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

Epimedium brevicomum leaves water extract exerted a potent and specific inhibition against yeast alpha-glucosidase, with 50% inhibition of activity (IC50) at 11.8 mu mol/L (or 2.01 mu g) Gallic Acid Equivalent (GAE)/mL. Several major flavonols from the leaves were evaluated for inhibitory activity. Baohuoside I exhibited strong inhibition against the alpha-glucosidase while icariin and epimedin A, B and C were weak or inactive. All compounds were inactive against pancreatic alpha-amylase. The IC50 of baohuoside I was 28.9 mu mol/L and its kinetic mode of inhibition was of the mixed type inhibition, with K-1 (inhibition constant for the formation of the baohuoside-enzyme complex) and K-2 (inhibition constant for the formation of the baohuoside-enzyme substrate complex) of 12.4 and 31.7 mu mol/L, respectively. Since its K-1 was lower than its K-2, 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 alpha-glucosidase inhibitory activity. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.