Superfund Research Program

Toxicant-Stimulated Disruption of Gestational Tissues with Implications for Adverse Pregnancy Outcomes

Project Leader: Sean Harris (University of Michigan)
Co-Investigators: Kelly M. Bakulski (University of Michigan), April Z. Gu (Cornell University), Chuanwu Xi (University of Michigan)
Grant Number: P42ES017198
Funding Period: 2010-2025

Project-Specific Links

Final Progress Reports

Year:   2019  2013 

Studies and Results

Dr. Loch-Caruso and her team of investigators propose a model of mechanisms by which di-2-ethylhexyl phthalate (DEHP) and trichloroethylene (TCE) target the placenta and extraplacental membranes to activate responses that may contribute to preterm birth and low birth weight. It is proposed that toxicants increase generation of reactive oxygen species in placenta and extraplacental membranes which subsequently stimulate release of proinflammatory cytokines, prostaglandins, and matrix metalloproteinases (MMPs), and increases cell death in the tissues.

Studies with the human placental cell line HTR-8/SVneo show that bioactive metabolites of DEHP and TCE increase generation of reactive oxygen species and activate response pathways relevant to preterm birth. Previously, the investigators reported that exposure of HTR-8/SVneo cells to the DEHP metabolite mono-2-ethylhexyl phthalate (MEHP) increases reactive oxygen species generation and cellular responses to reactive oxygen species, including oxidative DNA damage, activation of cell death response, and differential expression of genes sensitive to the changes in cellular reactive oxygen species, and induces gene expression of PTGS2, an enzyme important for synthesis of prostaglandins implicated in initiation of labor (Tetz, Cheng et al., 2013). In conducting studies on reactive oxygen species, the investigators' work identified potentially significant artifacts in a common method used to assess reactive oxygen species generation, the dichlorofluorescein assay (Tetz et al., 2013). New data show that primary placental macrophages respond to MEHP with increased expression of PTGS2, also. Similarly, the TCE metabolite S-(1,2)-dichlorovinyl cysteine (DCVC) increases reactive oxygen species generation, decreases cellular concentrations of the antioxidant glutathione, and increases release of the pro-inflammatory cytokine IL-6 at DCVC concentrations that have no significant effect on cell viability. Moreover, DCVC-stimulated release of IL-6 is inhibited by antioxidant treatments with Vitamin E and deferoxamine. These studies provide novel data in support of MEHP and DCVC stimulation of responses in placental cells that are relevant to adverse birth outcomes.

The investigators' data with pregnant rats show that daily exposure to 480 mg TCE/kg-d from day 6 through day 16 of gestation decreases fetal weight with no significant effect on maternal body weight or organ weight of maternal liver and kidney. Placentas from exposed litters show evidence of oxidative DNA damage with significantly increased formation of 8-hydroxydeoxyguanosine, and maternal serum shows significantly increased concentrations of the proinflammatory cytokine IL-6. The dose of TCE used is relevant to human occupational exposures but high for ambient environmental exposures (for example through drinking water). Recent work involves a transwell tissue culture model of human extraplacental membranes, in which the extraplacental membranes are affixed to a transwell insert to create a two-compartment culture system. Using this system, the investigators showed that human extraplacental membranes have a robust innate immune defense against infection to Group B Streptococcus (GBS; strain A909). Experiments with the transwell culture system, primary cultures of human amniotic cells, and choriodecidual punches show that the TCE bioactive metabolite DCVC suppresses innate immune defenses (e.g., cytokines and antimicrobial peptides) in human extraplacental membranes exposed to GBS.

Significance

Though incomplete, Dr. Loch-Caruso and her investigators' findings to date suggest that the metabolite MEHP and the metabolite DCVC activate responses in placental cells that are relevant to preterm birth. Experiments with pregnant rodents are providing further support for their over-arching hypothesis. By showing that toxicants activate pathways associated with labor, the investigators' data provide a foundation to further explore biological explanations for environmental pollutant exposure associations with preterm birth.