Influence of nitric oxide on the intracellular reduced glutathione pool: different cellular capacities and strategies to encounter nitric oxide-mediated stress.

Different cell types exhibit huge differences towards the cytotoxic action of NO. In search for an explanation, we used subtoxic concentrations of the NO-donors S-nitrosocysteine (SNOC) for short-term challenge and of (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1- ium-1,2-diolate (DETA/NO) for longer periods of exposure, respectively, and subtoxic concentrations of the oxidant H2O2 to determine the impact on intracellular reduced glutathione (GSH) concentrations. We find that GSH concentrations are always decreased, but that different cell types show different responses. Incubation of the relatively NO-sensitive murine lymphocytes with both NO-donors, but not with H2O2, resulted in a nearly complete loss of intracellular GSH. Short-term NO-treatment of P815 mastocytoma cells, also sensitive to NO-mediated cell death, decreased GSH to a similar extent only if either glutathione reductase (GSHR) activity or y-glutamylcysteine synthetase (gammaGCS) activity were inhibited concomitantly by specific inhibitors. Long-term NO-treatment of P815 cells, however, resulted in a significant decrease of GSH that could be further enhanced by inhibiting gammaGCS activity. In contrast, neither short-term nor long-term NO-exposure nor H2O2-treatment affected intracellular GSH levels of L929 fibroblasts, which were previously shown to be extremely resistant towards NO, whereas concomitant gammaGCS inhibition, but not GSHR inhibition, completely decreased GSH concentrations. These results show that different cell types use different pathways trying to maintain glutathione concentrations to cope with nitrosative stress, and the overall capability to maintain a critical amount of GSH correlates with susceptibility to NO-induced cell death.