Superoxide potently induces ceramide formation in glomerular endothelial cells

Recent evidence suggests that the sphingolipid-derived second messenger cer amide and oxidative stress are intimately involved in apoptosis induction. Here we report that exposure of microcapillary glomerular endothelial cells to superoxide-generating substances, including hypoxanthine/xanthine oxida se and the redox cyclers DMNQ and menadione results in a dose-dependent and delayed increase in the lipid signaling molecule ceramide. Long-term incub ation of endothelial cells for 2-30 h with either DMNQ or hypoxanthine/xant hine oxidase leads to a continuous increase in ceramide levels. In contrast , short-term stimulation for 1 min up to 1 h had no effect on ceramide form ation. The DMNQ-induced delayed ceramide formation is dose-dependently inhi bited by reduced glutathione, whereas oxidized glutathione was without effe ct. Furthermore, N-acetylcysteine completely blocks DMNQ-induced ceramide f ormation. Ah superoxide-generating substances were found to dose-dependentl y trigger endothelial cell apoptosis. In addition, glutathione and N-acetyl cysteine also prevented superoxide-induced apoptosis and implied that ceram ide represents an important mediator of superoxide-triggered cell responses like apoptosis. (C) 2001 Academic Press.