[Literature library] Human milk oligosaccharides and infant gut microbiota

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:
  1. Fucosylated (35-50%)
  2. Non-fucosylated neutral (42-55%)
  3. 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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[Literature Library] Human milk microbiota and oligosaccharides
 

WYE-EM-008-JAN-22