Alterations in plasma α- and γ-tocopherol concentrations in response to intravenous infusion of lipid emulsions in humans

Abstract

To study the fate of intravenously infused vitamin E, we infused lipid emulsions rich in γ-tocopherol (Intralipid, Kabi, Stockholm, Sweden), or in both α- and γ-tocopherols (Lipidem, Hausmann Laboratories, St Gallen, Switzerland); in normal human volunteers. Plasma γ-tocopherol levels increased in four subjects infused with Intralipid 10% (0.3 g triglyceride [TG]/kg/h for 6 hours) from 3 ± 1 to 25 ± 2 nmol/mL, but by 24 hours they decreased to 5 ± 1 nmol/mL. Although eight times more γ-tocopherol was infused, plasma α-tocopherol levels also increased from 26 ± 7 to 39 ± 9 nmol/mL at 8 hours and decreased to 24 ± 5 nmol/mL at 24 hours. Increases of α-tocopherol in the very-low-density lipoprotein (VLDL) density range occurred at 6 and 8 hours, while decreases occurred in low-density lipoprotein (LDL) and high-density lipoprotein (HDL) density ranges at 3, 6, 8, and 24 hours. Infusion of both emulsions in random order to six subjects at therapeutic rates (0.1 g/kg/h for 6 hours) resulted in (1) a threefold increase in plasma γ-tocopherol concentrations at 6 hours, (2) increases in plasma γ-tocopherol concentrations only with Lipidem (from 14.3 ± 1.0 nmol/mL at 0 hours to 18.4 ± 2.7 at 6 hours and 18.9 ± 1.1 at 24 hours), and (3) no decreases in lipoprotein α-tocopherol levels. In vitro incubations of emulsions with plasma (or isolated lipoprotein fractions) increased γ-tocopherol concentrations up to 10-fold, increased TG-rich fractions with α-tocopherol, and decreased α-tocopherol in the HDL density range, suggesting that HDL donates α-tocopherol to the TG-rich particles. These studies demonstrate that by 24 hours following infusion of γ-tocopherol-rich lipid emulsions, elevated plasma γ-tocopherol levels are not maintained and α-tocopherol levels remain increased only if the lipid emulsion contained added α-tocopherol.