On the mode of action of mirabegron

Unveiling the protective potential of mirabegron against thioacetamide-induced hepatic encephalopathy in rats: Insights into cAMP/PPAR-γ/p-ERK1/2/p S536 NF-κB p 65 and p-CREB/BDNF/TrkB in parallel with oxidative and apoptotic trajectories

Hepatic encephalopathy (HE) is one of the most prevalent and severe hepatic and brain disorders in which escalation of the oxidative, inflammatory and apoptotic trajectories pathologically connects acute liver injury with neurological impairment. Mirabegron (Mira) is a beta3 adrenergic receptor agonist with proven antioxidant and anti-inflammatory activities. The current research pointed to exploring Mira's hepato-and neuroprotective impacts against thioacetamide (TAA)-induced HE in rats. Rats were distributed into three experimental groups: the normal control group, the TAA group, received TAA (200 mg/kg/day for three consecutive days) and the Mira-treated group received Mira (10 mg/kg/day; oral gavage) for 15 consecutive days and intoxicated with TAA from the 13th to the 15th day of the experimental period. Mira counteracted hyperammonemia, enhanced rats' locomotor capability and motor coordination. It attenuated hepatic/neurological injuries by its antioxidant, anti-apoptotic as well as anti-inflammatory potentials. Mira predominantly targeted cyclic adenosine monophosphate (cAMP)/phosphorylated extracellular signal-regulated kinase (p-Erk1/2)/peroxisome proliferator-activated receptor gamma (PPARγ) dependent pathways via downregulation of p S536-nuclear factor kappa B p65 (p S536 NF-κB p 65)/tumor necrosis alpha (TNF-α) axis. Meanwhile, it attenuated nuclear factor erythroid 2-related factor (Nrf2) depletion in parallel with restoring of the neuroprotective defensive pathway by upregulation of cerebral cAMP/PPAR-γ/p-ERK1/2 and p-CREB/BDNF/TrkB besides reduction of GFAP immunoreactivity. Mira showed anti-apoptotic activity through inhibition of Bax immunoreactivity and elevation of Bcl2. To summarize, Mira exhibited a hepato-and neuroprotective effect against TAA-induced HE in rats via shielding antioxidant defense and mitigation of the pathological inflammatory and apoptotic axis besides upregulation of neuroprotective signaling pathways.

Mirabegron improves the irritative symptoms caused by BCG immunotherapy after transurethral resection of bladder tumors

BACKGROUND

This study aims to explore the efficacy and safety of mirabegron in treating irritative symptoms induced by intravesical immunotherapy with Bacillus Calmette-Guerin (BCG) after transurethral resection of bladder tumors (TURBT).

METHODS

A total of 160 patients subjected to TURBT was randomly divided into the mirabegron group and placebo group with 80 patients in each group. Then, the patients were administered 25 mg mirabegron or placebo daily, starting the first day after BCG infusion. The first BCG perfusion was conducted at least 2 weeks after TURBT. The 3-day bladder diaries were completed in all patients, 1 day before BCG perfusion, and on the 1st, 6th, and 13th days after the first BCG perfusion. Overactive bladder symptom scores were completed 1 day before BCG perfusion, and on the 6th and 13th days after the first BCG perfusion.

RESULTS

Symptom scores of bladder hyperactivity were significantly different between the two groups (p < 0.001). Also, the frequency of nocturia, pollakiuria, micturition urgency, urinary incontinence and was significantly lower in group 1 than that in group two (p < 0.05).

CONCLUSION

Our findings demonstrate that mirabegron is a valuable clinical drug for the management of irritative symptoms after TURBT with subsequent intravesical BCG perfusion.

Efficacy and tolerability of mirabegron in female patients with overactive bladder symptoms after surgical treatment for stress urinary incontinence

PURPOSE

To evaluate the efficacy and tolerability of mirabegron in females with overactive bladder (OAB) symptoms after surgical treatment for stress urinary incontinence (SUI).

MATERIALS AND METHODS

The study was conducted with a prospective, randomized and double-blinded design. 62 patients over the age of 40 who met the inclusion-exclusion criterias of the study were enrolled and randomly divided into two groups as Group A (mirabegron 50mg) and B (solifenacin 5mg). Patients were compared based on efficacy of treatment [Patient Perception of Bladder Condition (PPBC) scale and micturition diaries], safety of treatment (heart rate, systolic and diastolic blood pressure, adverse events), number of micturitions per day, patient's satisfaction status after treatment [Visual Analog Scale(VAS)] and quality of life.

RESULTS

The mean age of the population was 48.2±3.8 years and the duration of OAB symptoms was 5.9±2.9 months. Baseline values for the mean number of micturitions, volume voided in each micturition, nocturia episodes, urgency and urgency incontinence episodes were 15.3±0.34, 128±3.88mL, 3.96±1.67, 5.72±1.35 and 4.22±0.69, respectively. After treatment, values for these parameters were 11.7±0.29, 164.7±2.9mL, 2.25±0.6, 3.38±0.71, 2.31±0.49 respectively. Quality of life score, symptom bother score, VAS for treatment satisfaction score, PPBC score after treatment were 66.1±0.85, 43.7±0.77, 4.78±0.14, 4.78±0.14, respectively. There were no significant differences between two groups on any parameter. However, mirabegron showed better tolerability than solifenacin, particularly after 6 months.

CONCLUSION

Mirabegron is safe, effective and tolerable in the long-term treatment of females with OAB symptoms after surgery for stress urinary incontinence.

Mirabegron: potential off target effects and uses beyond the bladder

The β₃ -adrenoceptor was initially an attractive target for several pharmaceutical companies due to its high expression in rodent adipose tissue, where its activation resulted in decreased adiposity and improved metabolic outputs (such as glucose handling) in animal models of obesity and Type 2 diabetes. However, several drugs acting at the β₃ -adrenoceptor failed in clinical trials. This was thought to be due to their lack of efficacy at the human receptor. Recently, mirabegron, a β₃ -adrenoceptor agonist with human efficacy, was approved in North America, Europe, Japan and Australia for the treatment of overactive bladder syndrome. There are indications that mirabegron may act at other receptors/targets, but whether they have any clinical relevance is relatively unknown. Besides overactive bladder syndrome, mirabegron may have other uses such as in the treatment of heart failure or metabolic disease. This review gives an overview of the off-target effects of mirabegron and its potential use in the treatment of other diseases.

LINKED ARTICLES

This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc.

Recent advances in pharmacological management of urinary incontinence

Lower urinary tract symptoms-in particular, storage disorders (for example, urinary incontinence) as well as bladder underactivity-are major health-related problems that increase with age. Yet lower urinary tract symptoms remain under-diagnosed and poorly managed, and incontinence has been cited as the major reason for institutionalization in elderly populations and is one of the most common conditions in primary care practice. Although lifestyle and behavior therapy has been used as a useful treatment regimen for urge incontinence, medications (often used as adjunct) can provide additional benefit. This review will include current therapies used for treatment of urinary incontinence.

No. 353-Treatments for Overactive Bladder: Focus on Pharmacotherapy - An Addendum

OBJECTIVE

This technical update addendum reviews success rates and comparative evidence of the anticholinergic fesoterodine, as well as mechanism of action, safety profile, success rates, and comparative evidence of the β3 agonist mirabegron in the treatment of non-neurogenic overactive bladder syndrome (OAB). This adds to OAB pharmacotherapy recommendations initially published in 2012.

INTENDED USERS

Residents and other trainees, primary care practitioners, gynaecologists, urologists, urogynaecologists, and other health care providers who assess, counsel, and treat women with OAB.

TARGET POPULATION

Adult women with symptomatic OAB.

OPTIONS

This addition relates to fesoterodine, mirabegron, and anticholinergic-β3 agonist combination pharmacotherapy.

OUTCOMES

The outcomes of interest are clinical efficacy of fesoterodine compared with no treatment or other OAB therapies; mechanism of action and safety profile of mirabegron, clinical efficacy of mirabegron compared to no treatment or other OAB therapies; clinical efficacy of anticholinergic-β3 agonist combination pharmacotherapy for OAB.

EVIDENCE

PubMed, Medline, and the Cochrane Database were searched using the key words "fesoterodine" and "mirabegron." Results were restricted to English or French and human clinical and pharmacological research. Animal research and clinical studies including only male participants were excluded. Articles were included until the end of December 2016. Grey literature was not searched. Clinical practice guidelines, guidelines of specialty societies, and systematic reviews were included. RCTs and observational studies were included when evidence for the outcome of interest or in the target population was not available from systematic reviews. New studies not yet included in systematic reviews were also included. References of included articles were also searched to ensure comprehensive inclusion of relevant literature.

VALUES

The content and recommendations were drafted and agreed upon by the principal author, as well as members of the Urogynaecology Committee. The Board of the SOGC approved the final draft for publication. The quality of evidence was rated using the criteria described in the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology framework. The Summary of Findings is available upon request.

BENEFITS, HARMS, AND/OR COSTS

It is expected that this technical update will benefit patients with OAB by providing physicians and other interested health care providers with additional options for and knowledge of safe and effective OAB pharmacotherapy. The benefits clearly outweigh the potential harms or costs of implementation of this technical update, although there are no direct harms or costs identified. UPDATES: "Evidence will be reviewed 5 years after publication to decide whether all or part of the document should be updated. However, if important new evidence is published prior to the 5-year cycle, the review process may be accelerated for a more rapid update of some recommendations."

SPONSORS

Not applicable.

RECOMMENDATIONS

An Exploratory Study in Healthy Male Subjects of the Mechanism of Mirabegron-Induced Cardiovascular Effects

To explore the role of β₁ -adrenoceptors (ARs) in the heart rate response to the selective β₃ -adrenoceptor agonist mirabegron, 12 young male volunteers received single oral doses of the nonselective β_1/2 -AR antagonist propranolol (160 mg), the selective β₁ -AR antagonist bisoprolol (10 mg), or placebo on days 1 and 5 of each period in a 3-period crossover study. On day 5, dosing was followed by a supratherapeutic dose of mirabegron (200 mg). Vital signs, impedance cardiography, and plasma renin activity were collected. Mirabegron increased heart rate and systolic blood pressure and reduced stroke volume, whereas cardiac output and diastolic blood pressure were unaffected. Mirabegron-induced changes were attenuated by propranolol and bisoprolol. The data indicate that mirabegron has a positive chronotropic effect at supratherapeutic concentrations, which is at least partly mediated by stimulation of β₁ -AR.

Inhibition of cholinergic neurotransmission by β3-adrenoceptors depends on adenosine release and A1-receptor activation in human and rat urinary bladders

The direct detrusor relaxant effect of β₃-adrenoceptor agonists as a primary mechanism to improve overactive bladder symptoms has been questioned. Among other targets, activation of β₃-adrenoceptors downmodulate nerve-evoked acetylcholine (ACh) release, but there is insufficient evidence for the presence of these receptors on bladder cholinergic nerve terminals. Our hypothesis is that adenosine formed from the catabolism of cyclic AMP in the detrusor may act as a retrograde messenger via prejunctional A₁ receptors to explain inhibition of cholinergic activity by β₃-adrenoceptors. Isoprenaline (1 µM) decreased [³H]ACh release from stimulated (10 Hz, 200 pulses) human (-47 ± 5%) and rat (-38 ± 1%) detrusor strips. Mirabegron (0.1 µM, -53 ± 8%) and CL316,243 (1 µM, -37 ± 7%) mimicked isoprenaline (1 µM) inhibition, and their effects were prevented by blocking β₃-adrenoceptors with L748,337 (30 nM) and SR59230A (100 nM), respectively, in human and rat detrusor. Mirabegron and isoprenaline increased extracellular adenosine in the detrusor. Blockage of A₁ receptors with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 100 nM) or the equilibrative nucleoside transporters (ENT) with dipyridamole (0.5 µM) prevented mirabegron and isoprenaline inhibitory effects. Dipyridamole prevented isoprenaline-induced adenosine outflow from the rat detrusor, and this effect was mimicked by the ENT1 inhibitor, S-(4-nitrobenzyl)-6-thioinosine (NBTI, 30 µM). Cystometry recordings in anesthetized rats demonstrated that SR59230A, DPCPX, dipyridamole, and NBTI reversed the decrease in the voiding frequency caused by isoprenaline (0.1-1,000 nM). Data suggest that inhibition of cholinergic neurotransmission by β₃-adrenoceptors results from adenosine release via equilibrative nucleoside transporters and prejunctional A₁-receptor stimulation in human and rat urinary bladder.

On the Site and Mechanism of Action of β3-Adrenoceptor Agonists in the Bladder

The clinical success of mirabegron as the first β₃-adrenoceptor (AR) agonist for treatment of the overactive bladder (OAB) syndrome, has resulted in substantial interest in its site and mechanism of action. Even if the adrenergic innervation of the bladder and urethra has been well studied, the location(s) of β₃-ARs in different structures within the bladder wall and urethra, and the mode(s) of action of β₃-AR stimulation have still not been established. The recent demonstration of β₃-ARs on cholinergic nerve terminals with no immunoreactivity in urothelium or detrusor smooth muscle, is not in agreement with previous morphological studies, and functional data strongly suggest that β₃-ARs can be found these structures. However, recent studies suggest that the β₃-ARs on detrusor smooth muscle may not be the functionally most relevant. The assumption that β₃-AR activation during bladder filling inhibits acetylcholine release from parasympathetic neurons by a prejunctional mechanism and that this decreases bladder micromotions that generate afferent activity, is an attractive hypothesis. It does not exclude that other mechanisms may be contributing, and supports combined approaches to reduce afferent activity for treatment of the OAB syndrome.