Uptake and toxicity of copper oxide nanoparticles in C6 glioma cells

Copper oxide nanoparticles (CuO-NPs) are frequently used for many technical applications, but are also known for their cell toxic potential. In order to investigate a potential use of CuO-NPs as a therapeutic drug for glioma treatment, we have investigated the consequences of an application of CuO-NPs on the cellular copper content and cell viability of C6 glioma cells. CuO-NPs were synthesized by a wet-chemical method and were coated with dimercaptosuccinic acid and bovine serum albumin to improve colloidal stability in physiological media. Application of these protein-coated nanoparticles (pCuO-NPs) to C6 cells caused a strong time-, concentration- and temperature-dependent copper accumulation and severe cell death. The observed loss in cellular MTT-reduction capacity, the loss in cellular LDH activity and the increase in the number of propidium iodide-positive cells correlated well with the specific cellular copper content. C6 glioma cells were less vulnerable to pCuO-NPs compared to primary astrocytes and toxicity of pCuO-NPs to C6 cells was only observed for incubation conditions that increased specific cellular copper contents above 20 nmol copper per mg protein. Both cellular copper accumulation as well as the pCuO-NP-induced toxicity in C6 cells were prevented by application of copper chelators, but not by endocytosis inhibitors, suggesting that liberation of copper ions from the pCuO-NPs is the first step leading to the observed toxicity of pCuO-NP-treated glioma cells.