Lipopolysaccharide triggered TNF-α-induced hepatocyte apoptosis in a murine non-alcoholic steatohepatitis model

Background/Aims: Endogenous gut-derived bacterial endotoxins have been implicated as an important cofactor in the pathogenesis of liver injury, although their contribution to the progression of non-alcoholic steatohepatitis (NASH) remains unclear. Methods: Male C57BL/6 mice were fed a methionine-choline-deficient (MCD) diet or a standard diet for 17 days, following which they were injected with lipopolysaccharide (LPS) intraperitoneally and sacrificed after 6 h. In an in vitro experiment, RAW264.7 cells, a mouse macrophage cell line, and primary mouse hepatocytes were co-treated with hydrogen peroxide (H2O2) and LPS or tumour necrosis factor (TNF)-alpha. Results: Compared to the control mice, LPS treatment significantly increased hepatic TNF-alpha production in MCD mice. LPS also significantly increased TUNEL-positive cells, which were especially observed in the perivenular area. The apoptotic change was inhibited by co-treatment with a neutralizing anti-mouse TNF receptor antibody or pentoxifylline. In an in vitro experiment, treatment with H2O2 synergistically enhanced LPS-induced TNF-alpha production in RAW264.7 cells, accompanied by an up-regulation of CD14 mRNA. Moreover, co-treatment with TNF-alpha- and H2O2-induced apoptosis in primary hepatocytes, although neither TNF-alpha nor H2O2 could do so independently. Conclusions: LPS up-regulated TNF-alpha production, which induced hepatocyte apoptosis in a murine NASH. model. LPS may play a key role in the pathogenesis of NASH. (C) 2009 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.