The multiple effects of ethylenediaminetetraacetate in several model lipid peroxidation systems

Abstract

Experiments were performed which illustrate the various ways EDTA can influence lipid peroxidation. Either detergent-dispersed linoleate, or liposomes made from extracted microsomal phospholipids were utilized as substrates for peroxidation. Peroxidation was accomplished using Fe 2+ or Fe 3+. In systems utilizing Fe 2+, EDTA chelation facilitated Fe 2+ autoxidation which in turn caused peroxidation of detergent-dispersed linoleate. Peroxidation was not initiated during EDTA-Fe 2+ autoxidation when the substrate lipids were in a liposomal configuration. Systems utilizing Fe 3+ required an enzyme (either xanthine oxidase or NADPH-cytochrome P 450 reductase) to reduce the iron for peroxidative activity. EDTA chelation of Fe 3+ enhanced the xanthine oxidase and NADPH-cytochrome P 450 reductase-catalyzed peroxidation of detergent-dispersed linoleate, presumably by facilitating the reduction of Fe 3+. Catalase and mannitol inhibited both EDTA-Fe 2+- and EDTA-Fe 3+-dependent lipid peroxidation. EDTA-Fe 3+ was not capable of initiating peroxidation of phospholipid liposomes following enzymatic reduction by either enzyme, but ADP-chelated iron effectively initiated liposomal peroxidation in similar systems. With xanthine oxidase-catalyzed peroxidation of liposomes with ADP-Fe 3+, the inclusion of EDTA-Fe 3+ caused a modest enhancement of activity. EDTA-Fe 3+ greatly stimulated NADPH-cytochrome P 450 reductase-catalyzed peroxidation of liposomes with ADP-Fe 3+. In contrast, the addition of EDTA, rather than EDTA-Fe 3+ inhibited the liposomal peroxidation catalyzed by either enzyme with ADP-Fe 3+ when the EDTA concentration exceeded the concentration of Fe 3+.