Alpha-Tocopherol But Not Beta-Tocopherol Inhibits Thrombin-Induced PKC Activation and Endothelin Secretion in Endothelial Cells

Abstract

Production of endothelin by endothelial cells depends on protein-kinase C (PKC) stimulation which has been reported to be inhibited by alpha-tocopherol (alpha-Toch) but not by beta-tocopherol (beta-Toch). The goal of this study was to determine whether alpha-Toch and beta-Toch inhibit endothelin secretion by endothelial cells. and results In a first set of experiments, cultured bovine aortic endothelial cells (BAEC) were incubated for 48h with 100 micromol/l alpha-Toch or vehicle (0.1% ethanol), then cells were stimulated for 4 h or 20 h with thrombin. After stimulating bovine aortic endothelial cells with thrombin for 4 h, alpha-Toch inhibited PKC activity by 63% and endothelin secretion by 44%, whereas after 20 h of incubation with thrombin, alpha-Toch decreased the peptide secretion by 51%. In a second set of experiments, BAEC were incubated with increased concentrations (from 0 to 100 micromol/l) of alpha-Toch or beta-Toch, PKC activity and endothelin secretion were measured after thrombin stimulation as previously reported. In these experiments, alpha-Toch strongly inhibited thrombin-induced PKC activity and endothelin secretion in a dose-dependent manner, whereas beta-Toch was more than 10-fold less active than alpha-Toch in inhibiting these stimulations. Tocopherols (alpha-Toch + beta-Toch) produced a proportional correlation on both PKC stimulation and endothelin secretion by inhibiting the effect of thrombin. These data suggest that alpha-Toch strongly inhibits thrombin-induced endothelin secretion in vitro at least partly through PKC inhibition.