Cold induces catalytic iron release of cytochrome P-450 origin: A critical step in cold storage-induced renal injury

Earlier experimental studies have suggested a role for iron in cold-storage-induced organ injury. Whether the cytochrome P-450 enzymes, shown to be a source for iron in several injury models, contribute to cold-induced iron release is not known. Storage of human proximal tubular epithelial (RPTE) cells at 4 degreesC in the University of Wisconsin (UW) solution caused a significant and time-dependent increase in bleomycin-detectable iron (BDI). To identify the cellular source of BDI, RPTE cells were subfractionated and stored at 4 degreesC for 4 h. Bleomycin-detectable iron release was highest in the microsomes, next in the cytosol and none in the mitochondria. As microsomes are rich in iron-containing cytochrome P-450 enzymes, microsomes were cold stored with P-450 inhibitors, cimetidine and piperonyl butoxide. P-450 inhibitors significantly reduced cold-induced BDI release. Furthermore, cimetidine and iron chelator deferoxamine (DFO) significantly reduced cold-induced cell injury, suggesting a role for P-450-derived iron in cold-induced cell injury. In rat kidney experiments, BDI and LDH release were significantly higher in cold-stored kidneys than in control kidneys. Inclusion of cimetidine and DFO in the cold-storage solution significantly suppressed the BDI and LDH release, and reduced the ultrastructural changes. Our data demonstrate for the first time that cold-induced catalytic iron release may be at least in part of microsomal cytochrome P-450 origin, and that it participates in cold-storage-induced renal injury. In the clinical setting, sequestering free iron released during cold storage is possible and may prove to be useful in limiting organ injury.