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The internal dose makes the poison: higher internalization of polystyrene particles induce increased perturbation of macrophages
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Researchers exposed human macrophages, key immune cells, to polystyrene particles of different sizes and found that smaller particles were internalized more readily and caused greater cellular disruption. Nanoscale plastics triggered stronger inflammatory responses and more oxidative stress than larger microplastics. The study suggests that the amount of plastic actually absorbed by immune cells, not just the amount present in the environment, determines how harmful the exposure is.
Plastics are emerging pollutants of great concern. Macroplastics released in the environment degrade into microplastics and nanoplastics. Because of their small size, these micro and nano plastic particles can enter the food chain and contaminate humans with still unknown biological effects. Plastics being particulate pollutants, they are handled in the human body by scavenger cells such as macrophages, which are important players in the innate immune system. Using polystyrene as a model of micro and nanoplastics, with size ranging from under 100 nm to 6 microns, we have showed that although non-toxic, polystyrene nano and microbeads alter the normal functioning of macrophages in a size and dose-dependent manner. Alterations in the oxidative stress, lysosomal and mitochondrial functions were detected, as well as changes in the expression of various surface markers involved in the immune response such as CD11a/b, CD18, CD86, PD-L1, or CD204. For each beads size tested, the alterations were more pronounced for the cell subpopulation that had internalized the highest number of beads. Across beads sizes, the alterations were more pronounced for beads in the supra-micron range than for beads in the sub-micron range. Overall, this means that internalization of high doses of polystyrene favors the emergence of subpopulations of macrophages with an altered phenotype, which may not only be less efficient in their functions but also alter the fine balance of the innate immune system.
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Size-dependent internalization of polystyrene microplastics as a key factor in macrophages and systemic toxicity
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Researchers systematically tested how the size of polystyrene microplastics affects their uptake and toxicity in immune cells and mice. Smaller particles (0.5 micrometers) were taken up much more readily by immune cells and caused more damage, including mitochondrial dysfunction and cell death, compared to larger 5-micrometer particles. In living mice, smaller microplastics accumulated more in organs and caused broader changes in blood and metabolic markers, confirming that particle size is a key factor in microplastic toxicity.
Cellular internalization and release of polystyrene microplastics and nanoplastics
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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.
Polystyrene nanoplastics of different particle sizes regulate the polarization of pro-inflammatory macrophages
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Researchers exposed immune cells called macrophages to polystyrene nanoplastics of two different sizes (50 nm and 500 nm) and found that both sizes pushed the cells toward a pro-inflammatory state at higher concentrations. This means the immune cells shifted toward producing inflammation signals rather than healing signals after nanoplastic exposure. Since macrophages are a key defense in the gut, this inflammatory response could help explain how microplastics contribute to intestinal inflammation.
Effects of bisphenol A and nanoscale and microscale polystyrene plastic exposure on particle uptake and toxicity in human Caco-2 cells
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Researchers studied how human intestinal Caco-2 cells take up polystyrene plastic particles of five different sizes ranging from 300 nanometers to 6 micrometers. The study found that smaller particles were taken up at higher rates and that co-exposure with bisphenol A increased cellular toxicity, suggesting that nanoscale plastics may pose a greater risk to human intestinal cells than larger microplastics.
Bioaccumulation of differently-sized polystyrene nanoplastics by human lung and intestine cells
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Researchers examined how human lung and intestine cells take up polystyrene nanoplastics of different sizes, finding that smaller particles were internalized in greater numbers but at lower total mass compared to larger ones. When compared on a surface area basis, the uptake rates were similar across sizes, suggesting that surface interactions with cell membranes play a key role. The findings indicate that particle size is an important factor to consider when evaluating the health risks of nanoplastic exposure.
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