Abstract
BACKGROUND AND PURPOSE: Thiazolidinediones, acting as PPAR-γ ligands, reduce hepatic steatosis in humans and animals. However, the underlying mechanism of this action remains unclear. The purpose of this study was to investigate changes in hepatic metabolites and lipids in response to treatment with the thiazolidinedione pioglitazone in an animal model of obese Type 2 diabetes. EXPERIMENTAL APPROACH: Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats were orally administered either vehicle (control) or pioglitazone (30 mg·kg(-1) ) and fed a high-fat diet (60% kcal fat) for 12 weeks. Hepatic metabolites were analysed via metabolomic and lipidomic analyses. Gene expression and PLA(2) activity were analysed in livers from pioglitazone-treated and control rats. KEY RESULTS: OLETF rats that received pioglitazone showed decreased fat accumulation and improvement of lipid profiles in the liver compared to control rats. Pioglitazone treatment significantly altered levels of hepatic metabolites, including free fatty acids, lysophosphatidylcholines and phosphatidylcholines, in the liver. In addition, pioglitazone significantly reduced the expression of genes involved in hepatic de novo lipogenesis and fatty acid uptake and transport, whereas genes related to fatty acid oxidation were up-regulated. Gene expression and enzyme activity of PLA(2) , which hydrolyzes phosphatidylcholines to release lysophosphatidylcholines and free fatty acids, were significantly decreased in the livers of pioglitazone-treated rats compared to control rats. CONCLUSIONS AND IMPLICATIONS: Our results present evidence for the ameliorative effect of pioglitazone on hepatic steatosis, largely due to the regulation of lipid metabolism, including fatty acids, lysophosphatidylcholines, phosphatidylcholines and related gene-expression patterns.