title: Activation of TRPA1 channels by fenamate nonsteroidal anti-inflammatory drugs.
abstract: Transient receptor potential A1 (TRPA1) forms nonselective cation channels implicated in acute inflammatory pain and nociception. The mechanism of ligand activation of TRPA1 may involve either covalent modification of cysteine residues or conventional reversible ligand-receptor interactions. For certain electrophilic prostaglandins, covalent modification has been considered as the main mechanism involved in their stimulatory effect on TRPA1. Because some nonsteroidal anti-inflammatory drugs (NSAIDs) are structural analogs of prostaglandins, we examined several nonelectrophilic NSAIDs on TRPA1 activation using electrophysiological techniques and intracellular Ca(2+) measurements and found that a selected group of NSAIDs can act as TRPA1 agonists. Extracellularly applied flufenamic, niflumic, and mefenamic acid, as well as flurbiprofen, ketoprofen, diclofenac, and indomethacin, rapidly activated rat TRPA1 expressed in Xenopus oocytes and human TRPA1 endogenously expressed in WI-38 fibroblasts. Similarly, the NSAID ligands activated human TRPA1 inducibly expressed in HEK293 cells, but the responses were absent in uninduced and parental HEK293 cells. The response to fenamate agonists was blocked by TRPA1 antagonists, AP-18, HC-030031, and ruthenium red. At subsaturating concentrations, the fenamate NSAIDs also potentiate the activation of TRPA1 by allyl isothiocyanate, cinnamaldehyde, and cold, demonstrating positive synergistic interactions with other well-characterized TRPA1 activators. Importantly, among several thermosensitive TRP channels, the stimulatory effect is specific to TRPA1 because flufenamic acid inhibited TRPV1, TRPV3, and TRPM8. We conclude that fenamate NSAIDs are a novel class of potent and reversible direct agonists of TRPA1. This selective group of TRPA1-stimulating NSAIDs should provide a structural basis for developing novel ligands that noncovalently interact with TRPA1 channels.
authors.affiliation: Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH 43210, USA.
authors.forename: Hongzhen
authors.initials: H
authors.lastname: Hu
authors.forename: Jinbin
authors.initials: J
authors.lastname: Tian
authors.forename: Yingmin
authors.initials: Y
authors.lastname: Zhu
authors.forename: Chunbo
authors.initials: C
authors.lastname: Wang
authors.forename: Rui
authors.initials: R
authors.lastname: Xiao
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Herz
authors.forename: Jackie D
authors.initials: JD
authors.lastname: Wood
authors.forename: Michael X
authors.initials: MX
authors.lastname: Zhu
mesh_terms: D000818:Animals; D017487:Ankyrins; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D054361:Fenamates / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D015394:Molecular Structure; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D000074025:TRPA1 Cation Channel; D050052:TRPC Cation Channels; D050053:TRPM Cation Channels / Q000235:genetics / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D017487:Ankyrins; D000894:Anti-Inflammatory Agents, Non-Steroidal; D015220:Calcium Channels; D054361:Fenamates; D000074025:TRPA1 Cation Channel; D050052:TRPC Cation Channels; D050053:TRPM Cation Channels; C492297:TRPM8 protein, mouse; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; C480976:Trpa1 protein, rat; C486760:Trpv3 protein, mouse