Pro-oxidant-mediated hepatic fibrosis and effects of antioxidant intervention in murine dietary steatohepatitis.

The mechanistic significance of oxidative stress to fibrogenesis in the methionine and choline-deficient (MCD) diet-induced model of steatohepatitis was evaluated by antioxidant intervention, using either vitamin E or L-2-oxothiazolidine-4-carboxylate (OTC), a cysteine precursor that promotes glutathione synthesis. Significant depletion of hepatic reduced glutathione (GSH) and elevation of thiobarbituric acid reactive substances (TBARS) occurred from week 3 in association with hepatic injury in mice fed the MCD diet. Hepatic stellate cell (HSC) activation and increased collagen alpha1(I) mRNA expression, together with morphologic fibrosis were evident from week 5. Vitamin E repleted GSH, reduced TBARS, steatosis, inflammation, HSC activation and collagen alpha1(I) mRNA expression, and ameliorated fibrosis. Vitamin E did not effect the expression of either profibrogenic cytokines (transforming growth factor-beta 1, connective tissue growth factor) or matrix remodeling enzymes (tissue inhibitor of metalloproteinase-1 and -2, matrix metalloproteinase-2 and -13). Despite repletion of hepatic GSH in OTC-supplemented mice, the initial benefit in the reduction of hepatic TBARS and inhibition of collagen alpha1(I) mRNA expression at week 5, failed to protect these mice from hepatic injury or fibrosis at later time points. Oxidative stress or products of lipid peroxidation mediate HSC activation and collagen gene expression directly in the MCD model of steatohepatitis. Vitamin E but not glutathione augmentation can interrupt this pathogenic process.

COX-2 induction in mice with experimental nutritional steatohepatitis: Role as pro-inflammatory mediator.

The underlying mechanisms that perpetuate liver inflammation in nonalcoholic steatohepatitis are poorly understood. We explored the hypothesis that cyclooxygenase-2 (COX-2) can exert pro-inflammatory effects in metabolic forms of fatty liver disease. Male wild-type (WT) C57BL6/N or peroxisome proliferator-activated receptor alpha knockout (PPAR-alpha-/-) mice were fed a lipogenic, methionine- and choline-deficient (MCD) diet or the same diet with supplementary methionine and choline (control). COX-2 was not expressed in livers of mice fed the control diet. In mice fed the MCD diet, hepatic expression of COX-2 messenger RNA and protein occurred from day 5, continued to rise, and was 10-fold higher than controls after 5 weeks, thereby paralleling the development of steatohepatitis. Upregulation of COX-2 was even more pronounced in PPAR-alpha-/- mice. Induction of COX-2 was completely prevented by dietary supplementation with the potent PPAR-alpha agonist Wy-14,643 in WT but not PPAR-alpha-/- mice. COX-2 upregulation was preceded by activation of nuclear factor kappaB (NF-kappaB) and coincided with increased levels of tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-6, and intercellular adhesion molecule 1 (ICAM-1). Selective COX-2 inhibitors (celecoxib and NS-398) protected against the development of steatohepatitis in WT but not PPAR-alpha-/- mice. In conclusion, induction of COX-2 occurs in association with NF-kappaB activation and upregulation of TNF-alpha, IL-6, and ICAM-1 in MCD diet-induced steatohepatitis. PPAR-alpha suppresses both COX-2 and development of steatohepatitis, while pharmacological inhibition of COX-2 activity ameliorates the severity of experimental steatohepatitis. COX-2 may therefore be a pro-inflammatory mediator in metabolic forms of steatohepatitis.

Lipid peroxidation, stellate cell activation and hepatic fibrogenesis in a rat model of chronic steatohepatitis.

BACKGROUND/AIMS: We explored the involvement of cell types, cytokines and lipid peroxidation in a rat dietary model of fibrosing steatohepatitis. METHODS: Male rats were fed a high fat diet deficient in methionine and choline (MCD) for up to 17 weeks. Whole liver, hepatocytes and non-parenchymal cells were analysed for reduced glutathione (GSH) levels, products of lipid peroxidation (thiobarbituric acid reactive substances, TBARS), liver injury, and fibrosis. RESULTS: MCD diet-fed rats developed hepatic steatosis at week 2 and focal necroinflammatory change by week 5, while pericellular fibrosis evolved and progressed between weeks 12 and 17. Collagen alpha(1)(1) gene expression was upregulated by week 5 and increased fivefold by week 17. Stellate cells were the unique source of collagen gene expression. TIMP-1 and -2 were increased at week 12. Livers of MCD diet-fed rats exhibited lowered levels of GSH and elevated TBARS. Hepatocytes were the source of lipid peroxidation, and mRNA levels for TGFbeta1 were increased only in this cell type. CONCLUSIONS: The MCD model of 'fibrosing steatohepatitis' replicates the histologic features of human steatohepatitis, and the sequence of steatosis, inflammatory cell injury and fibrogenesis. The temporal sequence is consistent with a concept for involvement of oxidative injury in inflammatory recruitment and pathogenesis of hepatic fibrogenesis.