Peptides released by gastrointestinal digestión of milk and egg proteins as CCK and GLP-1 inducers

Abstract

During gastrointestinal digestion, food proteins are hydrolysed into peptides and free amino acids. These digestion products activate different receptors at intestinal level, among others, those involved in the secretion of satiety hormones by enteroendocrine cells. These cells sense the luminal contents and play an important role in regulating appetite, gastric emptying and ileal brake. The aim of this work is to evaluate the ability of gastrointestinal digests of casein, whey and egg white proteins to induce CCK and GLP-1 secretion, and to identify the molecules responsible for this effect. Gastrointestinal digests were prepared following an internationally harmonised digestion protocol and were assayed in an enteroendocrine cell model which had been previously validated with human digests obtained at jejunum2. Gastric and intestinal digests showed a different behaviour depending on the susceptibility of food proteins to the gastrointestinal enzymes. CCK release was rnaximised with intestinal digests from casein and whey protein. However, the gastric egg white digests, which contained undigested proteins and large peptides, induced CCK release to a larger extent than intestinal digests. For GLP-1, intestinal digests produced a higher hormonal secretion than the corresponding gastric digests. Non-digested proteins or free amino acids did not behaved as potent CCK and GLP-1 secretagogues, and therefore, peptides were pointed out as the molecules involved in enteroendocrine cell activation. Several synthetic peptides were also assayed under these conditions revealing that the ability of peptides to secrete hormones is related to the peptide size but also to peptide sequence. These results have physiological relevance dueto the location of CCK and GLP-1 secreting cells in the intestine and open the possibility to modulate food intake by controlling protein degradation and peptide release during gastrointestinal digestion.