Muscarinic receptors: What we know

The role of the cholinergic anti-inflammatory pathway in autoimmune rheumatic diseases

The cholinergic anti-inflammatory pathway (CAP) is a classic neuroimmune pathway, consisting of the vagus nerve, acetylcholine (ACh)-the pivotal neurotransmitter of the vagus nerve-and its receptors. This pathway can activate and regulate the activities of immune cells, inhibit cell proliferation and differentiation, as well as suppress cytokine release, thereby playing an anti-inflammatory role, and widely involved in the occurrence and development of various diseases; recent studies have demonstrated that the CAP may be a new target for the treatment of autoimmune rheumatic diseases. In this review, we will summarize the latest progress with the view of figuring out the role of the cholinergic pathway and how it interacts with inflammatory reactions in several autoimmune rheumatic diseases, and many advances are results from a wide range of experiments performed in vitro and in vivo.

MIST1, an Inductive Signal for Salivary Amylase in Mesenchymal Stem Cells

Sjögren’s syndrome (SjS) is an autoimmune disease that destroys the salivary glands and results in severe dry mouth. Mesenchymal stem cell (MSC) transplantation has been recently proposed as a promising therapy for restoring cells in multiple degenerative diseases. We have recently utilized advanced proteomics biochemical assays to identify the key molecules involved in the mesenchymal-epithelial transition (MET) of co-cultured mouse bone-marrow-derived MSCs mMSCs with primary salivary gland cells. Among the multiple transcription factors (TFs) that were differentially expressed, two major TFs were selected: muscle, intestine, and stomach expression-1 (MIST1) and transcription factor E2a (TCF3). These factors were assessed in the current study for their ability to drive the expression of acinar cell marker, alpha-salivary amylase 1 (AMY1), and ductal cell marker, cytokeratin19 (CK19), in vitro. Overexpression of MIST1-induced AMY1 expression while it had little effect on CK19 expression. In contrast, TCF3 induced neither of those cellular markers. Furthermore, we have identified that mMSCs express muscarinic-type 3 receptor (M3R) mainly in the cytoplasm and aquaporin 5 (AQP5) in the nucleus. While MIST1 did not alter M3R levels in mMSCs, a TCF3 overexpression downregulated M3R expressions in mMSCs. The mechanisms for such differential regulation of glandular markers by these TFs warrant further investigation.

Acetylcholinesterase and Butyrylcholinesterase – Important Enzymes of Human Body

The serine hydrolases and proteases are a ubiquitous group of enzymes that is fundamental to many critical lifefunctions. Human tissues have two distinct cholinesterase activities: acetylcholinesterase and butyrylcholinesterase. Acetylcholinesterase functions in the transmission of nerve impulses, whereas the physiological function of butyrylcholinesterase remains unknown. Acetylcholinesterase is one of the crucial enzymes in the central and peripheral nerve system. Organophosphates and carbamates are potent inhibitors of serine hydrolases and well suited probes for investigating the chemical reaction mechanism of the inhibition. Understanding the enzyme’s chemistry is essential in preventing and/or treating organophosphate and carbamate poisoning as well as designing new medicaments for cholinergic-related diseases like as Alzheimer’s disease.

Oxybutynin gel for the treatment of overactive bladder

INTRODUCTION

Overactive bladder (OAB) is a common condition that has a profound impact on an individual's overall health and quality of life. Muscarinic receptor antagonists are the mainstay of oral pharmacotherapy for OAB. While all of the medications in this class are significantly more effective than placebo, they are also associated with more adverse events that may limit their overall use. Transdermal application of oxybutynin has been shown to avoid first-pass metabolism and, thus, may be associated with fewer antimuscarinic side effects.

AREAS COVERED

This paper reviews the pharmacology of transdermal oxybutynin gel and summarizes the available data regarding this product in the treatment of OAB. It also discusses the role of this product in the OAB treatment armamentarium.

EXPERT OPINION

Oxybutynin transdermal gel has been shown to have significant advantages over placebo, in terms of urgency incontinence episodes, urinary frequency and voided volume in a Phase III study. Application site effects were higher in the gel group, but the incidence of antimuscarinic side effects were lower than those seen with oral preparations. The lower incidence of skin side effects, as compared with the transdermal patch, may confer a theoretical advantage toward the gel product. While promising, unanswered questions remain regarding persistence with treatment after this mode of therapy, and head-to-head comparisons with other antimuscarinics are absent.

In vitro safety pharmacology profiling: what else beyond hERG?

One of the main reasons for drug failures in clinical development, or postmarket launch, is lacking or compromised safety margins at therapeutic doses. Organ toxicity with poorly defined mechanisms and adverse drug reactions associated with on- and off-target effects are the major contributors to safety-related shortfalls of many clinical drug candidates. Therefore, to avoid high attrition rates in clinical trials, it is imperative to test compounds for potential adverse reactions during early drug discovery. Beyond a small number of targets associated with clinically acknowledged adverse drug reactions, there is little consensus on other targets that are important to consider at an early stage for in vitro safety pharmacology assessment. We consider here a limited number of safety-related targets, from different target families, which were selected as part of in vitro safety pharmacology profiling panels integrated in the drug-development process at Novartis. The best way to assess these targets, using a biochemical or a functional readout, is discussed. In particular, the importance of using cell-based profiling assays for the characterization of an agonist action at some GPCRs is highlighted. A careful design of in vitro safety pharmacology profiling panels allows better prediction of potential adverse effects of new chemical entities early in the drug-discovery process. This contributes to the selection of the best candidate for clinical development and, ultimately, should contribute to a decreased attrition rate.

Urinary incontinence in the aging female: etiology, pathophysiology and treatment options

Not only does the prevalence of incontinence increase with age, but the incidence does as well, in no small part due to the greater recognition of its signs and symptoms and the significant negative impact on quality of life. Elderly women differ from their younger counterparts by the presence of several physiologic changes in the urinary tract, as well as the presence of concomitant morbidity and polypharmacy. While the elderly have the same treatment options as younger women, they may experience a greater incidence of adverse events due to urologic and nonurologic factors. The objective of this article is to elucidate the unique changes in the elderly population and summarize the treatment options.

Update on the management of overactive bladder: patient considerations and adherence

Overactive bladder (OAB) is a common condition that causes a profound impact on an individual’s overall health and quality of life. Muscarinic receptor antagonists are the mainstay of oral pharmacotherapy for OAB. Although all of the medications in this class are significantly more effective than placebo, they are also associated with more adverse events that may limit their overall use. Although newer preparations of these medications have sought to improve tolerability and efficacy through alternative routes of delivery and once-daily dosing, improved adherence to treatment and treatment persistence continue to be an ongoing challenge. An improved understanding of the factors involved in persistence of medical OAB therapy is imperative in efforts to optimize therapeutic benefits in this chronic and potentially morbid condition.

Patient perspectives in the management of overactive bladder, focus on transdermal oxybutynin

Overactive bladder syndrome (OAB) is a constellation of distressing symptoms that significantly impair quality of life, sexual function, and work productivity, and imposes a significant economic burden to society. Pharmacological treatment with antimuscarinic agents, behavioral modification, bladder retraining, and/or pelvic floor exercises are often used alone or in combination as the mainstay treatment in the management of OAB. Oxybutynin has been used in the treatment of OAB for over 20 years with proven efficacy and is often the comparator in drug treatment trials. Oral formulations of oxybutynin have proven efficacy, but not without significant antimuscarinic effects, which reduce patient persistence with medical treatment. Low levels of patient persistence with oral formulations of oxybutynin provided an impetus for the development of a transdermal oxybutynin delivery system. The oxybutynin transdermal formulation has been found to have side effects similar to that of a placebo in randomized controlled trials while providing excellent efficacy. Patient persistence with therapy, improved quality of life, sexual function and interpersonal relationships have been observed with use of the transdermal oxybutynin delivery system. Its twice weekly dosing, low side effect profile, and high efficacy have made it a good choice for initial treatment of overactive bladder syndrome.

Antimuscarinics for the treatment of overactive bladder: a review of central nervous system effects

Antimuscarinic drugs commonly used to treat overactive bladder are often associated with central nervous system (CNS) side effects including cognitive dysfunction, memory impairment, dizziness, fatigue, and headache. New agents show reduced CNS penetrance and better selectivity for the M3 muscarinic receptor. However, changes associated with aging may lead to alterations in blood-brain barrier permeability. Therefore, use of antimuscarinics in the elderly or in patients with Alzheimer's disease presents a significant challenge. This review highlights muscarinic receptor distribution and function in the CNS, provides a description and incidence of CNS side effects with therapy, offers information specific to currently available agents, and describes the use of antimuscarinics in special populations including children, the elderly, and patients with Alzheimer's disease.

Management of detrusor-external sphincter dyssynergia

Detrusor-external sphincter dyssynergia (DSD) is a debilitating problem in patients with spinal cord injury. DSD carries a high risk of complications, and even life expectancy can be affected. The mainstay of treatment is the use of antimuscarinic medication and catheterization, but in those for whom this is not possible external sphincterotomy has been the traditional management route. External sphincterotomy, however, is associated with significant risks, including hemorrhage, erectile dysfunction and the need for repeat procedures, and over the last decade alternatives have been investigated, such as urethral stents and botulinum toxin injection. We present a review of DSD, including the current management strategies and prospects for future treatment.

Transdermal drug delivery treatment for overactive bladder

Overactive bladder is commonly treated with oral anticholinergic drugs such as oxybutynin chloride. Although oral anticholinergic agents have been effective in controlling urinary urgency and incontinence, adverse events, particularly dry mouth, often cause patients to discontinue oral therapy and to endure incontinence. Oxybutynin can be delivered transcutaneously, maintaining the efficacy of oral oxybutynin while significantly minimizing side effects (e.g., dry mouth) that may complicate therapy. By avoiding hepatic and gastrointestinal metabolism of oxybutynin, less N-desethyloxybutynin (N-DEO) is produced and this compound is deemed to be responsible for anticholinergic side effects such as dry mouth. This novel oxybutynin formulation offers patients with OAB and urge urinary incontinence a well-tolerated option for managing the symptoms of overactive bladder.

Solifenacin succinate for the treatment of symptoms of overactive bladder

BACKGROUND

Overactivity of the bladder detrusor muscle can result in urinary urgency, frequency, and incontinence. Antimuscarinic agents are the treatment of choice, as they reduce the contractility of this muscle. Solifenacin succinate (SOL) is a competitive muscarinic-receptor antagonist approved by the US Food and Drug Administration in late 2004 for the treatment of overactive bladder (OAB) with symptoms of urge urinary incontinence, urgency, and urinary frequency.

OBJECTIVE

This article reviews the current primary literature concerning the pharmacokinetics, efficacy, and tolerability of SOL in the treatment of OAB.

METHODS

Pertinent English-language articles were identified through a search of MEDLINE (1966-week 4, 2006), EMBASE (1991-first quarter of 2006), Current Contents/Clinical Medicine (week 10, 2005-week 9, 2006), the Cochrane Database of Systematic Reviews, MICROMEDEX Healthcare Series, and International Pharmaceutical Abstracts (1970-present). The search terms were overactive bladder, urinary incontinence, solifenacin, YM905, pharmacokinetics, and cost.

RESULTS

SOL is highly lipophilic (50:1 octanol:water distribution at pH 7.0), completely orally bioavailable, and 98% protein bound. It is metabolized by the cytochrome P450 3A isozyme, and approximately 50% of a dose is eliminated renally as parent compound, with 1 active and 3 inactive metabolites. In two 12-week Phase III studies, patients receiving SOL 5 or 10 mg had significant reductions compared with placebo in the numbers of voids (P < or = 0.01), incontinence episodes (P < or = 0.05), and urgency episodes (P < or = 0.01) per 24 hours; the volume voided per micturition was significantly increased (P < or = 0.01). In a study that compared SOL 5 and 10 mg with tolterodine extended release 4 mg, both agents were associated with significant reductions in the number of voids per 24 hours (-2.45 and -2.24 episodes, respectively; P = 0.004 for noninferiority). In a study of pooled data from two 12-week studies, patients who received SOL 5 or 10 mg reported significant improvements in a number of quality-of-life domains (P < or = 0.05). In a pooled analysis of 4 studies, the most common adverse effects (occurring in > or =3% of any group) in patients receiving SOL 5 mg (n = 266) and 10 mg (n = 612) were dry mouth (10.9% and 27.1%, respectively), constipation (5.3% and 12.9%), and blurred vision (4.5% and 4.7%).

CONCLUSIONS

In the studies reviewed, SOL was effective in the treatment of OAB with urge incontinence. Adverse effects included dry mouth, constipation, and blurred vision. Further studies are needed to determine the efficacy and tolerability of SOL in patients with hepatic or renal impairment.

Localization of M 2 and M 3 Muscarinic Receptors in Human Bladder Disorders and Their Clinical Correlations

PURPOSE

We studied the cellular localization of muscarinic receptor subtypes 2 and 3 in the human bladder and related any changes in overactive and painful bladder syndromes to measures of clinical dysfunction.

MATERIALS AND METHODS

Bladder specimens obtained from patients with painful bladder syndrome (11), idiopathic detrusor overactivity (12) and from controls with asymptomatic microscopic hematuria (16) were immunostained using specific antibodies to muscarinic receptor subtypes 2 and 3, and to vimentin, which is a marker for myofibroblasts. Immunostaining results were quantified with computerized image analysis and correlated with clinical dysfunction using frequency and urgency scores.

RESULTS

Muscarinic receptor subtype 2 and 3 immunoreactivity was observed in the urothelium, nerve fibers and detrusor layers. In addition, strong myofibroblast-like cell staining, similar to vimentin, was present in the suburothelial region and detrusor muscle. A significant increase in suburothelial myofibroblast-like muscarinic receptor subtype 2 immunoreactivity was seen in patients with painful bladder syndrome (p = 0.0062) and idiopathic detrusor overactivity (p = 0.0002), and in muscarinic receptor subtype 3 immunoreactivity in those with idiopathic detrusor overactivity (p = 0.0122) with a trend in painful bladder syndrome. Muscarinic receptor subtype 2 and 3 immunoreactivity significantly correlated with the urgency score (p = 0.0002 and 0.0206, respectively) and muscarinic receptor subtype 2 immunoreactivity correlated with the frequency score (p = 0.0029). No significant difference was seen in urothelial and detrusor muscarinic receptor subtypes 2 and 3 or vimentin immunostaining.

CONCLUSIONS

To our knowledge this is the first study to show the cellular localization of muscarinic receptor subtypes 2 and 3 in the human bladder. The increase in muscarinic receptor subtypes 2 and 3 immunostaining in myofibroblast-like cells in clinical bladder syndromes and its correlation with clinical scores suggests a potential role in pathophysiological mechanisms and the therapeutic effect of anti-muscarinic agents.

The puzzle of overactive bladder: controversies, inconsistencies, and insights

Overactive bladder (OAB) affects millions of individuals and may severely impair the quality of life of those affected. The contribution of human behavior to manifestations of this symptom complex remains poorly understood. Continued evolution of our understanding of the pathophysiology of OAB has identified contributory mechanisms, which in turn may open new therapeutic avenues. Recent improvements in drug delivery systems represent advances in the management of OAB. However, more complete symptom control with greater tolerability is desirable; this awaits the development of agents specific for newly emerging and as yet unidentified pathophysiologic pathways. Importantly, as understanding of outcomes assessment in OAB matures, refined assessments of disease severity, response to intervention, and patient preference should be possible.

Using anticholinergics to treat overactive bladder: the issue of treatment tolerability

Overactive bladder (OAB) is a chronic syndrome with debilitating symptoms that negatively affect health-related quality of life. Although anticholinergic agents have been first-line treatment for OAB for many years, the efficacious pharmacologic management of this condition has been compromised by concerns regarding tolerability. Anticholinergic agents prevent involuntary contractions of the bladder detrusor muscle by preventing acetylcholine from binding to the M2 and M3 muscarinic receptor subtypes. Anticholinergics are not tissue specific, and their use for treatment of OAB has been associated with side effects such as dry mouth, constipation, and blurred vision. Recent studies with extended-release formulations and newly developed receptor subtype-specific anticholinergic agents demonstrate that side effects are typically mild to moderate and generally tolerable, seldom leading to patient withdrawal. By incorporating patient-initiated dose adjustment into the protocol, the primary care physician can effectively manage adverse events associated with OAB without compromising efficacy. Recent dose-adjustment data with extended-release oxybutynin suggest that, given some control in the process, patients are willing to tolerate certain side effects in exchange for symptom relief.

Management of overactive bladder and urge urinary incontinence in the elderly patient

The symptoms of overactive bladder (OAB) and urge urinary incontinence may occur at any age but are particularly common among the elderly. These symptoms are associated with significant morbidity and often have a profound impact on patient quality of life. Urinary incontinence is an important contributor to the complications and economic cost of OAB for both community-dwelling and institutionalized elderly individuals. Many patients with OAB do not seek treatment because of embarrassment, fear of surgery, or the misperceptions that the problem is untreatable or is a normal and inevitable consequence of aging. Nonpharmacologic therapies improve bladder control by modifying lifestyle and behavior to prevent urine loss. This requires patient and caregiver motivation and can be time consuming. Improved results may be obtained by combining these strategies with pharmacotherapy or by means of pharmacotherapy alone. The most commonly used pharmacologic agents are the muscarinic receptor antagonists. These include oxybutynin, tolterodine, and three agents that have recently been approved for use in the United States: trospium, darifenacin, and solifenacin. In general, these therapies are well tolerated and safe; however, the selection of an optimal agent merits careful consideration. For elderly patients, important considerations include tolerability, absence of drug interactions, and the availability of a range of dosages to tailor treatment to individual patients. Primary care practitioners and geriatricians can have a key role in successful diagnosis and treatment of OAB. It is important for these physicians to realize that satisfactory outcomes may be achieved within the scope of a busy outpatient practice.

Potent anti-muscarinic activity in a novel series of quinuclidine derivatives

The synthesis and biological evaluation of a novel family of M(3) muscarinic antagonists are described. A systematic modification of the substituents to a novel alkyne-quinuclidine scaffold yielded original compounds displaying potent in vitro anticholinergic properties.

Inhibition of ligand binding to G protein-coupled receptors by arachidonic acid

Arachidonic acid (AA), released in response to muscarinic acetylcholine receptor (mAChR) stimulation, previously has been reported to function as a reversible feedback inhibitor of the mAChR. To determine if the effects of AA on binding to the mAChR are subtype specific and whether AA inhibits ligand binding to other G protein-coupled receptors (GPCRs), the effects of AA on ligand binding to the mAChR subtypes (M1, M2, M3, M4, and M5) and to the micro-opioid receptor, beta2-adrenergic receptor (beta2-AR), 5-hydroxytryptamine receptor (5-HTR), and nicotinic receptors were examined. AA was found to inhibit ligand binding to all mAChR subtypes, to the beta2-AR, the 5-HTR, and to the micro-opioid receptor. However, AA does not inhibit ligand binding to the nicotinic receptor, even at high concentrations of AA. Thus, AA inhibits several types of GPCRs, with 50% inhibition occurring at 3-25 MuM, whereas the nicotinic receptor, a non-GPCR, remains unaffected. Further research is needed to determine the mechanism by which AA inhibits GPCR function.

The q-t interval and antimuscarinic drugs

Antimuscarinic drugs form the mainstay of pharmacotherapy for the treatment of overactive bladder. The primary sites of activity of the agents for the desired therapeutic effect are the M3 and M2 receptors of the bladder. Drug interaction with other non-vesical muscarinic receptors produces a range of undesired adverse events. In general, certain adverse effects associated with antimuscarinic agents such as dry mouth (salivary) and constipation (colon) may be considered only bothersome, and somnolence and confusion (central nervous system) may be considered more serious in nature. However, effects on the myocardium are considered to be more significant safety issues and increased awareness and understanding of the effect of drugs on the myocardium, including the additional effects of drug-drug interaction, has increased a need for the evaluation of new drugs for cardiac safety. The role of genetics (and the identification of populations at risk) in the causation of congenital dysrhythmias has received specific attention in this area. New drugs now must undergo more intense scrutiny and cardiac testing to evaluate their effects on cardiac rate and rhythm, especially the QT interval. The recently approved agents (trospium, solifenacin, darifenacin) used for the treatment of overactive bladder have been rigorously evaluated for these effects.

Preview of new drugs for overactive bladder and incontinence: darifenacin, solifenacin, trospium, and duloxetine

This year, the US Food and Drug Administration will approve four new drugs indicated for the treatment of lower urinary tract dysfunction. Darifenacin, solifenacin, and trospium are antimuscarinic agents aimed at relieving the symptoms of overactive bladder and urge incontinence in men and women. Duloxetine will be the first drug approved for the treatment of female stress urinary incontinence. This article presents current data on the efficacy and tolerability of these new agents and invites the reader to decide whether they offer any potential advantages over existing therapies.

Antimuscarinic agents: Implications and concerns in themanagement of overactive bladder in the elderly

BACKGROUND

Overactive bladder (OAB) is a widespread problem that has a negative effect on quality of life, particularly among the elderly. Antimuscarinic agents are the only drug class with broad, accepted efficacy in the treatment of OAB. Their clinical usefulness, however, is limited by dose-dependent adverse effects. In the elderly, the most serious of these is central nervous system (CNS) dysfunction, including cognitive impairment.

OBJECTIVE

This article examines currently available antimuscarinic agents for the treatment of OAB in terms of their likelihood of causing CNS dysfunction by crossing the blood-brain barrier (BBB) and blocking muscarinic type 1 (Ml) receptor sites in the brain.

METHODS

Pertinent studies were selected from a comprehensive review of the OAB literature with a focus on muscarinic receptor-associated mechanisms leading to CNS adverse effects and their potential impact on elderly patients. MEDLINE was searched for articles published in the past 10 years, and additional articles were obtained from the reference lists of identified publications. Also searched were abstracts of recent meetings of the International Consultation on Incontinence, International Continence Society, American Urological Association, and European Association of Urology.

RESULTS

Antimuscarinic agents control involuntary detrusor muscle contractions through cholinergic blockade at the muscarinic receptors. The prevalence of OAB is highest in the elderly, the population most likely to be taking multiple anticholinergic medications and most vulnerable to the CNS adverse effects of these agents. Nonselective antimuscarinic agents that bind to the Ml receptor are most likely to cause significant cognitive adverse effects compared with the more selective antimuscarinic agents for the treatment of OAB.

CONCLUSIONS

When considering use of an antimuscarinic agent for the treatment of OAB in elderly patients, prescribers should routinely consider the agent's receptor selectivity and ability to cross the BBB. The medical history should include all current medications that may contribute to the anticholinergic burden and cognitive impairment. Patients and caregivers should be educated to recognize anticholinergic adverse effects.

Drug Treatment of Overactive Bladder

Overactive bladder (OAB) syndrome has been recognised by the International Continence Society as an important symptom syndrome that affects millions of people worldwide. Quality of life is affected in most people with OAB; however, the aetiology is unknown. Some researchers suggest that it is because of a damage to central inhibitory pathways or sensitisation of peripheral afferent terminals in the bladder, others suggest that it is a bladder muscle problem; the reality is probably a spectrum encompassing these two main explanations. Therefore, treatment is difficult and is aimed at alleviating symptoms (being those of urgency, with or without urge incontinence, usually with frequency and nocturia) rather than treating the cause. A thorough patient history and physical examination are required to establish a possible diagnosis. Frequency/volume charts form an important aid to the diagnosis. Once a presumptive diagnosis is made, conservative management forms the first line of treatment and includes lifestyle modifications, bladder training and pelvic floor exercises. If this fails, pharmacotherapy, in the form of anticholinergic drugs, is initiated. There are many antimuscarinic drugs, for example oxybutynin, tolterodine and trospium chloride. Each has a different specificity to bladder muscarinic receptors, thus producing different adverse effect profiles (e.g. dry mouth, blurred vision and constipation). Different individuals experience these adverse effects to different extents. New anticholinergic drugs, that have undergone phase III trials and are more specific to the muscarinic M3 human bladder receptor, are being introduced to the market in 2004 (e.g. solifenacin succinate and darifenacin). In addition to adverse effect profile, cost and improvement in quality of life are important factors in choosing treatment. Further research is being conducted on other types of drugs and different administration modalities, for example intravesical botulinum toxin A. Sacral nerve neuromodulation is emerging as a potential treatment, but if all treatments fail then surgery is the last resort.