Composition and structure elucidation of human milk glycosaminoglycans

To date, there is no complete structural characterization of human milk glycosaminoglycans (GAGs) available nor do any data exist on their composition in bovine milk. Total GAGs were determined and the extracts from human and bovine milk samples were subjected to digestion with specific enzymes, treatment with nitrous acid, and agarose-gel electrophoresis and to HPLC for their structural characterization. Quantitative analyses yielded ∼7 times more GAGs in human than in bovine milk. In particular, galactosaminoglycans, chondroitin sulfate (CS) and dermatan sulfate (DS), were found to differ considerably from one type of milk to the other. In fact, hardly any DS was observed in human milk, but a low-sulfated CS having a very low charge density of 0.36 was found. On the contrary, bovine milk galactosaminoglycans were demonstrated to be composed of ∼66% DS and 34% CS for a total charge density of 0.94. Structural analysis performed by heparinases showed the prevalence of fast-moving heparin (FM-Hep) more than heparan sulfate that account for ∼30-40% of total GAGs in both milk samples showing lower sulfation in human (2.03) compared to bovine (2.28). Hyaluronic acid was found in minor amounts. This study offers the first full characterization of the GAGs in human milk, providing useful data to gain a better understanding of their physiological role, as well as of their fundamental contribution to the health of the newborn.