Lipid peroxidation in erythrocyte membranes: cholesterol product analysis in photosensitized and xanthine oxidase-catalyzed reactions.

The effects of singlet oxygen- and oxygen radical-induced lipid peroxidation on cell membrane integrity were compared, using the human erythrocyte ghost as a model system. Resealed ghosts underwent lipid peroxidation and lysis (release of trapped glucose-6-P) when irradiated in the presence of uroporphyrin (UP) or when incubated with xanthine (X), xanthine oxidase (XO) and iron. The UP-sensitized process was inhibited by azide but not by phenolic antioxidants, consistent with singlet oxygen (nonradical) involvement. This was confirmed by showing that the predominant photoproduct of membrane cholesterol was the 5 alpha-hydroperoxide. Total hydroperoxide (LOOH) content in UP-photooxidized ghosts increased linearly during the prelytic lag and throughout the period of rapid lysis. Unlike the photoreaction, X/XO/iron-dependent peroxidation and lysis was inhibited by catalase, superoxide dismutase and phenolic antioxidants, indicating O2-/H2O2 intermediacy and a free radical mechanism. Correspondingly, only radical reaction products of cholesterol were formed, notably the 7 alpha-, 7 beta-hydroperoxide pair. Membrane lysis had a distinct lag as in photooxidation; however, the LOOH profile was more complex, with an initial lag followed by a sharp increase and then slow decline. X/XO/iron-induced lysis commenced when LOOH levels were 2-3 times higher than in photosensitized lysis, suggesting that the pathways of membrane lesion formation are different in the two systems.(ABSTRACT TRUNCATED AT 250 WORDS)