Distribution of lipid-soluble antioxidants in lipoproteins from healthy subjects. I. Correlation with plasma antioxidant levels arid composition of lipoproteins

The concentration of five lipid-soluble antioxidants (gamma- and alpha-toco pherol, lycopene, beta-carotene and ubiquinol-10) was measured in plasma an d very low-density, low-density and high-density lipoproteins (VLDL, LDL an d HDL) isolated from young healthy normocholesterolemic subjects. Alpha-toc opherol was the exclusive antioxidant whose plasma concentration significan tly correlated with the absolute concentration of total cholesterol (r=0.54 1, P<0.001). No correlation was found between plasma concentration and lipo protein content of alpha-tocopherol and ubiquinol-10, whereas it reached st atistically significant values for gamma-tocopherol, lycopene and beta-caro tene. The alpha-tocopherol content in VLDL and HDL, but not in LDL, was str ictly associated with the relative abundance of cholesterol and phospholipi ds in the lipoprotein particles. Moreover, the difference between alpha-toc opherol concentration in VLDL and LDL appeared to be strictly related to th e differences in cholesterol, phospholipids and triglycerides. The percent distribution of the total plasma pool of antioxidant in each lipoprotein cl ass revealed that gamma- and alpha-tocopherol were roughly equally distribu ted in LDL and HDL. On the other hand, lycopene, beta-carotene and ubiquino l-10 were preferentially sequestered in LDL. Finally, the absolute and rela tive concentration of alpha-tocopherol, but not that of other antioxidants, in HDL exhibited a statistically significant correlation with plasma HDL/L DL cholesterol ratio. These findings indicate that: (i) plasma concentratio ns of major lipid-soluble antioxidants are not always predictive of their l evels in lipoproteins and that, within individual lipoprotein classes, (ii) the lipid composition, metabolism and relative plasma concentration may si gnificantly affect their abundance. (C) 2000 Academic Press.