A comparison of the effects of polystyrene and polycaprolactone nanoplastics on macrophages.

Plastics are persistent in the environment, which suggests that they may induce adverse effects due to their progressive accumulation over time. This progressive accumulation is facilitated by the fact that macroplastics released in the environment progressively fragment into micro and nanoplastics, which are easily taken up by a wide range of living organisms. As these micro and nanoplastics are particulate materials, they are handled in these living organisms by specialized phagocytic cells, namely macrophages in vertebrates, opening the possibility that plastics accumulating in macrophages may elicit a variety of responses. Thus, one way of alleviating such accumulation in macrophages and in other cell types would be to use biodegradable plastics. Polycaprolactone is a biodegradable plastic showing favorable degradation characteristics in several environments. We thus investigated the responses of macrophages upon treatment with polycaprolactone nanobeads, using a combination of proteomics and validation experiments, and compared these results to the ones induced by polystyrene nanobeads. Many changes detected by proteomics, for example in the mitochondrial, lysosomal or reticulum proteins did not induce detectable physiological consequences. A slight decrease in the phagocytic capacity of polycaprolactone-treated cells was detected, but not for polystyrene-treated cells. We also showed that polycaprolactone nanobeads degrade within a few days in macrophages, modulating the macrophage responses. The derease in phagocytosis disappeared, while polystyrene induced a delayed surge in the phagocytic response. A delayed decrease in the secretion of pro-inflammatory cytokines was also observed in of polycaprolactone-treated cells, which may be linked to the release of hydroxycaproic acid.