Aspirin protects endothelial cells from oxidant damage via the nitric Oxide-cGMP pathway

Objectives - Aspirin is known to exert cytoprotection by presently unidentified mechanisms. This study investigates the involvement of nitric oxide ( NO) in antioxidant cellular protection induced by aspirin. Methods and Results - A 24-hour incubation with hydrogen peroxide markedly reduced viability of cultured endothelial cells. Preincubation with aspirin ( 3 to 30 mumol/L) protected endothelial cells from hydrogen peroxide - mediated toxicity and increased viability in a concentration-dependent fashion by up to 95% of control. This effect was specific in that other nonsteroidal anti-inflammatory drugs, such as salicylate or indomethacin, did not alter hydrogen peroxide toxicity. Aspirin-induced endothelial protection was abrogated in the presence of the NO scavenger PTIO ( 30 mumol/L) and the inhibitor of soluble guanylyl cyclase ODQ ( 1 mumol/L). Moreover, the L-arginine antagonist L-NMMA ( 25 mumol/L), but not its D-enantiomer, led to complete inhibition of aspirin-dependent cytoprotection. Correspondingly, aspirin enhanced NO synthase activity ( citrulline formation) and intracellular cyclic GMP accumulation in endothelial cells. Protein expression of endothelial NO synthase remained unaffected in the presence of aspirin. Conclusions - Our data suggest that endothelial NO synthase is a site of action of aspirin and that the NO/cyclic GMP system assumes a crucial function in mediating the cytoprotective action of aspirin.