Abstract
Banaba (Lagerstroemia speciosa L.) has been recognized as a folk medicine for diabetes in the Philippines. A hot water extract (HWE) of banaba leaves dose-dependently suppressed the elevation of blood glucose after oral administration of starch, but had no such effect after ingestion of glucose. The HWE was fractionated using HP-20 column chromatography, and its methanol fraction (HPME) was found to suppress the elevation of blood glucose after oral administration of starch. The inhibitory action of the HWE on activities of α-amylase and α-glucosidases was then examined in vitro. The HWE inhibited the activities of α-amylase, maltase, glucoamylase, sucrase and isomaltase, with estimated IC50 values of 0.53, 0.89, 1.24, 2.85 and 4.95mg/mL, respectively. The HPME also inhibited α-amylase and glucoamylase with IC50 values of 0.44 and 0.83mg/mL, respectively. These results suggest that the inhibitory effect of banaba on postprandial hyperglycemia is due to inhibition of α-amylase and α-glucosidases. Banaba may be a useful natural material for the prevention and therapy of diabetes.
