Activation of TRPA1 channels by fenamate nonsteroidal anti-inflammatory drugs.

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.

The effect of intravesical ketoprofen on acetylcholine-evoked urinary bladder contractility and detrusor overactivity in the anesthetized rabbit model.

Intraurethral procedures such as the transurethral resection of the prostate can generate detrusor overactivity and bladder irritability. The rabbit model of detrusor overactivity has proven to be an excellent model to study the effects of drugs on detrusor overactivity. Using this model, we evaluated the responses to intravesical ketoprofen. In this model, each rabbit is anesthetized and the right external carotid artery is cannulated for blood pressure monitoring. A catheter is inserted through the femoral artery and is used for administration of acetylcholine (Ach). The bladder is exposed and catheterized for bladder pressure monitoring and drug addition and the proximal urethra is ligated. Cystometry is performed, the bladder drained, and 20 ml buffer placed in the bladder. After 30 min Ach is injected proximal to the vesical artery and the response of the bladder and blood pressure is recorded. Ach administration is repeated at 10-min intervals until three consistent responses are obtained. The bladder is drained and 20 ml of ketoprofen (100 microM final concentration) is placed in the bladder. Ach injections are repeated as given above at 10 min intervals and observed for 4 h. At the end of the experiment, a second cystometry is performed. The following is a summary of the results: Ketoprofen had no effect on either micturition pressure or the intravesical volume at micturition. Ketoprofen administration resulted in a progressive 50% decrease in the response to Ach. Ketoprofen mediated a progressive decrease in detrusor overactivity amplitude and frequency, reaching a maximum at 120-180 min.