Critical O2 and NO concentrations in NO-induced cell death in a rat liver sinusoidal endothelial cell line

Nitric oxide (NO) plus oxygen (O-2) are known to cause cell damage via formation of reactive nitrogen species. NO itself directly inhibits cytochrome oxidase of the mitochondrial respiratory chain in competition with O-2, thus inducing a hypoxiclike injury. To assess the critical NO and O-2 concentrations for both mechanisms of NOinduced cell injury, cells of a rat liver sinusoidal endothelial cell line were incubated in the presence of the NO donor spermineNONOate at different O-2 concentrations, and their loss of viability was determined by the release of lactate dehydrogenase. Protection by ascorbic acid was used as indication for the involvement of reactive nitrogen species, whereas a hypoxiclike injury was indicated by the protective effects of glycine and glucose and the increase in NAD(P)H fluorescence. High concentrations of NO (approx. 10 M NO) and O-2 (21% O-2) were required to induce endothelial cell death mediated by formation of reactive nitrogen species. On the other hand, pathophysiologically relevant NO concentrations at low but physiological O2 concentrations (ca. 2 M NO at 5% O-2 and about 1 M NO at 2% O-2) induced hypoxic-like cell death in the endothelial cells that was prevented by the presence of glucose.