Peptidomic profiling of human and bovine milk and across infant digestion (622.5)

Abstract

Milk co‐evolved with mammalian infants to be nourishing and immunoprotective. Many milk proteins have no known function intact. However, fragments of milk proteins (peptides) released by enzymatic degradation have actions, including immune system modulation and antimicrobial action.The aims of this research were 3‐fold: 1) identify the extent of human and bovine milk protein proteolytic cleavage within the mammary gland and in the infant stomach; 2) identify the mechanisms for their release from the intact protein; and 3) identify peptide actions. Infant gastric aspirates were collected via a naso‐gastric tube 2 hours after feeding. Human milk, bovine milk and gastric aspirates were profiled for peptides by nano‐chip liquid chromatography quadrupole time‐of‐flight tandem mass spectrometry (Chip‐Q‐TOF). Hundreds of milk peptides were identified in both human and bovine milks, most of which derived from the casein family. Most peptides were present in all human milks and all bovine milks sampled. Many low abundant milk proteins were the source of numerous peptides, whereas some high abundant proteins yielded no peptides. All peptides were derived from specific portions of the parent protein. These findings suggest a well‐regulated proteolytic system in the mammary gland of both cows and humans. Bioinformatic analysis of the cleavage sites suggested several proteases native to milk were active both within the mammary gland and the infant stomach. In the stomach, despite evidence that the main gastric enzyme, pepsin, is non‐functional in infants, many of the proteolytic sites were consistent with pepsin cleavage. Over 10% of peptides identified in milks and gastric aspirates had over 50% sequence homology with peptides previously annotated for antimicrobial or immunomodulatory function. As an ensemble, human milk peptides inhibited in vitro growth of attenuated pathogenic strains of Escherichia coli and Staphylococcus aureus.