Activation of the human transient receptor potential vanilloid subtype 1 by essential oils.

Transient receptor potential vanilloid subtype 1 (TRPV1) is a non-selective cation channel activated by capsaicin. TRPV1 is expressed not only on human sensory neurons but also on human epidermal and hair follicle keratinocytes. Therefore, TRPV1 could have the potential to be a therapeutic target for skin disorders. To search for novel TRPV1 agonists, we screened 31 essential oils by using human TRPV1-expressing HEK293 cells. TRPV1 was activated by 4 essential oils: rose, thyme geraniol, palmarosa, and tolu balsam. The dose-response curves for TRPV1 activation by the essential oils revealed a rank order potency [the half-maximal effective concentration (EC(50))] of rose>palmarosa>thyme geraniol>tolu balsam, and rank order efficiency (% activity in response to 1 microM capsaicin) of tolu balsam>rose>palmarosa>thyme geraniol. Moreover, the dose-response curves for TRPV1 activation by citronellol (main constituent of rose oil) and geraniol (main constituent of thyme geraniol and palmarosa oils) were consistent with the potency and efficiency of each essential oil. In contrast, benzyl cinnamate and benzyl benzoate (main constituent of tolu balsam oil) and geranyl acetate (main constituent of thyme geraniol oil) did not show TRPV1 activity. In this first-of-its-kind study, we successfully investigated the role of some essential oils in promoting human TRPV1 activation, and also identified two monoterpenes, citronellol and geraniol, as new human TRPV1 agonists.