Protective Effects of Extracellular Glutathione Against Zn ²⁺-Induced Cell Death In Vitro and In Vivo

The central nervous system reserves high concentrations of free Zn ²⁺ in certain excitatory synaptic vesicles. In pathological conditions such as transient cerebral ischemia, traumatic brain injury, and kainic acid (KA)-induced seizure, free Zn²⁺ is released in excess at synapses, which causes neuronal and glial death. We report here that glutathione (GSH) can be used as an effective means for protection of neural cells from Zn²⁺-induced cell death in vitro and in vivo. Chronic treatment with 35 μM Zn²⁺ led to death of primary cortical neurons and primary astrocytes. The Zn²⁺ toxicity of cortical neurons was partially protected by 1 mM of GSH, whereas the Zn²⁺ toxicity of primary astrocyte cultures was blocked completely by 100 μM of GSH. To evaluate the beneficial effects of GSH in vivo, an excitotoxin-induced neural cell death model was established by intracerebroventricular (i.c.v.) injection of 0.94 nmol (0.2 μg) KA, which produced selective neuronal death, especially in CA1 and CA3 hippocampal regions. The i.c.v. co-injection of 200 pmol of GSH significantly attenuated KA-induced neuronal cell death and reactive gliosis in hippocampus. The results of this study suggest the contribution of Zn²⁺ in the excitotoxin-induced neural cell death model and a potential value of GSH as a therapeutic means against Zn ²⁺-induced pathogenesis in brain.