Mechanisms of H2O2-induced oxidative stress in endothelial cells.

Hydrogen peroxide, produced by inflammatory and vascular cells, induces oxidative stress that may contribute to endothelial dysfunction. In smooth muscle cells, H(2)O(2) induces production of O(2)*(-) by activating NADPH oxidase. However, the mechanisms whereby H(2)O(2) induces oxidative stress in endothelial cells are poorly understood. We examined the effects of H(2)O(2) on O(2)*(-) levels on porcine aortic endothelial cells (PAEC). Treatment with 60 micromol/L H(2)O(2) markedly increased intracellular O(2)*(-) levels (determined by conversion of dihydroethidium to hydroxyethidium) and produced cytotoxicity (determined by propidium iodide staining) in PAEC. Overexpression of human manganese superoxide dismutase in PAEC reduced O(2)*(-) levels and attenuated cytotoxicity resulting from treatment with H(2)O(2). L-NAME, an inhibitor of nitric oxide synthase (NOS), and apocynin, an inhibitor of NADPH oxidase, reduced O(2)*(-) levels in PAEC treated with H(2)O(2), suggesting that both NOS and NADPH oxidase contribute to H(2)O(2)-induced O(2)*(-) in PAEC. Inhibition of NADPH oxidase using apocynin and NOS rescue with L-sepiapterin together reduced O(2)*(-) levels in PAEC treated with H(2)O(2) to control levels. This suggests interaction-distinct NOS and NADPH oxidase pathways to superoxide. We conclude that H(2)O(2) produces oxidative stress in endothelial cells by increasing intracellular O(2)*(-) levels through NOS and NADPH oxidase. These findings suggest a complex interaction between H(2)O(2) and oxidant-generating enzymes that may contribute to endothelial dysfunction.