Influence of Dietary Vitamin E on the Intermembrane Transfer of α-Tocopherol as Mediated by an α-Tocopherol Binding Protein 1

Abstract

Abstract

The effect of dietary vitamin E on the intermembrane transfer of (3R)-α-tocopherol, a spontaneous process accelerated in the presence of an α-tocopherol binding protein (αTBP), was examined. The transfer activity of this cytosolic liver protein was assayed via in vitro transfer of (3R)-α-[³H]tocopherol (α[³H]T) from egg lecithin liposomes to human erythrocyte ghosts (EG). Male Fisher 344 rats (1 and 20 months old) were fed diets containing 0, 30, and 500 mg/kg vitamin E (d/-α-tocopheryl acetate) for 15 weeks. Liver cytosol fractions were assayed for α[³H]T transfer activity (αTTA). Among young rats, those fed vitamin E-deficient diets had the highest αTTA, 5.02 ± 3.10 pmole α[³H]T/min (mean ± SD), which was different (P < 0.05) from the spontaneous transfer rate of 2.10 pmole/min. Neither young rats fed 30 and 500 mg/kg vitamin E diets nor any of the aged rats showed αTTA which differed significantly from the spontaneous transfer rate. To examine the relationship between hepatic α-tocopherol levels and αTTA, α-tocopherol concentration per gram of wet liver was assayed by HPLC. A steep positive slope (6.39 ± 1.46 pmole min^-1 nmole g^-1) and strong correlation (r = 0.873) between hepatic α-tocopherol and αTTA were observed (P < 0.005) among young vitamin E-deficient rats. The data indicates that αTTA varies directly with hepatic α-tocopherol concentration when total liver vitamin E stores are very low. Thus, αTBP-mediated transfer of α-tocopherol may be manifest only when vitamin E status is compromised.