ACUTE-PHASE HEPATOCYTES REGULATE LIVER SINUSOIDAL CELL MEDIATOR PRODUCTION

Background: Overproduction of liver sinusoidal cell (LCS) mediators in response to endotoxemia or gramnegative infection that follows tissue injury may contribute to hepatic dysfunction. Objective: To better de fine the role of hepatocyte-derived acute-phase reactants in the regul ation of sinusoidal cell mediator production following sequential insu lts, we tested the hypothesis that interleukin-6 (IL-6) prestimulation alters hepatocyte regulation of lipopolysaccharide (LPS)-stimulated s inusoidal cell tumor necrosis factor (TNF), IL-6, and nitric oxide pro duction. Methods: Hepatocytes and LSCs were isolated from Wistar rats, and in vitro responses were compared between LSCs alone and hepatocyt e-LSC cocultures. Cocultures and LSCs alone were sequentially stimulat ed with IL-6 (5000 U/mL) then LPS (dose-response), and culture superna tants were analyzed for TNF (L929 cytolysis), IL-6 (7TD1 proliferation ), and nitric oxide (Griess reaction). induction of acute-phase protei n synthesis by the stimulation of hepatocytes with IL-6 and dexamethas one (0.1 mu mol/L) was assayed by methionine radiolabeling and SDS-PAG E (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Cocultu re levels of messenger RNA for TNF-alpha and IL-6 were examined by RNA extraction and reverse transcriptase polymerase chain reaction with s pecific primers. Results: Interleukin-6 and dexamethasone signal hepat ocyte acute-phase protein synthesis. Prestimulation of cocultures, but not of LSCs alone, with IL-6 inhibits LPS-stimulated IL-6 and nitric oxide production significantly. Bioactivity of TNF is reduced to a les ser extent. Polymerase chain reaction analysis demonstrated similar le vels of TNF and IL-6 message following sequential stimulation. Conclus ions: Interleukin-6-stimulated acute-phase hepatocytes limit LPS-stimu lated coculture cytokine bioactivity and nitric oxide production. This hepatocyte response may provide a local counterregulatory mechanism t o limit LSC-mediated injury.