Background: A therapeutic approach to treat diabetes is to decrease postprandial hyperglycemia. Alpha-glucosidase inhibitors from plant sources offer an attractive strategy for the control of hyperglycaemia. Smilax glabra Roxb is a medicinal plant in Asia, including Vietnam, for treatment of chronic diseases. However, antidiabetic activity, especially alpha-glucosidase inhibitors from this plant has not intensively investigated. This research was carried out to isolate the new alpha-glucosidase inhibitors from this plant for further study on their role in hyperglycemia control, as well as their potential application in the future.
Methods: Collumn chromatography combined with crystallization procedures were used to isolate active fractions and compounds. The chemical structures of the compounds were determined based on the analysis of the spectroscopic data, as well as MS data and comparison with the literature data. The α-glucosidase inhibitory activity was quantitative spectrophotometrically using p-nitrophenyl α-D-glucopyranoside as a substrate. The in vitro cytotoxicity of isolated compounds and fractions was determined using 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 extract of Smilax glabra Roxb growing in Vietnam. The two isolated compounds showed inhibitory activity against alpha-glucosidase with IC50 values of ca. 125 µg/mL and 38 µg/mL, respectively, about 4 and 13 fold higher than the reference compound acarbose (IC50 of ca. 525 µg/mL). The two active fractions F7 and F8, showed very promising inhibitory activities towards alpha-glucosidase with IC50 values of 5.5 and 5.8 µg/mL, respectively. Cytotoxicity data on mouse fibroblast NIH3T3 cells indicated that the most active compound and fractions are not toxic at concentrations that are much greater than IC50 values. Thus, for the first time, α-glucosidase inhibitory activity of astilbin, 5-O-caffeoylshikimic acid and two fractions of S. glabra are reported.
Conclusion: The isolated compounds and fractions, F7 and F8, significantly contribute to alpha-glucosidase inhibitory activity of the plant extract. Further works are needed to clarify their modes of action and potential application.