Functions of Milk Oligosaccharides

Human milk contains a large variety of oligosaccharides (HMOs) with the potential to modulate the gut flora, to affect different gastrointestinal activities and to influence inflammatory processes. Human intervention or clinical studies are still missing as the large amounts of milk oligosaccharides needed are not available yet. Therefore, there is great interest evaluating sources of oligosaccharides other than human milk. Although the amount of oligosaccharides in milk of most animal species is low compared to human milk, recent data indicate significant differences among milk from farm animals. Whether some of these oligosaccharides are good candidates for human studies needs to be further investigated. Currently, there is only a limited amount of quantitative data on the total amount of oligosaccharides and on individual components in animal milk, e. g. in bovine, goat or buffalo milk.

The HMO content is about 5 – 15 g/L. The quantity does not only depend on the lactational stage of the mother but is also affected by the expression of specific glycosyltransferases in the mammary gland. Genes coding for the blood group of the ABO(H), the Lewis type and the secretor status determine the presence of α1-2-, α1-3- and/or α1-4-fucosylated core structures of oligosaccharides. In addition, different patterns of sialylation (oligosaccharide bound N-acetylneuraminic acid), i.e., α2-3- and/or α2-6-linkages, were found and increase the variability of human milk oligosaccharides to a number of more than 150 compounds characterized so far.

Since the 1950s, oligosaccharides from human milk have been thought to be growth promoting factors for the bifidobacteria dominated gut flora mainly found in breast-fed infants. However, these carbohydrates may have more specific effects in the gastrointestinal tract by acting as soluble analogues to epithelial receptors for specific microbes and thus preventing their adhesion to the intestinal wall. Since the specificity required for this function is high, it might be expected that the anti-adhesive and even anti-infective properties vary individually.
In the presentation a brief summary will be given on the differences between human milk oligosaccharides and those from animals. The focus will be on the potential influence of a specific oligosaccharide pattern on biological processes within the intestinal tract and on systemic effects in inflammatory reactions.