The concentrations and distributions of major lipids (cholesterol, phospholipid, and triglyceride), tocopherol and carotenoids were determined in the plasma lipoprotein fractions (VLDL, LDL, and HDL) of (1) normal human subjects, (2) patients with hyperlipoproteinemia, and (3) patients with erythropoietic protoporphyria treated with oral beta-carotene and/or alpha-tocopherol. The distribution of tocopherol (in percent) was most closely correlated with the distribution of total lipids in the individual lipoproteins, while the major portion of beta-carotene was present in the low density lipoproteins, irrespective of the lipid distribution in the lipoproteins (except for one subject with hyperchylomicronemia). The alpha-tocopherol and beta-carotene concentrations of plasma and RBC in patients treated with tocopherol and carotene were determined periodically for a one-year period. Plasma and RBC tocopherol concentrations showed a rapid, parallel increase in response to tocopherol supplementation. In contrast, the plasma and RBC carotene concentrations showed a much slower and nonparallel increase in response to carotene administration. When carotene supplementation was stopped, the elevated carotene levels in both plasma and RBC persisted for several months; the elevated plasma carotene level persisted longer than the raised RBC carotene levels. These results suggest that alpha-tocopherol and beta-carotene are transported differently in the circulation and that the tissue storage and mobilization of these compounds are different.

Adult↗

PubMed1975

Comparison of exchange of alpha-tocopherol and free cholesterol between rat plasma lipoproteins and erythrocytes.

The simultaneous exchange of (3h)tocopherol and (14C)cholesterol between rat plasma, rat plasma lipoproteins, and RBC was studied in vitro to compare quantitavely (a) the fractional exchange rates and (b) the half-times for isotope equilibration. In all incubations of RBC with plasma or with plasma lipoprotein fractions, (14C)cholesterol approached equilibrium more rapidly than (3H)tocopherol. When the RBC contained the initial radioactivity, the half-times for equilibration with plasma of cholesterol and of tocopherol were 1.0 and 2.2 hr, respectively. However, the fractional exchange rates (KRBC leads to plasma) were 0.097/hr for cholesterol and 0.188/hr for tocopherol, indicating that the RBC tocopherol pool is turning over almost twice as rapidly as the RBC cholesterol pool. The rat plasma lipoproteins were separated into five fractions by successive ultracentrifugation. Only two fractions, the high density lipoproteins (d 1.063-1.21) and the very low density lipoproteins (d is less than 1.006), participated to a significant extent in the exchange of either tocopherol or cholesterol with RBC. Cholesterol exchange between individual rat plasma lipoproteins and RBC had the same half-times for isotope equilibrium for the very low and high density lipoproteins, and the RBC fractional exchange rates were proportional to the amount of cholesterol in the lipoproteins. In tocopherol exchange between individual rat plasma lipoproteins and RBC, the very low density lipoprotein tocopherol did not equilibrate completely with the RBC. However, the initial rate of tocopherol exchange appeared to be the same for very low and high density lipoproteins. The very low density lipoproteins were disrupted by repeated freezing and thawing or by dehydrating and rehydrating, and analysis of the resulting lipoproteins indicated that free cholesterol was associated more closely than tocopherol with the phospholipid-protein portion of the molecule, which is thought to be on the surface. This difference in distribution of tocopherol and free cholesterol within very low density lipoproteins could account for their different rates of exchange and for the nonequilibrium of tocopherol between RBC and very low density lipoproteins.

Acyltransferases↗

PubMed1973

Spectrophotometric method for determination of tocopherol in red blood cells.

A relatively rapid procedure is described for the spectrophotometric determination of total tocopherol in red blood cells (RBC) based on a modification of the original Emmerie-Engel reaction. The critical feature in this method is the presence of a large amount of an added antioxidant, pyrogallol or ascorbic acid, during the saponification and extraction stages and the use of thin-layer chromatography for tocopherol purification. The total tocopherol levels of plasma and erythrocytes were determined for a number of human subjects, for patients with abetalipoproteinemia, and for rats. It was found that these levels had a wide range in normal human subjects but that the ratio of RBC to plasma tocopherol was relatively constant and equal to 0.18, uncorrected, and 0.21 when both RBC and plasma values were corrected to 100% recovery. The RBC-to-plasma ratio for rats was 0.39. The accuracy of this ratio determined by the spectrophotometric procedure was verified by measuring the distribution of [(14)C]tocopherol in RBC and plasma when radioactive vitamin E was introduced into the blood by both in vitro and in vivo techniques. The addition of radioactive tocopherol to RBC or plasma at the initial stage of the analysis permits an accurate determination of the total tocopherol in RBC or plasma by calculations based on the recovery of the added isotope. This procedure for erythrocyte tocopherol analysis is compared with a gas-liquid chromatographic method in current use.

Abetalipoproteinemia↗