Extracellular and intracellular glutathione protects astrocytes from Zn²⁺-induced cell death

Free Zn²⁺ is released in excess at excitatory synapses in pathological conditions including transient global and focal cerebral ischemia, which causes neuronal and glial cell death. In the current study, we explored the mechanism underlying Zn²⁺-induced cell death in primary cortical astroglial cultures. Chronic treatment with 30-35 μM Zn²⁺ led to the death of 70-95% of astrocytes within 18 h, preceded by Zn²⁺ influx. Extracellular glutathione (GSH; 100 μM) completely blocked the Zn²⁺ influx and Zn²⁺ toxicity. The Zn²⁺ toxicity was also inhibited when intracellular GSH was increased. Conversely, it was aggravated when intracellular GSH was depleted by buthionine sulfoximine (BSO). Consistently, the level of cellular GSH was notably decreased with a concurrent increase in oxidized GSH in Zn²⁺-treated astrocytes. These results suggest that the disruption of proper maintenance of thiol homeostasis is a mechanism underlying Zn²⁺ toxicity in primary cortical astrocytes.