Published online Jul 7, 2015. doi: 10.3748/wjg.v21.i25.7754
Peer-review started: September 1, 2014
First decision: September 27, 2014
Revised: November 18, 2014
Accepted: January 8, 2015
Article in press: January 8, 2015
Published online: July 7, 2015
AIM: To investigate whether ezetimibe ameliorates hepatic steatosis and induces autophagy in a rat model of obesity and type 2 diabetes.
METHODS: Male age-matched lean control LETO and obese and diabetic OLETF rats were administered either PBS or ezetimibe (10 mg/kg per day) via stomach gavage for 20 wk. Changes in weight gain and energy intake were regularly monitored. Blood and liver tissue were harvested after overnight fasting at the end of study. Histological assessment was performed in liver tissue. The concentrations of glucose, insulin, triglycerides (TG), free fatty acids (FFA), and total cholesterol (TC) in blood and TG, FFA, and TG in liver tissue were measured. mRNA and protein abundance involved in autophagy was analyzed in the liver. To investigate the effect of ezetimibe on autophagy and reduction in hepatic fat accumulation, human Huh7 hepatocytes were incubated with ezetimibe (10 μmol/L) together with or without palmitic acid (PA, 0.5 mmol/L, 24 h). Transmission electron microscopy (TEM) was employed to demonstrate effect of ezetimibe on autophagy formation. Autophagic flux was measured with bafilomycin A1, an inhibitor of autophagy and following immunoblotting for autophagy-related protein expression.
RESULTS: In the OLETF rats that received ezetimibe (10 mg/kg per day), liver weight were significantly decreased by 20% compared to OLETF control rats without changes in food intake and body weight (P < 0.05). Lipid parameters including TG, FFA, and TC in liver tissue of ezetimibe-administrated OLETF rats were dramatically decreased at least by 30% compared to OLETF controls (P < 0.01). The serum glucose, insulin, HOMA-IR, and lipid profiles were also improved by ezetimibe (P < 0.05). In addition, autophagy-related mRNA expression including ATG5, ATG6, and ATG7 and the protein level of microtubule-associated protein light chain 3 (LC3) were significantly increased in the liver in rats that received ezetimibe (P < 0.05). Likewise, for hepatocytes cultured in vitro, ezetimibe treatment significantly decreased PA-induced fat accumulation and increased PA-reduced mRNA and protein expression involved in autophagy (P < 0.05). Ezetimibe-increased autophagosomes was observed in TEM analysis. Immunoblotting analysis of autophagy formation with an inhibitor of autophagy demonstrated that ezetimibe-increased autophagy resulted from increased autophagic flux.
CONCLUSION: The present study demonstrates that ezetimibe-mediated improvement in hepatic steatosis might involve the induction of autophagy.
Core tip: As an anti-hypercholesterolemia drug, ezetimibe is reported to improve metabolic disorders. Moreover, the hepatic expression of Niemann-Pick C1-like 1 protein, the target of ezetimibe, has led to increased interest in the effects, which have not been fully delineated, of ezetimibe on the liver. In the current study, ezetimibe treatment improved hepatic fat accumulation, which was accompanied by the induction of hepatic autophagy in obese and diabetic rats. In addition, in vitro hepatocytes treated with an inhibitor of autophagy showed that ezetimibe-induced autophagy resulted from an increase in autophagic flux. Therefore, ezetimibe-increased autophagy flux may play an important role in the improvement of hepatic steatosis.