title: Vitamin E inhibition on platelet procoagulant activity: involvement of aminophospholipid translocase activity.
abstract: BACKGROUND
  Activated platelets provide an important procoagulant surface, because exposed negatively charged phosphatidylserine (PS) is an important cofactor of the coagulation cascade. Aminophospholipid translocase (APLT) can transport PS from the outer to the inner membrane leaflet. Although vitamin E has been investigated for its anti-aggregating effect on platelets, its effect on platelet procoagulant activity has not been reported.
  
  
  METHODS
  Phorbol 12-myristate 13-acetate (PMA), a well-known PKC activator, and thrombin were used to induce PS exposure on platelet surface. The expression of PS was measured by annexin A5 binding with flow cytometry. Platelet procoagulant activity was measured by a prothrombinase assay. APLT activity was measured by flow cytometry by determining the percent of 1-palmitoyl-2-[6-[(7-nitro-2-1,3-benzoxadiazol-4-yl)amino]caproyl]-sn-glycero-3-phosphatidylserine (NBD-PS) translocated from the outer to the inner membrane leaflet. Inhibition effects of vitamin E on platelet aggregation were simultaneously measured by a Multiplate aggregometer, a Chrono-log aggregometer, and a PFA-100 system.
  
  
  RESULTS
  Vitamin E significantly attenuated PMA-induced conformational change of glycoprotein IIb/IIIa and P-selectin expression. Vitamin E significantly inhibited PMA and thrombin-induced PS externalization and reduced prothrombinase activity on platelet surfaces both in vitro and ex vivo. APLT activity was increased by vitamin E in a dose-dependent manner, indicating that reduced procoagulant activity may be attributed, at least in part, to this increased APLT activity. Vitamin E inhibited platelet aggregation induced by combined chemokine SDF-1 and low-dose ADP as well as by usual doses of ADP or collagen when measured by the Multiplate and Chrono-log aggregometers but not when measured by PFA-100.
  
  
  CONCLUSIONS
  These in vitro and ex vivo results showed that vitamin E inhibited platelet PS exposure and procoagulant activity partly by increasing APLT activity. These actions of vitamin E on platelet function provide new insights into the anticoagulation properties of vitamin E.
authors.affiliation: Department of Laboratory Medicine and Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Ji-Eun
authors.initials: JE
authors.lastname: Kim
authors.forename: Minje
authors.initials: M
authors.lastname: Han
authors.forename: Kyou-Sup
authors.initials: KS
authors.lastname: Hanl
authors.forename: Hyun Kyung
authors.initials: HK
authors.lastname: Kim
mesh_terms: D000328:Adult; D001777:Blood Coagulation / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D008297:Male; D010718:Phosphatidylserines / Q000096:biosynthesis / Q000097:blood; D049294:Phospholipid Transfer Proteins / Q000378:metabolism*; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014810:Vitamin E / Q000494:pharmacology*
chemical_list: D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; D014810:Vitamin E; D013755:Tetradecanoylphorbol Acetate