Lipid hydroperoxides (LOOHs) are potentially deleterious intermediates generated by activated oxygen attack on unsaturated lipids, phospholipids (PLs), and cholesterol in cell membranes. Singlet oxygen ()-derived LOOHs are of special interest because of the growing concern about cutaneous photoxicity resulting from 2-mediated photodynamic action of visible radiation or long wavelength ultraviolet radiation. It is proposed that LOOHs generated in or acquired by cell membranes can either undergo (i) glutathione/selenoperoxidase (GSH/GPX)-mediated two-electron reduction to relatively innocuous alcohols (detoxification) or (ii) iron-mediated one-electron reduction resulting in chain reactions that exacerbate peroxidative injury, possibly culminating in apoptotic or programmed cell deat (toxicity enhancement). Information is limited about the factors that might affect LOOH partitioning between pathways (i) and (ii) in a cell exposed to peroxidative stress. This question will be addressed by investigating both pathways in comprehensive fashion, first using cholesterol LOOHs and PLOOHs incorporated into model membranes and then photogenerated counterparts in various tumor cell lines. Several techniques developed in this laboratory will be used, including (i) high performance liquid chromatography with mercury cathode electrochemical detection [HPLC-EC(Hg)] for high-sensitivity monitorin of LOOH detoxification, and (ii) thin layer chromatography with phophorimaging radiodetection (TLC-PI) for assessing LOOH chain initiation potency (CIP), an index reflecting the degree of oxidation of a """"""""reporter"""""""" lipid, e.g. [14C] cholesterol. These approaches will be used in an effort to ascertain how changes in cellular selenium, iron, or a-tocopherol status might affect LOOH detoxification on the one hand, and toxicity enhancement leading to apoptotic cell death on the other. The studies are intended to provide new information about the dynamics of biologically important LOOHs and how cells respond to peroxidative challenges imposed by 1O2 and other activated species.
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