The Neuro-Urological Connection

The β3-Adrenergic Receptor: Structure, Physiopathology of Disease, and Emerging Therapeutic Potential

The discovery and characterization of the signal cascades of the β-adrenergic receptors have made it possible to effectively target the receptors for drug development. β-Adrenergic receptors are a class A rhodopsin type of G protein-coupled receptors (GPCRs) that are stimulated mainly by catecholamines and therefore mediate diverse effects of the parasympathetic nervous system in eliciting "fight or flight" type responses. They are detectable in several human tissues where they control a plethora of physiological processes and therefore contribute to the pathogenesis of several disease conditions. Given the relevance of the β-adrenergic receptor as a molecular target for many pathological conditions, this comprehensive review aims at providing an in-depth exploration of the recent advancements in β3-adrenergic receptor research. More importantly, we delve into the prospects of the β3-adrenergic receptor as a therapeutic target across a variety of clinical domains.

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.

Current and Emerging Pharmacological Targets and Treatments of Urinary Incontinence and Related Disorders

Overactive bladder syndrome with and without urinary incontinence and related conditions, signs, and disorders such as detrusor overactivity, neurogenic lower urinary tract dysfunction, underactive bladder, stress urinary incontinence, and nocturia are common in the general population and have a major impact on the quality of life of the affected patients and their partners. Based on the deliberations of the subcommittee on pharmacological treatments of the 7th International Consultation on Incontinence, we present a comprehensive review of established drug targets in the treatment of overactive bladder syndrome and the aforementioned related conditions and the approved drugs used in its treatment. Investigational drug targets and compounds are also reviewed. We conclude that, despite a range of available medical treatment options, a considerable medical need continues to exist. This is largely because the existing treatments are symptomatic and have limited efficacy and/or tolerability, which leads to poor long-term adherence. SIGNIFICANCE STATEMENT: Urinary incontinence and related disorders are prevalent in the general population. While many treatments have been approved, few patients stay on long-term treatment despite none of them being curative. This paper provides a comprehensive discussion of existing and emerging treatment options for various types of incontinence and related disorders.

Characterization of Urothelial Inclusions in Male Wistar Han Rats Treated Orally With the Novel α2A-Adrenoceptor Agonist Tasipimidine

Intracellular inclusions were observed in urinary bladder epithelium of male Wistar rats, following oral treatment with high doses of the α_2A-adrenoceptor agonist tasipimidine for 28 days. No cell death or inflammation was associated with the brightly eosinophilic inclusions. Electron microscopy (EM) studies showed that the inclusions represented intact or fragmented red blood cells (RBC) resulting from erythrophagocytosis, further supported by the presence of iron in urothelial cells. In addition, scattered iron-positive macrophages were observed in the submucosa and muscle layer, indicating microvascular leakage, as no major hemorrhage was evident. Despite the presence of inclusions, the urothelium showed normal uroplakin III distribution, normal cell turnover, and an absence of α-2u-globulin. It is, therefore, concluded that the inclusions were not associated with urothelial damage or increased renewal of the epithelium. This finding shows also that urothelial cells have the capability to phagocytize and break down RBCs originating from submucosal microvascular leakage. Similar changes were not observed in tasipimidine-treated beagle dogs (28 days), suggesting these findings were rat specific. The leakage of RBCs into the urothelium is suggested to be a consequence of exaggerated pharmacology leading to vasoconstriction of submucosal blood vessels in combination with transient increased bladder distension and pressure.

Design, synthesis and in vitro evaluation of a Dopa-organoboron compound that acts as a bladder relaxant through non-catecholamine receptors

Bladder relaxation through drug administration is an interesting topic in medicinal and combinatorial chemistry. In fact, compounds targeting catecholamine receptors [dopamine receptors and beta-adrenergic receptors (βAR) expressed in the bladder] are among the compounds commonly employed for this purpose. In particular, recent investigations have tended to focus on the β3-adrenoceptor (β3AR) as a target in the treatment of urinary incontinence and other disorders. However, organoboron compounds have been suggested as potent and efficient agents on these drug targets. In this work, through a docking study, we identified the parameters that induce a theoretical improvement in the affinity and activity of the organoboron compounds on the catecholamine receptors expressed in the bladder. Then, the identified potential drug, a boron-containing dopa-derivative named DPBX-L-Dopa, was synthesized and characterized. This compound induces a relaxation on the smooth muscle of the rat bladder, behaving as a weak relaxant compared to isoproterenol but with similar efficacy to BRL377, a selective β3AR agonist. However, unexpectedly, this effect was not blocked by propranolol or haloperidol at the concentrations at which they are able to block the catecholamine receptors in bladder tissue. In view of these results, the effect of DPBX-L-Dopa compound on the alpha 1 adrenergic receptors (α1AR) of aorta of the rats was also explored; however, no response of the tissue to this compound was obtained. The possible mechanisms of the action of this compound were explored and are discussed further.

β3-Adrenoceptor agonists for overactive bladder syndrome: Role of translational pharmacology in a repositioning clinical drug development project

β3-Adrenoceptor agonists were originally considered as a promising drug class for the treatment of obesity and/or type 2 diabetes. When these development efforts failed, they were repositioned for the treatment of the overactive bladder syndrome. Based on the example of the β3-adrenoceptor agonist mirabegron, but also taking into consideration evidence obtained with ritobegron and solabegron, we discuss challenges facing a translational pharmacology program accompanying clinical drug development for a first-in-class molecule. Challenges included generic ones such as ligand selectivity, species differences and drug target gene polymorphisms. Challenges that are more specific included changing concepts of the underlying pathophysiology of the target condition while clinical development was under way; moreover, a paucity of public domain tools for the study of the drug target and aspects of receptor agonists as drugs had to be addressed. Nonetheless, a successful first-in-class launch was accomplished. Looking back at this translational pharmacology program, we conclude that a specifically tailored and highly flexible approach is required. However, several of the lessons learned may also be applicable to translational pharmacology programs in other indications.

Combination histamine and serotonin treatment after simulated childbirth injury improves stress urinary incontinence

AIMS

Histamine and serotonin-related pharmaceuticals have the potential to modulate micturition and continence. The aim of this study was to determine if treatment with histamine and/or serotonin improves stress urinary incontinence (SUI) in female rats.

METHODS

Twenty-six age-matched female rats underwent pudendal nerve crush and vaginal distension (PNC + VD), to produce SUI. One week after injury, rats were treated subcutaneously with saline, histamine (1.1 μg), serotonin (2μg), or the combination of both twice daily for another week. A sham injured group received sham PNC + VD and were treated with saline (n = 7). Leak point pressure (LPP) testing with simultaneous external urethral sphincter (EUS) electromyography (EMG) was conducted 2 weeks after injury. The urethra was harvested for qualitative and quantitative histology. Data were analyzed with a one-way ANOVA and Student-Newman-Keuls posthoc test with P < 0.05 indicating statistically significant differences between groups.

RESULTS

Combination treatment significantly increased LPP after PNC + VD compared to injured sham treatment and treatment with either histamine or serotonin alone. Compared to injured sham treated rats, all three treatments significantly increased EUS EMG amplitude at both baseline and peak pressure and EUS EMG firing rate at peak pressure during LPP testing. There were more consistent urethral striated muscle fibers and thicker smooth and striated muscle with combination and histamine treatment. There was a statistically significant shift to a greater proportion of thicker collagen fibers in the urethra in serotonin and combination treated rats compared with injured sham treated rats.

CONCLUSIONS

Combination treatment was the most effective and may provide an effective therapy for SUI. Neurourol. Urodynam. 35:703-710, 2016. © 2015 Wiley Periodicals, Inc.

Therapeutic modulation of urinary bladder function: multiple targets at multiple levels

Storage dysfunction of the urinary bladder, specifically overactive bladder syndrome, is a condition that occurs frequently in the general population. Historically, pathophysiological and treatment concepts related to overactive bladder have focused on smooth muscle cells. Although these are the central effector, numerous anatomic structures are involved in their regulation, including the urothelium, afferent and efferent nerves, and the central nervous system. Each of these structures involves receptors for—and the urothelium itself also releases—many mediators. Moreover, hypoperfusion, hypertrophy, and fibrosis can affect bladder function. Established treatments such as muscarinic antagonists, β-adrenoceptor agonists, and onabotulinumtoxinA each work in part through their effects on the urothelium and afferent nerves, as do α1-adrenoceptor antagonists in the treatment of voiding dysfunction associated with benign prostatic hyperplasia; however, none of these treatments are specifically targeted to the urothelium and afferent nerves. It remains to be explored whether future treatments that specifically act at one of these structures will provide a therapeutic advantage.

Urinary urgency - translating the evidence base into daily clinical practice

AIM

To consider the currently available knowledge and understanding of the symptom of urgency.

MATERIALS & METHODS

Each faculty member reviewed the literature base of a different aspect of urgency and along with their personal clinical experience provided a base of evidence for discussion.

RESULTS

This overview summarises relevant published literature and the current clinical experience of the authors.

DISCUSSION

Whilst the mechanisms producing the sensation of urgency are still not fully understood and we are working within a definition that may complicate measurement and treatment, our pressing need is to effectively manage our patients for whom the practical nature of urgency can be all too apparent.

CONCLUSION

Health care professionals have an important role to play today in helping to alleviate the widespread problem of urgency and its consequences.

[Is medical therapy useful in the management of stress urinary incontinence?]

In Germany, only duloxetine is registered for treating stress urinary incontinence in adult women; duloxetine treatment for stress urinary incontinence in children or men is poorly investigated and still off-label. Trials in women based on the evidence level 1B and meta-analyses have demonstrated that duloxetine significantly reduced the frequency of incontinence episodes and increased incontinence-related quality of life. However, duloxetine must be used on a regular base to maintain these positive effects. Therefore, duloxetine seems to be especially indicated in women who refuse or cannot be subjected to physical or surgical treatment and are willing to accept the long-term use and possible side effects of the drug. Furthermore, duloxetine could be useful in women to support pelvic floor physiotherapy or in female patients awaiting incontinence surgery.

Alpha1 Adrenoceptors in Human Urinary Tract: Expression, Distribution and Clinical Implications

Adrenergic receptors (ARs) are a class of proteins belonging to the G protein-coupled receptor family. Pharmacological and molecular studies allowed dividing ARs into three different categories: α1, α2 and β. In this review, we focused on α1 ARs and α1 AR antagonists, since α 1 ARs play an important role in the pathophysiology of a number of urinary tract (UT) dysfunctions. α1 ARs are widely expressed in human UT; in particular, the three ureter areas (distal, medial and proximal) show different patterns of receptor expression (i.e. distal > medial = proximal), giving the molecular basis for the use of α1 ARs antagonist in the expulsive therapy of distal ureter calculi. Bladder areas are characterized by important differences among trigone, detrusor and neck, the first showing a different pattern of expression compared to the other parts. Further, there are evidences of both density and subtype gender-dependent expressions. α1 ARs expression in prostate and detrusor is a widely investigated area of research, mainly due to the clinical impact of benign prostatic hyperplasia (BPH). Urethra has not been well studied in human, although it plays a role in the control of continence.

Studies carried out on α1 AR subtype expression in the UT indicate that, although the presence of each subtype is observed, α1A firstly and then α1D ARs seem to be more expressed than α1B ARs. Thus, drugs that demonstrate high α1A/D AR selectivity have drawn the researchers’ attention. As it relates specifically to the α1 AR antagonists used in the treatment of lower UT symptoms, the concept of uroselectivity has been operationally defined; indeed, in a number of recent publications uroselectivity has been defined as the degree to which a given compound inhibits norepinephrine-induced increase in urinary muscle contractions and/or its propensity to generate unwanted cardiovascular effects, such as decreases in blood pressure.

Alpha1-, alpha2- and beta-adrenoceptors in the urinary bladder, urethra and prostate

1 We have systematically reviewed the presence, functional responses and regulation of alpha(1)-, alpha(2)- and beta-adrenoceptors in the bladder, urethra and prostate, with special emphasis on human tissues and receptor subtypes. 2 Alpha(1)-adrenoceptors are only poorly expressed and play a limited functional role in the detrusor. Alpha(1)-adrenoceptors, particularly their alpha(1A)-subtype, show a more pronounced expression and promote contraction of the bladder neck, urethra and prostate to enhance bladder outlet resistance, particularly in elderly men with enlarged prostates. Alpha(1)-adrenoceptor agonists are important in the treatment of symptoms of benign prostatic hyperplasia, but their beneficial effects may involve receptors within and outside the prostate. 3 Alpha(2)-adrenoceptors, mainly their alpha(2A)-subtype, are expressed in bladder, urethra and prostate. They mediate pre-junctional inhibition of neurotransmitter release and also a weak contractile effect in the urethra of some species, but not humans. Their overall post-junctional function in the lower urinary tract remains largely unclear. 4 Beta-adrenoceptors mediate relaxation of smooth muscle in the bladder, urethra and prostate. The available tools have limited the unequivocal identification of receptor subtypes at the protein and functional levels, but it appears that the beta(3)- and beta(2)-subtypes are important in the human bladder and urethra, respectively. Beta(3)-adrenoceptor agonists are promising drug candidates for the treatment of the overactive bladder. 5 We propose that the overall function of adrenoceptors in the lower urinary tract is to promote urinary continence. Further elucidation of the functional roles of their subtypes will help a better understanding of voiding dysfunction and its treatment.

Safety and tolerability of duloxetine in women with stress urinary incontinence

BACKGROUND

The serotonin/noradrenaline uptake inhibitor duloxetine has been shown to be effective in the medical treatment of stress urinary incontinence (SUI) in women.

AIM

To review the safety and tolerability of duloxetine with SUI.

METHODS

A systematic Medline search for the key word "duloxetine" was performed, and abstracts from recent international gynaecological and urological meetings were also considered.

RESULTS

Various unpleasant adverse effects exist, among which nausea is the most frequent, but is mild to moderate and transient in most cases. Dose escalation upon initiation of treatment improves the tolerability of duloxetine. The use of duloxetine appears safe as it lacks the cardiovascular adverse effects of older amine reuptake inhibitors.

CONCLUSIONS

Duloxetine has an acceptable safety profile. Dose escalation combined with patient counselling on the intensity and transient nature of adverse effects may help to further improve the benefit/tolerability ratio of duloxetine in the treatment of SUI.

Duloxetine in women awaiting surgery

Stress urinary incontinence (SUI) is a common condition affecting millions of women worldwide. It has a significant impact on the quality of life (psychosocial, social and economic well-being) of sufferers and their families. Until recently, treatment options for SUI were limited to conservative treatments such as pelvic floor muscle training, which usually has a poor compliance over time, or surgical procedures that carry the risk of complications and are mainly an option for more severely affected women. Duloxetine, a potent and relatively balanced serotonin and noradrenaline reuptake inhibitor, has been evaluated in phase II and phase III clinical trials and was found to be efficacious and safe in the treatment of women with moderate to severe SUI symptoms. Even in a subgroup of women with severe SUI awaiting surgery, with or without the presence of intrinsic sphincter deficiency, duloxetine was found to be effective. In addition, a good correlation was found between efficacy outcome measures and ratings of global impression scores. Women begin to perceive themselves as being better with treatment when their incontinence episodes frequency (IEF) decreases by 46% or their Incontinence Quality of Life (I-QOL) score improves by 6.3 points. The improvements in IEF and I-QOL obtained with duloxetine were well above these threshold levels, whereas these with placebo were not. All duloxetine responses were observed within 2 weeks. Overall, duloxetine is an effective treatment for a wide variety of women presenting with SUI symptoms. It has been approved in Europe for the treatment of women with moderate to severe SUI symptoms and is now available in many European countries.

The Rationale of Dual Serotonin/Noradrenaline Reuptake Inhibitors in the Management of Stress Urinary Incontinence

This paper aims at evaluating the role of serotonin (5-HT) and noradrenaline in the nervous control of urinary continence. Both α1-adrenergic and 5-HT2 receptors in the Onuf's nucleus help the guarding reflex; therefore the pharmacologic agents enhancing the effects of 5-HT and noradrenaline represent a promising choice in treating stress urinary incontinence. Duloxetine, a dual 5-HT/noradrenaline reuptake inhibitor, improves the external urethral sphincter contractility while increasing the activation of 5-HT2 and α1-adrenergic receptors thanks to the high concentrations of these monoamines in the Onuf's nucleus; it also plays a significant role in the management of stress urinary incontinence.

[Medical therapy of urinary incontinence]

Urinary incontinence has a high prevalence in both men and women. Women suffer predominantly from stress urinary incontinence and men from urge incontinence. Other types of incontinence are less frequent. Stress urinary incontinence is caused by an insufficient urethral closure mechanism and urge incontinence by uninhibited detrusor contractions. Medical treatment is beside other conservative options and operations only one part of the treatment strategy in incontinence. Duloxetine, a serotonine-norepinephrine reuptake inhibitor, is used to treat stress urinary incontinence, can increase activity of the external urethral sphincter and is able to reduce incontinence episodes in up to 64%. Antagonists of muscarinic receptors can reduce urgency, frequency and urge incontinence as well as increase bladder capacity significantly. In Germany, trospium chloride, tolterodine, solifenacin, oxybutynin and propiverine are available to treat urge incontinence. Efficacy of these agents are comparable. However, tolerability is different and side effects, especially dry mouth, often limit their use. None of the agents show ideal efficacy or tolerability in all patients and, therefore, new agents and formulations are currently under clinical investigation.