ALPHA-TOCOPHEROL AS A MODULATOR OF SMOOTH-MUSCLE CELL-PROLIFERATION

The effects of alpha-tocopherol and beta-tocopherol have been studied in rat and human aortic smooth muscle cells. alpha-tocopherol, but not beta-tocopherol, inhibited smooth muscle cell proliferation and prote in kinase C in a dose-dependent manner, at concentrations ranging from 10 to 50 mu M. beta-tocopherol added simultaneously with alpha-tocoph erol prevented both proliferation and protein kinase C inhibition. Pro tein kinase C inhibition was cell cycle-dependent and it was prevented by okadaic acid, a protein phosphatase inhibitor. Protein kinase C ac tivity measured from aortas of cholesterol-fed rabbits was also inhibi ted by alpha-tocopherol. By using protein kinase C (PKC) isoform-speci fic inhibitors and immunoprecipitation reactions it was found that PKC -alpha was selectively inhibited by alpha-tocopherol. Further, an acti vation of protein phosphatase 2A by alpha-tocopherol was found, which caused PKC-alpha dephosphorylation and inhibition. Ultimately, this ca scade of events at the level of cell signal transduction leads to the inhibition of smooth muscle cell proliferation.