Two processes responsible for chemiluminescence development in the course of iron-mediated lipid peroxidation

The kinetics of chemiluminescence (CL) accompanying Fe(2+)-induced lipid peroxidation (LPO) in liposome suspension has been investigated. A sequence of stages was observed, namely: (1) fast CL flash (FF); (2) latent period (LP); (3) slow CL flash (SF) and (4) stationary chemiluminescence (SL). The first three stages are known to reflect the Fe(2+)-mediated LPO process. In spite of the fact that at the stage of SL Fe2+ has completely oxidized and MDA has not accumulated, CL intensity was found to increase and after 0.5-1 h reached a value that was several times higher than SF amplitude. The maximal SL level was linearly dependent on the initial Fe2+ concentration and was not dependent on liposome concentration in the suspension. The nature of the processes responsible for CL emission at the stage of SL has been investigated using free radical reaction inhibitors and measurement of CL spectra. The SL spectrum was observed in the red region (lamda > 590 nm) in contrast to the SF CL spectrum (maximum at 540nm). SL amplitude was strongly inhibited by sodium azide (40%), superoxide dismutase (SOD) (30%), desferrioxamine and EDTA (30%), whereas mannitol, ethanol, alpha-tocopherol and butylated hydroxytoluene were ineffective. The data obtained indicate that CL at the stage of SL is not directly related to LPO process, i.e. lipid free radical recombination. The mechanism of stationary CL generation is discussed.