Novel Cholecystokinin Secretion-Stimulating Peptides from Oat Protein Hydrolysate: Sequence Identification and Insight into the Mechanism of Action

Cholecystokinin (CCK), secreted by enteroendocrine cells, plays a vital role in suppressing appetite. This study aimed to evaluate the in vivo effect of oat protein hydrolysate (OPH) on CCK secretion and elucidate the structural characteristics of the responsible peptides and their underlying mechanism of action. OPH was prepared by a simulated gastrointestinal digestion model. Intragastric administration of OPH in mice significantly increased plasma CCK levels. Using size exclusion column chromatography and liquid chromatography-tandem mass spectrometry, ten peptides were successfully identified, and their abilities to stimulate CCK secretion were evaluated in STC-1 cells. Four novel CCK secretion-stimulating peptides, including LLL, QQVFQPQ, QGDVVALPA, and DVNNNANQLEPR, were validated. Among them, QGDVVALPA exhibited the strongest activity. Inhibition experiments demonstrated that the calcium-sensing receptor and its coupled G-protein subtype G_q were involved in QGDVVALPA-stimulated CCK secretion. Additionally, downstream signaling molecules including intracellular Ca²⁺ and Ca²⁺/CaM-dependent protein kinase (CaMKII) were also required for QGDVVALPA to induce CCK secretion. Our findings highlight the potential of oat protein-derived hydrolysate and peptides as functional food ingredients to regulate satiety.