Extracts of Momordica charantia suppress postprandial hyperglycemia in rats

Momordica charantia (bitter melon) is commonly known as vegetable insulin, but the mechanisms underlying its hypoglycemic effect remain unclear. To address this issue, the effects of bitter melon extracts on postprandial glycemic responses have been investigated in rats. An aqueous extract (AE), methanol fraction (MF) and methanol insoluble fraction (MIF) were prepared from bitter melon. An oral sucrose tolerance test revealed that administration of AE, MF or MIF each significantly suppressed plasma glucose levels at 30 min as compared with the control. In addition, the plasma insulin level at 30 min was also significantly lower after MF administration than in the control in the oral sucrose tolerance test. By contrast, these effects of bitter melon extracts were not observed in the oral glucose tolerance test. In terms of mechanism, bitter melon extracts dose-dependently inhibited the sucrase activity of intestinal mucosa with ICsub(50) values of 8.3, 3.7 and 12.0 mg/mL for AE, MF and MIF, respectively. The fraction with a molecular weight of less than 1,300 (LT 1,300) obtained from MF inhibited the sucrase activity most strongly in an uncompetitive manner with an ICsub(50) value of 2.6 mg/mL. Taken together, these results demonstrated that bitter melon suppressed postprandial hyperglycemia by inhibition of alpha-glucosidase activity and that the most beneficial component is present in the LT 1,300 fraction obtained from MF.