Iron-dependent free radical reactions and renal ischemia are believed to be critical mediators of myohemoglobinuric acute renal failure. Thus, this study assessed whether catalytic iron exacerbates O2 deprivation-induced proximal tubular injury, thereby providing an insight into this form of renal failure. Isolated rat proximal tubular segments (PTS) were subjected to either hypoxia/reoxygenation (H/R: 27:15 min), ''chemical anoxia'' (antimycin A; 7.5 muM x 45 min), or continuous oxygenated incubation+/-ferrous (Fe2+) or ferric (Fe3+) iron addition. Cell injury (%lactic dehydrogenase [LDH] release), lipid peroxidation (malondialdehyde, [MDA]), and ATP depletion were assessed. Under oxygenated conditions, Fe2+ and Fe3+ each raised MDA (approximately 7-10X) and decreased ATP (approximately 25%). Fe2+, but not Fe3+, caused LDH release (31+/-2%). During hypoxia, Fe2+ and Fe3+ worsened ATP depletion; however, each decreased LDH release (approximately 31 to approximately 22%; P < 0.01). Fe2+-mediated protection was negated during reoxygenation because Fe3+ exerted its intrinsic cytotoxic effect (LDH release: Fe2+ alone, 31+/-2%; H/R 36+/-2%; H/R + Fe2+ 41+/-2%). However, Fe3+-mediated protection persisted throughout reoxygenation because it induced no direct cytotoxicity (H/R, 39+/-2%; H/R +Fe3+, 25+/-2%; P < 0.002). Fe3+ also decreased antimycin toxicity (41+/-4 vs. 25+/-3%; P < 0.001) despite inducing marked lipid peroxidation and without affecting ATP. These results indicate that catalytic iron can mitigate, rather than exacerbate, O2 deprivation/reoxygenation PTS injury.
