Prof Barbara Casadei FMedSci FRCP

Research Area: Integrative Physiology (Systems Biology)
Technology Exchange: Ex vivo models, In vivo imaging and Mouse models
Scientific Themes: Translational Medicine & Medical Technology and Cardiovascular Science
Keywords: Atrial fibrillation, diabetic cardiomyopathy, myocardial ischaemia and remodelling, nitric oxide, reactive oxygen species and myocardial electrophysiology
Web Links:
The Team

The Team

Our programme of work aims to understand nitric oxide (NO) and redox signalling in the healthy and diseased myocardium and explore the hypothesis that targeting relevant sources of NO and reactive oxygen species may open new therapeutic avenues for cardiovascular disease. 

This focus has underpinned a longstanding collaboration with Prof Keith Channon based on our common interest in NO-redox biology and complementary expertise. Our joint work has contributed to the award of a Fondation Leducq Transatlantic Network of Excellence on “Redox and Nitrosative Regulation of Cardiac Remodeling: Novel Therapeutic Approaches for Heart Failure”. 

As part of an EU consortium of investigators with a common interest in atrial fibrillation (EUTRAF http://www.eutraf.eu) we undertake preclinical studies using small molecules or gene transfer in large animal models of human disease, enabling crucial intermediate steps in the path leading to clinical translation of basic findings.

In addition, in collaboration with the University of Maastricht, we have developed techniques for evaluating the cardiac electrophysiological phenotype of murine models of human disease (e.g., in vivo programmed electrical stimulation and optical mapping in isolated hearts). In silico modelling in the context of human atrial fibrillation has also being developed in collaboration with Dr Blanca Rodriguez (Department of Computer Science, Oxford) and used as an hypothesis-generating tool to dissect the ion channels and transporters involved in the changes in action potential duration and calcium handling that are evoked by the activity of oxidase systems in atrial myocytes isolated from patients with atrial fibrillation. 

In parallel with investigations in human cardiac tissue and animal models, we have a strong focus on patient-based research comprising mechanistic in vivo and in vitro studies, prospective investigations in cohorts of patients and, more recently, clinical trials. In this respect, our research has been directed to the identification of biomarkers and therapeutic targets for the prediction and prevention of atrial fibrillation and other in-hospital complications in patients undergoing cardiac surgery and to studies of the role of NO released by the neuronal isoform of NO synthase in the regulation of vascular tone and arterial blood pressure in humans in vivo. Mechanistic patient-based investigations and a large outcome trial currently recruiting at the Department of Cardiothoracic Surgery of the Fuwai Hospital in Beijing involve collaboration with Prof Zhengming Chen and Prof Rory Collins in the Clinical Trial Service Unit of the University of Oxford. This work is funded by a British Heart Foundation Programme Grant and Chair to Prof Casadei.

Our group members are:

Dr Svetlana Reilly (MD, DPhil (Oxon), University Research Lecturer, BHF intermediate fellow) svetlana.reilly@cardiov.ox.ac.uk

Dr Ricardo Carnicer (DPhil, University Research Lecturer, BHF intermediate fellow) ricardo.carnicer@cardiov.ox.ac.uk

Dr Jillian Simon (postdoctoral researcher) jillian.simon@cardiov.ox.ac.uk

Dr Xing Liu (postdoctoral researcher) xing.liu@cardiov.ox.ac.uk

Dr Alice Recalde (postdoctoral researcher) alice.recalde@cardiov.ox.ac.uk

Dr Hannah Boycott (postdoctoral researcher) hannah.boycott@cardiov.ox.ac.uk

Dr Klemen Ziberna (MD, RDM PhD student) klemen.ziberna@cardiov.ox.ac.uk

Dr Rohan S. Wijesurendra (MBBChir MA, Clinical lecturer) rohan.wijesurendra@trinity.ox.ac.uk

Alexandra Mighiu (RDM PhD student) alexandra.mighiu@cardiov.ox.ac.uk

Maria Cristina Carena (Marie Curie early stage researcher) maria.carena@cardiov.ox.ac.uk

Matilde Stefanini (BHF PhD student) matilde.stefanini@cardiov.ox.ac.uk

Simona Mafrici (MD, DPhil student) simona.mafrici@cardiov.ox.ac.uk

Ritu Arya (Research Assistant) ritu.arya@cardiov.ox.ac.uk

Mary Norris (BSc, Clinical research nurse) mary.norris@cardiov.ox.ac.uk

Name Department Institution Country
Prof Keith Channon FMedSci FRCP Cardiovascular Medicine Oxford University, John Radcliffe Hospital United Kingdom
Prof Ulrich Schotten Physiology University of Maastricht Netherlands
Dr Sander Verheule Physiology University of Maastricht Netherlands
Prof David A Kass The Johns Hopkins University Medical Institutions United States
Professor Zhengming Chen (NDM) Oxford University, Richard Doll Building United Kingdom
Professor Sir Rory E Collins (NDM) Oxford University, Richard Doll Building United Kingdom
Prof Ajay M Shah FMedSci FRCP King's College London United Kingdom
Prof Hugh Watkins FRS FMedSci Cardiovascular Medicine Oxford University, West Wing, John Radcliffe Hospital United Kingdom
Dr Blanca Rodriguez Department of Computer Science, University of Oxford United Kingdom
Prof Charles Redwood Cardiovascular Medicine Oxford University, West Wing, John Radcliffe Hospital United Kingdom
Prof Stefan Neubauer FMedSci FRCP Cardiovascular Medicine Oxford University, John Radcliffe Hospital United Kingdom
Dr Gil Bub DPAG University of Oxford United Kingdom
Reilly SN, Liu X, Carnicer R, Recalde A, Muszkiewicz A, Jayaram R, Carena MC, Wijesurendra R, Stefanini M, Surdo NC et al. 2016. Up-regulation of miR-31 in human atrial fibrillation begets the arrhythmia by depleting dystrophin and neuronal nitric oxide synthase. Sci Transl Med, 8 (340), pp. 340ra74. | Show Abstract | Read more

Atrial fibrillation (AF) is a growing public health burden, and its treatment remains a challenge. AF leads to electrical remodeling of the atria, which in turn promotes AF maintenance and resistance to treatment. Although remodeling has long been a therapeutic target in AF, its causes remain poorly understood. We show that atrial-specific up-regulation of microRNA-31 (miR-31) in goat and human AF depletes neuronal nitric oxide synthase (nNOS) by accelerating mRNA decay and alters nNOS subcellular localization by repressing dystrophin translation. By shortening action potential duration and abolishing rate-dependent adaptation of the action potential duration, miR-31 overexpression and/or disruption of nNOS signaling recapitulates features of AF-induced remodeling and significantly increases AF inducibility in mice in vivo. By contrast, silencing miR-31 in atrial myocytes from patients with AF restores dystrophin and nNOS and normalizes action potential duration and its rate dependency. These findings identify atrial-specific up-regulation of miR-31 in human AF as a key mechanism causing atrial dystrophin and nNOS depletion, which in turn contributes to the atrial phenotype begetting this arrhythmia. miR-31 may therefore represent a potential therapeutic target in AF.

Agewall S, Camm J, Barón Esquivias G, Budts W, Carerj S, Casselman F, Coca A, De Caterina R, Deftereos S, Dobrev D et al. 2017. Guía ESC 2016 sobre el diagnóstico y tratamiento de la fibrilación auricular, desarrollada en colaboración con la EACTS Revista Española de Cardiología, 70 (1), pp. 50.e1-50.e84. | Read more

Kirchhof P, Benussi S, Kotecha D, Ahlsson A, Atar D, Casadei B, Castellá M, Diener HC, Heidbuchel H, Hendriks J et al. 2017. 2016 ESC Guidelines for the Management of Atrial Fibrillation Developed in Collaboration With EACTS. Rev Esp Cardiol (Engl Ed), 70 (1), pp. 50. | Read more

Kirchhof P, Benussi S, Kotecha D, Ahlsson A, Atar D, Casadei B, Castella M, Diener HC, Heidbuchel H, Hendriks J et al. 2016. 2016 ESC Guidelines for the management of atrial fibrillation developed in collaboration with EACTS. Eur J Cardiothorac Surg, 50 (5), pp. e1-e88. | Read more

Casadei B, Collins R, Zheng Z. 2016. Perioperative Rosuvastatin in Cardiac Surgery. N Engl J Med, 375 (9), pp. 903. | Read more

Kirchhof P, Benussi S, Kotecha D, Ahlsson A, Atar D, Casadei B, Castella M, Diener HC, Heidbuchel H, Hendriks J et al. 2016. 2016 ESC Guidelines for the management of atrial fibrillation developed in collaboration with EACTS. Eur Heart J, 37 (38), pp. 2893-2962. | Read more

Kirchhof P, Benussi S, Kotecha D, Ahlsson A, Atar D, Casadei B, Castella M, Diener HC, Heidbuchel H, Hendriks J et al. 2016. 2016 ESC Guidelines for the management of atrial fibrillation developed in collaboration with EACTS. Europace, 18 (11), pp. 1609-1678. | Read more

Zheng Z, Jayaram R, Jiang L, Emberson J, Zhao Y, Li Q, Du J, Guarguagli S, Hill M, Chen Z et al. 2016. Perioperative Rosuvastatin in Cardiac Surgery. N Engl J Med, 374 (18), pp. 1744-1753. | Show Abstract | Read more

BACKGROUND: Complications after cardiac surgery are common and lead to substantial increases in morbidity and mortality. Meta-analyses of small randomized trials have suggested that perioperative statin therapy can prevent some of these complications. METHODS: We randomly assigned 1922 patients in sinus rhythm who were scheduled for elective cardiac surgery to receive perioperative rosuvastatin (at a dose of 20 mg daily) or placebo. The primary outcomes were postoperative atrial fibrillation within 5 days after surgery, as assessed by Holter electrocardiographic monitoring, and myocardial injury within 120 hours after surgery, as assessed by serial measurements of the cardiac troponin I concentration. Secondary outcomes included major in-hospital adverse events, duration of stay in the hospital and intensive care unit, left ventricular and renal function, and blood biomarkers. RESULTS: The concentrations of low-density lipoprotein cholesterol and C-reactive protein after surgery were lower in patients assigned to rosuvastatin than in those assigned to placebo (P<0.001). However, the rate of postoperative atrial fibrillation did not differ significantly between the rosuvastatin group and the placebo group (21.1% and 20.5%, respectively; odds ratio 1.04; 95% confidence interval [CI], 0.84 to 1.30; P=0.72), nor did the area under the troponin I-release curve (102 ng×hour per milliliter and 100 ng×hour per milliliter, respectively; between-group difference, 1%; 95% CI, -9 to 13; P=0.80). Subgroup analyses did not indicate benefit in any category of patient. Rosuvastatin therapy did not result in beneficial effects on any of the secondary outcomes but was associated with a significant absolute (±SE) excess of 5.4±1.9 percentage points in the rate of postoperative acute kidney injury (P=0.005). CONCLUSIONS: In this trial, perioperative statin therapy did not prevent postoperative atrial fibrillation or perioperative myocardial damage in patients undergoing elective cardiac surgery. Acute kidney injury was more common with rosuvastatin. (Funded by the British Heart Foundation and others; STICS ClinicalTrials.gov number, NCT01573143.).

Antonopoulos AS, Margaritis M, Verheule S, Recalde A, Sanna F, Herdman L, Psarros C, Nasrallah H, Coutinho P, Akoumianakis I et al. 2016. Mutual Regulation of Epicardial Adipose Tissue and Myocardial Redox State by PPAR-γ/Adiponectin Signalling. Circ Res, 118 (5), pp. 842-855. | Show Abstract | Read more

RATIONALE: Adiponectin has anti-inflammatory effects in experimental models, but its role in the regulation of myocardial redox state in humans is unknown. Although adiponectin is released from epicardial adipose tissue (EpAT), it is unclear whether it exerts any paracrine effects on the human myocardium. OBJECTIVE: To explore the cross talk between EpAT-derived adiponectin and myocardial redox state in the human heart. METHODS AND RESULTS: EpAT and atrial myocardium were obtained from 306 patients undergoing coronary artery bypass grafting. Functional genetic polymorphisms that increase ADIPOQ expression (encoding adiponectin) led to reduced myocardial nicotinamide adenine dinucleotide phosphate oxidase-derived O2 (-), whereas circulating adiponectin and ADIPOQ expression in EpAT were associated with elevated myocardial O2 (-). In human atrial tissue, we demonstrated that adiponectin suppresses myocardial nicotinamide adenine dinucleotide phosphate oxidase activity, by preventing AMP kinase-mediated translocation of Rac1 and p47(phox) from the cytosol to the membranes. Induction of O2 (-) production in H9C2 cardiac myocytes led to the release of a transferable factor able to induce peroxisome proliferator-activated receptor-γ-mediated upregulation of ADIPOQ expression in cocultured EpAT. Using a NOX2 transgenic mouse and a pig model of rapid atrial pacing, we found that oxidation products (such as 4-hydroxynonenal) released from the heart trigger peroxisome proliferator-activated receptor-γ-mediated upregulation of ADIPOQ in EpAT. CONCLUSIONS: We demonstrate for the first time in humans that adiponectin directly decreases myocardial nicotinamide adenine dinucleotide phosphate oxidase activity via endocrine or paracrine effects. Adiponectin expression in EpAT is controlled by paracrine effects of oxidation products released from the heart. These effects constitute a novel defense mechanism of the heart against myocardial oxidative stress.

Kirchhof P, Benussi S, Kotecha D, Ahlsson A, Atar D, Casadei B, Castella M, Diener HC, Heidbuchel H, Hendriks J et al. 2016. [2016 ESC Guidelines for the management of atrial fibrillation developed in collaboration with EACTS]. Kardiol Pol, 74 (12), pp. 1359-1469. | Read more

Hashimoto T, Sivakumaran V, Carnicer R, Zhu G, Hahn VS, Bedja D, Recalde A, Duglan D, Channon KM, Casadei B, Kass DA. 2016. Tetrahydrobiopterin Protects Against Hypertrophic Heart Disease Independent of Myocardial Nitric Oxide Synthase Coupling. J Am Heart Assoc, 5 (3), pp. e003208. | Show Abstract | Read more

BACKGROUND: Nitric oxide synthase uncoupling occurs under conditions of oxidative stress modifying the enzyme's function so it generates superoxide rather than nitric oxide. Nitric oxide synthase uncoupling occurs with chronic pressure overload, and both are ameliorated by exogenous tetrahydrobiopterin (BH4)-a cofactor required for normal nitric oxide synthase function-supporting a pathophysiological link. Genetically augmenting BH4 synthesis in endothelial cells fails to replicate this benefit, indicating that other cell types dominate the effects of exogenous BH4 administration. We tested whether the primary cellular target of BH4 is the cardiomyocyte or whether other novel mechanisms are invoked. METHODS AND RESULTS: Mice with cardiomyocyte-specific overexpression of GTP cyclohydrolase 1 (mGCH1) and wild-type littermates underwent transverse aortic constriction. The mGCH1 mice had markedly increased myocardial BH4 and, unlike wild type, maintained nitric oxide synthase coupling after transverse aortic constriction; however, the transverse aortic constriction-induced abnormalities in cardiac morphology and function were similar in both groups. In contrast, exogenous BH4 supplementation improved transverse aortic constricted hearts in both groups, suppressed multiple inflammatory cytokines, and attenuated infiltration of inflammatory macrophages into the heart early after transverse aortic constriction. CONCLUSIONS: BH4 protection against adverse remodeling in hypertrophic cardiac disease is not driven by its prevention of myocardial nitric oxide synthase uncoupling, as presumed previously. Instead, benefits from exogenous BH4 are mediated by a protective effect coupled to suppression of inflammatory pathways and myocardial macrophage infiltration.

Fabritz L, Guasch E, Antoniades C, Bardinet I, Benninger G, Betts TR, Brand E, Breithardt G, Bucklar-Suchankova G, Camm AJ et al. 2016. Expert consensus document: Defining the major health modifiers causing atrial fibrillation: a roadmap to underpin personalized prevention and treatment. Nat Rev Cardiol, 13 (4), pp. 230-237. | Show Abstract | Read more

Despite remarkable advances in antiarrhythmic drugs, ablation procedures, and stroke-prevention strategies, atrial fibrillation (AF) remains an important cause of death and disability in middle-aged and elderly individuals. Unstructured management of patients with AF sharply contrasts with our detailed, although incomplete, knowledge of the mechanisms that cause AF and its complications. Altered calcium homeostasis, atrial fibrosis and ageing, ion-channel dysfunction, autonomic imbalance, fat-cell infiltration, and oxidative stress, in addition to a susceptible genetic background, contribute to the promotion, maintenance, and progression of AF. However, clinical management of patients with AF is currently guided by stroke risk parameters, AF pattern, and symptoms. In response to this apparent disconnect between the known pathophysiology of AF and clinical management, we propose a roadmap to develop a set of clinical markers that reflect the major causes of AF in patients. Thereby, the insights into the mechanisms causing AF will be transformed into a format that can underpin future personalized strategies to prevent and treat AF, ultimately informing better patient care.

Schwarzl M, Hamdani N, Seiler S, Alogna A, Manninger M, Reilly S, Zirngast B, Kirsch A, Steendijk P, Verderber J et al. 2015. A porcine model of hypertensive cardiomyopathy: implications for heart failure with preserved ejection fraction. Am J Physiol Heart Circ Physiol, 309 (9), pp. H1407-H1418. | Show Abstract | Read more

Heart failure with preserved ejection fraction (HFPEF) evolves with the accumulation of risk factors. Relevant animal models to identify potential therapeutic targets and to test novel therapies for HFPEF are missing. We induced hypertension and hyperlipidemia in landrace pigs (n = 8) by deoxycorticosteroneacetate (DOCA, 100 mg/kg, 90-day-release subcutaneous depot) and a Western diet (WD) containing high amounts of salt, fat, cholesterol, and sugar for 12 wk. Compared with weight-matched controls (n = 8), DOCA/WD-treated pigs showed left ventricular (LV) concentric hypertrophy and left atrial dilatation in the absence of significant changes in LV ejection fraction or symptoms of heart failure at rest. The LV end-diastolic pressure-volume relationship was markedly shifted leftward. During simultaneous right atrial pacing and dobutamine infusion, cardiac output reserve and LV peak inflow velocities were lower in DOCA/WD-treated pigs at higher LV end-diastolic pressures. In LV biopsies, we observed myocyte hypertrophy, a shift toward the stiffer titin isoform N2B, and reduced total titin phosphorylation. LV superoxide production was increased, in part attributable to nitric oxide synthase (NOS) uncoupling, whereas AKT and NOS isoform expression and phosphorylation were unchanged. In conclusion, we developed a large-animal model in which loss of LV capacitance was associated with a titin isoform shift and dysfunctional NOS, in the presence of preserved LV ejection fraction. Our findings identify potential targets for the treatment of HFPEF in a relevant large-animal model.

Schotten U, Hatem S, Ravens U, Jaïs P, Müller FU, Goette A, Rohr S, Antoons G, Pieske B, Scherr D et al. 2015. The European Network for Translational Research in Atrial Fibrillation (EUTRAF): objectives and initial results. Europace, 17 (10), pp. 1457-1466. | Show Abstract | Read more

Atrial fibrillation (AF) is the most common sustained arrhythmia in the general population. As an age-related arrhythmia AF is becoming a huge socio-economic burden for European healthcare systems. Despite significant progress in our understanding of the pathophysiology of AF, therapeutic strategies for AF have not changed substantially and the major challenges in the management of AF are still unmet. This lack of progress may be related to the multifactorial pathogenesis of atrial remodelling and AF that hampers the identification of causative pathophysiological alterations in individual patients. Also, again new mechanisms have been identified and the relative contribution of these mechanisms still has to be established. In November 2010, the European Union launched the large collaborative project EUTRAF (European Network of Translational Research in Atrial Fibrillation) to address these challenges. The main aims of EUTRAF are to study the main mechanisms of initiation and perpetuation of AF, to identify the molecular alterations underlying atrial remodelling, to develop markers allowing to monitor this processes, and suggest strategies to treat AF based on insights in newly defined disease mechanisms. This article reports on the objectives, the structure, and initial results of this network.

Hunter A, Holdsworth DA, D'Arcy J, Bailey K, Casadei B. 2015. Hypertension in the military patient. J R Army Med Corps, 161 (3), pp. 200-205. | Show Abstract | Read more

Hypertension and hypertension-related diseases are a leading cause of morbidity and mortality worldwide. A diagnosis of hypertension can have serious occupational implications for military personnel. This article examines the diagnosis and management of hypertension in military personnel, in the context of current international standards. We consider the consequences of hypertension in the military environment and potential military-specific issues relating to hypertension.

Jayaram R, Goodfellow N, Zhang MH, Reilly S, Crabtree M, De Silva R, Sayeed R, Casadei B. 2015. Molecular mechanisms of myocardial nitroso-redox imbalance during on-pump cardiac surgery. Lancet, 385 Suppl 1 pp. S49. | Show Abstract | Read more

BACKGROUND: The mechanism responsible for left ventricular dysfunction after cardiac surgery is only partly understood. In isolated rat hearts subjected to an ischaemia-reperfusion protocol, left ventricular dysfunction was associated with uncoupling of endothelial nitric oxide synthase (NOS) activity secondary to oxidation of the NOS cofactor, tetrahydrobiopterin (BH4). Here we investigated the effect of cardiopulmonary bypass and reperfusion on myocardial nitroso-redox balance in patients undergoing cardiac surgery. METHODS: From 116 patients who underwent elective cardiac surgery on cardiopulmonary bypass, paired samples of the right atrial appendages were obtained before venous cannulation of the right atrium and after myocardial reperfusion. Superoxide production from atrial samples was measured by lucigenin (5 μmol/L) enhanced chemiluminescence and 2-hydroxyethidium (2-OHE) detection by high-performance liquid chromatography (HPLC). BH4, oxidised biopterins, GTP-cyclohydrolase 1 (GTPCH-1, the rate-limiting enzyme in BH4 synthesis), and NOS activity ((14)C L-arginine to L-citrulline conversion) were measured by HPLC. FINDINGS: Atrial superoxide production increased significantly after reperfusion (from mean 37·83 relative light units per s per mg [SE 3·71] before cannulation to 65·02 [6·01] after reperfusion, p<0·0001; n=46 samples from 23 patients) due to increased mitochondrial and NOX2 oxidase activity (by 309% and 149%; p=0·002 and p=0·0002, respectively) and uncoupling of NOS activity. Atrial content of BH4 after perfusion was reduced (by 32%, p=0·001), as was activity of GTPCH1 (50%, p<0·0001). NOS activity decreased significantly after reperfusion (60%, p=0·0005) and this reduction was not affected by BH4 supplementation (10 μM) or NOX2 inhibition ex vivo. Instead, we identified increased endothelial NOS s-glutathionylation as the main mechanism for NOS uncoupling after reperfusion. Reversing NOS s-glutathionylation with dithiothreitol (100 μmol/L) completely restored NOS activity after reperfusion (p=0·34). INTERPRETATION: Our findings suggest that NOS s-glutathionylation, rather than BH4 depletion, accounts for NOS dysfunction in patients after cardiac surgery and cardiopulmonary bypass. FUNDING: British Heart Foundation.

Reilly S, Liu X, Carnicer R, Rajakumar T, Sayeed R, Krasopoulos G, Verheule S, Fulga T, Schotten U, Casadei B. 2015. Evaluation of the role of miR-31-dependent reduction in dystrophin and nNOS on atrial-fibrillation-induced electrical remodelling in man. Lancet, 385 Suppl 1 pp. S82. | Show Abstract | Read more

BACKGROUND: The management of atrial fibrillation remains a challenge. This condition remodels atrial electrical properties, which promote resistance to treatment. Although remodelling has long been a therapeutic target in atrial fibrillation, its causes remain incompletely understood. We aimed to evaluate the role of miR-31-dependent reduction in dystrophin and neuronal nitric oxide synthase (nNOS, also known as NOS1) on atrial electrical properties and atrial fibrillation inducibility. METHODS: We recruited 258 patients (209 patients in sinus rhythm and 49 with permanent atrial fibrillation) from the John Radcliffe Hospital, Oxford, UK; written informed consent was obtained from each participant. We also used a goat model of pacing-induced atrial fibrillation (24 with atrial fibrillation vs 20 controls in normal sinus rythm) and nNos-knock-out mice (n=28 compared with 27 wild-type littermates). Gene expression of miR-31, dystrophin, and nNOS was assessed by quantitative RT-PCR; protein content was measured by immunoblotting; NOS activity was evaluated with high-performance liquid chromatography; action potential duration (APD) and rate dependent adaptation were assessed by single-cell patch-clamping, and atrial fibrillation inducibility was evaluated by transoesophageal atrial burst stimulation. FINDINGS: We found that atrial-specific upregulation of miR-31 in human atrial fibrillation caused dystrophin (DYS) translational repression and accelerated mRNA degradation of nNOS leading to a profound reduction in atrial DYS and nNOS protein content and in nitric oxide availability. In human atrial myocytes obtained from patients in sinus rhythm, nNOS inhibition was sufficient to recapitulate hallmark features of remodelling induced by atrial fibrillation, such as shortening of APD and loss of APD rate-dependency, but had no effect in patients with atrial fibrillation. In mice, nNos gene deletion or inhibition shortened atrial APD and increased atrial fibrillation inducibility in vivo. Inhibition of miR-31 in human atrial fibrillation recovered DYS and nNOS, and normalised APD and APD rate-dependency. Prevention of miR-31 binding to nNOS 3'UTR recovered both nNOS protein and gene expression but had no effect on the DYS protein or mRNA level (consistent with the mRNA degradation of nNOS by miR-31). Prevention of miR-31 binding to DYS 3'UTR increased DYS protein but not mRNA is consistent with translation repression of DYS by miR-31; recovery of DYS protein increased nNOS protein but not mRNA in keeping with a stabilising effect of DYS on nNOS protein. In goats, a reduction in dystrophin and nNOS protein content was associated with upregulation of miR-31 in the atria but not in the ventricles. INTERPRETATION: The findings suggest that atrial-specific upregulation of miR-31 in human atrial fibrillation is a key mechanism causing atrial loss of dystrophin and nNOS; this loss leads to the electrical phenotype induced by atrial fibrillation. FUNDING: British Heart Foundation (BHF) Programme grant (for BC and XL), BHF Centre of Excellence in Oxford (SR), Leducq Foundation (in part for BC and SR), the European Union's seventh Framework Programme Grant Agree.

Linz D, van Hunnik A, Hohl M, Mahfoud F, Wolf M, Neuberger HR, Casadei B, Reilly SN, Verheule S, Böhm M, Schotten U. 2015. Catheter-based renal denervation reduces atrial nerve sprouting and complexity of atrial fibrillation in goats. Circ Arrhythm Electrophysiol, 8 (2), pp. 466-474. | Show Abstract | Read more

BACKGROUND: Atrial fibrillation (AF) leads to structural and neural remodeling in the atrium, which enhances AF complexity and perpetuation. Renal denervation (RDN) can reduce renal and whole-body sympathetic activity. Aim of this study was to determine the effect of sympathetic nervous system modulation by RDN on atrial arrhythmogenesis. METHODS AND RESULT: Eighteen goats were instrumented with an atrial endocardial pacemaker lead and a burst pacemaker. Percutaneous catheter-based RDN was performed in 8 goats (RDN-AF). Ten goats undergoing a sham procedure served as control (SHAM-AF). AF was induced and maintained by burst pacing for 6 weeks. High-resolution mapping was used to record epicardial conduction patterns of the right and left atrium. RDN reduced tyrosine hydroxylase-positive sympathetic nerve staining and resulted in lower transcardiac norepinephrine levels. This was associated with reduced expression of nerve growth factor-β, indicating less atrial nerve sprouting. Atrial endomysial fibrosis content was lower and myocyte diameter was smaller in RDN-AF. Median conduction velocity was higher (75 ± 9 versus 65 ± 10 cm/s, P = 0.02), and AF cycle length was shorter in RDN-AF compared with SHAM-AF. Left atrial AF complexity (4.8 ± 0.8 fibrillation waves/AF cycle length versus 8.5 ± 0.8 waves/AF cycle length, P = 0.001) and incidence of breakthroughs (2.0 ± 0.3 versus 4.3 ± 0.5 waves/AF cycle length, P = 0.059) were lower in RDN-AF compared with SHAM-AF. Blood pressure was normal and not significantly different between the groups. CONCLUSIONS: RDN reduces atrial sympathetic nerve sprouting, structural alterations, and AF complexity in goats with persistent AF, independent of changes in blood pressure.

Wijesurendra RS, Liu A, Casadei B, Robson MD, Neubauer S, Ferreira VM, Piechnik SK. 2015. Systolic ShMOLLI T1-mapping is feasible in tachyarrhythmia, with improved image quality compared to diastolic readout Journal of Cardiovascular Magnetic Resonance, 17 (Suppl 1), pp. Q5-Q5. | Read more

Wijesurendra R, Casadei B. 2015. Atrial supply-demand mismatch in atrial fibrillation: The missing link between rapid rate and atrial remodeling? Heart Rhythm, 12 (5), pp. 1001-1002. | Read more

Wijesurendra RS, Casadei B. 2015. Atrial fibrillation: effects beyond the atrium? Cardiovasc Res, 105 (3), pp. 238-247. | Show Abstract | Read more

Atrial fibrillation (AF) is the most common sustained clinical arrhythmia and is associated with significant morbidity, mostly secondary to heart failure and stroke, and an estimated two-fold increase in premature death. Efforts to increase our understanding of AF and its complications have focused on unravelling the mechanisms of electrical and structural remodelling of the atrial myocardium. Yet, it is increasingly recognized that AF is more than an atrial disease, being associated with systemic inflammation, endothelial dysfunction, and adverse effects on the structure and function of the left ventricular myocardium that may be prognostically important. Here, we review the molecular and in vivo evidence that underpins current knowledge regarding the effects of human or experimental AF on the ventricular myocardium. Potential mechanisms are explored including diffuse ventricular fibrosis, focal myocardial scarring, and impaired myocardial perfusion and perfusion reserve. The complex relationship between AF, systemic inflammation, as well as endothelial/microvascular dysfunction and the effects of AF on ventricular calcium handling and oxidative stress are also addressed. Finally, consideration is given to the clinical implications of these observations and concepts, with particular reference to rate vs. rhythm control.

Ferreira VM, Wijesurendra RS, Liu A, Greiser A, Casadei B, Robson MD, Neubauer S, Piechnik SK. 2015. Systolic ShMOLLI myocardial T1-mapping for improved robustness to partial-volume effects and applications in tachyarrhythmias. J Cardiovasc Magn Reson, 17 (1), pp. 77. | Show Abstract | Read more

BACKGROUND: T1-mapping using the Shortened Modified Look-Locker Inversion Recovery (ShMOLLI) technique enables non-invasive assessment of important myocardial tissue characteristics. However, tachyarrhythmia may cause mistriggering and inaccurate T1 estimation. We set out to test whether systolic T1-mapping might overcome this, and whether T1 values or data quality would be significantly different compared to conventional diastolic T1-mapping. METHODS: Native T1 maps were acquired using ShMOLLI at 1.5 T (Magnetom Avanto, Siemens Healthcare) in 10 healthy volunteers (5 male) in sinus rhythm, at varying prescribed trigger delay (TD) times: 0, 50, 100 and 150 ms (all "systolic"), 340 ms (MOLLI TD 500 ms, the conventional TD for ShMOLLI) and also "end diastolic". T1 maps were also acquired using a shorter readout, to explore the effect of reducing image readout time and sensitivity to systolic motion. The feasibility and image quality of systolic T1-mapping was tested in 15 patients with tachyarrhythmia (n = 13 atrial fibrillation, n = 2 sinus tachycardia; mean HR range 93-121 bpm). RESULTS: In healthy volunteers, systolic readout increased the thickness of myocardium compared to the diastolic readout. There was a small overall effect of TD on T1 values (p = 0.04), with slightly shorter T1 values in systole compared to diastole (maximum difference 10 ms). While there were apparent gender differences (with no effect of TD on T1 values in males, more marked differences in females, and exaggeration of this effect in thinner myocardial segments in females), dilatation and erosion of contours suggested that the effect of TD on T1 in females was almost entirely due to more partial-volume effects in diastole. All T1 maps were of excellent quality, but systolic TD and shorter readout were associated with less variability in segmental T1 values. In tachycardic patients, systolic acquisitions produced consistently excellent T1 maps (median R (2) = 0.993). CONCLUSIONS: In healthy volunteers, systolic ShMOLLI T1-mapping reduces T1 variability and reports clinically equivalent T1 values to conventional diastolic readout; slightly shorter T1 values in systole are mostly explained by reduced partial-volume effects due to the increase in functional myocardial thickness. In patients with tachyarrhythmia, systolic ShMOLLI T1-mapping is feasible, circumvents mistriggering and produces excellent quality T1 maps. This extends its clinical applicability to challenging rhythms (such as rapid atrial fibrillation) and aids the investigation of thinner myocardial segments. With further validation, systolic T1-mapping may become a new and convenient standard for myocardial T1-mapping.

Wijesurendra R, Casadei B. 2015. Atrial supply-demand mismatch in atrial fibrillation: The missing link between rapid rate and atrial remodeling? Heart Rhythm, 12 (5), pp. 1001-1002. | Read more

Antonopoulos AS, Margaritis M, Coutinho P, Shirodaria C, Psarros C, Herdman L, Sanna F, De Silva R, Petrou M, Sayeed R et al. 2015. Adiponectin as a link between type 2 diabetes and vascular NADPH oxidase activity in the human arterial wall: the regulatory role of perivascular adipose tissue. Diabetes, 64 (6), pp. 2207-2219. | Show Abstract | Read more

Oxidative stress plays a critical role in the vascular complications of type 2 diabetes. We examined the effect of type 2 diabetes on NADPH oxidase in human vessels and explored the mechanisms of this interaction. Segments of internal mammary arteries (IMAs) with their perivascular adipose tissue (PVAT) and thoracic adipose tissue were obtained from 386 patients undergoing coronary bypass surgery (127 with type 2 diabetes). Type 2 diabetes was strongly correlated with hypoadiponectinemia and increased vascular NADPH oxidase-derived superoxide anions (O2˙(-)). The genetic variability of the ADIPOQ gene and circulating adiponectin (but not interleukin-6) were independent predictors of NADPH oxidase-derived O2˙(-). However, adiponectin expression in PVAT was positively correlated with vascular NADPH oxidase-derived O2˙(-). Recombinant adiponectin directly inhibited NADPH oxidase in human arteries ex vivo by preventing the activation/membrane translocation of Rac1 and downregulating p22(phox) through a phosphoinositide 3-kinase/Akt-mediated mechanism. In ex vivo coincubation models of IMA/PVAT, the activation of arterial NADPH oxidase triggered a peroxisome proliferator-activated receptor-γ-mediated upregulation of the adiponectin gene in the neighboring PVAT via the release of vascular oxidation products. We demonstrate for the first time in humans that reduced adiponectin levels in individuals with type 2 diabetes stimulates vascular NADPH oxidase, while PVAT "senses" the increased NADPH oxidase activity in the underlying vessel and responds by upregulating adiponectin gene expression. This PVAT-vessel interaction is identified as a novel therapeutic target for the prevention of vascular complications of type 2 diabetes.

Cited:

27

Scopus

Simon JN, Duglan D, Casadei B, Carnicer R. 2014. Nitric oxide synthase regulation of cardiac excitation-contraction coupling in health and disease Journal of Molecular and Cellular Cardiology, 73 pp. 80-91. | Show Abstract | Read more

Significant advances in our understanding of the ability of nitric oxide synthases (NOS) to modulate cardiac function have provided key insights into the role NOS play in the regulation of excitation-contraction (EC) coupling in health and disease. Through both cGMP-dependent and cGMP-independent (e.g. S-nitrosylation) mechanisms, NOS have the ability to alter intracellular Ca 2+ handling and the myofilament response to Ca 2+ , thereby impacting the systolic and diastolic performance of the myocardium. Findings from experiments using nitric oxide (NO) donors and NOS inhibition or gene deletion clearly implicate dysfunctional NOS as a critical contributor to many cardiovascular disease states. However, studies to date have only partially addressed NOS isoform-specific effects and, more importantly, how subcellular localization of NOS influences ion channels involved in myocardial EC coupling and excitability. In this review, we focus on the contribution of each NOS isoform to cardiac dysfunction and on the role of uncoupled NOS activity in common cardiac disease states, including heart failure, diabetic cardiomyopathy, ischemia/reperfusion injury and atrial fibrillation. We also review evidence that clearly indicates the importance of NO in cardioprotection. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System". © 2014 Elsevier Ltd.

Jayaram R, Goodfellow N, Nahar K, Zhang M, Reilly S, Crabtree M, De Silva R, Sayeed R, Casadei B. 2014. P644Mechanisms of myocardial nitroso redox imbalance following elective cardiac surgery on cardiopulmonary bypass. Cardiovasc Res, 103 Suppl 1 (suppl 1), pp. S117. | Show Abstract | Read more

The mechanisms responsible for myocardial stunning after cardiac surgery are only partially understood, although ischemia - reperfusion (IR) injury associated with cardio pulmonary bypass (CPB) may play an important role. Reactive oxygen species and nitric oxide have been implicated in both myocardial injury and cardio protection suggesting that identification of their sources may refine therapeutic strategies. Here we investigated the effect of cardioplegia, CPB and reperfusion on myocardial nitroso--redox balance in patients after cardiac surgery.

Liu X, Reilly S, Carnicer R, Recalde A, Krasopoulos G, Sayeed R, Desilva R, Casadei B. 2014. P106Loss of myocardial nNOS in human atrial fibrillation (AF) shortens action potential duration (APD) by increasing Ito: Implications for AF-induced electrical remodelling. Cardiovasc Res, 103 Suppl 1 (suppl 1), pp. S18. | Show Abstract | Read more

Understanding the mechanism underlying atrial electrical remodelling in AF is of fundamental importance for the prevention and treatment of AF. We have recently found that neuronal nitric oxide synthase (nNOS) activity is dramatically reduced in atrial myocytes from patients with AF. Whether loss of nNOS activity contributes to AF-induced atrial electrical remodelling remains to be established.

Robinson P, Liu X, Zhang YH, Khandelwal A, Blagg B, Casadei B, Watkins H, Redwood C. 2014. P123The rescue of Ca2+ cycling abnormalities conferred by HCM-causing mutations with analogues of the green tea polyphenol epigallocatechin-3-gallate. Cardiovasc Res, 103 Suppl 1 (suppl 1), pp. S21. | Show Abstract | Read more

Mutations in thin filament regulatory proteins that cause hypertrophic cardiomyopathy (HCM) confer distinct primary alterations of cardiac contractility. We have shown that altered Ca2+-buffering by mutant thin filaments leads to altered Ca2+ handling and results in stimulation of Ca2+-dependent signalling pathways. To do this we have used adenoviral mediated expression of cTnT R92Q, cTnI R145G and α-TM D175N in adult guinea pig cardiomyocytes at a ratio of 1:1 with the endogenous protein. Simultaneous measurement of unloaded sarcomere-shortening and Ca2+ transients using fura-2 loading, showed the HCM mutations caused a significant decrease in the basal sarcomere length coupled with an increase in the diastolic Ca2+ concentration. The mechanism of alterations to EC-coupling was also investigated using tetracaine and caffeine challenging combined with simultaneous whole cell patch clamping. HCM mutant cells displayed reduced SR load (~1.4fold), slowed NCX calcium extrusion (~2.5fold), unchanged SERCA2 activity, increased ryanodine receptor leak (~5fold) and increased calcium buffering (~3fold). This was coupled to an increase in Ca2+ dependent NFAT nuclear localisation. Further studies using the green tea catechin, epigallocatechin gallate (EGCg) and sister compound epicatechin-3-gallate (ECG), have shown that the compounds can partiality reverse the increase in diastolic Ca2+ observed in cardiomyocytes containing HCM causing mutations. The mechanism is thought to be via an interaction with cTnC (measured using intrinsic cTnC tyrosine fluorescence) which in turn causes a reduction of in vitro thin filament Ca2+ affinity (measured using cTnC labelled with IAANS fluorophore at Cys 35). Data acquired so far suggests that catechins and their derivative compounds may provide a possible therapeutic approach for correcting Ca2+ regulation and Ca2+ dependent remodelling in HCM. We have recently obtained library of 37 EGCg analogues which we have screened for cTnC affinity and thin filament Ca2+ affinity. We have now identified several catechins with potentially greater efficacy than the parent compound, and plan to test their ability to rescue the cellular HCM phenotype characterised above.

Antonopoulos A, Margaritis M, Recalde A, Ciccone P, Reilly S, Shah A, Tousoulis D, Casadei B, Antoniades C, Channon KM. 2014. HFWM: - Title: Adiponectin and 4-hydroxynonenal as messengers in the cross-talk between the heart and epicardial adipose tissue regulating myocardial redox state in ischemic heart disease EUROPEAN JOURNAL OF HEART FAILURE, 16 pp. 105-105.

Sipido KR, Casadei B, Holvoet P, Janssens S, Luttun A, Sampaolesi M. 2014. Bedside to bench: a look at experimental research with a clinical trial checklist. Cardiovasc Res, 101 (1), pp. 1-3. | Read more

Antonopoulos AS, Margaritis M, Digby J, Petrou M, Ciccone P, Psarros C, Sayeed R, Casadei B, Channon KM, Antoniades C. 2013. A Novel Cross-Talk Between Epicardial Adipose Tissue and the Human Heart Regulates Myocardial Redox State in Ischaemic Heart Disease CIRCULATION, 128 (22),

Kirchhof P, Breithardt G, Aliot E, Al Khatib S, Apostolakis S, Auricchio A, Bailleul C, Bax J, Benninger G, Blomstrom-Lundqvist C et al. 2013. Personalized management of atrial fibrillation: Proceedings from the fourth Atrial Fibrillation competence NETwork/European Heart Rhythm Association consensus conference. Europace, 15 (11), pp. 1540-1556. | Show Abstract | Read more

The management of atrial fibrillation (AF) has seen marked changes in past years, with the introduction of new oral anticoagulants, new antiarrhythmic drugs, and the emergence of catheter ablation as a common intervention for rhythm control. Furthermore, new technologies enhance our ability to detect AF. Most clinical management decisions in AF patients can be based on validated parameters that encompass type of presentation, clinical factors, electrocardiogram analysis, and cardiac imaging. Despite these advances, patients with AF are still at increased risk for death, stroke, heart failure, and hospitalizations. During the fourth Atrial Fibrillation competence NETwork/European Heart Rhythm Association (AFNET/EHRA) consensus conference, we identified the following opportunities to personalize management of AF in a better manner with a view to improve outcomes by integrating atrial morphology and damage, brain imaging, information on genetic predisposition, systemic or local inflammation, and markers for cardiac strain. Each of these promising avenues requires validation in the context of existing risk factors in patients. More importantly, a new taxonomy of AF may be needed based on the pathophysiological type of AF to allow personalized management of AF to come to full fruition. Continued translational research efforts are needed to personalize management of this prevalent disease in a better manner. All the efforts are expected to improve the management of patients with AF based on personalized therapy.

Pinho-Gomes AC, Reilly S, Brandes RP, Casadei B. 2014. Targeting inflammation and oxidative stress in atrial fibrillation: role of 3-hydroxy-3-methylglutaryl-coenzyme a reductase inhibition with statins. Antioxid Redox Signal, 20 (8), pp. 1268-1285. | Show Abstract | Read more

SIGNIFICANCE: Atrial fibrillation (AF) is a burgeoning health-care problem, and the currently available therapeutic armamentarium is barely efficient. Experimental and clinical evidence implicates inflammation and myocardial oxidative stress in the pathogenesis of AF. RECENT ADVANCES: Local and systemic inflammation has been found to both precede and follow the new onset of AF, and NOX2-dependent generation of reactive oxygen species in human right atrial samples has been independently associated with the occurrence of AF in the postoperative period in patients undergoing cardiac surgery. Anti-inflammatory and antioxidant agents can prevent atrial electrical remodeling in animal models of atrial tachypacing and the new onset of AF after cardiac surgery, suggesting a causal relationship between inflammation/oxidative stress and the atrial substrate that supports AF. CRITICAL ISSUES: Statin therapy, by redressing the myocardial nitroso-redox balance and reducing inflammation, has emerged as a potentially effective strategy for the prevention of AF. Evidence indicates that statins prevent AF-induced electrical remodeling in animal models of atrial tachypacing and may reduce the new onset of AF after cardiac surgery. However, whether statins have antiarrhythmic properties in humans has yet to be conclusively demonstrated, as data from randomized controlled trials specifically addressing the relevance of statin therapy for the primary and secondary prevention of AF remain scanty. FUTURE DIRECTIONS: A better understanding of the mechanisms underpinning the putative antiarrhythmic effects of statins may afford tailoring AF treatment to specific clinical settings and patient's subgroups. Large-scale randomized clinical trials are needed to support the indication of statin therapy solely on the basis of AF prevention.

Margaritis M, Antonopoulos AS, Digby J, Lee R, Reilly S, Coutinho P, Shirodaria C, Sayeed R, Petrou M, De Silva R et al. 2013. Interactions between vascular wall and perivascular adipose tissue reveal novel roles for adiponectin in the regulation of endothelial nitric oxide synthase function in human vessels. Circulation, 127 (22), pp. 2209-2221. | Show Abstract | Read more

BACKGROUND: Adiponectin is an adipokine with potentially important roles in human cardiovascular disease states. We studied the role of adiponectin in the cross-talk between adipose tissue and vascular redox state in patients with atherosclerosis. METHODS AND RESULTS: The study included 677 patients undergoing coronary artery bypass graft surgery. Endothelial function was evaluated by flow-mediated dilation of the brachial artery in vivo and by vasomotor studies in saphenous vein segments ex vivo. Vascular superoxide (O2(-)) and endothelial nitric oxide synthase (eNOS) uncoupling were quantified in saphenous vein and internal mammary artery segments. Local adiponectin gene expression and ex vivo release were quantified in perivascular (saphenous vein and internal mammary artery) subcutaneous and mesothoracic adipose tissue from 248 patients. Circulating adiponectin was independently associated with nitric oxide bioavailability and O2(-) production/eNOS uncoupling in both arteries and veins. These findings were supported by a similar association between functional polymorphisms in the adiponectin gene and vascular redox state. In contrast, local adiponectin gene expression/release in perivascular adipose tissue was positively correlated with O2(-) and eNOS uncoupling in the underlying vessels. In ex vivo experiments with human saphenous veins and internal mammary arteries, adiponectin induced Akt-mediated eNOS phosphorylation and increased tetrahydrobiopterin bioavailability, improving eNOS coupling. In ex vivo experiments with human saphenous veins/internal mammary arteries and adipose tissue, we demonstrated that peroxidation products produced in the vascular wall (ie, 4-hydroxynonenal) upregulate adiponectin gene expression in perivascular adipose tissue via a peroxisome proliferator-activated receptor-γ-dependent mechanism. CONCLUSIONS: We demonstrate for the first time that adiponectin improves the redox state in human vessels by restoring eNOS coupling, and we identify a novel role of vascular oxidative stress in the regulation of adiponectin expression in human perivascular adipose tissue.

Shabeeh H, Melikian N, Dworakowski R, Casadei B, Chowienczyk P, Shah AM. 2013. Differential role of endothelial versus neuronal nitric oxide synthase in the regulation of coronary blood flow during pacing-induced increases in cardiac workload. Am J Physiol Heart Circ Physiol, 304 (9), pp. H1277-H1282. | Show Abstract | Read more

Endothelial nitric oxide synthase (eNOS) was assumed to be the only source of nitric oxide (NO) involved in the regulation of human coronary blood flow (CBF). However, our recent first-in-human study using the neuronal NOS (nNOS)-selective inhibitor S-methyl-L-thiocitrulline (SMTC) showed that nNOS-derived NO also plays a role. In this study, we investigated the relative contribution of nNOS and eNOS to the CBF response to a pacing-induced increase in cardiac workload. Incremental right atrial pacing was undertaken in patients with angiographically normal coronary arteries during intracoronary infusion of saline vehicle and then either SMTC or N(G)-monomethyl-l-arginine (l-NMMA; which inhibits both eNOS and nNOS). Intracoronary SMTC (0.625 μmol/min) and l-NMMA (25 μmol/min) reduced basal CBF to a similar extent (-19.2 ± 3.2% and 25.0 ± 2.7%, respectively; n = 10 per group). Pacing-induced increases in CBF were significantly blunted by l-NMMA (maximum CBF: 83.5 ± 14.2 ml/min during saline vs. 61.6 ± 9.5 ml/min during l-NMMA; P < 0.01). By contrast, intracoronary SMTC had no effect on the maximum CBF during pacing (98.5 ± 12.9 ml/min during saline vs. 102.1 ± 16.6 ml/min during SMTC; P = not significant). l-NMMA also blunted the pacing-induced increase in coronary artery diameter (P < 0.001 vs. saline), whereas SMTC had no effect. Our results confirm a role of nNOS in the regulation of basal CBF in humans but show that coronary vasodilation in response to a pacing-induced increase in cardiac workload is exclusively mediated by eNOS-derived NO.

Shabeeh H, Seddon M, Brett S, Melikian N, Casadei B, Shah AM, Chowienczyk P. 2013. Sympathetic activation increases NO release from eNOS but neither eNOS nor nNOS play an essential role in exercise hyperemia in the human forearm. Am J Physiol Heart Circ Physiol, 304 (9), pp. H1225-H1230. | Show Abstract | Read more

Nitric oxide (NO) release from endothelial NO synthase (eNOS) and/or neuronal NO synthase (nNOS) could be modulated by sympathetic nerve activity and contribute to increased blood flow after exercise. We examined the effects of brachial-arterial infusion of the nNOS selective inhibitor S-methyl-l-thiocitrulline (SMTC) and the nonselective NOS inhibitor N(G)-monomethyl-l-arginine (l-NMMA) on forearm arm blood flow at rest, during sympathetic activation by lower body negative pressure, and during lower body negative pressure immediately after handgrip exercise. Reduction in forearm blood flow by lower body negative pressure during infusion of SMTC was not significantly different from that during vehicle (-28.5 ± 4.02 vs. -34.1 ± 2.96%, respectively; P = 0.32; n = 8). However, l-NMMA augmented the reduction in forearm blood flow by lower body negative pressure (-44.2 ± 3.53 vs. -23.4 ± 5.71%; n = 8; P < 0.01). When lower body negative pressure was continued after handgrip exercise, there was no significant effect of either l-NMMA or SMTC on forearm blood flow immediately after low-intensity exercise (P = 0.91 and P = 0.44 for l-NMMA vs. saline and SMTC vs. saline, respectively; each n = 10) or high-intensity exercise (P = 0.46 and P = 0.68 for l-NMMA vs. saline and SMTC vs. saline, respectively; each n = 10). These results suggest that sympathetic activation increases NO release from eNOS, attenuating vasoconstriction. Dysfunction of eNOS could augment vasoconstrictor and blood pressure responses to sympathetic activation. However, neither eNOS nor nNOS plays an essential role in postexercise hyperaemia, even in the presence of increased sympathetic activation.

Shabeeh H, Khan S, Jiang B, Melikian N, Brett S, Casadei B, Chowienczyk P, Shah AM. 2012. First-In-Man Study of the Effects of Neuronal Nitric Oxide Synthase on Systemic Haemodynamics CIRCULATION, 126 (21),

Margaritis M, Antonopoulos A, Reilly S, Sayeed R, Petrou M, De Silva R, Bakogiannis C, Casadei B, Channon KM, Antoniades C. 2012. Adiponectin Improves Endothelial Redox State in Human Atherosclerosis by Phosphorylating eNOS and Improving Its Enzymatic Coupling CIRCULATION, 126 (21),

Idigo WO, Reilly S, Zhang MH, Zhang YH, Jayaram R, Carnicer R, Crabtree MJ, Balligand JL, Casadei B. 2012. Regulation of endothelial nitric-oxide synthase (NOS) S-glutathionylation by neuronal NOS: evidence of a functional interaction between myocardial constitutive NOS isoforms. J Biol Chem, 287 (52), pp. 43665-43673. | Show Abstract | Read more

Myocardial constitutive No production depends on the activity of both endothelial and neuronal NOS (eNOS and nNOS, respectively). Stimulation of myocardial β(3)-adrenergic receptor (β(3)-AR) produces a negative inotropic effect that is dependent on eNOS. We evaluated whether nNOS also plays a role in β(3)-AR signaling and found that the β(3)-AR-mediated reduction in cell shortening and [Ca(2+)](i) transient amplitude was abolished both in eNOS(-/-) and nNOS(-/-) left ventricular (LV) myocytes and in wild type LV myocytes after nNOS inhibition with S-methyl-L-thiocitrulline. LV superoxide (O(2)(·-)) production was increased in nNOS(-/-) mice and reduced by L-N(ω)-nitroarginine methyl ester (L-NAME), indicating uncoupling of eNOS activity. eNOS S-glutathionylation and Ser-1177 phosphorylation were significantly increased in nNOS(-/-) myocytes, whereas myocardial tetrahydrobiopterin, eNOS Thr-495 phosphorylation, and arginase activity did not differ between genotypes. Although inhibitors of xanthine oxidoreductase (XOR) or NOX2 NADPH oxidase caused a similar reduction in myocardial O(2)(·-), only XOR inhibition reduced eNOS S-glutathionylation and Ser-1177 phosphorylation and restored both eNOS coupled activity and the negative inotropic and [Ca(2+)](i) transient response to β(3)-AR stimulation in nNOS(-/-) mice. In summary, our data show that increased O(2)(·-) production by XOR selectively uncouples eNOS activity and abolishes the negative inotropic effect of β(3)-AR stimulation in nNOS(-/-) myocytes. These findings provide unequivocal evidence of a functional interaction between the myocardial constitutive NOS isoforms and indicate that aspects of the myocardial phenotype of nNOS(-/-) mice result from disruption of eNOS signaling.

Carnicer R, Hale AB, Suffredini S, Liu X, Reilly S, Zhang MH, Surdo NC, Bendall JK, Crabtree MJ, Lim GB et al. 2012. Cardiomyocyte GTP cyclohydrolase 1 and tetrahydrobiopterin increase NOS1 activity and accelerate myocardial relaxation. Circ Res, 111 (6), pp. 718-727. | Show Abstract | Read more

RATIONALE: Tetrahydrobiopterin (BH4) is an essential cofactor of nitric oxide synthases (NOS). Oral BH4 supplementation preserves cardiac function in animal models of cardiac disease; however, the mechanisms underlying these findings are not completely understood. OBJECTIVE: To study the effect of myocardial transgenic overexpression of the rate-limiting enzyme in BH4 biosynthesis, GTP cyclohydrolase 1 (GCH1), on NOS activity, myocardial function, and Ca2+ handling. METHODS AND RESULTS: GCH1overexpression significantly increased the biopterins level in left ventricular (LV) myocytes but not in the nonmyocyte component of the LV myocardium or in plasma. The ratio between BH4 and its oxidized products was lower in mGCH1-Tg, indicating that a large proportion of the myocardial biopterin pool was oxidized; nevertheless, myocardial NOS1 activity was increased in mGCH1-Tg, and superoxide release was significantly reduced. Isolated hearts and field-stimulated LV myocytes (3 Hz, 35°C) overexpressing GCH1 showed a faster relaxation and a PKA-mediated increase in the PLB Ser16 phosphorylated fraction and in the rate of decay of the [Ca2+]i transient. RyR2 S-nitrosylation and diastolic Ca2+ leak were larger in mGCH1-Tg and ICa density was lower; nevertheless the amplitude of the [Ca2+]i transient and contraction did not differ between genotypes, because of an increase in the SR fractional release of Ca2+ in mGCH1-Tg myocytes. Xanthine oxidoreductase inhibition abolished the difference in superoxide production but did not affect myocardial function in either group. By contrast, NOS1 inhibition abolished the differences in ICa density, Ser16 PLB phosphorylation, [Ca2+]i decay, and myocardial relaxation between genotypes. CONCLUSIONS: Myocardial GCH1 activity and intracellular BH4 are a limiting factor for constitutive NOS1 and SERCA2A activity in the healthy myocardium. Our findings suggest that GCH1 may be a valuable target for the treatment of LV diastolic dysfunction.

Adlam D, Herring N, Douglas G, De Bono JP, Li D, Danson EJ, Tatham A, Lu CJ, Jennings KA, Cragg SJ et al. 2012. Regulation of β-adrenergic control of heart rate by GTP-cyclohydrolase 1 (GCH1) and tetrahydrobiopterin. Cardiovasc Res, 93 (4), pp. 694-701. | Show Abstract | Read more

AIMS: Clinical markers of cardiac autonomic function, such as heart rate and response to exercise, are important predictors of cardiovascular risk. Tetrahydrobiopterin (BH4) is a required cofactor for enzymes with roles in cardiac autonomic function, including tyrosine hydroxylase and nitric oxide synthase. Synthesis of BH4 is regulated by GTP cyclohydrolase I (GTPCH), encoded by GCH1. Recent clinical studies report associations between GCH1 variants and increased heart rate, but the mechanistic importance of GCH1 and BH4 in autonomic function remains unclear. We investigate the effect of BH4 deficiency on the autonomic regulation of heart rate in the hph-1 mouse model of BH4 deficiency. METHODS AND RESULTS: In the hph-1 mouse, reduced cardiac GCH1 expression, GTPCH enzymatic activity, and BH4 were associated with increased resting heart rate; blood pressure was not different. Exercise training decreased resting heart rate, but hph-1 mice retained a relative tachycardia. Vagal nerve stimulation in vitro induced bradycardia equally in hph-1 and wild-type mice both before and after exercise training. Direct atrial responses to carbamylcholine were equal. In contrast, propranolol treatment normalized the resting tachycardia in vivo. Stellate ganglion stimulation and isoproterenol but not forskolin application in vitro induced a greater tachycardic response in hph-1 mice. β1-adrenoceptor protein was increased as was the cAMP response to isoproterenol stimulation. CONCLUSION: Reduced GCH1 expression and BH4 deficiency cause tachycardia through enhanced β-adrenergic sensitivity, with no effect on vagal function. GCH1 expression and BH4 are novel determinants of cardiac autonomic regulation that may have important roles in cardiovascular pathophysiology.

Antoniades C, Demosthenous M, Reilly S, Margaritis M, Zhang MH, Antonopoulos A, Marinou K, Nahar K, Jayaram R, Tousoulis D et al. 2012. Myocardial redox state predicts in-hospital clinical outcome after cardiac surgery effects of short-term pre-operative statin treatment. J Am Coll Cardiol, 59 (1), pp. 60-70. | Show Abstract | Read more

OBJECTIVES: The purpose of this study was to evaluate the role of the myocardial redox state in the development of in-hospital complications after cardiac surgery and the effect of statins on the myocardial redox state. BACKGROUND: Statins improve clinical outcome after cardiac surgery, but it is unclear whether they exert their effects by modifying the myocardial redox state. METHODS: We quantified myocardial superoxide anion (O(2)(-)) and peroxynitrite (ONOO(-)) and their enzymatic sources in samples of the right atrial appendage (RAA) from 303 patients undergoing cardiac surgery who were followed up until discharge, and in 42 patients who were randomized to receive 3-day treatment with atorvastatin 40 mg/d or placebo before surgery. The mechanisms by which atorvastatin modifies myocardial redox state were investigated in 26 RAA samples that were exposed to atorvastatin ex vivo. RESULTS: Atrial O(2)(-) (derived mainly from nicotinamide adenine dinucleotide phosphate [NADPH] oxidases) and ONOO(-) were independently associated with increased risk of atrial fibrillation, the need for post-operative inotropic support, and the length of hospital stay. Pre-operative atorvastatin treatment suppressed atrial NADPH oxidase activity and myocardial O(2)(-) and ONOO(-) production. Ex vivo incubation of RAA samples with atorvastatin induced a mevalonate-reversible and Rac1-mediated inhibition of NADPH oxidase. CONCLUSIONS: There is a strong independent association between myocardial O(2)(-)/ONOO(-) and in-hospital complications after cardiac surgery. Both myocardial O(2)(-) and ONOO(-) are reduced by pre-operative statin treatment, through a Rac1-mediated suppression of NADPH oxidase activity. These findings suggest that inhibition of myocardial NADPH oxidases may contribute to the beneficial effect of statins in patients undergoing cardiac surgery. (Effects of Atorvastatin on Endothelial Function, Vascular and Myocardial Redox State in High Cardiovascular Risk Patients; NCT01013103).

Cited:

39

Scopus

Oliveira SM, Zhang YH, Solis RS, Isackson H, Bellahcene M, Yavari A, Pinter K, Davies JK, Ge Y, Ashrafian H et al. 2012. AMP-Activated protein kinase phosphorylates cardiac troponin i and alters contractility of murine ventricular myocytes Circulation Research, 110 (9), pp. 1192-1201. | Show Abstract | Read more

Rationale: AMP-activated protein kinase (AMPK) is an important regulator of energy balance and signaling in the heart. Mutations affecting the regulatory γ2 subunit have been shown to cause an essentially cardiac-restricted phenotype of hypertrophy and conduction disease, suggesting a specific role for this subunit in the heart. Objective: The γ isoforms are highly conserved at their C-termini but have unique N-terminal sequences, and we hypothesized that the N-terminus of γ2 may be involved in conferring substrate specificity or in determining intracellular localization. Methods and Results: A yeast 2-hybrid screen of a human heart cDNA library using the N-terminal 273 residues of γ2 as bait identified cardiac troponin I (cTnI) as a putative interactor. In vitro studies showed that cTnI is a good AMPK substrate and that Ser150 is the principal residue phosphorylated. Furthermore, on AMPK activation during ischemia, Ser150 is phosphorylated in whole hearts. Using phosphomimics, measurements of actomyosin ATPase in vitro and force generation in demembraneated trabeculae showed that modification at Ser150 resulted in increased Ca sensitivity of contractile regulation. Treatment of cardiomyocytes with the AMPK activator 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) resulted in increased myocyte contractility without changing the amplitude of Ca transient and prolonged relaxation despite shortening the time constant of Ca transient decay (tau). Compound C prevented the effect of AICAR on myocyte function. These results suggest that AMPK activation increases myocyte contraction and prolongs relaxation by increasing myofilament Ca sensitivity. Conclusions: We conclude that cTnI phosphorylation by AMPK may represent a novel mechanism of regulation of cardiac function. © 2012 American Heart Association, Inc.

Cited:

46

Scopus

Zhang YH, Casadei B. 2012. Sub-cellular targeting of constitutive NOS in health and disease Journal of Molecular and Cellular Cardiology, 52 (2), pp. 341-350. | Show Abstract | Read more

Constitutive nitric oxide synthases (NOSs) are ubiquitous enzymes that play a pivotal role in the regulation of myocardial function in health and disease. The discovery of both a neuronal NOS (nNOS) and an endothelial NOS (eNOS) isoform in the myocardium and the availability of genetically modified mice with selective eNOS or nNOS gene deletion have been of crucial importance for understanding the role of constitutive nitric oxide (NO) production in the myocardium. eNOS and nNOS are homologous in structure and utilize the same co-factors and substrates; however, they differ in their subcellular localization, regulation, and downstream signaling, all of which may account for their distinct effects on excitation-contraction coupling. In particular, eNOS-derived NO has been reported to increase left ventricular (LV) compliance, attenuate beta-adrenergic inotropy and enhance parasympathetic/muscarinic responses, and mediate the negative inotropic response to β3 adrenoreceptor stimulation via cGMP-dependent signaling. Conversely, nNOS-derived NO regulates basal myocardial inotropy and relaxation by inhibiting the sarcolemmal Ca 2+ current (I Ca ) and promoting protein kinase A-dependent phospholamban (PLN) phosphorylation, independent of cGMP. By inhibiting the activity of myocardial oxidase systems, nNOS regulates the redox state of the myocardium and contributes to maintain eNOS "coupled" activity. After myocardial infarction, up-regulation of myocardial nNOS attenuates adverse remodeling and prevents arrhythmias whereas uncoupled eNOS activity in murine models of left ventricular pressure overload accelerates the progress towards heart failure. Here we review the evidence in support of the idea that NOS subcellular localization, mode of a ctivation, and downstream signaling account for the diverse and highly specialized actions of NO in the heart. This article is part of a Special Issue entitled "Local Signaling in Myocytes". © 2011 Elsevier Ltd.

Demosthenous M, Antoniades C, Reilly S, Margaritis M, Jayaram R, Tousoulis D, Antonopoulos AS, Channon KM, Stefanadis C, Casadei B. 2011. Myocardial Redox State Predicts Post-Operative Atrial Fibrillation in Cardiac Surgery CIRCULATION, 124 (21),

Margaritis M, Antoniades C, Tousoulis D, Demosthenous M, Antonopoulos AS, Bakogiannis C, Lymperiadis D, Psarros C, Casadei B, Stefanadis C. 2011. Systemic Lipid Peroxydation and Myocardial Superoxide/Peroxynitrite Anions as Predictors of Post-Operative Outcome in Cardiac Surgery CIRCULATION, 124 (21),

Zhang YH, Casadei B. 2012. Sub-cellular targeting of constitutive NOS in health and disease. J Mol Cell Cardiol, 52 (2), pp. 341-350. | Show Abstract | Read more

Constitutive nitric oxide synthases (NOSs) are ubiquitous enzymes that play a pivotal role in the regulation of myocardial function in health and disease. The discovery of both a neuronal NOS (nNOS) and an endothelial NOS (eNOS) isoform in the myocardium and the availability of genetically modified mice with selective eNOS or nNOS gene deletion have been of crucial importance for understanding the role of constitutive nitric oxide (NO) production in the myocardium. eNOS and nNOS are homologous in structure and utilize the same co-factors and substrates; however, they differ in their subcellular localization, regulation, and downstream signaling, all of which may account for their distinct effects on excitation-contraction coupling. In particular, eNOS-derived NO has been reported to increase left ventricular (LV) compliance, attenuate beta-adrenergic inotropy and enhance parasympathetic/muscarinic responses, and mediate the negative inotropic response to β3 adrenoreceptor stimulation via cGMP-dependent signaling. Conversely, nNOS-derived NO regulates basal myocardial inotropy and relaxation by inhibiting the sarcolemmal Ca(2+) current (I(Ca)) and promoting protein kinase A-dependent phospholamban (PLN) phosphorylation, independent of cGMP. By inhibiting the activity of myocardial oxidase systems, nNOS regulates the redox state of the myocardium and contributes to maintain eNOS "coupled" activity. After myocardial infarction, up-regulation of myocardial nNOS attenuates adverse remodeling and prevents arrhythmias whereas uncoupled eNOS activity in murine models of left ventricular pressure overload accelerates the progress towards heart failure. Here we review the evidence in support of the idea that NOS subcellular localization, mode of activation, and downstream signaling account for the diverse and highly specialized actions of NO in the heart. This article is part of a Special Issue entitled "Local Signaling in Myocytes".

Cited:

105

Scopus

Reilly SN, Jayaram R, Nahar K, Antoniades C, Verheule S, Channon KM, Alp NJ, Schotten U, Casadei B. 2011. Atrial Sources of Reactive Oxygen Species Vary With the Duration and Substrate of Atrial Fibrillation Implications for the Antiarrhythmic Effect of Statins CIRCULATION, 124 (10), pp. 1107-1U91. | Show Abstract | Read more

BACKGROUND-: An altered nitric oxide-redox balance has been implicated in the pathogenesis of atrial fibrillation (AF). Statins inhibit NOX2-NADPH oxidases and prevent postoperative AF but are less effective in AF secondary prevention; the mechanisms underlying these findings are poorly understood. METHODS AND RESULTS-: By using goat models of pacing-induced AF or of atrial structural remodeling secondary to atrioventricular block and right atrial samples from 130 patients undergoing cardiac surgery, we found that the mechanisms responsible for the NO-redox imbalance differ between atria and with the duration and substrate of AF. Rac1 and NADPH oxidase activity and the protein level of NOX2 and p22phox were significantly increased in the left atrium of goats after 2 weeks of AF and in patients who developed p ostoperative AF in the absence of differences in leukocytes infiltration. Conversely, in the presence of longstanding AF or atrioventricular block, uncoupled nitric oxide synthase activity (secondary to reduced BH4 content and/or increased arginase activity) and mitochondrial oxidases accounted for the biatrial increase in reactive oxygen species. Atorvastatin caused a mevalonate-reversible inhibition of Rac1 and NOX2-NADPH oxidase activity in right atrial samples from patients who developed postoperative AF, but it did not affect reactive oxygen species, nitric oxide synthase uncoupling, or BH4 in patients with permanent AF. CONCLUSIONS-: Upregulation of atrial NADPH oxidases is an early but transient event in the natural history of AF. Changes in the sources of reactive oxygen species with atrial remodeling may explain why statins are effective in the primary prevention of AF but not in its management. © 2011 American Heart Association, Inc.

Reilly SN, Jayaram R, Nahar K, Antoniades C, Verheule S, Channon KM, Alp NJ, Schotten U, Casadei B. 2011. Atrial sources of reactive oxygen species vary with the duration and substrate of atrial fibrillation: implications for the antiarrhythmic effect of statins. Circulation, 124 (10), pp. 1107-1117. | Show Abstract | Read more

BACKGROUND: An altered nitric oxide-redox balance has been implicated in the pathogenesis of atrial fibrillation (AF). Statins inhibit NOX2-NADPH oxidases and prevent postoperative AF but are less effective in AF secondary prevention; the mechanisms underlying these findings are poorly understood. METHODS AND RESULTS: By using goat models of pacing-induced AF or of atrial structural remodeling secondary to atrioventricular block and right atrial samples from 130 patients undergoing cardiac surgery, we found that the mechanisms responsible for the NO-redox imbalance differ between atria and with the duration and substrate of AF. Rac1 and NADPH oxidase activity and the protein level of NOX2 and p22phox were significantly increased in the left atrium of goats after 2 weeks of AF and in patients who developed postoperative AF in the absence of differences in leukocytes infiltration. Conversely, in the presence of longstanding AF or atrioventricular block, uncoupled nitric oxide synthase activity (secondary to reduced BH4 content and/or increased arginase activity) and mitochondrial oxidases accounted for the biatrial increase in reactive oxygen species. Atorvastatin caused a mevalonate-reversible inhibition of Rac1 and NOX2-NADPH oxidase activity in right atrial samples from patients who developed postoperative AF, but it did not affect reactive oxygen species, nitric oxide synthase uncoupling, or BH4 in patients with permanent AF. CONCLUSIONS: Upregulation of atrial NADPH oxidases is an early but transient event in the natural history of AF. Changes in the sources of reactive oxygen species with atrial remodeling may explain why statins are effective in the primary prevention of AF but not in its management.

Adlam D, De Bono JP, Danson EJ, Zhang MH, Casadei B, Paterson DJ, Channon KM. 2011. Telemetric analysis of haemodynamic regulation during voluntary exercise training in mouse models. Exp Physiol, 96 (11), pp. 1118-1128. | Show Abstract | Read more

Regular physical exercise reduces the risk of cardiovascular disease and improves outcome in patients with cardiovascular diseases. The dynamic changes in blood pressure and heart rate with acute exercise are independently predictive of prognosis. Quantification of the haemodynamic response to exercise training in genetically modified mouse models may provide insight into the molecular mechanisms underlying the beneficial effects of exercise. We describe, for the first time, the use of radiotelemetry to provide continuous blood pressure monitoring in C57BL/6J mice during a programme of voluntary wheel exercise with continuous simultaneous recording and analysis of wheel rotations and beat-by-beat haemodynamic parameters. We define distinct haemodynamic profiles at rest, during normal cage activity and during episodes of voluntary wheel running. We show that whilst cage activity is associated with significant rises both in blood pressure and in heart rate, voluntary wheel running leads to a further substantial rise in heart rate with only a small increment in blood pressure. With 5 weeks of chronic exercise training, resting heart rate progressively falls, but heart rate during episodes of wheel running initially increases. In contrast, there are minimal changes in blood pressure in response to chronic exercise training. Finally, we have quantified the acute changes in heart rate at the onset of and recovery from individual episodes of wheel running, revealing that changes in heart rate are extremely rapid and that the peak rate of change of heart rate increases with chronic exercise training. The results of this study have important implications for the use of genetically modified mouse models to investigate the beneficial haemodynamic effects of chronic exercise on blood pressure and cardiovascular diseases.

Margaritis M, Antoniades C, Tousoulis D, Demosthenous M, Antonopoulos AS, Bakogiannis C, Triantafillou C, Psarros C, Casadei B, Stefanadis C. 2011. Systemic and local myocardial redox state as predictors of post-operative outcome in patients undergoing coronary artery bypass grafting EUROPEAN HEART JOURNAL, 32 pp. 383-383.

Reilly S, Jayaram R, Nahar K, Antoniades C, Verheule S, Channon K, Alp N, Schotten U, Casadei B. 2011. Atrial sources of reactive oxygen species vary with the duration and substrate of atrial fibrillation: implications for the antiarrhythmic effect of statins EUROPEAN HEART JOURNAL, 32 pp. 942-942.

Kim YM, Sachedina A, Singh MH, Ray S, Zhang L, Ruiz-Lozano P, Verma S, Casadei B, Ashley EA, Backx PH. 2011. Modulation of atrial electrophysiology and oxidative stress by the endogenous peptide hormone apelin: implications in human atrial fibrillation EUROPEAN HEART JOURNAL, 32 pp. 941-942.

Carnicer R, Hale AB, Liu X, Bendall JK, Lim GBS, Alp NJ, Channon KM, Casadei B. 2011. Cardiomyocyte-targeted overexpression of GTP cyclohydrolase-1 increases nNOS activity and hastens myocardial relaxation EUROPEAN HEART JOURNAL, 32 pp. 154-154.

Antoniades C, Demosthenous M, Reilly S, Margaritis M, Jayaram R, Nahar K, Tousoulis D, Stefanadis C, Channon KM, Casadei B. 2011. Atorvastatin rapidly reduces myocardial superoxide and peroxynitrite generation in human atherosclerosis, by suppressing NADPH-oxidase activity independently of LDL lowering EUROPEAN HEART JOURNAL, 32 pp. 76-76.

Demosthenous M, Antoniades C, Tousoulis D, Margaritis M, Reilly S, Jayaram R, Antonopoulos AS, Channon KM, Stefanadis C, Casadei B. 2011. Myocardial superoxide and peroxynitrite as strong independent predictors of paroxysmal atrial fibrillation post-CABG EUROPEAN HEART JOURNAL, 32 pp. 470-471.

Antoniades C, Bakogiannis C, Leeson P, Guzik TJ, Zhang MH, Tousoulis D, Antonopoulos AS, Demosthenous M, Marinou K, Hale A et al. 2011. Rapid, direct effects of statin treatment on arterial redox state and nitric oxide bioavailability in human atherosclerosis via tetrahydrobiopterin-mediated endothelial nitric oxide synthase coupling. Circulation, 124 (3), pp. 335-345. | Show Abstract | Read more

BACKGROUND: Treatment with statins improves clinical outcome, but the exact mechanisms of pleiotropic statin effects on vascular function in human atherosclerosis remain unclear. We examined the direct effects of atorvastatin on tetrahydrobiopterin-mediated endothelial nitric oxide (NO) synthase coupling in patients with coronary artery disease. METHODS AND RESULTS: We first examined the association of statin treatment with vascular NO bioavailability and arterial superoxide (O(2)(·-)) in 492 patients undergoing coronary artery bypass graft surgery. Then, 42 statin-naïve patients undergoing elective coronary artery bypass graft surgery were randomized to atorvastatin 40 mg/d or placebo for 3 days before surgery to examine the impact of atorvastatin on endothelial function and O(2)(·-) generation in internal mammary arteries. Finally, segments of internal mammary arteries from 26 patients were used in ex vivo experiments to evaluate the statin-dependent mechanisms regulating the vascular redox state. Statin treatment was associated with improved vascular NO bioavailability and reduced O(2)(·-) generation in internal mammary arteries. Oral atorvastatin increased vascular tetrahydrobiopterin bioavailability and reduced basal and N-nitro-l-arginine methyl ester-inhibitable O(2)(·-) in internal mammary arteries independently of low-density lipoprotein lowering. In ex vivo experiments, atorvastatin rapidly improved vascular tetrahydrobiopterin bioavailability by upregulating GTP-cyclohydrolase I gene expression and activity, resulting in improved endothelial NO synthase coupling and reduced vascular O(2)(·-). These effects were reversed by mevalonate, indicating a direct effect of vascular hydroxymethylglutaryl-coenzyme A reductase inhibition. CONCLUSIONS: This study demonstrates for the first time in humans the direct effects of statin treatment on the vascular wall, supporting the notion that this effect is independent of low-density lipoprotein lowering. Atorvastatin directly improves vascular NO bioavailability and reduces vascular O(2)(·-) through tetrahydrobiopterin-mediated endothelial NO synthase coupling. These findings provide new insights into the mechanisms mediating the beneficial vascular effects of statins in humans. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01013103.

Adlam D, De Bono JP, Danson EJ, Zhang MH, Casadei B, Paterson DJ, Channon KM. 2011. Telemetric analysis of haemodynamic regulation during voluntary exercise training in mouse models Experimental Physiology, 96 (11), pp. 1118-1128. | Show Abstract | Read more

Regular physical exercise reduces the risk of cardiovascular disease and improves outcome in patients with cardiovascular diseases. The dynamic changes in blood pressure and heart rate with acute exercise are independently predictive of prognosis. Quantification of the haemodynamic response to exercise training in genetically modified mouse models may provide insight into the molecular mechanisms underlying the beneficial effects of exercise. We describe, for the first time, the use of radiotelemetry to provide continuous blood pressure monitoring in C57BL/6J mice during a programme of voluntary wheel exercise with continuous simultaneous recording and analysis of wheel rotations and beat-by-beat haemodynamic parameters. We define distinct haemodynamic profiles at rest, during normal cage activity and during episodes of voluntary wheel running. We show that whilst cage activity is associated with significant rises both in blood pressure and in heart rate, voluntary wheel running leads to a further substantial rise in heart rate with only a small increment in blood pressure. With 5 weeks of chronic exercise training, resting heart rate progressively falls, but heart rate during episodes of wheel running initially increases. In contrast, there are minimal changes in blood pressure in response to chronic exercise training. Finally, we have quantified the acute changes in heart rate at the onset of and recovery from individual episodes of wheel running, revealing that changes in heart rate are extremely rapid and that the peak rate of change of heart rate increases with chronic exercise training. The results of this study have important implications for the use of genetically modified mouse models to investigate the beneficial haemodynamic effects of chronic exercise on blood pressure and cardiovascular diseases. © 2011 The Physiological Society.

Cited:

117

Scopus

Antoniades C, Bakogiannis C, Leeson P, Guzik TJ, Zhang MH, Tousoulis D, Antonopoulos AS, Demosthenous M, Marinou K, Hale A et al. 2011. Rapid, direct effects of statin treatment on arterial redox state and nitric oxide bioavailability in human atherosclerosis via tetrahydrobiopterin- mediated endothelial nitric oxide synthase coupling Circulation, 124 (3), pp. 335-345. | Show Abstract | Read more

Background-: Treatment with statins improves clinical outcome, but the exact mechanisms of pleiotropic statin effects on vascular function in human atherosclerosis remain unclear. We examined the direct effects of atorvastatin on tetrahydrobiopterin-mediated endothelial nitric oxide (NO) synthase coupling in patients with coronary artery disease. Methods and Results-: We first examined the association of statin treatment with vascular NO bioavailability and arterial superoxide (O 2 .- ) in 492 patients undergoing coronary artery bypass graft surgery. Then, 42 statin-naïve patients undergoing elective coronary artery bypass graft surgery were randomized to atorvastatin 40 mg/d or placebo for 3 days before surgery to examine the impact of atorvastatin on endothelial function and O 2 .- generation in internal mammary arteries. Finally, segments of internal mammary arteries from 26 patients were used in ex vivo experiments to evaluate the statin-dependent mechanisms regulating the vascular redox state. Statin treatment was associated with improved vascular NO bioavailability and reduced O 2 .- generation in internal mammary arteries. Oral atorvastatin increased vascular tetrahydrobiopterin bioavailability and reduced basal and N-nitro-L-arginine methyl ester-inhibitable O 2 .- in internal mammary arteries independently of low-density lipoprotein lowering. In ex vivo experiments, atorvastatin rapidly improved vascular tetrahydrobiopterin bioavailability by upregulating GTP-cyclohydrolase I gene expression and activity, resulting in improved endothelial NO synthase coupling and reduced vascular O 2 .- . These effects were reversed by mevalonate, indicating a direct effect of vascular hydroxymethylglutaryl- coenzyme A reductase inhibition. Conclusions-: This study demonstrates for the first time in humans the direct effects of statin treatment on the vascular wall, supporting the notion that this effect is independent of low-density lipoprotein lowering. Atorvastatin directly improves vascular NO bioavailability and reduces vascular O 2 .- through tetrahydrobiopterin- mediated endothelial NO synthase coupling. These findings provide new insights into the mechanisms mediating the beneficial vascular effects of statins in humans. Clinical Trial Registration-: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01013103. © 2011 American Heart Association, Inc.

Antoniades C, Demosthenous M, Tousoulis D, Margaritis M, Antonopoulos A, Bakogiannis C, Triantafillou C, Channon KM, Casadei B, Stefanadis C. 2010. Myocardial Redox State Predicts Post-Operative Clinical Outcome in Patients Undergoing Elective CABG: The Role of NADPH-Oxidase and Uncoupled Nitric Oxide Synthase CIRCULATION, 122 (21),

Zhang Y-H, Zhang M-H, Redwood C, Casadei B. 2010. Attenuated Subsarcolemmal Protein Phosphatase 2A Activity is Responsible for the Enhanced L-Type Ca Channel Phosphorylation and Contraction in nNOS(-/-) Mice CIRCULATION, 122 (21),

Carnicer R, Hale AB, Liu X, Lim GB, Alp NJ, Channon KM, Casadei B. 2010. Cardiomyocyte-Targeted Overexpression of GTP Cyclohydrolase-1 Increases Myocyte Lusitropy and Reduces Superoxide Production CIRCULATION, 122 (21),

Antoniades C, Bakogiannis C, Tousoulis D, Reilly S, Zhang MH, Paschalis A, Antonopoulos AS, Demosthenous M, Miliou A, Psarros C et al. 2010. Preoperative atorvastatin treatment in CABG patients rapidly improves vein graft redox state by inhibition of Rac1 and NADPH-oxidase activity. Circulation, 122 (11 Suppl), pp. S66-S73. | Show Abstract | Read more

BACKGROUND: Statins improve clinical outcome of patients with atherosclerosis, but their perioperative role in patients undergoing coronary artery bypass grafting (CABG) is unclear. We hypothesized that short-term treatment with atorvastatin before CABG would improve the redox state in saphenous vein grafts (SVGs), independently of low-density lipoprotein cholesterol (LDL)-lowering. METHODS AND RESULTS: In a randomized, double-blind controlled trial, 42 statin-naïve patients undergoing elective CABG received atorvastatin 40 mg/d or placebo for 3 days before surgery. Circulating inflammatory markers and malondialdehyde (MDA) were measured before and after treatment. SVG segments were used to determine vascular superoxide (O(2)(*-)) and Rac1 activation. For ex vivo studies, SVG segments from 24 patients were incubated for 6 hours with atorvastatin 0, 5, or 50 μmol/L. Oral atorvastatin reduced vascular basal and NADPH-stimulated O(2)(*-) in SVGs (P<0.05 for all versus placebo) and reduced plasma MDA (P<0.05), independently of LDL-lowering and of changes in inflammatory markers. In SVGs exposed to atorvastatin ex vivo, without exposure to LDL, basal and NADPH-stimulated O(2)(·-) were significantly reduced (P<0.01 for both concentrations versus 0 μmol/L) in association with a striking reduction in Rac1 activation and 1 membrane-bound Rac1 and p67(phox) subunit. The antioxidant effects of atorvastatin were reversed by mevalonate, implying a dependence on vascular HMG-CoA reductase inhibition. CONCLUSIONS: Short-term treatment with atorvastatin 40 mg/d before CABG improves redox state in SVGs, by inhibiting vascular Rac1-mediated activation of NADPH-oxidase. These novel findings suggest that statin therapy should be maintained or initiated in patients undergoing CABG, independently of LDL levels. Clinical Trial Registration-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01013103.

Adlam D, De Bono JP, Danson E, Tatham A, Casadei B, Paterson DJ, Channon KM. 2010. Regulation of B-Adrenergic control of heart rate by GTP-Cycolhydolase 1 and Tetrahydrobiopterin EUROPEAN HEART JOURNAL, 31 (4), pp. 78-78.

Li L, Niederer SA, Idigo W, Zhang YH, Swietach P, Casadei B, Smith NP. 2010. A mathematical model of the murine ventricular myocyte: a data-driven biophysically based approach applied to mice overexpressing the canine NCX isoform. Am J Physiol Heart Circ Physiol, 299 (4), pp. H1045-H1063. | Show Abstract | Read more

Mathematical modeling of Ca(2+) dynamics in the heart has the potential to provide an integrated understanding of Ca(2+)-handling mechanisms. However, many previous published models used heterogeneous experimental data sources from a variety of animals and temperatures to characterize model parameters and motivate model equations. This methodology limits the direct comparison of these models with any particular experimental data set. To directly address this issue, in this study, we present a biophysically based model of Ca(2+) dynamics directly fitted to experimental data collected in left ventricular myocytes isolated from the C57BL/6 mouse, the most commonly used genetic background for genetically modified mice in studies of heart diseases. This Ca(2+) dynamics model was then integrated into an existing mouse cardiac electrophysiology model, which was reparameterized using experimental data recorded at consistent and physiological temperatures. The model was validated against the experimentally observed frequency response of Ca(2+) dynamics, action potential shape, dependence of action potential duration on cycle length, and electrical restitution. Using this framework, the implications of cardiac Na(+)/Ca(2+) exchanger (NCX) overexpression in transgenic mice were investigated. These simulations showed that heterozygous overexpression of the canine cardiac NCX increases intracellular Ca(2+) concentration transient magnitude and sarcoplasmic reticulum Ca(2+) loading, in agreement with experimental observations, whereas acute overexpression of the murine cardiac NCX results in a significant loss of Ca(2+) from the cell and, hence, depressed sarcoplasmic reticulum Ca(2+) load and intracellular Ca(2+) concentration transient magnitude. From this analysis, we conclude that these differences are primarily due to the presence of allosteric regulation in the canine cardiac NCX, which has not been observed experimentally in the wild-type mouse heart.

Ni J, McLoughlin RM, Brodovitch A, Moulin P, Brouckaert P, Casadei B, Feron O, Topley N, Balligand JL, Devuyst O. 2010. Nitric oxide synthase isoforms play distinct roles during acute peritonitis. Nephrol Dial Transplant, 25 (1), pp. 86-96. | Show Abstract | Read more

BACKGROUND: Acute peritonitis is the most frequent complication of peritoneal dialysis (PD). Increased nitric oxide (NO) release by NO synthase (NOS) isoforms has been implicated in acute peritonitis, but the role played by the NOS isoforms expressed in the peritoneum is unknown. METHODS: We investigated the structural and functional consequences of acute peritonitis induced by LPS in wild-type (WT) mice versus knockout mice (KO) for the endothelial NOS (eNOS), the inducible NOS (iNOS) or the neuronal NOS (nNOS). RESULTS: The level of NO metabolites (NOx) in the dialysate was maximal 18 h after LPS injection. LPS induced a significant increase in the transport of small solutes and decreased ultrafiltration in WT mice. These changes, which occurred without vascular proliferation, were paralleled by the upregulation of nNOS and eNOS, and the induction of iNOS. The transport modifications induced by LPS were significantly reversed in eNOS KO mice, but not modified in mice lacking iNOS or nNOS. In contrast, the increase of dialysate NOx was abolished in iNOS KO mice and significantly reduced in eNOS KO mice, but left unchanged in mice lacking nNOS. Mice lacking iNOS also showed more severe inflammatory changes, and a trend towards increased mortality following LPS. CONCLUSION: These data demonstrate specific roles for NOS isoforms in the peritoneal membrane and suggest that selective eNOS inhibition may improve peritoneal transport during acute peritonitis.

Bax JJ, Casadei B, Di Mario C, Fagard R, Filippatos G, Fox KA, Metra M, Nihoyannopoulos P, Perk J, Rademakers F et al. 2009. Highlights of the 2009 scientific sessions of the European Society of Cardiology. J Am Coll Cardiol, 54 (25), pp. 2447-2458. | Read more

Melikian N, Seddon MD, Casadei B, Chowienczyk PJ, Shah AM. 2009. Neuronal nitric oxide synthase and human vascular regulation. Trends Cardiovasc Med, 19 (8), pp. 256-262. | Show Abstract | Read more

Vascular blood flow and its distribution among different vascular beds are regulated by changes in microvascular tone. Nitric oxide (NO) plays a key role in the local paracrine regulation of vessel tone both under resting conditions and when blood flow increases in response to agonist stimulation or increased shear stress. The conventional notion that endothelial NO synthase (eNOS)-derived NO is largely responsible for both effects has been challenged by first-in-human studies with a selective inhibitor of neuronal NOS (nNOS), S-methyl-l-thiocitrulline (SMTC). These studies reveal that SMTC causes a reduction in basal blood flow in the normal human forearm and coronary circulations (that is reversed by l-arginine), without affecting the eNOS-mediated vasodilatation elicited by acetylcholine, substance P, or increased shear stress. S-methyl-l-thiocitrulline also inhibits mental stress-induced vasodilatation. These results are consistent with a significant body of experimental studies suggesting that nNOS plays an important role in the local regulation of vessel tone in other species, independent of the effects of nNOS-derived NO in the central nervous system. These emerging data suggest that eNOS and nNOS have distinct roles in the physiologic local regulation of human microvascular tone in vivo and pave the way for further detailed investigation of the relative contribution of nNOS and eNOS in vascular regulation in human disease.

Antoniades C, Van-Assche T, Shirodaria C, Diesch J, Antonopoulos AS, Lee J, Cunnington C, Tousoulis D, Stefanadis C, Casadei B et al. 2009. Preoperative sCD40L levels predict risk of atrial fibrillation after off-pump coronary artery bypass graft surgery. Circulation, 120 (11 Suppl), pp. S170-S176. | Show Abstract | Read more

BACKGROUND: The risk of atrial fibrillation (AF) after coronary bypass surgery has been related to redox state, inflammation, and ischemia. Platelet activation is common to all of these pathways. We investigated the relation between AF and preoperative soluble CD40 ligand (sCD40L), a proinflammatory marker released by activated platelets. Furthermore, we studied the role of inflammation, endothelial function, and redox state in this relation. METHODS AND RESULTS: sCD40L levels were measured in 144 patients in sinus rhythm the day before off-pump coronary artery surgery. Systemic inflammation was assessed from levels of C-reactive protein and soluble intercellular adhesion molecule-1, and endothelial function was assessed from the brachial artery flow-mediated dilatation response. Graft samples were collected during surgery to assess vascular redox state. AF occurred in 33% of patients after surgery, with 3% still in AF after 6 weeks. Preoperative sCD40L levels were significantly higher in those who developed in-hospital AF (odds ratio for a 1-SD increase in log[sCD40L]=1.97; 95% CI, 1.21 to 3.22; P=0.007; after adjustment for age, sex, Euroscore, and total duration of operation). sCD40L and vascular superoxide levels were higher in patients still in AF at 6 weeks, and endothelial function was lower, although the small number of events precluded statistical analysis in this group. Systemic endothelial function, redox state, and preoperative markers of systemic inflammation were not associated with in-hospital postoperative AF. CONCLUSIONS: Preoperative platelet activation, as assessed by sCD40L levels, is a novel predictor of postoperative AF, independent of systemic endothelial function, vascular redox state, and systemic inflammation.

Lim GBS, Zhang MH, Zhang YH, Casadei B. 2009. nNOS gene disruption reduces the diastolic calcium leak from the ryanodine receptor: implications for excitation-contraction coupling in heart failure EUROPEAN HEART JOURNAL, 30 pp. 175-176.

Reilly SN, Channon K, Alp NJ, Casadei B. 2009. Molecular mechanisms underlying the myocardial nitric oxide-redox imbalance in human atrial fibrillation EUROPEAN HEART JOURNAL, 30 pp. 824-825.

Sipido KR, Tedgui A, Kristensen SD, Pasterkamp G, Schunkert H, Wehling M, Steg PG, Eisert W, Rademakers F, Casadei B et al. 2009. Identifying needs and opportunities for advancing translational research in cardiovascular disease. Cardiovasc Res, 83 (3), pp. 425-435. | Read more

Zhang YH, Dingle L, Hall R, Casadei B. 2009. The role of nitric oxide and reactive oxygen species in the positive inotropic response to mechanical stretch in the mammalian myocardium. Biochim Biophys Acta, 1787 (7), pp. 811-817. | Show Abstract | Read more

The endothelial nitric oxide synthase (eNOS) has been implicated in the rapid (Frank-Starling) and slow (Anrep) cardiac response to stretch. Our work and that of others have demonstrated that a neuronal nitric oxide synthase (nNOS) localized to the myocardium plays an important role in the regulation of cardiac function and calcium handling. However, the effect of nNOS on the myocardial response to stretch has yet to be investigated. Recent evidence suggests that the stretch-induced release of angiotensin II (Ang II) and endothelin 1 (ET-1) stimulates myocardial superoxide production from NADPH oxidases which, in turn, contributes to the Anrep effect. nNOS has also been shown to regulate the production of myocardial superoxide, suggesting that this isoform may influence the cardiac response to stretch or ET-1 by altering the NO-redox balance in the myocardium. Here we show that the increase in left ventricular (LV) myocyte shortening in response to the application of ET-1 (10 nM, 5 min) did not differ between nNOS(-/-) mice and their wild type littermates (nNOS(+/+)). Pre-incubating LV myocytes with the NADPH oxidase inhibitor, apocynin (100 microM, 30 min), reduced cell shortening in nNOS(-/-) myocytes only but prevented the positive inotropic effects of ET-1 in both groups. Superoxide production (O(2)(-)) was enhanced in nNOS(-/-) myocytes compared to nNOS(+/+); however, this difference was abolished by pre-incubation with apocynin. There was no detectable increase in O(2)(-) production in ET-1 pre-treated LV myocytes. Inhibition of protein kinase C (chelerythrine, 1 microM) did not affect cell shortening in either group, however, protein kinase A inhibitor, PKI (2 microM), significantly reduced the positive inotropic effects of ET-1 in both nNOS(+/+) and nNOS(-/-) myocytes. Taken together, our findings show that the positive inotropic effect of ET-1 in murine LV myocytes is independent of nNOS but requires NADPH oxidases and protein kinase A (PKA)-dependent signaling. These results may further our understanding of the signaling pathways involved in the myocardial inotropic response to stretch.

Seddon M, Melikian N, Dworakowski R, Shabeeh H, Jiang B, Byrne J, Casadei B, Chowienczyk P, Shah AM. 2009. Effects of neuronal nitric oxide synthase on human coronary artery diameter and blood flow in vivo. Circulation, 119 (20), pp. 2656-2662. | Show Abstract | Read more

BACKGROUND: Nitric oxide (NO)-mediated local regulation of vascular tone is considered to involve endothelial NO synthase (eNOS). However, we recently reported that human forearm basal microvascular tone in vivo is tonically regulated by neuronal NO synthase (nNOS), in contrast to an acetylcholine-stimulated reduction in tone, which is eNOS dependent. Here, we investigated the in vivo effects of an nNOS-selective inhibitor, S-methyl-L-thiocitrulline (SMTC), on the human coronary circulation and on flow-mediated dilatation in the forearm. METHODS AND RESULTS: In patients with angiographically normal coronary arteries, intracoronary infusion of SMTC (0.625 micromol/min) reduced basal coronary blood flow by 34.1+/-5.2% (n=10; P<0.01) and epicardial coronary diameter by 3.6+/-1.2% (P=0.02) but had no effect on increases in flow evoked by intracoronary substance P (20 pmol/min). The nonselective NOS inhibitor N(G)-monomethyl-L-arginine (25 micromol/min) also reduced basal coronary flow (by 22.3+/-5.3%; n=8; P<0.01) but, in contrast to SMTC, inhibited substance P-induced increases in flow (P<0.01). In healthy volunteers, local infusion of SMTC (0.2 micromol/min) reduced radial artery blood flow by 36.0+/-6.4% (n=10; P=0.03) but did not affect flow-mediated dilatation (P=0.55). In contrast, N(G)-monomethyl-L-arginine (2 micromol/min) infusion reduced radial blood flow to a similar degree (by 39.7+/-11.8%; P=0.02) but also inhibited flow-mediated dilatation by approximately 80% (P<0.01). CONCLUSIONS: These data indicate that local nNOS-derived NO regulates basal blood flow in the human coronary vascular bed, whereas substance P-stimulated vasodilatation is eNOS mediated. Thus, nNOS and eNOS have distinct local roles in the physiological regulation of human coronary vascular tone in vivo.

Li L, Niederer SA, Idigo WO, Zhang Y, Casadei B, Smith NP. 2009. MODELLING CALCIUM HANDLING MECHANISMS IN NORMAL AND NEURONAL NITRIC OXIDE SYNTHASE KNOCK-OUT MOUSE HEARTS JOURNAL OF PHYSIOLOGICAL SCIENCES, 59 pp. 262-262.

Kristensen SD, Baumgartner H, Casadei B, Drexler H, Eeckhout E, Filippatos G, Fox KA, Perk J, Pierard LA, Poldermans D et al. 2008. Highlights of the 2008 Scientific Sessions of the European Society of Cardiology Munich, Germany, August 30 to September 3, 2008. J Am Coll Cardiol, 52 (24), pp. 2032-2042. | Read more

Kohler M, Pepperell JC, Casadei B, Craig S, Crosthwaite N, Stradling JR, Davies RJ. 2008. CPAP and measures of cardiovascular risk in males with OSAS. Eur Respir J, 32 (6), pp. 1488-1496. | Show Abstract | Read more

Obstructive sleep apnoea syndrome (OSAS) has been associated with hypertension, stroke and myocardial ischaemia in epidemiological and observational studies. Continuous positive airway pressure (CPAP) is the treatment of choice for OSAS, but the impact of this intervention on established risk factors for cardiovascular disease remains incompletely understood. A total of 102 males with moderate-to-severe OSAS were randomised to therapeutic (n = 51) or subtherapeutic (n = 51) CPAP treatment for 4 weeks to investigate the effects of active treatment on 24-h urinary catecholamine excretion, baroreflex sensitivity (BRS), arterial stiffness (augmentation index) and 24-h ambulatory blood pressure (ABP). After 4 weeks of therapeutic CPAP, significant reductions were seen in urine normetanephrine excretion (from mean+/-sd 179.7+/-80.1 to 132.7+/-46.5 micromol x mol(-1) creatinine) and augmentation index (from 14.5+/-11.3 to 9.1+/-13.8%) compared with the subtherapeutic control group. Furthermore, therapeutic CPAP significantly improved BRS (from 7.1+/-3.3 to 8.8+/-4.2 ms x mmHg(-1)) and reduced mean arterial ABP by 2.6+/-5.4 mmHg. In conclusion, treatment of obstructive sleep apnoea with continuous positive airway pressure may lower cardiovascular risk by reducing sympathetic nerve activity, ambulatory blood pressure and arterial stiffness and by increasing sensitivity of the arterial baroreflex.

Reilly SN, Schotten U, Alp NJ, Casadei B. 2008. Time-dependent regional differences in sources of oxidative stress in atrial fibrillation-induced remodelling EUROPEAN HEART JOURNAL, 29 pp. 288-289.

Zhang YH, Zhang MH, Sears CE, Redwood C, El-Armouche A, Kranias EG, Casadei B. 2008. Regulation of myocyte contractility by endogenous NO: role of protein phosphatase 2A and protein kinase A-dependent signalling EUROPEAN HEART JOURNAL, 29 pp. 631-631.

Idigo W, Zhang YH, Lygate C, Carnicer R, Dawson D, Casadei B. 2008. Is depressed myocyte contractility an early event in the natural history of heart failure? EUROPEAN HEART JOURNAL, 29 pp. 108-108.

Casadei B. 2008. Beta 3-adrenoceptors modulate left ventricular relaxation in the rat heart via the NO-cGMP-PKG pathway. Acta Physiol (Oxf), 193 (3), pp. 203. | Read more

Seddon MD, Chowienczyk PJ, Brett SE, Casadei B, Shah AM. 2008. Neuronal nitric oxide synthase regulates basal microvascular tone in humans in vivo. Circulation, 117 (15), pp. 1991-1996. | Show Abstract | Read more

BACKGROUND: Nitric oxide (NO) has a pivotal role in the regulation of vascular tone and blood flow, with dysfunctional release contributing to disease pathophysiology. These effects have been attributed to NO production by the endothelial NO synthase (eNOS); however, recent evidence suggests that a neuronal NO synthase (nNOS) may also be expressed in arterial vessels. METHODS AND RESULTS: We undertook a first-in-humans investigation of the role of nNOS in the local regulation of vascular blood flow in healthy subjects. Brachial artery infusion of the nNOS-specific inhibitor S-methyl-L-thiocitrulline (SMTC, 0.025 micromol/min to 0.2 micromol/min) caused a dose-dependent reduction in basal flow, with a 30.1+/-3.8% decrease at the highest dose (n=10; mean+/-SE; P<0.01). The effect of SMTC was abolished by coinfusion of the NO synthase substrate L-arginine but was unaffected by D-arginine. A similar reduction in basal flow with the nonselective NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA; 37.4+/-3.1%, n=10) required a 20-fold higher dose of 4 micromol/min. At doses that produced comparable reductions in basal flow, only L-NMMA (4 micromol/min) and not SMTC (0.2 micromol/min) inhibited acetylcholine-induced vasodilation; however, both SMTC and L-NMMA inhibited the forearm vasodilator response to mental stress. CONCLUSIONS: Basal forearm blood flow in humans is regulated by nNOS-derived NO, in contrast to the acetylcholine-stimulated increase in blood flow, which, as shown previously, is mediated primarily by eNOS. These data indicate that vascular nNOS has a distinct local role in the physiological regulation of human microvascular tone in vivo.

Zhang YH, Zhang MH, Sears CE, Emanuel K, Redwood C, El-Armouche A, Kranias EG, Casadei B. 2008. Reduced phospholamban phosphorylation is associated with impaired relaxation in left ventricular myocytes from neuronal NO synthase-deficient mice. Circ Res, 102 (2), pp. 242-249. | Show Abstract | Read more

Stimulation of nitric oxide (NO) release from the coronary endothelium facilitates myocardial relaxation via a cGMP-dependent reduction in myofilament Ca2+ sensitivity. Recent evidence suggests that NO released by a neuronal NO synthase (nNOS) in the myocardium can also hasten left ventricular relaxation; however, the mechanism underlying these findings is uncertain. Here we show that both relaxation (TR50) and the rate of [Ca2+]i transient decay (tau) are significantly prolonged in field-stimulated or voltage-clamped left ventricular myocytes from nNOS-/- mice and in wild-type myocytes (nNOS+/+) after acute nNOS inhibition. Disabling the sarcoplasmic reticulum abolished the differences in TR50 and tau, suggesting that impaired sarcoplasmic reticulum Ca2+ reuptake may account for the slower relaxation in nNOS-/- mice. In line with these findings, disruption of nNOS (but not of endothelial NOS) decreased phospholamban phosphorylation (P-Ser16 PLN), whereas nNOS inhibition had no effect on TR50 or tau in PLN-/- myocytes. Inhibition of cGMP signaling had no effect on relaxation in either group whereas protein kinase A inhibition abolished the difference in relaxation and PLN phosphorylation by decreasing P-Ser16 PLN and prolonging TR50 in nNOS+/+ myocytes. Conversely, inhibition of type 1 or 2A protein phosphatases shortened TR50 and increased P-Ser16 PLN in nNOS-/- but not in nNOS+/+ myocytes, in agreement with data showing increased protein phosphatase activity in nNOS-/- hearts. Taken together, our findings identify a novel mechanism by which myocardial nNOS promotes left ventricular relaxation by regulating the protein kinase A-mediated phosphorylation of PLN and the rate of sarcoplasmic reticulum Ca2+ reuptake via a cGMP-independent effect on protein phosphatase activity.

Lim G, Venetucci L, Eisner DA, Casadei B. 2008. Does nitric oxide modulate cardiac ryanodine receptor function? Implications for excitation-contraction coupling. Cardiovasc Res, 77 (2), pp. 256-264. | Show Abstract | Read more

Nitric oxide (NO) is a highly reactive, free radical signalling molecule that is constitutively released in cardiomyocytes by both the endothelial and neuronal isoforms of nitric oxide synthase (eNOS and nNOS, respectively). There are increasing data indicating that NO modulates various proteins involved in excitation-contraction coupling (ECC), and here we discuss the evidence that NO may modulate the function of the ryanodine receptor Ca(2+) release channel (RyR2) on the cardiac sarcoplasmic reticulum (SR). Both constitutive isoforms of NOS have been shown to co-immunoprecipitate with RyR2, suggesting that the channel may be a target protein for NO. eNOS gene deletion has been shown to abolish the increase in spontaneous Ca(2+) spark frequency in cardiomyocytes exposed to sustained stretch, whereas the effect of nNOS-derived NO on RyR2 function remains to be investigated. Single channel studies have been performed with RyR2 reconstituted in planar lipid bilayers and exposed to various NO donors and, under these conditions, NO appears to have a dose-dependent, stimulatory effect on channel open probability (P(open)). We discuss whether NO has a direct effect on RyR2 via covalent S-nitrosylation of reactive thiol residues within the protein, or whether there are downstream effects via cyclic nucleotides, phosphodiesterases, and protein kinases. Finally, we consider whether the proposed migration of nNOS from the SR to the sarcolemma in the failing heart may have consequences for the nitrosative vs. oxidative balance at the level of the RyR2, and whether this may contribute to an increased diastolic Ca(2+) leak, depleted SR Ca(2+) store, and reduced contractility in heart failure.

Kim YM, Kattach H, Ratnatunga C, Pillai R, Channon KM, Casadei B. 2008. Association of atrial nicotinamide adenine dinucleotide phosphate oxidase activity with the development of atrial fibrillation after cardiac surgery. J Am Coll Cardiol, 51 (1), pp. 68-74. | Show Abstract | Read more

OBJECTIVES: Our goal was to evaluate the role of myocardial nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity and plasma markers of oxidative stress in the pathogenesis of post-operative atrial fibrillation (AF). BACKGROUND: Atrial fibrillation is a common complication of cardiac surgery, leading to increased morbidity and prolonged hospitalization. Experimental evidence suggests that oxidative stress may be involved in the pathogenesis of AF; however, the relevance of this putative mechanism in patients undergoing cardiac surgery is unclear. METHODS: We measured basal and NADPH-stimulated superoxide production in right atrial appendage samples from 170 consecutive patients undergoing conventional coronary artery bypass surgery. Plasma markers of lipid and protein oxidation (thiorbabituric acid-reactive substances, 8-isoprostane, and protein carbonyls) were also measured in blood samples drawn from a central line before surgery and after reperfusion. RESULTS: Patients who developed AF after surgery (42%) were older and had a significantly increased atrial NADPH oxidase activity than patients who remained in sinus rhythm (SR) (in relative light units/s/mug protein: 4.78 +/- 1.44 vs. 3.53 +/- 1.04 in SR patients, p < 0.0001). Plasma markers of lipid and protein oxidation increased significantly after reperfusion; however, neither pre-operative nor post-operative measurements differed between patients who developed AF and those who remained in SR after surgery. Multivariate analysis identified atrial NADPH oxidase activity as the strongest independent predictor of post-operative AF (odds ratio 2.41; 95% confidence interval 1.71 to 3.40, p < 0.0001). CONCLUSIONS: Atrial NADPH oxidase activity is independently associated with an increased risk of post-operative AF, suggesting that this oxidase system may be a key mediator of atrial oxidative stress leading to the development of AF after cardiac surgery.

Seddon M, Shah AM, Casadei B. 2007. Cardiomyocytes as effectors of nitric oxide signalling. Cardiovasc Res, 75 (2), pp. 315-326. | Show Abstract | Read more

Nitric oxide (NO) generated constitutively within the heart has long been known to influence myocardial function; however, the precise nature of these effects has been controversial--at least in part--because of the experimental use of non-isoform-selective inhibitors of NO synthases (NOS) and unwarranted extrapolation from results obtained with NO donors. Recent studies using NOS-selective inhibitors and genetically modified models are beginning to redress the balance. It is well established that agonist-stimulated release of NO from eNOS in the coronary endothelium exerts paracrine effects on cardiomyocytes, predominantly affecting the timing of relaxation as well as myocardial oxygen consumption. A significant recent advance has been the finding that both eNOS and nNOS are constitutively expressed in distinct subcellular locations within cardiomyocytes. The relative autocrine role of these isoforms in the cardiomyocyte remains to be fully clarified but evidence suggests that the autocrine effects of nNOS may include the modulation of basal inotropy and relaxation, beta-adrenergic responsiveness, and the force-frequency relationship. Myocardial eNOS, on the other hand, may be involved in mediating the inotropic response to sustained stretch. These effects may change significantly in the diseased heart where the expression, activity and/or coupling of NOS isoforms to downstream effectors may be altered. In this article, we review the current understanding of this important but complex field, focussing particularly on contractile function and on recent advances in knowledge regarding the autocrine functions of nNOS-derived NO.

Casadei B. 2006. The emerging role of neuronal nitric oxide synthase in the regulation of myocardial function. Exp Physiol, 91 (6), pp. 943-955. | Show Abstract | Read more

The recent discovery of a NOS1 gene product (i.e. a neuronal-like isoform of nitric oxide synthase or nNOS) in the mammalian left ventricular (LV) myocardium has provided a new key for the interpretation of the complex experimental evidence supporting a role for myocardial constitutive nitric oxide (NO) production in the regulation of basal and beta-badrenergic cardiac function. Importantly, nNOS gene deletion has been associated with more severe LV remodelling and functional deterioration in murine models of myocardial infarction, suggesting that nNOS-derived NO may also be involved in the myocardial response to injury. To date, the mechanisms by which nNOS influences myocardial pathophysiology remain incompletely understood. In particular, it seems over simplistic to assume that all aspects of the myocardial phenotype of nNOS knockout (nNOS(-/-)) mice are a direct consequence of lack of NO production from this source. Emerging data showing co-localisation of xanthine oxidoreductase (XOR) and nNOS in the sarcoplasmic reticulum of rodents, and increased XOR activity in the nNOS(-/-) myocardium, suggest that nNOS gene deletion may have wider implications on the myocardial redox state. Similarly, the mechanisms regulating the targeting of myocardial nNOS to different subcellular compartments and the functional consequences of intracellular nNOS trafficking have not been fully established. Whether this information could be translated into a better understanding and management of human heart failure remains the most important challenge for future investigations.

Martin SR, Emanuel K, Sears CE, Zhang YH, Casadei B. 2006. Are myocardial eNOS and nNOS involved in the beta-adrenergic and muscarinic regulation of inotropy? A systematic investigation. Cardiovasc Res, 70 (1), pp. 97-106. | Show Abstract | Read more

OBJECTIVE: The role of constitutive nitric oxide (NO) production in the regulation of beta-adrenergic and muscarinic responses remains controversial. Conflicting data in left ventricular (LV) myocytes from eNOS knockout mice (eNOS-/-) have been ascribed to inconsistent experimental conditions (i.e., differences in the choice of controls, age of the mice, myocytes' stimulation frequency, and in the level of beta-adrenergic stimulation); however, the recent identification of a neuronal-like NO synthase (nNOS) in the LV myocardium has raised the possibility that this isoform may be involved in the modulation of beta-adrenergic and muscarinic responses. METHODS: To address these issues we recorded sarcomere shortening at 35 degrees C under basal conditions, in the presence of isoproterenol (ISO, 10-100 nmol/L) and of ISO plus carbamylcholine (CCh, 1 micromol/L) in LV myocytes isolated from eNOS-/- and nNOS-/- mice, their wild type littermates (eNOS+/+ and nNOS+/+) or C57BL/6J mice. eNOS-/- and control myocytes were studied at 1 and 3 Hz, in the presence of 10 and 100 nmol/L ISO, and responses were compared between young (3 months) and old (> or =12 months) mice. RESULTS: Contraction did not differ between young eNOS-/- and eNOS+/+ mice at all stages of the experimental protocol, either at 1 or 3 Hz or in response to 10 or 100 nmol/L ISO. However, myocytes from old eNOS-/- mice showed a reduced inotropic response to ISO compared with age-matched eNOS+/+ mice (P = 0.02). Similarly, there was a significant difference in the ISO response between eNOS+/+ and C57BL/6J myocytes (P < 0.01), suggesting that experimental variables such as age and the choice of control animals may have contributed to the inconsistency in the results reported in the literature. In contrast, nNOS-/- myocytes showed greater contraction and slower relaxation at all stages of the experimental protocol (P = 0.0003 and P = 0.01 vs. nNOS+/+ myocytes). CONCLUSIONS: Constitutive eNOS expression in murine LV myocytes is not essential for the muscarinic-mediated inhibition of beta-adrenergic signalling and does not appear to play a significant role in the regulation of basal and beta-adrenergic myocardial contraction. Our data suggest that nNOS is the myocardial constitutive isoform responsible for the NO-mediated autocrine regulation of myocardial inotropy and relaxation.

Dawson D, Lygate CA, Zhang MH, Hulbert K, Neubauer S, Casadei B. 2005. nNOS gene deletion exacerbates pathological left ventricular remodeling and functional deterioration after myocardial infarction. Circulation, 112 (24), pp. 3729-3737. | Show Abstract | Read more

BACKGROUND: The neuronal isoform of nitric oxide synthase (nNOS) has been implicated in the regulation of basal and beta-adrenergic inotropy in normal and chronically infarcted hearts. Furthermore, myocardial nNOS expression and activity increase in failing hearts, raising the possibility that nNOS may influence left ventricular (LV) remodeling progression and functional deterioration after myocardial infarction (MI). METHODS AND RESULTS: We compared LV remodeling at 1, 4, and 8 weeks after MI in nNOS-knockout mice (nNOS(-/-)) and their wild-type (WT) littermates matched for infarct size by using a highly accurate 3-dimensional echocardiographic technique. Basal LV hemodynamics and the inotropic response to dobutamine infusion (4 and 16 ng.g(-1).min(-1)) were also evaluated 8 weeks after MI. Sham-operated nNOS(-/-) mice showed enhanced basal LV contractility (P<0.03 versus WT, as evaluated by preload-recruitable stroke work) but an attenuated inotropic response to dobutamine infusion (P<0.01 versus WT). Both basal and beta-adrenergic LV relaxations were significantly impaired in nNOS(-/-) mice. Survival after MI did not differ between groups. However, nNOS(-/-) mice developed a faster and more severe LV dilation compared with WT mice (P<0.05 for both end-systolic and end-diastolic volume indices). WT mice maintained a positive inotropic response to dobutamine 8 weeks after MI. In contrast, infarcted nNOS(-/-) mice responded to dobutamine with a dramatic fall in LV contractility (P<0.01 for preload-recruitable stroke work). CONCLUSIONS: nNOS plays a crucial role in preventing adverse LV remodeling and maintaining myocardial beta-adrenergic reserve after MI. Taken together, our findings suggest that upregulation of myocardial nNOS in infarcted hearts may be an important adaptive mechanism.

Kim YM, Guzik TJ, Zhang YH, Zhang MH, Kattach H, Ratnatunga C, Pillai R, Channon KM, Casadei B. 2005. A myocardial Nox2 containing NAD(P)H oxidase contributes to oxidative stress in human atrial fibrillation. Circ Res, 97 (7), pp. 629-636. | Show Abstract | Read more

Human atrial fibrillation (AF) has been associated with increased atrial oxidative stress. In animal models, inhibition of reactive oxygen species prevents atrial remodeling induced by rapid pacing, suggesting that oxidative stress may play an important role in the pathophysiology of AF. NAD(P)H oxidase is a major source of superoxide in the cardiovascular system; however, whether this enzyme contributes to atrial oxidative stress in AF remains to be elucidated. We investigated the sources of superoxide production (using inhibitors and substrates of a range of oxidases, RT-PCR, immunofluorescence, and immunoblotting) in tissue homogenates and isolated atrial myocytes from the right atrial appendage (RAA) of patients undergoing cardiac surgery (n=54 in sinus rhythm [SR] and 15 in AF). A membrane-bound gp91phox containing NAD(P)H oxidase in atrial myocytes was the main source of atrial superoxide production in SR and in AF. NADPH-stimulated superoxide release from RAA homogenates was significantly increased in patients with AF in the absence of changes in mRNA expression of the p22phox and gp91phox subunits of the NAD(P)H oxidase. In contrast with findings in SR patients, NO synthases (NOSs) contributed significantly to atrial superoxide production in fibrillating atria, suggesting that increased oxidative stress in AF may lead to NOS "uncoupling." These findings indicate that a myocardial NAD(P)H oxidase and, to a lesser extent, dysfunctional NOS contribute significantly to superoxide production in the fibrillating human atrial myocardium and may play an important role in the atrial oxidative injury and electrophysiological remodeling observed in patients with AF.

Danson EJ, Zhang YH, Sears CE, Edwards AR, Casadei B, Paterson DJ. 2005. Disruption of inhibitory G-proteins mediates a reduction in atrial beta-adrenergic signaling by enhancing eNOS expression. Cardiovasc Res, 67 (4), pp. 613-623. | Show Abstract | Read more

OBJECTIVE: Cardiac parasympathetic nerve activity is reduced in most cardiovascular disease states, and this may contribute to enhanced cardiac sympathetic responsiveness. Disruption of inhibitory G-proteins (Gi) ablates the cholinergic pathway and increases cardiac endothelial nitric oxide (NO) synthase (eNOS) expression, suggesting that NO may offset the impaired attenuation of beta-adrenergic regulation of supraventricular excitability. To test this, we investigated the role of endogenous NO production on beta-adrenergic regulation of rate (HR), contraction (CR) and calcium (Ca2+) handling in atria following blockade of Gi-coupled muscarinic receptors. METHODS: Mice were administered pertussis toxin (PTx, n=105) or saline (C, n=100) intraperitoneally. After 3 days, we measured CR, HR, and NOS protein levels in isolated atria. Intracellular calcium (Ca2+) transients and Ca2+ current density (I(Ca)) were also measured in atrial myocytes. RESULTS: PTx treatment increased atrial myocyte eNOS protein levels compared to C (P<0.05). This did not affect basal atrial function but was associated with a significant reduction in the CR and HR response to isoprenaline (ISO) compared with C. NOS inhibition normalized responses in PTx atria with respect to responses in C atria (P<0.05), which were unaffected. Furthermore, PTx did not affect ISO-stimulated HR and CR in eNOS gene knockout mice (n=40). In agreement with these findings, the ISO-mediated increase in Ca2+ transient was suppressed in PTx-treated myocytes (P<0.05), whereas I(Ca) did not differ between groups. CONCLUSION: eNOS-derived NO inhibits beta-adrenergic responses following disruption of Gi signaling. This suggests that increased eNOS expression may be a compensatory mechanism which reduces beta-adrenergic regulation of heart rate when cardiac parasympathetic control is impaired.

Petersen SE, Selvanayagam JB, Francis JM, Myerson SG, Wiesmann F, Robson MD, Ostman-Smith I, Casadei B, Watkins H, Neubauer S. 2005. Differentiation of athlete's heart from pathological forms of cardiac hypertrophy by means of geometric indices derived from cardiovascular magnetic resonance. J Cardiovasc Magn Reson, 7 (3), pp. 551-558. | Show Abstract | Read more

PURPOSE: Determination of the underlying etiology of left ventricular hypertrophy (LVH) is a common, challenging, and critical clinical problem. The authors aimed to test whether pathological LVH, such as occurs in hypertrophic cardiomyopathy (HCM), hypertensive heart disease, or aortic stenosis, and physiological LVH in athletes, can be distinguished by means of left ventricular volume and geometric indices, derived from cardiovascular magnetic resonance imaging. METHODS: A total of 120 subjects were studied on a 1.5 Tesla MR (Sonata, Siemens Medical Solutions, Erlangen, Germany) scanner, comprising healthy volunteers (18), competitive athletes (25), patients with HCM (35), aortic stenosis (24), and hypertensive heart disease (18). Left ventricular mass index, ejection fraction, end-diastolic, end-systolic and stroke volume index, diastolic wall thickness, wall thickness ratio and diastolic and systolic wall-to-volume ratios were determined. RESULTS: Left ventricular (LV) mass indices were similar for all forms of LVH (p > 0.05), which were at least 35% higher than those obtained in healthy volunteers (p < 0.05). Multiple logistic regression showed that the percentage of correctly predicted diagnoses was 100% for athlete's heart, 80% for hypertrophic cardiomyopathy, 54% for aortic stenosis, and 22% for hypertensive heart disease. Using a receiver operating curve-determined cut-off value for diastolic wall-to-volume ratio of less than 0.15 mm x m2 x ml(-1), athletes' hearts could be differentiated from all forms of pathological cardiac hypertrophy with 99% specificity. CONCLUSIONS: Athlete's heart can be reliably distinguished from all forms of pathological cardiac hypertrophy using CMR-derived LV volume and geometric indices, but pathological forms of LVH present with overlapping cardiac hypertrophy phenotypes. This capability of CMR should be of high clinical value.

Casadei B, Abuzeid H. 2005. Is there a strong rationale for deferring elective surgery in patients with poorly controlled hypertension? J Hypertens, 23 (1), pp. 19-22. | Show Abstract | Read more

Hypertension remains one of the most common avoidable medical indications for deferring elective surgery, thereby increasing both the financial and emotional burden of having an operation. Although the evidence supporting the current guidelines on management of hypertension is among the best available in any field of medicine, our knowledge on whether high blood pressure (BP) is an independent perioperative risk factor is plagued by much uncertainty. Indeed, it is still unclear whether postponing surgery on the ground of elevated preoperative BP measurements will lead to a reduction in perioperative cardiac risk. Similarly, the importance of multiple versus isolated BP measurements in predicting perioperative complications has not yet been assessed. As most studies have evaluated the predictive value of diastolic BP, the risk of perioperative cardiovascular events associated with isolated systolic hypertension remains uncertain. With no controlled evidence to address these issues, no firm recommendations can be made to improve patients' safety. These important issues now need to be addressed by modern clinical trials.

Sears CE, Ashley EA, Casadei B. 2004. Nitric oxide control of cardiac function: is neuronal nitric oxide synthase a key component? Philos Trans R Soc Lond B Biol Sci, 359 (1446), pp. 1021-1044. | Show Abstract | Read more

Nitric oxide (NO) has been shown to regulate cardiac function, both in physiological conditions and in disease states. However, several aspects of NO signalling in the myocardium remain poorly understood. It is becoming increasingly apparent that the disparate functions ascribed to NO result from its generation by different isoforms of the NO synthase (NOS) enzyme, the varying subcellular localization and regulation of NOS isoforms and their effector proteins. Some apparently contrasting findings may have arisen from the use of non-isoform-specific inhibitors of NOS, and from the assumption that NO donors may be able to mimic the actions of endogenously produced NO. In recent years an at least partial explanation for some of the disagreements, although by no means all, may be found from studies that have focused on the role of the neuronal NOS (nNOS) isoform. These data have shown a key role for nNOS in the control of basal and adrenergically stimulated cardiac contractility and in the autonomic control of heart rate. Whether or not the role of nNOS carries implications for cardiovascular disease remains an intriguing possibility requiring future study.

Khoo JP, Alp NJ, Bendall JK, Kawashima S, Yokoyama M, Zhang YH, Casadei B, Channon KM. 2004. EPR quantification of vascular nitric oxide production in genetically modified mouse models. Nitric Oxide, 10 (3), pp. 156-161. | Show Abstract | Read more

With increasing use of genetically modified mice to study endothelial nitric oxide (NO) biology, methods for reliable quantification of vascular NO production by mouse tissues are crucial. We describe a technique based on electron paramagnetic resonance (EPR) spectroscopy, using colloid iron (II) diethyldithiocarbamate [Fe(DETC)2], to trap NO. A signal was seen from C57BL/6 mice aortas incubated with Fe(DETC)2, that increased 4.7-fold on stimulation with calcium ionophore A23187 [3.45+/-0.13 vs 0.73+/-0.13au (arbitrary units)]. The signal increased linearly with incubation time (r(2) = 0.93), but was abolished by addition of N(G)-nitro-l-arginine methyl ester (L-NAME) or endothelial removal. Stimulated aortas from eNOS knockout mice had virtually undetectable signals (0.14+/-0.06 vs 3.17+/-0.21 au in littermate controls). However, the signal was doubled from mice with transgenic eNOS overexpression (7.17+/-0.76 vs 3.37+/-0.43 au in littermate controls). We conclude that EPR is a useful tool for direct NO quantification in mouse vessels.

Casadei B, Sears CE. 2003. Nitric-oxide-mediated regulation of cardiac contractility and stretch responses. Prog Biophys Mol Biol, 82 (1-3), pp. 67-80. | Show Abstract | Read more

In the heart, nitric oxide (NO) is constitutively produced by the vascular and endocardial endothelium, the cardiomyocytes and the autonomic nerves. Whereas stimulation of NO release from the vascular endothelium has consistently been shown to quicken the onset of left ventricular (LV) relaxation and cause a small reduction in peak contraction, the role of myocardial NO production in regulating cardiac function appears to be more complex and controversial. Some studies have shown that non-isoform-specific inhibition of NO synthesis with L-arginine analogues has no effect on basal contraction in LV myocytes. However, others have demonstrated that stimulation of myocardial NO production can offset the increase in contraction in response to a rise in intracellular Ca(2+). Cardiac NO production is also activated by stretch and under these conditions NO has been shown to facilitate the Frank-Starling response and to contribute to the increase in intracellular Ca(2+) transients that mediates the slow increase in contraction in response to stretch (i.e., the Anrep effect). These findings suggest that NO can mediate diverse and even contrasting actions within the myocardium, a notion that is difficult to reconcile with the early description of NO as a highly reactive and diffusible molecule possessing minimal specificity in its interactions. The purpose of this short review is to revisit some of the 'controversial' aspects of NO-mediated regulation of myocardial function, taking into account our current understanding of how mammalian cells may target and regulate the synthesis of NO in such a way that NO can serve diverse physiological functions.

Sears CE, Bryant SM, Ashley EA, Lygate CA, Rakovic S, Wallis HL, Neubauer S, Terrar DA, Casadei B. 2003. Cardiac neuronal nitric oxide synthase isoform regulates myocardial contraction and calcium handling. Circ Res, 92 (5), pp. e52-e59. | Show Abstract | Read more

A neuronal isoform of nitric oxide synthase (nNOS) has recently been located to the cardiac sarcoplasmic reticulum (SR). Subcellular localization of a constitutive NOS in the proximity of an activating source of Ca2+ suggests that cardiac nNOS-derived NO may regulate contraction by exerting a highly specific and localized action on ion channels/transporters involved in Ca2+ cycling. To test this hypothesis, we have investigated myocardial Ca2+ handling and contractility in nNOS knockout mice (nNOS-/-) and in control mice (C) after acute nNOS inhibition with 100 micromol/L L-VNIO. nNOS gene disruption or L-VNIO increased basal contraction both in left ventricular (LV) myocytes (steady-state cell shortening 10.3+/-0.6% in nNOS-/- versus 8.1+/-0.5% in C; P<0.05) and in vivo (LV ejection fraction 53.5+/-2.7 in nNOS-/- versus 44.9+/-1.5% in C; P<0.05). nNOS disruption increased ICa density (in pA/pF, at 0 mV, -11.4+/-0.5 in nNOS-/- versus -9.1+/-0.5 in C; P<0.05) and prolonged the slow time constant of inactivation of ICa by 38% (P<0.05), leading to an increased Ca2+ influx and a greater SR load in nNOS-/- myocytes (in pC/pF, 0.78+/-0.04 in nNOS-/- versus 0.64+/-0.03 in C; P<0.05). Consistent with these data, [Ca2+]i transient (indo-1) peak amplitude was greater in nNOS-/- myocytes (410/495 ratio 0.34+/-0.01 in nNOS-/- versus 0.31+/-0.01 in C; P<0.05). These findings have uncovered a novel mechanism by which intracellular Ca2+ is regulated in LV myocytes and indicate that nNOS is an important determinant of basal contractility in the mammalian myocardium. The full text of this article is available at http://www.circresaha.org.

Ashley EA, Sears CE, Bryant SM, Watkins HC, Casadei B. 2002. Cardiac nitric oxide synthase 1 regulates basal and beta-adrenergic contractility in murine ventricular myocytes. Circulation, 105 (25), pp. 3011-3016. | Show Abstract | Read more

BACKGROUND: Evidence indicates that myocardial NO production can modulate contractility, but the source of NO remains uncertain. Here, we investigated the role of a type 1 NO synthase isoform (NOS1), which has been recently localized to the cardiac sarcoplasmic reticulum, in the regulation of basal and beta-adrenergic myocardial contraction. METHODS AND RESULTS: Contraction was assessed in left ventricular myocytes isolated from mice with NOS1 gene disruption (NOS1(-/-) mice) and their littermate controls (NOS1(+/+) mice) at 3 stimulation frequencies (1, 3, and 6 Hz) in basal conditions and during beta-adrenergic stimulation with isoproterenol (2 nmol/L). In addition, we examined the effects of acute specific inhibition of NOS1 with vinyl-L-N-5-(1-imino-3-butenyl)-L-ornithine (L-VNIO, 500 micromol/L). NOS1((-/-)) myocytes exhibited greater contraction at all frequencies (percent cell shortening at 6 Hz, 10.7+/-0.92% in NOS1(-/-) myocytes versus 7.21+/-0.8% in NOS1(+/+) myocytes; P<0.05) with a flat frequency-contraction relationship. Time to 50% relaxation was increased in NOS1(-/-) myocytes at all frequencies (at 6 Hz, 26.53+/-1.4 ms in NOS1(-/-) myocytes versus 21.27+/-1.3 ms in NOS1(+/+) myocytes; P<0.05). L-VNIO prolonged time to 50% relaxation at all frequencies (at 6 Hz, 21.28+/-1.7 ms in NOS1(+/+) myocytes versus 26.45+/-1.4 ms in NOS1(+/+)+L-VNIO myocytes; P<0.05) but did not significantly increase basal contraction. However, both NOS1(-/-) myocytes and NOS1(+/+) myocytes treated with L-VNIO showed a greatly enhanced contraction in response to beta-adrenergic stimulation (percent increase in contraction at 6 Hz, 25.2+/-10.8 in NOS1(+/+) myocytes, 68.2+/-11.2 in NOS1(-/-) myocytes, and 65.1+/-13.2 in NOS1(+/+)+L-VNIO myocytes; P<0.05). CONCLUSIONS: NOS1 disruption enhances basal contraction and the inotropic response to beta-adrenergic stimulation in murine ventricular myocytes. These findings indicate that cardiac NOS1-derived NO plays a significant role in the autocrine regulation of myocardial contractility.

Kardos A, Watterich G, Casadei B, Rudas L. 2002. Baroreflex sensitivity: population values. Acta Cardiol, 57 (1), pp. 41-42.

Casadei B. 2001. Vagal control of myocardial contractility in humans. Exp Physiol, 86 (6), pp. 817-823. | Show Abstract | Read more

Until about 40 years ago, it was thought that the parasympathetic innervation of the mammalian heart was confined to supraventricular structures. Hence, neither the vagus nor its primary neurotransmitter, acetylcholine (ACh), were believed to have significant effects on the inotropic state of the ventricles or on their excitability. However, it is now well-established that vagal/muscarinic stimulation prolongs ventricular refractoriness in humans and has a small but distinct negative inotropic effect on the left ventricle, which is accentuated in the presence of elevated sympathetic activity (Löffelholz & Pappano, 1985). This brief review will consider the evidence for a vagal/ muscarinic regulation of left ventricular (LV) function in humans and discuss the mechanisms that may be responsible for this effect.

Ashley EA, Bryant S, Sears C, Kim YM, Watkins H, Casadei B. 2001. Enhancement of beta adrenergic responsiveness in myocytes lacking nitric oxide synthase 1 CIRCULATION, 104 (17), pp. 51-52.

Bryant SM, Sears CE, Wallis H, Casadei B. 2001. Mechanical and electrophysiological properties of murine hypertrophied left ventricular myocytes EUROPEAN HEART JOURNAL, 22 pp. 55-55.

Sears C, Bryant S, Wallis H, Ashley E, Casadei B. 2001. Effect of disruption of the nNOS gene on myocardial calcium current and contraction EUROPEAN HEART JOURNAL, 22 pp. 55-55.

Bryant SM, Sears CE, Rigg L, Terrar DA, Casadei B. 2001. Nitric oxide does not modulate the hyperpolarization-activated current, I(f), in ventricular myocytes from spontaneously hypertensive rats. Cardiovasc Res, 51 (1), pp. 51-58. | Show Abstract | Read more

OBJECTIVE: : In sinoatrial (SA) node cells, nitric oxide (NO) exerts a dual effect on the hyperpolarization-activated current, I(f), i.e. in basal conditions NO enhances I(f) whereas in the presence of beta-adrenergic stimulation it decreases it. Recent studies have shown that I(f) is present in ventricular myocytes from hypertrophied or failing hearts where it may promote abnormal automaticity. Since these pathological conditions are associated with increased sympathetic tone and upregulation of myocardial NO production, we set out to investigate whether I(f) is similarly modulated by NO in hypertrophied ventricular myocytes. METHODS: Left ventricular myocytes were isolated from 18-20-month-old spontaneously hypertensive rats (SHRs). Membrane current was measured under whole-cell or amphotericin-perforated patch-clamp conditions, at 35 degrees C. RESULTS: Application of diethylamine-NO (DEA-NO, 1-100 microM) did not alter the amplitude or voltage dependence of activation of I(f) under basal conditions (half-activation voltage, V(h): control -82.9+/-2.6, DEA-NO -84.0+/-2.6 mV). Similarly, I(f) was not affected by the inhibition of endogenous NO production (L-NMMA, 500 microM) or guanylate cyclase (ODQ, 10 microM). Forskolin (10 microM) or isoprenaline (100 nM) elicited a positive shift in V(h) but subsequent application of DEA-NO did not further affect the properties of I(f). CONCLUSIONS: Our results show that, unlike in SA node cells, in SHR ventricular myocytes basal and adrenergically stimulated I(f) is not modulated by exogenous NO or by constitutive NO or cGMP production.

Thornton JM, Guz A, Murphy K, Griffith AR, Pedersen DL, Kardos A, Leff A, Adams L, Casadei B, Paterson DJ. 2001. Identification of higher brain centres that may encode the cardiorespiratory response to exercise in humans. J Physiol, 533 (Pt 3), pp. 823-836. | Show Abstract | Read more

1. Positron emission tomography (PET) was used to identify the neuroanatomical correlates underlying 'central command' during imagination of exercise under hypnosis, in order to uncouple central command from peripheral feedback. 2. Three cognitive conditions were used: condition I, imagination of freewheeling downhill on a bicycle (no change in heart rate, HR, or ventilation, V(I)): condition II, imagination of exercise, cycling uphill (increased HR by 12 % and V(I) by 30 % of the actual exercise response): condition III, volitionally driven hyperventilation to match that achieved in condition II (no change in HR). 3. Subtraction methodology created contrast A (II minus I) highlighting cerebral areas involved in the imagination of exercise and contrast B (III minus I) highlighting areas activated in the direct volitional control of breathing (n = 4 for both; 8 scans per subject). End-tidal P(CO(2)) (P(ET,CO(2))) was held constant throughout PET scanning. 4. In contrast A, significant activations were seen in the right dorso-lateral prefrontal cortex, supplementary motor areas (SMA), the right premotor area (PMA), superolateral sensorimotor areas, thalamus, and bilaterally in the cerebellum. In contrast B, significant activations were present in the SMA and in lateral sensorimotor cortical areas. The SMA/PMA, dorso-lateral prefrontal cortex and the cerebellum are concerned with volitional/motor control, including that of the respiratory muscles. 5. The neuroanatomical areas activated suggest that a significant component of the respiratory response to 'exercise', in the absence of both movement feedback and an increase in CO(2) production, can be generated by what appears to be a behavioural response.

Bryant S, Sears C, Wallis HL, Casadei B. 2001. Mechanical and electrophysiological properties of left ventricular myocytes in catecholamine-induced hypertrophy in mice JOURNAL OF PHYSIOLOGY-LONDON, 533 pp. 27P-27P.

Sears CE, Bryant SM, Wallis HL, Ashley EA, Casadei B. 2001. Electrophysiological and mechanical properties of ventricular myocytes isolated from wild-type mice and mice with disruption of the neuronal nitric oxide synthase gene JOURNAL OF PHYSIOLOGY-LONDON, 533 pp. 35P-36P.

Ashley EA, Naoumova D, Casadei B. 2001. Isolated mouse ventricular cells exhibit a negative contraction frequency response JOURNAL OF PHYSIOLOGY-LONDON, 533 pp. 46P-47P.

Casadei B. 2001. Parasympathetic regulation of cardiac function in man JOURNAL OF PHYSIOLOGY-LONDON, 533 pp. 8S-8S.

Kardos A, Watterich G, de Menezes R, Csanády M, Casadei B, Rudas L. 2001. Determinants of spontaneous baroreflex sensitivity in a healthy working population. Hypertension, 37 (3), pp. 911-916. | Show Abstract | Read more

Baroreflex sensitivity (BRS) by the spontaneous sequence technique has been widely used as a cardiac autonomic index for a variety of pathological conditions. However, little information is available on determinants of the variability of spontaneous BRS and on age-related reference values of this measurement in a healthy population. We evaluated BRS as the slope of spontaneous changes in systolic blood pressure (BP) and pulse interval from 10 minutes BP (Finapres) and ECG recordings in 1134 healthy volunteers 18 to 60 years of age. Measurement of BRS could be obtained in 90% of subjects. Those with unmeasurable spontaneous BRS had a slightly lower heart rate but were otherwise not different from the rest of the population. BRS was inversely related to age (lnBRS, 3.24-0.03xage; r(2)=0.23; P:<0.0001) in both genders. In addition, univariate analysis revealed a significant inverse correlation between BRS and heart rate, body mass index, and BP. Sedentary lifestyle and regular alcohol consumption were also associated with lower BRS. However, only age, heart rate, systolic and diastolic BP, body mass index, smoking, and gender were independent predictors of BRS in a multivariate model, accounting for 47% of the variance of BRS. The present study provides reference values for spontaneous BRS in a healthy white population. Only approximately half of the variability of BRS could be explained by anthropometric variables and common risk factors, which suggests that a significant proportion of interindividual differences may reflect genetic heterogeneity.

Elsheikh M, Casadei B, Conway GS, Wass JA. 2001. Hypertension is a major risk factor for aortic root dilatation in women with Turner's syndrome. Clin Endocrinol (Oxf), 54 (1), pp. 69-73. | Show Abstract | Read more

Women with Turner's syndrome (TS) have a threefold increase in mortality, primarily as a result of their cardiovascular complications. Recently, the risk of fatal aortic dissection has come to light as a major cause of mortality in women with TS. The aim of this study was to assess the prevalence of aortic root dilatation in a group of women with TS and to investigate the factors contributing to its development. Thirty-eight women with TS attending a dedicated adult Turner clinic were examined clinically and by M-mode and two-dimensional echocardiography on at least one occasion. Aortic root dilatation was defined as an aortic root diameter greater than the 95th centile for body surface area. Fasting serum lipid concentrations were measured in all women. Additionally, 18 subjects underwent noninvasive assessment of central arterial stiffness using applanation tonometry. Fifty percent of subjects were hypertensive and a similar number had an abnormal echocardiogram. A bicuspid aortic valve was present in 33% of subjects, 16 women (42%) had ascending aortic root dilatation. This was associated with a bicuspid aortic valve in four women and hypertension in 11. Two women had isolated aortic root dilatation. Aortic root diameter was significantly associated with systolic blood pressure (r = 0.5, P = 0.003) and left ventricular thickness (r = 0.5, P = 0.02). There was no association with serum lipids or arterial compliance. Structural cardiac abnormalities are present in up to 50% of women with Turner's syndrome. Aortic root dilatation is a significant risk in women with Turner's syndrome and is closely dependent on blood pressure. Aortic root dilatation does not appear to be related to atherosclerosis and is more likely to be due to a mesenchymal defect. Regular surveillance of the aortic root diameter is essential in all women with Turner's syndrome and hypertension should be treated aggressively when present in order to minimize the risk of potentially fatal aortic dissection.

El-Omar M, Kardos A, Casadei B. 2001. Mechanisms of respiratory sinus arrhythmia in patients with mild heart failure. Am J Physiol Heart Circ Physiol, 280 (1), pp. H125-H131. | Show Abstract

The high-frequency (HF) component of the heart rate variability (HRV) is regarded as an index of cardiac vagal responsiveness. However, when vagal tone is decreased, nonneural mechanisms could account for a significant proportion of the HF component. To test this hypothesis, we examined the HRV spectral power in 20 patients with mild chronic heart failure (CHF) and 11 controls before and during ganglion blockade with trimethaphan camsylate (3-6 mg/min iv). A small HF component was still present during ganglion blockade, and its amplitude did not differ between CHF patients and controls. The average contribution of nonneural oscillations to the HF component was 15% (range 1-77%) in patients with CHF and 3% (range 0. 7-30%) in healthy controls (P < 0.005). During controlled breathing at 0.16 Hz, however, it decreased to 1% (range 0.2-13%) in healthy controls and 5% (range 1-44%) in CHF patients. Our results indicate that the HF component can significantly overestimate cardiac vagal responsiveness in patients with mild CHF. This bias is improved by controlled breathing, since this maneuver increases the vagal contribution to HF without affecting its nonneural component.

Musialek P, Rigg L, Terrar DA, Paterson DJ, Casadei B. 2000. Role of cGMP-inhibited phosphodiesterase and sarcoplasmic calcium in mediating the increase in basal heart rate with nitric oxide donors. J Mol Cell Cardiol, 32 (10), pp. 1831-1840. | Show Abstract | Read more

Nitric oxide (NO) donors increase heart rate (HR) through a guanylyl cyclase-dependent stimulation of the pacemaker current I(f), without affecting basal I(Ca-L). The activity of I(f)is known to be enhanced by cyclic nucleotides and by an increase in cytosolic Ca(2+). We examined the role of cGMP-dependent signaling pathways and intracellular Ca(2+)stores in mediating the positive chronotropic effect of NO donors. In isolated guinea pig atria, the increase in HR in response to 1-100 micromol/l 3-morpholino-sydnonimine (SIN-1; with superoxide dismutase, n=6) or diethylamine-NO (DEA-NO, n=8) was significantly attenuated by blockers of the cGMP-inhibited phosphodiesterase (PDE3; trequinsin, milrinone or Ro-13-6438, n=22). In addition, the rate response to DEA-NO or sodium nitroprusside (SNP) was significantly reduced following inhibition of PKA (KT5720 or H-89, n=15) but not PKG (KT5728 or Rp-8-pCPT-cGMPs, n=16). Suppression of sarcoplasmic (SR) Ca(2+)release by pretreatment of isolated atria with ryanodine or cyclopiazonic acid (2 micromol/l and 60 micromol/l, n=16) significantly reduced the chronotropic response to 1-100 micromol/l SIN-1 or DEA-NO. Moreover, in isolated guinea pig sinoatrial node cells 5 micromol/l SNP significantly increased diastolic and peak Ca(2+)fluorescence (+13+/-1% and +28+/-1%, n=6, P<0.05). Our findings are consistent with a functionally significant role of cAMP/PKA signaling (via cGMP inhibition of PDE3) and SR Ca(2+)in mediating the positive chronotropic effect of NO donors.

Keavney B, Bird R, Caiazza A, Casadei B, Conway J. 2000. Measurement of blood pressure using the auscultatory and oscillometric methods in the same cuff deflation: validation and field trial of the A&D TM2421 monitor. J Hum Hypertens, 14 (9), pp. 573-579. | Show Abstract | Read more

We have evaluated under laboratory validation conditions and in an extensive field trial the behaviour of an ambulatory monitoring device that is capable of recording both by the Korotkoff-sound and oscillometric methods in a single cuff deflation (TM2421: A&D Co, Tokyo, Japan). The effects of subject age and blood pressure (BP) level on the accuracy and field reliability of the two methods implemented in the device have been determined. In the validation phase, automatic BP measurements were compared with readings by two trained observers in 96 subjects, and the results compared with the AAMI criteria for automatic BP monitors. In the field trial phase, the performances of Korotkoff-sound and oscillometric methods over a 24-h period of ambulatory BP monitoring were compared in 515 subjects, with analysis of the agreement between the two methods in patients where both provided satisfactory recordings. In the validation phase, the Korotkoff-sound method gave satisfactory results for both systolic and diastolic BP, but the oscillometric technique narrowly failed to meet the AAMI criteria for the measurement of either systolic or diastolic BP. In the field trial, the K-sound method failed to record BP accurately in 12% of subjects whereas the oscillometric method was successful in all of these. Where both methods provided technically adequate records, agreement between mean values for each method was close. In 18% of patients, the availability of the oscillometric measurement as a 'back-up' method for the K-sound method significantly improved the number of available measurements in the monitoring period, which should result in improved accuracy and reproducibility of the ambulatory mean values.

Musialek P, Casadei B. 2000. Nitrovasodilators and heart rate: more than the arterial baroreflex. Cardiovasc Res, 47 (2), pp. 404-405. | Read more

Musialek P, Paterson DJ, Casadei B. 2000. Cyclic GMP-inhibited phosphodiesterase of cAMP and protein kinase A play an important part in the positive chronotropic response to NO donors EUROPEAN HEART JOURNAL, 21 pp. 47-47.

Sears CE, Bryant SM, Rigg L, Terrar DA, Casadei B. 2000. Does nitric oxide regulate the hyperpolarisation-activated inward current in ventricular myocytes from spontaneously hypertensive rats? EUROPEAN HEART JOURNAL, 21 pp. 65-65.

Mohan RM, Choate JK, Golding S, Herring N, Casadei B, Paterson DJ. 2000. Peripheral pre-synaptic pathway reduces the heart rate response to sympathetic activation following exercise training: role of NO. Cardiovasc Res, 47 (1), pp. 90-98. | Show Abstract | Read more

OBJECTIVES: We tested the hypothesis that the attenuated heart rate (HR) response to sympathetic activation following swim training in the guinea pig (Cavia porcellus) results from a peripheral modulation of pacemaking by nitric oxide (NO). METHODS: Nitric oxide synthase (NOS) inhibition on the increase in heart rate with sympathetic nerve stimulation (SNS) was investigated in the isolated guinea pig double atrial/right stellate ganglion preparation from exercise trained (6-weeks swimming, n=20) and sedentary animals (n=20). Western blot analysis for neuronal nitric oxide synthase (nNOS) was performed on the stellate ganglion from both groups. RESULTS: Relative to the control group, the exercise group demonstrated typical exercise adaptations of increased ventricular weight/body weight ratio, enhanced skeletal muscle citrate synthase activity and higher concentrations of [3H]ouabain binding sites in both skeletal and cardiac tissue (P<0.05). The increase in heart rate (bpm) with SNS significantly decreased in the exercise group (n=16) compared to the sedentary group (n=16) from 30+/-5 to 17+/-3 bpm at 1 Hz; 67+/-7 to 47+/-4 bpm at 3 Hz; 85+/-9 to 63+/-4 bpm at 5 Hz and 101+/-9 to 78+/-5 bpm at 7 Hz stimulation (P<0.05). The increase in heart rate with cumulative doses (0.1-10 microM) or a single dose (0.1 microM) of bath-applied norepinephrine expressed as the effective doses at which the HR response was 50% of the maximum response (EC50) were similar in both exercise (EC50 -6.08+/-0.16 M, n=8) and sedentary groups (EC50 -6.18+/-0.07 M, n=7). Trained animals had significantly more nNOS protein in left stellate ganglion compared to the sedentary group. In the exercise group, the non-isoform selective NOS inhibitor, N-omega nitro-L-arginine (L-NA, 100 microM) caused a small but significant increase in the heart rate response to SNS. However, the positive chronotropic response to sympathetic nerve stimulation remained significantly attenuated in the exercise group compared to the sedentary group during NOS inhibition (P<0.05). CONCLUSIONS: Our results indicate that there is a significant peripheral pre-synaptic component reducing the HR response to sympathetic activation following training, although NO does not play a dominant role in this response.

Kardos A, Taylor DJ, Thompson C, Styles P, Hands L, Collin J, Casadei B. 2000. Sympathetic denervation of the upper limb improves forearm exercise performance and skeletal muscle bioenergetics. Circulation, 101 (23), pp. 2716-2720. | Show Abstract | Read more

BACKGROUND: Sympathetic activation may limit exercise performance by restraining muscle blood flow or by negatively affecting skeletal muscle metabolic behavior. To test this hypothesis, we studied the effect of thoracoscopic sympathetic trunkotomy (TST) on forearm exercise duration, blood flow, and muscle bioenergetics in 13 patients with idiopathic palmar hyperhidrosis. METHODS AND RESULTS: Heart rate and beat-by-beat mean arterial pressure were recorded at rest and during right and left rhythmic handgrip before and 4 to 7 weeks after right TST. Forearm blood flow was measured bilaterally at rest and on the right during exercise. Right forearm muscle phosphocreatine content and intracellular pH were assessed by (31)phosphorus magnetic resonance spectroscopy. After right TST, exercise duration increased from 8.9+/-1.4 to 13.4+/-1.8 minutes (P<0.0001) with the right forearm and from 5.7+/-0.4 to 7.6+/-0.9 minutes (P<0.05) with the left (P<0.05 for the interaction between treatment and side). Right forearm blood flow at rest was 66% higher (P<0.01) after right TST, but this difference decreased as the exercise progressed. After right TST, a significant reduction occurred in muscle acidification and phosphocreatine depletion during ipsilateral forearm exercise. This was associated with a significantly reduced mean arterial pressure response to right handgrip, whereas the pressor response to left handgrip did not change. CONCLUSIONS: Sympathetic denervation of the upper limb significantly improves forearm skeletal muscle bioenergetics and exercise performance in patients with idiopathic palmar hyperhidrosis.

Bryant SM, Sears CE, Rigg L, Terrar DA, Casadei B. 2000. Does nitric oxide regulate the hyperpolarisation-activated inward current in ventricular myocytes from spontaneously hypertensive rats? JOURNAL OF PHYSIOLOGY-LONDON, 525 pp. 91P-91P.

Kardos A, Watterich G, Csanady M, Casadei B, Rudas L. 2000. Determinants of spontaneous baroreflex sensitivity in a healthy working population JOURNAL OF HYPERTENSION, 18 pp. S75-S75.

Paterson DJ, Thornton JM, Murphy K, Griffith A, Pedersen D, Leff A, Adams L, Casadei B, Guz A. 2000. Higher centres encode cardiorespiratory response to exercise without movement feedback FASEB JOURNAL, 14 (4), pp. A646-A646.

Elsheikh M, Bird R, Casadei B, Conway GS, Wass JA. 2000. The effect of hormone replacement therapy on cardiovascular hemodynamics in women with Turner's syndrome. J Clin Endocrinol Metab, 85 (2), pp. 614-618. | Show Abstract | Read more

Women with Turner's syndrome, the majority of whom are estrogen deficient, have an increased incidence of coronary artery disease. The aim of this study was to assess the effects of hormone replacement therapy (HRT) on central arterial hemodynamics, insulin sensitivity, and lipids in adults with Turner's syndrome. Twenty-one women with Turner's syndrome were studied prospectively, on and off 3 months of estradiol valerate in combination with levonorgestrel. The following measurements were made: body mass index, waist/hip ratio, serum lipids, fasting insulin and glucose, and mean arterial blood pressure. Aortic root pressure and waveforms were estimated noninvasively and the augmentation index (AI), a measure of aortic stiffness, was calculated. The AI was significantly lower during estrogen therapy (22% vs. 15%; P = 0.008), suggesting a reduction in central arterial stiffness. Fasting insulin and glucose concentrations were also significantly lower during HRT (P = 0.01 and P = 0.0004, respectively). There was no difference in body mass index, serum lipids, or brachial and aortic blood pressures on and off treatment. Total cholesterol was correlated with the AI (r = 0.4; P = 0.03). These results suggest that HRT in women with Turner's syndrome has a favorable effect on central arterial hemodynamics and insulin sensitivity. The lack of effect on serum lipids suggests that the effects of HRT on aortic compliance may be mediated by an improvement in endothelial function.

Musialek P, Nash M, Thornton J, Casadei B, Paterson DJ. 2000. The nitric oxide donor sodium nitroprusside increases heart rate in the absence of changes in arterial blood pressure when applied topically to the sino-atrial node in the anaesthetised pig JOURNAL OF PHYSIOLOGY-LONDON, 523 pp. 267P-268P.

Casadei B, Paterson DJ. 2000. Should we still use nitrovasodilators to test baroreflex sensitivity? J Hypertens, 18 (1), pp. 3-6. | Read more

Kardos A, Taylor DJ, Thompson C, Styles P, Hands L, Collin J, Casadei B. 2000. Sympathetic denervation of the upper limb improves forearm exercise performance and skeletal muscle bioenergetics Heart, 83 (SUPPL. 1), | Show Abstract

Background. Sympathetic activation may limit exercise performance by restraining muscle blood flow or by negatively affecting skeletal muscle metabolic behavior. To test this hypothesis we studied the effect of thoracoscopic sympathetic trunkotomy (TST) on forearm exercise duration, blood flow, and muscle bioenergetics in 13 patients with idiopathic palmar hyperhidrosis. Methods and Results. Heart rate and beat-by-beat mean arterial pressure (MAP) were recorded at rest and during right and left rhythmic handgrip before and 4-7 weeks after right TST. Forearm blood flow (FBF) was measured bilaterally at rest and on the right during exercise. Right forearm muscle phosphocreatine content and intracellular pH were assessed by 31 P magnetic resonance spectroscopy. After right TST, exercise duration increased from 8.9±1.4 to 13.4±1.8 minutes (P < 0.0001) with the right forearm and from 5.7±0.4 to 7.6±0.9 minutes (P < 0.05) with the left (P < 0.05 for the interaction between treatment and side). Right FBF at rest was 66% higher (P < 0.01) after right TST, but this difference decreased as the exercise progressed. After right TST there was a significant reduction in muscle acidification and phosphocreatine depletion during ipsilateral forearm exercise. This was associated with a significantly reduced MAP response to right handgrip, whereas the pressor response to left handgrip did not change. Discussion. Sympathetic denervation of the upper limb significantly improves forearm skeletal muscle bioenergetics and exercise performance in patients with idiopathic palmar hyperhidrosis. Our findings suggest that inhibition of adrenergic activity might improve skeletal muscle abnormalities in conditions characterized by sympathetic hyperactivity, such as heart failure.

Musialek P, Paterson DJ, Casadei B. 2000. cGMP-inhibited phosphodiesterase of cAMP (PDE3) and protein kinase a (PKA) play an important role in eliciting the positive chronotropic effect of Nitric Oxide (NO) donors Heart, 83 (SUPPL. 1), | Show Abstract

Background: NO donors exert a positive chronotropic effect by stimulating the pacemaker current I f in sino-atrial node cells via a mechanism requiring guanylyl cyclase (GC) and cGMP, and involving mobilization of sarcoplasmic (SR) Ca 2+ . Cyclic GMP can directly stimulate If but it is ∼10-fold less potent than the 'physiological' I f -gating nucleotide, cAMP. In ventricular myocytes, NO can increase cAMP levels through a cGMP-dependent inhibition of PDE3. Aim: To elucidate the role of PDE3, PKA and PKG in mediating the NO-I f -dependent increase in HR. Methods and Results: In isolated guinea-pig atria with basal HR (B/L) of 174±3 bpm (n=69), we evaluated the HR response to increasing concentrations (from 0.1 to 100μmol/L) of the NO donors DEA-NO (n=8) or SIN-1 (+SOD 100 U/mL, n=6) or to 10 μmol/L SNP (n=9), (1) alone, and (2) after pretreatment (ca. 40min) with inhibitors of (i) PDE3 (milrinone, trequinsin or Ro-13-6482, n=22) or (ii) PKA (KT5720 or H-89, n=15) or (iii) PKG (KT5823 or Rp-8-pCPT-cGMPs, n=16). Whereas PKG inhibition had no effect on the magnitude of the increase in HR with DEA-NO (see Fig; bars show the peak increase in HR, mean± SEM; =p < 0.05 vs. B/L, †=p < 0.05 vs. the HR response DEA-NO alone), inhibition of PDE3 or PKA markedly attenuated the HR response to DEA-NO (and, similarly, to SIN-1 or SNP; not shown). Conclusion: cGMP-PDE3-cAMP signalling plays a significant part in eliciting the 'direct' positive chronotropic response to NO donors. Since PKA is known to stimulate SR Ca 2+ release by phosphorylating ryanodine receptors, the present findings provide an important link between the activation of GC with NO donors and the NO-dependent mobilization of SR Ca 2+ in SA node which we reported previously. (Graph Presented).

Carnicer R, Suffredini S, Liu X, Reilly S, Simon JN, Surdo NC, Zhang YH, Lygate CA, Channon KM, Casadei B. 2017. The Subcellular Localisation of Neuronal Nitric Oxide Synthase Determines the Downstream Effects of NO on Myocardial Function. Cardiovasc Res, 113 (3), pp. 321-331. | Read more

Wijesurendra RS, Liu A, Eichhorn C, Ariga R, Levelt E, Clarke WT, Rodgers CT, Karamitsos TD, Bashir Y, Ginks M et al. 2016. Lone Atrial Fibrillation Is Associated With Impaired Left Ventricular Energetics That Persists Despite Successful Catheter Ablation. Circulation, 134 (15), pp. 1068-1081. | Show Abstract | Read more

BACKGROUND: Lone atrial fibrillation (AF) may reflect a subclinical cardiomyopathy that persists after sinus rhythm (SR) restoration, providing a substrate for AF recurrence. To test this hypothesis, we investigated the effect of restoring SR by catheter ablation on left ventricular (LV) function and energetics in patients with AF but no significant comorbidities. METHODS: Fifty-three patients with symptomatic paroxysmal or persistent AF and without significant valvular disease, uncontrolled hypertension, coronary artery disease, uncontrolled thyroid disease, systemic inflammatory disease, diabetes mellitus, or obstructive sleep apnea (ie, lone AF) undergoing ablation and 25 matched control subjects in SR were investigated. Magnetic resonance imaging quantified LV ejection fraction (LVEF), peak systolic circumferential strain (PSCS), and left atrial volumes and function, whereas phosphorus-31 magnetic resonance spectroscopy evaluated ventricular energetics (ratio of phosphocreatine to ATP). AF burden was determined before and after ablation by 7-day Holter monitoring; intermittent ECG event monitoring was also undertaken after ablation to investigate for asymptomatic AF recurrence. RESULTS: Before ablation, both LV function and energetics were significantly impaired in patients compared with control subjects (LVEF, 61% [interquartile range (IQR), 52%-65%] versus 71% [IQR, 69%-73%], P<0.001; PSCS, -15% [IQR, -11 to -18%] versus -18% [IQR, -17% to -19%], P=0.002; ratio of phosphocreatine to ATP, 1.81±0.35 versus 2.05±0.29, P=0.004). As expected, patients also had dilated and impaired left atria compared with control subjects (all P<0.001). Early after ablation (1-4 days), LVEF and PSCS improved in patients recovering SR from AF (LVEF, 7.0±10%, P=0.005; PSCS, -3.5±4.3%, P=0.001) but were unchanged in those in SR during both assessments (both P=NS). At 6 to 9 months after ablation, AF burden reduced significantly (from 54% [IQR, 1.5%-100%] to 0% [IQR 0%-0.1%]; P<0.001). However, LVEF and PSCS did not improve further (both P=NS) and remained impaired compared with control subjects (P<0.001 and P=0.003, respectively). Similarly, there was no significant improvement in atrial function from before ablation (P=NS), and this remained lower than in control subjects (P<0.001). The ratio of phosphocreatine to ATP was unaffected by heart rhythm during assessment and AF burden before ablation (both P=NS). It was unchanged after ablation (P=0.57), remaining lower than in control subjects regardless of both recovery of SR and freedom from recurrent AF (P=0.006 and P=0.002, respectively). CONCLUSIONS: Patients with lone AF have impaired myocardial energetics and subtle LV dysfunction, which do not normalize after ablation. These findings suggest that AF may be the consequence (rather than the cause) of an occult cardiomyopathy, which persists despite a significant reduction in AF burden after ablation.

Simon JN, Ziberna K, Casadei B. 2016. Compromised redox homeostasis, altered nitroso-redox balance, and therapeutic possibilities in atrial fibrillation. Cardiovasc Res, 109 (4), pp. 510-518. | Show Abstract | Read more

Although the initiation, development, and maintenance of atrial fibrillation (AF) have been linked to alterations in myocyte redox state, the field lacks a complete understanding of the impact these changes may have on cellular signalling, atrial electrophysiology, and disease progression. Recent studies demonstrate spatiotemporal changes in reactive oxygen species production shortly after the induction of AF in animal models with an uncoupling of nitric oxide synthase activity ensuing in the presence of long-standing persistent AF, ultimately leading to a major shift in nitroso-redox balance. However, it remains unclear which radical or non-radical species are primarily involved in the underlying mechanisms of AF or which proteins are targeted for redox modification. In most instances, only free radical oxygen species have been assessed; yet evidence from the redox signalling field suggests that non-radical species are more likely to regulate cellular processes. A wider appreciation for the distinction of these species and how both species may be involved in the development and maintenance of AF could impact treatment strategies. In this review, we summarize how redox second-messenger systems are regulated and discuss the recent evidence for alterations in redox regulation in the atrial myocardium in the presence of AF, while identifying some critical missing links. We also examine studies looking at antioxidants for the prevention and treatment of AF and propose alternative redox targets that may serve as superior therapeutic options for the treatment of AF.

Reilly SN, Liu X, Carnicer R, Recalde A, Muszkiewicz A, Jayaram R, Carena MC, Wijesurendra R, Stefanini M, Surdo NC et al. 2016. Up-regulation of miR-31 in human atrial fibrillation begets the arrhythmia by depleting dystrophin and neuronal nitric oxide synthase. Sci Transl Med, 8 (340), pp. 340ra74. | Show Abstract | Read more

Atrial fibrillation (AF) is a growing public health burden, and its treatment remains a challenge. AF leads to electrical remodeling of the atria, which in turn promotes AF maintenance and resistance to treatment. Although remodeling has long been a therapeutic target in AF, its causes remain poorly understood. We show that atrial-specific up-regulation of microRNA-31 (miR-31) in goat and human AF depletes neuronal nitric oxide synthase (nNOS) by accelerating mRNA decay and alters nNOS subcellular localization by repressing dystrophin translation. By shortening action potential duration and abolishing rate-dependent adaptation of the action potential duration, miR-31 overexpression and/or disruption of nNOS signaling recapitulates features of AF-induced remodeling and significantly increases AF inducibility in mice in vivo. By contrast, silencing miR-31 in atrial myocytes from patients with AF restores dystrophin and nNOS and normalizes action potential duration and its rate dependency. These findings identify atrial-specific up-regulation of miR-31 in human AF as a key mechanism causing atrial dystrophin and nNOS depletion, which in turn contributes to the atrial phenotype begetting this arrhythmia. miR-31 may therefore represent a potential therapeutic target in AF.

Zheng Z, Jayaram R, Jiang L, Emberson J, Zhao Y, Li Q, Du J, Guarguagli S, Hill M, Chen Z et al. 2016. Perioperative Rosuvastatin in Cardiac Surgery. N Engl J Med, 374 (18), pp. 1744-1753. | Show Abstract | Read more

BACKGROUND: Complications after cardiac surgery are common and lead to substantial increases in morbidity and mortality. Meta-analyses of small randomized trials have suggested that perioperative statin therapy can prevent some of these complications. METHODS: We randomly assigned 1922 patients in sinus rhythm who were scheduled for elective cardiac surgery to receive perioperative rosuvastatin (at a dose of 20 mg daily) or placebo. The primary outcomes were postoperative atrial fibrillation within 5 days after surgery, as assessed by Holter electrocardiographic monitoring, and myocardial injury within 120 hours after surgery, as assessed by serial measurements of the cardiac troponin I concentration. Secondary outcomes included major in-hospital adverse events, duration of stay in the hospital and intensive care unit, left ventricular and renal function, and blood biomarkers. RESULTS: The concentrations of low-density lipoprotein cholesterol and C-reactive protein after surgery were lower in patients assigned to rosuvastatin than in those assigned to placebo (P<0.001). However, the rate of postoperative atrial fibrillation did not differ significantly between the rosuvastatin group and the placebo group (21.1% and 20.5%, respectively; odds ratio 1.04; 95% confidence interval [CI], 0.84 to 1.30; P=0.72), nor did the area under the troponin I-release curve (102 ng×hour per milliliter and 100 ng×hour per milliliter, respectively; between-group difference, 1%; 95% CI, -9 to 13; P=0.80). Subgroup analyses did not indicate benefit in any category of patient. Rosuvastatin therapy did not result in beneficial effects on any of the secondary outcomes but was associated with a significant absolute (±SE) excess of 5.4±1.9 percentage points in the rate of postoperative acute kidney injury (P=0.005). CONCLUSIONS: In this trial, perioperative statin therapy did not prevent postoperative atrial fibrillation or perioperative myocardial damage in patients undergoing elective cardiac surgery. Acute kidney injury was more common with rosuvastatin. (Funded by the British Heart Foundation and others; STICS ClinicalTrials.gov number, NCT01573143.).

Antonopoulos AS, Margaritis M, Verheule S, Recalde A, Sanna F, Herdman L, Psarros C, Nasrallah H, Coutinho P, Akoumianakis I et al. 2016. Mutual Regulation of Epicardial Adipose Tissue and Myocardial Redox State by PPAR-γ/Adiponectin Signalling. Circ Res, 118 (5), pp. 842-855. | Show Abstract | Read more

RATIONALE: Adiponectin has anti-inflammatory effects in experimental models, but its role in the regulation of myocardial redox state in humans is unknown. Although adiponectin is released from epicardial adipose tissue (EpAT), it is unclear whether it exerts any paracrine effects on the human myocardium. OBJECTIVE: To explore the cross talk between EpAT-derived adiponectin and myocardial redox state in the human heart. METHODS AND RESULTS: EpAT and atrial myocardium were obtained from 306 patients undergoing coronary artery bypass grafting. Functional genetic polymorphisms that increase ADIPOQ expression (encoding adiponectin) led to reduced myocardial nicotinamide adenine dinucleotide phosphate oxidase-derived O2 (-), whereas circulating adiponectin and ADIPOQ expression in EpAT were associated with elevated myocardial O2 (-). In human atrial tissue, we demonstrated that adiponectin suppresses myocardial nicotinamide adenine dinucleotide phosphate oxidase activity, by preventing AMP kinase-mediated translocation of Rac1 and p47(phox) from the cytosol to the membranes. Induction of O2 (-) production in H9C2 cardiac myocytes led to the release of a transferable factor able to induce peroxisome proliferator-activated receptor-γ-mediated upregulation of ADIPOQ expression in cocultured EpAT. Using a NOX2 transgenic mouse and a pig model of rapid atrial pacing, we found that oxidation products (such as 4-hydroxynonenal) released from the heart trigger peroxisome proliferator-activated receptor-γ-mediated upregulation of ADIPOQ in EpAT. CONCLUSIONS: We demonstrate for the first time in humans that adiponectin directly decreases myocardial nicotinamide adenine dinucleotide phosphate oxidase activity via endocrine or paracrine effects. Adiponectin expression in EpAT is controlled by paracrine effects of oxidation products released from the heart. These effects constitute a novel defense mechanism of the heart against myocardial oxidative stress.

Hashimoto T, Sivakumaran V, Carnicer R, Zhu G, Hahn VS, Bedja D, Recalde A, Duglan D, Channon KM, Casadei B, Kass DA. 2016. Tetrahydrobiopterin Protects Against Hypertrophic Heart Disease Independent of Myocardial Nitric Oxide Synthase Coupling. J Am Heart Assoc, 5 (3), pp. e003208. | Show Abstract | Read more

BACKGROUND: Nitric oxide synthase uncoupling occurs under conditions of oxidative stress modifying the enzyme's function so it generates superoxide rather than nitric oxide. Nitric oxide synthase uncoupling occurs with chronic pressure overload, and both are ameliorated by exogenous tetrahydrobiopterin (BH4)-a cofactor required for normal nitric oxide synthase function-supporting a pathophysiological link. Genetically augmenting BH4 synthesis in endothelial cells fails to replicate this benefit, indicating that other cell types dominate the effects of exogenous BH4 administration. We tested whether the primary cellular target of BH4 is the cardiomyocyte or whether other novel mechanisms are invoked. METHODS AND RESULTS: Mice with cardiomyocyte-specific overexpression of GTP cyclohydrolase 1 (mGCH1) and wild-type littermates underwent transverse aortic constriction. The mGCH1 mice had markedly increased myocardial BH4 and, unlike wild type, maintained nitric oxide synthase coupling after transverse aortic constriction; however, the transverse aortic constriction-induced abnormalities in cardiac morphology and function were similar in both groups. In contrast, exogenous BH4 supplementation improved transverse aortic constricted hearts in both groups, suppressed multiple inflammatory cytokines, and attenuated infiltration of inflammatory macrophages into the heart early after transverse aortic constriction. CONCLUSIONS: BH4 protection against adverse remodeling in hypertrophic cardiac disease is not driven by its prevention of myocardial nitric oxide synthase uncoupling, as presumed previously. Instead, benefits from exogenous BH4 are mediated by a protective effect coupled to suppression of inflammatory pathways and myocardial macrophage infiltration.

Antonopoulos AS, Margaritis M, Coutinho P, Shirodaria C, Psarros C, Herdman L, Sanna F, De Silva R, Petrou M, Sayeed R et al. 2015. Adiponectin as a link between type 2 diabetes and vascular NADPH oxidase activity in the human arterial wall: the regulatory role of perivascular adipose tissue. Diabetes, 64 (6), pp. 2207-2219. | Show Abstract | Read more

Oxidative stress plays a critical role in the vascular complications of type 2 diabetes. We examined the effect of type 2 diabetes on NADPH oxidase in human vessels and explored the mechanisms of this interaction. Segments of internal mammary arteries (IMAs) with their perivascular adipose tissue (PVAT) and thoracic adipose tissue were obtained from 386 patients undergoing coronary bypass surgery (127 with type 2 diabetes). Type 2 diabetes was strongly correlated with hypoadiponectinemia and increased vascular NADPH oxidase-derived superoxide anions (O2˙(-)). The genetic variability of the ADIPOQ gene and circulating adiponectin (but not interleukin-6) were independent predictors of NADPH oxidase-derived O2˙(-). However, adiponectin expression in PVAT was positively correlated with vascular NADPH oxidase-derived O2˙(-). Recombinant adiponectin directly inhibited NADPH oxidase in human arteries ex vivo by preventing the activation/membrane translocation of Rac1 and downregulating p22(phox) through a phosphoinositide 3-kinase/Akt-mediated mechanism. In ex vivo coincubation models of IMA/PVAT, the activation of arterial NADPH oxidase triggered a peroxisome proliferator-activated receptor-γ-mediated upregulation of the adiponectin gene in the neighboring PVAT via the release of vascular oxidation products. We demonstrate for the first time in humans that reduced adiponectin levels in individuals with type 2 diabetes stimulates vascular NADPH oxidase, while PVAT "senses" the increased NADPH oxidase activity in the underlying vessel and responds by upregulating adiponectin gene expression. This PVAT-vessel interaction is identified as a novel therapeutic target for the prevention of vascular complications of type 2 diabetes.

Carnicer R, Hale AB, Suffredini S, Liu X, Reilly S, Zhang MH, Surdo NC, Bendall JK, Crabtree MJ, Lim GB et al. 2012. Cardiomyocyte GTP cyclohydrolase 1 and tetrahydrobiopterin increase NOS1 activity and accelerate myocardial relaxation. Circ Res, 111 (6), pp. 718-727. | Show Abstract | Read more

RATIONALE: Tetrahydrobiopterin (BH4) is an essential cofactor of nitric oxide synthases (NOS). Oral BH4 supplementation preserves cardiac function in animal models of cardiac disease; however, the mechanisms underlying these findings are not completely understood. OBJECTIVE: To study the effect of myocardial transgenic overexpression of the rate-limiting enzyme in BH4 biosynthesis, GTP cyclohydrolase 1 (GCH1), on NOS activity, myocardial function, and Ca2+ handling. METHODS AND RESULTS: GCH1overexpression significantly increased the biopterins level in left ventricular (LV) myocytes but not in the nonmyocyte component of the LV myocardium or in plasma. The ratio between BH4 and its oxidized products was lower in mGCH1-Tg, indicating that a large proportion of the myocardial biopterin pool was oxidized; nevertheless, myocardial NOS1 activity was increased in mGCH1-Tg, and superoxide release was significantly reduced. Isolated hearts and field-stimulated LV myocytes (3 Hz, 35°C) overexpressing GCH1 showed a faster relaxation and a PKA-mediated increase in the PLB Ser16 phosphorylated fraction and in the rate of decay of the [Ca2+]i transient. RyR2 S-nitrosylation and diastolic Ca2+ leak were larger in mGCH1-Tg and ICa density was lower; nevertheless the amplitude of the [Ca2+]i transient and contraction did not differ between genotypes, because of an increase in the SR fractional release of Ca2+ in mGCH1-Tg myocytes. Xanthine oxidoreductase inhibition abolished the difference in superoxide production but did not affect myocardial function in either group. By contrast, NOS1 inhibition abolished the differences in ICa density, Ser16 PLB phosphorylation, [Ca2+]i decay, and myocardial relaxation between genotypes. CONCLUSIONS: Myocardial GCH1 activity and intracellular BH4 are a limiting factor for constitutive NOS1 and SERCA2A activity in the healthy myocardium. Our findings suggest that GCH1 may be a valuable target for the treatment of LV diastolic dysfunction.

Antoniades C, Demosthenous M, Reilly S, Margaritis M, Zhang MH, Antonopoulos A, Marinou K, Nahar K, Jayaram R, Tousoulis D et al. 2012. Myocardial redox state predicts in-hospital clinical outcome after cardiac surgery effects of short-term pre-operative statin treatment. J Am Coll Cardiol, 59 (1), pp. 60-70. | Show Abstract | Read more

OBJECTIVES: The purpose of this study was to evaluate the role of the myocardial redox state in the development of in-hospital complications after cardiac surgery and the effect of statins on the myocardial redox state. BACKGROUND: Statins improve clinical outcome after cardiac surgery, but it is unclear whether they exert their effects by modifying the myocardial redox state. METHODS: We quantified myocardial superoxide anion (O(2)(-)) and peroxynitrite (ONOO(-)) and their enzymatic sources in samples of the right atrial appendage (RAA) from 303 patients undergoing cardiac surgery who were followed up until discharge, and in 42 patients who were randomized to receive 3-day treatment with atorvastatin 40 mg/d or placebo before surgery. The mechanisms by which atorvastatin modifies myocardial redox state were investigated in 26 RAA samples that were exposed to atorvastatin ex vivo. RESULTS: Atrial O(2)(-) (derived mainly from nicotinamide adenine dinucleotide phosphate [NADPH] oxidases) and ONOO(-) were independently associated with increased risk of atrial fibrillation, the need for post-operative inotropic support, and the length of hospital stay. Pre-operative atorvastatin treatment suppressed atrial NADPH oxidase activity and myocardial O(2)(-) and ONOO(-) production. Ex vivo incubation of RAA samples with atorvastatin induced a mevalonate-reversible and Rac1-mediated inhibition of NADPH oxidase. CONCLUSIONS: There is a strong independent association between myocardial O(2)(-)/ONOO(-) and in-hospital complications after cardiac surgery. Both myocardial O(2)(-) and ONOO(-) are reduced by pre-operative statin treatment, through a Rac1-mediated suppression of NADPH oxidase activity. These findings suggest that inhibition of myocardial NADPH oxidases may contribute to the beneficial effect of statins in patients undergoing cardiac surgery. (Effects of Atorvastatin on Endothelial Function, Vascular and Myocardial Redox State in High Cardiovascular Risk Patients; NCT01013103).

Cited:

105

Scopus

Reilly SN, Jayaram R, Nahar K, Antoniades C, Verheule S, Channon KM, Alp NJ, Schotten U, Casadei B. 2011. Atrial Sources of Reactive Oxygen Species Vary With the Duration and Substrate of Atrial Fibrillation Implications for the Antiarrhythmic Effect of Statins CIRCULATION, 124 (10), pp. 1107-1U91. | Show Abstract | Read more

BACKGROUND-: An altered nitric oxide-redox balance has been implicated in the pathogenesis of atrial fibrillation (AF). Statins inhibit NOX2-NADPH oxidases and prevent postoperative AF but are less effective in AF secondary prevention; the mechanisms underlying these findings are poorly understood. METHODS AND RESULTS-: By using goat models of pacing-induced AF or of atrial structural remodeling secondary to atrioventricular block and right atrial samples from 130 patients undergoing cardiac surgery, we found that the mechanisms responsible for the NO-redox imbalance differ between atria and with the duration and substrate of AF. Rac1 and NADPH oxidase activity and the protein level of NOX2 and p22phox were significantly increased in the left atrium of goats after 2 weeks of AF and in patients who developed p ostoperative AF in the absence of differences in leukocytes infiltration. Conversely, in the presence of longstanding AF or atrioventricular block, uncoupled nitric oxide synthase activity (secondary to reduced BH4 content and/or increased arginase activity) and mitochondrial oxidases accounted for the biatrial increase in reactive oxygen species. Atorvastatin caused a mevalonate-reversible inhibition of Rac1 and NOX2-NADPH oxidase activity in right atrial samples from patients who developed postoperative AF, but it did not affect reactive oxygen species, nitric oxide synthase uncoupling, or BH4 in patients with permanent AF. CONCLUSIONS-: Upregulation of atrial NADPH oxidases is an early but transient event in the natural history of AF. Changes in the sources of reactive oxygen species with atrial remodeling may explain why statins are effective in the primary prevention of AF but not in its management. © 2011 American Heart Association, Inc.

Cited:

117

Scopus

Antoniades C, Bakogiannis C, Leeson P, Guzik TJ, Zhang MH, Tousoulis D, Antonopoulos AS, Demosthenous M, Marinou K, Hale A et al. 2011. Rapid, direct effects of statin treatment on arterial redox state and nitric oxide bioavailability in human atherosclerosis via tetrahydrobiopterin- mediated endothelial nitric oxide synthase coupling Circulation, 124 (3), pp. 335-345. | Show Abstract | Read more

Background-: Treatment with statins improves clinical outcome, but the exact mechanisms of pleiotropic statin effects on vascular function in human atherosclerosis remain unclear. We examined the direct effects of atorvastatin on tetrahydrobiopterin-mediated endothelial nitric oxide (NO) synthase coupling in patients with coronary artery disease. Methods and Results-: We first examined the association of statin treatment with vascular NO bioavailability and arterial superoxide (O 2 .- ) in 492 patients undergoing coronary artery bypass graft surgery. Then, 42 statin-naïve patients undergoing elective coronary artery bypass graft surgery were randomized to atorvastatin 40 mg/d or placebo for 3 days before surgery to examine the impact of atorvastatin on endothelial function and O 2 .- generation in internal mammary arteries. Finally, segments of internal mammary arteries from 26 patients were used in ex vivo experiments to evaluate the statin-dependent mechanisms regulating the vascular redox state. Statin treatment was associated with improved vascular NO bioavailability and reduced O 2 .- generation in internal mammary arteries. Oral atorvastatin increased vascular tetrahydrobiopterin bioavailability and reduced basal and N-nitro-L-arginine methyl ester-inhibitable O 2 .- in internal mammary arteries independently of low-density lipoprotein lowering. In ex vivo experiments, atorvastatin rapidly improved vascular tetrahydrobiopterin bioavailability by upregulating GTP-cyclohydrolase I gene expression and activity, resulting in improved endothelial NO synthase coupling and reduced vascular O 2 .- . These effects were reversed by mevalonate, indicating a direct effect of vascular hydroxymethylglutaryl- coenzyme A reductase inhibition. Conclusions-: This study demonstrates for the first time in humans the direct effects of statin treatment on the vascular wall, supporting the notion that this effect is independent of low-density lipoprotein lowering. Atorvastatin directly improves vascular NO bioavailability and reduces vascular O 2 .- through tetrahydrobiopterin- mediated endothelial NO synthase coupling. These findings provide new insights into the mechanisms mediating the beneficial vascular effects of statins in humans. Clinical Trial Registration-: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01013103. © 2011 American Heart Association, Inc.

Seddon MD, Chowienczyk PJ, Brett SE, Casadei B, Shah AM. 2008. Neuronal nitric oxide synthase regulates basal microvascular tone in humans in vivo. Circulation, 117 (15), pp. 1991-1996. | Show Abstract | Read more

BACKGROUND: Nitric oxide (NO) has a pivotal role in the regulation of vascular tone and blood flow, with dysfunctional release contributing to disease pathophysiology. These effects have been attributed to NO production by the endothelial NO synthase (eNOS); however, recent evidence suggests that a neuronal NO synthase (nNOS) may also be expressed in arterial vessels. METHODS AND RESULTS: We undertook a first-in-humans investigation of the role of nNOS in the local regulation of vascular blood flow in healthy subjects. Brachial artery infusion of the nNOS-specific inhibitor S-methyl-L-thiocitrulline (SMTC, 0.025 micromol/min to 0.2 micromol/min) caused a dose-dependent reduction in basal flow, with a 30.1+/-3.8% decrease at the highest dose (n=10; mean+/-SE; P<0.01). The effect of SMTC was abolished by coinfusion of the NO synthase substrate L-arginine but was unaffected by D-arginine. A similar reduction in basal flow with the nonselective NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA; 37.4+/-3.1%, n=10) required a 20-fold higher dose of 4 micromol/min. At doses that produced comparable reductions in basal flow, only L-NMMA (4 micromol/min) and not SMTC (0.2 micromol/min) inhibited acetylcholine-induced vasodilation; however, both SMTC and L-NMMA inhibited the forearm vasodilator response to mental stress. CONCLUSIONS: Basal forearm blood flow in humans is regulated by nNOS-derived NO, in contrast to the acetylcholine-stimulated increase in blood flow, which, as shown previously, is mediated primarily by eNOS. These data indicate that vascular nNOS has a distinct local role in the physiological regulation of human microvascular tone in vivo.

Zhang YH, Zhang MH, Sears CE, Emanuel K, Redwood C, El-Armouche A, Kranias EG, Casadei B. 2008. Reduced phospholamban phosphorylation is associated with impaired relaxation in left ventricular myocytes from neuronal NO synthase-deficient mice. Circ Res, 102 (2), pp. 242-249. | Show Abstract | Read more

Stimulation of nitric oxide (NO) release from the coronary endothelium facilitates myocardial relaxation via a cGMP-dependent reduction in myofilament Ca2+ sensitivity. Recent evidence suggests that NO released by a neuronal NO synthase (nNOS) in the myocardium can also hasten left ventricular relaxation; however, the mechanism underlying these findings is uncertain. Here we show that both relaxation (TR50) and the rate of [Ca2+]i transient decay (tau) are significantly prolonged in field-stimulated or voltage-clamped left ventricular myocytes from nNOS-/- mice and in wild-type myocytes (nNOS+/+) after acute nNOS inhibition. Disabling the sarcoplasmic reticulum abolished the differences in TR50 and tau, suggesting that impaired sarcoplasmic reticulum Ca2+ reuptake may account for the slower relaxation in nNOS-/- mice. In line with these findings, disruption of nNOS (but not of endothelial NOS) decreased phospholamban phosphorylation (P-Ser16 PLN), whereas nNOS inhibition had no effect on TR50 or tau in PLN-/- myocytes. Inhibition of cGMP signaling had no effect on relaxation in either group whereas protein kinase A inhibition abolished the difference in relaxation and PLN phosphorylation by decreasing P-Ser16 PLN and prolonging TR50 in nNOS+/+ myocytes. Conversely, inhibition of type 1 or 2A protein phosphatases shortened TR50 and increased P-Ser16 PLN in nNOS-/- but not in nNOS+/+ myocytes, in agreement with data showing increased protein phosphatase activity in nNOS-/- hearts. Taken together, our findings identify a novel mechanism by which myocardial nNOS promotes left ventricular relaxation by regulating the protein kinase A-mediated phosphorylation of PLN and the rate of sarcoplasmic reticulum Ca2+ reuptake via a cGMP-independent effect on protein phosphatase activity.

Dawson D, Lygate CA, Zhang MH, Hulbert K, Neubauer S, Casadei B. 2005. nNOS gene deletion exacerbates pathological left ventricular remodeling and functional deterioration after myocardial infarction. Circulation, 112 (24), pp. 3729-3737. | Show Abstract | Read more

BACKGROUND: The neuronal isoform of nitric oxide synthase (nNOS) has been implicated in the regulation of basal and beta-adrenergic inotropy in normal and chronically infarcted hearts. Furthermore, myocardial nNOS expression and activity increase in failing hearts, raising the possibility that nNOS may influence left ventricular (LV) remodeling progression and functional deterioration after myocardial infarction (MI). METHODS AND RESULTS: We compared LV remodeling at 1, 4, and 8 weeks after MI in nNOS-knockout mice (nNOS(-/-)) and their wild-type (WT) littermates matched for infarct size by using a highly accurate 3-dimensional echocardiographic technique. Basal LV hemodynamics and the inotropic response to dobutamine infusion (4 and 16 ng.g(-1).min(-1)) were also evaluated 8 weeks after MI. Sham-operated nNOS(-/-) mice showed enhanced basal LV contractility (P<0.03 versus WT, as evaluated by preload-recruitable stroke work) but an attenuated inotropic response to dobutamine infusion (P<0.01 versus WT). Both basal and beta-adrenergic LV relaxations were significantly impaired in nNOS(-/-) mice. Survival after MI did not differ between groups. However, nNOS(-/-) mice developed a faster and more severe LV dilation compared with WT mice (P<0.05 for both end-systolic and end-diastolic volume indices). WT mice maintained a positive inotropic response to dobutamine 8 weeks after MI. In contrast, infarcted nNOS(-/-) mice responded to dobutamine with a dramatic fall in LV contractility (P<0.01 for preload-recruitable stroke work). CONCLUSIONS: nNOS plays a crucial role in preventing adverse LV remodeling and maintaining myocardial beta-adrenergic reserve after MI. Taken together, our findings suggest that upregulation of myocardial nNOS in infarcted hearts may be an important adaptive mechanism.

Identification of the atrial transcriptional signature of patients who develop atrial fibrillation

Microarray expression analyses have identified differences in the expression of gene sets related to ion channel function and transcription factors in atrial tissue from patients with paroxysmal or persistent atrial fibrillation (AF) versus normal sinus rhythm (SR) and differential expression of miRs involved in the regulation of ion channel subunits have been identified between similar patient groups. However, it is unclear whether these changes are a cause or a consequence of AF. So far, most ...

View project

The role of nitric oxide synthase and its cofactor BH4 in diabetic cardiomyopathy

A high percentage of diabetic patients develop a distinct type of heart disease known as diabetic cardiomyopathy. The mechanisms underlying this condition are only partially understood and specific therapies are lacking. We have investigated the molecular signature of diabetes in heart cells/muscle of patients and animal models and discovered that cardiac dysfunction is prevented by increasing the myocardial level of tetrahydrobiopterin (BH4). BH4 is a key cofactor of nitric oxide synthase ...

View project

1462