Cytotoxic effects of polystyrene nanoplastics with different surface functionalization on human HepG2 cells

Nanoplastics in the environment lead to the human exposure to these particles. However, the consequences of this exposure are not yet fully understood. Here, the cytotoxicity of polystyrene nanoparticles (PS-NPs) with a uniform size (50 nm) but distinct surface functionalization (pristine polystyrene, PS; carboxy and amino functionalized, PS-COOH and PS-NH₂, respectively), and at an exposure dosage of 10, 50 and 100 μg/mL, were assessed in the human hepatocellular carcinoma (HepG2) cell line. Although all PS-NPs could be internalized by the HepG2 cells, according to the fluorescent intensities, more of PS-COOH and PS-NH₂ than PS, accumulated in the cells. The cell viability was significantly affected in a positively dose-related manner. Functionalized PS-NPs exhibited greater inhibition of cell viability than PS, and the viability inhibition peaked (46%) at 100 μg/mL of PS-NH₂ exposure. Superoxide dismutase (SOD) activity was maximum when HepG2 cells were exposed to 10 μg/mL of PS-COOH (1.8 folds higher than that without PS-COOH exposure). The glutathione (GSH) content was maximum when the cells were treated with 50 μg/mL of PS (3.75 fold increase compared to untreated cells). Although the difference in inhibition of cell viability was not significant between PS-NH₂ and PS-COOH exposure, 100 μg/mL of PS-NH₂ exposure caused the most severe oxidative stress due to dramatically increased accumulation of malondialdehyde (MDA); however, a decrease in the antioxidants levels as the SOD activity and GSH content were also found. The results demonstrated that the cellular oxidative damage occurred and that the antioxidation enzymes may not be able to maintain the balance between the generation of oxidant species and the antioxidant defense. Consequently, 100 μg/mL of PS-NH₂ exposure triggered the destruction of antioxidant structures. This study defines the cytotoxic effects of PS-NPs on HepG2 cells and emphasizes the significance of investigating the cytotoxic outcomes of nanoplastics in humans.