Advances in the management of constipation-predominant irritable bowel syndrome: the role of linaclotide

Effect of Organic Solvents on the Activity, Stability and Secondary Structure of asclepain cI, Using FTIR and Molecular Dynamics Simulations

The present study aims at understanding the effect of organic solvents on the specific proteolytic activity and operational stability of asclepain cI in aqueous-organic media, using correlations between geometrical and structural parameters of asclepain cI. These correlations were determined by molecular dynamics (MD) simulations and the secondary structure of the enzyme validated by Fourier-transform Infrared (FTIR) spectroscopy. Asclepain cI exhibited significantly higher catalytic potential in 29 of the 42 aqueous-organic media tested, composed by 0.1 mM TRIS hydrochloride buffer pH 8 (TCB) and an organic solvent, than in buffer alone. Asclepain cI in water-organic miscible systems showed high FTIR spectral similarity with that obtained in TCB, while in immiscible systems the enzyme acquired different secondary structures than in buffer. Among the conditions studied, asclepain cI showed the highest catalytic potential in 50% v/v ethyl acetate in TCB. According to MD simulations, that medium elicited solvation and flexibility changes around the active center of asclepain cI and conducted to a new secondary structure with the active center preserved. These results provide valuable insights into the elucidation of the molecular mechanism of asclepain cI tolerance to organic solvents and pave the way for its future application for the synthesis of peptides in aqueous-organic media.

Enzymatic synthesis of new antimicrobial peptides for food purposes

Growing consumer awareness of the potential negative health effects of synthetic antibiotics has prompted the search for more natural preservatives that can improve the safety and quality of food. In this study we report the enzymatic synthesis of N-α-[Carbobenzyloxy]-Ile-Gln (Z-IQ) which is the precursor of Ile-Gln (IQ), a new antibacterial dipeptide, using an aqueous-organic biphasic system formed by 50% (v/v) ethyl acetate in 0.1 M Tris - HCl buffer pH 8. A partially purified proteolytic extract from the fruits of Solanum granuloso leprosum, named granulosain, proved to be a robust biocatalyst for the synthesis of Z-IQ, eliciting 71 ± 0.10% maximal peptide yield in the above described conditions. After cleaving and purifying IQ dipeptide, antimicrobial activity was assayed against Staphylococcus aureus ATCC 25923, Staphylococcus hominis A17771, and Staphylococcus aureus C00195, and MIC values between 118 ± 0.01 μg/mL and 133.7 ± 0.05 μg/mL were obtained. In addition, IQ showed MIC of 82.4 ± 0.01 μg/mL and 85.0 ± 0.00 μg/mL against Escherichia coli ATCC 25922 and Escherichia coli A17683, respectively. IQ did not show inhibitory activity against single-drug resistance (SDR) strains, such as Klebsiella oxytoca A19438 (SDR) and Pseudomonas aeruginosa C00213 (SDR), and against multidrug-resistant Enterococcus faecalis I00125 (MDR). IQ also caused growth inhibition of Helicobacter pylori NCTC 11638 and three wild-type H. pylori strains, which are sensitive to AML, MTZ, LEV and CLA (H. pylori 659), resistant to LEV (H. pylori 661 SDR), and resistant to MTZ (H. pylori 662 SDR). Finally, this study contributes with a new dipeptide (IQ) that can be used as an antimicrobial agent for food preservation or as a safe ingredient of functional foods.

Structural insight into guanylyl cyclase receptor hijacking of the kinase-Hsp90 regulatory mechanism

Membrane receptor guanylyl cyclases play a role in many important facets of human physiology, ranging from regulation of blood pressure to the regulation of intestinal fluid secretion. The structural mechanisms which influence the regulation of these important physiological effects have yet to be explored. We present the 3.9 Å resolution cryoEM structure of the human membrane receptor guanylyl cyclase GC-C in complex with Hsp90 and its co-chaperone Cdc37, providing insight into the mechanism of Cdc37 mediated binding of GC-C to the Hsp90 regulatory complex. As a membrane protein and non-kinase client of Hsp90-Cdc37, this work shows remarkable plasticity of Cdc37 to interact with a broad array of clients having significant sequence variation. Further, this work shows how membrane receptor guanylyl cyclases hijack the regulatory mechanisms used for active kinases to facilitate their regulation. Given the known druggability of Hsp90, these insights can guide the further development of mGC targeted therapeutics and lead to new avenues to treat hypertension, inflammatory bowel disease, and other mGC related conditions.

Oral Phyto-thymol ameliorates the stress induced IBS symptoms

Physical stressors play a crucial role in the progression of irritable bowel syndrome (IBS). Here we report a heterogeneous physical stress induced IBS rat model which shows depression and subsequent modulation of IBS by oral treatment of thymol. Oral administration of Thymol reduces the stress induced IBS significantly altering the stress induced gastrointestinal hypermotility, prolonged the whole gut transit time, and increased abdominal withdrawal reflex suggesting gastrointestinal hypermotility and visceral discomfort caused the onset of depression. Immunohistochemical analysis in small intestine and colon of rats shows the decreased 5-HT3AR expression level while thymol treatment normalized the 5-HT3AR expression in the stressed rats. Molecular docking studies showed that thymol competes with endogenous serotonin and an antagonist, Tropisetron and all have similar binding energies to 5-HT3AR. Molecular dynamics simulations revealed that thymol and tropisetron might have similar effects on 5-HT3AR. Our study suggest that thymol improves IBS symptoms through 5-HT3AR, could be useful for the treatment of IBS.

Plecanatide: a new guanylate cyclase agonist for the treatment of chronic idiopathic constipation

Chronic constipation affects millions of Americans, consumes significant healthcare resources, and significantly affects quality of life (QOL). Recently, several new treatment options have become available for the treatment of constipation, including intestinal secretagogues such as lubiprotone, and linaclotide, prokinetics such as prucalopride, and bile acid transporter antagonists. Plecanatide is the newest of the secretagogue class of compounds that has been approved by the US Food and Drug Administration for the treatment of adults with chronic idiopathic constipation (CIC) in the USA. It is a guanylate cyclase agonist, and a 16 amino acid synthetic peptide that is a structural analog of human uroguanylin. Two large randomized, double-blind, placebo-controlled studies assessed the efficacy and safety of plecanatide in CIC patients (Rome III). Both doses of plecanatide, 3 mg and 6 mg resulted in a significantly greater percentage of patients who were durable overall complete spontaneous bowel movement (CSBM) responders (primary endpoint) compared with those who received placebo (plecanatide 3 mg, 21.0%; plecanatide 6 mg, 19.5%; placebo, 10.2%; p < 0.001 for each drug dose versus placebo). Plecanatide treatment also significantly reduced the severity of other CIC symptoms (straining effort, stool consistency, bloating). Also, plecanatide-treated patients reported high levels of satisfaction and improved QOL and desire to continue treatment. The rate of treatment-emergent adverse events with plecanatide was low, including rates of diarrhea (5%). Plecanatide is a luminally acting secretagogue that is efficacious and safe for the treatment of CIC. This article provides an overview of plecanatide in the management of adults with CIC.

Oral treatment with plecanatide or dolcanatide attenuates visceral hypersensitivity via activation of guanylate cyclase-C in rat models

AIM

To investigate the effects of plecanatide and dolcanatide on maintenance of paracellular permeability, integrity of tight junctions and on suppression of visceral hypersensitivity.

METHODS

Transport of fluorescein isothiocyanate (FITC)-dextran was measured to assess permeability across cell monolayers and rat colon tissues. Effects of plecanatide and dolcanatide on the integrity of tight junctions in Caco-2 and T84 monolayers and on the expression and localization of occludin and zonula occludens-1 (ZO-1) were examined by immunofluorescence microscopy. Anti-nociceptive activity of these agonists was evaluated in trinitrobenzene sulfonic acid (TNBS)-induced inflammatory as well as in non-inflammatory partial restraint stress (PRS) rat models. Statistical significance between the treatment groups in the permeability studies were evaluated using unpaired t-tests.

RESULTS

Treatment of T84 and Caco-2 monolayers with lipopolysaccharide (LPS) rapidly increased permeability, which was effectively suppressed when monolayers were also treated with plecanatide or dolcanatide. Similarly, when T84 and Caco-2 monolayers were treated with LPS, cell surface localization of tight junction proteins occludin and ZO-1 was severely disrupted. When cell monolayers were treated with LPS in the presence of plecanatide or dolcanatide, occludin and ZO-1 were localized at the cell surface of adjoining cells, similar to that observed for vehicle treated cells. Treatment of cell monolayers with plecanatide or dolcanatide without LPS did not alter permeability, integrity of tight junctions and cell surface localization of either of the tight junction proteins. In rat visceral hypersensitivity models, both agonists suppressed the TNBS-induced increase in abdominal contractions in response to colorectal distension without affecting the colonic wall elasticity, and both agonists also reduced colonic hypersensitivity in the PRS model.

CONCLUSION

Our results suggest that activation of GC-C signaling might be involved in maintenance of barrier function, possibly through regulating normal localization of tight junction proteins. Consistent with these findings, plecanatide and dolcanatide showed potent anti-nociceptive activity in rat visceral hypersensitivity models. These results imply that activation of GC-C signaling may be an attractive therapeutic approach to treat functional constipation disorders and inflammatory gastrointestinal conditions.

Cellular mechanism for herbal medicine Junchoto to facilitate intestinal Cl-/water secretion that involves cAMP-dependent activation of CFTR

Constipation is a common symptom frequently compromising the quality of daily life. Several mechanistically different drugs have been used to mitigate constipation, including Japanese herbal (Kampo) medicines. However, the mechanisms of their actions are often not well understood. Here we aimed to investigate the molecular mechanisms underlying the effects of Junchoto (JCT), a Kampo medicine empirically prescribed for chronic constipation. Cl⁻ channel activity was measured by the patch-clamp method in human cystic fibrosis transmembrane conductance regulator (CFTR)-expressing HEK293T cells and human intestinal Caco-2 cells. cAMP was measured by a luciferase-based assay. Cell volume change was measured by a particle-sizing and particle-counting analyzer and video-microscopic measurement. In both CFTR-expressing HEK293T and Caco-2 cells, JCT dose-dependently induced whole-cell currents showing typical biophysical and pharmacological features of CFTR. Robust expression of CFTR was confirmed by RT-PCR and Western blotting in Caco-2 cells. Luciferase-based measurement revealed that JCT increases intracellular cAMP levels. Administration of the adenylate cyclase inhibitor SQ22536 or CFTR inhibitor-172, or treatment with small interfering RNAs (siRNA) targeting CFTR, abolished JCT-induced whole-cell currents, suggesting that elevated intracellular cAMP by JCT causes activation of CFTR in Caco-2 cells. Finally, blockade of CFTR activity by CFTR inhibitor-172 or siRNA-knockdown of CFTR or application of SQ22536 markedly reduced the degree of cell volume decrease induced by JCT. JCT can induce a Cl⁻ efflux through the CFTR channel to promote water secretion, and this effect is likely mediated by increased cAMP production.

Mashiningan Improves Opioid-Induced Constipation in Rats by Activating Cystic Fibrosis Transmembrane Conductance Regulator Chloride Channel

Opioid receptor stimulants are analgesics used in patients with and without cancer; however, they often cause constipation, resulting in poor adherence and deterioration of the quality of life. Hence, suitable treatments for constipation are required. In this study, we investigated the pharmacological mechanisms of action of mashiningan (MNG), a Kampo medicine used to treat constipation, and evaluated the effect of MNG on opioid-induced constipation in rats. MNG (100 or 300 mg/kg) was orally administered to normal or codeine phosphate (CPH)-induced constipation in rats, and its effect was evaluated on the basis of fecal counts, characteristics, and weight. Small intestinal fluid secretion was measured after treatment with MNG alone or coadministration with a cystic fibrosis transmembrane conductance regulator (CFTR)-specific inhibitor (CFTRinh-172). The effects of MNG on the CFTR and type-2 chloride channel were determined using patch-clamp or short-circuit current experiments, respectively. MNG increased the fecal weight and proportion of soft feces in normal rats. CPH-induced constipation in rats decreased fecal counts and weight, whereas MNG prevented these effects and increased the proportion of soft feces. MNG increased the electronic chloride current, and this effect was inhibited by the CFTRinh-172 in the CFTR assay. Furthermore, MNG increased small intestinal fluid secretion, and this effect was abolished by coadministration with the CFTRinh-172. MNG improved opioid-induced constipation in rats, and this improvement may have been mediated by increasing intestinal fluid secretion via CFTR chloride channel activation. Therefore, MNG is expected as a medicine of the treatment of constipation in patients taking opioids.

New and emerging therapies for the treatment of irritable bowel syndrome: an update for gastroenterologists

Irritable bowel syndrome is a functional bowel disorder with gastrointestinal symptoms (e.g. abdominal pain, straining, urgency, incomplete evacuation, nausea, and bloating) that occur alongside bowel function alterations (i.e. constipation, diarrhea, or both). Patients with irritable bowel syndrome may also experience comorbid anxiety and depression. Irritable bowel syndrome is common, with a prevalence estimated between 3% and 28%, affecting patient health and quality of life. Patients with moderate or severe irritable bowel syndrome generally seek medical care, whereas those with milder symptoms may choose self-management. Most patients with irritable bowel syndrome receive outpatient care, but irritable bowel syndrome-related hospitalizations do occur. The pathophysiology of irritable bowel syndrome is multifactorial (i.e. genetics, immune components, changes in the gut microbiota, disturbances in physiologic stress response systems, and psychosocial factors). Management of irritable bowel syndrome can include lifestyle changes, dietary interventions, counseling, psychologic medication, and agents that affect gastrointestinal motility. A number of therapies have emerged in recent years with clinical trial data demonstrating efficacy and safety for patients with irritable bowel syndrome, including agents that target gastrointestinal motility (i.e. linaclotide), gastrointestinal opioid receptors (i.e. asimadoline, eluxadoline), and gut microbiota (i.e. rifaximin). Linaclotide has been shown to significantly improve stool frequency and abdominal pain compared with placebo in constipation-predominant irritable bowel syndrome (number needed to treat, 5.1). Asimadoline shows efficacy in patients with moderate-to-severe irritable bowel syndrome-related pain. Rifaximin provided adequate relief of global irritable bowel syndrome symptoms versus placebo for a significantly greater percentage of patients with diarrhea-predominant irritable bowel syndrome (p < 0.001). Management that encompasses all aspects of irritable bowel syndrome (gastrointestinal symptoms) and comorbid psychologic symptoms (e.g. anxiety or depression) is important for improving overall patient health and well-being.

Rare medical manifestations of severe restricting and purging: "Zebras," missed diagnoses, and best practices

OBJECTIVE

Medical problems that arise due to severe restricting and/or purging may be misdiagnosed or suboptimally treated, from outpatient clinics to top medical hospitals. A symptom may be presumed to be a psychological manifestation of the eating disorder and inappropriately dismissed for further medical evaluation. Alternatively, a detailed medical workup may be performed, overlooking a classic relationship between starvation and a physical finding, which delays referral to eating disorder care. This review article focuses on rare medical issues (also called "zebras" in medical training), diagnoses that may be missed in patients with eating disorders, and best practices for management, organized by organ system.

METHOD

A PubMed search was performed, using search terms "eating disorder," "anorexia nervosa," and "bulimia nervosa" in combination with different words for each organ system and known medical manifestations of severe eating disorders, with high quality and relevant studies from the past 20 years cited.

DISCUSSION

Adults with eating disorders may present with extreme organ dysfunction and atypical signs and symptoms of typical medical problems. Timely diagnosis, risk awareness, appropriate treatment, and avoidance of harm are all vital. With judicious management and nutritional rehabilitation, most of these complications will significantly improve or resolve. ©

New pharmacological treatment options for irritable bowel syndrome with constipation

INTRODUCTION

Constipation predominant irritable bowel syndrome (IBS-C) is a common disorder and accounts for a large number of ambulatory visits. Sensory abnormalities, that is, presence of abdominal pain and discomfort, distinguish IBS-C from chronic idiopathic constipation.

AREA COVERED

This review focuses on the pharmacology, efficacy, safety, and future of prucalopride, YKP-10811, DSP-6952, dexloxiglumide, linaclotide, plecanatide, tenapanor, and elobixibat.

EXPERT OPINION

It is now well established that treatment focusing only on bowel transit provides incomplete relief to patients with IBS-C. Improved understanding of pathophysiology of IBS-C has led to use of sensory end points like complete spontaneous bowel movements and the FDA combined end point (abdominal pain and complete spontaneous bowel movements) in clinical trials. A number of drugs are in development and provide hope for this challenging group of patients. However, because of recent failures secondary to ineffectiveness and/or adverse events, we cautiously await how clinical data play out in larger studies and in clinical practice.

Defecating Disorders: A Common Cause of Constipation in Women

Defecating disorders are a common and complex problem. There are a range of anatomical and functional bowel abnormalities that can lead to this condition. Treatment is difficult and needs a multidisciplinary approach. First line treatment for defecating disorders is conservative. For those that fail conservative treatment, some may respond to surgical therapy but with variable results. The aim of this review is to offer an overview of defecating disorders as well as provide an algorithm on how to diagnose and treat them with the help of a multidisciplinary and multimodal approach.

Potential Causes and Present Pharmacotherapy of Irritable Bowel Syndrome: An Overview

BACKGROUND

Irritable bowel syndrome (IBS) is currently one of the most common disorders of the digestive system in the Western society. Almost 2 out of 10 people suffer from IBS with women being more affected than men. IBS is associated with abdominal pain, bloating and altered stool consistency and imposes a heavy burden for the affected patients.

SUMMARY

The pathophysiology of IBS remains elusive although potential causes have been suggested, such as a deranged brain-gut signaling, hypersensitivity of visceral sensory afferent fibers, bacterial gastroenteritis, small intestinal bacterial overgrowth (SIBO), genetic alterations and food sensitivity. Targets for the pharmacotherapy of IBS include the serotonergic and opioidergic system, and the microbial population of the gut. Alternative therapies like traditional Chinese medicine have shown some success in the combat against IBS. Key Messages: Many therapeutics for the treatment of IBS have emerged in the past; however, only a few have met up with the expectations in larger clinical trials. Additionally, the multifactorial etiology of IBS and its variety of cardinal symptoms requires an individual set of therapeutics. This review provides a short overview of potential causes and current pharmacological therapeutics and of additional and alternative therapies for IBS.

Stress-induced visceral pain: toward animal models of irritable-bowel syndrome and associated comorbidities

Visceral pain is a global term used to describe pain originating from the internal organs, which is distinct from somatic pain. It is a hallmark of functional gastrointestinal disorders such as irritable-bowel syndrome (IBS). Currently, the treatment strategies targeting visceral pain are unsatisfactory, with development of novel therapeutics hindered by a lack of detailed knowledge of the underlying mechanisms. Stress has long been implicated in the pathophysiology of visceral pain in both preclinical and clinical studies. Here, we discuss the complex etiology of visceral pain reviewing our current understanding in the context of the role of stress, gender, gut microbiota alterations, and immune functioning. Furthermore, we review the role of glutamate, GABA, and epigenetic mechanisms as possible therapeutic strategies for the treatment of visceral pain for which there is an unmet medical need. Moreover, we discuss the most widely described rodent models used to model visceral pain in the preclinical setting. The theory behind, and application of, animal models is key for both the understanding of underlying mechanisms and design of future therapeutic interventions. Taken together, it is apparent that stress-induced visceral pain and its psychiatric comorbidities, as typified by IBS, has a multifaceted etiology. Moreover, treatment strategies still lag far behind when compared to other pain modalities. The development of novel, effective, and specific therapeutics for the treatment of visceral pain has never been more pertinent.