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Nanoplastics Can Enter Cells and Impair Immune Function

Polystyrene nanoplastics inhibit key signalling pathways involved in the activation of immune cells, impairing immune responses.

In a study conducted by Professor Xu Mingkai from the Institute of Applied Ecology (IAE) of the Chinese Academy of Sciences and colleagues, the team looked at the toxic effects and underlying mechanisms of polystyrene nanoplastics on immune cells and found that these nanoplastics inhibit key signalling pathways that activate immune cells.

Plastic pollution is one of the biggest problems in the world today, where we produce about 300 million tonnes of plastic waste every year. With much attention centred around microplastics in recent years, scientists are now considering the further fragmentation of these microplastics to the sub-micrometre scale. While the scientific community is still debating on the limits of what can be considered a nanoplastic, it is without a doubt that this environmental pollutant is a cause for greater concern.

When plastic waste is released into the environment, it will break down into smaller pieces via different physical, chemical, and biological processes. Microplastics can be ingested by different organisms and accumulate in the body. Several studies have since found microplastics in the respiratory and digestive tract and have shown that the infiltration of these microplastics into these systems can attack other organs as well.

Nanoplastics, being smaller in size with more physiologically penetrating features, are considered more toxic than microplastics. However, due to technical limitations of detecting nanoplastics, not many studies have been done to investigate its biological toxicity.

In light of this, Prof. Xu and colleagues investigated the toxicological effects on T cells by utilising four representative polystyrene nanoplastics (PS-NPs) with different surface charges and particle sizes. Their study would provide greater insight into the assessment of the risk PS-NP pollution poses to human health.

To evaluate the cytotoxic characteristics of PS-NPs, the team had to find out the internalisation efficiency of these particles by cells. They carried out transmission electron microscopy and flow cytometry assays and found that both 20 nm and 50 nm PS-NPs could be taken up into murine splenocytes in a dose-dependent manner.

The team then carried out MTS assay to find out the viability of murine splenocytes after being treated with PS-NPs. They observed that PS-NPs decreased the viability of murine splenocytes at high concentrations. Through a western blot analysis, the team was also able to confirm that PS-NPs induced apoptosis as well and that positively charged 20 nm PS-NPs exerted the greatest effect on the cells. It is suggested that positively charged nanoparticles are more harmful as they could pass through the phospholipid bilayer with relative ease and cause more plasma membrane damage than nanoparticles with a negative charge or no charge.

Prof. Xu and colleagues were also able to demonstrate how exposure to nanoplastics influenced the regulation of key signalling pathways involved in T cell activation and function. These results predict that above a certain concentration, nanoplastics can damage the spleen in mammals and impair immune function. Furthermore, apart from affecting immune function, these pathways also regulate a variety of physiological functions as well, suggesting that PS-NPs might pose more diverse risks to animal and human health beyond just immune responses and warrant more attention. [APBN]

Source: Li et al. (2022). In vitro study on the toxicity of nanoplastics with different charges to murine splenic lymphocytes. Journal of Hazardous Materials, 424, 127508.