Gluten Metabolism in Humans. Involvement of the Gut Microbiota.

Gluten proteins are the major storage proteins that are deposited in the starchy endosperm cells of developing wheat grain. These proteins have the capacity to form a viscoelastic network, and thus wheat is used in numerous processed foods. Therefore, a large amount of gluten protein is ingested by humans. However, because of their high proline and glutamine content, gluten peptides are relatively resistant to complete digestion by human digestive proteases because those enzymes are deficient in prolyl endopeptidasic activity. The incomplete digestion of gluten proteins generates high molecular weight oligopeptides that remain in the lumen of the small intestine; some of these are capable of triggering the inflammatory process associated with celiac disease (CD). Nevertheless, there are several reasons why gut microbiota should be taken into account when considering the metabolism of proteins in the human intestine. For example, there are bacteria in the oral cavity that have the ability to hydrolyze gluten peptides, and there are bacteria in the large intestine with the ability to digest gliadin peptides. These bacteria could generate different digestion processes for gluten proteins in CD patients and in healthy people. Therefore, this review examines gluten metabolism throughout the gastrointestinal tract, and the role of the gut microbiota in this process. © 2014 Elsevier Inc. All rights reserved.