PREVENTION OF DOPAMINE-INDUCED CELL-DEATH BY THIOL ANTIOXIDANTS - POSSIBLE IMPLICATIONS FOR TREATMENT OF PARKINSONS-DISEASE

We have recently shown that dopamine (DA) can trigger apoptosis, an ac tive program of cellular self destruction in various neuronal cultures and proposed that inappropriate activation of apoptosis by DA and or its oxidation products may initiate nigral cell loss in Parkinson's di sease (PD). Since DA toxicity may be mediated via generation of oxygen -free radical species, we examined whether DA-induced cell death in PC 12 cells may be inhibited by antioxidants. We have found that the thio l containing compounds, reduced glutathione (GSH), N-acetyl-cysteine ( NAG), and dithiothreitol (DTT) were markedly protective, while vitamin s C and E had lesser or no effect. The thiol antioxidants and vitamin C but not vitamin E, prevented dopamine autooxidation and production o f dopamine-melanin, Their protective effect has also manifested by inh ibiting DA-induced apoptosis; DNA fragmentation was prevented as was s hown histochemically by the in situ end-labeled DNA technique (TUNEL), Intracellular GSH and other thiols constitute an important natural de fense against oxidative stress. We have found that depletion of cellul ar GSH by the addition of phoron, a substrate of glutathione transfera se, and buthionine sulfoximine (BSO), an inhibitor of gamma-glutamyl t ranspeptidase, significantly enhanced DA toxicity. Cotreatment with NA C rescued the cells from the toxic effect of BSO + DA, and phoron + DA , while addition of Cf SW provided only partial protection from BSO DA-toxicity. Our data indicate that the thiol family of antioxidants, but not vitamins C and E, are highly effective in rescuing cells from DA-induced apoptosis. Further study of the mechanisms underlying the u nique protective capacity of thiol antioxidants may lead to the develo pment of new neuroprotective therapeutic strategies for PD. (C) 1996 A cademic Press, Inc.