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Implication of ferroptosis in hepatic toxicity upon single or combined exposure to polystyrene microplastics and cadmium
Summary
This study found that polystyrene microplastics combined with cadmium caused more severe liver damage in mice than either pollutant alone. The microplastics absorbed cadmium on their surface, increasing the amount of the toxic metal delivered to liver cells, and triggered a type of cell death called ferroptosis. This is concerning because microplastics in the environment commonly carry heavy metals, meaning the combined exposure people face may be more harmful than we thought.
Microplastics (MPs) are a newly emerging type of pollutants. To date, MPs have been found in the atmosphere, soil, water, and even in human samples, posing a non-negligible threat to humans. Furthermore, multiple heavy metals have been found to co-exist with MPs or be absorbed by MPs. This leads to a widespread concern about their combined toxicity, which is currently elusive. Herein, we investigated the single or combined toxic effects of polystyrene MPs (PS-MPs) and cadmium chloride (CdCl) on the liver and hepatocytes. After co-incubation, cadmium (Cd) can be absorbed by PS-MPs, resulting in physiochemical alterations of PS-MPs. In vivo and in vitro experiments revealed that PS-MPs solely or together with CdCl induced ferroptosis in hepatocytes, a newly defined programmed cell death characterized by lipid oxidation and iron accumulation. PS-MPs exerted more ferroptotic effect on hepatocytes than CdCl, and combined exposure to PS-MPs and CdCl enhanced their ferroptotic effect, mainly by stimulating reactive oxygen species (ROS) production and inhibiting antioxidant activity. Upon single or combined exposure to PS-MPs and CdCl, the induction of ferroptosis in hepatocytes can be inhibited by N-acetyl-cysteine (NAC, an ROS scavenger), deferoxamine (DFO, an iron chelator), and particularly ferrostatin-1 (Fer-1, a specific ferroptosis inhibitor). Fer-1 efficiently rescued the cell viability of hepatocytes upon exposure to PS-MPs and CdCl through enhancing the antioxidant system via upregulating GPX4 and SLC7A11. These findings would contribute to an in-depth understanding of the single and combined toxicity of microplastics and cadmium.