57 Nanoplastics are taken up by the oocyte and delay embryo development

The ubiquity of micro- and nanoplastics (MNPs) has recently gained increasing attention due to their potential health effects. MNPs have been observed to pass biological barriers including the reproductive tract in rodents, but thus far there is little information on the impact of MNPs on early life. To investigate the effect of MNPs on oocytes and early embryonic development we made use of the bovine IVF model, which also resembles the human periconception phase owing to the large similarities between cow and human. We exposed maturing bovine cumulus–oocyte complexes (COCs) to nanoplastics (NPs; <1 µm) to assess whether such exposure affects embryo development and the transcriptome of the COCs. We discovered that during IVM, 50-nm polystyrene NPs enter the oocyte and hamper oocyte nuclear maturation rate at a concentration of 3 µg mL⁻¹ (66.1% in NP exposure group vs. 81.0% in the control group). To investigate the underlying mechanisms, RNA-seq was used on RNA isolated from COCs, originating from slaughterhouse ovaries, that were exposed to 50-nm polystyrene NPs (3 µg mL⁻¹) during the 23-h IVM. Gene Set Enrichment Analysis (GSEA) was performed using Kyoto Encyclopedia of Genes and Genomes pathway and gene ontology database. Additionally, IVF and in vitro embryo production (IVEP) were performed to determine whether the oocyte developmental competence was affected. In total, IVF and IVEP were performed on 298 COCs per treatment group in four replicates. Several 231 and 223 cleaved embryos were evaluated in the NP exposure and control group, respectively. A generalized Linear Model with binary logistic regression followed by Bonferroni adjustment for multiple comparisons was used for statistical analysis. A P-value < 0.05 was considered statistically significant. Following GSEA, pathways related to negative regulation of the developmental process were upregulated, and mitochondrial function was downregulated after 50-nm NP exposure of COCs during IVM. The cleavage rates on Day 5 and blastocyst rates on Day 8 were not significantly different between the two groups. Notably, on Day 7 of IVEP, a significant decrease was observed in blastocyst rate in the exposure group (29.2 ± 4.4%) compared with the control group (36.2 ± 5.8%), in line with the observed outcome of the pathway analysis for development. In summary, exposure to NPs during IVM appears to affect mitochondrial functions and results in a temporal delay in early embryonic development. Further investigations are ongoing to investigate the potential impact of NPs on mitochondrial function and embryonic development.