Limited passage and functional effects of polystyrene micro- and nanoplastics in a physiologically-relevant in vitro human placental co-culture model.

The placenta plays a crucial role during pregnancy, yet effective in vitro models for placental toxicity testing are limited. In this study, a Transwell co-culture model combining BeWo b30 and HUVEC cells was developed and characterized, and used to study the transport and effects of polystyrene micro- and nanoplastics (PS-MNPs). After 72 h, 8.7 % of 50 nm and 1.2 % of 200 nm of fluorescent (F)PS-MNPs were detected on the basolateral side, while 1000 nm FPS-MNPs were undetectable. Confocal microscopy showed the uptake of 50 and 200 nm FPS-MNPs by the BeWo b30 and HUVEC cell layer, whereas the 1000 nm FPS-MNPs were only found within the BeWo b30 cell layer. Exposure to PS-MNPs (sizes of 50, 200 and 1000 nm at concentrations of 1-10 µg/mL) did not result in an effect on mitochondrial activity, oxidative stress and gene expression of several functional markers and steroidogenic enzymes. However, LC/MS-MS analysis of the culture media showed a decrease of 17 % in the level of 17-alpha-estradiol after 72-hour exposure to 1 µg/mL 50 nm PS-MNPs compared to vehicle control. Overall, our data showed limited effects of PS-MNPs on placental cell function in vitro, but FPS-MNPs were internalized and detected on the basolateral side in the co-culture. This warrants further studies on effects of MNPs on placental cell function, and particularly steroidogenesis, to assess the potential effects of MNPs during pregnancy.