Ferritin and superoxide-dependent lipid peroxidation.

Abstract

Ferritin was found to promote the peroxidation of phospholipid liposomes, as evidenced by malondialdehyde formation, when incubated with xanthine oxidase, xanthine, and ADP.Activity was inhibited by superoxide dkmutase but markedly stimulated by the addition of catalase.Xanthine oxidase-dependent iron release from ferritin, measured spectrophotometrically using the ferrous iron chelator 2,2'-dipyridyl, was also inhibited by superoxide dismutase, suggesting that superoxide can mediate the reductive release of iron from ferritin.Potassium superoxide in crown ether also promoted superoxide dismutase-inhibitable release of iron from ferritin.Catalase had little effect on the rate of iron release from ferritin; thus hydrogen peroxide appears to inhibit lipid peroxidation by preventing the formation of an initiating species rather than by inhibiting iron release from ferritin.EPR spin trapping with 5,5-dimethyl-l-pyrroline-N-oxide was used to observe free radical production in this system.Addition of ferritin to the xanthine oxidase system resulted in loss of the superoxide spin trap adduct suggesting an interaction between superoxide and ferritin.The resultant spectrum was that of a hydroxyl radical spin trap adduct which was abolished by the addition of catalase.These data suggest that ferritin may function in vivo as a source of iron for promotion of superoxide-dependent lipid peroxidation.Stimulation of lipid peroxidation but inhibition of hydroxyl radical formation by catalase suggests that, in this system, initiation is not via an iron-catalyzed Haber-Weiss reaction.Cellular damage resulting from ischemia (l), hyperoxia (2), redox cycling (3), and other oxygen-associated toxicities is often attributed to enhanced production of superoxide (0;) with biochemical alterations reported to include peroxidation of membrane phospholipids (4) and DNA degradation (5).However, in aqueous media 0, is relatively unreactive toward most organic compounds (6); thus its proposed deleterious effects may be the result of its participation in reactions leading to other more reactive species.Superoxide-dependent formation of more reactive radicals such as the hydroxyl radical (.OH) requires the presence of transition metal ions such as copper or iron (4).The most widely proposed mech-