Comparison of receptor binding characteristics of commonly used muscarinic antagonists in human bladder detrusor and mucosa

The effect of sacral nerve root magnetic stimulation on bladder urodynamics and M3 receptor expression in rats with neurogenic bladder

Objective

To investigate the effect of sacral nerve root magnetic stimulation(SMS) on bladder urodynamics and M3 receptor expression in rats with neurogenic bladder.

Methods

30 adult female SD rats were randomly divided into Normal Group, Model Group, and Magnetic Stimulation Group, with 10 rats in each group. The Model Group and Magnetic Stimulation Group used the spinal cord transtion method to establish the neurogenic bladder animal model. After successful modeling, the Magnetic Stimulation Group received magnetic stimulation treatment once per day for 8 consutive weeks. After 8 weeks, bladder urodynamics were measured under anesthesia, rats were sacrificed, and bladder detrusor muscle tissue was collected for histological and ultrastructural observation, and M3 receptor expression levels were measured.

Results

The maximum bladder capacity and bladder compliance in the Magnetic Stimulation Group were higher than those in the Model Group (all P < 0. 05), and the leak point pressure was lower than that in the Model Group (P < 0. 05); there were no significant differences between the Magnetic Stimulation Group and the Normal Group in these three parameters (all P > 0. 05). H&E staining of bladder detrusor muscle tissue in the Magnetic Stimulation Group revealed minimal neutrophil infiltration. Moreover, the morphology and arrangement of the mucosal epithelial cells were closer to those observed in the Normal Group when compared with the Model Group. Under transmission electron microscopy, detrusor muscle cells had a smooth surface, slightly widened intercellular spaces, relatively uniform arrangement, and relatively intact mitochondrial structure. The expression level of M3 receptors in the bladder detrusor muscle tissue of the Magnetic Stimulation Group was significantly higher than that in the Normal Group and the Model Group (all P < 0. 05); there was no significant difference between the Model Group and the Normal Group (P > 0. 05).

Conclusion

Sacral nerve root magnetic stimulation has a certain effect on improving bladder function in rats with neurogenic bladder, which may be related to the increased expression level of M3 receptors in the bladder detrusor muscle tissue.

Assessing the anticholinergic cognitive burden classification of putative anticholinergic drugs using drug properties

AIMS

This study evaluated the use of machine learning to leverage drug absorption, distribution, metabolism and excretion (ADME) data together with physicochemical and pharmacological data to develop a novel anticholinergic burden scale and compare its performance to previously published scales.

METHODS

Experimental and in silico ADME, physicochemical and pharmacological data were collected for antimuscarinic activity, blood-brain barrier penetration, bioavailability, chemical structure and P-glycoprotein (P-gp) substrate profile. These five drug properties were used to train an unsupervised model to assign anticholinergic burden scores to drugs. The model performance was evaluated through 10-fold cross-validation and compared with the clinical Anticholinergic Cognitive Burden (ACB) scale and nonclinical Anticholinergic Toxicity Scores (ATS) scale, which is based primarily on muscarinic binding affinity.

RESULTS

In silico software (ADMET Predictor) used for screening drugs for their blood-brain barrier (BBB) penetration correctly identified some drugs that do not cross the BBB. The mean area under the curve for the unsupervised and ACB scale based on the five selected variables was 0.76 and 0.64, respectively. The unsupervised model agreed with the ACB scale on the classification of more than half of the drugs (49 of 88) agreed on the classification of less than half the drugs in the ATS scale (12 of 25).

CONCLUSIONS

Our findings suggest that the commonly used ACB scale may misclassify certain drugs due to their inability to cross the BBB. By contrast, the ATS scale would misclassify drugs solely depending on muscarinic binding affinity without considering other drug properties. Machine learning models can be trained on these features to build classification models that are easy to update and have greater generalizability.

Urinary Incontinence and Pelvic Organ Prolapse in Women

BACKGROUND

Pelvic floor disorders are common, especially in pregnancy and after delivery, in the postmenopausal period, and old age, and they can significantly impact on the patient's quality of life.

METHODS

This narrative review is based on publications retrieved by a selective search of the literature, with special consideration to original articles and AWMF guidelines.

RESULTS

Pelvic floor physiotherapy (evidence level [EL] 1), the use of pessaries (EL2), and local estrogen therapy can help alleviate stress/urge urinary incontinence and other symptoms of urogenital prolapse. Physiotherapy can reduce urinary incontinence by 62% during pregnancy and by 29% 3-6 months post partum. Anticholinergic and β-sympathomimetic drugs are indicated for the treatment of an overactive bladder with or without urinary urge incontinence (EL1). For patients with stress urinary incontinence, selective serotonin-noradrenaline reuptake inhibitors can be prescribed (EL1). The tension-free tape is the current standard of surgical treatment (EL1); in an observational follow-up study, 87.2% of patients were satisfied with the outcome 17 years after surgery. Fascial reconstruction techniques are indicated for the treatment of primary pelvic organ prolapse, and mesh-based surgical procedures for recurrences and severe prolapse (EL1).

CONCLUSION

Urogynecological symptoms should be specifically asked about by physicians of all relevant specialties; if present, they should be treated conservatively at first. Structured surgical techniques with and without mesh are available for the treatment of urinary incontinence and pelvic organ prolapse. Preventive measures against pelvic floor dysfunction should be offered during pregnancy and post partum.

Novel Potent Muscarinic Receptor Antagonists: Investigation on the Nature of Lipophilic Substituents in the 5- and/or 6-Positions of the 1,4-Dioxane Nucleus

A series of novel 1,4-dioxane analogues of the muscarinic acetylcholine receptor (mAChR) antagonist 2 was synthesized and studied for their affinity at M₁–M₅ mAChRs. The 6-cyclohexyl-6-phenyl derivative 3b, with a cis configuration between the CH₂N⁺(CH₃)₃ chain in the 2-position and the cyclohexyl moiety in the 6-position, showed pK_i values for mAChRs higher than those of 2 and a selectivity profile analogous to that of the clinically approved drug oxybutynin. The study of the enantiomers of 3b and the corresponding tertiary amine 33b revealed that the eutomers are (2S,6S)-(−)-3b and (2S,6S)-(−)-33b, respectively. Docking simulations on the M₃ mAChR-resolved structure rationalized the experimental observations. The quaternary ammonium function, which should prevent the crossing of the blood–brain barrier, and the high M₃/M₂ selectivity, which might limit cardiovascular side effects, make 3b a valuable starting point for the design of novel antagonists potentially useful in peripheral diseases in which M₃ receptors are involved.

Muscarinic receptor binding of fesoterodine, 5-hydroxymethyl tolterodine, and tolterodine in rat tissues after the oral, intravenous, or intravesical administration

The present study aimed to characterize muscarinic receptor binding of fesoterodine, 5-hydroxymethyl tolterodine (5-HMT), and tolterodine in bladder and other tissues of rats after their oral, intravenous, or intravesical administration. Muscarinic receptors in tissues were measured by using [N-methyl-³H]scopolamine methyl chloride ([³H]NMS). The in vitro binding affinity for muscarinic receptors was the highest by 5-HMT, followed by tolterodine and fesoterodine. Fesoterodine exhibited lower affinity in rat submaxillary gland than in detrusor muscle and urothelium. Muscarinic binding affinities of 5-HMT and tolterodine were similar among tissues. The duration of binding of oral fesoterodine to muscarinic receptors was longer in bladder than in submaxillary gland, heart, and lung, and its binding was little observed in colon and cerebral cortex. Binding activity of intravenous 5-HMT to muscarinic receptors was significantly observed in all tissues, except cerebral cortex, with a longer duration in bladder. Significant binding of bladder detrusor and urothelial muscarinic receptors was observed following intravesical instillation of 5-HMT. This selectivity may be attributed to the direct blockade of bladder receptors by excreted urinary 5-HMT. Thus, fesoterodine may be efficacious as a treatment for patients with overactive bladder.

Mirabegron: a Beta-3 agonist for overactive bladder

OBJECTIVE

To review the literature regarding the efficacy and safety of mirabegron for the treatment of overactive bladder (OAB).

DATA SOURCES

A literature search was performed using MEDLINE (PubMed) prior to December 31, 2013, using the terms "mirabegron" and "randomized-controlled trial."

STUDY SELECTION/DATA EXTRACTION

All published, double-blind, randomized-controlled trials assessing mirabegron were included. Articles were reviewed and included if mirabegron was used as monotherapy and if the primary outcome analyzed drug efficacy.

DATA SYNTHESIS

The efficacy of mirabegron for the treatment of OAB has been demonstrated in the selected five randomized, placebo-controlled trials. The majority of these trials lasted 12 weeks and compared various doses of mirabegron with placebo and/or tolterodine extended-release (ER). Primary efficacy outcomes for the trials included mean number of micturitions per 24 hours and mean number of incontinence episodes per 24 hours. Included trials showed statistically significant reductions in both efficacy outcomes for various doses of mirabegron when compared with placebo.

CONCLUSION

Based on the trials reviewed, mirabegron has been efficacious in reducing mean number of micturitions and incontinence episodes per 24 hours, as well as in improving other secondary outcomes such as OAB symptoms and quality-of-life measures. Common adverse drug events seen with mirabegron include: hypertension, nasopharyngitis, urinary tract infections, headache, constipation, upper respiratory tract infection, arthralgia, diarrhea, tachycardia, abdominal pain, and fatigue. Given the efficacy and safety data currently available, mirabegron represents a reasonable alternative to antimuscarinics for patients with OAB. Future studies are needed to determine the utility of mirabegron for OAB in a variety of demographics.

Phencynonate S-isomer as a eutomer is a novel central anticholinergic drug for anti-motion sickness

To compare and evaluate the differences of stereoselective activity, the binding affinity, metabolism, transport and molecular docking of phencynonate isomers to muscarinic acetylcholine receptor (mAChR) were investigated in this study. The rotation stimulation and locomotor experiments were used to evaluate anti-motion sickness effects. The competitive affinity with [3H]-QNB and molecular docking were used for studying the interactions between the two isomers and mAChR. The stereoselective mechanism of isomers was investigated by incubation with rat liver microsomes, a protein binding assay and membrane permeability assay across a Caco-2 cell monolayer using a chiral column HPLC method. The results indicated that S-isomer was more effective against motion sickness and had not anxiogenic action at therapeutic doses. S-isomer has the higher affinity and activity for mAChR in cerebral cortex and acted as a competitive mAChR antagonist. The stereoselective elimination of S-isomer was primarily affected by CYP1B1 and 17A1 enzymes, resulting in a higher metabolic stability and slower elimination. Phencynonate S isomer, as a eutomer and central anticholinergic chiral drug, is a novel anti-motion sickness drug with higher efficacy and lower central side effect. Our data assisted the development of a novel drug and eventual use of S-isomer in clinical practice.

Basic and clinical aspects of antimuscarinic agents used to treat overactive bladder

Antimuscarinic agents are now widely used as the pharmacological therapy for overactive bladder (OAB) because neuronal (parasympathetic nerve) and non-neuronal acetylcholine play a significant role for the bladder function. In this review, we will highlight basic and clinical aspects of eight antimuscarinic agents (oxybutynin, propiverine, tolterodine, solifenacin, darifenacin, trospium, imidafenacin, and fesoterodine) clinically used to treat urinary dysfunction in patients with OAB. The basic pharmacological characteristics of these eight antimuscarinic agents include muscarinic receptor subtype selectivity, functional bladder selectivity, and muscarinic receptor binding in the bladder and other tissues. The measurement of drug-receptor binding after oral administration of these agents allows for clearer understanding of bladder selectivity by the integration of pharmacodynamics and pharmacokinetics under in vivo conditions. Their central nervous system (CNS) penetration potentials are also discussed in terms of the feasibility of impairments in memory and cognitive function in elderly patients with OAB. The clinical aspects of efficacy focus on improvements in the daytime urinary frequency, nocturia, bladder capacity, the frequency of urgency, severity of urgency, number of incontinence episodes, OAB symptom score, and quality of life (QOL) score by antimuscarinic agents in patients with OAB. The safety of and adverse events caused by treatments with antimuscarinic agents such as dry mouth, constipation, blurred vision, erythema, fatigue, increased sweating, urinary retention, and CNS adverse events are discussed. A dose-dependent relationship was observed with adverse events, because the risk ratio generally increased with elevations in the drug dose of antimuscarinic agents. Side effect profiles may be additive to or contraindicated by other medications.

Acetylcholinesterase Inhibitors and Drugs Acting on Muscarinic Receptors- Potential Crosstalk of Cholinergic Mechanisms During Pharmacological Treatment

BACKGROUND

Pharmaceuticals with targets in the cholinergic transmission have been used for decades and are still fundamental treatments in many diseases and conditions today. Both the transmission and the effects of the somatomotoric and the parasympathetic nervous systems may be targeted by such treatments. Irrespective of the knowledge that the effects of neuronal signalling in the nervous systems may include a number of different receptor subtypes of both the nicotinic and the muscarinic receptors, this complexity is generally overlooked when assessing the mechanisms of action of pharmaceuticals.

METHODS

We have search of bibliographic databases for peer-reviewed research literature focused on the cholinergic system. Also, we have taken advantage of our expertise in this field to deduce the conclusions of this study.

RESULTS

Presently, the life cycle of acetylcholine, muscarinic receptors and their effects are reviewed in the major organ systems of the body. Neuronal and non-neuronal sources of acetylcholine are elucidated. Examples of pharmaceuticals, in particular cholinesterase inhibitors, affecting these systems are discussed. The review focuses on salivary glands, the respiratory tract and the lower urinary tract, since the complexity of the interplay of different muscarinic receptor subtypes is of significance for physiological, pharmacological and toxicological effects in these organs.

CONCLUSION

Most pharmaceuticals targeting muscarinic receptors are employed at such large doses that no selectivity can be expected. However, some differences in the adverse effect profile of muscarinic antagonists may still be explained by the variation of expression of muscarinic receptor subtypes in different organs. However, a complex pattern of interactions between muscarinic receptor subtypes occurs and needs to be considered when searching for selective pharmaceuticals. In the development of new entities for the treatment of for instance pesticide intoxication, the muscarinic receptor selectivity needs to be considered. Reactivators generally have a muscarinic M2 receptor acting profile. Such a blockade may engrave the situation since it may enlarge the effect of the muscarinic M3 receptor effect. This may explain why respiratory arrest is the major cause for deaths by esterase blocking.

Medical management of neurogenic bladder with oral therapy

This is a review of the most current literature on medical management of the neurogenic bladder (NGB) to treat detrusor overactivity (DO), improve bladder compliance and treat urinary incontinence. The use of antimuscarinics, alpha blockers, tricyclic antidepressants, desmopressin and mirabegron will be discussed along with combination therapy to improve efficacy. These medical therapies will be the focus of this review with surgical therapy and botulinum toxin injections being the subject of other articles in this series.

Concomitant use of acetylcholine esterase inhibitors and urinary antispasmodics among Finnish community-dwelling persons with Alzheimer disease

Concomitant use of acetylcholine esterase inhibitors (AChEIs) and anticholinergic drugs, such as urinary antispasmodics (UA), is generally considered as inappropriate because of their opposite pharmacological actions. However, prevalence and the duration or factors associated with concomitant use have not been previously studied among community-dwelling persons with Alzheimer disease (AD). The aim of this study was to examine the prevalence and duration of concomitant use of AChEIs and UAs among community-dwelling persons with AD and factors associated with concomitant use. Register-based data of the MEDALZ-2005 Study included all community-dwelling persons with clinically diagnosed AD at the end of year 2005 in Finland. Persons using AChEI drugs during the 4-year follow-up (2006-2009) were included in the present study (n = 20,442). Among AChEI users, 1576 persons used UA during the follow-up. Prevalence of concomitant use of AChEIs and UAs was 7.3% (n = 1491) during the 4-year follow-up. The median duration of concomitant use was 236 days. Factors associated with concomitant use were age younger than 80 years (odds ratio [OR], 1.20; 95% confidence interval [CI], 1.08-1.34), male sex (OR, 1.16; 95% CI, 1.04-1.30), Parkinson disease (OR, 1.98; 95% CI, 1.55-2.52), diabetes (OR, 1.25; 95% CI, 1.08-1.45), and prostatic cancer (OR, 1.54; 95% CI, 1.13-2.09). Despite their antagonizing action, concomitant use of AChEIs and UAs was quite common among Finnish community-dwelling persons with AD. In addition, duration of concomitant use was comparatively long. It is recommended to consider some other options than UAs to treat urinary incontinence among persons with AD.

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

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Muscarinic receptors increase smooth muscle tone in airways and urinary bladder.

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β-Adrenoceptors relax smooth muscle tone and oppose muscarinic contraction.

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Opposition involves transmitter release, signal transduction and receptor expression.

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This supports the combined use of muscarinic antagonists and β-adrenoceptor agonists.

Muscarinic receptor antagonists and β-adrenoceptor agonists are used in the treatment of obstructive airway disease and overactive bladder syndrome. Here we review the pharmacological rationale for their combination. Muscarinic receptors and β-adrenoceptors are physiological antagonists for smooth muscle tone in airways and bladder. Muscarinic agonism may attenuate β-adrenoceptor-mediated relaxation more than other contractile stimuli. Chronic treatment with one drug class may regulate expression of the target receptor but also that of the opposing receptor. Prejunctional β₂-adrenoceptors can enhance neuronal acetylcholine release. Moreover, at least in the airways, muscarinic receptors and β-adrenoceptors are expressed in different locations, indicating that only a combined modulation of both systems may cause dilatation along the entire bronchial tree. While all of these factors contribute to a rationale for a combination of muscarinic receptor antagonists and β-adrenoceptor agonists, the full value of such combination as compared to monotherapy can only be determined in clinical studies.

Different muscarinic receptor subtypes modulate proliferation of primary human detrusor smooth muscle cells via Akt/PI3K and map kinases

While acetylcholine (ACh) and muscarinic receptors in the bladder are mainly known for their role in the regulation of smooth muscle contractility, in other tissues they are involved in tissue remodelling and promote cell growth and proliferation. In the present study we have used primary cultures of human detrusor smooth muscle cells (HDSMCs), in order to investigate the role of muscarinic receptors in HDSMC proliferation. Samples were obtained as discarded tissue from men >65 years undergoing radical cystectomy for bladder cancer and cut in pieces that were either immediately frozen or placed in culture medium for the cell culture establishment. HDSMCs were isolated from samples, propagated and maintained in culture. [(3)H]-QNB radioligand binding on biopsies revealed the presence of muscarinic receptors, with a Kd of 0.10±0.02nM and a Bmax of 72.8±0.1fmol/mg protein. The relative expression of muscarinic receptor subtypes, based on Q-RT-PCR, was similar in biopsies and HDSMC with a rank order of M2≥M3>M1>M4>M5. The cholinergic agonist carbachol (CCh, 1-100μM) concentration-dependently increased [(3)H]-thymidine incorporation (up to 46±4%). This was concentration-dependently inhibited by the general muscarinic receptor antagonist atropine and by subtype-preferring antagonists with an order of potency of darifenacin >4-DAMP>AF-DX 116. The CCh-induced cell proliferation was blocked by selective PI-3 kinase and ERK activation inhibitors, strongly suggesting that these intracellular pathways mediate, at least in part, the muscarinic receptor-mediated cell proliferation. This work shows that M2 and M3 receptors can mediate not only HDSM contraction but also proliferation; they may also contribute bladder remodelling including detrusor hypertrophy.

Fesoterodine, its active metabolite, and tolterodine bind selectively to muscarinic receptors in human bladder mucosa and detrusor muscle

OBJECTIVE

To comparatively characterize the binding activity of fesoterodine, its active metabolite (5-hydroxymethyl tolterodine [5-HMT]), and tolterodine in the human bladder mucosa, detrusor muscle, and parotid gland.

MATERIALS AND METHODS

Muscarinic receptors in the homogenates of human bladder mucosa, detrusor muscle, and parotid gland were measured by a radioligand binding assay using [N-methyl-(3)H] scopolamine methyl chloride.

RESULTS

Fesoterodine, 5-HMT, and tolterodine competed with [N-methyl-(3)H] scopolamine methyl chloride for binding sites in the bladder mucosa, detrusor muscle, and parotid gland in a concentration-dependent manner. The affinity for muscarinic receptors of these agents was significantly greater in the bladder than in the parotid gland, suggesting pharmacologic selectivity for the bladder over the parotid gland. The bladder selectivity was larger for fesoterodine and 5-HMT than for tolterodine. Fesoterodine, 5-HMT, and tolterodine resulted in significantly increased (two- to five-fold) values of the apparent dissociation constant for specific [N-methyl-(3)H] scopolamine methyl chloride binding in the detrusor muscle and parotid gland, with little effect on the corresponding values of the maximal number of binding sites. This finding indicates that these agents bind to the human muscarinic receptors in a competitive and reversible manner.

CONCLUSION

Fesoterodine and 5-HMT bind to the muscarinic receptors with greater affinity in the human bladder mucosa and detrusor muscle than in the parotid gland in a competitive and reversible manner.

Investigation of ex vivo stability of fesoterodine in human plasma and its simultaneous determination together with its active metabolite 5-HMT by LC-ESI-MS/MS: Application to a bioequivalence study

Fesoterodine is a non-selective muscarinic-receptor antagonist, used in the treatment of overactive bladder syndrome. A highly sensitive, selective and rapid method has been developed for the simultaneous determination of fesoterodine and its active metabolite, 5-hydroxymethyl tolterodine (5-HMT) in human plasma by liquid chromatography-tandem mass spectrometry (LC-ESI-MS/MS). Due to rapid conversion of parent drug to 5-HMT, ex vivo stability of fesoterodine in human plasma was extensively studied to optimize the extraction protocol. The analytes and their deuterated analogs were quantitatively extracted from 100μL human plasma by liquid-liquid extraction in methyl tert-butyl ether: n-hexane. The chromatographic separation of analytes was achieved on a Kromasil C18 (100mm×4.6mm, 5μm) column under isocratic conditions. The method was validated over a dynamic concentration range of 0.01-10ng/mL for both the analytes. Ion-suppression effects were investigated by post-column infusion of analytes. The precision (% CV) values for the calculated slopes of calibration curves, which would reflect the relative matrix effect, were less than 1.5% for both the analytes. The intra-batch and inter-batch precision (% CV) across quality control levels varied from 1.82 to 3.73% and the mean extraction recovery was >96% for both the analytes. The method was successfully applied to a bioequivalence study of 8mg fesoterodine tablet formulation (test and reference) in 12 healthy Indian subjects under fasted and fed condition. The assay reproducibility estimated by reanalysis of incurred samples showed a change of ±12.0%.

Autonomic nervous control of the urinary bladder

The autonomic nervous system plays an important role in the regulation of the urinary bladder function. Under physiological circumstances, noradrenaline, acting mainly on β(3) -adrenoceptors in the detrusor and on α(1) (A) -adrenoceptors in the bladder outflow tract, promotes urine storage, whereas neuronally released acetylcholine acting mainly on M(3) receptors promotes bladder emptying. Under pathophysiological conditions, however, this system may change in several ways. Firstly, there may be plasticity at the levels of innervation and receptor expression and function. Secondly, non-neuronal acetylcholine synthesis and release from the urothelium may occur during the storage phase, leading to a concomitant exposure of detrusor smooth muscle, urothelium and afferent nerves to acetylcholine and noradrenaline. This can cause interactions between the adrenergic and cholinergic system, which have been studied mostly at the post-junctional smooth muscle level until now. The implications of such plasticity are being discussed.

Overview of muscarinic receptor subtypes

The physiological role of muscarinic receptors is highly complex and, although not completely understood, has become clearer over the last decade. Recent pharmacological evidence with novel compounds, together with data from transgenic mice, suggests that all five subtypes have defined functions in the nervous system as well as mediating the non neuronal, hormonal actions of acetylcholine. Numerous novel agonists, allosteric regulators, and antagonists have now been identified with authentic subtype specificity in vitro and in vivo. These compounds provide additional pharmacological opportunities for selective subtype modulation as well as a new generation of muscarinic receptor-based therapeutics.

Muscarinic agonists and antagonists: effects on the urinary bladder

Voiding of the bladder is the result of a parasympathetic muscarinic receptor activation of the detrusor smooth muscle. However, the maintenance of continence and a normal bladder micturition cycle involves a complex interaction of cholinergic, adrenergic, nitrergic and peptidergic systems that is currently little understood. The cholinergic component of bladder control involves two systems, acetylcholine (ACh) released from parasympathetic nerves and ACh from non-neuronal cells within the urothelium. The actions of ACh on the bladder depend on the presence of muscarinic receptors that are located on the detrusor smooth muscle, where they cause direct (M₃) and indirect (M₂) contraction; pre-junctional nerve terminals where they increase (M₁) or decrease (M₄) the release of ACh and noradrenaline (NA); sensory nerves where they influence afferent nerve activity; umbrella cells in the urothelium where they stimulate the release of ATP and NO; suburothelial interstitial cells with unknown function; and finally, other unidentified sites in the urothelium from where prostaglandins and inhibitory/relaxatory factors are released. Thus, the actions of muscarinic receptor agonists and antagonists on the bladder may be very complex even when considering only local muscarinic actions. Clinically, muscarinic antagonists remain the mainstay of treatment for the overactive bladder (OAB), while muscarinic agonists have been used to treat hypoactive bladder. The antagonists are effective in treating OAB, but their precise mechanisms and sites of action (detrusor, urothelium, and nerves) have yet to be established. Potentially more selective agents may be developed when the cholinergic systems within the bladder are more fully understood.

Comparative analysis of the effects of antimuscarinic agents on bladder functions in both nonhuman primates and rodents

Both the physiological role of muscarinic receptors for bladder function and the therapeutic efficacy of antimuscarinic agents for overactive bladder syndrome are well documented. We investigated the effect of antimuscarinic agents with different subtype selectivity on urodynamic parameters in nonhuman primates and rodents and compared plasma levels of these agents between species. Anesthetized rhesus monkeys were transurethrally catheterized, and the bladder was infused with saline. Urodynamic parameters were measured before and after intravenous drug administration. Tolterodine (nonselective) and oxybutynin (moderately M(3)-selective) increased bladder capacity at lower doses than those required to decrease micturition pressure. However, higher doses of darifenacin (M(3)-selective) were needed to increase the bladder capacity than those needed to decrease the micturition pressure. In rats, tolterodine had no effect on the bladder capacity but decreased the micturition pressure at all of the doses administered. Oxybutynin also decreased micturition pressure and increased bladder capacity at the highest dose. Plasma levels of these drugs overlap in both species. These results suggest that, in addition to the M(3) receptor, other muscarinic receptor subtypes contribute to regulate bladder storage function in nonhuman primates, since less subtype-selective tolterodine and oxybutynin showed higher specificity to the bladder capacity effect than the effect on micturition pressure compared with M(3)-selective darifenacin. In addition, the role of muscarinic receptors in bladder storage function varies between primates and rodents. Compared with rodents, muscarinic receptors may play a more active role during the storage phase to regulate the functional bladder capacity in primates.

Muscarinic acetylcholine receptors in the urinary tract

Muscarinic receptors comprise five cloned subtypes, encoded by five distinct genes, which correspond to pharmacologically defined receptors (M(1)-M(5)). They belong to the family of G-protein-coupled receptors and couple differentially to the G-proteins. Preferentially, the inhibitory muscarinic M(2) and M(4) receptors couple to G(i/o), whereas the excitatory muscarinic M(1), M(3), and M(5) receptors preferentially couple to G(q/11). In general, muscarinic M(1), M(3), and M(5) receptors increase intracellular calcium by mobilizing phosphoinositides that generate inositol 1,4,5-trisphosphate (InsP3) and 1,2-diacylglycerol (DAG), whereas M(2) and M(4) receptors are negatively coupled to adenylyl cyclase. Muscarinic receptors are distributed to all parts of the lower urinary tract. The clinical use of antimuscarinic drugs in the treatment of detrusor overactivity and the overactive bladder syndrome has focused interest on the muscarinic receptors not only of the detrusor, but also of other components of the bladder wall, and these have been widely studied. However, the muscarinic receptors in the urethra, prostate, and ureter, and the effects they mediate in the normal state and in different urinary tract pathologies, have so far not been well characterized. In this review, the expression of and the functional effects mediated by muscarinic receptors in the bladder, urethra, prostate, and ureters, under normal conditions and in different pathologies, are discussed.

Pharmacologic therapy for the neurogenic bladder

This article is a review of the current and past literature on medical management of the neurogenic bladder, with a particular focus on spinal cord injury and multiple sclerosis. The use of antimuscarinics, αα-blocker, and tricyclic antidepressants and their combined use are discussed along with new therapies in human and animal trials.

Role of fesoterodine in the treatment of overactive bladder

Muscarinic receptors have long been the target receptors for treatment of patients with overactive bladder (OAB). These patients experience symptoms of urgency, urinary frequency and nocturia, with or without urge incontinence (the involuntary leakage of urine associated with urge). Fesoterodine, a pro-drug, structurally and functionally related to tolterodine, is the newest agent developed for the treatment of OAB. Fesoterodine is broken down to the active metabolite, 5-hydroxy-methyl-tolterodine (5-HMT) by non-specific esterases. This metabolism results in the complete breakdown of the parent compound and is responsible for dose related improvements in clinical efficacy and health related quality of life. Like other antimuscarinic agents including tolterodine, fesoterodine is associated with improvements in clinical variables related both to bladder filling (decreasing micturition frequency and increasing mean voided volume) and urgency (urgency and urge incontinence episodes). Improvements in health related quality of life following treatment with fesoterodine is indicated by improvements in 7 of the 9 variables measured by the King’s Health Questionnaire. Also like other antimuscarinic agents, fesoterodine use is associated with adverse events including dry mouth. However the incidence of dry mouth is reduced with fesoterodine, compared to oxybutynin, due to the improved bladder selectivity of 5-HMT.

Fesoterodine for the treatment of overactive bladder

OBJECTIVE

To review pharmacologic, pharmacokinetic, efficacy, and safety data for fesoterodine and determine its role in the treatment of overactive bladder.

DATA SOURCES

A MEDLINE search (1966-July 2009) was conducted using the key words fesoterodine, tolterodine, muscarinic receptor antagonist, anticholinergic, overactive bladder, urge incontinence, efficacy, safety, adverse effect, pharmacology, pharmacokinetic, and receptor binding.

STUDY SELECTION AND DATA EXTRACTION

All articles written in English that were identified from the data sources were evaluated, prioritizing randomized, controlled trials with human data. The references of published articles that we identified were examined for any additional studies appropriate for the review.

DATA SYNTHESIS

Fesoterodine, a competitive muscarinic receptor antagonist, is converted to its active metabolite, 5-hydroxymethyltolterodine, by nonspecific esterases, bypassing the cytochrome P450 system. Two randomized controlled Phase 3 trials examined the safety and efficacy of fesoterodine in the treatment of overactive bladder. Fesoterodine was found to produce significant improvements in the treatment of overactive bladder symptoms compared with placebo. Post hoc analysis of these trials demonstrated significant improvements in health-related quality of life in patients with overactive bladder. Only one study included tolterodine, and direct comparisons between fesoterodine and tolterodine were not conducted. The most common treatment-emergent adverse effects associated with fesoterodine included dry mouth, constipation, urinary tract infection, and headache.

CONCLUSIONS

Fesoterodine appears to be effective and generally safe for the treatment of overactive bladder. The efficacy and safety of fesoterodine in overactive bladder treatment seem to be at least similar to that of tolterodine. Although additional comparative trials are needed, based on available data, it does not appear that fesoterodine provides a substantial advantage over extended-release tolterodine in either efficacy or safety.