Mulberry leaf polyphenols attenuated postprandial glucose absorptionviainhibition of disaccharidases activity and glucose transport in Caco-2 cells

The present study attempted to evaluate the mechanism of action and bioactivity of mulberry leaf polyphenols (MLPs) in type-2 diabetes prevention via inhibition of disaccharidase and glucose transport. MLPs were purified with D101 resin and the main composition was determined as chlorogenic acid, rutin, benzoic acid and hyperoside. MLPs demonstrated a strong inhibitory effect on disaccharidases derived from both mouse and Caco-2 cells, and the order of IC50 value was: murine sucrase (7.065 mg mL-1) > murine maltase (4.037 mg mL-1) > Caco-2 cell maltase (0.732 mg mL-1) > Caco-2 cell sucrase (0.146 mg mL-1). MLPs showed the strongest inhibitory effect on sucrase derived from Caco-2 cells and played a role in lowering postprandial glucose mainly by inhibiting sucrase activity. The Caco-2 monolayer cell model was established to simulate the glucose transport process in the human small intestine. We found that within the concentration range of 0.5-2 mg mL-1, MLPs significantly inhibited glucose transport, and the inhibition rate increased with time and dose. The effect of phlorizin (SGLT1 inhibitor) in the control group showed a similar effect on glucose transport, revealing that MLPs may inhibit glucose transport mainly by inhibiting the SGLT1 transporter. RT-qPCR analysis confirmed that MLPs inhibited glucose absorption by suppressing the SGLT1-GLUT2 pathway via downregulation of the mRNA expression of phospholipase, protein kinase A and protein kinase C.