Cu(I)/Cu(II) Released by Cu Nanoparticles Revealed Differential Cellular Toxicity Related to Mitochondrial Dysfunction

Cu-based nanoparticles (NPs) have been increasingly fabricated, and different Cu species (i.e., Cu⁺ and Cu²⁺) of these NPs are tuned to achieve differential physicochemical properties. Although ion release is one of the major toxic mechanisms of Cu-based NPs, differences in cytotoxicity between released Cu(I) and Cu(II) ions are largely unknown. In this study, the A549 cells exhibited a lower tolerance to Cu(I) compared with Cu(II) accumulation. Bioimaging of labile Cu(I) indicated that the change of the Cu(I) level upon CuO and Cu₂O exposure displayed different trends. We then developed a novel method to selectively release Cu(I) and Cu(II) ions within the cells by designing Cu_xS shells for Cu₂O and CuO NPs, respectively. This method confirmed that Cu(I) and Cu(II) exhibited different cytotoxicity mechanisms. Specifically, excess Cu(I) induced cell death through mitochondrial fragmentation, which further led to apoptosis, whereas Cu(II) resulted in cell cycle arrest at the S phase and induced reactive oxygen species generation. Cu(II) also led to mitochondrial fusion, which was likely due to the influence of the cell cycle. Our study first uncovered the difference between the cytotoxicity mechanisms of Cu(I) and Cu(II), which could be greatly beneficial for the green fabrication of engineered Cu-based NPs.