Glutathione prevented dopamine-induced apoptosis of melanocytes and its signaling

Abstract

Dopamine (DA), a monoamine neurotransmitter, is a well-known neurotoxin and plays an etiologic role in neurodegenerative disorders such as Parkinson's disease. DA exerts its toxic effect by generation of reactive oxygen species and quinone product. Vitiligo, a depigmentary disorder of the skin and hair characterized by selective destruction of melanocytes, has been reported to show increased levels of DA with onset and progression of the disease. The aim of this study is to investigate the cytotoxic effect of DA on melanocytes and to search for protective antioxidants against DA-induced toxicity. In addition, molecular mechanism of cell death was also investigated. Cells were treated with DA and cell viabilities were measured by crystal violet staining method. To investigate the cytoprotective activity of various antioxidants, vitamin C, vitamin E, Trolox, quercetin, N-acetylcysteine (NAC) and l-glutathione (GSH) were used. To study cytoprotective effects of NAC and GSH, Mel-Ab cells and cultured normal human melanocytes were pretreated with NAC or GSH, then DA solution was added. DA-induced apoptosis and activation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) were also observed by flow cytometric analysis and Western blotting. The viability of DA-treated Mel-Ab cells significantly decreased in a dose-dependent manner while keratinocytes were much more resistant to DA-toxicity, which was a consistent finding with the selective melanocyte loss observed in vitiligo. Among various antioxidants used in this study, only thiol-containing antioxidants such as NAC or GSH inhibited both JNK and p38 MAPK activation and apoptosis, indicating the unique protective capacity of thiol compounds. Cultured normal human melanocytes were also susceptible to DA and thiol compounds were very efficiently protective against DA-induced cytotoxicity. DA-induced apoptosis and cytoprotective effect of thiol compounds shown in this study could be a clue to understand pathogenesis of viltigo and provide a new therapeutic strategy.