Vitamin E and arachidonic acid metabolism in cultured human endothelial cells.

A novel approach to study the metabolism of nutrients in human cells was developed. The incorporation and depletion of 2R,4$\sp\prime$R,8$\sp\prime$R-$\alpha$-tocopherol (RRR-$\alpha$-T), a natural form of vitamin E, and its subsequent effect on the metabolism of arachidonic acid were conducted on human umbilical vein endothelial cells (HUVECs) in culture. HUVECs incorporated physiological and pharmacological concentrations of RRR-$\alpha$-T in a time- and dose-dependent manner. Incorporated tocopherol was found mainly associated with membrane fractions of the cell. This stimulatory activity of tocopherol has an absolute structural requirement for both free hydroxyl moiety and the hydrophobic phytyl side chain, although the position and the presence of the methyl groups attached to the aromatic moiety are not required for its activity. Direct analysis of enzymes involved in phospholipid metabolism indicated that tocopherol-enrichment caused an increase in phospholipase A$\sb2$ activity without affecting the activities of lysophospholipase or acylCoA-acyltransferase. Hydrogen peroxide when combined with $\alpha$-tocopherol synergistically stimulated basal release of PGI$\sb2$ from endothelial cells. $\alpha$-tocopherol potentiates PGI$\sb2$ synthesis when challenged with exogenous arachidonic acid. (Abstract shortened by UMI.