Inhibitory actions of Pseuderanthemum palatiferum(Nees) Radlk. leaf ethanolic extract and its phytochemicals against carbohydrate-digesting enzymes

摘要

Objective: To investigate the effects of the leaf ethanolic extract of Pseuderanthemum palatiferum（PPE） and its isolated phytochemicals, stigmasterol and sitosterol-3-O-b-Dglucopyranoside, against a-amylase and a-glucosidase enzyme activities both in vitro and in vivo.Methods: A concentration of maltose, which is a product released in a-amylase-catalyzing reaction, was used as an index of in vitro a-amylase activity. Meanwhile, in vitro a-glucosidase enzyme activity was indicated by the amount of liberated p-nitrophenol in a-glucosidase-catalyzing reaction. In vivo a-amylase and a-glucosidase enzyme activities were evaluated in the normal rats by using oral starch tolerance test and oral sucrose tolerance test, respectively.Results: PPE exerted a concentration-dependent inhibitory action against both aamylase and a-glucosidase in vitro with the IC50 values of（11.79 ± 8.10） mg/m L and（1.00 ± 0.11） mg/m L, respectively. Stigmasterol and sitosterol-3-O-b-D-glucopyranoside also exerted an in vitro a-amylase inhibition with the IC50 values of（59.41 ± 8.22） mg/m L and（111.19 ± 9.02） mg/m L, respectively. However, these phytochemicals did not produce a concentration-dependent inhibition against in vitro a-glucosidase activity. PPE and its isolated phytochemicals significantly decreased the blood glucose levels at t = 30 min in the oral starch tolerance test. From the sucrose tolerance test, only PPE but not its isolated phytochemicals significantly caused a depletion in the blood glucose levels at t = 30 min Conclusions: These results indicate an inhibitory action against carbohydrate-digesting enzymes as the anti-diabetic mechanism of action of PPE. Nonetheless, further clinical study is required to justify its role in the treatment of diabetes.