Cereal chemistry, molecular biology, and toxicity in coeliac disease

Association of whole grain, refined grain, and cereal consumption with gastric cancer risk: A meta-analysis of observational studies

Many studies have analyzed the relationship between cereal, whole, or refined grain and the risk of gastric cancer (GC) and have yielded mixed results. Therefore, we performed a meta-analysis of observational studies to summarize the available evidence on this topic. Databases such as PubMed, EMBASE, Web of Science, MEDLINE, and the Cochrane Library were searched for studies focusing on these associations from inception to October 2017. Summary odd ratios (OR) and 95% confidence intervals (CI) were calculated by using either a random- or fixed-effect model according to the between-studies heterogeneity. Subgroup analysis was also performed. In total, eleven studies that included 530,176 participants were identified. In a pooled analysis of all studies, cereal exposure was not associated with GC risk (OR, 1.11, 95%CI, 0.85-1.36). Specific analyses indicated that whole grain consumption was associated with decreased GC risk (OR, 0.61, 95%CI, 0.40-0.83) and that refined grain consumption was associated with increased GC risk (OR, 1.65, 95%CI, 1.36-1.94). Higher whole grain and lower refined grain intake but not cereal consumption reduces GC risk. This study has been registered at ClinicalTrials.gov (ID: NCT03419663).

The toxic alpha-gliadin peptide 31-43 enters cells without a surface membrane receptor

Alpha-gliadin peptide 31-43 is considered to be the main peptide responsible for the innate immune response in celiac disease patients. Recent evidence indicates that peptide 31-43 rapidly enters cells and interacts with the early endocytic vesicular compartment. However, the mechanism of its uptake is not completely understood. Our aim is to characterize, isolate and identify possible cell surface proteins involved in peptide 31-43 internalization by Caco-2 cells. In this study, we used a chemical cross-linker to block peptide 31-43 on cell surface proteins, and pulled-down peptide-proteins complexes using antibodies raised against peptide 31-43. Through this experimental approach, we did not observe any specific complex between cell proteins and peptide 31-43 in Coomassie-stained denaturating gels or by Western blotting. We also found that type 2 transglutaminase was not necessary for peptide 31-43 internalization, even though it had a regulatory role in the process. Finally, we demonstrated that peptide 31-43 did not behave as a classical ligand, indeed the labeled peptide did not displace the unlabeled peptide in a competitive binding assay. On the basis of these findings and of previous evidence demonstrating that peptide 31-43 is able to interact with a membrane-like environment in vitro, we conclude that membrane composition and organization, rather than a specific receptor protein, may have a major role in peptide 31-43 internalization by cells.

Endocytosis and transcytosis of gliadin peptides

Background

Celiac disease (CD) is a frequent inflammatory intestinal disease, with a genetic background, caused by gliadin-containing food. Some gliadin peptides are not digested by intestinal proteases and can have different biological effects. Gliadin peptides can induce innate and adaptive T cell-mediated immune responses. The major mediator of the stress and innate immune response to gliadin peptides (i.e., peptides 31–43 and 31–55) is the cytokine interleukin-15 (IL-15). Other peptides such as the 33 mer containing the P57–68 sequence, after tissue transglutaminase deamidation, are well presented to T cell in the intestine and can induce an adaptive immune response.

Findings

In this paper, we review the recent studies on the digestion of gliadin and the peptides released by the digestion process. We will also discuss the mechanisms responsible for the internalization and transcytosis of indigested gliadin peptides in the intestinal epithelium.

Conclusions

Gliadin is not completely digested by the intestinal proteases producing bioactive peptides that have different biological effects. These peptides are internalized in the cells by an active process of endocytosis and can traverse the intestinal mucosa with different kinetics and immunological effects. In vivo findings will also be discussed.

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.

Celiac disease in an adult Turkish population with type 1 diabetes mellitus

Celiac disease is a frequent cause of morbidity among patients with type 1 diabetes mellitus. In this study our objective was to determine the prevalance of celiac diasease in a Turkish adult population with type 1 diabetes mellitus. Patients included 122 type 1 diabetes cases from adult diabetes clinic. Total IgA and IgA-antiendomysial antibody (AEA) assays were performed. Patients positive for IgA-AEA were asked to undergo small intestinal biopsy. Of the 122 patients, none was IgA deficient and 3 had positive IgA-AEA results (2.45%). All three of these patients had biopsies diagnostic of celiac disease. The body mass index (BMI) values of patients with positive AEA were significantly lower than normal (P = 0.024). Among the gastrointestinal complaints there was an association between early satiety and AEA positivity (P = 0.02). None of the other gastrointestinal complaints or age, duration of diabetes, glycosylated hemoglobin values, or insulin doses used were found to be related to AEA positivity. Celiac disease has a high prevalence among Turkish paients with type 1 diabetes mellitus. Screening for IgA-AEA during routine investigations of type 1 diabetic patients is important to prevent celiac-associated symptoms.

The immune recognition of gluten in coeliac disease

Coeliac disease, the most common intestinal disorder of western populations, is an autoimmune enteropathy caused by an abnormal immune response to dietary gluten peptides that occurs in genetically susceptible individuals carrying the HLA-DQ2 or -DQ8 haplotype. Despite the recent progresses in understanding the molecular mechanisms of mucosal lesions, it remains unknown how increased amounts of gluten peptides can enter the intestinal mucosa to initiate the inflammatory cascade. Current knowledge indicates that different gluten peptides are involved in the disease process in a different manner, some fragments being 'toxic' and others 'immunogenic'. Those defined as 'toxic' are able to induce mucosal damage either when added in culture to duodenal endoscopic biopsy or when administered in vivo, while those defined as 'immunogenic' are able to specifically stimulate HLA-DQ2- or DQ8-restricted T cell clones isolated from jejunal mucosa or peripheral blood of coeliac patients. These peptides are able to trigger two immunological pathways: one is thought to be a rapid effect on the epithelium that involves the innate immune response and the other represents the adaptive immune response involving CD4+ T cells in the lamina propria that recognize gluten epitopes processed and presented by antigen presenting cells. These findings are the subject of the present review.

Wheat gliadin induces apoptosis of intestinal cells via an autocrine mechanism involving Fas-Fas ligand pathway

Wheat gliadin and other cereal prolamins have been said to be involved in the pathogenic damage of the small intestine in celiac disease via the apoptosis of epithelial cells. In the present work we investigated the mechanisms underlying the pro-apoptotic activity exerted by gliadin-derived peptides in Caco-2 intestinal cells, a cell line which retains many morphological and enzymatic features typical of normal human enterocytes. We found that digested peptides from wheat gliadins (i) induce apoptosis by the CD95/Fas apoptotic pathway, (ii) induce increased Fas and FasL mRNA levels, (iii) determine increased FasL release in the medium, and (iv) that gliadin digest-induced apoptosis can be blocked by Fas cascade blocking agents, i.e. targeted neutralizing antibodies. This favors the hypothesis that gliadin could activate an autocrine/paracrine Fas-mediated cell death pathway. Finally, we found that (v) a small peptide (1157 Da) from durum wheat, previously proposed for clinical practice, exerted a powerful protective activity against gliadin digest cytotoxicity.

Clarification of Muscat musts using wheat proteins and the flotation technique

The bovine spongiform encephalopathy (BSE, mad cow) crisis has led some wine-makers to question gelatin as a fining agent and to reject the use of these animal proteins. The search for a substitute for gelatin was begun by comparing vegetable proteins (particularly gluten) with gelatin fining treatments. Clairette de Die (French-controlled appellation) is a sparkling sweet wine. The alcoholic fermentation begins in a tank, continues in a crown-cap bottle, and stops before the complete consumption of sugar. All particles present in the bottle have to be removed before corking, and it is important to have a must as clear as possible. This study concerned the clarifying of a Muscat must, treated with pectinases, using a very efficient flotation technique. The must is fined with bentonite/silica/protein (fish gelatin, wheat gluten, or lupin isolate) to induce flocculation and then pressurized (6 bar). After depressurization, microbubbles cling to flocculates and climb to the top of the flotation tank (this flotation foam is clarified using a rotary filter). At laboratory scale, gluten (20 g/hL) and gelatin (10 g/hL) (each combined with bentonite and silica gel) gave turbidities of 50 and 35 NTU, respectively (6.5 and 4.1% of that of the nontreated must). The Muscat must was also clarified by static settling. The turbidity decreased by 86% for the gluten/bentonite fining and by 60% for the gelatin/bentonite fining. Visually, gluten flocculation takes longer to occur and flocculates sedimentation is longer than with gelati, but the removal of insoluble particles is more complete and leads to lower turbidities. At an industrial scale, gluten (20 g/hL) and gelatin (10 g/hL) (each combined with bentonite and silica gel) gave turbidities of 60 and 48 NTU, respectively. Turbidities measured in the tanks 14 h after the flotation showed a better efficiency for the wheat gluten (24 NTU) compared to gelatin (28 NTU). This is explained by the static settling that completed the clarifying effect of the flotation. The last experiment showed comparable efficiencies for wheat gluten and lupin proteins. BSE caused a situation of crisis (in Europe particularly) leading the public and wine-makers to lose their confidence in the use of gelatin as fining agent and to reject animal proteins in general. It is proposed here that vegetable proteins could efficiently replace gelatin.

Evaluation of intestinal permeability and gluten sensitivity in Soft-Coated Wheaten Terriers with familial protein-losing enteropathy, protein-losing nephropathy, or both

OBJECTIVE

To evaluate intestinal permeability and gluten sensitivity in a family of Soft-Coated Wheaten Terriers (SCWT) affected with protein-losing enteropathy (PLE), protein-losing nephropathy (PLN), or both.

ANIMALS

6 affected adult dogs.

PROCEDURE

Intestinal biopsy specimens, urine protein-to-creatinine ratio, serum concentrations of albumin and globulin, and concentration of alpha1-protease inhibitor in feces were evaluated before, during, and 13 weeks after daily administration of 10 g of gluten for 7 weeks. Eosinophils and lymphocytes-plasmacytes were enumerated in intestinal biopsy specimens. Intestinal permeability was evaluated before and during the sixth week of gluten administration via cellobiose-mannitol and chromium-EDTA absorption tests.

RESULTS

Serum globulin concentration decreased significantly after prolonged administration of gluten. Although not significant, there was an increase in lymphocytes-plasmacytes and a decrease in eosinophils in intestinal biopsy specimens. Furthermore, these counts were greater than those reported for clinically normal dogs. Gluten administration did not increase intestinal permeability.

CONCLUSIONS AND CLINICAL RELEVANCE

Daily administration of gluten was associated with a significant decrease in serum globulin concentration in SCWT affected with PLE or PLN, but other variables remained unchanged. Although enhanced wheat-gluten sensitivity may be one factor involved in the pathogenesis of PLE or PLN in SCWT, this syndrome does not appear to be the result of a specific sensitivity to gluten.

T cells from the small intestinal mucosa of a DR4, DQ7/DR4, DQ8 celiac disease patient preferentially recognize gliadin when presented by DQ8

CD is an immunologic disease of the small intestine which is precipitated by ingestion of wheat gliadin. Most patients carry the HLA-DQ (alpha 1*0501, beta 1*0201) (DQ2) heterodimer. We recently reported that a preponderance of gliadin-specific T cells from the small intestinal mucosa of DQ2-positive CD patients were restricted by this DQ heterodimer. However, a small percentage of CD patients do not carry this DQ heterodimer, and most of them instead carry DQ (alpha 1*0301, beta 1*0302) (DQ8). Here we report that a majority of gliadin-specific T cells from the small intestinal mucosa of a DR4,DQ7/DR4,DQ8 heterozygous CD patient are restricted by DQ8. Thus, preferential presentation of gliadin-derived peptides to T cells by the CD-associated DQ2 and DQ8 molecules may be an initial and important immunopathogenic step in CD.

T cells from the peripheral blood of coeliac disease patients recognize gluten antigens when presented by HLA-DR, -DQ, or -DP molecules

Coeliac disease (CD) is a T-cell mediated immunological disease of the small intestine which is precipitated in susceptible individuals by ingestion of gluten. We recently reported that gliadin-specific T cells can be found in the small intestinal mucosa of CD patients, and that a preponderance of these T cells was restricted by the CD-associated DQ(alpha 1*0501,beta 1*0201) heterodimer. Here we report studies on whether the same is found for gliadin specific T cells in the peripheral blood of CD patients. T-cell responses towards gluten antigens in vitro were found for both most CD patients and healthy controls. Gluten-specific T-cell clones (TCC) were established from four CD patients. Although a large proportion of these TCC were restricted by DQ molecules, including the CD-associated DQ(alpha 1*0501,beta 1*0201) heterodimer, several were restricted instead by DR or DP molecules. Thus, gluten-derived peptides can be presented to T cells by several different HLA class-II molecules, and the preferential DQ(alpha 1*0501,beta 1*0201) restriction of gluten-specific T cells in the small intestinal mucosa of CD patients is less pronounced than for similar T cells in the peripheral blood.

Gliadin-specific, HLA-DQ(alpha 1*0501,beta 1*0201) restricted T cells isolated from the small intestinal mucosa of celiac disease patients

Celiac disease (CD) is most probably an immunological disease, precipitated in susceptible individuals by ingestion of wheat gliadin and related proteins from other cereals. The disease shows a strong human HLA association predominantly to the cis or trans encoded HLA-DQ(alpha 1*0501,beta 1*0201) (DQ2) heterodimer. T cell recognition of gliadin presented by this DQ heterodimer may thus be of immunopathogenic importance in CD. We therefore challenged small intestinal biopsies from adult CD patients on a gluten-free diet in vitro with gluten (containing both gliadin and other wheat proteins), and isolated activated CD25+ T cells. Polyclonal T cell lines and a panel of T cell clones recognizing gluten were established. They recognized the gliadin moiety of gluten, but not proteins from other cereals. Inhibition studies with anti-HLA antibodies demonstrated predominant antigen presentation by HLA-DQ molecules. The main antigen-presenting molecule was established to be the CD-associated DQ(alpha 1*0501, beta 1*0201) heterodimer. The gluten-reactive T cell clones were CD4+, CD8-, and carried diverse combinations of T cell receptor (TCR) V alpha and V beta chains. The findings suggest preferential mucosal presentation of gluten-derived peptides by HLA-DQ(alpha 1*0501, beta 1*0201) in CD, which may explain the HLA association.