Zinc protects against oxidative damage in cultured human retinal pigment epithelial cells

This study was undertaken to determine whether bioavailable zinc can influe nce the effects of oxidative stress on cultured human retinal pigment epith elial (RPE) cells. RPE cells were maintained for 7 d in culture medium cont aining 14 mu M total zinc, or in medium containing 0.55 mu M total zinc. Af ter 1 week, MTT assays were performed to determine the relative cytotoxicit y of H2O2 or paraquat on RPE cells. Conjugated dienes and thiobarbituric ac id reactive substances (TBARS) were measured in RPE cells treated with 0, 0 .5 mM H2O2, 10 mu M FeSO4 +/- 0.5 mM H2O2 or 10 mu M FeSO4 + xanthine/xanth ine oxidase for 24 h or paraquat for 7 d. Oxidized proteins were determined by the formation of carbonyl residues. The antioxidants metallothionein, c atalase, superoxide dismutase, and glutathione peroxidase were also measure d. The MTT assays showed that zinc protected cultured RPE from the toxicity of H2O2 and paraquat. RPE cells in 0.55 mu M zinc medium contained higher levels of TBARS, conjugated dienes and protein carbonyls due to the oxidati ve stresses, compared to cells in 14 mu M zinc. Catalase and MT content wer e reduced in cells cultured in 0.55 mu M zinc medium and were reduced addit ionally when treated with above stresses. Superoxide dismutase activity inc reased in 0.55 mu M zinc medium in response to these stresses. Our results show RPE cells cultured in zinc-reduced medium are more susceptible to oxid ative insult. (C) 1999 Elsevier Science Inc.