The Role Of Fucosylated And Sialylated Human Milk Oligosaccharides In Infant Nutrition
Human milk oligosaccharides are the third most abundant component of human milk after lactose and lipids, reaching between 5 and 20 g/L in mature human milk.
The HMOs are all based on five monosaccharides; glucose, galactose, N-acetyl-glucosamine, fucose, and sialic acid, also known as N-acetylneuraminic acid . The monosaccharides fucose and sialic acid are also somewhat unusual and interesting. Fucose is structurally different from other 6-carbon monosaccharides present in mammals as it lacks a hydroxyl group on the carbon at the 6-position (C-6) and it has, the L-configuration whereas most other monosaccharides have the D-configuration . Sialic acid is not only a component of HMOs but is also very important in brain development . There are three major types of HMOs: (1) fucosylated HMOs such as 2′-fucosyllactose (2′-FL), (2) sialylated HMOs such as 3’-sialyllactose (3’-SL) and (3) neutral HMOs such as lacto-N-neotetraose (LNnT). The most abundant HMO in breast milk of about 80% of all women is 2′-FL, which constitutes up to 30% of the total HMOs . There are also wide differences in the production of HMOS by individual women. This is due to the presence or absence of the fucosyltransferase 2 (FUT2) secretor gene. Women with an active FUT2 enzyme are referred to as Secretors as they secrete a substantial amount of 2′-FL. Women with an inactive FUT2 secretor gene lack 2′-FL and are referred to as Non-secretors. The abundance of 2′FL in breast milk is an indicator of secretor status .