MITOCHONDRIAL IMPAIRMENT AS AN EARLY EVENT IN THE PROCESS OF APOPTOSIS INDUCED BY GLUTATHIONE DEPLETION IN NEURONAL CELLS - RELEVANCE TO PARKINSONS-DISEASE

In Parkinson's disease (PD), dopaminergic cell death in the substantia nigra was associated with a profound glutathione (GSH) decrease and a mitochondrial dysfunction. The fall in GSH concentration seemed to ap pear before the mitochondrial impairment and the cellular death, sugge sting that a link may exist between these events. The relationships be tween GSH depletion, reactive oxygen species (ROS) production, mitocho ndrial dysfunction and the mode of cell death in neuronal cells remain to be resolved and will provide important insights into the etiology of Parkinson's disease. An approach to determine the role of GSH in th e mitochondrial function and in neurodegeneration was to create a sele ctive depletion of GSH in a neuronal cell line in culture (NS20Y) by i nhibiting its biosynthesis with L-buthionine-(S,R)-sulfoximine (BSO), a specific inhibitor of gamma-glutamylcysteine synthetase. This treatm ent led to a nearly complete GSH depletion after 24 hr and induced cel lular death via an apoptotic pathway after 5 days of BSO treatment. By using the reactive oxygen species sensitive probe 2',7'-dichlorofluor escin, we observed that the rapid GSH depletion was accompanied, early in the process, by a strong and transient intracellular increase in r eactive oxygen species evidenced after 1 hr with BSO, culminating afte r 3 hr when the GSH level decreased to 30% of normal. GSH depletion in duced a loss of mitochondrial function after 48 hr of BSO treatment. I n particular, the activities of complexes I, II and IV of the respirat ory chain were decreased by 32, 70 and 65%, respectively as compared t o controls. These results showed the crucial role of GSH for maintaini ng the integrity of mitochondrial function in neuronal cells. Oxidativ e stress and mitochondrial impairment, preceding DNA fragmentation cou ld be early events in the apoptotic process induced by GSH depletion. Our data are consistent with the hypothesis that GSH depletion could c ontribute to neuronal apoptosis in Parkinson's disease through oxidati ve stress and mitochondrial dysfunction. (C) 1998 Elsevier Science Inc .