Analysis of sequential hair segments reflects changes in the metabolome across the trimesters of pregnancy

Abstract

The hair metabolome has been recognized as a valuable source of information in pregnancy research, as it provides stable metabolite information that could assist with studying biomarkers or metabolic mechanisms of pregnancy and its complications. We tested the hypothesis that hair segments could be used to reflect a metabolite profile containing information from both endogenous and exogenous compounds accumulated during the nine months of pregnancy. Segments of hair samples corresponding to the trimesters were collected from 175 pregnant women in New Zealand. The hair samples were analysed using gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. In healthy pregnancies, 56 hair metabolites were significantly different between the first and second trimesters, while 62 metabolites were different between the first and third trimesters (p < 0.05). Additionally, three metabolites in the second trimester hair samples were significantly different between healthy controls and women who delivered small-for-gestational-age infants (p < 0.05), and ten metabolites in third trimester hair were significantly different between healthy controls and women with gestational diabetes mellitus (p < 0.01). The findings from this pilot study provide improved insight into the changes of the hair metabolome during pregnancy, as well as highlight the potential of the maternal hair metabolome to differentiate pregnancy complications from healthy pregnancies.

Figure 1

(A) Partial least squares-discriminant analysis (PLS-DA) of healthy pregnancy controls; first-trimester hair segments (red), second trimester (green), third trimester (blue). (B) Leave-one-out cross validation for PLS-DA.

Figure 2

Heat map shows metabolites that differed significantly across the trimesters of normal pregnancies. Red colors represent higher metabolite concentrations, while green colors indicate lower metabolite levels. The relative concentration of metabolite was scaled to have the mean of 0 and standard deviation of 1 (z-score). Only metabolites with p-value and q-value less than 0.05 between trimesters are shown.

Figure 3

Heat map shows the altered metabolic pathways across the trimesters of normal pregnancies. Red colors represent higher metabolic activities, while green colors indicate lower metabolic activities. The metabolic activity of metabolic pathway was scaled to have the mean of 0 and standard deviation of 1 (z-score). Only metabolic pathways with p-value and q-value less than 0.05 between trimesters are shown.

Figure 4

A metabolic network showing how trimester-related metabolic pathways are interconnected with common metabolites. The metabolic pathways are connected by Kamada-Kawai layout that relates the layout of metabolites to a dynamic spring system and minimizes metabolic reactions between metabolites within a metabolic network. The metabolites placed closer together will have stronger springs strength which are calculated by the inverse proportion to the square of the shortest graphical distance between two metabolites (the spring attraction was set to 68). The significantly altered metabolites throughout pregnancy are shown by the red circles and the non-significant metabolites by yellow circles. The red lines connect the significant metabolites. The topology of network is organized to have the most connected metabolites situated in the center of network.

Figure 5

The ratio of hair metabolite levels collected from normal pregnancies as opposed to gestational diabetes mellitus (GDM) at second trimester and third trimester. Red circles represent metabolite level in maternal hairs collected from GDM. Blue triangles represent metabolite level in maternal hairs collected from normal pregnancies that were set to 0. The metabolite levels in GDM relative to the normal pregnancy were adjusted using log 2 scale. Standard deviations are shown by vertical lines. Red asterisks (*) indicate metabolites with p-values and q-values less than 0.01 and 0.17, respectively.

Figure 6

The ratio of hair metabolite levels collected from normal pregnancy as opposed to small for gestational age (SGA) at second trimester and third trimester. Red circles represent metabolite level in maternal hairs collected from SGA. Blue triangles represent metabolite level in maternal hairs collected from normal pregnancy that were set to 0. The metabolite levels relative to the normal pregnancy were adjusted using log₂ scale. Standard deviations are shown by vertical lines. Red asterisks (*) indicate metabolites with p-values and q-values less than 0.05 and 0.6, respectively.

Figure 7

Representation of the hair segmentation.