Danchunhwan water extract prevents apoptotic death by peroxynitrite and nitric oxide in human dopaminergic neuroblastoma SH-SY5Y cells

Graphene quantum dot antioxidant and proautophagic actions protect SH-SY5Y neuroblastoma cells from oxidative stress-mediated apoptotic death

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP). GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical (^•OH), superoxide anion (O₂^•-), and lipid peroxidation. Nonselective antioxidants, ^•OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing ^•OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagy-limiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proautophagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH₄Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both ^•OH/NO scavenging and induction of cytoprotective autophagy.

Green tea polyphenols enhance sodium nitroprusside-induced neurotoxicity in human neuroblastoma SH-SY5Y cells

Oxidative stress is a main mediator in nitric oxide (NO) -induced neurotoxicity and has been implicated in the pathogenesis of many neurodegenerative disorders. Green tea polyphenols are usually expected as potent chemo-preventive agents due to their ability of scavenging free radicals and chelating metal ions. However, not all the actions of green tea polyphenols are necessarily beneficial. In the present study, we demonstrated that higher-concentration green tea ployphenols significantly enhanced the neurotoxicity by treatment of sodium nitroprusside (SNP), a nitric oxide donor. SNP induced apoptosis in human neuroblastoma SH-SY5Y cells in a concentration and time-dependent manner, as estimated by cell viability assessment, FACScan analysis and DNA fragmentation assay, whereas treatment with green tea polyphenols alone had no effect on cell viability. Pre-treatment with lower-dose green tea polyphenols (50 and 100 microm) had only a slightly deleterious effect in the presence of SNP, while higher-dose green tea polyphenols (200 and 500 microm) synergistically damaged the cells severely. Further research showed that co-incubation of green tea polyphenols and SNP caused loss of mitochondrial membrane potential, depletion of intracellular GSH and accumulation of reactive oxygen species, and exacerbated NO-induced neuronal apoptosis via a Bcl-2 sensitive pathway.