Duodenal Secretion Research Articles

Abstract IA019: Clinical trials of GUCY2C (GCC) agonists for colorectal cancer prevention

Abstract Guanylyl cyclase C (GUCY2C), expressed on intestinal epithelial cells, is the receptor for heat-stable enterotoxins (STs) produced by diarrheagenic bacteria. Fluid secretion reflects ST activation of GUCY2C, which produces cyclic (c)GMP activating ion channels. Beyond toxins, GUCY2C binds uroguanylin in small intestine and guanylin in colorectum, which also stimulate secretion. This mechanism is the basis for the oral agonists linaclotide (ST analog) and plecanatide (uroguanylin analog) to treat constipation. Guanylin is the most commonly lost gene product, while GUCY2C expression is retained, in colorectal tumors. Eliminating GUCY2C promotes tumor formation, while oral GUCY2C agonists or transgenic guanylin reduce intestinal tumors, in mice. These data support a hypothesis in which loss of guanylin silencing GUCY2C is a key step in intestinal transformation which can be prevented by oral GUCY2C agonists. However, GUCY2C agonists are formulated for duodenal activity, without bioavailability in the colorectum. Here, we explored whether this pharmacokinetic (PK) barrier could be abrogated with high doses (HD) of linaclotide. Indeed, HD linaclotide induced a cGMP response in mucosal biopsies obtained by colonoscopy following oral polyethylene glycol (PEG) preparation. This cGMP response was validated by VASP phosphorylation and suppression of crypt proliferation. Similarly, HD linaclotide induced cGMP in colon biopsies obtained by sigmoidoscopy following oral PEG. However, HD linaclotide failed to induce cGMP in colon biopsies obtained by sigmoidoscopy i n the absence of oral PEG . Thus, oral PEG abrogated the PK barrier, delivering linaclotide to the colorectum. Unfortunately, dolcanatide, a proteolysis-resistant analog of plecanatide, also failed to overcome the colorectal PK barrier, although it produced duodenal secretion and diarrhea. Thus, guanylin loss silencing GUCY2C appears to be a key step in intestinal transformation. Preclinical models suggest that oral GUCY2C agonists stimulate GUCY2C signaling, opposing tumorigenesis. However, translation of these observations appears to be constrained by a PK barrier, reflecting agonists formulated for duodenal activity, without colorectal bioavailability. Exploiting GUCY2C for chemoprevention awaits agonists formulated for the colorectum. We are exploring the ability of GUCY2C agonists to activate cGMP in duodenum (within the PK barrier), as a prelude to trials in patients with FAP at risk for duodenal tumors. Citation Format: Scott A. Waldman. Clinical trials of GUCY2C (GCC) agonists for colorectal cancer prevention [abstract]. In: Proceedings of the Second Biennial NCI Meeting: Translational Advances in Cancer Prevention Agent Development (TACPAD); 2022 Sep 7-9. Philadelphia (PA): AACR; Can Prev Res 2022;15(12 Suppl_2): Abstract nr IA019.

Influence of the water of the Izhevsk mineral spring on duodenal secretion

By now, a wealth of practical experience has been accumulated on the positive results of the action of Izhevsk mineral water in diseases of the gastrointestinal tract and liver, as evidenced by numerous reviews of professors-clinicians and practical doctors. However, observing in the sanatorium of the Izhevsk mineral spring patients suffering from decreased secretion and achilia of the stomach, catarrhal state of the biliary tract of the liver, one has to be surprised at the rapidly advancing positive results that are obtained after a month of treatment with water. Belching, heartburn, nausea, vomiting and diarrhea in patients with subacid catarrhs ​​and stomach achilia disappear amazingly quickly, liver soreness disappears in inflammatory processes of the biliary tract, food digestibility and weight gain increase. Research and observation by prof. BA Voltaire, Dr. Vilensky and Lande of gastric secretions during treatment with Izhevsk water show that St. HC1 and total acidity with subacid catarrh increases relatively little, while with complete organic achilia of St. HC1 did not appear at all or appeared in the form of traces, meanwhile, pronounced dyspeptic phenomena almost completely disappear ?, therefore, naturally, we had to assume that there were changes in the secretion of the pancreas and liver, and that their secretion increased under the influence of treatment with Izhevsk water. From this side, the water of the Izhevsk mineral spring has not yet been studied by anyone.

Reduced acetylcholine and elevated muscarinic receptor 2 in duodenal mucosa contribute to the impairment of mucus secretion in 6-hydroxydopamine-induced Parkinson's disease rats.

Patients with Parkinson's disease (PD) have a higher incidence rate of duodenal ulcers. The mucus barrier provides the first line of defense for duodenal mucosal protection. However, it is unknown whether duodenal mucus secretion is affected in PD. In the present study, we used the rats microinjected 6-hydroxydopamine (6-OHDA) into the bilateral substantia nigra to investigate duodenal mucus secretion and potential therapeutic targets in duodenal ulcer in PD. Alcian blue-periodic acid-Schiff, transmission electron microscopy, immunofluorescence, duodenal mucosal incubation, and enzyme-linked immunosorbent assays were used. The 6-OHDA rats exhibited mucin accumulation and retention in duodenal goblet cells. Mucin granules were unable to fuse with the apical membranes of goblet cells, and the exocytosis ratio of goblet cells was significantly reduced. Moreover, decreased acetylcholine and increased muscarinic receptor 2 (M2R) levels were detected in the duodenal mucosa of 6-OHDA rats. Bilateral vagotomy rats were also characterized by defective duodenal mucus secretion and decreased acetylcholine with increased M2R levels in the duodenal mucosa. Application of the cholinomimetic drug carbachol or blocking M2R with methoctramine significantly promoted mucus secretion by goblet cells and increased MUC2 content in duodenal mucosa-incubated solutions from 6-OHDA and vagotomy rats. We conclude that the reduced acetylcholine and increased M2R contribute to the impaired duodenal mucus secretion of 6-OHDA rats. The study provides new insights into the mechanism of duodenal mucus secretion and potential therapeutic targets for the treatment of duodenal ulcers in PD patients.

Role of Serosal TRPV4-Constituted SOCE Mechanism in Secretagogues-Stimulated Intestinal Epithelial Anion Secretion.

As little is known about the role of calcium (Ca2+) signaling mediating the small intestinal epithelial anion secretion, we aimed to study its regulatory role in secretagogue-stimulated duodenal anion secretion and the underlying molecular mechanisms. Therefore, intestinal anion secretion from native mouse duodenal epithelia was examined with Ussing chambers to monitor PGE2-, 5-HT-, and CCh-induced short-circuit currents (I sc). PGE2 (10 μM) and 5-HT (10 μM) induced mouse duodenal I sc, markedly attenuated by serosal Ca2+-free solution and selective blockers of store-operated Ca2+ channels on the serosal side of the duodenum. Furthermore, PGE2- and 5-HT-induced duodenal I sc was also inhibited by ER Ca2+ chelator TPEN. However, dantrolene, a selective blocker of ryanodine receptors, inhibited PGE2-induced duodenal I sc, while LiCl, an inhibitor of IP3 production, inhibited 5-HT-induced I sc. Moreover, duodenal I sc response to the serosal applications of both PGE2 and 5-HT was significantly attenuated in transient receptor potential vanilloid 4 (TRPV4) knockout mice. Finally, mucosal application of carbachol (100 μM) also induced duodenal I sc via selective activation of muscarinic receptors, which was significantly inhibited in serosal Ca2+-free solution but neither in mucosal Ca2+-free solution nor by nifedipine. Therefore, the serosal TRPV4-constituted SOCE mechanism is likely universal for the most common and important secretagogues-induced and Ca2+-dependent intestinal anion secretion. These findings will enhance our knowledge about gastrointestinal (G.I.) epithelial physiology and the associated G.I. diseases, such as diarrhea and constipation.

Pancreatic atrophy and exocrine insufficiency associate with the presence of diabetes in chronic pancreatitis patients, but additional mediators are operative

Objectives Diabetes mellitus is a frequent complication of chronic pancreatitis (CP) and has traditionally been considered to develop as a consequence of pancreatic islet cell loss. However, additional mechanisms may be operative including accumulation of pancreatic fat and fibrosis. We used advanced magnetic resonance imaging (MRI) to study pancreatic morphology and exocrine function in a reference population and in CP patients with and without diabetes. Methods This was a cross-sectional mono centre study. All subjects underwent advanced MRI including assessment of pancreatic ductal parameters (Cambridge classification and main pancreatic duct diameter), parenchymal parameters (DIXON technique and diffusion weighted imaging as proxies for pancreatic fat content and fibrosis, as well as pancreatic volume segmentation). Pancreatic exocrine function was determined as duodenal secretion following secretin stimulation and by the faecal elastase test. Results The study included 76 patients with definite CP of whom 23 (30.1%) had diabetes and 23 sex- and age matched healthy volunteers. Compared to their non-diabetic counterparts, diabetic patients were characterised by a low pancreatic volume (20 vs. 36 ml; p = .02) and impaired pancreatic exocrine function (faecal elastase 19 vs. 48 µg/g; p = .008), while no difference between patients with and without diabetes were seen in relation to MRI derived proxies for fibrosis and pancreatic fat accumulation and pancreatic duct parameters. A large proportion of non-diabetic patients (49%) had similar morphological and functional characteristics as patients with diabetes. Conclusion Pancreatic atrophy and exocrine insufficiency are present in most CP patients with diabetes, but additional mediators seem to be operative in post pancreatitis diabetes mellitus.

Thyrotropin releasing hormone (TRH) in the brainstem: Role of Pavlov’s vagally mediated cephalic phase of gastric secretion

Pavlov’s seminal observation that sham feeding in dogs stimulates gastric acid secretion through the vagus nerve pioneered the concept of the cephalic phase of digestion. This has been subsequently extended to a wide range of mammals including humans. In the last decades, experimental evidence in rats established that the three amino acid peptide thyrotropinreleasing hormone (TRH) expressed in the brainstem plays a key role in the vagal stimulation of digestive secretory-motor function. The dorsal motor nucleus of the vagus (DMN) neurons expresses TRH receptor subtype 1 (TRH-R1) and receives input of TRH containing fibers arising from TRH synthesizing neurons in medullary raphe nuclei. The activation of TRHTRH-R1 signaling excites the firing of DMN neurons leading to the activation of vagal efferent discharges and gastric myenteric cholinergic neurons. This results in a vagally mediated and atropine-sensitive stimulation of gastric secretory and propulsive motor function, along with duodenal and pancreatic secretion. Importantly, the blockade of TRH or TRH-R1 in the brainstem inhibits the gastric acid response to sham feeding in rats. Collectively, these convergent data support the physiological relevance of medullary TRHTRH-R1 signaling as the end effector of the vagally mediated stimulation of digestive process in the cephalic phase.

Xenin-25 induces anion secretion by activating noncholinergic secretomotor neurons in the rat ileum.

Xenin-25 is a neurotensin-like peptide that is secreted by enteroendocrine cells in the small intestine. Xenin-8 is reported to augment duodenal anion secretion by activating afferent neural pathways. The intrinsic neuronal circuits mediating the xenin-25-induced anion secretion were characterized using the Ussing-chambered, mucosa-submucosa preparation from the rat ileum. Serosal application of xenin-25 increased the short-circuit current in a concentration-dependent manner. The responses were abolished by the combination of Cl--free and -free solutions. The responses were almost completely blocked by TTX (10-6 M) but not by atropine (10-5 M) or hexamethonium (10-4 M). The selective antagonists for neurotensin receptor 1 (NTSR1), neurokinin 1 (NK1), vasoactive intestinal polypeptide (VIP) receptors 1 and 2 (VPAC1 and VPAC2, respectively), and capsaicin, but not 5-hydroxyltryptamine receptors 3 and 4 (5-HT3 and 5-HT4), NTSR2, and A803467, inhibited the responses to xenin-25. The expression of VIP receptors (Vipr) in rat ileum was examined using RT-PCR. The Vipr1 PCR products were detected in the submucosal plexus and mucosa. Immunohistochemical staining showed the colocalization of NTSR1 and NK1 with substance P (SP)- and calbindin-immunoreactive neurons in the submucosal plexus, respectively. In addition, NK1 was colocalized with noncholinergic VIP secretomotor neurons. Based on the results from the present study, xenin-25-induced Cl-/ secretion is involved in NTSR1 activation on intrinsic and extrinsic afferent neurons, followed by the release of SP and subsequent activation of NK1 expressed on noncholinergic VIP secretomotor neurons. Finally, the secreted VIP may activate VPAC1 on epithelial cells to induce Cl-/ secretion in the rat ileum. Activation of noncholinergic VIP secretomotor neurons by intrinsic primary afferent neurons and extrinsic afferent neurons by postprandially released xenin-25 may account for most of the neurogenic secretory response induced by xenin-25. NEW & NOTEWORTHY This study is the first to investigate the intrinsic neuronal circuit responsible for xenin-25-induced anion secretion in the rat small intestine. We have found that nutrient-stimulated xenin-25 release may activate noncholinergic vasoactive intestinal polypeptide (VIP) secretomotor neurons to promote Cl-/ secretion through the activation of VIP receptor 1 on epithelial cells. Moreover, the xenin-25-induced secretory responses are mainly linked with intrinsic primary afferent neurons, which are involved in the activation of neurotensin receptor 1 and neurokinin 1 receptor.

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

Although ClC-2 channels are important in colonic Cl- secretion, it is unclear about their roles in small intestinal anion secretion. Therefore, we sought to examine whether ClC-2 channels play important roles in anion secretion, particularly duodenal bicarbonate secretion (DBS). Duodenal mucosae from mice were stripped of seromuscular layers and mounted in Ussing chambers. Both duodenal short-circuit current (Isc) and HCO3- secretion in vitro were simultaneously recorded. DBS in vivo was measured by a CO2-sensitive electrode. Lubiprostone, a selective ClC-2 activator, concentration-dependently increased both duodenal Isc and DBS only when applied basolaterally, but not when applied apically. Removal of extracellular Cl- abolished lubiprostone-induced duodenal Isc, but did not alter HCO3- secretion even in the presence of DIDS, a Cl-/HCO3- exchanger inhibitor. However, further addition of glibenclamide, a CFTR channel blocker, abolished lubiprostone-evoked HCO3- secretion. Moreover, lubiprostone-induced HCO3- secretion was impaired in CFTR-/- mice compared to wild-type littermates. Luminal perfusion of duodenal lumen with lubiprostone did not alter basal DBS in vivo, but lubiprostone (i.p.) was able to induce DBS, which was also significantly inhibited by Cd2+, a ClC-2 channel blocker. [Ca2+]cyt level, Ca2+-activated K+ channel- and cAMP-mediated duodenal Isc, and HCO3- secretion were unchanged by lubiprostone. We have provided the first evidence for the novel functional role of basolateral ClC-2 channels in the regulation of duodenal anion secretion.

Proteolytic Degradation of reduced Human Beta Defensin 1 generates a Novel Antibiotic Octapeptide

Microbial resistance against clinical used antibiotics is on the rise. Accordingly, there is a high demand for new innovative antimicrobial strategies. The host-defense peptide human beta-defensin 1 (hBD-1) is produced continuously by epithelial cells and exhibits compelling antimicrobial activity after reduction of its disulphide bridges. Here we report that proteolysis of reduced hBD-1 by gastrointestinal proteases as well as human duodenal secretions produces an eight-amino acid carboxy-terminal fragment. The generated octapeptide retains antibiotic activity, yet with distinct characteristics differing from the full-length peptide. We modified the octapeptide by stabilizing its termini and by using non-natural D-amino acids. The native and modified peptide variants showed antibiotic activity against pathogenic as well as antibiotic-resistant microorganisms, including E. coli, P. aeruginosa and C. albicans. Moreover, in an in vitro C. albicans infection model the tested peptides demonstrated effective amelioration of C. albicans infection without showing cytotoxity on human cells. In summary, protease degradation of hBD-1 provides a yet unknown mechanism to broaden antimicrobial host defense, which could be used to develop defensin-derived therapeutic applications.

Method Performance of Bicarbonate and Electrolytes by Use of Duodenal Fluid for Assessment of Exocrine Pancreatic Function.

Evaluation of exocrine pancreatic insufficiency is challenging for both clinicians and laboratories. Indirect pancreatic function tests such as serum trypsinogen, fecal elastase, and fecal fat measurements are moderately sensitive for diagnosis of advanced chronic pancreatitis but show reduced sensitivity and specificity for diagnosis of early disease. An alternative is the endoscopic pancreatic function test, which uses duodenal secretions after administration of IV secretin. Samples are collected at various times via the endoscopic tube and then analyzed for bicarbonate, sodium, potassium, and chloride. Precision, linearity, method comparison, and stability studies were performed on the Beckman Coulter AU5822 chemistry analyzer with duodenal fluid. Comparison with the Vitros 4600 dry slide chemistry instrument was used to interrogate differences between methods. All assays produced a CV <2% without any measurable effects from the endoscopy fluid matrix and showed acceptable imprecision near the limit of detection (CV < 5%). All analytes showed linear dilution across the analytical measuring range. All the calculated error biases from dilutions were within 50% of the CLIA-allowable error for serum for each of the respective analytes. The calculated slopes ranged from 0.841 to 1.274 when compared to the Vitros 4600. Stability studies demonstrated that sodium, potassium, chloride, and bicarbonate remained stable after storage at -20 °C and after multiple freeze-thaw cycles. The percent change for all analytes was <5% mmol/L. The AU5800 series demonstrated adequate performance for the analysis of bicarbonate in duodenal fluid and therefore can be used for assessment of exocrine pancreatic function. However, notable discrepancies were observed for sodium, potassium, and chloride between the AU5800 series and the Vitros 4600.

Comparative Evaluation of Gastroduodenostomy and Gastrojejunostomy for Stomach Reconstruction Following Partial Gastrectomy in Dogs

The present experimental study was aimed to perform partial gastrectomy through surgical excision the distal part of the stomach in dogs (approximately 1/5 stomach size), and then performing two types of reconstruction techniques: Gastroduodenostomy (Billroth I) and Gastrojejunostomy (Billroth II). The current experimental study was carried out on 10 apparently healthy mongrel dogs (7 males and 3 non-pregnant females), aging (8 months to 2 years old) and weighing (12 to 30 kg). Two types of surgical technique were used: A. Billroth I (Gastroduodenostomy): Partial gastroectomy with gastroduodenal anastomosis (5 dogs were used) B. Billroth II (Gastrojejunostomy): Partial gastroectomy with gastrojejunal anastomosis (5 dogs were used). All dogs recovered from anesthesia with no complications during the surgery and recovery. There was no evidence of wound infection. Dogs started to eat on Day 3 after surgery without any sign of regurgitation. No serious postoperative complications were observed. There were no signs of premature vasomotor disturbances, such as dizziness, weakness and alimentary disorders. One month after surgery radiographic findings cleared that there was neither stricture, narrowing, obstruction nor leakage at site of anastomosis in both groups. On conclusion; Both Billroth I and Billroth II might be considered as suitable approaches for reconstructing gastro-intestinal tract following partial gastrectomy in dogs with no particular difference in clinical and para-clinical parameters in dogs. Billroth I doesn’t change the normal anatomy and function of the digestive system as performed anastomosis of the stomach stump to the duodenum, it’s conductive to the digestion of food falling from the stomach into the intestine mixing with pancreatic, duodenal and biliary secretion while in Billroth II mixing process occurs in the jejunum. The time consumed during Billroth II operation was higher than Billroth I also the risk adjusted complication rate was also higher in Billroth II group. Billroth I method should be the first choice after a distal gastrectomy as long as the anatomic and oncological environment allows us to perform it.

Molecular mechanisms of calcium signaling in the modulation of small intestinal ion transports and bicarbonate secretion.

Background and Purpose: Although Ca2+ signaling may stimulate small intestinal ion secretion, little is known about its critical role and the molecular mechanisms of Ca2+-mediated biological action.Key ResultsActivation of muscarinic receptors by carbachol(CCh) stimulated mouse duodenal Isc, which was significantly inhibited in Ca2+-free serosal solution and by several selective store-operated Ca2+ channels(SOC) blockers added to the serosal side of duodenal tissues. Furthermore, we found that CRAC/Orai channels may represent the molecular candidate of SOC in intestinal epithelium. CCh increased intracellular Ca2+ but not cAMP, and Ca2+ signaling mediated duodenal Cl- and HCO3- secretion in wild type mice but not in CFTR knockout mice. CCh induced duodenal ion secretion and stimulated PI3K/Akt activity in duodenal epithelium, all of which were inhibited by selective PI3K inhibitors with different structures. CCh-induced Ca2+ signaling also stimulated the phosphorylation of CFTR proteins and their trafficking to the plasma membrane of duodenal epithelial cells, which were inhibited again by selective PI3K inhibitors.Materials and MethodsFunctional, biochemical and morphological experiments were performed to examine ion secretion, PI3K/Akt and CFTR activity of mouse duodenal epithelium. Ca2+ imaging was performed on HT-29 cells.Conclusions and ImplicationsCa2+ signaling plays a critical role in intestinal ion secretion via CRAC/Orai-mediated SOCE mechanism on the serosal side of epithelium. We also demonstrated the molecular mechanisms of Ca2+ signaling in CFTR-mediated secretion via novel PI3K/Akt pathway. Our findings suggest new perspectives for drug targets to protect the upper GI tract and control liquid homeostasis in the small intestine.

Can we better predict the biologic behavior of incidental IPMN? A comprehensive analysis of molecular diagnostics and biomarkers in intraductal papillary mucinous neoplasms of the pancreas.

Predicting the biologic behavior of intraductal papillary mucinous neoplasm (IPMN) remains challenging. Current guidelines utilize patient symptoms and imaging characteristics to determine appropriate surgical candidates. However, the majority of resected cysts remain low-risk lesions, many of which may be feasible to have under surveillance. We herein characterize the most promising and up-to-date molecular diagnostics in order to identify optimal components of a molecular signature to distinguish levels of IPMN dysplasia. A comprehensive systematic review of pertinent literature, including our own experience, was conducted based on the PRISMA guidelines. Molecular diagnostics in IPMN patient tissue, duodenal secretions, cyst fluid, saliva, and serum were evaluated and organized into the following categories: oncogenes, tumor suppressor genes, glycoproteins, markers of the immune response, proteomics, DNA/RNA mutations, and next-generation sequencing/microRNA. Specific targets in each of these categories, and in aggregate, were identified by their ability to both characterize a cyst as an IPMN and determine the level of cyst dysplasia. Combining molecular signatures with clinical and imaging features in this era of next-generation sequencing and advanced computational analysis will enable enhanced sensitivity and specificity of current models to predict the biologic behavior of IPMN.

Luminal chemosensing in the gastroduodenal mucosa.

We report recently published knowledge regarding gut chemosensory mechanisms focusing on nutrient-sensing G protein-coupled receptors (GPCRs) expressed on gut enteroendocrine cells (EECs), tuft cells, and in afferent nerves in the gastroduodenal mucosa and submucosa. Gene profiling of EECs and tuft cells have revealed expression of a variety of nutrient-sensing GPCRs. The density of EEC and tuft cells is altered by luminal environmental changes that may occur following bypass surgery or in the presence of mucosal inflammation. Some EECs and tuft cells are directly linked to sensory nerves in the subepithelial space. Vagal afferent neurons that innervate the intestinal villi express nutrient receptors, contributing to the regulation of duodenal anion secretion in response to luminal nutrients. Nutrients are also absorbed via specific epithelial transporters. Gastric and duodenal epithelial cells are continually exposed to submolar concentrations of nutrients that activate GPCRs expressed on EECs, tuft cells, and submucosal afferent nerves and are also absorbed through specific transporters, regulating epithelial cell proliferation, gastrointestinal physiological function, and metabolism. The chemical coding and distribution of EECs and tuft cells are keys to the development of GPCR-targeted therapies.

Ubiquitously expressed Human Beta Defensin 1 (hBD1) forms bacteria-entrapping nets in a redox dependent mode of action.

Ever since the discovery of endogenous host defense antimicrobial peptides it has been discussed how these evolutionary conserved molecules avoid to induce resistance and to remain effective. Human ß-defensin 1 (hBD1) is an ubiquitously expressed endogenous antimicrobial peptide that exhibits qualitatively distinct activities between its oxidized and reduced forms. Here, we explore these antimicrobial mechanisms. Surprisingly, using electron microscopy we detected a so far unknown net-like structure surrounding bacteria, which were treated with the reduced but not the oxidized form of hBD1. A transmigration assay demonstrated that hBD1-derived nets capture bacteria and inhibit bacterial transmigration independent of bacterial killing. The presence of nets could completely prevent migration of hBD1 resistant pathogens and are stable in the presence of human duodenal secretion with a high amount of proteases. In contrast to HD6, cysteins are necessary for net formation. This redox-dependent function serves as an additional mechanism of action for hBD1 and differs from net formation by other defensins such as Paneth cell-derived human α-defensin 6 (HD6). While hBD1red and hBD1ox have distinct antimicrobial profiles and functions, only the reduced form provides additional host protection by entrapping bacteria in extracellular net structures preventing bacterial invasion. Better understanding of the modes of action of endogenous host peptides will help to find new antimicrobial strategies.

Constipation-Predominant Irritable Bowel Syndrome Females Have Normal Colonic Barrier and Secretory Function.

The objective of this study was to determine whether constipation-predominant irritable bowel syndrome (IBS-C) is associated with changes in intestinal barrier and secretory function. A total of 19 IBS-C patients and 18 healthy volunteers (all females) underwent saccharide excretion assay (0.1 g 13C mannitol and 1 g lactulose), measurements of duodenal and colonic mucosal barrier (transmucosal resistance (TMR), macromolecular and Escherichia coli Bio-Particle translocation), mucosal secretion (basal and acetylcholine (Ach)-evoked short-circuit current (Isc)), in vivo duodenal mucosal impedance, circulating endotoxins, and colonic tight junction gene expression. There were no differences in the in vivo measurements of barrier function between IBS-C patients and healthy controls: cumulative excretion of 13C mannitol (0-2 h mean (s.e.m.); IBS-C: 12.1 (0.9) mg vs. healthy: 13.2 (0.8) mg) and lactulose (8-24 h; IBS-C: 0.9 (0.5) mg vs. healthy: 0.5 (0.2) mg); duodenal impedance IBS-C: 729 (65) Ω vs. healthy: 706 (43) Ω; plasma mean endotoxin activity level IBS-C: 0.36 (0.03) vs. healthy: 0.35 (0.02); and in colonic mRNA expression of occludin, zonula occludens (ZO) 1-3, and claudins 1-12 and 14-19. The ex vivo findings were consistent, with no group differences: duodenal TMR (IBS-C: 28.2 (1.9) Ω cm2 vs. healthy: 29.8 (1.9) Ω cm2) and colonic TMR (IBS-C: 19.1 (1.1) Ω cm2 vs. healthy: 17.6 (1.7) Ω cm2); fluorescein isothiocyanate (FITC)-dextran (4 kDa) and E. coli Bio-Particle flux. Colonic basal Isc was similar, but duodenal basal Isc was lower in IBS-C (43.5 (4.5) μA cm-2) vs. healthy (56.9 (4.9) μA cm-2), P=0.05. Ach-evoked ΔIsc was similar. Females with IBS-C have normal colonic barrier and secretory function. Basal duodenal secretion is decreased in IBS-C.

Xenin Augments Duodenal Anion Secretion via Activation of Afferent Neural Pathways.

Xenin-25, a neurotensin (NT)-related anorexigenic gut hormone generated mostly in the duodenal mucosa, is believed to increase the rate of duodenal ion secretion, because xenin-induced diarrhea is not present after Roux-en-Y gastric bypass surgery. Because the local effects of xenin on duodenal ion secretion have remained uninvestigated, we thus examined the neural pathways underlying xenin-induced duodenal anion secretion. Intravenous infusion of xenin-8, a bioactive C-terminal fragment of xenin-25, dose dependently increased the rate of duodenal HCO3- secretion in perfused duodenal loops of anesthetized rats. Xenin was immunolocalized to a subset of enteroendocrine cells in the rat duodenum. The mRNA of the xenin/NT receptor 1 (NTS1) was predominantly expressed in the enteric plexus, nodose and dorsal root ganglia, and in the lamina propria rather than in the epithelium. The serosal application of xenin-8 or xenin-25 rapidly and transiently increased short-circuit current in Ussing-chambered mucosa-submucosa preparations in a concentration-dependent manner in the duodenum and jejunum, but less so in the ileum and colon. The selective antagonist for NTS1, substance P (SP) receptor (NK1), or 5-hydroxytryptamine (5-HT)3, but not NTS2, inhibited the responses to xenin. Xenin-evoked Cl- secretion was reduced by tetrodotoxin (TTX) or capsaicin-pretreatment, and abolished by the inhibitor of TTX-resistant sodium channel Nav1.8 in combination with TTX, suggesting that peripheral xenin augments duodenal HCO3- and Cl- secretion through NTS1 activation on intrinsic and extrinsic afferent nerves, followed by release of SP and 5-HT. Afferent nerve activation by postprandial, peripherally released xenin may account for its secretory effects in the duodenum.

Effects of Helicobacter pylori Infection on the Expressions and Functional Activities of Human Duodenal Mucosal Bicarbonate Transport Proteins.

The mechanisms for Helicobacter pylori (H. pylori)-induced duodenal ulcerogenesis are not fully understood. In this study, we investigated the effects of H. pylori infection on the expressions and functional activities of human duodenal mucosal bicarbonate transport proteins and hope to further clarify the pathogenesis of H. pylori-associated duodenal ulcer. The experiments were performed in the patients with H. pylori-associated duodenal ulcers, H. pylori-associated chronic gastritis, and H. pylori-negative healthy subjects. Duodenal mucosal bicarbonate secretion was measured by Ussing Chamber technology. The expressions of duodenal mucosal bicarbonate transport proteins, CFTR (cystic fibrosis transmembrane conductance regulator) and SLC26A6 (solute-linked carrier 26 gene A6), in the patients with H. pylori-associated duodenal ulcers were markedly lower than those in healthy controls. Basal and both forskolin- and prostaglandin E2 -stimulated duodenal mucosal bicarbonate secretions in the patients with H. pylori-associated duodenal ulcers were also lower than those in healthy controls. After anti-H. pylori treatment for H. pylori-associated duodenal ulcers, duodenal mucosal bicarbonate secretion and CFTR and SLC26A6 expressions in H. pylori-eradicated patients recovered to levels comparable to healthy controls, but those were found to be not significantly altered in non-H. pylori-eradicated patients. The further results showed that decreases in the H. pylori-induced CFTR and SLC26A6 expression were related to the severity and virulent factors of H. pylori infection. H. pylori infection impairs the expressions and functional activities of duodenal mucosal bicarbonate transport proteins, CFTR and SLC26A6, which contributes to the development of duodenal ulcer.

Estudio experimental de la ulcera péptica. La acidez gástrica frente a las técnicas de la gastrectomía

La obtención experimental de úlceras pépticas similares a las humanas viene efectúandose desde el siglo pasado. Con tal finalidad se han utilizado una serie de experimentos que los podemos agrupar considerando los "factores locales" que entran en juego, (irritantes del estómago, traumatismos de la pared abdominal, exposición a los rayos X, infección, obstáculos en las funciones pilórica y duodenal y obstáculos en el sistema circulatorio), los "factores sistémicos" que actúan sobre el estómago y duodeno (quemaduras, cincofeno, inmunización, transtornos de la nutrición y alteraciones endócrinas) y su producción experimental por "métodos quirúrgicos" (gastroenterostomía y desviación de las secreciones duodenales) entre los que se consideran diferentes factores, tales como la nutrición, acidez, suceptibilidad de la mucosa, factor mecánico, traumatismo operatorio, espasmo yeyunal y acción protectora de las secreciones duodenales.

Cholecystokinin but not ghrelin stimulates mucosal bicarbonate secretion in rat duodenum: Independence of feeding status and cholinergic stimuli

Cholecystokinin (CCK) is an important regulator of food digestion but its influence on small intestinal secretion has received little attention. We characterized effects of CCK-8, ghrelin and some related peptides on duodenal HCO3− secretion in vivo and demonstrated CCK-induced calcium signaling in acutely isolated enterocytes.A segment of proximal duodenum with intact blood supply was cannulated in situ in anaesthetized rats. Mucosal HCO3− secretion was continuously recorded (pH-stat). Peptides were administrated to the duodenum by close intra-arterial infusion. Clusters of duodenal enterocytes were attached to the bottom of a perfusion chamber. The intracellular calcium concentration ([Ca2+]i) was examined by dual-wavelength imaging.CCK-8 (3.0, 15 and 60 pmol/kg,h) caused dose-dependent increases (p<0.01) in duodenal alkaline secretion in both overnight fasted and continuously fed animals. The CCK1R-antagonist devazepide but neither the CCK2R-antagonist YMM022 nor the melatonin MT2-selective antagonist luzindole inhibited the rise in secretion. Atropine decreased sensitivity to CCK-8. The appetite-related peptide ghrelin was without effect on the duodenal secretion in fasted as well as fed animals. Superfusion with CCK-8 (1.0-50 nM) induced [Ca2+]i signaling in acutely isolated duodenal enterocytes. After an initial peak response, [Ca2+]i returned to near basal values within 3–5min. Devazepide but not YMM022 inhibited this [Ca2+]i response.Low doses of CCK-8 stimulate duodenal alkaline secretion and induce enterocyte [Ca2+]i signaling by an action at CCK1 receptors. The results point to importance of CCK in the rapid postprandial rise in mucosa-protective duodenal secretion.