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

Abstract

Objective: To investigate the effects of the leaf ethanolic extract of Pseuderanthemum palatiferum (PPE) and its isolated phytochemicals, stigmasterol and sitosterol-3-O-β-d-glucopyranoside, against α-amylase and α-glucosidase enzyme activities both in vitro and in vivo. Methods: A concentration of maltose, which is a product released in α-amylase-catalyzing reaction, was used as an index of in vitro α-amylase activity. Meanwhile, in vitro α-glucosidase enzyme activity was indicated by the amount of liberated p-nitrophenol in α-glucosidase-catalyzing reaction. In vivo α-amylase and α-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 α-amylase and α-glucosidase in vitro with the IC50 values of (11.79 ± 8.10) mg/mL and (1.00 ± 0.11) mg/mL, respectively. Stigmasterol and sitosterol-3-O-β-d-glucopyranoside also exerted an in vitro α-amylase inhibition with the IC50 values of (59.41 ± 8.22) μg/mL and (111.19 ± 9.02) μg/mL, respectively. However, these phytochemicals did not produce a concentration-dependent inhibition against in vitro α-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.

Keywords

• Pseuderanthemum palatiferum
• Diabetes mellitus
• α-Amylase
• α-Glucosidase
• Postprandial blood glucose