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.