Accumulating evidence has demonstrated the association between alcohol overconsumption and the development of insulin resistance. However, the underlying mechanisms are not completely understood. To investigate the requirement and sufficiency of hepatocyte toll-like receptor 4 (TLR4) in alcohol-induced insulin resistance, we used two mouse models (Tlr4^fl/fl and Tlr4^LoxTB) that allow ablation of TLR4 only in hepatocytes (Tlr4^LKO) and restoration of endogenous TLR4 expression in hepatocytes on a TLR4-null background (Tlr4^LoxTB × Alb-Cre), respectively. A Lieber-DeCarli feeding model was used to induce glucose intolerance and insulin resistance in mice. Glucose tolerance test, insulin tolerance test, and insulin signaling experiments were performed to examine systemic and tissue-specific insulin sensitivity. We found that alcohol-fed hepatocyte TLR4 deficient mice (Tlr4^LKO) had lower blood glucose levels in response to intraperitoneal injection of insulin. Moreover, increased phosphorylation of glycogen synthase kinase-3β (GSK3β) was observed in the liver of Tlr4^LKO mice after chronic alcohol intake. In contrast, when hepatic TLR4 was reactivated in mice (Tlr4^LoxTB × Alb-Cre), alcohol feeding caused glucose intolerance in these mice compared with littermate controls (Tlr4^LoxTB). In addition, AKT phosphorylation was dramatically reduced in the liver and epididymal white adipose tissue (eWAT) of alcohol-fed Tlr4^LoxTB × Alb-Cre mice, which was similar to that of mice with whole-body TLR4 reactivation (Tlr4^LoxTB × Zp3-Cre). Collectively, these findings suggest that hepatocyte TLR4 is both required and sufficient in the development of insulin resistance induced by alcohol overconsumption.

Interactions between alcohol and nutrition play an important role in the development and progression of alcohol-associated liver disease (ALD). Although dietary cholesterol was shown to exacerbate fatty liver and liver injury in alcohol-fed mice, findings regarding the combined effect of dietary cholesterol and heavy alcohol drinking on cholesterol homeostasis remain controversial. Ezetimibe has been widely used as a cholesterol-lowering drug in hypercholesterolemic subjects. It is not fully understood whether ezetimibe blunts the adverse effect of cholesterol on lipid and biliary bile acid metabolism in alcohol-exposed mice. In the current study, wild-type mice were subjected to NIAAA alcohol feeding model. Dietary cholesterol (0.2%, w/v) and ezetimibe (0.001%, w/v) were added to the liquid diets. Cholesterol and triglyceride contents in the liver and circulation were determined. Biliary bile acid composition, as well as hepatic and circulating inflammatory markers were analyzed. We found that ezetimibe protected mice from the synergistic effects of dietary cholesterol and alcohol on hepatic triglyceride accumulation, which was accompanied by enhanced expression of genes involved in hepatic beta oxidation. Dietary cholesterol caused great increases in liver cholesterol content and dramatic reductions in the expression of hepatic cholesterol biosynthetic genes in both control- and alcohol-fed mice. These changes were normalized by ezetimibe treatment. Ezetimibe attenuated dietary cholesterol-induced elevations in total biliary bile acids. Moreover, mice fed a diet containing both cholesterol and alcohol exhibited increased expression of monocyte chemoattractant protein 1 (Mcp1) and tumor necrosis factor alpha (Tnfα) in the distal small intestine. Collectively, our findings indicate that ezetimibe effectively mitigates the adverse effects of dietary cholesterol and alcohol consumption on hepatic lipid accumulation and liver injury.