Graphene quantum dots protect SH-SY5Y neuronal cells from SNP-induced apoptotic death

Abstract

Introduction: We examined the molecular mechanisms of graphene quantum dot (GQD)- mediated protection of SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP). Methods: GQD was produced by electrochemical oxidation of graphite and characterized by AFM, UVVIS and FTIR spectroscopy. The antioxidant activity of GQD in cell-free conditions was assessed by DPPH, NBT and EPR analysis. The neuroprotective potential of GQD was determined by cell viability assays MTT, CV. Flow cytometry was used to assess markers of apoptosis and GQD scavenging of intracellular ROS/RNS as well. Cellular internalization of GQD was determined using TEM. Results: GQD prevented SNP-induced apoptosis, caspase activation and mitochondrial depolarization in neuroblastoma cells. Although GQD diminished the NO levels in SNP-treated cells, NO scavengers displayed only a slight protection. GQD significantly protected SH-SY5Y cells from neurotoxicity of lightexhausted SNP, incapable of producing NO, implying that protective mechanism is independent of NO-scavenging. GQD reduced SNP-triggered increase in intracellular levels of ROS, particularly •OH, O2•− in cells and cell-free condition. Nonselective antioxidants, •OH scavengers and iron chelators, mimicked GQD cytoprotection, indicating that GQD protect cells by neutralizing •OH generated in the Fenton reaction. Cellular GQD internalization was required for optimal protection since the removal of extracellular GQD by extensive washing partly diminished their protective effect, suggesting that GQD exerted neuroprotective effect intra- and extracellularly. Conclusion: By demonstrating that GQD protect neuroblastoma cells from SNP-induced apoptosis by •OH/NO scavenging, our results suggest that GQD could be valuable candidates for treatment of neurodegenerative diseases associated with oxidative/nitrosative stress.