TRP Channel Agonists Activate Different Afferent Neuromodulatory Mechanisms in Guinea Pig Urinary Bladder

Research Progress on TRPA1 in Diseases

For a long time, the physiological activity of TRP ion channels and the response to various stimuli have been the focus of attention, and the physiological functions mediated by ion channels have subtle links with the occurrence of various diseases. Our group has been engaged in the study of ion channels. In recent years, the report rate of TRPA1, the only member of the TRPA subfamily in the newly described TRP channel, has been very high. TRPA1 channels are not only abundantly expressed in peptidergic nociceptors but are also found in many nonneuronal cell types and tissues, and through the regulation of Ca2+ influx, various neuropeptides and signaling pathways are involved in the regulation of nerves, respiration, circulation, and various diseases and inflammation throughout the body. In this review, we mainly summarize the effects of TRPA1 on various systems in the body, which not only allows us to have a more systematic and comprehensive understanding of TRPA1 but also facilitates more in-depth research on it in the future.

H2O2 enhances the spontaneous phasic contractions of isolated human-bladder strips via activation of TRPA1 channels on sensory nerves and the release of substance P and PGE2

Several studies have indicated that reactive oxygen species (ROS) can lead to detrusor overactivity (DO), but the underlying mechanisms are not known. Hydrogen dioxide (H2O2) is used commonly to investigate the effects of ROS. In present study, we investigated the effects of H2O2 on phasic spontaneous bladder contractions (SBCs) of isolated human-bladder strips (iHBSs) and the underlying mechanisms. Samples of bladder tissue were obtained from 26 patients undergoing cystectomy owing to bladder cancer. SBCs of iHBSs were recorded in organ-bath experiments. H2O2 (1μM-10mM) concentration-dependently increased the SBCs of iHBSs. These enhancing effects could be mimicked by an agonist of transient receptor potential (TRP)A1 channels (allyl isothiocyanate) and blocked with an antagonist of TRPA1 channels (HC030031; 10 μM). H2O2 induced enhancing effects also could be attenuated by desensitizing sensory afferents with capsaicin (10 μM), blocking nerve firing with TTX (1 μM), blocking neurokinin effects with NK2 receptor antagonist (SR48968, 10 μM), and blocking PGE2 synthesis with indomethacin (10 μM), respectively. Our study: (i) suggests activation of TRPA1 channels on bladder sensory afferents, and then release of substance P or PGE2 from sensory nerve terminals, contribute to the H2O2-induced enhancing effects on SBCs of iHBSs; (ii) provides insights for the mechanisms underlying ROS leading to DO; (iii) indicates that targeting TRPA1 channels might be the promising strategy against overactive bladder in conditions associated with excessive production of ROS.

Drugs Currently Undergoing Preclinical or Clinical Trials for the Treatment of Overactive Bladder: A Review

Background

Overactive bladder (OAB) is a common clinical condition for which current drug treatment comprises drugs blocking the cholinergic nerve supply, or augmenting the adrenergic nerve supply, to the detrusor muscle of the urinary bladder. Current treatments have drawbacks, including lack of efficacy and the development of adverse effects in some patients. Hence, new and better drugs for treating OAB will be clinically useful.

Objective

This review is meant to provide information on drugs currently undergoing preclinical or clinical trials for the treatment of OAB published in journal articles or elsewhere.

Methods

The cited articles were retrieved from PubMed and Google Scholar from January 1, 1990, to December 31, 2021. The search terms used were contraction or contractility, detrusor, inhibition, isolated or in vitro, in vivo, overactive bladder, and relaxant effect or relaxation.

Results

There are 4 classes of new drugs under various stages of development for the treatment of OAB. These are drugs acting on the autonomic nerve supply to the detrusor muscle of the urinary bladder that include the anticholinergics tarafenacin and afacifenacin and the β₃ adrenoceptor agonists solabegron and ritobegron; drugs acting on ion channels in the detrusor muscle (eg, potassium channel openers and calcium channel blockers), drugs acting on cellular enzymes like phosphodiesterase-5 inhibitors and Rho kinase inhibitors, and drugs acting on miscellaneous targets (eg, pregabalin and trimetazidine).

Conclusions

Drugs currently used to treat OAB target only the cholinergic and adrenergic cellular signalling pathways. There are many other drugs under trial targeting other cellular pathways that may be useful for treating OAB. Their approval for clinical use might improve the treatment of patients with OAB. (Curr Ther Res Clin Exp. 2022; 83:XXX–XXX)