ROLE OF OXIDATIVE STRESS AND THE GLUTATHIONE SYSTEM IN LOSS OF DOPAMINE NEURONS DUE TO IMPAIRMENT OF ENERGY-METABOLISM

Alterations in the glutathione system and impairment in energy metabol ism have both been implicated in the loss of dopamine neurons in Parki nson's disease. This study examined the importance of cellular glutath ione and the involvement of oxidative stress in the loss of mesencepha lic dopamine and GABA neurons due to inhibition of energy metabolism w ith malonate, the reversible, competitive inhibitor of succinate dehyd rogenase. Consistent with previous findings, exposure to malonate for 24 h followed by 48 h of recovery caused a dose-dependent loss of the dopamine population with little effect on the GABA population. Toxicit y was assessed by simultaneous measurement of the high-affinity uptake of [H-3]dopamine and [C-14]GABA. Total glutathione content in rat mes encephalic cultures was decreased by 65% with a 24-h pretreatment with 10 mu M buthionine sulfoxamine. This reduction in glutathione level g reatly potentiated damage to both the dopamine and GABA populations an d removed the differential susceptibility between the two populations in response to malonate, These findings point to a role for oxidative stress occurring during energy impairment by malonate. Consistent with this, several spin-trapping agents, alpha-phenyl-tert-butyl nitrone a nd two cyclic nitrones, MDL 101,002 and MDL 102,832, completely preven ted malonate-induced damage to the dopamine neurons in the absence of buthionine sulfoxamine. The spin-trapping agents also completely preve nted toxicity to both the dopamine and GABA populations when cultures were exposed to malonate after pretreatment with buthionine sulfoxamin e to reduce glutathione levels. Counts of tyrosine hydroxylase-positiv e neurons verified enhancement of cell loss by buthionine sulfoxamine plus malonate and protection against cell loss by the spin-trapping ag ents. NMDA receptors have also been shown to play a role in malonate-i nduced dopamine cell loss and are associated with the generation of fr ee radicals, Consistent with this, toxicity to the dopamine neurons du e to a 1-h exposure to 50 mu M glutamate was attenuated by the nitrone spin traps. These findings provide evidence for an oxidative challeng e occurring during inhibition of energy metabolism by malonate and sho w that glutathione is an important neuroprotectant for midbrain neuron s during situations when energy metabolism is impaired.