Effect of aluminum ion on Fe(2+)-induced lipid peroxidation in phospholipid liposomes under acidic conditions.

The effects of Al3+ on Fe(2+)-induced lipid peroxidation in phospholipid liposomes consisting of phosphatidylcholine (PC) and phosphatidylserine (PS) were examined under acidic conditions. The stimulatory effect of Al3+ on Fe(2+)-induced lipid peroxidation in the liposomes showed a biphasic response against pH variation, and the maximum stimulation was observed around pH 6.0. In addition, it was found that the stimulatory effect of Al3+ on the lipid peroxidation was dependent on the proportion of PS in the liposomes. On the other hand, the lipid peroxidation in PC liposomes was not stimulated by the addition of Al3+. From these findings, it is suggested that the Al3+ effect on Fe(2+)-induced lipid peroxidation under acidic conditions is largely dependent on the phospholipid composition. Trivalent cations such as Tb3+ and Ga3+ also stimulated Fe(2+)-induced lipid peroxidation in PC/PS liposomes under acidic conditions, but divalent cations (Zn2+ and Mn2+) showed no stimulatory effect. The extents of Fe2+ disappearance and Fe3+ formation during the reaction were enhanced by the addition of Al3+ or Ga2+, but Tb3+ had no effect on Fe2+ disappearance. The results with 1,6-diphenyl-1,3,5-hexatriene (DPH) showed that the fluorescence anisotropy of DPH-labeled PC/PS liposomes under acidic conditions was increased by the addition of Al3+. Furthermore, there is a relation between the extents of the fluorescence anisotropy of the complex and TBARS production. In contrast, the fluorescence anisotropy of DPH molecules embedded in PC liposomes was not changed by the addition of Al3+. Based on these results, a possible mechanism of the stimulatory effect of Al3+ on Fe(2+)-induced lipid peroxidation under acidic conditions is discussed.