Structural characteristics of HMOs
- More than 200 different structures have been identified so far
- The diversity and composition of HMOs vary significantly between individual woman and lactation stages of the same woman
- 3 main HMO structural groups:
- Fucosylated (35-50%)
- Non-fucosylated neutral (42-55%)
- Sialylated (12-14%)
HMO utilization strategies of Bifidobacteria
- Genes encoding specific HMO degrading enzymes (glycosidase and transporter) are particularly found in Bifidobacteria
- 2 primary utilization strategies:
- Intracellular way: transporter-dependent
- Extracellular way: glycosidase-dependent
HMO utilization strategies of Bacteroides and Lactobacillus
- HMOs are degraded by Bacteroides to various degrees via a variety of strategies
- Information on HMO utilization strategy of Lactobacillus species is very limited
Cross-feeding effects
- HMOs are partially or completely degraded in the infant colon
- HMO degradation products of a certain bacterial strain can be further degraded by the other strains
- Cross-feeding promotes metabolism of HMOs to the greatest extent, and the growth of non-HMO consumers
- This mechanism is especially important among bifidobacterial species
Associated effects of HMOs
On immune functions
- Direct: by regulating gene expression of epithelial cells, immune cell responses, or immune function in the intestine and other sites
- Indirect: by modulating infant microbiota composition and the metabolites
On intestinal immunity
- The structural similarity of HMOs to the surface glycans of gut epithelial cells enables them to prevent pathogenic infections by binding pathogens to gut epithelial cells
- HMOs can regulate gene expression of gut epithelial cells, which further blocks the contact between pathogens and gut epithelial cells
- HMOs individually or in combination promote the maturation of intestinal epithelium cells
- LNnT and 6’-SL: reduce cell proliferation
- LNnT: reduce permeability of epithelial cells
- 2’-FL, 3-FL and 6’-SL: reduce cell proliferation, promote differentiation and maturation of epithelial cells
On infant microbiome
- Cross-feeding on HMOs contributes to establishment of infant microbiome, by supporting colonization of various bacteria
- HMOs selectively promote the growth of beneficial bacteria
- 2’-FL and LNnT supplemented infant formula could shift the microbiota composition of cesarean section infant group closer to that of the vaginal delivery infant group
Abbreviations:
LNnT = Lacto-N-Neotetraose; 6’-SL = 6’-Sialyllactose; 2’-FL = 2’-Fucosyllactose; 3-FL = 3-Fucosyllactose
Link to the abstract:
https://pubmed.ncbi.nlm.nih.gov/34823774/
Reference:
Zhang B et al. Human milk oligosaccharides and infant gut microbiota: Molecular structures, utilization strategies and immune function. Carbohydr Polym. 2022;276:118738.
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WYE-EM-008-JAN-22