Organophosphate Flame Retardants, Highly Fluorinated Chemicals, and Biomarkers of Placental Development and Disease During Mid-Gestation

Abstract

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) and organophosphate flame retardants (OPFRs) are chemicals that may contribute to placenta-mediated complications and adverse maternal-fetal health risks. Few studies have investigated these chemicals in relation to biomarkers of effect during pregnancy. We measured 12 PFASs and four urinary OPFR metabolites in 132 healthy pregnant women during mid-gestation and examined a subset with biomarkers of placental development and disease (n = 62). Molecular biomarkers included integrin alpha-1 (ITGA1), vascular endothelial-cadherin (CDH5), and matrix metalloproteinase-1 (MMP1). Morphological endpoints included potential indicators of placental stress and the extent of cytotrophoblast (CTB)-mediated uterine artery remodeling. Serum PFASs and urinary OPFR metabolites were detected in ∼50%-100% of samples. The most prevalent PFASs were perfluorononanoic acid (PFNA), perfluorooctanoic acid (PFOA), and perfluorooctane sulfonic acid (PFOS), with geometric mean (GM) levels of ∼1.3-2.8 (95% confidence limits from 1.2-3.1) ng/ml compared to ≤0.5 ng/ml for other PFASs. Diphenyl phosphate (DPhP) and bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) were the most prevalent OPFR metabolites, with GMs of 2.9 (95% CI: 2.5-3.4) and 3.6 (95% CI: 2.2-3.1) ng/ml, respectively, compared to <1 ng/ml for bis(2-chloroethyl) phosphate (BCEP) and bis(1-chloro-2-propyl) phosphate (BCIPP). We found inverse associations of PFASs or OPFRs with ITGA1 or CDH5 immunoreactivity and positive associations with indicators of placental stress in multiple basal plate regions, indicating these chemicals may contribute to abnormal placentation and future health risks. Associations with blood pressure and lipid concentrations warrant further examination. This is the first study of these chemicals with placental biomarkers measured directly in human tissues and suggests specific biomarkers are sensitive indicators of exposure during a vulnerable developmental period.

Keywords: biomonitoring; birth outcomes; cytotrophoblast differentiation; developmental/reproductive health effects; endocrine disruption; flame retardants; maternal health; perfluoroalkyl and polyfluoralkyl substances; preeclampsia; pregnancy complications.

Figure 1.

Study population and biological sample collection at the Women’s Options Center (WOC) in Northern California from 2014 to 2016. Tissue samples and questionnaire data were obtained from 138 pregnant women undergoing elective terminations during mid-gestation. Perfluoroalkyl and polyfluoroalkyl substances and organophosphate flame retardants metabolite levels were measured in 132 matched serum and urine samples, respectively. We then evaluated a subset of matched placental samples for molecular (n = 62) and morphological (n = 61) biomarkers of placental development and disease.

Figure 2.

Human placental villous cytotrophoblast (CTB) differentiation at the maternal-fetal interface. A, Anatomy of the human placenta. Chorionic villi are the functional units. The histology of the boxed area is shown in the panel to the right. B, Depiction of the maternal-fetal interface at the cellular level. The mononuclear cytotrophoblasts (CTB) of the (early gestation) chorionic villi fuse to become multinuclear syncytiotrophoblasts (STBs), which form the surface of the placenta. Floating villi are perfused by maternal blood. Anchoring villi give rise to invasive interstitial CTBs (CTBi) that emigrate from the chorionic villi via cell columns that attach the placenta to the maternal unit and infiltrate the uterine wall. Maternal cells in this region include the decidua, remodeled uterine blood vessels, which are lined by cytotrophoblasts (CTBe), and immune cells. During vascular invasion, the cells breach both veins and arteries, but they have more extensive interactions with the arterial portion of the uterine vasculature. Here, they replace the endothelial lining and intercalate within the smooth muscle walls of the spiral arteries, producing hybrid vessels that are composed of both embryonic/fetal and maternal cells. Vascular invasion connects the uterine circulation to the intervillous space where maternal blood perfuses the chorionic villi. Immunoreactivity of molecular biomarkers was evaluated in five zones (I–V) corresponding to different stages of CTB differentiation: (I) CTB progenitors in floating villi (FV); (II) CTBs of the proximal (AVp) and (III) distal (AVd) anchoring villi; (IV) invading interstitial CTBs (CTBi); and (V) endovascular CTBs (CTBe) that remodel the uterine vasculature. Image and text reproduced from Varshavsky et al. (2020b) (Environmental Health); originally modified from Damsky et al. (1992) and Maltepe and Fisher (2015).

Figure 3.

Correlation of serum perfluoroalkyl and polyfluoroalkyl substances and urinary organophosphate flame retardants metabolite levels among pregnant women during mid-gestation (N = 132; 2014–2016). Rank order correlation assessed using censored Kendall’s Tau Correlation Coefficients which accounts for bivariate left-censored chemical data (below detection limit). Values represent magnitude and shading denotes direction of correlation (red = decreasing; blue = increasing), while “X” symbol denotes lack of statistical significance (p > .05).

Figure 4.

Correlation of (A) serum perfluoroalkyl and polyfluoroalkyl substances and (B) urinary organophosphate flame retardants metabolite levels with placental biomarkers among pregnant women during mid-gestation (N = 62; 2014–2016). Rank order correlation assessed using censored Kendall’s Tau Correlation Coefficients which accounts for left-censored chemical data (below detection limit). Color denotes significance (p < .05). dAV, Anchoring villi (distal); pAV, Anchoring villi (proximal); eCTB, Endovascular CTB; iCTB, Interstitial CTB; FV, Floating villi (bilayer); bpFD, % Fibrinoid deposition in basal plate; fvFD, % Floating villi with fibrinoid deposition; mBV, % CTB-modulated blood vessels; WBC, White blood cell count.

Figure 5.

Correlation of PFOA and PFNA levels with total lipid levels in maternal serum among pregnant women during mid-gestation (N = 132; 2014–2016). Rank order correlation assessed using Kendall’s Tau Correlation.