Introduction: Exposure to air pollutants such as black carbon (BC) during pregnancy is associated with adverse outcomes including low birth weight and preterm birth. BC nanoparticles have a mean diameter ranging between 10-100 nm which allows them to cross the alveolar epithelial barrier and enter the systemic circulation where they have been identified in a variety of different tissues including the placenta. Currently, the transport mechanisms underlying uptake of pollutant particles in the placenta are not fully understood; this study aims to elucidate the mechanisms responsible.

Methods: Syncytialised BeWo and trophoblast stem cell (TSC)-derived syncytiotrophoblasts were treated with 0.1-10 μg/ml polystyrene nanoparticles (50 nm) and carbon quantum dots (5 nm) to model BC. Using fluorescence microscopy, cellular uptake of particles was visualised and then quantified (n=5). Uptake of different dose treatments were compared with Wilcoxon test with Bonferroni correction. Samples were also stained with endocytic antibodies to track the trafficking of particles through different intracellular vesicles.

Results: Polystyrene nanoparticles were visualised in syncytialised BeWo trophoblast cell line cultures with uptake occurring in a dose-dependent manner. Particles were rapidly taken up in the first 16 hours of culture where they progressively co-localised with early endosomes, late endosomes and lysosomes. The rate of nanoparticles internalisation slowed after 24 hours. Preliminary data from TSC derived syncytiotrophoblasts treated with carbon quantum dots suggests particles are internalised quicker, visualised intracellularly in the first 2 hours of culture with particles colocalising with endocytic vesicles and lysosomes.

Conclusion: Uptake of pollutant nanoparticles by placental syncytiotrophoblasts is dependent on dose and particle diameter with smaller 5 nm particles internalised quicker than 50 nm polystyrene particles. However, the different cell models used may also influence uptake kinetics. The results from this study will further our understanding of pollutant uptake by the placenta and provide an insight into what extent the trophoblast layer acts as a barrier against carbon-based nanoparticles.