Assessing antioxidant responses in C6 and U-87 MG cell lines exposed to high copper levels

Abstract

Copper excess has been tested as an anticancer therapy, due to its properties to generate oxidative stress resulting in tumoral cell death. Thus, this study aimed to evaluate the impact of copper excess on oxidative stress and antioxidant responses in glioma cells, establishing the antioxidant system as a target of copper toxicity in tumoral cells. C6 and U-87 MG cells were exposed to CuSO₄ (0–600 μM) for 24-48 h. SOD, CAT, GPx, GR, and CK activities, protein and non-protein thiol levels (PSH and NPSH), and O₂⁻ production were assessed, alongside SOD1, GPx1, and GR gene expression. Results revealed a decrease in GPx, GR, and CAT activity after CuSO₄ exposure in both cell lines over 24-48 h, while SOD activity initially increased, then declined after 48 h. CK activity was also decreased in C6 cells. NPSH and PSH levels dropped after 24 h, and O₂⁻ production was observed in all CuSO₄ concentrations. GR mRNA was reduced in both cell lines, contrasting with increased GPx1 mRNA in C6. U-87 MG cells exhibited higher levels of SOD1 mRNA, while C6 cells displayed lower expression. Our findings suggest that copper excess limits antioxidant enzyme activity and thiol levels, particularly in the C6 cells, likely attributable to oxidative stress or direct copper-enzyme interactions. Moreover, our results imply differences in copper toxicity regarding the cell lineage used, highlighting the importance of analyzing high copper levels effects in different models. Moreover, it could be proposed that the antioxidant system is a target of copper toxicity, contributing to glioma cell death.