Distribution of alpha-tocopherol in human plasma lipoproteins

Lipoproteins were removed from human plasma by ultracentrifugation at a density of 1.225. Three classes of lipoproteins were then separated by 4% Agarose-column chromatography: very low density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). A sensitive high performance liquid chromatography method with a fluorescence detector was used to estimate alpha-tocopherol in plasma and in column eluates. Total plasma tocopherol was not significantly different in males (n = 6) and females (n = 6) and almost all of the vitamin was recovered in the isolated lipoproteins. Although LDL and HDL were the main carriers of alpha-tocopherol in both males and females, more tocopherol was found in LDL than in HDL in males but the opposite was true in females. The distribution of alpha-tocopherol in males was: VLDL, 8%; LDL, 59%; and HDL, 33% whereas that in females was VLDL, 2%; LDL, 42%; HDL, 56%. The distribution of protein in lipoprotein from males was: VLDL, 4%, LDL, 37%; and HDL, 59% and in females: VLDL, 2%; LDL, 25%; and HDL, 73%. The alpha-tocopherol concentration (expressed as microgram alpha-tocopherol/mg protein) in lipoproteins differed little between the sexes. The values in males were: VLDL, 7.0; LDL, 4.3; and HDL, 1.5, in females: VLDL, 3.9; LDL, 4.7; and HDL, 2.1. The data suggest that the different distribution of alpha-tocopherol in plasma lipoproteins in males and females is due to the different levels of proteins in those lipoprotein fractions. Overall, tocopherol and protein levels were highly correlated in HDL, a lower correlation was found in LDL.