Metabolomics analysis of maternal serum exposed to high air pollution during pregnancy and risk of autism spectrum disorder in offspring

Abstract

Background: Previously, numerous epidemiologic studies reported an association between autism spectrum disorder (ASD) and exposure to air pollution during pregnancy. However, there have been no metabolomics studies investigating the impact of pregnancy pollution exposure to ASD risk in offspring.

Objectives: To identify differences in maternal metabolism that may reflect a biological response to exposure to high air pollution in pregnancies of offspring who later did or did not develop ASD.

Methods: We obtained stored mid-pregnancy serum from 214 mothers who lived in California's Central Valley and experienced the highest levels of air pollution during early pregnancy. We estimated each woman's average traffic-related air pollution exposure (carbon monoxide, nitric oxides, and particulate matter <2.5 μm) during the first trimester using the California Line Source Dispersion Model, version 4 (CALINE4). By utilizing liquid chromatography-high resolution mass spectrometry, we identified the metabolic profiles of maternal serum for 116 mothers with offspring who later developed ASD and 98 control mothers. Partial least squares discriminant analysis (PLS-DA) was employed to select metabolic features associated with air pollution exposure or autism risk in offspring. We also conducted extensive pathway enrichment analysis to elucidate potential ASD-related changes in the metabolome of pregnant women.

Results: We extracted 4022 and 4945 metabolic features from maternal serum samples in hydrophilic interaction (HILIC) chromatography (positive ion mode) and C18 (negative ion mode) columns, respectively. After controlling for potential confounders, we identified 167 and 222 discriminative features (HILIC and C18, respectively). Pathway enrichment analysis to discriminate metabolic features associated with ASD risk indicated various metabolic pathway perturbations linked to the tricarboxylic acid (TCA) cycle and mitochondrial function, including carnitine shuttle, amino acid metabolism, bile acid metabolism, and vitamin A metabolism.

Conclusion: Using high resolution metabolomics, we identified several metabolic pathways disturbed in mothers with ASD offspring among women experiencing high exposure to traffic-related air pollution during pregnancy that were associated with mitochondrial dysfunction. These findings provide us with a better understanding of metabolic disturbances involved in the development of ASD under adverse environmental conditions.

Keywords: Air pollution exposure; Autism spectrum disorder (ASD); Metabolomics; Mitochondria; Pregnancy.

Fig. 1.

Metabolic pathways associated with ASD using HILIC with positive ESI and C18 with negative ESI. HILIC: hydrophilic interaction liquid chromatography; ESI: electron spray ionization.

Fig. 2.

Identification of metabolic features associated with ASD risk in offspring during pregnancy. A) Type 1 Manhattan plot for features in the HILIC column (positive ion mode), VIP score vs m/z. 167 m/z features were found above the VIP≥2 threshold. Red dots indicate features that were increased, and green dots features that were decreased in maternal mid-pregnancy serum of offspring with autism; B) Type 1 Manhattan plot for features in the C18 column (negative ion mode), VIP score vs m/z. 222 m/z features were found above the VIP≥2 threshold. C) Volcano plot for features in the HILIC column; D) Volcano plot for features in the C18 column. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3.

Altered metabolic pathways observed in mothers with ASD offspring under exposure to high levels of air pollution during pregnancy. Red circles represent higher metabolite levels, while green circles indicate lower metabolite levels. ADP: adenosine diphosphate; AMP: adenosine monophosphate; LCFA: long-chain fatty acids; NADH: nicotinamide adenine dinucleotide; PKCδ: protein kinase Cδ; Rol: retinol complex; PDHC: pyruvate dehydrogenase; PDK2: pyruvate dehydrogenase kinase 2; PDK2-Pase: pyruvate dehydrogenase kinase 2-phosphatase; Cyt c³⁺: cytochrome C³⁺; TCA: tricarboxylic acid cycle; 7α–OH–4-CA: 7α-Hydroxy-3-oxo-4- cholestenoate.