Binding effects of Alpinia galanga oil and its nanoemulsion 1 to GABAA receptors in rat cortical membranes

Abstract

Anesthetic activity of Alpinia galanga oil (AGO) has been reported however the mechanism of action in mammals has not been clear. In the present study, the binding effects of AGO and its three active components to gamma-aminobutyric acid type A (GABAA) receptor in cortical membranes of Sprague-Dawley rats were firstly investigated using a [3H]muscimol binding assay. Dimethyl sulfoxide (DMSO) was used to deliver these test samples. The results showed that only AGO and methyl eugenol displayed positive modulation at the highest concentration whereas 1,8-cineole and 4-allylphenyl acetate were inactive. An oil-in-water nanoemulsion containing 20%w/w AGO (NE-AGO) was formulated to deliver AGO instead of DMSO. This NE-AGO significantly enhanced a specific [3H]muscimol binding to 179% of the control with EC50 of 391 µg/mL. The result correlates well to the amount of methyl eugenol in AGO. This result confirms that the anesthetic activity of AGO and methyl eugenol is associated with GABAA receptor modulation, while that of 1,8-cineole and 4-allylphenyl acetate is not and may instead be related to other mechanisms. AGO showed well-tolerated by human cells. Therefore, the formulated NE-AGO might be a promising alternative anesthetic product for humans.