Hypoglycemic effect of aspalathin is related to increased GLUT4 translocation to plasma membrane via AMPK activation. In addition, aspalathin reduces the gene expression of hepatic enzymes related to glucose production and lipogenesis. These results strongly suggest that aspalathin has anti-diabetic potential.

The effects of oryzanol and ferulic acid on the glucose metabolism of high-fat-fed mice were investigated. Male C57BL/6N mice were randomly divided into 4 groups: NC group fed with normal control diet; HF group fed with high-fat (17%) diet; HF-O group fed with high-fat diet supplemented with 0.5% oryzanol; and HF-FA group fed with high-fat diet supplemented with 0.5% ferulic acid. All animals were allowed free access to the experimental diets and water for 7 wk. At the end of the experimental period, the HF-O and HF-FA groups exhibited significantly lower blood glucose level and glucose-6-phosphatase (G6pase) and phosphoenolpyruvate carboxykinase (PEPCK) activities, and higher glycogen and insulin concentrations and glucokinase (GK) activity compared with NC and HF groups. The results of this study illustrate that both oryzanol and ferulic acid could reduce the risk of high-fat diet-induced hyperglycemia via regulation of insulin secretion and hepatic glucose-regulating enzyme activities.

There have been studies on health beneficial effects of ginger and its components. However, there still remain certain aspects that are not well defined in their anti-hyperglycemic effects. Our aims were to find evidence of possible mechanisms for antidiabetic action of [6]-gingerol, a pungent component of ginger, employing a rat skeletal muscle-derived cell line, a rat-derived pancreatic β-cell line, and type 2 diabetic model animals. The antidiabetic effect of [6]-gingerol was investigated through studies on glucose uptake in L6 myocytes and on pancreatic β-cell protective ability from reactive oxygen species (ROS) in RIN-5F cells. Its in vivo effect was also examined using obese diabetic db/db mice. [6]-Gingerol increased glucose uptake under insulin absent condition and induced 5' adenosine monophosphate-activated protein kinase phosphorylation in L6 myotubes. Promotion by [6]-gingerol of glucose transporter 4 (GLUT4) translocation to plasma membrane was visually demonstrated by immunocytochemistry in L6 myoblasts transfected with glut4 cDNA-coding vector. [6]-Gingerol suppressed advanced glycation end product-induced rise of ROS levels in RIN-5F pancreatic β-cells. [6]-Gingerol feeding suppressed the increases in fasting blood glucose levels and improved glucose intolerance in db/db mice. [6]-Gingerol regulated hepatic gene expression of enzymes related to glucose metabolism toward decreases in gluconeogenesis and glycogenolysis as well as an increase in glycogenesis, thereby contributing to reductions in hepatic glucose production and hence blood glucose concentrations. These in vitro and in vivo results strongly suggest that [6]-gingerol has antidiabetic potential through multiple mechanisms.

Previous studies have demonstrated antidiabetic effects for rooibos (Aspalathus linearis) and aspalathin (ASP), one of its main polyphenols. Rooibos, an endemic plant of South Africa, is well-known for its use as herbal tea. Green ('unfermented') rooibos has been shown to contain more ASP than 'fermented' rooibos tea, currently the major product. In the present study, we investigated the antidiabetic effect of green rooibos extract (GRE) through studies on glucose uptake in L6 myotubes and on pancreatic β-cell protective ability from reactive oxygen species (ROS) in RIN-5F cells. Its in vivo effect was also examined using obese diabetic KK-A(y) mice. GRE increased glucose uptake under insulin absent condition and induced phosphorylation of 5'-adenosine monophosphate-activated protein kinase (AMPK) in L6 myotubes as previously demonstrated for ASP. In addition to AMPK, GRE also promoted phosphorylation of Akt, another promoter of glucose transporter 4 (GLUT4) translocation, in L6 myotubes unlike ASP, suggesting an involvement of GRE component(s) other than ASP in Akt phosphorylation. Promotion of GLUT4 translocation to the plasma membrane by GRE in L6 myotubes was demonstrated by Western blotting analysis. GRE suppressed the advanced glycation end products (AGEs)-induced increase in ROS levels in RIN-5F pancreatic β-cells. Subchronic feeding with GRE suppressed the increase in fasting blood glucose levels in type 2 diabetic model KK-A(y) mice. These in vitro and in vivo results strongly suggest that GRE has antidiabetic potential through multiple modes of action.

The comparative effects of oryzanol and ferulic acid on the lipid metabolism and antioxidative status of high fat-fed mice were investigated. The mice were given a diet containing 17% fat (HF), supplemented with oryzanol (HF-O) or ferulic acid for 7 weeks. The control mice (NC) were fed with normal diet. The HF mice exhibited increased body weight gain, plasma and hepatic total cholesterol and triglyceride concentrations, and lipid peroxidation rate, and reduced high-density lipoprotein cholesterol level. In general, they also showed lower hepatic antioxidant and higher lipid-regulating enzymes activities relative to that of NC group. Addition of oryzanol or ferulic acid in the diet counteracted these high fat-induced hyperlipidemia and oxidative stress via increased faecal lipid excretion and regulation of antioxidant and lipogenic enzymes activities. This study illustrates that oryzanol and ferulic acid have relatively similar hypolipidemic actions and could be effective in lowering the risk of high fat diet-induced obesity.