Acetylcholinesterase inhibition of oil from Acorus calamus rhizome

Acorus calamus L. has been used in traditional Indian prescriptions and its beneficial effects on memory disorder, learning performance and other aspects of ageing effect have been reported [1]. The hydro-alcoholic extract and essential oil of Indian Acorus calamus rhizomes were tested for in vitro AChE inhibitory activity based on Ellman's method in 96-well micro plates [2] using acetylcholinesterase (AChE) from bovine erythrocytes. The hydro-alcoholic extract gave an inhibition of AChE (IC₅₀ value 182.31±16.78µg/mL) but the oil was stronger (IC₅₀ value 106.75±8.08µg/mL). GC analysis of the oil was performed on a Varian 3400 programmable capillary GC, using D.B.5 'Wax' capillary column [30m x 0.32mm i.d., film thickness 0.25µ]. Oven temperature was programmed at 140–180⁰C, at 3⁰C/min and held isothermal at 180⁰C for 7.67 minutes. Injector temperature was 210⁰C; Detector temperature was 250⁰C [FID]; carrier gas Helium. 2µL samples were injected with the Frit-splitter at ratio 12:1. GC analysis of the oil revealed that β-asarone 1 was the major constituent (52.33% w/w with respect to dried rhizomes) while α-asarone content was 1.026% w/w. 1 and α-asarone (the trans isomer of 1) were tested for AChE inhibition and found to have IC₅₀ values of 3.33±0.02µM and 46.38±2.69µM respectively. Physostigmine was used as standard and showed inhibition of AChE with an IC₅₀ value of 0.28±0.015µM.

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The AChE-inhibitory activity of the oil can be ascribed to β-asarone. Since cognitive performance and memory are related to acetylcholine levels, the AChE inhibitory effect of the plant may account for its traditional use.

Acknowledgements: Commonwealth Fellowship for financial support. for PKM.

References: 1. Howes, M.R., Houghton, P.J. (2003), Pharmacol. Biochem. Behavior 75: 513–527. 2. Perry, N.S.L. et al. (2000), J. Pharm. Pharmacol. 52: 895–902.