Hyperresponsiveness of the mucosal barrier in Crohn's disease is not tumor necrosis factor-dependent

Angiocrine Regulation of Epithelial Barrier Integrity in Inflammatory Bowel Disease

Inflammatory bowel disease describes chronic inflammatory disorders. The incidence of the disease is rising. A major step in disease development is the breakdown of the epithelial cell barrier. Numerous blood vessels are directly located underneath this barrier. Diseased tissues are heavily vascularized and blood vessels significantly contribute to disease progression. The gut-vascular barrier (GVB) is an additional barrier controlling the entry of substances into the portal circulation and to the liver after passing the first epithelial barrier. The presence of the GVB rises the question, whether the vascular and endothelial barriers may communicate bi-directionally in the regulation of selective barrier permeability. Communication from epithelial to endothelial cells is well-accepted. In contrast, little is known on the respective backwards communication. Only recently, perfusion-independent angiocrine functions of endothelial cells were recognized in a way that endothelial cells release specific soluble factors that may directly act on the epithelial barrier. This review discusses the putative involvement of angiocrine inter-barrier communication in the pathogenesis of IBD.

Macrophage Deficiency Makes Intestinal Epithelial Cells Susceptible to NSAID-Induced Damage

Objectives

In Crohn's disease (CD), the mechanisms underlying the regulation by granulocyte-macrophage colony-stimulating factor (GM-CSF) of mucosal barrier function in the ileum are unclear. We analyzed the molecular mechanisms underlying the regulation by GM-CSF of the mucosal barrier function.

Methods

We examined the role of GM-CSF in the intestinal barrier function in CD at the molecular-, cellular-, and animal-model levels.

Results

Macrophages directly secreted GM-CSF, promoting intestinal epithelial proliferation and inhibiting apoptosis, which maintained intestinal barrier function. Macrophages were absent in NSAID-induced ileitis, causing GM-CSF deficiency, increasing the apoptosis rate, decreasing the proliferation rate, increasing inter- and paracellular permeabilities, decreasing the TJP levels, and reducing the numbers of mesenteric lymph nodes, memory T cells, and regulatory T cells in Csf1^op/op transgenic mice.

Conclusions

GM-CSF is required for the maintenance of intestinal barrier function. Macrophages directly secrete GM-CSF, promoting intestinal epithelial proliferation and inhibiting apoptosis.

Immunity, microbiota and kidney disease

The recognition that intestinal microbiota exert profound effects on human health has led to major advances in our understanding of disease processes. Studies over the past 20 years have shown that host components, including components of the host immune system, shape the microbial community. Pathogenic alterations in commensal microorganisms contribute to disease manifestations that are generally considered to be noncommunicable, such as inflammatory bowel disease, diabetes mellitus and liver disease, through a variety of mechanisms, including effects on host immunity. More recent studies have shed new light on how the immune system and microbiota might also drive the pathogenesis of renal disorders. In this Review, we discuss the latest insights into the mechanisms regulating the microbiome composition, with a focus both on genetics and environmental factors, and describe how commensal microorganisms calibrate innate and adaptive immune responses to affect the activation threshold for pathogenic stimulations. We discuss the mechanisms that lead to intestinal epithelial barrier inflammation and the relevance of certain bacteria to the pathogenesis of two common kidney-based disorders: hypertension and renal stone disease. Limitations of current approaches to microbiota research are also highlighted, emphasizing the need to move beyond studies of correlation to causation.

Effects of Anti-Cytokine Antibodies on Gut Barrier Function

Anti-cytokine antibodies are used in treating chronic inflammatory diseases and autoimmune diseases such as inflammatory bowel disease and rheumatic diseases. Patients with these diseases often have a compromised gut barrier function, suggesting that anti-cytokine antibodies may contribute to the re-establishment of gut barrier integrity, in addition to their immunomodulatory effects. This paper reviews the effects of anti-cytokine antibodies on gut barrier function and their mechanisms.

Assessing intestinal permeability in Crohn's disease patients using orally administered 52Cr-EDTA

Background

Intestinal permeability can be assessed by monitoring renal excretion of orally administered radioactively ⁵¹Cr-labeled ethylenediaminetetraacetic acid (⁵¹Cr-EDTA). Although considered safe, patient participation in using radio-labeled tracers is low. Here, we used orally administered ⁵²Cr-EDTA as non-radioactive alternative to assess intestinal permeability in CD and analyzed the association with disease activity, disease location and gut microbial dysbiosis.

Materials and methods

60 CD patients with low (n = 25) and increased (n = 35) fecal calprotectin levels (cut-off: 100 μg/g feces) ingested 20 mL ⁵²Cr-EDTA (20 mmol/L) solution whereafter 24-h urine was collected. Urinary ⁵²Cr-EDTA concentrations were quantified using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Fecal Enterobacteriaceae and Faecalibacterium prausnitzii were quantified using FISH. Correlations between urinary ⁵²Cr-EDTA excretion and other parameters were established using nonparametric Spearman’s correlation coefficients (ρ).

Results

CD patients with increased fecal calprotectin levels (> 100 μg/g) demonstrated an elevated urinary ⁵²Cr-EDTA/creatinine ratio (772 vs. 636 μmol/mol, P = 0.132). Patients with primarily colonic disease showed the highest ⁵²Cr-EDTA excretion. Importantly, a positive correlation was observed for the urinary ⁵²Cr-EDTA/creatinine ratio and fecal calprotectin levels (ρ = 0.325, P < 0.05). Finally, urinary ⁵²Cr-EDTA/creatinine ratio negatively correlated with the relative abundance of Faecalibacterium prausnitzii (ρ = -0.221, P = 0.092), while positively correlating with Enterobacteriaceae (ρ = 0.202, P = 0.126).

Conclusions

Orally administered and renal excreted ⁵²Cr-EDTA may be used to assess intestinal permeability in CD and correlates with fecal calprotectin levels and bacterial species relevant to CD. This test may improve non-invasive detection of disease exacerbations and help monitor disease activity.

Infliximab restores colonic barrier to adherent-invasive E. coli in Crohn's disease via effects on epithelial lipid rafts

OBJECTIVE

Infliximab is important in the therapeutic arsenal of Crohn's disease (CD). However, its effect on mucosal barrier function is not fully understood. Adherent-invasive Escherichia coli (AIEC) are important in CD pathophysiology, but the transmucosal uptake routes are partly unknown. We investigated effects of infliximab on uptake of colon-specific AIEC HM427 across CD colonic mucosa.

MATERIALS AND METHODS

Endoscopic biopsies from non-inflamed colon of seven patients with CD, before and after two infliximab infusions, and eight non-inflammation controls, were mounted in Ussing chambers. Paracellular permeability (⁵¹Cr-EDTA) and transmucosal passage of GFP-expressing HM427 were studied. Mechanisms of HM427 transepithelial transport were investigated in Caco-2 monolayers treated with TNF, in the presence of infliximab and/or endocytosis inhibitors.

RESULTS

Before infliximab treatment, colonic passage of HM427 [CD: 2475 CFU (450-3000); controls 1163(225-1950)] and ⁵¹Cr-EDTA permeability were increased in CD (p < .05), but were restored to control levels by infliximab (CD: 150 (18.8-1069)). In TNF-exposed Caco-2 monolayers HM427 transport and lipid rafts/HM427 co-localization was decreased by infliximab. The lipid raft inhibitor methyl-β-cyclodextrin decreased HM427 transport.

CONCLUSION

Infliximab restored the colonic barrier to AIEC in CD; an effect partially mediated by blocking lipid rafts in epithelial cells. This ability likely contributes to infliximab's clinical efficacy in colonic CD.

Interplay of GTPases and Cytoskeleton in Cellular Barrier Defects during Gut Inflammation

An essential role of the intestine is to build and maintain a barrier preventing the luminal gut microbiota from invading the host. This involves two coordinated physical and immunological barriers formed by single layers of intestinal epithelial and endothelial cells, which avoid the activation of local immune responses or the systemic dissemination of microbial agents, and preserve tissue homeostasis. Accordingly, alterations of epithelial and endothelial barrier functions have been associated with gut inflammation, for example during inflammatory bowel disease (IBD). The discriminative control of nutriment uptake and sealing toward potentially pathological microorganisms requires a profound regulation of para- and transcellular permeability. On the subcellular level, the cytoskeleton exerts key regulatory functions in the maintenance of cellular barriers. Increased epithelial/endothelial permeability occurs primarily as a result of a reorganization of cytoskeletal–junctional complexes. Pro-inflammatory mediators such as cytokines can induce cytoskeletal rearrangements, causing inflammation-dependent defects in gut barrier function. In this context, small GTPases of the Rho family and large GTPases from the Dynamin superfamily appear as major cellular switches regulating the interaction between intercellular junctions and actomyosin complexes, and in turn cytoskeleton plasticity. Strikingly, some of these proteins, such as RhoA or guanylate-binding protein-1 (GBP-1) have been associated with gut inflammation and IBD. In this review, we will summarize the role of small and large GTPases for cytoskeleton plasticity and epithelial/endothelial barrier in the context of gut inflammation.

The intestinal barrier: a fundamental role in health and disease

The gastrointestinal mucosa constitutes a critical barrier where millions of microbes and environmental antigens come in close contact with the host immune system. Intestinal barrier defects have been associated with a broad range of diseases and therefore denote a new therapeutic target. Areas covered: This review is based on an extensive literature search in PubMed of how the intestinal barrier contributes to health and as a trigger for disease. It discusses the anatomy of the intestinal barrier and explains the available methods to evaluate its function. Also reviewed is the importance of diet and lifestyle factors on intestinal barrier function, and three prototypes of chronic diseases (inflammatory bowel disease, celiac disease and nonalcoholic fatty liver disease) that have been linked to barrier defects are discussed. Expert commentary: The intestinal barrier has been investigated by various methods, but correlation of results across studies is difficult, representing a major shortcoming in the field. New upcoming techniques and research on the effect of barrier-restoring therapeutics may improve our current understanding of the gut barrier, and provide a step forward towards personalised medicine.

Noncoding Transcribed Ultraconserved Region (T-UCR) uc.261 Participates in Intestinal Mucosa Barrier Damage in Crohn's Disease

BACKGROUND

To date, 481 ultraconserved regions (UCRs) have been discovered in human genome. We aimed to investigate the transcribed UCR (T-UCR) characteristics in Crohn's disease (CD ) and determine whether T-UCR uc.261 participated in intestinal mucosa barrier damage.

METHODS

T-UCRs were screened in active CD mucosa using the Arraystar Human T-UCR Microarray and validated with quantitative real-time reverse transcription PCR, together with tight junction proteins (TJPs) including junctional adhesion molecule-A, occludin, claudin-1, and zonula occluden-1. T-UCR uc.261 in active CD mucosa was validated by RNA fluorescence in situ hybridization. Caco2 and T84 cells were employed to determine transepithelial electrical resistance. Cdc42, protein kinase C ζ, PAR3, and PAR6 were assessed with quantitative real-time reverse transcription PCR and Western blotting. The assembly of TJPs was detected using cell immunofluorescence assay.

RESULTS

Four T-UCRs were significantly upregulated (uc.290-, uc.144-, uc.261-, and uc.477+) and 4 T-UCRs were downregulated (uc.166-, uc.141-, uc.478+, and uc.479+). Uc.261 was inversely correlated with transepithelial electrical resistance during tight junction formation. The levels of TJPs were diminished in active CD mucosa. Most uc.261s were located in the cytoplasm of colonic epithelial cells. Overexpression of uc.261 reduced transepithelial electrical resistance, inhibited the expression and assembly of TJPs, activated Cdc42, and suppressed protein kinase C ζ. Silencing of uc.261 in TNF-α-treated cells reversed the tight junction damage.

CONCLUSIONS

Overexpression of uc.261 participates in intestinal mucosa barrier damage. Suppression of uc.261 reverses the damage to tight junction in inflammation. Attenuation of uc.261 overexpression might be a rational strategy to manage patients with CD.

Intestinal Permeability in Inflammatory Bowel Disease: Pathogenesis, Clinical Evaluation, and Therapy of Leaky Gut

The pathogenesis of inflammatory bowel disease (IBD) is multifactorial with data suggesting the role of a disturbed interaction between the gut and the intestinal microbiota. A defective mucosal barrier may result in increased intestinal permeability which promotes the exposition to luminal content and triggers an immunological response that promotes intestinal inflammation. IBD patients display several defects in the many specialized components of mucosal barrier, from the mucus layer composition to the adhesion molecules that regulate paracellular permeability. These alterations may represent a primary dysfunction in Crohn's disease, but they may also perpetuate chronic mucosal inflammation in ulcerative colitis. In clinical practice, several studies have documented that changes in intestinal permeability can predict IBD course. Functional tests, such as the sugar absorption tests or the novel imaging technique using confocal laser endomicroscopy, allow an in vivo assessment of gut barrier integrity. Antitumor necrosis factor-α (TNF-α) therapy reduces mucosal inflammation and restores intestinal permeability in IBD patients. Butyrate, zinc, and some probiotics also ameliorate mucosal barrier dysfunction but their use is still limited and further studies are needed before considering permeability manipulation as a therapeutic target in IBD.

Prevalence of Mycobacterium avium subsp. paratuberculosis and Escherichia coli in blood samples from patients with inflammatory bowel disease

Mycobacterium avium subsp. paratuberculosis (MAP) and adherent-invasive Escherichia coli (AIEC) have been implicated as primary triggers in Crohn's disease (CD). In this study, we evaluated the prevalence of MAP and E. coli (EC) DNA in peripheral blood from 202 inflammatory bowel disease (IBD) patients at various disease periods and compared against 24 cirrhotic patients with ascites (CIR) (non-IBD controls) and 29 healthy controls (HC). MAP DNA was detected by IS900-specific nested PCR, EC DNA by malB-specific nested PCR and AIEC identity, in selected samples, by sequencing of fimH gene. CD patients with active disease showed the highest MAP DNA prevalence among IBD patients (68 %). Infliximab treatment resulted in decreased MAP detection. CIR patients had high individual and coinfection rates (75 % MAP, 88 % EC and 67 % MAP and EC), whilst HC controls had lower MAP prevalence (38 %) and EC was undetectable in this control group. EC DNA prevalence in IBD patients was highly associated with CD, and 80 % of EC from the selected samples of CD patients analyzed carried the fimH30 allele, with a mutation strongly associated with AIEC. Our results show that coinfection with MAP and AIEC is common and persistent in CD, although the high MAP and EC detection in CIR patients suggested that colonization is, at least, partially dependent on increased gut permeability. Nevertheless, facilitative mechanisms between a susceptible host and these two potential human pathogens may allow their implication in CD pathogenesis.

Biological pathways involved in the development of inflammatory bowel disease

Apoptosis, autophagy and necrosis are three distinct functional types of the mammalian cell death network. All of them are characterized by a number of cell's morphological changes. The inappropriate induction of cell death is involved in the pathogenesis of a number of diseases.Pathogenesis of inflammatory bowel diseases (ulcerative colitis, Crohn's disease) includes an abnormal immunological response to disturbed intestinal microflora. One of the most important reason in pathogenesis of chronic inflammatory disease and subsequent multiple organ pathology is a barrier function of the gut, regulating cellular viability. Recent findings have begun to explain the mechanisms by which intestinal epithelial cells are able to survive in such an environment and how loss of normal regulatory processes may lead to inflammatory bowel disease (IBD).This review focuses on the regulation of biological pathways in development and homeostasis in IBD. Better understanding of the physiological functions of biological pathways and their influence on inflammation, immunity, and barrier function will simplify our expertice of homeostasis in the gastrointestinal tract and in upgrading diagnosis and treatment.

Central role of the gut epithelial barrier in the pathogenesis of chronic intestinal inflammation: lessons learned from animal models and human genetics

The gut mucosa is constantly challenged by a bombardment of foreign antigens and environmental microorganisms. As such, the precise regulation of the intestinal barrier allows the maintenance of mucosal immune homeostasis and prevents the onset of uncontrolled inflammation. In support of this concept, emerging evidence points to defects in components of the epithelial barrier as etiologic factors in the pathogenesis of inflammatory bowel diseases (IBDs). In fact, the integrity of the intestinal barrier relies on different elements, including robust innate immune responses, epithelial paracellular permeability, epithelial cell integrity, as well as the production of mucus. The purpose of this review is to systematically evaluate how alterations in the aforementioned epithelial components can lead to the disruption of intestinal immune homeostasis, and subsequent inflammation. In this regard, the wealth of data from mouse models of intestinal inflammation and human genetics are pivotal in understanding pathogenic pathways, for example, that are initiated from the specific loss of function of a single protein leading to the onset of intestinal disease. On the other hand, several recently proposed therapeutic approaches to treat human IBD are targeted at enhancing different elements of gut barrier function, further supporting a primary role of the epithelium in the pathogenesis of chronic intestinal inflammation and emphasizing the importance of maintaining a healthy and effective intestinal barrier.

Abnormal intestinal permeability in Crohn's disease pathogenesis

Increased small intestinal permeability is a longstanding observation in both Crohn's disease patients and in their healthy, asymptomatic first-degree relatives. However, the significance of this compromised gut barrier function and its place in the pathogenesis of the disease remains poorly understood. The association between abnormal small intestinal permeability and a specific mutation in the NOD2 gene, which functions to modulate both innate and adaptive immune responses to intestinal bacteria, suggests a common, genetically determined pathway by which an abnormal gut barrier could result in chronic intestinal inflammation. Furthermore, rodent colitis models show that gut barrier defects precede the development of inflammatory changes. However, it remains possible that abnormal permeability is simply a consequence of mucosal inflammation. Further insight into whether abnormal barrier function is the cause or consequence of chronic intestinal inflammation will be crucial to understanding the role of intestinal permeability in the pathogenesis of Crohn's disease.

Anti-TNF-α antibodies improve intestinal barrier function in Crohn's disease

BACKGROUND AND AIMS

Intestinal barrier function in Crohn's disease patients and their first degree healthy relatives is impaired. The increased intestinal permeability may result in an enhanced mucosal immune response and thereby aggravate intestinal inflammation. Humanised anti-TNF-α antibodies have been shown to be effective in the treatment of active Crohn's disease and in the treatment of entero-cutaneous fistula. The aim of the present study was to investigate the influence of anti-TNF-α antibody (infliximab) treatment on the intestinal barrier function of patients with active Crohn's disease.

METHODS

The differential intestinal uptake of lactulose and mannitol was measured to quantify intestinal permeability in patients with long standing active Crohn's disease (n=17) directly before and seven days after treatment with infliximab (5 mg/kg bodyweight). In parallel, intestinal permeability was studied in a healthy control group (n=20). Serum samples were analysed with pulsed amperometric detection after separation on an anion exchange column.

RESULTS

Intestinal permeability was significantly increased in all patients with Crohn's disease (L/M ratio 0.24±0.17) prior to infliximab treatment compared to the control group (L/M ratio 0.01±0.02; p-value <1×10(-7)). Treatment of patients with infliximab resulted in a marked decrease of intestinal permeability as measured by L/M ratio from 0.24±0.17 before to 0.02±0.02 (p-value <1×10(-7)) seven days after infliximab application.

CONCLUSIONS

Treatment with anti-TNF-α antibodies improved impaired intestinal barrier function in patients with Crohn's disease. This effect may correlate to the well documented anti-inflammatory effect of TNF-α blockade in this intestinal disease.

Effect of COX-2 inhibitor lumiracoxib and the TNF-α antagonist etanercept on TNBS-induced colitis in Wistar rats

Crohn's disease (CD) is associated with gut barrier dysfunction. Besides the baseline barrier defect, a subgroup of patients also expresses an intestinal barrier hyperresponsiveness to nonsteroidal anti-inflammatory drugs. On the other hand, the anti-tumour necrosis factor alpha (TNF-α) treatment has brought benefits to these patients. Thus, this study aimed to evaluate the effect of lumiracoxib, a selective-cyclooxygenase-2 (COX-2) inhibitor, and Etanercept (ETC), a TNF-α antagonist on the 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced experimental colitis. A total of 47 Wistar rats were randomized into seven groups, as follows: (1) Sham: sham induced-colitis; (2) TNBS: nontreated induced-colitis; (3) Lumiracoxib control; (4) Lumiracoxib-treated induced-colitis; (5) ETC control; (6) ETC-treated induced-colitis; (7) Lumiracoxib-ETC-treated induced-colitis. Rats from groups 6 and 7 presented significant improvement of macroscopic and histopathological damages in the distal colon. The gene expression of COX-2 mRNA, as well of TNF-α mRNA, decreased significantly in groups 6 and 7 compared to the TNBS nontreated and lumiracoxib-treated groups. The treatment only with lumiracoxib did not reduce the inflammation on TNBS-induced experimental colitis. ETC attenuated the damage seen in the colon and reduced the inflammation caused by TNBS. Our results suggest that down-regulation of TNF-α and COX-2 resulted in a decrease in inflammation caused by TNBS and thus provided some protection from the colonic damage caused by TNBS.

Granulocyte macrophage-colony-stimulating factor autoantibodies and increased intestinal permeability in Crohn disease

BACKGROUND

Alterations in intestinal permeability have been implicated in the pathogenesis of Crohn disease (CD). We have reported that granulocyte macrophage-colony-stimulating factor (GM-CSF) is required for mucosal barrier function in mice, and elevated neutralizing GM-CSF autoantibodies (Ab) are associated with stricturing ileal disease and surgery in patients with CD. We hypothesized that children with CD with elevated GM-CSF Ab would exhibit increased intestinal permeability.

PATIENTS AND METHODS

Subjects were divided into 3 groups: 15 with CD and high GM-CSF Ab (≥ 1.6 μg/mL, GM-CSF Ab Hi), 12 with CD and low GM-CSF Ab (<1.6 μg/mL, GM-CSF Ab Lo), and 15 healthy controls. Subjects ingested a lactulose:mannitol (L:M) solution, and urinary excretion of LM was measured by high-performance liquid chromatography. Serum GM-CSF Ab, endotoxin core Ab (EndoCAb), and lipopolysaccharide-binding protein (LBP), and fecal S100A12 were determined by enzyme-linked immunosorbent assay.

RESULTS

The CD groups did not vary by age, sex, disease location, or activity. Neither systemic (serum LBP) nor mucosal (fecal S100A12) inflammation differed between the CD groups. Intestinal permeability as measured by the urine L:M ratio and endotoxin exposure as measured by serum EndoCAb were increased in the GM-CSF Ab Hi group compared to the GM-CSF Ab Lo group and controls.

CONCLUSIONS

Patients with CD with elevated GM-CSF Ab exhibit an increase in bowel permeability relative to patients with CD with lower levels of GM-CSF Ab in the absence of differences in systemic or intestinal inflammation. Therapies that target the mucosal barrier may be of particular benefit in this subgroup of patients with CD.

Crohn's disease: evidence for involvement of unregulated transcytosis in disease etio-pathogenesis

Crohn's disease (CD) is a chronic inflammatory bowel disease. Research has identified genetic predisposition and environmental factors as key elements in the development of the disease. However, the precise mechanism that initiates immune activation remains undefined. One pathway for luminal antigenic molecules to enter the sterile lamina propria and activate an immune response is via transcytosis. Transcytosis, although tightly regulated by the cell, has the potential for transepithelial transport of bacteria and highly antigenic luminal molecules whose uncontrolled translocation into the lamina propria can be the source of immune activation. Viewed as a whole, the evidence suggests that unregulated intestinal epithelial transcytosis is involved in the inappropriate presentation of immunogenic luminal macromolecules to the intestinal lamina propria. Thus fulfilling the role of an early pre-morbid mechanism that can result in antigenic overload of the lamina propria and initiate an immune response culminating in chronic inflammation characteristic of this disease. It is the aim of this paper to present evidence implicating enterocyte transcytosis in the early etio-pathogenesis of CD.

Effect of COX-2 inhibitor after TNBS-induced colitis in Wistar rats

Inflammatory bowel disease (IBD) is a common chronic gastrointestinal disorder characterized by alternating periods of remission and active intestinal inflammation. Some studies suggest that antiinflammatory drugs are a promising alternative for treatment of the disease. Thus, this study aimed to evaluate the effect of lumiracoxib, a selective-cyclooxygenase-2 (COX-2) inhibitor, on 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced experimental colitis. Wistar rats (n = 25) were randomized into four groups, as follows: Group (1) Sham group: sham induced-colitis rats; Group (2) TNBS group: nontreated induced-colitis rats; Group (3) Lumiracoxib control group; and Group (4) Lumiracoxib-treated induced-colitis rats. Our results showed that rats from groups 2 and 4 presented similar histopathological damage and macroscopic injury in the distal colon as depicted by significant statistically differences (P < 0.01; P < 0.05) compared to the other two groups. Weak expression of COX-2 mRNA was detected in normal colon cells, while higher levels of COX-2 mRNA were detected in group 2 and group 4. Therapy with lumiracoxib reduced COX-2 expression by 20-30%, but it was still higher and statistically significant compared to data obtained from the lumiracoxib control group. Treatment with the selective COX-2 inhibitor lumiracoxib did not reduce inflammation-associated colonic injury in TNBS-induced experimental colitis. Thus, the use of COX-2 inhibitors for treating IBD should be considered with caution and warrants further experimental investigation to elucidate their applicability.

Protective effect of octreotide and infliximab in an experimental model of indomethacin-induced inflammatory bowel disease

Indomethacin administration in animals increases permeability of the small intestine, leading to inflammation that mimics Crohn's disease. Nonsteroidal anti-inflammatory drugs increase the permeability of the intestinal epithelial barrier and should therefore be used with caution in patients with Crohn's disease. We analyzed the protective effects of octreotide and the tumor necrosis factor-alpha inhibitor infliximab in a rat model of indomethacin-induced enterocolitis. Male Wistar rats received 20 mg of infliximab or 10 mug of octreotide 24 h prior to injection with indomethacin. Intestinal permeability was analyzed using Cr-51-ethylenediaminetetraacetic acid clearance. No microscopic or macroscopic alterations were observed in the rats receiving infliximab or octreotide, both of which increased permeability (P < 0.001 versus controls). Our macroscopic and microscopic findings might be related to the low specificity of infliximab and suggest that cytokines affect the intestinal epithelial barrier, as evidenced by the protective effect that infliximab had on the permeability parameters evaluated.

Targeting TNFalpha rapidly reduces density of dendritic cells and macrophages in psoriatic plaques with restoration of epidermal keratinocyte differentiation

BACKGROUND

The cytokine network theory for psoriasis postulates a key role for TNFalpha in mediating inflammation and altered epidermal differentiation.

OBJECTIVE

This study defines responses following administration of adalimumab, a TNFalpha inhibitor, in pre-psoriatic skin (PN) and lesional psoriatic plaques (PP) skin.

METHODS

PN and PP skin before and after treatment were biopsied at days 2, 7, 28 and 84 (n=6 different patients). Cryosections were immunohistochemically stained to detect TNFalpha and other relevant markers in epidermal and dermal compartments. Detection of apoptosis utilized antibody specific for activated caspase 3. Semiquantitative assessments and statistical analysis was performed for each staining profile.

RESULTS

TNFalpha+ cells were increased in PP skin. PP skin was also characterized by a four-fold increase in number of CD68+ macrophages as well as eight-fold increase in CD11c+ dermal dendritic cells (DCs) compared to PN skin. By two-color immunofluorescence staining, both CD68+ cells as well as CD11c+ cells expressed TNFalpha. Following initiation of adalimumab therapy, CD11c+ cells, significantly decreased in PP skin at days 7, 28, and 84, while CD68+ and CD14+ cells decreased at days 28 and 84. Other markers for DCs (CD83, CD86) showed decreases at days 7, 28, and 84. Reduction in DCs, macrophages or T cells was not accompanied by increased activated caspase 3-positive cells. When a keratinocyte terminal differentiation marker was examined, adalimumab triggered rapid restoration of loricrin expression (beginning on day 2), with loss of aberrant differentiation marker, keratin 17 (K17).

CONCLUSION

Adalimumab impacts dermal-based immunocytes, and the epidermal compartment also responds by restoration of normal differentiation without detectable apoptosis.

Altered permeability in inflammatory bowel disease: pathophysiology and clinical implications

PURPOSE OF REVIEW

To present the mechanisms behind barrier disturbance in inflammatory bowel disease and their functional consequences.

RECENT FINDINGS

A reduction in tight junction strands, strand breaks and alteration of tight junction protein content and composition characterize Crohn's disease. In ulcerative colitis, epithelial leaks appear early as a result of microerosions, upregulated epithelial apoptosis and tight junction protein changes with pronounced increases in claudin-2. T-helper type 1 cytokine effects by interferon-gamma and tumour necrosis factor alpha are important for epithelial damage in Crohn's disease. Interleukin-13 is the key effector cytokine in ulcerative colitis, stimulating epithelial cell apoptosis, and can upregulate claudin-2 expression. Together with interleukin-13-induced epithelial restitution arrest, this may explain why ulcer lesions occur in early stages of ulcerative colitis but are only observed in advanced inflammatory stages in Crohn's disease.

SUMMARY

Barrier dysfunction in inflammatory bowel disease contributes to diarrhea by a leak flux mechanism and can cause mucosal inflammation secondary to luminal antigen uptake. Barrier abnormalities, such as epithelial tight junction changes and apoptotic leaks, gross mucosal lesions, and epithelial restitution arrest are responsible for these abnormalities and are the result of immune dysregulation. Studying the underlying mechanisms is important in understanding the pathophysiology of inflammatory bowel disease and developing therapeutic strategies.

LIGHT signals directly to intestinal epithelia to cause barrier dysfunction via cytoskeletal and endocytic mechanisms

BACKGROUND & AIMS

LIGHT (lymphotoxin-like inducible protein that competes with glycoprotein D for herpes virus entry on T cells) is a tumor necrosis factor core family member that regulates T-cell activation and causes experimental inflammatory bowel disease. Additional data suggest that LIGHT may be involved in the pathogenesis of human inflammatory bowel disease. The aim of this study was to determine if LIGHT is capable of signaling directly to intestinal epithelia and to define the mechanisms and consequences of such signaling.

METHODS

The effects of LIGHT and interferon-gamma on barrier function, cytoskeletal regulation, and tight junction structure were assessed in mice and intestinal epithelial monolayers.

RESULTS

LIGHT induced barrier loss in cultured epithelia via myosin II regulatory light chain (MLC) phosphorylation; both barrier loss and MLC phosphorylation were reversed by MLC kinase (MLCK) inhibition. Pretreatment with interferon-gamma, which induced lymphotoxin beta receptor (LT beta R) expression, was required for these effects, and neither barrier dysfunction nor intestinal epithelial MLC phosphorylation occurred in LT beta R knockout mice. In cultured monolayers, endocytosis of the tight junction protein occludin correlated with barrier loss. Internalized occludin colocalized with caveolin-1. LIGHT-induced occludin endocytosis and barrier loss were both prevented by inhibition of caveolar endocytosis.

CONCLUSIONS

T cell-derived LIGHT activates intestinal epithelial LT beta R to disrupt barrier function. This requires MLCK activation and caveolar endocytosis. These data suggest a novel role for LIGHT in disease pathogenesis and suggest that inhibition of MLCK-dependent caveolar endocytosis may represent an approach to restoring barrier function in inflammatory bowel disease.

Enteric glia regulate intestinal barrier function and inflammation via release of S-nitrosoglutathione

BACKGROUND & AIMS

Barrier functions across epithelia and endothelia are essential for homeostatic tissue regulation. Astroglia interact with cerebral endothelia to maintain the blood-brain barrier. Whether similar interactions between astrocyte-like enteric glia and epithelia regulate intestinal barrier function is not known.

METHODS

Fluorescent permeability markers were used to measure intestinal barrier function in vivo after conditional ablation of enteric glia in transgenic mice. Enteric glial cell regulation of epithelial barrier integrity then was modeled in vitro using coculture. Glial-derived barrier-inducing factors were characterized using size-exclusion chromatography and mass spectrometry. Epithelial barrier integrity was assessed by transepithelial resistance readings and by quantitative measurement of tight-junction-associated protein expression by quantitative polymerase chain reaction and Western blot.

RESULTS

We show that ablation of enteric glial cells in transgenic mice causes intestinal mucosal barrier dysfunction, resulting in inflammation. Glial-derived s-nitrosoglutathione (GSNO) was identified as a potent inducer of mucosal barrier function in vitro and in vivo and of attenuated tissue inflammation after ablation of enteric glia in transgenic mice. GSNO regulation of mucosal barrier function was associated directly with an increased expression of perijunctional F-actin and tight-junction-associated proteins zonula occludens-1 and occludin. GSNO also significantly restored mucosal barrier function in colonic biopsy specimens from patients with Crohn's disease, a well-described inflammatory permeability disorder associated with enteric glial-cell disruption.

CONCLUSIONS

Enteric glia therefore share the ability of astrocytes to regulate tight-junction integrity, and cellular interactions comparable with those maintaining blood-brain barrier function also regulate epithelial permeability at mucosal surfaces.

Mechanism of glucocorticoid regulation of the intestinal tight junction barrier

A defective intestinal epithelial tight junction (TJ) barrier has been proposed as an important pathogenic factor contributing to the intestinal inflammation of Crohn's disease. Glucocorticoids are first-line therapeutic agents for the treatment of moderate to severe Crohn's disease. Glucocorticoid treatment has been shown to induce retightening of the intestinal TJ barrier defect in Crohn's disease patients. However, the mechanisms that mediate the glucocorticoid therapeutic action on intestinal TJ barrier function remain unknown. The aim of this study was to elucidate the mechanism of glucocorticoid modulation of the intestinal epithelial TJ barrier using an in vitro model system. Filter-grown Caco-2 intestinal epithelial cells were used as an in vitro model to examine the effects of glucocorticoids on basal intestinal epithelial TJ barrier function and on TNF-alpha-induced disruption of the TJ barrier. Glucocorticoids (prednisolone and dexamethasone) did not have a significant effect on baseline Caco-2 TJ barrier function but prevented the TNF-alpha-induced increase in Caco-2 TJ permeability. The glucocorticoid protective effect against the TNF-alpha-induced increase in Caco-2 TJ permeability required activation of the glucocorticoid receptor (GR) complex. The activation of the GR complex resulted in GR complex binding to the glucocorticoid response element (GRE) site on DNA and activation of a GR-responsive promoter. Glucocorticoids inhibited the TNF-alpha-induced increase in myosin light chain kinase (MLCK) protein expression, a key process mediating the TNF-alpha increase in intestinal TJ permeability. The glucocorticoid inhibition of the TNF-alpha-induced increase in MLCK protein expression was due to the binding of the GR complex to a GRE binding site on the MLCK promoter region suppressing the TNF-alpha-induced activation. Glucocorticoids inhibit the TNF-alpha-induced increase in Caco-2 TJ permeability. The prednisolone protective action was mediated by binding of activated GR complex to the GRE site on the MLCK promoter, suppressing the TNF-alpha-induced increase in MLCK gene activity, protein expression, and subsequent opening of the intestinal TJ barrier.

IFN-gamma-induced TNFR2 expression is required for TNF-dependent intestinal epithelial barrier dysfunction

BACKGROUND & AIMS

Tumor necrosis factor (TNF) plays a critical role in intestinal disease. In intestinal epithelia, TNF causes tight junction disruption and epithelial barrier loss by up-regulating myosin light chain kinase (MLCK) activity and expression. The aim of this study was to determine the signaling pathways by which TNF causes intestinal epithelial barrier loss.

METHODS

Caco-2 cells that were either nontransfected or stably transfected with human TNF receptor 1 (TNFR1) or TNFR2 and mouse colonocytes were used for physiologic, morphologic, and biochemical analyses.

RESULTS

Colitis induced in vivo by adoptive transfer of CD4(+)CD45RB(hi) T cells was associated with increased epithelial MLCK expression and myosin II regulatory light chain (MLC) phosphorylation as well as morphologic tight junction disruption. In vitro studies showed that TNF caused similar increases in MLCK expression and MLC phosphorylation, as well as barrier dysfunction, in Caco-2 monolayers only after interferon (IFN)-gamma pretreatment. This reductionist model was therefore used to determine the molecular mechanism by which IFN-gamma and TNF synergize to cause intestinal epithelial barrier loss. IFN-gamma priming increased TNFR1 and TNFR2 expression, and blocking antibody studies showed that TNFR2, but not TNFR1, was required for TNF-induced barrier dysfunction. Transgenic TNFR2, but not TNFR1, expression allowed IFN-gamma-independent TNF responses.

CONCLUSIONS

IFN-gamma primes intestinal epithelia to respond to TNF by inducing TNFR2 expression, which in turn mediates TNF-induced MLCK-dependent barrier dysfunction. The data further suggest that epithelial TNFR2 blockade may be a novel approach to restore barrier function in intestinal disease.