Human milk glycosaminoglycans. Handbook on dietary and nutritional aspects of human breast milk

Glycosaminoglycans (GAGs) are natural complex linear heteropolysaccharides able to regulate many cellular events and physiological processes due to their strong interactive capacity. This chapter focuses not only on the recent comparative results on structural characterization of human and bovine milk GAGs, but also provides the first quantitative data on GAGs content both in term and preterm milk during the first month of lactation. Great differences exist between human and bovine milk under qualitative and quantitative point of view. In particular, chondroitin sulfate (CS) and dermatan sulfate (DS) differ considerably between the two types of milk. Hardly any DS is observed in human milk, on the contrary a low-sulfated CS is found in large amount. Furthermore, structural analysis shows the prevalence of fast-moving heparin (FM-Hep) that account for ~30-40% of total GAGs in both milks. Hyaluronic acid is present in minor amounts. Under quantitative point of view, GAG content in human milk was about 7 times higher compared to bovine milk. During the first month of lactation total GAG concentration shows a progressive decrease both in term and preterm milks, with absolute amounts constantly and significantly higher in preterm milk. The highest values are present at day 4 (9.3 g/L in preterm milk and 3.8 in term milk), followed by a decrease to 4.3 and 0.4 g/L respectively at day 30. As a consequence, breastfed infants ingest daily consistent amounts of GAGs which, due to their particular structure, may play an active role in the defence mechanisms of the newborn. In fact, as at intestinal level no specific enzyme is present, undigested human milk GAGs could play an important role as glycomimetics against several pathogens (viruses, bacteria and their toxins) through a receptor-like mechanism which prevents their adhesion to intestinal cells. Furthermore, human milk GAGs, due to their well known antioxidant and antiiflammatory activities, may play important defence roles. Finally, once in the colon, they could be degraded by resident bacteria and, behaving as prebiotics, contribute to stimulate the development of the bifidigenic microflora.