HEPATOCYTE-DERIVED INTERLEUKIN-6 AND TUMOR-NECROSIS-FACTOR-ALPHA MEDIATE THE LIPOPOLYSACCHARIDE-INDUCED ACUTE-PHASE RESPONSE AND NITRIC-OXIDE RELEASE BY CULTURED RAT HEPATOCYTES

The regulation of acute-phase protein production and nitric oxide (NO) release in lipopolysaccharide-induced liver injury is thought to occu r in response to monocytes/macrophages and Kupffer-cell-derived cytoki nes. In this study, we used primary cultured rat hepatocytes maintaine d as a differentiated phenotype to investigate the direct effects of e ndotoxin (lipopolysaccharide) on the production of the acute-phase pro teins and on NO release. Lipopolysaccharide (10 mu g/ml) increased the production of alpha(2)-macroglobulin 2.5-fold compared to untreated c ultures and decreased the production of albumin by 50%. The effect of lipopolysaccharide was mimicked by adding interleukin-6 (IL-6) and tum or-necrosis factor alpha (TNF-alpha), cytokines being induced by treat ment of hepatocytes with lipopolysaccharide. Maximal TNF-alpha (600 pg /ml) and IL-6 (1800 pg/ml) concentrations were observed 4 h and 6 h af ter lipopolysaccharide stimulation, respectively. The lipopolysacchari de-induced acute-phase protein response was blocked by anti-(IL-6) but not by anti-(TNF-alpha) IgG. The latter reduced the lipopolysaccharid e-induced IL-6 production by 60%. Besides its effects on the acute-pha se proteins, endotoxin caused a significant increase in NO production in cultured rat hepatocytes. Unlike anti-(IL-6) IgG, anti-(TNF-alpha) IgG reduced the lipopolysaccharide-induced NO production by 50% indica ting that endotoxin-induced NO production is partially mediated by TNF -alpha but not by IL-6. Preculture with gadolinium chloride (GdCl3), a n inhibitor of Kupffer cells, did not change the response of hepatocyt es to lipopolysaccharide indicating that the observed findings are dir ect endotoxin effects on hepatocytes. The data demonstrate that by the ir production of TNF-alpha and IL-6 rat hepatocytes respond to lipopol ysaccharide treatment with an IL-6 mediated acute-phase protein and a TNF-alpha-mediated NO production. These features have previously been attributed to monocytes/macrophages and Kupffer cells.