Effects of calcium channel antagonists on LPS-induced hepatic iNOS expression

The onset of liver injury is a,pivotal event during endotoxemia. Lipopolysa ccharide (LPS) activates the Kupffer cells (KC), the resident macrophages o f the liver, to generate an abundance of inflammatory substances, including nitric oxide (NO). Elevated levels of NO are thought to contribute to the propagation of liver injury during sepsis. Calcium, a major second messenge r in several cellular signaling events, is required by the KC for the gener ation of inducible nitric oxide synthase (iNOS). The purpose of this study was to determine whether calcium channel antagonists limit hepatic injury a nd iNOS expression in vivo following LPS exposure and to evaluate their eff ects on the regulation of iNOS expression in cultured KC. In rats subjected to LPS for 6 h, the serum alanine aminotransferase (ALT) level was elevate d significantly; this response was accompanied by an increase in iNOS mRNA formation in the intact liver. Pretreatment of rats with calcium channel an tagonists (i.e., diltiazem, nifedipine, or verapamil) before LPS exposure a ttenuated the serum ALT level and iNOS mRNA expression in the liver. Pretre atment of cultured KC with calcium channel antagonists for 1 h followed by the addition of LPS markedly repressed iNOS protein and mRNA expression. Ti me-course studies revealed that calcium channel antagonists were most effec tive at inhibiting LPS-induced iNOS mRNA formation by KC when added before LPS. Treatment of KC with calcium channel antagonists prior to the addition of LPS decreased nuclear levels of the p65 subunit of nuclear factor-kappa B and prevented the LPS-dependent degradation of the inhibitory protein I kappa B alpha. Thus our findings indicate that under endotoxemic conditions calcium channel antagonists limit hepatocellular injury that is accompanie d by an inhibition of LPS-mediated iNOS expression in rat liver KC.