bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of apolipoprotein D in the transport of bilirubin in plasma
Authors: Goessling Wolfram , Zucker Stephen D.
Published: December 2017

Apolipoprotein D (apo D) is a 30-kDa glycoprotein of unknown function that is associated with high-density lipoproteins (HDL). Because unconjugated bilirubin has been shown to bind apo D with a 0.8:1 stoichiometry, we examined the contribution of this protein to transport of bilirubin in human plasma. Density gradient centrifugation analysis using physiological concentrations of [14C]bilirubin reveals that 9% of unconjugated bilirubin is associated with HDL, with the remaining pigment bound primarily to serum proteins (i.e., albumin). The percentage of total plasma bilirubin bound to HDL was found to increase proportionally with bilirubin concentration. Affinity of human apo D for bilirubin was determined by steady-state fluorescence quenching, with Scatchard analysis demonstrating a single binding site for unconjugated bilirubin with an affinity constant ( Ka) of ∼3 × 107M−1. Incorporation of apo D into phosphatidylcholine vesicles had no effect on Ka, suggesting that a lipid environment does not alter the affinity of the protein for bilirubin. Using stopped-flow techniques, the first-order rate constant for bilirubin dissociation from apo D was measured at 5.4 s−1(half-time = 129 ms). Our findings indicate that HDL is the principal nonalbumin carrier of bilirubin in human plasma and further support the proposition that the affinity of HDL for bilirubin is primarily the result of binding to apo D.
Effects of M1 and CCK antagonists on latency of pancreatic amylase response to intestinal stimulants
Authors: Niebergall-Roth Elke , Teyssen Stephan , Singer Manfred V.
Published: December 2017

In six conscious dogs with gastric and duodenal cannulas, secretin (164 pmol · kg−1· h−1iv) was given to provide a flow of pancreatic juice of ∼1 drop/s. Amylase activity was measured in each drop before and after rapid intravenous injection of caerulein (7.4 pmol/kg) or intraduodenal injection of l-tryptophan (1 mmol), sodium oleate (3 mmol), and HCl (3 mmol). All experiments were repeated in the presence of the M1 receptor antagonist telenzepine (81 nmol · kg−1· h−iv) and the cholecystokinin (CCK) receptor antagonist L-364718 (0.1 mg/kg iv). Latency of amylase response (time between injection of stimulant and sustained increase in amylase activity greater than mean + 3 SD of prestimulatory activity) to tryptophan (17 ± 7 s; n = 6) and oleate (16 ± 5 s) was significantly ( P < 0.05) shorter than to caerulein (28 ± 4 s) and HCl (120 ± 47 s). Telenzepine significantly increased the latency of amylase response to tryptophan and oleate by >10-fold but not the latency to caerulein or HCl. L-364718 abolished the amylase response to all stimulants. These findings indicate that the early amylase response to intraduodenal tryptophan and oleate is mediated by a neural enteropancreatic reflex ending on M1 receptors rather than by hormone release. However, the activation of (possibly vagal) CCK receptors is essential to run the reflex. The early amylase response to intraduodenal HCl is probably mediated by the release of CCK into the blood circulation.
ATP-dependent GSH and glutathioneS-conjugate transport in skate liver: role of an Mrp functional homologue
Authors: Rebbeor James F. , Connolly Gregory C. , Henson John H. , Boyer James L. , Ballatori Nazzareno
Published: December 2017

Multidrug resistance-associated proteins 1 and 2 (Mrp1 and Mrp2) are thought to mediate low-affinity ATP-dependent transport of reduced glutathione (GSH), but there is as yet no direct evidence for this hypothesis. The present study examined whether livers from the little skate ( Raja erinacea) express an Mrp2 homologue and whether skate liver membrane vesicles exhibit ATP-dependent GSH transport activity. Antibodies directed against mammalian Mrp2-specific epitopes labeled a 180-kDa protein band in skate liver plasma membranes and stained canaliculi by immunofluorescence, indicating that skate livers express a homologous protein. Functional assays of Mrp transport activity were carried out using3H-labeled S-dinitrophenyl-glutathione (DNP-SG). DNP-SG was accumulated in skate liver membrane vesicles by both ATP-dependent and ATP-independent mechanisms. ATP-dependent DNP-SG uptake was of relatively high affinity [Michaelis-Menten constant ( Km) = 32 ± 9 μM] and was cis-inhibited by known substrates of Mrp2 and by GSH. Interestingly, ATP-dependent transport of3H-labeled S-ethylglutathione and3H-labeled GSH was also detected in the vesicles. ATP-dependent GSH transport was mediated by a low-affinity pathway ( Km= 12 ± 2 mM) that was cis-inhibited by substrates of the Mrp2 transporter but was not affected by membrane potential or pH gradient uncouplers. These results provide the first direct evidence for ATP-dependent transport of GSH in liver membrane vesicles and support the hypothesis that GSH efflux from mammalian cells is mediated by members of the Mrp family of proteins.
Impact of intrinsic blood flow regulation in cirrhosis: maintenance of hepatic arterial buffer response
Authors: Richter Sven , Mücke Isabella , Menger Michael D. , Vollmar Brigitte
Published: December 2017

The hepatic arterial buffer response (HABR) effectively controls total blood perfusion in normal livers, but little is known about blood flow regulation in cirrhosis. We therefore studied the impact of HABR on blood perfusion of cirrhotic livers in vivo. After 8-wk CCl4treatment to induce cirrhosis, 18 anesthetized rats (and 18 noncirrhotic controls) were used to simultaneously assess portal venous and hepatic arterial inflow with miniaturized ultrasonic flow probes. Stepwise hepatic arterial blood flow (HAF) or portal venous blood flow (PVF) reduction was performed. Cirrhotic livers revealed a significantly reduced total hepatic blood flow (12.3 ± 0.9 ml/min) due to markedly diminished PVF (7.3 ± 0.8 ml/min) but slightly increased HAF (5.0 ± 0.6 ml/min) compared with noncirrhotic controls (19.0 ± 1.6, 15.2 ± 1.3, and 3.8 ± 0.4 ml/min). PVF reduction caused a significant HABR, i.e., increase of HAF, in both normal and cirrhotic livers; however, buffer capacity of cirrhotic livers exceeded that of normal livers ( P < 0.05) by 1.7- to 4.5-fold (PVF 80% and 20% of baseline). Persistent PVF reduction for 1, 2, and 6 h demonstrated constant HABR in both groups. Furthermore, HABR could be repetitively provoked, as analyzed by intermittent PVF reduction. HAF reduction did not induce changes of portal flow in either group. Because PVF is reduced in cirrhosis, the maintenance of HAF and the preserved HABR must be considered as a protective effect on overall hepatic circulation, counteracting impaired nutritive blood supply via the portal vein.
Molecular Physiology and Pathophysiology of Tight Junctions I. Biogenesis of tight junctions and epithelial polarity
Authors: Cereijido M. , Shoshani L. , Contreras R. G.
Published: December 2017

The tight junction (TJ) was first noticed through its ability to control permeation across the paracellular route, but the homologies of its molecular components with peptides that participate in tumor suppression, nuclear addressing, and cell proliferation indicate that it may be involved in many other fundamental functions. TJs are formed by a dozen molecular species that assemble through PDZ and other protein-protein clustering promoting sequences, in response to the activation of E-cadherin. The TJ occupies a highly specific position between the apical and the basolateral domains. Its first molecular components seem to be delivered to such a position by addressing signals in their molecule and, once anchored, serve as a clustering nucleus for further TJ-associated molecules. Although in mature epithelial cells TJs and E-cadherin do not colocalize, a complex chain of reactions goes from one to the other that involves α-, β-, and γ-catenins, two different G proteins, phospholipase C, protein kinase C, calmodulin, mitogen-activated protein kinase, and molecules pertaining to the cytoskeleton, which keep the TJ sensitive to physiological requirements and local conditions (notably to Ca2+-dependent cell-cell contacts) throughout the life of the epithelium.
Identification of genes involved in mucosal defense and inflammation associated with normal enteric bacteria
Authors: Ogawa Hitoshi , Fukushima Kouhei , Sasaki Iwao , Matsuno Seiki
Published: December 2017

Normal luminal bacteria and their products play a role in experimental colitis and inflammatory bowel disease. However, what molecules from what cells are responsible for mounting and maintaining the mucosal defense against luminal flora is still uncertain. The aim of this study was to identify epithelial gene products involved in mucosal defense and inflammation associated with ubiquitous enteric bacteria. Germ-free ICR mice were given an oral bacterial suspension prepared from conventional components (bacterial reconstitution). Small intestinal and colonic epithelial cells were isolated from bacteria-reconstituted, germ-free, and specific pathogen-free mice. Differential gene expression was investigated by differential display, Northern blot, and sequence analysis. Bacterial reconstitution resulted in acute but self-limited colitis. In epithelial cells, we observed the induction of small intestine-specific genes of the cryptdin family and colon-specific expression of serum amyloid A1 gene. This novel approach allows the identification of known and novel gene products involved in mucosal defense against luminal microorganisms and the associated inflammatory response.
The metabolism of gastrin-52 and gastrin-6 in pigs
Authors: Hansen C. Palnæs , Goetze J. P. , Stadil F. , Rehfeld J. F.
Published: December 2017

The kinetics and metabolism in various organs of three bioactive products of progastrin, the small sulfated and nonsulfated gastrin-6 and the large nonsulfated gastrin-52, were examined during intravenous administration in anesthetized pigs. The kidney, hindlimb, liver, head, and gut eliminated the hexapeptides efficiently, with a fractional extraction ranging from 0.50 to 0.28 ( P < 0.001–0.05). No metabolism was recorded in the lungs, and sulfation was without influence on the extraction of gastrin-6. Gastrin-52 was eliminated only in the kidney and the head, with a fractional extraction between 0.23 and 0.11 ( P < 0.01–0.05). The half-life of sulfated and nonsulfated gastrin-6 was 1.5 ± 0.4 and 1.4 ± 0.3 min, the metabolic clearance rate (MCR) was 80.8 ± 7.6 and 116.0 ± 13.5 ml · kg−1· min−1( P < 0.05), and the apparent volume of distribution (Vdss) was 199.3 ± 70.1 and 231.4 ± 37.3 ml/kg, respectively. The decay of gastrin-52 in plasma was biexponential. The half-lives of this biexponential after a bolus injection were 3.9 ± 0.5 ( T1/2α) and 25.7 ± 1.4 ( T1/2β) min, and the MCR and Vdsswere 4.2 ± 0.4 ml · kg−1· min−1and 116.2 ± 16.2 ml/kg1. We conclude that there is a differential elimination of progastrin products in splanchnic and nonsplanchnic tissue, which depends on the chain length of the peptides. Sulfation of gastrin-6 had no influence on the organ-specific extraction but reduced the MCR. Our results are in keeping with previous studies of nonsulfated gastrin-17, which is extracted in the kidney, head, limb, and gut but not in the liver.
TNF-α activates solitary nucleus neurons responsive to gastric distension
Authors: Emch Gregory S. , Hermann Gerlinda E. , Rogers Richard C.
Published: December 2017

Tumor necrosis factor-α (TNF-α) is liberated as part of the immune response to antigenic challenge, carcinogenesis, and radiation therapy. Previous studies have implicated elevated circulating levels of this cytokine in the gastric hypomotility associated with these disease states. Our earlier studies suggest that a site of action of TNF-α may be within the medullary dorsal vagal complex. In this study, we describe the role of TNF-α as a neuromodulator affecting neurons in the nucleus of the solitary tract that are involved in vago-vagal reflex control of gastric motility. The results presented herein suggest that TNF-α may induce a persistent gastric stasis by functioning as a hormone that modulates intrinsic vago-vagal reflex pathways during illness.
Effect of galanin and galanin antagonists on peristalsis in esophageal smooth muscle in the opossum
Authors: Yamato Shigeru , Hirano Ikuo , Goyal Raj K.
Published: December 2017

Galanin, a neuropeptide that is widely distributed in the esophageal nerves, is known to exert a neuromodulatory action in the gut. These studies examined the effect of galanin and galanin antagonists on esophageal peristalsis in anesthetized opossums in vivo. Intraluminal esophageal pressures were recorded at 1, 3, 5, 7, and 9 cm above the lower esophageal sphincter. Esophageal peristaltic contractions were induced by swallow and short- (1-s) and long-train (10-s) vagal stimulation (VS). Galanin (1 nmol/kg) inhibited the amplitude of swallow-induced peristaltic contractions and increased peristaltic velocity by enlarging the latency periods in the upper part of the esophagus and reducing them in the lower part. Galinin nearly abolished esophageal contractions caused by short-train VS at 5 Hz and inhibited the contractions at 10 Hz. Galanin increased latency periods induced by short-train VS with little change in the velocity of peristalsis and reduced the amplitude of both A (cholinergic) and B (noncholinergic) contractions due to long-train VS. However, the decrease in amplitude of B contractions was more marked. Galantide (3 nmol/kg) antagonized the inhibitory action of exogenous galanin on esophageal contractions elicited by short-train VS, but by itself galantide had no significant effect on esophageal contractions. In conclusion, exogenous galanin inhibits the amplitude of swallow-induced peristaltic contractions and converts them into nonperistaltic contractions by inhibiting both the cholinergic and noncholinergic components.
Novel goblet cell gene related to IgGFcγBP is regulated in adapting gut after small bowel resection
Authors: Rubin Deborah C. , Swietlicki Elzbieta A. , Iordanov Hristo , Fritsch Christine , Levin Marc S.
Published: December 2017

The loss of functional small bowel surface area leads to a well-described adaptive response in the remnant intestine. To elucidate its molecular regulation, a cohort of cDNAs were cloned using a rat gut resection model and subtractive/differential hybridization cloning techniques. This study reports a novel cDNA termed “ileal remnant repressed” (IRR)-219, which shares 80% nucleotide identity with the 3′end of a human intestinal IgG Fc binding protein (IgGFcγBP) and is homologous to human and rat mucins. IRR-219 mRNA is expressed in intestine and colon only. At 48 h after 70% intestinal resection, mRNA levels decreased two- to fivefold in the adaptive small bowel but increased two- to threefold in the colon. Expression of IRR-219 was suppressed in adaptive small bowel as late as 1 wk after resection. IRR-219 expression is also regulated during gut ontogeny. In situ hybridization revealed IRR-219 expression in small intestinal and colonic goblet cells only. Its unique patterns of expression during ontogeny and after small bowel resection suggest distinctive roles in small bowel and colonic adaptation.
Time course inhibition of gastric and platelet COX activity by acetylsalicylic acid in humans
Authors: Feldman Mark , Shewmake Kenneth , Cryer Byron
Published: December 2017

Aspirin causes peptic ulcers predominately by reducing gastric mucosal cyclooxygenase (COX) activity and prostaglandin synthesis. Because aspirin circulates for only a few hours, we hypothesized that aspirin's inhibitory effect on gastric COX activity must be prolonged. We performed a placebo-controlled experiment in healthy humans to determine the duration of inhibition of aspirin on gastric mucosal COX activity (PGE2 and PGF2α synthesis rates). Recovery of gastric COX activity after stopping aspirin was slow and linear. Seventy-two hours after 325-mg aspirin, gastric COX activity was still reduced by 57% ( P < 0.001). Duration of inhibition of gastric COX activity was estimated to be 7–8 days after 325-mg aspirin and 5 days after 81-mg aspirin. Recovery of gastric prostaglandin synthesis after 325-mg but not after 81-mg aspirin occurred at slower rates in subjects with Helicobacter pylori-associated gastritis than in those with normal histology. In conclusion, aspirin inhibits gastric COX activity for much longer than predicted from its pharmacokinetic profile, explaining why aspirin at widely spaced intervals is ulcerogenic.
A primary culture of guinea pig gallbladder epithelial cells that is responsive to secretagogues
Authors: Gunter-Smith Pamela J. , Abdulkadir Oluwakemi , Hammonds-Odie Latanya , Scanlon Mary , Terrell Raquel
Published: December 2017

We have developed a cell culture of guinea pig gallbladder epithelial cells with which to study ion transport. When grown on permeable supports, the cultured epithelia developed a transepithelial resistance ( Rt) of ∼500 Ω · cm2. The epithelial cell origin of the cell culture was further confirmed by immunocytochemical localization of cytokeratin. Ionomycin and forskolin increased transepithelial voltage and short-circuit current ( Isc) and decreased Rt. The response to ionomycin was transient, whereas that to forskolin was sustained. Both were attenuated by replacement of Cl−and/or HCO3−. Mucosal addition of the anion transport inhibitors DIDS or diphenylamine-2-carboxylic acid (DPC) blocked the response to ionomycin. The response to forskolin was blocked by DPC but not by DIDS. Ionomycin, but not forskolin, increased intracellular Ca2+concentration in fura 2-loaded cells. PGE2, histamine, vasoactive intestinal polypeptide, and secretin elicited a sustained increase in Isc. Responses to ATP and CCK were transient. Thus cultured guinea pig gallbladder epithelia display the range of responses observed in the native tissue and are an appropriate model for studies of ion transport in gallbladder and intestinal epithelia.
Regulation of IGFBP-4 levels in human intestinal muscle by an IGF-I-activated, confluence-dependent protease
Authors: Kuemmerle John F. , Teng Baiqin
Published: December 2017

Human intestinal smooth muscle cells in culture produce insulin-like growth factor-I (IGF-I), IGF binding protein-3 (IGFBP-3), IGFBP-4, and IGFBP-5, which can modulate the effects of IGF-I on growth. This study examined the role of IGFBP-4 on IGF-I-induced growth and the mechanisms regulating IGFBP-4 levels. IGFBP-4 inhibited IGF-I-induced [3H]thymidine incorporation. IGFBP-4 mRNA levels were not altered by IGF-I. IGF-I caused a concentration-dependent activation of an endogenous IGFBP-4 protease, resulting in time-dependent degradation of intact IGFBP-4 into inactive fragments. Protease activity was measured in a cell-free assay using smooth muscle cell conditioned medium containing the IGFBP-4 protease. The protease was inhibited by EDTA and benzamidine. Protease activity was highest in proliferating cells and lowest in postconfluent cells. The role of endogenous IGF-I in regulating IGFBP-4 degradation was confirmed by the ability of an IGF-I antagonist to inhibit IGF-I-activated IGFBP-4 proteolysis in intact cells. We conclude that in human intestinal smooth muscle cells levels of secreted IGFBP-4 are determined by the confluence-dependent production of a cation-dependent serine protease that is activated by endogenous IGF-I.
Site-specific DNA methylation contributes to neurotensin/neuromedin N expression in colon cancers
Authors: Dong Zizheng , Wang Xiaofu , Evers B. Mark
Published: December 2017

The neurotensin/neuromedin N (NT/N) gene is expressed in fetal colon, repressed in newborn and adult colon, and reexpressed in ∼25% of colon cancers. Our purpose was to determine the effect of gene methylation on NT/N silencing in colon cancers. We found that the NT/N gene was expressed in human colon cancer cell line KM12C but not in KM20 colon cancer cells. Bisulfite genomic sequencing demonstrated that all CpG dinucleotides in the region from −373 to +100 of the NT/N promoter, including a CpG site in a distal consensus AP-1 site, were methylated in KM20 but unmethylated in KM12C cells. Treatment of KM20 cells with demethylating agent 5-azacytidine induced NT/N expression, suggesting a role for DNA methylation in silencing of NT/N in colon cancers. To better elucidate the mechanisms responsible for NT/N repression by DNA methylation, we performed gel shift assays using an oligonucleotide probe corresponding to the distal AP-1 consensus sequence of the NT/N promoter. Methylation of the oligonucleotide probe inhibited protein binding to the distal AP-1 site of the NT/N promoter, suggesting a potential mechanism of NT/N gene repression in colon cancers. We show that DNA methylation plays a role in NT/N gene silencing in the human colon cancer KM20 and that NT/N expression in KM12C cells is associated with demethylation of the CpG sites. DNA methylation likely contributes to NT/N gene expression noted in human colon cancers.
Poly(ADP-ribose) polymerase is affected early by thyroid state during liver regeneration in rats
Authors: Cesarone C. F. , Scarabelli L. , Demori I. , Balocco S. , Fugassa E.
Published: December 2017

Poly(ADP-ribose) polymerase (PARP), a nuclear enzyme involved in DNA synthesis, DNA repair, and cell replication and transformation, also plays a role in the early steps of liver regeneration induced by partial hepatectomy (PH). PARP and DNA topoisomerase I (Topo I) activities and de novo DNA synthesis were studied during liver regeneration in rats with altered thyroid state. Hepatic PARP activity, evaluated as [32P]NAD incorporated into isolated liver nuclei, was inhibited in hyperthyroid rats and increased in hypothyroid animals. In both euthyroid and hyperthyroid rats PARP activity was rapidly stimulated, peaking 6 h after PH. In hypothyroid animals, an early decrease in activity was found, at a minimum of 6 h after PH, followed by an early onset of DNA synthesis. An inverse relationship between PARP and Topo I activities was a shared feature among euthyroid, hypothyroid, and hyperthyroid rats. Together these data show that, in replicating hepatocytes, thyroid hormones exert a regulatory role on PARP activity, which reflects the control of a number of nuclear proteins involved in DNA metabolism.
Transcription factor NF-κB participates in regulation of epithelial cell turnover in the colon
Authors: Inan Mehmet Sait , Tolmacheva Veronica , Wang Qiang-Shu , Rosenberg Daniel W. , Giardina Charles
Published: December 2017

The transcription factor nuclear factor (NF)-κB regulates the expression of genes that can influence cell proliferation and death. Here we analyze the contribution of NF-κB to the regulation of epithelial cell turnover in the colon. Immunohistochemical, immunoblot, and DNA binding analyses indicate that NF-κB complexes change as colonocytes mature: p65-p50 complexes predominate in proliferating epithelial cells of the colon, whereas the p50-p50 dimer is prevalent in mature epithelial cells. NF-κB1 (p50) knockout mice were used to study the role of NF-κB in regulating epithelial cell turnover. Knockout animals lacked detectable NF-κB DNA binding activity in isolated epithelial cells and had significantly longer crypts with a more extensive proliferative zone than their wild-type counterparts (as determined by proliferating cell nuclear antigen staining and in vivo bromodeoxyuridine labeling). Gene expression profiling reveals that the NF-κB1 knockout mice express the potentially growth-enhancing tumor necrosis factor (TNF)-α and nerve growth factor-α genes at elevated levels, with in situ hybridization localizing some of the TNF-α expression to epithelial cells. TNF-α is NF-κB regulated, and its upregulation in NF-κB1 knockouts may result from an alleviation of p50-p50 repression. NF-κB complexes may therefore influence cell proliferation in the colon through their ability to selectively activate and/or repress gene expression.
Hepatic neovascularization after partial portal vein ligation: novel mechanism of chronic regulation of blood flow
Authors: Yokoyama Yukihiro , Baveja Rajiv , Sonin Natalie , Clemens Mark G. , Zhang Jian X.
Published: December 2017

The present study was undertaken to investigate hepatic microcirculatory response following partial portal vein ligation (PPVL) in rats. Portal pressure was markedly increased 2–6 wk after PPVL, but no significant reduction in sinusoidal perfusion and hepatocellular injury were detected. However, marked neovascularization was observed in PPVL rats using intravital microscopy and scanning electron microscopy (SEM). Extremely high red blood cell velocity (2,000–4,900 μm /s) was seen in these vessels. Injection of fluorescein sodium via the carotid artery revealed that the neovessels originated from the hepatic arterial vasculature. This was further confirmed by clamping the common hepatic artery and phenylephrine injection from the carotid artery. These vessels maintained sufficient flow after massive sinusoidal shutdown elicited by the portal infusion of endothelin receptor B agonist IRL-1620. SEM also showed extensive neovascularization at the hilum. Additionally, clamping the portal vein decreased sinusoidal perfusion only by 9.5% in PPVL, whereas a 71.2% decrease was observed in sham. These results strongly suggest that the liver maintains its microcirculatory flow by vascular remodeling from the hepatic arterial vasculature following PPVL.
II. Stress and intestinal barrier function
Authors: Söderholm Johan D. , Perdue Mary H.
Published: December 2017

The influence of stress on the clinical course of a number of intestinal diseases is increasingly being recognized, but the underlying mechanisms are largely unknown. This themes article focuses on recent findings related to the effects of stress on mucosal barrier function in the small intestine and colon. Experiments using animal models demonstrate that various types of psychological and physical stress induce dysfunction of the intestinal barrier, resulting in enhanced uptake of potentially noxious material (e.g., antigens, toxins, and other proinflammatory molecules) from the gut lumen. Evidence from several studies indicates that in this process, mucosal mast cells play an important role, possibly activated via neurons releasing corticotropin-releasing hormone and/or acetylcholine. Defining the role of specific cells and mediator molecules in stress-induced barrier dysfunction may provide clues to novel treatments for intestinal disorders.
III. Stress-related alterations of gut motor function: role of brain corticotropin-releasing factor receptors
Authors: Taché Yvette , Martinez Vicente , Million Mulugeta , Wang Lixin
Published: December 2017

Alterations of gastrointestinal (GI) motor function are part of the visceral responses to stress. Inhibition of gastric emptying and stimulation of colonic motor function are the commonly encountered patterns induced by various stressors. Activation of brain corticotropin-releasing factor (CRF) receptors mediates stress-related inhibition of upper GI and stimulation of lower GI motor function through interaction with different CRF receptor subtypes. CRF subtype 1 receptors are involved in the colonic and anxiogenic responses to stress and may have clinical relevance in the comorbidity of anxiety/depression and irritable bowel syndrome.
III. Shigellosis: from symptoms to molecular pathogenesis
Authors: Sansonetti Philippe J.
Published: December 2017

Interaction of Shigella flexneri with epithelial cells includes contact of bacteria with the cell surface and release of Ipa proteins through a specialized type III secreton. A complex signaling process involving activation of small GTPases of the Rho family and c- src causes major rearrangements of the subcortical cytoskeleton, thereby allowing bacterial entry by macropinocytosis. After entry, shigellae escape to the cell cytoplasm and initiate intracytoplasmic movement through polar nucleation and assembly of actin filaments caused by bacterial surface protein IcsA, which binds and activates neuronal Wiskoff-Aldrich syndrome protein (N-WASP), thus inducing actin nucleation in an Arp 2/3-dependent mechanism. Actin-driven motility promotes efficient colonization of the host cell cytoplasm and rapid cell-to-cell spread via protrusions that are engulfed by adjacent cells in a cadherin-dependent process. Bacterial invasion turns infected cells to strongly proinflammatory cells through sustained activation of nuclear factor-κB. A major consequence is interleukin (IL)-8 production, which attracts polymorphonuclear leukocytes (PMNs). On transmigration, PMNs disrupt the permeability of this epithelium and promote its invasion by shigellae. At the early stage of infection, M cells of the follicle-associated epithelium allow bacterial translocation. Subsequent apoptotic killing of macrophages in a caspase 1-dependent process causes the release of IL-1β and IL-18, which accounts for the initial steps of inflammation.
Electrophysiological effects of GABA on cat pancreatic neurons
Authors: Sha L. , Miller S. M. , Szurszewski J. H.
Published: December 2017

In mammalian peripheral sympathetic ganglia GABA acts presynaptically to facilitate cholinergic transmission and postsynaptically to depolarize membrane potential. The GABA effect on parasympathetic pancreatic ganglia is unknown. We aimed to determine the effect of locally applied GABA on cat pancreatic ganglion neurons. Ganglia with attached nerve trunks were isolated from cat pancreata. Conventional intracellular recording techniques were used to record electrical responses from ganglion neurons. GABA pressure microejection depolarized membrane potential with an amplitude of 17.4 ± 0.7 mV. Electrically evoked fast excitatory postsynaptic potentials were significantly inhibited (5.4 ± 0.3 to 2.9 ± 0.2 mV) after GABA application. GABA-evoked depolarizations were mimicked by the GABAAreceptor agonist muscimol and abolished by the GABAAreceptor antagonist bicuculline and the Cl−channel blocker picrotoxin. GABA was taken up and stored in ganglia during preincubation with 1 mM GABA; β-aminobutyric acid application after GABA loading significantly ( P < 0.05) increased depolarizing response to GABA (15.6 ± 1.0 vs. 7.8 ± 0.8 mV without GABA preincubation). Immunolabeling with antibodies to GABA, glial cell fibrillary acidic protein, protein gene product 9.5, and glutamic acid decarboxylase (GAD) immunoreactivity showed that GABA was present in glial cells, but not in neurons, and that glial cells did not contain GAD, whereas islet cells did. The data suggest that endogenous GABA released from ganglionic glial cells acts on pancreatic ganglion neurons through GABAAreceptors.
Molecular and functional evidence for electrogenic and electroneutral Na+-HCO 3 − cotransporters in murine duodenum
Authors: Praetorius J. , Hager H. , Nielsen S. , Aalkjaer C. , Friis U. G. , Ainsworth M. A. , Johansen T.
Published: December 2017

Inward Na+-HCO[Formula: see text]cotransport has previously been demonstrated in acidified duodenal epithelial cells, but the identity and localization of the mRNAs and proteins involved have not been determined. The molecular expression and localization of Na+-HCO[Formula: see text]cotransporters (NBCs) were studied by RT-PCR, sequence analysis, and immunohistochemistry. By fluorescence spectroscopy, the intracellular pH (pHi) was recorded in suspensions of isolated murine duodenal epithelial cells loaded with 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Proximal duodenal epithelial cells expressed mRNA encoding two electrogenic NBC1 isoforms and the electroneutral NBCn1. Both NBC1 and NBCn1 were localized to the basolateral membrane of proximal duodenal villus cells, whereas the crypt cells did not label with the anti-NBC antibodies. DIDS or removal of extracellular Cl−increased pHi, whereas an acidification was observed on removal of Na+or both Na+and Cl−. The effects of inhibitors and ionic dependence of acid/base transporters were consistent with both inward and outward Na+-HCO[Formula: see text] cotransport. Hence, we propose that NBCs are involved in both basolateral electroneutral HCO[Formula: see text] transport as well as basolateral electrogenic HCO[Formula: see text] transport in proximal duodenal villus cells.
Regulation of slow wave frequency by IP3-sensitive calcium release in the murine small intestine
Authors: Malysz John , Donnelly Graeme , Huizinga Jan D.
Published: December 2017

Slow waves determine frequency and propagation characteristics of contractions in the small intestine, yet little is known about mechanisms of slow wave regulation. We propose a role for intracellular Ca2+, inositol 1,4,5,-trisphosphate (IP3)-sensitive Ca2+release, and sarcoplasmic reticulum (SR) Ca2+content in the regulation of slow wave frequency because 1) 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid-AM, a cytosolic Ca2+chelator, reduced the frequency or abolished the slow waves; 2) thapsigargin and cyclopiazonic acid (CPA), inhibitors of SR Ca2+-ATPase, decreased slow wave frequency; 3) xestospongin C, a reversible, membrane-permeable blocker of IP3-induced Ca2+release, abolished slow wave activity; 4) caffeine and phospholipase C inhibitors (U-73122, neomycin, and 2-nitro-4-carboxyphenyl- N, N-diphenylcarbamate) inhibited slow wave frequency; 5) in the presence of CPA or thapsigargin, stimulation of IP3synthesis with carbachol, norepinephrine, or phenylephrine acting on α1-adrenoceptors initially increased slow wave frequency but thereafter increased the rate of frequency decline, 6) thimerosal, a sensitizing agent of IP3receptors increased slow wave frequency, and 7) ryanodine, a selective modulator of Ca2+-induced Ca2+release, had no effect on slow wave frequency. In summary, these data are consistent with a role of IP3-sensitive Ca2+release and the rate of SR Ca2+refilling in regulation of intestinal slow wave frequency.
Decreased orexigenic response to neuropeptide Y in rats with obstructive cholestasis
Authors: Rioux Kevin P. , Le Tai , Swain Mark G.
Published: December 2017

Neuropeptide Y (NPY) is a key factor in the neurochemical control of food intake, and obstructive cholestasis can be associated with disturbances in food intake. Our aim in this study was to determine whether obstructive cholestasis in the rat is associated with defective central responsiveness to NPY. Cholestasis was induced in rats by surgical bile duct resection. Rats with obstructive cholestasis exhibited a 20% reduction in food intake 2 days after laparotomy (compared with sham-resected controls) that had resolved by 4 days after surgery. Responsiveness to the orexigenic action of NPY was tested by measuring food intake after intracerebroventricular injection of NPY. In sham-resected rats, NPY infusion strikingly increased food intake, whereas bile duct-resected (BDR) rats showed a consistent significantly impaired feeding response to NPY at postlaparotomy days 2, 4, and 7. Separate experiments measured specific binding of [3H]NPY to hypothalamic receptors. Fos protein expression was measured in the hypothalamic paraventricular nucleus (PVN) as a marker of NPY-induced neuronal activation. The decreased orexigenic responsiveness to NPY was not caused by altered NPY binding at hypothalamic receptors or its ability to activate neurons in the PVN. Therefore, cholestatic rats demonstrate an attenuated NPY-induced orexigenic drive that occurs early after biliary obstruction, when cholestatic rats exhibit reduced food intake, and persists despite the return of food intake to normal levels and the presence of intact central NPY-related neuronal pathways.
V. Stress and irritable bowel syndrome
Authors: Mayer Emeran A. , Naliboff Bruce D. , Chang Lin , Coutinho Santosh V.
Published: December 2017

Different types of stress play important roles in the onset and modulation of irritable bowel syndrome (IBS) symptoms. The physiological effects of psychological and physical stressors on gut function and brain-gut interactions are mediated by outputs of the emotional motor system in terms of autonomic, neuroendocrine, attentional, and pain modulatory responses. IBS patients show an enhanced responsiveness of this system manifesting in altered modulation of gastrointestinal motility and secretion and in alterations in the perception of visceral events. Functional brain imaging techniques are beginning to identify brain circuits involved in the perceptual alterations. Animal models have recently been proposed that mimic key features of the human syndrome.
IV.Helicobacter pyloristrain-specific activation of signal transduction cascades related to gastric inflammation
Authors: Peek Richard M.
Published: December 2017

Helicobacter pylori strains that possess the cag pathogenicity island induce more severe gastritis and augment the risk of developing peptic ulcer disease and distal gastric cancer. A specific mechanism by which cag+strains may enhance gastritis is strain-selective regulation of interleukin (IL)-8 production. On contact with gastric epithelial cells, H. pylori activates multiple signal transduction cascades that regulate IL-8 secretion, including nuclear factor-κB and mitogen-activated protein kinases, and these events are dependent on genes within the cagisland. An independent effect of cag-mediated cellular contact is translocation and phosphorylation of H. pyloriproteins within the host epithelial cell. The redundancy of intracellular signaling cascades activated by H. pylori and the divergent epithelial cell responses induced by components of the cag island may contribute to the ability of this organism to persist for decades within the gastric niche.
Staphylococcal enterotoxin B potentiates LPS-induced hepatic dysfunction in chronically catheterized rats
Authors: Beno David W. A. , Uhing Michael R. , Goto Masakatsu , Chen Yong , Jiyamapa-Serna Vanida A. , Kimura Robert E.
Published: December 2017

Most models of liver dysfunction in sepsis use endotoxin (lipopolysaccharide; LPS) to induce a pathophysiological response. In our study published in this issue (Beno DWA, Uhing MR, Goto M, Chen Y, Jiyamapa-Serna VA, and Kimura RE. Am J Physiol Gastrointest Liver Physiol 280: G858–G865, 2001), the adverse effect of LPS on hepatic function in vivo was only significant at relatively high LPS doses despite high tumor necrosis factor-α concentrations. However, many patients with sepsis are exposed to multiple bacterial toxins that may augment the immune response, resulting in increased hepatic dysfunction. We have developed a model of polymicrobial sepsis by parentally administering a combination of staphylococcal enterotoxin B (SEB) and LPS. Using this model, we demonstrate that SEB (50 μg/kg) potentiates the effect of LPS-induced hepatic dysfunction as measured by decreased rates of biliary indocyanine green clearance and bile flow. These increases were most pronounced with doses of 10 and 100 μg/kg LPS, doses that by themselves do not induce hepatic dysfunction. This may explain the seemingly increased incidence and severity of liver dysfunction in sepsis, and it suggests that the exclusive use of LPS for replicating septic shock may not be relevant for studies of hepatic dysfunction.
MEK inhibits secretin release and pancreatic secretion: roles of secretin-releasing peptide and somatostatin
Authors: Li James P. , Lee Kae Yol , Chang Ta-Min , Chey William Y.
Published: December 2017

We investigated the mechanism of action of methionine enkephalin (MEK) on HCl-stimulated secretin release and pancreatic exocrine secretion. Anesthetized rats with pancreatobiliary cannulas and isolated upper small intestinal loops were perfused intraduodenally with 0.01 N HCl while bile and pancreatic juice were diverted. The effect of intravenous MEK on acid-stimulated secretin release and pancreatic exocrine secretion was then studied with or without coinfusion of naloxone, an anti-somatostatin (SS) serum, or normal rabbit serum. Duodenal acid perfusate, which contains secretin-releasing peptide (SRP) activity, was collected from donor rats with or without pretreatment with MEK, MEK + naloxone, or MEK + anti-SS serum, concentrated by ultrafiltration, and neutralized. The concentrated acid perfusate (CAP), which contains SRP bioactivity, was infused intraduodenally into recipient rats. MEK increased plasma SS concentration and inhibited secretin release and pancreatic fluid and bicarbonate secretion dose-dependently. The inhibition was partially reversed by naloxone and anti-SS serum but not by normal rabbit serum. In recipient rats, CAP increased plasma secretin level and pancreatic secretion. CAP SRP bioactivity decreased when it was collected from MEK-treated donor rats; this was partially reversed by coinfusion with naloxone or anti-SS serum. These results suggest that in the rat, MEK inhibition of acid-stimulated pancreatic secretion and secretin release involves suppression of SRP activity release. Thus the MEK inhibitory effect appears to be mediated in part by endogenous SS.
VI.Entamoeba histolytica: parasite-host interactions
Authors: Stanley Samuel L. , Reed Sharon L.
Published: December 2017

The protozoan intestinal parasite Entamoeba histolytica remains a significant cause of morbidity and mortality worldwide. E. histolytica causes two major clinical syndromes, amebic colitis and amebic liver abscess. Recent advances in the development of in vitro and in vivo models of disease, new genetic approaches, the identification of key E. histolytica virulence factors, and the recognition of crucial elements of the host response to infection have led to significant insights into the pathogenesis of amebic infection. E. histolytica virulence factors include 1) a surface galactose binding lectin that mediates E. histolyticabinding to host cells and may contribute to amebic resistance to complement, 2) amebapores, small peptides capable of lysing cells, which may play a role in killing intestinal epithelial cells, hepatocytes, and host defense cells, and 3) a family of secreted cysteine proteinases that play a key role in E. histolytica tissue invasion, evasion of host defenses, and parasite induction of gut inflammation. Amebae can both lyse host cells and induce their suicide through programmed cell death. The host response is also an important factor in the outcome of infection, and neutrophils may play a key role in contributing to the tissue damage seen in amebiasis and in controlling amebic infection.
Production of MDC/CCL22 by human intestinal epithelial cells
Authors: Berin M. Cecilia , Dwinell Michael B. , Eckmann Lars , Kagnoff Martin F.
Published: December 2017

The intestinal mucosa contains a subset of lymphocytes that produce Th2 cytokines, yet the signals responsible for the recruitment of these cells are poorly understood. Macrophage-derived chemokine (MDC/CCL22) is a recently described CC chemokine known to chemoattract the Th2 cytokine producing cells that express the receptor CCR4. The studies herein demonstrate the constitutive production of MDC/CCL22 in vivo by human colon epithelium and by epithelium of human intestinal xenografts. MDC/CCL22 mRNA expression and protein secretion was upregulated in colon epithelial cell lines in response to proinflammatory cytokines or infection with enteroinvasive bacteria. Inhibition of nuclear factor (NF)-κB activation abolished MDC/CCL22 expression in response to proinflammatory stimuli, demonstrating that MDC/CCL22 is a NF-κB target gene. In addition, tumor necrosis factor-α-induced MDC/CCL22 secretion was differentially modulated by Th1 and Th2 cytokines. Supernatants from the basal, but not apical, side of polarized epithelial cells induced a MDC/CCL22-dependent chemotaxis of CCR4-positive T cells. These studies demonstrate the constitutive and regulated production by intestinal epithelial cells of a chemokine known to function in the trafficking of T cells that produce anti-inflammatory cytokines.
Angiotensin II type 2 receptor-mediated duodenal mucosal alkaline secretion in the rat
Authors: Johansson Berndt , Holm Mathias , Ewert Sara , Casselbrant Anna , Pettersson Anders , Fändriks Lars
Published: December 2017

The aims of this study were to elucidate the distribution of angiotensin receptors (AT1and AT2) in the duodenal wall and to investigate whether AT2receptors are involved in the regulation of duodenal mucosal alkaline secretion, which is of importance for the mucosal defense against gastric acid. Immunohistochemistry was used to locate AT1and AT2receptors in chloralose-anesthetized rats. Duodenal mucosal alkaline output was measured by use of in situ pH-stat titration. Immunohistochemistry demonstrated a distinct staining for both AT1and AT2receptors in the lamina propria of the villi and also for AT1receptors in the muscularis interna. When angiotensin II was infused in the presence of the AT1receptor antagonist losartan, mucosal alkaline secretion increased by ∼50%. This response was inhibited by the AT2receptor antagonist PD-123319. The AT2receptor agonist CGP-42112A increased mucosal alkaline secretion by ∼50%. This increase was absent in the presence of PD-123319 but not in the presence of losartan or the local anesthetic lidocaine. We conclude that angiotensin II stimulates duodenal mucosal alkaline secretion by activation of AT2receptors located in the duodenal mucosa/submucosa.
Role of protein tyrosine phosphorylation in acetaldehyde-induced disruption of epithelial tight junctions
Authors: Atkinson K. J. , Rao R. K.
Published: December 2017

Acetaldehyde-induced cytotoxicity is an important factor in pathogenesis of alcohol-related diseases; however, the mechanism of this toxicity is unknown. We recently showed that acetaldehyde increases epithelial paracellular permeability. We asked whether protein tyrosine phosphorylation via modulation of tyrosine kinases and/or PTPases is a mechanism involved in acetaldehyde-induced disruption of the tight junctions in the Caco-2 cell monolayer. Immunofluorescence localization of occludin and ZO-1 showed disruption of the tight junctions in acetaldehyde-treated cell monolayer. Administration of genistein prevented acetaldehyde-induced permeability. Acetaldehyde increased tyrosine phosphorylation of three clusters of proteins with molecular masses of 30–50, 60–90, and 110–150 kDa; three of these proteins were ZO-1, E-cadherin, and β-catenin. Acetaldehyde reduced PTPase activity in plasma membrane and soluble fractions, whereas tyrosine kinase activity remained unaffected. Treatment with acetaldehyde resulted in a 97% loss of protein tyrosine phosphatase (PTP)1B activity and a partial reduction of PTP1C and PTP1D activities. These results strongly suggest that acetaldehyde inhibits PTPases to increase protein tyrosine phosphorylation, which may result in disruption of the tight junctions.
Impairment of H+-K+-ATPase-dependent proton transport and inhibition of gastric acid secretion by ethanol
Authors: del Valle Juan C. , Salvatella María , Rossi Irma , Andrade Ramón , Gutiérrez Yolanda , Pereda Carmen , Samper Begoña , Felíu Juan E.
Published: December 2017

Ethanol (1–20% vol/vol) caused a dose-dependent reduction in the basal rate of acid formation in isolated rabbit gastric glands with a calculated EC50value of 4.5 ± 0.2%. Ethanol also reduced ATP levels in isolated gastric glands and in cultured parietal cells (EC50: 8.8 ± 0.4% and 8.5 ± 0.2%, respectively) and decreased both basal and forskolin-stimulated cAMP levels. In studies carried out in gastric gland microsomes, ethanol inhibited the hydrolytic activity of H+-K+-ATPase (EC50: 8.5 ± 0.6%), increased passive proton permeability (EC50: 7.9%), and reduced H+-K+-ATPase-dependent proton transport (EC50: 3%). Our results show that the inhibition of gastric acid secretion observed at low concentrations of ethanol (≤5%) is mainly caused by the specific impairment of H+-K+-ATPase-dependent proton transport across cell membranes rather than inhibition of the hydrolytic activity of H+-K+-ATPase, reduction in the cellular content of ATP, or increase in the passive permeability of membranes to protons, although these changes, in combination, must be relevant at concentrations of ethanol ≥7%.