Amino acids-modified chitosan nanoparticles for chelating Cu2+ to suppress the cytotoxicity of CuO nanoparticles
The extensive development and application of engineered nanoparticles (NPs) worldwide in various sectors have gained increased concern due to their potential hazards to human beings and the environment. Thus, a simple, economical and effective method able to suppress the toxicity of metal-based nanomaterials is becoming more urgent. In this study, glutaraldehyde-crosslinked chitosan nanoparticles (CS NPs) were prepared and further modified with lysine (Ly-CS), glutamic acid (Glu-CS), or sodium borohydride (NaBH4) reduction (R-CS), which were used to suppress cytotoxicity induced by copper oxide NPs (CuO NPs) by chelation of the intracellularly released copper ions. All three kinds of CS NPs had a similar size of ~100 nm in a dry state and ~200 nm in cell culture medium, as analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dynamic light scattering (DLS). The chelating efficiency of different CS NPs followed the order of Ly-CS>Glu-CS>R-CS NPs. The CS NPs showed minimal or no toxicity to three different cell lines (HepG2, A549 and RAW264.7 cells) at 100 g/mL with a similar cell internalization and exocytosis process. Comparatively, the RAW264.7 cells exhibited higher endocytosis and exocytosis rate, which was revealed by both flow cytometry and confocal laser scanning microscopy (CLSM). The CS NPs were found in the form of agglomerates inside the A549 cells and RAW264.7 cells, and the amount of agglomerates inside RAW264.7 cells decreased significantly with prolonged incubation. All three CS NPs, especially Ly-CS and Glu-CS NPs, could efficiently suppress the cytotoxicity induced by CuO NPs, and reduce the intracellular reactive oxygen species (ROS) level.