Substrate specificity of exopeptidases in small intestinal mucosa determines the structure of food-derived collagen peptides in rat lumen and blood

Gly-Pro-Hyp-Gly is the most common motif in collagen. Ingestion of collagen hydrolysate (CH) has been reported to significantly increase Pro-Hyp and Hyp-Gly in human peripheral blood. However, the elevation of Gly-Pro content remains negligible. This study seeks to elucidate the underlying reasons behind the bioavailability of CH-derived peptides using in vivo and in vitro digestion. After oral administration of CH (800 mg/kg body weight) to rats, Pro-Hyp significantly increased in the lumen, small intestinal tissue, and blood from the abdominal vein, while only negligible amounts of Gly-Pro were detected. In vitro digestion of CH by digestive exopeptidases, including aminopeptidase N, leucine aminopeptidase, and carboxypeptidase A predominantly generated Gly-Pro. Interestingly, the digestion of CH with crude extract of small intestinal mucosa predominantly generated Pro-Hyp and negligible amounts of Gly-Pro. Furthermore, synthetic Gly-Pro was rapidly degraded by crude extract of the intestinal mucosa, while Pro-Hyp showed higher resistance. These facts indicate prolidase activity in the mucosa plays a crucial role in determining collagen-derived peptides in the body.