CB1 receptor blockade ameliorates hepatic fat infiltration and inflammation and increases Nrf2-AMPK pathway in a rat model of severely uncontrolled diabetes

Abstract

Previous studies have shown that the CB1 receptor antagonist reverses steatohepatitis and its related features of metabolic syndrome, such as obesity and type 2 diabetes. However, the beneficial effects of CB1 receptor blockade on hepatic steatosis and inflammation have not been investigated independently of its effects on body weight and glycemic control. At 32 weeks of age, OLETF rats were administered with rimonabant (10 mg.kg(-1).day(-1)) by oral gavage for 6 weeks. No significant changes in body weight, OGTT, and serum glucose were observed in spite of rimonabant-decreased food intake. Moreover, there was a significant difference between initial and final body weight, regardless of rimonabant administration, indicating that OLETF rats were severely diabetic rats. Rimonabant administration significantly decreased serum liver enzyme levels such as ALT and AST, hepatic fat accumulation, lipid peroxidation, and cell death as demonstrated by the number of TUNEL-positive cells in severely uncontrolled diabetic OLETF rats. Significant decreases in hepatic gene expression of proinflammatory cytokines (CD11b, F4/80, MCP1, and TNF alpha), negative inflammatory mediators (SOCS1 and SOCS3), and fibrosis-related proteins (TGF beta, collagen 1, and TIMP1) were found in rimonabant-treated OLETF rats. Six-week administration of rimonabant significantly upregulated mRNA levels of CPT1 alpha and PPAR alpha related to beta-oxidation. Moreover, significant increases in Nrf2 gene expression and its downstream genes, NQO1, GSAT, HO-1, and TXNRD1 along with increased AMPK phosphorylation were noted in uncontrolled diabetic rats treated with rimonabant. The observed potent inhibitory effects of CB1 receptor blockade on hepatic fat infiltration and cellular death in severely uncontrolled diabetic rats indicate that CB1 receptor is a possible therapeutic target. Increased Nrf2 and AMPK phosphorylation may play a role in the mechanism of rimonabant action.