The α-glucosidase inhibiting isoflavones isolated from belamcanda chinensis leaf extract

The dried rhizome of Belamcanda chinensis is an important Chinese traditional medicine used for the treatment of inflammation and many other disorders. Previously, we reported the hypo- and antihyper-glycemic effects of the aqueous leaf extract of B. chinensis (BCL) and identified the isoflavones as its principal active fraction. In the present study, the α-glucosidase inhibitory effect of BCL and its rough isoflavone preparation (BIF) was tested in vitro and in vivo. Thirteen isoflavones were isolated from BCL and their α-glucosidase inhibitory activity was screened in vitro. The results showed that BCL (500 and 1000 mg/kg) and BIF (250 and 500 mg/kg) greatly inhibited the increase in blood glucose level after 5 g/kg starch loading in normal mice. Six out of the thirteen isoflavones (swertisin, 2'-O-rhamnosylswertisin, genistein, genistin, mangiferin and daidzin) exhibited strong α-glucosidase inhibitory activity in vitro. HPLC analysis showed that swertisin was the most abundant isoflavone in BCL accounting for 1.24% of BCL, 7.44% of BIF, and 11.24% of the total isoflavone fraction of BCL, respectively. These results demonstrate that BCL possesses significant α-glucosidase inhibitory activity and swertisin may be the principal active component of BCL in α-glucosidase inhibition.