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

Abstract

Introduction Production of endothelin by endothelial cells depends on protein-kinase C (PKC) stimulation which has been reported to be inhibited by alpha-tocopherol (α-Toch) but not by beta-tocopherol (β-Toch). The goal of this study was to determine whether α-Toch and β-Toch inhibit endothelin secretion by endothelial cells.

Methods and results In a first set of experiments, cultured bovine aortic endothelial cells (BAEC) were incubated for 48 h with 100 μmol/l α-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, α-Toch inhibited PKC activity by 63% and endothelin secretion by 44%, whereas after 20 h of incubation with thrombin, α-Toch decreased the peptide secretion by 51%. In a second set of experiments, BAEC were incubated with increased concentrations (from 0 to 100 μmol/l) of α-Toch or β-Toch, PKC activity and endothelin secretion were measured after thrombin stimulation as previously reported. In these experiments, α-Toch strongly inhibited thrombin-induced PKC activity and endothelin secretion in a dose-dependent manner, whereas β-Toch was more than 10-fold less active than α-Toch in inhibiting these stimulations. Tocopherols (α-Toch + β-Toch) produced a proportional correlation on both PKC stimulation and endothelin secretion by inhibiting the effect of thrombin.

Conclusion These data suggest that α-Toch strongly inhibits thrombin-induced endothelin secretion in vitro at least partly through PKC inhibition.