Inhibition of acetylcholinesterase activity by tea tree oil and constituent terpenoids

In vitro inhibition of bovine erythrocyte acetylcholinesterase (AChE) activity by tea tree oil was investigated. The main constituents in the tea tree oil batch used for the analysis of AChE inhibition were terpinen-4-ol (35.6%), γ-terpinene (19.5%), α-terpinene (8.3%), p-cymene (7.2%) and 1,8-cineole (4.4%). AChE was measured by a colorimetric method. IC50 values were obtained for tea tree oil and α-pinene and were 51.2 µg/ml and 57.1 µg/ml, respectively. Tea tree oil was found to contain mixed-type inhibitors; a mixture of main constituents and main constituents showed competitive inhibition.