Failure of the gut barrier system enhances liver injury in rats: protection of hepatocytes by gut-derived hepatocyte growth factor.

Abstract

Clinical and experimental studies suggest that impairment of the mucosal barrier system increases gut-derived endotoxin in the portal blood, which causes liver injury. The aim of this study was to elucidate the mechanism of liver injury caused by gut defence failure. Wistar rats were administered either enteral lipopolysaccharide (LPS) or LPS via the portal vein. Blood samples were collected via the inferior vena cava at necropsy. Serum aspartate transaminase (AST) and alanine transaminase (ALT) were analysed by standard enzymatic procedures and cytokines [tumour necrosis factor-alpha, interleukin (IL)-1beta, interferon-gamma, IL-6 and hepatocyte growth factor (HGF)] were measured by enzyme-linked immunosorbent assay. Livers were removed and snap-frozen in liquid nitrogen. CD14, CD68, Toll-like receptor (TLR) 2, TLR4 and Fas ligand (FasL) were analysed immunohistochemically. Expression of TLR2, TLR4 and CD14 mRNA was determined by reverse transcriptase-polymerase chain reaction. In enterally-treated rats, AST and ALT were not increased and cytokine levels were under the limits of detection in the absence of a rise in HGF. Enteral administration of LPS increased HGF dose-dependently. Injection of LPS in the portal vein resulted in significant increases in AST, ALT, tumour necrosis factor-alpha, IL-1beta, interferon-gamma and IL-6 levels, but no change in HGF levels. Immunohistochemical analysis revealed that intraportal LPS administration increased CD14, TLR4, CD68 and FasL. Reverse transcriptase-polymerase chain reaction analysis demonstrated that TLR4 mRNA expression was upregulated 0.5 h after intraportal LPS administration. s Our data suggest that Kupffer cell activation mediated by intraportal LPS via TLR4 is involved in liver injury, possibly through both tumour necrosis factor-alpha/IL-1beta and FasL, and that lack of HGF activity in the impaired gut could not counteract liver injury.