The effect of microplastic-polystyrene exposure on mouse embryogenesis in vitro

Abstract

Rising plastic production over recent decades has driven a corresponding increase in plastic pollution. As a result, researchers are investigating the impact that this may have on our environment. Recent studies have documented the presence of microplastics (MPs), small plastic particles <5mm in size, in our water, food, and human tissue. The effect of this plastic ingestion, internalization, and accumulation in the body is not fully understood. Studies of MP exposure in reproductive tissues suggest toxicity that may impair fertility and affect offspring. The underlying mechanisms of the pathways driving these effects have not been elucidated. Defining how microplastics can disrupt reproductive processes like embryogenesis is essential to clarify the impact of escalating environmental MP burden on maternal-fetal interactions and pregnancy outcomes.Here, we collected fertilized embryos from pregnant mice at 0.5 days post coitum (dpc) and incubated them until blastocyst stage (3.5 dpc) in control media culture or media containing either 0.1 µg/mL, 1.0 µg/mL, or 5.0 µg/mL of 5.0 µm Polystyrene beads. Preimplantation embryos were imaged by light microscopy to quantify the blastocyst formation rates. Fluorescent light microscopy on 4.5 dpc was performed to determine whether polystyrene microplastics (MP-PS) beads were present on the blastocyst surface or inside the blastocele. To assess if plastic-associated chemicals were the source of any observed cytotoxicity, additional experiments were conducted using embryos cultured in media containing MP-PS leachate. Finally, embryos were assessed for signs of oxidative stress. While no significant differences in blastocyst formation were observed between the control, 0.1 µg/mL, and 1.0 µg/mL groups, the embryos exposed to 5.0 µg/mL of polystyrene beads showed significant decline in blastocyst formation at 3.5 dpc. Embryos grown in solutions containing only the leachate from MP-PS beads showed no significant differences in blastocyst formation rates compared to the control group. Imaging revealed MP-PS beads on the surface of the blastocyst and within the blastocele in the 1.0 µg/mL and 5.0 µg/mL groups, though the bead internalization was infrequent. Finally, embryos cultured in 5.0 µg/mL MP-PS beads exhibited significant signs of oxidative stress compared to the embryos grown in the control media. The observed reduction in blastocyst formation rate indicates cytotoxic effects associated with MP-PS bead exposure. Delayed blastocyst formation rates are frequently linked to underlying genetic or chromosomal abnormalities that compromise proliferative capacity during early embryogenesis. The detection of MP-PS beads adherent to the blastocyst surface and within the blastocele cavity supports direct interaction with trophoblast cells. These findings suggest that MP-PS particles are recognized at the cell membrane, undergo binding, and are subsequently internalized via an as yet undefined uptake mechanism. Such internalization may disrupt cellular integrity and developmental programming, with potential adverse consequences for embryonic viability and placental development. Previous studies suggested that microplastic exposure may lead to increased reactive oxygen species (ROS) accumulation and eventual oxidative stress in tissues. Confirmation of these findings suggests that the delayed blastocyst formation witnessed among experimental groups could be due to increased oxidative stress caused by the MP-PS bead presence.