Young apple polyphenols as natural α-glucosidase inhibitors: In vitro and in silico studies

In this study, the inhibitory activity of young apple polyphenols (YAP) on α-glucosidase was investigated. Composition and inhibition analyses suggested that tannic acid (TA), (-)-epicatechin (EC) and phlorizin (PH) were the main active constituents in YAP showing α-glucosidase inhibition. PH was a competitive inhibitor, while YAP, TA and EC were the mixed-type ones. YAP, TA, PH and EC quenched the fluorescence spectrum of α-glucosidase significantly. Interestingly, the constants that indicate binding interaction between α-glucosidase and TA, PH, EC, including reciprocal of competitive inhibition constant (1/K_ic), fluorescence quenching constant (K_FQ) and binding energy (E_b), were shown similar orders as TA > PH > EC, contrary to IC₅₀ values. This indicates that binding interactions between polyphenols and α-glucosidase caused the enzyme inhibition. Additionally, potential enzyme unfolding by polyphenols interactions indicated by red-shift of maximum emission wavelength is supported by the decrease in α-helix and β-sheet contents of the enzyme. Conclusively, the α-glucosidase inhibition indicates that YAP may have potentials in alleviation of type 2 diabetes symptom.