Introduction: Triphenyl phosphate (TPHP) is a chemical flame retardant and plasticizer which is added to consumer and industrial products. The developmental origins of health and disease hypothesis postulate that in utero exposures can have later-in-life effects on the developing fetus and can alter fetal gene expression. This study aimed to determine whether epigenetic modifications occurred following in utero TPHP exposure in mice and whether these changes were dose and/or sex-dependent.
Methods: Pregnant C57Bl/6 mice were treated with 0, 5, 25, or 50 mg/kg of TPHP on gestational days (GD) 8, 10, 12, and 14 via intraperitoneal injection and fetal livers were collected on GD 19. Changes in the levels of acetylation of H3 and H4, as well as methylation of H3K9 and global DNA methylation were assessed in the fetal livers by western blot.
Results: Results showed that there was a significant decrease in fetal DNA methylation following in utero exposure to 50 mg/kg TPHP compared to the control (0 mg/kg) independent of the sex of the fetus. While there were no significant alterations compared to controls in any histone modifications at any dose or sex following in utero TPHP exposure, we did note a decrease (t test, p = .025) in the levels of acetylated H3 in males versus females following a maternal dose of 25 mg/kg. The monomethylated H3K9 levels were also increased in females versus males following exposure to TPHP at 5 mg/kg (p = .018) and 25 mg/kg (p = .027) when analyzed via unpaired t tests, although not significantly different from controls.
Discussion: The results suggest that gestational TPHP exposure can induce epigenetic modifications in murine fetal tissue. Specifically, global DNA methylation levels were downregulated in response to TPHP. Additionally, males appear to be more sensitive to TPHP-induced histone modifications than females. These data support the need for further studies investigating the impacts of gestational TPHP exposure on the developing fetus.
Keywords: DNA methylation; acetylated H3; fetal liver; histone modifications; monomethylated H3K9; triphenyl phosphate.
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