Flavonolignans isolated from Silybum marianum act as α-glucosidase inhibitors

Abstract

Silybin (Silibinin), a key flavonolignan in Silybum marianum, has been reported to possess significant α-glucosidase inhibitory activity. The aim of present study was to explore α-glucosidase inhibitory potential for individual flavonolignans including silibinin. Six Flavonolignans (1-6) were isolated from the MeOH extract of S. marianum seeds and examined α-glucosidase inhibition. All flavonolignans (1-6) showed potent inhibitions against α-glucosidase, with flavonolignan 3 emerging as the most potent inhibitor (IC50=18.0 μM), showing three times the activity of 4 (silybin, IC50=53.0 μM). Detailed kinetic behaviors of α-glucosidase inhibitors were explored by analyzing changes in Km and Vmax, the ratios of KI / KIS and Kik / Kiv, as well as the fluorescence quenching effect. All flavonolignans were identified as mixed-type I inhibitors, exhibiting a higher affinity for the free enzyme compared to the enzyme-substrate complex (KI < KIS). The binding affinity (Ksv) between the enzyme and the inhibitors was determined through fluorescence quenching, which correlated positively with the inhibitory potency (IC50) of flavonolignans. This study represents the first comprehensive investigation into the α-glucosidase inhibitory effects of individual flavonolignans.