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Y.H. Yoon, M.H. Yoo, J. Koh; Protection Against Zinc-Induced Oxidative Injury in Retinal Cell Culture bt Pyruvate and Oxaloacetate . Invest. Ophthalmol. Vis. Sci. 2003;44(13):467.
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Purpose: Cytotoxcity mediated by endogenous synaptic zinc contributes to cell death in certain cases of acute brain injury. Retina belongs to the central nervous system and contains substantial amounts of releasable zinc. Hence. it seems possible that zinc toxicity may be a contributing factor in certain retinal diseases. In the present study, we examined the characteristics of zinc-induced cytotoxicity in primary culture of rat retinal cells. Methods: Retinal cell cultures were prepared from new born SD rat pups, and exposed to zinc in serum free MEM after 10 days in vitro. Cell death was quantified by LDH release assay. Levels of NAD+ was measured by enzymatic cycling assays. ATP levels were measured with the luciferin-luciferase method. Production of reactive oxygen species in cells was visualized with DCF fluorescence microscopy. Results: Exposure of retinal cultures for 15 min to 300 - 500 mM zinc induced gradual cell body swelling and cell lysis accompanied by the release of LDH into the medium over the following 6 - 10 h. Indicating that zinc cytotoxicity is mediated by oxidative stress, it was accompanied by increased levels of reactive oxygen species, and attenuated by an antioxidant trolox. Preceding cell lysis, levels of NAD+ and ATP decreased drastically. Indicating the role of poly(ADP-ribose) polymerase (PARP), the PARP inhibitor attenuated NAD+ and ATP depletion as well as zinc-induced cell death. Pyruvate and oxaloacetate (OAA) have been shown to markedly protect against oxidative injury as well as zinc toxicity in other cell systems. Likewise, pyruvate and OAA protected retinal cells against NAD+ and ATP depletion as well as death induced by H2O2 and zinc. Lactate, on the other hand, had no protective effect. Conclusions: As in other areas of the CNS, cytotoxicity mediated by endogenous zinc may contribute to cell death in retina. Present results suggest that PARP inhibitors, pyruvate and OAA may prove effective in ameliorating retinal neuronal cell death where zinc toxicity or oxidative stress is involved.
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