Carotenoid composition and antioxidant potential in subfractions of human low-density lipoprotein

Carotenoids and vitamin E are transported in human plasma complexed with li poproteins. The bulk of them are associated with low-density lipoprotein (L DL), in which form they may act as antioxidants and thus delay the onset of atherosclerosis. We used a simple, rapid, ultracentrifugation technique to fractionate plasma lipoproteins in self-generating gradients of iodixanol (Optiprep(TM)), a non-ionic iodinated density gradient medium. The caroteno id content and composition of a number of LDL subfractions was determined b y reversed-phase high-performance liquid chromatography. Lycopene, beta-car otene and beta-cryptoxanthin were mainly located in the larger, less-dense LDL particles whereas lutein and zeaxanthin were found preferentially in th e smaller, more dense LDL particles. When the antioxidant content of these fractions was expressed per milligram of LDL protein, significantly lower c oncentrations of carotenoid and vitamin E were found to be associated with the smaller, protein-rich fractions of LDL. Strong positive correlations we re found between total carotenoid and Vitamin E plasma concentrations and t he lag-time of Cu2+-mediated oxidation of LDL subfractions The more dense L DL subfractions, which had lower levels of these antioxidants, were more re adily oxidized, highlighting their possible role in atherosclerotic events.