Coeliac disease: a critical review of aetiology and pathogenesis

Use of Response Surface Methodology to Optimize Gluten-Free Bread Fortified with Soy Flour and Dry Milk

The percentages of soy flour (X1) and dry milk (X2) were varied for the production of gluten-free bread to optimize batter softness (Y1), specific volume (Y2), crumb grain score (Y3), bread score (Y4) and bread protein content (Y5). A central composite design was used and second-order models for Y1 were employed to generate response surfaces. When bread protein content was decreased from 10 to 3%, specific volume increased from 3.2 to 4.6 cm3/g and bread score increased too. Nevertheless, the highest crumb grain score was obtained at 7.3% of bread protein content. The results demonstrated that a gluten-free bread can be prepared by adding 7.5% soy flour and 7.8% dry milk to a previously developed formulation, increasing its protein content from 1 to 7.3% and modifying in a small degree, its sensory quality.

Qualitative and quantitative analysis of wheat gluten proteins by liquid chromatography and electrospray mass spectrometry

Based on analysis by liquid chromatography/electrospray ionisation mass spectrometry, we have developed a new method for fast and sensitive fingerprinting of gliadins and glutenins in wheat flour. Using this procedure the two protein fractions from seven durum wheat varieties have been analysed by high resolution high performance liquid chromatographic separation coupled to accurate determination of molecular mass. In this way, the molecular mass of the single components from both gliadin and glutenin fractions were measured and more than forty components were detected for each fraction indicating a high heterogeneity. Although the chromatographic profiles were similar, the molecular masses of protein components with similar retention times among the varieties were often different. The difference ranged from a few mass units corresponding to single amino acid substitution(s) up to thousands implying peptide deletion or insertion along the protein chain. Two components representing about a half of the gliadin fraction, e.g. gamma(2)- and gamma(3)-gliadin, were identified through the N-terminal sequence and molecular mass determination. We suggest the use of the high level and the molecular mass of these gliadin components as markers to detect traces of wheat in gluten-free food preparations for celiac patients.

Changes in jejunal mucosa after long-term feeding of germfree rats with gluten

BACKGROUND

Coeliac disease (CD) or gluten-sensitive enteropathy is a chronic gastrointestinal disease of children and adults. An experimental model using inbred germfree rats has been developed to study the effects of intragastric gliadin application on intestinal mucosa.

METHODS

AVN strain Wistar rats (inbred F 87)-germfree were used. Gliadin was applied by intragastric probe from birth until day 63 (0.5-5 mg of gliadin per immunization). Intraepithelial lymphocytes (IEL) were separated from the jejunum, and surface marker characterization was performed using flow cytometry. Isolated IEL were labelled with fluorescein isothiocyanate and injected into control jejunal loops. After 1 h and 6 h the abdominal cavity was reopened. The samples of jejunum were fixed.

RESULTS

Prolonged application of gliadin led to the shortening of jejunal villi, crypt hyperplasia, increased number of mitoses in the crypt epithelium, and increased number of IEL-characteristic CD8+, RGL-1+, and TcR alpha/beta +. Transfer of IEL separated from rats fed with gliadin into the intestinal loops of untreated rats led to tight junctions in the enterocytes of the intestinal loops. The IEL isolated from controls (albumin-treated) induced no mucosal changes in intestinal loops.

CONCLUSION

These data suggest that IEL isolated from gliadin-treated rats transfer mucosal damage and that gluten-induced enteropathy has an autoimmune component.

Natural killer cell activity in coeliac disease: effect of in vitro treatment on effector lymphocytes and/or target lymphoblastoid, myeloid and epithelial cell lines with gliadin

To analyze the possible involvement of natural killer (NK) cell activity in the pathogenetic mechanism of coeliac disease (CD) we measured the spontaneous cytotoxic cell activity of peripheral blood mononuclear cells (PMNC) from patients with CD and from healthy donors. No significant differences were found between the NK cell activity of PMNC from healthy donors and from patients with CD using a standard 51 Cr release assay. However, a 30-min treatment of PMNC with gliadin inhibited NK cell activity in patients with CD. On the other hand, a 1-d incubation with gliadin induced cytotoxic cell activity of PMNC against the NK-resistant target cells such as the epithelial HT-29 and the lymphoblastoid RAJI cell lines, suggesting that activation of PMNC by cultivation with gliadin can occur.

Morphological factors influencing transepithelial conductance in a rabbit model of ileitis

BACKGROUND & AIMS

Infection of rabbits with coccidia (Eimeria magna) causes chronic ileal inflammation and diarrhea. Inflamed ileum also shows decreased transmural conductance. The aim of this study was to characterize morphological factors known to affect paracellular permeability that may alter transmural conductance in inflamed ileum.

METHODS

Ileal mucosa was mounted in Ussing chambers for study of [3H]mannitol and [3H]inulin fluxes. Light and electron microscopy were used for morphometric studies. Alterations in the zonula occludens of epithelial cells were evaluated in freeze-fracture replicas.

RESULTS

Inflamed ileum showed diminished paracellular fluxes. Inoculated rabbits showed marked lymphoplasmocytic infiltration and villus blunting in ileum. Villus linear junctional density was unaffected. However, total villus apical surface area per square centimeter of tissue was reduced in inflamed ileum, causing a diminished total villus linear junctional pathway per square centimeter of apical surface. Villus zonula occludens strand number was reduced in inflamed ileum, whereas the frequency of both villus and crypt lateral surface extrajunctional strands increased.

CONCLUSIONS

Chronic inflammation exerts a profound effect on ileal paracellular permeability. Morphological data suggest that this effect may be caused in part by alterations in inflamed ileal mucosal structure and tight junctional organization and density, particularly on villi.

Characterization of distinct alpha- and gamma-type gliadins and low molecular weight components from wheat endosperm as coeliac immunoreactive proteins

Distinct alpha- and gamma-type gliadins, as well as a few low molecular weight components have been identified as coeliac immunoreactive proteins from a chloroform/methanol extract from wheat endosperm. Characterization of these components involved the combination of reverse-phase high-performance liquid chromatography, immunoblotting following SDS-PAGE using a coeliac serum and microsequencing analysis. This has allowed the identification of a group of gliadins with different molecular weights, according to their N-terminal amino-acid sequence: five alpha-type gliadins of 31, 35, 38 and two of 45 kDa, one gamma 2-type gliadin of 40 kDa, two gamma 3-type gliadins of 31, and 50 kDa, and two gamma-type gliadins with an atypical gliadin N-terminal of 31, and 40 kDa, as well as a few unidentified low molecular weight components and three N-terminal blocked proteins, all exhibiting similar antigenicity.

Coeliac disease, enamel defects and HLA typing

The presence of dental enamel defects in coeliac disease and their relation to hypocalcaemia or a particular HLA class in 82 Italian children with coeliac disease was studied. Demarcated opacities or hypoplasia were detected in 23 subjects (group 1) while minimal or no dental lesions were found in the remaining 59 patients (group 2); in 189 normal controls, enamel lesions were significantly less frequent than in patients with coeliac disease (14.8% versus 28.0%; p < 0.005). No statistically significant differences were found for age at diagnosis and calcium concentrations between groups 1 and 2. Regression analysis showed a correlation between age at diagnosis and number of teeth with enamel defects. In our patients, the presence of HLA DR3 antigen significantly increased the risk of dental lesions, while genotype DR5,7 seemed to protect against enamel defects. A logistic regression analysis of the variables age, serum calcium concentrations, number of affected teeth, type of enamel defect and DR antigens showed that only DR antigens discriminated coeliac disease patients with from those without enamel defects.

HLA susceptibility genes in celiac disease: genetic mapping and role in pathogenesis

The overrepresentation of particular HLA alleles in patients with celiac disease was first noted two decades ago. Several lines of evidence obtained during the last years strongly suggest that a particular HLA-DQ heterodimer, encoded by the DQA1*0501 and DQB1*0201 genes in cis or trans configuration, confers the primary disease susceptibility. This paper reviews the evidence behind this concept and discusses how this particular DQ molecule may be involved in the pathogenesis.

Mathematical correlation between villus height and the nutritional state in Sprague-Dawley rats

Three different experiments were carried out on growing male Sprague-Dawley rats. In the first experiment, dietary nitrogen was given in casein at four different protein values ranging from 5 to 16%. Rats were fed ad libitum for 21 days. In the second experiment, which lasted 17 days, animals were given three diets that differed in the molecular form of the nitrogen supply - that is, proteins or peptides. The protein value (N x 6.25) was 10% in each diet. In the third experiment, malnourished rats were refed diets with a protein value of 15% (N x 6.25) for eight days. The dietary nitrogen was either in the form of protein, peptide, or amino acid. Body weight was recorded daily. At the end of each experiment the intestinal villus height was measured by light microscopy. Data were statistically analysed by Exner's coefficient. The results assessed the validity of the correlation between villus height and gain in body weight.

Characterization of the gliadin-derived peptides which are biologically active in coeliac disease

Reversed-phase HPLC on C18 silica gel at pH 3.5 was used to separate peptides in fraction 9, a mixture of peptides of unknown composition obtained from an enzymic digest of wheat gliadin. This fraction, which has been shown to be toxic to individuals with coeliac disease, yielded a principal peak as well as many minor peaks after HPLC. The significant peaks were subjected to amino acid analysis. The principal peak obtained was purified by rechromatography at pH 6.0 and shown to contain a dodecapeptide of sequence H-Arg-Pro-Gln-Gln-Pro-Tyr-Pro-Gln-Pro-Gln-Pro-Gln-OH. This peptide may have been derived from regions in the A-gliadin molecule corresponding to amino acids numbered 75-86 or from homologous regions in other gliadin molecules. Preliminary results indicate that it is active in two in vitro models of coeliac disease and that it could be the source of one of the undigested peptides (Hexapeptide II, (Glx)3, (Pro)2, Tyr) obtained from coeliac mucosal digestion of fraction 9. Some active serine-containing peptides were also obtained from chromatography at pH 3.5 and attempts are being made to correlate these with the other undigested peptide (Hexapeptide I) of composition (Glx)3, (Pro)2, Ser, obtained after coeliac mucosal digestion of fraction 9.

Gliadin uptake in human enterocytes. Differences between coeliac patients in remission and control individuals

The pepsin trypsin digest of the wheat prolamin gliadin (PT-gliadin) is deleterious to the small intestinal mucosa of coeliac patients. The handling of PT-gliadin by the intestinal epithelium in coeliac patients in remission and control individuals was investigated by in vivo instillation of PT-gliadin. The uptake of PT-gliadin was monitored by immunofluorescence microscopy of intestinal biopsy specimens, using affinity purified PT-gliadin antibodies. Control individuals show weak staining in the apical region of the enterocytes thereby showing an uptake of PT-gliadin. Coeliac patients have a conspicuous fluorescence in relation to the lateral membrane/intercellular space of enterocytes and intense staining intracellularly in the apical region. There is only weak staining in the enterocytes after the instillation was terminated, indicating an intracellular clearance. The study shows that normal enterocytes are able to take up PT-gliadin. The increased uptake in coeliac patients might be of importance for the pathogenesis either by direct toxicity or by presentation to immunocompetent cells. Furthermore, the results are in agreement with the suggestion of a functional alteration in the zonula occludens in the intestinal epithelium of coeliac patients.

Identification of the three major coeliac immunoreactive proteins and one alpha-amylase inhibitor from oat endosperm

Six chloroform/methanol-soluble proteins from oat endosperm (Avena sativa) have been isolated and characterized by a purification procedure based on extraction with volatile solvents, followed by reversed-phase high performance liquid chromatography. Three of these proteins, with an assessed molecular weight of 25,000, 27,000 and 32,000 Da, respectively, have been identified by immunoblotting using coeliac sera, as the major coeliac serum IgA-binding components of oat endosperm. The N-terminal amino acid sequence of these proteins indicates that they correspond to alpha 2, gamma 4, and gamma 3 avenins, respectively. We have tentatively named them 'coeliac immunoreactive proteins'. Another chloroform/methanol oat component shows weak alpha-amylase inhibitory activity and exhibits strong homology (60% identity) at the N-terminus with the alpha-amylase inhibitor from ragi (Eleusine coracana).

Diabetes-related autoantibodies do appear in children with coeliac disease

Humoral immune factors related to type 1 diabetes have been investigated in children with coeliac disease. Anti-insulin (IAAb), immunoglobulin (alpha IgAb), islet cell (ICA) and glucagon autoantibodies were examined in 15 children with coeliac disease at diagnosis (group 1), in 15 children with coeliac disease following a gluten-free diet (group 2) and in 30 control patients (groups 3 and 4). IAAb were present in 27% of group 1 and in 20% of group 2 patients and alpha IgAb were significantly increased in group 1 and 2 patients; two patients in group 2 were positive for ICA; none of the coeliac disease patients were positive for anti-glucagon antibodies. The levels of anti-gliadin antibodies in group 1 were positively correlated with those of alpha IgAb. Coeliac disease-related HLA antigens were not correlated with antibody presence. The presence of diabetes-related humoral immune factors in coeliac disease raises the question as to whether or not they are predictive of subclinical pancreatic damage or whether they are simply indicators of a more general autoimmune diathesis.

Purification and characterisation of antigenic gliadins in coeliac disease

Two gliadins, known to be especially antigenic in coeliac disease, were purified to homogeneity by a series of ion-exchange chromatography steps. Their N-terminal amino acid sequences showed minor differences but clearly classified them as gamma-type gliadins. The purified gliadins were further characterised with respect to amino acid composition, molecular mass and E1(1%)cm at 276 nm. Based on these properties it is suggested that one of them is identical to a gamma-type gliadin, earlier characterised by its nucleotide sequence, whereas the other has not previously been described. The purification procedure may form the basis for the development of a more differentiated analysis of circulating antibodies for diagnosis and makes clinical testing of the toxicity of defined gliadin peptides feasible.

Self-management of dietary compliance in coeliac disease by means of ELISA "home test" to detect gluten

To improve compliance with a gluten-free diet in coeliac disease a simple prototype test kit was developed to detect gluten in foods for use at home. The test is based on monoclonal antibodies to heat-stable gluten proteins which crossreact appropriately with barley and rye proteins. It is suitable for use with a wide range of raw or cooked foods. The food is extracted with dilute hydrochloric acid and 1 drop of the extract transferred to an antibody-coated tube; enzyme-labelled gluten detection antibody is added and after 3 min the tube is washed and colour developer is added. The reaction is stopped after 2 min, stabilising the blue colour. The home kit was compared with a quantitative laboratory kit, and the qualitative agreement was very good. The kit could distinguish foods with trace gluten contents (acceptable for a "gluten-free" diet) from those with a slightly higher but unacceptable gluten content. In a trial of the prototype kit by 47 coeliac disease patients of diverse ages and educational backgrounds, 93% of tests correctly identified foods as acceptable or unacceptable.

A physical approach to coeliac disease

The morphological changes used to confirm a diagnosis of coeliac disease (CD) are precisely those predicted if the surface energy of the interface between duodenal epithelium and the luminal contents were raised to levels comparable to those demonstrated by the hydrophobic nature of the stomach wall. This hypothesis pursues the concept that, in coeliac patients, the gastric mucosal barrier (GMB) is effectively extended from the stomach to coat the duodenum, thus closing the window of absorption in the Gl tract. If studies are correct which indicate that the GMB is a physical reality provided by an adsorbed monolayer of surface-active phospholipid (surfactant) which renders surfaces hydrophobic, then it could also act as a barrier to the absorption of nutrients in the duodenum. Gluten, or its more active polypeptide fragment gliadin, exacerbates the situation in CD by acting as very effective carriers for the insoluble phospholipid which is deposited at the duodenal surface where they are digested by brush-border and pancreatic enzymes.

Antibody response reveal differences in oral tolerance to wheat and maize grain protein fractions

The influence of diet on humoral immune responses to gluten- and maize-derived proteins was examined using ELISA and protein blotting techniques. Mice raised on the maize-based (gluten-free) diet responded well to parenteral immunization with each of six gluten-derived protein preparations (whole gliadin, two omega-gliadin fractions, wheat salt-soluble proteins, a peptic-tryptic digest and a subtilisin digest of gluten), as serum antibody levels increased at least 300-fold in each case. In contrast, mice raised on the wheat-based diet responded poorly to immunization with either whole gliadin or omega-gliadin and were virtually non-responsive to enzymic digest of gluten. Diet had little effect on the magnitude of the antibody response to wheat salt-soluble proteins, with both groups showing a 300-fold increase in titre. Similarly, tolerance to alpha-zeins, the alcohol-soluble proteins of maize, did not occur on either diet. However, some oral tolerance was observed to maize glutelin. The specificity of the various antibody responses was then analysed by immunoblotting. Following immunization with gluten proteins or digests, antibodies from the maize-fed mice bound more or less equally to each of the main gliadin bands and to the glutenins while the mice on the wheat-based diet had antibody specific for omega-gliadin proteins. Serum antibodies from the maize-fed mice, immunized with either alpha-zein or maize glutelin, showed even labelling of the major maize endosperm proteins while antibodies from mice on the wheat diet showed strong labelling of the Mr 27,000 and 58,000 bands. These results show that diet influenced the specificity, as well as the magnitude of serum antibody responses to cereal proteins. In addition, oral tolerance appeared to affect the humoral response to some cereal proteins more than others. Both of these findings have important implications for our understanding of coeliac disease.

Use of physiological substrates for zymograms of disaccharidases after separation in immobilized pH gradients

A new technique is described for in situ visualization of the activity of intestinal disaccharidases after isoelectric focusing in immobilized pH gradients using their physiological substrates. The reaction principle is based on the oxidation of D-glucose, liberated by the disaccharidases, into D-gluconolactone and the production of NADH by glucose dehydrogenase. At the sites of enzymatic activity, tetrazolium salts present in the reaction mixture are reduced to relatively water-insoluble formazans by NADH. The rate of formazan production is increased by the presence of phenazine methosulfate. An additional modification of the technique involves the use of polyvinyl alcohol in the substrate solution. Due to the increase in the viscosity of the substrate solution, leakage of the enzyme from the IPG gels is minimized. Incubation times can thus be prolonged without loss of resolution and band-blurring.

Immunological studies of patients with Down's syndrome. Measurements of autoantibodies and serum antibodies to dietary antigens in relation to zinc levels

Recurrent diarrhoea and weight loss in many adult patients with Down's syndrome (DS), initiated a search for malabsorption based on determination of serum IgG and IgA antibody levels to dietary antigens. The results were compared with measurements of autoantibodies and serum zinc levels. DS patients had increased IgG and IgA activities to gluten proteins, casein and ovalbumin compared with an age- and sex-matched group of other mentally retarded patients in the same institution. Intestinal biopsy was performed in six of the 38 patients; one had total and one partial villous atrophy. Serum zinc was significantly lower in DS patients (median 14.7 mumol/l, range 5.5-20 mumol/l) than in the controls (median 16.4 mumol/l, range 12.7-19.5 mumol/l). DS patients with increased IgA activity to gluten weighed less and had lower concentrations of zinc in serum than DS patients with normal IgA activity. Twenty-eight per cent of the DS patients had autoantibodies to the thyroid gland. Our results suggest intestinal malfunction in DS, perhaps related to a defect of immune regulation caused by reduced levels of zinc in serum.

The prolamin antibody reactivity against hordein polypeptides in sera from patients with coeliac disease

The antibody reactivity against the barley prolamin, hordein, was investigated by an immunoblotting technique, in sera from patients with untreated coeliac disease, patients with other gastrointestinal diseases and healthy controls. No characteristic hordein polypeptide antibody pattern could be connected to coeliac disease, as observed in a similar study using different fractions of the wheat prolamin, gliadin. Gliadin- and hordein-immunoadsorbent column experiments demonstrated that the prolamin reactivity originates from the same population of antibodies. It is speculated that distinct antigenic epitopes characteristic for untreated coeliac disease, might reside within a N-terminal repeat region of gliadin.

Amino acid composition of peptides remaining after in vitro digestion of a gliadin sub-fraction with duodenal mucosa from patients with coeliac disease

Sub-fraction 9-2, derived from fraction 9 of a peptic-tryptic-pancreatinic digest of wheat gliadin and previously shown to be toxic to individuals with coeliac disease, was digested in vitro with duodenal mucosa from patients with coeliac disease in remission and with mucosa from normals. Digestion products from coeliac mucosa caused damage to rat liver lysosomes in contrast to digestion products from normal mucosa which had practically no effects on the lysosomes. Ion exchange chromatography of the digestion products, followed by gel permeation chromatography to remove tissue proteins and amino acids allowed the separation of small peptides. Purification of the peptide residues by reversed-phase HPLC on a C18 column resulted in four subfractions, two of which were cytotoxic to rat liver lysosomes. Amino acid analysis of these latter peptide fractions showed that they were both rich in glutamine/glutamic acid, proline, serine and tyrosine. The results support the hypothesis of defective mucosal digestion as being the aetiology of coeliac disease and suggest that the causative agents are small peptides of apparent Mr congruent to 700 Da, with amino acid analysis corresponding to (Glx)3, (Pro)2, Ser and (Glx)3, (Pro)2, Tyr. These hexapeptides are likely to be H-Pro-Ser-Glx-Glx-Glx-Pro-OH and H-Glx-Glx-Pro-Tyr-Pro-Glx-OH.

In vivo induction of gliadin-mediated enterocyte damage in rats by the mannosidase inhibitor, swainsonine: a possible animal model for celiac disease

Simultaneous feeding of gliadin and swainsonine, an inhibitor of alpha-D-mannosidases, in rats disturbed enterocytic maturation as shown by a marked loss of activities of alkaline phosphatase and gamma-glutamyltransferase. Morphologically, simultaneous treatment with gliadin and swainsonine caused destruction and decreased density of microvilli, as shown by electron microscopy. Neither gliadin nor swainsonine when given alone had significant effects on enterocytic enzyme activities or enterocytic morphology. Binding of enterocytic glycoproteins to both gliadin-Sepharose and concanavalin A-Sepharose was significantly increased in rats treated with swainsonine. Because swainsonine causes the formation of hybrid-type oligosaccharides with a high binding affinity to mannose-specific lectins, the observed alterations of enterocytic maturation and morphology are presumably caused by the increased binding of gliadin to enterocytic glycoproteins. A possible analogy in the etiology of celiac disease is discussed.