Nociceptive transient receptor potential ankyrin 1 (TRPA1) in sensory neurons are targets of the antifungal drug econazole.

Background: Econazole is a widely used imidazole derivative antifungal for treating skin infections. The molecular targets for its frequent adverse effects of skin irritation symptoms, such as pruritus, burning sensation, and pain, have not been clarified. Transient receptor potential (TRP) channels, non-selective cation channels, are mainly expressed in peripheral sensory neurons and serve as sensors for various irritants.

Methods: We investigated the effect of econazole on TRP channel activation by measuring intracellular calcium concentration ([Ca²⁺]_i) through fluorescent ratio imaging in mouse dorsal root ganglion (DRG) neurons isolated from wild-type, TRPA1^(-/-) and TRPV1^(-/-) mice, as well as in heterologously TRP channel-expressed cells. A cheek injection model was employed to assess econazole-induced itch and pain in vivo.

Results: Econazole evoked an increase in [Ca²⁺]_i, which was abolished by the removal of extracellular Ca²⁺ in mouse DRG neurons. The [Ca²⁺]_i responses to econazole were suppressed by a TRPA1 blocker but not by a TRPV1 blocker. Attenuation of the econazole-induced [Ca²⁺]_i responses was observed in the TRPA1^(-/-) mouse DRG neurons but was not significant in the TRPV1^(-/-) neurons. Econazole increased the [Ca²⁺]_i in HEK293 cells expressing TRPA1 (TRPA1-HEK) but not in those expressing TRPV1, although at higher concentrations, it induced Ca²⁺ mobilization from intracellular stores in untransfected naïve HEK293 cells. Miconazole, which is a structural analog of econazole, also increased the [Ca²⁺]_i in mouse DRG neurons and TRPA1-HEK, and its nonspecific action was larger than econazole. Fluconazole, a triazole drug failed to activate TRPA1 and TRPV1 in mouse DRG neurons and TRPA1-HEK. Econazole induced itch and pain in wild-type mice, with reduced responses in TRPA1^(-/-) mice.

Conclusions: These findings suggested that the imidazole derivatives econazole and miconazole may induce skin irritation by activating nociceptive TRPA1 in the sensory neurons. Suppression of TRPA1 activation may mitigate the adverse effects of econazole.