Multiple cytokines are required to induce hepatocyte nitric oxide production and inhibit total protein synthesis

The etiology and mechanisms by which severe trauma or sepsis induce hepatic failure are unknown. Previously we showed that Kupffer cells (KC), the fixed macrophages of the liver, induce a profound decrease in hepatocyte (HC) total-protein synthesis when exposed to endotoxin. Furthermore we demonstrated that endotoxin-activated KCs induce these changes in HC protein synthesis through the induction of a novel L-arginine-dependent biochemical pathway within the HC. In this pathway, the guanido nitrogen of L-arginine is converted to the highly reactive molecule nitric oxide (NO ·). To identify the KC factors that act as signals for induction of HC NO · biosynthesis, recombinant cytokines were added to HC cultures and HC nitrogen oxide production and protein synthesis levels were determined. We found that no single cytokine, but rather a specific combination of tumor necrosis factor, interleukin-1, interferon-gamma, and endotoxin, were required for maximal induction of HC nitrogen oxide production. This specific combination of cytokines induced a 248.8 ± 26.0 μmol/L (micromolar) increase in HC nitrogen oxide production and simultaneously inhibited HC total protein synthesis by 36.1% ± 3.1%. These data demonstrate that multiple cytokines, produced by endotoxin-activated KC, induce the production of NO · within HC, which in turn leads to the inhibition of HC total-protein synthesis.