Use of muscarinic agonists in the treatment of Sjögren's syndrome

Pharmacological and Electroceutical Targeting of the Cholinergic Anti-Inflammatory Pathway in Autoimmune Diseases

Continuous dialogue between the immune system and the brain plays a key homeostatic role in various immune responses to environmental cues. Several functions are under the control of the vagus nerve-based inflammatory reflex, a physiological mechanism through which nerve signals regulate immune functions. In the cholinergic anti-inflammatory pathway, the vagus nerve, its pivotal neurotransmitter acetylcholine, together with the corresponding receptors play a key role in modulating the immune response of mammals. Through communications of peripheral nerves with immune cells, it modulates proliferation and differentiation activities of various immune cell subsets. As a result, this pathway represents a potential target for treating autoimmune diseases characterized by overt inflammation and a decrease in vagal tone. Consistently, converging observations made in both animal models and clinical trials revealed that targeting the cholinergic anti-inflammatory pathway using pharmacologic approaches can provide beneficial effects. In parallel, bioelectronic medicine has recently emerged as an alternative approach to managing systemic inflammation. In several studies, nerve electrostimulation was reported to be clinically relevant in reducing chronic inflammation in autoimmune diseases, including rheumatoid arthritis and diabetes. In the future, these new approaches could represent a major therapeutic strategy for autoimmune and inflammatory diseases.

Outline of Salivary Gland Pathogenesis of Sjögren's Syndrome and Current Therapeutic Approaches

Sjögren's syndrome (SS) is an autoimmune disease characterized by the involvement of exocrine glands such as the salivary and lacrimal glands. The minor salivary glands, from which tissue samples may be obtained, are important for the diagnosis, evaluation of therapeutic efficacy, and genetic analyses of SS. In the onset of SS, autoantigens derived from the salivary glands are recognized by antigen-presenting dendritic cells, leading to the activation of T and B cells, cytokine production, autoantibody production by plasma cells, the formation of ectopic germinal centers, and the destruction of salivary gland epithelial cells. A recent therapeutic approach with immune checkpoint inhibitors for malignant tumors enhances the anti-tumor activity of cytotoxic effector T cells, but also induces SS-like autoimmune disease as an adverse event. In the treatment of xerostomia, muscarinic agonists and salivary gland duct cleansing procedure, as well as sialendoscopy, are expected to ameliorate symptoms. Clinical trials on biological therapy to attenuate the hyperresponsiveness of B cells in SS patients with systemic organ involvement have progressed. The efficacy of treatment with mesenchymal stem cells and chimeric antigen receptor T cells for SS has also been investigated. In this review, we will provide an overview of the pathogenesis of salivary gland lesions and recent trends in therapeutic approaches for SS.

Gastrointestinal involvement in systemic sclerosis: An updated review

The gastrointestinal tract (GI) is the second most affected organ system in individuals suffering from systemic/localized scleroderma (SSc) or localized scleroderma. SSc can affect any part of the GI, between the oral cavity and anorectum. The annual incidence of SSc in the United States is estimated to be 19.3 cases per million adults, with the highest incidence reported in people aged 44 to 55. Females are 5 times more likely than males to suffer from SSc. Morbidity and mortality rates associated with SSc are predominantly elevated among patients with GI manifestations. Esophageal and intestinal manifestations impact 90% and 40% to 70% of patients with systemic scleroderma, respectively. SSc patients are known to suffer from small bowel hypomotility and small intestinal bacterial overgrowth, which cause malabsorption and malnutrition, ultimately contributing to the 50% mortality rate. Fecal incontinence is a common symptom of SSc that can lead to depression. SSc patients may suffer from gastrointestinal complications that can negatively impact their quality of life on a daily basis. Multidisciplinary approaches are necessary for systematically managing gastrointestinal complications associated with SSc. A prospective study should focus on developing targeted therapies to improve recovery patterns and prognosis in cases of SSc. This article summarizes the epidemiology, commonly reported clinical manifestations, complications, and available treatments for treating GI pathology in SSc patients.

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.

Aging-Related Metabolic Dysfunction in the Salivary Gland: A Review of the Literature

Aging-related salivary dysfunction commonly induces the poor oral health, including decreased saliva flow and dental caries. Although the clinical significance of the salivary glands is well-known, the complex metabolic pathways contributing to the aging-dysfunction process are only beginning to be uncovered. Here, we provide a comprehensive overview of the metabolic changes in aging-mediated salivary gland dysfunction as a key aspect of oral physiology. Several metabolic neuropeptides or hormones are involved in causing or contributing to salivary gland dysfunction, including hyposalivation and age-related diseases. Thus, aging-related metabolism holds promise for early diagnosis, increased choice of therapy and the identification of new metabolic pathways that could potentially be targeted in salivary gland dysfunction.

Functionally selective and biased agonists of muscarinic receptors

Disruption of cholinergic signalling via muscarinic receptors is associated with various pathologies, like Alzheimer's disease or schizophrenia. Selective muscarinic agonists possess therapeutic potential in the treatment of diabetes, pain or Sjögren's syndrome. The orthosteric binding site of all subtypes of the muscarinic receptor is structurally identical, making the development of affinity-based selective agonists virtually impossible. Some agonists, however, are functionally selective; they activate only a subset of receptors or signalling pathways. Others may stabilise specific conformations of the receptor leading to non-uniform modulation of individual signalling pathways (biased agonists). Functionally selective and biased agonists represent a promising approach for selective activation of individual subtypes of muscarinic receptors. In this work we review chemical structures, receptor binding and agonist-specific conformations of currently known functionally selective and biased muscarinic agonists in the context of their intricate intracellular signalling. Further, we take a perspective on the possible use of biased agonists for tissue and organ-specific activation of muscarinic receptors.

Reactivity of human labial glands in response to cevimeline treatment

Among the pathologies affecting the salivary glands, the Sjögren's syndrome (SS), an autoimmune disease, causes progressive destruction of the glandular tissue. The effect of SS is particularly evident on the labial glands and the morphological analysis of these minor glands is considered useful for diagnosis. Cevimeline hydrochloride (SNI), a selective muscarinic agonist drug, is one of the elective treatments for the hyposalivation due to SS, acting not only on major salivary glands, but also on labial glands since their secretion is primarily under parasympathetic control. Aim of this study is to describe the morphology of human labial glands treated with SNI by light, transmission, and high-resolution scanning electron microscopy. Moreover, a morphometric analysis was applied to the light and transmission electron microscopy micrographs to obtain data that were then compared with analogous data collected on control and carbachol-treated labial glands. Following SNI administration, the mucous tubules exhibited enlarged lumina, which were filled with a dense mucous secretion. Occasionally, small broken debris of the cells were retrieved into the lumen. In the mucous secretory cells, some mucous droplets fused to form a large vacuole-like structure. Similarly, the seromucous acini showed both dilated lumina and canaliculi. These above reported signs of secretion were confirmed through morphometric analysis and a milder action of SNI than carbachol on labial parenchyma was observed. This study confirmed that SNI also evoked secretion on labial glands and that its effect is more physiologic than that of the pan-muscarinic agonists.

Investigation of Changes in Saliva in Radiotherapy-Induced Head Neck Cancer Patients

The intact function of the salivary glands is of utmost importance for oral health. During radiotherapy in patients with head and neck tumors, the salivary glands can be damaged, causing the composition of saliva to change. This leads to xerostomia, which is a primary contributor to oral mucositis. Medications used for protective or palliative treatment often show poor efficacy as radiation-induced changes in the physico-chemical properties of saliva are not well understood. To improve treatment options, this study aimed to carefully examine unstimulated whole saliva of patients receiving radiation therapy and compare it with healthy unstimulated whole saliva. To this end, the pH, osmolality, electrical conductivity, buffer capacity, the whole protein and mucin concentrations, and the viscoelastic and adhesive properties were investigated. Moreover, hyaluronic acid was examined as a potential candidate for a saliva replacement fluid. The results showed that the pH of radiation-induced saliva shifted from neutral to acidic, the osmolality increased and the viscoelastic properties changed due to a disruption of the mucin network and a change in water secretion from the salivary glands. By adopting an aqueous 0.25% hyaluronic acid formulation regarding the lost properties, similar adhesion characteristics as in healthy, unstimulated saliva could be achieved.

A review of isolation methods, structure features and bioactivities of polysaccharides from Dendrobium species

Dendrobium, orchid, is a traditional Chinese herb medicine applied extensively as tonic and precious food for thou-sands of years recorded in ancient Chinese medical book "Shen Nong's Materia Medica". It's well known that bioactivities are usually related to the ingredients' basis. Based on the previous research, Dendrobium species contain amino acid, sesquiterpenoids, alkaloids and polysaccharides. As the bioactive substances, carbohydrate shows extensive activities in antitumor, antiglycation, immune-enhancing, antivirus, antioxidant, antitumor and etc. Therefore, as the main biologically active substance, the exact structures and latent activities of polysaccharides from Dendrobium species are widely focused on. In this review, we focus on the advancements of extraction methods and diversity of structures and bioactivities of polysaccharides obtained from Dendrobium species.

Pilocarpine induces the residual secretion of salivary fluid in perfused submandibular glands of rats

Pilocarpine is an M3 muscarinic agonist that is widely used for the treatment of xerostomia caused by various diseases and medical conditions. Pilocarpine induced the secretion of salivary fluid in perfused submandibular glands of rats. The secretion of salivary fluid observed after removal of pilocarpine was referred to as residual fluid secretion. The volume of fluid and time of the residual secretion depended on the dose of pilocarpine. Such a residual effect of pilocarpine was observed on fluid secretion via the paracellular pathway and oxygen consumption. When a muscarinic antagonist was added to the perfusate immediately after cessation of pilocarpine, residual secretion of salivary fluid did not occur. These observations indicate that the residual secretion of salivary fluid is a characteristics of the interaction of pilocarpine with muscarinic receptors.

Saliva: An all-rounder of our body

Saliva is a multifaceted bodily fluid that is often taken for granted but is indispensable for oral health and overall well-being in humans. Although mainly comprised of water (99.5%), proteins, ions and enzymes turn saliva into a viscoelastic solution that performs a variety of vital tasks. This review article gives a brief overview of the salivary gland system, as well as the composition, output and functions of saliva. It also addresses the current applications of saliva for diagnostic purposes, the clinical relevance of saliva in oral diseases as well as current treatment options.

How to treat Sjögren's syndrome

SS is a chronic, autoimmune disease of unknown aetiology for which there is no known curative treatment. Although dryness of the eyes and mouth are the classically described features, patients often experience drying of other mucosal surfaces and systemic manifestations, including fatigue and arthralgia. There is an association with other autoimmune diseases, especially thyroid disease, coeliac disease and primary biliary cholangitis. Systemic features may affect up to 70% and include inflammatory arthritis, skin involvement, haematological abnormalities, neuropathies, interstitial lung disease and a 5-10% lifetime risk of B cell lymphoma. Treatment should aim to empower patients to manage their condition; conserve, replace and stimulate secretions; prevent damage; and suppress underlying systemic disease activity.

Contribution of HIV Infection, AIDS, and Antiretroviral Therapy to Exocrine Pathogenesis in Salivary and Lacrimal Glands

The structure and function of exocrine glands are negatively affected by human immunodeficiency virus (HIV) infection and its co-morbidities, including innate and adaptive immune responses. At the same time, exocrine function may also be influenced by pharmacotherapies directed at the infectious agents. Here, we briefly review the role of the salivary glands and lacrimal glands in normal physiology and exocrine pathogenesis within the context of HIV infection and acquired immune deficiency syndrome (AIDS), including the contribution of antiretroviral therapies on both. Subsequently, we discuss the impact of HIV infection and the types of antiretroviral therapy on disease management and therapy development efforts.

Salivary hypofunction: An update on therapeutic strategies

OBJECTIVE

To perform a literature review addressing the therapeutic strategies for salivary hypofunction.

BACKGROUND

Qualitative and quantitative salivary dysfunctions predispose to changes in the oral mucosa and teeth, cause impairment to oral functions and negative impact on quality of life.

MATERIALS AND METHODS

A MEDLINE/PubMed search was conducted using the terms "Xerostomia" AND, "Saliva Artificial" OR, "Citric Acid," "Malic Acid," "Chewing Gum," "Acupuncture" OR, "Pilocarpine" OR, "Bethanechol" OR, "Cevimeline" OR, "Hyperbaric Oxygen Therapy" OR, "Stem Cell Therapy" OR "Genetic Therapy" and their Mesh Terms.

RESULTS

We selected 25 clinical trials investigating the effects of salivary substitutes, chewing gum, malic and citric acids, pilocarpine, cevimeline, bethanechol, acupuncture, hyperbaric oxygen therapy and regenerative therapies on salivary hypofunction. In most studies, the number of participants was low and the follow-up times short. The therapeutic modalities were classified according to the level of evidence on salivary dysfunction.

CONCLUSIONS

Pilocarpine and cevimeline had the strongest evidence of beneficial effect on salivary hypofunction. Citric and malic acids increase salivary flow but also increase the risk of erosion and dental caries. There are no controlled clinical trials supporting the efficacy of acupuncture, stem cell therapy and gene therapy on salivary dysfunction, although clinical observations suggest a promising effect. There is no evidence supporting salivary substitutes, chewing gum, bethanechol or hyperbaric oxygen on the treatment of salivary hypofunction.

Is it Sjögren's syndrome or burning mouth syndrome? Distinct pathoses with similar oral symptoms

Sjögren's syndrome (SS) and burning mouth syndrome (BMS) typically occur in postmenopausal women. Although these conditions have significantly different etiopathogeneses, patients with SS or BMS often present with analogous oral complaints. The similarities between the two conditions have led to considerable confusion on the part of medical and dental practitioners, and those with BMS or SS often wait years to receive a diagnosis. Therefore, it is imperative for clinicians to understand the characteristic subjective and objective features of each disease and how these can be used to distinguish them. This review will discuss the proposed etiology, clinical manifestations, histopathology, diagnostic criteria, and patient management of SS and BMS. We also identify key differences between the two pathoses that aid in establishing the correct diagnosis. Recognition of the defining features of each condition will lead to reduced time to diagnosis and improved patient management for these poorly understood conditions.

Dysfunctional tear syndrome: dry eye disease and associated tear film disorders - new strategies for diagnosis and treatment

Dysfunctional tear syndrome (DTS) is a common and complex condition affecting the ocular surface. The health and normal functioning of the ocular surface is dependent on a stable and sufficient tear film. Clinician awareness of conditions affecting the ocular surface has increased in recent years because of expanded research and the publication of diagnosis and treatment guidelines pertaining to disorders resulting in DTS, including the Delphi panel treatment recommendations for DTS (2006), the International Dry Eye Workshop (DEWS) (2007), the Meibomian Gland Dysfunction (MGD) Workshop (2011), and the updated Preferred Practice Pattern guidelines from the American Academy of Ophthalmology pertaining to dry eye and blepharitis (2013). Since the publication of the existing guidelines, new diagnostic techniques and treatment options that provide an opportunity for better management of patients have become available. Clinicians are now able to access a wealth of information that can help them obtain a differential diagnosis and treatment approach for patients presenting with DTS. This review provides a practical and directed approach to the diagnosis and treatment of patients with DTS, emphasizing treatment that is tailored to the specific disease subtype as well as the severity of the condition.

Trends in the Evolution of Snake Toxins Underscored by an Integrative Omics Approach to Profile the Venom of the Colubrid Phalotris mertensi

Only few studies on snake venoms were dedicated to deeply characterize the toxin secretion of animals from the Colubridae family, despite the fact that they represent the majority of snake diversity. As a consequence, some evolutionary trends observed in venom proteins that underpinned the evolutionary histories of snake toxins were based on data from a minor parcel of the clade. Here, we investigated the proteins of the totally unknown venom from Phalotris mertensi (Dipsadinae subfamily), in order to obtain a detailed profile of its toxins and to appreciate evolutionary tendencies occurring in colubrid venoms. By means of integrated omics and functional approaches, including RNAseq, Sanger sequencing, high-resolution proteomics, recombinant protein production, and enzymatic tests, we verified an active toxic secretion containing up to 21 types of proteins. A high content of Kunitz-type proteins and C-type lectins were observed, although several enzymatic components such as metalloproteinases and an L-amino acid oxidase were also present in the venom. Interestingly, an arguable venom component of other species was demonstrated as a true venom protein and named svLIPA (snake venom acid lipase). This finding indicates the importance of checking the actual protein occurrence across species before rejecting genes suggested to code for toxins, which are relevant for the discussion about the early evolution of reptile venoms. Moreover, trends in the evolution of some toxin classes, such as simplification of metalloproteinases and rearrangements of Kunitz and Wap domains, parallel similar phenomena observed in other venomous snake families and provide a broader picture of toxin evolution.

Safety of treatments for primary Sjögren's syndrome

INTRODUCTION

Primary Sjögren's syndrome (pSS) is a disabling auto-immune disease, affecting exocrine glands and several organs.

AREAS COVERED

In this review we analyze the safety of therapies used in pSS. Symptomatic treatment is widely applied due to the good supportive effect and good safety profile. Systemic stimulation of tears and saliva can be successful in pSS. However, cumbersome adverse events can influence the tolerability of this therapy. Evidence for the effectiveness of synthetic DMARDs therapies in pSS is limited, while there is a risk of adverse events. Several studies on biologic DMARD treatment of pSS patients have shown promising efficacy and safety results.

EXPERT OPINION

The safety of symptomatic treatment of pSS is very good. However, systemic therapy is necessary to achieve long-term relieve and prevention of organ-damage. Synthetic DMARDs have not shown much efficacy in earlier studies, and their benefits do not weigh up to the possible harms, while biologic DMARDs show promising results regarding efficacy and cause mostly mild adverse events. Many questions remain unanswered regarding safety of DMARDs in pSS. There is a need for well designed studies, in which safety should be evaluated in a uniform manner to be able to compare the results between studies.

Adult stem cells and tissue engineering strategies for salivary gland regeneration: a review

Saliva is an important compound produced by the salivary glands and performs numerous functions. Hyposalivation (dry mouth syndrome) is a deleterious condition often resulting from radiotherapy for patients with head and neck cancer, Sjogren's Syndrome, or as a side effect of certain medications. Hyposalivation negatively affects speaking, mastication, and swallowing in afflicted patients, greatly reducing their quality of life. Current treatments for this pathology include modifying lifestyle, synthetic saliva supplementation, and the utilization of salivary gland stimulants and sialagogues. However, many of these treatments do not address the underlying issues and others are pervaded by numerous side effects. In order to address the shortcomings related to current treatment modalities, many groups have diverted their attention to utilizing tissue engineering and regenerative medicine approaches. Tissue engineering is defined as the application of life sciences and materials engineering toward the development of tissue substitutes that are capable of mimicking the structure and function of their natural analogues within the body. The general underlying strategy behind the development of tissue engineered organ substitutes is the utilization of a combination of cells, biomaterials, and biochemical cues intended to recreate the natural organ environment. The purpose of this review is to highlight current bioengineering approaches for salivary gland tissue engineering and the adult stem cell sources used for this purpose. Additionally, future considerations in regard to salivary gland tissue engineering strategies are discussed.

Immunolocalization of AQP5 in resting and stimulated normal labial glands and in Sjögren's syndrome

OBJECTIVE

In our current work, in vivo examination of AQP5 distribution in labial salivary glands following stimulation of secretion has been carried out in normal individuals and in patients with Sjögren's syndrome.

SUBJECTS AND METHODS

For this study, we selected five patients with primary Sjögren's syndrome (mean age 62.4 ± 10.6 s.d. years) diagnosed in accordance with the European Cooperative Community classification criteria. There were five patients (mean age 27 ± 2.5 s.d. years) in the control group. The subcellular distribution of AQP5 in human labial gland biopsies was determined with light and immunoelectron microscopy before and 30 min after administration of oral pilocarpine.

RESULTS

In unstimulated control and Sjögren's labial glands, AQP5 is about 90% localized in the apical plasma membrane, with only rarely associated gold particles with intracellular membrane structures. We have found no evidence of pilocarpine-induced changes in localization of AQP5 in either healthy individuals or patients with Sjögren's syndrome.

CONCLUSIONS

Our studies indicate that neither Sjögren's syndrome itself, nor muscarinic cholinergic stimulation in vivo caused any significant changes in the distribution of AQP5 in the labial salivary gland cells.

Hypersensitive mAChRs are involved in the epiphora of transplanted glands

Autologous transplantation of the submandibular gland is an effective treatment for severe dry eye syndrome. However, more than 40% of patients experience epiphora 3 to 6 months after transplantation. The underlying mechanism of epiphora remains to be elucidated. To investigate the potential roles of muscarinic acetylcholine receptors (mAChRs) in the induction of epiphora in transplanted glands, we assessed and found elevated mRNA and protein expression of M1- and M3-mAChR in transplanted glands from epiphora patients. The content of inositol 1, 4, 5-trisphosphate was also elevated. Moreover, carbachol (5 and 10 µM) induced greater increase of [Ca(2+)]i in isolated epiphora submandibular cells than in controls. Although aquaporin-5 (AQP5) content and distribution in the apical and lateral plasma of epiphora glands did not change, AQP5 content was reduced in lipid microdomains (lipid rafts and caveolae) but increased in non-lipid microdomains compared with controls. Carbachol (10 µM) increased the ratio of non-lipid microdomain to total AQP5 in the cultured control submandibular gland tissue. Taken together, these results indicated that hypersensitive mAChRs might be involved in the epiphora of transplanted submandibular glands by modulating AQP5 trafficking.

Visante optical coherence tomography and tear function test evaluation of cholinergic treatment response in patients with sjögren syndrome

PURPOSE

To evaluate tear meniscus changes in patients with Sjögren syndrome (SS) receiving oral pilocarpine with Visante optical coherence tomography (OCT).

METHODS

Eight patients with primary SS were recruited in this prospective interventional case series study. Patients received pilocarpine tablets twice a day for 3 months. Visual analog scale assessment for dry eye and dry mouth symptoms was carried out. Patients underwent OCT and slit-lamp microscopy graticule scale tear meniscus height (TMH) measurements, strip meniscometry testing, tear film breakup time measurement, fluorescein and Rose Bengal staining, and the Schirmer 1 test. The data were analyzed 1 week, 1 month, and 3 months after treatment. Mann-Whitney test was performed.

RESULTS

Visual analog scale assessment showed a significant time-wise improvement (P < 0.05). OCT and graticule scale TMH measurements significantly improved after 1 week (P < 0.05), 1 month, and 3 months of treatment (P < 0.001). Strip meniscometry, mean tear film stability, and fluorescein and Rose Bengal scores remained improved 3 months after treatment (P < 0.001), whereas Schirmer 1 test values tended to improve without statistical significance.

CONCLUSIONS

Visante OCT was effective in monitoring tear meniscus changes during the course of treatment noninvasively and quickly. Oral pilocarpine seemed to be effective in improving TMH, and the signs and symptoms of dryness in patients with SS.

Treating Sjögren's Syndrome: Insights for the Clinician

Sjögren's syndrome (SS) is a systemic autoimmune disease that affects the exocrine glands, mainly the salivary and lachrymal glands, with consequent persistent dryness of the mouth and eyes. In addition to the clinical manifestations related to the exocrine gland involvement, a consistent prevalence of patients may present systemic manifestations. Some of these can be ascribed to the periepithelial extension of lymphocytic infiltration whilst others are determined by an immunomediated process affecting small- or medium-size vessels. While the use of tear and saliva substitutes and local or systemic stimulation of residual secretions represent the mainstays of the therapy of sicca component, different immunomodulating or immunosuppressive agents are usually required to treat extraglandular features, similarly to what happens in other connective tissue diseases. In the last few years, the advancement in the understanding the pathogenetic mechanisms of this disorder and the availability of new biologic target therapies seem to offer completely new therapeutic options. The use of B cell depleting or modulating therapies has achieved promising results.

Cholinergic involvement and manipulation approaches in multiple system disorders

Within the autonomic system, acetylcholine signaling contributes simultaneously and interactively to cognitive, behavioral, muscle and immune functions. Therefore, manipulating cholinergic parameters such as the activities of the acetylcholine hydrolyzing enzymes in body fluids or the corresponding transcript levels in blood leukocytes can change the global status of the autonomic system in treated individuals. Specifically, cholinesterase activities are subject to rapid and effective changes. The enzyme activity baseline increases with age and body mass index and depends on gender and ethnic origin. Also, the corresponding DNA (for detecting mutations) and RNA (for measuring specific mRNA transcripts) of cholinergic genes present individual variability. In leukocytes, acetylcholine inhibits the production of pro-inflammatory cytokines, suggesting relevance of cholinergic parameters to both the basal levels and to disease-induced inflammation. Inversely, acetylcholine levels increase under various stress stimuli, inducing changes in autonomic system molecules (e.g., pro-inflammatory cytokines) which can penetrate the brain; therefore, manipulating these levels can also effect brain reactions, mainly of anxiety, depression and pain. Additionally, neurodegenerative diseases often involve exacerbated inflammation, depression and anxiety, providing a focus interest group for cholinergic manipulations. In Alzheimer's disease, the systemic cholinergic impairments reflect premature death of cholinergic neurons. The decline of cholinesterases in the serum of Parkinson's disease and post- stroke patients, discovery of the relevant microRNAs and the growing range of use of anticholinesterase medications all call for critical re-inspection of established and novel approaches for manipulating cholinergic parameters.

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.

Effect of topically applied epithelial sodium channel inhibitors on tear production in normal mice and in mice with induced aqueous tear deficiency

PURPOSE

Dry eye syndromes affect a significant proportion of the population worldwide with reported prevalence ranging from 6% to more than 34%. Patients with dry eye can experience intense pain due to eye irritation, gritty/scratchy feeling in the eyes, blurry vision, and light sensitivity. Available treatments for dry eye syndromes remain mainly palliative. The purpose of the present study was to test the hypothesis that inhibiting sodium absorption via the epithelial sodium channel (ENaC) will increase ocular hydration in both normal as well as in animals with experimentally induced dry eye.

METHODS

ENaC inhibitors were dissolved in an aqueous buffer that mimics the composition of tears and were applied topically to the ocular surface of isoflurane-anesthetized mice. The effect of ENaC inhibitors was compared with that of the secretagogue uridine triphosphate (UTP; 1%), a purinergic receptor agonist which was shown to increase tear volume in animals. Tear production was measured for 10 s using phenol red-impregnated cotton threads. Fluorescein staining that assesses ocular surface damage was performed at baseline and then at days 1, 2, and 3 after the induction of dry eye in mice.

RESULTS

Our data show that the inhibition of ENaC led to a time- and concentration-dependent increase in tear volume in normal mice. The effect of ENaC inhibition after a single application outperformed UTP, as it was long-lasting with tear volume still above baseline values 8 h postdosing. ENaC inhibition, which led to increased tear production, improved fluorescein scores in our dry eye model, when compared with nontreated or animals treated with buffer or UTP.

CONCLUSION

We conclude that the inhibition of ENaC provides long-lasting increases in ocular surface hydration and that ENaC blockers could provide an effective new therapy for chronic dry eye.

Human mesenchymal stem cells cultured with salivary gland biopsies adopt an epithelial phenotype

Sjogren's syndrome and radiotherapy for head and neck cancer result in severe xerostomia and irreversible salivary gland damage for which no effective treatment is currently available. Cell culture methods of primary human salivary gland epithelial cells (huSGs) are slow and cannot provide a sufficient number of cells. In addition, the majority of cultured huSGs are of a ductal phenotype and thus not fluid/saliva secretory cells. Some reports indicated that mesenchymal stem cells (MSCs) possessed the potential to differentiate into epithelial cells. To test this hypothesis with huSGs, a coculture system containing 2 chambers separated by a polyester membrane was used to study the capacity of human MSCs to adopt an epithelial phenotype when cocultured with human salivary gland biopsies. Results were that 20%-40% of cocultured MSCs expressed tight junction proteins [claudin-1 (CLDN-1), -2, -3, and -4; occludin; junctional adhesion molecule-A; and zonula occludens-1] as well as other epithelial markers [aquaporin-5, α-amylase (α-AMY), and E-cadherin], and generated a higher transepithelial electrical resistance. Electron microscopy demonstrated that these MSCs had comparable cellular structures to huSGs, such as tight junction structures and numerous secretory granules. Quantitative real time (RT)-polymerase chain reaction revealed an upregulation of several salivary genes (aquaporin-5, AMY, and CLDN-2). Moreover, the amounts of α-AMY detected in cocultured MSCs were comparable to those detected in huSGs control cultures. These data suggest that cocultured MSCs can demonstrate a temporary change into a salivary gland acinar phenotype.

Matrigel improves functional properties of primary human salivary gland cells

Currently, there is no effective treatment available to patients with irreversible loss of functional salivary acini caused by Sjogren's syndrome or after radiotherapy for head and neck cancer. A tissue-engineered artificial salivary gland would help these patients. The graft cells for this device must establish tight junctions in addition to being of fluid-secretory nature. This study analyzed a graft source from human salivary glands (huSG) cultured on Matrigel. Cells were obtained from parotid and submandibular glands, expanded in vitro, and then plated on either Matrigel-coated (2 mg/mL) or uncoated culture dish. Immunohistochemistry, transmission electron microscopy, quantitative real-time-polymerase chain reaction, Western blot, and transepithelial electrical resistance were employed. On Matrigel, huSG cells adopted an acinar phenotype by forming three-dimensional acinar-like units (within 24 h of plating) as well as a monolayer of cells. On uncoated surfaces (plastic), huSG cells only formed monolayers of ductal cells. Both types of culture conditions allowed huSG cells to express tight junction proteins (claudin-1, -2, -3, -4; occludin; JAM-A; and ZO-1) and adequate transepithelial electrical resistance. Importantly, 99% of huSG cells on Matrigel expressed α-amylase and the water channel protein Aquaporin-5, as compared to <5% of huSG cells on plastic. Transmission electron microscopy confirmed an acinar phenotype with many secretory granules. Matrigel increased the secretion of α-amylase two to five folds into the media, downregulated certain salivary genes, and regulated the translation of acinar proteins. This three-dimensional in vitro serum-free cell culture method allows the organization and differentiation of huSG cells into salivary cells with an acinar phenotype.

Diagnostic significance of measuring antibodies to cyclic type 3 muscarinic acetylcholine receptor peptides in primary Sjogren's syndrome

OBJECTIVE

SS is an autoimmune disease characterized by salivary and lacrimal gland dysfunction leading to dry mouth (xerostomia) and dry eyes (xerophthalmia). Anti-muscarinic acetylcholine type-3 receptor (anti-M3R) autoantibodies have been shown to be a good serum marker in primary SS (pSS). The aim of this study was to assess the clinical correlations of anti-M3R-derived peptide antibodies in patients with pSS.

METHODS

Sequences of the first to fourth cycle-M3R (c1M3R-c4M3R)-derived peptide was synthesized by a solid-phase technique on an Applied Biosytems Peptide Synthesizer. Synthesized cM3R peptide (cM3RP) was used as substrate in an ELISA to detect IgG anti-cM3RP antibodies in serum samples of patients and controls. The clinical and biological parameters of the diseases were also evaluated. The EULAR SS disease activity index (ESSDAI) score was used to measure disease activity in patients with primary SS.

RESULTS

(i) Anti-c2M3RP antibodies were highly prevalent in pSS patients, and the titre is much higher than anti-c1,3,4M3RP antibodies. (ii) The prevalence of anti-c2M3RP antibodies in pSS, SLE, RA and healthy controls was 62.2, 7.1, 5.3 and 1.6%, respectively. The prevalence of anti-linear-2-M3RP antibodies in pSS, SLE and RA patients and healthy controls were 56.1, 20.0, 14.7 and 9.4%. (iii) The specificity of anti-c2M3RP antibodies was 95.1%, much higher than that of linear polypeptide (84.7%) for pSS diagnosis. (iv) In pSS patients, anti-c2M3RP positivity had significantly increased frequency in patients who were RF or ANA positive, and had several haematological abnormalities, such as leucopenia, anaemia and thrombocytopenia. Furthermore, the ESSDAI score was significantly higher in anti-c2M3RP-positive pSS patients (P <  0.05).

CONCLUSION

Anti-c2M3RP antibody was highly specific for patients with pSS. The presence of anti-c2M3RP antibody in pSS indicates that c2M3RP may act as an autoantigen that may play a role in the pathogenesis of pSS.

Comparison of the effects of pilocarpine and cevimeline on salivary flow

OBJECTIVE

The aim of the present study was to compare the effect of low-dose pilocarpine and cevimeline as stimulants for salivary flow in healthy subjects.

METHODS

In this cross-over clinical trial with a 1-week washout period, 40 male volunteers were submitted to an oral dose of pilocarpine 1% (Salagen) -60 microg kg(-1) body-weight (Group 1) or Cevimeline (Evoxac) -30 mg (Group 2). Saliva samples were collected and the salivary flow rate was measured (ml min(-1)) at baseline and 20, 40, 60, 80, 140 and 200 min after administration of drugs. In addition, salivary secretion was also measured under mechanical stimulation to observe salivary gland function.

RESULTS

The data were analyzed by Friedman and Wilcoxon signed-rank tests (significance level = 5%). Pilocarpine and cevimeline significantly increased salivary flow 140 min after intake. There was a significant higher secretion with cevimeline 140 and 200 min after administration. There were no differences seen among subjects in the salivary glands function by mechanical stimulation.

CONCLUSION

Both drugs showed efficacy in increasing the salivary flow in healthy volunteers, but cevimeline was more effective than pilocarpine.

Pilocarpine-induced salivary fluid secretion in the perfused submandibular gland of the rat

Xerostomia is the symptom of dry mouth often seen in patients who receive head and neck radiation therapy or in patients who have Sjögren's syndrome. The primary treatment to relieve xerostomia symptom is oral administration of pilocarpine, a parasympathomimetic agent with muscarinic action. Increase in salivary secretion induced by systemic administration of pilocarpine is considered to be mediated by actions on muscarinic cholinergic receptors in the central nervous system and salivary glands. In this study, we investigated the direct effect of pilocarpine on salivary fluid secretion in the isolated, perfused rat submandibular gland. Pilocarpine provoked salivary fluid secretion in a dose-dependent manner. The Na(+)-channel blocker tetrodotoxin had almost no effect on the pilocarpine-induced salivary fluid secretion, indicating that pilocarpine directly stimulates submandibular gland. Pilocarpine induced an increase in intracellular Ca(2+) concentration in dispersed submandibular gland cells at 37 degrees C, but not 25 degrees C. The salivary fluid secretion induced by pilocarpine was consisted of a rapid and transient phase and a subsequent sustained phase, which profile was different from that evoked by carbachol, another typical muscarinic agonist. Pilocarpine also induced Lucifer yellow secretion via paracellular route.

Central muscarinic receptor subtypes involved in pilocarpine-induced salivation, hypertension and water intake

BACKGROUND AND PURPOSE

Recent evidence has suggested that pilocarpine (ACh receptor agonist) injected peripherally may act centrally producing salivation and hypertension. In this study, we investigated the effects of specific M(1) (pirenzepine), M(2)/M(4) (methoctramine), M(1)/M(3) (4-DAMP) and M(4) (tropicamide) muscarinic receptor subtype antagonists injected into the lateral cerebral ventricle (LV) on salivation, water intake and pressor responses to peripheral pilocarpine.

EXPERIMENTAL APPROACH

Male Holtzman rats with stainless steel cannulae implanted in the LV were used. Salivation was measured in rats anaesthetized with ketamine (100 mg per kg body weight) and arterial pressure was recorded in unanaesthetized rats.

KEY RESULTS

Salivation induced by i.p. pilocarpine (4 micromol per kg body weight) was reduced only by 4-DAMP (25-250 nmol) injected into the LV, not by pirenzepine, methoctramine or tropicamide at the dose of 500 nmol. Pirenzepine (0.1 and 1 nmol) and 4-DAMP (5 and 10 nmol) injected into the LV reduced i.p. pilocarpine-induced water intake, whereas metoctramine (50 nmol) produced nonspecific effects on ingestive behaviours. Injection of pirenzepine (100 nmol) or 4-DAMP (25 and 50 nmol) into the LV reduced i.v. pilocarpine-induced pressor responses. Tropicamide (500 nmol) injected into the LV had no effect on pilocarpine-induced salivation, pressor responses or water intake.

CONCLUSIONS AND IMPLICATIONS

The results suggest that central M(3) receptors are involved in peripheral pilocarpine-induced salivation and M(1) receptors in water intake and pressor responses. The involvement of M(3) receptors in water intake and pressor responses is not clear because 4-DAMP blocks both M(1) and M(3) receptors.

Selectivity of agonists for the active state of M1 to M4 muscarinic receptor subtypes

We measured the intrinsic relative activity (RA(i)) of muscarinic agonists to detect possible selectivity for receptor subtypes and signaling pathways. RA(i) is a relative measure of the microscopic affinity constant of an agonist for the active state of a GPCR expressed relative to that of a standard agonist. First, we estimated RA(i) values for a panel of agonists acting at the M(4) muscarinic receptor coupled to three distinct G-protein pathways: G(i) inhibition of cAMP accumulation, G(s) stimulation of cAMP accumulation, and G alpha(15) stimulation of phosphoinositide hydrolysis. Our results show similar RA(i) values for each agonist, suggesting that the same active state of the M(4) receptor triggers the activation of the three G proteins. We also estimated RA(i) values for agonists across M(1) to M(4) muscarinic subtypes stably transfected in Chinese hamster ovary cells. Our results show selectivity of McN-A-343 [4-I-[3-chlorophenyl]carbamoyloxy)-2-butynyltrimethylammnonium chloride] for the M(1) and M(4) subtypes and selectivity of pilocarpine for the M(1) and M(3) subtypes. The other agonists tested lacked marked selectivity among M(1) to M(4) receptors. Finally, we estimated RA(i) values from published literature on M(1), M(2), and M(3) muscarinic responses and obtained results consistent with our own studies. Our results show that the RA(i) estimate is a useful receptor-dependent measure of agonist activity.

Cholinergic treatments with emphasis on m1 muscarinic agonists as potential disease-modifying agents for Alzheimer's disease

The only prescribed drugs for treatment of Alzheimer's disease (AD) are acetylcholinesterase inhibitors (e.g., donepezil, rivastigmine, galantamine, and tacrine) and memantine, an NMDA antagonist. These drugs ameliorate mainly the symptoms of AD, such as cognitive impairments, rather than halting or preventing the causal neuropathology. There is currently no cure for AD and there is no way to stop its progression, yet there are numerous therapeutic approaches directed against various pathological hallmarks of AD that are extensively being pursued. In this context, the three major hallmark characteristics of AD (i.e., the CNS cholinergic hypofunction, formation of beta-amyloid plaques, and tangles containing hyperphosphorylated tau proteins) are apparently linked. Such linkages may have therapeutic implications, and this review is an attempt to analyze these versus the advantages and drawbacks of some cholinergic compounds, such as acetylcholinesterase inhibitors, M1 muscarinic agonists, M2 antagonists, and nicotinic agonists. Among the reviewed treatments, M1 selective agonists emerge, in particular, as potential disease modifiers.

Effect of the H2 receptor antagonist nizatidine on xerostomia in patients with primary Sjögren's syndrome

In Sjögren's syndrome (SS), oral dryness (xerostomia) is frequently the most bothersome symptom. An H2 histamine receptor antagonist is often administered to SS patients to treat associated superficial gastritis. The aim of the present study was to assess the ability of nizatidine, an H2 receptor antagonist, to also relieve xerostomia in patients with primary SS. Twenty-seven patients with primary SS were randomly assigned to receive nizatidine (n=14, 300 mg a day) or another H2 blocker, famotidine (n=13, 40 mg a day; control), were followed for eight weeks, and were asked for both subjective and objective assessments of oral dryness using a visual analog scale (VAS; 1-100 mm) and the Saxon's test, respectively. Patients receiving oral nizatidine, but not famotidine, obtained significant objective relief from their xerostomia (Saxon's test; baseline, 0.57 g/2 min; after eight weeks, 0.90 g/2 min, P<0.05). VAS scores indicated that nizatidine also provides mild improvement (20% improvement over baseline) of xerostomia-related clinical conditions, including mouth dryness and difficulty in chewing, tasting and swallowing food. Both drugs were generally well tolerated, without adverse effects. The present preliminary study suggests that nizatidine may represent a new option for the treatment of xerostomia in SS.

Mechanism of salivary secretion enhancement by Byakkokaninjinto

Byakkokaninjinto (BN) is a Kampo preparation used for the treatment of xerostomia induced by drug, ageing, Sjogren syndrome, etc. The mechanism for BN to induce salivary secretion has not been made clear. In this study, various rat thirst models were prepared using muscarinic receptor blockers, such as 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) and atropine, or adrenoceptor blockers, such as phentolamine and propranolol, in order to investigate the efficiency of BN. When BN was orally administered to the rats in the dose range of 100 to 300 mg/kg, the salivary secretion increased in a dose-dependent manner. The suppression of salivary secretion induced by phentolamine, atropine, and 4-DAMP was recovered by the additional treatment of BN. Interestingly, BN treatment increased the expression of aquaporin 5 in rats, which is known to regulate salivary secretion from the submandibular gland. These results suggested that BN increased the expression of aquaporin 5 through activation of muscarinic M3 receptor and enhanced salivary secretion.

Distinct pathways of ERK activation by the muscarinic agonists pilocarpine and carbachol in a human salivary cell line

Cholinergic-muscarinic receptor agonists are used to alleviate mouth dryness, although the cellular signals mediating the actions of these agents on salivary glands have not been identified. We examined the activation of ERK1/2 by two muscarinic agonists, pilocarpine and carbachol, in a human salivary cell line (HSY). Immunoblot analysis revealed that both agonists induced transient activation of ERK1/2. Whereas pilocarpine induced phosphorylation of the epidermal growth factor (EGF) receptor, carbachol did not. Moreover, ERK activation by pilocarpine, but not carbachol, was abolished by the EGF receptor inhibitor AG-1478. Downregulation of PKC by prolonged treatment of cells with the phorbol ester PMA diminished carbachol-induced ERK phosphorylation but had no effect on pilocarpine responsiveness. Depletion of intracellular Ca2+ ([Ca2+]i by EGTA did not affect ERK activation by either agent. In contrast to carbachol, pilocarpine did not elicit [Ca2+]i mobilization in HSY cells. Treatment of cells with the muscarinic receptor subtype 3 (M3) antagonist N-(3-chloropropyl)-4-piperidnyl diphenylacetate decreased ERK responsiveness to both agents, whereas the subtype 1 (M1) antagonist pirenzepine reduced only the carbachol response. Stimulation of ERKs by pilocarpine was also decreased by M3, but not M1, receptor small interfering RNA. The Src inhibitor PP2 blocked pilocarpine-induced ERK activation and EGF receptor phosphorylation, without affecting ERK activation by carbachol. Our results demonstrate that the actions of pilocarpine and carbachol in salivary cells are mediated through two distinct signaling mechanisms-pilocarpine acting via M3 receptors and Src-dependent transactivation of EGF receptors, and carbachol via M1/M3 receptors and PKC-converging on the ERK pathway.

Muscarinic acetylcholine receptors: mutant mice provide new insights for drug development

Muscarinic acetylcholine receptors (mAChRs), M(1)-M(5), regulate the activity of numerous fundamental central and peripheral functions. The lack of small-molecule ligands that can block or activate specific mAChR subtypes with high selectivity has remained a major obstacle in defining the roles of the individual receptor subtypes and in the development of novel muscarinic drugs. Recently, phenotypic analysis of mutant mouse strains deficient in each of the five mAChR subtypes has led to a wealth of new information regarding the physiological roles of the individual receptor subtypes. Importantly, these studies have identified specific mAChR-regulated pathways as potentially novel targets for the treatment of various important disorders including Alzheimer's disease, schizophrenia, pain, obesity and diabetes.