a-967079 and allyl-isothiocyanate

Topics: Acetanilides; Animals; Antigens, CD; Antigens, Differentiation, T-Lymphocyte; Calcium; CD28 Antigens; CD3 Complex; Computer Simulation; Concanavalin A; Gene Expression Regulation; Humans; Immunity, Cellular; Interferon-gamma; Interleukin-2; Interleukin-2 Receptor alpha Subunit; Isothiocyanates; Lectins, C-Type; Mice; Oximes; Primary Cell Culture; Purines; T-Lymphocytes; TRPA1 Cation Channel; Tumor Necrosis Factor Receptor Superfamily, Member 7; Tumor Necrosis Factor-alpha

The transient receptor potential ankyrin 1 (TRPA1) channel functions as an irritant sensor and is a therapeutic target for treating pain, itch, and respiratory diseases. As a ligand-gated channel, TRPA1 can be activated by electrophilic compounds such as allyl isothiocyanate (AITC) through covalent modification or activated by noncovalent agonists through ligand binding. However, how covalent modification leads to channel opening and, importantly, how noncovalent binding activates TRPA1 are not well-understood. Here we report a class of piperidine carboxamides (PIPCs) as potent, noncovalent agonists of human TRPA1. Based on their species-specific effects on human and rat channels, we identified residues critical for channel activation; we then generated binding modes for TRPA1-PIPC interactions using structural modeling, molecular docking, and mutational analysis. We show that PIPCs bind to a hydrophobic site located at the interface of the pore helix 1 (PH1) and S5 and S6 transmembrane segments. Interestingly, this binding site overlaps with that of known allosteric modulators, such as A-967079 and propofol. Similar binding sites, involving π-helix rearrangements on S6, have been recently reported for other TRP channels, suggesting an evolutionarily conserved mechanism. Finally, we show that for PIPC analogs, predictions from computational modeling are consistent with experimental structure-activity studies, thereby suggesting strategies for rational drug design.

Topics: Animals; Binding Sites; Calcium Channels; Drug Design; Humans; Isothiocyanates; Ligands; Models, Structural; Molecular Docking Simulation; Mutagenesis; Oximes; Piperidines; Propofol; Protein Domains; Rats; Species Specificity; TRPA1 Cation Channel

The nonselective cation channel transient receptor potential ankryn subtype family 1 (TRPA1) is expressed in neurons of dorsal root ganglia and trigeminal ganglia and also in vagal afferent neurons that innervate the lungs and gastrointestinal tract. Many TRPA1 agonists are reactive electrophilic compounds that form covalent adducts with TRPA1. Allyl isothiocyanate (AITC), the common agonist used to identify TRPA1, contains an electrophilic group that covalently binds with cysteine residues of TRPA1 and confers a structural change on the channel. There is scientific motivation to identify additional compounds that can activate TRPA1 with different mechanisms of channel gating. We provide evidence that ethyl vanillin (EVA) is a TRPA1 agonist. Using fluorescent calcium imaging and whole-cell patch-clamp electrophysiology on dissociated rat vagal afferent neurons and TRPA1-transfected COS-7 cells, we discovered that EVA activates cells also activated by AITC. Both agonists display similar current profiles and conductances. Pretreatment with A967079, a selective TRPA1 antagonist, blocks the EVA response as well as the AITC response. Furthermore, EVA does not activate vagal afferent neurons from TRPA1 knockout mice, showing selectivity for TRPA1 in this tissue. Interestingly, EVA appears to be pharmacologically different from AITC as a TRPA1 agonist. When AITC is applied before EVA, the EVA response is occluded. However, they both require intracellular oxidation to activate TRPA1. These findings suggest that EVA activates TRPA1 but via a distinct mechanism that may provide greater ease for study in native systems compared with AITC and may shed light on differential modes of TRPA1 gating by ligand types.

Topics: Animals; Benzaldehydes; Chlorocebus aethiops; COS Cells; HEK293 Cells; Humans; Isothiocyanates; Male; Mice; Neurons, Afferent; Nodose Ganglion; Oximes; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; TRPA1 Cation Channel; TRPC Cation Channels

Methylglyoxal (MG), a highly reactive dicarbonyl substance, is known as an endogenous carbonyl stress-inducing substance related to various disease states. Irritable bowel syndrome (IBS) is one of the most frequently encountered gastrointestinal disorders and MG is considered to be its causal substance. An increased serum 5-hydroxytryptamine (5-HT) level is related to IBS symptoms and the majority of 5-HT originates from enterochromaffin (EC) cells in the intestine. Here we examine the mechanisms of MG-induced 5-HT secretion using RIN-14B cells derived from a rat pancreatic islet tumor since these cells are used as a model for EC cells. MG increased the intracellular Ca(2+) concentration ([Ca(2+)]i) and 5-HT secretion, both of which were inhibited by the removal of extracellular Ca(2+) and specific transient receptor potential ankyrin 1 (TRPA1) antagonists. MG elicited an inward current under voltage-clamped conditions. Prior application of MG evoked reciprocal suppression of subsequent [Ca(2+)]i responses to allylisothiocyanate, a TRPA1 agonist, and vice versa. Glyoxal, an analog of MG, also evoked [Ca(2+)]i and secretory responses but its potency was much lower than that of MG. The present results suggest that MG promotes 5-HT secretion through the activation of TRPA1 in RIN-14B cells. These results may indicate that TRPA1 is a promising target for the treatment of IBS and that the RIN-14B cell line is a useful model for investigation of IBS.

Topics: Acetanilides; Adenoma, Islet Cell; Animals; Calcium; Cell Line, Tumor; Formazans; Glyoxal; Isothiocyanates; Membrane Potentials; Neuroendocrine Tumors; Oximes; Patch-Clamp Techniques; Purines; Pyruvaldehyde; Rats; Serotonin; TRPA1 Cation Channel; TRPC Cation Channels

The aim of this research was to assess the antinociceptive activity of the transient receptor potential (TRP) channel TRPV1, TRPM8, and TRPA1 antagonists in neurogenic, tonic, and neuropathic pain models in mice. For this purpose, TRP channel antagonists were administered into the dorsal surface of a hind paw 15 min before capsaicin, allyl isothiocyanate (AITC), or formalin. Their antiallodynic and antihyperalgesic efficacies after intraperitoneal administration were also assessed in a paclitaxel-induced neuropathic pain model. Motor coordination of paclitaxel-treated mice that received these TRP channel antagonists was investigated using the rotarod test. TRPV1 antagonists, capsazepine and SB-366791, attenuated capsaicin-induced nociceptive reaction in a concentration-dependent manner. At 8 µg/20 µl, this effect was 51% (P<0.001) for capsazepine and 37% (P<0.05) for SB-366791. A TRPA1 antagonist, A-967079, reduced pain reaction by 48% (P<0.05) in the AITC test and by 54% (P<0.001) in the early phase of the formalin test. The test compounds had no influence on the late phase of the formalin test. In paclitaxel-treated mice, they did not attenuate heat hyperalgesia but N-(3-aminopropyl)-2-{[(3-methylphenyl)methyl]oxy}-N-(2-thienylmethyl) benzamide hydrochloride salt (AMTB), a TRPM8 antagonist, reduced cold hyperalgesia and tactile allodynia by 31% (P<0.05) and 51% (P<0.01), respectively. HC-030031, a TRPA1 channel antagonist, attenuated tactile allodynia in the von Frey test (62%; P<0.001). In conclusion, distinct members of TRP channel family are involved in different pain models in mice. Antagonists of TRP channels attenuate nocifensive responses of neurogenic, tonic, and neuropathic pain, but their efficacies strongly depend on the pain model used.

Topics: Acetanilides; Analgesics; Animals; Benzamides; Capsaicin; Cold Temperature; Disease Models, Animal; Formaldehyde; Hyperalgesia; Isothiocyanates; Male; Mice; Neuralgia; Oximes; Paclitaxel; Pain Measurement; Purines; Thiophenes; Touch; Transient Receptor Potential Channels; TRPA1 Cation Channel; TRPM Cation Channels; TRPV Cation Channels