Microsomal lipid peroxidation. I. Characterization of the role of iron and NADPH
Kornbrust, D.J.; Mavis, R.D.
Molecular Pharmacology 17(3): 400-407
1980
ISSN/ISBN: 0026-895X PMID: 6771519 Document Number: 167327
A number of pathological conditions stemming primarily from exposure to toxic chemicals are believed to be manifested through a process of lipid peroxidation. The NADPH/Fe-dependent peroxidation of lipids in rat liver microsomes was dependent on the presence of free ferrous Fe. High concentrations of Fe2+ initiated microsomal lipid peroxidation at an initial rate which was independent of NADPH. With Fe3+, lower Fe2+ concentrations, or longer incubation times, NADPH stimulated microsomal lipid peroxidation and this stimulation was blocked by cytochrome c, which is capable of accepting electrons from the microsomal NADPH-cytochrome P-450 reductase. NADPH did not induce peroxidation in the absence of Fe, nor did ferric Fe in the absence of NADPH. Thus the role of NADPH appears to be maintenance of Fe in the reduced Fe2+ state. The presence of superoxide dismutase, catalase, or the hydroxyl radical scavengers ethanol or thiourea had little or no effect on the Fe-initiated peroxidation, ruling out dependence on reduced states of O. Complete chelation of Fe by EDTA completely inhibited peroxidation and no stimulation by either EDTA or ADP was observed over the peroxidation produced by free Fe alone. Preincubation of microsomes in the absence of Fe did not enhance the peroxidation rate upon subsequent addition of Fe, suggesting that Fe acts by initiating peroxidative decomposition of membrane lipids rather than by catalyzing the breakdown of preformed hydroperoxides. Liposomes of extracted microsomal lipid also underwent peroxidation in the presence of ferrous Fe at a rate comparable to that of intact microsomes. Ascorbate stimulated Fe-induced liposomal peroxidation but had no effect in the absence of Fe. H2O2 did not enhance Fe-induced liposomal peroxidation and inhibited at high concentrations, ruling out a role for hydroxyl radicals produced by reduction of H2O2 by Fe2+.