Comparison of the effect of alpha-pinene and quercetin on the activity of acetylcholinesterase

Decreased synthesis or increased hydrolysis of acetylcholine in the cholinergic system is one of the causes of Alzheimer's disease. Acetylcholinesterase enzyme inhibition is a therapeutic strategy. A number of natural plant compounds with biological properties such as neuroprotective, antioxidant, antianxiety and antimicrobial effects have been investigated in recent years, which alpha-pinene and quercetin, respectively, from the subgroup of monoterpenoids and flavonols, are among them. Ellman's method was used for determination of inhibition percentage, IC50 value and kinetic type of acetylcholinesterase inhibition. The antioxidant activity of alpha-pinene and quercetin was evaluated s and the results were reported based on the EC50 index. Finally, molecular docking studies were performed to evaluate the above results. Examining the percentage of enzyme inhibition for galantamine, alpha-pinene and quercetin showed IC50 values of 0.001, 0.25 and 15.75 mM respectively. Kinetics of enzyme inhibition by these compounds showed a mixed inhibition pattern (uncompetitive-noncompetitive) for both alpha-pinene and quercetin. Using ascorbate as positive control (EC50= 22.6 µM, antioxidant capacity of alpha-pinene and quercetin were (EC50=1.22 mM) and (EC50=29.5 µM), respectively. Finally, molecular docking studies showed the binding energy for the best state of alpha-pinene and quercetin to be -5.6 and -0.9 kcal/mol, respectively. The results obtained from this study show that both alpha-pinene and quercetin have inhibitory properties of acetylcholinesterase enzyme, but the antioxidant power of quercetin is higher than alpha-pinene. The results of the molecular docking studies were consistent with the experimental results.