EXTRACELLULAR IRON(II) CAN PROTECT CELLS FROM HYDROGEN-PEROXIDE

We hypothesized that exposure of cells to H2O2 plus Fe2+ would increas e formation of cell-derived Lipid peroxides that would inactivate pros taglandin H synthase, resulting in decreased prostaglandin synthesis, Therefore, we treated human endothelial cells with 0-100 mu M H2O2 fol lowed immediately by addition of 0-200 mu M Fe2+, After oxidant exposu re, cells were stimulated with 20 mu M arachidonic acid to induce pros taglandin I-2 (PGI(2)) synthesis, Adding 100 mu M H2O2 prior to arachi donic acid decreased PGI(2) synthesis more than 80%. However, to our s urprise, the addition of Fe2+, in increasing amounts, progressively pr otected PGI(2) synthesis against the harmful effects of H2O2. A ratio of one part H2O2 to two parts Fe2+ offered almost complete protection, whereas Fe3+ did not protect PGI(2) synthesis from H2O2, We found tha t 100 mu M H2O2 was not cytolytic; however 250 mu M H2O2 was cytolytic ; Fe2+ protected against this cytotoxicity. In addition, extracellular Fe2+ prevented the rise in intracellular calcium caused by H2O2 and e xtracellular Fe2+ preserved intracellular glutathione in H2O2-exposed cells, Electron paramagnetic resonance spin trapping demonstrated that extracellular Fe2+ generated the hydroxyl free radical, HO., outside the cell, We speculate that extracellular Fe2+ protects the intracellu lar space from H2O2 by initiating the Fenton reaction outside the cell , This reductive cleavage of H2O2 generates HO. in the extracellular s pace, where much of the HO. will react with noncellular components, th ereby protecting the cell interior. (C) 1996 Academic Press, Inc.