Toxicity of surface-modified copper oxide nanoparticles in a mouse macrophage cell line: interplay of particles, surface coating and particle dissolution

Copper oxide nanoparticles (CuO NPs) are used in numerous applications including antimicrobial agents, semiconductors, chemical sensors, catalysts and others. However, their high toxic potential and growing industrial production increases the concern for health and environmental risks. The present study aimed to investigate the toxicity of pristine versus surface-modified CuO NPs in relation to their stability/dissolution in cell culture medium, cellular uptake, cytotoxicity and ROS production in mouse macrophages RAW264.7. Our results showed that NPs modified with different coating agents [citrate (CIT), ascorbate (ASC), polyethyleneimine (PEI) and polyvinylpyrollidone (PVP)] affected the dissolution of the NPs in water but not in cell culture medium. Further, in vitro testing demonstrated that PEI-coated NPs were most cytotoxic while ASC-coated material exerted the lowest cytotoxicity. The anionic coatings CIT and ASC also provided protection against CuO NPs-induced oxidative stress and decreased levels of ROS production. Cellular internalization assessed by TEM was detected in cells exposed to CIT, ASC, PVP-coated and pristine NPs but not PEI-CuO NPs. Intracellular Cu content in cells tended to decrease with time, resulting in reduced cell/total Cu ratios, with the highest reduction noted for cells exposed to uncoated NPs. Overall, the toxicity of the surface-modified CuO NPs could be explained by synergistic interactions between the NPs, their dissolution, and the toxicity of the coating agents.