Oat fiber attenuates circulating oxysterols levels and hepatic inflammation via targeting TLR4 signal pathway in LDL receptor knockout mice

Impact of Oat (Avena sativa L.) on Metabolic Syndrome and Potential Physiological Mechanisms of Action: A Current Review

Oat (Avena sativa L.), an annual herbaceous plant belonging to the Gramineae family, is widely grown in various regions including EU, Canada, America, Australia, etc. Due to the nutritional and pharmacological values, oats have been developed into various functional food including fermented beverage, noodle, cookie, etc. Meanwhile, numerous studies have demonstrated that oats may effectively improve metabolic syndrome, such as dyslipidemia, hyperglycemia, atherosclerosis, hypertension, and obesity. However, the systematic pharmacological mechanisms of oats on metabolic syndrome have not been fully revealed. Therefore, in order to fully explore the benefits of oat in food industry and clinic, this review aims to provide up-to-date information on oat and its constituents, focusing on the effects on metabolic syndrome.

Oat Fiber Modulates Hepatic Circadian Clock via Promoting Gut Microbiota-Derived Short Chain Fatty Acids

The biological alteration of circadian rhythm was found to be related to the development of metabolic disorders. Our previous studies reported that impaired lipid metabolism caused by a high-fat diet was improved by oat fiber, but did not attempt to answer whether the improvement is mechanistically linked to circadian rhythm. By focusing on circadian alteration, the present study aimed to elucidate the effect of gut microbiota-derived short chain fatty acids (SCFAs) on circadian rhythm in a high-fat diet experimental paradigm with and without dietary oat fiber feeding. The results showed that oat fiber prevented the production of obesity and dyslipidemia caused by a high-fat diet in C57BL/6 mice. From a circadian perspective specifically, a high-fat diet disrupted the hepatic circadian protein expressions of the liver clock genes, which were in parallel with the altered oscillation of serum triglycerides, low-density lipoprotein cholesterol, fasting insulin, and the homeostasis model assessment-insulin resistance index. Oat fiber, by contrast, reversed these disrupted diurnal oscillations. Most interestingly, what a high-fat diet induced and what oat fiber prevented were dictated in a close oscillation pattern resembling that of SCFA production facilitated by the intestinal microbiome. Given the results from the present study and from others that demonstrated the role played by SCFAs in regulating circadian rhythm, we conclude that the beneficial effects of oat fiber are likely mediated by complex processes involving multiple mechanisms including a signal transduction pathway of gut microbiota-derived SCFAs to hepatic circadian protein expression to lipid and other metabolic oscillations. The latter warrants more investigation to further determine whether the circadian rhythm pathway has any major and causal significance for the outcome measures in the prevention and treatment of metabolic disorders in humans.