Fe(2+)-induced lipid peroxidation kinetics in liposomes: the role of surface Fe2+ concentration in switching the reaction from acceleration to decay.

Kinetics of malonyldialdehyde (MDA) accumulation, Fe2+ oxidation, and chemiluminescence (CL) at different initial iron ([Fe2+]) and liposome ([L]) concentrations were measured in liposome suspension. Above certain critical Fe2+ concentrations ([Fe2+]*) the latent period (LP) of LPO development was observed. The method of [Fe2+]* estimation by the dependence of LP value (tau) on [Fe2+] was elaborated. The increase of [L] resulted in decrease of tau and increase of delta MDA as well as SF CL amplitude. [Fe2+]* value changed from 10 to 50 microM with change of [L] from 1 to 4 mg/ml, so that the ratio [Fe2+]*/[L] was kept constant. This may be explained under the assumption that the major part of Fe2+ is bound by the membranes. At concentrations of Fe2+ higher than the critical one, iron chelators (desferrioxamine, o-phenanthroline, and EDTA) and cations (Eu3+, Ca2+, and Fe3+) decreased tau without any essential influence on the CL "slow flash" amplitude (h). Apparently, the only result of iron complexones and cations on LPO is the decrease of Fe2+ ion concentration on the membrane surface. Thus, [Fe2+]* value and surface concentration of Fe2+ are the main parameters determining both kinetics and efficiency of Fe(2+)-induced LPO in membrane systems.