α-Glucosidase Inhibitory Activity of the Extracts and Major Phytochemical Components of Smilax glabra Roxb

Background: A therapeutic approach to treat diabetes is to decrease postprandial hyperglycemia. α-Glucosidase inhibitors from plant sources offer an attractive strategy for the control of hyperglycemia. Smilax glabra Roxb is a medicinal plant found in Asia, including Vietnam, which is used in the treatment of chronic diseases. However, the antidiabetic activity and the identification of α-glucosidase inhibitors from this plant have not been intensively investigated. This research was carried out to determine the α-glucosidase inhibitory activity of the extracts and that of the major phytochemical components of Smilax glabra Roxb. This could lead to further studies on the role of these compounds in hyperglycemia control, as well as identify their potential future applications. Methods: Column chromatography combined with crystallization procedures were used to isolate active fractions and two major compounds. The chemical structures of these compounds were determined by analysis of their NMR spectroscopic data, as well as MS data and comparisons made with the literature data. The α-glucosidase inhibitory activity was determined spectrophotometrically using p-nitrophenyl α-D-glucopyranoside as a substrate. The in vitro cytotoxicity of the isolated compounds and fractions was determined using the MTT assay. Results: The two major compounds, astilbin and 5-O-caffeoylshikimic acid together with two very active fractions, F7 and F8, were isolated from the rhizome. The two major compounds had α- glucosidase inhibitory activities with IC50 values of ca. 125 µg/mL and 38 µg/mL, respectively which are about 4 and 13 folds higher activity than the reference compound acarbose (IC50 of ca. 525 µg/mL). Fractions F7 and F8 showed very promising inhibitory activities towards α-glucosidase with IC50 values of 5.5 and 5.8 µg/mL, respectively. Cytotoxicity data on mouse fibroblast NIH3T3 cells indicated that the active compounds and fractions were not toxic at concentrations that are greater than their respective IC50 values. The α-glucosidase inhibitory activity of 5-Ocaffeoylshikimic acid and that of the two active fractions are reported here for the first time. Conclusion: The two major isolated compounds and fractions, F7 and F8, significantly contribute to the α-glucosidase inhibitory activity of S. glabra Roxb extract. Further work is needed to clarify their modes of action and potential application.