Identification of Human Acetylcholinesterase Inhibitors from the Constituents of EGb761 by Modeling Docking and Molecular Dynamics Simulations

Aim and Objective: EGb761, a standardized and well-defined product extract of Ginkgo biloba leaves, has beneficial role in the treatment of multiple diseases, particularly Alzheimer's disease (AD). Identification of natural acetylcholinesterase (AChE) inhibitors from EGb761 would provide a novel therapeutic approach against the Alzheimer's disease. Material and Method: A series of 21 kinds of promising EGb761 compounds were selected, and subsequently evaluated for their potential ability to bind AChE enzyme by molecular docking and a deep analysis of protein surface pocket features. Results: Docking results indicated that these compounds can bind tightly with the active site of human AChE, with favorable distinct interactions around several important residues Asp74, Leu289, Phe295, Ser293, Tyr341, Trp286 and Val294 in the active pocket. Most EGB761 compounds could form the hydrogen bond interactions with the negatively charged Asp74 and Phe295 residues. Among these compounds, diosmetin is the one with the best-predicted docking score while three key hydrogen bonds can be formed between small molecule and corresponding residues of the binding site. Besides, other three compounds luteolin, apigenin, and isorhamnetin have better predicted docking scores towards AChE than other serine proteases, i.e Elastase, Tryptase, Factor XA, exhibiting specificity for AChE inhibition. The RMSD and MM-GBSA results from molecular dymamic simulations indicated that the docking pose of diosmetin-AChE complex displayed highly stable, which can be used for validating the accuracy of molecular docking study. Subsequently, the AChE inhibitory activities of these compounds were evaluated by the Ellman's colorimetric method. Conclusion: The obtained results revealed that all the four compounds exhibited modest AChE inhibitory activity, among which Diosmetin manifested remarkable anti-AChE activity, comparable with the reference compound, Physostigmine. It can be deduced that these EGB761 compounds can be regarded as a promising starting point for developing AChE inhibitors against AD.