Thymol and related alkyl phenols activate the hTRPA1 channel.
OBJECTIVE
Thymol, a major component of thyme and oregano, has medical uses in oral care products as an astringent and antibiotic. Its distinctive sharp odour and pungent flavour are considered aversive properties. The molecular basis of these aversive properties is not well understood.


METHODS
The ability of thymol to activate human transient receptor potential channel A1 (hTRPA1) expressed in stably transfected human embryonic kidney 293 (HEK293) cells was measured by membrane potential and calcium-sensitive dyes in a fluorescence-imaging plate reader (FLIPR) assay. Direct activation of hTRPA1 currents was measured by whole-cell voltage clamp recording. Intracellular calcium changes were measured using fura-2 dye. The FLIPR assay was also used to measure membrane potential changes elicited by thymol after pretreatment with camphor, a known TRPA1 inhibitor. The ability of related alkyl phenols to activate hTRPA1 was also determined.


RESULTS
Thymol potently activated a membrane potential response and intracellular calcium increase in hTRPA1-expressing HEK293 cells in a concentration-dependent manner. Activation by thymol desensitized hTRPA1 to further exposure to thymol or the known ligand allyl isothiocyanate (AITC). The related phenols 2-tert-butyl-5-methylphenol, 2,6-diisopropylphenol (propofol) and carvacrol also activated hTRPA1. Phenols with less bulky carbon substitutions and lower logP values were less potent in general. The response to thymol was blocked by camphor.


CONCLUSIONS
These results suggest a role for hTRPA1 activation in the reported pungent and aversive properties of some of these pharmaceutically important phenols.
Lee
S P
SP
Discovery Research, Redpoint Bio Corporation, Ewing, NJ, USA.
Buber
M T
MT
Yang
Q
Q
Cerne
R
R
Cortés
R Y
RY
Sprous
D G
DG
Bryant
R W
RW
D000890:Anti-Infective Agents / Q000008:administration & dosage / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005470:Fluorometry / Q000379:methods; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D009419:Nerve Tissue Proteins / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010636:Phenols / Q000008:administration & dosage / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D000074025:TRPA1 Cation Channel; D013943:Thymol / Q000008:administration & dosage / Q000494:pharmacology*; D050051:Transient Receptor Potential Channels / Q000187:drug effects* / Q000378:metabolism
D000890:Anti-Infective Agents; D015220:Calcium Channels; D009419:Nerve Tissue Proteins; D010636:Phenols; D000074025:TRPA1 Cation Channel; C473350:TRPA1 protein, human; D050051:Transient Receptor Potential Channels; D013943:Thymol; D002118:Calcium