Exposure to flame retardant chemicals is relatively ubiquitous among the general public, and research has demonstrated that these contaminants can pass from a mother to her baby through the placenta. During fetal development, the placenta serves as an endocrine organ and is responsible for nutrient, waste, and gas exchange as well as protection from the maternal immune system and pathogens. Thus, it is suspected that the placenta is a target of endocrine-disrupting chemicals, such as flame retardants. Recently, we conducted a study that measured brominated flame retardant levels in human placental tissues from a group of women in North Carolina.
Our research group measured a suite of polybrominated diphenyl ether (PBDEs), 2,4,6-tribromophenol, and thyroid hormone levels (T4, T3 and rT3) in each tissue sample. Significant associations were observed between the flame retardants and thyroid hormone levels in the placenta, although the associations were opposite in direction depending on the sex of the fetus. Further, we found that concentrations were significantly higher in the placental tissues if the placenta was associated with a male infant, compared to a female infant (see Leonetti et al. 2016). In collaboration with a lab at NCSU, we have explored the toxicokinetics of a PBDE mixture using pregnant Wistar rats as a model. We sought to understand the tissue-specific accumulation of PBDEs in the placenta and the impact on thyroid hormone regulation. We found that PBDEs accumulated in the fetal portion of the placenta at 2-3 times higher concentrations than the maternal portion of the placenta. We also observed a significant effect on dam serum thyroid hormone levels but did not see any effects in the placenta or fetus (see Ruis et al. 2019).
The factors or variables driving this difference in flame retardant accumulation are unclear, but we are conducting further research to determine if this may be related to differences in metabolism or differences in transport of the flame retardants and thyroid hormones across the placental barrier. We are currently exploring the effects of flame retardants on thyroid and estrogen regulation and metabolism using placental cell lines, animal models, as well as ex vivo human placental tissue. This research has been supported by a grant from the National Institute of Environmental Health Sciences (R01ES020430).
For more information about flame retardants, please check out this Factsheet from the National Institute of Health.
Associated Publications
Gaballah, S., Horman, B., St Armour, G., Hoffman, K., Patisaul, H.B., Stapleton, H.M. 2023. OR06-02 Placental Distribution of Polybrominated Diphenyl Ethers (PBDEs) and Thyroid Hormones across Gestation in PBDE-Exposed Wistar Rats. Journal of the Endocrine Society, 7. https://doi.org/10.1210/jendso/bvad114.1048
Ruis, M., Hoffman, K., Stapleton, H.M. 2023. Brominated Flame Retardants and Legacy Organochlorines in Archived Human Placenta Samples: Sex Differences, Temporal Analysis and Associations with Infant Birth Weight. Chemosphere, 322: 138170. https://doi.org/10.1016/j.chemosphere.2023.138170.
Rock, K.D., St Armour, G., Horman, B., Phillips, A., Ruis, M., Stewart, A.K., Jima, D., Muddiman, D.C., Stapleton, H.M., Patisaul, H.B. 2020. Effects of Prenatal Exposure to a Mixture of Organophosphate Flame Retardants on Placental Gene Expression and Serotonergic Innervation in the Fetal Rat Brain. Toxicological Sciences, 176(1): 202-223. https://doi.org/10.1093/toxsci/kfaa046
Ruis, M.T., Rock, K.D., Hall, S.M., Horman, B., Patisaul, H.B., Stapleton, H.M. 2019. Polybrominated Diphenyl Ethers Concentrate in the Fetal Portion of the Placenta: Implications for Thyroid Hormone Dysregulation. Endocrinology, 160(11), 2748-2758. https://pubmed.ncbi.nlm.nih.gov/31555822/
Rock, K.D., Horman, B., Phillips, A.L., McRitchie, S.L., Watson, S., Deese-Spruil, J., Sumner, S., Stapleton, H.M., Patisaul, H.B. 2018. EDC Impact: Molecular Effects of Developmental FM 550 Exposure in Wistar Rat Placenta and Fetal Forebrain. Endocrine Connections, 7(2): 305-324. https://pubmed.ncbi.nlm.nih.gov/29351906/
Leonetti, C.P., Butt, C.M., Stapleton, H.M. 2018. Disruption of Thyroid Hormone Sulfotransferase Activity by Brominated Flame Retardant Chemicals in the Human Choriocarcinoma Placenta Cell Line, BeWo. Chemosphere, 197: 81-88. https://pubmed.ncbi.nlm.nih.gov/29331935/
Baldwin, K.R., Phillips, A.L., Horman, B., Arambula, S.E., Rebuli, M.E., Stapleton, H.M., Patisaul, H.B. 2017. Sex Specific Placental Accumulation and Behavioral Effects of Developmental Firemaster 550 Exposure in Wistar Rats. Scientific Reports, 7: 7118. https://doi.org/10.1038/s41598-017-07216-6
Leonetti, C., Butt, C.M, Hoffman, K., Hammel, S.C., Miranda, M.L., Stapleton, H.M. 2016. Brominated Flame Retardants in Placental Tissues: Associations with Infant Sex and Thyroid Hormone Endpoints. Environmental Health, 15(1): 113-122. https://pubmed.ncbi.nlm.nih.gov/27884139/
Leonetti, C., Butt, C.M., Hoffman, K., Miranda, M.L., Stapleton, H.M. 2016. Concentrations of Polybrominated Diphenyl Ethers (PBDEs) and 2,4,6-Tribromophenol in Human Placental Tissues. Environment International, 88: 23-29. https://pubmed.ncbi.nlm.nih.gov/26700418/