SELECTIVE ROLE OF GLUTATHIONE IN PROTECTING HUMAN NEURONAL CELLS FROMDOPAMINE-INDUCED APOPTOSIS

The role of glutathione and other antioxidants in dopamine-induced apo ptosis has been analyzed in cultures of the human neuronal cell line N MB. Apoptosis, induced by 0.1-0.3 mM dopamine, was blocked by glutathi one in a dose- and time-dependent manner. This was observed by monitor ing cell morphology, cell viability, and the release of the cytosolic enzyme lactate dehydrogenase into the culture medium. L-Cysteine and N -acetylcysteine had a similar effect in protecting against dopamine ne urotoxicity, but at lower concentrations than glutathione. The dopamin e-induced alteration in the cell cycle profile;detected by flow cytome try (FAGS), and intranucleosomal DNA fragmentation, were both blocked by glutathione. Treatment of NMB cells with buthionine sulfoximine, an irreversible inhibitor of gamma-glutamylcysteine synthetase, increase d the neurotoxic effect of, dopamine, suggesting that endogenous gluta thione participates in reducing dopamine neurotoxicity. The relationsh ip between glutathione and dopamine was further investigated by testin g the effect of dopamine on the endogenous glutathione level. Dopamine decreased glutathione levels within 16-24 hr; however, this effect wa s preceded by a transient increase in the level of the tripeptide with in the first 0.5-7 hr. Two other types of endogenous antioxidants, (+) -alpha-tocopherol (vitamin E) and ascorbic acid (vitamin C), were test ed; vitamin E (at 1-100 mu g/ml) was inactive against dopamine toxicit y, whereas vitamin C had no effect at 0.05-0.2 mM, but increased dopam ine toxicity at 0.5-2 mM. The results indicate-that glutathione has a selective role in protecting human neural cells from the toxic effect of dopamine; This study may contribute, therefore, to a better underst anding of the mechanisms underling the excessive loss of dopaminergic neurons in neurodegenerative diseases, such as Parkinsonism, and in th e aging process. Copyright (C) 1996 Elsevier Science Ltd