Graphene quantum dots protect SH-SY5Y cells from SNP-induced neurotoxicity by ROS/RNS scavenging

Abstract

We here investigated the ability of graphene quantum dots (GQD), graphene nanoparticles with antioxidative capacity, to protect SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP). Although GQD diminished the levels of nitric oxide (NO) in both cell free condition and SNPexposed cells, NO scavengers (PTIO and uric acid), displayed only slight protection from SNP, suggesting that NO scavenging was not the main protective mechanism of GQD. Moreover, GQD significantly protected SH-SY5Y cells from neurotoxicity of light exhausted SNP, incapable of producing NO, implying the existence of protective mechanism independent of NO-scavenging. GQD lowered the increase in the concentration of hydroxyl radical (•OH) and superoxide anion (O2•−) caused by SNP both in the cell-free condition and inside cells, as well as ensuing oxidative stress and lipid peroxidation. Nonspecific antioxidants (glutathione, NAC), •OH scavenger (DMSO), and iron chelators (DTPA, BPDSA), but not superoxide dismutase, mimicked the cytoprotective activity of GQD, suggesting that GQD protect cells by neutralizing •OH generated in the presence of iron released from SNP. GQD were readily internalized by SH-SY5Y cells, while extensive washing of cells pre-incubated with GQD only partly reduced their protective activity, suggesting that GQD exerted neuroprotective effect both intra- and extracellularly. By demonstrating that GQD protect neuroblastoma cells from SNP-induced neurotoxicity by both extracellular •OH/NO scavenging and some unknown intracellular mechanism, our results suggest that GQD could be valuable candidate for treatment of neurodegenerative and neuroinflammatory disorders associated with oxidative/nitrosative stress.