Antioxidant Activity of Low-Density Lipoprotein

Oxidation of low-density lipoprotein (LDL) is of great interest for epidemiological and clinical diagnostic reasons, as well as for basic scientific research, because it is thought to precede the development of atherosclerotic lesions (1 ). Measurement of individual antioxidants such as α-tocopherol, is, of course, a primary route to the study of LDL oxidation. However, such measurements are not always possible and do not take into account the potential contribution to the antioxidant activity of LDL from a wide variety of different antioxidants whose exact nature may not be known. Oxidized LDL can itself be quantitatively measured (2 ) as well as LDL oxidizability (3 –5 ). However, the measurement of LDL oxidizability involves a prolonged and variable incubation period and the results obtained from the studies previously quoted are, in a number of respects, contradictory. LDL oxidizability measurements clearly reflect a number of factors other than the antioxidant content of LDL (for example, the presence of pre-formed lipid hydroperoxides and the ratio of saturated to unsaturated fatty acids) (6 ), which may, of course, be a desirable feature because oxidized LDL itself is the end product of a multi-factorial process.