Novel Dipeptidyl Peptidase IV Inhibitory and Antioxidant Peptides Derived from Human Gastrointestinal Endogenous Proteins

Human gastrointestinal endogenous proteins (GEP) include the proteins mucins, serum albumin, digestive enzymes, and proteins from sloughed epithelial and microbial-cells. GEP play a vital role in the digestion of food, but are also simultaneously digested by proteases and peptidases of the gastrointestinal tract (GIT). Recent studies suggest that during gastrointestinal digestion, similar to dietary proteins, GEP may also give rise to bioactive peptides. In the present study, the protein sequences of 11 representative GEP were subjected to simulated in silico GIT (SIGIT) digestion. Following SIGIT digestion, 19 novel GEP-derived peptide sequences were selected using quantitative structure activity relationship rules for chemical synthesis. The peptides were then tested for their in vitro dipeptidyl peptidase IV (DPP-IV) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition, and for their ferric reducing antioxidant power (FRAP). Two novel DPP-IV inhibitory peptides with the amino acid sequences RPCF (IC₅₀ = 800.51 ± 49.00 µM) and MIM (IC₅₀ = 1056.78 ± 61.11 µM), and five novel antioxidant peptides CCK, RPCF, CRPK, QQCP and DCR were identified. The results of this study indicate that GEP are a significant source of bioactive peptides with potential novel bioactive peptide fragments within their sequences.