Alterations of the intestinal transport and processing of gliadin peptides in celiac disease

Exopeptidase combination enhances the degradation of isotopically labelled gluten immunogenic peptides in humans

Introduction

Celiac disease is a common autoimmune-like enteropathy caused by an aberrant response to incompletely digested dietary gluten. Gluten immunogenic peptides including the immunodominant 33-mer are thought to be resistant to proteolytic digestion by human gastrointestinal peptidases. We developed a novel enzyme therapy approach to support gluten peptide digestion using a combination of two tandem-acting exopeptidases, AMYNOPEP, that complement the intrinsic enzymatic activity of intestinal brush border enterocytes.

Methods

We evaluated the effects of AMYNOPEP supplementation on 33-mer degradation in vitro and in vivo. In a cross-over clinical study, healthy volunteers with no gastrointestinal disorders were given stable isotope (SI) labelled 33-mer peptides in the presence of varying peptide substrates and caloric loads, with and without AMYNOPEP. 33-mer degradation products (SI-labelled single amino acids) were measured in the blood plasma using LC-MS/MS.

Results

AMYNOPEP achieved rapid, complete amino-to-carboxyl terminal degradation of the 33-mer in vitro, generating single amino acids and dipeptides. In healthy volunteers, AMYNOPEP supplementation significantly increased 33-mer degradation and absorption of SI-labelled amino acids even in the presence of competing substrates. Specifically, we observed a 2.8-fold increase in the Cmax of stable isotope-labelled amino acids in the presence of wheat gluten. The absorption kinetics of labelled amino acids derived from 33-mer digestion with AMYNOPEP closely resembled that of SI-labelled X-Proline dipeptides administered without enzyme supplementation, highlighting the rapid hydrolytic activity of AMYNOPEP on polypeptides.

Conclusions

AMYNOPEP achieved complete degradation of the 33-mer into single amino acids and dipeptides in vitro and significantly improved 33-mer degradation kinetics in healthy volunteers, as measured by labelled amino acid detection, warranting further investigation into the potential therapeutic benefits of exopeptidase combinations for patients with gluten-related health disorders including celiac disease.

Association of dietary intake and serum concentration of omega-3 fatty acids on celiac disease: evidence from observational study and Mendelian randomization

OBJECTIVE

The association between omega-3 fatty acids (O3FA) and celiac disease lacks sufficient investigation.

METHODS

Utilizing data gleaned from the 2009 to 2014 National Health and Nutrition Examination Survey (NHANES), this research comprises a sample of 13 403 adults, each aged 20 years and above. We conducted a multivariable logistic regression analysis to assess the association between dietary intake of O3FA and celiac disease. Subsequently, a two-sample Mendelian randomization was performed to estimate the unconfounded causal relationship between serum O3FA and celiac disease. The principal analytical strategy utilized the inverse-variance weighted methodology.

RESULTS

In this cross-sectional study, 48 occurrences (0.36%) of celiac disease were encompassed. In the multivariable model, there was no association between dietary intake of O3FA and cases of celiac disease (odds ratio: 1.12, 95% confidence interval: 0.47-2.66, P  = 0.792). However, serum levels of O3FA determined by genetic assay were correlated with celiac disease (inverse-variance weighted, β = 0.2439, P  = 0.0287), with no evidence of horizontal pleiotropy ( P  = 0.3689).

CONCLUSION

The dietary consumption of O3FA did not exhibit an association with the risk of celiac disease in this cross-sectional investigation. However, a correlation between celiac disease and serum levels of O3FA was observed in the Mendelian randomization. Further investigations, including human clinical trials, are warranted.

Prevalence of autoimmune, cholestatic and nonalcoholic fatty liver disease in celiac disease

BACKGROUND

While there is higher prevalence of autoimmune, cholestatic and fatty liver disease in celiac disease (CeD), most data is from small-scale studies. We evaluated the prevalence and risk factors of the same using large cohort data.

METHODS

A population-based cross-sectional study was conducted using Explorys, a multi-institutional database. Prevalence and risk factors of autoimmune hepatitis (AIH), primary biliary cholangitis (PBC), primary sclerosing cholangitis (PSC) and nonalcoholic fatty liver disease (NAFLD) in CeD were assessed.

RESULTS

Out of 70 352 325 subjects, 136 735 had CeD (0.19%). The prevalence of AIH (0.32%), PBC (0.15%), PSC (0.004%) and NAFLD (0.7%) were high in CeD. After adjusting for age, gender, Caucasian race and anti-tissue transglutaminase antibody (anti-TTG), CeD subjects had higher odds of AIH [adjusted odds ratio (aOR) 7.06, 95% confidence interval (CI) 6.32-7.89] and PBC (aOR 4.16, 95% CI 3.46-5.0). Even after adjusting for CeD, anti-TTG positivity concurred with higher odds of AIH (aOR 4.79, 95% CI 3.88-5.92) and PBC (aOR 9.22, 95% CI 7.03-12.1). After adjusting for age, gender, Caucasian race, diabetes mellitus (DM), obesity, hypothyroidism and metabolic syndrome, there was higher prevalence of NAFLD in CeD, with the aOR in the presence of DM type 1 being 2.1 (95% CI 1.96-2.25), and in the presence of DM type 2 being 2.92 (95% CI 2.72-3.14).

CONCLUSION

Subjects with CeD are more likely to have AIH, PBC, PSC and NAFLD. AIH and PBC have higher odds in the presence of anti-TTG. The odds of NAFLD in CeD are high regardless of type of DM.

Measuring intestinal permeability in celiac disease ex vivo, using Ussing chambers

Multicellular organisms need epithelial barriers to remain compartmentalized and protected from external influences. Although much progress has been made in understanding barrier integrity disruption in Celiac disease (CD), the regulatory and genetic mechanisms underlying the increased intestinal epithelial flux are still unknown. As we learn more about the regulation of permeability in homeostasis and pathogenesis, we will be able to develop strategies to strengthen the epithelial barrier function in intestinal disorders, including CD. For this purpose, Ussing chambers are increasingly used in native tissue, such as gut mucosa or cell monolayers, to assess the integrity of the barrier. In particular, the Ussing chambers allow the measurement of paracellular and transcellular parameters of CD small intestinal biopsies under physiologically specific conditions. In diverse types of diseases, this method is commonly used to determine epithelial barrier defects, but its application to CD has not yet been widely expanded. To provide a great model of barrier ex vivo studies in CD, we facilitate a standard protocol to measure paracellular and transcellular permeability using the Ussing chamber.

A case for improved assessment of gut permeability: a meta-analysis quantifying the lactulose:mannitol ratio in coeliac and Crohn's disease

BACKGROUND

A widely used method in assessing small bowel permeability is the lactulose:mannitol test, where the lactulose:mannitol ratio (LMR) is measured. However, there is discrepancy in how the test is conducted and in the values of LMR obtained across studies. This meta-analysis aims to determine LMR in healthy subjects, coeliac and Crohn's disease.

METHODS

A literature search was performed using PRISMA guidance to identify studies assessing LMR in coeliac or Crohn's disease. 19 studies included in the meta-analysis measured gut permeability in coeliac disease, 17 studies in Crohn's disease. Outcomes of interest were LMR values and comparisons of standard mean difference (SMD) and weighted mean difference (WMD) in healthy controls, inactive Crohn's, active Crohn's, treated coeliac and untreated coeliac. Pooled estimates of differences in LMR were calculated using the random effects model.

RESULTS

Pooled LMR in healthy controls was 0.014 (95% CI: 0.006-0.022) while pooled LMRs in untreated and treated coeliac were 0.133 (95% CI: 0.089-0.178) and 0.037 (95% CI: 0.019-0.055). In active and inactive Crohn's disease, pooled LMRs were 0.093 (95% CI: 0.031-0.156) and 0.028 (95% CI: 0.015-0.041). Significant differences were observed in LMR between: (1) healthy controls and treated coeliacs (SMD = 0.409 95% CI 0.034 to 0.783, p = 0.032), (2) healthy controls and untreated coeliacs (SMD = 1.362 95% CI: 0.740 to 1.984, p < 0.001), (3) treated coeliacs and untreated coeliacs (SMD = 0.722 95% CI: 0.286 to 1.157, p = 0.001), (4) healthy controls and inactive Crohn's (SMD = 1.265 95% CI: 0.845 to 1.686, p < 0.001), (5) healthy controls and active Crohn's (SMD = 2.868 95% CI: 2.112 to 3.623, p < 0.001), and (6) active Crohn's and inactive Crohn's (SMD = 1.429 (95% CI: 0.580 to 2.278, p = 0.001). High heterogeneity was observed, which was attributed to variability in protocols used across different studies.

CONCLUSION

The use of gut permeability measurements in screening and monitoring of coeliac and Crohn's disease is promising. LMR is useful in performing this function with significant limitations. More robust alternative tests with higher degrees of clinical evidence are needed if measurements of gut permeability are to find widespread clinical use.

Larazotide acetate for treatment of celiac disease: A systematic review and meta-analysis of randomized controlled trials

PURPOSE

The standard of care for treatment of celiac disease (CD) is a stringent lifetime gluten-free diet (GFD). Larazotide acetate (AT-1001) is an anti-zonulin which functions as a gut permeability regulator for treatment of CD. We endeavored to conduct a systematic review and meta-analysis of all randomized controlled trials (RCTs) which studied the efficacy and safety of AT-1001 in patients with CD.

METHODS

We examined four databases from inception to 20-August-2020. We pooled continuous outcomes as mean difference and dichotomous outcomes as risk ratio with 95% confidence interval under the fixed-effects meta-analysis model.

RESULTS

Four RCTs met our eligibility criteria, comprising 626 patients (AT-1001, n=465, placebo, n=161). Three and two RCTs reported outcomes of patients undergoing gluten challenge (intake of 2.4-2.7 grams of gluten/day) and GFD, respectively. For change in lactulose-to-mannitol ratio, the endpoint did not significantly differ between AT-1001 and placebo groups, irrespective of the gluten status. Subgroup analysis of patients undergoing gluten challenge showed AT-1001 treatment (compared with placebo) significantly correlated with better symptomatic improvement in the two endpoints of change in total gastrointestinal symptom rating scale (total GSRS) and CD-specific GSRS (CD-GSRS). However, no significant difference was noted among patients undergoing GFD for the abovementioned two efficacy endpoints. Compared with placebo, AT-1001 favorably reduced the adverse event (AE) of gluten-related diarrhea in patients who underwent gluten challenge. Other AEs were comparable between both AT-1001 and placebo groups.

CONCLUSIONS

AT-1001 is largely well-endured and seems somehow superior to placebo in alleviating gastrointestinal symptoms among CD patients undergoing gluten challenge. Nevertheless, additional RCTs are warranted to validate these findings.

Anaphylactic Food Allergy After Roux-en-Y Gastric Bypass

The prevalence of obesity in the United States is projected to increase as high as 85% by 2030. Weight loss is associated with improved morbidity and mortality outcomes. Roux-en-Y gastric bypass (RYGB) is an effective procedure recommended for individuals with morbid obesity for weight loss. We report the case of a patient who developed worsening food allergic reactions after RYGB surgery that progressed to an anaphylactic reaction. A 36-year-old female developed an anaphylactic reaction to an ingredient in guacamole eight years after RYGB surgery. Prior to the surgery, she had symptoms consistent with oral allergy syndrome. After the gastric bypass, however, she experienced worsening symptoms. On this occasion, she developed throat tightness prompting a visit to the emergency department where she required emergent intubation for airway protection. Blood testing to assess for an immunoglobin E-mediated allergy to common foods was negative. Despite the negative test, the allergist maintained a high suspicion for the progression of food-pollen syndrome following gastric bypass. Disruption of protein digestion from stomach bypass surgery may result in dietary proteins large enough to elicit immune responses being presented to the immune-rich intestinal mucosa. Additional consideration should be given to patients with a preexisting history of food allergic reactions undergoing RGYB surgery.

An updated overview on celiac disease: from immuno-pathogenesis and immuno-genetics to therapeutic implications

INTRODUCTION

Celiac disease (CD) is an autoimmune enteropathy triggered by ingestion of gluten. While presenting many similarities with other autoimmune diseases, celiac disease is unique in that the external trigger, gluten, and the genetic background necessary for disease development (HLA DQ2/DQ8) are well described. The prevalence of celiac disease is dramatically increasing over the years and new epidemiologic data show changes regarding age of onset and symptoms. A better understanding of CD-pathogenesis is fundamental to highlight the reasons of this rise of celiac diagnoses.

AREAS COVERED

In this review we describe CD-pathogenesis by dissecting all the components necessary to lose tolerance to gluten (ingestion of gluten, genetic predisposition, loss of barrier function and immune response). Additionally, we also highlight the role that microbiome plays in celiac disease as well as new proposed therapies and experimental tools.

EXPERT OPINION

Prevalence of autoimmune diseases is increasing around the world. As a result, modern society is strongly impacted by a social and economic burden. Given the unique characteristics of celiac disease, a better understanding of its pathogenesis and the factors that contribute to it may shed light on other autoimmune diseases for which external trigger and genetic background are not known.

Cytokine-Mediated Crosstalk between Immune Cells and Epithelial Cells in the Gut

Cytokines are small proteins that are secreted by a vast majority of cell types in the gut. They not only establish cell-to-cell interactions and facilitate cellular signaling, but also regulate both innate and adaptive immune responses, thereby playing a central role in genetic, inflammatory, and infectious diseases of the gut. Both, immune cells and gut epithelial cells, play important roles in intestinal disease development. The epithelium is located in between the mucosal immune system and the gut microbiome. It not only establishes an efficient barrier against gut microbes, but it also signals information from the gut lumen and its composition to the immune cell compartment. Communication across the epithelial cell layer also occurs in the other direction. Intestinal epithelial cells respond to immune cell cytokines and their response influences and shapes the microbial community within the gut lumen. Thus, the epithelium should be seen as a translator or a moderator between the microbiota and the mucosal immune system. Proper communication across the epithelium seems to be a key to gut homeostasis. Indeed, current genome-wide association studies for intestinal disorders have identified several disease susceptibility loci, which map cytokine signatures and their related signaling genes. A thorough understanding of this tightly regulated cytokine signaling network is crucial. The main objective of this review was to shed light on how cytokines can orchestrate epithelial functions such as proliferation, cell death, permeability, microbe interaction, and barrier maintenance, thereby safeguarding host health. In addition, cytokine-mediated therapy for inflammation and cancer are discussed.

The gliadin p31-43 peptide: Inducer of multiple proinflammatory effects

Coeliac disease (CD) is the prototype of an inflammatory chronic disease induced by food. In this context, gliadin p31-43 peptide comes into the spotlight as an important player of the inflammatory/innate immune response to gliadin in CD. The p31-43 peptide is part of the p31-55 peptide from α-gliadins that remains undigested for a long time, and can be present in the small intestine after ingestion of a gluten-containing diet. Different biophysical methods and molecular dynamic simulations have shown that p31-43 spontaneously forms oligomeric nanostructures, whereas experimental approaches using in vitro assays, mouse models, and human duodenal tissues have shown that p31-43 is able to induce different forms of cellular stress by driving multiple inflammatory pathways. Increased proliferative activity of the epithelial cells in the crypts, enterocyte stress, activation of TG2, induction of Ca²⁺, IL-15, and NFκB signaling, inhibition of CFTR, alteration of vesicular trafficking, and activation of the inflammasome platform are some of the biological effects of p31-43, which, in the presence of appropriate genetic susceptibility and environmental factors, may act together to drive CD.

Coeliac Disease and Mast Cells

Over the last decades, there has been an impressive progress in our understanding of coeliac disease pathogenesis and it has become clear that the disorder is the final result of complex interactions of environmental, genetic, and immunological factors. Coeliac disease is now considered a prototype of T-cell-mediated disease characterized by loss of tolerance to dietary gluten and the targeted killing of enterocytes by T-cell receptor αβ intraepithelial lymphocytes. Accumulating evidence, however, indicates that the induction of a gluten-specific T helper-1 response must be preceded by the activation of the innate immune system. Mast cells are key players of the innate immune response and contribute to the pathogenesis of a multitude of diseases. Here, we review the results of studies aimed at investigating the role of mast cells in the pathogenesis of coeliac disease, showing that these cells increase in number during the progression of the disease and contribute to define a pro-inflammatory microenvironment.

The human duodenal mucosa harbors all components for a local renin angiotensin system

The renin-angiotensin system (RAS) is present in the gastrointestinal (GI) tract but remains to be fully characterized, particularly in man. The duodenum plays a role in both the upper and lower GI regulation, as well as in distant organs. The present study investigates the presence and functional potential of RAS in the human duodenal mucosa of healthy individuals. Endoscopically acquired mucosal biopsies from healthy volunteers were examined using western blot, immunohistochemistry, and ELISA. Functionality was examined by using Ussing chambers and recording duodenal transmucosal potential difference (PD) and motility in vivo Angiotensinogen, Angiotensin II (AngII) and its receptors (AT1R, AT2R) as well as to the RAS associated enzymes renin, ACE, and neprylisin were detected in all samples of duodenal mucosa. Migrating motility complex induced elevations of transmucosal PD were significantly larger after per-oral administration of the AT1R receptor antagonist candesartan. Fasting duodenal motility per se was not influenced by candesartan. The epithelial current produced by duodenal mucosae mounted in Ussing chambers increased significantly after addition of AngII to specimens where the AT1R was blocked using losartan. The epithelial current also increased after addition of the AT2R-selective agonist C21. Immunostaining and pharmacological data demonstrate the presence of a local RAS in the human duodenal mucosa with capacity to influence epithelial ion transport by way of particulary the AT2R.

IL-10 signaling prevents gluten-dependent intraepithelial CD4+ cytotoxic T lymphocyte infiltration and epithelial damage in the small intestine

Breach of tolerance to gluten leads to the chronic small intestinal enteropathy celiac disease. A key event in celiac disease development is gluten-dependent infiltration of activated cytotoxic intraepithelial lymphocytes (IELs), which cytolyze epithelial cells causing crypt hyperplasia and villous atrophy. The mechanisms leading to gluten-dependent small intestinal IEL infiltration and activation remain elusive. We have demonstrated that under homeostatic conditions in mice, gluten drives the differentiation of anti-inflammatory T cells producing large amounts of the immunosuppressive cytokine interleukin-10 (IL-10). Here we addressed whether this dominant IL-10 axis prevents gluten-dependent infiltration of activated cytotoxic IEL and subsequent small intestinal enteropathy. We demonstrate that IL-10 regulation prevents gluten-induced cytotoxic inflammatory IEL infiltration. In particular, IL-10 suppresses gluten-induced accumulation of a specialized population of cytotoxic CD4⁺CD8αα⁺ IEL (CD4⁺ CTL) expressing Tbx21, Ifng, and Il21, and a disparate non-cytolytic CD4⁺CD8α^- IEL population expressing Il17a, Il21, and Il10. Concomitantly, IL-10 suppresses gluten-dependent small intestinal epithelial hyperproliferation and upregulation of stress-induced molecules on epithelial cells. Remarkably, frequencies of granzyme B⁺CD4⁺CD8α⁺ IEL are increased in pediatric celiac disease patient biopsies. These findings demonstrate that IL-10 is pivotal to prevent gluten-induced small intestinal inflammation and epithelial damage, and imply that CD4⁺ CTL are potential new players into these processes.

Gluten Immunogenic Peptides as Standard for the Evaluation of Potential Harmful Prolamin Content in Food and Human Specimen

Gluten is a complex mixture of storage proteins in cereals like wheat, barley, and rye. Prolamins are the main components of gluten. Their high content in proline and glutamine makes them water-insoluble and difficult to digest in the gastrointestinal tract. Partial digestion generates peptide sequences which trigger immune responses in celiac and gluten-sensitive patients. Gluten detection in food is challenging because of the diversity, in various food matrices, of protein proportions or modifications and the huge number of immunogenic sequences with differential potential immunoactivity. Attempts to develop standard reference materials have been unsuccessful. Recent studies have reported the detection of a limited number of dominant Gluten Immunogenic Peptides (GIP) that share similarities to epitopes presented in the α-gliadin 33-mer, which showed to be highly proteolytic resistant and is considered to be the most immunodominant peptide within gluten in celiac disease (CD). GIP were detectable and quantifiable in very different kind of difficult to analyze food, revealing the potential immunogenicity by detecting T-cell activity of celiac patients. But GIP were also found in stool and urine of celiac patients on a supposedly gluten-free diet (GFD), showing the capacity to resist and be absorbed and excreted from the body, providing the first simple and objective means to assess adherence to the GFD. Methods to specifically and sensitively detect the most active GIP in food and biological fluids are rational candidates may use similar analytical standard references for determination of the immunopathological risk of gluten exposure in gluten-related diseases.

Green Tea Polyphenols Mitigate Gliadin-Mediated Inflammation and Permeability in Vitro

SCOPE

Green tea, a polyphenol-rich beverage, has been reported to mitigate a number of inflammatory and hypersensitivity disorders in laboratory models, and has been shown to moderate pathways related to food allergies in vitro. The present study investigates the impact of decaffeinated green tea extract (GTE) on the digestion of gliadin protein in vitro and the effect of physical interactions with GTE on the ability of gliadin to stimulate celiac disease-related symptoms in vitro.

METHODS AND RESULTS

Complexation of GTE and gliadin in vitro is confirmed by monitoring increases in turbidity upon titration of GTE into a gliadin solution. This phenomenon is also observed during in vitro digestion when gliadin is exposed to the digestive proteases pepsin and trypsin. SDS-PAGE and enzymatic assays reveal that GTE inhibits digestive protease activity and gliadin digestion. In differentiated Caco-2 cell monolayers as a model of the small intestinal epithelium, complexation of gliadin with GTE reduces gliadin-stimulated monolayer permeability and the release of interleukin (IL)-6 and IL-8.

CONCLUSION

There are potential beneficial effects of GTE as an adjuvant therapy for celiac disease through direct interaction between gliadin proteins and green tea polyphenols.

A New Proposal for the Pathogenic Mechanism of Non-Coeliac/Non-Allergic Gluten/Wheat Sensitivity: Piecing Together the Puzzle of Recent Scientific Evidence

Non-coeliac/non-allergic gluten/wheat sensitivity (NCG/WS) is a gluten-related disorder, the pathogenesis of which remains unclear. Recently, the involvement of an increased intestinal permeability has been recognized in the onset of this clinical condition. However, mechanisms through which it takes place are still unclear. In this review, we attempt to uncover these mechanisms by providing, for the first time, an integrated vision of recent scientific literature, resulting in a new hypothesis about the pathogenic mechanisms involved in NCG/WS. According to this, the root cause of NCG/WS is a particular dysbiotic profile characterized by decreased butyrate-producing-Firmicutes and/or Bifidobacteria, leading to low levels of intestinal butyrate. Beyond a critical threshold of the latter, a chain reaction of events and vicious circles occurs, involving other protagonists such as microbial lipopolysaccharide (LPS), intestinal alkaline phosphatase (IAP) and wheat α-amylase trypsin inhibitors (ATIs). NCG/WS is likely to be a multi-factor-onset disorder, probably transient and preventable, related to quality and balance of the diet, and not to the presence of gluten in itself. If future studies confirm our proposal, this would have important implications both for the definition of the disease, as well as for the prevention and therapeutic-nutritional management of individuals with NCG/WS.

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.

Soluble Syndecan-1: A Novel Biomarker of Small Bowel Mucosal Damage in Children with Celiac Disease

BACKGROUND

Syndecan-1 (SDC1) is essential for maintaining normal epithelial barrier. Shedding of SDC1 ectodomain, reflected by serum soluble syndecan-1 (SSDC1) levels, is regulated by inflammation. Increased intestinal permeability plays a central role in celiac disease (CD). The association between SSDC1 levels and mucosal damage in CD has not been evaluated.

AIMS

To evaluate serum SSDC1 levels in children with CD and to determine its relationship with histological grading classified by modified Marsh criteria.

METHODS

This is a cross-sectional, pilot study, in which serum SSDC1 was analyzed by ELISA in a cohort of 49 untreated children with CD and 15 children with nonspecific abdominal pain (AP). CD was diagnosed based on positive celiac serology and small intestinal biopsy. SSDC1 levels at the time of biopsy were correlated with Marsh grading. Controls were defined by AP, negative celiac serology, normal upper endoscopy, and small intestinal biopsies.

RESULTS

SSDC1 levels were significantly higher in CD patients compared to AP controls (116.2 ± 161 vs. 41.3 ± 17.5 ng/ml, respectively, p < 0.01). SSDC1 levels were significantly higher in patients with Marsh 3c lesion compared to AP controls (170.6 ± 201 vs. 41.3 ± 17.5 ng/ml, respectively, p < 0.05). SSDC1 concentrations displayed a significant correlation with mucosal damage defined by Marsh (r = 0.39, p < 0.05).

CONCLUSION

This is the first study demonstrating elevated levels of serum SSDC1 in children with CD. Our results suggest that SSDC1 is a potentially novel marker of intestinal mucosal damage in patients with CD. Its applicability as a surrogate biomarker in CD remains to be determined.

Active and passive involvement of claudins in the pathophysiology of intestinal inflammatory diseases

Intestinal inflammatory diseases, four of which are discussed here, are associated with alterations of claudins. In ulcerative colitis, diarrhea and antigen entry into the mucosa occurs. Claudin-2 is upregulated but data on other claudins are still limited or vary (e.g., claudin-1 and -4). Apart from that, tight junction changes contribute to diarrhea via a leak flux mechanism, while protection against antigen entry disappears behind epithelial gross lesions (erosions) and apoptotic foci. Crohn's disease is additionally characterized by a claudin-5 and claudin-8 reduction which plays an active role in antigen uptake already before gross lesions appear. In microscopic colitis (MC), upregulation of claudin-2 expression is weak and a reduction in claudin-4 may be only passively involved, while sodium malabsorption represents the main diarrheal mechanism. However, claudin-5 is removed from MC tight junctions which may be an active trigger for inflammation through antigen uptake along the so-called leaky gut concept. In celiac disease, primary barrier defects are discussed in the context of candidate genes as PARD3 which regulate cell polarity and tight junctions. The loss of claudin-5 allows small antigens to invade, while the reductions in others like claudin-3 are rather passive events. Taken together, the specific role of single tight junction proteins for the onset and perpetuation of inflammation and the recovery from these diseases is far from being fully understood and is clearly dependent on the stage of the disease, the background of the other tight junction components, the transport activity of the mucosa, and the presence of other barrier features like gross lesions, an orchestral interplay which is discussed in this article.

Intestinal barrier dysfunction: implications for chronic inflammatory conditions of the bowel

The intestinal epithelium of adult humans acts as a differentially permeable barrier that separates the potentially harmful contents of the lumen from the underlying tissues. Any dysfunction of this boundary layer that disturbs the homeostatic equilibrium between the internal and external environments may initiate and sustain a biochemical cascade that results in inflammation of the intestine. Key to such dysfunction are genetic, microbial and other environmental factors that, singularly or in combination, result in chronic inflammation that is symptomatic of inflammatory bowel disease (IBD). The aim of the present review is to assess the scientific evidence to support the hypothesis that defective transepithelial transport mechanisms and the heightened absorption of intact antigenic proinflammatory oligopeptides are important contributing factors in the pathogenesis of IBD.

Celiac disease in children

Celiac disease is an autoimmune enteropathy, triggered by ingestion of gluten in genetically predisposed individuals. Since the use of anti-transglutaminase and anti-endomysium antibodies in the early 1990s, two main groups of clinical presentation can be identified: patients with a symptomatic form of the disease, and patients with a pauci (a)-symptomatic form detected during the work-up of another autoimmune disease or due to a family history of celiac disease. The prevalence of both forms of the disease is currently estimated between 1/100 and 1/400. Classical form of the disease is characterized by occurrence of diarrhoea, failure to thrive, and abdominal bloating in young infants in the months following gluten introduction. Serological tests show high level of anti-transglutaminase and anti-endomysium antibodies. Until recently, the diagnosis required duodenal biopsies that show villous atrophy. HLA genotype can help for diagnosis: the absence of the HLA-DQ2 or DQ8 alleles has a high negative predictive value. European guidelines recently proposed to reconsider the need for systematic endoscopy in typical symptomatic forms with high level of anti-transglutaminase and positive anti-endomysium. These recommendations are being assessed now. Currently, the gluten-free diet remains the only effective treatment for celiac disease. Children with celiac disease have to exclude from their diet all products containing wheat, barley and rye. Gluten-free diet causes clinical remission within a few weeks, but normalization of the small bowel mucosa and negativity of anti-transglutaminase antibodies are obtained in several months or even years. Gluten-free diet is useful to obtain clinical assessment, but also to prevent long-term complications of celiac disease, mainly osteoporosis, other autoimmune diseases, decreased fertility and cancers.

Non-celiac wheat sensitivity: differential diagnosis, triggers and implications

Non allergy-non-celiac wheat sensitivity (NCWS) has become a common and often overrated diagnosis. Skepticism mainly relates to patients with prominent intestinal symptoms in the absence of general or intestinal signs of inflammation. There is consensus that the major wheat sensitivities, celiac disease and wheat allergy, have to be ruled out which may be difficult for wheat allergy. The non-inflammatory intolerances to carbohydrates, mainly lactose and FODMAPs (fermentable oligi-, di-, monosaccharides and polyols), which cause bloating or diarrhoea, can usually be excluded clinically or by simple tests. Recent studies and experimental data strongly indicate that NCWS exists in a substantial proportion of the population, that it is an innate immune reaction to wheat and that patients often present with extraintestinal symptoms, such as worsening of an underlying inflammatory disease in clear association with wheat consumption. Wheat amylase-trypsin inhibitors (ATIs) have been identified as the most likely triggers of NCWS. They are highly protease resistant and activate the toll-like receptor 4 (TLR4) complex in monocytes, macrophages and dendritic cells of the intestinal mucosa. Non-gluten containing cereals or staples display no or little TLR4 stimulating activity. Wheat ATIs are a family of up to 17 similar proteins of molecular weights around 15 kD and represent 2-4% of the wheat protein. With oral ingestion they costimulate antigen presenting cells and promote T cell activation in celiac disease, but also in other immune-mediated diseases within and outside the GI tract.

Larazotide acetate for persistent symptoms of celiac disease despite a gluten-free diet: a randomized controlled trial

BACKGROUND & AIMS

Celiac disease (CeD) is a prevalent autoimmune condition. Recurrent signs and symptoms are common despite treatment with a gluten-free diet (GFD), yet no approved or proven nondietary treatment is available.

METHODS

In this multicenter, randomized, double-blind, placebo-controlled study, we assessed larazotide acetate 0.5, 1, or 2 mg 3 times daily to relieve ongoing symptoms in 342 adults with CeD who had been on a GFD for 12 months or longer and maintained their current GFD during the study. The study included a 4-week placebo run-in, 12 weeks of treatment, and a 4-week placebo run-out phase. The primary end point was the difference in average on-treatment Celiac Disease Gastrointestinal Symptom Rating Scale score.

RESULTS

The primary end point was met with the 0.5-mg dose of larazotide acetate, with fewer symptoms compared with placebo by modified intention to treat (n = 340) (analysis of covariance, P = .022; mixed model for repeated measures, P = .005). The 0.5-mg dose showed an effect on exploratory end points including a 26% decrease in celiac disease patient-reported outcome symptomatic days (P = .017), a 31% increase in improved symptom days (P = .034), a 50% or more reduction from baseline of the weekly average abdominal pain score for 6 or more of 12 weeks of treatment (P = .022), and a decrease in the nongastrointestinal symptoms of headache and tiredness (P = .010). The 1- and 2-mg doses were no different than placebo for any end point. Safety was comparable with placebo.

CONCLUSIONS

Larazotide acetate 0.5 mg reduced signs and symptoms in CeD patients on a GFD better than a GFD alone. Although results were mixed, this study was a successful trial of a novel therapeutic agent targeting tight junction regulation in patients with CeD who are symptomatic despite a GFD. Clinicaltrials.gov: NCT01396213.

Claudin-related intestinal diseases

With up to 200 m(2) the human intestine is the organ with the largest absorptive surface of the body. It is lined by a single layer of epithelial cells that separates the host from the environment. The intestinal epithelium provides both, selective absorption of nutrients, ions, and water but also a highly effective barrier function which includes the first line of defense against environmental antigens. The paracellular part of this barrier function is provided by tight junction (TJ) proteins, especially the large family of claudins. Changes in abundance or molecular structure of claudins can generally result in three typical effects, (i) decreased absorptive passage, (ii) increased secretory passage of small solutes and water causing leak flux diarrhea and (iii) increased absorptive passage of macromolecules which may induce inflammatory processes. Several intestinal diseases are associated with such changes that can result in intestinal inflammation and symptoms like weight loss, abdominal pain or diarrhea. This review summarizes our current knowledge on barrier dysfunction and claudin dysregulation in several intestinal diseases gastroenterologists are often faced with, like inflammatory bowel disease, microscopic colitis, celiac disease, irritable bowel syndrome, gallstones and infectious diseases like HIV enteropathy, Campylobacter jejuni and Clostridium perfringens infection.

Claudin-2 as a mediator of leaky gut barrier during intestinal inflammation

The epithelial tight junction determines the paracellular water and ion movement in the intestine and also prevents uptake of larger molecules, including antigens, in an uncontrolled manner. Claudin-2, one of the 27 mammalian claudins regulating that barrier function, forms a paracellular channel for small cations and water. It is typically expressed in leaky epithelia like proximal nephron and small intestine and provides a major pathway for the paracellular transport of sodium, potassium, and fluid. In intestinal inflammation (Crohn's disease, ulcerative colitis), immune-mediated diseases (celiac disease), and infections (HIV enteropathy), claudin-2 is upregulated in small and large intestine and contributes to diarrhea via a leak flux mechanism. In parallel to that upregulation, other epithelial and tight junctional features are altered and the luminal uptake of antigenic macromolecules is enhanced, for which claudin-2 may be partially responsible through induction of tight junction strand discontinuities.

Epithelial transport of immunogenic and toxic gliadin peptides in vitro

Scope

Celiac disease is an autoimmune disorder caused by failure of oral tolerance against gluten in genetically predisposed individuals. The epithelial translocation of gluten-derived gliadin peptides is an important pathogenetic step; the underlying mechanisms, however, are poorly understood. Thus, we investigated the degradation and epithelial translocation of two different gliadin peptides, the toxic P31–43 and the immunogenic P56–68. As the size, and hence, the molecular weight of peptides might have an effect on the transport efficiency we chose two peptides of the same, rather short chain length.

Methods and Results

Fluorescence labeled P31–43 and P56–68 were synthesized and studied in a transwell system with human enterocytes. Fluorometric measurements were done to reveal antigen translocation and flow cytometry as well as confocal microscopy were used to investigate cellular uptake of peptides. Structural changes of these peptides were analysed by MALDI-TOF-MS. According to fluorescence intensities, significantly more P31–43 compared to P56–68 was transported through the enterocyte layer after 24 h incubation. In contrast to previous reports, however, mass spectrometric data do not only show a time-dependent cleavage of the immunogenic P56–68, but we observed for the first time the degradation of the toxic peptide P31–43 at the apical side of epithelial cells.

Conclusion

Considering the degradation of gliadin peptides by enterocytes, measurement of fluorescence signals do not completely represent translocated intact gliadin peptides. From our experiments it is obvious that even short peptides can be digested prior to the translocation across the epithelial barrier. Thus, the chain length and the sensibility to degradations of gliadin peptides as well as the integrity of the epithelial barrier seem to be critical for the uptake of gliadin peptides and the subsequent inflammatory immune response.

Seroreactive marker for inflammatory bowel disease and associations with antibodies to dietary proteins in bipolar disorder

OBJECTIVES

Immune sensitivity to wheat glutens and bovine milk caseins may affect a subset of individuals with bipolar disorder. Digested byproducts of these foods are exorphins that have the potential to impact brain physiology through action at opioid receptors. Inflammation in the gastrointestinal (GI) tract might accelerate exposure of food antigens to systemic circulation and help explain elevated gluten and casein antibody levels in individuals with bipolar disorder.

METHODS

We measured a marker of GI inflammation, anti-Saccharomyces cerevisiae antibodies (ASCA), in non-psychiatric controls (n = 207), in patients with bipolar disorder without a recent onset of psychosis (n = 226), and in patients with bipolar disorder with a recent onset of psychosis (n = 38). We compared ASCA levels to antibodies against gluten, casein, Epstein-Barr virus (EBV), herpes simplex virus 1 (HSV-1), influenza A, influenza B, measles, and Toxoplasma gondii.

RESULTS

Elevated ASCA conferred a 3.5-4.4-fold increased odds ratio of disease association (age-, race-, and gender-corrected multinomial logistic regressions, p ≤ 0.00001) that was independent of type of medication received. ASCA correlated with food antibodies in both bipolar disorder groups (R(2)  = 0.29-0.59, p ≤ 0.0005), and with measles and T. gondii immunoglobulin G (IgG) in the recent onset psychosis bipolar disorder group (R(2)  = 0.31-0.36, p ≤ 0.004-0.01).

CONCLUSIONS

Elevated seropositivity of a GI-related marker and its association with antibodies to food-derived proteins and self-reported GI symptoms suggest a GI comorbidity in at least a subgroup of individuals with bipolar disorder. Marker seroreactivity may also represent part of an overall heightened activated immune state inherent to this mood disorder.

Abnormal apical-to-basal transport of dietary ovalbumin by secretory IgA stimulates a mucosal Th1 response

In celiac disease, enhanced permeability to gliadin peptides can result from their apico-basal transport by secretory immunoglobulin A1 (SIgA1) binding to the CD71 receptor ectopically expressed at the gut epithelial surface. Herein, we have established a mouse model in which there is apico-basal transport of the model antigen ovalbumin (OVA) by specific SIgA1 and have analyzed local T-cell activation. Transgenic DO11.10 mice were grafted with a hybridoma-secreting OVA-specific humanized IgA1, which could bind mouse CD71 and which were released in the intestinal lumen as SIgA. CD71 expression was induced at the gut apical surface by treating the mice with tyrphostin A8. Following gavage of the mice with OVA, OVA-specific CD4⁺ T cells isolated from the mesenteric lymph nodes displayed higher expression of the activation marker CD69 and produced more interferon gamma in mice bearing the hybridoma-secreting OVA-specific IgA1, than in ungrafted mice or in mice grafted with an irrelevant hybridoma. These results indicate that the protective role of SIgA1 might be jeopardized in human pathological conditions associated with ectopic expression of CD71 at the gut surface.

Gliadin fragments and a specific gliadin 33-mer peptide close KATP channels and induce insulin secretion in INS-1E cells and rat islets of langerhans

In non-obese diabetic (NOD) mice, diabetes incidence is reduced by a gluten-free diet. Gluten peptides, such as the compound gliadin, can cross the intestinal barrier and may directly affect pancreatic beta cells. We investigated the effects of enzymatically-digested gliadin in NOD mice, INS-1E cells and rat islets. Six injections of gliadin digest in 6-week-old NOD mice did not affect diabetes development, but increased weight gain (20% increase by day 100). In INS-1E cells, incubation with gliadin digest induced a dose-dependent increase in insulin secretion, up to 2.5-fold after 24 hours. A similar effect was observed in isolated rat islets (1.6-fold increase). In INS-1E cells, diazoxide reduced the stimulatory effect of gliadin digest. Additionally, gliadin digest was shown to decrease current through K_ATP-channels. A specific gliadin 33-mer had a similar effect, both on current and insulin secretion. Finally, INS-1E incubation with gliadin digest potentiated palmitate-induced insulin secretion by 13% compared to controls. Our data suggest that gliadin fragments may contribute to the beta-cell hyperactivity observed prior to the development of type 1 diabetes.

Pepsin digest of wheat gliadin fraction increases production of IL-1β via TLR4/MyD88/TRIF/MAPK/NF-κB signaling pathway and an NLRP3 inflammasome activation

Celiac disease (CD) is a gluten-responsive, chronic inflammatory enteropathy. IL-1 cytokine family members IL-1β and IL-18 have been associated with the inflammatory conditions in CD patients. However, the mechanisms of IL-1 molecule activation in CD have not yet been elucidated. We show in this study that peripheral blood mononuclear cells (PBMC) and monocytes from celiac patients responded to pepsin digest of wheat gliadin fraction (PDWGF) by a robust secretion of IL-1β and IL-1α and a slightly elevated production of IL-18. The analysis of the upstream mechanisms underlying PDWGF-induced IL-1β production in celiac PBMC show that PDWGF-induced de novo pro-IL-1β synthesis, followed by a caspase-1 dependent processing and the secretion of mature IL-1β. This was promoted by K+ efflux and oxidative stress, and was independent of P2X7 receptor signaling. The PDWGF-induced IL-1β release was dependent on Nod-like receptor family containing pyrin domain 3 (NLRP3) and apoptosis-associated speck like protein (ASC) as shown by stimulation of bone marrow derived dendritic cells (BMDC) from NLRP3(-/-) and ASC(-/-) knockout mice. Moreover, treatment of human PBMC as well as MyD88(-/-) and Toll-interleukin-1 receptor domain-containing adaptor-inducing interferon-β (TRIF)(-/-) BMDC illustrated that prior to the activation of caspase-1, the PDWGF-triggered signal constitutes the activation of the MyD88/TRIF/MAPK/NF-κB pathway. Moreover, our results indicate that the combined action of TLR2 and TLR4 may be required for optimal induction of IL-1β in response to PDWGF. Thus, innate immune pathways, such as TLR2/4/MyD88/TRIF/MAPK/NF-κB and an NLRP3 inflammasome activation are involved in wheat proteins signaling and may play an important role in the pathogenesis of CD.

Structural analysis and Caco-2 cell permeability of the celiac-toxic A-gliadin peptide 31-55

Celiac disease is a chronic enteropathy caused by the ingestion of wheat gliadin and other cereal prolamines. The synthetic peptides 31-43 (P31-43) and 31-49 (P31-49) from A-gliadin are considered to be model peptides for studying innate immunity in celiac disease. Our previous study demonstrated that P31-43 and P31-49 are encrypted within peptide 31-55 (P31-55), which is naturally released from gastropancreatic digestion and is not susceptible to hydrolysis by brush border membrane enzymes. Here, we analyzed the permeability of P31-55 through the epithelial cell layer of confluent Caco-2 cells using high-performance liquid chromatography, mass spectrometry, and fluorescence-activated cell sorting. Twenty-three percent of the P31-55 added to the apical chamber was transported to the basolateral chamber after 4 h of incubation without being degraded by hydrolysis. Treatment of Caco-2 cells with whole gliadin digests extracted from a common wheat cultivar increased the epithelial P31-55 translocation by approximately 35%. Moreover, we observed an atypical chromatographic profile consisting of a double peak. Chromatography using different column temperatures and circular dichroism highlighted the presence of more conformational structures around the amide bond of the two adjacent prolines 38 and 39. These findings confirm that P31-55 is gastrointestinally resistant and is permeable across a Caco-2 monolayer. Moreover, we hypothesize that the various conformations of P31-55 may play a role in the activation of innate immunity.

Anti-gluten immune response following Toxoplasma gondii infection in mice

Gluten sensitivity may affect disease pathogenesis in a subset of individuals who have schizophrenia, bipolar disorder or autism. Exposure to Toxoplasma gondii is a known risk factor for the development of schizophrenia, presumably through a direct pathological effect of the parasite on brain and behavior. A co-association of antibodies to wheat gluten and to T. gondii in individuals with schizophrenia was recently uncovered, suggesting a coordinated gastrointestinal means by which T. gondii and dietary gluten might generate an immune response. Here, we evaluated the connection between these infectious- and food-based antigens in mouse models. BALB/c mice receiving a standard wheat-based rodent chow were infected with T. gondii via intraperitoneal, peroral and prenatal exposure methods. Significant increases in the levels of anti-gluten IgG were documented in all infected mice and in offspring from chronically infected dams compared to uninfected controls (repetitive measures ANOVAs, two-tailed t-tests, all p≤0.00001). Activation of the complement system accompanied this immune response (p≤0.002–0.00001). Perorally-infected females showed higher levels of anti-gluten IgG than males (p≤0.009) indicating that T. gondii-generated gastrointestinal infection led to a significant anti-gluten immune response in a sex-dependent manner. These findings support a gastrointestinal basis by which two risk factors for schizophrenia, T. gondii infection and sensitivity to dietary gluten, might be connected to produce the immune activation that is becoming an increasingly recognized pathology of psychiatric disorders.

A randomized, double-blind study of larazotide acetate to prevent the activation of celiac disease during gluten challenge

OBJECTIVES

In patients with celiac disease, enteropathy is caused by the entry of gluten peptides into the lamina propria of the intestine, in which their immunogenicity is potentiated by tissue transglutaminase (tTG) and T-helper type 1-mediated immune responses are triggered. Tight junction disassembly and paracellular permeability are believed to have an important role in the transport of gluten peptides to the lamina propria. Larazotide acetate is a tight-junction regulator peptide that, in vitro, prevents the opening of intestinal epithelial tight junctions. The aim of this study was to evaluate the efficacy and tolerability of larazotide acetate in protecting against gluten-induced intestinal permeability and gastrointestinal symptom severity in patients with celiac disease.

METHODS

In this dose-ranging, placebo-controlled study, 86 patients with celiac disease controlled through diet were randomly assigned to larazotide acetate (0.25, 1, 4, or 8 mg) or placebo three times per day with or without gluten challenge (2.4 g/day) for 14 days. The primary efficacy outcome was the urinary lactulose/mannitol (LAMA) fractional excretion ratio. Secondary endpoints included gastrointestinal symptom severity, quality-of-life measures, and antibodies to tTG.

RESULTS

LAMA measurements were highly variable in the outpatient setting. The increase in LAMA ratio associated with the gluten challenge was not statistically significantly greater than the increase in the gluten-free control. Among patients receiving the gluten challenge, the difference in the LAMA ratios for the larazotide acetate and placebo groups was not statistically significant. However, larazotide acetate appeared to limit gluten-induced worsening of gastrointestinal symptom severity as measured by the Gastrointestinal Symptom Rating Scale at some lower doses but not at the higher dose. Symptoms worsened significantly in the gluten challenge-placebo arm compared with the placebo-placebo arm, suggesting that 2.4 g of gluten per day is sufficient to induce reproducible gluten toxicity. Larazotide acetate was generally well tolerated. No serious adverse events were observed. The most common adverse events were headache and urinary tract infection.

CONCLUSIONS

LAMA variability in the outpatient setting precluded accurate assessment of the effect of larazotide acetate on intestinal permeability. However, some lower doses of larazotide acetate appeared to prevent the increase in gastrointestinal symptom severity induced by gluten challenge.

Interactions among secretory immunoglobulin A, CD71, and transglutaminase-2 affect permeability of intestinal epithelial cells to gliadin peptides

BACKGROUND & AIMS

The transferrin receptor (CD71) is up-regulated in duodenal biopsy samples from patients with active celiac disease and promotes retrotransport of secretory immunoglobulin A (SIgA)-gliadin complexes. We studied intestinal epithelial cell lines that overexpress CD71 to determine how interactions between SIgA and CD71 promote transepithelial transport of gliadin peptides.

METHODS

We analyzed duodenal biopsy specimens from 8 adults and 1 child with active celiac disease. Caco-2 and HT29-19A epithelial cell lines were transfected with fluorescence-labeled small interfering RNAs against CD71. Interactions among IgA, CD71, and transglutaminase 2 (Tgase2) were analyzed by flow cytometry, immunoprecipitation, and confocal microscopy. Transcytosis of SIgA-CD71 complexes and intestinal permeability to the gliadin 3H-p31-49 peptide were analyzed in polarized monolayers of Caco-2 cells.

RESULTS

Using fluorescence resonance energy transfer and in situ proximity ligation assays, we observed physical interactions between SIgA and CD71 or CD71 and Tgase2 at the apical surface of enterocytes in biopsy samples and monolayers of Caco-2 cells. CD71 and Tgase2 were co-precipitated with SIgA, bound to the surface of Caco-2 cells. SIgA-CD71 complexes were internalized and localized in early endosomes and recycling compartments but not in lysosomes. In the presence of celiac IgA or SIgA against p31-49, transport of intact 3H-p31-49 increased significantly across Caco-2 monolayers; this transport was inhibited by soluble CD71 or Tgase2 inhibitors.

CONCLUSIONS

Upon binding to apical CD71, SIgA (with or without gliadin peptides) enters a recycling pathway and avoids lysosomal degradation; this process allows apical-basal transcytosis of bound peptides. This mechanism is facilitated by Tgase2 and might be involved in the pathogenesis of celiac disease.

Celiac disease, inflammation and oxidative damage: a nutrigenetic approach

Celiac disease (CD), a common heritable chronic inflammatory condition of the small intestine caused by permanent intolerance to gluten/gliadin (prolamin), is characterized by a complex interplay between genetic and environmental factors. Developments in proteomics have provided an important contribution to the understanding of the biochemical and immunological aspects of the disease and the mechanisms involved in toxicity of prolamins. It has been demonstrated that some gliadin peptides resistant to complete proteolytic digestion may directly affect intestinal cell structure and functions by modulating gene expression and oxidative stress. In recent years, the creation of the two research fields Nutrigenomics and Nutrigenetics, has enabled the elucidation of some interactions between diet, nutrients and genes. Various dietary components including long chain ω-3 fatty acids, plant flavonoids, and carotenoids have been demonstrated to modulate oxidative stress, gene expression and production of inflammatory mediators. Therefore their adoption could preserve intestinal barrier integrity, play a protective role against toxicity of gliadin peptides and have a role in nutritional therapy of celiac disease.

Ascorbate-dependent decrease of the mucosal immune inflammatory response to gliadin in coeliac disease patients

BACKGROUND

The IL-15/NF-κB axis has an important role in coeliac disease (CD) and may represent a molecular target for immunomodulation. Ascorbate (vitamin C) is known to show inhibitory effects on NF-κB. Therefore, we studied if ascorbate supplementation to gliadin gliadin-stimulated biopsy culture could down-regulate the mucosal immune response to gliadin in CD.

METHODS

Duodenal biopsy explants from treated CD patients were gliadin challenged in vitro (100 μg/ml) with and without 20mM ascorbate. An extra tissue explant in basal culture was used as internal control. Secretion levels of nitrites (3h), and IFNγ, TNFα, IFNα, IL-17, IL-13, and IL-6 (24h) were measured on the supernatants. IL-15 was assayed by western-blot on whole protein duodenal explants.

RESULTS

The addition of ascorbate to in vitro culture gliadin-challenged biopsies blocked the secretion of nitrites (p=0.013), IFNγ (p=0.0207), TNFα (p=0.0099), IFNα (p=0.0375), and IL-6 (p=0.0036) compared to samples from non-ascorbate supplemented culture. Cytokine secretion was downregulated by ascorbate even to lower values than those observed in basal cultures (IFNγ: p=0.0312; TNFα: p=0.0312; IFNα: p=0.0312; and IL-6: p=0.0078). Gliadin-challenge induced IL-15 production in biopsies from treated CD patients, while the addition of ascorbate to culture medium completely inhibited IL-15 production. Moreover, the inhibition of IL-15 by ascorbate took place even in the only treated CD-patient who had basal IL-15 production.

CONCLUSIONS

Ascorbate decreases the mucosal inflammatory response to gluten in an intestinal biopsy culture model, so it might have a role in future supplementary therapy in CD.

Non-dietary therapeutic clinical trials in coeliac disease

Coeliac disease is a permanent immunological intolerance to gluten proteins in genetically predisposed individuals. The only management is life-long strict adherence to a gluten-free diet. Unfortunately, compliance with gluten-free diet is very difficult in practice due to the widespread presence of gluten in Western diets. For this reason, about 50% of coeliacs following a gluten-free diet continue to suffer from symptoms and present with autoantibodies and/or villous atrophy while on a gluten-free diet. It is therefore important to explore new therapies to improve the management of coeliac disease. To date, five experimental therapies have been tested in randomized and controlled clinical trials. Larazotide acetate reduces the para-cellular passage of gluten to the lamina propria by preventing the opening of intercellular tight junctions. The endopeptidases ALV003 and AN-PEP break down gluten to produce less or non-toxic peptide fragments. A therapeutic vaccine is being tested with the aim of developing gluten tolerance. Finally, infection with the nematode Necator americanus and treatment with the CCR9 antagonist Traficet-EN have also been reported. While substantial progress has been made in the last few years, it is important to remember that all these investigational therapies are in research stage and are generally being considered as "adjunctive" therapies to the gluten-free diet and not as substitutes of the gluten-free diet at this point in time.

Selected disorders of malabsorption

Malabsorption syndrome encompasses numerous clinical entities that result in chronic diarrhea, abdominal distention, and failure to thrive. These disorders may be congenital or acquired and include cystic fibrosis and Shwachman-Diamond syndrome; the rare congenital lactase deficiency; glucose-galactose malabsorption; sucrase-isomaltase deficiency; adult-type hypolactasia leading to acquired lactose intolerance. The pathology may be due to impairment in absorption or digestion of nutrients resulting in Nutritional deficiency, gastrointestinal symptoms, and extra gastrointestinal symptoms. Treatment is aimed at correcting the deficiencies and symptoms to improve quality of life. Common disorders of malabsorption celiac disease, pernicious anemia, and lactase deficiency are discussed in this article.

Paracellular versus transcellular intestinal permeability to gliadin peptides in active celiac disease

The intestinal permeability of undegraded α9-gliadin peptide 31-49 (p31-49) and 33-mer gliadin peptides is increased in active celiac disease. Two distinct transport pathways have been proposed: paracellular leakage through epithelial tight junctions and protected transcellular transport. To analyze the relative contribution of these pathways, we compared mucosa-to-serosa permeability of small and large permeability markers [ionic conductance (G), mannitol, 182 Da; horseradish peroxidase, 40 kDa] and gliadin peptides [33-mer (p56-88, 3900 Da), 19-mer (p31-49, 2245 Da; and p202-220, 2127 Da), and 12-mer (p57-68, 1453 Da)] in duodenal biopsy specimens mounted in Ussing chambers. The permeability of intact peptides was much higher for p31-49 or 33-mer than for horseradish peroxidase, p202-220, and p57-68. A positive correlation was observed between G, an index of paracellular diffusion of ions, and mannitol permeability. The absence of correlation between G and permeability to intact 33-mer or p31-49 did not favor paracellular diffusion of the peptides. Immunofluorescence studies indicated that 33-mer enters the early endosome antigen 1-positive compartment but escapes the lysosomal-associated protein 2-positive compartment. The results underline that mannitol and ionic conductance G cannot be considered markers of permeability to gliadin peptides. In active celiac disease, increases in transcellular permeability to intact gliadin peptides might be considered in treatment strategies aimed at controlling epithelial permeability to gluten.

Bio-physical characteristics of gastrointestinal mucosa of celiac patients: comparison with control subjects and effect of gluten free diet-

Background

Intestinal mucosa is leaky in celiac disease (CD), and this alteration may involve changes in hydrophobicity of the mucus surface barrier in addition to alteration of the epithelial barrier. The aims of our study were i) to compare duodenal hydrophobicity as an index of mucus barrier integrity in CD patients studied before (n = 38) and during gluten- free diet (GFD, n = 68), and in control subjects (n = 90), and ii) to check for regional differences of hydrophobicity in the gastro-intestinal tract.

Methods

Hydrophobicity was assessed by measurement of contact angle (CA) (Rame Hart 100/10 goniometer) generated by a drop of water placed on intestinal mucosal biopsies.

Results

CA (mean ± SD) of distal duodenum was significantly lower in CD patients (56° ± 10°)) than in control subjects (69° ± 9°, p < 0.0001), and persisted abnormal in patients studied during gluten free diet (56° ± 9°; p < 0.005). CA was significantly higher (62° ± 9°) in histologically normal duodenal biopsies than in biopsies with Marsh 1-2 (58° ± 10°; p < 0.02) and Marsh 3 lesions (57° ± 10°; p < 0.02) in pooled results of all patients and controls studied. The order of hydrofobicity along the gastrointestinal tract in control subjects follows the pattern: gastric antrum > corpus > rectum > duodenum > oesophagus > ileum.

Conclusions

We conclude that the hydrophobicity of duodenal mucous layer is reduced in CD patients, and that the resulting decreased capacity to repel luminal contents may contribute to the increased intestinal permeability of CD. This alteration mirrors the severity of the mucosal lesions and is not completely reverted by gluten-free diet. Intestinal hydrophobicity exhibits regional differences in the human intestinal tract.

Correction of gliadin transport within enterocytes through celiac disease serum

Celiac disease (CD) is caused by loss of tolerance toward gluten and related cereal products. The delivery of gliadin peptides (GP) to HLA-DR-positive late endosomes (LE) of enterocytes is required for antigen presentation and tolerance generation. We hypothesized that anti-gliadin antibodies in CD serum modify gliadin transport into LE within enterocytes. CD and control duodenal biopsies were incubated with digests of gluten as well as with serum of CD patients. Lissamin-labeled GP AA31-43 and AA56-68 were endocytozed by Caco-2 cells with serum of CD- or control patients. Colocalization of gliadin with the LE marker LAMP-2 and cathepsin D was determined and quantified on immunofluorescence and immunoelectron microscopical level. Up to 13% of internalized gliadin was located in LE of CD biopsies incubated with CD serum compared with less than 4% in CD biopsies without CD serum as well as in control biopsies. In Caco-2 cells, the colocalization coefficient of GP AA31-43 and LE was 0.82 with CD serum, 0.42 with control serum, and 0.48 with culture medium. Incubation with CD serum can direct GP AA31-43 into LE of enterocytes which is required for antigen presentation.

The frontiers of mass spectrometry-based techniques in food allergenomics

In the last years proteomic science has started to provide an important contribution to the disclosure of basic aspects of food-related diseases. Among these, the identification of proteins involved in food allergy and their mechanism of activation of toxicity. Elucidation of these key issues requires the integration of clinical, immunological, genomic and proteomic approaches. These combined research efforts are aimed to obtain structural and functional information to assist the development of novel, more reliable and powerful diagnostic protocols alternative to the currently available procedures, mainly based on food challenge tests. Another crucial aspect related to food allergy is the need for methods to detect trace amounts of allergenic proteins in foods. Mass spectrometry is the only non-immunological method for high-specificity and high-sensitivity detection of allergens in foods. Nowadays, once provided the appropriate sample handling and the correct operative conditions, qualitative and quantitative determination of allergens in foods and ingredients can be efficiently obtained by MALDI-TOF-MS and LC-MS/MS methods, with limits of detection and quantification in the low-ppb range. The availability of accurate and fast alternatives to immunological ELISA tests may also enable the development of novel therapeutic strategies and food processing technologies to aid patients with food allergy or intolerance, and to support allergen labelling and certification processes, all issues where the role of proteomic science is emerging.

[Immunogenetics of celiac disease]

Celiac disease is an auto-immune enteropathy involving genetic factors. It is associated in almost all the patients, to specific susceptibility alleles encoding histocompatibility antigens (HLA for human leucocyte antigen), specifically certain variants of the HLA-DQ2, and the HLA-DQ8 HLA class II molecules. Its estimated prevalence is 1% in the european and north-american populations. However, although these alleles represent the main genetic factor for this disease, they do not explain it on their own, as they are expressed by up to 30% of the population. Recent immunological advances allowed identifying the immunodominant epitopes of gluten, to establish the role of tissue transglutaminase in the disease and to define at the atomic level the presentation of these antigens by the HLA-DQ molecule. It is noteworthy that the HLA susceptibility alleles only account for 40% of the whole genetic risk, and the challenge is now to explain the remaining 60%. Genome-wide association studies using the DNA arrays technology to screen single nucleotide polymorphisms to pinpoint candidate regions and genes, have started to provide answers, but contradictory results sometimes still persist. Most of the genes emerging as statistically significantly associated with celiac disease are involved in the immune response, and suggest that the situation is complex.

Zonulin and its regulation of intestinal barrier function: the biological door to inflammation, autoimmunity, and cancer

The primary functions of the gastrointestinal tract have traditionally been perceived to be limited to the digestion and absorption of nutrients and to electrolytes and water homeostasis. A more attentive analysis of the anatomic and functional arrangement of the gastrointestinal tract, however, suggests that another extremely important function of this organ is its ability to regulate the trafficking of macromolecules between the environment and the host through a barrier mechanism. Together with the gut-associated lymphoid tissue and the neuroendocrine network, the intestinal epithelial barrier, with its intercellular tight junctions, controls the equilibrium between tolerance and immunity to non-self antigens. Zonulin is the only physiological modulator of intercellular tight junctions described so far that is involved in trafficking of macromolecules and, therefore, in tolerance/immune response balance. When the finely tuned zonulin pathway is deregulated in genetically susceptible individuals, both intestinal and extraintestinal autoimmune, inflammatory, and neoplastic disorders can occur. This new paradigm subverts traditional theories underlying the development of these diseases and suggests that these processes can be arrested if the interplay between genes and environmental triggers is prevented by reestablishing the zonulin-dependent intestinal barrier function. This review is timely given the increased interest in the role of a "leaky gut" in the pathogenesis of several pathological conditions targeting both the intestine and extraintestinal organs.

Epithelial transport and deamidation of gliadin peptides: a role for coeliac disease patient immunoglobulin A

In coeliac disease, the intake of dietary gluten induces small-bowel mucosal damage and the production of immunoglobulin (Ig)A class autoantibodies against transglutaminase 2 (TG2). We examined the effect of coeliac patient IgA on the apical-to-basal passage of gluten-derived gliadin peptides p31-43 and p57-68 in intestinal epithelial cells. We demonstrate that coeliac IgA enhances the passage of gliadin peptides, which could be abolished by inhibition of TG2 enzymatic activity. Moreover, we also found that both the apical and the basal cell culture media containing the immunogenic gliadin peptides were able to induce the proliferation of deamidation-dependent coeliac patient-derived T cells even in the absence of exogenous TG2. Our results suggest that coeliac patient IgA could play a role in the transepithelial passage of gliadin peptides, a process during which they might be deamidated.