Acute-phase hepatocytes regulate liver sinusoidal cell mediator production
P. Bankey, M. Prager, D. Geldon, S. Taylor and K. McIntyre
Department of Surgery, University of Texas, Southwestern Medical Center, Dallas.
BACKGROUND: Overproduction of liver sinusoidal cell (LCS) mediators in
response to endotoxemia or gram-negative infection that follows tissue
injury may contribute to hepatic dysfunction. OBJECTIVE: To better define
the role of hepatocyte-derived acute-phase reactants in the regulation of
sinusoidal cell mediator production following sequential insults, we tested
the hypothesis that interleukin-6 (IL-6) prestimulation alters hepatocyte
regulation of lipopolysaccharide (LPS)-stimulated sinusoidal cell tumor
necrosis factor (TNF), IL-6, and nitric oxide production. METHODS:
Hepatocytes and LSCs were isolated from Wistar rats, and in vitro responses
were compared between LSCs alone and hepatocyte-LSC cocultures. Cocultures
and LSCs alone were sequentially stimulated with IL-6 (5000 U/mL) then LPS
(dose-response), and culture supernatants were analyzed for TNF (L929
cytolysis), IL-6 (7TD1 proliferation), and nitric oxide (Griess reaction).
Induction of acute-phase protein synthesis by the stimulation of
hepatocytes with IL-6 and dexamethasone (0.1 mumol/L) was assayed by
methionine radiolabeling and SDS-PAGE (sodium dodecyl
sulfate-polyacrylamide gel electrophoresis). Coculture levels of messenger
RNA for TNF-alpha and IL-6 were examined by RNA extraction and reverse
transcriptase polymerase chain reaction with specific primers. RESULTS:
Interleukin-6 and dexamethasone signal hepatocyte 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 lesser extent. Polymerase chain reaction
analysis demonstrated similar levels of TNF and IL-6 message following
sequential stimulation. CONCLUSIONS: Interleukin-6-stimulated acute-phase
hepatocytes limit LPS-stimulated coculture cytokine bioactivity and nitric
oxide production. This hepatocyte response may provide a local
counterregulatory mechanism to limit LSC-mediated injury.
