Effect of Antioxidants on Oxidative Modification of LDL

Human low density lipoprotein (LDL) with a molecular mass of 2.5 million contains on average 1300 molecules of polyunsaturated fatty acids (PUFAs) bound in the different lipid classes. The predominant antioxidant in LDL is a-tocopherol, with an average of 6 molecules in each LDL particle. The other substances with potential antioxidant activity are: gamma-tocopherol, β-carotene, a-carotene, lycopene, cryptoxanthin, cantaxanthin, phytofluene and ubiquinol-10. Each is present in amounts of only 1/ 20th to 1/300th of that of a-tocopherol. If LDL is exposed to oxidative conditions (Cuions, macrophages) a lag phase precedes the oxidation of PUFAs. During the lag phase the antioxidants disappear with a-tocopherol the first to go and β-carotene the last.The lag phase, which can readily be determined, is an index of the oxidation resistance of LDL. If LDL is loaded with vitamin E in vitro its oxidation resistance increases linearly with its a-tocopherol content according to the equation, y=kx+a. The same relation...