The role of the transient receptor potential ankyrin type-1 (TRPA1) channel in migraine pain: evaluation in an animal model.

BACKGROUND: Clinical and experimental studies have pointed to the possible involvement of the transient receptor potential ankyrin type-1 (TRPA1) channels in migraine pain. In this study, we aimed to further investigate the role of these channels in an animal model of migraine using a novel TRPA1 antagonist, ADM_12, as a probe. METHODS: The effects of ADM_12 on nitroglycerin-induced hyperalgesia at the trigeminal level were investigated in male rats using the quantification of nocifensive behavior in the orofacial formalin test. The expression levels of the genes coding for c-Fos, TRPA1, calcitonin gene-related peptide (CGRP) and substance P (SP) in peripheral and central areas relevant for migraine pain were analyzed. CGRP and SP protein immunoreactivity was also evaluated in trigeminal nucleus caudalis (TNC). RESULTS: In rats bearing nitroglycerin-induced hyperalgesia, ADM_12 showed an anti-hyperalgesic effect in the second phase of the orofacial formalin test. This effect was associated to a significant inhibition of nitroglycerin-induced increase in c-Fos, TRPA1 and neuropeptides mRNA levels in medulla-pons area, in the cervical spinal cord and in the trigeminal ganglion. No differences between groups were seen as regards CGRP and SP protein expression in the TNC. CONCLUSIONS: These findings support a critical involvement of TRPA1 channels in the pathophysiology of migraine, and show their active role in counteracting hyperalgesia at the trigeminal level.

Cardamonin, a Novel Antagonist of hTRPA1 Cation Channel, Reveals Therapeutic Mechanism of Pathological Pain.

The increasing demand for safe and effective treatments of chronic pain has promoted the investigation of novel analgesic drugs. Some herbals have been known to be able to relieve pain, while the chemical basis and target involved in this process remained to be clarified. The current study aimed to find anti-nociceptive candidates targeting transient receptor potential ankyrin 1 (TRPA1), a receptor that implicates in hyperalgesia and neurogenic inflammation. In the current study, 156 chemicals were tested for blocking HEK293/TRPA1 ion channel by calcium-influx assay. Docking study was conducted to predict the binding modes of hit compound with TRPA1 using Discovery Studio. Cytotoxicity in HEK293 was conducted by Cell Titer-Glo assay. Additionally, cardiotoxicity was assessed via xCELLigence RTCA system. We uncovered that cardamonin selectively blocked TRPA1 activation while did not interact with TRPV1 nor TRPV4 channel. A concentration-dependent inhibitory effect was observed with IC50 of 454 nM. Docking analysis of cardamonin demonstrated a compatible interaction with A-967079-binding site of TRPA1. Meanwhile, cardamonin did not significantly reduce HEK293 cell viability, nor did it impair cardiomyocyte constriction. Our data suggest that cardamonin is a selective TRPA1 antagonist, providing novel insight into the target of its anti-nociceptive activity.

Development of novel azabenzofuran TRPA1 antagonists as in vivo tools.

The transient receptor potential ankyrin 1 (TRPA1) channel is activated by noxious stimuli including chemical irritants and endogenous inflammatory mediators. Antagonists of this channel are currently being investigated for use as therapeutic agents for treating pain, airway disorders, and itch. A novel azabenzofuran series was developed that demonstrated in vitro inhibition of allyl isothiocyanate (AITC)-induced (45)Ca(2+) uptake with nanomolar potencies against both human and rat TRPA1. From this series, compound 10 demonstrated in vivo target coverage in an AITC-induced flinching model in rats while providing unbound plasma concentrations up to 16-fold higher than the TRPA1 rat IC50.

Effects of intravenous administration of recombinant Phα1ß toxin in a mouse model of fibromyalgia.

This study investigated the effects of intravenous (iv) administration of recombinant Phα1ß toxin, pregabalin, and diclofenac by the intrathecal route using an animal model fibromyalgia (FM). The reserpine administration (0.25 mg/kg s. c) once daily for three consecutive days significantly induced hyperalgesia, immobility time, and sucrose consumption in mice on the 4th day. Reserpine caused hyperalgesia on the mechanical and thermal hyperalgesia on the 4th day was reverted by recombinant Phα1ß (0.2 mg/kg iv) and pregabalin (1.25 µmol/site i. t) treatments. In contrast, diclofenac (215 nmol/site i. t) was ineffective. Recombinant Phα1ß toxin, pregabalin, and diclofenac did not affect the depressive-like behavioural effect induced by reserpine on mice during the forced swim and sucrose consumption tests. The data confirmed the analgesic effect of the recombinant Phα1ß toxin administered intravenously in a fibromyalgia mouse model.

Niosomal Formulation of a Lipoyl-Carnosine Derivative Targeting TRPA1 Channels in Brain.

The transient receptor potential akyrin type-1 (TRPA1) is a non-selective cation channel playing a pivotal role in pain sensation and neurogenic inflammation. TRPA1 channels expressed in the central nervous system (CNS) have a critical role in the modulation of cortical spreading depression (CSD), which is a key pathophysiological basis of migraine pain. ADM_09 is a recently developed lipoic acid-based TRPA1 antagonist that is able to revert oxaliplatin-induced neuropathic pain and inflammatory trigeminal allodynia. In this context, aiming at developing drugs that are able to target TRPA1 channels in the CNS and promote an antioxidant effect, permeability across the blood-brain barrier (BBB) represents a central issue. Niosomes are nanovesicles that can be functionalized with specific ligands selectively recognized by transporters expressed on the BBB. In this work, the activity of ADM_09 on neocortex cultures was studied, and an efficient formulation to cross the BBB was developed with the aim of increasing the concentration of ADM_09 into the brain and selectively delivering it to the CNS rapidly after parenteral administration.

The involvement of the TRPA1 receptor in a mouse model of sympathetically maintained neuropathic pain.

Sympathetic fibres maintain some forms of neuropathic pain, but the underlying mechanisms are poorly understood. Therefore, this study investigated the possible involvement of transient receptor potential ankyrin 1 (TRPA1) and the role of the sympathetic nervous system (involved in sympathetically maintained neuropathic pain) in a model of neuropathic pain induced by sciatic nerve chronic constriction injury (CCI) in mice. Systemic injection of the selective TRPA1 antagonist HC-030031 reversed the mechanical and cold allodynia that was induced by sciatic nerve chronic constriction injury (CCI). Nerve injury also sensitised mice to nociception, which was induced by the intraplantar injection of a low dose of the TRPA1 agonist allyl isothiocyanate without changing TRPA1 immunoreactivity in the injected paw. Furthermore, chemical sympathectomy produced by guanethidine largely prevented CCI-induced mechanical and cold allodynia. CCI also induced a norepinephrine-triggered nociception that was inhibited by an α-adrenoceptor antagonist, norepinephrine transporter block and monoamine oxidase inhibition. Finally, the peripheral injection of HC-030031 also largely reduced CCI-induced norepinephrine nociception and mechanical or cold allodynia. Taken together, the present findings reveal a critical role of TRPA1 in mechanical and cold hypersensitivity and norepinephrine hypersensitivity following nerve injury. Finally, our results suggest that TRPA1 antagonism may be useful to treat patients who present sympathetically maintained neuropathic pain.