Zinc release contributes to hypoglycemia-induced neuronal death

Neurons exposed to zinc exhibit activation of poly(ADP-ribose) polymerase-1 (PARP-1), an enzyme that normally participates in DNA repair but promotes cell death when extensively activated. Endogenous, vesicular zinc in brain is released to the extracellular space under conditions causing neuronal depolarization. Here, we used a rat model of insulin-induced hypoglycemia to assess the role of zinc release in PARP-1 activation and neuronal death after severe hypoglycemia. Zinc staining with N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide (TSQ) showed depletion of presynaptic vesicular zinc from hippocampal mossy fiber terminals and accumulation of weakly bound zinc in hippocampal CA1 cell bodies after severe hypoglycemia. Intracerebroventricular injection of the zinc chelator calcium ethylene-diamine tetraacetic acid (CaEDTA) blocked the zinc accumulation and significantly reduced hypoglycemia-induced neuronal death. CaEDTA also attenuated the accumulation of poly(ADP-ribose), the enzymatic product of PARP-1, in hippocampal neurons. These results suggest that zinc translocation is an intermediary step linking hypoglycemia to PARP-1 activation and neuronal death.