EVIDENCE FOR GENERATION OF OXIDATIVE STRESS IN BRAIN BY MPTP - IN-VITRO AND IN-VIVO STUDIES IN MICE

The role of oxidative stress in 1-methyl-4-phenyl-1,2,3,6-tetrahydropy ridine (MPTP)-mediated neurotoxicity is as yet unclear and the evidenc e for generation of oxygen free radicals as a primary event in the neu rotoxicity is yet to be demonstrated. The present study was undertaken to ascertain the potential role of oxidative damage, and the protecti ve role, if any, of the antioxidant, glutathione (GSH), in MPTP-induce d neurotoxicity. Exposure of sagittal slices of mouse brain to MPTP re sulted in significant increases of reactive oxygen species (ROS) and m alondialdehyde (MDA, the product of lipid peroxidation) and decreases in GSH content. Pretreatment of mouse brain slices, in vitro, with GSH or GSH isopropyl ester attenuated MPTP toxicity as assessed by the ti ssue activity of the mitochondrial enzyme, NADH-dehydrogenase (NADH-DH ), and by leakage of the cytosolic enzyme, lactate dehydrogenase (LDH) , from the slice into the medium. In vivo administration of MPTP (30 m g/kg body weight, s.c.), to mice resulted in significant lowering of G SH in the striatum and midbrain, 2 h after dosage; ROS levels in the s triatum and midbrain increased after 3 and 8 h, respectively. In the s triatum significant inhibition of rotenone-sensitive NADH ubiquinone-l oxido-reductase (Complex 1) was observed transiently 1 h after MPTP a dministration. The enzyme activity recovered thereafter; significant i nhibition of mitochondrial Complex I was observed in the striatum only 18 h after MPTP dose. In the midbrain, mitochondrial Complex I was in hibited only 18 h after MPTP dose; no change was observed at the early time points examined. Thus, the depletion of GSH and increased ROS fo rmation preceded the inhibition of the mitochondrial enzyme in the mid brain. Evidence presented herein from both in vitro and in vivo studie s support that MPTP exposure generates ROS resulting in oxidative stre ss.