Structures and application of oligosaccharides in human milk

Abstract

Comparative study of the oligosaccharide profiles of individual human milk revealed the presence of three different patterns. Four oligosaccharides containing the Fucalpha1-2Gal group were missing in the milk of non-secretor, and three oligosaccharides containing the Fucalpha1-4GlcNAc group were missing in the milk of Lewis negative individuals. Disappearance of some major oligosaccharides in these samples led to the finding of five novel minor oligosaccharides, which were hidden under the missing oligosaccharides. Following these studies, structures of many novel milk oligosaccharides were elucidated. At least 13 core oligosaccharides were found in these oligosaccharides. By adding alpha-fucosyl residues and sialic acid residues to these core oligosaccharides, more than one hundred oligosaccharides were formed. All these oligosaccharides contain lactose at their reducing termini. This evidence, together with the deletion phenomena found in the milk oligosaccharides of non-secretor and Lewis negative individuals, suggested that the oligosaccharides are formed from lactose by the concerted action of glycosyltransferases, which are responsible for elongation and branching of the Galbeta1-4GlcNAc group in the sugar chains of glycoconjugates on the surface of epithelial cells. Therefore, oligosaccharides in human milk could include many structures, starting from the Galbeta1-4GlcNAc group in the sugar chains of various glycoconjugates. Many lines of evidence recently indicated that virulent enteric bacteria and viruses start their infection by binding to particular sugar chains of glycoconjugates on the target cell surfaces. Therefore, milk oligosaccharides could be useful for developing drugs, which inhibit the infection of bacteria and viruses.

Figure 1.

Three typical fingerprinting patterns obtained from the oligosaccharide fraction of milk sample, collected from a single donor. The fraction numbers as indicated by “TUBE NUMBER” in abscissa were obtained by Sephadex G-25 column chromatography of human milk oligosaccharide fraction. Aliquot of the fractions were spotted at the origin of a sheet of a filter paper, and subjected to chromatography using ethylacetate/pyridine/acetic acid/water (5:5:1:3) as solvent. Black spots represent oligosaccharides visualized by alkaline-AgNO₃ reagent, and hatched ones encircled by black line represent those detected by both alkaline-AgNO₃ reagent and thiobarbituric acid reagent. Spots shown by dotted lines were missing in the pattern. Grey spots detected at the positions of missing oligosaccharides are minor oligosaccharides hidden under the major oligosaccharides. A, the pattern obtained from milk samples of Le^a+b+ individuals; B, the pattern obtained from milk samples of Le^a+b− (non-secretor) individuals; C, the pattern obtained from milk samples of Le^a−b− individuals. Revised from the figure in Glycoconj. J. 17, 443–464 (2000) with kind permission from Springer Science+Business media.

Figure 2.

Elongation of lactose and N-acetyllactosamine group of the sugar chain of glycoconjugates by the action of iGnT and IGnT. R represents the aglycon moieties of glycoconjugates. Revised from the figure in Chang Gung Medical J. 26, 620–636 (2003).

Figure 3.

Biosynthetic pathways leading to various core oligosaccharides from GlcNAcβ1-3Galβ1-4Glc and GlcNAcβ1-6(GlcNAcβ1-3)Galβ1-4Glc.

Figure 4.

Structures of milk oligosaccharides containing the sialyl-Le^a group (A–D), and three human milk oligosaccharides (C–E), which do not contain the known core oligosaccharides. Taken from the figure in Chang Gung Medical J. 26, 620–636 (2003).