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Quantitation of the immunodominant 33-mer peptide from α-gliadin in wheat flours

by luciano

In wheat there are multiple fractions able to activate the adverse response of the human immune system. Among these fractions the most active is that called 33-mer because it is the most resistant to human digestion and because it contains six copies of the three toxic epitopes and its intermolecular bonds are very strong. It is therefore important to know the quantity of this fraction in the grains. The study of which some parts are reported, examined 57 different types of wheat, ancient and modern, noting that the difference, in all soft wheat and spelt flour, of 33-mer is wide: from 90.9 to 602.6 μg / g made with flour. On the other hand, its presence in monococcum wheat and durum wheat was not detected. These results take on great importance because they allow grains to be chosen with limited or no presence of this important toxic fraction for products that are more suitable for non-celiac gluten sensitive people or those suffering from gluten disorders.

“All gluten protein fractions, namely the alcohol-soluble prolamins and the insoluble glutelins, contain CD-active epitopes3. The prolamin fraction is particularly rich in proline and glutamine and the numerous proline residues lead to a high resistance to complete proteolytic digestion by human gastric, pancreatic, and brushborder enzymes. Studies by Shan et al. (2002) showed that a large 33-mer peptide (LQLQPFPQPQLPYPQPQLPYPQPQLPYPQPQPF) from α2-gliadin (position in the amino acid sequence of α2-gliadin: 56–88) is resistant to cleavage by intestinal peptidases4,5. The 33-mer is widely called the most immunodominant gluten peptide4,6,7, because it contains three overlapping T-cell epitopes, namely PFPQPQLPY (DQ2.5-glia-α1a, one copy), PYPQPQLPY (DQ2.5-glia-α1b, two copies) and PQPQLPYPQ (DQ2.5-glia-α2, three copies)3, which result in the initiation of a strong immune response.

Simultaneously identify the gluten peptides that are most active in activating the human immune system

by luciano

The method aims to identify, through the use of specific antibodies, the most toxic peptides instead of, as with the usual methods used today, the total gluten content. Considering that the research is also focused on producing grains with smaller amounts of toxic peptides, as well as using specific pools of enzymes / bacteria / etc in the preparation of products with the same purpose, the possibility of identifying and “weighing” only the presence, in the final product, more active peptides become a very useful tool. The highlighted study traces the history of the methods used to quantify gluten in food and presents advantages and limitations of the new method. All the methods mentioned, including the new method, have been developed to be able to certify whether a food is safe for celiacs or not, but the new methods become even more interesting for non-celiac and / or pre-celiac gluten sensitive subjects. The toxic fraction harmful to celiacs is the same as in people who are sensitive to gluten NOT celiac (1) but has a very different and less harmful impact: the new method is, therefore, very useful also in this case with the advantage of being able to have a greater tolerance in the result.

NEW IMMUNOCHEMICAL DETECTION METHODS

“Techniques that allow for the simultaneous detection of multiple different peptides are avail able, and are making their way into the field of food allergen detection. Another interesting possibility in gluten detection with the use of a multiplex immunoassay is to narrow down the focus even further to the harmful gluten epitopes. If antibodies were raised against the most relevant gluten epitopes, the detection of these specific epitopes could prove more relevant than detecting the total gluten content. A multiplex immunoassay can be updated by adding antibodies against more epitopes, and therefore can keep up with our increasing knowledge on harmful gluten epitopes. Also, by combining antibodies against the most relevant epitopes in a single detection method, the possibility of a false negative result decreases. Van den Broeck et al have investigated the possibilities of breeding a wheat variety with reduced CD-epitopes, based on small varieties in amino acid sequences between different gluten peptides (van den Broeck et al., 2011). If such a wheat variety could be bred, quantifying the total gluten content of food products containing this variety would be less appropriate. However, a detection method that can detect the presence of the harmful epitopes in these products would be very welcome. If the obstacles for developing a multiplex immunoassay can be overcome, this detection method would help providing consumers with more accurate food labels. This would further improve both food safety and the variety of choice in food products for CD patients everywhere”.

Depeening

Immunochemical Detection Methods for Gluten in Food Products: Where Do We Go from Here?

Note:

(1) – Gluten Immunogenic Peptides as Standard for the Evaluation of Potential Harmful Prolamin Content in Food and Human Specimen.

Ángel Cebolla , María de Lourdes Moreno , Laura Coto and Carolina Sousa

Published: 5 December 2018