Evaluation of α-glucosidase inhibition potential of some flavonoids from Epimedium brevicornum

- Epimedium brevicornum water extract is a potent inhibitor of yeast α-glucosidase.
- Baohuoside I, a flavonol of the leave, was identified as one of the bioactive.
- Baohuoside I kinetic mode of inhibition was of the mixed type inhibition.
- Structure-activity relationship indicated the C7-OH is important for inhibition.

Epimedium brevicornum leaves water extract exerted a potent and specific inhibition against yeast α-glucosidase, with 50% inhibition of activity (IC50) at 11.8 μmol/L (or 2.01 μg) Gallic Acid Equivalent (GAE)/mL. Several major flavonols from the leaves were evaluated for inhibitory activity. Baohuoside I exhibited strong inhibition against the α-glucosidase while icariin and epimedin A, B and C were weak or inactive. All compounds were inactive against pancreatic α-amylase. The IC50 of baohuoside I was 28.9 μmol/L and its kinetic mode of inhibition was of the mixed type inhibition, with K1 (inhibition constant for the formation of the baohuoside-enzyme complex) and K2 (inhibition constant for the formation of the baohuoside-enzyme-substrate complex) of 12.4 and 31.7 μmol/L, respectively. Since its K1 was lower than its K2, it would indicate that baohuoside I tends to bind more easily and firmly to the free enzyme than to the enzyme-substrate complex. The fact that icariin, which has no free C4′-OH and C7-OH, showed weak inhibition while baohuoside I, which has no free C4′-OH but free C7-OH, showed strong inhibition, indicates the primary importance of the A-ring C7-OH for α-glucosidase inhibitory activity.