Inhibitory kinetics and mechanism of active compounds in green walnut husk against α-glucosidase: Spectroscopy and molecular docking analyses

Abstract

Inhibiting the activity of α-glucosidase is considered an effective strategy to regulate blood sugar levels and manage food-linked hyperglycemia. Green walnut husk (GWH) is the main processing by-product of walnut, still rich in natural bioactive compounds with α-glucosidase inhibition. The objective of this study was to screen the specific components in GWH responsible for the α-glucosidase inhibitory effects and investigate the mechanisms through enzyme kinetic analysis, multi-spectroscopic techniques, and molecular docking analysis. Affinity ultrafiltration-liquid-chromatography-mass spectrometry was employed to rapidly screen and identify the bioactive compounds with α-glucosidase inhibition. Catechin, hyperoside, and quercetin exhibited significant α-glucosidase inhibitory activities with IC50 values of 12.78, 77.24, and 92.87 μg/mL, respectively. The inhibition kinetic analysis indicated that catechin and quercetin were competitive inhibitors, while hyperoside was an uncompetitive inhibitor. UV spectra, Fourier-transform infrared spectroscopy, and fluorescence quenching demonstrated that these inhibitions led to the conformational changes of α-glucosidase. Circular dichroism spectra suggested that α-glucosidase secondary structures were induced by inhibitors. The molecular docking analysis illustrated that the interaction forces between inhibitors and α-glucosidase were hydrogen bonds and hydrophobic interactions, with the binding energy of −8.3, −9.5, and −9.5 kcal/mol, respectively. Therefore, GWH provided a potential source for developing natural α-glucosidase inhibitors.