Activation of TRPA1 channels by Fenamate NSAIDs

Abstract

TRPA1 forms non‐selective cation channels in polymodal nociceptors and can be activated by electrophilic prostaglandins and pungent chemicals through covalent modification. In the present study, we tested the activity of a group of non‐steroidal anti‐inflammatory drugs (NSAIDs) using electrophysiological techniques and intracellular Ca2+ measurements. We found that specific NSAIDs can act as full agonists of TRPA1, while others are partial agonists or inactive. 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 in WI‐38 fibroblasts. These same NSAIDs activated human TRPA1 inducibly expressed in HEK293 cells, but the responses were absent in uninduced and parental HEK293 cells. Responses to fenamate agonists were blocked by TRPA1 antagonists, AP‐18, HC‐030031, and ruthenium red. Washout of agonist led to a rapid transition to a resting state. At subsaturating concentrations, the fenamate NSAIDs potentiated the activation of TRPA1 by AITC, cinnamaldehyde, and cold, demonstrating positive synergistic interactions. The stimulatory effect was 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.