Placental Metabolomics of Fetal Growth Restriction

Abstract

Fetal growth restriction is an obstetrical pathological condition that causes high neonatal mortality and morbidity. The mechanisms of its onset are not completely understood. Metabolites were extracted from 493 placentas from non-complicated pregnancies in Hamilton Country, TN (USA), and analyzed by gas chromatography-mass spectrometry (GC-MS). Newborns were classified according to raw fetal weight (low birth weight (LBW; <2500 g) and non-low birth weight (Non-LBW; >2500 g)), and according to the calculated birth weight centile as it relates to gestational age (small for gestational age (SGA), large for gestational age (LGA), and adequate for gestational age (AGA)). Mothers of LBW infants had a lower pre-pregnancy weight (66.2 ± 17.9 kg vs. 73.4 ± 21.3 kg, p < 0.0001), a lower body mass index (BMI) (25.27 ± 6.58 vs. 27.73 ± 7.83, p < 0.001), and a shorter gestation age (246.4 ± 24.0 days vs. 267.2 ± 19.4 days p < 0.001) compared with non-LBW. Marital status, tobacco use, and fetus sex affected birth weight centile classification according to gestational age. Multivariate statistical comparisons of the extracted metabolomes revealed that asparagine, aspartic acid, deoxyribose, erythritol, glycerophosphocholine, tyrosine, isoleucine, serine, and lactic acid were higher in both SGA and LBW placentas, while taurine, ethanolamine, β-hydroxybutyrate, and glycine were lower in both SGA and LBW. Several metabolic pathways are implicated in fetal growth restriction, including those related to the hypoxia response and amino-acid uptake and metabolism. Inflammatory pathways are also involved, suggesting that fetal growth restriction might share some mechanisms with preeclampsia.

Keywords: fetal growth restriction; low birth weight; metabolomics; small for gestational age.

Figure 1

Classification models: (A1). Two class (LBW vs. non-LBW) PLS-DA score plot. (A2). VIP metabolites heat-map selected by the dichotomic classification. (B1) Three class (SGA, AGA, and LGA) PLS-DA score plot. (B2) VIP metabolites heat-map selected by the three-class classification. Abbreviations: LBW: low birth weight; PLS-DA: partial least square discriminant analysis; VIP: variable important in projection; SGA: small for gestational age; AGA: adequate for gestational age; LGA: large for gestational age.

Figure 2

Relevant metabolites selected in all class comparisons. (A) Heatmap reporting the ANOVA selected metabolites. Cluster analysis allowed for the recognition of three groups of metabolites based on their concentration mean levels in the three classes (SGA: small for gestational age; AGA: adequate for gestational age; LGA: large for gestational age). (B) Volcano plot of the analyzed metabolites comparing LBW to non-LBW placentae, highlighting the ones showing a p-value < 0.05 and a large fold change (>2.0 or <0.5); in red are the metabolites with a lower concentration in LBW, while in blue are the metabolites with a higher concentration in LBW. (C). UpSet diagram reporting the relevant metabolite selection among the various strategies. Set size indicates the number of metabolites involved in each metabolite selection strategy, while intersection size indicates the number of metabolites selected from each strategy combination.

Figure 3

Box and whisker plot of the VIP metabolites. Red boxes represent the placentae of small for gestational age (SGA) newborns (n = 118), yellow represents the adequate for gestational age (AGA) placentae (n = 326), green represents the large for gestational age (LGA) placentae (n = 49), blue represents the placentae of low birth weight baby (LBW) (n = 124), while purple represents the non-low birth weight baby (non-LBW) (n = 369). The y axes represent the normalized metabolite chromatographic area. GPC = Glycerophosphocoline; HBA = Hydroxybutyric acid; ns = not significance. Ns indicated not significant difference in concentration, * p-value < 0.05, ** p-value < 0.01, *** p-value < 0.001.

Figure 4

Metabolic pathways showing the interplay of selected metabolites.