Cholera Toxin-induced Fluid Secretion Research Articles

Calcimimetic acts on enteric neuronal CaSR to reverse cholera toxin-induced intestinal electrolyte secretion

Treatment of acute secretory diarrheal illnesses remains a global challenge. Enterotoxins produce secretion through direct epithelial action and indirectly by activating enteric nervous system (ENS). Using a microperfused colonic crypt technique, we have previously shown that R568, a calcimimetic that activates the calcium-sensing receptor (CaSR), can act on intestinal epithelium and reverse cholera toxin-induced fluid secretion. In the present study, using the Ussing chamber technique in conjunction with a tissue-specific knockout approach, we show that the effects of cholera toxin and CaSR agonists on electrolyte secretion by the intestine can also be attributed to opposing actions of the toxin and CaSR on the activity of the ENS. Our results suggest that targeting intestinal CaSR might represent a previously undescribed new approach for treating secretory diarrheal diseases and other conditions with ENS over-activation.

The efficacy of a sulphated polysaccharide fraction from Hypnea musciformis against diarrhea in rodents

Seaweeds are sources of diverse bioactive compounds, such as sulphated polysaccharides. This study was designed to evaluate the chemical composition and anti-diarrheal activity of a fraction of sulphated polysaccharide (PLS) obtained from the red seaweed Hypnea musciformis in different animal models, and to elucidate the underlying mechanisms. PLS was obtained by aqueous extraction, with a yield of 31.8% of the seaweed dry weight. The total carbohydrate content accounted for 99% of the sample. The sulfate content of the polysaccharide was 5.08% and the percentage of carbon was 25.98%. Pretreatment with all doses of PLS inhibited castor oil-induced diarrhea, with reduction of the total amount of stool, diarrheal stools, and the severity of diarrhea. PLS (90mg/Kg) decreased castor oil- and PGE2-induced enteropooling. In addition, PLS (90mg/Kg) increased the Na+/K+-ATPase activity in the small intestine and reduced gastrointestinal transit, possibly via activation of cholinergic receptors. Interestingly, the cholera toxin-induced fluid secretion and Cl− ion levels decreased in the intestinal contents of the animals pretreated with PLS (90mg/kg), probably via reduction of toxin—GM1 receptor binding. In conclusion, PLS exerts anti-diarrheal activity by increasing Na+/K+-ATPase activity, inhibiting gastrointestinal motility, and blocking the toxin—GM1 receptor binding.

Oridonin: A small molecule inhibitor of cystic fibrosis transmembrane conductance regulator (CFTR) isolated from traditional Chinese medicine

The cystic fibrosis transmembrane conductance regulator (CFTR) is an epithelial chloride channel regulating the transepithelial transport of electrolyte and water. In the recent years, CFTR chloride channel becomes the new molecular target of treating secretory diarrhea. The objective of this study is to find out a novel CFTR inhibitor from traditional Chinese medicine (TCM) and study on its pharmacological activity. About 34,000 factions of TCM extracts were screened by high throughput screening (HTS) in this research. We found that Rabdosia rubescens show a potent inhibition on CFTR. Under the bio-active analysis guidance, an ent-kaurane diterpenoid — oridonin (PubChem CID: 34378) was isolated from R. rubescens. A series of intensive studies showed that oridonin remarkably reduced iodide influx in wt-CFTR and ΔF508-CFTR FRT epithelial cells in a dose-dependent and irreversible way. Oridonin sharply blocked FSK-stimulated short-circuit current in both rats and mice intestine in vitro. In mouse closed-loop model, oridonin reduced cholera toxin-induced fluid secretion significantly over 6hours in vivo. Thus we concluded that oridonin is a new inhibitor of CFTR Cl− channel. It will be a good leading compound for developing the new drug of cholera toxin-induced secretory diarrhea.

CFTR channel pharmacology: insight from a flock of clones. Focus on “Divergent CFTR orthologs respond differently to the channel inhibitors CFTRinh-172, glibenclamide, and GlyH-101”

how do you identify drug-binding sites on an ion channel when you don't have a crystal structure? In the case of the cystic fibrosis transmembrane conductance regulator (CFTR), which plays a pivotal role in transepithelial ion transport, several approaches have been tried, including 1 ) targeting

Nanomolar CFTR Inhibition by Pore-Occluding Divalent Polyethylene Glycol-Malonic Acid Hydrazides

Inhibitors of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel have potential application as antisecretory therapy in cholera. We synthesized mono- and divalent CFTR inhibitors consisting of a malonic acid hydrazide (MalH) coupled via a disulfonic stilbene linker to polyethylene glycols (PEGs; 0.2-100 kDa). IC50 values for CFTR inhibition were 10-15 microM for the monovalent MalH-PEGs, but substantially lower for divalent MalH-PEG-MalH compounds, decreasing from 1.5 to 0.3 microM with increasing PEG size and showing positive cooperativity. Whole-cell patch-clamp showed voltage-dependent CFTR block with inward rectification. Outside-out patch-clamp showed shortened single-channel openings, indicating CFTR pore block from the extracellular side. Luminally added MalH-PEG-MalH blocked by >90% cholera toxin-induced fluid secretion in mouse intestinal loops (IC50 approximately 10 pmol/loop), and greatly reduced mortality in a suckling mouse cholera model. These conjugates may provide safe, inexpensive antisecretory therapy.

Luminally active, nonabsorbable CFTR inhibitors as potential therapy to reduce intestinal fluid loss in cholera

Enterotoxin-mediated secretory diarrheas such as cholera involve chloride secretion by enterocytes into the intestinal lumen by the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. We previously identified glycine hydrazide CFTR blockers that by electrophysiological studies appeared to block the CFTR anion pore at its lumen-facing surface. Here, we synthesize highly water-soluble, nonabsorbable malondihydrazides by coupling 2,4-disulfobenzaldehyde, 4-sulfophenylisothiocyante, and polyethylene glycol (PEG) moieties to 2-naphthalenylamino-[(3,5-dibromo-2,4-dihydroxyphenyl) methylene] propanedioic acid dihydrazide, and aminoacethydrazides by coupling PEG to [(N-2-naphthalenyl)-2-(2-hydroxyethyl)]-glycine-2-[(3,5-dibromo-2,4-dihydroxyphenyl) methylene] hydrazide. Compounds rapidly, fully and reversibly blocked CFTR-mediated chloride current with Ki of 2-8 microM when added to the apical surface of epithelial cell monolayers. Compounds did not pass across Caco-2 monolayers, and were absorbed by <2%/hr in mouse intestine. Luminally added compounds blocked by >90% cholera toxin-induced fluid secretion in mouse intestinal loops, without inhibiting intestinal fluid absorption. These orally administered, nonabsorbable, nontoxic CFTR inhibitors may reduce intestinal fluid losses in cholera.

Thiazolidinone CFTR inhibitor identified by high-throughput screening blocks cholera toxin–induced intestinal fluid secretion

Secretory diarrhea is the leading cause of infant death in developing countries and a major cause of morbidity in adults. The cystic fibrosis transmembrane conductance regulator (CFTR) protein is required for fluid secretion in the intestine and airways and, when defective, causes the lethal genetic disease cystic fibrosis. We screened 50,000 chemically diverse compounds for inhibition of cAMP/flavone–stimulated Cl– transport in epithelial cells expressing CFTR. Six CFTR inhibitors of the 2-thioxo-4-thiazolidinone chemical class were identified. The most potent compound discovered by screening of structural analogs, CFTRinh-172, reversibly inhibited CFTR short-circuit current in less than 2 minutes in a voltage-independent manner with KI approximately 300 nM. CFTRinh-172 was nontoxic at high concentrations in cell culture and mouse models. At concentrations fully inhibiting CFTR, CFTRinh-172 did not prevent elevation of cellular cAMP or inhibit non-CFTR Cl– channels, multidrug resistance protein-1 (MDR-1), ATP-sensitive K+ channels, or a series of other transporters. A single intraperitoneal injection of CFTRinh-172 (250 μg/kg) in mice reduced by more than 90% cholera toxin–induced fluid secretion in the small intestine over 6 hours. Thiazolidinone CFTR inhibitors may be useful in developing large-animal models of cystic fibrosis and in reducing intestinal fluid loss in cholera and other secretory diarrheas.

Thiazolidinone CFTR inhibitor identified by high-throughput screening blocks cholera toxin-induced intestinal fluid secretion.

Secretory diarrhea is the leading cause of infant death in developing countries and a major cause of morbidity in adults. The cystic fibrosis transmembrane conductance regulator (CFTR) protein is required for fluid secretion in the intestine and airways and, when defective, causes the lethal genetic disease cystic fibrosis. We screened 50,000 chemically diverse compounds for inhibition of cAMP/flavone-stimulated Cl(-) transport in epithelial cells expressing CFTR. Six CFTR inhibitors of the 2-thioxo-4-thiazolidinone chemical class were identified. The most potent compound discovered by screening of structural analogs, CFTR(inh)-172, reversibly inhibited CFTR short-circuit current in less than 2 minutes in a voltage-independent manner with K(I) approximately 300 nM. CFTR(inh)-172 was nontoxic at high concentrations in cell culture and mouse models. At concentrations fully inhibiting CFTR, CFTR(inh)-172 did not prevent elevation of cellular cAMP or inhibit non-CFTR Cl(-) channels, multidrug resistance protein-1 (MDR-1), ATP-sensitive K(+) channels, or a series of other transporters. A single intraperitoneal injection of CFTR(inh)-172 (250 micro g/kg) in mice reduced by more than 90% cholera toxin-induced fluid secretion in the small intestine over 6 hours. Thiazolidinone CFTR inhibitors may be useful in developing large-animal models of cystic fibrosis and in reducing intestinal fluid loss in cholera and other secretory diarrheas.

The role of TNF-alpha in cholera toxin induced fluid secretion in the rat jejunum

The role of TNF-alpha in cholera toxin induced fluid secretion in the rat jejunum

The role of TNF-alpha in cholera toxin induced fluid secretion in the rat jejunum

The role of TNF-alpha in cholera toxin induced fluid secretion in the rat jejunum

Effect of cholera toxin on passive transepithelial transport of 51Cr-ethylenediaminetetraacetic acid and 14C-mannitol in rat jejunum.

Intestinal fluid secretion, mainly derived from the crypts, induced, for example, by cholera toxin, decreases the passive transport of small hydrophilic molecules into the lumen. However, the effect of the fluid secretion on the passive absorption of these substances and thus on the permeability of the villus absorptive area is not known. Therefore, the transport rates of 51Cr-ethylenediaminetetraacetic acid (EDTA) and 14C-mannitol from lumen to plasma and from plasma to lumen were recorded in jejunal loops of anaesthetized rats during cholera toxin-induced fluid secretion in the absence and presence of glucose in the intestinal lumen and expressed as clearance (microL (min g)(-1)). The results showed that the cholera toxin induced fluid secretion and abolished the passive absorption of 51Cr-EDTA both in the absence and presence of luminal glucose during a high perfusion rate (0.5 mL min(-1)). The clearance of mannitol was also inhibited at the low perfusion rate (0.2 mL min-1) with the glucose-free perfusate but only reduced with the glucose perfusate. The results show that mechanisms activated by cholera toxin inhibit the passive absorption of inert hydrophilic substances. This is proposed to be mainly caused by a reduction in the accessibility of the villus epithelium to the luminal content. Furthermore, the secretion seems predominantly to inhibit the passive absorption at the basal parts of the villus while the absorption rate at the villus tips is better preserved. The results also show that the intestinal absorption and secretion of fluid takes place at different locations (villus and crypts, respectively).

Mechanisms of Cholera Toxin‐Induced Diarrhea

In the pathogenesis of cholera, cyclic adenosine monophosphate, 5-hydroxytryptamine, prostaglandins, and the function of neuronal structures have been implicated. To elucidate the role of different isoforms of cyclooxygenase (COX)-1 and COX-2, selective COX-2 inhibitors were used. The selective COX-2 inhibitors NS-398 and DFU completely suppressed cholera toxin-induced prostaglandin E2 biosynthesis and caused a dose-dependent inhibition of cholera toxin-induced fluid secretion in the rat jejunum in vivo. Constitutive expression of COX-1 but also of COX-2 mRNA was found in mucosal scrapings of the rat jejunum. Cholera toxin had no effect on COX-1 as well as COX-2 mRNA expression. Treatment of rats with dexamethasone did not effect cholera toxin-induced prostaglandin E2 biosynthesis and did not influence the expression of COX-2 mRNA, further substantiating that cholera toxin does not cause an induction of COX-2 mRNA. Treatment of rats with E. coli lipopolysaccharide caused a marked increase in COX-2 mRNA expression that was inhibited by dexamethasone. In conclusion, the results provide evidence that cholera toxin, in addition to other mediators, uses prostaglandin E2 to exert its secretory effect and that in the case of cholera toxin prostaglandins are metabolized via COX-2.

The inhibition of cholera toxin-induced 5-HT release by the 5-HT(3) receptor antagonist, granisetron, in the rat.

1. The secretagogue 5-hydroxytryptamine (5-HT) is implicated in the pathophysiology of cholera. 5-HT released from enterochromaffin cells after cholera toxin exposure is thought to activate non-neuronally (5-HT(2) dependent) and neuronally (5-HT(3) dependent) mediated water and electrolyte secretion. CT-secretion can be reduced by preventing the release of 5-HT. Enterochromaffin cells possess numerous receptors that, under basal conditions, modulate 5-HT release. 2. These include basolateral 5-HT(3) receptors, the activation of which is known to enhance 5-HT release. 3. Until now, 5-HT(3) receptor antagonists (e.g. granisetron) have been thought to inhibit cholera toxin-induced fluid secretion by blockading 5-HT(3) receptors on secretory enteric neurones. Instead we postulated that they act by inhibiting cholera toxin-induced enterochromaffin cell degranulation. 4. Isolated intestinal segments in anaesthetized male Wistar rats, pre-treated with granisetron 75 microg kg(-1), lidoocaine 6 mg kg(-1) or saline, were instilled with a supramaximal dose of cholera toxin or saline. Net fluid movement was determined by small intestinal perfusion or gravimetry and small intestinal and luminal fluid 5-HT levels were determined by HPLC with fluorimetric detection. 5. Intraluminal 5-HT release was proportional to the reduction in tissue 5-HT levels and to the onset of water and electrolyte secretion, suggesting that luminal 5-HT levels reflect enterochromaffin cell activity. 6. Both lidocaine and granisetron inhibited fluid secretion. However, granisetron alone, and proportionately, reduced 5-HT release. 7. The simultaneous inhibition of 5-HT release and fluid secretion by granisetron suggests that 5-HT release from enterochromaffin cells is potentiated by endogenous 5-HT(3) receptors. The accentuated 5-HT release promotes cholera toxin-induced fluid secretion.

A novel plant-derived inhibitor of cAMP-mediated fluid and chloride secretion.

We have identified an agent (SP-303) that shows efficacy against in vivo cholera toxin-induced fluid secretion and in vitro cAMP-mediated Cl- secretion. Administration of cholera toxin to adult mice results in an increase in fluid accumulation (FA) in the small intestine (FA ratio = 0.63 vs. 1.86 in control vs. cholera toxin-treated animals, respectively). This elevation in FA induced by cholera toxin was significantly reduced (FA ratio = 0.70) in animals treated with a 100 mg/kg dose of SP-303 at the same time as the cholera treatment. Moreover, when SP-303 was administered 3 h after cholera toxin, a dose-dependent inhibition of FA levels was observed with a half-maximal inhibitory dose of 10 mg/kg. In Ussing chamber studies of Caco-2 or T84 monolayer preparations, SP-303 had a significant effect on both basal current and forskolin-stimulated Cl- current. SP-303 also induced an increase in resistance that paralleled the observed decrease in current. These data suggest that SP-303 has an inhibitory effect on cAMP-mediated Cl- and fluid secretion. Thus SP-303 may prove to be a useful broad-spectrum antidiarrheal agent.

Effects of Hange-shashin-to on cholera toxin-induced fluid secretion in the small intestine of rats.

The effects of Hange-shashin-to (TJ-14) on cholera toxin-induced intestinal fluid secretion were studied to elucidate the mechanism by which this kampo medicine manifests antidiarrheal effects. TJ-14 suppressed the intestinal fluid secretion induced by cholera toxin (1 microg/rat) in a dose-dependent manner at doses between 125 and 1000 mg/kg. It also inhibited the luminal prostaglandin E2 (PGE2) level. On the other hand, serotonin (5-HT) release was not affected by TJ-14. Subcutaneous injection of indomethacin at 10 mg/kg or ondansetron at 100 microg/kg significantly suppressed intestinal secretion. The luminal PGE2 level was also inhibited by indomethacin (10 mg/kg, s.c.). TJ-14, even at 10(-4) g/ml, had little effect on the phasic contraction of isolated guinea pig ileum induced by 5-HT (2 x 10(-6) g/ml), while ondansetron suppressed the phasic contraction caused by 5-HT. These results indicate that TJ-14 is useful in suppressing cholera toxin-stimulated intestinal fluid secretion, and that this effect is partially due to its suppressive action on the PGE2 level.

Identification of an active site in the antisecretory factor protein

The antisecretory factor (AF) is a new regulatory protein, produced in the human pituitary gland, which reverses intestinal fluid secretion induced by cholera toxin. We have previously described the cDNA-cloning and characterization of the expressed gene. The aim of this study was to identify the region responsible for the antisecretory activity in the AF-molecule. The recombinant full-length AF has an increased ability to inhibit hypersecretion after treatment with trypsin, indicating that the activity of AF is achieved by smaller peptide fragments. To localize the active region of AF, we expressed truncated forms of the recombinant protein and examined their antisecretory activity against cholera toxin-induced fluid secretion in rat. Nine recombinant AF peptides and four smaller peptides made by solid phase synthesis were tested. Five of the peptides lacked all activity, whereas seven of them were highly active, a dose between 4 and 15 pmol causing a half-maximal inhibition. All the active peptides contained amino acid 36–42 of the AF sequence, whereas none of the inactive peptides contained this sequence. Our results suggest that the site of the antisecretory activity resides in a small region (I)VCHSKTR between position 35 and 42 of the AF molecule.

Treating diarrhoea: what might the pituitary offer?

See article on page 642 Administration of cholera toxin to an animal can protect it against subsequent administration of the toxin or viable Vibrio cholerae . This protection is usually...

Effect of ganglionic blocking compounds on in-vivo fluid secretion in the rat small intestine.

It is well-known that enteric, secreto-motor nerves mediate cholera toxin-induced fluid secretion in the rat small intestine. This notion is, in part, derived from experiments on anaesthetized animals in which the response to cholera toxin was antagonized by the ganglionic nicotinic receptor antagonist, hexamethonium. In the current study, such anti-secretory action of ganglionic blocking compounds was analysed in an experiment designed to minimize any possible negative effect of general anaesthesia on intestinal secretion. Rats were anaesthetized with ether for 5-10 min, during which time a jejunal loop (10-12 cm) was constructed. The loop was challenged with one of the secretagogues, cholera toxin, prostaglandin E1 (PGE1) or okadaic acid. Saline (control) or either of the ganglionic blockers, hexamethonium and chlorisondamine, was administered intravenously. The rats were killed 5 h (cholera toxin) or 1.5 h (PGE1 and okadaic acid) after challenge, and the amount of fluid accumulated in the loops was determined. Cholera toxin-induced secretion was unchanged by hexamethonium but reduced by approximately 80% by chlorisondamine. The difference in effect between the two blockers might relate to the duration of ganglionic blockade. Chlorisondamine blocked secretion induced by either PGE1 or okadaic acid by approximately 60%. It is suggested that the anti-secretory effect of ganglionic blocking compounds might be a result of blockade of secreto-motor nerves but other mechanisms, for example interference with haemodynamic factors, cannot be ruled out.

Nitric oxide counteracts 5-hydroxytryptamine- and cholera toxin-induced fluid secretion and enhances the effect of oral rehydration solution

The effects of pharmacological modulation of the nitric oxide (NO) pathway on intestinal fluid transport were studied in a model of ligated jejunal loops of anaesthetized rats in vivo. Close intraarterial infusion of 5-hydroxytryptamine (5-HT) (0.16 μg/min) induced net fluid secretion. Intravenous infusion of the NO synthase inhibitor N ω-nitro- l-arginine methyl ester ( l-NAME) (0.55 mg/kg per min) reversed net fluid absorption in controls to net secretion and significantly enhanced 5-HT-induced fluid secretion. 5-HT-induced net fluid secretion was inhibited by intravenous infusion of l-arginine (8.88 mg/kg per min), sodium nitroprusside (22.2 μg/kg per min), or 3-morpholino sydnonimine (SIN-1) (22.2 μg/kg per min). Intraluminal instillation of cholera toxin (0.5 μg/ml) induced net secretion, which was significantly enhanced by l-NAME and reduced by l-arginine. Another series of experiments was performed using a model of luminally perfused jejunal loops. Cholera toxin (10 μg/ml) induced profuse net fluid secretion also in this model. l-Arginine and sodium nitroprusside significantly enhanced net fluid absorption compared to controls and abolished the secretory effect of cholera toxin. Luminal perfusion with oral rehydration solution enhanced net absorption of fluid in controls and reversed cholera toxin-induced secretion to absorption. Intravenous infusion, but not intraluminal administration, of l-arginine significantly enhanced the antisecretory effect of oral rehydration solution. These results give further support to the existence of an intestinal NO-mediated proabsorptive tone, which also downregulates fluid secretion elicited by different enterotoxins or mediators of secretion. Intravenous administration of exogenous sources of NO counteracts intestinal fluid accumulation and augments the antisecretory effect of oral rehydration solution, findings which may lead to therapeutic consequences.

Molecular Cloning and Expression of a Pituitary Gland Protein Modulating Intestinal Fluid Secretion

Antisecretory factor (AF) is a protein known to inhibit intestinal fluid secretion induced by cholera toxin. cDNA clones, expressing immunoreactivity to AF were isolated from a human pituitary gland library and sequenced. The sequence contained 1309 base pairs plus a poly(A) tail; Northern blot analysis of pituitary RNA confirmed this size. One large open reading frame was found to code for 382 amino acids. The protein was expressed in pGEX-lambda 1T/Escherichia coli and purified. The recombinant AF was extremely potent, 9 ng (2.10(-13) mol), giving a significant antisecretory activity against cholera toxin-induced fluid secretion in rat. Antiserum against recombinant AF was used in immunohistochemical and Western blot analysis. Sections from human pituitary glands manifested specific intracellular staining in cells exclusively located in the anterior part. Both recombinant AF and AF extracted from pituitary gland appeared in SDS-polyacrylamide to have a molecular mass of 60 kDa, although the renal value was 41 kDa. The protein sequence manifested homology (29% identity) with one protein, a putative Saccharomyces cerevisiae 30-kDa protein of unknown function.