Gliadin, zonulin and gut permeability: Effects on celiac and non-celiac intestinal mucosa and intestinal cell lines

Orally Based Diagnosis of Celiac Disease: Current Perspectives

Celiac disease (CD) is a lifelong immune-mediated disorder caused by the ingestion of wheat gluten in genetically susceptible persons. Most cases of CD are atypical and remain undiagnosed, which exposes the individuals to the risk of life-threatening complications. Serologic endomysial and tissue transglutaminase antibody tests are used to screen at-risk individuals, although a firm diagnosis requires demonstration of characteristic histopathologic findings in the small-intestinal mucosa. A gluten challenge, with a repeat biopsy to demonstrate recurrence of histopathologic changes in the intestinal mucosa after the re-introduction of gluten, is considered for those persons in whom diagnosis remains in doubt. In this paper, we review studies that evaluated: (1) the possibility of using oral mucosa for the initial diagnosis of CD or for local gluten challenge; and (2) the possibility of using salivary CD-associated antibodies as screening tests. Our review shows that orally based diagnosis of CD is attractive and promising, although additional evaluations with standardized collection and analysis methods are needed. There is some evidence of a dissociation between systemic and oral mucosal immune responses in CD. The hypothesis that gluten could stimulate naïve lymphocytes directly in the oral cavity would have important implications for the understanding, diagnosis, and management of CD.

Celiac disease

PURPOSE OF REVIEW

Research in celiac disease is unraveling new findings at a high rate, and major advances seem to occur in all areas such as genetics, environmental factor, pathophysiology, and even prospective therapeutic implications.

RECENT FINDINGS

New insight is being gained into the interplay between genetic and environmental factors causing celiac disease. In addition to the known human leukocyte antigen haplotypes, genome-wide studies have now identified additional susceptibility loci and the majority of newly discovered risk regions harbor genes controlling immune pathways. The mechanism of translocation of gliadin peptides across the intestinal barrier has been the subject of much investigation, and there is now evidence that the toxic 33-mer peptide can also be translocated transcellularly. As for the paracellular route, this appears to be enhanced by gliadin's stimulation of zonulin release. The growing role of the innate immunity is being recognized and the increased expression of some Toll-like receptors appears to delineate a new inherent defect in this branch of innate immunity. Finally, new perspectives are opening in the treatment of celiac disease based on new detoxified grains, enzymatic degradation of gluten, and prevention of its crossing the mucosal barrier.

SUMMARY

The pace of new knowledge in this 'ancient' disease is very fast, and this review outlines the principal lines of such exciting developments.

Systematic review: The evidence base for long-term management of coeliac disease

BACKGROUND

While gluten-free diet is an effective treatment for coeliac disease, the need for and goals of long-term management of patients are poorly defined.

AIM

To review systematically the complications and associations of coeliac disease, to identify potential risk factors, to define ways of assessing risk factors and to provide a strategy for management.

METHODS

Review of medical literature from 1975.

RESULTS

There is an increasing list of potential complications and/or conditions associated with coeliac disease, in particular, autoimmune disease, malignancy and bone disease. Risk factors that may predict or influence long-term outcomes include genetic susceptibility, environmental factors predominantly gluten ingestion, persistent small intestinal inflammation/injury and nutritional deficiencies. Genotyping of patients is yet to have an established clinical role in long-term management. Assessment of adherence to the gluten-free diet largely relies upon skilled dietary history, but the ultimate test is duodenal histopathology, which is the only currently established means of assessing healing. Symptoms, serology or other non-invasive means are poor predictors of healing and the likelihood of complications.

CONCLUSION

Evidence (albeit limited) that adherence to a gluten-free diet and mucosal healing prevent and/or ameliorate complications indicates that a planned long-term strategy for follow-up is essential.

Higher constitutive IL15R alpha expression and lower IL-15 response threshold in coeliac disease patients

The IL-15 triggering effect of gliadin is not exclusive to coeliac disease (CD) patients, whereas the secondary response is CD specific. We have studied the expression of the IL-15 receptor, and the IL-15 response upon stimulation, in non-CD and CD patients, and the possible existence of a lower immunological threshold in the latter. Forty-two CD patients (20 on a gluten-containing diet, GCD, and 22 on gluten-free diet, GFD) and 24 non-CD healthy individuals were studied. IL15R alpha mRNA expression, and tissue characterization, were assayed in the duodenum. Biopsies from six CD patients on GFD and 10 non-CD individuals were studied in vitro using organ culture in basal conditions, as well as after IL-15 stimulation discarding basal IL-15 production. Secretion of immune mediators was measured in the culture supernatants. IL15R alpha mRNA expression was increased in CD patients, as compared with non-CD controls (on GFD P = 0.0334, on GCD P = 0.0062, respectively), and confirmed also by immunofluorescence. No differences were found between CD patients on GFD and on GCD. After in vitro IL-15 stimulation, IL15R alpha expression was only triggered in non-CD controls (P = 0.0313), though it remained increased in CD patients. Moreover, IL-15 induced a more intense immunological response in CD patients after triggering the production of both nitrites and IFN gamma (P = 0.0313, P = 0.0313, respectively). Gliadin-induced IL15 has a lower response threshold in CD patients, leading to the production of other immune mediators and the development of the intestinal lesion, and thus magnifying its effects within the CD intestine.

Effect of gluten-free diet on preventing recurrence of gastroesophageal reflux disease-related symptoms in adult celiac patients with nonerosive reflux disease

BACKGROUND AND AIM

In celiac disease (CD) the role of a gluten-free diet (GFD) on gastroesophageal reflux disease-related symptoms (GERD-rs) is unclear. The aim of this study was to establish the recurrence of GERD-rs, in CD patients with nonerosive reflux disease (NERD).

METHODS

From a total of 105 adult CD patients observed, 29 who presented with the NERD form were enrolled in the study. Thirty non-CD patients with NERD were studied as controls. Recurrence of GERD-rs was clinically assessed at 6, 12, 18, and 24 months follow-up (FU) after withdrawal of initial proton-pump inhibitor (PPI) treatment for 8 weeks.

RESULTS

GERD-rs were resolved in 25 (86.2%) CD patients and in 20 (66.7%) controls after 8 weeks of PPI treatment. In the CD group, recurrence of GERD-rs was found in five cases (20%) at 6 months but in none at 12, 18, and 24 months while in the control group recurrence was found in six of 20 controls (30%), in another six (12/20, 60%), in another three (15/20, 75%), and in another two (17/20, 85%) at 6, 12, 18, and 24 months FU respectively.

CONCLUSIONS

The present study is the first to have evaluated the effect of a GFD in the nonerosive form of GERD in CD patients, by means of clinical long-term follow-up, suggesting that GFD could be a useful approach in reducing GERD symptoms and in the prevention of recurrence.

Celiac disease pathogenesis: the proinflammatory cytokine network

In susceptible individuals, the adaptive response, mediated by the activation of antigen-specific T lymphocytes, drives a proinflammatory response, which ends in an immune-mediated enteropathy characterized by villous atrophy, crypt hyperplasia, and recruitment of intraepithelial lymphocytes. In addition, some gluten peptides are able to induce an innate immune response in intestinal mucosa. The molecular mechanisms and the cells involved in the initial stages of the gluten-intestinal mucosa interaction are poorly understood to date. There is evidence of a direct toxic effect of gluten peptides in several biological models. However, the failure to control the inflammatory response may be one of the factors underlying gluten intolerance in these individuals. The cytokine network involved in celiac disease is characterized by abundant interferon-gamma in the intestinal mucosa. In addition, the production of interleukin (IL)-15, IL-18, and IL-21 is linked to gluten intake, which can drive the inflammatory response probably sustained by IL-18, IL-21, and perhaps IL-27 through STAT1 and STAT5 pathways, whereas neither IL-12 nor IL-23 plays a significant role in pathogenic mechanisms. Herein we describe the involvement of these activation pathways in the context of the pathogenesis of celiac disease.

Gliadin induces an increase in intestinal permeability and zonulin release by binding to the chemokine receptor CXCR3

BACKGROUND & AIMS

Celiac disease is an immune-mediated enteropathy triggered by gliadin, a component of the grain protein gluten. Gliadin induces an MyD88-dependent zonulin release that leads to increased intestinal permeability, a postulated early element in the pathogenesis of celiac disease. We aimed to establish the molecular basis of gliadin interaction with intestinal mucosa leading to intestinal barrier impairment.

METHODS

Alpha-gliadin affinity column was loaded with intestinal mucosal membrane lysates to identify the putative gliadin-binding moiety. In vitro experiments with chemokine receptor CXCR3 transfectants were performed to confirm binding of gliadin and/or 26 overlapping 20mer alpha-gliadin synthetic peptides to the receptor. CXCR3 protein and gene expression were studied in intestinal epithelial cell lines and human biopsy specimens. Gliadin-CXCR3 interaction was further analyzed by immunofluorescence microscopy, laser capture microscopy, real-time reverse-transcription polymerase chain reaction, and immunoprecipitation/Western blot analysis. Ex vivo experiments were performed using C57BL/6 wild-type and CXCR3(-/-) mouse small intestines to measure intestinal permeability and zonulin release.

RESULTS

Affinity column and colocalization experiments showed that gliadin binds to CXCR3 and that at least 2 alpha-gliadin 20mer synthetic peptides are involved in this binding. CXCR3 is expressed in mouse and human intestinal epithelia and lamina propria. Mucosal CXCR3 expression was elevated in active celiac disease but returned to baseline levels following implementation of a gluten-free diet. Gliadin induced physical association between CXCR3 and MyD88 in enterocytes. Gliadin increased zonulin release and intestinal permeability in wild-type but not CXCR3(-/-) mouse small intestine.

CONCLUSIONS

Gliadin binds to CXCR3 and leads to MyD88-dependent zonulin release and increased intestinal permeability.

Elevated serum anti-Saccharomyces cerevisiae, anti-I2 and anti-OmpW antibody levels in patients with suspicion of celiac disease

OBJECTIVES

Expression of anti-Saccharomyces cerevisiae antibodies (ASCA) identifies patients and individuals at risk for Crohn's disease and has also been reported in 40-60% of celiac disease (CD) cases, suggesting a role of host response to enteric microbiota in the development of inflammatory lesions. In this prospective study in patients with suspicion of CD, we evaluate the frequency and association of ASCA to serological responses for other host microbial targets formally associated with Crohn's disease, including the Pseudomonas fluorescens associated sequence I2 and a Bacteroides caccae TonB-linked outer membrane protein, OmpW.

METHODS

Small bowel mucosal biopsies were taken from 242 patients with suspicion of CD, their sera were tested for antibodies to tissue transglutaminase (tTG), ASCA, I2, and OmpW. Eighty adult healthy blood donors were used as controls.

RESULTS

The diagnosis of CD was confirmed on biopsy in 134 cases. The occurrence of ASCA and I2 positivity was significantly higher in adult CD patients than in patients with non-CD disease. Anti-I2 levels in the sera were significantly higher in adult CD patients than in non-CD disease or the controls and anti-OmpW levels in CD and non-CD patients when compared to controls. Positive seroreactivity to OmpW seemed to increase with age. Of the CD patients, 90% were seropositive for at least one microbial antigen tested.

CONCLUSIONS

This study demonstrates a mosaic of disease-related serological responses to microbial antigens in patients with CD. Immune responses to commensal enteric bacteria may play a role in the small intestine mucosal damage in CD.

Parallels between pathogens and gluten peptides in celiac sprue

Pathogens are exogenous agents capable of causing disease in susceptible organisms. In celiac sprue, a disease triggered by partially hydrolyzed gluten peptides in the small intestine, the offending immunotoxins cannot replicate, but otherwise have many hallmarks of classical pathogens. First, dietary gluten and its peptide metabolites are ubiquitous components of the modern diet, yet only a small, genetically susceptible fraction of the human population contracts celiac sprue. Second, immunotoxic gluten peptides have certain unusual structural features that allow them to survive the harsh proteolytic conditions of the gastrointestinal tract and thereby interact extensively with the mucosal lining of the small intestine. Third, they invade across epithelial barriers intact to access the underlying gut-associated lymphoid tissue. Fourth, they possess recognition sequences for selective modification by an endogenous enzyme, transglutaminase 2, allowing for in situ activation to a more immunotoxic form via host subversion. Fifth, they precipitate a T cell–mediated immune reaction comprising both innate and adaptive responses that causes chronic inflammation of the small intestine. Sixth, complete elimination of immunotoxic gluten peptides from the celiac diet results in remission, whereas reintroduction of gluten in the diet causes relapse. Therefore, in analogy with antibiotics, orally administered proteases that reduce the host's exposure to the immunotoxin by accelerating gluten peptide destruction have considerable therapeutic potential. Last but not least, notwithstanding the power of in vitro methods to reconstitute the essence of the immune response to gluten in a celiac patient, animal models for the disease, while elusive, are likely to yield fundamentally new systems-level insights.

Oxidative stress-induced disruption of epithelial and endothelial tight junctions

Mounting body of evidence indicates that the disruption of epithelial tight junctions and resulting loss of barrier function play a crucial role in the pathogenesis of a variety of gastrointestinal, hepatic, pulmonary, kidney and ocular diseases. Increased production of inflammatory mediators such as cytokines and reactive oxygen species disrupt the epithelial and endothelial barrier function by destabilizing tight junctions. Oxidative stress induced by various reactive oxygen species such as hydrogen peroxide, nitric oxide, peroxynitrite and hypochlorous acid disrupt the epithelial and endothelial tight junctions in various tissues. The mechanism involved in oxidative stress-induced disruption of tight junction includes protein modification such as thiol oxidation, phosphorylation, nitration and carbonylation. The role of signaling molecules such as protein kinases and protein phosphatases in regulation of tight junctions is discussed in this article. Understanding such mechanisms in oxidative stress-induced disruption of epithelial and endothelial barrier functions is likely to provide insight into the pathogenesis of various inflammatory diseases, and may form a basis for the design of treatment strategies for different diseases.

Imbalance in the composition of the duodenal microbiota of children with coeliac disease

Coeliac disease (CD) is the most common immune-mediated enteropathy characterized by chronic inflammation of the small intestinal mucosa. The ingestion of gluten is responsible for the symptoms of CD, but other environmental factors are also thought to play a role in this disorder. In this study, the composition of the duodenal microbiota of coeliac children with active disease, symptom-free CD patients on a gluten-free diet and control children was determined. Bacteriological analyses of duodenal biopsy specimens were carried out by fluorescent in situ hybridization coupled with flow cytometry. The proportions of total bacteria and Gram-negative bacteria were significantly higher in CD patients with active disease than in symptom-free CD patients and controls. Bacteroides and Escherichia coli groups were significantly more abundant in CD patients with active disease than in controls, whilst these bacterial deviations were normalized in symptom-free CD patients. The ratio of Lactobacillus--Bifidobacterium to Bacteroides--E. coli was significantly reduced in coeliac patients with either active or inactive disease compared with controls. The differences in Atopobium, Eubacterium rectale--Clostridium coccoides, Clostridium histolyticum, Clostridium lituseburense, sulphate-reducing bacteria and Faecalibacterium prausnitzii populations among the three groups of children were less relevant. Overall, the higher incidence of Gram-negative and potentially pro-inflammatory bacteria in the duodenal microbiota of coeliac children was linked to the symptomatic presentation of the disease and could favour the pathological process of the disorder.

Clinical, subclinical and potential autoimmune diseases in an Italian population of children with coeliac disease

BACKGROUND Several studies have suggested a link between coeliac disease and other autoimmune diseases. AIM To compare the presence of autoimmune disease in children with coeliac disease and in controls. METHODS When coeliac disease was diagnosed, 267 children were evaluated for clinical autoimmune disease (with signs/symptoms), subclinical autoimmune disease (with autoantibodies and subclinical impairment of the target organ) or potential autoimmune disease (with autoantibodies only) and compared with 220 healthy controls. 170 coeliac disease patients were followed up for a mean 47 +/- 31 months, in complete remission on a gluten-free diet. Ninety-nine controls were followed up for 45 +/- 33 months. RESULTS When coeliac disease was diagnosed, 71 (27%) children had autoimmune disease vs. 1% among the controls (P < 0.001): 31 had clinical autoimmune disease and 40 had subclinical or potential autoimmune disease. During the follow-up, the clinical autoimmune disease cases slightly decreased from 12% to 11%, while the potential autoimmune disease cases increased from 14% to 21%. Of the 99 controls, none had any variation in their autoantibody profile. CONCLUSIONS Gluten-free diet does not modify the natural history of autoimmunity in patients with coeliac disease. However, gluten-free diet seems to produce a favourable effect on the previously present clinical autoimmune disease and to prevent the development of new clinical autoimmune disease, but does not affect the onset of potential autoimmunity, which tends to increase with time.

Is there an association between coeliac disease and inflammatory bowel diseases? A study of relative prevalence in comparison with population controls

OBJECTIVE

The relationship between coeliac disease and inflammatory bowel disease (IBD) is controversial. The aim of this study was to determine the prevalence of coeliac disease in IBD and the prevalence of IBD in coeliac disease.

MATERIAL AND METHODS

Patients were enrolled from specialist IBD and coeliac clinics. Antigliadins, endomysial, tissue transglutaminase antibody and total IgA levels were measured in IBD patients. Patients with positive antibodies were offered a duodenal biopsy. The notes on coeliac patients were reviewed for colonoscopic and biopsy findings. Controls were recruited from the local population.

RESULTS

The study included 305 patients with coeliac disease, 354 with IBD and 601 healthy controls. The IBD group comprised 154 ulcerative colitis (UC) cases, 173 Crohn's disease, 18 indeterminate colitis and 9 cases of microscopic colitis. Forty-seven patients had positive antibodies and 3 had villous atrophy on biopsy. All three patients had positive anti-tissue transglutaminase antibodies but only two were endomysial antibody (EMA) positive. Ten coeliac patients had IBD (5 UC and 5 lymphocytic colitis). Five controls had coeliac disease and 2 had IBD (1 Crohn's disease and 1 UC). Stepwise multiple logistic regression showed only antibody positivity as being significant (p<0.0001).

CONCLUSIONS

The prevalence of IBD in coeliac disease was increased 10-fold compared with that in controls (odds ratio 9.98, 95% CI 2.8-45.9, p=0.0006), while the prevalence of coeliac disease in IBD was comparable with that in controls (odds ratio 1.02, 95% CI, 0.24-4.29, p=1.0).

The safety, tolerance, pharmacokinetic and pharmacodynamic effects of single doses of AT-1001 in coeliac disease subjects: a proof of concept study

BACKGROUND

Lifelong adherence to a strict gluten-free diet is the cornerstone of coeliac disease treatment. Elucidation of disease pathogenesis has created opportunities for novel therapeutic approaches to coeliac disease. AT-1001 is an inhibitor of paracellular permeability whose structure is derived from a protein secreted by Vibrio cholerae.

AIM

To determine the safety and tolerability of 12 mg doses of AT-1001 in coeliac disease subjects challenged with gluten.

METHODS

An in-patient, double-blind, randomized placebo-controlled safety study utilizing intestinal permeability, measured via fractional excretions of lactulose and mannitol, as an exploratory measure of drug efficacy.

RESULTS

Compared to placebo, no increase in adverse events occurred in patients exposed to AT-1001. Following acute gluten exposure, a 70% increase in intestinal permeability was detected in the placebo group, while none was seen in the AT-1001 group. Interferon-gamma levels increased in four of seven patients (57%) of the placebo group, but only in four of 14 patients (29%) of the AT-1001 group. Gastrointestinal symptoms were more frequently detected in the placebo group when compared to the AT-1001 group (P = 0.018).

CONCLUSIONS

AT-1001 is well tolerated and appears to reduce intestinal barrier dysfunction, proinflammatory cytokine production, and gastrointestinal symptoms in coeliacs after gluten exposure.

Mechanisms of disease: protease functions in intestinal mucosal pathobiology

Of all our organ systems, the gastrointestinal tract contains the highest levels of endogenous and exogenous proteases (also known as proteinases and peptidases); however, our understanding of their functions and interactions within the gastrointestinal tract is restricted largely to nutrient digestion. The gut epithelium is a sensor of the luminal environment, not only controlling digestive, absorptive and secretory functions, but also relaying information to the mucosal immune, vascular and nervous systems. These functions involve a complex array of cell types that elaborate growth factors, cytokines and extracellular matrix (ECM) proteins, the activity and availability of which are regulated by proteases. Proteolytic activity must be tightly regulated in the face of diverse environmental challenges, because unrestrained or excessive proteolysis leads to pathological gastrointestinal conditions. Moreover, enteric microbes and parasites can hijack proteolytic pathways through 'pathogen host mimicry'. Understanding how the protease balance is maintained and regulated in the intestinal epithelial cell microenvironment and how proteases contribute to physiological and pathological outcomes will undoubtedly contribute to the identification of new potential therapeutic targets for gastrointestinal diseases.

Possible drug targets for celiac disease

Celiac disease (CD) is an intestinal disorder caused by an altered immune response against wheat gluten, a common dietary antigen, and related cereal proteins. Both CD4+ and CD8+ T cells have a role in inducing the intestinal damage, although recent studies have also pinpointed the involvement of the innate immune response in CD pathogenesis. So far, the only available treatment for CD is the strict avoidance of gluten in the diet, but the poor compliance and the associated complications demand alternative therapies. During the last decade, the knowledge of genetic, molecular and cellular mechanisms leading to CD pathogenesis made great progress. The improved understanding of gluten peptides activating either adaptive or innate immune response, of HLA restriction molecules, as well as of cytokines that mediate most of the inflammatory reactions, opens several new promising perspectives for therapeutic intervention. This review discusses both molecular and cellular strategies to treat CD, including the use of proteolytic enzymes active on gluten peptides, antibodies neutralising IL-15 and IFN-gamma, drugs targeting HLA, regulatory cytokines and T cells.

Gliadin peptides activate blood monocytes from patients with celiac disease

To elucidate the role of innate immune responses in celiac disease, we investigated the effect of gliadin on blood monocytes from patients with celiac disease. Gliadin induced substantial TNF-alpha and IL-8 production by monocytes from patients with active celiac disease, lower levels by monocytes from patients with inactive celiac disease, and even lower levels by monocytes from healthy donors. In healthy donor monocytes gliadin induced IL-8 from monocytes expressing HLA-DQ2 and increased monocyte expression of the costimulatory molecules CD80 and CD86, the dendritic cell marker CD83, and the activation marker CD40. Gliadin also increased DNA binding activity of NF-kappaB p50 and p65 subunits in monocytes from celiac patients, and NF-kappaB inhibitors reduced both DNA binding activity and cytokine production. Thus, gliadin activation of HLA-DQ2(+) monocytes leading to chemokine and proinflammatory cytokine production may contribute to the host innate immune response in celiac disease.

A unified hypothesis of coeliac disease with implications for management of patients

This mini-review presents the research carried out within the context of two of the main hypotheses of the aetiology of coeliac disease. The enzymopathic hypothesis of the disease has been placed clearly as the underlying deficiency causing increased levels of toxic peptides, while the immunological hypothesis has been implicated in the pathogenesis of the disorder as the result of the action of undigested peptides in the small intestine. As a consequence, we are proposing a unified hypothesis of coeliac disease, which takes into account the actions of these undigested peptides through their direct cytotoxicity and their immunoactivity. At the same time, work aimed at defining some of these biologically active peptides, which could be said to be involved in the aetiopathogenesis of coeliac disease, will be reported. The review also focusses on the use of enzyme therapy for management of the disease, which when used in conjunction with the gluten-free diet, offers a safeguard against damage to the small intestine caused by small amounts of gluten.