Chloride Secretagogues Research Articles

Use of prucalopride in adults with chronic idiopathic constipation

ABSTRACTIntroduction: Prucalopride is a selective 5-HT4 receptor agonist with colonic prokinetic activity. It was recently approved by the FDA for the treatment of chronic idiopathic constipation. Before this approval, there were limited options to improve colonic motility in the treatment of chronic idiopathic constipation.Areas covered: We systematically searched PubMed, Embase, ClinicalTrials.gov, and international conference presentations, and we reviewed all studies that evaluated prucalopride for the treatment of chronic idiopathic constipation in adults. In this review, we discuss the pharmacokinetics, pharmacodynamics, receptor interactions, phase I-IV clinical trials, and safety outcomes of prucalopride in adults, including the elderly.Expert opinion: Prucalopride is an effective agent to improve colonic motility, decrease colonic transit time, and increase complete spontaneous bowel movements in patients with chronic idiopathic constipation. Unlike previously available 5-HT4 receptor agonists such as cisapride and tegaserod, prucalopride does not interact with the cardiac hERG potassium channels or other serotonergic receptors in blood vessels and is not associated with an increase in major adverse cardiovascular events. Additionally, prucalopride has demonstrated promise in the treatment of gastroparesis, post-operative ileus, and opioid-induced constipation. Prucalopride directly stimulates colonic motility, differentiating it from all other medications (exclusively osmotic or chloride secretagogues) approved for chronic constipation in the last decade.

Rectification of oxygen transfer through the rat colonic epithelium.

AIMTo assess whether higher sensitivity of colonic epithelium to hypoxia at the serosal side is associated with oxygen transfer asymmetry.METHODSRats were fed either with normal chow or a low-sodium diet. Tissues were mounted as flat sheets in a modified, airtight Ussing chamber with oxygen meters in each hemichamber. Mucosal samples from normal diet animals were studied under control conditions, in low-chloride solution and after adding chloride secretion inhibitors and chloride secretagogues. Samples from sodium-deprived rats were studied before and after ouabain addition. In separate experiments, the correlation between short-circuit current and oxygen consumption was analyzed. Finally, hypoxia was induced in one hemichamber to assess the relationship between its oxygen content and the oxygen pressure difference between both hemichambers.RESULTSIn all studied conditions, oxygen consumption was larger in the serosal hemichamber than in the mucosal one (P = 0.0025 to P < 0.0001). Short-circuit current showed significant correlation with both total oxygen consumption (r = 0.765; P = 0.009) in normoxia and oxygen consumption in the serosal hemichamber (r = 0.754; P = 0.011) during mucosal hypoxia, but not with oxygen consumption in the mucosal hemichamber. When hypoxia was induced in the mucosal hemichamber, an oxygen pressure difference of 13 kPa with the serosal hemichamber was enough to keep its oxygen content constant. However, when hypoxia was induced in the serosal hemichamber, the oxygen pressure difference with the mucosal hemichamber necessary to keep its oxygen content constant was 40 kPa (P < 0.0001).CONCLUSIONSerosal oxygen supply is more readily available to support short-circuit current. This may be partly due to a rectifying behavior of transepithelial oxygen transfer.

Gastric inhibitory peptide, serotonin, and glucagon are unexpected chloride secretagogues in the rectal gland of the skate (Leucoraja erinacea)

Since the discovery of the rectal gland of the dogfish shark 50 years ago, experiments with this tissue have greatly aided our understanding of secondary active chloride secretion and the secretagogues responsible for this function. In contrast, very little is known about the rectal gland of skates. In the present experiments, we performed the first studies in the perfused rectal gland of the little skate (Leucoraja erinacea), an organ weighing less than one-tenth of the shark rectal gland. Our results indicate that the skate gland can be studied by modified perfusion techniques and in primary culture monolayers, and that secretion is blocked by the inhibitors of membrane proteins required for secondary active chloride secretion. Our major finding is that three G protein-coupled receptor agonists, the incretin gastric inhibitory polypeptide (GIP), also known as glucose-dependent insulinotropic peptide, as well as glucagon and serotonin, are unexpected potent chloride secretagogues in the skate but not the shark. Glucagon stimulated chloride secretion to a mean value of 1,661 ± 587 μeq·h(-1)·g(-1) and serotonin stimulated to 2,893 ± 699 μeq·h(-1)·g(-1). GIP stimulated chloride secretion to 3,733 ± 679 μeq·h(-1)·g(-1) and significantly increased tissue cAMP content compared with basal conditions. This is the first report of GIP functioning as a chloride secretagogue in any species or tissue.

Resveratrol Enhances Airway Surface Liquid Depth in Sinonasal Epithelium by Increasing Cystic Fibrosis Transmembrane Conductance Regulator Open Probability

BackgroundChronic rhinosinusitis engenders enormous morbidity in the general population, and is often refractory to medical intervention. Compounds that augment mucociliary clearance in airway epithelia represent a novel treatment strategy for diseases of mucus stasis. A dominant fluid and electrolyte secretory pathway in the nasal airways is governed by the cystic fibrosis transmembrane conductance regulator (CFTR). The objectives of the present study were to test resveratrol, a strong potentiator of CFTR channel open probability, in preparation for a clinical trial of mucociliary activators in human sinus disease. MethodsPrimary sinonasal epithelial cells, immortalized bronchoepithelial cells (wild type and F508del CFTR), and HEK293 cells expressing exogenous human CFTR were investigated by Ussing chamber as well as patch clamp technique under non-phosphorylating conditions. Effects on airway surface liquid depth were measured using confocal laser scanning microscopy. Impact on CFTR gene expression was measured by quantitative reverse transcriptase polymerase chain reaction.ResultsResveratrol is a robust CFTR channel potentiator in numerous mammalian species. The compound also activated temperature corrected F508del CFTR and enhanced CFTR-dependent chloride secretion in human sinus epithelium ex vivo to an extent comparable to the recently approved CFTR potentiator, ivacaftor. Using inside out patches from apical membranes of murine cells, resveratrol stimulated an ~8 picosiemens chloride channel consistent with CFTR. This observation was confirmed in HEK293 cells expressing exogenous CFTR. Treatment of sinonasal epithelium resulted in a significant increase in airway surface liquid depth (in µm: 8.08+/-1.68 vs. 6.11+/-0.47,control,p<0.05). There was no increase CFTR mRNA. ConclusionResveratrol is a potent chloride secretagogue from the mucosal surface of sinonasal epithelium, and hydrates airway surface liquid by increasing CFTR channel open probability. The foundation for a clinical trial utilizing resveratrol as a therapeutic intervention to increase mucociliary transport and airway surface liquid hydration in sinus disease is strongly supported by these findings.

The role of rectal chloride secretion in childhood constipation

Disturbance in fluid secretion, driven by chloride secretion, might play a role in constipation. However, disturbed chloride secretion in those patients has yet to be evaluated. Therefore, the aim of this study was to compare chloride secretion in rectal biopsies of children with functional constipation (FC) to those without constipation. To measure changes in short circuit current (I(sc) in μA cm(-2)) reflecting chloride secretion, intestinal biopsies from children with constipation, to either exclude or diagnose Hirschsprung's disease, and from children without constipation (controls) undergoing colonoscopy for screening of familial adenomatous polyposis, juvenile polyps or inflammatory bowel disease (IBD), were compared and studied in Ussing chambers. Following electrogenic sodium absorption blockade by amiloride, chloride secretory responses to calcium-linked (histamine, carbachol) and cAMP-linked (IBMX/forskolin) secretagogues were assessed. Ninety-six patients (46 FC) participated; nine FC patients (n = 1 congenital syndrome and n = 8 technical problems) and 13 controls (n = 6 IBD; n = 7 technical problems) were excluded. No significant difference was found in mean (±SE) basal chloride currents between children with FC and controls (9.6 ± 1.1 vs 9.2 ± 0.8; P = 0.75, respectively). Responses to calcium-linked chloride secretagogues (histamine and carbachol) were significantly higher in controls (33.0 ± 3.0 vs 24.5 ± 2.3; P = 0.03 and 33.6 ± 3.4 vs 26.4 ± 2.7; P = 0.05 following histamine and carbachol, respectively). Calcium-linked chloride secretion is disturbed in children with FC. Whether this defect occurs at the level of histamine receptors, components of receptor-linked signal transduction pathways or basolateral Ca(2+) -sensitive K(+) channels enhancing the electrical driving force for apical chloride secretion, remains to be explored.

Apical leptin induces chloride secretion by intestinal epithelial cells and in a rat model of acute chemotherapy-induced colitis

The purpose of this study was to investigate whether luminal leptin alters ion transport properties of the intestinal epithelium under acute inflammatory conditions. Monolayers of human intestinal T(84) epithelial cells and a rat model of chemotherapy-induced enterocolitis were used. Cells were treated with leptin and mounted in Ussing chambers to measure basal and secretagogue-induced changes in transepithelial short-circuit current (I(sc)). Furthermore, the role of MAPK and phosphatidylinositol 3-kinase (PI3K) signaling pathways in mediating responses to leptin was investigated. Acute colitis in Sprague-Dawley rats was induced by intraperitoneal injection of 40 mg/kg methotrexate. Leptin (100 ng/ml) induced a time-dependent increase in basal I(sc) in T(84) intestinal epithelial cells (P < 0.01). Moreover, pretreatment of T(84) cells with leptin for up to 1 h significantly potentiated carbachol- and forskolin-induced increases in I(sc). Pretreatment with an inhibitor of MAPK abolished the effect of leptin on basal, carbachol- and forskolin-induced chloride secretion (P < 0.05). However, the PI3K inhibitor, wortmannin, only blunted the effect of leptin on forskolin-induced increases in I(sc). Furthermore, leptin treatment evoked both ERK1/2 and Akt1 phosphorylation in T(84) cells. In the rat model, luminal leptin induced significant increases in I(sc) across segments of proximal and, to a lesser extent, distal colon (P < 0.05). We conclude that luminal leptin is likely an intestinal chloride secretagogue, particularly when present at elevated concentrations and/or in the setting of inflammation. Our findings may provide a mechanistic explanation, at least in part, for the clinical condition of secretory diarrhea both in hyperleptinemic obese patients and in patients with chemotherapy-induced intestinal inflammation.

Influence of weaning and effect of post weaning dietary zinc and copper on electrophysiological response to glucose, theophylline and 5-HT in piglet small intestinal mucosa

This study aimed to examine how weaning and how dietary zinc and/or copper fed post weaning may affect the electrophysiological response to glucose and to chloride secretagogues in piglet small intestine in vitro. Study 1 included 54 piglets (six litters of nine piglets). One piglet from every litter was killed 1 day before weaning. The remaining 48 piglets were allocated at weaning (28 d) to four dietary zinc treatments and subsequently killed 1–2, 5–6 or 14–15 days after weaning. Study 2 included 48 piglets (six litters of eight piglets) allocated to four dietary treatments, consisting of high or low dietary zinc with or without high dietary copper. All piglets in study 2 were killed 5–7 days after weaning. The in vitro studies in Ussing chambers showed that weaning resulted in increased ileal glucose absorption as well as increased neuroendocrine-regulated (activated by 5-HT) and cAMP-dependent (activated by theophylline) chloride secretion. High zinc supplementation reduced the responses to 5-HT and theophylline. The study did not reveal any influence of copper on these parameters. It is concluded that the positive effect of zinc supplementation on diarrhoea in weaned piglets may be due to zinc reducing the intestinal mucosal susceptibility to secretagogues that activate chloride secretion.

Activation of Chloride Secretion in Cystic Fibrosis Cells and Tissues by the Substituted Imidazole SRI 2931

Recent interest in nucleotides and related agents as part of clinical trials in cystic fibrosis (CF) therapy have elicited efforts to identify novel compounds capable of activating transepithelial chloride (Cl(-)) transport in CF cells and tissues. From a library of nucleosides, bases, and other substituted heterocycles, 341 compounds were screened for their ability to activate anion transport in CF cells grown on permeable supports. One compound, SRI 2931, was found to confer prolonged and potent activity when administered to the apical surfaces of CF pancreatic epithelial cells, primary CF nasal epithelial cells, non-CF human colonic epithelial cells, and intact tissue taken from mouse models for CF. Concentrations of SRI 2931 (20 microM), which activated Cl(-) transport, had minimal effect on cell proliferation. SRI 2931 was not calcium (Ca(2+)) or cAMP dependent, suggesting important differences from conventional chloride secretagogues. The compound selectively released ATP from the apical, but not basolateral, surfaces of CF cells grown on permeable supports. The magnitude, longevity, and mechanism of action of the response provide a tool for dissecting pathways of epithelial ATP extracellular signaling and Cl(-) permeability.

Bradykinin increases IL-8 generation in airway epithelial cells via COX-2-derived prostanoids.

Interleukin (IL)-8, the C-X-C chemokine, is a potent neutrophil chemoattractant that has been implicated in a number of inflammatory airway diseases such as cystic fibrosis. Here we tested the hypothesis that bradykinin, an inflammatory mediator and chloride secretagogue, would increase IL-8 generation in airway epithelial cells through autocrine generation of endogenous prostanoids. Bradykinin increased IL-8 generation in both a non-cystic fibrosis (A549) and cystic fibrosis epithelial cell line (CFTE29) that was inhibited by the nonselective cyclooxygenase (COX) inhibitor indomethacin and the COX-2 selective inhibitor NS-398. COX-2 was the only isoform of COX expressed in both cell lines. Furthermore, the COX substrate arachidonic acid and exogenous prostaglandin E(2) both increased IL-8 release in A549 cells. These results suggest that bradykinin may contribute to neutrophilic inflammation in the airway by generation of IL-8 from airway epithelial cells. The dependence of this response on endogenous production of prostanoids by COX-2 suggests that selective COX-2 inhibitors may have a role in the treatment of airway diseases characterized by neutrophilic inflammation such as cystic fibrosis or chronic obstructive pulmonary disease.

Fish oil supplementation does not impair the gut immune response to Trichinella spiralis infection in rats.

Fish oil has been recommended as a source of omega-3 fatty acids for preterm infants and for therapy of some inflammatory diseases. Because fish oil supplementation could downregulate the host's immune response, we studied the gut inflammatory response to an enteric infection in 72 rats assigned to three dietary groups with differing fatty acid profile: 1) fish oil, rich in eicosapentaenoic and docosahexaenoic acid; 2) olive oil, containing 71% monounsaturated fat; and 3) rat chow, containing 57% saturated fat. One half (n = 36) of the rats were infected with Trichinella spiralis larvae; the other half served as controls. The inflammatory response to initial infection (study 1), and type I hypersensitivity response to a subsequent parasite-derived antigenic challenge (study 2) were assessed. Jejunal inflammatory cell infiltrate, mean villus height, disaccharidase levels, changes in short-circuit current in response to glucose absorption, and chloride secretagogues (study 1) were measured 9 days after infection. Short-circuit current changes induced by chloride secretion were measured when the proximal jejunum was challenged with T. spiralis-derived antigen 40 days after infection (study 2). In study 1, jejunal tissue from infected animals had more eosinophilic infiltrate, lower disaccharidase levels, and less glucose absorptive and chloride secretory capacity than tissue from noninfected animals. In study 2, the jejunum of infected animals showed an antigen-induced chloride secretory response, whereas no response was obtained from jejunal tissue from noninfected animals. Type of diet did not affect the response in either study. Under the conditions of this experiment, fish oil supplementation did not interfere with the local intestinal inflammatory response after T. spiralis infection.

The primary and final effector mechanisms required for kinin-induced epithelial chloride secretion.

The short-circuit current technique was used to examine the effects of N2-L-lysylbradykinin (LBK) on chloride secretion in the mucosae of the mouse intestine. It was found to be a potent chloride secretagogue in the mucosa lining the colon, jejunum, and cecum, as it is in most mammals, with 2 nM being sufficient to cause half-maximal secretion. The extent of the responses was in the order cecum > colon > jejunum. In cystic fibrosis (CF) null mice, with no CF transmembrane conductance regulator (CFTR) chloride channels, LBK caused no chloride secretion, but transporting activities for other ions were revealed. Introduction of the human CF gene into the genome of CF null mice at the zygote stage restored the chloride secretory activity of LBK, with only minor differences in potency. In mice in which the kinin B2 receptor gene had been disrupted, LBK had no effect, whereas the responses to forskolin were unchanged. Thus the acute effects of kinins on chloride secretion depend uniquely on kinin B2 receptors and CFTR chloride channels, which form the primary and final effector mechanisms of the secretory process.

AMP and microamps: neutrophil-derived chloride secretagogue identified.

AMP and microamps: neutrophil-derived chloride secretagogue identified.

Chloride secretagogues stimulate inositol phosphate formation in shark rectal gland tubules cultured in suspension

Neuroendocrine activation of transepithelial chloride secretion by shark rectal gland cells is associated with increases in cellular cAMP, cGMP, and free calcium concentrations. We report here on the effects of several chloride secretagogues on inositol phosphate formation in cultured rectal gland tubules. Vasoactive intestinal peptide (VIP), atriopeptin (AP), and ionomycin increase the total inositol phosphate levels of cultured tubules, as measured by ion exchange chromatography. Forskolin, a potent chloride secretagogue, has no effect on inositol phosphate formation. The uptake of 3H-myo-inositol into phospholipids is very slow, preventing the detection of increased levels of inositol trisphosphate. However, significant increases in inositol monophosphate (IP1) and inositol biphosphate (IP2) were measured. The time course of VIP- and AP-stimulated IP1 and IP2 formation is similar to the effects of these agents on the short-circuit current responses of rectal gland monolayer cultures. In addition, aluminum fluoride, an artificial activator of guanine nucleotide-binding proteins, stimulates IP1 and IP2 formation. We conclude that rectal gland cells contain VIP and AP receptors coupled to the activation of phospholipase C. Coupling may be mediated by G-proteins. Receptor-stimulated increases in inositol phospholipid metabolism is one mechanism leading to increased intracellular free calcium concentrations, an important regulatory event in the activation of transepithelial chloride secretion by shark rectal gland epithelial cells.

Neuropeptide Y antagonises secretagogue evoked chloride transport in rat jejunal epithelium

Neuropeptide Y (NPY) inhibits electrogenic Cl secretion in rat jejunal epithelium under voltage clamp conditions. This effect is dependent upon endogenous eicosanoid formation since it is blocked by the cyclooxygenase inhibitor, piroxicam, which itself has an inhibitory action upon chloride secretion. A number of chloride secretagogues have been examined for their ability to restore the antisecretory effects of NPY. Data presented here shows that NPY responsiveness is restored, in piroxicam pretreated tissues, by vasoactive intestinal polypeptide (VIP), forskolin, prostaglandin E2 (PGE2) isobutyl-1-methyl-xanthine (IBMX) and dibutyryl cAMP added prior to the neuropeptide. While all these agents cause chloride secretion by elevating intracellular cAMP, NPY is also effective in inhibiting the secretory effects of carbachol (CCh) and substance P (SP), agents believed to act by raising intracellular calcium (Cai). Although there is evidence that NPY can inhibit adenylate cyclase, its ability to attenuate chloride secretion brought about by secretagogues acting through both adenylate cyclase and calcium mechanisms, implies that NPY has either a more general fundamental mechanism or has multiple interactions with different second messenger systems.