Transient Receptor Potential Ankyrin Type Research Articles

A synergistic effect of simultaneous TRPA1 and TRPV1 activations on vagal pulmonary C-fiber afferents.

Transient receptor potential ankyrin type 1 (TRPA1) and vanilloid type 1 (TRPV1) receptors are coexpressed in vagal pulmonary C-fiber sensory nerves. Because both these receptors are sensitive to a number of endogenous inflammatory mediators, it is conceivable that they can be activated simultaneously during airway inflammation. This study aimed to determine whether there is an interaction between these two polymodal transducers upon simultaneous activation, and how it modulates the activity of vagal pulmonary C-fiber sensory nerves. In anesthetized, spontaneously breathing rats, the reflex-mediated apneic response to intravenous injection of a combined dose of allyl isothiocyanate (AITC, a TRPA1 activator) and capsaicin (Cap, a TRPV1 activator) was ∼202% greater than the mathematical sum of the responses to AITC and Cap when they were administered individually. Similar results were also observed in anesthetized mice. In addition, the synergistic effect was clearly demonstrated when the afferent activity of single vagal pulmonary C-fiber afferents were recorded in anesthetized, artificially ventilated rats; C-fiber responses to AITC, Cap and AITC + Cap (in combination) were 0.6 ± 0.1, 0.8 ± 0.1, and 4.8 ± 0.6 impulses/s (n = 24), respectively. This synergism was absent when either AITC or Cap was replaced by other chemical activators of pulmonary C-fiber afferents. The pronounced potentiating effect was further demonstrated in isolated vagal pulmonary sensory neurons using the Ca(2+) imaging technique. In summary, this study showed a distinct positive interaction between TRPA1 and TRPV1 when they were activated simultaneously in pulmonary C-fiber sensory nerves.

Structure–affinity relationships and pharmacological characterization of new alkyl-resorcinol cannabinoid receptor ligands: Identification of a dual cannabinoid receptor/TRPA1 channel agonist

In our ongoing program aimed at deeply investigating the endocannabinoid system (ES), a set of new alkyl-resorcinol derivatives was prepared focusing on the nature and the importance of the carboxamide functionality. Binding studies on CB1 and CB2 receptors, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH) showed that some of the newly developed compounds behaved as very potent cannabinoid receptor ligands (Ki in the nanomolar range) while, however, none of them was able to inhibit MAGL and/or FAAH.Derivative 11 was a potent CB1 and CB2 ligand, with Ki values similar to WIN 55,212, exhibiting a CB1 and CB2 agonist profile in vitro. In the formalin test of peripheral acute and inflammatory pain in mice, this compound showed a weak and delayed antinociceptive effect against the second phase of the nocifensive response, exhibiting, interestingly, a quite potent transient receptor potential ankyrin type-1 (TRPA1) channel agonist activity. Moreover, derivative 14, characterized by lower affinity but higher CB2 selectivity than 11, proved to behave as a weak CB2 competitive inverse agonist.

A synergistic effect of TRPV1 and TRPA1 activations in vagal pulmonary C fibers (712.16)

Recent studies suggest that transient receptor potential ankyrin type 1 (TRPA1) channels can be activated by a number of inflammatory mediators and are largely co‐expressed with TRPV1 in a subset of vagal bronchopulmonary C‐fibers. This study was carried out to determine whether there is an interaction between these two polymodal transducers, TRPV1 and TRPA1, upon simultaneous activation. Pulmonary chemoreflex responses were compared in anesthetized, spontaneously breathing rats when intravenous injections of capsaicin (Cap, a TRPV1 activator; 0.75 µg/kg) and allyl isothiocyanate (AITC, a TRPA1 activator; 0.8‐1.2 mg/kg) were administered individually first and then in combination at 20 min intervals. The apneic ratios triggered by Cap alone and AITC alone were 2.2 ± 0.6 and 2.0 ± 0.9, respectively; intravenous injection of the combined dose (Cap + AITC) elevated the apneic ratio to 12.8 ± 2.4 which is ~255% greater than the mathematical sum of TRPV1 and TRPA1 responses (P<0.05, n=6). The synergistic effect was also observed in the study of chemoreflex responses in anesthetized mice (~450% greater than the mathematical sum of TRPV1 and TRPA1 responses, P<0.05, n=6; 1.3 ± 0.2, 1.1 ± 0.0, and 12.3 ± 2.9 for Cap alone, AITC alone, and Cap + AITC, respectively). Furthermore, when both TRPV1 and TRPA1 were activated simultaneously, the C‐fiber responses, recorded by the single‐fiber recording technique, were markedly amplified: responses to Cap alone, AITC alone and Cap + AITC were 4.3 ± 0.5, 3.4 ± 0.8 and 27.2 ± 3.4 impulses/s, respectively (~468% greater than the mathematical sum of TRPV1 and TRPA1 responses, P<0.05, n=24). These results clearly demonstrated a positive interaction between TRPV1 and TRPA1 activations at the pulmonary C‐fiber endings. The underlying mechanism of this synergistic effect remains to be determined. (Supported by NIH grant HL96914 and DoD grant W81XWH‐10‐2‐0189).

Piperazinyl carbamate fatty acid amide hydrolase inhibitors and transient receptor potential channel modulators as “dual-target” analgesics

We showed previously that inhibiting fatty acid amide hydrolase (FAAH), an endocannabinoid degrading enzyme, and transient receptor potential vanilloid type-1 (TRPV1) channels with the same molecule, the naturally occurring N-arachidonoyl-serotonin (AA-5-HT), produces more efficacious anti-nociceptive and anti-hyperalgesic actions than the targeting of FAAH or TRPV1 alone. We also reported the synthesis of some piperazinyl carbamates as “dual” FAAH inhibitors and either antagonists at TRPV1 or agonists/desensitizers of the transient receptor potential ankyrin type-1 (TRPA1) cannel, another target for analgesic drugs. We investigated here if two such compounds, the FAAH/TRPV1 blocker OMDM198 and the FAAH inhibitor/TRPA1 agonist, OMDM202, exert anti-nociceptive actions in the formalin test of pain in mice, and through what mechanism. Both compounds inhibited the second phase of the response to formalin, the effect being maximal at 3mg/kg, i.p. Antagonism of CB1 or CB2 receptors with AM251 or AM630 (1mg/kg, i.p.), respectively, reversed this effect. A TRPV1 agonist, palvanil (0.1mg/kg, i.p.), also reversed the analgesic effect of OMDM198. OMDM202 action was also antagonized by a per se inactive dose of the selective TRPA1 blocker, AP-18 (0.05mg/kg, i.p.), but not by a TRPV1 antagonist. AP-18 at higher doses (0.1–0.2mg/kg) inhibited both the first and second phase of the formalin response. The effects of OMDM198 and OMDM202 were accompanied by elevation of anandamide levels in the spinal cord. OMDM198 (0.1–5.0mg/kg, i.p.) also reversed carrageenan-induced oedema and thermal hyperalgesia in mice with efficacy similar to that of AA-5-HT. These data suggest that “dual” fatty acid amide hydrolase and transient receptor potential channel modulators should be clinically evaluated as novel analgesics.

The cannabinoid TRPA1 agonist cannabichromene inhibits nitric oxide production in macrophages and ameliorates murine colitis

The non-psychotropic cannabinoid cannabichromene is known to activate the transient receptor potential ankyrin-type1 (TRPA1) and to inhibit endocannabinoid inactivation, both of which are involved in inflammatory processes. We examined here the effects of this phytocannabinoid on peritoneal macrophages and its efficacy in an experimental model of colitis. Murine peritoneal macrophages were activated in vitro by LPS. Nitrite levels were measured using a fluorescent assay; inducible nitric oxide (iNOS), cyclooxygenase-2 (COX-2) and cannabinoid (CB1 and CB2 ) receptors were analysed by RT-PCR (and/or Western blot analysis); colitis was induced by dinitrobenzene sulphonic acid (DNBS). Endocannabinoid (anandamide and 2-arachidonoylglycerol), palmitoylethanolamide and oleoylethanolamide levels were measured by liquid chromatography-mass spectrometry. Colonic inflammation was assessed by evaluating the myeloperoxidase activity as well as by histology and immunohistochemistry. LPS caused a significant production of nitrites, associated to up-regulation of anandamide, iNOS, COX-2, CB1 receptors and down-regulation of CB2 receptors mRNA expression. Cannabichromene significantly reduced LPS-stimulated nitrite levels, and its effect was mimicked by cannabinoid receptor and TRPA1 agonists (carvacrol and cinnamaldehyde) and enhanced by CB1 receptor antagonists. LPS-induced anandamide, iNOS, COX-2 and cannabinoid receptor changes were not significantly modified by cannabichromene, which, however, increased oleoylethanolamide levels. In vivo, cannabichromene ameliorated DNBS-induced colonic inflammation, as revealed by histology, immunohistochemistry and myeloperoxidase activity. Cannabichromene exerts anti-inflammatory actions in activated macrophages - with tonic CB1 cannabinoid signalling being negatively coupled to this effect - and ameliorates experimental murine colitis.

Role of Transient Receptor Potential and Acid-sensing Ion Channels in Peripheral Inflammatory Pain

Pain originating in inflammation is the most common pathologic pain condition encountered by the anesthesiologist whether in the context of surgery, its aftermath, or in the practice of pain medicine. Inflammatory agents, released as components of the body's response to peripheral tissue damage or disease, are now known to be collectively capable of activating transient receptor potential vanilloid type 1, transient receptor potential vanilloid type 4, transient receptor potential ankyrin type 1, and acid-sensing ion channels, whereas individual agents may activate only certain of these ion channels. These ionotropic receptors serve many physiologic functions-as, indeed, do many of the inflammagens released in the inflammatory process. Here, we introduce the reader to the role of these ionotropic receptors in mediating peripheral pain in response to inflammation.