Changes in the relative amounts of α2-3 and α2-6 linked sialic acid on free and protein-bound milk oligosaccharides during lactation
(English)Manuscript (preprint) (Other academic)
Human milk contains large amounts of oligosaccharides, both in free and protein-bound forms. Sialic acid is a common constituent of milk oligosaccharides and is present α2-3 or α2-6 linked to galactose, α2-6 to N-acetyl glucosamine or α2-6 to N-acetyl galactosamine. High-performance anionexchange chromatography with pulsed amperometric detection (HPAEC-PAD) was used to quantify four major sialylated milk oligosaccharides. The concentrations of the individual oligosaccharides were analyzed in milk from five donors, followed separately during six to nine months of lactation. The oligosaccharides containing sialic acid a2-6 linked to galactose ( 6-sialyl lactose and LSTc) decreased more than tenfold during lactation. In contrast, the concentration of 3-sialyl lactose (3-SL) containing sialic acid a2-3 linked to galactose remained constant during nine months of lactation. Disialyl lacto-Ntetraose (DSLNT) which contain sialic acid linked α2-3 to Gal and α2-6 to GlcNAc decreased approximately threefold during lactation. Lectin ELISA was used to analyze sialic acid on the secreted milk glycoprotein bile-salt-stimulated lipase (BSSL ). There was a gradual decrease in the binding of Sambucus Nigra lectin to BSSL, indicating decreased amount of α2-6 linked sialic acid during lactation. In contrast, binding of Maackia Amurensis lectin remained constant, indicating a constant expression of α2-3 linked sialic acid on BSSL during lactation. This suggests a shift from preferentially 6-linked to 3-linked sialic acid on free and protein-bound oligosaccharides during lactation. The shift may reflect changes in sialyltransferase activities and, on a higher level, changes in the population of mammary epithelial cells. This finding may be of importance for the development of a correct immune response to environmental challenges.
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:liu:diva-80000OAI: oai:DiVA.org:liu-80000DiVA: diva2:545000