Iron (III) stimulation of lipid hydroperoxide-dependent lipid peroxidation.

In an experimental system where both Fe2+ autoxidation and generation of reactive oxygen species is negligible, the effect of FeCl2 and FeCl3 on the peroxidation of phosphatidylcholine (PC) liposomes containing different amounts of lipid hydroperoxides (LOOH) was studied; Fe2+ oxidation, oxygen consumption and oxidation index of the liposomes were measured. No peroxidation was observed at variable FeCl2/FeCl3 ratio when PC liposomes deprived of LOOH by triphenylphosphine treatment were utilized. By contrast, LOOH containing liposomes were peroxidized by FeCl2. The FeCl2 concentration at which Fe2+ oxidation was maximal, defined as critical Fe2+ concentration [Fe2+], depended on the LOOH concentration and not on the amount of PC liposomes in the assay. The LOOH-dependent lipid peroxidation was stimulated by FeCl3 addition; the oxidized form of the metal increased the average length of radical chains, shifted to higher values the [Fe2+] and shortened the latent period. The iron chelator KSCN exerted effects opposite to those exerted by FeCl3 addition. The experimental data obtained indicate the kinetics of LOOH-dependent lipid peroxidation depends on the Fe2+/Fe3+ ratio at each moment during the time course of lipid peroxidation. The results confirm that exogenously added FeCl3 does not affect the LOOH-independent but the LOOH-dependent lipid peroxidation; and suggest that the Fe3+ endogenously generated exerts a major role in the control of the LOOH-dependent lipid peroxidation.