Human Milk K-Casein and Inhibition of Helicobacter pylori Adhesion to Human Gastric Mucosa

Readily digested caseins, which account for almost half of the protein content in human milk, are important as nutritional protein for breast-fed infants. It has also been advocated that part of the antimicrobial activity of human milk resides in the caseins, most likely the glycosylated K-casein. To explore this possibility, we purified K-casein from human milk to homogeneity by a two-step size-exclusion chromatography procedure. Purified human K-casein, in contrast to K-casein purified from bovine milk, effectively inhibited the cell lineage-specific adhesion of fluoroisothiocyanate-labeled Helicobacter pylori to human gastric surface mucous cells. The inhibitory activity was abolished by metaperiodate oxidation and considerably reduced by preincubation with α-L-fucosidase but not with α-N-acetylneuraminidase or endo-β-galactosidase. These results strongly support the view that fucose containing carbohydrate moieties of human K-casein are important for inhibition of H. pylori adhesion and, thus, infection. They also suggest that breast-feeding may protect from infection by H. pylori during early life and that species-specific glycosylation patterns, as illustrated by human and bovine κ-casein, partly determine both the narrow host spectrum of this human gastric pathogen and the capacity to resist infection.