Oxidative stress contributes to memory impairment and neuronal damage in experimental cerebral hypoperfusion
Farkas E., Mracsko E., Krecsmarik M., Karg E., Penke B., Bari F.
The permanent, bilateral occlusion of the common carotid arteries of rats (2VO) has been widely used as a model for chronic cerebral hypoperfusion as it occurs in aging and dementia. 2VO in experimental animals leads to memory dysfunction and a progressive loss of hippocampal pyramidal neurons. However, the potential mechanisms of neuronal damage after the onset of 2VO have not been identified. The present investigation set out to determine whether oxidative stress may contribute to the 2VO-induced memory impairment and neurodegeneration. Treatments with the antioxidant alpha-tocopherol were employed as pharmacological means to counteract and, thus, confirm the incidence of oxidative stress in the 2VO model. 2VO was imposed on male Wistar rats (n=70). Sham-operated animals (SHAM) served as controls (n=66). Half of the animals were pre- or post-treated repeatedly with alpha-tocopherol (5 x 100 mg/kg daily, i.p.), the other half received soybean oil, the vehicle of alpha-tocopherol. One week after the onset of 2VO, the spatial learning capacity of the animals was assessed in the Morris water maze (n=65). After testing, hippocampal slices were stained with cresyl violet in order to examine the pyramidal cell layer integrity. The density of MAP-2-positive dendrites and the level of OX-42-labeled microglial activation were determined immunocytochemically. The amount of nitrotyrosine (generated by the free radical peroxinitrite) was determined with Western blotting (n=32). Alpha-tocopherol concentration was determined in the peripheral tissues, blood and brain with HPLC (n=39) . Alpha-tocopherol attenuated the 2VO-induced learning impairment. The treatments with alpha-tocopherol, and particularly the post-treatment, prevented the 2VO-induced pyramidal cell death and the activation of microglia in the hippocampus CA1 region, and the degeneration of MAP-2-positive dendrites in the CA3 region, determined 2 weeks after the onset of 2VO. The amount of nitrotyrosine in the hippocampus was moderately elevated as compared with SHAM controls on days 3 and 7 (relative optical density: 0.87±0.11 vs. 0.75±0.10, and 0.98±0.03 vs. 0.86±0.10, respectively), but was not affected on day 1 after the initiation of 2VO. The alpha-tocopherol concentration was considerably elevated in the peripheral tissues and the blood, while only moderate accumulation of alpha-tocopherol was detected in the hippocampus (31.99±1.79 vs. 28.98±1.36 nmol/g). The data suggests that oxidative neuronal injury plays a role in the 2VO-related neurodegenerative processes. Further, alpha-tocopherol appears beneficial in combating the cerebral hypoperfusion-related neuronal damage. Finally, the observation that the post-treatment achieved better neuroprotection than the pretreatment may imply that the increased availability of alpha-tocopherol at the time of an ongoing ischemic injury may be required for a better neurological outcome from the insult.