SPI-0211 activates T84 cell chloride transport and recombinant human ClC-2 chloride currents

Review of the Patient Burden and Therapeutic Landscape of Irritable Bowel Syndrome with Constipation in the United States

Irritable bowel syndrome (IBS) is a common disorder of the gut-brain axis. IBS with constipation (IBS-C) accounts for approximately one-third of IBS cases and is associated with substantial burden of illness and decreased quality of life. This narrative review provides an overview of the current and upcoming treatment options and disease management for IBS-C from a US perspective and discusses the importance of the relationship between patient and health care provider in diagnosis and treatment. A positive diagnostic strategy for IBS-C is recommended, based on clinical history, physical examination, and minimal laboratory tests. An effective communication strategy between patients and health care professionals is essential to ensure early diagnosis and reduce both health care costs and overall disease burden. Treatment typically begins with lifestyle interventions and nonpharmacologic options, such as dietary interventions, fiber supplements, and osmotic laxatives. In patients with inadequate response to these therapies, 4 currently available therapies (lubiprostone, linaclotide, plecanatide, and tenapanor) approved by the US Food and Drug Administration may relieve IBS-C symptoms. These agents are generally well tolerated and efficacious in improving IBS-C symptoms, including constipation and abdominal pain. In patients with persistent abdominal pain and/or psychological symptoms, brain-gut behavioral therapy or neuromodulator therapy may be beneficial.

Efficacy of lubiprostone for functional constipation treatment in adolescents and children: Randomized controlled trial

OBJECTIVES

Adolescent and pediatric functional constipation (FC) is a common clinical problem. Currently, data on lubiprostone for the treatment of pediatric FC are scarce. This study investigated the efficacy and safety of lubiprostone in the treatment of pediatric FC.

METHODS

In a single-blinded, randomized controlled study, we included 280 patients aged 8-18 years with FC. Patients were randomized either to a weight-based lubiprostone dose (n = 140) or conventional laxatives (n = 140), including lactulose, bisacodyl, or sodium picosulfate, for 12 weeks, followed by 4 weeks posttreatment follow-up.

RESULTS

Improvement in constipation was achieved in 128 (91.4%) patients in the lubiprostone group, and in 48 (34.3%) patients of the conventional therapy group (p < 0.001) and was sustained after treatment discontinuation. One quarter of the lubiprostone group experienced the first spontaneous bowel motion within 48 h after dose initiation. A total of 75.7% of the lubiprostone group could achieve and sustain Bristol stool form of 3 or 4 during the last 4 weeks of therapy and through the 4 weeks of follow-up versus 50 (35.7%) patients in the conventional therapy group (p < 0.001). No life-threatening adverse drug reactions were encountered, and no treatment-related discontinuation. Mild self-limited colicky abdominal pain and headache were the most prevalent side effects in the lubiprostone group.

CONCLUSIONS

Lubiprostone is an effective and well-tolerated pharmacotherapy for youthful age and pediatric age groups, which may alter the paradigm of pediatric FC treatment.

Factors associated with long-term efficacy of lubiprostone for chronic constipation

The prevalence of chronic constipation in Japan is increasing, and is presently almost 1 in 5 people. Because constipation is common, especially in older patients, to avoid adverse events and polypharmacy, simple treatments at low doses are generally desired. Although the chloride channel activator lubiprostone is candidate drug that may solve these problems, factors associated with the long-term efficacy of lubiprostone monotherapy for chronic constipation in treatment-naive patients remain unclear. We here retrospectively investigated the clinical characteristics and factors of patients who achieved long-term constipation improvement with lubiprostone monotherapy. Seventy-four patients with chronic constipation treated with lubiprostone monotherapy (24 or 48 μg/day) from January 2017 to August 2018 were reviewed. Patient characteristics and clinical time-courses were compared between those who sustained improvement for 6 months, and those who became refractory to treatment. In 54 patients (76.1%), constipation improved by lubiprostone administration for 6 months. On multivariate analysis, a significant clinical factor associated with sustained improvement was a starting lubiprostone dose of 24 μg/day (odds ratio: 5.791; 95% confidence interval: 1.032-32.498; p = 0.046). A starting lubiprostone dose of 24 μg/day has efficacy to improve chronic constipation and to prevent adverse events of nausea and diarrhea in Japanese patients.

Olfactory neuronal cells as a promising tool to realize the "druggable genome" approach for drug discovery in neuropsychiatric disorders

"Druggable genome" is a novel concept that emphasizes the importance of using the information of genome-wide genetic studies for drug discovery and development. Successful precedents of "druggable genome" have recently emerged for some disorders by combining genomic and gene expression profiles with medical and pharmacological knowledge. One of the key premises for the success is the good access to disease-relevant tissues from "living" patients in which we may observe molecular expression changes in association with symptomatic alteration. Thus, given brain biopsies are ethically and practically difficult, the application of the "druggable genome" approach is challenging for neuropsychiatric disorders. Here, to fill this gap, we propose the use of olfactory neuronal cells (ONCs) biopsied and established via nasal biopsy from living subjects. By using candidate genes that were proposed in a study in which genetic information, postmortem brain expression profiles, and pharmacological knowledge were considered for cognition in the general population, we addressed the utility of ONCs in the "druggable genome" approach by using the clinical and cell resources of an established psychosis cohort in our group. Through this pilot effort, we underscored the chloride voltage-gated channel 2 (CLCN2) gene as a possible druggable candidate for early-stage psychosis. The CLCN2 gene expression was associated with verbal memory, but not with other dimensions in cognition, nor psychiatric manifestations (positive and negative symptoms). The association between this candidate molecule and verbal memory was also confirmed at the protein level. By using ONCs from living subjects, we now provide more specific information regarding molecular expression and clinical phenotypes. The use of ONCs also provides the opportunity of validating the relationship not only at the RNA level but also protein level, leading to the potential of functional assays in the future. Taken together, we now provide evidence that supports the utility of ONCs as a tool for the "druggable genome" approach in translational psychiatry.

The ClC-2 Chloride Channel Activator, Lubiprostone, Improves Intestinal Barrier Function in Biopsies from Crohn’s Disease but Not Ulcerative Colitis Patients

The prostone analog, lubiprostone, is approved to manage constipation-predominant irritable bowel syndrome. Lubiprostone also protects intestinal mucosal barrier function in animal models of colitis. The aim of this study was to determine if lubiprostone improves barrier properties in isolated colonic biopsies from Crohn’s disease (CD) and ulcerative colitis (UC) patients. Sigmoid colon biopsies from healthy subjects, CD and UC patients in remission, and CD patients with active disease were mounted in Ussing chambers. Tissues were treated with lubiprostone or vehicle to determine the effects on transepithelial electrical resistance (TER), FITC-dextran 4kD (FD4) permeability, and electrogenic ion transport responses to forskolin and carbachol. Localization of the tight junction protein, occludin, was determined by immunofluorescence. Lubiprostone significantly increased ion transport across control, CD and UC remission biopsies but not active CD. Lubiprostone selectively improved TER in both CD remission and active disease biopsies but not in control or UC biopsies. The improved TER was associated with increased membrane localization of occludin. Lubiprostone selectively improved barrier properties of biopsies from CD patients vs. UC and independent of an ion transport response. These data indicate that lubiprostone has potential efficacy in improving mucosal integrity in Crohn’s disease.

Development and validation of a highly sensitive and selective LC-MS/MS method for the determination of 15-hydroxylubiprostone in human plasma: Application to a pharmacokinetic study in healthy Chinese volunteers

Lubiprostone, a derivative of prostaglandin E1, is the first chemical-type constipation treatment approved by FDA. Lubiprostone has low systemic exposure after oral administration. Therefore, it is recommended that 15-hydroxylubiprostone, which is a dominant active metabolite of lubiprostone, be used as the pharmacokinetic evaluation indicator. Due to the microdosage of the lubiprostone capsules, it is difficult to develop a highly sensitive bioanalytical method for 15-hydroxylubiprostone.In this study, a highly sensitive and selective liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method has been established and fully validated for the quantification of 15-hydroxylubiprostone in human plasma, and the validated bioanalytical method has been applied to a pharmacokinetic study of lubiprostone capsules successfully.The pharmacokinetics of 15-hydroxylubiprostone were observed after fed administration in healthy Chinese volunteers. The C_max and AUC_0-t were 75.8 ± 57.6 pg/mL and 222 ± 68.0 pg·h/mL for 15-hydroxylubiprostone.This study investigated the pharmacokinetic properties of 15-hydroxylubiprostone under fed conditions in healthy Chinese volunteers and would provide clinical guidance for the application and further development of lubiprostone capsules.

Enantio-, Diastereo- and Regioselective Synthesis of Chiral Cyclic and Acyclic gem-Difluoromethylenes by Palladium-Catalyzed [4+2] Cycloaddition

gem-Difluoromethylene moieties are attractive in medicinal chemistry due to their ability to mimic other more ubiquitous functional groups. Thus, effective asymmetric methods for their construction are highly desirable, especially for the industrial production of chiral drugs. Using a Pd-catalyzed asymmetric [4+2] cycloaddition between substituted-2-alkylidenetrimethylene carbonates and gem-difluoroalkyl ketones, we were able to easily access chiral 1,3-dioxanes that contain a tetrasubstituted difluoroalkyl stereogenic center in cyclic and acyclic skeletons. A novel phosphoramidite ligand, which contains a bulky 1,1-dinaphthylmethanamino moiety, was developed to provide the products in high yield with excellent enantio-, diastereo-, and regioselectivity. Strikingly, the gem-difluoro substitution pattern promotes the reaction, and pentafluoroethylketone, an α,α-difluorinated β-ketoester, and a β-ketosulfone are suitable substrates for this method.

Lubiprostone is non-selective activator of cAMP-gated ion channels and Clc-2 has a minor role in its prosecretory effect in intestinal epithelial cells

Loss of prosecretory Cl- channel CFTR activity is considered as the key cause of gastrointestinal disorders in cystic fibrosis including constipation and meconium ileus. Clc-2 is proposed as an alternative Cl- channel in intestinal epithelia that can compensate for CFTR loss-of-function. Lubiprostone is an FDA-approved drug with Clc-2 activation as its presumed mechanism of action. However, relative contribution of Clc-2 in intestinal Cl- secretion and the mechanism of action of lubiprostone remain controversial due to lack of selective Clc-2 inhibitors. Using recently identified selective Clc-2 inhibitor AK-42, we characterized the roles of Clc-2 in Cl- secretion in human intestinal epithelial T84 cells. Clc-2 inhibitor AK-42 had minimal (15%) inhibitory effect on secretory short-circuit current (Isc) induced by cAMP agonists, where subsequently applied CFTR inhibitor (CFTRinh-172) caused 2-3 fold greater inhibition. Similarly, AK-42 inhibited lubiprostone-induced secretory Isc by 20%, whereas CFTRinh-172 caused 2-3 fold greater inhibition. In addition to increasing CFTR and Clc-2-mediated apical Cl- conductance, lubiprostone increased basolateral membrane K+ conductance, which was completely reversed by cAMP-activated K+ channel inhibitor BaCl2 All components of lubiprostone-induced secretion (Clc-2, CFTR and K+ channels) were inhibited by ~65% with the extracellular Ca2+-sensing receptor (CaSR) activator cinacalcet that stimulates cAMP hydrolysis. Lastly, EP4 prostaglandin receptor inhibitor GW627368 pretreatment inhibited lubiprostone-induced secretion by 40% without any effect on forskolin response. Our findings suggest that Clc-2 has minor role in cAMP-induced intestinal Cl- secretion; and lubiprostone is not a selective Clc-2 activator, but general activator of cAMP-gated ion channels in human intestinal epithelial cells. Significance Statement Cl- channel Clc-2 activation is the proposed mechanism of action of the FDA-approved constipation drug lubiprostone. Using first-in-class selective Clc-2 inhibitor AK-42, we showed that Clc-2 has minor contribution in intestinal Cl- secretion induced by lubiprostone and cAMP agonists. We also found that lubiprostone is a general activator of cAMP-gated ion channels in human intestinal epithelial cells (via EP4 receptors). Our findings clarify the roles of Clc-2 in intestinal Cl- secretion and elucidate the mechanism of action of approved-drug lubiprostone.

Intestinal secretory mechanisms and diarrhea

One of the primary functions of the intestinal epithelium is to transport fluid and electrolytes to and from the luminal contents. Under normal circumstances, absorptive and secretory processes are tightly regulated such that absorption predominates, thereby enabling conservation of the large volumes of water that pass through the intestine each day. However, in conditions of secretory diarrhea, this balance becomes dysregulated, so that fluid secretion, driven primarily by Cl- secretion, overwhelms absorptive capacity, leading to increased loss of water in the stool. Secretory diarrheas are common and include those induced by pathogenic bacteria and viruses, allergens, and disruptions to bile acid homeostasis, or as a side effect of many drugs. Here, we review the cellular and molecular mechanisms by which Cl- and fluid secretion in the intestine are regulated, how these mechanisms become dysregulated in conditions of secretory diarrhea, currently available and emerging therapeutic approaches, and how new strategies to exploit intestinal secretory mechanisms are successfully being used in the treatment of constipation.

Receptor-mediated activation of CFTR via prostaglandin signaling pathways in the airway

Cystic fibrosis (CF) is a genetic disease caused by mutations of the gene encoding a cAMP-activated Cl^- channel, the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR modulator therapies consist of small-molecule drugs that rescue mutant CFTR. Regimens of single or combinations of CFTR modulators still rely on endogenous levels of cAMP to regulate CFTR activity. We investigated CFTR activation by the natural mediator prostaglandin E2 (PGE2) and lubiprostone (a Food and Drug Administration-approved drug known to target prostaglandin receptors) and tested the hypothesis that receptor-mediated CFTR activators can be used in combination with currently available CFTR modulators to increase function of mutant CFTR. Primary-cultured airway epithelia were assayed in Ussing chambers. Experimental CFTR activators and established CFTR modulators were applied for 24 h and/or acutely and analyzed for their effect on CFTR activity as measured by changes in short-circuit current (I_SC). In non-CF airway epithelia, acute application of lubiprostone and PGE2 activated CFTR to the levels comparable to forskolin (Fsk). Pretreatment (24 h) with antagonists to prostaglandin receptors EP2 and EP4 abolished the ability of lubiprostone to acutely activate CFTR. In F508del homozygous airway epithelia pretreated with the triple combination of elexacaftor, tezacaftor, and ivacaftor (ELEXA/TEZ/IVA; i.e., Trikafta), acute application of lubiprostone was able to maximally activate CFTR. Prolonged (24 h) cotreatment of F508del homozygous epithelia with ELEXA/TEZ/IVA and lubiprostone increased acute CFTR activation by ∼60% compared with the treatment with ELEXA/TEZ/IVA alone. This work establishes the feasibility of targeting prostaglandin receptors to activate CFTR on the airway epithelia and demonstrates that cotreatment with lubiprostone can further restore modulator-rescued CFTR.

Opioid-Related Constipation

Opioid-related constipation encompasses constipation directly caused by opioid use (opioid-induced constipation [OIC]) as well as pre-existing constipation worsened by opioid use (opioid-exacerbated constipation [OEC]). Over-the-counter laxatives should be used as first-line agents for both OIC and OEC, given their efficacy, low cost, and high safety profiles. Symptoms of OIC and responses to therapy can be assessed with the Bowel Function Index. Individuals with OIC refractory to laxatives may be responsive to peripherally acting μ-opioid receptor antagonists. Although data supporting the superiority of one prescription agent over another is lacking, all have proven effective for the treatment of OIC.

Review of the Safety Profiles of Laxatives in Pregnant Women

Chronic constipation is one of the most common complaints seen in the gastroenterology clinic and is particularly prevalent in women. Women who become pregnant may suffer from existing constipation or develop constipation de novo. A thorough understanding of the safety of laxative therapies during pregnancy and the postpartum period is essential to successfully treating these women. Current understanding of the safety of both over the counter and prescription laxatives has not been adequately evaluated. In this article we provide an updated and comprehensive review of the safety profiles of laxatives that are currently used for the treatment of chronic constipation to aid the clinician in risk-benefit discussions with women who are currently or planning to become pregnant.

The Progress of Intestinal Epithelial Models from Cell Lines to Gut-On-Chip

Over the past years, several preclinical in vitro and ex vivo models have been developed that helped to understand some of the critical aspects of intestinal functions in health and disease such as inflammatory bowel disease (IBD). However, the translation to the human in vivo situation remains problematic. The main reason for this is that these approaches fail to fully reflect the multifactorial and complex in vivo environment (e.g., including microbiota, nutrition, and immune response) in the gut system. Although conventional models such as cell lines, Ussing chamber, and the everted sac are still used, increasingly more sophisticated intestinal models have been developed over the past years including organoids, InTESTine™ and microfluidic gut-on-chip. In this review, we gathered the most recent insights on the setup, advantages, limitations, and future perspectives of most frequently used in vitro and ex vivo models to study intestinal physiology and functions in health and disease.

Focus on Pharmacotherapy for Irritable Bowel Syndrome with Constipation

Irritable bowel syndrome with constipation is a common disorder that significantly impairs quality of life. There are now multiple classes of therapeutics that have been shown via rigorous clinical testing to improve the abdominal and bowel symptoms attributed to irritable bowel syndrome with constipation. These include the secretagogues (lubiprostone, linaclotide, plecanatide, tenapenor) and the prokinetic agent tegaserod. This article highlights the pivotal evidence for these agents and most recent treatment guidance from the major North American gastroenterological societies. When pharmaceuticals are used, a patient-specific approach based on efficacy, safety, tolerability, access, and affordability is recommended.

Open-label study to evaluate the treatment continuation rate after a dose reduction of lubiprostone due to onset of adverse events

OBJECTIVE

To investigate the continuation rate with a reduced lubiprostone dose (12 mcg twice daily, BD) after the onset of adverse events (AEs) in patients with chronic constipation (CC).

METHODS

In this exploratory, open-label, multicenter study, patients with CC received lubiprostone 24 mcg BD and the dose was reduced to 12 mcg BD in subjects experiencing AEs. The primary objective was the continuation rate after dose reduction due to nausea/vomiting. Secondary objectives included the continuation rate after dose reduction due to diarrhea/any AE and efficacy, including changes in number of weekly bowel movements and Bristol Stool Form Scale.

RESULTS

Of the 146 patients included in the study, 42 (28.8%) received lubiprostone 12 mcg BD (dose-reduced group) due to any AE. Thirty-six (85.7%) subjects in the dose-reduced group continued treatment and completed the study. 22/27 (81.5%) and 17/19 (89.5%) patients in whom the dose was reduced due to nausea/vomiting or diarrhea, respectively, continued treatment. There was no clinically relevant difference in efficacy after dose reduction.

CONCLUSION

These results suggest that treatment withdrawal due to AEs associated with lubiprostone 24 mcg BD could be minimized in patients with CC after dose reduction to 12 mcg BD, thus resulting in improved long-term outcomes.

CLINICAL TRIAL REGISTRATION

Japan Registry of Clinical Trials (https://jrct.niph.go.jp/latest-detail/jRCTs031180069).

ACG Clinical Guideline: Management of Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a highly prevalent, chronic disorder that significantly reduces patients' quality of life. Advances in diagnostic testing and in therapeutic options for patients with IBS led to the development of this first-ever American College of Gastroenterology clinical guideline for the management of IBS using Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) methodology. Twenty-five clinically important questions were assessed after a comprehensive literature search; 9 questions focused on diagnostic testing; 16 questions focused on therapeutic options. Consensus was obtained using a modified Delphi approach, and based on GRADE methodology, we endorse the following: We suggest that a positive diagnostic strategy as compared to a diagnostic strategy of exclusion be used to improve time to initiating appropriate therapy. We suggest that serologic testing be performed to rule out celiac disease in patients with IBS and diarrhea symptoms. We suggest that fecal calprotectin be checked in patients with suspected IBS and diarrhea symptoms to rule out inflammatory bowel disease. We recommend a limited trial of a low fermentable oligosaccharides, disacchardies, monosaccharides, polyols (FODMAP) diet in patients with IBS to improve global symptoms. We recommend the use of chloride channel activators and guanylate cyclase activators to treat global IBS with constipation symptoms. We recommend the use of rifaximin to treat global IBS with diarrhea symptoms. We suggest that gut-directed psychotherapy be used to treat global IBS symptoms. Additional statements and information regarding diagnostic strategies, specific drugs, doses, and duration of therapy can be found in the guideline.

Development and validation of a potent and specific inhibitor for the CLC-2 chloride channel

CLC-2 is a voltage-gated chloride channel that is widely expressed in mammalian tissues. In the central nervous system, CLC-2 appears in neurons and glia. Studies to define how this channel contributes to normal and pathophysiological function in the central nervous system raise questions that remain unresolved, in part due to the absence of precise pharmacological tools for modulating CLC-2 activity. Herein, we describe the development and optimization of AK-42, a specific small-molecule inhibitor of CLC-2 with nanomolar potency (IC50 = 17 ± 1 nM). AK-42 displays unprecedented selectivity (>1,000-fold) over CLC-1, the closest CLC-2 homolog, and exhibits no off-target engagement against a panel of 61 common channels, receptors, and transporters expressed in brain tissue. Computational docking, validated by mutagenesis and kinetic studies, indicates that AK-42 binds to an extracellular vestibule above the channel pore. In electrophysiological recordings of mouse CA1 hippocampal pyramidal neurons, AK-42 acutely and reversibly inhibits CLC-2 currents; no effect on current is observed on brain slices taken from CLC-2 knockout mice. These results establish AK-42 as a powerful tool for investigating CLC-2 neurophysiology.

Short Chain Fatty Acids Effect on Chloride Channel ClC-2 as a Possible Mechanism for Lubiprostone Intestinal Action

Lubiprostone, a 20-carbon synthetic fatty acid used for the treatment of constipation, is thought to act through an action on Cl⁻ channel ClC-2. Short chain fatty acids (SCFAs) are produced and absorbed in the distal intestine. We explore whether SCFAs affect ClC-2, re-examine a possible direct effect of lubiprostone on ClC-2, and use mice deficient in ClC-2 to stringently address the hypothesis that the epithelial effect of lubiprostone targets this anion channel. Patch-clamp whole cell recordings of ClC-2 expressed in mammalian cells are used to assay SCFA and lubiprostone effects. Using chamber measurements of ion current in mice deficient in ClC-2 or CFTR channels served to analyze the target of lubiprostone in the distal intestinal epithelium. Intracellular SCFAs had a dual action on ClC-2, partially inhibiting conduction but, importantly, facilitating the voltage activation of ClC-2. Intra- or extracellular lubiprostone had no effect on ClC-2 currents. Lubiprostone elicited a secretory current across colonic epithelia that was increased in mice deficient in ClC-2, consistent with the channel’s proposed proabsorptive function, but absent from those deficient in CFTR. Whilst SCFAs might exert a physiological effect on ClC-2 as part of their known proabsorptive effect, ClC-2 plays no part in the lubiprostone intestinal effect that appears mediated by CFTR activation.

Risk Factors for Adverse Events in Patients with Chronic Constipation Following Lubiprostone Administration

INTRODUCTION

Lubiprostone is an effective treatment of chronic constipation (CC). However, as with other stimulant or osmotic laxatives, adverse events (AEs) can make it difficult to continue treatment. This article investigates AE risk factors associated with lubiprostone.

METHODS

We retrospectively analyzed all 1,338 Japanese patients with CC treated at our hospital from October 2013 to July 2017. All patients were diagnosed with constipation as defined by the Roma III criteria. Enrolled patients received lubiprostone orally (24 or 48 μg daily), after which we investigated the incidence of AEs. The causative factors for diarrhea and nausea, the most common AEs, were examined by the backward logistic regression model.

RESULTS

Two hundred eight (15.5%) experienced at least 1 AE. No serious AEs were associated with the study drug. The AEs reported by >1% of patients overall were diarrhea (6.1%) and nausea (4.2%). We performed a multivariate logistic regression using a backward variable selection method to investigate AE risk factors. Factors associated with higher incidence of diarrhea were patient age of 65 years or more (odds ratio: [95% confidence interval]; p value) (2.09: [1.05-4.16]; 0.035). Factors associated with greater likelihood of nausea included female gender (1.99: [1.10-3.61]; 0.023), and the chief complaint was a patient complaining of abdominal pain and fullness (2.07: [1.01-4.22]; 0.046).

CONCLUSIONS

Understanding AE risk factors can help avoid unnecessary AEs and promote more effective treatment.

Physiological Significance of Ion Transporters and Channels in the Stomach and Pathophysiological Relevance in Gastric Cancer

Gastric cancer (GC) is a highly invasive and fatal malignant disease that accounts for 5.7% of new global cancer cases and is the third leading cause of cancer-related death. Acid/base homeostasis is critical for organisms because protein and enzyme function, cellular structure, and plasma membrane permeability change with pH. Various ion transporters are expressed in normal gastric mucosal epithelial cells and regulate gastric acid secretion, ion transport, and fluid absorption, thereby stabilizing the differentiation and homeostasis of gastric mucosal epithelial cells. Ion transporter dysfunction results in disordered ion transport, mucosa barrier dysfunction, and acid/base disturbances, causing gastric acid-related diseases such as chronic atrophic gastritis (CAG) and GC. This review summarizes the physiological functions of multiple ion transporters and channels in the stomach, including Cl⁻ channels, Cl⁻/HCO₃⁻ exchangers, sodium/hydrogen exchangers (NHEs), and potassium (K⁺) channels, and their pathophysiological relevance in GC.

Herbal components of Japanese Kampo medicines exert laxative actions in colonic epithelium cells via activation of BK and CFTR channels

Japanese Kampo medicines Junchoto and Mashiningan are mixtures of numerous herbal plant extracts and empirically known to exert laxative actions by stimulating fluid secretion in the colonic epithelium. However, it is unknown which and how the herbal components of these crude Kampo drugs are effective to stimulate ion effluxes causing fluid secretion. Here, we selected four herbal components of Junchoto and Mashiningan, Mashinin (MSN), Kyonin (KYN), Tonin (TON), and Daio (DIO), which are putatively laxatives, and examined their effects on the ion channel activity of human colonic epithelial Caco-2 cells. Patch clamp analyses revealed that MSN activated whole-cell current characteristics of the cystic fibrosis transmembrane conductance regulator (CFTR) channel, whereas KYN, TON, and DIO activated the large-conductance and voltage-activated K⁺ (BK) channel. Furthermore, electronic cell sizing showed that MSN induced secretory volume decrease (SVD) sensitivity to a CFTR blocker, whereas TON, KYN, and DIO induced SVD sensitivity to a K⁺ channel blocker. In conclusion, MSN and TON, KYN, and DIO promote fluid secretion from colonic epithelial cells by activating CFTR and BK channels. Thus, Japanese Kampo medicines, Junchoto and Mashiningan, exert anti-constipation actions by inducing KCl efflux through the combined actions of CFTR- and BK-stimulating herbal components.

Evaluation and Comparison of Daiokanzoto and Lubiprostone for Constipation: A Retrospective Cohort Study

Daiokanzoto (DKT) and lubiprostone (LPS) are drugs used for constipation, but few studies have compared them. This study examined the effectiveness, adverse events, and medical economic efficiency of DKT and LPS for constipation. Patients who received DKT (DKT group) and those who received LPS (LPS group) during admission to Ogaki Municipal Hospital between November 2012 and May 2016 were enrolled. Drug efficacy was evaluated based on the median value of bowel movement frequency over 1 week before and after drug administration, and their safety was evaluated by the presence or absence of diarrhea, abdominal pain, nausea, and vomiting. To assess medical economic efficiency, drug costs for constipation per week were calculated. The median values (quartile ranges) of bowel movement frequency at 1 week after drug administration were 8.5 (6.0-12.0) in the DKT group and 5 (3.0-7.0) in the LPS group, which was significantly different (p < 0.01). Diarrhea occurred significantly less often in the DKT group (4 cases) than in the LPS group (17 cases) (p < 0.01). The median cost of drugs administered for constipation for 1 week was significantly lower in the DKT group (631 [quartile range, 513-653] yen) than in the LPS group (1431 [1135-2344] yen) (p < 0.01). DKT had a higher immediate effect on constipation and was associated with more frequent bowel movement and fewer adverse events of diarrhea than LPS, suggesting that it may be effective and safe for treating constipation, and DKT is inexpensive.

Functional Role of Basolateral ClC-2 Channels in the Regulation of Duodenal Anion Secretion in Mice

BACKGROUND

Although ClC-2 channels are important in colonic Cl^- secretion, it is unclear about their roles in small intestinal anion secretion. Therefore, we sought to examine whether ClC-2 channels play important roles in anion secretion, particularly duodenal bicarbonate secretion (DBS).

METHODS

Duodenal mucosae from mice were stripped of seromuscular layers and mounted in Ussing chambers. Both duodenal short-circuit current (I_sc) and HCO₃^- secretion in vitro were simultaneously recorded. DBS in vivo was measured by a CO₂-sensitive electrode.

RESULTS

Lubiprostone, a selective ClC-2 activator, concentration-dependently increased both duodenal I_sc and DBS only when applied basolaterally, but not when applied apically. Removal of extracellular Cl^- abolished lubiprostone-induced duodenal I_sc, but did not alter HCO₃^- secretion even in the presence of DIDS, a Cl^-/HCO₃^- exchanger inhibitor. However, further addition of glibenclamide, a CFTR channel blocker, abolished lubiprostone-evoked HCO₃^- secretion. Moreover, lubiprostone-induced HCO₃^- secretion was impaired in CFTR^-/- mice compared to wild-type littermates. Luminal perfusion of duodenal lumen with lubiprostone did not alter basal DBS in vivo, but lubiprostone (i.p.) was able to induce DBS, which was also significantly inhibited by Cd²⁺, a ClC-2 channel blocker. [Ca²⁺]_cyt level, Ca²⁺-activated K⁺ channel- and cAMP-mediated duodenal I_sc, and HCO₃^- secretion were unchanged by lubiprostone.

CONCLUSIONS

We have provided the first evidence for the novel functional role of basolateral ClC-2 channels in the regulation of duodenal anion secretion.

Efficacy of Lubiprostone for the Treatment of Opioid-Induced Constipation, Analyzed by Opioid Class

Objectives

To examine the efficacy and safety of lubiprostone for the treatment of opioid-induced constipation (OIC) in patients by opioid class received.

Design

Data were pooled from three phase III, randomized, double-blind, placebo-controlled studies.

Subjects/Setting

Adults with chronic noncancer pain receiving opioid therapy for 30 or more days and diagnosed with OIC.

Methods

Overall mean change from baseline in spontaneous bowel movement (SBM) frequency, overall treatment response (≥1 SBM/week improvement over baseline SBM frequency in all treatment weeks with available data and ≥3 SBMs/week for ≥9 of the 12 weeks of treatment), and OIC-related symptoms were examined in patients taking opioids. Data were pooled and analyzed by opioid group.

Results

In patients receiving phenanthrene opioids (e.g., oxycodone; N = 1,159), lubiprostone significantly increased overall mean changes in SBM frequency from baseline (P = 0.0001), increased overall response rate (P = 0.0024), and improved OIC symptoms (P ≤ 0.0229) vs placebo. Patients receiving phenylpiperidine opioids (e.g., fentanyl; N = 137) had significant improvement in SBM frequency (P = 0.0129) and favorable trends in response rates (21.4% vs 9.8%; P = 0.0723) and OIC symptoms vs placebo. Efficacy was not observed in overall analyses of patients receiving diphenylheptane opioids (e.g., methadone), although an increase in SBM frequency was observed in patients who received a morphine-equivalent daily dose of 200 or fewer mg, suggesting a dose-dependent negative interference of this opioid class on lubiprostone effects. For all groups, the lubiprostone adverse event profile was similar; the most common treatment-emergent adverse events were nausea and diarrhea.

Conclusions

In patients using commonly prescribed opioids, lubiprostone is effective and generally well tolerated for the treatment of OIC.

Physiology of Electrolyte Transport in the Gut: Implications for Disease

We now have an increased understanding of the genetics, cell biology, and physiology of electrolyte transport processes in the mammalian intestine, due to the availability of sophisticated methodologies ranging from genome wide association studies to CRISPR-CAS technology, stem cell-derived organoids, 3D microscopy, electron cryomicroscopy, single cell RNA sequencing, transgenic methodologies, and tools to manipulate cellular processes at a molecular level. This knowledge has simultaneously underscored the complexity of biological systems and the interdependence of multiple regulatory systems. In addition to the plethora of mammalian neurohumoral factors and their cross talk, advances in pyrosequencing and metagenomic analyses have highlighted the relevance of the microbiome to intestinal regulation. This article provides an overview of our current understanding of electrolyte transport processes in the small and large intestine, their regulation in health and how dysregulation at multiple levels can result in disease. Intestinal electrolyte transport is a balance of ion secretory and ion absorptive processes, all exquisitely dependent on the basolateral Na⁺ /K⁺ ATPase; when this balance goes awry, it can result in diarrhea or in constipation. The key transporters involved in secretion are the apical membrane Cl^- channels and the basolateral Na⁺ -K⁺ -2Cl^- cotransporter, NKCC1 and K⁺ channels. Absorption chiefly involves apical membrane Na⁺ /H⁺ exchangers and Cl^- /HCO₃ ^- exchangers in the small intestine and proximal colon and Na⁺ channels in the distal colon. Key examples of our current understanding of infectious, inflammatory, and genetic diarrheal diseases and of constipation are provided. © 2019 American Physiological Society. Compr Physiol 9:947-1023, 2019.

Pathophysiology and management of opioid-induced constipation: European expert consensus statement

Background

Opioid-induced bowel dysfunction is a complication of opioid therapy, in which constipation is the most common and problematic symptom. However, it is frequently under-recognised and thus effective management is often not instituted despite a number of treatment options.

Objective

The central objective of this study is to provide a summary of the pathophysiology and clinical evaluation of opioid-induced constipation and to provide a pragmatic management algorithm for day-to-day clinical practice.

Methods

This summary and the treatment algorithm is based on the opinion of a European expert panel evaluating current evidence in the literature.

Results

The pathophysiology of opioid-induced constipation is multi-faceted. The key aspect of managing opioid-induced constipation is early recognition. Specific management includes increasing fluid intake, exercise and standard laxatives as well as addressing exacerbating factors. The Bowel Function Index is a useful way of objectively evaluating severity of opioid-induced constipation and monitoring response. Second-line treatments can be considered in those with recalcitrant symptoms, which include gut-restricted or peripherally acting mu-opioid receptor antagonists. However, a combination of interventions may be needed.

Conclusion

Opioid-induced constipation is a common, yet under-recognised and undertreated, complication of opioid therapy. We provide a pragmatic step-wise approach to opioid-induced constipation, which should simplify management for clinicians.

Experimental Paradigm for the Assessment of the Non-pharmacological Mechanism of Action in Medical Device Classification: The Example of Glycerine as Laxative

The evolution of medical devices has led to the introduction of medical devices that include "substances" and which, due to their presentation and sites of application may resemble medicinal products. The difference between substance-based medical devices and medicinal products lies in the proper definition of the principal mechanism of action. The major problem at the moment is the lack of a proper procedure for the demonstration of a mechanism that is "not pharmacological, immunological or metabolic." We aimed to design an experimental set up to demonstrate the difference between the mechanism of action of two substances used commonly for the treatment of constipation, lubiprostone (example of medicinal product) and glycerine (example of medical device). By implementing cellular models and molecular analyses we demonstrate the difference in their mechanism of action. This set up can be considered an example on the possibility to define a paradigm for the case by case study of the mechanism of action of substances and combination of substances in medical devices.

Gut Movements: A Review of the Physiology of Gastrointestinal Transit

The well-regulated mechanisms of intestinal transit favor aboral movement of intestinal contents during the formation of normal stool. Electrical pacemakers initiate mechanical smooth muscular propulsion under regulation by the enteric nervous system-a function of the "brain-gut axis." Several unique intestinal motor patterns function in concert to enhance the activities of intestinal transit. Development of pharmacologic targets of intestinal transit mechanisms afford clinicians control in the management of functional gastrointestinal disorders. This review highlights the important physiologic events of intestinal transit, discusses selected pharmacologic and neuromodulators involved in these processes, and provides relevant clinical correlates to physiologic events.

Chronic stress-associated visceral hyperalgesia correlates with severity of intestinal barrier dysfunction

In humans, chronic psychological stress is associated with increased intestinal paracellular permeability and visceral hyperalgesia, which is recapitulated in the chronic intermittent water avoidance stress (WAS) rat model. However, it is unknown whether enhanced visceral pain and permeability are intrinsically linked and correlate. Treatment of rats with lubiprostone during WAS significantly reduced WAS-induced changes in intestinal epithelial paracellular permeability and visceral hyperalgesia in a subpopulation of rats. Lubiprostone also prevented WAS-induced decreases in the epithelial tight junction protein, occludin (Ocln). To address the question of whether the magnitude of visceral pain correlates with the extent of altered intestinal permeability, we measured both end points in the same animal because of well-described individual differences in pain response. Our studies demonstrate that visceral pain and increased colon permeability positively correlate (0.6008, P = 0.0084). Finally, exposure of the distal colon in control animals to Ocln siRNA in vivo revealed that knockdown of Ocln protein inversely correlated with increased paracellular permeability and enhanced visceral pain similar to the levels observed in WAS-responsive rats. These data support that Ocln plays a potentially significant role in the development of stress-induced increased colon permeability. We believe this is the first demonstration that the level of chronic stress-associated visceral hyperalgesia directly correlates with the magnitude of altered colon epithelial paracellular permeability.

CLC Chloride Channels and Transporters: Structure, Function, Physiology, and Disease

CLC anion transporters are found in all phyla and form a gene family of eight members in mammals. Two CLC proteins, each of which completely contains an ion translocation parthway, assemble to homo- or heteromeric dimers that sometimes require accessory β-subunits for function. CLC proteins come in two flavors: anion channels and anion/proton exchangers. Structures of these two CLC protein classes are surprisingly similar. Extensive structure-function analysis identified residues involved in ion permeation, anion-proton coupling and gating and led to attractive biophysical models. In mammals, ClC-1, -2, -Ka/-Kb are plasma membrane Cl−channels, whereas ClC-3 through ClC-7 are 2Cl−/H+-exchangers in endolysosomal membranes. Biological roles of CLCs were mostly studied in mammals, but also in plants and model organisms like yeast and Caenorhabditis elegans. CLC Cl−channels have roles in the control of electrical excitability, extra- and intracellular ion homeostasis, and transepithelial transport, whereas anion/proton exchangers influence vesicular ion composition and impinge on endocytosis and lysosomal function. The surprisingly diverse roles of CLCs are highlighted by human and mouse disorders elicited by mutations in their genes. These pathologies include neurodegeneration, leukodystrophy, mental retardation, deafness, blindness, myotonia, hyperaldosteronism, renal salt loss, proteinuria, kidney stones, male infertility, and osteopetrosis. In this review, emphasis is laid on biophysical structure-function analysis and on the cell biological and organismal roles of mammalian CLCs and their role in disease.

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.

Randomized clinical trial: efficacy and safety of plecanatide in the treatment of chronic idiopathic constipation

BACKGROUND

Plecanatide, with the exception of a single amino acid replacement, is identical to human uroguanylin and is approved in the United States for adults with chronic idiopathic constipation (CIC). This double-blind, placebo-controlled, phase III study evaluated the efficacy and safety of plecanatide versus placebo in CIC.

METHODS

Adults meeting modified Rome III CIC criteria were randomized to plecanatide 3 mg (n = 443), 6 mg (n = 449), or placebo (n = 445). Patients recorded bowel movement (BM) characteristics [including spontaneous BMs (SBMs) and complete SBMs (CSBMs)] and rated CIC symptoms in daily electronic diaries. The primary endpoint was the percentage of durable overall CSBM responders (weekly responders for ⩾9 of 12 treatment weeks, including ⩾3 of the last 4 weeks). Weekly responders had ⩾3 CSBMs/week and an increase of ⩾1 CSBM from baseline for the same week.

RESULTS

A significantly greater percentage of durable overall CSBM responders resulted with each plecanatide dose compared with placebo (3 mg = 20.1%; 6 mg = 20.0%; placebo = 12.8%; p = 0.004 each dose). Over the 12 weeks, plecanatide significantly improved stool consistency and stool frequency. Significant increases in mean weekly SBMs and CSBMs began in week 1 and were maintained through week 12 in plecanatide-treated patients. Adverse events were mostly mild/moderate, with diarrhea being the most common (3 mg = 3.2%; 6 mg = 4.5%; placebo = 1.3%).

CONCLUSIONS

Plecanatide resulted in a significantly greater percentage of durable overall CSBM responders and improved stool frequency and secondary endpoints. Plecanatide was well tolerated; the most common AE, diarrhea, occurred in a small number of patients.[ClinicalTrials.gov identifier: NCT02122471].

Research and progress on ClC‑2 (Review)

Chloride channel 2 (ClC-2) is one of the nine mammalian members of the ClC family. The present review discusses the molecular properties of ClC‑2, including CLCN2, ClC‑2 promoter and the structural properties of ClC‑2 protein; physiological properties; functional properties, including the regulation of cell volume. The effects of ClC‑2 on the digestive, respiratory, circulatory, nervous and optical systems are also discussed, in addition to the mechanisms involved in the regulation of ClC‑2. The review then discusses the diseases associated with ClC‑2, including degeneration of the retina, Sjögren's syndrome, age‑related cataracts, degeneration of the testes, azoospermia, lung cancer, constipation, repair of impaired intestinal mucosa barrier, leukemia, cystic fibrosis, leukoencephalopathy, epilepsy and diabetes mellitus. It was concluded that future investigations of ClC‑2 are likely to be focused on developing specific drugs, activators and inhibitors regulating the expression of ClC‑2 to treat diseases associated with ClC‑2. The determination of CLCN2 is required to prevent and treat several diseases associated with ClC‑2.

Luminally Acting Agents for Constipation Treatment: A Review Based on Literatures and Patents

Constipation is one of the most frequently reported gastrointestinal (GI) disorders that negatively impacts quality of life and is associated with a significant economic burden to the patients and society. Traditional treatments including lifestyle modification and laxatives are often ineffective in the more severe forms of constipation and over the long term. New medications targeting at intestinal chloride channels and colonic serotonin receptors have been demonstrated effective in recent years. Emerging agents focusing on improving intestinal secretion and/or colonic motility have been shown effective in animal models and even in clinical trials. Recognization of the role of cystic fibrosis transmembrane regulator (CFTR) and calcium-activated chloride channels (CaCCs) in intestine fluid secretion and motility modulation makes CFTR and CaCCs promising molecule targets for anti-constipation therapy. Although there are multiple choices for constipation treatment, there is still a recognized need for new medications in anti-constipation therapy. The present review covers the discovery of luminally acting agents for constipation treatment described in both patents (2011–present) and scientific literatures.

Lubiprostone improves visualization of small bowel for capsule endoscopy: a double-blind, placebo-controlled 2-way crossover study

BACKGROUND AND STUDY AIMS

 Lubiprostone has been reported to be an anti-constipation drug. The aim of the study was to investigate the usefulness of lubiprostone both for bowel preparation and as a propulsive agent in small bowel endoscopy.

PATIENTS AND METHODS

 This was a double-blind, placebo-controlled, 2-way crossover study of subjects who volunteered to undergo capsule endoscopy (CE). A total of 20 subjects (16 male and 4 female volunteers) were randomly assigned to receive a 24-μg tablet of lubiprostone 120 minutes prior to capsule ingestion for CE (L regimen), or a placebo tablet 120 minutes prior to capsule ingestion for CE (P regimen). Main outcome was gastric transit time (GTT) and small-bowel transit time (SBTT). Secondary outcome was adequacy of small-bowel cleansing and the fluid score in the small bowel. The quality of the capsule endoscopic images and fluid in the small bowel were assessed on 5-point scale.

RESULTS

 The capsule passed into the small bowel in all cases. Median GTT was 57.3 (3 - 221) minutes for the P regimen and 61.3 (10 - 218) minutes for the L regimen ( P  = 0.836). Median SBTT was 245.0 (164 - 353) minutes for the P regimen and 228.05 (116 - 502) minutes for the L regimen ( P  = 0.501). The image quality score in the small bowel was 3.05 ± 1.08 for the P regimen and 3.80 ± 0.49 for the L regimen ( P  < 0.001). The fluid score in the small bowel was 2.04 ± 1.58 for the P regimen and 2.72 ± 1.43 for the L regimen ( P  < 0.001). There was a significant difference between the 2 regimens with regard to image quality. The fluid score was more plentiful for the L regimen than for the P regimen. There were no cases of capsule retention or serious adverse events in this study.

CONCLUSION

 Our study showed that use of lubiprostone prior to CE significantly improved visualization of the small bowel during CE as a result of inducing fluid secretion into the small bowel.

Identification of the fatty acid activation site on human ClC-2

Fatty acids (including lubiprostone and cobiprostone) are human ClC-2 (hClC-2) Cl^- channel activators. Molecular and cellular mechanisms underlying this activation were examined. Role of a four-amino acid PKA activation site, RGET₆₉₁, of hClC-2 was investigated using wild-type (WT) and mutant (AGET, RGEA, and AGAA) hClC-2 expressed in 293EBNA cells as well as involvement of PKA, intracellular cAMP concentration ([cAMP]_i), EP₂, or EP₄ receptor agonist activity. All fatty acids [lubiprostone, cobiprostone, eicosatetraynoic acid (ETYA), oleic acid, and elaidic acid] caused significant rightward shifts in concentration-dependent Cl^- current activation (increasing EC₅₀s) with mutant compared with WT hClC-2 channels, without changing time and voltage dependence, current-voltage rectification, or methadone inhibition of the channel. As with lubiprostone, cobiprostone activation of hClC-2 occurred with PKA inhibitor (myristoylated protein kinase inhibitor) present or when using double PKA activation site (RRAA₆₅₅/RGEA₆₉₁) mutant. Cobiprostone did not activate human CFTR. Fatty acids did not increase [cAMP]_i in hClC-2/293EBNA or T84 cells. Using T84 CFTR knockdown cells, cobiprostone increased hClC-2 Cl^- currents without increasing [cAMP]_i, while PGE₂ and forskolin-IBMX increased both. Fatty acids were not agonists of EP₂ or EP₄ receptors. L-161,982, a supposed EP₄-selective inhibitor, had no effect on lubiprostone-activated hClC-2 Cl^- currents but significantly decreased T84 cell barrier function measured by transepithelial resistance and fluorescent dextran transepithelial movement. The present findings show that RGET₆₉₁ of hClC-2 (possible binding site) plays an important functional role in fatty acid activation of hClC-2. PKA, [cAMP]_i, and EP₂ or EP₄ receptors are not involved. These studies provide the molecular basis for fatty acid regulation of hClC-2.

MDCK cells are capable of water secretion and reabsorption in response to changes in the ionic environment

A prerequisite for tissue electrolyte homeostasis is highly regulated ion and water transport through kidney or intestinal epithelia. In the present work, we monitored changes in the cell and luminal volumes of type II Madin-Darby canine kidney (MDCK) cells grown in a 3D environment in response to drugs, or to changes in the composition of the basal extracellular fluid. Using fluorescent markers and high-resolution spinning disc confocal microscopy, we could show that lack of sodium and potassium ions in the basal fluid (tetramethylammonium chloride (TMACl) buffer) induces a rapid increase in the cell and luminal volumes. This transepithelial water flow could be regulated by inhibitors and agonists of chloride channels. Hence, the driving force for the transepithelial water flow is chloride secretion, stimulated by hyperpolarization. Chloride ion depletion of the basal fluid (using sodium gluconate buffer) induces a strong reduction in the lumen size, indicating reabsorption of water from the lumen to the basal side. Lumen size also decreased following depolarization of the cell interior by rendering the membrane permeable to potassium. Hence, MDCK cells are capable of both absorption and secretion of chloride ions and water; negative potential within the lumen supports secretion, while depolarizing conditions promote reabsorption.

Persistent constipation and abdominal adverse events with newer treatments for constipation

Background

Clinical trials of several new treatments for opioid-induced constipation (OIC), chronic idiopathic constipation (CIC) and constipation-predominant irritable bowel syndrome (IBS-C) have focused on differences between subjects relieved of constipation with placebo and active treatment. Patients and clinicians however, are more interested in the probability these treatments provide actual relief of constipation and its associated symptoms.

Methods

We searched the medical literature using MEDLINE and Cochrane central register of controlled trials. Randomised, placebo-controlled trials that examined the use of methylnaltrexone, naloxegol, lubiprostone, prucalopride or linaclotide in adults with OIC, CIC and IBS-C were eligible for inclusion. The primary efficacy measure was relief of constipation. Adverse event data for abdominal symptoms were also analysed.

Key results and findings

25 publications were included in our analyses. The proportion of constipated individuals with active treatment was significantly lower than the proportion with placebo; however, in 15 of these 20 trials analysed, a majority of patients remained constipated with active treatment. Analyses of adverse event data revealed that the percentage of participants who experienced abdominal pain, diarrhoea and flatulence with active treatment was higher than that with placebo in the majority of trials analysed.

Conclusions

Newer pharmacological treatments for constipation are superior to placebo in relieving constipation, but many patients receiving active treatment may remain constipated. In addition, all 5 of the treatments studied are accompanied by no change or a possible increase in the prevalence of abdominal symptoms, such as abdominal pain, diarrhoea and flatulence.

Lithocholic acid attenuates cAMP-dependent Cl- secretion in human colonic epithelial T84 cells

Bile acids (BAs) play a complex role in colonic fluid secretion. We showed that dihydroxy BAs, but not the monohydroxy BA lithocholic acid (LCA), stimulate Cl(-) secretion in human colonic T84 cells (Ao M, Sarathy J, Domingue J, Alrefai WA, Rao MC. Am J Physiol Cell Physiol 305: C447-C456, 2013). In this study, we explored the effect of LCA on the action of other secretagogues in T84 cells. While LCA (50 μM, 15 min) drastically (>90%) inhibited FSK-stimulated short-circuit current (Isc), it did not alter carbachol-stimulated Isc LCA did not alter basal Isc, transepithelial resistance, cell viability, or cytotoxicity. LCA's inhibitory effect was dose dependent, acted faster from the apical membrane, rapid, and not immediately reversible. LCA also prevented the Isc stimulated by the cAMP-dependent secretagogues 8-bromo-cAMP, lubiprostone, or chenodeoxycholic acid (CDCA). The LCA inhibitory effect was BA specific, since CDCA, cholic acid, or taurodeoxycholic acid did not alter FSK or carbachol action. While LCA alone had no effect on intracellular cAMP concentration ([cAMP]i), it decreased FSK-stimulated [cAMP]i by 90%. Although LCA caused a small increase in intracellular Ca(2+) concentration ([Ca(2+)]i), chelation by BAPTA-AM did not reverse LCA's effect on Isc LCA action does not appear to involve known BA receptors, farnesoid X receptor, vitamin D receptor, muscarinic acetylcholine receptor M3, or bile acid-specific transmembrane G protein-coupled receptor 5. LCA significantly increased ERK1/2 phosphorylation, which was completely abolished by the MEK inhibitor PD-98059. Surprisingly PD-98059 did not reverse LCA's effect on Isc Finally, although LCA had no effect on basal Isc, nystatin permeabilization studies showed that LCA both stimulates an apical cystic fibrosis transmembrane conductance regulator Cl(-) current and inhibits a basolateral K(+) current. In summary, 50 μM LCA greatly inhibits cAMP-stimulated Cl(-) secretion, making low doses of LCA of potential therapeutic interest for diarrheal diseases.

[Current issues on the treatment of chronic constipation]

Chronic constipation is a very common clinical problem with its prevalence of up to 14% in the general population. It is not a life-threatening disease, but since patient's satisfaction to the treatment is known to be as low as 50%, chronic constipation still remains a clinically challenging problem. Fortunately, many new treatments have been introduced or are to be introduced in the near future. This article will review the basic concepts and the results of recent studies on the new treatments for chronic constipation.

Opioid-induced constipation: advances and clinical guidance

Currently opioids are the most frequently used medications for chronic noncancer pain. Opioid-induced constipation is the most common adverse effect associated with prolonged use of opioids, having a major impact on quality of life. There is an increasing need to treat opioid-induced constipation. With the recent approval of medications for the treatment of opioid-induced constipation, there are several therapeutic approaches. This review addresses the clinical presentation and diagnosis of opioid-induced constipation, barriers to its diagnosis, effects of opioids in the gastrointestinal tract, differential tolerance to opiates in different gastrointestinal organs, medications approved and in development for the treatment of opioid-induced constipation, and a proposed clinical management algorithm for treating opioid-induced constipation in patients with noncancer pain.

Pharmaceutical Activation or Genetic Absence of ClC-2 Alters Tight Junctions During Experimental Colitis

BACKGROUND

We have previously reported that the ClC-2 chloride channel has an important role in regulation of tight junction barrier function during experimental colitis, and the pharmaceutical ClC-2 activator lubiprostone initiates intestinal barrier repair in ischemic-injured intestine. Thus, we hypothesized that pharmaceutical ClC-2 activation would have a protective and therapeutic effect in murine models of colitis, which would be absent in ClC-2 mice.

METHODS

We administered lubiprostone to wild-type or ClC-2 mice with dextran sulfate sodium (DSS) or 2, 4, 5-trinitrobenzene sulfonic acid-induced colitis. We determined the severity of colitis and assessed intestinal permeability. Selected tight junction proteins were analyzed by Western blotting and immunofluorescence/confocal microscopy, whereas proliferative and differentiated cells were examined with special staining and immunohistochemistry.

RESULTS

Oral preventive or therapeutic administration of lubiprostone significantly reduced the severity of colitis and reduced intestinal permeability in both DSS and trinitrobenzene sulfonic acid-induced colitis. Preventive treatment with lubiprostone induced significant recovery of the expression and distribution of selected sealing tight junction proteins in mice with DSS-induced colitis. In addition, lubiprostone reduced crypt proliferation and increased the number of differentiated epithelial cells. Alternatively, when lubiprostone was administered to ClC-2 mice, the protective effect against DSS colitis was limited.

CONCLUSIONS

This study suggests a central role for ClC-2 in restoration of barrier function and tight junction architecture in experimental murine colitis, which can be therapeutically targeted with lubiprostone.

ClC-2 regulation of intestinal barrier function: Translation of basic science to therapeutic target

The ClC-2 chloride channel is a member of the voltage-gated chloride channel family. ClC-2 is involved in various physiological processes, including fluid transport and secretion, regulation of cell volume and pH, maintaining the membrane potential of the cell, cell-to-cell communication, and tissue homeostasis. Recently, our laboratory has accumulated evidence indicating a critical role of ClC-2 in the regulation of intestinal barrier function by altering inter-epithelial tight junction composition. This review will detail the role of ClC-2 in intestinal barrier function during intestinal disorders, including experimental ischemia/reperfusion injury and dextran sodium sulfate (DSS)-induced inflammatory bowel disease. Details of pharmacological manipulation of ClC-2 via prostone agonists will also be provided in an effort to show the potential therapeutic relevance of ClC-2 regulation, particularly during intestinal barrier disruption.

Genetic Ablation of the ClC-2 Cl- Channel Disrupts Mouse Gastric Parietal Cell Acid Secretion

The present studies were designed to examine the effects of ClC-2 ablation on cellular morphology, parietal cell abundance, H/K ATPase expression, parietal cell ultrastructure and acid secretion using WT and ClC-2^-/- mouse stomachs. Cellular histology, morphology and proteins were examined using imaging techniques, electron microscopy and western blot. The effect of histamine on the pH of gastric contents was measured. Acid secretion was also measured using methods and secretagogues previously established to give maximal acid secretion and morphological change. Compared to WT, ClC-2^-/- gastric mucosal histological organization appeared disrupted, including dilation of gastric glands, shortening of the gastric gland region and disorganization of all cell layers. Parietal cell numbers and H/K ATPase expression were significantly reduced by 34% (P<0.05) and 53% (P<0.001) respectively and cytoplasmic tubulovesicles appeared markedly reduced on electron microscopic evaluation without evidence of canalicular expansion. In WT parietal cells, ClC-2 was apparent in a similar cellular location as the H/K ATPase by immunofluorescence and appeared associated with tubulovesicles by immunogold electron microscopy. Histamine-stimulated [H⁺] of the gastric contents was significantly (P<0.025) lower by 9.4 fold (89%) in the ClC-2^-/- mouse compared to WT. Histamine/carbachol stimulated gastric acid secretion was significantly reduced (range 84–95%, P<0.005) in ClC-2^-/- compared to WT, while pepsinogen secretion was unaffected. Genetic ablation of ClC-2 resulted in reduced gastric gland region, reduced parietal cell number, reduced H/K ATPase, reduced tubulovesicles and reduced stimulated acid secretion.