Cytotoxicity of dopaminochrome in the mesencephalic cell line, MN9D, is dependent upon oxidative stress.

Parkinson disease is a specific form of neurodegeneration characterized by a loss of nigra-striatal dopaminergic neurons in the midbrain of humans. The disease is also characterized by an increase in oxidative stress and a loss of glutathione in the midbrain region. A potential link between all these factors is the oxidation of dopamine to dopaminochrome (DAC). Using the murine mesencephalic cell line MN9D, we have shown that DAC [50-250 microM] leads to cell death in a concentration-dependent manner, whereas oxidized l-dopa, dopachrome [50-250 microM], is only toxic at the highest concentration used. Furthermore, chronic exposure of MN9D cells to low concentrations of DAC [50-100 microM] is cytotoxic between 48 and 96 h. DAC also increases superoxide production within MN9D cells as indicated by dihydroethidium fluorescence, that can be prevented by co-administration with the antioxidant, N-acetylcysteine [5 mM]. Moreover, the cytotoxicity induced by DAC can also be prevented by administration of N-acetylcysteine [1-5mM]. Finally, depletion of reduced glutathione in MN9D cells by buthionine sulfoximine [50-100 microM] administration significantly enhances the cytotoxic effect of low concentrations of DAC [50-100 microM] and DAC [175 microM] itself reduces the proportion of oxidized glutathione in total glutathione within 30 min of administration in MN9D cells. Overall, we have shown that DAC causes MN9D cell death in an oxidatively dependent manner that appears closely linked with a rapid loss of reduced glutathione. These findings have implications for understanding the pathogenesis of neurodegenerative pathways in Parkinson disease.