Human placenta is a multifunctional interface between maternal and fetal blood. Studying the impact of pollutants on this organ is crucial because many xenobiotics in maternal blood can accumulate in placental cells or pass into the fetal circulation. Benzo(a)pyrene (BaP) and cerium dioxide nanoparticles (CeO2 NP), which share the same emission sources, are found in ambient air pollution and also in maternal blood. The aim of the study was to depict the main signaling pathways modulated after exposure to BaP or CeO2 NP vs. co-exposure on both chorionic villi explants and villous cytotrophoblasts isolated from human term placenta. At nontoxic doses of pollutants, BaP is bioactivated by AhR xenobiotic metabolizing enzymes, leading to DNA damage with an increase in γ-H2AX, the stabilization of stress transcription factor p53, and the induction of its target p21. These effects are reproduced in co-exposure with CeO2 NP, except for the increase in γ-H2AX, which suggests a modulation of the genotoxic effect of BaP by CeO2 NP. Moreover, CeO2 NP in individual and co-exposure lead to a decrease in Prx-SO3, suggesting an antioxidant effect. This study is the first to identify the signaling pathways modulated after co-exposure to these two pollutants, which are common in the environment.

The human placenta is a transitory organ essential for fetal development, whose functions can be disrupted by xenobiotics in maternal blood. Benzo-[a]-pyrene (B[a]P) is a carcinogenic, mutagenic and reprotoxic pollutant as well as an endocrine disruptor that can be internalized in the human body by respiratory exposure. Cerium dioxide nanoparticles (CeO2 NP) have been introduced into our environment, mainly for their catalytic properties and share the same emission sources as B[a]P (cigarette smoke and diesel engine exhaust). The aim of our study is to determine the impact of these two atmospheric pollutants on the human placenta in concomitant exposure, in order to get closer to the environmental reality. Chorionic villi and villous cytotrophoblasts (VCT) from human placentas at term of pregnancy were exposed in vitro to the pollutants. The internalization of the pollutants was observed by confocal and Raman microscopy. Cytotoxicity was assessed using WST-1 test and extracellular LDH assay. Placental endocrine activity was assessed by ELISA. The signaling pathways impacted have been studied by Western Blot, RT-qPCR and IHC. CeO2 NP and B[a]P can be internalized within the chorionic villi. B[a]P alone or in co-exposure with CeO2 NP activate the metabolic pathway of the aryl hydrocarbon receptor (AhR), causing DNA damage. B[a]P also stabilizes the stress transcription factor p53 and its transcriptional target p21. Although these two pollutants do not cause major toxicity on term human trophoblasts after in vitro exposures, cellular stress markers are induced.

The placenta is a multifunctional organ essential for fetal development and growth, but also represents a barrier for the fetus against many xenobiotics. Benzo-(a)-pyrene (BaP) is a pollutant already known as a mutagenic and reprotoxic carcinogen as well as an endocrine disruptor, which can bypass the placental barrier. Cerium dioxide nanoparticles (CeO2 NPs) are new pollutants that currently share the same emission sources as BaP (cigarette smoke, diesel engine exhaust…). In order to understand their impact on human health, in 2010 the OECD included CeO₂ NPs in the priority list of nanomaterials requiring urgent assessment. The aim of our study is to identify the cellular effects and the mechanisms of action of these two atmospheric pollutants on the human placental barrier when they are in concomitant exposure, in order to get closer to the environmental reality. The chosen concentrations ratio is of 10 µg/cm2 of NPs CeO2 for 1 µM of BaP, which corresponds to the quantity of BaP necessary to cover the surface of the NPs when they are encountered together. Cytotoxicity was assessed using a metabolic activity test of the mitochondrial dehydrogenase (WST-1 test) and the release of LDH on villous cytotrophoblasts isolated from term human placentas. A Cell Stress Array protein-on-chip study was performed to identify the modulated signaling pathways after exposure to these two pollutants. The results obtained were confirmed by Western Blot, IHC and RTq-PCR. The endocrine function was assessed by hCG dosage in the culture medium after exposure to these pollutants. We have shown that the two pollutants are not toxic for cytotrophoblasts at realistic exposure doses. However, BaP alone or in co-exposure to CeO2 NPs activates the pathway of xenobiotic metabolism through the aryl hydrocarbon receptor (AhR), stabilizes the stress transcription factor p53 and its transcriptional target p21, without modifying the antioxidant enzyme levels. On the contrary, CeO2 NPs seem rather to have an antioxidant effect and decrease the levels of factors such as HIF-1α, HIF-2α, p38 and NFκB. These diminishing effects are potentiated after co-exposure to both pollutants. The Cell Stress Array highlights a large number of actors, whose protein levels decrease during co-exposure compared to individual exposures, in particular those of the p53 pathway and HIF. These results open up new perspectives for describing the mechanisms by which these two atmospheric pollutants alter the functioning of the placenta of exposed pregnant women

The human placenta is a transient organ essential for pregnancy maintenance, fetal development and growth. It has several functions, including that of a selective barrier against pathogens and xenobiotics from maternal blood. However, some pollutants can accumulate in the placenta or pass through with possible repercussions on pregnancy outcomes. Cerium dioxide nanoparticles (CeO2 NPs), also termed nanoceria, are an emerging pollutant whose impact on pregnancy is starting to be defined. CeO2 NPs are already used in different fields for industrial and commercial applications and have even been proposed for some biomedical applications. Since 2010, nanoceria have been subject to priority monitoring by the Organization for Economic Co-operation and Development in order to assess their toxicity. This review aims to summarize the current methods and models used for toxicology studies on the placental barrier, from the basic ones to the very latest, as well as to overview the most recent knowledge of the impact of CeO2 NPs on human health, and more specifically during the sensitive window of pregnancy. Further research is needed to highlight the relationship between environmental exposure to CeO2 and placental dysfunction with its implications for pregnancy outcome.