Inorganic iron effects on in vitro hypoxic proximal renal tubular cell injury

Abstract

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 μM × 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 (∼ 7-10×) and decreased ATP (∼ 25%). Fe2+, but not Fe3+, caused LDH release (31±2%). During hypoxia, Fe2+ and Fe3+ worsened ATP depletion; however, each decreased LDH release (∼ 31 to ∼ 22%; P < 0.01). Fe2+-mediated protection was negated during reoxygenation because Fe2+ 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.