Neuroprotective effect of 3-morpholinosydnonimine against Zn²⁺-induced PC12 cell death

Excessive intracellular accumulation of zinc (Zn²⁺) is neurotoxic and contributes to a number of neuropathological conditions. Here, we investigated the protective effect of 3-morpholinosydnonimine (SIN-1) against Zn²⁺-induced neuronal cell death in differentiated PC12 cells. We found that Zn²⁺-induced PC12 cell death was reduced in a concentration-dependent manner by pretreatment with SIN-1. The intracellular accumulation of Zn²⁺ was not affected by pretreatment with SIN-1, indicating that SIN-1-induced neuroprotection was not attributable to reduced influx of Zn²⁺ into cells. SIN-1C, the stable decomposition product of SIN-1, failed to prevent Zn²⁺-induced cell death. Furthermore, the protective effect of SIN-1 against Zn²⁺-induced PC12 cell death was almost completely abolished by uric acid, a free radical scavenger, suggesting that reactive oxygen and nitrogen species generated by SIN-1 may contribute to the protective effect. SIN-1 prevented the inactivation of glutathione reductase (GR) and the increase in the ratio of oxidized glutathione/total glutathione (GSSG/total GSH) induced by Zn²⁺. Addition of membrane permeable GSH ethyl ester (GSH-EE) to PC12 cells prior to Zn²⁺ treatment significantly increased cell viability. We therefore conclude that SIN-1 may exert neuroprotective effect against Zn²⁺-induced cell death in differentiated PC12 cells by preventing inhibition of GR and increase in GSSG/total GSH ratio.