Intestinal permeability in patients with Crohn's disease and their first degree relatives

Increased Intestinal Permeability and Decreased Resiliency of the Intestinal Barrier in Alcoholic Liver Disease

INTRODUCTION

Only 20%-30% of individuals with alcohol use disorder (AUD) develop alcoholic liver disease (ALD). While the development of gut-derived endotoxemia is understood to be a required cofactor, increased intestinal permeability in ALD is not completely understood.

METHODS

We recruited 178 subjects-58 healthy controls (HCs), 32 with ALD, 53 with AUD but no liver disease (ALC), and 35 with metabolic dysfunction-associated steatotic liver disease (MASLD). Intestinal permeability was assessed by a sugar cocktail as a percentage of oral dose. The permeability test was repeated after an aspirin challenge in a subset.

RESULTS

Five-hour urinary lactulose/mannitol ratio (primarily representing small intestinal permeability) was not statistically different in HC, ALC, ALD, and MASLD groups ( P = 0.40). Twenty-four-hour urinary sucralose (representing whole gut permeability) was increased in ALD ( F = 5.3, P < 0.01) and distinguished ALD from ALC; 24-hour sucralose/lactulose ratio (primarily representing colon permeability) separated the ALD group ( F = 10.2, P < 0.01) from the MASLD group. After aspirin challenge, intestinal permeability increased in all groups and ALD had the largest increase.

DISCUSSION

In a group of patients, we confirmed that (i) the ALD group has increased intestinal permeability compared with the HC, ALC, or MASLD group. In addition, because small bowel permeability (lactulose/mannitol ratio) is normal, the disruption of intestinal barrier seems to be primarily in the large intestine; (ii) decreased resiliency of intestinal barrier to injurious agents (such as NSAID) might be the mechanism for gut leak in subset of AUD who develop ALD.

Chronic exposure to synthetic food colorant Allura Red AC promotes susceptibility to experimental colitis via intestinal serotonin in mice

Chemicals in food are widely used leading to significant human exposure. Allura Red AC (AR) is a highly common synthetic colorant; however, little is known about its impact on colitis. Here, we show chronic exposure of AR at a dose found in commonly consumed dietary products exacerbates experimental models of colitis in mice. While intermittent exposure is more akin to a typical human exposure, intermittent exposure to AR in mice for 12 weeks, does not influence susceptibility to colitis. However, exposure to AR during early life primes mice to heightened susceptibility to colitis. In addition, chronic exposure to AR induces mild colitis, which is associated with elevated colonic serotonin (5-hydroxytryptamine; 5-HT) levels and impairment of the epithelial barrier function via myosin light chain kinase (MLCK). Importantly, chronic exposure to AR does not influence colitis susceptibility in mice lacking tryptophan hydroxylase 1 (TPH1), the rate limiting enzyme for 5-HT biosynthesis. Cecal transfer of the perturbed gut microbiota by AR exposure worsens colitis severity in the recipient germ-free (GF) mice. Furthermore, chronic AR exposure elevates colonic 5-HT levels in naïve GF mice. Though it remains unknown whether AR has similar effects in humans, our study reveals that chronic long-term exposure to a common synthetic colorant promotes experimental colitis via colonic 5-HT in gut microbiota-dependent and -independent pathway in mice.

Dietary nanoparticles compromise epithelial integrity and enhance translocation and antigenicity of milk proteins: An in vitro investigation

Nanoparticles (NPs) are increasingly being used in the food sector, yet little is known about the potential health risks associated with oral exposure to dietary NPs. In this study, the most widely used NPs in food industry including food grade silicon dioxide (SiO₂), titanium dioxide (TiO₂) and silver (Ag), along with their non-food grade and bulk counterparts, are characterized for physicochemical properties and molecular, cellular, and intracellular effects on human intestinal epithelial cells (Caco-2 and HIEC-6). Silver NPs are the most cytotoxic and induce significant cellular changes in oxidative stress, Ca²⁺ flux and mitochondria function, leading to cellular junction disruption at the lowest exposure concentration. At higher testing concentrations, NPs but not microparticles of SiO₂ and TiO₂ cause sublethal cellular responses and remodel tight junctions without impairing epithelial integrity. To relate the cellular results to key events in GI disorder progression, NPs are exposed to an in vitro co-culture model for cow's milk allergy comprised of Caco-2 and allergy sera-primed mast cells (LUVA). All particle treatments increase the allergen delivery across intestinal epithelium and subsequent allergy responses. Overall, the study has identified a particle-dependent alteration in intestinal epithelium and highlighted potential safety concerns of dietary NPs.

Results of the Seventh Scientific Workshop of ECCO: Precision Medicine in IBD-Prediction and Prevention of Inflammatory Bowel Disease

Inflammatory bowel disease [IBD] is a complex chronic disorder with no clear aetiology and no known cure. Despite recent advances in overall disease management and improved therapeutics, patients with IBD still experience a substantial burden. Furthermore, as the incidence continues to increase in developing areas of the world, it is expected that the burden of IBD to society will increase and exert tremendous pressure on health care systems worldwide. Therefore, new strategies to prevent the global increase of IBD are urgently required. Data are being progressively acquired on the period preceding disease diagnosis, which support the concept that IBD has a preclinical period that may reveal the triggers of disease and may be amenable to early intervention. Having a better knowledge of this preclinical period will increase the potential not only for improved understanding of disease pathogenesis and improved therapeutics, but also for disease prediction and prevention.

The Role of Intestinal Permeability in Gastrointestinal Disorders and Current Methods of Evaluation

An increased intestinal permeability has been described in various gastrointestinal and non-gastrointestinal disorders. Nevertheless, the concept and definition of intestinal permeability is relatively broad and includes not only an altered paracellular route, regulated by tight junction proteins, but also the transcellular route involving membrane transporters and channels, and endocytic mechanisms. Paracellular intestinal permeability can be assessed in vivo by using different molecules (e.g., sugars, polyethylene glycols, ⁵¹Cr-EDTA) and ex vivo in Ussing chambers combining electrophysiology and probes of different molecular sizes. The latter is still the gold standard technique for assessing the epithelial barrier function, whereas in vivo techniques, including putative blood biomarkers such as intestinal fatty acid-binding protein and zonulin, are broadly used despite limitations. In the second part of the review, the current evidence of the role of impaired barrier function in the pathophysiology of selected gastrointestinal and liver diseases is discussed. Celiac disease is one of the conditions with the best evidence for impaired barrier function playing a crucial role with zonulin as its proposed regulator. Increased permeability is clearly present in inflammatory bowel disease, but the question of whether this is a primary event or a consequence of inflammation remains unsolved. The gut-liver axis with a crucial role in impaired intestinal barrier function is increasingly recognized in chronic alcoholic and metabolic liver disease. Finally, the current evidence does not support an important role for increased permeability in bile acid diarrhea.

All disease begins in the (leaky) gut: role of zonulin-mediated gut permeability in the pathogenesis of some chronic inflammatory diseases

Improved hygiene leading to reduced exposure to microorganisms has been implicated as one possible cause for the recent "epidemic" of chronic inflammatory diseases (CIDs) in industrialized countries. That is the essence of the hygiene hypothesis that argues that rising incidence of CIDs may be, at least in part, the result of lifestyle and environmental changes that have made us too "clean" for our own good, so causing changes in our microbiota. Apart from genetic makeup and exposure to environmental triggers, inappropriate increase in intestinal permeability (which may be influenced by the composition of the gut microbiota), a "hyper-belligerent" immune system responsible for the tolerance-immune response balance, and the composition of gut microbiome and its epigenetic influence on the host genomic expression have been identified as three additional elements in causing CIDs. During the past decade, a growing number of publications have focused on human genetics, the gut microbiome, and proteomics, suggesting that loss of mucosal barrier function, particularly in the gastrointestinal tract, may substantially affect antigen trafficking, ultimately influencing the close bidirectional interaction between gut microbiome and our immune system. This cross-talk is highly influential in shaping the host gut immune system function and ultimately shifting genetic predisposition to clinical outcome. This observation led to a re-visitation of the possible causes of CIDs epidemics, suggesting a key pathogenic role of gut permeability. Pre-clinical and clinical studies have shown that the zonulin family, a group of proteins modulating gut permeability, is implicated in a variety of CIDs, including autoimmune, infective, metabolic, and tumoral diseases. These data offer novel therapeutic targets for a variety of CIDs in which the zonulin pathway is implicated in their pathogenesis.

Acid-functionalized single-walled carbon nanotubes alter epithelial tight junctions and enhance paracellular permeability

Due to their unique properties, carbon nanotubes (CNTs) are being widely explored for industrial and medical applications. This has necessitated a thorough assessment of the effect of CNTs on human and animal physiology and health. Impact of CNTs on epithelial tight junctions has not been evaluated in the context of their toxic effects in many biological systems. In the present study, we examined the effect of acid functionalized single-walled carbon nanotubes (AF-SWCNTs) on the function and expression of two tight junction proteins (ZO-1 and occludin) in the Madin-Darby canine kidney (MDCK) cell line. Treatment of MDCK cells with AF-SWCNT resulted in a downregulation of tight junction proteins, decreased trans-epithelial electrical resistance (TER), increased paracellular permeability, and disruption of tight junctions. Taken together, our data demonstrate that AF-SWCNT disrupts tight junction barrier by downregulating tight junction proteins in MDCK epithelial cells.

Gut Barrier Dysfunction-A Primary Defect in Twins with Crohn's Disease Predominantly Caused by Genetic Predisposition

BACKGROUND AND AIMS

The aetiology of Crohn's disease is poorly understood. By investigating twin pairs discordant for Crohn's disease, we aimed to assess whether the dysregulated barrier represents a cause or a consequence of inflammation and to evaluate the impact of genetic predisposition on barrier function.

METHODS

Ileal biopsies from 15 twin pairs discordant for Crohn's disease [monozygotic n = 9, dizygotic n = 6] and 10 external controls were mounted in Ussing chambers to assess paracellular permeability to 51Chromium [Cr]-EDTA and trancellular passage to non-pathogenic E. coli K-12. Experiments were performed with and without provocation with acetylsalicylic acid. Immunofluorescence and ELISA were used to quantify the expression level of tight junction proteins.

RESULTS

Healthy co-twins and affected twins displayed increased 51Cr-EDTA permeability at 120 min, both with acetylsalicylic acid [p < 0.001] and without [p < 0.001] when compared with controls. A significant increase in 51Cr-EDTA flux was already seen at 20 min in healthy monozygotic co-twins compared with controls [p≤0.05] when stratified by zygosity, but not in healthy dizygotic co-twins. No difference in E. coli passage was observed between groups. Immunofluorescence of the tight junction proteins claudin-5 and tricellulin showed lower levels in healthy co-twins [p < 0.05] and affected twins [p < 0.05] compared with external controls, while ELISA only showed lower tricellulin in Crohn's disease twins [p < 0.05].

CONCLUSION

Our results suggest that barrier dysfunction is a primary defect in Crohn's disease, since changes were predominantly seen in healthy monozygotic co-twins. Passage of E. coli seems to be a consequence of inflammation, rather than representing a primary defect.

Genetic and Transcriptomic Bases of Intestinal Epithelial Barrier Dysfunction in Inflammatory Bowel Disease

BACKGROUND

Intestinal barrier defects are common in patients with inflammatory bowel disease (IBD). To identify which components could underlie these changes, we performed an in-depth analysis of epithelial barrier genes in IBD.

METHODS

A set of 128 intestinal barrier genes was selected. Polygenic risk scores were generated based on selected barrier gene variants that were associated with Crohn's disease (CD) or ulcerative colitis (UC) in our study. Gene expression was analyzed using microarray and quantitative reverse transcription polymerase chain reaction. Influence of barrier gene variants on expression was studied by cis-expression quantitative trait loci mapping and comparing patients with low- and high-risk scores.

RESULTS

Barrier risk scores were significantly higher in patients with IBD than controls. At single-gene level, the associated barrier single-nucleotide polymorphisms were most significantly enriched in PTGER4 for CD and HNF4A for UC. As a group, the regulating proteins were most enriched for CD and UC. Expression analysis showed that many epithelial barrier genes were significantly dysregulated in active CD and UC, with overrepresentation of mucus layer genes. In uninflamed CD ileum and IBD colon, most barrier gene levels restored to normal, except for MUC1 and MUC4 that remained persistently increased compared with controls. Expression levels did not depend on cis-regulatory variants nor combined genetic risk.

CONCLUSIONS

We found genetic and transcriptomic dysregulations of key epithelial barrier genes and components in IBD. Of these, we believe that mucus genes, in particular MUC1 and MUC4, play an essential role in the pathogenesis of IBD and could represent interesting targets for treatment.

Host-probiotic interaction: new insight into the role of the endocannabinoid system by in vivo and ex vivo approaches

The endocannabinoid system plays an important role in regulating inflammation in several chronic or anomalous gut inflammatory diseases. In vivo and ex vivo studies showed that 30 days treatment with a probiotic mix activated the endocannabinoid system in zebrafish. These results highlight the potential of this probiotic mixture to regulate immune cell function, by inducing gene expression of toll-like receptors and other immune related molecules. Furthermore, TUNEL assay showed a decrease in the number of apoptotic cells, and this finding was supported by a reduction in pro-apoptotic factors and an increase in anti-apoptotic molecules. The results presented here strengthen the molecular mechanisms activated by probiotic mix controlling immune response and inflammation.

Zonulin transgenic mice show altered gut permeability and increased morbidity/mortality in the DSS colitis model

Increased small intestinal permeability (IP) has been proposed to be an integral element, along with genetic makeup and environmental triggers, in the pathogenies of chronic inflammatory diseases (CIDs). We identified zonulin as a master regular of intercellular tight junctions linked to the development of several CIDs. We aim to study the role of zonulin-mediated IP in the pathogenesis of CIDs. Zonulin transgenic Hp2 mice (Ztm) were subjected to dextran sodium sulfate (DSS) treatment for 7 days, followed by 4-7 days' recovery and compared to C57Bl/6 (wild-type (WT)) mice. IP was measured in vivo and ex vivo, and weight, histology, and survival were monitored. To mechanistically link zonulin-dependent impairment of small intestinal barrier function with clinical outcome, Ztm were treated with the zonulin inhibitor AT1001 added to drinking water in addition to DSS. We observed increased morbidity (more pronounced weight loss and colitis) and mortality (40-70% compared with 0% in WT) at 11 days post-DSS treatment in Ztm compared with WT mice. Both in vivo and ex vivo measurements showed an increased IP at baseline in Ztm compared to WT mice, which was exacerbated by DSS treatment and was associated with upregulation of zonulin gene expression (fourfold in the duodenum, sixfold in the jejunum). Treatment with AT1001 prevented the DSS-induced increased IP both in vivo and ex vivo without changing zonulin gene expression and completely reverted morbidity and mortality in Ztm. Our data show that zonulin-dependent small intestinal barrier impairment is an early step leading to the break of tolerance with subsequent development of CIDs.

Management Strategies to Improve Outcomes of Patients With Inflammatory Bowel Diseases

Strategies for management of inflammatory bowel diseases are shifting from simple control of symptoms toward full control of these diseases (clinical and endoscopic remission), with the final aim of blocking their progression and preventing bowel damage and disability. New goals have been proposed for treatment, such as treat to target and tight control based on therapeutic monitoring and early intervention. For patients who achieve clinical remission, there is often interest in discontinuation of therapy due to safety or economic concerns. We review the evidence supporting these emerging paradigms, the reasons that early effective treatment can alter progression of inflammatory bowel diseases, the importance of examining objective signs of inflammation, and the safety of reducing treatment dosage. We also discuss recent findings regarding personalization of care, including factors that predict patient outcomes and response to therapies, as well as preventative strategies.

Mechanisms of Intestinal Epithelial Barrier Dysfunction by Adherent-Invasive Escherichia coli

Pathobiont expansion, such as that of adherent-invasive Escherichia coli (AIEC), is an emerging factor associated with inflammatory bowel disease. The intestinal epithelial barrier is the first line of defense against these pathogens. Inflammation plays a critical role in altering the epithelial barrier and is a major factor involved in promoting the expansion and pathogenesis of AIEC. AIEC in turn can exacerbate intestinal epithelial barrier dysfunction by targeting multiple elements of the barrier. One critical element of the epithelial barrier is the tight junction. Increasing evidence suggests that AIEC may selectively target protein components of tight junctions, leading to increased barrier permeability. This may represent one mechanism by which AIEC could contribute to the development of inflammatory bowel disease. This review article discusses potential mechanisms by which AIEC can disrupt epithelial tight junction function and intestinal barrier function.

Zonulin, a regulator of epithelial and endothelial barrier functions, and its involvement in chronic inflammatory diseases

Beside digesting nutrients and absorbing solutes and electrolytes, the intestinal epithelium with its barrier function is in charge of a tightly controlled antigen trafficking from the intestinal lumen to the submucosa. This trafficking dictates the delicate balance between tolerance and immune response causing inflammation. Loss of barrier function secondary to upregulation of zonulin, the only known physiological modulator of intercellular tight junctions, leads to uncontrolled influx of dietary and microbial antigens. Additional insights on zonulin mechanism of action and the recent appreciation of the role that altered intestinal permeability can play in the development and progression of chronic inflammatory disorders has increased interest of both basic scientists and clinicians on the potential role of zonulin in the pathogenesis of these diseases. This review focuses on the recent research implicating zonulin as a master regulator of intestinal permeability linked to the development of several chronic inflammatory disorders.

Gastrointestinal comorbidities in patients with psoriatic arthritis

Comorbidities associated with psoriatic arthritis (PsA) include cardiovascular diseases, diabetes mellitus, and obesity. This study evaluated the association between PsA and common gastrointestinal (GI) diseases. A retrospective study was performed in Israel's largest health care provider database between 2002 and 2013. 3161 PsA patients were matched for age and sex with 31610 randomly selected patients. We searched these patients' records for the presence of peptic ulcer disease (PUD), reflux esophagitis, Crohn's disease, ulcerative colitis, irritable bowel syndrome (IBS) and celiac disease. T-test was used to compare continuous variables and a Chi-square test was used for categorical variables. Multivariate logistic regression models were used to assess the association between PsA and GI comorbidities. PsA was associated with Crohn's disease (OR 2.4, 95 %CI: 1.75-3.32, p < 0.0001), ulcerative colitis (OR 2.1, 95 %CI: 1.33-3.26, p = 0.001), reflux esophagitis (OR 1.6, 95 %CI: 1.44-1.78, p < 0.0001), PUD (OR 1.5, 95 %CI: 1.31-1.63, p < 0.0001) and IBS (OR 1.4, 95 %CI: 1.01-1.86, p = 0.045). After controlling for known risk factors, the association remained significant between PsA and Crohn's disease (OR 2.2, 95 %CI: 1.59-3.03, p < 0.0001), ulcerative colitis (OR 1.9, 95 %CI: 1.21-3.00, p = 0.005), reflux esophagitis (OR 1.5, 95 %CI: 1.31-1.63, p < 0.0001), and PUD (OR 1.3, 95 %CI: 1.12-1.47, p < 0.0001). No significant association was found between PsA and celiac disease. In the current study PsA was associated with gastrointestinal morbidities including Crohn's disease, ulcerative colitis, PUD and IBS. Physicians treating patients with PsA should be aware of these associations.

Intra-Individual Variation in Serum AZT Concentration is Not Related to Intestinal Absorption or Small Intestinal Inflammatory Changes in Human Immunodeficiency Virus-Infected Subjects

3′-Azido-3′-deoxythymidine (AZT; zidovudine) either alone or in combination with didanosine or another nucleoside analogue is the first-line treatment for patients with human immunodeficiency virus (HIV) infection, many of whom have concurrent gastrointestinal (GI) disease. This study assessed whether the absorption of AZT was affected by GI disease. The absorption and pharmacokinetics of AZT in 23 HIV-infected individuals was measured after a single dose of AZT and was related in 12 patients to small intestinal function. Levels of AZT and its metabolite 5′-glucopyranuronosylthymidine (G-AZT) were measured by radioimmunoassay. Intestinal permeability was assessed by differential urinary excretion of orally administered lactulose/1-rhamnose; absorptive capacity was measured simultaneously by the urinary excretion of 3-o-methyl-D-glucose, d-xylose and 1-rhamnose. Small intestinal inflammation was assessed by faecal excretion of indium-labelled neutrophils. Peak levels of AZT in serum varied between 170 and 1820 ng mL−1. The metabolite G-AZT was present in serum at peak concentrations varying from 1020 to 9930 ng mL−1. There was up to a sevenfold variation in the area under the curve (AUC). The time to maximum serum concentration for AZT was between 30 and 120 min, with an absorption half-life of between 2 and 38 min. The median elimination half-life was 57 min (range 46–72 min), close to the predicted half-life of 60 min. Intestinal permeability was increased in six of the 12 subjects studied and eight had evidence of reduced absorptive capacity. Ten of the 12 patients had evidence of small intestinal inflammation. We concluded that neither changes in permeability nor absorptive capacity influenced the absorption of AZT. There was no relationship between the presence of intestinal inflammation and AZT absorption. This study showed a significant intra-individual variation of serum AZT levels which cannot be explained on the basis of altered intestinal absorptive capacity or intestinal inflammatory changes.

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.

Chasing a ghost?--Issues with the determination of circulating levels of endotoxin in human blood

Reliable quantification of bacterial products such as endotoxin is important for the diagnosis of Gram-negative infection and for the monitoring of its treatment. Further, it is important to identify patients with persistent subclinical level of bacterial products in their systemic circulation as data from animal studies also suggest this may be correlated with the onset of metabolic syndrome. In this review, we first aim to describe the principles of the Limulus amoebocyte lysate (LAL) test, an assay that is used to quantify endotoxin, and the various shortcomings that must be addressed before it can become a reliable means of quantifying endotoxin in samples derived from blood. We then review published data regarding endotoxin levels in healthy subjects and those with sepsis, inflammatory bowel disease, liver disorders and metabolic disorders such as obesity and diabetes. We also review the evidence regarding influence of macronutrients in augmenting the levels of systemic endotoxin. The results of this review show that reported mean levels of endotoxin in the systemic circulation of healthy humans and of those with various clinical disorders vary over a wide range. Further, this review shows that a significant proportion of this variation can be related to the method that was used to prepare plasma and serum samples prior to assay and its ability to reduce the effect of various blood borne factors that interfere with the LAL assay.

Diagnostic and Prognostic Microbial Biomarkers in Inflammatory Bowel Diseases

The microbiome plays multifaceted roles in the pathogenesis of inflammatory bowel diseases (IBD). Accordingly, the clinical challenge of patient heterogeneity in disease phenotype and response to treatment should in part be addressed by biomarkers that detect the host response to microbiota, and the levels of microbial taxa and products eliciting the host response in susceptible individuals. Molecular analysis has revealed much evidence for microbial taxonomic membership and microbial products in association with IBD, but their utility as clinical biomarkers is still in its infancy. A rich area of progress has been the development and validation of host serologic microbial biomarkers, which have achieved a distinctive position in the diagnosis and prognosis in IBD, and as a template for defining other categories of microbial biomarkers in disease state and phenotype.

Immunology of inflammatory bowel disease and molecular targets for biologics

Inflammatory bowel disease (IBD) is an immune-mediated disease and involves a complex interplay of host genetics and environmental influences. Recent advances in the field, including data from genome-wide association studies and microbiome analysis, have started to unravel the complex interaction between host genetics and environmental influences in the pathogenesis of IBD. A drawback of current clinical trials is inadequate or lack of immune phenotyping of patients. However, recent advances in high-throughput technologies provide an opportunity to monitor the dynamic and complex immune system, which may to lead to a more personalized treatment approach in IBD.

The role of Haptoglobin and its related protein, Zonulin, in inflammatory bowel disease

Crohn's disease (CD) and ulcerative colitis (UC), collectively called inflammatory bowel disease (IBD), are immune-mediated conditions characterized by a chronic inflammation of the gut. Their precise etiology is unknown, although an increased intestinal permeability has been shown to play a central role in the pathogenesis of IBD. The intestinal epithelium provides the largest interface between the external environment and the host, and is thus a crucial regulation site of innate and adaptive immunity. Zonulin is one of the few known physiological mediators of paracellular intestinal permeability. It was found upregulated in different immune diseases like Celiac disease and Type 1 Diabetes (T1D). Recently, human zonulin was identified as prehaptoglobin-2 (pre-HP2) which before only had been regarded as the inactive precursor for HP2. Haptoglobin (HP) is a hemoglobin-binding protein with immunomodulatory properties. Its gene harbors a common polymorphism with 2 different alleles: HP1 and HP2. Allele HP2 and genotype HP22 has been shown to be overrepresented in different immune diseases like Rheumatoid Arthritis (RA), Systemic Lupus Erythematosus (SLE) and T1D, and has also been found to be more frequent in patients with IBD (UC and CD) than in healthy controls.   In order to get some clues about the mechanism of action of HP(2) in IBD pathogenesis, we here review the current state of knowledge about zonulin and haptoglobin structure and function, and their plausible role in immune mediated diseases with an emphasis on IBD.

Analysis of single nucleotide polymorphisms in the region of CLDN2-MORC4 in relation to inflammatory bowel disease

AIM: To investigate a possible genetic influence of claudin (CLDN)1, CLDN2 and CLDN4 in the etiology of inflammatory bowel disease.

METHODS: Allelic association between genetic regions of CLDN1, CLDN2 or CLDN4 and patients with inflammatory bowel disease, Crohn’s disease (CD) or ulcerative colitis were investigated using both a case-control study approach (one case randomly selected from each of 191 Swedish inflammatory bowel disease families and 333 controls) and a family-based study (463 non-Swedish European inflammatory bowel disease -families). A nonsynonymous coding single nucleotide polymorphism in MORC4, located on the same linkage block as CLDN2, was investigated for association, as were two novel CLDN2 single nucleotide polymorphism markers, identified by resequencing.

RESULTS: A single nucleotide polymorphism marker (rs12014762) located in the genetic region of CLDN2 was significantly associated to CD (case-control allelic OR = 1.98, 95%CI: 1.17-3.35, P = 0.007). MORC4 was present on the same linkage block as this CD marker. Using the case-control approach, a significant association (case control allelic OR = 1.61, 95%CI: 1.08-2.41, P = 0.018) was found between CD and a nonsynonymous coding single nucleotide polymorphism (rs6622126) in MORC4. The association between the CLDN2 marker and CD was not replicated in the family-based study. Ulcerative colitis was not associated to any of the single nucleotide polymorphism markers.

CONCLUSION: These findings suggest that a variant of the CLDN2-MORC4 region predisposes to CD in a Swedish population.

Mathematical modelling to restore circulating IGF-1 concentrations in children with Crohn's disease-induced growth failure: a pharmacokinetic study

OBJECTIVES

Children with Crohn's disease grow poorly, and inflammation depresses the response of insulin-like growth factor-1 (IGF-1) to growth hormone. Correcting the inflammation normalises growth velocity; however, removing inflammation cannot be achieved in all children. Our lack of understanding of IGF-1 kinetics has hampered its use, particularly as high IGF-1 concentrations over long periods may predispose to colon cancer. We hypothesised that mathematical modelling of IGF-1 would define dosing regimes that return IGF-1 concentrations into the normal range, without reaching values that risk cancer.

DESIGN

Pharmacokinetic intervention study.

SETTING

Tertiary paediatric gastroenterology unit.

PARTICIPANTS

8 children (M:F; 4:4) entered the study. All completed: 5 South Asian British; 2 White British; 1 African British.

INCLUSION CRITERIA

Children over 10 years with active Crohn's disease (C reactive protein >10 mg/l or erythrocyte sedimentation rate >25 mm/h) and height velocity <-2 SD score.

EXCLUSION CRITERIA

closed epiphyses; corticosteroids within 3 months; neoplasia or known hypersensitivity to recombinant human IGF-1 (rhIGF-1).

INTERVENTIONS

Subcutaneous rhIGF-1 (120 μg/kg) per dose over two admissions: the first as a single dose and the second as twice daily doses over 5 days.

PRIMARY OUTCOME

Significant increase in circulating IGF-1.

SECONDARY OUTCOMES

Incidence of side effects of IGF-1. A mathematical model of circulating IGF-1 (Ac) was developed to include parameters of endogenous synthesis (Ksyn); exogenous uptake (Ka) from the subcutaneous dose (As): and IGF-1 clearance: where dAc/dt=Ksyn - Kout×Ac+Ka×As.

RESULTS

Subcutaneous IGF-1 increased concentrations, which were maintained on twice daily doses. In covariate analysis, disease activity reduced Ksyn (p<0.001). Optimal dosing was derived from least squares regression fitted to a dataset of 384 Crohn's patients, with model parameters assigned by simulation.

CONCLUSIONS

By using age, weight and disease activity scaling in IGF-1 dosing, over 95% of children will have normalised IGF-1 concentrations below +2.5 SDs of the normal population mean, a level not associated with cancer risk.

Human β-defensin 3 peptide is increased and redistributed in Crohn's ileitis

BACKGROUND

Antimicrobial peptides (AMPs) maintain a sterile environment in intestinal crypts, limiting microbial colonization and invasion. Decreased AMP expression is proposed to increase the risk for inflammatory bowel disease. Expression and function of inducible AMPs, human β-defensin 2 and 3 (hBD-2 and hBD-3), remain poorly characterized in healthy and chronically inflamed intestine.

METHODS

Peptide concentrations of hBD-2 and hBD-3 in serum and intestinal biopsies of subjects with ulcerative colitis and Crohn's disease (CD), and those of healthy subjects were measured by ELISA. Messenger RNA of hBD-2 and hBD-3 was quantified by quantitative PCR in biopsies from the terminal ileum (TI) of patients with CD and healthy controls. Peptide localization of hBD-3 in the TI was visualized by confocal microscopy.

RESULTS

Immunoreactive hBD-3 peptide is present in the TI and colon in healthy subjects. In the TI of patients with CD, hBD-3, but not hBD-2 peptide, is increased 4-fold, whereas hBD-2 peptide is elevated in the serum. Messenger RNA of hBD-3 in the CD TI remains unchanged and does not correlate with hBD-3 peptide expression. However, hBD-3 is localized to Paneth cell granules and the apical surface of the healthy columnar epithelium. In CD, hBD-3 peptide location switches to the basolateral surface of the columnar epithelium and is diffusely distributed within the lamina propria.

CONCLUSION

The peptide hBD-3 throughout the healthy gastrointestinal tract suggests a role in maintaining balance between host defenses and commensal microbiota. Increased and relocalized secretion of hBD-3 toward the lamina propria in the CD TI indicates possible local immunomodulation during chronic inflammation, whereas increased serum hBD-2 in CD implicates its systemic antimicrobial and immunomodulatory role.

Probiotic-induced apoptosis and its potential relevance to mucosal inflammation of gastrointestinal tract

In this short review we attempt to establish and/or strengthen connections between probiotics administration and apoptotic pathway in gastrointestinal tract. The disturbance of apoptosis is mainly deliberated in the framework of insufficient removal of immuno-effector cells that may cause autoimmunity. In the context of the inflammatory bowel disease (IBD) and necrotizing enterocolitis (NEC), the commensal bacteria and their products effect on gut and immune cell survival are illustrated. The multitude of mechanisms of probiotics to induce cell death is shortly summarized and some aspects of it are being discussed in greater detail. The mechanism of intestinal cell death induced by probiotic administration and its influence on the immune system and potential benefits of apoptosis induction during probiotic therapy is indicated.

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 JAK2 variant rs10758669 in Crohn's disease: altering the intestinal barrier as one mechanism of action

PURPOSE

The aetiology of intestinal barrier dysfunction in Crohn's disease (CD) is poorly understood. Associations in relatives of CD families suggest a genetic basis, but the relevant variants are still unknown. We hypothesized that variants in genes occurring in pathways such as autophagy and IL23 signalling might contribute to CD by altering intestinal permeability.

METHODS

We analysed five variants (rs10758669 within JAK2, rs744166 within STAT3, rs4958847, rs11747270 and rs13361189 within IRGM) in adult German inflammatory bowel disease patients (CD, n = 464; ulcerative colitis (UC), n = 292) and matched healthy controls (n = 508). These data were correlated with gastrointestinal permeability as assessed by lactulose/mannitol ratio in CD patients (n = 141) in remission.

RESULTS

Our data confirm the association between JAK2 rs10758669 (p = 0.026, OR = 1.25, 95% CI = 1.04-1.50) and STAT3 rs744166 (p = 0.04, OR = 0.83, 95% CI = 0.688-0.998) with CD, but not UC. With respect to all the analysed IRGM variants, no association was found to either CD or UC. Among CD patients, an increased intestinal permeability was detected in 65 out of 141 patients (46.1%). Most importantly, patients carrying the C risk allele within JAK2 rs10758669 displayed an increased permeability more often compared with patients without the C allele (p = 0.004). No association with intestinal permeability was found for STAT3 rs744166 and all IRGM variants.

CONCLUSIONS

JAK2 rs10758669 and STAT3 rs744166 increase susceptibility for CD. We show that the A>C substitution in rs10758669 of the JAK2 gene is associated with increased intestinal permeability. Altering intestinal barrier function might thus be one mechanism how JAK2 contributes to CD pathogenesis.

Lipid rafts are disrupted in mildly inflamed intestinal microenvironments without overt disruption of the epithelial barrier

Intestinal epithelial barrier disruption is a feature of inflammatory bowel disease (IBD), but whether barrier disruption precedes or merely accompanies inflammation remains controversial. Tight junction (TJ) adhesion complexes control epithelial barrier integrity. Since some TJ proteins reside in cholesterol-enriched regions of the cell membrane termed lipid rafts, we sought to elucidate the relationship between rafts and intestinal epithelial barrier function. Lipid rafts were isolated from Caco-2 intestinal epithelial cells primed with the proinflammatory cytokine interferon-γ (IFN-γ) or treated with methyl-β-cyclodextrin as a positive control for raft disruption. Rafts were also isolated from the ilea of mice in which colitis had been induced in conjunction with in vivo intestinal permeability measurements, and lastly from intestinal biopsies of ulcerative colitis (UC) patients with predominantly mild or quiescent disease. Raft distribution was analyzed by measuring activity of the raft-associated enzyme alkaline phosphatase and by performing Western blot analysis for flotillin-1. Epithelial barrier integrity was estimated by measuring transepithelial resistance in cytokine-treated cells or in vivo permeability to fluorescent dextran in colitic mice. Raft and nonraft fractions were analyzed by Western blotting for the TJ proteins occludin and zonula occludens-1 (ZO-1). Our results revealed that lipid rafts were disrupted in IFN-γ-treated cells, in the ilea of mice with subclinical colitis, and in UC patients with quiescent inflammation. This was not associated with a clear pattern of occludin or ZO-1 relocalization from raft to nonraft fractions. Significantly, a time-course study in colitic mice revealed that disruption of lipid rafts preceded the onset of increased intestinal permeability. Our data suggest for the first time that lipid raft disruption occurs early in the inflammatory cascade in murine and human colitis and, we speculate, may contribute to subsequent disruption of epithelial barrier function.

Adherent-invasive Escherichia coli induce claudin-2 expression and barrier defect in CEABAC10 mice and Crohn's disease patients

BACKGROUND

Abnormal expression of CEACAM6 observed on the ileal epithelium in Crohn's disease (CD) patients allows adherent-invasive Escherichia coli (AIEC) to colonize gut mucosa. Since intestinal permeability is significantly increased in CD patients, we aimed at investigating whether and how AIEC alter barrier function.

METHODS

Tissue microarray was performed on ileal biopsies from CD patients in quiescent and active phases. CEABAC10 or wildtype mice were orally challenged with 10(9) bacteria. Intestinal permeability was assessed by measuring 4 kDa dextran-FITC flux in serum, barrier integrity was analyzed using biotin tracer experiment, and claudin-2 protein immunostaining. Bacterial translocation was analyzed in Ussing chambers.

RESULTS

Pore-forming tight junction protein claudin-2 is strongly expressed in the ileum of 51% patients in quiescent phase and in 49% of the patients with active CD. Infection of CEABAC10 transgenic mice expressing human CEACAMs with AIEC, but not with nonpathogenic E. coli, led to a significant 3.0-fold increase in intestinal permeability and to disruption of mucosal integrity in a type 1 pili-dependent mechanism. This is consistent with the claudin-2 abnormal expression at the plasma membrane of intestinal epithelial cells observed in AIEC-infected CEABAC10 mice. AIEC bacteria were able to translocate through CEABAC10 intestinal mucosa.

CONCLUSIONS

These findings strongly support the hypothesis that AIEC type 1 pili-mediated interaction with CEACAM6 abnormally expressed in the quiescent phase of CD may disrupt intestinal barrier integrity before the onset of inflammation. Thus, therapeutic targeting claudin-2 induced by AIEC infection could be a new clinical strategy for preserving intestinal barrier function in CD patients.

Systemic antibody responses to gut microbes in health and disease

Gastrointestinal commensal microbes usually exist in mutualistic relationship with their mammalian host. This relationship exists even though the mammalian host immune system is equipped with exquisite sensors for microbial chemical structures which trigger powerful immune defense mechanisms. Such beneficial mutualism is specifically maintained at the gut mucosal interface by a variety of physical and bioactive barriers as well as specific immunregulatory mechanisms. In addition, there is a strict compartmentalization between systemic and gut mucosal immunity--at least in inbred mice--which focuses adaptive immunity to gut microbes specifically to the gut tissue and the gut lumen. Only in circumstances of increased gut microbial exposure due to elevated gut epithelial permeability, due to genetic deficiencies in local defense mechanisms, due to imbalances in local immune regulation or in case of gastrointestinal pathogenic bacterial infections this compartmentalization is broken and systemic immune responses to gut microbes are induced, which manifest for example as systemic antibody responses specific for gut microbial antigens. Here we briefly discuss the abundance of systemic antibody responses to commensal gut bacteria in healthy humans and how it is altered in situations with chronic enteropathies such as in inflammatory bowel disease and HIV-1 infection or infection with gut bacterial pathogens.

Subclinical intestinal inflammation in siblings of children with Crohn's disease

BACKGROUND

Intestinal permeability and altered inflammatory responses, along with genetic and environmental factors, likely contribute to the pathogenesis of Crohn's disease.

AIMS

This study aimed to assess the presence and prevalence of subclinical intestinal inflammation among apparently healthy, first-degree relatives of pediatric patients with Crohn's disease, using non-invasive fecal markers.

METHODS

Stool samples were collected from 13 patients with Crohn's disease, 36 siblings and 41 parents. S100A12 levels were measured using an in-house ELISA assay and calprotectin levels were determined using the PhiCal test, with levels compared to normal healthy population controls.

RESULTS

Fecal S100A12 levels in siblings (median, 14 mg/kg; 95% confidence interval [CI], 9-32 mg/kg) and patients (71 mg/kg; CI 4-286 mg/kg) differed significantly from pediatric controls (1 mg/kg; CI 1-5 mg/kg; p < 0.001). In contrast, fecal calprotectin levels in siblings (22 mg/kg; CI 15-31 mg/kg) were lower than that of pediatric controls (31 mg/kg; CI 19-52 mg/kg; p = 0.03). Fecal markers were not elevated in parents compared to adult controls.

CONCLUSIONS

This study provides further evidence of subclinical intestinal inflammation amongst first-degree relatives of patients with Crohn's disease. The presence of sub-clinical gut inflammation may be a risk factor for the subsequent development of Crohn's disease.

The interaction of gut microbes with host ABC transporters

ATP binding cassette (ABC) transporters are increasingly recognized for their ability to modulate the absorption, distribution, metabolism, secretion and toxicity of xenobiotics. In addition to their essential function in drug resistance, there is also emerging evidence documenting the important role ABC transporters play in tissue defense. In this respect, the gastrointestinal tract represents a critical vanguard of defense against oral exposure of drugs while at the same time functions as a physical barrier between the lumenal contents (including bacteria) and the intestinal epithelium. Given emerging evidence suggesting that multidrug resistance protein (MDR) plays an important role in host-bacterial interactions in the gastrointestinal tract, this review will discuss the interplay between MDR of the intestinal epithelial cell barrier and gut microbes in health and disease. In particular, we will explore host-microbe interactions involving three apically restricted ABC transporters of the intestinal epithelium; P-glycoprotein (P-gp), multidrug resistance-associated protein 2 (MRP2) and cystic fibrosis transmembrane regulator (CFTR).

Adrenomedullin treatment reduces intestinal inflammation and maintains epithelial barrier function in mice administered dextran sulphate sodium

Hyperactivation and hyperpermeability of the intestinal epithelium is a hallmark of IBD. AM has been shown to reduce the severity of colitis in the acetic acid and TNBS-induced colitis model, however the mechanism of the therapeutic effect of AM against the colitis has not been clarified. Here, we show that the protective capability of AM is associated with suppression of inflammation and maintenance of the intestinal epithelial barrier function. In the DSS-induced colitis model, intra-rectal AM-treated mice showed a reduction in loss of body weight and severity of colitis. AM-treatment suppressed phosphorylation of STAT1 and STAT3 in the colonic epithelium, and altered the cytokine balance in the intestinal T cells, with lower levels of IFN-gamma and TNF-alpha but higher levels of TGF-beta. Expression of the epithelial intercellular junctions such as tight and adherence junctions were sustained in the AM-treated mice. In contrast, the epithelial junctions were down-regulated in the control mice, leading to loss of epithelial barrier integrity and enhanced permeability. Collectively, these data indicate a broad spectrum of AM-induced effects with respect to protection against DSS-induced colitis, and suggest a potential therapeutic value of this treatment for IBD.

Role of Klebsiella and collagens in Crohn's disease: a new prospect in the use of low-starch diet

Crohn's disease is suggested to result from a microbially triggered immune-mediated autoimmune process, involving mainly the terminal ileum and ileo-caecal junction. Klebsiella pneumoniae shares certain molecular structures present in pullulanase pulA and pulD secretion enzymes with various self-antigens present in collagens and HLA-B27 molecules, respectively. A link exists between high dietary starch intake and the growth of intestinal microflora, involving especially Klebsiella microbes. Increased exposure to Klebsiella in the gut as the result of high starch intake would lead to high production of antiKlebsiella antibodies as well as autoantibodies to the cross-reactive self-antigens with the resultant inflammation at the pathological sites. Eradication of these microbes from the gut in patients with Crohn's disease with the use of low-starch diet and antibacterial agents as well as immunomodulatory measures could be beneficial in the management of this disease.

Enteropathic spondyloarthropathy: A common genetic background with inflammatory bowel disease?

The association between spondyloarthropathy and inflammatory bowel disease (IBD) is largely established, although prevalence is variable because of different population selection and diagnostic methodologies. Most studies indicate that as many as 10%-15% of cases of IBD are complicated by ankylosing spondylitis (AS) or other forms of spondylarthritis (SpA). Of note, ileal inflammation resembling IBD has been reported in up to two thirds of cases of SpA, and it has been suggested that the presence of ileitis is associated with the chronicity of articular complications. Although this observation is of interest to unravel the pathophysiology of the disease, systematic screening of patients with SpA by ileocolonoscopy is not indicated in the absence of gut symptoms, as only a small proportion of patients with subclinical gut inflammation will develop overt IBD over time. The existence of familial clustering of both IBD and AS, the coexistence of both conditions in a patient, the evidence of an increased risk ratio among first- and second-degree relatives of affected AS or IBD patients and finally, the increased cross-risk ratios between AS and IBD, strongly suggest a shared genetic background. So far, however, IL23R is the only identified susceptibility gene shared by both IBD and AS. Although functional studies are still needed to better understand its pathogenic role, great effort is being spent therapeutically targeting this pathway that may prove effective for both disorders.

Probiotic mixture VSL#3 protects the epithelial barrier by maintaining tight junction protein expression and preventing apoptosis in a murine model of colitis

Changes in epithelial tight junction protein expression and apoptosis increase epithelial permeability in inflammatory bowel diseases. The effect of the probiotic mixture VSL#3 on the epithelial barrier was studied in dextran sodium sulfate (DSS)-induced colitis in mice. Acute colitis was induced in BALB/c mice (3.5% DSS for 7 days). Mice were treated with either 15 mg VSL#3 or placebo via gastric tube once daily during induction of colitis. Inflammation was assessed by clinical and histological scores. Colonic permeability to Evans blue was measured in vivo. Tight junction protein expression and epithelial apoptotic ratio were studied by immunofluorescence and Western blot. VSL#3 treatment reduced inflammation (histological colitis scores: healthy control 0.94 +/- 0.28, DSS + placebo 14.64 +/- 2.55, DSS + VSL#3 8.43 +/- 1.82; P = 0.011). A pronounced increase in epithelial permeability in acute colitis was completely prevented by VSL#3 therapy [healthy control 0.4 +/- 0.07 (extinction/g), DSS + placebo 5.75 +/- 1.67, DSS + VSL#3 0.26 +/- 0.08; P = 0.003]. In acute colitis, decreased expression and redistribution of the tight junction proteins occludin, zonula occludens-1, and claudin-1, -3, -4, and -5 were observed, whereas VSL#3 therapy prevented these changes. VSL#3 completely prevented the increase of epithelial apoptotic ratio in acute colitis [healthy control 1.58 +/- 0.01 (apoptotic cells/1,000 epithelial cells), DSS + placebo 13.33 +/- 1.29, DSS + VSL#3 1.72 +/- 0.1; P = 0.012]. Probiotic therapy protects the epithelial barrier in acute colitis by preventing 1) decreased tight junction protein expression and 2) increased apoptotic ratio.

Induction of persistent colitis by a human commensal, enterotoxigenic Bacteroides fragilis, in wild-type C57BL/6 mice

Enterotoxigenic Bacteroides fragilis (ETBF) causes diarrhea and is implicated in inflammatory bowel diseases and colorectal cancer. The only known ETBF virulence factor is the Bacteroides fragilis toxin (BFT), which induces E-cadherin cleavage, interleukin-8 secretion, and epithelial cell proliferation. A murine model for ETBF has not been characterized. Specific pathogen-free (SPF) C57BL/6J or germfree 129S6/SvEv mice were orally inoculated with wild-type ETBF (WT-ETBF) strains, a nontoxigenic WT strain of B. fragilis (WT-NTBF), WT-NTBF overexpressing bft (rETBF), or WT-NTBF overexpressing a biologically inactive mutated bft (rNTBF). In SPF and germfree mice, ETBF caused colitis but was lethal only in germfree mice. Colonic histopathology demonstrated mucosal thickening with inflammatory cell infiltration, crypt abscesses, and epithelial cell exfoliation, erosion, and ulceration. SPF mice colonized with rETBF mimicked WT-ETBF, whereas rNTBF caused no histopathology. Intestinal epithelial E-cadherin was rapidly cleaved in vivo in WT-ETBF-colonized mice and in vitro in intestinal tissues cultured with purified BFT. ETBF mice colonized for 16 months exhibited persistent colitis. BFT did not directly induce lymphocyte proliferation, dendritic cell stimulation, or Toll-like receptor activation. In conclusion, WT-ETBF induced acute then persistent colitis in SPF mice and rapidly lethal colitis in WT germfree mice. Our data support the hypothesis that chronic colonization with the human commensal ETBF can induce persistent, subclinical colitis in humans.

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.

Chemokines and chemokine receptors in mucosal homeostasis at the intestinal epithelial barrier in inflammatory bowel disease

Chemokines, a large family of small chemoattractive cytokines, and their receptors play an integral role in the regulation of the immune response and homeostasis. The ability of chemokines to attract specific populations of immune cells sets them apart from other chemoattractants. Chemokines produced within the gastrointestinal mucosa are critical players in directing the balance between physiological and pathophysiological inflammation in health, inflammatory bowel disease (IBD), and the progression to colon cancer. In addition to the well-characterized role of chemokines in directed trafficking of immune cells to the gut mucosa, the expression of chemokine receptors on the cells of the epithelium makes them active participants in the chemokine signaling network. Recent findings demonstrate an important role for chemokines and chemokine receptors in epithelial barrier repair and maintenance as well as an intricate involvement in limiting metastasis of colonic carcinoma. Increased recognition of the association between barrier defects and inflammation and the subsequent progression to cancer in IBD thus implicates chemokines as key regulators of mucosal homeostasis and disease pathogenesis.

Dynamics of enterocyte tight junctions: effect of experimental colitis and two different anti-TNF strategies

An alteration of the intestinal barrier is considered to represent an early step in pathogenesis of Crohn's disease. The integrity of intestinal barrier function is guaranteed among other factors by enterocyte tight junction (TJ) proteins. Clinical and experimental data indicate the TNF-alpha to be the major responsible factor for these defects. In the present study we investigated the very early effects of DNBS-ethanol colitis on ileal enterocyte TJ proteins [occludin, zonula occludens-1 (ZO-1), claudin-2] in controls, mice treated with infliximab (IFX) or with etanercept (ETC), and in knockout mice for the TNF-alpha receptor 1 (TNFR-1(-/-)). Circulating TNF-alpha levels were effectively reduced by IFX and ETC (P < 0.01, both) at 3 and at 6 h. DNBS colitis induced disappearance of occludin and ZO-1 from enterocyte cell-cell contact, whereas claudin-2, absent under control conditions, appeared in the ileal epithelium. These alterations were prevented equally by both treatments, IFX and ETC, and in TNFR-1(-/-) animals. DNBS colitis induced a very rapid loss of occludin and ZO-1 from ileal TJ together with an upregulation of claudin-2. Our data are consistent with the hypothesis that TNF-alpha is involved in early TJ rearrangement and that its effects are mediated through TNFR-1. Despite clinical differences, both anti-TNF treatments were equally effective in the present setting.

A common genetic background for inflammatory bowel disease and ankylosing spondylitis: a genealogic study in Iceland

OBJECTIVE

Patients with ankylosing spondylitis (AS) and approximately 50% of their first-degree relatives may have a genetic abnormality that results in subclinical intestinal inflammation. This study was undertaken to examine the familial occurrence and cosegregation of AS and inflammatory bowel disease (IBD) in order to determine whether there is a shared genetic risk factor in families.

METHODS

The Icelandic genealogy database and population-wide data on all living Icelanders diagnosed as having AS (n = 205) and/or IBD (n = 1,352) were used to estimate the risk ratios of AS for relatives of patients with AS, the risk ratios of IBD for relatives of patients with IBD, and the cross-risk ratios of AS for relatives of patients with IBD or of IBD for relatives of patients with AS. The mean kinship coefficients for each disease were calculated. The control population for disease risk calculations comprised 10,000-100,000 sets of matched Icelandic subjects.

RESULTS

First-, second-, and third-degree relatives of patients with AS had risk ratios of 94, 25, and 3.5, respectively, indicating an increased risk of developing AS (each P < 0.0005), while first-, second-, and third-degree relatives of patients with IBD had risk ratios for IBD of 4.4, 2.2, and 1.4, respectively (each P < 0.0001). The cross-risk ratios of IBD were 3.0 and 2.1 in first- and second-degree relatives of patients with AS, respectively, and were the same for AS in first- and second-degree relatives of patients with IBD. With the exception of Crohn's disease, the risk of having AS, ulcerative colitis, or IBD in spouses of patients with these diseases did not differ significantly from that in controls. Calculation of the kinship coefficients confirmed these patterns of familial risk.

CONCLUSION

Patients with AS or IBD in Iceland are significantly more related to each other than are randomly sampled control subjects, in terms of an increased risk of either or both conditions developing in third-degree relatives. These findings suggest that one or more undiscovered genetic variants may underlie the risk of both diseases.

CARD15/NOD2 is required for Peyer's patches homeostasis in mice

Background

CARD15/NOD2 mutations are associated with susceptibility to Crohn's Disease (CD) and Graft Versus Host Disease (GVHD). CD and GVHD are suspected to be related with the dysfunction of Peyer's patches (PP) and isolated lymphoid follicles (LFs). Using a new mouse model invalidated for Card15/Nod2 (KO), we thus analysed the impact of the gene in these lymphoid formations together with the development of experimental colitis.

Methodology/Principal Findings

At weeks 4, 12 and 52, the numbers of PPs and LFs were higher in KO mice while no difference was observed at birth. At weeks 4 and 12, the size and cellular composition of PPs were analysed by flow cytometry and immunohistochemistry. PPs of KO mice were larger with an increased proportion of M cells and CD4⁺ T-cells. KO mice were also characterised by higher concentrations of TNFα, IFNγ, IL12 and IL4 measured by ELISA. In contrast, little differences were found in the PP-free ileum and the spleen of KO mice. By Ussing chamber experiments, we found that this PP phenotype is associated with an increased of both paracellular permeability and yeast/bacterial translocation. Finally, KO mice were more susceptible to the colitis induced by TNBS.

Conclusions

Card15/Nod2 deficiency induces an abnormal development and function of the PPs characterised by an exaggerated immune response and an increased permeability. These observations provide a comprehensive link between the molecular defect and the Human CARD15/NOD2 associated disorders: CD and GVHD.

Bacterial peptidoglycan breaks down intestinal tolerance via mast cell activation: the role of TLR2 and NOD2

Intestinal microbes are believed to be involved in the pathogenesis of inflammatory bowel disease. Microbes and their products are generally well tolerated by intestinal epithelial cells in the intestinal tract of healthy individuals. It is of significance to understand what breaks down the established tolerance leading to intestinal barrier dysfunction and intestinal inflammation. T84 monolayer transported peptidoglycan (PGN) was determined by enzyme-linked immune assay. Mast cell line HMC-1 cell activation in response to PGN stimulation was observed with electron microscopy and measurement of histamine release. T84 monolayer barrier function was determined by recording the transepithelial electric resistance (TER) and measuring the permeability in response to PGN-induced HMC-1 cell activation. Expression of Toll-like receptor (TLR) 2 and nucleotide-binding oligomerization domain (NOD) 2 were determined by immunocytochemistry, real-time reverse transcription (RT)-PCR and Western blot. Exposure to PGN alone did not alter TER and permeability of T84 monolayers. T84 monolayers transported PGN from the apical chamber to the basal chamber of transwell system. TLR2 expressed on the surface of HMC-1 cells. HMC-1 cells absorbed PGN. HMC-1 cells released histamine in response to the PGN stimulation, which was blocked by pretreatment with antibodies or small interfering RNA against TLR2 or NOD2. In a co-culture system, T84 monolayer transported PGN activated HMC-1 cells and increased the horseradish peroxidase flux. TLR2 mediated the PGN-absorption in HMC-1 cells. Blockade of TLR2 or NOD2 abolished PGN-induced HMC-1 cell activation and T84 monolayer barrier dysfunction. T84 monolayer transported PGN activates HMC-1 cells to release chemical mediators to induce T84 monolayer dysfunction that are mediated by TLR2 and NOD2.

Genetics of the innate immune response in inflammatory bowel disease

The discovery of nucleotide-binding oligomerization domain 2/caspase recruitment domain-containing protein 15 (NOD2/CARD15) as the first susceptibility gene in Crohn's disease (CD) has shifted the focus of research into the pathogenesis of inflammatory bowel disease (IBD) firmly to the innate immune response and the integrity of the epithelial barrier. The subsequent implication in IBD of variant alleles of OCTN, DLG5, MDR1, and TLRs has provided further support for a new, more complex model of innate immunity function in the gastrointestinal tract. In this review, we examine the recent advances in our understanding of the influence of genetics of the innate immune response on IBD. We will focus on germline variation of genes encoding pathogen-recognition receptors, proteins involved in epithelial homeostasis and secreted antimicrobial proteins.

Colonic luminal proteases activate colonocyte proteinase-activated receptor-2 and regulate paracellular permeability in mice

Luminal activation of protease-activated receptors-2 (PAR(2)) on colonocytes by trypsin or PAR(2)-activating peptide increases colonic paracellular permeability (CPP). The aim of this study was to evaluate the role of proteases from endogenous and bacterial origin in the modulation of CPP and colonocyte PAR(2) expression in mice. CPP was assessed with (51)Cr-EDTA after intracolonic administration of different protease inhibitors. After 12 days of oral antibiotic treatment, measurements of colonic luminal serine protease activity (CLSPA), CPP, mucosal mouse mast cell proteinase-1 (MMCP-1) content, immunochemistry of PAR(2) and assessment of effects of PAR(2) agonist (SLIGRL) and mast cell degranulator (C48/80) on CPP in Ussing chambers were performed. Immunochemistry was repeated after intracolonic trypsin administration. Colonic infusion of protease inhibitors significantly reduced CPP. In antibiotic-treated mice, CLSPA was reduced coupled with a decrease in PAR(2) expression, but with no change in CPP and MMCP-1 content. Trypsin administration restored PAR(2) expression. The increase in CPP induced by SLIGRL and C48/80 was reduced after antibiotic treatment. Protease activity of colonic content plays an important role in the regulation of mucosal barrier through activation of PAR(2).

Hypothesis about mechanisms through which nicotine might exert its effect on the interdependence of inflammation and gut barrier function in ulcerative colitis

Ulcerative colitis (UC) is characterized by impairment of the epithelial barrier and the formation of ulcer-type lesions, which result in local leaks and generalized alterations of mucosal tight junctions. Ultimately, this results in increased basal permeability. Although disruption of the epithelial barrier in the gut is a hallmark of inflammatory bowel disease and intestinal infections, it remains unclear whether barrier breakdown is an initiating event of UC or rather a consequence of an underlying inflammation, evidenced by increased production of proinflammatory cytokines. UC is less common in smokers, suggesting that the nicotine in cigarettes may ameliorate disease severity. The mechanism behind this therapeutic effect is still not fully understood, and indeed it remains unclear if nicotine is the true protective agent in cigarettes. Nicotine is metabolized in the body into a variety of metabolites and can also be degraded to form various breakdown products. It is possible these metabolites or degradation products may be the true protective or curative agents. A greater understanding of the pharmacodynamics and kinetics of nicotine in relation to the immune system and enhanced knowledge of gut permeability defects in UC are required to establish the exact protective nature of nicotine and its metabolites in UC. This review suggests possible hypotheses for the protective mechanism of nicotine in UC, highlighting the relationship between gut permeability and inflammation, and indicates where in the pathogenesis of the disease nicotine may mediate its effect.

Molecular pathogenesis of inflammatory bowel disease: genotypes, phenotypes and personalized medicine

Crohn's disease (CD) and ulcerative colitis (UC), also known as inflammatory bowel diseases (IBD), are characterized by chronic inflammation of the gastrointestinal tract. IBD is among the few complex diseases for which several genomic regions and specific genes have been identified and confirmed in multiple replication studies. We will review the different loci implicated in disease risk in the context of three proposed mechanisms leading to chronic inflammation of the gut mucosa: 1) deregulation of the innate immune response to enteric microflora or pathogens; 2) increased permeability across the epithelial barrier; and 3) defective regulation of the adaptive immune system. As our knowledge of genetic variation, analytical approaches and technology improves, additional genetic risk factors are expected to be identified. With the identification of novel risk variants, additional pathophysiological mechanisms are likely to emerge. The resulting discoveries will further our molecular understanding of IBD, potentially leading to improved disease classification and rational drug design. Moreover, these approaches and tools can be applied in the context of variable drug response with the goal of providing more personalized clinical management of patients with IBD.