Endotoxemia correlates with nonalcoholic steatohepatitis induced by methionine and choline deficient diet in mice

Nonalcoholic steatohepatitis (NASH) is a disease characterized by fat and inflammation in the liver that can lead to cirrhosis. Previous studies suggested that gut‐derived endotoxin plays a significant role in the pathogenesis of NASH. Therefore, the aim of the present study was to characterize NASH in relationship to endotoxemia. To model NASH, male C57LB/6 mice (4–6 wk) were fed a methionine and choline deficient diet (MCDD); mice fed a similar diet with adequate amounts of methionine and choline (control diet; CD) served as controls. After 3 wks of feeding, extensive necroinflammation was observed in MCDD‐fed mice as indicated by the accumulation of neutrophils, induction of ICAM‐1 mRNA expression, and elevated serum transaminase activity. Expression of Collagen I was also significantly up‐regulated in MCDD‐fed mice demonstrating early fibrotic changes. Blood samples were collected from the portal vein at sacrifice and endotoxin was measured in the platelet‐rich plasma fraction using a kinetic limulus assay. Portal vein endotoxin values in MCDD‐fed mice (100.7 ± 26.7 pg/ml) were significantly higher than CD‐fed mice (44.4 ± 18.4 pg/ml), indicating endotoxin leakage into hepatic circulation. To further index endotoxemia, expression of toll‐like receptor‐4 (TLR‐4) was measured using QRT‐PCR and was increased 5–fold in MCDD‐fed mice. Consistent with our hypothesis, there was a significant direct correlation between the expression of TLR‐4 and ICAM‐1. Expression of TLR‐4 levels also correlated with the extent of induction of collagen mRNA levels. These findings are consistent with the idea that endotoxemia plays an important role in MCDD‐induced NASH.