Search

To test the hypothesis that metformin protects against fructose-induced steatosis, and if so, to elucidate underlying mechanisms, C57BL/6J mice were either fed 30% fructose solution or plain water for 8 weeks. Some of the animals were concomitantly treated with metformin (300 mg/kg body weight/day) in the drinking solution. While chronic consumption of 30% fructose solution caused a significant increase in hepatic triglyceride accumulation and plasma alanine-aminotransferase levels, this effect of fructose was markedly attenuated in fructose-fed mice concomitantly treatment with metformin. The protective effects of the metformin treatment on the onset of fructose-induced non-alcoholic fatty liver disease (NAFLD) were associated with a protection against the loss of the tight junction proteins occludin and zonula occludens 1 in the duodenum of fructose-fed mice and the increased translocation of bacterial endotoxin found in mice only fed with fructose. In line with these findings, in metformin-treated fructose-fed animals, hepatic expression of genes of the toll-like receptor-4-dependent signalling cascade as well as the plasminogen-activator inhibitor/cMet-regulated lipid export were almost at the level of controls. Taken together, these data suggest that metformin not only protects the liver from the onset of fructose-induced NAFLD through mechanisms involving its direct effects on hepatic insulin signalling but rather through altering intestinal permeability and subsequently the endotoxin-dependent activation of hepatic Kupffer cells.

Plasminogen activator inhibitor-1 (PAI-1) is an acute-phase protein known to be involved in alcoholic liver disease and hepatic fibrosis. In the present study, the hypothesis that PAI-1 is causally involved in the onset of fructose-induced hepatic steatosis was tested in a mouse model. Wild-type C57BL/6J and PAI-1⁻/⁻ mice were fed with 30% fructose solution or water for 8 weeks. Markers of hepatic steatosis, expression of PAI-1, apolipoprotein B (ApoB), cluster of differentiation 1d (CD1d), markers of natural killer T (NKT) cells, protein levels of phospho-c-Met and tumor necrosis factor-α (TNF-α) were determined. Activity of the microsomal triglyceride transfer protein (MTTP) was measured in liver tissue. In comparison with water controls, chronic intake of 30% fructose solution caused a significant increase in hepatic triglycerides, PAI-1 expression and plasma alanine aminotransferase levels in wild-type mice. This effect of fructose feeding was markedly attenuated in PAI-1⁻/⁻ mice. Despite no differences in portal endotoxin levels and hepatic TNF-α protein levels between fructose-fed groups, the protective effect of the loss of PAI-1 against the onset of fructose-induced steatosis was associated with a significant increase in phospho-c-Met, phospho Akt, expression of ApoB and activity of MTTP in livers of PAI-1⁻/⁻ mice in comparison with fructose-fed wild types. Moreover, in PAI-1⁻/⁻ mice, expressions of CD1d and markers of CD1d-reactive NKT cells were markedly higher than in wild-type mice; however, expression of markers of activation of CD1d-reactive NKT cells (eg, interleukin-15 and interferon-γ) were only found to be increased in livers of fructose-fed PAI-1⁻/⁻ mice. Taken together, these data suggest that PAI-1 has a causal role in mediating the early phase of fructose-induced liver damage in mice through signaling cascades downstream of Kupffer cells and TNF-α.