Inhibition mechanism of fisetin on acetylcholinesterase and its synergistic effect with galantamine

Abstract

The search for acetylcholinesterase (AChE) inhibitors produced by natural sources is of great significance for the prevention and therapy of Alzheimer's disease and has been widely concerned. In this study, fisetin, a flavonoid compound of plant origin, displayed a mixed inhibition mode on AChE (IC50 = 8.88 ± 0.14 μM). Fluorescence spectra analysis revealed that fisetin statically quenched AChE fluorescence, and the ground state complex was formed by hydrogen bonds and hydrophobic interactions. Circular dichroism assays showed that fisetin induced AChE structure loosened with a decrease in α-helix structure (from 20.6 % to 19.5 %). Computer simulation exhibited that fisetin bound to both the peripheral anionic site (PAS) and the catalytic active site (CAS) and increased the stability of the AChE. Interestingly, the combination of fisetin and galantamine enhanced the binding affinity between AChE and galantamine and induced AChE structure further loosened, while the inhibition mode was still the mixed type. The heatmap analysis indicated that galantamine (0.2 μM) combined with fisetin (2.25 μM) had a significant synergy on AChE inhibition, probably because fisetin binding at the PAS-AChE induced conformation changes of the gorge and CAS, which enhanced galantamine binding affinity with CAS, and a further loose structure of AChE was induced by the mixture, so finally the interaction between the substrate and AChE was strongly affected. This work may offer a theoretical reference for the functional research of fisetin as a potential AChE inhibitor and an enhanced supplement for galantamine.