Uptake of polystyrene nanoplastics by cumulus-oocyte complexes impairs oocyte and embryo development

Nanoplastics (NPs), plastic particles smaller than 1 μm, have gained increasing attention due to their potential health effects. Experimental studies in animals have shown that NPs can pass biological barriers, reach the female reproductive tract, and enter the ovary. Their presence in the ovary might have profound consequences for reproductive endpoints, such as oocyte development. This study aimed to investigate the uptake and associated effects of polystyrene (PS) NPs on oocyte and embryo development using a bovine in vitro fertilization (IVF) model. Bovine cumulus-oocyte complexes (COCs) were exposed to pristine PS-NPs (50 nm or 200 nm) at different doses during in vitro maturation (23 h), followed by IVF and embryo culture. RNA sequencing was performed to investigate mechanisms involved in possible effects on oocyte maturation. Confocal microscopy confirmed the internalization of 50 nm and 200 nm PS-NPs into cumulus cells, however, only 50 nm particles were able to transfer into oocytes. Additionally, exposure to 50 nm PS-NPs at 3 μg/mL significantly delayed oocyte nuclear maturation and early embryo development. At this dose, RNA sequencing did not identify differentially expressed genes in the COCs, however, gene set enrichment analyses did indicate effects on mitochondrial processes. Nevertheless, subsequent analysis on mitochondrial activity remained unaffected. Our findings suggest that while 50 nm PS-NPs can penetrate the zona pellucida and impair oocyte maturation, their effects may not be driven by major transcriptomic or mitochondrial functional alterations.