Direct induction of CCK and GLP-1 release from murine endocrine cells by intact dietary proteins

Scope: Consumption of high-protein diets cause elevated levels of CCK and GLP-1. Although unknown, this might be due to protein breakdown by various proteases that originate from the gastrointestinal tract. This study investigated which dietary proteins, hydrolysates, or synthetic-peptides are most potent to affect secretion of CCK and GLP-1 in STC-1 cells known for satiety hormone release. Methods and results: Addition of intact proteins to STC-1 cells exerted strong effects on secretion of satiety hormones. Casein, whey, and pea showed strongest effects on CCK release, whereas casein, codfish, egg, and wheat showed most pronounced effects on GLP-1 release. Egg-hydrolysate stimulated release of CCK and GLP-1, whereas all other tested hydrolysates and synthetic-peptides showed no significant effects on hormone release. Addition of a combination of trypsin and casein-hydrolysate, codfish, egg, egg-hydrolysate, sodium-casein, wheat-hydrolysate, or wheat resulted in additional stimulation of CCK release, compared to only the protein. Addition of a combination of DPP-IV and egg-hydrolysate, ovomucoid, or sodium-casein decreased GLP-1 levels. Conclusion: This study showed that specific intact, or partially digested proteins, in contrast to protein-hydrolysates and synthetic-peptides, stimulated hormone release. We conclude that intact proteins exert strong effects on satiety hormone release, and may therefore provide potent dietary supplements for prevention or treatment of obesity.