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The potential medical applications of nanoparticles warrant their investigation in terms of biodistribution and safety during pregnancy. The transport of silica nanoparticles (NPs) across the placenta was investigated using two models of maternal-fetal transfer in human placenta, namely, the BeWo b30 choriocarcinoma cell line and the ex vivo perfused human placenta. Nanotoxicity in BeWo cells was examined by the MTT assay and demonstrated decreased cell viability at concentrations greater than 100 μg/mL. In the placental perfusion experiments, antipyrine crossed the placenta rapidly, with a fetal/maternal ratio of 0.97 ± 0.10 after 2 hours. In contrast, the percentage of silica NPs reaching the fetal perfusate after 6 hours was limited to 4.2 ± 4.9% and 4.6 ± 2.4% for 25-nm and 50-nm NPs, respectively. The transport of silica NPs across the BeWo cells was also limited, with an apparent permeability of only 1.54 × 10−6 ± 1.56 × 10−6 cm/sec. Using confocal microscopy, there was visual confirmation of particle accumulation in both BeWo cells and in perfused placental tissue. Despite the low transfer of silica NPs to the fetal compartment, questions regarding biocompatibility could limit the application of unmodified silica NPs in biomedical imaging or therapy.

Advances in biomedical nanotechnology raise hopes in patient populations but may also raise questions regarding biodistribution and biocompatibility, especially during pregnancy. Special consideration must be given to the placenta as a biological barrier because a pregnant woman's exposure to nanoparticles could have significant effects on the fetus developing in the womb. Therefore, the purpose of this study is to optimize an in vitro model for characterizing the transport of nanoparticles across human placental trophoblast cells. The growth of BeWo (clone b30) human placental choriocarcinoma cells for nanoparticle transport studies was characterized in terms of optimized Transwell® insert type and pore size, the investigation of barrier properties by transmission electron microscopy, tight junction staining, transepithelial electrical resistance, and fluorescein sodium transport. Following the determination of nontoxic concentrations of fluorescent polystyrene nanoparticles, the cellular uptake and transport of 50 nm and 100 nm diameter particles was measured using the in vitro BeWo cell model. Particle size measurements, fluorescence readings, and confocal microscopy indicated both cellular uptake of the fluorescent polystyrene nanoparticles and the transcellular transport of these particles from the apical (maternal) to the basolateral (fetal) compartment. Over the course of 24 hours, the apparent permeability across BeWo cells grown on polycarbonate membranes (3.0 µm pore size) was four times higher for the 50 nm particles compared with the 100 nm particles. The BeWo cell line has been optimized and shown to be a valid in vitro model for studying the transplacental transport of nanoparticles. Fluorescent polystyrene nanoparticle transport was size-dependent, as smaller particles reached the basal (fetal) compartment at a higher rate

Placenta perfusion models are very effective when studying the placental mechanisms in order to extrapolate to reallife situations. The models are most often used to investigate the transport of substances between mother and foetus, including the potential metabolism of these. We have studied the relationships between maternal and foetal exposures to various compounds including pollutants such as polychlorinated biphenyls, polybrominated flame retardants, nanoparticles as well as recombinant human antibodies. The compounds have been studied in the human placenta perfusion model and to some extent in vitro with an established human monolayer trophoblast cell culture model. Results from our studies distinguish placental transport of substances by physicochemical properties, adsorption to placental tissue, binding to transport and receptor proteins and metabolism. We have collected data from different classes of chemicals and nanoparticles for comparisons across chemical structures as well as different test systems. Our test systems are based on human material to bypass the extrapolation from animal data. By combining data from our two test systems, we are able to rank and compare the transport of different classes of substances according to their transport ability. Ultimately, human data including measurements in cord blood contribute to the study of placental transport.With our work, we contribute to the paradigm shift in toxicology research from the use of animal studies towards alternative models with high relevance to human beings. Modes of actions, exposures and analysis can be studied with modelling, new omics technologies and in silico testing, preferably including study material of human origin [1,2]. Replacement of animal use in this area calls for human mechanistic and human toxicity pathway analysis bridged with exposure information as currently developed in the USA in the report Toxicity Testing in the 21st Century: A Vision and a Strategy [3], which also includes transport studies across cellular barriers such as the placenta.Risks from prenatal exposure to environmental toxicants are highly dependent on placental transport of substances from the maternal circulation to the foetal circulation. The presence of a substance in human cord blood is the ultimate demonstration of transport during pregnancy. Placental transport kinetics can be investigated by using the human dually perfused recirculating placental perfusion model and the BeWo cell transfer model.In the placental perfusion model, a human term placenta is obtained directly after birth and a single cotyledon is reperfused in the laboratory set-up. Foetal and maternal circulations are re-established by a pump system, and the transport of a chosen test substance can be investigated. This perfusion model is a simplified model of placental transport, and it does not take all the physiological and biochemical variables in the mother and foetus into account. The model can only represent transport in the late third trimester. However, the ass...

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