Overactive bladder (OAB) is a symptom complex that may have many underlying contributing urological pathologies, among which metabolic syndrome is a known risk factor. Current treatment for OAB includes oral antimuscarinics or beta 3 agonists.... However, there is still some patients having poor results and needing new treatment options. The established causes of underactive bladder include neurogenic, myogenic, aging, and medication side effects. Currently, the pharmacotherapy for acontractile detrusor (AD) is still disappointing. During the past years, our studies have linked chloride channels to OAB. Significantly increased molecular expressions of CLC-3 and CLCA4 chloride channels on bladder smooth muscle has been disclosed using a cyclophosphamide (CYP) induced rat OAB model. Increased voiding frequency and non-voiding contractions in CYP-induced OAB rat could be ameliorated by intravesical instillation of chloride channel blockers, implying the potential therapeutic effect of calcium activated chloride channel blockers (CaCC) on OAB. TMEM16A was recently identified as a CaCC. Evidence has also been reported for TMEM16A involvement in intestinal and vascular smooth muscle contraction. Specific TMEM16A channel blockers and activators have also been developed. However, the role of TMEM16A on bladder smooth muscle has not been elucidated. We therefore implement a fructose feeding rat (FFR) model of metabolic syndrome to investigate the effects of inhibition or activation of TMEM16A CaCC on bladder smooth muscle tissue between normal, metabolic syndrome induced OAB and AD in rats.

50 FFRs were fed a fructose rich diet while 25 control animals received standard rat chow for 6 months. Based on the results of cystometric presentation at month 6, FFRs were categorized into 3 groups: NDF group (normal detrusor function), OAB group and AD group. The basal pressure, maximum bladder voiding pressure, intercontraction interval and spontaneous contraction activity were recorded. Then the urinary bladder was harvested. We  conducted a strategy using organ bath isometric tension experiments to involve: ①Inhibitory concentration-response curve (CRC)  of traditional chloride channel blockers (niflumic acid (NFA)) and TMEM16A blockers (T16inh-A01 and N-((4-methoxy)-2-naphthyl)-5-nitroanthranilic acid (MONNA)) on carbachol (CCh)-induced tonic contractions in control, NDF and OAB rats.  ②CRC of TMEM16A activator (N-(2-methoxyethyl)-N-(4-phenyl-2-thiazolyl)- 2,3,4-trimethoxybenzeneacetamide (Eact ))-induced tonic contractions in control, NDF and AD rats. The results of inhibitory CRC and IC50 for TMEM16A blockers and CRC for TMEM16A activator among control, NDF, OAB and control, NDF, AD groups were compared.

①The CCh-induced contractions (at ED80) could be inhibited by pretreatment of NFA, T16inh-A01 and MONNA in a concentration-dependent manner in control, NDF and OAB groups (Figure 1A, 1B, 1C). The IC50 of NFA, T16inh-A01 and MONNA in the three groups are shown in Table. The inhibitory effects of TMEM16A blockers (T16inh-A01 and MONNA) on CCh-induced contraction are more potent than those of traditional chloride channel blockers (NFA) In addition, there was a significant greater inhibition of tension for NFA (10^-4~10^-1M), T16inh-A01 (10^-5~10^-2M) and MONNA (10^-4~10^-1M) in OAB group than in control group. Also, there was a significant greater inhibition of contraction percentage in OAB group than in control group using T16inh-A01, MONNA (at the concentration of 10^-4M) but not NFA. ②Eact could induce tonic contraction on isolated rat detrusor in control, NDF, and AD groups. The contractility increased as the concentration of Eact increased (Figure 1D). The ED80 for Eact was 1.7x10-5M.

The results showed that pretreatment of traditional chloride channel blockers (NFA) or TMEM16A blockers (T16inh-A01 and MONNA) could inhibit the CCh-induced tonic contraction in bladder smooth muscle tissue of control, NDF and OAB rats with metabolic syndrome. The inhibition effects are more potent using TMEM16A blockers than traditional chloride channel blockers. The detrusor contractility in OAB group was more susceptive to inhibition of chloride channel blockers than that in control group. On the other hand, treatment of TMEM16A activator (Eact) could trigger the tonic contractions of bladder smooth muscle tissue in control, NDF and AD rats. Taking these results together, there may be an important role of TMEM16A CaCC on bladder smooth muscle in metabolic syndrome-induced OAB and AD rats. Thus, the TMEM16A blockers may provide novel therapeutic agents for OAB and TMEM16A activators, for UAB respectively.

This study demonstrated the inhibitory effects of TMEM16A blockers and the activating effects of Eact on bladder smooth muscle contraction in metabolic syndrome induced OAB and AD rats respectively, indicating the novel therapeutic target of TMEM16A CaCC for OAB and AD.