Potential host-defense role of a human milk vitamin B-12-binding protein, haptocorrin, in the gastrointestinal tract of breastfed infants, as assessed with porcine haptocorrin in vitro.
BACKGROUND
Limited information exists on the biological role of a vitamin B-12-binding protein, haptocorrin, in human milk. The expression of haptocorrin by human mammary epithelial cells and its presence in human milk suggest a potential physiologic function in breastfed infants.


OBJECTIVE
We investigated the extent to which haptocorrin could withstand proteolytic degradation and exert antimicrobial activity under in vitro conditions designed to simulate the gastrointestinal tract of breastfed infants.


METHODS
An in vitro model that simulates infant gastric and intestinal digestion was developed. The structural stability of porcine haptocorrin after exposure to digestive enzymes (pepsin and pancreatin) was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blot analysis, column chromatography, and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The antimicrobial activity of haptocorrin was determined by incubating haptocorrin with enteropathogenic Escherichia coli O127 strain 2348/69 and monitoring bacterial growth.


RESULTS
The structural analysis of haptocorrin exposed to enzymes did not show a decrease in molecular weight, which indicated that haptocorrin can survive proteolytic degradation. Both haptocorrin exposed to digestive enzymes and undigested haptocorrin inhibited the growth of enteropathogenic E. coli and did so to a similar extent. Thus, haptocorrin in vitro not only retains its structure after exposure to proteases but also exhibits antimicrobial activity.


CONCLUSIONS
These results suggest that haptocorrin may exert a host-defense function against pathogens in the gastrointestinal tracts of breastfed infants.
Adkins
Yuriko
Y
Department of Nutrition, the University of California, Davis, CA 95616, USA.
Lönnerdal
Bo
B
D000818:Animals; D015153:Blotting, Western; D001942:Breast Feeding; D002845:Chromatography; D004064:Digestive System / Q000254:growth & development / Q000382:microbiology; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development*; D006801:Humans; D008892:Milk / Q000276:immunology; D008895:Milk, Human / Q000276:immunology*; D008970:Molecular Weight; D010447:Peptide Hydrolases / Q000494:pharmacology; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013552:Swine; D014155:Transcobalamins / Q000737:chemistry / Q000494:pharmacology / Q000502:physiology*
D014155:Transcobalamins; D010447:Peptide Hydrolases