Hypoglycemic Efficacy of Guava Leaf Extract

[[abstract]]Compendium of Materia Medica indicated that guava leaves may be used for treating subjects with diabetic conditions. Due to subtropical climate conditions, guava tree can be cultivated in large quantity throughout the year in Taiwan. We cooperated with guava framers and the farmer’s union at Shetou(社頭) District of Chunghwa County to study the blood glucose lowering potential of guava leaf by examining if guava leaf extract can inhibit protein tyrosine phosphatase-1B enzymatic activity. Guava leaf was extracted with methanol extensively, and the extract was condensed for further partitioning. Solvents of different polarities were used in the serial partitioning; they include hexane, ethyl acetate, butanol and water. Guava leaf was also extracted directly with hot water, so a total of six fractions were obtained. These fractions were concentrated and tested for their effects on protein tyrosine phosphatase-1B (PTP-1B) enzymatic activity, which plays a major role at controlling insulin signaling and circulating blood glucose levels. The water-soluble concentrate has an IC50 of 0.031 ±0.004 mg/mL when inhibiting protein tyrosine phosphatase-1B, while direct hot water extract has an of IC50 of 0.033 ±0.001 mg/mL, these two water soluble fractions are more potent than other fractions at inbiting PTP-1B enzyme activity in vitro. Therefore, it is suggested that guava leaf tea can inhibit protein tyrosine phosphatase-1B activity, and the active ingredient be water-soluble