Extracellular accumulation of nitric oxide, hydrogen peroxide, and glutamate in astrocytic cultures following glutathione depletion, complex I inhibition, and/or lipopolysaccharide-induced activation

Abstract

Dopaminergic neuronal death in substantia nigra in Parkinson’s disease is accompanied by depletion of reduced glutathione levels and inhibition of complex I activity which occur partially in normal or activated cells. The relationship between neuronal death and altered glial function is not known, but this may involve the release of toxic mediators from astrocytes and microglia, which in turn cause neuronal injury. We have examined the effects of l-buthionine-[ S, R]-sulfoximine ( l-BSO)-induced glutathione depletion, inhibition of complex I activity by 1-methyl-4-phenylpyridinium (MPR +), and/or lipopolysaccharide (LPS)-induced activation on the extracellular accumulation of nitric oxide (NO), hydrogen peroxide (H 2O 2), and glutamate in primary cultures of rat forebrain astrocytes. Depletion of glutathione levels by up to 90% did not alter NO, H 2O 2, or glutamate levels in cultured astrocytes. Inhibition of complex I activity by up to 43% had no effect on extracellular NO accumulation, but increased H 2O 2 and glutamate levels. LPS-induced activation of cultured astrocytes increased extracellular levels of NO, H 2O 2, and glutamate. Extracellular accumulation of NO and H 2O 2 caused by LPS was markedly less in glutathione-depleted or complex I-inhibited astrocytic cultures compared to normal astrocytic cultures. In conclusion, complex I inhibition or activation of glial cells, alone or in combination with glutathione depletion, results in the extracellular accumulation of glutamate and the formation of NO and H 2O 2, which in turn may form highly toxic peroxynitrite and hydroxyl radicals. Thus, altered glial function leading to oxidative stress and excitotoxicity may contribute to the initiation or progression of neuronal death in substantia nigra in Parkinson’s disease.