Suppression of lipopolysaccharide-induced nitric oxide synthase expressionby platelet-activating factor receptor antagonists in the rat liver and cultured rat Kupffer cells

Excessive nitric oxide (NO) generated by hepatic cells in response to lipop olysaccharide (LPS) and inflammatory substances (e.g., platelet-activating factor [PAF]) is a key contributor to the pathophysiological outcomes obser ved in the liver during sepsis. In rats subjected to liver-focused endotoxe mia, inducible nitric oxide synthase (iNOS) levels in the intact liver were elevated by 6 hours; cell-specific expression of iNOS messenger RNA (mRNA) was Kupffer cells (KCs), endothelial cells, and hepatocytes. Elevated seru m alanine transaminase (ALT) levels at 6 hours confirmed hepatic damage. Pr etreatment of endotoxemic rats with PAF receptor antagonists BN 50739 or WE B 2170 reduced serum ALT and iNOS mRNA levels in the intact liver. Pretreat ment of cultured KCs with BN 50739 or WEB 2170 inhibited both LPS and PAF-i nduced iNOS RNA formation, in addition, LPS-induced iNOS protein levels in KCs pretreated with BN 50739 or WEB 2170 were decreased. Exposure of KCs to either LPS or PAF caused the translocation of the p65 subunit of nuclear f actor kappa B (NF-kappa B) into the nucleus and this process was attenuated by BN 50739 and WEB 2170. There was concomitant inhibition of LPS-dependen t degradation of the inhibitory protein I kappa B alpha and increase in int racellular Ca2+ in KC treated with BN 50739 or WEB 2170. Also, in KCs, LPS was able to induce iNOS mRNA expression independent of CD14. This response was inhibited by pretreatment of KCs with either BN 50739 or WEB 2170. Our findings indicate that PAF receptor antagonists convey protection against h epatocellular injury accompanied by a decrease in nitric oxide (NO) formati on in the livers of endotoxemic rats.