Association of polybrominated diphenyl ether (PBDE) levels with biomarkers of placental development and disease during mid-gestation

Abstract

Background: Polybrominated diphenyl ether (PBDE) exposures have been associated with adverse pregnancy outcomes. A hypothesized mechanism is via alterations in placental development and function. However, we lack biomarkers that can be used as early indicators of maternal/fetal response to PBDE exposures and/or perturbations in placental development or function.

Methods: To evaluate the relationship between PBDE levels and placental biomarkers during mid-gestation of human pregnancy (n = 62), we immunolocalized three molecules that play key roles in cytotrophoblast (CTB) differentiation and interstitial/endovascular uterine invasion-integrin alpha-1 (ITGA1), vascular endothelial-cadherin (CDH5), and metalloproteinase-1 (MMP1)-and assessed three morphological parameters as potential indicators of pathological alterations using H&E-stained tissues-leukocyte infiltration, fibrinoid deposition, and CTB endovascular invasion. We evaluated associations between placental PBDE levels and of biomarkers of placental development and disease using censored Kendall's tau correlation and linear regression methods.

Results: PBDEs were detected in all placental samples. We observed substantial variation in antigen expression and morphological endpoints across placental regions. We observed an association between PBDE concentrations and immunoreactivity of endovascular CTB staining with anti-ITGA1 (inverse) or interstitial CTBs staining with anti-CDH5 (positive).

Conclusions: We found several molecular markers that may be sensitive placental indicators of PBDE exposure. Further, this indicates that placental biomarkers of development and disease could be useful barometers of exposure to PBDEs, a paradigm that could be extended to other environmental chemicals and placental stage-specific antigens.

Keywords: Biomonitoring; Birth outcomes; Cytotrophoblast differentiation; Developmental/reproductive health effects; Endocrine disruption; Flame retardants; Maternal health; Preeclampsia; Pregnancy complications.

Fig. 1

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 modified from Maltepe and Fisher, 2015; Damsky et al., 1992 (Damsky et al., 1992; Maltepe and Fisher, 2015)

Fig. 2

Participant recruitment and biological samples collected at the Women’s Options Center (WOC) in Northern California from 2014 to 16. We obtained tissue samples and questionnaire data from 138 pregnant women undergoing elective terminations during mid-gestation. Polybrominated diphenyl ether (PBDE) levels were measured in 135 placental samples. After excluding twins, PBDE measurements were obtained for 130 matched samples of maternal serum, fetal liver, and the placenta. Then we evaluated a subset of placental samples for molecular (n = 62) and morphological (n = 61) biomarkers of placental development and disease

Fig. 3

Immunoreactivity of ITGA1, CDH5, and MMP1 as a function of cytotrophoblast (CTB) differentiation/invasion during mid-gestation (n = 62). The following cell types were scored: 1) CTBs in floating villi (FV); anchoring villi CTBs in the 2) proximal (pAV) and 3) distal (dAV) regions of cell columns; 4) invasive interstitial CTBs (iCTB); and 5) endovascular CTBs (eCTB). CTB immunoreactivity in each region was scored based on the percent of cells that stained for each biomarker in that region: 1) < 25% (−), 2) 25–75% (−/+), or 3) > 75% (+). Staining patterns varied by antigen and CTB subtype (p < 0.001; Fisher’s exact test)

Fig. 4

Wet-weight placental (a) BDE-47 and (b) åPBDE4 molecular immunoreactivity by placental region/cell type during mid-gestation (n = 62). åPBDE4 = BDE-47 + − 99 + − 100 + − 153. Red asterisks denote significance or marginal significance (where: *p < 0.10; **p < 0.05; and ***p < 0.01) from bivariate censored MLE regression models evaluating the percent (%) difference in placental PBDE levels between moderate or high immunoreactivity compared to low immunoreactivity/referent group: 25–75% (−/+) or > 75% (+) compared to < 25% (−)