The pharmacological rationale for combining muscarinic receptor antagonists and β-adrenoceptor agonists in the treatment of airway and bladder disease

Genomic crosstalk between carbachol, a muscarinic receptor agonist, and the long-acting β2-adrenoceptor agonist, indacaterol, in human airway epithelial cells

Many patients with chronic obstructive pulmonary disease are susceptible to recurrent exacerbations. In this study, we hypothesized that endogenous acetylcholine (ACh) may act as a proinflammatory mediator because long-acting muscarinic receptor antagonists protect against exacerbations, which have an inflammatory basis. This possibility was explored by determining if carbachol (CCh), a stable ACh analog, was a genomic stimulus in BEAS-2B bronchial epithelial cells. The ability of CCh to interact with indacaterol (Ind), a long-acting β2-adrenoceptor agonist, was also assessed given that (1) sympathomimetic bronchodilators can promote adverse gene expression changes in airway structural cells, and (2) crosstalk between β2-adrenoceptor and Gq-coupled muscarinic receptor agonists is well described. Unlike Ind, which induced 624 unique genes, CCh was a relatively weak genomic stimulus, implying that ACh may not behave as a proinflammatory mediator as hypothesized. Nevertheless, checkerboard assays using BEAS-2B cells expressing a cAMP-response element luciferase reporter determined that CCh interacted with Ind in a supra-additive manner and that this interaction was replicated on 39 Ind-regulated genes. Functional annotation of the Ind-regulated transcriptomes identified "transcription" and "signalling" as the dominant themes, with gene ontology terms associated with "inflammation" and "immune processes" being highly represented. A comparable gene ontology signature was obtained when Ind and CCh were combined; however, the number, magnitude and duration of gene expression changes were significantly enhanced. If genomic interactions occur between a long-acting β2-adrenoceptor agonist and ACh in vivo, then they may enhance the expression of adverse-effect genes that could maintain, or even augment, features of lung pathology in chronic obstructive pulmonary disease. SIGNIFICANCE STATEMENT: Long-acting muscarinic receptor antagonists reduce exacerbation risk in chronic obstructive pulmonary disease, implying the etiology could have an inflammatory basis mediated by acetylcholine. However, in BEAS-2B cells, carbachol was a weak genomic stimulus, although it enhanced changes in indacaterol-regulated gene expression. Functional annotation of carbachol + indacaterol-regulated genes identified gene ontology terms associated with several themes, including inflammation. Interaction between a long-acting β2-adrenoceptor agonist and endogenous acetylcholine could, paradoxically, augment airway inflammation in patients with chronic obstructive pulmonary disease.

Anti-carcinogenic effects of arecaidine but-2-ynyl ester tosylate on breast cancer: proliferation inhibition and activation of apoptosis

BACKGROUND

Breast cancer (BC) is the most prevalent cancer among women globally and is notoriously difficult to treat due to its heterogeneous nature and the lack of an effective treatment. Muscarinic receptors (MRs), which serve as key regulators in the parasympathetic nervous system, exhibit significant regulatory functions in non-neural cells. Recent studies suggest that modulating MR activity can elicit anti-carcinogenic effects across various malignancies, stimulating interest in their oncological implications. To investigate this further, we explored the anti-carcinogenic effects of arecaidine but-2-ynyl ester tosylate (ABET), a potential M2 receptor activator, in BC cells using several cellular and molecular assays.

METHODS AND RESULTS

Molecular docking assays were employed to confirm the binding affinity of ABET to M2/M4 receptors. Subsequently, we evaluated the impact of ABET on cell viability, proliferation, clonogenicity, and migration in MDA-MB-231 and MCF-7 BC cell lines. Computational analysis revealed preferential binding of ABET to M2 and M4 receptors. In-vitro experiments demonstrated that ABET markedly inhibits viability, growth, clonogenicity, and migration in BC cells. Notably, ABET induced cell cycle arrest in MDA-MB-231 cells and promoted apoptotic cell death in MCF-7 cells. Furthermore, ABET downregulated key proliferation- and cell cycle-associated genes, including CCND1, CDK6, and MKI67.

CONCLUSIONS

Our findings underscore ABET as a promising therapeutic candidate for BC treatment, capable of suppressing cell growth, survival, and migration. Additional in-vivo studies are necessary to validate ABET's anti-neoplastic efficacy and evaluate its feasibility as novel therapeutic agent in BC management.

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.

Survivin knockdown alleviates pathological hydrostatic pressure-induced bladder smooth muscle cell dysfunction and BOO-induced bladder remodeling via autophagy

Aim: Bladder outlet obstruction (BOO) leads to bladder wall remodeling accompanying the progression from inflammation to fibrosis where pathological hydrostatic pressure (HP)-induced alteration of bladder smooth muscle cells (BSMCs) hypertrophic and excessive extracellular matrix (ECM) deposition play a pivotal role. Recently, we have predicted survivin (BIRC5) as a potential hub gene that might be critical during bladder fibrosis by bioinformatics analyses from rat BOO bladder, but its function during BOO progression remains unknown. Here, we investigated the role of survivin protein on bladder dysfunction of BOO both in vitro and in vivo. Methods: Sprague-Dawley female rats were divided into three groups: control group, BOO group, and BOO followed by the treatment with YM155 group. Bladder morphology and function were evaluated by Masson staining and urodynamic testing. To elucidate the underlying mechanism, hBSMCs were subjected to pathological HP of 200 cm H2O and co-cultured with the presence or absence of survivin siRNA and/or autophagy inhibitor 3-MA. Autophagy was evaluated by the detection of Beclin1 and LC3B-II expression, proliferation was conducted by the EdU analysis and PCNA expression, and fibrosis was assessed by the examination of Col 1 and Fn expression. Results: BOO led to a gradual alteration of hypertrophy and fibrosis of the bladder, and subsequently induced bladder dysfunction accompanied by increased survivin expression, while these histological and function changes were attenuated by the treatment with YM155. HP significantly increased survivin expression, upregulated Col1 and Fn expression, enhanced proliferation, and downregulated autophagy markers, but these changes were partially abolished by survivin siRNA treatment, which was consistent with the results of the BOO rat experiment. In addition, the anti-fibrotic and anti-proliferative effects of the survivin siRNA treatment on hBSMCs were diminished after the inhibition of autophagy by the treatment with 3-MA. Conclusion: In summary, the upregulation of survivin increased cell proliferation and fibrotic protein expression of hBSMC and drove the onset of bladder remodeling through autophagy during BOO. Targeting survivin in pathological hBSMCs could be a promising way to anti-fibrotic therapeutic approach in bladder remodeling secondary to BOO.

Inhibition of Human Prostate and Bladder Smooth Muscle Contraction, Vasoconstriction of Porcine Renal and Coronary Arteries, and Growth-Related Functions of Prostate Stromal Cells by Presumed Small Molecule Gαq/11 Inhibitor, YM-254890

Introduction: Lower urinary tract symptoms (LUTS) involve benign prostatic hyperplasia (BPH) and overactive bladder (OAB). Standard-of-care medical treatment includes α1-blockers and antimuscarinics for reduction of prostate and detrusor smooth muscle tone, respectively, and 5α-reductase inhibitors (5-ARI) to prevent prostate growth. Current medications are marked by high discontinuation rates due to unfavourable balance between efficacy and treatment-limiting side effects, ranging from dry mouth for antimuscarinics to cardiovascular dysregulation and a tendency to fall for α1-blockers, which results from hypotension, due to vasorelaxation. Agonist-induced smooth muscle contractions are caused by activation of receptor-coupled G-proteins. However, little is known about receptor- and organ-specific differences in coupling to G-proteins. With YM-254890, a small molecule inhibitor with presumed specificity for Gαq/11 became recently available. Here, we investigated effects of YM-254890 on prostate, bladder and vascular smooth muscle contraction, and on growth-related functions in prostate stromal cells.

Methods: Contractions of human prostate and detrusor tissues, porcine renal and coronary arteries were induced in an organ bath. Proliferation (EdU assay), growth (colony formation), apoptosis and cell death (flow cytometry), viability (CCK-8) and actin organization (phalloidin staining) were studied in cultured human prostate stromal cells (WPMY-1).

Results: Contractions by α1-adrenergic agonists, U46619, endothelin-1, and neurogenic contractions were nearly completely inhibited by YM-254890 (30 nM) in prostate tissues. Contractions by cholinergic agonists, U46619, endothelin-1, and neurogenic contractions were only partly inhibited in detrusor tissues. Contractions by α1-adrenergic agonists, U46619, endothelin-1, and neurogenic contractions were strongly, but not fully inhibited in renal arteries. Contractions by cholinergic agonists were completely, but by U46619 and endothelin-1 only strongly inhibited, and neurogenic contractions reduced by half in coronary arteries. YM-254890 had no effect on agonist-independent contractions induced by highmolar (80 mM) potassium chloride (KCl). Neurogenic detrusor contractions were fully sensitive to tetrodotoxin. In WPMY-1 cells, YM-254890 caused breakdown of actin polymerization and organization, and obvious, but clearly limited decreases of proliferation rate, colony formation and viability, and slightly increased apoptosis.

Conclusion: Intracellular post-receptor signaling pathways are shared by Gαq-coupled contractile receptors in multiple smooth muscle-rich organs, but to different extent. While inhibition of Gαq/11 causes actin breakdown, anti-proliferative effects were detectable but clearly limited. Together this may aid in developing future pharmaceutical targets for LUTS and antihypertensive medication.

Inhibition of Full Smooth Muscle Contraction in Isolated Human Detrusor Tissues by Mirabegron Is Limited to Off-Target Inhibition of Neurogenic Contractions

Mirabegron is used for treatment of storage symptoms in overactive bladder (OAB) caused by spontaneous bladder smooth muscle contractions. However, owing to limitations in available studies using human tissues, central questions are still unresolved, including mechanisms underlying improvements by mirabegron and its anticontractile effects in the detrusor. Here, we assessed concentration-dependent mirabegron effects on contractions of human detrusor tissues in frequency-response curves and concentration-response curves for different cholinergic and noncholinergic agonists. Detrusor tissues were sampled from patients undergoing radical cystectomy. Contractions were induced by electric field stimulation (EFS) and by cumulative concentrations of cholinergic agonists, endothelin-1, and the thromboxane A2 analog U46619. EFS-induced contractions were inhibited using 10 µM mirabegron, but not using 1 µM. Inhibition by 10 µM mirabegron was resistant to the β 3-adrenergic antagonist L-748,337. Concentration-dependent contractions by carbachol were not inhibited by 1 µM or 10 µM mirabegron. Concentration-response curves for methacholine were slightly right-shifted by 10 µM, but not 1 µM mirabegron. Concentration-dependent contractions by endothelin-1 or U46619 were not changed by mirabegron. In contrast, the muscarinic antagonist tolterodine right-shifted concentration-response curves for carbachol and methacholine and inhibited EFS-induced contractions. In conclusion, inhibition of neurogenic contractions in isolated detrusor tissues by mirabegron requires concentrations highly exceeding known plasma levels during standard dosing and the known binding constant (Ki values) for β 3-adrenoceptors. Full contractions by cholinergic agonists, endothelin-1, and U46619 are not affected by therapeutic concentrations of mirabegron. Improvements of storage symptoms are most likely not imparted by inhibition of β 3-adrenoceptors in the bladder wall itself. SIGNIFICANCE STATEMENT: Mirabegron is used for overactive bladder (OAB) treatment, but the underlying mechanisms are unclear, and preclinical and clinical findings are controversial due to limitations in available studies. Our findings suggest that inhibition of detrusor contractions by mirabegron is limited to neurogenic contractions, which requires unphysiologic concentrations and does not involve β 3-adrenoceptors. Mechanisms accounting for improvements of OAB by mirabegron are located outside the urinary bladder.

Does coupling to ADP ribosylation factor 6 explain differences between muscarinic and other receptors in interaction with β-adrenoceptor-mediated smooth muscle relaxation?

Numerous studies in airways, ileum, and urinary bladder have demonstrated that relaxation by β-adrenoceptor agonists has lower potency and/or efficacy when contraction was elicited by muscarinic receptor agonists as compared to other G-protein-coupled receptors, KCl, or basal tone, but the molecular mechanisms behind this relative resistance remain unclear. A paper by Huang et al. in this issue demonstrates that NAV2729, an inhibitor of ADP ribosylation factor 6, inhibits contraction of isolated blood vessels elicited by muscarinic receptor agonists, but not by α₁-adrenoceptor agonists or KCl. Against this background, we discuss the role of ADP ribosylation factor 6 in cellular responses to G-protein-coupled receptor stimulation. While ADP ribosylation factor 6 apparently is the only promising molecular explanation for the relative resistance of smooth muscle contraction elicited by muscarinic agonists, the existing data are insufficient for a robust conclusion.

Inhibition of neurogenic contractions in renal arteries and of cholinergic contractions in coronary arteries by the presumed inhibitor of ADP-ribosylation factor 6, NAV2729

NAV2729 is a presumed inhibitor of the monomeric GTPase ADP ribosylation factor 6 (ARF6) and inhibits smooth muscle contraction outside the cardiovascular system. Its effects on vascular smooth muscle contraction or a possible role of ARF6 in vasocontraction have not yet been examined. Here, we report effects of NAV2729 on neurogenic and agonist-induced contractions in renal interlobar and coronary arteries. Contractions of pig interlobar and coronary arteries were induced in an organ bath by agonists or by electric field stimulation (EFS). Owing to divergent characteristics of both vessel types, EFS-induced contractions were only examined in interlobar arteries, and contractions by agonists acting on muscarinic receptors only in coronary arteries. NAV2729 inhibited frequency-dependent EFS-induced contractions of interlobar arteries. The degree of inhibition was similar using 5 µM and 10 µM NAV2729. Inhibition of EFS-induced contractions was resistant to a nitric oxide synthase inhibitor and to diclofenac. The neurogenic and adrenergic character of EFS-induced contractions was confirmed by inhibition by tetrodotoxin and prazosin. In coronary arteries, NAV2729 (5 µM) inhibited concentration-dependent contractions induced by carbachol and methacholine. Contractions induced by α₁-adrenergic agonists, endothelin-1, the thromboxane receptor agonist U46619, or serotonin remained unchanged by NAV2729 in both vessel types. NAV2729 inhibits neurogenic contractions in interlobar arteries and contractions induced by cholinergic agonists in coronary arteries. In both vessel types, NAV2729 does not inhibit contractions induced by receptor agonists other than those acting on muscarinic receptors. Addressing effects in other vessels and in other smooth muscle–rich organs merits further attention.

Validation of Fenoterol to Study β2-Adrenoceptor Function in the Rat Urinary Bladder

Fenoterol is a β2-adrenoceptor (AR)-selective agonist that is commonly used to investigate relaxation responses mediated by β2-AR in smooth muscle preparations. Some data have questioned this because fenoterol had low potency in the rat urinary bladder when a muscarinic agonist was used as a pre-contraction agent and because some investigators proposed that fenoterol may act in part via β3-AR. We designed the present study to investigate whether fenoterol is a proper pharmacological tool to study β2-AR-mediated relaxation responses in the rat urinary bladder. Firstly, we have compared the effect of pre-contraction agents on fenoterol potency and found that fenoterol potency was about 1.5 log units greater against KCl than carbachol (pEC50 7.19 ± 0.66 and 5.62 ± 1.09 of KCl and of carbachol, respectively). To test the selectivity of fenoterol, we have determined the effects of the β2-AR antagonist ICI 118,551 and the β3-AR antagonist L 748,337 on relaxation responses to fenoterol. While 300 nM L 748,337 had little effect on the potency of fenoterol (pEC50 6.56 ± 0.25 and 6.33 ± 0.61 in the absence and presence of L 748,337, respectively), the relaxation curve for fenoterol was right-shifted in the presence 300 nM ICI 118,551 (pEC50 5.03 ± 0.18). Thus, we conclude that fenoterol is a proper pharmacological tool to assess β2-AR-mediated responses in the rat urinary bladder and most likely in other smooth-muscle preparations containing multiple subtypes of the β-AR.

Inhaled β2 Adrenergic Agonists and Other cAMP-Elevating Agents: Therapeutics for Alveolar Injury and Acute Respiratory Disease Syndrome?

Inhaled long-acting β-adrenergic agonists (LABAs) and short-acting β-adrenergic agonists are approved for the treatment of obstructive lung disease via actions mediated by β2 adrenergic receptors (β2-ARs) that increase cellular cAMP synthesis. This review discusses the potential of β2-AR agonists, in particular LABAs, for the treatment of acute respiratory distress syndrome (ARDS). We emphasize ARDS induced by pneumonia and focus on the pathobiology of ARDS and actions of LABAs and cAMP on pulmonary and immune cell types. β2-AR agonists/cAMP have beneficial actions that include protection of epithelial and endothelial cells from injury, restoration of alveolar fluid clearance, and reduction of fibrotic remodeling. β2-AR agonists/cAMP also exert anti-inflammatory effects on the immune system by actions on several types of immune cells. Early administration is likely critical for optimizing efficacy of LABAs or other cAMP-elevating agents, such as agonists of other Gs-coupled G protein-coupled receptors or cyclic nucleotide phosphodiesterase inhibitors. Clinical studies that target lung injury early, prior to development of ARDS, are thus needed to further assess the use of inhaled LABAs, perhaps combined with inhaled corticosteroids and/or long-acting muscarinic cholinergic antagonists. Such agents may provide a multipronged, repurposing, and efficacious therapeutic approach while minimizing systemic toxicity. SIGNIFICANCE STATEMENT: Acute respiratory distress syndrome (ARDS) after pulmonary alveolar injury (e.g., certain viral infections) is associated with ∼40% mortality and in need of new therapeutic approaches. This review summarizes the pathobiology of ARDS, focusing on contributions of pulmonary and immune cell types and potentially beneficial actions of β2 adrenergic receptors and cAMP. Early administration of inhaled β2 adrenergic agonists and perhaps other cAMP-elevating agents after alveolar injury may be a prophylactic approach to prevent development of ARDS.

Three-dimensional imaging on a chip using optofluidics light-sheet fluorescence microscopy

Volumetric, sub-micron to micron level resolution imaging is necessary to assay phenotypes or characteristics at the sub-cellular/organelle scale. However, three-dimensional fluorescence imaging of cells is typically low throughput or compromises on the achievable resolution in space and time. Here, we capitalise on the flow control capabilities of microfluidics and combine it with microoptics to integrate light-sheet based imaging directly into a microfluidic chip. Our optofluidic system flows suspended cells through a sub-micrometer thick light-sheet formed using micro-optical components that are cast directly in polydimethylsiloxane (PDMS). This design ensures accurate alignment, drift-free operation, and easy integration with conventional microfluidics, while providing sufficient spatial resolution, optical sectioning and volumetric data acquisition. We demonstrate imaging rates of 120 ms per cell at sub-μm resolution, that allow extraction of complex cellular phenotypes, exemplified by imaging of cell clusters, receptor distribution, and the analysis of endosomal size changes.

A Patent Review on the Current Developments of Benzoxazoles in Drug Discovery

The benzoxazole moiety is widely found in various natural compounds, which are often found to be biologically active. Due to its versatile biological properties, benzoxazole has been incorporated as an essential pharmacophore and substructure in many medicinal compounds. In the past years, numerous benzoxazole derivatives have been synthesised and evaluated for their biological potential. The wide range in therapeutic potential of benzoxazole derivatives is related to the favourable interactions of the benzoxazole moiety with different protein targets. Herein we review the biological activities of benzoxazole derivatives patented within the past six years. Using the Lens database, granted patents issued from 2015 to 2020 were retrieved. The patented benzoxazole derivatives demonstrated excellent activity against various protein targets and diseases, with some reaching clinical trial stage. Pharmacological and medicinal aspects of patented benzoxazole derivatives are discussed. The recent development and drawbacks are also reviewed.

Role of Airway Smooth Muscle in Inflammation Related to Asthma and COPD

Airway smooth muscle contributes to both contractility and inflammation in the pathophysiology of asthma and COPD. Airway smooth muscle cells can change the degree of a variety of functions, including contraction, proliferation, migration, and the secretion of inflammatory mediators (phenotype plasticity). Airflow limitation, airway hyperresponsiveness, β₂-adrenergic desensitization, and airway remodeling, which are fundamental characteristic features of these diseases, are caused by phenotype changes in airway smooth muscle cells. Alterations between contractile and hyper-contractile, synthetic/proliferative phenotypes result from Ca²⁺ dynamics and Ca²⁺ sensitization. Modulation of Ca²⁺ dynamics through the large-conductance Ca²⁺-activated K⁺ channel/L-type voltage-dependent Ca²⁺ channel linkage and of Ca²⁺ sensitization through the RhoA/Rho-kinase pathway contributes not only to alterations in the contractile phenotype involved in airflow limitation, airway hyperresponsiveness, and β₂-adrenergic desensitization but also to alteration of the synthetic/proliferative phenotype involved in airway remodeling. These Ca²⁺ signal pathways are also associated with synergistic effects due to allosteric modulation between β₂-adrenergic agonists and muscarinic antagonists. Therefore, airway smooth muscle may be a target tissue in the therapy for these diseases. Moreover, the phenotype changing in airway smooth muscle cells with focuses on Ca²⁺ signaling may provide novel strategies for research and development of effective remedies against both bronchoconstriction and inflammation.

Fixed dose drug combinations - are they pharmacoeconomically sound? Findings and implications especially for lower- and middle-income countries

Introduction: There are positive aspects regarding the prescribing of fixed dose combinations (FDCs) versus prescribing the medicines separately. However, these have to be balanced against concerns including increased costs and their irrationality in some cases. Consequently, there is a need to review their value among lower- and middle-income countries (LMICs) which have the greatest prevalence of both infectious and noninfectious diseases and issues of affordability.Areas covered: Review of potential advantages, disadvantages, cost-effectiveness, and availability of FDCs in high priority disease areas in LMICs and possible initiatives to enhance the prescribing of valued FDCs and limit their use where there are concerns with their value.Expert commentary: FDCs are valued across LMICs. Advantages include potentially improved response rates, reduced adverse reactions, increased adherence rates, and reduced costs. Concerns include increased chances of drug:drug interactions, reduced effectiveness, potential for imprecise diagnoses and higher unjustified prices. Overall certain FDCs including those for malaria, tuberculosis, and hypertension are valued and listed in the country's essential medicine lists, with initiatives needed to enhance their prescribing where currently low prescribing rates. Proposed initiatives include robust clinical and economic data to address the current paucity of pharmacoeconomic data. Irrational FDCs persists in some countries which are being addressed.

Pharmacology and Therapeutics of Bronchodilators Revisited

Bronchodilators remain the cornerstone of the treatment of airway disorders such as asthma and chronic obstructive pulmonary disease (COPD). There is therefore considerable interest in understanding how to optimize the use of our existing classes of bronchodilator and in identifying novel classes of bronchodilator drugs. However, new classes of bronchodilator have proved challenging to develop because many of these have no better efficacy than existing classes of bronchodilator and often have unacceptable safety profiles. Recent research has shown that optimization of bronchodilation occurs when both arms of the autonomic nervous system are affected through antagonism of muscarinic receptors to reduce the influence of parasympathetic innervation of the lung and through stimulation of β 2-adrenoceptors (β 2-ARs) on airway smooth muscle with β 2-AR-selective agonists to mimic the sympathetic influence on the lung. This is currently achieved by use of fixed-dose combinations of inhaled long-acting β 2-adrenoceptor agonists (LABAs) and long-acting muscarinic acetylcholine receptor antagonists (LAMAs). Due to the distinct mechanisms of action of LAMAs and LABAs, the additive/synergistic effects of using these drug classes together has been extensively investigated. More recently, so-called "triple inhalers" containing fixed-dose combinations of both classes of bronchodilator (dual bronchodilation) and an inhaled corticosteroid in the same inhaler have been developed. Furthermore, a number of so-called "bifunctional drugs" having two different primary pharmacological actions in the same molecule are under development. This review discusses recent advancements in knowledge on bronchodilators and bifunctional drugs for the treatment of asthma and COPD. SIGNIFICANCE STATEMENT: Since our last review in 2012, there has been considerable research to identify novel classes of bronchodilator drugs, to further understand how to optimize the use of the existing classes of bronchodilator, and to better understand the role of bifunctional drugs in the treatment of asthma and chronic obstructive pulmonary disease.

Urinary Bladder Weight and Function in a Rat Model of Mild Hyperglycemia and Its Treatment With Dapagliflozin

Hypertrophy and dysfunction of the urinary bladder are consistently observed in animal models of type 1 and less consistently in those of type 2 diabetes. We have tested the effects of mild hyperglycemia (n = 10 per group) in a randomized, blinded study and, in a blinded pilot study, of type 2 diabetes (n = 6 per group) and its treatment with dapagliflozin (1 mg/kg per day) on weight, contraction, and relaxation of the rat bladder. Based on a combination of high-fat diet and a low dose of streptozotocin, animals in the main study reached a mean peak blood glucose level of about 300 mg/dl, which declined to 205 mg/dl at study end. This was associated with a small, if any, increase in bladder weight. In a pooled analysis of all animals of the main and the pilot study, we detected a correlation of moderate strength between blood glucose and bladder weight (r² = 0.2013; P = 0.0003 for Pearson correlation coefficient). Neither the main nor the pilot study found evidence for an altered contractility (responses to carbachol or KCl) or relaxation (responses to isoprenaline, fenoterol, CL 316,243, or forskolin). Treatment with dapagliflozin in the absence of hyperglycemia increased diuresis in the main study by 43% relative to control and increased bladder weight by 15% in the pooled groups of both studies (post hoc analysis). We conclude that mild hyperglycemia has no major effects on bladder hypertrophy or function.

β3 -Adrenoceptors in the normal and diseased urinary bladder-What are the open questions?

β₃ -Adrenoceptor agonists are used in the treatment of overactive bladder syndrome. Although the relaxant response to adrenergic stimulation in human detrusor smooth muscle cells is mediated mainly via β₃ -adrenoceptors, the plasma concentrations of the therapeutic dose of mirabegron, the only clinically approved β₃ -adrenoceptor agonist, are considerably lower than the EC₅₀ for causing direct relaxation of human detrusor, suggesting a mechanism of action other than direct relaxation of detrusor smooth muscle. However, the site and mechanism of action of β₃ -adrenoceptor agonists in the bladder have not been firmly established. Postulated mechanisms include prejunctional suppression of ACh release from the parasympathetic nerves during the storage phase and inhibition of micro-contractions through β₃ -adrenoceptors on detrusor smooth muscle cells or suburothelial interstitial cells. Implications of possible desensitization of β₃ -adrenoceptors in the bladder upon prolonged agonist exposure and possible causes of rarely observed cardiovascular effects of mirabegron are also discussed. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Pharmacological characterization of DA-8010, a novel muscarinic receptor antagonist selective for urinary bladder over salivary gland

Several antimuscarinics have been commonly used for overactive bladder patients, but dry mouth as a major anticholinergic side effect remains a shortcoming to limit long-term use. The aim of this study was to elucidate the pharmacological properties of DA-8010, a novel muscarinic receptor antagonist selective for urinary bladder over salivary gland. DA-8010 exhibited a high binding affinity for human muscarinic M₃ receptor with pK_i of 8.81 ± 0.05 and great potencies for human M₃ receptor and rat bladder preparation. The potency of DA-8010 for bladder smooth muscle cells was 3.6-fold higher than that for salivary gland cells isolated from mice. Intravenous administration of DA-8010 dose-dependently inhibited rhythmic urinary bladder contractions induced by distension in rats, indicating the most potent activity (ID₃₀ = 0.08 mg/kg) among the antimuscarinics tested. Taken together with the inhibitory effects of DA-8010 and other antimuscarinics on carbachol-induced salivary secretion in rats, the in vivo functional selectivity of DA-8010 for urinary bladder over salivary gland was 3.1-fold, 3.2-fold and 5.2-fold greater than those observed for solifenacin, oxybutynin and darifenacin, respectively. Furthermore, oral administration of DA-8010 in mice resulted in more selective and persistent binding for muscarinic receptors in the bladder rather than in the submaxillary gland, in comparison with other antimuscarinics. These findings suggest that DA-8010 is a potent muscarinic M₃ receptor antagonist to be highly selective for bladder over salivary gland, which might be a promising agent with greater efficacy and less dry mouth in the treatment of overactive bladder.

Involvement of Allosteric Effect and KCa Channels in Crosstalk between β₂-Adrenergic and Muscarinic M₂ Receptors in Airway Smooth Muscle

To advance the development of bronchodilators for asthma and chronic obstructive pulmonary disease (COPD), this study was designed to investigate the mechanism of functional antagonism between β₂-adrenergic and muscarinic M₂ receptors, focusing on allosteric effects and G proteins/ion channels coupling. Muscarinic receptor antagonists (tiotropium, glycopyrronium, atropine) synergistically enhanced the relaxant effects of β₂-adrenergic receptor agonists (procaterol, salbutamol, formoterol) in guinea pig trachealis. This crosstalk was inhibited by iberitoxin, a large-conductance Ca²⁺-activated K⁺ (K_Ca) channel inhibitor, whereas it was increased by verapamil, a L-type voltage-dependent Ca²⁺ (VDC) channel inhibitor; additionally, it was enhanced after tissues were incubated with pertussis or cholera toxin. This synergism converges in the G proteins (G_i, G_s)/K_Ca channel/VDC channel linkages. Muscarinic receptor antagonists competitively suppressed, whereas, β₂-adrenergic receptor agonists noncompetitively suppressed muscarinic contraction. In concentration-inhibition curves for β₂-adrenergic receptor agonists with muscarinic receptor antagonists, EC₅₀ was markedly decreased, and maximal inhibition was markedly increased. Hence, muscarinic receptor antagonists do not bind to allosteric sites on muscarinic receptors. β₂-Adrenergic receptor agonists bind to allosteric sites on these receptors; their intrinsic efficacy is attenuated by allosteric modulation (partial agonism). Muscarinic receptor antagonists enhance affinity and efficacy of β₂-adrenergic action via allosteric sites in β₂-adrenergic receptors (synergism). In conclusion, K_Ca channels and allosterism may be novel targets of bronchodilator therapy for diseases such as asthma and COPD.

Inhaled therapies in patients with moderate COPD in clinical practice: current thinking

COPD is a complex, heterogeneous condition. Even in the early clinical stages, COPD carries a significant burden, with breathlessness frequently leading to a reduction in exercise capacity and changes that correlate with long-term patient outcomes and mortality. Implementation of an effective management strategy is required to reduce symptoms, preserve lung function, quality of life, and exercise capacity, and prevent exacerbations. However, current clinical practice frequently differs from published guidelines on the management of COPD. This review focuses on the current scientific evidence and expert opinion on the management of moderate COPD: the symptoms arising from moderate airflow obstruction and the burden these symptoms impose, how physical activity can improve disease outcomes, the benefits of dual bronchodilation in COPD, and the limited evidence for the benefits of inhaled corticosteroids in this disease. We emphasize the importance of maximizing bronchodilation in COPD with inhaled dual-bronchodilator treatment, enhancing patient-related outcomes, and enabling the withdrawal of inhaled corticosteroids in COPD in well-defined patient groups.

Selective inhibition of histamine-evoked Ca2+ signals by compartmentalized cAMP in human bronchial airway smooth muscle cells

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β₂-adrenoceptors, via cAMP and PKA, inhibit histamine-evoked Ca²⁺ signals in human bronchial airway smooth muscle cells.

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Responses to other Ca²⁺-mobilizing receptors are unaffected or minimally affected by cAMP.

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There is no consistent relationship between the amounts of cAMP produced by different stimuli and inhibition of histamine-evoked Ca²⁺ release.

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Local delivery of cAMP within hyperactive signaling junctions stimulates PKA.

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PKA inhibits an early step in the signaling pathway activated by H₁ histamine receptors.

Intracellular Ca²⁺ and cAMP typically cause opposing effects on airway smooth muscle contraction. Receptors that stimulate these pathways are therapeutic targets in asthma and chronic obstructive pulmonary disease. However, the interactions between different G protein-coupled receptors (GPCRs) that evoke cAMP and Ca²⁺ signals in human bronchial airway smooth muscle cells (hBASMCs) are poorly understood. We measured Ca²⁺ signals in cultures of fluo-4-loaded hBASMCs alongside measurements of intracellular cAMP using mass spectrometry or [³H]-adenine labeling. Interactions between the signaling pathways were examined using selective ligands of GPCRs, and inhibitors of Ca²⁺ and cAMP signaling pathways. Histamine stimulated Ca²⁺ release through inositol 1,4,5-trisphosphate (IP₃) receptors in hBASMCs. β₂-adrenoceptors, through cAMP and protein kinase A (PKA), substantially inhibited histamine-evoked Ca²⁺ signals. Responses to other Ca²⁺-mobilizing stimuli were unaffected by cAMP (carbachol and bradykinin) or minimally affected (lysophosphatidic acid). Prostaglandin E₂ (PGE₂), through EP₂ and EP₄ receptors, stimulated formation of cAMP and inhibited histamine-evoked Ca²⁺ signals. There was no consistent relationship between the inhibition of Ca²⁺ signals and the amounts of intracellular cAMP produced by different stimuli. We conclude that β-adrenoceptors, EP₂ and EP₄ receptors, through cAMP and PKA, selectively inhibit Ca²⁺ signals evoked by histamine in hBASMCs, suggesting that PKA inhibits an early step in H₁ receptor signaling. Local delivery of cAMP within hyperactive signaling junctions mediates the inhibition.

Structure-Based Design and Discovery of New M2 Receptor Agonists

Muscarinic receptor agonists are characterized by apparently strict restraints on their tertiary or quaternary amine and their distance to an ester or related center. On the basis of the active state crystal structure of the muscarinic M₂ receptor in complex with iperoxo, we explored potential agonists that lacked the highly conserved functionalities of previously known ligands. Using structure-guided pharmacophore design followed by docking, we found two agonists (compounds 3 and 17), out of 19 docked and synthesized compounds, that fit the receptor well and were predicted to form a hydrogen-bond conserved among known agonists. Structural optimization led to compound 28, which was 4-fold more potent than its parent 3. Fortified by the discovery of this new scaffold, we sought a broader range of chemotypes by docking 2.2 million fragments, which revealed another three micromolar agonists unrelated either to 28 or known muscarinics. Even pockets as tightly defined and as deeply studied as that of the muscarinic reveal opportunities for the structure-based design and the discovery of new chemotypes.

Double bronchodilation in chronic obstructive pulmonary disease: a crude analysis from a systematic review

OBJECTIVE

The combination of a long-acting muscarinic antagonist (LAMA) and a long-acting β₂-agonist (LABA) in a single inhaler is a viable treatment option for patients with chronic obstructive pulmonary disease (COPD). Here, we systematically review the current knowledge on double bronchodilation for the treatment of COPD, with a specific focus on its efficacy versus placebo and/or monotherapy bronchodilation.

METHODS

A systematic review of clinical trials investigating LABA/LAMA combination therapies was conducted. Articles were retrieved from PubMed, Embase, and Scopus on June 26, 2016. We specifically selected clinical trials with a randomized controlled or crossover design published in any scientific journal showing the following characteristics: 1) comparison of different LABA/LAMA combinations in a single inhaler for patients with COPD, 2) dose approved in Europe, and 3) focus on efficacy (versus placebo and/or bronchodilator monotherapy) in terms of lung function, respiratory symptoms, or exacerbations.

RESULTS

We analyzed 26 clinical trials conducted on 24,338 patients. All LABA/LAMA combinations were consistently able to improve lung function compared with both placebo and bronchodilator monotherapy. Improvements in symptoms were also consistent versus placebo, showing some lack of correlation for some clinical end points and combinations versus monotherapy bronchodilation. Albeit being an exploratory end point, exacerbations showed an improvement with LABA/LAMA combinations over placebo in some trials; however, scarce information was available in comparison with bronchodilator monotherapy in most studies.

CONCLUSION

Our data show consistent improvements for LABA/LAMA combinations, albeit with some variability (depending on the clinical end point, the specific combination, and the comparison group). Clinicians should be aware that these are average differences. All treatments should be tailored at the individual level to optimize clinical outcomes.

Drugs Interfering with Muscarinic Acetylcholine Receptors and Their Effects on Place Navigation

Muscarinic acetylcholine receptors (mAChRs) have been found to regulate many diverse functions, ranging from motivation and feeding to spatial navigation, an important and widely studied type of cognitive behavior. Systemic administration of non-selective antagonists of mAChRs, such as scopolamine or atropine, have been found to have adverse effects on a vast majority of place navigation tasks. However, many of these results may be potentially confounded by disruptions of functions other than spatial learning and memory. Although studies with selective antimuscarinics point to mutually opposite effects of M1 and M2 receptors, their particular contribution to spatial cognition is still poorly understood, partly due to a lack of truly selective agents. Furthermore, constitutive knock-outs do not always support results from selective antagonists. For modeling impaired spatial cognition, the scopolamine-induced amnesia model still maintains some limited validity, but there is an apparent need for more targeted approaches such as local intracerebral administration of antagonists, as well as novel techniques such as optogenetics focused on cholinergic neurons and chemogenetics aimed at cells expressing metabotropic mAChRs.

Involvement of Ca2+ Signaling in the Synergistic Effects between Muscarinic Receptor Antagonists and β₂-Adrenoceptor Agonists in Airway Smooth Muscle

Long-acting muscarinic antagonists (LAMAs) and short-acting β₂-adrenoceptor agonists (SABAs) play important roles in remedy for COPD. To propel a translational research for development of bronchodilator therapy, synergistic effects between SABAs with LAMAs were examined focused on Ca²⁺ signaling using simultaneous records of isometric tension and F340/F380 in fura-2-loaded tracheal smooth muscle. Glycopyrronium (3 nM), a LAMA, modestly reduced methacholine (1 μM)-induced contraction. When procaterol, salbutamol and SABAs were applied in the presence of glycopyrronium, relaxant effects of these SABAs are markedly enhanced, and percent inhibition of tension was much greater than the sum of those for each agent and those expected from the BI theory. In contrast, percent inhibition of F340/F380 was not greater than those values. Bisindolylmaleimide, an inhibitor of protein kinase C (PKC), significantly increased the relaxant effect of LAMA without reducing F340/F380. Iberiotoxin, an inhibitor of large-conductance Ca²⁺-activated K⁺ (K_Ca) channels, significantly suppressed the effects of these combined agents with reducing F340/F380. In conclusion, combination of SABAs with LAMAs synergistically enhances inhibition of muscarinic contraction via decreasing both Ca²⁺ sensitization mediated by PKC and Ca²⁺ dynamics mediated by K_Ca channels. PKC and K_Ca channels may be molecular targets for cross talk between β₂-adrenoceptors and muscarinic receptors.

Cost-effectiveness and budget impact of the fixed-dose dual bronchodilator combination tiotropium-olodaterol for patients with COPD in the Netherlands

Purpose

The fixed-dose dual bronchodilator combination (FDC) of tiotropium and olodaterol showed increased effectiveness regarding lung function and health-related quality of life in patients with chronic obstructive pulmonary disease (COPD) compared with the use of its mono-components. Yet, while effectiveness and safety have been shown, the health economic implication of this treatment is still unknown. The aim of this study was to assess the cost–utility and budget impact of tiotropium–olodaterol FDC in patients with moderate to very severe COPD in the Netherlands.

Patients and methods

A cost–utility study was performed, using an individual-level Markov model. To populate the model, individual patient-level data (age, height, sex, COPD duration, baseline forced expiratory volume in 1 second) were obtained from the tiotropium–olodaterol TOnado trial. In the model, forced expiratory volume in 1 second and patient-level data were extrapolated to utility and survival, and treatment with tiotropium–olodaterol FDC was compared with tiotropium. Cost–utility analysis was performed from the Dutch health care payer’s perspective using a 15-year time horizon in the base-case analysis. The standard Dutch discount rates were applied (costs: 4.0%; effects: 1.5%). Both univariate and probabilistic sensitivity analyses were performed. Budget impact was annually assessed over a 5-year time horizon, taking into account different levels of medication adherence.

Results

As a result of cost increases, combined with quality-adjusted life-year (QALY) gains, results showed that tiotropium–olodaterol FDC had an incremental cost-effectiveness ratio of €7,004/QALY. Without discounting, the incremental cost-effectiveness ratio was €5,981/QALY. Results were robust in univariate and probabilistic sensitivity analyses. Budget impact was estimated at €4.3 million over 5 years assuming 100% medication adherence. Scenarios with 40%, 60%, and 80% adherence resulted in lower 5-year incremental cost increases of €1.7, €2.6, and €3.4 million, respectively.

Conclusion

Tiotropium–olodaterol FDC can be considered a cost-effective treatment under current Dutch cost-effectiveness thresholds.

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.

Research and development of bronchodilators for asthma and COPD with a focus on G protein/KCa channel linkage and β2-adrenergic intrinsic efficacy

Bronchodilators are used to improve symptoms and lung function in asthma and COPD. Airway smooth muscle tone is regulated by both muscarinic and β2-adrenergic receptor activity. Large-conductance Ca(2+)-activated K(+) (KCa) channels are activated by β2-adrenergic receptor agonists, via Gs, and suppressed by muscarinic receptor antagonists via Gi. This functional antagonism converges on the G protein/KCa channel linkages. Membrane potential regulated by KCa channels contributes to airway smooth muscle tension via Ca(2+) influx passing through voltage-dependent Ca(2+) (VDC) channels. The Gs/KCa/VDC channel linkage is a key process in not only physiological effects, but also in dysfunction of β2-adrenergic receptors and airway remodeling. Moreover, this pathway is involved in the synergistic effects between β2-adrenergic receptor agonists and muscarinic receptor antagonists. Intrinsic efficacy is also an important characteristic for both maintenance and loss of β2-adrenergic action. Allosteric modulators of G protein-coupled receptors contribute not only to this synergistic effect between β2-adrenergic and muscarinic M2 receptors, but also to intrinsic efficacy. The effects of weak partial agonists are suppressed by lowering receptor number, disordering receptor function, and enhancing functional antagonism; in contrast, those of full or strong partial agonists are not suppressed. Excessive exposure to full agonists causes β2-adrenergic desensitization; in contrast, exposure to partial agonists does not cause desensitization. Intrinsic efficacy may provide the rationale for the clinical use of β2-adrenergic receptor agonists in asthma and COPD. In conclusion, the G protein/KCa linkage and intrinsic efficacy (allosteric effects) may be therapeutic targets for research and development of novel agents against both airway obstruction and airway remodeling.

Bronchodilators, receptors and cross-talk: Together is better?

The most widely used maintenance therapies in chronic obstructive pulmonary disease (COPD) are long-acting muscarinic antagonists (LAMAs), and a number of these drugs are now available in combination with long-acting β2-agonists (LABAs). LAMAs inhibit the parasympathetic muscarinic pathway, while LABAs, as sympathomimetics, reduce airway smooth muscle (ASM) tone. As well as directly controlling the constriction and relaxation of ASM, muscarinic and adrenergic receptors are found on inflammatory cells, and drugs that target these receptors may also reduce inflammation in COPD. Evidence suggests that the muscarinic and adrenergic pathways cross-talk at the level of neuronal input to the ASM via second-messenger pathways within ASM cells. Although the cross-talk is not completely understood, pharmacologically targeting both pathways in COPD can maximize bronchodilation. Combining LAMAs and LABAs demonstrated improved efficacy compared with the individual therapies and so, for greater convenience, several fixed-dose combinations for once-daily use have been developed. These fixed-dose combinations demonstrate improvements in both lung-function and patient-reported outcomes compared with well-established monotherapies, with similar tolerability profiles to the individual agents.

Profile of a fixed-dose combination of tiotropium/olodaterol and its potential in the treatment of COPD

Chronic obstructive pulmonary disease (COPD) is a progressive, debilitating disorder that results in frequent exacerbations and impacts quality of life. It represents a growing burden of health care cost, both from societal and economic perspectives. Short- and long-acting bronchodilators remain the mainstay of therapy in COPD patients. New fixed-dose combination inhalers with novel pharmacological combinations of long-acting β2-agonists and muscarinic antagonists and delivered once-daily through a variety of devices are currently being developed and licensed for the treatment of COPD. There is mounting research suggesting that combining a fixed dose of a β2-agonist and a muscarinic antagonist achieves better bronchodilation and clinical outcomes compared with either agent alone. These once-daily dosing inhalers are anticipated to impact favorably on patient preference and compliance. This review examines the fixed-dose combination of tiotropium bromide and olodaterol delivered by a Respimat(®) Soft Mist™ inhaler at doses of 2.5/5 μg and 5/5 μg in moderate-to-very-severe COPD, and its potential role in COPD compared with other long-acting β2-agonist with long-acting muscarinic antagonist combinations and delivery devices.

β3-Adrenoceptor-mediated relaxation of rat and human urinary bladder: roles of BKCa channels and Rho kinase

Previous studies suggest that the large-conductance Ca(2+)-activated K(+) (BKCa) channel and Rho-kinase play major roles in the control of urinary bladder tone. Here, we investigated their involvement in β-adrenoceptor (AR)-mediated relaxation of rat and human bladder. Concentration-response curves of isoprenaline and mirabegron-induced bladder relaxation were generated against passive tension and KCl- and carbachol-induced tone, in the absence or presence of the BKCa channel inhibitor iberiotoxin (100 nM) or the Rho-kinase inhibitor Y27,632 (1 μM). Myosin light chain (MLC) phosphorylation was studied by Western blot. In rat, iberiotoxin only slightly altered isoprenaline- and mirabegron-induced relaxation against KCl-induced tone but attenuated relaxation by both agonists against carbachol-induced tone. Y27,632 enhanced isoprenaline- or mirabegron-induced relaxation only against carbachol-induced tone. In humans, iberiotoxin slightly enhanced relaxation by both agonists against carbachol-induced pre-contraction. Y27,632 did not change isoprenaline-induced relaxation but enhanced that by mirabegron. Under passive tension, MLC phosphorylation was markedly reduced by both β-AR agonists, an effect insensitive to Y27,632. In the presence of carbachol, both β-AR agonists increased MLC phosphorylation, an effect reduced by Y27,632 only in the presence of 1 μM carbachol. These results indicate that the extent of BKCa channel and Rho-kinase involvement in relaxation induced by β-AR agonists depends on pre contractile stimulus and species.

The odd sibling: features of β3-adrenoceptor pharmacology

β3-Adrenoceptor agonists have recently been introduced for the treatment of overactive urinary bladder syndrome. Their target, the β3-adrenoceptor, was discovered much later than β1- and β2-adrenoceptors and exhibits unique properties which make extrapolation of findings from the other two subtypes difficult and the β3-adrenoceptor a less-understood subtype. This article discusses three aspects of β3-adrenoceptor pharmacology. First, the ligand-recognition profile of β3-adrenoceptors differs considerably from that of the other two subtypes, i.e., many antagonists considered as nonselective actually are β3-sparing, including propranolol or nadolol. Many agonists and antagonists classically considered as being β3-selective actually are not, including BRL 37,344 ((±)-(R*,R*)-[4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]phenoxy] acetic acid sodium hydrate) or SR 59,230 (3-(2-ethylphenoxy)-[(1S)-1,2,3,4-tetrahydronaphth-1-ylamino]-(2S)-2-propanol oxalate). Moreover, the binding pocket apparently differs between the human and rodent β3-adrenoceptor, yielding considerable species differences in potency. Second, the expression pattern of β3-adrenoceptors is more restricted than that of other subtypes, particularly in humans; this makes extrapolation of rodent findings to the human situation difficult, but it may result in a smaller potential for side effects. The role of β3-adrenoceptor gene polymorphisms has insufficiently been explored and may differ even between primate species. Third, β3-adrenoceptors lack the phosphorylation sites involved in agonist-induced desensitization of the other two subtypes. Thus, they exhibit downregulation and/or desensitization in some, but not other, cell types and tissues. When desensitization occurs, it most often is at the level of mRNA or signaling molecule expression. All three of these factors have implications for future studies to better understand the β3-adrenoceptor as a novel pharmacological target.

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.