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

Minh Anh Thu Phan, Jin Wang, Jingyi Tang, Yan Zhi Lee, Ken Ng, 

Abstract

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 

 brevicornum leaves were of HPLC purified grade (>98% pure) and were purchased from Chengdu Biopurify Pty. Ltd. (Chengdu, China)