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The pro-algesic transient receptor potential ankyrin 1 (TRPA1) channel, expressed by a subpopulation of primary sensory neurons, has been implicated in various pain models in mice. However, evidence in rats indicates that TRPA1 conveys nociceptive signals elicited by channel activators, but not those associated with tissue inflammation or nerve injury. Here, in rats, we explored the TRPA1 role in mechanical allodynia associated with stimulation of peptidergic primary sensory neurons (neurogenic inflammation) and moderate (partial sciatic nerve ligation, pSNL) or severe (chronic constriction injury, CCI) sciatic nerve injury.Acute nociception and mechanical hypersensitivity associated with neurogenic inflammation and sciatic nerve injury (pSNL and CCI) were investigated in rats with TRPA1 pharmacological antagonism or genetic silencing. TRPA1 presence and function were analysed in cultured rat Schwann cells.Hind paw mechanical allodynia (HPMA), but not acute nociception, evoked by local injection of capsaicin or allyl isothiocyanate, the TRP vanilloid 1 (TRPV1) or the TRPA1 activators was mediated by CGRP released from peripheral sensory nerve terminals. CGRP-evoked HPMA was sustained by a ROS-dependent TRPA1 activation, probably in Schwann cells. HPMA evoked by pSNL, but not that evoked by CCI, was mediated by ROS and TRPA1 without the involvement of CGRP.As found in mice, TRPA1 mediates mechanical allodynia associated with neurogenic inflammation and moderate nerve injury in rats. The channel contribution to mechanical hypersensitivity is a common feature in rodents and might be explored in humans.

Background and Purpose The mechanism of the antimigraine action of butterbur [Petasites hybridus (L.) Gaertn.] is unknown. Here, we investigated the ability of isopetasin, a major butterbur constituent, to specifically target the transient receptor ankyrin 1 (TRPA1) channel and to affect functional responses relevant to migraine. Experimental Approach Single cell calcium imaging and patch-clamp recordings in human and rodent TRPA1-expressing cells, neurogenic motor responses in isolated rat/mouse urinary bladder, release of calcitonin gene-related peptide (CGRP) from mouse spinal cord in vitro, and facial rubbing in mice and meningeal blood flow in rat were examined. Key Results Isopetasin produced (i) calcium responses and currents in rat/mouse trigeminal ganglion (TG) neurons and in cells expressing the human TRPA1, (ii) substance P-mediated contractions of isolated rat urinary bladders and (iii) CGRP release from mouse dorsal spinal cord, responses that were selectively abolished by TRPA1 genetic deletion/pharmacological antagonism. Pre-exposure to isopetasin produced marked desensitisation of allyl isothiocyanate (AITC, TRPA1 agonist)- or capsaicin (TRPV1 agonist)-evoked currents in rat TG neurons, contractions of rat or mouse urinary bladder and CGRP release from mouse central terminals of primary sensory neurons. Repeated intragastric administration of isopetasin attenuated mouse facial rubbing, evoked by local AITC or capsaicin, and dilation of rat meningeal arteries by acrolein or ethanol (TRPA1 and TRPV1 agonists, respectively). Conclusion and Implications TRPA1 agonism by isopetasin results in excitation of neuropeptide-containing nociceptors that is followed by remarkable heterologous neuronal desensitisation. Such attenuation in pain and neurogenic inflammation may account for the antimigraine action of butterbur.

BACKGROUND AND PURPOSE Peptides from venomous animals have long been important tools for understanding pain mechanisms and for the discovery of pain treatments. Here, we hypothesized that Phα1β, a peptide purified from the armed spider Phoneutria nigriventer venom, produces analgesia by blocking the transient receptor potential ankyrin 1 (TRPA1) channel. EXPERIMENTAL APPROACH Cultured rat dorsal root ganglion (DRG) neurons, human IMR90 fibroblasts or HEK293 cells expressing the human TRPA1 (hTRPA1-HEK293), TRPV1 (hTRPV1-HEK293) or TRPV4 (hTRPV4-HEK293), were used for calcium imaging and electrophysiology. Pain-like responses induced by TRPA1, TRPV1 or TRPV4 agonists or by bortezomib were also investigated in mice. KEY RESULTS Phα1β selectively inhibited calcium responses and currents evoked by the TRPA1 agonist, allyl isothiocyanate (AITC), on hTRPA1-HEK293, IMR90 fibroblasts and DRG neurons. Phα1β did not affect calcium responses evoked by selective TRPV1 (capsaicin) or TRPV4 (GSK 1016790A) agonists on the various cell types. Intrathecal (i.t.) and intraplantar (i.pl.) administration of low doses of Phα1β (up to 300 pmol per paw) attenuated acute nociception and mechanical and cold hyperalgesia evoked by AITC (i.t or i.pl), without affecting responses produced by capsaicin or hypotonic solution. Notably, Phα1β abated the TRPA1-dependent neuropathic pain-like responses induced by bortezomib. Finally, in vitro and in vivo inhibition of TRPA1 by Phα1β was recapitulated by a recombinant version of the peptide, CTK 01512-2. CONCLUSIONS AND IMPLICATIONS Phα1β and CTK 01512-2 selectively target TRPA1, but not other TRP channels. This specific action underlines the potential of Phα1β and CTK 01512-2 for pain treatment.

A complex network of many interacting mechanisms orchestrates immune and inflammatory responses. Among these, the cation channels of the transient receptor potential (TRP) family expressed by resident tissue cells, inflammatory and immune cells and distinct subsets of primary sensory neurons, have emerged as a novel and interrelated system to detect and respond to harmful agents. TRP channels, by means of their direct effect on the intracellular levels of cations and/or through the indirect modulation of a large series of intracellular pathways, orchestrate a range of cellular processes, such as cytokine production, cell differentiation and cytotoxicity. The contribution of TRP channels to the transition of inflammation and immune responses from a defensive early response to a chronic and pathological condition is also emerging as a possible underlying mechanism in various diseases. This review discusses the roles of TRP channels in inflammatory and immune cell function and provides an overview of the effects of inflammatory and immune TRP channels on the pathogenesis of human diseases.

Background and Purpose Although still used by hundreds of millions of people worldwide, the mechanism of the analgesic action of the pyrazolone derivatives (PDs), dipyrone, propyphenazone and antipyrine remains unknown. The transient receptor potential ankyrin 1 (TRPA1) channel, expressed by nociceptors, is emerging as a major pain transduction pathway. We hypothesized that PDs target the TRPA1 channel and by this mechanism produce their analgesic effect.

The mechanism of the anti-migraine action of extracts of butterbur [Petasites hybridus (L.) Gaertn.] is unknown. Here, we investigated the ability of isopetasin, a major constituent of these extracts, to specifically target TRPA1 channel and to affect functional responses relevant to migraine.Single-cell calcium imaging and patch-clamp recordings in human and rodent TRPA1-expressing cells, neurogenic motor responses in rodent isolated urinary bladder, release of CGRP from mouse spinal cord in vitro and facial rubbing in mice and meningeal blood flow in rats were examined.Isopetasin induced (i) calcium responses and currents in rat/mouse trigeminal ganglion (TG) neurons and in cells expressing the human TRPA1, (ii) substance P-mediated contractions of rat isolated urinary bladders and (iii) CGRP release from mouse dorsal spinal cord, responses that were selectively abolished by genetic deletion or pharmacological antagonism of TRPA1 channels. Pre-exposure to isopetasin produced marked desensitization of allyl isothiocyanate (AITC, TRPA1 channel agonist)- or capsaicin (TRPV1 channel agonist)-evoked currents in rat TG neurons, contractions of rat or mouse bladder and CGRP release from mouse central terminals of primary sensory neurons. Repeated intragastric administration of isopetasin attenuated mouse facial rubbing, evoked by local AITC or capsaicin, and dilation of rat meningeal arteries by acrolein or ethanol (TRPA1 and TRPV1 channel agonists respectively).Activation of TRPA1 channels by isopetasin results in excitation of neuropeptide-containing nociceptors, followed by marked heterologous neuronal desensitization. Such atten uation in pain and neurogenic inflammation may account for the anti-migraine action of butterbur.