Nitric oxide inhibits peroxide-mediated endothelial toxicity

Background. Oxidant molecules and nitric oxide (NO) have each been implicated as mediators of endothelial cell damage, but the biologic effect of these molecules acting in concert is incompletely understood. Materials and methods. We studied the effects of an NO donor, S-nitroso-acetyl-D,L- penicillamine (SNAP), in combination with the peroxidants tert-butyl hydroperoxide (TBH) and hydrogen peroxide (H₂O₂) on rabbit aortic endothelial cells in culture. Cell viability was assessed using Alamar blue, a nontoxic dye indicator of cell metabolism. Lipid peroxidation was assessed using a chemiluminescent single-photon counting technique. Results. After 90 min exposure to test reagents, there was concentration-dependent cytotoxicity for both TBH and H₂O₂. Peroxidant-induced cytotoxicity was significantly ameliorated by SNAP (10^-4-10^-3 M). N-Acetylpenicillamine and NO-depleted SNAP failed to demonstrate a cytoprotective effect against peroxidant cellular injury, thus implicating NO as the agent responsible for the protective effect. SNAP reduced lipid peroxidation caused by 10^-3 M TBH in a dose-dependent manner. Preincubation of cells with SNAP before exposure to peroxidants alone had no effect on toxicity. Conclusions. NO is cytoprotective to the endothelium in the presence of peroxidants through a reduction of lipid peroxidation.