101: Unbiased metabolomics reveals polycyclic aromatic hydrocarbon exposure is associated with alterations in placental glutamate metabolism

Abstract

Prenatal exposure to polycyclic aromatic hydrocarbons (PAHs) is associated with adverse outcomes including small for gestational age infants. Exposure to PAHs largely comes from tobacco smoke, consumption of grilled meat and through the environment due to the incomplete combustion of fossil fuels. We have previously shown that PAH exposure disrupts the placental transcriptome. In this study we utilized unbiased metabolomics of the placenta to measure alterations of the placental metabolome with PAH exposures. Placental levels (N=30) of the PAHs benzo[a]pyrene (BaP), and benzo[b] fluoranthene (BbF) were measured using gas chromatography followed by quadrupole mass spec. Quantitation was performed using external calibration curves. Metabolites were extracted from 100mg of placenta tissue, and subjected to liquid chromatography-mass spectrometry. Identified metabolites were quantified by normalizing against their respective internal standard. Metabolites which were identified from differential analyses between high and low PAH exposures were mapped to the Human Metabolome Database (HMDB) using CAS numbers and uploaded to MetaboAnalyst. Six metabolites were found to be differentially regulated between the high and low exposure groups including 4-hydroxy-L-glutamic acid (0.97 log fold change, p=0.001), D-gluconic acid (1.34 log fold change, p=0.002) and D-saccharic acid 1,4-lactone (-2.52 log fold change, p< 0.01). Analysis of pathways which are enriched for these metabolites revealed an alteration in “D-glutamine and D-glutamate metabolism,” p=0.018 and “Alanine, aspartate and glutamate metabolism,” p=0.039. We found alterations of metabolites in the glutamine and glutamate metabolism pathways by virtue of PAH exposure level in the placenta. Glutamine and glutamate exchange in the placenta is important to supply the growing fetus with the appropriate amino acids for growth. Such alterations in metabolism due to environmental exposures warrant further study to determine underlying causes of the growth restriction observed in these infants.