The effects of a new selective beta3-adrenoceptor agonist (GW427353) on spontaneous activity and detrusor relaxation in human bladder

OBJECTIVE: To examine the effects of a new selective beta3-adrenoceptor agonist, GW427353 on human detrusor function, as beta2- and beta3-adrenoceptors have been identified in the bladder, and can mediate detrusor relaxation, but beta3-adrenoceptors are less widely distributed and beta3-adrenoceptor agonists should have the therapeutic advantage of producing fewer treatment side-effects. PATIENTS AND METHODS: 'Normal' human detrusor was retrieved from 12 patients (mean age 56 years) at cystectomy and from organ donors. Detrusor strips (4 x 1 x 1 mm) were mounted in superfused organ baths. Tone was induced with carbachol (5 x 10(-7)m) before applying either a nonselective beta-adrenoceptor agonist (isoprenaline) or GW427353 (with or without the beta3-adrenoceptor antagonist, SR59230A). In addition, the effect of GW427353 was tested on intrinsic nerve-evoked smooth muscle contraction over time. Effects on spontaneous activity were also recorded. RESULTS: GW427353 produced significant relaxation at concentrations of >10(-7)m; isoprenaline produced a significant effect from 10(-6)m, but otherwise both agonists had similar effects. The addition of SR59230A (10(-7)m), produced partial inhibition of the GW427353 response. GW427353 at 10(-6)m significantly reduced spontaneous activity within 10 min of incubation, and at higher concentrations (>5 x 10(-6)m) inhibited detrusor contractions evoked by electrical field stimulation. CONCLUSION: Neuropathic bladder dysfunction is characterized by increased spontaneous activity and involuntary detrusor contractions, which can result in urinary frequency, urgency, nocturia and incontinence. The novel feature of GW427353 is the ability to suppress spontaneous activity and produce significant relaxation in human detrusor tissue at low concentrations, whilst also inhibiting evoked detrusor contractions at higher concentrations.     

Beta3-adrenoceptors in urinary bladder

The beta-adrenoceptor (AR) is currently classified into beta(1), beta(2), and beta(3) subtypes. A third subtype, beta(3)-AR, was first identified in adipose tissue, but has also been identified in smooth muscle tissue, particularly in the gastrointestinal tract and urinary bladder smooth muscle. There is a predominant expression of beta(3)-AR messenger RNA (mRNA) in human bladder, with 97% of total beta-AR mRNA being represented by the beta(3)-AR subtype and only 1.5 and 1.4% by the beta(1)-AR and beta (2)-AR subtypes, respectively. Moreover, the presence of beta(1)-, beta(2)-, and beta(3)-AR mRNAs in the urothelium of human bladder has been identified. The distribution of beta-AR subtypes mediating detrusor muscle relaxation is species dependent, the predominant subtype being the beta(3)-AR in humans. Recent studies have suggested that cAMP-dependent routes are not exclusive mechanisms triggering the beta-AR-mediated relaxation of smooth muscle. It has been demonstrated in rats detrusor muscle that cAMP plays a greater role in beta-adrenergic relaxation against basal tone than against KCl-induced tone and that conversely calcium-activated K(+) channels (BKca channels) play a greater role under the latter circumstances. In rat models, beta(3)-AR agonists increase bladder capacity without influencing bladder contraction and have only weak cardiovascular side effects. Although this evidence points toward the clinical utility of beta(3)-AR agonists as therapy for overactive bladder (OAB), pharmacological differences exist between rat and human beta(3)-ARs. Development of compounds with high selectivity for the human beta(3)-AR, identified by screening techniques using cell lines transfected with the human beta(1)-, beta(2)-, and beta(3)-AR genes, may mitigate against such problems. The association between the tryptophan 64 arginine polymorphism in the beta(3)-AR gene and idiopathic OAB is discussed.     

Effects of intravenous and infravesical administration of suramin,terazosin and BMY 7378 on bladder instability in conscious rats with bladder outlet obstruction

OBJECTIVE: To evaluate the effect of the nonselective purinergic antagonist suramin and the alpha1-adrenergic antagonists, terazosin and BMY 7378, given intravenously or infused directly into the bladder during cystometry in conscious rats with bladder outlet obstruction induced by urethral ligation. MATERIALS AND METHODS: Cystometry was performed in conscious female rats recording bladder volume capacity (BVC), evaluated as the amount of saline infused between two voiding cycles, and micturition volume (MV). Changes in frequency and amplitude of spontaneous non-voiding bladder contractions (NVC) were also recorded. The effects of the intravenous administration of suramin (100 mg/kg), BMY 7378 (1 mg/kg), and terazosin (0.3 mg/kg) on NVC, BVC and MV were evaluated in obstructed rats with bladder infusion of saline. The effects of infravesical infusion of suramin (3-10 micromol/L), terazosin (1 micromol/L) and BMY 7378 (10 micromol/L) were also evaluated and compared with values observed in control rats during saline infusion into the bladder. RESULTS: Intravenous injection with suramin had no effects on NVC, BVC and MV, but suramin infused into the bladder induced a consistent reduction in the amplitude of NVC (significantly different from matched control animals) with a tendency to reduce their frequency. BVC and MV were slightly but significantly decreased by infravesical infusion of suramin. In contrast, BMY 7378 and terazosin, given intravenously, were extremely potent at inhibiting the frequency and amplitude of the NVC, but were inactive on NVC when infused into bladder. CONCLUSIONS: These findings confirm a role for alpha1-adrenergic receptors in bladder instability caused by bladder outlet obstruction. In addition, a purinergic neurotransmitter, presumably ATP, is shown to be involved.     

Effects of selective beta2 and beta3-adrenoceptor agonists on detrusor hyperreflexia in conscious cerebral infarcted rats

PURPOSE: We evaluated the effects of beta-adrenoceptor agonists on detrusor hyperreflexia in cerebral infarcted rats. MATERIALS AND METHODS: To produce cerebral infarction in Sprague-Dawley rats the left middle cerebral artery was occluded by introducing a monofilament nylon thread into the artery. In sham operated rats the same artery was exposed but not occluded. After these operations cystometric and cardiovascular experiments were performed with no anesthesia or restraint. RESULTS: After the operation bladder capacity was significantly decreased and voiding pressure was significantly increased in cerebral infarcted but not in sham operated animals. The difference in cerebral infarcted and sham operated rats was significant for each parameter (p <0.01). Post-void residual urine volume was not affected in either group. In the cerebral infarction group intravenous administration of CL316243 ([R,R]-5-2-[[2-(3-chlorophenyl-2-hydroxyethyl]-amino]propyl] -1,3-benzodioxole-2,2-dicarboxylate) (Kissei Central Laboratories, Hotaka, Japan) a selective beta3-adrenoceptor agonist, significantly increased bladder capacity at 10 and 100 microgram./kg. without affecting voiding pressure or post-void residual urine volume. Procaterol, a selective beta2-adrenoceptor agonist, significantly increased bladder capacity and post-void residual urine volume at 10 microgram/kg. intravenously without affecting voiding pressure. In separate experiments procaterol (1 to 100 microgram./kg. intravenously) decreased mean blood pressure and increased heart rate in a dose dependent manner. In contrast, the effects of CL316243 (0.1 to 100 microgram./kg. intravenously) on mean blood pressure and heart rate were minimal. CONCLUSIONS: These results indicate that in cerebral infarcted rats detrusor hyperreflexia can be suppressed by the selective beta3-adrenoceptor agonist CL316243 without increasing post-void residual volume and without significant cardiovascular side effects. If the current results hold true in humans, selective beta3-adrenoceptor agonists may prove useful for treating detrusor hyperreflexia associated with cerebral infarction.     

The restorative effect of a selective cyclooxygenase-2 inhibitor on urothelial cell-cell interactions after partial bladder outlet obstruction in rats

OBJECTIVE: To determine the changes in cyclooxygenase-2 (COX-2), E-cadherin and alpha-catenin expression after partial bladder outlet obstruction (PBOO), and whether a selective COX-2 inhibitor (celecoxib) might inhibit COX-2 expression and have beneficial effects on urothelial cell-to-cell interactions in rats subjected to PBOO. MATERIALS AND METHODS: Thirty-six male rats were divided into six equal groups; celecoxib was administered after creating PBOO for 1 and 4 weeks in groups 1 and 2, respectively. Two further obstructed groups (3 and 4, PBOO for 1 and 4 weeks, respectively) received no treatment. Sham-operated animals served as controls (group 5 and 6, assessed at 1 and 4 weeks, respectively). After 1 and 4 weeks of PBOO or a sham procedure the bladder weight was recorded before sampling the bladder for Western blotting and immunohistological analysis, to assess the expressions of COX-2 and adherens proteins, E-cadherin and alpha-catenin. Urothelial cell-to-cell interactions were evaluated using electron microscopy. RESULTS: The bladder mass increased rapidly during the first 7 days after PBOO in groups 1-4 compared with 5 and 6 (P < 0.05). While the bladder mass then continued to increase for the next 21 days in group 4, it was constant in group 2 (P < 0.001). Immunohistochemical staining and Western blotting analyses showed that E-cadherin and alpha-catenin expression were reversibly decreased in rats with PBOO, while COX-2 protein expression was up-regulated. After giving celecoxib there was a significant decrease in COX-2 expression and a restoration of intercellular adherens junctions and desmosomes, as assessed on electron microscopy and expression of adherens proteins combined. CONCLUSION: The increase in COX-2 expression attributable to hypoxia and the tensile strength of bladder wall was attenuated by celecoxib. Selective COX-2 inhibitors have important restorative effects on intercellular adherens junctions and desmosomes in PBOO.     

Role of beta-adrenoceptor subtypes in mediating relaxation of the pig bladder trigonal muscle in vitro

AIMS: To investigate the role of beta-adrenoceptor subtypes in mediating relaxation of the pig bladder trigonal muscle in vitro. MATERIALS AND METHODS: Longitudinal strips of trigonal muscle were isolated, and the mucosa and serosa removed. Tissues were precontracted with KCl, and beta-adrenoceptor agonists (isoprenaline or salbutamol) were added cumulatively, and concentration-relaxation curves (CRCs) were obtained. CRCs to agonists were obtained in the absence and presence of antagonists and antagonist affinity values were calculated. RESULTS: Isoprenaline (non-selective beta-agonist) relaxed with high potency (pEC(50) = 7.2). Propranolol antagonized CRCs to isoprenaline with a high affinity (apparent pK(B) = 8.8), but the Schild plot had a slope significantly (P < 0.01) less than unity (0.61), suggesting that responses were mediated by more than one beta-adrenoceptor subtype. CGP20712A (beta(1)-antagonist) antagonized responses to isoprenaline with a low affinity (apparent pK(B) = 5.13), indicating beta(1)-adrenoceptors did not participate in the response. The affinity of ICI118551 (beta(2)-antagonist) for antagonism of responses to isoprenaline was also relatively low (apparent pK(B) = 6.9), and the Schild slopes were significantly (P < 0.01) less than unity (0.58). SR59230A (beta(3)-antagonist) antagonized CRCs to isoprenaline with a relatively low affinity (apparent pK(B) = 7.5), and with a Schild slope significantly (P < 0.01) less than unity (0.86), indicating that responses may be mediated by more than one beta-adrenoceptor subtype. In contrast to that observed with isoprenaline, the beta(2)-adrenoceptor selective agonist salbutamol induced relaxation with a relatively low potency (pEC(50) = 6.6) and with maximum responses of 80% of that to isoprenaline. ICI118551 competitively antagonized (Schild plot of unity) responses to salbutamol with a high affinity (pA2 = 8.3). CONCLUSIONS: These data suggest that beta-adrenoceptor mediated responses to isoprenaline of the bladder trigone are mediated via both the beta(2)- and beta(3)-adrenoceptor subtypes whilst responses to salbutamol appear to be mediated only via the beta(2)-adrenoceptor.     

Patient‐reported outcomes with the β3‐adrenoceptor agonist mirabegron in a phase III trial in patients with overactive bladder

Aims

To assess patient‐reported outcomes (PROs) in patients with overactive bladder (OAB) receiving the novel β₃‐adrenoceptor agonist mirabegron.

Methods

Data from a randomised, double‐blind, controlled phase III trial in 1,987 patients aged ≥18 years with OAB symptoms for ≥3 months were analysed. Patients received placebo, mirabegron 50 or 100 mg/day, or tolterodine extended release (ER) 4 mg orally once daily for 12 weeks after a 2‐week placebo run‐in. Prespecified analysis of PROs (changes in OAB Questionnaire [OAB‐q], Patient Perception of Bladder Condition [PPBC], and Work Productivity and Activity Impairment: Specific Health Problem [WPAI‐SHP] instrument) in patients treated with mirabegron 50 mg/day, tolterodine ER 4 mg/day or placebo is reported. Post‐hoc analyses of OAB‐q, PPBC and the Treatment Satisfaction‐Visual Analogue Scale (TS‐VAS) in patients who were incontinent at baseline are also reported.

Results

Significant improvements over placebo in OAB‐q coping and concern from baseline to final visit were observed with mirabegron 50 mg/day. No significant improvements in these parameters were observed with tolterodine ER 4 mg/day. Mirabegron 50 mg/day significantly increased the proportion of patients showing a PPBC improvement over placebo. Mirabegron 50 mg/day also produced greater improvements in WPAI‐SHP presenteeism and greater reductions in absenteeism and overall work impairment than placebo or tolterodine ER 4 mg/day. The impact of mirabegron 50 mg/day treatment on PROs in the incontinent population appears to be greater than that in the overall OAB population.

Conclusions

At the approved dose of 50 mg/day, mirabegron significantly improves OAB patients' perception of disease and quality of life, independent of whether they are incontinent at baseline. Neurourol. Urodynam. 35:987–994, 2016. © 2015 The Authors. Neurourology and Urodynamics published by Wiley Periodicals, Inc.