Toxicity of CuO nanoparticles and Cu ions to tight epithelial cells from Xenopus laevis (A6): Effects on proliferation, cell cycle progression and cell death

► All three Cu forms tested cause cell cycle arrest and cell death via apoptosis. ► Toxicity pattern of the 3 Cu forms is: poly-CuO NPs > CuO NPs (6 nm) > Cu ions. ► Effects of Cu depend on cell state (dividing or differentiated).