Hydrogen peroxide promotes endothelial dysfunction by stimulating multiple sources of superoxide anion radical production and decreasing nitric oxide bioavailability

Hydrogen peroxide (H2O2) is an oxidant implicated in cell signalling and various pathologies, yet relatively little is known about its impact on endothelial cell function. Herein we studied the functional and biochemical changes in aortic vessels and cultured porcine aortic endothelial cells (PAEC) exposed to H2O2. Exposure of aortic rings to 25 or 50 mu M, but not 10 mu M, H2O2 for 60min prior to constriction significantly decreased subsequent relaxation in response to acetylcholine (ACh), but not the nitric oxide ((NO)-N-center dot) donor sodium nitroprusside. Treatment of PAEC with 50 mu M H2O2 significantly decreased ACh-induced accumulation of (NO)-N-center dot, as measured with a (NO)-N-center dot-selective electrode, yet such treatment increased nitric oxide synthase activity similar to 3-fold, as assessed by conversion of L-arginine to L-citrulline. Decreased (NO)-N-center dot bioavailability was reflected in decreased cellular cGMP content, associated with increased superoxide anion radical (O-2(-center dot)), and overcome by addition of polyethylene glycol superoxide dismutase. Increased cellular O-2(-center dot) production was inhibited by allopurinol, diphenyliodonium and rotenone in an additive manner. The results show that exposure of endothelial cells to H2O2 decreases the bioavailability of agonist-induced (NO)-N-center dot as a result of increased production of O-2(-center dot) likely derived from xanthine oxidase, NADPH-oxidase and mitochondria. These processes could contribute to H2O2-induced vascular dysfunction that may be relevant under conditions of oxidative stress such as inflammation. Copyright (c) 2007 S. Karger AG, Basel.