Clioquinol and Pyrithione Activate TRPA1 by Increasing Intracellular Zn

The antifungal and amoebicidal drug clioquinol (CQ) was withdrawn from the market when it was linked to an epidemic of subacute myelo-optico-neuropathy (SMON). Clioquinol exerts its anti-parasitic actions by acting as a Cu/Zn chelator and ionophore. Here we show that local injections of CQ produce mechanical hyperalgesia and cold hypersensitivity through a mechanism involving TRPA1 in mice. We also show that CQ activates TRPA1 in a Zn²⁺ -dependent manner. Using a different Zn²⁺ -ionophore, zinc pyrithione (ZnPy), we demonstrate that low, nanomolar concentrations of intracellular Zn²⁺ ([Zn²⁺]¡) stimulate TRPA1. Direct application of Zn²⁺ to the intracellular face of excised, inside-out patches activates TRPA1 with an EC 50 value of 7.5 ± 1 nM. TRPA1 is expressed in a subpopulation of nociceptive dorsal root ganglion (DRG) neurons, where it acts as a sensory receptor for environmental irritants and oxidants. Using cultured DRG neurons from wild-type and TRPA1-deficient mice, we demonstrate that TRPA1 is the principal excitatory receptor for increased [Zn²⁺]¡ in DRG neurons. In conclusion, we have discovered that TRPA1 acts a sensor of intracellular Zn²⁺, and that Zn²⁺ ionophores, such as CQ and ZnPy, activate TRPA1 by increasing [Zn²⁺]¡. We also demonstrate that CQ-evoked mechanical hyperalgesia and cold allodynia require TRPA1 in vivo.