Rice Bran Oil Improves Insulin Resistance by Affecting the Expression of Antioxidants and Lipid-Regulatory Genes.

Abstract

The present study investigated the molecular effects of rice bran oil (RBO) on lipid-regulatory genes (sterol regulatory element binding protein-1 [Srebf1] and peroxisome proliferator-activated receptors-α [Ppara]) and the expression of catalase (CAT) and superoxide dismutase (SOD1) genes in insulin-resistant rats. Rats were divided into five groups: animals that received standard diet (control); rats fed standard diet containing RBO as the sole source of fat (RBO); a high-fructose diet (HFD) group, which was further divided into two subgroups: rats fed HFD either for only 1 month (HFD1) or for 2 months (HFD2) and rats fed HFD containing RBO for 1 month; while rats in the last group fed HFD for 30 days then treated with RBO for another 30 days. The HFD induced a state of insulin resistance (IR) as indicated by the hyperinsulinemia and elevated homeostasis model assessment insulin resistance index. Hepatic lipid levels and radical scavenging enzymes were altered by the HFD. Lipid-regulatory genes, Srebf1 and Ppara, were upregulated while Sod1 and Cat were downregulated in insulin-resistant rats. Addition of RBO to the two diet regimens alleviated the disorders of IR to some extent. RBO reduced the hepatic levels of triacylglycerol, malondialdehyde, SREBP, and PPAR-α mRNA. Hepatic SOD and CAT were elevated at gene and protein levels. The HFD induces de novo lipogenesis by upregulating the lipid-regulatory genes resulting in increased serum and hepatic triacylglycerol. Moreover, IR induced by the HFD caused a state of oxidative stress. Supplementation of RBO to fructose-fed rats not only improves insulin resistance but also downregulates lipogenic genes and improves the unbalanced oxidative status.