Mirabegron 25 mg Monotherapy Is Safe but Less Effective in Male Patients With Overactive Bladder and Bladder Outlet Obstruction

Ligand-Receptor Interactions and Structure-Function Relationships in Off-Target Binding of the β3-Adrenergic Agonist Mirabegron to α1A-Adrenergic Receptors

The β3-adrenoceptor agonist mirabegron is available for the treatment of storage symptoms of overactive bladder, including frequency, urgency, and incontinence. The off-target effects of mirabegron include binding to α1-adrenoceptors, which are central in the treatment of voiding symptoms. Here, we examined the structure-function relationships in the binding of mirabegron to a cryo-electron microscopy structure of α1A. The binding was simulated by docking mirabegron to a 3D structure of a human α1A-adrenoceptor (7YMH) using Autodock Vina. The simulations identified two binding states: slope orientation involving 10 positions and horizontal binding to the receptor surface involving 4 positions. No interactions occurred with positions constituting the α1A binding pocket, including Asp-106, Ser-188, or Phe-312, despite the positioning of the phenylethanolamine moiety in transmembrane regions close to the binding pocket by contact with Phe-288, -289, and Val-107. Contact with the unique positions of α1A included the transmembrane Met-292 during slope binding and exosite Phe-86 during horizontal binding. Exosite binding in slope orientation involved contact of the anilino part, rather than the aminothiazol end, to Ile-178, Ala-103, and Asn-179. In conclusion, contact with Met-292 and Phe-86, which are unique positions of α1A, accounts for mirabegron binding to α1A. Because of its lack of interactions with the binding pocket, mirabegron has lower affinity compared to α1A-blockers and no effects on voiding symptoms.

Adrenoceptors in the Lower Urinary Tract

Adrenoceptors importantly contribute to the physiological regulation of lower urinary tract (LUT) function and have become a target of several clinically successful treatments for major LUT diseases. In the bladder dome, β-adrenoceptor subtypes are found in multiple cell types and mediate relaxation of detrusor smooth muscle, perhaps partly indirectly by acting on afferent nerves and cells of the mucosa. β3-adrenoceptor agonists such as mirabegron and vibegron are used to treat overactive bladder syndrome. In the bladder trigone and urethra, α1-adrenoceptors cause contraction and thereby physiologically contribute to bladder outlet resistance. α1-adrenoceptors in the prostate also cause contraction and pathophysiologically elevate bladder outlet resistance leading to voiding dysfunction in benign prostatic hyperplasia. α1-adrenoceptor antagonist such as tamsulosin is widely used as a first-line option to treat LUT symptoms in men, but it remains unclear to which extent and how smooth muscle relaxation contributes to symptom relief.

Treatment Algorithm for Management of Benign Prostatic Obstruction: An Overview of Current Techniques

The management of benign prostatic obstruction (BPO) should involve a treatment algorithm that takes into account prostate size, and patient's symptoms and preference with the aim of helping with urinary symptoms and enhance quality of life. The diagnostic assessment for men with lower urinary tract symptoms (LUTS) should be comprehensive to help choose the best management strategy. Strategies from lifestyle modifications to medical treatment with alpha blockers and/or 5-alpha-reductase inhibitors to surgical procedures can all be used in the management algorithm. Surgical management ranges from transurethral resection of prostate (TURP) to minimally invasive surgical therapies (MIST) including laser therapies such as Holmium laser enucleation (HoLEP) and photoselective vaporisation (PVP), aquablation, Rezūm system, prostate artery embolisation (PAE), prostatic urethral lift (PUL), temporary implantable nitinol device (iTind) and Optilume BPH catheter system. BPO is a common urological condition that has a significant impact on quality of life and economic burden globally and is likely to become increasingly prevalent with an ageing population. Selecting the most appropriate treatment modality will depend on the individual patient preferences, availability of resources, cost, anatomical factors and the goals of treatment.

Current optimal pharmacologic therapies for overactive bladder

INTRODUCTION

Overactive bladder (OAB) is a common syndrome in adults. Current pharmacologic treatment includes antimuscarinic agents and β-3 adrenoceptor agonists. For non-responders to oral medication, intravesical injection of botulinum toxin A (BoNT-A) is an effective option. However, these treatments have potential adverse events and should be cautiously selected for appropriate patients. This review presents the recently published results of clinical trials and studies for patients with OAB and the underlying pathophysiology of OAB. Appropriate medical therapy based on pathophysiology of OAB is also presented.

AREAS COVERED

Literature search from Pubmed from 2001 to 2023 including clinical background, pharmacology, and clinical studies for OAB medications.

EXPERT OPINION

Treatment of OAB syndrome with any antimuscarinic or β-3 adrenoceptor agonist is feasible as a first-line approach. For patients with suboptimal therapeutic effect to full-dose antimuscarinics or mirabegron, combination with both drugs can improve efficacy. Intravesical BoNT-A 100-U injection provides therapeutic effects for refractory OAB. Patients who are refractory to initial pharmacotherapies should be investigated for the underlying pathophysiology; then an appropriate medication can be added, such as an α1-blocker or anti-inflammatory agents. Patient education about behavioral modification and therapies should always be provided with oral medication or BoNT-A injection for OAB patients.

Treating LUTS in Men with Benign Prostatic Obstruction: A Review Article

Benign prostatic obstruction (BPO) is a prevalent condition that affects men, primarily toward their old age. The condition is often accompanied by lower urinary tract symptoms (LUTS), which can significantly impair a patient's quality of life and lead to other medical complications. Accurate diagnosis of BPO is essential for effective management of complications secondary to BPO, and treatment plans should be tailored patients, and occasionally according to surgeon experience. As such, this literature review aims to analyze the current available data on male LUTS secondary to BPO by providing a comprehensive overview of relevant studies, as well as the surgical and medical management guidelines from the Canadian Urological Association (CUA), American Urological Association (AUA), and European Association of Urology (EAU). By synthesizing the existing literature, this review purports to summarize the current body of knowledge surrounding BPO and male LUTS, and support healthcare providers in making informed decisions about the management of male LUTS secondary to BPO, ultimately improving patient outcomes and quality of life.

Molecular and Morphological Characteristics of the De-Obstructed Rat Urinary Bladder—An Update

Many patients with outlet obstruction secondary to prostatic enlargement have lower urinary tract symptoms (LUTSs) and an increased frequency of micturition. The standard treatment is transurethral resection of the prostate (TURP), which alleviates obstruction and symptoms. However, after TURP, 20–40 percent of patients continue to experience LUTSs. The aim of the present study in rats was to identify the mechanisms that do not normalize after the removal of the obstruction and that could explain the persisting symptoms. We had microarray data from control, obstructed, and de-obstructed female rat bladders, which made it possible to study 14,553 mRNA expressions. We also had a bank of electron micrographs from similar detrusors. Microarrays: There were significant differences between the control and obstructed bladders for 1111 mRNAs. The obstructed and de-obstructed bladders differed significantly for 1059 mRNAs. The controls and the de-obstructed bladders differed significantly for 798 mRNAs. We observed many mRNAs that were increased in the obstructed bladder and then decreased to control levels after de-obstruction, and many mRNAs that were decreased in the obstructed bladder and then increased following de-obstruction. mRNAs that were significantly higher or lower in the de-obstructed bladder than in the control bladder were also found. Ultrastructure: The detrusor cells in the obstructed bladders had cross-sectional areas that were much larger than those in the controls. The control cells had smooth outlines and similar cross-sectional areas. The de-obstructed detrusor cells had larger cross-sectional areas than the controls, as well as corrugated surfaces. The cell areas varied, suggesting that the shrinkage of the de-obstructed cells was not even. We did not find any points of contact of the gap junction plaque type between the detrusor cells. There were abundant finger-like processes between the detrusor cells in the obstructed and in de-obstructed bladders, which were only occasionally found in the control detrusors. They are the only possible localization for gap junction channels. The de-obstructed rat bladder is not an organ with properties intermediate between those of the control and obstructed bladders. Instead, de-obstructed bladders have gene expressions, morphologies, and functional properties of the individual cells and their organization, which make them distinctly different from both control and obstructed bladders.

Chapter 4: Treatment of overactive bladder in men: Is it really different?

INTRODUCTION

Overactive bladder (OAB) in men is a topic that is gaining increasing attention as there is a wider understanding that OAB is not a female condition. There are several treatments; however, data in male populations are lacking compared to female cohorts. The high likelihood of concomitant benign prostatic hyperplasia (BPH) and benign prostatic obstruction (BPO) adds to the complexity of the treatment algorithm. The overlap in urinary storage symptoms also makes the interpretation of the literature challenging.

METHODS

Articles that evaluated men with OAB and men with OAB and BPH/BPO were evaluated and assessed.

RESULTS

Behavioral interventions can offer a significant benefit to male patients with OAB. Medical therapies that have been studied in men with OAB include anticholinergics, beta-3 agonists, and phosphodiesterase-5 inhibits. These agents can be offered in addition to alpha-blockers for men with coexisting BPH/BPO. The literature on Onabotulinumtoxin-A and neuromodulation modulation in the male population is growing and shows promising results.

CONCLUSION

Male OAB is complex; however, there is a growing body of literature to help guide treatments. Many treatments are available and they have shown considerable success.

Antagonism of α1-adrenoceptors by β3-adrenergic agonists: Structure-function relations of different agonists in prostate smooth muscle contraction

Effects of β₃-adrenergic agonists on prostate smooth muscle contraction are poorly characterized, although mirabegron is used for treatment of lower urinary tract symptoms. Off-target effects of several β₃-adrenergic agonists include antagonism of α₁-adrenoceptors. Proposed, but unconfirmed explanations include phenylethanolamine backbones, found in some β₃-adrenergic agonists and imparting interaction with catecholamine binding pockets of adrenoceptors. Here, we examined effects of β₃-adrenergic agonists on contractions of human prostate tissues, including ZD7114 (without phenylethanolamine moiety), ZD2079 (phenylethanolamine backbone), BRL37344 and CL316243 (chloride-substituted phenylethanolamine deriatives). Prostate tissues were obtained from radical prostatectomy. Contractions by α₁-adrenergic agonists and electric field stimulation (EFS) were studied in an organ bath. ZD7114 (10 µM) right-shifted concentration responses curves for α₁-adrenergic agonists, resulting in increased EC₅₀ values for phenylephrine, methoxamine and noradrenaline up to one magnitude, without affecting E_max values. ZD7114 (10 µM) inhibited EFS-induced contractions, resulting in reduced E_max values. All effects of ZD7114 were resistant to the β₃-adrenergic antagonist L-748337, including increases in EC₅₀ values for α₁-adrenergic agonists, up to more than two magnitudes. Using 10 µM, neither ZD2079, BRL37344 or CL316243 affected α₁-adrenergic or EFS-induced contractions. At escalated concentrations, BRL37344 (200 µM) right-shifted concentration response curves for phenylephrine, increased EC₅₀ values for phenylephrine, and inhibited EFS-induced contractions, while CL316243 (300 µM) did not affect phenylephrine- or EFS-induced contractions. In conclusion, phenylethanolamine backbones are not decisive to impart α₁-adrenoceptor antagonism to β₃-agonists. Effects of β₃-adrenergic agonists on prostate smooth muscle contraction are limited to off-target effects, including α₁-adrenoceptor antagonism by ZD7114 and BRL37344.

Concentration-dependent alpha1-Adrenoceptor Antagonism and Inhibition of Neurogenic Smooth Muscle Contraction by Mirabegron in the Human Prostate

Introduction: Mirabegron is available for treatment of storage symptoms in overactive bladder, which may be improved by β₃-adrenoceptor-induced bladder smooth muscle relaxation. In addition to storage symptoms, lower urinary tract symptoms in men include obstructive symptoms attributed to benign prostatic hyperplasia, caused by increased prostate smooth muscle tone and prostate enlargement. In contrast to the bladder and storage symptoms, effects of mirabegron on prostate smooth muscle contraction and obstructive symptoms are poorly understood. Evidence from non-human smooth muscle suggested antagonism of α₁-adrenoceptors as an important off-target effect of mirabegron. As α₁-adrenergic contraction is crucial in pathophysiology and medical treatment of obstructive symptoms, we here examined effects of mirabegron on contractions of human prostate tissues and on proliferation of prostate stromal cells.

Methods: Contractions were induced in an organ bath. Effects of mirabegron on proliferation, viability, and cAMP levels in cultured stromal cells were examined by EdU assays, CCK-8 assays and enzyme-linked immunosorbent assay.

Results: Mirabegron in concentrations of 5 and 10 μM, but not 1 µM inhibited electric field stimulation-induced contractions of human prostate tissues. Mirabegron in concentrations of 5 and 10 µM shifted concentration response curves for noradrenaline-, methoxamine- and phenylephrine-induced contractions to the right, including recovery of contractions at high concentrations of α₁-adrenergic agonists, increased EC₅₀ values, but unchanged E_max values. Rightshifts of noradrenaline concentration response curves and inhibition of EFS-induced contractions were resistant to L-748,337, l-NAME, and BPIPP. 1 µM mirabegron was without effect on α₁-adrenergic contractions. Endothelin-1- and U46619-induced contractions were not affected or only inhibited to neglectable extent. Effects of mirabegron (0.5–10 µM) on proliferation and viability of stromal cells were neglectable or small, reaching maximum decreases of 8% in proliferation assays and 17% in viability assays. Mirabegron did not induce detectable increases of cAMP levels in cultured stromal cells.

Conclusion: Mirabegron inhibits neurogenic and α₁-adrenergic human prostate smooth muscle contractions. This inhibition may be based on antagonism of α₁-adrenoceptors by mirabegron, and does not include activation of β₃-adrenoceptors and requires concentrations ranging 50-100fold higher than plasma concentrations reported from normal dosing. Non-adrenergic contractions and proliferation of prostate stromal cells are not inhibited by mirabegron.

Efficacy and Safety of Mirabegron in Men with Overactive Bladder Symptoms and Benign Prostatic Hyperplasia

PURPOSE OF REVIEW

To review the efficacy and safety of mirabegron in men with overactive bladder (OAB) and benign prostatic hyperplasia (BPH).

RECENT FINDINGS

Numerous studies have shown mirabegron to be efficacious and safe in treating symptoms of OAB. More recent studies evaluating the use of mirabegron in men with OAB and BPH have also shown the medication to be effective with few adverse side effects when used as monotherapy or in combination therapy. Mirabegron is an effective and safe treatment for men with OAB and BPH.

Beyond Antimuscarinics: A Review of Pharmacological and Interventional Options for Overactive Bladder Management in Men

CONTEXT

The role of overactive bladder (OAB) treatment in women beyond antimuscarinics has been evaluated extensively. Beta-3 agonists, botulinum toxin-A (BTX-A), and nerve stimulation are indicated in these patients. However, data on male patients in this clinical scenario are scarce.

OBJECTIVE

The aim of this systematic review was to evaluate the evidence on treatment options beyond antimuscarinics in men with OAB.

EVIDENCE ACQUISITION

A search of PubMed, EMBASE, Scopus, Web of science, Cochrane Central Register of Controlled Trials, and Cochrane Central Database of Systematic Reviews databases was performed for relevant articles published between January 2000 and October 2020, using the following Medical Subject Headings: "male/man," "LUTS," "overactive bladder," "storage symptoms," "urgency," "nocturia," "incontinence," "beta-3 agonist," "PDE-5 inhibitors," "botulinum toxin," "sacral nerve stimulation/neurostimulation," "percutaneous/transcutaneous tibial nerve stimulation," "PTENS," and "combination therapy." Evidence acquisition was performed according to Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. PROSPERO registration number is CRD42020201223.

EVIDENCE SYNTHESIS

Overall, 24 studies were retrieved. In male OAB, mirabegron (MIRA) is the most intensively investigated pharmacological option. A pooled analysis of five randomized clinical trials (RCTs), including 1187 patients, concluded that MIRA 50 mg was associated with a greater reduction in frequency versus placebo (-0.37, 95% confidence interval [CI]: -0.74, -0.01, p <  0.05). A pooled analysis of three RCTs, including 1317 male patients, has also shown that the addition of MIRA 50 mg in men receiving the α₁-blocker tamsulosin improved the mean number of micturitions per day (-0.27, 95% CI: -0.46 to -0.09, p <  0.05), urgency episodes (-0.50, 95% CI: -0.77 to -0.22, p <  0.05), total OAB symptom score (-0.66, 95% CI: -1.00 to -0.38, p <  0.05), and mean volume voided (+10.76 ml, 95% CI: 4.87-16.64, p <  0.05). MIRA treatment is well tolerated in men. Other pharmacological treatment options, such as phosphodiesterase-5 (PDE-5) inhibitors, should be considered investigational. BTX-A seems to be effective as third-line treatment in male OAB patients. A higher rate of intermittent self-catheterization (5-42%) is observed in male than in female patients. Data on nerve stimulation are scarce.

CONCLUSIONS

MIRA has the most robust data in terms of safety and efficacy in this patient population. Preliminary data in men suggest that BTX-A is indicated as an interventional treatment. Evidence for PDE-5 inhibitors and nerve stimulation is too limited to provide recommendations. Future studies in this population should aim to better define the best treatment sequence and to identify predictors for treatment response and failure, to determine a therapeutic approach tailored to patients' characteristics.

PATIENT SUMMARY

Overactive bladder is highly prevalent in men. Mirabegron 50 mg is the treatment option supported by the highest level of evidence when antimuscarinics failed. Botulinum toxin A injections seems to be an effective treatment as interventional option. Roles of nerve stimulation and phosphodiesterase inhibitors in male OAB patients are still to be defined.

Intravesical prostatic protrusion does not compromise the therapeutic effects of Mirabegron in male patients with overactive bladder

AIMS

Intravesical prostatic protrusion (IPP) is associated with the degree of benign prostatic obstruction. We evaluated the effects of Mirabegron, a selective β3 adrenoceptor agonist, on overactive bladder (OAB) in male patients with different degrees of IPP.

METHODS

About 185 male patients ≥40 years with lower urinary tract symptoms were recruited from a tertiary referral center. OAB was defined by the overactive bladder symptom score (OABSS) urgency score of ≥2 and sum score of ≥3. IPP was measured in the midsagittal section using transrectal ultrasound and patients were divided into IPP ≤5 mm and IPP >5 mm groups. Outcomes were assessed at the baseline, 4, and 12 weeks.

RESULTS

About 104 patients (56.2%) were diagnosed with OAB and received Mirabegron (50 mg) daily use. Both IPP groups (≤5 and >5 mm) had similar baseline OABSS and International Prostate Symptom Scores (IPSS). Four-week Mirabegron usage was associated with significant decreases in both symptom score measurements, OABSS: IPP ≤5 mm -27.4% and IPP >5 mm -19.7% (P = .419) and IPSS: -32% and -22.5% (P = .202), respectively. Urgency, urge incontinence, and nocturia sub-scores were decreased in both groups, -26.3% and -27.4% (P = .690), 53.3% and 46.2% (P = .916), and 20.8% and 15.4% (P = .958). Effects were maintained at 12 weeks. We found no significant improvement in the frequency sub-score in either group. One patient stopped medication because of intolerable hypertension. Most frequent adverse event was increased residual urine (≥50 mL higher than baseline), IPP ≤5 mm 9.2% and IPP >5 mm 5.1% (P = .707), but no case had acute urinary retention.

CONCLUSIONS

Mirabegron is an effective drug to treat male OAB regardless of IPP grade.

Effect of mirabegron on erectile function in sexually active men with bothersome overactive bladder symptoms

BACKGROUND

To evaluate the change of erectile function (EF) in sexually active male overactive bladder (OAB) patients treated with Mirabegron. Mirabegron, a selective β3 adrenoceptor agonist, approved for the treatment of OAB, has been reported to relax human and rat corpus cavernosum and might have beneficial effect on EF.

METHODS

A total of 128 consecutive men with lower urinary tract symptoms attended urology outpatient clinic were evaluated for OAB and EF. Thirty-four sexually active OAB patients were prospectively enrolled in this study and received mirabegron 50 mg oral once a day. The evaluation of EF and OAB was based on a self-administered questionnaire containing International Index of Erectile Function (IIEF-5) and OAB symptom score (OABSS), respectively. Men with an OABSS urgency score of ≥2 and sum score of ≥3 were considered to have OAB. The therapeutic outcomes were assessed at baseline, 4, and 12 weeks.

RESULTS

Mirabegron usage was associated with a statistically significant improvement of OAB symptoms (OABSS 32.1% decrease) at 4-week follow-up and the therapeutic effects were maintained at 12-week follow-up. Mirabegron usage did not improve EF (IIEF-5 4.9% decrease at 4-week; p = 0.106, and 9.1% decrease at 12-week follow-up; p = 0.077). However, the IIEF-5 was significantly decreased in the higher baseline IIEF-5 (≥17) group (11.7% decrease; p = 0.044), noncoronary artery disease (13.2%; p = 0.007), or non-DM group (13.9% decrease; p = 0.021) at 12-week follow-up.

CONCLUSION

This preliminary study demonstrates that mirabegron treatment of men with OAB improved OAB symptoms, but has no beneficial effect on EF.

Precision medicine in the diagnosis and treatment of male lower urinary tract symptoms suggestive of benign prostatic hyperplasia

Male lower urinary tract symptoms (LUTSs) are highly prevalent in men and the incidence increases with aging. The pathophysiology of male LUTSs might be bladder outlet dysfunctions such as bladder neck (BN) dysfunction, benign prostatic obstruction, and poor relaxation of external sphincter and bladder dysfunctions such as detrusor overactivity (DO), detrusor underactivity, DO, and inadequate contractility. Male LUTSs include voiding and storage symptoms, and precision diagnosis should not be done based on the symptoms alone. Videourodynamic study provides a thorough look at the bladder and bladder outlet and can clearly demonstrate the underlying pathophysiology when the initial medication fails to relieve LUTS. Medical treatment should be given based on the underlying pathophysiology of LUTS, and surgical intervention to remove prostate should only be performed when a definite bladder outlet obstruction due to prostatic obstruction has been confirmed by invasive urodynamic study.

Individualizing medical treatment of overactive bladder

Overactive bladder (OAB) syndrome is highly prevalent in both men and women and might have negative impact on quality of life. Clinical trials of OAB usually highly select participants that may not reflect the real-world practice of OAB patients. The spectrum of OAB includes patients with idiopathic, neuropathic, with bladder outlet obstruction, and patients in elderly and medical comorbidities. Patients might have poor response to OAB medication or have adverse events after treatment. Therefore, treatment of OAB should be individualized to obtain therapeutic efficacy and avoid unacceptable adverse events. This article reviews the recently published literature and provides a guide for physicians to choose the appropriate treatment for different OAB patients.