Monoterpenoid agonists of TRPV3

Abstract

Background and purpose: Transient receptor potential (TRP) V3 is a thermosensitive ion channel expressed predominantly in the skin and neural tissues. It is activated by warmth and the monoterpene camphor and has been hypothesized to be involved in skin sensitization. A selection of monoterpenoid compounds was tested for TRPV3 activation to establish a structure-function relationship. The related channel TRPM8 is activated by cool temperatures and a number of chemicals, among them the monoterpene (-)-menthol. The overlap of the receptor pharmacology between the two channels was investigated.

Experimental approach: Transfected HEK293 cells were superfused with the test substances. Evoked currents were measured in whole cell patch clamp measurements. Dose-response curves for the most potent agonists were obtained in Xenopus laevis oocytes.

Key results: Six monoterpenes significantly more potent than camphor were identified: 6-tert-butyl-m-cresol, carvacrol, dihydrocarveol, thymol, carveol and (+)-borneol. Their EC(50) is up to 16 times lower than that of camphor. All of these compounds carry a ring-located hydroxyl group and neither activates TRPM8 to a major extent.

Conclusions and implications: Terpenoids have long been recognized as medically and pharmacologically active compounds, although their molecular targets have only partially been identified. TRPV3 activation may be responsible for several of the described effects of terpenoids. We show here that TRPV3 is activated by a number of monoterpenes and that a secondary hydroxyl-group is a structural requirement.

Figure 1

Representative current traces illustrating the screening of monoterpenes for TRPV3 activation. HEK293 cells transfected with TRPV3 were held in the whole-cell voltage-clamp mode at −40 mV and superfused as indicated. (a) Representative response of one cell to dihydrocarveol and camphor. (b) Representative response of the same cell to (+)-dihydrocarvone. (c) Assay in an untransfected cell. Note that neither camphor nor the other two monoterpenes evoked any current. (d) TRPV3 expressing cell superfused with icilin.

Figure 2

(a) Representative recordings in Xenopus oocytes for the establishment of dose–response curves. (b) Dose–response curves constructed from mean values of three to five experiments fitted by the Hill equation.

Figure 3

Activation of TRPM8 by potent TRPV3 monoterpenoid agonists. (a) Representative current trace of a TRPM8 expressing HEK293 cell. The cell was held in the voltage clamp mode at −40 mV and transiently superfused with (−)-menthol (2 mM) and carveol (2 mM) as indicated. (b) Equivalent stimulation of an untransfected cell did not result in any response to either (−)-menthol or carveol (c) Summary of the evoked currents relative to that evoked by (−)-menthol; all compounds were applied at a concentration of 2 mM. Values shown are means±s.d.