Does size matter? A proteomics-informed comparison of the effects of polystyrene beads of different sizes on macrophages

Plastics are one of the most preoccupying emerging pollutants. Macroplastics released into the environment degrade into microplastics and nanoplastics. Because of their small size, these micro and nano plastic particles can enter the food chain and, in addition to their ecotoxicological effects, 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 immune system. In order to get a better appraisal of the effects of plastic particles on macrophages, we have studied the effects of unmodified polystyrene particles of 0.1, 1 and 10 micrometers of diameter, by a combination of proteomics and targeted validation experiments. Proteomics showed important adaptive changes of the proteome in response to exposure to plastics, with more than one third of the detected proteins showing a significance change in their abundance in response to cell exposure to at least one plastic bead size. These changes affected for example mitochondrial, lysosomal or cytoskeletal proteins. Although an increase in the mitochondrial transmembrane potential was detected in response to 10 micrometer beads, no alteration in cell viability was observed. Similarly, no lysosomal dysfunction and no alteration in the phagocytic capability of the cells was observed in response to exposure to plastics. When the inflammatory response was examined, no increase in the secretion of tumor necrosis factor or interleukin 6 was observed. Oppositely, the secretion of these cytokines in response to lipopolysaccharide was observed after exposure to plastics, which suggested a decreased ability of macrophages to respond to bacterial infection. In conclusion, these results provide a better understanding of the responses of macrophages to exposure to polystyrene particles of different sizes.