Mulberry Leaf Extract Reduces Postprandial Hyperglycemia with Few Side Effects by Inhibiting α-Glucosidase in Normal Rats

Mulberry (Morus alba L.) leaf extract (MLE) was investigated as a potent plant-derived a-glucosidase inhibitor with low alpha-amylase inhibitory activity. MLE was prepared by heating in an autoclave at 121 degrees C for 15 minutes, and its in vitro and in vivo antihyperglycemic activities were investigated. The adverse side effects of MLE were analyzed by measuring the weight and volume of the cecum, stool color, starch content in the cecum, and the integrity of intestinal transporting capacity. The in vitro inhibitory activity of MLE on intestinal alpha-glucosidase was potent and that on intestinal alpha-amylase was very weak compared with acarbose. Sugar loading tests with starch, maltose, and sucrose showed that MLE may reduce postprandial increases in blood glucose by acting as an intestinal alpha-glucosidase inhibitor. Feeding tests suggested that MLE may exhibit fewer adverse side effects than other alpha-glucosidase inhibitors, such as abdominal flatulence and meteorism, which are attributed to the impaired digestion of starch by strong inhibition of intestinal alpha-amylase. These results suggest that MLE could be used in the development of pharmaceutical foods to control the blood glucose levels of diabetic patients by inhibiting intestinal alpha-glucosidase with reduced side effects.