OXIDATION OF LIPIDS IN LOW-DENSITY-LIPOPROTEIN PARTICLES

This study was undertaken to understand further the mechanisms and dyn amics of the oxidation of lipids in low density lipoprotein (LDL) part icles, aiming specifically at elucidating the material balance between oxygen uptake and products found and also the relative susceptibiliti es to oxidation of cholesteryl ester in the core and phosphatidylcholi ne in the outer monolayer in the LDL particles. It was found that cons iderable amount of oxygen uptake could not be accounted for by conjuga ted diene or total peroxides. Total peroxide was measured from the pho sphine oxide formed from triphenylphosphine or diphenylpyrenylphosphin e by reduction of peroxides. Cholesteryl ester hydroperoxides and phos phatidylcholine hydroperoxides were the major peroxides formed in LDL oxidation, but they accounted for about 60% of total peroxide. Cholest erol was also oxidized, but its oxidation was significant only at the later stages of the reaction. It was also found that the oxidizability of cholesteryl ester relative to phosphatidylcholine was larger withi n the LDL particle than in homogeneous solution and this was interpret ed in the context of the physical properties of LDL particle.