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Results for “Intestinal Barrier Function”

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At least 865 records · Page 48Linked to original sources

PubMed2000

Poly (ADP-ribose) synthetase mediates intestinal mucosal barrier dysfunction after mesenteric ischemia.

Peroxynitrite-mediated DNA strand breaks trigger poly (ADP-ribose) synthetase (PARS) activation, resulting in intracellular energetic failure and organ dysfunction. We investigated the role of PARS activation on the inflammatory and functional response of the intestine to mesenteric ischemia-reperfusion injury. Anesthetized rats exposed to 15 min occlusion of the superior mesenteric artery showed an increased mucosal PARS activity (ex vivo incorporation of radiolabelled NAD+ in gut mucosal scrapings) as soon as 10 min after reperfusion. During the first 30 min of reperfusion, significant mucosal damage developed, as well as mucosal hyperpermeability to a 4000 MW fluorescent dextran (FD4). These alterations were significantly reduced by treatment with the NO synthase inhibitor L-NMA, which blocks the production of peroxynitrite, as well as with the PARS inhibitors 3-aminobenzamide and nicotinamide, whereas they were markedly enhanced by the glutathione depletor L-buthionine-(S,R)-sulfoximine. Also, PARS inhibition significantly reduced ileal neutrophil infiltration (myeloperoxidase activity) at 3 h reperfusion. In a second set of experiments, the effects of 15 or 30 min ischemia followed by 3 h reperfusion were evaluated in PARS knockout and wild-type mice. Significant protection against histological damage, neutrophil infiltration, and mucosal barrier failure (evaluated by the mucosal-to-serosal FD4 clearance of everted ileal sacs incubated ex vivo) was noted in PARS knockout mice, who also showed reduced alterations in remote organs, as shown by lesser lipid peroxidation (malondialdehyde formation) and neutrophil infiltration in the lung and liver. In conclusion, PARS plays a crucial role in mediating intestinal injury and dysfunction in the early and late phases of mesenteric reperfusion. Pharmacological inhibition of PARS may be a novel approach to protect tissues from reperfusion-related damage.

Animals↗

PubMed1994

Cryptosporidium parvum infection of intestinal epithelium: morphologic and functional studies in an in vitro model.

A monolayer of mature polarized colonic epithelial cells (T84) able to generate and maintain a barrier to macromolecular flow was used to study pathophysiologic events that occur on microvillus cell exposure to Cryptosporidium parvum. By 24-48 h, several life cycle forms were seen in parasitophorous vacuoles near the apical cell surface, along with a time- and oocyst dose-dependent reduction in epithelial barrier function. As few as 10(5) organisms constituted a successful infecting dose, and heat inactivation of organisms markedly reduced the monolayer barrier alteration. Horseradish peroxidase flux studies demonstrated a substantial increase in macromolecular permeability of the monolayer, and lactate dehydrogenase determinations indicated modest injury of the T84 epithelial cells on exposure to oocysts. Thus, disruption of the epithelial cell barrier, not just opening of transcellular channels for ion flow as reported previously, is responsible for the effects of C. parvum oocysts on intestinal epithelium.

Animals↗

PubMed2004

Compartmentalization of the mucosal immune responses to commensal intestinal bacteria.

Mammals coexist with a luxuriant load of bacteria in the lower intestine (up to 10(12) organisms/g of intestinal contents). Although these bacteria do not cause disease if they remain within the intestinal lumen, they contain abundant immunostimulatory molecules that trigger immunopathology if the bacteria penetrate the body in large numbers. The physical barrier consists only of a single epithelial cell layer with overlying mucus, but comparisons between animals kept in germ-free conditions and those colonized with bacteria show that bacteria induce both mucosal B cells and some T cell subsets; these adaptations are assumed to function as an immune barrier against bacterial penetration, but the mechanisms are poorly understood. In mice with normal intestinal flora, but no pathogens, there is a secretory IgA response against bacterial membrane proteins and other cell wall components. Whereas induction of IgA against cholera toxin is highly T help dependent, secretory IgA against commensal bacteria is induced by both T independent and T dependent pathways. When animals are kept in clean conditions and free of pathogens, there is still a profound intestinal secretory IgA response against the commensal intestinal flora. However, T dependent serum IgG responses against commensal bacteria do not occur in immunocompetent animals unless they are deliberately injected intravenously with 10(4) to 10(6) organisms. In other words, unmanipulated pathogen-free mice are systemically ignorant but not tolerant of their commensal flora despite the mucosal immune response to these organisms. In mice that are challenged with intestinal doses of commensal bacteria, small numbers of commensals penetrate the epithelial cell layer and survive within dendritic cells (DC). These commensal-loaded DC induce IgA, but because they are confined within the mucosal immune system by the mesenteric lymph nodes, they do not induce systemic immune responses. In this way the mucosal immune responses to commensals are geographically and functionally separated from systemic immunity.

Animals↗

PubMed2000

Regulation of intestinal blood flow.

The gastrointestinal system anatomically is positioned to perform two distinct functions: to digest and absorb ingested nutrients and to sustain barrier function to prevent transepithelial migration of bacteria and antigens. Alterations in these basic functions contribute to a variety of clinical scenarios. These primary functions intrinsically require splanchnic blood flow at both the macrovascular and microvascular levels of perfusion. Therefore, a greater understanding of the mechanisms that regulate intestinal vascular perfusion in the normal state and during pathophysiological conditions would be beneficial. The purpose of this review is to summarize the current understanding regarding the regulatory mechanisms of intestinal blood flow in fasted and fed conditions and during pathological stress.

Animals↗

PubMed2006

Role of intestinal function in cachexia.

PURPOSE OF REVIEW: Cachexia is a prominent feature in many chronic diseases, but its pathogenesis is still not fully understood. This article reviews recent research into the role of the gut barrier in the pathogenesis of inflammation and cachexia with special emphasis on two potentially catabolic diseases: liver cirrhosis and chronic heart failure. RECENT FINDINGS: There is increasing evidence that catabolic diseases such as liver cirrhosis and chronic heart failure are associated with increased gut permeability, endotoxemia and enhanced expression of proinflammatory cytokines. In liver cirrhosis normalization of portal hypertension by insertion of a transjugular intrahepatic portosystemic stent shunt obviously causes improvement not only of gut barrier function, but also of nutritional status. SUMMARY: Although its pathogenesis is not yet completely understood, proinflammatory cytokines have been implicated in the onset and progression of cachexia. Recent data support the hypothesis that impaired gut barrier function and increased permeability further translocation of endotoxins. Increased endotoxemia might be a potent trigger of systemic inflammatory response which is involved in the pathogenesis of the cachexia syndrome. Thus, it is tempting to speculate that therapeutic strategies for the improvement of gut barrier function will concomitantly improve nutritional status.

Bacterial Translocation↗

PubMed2004

Electroporation-mediated delivery of molecules to model intestinal epithelia.

This study was conducted to determine if electroporation can deliver membrane-impermeant molecules intracellularly to intact, physiologically competent monolayers that mimic the intestinal epithelium. In addition, the long-term effects of electroporation on these monolayers were studied to determine the kinetics with which monolayers recover barrier function. Caco-2 and T84 cells were electroporated as monolayers using calcein and fluorescein-labeled bovine serum albumin as marker molecules for measuring delivery into cells. Confocal microscopy and flow cytometry were used, respectively, to visualize and quantify uptake of these molecules. Transepithelial resistance was used as a measure of physiologic barrier function. We found that intracellular uptake of calcein and bovine serum albumin occurred uniformly throughout both types of model epithelia and increased as a function of voltage, pulse length, and pulse number. There was no significant difference in uptake resulting from single and multiple pulses of the same total exposure time. We also observed that monolayers exposed to electroporation that induced uptake of up to 10(6) molecules/cell were able to recover normal barrier function within one day. These findings suggest that electroporation may be useful for intracellular delivery into monolayers to study epithelial biology and, possibly, for drug delivery to intestinal epithelium.

Animals↗

PubMed2002

Intestinal adaptation in short bowel syndrome.

Regaining enteral autonomy after extensive small bowel resection is dependent on intestinal adaptation. This adaptational process is characterized by hyperplastic growth of the remaining gut, which is accompanied by both an increase of cell division at the level of the crypt cells and by an increased rate of programmed cell death (apoptosis). Apart from the absorptive function, the small bowel also has a barrier function and plays an important role in interorgan metabolism. Also, these functions are greatly affected by a massive intestinal resection and subsequent recovery by intestinal adaptation. This review aims to give an overview of the debilitating effects of massive intestinal resection on gut function and subsequently discusses intestinal adaptation and possible factors stimulating adaptation.

Adaptation, Physiological↗

PubMed1999

Diagnosis and management of small intestinal diseases.

Advances in the diagnosis and management of small bowel diseases are the subject of this review. Topics covered include improving the specificity of breath tests for bacterial overgrowth; small bowel enteroscopy; early diagnosis of mesenteric ischemia; the use of polymerase chain reaction for diagnosing central nervous system involvement in Whipple's disease; progress in defining the cause and pathogenesis of chronic idiopathic intestinal pseudoobstruction and the Peutz-Jeghers syndrome; defining the role of gut barrier function in health and disease; the therapeutic role for bile acid-binding resins in diarrhea after refeeding in critically ill patients; use of genetic techniques and topical steroid therapy in treating graft-versus-host disease; and the beneficial effects of combination hormonal therapy in occult gastrointestinal blood loss resulting from angiodysplasia.

Journal Article↗

PubMed2003

Targeting enteric bacteria in treatment of inflammatory bowel diseases: why, how, and when.

PURPOSE: This review discusses the role of bacterial adjuvants and antigens in induction and reactivation of chronic intestinal inflammation in susceptible hosts; discusses the results of recent therapeutic trials of antibiotics, probiotics, and prebiotics; and suggests future treatment strategies. RECENT FINDINGS: Bacterial adjuvants, including peptidoglycan, lipopolysaccharide, and DNA (CpG) bind to membrane-bound toll-like receptors (TLR-2, 4, and 9. respectively) or cytoplasmic (NOD1 and NOD2) receptors (pattern recognition receptors) that activate nuclear factor-kappaB and transcription of many proinflammatory cytokines and adhesion, costimulatory, and major histocompatibility complex class II molecules. Experimental enterocolitis does not occur in a sterile (germ-free) environment and is prevented and treated by broad-spectrum antibiotics. Individual nonpathogenic intestinal bacterial species selectively induce experimental colitis, with host specificity. Crohn disease and ulcerative colitis patients exhibit pathogenic immune responses (loss of immunologic tolerance) to multiple normal enteric bacterial species and serologic responses to Mycobacterium paratuberculosis. Metronidazole and ciprofloxacin selectively treat colonic Crohn disease, but not ulcerative colitis or ileal Crohn disease, and may prevent recurrence of postoperative Crohn disease. Certain probiotic species decrease relapse of ulcerative colitis and chronic pouchitis and delay onset of pouchitis. SUMMARY: Normal, nonpathogenic enteric bacteria induce and perpetuate chronic intestinal inflammation in genetically susceptible hosts with defective immunoregulation, bacterial clearance, or mucosal barrier function. Altering the composition and decreasing mucosal adherence/invasion of commensal bacteria with antibiotics, probiotics, and prebiotics can potentially prevent and treat Crohn disease, pouchitis, and possibly ulcerative colitis, but optimal treatments have not yet been identified.

Journal Article↗

PubMed1996

Induction of NGAL synthesis in epithelial cells of human colorectal neoplasia and inflammatory bowel diseases.

In inflammatory and neoplastic disorders of the colon a defect barrier function of the mucosa may result in absorption of bacterial products from the intestinal lumen. These products may further recruit inflammatory cells and thus augment the inflammatory response. A novel lipocalin in neutrophils, neutrophil gelatinase associated lipocalin (NGAL), with the ability to bind bacterial formylpeptides, has been described and therefore it is of interest to investigate the expression of this protein in diseases of the colon. Expression of NGAL was investigated by immunohistochemistry and by mRNA in situ hybridisation in normal colon and in neoplastic and inflammatory colorectal diseases. A very high expression of NGAL was seen in colonic epithelium in areas of inflammation, both in non-malignant epithelium (diverticulitis, inflammatory bowel disease, and appendicitis) as well as in premalignant and malignant neoplastic lesions of the colon. In adenocarcinoma, the NGAL expression was especially abundant in the transitional mucosa and in the superficial ulcerated area. On the other hand, no NGAL expression could be detected in lymph node metastases from these adenocarcinomas. A weak expression of NGAL in some epithelial cells was only occasionally seen in normal colon. In conclusion, NGAL synthesis is induced in epithelial cells in inflammatory and neoplastic, colorectal diseases. NGAL may serve an important anti-inflammatory function as a scavenger of bacterial products.

Acute-Phase Proteins↗

PubMed2005

In vitro evaluation of the effect of the opioid antagonist N-methylnaltrexone on motility of the equine jejunum and pelvic flexure.

REASONS FOR PERFORMING STUDY: Although potent analgesics, opioids decrease intestinal activity, leading to ileus in many species. N-methylnaltrexone (MNTX), an opioid antagonist which does not cross the blood-brain barrier and antagonises the morphine effect on the intestine, directly stimulates motility and restores function without affecting analgesic properties. While its use has been reported in human subjects, there is no information with regard to its usage in the horse. OBJECTIVES: To determine whether MNTX has an effect on contractile activity of the equine jejunum and pelvic flexure. METHODS: Using circular smooth muscle strips obtained from 8 mature horses, increasing concentrations of MNTX were added to tissue baths in the range of 1 x 10(-9) to 1 x 10(-5) mol/l, and contractile responses were recorded for 3 mins. Data were analysed using a repeated measures ANOVA to determine whether there was a significant drug effect compared to baseline activity. Data were analysed between the jejunum and pelvic flexure using a Mann-Whitney U test. Statistical significance was established as P < 0.05. RESULTS: The administration of MNTX significantly increased the contractile frequency and amplitude at all concentrations relative to baseline (P < 0.0001) for the jejunum. The response was greatest at 1 x 10(-7) mol/l (P = 0.0005), with a mean difference from baseline of 115.12 g/cm2. The highest concentration evaluated (1 x 10(-5) mol/l) had a mean contractile strength of 69.76 g/cm2, which was significantly greater than baseline activity (P = 0.04). A significant increase in contractile activity for the colon was detected at 3 x 10(-7) mol/l and all subsequent concentrations (P < 0.04). Unlike the jejunum, the contractile activity of the pelvic flexure increased progressively with the addition of each subsequent concentration. CONCLUSIONS: N-methylnaltrexone has a direct effect on circular smooth muscle of the equine jejunum and pelvic flexure resulting in an increase in contractile activity. POTENTIAL RELEVANCE: N-methylnaltrexone could potentially be used in conjunction with morphine to provide potent and effective analgesia without compromising intestinal function. Further in vivo investigations are required to determine whether this agent antagonises morphine's effect on motility.

Analysis of Variance↗

PubMed1999

[Enteral nutrition and the critically ill patient].

Critically ill patients often suffer from malnutrition y loss of muscle weight throughout the whole time they are ill, even when they receive nutritional therapy, due to the tremendous amount of stress they undergo accompanied by a high degree of hypercatabolism. The most recent theories all coincide in the importance of the intestine as the preferred way for nutrients to enter the bodies of these patients because besides fulfilling its function to absorb and digest nutrients, the intestine plays an important role as a barrier to bacteria and their toxins. For these reasons, enteral nutrition should be the first option to consider whenever we must feed a critically ill patient by artificial means.

Critical Care↗

PubMedDate not supplied

2002 Harry M. Vars Research Award. Keratinocyte growth factor stimulates the recovery of epithelial structure and function in a mouse model of total parenteral nutrition.

BACKGROUND: Keratinocyte growth factor (KGF) increases intestinal growth and is expressed by intestinal intraepithelial lymphocytes (IEL). Because total parenteral nutrition (TPN) leads to villus atrophy and a loss of epithelial function, we hypothesized that KGF administration could reverse these changes. METHODS: Mice were randomized into three groups: oral feeding (Control); TPN; or TPN with recombinant human KGF. Mice were killed at 7 days, and the small bowel was harvested for histology, DNA, and protein content analysis. Epithelial cell proliferation was studied by 5-bromo-2-deoxyuridine (BrdU) incorporation, and apoptosis was detected by flow cytometry with Annexin V staining. Epithelial ion transport function was studied by Ussing chambers. Epithelial barrier function was assessed with transepithelial resistance and transmural passage of 3H-mannitol. Epithelial KGF receptors expression was studied by using reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot. RESULTS: TPN decreased intestinal DNA, protein content, villus height, and crypt cell proliferation. TPN also resulted in an increase in epithelial cell apoptosis. KGF administration significantly stimulated the recovery of mucosal structures including intestinal protein and DNA content, villus height, and crypt cell proliferation, and decreased epithelial apoptosis. KGF also up-regulate the epithelial KGF receptor expression. Moreover, KGF attenuated the TPN-induced increase in ion transport and increased the epithelial barrier function. CONCLUSIONS: KGF administration reversed many of the adverse epithelial changes associated with TPN administration. Additionally, KGF up-regulated epithelial KGF receptor expression. It is possible that KGF may have a therapeutic efficacy in patients who are receiving TPN.

Animals↗

PubMed2006

Microvascular and epithelial permeability measurements in laboratory animals.

Disruption of the mucosal permeability barrier is an acute life-threatening consequence of intestinal transplantation. The major aim of organ preservation techniques is to maintain the mucosal barrier and its function. Thus, assessment of microvascular and epithelial permeability is an important tool to determine the efficacy of therapeutic interventions. The use of murine models is particularly advantageous, as numerous immunological approaches (e.g., monoclonal antibodies) and genetically modified animal strains have been developed. Large animal models are also useful because they allow online detection of mucosal permeability changes. In this review, we summarize the available methodologies for measuring microvascular and epithelial permeability in the intestines of laboratory animals. We describe the advantages of various photometric and intravital microscopic methods for the assessment of microvascular permeability. Techniques that determine the inward and outward direction of mucosal permeability changes (including radioenzymatic, fluorimetric, and intravital microscopy methods) are also discussed.

Animals↗

PubMed1985

The effect of cyclophosphamide and vincristine on intestinal protein loss in rats.

24 and 48 hours after a single intraperitoneal dose of 80 mg/kg cyclophosphamide (I. group) and 0.20 mg/kg vincristine (II. group) the intestinal protein loss has been studied using the 51CrCl3 isotope method. 16 animals were used as control (III. group). In case of both cytostatics, the intestinal protein loss was significantly higher. Histologically the small bowel mucosa, on the first day after injection, showed, in the crypts, necrotic cells and mitoses arrested in metaphase. By the second day, after injection, severe villous atrophy and occasional mucosal erosions were seen. The causes of these changes are discussed together with the question of the disrupted barrier function of the small bowel.

Animals↗

PubMed2003

Gene alteration of intestinal intraepithelial lymphocytes with administration of total parenteral nutrition.

BACKGROUND: Total parenteral nutrition (TPN) is associated with sepsis and loss of immune reactivity. The authors previously have shown that changes in the intestinal mucosal immune system--ie, intraepithelial lymphocytes (IEL)--lead to a loss of epithelial barrier function. This may be a mechanism by which bacteria and toxins endanger individuals receiving TPN. To identify altered IEL gene expression during TPN administration, microarray assays were used. METHODS: Mice received oral feeding (control) or TPN for 7 days. Small bowel IEL were separated and retained, RNA purified, and microarray assays performed (Affymetrix system, 12,491 genes). Results were expressed as quantile-normalized trimmed-means. Significance equals a greater than 2-fold change (TPN v control), P <.01 (t test) or greater than 3-fold, P <.05. RESULTS: In the TPN group 88, IEL genes were significantly up regulated and 114 downregulated (v control). Of these genes, 4 were identified to have highest degree of upregulation (FK506-binding protein 5; mannose-binding lectin, metallothionein 1 and 2), 2 were highly downregulated (microsomal epoxide hydrolase 1 and cytochrome P450 1a1). These genes were found to have high potential for immune-modulatory effects. CONCLUSIONS: The observed alterations in IEL gene expression may have an important role in the altered immune response with TPN and may relate to the increase in sepsis with TPN administration.

Animals↗

PubMed2004

Mechanisms of diarrhea in the interleukin-2-deficient mouse model of colonic inflammation.

Colitis in interleukin-2-deficient (IL-2(-/-)) mice resembles ulcerative colitis in humans. We studied epithelial transport and barrier function in IL-2(-/-) mice and used this model to characterize mechanisms of diarrhea during intestinal inflammation. (22)Na(+) and (36)Cl(-) fluxes were measured in proximal colon. Net Na(+) flux was reduced from 4.0 +/- 0.5 to 0.8 +/- 0.5 micromol.h(-1).cm(-2), which was paralleled by diminished mRNA and protein expression of the Na(+)/H(+) exchanger NHE3. Net Cl(-) flux was also decreased from 2.2 +/- 1.6 to -2.7 +/- 0.6 micromol.h(-1).cm(-2), indicating impaired Na(+)-Cl(-) absorption. In distal colon, aldosterone-induced electrogenic Na(+) absorption was 6.1 +/- 0.9 micromol.h(-1).cm(-2) in controls and was abolished in IL-2(-/-) mice. Concomitantly, mRNA expression of beta- and gamma-subunits of the epithelial sodium channel (ENaC) was reduced. Epithelial barrier was studied in proximal colon by impedance technique and mannitol fluxes. In contrast to ulcerative colitis, epithelial resistance was increased and mannitol fluxes were decreased in IL-2(-/-) mice. This was in accord with the findings of reduced ion transport as well as increased expression of tight junction proteins occludin and claudin-1, -2, -3, and -5. In conclusion, the IL-2(-/-) mucosa exhibits impaired electroneutral Na(+)-Cl(-) absorption and electrogenic Na(+) transport due to reduced mRNA and protein expression of NHE3 and ENaC beta- and gamma-subunit mRNA. This represents a model of early intestinal inflammation with absorptive dysfunction due to impaired transport protein expression/function while epithelial barrier is still intact. Therefore, this model is ideal to study regulation of transporter expression independent of barrier defects.

Animals↗

PubMed1999

Regional crypt function in rat large intestine in relation to fluid absorption and growth of the pericryptal sheath.

1. Confocal microscopic studies of rat colonic mucosa showed that the pericryptal sheath surrounding distal colonic crypts is an effective barrier both to dextran and NaCl movement, whereas no such structure surrounds the caecal crypts. 2. The distal colonic pericryptal barrier was functionally demonstrated by accumulation of Sodium Green within the pericryptal space. After exposure to benzamil, Sodium Green accumulation was decreased. Fluorescein isocyanate-labelled dextran (FITC dextran; molecular mass 10000 Da) was accumulated in the crypt lumens and pericryptal spaces. Both dextran and Sodium Green accumulation were absent from the pericryptal zone surrounding caecal crypts. 3. Low dietary Na+ intake raised rat plasma aldosterone and stimulated distal pericryptal sheath growth and adhesiveness as shown by increased amounts of F-actin, smooth muscle actin, beta-catenin and E-cadherins in the pericryptal zone. It also raised the capacity of the distal colon to dehydrate against a high luminal hydraulic resistance. This linkage indicates that trophic effects on the colon resulting from a low Na+ diet are not confined solely to effects on transepithelial Na+ transport, but are observed in the pericryptal sheath. 4. A computer model of crypt function confirms that a pericryptal sheath with low permeability to NaCl is an essential component of the crypt dehydrating mechanism.

Actins↗