Abstract
Little is known about the pharmacological activity of Monarda fistulosa L. essential oils. To address this issue, we isolated essential oils from the flowers and leaves of M. fistulosa and analyzed their chemical composition. We also analyzed the pharmacological effects of M. fistulosa essential oils on transient receptor potential (TRP) channel activity, as these channels are known targets of various essential oil constituents. Flower (MEOFl) and leaf (MEOLv) essential oils were comprised mainly of monoterpenes (43.1% and 21.1%) and oxygenated monoterpenes (54.8% and 77.7%), respectively, with a high abundance of monoterpene hydrocarbons, including p-cymene, γ-terpinene, α-terpinene, and α-thujene. Major oxygenated monoterpenes of MEOFl and MEOLv included carvacrol and thymol. Both MEOFl and MEOLv stimulated a transient increase in intracellular free Ca2+ concentration ([Ca2+]i) in TRPA1 but not in TRPV1 or TRPV4-transfected cells, with MEOLv being much more effective than MEOFl. Furthermore, the pure monoterpenes carvacrol, thymol, and β-myrcene activated TRPA1 but not the TRPV1 or TRPV4 channels, suggesting that these compounds represented the TRPA1-activating components of M. fistulosa essential oils. The transient increase in [Ca2+]i induced by MEOFl/MEOLv, carvacrol, β-myrcene, and thymol in TRPA1-transfected cells was blocked by a selective TRPA1 antagonist, HC-030031. Although carvacrol and thymol have been reported previously to activate the TRPA1 channels, this is the first report to show that β-myrcene is also a TRPA1 channel agonist. Finally, molecular modeling studies showed a substantial similarity between the docking poses of carvacrol, thymol, and β-myrcene in the binding site of human TRPA1. Thus, our results provide a cellular and molecular basis to explain at least part of the therapeutic properties of these essential oils, laying the foundation for prospective pharmacological studies involving TRP ion channels.
Highlights
The genus Monarda L. (Lamiaceae) includes 20 species native to the United States [1] and is divided into two distinct subgenera, Monarda and Cheilyctis [2]
The chemical composition and biological activity of essential oils can be affected by many factors, including which part of the plant is used for essential oil isolation [39]
The chemical composition of these essential oils was evaluated using gas chromatography-flame ionization detector (GC-Flame ionization detector (FID)) and gas chromatography-mass spectrometry (GC-MS) simultaneously, and Tables 2 and 3 summarize the compounds identified, percentage composition, and relative retention indices (RRI)
Summary
The genus Monarda L. (Lamiaceae) includes 20 species native to the United States [1] and is divided into two distinct subgenera, Monarda and Cheilyctis [2]. (Lamiaceae) includes 20 species native to the United States [1] and is divided into two distinct subgenera, Monarda and Cheilyctis [2]. Essential oils of Monarda species have been reported to be rich in oxygenated monoterpenes, leading to differentiation into the following chemotypes: thymol, carvacrol, borneol, and geraniol [10].
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