Citation: Khumpirapang, N.;
Suknuntha, K.; Wongrattanakamon, P.;
Jiranusornkul, S.; Anuchapreeda, S.;
Wellendorph, P.; Müllertz, A.; Rades,
T.; Okonogi, S. The Binding of Alpinia
galanga Oil and Its Nanoemulsion to
Mammal GABA
A
Receptors Using
Rat Cortical Membranes and an In
Silico Modeling Platform.
Pharmaceutics 2022, 14, 650.
https://doi.org/10.3390/
pharmaceutics14030650
Academic Editor:
Aristeidis Dokoumetzidis
Received: 21 February 2022
Accepted: 14 March 2022
Published: 16 March 2022
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pharmaceutics
Article
The Binding of Alpinia galanga Oil and Its Nanoemulsion to
Mammal GABA
A
Receptors Using Rat Cortical Membranes and
an In Silico Modeling Platform
Nattakanwadee Khumpirapang
1
, Krit Suknuntha
2
, Pathomwat Wongrattanakamon
3
, Supat Jiranusornkul
3
,
Songyot Anuchapreeda
4,5
, Petrine Wellendorph
6
, Anette Müllertz
7
, Thomas Rades
7
and Siriporn Okonogi
3,5,
*
1
Department of Pharmaceutical Chemistry and Pharmacognosy, Faculty of Pharmaceutical Sciences, Naresuan
University, Phitsanulok 65000, Thailand; nattakanwadeek@nu.ac.th
2
Department of Pharmaceutical Chemistry, Faculty of Pharmaceutical Sciences, Prince of Songkla University,
Songkhla 90112, Thailand; krit@pharmacy.psu.ac.th
3
Department of Pharmaceutical Sciences, Faculty of Pharmacy, Chiang Mai University,
Chiang Mai 50200, Thailand; pathomwat.w@cmu.ac.th (P.W.); supat.jira@cmu.ac.th (S.J.)
4
Department of Medical Technology, Faculty of Associated Medical Sciences, Chiang Mai University,
Chiang Mai 50200, Thailand; songyot.anuch@cmu.ac.th
5
Research Center of Pharmaceutical Nanotechnology, Faculty of Pharmacy, Chiang Mai University,
Chiang Mai 50200, Thailand
6
Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of
Copenhagen, 2100 Copenhagen, Denmark; pw@sund.ku.dk
7
Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen,
2100 Copenhagen, Denmark; anette.mullertz@sund.ku.dk (A.M.); thomas.rades@sund.ku.dk (T.R.)
* Correspondence: siriporn.okonogi@cmu.ac.th; Tel.: +66-5394-4311
Abstract: The anesthetic effect of Alpinia galanga oil (AGO) has been reported. However, knowledge of
its pathway in mammals is limited. In the present study, the binding of AGO and its key compounds,
methyl eugenol, 1,8-cineole, and 4-allylphenyl acetate, to gamma-aminobutyric acid type A (GABA
A
)
receptors in rat cortical membranes, was investigated using a [
3
H]muscimol binding assay and an
in silico modeling platform. The results showed that only AGO and methyl eugenol displayed a
positive modulation at the highest concentrations, whereas 1,8-cineole and 4-allylphenyl acetate were
inactive. The result of AGO correlated well to the amount of methyl eugenol in AGO. Computational
docking and dynamics simulations into the GABA
A
receptor complex model (PDB: 6X3T) showed
the stable structure of the GABA
A
receptor–methyl eugenol complex with the lowest binding energy
of −22.16 kcal/mol. This result shows that the anesthetic activity of AGO and methyl eugenol in
mammals is associated with GABA
A
receptor modulation. An oil-in-water nanoemulsion containing
20% w/w AGO (NE-AGO) was formulated. NE-AGO showed a significant increase in specific
[
3
H]muscimol binding, to 179% of the control, with an EC
50
of 391 μg/mL. Intracellular studies show
that normal human cells are highly tolerant to AGO and the nanoemulsion, indicating that NE-AGO
may be useful for human anesthesia.
Keywords: Alpinia galanga; essential oil; mammal anesthesia; anesthetic pathway; positive allosteric
modulation; binding assay
1. Introduction
Alpinia galanga, an edible plant of the Zingiberaceae family, is widely cultivated in
Southeast Asian countries [1]. It is well-known in Asian folk medicine and has been used
for centuries as a food additive, an antimicrobial agent, a local anesthetic, an analgesic,
and an antipruritic [2,3]. Three important compounds, methyl eugenol, 1,8-cineole, and
4-allylphenyl acetate, were reported in A. galanga oil (AGO) [4]. Recently, AGO has been
shown to have an anesthetic effect in fish [5]. Further, 1,8-cineole has been shown to reduce
Pharmaceutics 2022, 14, 650. https://doi.org/10.3390/pharmaceutics14030650 https://www.mdpi.com/journal/pharmaceutics