Antioxidant Role of Oleuropein on Midbrain and Dopaminergic Neurons of Substantia Nigra in Aged Rats

Background: Oleuropein is a phenolic compound which is present in the olive leaf extract. The purpose of the present study was to investigate the neuroprotective effect of oleuropein as an antioxidant agent on the substantia nigra in aged rats. Methods: Twenty 18-month-old Wistar rats (450-550 g) were randomly divided into control and experimental groups. The experimental group received a daily single dose of 50 mg/kg of oleuropein by oral gavage for 6 months. The control group received only distilled water. All rats were sacrificed two hours after the last gavage and the brains were removed and midbrains were cut. One part of the midbrains were homogenized and centrifuged. The tissue supernatant was assayed for lipid peroxidation (LPO) and antioxidant enzyme activities. The other part of midbrains fixed and embedded in paraffin, then processed for Nissl and immunohistochemistry (IHC) staining. Data was analyzed using SPSS by t-test. Differences were considered significant for P<0.05. Results: The level of LPO in midbrain of the rats was decreased significantly in the experimental group, but superoxide dismutase, catalase and glutathione peroxidase activities were increased in experimental group compared to control group (P<0.05). Morphometric analyses showed significantly that the experimental group had more neurons in substantia nigra pars compacta (SNc) either in Nissl or IHC staining when compared to control (P<0.05). Conclusion: The results of the present study indicate that treatment of the old rats with oleuropein reduces the oxidative damage in SNc by increasing the antioxidant enzyme activities.