Discrimination between RRR- and all-racemic-alpha-tocopherols labeled with deuterium by patients with abetalipoproteinemia.

The ability to discriminate between stereoisomers of alpha-tocopherol was studied in five patients with abetalipoproteinemia (ABL) because an impairment in secretion of apolipoprotein B-containing lipoproteins might impede the normally enhanced plasma transport of RRR-alpha-tocopherol. An oral dose containing 3.7 g of each 2R, 4'R,8'R-alpha-[5-C2H3]tocopheryl acetate (d3RRR-alpha-tocopheryl acetate) and 2RS,4'RS,8'RS-alpha-[5,7-(C2H3)2]tocopheryl acetate (d6 all rac-alpha-tocopheryl acetate) was administered, then the labeled and unlabeled alpha-tocopherol contents of plasma and red blood cells from multiple blood samples obtained at selected times up to 72 h following the dose were quantitated. ABL plasma contained about 1%-10% of the d3-RRR-alpha-tocopherol concentrations of normal subjects given only 150 mg of each isotope. Three of the patients discriminated between forms of alpha-tocopherol with ratios of RRR-/allrac-alpha-tocopherol > or = 1.8, similar to normals. These data suggest that the hepatic tocopherol binding protein is present and functional in ABL patients. Although two of the patients did not discriminate between stereoisomers of alpha-tocopherol, it is likely that this resulted from nearly a complete block in very low density lipoprotein (VLDL) secretion. Thus, the ability of ABL patients to absorb and transport orally administered vitamin E is markedly impaired and variable among patients.