Gluten, gliadin and GIP


What is gluten?

Gluten is a mixture of proteins present in grains as  wheat, barley and rye, and some varieties of oats 12. Wheat gluten is composed of two types of proteins: gliadins (soluble in alcohol) and glutenins (insoluble in alcohol). Although most dietary proteins are digested to single amino acids, dipeptides or tripeptides by gastrointestinal proteases, gluten proteins are not fully digested by gastric, pancreatic and intestinal membrane proteases and remain in the gastrointestinal tract, where one part goes through the mucous membrane and the other part is excreted in stool. It has also been proved that GIP can also be excreted in the urine within a few hours of gluten consumption 11,13,16.


What is gliadin?

Gliadin is a mixture of alcohol-soluble gluten proteins that contain some of the immunogenic peptides, which are toxic for celiac patients. Gliadin contains several components, which can be divided into groups: α, β, and γand ω. Among the most toxic peptides, the α-gliadin 33-mer is one that is resistant to digestion and was identified as one of the main immunogenic peptides for celiac patients 1.


What are GIP?

The peptide complex that generates most of the immunotoxic reaction to gluten in celiac patients are Gluten Immunogenic Peptides (GIP). They are fragments of gluten proteins that are resistant to gastrointestinal digestion and trigger immunologic reactions in celiac patients. GIP determination can be simplified by quantifying the peptides that are similar to those found in the α-gliadin 33-mer sequence, the dominating immunogenic peptide in wheat gluten, which reacts to the monoclonal antibodies G12 14 and A1 used in the iVYDAL In Vitro Diagnostics® products, technology developed and patented by the University of Seville and Biomedal SL.

The resistance of GIP to gastrointestinal digestion ensures that a significant part of the gluten ingested is excreted. Therefore, the detection of GIP in feces and urine is a precise and direct marker for the monitoring of the gluten-free diet 15,16.


Which methodology is used to detect and quantify GIP?

The methodology is based on the detection and quantification of GIP in human samples (stools or urine) via the specific monoclonal antibodies, A1 or G12, which recognize epitopes in those peptides 14 . The techniques employed are sandwich enzyme-linked immunosorbent assay (ELISA) and lateral flow immunochromatography (LFIA).