Black raspberry extract stimulates glucose uptake via adenosine monophosphate-activated protein kinase and phosphatidylinositol-3 kinase pathways in skeletal muscle cells

Abstract

Black raspberry (Rubus occidentalis) shows beneficial health effects, such as antioxidant, anti-inflammatory, chemopreventive, antiproliferative, and antihyperglycemic activities. The present study investigated the antihyperglycemic activity of black raspberry extract (BRE) and potential mechanisms in skeletal muscle cells. Differentiated C2C12 myotubes were treated with the BRE (1–1000 μg/mL) or metformin (1 mM). The protein levels of various insulin signaling targets were measured by western blot analysis. BRE significantly increased glucose uptake by upregulated insulin receptor and phosphatidylinositol-3 kinase (PI3K) in C2C12 cells, leading to enhanced translocation of glucose transporter 4 (GLUT4) to the plasma membrane. The expression of phosphorylated (p)-adenosine monophosphate-activated protein kinase (AMPK) was also enhanced by treatment with BRE, this resulting in stimulation of GLUT4 translocation to the plasma membrane and hence glucose uptake in skeletal muscles. These results suggest that BRE has an antihyperglycemic effect by stimulating GLUT4 translocation to the plasma membrane via activating the PI3K and AMPK pathways in skeletal muscle cells, thereby upregulating glucose uptake. Black raspberry is a potential functional food and has important implications for preventing and treating type-2 diabetes. In addition, our study found that the flavonoids fraction is the main contributor fraction to promote glucose uptake in C2C12 cells.