Triterpene alcohols and sterols from rice bran lower postprandial glucose-dependent insulinotropic polypeptide release and prevent diet-induced obesity in mice

Abstract

Obesity is now a worldwide health problem. Glucose-dependent insulinotropic polypeptide (GIP) is a gut hormone that is secreted following the ingestion of food and modulates energy metabolism. Previous studies reported that lowering diet-induced GIP secretion improved energy homeostasis in animals and humans, and attenuated diet-induced obesity in mice. Therefore, food-derived GIP regulators may be used in the development of foods that prevent obesity. Rice bran oil and its components are known to have beneficial effects on health. Therefore, the aim of the present study was to clarify the effects of the oil-soluble components of rice bran on postprandial GIP secretion and obesity in mice. Triterpene alcohols [cycloartenol (CA) and 24-methylene cycloartanol (24Me)], β-sitosterol, and campesterol decreased the diet-induced secretion of GIP in C57BL/6J mice. Mice fed a high-fat diet supplemented with a triterpene alcohol and sterol preparation (TASP) from rice bran for 23 wk gained less weight than control mice. Indirect calorimetry revealed that fat utilization was higher in TASP-fed mice than in control mice. Fatty acid oxidation-related gene expression in the muscles of mice fed a TASP-supplemented diet was enhanced, whereas fatty acid synthesis-related gene expression in the liver was suppressed. The treatment of HepG2 cells with CA and 24Me decreased the gene expression of sterol regulatory element-binding protein (SREBP)-1c. In conclusion, we clarified for the first time that triterpene alcohols and sterols from rice bran prevented diet-induced obesity by increasing fatty acid oxidation in muscles and decreasing fatty acid synthesis in the liver through GIP-dependent and GIP-independent mechanisms.

Effects of feeding outer bran fraction of rice on lipid accumulation and fecal excretion in rats

“…34) In addition, triterpene alcohols and sterols from rice bran inhibited postprandial release of glucose-dependent insulinotropic polypeptide (GIP), which promotes weight gain and insulin resistance, and prevent diet-induced obesity in mice. 35) Since γ-oryzanol is a mixture of ferulic acid esters of phytosterols and triterpene alcohols, 36) OBFR might contain higher amount of triterpene alcohols compared to WRB and increase energy expenditure via inhibition of GIP release. Moreover, rice bran contains functional components other than γ-oryzanol, phytic acid, and dietary fiber such as vitamins, essential minerals, protease inhibitors, and amylase inhibitors.…”

Triterpene alcohols and sterols from rice bran reduce postprandial hyperglycemia in rodents and humans

“…Our previous study showed that the absorption of TASP components (CA and 24Me) was slow and their blood levels reached a maximum concentration no earlier than 3–6 h after TASP ingestion in mice. Furthermore, dietary ingestion of TASP for 7 weeks did not change the metabolic gene expression levels in the skeletal muscle in mice . Therefore, dietary TASP is not likely to lower postprandial blood glucose levels by increasing glucose uptake into the skeletal muscles.…”

“…We previously demonstrated triterpene alcohol and sterol preparation (TASP) from rice bran lowered postprandial glucose‐dependent insulinotropic polypeptide (GIP) secretion and prevented obesity induced by a high‐fat diet in mice . GIP is a gut hormone secreted from enteroendocrine K cells into the bloodstream after food consumption .…”

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

“…Consequently, the inhibitory effect of RBO may be due to the unsaponifiable matter, which downregulates SREBP-1c (Ham et al, 2016). Fukuoka et al (2014) showed that treatment of HepG2 cells with triterpene alcohols, the characteristic components of RBO, decreased the gene expression of Srebf1_v3. Moreover, the expression of Srebf1_v3 was previously reported to be directly regulated by insulin (O'Brien, Streeper, Ayala, Stadelmaier, & Hornbuckle, 2001).…”