Abstract

The transient receptor potential melastin 8 ion channel (TRPM8) is implicated in bladder sensing but limited information on TRPM8 antagonists in bladder overactivity is available. This study characterizes a new TRPM8-selective antagonist (DFL23448 [5-(2-ethyl-2H-tetrazol-5-yl)-2-(3-fluorophenyl)-1,3-thiazol-4-ol]) and evaluates it in cold-induced behavioral tests and tests on bladder function and experimental bladder overactivity in vivo in rats. DFL23448 displayed IC₅₀ values of 10 and 21 nM in hTRPM8 human embryonic kidney 293 cells activated by Cooling Agent 10 or cold, but it had limited activity (IC₅₀ > 10 μM) at transient receptor potential vanilloids TRPV1, TRPA1, or TRPV4 or at various G protein–coupled receptors. In rats, DFL23448 administered intravenously or orally had a half-life of 37 minutes or 4.9 hours, respectively. DLF23448 (10 mg/kg i.v.) reduced icilin-induced “wet dog–like” shakes in rats. Intravesical DFL23448 (10 mg/l), but not vehicle, increased micturition intervals, micturition volume, and bladder capacity. During bladder overactivity by intravesical prostaglandin E₂ (PGE₂), vehicle controls exhibited reductions in micturition intervals, micturition volumes, and bladder capacity by 37%–39%, whereas the same parameters only decreased by 12%–15% (P < 0.05–0.01 versus vehicle) in DFL23448-treated rats. In vehicle-treated rats, but not in DFL23448-treated rats, intravesical PGE₂ increased bladder pressures. Intravenous DFL23448 at 10 mg/kg, but not 1 mg/kg DFL23448 or vehicle, increased micturition intervals, micturition volumes, and bladder capacity. During bladder overactivity by intravesical PGE₂, micturition intervals, micturition volumes, and bladder capacity decreased in vehicle– and 1 mg/kg DFL23448–treated rats, but not in 10 mg/kg DFL23448–treated rats. Bladder pressures increased less in rats treated with DFL23448 10 mg/kg than in vehicle– or 1 mg/kg DFL23448–treated rats. DFL23448 (10 mg/kg i.v.), but not vehicle, prevented cold stress–induced bladder overactivity. Our results support a role for bladder TRPM8-mediated signals in experimental bladder overactivity.