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Cellular internalization and release of polystyrene microplastics and nanoplastics
Summary
Scientists studied how polystyrene plastic particles of different sizes enter and exit living cells. They found that particles 50 and 500 nanometers in size can penetrate cell membranes and get taken up through multiple pathways, while 5-micrometer particles are too large to enter cells. This research helps explain why smaller nanoplastics may be more harmful to human health, as they can more easily get inside our cells and accumulate there.
Microplastics and nanoplastics can accumulate in organisms after being ingested, be transported in the food web, and ultimately threaten human health. An understanding of the cellular internalization and release of micro(nano)plastics is important to predict their cytotoxicity. In this study, 50 nm, 500 nm and 5 μm polystyrene particles (PS50, PS500 and PS5000) were exposed to both model cell membranes and rat basophilic leukemia (RBL-2H3) cells. PS50 and PS500 absorb on the model membrane due to hydrophobic interactions and Van der Waals' forces, and may also penetrate the model membrane. PS50 and PS500 are internalized into living cells via both passive membrane penetration and active endocytosis. The passive membrane penetration is due to the partition of polystyrene particles in the water-phospholipid system. The endocytosis of PS50 occurs through the clathrin-mediated pathway, the caveolin-mediated pathway and macropinocytosis, but endocytosis of PS500 is mainly via the macropinocytosis. PS5000 cannot adhere to the cell membrane or be internalized into cells due to its large size and weak Brownian motion. The endocytosed PS50 and PS500 mainly accumulate in the lysosomes. The passively internalized PS50 and PS500 initially distribute in the cytoplasm not in lysosomes, but are transported to lysosomes with energy supply. PS50 and PS500 are excreted from cells via energy-free penetration and energy-dependent lysosomal exocytosis. The masses of the internalized PS50 inside the cells and the excreted PS50 outside the cells were both higher than the masses of PS500, indicating that the smaller particles are more easily enter or leave cells than do their larger counterparts. Our findings will contribute to the risk assessment of micro(nano)plastics and their safe application.
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