Vitamin E inhibits platelet phospholipase A 2

Abstract

One of the most important functions of phospholipase A 2 is the release of arachidonic acid from membrane phospholipids for the synthesis of biologically active eicosanoids. We have demonstrated in our laboratory that vitamin E inhibits platelet phospholipase A 2 in a dose-dependent manner. Rats fed a 100 ppm or a 1000 ppm vitamin E diet exhibit diminished phospholipase A 2 activity compared to those fed a vitamin E-free diet. Addition of vitamin E to a sonicated platelet suspension resulted in further suppression of the phospholipase A 2 activity in all groups of rats. In order to gain insight into the mechanism of vitamin E inhibition of platelet phospholipase A 2, we partially purified this enzyme by gel filtration chromatography. Enzyme activity was localized in the soluble supernatant fraction of a high-speed spin. This partially purified rat platelet phospholipase A 2 had an absolute requirement for Ca 2+ and was inhibited by various forms of tocopherol. Tocol inhibited the enzyme to a greater extent than either d- or dl-α-tocopherol, while there was little or no effect from dl-α-tocopherol acetate. These results emphasize the importance of the hydroxyl moiety on the chromanol of the vitamin E molecule for its inhibitory action, compared to that of the methyl groups which are absent in tocol. This inhibitory action of vitamin E on platelet phospholipase A 2 suggests a crucial function for vitamin E in regulating arachidonate release from the membrane phospholipids and its subsequent metabolism.