Advanced glycation end products elicit externalization of phosphatidylserine in a subpopulation of platelets via 5-HT2A/2Creceptors

Advanced glycation end products (AGE) are substantially elevated in individuals with diabetes and/or chronic kidney disease (CKD). These patients are at greatly increased risk of cardiovascular events. The purpose of this study was to investigate the novel hypothesis that AGE elicit externalization of the platelet membrane phospholipid phosphatidylserine (PS). This contributes to hemostasis through propagation of the coagulation cascade leading to thrombus formation. Platelet-rich plasma (PRP) was prepared by differential centrifugation, and PS externalization was quantified by a fluorescence-activated cell sorter using annexin V-FITC. Human serum albumin (HSA)-AGE was generated by incubating HSA with glucose for 2, 4, or 6 wk, and total HSA-AGE was assessed by fluorescence intensity. The 2-wk HSA-AGE preparation (0–2 mg/ml) stimulated a concentration-dependent increase in PS externalization in a subpopulation of platelets that was threefold at 2 mg/ml. In contrast, the 4- and 6-wk preparations were maximal at 0.5 mg/ml and fivefold in magnitude. These effects mirrored the change in total HSA-AGE content of the preparations. The PS response was maximal at 10 min and inhibited by the PKC-δ inhibitor rottlerin and the serotonin [5-hydroxytryptamine (5-HT)]2A/2Creceptor antagonist ritanserin in a dose-dependent manner. Moreover, the 5-HT2A/2Creceptor agonist 1,2,5-dimethoxy-4-iodophenyl-2-aminopropane mimicked the effect of HSA-AGE on PS externalization. These data demonstrate, for the first time, that HSA-AGE stimulates PS externalization in a subpopulation of platelets via the 5-HT2A/2Creceptor. This may have important consequences for platelet involvement in inflammatory responses and the increased cardiovascular risk observed in individuals with diabetes and/or CKD.