Lipopolysaccharide prevents cell death caused by glutathione depletion: possible mechanisms of protection

Glutathione is an important cellular antioxidant present at high concentrations in the brain. We have previously demonstrated that depletion of glutathione in mesencephalic cultures results in cell death and that the presence of glia is necessary for the expression of toxicity. Cell death following glutathione depletion can be prevented by inhibition of lipoxygenase activity, implicating arachidonic acid metabolism in the toxic events. In this study we examined the effect of glial activation, known to cause secretion of cytokines and release of arachidonic acid, on the toxicity induced by glutathione depletion. Our data show that treatment with the endotoxin lipopolysaccharide activated glial cells in mesencephalic cultures, increased interleukin-1β in microglia and caused depletion of glutathione. The overall effect of lipopolysaccharide treatment, however, was protection from damage caused by glutathione depletion. Addition of cytokines or growth factors, normally secreted by activated glia, did not modify L-buthionine sulfoximine toxicity, although basic fibroblast growth factor provided some protection. A large increase in the protein content and the activity of Mn–superoxide dismutase, observed after lipopolysaccharide treatment, may indicate a role for this mitochondrial antioxidant enzyme in the protective effect of lipopolysaccharide. This was supported by the suppression of toxicity by exogenous superoxide dismutase. Our data suggest that superoxide contributes to the damage caused by glutathione depletion and that up-regulation of superoxide dismutase may offer protection in neurodegenerative diseases associated with glutathione depletion and oxidative stress.