Uncovering the gap: Coeliac disease knowledge among healthcare professionals in the Danube region.

BACKGROUND: Several studies have shown that the knowledge about coeliac disease (CD) is not satisfactory among healthcare professionals (HCP). The aim of our study was to assess the knowledge of HCPs about CD in the Danube region. METHODS: HCPs from 8 countries in the Danube region were asked to complete the web-based questionnaire about CD. Scores of HCPs were compared according to their speciality, work experience and country of residence. The results were compared with the results of a similar study conducted in Central Europe within the Focus IN CD project in 2016. RESULTS: Questionnaire was completed by 799 HCPs from Austria, Croatia, Czech Republic, Hungary, Moldova, Romania, Serbia, and Slovenia. Mean score achieved by HCPs was 52.2%. Paediatric gastroenterologists scored the highest (75.3%). Comparing the data with the study conducted in Central Europe in 2016, we found a significant rise (p < 0.001) in the knowledge of paediatric gastroenterologists. Also, HCPs who previously took part in the Focus IN CD project, achieved higher score (61.1% vs. 50.8%; p < 0.001). CONCLUSION: The knowledge about CD among HCPs in Danube region is not satisfactory. There has been a significant increase in the knowledge of paediatric gastroenterologists, showing the benefit of various awareness raising activities that were carried out recently.

ESPGHAN Position Paper on Management and Follow-up of Children and Adolescents With Celiac Disease.

OBJECTIVES: To gather the current evidence and to offer recommendations for follow-up and management. METHODS: The Special Interest Group on Celiac Diseases of the European Society of Paediatric Gastroenterology Hepatology and Nutrition formulated ten questions considered to be essential for follow-up care. A literature search (January 2010-March 2020) was performed in PubMed or Medline. Relevant publications were identified and potentially eligible studies were assessed. Statements and recommendations were developed and discussed by all coauthors. Recommendations were voted upon: joint agreement was set as at least 85%. RESULTS: Publications (n = 2775) were identified and 164 were included. Using evidence or expert opinion, 37 recommendations were formulated on: The need to perform follow-up, its frequency and what should be assessed, how to assess adherence to the gluten-free diet, when to expect catch-up growth, how to treat anemia, how to approach persistent high serum levels of antibodies against tissue-transglutaminase, the indication to perform biopsies, assessment of quality of life, management of children with unclear diagnosis for which a gluten-challenge is indicated, children with associated type 1 diabetes or IgA deficiency, cases of potential celiac disease, which professionals should perform follow-up, how to improve the communication to patients and their parents/caregivers and transition from pediatric to adult health care. CONCLUSIONS: We offer recommendations to improve follow-up of children and adolescents with celiac disease and highlight gaps that should be investigated to further improve management.

Clinical Presentation in Children With Coeliac Disease in Central Europe.

OBJECTIVES: During the past decades, there has been a shift in the clinical presentation of coeliac disease (CD) to nonclassical, oligosymptomatic, and asymptomatic forms. We assessed clinical presentation of CD in children and adolescents in Central Europe. METHODS: Paediatric gastroenterologists in 5 countries retrospectively reported data of their patients diagnosed with CD. Clinical presentation was analyzed and the differences among very young (<3 years) and older children and adolescents were studied. RESULTS: Data from 653 children and adolescents (median age 7 years 2 months; 63.9% girls) from Croatia, Germany, Hungary, Italy, and Slovenia were available for the analysis. One fifth (N = 134) of all children were asymptomatic. In symptomatic children, the most common leading symptom was abdominal pain (33.3%), followed by growth retardation (13.7%) and diarrhoea (13.3%). The majority of symptomatic children (47.6%; N = 247) were polysymptomatic. Abdominal pain was the most common symptom in polysymptomatic (66.4%) as well as in monosymptomatic children (29.7%). Comparing clinical presentation of CD in very young children (younger than 3 years) with older children (3 years or older), we found that symptoms and signs of malabsorption were significantly more common in younger (P < 0.001), whereas abdominal pain and asymptomatic presentation were more common in older children and adolescents (both P < 0.001). CONCLUSION: In children with CD, abdominal pain has become the most common symptom. However, in younger children, symptoms of malabsorption are still seen frequently. This raises a question about the underlying mechanism of observed change in clinical presentation in favour of nonclassical presentation and asymptomatic disease at certain age.

The Knowledge About Celiac Disease Among Healthcare Professionals and Patients in Central Europe.

OBJECTIVES: Celiac disease (CD) remains undiagnosed for a long time in many adult and pediatric patients. We assessed the knowledge about CD among healthcare professionals (HCPs) and CD patients in Central Europe (CE). METHODS: HCPs and CD patients from 5 CE countries were asked to complete the web-based questionnaire about CD. The questions were divided into subsections on epidemiology, clinical presentation, diagnostics, treatment, and follow-up. Achieved scores of different specialists managing patients with CD were compared and regional differences in patients' knowledge were analyzed. RESULTS: Questionnaire was completed by 1381 HCPs and 2262 CD patients or their caregivers from Croatia, Hungary, Germany, Italy, and Slovenia. Mean score achieved by HCPs was 50.9%, and by CD patients 56.4%. Pediatric gastroenterologists scored the highest (69.4%; P < 0.001). There were significant differences in knowledge of patients from different CE regions with German participants scoring the highest (58.3%). Members of CD societies scored higher compared with nonmembers (mean score 58% vs 53.2%; P < 0.001) and patients diagnosed less than 5 years ago scored higher compared with those diagnosed more than 10 years ago (mean score 57.3% vs 54.6%; P < 0.001). CONCLUSIONS: The knowledge about CD among HCPs and CD patients is not satisfactory. Further awareness-raising and learning activities are needed to improve HCPs' knowledge and to minimize the number of unrecognized patients and unnecessary diagnostic delays. Patients should be better informed about their disease to reach higher compliance with the gluten-free diet.

Biochemical Characterisation of Human Transglutaminase 4.

Transglutaminases are protein-modifying enzymes involved in physiological and pathological processes with potent therapeutic possibilities. Human TG4, also called prostate transglutaminase, is involved in the development of autoimmune and tumour diseases. Although rodent TG4 is well characterised, biochemical characteristics of human TG4 that could help th e understanding of its way of action are not published. First, we analysed proteomics databases and found that TG4 protein is present in human tissues beyond the prostate. Then, we studied in vitro the transamidase activity of human TG4 and its regulation using the microtitre plate method. Human TG4 has low transamidase activity which prefers slightly acidic pH and a reducing environment. It is enhanced by submicellar concentrations of SDS suggesting that membrane proximity is an important regulatory event. Human TG4 does not bind GTP as tested by GTP-agarose and BODIPY-FL-GTPγS binding, and its proteolytic activation by dispase or when expressed in AD-293 cells was not observed either. We identified several potential human TG4 glutamine donor substrates in the AD-293 cell extract by biotin-pentylamine incorporation and mass spectrometry. Several of these potential substrates are involved in cell-cell interaction, adhesion and proliferation, suggesting that human TG4 could become an anticancer therapeutic target.

Diagnostic Delays in Children With Coeliac Disease in the Central European Region.

OBJECTIVES: Coeliac disease (CD) is a systemic autoimmune disorder affecting about 1% of the population. Many patients remain undiagnosed or are diagnosed with substantial delay. We assessed diagnostic delays in symptomatic CD children in Central Europe (CE). METHODS: Paediatric gastroenterologists in 5 CE countries retrospectively reported data of their patients diagnosed in 2016. Age at first CD-related symptom(s), first visit to paediatric gastroenterologist and confirmed diagnosis were used to determine diagnostic delays. RESULTS: Data from 393 children (65% girls, median age 7 years, range 7 months to 18.5 years) from Croatia, Hungary, Germany, Italy, and Slovenia were analysed. Median duration from first symptom(s) to visit to paediatric gastroenterologist was 5 months (range 0-10 years; preschool 4 months, school-aged 5 months), and further duration until final diagnosis was 1 month (range 0-5 years) with significant regional differences (P < 0.001). Median diagnostic delay was 6 months (range 0-10 years; preschool 5 months, school-aged 7 months). Type of clinical presentation had little, however, significant effect on delays. Reduced body mass in delays longer than 3 years compared with delays shorter than 1 year was found (z score -0.93 vs -0.39, P < 0.05). CONCLUSIONS: Time from first symptoms to CD diagnosis in children in 5 CE countries is slightly shorter compared with few other small paediatric studies, and significantly shorter than reported for adults. Nevertheless, delays of more than 3 years in 6.6% of children are worrisome. Raising awareness about the variable symptoms and implementation of reliable diagnostic tools will further reduce diagnostic delays.

Accuracy in Diagnosis of Celiac Disease Without Biopsies in Clinical Practice.

BACKGROUND & AIMS: The guidelines of the European Society of Pediatric Gastroenterology, Hepatology, and Nutrition allow for diagnosis of celiac disease without biopsies in children with symptoms and levels of immunoglobulin A against tissue-transglutaminase (TGA-IgA) 10-fold or more the upper limit of normal (ULN), confirmed by detection of endomysium antibodies (EMA) and positivity for HLA-DQ2/DQ8. We performed a large, international prospective study to validate this approach. METHODS: We collected data from consecutive pediatric patients (18 years or younger) on a gluten-containing diet who tested positive for TGA-IgA from November 2011 through May 2014, seen at 33 pediatric gastroenterology units in 21 countries. Local centers recorded symptoms; measurements of total IgA, TGA, and EMA; and histopathology findings from duodenal biopsies. Children were considered to have malabsorption if they had chronic diarrhea, weight loss (or insufficient gain), growth failure, or anemia. We directly compared central findings from 16 antibody tests (8 for TGA-IgA, 1 for TGA-IgG, 6 for IgG against deamidated gliadin peptides, and 1 for EMA, from 5 different manufacturers), 2 HLA-DQ2/DQ8 tests from 2 manufacturers, and histopathology findings from the reference pathologist. Final diagnoses were based on local and central results. If all local and central results were concordant for celiac disease, cases were classified as proven celiac disease. Patients with only a low level of TGA-IgA (threefold or less the ULN) but no other results indicating celiac disease were classified as no celiac disease. Central histo-morphometry analyses were performed on all other biopsies and cases were carefully reviewed in a blinded manner. Inconclusive cases were regarded as not having celiac disease for calculation of diagnostic accuracy. The primary aim was to determine whether the nonbiopsy approach identifies children with celiac disease with a positive predictive value (PPV) above 99% in clinical practice. Secondary aims included comparing performance of different serological tests and to determine whether the suggested criteria can be simplified. RESULTS: Of 803 children recruited for the study, 96 were excluded due to incomplete data, low level of IgA, or poor-quality biopsies. In the remaining 707 children (65.1% girls; median age, 6.2 years), 645 were diagnosed with celiac disease, 46 were found not to have celiac disease, and 16 had inconclusive results. Findings from local laboratories of TGA-IgA 10-fold or more the ULN, a positive result from the test for EMA, and any symptom identified children with celiac disease (n = 399) with a PPV of 99.75 (95% confidence interval [CI], 98.61-99.99); the PPV was 100.00 (95% CI, 98.68-100.00) when only malabsorption symptoms were used instead of any symptom (n = 278). Inclusion of HLA analyses did not increase accuracy. Findings from central laboratories differed greatly for patients with lower levels of antibodies, but when levels of TGA-IgA were 10-fold or more the ULN, PPVs ranged from 99.63 (95% CI, 98.67-99.96) to 100.00 (95% CI, 99.23-100.00). CONCLUSIONS: Children can be accurately diagnosed with celiac disease without biopsy analysis. Diagnosis based on level of TGA-IgA 10-fold or more the ULN, a positive result from the EMA tests in a second blood sample, and the presence of at least 1 symptom could avoid risks and costs of endoscopy for more than half the children with celiac disease worldwide. HLA analysis is not required for accurate diagnosis. Clinical Trial Registration no: DRKS00003555.

A Prospective Study on the Usefulness of Duodenal Bulb Biopsies in Celiac Disease Diagnosis in Children: Urging Caution.

OBJECTIVES: Several recent celiac disease guidelines recommend the acquisition of duodenal bulb biopsies for diagnostics. This is in conflict with previously reported evidence and routine practice from the 1960s onward. We reopened the issue in a prospective multicenter study and used morphometric variables in evaluating the usefulness of bulb biopsies in children. We further sought to establish whether deposits of IgA targeting bulb transglutaminase 2 (TG2) could be of diagnostic help. METHODS: Diagnoses of celiac disease were based on clinic and distal duodenal histopathology statements. Centralized reading of villous height (VH) to crypt depth (CrD) ratios and IgA deposits was performed on anatomical duodenal bulb specimens. All children participating also underwent routine investigations for other diseases. RESULTS: Twenty-two children had celiac disease, and another 22 served as non-celiac disease controls. The quality of the anatomical bulb specimens was unsatisfactory for reliable morphometric measurements in 20 out of 44 (45%) patients even after recuttings. All celiac disease patients had VH:CrD<2.0 (mean 0.2) but also 10 out of 13 (77%) non-celiac control patients had an injured bulb mucosal lining (mean 1.3) even up to false-positive "flat lesion". Bulb IgA deposits were able to separate celiac disease from disease controls. CONCLUSIONS: Morphological injury is common in the anatomical bulb even without celiac disease, increasing the risk of false-positive diagnoses. Premature conclusions might have been drawn on current care guidelines as to celiac disease diagnosis based solely on anatomical bulb specimens. Bulb mucosal IgA targeting TG2 in poor quality biopsy specimens is a powerful clinical tool in finding celiac disease patients.

Celiac disease patient IgA antibodies induce endothelial adhesion and cell polarization defects via extracellular transglutaminase 2.

We have recently found that celiac disease patient serum-derived autoantibodies targeted against transglutaminase 2 interfere with several steps of angiogenesis, including endothelial sprouting and migration, though the mechanism involved remained to be fully characterized. This study now investigated the processes underlying the antiangiogenic effects exerted by celiac disease patient antibodies on endothelial cells, with particular regard to the adhesion, migration, and polarization signaling pathway. We observed that celiac IgA reduced endothelial cell numbers by affecting adhesion without increasing apoptosis. Endothelial cells in the presence of celiac IgA showed weak attachment, a high susceptibility to detach from fibronectin, and a disorganized extracellular matrix due to a reduction of protein cross-links. Furthermore, celiac patient IgA led to secretion of active transglutaminase 2 from endothelial cells into the culture supernatants. Additionally, cell surface transglutaminase 2 mediated integrin clustering in the presence of celiac IgA was coupled to augmented expression of ß1-integrin. We also observed that celiac patient IgA-treated endothelial cells had migratory defects and a less polarized phenotype when compared to control groups, and this was associated with the RhoA signaling pathway. These biological effects mediated by celiac IgA on endothelial cells were partially influenced but not completely abolished by R281, an irreversible extracellular transglutaminase 2 enzymatic activity inhibitor. Taken together, our results imply that celiac patient IgA antibodies disturb the extracellular protein cross-linking function of transglutaminase 2, thus altering cell-extracellular matrix interactions and thereby affecting endothelial cell adhesion, polarization, and motility.

Management of coeliac disease patients after the confirmation of diagnosis in Central Europe.

BACKGROUND: Recently published paediatric guidelines for diagnosing coeliac disease do not include recommendations on the follow-up of coeliac disease patients. GOAL: The aim of this study was to assess the management practices and experience of coeliac disease patients with their follow-up appointments in Central Europe. STUDY: Gastroenterologists and coeliac disease patients in five Central European countries were asked to complete the web-based questionnaire focusing on coeliac disease management practices. RESULTS: Answers from 147 gastroenterologists and 2041 coeliac disease patients were available for the analysis. More than half of the gastroenterologists (58.5%) schedule the first follow-up visit within 3 months after the diagnosis. At follow-up, tissue transglutaminase antibodies are checked in almost all patients (95.9%). Approximately two-thirds (60.7%) of gastroenterologists refer all of their patients to the dietitian at diagnosis. Similarly, 42.8% of coeliac disease patients reported that they had not been appointed to a dietitian. Almost one-third of coeliac disease patients (30.8%) reported that they had no follow-up appointments with gastroenterologist at all. CONCLUSIONS: Follow-up of coeliac disease patients is suboptimal in Central Europe. Many patients are not followed regularly. A lot of patients are not referred to a dietitian. The recommendations on the optimal follow-up of coeliac disease patients are needed in order to improve patient care.

Increased heat shock protein 72 expression in celiac disease.

BACKGROUND AND OBJECTIVES: Heat shock protein (HSP) 72, a known chaperone, has potential epithelial barrier protecting, antiapoptotic, and immune system regulatory effects; therefore, our aim was to study its involvement in the pathology of celiac disease (CD). PATIENTS AND METHODS: Duodenal biopsy specimens were collected from children with untreated and treated CD and from controls. mRNA expression, protein level, and localization of HSP72 were determined. RESULTS: Elevated HSP72 mRNA expression and higher protein levels were found in the duodenal mucosa of children with untreated CD as well as in children with treated CD compared with those in controls. In the duodenal mucosa of children with treated CD, HSP72 mRNA expression was decreased and HSP72 protein levels were lower than those in children with untreated CD. We detected intensive HSP72 staining in the villous enterocytes and immune cells of the lamina propria in the duodenal villi of children with untreated CD compared with that in controls. CONCLUSIONS: The increased expression and altered localization of HSP72 in CD indicate that HSP72 should have a role in protection against gliadin-induced cytotoxicity. HSP72 may exert antiapoptotic effect and contribute to preservation of intestinal epithelial barrier integrity. Moreover, HSP72 as a ligand of TLR2 and TLR4 may promote innate immune responses and warn the cells of the potential injury.

The Use of Biopsy and "No-Biopsy" Approach for Diagnosing Paediatric Coeliac Disease in the Central European Region.

OBJECTIVES: The current European Society for Paediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) guidelines introduced the option to diagnose coeliac disease (CD) in children and adolescents without upper endoscopy if the defined criteria are met. The aim of our study was to evaluate how frequently paediatric gastroenterologists in Central Europe used the "no-biopsy" approach and how often the duodenal biopsy could have been omitted. METHODS: Medical records of patients aged < 19 years diagnosed with CD in 2016 from five European countries were analysed, focusing on levels of transglutaminase antibodies (TGA) at the time of diagnosis and on whether the diagnosis was confirmed using duodenal biopsy or "no-biopsy" approach. Clinical presentation and delays until final diagnosis were analysed according to diagnostic approach. RESULTS: Data from 653 children (63.9% female, median age: 7 years, range: 7 months-18.5 years) from Croatia, Hungary, Germany, Italy, and Slovenia were analysed. One fifth (n = 134) of included children were asymptomatic at diagnosis. Of 519 symptomatic children, 107 (20.6%) were diagnosed by the "no-biopsy" approach. Out of the remaining 412 children who underwent duodenal biopsies, 214 (51.9%) had TGA ≥ 10 times upper level of normal (ULN) and would have been eligible for the "no-biopsy" approach. Signs and symptoms of malabsorption were more frequent in children diagnosed without duodenal biopsies. There were no differences in diagnostic delays with respect to the diagnostic approach. CONCLUSION: In this cohort, about 60% of symptomatic CD patients could have been diagnosed without duodenal biopsies. The aim of the "no-biopsy" approach was to make the diagnostic procedure less challenging without compromising its reliability. However, this option was applied only in 20%, in spite of fewer burdens to the family and reduced costs. The reasons for this discrepancy are unknown. Physicians should be made more aware about the reliability of CD diagnosis without biopsies when the ESPGHAN guidelines for CD diagnosis are followed.

The role of gluten consumption at an early age in celiac disease development: a further analysis of the prospective PreventCD cohort study.

Background: We previously found that the introduction of small quantities of gluten at 4-6 mo of age did not reduce the risk of celiac disease (CD) in a group of high-risk children. However, the consumption of high amounts of gluten early in life has been suggested to increase CD risk.Objective: The aim of this study was to evaluate this hypothesis by using data from the previous study of the PreventCD trial (www.preventcd.com).Design: Gluten intake was prospectively quantified by using specific food records between 11 and 36 mo of age in 715 children positive for the human leukocyte antigen (HLA)-DQ2 and/or HLA-DQ8 from 5 European countries. According to the PreventCD protocol, infants received 100 mg immunologically active gluten/d or placebo from 4 to 6 mo of age, with a stepwise and fixed gluten increase until age 10 mo and unrestricted intake thereafter. The primary outcome of the present study was the impact of the amount of gluten consumed from age 10 mo onward on CD development.Results: Mean daily gluten intakes from 10 mo onward were significantly different between countries for children at all ages (P < 0.001) but not between children who developed CD and those who did not within the same country (P > 0.05). The variables country, sex, intervention group, and gluten consumption pattern did not show significant associations with CD development risk (HRs not significant). In addition, the interaction between HLA risk group and gluten consumption pattern showed no significant risk on CD development, except for the DQ2.2/DQ7 haplotype (HR: 5.81; 95% CI: 1.18, 28.74; P = 0.031).Conclusions: Gluten consumption patterns as well as the amount of gluten consumed at 11-36 mo of age do not influence CD development for most related HLA genotypes in children with a genetic risk. This study reports the gluten consumption pattern in children at risk of CD from different European countries. This trial was registered at www.controlled-trials.com as ISRCTN74582487.

Thioredoxin is involved in endothelial cell extracellular transglutaminase 2 activation mediated by celiac disease patient IgA.

PURPOSE: To investigate the role of thioredoxin (TRX), a novel regulator of extracellular transglutaminase 2 (TG2), in celiac patients IgA (CD IgA) mediated TG2 enzymatic activation. METHODS: TG2 enzymatic activity was evaluated in endothelial cells (HUVECs) under different experimental conditions by ELISA and Western blotting. Extracellular TG2 expression was studied by ELISA and immunofluorescence. TRX was analysed by Western blotting and ELISA. Serum immunoglobulins class A from healthy subjects (H IgA) were used as controls. Extracellular TG2 enzymatic activity was inhibited by R281. PX12, a TRX inhibitor, was also employed in the present study. RESULTS: We have found that in HUVECs CD IgA is able to induce the activation of extracellular TG2 in a dose-dependent manner. Particularly, we noted that the extracellular modulation of TG2 activity mediated by CD IgA occurred only under reducing conditions, also needed to maintain antibody binding. Furthermore, CD IgA-treated HUVECs were characterized by a slightly augmented TG2 surface expression which was independent from extracellular TG2 activation. We also observed that HUVECs cultured in the presence of CD IgA evinced decreased TRX surface expression, coupled with increased secretion of the protein into the culture medium. Intriguingly, inhibition of TRX after CD IgA treatment was able to overcome most of the CD IgA-mediated effects including the TG2 extracellular transamidase activity. CONCLUSIONS: Altogether our findings suggest that in endothelial cells CD IgA mediate the constitutive activation of extracellular TG2 by a mechanism involving the redox sensor protein TRX.

Gluten-dependent intestinal autoimmune response.

Celiac disease is a multi-systemic autoimmune disease of the small bowel induced by gluten in genetically predisposed subjects. Highly specific and gluten-dependent production of auto-antibodies targeting self-proteins of the transglutaminase family occurs in the intestinal mucosa. These anti-transglutaminase antibodies are found deposited in intestinal and extra-intestinal tissue where they might exert biological effects, together with the intestinal mucosal gliadin-specific T lymphocytes. We conducted a brief review on antitransglutaminase antibodies effects, discussing their roles in the pathogenesis of several clinical manifestations of celiac disease.

Transglutaminase 2 is expressed and active on the surface of human monocyte-derived dendritic cells and macrophages.

The multifunctional enzyme, transglutaminase 2 (TG2), can be found intracellularly, in the extracellular matrix and on the cell surface. Cell surface TG2 (csTG2) could not be detected by TG2-specific antibodies or autoantibodies on immunocompetent cells. A supposedly csTG2-specific antibody, 6B9, was recently shown to actually react with CD44. Though the importance of TG2-mediated deamidation of gluten in the pathogenesis of celiac disease has been well recognized, it is not known in which intestinal cells or cell compartment the deamidation occurs. Duodenal dendritic cells (DCs) can be directly involved in gluten-reactive T-cell activation. Here we use blood monocyte-derived dendritic cells (iDC) and macrophages (MPhi) as a model for intestinal antigen-presenting cells (APCs) and show that they contain large amounts of TG2. We found that TG100, a commercial TG2-specific monoclonal antibody can recognize TG2 on the surface of these cells, that is monocyte-derived APCs express surface-associated TG2. TG2 expression was found on the surface of individual tunica propria cells in frozen small bowel tissue sections from both normal and celiac subjects. We also demonstrate that the pool of TG2 on the surface of iDCs can be catalytically active, hence it might directly be involved in the deamidation of gliadin peptides. Bacterial lipopolysaccharide (LPS) increased the level of TG2 on the surface of maturing DCs, supporting the hypothesis that an unspecific inflammatory process in the gut may expose more transglutaminase activity.

Functional significance of five noncanonical Ca2+-binding sites of human transglutaminase 2 characterized by site-directed mutagenesis.

The multifunctional tissue transglutaminase 2 (TG2) has a four-domain structure with several Ca(2+)-regulated biochemical activities, including transglutamylation and GTP hydrolysis. The structure of the Ca(2+)-binding form of the human enzyme is not known, and its Ca(2+)-binding sites have not been fully characterized. By mutagenesis, we have targeted its active site Cys, three sites based on homology to Ca(2+)-binding residues of epidermal transglutaminase and factor XIIIa (S1-S3), and two regions with negative surface potentials (S4 and S5). CD spectroscopy, antibody-binding assay and GTPase activity measurements indicated that the amino acid substitutions did not cause major structural alterations. Calcium-45 equilibrium dialysis and isothermal calorimetric titration showed that both wild-type and active site-deleted enzymes (C277S) bind six Ca(2+). Each of the S1-S5 mutants binds fewer than six Ca(2+), S1 is a strong Ca(2+)-binding site, and mutation of one site resulted in the loss of more than one bound Ca(2+), suggesting cooperativity among sites. All mutants were deficient in transglutaminase activity, and GTP inhibited remnant activities. Like those of the wild-type enzyme, the GTPase activities of the mutants were inhibited by Ca(2+), except in the case of the S4 and S5 mutants, which exhibited increased activity. TG2 is the major autoantigen in celiac disease, and testing the reactivity of mutants with autoantibodies from celiac disease patients revealed that S4 strongly determines antigenicity. It can be concluded that five of the Ca(2+)-binding sites of TG2 influence its transglutaminase activity, two sites are involved in the regulation of GTPase activity, and one determines antigenicity for autoantibodies in celiac patients.

Anti-microbial antibodies in celiac disease: trick or treat?

AIM: To determine the prevalence of a new set of anti-glycan and anti-outer membrane protein (anti-OMP) antibodies in a Hungarian cohort of adult Celiac disease (CD) patients. METHODS: 190 consecutive CD patients [M/F: 71/119, age:39.9 (SD:14.1) years], 100 healthy, and 48 gastrointestinal controls were tested for glycan anti-Saccharomyces cerevisiae (gASCA), anti-laminaribioside (ALCA), anti-chitobioside, anti-mannobioside, anti-OMP antibodies and major NOD2/CARD15 mutations. Thirty out of 82 CD patients enrolled at the time of diagnosis were re-evaluated for the same antibodies after longstanding gluten-free diet (GFD). RESULTS: 65.9% of the CD patients were positive for at least one of the tested antibodies at the time of the diagnosis. Except anti-OMP and ALCA, anti-microbial antibodies were exclusively seen in untreated CD; however, the overall sensitivity was low. Any glycan positivity (LR+: 3.13; 95% CI: 2.08-4.73) was associated with an increased likelihood ratio for diagnosing CD. Significant correlation was found between the levels of anti-glycan and anti-endomysial or anti-transglutaminase antibodies. Anti-glycan positivity was lost after longstanding GFD. Anti-glycan antibody titers were associated with symptoms at presentation, but not the presence of NOD2/CARD15 mutations. Patients with severe malabsorption more frequently had multiple antibodies at diagnosis (P = 0.019). CONCLUSION: The presence of anti-glycan antibodies in CD seems to be secondary to the impaired small bowel mucosa which can lead to increased antigen presentation. Furthermore, anti-glycan positivity may be considered an additional marker of CD and dietary adherence.

Coeliac autoantibodies can enhance transamidating and inhibit GTPase activity of tissue transglutaminase: dependence on reaction environment and enzyme fitness.

Modification of the enzymatic functions of tissue transglutaminase (TG2) by anti-TG2 autoantibodies may play a role in manifestations of coeliac disease. Our aim was to evaluate the effect of coeliac autoantibodies on reactions catalysed by TG2 by a systematic biochemical approach, and in relation to observed clinical presentation type. Coeliac antibodies did not have significant inhibitory effect on transamidation/deamidation activity of TG2 as measured by amine-incorporation into solid and immobilised casein and by ultraviolet kinetic assay. In contrast, immunoglobulins from patients with severe malabsorption enhanced the reaction velocity to 105.4-242.2%. This activating effect was dose-dependent, most pronounced with immobilised glutamine-acceptor substrates, and correlated inversely with the basal specific activity of the enzyme and with dietary treatment. A similar activation could be demonstrated also with the TG2-specific fraction of autoantibodies and in transamidation activity assays which use fibronectin-bound TG2 and thereby mimic in vivo conditions. These results suggest that coeliac antibodies may stabilise the enzyme in a catalytically advantageous conformation. GTPase activity of TG2 decreased to 67.0-73.4% in the presence of antibodies raising the possibility that inhibition of GTPase activity may affect cellular signalling in case coeliac autoantibodies would reach intracellular compartments.