Gluten Immunogenic Peptides as Standard for the Evaluation of Potential Harmful Prolamin Content in Food and Human Specimen

Abstract

Gluten is a complex mixture of storage proteins in cereals like wheat, barley and rye. Prolamins are the main components of gluten. Their high content in proline and glutamine makes them water-insoluble and difficult to digest in the gastrointestinal tract. Partial digestion generates peptide sequences which trigger immune responses in celiac and gluten-sensitive patients. Gluten detection in food is challenging because of the diversity, in various food matrices, of protein proportions and their immunogenicity. Attempts to develop standard reference materials have been unsuccessful. We present here a summary of recent studies reporting the detection of dominant Gluten Immunogenic Peptides (GIP) sharing epitopes presented in the α-gliadin 33-mer, the most important celiac disease-immunogenic sequence within gluten. GIP were not only detectable and quantifiable in very different kind of difficult to analyze food, but also in stool and urine of celiac patients on a supposedly gluten-free diet (GFD), providing the first simple and objective means to assess adherence to the GFD. Methods to specifically and sensitively detect the most active GIP in food and biological fluids are rational candidates may use similar analytical standard references for determination of the immunopathological risk of gluten exposure in gluten-related diseases.

How to manage celiac disease and gluten-free diet during the COVID-19 era: proposals from a tertiary referral center in a high-incidence scenario

“…Furthermore, the availability of novel point-of-care (POC) testing may be of help during telemedicine counselling. Patients can verify the correctness of their GFD by themselves via POC tests that detect the presence of gluten peptides in urine [ 56 ], They can then discuss the test result with their nutritionist and/or gastroenterologist during a later telemedicine session. These tests can also be repeated during lockdown and quarantine to verify GF products of uncertain quality.…”

Exposure sources, amounts and time course of gluten ingestion and excretion in patients with coeliac disease on a gluten‐free diet

“…In Europe, there was negligible gluten content in the 205 commercially available gluten‐free foods tested, 35 whereas in a US study approximately 5% of the 158 gluten‐free products tested above levels of 20 ppm 36 . Furthermore, these studies might be underestimating gluten content because they typically utilised the R5 antibody sandwich ELISA method which produced high variation of results in interlaboratory proficiency studies 37 and does not detect small hydrolysed gluten fragments or some of the most immunogenic gluten peptides 38,39 . In a systematic review of 24 cross‐sectional studies, gluten contamination of both processed foods (13.2%) and raw ingredients (41.3%) 40 was common.…”

The Gluten Gene: Unlocking the Understanding of Gluten Sensitivity and Intolerance

“… 34 , 69 Two peptides that have attracted most attention and remain intact in the digestive process are the 33-mer (p55–87) and the 25-mer (p31–55) located in the α-gliadins encoded by the Gli-D2 locus on chromosome 6D. 73 , 74 Of these two peptides, the 33-mer is the most digestion-resistant peptide with high immunogenic properties (contains DQ2.5-glia-α1a, DQ2.5-glia-α1b, and DQ2.5-glia-α2 epitopes). 75 , 76 During or after absorption of partially digested gliadin peptides into the lamina propria, specific glutamine residues of the 33-mer peptide are susceptible to pH-dependent transamidation (covalent cross-linking to free amines, for example, lysine residues in other proteins) or direct deamidation to glutamate through the action of extracellular tissue transglutaminase (tTG) expressed in inflamed host tissues.…”