bluuebunny/crossref_metadata_2025 huggingface dataset:
HNF-1α and endodermal transcription factors cooperatively activateFabpl: MODY3 mutations abrogate cooperativity
Authors: Divine Joyce K. , McCaul Sean P. , Simon Theodore C.
Published: March 2015

Hepatocyte nuclear factor (HNF)-1α plays a central role in intestinal and hepatic gene regulation and is required for hepatic expression of the liver fatty acid binding protein gene ( Fabpl). An Fabpl transgene was directly activated through cognate sites by HNF-1α and HNF-1β, as well as five other endodermal factors: CDX-1, C/EBPβ, GATA-4, FoxA2, and HNF-4α. HNF-1α activated the Fabpl transgene by as much as 60-fold greater in the presence of the other five endodermal factors than in their absence, accounting for up to one-half the total transgene activation by the group of six factors. This degree of synergistic interaction suggests that multifactor cooperativity is a critical determinant of endodermal gene activation by HNF-1α. Mutations in HNF-1α that result in maturity onset diabetes of the young (MODY3) provide evidence for the in vivo significance of these synergistic interactions. An R131Q HNF-1α MODY3 mutant exhibits complete loss of synergistic activation in concert with the other endodermal transcription factors despite wild-type transactivation ability in their absence. Furthermore, whereas wild-type HNF-1α exhibited pairwise cooperative synergy with each of the other five factors, the R131Q mutant could synergize only with GATA-4 and C/EBPβ. Selective loss of synergy with other endodermal transcription factors accompanied by retention of native transactivation ability in an HNF-1α MODY mutant suggests in vivo significance for cooperative synergy.
Activation of AMP-activated protein kinase reduces cAMP-mediated epithelial chloride secretion
Authors: Walker John , Jijon Humberto B. , Churchill Thomas , Kulka Marianne , Madsen Karen L.
Published: March 2015

AMP-activated protein kinase (AMPK) is activated in response to fluctuations in cellular energy status caused by oxidative stress. One of its targets is the cystic fibrosis transmembrane conductance regulator (CFTR), which is the predominant Cl-secretory channel in colonic tissue. The aim of this study was to determine the role of AMPK in the modulation of colonic chloride secretion under conditions of oxidative stress and chronic inflammation. Chloride secretion and AMPK activity were examined in colonic tissue from adult IL-10-deficient and wild-type 129 Sv/Ev mice in the presence and absence of pharmacological AMPK inhibitors and activators, respectively. Apical levels of CFTR were measured in brush-border membrane vesicles. Cell culture studies in human colonic T84 monolayers examined the effect of hydrogen peroxide and pharmacological activation of AMPK on forskolin-stimulated chloride secretion. Inflamed colons from IL-10-deficient mice exhibited hyporesponsiveness to forskolin stimulation in association with reductions in surface CFTR expression and increased AMPK activity. Inhibition of AMPK restored tissue responsiveness to forskolin, whereas stimulation of AMPK with 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) induced tissue hyporesponsivness in wild-type mice. T84 cells exposed to hydrogen peroxide demonstrated a time-dependent increase in AMPK activity and reduction of forskolin-stimulated chloride secretion. Inhibition of AMPK prevented the reduction in chloride secretion. Treatment of cells with the AMPK activator, AICAR, resulted in a decreased chloride secretion. In conclusion, AMPK activation is linked with reductions in cAMP-mediated epithelial chloride flux and may be a contributing factor to the hyporesponsiveness seen under conditions of chronic inflammation.
Physiological role of neuropeptide Y in the regulation of the ascending phase of the peristaltic reflex
Authors: Grider John R. , Langdon Lea E.
Published: March 2015

The physiological role of neuropeptide Y (NPY) and of specific NPY receptors in regulating the intestinal peristaltic reflex was examined in three-compartment flat-sheet preparations of rat colon. Graded muscle stretch or mucosal stimulation applied to the central compartment inhibited NPY release in the orad compartment where ascending contraction was measured. NPY and the Y1-receptor agonist [Leu31, Pro34]NPY inhibited, whereas the selective Y1-receptor antagonist BIBP 3226 augmented ascending contraction and substance P (SP) release in the orad compartment induced by muscle stretch or mucosal stimulation. Neither agonist nor antagonist had any effect on descending relaxation or VIP release in the caudad compartment. The Y2-receptor agonist NPY13-36 and antagonist BIIE 0246 had no effect on peptide release or mechanical response. The results indicate that suppression of a tonic inhibitory influence of NPY neurons on excitatory neurotransmitter release contributes substantially to the orad contractile phase of the peristaltic reflex. The effect of NPY on neurotransmitter release is mediated by Y1 receptors.
Mesenchymal IGF-I overexpression: paracrine effects in the intestine, distinct from endocrine actions
Authors: Williams Kristen L. , Fuller C. Randall , Fagin James , Lund P. Kay
Published: March 2015

Local IGF-I expression is frequently increased in intestinal mesenchyme during adaptive growth of intestinal epithelium, but paracrine growth effects of IGF-I in vivo are not defined. We tested whether overexpression of IGF-I in intestinal mesenchyme increases epithelial growth and if effects are distinct from known effects of circulating IGF-I. SMP8-IGF-I-transgenic (TG) mice overexpress IGF-I driven by an α-smooth muscle actin promoter. Mucosal and muscularis growth were assessed in the jejunum, ileum, and colon of SMP8-IGF-I-TG mice and wild-type littermates. Abundance of the SMP8-IGF-I transgene and IGF binding protein (IGFBP)-3 and -5 mRNAs was determined. Mucosal growth was increased in SMP8-IGF-I-TG ileum but not jejunum or colon; muscularis growth was increased throughout the bowel. IGFBP-5 mRNA was increased in SMP8-IGF-I-TG jejunum and ileum and was specifically upregulated in ileal lamina propria. Overexpression of IGF-I in intestinal mesenchymal cells has preferential paracrine effects on the ileal mucosal epithelium and autocrine effects on the muscularis throughout the bowel. Locally expressed IGF-I has distinct actions on IGFBP expression compared with circulating IGF-I.
I. Age-related changes in the enteric nervous system
Authors: Wade Paul R.
Published: March 2015

As we enter the 21st century, the segment of the population that is the most rapidly expanding is that comprised of individuals 85 yr of age and older. Dysfunctions of the gastrointestinal (GI) system, including dysphagia, constipation, diarrhea, and irritable bowel syndrome are more common complaints of the elderly, yet our knowledge of the aging GI tract is incomplete. Compared with the rapid advances in the neurobiology of aging in the central nervous system, the understanding of age-related changes in the enteric nervous system (ENS) is poor. In this brief review, I recap experiments that reveal neurodegenerative changes and their functional correlates in the ENS of mice, rats, and guinea pigs. Clinical literature seems indicative of similar structural and functional age-related changes in the human ENS. Current studies that address the mechanisms underlying age-related changes in the ENS are introduced. The future directions for this field include physiological and pharmacological studies, especially at cellular and molecular levels. Research in the aging ENS is poised to make major advances, and this new knowledge will be useful for clinicians seeking to better understand and treat GI dysfunction in the elderly.
Mechanism of the alcohol cyclic pattern: role of catecholamines
Authors: Li Jun , French Barbara A. , Fu Paul , Bardag-Gorce Fawzia , French Samuel W.
Published: March 2015

The cause of the urinary alcohol level (UAL) cycle in rats fed ethanol at a constant rate has been shown to involve the hypothalamic-pituitary thyroid axis. Because the effect of thyroid hormone on the metabolic rate is augmented by catecholamines, the role of catecholamines was investigated by using the intragastric ethanol feeding model of alcoholic liver disease in which the UAL cycles over a 6- to 10-day period. The diet was supplemented with ephedrine and caffeine to test the hypothesis that the UAL cycle involves catecholamines. The UAL was followed to see whether the cycle was ablated by catecholamine supplements. Ethanol fed alone increased the blood levels of catecholamines significantly more than did ephedrine fed alone. However, blood catecholamine levels were significantly higher when ethanol was fed with ephedrine compared with the sum of ethanol and ephedrine fed alone. This indicated that the effect of ethanol and ephedrine were synergistic. The UAL cycle was completely ablated in the ethanol + ephedrine-fed rats. These rats tolerated a much higher dose of ethanol, indicating that they metabolized alcohol faster due to an increase in metabolic rate caused by ephedrine. In the ethanol + ephedrine-fed rats the liver pathology included significantly higher alanine amino transferase (ALT) in the blood and centrilobular ischemic necrosis in the liver. Necrosis was not present in the rats fed ephedrine alone. In conclusion, catecholamine supplements prevented the UAL cycle by increasing the metabolic rate to the point at which fluctuations in the metabolic rate caused by alcohol were prevented.
Abdominal irradiation increases inflammatory cytokine expression and activates NF-κB in rat ileal muscularis layer
Authors: Linard C. , Ropenga A. , Vozenin-Brotons M. C. , Chapel A. , Mathe D.
Published: March 2015

The small bowel is an important dose-limiting organ in abdominal radiotherapy because irradiation can cause acute enteritis that, in turn, leads to progressively reduced motility and finally, in a later phase, to fibrosis. Because these clinical symptoms may be caused by the early stage of an inflammatory process, we characterized the radiation-induced intestinal inflammation in rats. Abdominal γ-irradiation (10-Gy) induced a cascade of inflammatory events characterized by an early (6 h after exposure) increase in IL-1β, TNF-α, and IL-6 mRNA levels in the rat ileal muscularis layer. IL-8 [a cytokine-induced neutrophil chemoattractant (CINC)] mRNA appeared later (at 3 days). The expression of TGF-β (a profibrotic cytokine) was higher in irradiated than control tissue at day 1, whereas IL-10 (an anti-inflammatory cytokine) expression vanished completely. Despite strong IL-1ra expression, the IL-1ra/IL-1β ratio, which is an indicator of inflammatory balance, was -41% at day 1 in irradiated compared with control tissue. The nuclear transcription factors NF-κB and activator protein-1 (AP-1) govern transcription of these genes, directly or indirectly. Although expression of the subunits of NF-κB (p65, p50) and AP-1 (c- fos, c- jun) did not increase, irradiation caused a rapid and persistent translocation of p65 and p50. An imbalance between proinflammatory and anti-inflammatory mediators may contribute to perpetuating intestinal inflammation, thus making it chronic.
Cultured gallbladder epithelial cells synthesize apolipoproteins A-I and E
Authors: Lee Jin , Tauscher Aimee , Seo Dong Wan , Oram John F. , Kuver Rahul
Published: March 2015

Gallbladder epithelial cells (GBEC) are exposed to high and fluctuating concentrations of biliary cholesterol on their apical (AP) surface. GBEC absorb and efflux cholesterol, but the mechanisms of cholesterol uptake, intracellular trafficking, and efflux in these cells are not known. We previously reported that ATP binding cassette (ABC)A1 mediates basolateral (BL) cholesterol efflux in cultured polarized GBEC. In addition, the nuclear hormone receptors liver X receptor (LXR)α and retinoid X receptor (RXR) mediate both AP and BL cholesterol efflux. An interesting finding from our previous study was that apolipoprotein (apo)A-I applied to the AP surfaces of cells elicited BL ABCA1-mediated cholesterol efflux. Because ABCA1-mediated cholesterol efflux requires the presence of a cholesterol acceptor, we hypothesized that GBEC synthesize and secrete endogenous apo into the BL compartment. Here, we demonstrate that cholesterol loading of cells with model bile and AP apoA-I treatment is associated with an increase in the synthesis of apoE mRNA and protein. Furthermore, apoE is secreted into the BL compartment. LXRα/RXR ligands stimulate the synthesis of endogenous apoA-I mRNA and protein, as well as apoE mRNA. BL secretion of apoA-I is elicited by LXRα/RXR ligands. Therefore, GBEC synthesize apoA-I and -E and efflux cholesterol using ABCA1- and non-ABCA1- mediated pathways. These processes may alter gallbladder biliary cholesterol concentrations and thereby influence gallstone formation.
II. Intestinal epithelial cell exosomes: perspectives on their structure and function
Authors: van Niel Guillaume , Heyman Martine
Published: March 2015

Intestinal epithelial cells (IEC) are located at the strategic interface between the external environment and the most extensive lymphoid compartment in the body. Besides their central role in the absorption of nutrients, they also provide sample information to the immune system on soluble or particulate antigens present in the intestinal lumen. Like professional antigen-presenting cells, IEC have recently been shown to secrete 30- to 90-nm diameter vesicles named exosomes from their apical and basolateral surfaces. These vesicles carry molecules that are implicated in adhesion and antigen presentation, such as major histocompatibility complex (MHC) class I molecules, MHC class II molecules, CD63, CD26/dipeptidyl-peptidase IV, tetraspan proteins, and A33 antigen. IEC exosomes therefore, constitute a link by which IEC may influence antigen presentation in the mucosal or systemic immune system independent of direct cellular contact with effector cells.
Measuring esophageal distension by high-frequency intraluminal ultrasound probe
Authors: Rhee Poong-Lyul , Liu Jianmin , Puckett James L. , Mittal Ravinder K.
Published: March 2015

Distension of the esophagus can cause heartburn and chest pain; however, none of the available techniques to study the esophagus measure esophageal distension. We evaluated the technique of high-frequency intraluminal ultrasound probe (HFIUS) to measure the esophageal cross-sectional area (CSA) during gastroesophageal reflux (GER). The following methods were used: 1) the CSA of agarose gel tubes of known dimensions were measured using ultrasound probes; 2) seven normal subjects were studied to evaluate the esophageal CSA during different bolus volumes (1, 5, 10, 15, and 20 ml) of water swallows (WS); and 3) simultaneous pressures, pH, and ultrasound images of the esophagus were recorded in healthy subjects. In vitro studies showed that the HFIUS measured the CSA of the tubes accurately. The maximal CSA of the distal esophagus during WS with boluses of 1, 5, 10, 15, and 20 ml were 54, 101, 175, 235, and 246 mm2, respectively. Esophageal contents during 62 episodes of transient lower esophageal sphincter relaxations, 29 pH positive, and 33 pH negative GER episodes revealed that reflux of air into the esophagus occurred more frequently than liquid. The median CSA and estimated diameter of the esophagus during liquid GER was 44.1 mm2 and 7.5 mm, respectively. We conclude that HFIUS is a valid technique to measure the CSA of the esophagus in vivo during GER. Distension of the esophagus during physiological GER is relatively small.
DMT1 and FPN1 expression during infancy: developmental regulation of iron absorption
Authors: Leong Weng-In , Bowlus Christopher L. , Tallkvist Jonas , Lönnerdal Bo
Published: March 2015

Two iron transporters, divalent metal transporter1 (DMT1) and ferroportin1 (FPN1) have been identified; however, their role during infancy is unknown. We investigated DMT1, FPN1, ferritin, and transferrin receptor expression, iron absorption and tissue iron in iron-deficient rat pups, iron-deficient rat pups given iron supplements, and controls during early ( day 10) and late infancy ( day 20). With iron deficiency, DMT1 was unchanged and FPN1 was decreased (-80%) at day 10. Body iron uptake, mucosal iron retention, and total iron absorption were unchanged. At day 20, DMT1 increased fourfold and FPN1 increased eightfold in the low-Fe group compared with controls. Body iron uptake and total iron absorption were increased, and mucosal iron retention was decreased with iron deficiency. Iron supplementation normalized expression levels of the transporters, body iron uptake, mucosal iron retention, and total iron absorption of the low-Fe group to those of controls at day 20. In summary, the molecular mechanisms regulating iron absorption during early infancy differ from late infancy when they are similar to adult animals, indicating developmental regulation of iron absorption.
Cholinergic and nitrergic regulation of in vivo giant migrating contractions in rat colon
Authors: Li Mona , Johnson Christopher P. , Adams Mark B. , Sarna Sushil K.
Published: March 2015

The aim of this study was to characterize in vivo rat colonic motor activity in normal and inflamed states and determine its neural regulation. Circular muscle contractions were recorded by surgically implanted strain-gauge transducers. The rat colon exhibited predominantly giant migrating contractions (GMCs) whose frequency decreased distally. Only a small percentage of these GMCs propagated in the distal direction; the rest occurred randomly. Phasic contractions were present, but their amplitude was very small compared with that of GMCs. Inflammation induced by oral administration of dextran sodium sulfate suppressed the frequency of GMCs in the proximal and middle but not in the distal colon. Frequency of GMCs was suppressed by intraperitoneally administered atropine and 4-diphenylacetoxy- N-methyl-piperidine methiodide and was enhanced by N w-nitro-l-arginine methyl ester. Serotonin, tachykinin, and calcitonin gene-related peptide receptor or receptor subtype antagonists as well as guanethidine and suramin had no significant effect on the frequency of GMCs. Verapamil transiently suppressed the GMCs. In conclusion, unlike the canine and human colons, the rat colon exhibits frequent GMCs and their frequency is suppressed in inflammation. In vivo GMCs are stimulated by neural release of acetylcholine that acts on M3 receptors. Constitutive release of nitric oxide may partially suppress their frequency.
Stimulation of neurons in rat ARC inhibits gastric acid secretion via hypothalamic CRF1/2- and NPY-Y1 receptors
Authors: Tebbe Johannes J. , Mronga Silke , Schäfer Martin K.-H. , Rüter Jens , Kobelt Peter , Mönnikes Hubert
Published: March 2015

Neuropeptide Y (NPY) neuronal projections from the arcuate nucleus (ARC) have been proposed to target corticotropin-releasing factor (CRF)-positive neurons in the paraventricular nucleus (PVN) as part of the ARC-PVN axis. The existence of a positive feedback loop involving CRF receptors in the PVN has been suggested. Exogenous NPY and CRF in the PVN have been shown to inhibit gastric acid secretion. Recently, we have demonstrated that activation of ARC neurons inhibits gastric acid secretion via vagal pathways. To what extent NPY- and CRF-mediated mechanisms in the PVN contribute to the CNS modulation of gastric acid secretion is still an open question. In the present study, we performed consecutive bilateral microinjections of antagonists to NPY receptor subtypes Y1 and Y2 and to CRF1/2 receptors in the PVN and of the excitatory amino acid kainate in the ARC to assess the role of NPY- and CRF-mediated mechanisms in the kainate-induced effects on gastric acid secretion. Gastric acid secretion was measured at the basal condition and during pentagastrin (16 μg/kg body wt) stimulation. Microinjection of vehicle in the PVN and kainate in the ARC decreased gastric acid secretion. Microinjection of the specific NPY-Y1 receptor antagonist BIBP-3226 (200 pmol) and the nonspecific CRF1/2 antagonist astressin (30 pmol) in the PVN abolished the inhibitory effect of neuronal activation in the ARC by kainate on gastric acid secretion. The CRF antagonist astressin was more effective. Pretreatment with the NPY-Y2 receptor antagonist BIIE-0246 (120 pmol) in the PVN had no significant effect. Our results indicate that activation of neurons in the ARC inhibits gastric acid secretion via CRF1/2 and NPY-Y1 receptor-mediated pathways in the PVN.
Effects of PGE2 in guinea pig colonic myenteric ganglia
Authors: Manning Brian P. , Sharkey Keith A. , Mawe Gary M.
Published: March 2015

PGE2 is a proinflammatory mediator that can influence many cell types. This study was conducted to determine whether PGE2 alters the electrical activity of distal colonic myenteric neurons, because colitis is typically associated with altered motility and changes in neural signaling may be involved. The electrical properties of intact myenteric neurons were evaluated with intracellular microelectrodes. Acute application of PGE2 elicited a prolonged depolarization in both AH and S neurons with little effect on input resistance or electrical excitability. PGE2 effects were suppressed by tetrodotoxin (TTX) or neurokinin (NK) receptor antagonists, indicating that PGE2 acts directly and indirectly to depolarize colonic neurons. PGE2-evoked depolarization was concentration dependent (∼3 μM EC50) and was attenuated by the E prostanoid (EP)1/2 receptor antagonist, AH-6809. When preparations were maintained for 48 h in the presence of the stable PGE2analog PGE2-ethanolamide (10 μM), neurons exhibited a significant membrane depolarization and enhanced excitability. These results suggest that PGE2 can play a role in altered motility in colitis by evoking changes in the electrical properties of myenteric neurons.
Mechanical properties in the human gastric antrum using B-mode ultrasonography and antral distension
Authors: Gregersen H. , Gilja O. H. , Hausken T. , Heimdal A. , Gao C. , Matre K. , Ødegaard S. , Berstad A.
Published: March 2015

The aims of this study were to investigate gastric antral geometry and stress-strain properties by using transabdominal ultrasound scanning during volume-controlled distensions in the human gastric antrum. Seven healthy volunteers underwent stepwise inflation of a bag located in the antrum with volumes up to 60 ml. The stretch ratio and Cauchy stress and strain were calculated from measurements of pressure, diameter, and wall thickness. A second distension series was conducted in three volunteers during administration of the anticholinergic drug butylscopolamine. Analysis of stretch ratios demonstrated positive strain in the circumferential direction, negative strain in the radial direction, and no strain in the longitudinal direction. The stress-strain relation was exponential and did not differ without or with the administration of butylscopolamine. The wall stress was decomposed into its active and passive components. The well-known length-tension diagram from in vitro studies of smooth muscle strips was reproduced. The maximum active tension appeared at a volume of 50 ml, corresponding to a stretch ratio of 1.5. We conclude that the method provides measures of antral biomechanical wall properties and can be used to reproduce the muscle length-tension diagram in humans.
Tumor necrosis factor-α-associated lysosomal permeabilization is cathepsin B dependent
Authors: Werneburg Nathan W. , Guicciardi M. Eugenia , Bronk Steven F. , Gores Gregory J.
Published: March 2015

Cathepsin B (Cat B) is released from lysososomes during tumor necrosis factor-α (TNF-α) cytotoxic signaling in hepatocytes and contributes to cell death. Sphingosine has recently been implicated in lysosomal permeabilization and is increased in the liver by TNF-α. Thus the aims of this study were to examine the mechanisms involved in TNF-α-associated lysosomal permeabilization, especially the role of sphingosine. Confocal microscopy demonstrated Cat B-green fluorescent protein and LysoTracker Red were both released from lysosomes after treatment of McNtcp.24 cells with TNF-α/actinomycin D, a finding compatible with lysosomal destabilization. In contrast, endosomes labeled with Texas Red dextran remained intact, suggesting lysosomes were specifically targeted for permeabilization. LysoTracker Red was released from lysosomes in hepatocytes treated with TNF-α or sphingosine in Cat B(+/+) but not Cat B(−/−) hepatocytes, as assessed by a fluorescence-based assay. With the use of a calcein release assay in isolated lysosomes, sphingosine permeabilized liver lysosomes isolated from Cat B(+/+) but not Cat B(−/−) liver. C6ceramide did not permeabilize lysosomes. In conclusion, these data implicate a sphingosine-Cat B interaction inducing lysosomal destabilization during TNF-α cytotoxic signaling.
Activation of TGF-β-Smad signaling pathway following polyamine depletion in intestinal epithelial cells
Authors: Liu Lan , Santora Rachel , Rao Jaladanki N. , Guo Xin , Zou Tongtong , Zhang Huifang M. , Turner Douglas J. , Wang Jian-Ying
Published: March 2015

Smad proteins are transcription activators that are critical for transmitting transforming growth factor-β (TGF-β) superfamily signals from the cell surface receptors to the nucleus. Our previous studies have shown that cellular polyamines are essential for normal intestinal mucosal growth and that a decreased level of polyamines inhibits intestinal epithelial cell proliferation, at least partially, by increasing expression of TGF-β/TGF-β receptors. The current study went further to determine the possibility that Smads are the downstream intracellular effectors of activated TGF-β/TGF-β receptor signaling following polyamine depletion. Studies were conducted in IEC-6 cells derived from rat small intestinal crypts. Depletion of cellular polyamines by α-difluoromethylornithine (DFMO) increased basal levels of Smad3 and Smad4 proteins, induced their nuclear translocation, and stimulated Smad sequence-specific DNA-binding activity. Polyamine depletion-induced Smads were also associated with a significant increase in transcription activation as measured by luciferase reporter gene activity of Smad-dependent promoters. Inhibition of Smads by a dominant-negative mutant Smad4 in the DFMO-treated cells prevented the increased Smad transcription activation. Polyamine-deficient cells highly expressed TGF-β and were growth-arrested at the G1phase. Inhibition of TGF-β by treatment with either immunoneutralizing anti-TGF-β antibody or TGF-β antisense oligodeoxyribonucleotides not only blocked the induction of Smad activity but also decreased the Smad-mediated transcriptional activation in polyamine-depleted cells. These findings suggest that Smads are involved in the downstream cellular processes mediated by cellular polyamines and that increased TGF-β/TGF-β receptor signaling following polyamine depletion activates Smads, thus resulting in the stimulation of Smad target gene expression.
Chronic EtOH administration alters liver Mg2+homeostasis
Authors: Young Andrew , Cefaratti Christie , Romani Andrea
Published: March 2015

Ethanol (EtOH) administration to rats for 4 wk markedly decreased Mg2+content in several tissues, including liver. Total cellular Mg2+accounted for 26.8 ± 2.4 vs. 36.0 ± 1.4 nmol Mg2+/mg protein in hepatocytes from EtOH-fed and control rats, respectively, and paralleled a 13% decrease in cellular ATP content. Stimulation of α1- or β-adrenergic receptor or acute EtOH administration did not elicit an extrusion of Mg2+from liver cells of EtOH-fed rats while releasing 5% of total tissue Mg2+content from hepatocytes of control rats. Despite the 25% decrease in Mg2+content, hepatocytes from EtOH-fed rats did not accumulate Mg2+following stimulation of protein kinase C signaling pathway, whereas control hepatocytes accumulated ∼2 nmol Mg2+· mg protein−1· 4 min−1. Together, these data indicate that Mg2+homeostasis and transport are markedly impaired in liver cells after prolonged exposure to alcohol. The inability of liver cells, and possibly other tissues, to accumulate Mg2+can help explain the reduction in tissue Mg2+content following chronic alcohol consumption.
Feeding natural hydrophilic bile acids inhibits intestinal cholesterol absorption: studies in the gallstone-susceptible mouse
Authors: Wang David Q.-H. , Tazuma Susumu , Cohen David E. , Carey Martin C.
Published: March 2015

We explored the influence of the hydrophilic-hydrophobic balance of a series of natural bile acids on cholesterol absorption in the mouse. Male C57L/J mice were fed standard chow or chow supplemented with 0.5% cholic; chenodeoxycholic; deoxycholic; dehydrocholic; hyocholic; hyodeoxycholic; α-, β-, or ω-muricholic; ursocholic; or ursodeoxycholic acids for 7 days. Biliary bile salts were measured by reverse-phase HPLC, and hydrophobicity indices were estimated by Heuman's method. Cholesterol absorption efficiency was determined by a plasma dual-isotope ratio method. In mice fed chow, natural proportions of tauro-β-muricholate (42 ± 6%) and taurocholate (50 ± 7%) with a hydrophobicity index of -0.35 ± 0.04 produced cholesterol absorption of 37 ± 5%. Because bacterial and especially hepatic biotransformations of specific bile acids occurred, hydrophobicity indices of the resultant bile salt pools differed from fed bile acids. We observed a significant positive correlation between hydrophobicity indices of the bile salt pool and percent cholesterol absorption. The principal mechanism whereby hydrophilic bile acids inhibit cholesterol absorption appears to be diminution of intraluminal micellar cholesterol solubilization. Gene expression of intestinal sterol efflux transporters Abcg5 and Abcg8 was upregulated by feeding cholic acid but not by hydrophilic β-muricholic acid nor by hydrophobic deoxycholic acid. We conclude that the hydrophobicity of the bile salt pool predicts the effects of individual fed bile acids on intestinal cholesterol absorption. Natural α- and β-muricholic acids are the most powerful inhibitors of cholesterol absorption in mice and might act as potent cholesterol-lowering agents for prevention of cholesterol deposition diseases in humans.
Downregulation of nNOS and synthesis of PGs associated with endotoxin-induced delay in gastric emptying
Authors: Calatayud Sara , García-Zaragozá Eugenia , Hernández Carlos , Quintana Elsa , Felipo Vicente , Esplugues Juan Vicente , Barrachina María Dolores
Published: March 2015

A single intraperitoneal injection of endotoxin (40 μg/kg) significantly delayed gastric emptying of a solid nutrient meal. Blockade of nitric oxide synthase (NOS) with 30 mg/kg ip N G-nitro-l-arginine methyl ester or 20 mg/kg ip 7-nitroindazole [neuronal NOS (nNOS) inhibitor] significantly delayed gastric emptying in control animals but failed to modify gastric emptying in endotoxin-treated rats. Administration of 2.5, 5, and 10 mg/kg ip N 6-iminoethyl-l-lysine [inducible NOS (iNOS) inhibitor] had no effect in either experimental group. Indomethacin (5 mg/kg sc), NS-398 (cyclooxygenase-2 inhibitor; 10 mg/kg ip), and dexamethasone (10 mg/kg sc) but not quinacrine (20 mg/kg ip) significantly prevented delay in gastric emptying induced by endotoxin but failed to modify gastric emptying in vehicle-treated animals. Ca2+-dependent NOS activity in the antrum pylorus of the stomach was diminished by endotoxin, whereas Ca2+-independent NOS activity was not changed. In addition, decreased nNOS mRNA and protein were observed in the antrum pylorus of endotoxin-treated rats. Our results suggest that downregulation of nNOS in the antrum pylorus of the stomach and synthesis of prostaglandins mediate the delay in gastric emptying of a solid nutrient meal induced by endotoxin.
Regulation of intestinal NaPi-IIb cotransporter gene expression by estrogen
Authors: Xu Hua , Uno Jennifer K. , Inouye Michael , Xu Liping , Drees Jason B. , Collins James F. , Ghishan Fayez K.
Published: March 2015

The current experiments were designed to study the effect of β-estradiol on type IIb sodium-coupled phosphate (NaPi-IIb) cotransporter gene expression. Uptake studies with intestinal brush-border membrane vesicles (BBMV) showed that estrogen treatment increased sodium-dependent phosphate absorption by ∼45% in rat intestine. Northern blot analysis indicated that NaPi-IIb mRNA expression was increased by ∼50% after estrogen treatment. Western blot analysis also detected an increase in BBMV NaPi-IIb protein expression in estrogen-treated rats. In human intestinal Caco-2 cells, NaPi-IIb mRNA abundance was increased ∼60% after estrogen treatment, and this increase could be abolished by inhibition of gene transcription. Transfection studies with human NaPi-IIb promoter reporter constructs showed that the promoter was responsive to estrogen treatment. These studies demonstrate for the first time that estrogen stimulates intestinal sodium-dependent phosphate absorption in female rats. This stimulation is associated with increased NaPi-IIb mRNA and protein expression. Thus the effect of estrogen on intestinal Pi absorption may be partially due to activation of NaPi-IIb gene transcription.
Muscularis mucosae contraction evokes colonic secretion via prostaglandin synthesis and nerve stimulation
Authors: Percy W. H. , Fromm T. H. , Wangsness C. E.
Published: March 2015

This in vitro study tested the hypothesis that muscularis mucosae contractile activity contributes to rabbit colonic mucosal function by mechanisms other than simple mechanical deformation of the epithelium. Experiments were performed by using a technique that allows simultaneous recording of muscle activity and transmucosal potential difference, a measure of epithelial ion transport. ATP, bradykinin, histamine, PGE2, PGF1α, and PGF2α elicited muscularis mucosae contractions that were resistant to atropine and TTX. Only ATP-induced contractions were indomethacin sensitive, and only those to dimethylphenylpiperazinium iodide (DMPP) were reduced by atropine. All agonist-evoked increases in transmucosal potential difference were atropine resistant, and, with the exception of those to PGE2, PGF2α, and VIP, they were also TTX sensitive. Mucosal responses to ATP, bradykinin, and histamine were indomethacin sensitive, whereas those to DMPP, the prostaglandins, and VIP were not. When cyclooxygenase activity or the mucosal innervation was compromised, even maximal muscularis mucosae contractions did not produce large secretory responses. It is concluded that contraction-related prostaglandin synthesis and noncholinergic secretomotor neuron stimulation represent the physiological transduction mechanism through which muscularis mucosae motor activity is translated into mucosal secretion.
Ontogenic regulation of folate transport across rat jejunal brush-border membrane
Authors: Balamurugan Krishnaswamy , Said Hamid M.
Published: March 2015

Folate is an essential micronutrient that in mammals must be obtained from exogenous sources via intestinal absorption. Previous studies from our laboratory and others have demonstrated that folate absorption from the small intestine is mediated via the reduced-folate carrier (RFC). The goal of this study was to determine whether the initial step of folate uptake by intestinal epithelial cells, i.e., transport across the brush-border membrane (BBM) of the polarized enterocytes, is ontogenically regulated, and if so, to determine the molecular mechanism involved. Purified BBM vesicles (BBMV) isolated from suckling, weanling, and adult rats were used in this study. The initial rate of carrier-mediated uptake of a physiological concentration of folic acid (0.1 μM) by jejunal BBMV was found to be significantly ( P < 0.01) higher in suckling compared with weanling rats, which was, in turn, significantly ( P < 0.01) higher than that in adult rats. This decline in carrier-mediated folate uptake with maturation was found to be mediated via a decrease in the maximum velocity of the folate uptake process (6.55 ± 0.87, 2.16 ± 0.10, 0.90 ± 0.16 pmol·mg protein-1·10 s-1for suckling, weanling, and adult rats, respectively), with no changes in its apparent Km. Western blot analysis of BBM protein and real-time PCR showed RFC protein and mRNA levels, respectively, to be significantly ( P < 0.01 for both) higher in suckling compared with weanling rats, which were in turn significantly ( P < 0.01 for both) higher than that in adult rats. These changes were found by nuclear run-on assay to be associated with a parallel decline in the RFC transcriptional rate in jejunal epithelia with maturation. In situ hybridization showed a similar pattern of RFC message distribution along crypt/villus axis in suckling and adult rat jejunum. These results demonstrate for the first time that folate transport across the intestinal BBM is under ontogenic regulation during early stages of life and that this regulation involves a transcriptional regulatory mechanism(s).
Molecular and functional characterization of ERG, KCNQ, and KCNE subtypes in rat stomach smooth muscle
Authors: Ohya Susumu , Asakura Keiichi , Muraki Katsuhiko , Watanabe Minoru , Imaizumi Yuji
Published: March 2015

Contribution of K+ channels derived from the expression of ERG, KCNQ, and KCNE subtypes, which are responsible for rapidly and slowly activating delayed rectifier K+ currents ( I Kr and I Ks, respectively) in cardiac myocytes, to membrane currents was examined in stomach circular smooth muscle cells (SMCs). The region-qualified multicell RT-PCR showed that ERG1/KCNE2 transcripts were expressed in rat stomach fundus and antrum SMCs and that KCNQ1/KCNE1 transcripts were expressed in antrum but not fundus. Western blotting and immunocytochemical analyses indicate that ERG1 proteins were substantially expressed in both regions, whereas KCNE1 proteins were faintly expressed in antrum and not in fundus. Both I Kr- and I Ks-like currents susceptible to E-4031 and indapamide, respectively, were identified in circular SMCs of antrum but only I Kr-like current was identified in fundus. It is strongly suggested that I Kr- and I Ks-like currents functionally identified in rat stomach SMCs are attributable to the expression of ERG1/KCNE2 and KCNQ1/KCNE1, respectively. The membrane depolarization by 1 μM E-4031 indicates the contribution of K+ channels encoded by ERG1/KCNE2 to the resting membrane potential in stomach SMCs.
Expression and function of 5-HT3receptors in the enteric neurons of mice lacking the serotonin transporter
Authors: Liu Min-Tsai , Rayport Stephen , Jiang Yan , Murphy Dennis L. , Gershon Michael D.
Published: March 2015

The actions of enteric 5-HT are terminated by 5-HT transporter (SERT)-mediated uptake, and gastrointestinal motility is abnormal in SERT −/− mice. We tested the hypothesis that adaptive changes in enteric 5-HT3receptors help SERT −/− mice survive despite inefficient 5-HT inactivation. Expression of mRNA encoding enteric 5-HT3Asubunits was similar in SERT +/+ and −/− mice, but that of 5-HT3Bsubunits was fourfold less in SERT −/− mice. 5-HT3BmRNA was found, by in situ hybridization, in epithelial cells and enteric neurons. 5-HT evoked a fast inward current in myenteric neurons that was pharmacologically identified as 5-HT3mediated. The EC50of the 5-HT response was lower in SERT +/+ (18 μM) than in SERT −/− (36 μM) mice and desensitized rapidly in a greater proportion of SERT −/− neurons; however, peak amplitudes, steady-state current, and decay time constants were not different. Adaptive changes thus occur in the subunit composition of enteric 5-HT3receptors of SERT −/− mice that are reflected in 5-HT3receptor affinity and desensitization.
Prevention of hepatic ischemia-reperfusion injury by green tea extract
Authors: Zhong Zhi , Froh Matthias , Connor Henry D. , Li Xiangli , Conzelmann Lars O. , Mason Ronald P. , Lemasters John J. , Thurman Ronald G.
Published: March 2015

These experiments were designed to determine whether green tea extract (GTE), which contains polyphenolic free radical scavengers, prevents ischemia-reperfusion injury to the liver. Rats were fed a powdered diet containing 0–0.3% GTE starting 5 days before hepatic warm ischemia and reperfusion. Free radicals in bile were trapped with the spin-trapping reagent α-(4-pyridyl-1-oxide)- N- tert-butylnitrone (4-POBN) and measured using electron spin resonance spectroscopy. Hepatic ischemia-reperfusion increased transaminase release and caused pathological changes including focal necrosis and hepatic leukocyte infiltration in the liver. Transaminase release was diminished by over 85% and pathological changes were almost totally blocked by 0.1% dietary GTE. Ischemia-reperfusion increased 4-POBN/radical adducts in bile nearly twofold, an effect largely blocked by GTE. Epicatechin, one of the major green tea polyphenols, gave similar protection as GTE. In addition, hepatic ischemia-reperfusion activated NF-κB and increased TNF-α mRNA and protein expression. These effects were all blocked by GTE. Taken together, these results demonstrate that GTE scavenges free radicals in the liver after ischemiareoxygenation, thus preventing formation of toxic cytokines. Therefore, GTE could prove to be effective in decreasing hepatic injury in disease states where ischemia-reperfusion occurs.
Hemorrhage induces the rapid development of hepatic insulin resistance
Authors: Ma Yuchen , Wang Ping , Kuebler Joachim F. , Chaudry Irshad H. , Messina Joseph L.
Published: March 2015

Hyperglycemia is an early metabolic response to trauma and hemorrhage. The role of hepatic insulin resistance to the development of this hyperglycemia is not well understood. The aim of this study was to determine whether the liver becomes insulin resistant and to identify the particular hepatic insulin signaling pathways that may be compromised following trauma and hemorrhage. Male adult rats were bled to a mean arterial pressure of 40 mmHg and maintained at that pressure for 90 min followed by resuscitation with Ringer lactate. Data showed that trauma and hemorrhage rapidly induced profound hyperinsulinemia in combination with significant hyperglycemia, suggesting the development of insulin resistance. After trauma and hemorrhage, hepatic insulin signaling via the insulin-induced phosphatidylinositol 3 (PI3)-kinase-Akt pathway was abolished, whereas ERK1/2 signaling was relatively normal. The regulation (inhibition) of a hepatic-, insulin-, and the PI3-kinase-dependent gene, IGF binding protein-1, was also lost. The present study provides convincing evidence of a rapid onset hepatic insulin resistance following a combination of trauma and hemorrhage.
Neuromedin U acts in the central nervous system to inhibit gastric acid secretion via CRH system
Authors: Mondal Muhtashan S. , Date Yukari , Murakami Noboru , Toshinai Koji , Shimbara Takuya , Kangawa Kenji , Nakazato Masamitsu
Published: March 2015

Neuromedin U (NMU) is a hypothalamic peptide involved in energy homeostasis and stress responses. NMU, when administered intracerebroventricularly, decreases food intake and body weight while increasing body temperature and heat production. In addition, NMU, acting via the corticotropin-releasing hormone (CRH) system, induces gross locomotor activity and stress responses. We studied the effect of intracerebroventricularly administered NMU (0.5–4 nmol) in the regulation of gastric functions in conscious rats. Intracerebroventricular administration of NMU significantly decreased gastric acid output to 30–60% and gastric emptying to 35–70% in a dose-dependent manner. Vagotomy did not abolish the inhibitory effect of NMU on pentagastrin-induced gastric acid secretion. Pretreatment with indomethacin (10 mg/kg), an inhibitor of prostaglandin synthesis, also did not affect NMU-induced acid inhibition. Pretreatment with anti-CRH IgG (1 μg/rat), however, completely blocked NMU-induced acid inhibition ( P < 0.01). Administration of yohimbine (4 mg/kg), an α2-adrenergic receptor antagonist, also abolished NMU-induced acid inhibition ( P < 0.01). These findings suggest that NMU is critical in the central regulation of gastric acid secretion via CRH.
Iron Imports. I. Intestinal iron absorption and its regulation
Authors: Frazer David M. , Anderson Gregory J.
Published: March 2015

Our knowledge of how the body absorbs iron from the diet and how this process is controlled has increased at a rapid rate in recent years. The identification of key molecules, including the iron regulatory peptide hepcidin, and the analysis of how they are regulated and interact have led to the development of an integrated model for the control of iron absorption by body iron requirements. Research now focuses on the role of the liver as the primary regulator of iron absorption, and this review considers some of the recent highlights and controversies in this area.
The importance of mucus layers and bicarbonate transport in preservation of gastric juxtamucosal pH
Authors: Phillipson Mia , Atuma Christer , Henriksnäs Johanna , Holm Lena
Published: March 2015

Mucus thickness is suggested to be related to mucosal protection. We therefore investigated the importance of the removable mucous layer and epithelial bicarbonate transport in preservation of the gastric juxtamucosal pH (pHjm) during luminal acid. Anesthetized rats were prepared for intravital microscopy of the gastric mucosa, and pHjmwas measured with pH-sensitive microelectrodes. The mucus was either left intact (IM) or removed (MR) down to the firmly attached mucous layer, and HCl (pH 1) was applied luminally. Removal of the loosely adherent mucous layer did not influence the pHjmduring luminal acid (pentagastrin: IM/MR 7.03 ± 0.09/6.82 ± 0.19; pentagastrin + indomethacin: IM/MR 6.89 ± 0.20/6.95 ± 0.27; ranitidine: IM/MR 2.38 ± 0.64/2.97 ± 0.62), unless prostaglandin synthesis and acid secretion were inhibited (ranitidine + indomethacin: IM/MR 2.03 ± 0.37/1.66 ± 0.18). Neutral pHjmis maintained during endogenous acid secretion and luminal pH 1, unless DIDS was applied luminally, which resulted in a substantially decreased pHjm(1.37 ± 0.21). Neutral pHjmis maintained by a DIDS-sensitive bicarbonate transport over the surface epithelium. The loosely adherent mucous layer only contributes to maintaining pHjmduring luminal pH 1 if acid secretion and prostaglandin synthesis are inhibited.
Alterations in Muc2 biosynthesis and secretion during dextran sulfate sodium-induced colitis
Authors: Renes Ingrid B. , Boshuizen Jos A. , Van Nispen Daniëlle J. P. M. , Bulsing Nathalie P. , Büller Hans A. , Dekker Jan , Einerhand Alexandra W. C.
Published: March 2015

To gain insight into mucin 2 (Muc2) synthesis and secretion during dextran sulfate sodium (DSS)-induced colitis, rats were treated with DSS for 7 days. Colonic segments were excised on days 0 (control), 2 (onset of disease), 7 (active disease), and 14(regenerative phase) for histological evaluation. Explants were metabolically labeled with35S-labeled amino acids or [35S]sulfate followed by chase incubation. Homogenates were analyzed by SDS-PAGE and35S-labeled Muc2 was quantified. Also, total Muc2 protein and mRNA were quantified. DSS-induced crypt loss, ulcerations, and concomitant goblet cell loss were most pronounced in the distal colon. Muc2 precursor synthesis increased progressively in the proximal colon but was unaltered in the distal colon during onset and active disease. During the regenerative phase, Muc2 precursor synthesis levels normalized in the proximal colon but increased in the distal colon. Total Muc2 levels paralleled the changes seen in Muc2 precursor synthesis levels. During each disease phase, total Muc2 secretion was unaltered in the proximal and distal colon. [35S]sulfate incorporation into Muc2 only decreased in the proximal colon during active disease and the regenerative phase, whereas secretion of [35S]sulfate-labeled Muc2 increased. During the regenerative phase, Muc2 mRNA levels were downregulated in both colonic segments. In conclusion, DSS-induced loss of goblet cells was accompanied by an increase or maintenance of Muc2 precursor synthesis, total Muc2 levels, and Muc2 secretion. In the proximal colon, Muc2 became undersulfated, whereas sulfated Muc2 was preferentially secreted. Collectively, these data suggest specific adaptations of the mucus layer to maintain the protective capacities during DSS-induced colitis.