Acute Embryotoxicity of Mono-2-Ethylhexyl Phthalate (MEHP) in Mice: Nutrition, Epigenomics, and Environment.

Abstract

Mono-2-ethylhexyl phthalate (MEHP) is the primary metabolite of di-2-ethylhexyl phthalate (DEHP), a ubiquitous toxicant used in the production of plastics. Studies have associated prenatal phthalate exposure with a spectrum of adverse health outcomes including neurodevelopmental disorders, although mechanisms are unknown. The importance of adequate fetal nutrition for neurodevelopment has been well-studied, but the role of histiotrophic nutrition pathways (HNPs) in embryonic development is not well characterized. This work aimed to 1) characterize mechanisms by which nutrient starvation may alter epigenetic programming during development, 2) evaluate the teratogenic potential of MEHP exposure, 3) examine MEHP’s impact on HNPs and epigenetic programming, and 4) contrast the transcriptomic and epigenomic effects of MEHP exposure and adverse neurodevelopmental outcomes. Whole embryo culture was used to investigate rodent conceptuses during early organogenesis. Treatment with leupeptin, a protease inhibitor known to decrease HNPs, altered one-carbon (C1) metabolism and decreased global DNA methylation in the embryo (EMB) and visceral yolk sac (VYS). MEHP treatment reduced embryonic growth, increased the prevalence of open neural tubes (NTD) in EMB, and increased susceptibility to oxidation. After 6-h MEHP treatment, decreased EMB and VYS expression of genes in pathways involved in the metabolism of amino acids, energy metabolism, and oxidative phosphorylation occurred. Total HNP function, defined as the clearance of extra-conceptal proteins into the conceptal tissues and fluids, was reduced in a dose-dependent manner after 3-h MEHP treatment. C1 metabolism was increased by 24-h MEHP treatment, suggesting time-dependent response in nutrient uptake and metabolism due to exposures. Global embryonic DNA methylation was decreased after 24 h exposure to MEHP and in EMB with NTDs. Global histone methylation at the H3K4 and H3K27 loci was increased in EMBs with NTDs and treated VYSs. Parallel transcriptomic and epigenomic analysis examined the effects of MEHP treatment and also NTD status. Pathway analysis of expression and DNA methylation data revealed disrupted nutrient metabolism, increased xenobiotic metabolism, and induction of pathways governing cellular fate such as increased autophagy. This research demonstrates that MEHP may induce nutrient starvation and redox control of autophagy (NSRCA), and these findings suggest that NSRCA may play a crucial role in teratogenesis.