Role of Human Milk Oligosaccharides in Feto‐placental Endothelial Function in Gestational Diabetes Mellitus
Authors: Jantscher‐Krenn Evelyn , Aigner Johanna , Lam Uyen , van Poppel Mireille , Bode Lars , Desoye Gernot 
Published: November 2023

Background & Objective

Human milk oligosaccharides (HMO) are a diverse group of highly bioactive glycans in breast milk. We have recently shown that HMO are also present in maternal serum early in pregnancy. This raises the question whether HMO can cross the placental barrier and reach the fetal circulation. If so, HMO might directly impact the feto‐placental unit, potentially affecting endothelial functions in the placenta and fetal vasculature with implications for placental development and fetal programming. Therefore, potential changes in HMO composition/concentration due to maternal metabolic derangements such as in gestational diabetes mellitus (GDM) might contribute to altered vascular functions as seen in GDM. Thus, we here asked a) whether HMO can indeed be detected in cord blood serum, b) whether their composition and concentration are different in GDM pregnancies, and c) whether HMO impact feto‐placental endothelial cells.

Methods

HMO were isolated from mixed cord blood serum samples collected from healthy (n=21) and GDM (n=20) term pregnancies at the university hospital. Briefly, after addition of the internal standard raffinose, serum was delipidated, deproteinated and desalted. Following 2AB‐labeling, purified HMO were analyzed using HPLC with fluorescence detection. Peaks were annotated according to retention times of HMO standards. Identity of most prominent HMO peaks was confirmed by exoglycosidase digest. Primary feto‐placental endothelial cells (fpEC) were isolated from healthy term pregnancies (n=15). To investigate the effects of HMO on fpEC, cells were pre‐treated with HMO isolated from breast milk (24h) and subjected to an in vitro 2D network formation assay.

Results

HPLC‐FL analysis of cord blood serum revealed the presence of 15 HMO, with a total concentration of 667±252ng/ml (mean±SD). The most abundant HMO were 3′Sialyllactose, 2′Fucosyllactose, Lactodifucotetraose, and two oligosaccharides also found in maternal serum but not in human milk, 3′‐ and 6′Sialyl‐N‐acetyllactoseamine. Total HMO concentrations were not different in GDM versus healthy pregnancies. However, cord blood 3′SL concentration was higher in GDM compared to normal pregnancies (187±80ng/ml vs. 140±43ng/ml, p=0.0384). In network formation assays, 125ug/ml pooled HMO increased total tube length in fpEC by 35± 27% (p=0.018).

Conclusion

Our study provides the first evidence that HMO are present in the fetal circulation and affect fpEC in vitro, pointing towards a previously unappreciated biological role of HMO in the feto‐placental unit. The higher concentration of 3′SL in cord blood of GDM pregnancies suggests a contribution to altered endothelial function in GDM and warrants further investigations.

Support or Funding Information

The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007‐2013/under REA grant agreement number 627056.