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Lipid peroxidation in erythrocyte membranes: Cholesterol product analysis in photosensitized and xanthine oxidase‐catalyzed reactions
Author(s) -
Girotti Albert W.,
Bachowski Gary J.,
Jordan John E.
Publication year - 1987
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02537268
Subject(s) - chemistry , lipid peroxidation , lysis , hydroxyl radical , xanthine oxidase , catalase , superoxide dismutase , singlet oxygen , biochemistry , radical , photochemistry , oxygen , antioxidant , enzyme , organic chemistry
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 5α‐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 O 2 − /H 2 O 2 intermediacy and a free radical mechanism. Correspondingly, only radical reactions products of cholesterol were formed, notably the 7α‐, 7β‐hydroperoxide pair. Membranes 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. In low concentrations, ascorbate exacerbated the damaging effects of photoperoxidation, switching the reaction from primarily singled oxygen‐ to oxygen radical‐dependence, as indicated by cholesterol product analysis.