Nociceptive TRP channels function as molecular target for several antifungal drugs

Background/objectives

Topically applied antifungal agents can induce adverse effects, such as pain and irritation. The transient receptor potential (TRP) channels—TRPA1 and TRPV1—mainly expressed in sensory neurons, act as sensors for detecting irritants. This study aims to evaluate the involvement of nociceptive channels in topical antifungal-induced pain and irritation. We tested nine topical antifungals belonging five classes: isoconazole, econazole, miconazole, clotrimazole, and ketoconazole as imidazoles; liranaftate as a thiocarbamate; terbinafine as an allylamine; amorolfine as a morpholine; and butenafine as a benzylamine.

Methods

Intracellular calcium concentrations ([Ca²⁺]_i) and membrane currents in response to antifungals were measured to estimate channel activity using heterologously expressing cells and isolated mouse sensory neurons.

Results

In mouse TRPA1-expressing cells, all the tested drugs induced an increase in [Ca²⁺]_i, which was abrogated or reduced by a TRPA1 blocker. Although many drugs evoked the TRPA1-nonspecific [Ca²⁺]_i response at high concentrations, responses to clotrimazole, ketoconazole, and liranaftate were TRPA1 specific and elicited current responses in TRPA1-expressing cells. In mouse TRPV1-expressing cells, clotrimazole and ketoconazole elicited [Ca²⁺]_i and current responses. In mouse sensory neurons, liranaftate-induced increase in [Ca²⁺]_i was abrogated by a TRPA1 blocker and Trpa1 deletion. Responses to ketoconazole were inhibited by TRPA1 and TRPV1 blockers and by the genetic deletion of either channel.

Conclusion

These results suggest that topical antifungal-induced pain and irritation are attributable to the activation of nociceptive TRPA1 and/or TRPV1 channel/s. Consequently, caution should be exercised in the use of topical antifungals with symptoms of pain.