Stimulation of Fe 2+-induced lipid peroxidation in phosphatidylcholine liposomes by aluminium ions at physiological pH

Abstract

The effects of aluminium ions on Fe 2+-induced lipid peroxidation in egg yolk phosphatidylcholine liposomes were examined under various conditions. The degree of Fe 2+-induced lipid peroxidation of the liposomes was dependent on pH of the reaction mixture: pH 5.0 > pH 7.4. However, Fe 2+ did not induce lipid peroxidation in the liposomes at pH 9.0. The addition of AlCl 3, to the liposomal suspension resulted in a marked stimulation of Fe 2+-induced liposomal peroxidation at pH 7.4, depending on the concentration of AlCl 3. On the other hand, Fe 3+, Cu 2+, Pb 2+, Cd 2+ and Cr 6+ did not induce lipid peroxidation in the liposomes at pH 7.4 regardless of the presence and absence of AlCl 3. Fe 3+ enhanced Fe 2+-induced liposomal peroxidation at pH 7.4 but is unrelated to the stimulatory effect of AlCl 3. In the absence of AlCl 3, Fe 2+-induced liposomal peroxidation was observed after a lag phase of about 15 min. The lag phase of the reaction was shortened by the addition of AlCl 3 in a dose-dependent fashion. The shortening of the lag phase was also observed by the decrease of Fe 2+ concentration or by the co-presence of Fe 3+ in the reaction mixture. In addition, it was found that AlCl 3 stimulates Fe 2+ disappearance and Fe 3+ formation. The addition of AJC1 3 to the liposomal suspension at pH 7.4 resulted in a marked increase of the turbidity of the suspension. On the other hand, the turbidity of the liposomal suspension at pH 5.0 did not change by the addition of AlCl 3. Furthermore, addition of AlCl 3 at the same concentration to the buffer system without the liposomes did not cause an appreciable increase of the turbidity. From these results, it is suggested that Al 3+ promotes aggregation of the liposomes. In addition, it was found that there is a good correlation between the stimulatory effect of Al 3+ and the turbidity change of the suspension over the concentration range of AlCl 3 tested (0.1–1.0 mM). On the basis of these results, the stimulatory effect of Al 3+ on Fe 2+-induced lipid peroxidation of the liposomes is discussed in relation to the liposomal aggregation.