Discovery and development of antisecretory drugs for treating diarrheal diseases

The health benefits of dietary polyphenols on pediatric intestinal diseases: Mechanism of action, clinical evidence and future research progress

Pediatric intestinal development is immature, vulnerable to external influences and produce a variety of intestinal diseases. At present, breakthroughs have been made in the treatment of pediatric intestinal diseases, but there are still many challenges, such as toxic side effects, drug resistance, and the lack of more effective treatments and specific drugs. In recent years, dietary polyphenols derived from plants have become a research hotspot in the treatment of pediatric intestinal diseases due to their outstanding pharmacological activities such, as anti-inflammatory, antibacterial, antioxidant and regulation of intestinal flora. This article reviewed the mechanism of action and clinical evidence of dietary polyphenols in the treatment of pediatric intestinal diseases, and discussed the influence of physiological characteristics of children on the efficacy of polyphenols, and finally prospected the new dosage forms of polyphenols in pediatrics.

Anti-diarrheal effect of piperine possibly through the interaction with inflammation inducing enzymes: In vivo and in silico studies

Piperine is a natural alkaloid that possesses a variety of therapeutic properties, including anti-inflammatory, antioxidant, antibacterial, and anticarcinogenic activities. The present study aims to assess the medicinal benefits of piperine as an anti-diarrheal agent in a chick model by utilizing in vivo and in silico techniques. For this, castor oil was administered orally to 2-day-old chicks to cause diarrhea. Bismuth subsalicylate (10 mg/kg), loperamide (3 mg/kg), and nifedipine (2.5 mg/kg) were used as positive controls, while the vehicle was utilized as a negative control. Two different doses (25 and 50 mg/kg b.w.) of the test sample (piperine) were administered orally, and the highest dose was tested with standards to investigate the synergistic activity of the test sample. In our findings, piperine prolonged the latent period while reducing the number of diarrheal feces in the experimental chicks during the monitoring period (4 h). At higher doses, piperine appears to reduce diarrheal secretion while increasing latency in chicks. Throughout the combined pharmacotherapy, piperine outperformed bismuth subsalicylate and nifedipine in terms of anti-diarrheal effects with loperamide. In molecular docking, piperine exhibited higher binding affinities towards different inflammatory enzymes such as cyclooxygenase 1 (-7.9 kcal/mol), cyclooxygenase 2 (-8.4 kcal/mol), nitric oxide synthases (-8.9 kcal/mol), and L-type calcium channel (-8.8 kcal/mol), indicating better interaction of PP with these proteins. In conclusion, piperine showed a potent anti-diarrheal effect in castor oil-induced diarrheal chicks by suppressing the inflammation and calcium ion influx induced by castor oil.

A Review Of Preclinical Tools To Validate Anti-Diarrheal Agents

BACKGROUND

Since their inception, preclinical experimental models have played an important role in investigating and characterizing disease pathogenesis. These in vivo, ex vivo, and in vitro preclinical tests also aid in identifying targets, evaluating potential therapeutic drugs, and validating treatment protocols.

INTRODUCTION

Diarrhea is a leading cause of mortality and morbidity, particularly among children in developing countries, and it represents a huge health-care challenge on a global scale. Due to its chronic manifestations, alternative anti-diarrheal medications must be tested and developed because of the undesirable side effects of currently existing anti-diarrheal drugs.

METHODS

Several online databases, including Science Direct, PubMed, Web of Science, Google Scholar and Scopus, were used in the literature search. The datasets were searched for entries of studies up to May, 2022.

RESULTS

The exhaustive literature study provides a large number of in vivo, in vitro and ex vivo models, which have been used for evaluating the mechanism of the anti-diarrheal effect of drugs in chemically-, pathogen-, disease-induced animal models of diarrhea. The advances and challenges of each model were also addressed in this review.

CONCLUSION

This review encompasses diverse strategies for screening drugs with anti-diarrheal effects and covers a wide range of pathophysiological and molecular mechanisms linked to diarrhea, with a particular emphasis on the challenges of evaluating and predictively validating these experimental models in preclinical studies. This could also help researchers find a new medicine to treat diabetes more effectively and with fewer adverse effects.

Loss of Serum Glucocorticoid-Inducible Kinase 1 SGK1 Worsens Malabsorption and Diarrhea in Microvillus Inclusion Disease (MVID)

Microvillus inclusion disease (MVID), a lethal congenital diarrheal disease, results from loss of function mutations in the apical actin motor myosin VB (MYO5B). How loss of MYO5B leads to both malabsorption and fluid secretion is not well understood. Serum glucocorticoid-inducible kinase 1 (SGK1) regulates intestinal carbohydrate and ion transporters including cystic fibrosis transmembrane conductance regulator (CFTR). We hypothesized that loss of SGK1 could reduce CFTR fluid secretion and MVID diarrhea. Using CRISPR-Cas9 approaches, we generated R26^CreER;MYO5B^f/f conditional single knockout (cMYO5BKO) and R26^CreER;MYO5B^f/f;SGK1^f/f double knockout (cSGK1/MYO5B-DKO) mice. Tamoxifen-treated cMYO5BKO mice resulted in characteristic features of human MVID including severe diarrhea, microvillus inclusions (MIs) in enterocytes, defective apical traffic, and depolarization of transporters. However, apical CFTR distribution was preserved in crypts and depolarized in villus enterocytes, and CFTR high expresser (CHE) cells were observed. cMYO5BKO mice displayed increased phosphorylation of SGK1, PDK1, and the PDK1 target PKCι in the intestine. Surprisingly, tamoxifen-treated cSGK1/MYO5B-DKO mice displayed more severe diarrhea than cMYO5BKO, with preservation of apical CFTR and CHE cells, greater fecal glucose and reduced SGLT1 and GLUT2 in the intestine. We conclude that loss of SGK1 worsens carbohydrate malabsorption and diarrhea in MVID.

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.

Antidiarheal activity of catechol and ethyl 5, 8,11,14,17 - icosapentanoate-rich fraction of Annona senegalensis stem bark

Background and aim

Secretory diarrhea is the most common type of diarrhea. This study aimed at exploring the possible mechanism of antisecretory action of Annona senegalensis stem bark and to identify the bioactive compounds.

Experimental procedure

The ability of three crude extract; aqueous, dichloromethane and hexane stem bark extracts to inhibit castor oil-induced stooling in albino rats were assessed. Bioactivity guided fractionation of the most active extract was done using solvent-solvent partitioning (with hexane, dichloromethane, ethylacetate) and column chromatography. In vitro antioxidant activity of the most active sub-fraction was done using standard methods. The most active sub-fraction (25 mg/kg b. wt.) was administered to castor oil-induced diarrheal rats. Diarrheal rats small intestinal malondialdehyde concentration, antioxidant enzyme, cyclooxygenase II and Na+- K+ ATPase activities were determined using standard procedures. GC-MS analysis was done to identify the chemical compounds in the sub-fraction.

Result and conclusion

Aqueous extract significantly decreased the number of wet stools. Sub-fraction 1 of ethylacetate fraction of aqueous stem bark extract (EFAS1) showed the highest stool inhibition. The H2O2 scavenging activity of EFAS1 was significantly greater than ascorbic acid. The sub-fraction significantly increased (p < 0.05) the activity of catalase and Na+- K+ ATPase activities but significantly decreased the concentration of malondialdehyde and cyclooxygenase II activity. GC-MS analysis revealed that EFAS1 is rich in catechol, n-hexadecanoic acid and ethyl-5,8,11,14,17-icosapentanoate. The sub-fraction exerts its antisecretory activity by its antioxidative, inhibition of prostaglandin synthesis and stimulation of Na+- K+ ATPase properties due to the presence of catechol, n-hexedecanoic acid and ethyl-5,8,11,14,17-icosapentanoate.

Paracellular Filtration Secretion Driven by Mechanical Force Contributes to Small Intestinal Fluid Dynamics

Studies of fluid secretion by the small intestine are dominated by the coupling with ATP-dependent generation of ion gradients, whereas the contribution of filtration secretion has been overlooked, possibly by the lack of a known mechanistic basis. We measured apical fluid flow and generation of hydrostatic pressure gradients by epithelia of cultured mouse enterocytes, Caco-2 and T-84 cells, and fibroblasts exposed to mechanical force provided by vigorous aeration and in response to ion gradients, inhibitors of ion channels and transporters and in vitro using intact mouse and rat small intestine. We describe herein a paracellular pathway for unidirectional filtration secretion that is driven by mechanical force, requires tight junctions, is independent of ionic and osmotic gradients, generates persistent hydrostatic pressure gradients, and would contribute to the fluid shifts that occur during digestion and diarrhea. Zinc inhibits the flow of fluid and the paracellular marker fluorescein isothyocyanate conjugated dextran (MW = 4 kD) across epithelia of cultured enterocytes (>95%; p < 0.001) and intact small intestine (>40%; p = 0.03). We propose that mechanical force drives fluid secretion through the tight junction complex via a “one-way check valve” that can be regulated. This pathway of filtration secretion complements chloride-coupled fluid secretion during high-volume fluid flow. The role of filtration secretion in the genesis of diarrhea in intact animals needs further study. Our findings may explain a potential linkage between intestinal motility and intestinal fluid dynamics.

Pharmacological and Parenteral Nutrition-Based Interventions in Microvillus Inclusion Disease

Microvillus inclusion disease (MVID) is a rare inherited and invariably fatal enteropathy, characterized by severe intractable secretory diarrhea and nutrient malabsorption. No cure exists, and patients typically die during infancy because of treatment-related complications. The need for alternative treatment strategies is evident. Several pharmacological interventions with variable successes have been tried and reported for individual patients as part of their clinical care. Unfortunately, these interventions and their outcomes have remained hidden in case reports and have not been reviewed. Further, recent advances regarding MVID pathogenesis have shed new light on the outcomes of these pharmacological interventions and offer suggestions for future clinical research and trials. Hence, an inventory of reported pharmacological interventions in MVID, their rationales and outcomes, and a discussion of these in the light of current knowledge is opportune. Together with a discussion on MVID-specific pharmacokinetic, -dynamic, and -genetic concerns that pose unique challenges regarding pharmacological strategies, we envision that this paper will aid researchers and clinicians in their efforts to develop pharmacological interventions to combat this devastating disease.

What's in the pipeline for lower functional gastrointestinal disorders in the next 5 years?

The overall objectives of this review are to summarize actionable biomarkers for organic etiology of lower functional gastrointestinal disorders (FGIDs) that lead to individualized treatment for their FGIDs and to assess the pipeline for novel approaches to the management of constipation, diarrhea, and chronic abdominal pain in lower FGIDs. The new approaches to therapy include ion exchangers/transporters for functional constipation (sodium-glucose cotransporter 1, Na+/H+ exchanger 3, and solute carrier family 26 member 3 inhibitors), bile acid modulators for constipation such as ileal bile acid transporter inhibitors and fibroblast growth factor 19 analog for functional constipation, and bile acid sequestrants or farnesoid X receptor agonists for functional diarrhea. Treatment for chronic abdominal pain remains an unmet need in patients with lower FGIDs, and promising novel approaches include delayed-release linaclotide, nonclassical opioid visceral analgesics, and selective cannabinoid receptor agonists. The role of probiotics, fecal microbial transplantation, and possible future microbiome therapies is discussed.

NHERF3 is necessary for Escherichia coli heat-stable enterotoxin-induced inhibition of NHE3: differences in signaling in mouse small intestine and Caco-2 cells

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of childhood death from diarrhea and the leading cause of Traveler's diarrhea. E. coli heat-stable enterotoxin (ST) is a major virulence factor of ETEC and inhibits the brush border Na/H exchanger NHE3 in producing diarrhea. NHE3 regulation involves multiprotein signaling complexes that form on its COOH terminus. In this study, the hypothesis was tested that ST signals via members of the Na/H exchanger regulatory factor (NHERF) family of scaffolding proteins, NHERF2, which had been previously shown to have a role, and now with concentration on a role for NHERF3. Two models were used: mouse small intestine and Caco-2/BBe cells. In both models, ST rapidly increased intracellular cGMP, inhibited NHE3 activity, and caused a quantitatively similar decrease in apical expression of NHE3. The transport effects were NHERF3 and NHERF2 dependent. Also, mutation of the COOH-terminal amino acids of NHERF3 supported that NHERF3-NHERF2 heterodimerization was likely to account for this dual dependence. The ST increase in cGMP in both models was partially dependent on NHERF3. The intracellular signaling pathways by which ST-cGMP inhibits NHE3 were different in mouse jejunum (activation of cGMP kinase II, cGKII) and Caco-2 cells, which do not express cGKII (elevation of intracellular Ca²⁺ concentration [Ca²⁺]_i). The ST elevation of [Ca²⁺]_i was from intracellular stores and was dependent on NHERF3-NHERF2. This study shows that intracellular signaling in the same diarrheal model in multiple cell types may be different; this has implications for therapeutic strategies, which often assume that models have similar signaling mechanisms.

Origanum majorana L. extract exhibit positive cooperative effects on the main mechanisms involved in acute infectious diarrhea

ETHNOPHARMACOLOGICAL RELEVANCE

Origanum majorana L. (Lamiaceae) is commonly used in Moroccan folk medicine to treat infantile colic, abdominal discomfort and diarrhea. Liquid stools and abdominal discomfort observed in acute infectious diarrhea are the consequences of imbalance between intestinal water secretion and absorption in the lumen, and relaxation of smooth muscle surrounding the intestinal mucosa.

AIM OF THE STUDY

The objective of our study was to see if aqueous extract of Origanum majorana L. (AEOM) may exhibit an effect on those deleterious mechanisms.

MATERIALS AND METHODS

The effect of AEOM on electrogenic Cl^- secretion and Na⁺ absorption, the two main mechanisms underlying water movement in the intestine, was assessed on intestinal pieces of mice intestine mounted, in vitro, in Ussing chambers. AEOM effect on muscle relaxation was measured on rat intestinal smooth muscle mounted in an isotonic transducer.

RESULTS

1) AEOM placed on the serosal (i.e. blood) side of the piece of jejunum entirely inhibited in a concentration-dependent manner the Forskolin-induced electrogenic chloride secretion, with an IC₅₀ = 654 ± 8 µg/mL. 2) AEOM placed on the mucosal (i.e. luminal) side stimulated in a concentration-dependent manner an electrogenic Na⁺ absorption, with an IC₅₀ = 476.9 ± 1 µg/mL. 3) AEOM (1 mg/mL) inhibition of Forskolin-induced electrogenic secretion was almost entirely prevented by prior exposure to Ca⁺⁺ channels or neurotransmitters inhibitors. 4) AEOM (1 mg/mL) proabsorptive effect was greater in the ileum and progressively declined in the jejunum, distal colon and proximal colon (minimal). 5) AEOM inhibited in a concentration-dependent manner smooth muscle Carbachol or KCl induced contraction, with an IC₅₀ = 1.64 ± 0.2 mg/mL or 1.92 ± 0.8 mg/mL, respectively.

CONCLUSION

the present results indicate that aqueous extract of Origanum majorana L. exhibit positive cooperative effects on the main mechanisms that are involved in acute infectious diarrhea.

Cystic fibrosis transmembrane conductance regulator (CFTR) and autophagy: hereditary defects in cystic fibrosis versus gluten-mediated inhibition in celiac disease

Cystic Fibrosis (CF) is the most frequent lethal monogenetic disease affecting humans. CF is characterized by mutations in cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel whose malfunction triggers the activation of transglutaminase-2 (TGM2), as well as the inactivation of the Beclin-1 (BECN1) complex resulting in disabled autophagy. CFTR inhibition, TGM2 activation and BECN1 sequestration engage in an ‘infernal trio’ that locks the cell in a pro-inflammatory state through anti-homeostatic feedforward loops. Thus, stimulation of CFTR function, TGM2 inhibition and autophagy stimulation can be used to treat CF patients. Several studies indicate that patients with CF have a higher incidence of celiac disease (CD) and that mice bearing genetically determined CFTR defects are particularly sensitive to the enteropathogenic effects of the orally supplied gliadin (a gluten-derived protein). A gluten/gliadin-derived peptide (P31–43) inhibits CFTR in mouse intestinal epithelial cells, causing a local stress response that contributes to the immunopathology of CD. In particular, P31–43-induced CFTR inhibition elicits an epithelial stress response perturbing proteostasis. This event triggers TGM2 activation, BECN1 sequestration and results in molecular crosslinking of CFTR and P31-43 by TGM2. Importantly, stimulation of CFTR function with a pharmacological potentiator (Ivacaftor), which is approved for the treatment of CF, could attenuate the autophagy-inhibition and pro-inflammatory effects of gliadin in preclinical models of CD. Thus, CD shares with CF a common molecular mechanism involving CFTR inhibition that might respond to drugs that intercept the "infernal trio". Here, we highlight how drugs available for CF treatment could be repurposed for the therapy of CD.

Effect of New Derivatives of 2-Aminothiophene-3-Carboxylic Acid on Calcium-Activated Chloride Currents in Rat Neurons

Using the patch-clamp method in the whole-cell configuration, we showed that the new derivatives of 2-aminothiophene-3-carboxylic acid, which were synthesized by us earlier, can both block (compound 1) and potentiate (compound 2) calcium-activated chloride currents in single rat cerebellar Purkinje cells.

Fluorescence-Based High Throughput Screening Technologies for Natural Chloride Ion Channel Blockers

Chloride channels represent a group of potential drug targets; their blockers showed significant protecting effect on impaired cells by modulating apoptosis, autophagy, and other cell signals. However, clinical drugs with chloride channel inhibitory properties have not yet been developed. Natural product extract becomes an underlying candidate satisfied the clinical requirements for its low toxicity, low cost, and abundant sources. Here, a fluorescence-based EYFP-H148Q/I153L-HeLa cell line model was constructed by molecular cloning and verified by real-time polymerase chain reaction and Western blotting assay. By using this chloride channel blocker screening model, seven hit compounds chosen from 6988 natural compounds showed the channel blocking activity. Then the hit compounds were further validated by electrophysiological patch-clamp analysis. Our study preliminarily identified PC-4 as a new chloride channel inhibitor and demonstrated the reliability and sensitivity of fluorescence-based high throughput screening technologies for discovery of biologically active compounds from natural herbal compounds.

Antidiarrheal activity of α-terpineol in mice

Diarrhea is one of the leading causes of infant death in the world accounting for high child mortality rate. It is also present in different pathophysiologies related to several etiological agents. The aim of this study is to investigate the antidiarrheal effect of α -Terpineol (α-TPN) in different diarrhea models in rodents. The antidiarrheal effect of α-TPN in the treatment of acute diarrhea and enteropooling induced by castor oil or PGE₂ in Swiss mice pretreated orally with saline (NaCl 0.9%), Loperamide (5 mg/kg) and α-TPN (6.25, 12.5, 25 and 50 mg/kg) was analyzed. Additionally, parameters of severity, total weight of faeces and post-treatment for 4 h were evaluated. Modulation of the opioid and cholinergic pathways was performed and intestinal transit model using activated charcoal as marker was also used. The effect of α-TPN on secretory diarrhea was investigated using the model of fluid secretion in intestinal loops isolated from cholera toxin-treated mice. α-TPN showed antidiarrheal effect (*p < 0.05), reducing the total stool amount (*55%, *48%, *44%, *24%) and diarrheal (*47%, *66%; *56%, 10%) respectively for the doses tested. All doses investigated in the enteropooling test presented significant changes (*46%, *78%, *66%, *41% respectively) in relation to the control. α-TPN through the muscarinic pathway reduced the gastrointestinal transit (*31%), besides inhibiting PGE₂-induced diarrhea (*39%). α-TPN also reduced fluid formation and loss of Cl^- ions, by interacting directly with GM1 receptors and cholera toxin, thus increasing the uptake of intestinal fluids. The results suggest an anti-diarrheal activity of α-TPN due to its anticholinergic action, ability to block PGE₂ and GM1 receptors and interaction with cholera toxin in secretory diarrhea, making it a promising candidate drug for the treatment of diarrheal diseases.

A pathogenic role for cystic fibrosis transmembrane conductance regulator in celiac disease

Intestinal handling of dietary proteins usually prevents local inflammatory and immune responses and promotes oral tolerance. However, in ~ 1% of the world population, gluten proteins from wheat and related cereals trigger an HLA DQ2/8‐restricted T_H1 immune and antibody response leading to celiac disease. Prior epithelial stress and innate immune activation are essential for breaking oral tolerance to the gluten component gliadin. How gliadin subverts host intestinal mucosal defenses remains elusive. Here, we show that the α‐gliadin‐derived LGQQQPFPPQQPY peptide (P31–43) inhibits the function of cystic fibrosis transmembrane conductance regulator (CFTR), an anion channel pivotal for epithelial adaptation to cell‐autonomous or environmental stress. P31–43 binds to, and reduces ATPase activity of, the nucleotide‐binding domain‐1 (NBD1) of CFTR, thus impairing CFTR function. This generates epithelial stress, tissue transglutaminase and inflammasome activation, NF‐κB nuclear translocation and IL‐15 production, that all can be prevented by potentiators of CFTR channel gating. The CFTR potentiator VX‐770 attenuates gliadin‐induced inflammation and promotes a tolerogenic response in gluten‐sensitive mice and cells from celiac patients. Our results unveil a primordial role for CFTR as a central hub orchestrating gliadin activities and identify a novel therapeutic option for celiac disease.

Prevention and treatment of secretory diarrhea by the lysophosphatidic acid analog Rx100

IMPACT STATEMENT

A critical barrier in treating diarrheal disease is easy-to-use effective treatments. Rx100 is a first in class, novel small molecule that has shown efficacy after both subcutaneous and oral administration in a mouse cholera-toxin- and Citrobacter rodentium infection-induced diarrhea models. Our findings indicate that Rx100 a metabolically stable analog of the lipid mediator lysophosphatidic acid blocks activation of CFTR-mediated secretion responsible for fluid discharge in secretory diarrhea. Rx100 represents a new treatment modality which does not directly block CFTR but attenuates its activation by bacterial toxins. Our results provide proof-of-principle that Rx100 can be developed for use as an effective oral or injectable easy-to-use drug for secretory diarrhea which could significantly improve care by eliminating the need for severely ill patients to regularly consume large quantities of oral rehydration therapies and offering options for pediatric patients.

The Zinc Sensing Receptor, ZnR/GPR39, in Health and Disease

A distinct G-protein coupled receptor that senses changes in extracellular Zn²⁺, ZnR/GPR39, was found in cells from tissues in which Zn²⁺ plays a physiological role. Most prominently, ZnR/GPR39 activity was described in prostate cancer, skin keratinocytes, and colon epithelial cells, where zinc is essential for cell growth, wound closure, and barrier formation. ZnR/GPR39 activity was also described in neurons that are postsynaptic to vesicular Zn²⁺ release. Activation of ZnR/GPR39 triggers Gαq-dependent signaling and subsequent cellular pathways associated with cell growth and survival. Furthermore, ZnR/GPR39 was shown to regulate the activity of ion transport mechanisms that are essential for the physiological function of epithelial and neuronal cells. Thus, ZnR/GPR39 provides a unique target for therapeutically modifying the actions of zinc in a specific and selective manner.

Targeting Small Bowel Receptors to Treat Constipation and Diarrhea

BACKGROUND

The options for the treatment of diarrhea and constipation are evolving as emerging therapies target small bowel receptors. The goal of this review is to discuss small bowel receptors involved in intestinal absorption, secretion, and motility. The review highlights therapies already approved or currently being studied for the modulation of these receptors.

METHODS

The articles cited in this review focus on the molecular level of pathways involved in diarrhea and constipation, and highlight the respective pharmacotherapies.

RESULTS

The majority of the studies in the current literature investigate the effects of both the small and large intestine receptors on diarrhea and constipation. There are fewer studies that isolate the effects of these receptors solely on the small bowel, and focusing more on the receptors found distinctly in the small intestine may be an area of interest for future studies as this can inspire more targeted therapies.

Antidiarrheal Drug Therapy

INTRODUCTION

Acute diarrhea often runs a self-limited course and little by way of treatment is needed except for oral rehydration therapy. Chronic diarrhea poses a longer-term problem. If not treatable with specific therapy aimed at the underlying pathophysiology, chronic diarrhea often needs long-term symptomatic therapy.

PURPOSE OF REVIEW

This paper aims to examine the options for symptomatic, nonspecific treatment of diarrhea.

RECENT FINDINGS

The most frequently used therapies are opiate antidiarrheal drugs. These drugs are effective for a wide variety of diarrheal conditions and generally can be used safely if monitored closely. They work by slowing motility and allowing more time for absorption. They vary in potency and in addictive liability. In recent years, a variety of other drugs have been developed, which provide more targeted therapy that can mitigate diarrhea in specific situations. These drugs work on other regulatory pathways in the gut or on mucosal absorptive mechanisms. There is evidence for efficacy for both traditional and newer agents used for the symptomatic management of diarrhea. Opiates are used most often for this indication. Other agents may benefit individuals, but further research is needed to establish indications and best practices.

CFTR-NHERF2-LPA₂ Complex in the Airway and Gut Epithelia

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP- and cGMP-regulated chloride (Cl⁻) and bicarbonate (HCO₃⁻) channel localized primarily at the apical plasma membrane of epithelial cells lining the airway, gut and exocrine glands, where it is responsible for transepithelial salt and water transport. Several human diseases are associated with altered CFTR channel function. Cystic fibrosis (CF) is caused by the absence or dysfunction of CFTR channel activity, resulting from mutations in the gene. Secretory diarrhea is caused by the hyperactivation of CFTR channel activity in the gastrointestinal tract. CFTR is a validated target for drug development to treat CF, and extensive research has been conducted to develop CFTR inhibitors for therapeutic interventions of secretory diarrhea. The intracellular processing, trafficking, apical membrane localization, and channel function of CFTR are regulated by dynamic protein–protein interactions in a complex network. In this paper, we review the current knowledge of a macromolecular complex of CFTR, Na⁺/H⁺ exchanger regulatory factor 2 (NHERF2), and lysophosphatidic acids (LPA) receptor 2 (LPA₂) at the apical plasma membrane of airway and gut epithelial cells, and discuss its relevance in human physiology and diseases. We also explore the possibilities of targeting this complex to fine tune CFTR channel activity, with a hope to open up new avenues to develop novel therapies for CF and secretory diarrhea.

The Zn2+-sensing receptor, ZnR/GPR39, upregulates colonocytic Cl- absorption, via basolateral KCC1, and reduces fluid loss

Administration of zinc, as a complement to oral rehydration solutions, effectively diminishes duration and severity of diarrhea, but it is not known whether it merely fulfills a nutritional deficiency, or if zinc has a direct role of regulating solute absorption. We show that Zn2+ acts via a specific receptor, ZnR/GPR39, to reduce fluid loss. Intestinal fluid secretion triggered by cholera toxin (CTx) was lower in WT mice compared to ZnR/GPR39 KO. In the absence of dietary Zn2+ we observed similar fluid accumulation in WT and ZnR/GPR39 KO mice, indicating that Zn2+ and ZnR/GPR39 are both required for a beneficial effect of Zn2+ in diarrhea. In primary colonocytes and in Caco-2 colonocytic cells, activation of ZnR/GPR39 enhanced Cl- transport, a critical factor in diarrhea, by upregulating K+/Cl- cotransporter (KCC1) activity. Importantly, we show basolateral expression of KCC1 in mouse and human colonocytes, thus identifying a novel Cl- absorption pathway. Finally, inhibition of KCC-dependent Cl- transport enhanced CTx-induced fluid loss. Altogether, our data indicate that Zn2+ acting via ZnR/GPR39 has a direct role in controlling Cl- absorption via upregulation of basolateral KCC1 in the colon. Moreover, colonocytic ZnR/GPR39 and KCC1 reduce water loss during diarrhea and may therefore serve as effective drug targets.

The Contributions of Human Mini-Intestines to the Study of Intestinal Physiology and Pathophysiology

The lack of accessibility to normal and diseased human intestine and the inability to separate the different functional compartments of the intestine even when tissue could be obtained have held back the understanding of human intestinal physiology. Clevers and his associates identified intestinal stem cells and established conditions to grow "mini-intestines" ex vivo in differentiated and undifferentiated conditions. This pioneering work has made a new model of the human intestine available and has begun making contributions to the understanding of human intestinal transport in normal physiologic conditions and the pathophysiology of intestinal diseases. However, this model is reductionist and lacks many of the complexities of normal intestine. Consequently, it is not yet possible to predict how great the advances using this model will be for understanding human physiology and pathophysiology, nor how the model will be modified to include multiple other intestinal cell types and physical forces necessary to more closely approximate normal intestine. This review describes recent studies using mini-intestines, which have readdressed previously established models of normal intestinal transport physiology and newly examined intestinal pathophysiology. The emphasis is on studies with human enteroids grown either as three-dimensional spheroids or two-dimensional monolayers. In addition, comments are provided on mouse studies in cases when human studies have not yet been described.

Pathophysiology, Evaluation, and Management of Chronic Watery Diarrhea

Chronic watery diarrhea poses a diagnostic and therapeutic challenge and is often a disabling condition for patients. Although acute diarrhea is likely to be caused by infection, the causes of chronic diarrhea (>4 weeks in duration) are more elusive. We review the pathophysiology, diagnosis, and treatment of chronic diarrhea. Drawing on recent insights into the molecular mechanisms of intestinal epithelial transport and barrier function, we discuss how diarrhea can result from a decrease in luminal solute absorption, an increase in secretion, or both, as well as derangements in barrier properties. We also describe the various extraepithelial factors that activate diarrheal mechanisms. Finally, clinical evaluation and tests used in the assessment of patients presenting with chronic diarrhea are reviewed, and an algorithm guiding therapeutic decisions and pharmacotherapy is presented.

Molecular modelling and molecular dynamics of CFTR

The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a member of the ATP-binding cassette (ABC) transporter superfamily that functions as an ATP-gated channel. Considerable progress has been made over the last years in the understanding of the molecular basis of the CFTR functions, as well as dysfunctions causing the common genetic disease cystic fibrosis (CF). This review provides a global overview of the theoretical studies that have been performed so far, especially molecular modelling and molecular dynamics (MD) simulations. A special emphasis is placed on the CFTR-specific evolution of an ABC transporter framework towards a channel function, as well as on the understanding of the effects of disease-causing mutations and their specific modulation. This in silico work should help structure-based drug discovery and design, with a view to develop CFTR-specific pharmacotherapeutic approaches for the treatment of CF in the context of precision medicine.

Chemotherapy-Induced Constipation and Diarrhea: Pathophysiology, Current and Emerging Treatments

Gastrointestinal (GI) side-effects of chemotherapy are a debilitating and often overlooked clinical hurdle in cancer management. Chemotherapy-induced constipation (CIC) and Diarrhea (CID) present a constant challenge in the efficient and tolerable treatment of cancer and are amongst the primary contributors to dose reductions, delays and cessation of treatment. Although prevalence of CIC is hard to estimate, it is believed to affect approximately 16% of cancer patients, whilst incidence of CID has been estimated to be as high as 80%. Despite this, the underlying mechanisms of both CID and CIC remain unclear, but are believed to result from a combination of intersecting mechanisms including inflammation, secretory dysfunctions, GI dysmotility and alterations in GI innervation. Current treatments for CIC and CID aim to reduce the severity of symptoms rather than combating the pathophysiological mechanisms of dysfunction, and often result in worsening of already chronic GI symptoms or trigger the onset of a plethora of other side-effects including respiratory depression, uneven heartbeat, seizures, and neurotoxicity. Emerging treatments including those targeting the enteric nervous system present promising avenues to alleviate CID and CIC. Identification of potential targets for novel therapies to alleviate chemotherapy-induced toxicity is essential to improve clinical outcomes and quality of life amongst cancer sufferers.

Pathophysiological mechanisms of diarrhea caused by the Vibrio cholerae O1 El Tor variant: an in vivo study in mice

Cholera is caused by infection with Vibrio cholerae. This study aimed to investigate the pathophysiology of diarrhea caused by the V. cholerae O1 El Tor variant (EL), a major epidemic strain causing severe diarrhea in several regions. In the ligated ileal loop model of EL-induced diarrhea in the ICR mice, a cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor and a calcium-activated chloride channel (CaCC) inhibitor similarly inhibited intestinal fluid secretion. In addition, barrier disruption and NF-κB-mediated inflammatory responses, e.g., iNOS and COX-2 expression, were observed in the infected ileal loops. Interestingly, intestinal fluid secretion and barrier disruption were suppressed by NF-κB and COX-2 inhibitors, whereas an iNOS inhibitor suppressed barrier disruption without affecting fluid secretion. Furthermore, EP2 and EP4 PGE2 receptor antagonists ameliorated the fluid secretion in the infected ileal loops. The amount of cholera toxin (CT) produced in the ileal loops by the EL was ∼2.4-fold of the classical biotype. The CT transcription inhibitor virstatin, a toll-like receptor-4 (TLR-4) antibody and a CT antibody suppressed the EL-induced intestinal fluid secretion, barrier disruption and COX-2 expression. The CT at levels detected during EL infection induced mild intestinal barrier disruption without inducing inflammatory responses in mouse intestine. Collectively, this study indicates that CT-induced intestinal barrier disruption and subsequent TLR-4-NF-κB-mediated COX-2 expression are involved in the pathogenesis of EL-induced diarrhea and represent promising novel therapeutic targets of cholera.

The Effect of G-ORS Along With Rice Soup in the Treatment of Acute Diarrhea in Children: A Single-Blind Randomized Controlled Trial

Background

The world health organization guidelines for treatment of diarrhea in children emphasize on continued feeding together with prescription of oral rehydration solution (ORS) and supplementary zinc therapy. However, conflicting viewpoints exist regarding the optimal diet and dietary ingredients for children with diarrhea. Moreover, few studies have investigated the effect of rice soup along with ORS in the treatment of this disease.

Objectives

This study aimed to explore effects of simultaneous taking of glucose oral rehydration solution (G-ORS) and rice soup in the treatment of acute diarrhea in 8 to 24-month-old children.

Patients and Methods

This single-blind controlled clinical trial was conducted in the pediatric ward of 22nd of Bahman hospital, Gonabad, Iran between June 2013 and February 2014. Forty children aged 8-24 months with acute diarrhea were randomly assigned into an intervention group (G-ORS plus rice soup group) comprising 20 babies and a control group (G-ORS) of 20 children based on balanced blocking randomization. The variables under investigation were diarrhea duration, patient hospitalization, need for intravenous (IV) fluids and stool output frequency. Data was analyzed using independent samples t and chi-square test.

Results

At the end of study, the time for treating acute watery diarrhea in the intervention and control groups were 21.10 ± 8.81 and 34.55 ± 5.82 hours (P < 0.001) and hospital stay were 34.05 ± 6.62 and 40.20 ± 6.32 hours (P = 0.005). Moreover, stool output frequency were 4.20 ± 0.95 and 8.00 ± 1.37 (P < 0.001) in the first 24 hours, and 2.18 ± 0.60 and 2.80 ± 0.76 (P = 0.03) in the second 24 hours of treatment in intervention and control groups, respectively.

Conclusions

Rice soup regimen was highly effective and inexpensive in the treatment of acute diarrhea in children. Thus, in addition to the common treatment by G-ORS, rice soup can be consumed simultaneously with G-ORS.

Electrophysiological Studies into the Safety of the Anti-diarrheal Drug Clotrimazole during Oral Rehydration Therapy

Background and Aims

Morbidity and mortality from acute diarrheal disease remains high, particularly in developing countries and in cases of natural or man-made disasters. Previous work has shown that the small molecule clotrimazole inhibits intestinal Cl^- secretion by blocking both cyclic nucleotide- and Ca²⁺-gated K⁺ channels, implicating its use in the treatment of diarrhea of diverse etiologies. Clotrimazole, however, might also inhibit transporters that mediate the inwardly directed electrochemical potential for Na⁺-dependent solute absorption, which would undermine its clinical application. Here we test this possibility by examining the effects of clotrimazole on Na⁺-coupled glucose uptake.

Materials and Methods

Short-circuit currents (Isc) following administration of glucose and secretagogues were studied in clotrimazole-treated jejunal sections of mouse intestine mounted in Ussing chambers.

Results

Treatment of small intestinal tissue with clotrimazole inhibited the Cl^- secretory currents that resulted from challenge with the cAMP-agonist vasoactive intestinal peptide (VIP) or Ca²⁺-agonist carbachol in a dose-dependent fashion. A dose of 30 μM was effective in significantly reducing the Isc response to VIP and carbachol by 50% and 72%, respectively. At this dose, uptake of glucose was only marginally affected (decreased by 14%, p = 0.37). There was no measurable effect on SGLT1-mediated sugar transport, as uptake of SGLT1-restricted 3-O-methyl glucose was equivalent between clotrimazole-treated and untreated tissue (98% vs. 100%, p = 0.90).

Conclusion

Treatment of intestinal tissue with clotrimazole significantly reduced secretory responses caused by both cAMP- and Ca²⁺-dependent agonists as expected, but did not affect Na⁺-coupled glucose absorption. Clotrimazole could thus be used in conjunction with oral rehydration solution as a low-cost, auxiliary treatment of acute secretory diarrheas.

In acute infectious diarrhea, the active secretion of Cl^- ions contributes to the secondary loss of Na⁺ and water from the intestine. Apical Cl^- secretion from intestinal epithelial cells is dependent upon cyclic nucleotide- and Ca²⁺-dependent intracellular signals and requires the concomitant transport of K⁺ through basolateral K⁺ channels for maintenance of an electroneutral state. Hence, when efflux of K⁺ in enterocytes is blocked, Cl^- secretion necessarily shuts down. The FDA-approved antifungal drug clotrimazole has been demonstrated to be a potent blocker of basolateral cAMP- and Ca²⁺-gated K⁺ channels in enterocytes, and therefore likely has therapeutic efficacy for secretory diarrheas. One important concern that could compromise its clinical applicability as a novel anti-diarrheal drug, however, is that clotrimazole might affect intestinal Na⁺-coupled glucose absorption, which constitutes the physiological basis of oral rehydration therapies and is thus critical for the efficacy of the current golden standard treatment for acute infectious diarrheal diseases. In this work, we demonstrate that clotrimazole effectively blocks Cl^- secretion in mouse intestine after stimulation with secretory stimuli, without affecting the capacity to take up Na⁺ and glucose. These results pave the way towards further clinical development of clotrimazole as a new pharmacologic strategy for acute diarrheal disease.

Benzopyrimido-pyrrolo-oxazine-dione (R)-BPO-27 Inhibits CFTR Chloride Channel Gating by Competition with ATP

We previously reported that benzopyrimido-pyrrolo-oxazinedione BPO-27 [6-(5-bromofuran-2-yl)-7,9-dimethyl-8,10-dioxo-11-phenyl-7,8,9,10-tetrahydro-6H-benzo[b]pyrimido [4',5':3,4]pyrrolo [1,2-d][1,4]oxazine-2-carboxylic acid] inhibits the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel with low nanomolar potency and reduces cystogenesis in a model of polycystic kidney disease. We used computational chemistry and patch-clamp to show that enantiomerically pure (R)-BPO-27 inhibits CFTR by competition with ATP, whereas (S)-BPO-27 is inactive. Docking computations using a homology model of CFTR structure suggested that (R)-BPO-27 binds near the canonical ATP binding site, and these findings were supported by molecular dynamics simulations showing a lower binding energy for the (R) versus (S) stereoisomers. Three additional lower-potency BPO-27 analogs were modeled in a similar fashion, with the binding energies predicted in the correct order. Whole-cell patch-clamp studies showed linear CFTR currents with a voltage-independent (R)-BPO-27 block mechanism. Single-channel recordings in inside-out patches showed reduced CFTR channel open probability and increased channel closed time by (R)-BPO-27 without altered unitary channel conductance. At a concentration of (R)-BPO-27 that inhibited CFTR chloride current by ∼50%, the EC50 for ATP activation of CFTR increased from 0.27 to 1.77 mM but was not changed by CFTRinh-172 [4-[[4-oxo-2-thioxo-3-[3-trifluoromethyl)phenyl]-5-thiazolidinylidene]methyl]benzoic acid], a thiazolidinone CFTR inhibitor that acts at a site distinct from the ATP binding site. Our results suggest that (R)-BPO-27 inhibition of CFTR involves competition with ATP.

ErbB small molecule tyrosine kinase inhibitor (TKI) induced diarrhoea: Chloride secretion as a mechanistic hypothesis

Diarrhoea is a common, debilitating and potentially life threatening toxicity of many cancer therapies. While the mechanisms of diarrhoea induced by traditional chemotherapy have been the focus of much research, the mechanism(s) of diarrhoea induced by small molecule ErbB TKI, have received relatively little attention. Given the increasing use of small molecule ErbB TKIs, identifying this mechanism is key to optimal cancer care. This paper critically reviews the literature and forms a hypothesis that diarrhoea induced by small molecule ErbB TKIs is driven by intestinal chloride secretion based on the negative regulation of chloride secretion by ErbB receptors being disrupted by tyrosine kinase inhibition.