Anti-acetylcholinesterase mechanism of kaempferol and its synergistic effect with galanthamine hydrobromide

Kaempferol, a natural flavonoid compound, was found to suppress the activity of AChE in a reversible mixedinhibition with an IC50 value of 12.43 +/- 0.19 mu M. Fluorescence spectra showed that the fluorescence burst mechanism of kaempferol on AChE was of static burst type, and it was coupled with AChE to form a complex with a moderate binding affinity driven mainly by hydrogen bonding and hydrophobic interactions. The analysis of circular dichroism spectra found that kaempferol induced structural relaxation of AChE with a decrease in alpha-helix content (from 19.64% to 18.02%). Computer simulation showed that kaempferol was a two-site inhibitor that bound to both the catalytic active site (Trp86, Glu202, Tyr337) and peripheral anionic site (Tyr72, Asp74, Tyr124 and Tyr341) of AChE, inducing the enzyme structure to become more stable, then the substrate was prevented from binding to the active site of AChE, and the catalytic activity of AChE was inhibited. Moreover, kaempferol binding at the PAS-AChE site induced a conformational change of AChE that may increase the binding affinity of galanthamine to the enzyme, and thus kaempferol and galanthamine synergistically inhibited the activity of AChE. This work may offer novel insights into the development of kaempferol as a food functional factor for the cure of AD.