Increased susceptibility to experimental steatohepatitis induced by methionine-choline deficiency in HBs-Tg mice

BACKGROUND: Worldwide, about 25% of individuals with chronic hepatitis B have fatty liver disease. Lipogenic diets that are completely devoid of methionine and choline induce nonalcoholic fatty liver disease. However, no animal model of nonalcoholic steatohepatitis associated with HBV infection is available, and the influence of viral infection on nutritional hepatic steatosis is unclear. METHODS: We used HBV surface antigen transgenic mice (HBs-Tg mice), which mimic healthy human carriers with hepatitis B surface antigen. The mice were fed with a high-fat methionine-choline-deficient diet (MCD) to build a reliable rodent nutritional model of nonalcoholic steatohepatitis associated with HBV infection, and the changes in body weight and serum triglycerides were measured. Hepatocyte ballooning changes were determined by hematoxylin and eosin staining. The extent of hepatic fat accumulation was evaluated by oil red O staining. Immunohistochemical assays were performed to detect proliferating cell nuclear antigen as an index of cell proliferation. RESULTS: MCD feeding provoked systemic weight loss and liver injury. MCD feeding caused more macrovesicular fat droplets and fat accumulation in the livers of HBs-Tg mice than in wild-type C57BL/6 mice. In addition, within 30 days of MCD exposure, more PCNA-positive nuclei were found in the livers of HBs-Tg mice. CONCLUSIONS: HBs-Tg mice fed with a lipogenic MCD form more macrovesicular fat droplets earlier, coincident with more hepatocyte proliferation, resulting in the appearance of increased susceptibility to experimental steatohepatitis in these mice.

Γ-Aminobutyric acid promotes methionine-choline deficient diet-induced nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis（NASH） is one of the most common liver diseases and a major cause of liver fibrosis worldwide.r-Aminobutyric acid（GABA） is one of the most abundant inhibitory neurotransmitters in the central nervous system.Recently,it has been reported that GABAergic signaling pathways are found in various non-neuronal tissues including the immune system and play a functional role.In the present study,we investigated whether administration of GABA has effects on NASH through its immunomodulatory effects.To test this hypothesis,C57BL/6 mice were fed a methionine-choline-deficient（MCD） diet for 8 weeks.After four weeks into MCD feeding,mice were provided with plain water（control） or water containing 2 mg/mL of GABA for the subsequent 4 weeks.Using this MCD diet-induced NASH model,we found that mice receiving GABA showed more severe steatohepatitis and liver fibrosis than control mice.This increased liver damage was confirmed by higher levels of serum alanine transaminase（ALT） and aspartate aminotransferase（AST） compared to the control group.In accordance with increased liver steatohepatitis,NASH-related and inflammatory gene expression（collagen al,tissue inhibitor of metalloproteinase-1,TNF-α） in the liver was markedly increased in GABA-treated mice.Furthermore,GABA directly enhanced production of inflammatory cytokines including IL-6 and TNF-α in LPS activated RAW macrophage cells and increased TIB-73 hepatocyte death.Such effects were abolished when GABA was treated with bicuculline,a competitive antagonist of GABA receptors.These results suggest that oral administration of GABA may be involved in changes of the liver immune milieu and conferred detrimental effects on NASH progression.