The sugar permeability test reflects disease activity in children and adolescents with inflammatory bowel disease

Fmo5 plays a sex-specific role in goblet cell maturation and mucus barrier formation

The intestine plays a key role in metabolism, nutrient and water absorption, and provides both physical and immunological defense against dietary and luminal antigens. The protective mucus lining in the intestine is a critical component of intestinal barrier function that when compromised, can lead to dysfunctional intestinal barriers that are a defining characteristic of inflammatory bowel disease (IBD), among other intestinal diseases. Here, we define a new role for the flavin-containing monooxygenase family of enzymes in maintaining a healthy intestinal epithelium. In nematodes, we find that Cefmo-2 is necessary and sufficient for proper intestinal barrier function, intestinal actin expression, and is induced by intestinal damage. In mice, we utilize an intestine-specific, inducible knockout model of the prevalent gut Fmo (Fmo5) and find striking phenotypes within two weeks of knockout. These phenotypes include sex-dependent changes in colon epithelial histology, goblet cell localization and maturation factors, and mucus barrier formation. Each of these changes are significantly more severe in female mice, plausibly mirroring differences observed in some types of IBD in humans. Looking further at these phenotypes, we find increased protein folding stress in Fmo5 knockout animals and successfully rescue the severe female phenotype with addition of a chemical ER chaperone. Together, our results identify a new role for Fmo5 in the mammalian intestine and support a key role for Fmo5 in maintenance of ER/protein homeostasis and proper mucus barrier formation.

First-in-Human Assessment of Gut Permeability in Crohn's Disease Patients Using Fluorophore Technology

Background and Aims

The dual sugar absorption test as a classic measure of human intestinal permeability has limited clinical utility due to lengthy and cumbersome urine collection, assay variability, and long turnaround. We aimed to determine if the orally administered fluorophore MB-102 (relmapirazin) (molecular weight [MW] = 372) compares to lactulose (L) (MW = 342) and rhamnose (R) (MW = 164)-based dual sugar absorption test as a measure of gut permeability in people with a spectrum of permeability including those with Crohn's disease (CD).

Methods

We performed a single-center, randomized, open-label, crossover study comparing orally administered MB-102 (1.5 or 3.0 mg/kg) to L (1000 mg) and R (200 mg). Adults with active small bowel CD on magnetic resonance enterography (cases) and healthy adults (controls) were randomized to receive either MB-102 or L and R on study day 1, and the other tracer 3 to 7 days later. Urine was collected at baseline and 1, 2, 4, 6, 8, 10, and 12 hours after tracer ingestion to calculate the cumulative urinary percent excretion of MB-102 and L and R.

Results

Nine cases and 10 controls completed the study without serious adverse events. Urinary recovery of administered MB-102 correlated with recovery of lactulose (r-squared = 0.83) for all participants. MB-102 urine recovery was also tracked with the L:R ratio urine recovery (r-squared = 0.57). In controls, the percentages of L and MB-102 recovered were similar within a narrow range, unlike in CD patients.

Conclusion

This first-in-human study of an orally administered fluorophore to quantify gastrointestinal permeability in adults with CD demonstrates that MB-102 is well tolerated, and its recovery in urine mirrors that of percent L and the L:R ratio.

Intestinal Membrane Function in Inflammatory Bowel Disease

Inflammatory bowel disease is a set of chronic inflammatory diseases that mainly develop in the gastrointestinal mucosa, including ulcerative colitis and Crohn's disease. Gastrointestinal membrane permeability is an important factor influencing the pharmacological effects of pharmaceuticals administered orally for treating inflammatory bowel disease and other diseases. Understanding the presence or absence of changes in pharmacokinetic properties under a disease state facilitates effective pharmacotherapy. In this paper, we reviewed the gastrointestinal membrane function in ulcerative colitis and Crohn's disease from the perspective of in vitro membrane permeability and electrophysiological parameters. Information on in vivo permeability in humans is summarized. We also overviewed the inflammatory bowel disease research using gut-on-a-chip, in which some advances have recently been achieved. It is expected that these findings will be exploited for the development of therapeutic drugs for inflammatory bowel disease and the optimization of treatment options and regimens.

Increased Gut Permeability in First-degree Relatives of Children with Irritable Bowel Syndrome or Functional Abdominal Pain

BACKGROUND & AIMS

Increased gut permeability might contribute to the pathogenesis of irritable bowel syndrome or functional abdominal pain (IBS or FAP). We investigated whether siblings and parents of children with IBS or FAP have increased gut permeability.

METHODS

We performed permeability tests (using sucrose, lactulose, mannitol, and sucralose) on 29 siblings and 43 parents of children with IBS or FAP, and 43 children (controls) and 42 parents of controls, from primary and secondary care. Permeability studies were repeated in 7 siblings and 37 parents of children with IBS or FAP and 23 controls and 36 parents of controls following ingestion of 400 mg of ibuprofen. Percent recovery of sucrose was calculated based on analyses of urine collected overnight; the lactulose/mannitol ratio and percent recovery of sucralose were based on analyses of urine samples collected over a 24-hour period.

RESULTS

When we controlled for age, sex, and family membership, siblings of children with IBS or FAP had increased small bowel permeability (urinary lactulose/mannitol ratio) vs controls (P = .004). There was no difference in gastroduodenal (percent sucrose recovery) or colonic (percent sucralose recovery) permeability between groups. Similarly, parents of children with IBS or FAP also had increased small bowel permeability, compared with parents of controls (P = .015), with no differences in gastric or colonic permeability. After administration of ibuprofen, gastroduodenal and small bowel permeability tended to be greater in IBS or FAP siblings (P = .08) and gastroduodenal permeability tended to be greater in IBS or FAP parents (P = .086).

CONCLUSIONS

Siblings and parents of children with IBS or FAP have increased baseline small intestinal permeability compared with control children and their parents. These results indicate that there are familial influences on gastrointestinal permeability in patients with IBS or FAP.

Comparison of the Intestinal Drug Permeation and Accumulation Between Normal Human Intestinal Tissues and Human Intestinal Tissues With Ulcerative Colitis

The purpose of this study was to examine drug absorption profile utilizing human intestinal tissues from ulcerative colitis (UC) patients and to compare with normal tissues from intestinal cancer patients. Human intestinal tissues from UC and cancer patients mounted in a mini-Ussing chamber were used to evaluate the permeation of drugs, including FD-4, a very low permeable marker, rebamipide, a low permeable marker, and metoprolol, a high permeable marker. The transport index, an index of sum of permeated and tissue-accumulated molecules, of the model drugs was in accordance with their absorption rank order, and was almost kept constant irrespective of autopsy grade based on tissue fibrosis. On the other hand, UC tissues of grade 2 showed the decreased X^corr, an index of permeated amount of molecules and increased T^corr, an index of tissue-accumulated molecules for every tested compound. Our finding of the transport characteristics in intestinal tissues of severe UC patients in mini-Ussing chamber system demonstrated that autopsy grade of UC patients did not drastically change membrane permeability of the tested compounds. Furthermore, it was suggested that morphological changes of intestinal tissues caused by fibrosis led to limited permeation and subsequently increased accumulation with little change of total absorption.

SRC-3 protects intestine from DSS-induced colitis by inhibiting inflammation and promoting goblet cell differentiation through enhancement of KLF4 expression

Goblet cell loss, which leads to the reduction of mucin secretion, is a hallmark of ulcerative colitis (UC). We previously reported that steroid receptor coactivator 3 (SRC-3), a transcriptional coactivator, contributes to host defense against Citrobacter rodentium by recruiting neutrophils, suggesting a role of SRC-3 in intestine homeostasis. However, the biological role of SRC-3 in UC remains unclear. Here, we showed that SRC-3^-/- mice were more susceptible to dextran sulfate sodium (DSS)-induced colitis compared with wild-type mice after oral administration of 2% DSS dissolved in drinking water. After oral administration of 2% DSS, SRC-3^-/- mice displayed higher mortality rate, significant body weight loss, and higher clinical symptom scores compared to wild-type mice. SRC-3^-/- mice suffered a severe loss of mature colonic goblet cells, leading to more severe histopathology and more proinflammatory cytokine production. Mechanistically, SRC-3^-/- mice exhibited a decreased expression of transcription factor KLF4 in the colons, which is responsible for colonic goblet cell differentiation and maturation. At the molecular level, SRC-3 cooperated with c-Fos to promote KLF4 expression at the transcriptional level. These results demonstrate that SRC-3 can ameliorate DSS-induced colitis by inhibiting inflammation and promoting colonic goblet cell differentiation and maturation through enhancing the expression of transcriptional factor KLF4, which is responsible for colonic goblet cell differentiation and maturation.

Peroxisome proliferator-activated receptor gamma activation promotes intestinal barrier function by improving mucus and tight junctions in a mouse colitis model

BACKGROUND AND AIMS

Defects in mucus and intestinal epithelia can lead to intestinal inflammation in colitis. Reduced peroxisome proliferator-activated receptor gamma (PPAR_γ) in the mucosa may contribute to inflammation. However, the roles of PPAR_γ in the intestinal barrier remain poorly understood.

METHODS

Chronic colitis was induced in C57BL/6 mice by administration of dextran sulfate sodium (DSS) for 27 days. Three days before DSS treatment, mice were treated with the PPAR_γ agonist rosiglitazone (Ro) orally at 20 mg kg^-1 day^-1.

RESULTS

The colitis based on disease activity index and colonic histopathology was significantly ameliorated in the DSS + Ro group. Additionally, mice in the DSS + Ro group had a thicker mucous layer than those in DSS + NS group, and muc2 mRNA expression was elevated significantly along with the mouse atonal homolog, SAM-pointed domain-containing Ets-like factor, and anterior gradient 2 genes. Moreover, tight junctions were up-regulated, whereas long myosin light chain kinase and phosphorylation of the myosin II light chain were lower in DSS + Ro mice. Similarly, after HT-29 and Caco-2 cells were treated by LPS or LPS + Ro, PPAR_γ activation by Ro could effectively improve the intestinal barrier, including intestinal mucus and tight junctions.

CONCLUSIONS

Our results demonstrate that activated PPAR_γ could effectively promote intestinal mucus integrity by increasing the number of goblet cells, the glycosylation of mucins, and tight junctions via an MLCK-dependent mechanism.

Protein losing enteropathy: comprehensive review of the mechanistic association with clinical and subclinical disease states

Protein losing enteropathy (PLE) has been associated with more than 60 different conditions, including nearly all gastrointestinal diseases (Crohn’s disease, celiac, Whipple’s, intestinal infections, and so on) and a large number of non-gut conditions (cardiac and liver disease, lupus, sarcoidosis, and so on). This review presents the first attempt to quantitatively understand the magnitude of the PLE in relation to the associated pathology for three different disease categories: 1) increased lymphatic pressure (e.g., lymphangiectasis); 2) diseases with mucosal erosions (e.g., Crohn’s disease); and 3) diseases without mucosal erosions (e.g., celiac disease). The PLE with lymphangiectasis results from rupture of the mucosal lymphatics, with retrograde drainage of systemic lymph into the intestinal lumen with the resultant loss of CD4 T cells, which is diagnostic. Mucosal erosion PLE results from macroscopic breakdown of the mucosal barrier, with the epithelial capillaries becoming the rate-limiting factor in albumin loss. The equation derived to describe the relationship between the reduction in serum albumin (C_P) and PLE indicates that gastrointestinal albumin clearance must increase by at least 17 times normal to reduce the C_P by half. The strengths and limitations of the two quantitative measures of PLE (⁵¹Cr-albumin or α₁-antitrypsin [αAT] clearance) are reviewed. αAT provides a simple quantitative diagnostic test that is probably underused clinically. The strong, unexplained correlation between minor decreases in C_P and subsequent mortality in seemingly healthy individuals raises the question of whether subclinical PLE could account for the decreased C_P and, if so, could the mechanism responsible for PLE play a role in the increased mortality? A large-scale study correlating αAT clearance with serum albumin concentrations will be required in order to determine the role of PLE in the regulation of the serum albumin concentration of seemingly healthy subjects.

The Effect of DA-6034 on Intestinal Permeability in an Indomethacin-Induced Small Intestinal Injury Model

Background/Aims

DA-6034 has anti-inflammatory activities and exhibits cytoprotective effects in acute gastric injury models. However, explanations for the protective effects of DA-6034 on intestinal permeability are limited. This study sought to investigate the effect of DA-6034 on intestinal permeability in an indomethacin-induced small intestinal injury model and its protective effect against small intestinal injury.

Methods

Rats in the treatment group received DA-6034 from days 0 to 2 and indomethacin from days 1 to 2. Rats in the control group received indomethacin from days 1 to 2. On the fourth day, the small intestines were examined to compare the severity of inflammation. Intestinal permeability was evaluated by using fluorescein isothiocyanate-labeled dextran. Western blotting was performed to confirm the association between DA-6034 and the extracellular signal-regulated kinase (ERK) pathway.

Results

The inflammation scores in the treatment group were lower than those in the control group, but the difference was statistically insignificant. Hemorrhagic lesions in the treatment group were broader than those in the control group, but the difference was statistically insignificant. Intestinal permeability was lower in the treatment group than in the control group. DA-6034 enhanced extracellular signal-regulated kinase expression, and intestinal permeability was negatively correlated with ERK expression.

Conclusions

DA-6034 may decrease intestinal permeability in an indomethacin-induced intestinal injury model via the ERK pathway.

A relaxometric method for the assessment of intestinal permeability based on the oral administration of gadolinium-based MRI contrast agents

Herein, a new relaxometric method for the assessment of intestinal permeability based on the oral administration of clinically approved gadolinium (Gd)-based MRI contrast agents (CAs) is proposed. The fast, easily performed and cheap measurement of the longitudinal water proton relaxation rate (R1) in urine reports the amount of paramagnetic probe that has escaped the gastrointestinal tract. The proposed method appears to be a compelling alternative to the available methods for the assessment of intestinal permeability. The method was tested on the murine model of dextran sulfate sodium (DSS)-induced colitis in comparison with healthy mice. Three CAs were tested, namely ProHance®, MultiHance® and Magnevist®. Urine was collected for 24 h after the oral ingestion of the Gd-containing CA at day 3-4 (severe damage stage) and day 8-9 (recovery stage) after treatment with DSS. The Gd content in urine measured by (1)H relaxometry was confirmed by inductively coupled plasma-mass spectrometry (ICP-MS). The extent of urinary excretion was given as a percentage of excreted Gd over the total ingested dose. The method was validated by comparing the results obtained with the established methodology based on the lactulose/mannitol and sucralose tests. For ProHance and Magnevist, the excreted amounts in the severe stage of damage were 2.5-3 times higher than in control mice. At the recovery stage, no significant differences were observed with respect to healthy mice. Overall, a very good correlation with the lactulose/mannitol and sucralose results was obtained. In the case of MultiHance, the percentage of excreted Gd complex was not significantly different from that of control mice in either the severe or recovery stages. The difference from ProHance and Magnevist was explained on the basis of the (known) partial biliary excretion of MultiHance in mice.

Genes involved in the regulation of intestinal permeability and their role in ulcerative colitis

OBJECTIVE

Genome-wide association studies have identified single nucleotide polymorphisms in genes that might influence intestinal barrier function (HNF4A, ECM1, CDH1 and LAMB1) to increase the risk for ulcerative colitis (UC). The aim of our study was to detect causative sequence alterations and provide a functional link to a disturbed intestinal permeability (IP) in UC.

METHODS

A total of 19 UC patients with increased IP (lactulose/mannitol ratio measured by sugar drink test) were identified from a large database, and exon/intron boundaries, coding and promoter regions of HNF4A, ECM1, CDH1 and LAMB1 were sequenced. Variants with putative protein alterations were studied for an association with IP in 82 UC patients. A case-control analysis including a genotype phenotype correlation was performed in 743 patients with inflammatory bowel disease (IBD) and 473 healthy controls.

RESULTS

In UC patients, we identified 11 missense-mutations, 12 synonymous mutations, one putative promoter variant and three variants in introns close to the intron/exon boundaries (CDH1, HNF4A). For several variants prediction tools revealed damaging protein alterations. None of the studied variants, however, showed an association with an increased IP in UC. In the case-control analysis, the frequency of all investigated variants did not differ between UC or Crohn's disease and healthy controls. Furthermore, no significant association was found to a distinct phenotype.

CONCLUSIONS

Despite our large sequencing approach, we could not identify protein altering variants in the genes HNF4A, ECM1, CDH1 and LAMB1 which could explain an impaired intestinal barrier function in UC. The functional relevance of these genes in IBD remains unknown.

Validating biomarkers of treatable mechanisms in irritable bowel syndrome

BACKGROUND

A valid biomarker is 'an indicator of normal biologic or pathogenic processes, or pharmacological responses to a therapeutic intervention'. There is no validated biomarker for irritable bowel syndrome (IBS). The aim of the study was to assess ability of three quantitative traits to identify treatable processes to discriminate between IBS-diarrhea (IBS-D) patients, IBS-constipation (IBS-C) patients and healthy volunteers (HV).

METHODS

In 30 HV, 30 IBS-C patients and 64 IBS-D patients, we characterized bowel symptoms and quantitated pathophysiological mechanisms: bile acid (BA) synthesis (serum C4 and FGF19), fecal BA and fat, colonic transit (CT), and intestinal permeability (IP). We used multiple logistic regression and receiver-operating characteristic (ROCAUC ) to appraise three factors (fecal BA, CT, and IP) individually and in combination to identify discriminant targets for treatment in IBS.

KEY RESULTS

There were significant associations between the three subgroups and symptoms reflecting bowel function and the quantitative traits. There were significant associations between fecal BA and CT at 48 h (r = 0.43; p < 0.001) and between fecal BA and IP (r = 0.23; p = 0.015). Individually, fecal BA and CT48 (but not IP) were significant independent predictors for distinguishing HV from IBS. In combination, they discriminated HV from IBS-D patients (ROCAUC 0.70), HV from IBS-C patients (ROCAUC 0.73), and IBS-C patients from IBS-D patients (ROCAUC 0.86). Colonic transit and fecal BA excretion together discriminate between healthy volunteers and IBS-C patients or IBS-D patients, or between the IBS subgroups with 75-90% specificity at 60% sensitivity.

CONCLUSIONS & INFERENCES

Colonic transit and fecal BA individually and together constitute useful biomarkers to identify treatable mechanisms in IBS and to differentiate subgroups of IBS.

TNFR2 activates MLCK-dependent tight junction dysregulation to cause apoptosis-mediated barrier loss and experimental colitis

BACKGROUND & AIMS

Tight junction dysregulation and epithelial damage contribute to barrier loss in patients with inflammatory bowel disease. However, the mechanisms that regulate these processes and their relative contributions to disease pathogenesis are not completely understood. We investigated these processes using colitis models in mice.

METHODS

We induced colitis by adoptive transfer of CD4(+)CD45RB(hi) cells or administration of dextran sulfate sodium to mice, including those deficient in tumor necrosis factor receptor (TNFR) 1, TNFR2, or the long isoform of myosin light chain kinase (MLCK). Intestinal tissues and isolated epithelial cells were analyzed by immunoblot, immunofluorescence, enzyme-linked immunosorbent assay, and real-time polymerase chain reaction assays.

RESULTS

Induction of immune-mediated colitis by CD4(+)CD45RB(hi) adoptive transfer increased intestinal permeability, epithelial expression of claudin-2, the long isoform of MLCK, and TNFR2 (but not TNFR1) and phosphorylation of the myosin II light chain. Long MLCK upregulation, myosin II light chain phosphorylation, barrier loss, and weight loss were attenuated in TNFR2(-/-) , but not TNFR1(-/-) , recipients of wild-type CD4(+)CD45RB(hi) cells. Similarly, long MLCK(-/-) mice had limited increases in myosin II light chain phosphorylation, claudin-2 expression, and intestinal permeability and delayed onset of adoptive transfer-induced colitis. However, coincident with onset of epithelial apoptosis, long MLCK(-/-) mice ultimately developed colitis. This indicates that disease progresses via apoptosis in the absence of MLCK-dependent tight junction regulation. In support of this conclusion, long MLCK(-/-) mice were not protected from epithelial apoptosis-mediated, damage-dependent dextran sulfate sodium colitis.

CONCLUSIONS

In immune-mediated inflammatory bowel disease models, TNFR2 signaling increases long MLCK expression, resulting in tight junction dysregulation, barrier loss, and induction of colitis. At advanced stages, colitis progresses by apoptosis and mucosal damage that result in tight junction- and MLCK-independent barrier loss. Therefore, barrier loss in immune-mediated colitis occurs via two temporally and morphologically distinct mechanisms. Differential targeting of these mechanisms can lead to improved inflammatory bowel disease therapies.

Chronic immune activation in common variable immunodeficiency (CVID) is associated with elevated serum levels of soluble CD14 and CD25 but not endotoxaemia

Common variable immunodeficiency (CVID), the most frequent symptomatic immunoglobulin primary immunodeficiency, is associated with chronic T cell activation and reduced frequency of CD4(+) T cells. The underlying cause of immune activation in CVID is unknown. Microbial translocation indicated by elevated serum levels of lipopolysaccharide and soluble CD14 (sCD14) has been linked previously to systemic immune activation in human immunodeficiency virus/acquired immune deficiency syndrome (HIV-1/AIDS), alcoholic cirrhosis and other conditions. To address the mechanisms of chronic immune activation in CVID, we performed a detailed analysis of immune cell populations and serum levels of sCD14, soluble CD25 (sCD25), lipopolysaccharide and markers of liver function in 35 patients with CVID, 53 patients with selective immunoglobulin (Ig)A deficiency (IgAD) and 63 control healthy subjects. In CVID subjects, the concentration of serum sCD14 was increased significantly and correlated with the level of sCD25, C-reactive protein and the extent of T cell activation. Importantly, no increase in serum lipopolysaccharide concentration was observed in patients with CVID or IgAD. Collectively, the data presented suggest that chronic T cell activation in CVID is associated with elevated levels of sCD14 and sCD25, but not with systemic endotoxaemia, and suggest involvement of lipopolysaccharide-independent mechanisms of induction of sCD14 production.

Increased small intestinal permeability in ulcerative colitis: rather genetic than environmental and a risk factor for extensive disease?

BACKGROUND

A disturbed epithelial barrier could play a pivotal role in ulcerative colitis (UC). We performed a family-based study analyzing in vivo gastrointestinal permeability in patients with UC, their healthy relatives, spouses, and controls.

METHODS

In total, 89 patients with UC in remission, 35 first-degree relatives (UC-R), 24 nonrelated spouses (UC-NR), and 99 healthy controls (HC) were studied. Permeability was assessed by a sugar-drink test using sucrose (gastroduodenal permeability), lactulose/mannitol (intestinal permeability), and sucralose (colonic permeability). Data were correlated with clinical characteristics including medical treatment.

RESULTS

Increased intestinal permeability was detected significantly more often in UC patients in remission (25/89, 28.1%) compared with HC (6/99, 6.1%; P < 0.001). Similar results were obtained in UC-R (7/35, 20.0%; P = 0.01 compared with HC) regardless of sharing the same household with the patients or not. No difference was found between UC-NR (3/24, 12.5%) and HC. Notably, in UC patients increased intestinal permeability was found in 12/28 patients (42.9%) with pancolitis, 7/30 (23.3%) patients with left-sided colitis, and in 2/19 (10.5%) patients with proctitis (P = 0.04). Gastroduodenal and colonic permeability were similar in all groups. Among patients on azathioprine, increased intestinal permeability was only seen in 1/18 (5.6%) patients. In contrast, in 24/70 (34.3%) patients without azathioprine, an increased intestinal permeability was found (P = 0.005).

CONCLUSIONS

An increased intestinal but not colonic permeability was found in UC patients in clinical remission that could mark a new risk factor for extensive disease location. Similar findings in healthy relatives but not spouses suggest that this barrier defect is genetically determined.

The gut barrier: new acquisitions and therapeutic approaches

The intestinal barrier serves 2 critical functions for the survival of the individual: first, it allows nutrient absorption and second, it defends the body from dangerous macromolecule penetration. It is a complex multilayer system, consisting of an external "anatomic" barrier and an inner "functional" immunological barrier. The interaction of these 2 barriers enables equilibrated permeability to be maintained. Many factors can alter this balance: gut microflora modifications, mucus layer alterations, and epithelial damage can increase intestinal permeability, allowing the translocation of luminal content to the inner layer of intestinal wall. Several techniques are now available that enable us to study gut permeability: "in vitro" models (Caco-2 and HT29-MTX cells) and "in vivo" not invasive tests (sugar tests and radioisotope scanning tests) are used to estimate permeability and to suggest molecular pathophysiological mechanisms of intestinal permeability in health and diseases. Many medicinal products used in the treatment of gastrointestinal diseases have also found to play an active role in modulate intestinal permeability: corticosteroids, 5-aminosalicylic acid, anti-tumor necrosis factor, probiotics, and mucosal protectors, like gelatin tannate. This review will particularly address the role of the gut barrier in maintaining intestinal permeability (microbiota, mucus, and epithelial cells), the techniques used for estimating intestinal permeability and the therapeutic approaches able to modify it.

Urine sugars for in vivo gut permeability: validation and comparisons in irritable bowel syndrome-diarrhea and controls

Mucosal barrier dysfunction contributes to gastrointestinal diseases. Our aims were to validate urine sugar excretion as an in vivo test of small bowel (SB) and colonic permeability and to compare permeability in patients with irritable bowel syndrome-diarrhea (IBS-D) to positive and negative controls. Oral lactulose (L) and mannitol (M) were administered with (99m)Tc-oral solution, (111)In-oral delayed-release capsule, or directly into the ascending colon (only in healthy controls). We compared L and M excretion in urine collections at specific times in 12 patients with IBS-D, 12 healthy controls, and 10 patients with inactive or treated ulcerative or microscopic colitis (UC/MC). Sugars were measured by high-performance liquid chromatography-tandem mass spectrometry. Primary endpoints were cumulative 0-2-h, 2-8-h, and 8-24-h urinary sugars. Radioisotopes in the colon at 2 h and 8 h were measured by scintigraphy. Kruskal-Wallis and Wilcoxon tests were used to assess the overall and pairwise associations, respectively, between group and urinary sugars. The liquid in the colon at 2 h and 8 h was as follows: health, 62 ± 9% and 89 ± 3%; IBS-D, 56 ± 11% and 90 ± 3%; and UC/MC, 35 ± 8% and 78 ± 6%, respectively. Liquid formulation was associated with higher M excretion compared with capsule formulation at 0-2 h (health P = 0.049; IBS-D P < 0.001) but not during 8-24 h. UC/MC was associated with increased urine L and M excretion compared with health (but not to IBS-D) at 8-24 h, not at 0-2 h. There were significant differences between IBS-D and health in urine M excretion at 0-2 h and 2-8 h and L excretion at 8-24 h. Urine sugars at 0-2 h and 8-24 h reflect SB and colonic permeability, respectively. IBS-D is associated with increased SB and colonic mucosal permeability.

Increased intestinal permeability in inflammatory bowel diseases assessed by iohexol test

AIM

To study intestinal permeability (IP) and its relationship to the disease activity in patients with inflammatory bowel diseases (IBD) - Crohn's disease (CD) and ulcerative colitis (UC).

METHODS

Fifty-eight patients with active IBD (32 with CD and 26 with UC) and 25 healthy controls consented to participate in the study. The clinical activity of CD was estimated using the Crohn's Disease Activity Index (CDAI), and the endoscopic activity of UC using the Mayo scoring system. IP was assessed by the rise in levels of iohexol, which was administered orally (25 mL, 350 mg/mL) 2 h after breakfast. Three and six hours later serum (SIC mg/L) and urine (UIC g/mol) iohexol concentrations were determined by a validated HPLC-UV technique.

RESULTS

In the CD group, SIC values at 3 h (2.95 ± 2.11 mg/L) and at 6 h after ingestion (2.63 ± 2.18 mg/L) were significantly higher compared to those of healthy subjects (1.25 ± 1.40 mg/L and 1.11 ± 1.10 mg/L, respectively, P < 0.05). UIC (g/mol) values were also higher in patients, but the differences were significant only for UIC at 6 h. Significant positive correlation (P < 0.05) was found between the CDAI and IP, assessed by SIC at 3 h (r = 0.60) and 6 h (r = 0.74) after the ingestion. In comparison to controls, SIC and UIC of UC patients were higher in the two studied periods, but the differences were significant at 6 h only. Significantly higher values of SIC (P < 0.05) were found in patients with severe endoscopic activity of UC compared to those of patients with mild and moderate activity (3.68 ± 3.18 vs 0.92 ± 0.69 mg/L).

CONCLUSION

Serum levels of iohexol at 3 h and 6 h after its ingestion reflect increased IP, which is related to the disease activity in patients with IBD.

Increased intestinal permeability in inflammatory bowel diseases assessed by iohexol test

AIM: To study intestinal permeability (IP) and its relationship to the disease activity in patients with inflammatory bowel diseases (IBD) - Crohn’s disease (CD) and ulcerative colitis (UC).

METHODS: Fifty-eight patients with active IBD (32 with CD and 26 with UC) and 25 healthy controls consented to participate in the study. The clinical activity of CD was estimated using the Crohn’s Disease Activity Index (CDAI), and the endoscopic activity of UC using the Mayo scoring system. IP was assessed by the rise in levels of iohexol, which was administered orally (25 mL, 350 mg/mL) 2 h after breakfast. Three and six hours later serum (SIC mg/L) and urine (UIC g/mol) iohexol concentrations were determined by a validated HPLC-UV technique.

RESULTS: In the CD group, SIC values at 3 h (2.95 ± 2.11 mg/L) and at 6 h after ingestion (2.63 ± 2.18 mg/L) were significantly higher compared to those of healthy subjects (1.25 ± 1.40 mg/L and 1.11 ± 1.10 mg/L, respectively, P < 0.05). UIC (g/mol) values were also higher in patients, but the differences were significant only for UIC at 6 h. Significant positive correlation (P < 0.05) was found between the CDAI and IP, assessed by SIC at 3 h (r = 0.60) and 6 h (r = 0.74) after the ingestion. In comparison to controls, SIC and UIC of UC patients were higher in the two studied periods, but the differences were significant at 6 h only. Significantly higher values of SIC (P < 0.05) were found in patients with severe endoscopic activity of UC compared to those of patients with mild and moderate activity (3.68 ± 3.18 vs 0.92 ± 0.69 mg/L).

CONCLUSION: Serum levels of iohexol at 3 h and 6 h after its ingestion reflect increased IP, which is related to the disease activity in patients with IBD.

Targeted epithelial tight junction dysfunction causes immune activation and contributes to development of experimental colitis

BACKGROUND & AIMS

Inflammatory bowel disease (IBD) is a multifactorial disease thought to be caused by alterations in epithelial function, innate and adaptive immunity, and luminal microbiota. The specific role of epithelial barrier function remains undefined, although increased activity of intestinal epithelial myosin light chain kinase (MLCK), which is the primary mechanism of tumor necrosis factor-induced barrier dysfunction, occurs in human IBD. Our aim was to determine whether, in an intact epithelium, primary dysregulation of the intestinal epithelial barrier by pathophysiologically relevant mechanisms can contribute to development of colitis.

METHODS

We developed transgenic (Tg) mice that express constitutively active MLCK (CA-MLCK) specifically within intestinal epithelia. Their physiology, immune status, and susceptibility to disease were assessed and compared with non-Tg littermate controls.

RESULTS

CA-MLCK Tg mice demonstrated significant barrier loss but grew and gained weight normally and did not develop spontaneous disease. CA-MLCK Tg mice did, however, develop mucosal immune activation demonstrated by increased numbers of lamina propria CD4(+)lymphocytes, redistribution of CD11c+cells, increased production of interferon-gamma and tumor necrosis factor, as well as increased expression of epithelial major histocompatibility complex class I. When challenged with CD4+CD45+Rb(hi) lymphocytes, Tg mice developed an accelerated and more severe form of colitis and had shorter survival times than non-Tg littermates.

CONCLUSIONS

Primary pathophysiologically relevant intestinal epithelial barrier dysfunction is insufficient to cause experimental intestinal disease but can broadly activate mucosal immune responses and accelerate the onset and severity of immune-mediated colitis.

Intestinal barrier dysfunction in inflammatory bowel diseases

The etiology of human inflammatory bowel diseases (IBDs) is believed to involve inappropriate host responses to the complex commensal microbial flora in the gut, although an altered commensal flora is not completely excluded. A multifunctional cellular and secreted barrier separates the microbial flora from host tissues. Altered function of this barrier remains a major largely unexplored pathway to IBD. Although there is evidence of barrier dysfunction in IBD, it remains unclear whether this is a primary contributor to disease or a consequence of mucosal inflammation. Recent evidence from animal models demonstrating that genetic defects restricted to the epithelium can initiate intestinal inflammation in the presence of normal underlying immunity has refocused attention on epithelial dysfunction in IBD. We review the components of the secreted and cellular barrier, their regulation, including interactions with underlying innate and adaptive immunity, evidence from animal models of the barrier's role in preventing intestinal inflammation, and evidence of barrier dysfunction in both Crohn's disease and ulcerative colitis.

Measurement of intestinal mucosal permeability in dogs with lymphocytic-plasmacytic enteritis

Lymphocytic-plasmacytic enteritis (LPE) is a type of canine inflammatory bowel disease (IBD). One of its most probable causes is a defect in the mucosal permeability barrier. In the present study, intestinal permeability in LPE dogs was examinated to evaluate its clinical value. Twenty-nine dogs with LPE diagnosed by clinical and histological examinations were included in this study. Intestinal permeability was evaluated by measuring the ratio of the concentrations of two sugars (lactulose (L) and rhamnose (R)) with different molecular weights in urine samples after oral administration of a solution containing them. Biopsy specimens of duodenum were evaluated according to histological criteria. The urinary L:R ratio in the 29 LPE dogs (1.68 +/- 1.17, mean +/- SD) was significantly higher than that in the 10 healthy control dogs (0.75 +/- 0.38, P<0.01). In the LPE dogs, a weak correlation was observed between the histopathological grading score of the duodenum and the urinary L:R ratio (r=0.408, P<0.05). The urinary L:R ratio in the 20 dogs showing hypoalbuminemia (< 2.5 g/dl) was significantly higher than that in the 9 dogs with normal serum albumin levels > 2.5 g/dl (P<0.01). In conclusion, permeability of the intestinal mucosa as determined by the urinary L:R ratio could be a useful laboratory parameter for evaluating intestinal damage in LPE dogs.

Invasive Escherichia coli are a feature of Crohn's disease

Crohn's disease (CD) and ulcerative colitis (UC) are idiopathic inflammatory conditions of the gut. Our goal was to investigate if invasive Escherichia coli strains were present in patients with inflammatory bowel disease (IBD). Bacterial strains were isolated from biopsy material obtained from normal controls, and patients with a clinical diagnosis of CD and UC. Invasive bacteria were characterized by gentamicin protection assay and biochemical profiling (Api-20E). Strains were characterized by induction of cytokine expression in epithelial and macrophage cell cultures, measurement of epithelial barrier function, and confocal microscopy. Of all invasive bacterial strains in CD 98.9% were identified as E. coli as opposed to 42.1% in UC and 2.1% in normal controls. Epithelial invasion in vitro was significantly higher for CD-associated E. coli (8.4%, +/-5.5 of initial inoculum (I/O)) in comparison to UC (2.5%, +/-0.4 I/O), but highest for strains from inflamed CD tissue (11.3%, +/-4.3 I/O). Both, CD and UC E. coli strains induced high mean TNF-alpha expression in macrophage cell lines (2604.8 pg/10(5) cells, +/-447.4; 2,402.6 pg/10(5) cells, +/-476.3, respectively), but concentrations were significantly higher for isolates from inflamed CD tissue (3071.3 pg/10(5) cells, +/-226.0). Invasive E. coli from IBD tissue induced similar concentrations of interleukin (IL)-8 in epithelial cell cultures, but strains from inflamed CD tissue induced significantly less epithelial IL-8 (674.1 pg/10(5) cells, +/-58.0 vs 920.5 pg/10(5) cells, +/-94.6). IBD-associated E. coli strains significantly decreased transepithelial resistance, induced disorganization of F-actin and displacement of ZO-1, and E-cadherin from the apical junctional complex (AJC). In comparison to normal controls and UC, E. coli are more prevalent in CD, are highly invasive, and do not encode for known effector proteins. E. coli strains from IBD patients regulate cytokine expression and epithelial barrier function, two pathological features of IBD.

Citrobacter rodentium infection causes iNOS-independent intestinal epithelial dysfunction in mice

Attaching-effacing bacteria are major causes of infectious diarrhea in humans worldwide. Citrobacter rodentium is an attaching-effacing enteric pathogen that causes transmissible murine colonic mucosal hyperplasia. We characterized colonic inflammation and ion transport at 3, 7, 10, 30, and 60 d after infection of C57Bl/6 mice with C. rodentium. Macroscopic damage score was significantly increased 7 and 10 d after infection. Colonic wall thickness was increased at 7, 10, 30, and 60 d. Myeloperoxidase (MPO) activity was significantly increased at 3, 7, and 10 d and returned to control levels by days 30 and 60. The expressions of inducible nitric oxide synthase and cyclooxygenase-2 were increased by C. rodentium infection. Significant reductions in the epithelial secretory response to carbachol, but not to electrical field stimulation or forskolin, were observed at 3 and 10 d of infection. Translocation of enteric bacteria into the mesenteric lymph nodes was observed 10 d following infection. There was no difference in response to infection between animals deficient in inducible nitric oxide synthase and wild-type controls. The COX-2 inhibitor rofecoxib caused decreased wall thickness and MPO activity at day 10. However, COX-2 inhibition did not alter infection-induced changes in ion transport. Citrobacter rodentium infection causes colonic inflammation, mucosal hyperplasia, and nitric-oxide-independent epithelial dysfunction in association with increased permeability to luminal bacteria.

Serum lipopolysaccharide-binding protein in endotoxemic patients with inflammatory bowel disease

BACKGROUND

In inflammatory bowel disease (IBD), enhanced inflammatory activity in the gut is thought to increase the risk of bacterial translocation and endotoxemia. By searching for signs of endotoxin-signaling cascade activation, including augmented levels of endotoxin, lipopolysaccharide-binding protein (LBP), and soluble CD14 receptor (sCD14), this prospective study sought to establish whether endotoxemia could contribute to greater clinical activity of disease.

METHODS

Concentrations of plasma endotoxin, LBP, sCD14, several cytokines, acute phase proteins and clinical activity indices were determined in 104 patients with Crohn's disease (CD) and 52 patients with ulcerative colitis (UC).

RESULTS

Endotoxemia was present in 48% of the patients with CD and in 28% of the patients with UC. The mean LBP was higher in patients with active CD (23.1 +/- 13.7 microg/mL) and UC (21.4 +/- 10.9 microg/mL) than in healthy controls (7.2 +/- 1.8 microg/mL; P < 0.01). Elevated serum concentrations of endotoxin and LBP were even detected in patients with inactive CD. Among the patients with active IBD, those with higher endotoxin levels had the worst clinical activity scores and the highest LBP levels. Treatment normalized LBP concentrations, from 29.1 +/- 13.0 to 15.2 +/- 7.3 microg/mL; (P < 0.05) in active CD and from 21.7 +/- 9.8 to 13.6 +/- 5.7 microg/mL; (P < 0.01) in active UC, along with normalizing endotoxin and sCD14 plasma concentrations.

CONCLUSIONS

Patients with IBD show increased serum levels of endotoxin, LBP and sCD14. This alteration correlates with disease activity, with normal levels recovered after treatment, although less completely in Crohn's disease, and parallels a rise in proinflammatory cytokines, suggesting a contribution of bacterial products to the inflammatory cascade in these patients.

Increased intestinal permeability and NOD2 variants in familial and sporadic Crohn's disease

BACKGROUND

Abnormal barrier function may be genetically determined in Crohn's disease.

AIM

To examine the role of abnormal intestinal permeability in genetic predisposition in multiplex vs. sporadic Crohn's disease families.

METHODS

Intestinal permeability was measured in patients, relatives and partners by means of lactulose/mannitol test. Healthy subjects from the hospital staff served as controls. CARD15 mutations were investigated in sporadic and familial Crohn's disease patients and in a group of blood donors.

RESULTS

The median lactulose/mannitol ratio was increased significantly in Crohn's disease patients vs. their relatives [0.03 (0.01-0.24) vs. 0.01 (0.003-0.19), P=0.005]. The percentage of abnormal tests was significantly higher in familial vs. sporadic first-degree relatives of Crohn's disease patients (29% vs. 11%, P=0.0281). Abnormal permeability occurred significantly more frequent in patients with familial Crohn's disease carrying the frameshift mutation. The frameshift mutation 3020 insC was associated with increased permeability in 75% in the multiplex and in 61% of the sporadic CD patients. One partner had abnormal lactulose/mannitol ratio. Conclusion Intestinal permeability is raised in Crohn's disease patients and relatives, with higher rates in familial vs. sporadic healthy relatives. CARD15 mutations are associated with abnormal permeability in ileal Crohn's disease.

Evidence for a genetic defect in oral tolerance induction in inflammatory bowel disease

BACKGROUND

Previous studies have suggested that there may be a defect in the control of immune responses locally in the intestines of patients with inflammatory bowel disease (IBD). Recently, we documented a failure to induce oral tolerance to a fed soluble protein antigen, keyhole limpet hemocyanin (KLH), in IBD patients. Both Crohn's disease (CD) and ulcerative colitis (UC) appear to be multigenic disorders with evidence of familial segregation. In this study, we analyzed multiplex IBD families to determine whether the defect in oral tolerance induction is genetically regulated.

METHODS

Patients and first-degree relatives from 6 multiplex families were fed KLH 50 mg on days 0 to 5 and 10 to 15, followed by subcutaneous immunizations on days 26 and 35. Blood was obtained and analyzed for KLH-specific T cell proliferative responses and cytokine production. Intestinal permeability was also assessed.

RESULTS

In contrast to normal controls, all IBD patients, save 1 (10 patients out of 11 tested P<.0001 versus normal controls), failed to develop oral tolerance to KLH. Furthermore, in 3 of the 4 CD families, at least 1 unaffected family member (total of 5/14 unaffected individuals, P=.002 versus normal controls) also failed to tolerize. This is in sharp contrast to unaffected individuals with no family history of IBD (1/31 tested to date).

CONCLUSIONS

This failure of tolerance induction could not be attributed to increased intestinal permeability. In the UC families, the defect in tolerance segregated with disease. These data support a genetic defect in tolerance induction in CD.

Bronchial Hyperresponsiveness in Patients with Inflammatory Bowel Disease

Pulmonary complications have been described in patients with inflammatory bowel disease. The aim of this study was to evaluate bronchial hyppersponsiveness (BHR) in patients with Crohn's disease (CD) and ulcerative colitis (UC). Fifteen patients (8 men, 7 women, mean age: 42.20 ± 12.20 years) participated in the study. None of the patients had a prior history of respiratory disease or suffered from other systematic disease. Skin prick tests for common allergens (such as pollens, mites, foods and moulds) were administered to all patients of the study. The control group included 15 healthy volunteers (10 men, 5 women, mean age: 40.33 ± 5.06 years). The skin tests showed that 3 of 15 patients with inflammatory bowel disease were sensitive to common allergens (two patients to mix grasses and one to D. Pteronysinnus). In the control group, one subject was sensitive to D. Pteronysinnus. BHR was estimated after methacholine challenge. The frequency of BHR among the patients with inflammatory bowel disease was 7 of 15 (46.60%), compared with only one in the control group who was positive at the maximum dosage of methacholine (16 mg/dl). Our results indicate that there is an increased frequency of BHR in patients with inflammatory bowel disease.

Galanin contributes to the excess colonic fluid secretion observed in dextran sulfate sodium murine colitis

Galanin is present in enteric nerves lining the gastrointestinal (GI) tract where it is normally involved in regulating intestinal motility by binding to the galanin-1 receptor (Gal1R) subtype expressed by smooth muscle cells. In contrast, although epithelial cells lining the colon do not normally express Gal1R, this protein is up-regulated by the inflammation-associated transcription factor NF-kappaB. We previously showed that the murine colitis induced by dextran sulfate sodium (DSS) was associated with increased Gal1R expression as well as by increased colonic fluid secretion. Although Gal1R up-regulation by colonic epithelial cells results in increased intestinal Cl- secretion, the relative contributions of galanin to this excess colonic fluid secretion could not be determined. We therefore created a mouse genetically incapable of synthesizing Gal1R (GAL1R-/- mice). We herein demonstrate that both wild-type and GAL1R-/- mice developed identical histologic lesions in response to DSS. This was characterized by a marked inflammatory infiltrate, activation of NF-kappaB in both enterocytes and enteric nerves, and a threefold increase in neuronal galanin. Colonic fluid secretion, while increased, was approximately half that in GAL1R-/- mice as compared with their wild-type littermates. Overall, then, these findings strongly suggest that approximately half of the increase in colonic fluid secretion in DSS colitis is due to up-regulation of the Gal1R.

A porous defense: the leaky epithelial barrier in intestinal disease

A critical function of the intestinal mucosa is to form a barrier that separates luminal contents from the interstitium. This intestinal barrier is compromised in a number of intestinal diseases, most notably inflammatory bowel disease. In vitro studies have demonstrated that cytokines elaborated by immune cells can cause the mucosal barrier to become leaky; these cytokines are known to be increased in intestinal mucosa involved in inflammatory bowel disease. Detailed information describing the mechanisms by which altered cytokine signaling occurs is not available, but recent data implicate the cytoskeleton within epithelial cells as a critical regulator of the mucosal barrier under physiological and pathophysiological conditions. Using available data, we describe a model of intestinal disease where an initial insult to the epithelial barrier may trigger a self-amplifying cycle of immune activation, cytokine release, and further barrier dysfunction. This model is supported by the observation that pharmacological abrogation of cytokine signaling corrects both barrier defects and clinical disease in animal models and human patients, although such therapy clearly has multiple mechanisms. Other therapeutic targets that represent strategies to prevent or reverse disease processes are also considered. The overarching hypothesis is that modulation of the mucosal epithelial barrier plays a critical role in the initiation and propogation of inflammatory intestinal diseases.

Do high serum levels of anti-Saccharomyces cerevisiae antibodies result from a leakiness of the gut barrier in Crohn's disease?

OBJECTIVES

To examine the relationship between serum levels of anti-Saccharomyces cerevisiae antibodies (ASCAs) and intestinal permeability at a given time (hypothesis 1) and the probability of increased ASCA serum levels with increased intestinal permeability (hypothesis 2) in patients with Crohn's disease.

METHODS

Each hypothesis was tested retrospectively with its own study population: group A for hypothesis 1 and group B for hypothesis 2. Intestinal permeability was measured by lactulose/mannitol test and ASCAs were quantified by using ELISA. Patients received either no treatment or 5-aminosalicylates. The lactulose/mannitol test and sampling of sera for ASCA assessment had to be performed within 1 month in group A. In group B the highest intestinal permeability value obtained from among at least three measurements made during different stages of disease activity was chosen for evaluation.

RESULTS

Both study populations consisted of 140 patients with Crohn's disease. Elevated IgG ASCAs were detected in 64% (90/140) in group A compared with 65% (91/140) in group B. In group A, 64% (90/140) and in group B 66% (92/140) were IgA ASCA positive. Correlation analysis showed a tendency for a positive relationship between IgG ASCAs and intestinal permeability in group A (tau = 0.16, P = 0.07) and in group B (tau = 0.16, P = 0.06). A positive trend was seen for the combination of high intestinal permeability and high IgG ASCAs in group B (chi-squared test, P = 0.07).

CONCLUSION

Elevated serum levels of anti-S. cerevisiae antibodies do not seem to result primarily from a defect of the gut barrier. This observation points to an intrinsic pathomechanism in the development of increased ASCA serum levels.

The mechanisms of prednisone inhibition of inflammation in Crohn's disease involve changes in intestinal permeability, mucosal TNFalpha production and nuclear factor kappa B expression

BACKGROUND

The clinical course of Crohn's disease after the induction of remission with medical therapy is characterized by unpredictable relapse.

AIM

To evaluate three surrogate markers, intestinal permeability, mucosal TNFalpha and nuclear factor (NF)-kappaB/IkappaBalpha expression, in order to determine the relationship of these parameters to clinical relapse.

METHODS

Thirty patients with active Crohn's disease were treated with a 10 week course of prednisone using a tapering dosing regimen. Intestinal permeability (lactulose/mannitol [L/M ratio]) was determined at baseline and at the end of prednisone tapering. TNFalpha production and the levels of expression of NF-kappaB/IkappaBalpha were measured in colonic mucosal biopsies obtained after the induction of remission.

RESULTS

Twenty-two patients (73%) achieved remission and 50% of patients experienced a clinical relapse during the ensuing 12 months. Treatment with prednisone resulted in a significant decrease in the L/M ratio. Of the patients that relapsed, 75% had a raised L/M ratio at the time of remission compared with 20% of patients with a normal L/M ratio (P < 0.008; hazard ratio = 6.094; CI 1.55, 17.43). Mucosal TNFalpha production was greater in relapsers compared with those who remained in remission. The levels of NF-kappaB in relapsers were significantly greater and levels of cytosolic IkappaBalpha were significantly lower compared with those measured in patients who remained in remission.

CONCLUSIONS

These findings underscore the importance of incorporating biological parameters of inflammation in determining the clinical course of Crohn's disease.

Intestinal barrier: an interface between health and disease

The intestine constitutes the largest interface between a person and his or her environment, and an intact intestinal barrier is thus essential in maintaining health and preventing tissue injury and several diseases. The intestinal barrier has various immunological and non-immunological components. The epithelial barrier is one of the most important non-immunological components. Hyperpermeability of this barrier is believed to contribute to the pathogenesis of several gastrointestinal disorders including inflammatory bowel disease, celiac disease and food allergy. Hence, assessing barrier integrity is of the utmost importance. One of the more quantitative gauges for this assessment is transepithelial permeability of various molecular probes, among which sugars are commonly used. Measures of intestinal permeability might also be useful as markers for assessment of prognosis and follow up in various gastrointestinal disorders. The present article is a review of the normal and abnormal functioning of the intestinal barrier, the diseases that can result from loss of barrier integrity, and some promising agents and strategies for restoring barrier normality and integrity.

Use of Lactobacillus-GG in paediatric Crohn's disease

The potential role of luminal bacteria in initiating the abnormal immune response seen in inflammatory bowel disease is stressed by many observations. A defect in mucosal barrier function could allow luminal bacterial antigens to initiate the chronic relapsing inflammation in Crohn's disease. The potential role of luminal bacteria in initiating the abnormal immune response seen in inflammatory bowel disease is stressed by many observations. A pilot study to investigate the possible effect of Lactobacillus GG in children with active Crohn's disease was conducted. Four male patients were enrolled, median age 14.5 years (range 10-18). In terms of clinical outcome, the patients showed significant improvement. In three patients on Lactobacillus GG, it was possible to taper the dose of steroids. Thus, although our data are obviously very preliminary, Lactobacillus GG appears to be effective in improving the clinical status of children with Crohn's disease. A multicentre study is currently being carried out in 7 US University centres in a randomized, double-blind, placebo-controlled fashion to establish the efficacy of this probiotic in children with Crohn's disease.

Anti-tumor necrosis factor treatment restores the gut barrier in Crohn's disease

OBJECTIVES

A primary defect of the tight junctions and, hence, increased intestinal epithelial permeability has been proposed as a basic pathogenic event in Crohn's disease. Challenge of the mucosal immune system by the commensal gut flora would then result in chronic inflammation. Alternatively, increased permeability could be the result of inflammation. Our aim was to study intestinal permeability in refractory Crohn's disease before and after treatment with monoclonal chimeric antibodies directed against tumor necrosis factor (TNF) to investigate whether the abnormal permeability persists after control of inflammation.

METHODS

Twenty-three patients with active Crohn's disease were evaluated before and 4 wk after a single infusion of 5 mg/kg infliximab. Intestinal permeability was studied by measurement of urinary excretion of 51Cr-EDTA after oral intake.

RESULTS

The increased permeation of 51Cr-EDTA through the small intestine (1.63% interquartile range [IQR] 1.06-2.07) and the overall permeation (3.27% IQR 2.40-4.38) before therapy decreased significantly after infliximab infusion to values (1.04% IQR 0.74-1.54 and 2.42% IQR 2.03-2.80, respectively) in the range of those found in normal volunteers (1.12% IQR 0.85-1.58 and 2.28% IQR 1.88-2.86, respectively).

CONCLUSION

Inhibiting the proinflammatory cytokine tumor necrosis factor dramatically reduces gut inflammation and largely restores the gut barrier in Crohn's disease. Our data confirm the central role of TNF in gut barrier modulation in inflammatory conditions in vivo.

Etiopathogenesis of inflammatory bowel disease: the importance of the pediatric perspective

Inflammatory bowel disease (IBD) is now recognized as a common chronic disease affecting children and adolescents. This article will review recent advances made in the fields of genetics, epidemiology, gut ecology, and immunology regarding the etiopathogenesis of IBD, with particular emphasis on the contributions made by pediatric studies. Areas where further study of the pediatric age group would be beneficial will be highlighted.

Antibody response to dietary and autoantigens in G alpha i2-deficient mice

BACKGROUND

Mice with a targeted mutation in the G protein subunit G alpha i2 gene develop a colonic mucosal inflammation, with a highly activated B-cell response. We wanted to investigate whether this increased B-cell activity was directed against dietary antigens and/or various self tissues.

METHODS

The level of antibodies specific for dietary (gliadin, soya and fish meal) antigens was measured by ELISA. Reactivity against self antigens was measured by immunohistochemistry on cryo-sectioned mouse and rat tissue. Sera and intestinal lavages were analysed from G alpha i2-/- mice before and after development of colitis and in age-matched wild type litter mates.

RESULTS

Titres of antibodies against dietary antigens were significantly enhanced both in serum and in large intestinal lavages from G alpha i2-/- mice with ongoing colitis but not prior to disease, as compared to wild type mice. The autoreactivity to self tissues was significantly increased in G alpha i2-/- mice both before and after development of colitis as compared to litter mate control animals. Self tissue reactivity was directed not only against epithelial cells of the colon, small intestine and gastric glands, but also against smooth muscle cells, hepatocytes, bile duct cells, renal tubule and collecting tubule cells of the kidney. In analogy to human ulcerative colitis, autoantibodies against epithelial cells, bile duct epithelium and neutrophil granulocytes were found.

CONCLUSIONS

Earlier increase in levels of autoantibodies (before onset of colitis) than of food antibodies (after onset of colitis) suggests the latter response to be a secondary phenomenon to e.g. a destroyed barrier function.

Effects of therapy with lansoprazole on intestinal permeability and inflammation in young cystic fibrosis patients

BACKGROUND

Defective pancreatic bicarbonate secretion with low intestinal pH or intestinal inflammation of any origin increase intestinal permeability in cystic fibrosis (CF).

METHODS

In this open study, the authors evaluated the effect of a proton-pump inhibitor on intestinal permeability and inflammation in 14 young, pancreatic-insufficient CF patients. Permeability was measured by a three-sugar permeability test before and after 1 year of lansoprazole use, and urinary nitric oxide (NO) oxidation products were assessed before and during that year as a marker of inflammation.

RESULTS

After 1 year of lansoprazole use, median urinary recovery percentages changed from 2.5% to 1.7% (P = 0.064), from 24.9% to 24.5% (no significance), and from 10.5% to 11.1% (no significance) for lactulose, mannitol, and L-rhamnose, respectively. Despite the fact that the median urinary excretion ratios decreased from 0.108 to 0.083 (P = 0.03) and from 0.246 to 0.176 (P = 0.016) for lactulose and mannitol and for lactulose and rhamnose, respectively, they both remained increased. Median urinary NO products-to-creatinine ratios were 0.287 for CF patients before lansoprazole and 0.130 for healthy control participants (P = 0.002). Although there was a tendency toward a decrease in the NO products-to-creatinine ratio during treatment, this was not significant at the end point.

CONCLUSIONS

Intestinal permeability is considerably increased in CF patients and is partly corrected after the use of a proton-pump inhibitor for 1 year, which may point to a harmful effect of the acid luminal contents on the tight junctional related paracellular permeability pathway. The start and end values for the NO products-to-creatinine ratio in CF patients were not significantly different, but were considerably increased when compared with control participants (P = 0.002).

Increased intestinal permeability precedes the onset of Crohn's disease in a subject with familial risk

Increased intestinal permeability to several specific molecular probes has been observed in patients with Crohn's disease and their first-degree relatives. A positive family history is also a potent risk factor for inflammatory bowel disease. Although it has been argued that increased permeability in relatives may confer an increased future risk of developing Crohn's disease, long-term follow-up of such family members has been lacking. We describe a 24-year-old woman with a positive family history of Crohn's disease who had an elevated gut permeability to (51)Cr-EDTA at age 13, as part of a cross-sectional cohort study in patients and their first-degree relatives. She was asymptomatic at the time, and extensive investigation found no evidence of microscopic or macroscopic Crohn's disease. Repeat investigation because of symptom onset at age 21 revealed ileocolonic Crohn's disease, which required treatment with systemic corticosteroids to induce a clinical remission. In this case, a permeability defect was clearly identified to precede the onset of Crohn's disease in a subject at increased risk. This observation provides support for the hypothesis that increased gut permeability to macromolecules is an early step in the pathogenesis of this disorder.

Diagnostic markers of inflammatory bowel disease

The diagnosis of inflammatory bowel disease is usually straightforward, based on a detailed history and physical examination, along with standard radiographic and endoscopic investigations, biopsies, and laboratory parameters. More challenging is the search for clinically useful, noninvasive markers for Crohn disease and ulcerative colitis to accurately screen cases with nonspecific and indolent symptoms. Equally required are diagnostic markers that discriminate between these two disorders in cases with indeterminate colitis. Another dilemma for clinicians is that there are no simple measures to observe disease activity and predict relapses. This review describes the recent advances in diagnostic markers that afford the ability to screen for inflammatory bowel disease, discriminate between its types, and monitor disease activity. These include serological, fecal, and tissue markers; permeability tests; and diagnostic imaging using color Doppler ultrasonography.

Recent advances in the diagnosis and treatment of pediatric inflammatory bowel disease

The diagnosis and management of inflammatory bowel disease (IBD) in children and adolescents is a challenge to patients, their families, and to the healthcare team. This review highlights recent advances in the epidemiology, diagnosis, and management of pediatric IBD. Among the most prominent advances are the new diagnostic serologic assays that can help screen for IBD in the absence of physical signs of disease and help discriminate between ulcerative and Crohn's colitis. Other tests have been identified as potential noninvasive markers of disease activity, including color Doppler abdominal ultrasound and sugar permeability tests. Recent advances in pharmacogenetics afford clinicians the ability to optimize and individualize therapy using azathioprine or 6-mercaptopurine. Finally, bone health has come forth as a major issue in the complete management of pediatric IBD.

Bronchial hyperresponsiveness in children and adolescents with Crohn's disease

Pulmonary manifestations have been described in Crohn's disease (CD). Bronchial responsiveness to methacholine (MCh) was evaluated in 14 children with CD with no evidence of airway disease, 10 asthmatics, and 10 healthy subjects. In patients with CD total blood eosinophils and serum IgE were 0.20 x 10(9) x L(-1) (95% CI -1.68 to 2.08) and 138.4 kU x L(-)(1) (95% CI 18.84 to 257.96), respectively. Three patients with CD had positive prick tests. Bronchial hyperresponsiveness (BHR) was demonstrated in 10 patients with CD (71%) and in the asthmatics, but not in control subjects. In patients with CD PD(20) appeared significantly greater than in asthmatics (699 microg [95% CI 238 to 1,115] versus 104 microg [95% CI 37.35 to 293]; p < 0.05), and was not related either to baseline FEV(1) or IgE or eosinophils (r = 0.32; r = -0.5; r = -0.15, p = NS, respectively). Neither activity nor treatment or duration of CD affected BHR. Five nonatopic CD patients underwent a second MCh challenge over a 25-mo period: the PD(20) appeared significantly greater than basal PD(20) (1,941 microg versus 575 microg, p < 0.05, respectively), in the absence of significant changes of disease activity. BHR might be the expression of subclinical airway inflammation, a phenomenon which can be responsible for the development of various pulmonary manifestations in CD.

Intestinal permeability, leaky gut, and intestinal disorders

A major task of the intestine is to form a defensive barrier to prevent absorption of damaging substances from the external environment. This protective function of the intestinal mucosa is called permeability. Clinicians can use inert, nonmetabolized sugars such as mannitol, rhamnose, or lactulose to measure the permeability barrier or the degree of leakiness of the intestinal mucosa. Ample evidence indicates that permeability is increased in most patients with Crohn's disease and in 10% to 20% of their clinically healthy relatives. The abnormal leakiness of the mucosa in Crohn's patients and their relatives can be greatly amplified by aspirin preadministration. Permeability measurements in Crohn's patients reflect the activity, extent, and distribution of the disease and may allow us to predict the likelihood of recurrence after surgery or medically induced remission. Permeability is also increased in celiac disease and by trauma, burns, and nonsteroidal anti-inflammatory drugs. The major determinant of the rate of intestinal permeability is the opening or closure of the tight junctions between enterocytes in the paracellular space. As we broaden our understanding of the mechanisms and agents that control the degree of leakiness of the tight junctions, we will be increasingly able to use permeability measurements to study the etiology and pathogenesis of various disorders and to design or monitor therapies for their management.