Effects of Iron Chelates on the Transferrin-Free Culture of Rat Dermal Fibroblasts through Active Oxygen Generation

Effects of nonchelating and chelating agents at 10 mM on the serum-free culture of rat dermal fibroblasts were investigated. A strong iron-chelating agent, iminodiacetic acid (IDA), and a weak one, dihydroxyethylglycine (DHEG), decreased iron permeation into preconfluent fibroblasts. A weak iron-chelating agent, glycylglycine (GG), a nonchelating agent, N-2-hydroxyethylpiperazine -N'-2-ethanesulfonic acid (HEPES), and human apotransferrin ($10 \mug/ml$) increased the permeation with time. Iron may be essential for survival of fibroblasts because subconfluent fibroblasts exposed to$100 \muM FeSO_4$in combination with transferrin, HEPES, or GG significantly decreased to release lactate dehydrogenase into the medium. Superoxide dismutase and dimethyl sulfoxide blocked the enzyme release, suggesting that Superoxide and hydroxyl radical induce cellular damage but hydrogen peroxide (H2O 2) generated by Superoxide dismutation does not. GG significantly reduced H2O 2cytotoxicity. DHEG acted as a potent promoter of the iron-stimulated cellular damage if ascorbate or H2O 2was added to the medium. FeSO4and FeCl3(50 to$100 \muM$) individually combined with IDA maximally promoted fibroblast proliferation. Ascorbate increased formation of thiobarbituric acid-reactive substances from deoxyribose in the medium supplemented with FeSO4and either IDA or DHEG. Conversely, ascorbate decreased the formation in the medium with FeSO4and with or without other agents. Fibroblast proliferation may thus be stimulated through the active oxygen generation mediated by a redox-cycling between Fe3+and Fe2+, which are dissolved in the medium at a high concentration, rather than through delivery of iron into the cells.