Hydrogen sulfide ameliorates zinc-induced cell death in neuroblastoma SH-SY5Y cells

Previous reports have demonstrated that excess zinc (Zn²⁺) released from nerve terminals following cerebral ischemia causes brain injury. Therefore, the disturbance of Zn²⁺ homeostasis in the brain is thought to be closely linked to neurotoxicity. Recently, hydrogen sulfide (H₂S), a gaseous mediator, has been reported to ameliorate ischemic brain injury. However, its mechanism is not fully understood. In this study, we examined whether sodium hydrogen sulfide (NaHS), an H₂S donor, protects against Zn²⁺ cytotoxicity using human neuroblastoma SH-SY5Y cells. NaHS dose-dependently prevented cell death caused by Zn²⁺ exposure. Treatment of cells with NaHS just before Zn²⁺ exposure exerted the most potent protection. Zn²⁺ induced loss of intracellular NAD⁺ and ATP and mitochondrial dysfunctions, resulting in cytotoxicity associated with failure of energy production; however, NaHS prevented these Zn²⁺-induced events. In addition, NaHS suppressed Zn²⁺-dependent activation of metal-responsive transcription factor-1 and induction of metallothionein gene expression. Zn²⁺ imaging with the Zn²⁺-specific fluorescent indicator FluoZin-3 revealed that NaHS abolished the elevation of intracellular Zn²⁺ levels after Zn²⁺ exposure. These results suggest that entry of Zn²⁺ into cells was suppressed by NaHS. The measurement of H₂S derived from NaHS by o-fluorinated-azido-capped rhodamine (Rho-N₃F₂), a reaction-based H₂S probe, revealed that H₂S levels in aqueous solutions were markedly reduced in the presence of Zn²⁺. This finding suggests the possibility that H₂S reacts directly with Zn²⁺ and decreases extracellular Zn²⁺ levels. Taken together, we conclude that the protection of NaHS against Zn²⁺ cytotoxicity is exerted by inhibiting entry of Zn²⁺ into SH-SY5Ycells.