A comparative study on constituents of Citrus medica, Citrus paradisi and Citrus limetta essential oils and their inhibitory effect on acetylcholinesterase

Medicinal plants have been used since ancient times to treat various diseases. Citrus fruits are rich sources of antioxidant compounds in addition to being eaten. One of the important goals in the treatment of Alzheimer's disease is to inhibit the acetylcholinesterase. The aim of this study was to investigate the constituents of the essential oils of the citron, grapefruit and sweet lemon skin and their effect on kinetic properties of the acetylcholinesterase. The extraction of the essential oil was done by the Clevenger apparatus and their constituents were identified by GC/Mass. The activity of the enzyme was measured under incubation conditions with different amounts of essential oils, and according to the changes in the kinetic parameters of the enzyme, the effect and type of inhibition were concluded. The monoterpenes constitute the highest percentage of the essential oils. Lemon essential oil showed the highest acetylcholinesterase inhibitory effect of 60.09% at a concentration of 1.45 mg/mL. The amounts of IC50 for the citron, grapefruit and sweet lemon were obtained 1.42, 1.21 and 1.23 mg/mL respectively. The results showed that the essential oil of citron, grapefruit and sweet lemon reduced the activity of acetylcholinesterase in a concentration-dependent manner and respectively by mixed, competitive and non-competitive inhibition. It is also expected that the difference in the type of inhibition was due to the different constituents of the essential oils. According to our results, the citrus essential oil could have a good potential for further research and formulation with the aim of replacing synthetic drugs.