Abstract
New developments in lipid peroxidation are presented. Amongst many biological components lipids are the most susceptible to oxidation since they contain polyunsaturated fatty acids (PUFA). PUFA is oxidized by a free radical chain mechanism in which one radical results in the formation of hundreds of lipid hydroperoxides. Oxidation of arachidonic acid gives polyoxygenated products including isoprostanes, useful as markers of a nonenzymatic oxidation in vivo. The oxidizability of PUFA in homogeneous solution depends on the number of bisallylic positions available for oxidation. In contrast, the oxidizability of PUFA in aqueous micelles decreases with an increasing number of bisallylic sites. Peroxyl radicals derived from docosahexaenoate are considered to be more polar than those from linoleate because the ratio of oxygen uptake to substrate consumption increased from 1 to 3.4 with an increasing number of unsaturation. The rate of disappearance of butyl hydroxytoluene situated in the core of micelles decreased with an increasing number of unsaturation during the oxidation of PUFA. Polar peroxyl radicals from highly unsaturated fatty acid methyl ester would thus appear to migrate from the core to micelle surface with consequent reduction in rate of oxidation by enhancing the rate of termination and reducing the rate of propagation. The authors have established a reliable method for evaluating the regioisomeric composition of Ch 18 : 2-O (O) H in human plasma, with no affect on artifactual oxidation during sample treatment and analysis. All four regioisomers of Ch 18 : 2-O (O) H were detected in blood plasma from healthy young subjects. The 13 ZE-Ch 18 : 2-O (O) H isomer was not a major product produced through the enzymatic oxidation of Ch 18 : 2. Free radical-mediated oxidation of polyunsaturated lipids appears from the present findings to be an ongoing process within normal healthy individuals.
