A Rice Bran Oil Diet Increases LDL-Receptor and HMG-CoA Reductase mRNA Expressions and Insulin Sensitivity in Rats with Streptozotocin/Nicotinamide-Induced Type 2 Diabetes

Abstract

A rice bran oil (RBO) diet can reduce plasma lipids; this was attributed to the specific components, gamma-oryzanol and gamma-tocotrienol, which individually were shown to be hypocholesterolemic; however, the mechanism of their effects on diabetic hyperlipidemia and the development of diabetes is not known. Rats with streptozotocin/nicotinamide-induced type 2 diabetes were divided into control, RO10, and RO15 groups, and fed cholesterol-free diets containing 0, 10, and 15 g RBO with 0, 352, and 528 g gamma-oryzanol and 0, 6.0 and 9.0 mg gamma-tocotrienol/100 g diet for 4 wk. Diabetic rats fed the RBO diet had greater insulin sensitivity (P = 0.02) than rats fed the control diet. Diabetic rats fed the RBO diet also had lower plasma triglyceride (P = 0.003), LDL cholesterol (P = 0.028), and hepatic triglyceride concentrations (P = 0.04), as well as greater fecal neutral sterol and bile acid excretion than those fed the control diet. After 4 wk, there was an approximately 100% (P < 0.001) increase in the abundance of hepatic cholesterol 7alpha-hydroxylase, an 89% (P < 0.001) increase in the hepatic LDL-receptor, and a 50% (P < 0.001) increase in hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase mRNA in rats fed the RBO diet compared with those fed the control diet. These findings support the conclusion that a rice bran oil-containing diet can significantly suppress hyperlipidemic and hyperinsulinemic responses in diabetic rats. The high contents of gamma-oryzanol and gamma-tocotrienol in RBO can lead to increased fecal neutral sterol and bile acid excretion, via upregulation of cholesterol synthesis and catabolism.

Supercritical CO₂ Extraction of Rice Bran Oil –the Technology, Manufacture, and Applications

“…RBO is the richest source of natural oryzanols. RBO phytochemicals have wide range of positive health properties, including hypolipidemic, anti-atherogenic, and anti-diabetic properties 15 . At present, RBO supplements are now being recommended as a good source of these bioactive compounds.…”

Tocotrienols and its impact in cardiovascular health

“…43 Tocotrienol, not only of palm oil origin, but also isolated from rice bran show cholesterol lowering properties. 44,45 Amaranth oil, containing tocotrienol, possesses hypocholesterolemic properties as well. 46 A human study with 28 hypercholesterolemic subjects has been executed in 5 phases of 35 days each.…”

Multifaceted role of tocotrienols in cardioprotection supports their structure: function relation

“…Interestingly, c-and d-tocotrienol, which lacked the 5-methyl substituents present in a-tocotrienol, were shown to possess significantly greater HMGR suppression (Pearce et al 1994). Tocotrienol not only of palm oil origin but also isolated from rice bran shows cholesterol-lowering properties (Chen and Cheng 2006;Pearce et al 1992b).…”