Deamidation and cross-linking of gliadin peptides by transglutaminases and the relation to celiac disease

Bacteria: Potential Make-or-Break Determinants of Celiac Disease

Celiac disease is an autoimmune disease triggered by dietary gluten in genetically susceptible individuals that primarily affects the small intestinal mucosa. The sole treatment is a gluten-free diet that places a social and economic burden on patients and fails, in some, to lead to symptomatic or mucosal healing. Thus, an alternative treatment has long been sought after. Clinical studies on celiac disease have shown an association between the presence of certain microbes and disease outcomes. However, the mechanisms that underlie the effects of microbes in celiac disease remain unclear. Recent studies have employed disease models that have provided insights into disease mechanisms possibly mediated by bacteria in celiac disease. Here, we have reviewed the bacteria and related mechanisms identified so far that might protect from or incite the development of celiac disease. Evidence indicates bacteria play a role in celiac disease and it is worth continuing to explore this, particularly since few studies, to the best of our knowledge, have focused on establishing a mechanistic link between bacteria and celiac disease. Uncovering host-microbe interactions and their influence on host responses to gluten may enable the discovery of pathogenic targets and development of new therapeutic or preventive approaches.

Production of Antibodies to Peptide Targets Using Hybridoma Technology

Hybridoma technology is a well-established and indispensable tool for generating high-quality monoclonal antibodies and has become one of the most common methods for monoclonal antibody production. In this process, antibody-producing B cells are isolated from mice following immunization of mice with a specific immunogen and fused with an immortal myeloma cell line to form antibody-producing hybridoma cell lines. Hybridoma-derived monoclonal antibodies not only serve as powerful research and diagnostic reagents but have also emerged as the most rapidly expanding class of therapeutic biologicals. In spite of the development of new high-throughput monoclonal antibody generation technologies, hybridoma technology still is applied for antibody production due to its ability to preserve innate functions of immune cells and to preserve natural cognate antibody paring information. In this chapter, an overview of hybridoma technology and the laboratory procedures used for hybridoma production and antibody screening of peptide-specific antibodies are presented.

A Comprehensive Review of the Neurological Manifestations of Celiac Disease and Its Treatment

Celiac disease (CD) is a common chronic inflammatory disorder occurring in genetically predisposed individuals secondary to gluten ingestion. CD usually presents with gastrointestinal symptoms such as pain, bloating, flatulence, and constipation or diarrhea. However, individuals can present in a nonclassical manner with only extraintestinal symptoms. The neurological manifestations of CD include ataxia, cognitive impairment, epilepsy, headache, and neuropathy. A lifelong gluten-free diet is the current recommended treatment for CD. This review discusses the relevant neurological manifestations associated with CD and the novel therapeutics. Further research is required to get a better understanding of the underlying pathophysiology of the neurological manifestations associated with CD. Clinicians should keep CD in the differential diagnosis in individuals presenting with neurological dysfunction of unknown cause.

Tissue Transglutaminase but Not Microbial Transglutaminase Is Inhibited by Exogenous Oxidative Substances in Celiac Disease

Enzymatic modification of gliadin peptides by human transglutaminase 2 (TG2) is a central step in celiac disease (CD) pathogenesis. Microbial transglutaminase (mTG) mimics the enzymatic function of TG2 and might play a role in CD. TG2 is inhibited by endogenous oxidative endoplasmic reticulum-resident protein 57 (ERp57), but data about mTG are lacking. We investigated the localization of ERp57 in duodenal biopsies and examined inhibition of TG2, and mTG by competitive, and oxidative molecules. Localization of ERp57 was investigated in duodenal biopsies from CD, and control patients by electron microcopy. Inhibition of TG2 and mTG was analyzed on an in vitro level using a photometric assay. ERp57 was observed within the lamina propria and its abundance within the endoplasmic reticulum (ER) was reduced in CD patients. TG2 was oxidatively inhibited by up to 95% by PX12 (p < 0.001) and L-cystine (p < 0.001), whereas mTG remained unaffected. The reduced presence of ERp57 within the ER of CD biopsies suggests a regulatory function of this protein within CD pathogenesis. PX12 and L-cystine oxidatively inhibit TG2 and might serve as treatment options in CD. mTG is poorly regulated and could contribute to the accumulation of immunogenic peptides within the gut with potential pathogenic effects.

Acid Hydrolysis of Gluten Enhances the Skin Sensitizing Potential and Drives Diversification of IgE Reactivity to Unmodified Gluten Proteins

SCOPE

Personal care products containing hydrolyzed gluten have been linked to spontaneous sensitization through the skin, however the impact of the hydrolysate characteristics on the sensitizing capacity is generally unknown.

METHODS AND RESULTS

The physicochemical properties of five different wheat-derived gluten products (one unmodified, one enzyme hydrolyzed, and three acid hydrolyzed) are investigated, and the skin sensitizing capacity is determined in allergy-prone Brown Norway rats. Acid hydrolyzed gluten products exhibited the strongest intrinsic sensitizing capacity via the skin. All hydrolyzed gluten products induced cross-reactivity to unmodified gluten in the absence of oral tolerance to wheat, but were unable to break tolerance in animals on a wheat-containing diet. Still, the degree of deamidation in acid hydrolyzed products is associated with product-specific sensitization in wheat tolerant rats. Sensitization to acid hydrolyzed gluten products is associated with a more diverse IgE reactivity profile to unmodified gluten proteins compared to sensitization induced by unmodified gluten or enzyme hydrolyzed gluten.

CONCLUSION

Acid hydrolysis enhances the skin sensitizing capacity of gluten and drives IgE reactivity to more gluten proteins. This property of acid hydrolyzed gluten may be related to the degree of product deamidation, and could be a strong trigger of wheat allergy in susceptible individuals.

Evaluation of the discriminatory potential of antibodies created from synthetic peptides derived from wheat, barley, rye and oat gluten

Celiac disease (CD) is triggered by ingestion of gluten-containing cereals such as wheat, barley, rye and in some cases oat. The only way for affected individuals to avoid symptoms of this condition is to adopt a gluten-free diet. Thus, gluten-free foodstuffs need to be monitored in order to ensure their innocuity. For this purpose, commercial immunoassays based on recognition of defined linear gluten sequences are currently used. These immunoassays are designed to detect or quantify total gluten regardless of the cereal, and often result in over or underestimation of the exact gluten content. In addition, Canadian regulations require a declaration of the source of gluten on the label of prepackaged foods, which cannot be done due to the limitations of existing methods. In this study, the development of new antibodies targeting discrimination of gluten sources was conducted using synthetic peptides as immunization strategy. Fourteen synthetic peptides selected from unique linear amino acid sequences of gluten were bioconjugated to Concholepas concholepas hemocyanin (CCH) as protein carrier, to elicit antibodies in rabbit. The resulting polyclonal antibodies (pAbs) successfully discriminated wheat, barley and oat prolamins during indirect ELISA assessments. pAbs raised against rye synthetic peptides cross-reacted evenly with wheat and rye prolamins but could still be useful to successfully discriminate gluten sources in combination with the other pAbs. Discrimination of gluten sources can be further refined and enhanced by raising monoclonal antibodies using a similar immunization strategy. A methodology capable of discriminating gluten sources, such as the one proposed in this study, could facilitate compliance with Canadian regulations on this matter. This type of discrimination could also complement current immunoassays by settling the issue of over and underestimation of gluten content, thus improving the safety of food intended to CD and wheat-allergic patients.

Co-Silencing of Tissue Transglutaminase-2 and Interleukin-15 Genes in a Celiac Disease Mimetic Mouse Model Using a Nanoparticle-in-Microsphere Oral System

Celiac disease is a chronic inflammatory condition characterized by activation of the immune system in response to deamidation of gluten peptides brought about by tissue transglutaminase-2 (TG2). Overexpression of interleukin-15 (IL-15) in the intestinal epithelium and the lamina propria leads to the dysregulation of the immune system, leading to epithelial damage. The goal of this study was to develop an RNA interference therapeutic strategy for celiac disease using a combination of TG2 and IL-15 gene silencing in the inflamed intestine. TG2 and IL-15 silencing siRNA sequences, along with scrambled control, were encapsulated in a nanoparticle-in-microsphere oral system (NiMOS) and administered in a poly(I:C) mouse model of celiac disease. Single TG2 and IL-15 siRNA therapy and the combination showed effective gene silencing in vivo. Additionally, it was found that IL-15 gene silencing alone and combination in the NiMOS significantly reduced other proinflammatory cytokines. The tissue histopathology data also confirmed a reduction in immune cell infiltration and restoration of the mucosal architecture and barrier function in the intestine upon treatment. Overall, the results of this study show evidence that celiac disease can be potentially treated with an oral microsphere formulation using a combination of TG2 and IL-15 RNA interference therapeutic strategies.

Epitope-directed monoclonal antibody production using a mixed antigen cocktail facilitates antibody characterization and validation

High quality, well-validated antibodies are needed to mitigate irreproducibility and clarify conflicting data in science. We describe an epitope-directed monoclonal antibody (mAb) production method that addresses issues of antibody quality, validation and utility. The workflow is illustrated by generating mAbs against multiple in silico-predicted epitopes on human ankyrin repeat domain 1 (hANKRD1) in a single hybridoma production cycle. Antigenic peptides (13-24 residues long) presented as three-copy inserts on the surface exposed loop of a thioredoxin carrier produced high affinity mAbs that are reactive to native and denatured hANKRD1. ELISA assay miniaturization afforded by novel DEXT microplates allowed rapid hybridoma screening with concomitant epitope identification. Antibodies against spatially distant sites on hANKRD1 facilitated validation schemes applicable to two-site ELISA, western blotting and immunocytochemistry. The use of short antigenic peptides of known sequence facilitated direct epitope mapping crucial for antibody characterization. This robust method motivates its ready adoption for other protein targets.

The Gluten Gene: Unlocking the Understanding of Gluten Sensitivity and Intolerance

Wheat flour is one of the most important food ingredients containing several essential nutrients including proteins. Gluten is one of the major protein components of wheat consisted of glutenin (encoded on chromosome 1) and gliadin (encoded on chromosome 1 and 6) and there are around hundred genes encoding it in wheat. Gluten proteins have the ability of eliciting the pathogenic immune responses and hypersensitivity reactions in susceptible individuals called “gluten-related disorders (GRDs)”, which include celiac disease (CD), wheat allergy (WA), and non-celiac gluten sensitivity (NCGS). Currently removing gluten from the diet is the only effective treatment for mentioned GRDs and studies for the appropriate and alternative therapeutic approaches are ongoing. Accordingly, several genetic studies have focused on breeding wheat with low immunological properties through gene editing methods. The present review considers genetic characteristics of gluten protein components, focusing on their role in the incidence of gluten-related diseases, and genetic modifications conducted to produce wheat with less immunological properties.

Gluten Free Diet for the Management of Non Celiac Diseases: The Two Sides of the Coin

A lifelong adherence to a gluten-free (GF) diet is currently the only treatment for Celiac disease (CD), an autoimmune disorder that arises after gluten ingestion in individuals who are genetically predisposed. The gluten intake exerts toxic effects through several pathways involving gut barrier integrity, intestinal microbiota composition and immune system stimulation. However, despite the great benefit of GF diet for CD patients, its use has been debated. Indeed, individuals who adopt this diet regime may be at risk of nutrient deficiencies. Emerging evidence supports a beneficial effect of a GF diet also for other pathological conditions, including gluten-related disorders (GRD) often associated to CD, such as Non celiac gluten sensitivity (NCGS) and Dermatitis Herpetiforme (DH) as well as Irritable bowel syndrome (IBS) and Diabetes. This suggests a pathogenic role of gluten in these conditions. Despite the growing popularity of GF diet among consumers, to date, there are limited evidences supporting its use for the management of non-celiac diseases. Therefore, in this review, we discuss whether the GF diet could really improve the general quality of life of patients with GRD and non-GRD conditions, keeping in mind its sensorial limitations and nutritional inadequacies. In addition, we discuss the current motivations, leading to the use of a GF diet, despite the inferior quality of GF products respect to those containing gluten.

Celiac Disease and Non-celiac Wheat Sensitivity: State of Art of Non-dietary Therapies

Gluten related disorders (GRD), which include celiac disease, non-celiac wheat sensitivity and wheat allergy are heterogeneous conditions triggered by ingestion of gluten-containing grains. Together, their prevalence is estimated to be ~5% in the general population, however, in the last years the number of diagnoses has been rapidly increasing. To this day, the gold standard treatment for these disorders is the complete removal of gluten-containing grains from the diet. Although this therapy results effective in the majority of patients, up to 30% of individuals affected by GRD continue to present persistent symptoms. In addition, gluten-free diet has been shown to have poor nutritional quality and to cause a socio-economic burden in patients' quality of life. In order to respond to these issues, the scientific community has been focusing on finding additional and adjuvant non-dietary therapies. In this review, we focus on two main gluten related disorders, celiac disease and non-celiac wheat sensitivity. We delineate the actual knowledge about potential treatments and their relative efficacy in pre-clinical and clinical trials.

The use of microbial transglutaminase in a bread system: A study of gluten protein structure, deamidation state and protein digestion

Microbial transglutaminase (mTG) catalyses the formation of protein crosslinks, deamidating glutamine in a side-reaction. Gluten deamidation by human tissue transglutaminase is critical to activate celiac disease pathogenesis making the addition of mTG to wheat-based products controversial. The ability of mTG (0-2000 U.kg^-1) to alter gluten's structure, digestibility and the deamidation state of six immunogenic gluten peptides within bread was investigated. Gluten's structure was altered when mTG exceeded 100 U.kg^-1, determined by confocal microscopy, extractability and free sulfhydryl assays. The effect of mTG on six immunogenic peptides was investigated by in vitro digestion (INFOGEST) and mass spectrometry. The addition of mTG to bread (0-2000 U.kg^-1) did not alter the deamidation state or digestibility of the immunogenic peptides investigated. Overall, this investigation indicated that the addition of mTG to bread does not create activated gluten peptides. This analysis provides evidence for risk assessments of mTG as a food processing aid.

Pharmacokinetics and Biodistribution Analysis of Small Interference RNA for Silencing Tissue Transglutaminase-2 in Celiac Disease After Oral Administration in Mice Using Gelatin-Based Multicompartmental Delivery Systems

Background: RNA interference (RNAi) therapy has tremendous potential in treating diseases that are characterized by overexpression of genes. However, the biggest challenge to utilize the therapy is to engineer delivery systems that can efficiently transport small interfering RNA (siRNA) to appropriate target sites. Our objective in this study was to develop and evaluate multi-compartmental systems for the oral delivery of siRNA that targets the overexpressed TG2 gene (TG2-siRNA) in the small intestine for the treatment of celiac disease (CD). Materials and Methods: Two types of multicompartmental systems were developed and evaluated: (1) a solid-in-solid multicompartmental system featuring "nanoparticle in microsphere oral system (NiMOS)" where type B gelatin nanoparticles containing TG2-siRNA (TG2-NiMOS) were encapsulated within poly(ɛ-caprolactone) (PCL) based microspheres, and (2) a solid-in-liquid multicompartmental system, "Nanoparticle-in-Emulsion (NiE)" consisting of type-B gelatin nanoparticles containing TG2-siRNA encapsulated within safflower oil containing water-in-oil-in-water (W/O/W) multiple emulsion (TG2-NiE). Results: Evaluation of the biodistribution and pharmacokinetics (PK) after a single oral dose of siRNA containing multicompartmental systems to C57BL/6 mice showed that TG2-siRNA was delivered to the small intestine (duodenum, jejunum and ileum), and colon with minimal systemic exposure via both TG2-NiE and TG2-NiMOS systems. TG2-siRNA exposure (AUC_0-t) in the duodenum, jejunum, ileum and colon was 56.4-, 34.3-, 85.5- and 35.5-fold greater for the TG2-NiMOS formulation, relative to the TG2-NiE formulation. Conclusion: The results of this study suggest that TG2-NiMOS formulation was more superior than TG2-NiE formulation in facilitating intestinal delivery of siRNA via the oral route of administration and can be potentially used in the treatment of CD.

Peptides, Antibodies, Peptide Antibodies and More

The applications of peptides and antibodies to multiple targets have emerged as powerful tools in research, diagnostics, vaccine development, and therapeutics. Antibodies are unique since they, in theory, can be directed to any desired target, which illustrates their versatile nature and broad spectrum of use as illustrated by numerous applications of peptide antibodies. In recent years, due to the inherent limitations such as size and physical properties of antibodies, it has been attempted to generate new molecular compounds with equally high specificity and affinity, albeit with relatively low success. Based on this, peptides, antibodies, and peptide antibodies have established their importance and remain crucial reagents in molecular biology.

Immunoreactivity of Gluten-Sensitized Sera Toward Wheat, Rice, Corn, and Amaranth Flour Proteins Treated With Microbial Transglutaminase

The aim of this study was to analyze the effects of microbial transglutaminase (mTG) on the immunoreactivity of wheat and gluten-free cereals flours to the sera of patients with celiac disease (CD) and non-celiac gluten sensitivity (NCGS). Both doughs and sourdoughs, the latter prepared by a two-step fermentation with Lactobacillus sanfranciscensis and Candida milleri, were studied. In order to evaluate the IgG-binding capacity toward the proteins of the studied flours, total protein as well as protein fractions enriched in albumins/globulins, prolamins and glutelins, were analyzed by SDS-PAGE and enzyme-linked immunosorbent assay (ELISA). Results showed that while mTG modified both gluten and gluten-free flour by increasing the amount of cross-linked proteins, it did not affect the serum's immune-recognition. In fact, no significant differences were observed in the immunoreactivity of sera from CD and NCGS patients toward wheat and gluten-free protein extracts after enzyme treatment, nor did this biotechnological treatment affect the immunoreactivity of control samples or the sera of healthy patients. These results suggest that mTG may be used as a tool to create innovative gluten and gluten-free products with improved structural properties, without increasing the immune-reactivity toward proteins present either in doughs or in sourdoughs.

Intracellular Localization of Microbial Transglutaminase and Its Influence on the Transport of Gliadin in Enterocytes

OBJECTIVE

Celiac disease (CD) is a systemic inflammatory disorder, characterized by the destruction of duodenal epithelium. The CD8 T cells involved are associated with cross-presentation. In addition to other factors, the rising prevalence of CD might be induced by microbial transglutaminase (mTG) an enzyme frequently used in food production that shares enzymatic and antigenic properties of tissue transglutaminase (TG2), the autoantigen in CD. We hypothesized that mTG and gliadin are transported into the endoplasmic reticulum (ER), indicating cross-presentation of both antigens.

METHODS

Apical incubation of duodenal biopsies from CD and control patients was performed with mTG alone or with mTG and simultaneously with Frazer's fraction. Evaluation was carried out by immunofluorescence and electron microscopy.

RESULTS

Approximately 6% to 9% of the intracellular mTG and gliadin were transported to the ER of enterocytes. RACE cells (Rapid uptake of Antigen into the Cytosol of Enterocytes) displayed an enhanced antigen uptake into a dilated ER. mTG strongly localized at the basolateral membrane and the lamina propria.

CONCLUSIONS

mTG and gliadin are transported to the ER of enterocytes and to a greater extent to the ER of RACE cells, suggesting cross-presentation of exogenous antigens. The strong localization of mTG at the basolateral membrane and the lamina propria may also indicate a potential antigenic interaction with cells of the immune system. Since mTG may not only been taken up with food stuffs but could also be released by bacteria within the intestinal microbiota, further investigations are needed regarding the role of mTG in CD pathogenesis.

Synthetic Neoepitopes of the Transglutaminase-Deamidated Gliadin Complex as Biomarkers for Diagnosing and Monitoring Celiac Disease

BACKGROUND & AIMS

Celiac disease (CeD) has characteristics of an autoimmune disease, such as increased antibody levels to tissue transglutaminase (tTG). However, assays to measure these biomarkers in blood samples do not identify patients with sufficient accuracy for diagnosis or monitoring of CeD. We aimed to discover biomarkers of CeD derived from neoepitopes of deamidated gliadin peptides (DGP) and tTG fragments and to determine if immune reactivity against these epitopes can identify patients with CeD with mucosal healing.

METHODS

We analyzed serum samples from 90 patients with biopsy-proven CeD and 79 healthy individuals (controls) for immune reactivity against the tTG-DGP complex (discovery cohort). A fluorescent peptide microarray platform was used to estimate the antibody-binding intensity of each synthesized tTG-DGP epitope. We validated our findings in 82 patients with newly diagnosed CeD and 217 controls. We tested the ability of our peptide panel to identify patients with mucosal healing (based on the histologic analysis) using serum samples from patients with treated and healed CeD (n = 85), patients with treated but unhealed CeD (n = 81; villous atrophy despite a adhering a gluten-free diet), patients with untreated CeD (n = 82) and disease controls (n = 27), villous atrophy without CeD), and healthy controls (n = 217). Data were analyzed using principal component analysis followed by machine learning and support vector machine modeling.

RESULTS

We identified 172 immunogenic epitopes of the tTG-DGP complex. We found significantly increased immune reactivity against these epitopes vs controls. In the both cohort, the set of neoepitopes derived from the tTG-DGP complex identified patients with CeD with 99% sensitivity and 100% specificity. Serum samples from patients with untreated CeD had the greatest mean antibody-binding intensity against the tTG-DGP complex (32.5 ± 16.4). The average antibody-binding intensity was significantly higher in serum from patients with treated but unhealed CeD mucosa (15.1 ± 7.5) than in patients with treated and healed CeD mucosa (5.5 ± 3.4) (P < .001). The assay identified patients with mucosa healing status with 84% sensitivity and 95% specificity.

CONCLUSIONS

We identified immunogenic epitopes of the tTG-DGP complex, and found that an assay to measure the immune response to epitopes accurately identified patients with CeD, as well as patients with mucosal healing. This biomarker assay might be used in detection and monitoring of patients with CeD.

Microbial transglutaminase in noodle and pasta processing

Nowadays, there is an aggressive rate in consumption of noodles and pasta products throughout the world. Consumer acceptability and preference of these functional products can be promoted by the discovery of novel knowledge to improve their formulation and quality. The development of fortified-formulations for noodles and pasta products based on microbial transglutaminase (MTGase) can guarantee the shelf life extension with minimum quality losses. The current review focuses on recent trends and future prospects of MTGase utilization in the structural matrix of noodles and pasta products and represents the quality changes of cooking loss, texture, microstructure, color and sensory attributes of the MTGase-incorporated products. Digestibility, nutritional and health aspects of the MTGase-enriched formulations are also reviewed with a vision toward physical functions and safety outcomes of MTGases isolated from new microbial sources. The high potential of MTGase in developing commercial noodles and pasta products is successfully demonstrated. MTGase by modifying the crystallinity or molecular structure via covalent crosslinks between protein molecules strengthens the doughs stability and the textural characteristics of final products with the low- or high-protein flour. Compared with the control samples, the MTGase-supplemented products indicate slower digestion rates and better sensory and cooking properties without any remarkable color instability.

Microbial Transglutaminase Used in Bread Preparation at Standard Bakery Concentrations Does Not Increase Immunodetectable Amounts of Deamidated Gliadin

The effect of standard bakery concentrations of microbial transglutaminase (MTG) in wheat bread preparation on the immunoreactivity of sera of celiac disease (CD) patients was investigated. Immunoblotting using monoclonal antibodies specific to unmodified and/or deamidated gliadin showed no differences between control bread and MTG bread. Deamidation of gliadin could not be detected at standard MTG concentrations. Sera of CD patients were characterized using anti-gliadin and anti-deamidated gliadin peptide (DGP) enzyme-linked immunosorbent assay and grouped into DGP high- and low-titer pools. The recognition pattern obtained after using both CD sera pools for immunoblotting did not reveal differences between control and MTG-treated bread protein extracts. Our results indicate that MTG treatment of wheat bread prepared with typical MTG concentrations used in standard bakery processes does not lead to immunodetectable amounts of CD immunotoxic deamidated gliadins.

Peptide Antibodies in Clinical Laboratory Diagnostics

Peptide antibodies, with their high specificities and affinities, are invaluable reagents for peptide and protein recognition in biological specimens. Depending on the application and the assay, in which the peptide antibody is to used, several factors influence successful antibody production, including peptide selection and antibody screening. Peptide antibodies have been used in clinical laboratory diagnostics with great success for decades, primarily because they can be produced to multiple targets, recognizing native wildtype proteins, denatured proteins, and newly generated epitopes. Especially mutation-specific peptide antibodies have become important as diagnostic tools in the detection of various cancers. In addition to their use as diagnostic tools in malignant and premalignant conditions, peptide antibodies are applied in all other areas of clinical laboratory diagnostics, including endocrinology, hematology, neurodegenerative diseases, cardiovascular diseases, infectious diseases, and amyloidoses.

Involvement of cell surface TG2 in the aggregation of K562 cells triggered by gluten

Gluten-induced aggregation of K562 cells represents an in vitro model reproducing the early steps occurring in the small bowel of celiac patients exposed to gliadin. Despite the clear involvement of TG2 in the activation of the antigen-presenting cells, it is not yet clear in which compartment it occurs. Herein we study the calcium-dependent aggregation of these cells, using either cell-permeable or cell-impermeable TG2 inhibitors. Gluten induces efficient aggregation when calcium is absent in the extracellular environment, while TG2 inhibitors do not restore the full aggregating potential of gluten in the presence of calcium. These findings suggest that TG2 activity is not essential in the cellular aggregation mechanism. We demonstrate that gluten contacts the cells and provokes their aggregation through a mechanism involving the A-gliadin peptide 31-43. This peptide also activates the cell surface associated extracellular TG2 in the absence of calcium. Using a bioinformatics approach, we identify the possible docking sites of this peptide on the open and closed TG2 structures. Peptide docks with the closed TG2 structure near to the GTP/GDP site, by establishing molecular interactions with the same amino acids involved in stabilization of GTP binding. We suggest that it may occur through the displacement of GTP, switching the TG2 structure from the closed to the active open conformation. Furthermore, docking analysis shows peptide binding with the β-sandwich domain of the closed TG2 structure, suggesting that this region could be responsible for the different aggregating effects of gluten shown in the presence or absence of calcium. We deduce from these data a possible mechanism of action by which gluten makes contact with the cell surface, which could have possible implications in the celiac disease onset.

Assessment of a Test for the Screening and Diagnosis of Celiac Disease

BACKGROUND

Celiac disease (CD) is an immune-mediated intolerance to dietary gluten, affecting genetically predisposed individuals. ELISA-based serological tests help to decide if further duodenal biopsy is necessary, for this the diagnostic kits have to be accurate, specific, and sensible. In this study, we investigate the performance of an ELISA that uses the purified cross-linked complex of tissue transglutaminase and gliadin, referred as the "neoepitope" (AESKULISA® tTG New Generation), as antigen.

METHODS

We evaluated 41 newly diagnosed celiac patients, 18 celiac patients on gluten-free diet, and 169 controls, comprising healthy subjects, patients affected by other autoimmune diseases, and patients affected by several non-autoimmune diseases.

RESULTS AND CONCLUSION

The assay has an excellent performance. Due to its high level of diagnostic accuracy, this assay constitutes a new approach for the screening of celiac patients not only for the diagnosis of CD, but also for monitoring patients on gluten-free diet and their compliance. Moreover, cases of neoepitope-positive subjects who were tested negative with "classical" serological markers could have a predictive value for this pathology. This aspect will require further studies of elaboration.

The Role of Gluten in Celiac Disease and Type 1 Diabetes

Celiac disease (CD) and type 1 diabetes (T1D) are autoimmune conditions in which dietary gluten has been proven or suggested to play a pathogenic role. In CD; gluten is established as the instigator of autoimmunity; the autoimmune process is halted by removing gluten from the diet; which allows for resolution of celiac autoimmune enteropathy and subsequent normalization of serological markers of the disease. However; an analogous causative agent has not yet been identified for T1D. Nevertheless; the role of dietary gluten in development of T1D and the potentially beneficial effect of removing gluten from the diet of patients with T1D are still debated. In this review; we discuss the comorbid occurrence of CD and T1D and explore current evidences for the specific role of gluten in both conditions; specifically focusing on current evidence on the effect of gluten on the immune system and the gut microbiota.

Possible association between celiac disease and bacterial transglutaminase in food processing: a hypothesis

The incidence of celiac disease is increasing worldwide, and human tissue transglutaminase has long been considered the autoantigen of celiac disease. Concomitantly, the food industry has introduced ingredients such as microbial transglutaminase, which acts as a food glue, thereby revolutionizing food qualities. Several observations have led to the hypothesis that microbial transglutaminase is a new environmental enhancer of celiac disease. First, microbial transglutaminase deamidates/transamidates glutens such as the endogenous human tissue transglutaminase. It is capable of crosslinking proteins and other macromolecules, thereby changing their antigenicity and resulting in an increased antigenic load presented to the immune system. Second, it increases the stability of protein against proteinases, thus diminishing foreign protein elimination. Infections and the crosslinked nutritional constituent gluten and microbial transglutaminase increase the permeability of the intestine, where microbial transglutaminases are necessary for bacterial survival. The resulting intestinal leakage allows more immunogenic foreign molecules to induce celiac disease. The increased use of microbial transglutaminase in food processing may promote celiac pathogenesis ex vivo, where deamidation/transamidation starts, possibly explaining the surge in incidence of celiac disease. If future research substantiates this hypothesis, the findings will affect food product labeling, food additive policies of the food industry, and consumer health education.

novPTMenzy: a database for enzymes involved in novel post-translational modifications

With the recent discoveries of novel post-translational modifications (PTMs) which play important roles in signaling and biosynthetic pathways, identification of such PTM catalyzing enzymes by genome mining has been an area of major interest. Unlike well-known PTMs like phosphorylation, glycosylation, SUMOylation, no bioinformatics resources are available for enzymes associated with novel and unusual PTMs. Therefore, we have developed the novPTMenzy database which catalogs information on the sequence, structure, active site and genomic neighborhood of experimentally characterized enzymes involved in five novel PTMs, namely AMPylation, Eliminylation, Sulfation, Hydroxylation and Deamidation. Based on a comprehensive analysis of the sequence and structural features of these known PTM catalyzing enzymes, we have created Hidden Markov Model profiles for the identification of similar PTM catalyzing enzymatic domains in genomic sequences. We have also created predictive rules for grouping them into functional subfamilies and deciphering their mechanistic details by structure-based analysis of their active site pockets. These analytical modules have been made available as user friendly search interfaces of novPTMenzy database. It also has a specialized analysis interface for some PTMs like AMPylation and Eliminylation. The novPTMenzy database is a unique resource that can aid in discovery of unusual PTM catalyzing enzymes in newly sequenced genomes.

Database URL: http://www.nii.ac.in/novptmenzy.html

Sourdough fermentation of wheat flour does not prevent the interaction of transglutaminase 2 with α2-gliadin or gluten

The enzyme transglutaminase 2 (TG2) plays a crucial role in the initiation of celiac disease by catalyzing the deamidation of gluten peptides. In susceptible individuals, the deamidated peptides initiate an immune response leading to celiac disease. Several studies have addressed lactic fermentation plus addition of enzymes as a means to degrade gluten in order to prevent adverse response in celiacs. Processing for complete gluten degradation is often harsh and is not likely to yield products that are of comparable characteristics as their gluten-containing counterparts. We are concerned that incomplete degradation of gluten may have adverse effects because it leads to more available TG2-binding sites on gluten peptides. Therefore, we have investigated how lactic acid fermentation affects the potential binding of TG2 to gluten protein in wheat flour by means of estimating TG2-mediated transamidation in addition to measuring the available TG2-binding motif QLP, in α₂-gliadin. We show that lactic fermentation of wheat flour, as slurry or as part of sourdough bread, did not decrease the TG2-mediated transamidation, in the presence of a primary amine, to an efficient level (73%–102% of unfermented flour). Nor did the lactic fermentation decrease the available TG2 binding motif QLP in α₂-gliadin to a sufficient extent in sourdough bread (73%–122% of unfermented control) to be useful for celiac safe food.

Production and Screening of Monoclonal Peptide Antibodies

Hybridoma technology is a remarkable and indispensable tool for generating high-quality monoclonal antibodies. Hybridoma-derived monoclonal antibodies not only serve as powerful research and diagnostic reagents, but have also emerged as the most rapidly expanding class of therapeutic biologicals. In this chapter, an overview of hybridoma technology and the laboratory procedures used routinely for hybridoma production and antibody screening are presented, including characterization of peptide antibodies.

Microbial transglutaminase treatment in pasta-production does not affect the immunoreactivity of gliadin with celiac disease patients' sera

The effect of microbial transglutaminase (MTG)-treatment of pasta-dough on the immunoreactivity with celiac disease patient's sera has been investigated. Modification by MTG has been proven by determination of the MTG reaction product ε-(γ-glutamyl)lysine (3.63 μmol/g protein), which was not detectable in non-MTG-treated pasta. Antigenicity has been analyzed by immunoblotting and ELISA using gliadin-extracts from pasta and MTG-treated pasta. Immunoblotting showed that the antibody-population (antigliadin antibodies and antideamidated gliadin antibodies) of the sera is specific for every individual patient. Immunoblotting and ELISA showed that there is no difference in immunoreactivity of gliadin extracted from pasta and MTG-pasta. Recognition pattern and intensity in Western blot as well as antibody titer has also been identical even for sera with a high antideamidated gliadin antibody titer. These results indicate no difference between pasta-gliadin and MTG-pasta-gliadin and especially no increased deamidation in pasta-gliadin by MTG-treatment.

The gluten-free diet: testing alternative cereals tolerated by celiac patients

A strict gluten-free diet (GFD) is the only currently available therapeutic treatment for patients with celiac disease, an autoimmune disorder of the small intestine associated with a permanent intolerance to gluten proteins. The complete elimination of gluten proteins contained in cereals from the diet is the key to celiac disease management. However, this generates numerous social and economic repercussions due to the ubiquity of gluten in foods. The research presented in this review focuses on the current status of alternative cereals and pseudocereals and their derivatives obtained by natural selection, breeding programs and transgenic or enzymatic technology, potential tolerated by celiac people. Finally, we describe several strategies for detoxification of dietary gluten. These included enzymatic cleavage of gliadin fragment by Prolyl endopeptidases (PEPs) from different organisms, degradation of toxic peptides by germinating cereal enzymes and transamidation of cereal flours. This information can be used to search for and develop cereals with the baking and nutritional qualities of toxic cereals, but which do not exacerbate this condition.

A novel algorithm for the diagnosis of celiac disease and a comprehensive review of celiac disease diagnostics

There is an urgent clinical need for a better laboratory celiac disease diagnosis with both less false positive results and minimal underdetection. The aim of the present study was to evaluate the performance and diagnostic accuracy of different assays in an outpatient population setting for the diagnosis for celiac disease (CD) in order to design an optimal algorithm. We used 15 different ELISA assays to assess 47 blood samples of newly diagnosed children (positive biopsy results) and 52 samples from age- and sex-matched children with negative biopsy results for CD. Scoring criteria were established for grading the assays performance and characteristics. The combined gliadin and tTG assays exhibited the best sensitivity (100%). The addition of other assays to the CeliCheck neo-epitopes assay improved specificity so that the final algorithm had 100% sensitivity, 96.2% specificity, and 98.1% accuracy. The clinical demand for both maximal sensitivity and maximal specificity cannot be achieved with a single test. Using a combination of a sensitive assay together with specific assays improved celiac disease detection rates, with an acceptable number of false positive results. This model, however, needs to be confirmed prospectively in both children and adults.

Dermatitis herpetiformis: from the genetics to the development of skin lesions

Dermatitis herpetiformis (DH) is a rare autoimmune disease linked to gluten sensitivity with a chronic-relapsing course. It is currently considered to be the specific cutaneous manifestation of celiac disease (CD). Both conditions are mediated by the IgA class of autoantibodies, and the diagnosis of DH is dependent on the detection of granular deposits of IgA in the skin. There is an underlying genetic predisposition to the development of DH, but environmental factors are also important. This paper describes these different factors and discusses the known mechanism that lead to the development of skin lesions.

Gluten sensitivity: problems of an emerging condition separate from celiac disease

Gluten sensitivity appears to be emerging as a separate condition from celiac disease, yet no clear definition or diagnosis exists. As a result, patients with gluten sensitivity experience delayed diagnosis and continuing symptoms if they consume gluten. This emerging medical problem may involve human genetics, plant genetic modifications, gluten as a food additive, environmental toxins, hormonal influences, intestinal infections and autoimmune diseases. The treatment is similar to that for celiac disease - a gluten-free diet. The use of a gluten-free diet or an elimination diet is encouraged in assisting people to determine whether or not they are gluten sensitive. It is time to not only recognize, but to treat and further research gluten sensitivity, as unconfirmed environmental factors continue to spread this problem further into the general population.

Design of a peptide for immunodetection of IgA antigliadin antibody for the purpose of screening of celiac disease

Celiac disease (CD) is gluten induced enteropathy which requires jejunal biopsy for diagnosis. To select the patients for endoscopoic procedure some serologic tests are popular in clinical practice for screening of CD. Although gliadin is one of the key immuno activator of the disease; serological screening by immuno-detection of gliadin is not recommended. In this context we have designed a peptide using tools of computational biology keeping molecular pathogenesis of the disease into consideration such that antigliadin antibody detection based sensitive and specific cost effective tool for screening of celiac disease can be developed. The designed peptide QPFPEP interacts in a stable manner with dimeric immunoglobin A1 molecule and its parent peptide QPFPQP are sequentially present in maximum number of gliadin epitopes. This hexapeptide is predicted to interact with dimeric IgA1, which increases in the biofluids of the CD patients.

ABBREVIATIONS

CD - Celiac disease, TT - Tissue transglutamase, IgA - Immunoglobulin A, AGA - antigliadin antibody, Immunoglobulin G - IgG.

Production and characterization of peptide antibodies

Proteins are effective immunogens for generation of antibodies. However, occasionally the native protein is known but not available for antibody production. In such cases synthetic peptides derived from the native protein are good alternatives for antibody production. These peptide antibodies are powerful tools in experimental biology and are easily produced to any peptide of choice. A widely used approach for production of peptide antibodies is to immunize animals with a synthetic peptide coupled to a carrier protein. Very important is the selection of the synthetic peptide, where factors such as structure, accessibility and amino acid composition are crucial. Since small peptides tend not to be immunogenic, it may be necessary to conjugate them to carrier proteins in order to enhance immune presentation. Several strategies for conjugation of peptide-carriers applied for immunization exist, including solid-phase peptide-carrier conjugation and peptide-carrier conjugation in solution. Upon immunization, adjuvants such as Al(OH)(3) are added together with the immunogenic peptide-carrier conjugate, which usually leads to high-titred antisera. Following immunization and peptide antibody purification, the antibodies are characterized based on their affinity or specificity. An efficient approach for characterization of peptide antibodies is epitope mapping using peptide based assays. This review describes standard solid-phase approaches for generation of peptide antibodies with special emphasis on peptide selection, generation of peptide conjugates for immunization and characterization of the resulting peptide antibodies.

Novel trends in celiac disease

Celiac disease (CD) is one of the most common food intolerances in developed world. It affects genetically susceptible individuals and has severe consequences if it remains undiagnosed. A disease known for more than a century, it is still the focus for experts from various fields of research and development. Geneticists, pathologists, immunologists, food engineers and dieticians share their knowledge and expertise to improve the conditions of CD patients. With new insights in the pathomechanism of gluten processing and antigen presentation in CD, it was possible to improve the diagnostic antigen mimicking the primary epitope in CD. These celiac neo-epitopes are comprised of a complex of gliadin peptides crosslinked with transglutaminase (tTg). They are an early diagnostic marker for CD which occurs up to 6 months earlier than classical markers known to miss a certain amount of CD patients.

Novel screening assay performance in pediatric celiac disease and adult dermatitis herpetiformis

OBJECTIVES

: Several serologic assays are commercially available to aid in the diagnosis of gluten-sensitive enteropathy (GSE). Our objective in this study was to assess the performance of a novel combined antigen-screening assay for GSE.

PATIENTS AND METHODS

: Deidentified sera from 111 pediatric patients suspected of having celiac disease (CD), 130 adults diagnosed with dermatitis herpetiformis (DH), and 77 pediatric and 49 adult normal controls were included in the study. Sera from 10 patients submitted to our laboratory for GSE testing with IgA deficiency and IgG antibodies against 1 or more of the traditional serologic markers associated with GSE were also included. All sera were screened for antibodies (IgA and IgG) against tissue transglutaminase (tTG) and deamidated gliadin peptides (DGP) by enzyme immunoassay (EIA) in a single test well. In addition, all sera were assessed for each individual marker and isotype using separate EIAs.

RESULTS

: The IgA/IgG anti-tTG/DGP EIA screen was 92.6% sensitive and 94.3% specific in pediatric CD and detected 1 patient (Marsh 3c) who was IgA anti-tTG negative; this patient was not IgA deficient (<7.0 mg/dL). All 10 IgA-deficient sera gave positive results by the tTG/DGP EIA screen. Sensitivity and specificity of the tTG/DGP EIA screen in retrospective and prospective DH were 65% and 100% versus 62% and 100%, respectively.

CONCLUSIONS

: The new IgA/IgG anti-tTG/DGP EIA screen was slightly more sensitive than IgA anti-tTG alone in pediatric CD. This novel screening assay may allow the current recommendation of measuring total serum IgA in suspected GSE patients to be eliminated.

Diagnostic challenges in celiac disease and the role of the tissue transglutaminase-neo-epitope

The diagnosis of celiac disease (CD) remains a clinical challenge based on the incomplete specificity and sensitivity rates of current non-invasive tests. Furthermore, histological assessments fail to identify all overt cases and, in particular, do not manifest pathognomonic alterations in silent cases. Accordingly, the majority of CD cases are diagnosed with great delay. Recent research into the pathogenesis of CD, allowed us to identify a neo-antigen that appears to be the most promising serological tool for the detection of anti-tissue transglutaminase as well as anti-gliadin antibodies.

Deamidation of gliadin peptides in lamina propria: implications for celiac disease

Activation of small intestinal gluten-reactive CD4(+) T-cells is a critical event in celiac disease. Deamidation of specific glutamine residues by tissue transglutaminase enhances the binding of T-cell activating gliadin epitopes to DQ2, increasing T-cell recognition. Our purpose was to investigate whether deamidated gliadin epitopes can be generated in the small intestinal mucosa by tissue transglutaminase and to characterize the location of the process. Intestinal explants from pig intestine and frozen biopsy slices from human and rat intestine were incubated with alpha-gliadin peptides containing the immunodominant motif. Monoclonal antibodies specifically recognizing the non-deamidated and/or the deamidated epitope were used for immunofluorescence studies. We conclude that endogenous tissue transglutaminase can mediate extracellular deamidation of gliadin peptides in the lamina propria. Gliadin peptides with more than one recognition site can be simultaneously cross-linked and deamidated extracellularly in the lamina propria, and might be of importance for the antibody response seen in untreated celiac disease patients.