Neutral lipid transfer protein does not regulate α-tocopherol transfer between human plasma lipoproteins

Vitamin E has no known plasma carrier protein and is transported by plasma lipoproteins. The site of association of vitamin E in the lipoprotein particle and the mode of transfer of vitamin E between plasma lipoproteins have not been ascertained. Since neutral lipids (triglycerides and cholesterol esters) exchange between plasma lipoproteins by processes mediated by neutral lipid transfer protein, we questioned that if vitamin E, a hydrophobic molecule, is carried in the core of the lipoprotein particle then its transfer between plasma lipoproteins may be mediated by neutral lipid transfer protein. Transfer of D-α(5-methyl-³H)tocopherol from in vitro-labeled human plasma lipoprotein fractions to other plasma lipoproteins was measured under incubation conditions that were designed to yield markedly differing degrees of neutral lipid exchange. Despite the presence of the d>1.21 g/ml lipoprotein-poor plasma fraction or purified lipid transfer protein that resulted in up to a 10-fold increase in neutral lipid transfer, vitamin E transfer between very low density lipoproteins, low density and high density lipoproteins remained constant. Even excess amounts of lipid transfer protein, which caused triglyceride transfer between very low density and high density lipoproteins to reach saturation, failed to affect significantly vitamin E transfer. Vitamin E distribution between lipoprotein fractions did correlate with lipoprotein mass ratios. Vitamin E transfer was higher as the protein ratio of acceptor lipoproteins to donor lipoproteins increased. We conclude that vitamin E transfer between lipoproteins is not dependent primarily on neutral lipid transfer protein and is not mediated via neutral lipid transfer.