Inhibition of platelet adherence to mononuclear cells by alpha-tocopherol: role of P-selectin.

Abstract

Platelet-leukocyte interaction is an early important event for thrombogenesis, and this process is mainly mediated by P-selectin on platelets. Although alpha-tocopherol has been shown to inhibit thrombotic disorders, the effect of alpha-tocopherol on platelet P-selectin expression and platelet-leukocyte interaction is little known. We examined whether alpha-tocopherol inhibited human platelet P-selectin expression and platelet-leukocyte interaction. Alpha-tocopherol (50 to 500 microg/mL) inhibited thrombin-induced or phorbol 12-myristate 13-acetate (PMA)-induced P-selectin expression on platelets. alpha-Tocopherol suppressed platelet-mononuclear cell (MNC) interaction, platelet aggregation, and platelet protein kinase C (PKC) activity stimulated with either PMA (100 nmol/L) or thrombin. Inhibitory actions of alpha-tocopherol against the platelet functions were mimicked by staurosporine, a selective PKC inhibitor. After oral supplementation of alpha-tocopherol (300 mg/d for 3 weeks) in healthy subjects, thrombin-mediated or PMA-mediated P-selectin expression, platelet-MNC interaction, and platelet aggregation ex vivo were suppressed. alpha-Tocopherol inhibited P-selectin expression on human platelets and thereby attenuated platelet-MNC interactions, which were mediated at least in part by the inhibition of intraplatelet PKC activity. These actions of alpha-tocopherol on platelet functions provide new insights into the antithromboatherogenic properties of alpha-tocopherol.