Peptides identified in egg white gastrointestinal digest as inducers of anorexigenic hormones in STC-1 cells

Abstract

Dietary proteins are potent inducers of satiety and suppress short-term food intake. Protein digestion products can actas pre-absorptive signaling molecules, able to actívate enteroendocrine cells which release a variety of hormones, such as CCK or GLP-1. These hormones modulate the progress of the digestion and satiety. The aim of this work was to investigate the effects of egg white gastrointestinal digests and specific peptides released during digestion on CCK and GLP-1 secretion in enteroendocrine cells. Digests were characterized by mass spectrometry and amino acid analysis and assayed in STC-1 cells. This enteroendocrine cellular model had been previously validated with human jejunal digests in our research group. At the end of the egg white gastrointestinal digestion, 28% of the total nitrogen content corresponded to free amino acids, while the rest was in the form of peptides and intact protein. In fact, traces of ovalbumin and ovalbumin-Y were still detected by SDS-PAGE at the end of the digestion process. In arder to identify the molecules involved in hormonal secretion, intestinal digests were fractionated by size exclusion chromatography (SEC) into three different fractions: > 3 kDa, 3-0.5 kDa and <0.5 kDa, In addition, purified proteins and mixture of free a mino acids were also assayed in this cell line. The highest GLP-1 response was obtained with intestinal digests and SEC-intestinal fractions containing medium-size peptides, between 0.5 and 3 kDa, whereas a mixture of free ami no acids did not induce the release of this hormone. The mixture of free amino acids induced only a weak CCK secretion/which was maximized with peptides1 although peptide size did not clearly influenced CCK response. Interestingly, peptide sequences triggering CCK secretion showed different structural characteristics than those inducing GLP-1 release. This work opens new insights into the field of nutrient sensing at the gastrointestinal tract.