Dissemination of peroxidative stress via intermembrane transfer of lipid hydroperoxides: Model studies with cholesterol hydroperoxides

Lipid hydroperoxides (LOOHs) can be generated in cells when cholesterol (Ch ) and other unsaturated lipids in cell membranes are degraded under conditi ons of oxidative stress. If LOOHs escape reductive detoxification by glutat hione-dependent seIenoperoxidases, they may undergo iron-catalyzed one-elec tron reduction to free radical species, thus triggering peroxidative chain reactions which exacerbate oxidative membrane damage. LOOHs are more polar than parent lipids and much longer-lived than free radical precursors or pr oducts. Accordingly, intermembrane transfer of LOOHs (analogous to that of unoxidized precursors) might be possible, and this could jeopardize accepto r membranes. We have investigated this possibility, using photoperoxidized [C-14]Ch-labeled erythrocyte ghosts as cholesterol hydroperoxide (ChOOH) do nors and unilamellar liposomes [e.g., dimyristogl-phosphatidylcholine/Ch, 9 :1 mol/mol] as accepters. ChOOH material consisted mainly of 5 alpha-hydrop eroxide, a singlet oxygen adduct. Time-dependent transfer of ChOOH versus C h at 37 degrees C was determined, using high-performance liquid and thin-la yer chromatographic methods to analyze liposomal extracts for these species . A typical experiment in which the starting ChOOH/Ch mol ratio in ghosts w as similar to 0.05 showed that the initial transfer rate of ChOOH was simil ar to 16 times greater than that of parent Ch. Using [C-14]Ch as a reporter in liposome accepters, we found that transfer-acquired ChOOHs, when expose d to a lipophilic iron chelate and ascorbate, could trigger strong peroxida tive chain reactions, as detected by accumulation of [C-14]Ch oxidation pro ducts. These findings support the hypothesis that intermembrane transfer of ChOOHs can contribute to their prooxidant membrane damaging and cytotoxic potential. (C) 2000 Academic Press.