Clioquinol and pyrithione activate TRPA1 by increasing intracellular Zn2+

The antifungal and amoebicidal drug clioquinol (CQ) was withdrawn from the market when it was linked to an epidemic of subacute myelo-optico-neuropathy (SMON).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+](i)) stimulate TRPA1. Direct application of Zn2+ to the intracellular face of excised, inside-out patches activates TRPA1 with an EC50 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+](i) 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+](i). We also demonstrate that CQ-evoked mechanical hyperalgesia and cold allodynia require TRPA1 in vivo.