Anti-diabetic activity of a polyphenol-rich extract from Phellinus igniarius in KK-Ay mice with spontaneous type 2 diabetes mellitus.

The present study investigated the anti-diabetic activity and potential mechanisms of the polyphenol rich extract from Phellinus igniarius (PI-PRE) in vitro and in vivo. Four main phenolic compounds of PI-PRE were purified and identified as 7,8-dihydroxycoumarin, 3,4-dihydroxybenzalacetone, 7,3'-dihydroxy-5'-methoxyisoflavone and inoscavin C by the off-line semipreparative liquid chromatography-nuclear magnetic resonance protocol. In vitro, PI-PRE stimulated GLUT4 translocation by 2.34-fold and increased glucose uptake by 1.73-fold in L6 cells. However, the selective AMP-activated protein kinase (AMPK) inhibitor, compound C, completely reversed the PI-PRE-induced GLUT4 translocation. In vivo, KK-Ay mice treated with PI-PRE for four weeks had lower fasting blood glucose levels, as well as other blood-lipid indexes, compared with the vehicle control group. Mechanistic studies showed that the expressions of p-AMPKα and GLUT4 were significantly increased by treatment with PI-PRE in L6 cells. In KK-Ay mice, the expression of p-AMPKα was enhanced in the liver and skeletal muscle, and the expression of GLUT4 was increased in skeletal muscle. These findings suggest that PI-PRE possesses potential anti-diabetic effects including improving glucose tolerance, reducing hyperglycemia, and normalizing insulin levels. These effects are partly due to the activation of GLUT4 translocation via the modulation of the AMPK pathway.