Prevention by mannan and other sugars of in vitro damage of rat fetal small intestine induced by cereal prolamin peptides toxic for human celiac intestine

Cell Agglutinating Activity of A-Gliadin-Related Synthetic Peptides

Previous studies have suggested that various A-gliadin-derived peptides actively agglutinate K562CS) cells. These active peptides showed the following common sequences: pro-ser-gln-gln and gln-gln-gln-pro. In this study, we have synthesised and tested the following toxic fragments: the peptide with the 31–55 amino acid sequence, which contains both the toxic sequences, and the peptides 31–43 and 44–55, which contain the sequences gln-gln-gln-pro, and pro-ser-gln-gln, respectively. Both the peptides with either the gln-gln-gln-pro or pro-ser-gln-gln sequences were active in agglutinating all cells. However, the peptide 44–55 agglutinated 100% of the cells at a concentration two times greater than the peptide 31–43. This suggests a relationship between the gln-gln-gln-pro and pro-ser-gln-gln sequences and the damaging effect of gliadins on the coeliac small intestine in individuals affected by coeliac disease. Moreover mannan and oligomers of N-acetylglucosamine were found to be able to prevent the cell-agglutinating activity of the active peptides.

In VitroSystems for the Study of Cereal Proteins Toxic in Coeliac Disease

For a number of years, we have been carrying out investigations intended to clarify the nature of the toxic gliadin peptides, and whether different species and/or cultivars of wheat are tolerated to varying extents by people suffering from coeliac disease. Our investigations have been carried out using three main biological systems: 1) cultures of biopsy specimens of human intestinal mucosa; 2) cultures of rat fetal intestine; and 3) cultures of erythroid K562(S) cells.

Using these systems, we have tested several peptide mixtures prepared from gliadin and non-gliadin fractions extracted from wheats having various degrees of ploidy and from other cereals. Fraction preparation has been carried out by means of sequential digestion with pepsin and trypsin under experimental conditions simulating protein digestion in man. The results obtained indicate that the pathological symptoms associated with intolerance to gluten are largely due to the cytotoxic activity of wheat gliadin peptides toward immature enterocytes.

In vitro cytotoxic effect of bread wheat gliadin on the LoVo human adenocarcinoma cell line

The pathogenesis of celiac disease is not completely understood but, although the initial step of the process is still unclear, an altered immune response seems to play a major role. Previous studies of the biological properties of gliadin have highlighted its cytotoxic effects, and the aim of this study was to develop an in vitro technique to study them. The LoVo (human colon adenocarcinoma) cell line grown in two-dimensional cultures was exposed to different concentrations of digested bread wheat gliadin (62, 125, 250, 500 and 750 microg/ml) for 48 h, after which cell growth and oxidative balance (the content of reduced glutathione (GSH), and peroxidase, transferase and reductase activity) was evaluated. Other food proteins were used as controls. Our data revealed a statistically significant inhibition of cell growth in proportion to the gliadin concentration (from 26 to 100%), combined with a decrease in GSH content (-38% at 500 microg/ml) and reduced enzymatic activity (-30% at 500 microg/ml). The controls did not show any noxious effect. Our results confirm the usefulness of LoVo cells in evaluating gliadin cytotoxicity and that they can be used to investigate the biological properties of gliadin.

In vitro screening of food peptides toxic for coeliac and other gluten-sensitive patients: a review

Experience gained through investigations on coeliac disease makes it possible to propose a screening method based on agglutination of isolated K562(S) cells to evaluate the occurrence in food protein of amino acid sequences that are able to adversely affect coeliac and related gluten-sensitive patients. The method consists of in vitro sequential peptic and tryptic digestion of food protein fractions under optimal pH, temperature and time conditions and in vitro incubation of the digest with K562(S) cells; the toxic potential is detected as an agglutination of K 562 (S) cells after a short incubation. Other in vitro test systems, including atrophic coeliac intestinal mucosa and rat fetal intestine, can be used to confirm the results obtained with the isolated cells. A fractionation step of the proteolytic digest on a sepharose-mannan column before exposure of the in vitro systems to the separated peptide fractions adds to the sensitivity of the method. This screening method is not only very useful to investigate action mechanisms in coeliac disease, but also to assess the safety of genetically-modified plant foods and novel foods for gluten-sensitive patients.

Binding of gliadin to lymphoblastoid, myeloid and epithelial cell lines

The aim of our work was to investigate the in vitro reactivity of gliadin peptides of natural and synthetic origin with various cell lines. We have found that all tested cell lines of human, mouse and rat origin were agglutinated by enzymically digested gliadin (peptic-tryptic- and peptic-tryptic pancreatic digest of alpha-gliadin) in a concentration dependent manner. In order to test the specificity of binding, inhibition studies were performed using a panel of sugars as well as natural and synthetic peptides derived from gliadin. We have found that among twelve tested sugars only fetuin and phosphomannan were able to inhibit the agglutination of K562 cells with peptic-tryptic- but not with peptic-tryptic pancreatic digest of alpha-gliadin. The lack of inhibition by gliadin peptides and most of the saccharides suggests that agglutinating activity of gliadin is the result of a nonspecific binding of gliadin to the cell membrane.

Agglutinating activity of wheat gliadin peptide fractions in coeliac disease

The K 562 (S) cell agglutinating activity of peptides obtained from in vitro digestion of bread wheat gliadins has been shown to be associated with a small fraction (coded as Fraction C), that can be easily separated by affinity chromatography of the whole digest on a sepharose 6-B-mannan or sepharose 6-B-oligomers of N-acetyl-glucosamine. Although the whole gliadin digests from 12 durum wheat varieties were unable to agglutinate K 562 (S) cells, all these digests were found to contain an active Fraction C. The lack of agglutinating activity of the whole durum wheat gliadin digests has been shown to be associated with the presence in these digests of another peptide fraction (coded as Fraction B) that is eluted much earlier from the sepharose 6-B-mannan column and is able to inhibit the cell agglutinating activity of Fraction C. Such an active Fraction B is not present in bread wheat gliadin peptides, although peptides with the same elution profile as Fraction B have been detected.

Mannan and oligomers of N-acetylglucosamine protect intestinal mucosa of celiac patients with active disease from in vitro toxicity of gliadin peptides

Wheat flour and other cereals toxic for celiac patients contain an alcohol-soluble protein fraction that, under experimental conditions simulating in vivo protein digestion, yields peptides that agglutinate undifferentiated K 562(S) cells. In contrast, cereals well tolerated in celiac disease (i.e., rice and maize) do not. Furthermore, purified A-gliadin peptides that damage in vitro-cultured flat celiac mucosa are powerful agglutinins for K 562(S) cells, whereas A-gliadin peptides that do not show any adverse in vitro effect on celiac intestine lack agglutinating activity. Mannan, acetylglucosamine, and its oligomers (N,N'-diacetylchitobiose and N,N',N"-triacetylchitotriose) were able to prevent and reverse cell agglutination induced by peptides from all the toxic cereals. Moreover, mannan and N,N',N"-triacetylchitotriose exhibited a protective effect on intestinal mucosa specimens of patients with active celiac disease cultured with wheat protein-derived peptides. These data are consistent with the hypothesis that the agglutinating and toxic peptides are bound by carbohydrates.