title: Increased prothrombin activation in protein S-deficient plasma under flow conditions on endothelial cell matrix: an independent anticoagulant function of protein S in plasma.
abstract: Protein S is a vitamin K-dependent nonenzymatic coagulation factor involved in the regulation of activated protein C (aPC). In this study, we report an aPC-independent anticoagulant function of protein S in plasma under flow conditions. Plasma, anticoagulated with low-molecular-weight heparin allowing tissue factor-dependent prothrombin activation, was perfused at a wall shear rate of 100 s-1 over tissue factor containing matrices of stimulated endothelial cells placed in a perfusion chamber. Fractions were collected in time at the outlet and prothrombin activation was determined by measuring the activation fragment F1+2 of prothrombin. In normal plasma, a time-dependent prothrombin activation was detected by the generation of fragment1+2. Prothrombin activation had ceased after 12 minutes perfusion, independent of the amount of tissue factor present in the matrix. Depletion of protein S from plasma or inhibition of protein S in plasma by monoclonal antibodies induced a 5- to 25-fold increase of prothrombin activation on the procoagulant endothelial cell matrix. A prolonged prothrombin activation was detected in protein S-depleted plasma up to 20 minutes after onset of the thrombin generation. The increased prothrombin activation in protein S-depleted plasma could not be explained by the absence of the cofactor function of protein S for aPC because depletion of protein C from plasma did not result in increased prothrombin activation. These data provide further evidence for a strong anticoagulant function of protein S in plasma independent from activated protein C.
authors.affiliation: Department of Haematology, University Hospital Utrecht, The Netherlands.
authors.forename: C
authors.initials: C
authors.lastname: van't Veer
authors.forename: T M
authors.initials: TM
authors.lastname: Hackeng
authors.forename: D
authors.initials: D
authors.lastname: Biesbroeck
authors.forename: J J
authors.initials: JJ
authors.lastname: Sixma
authors.forename: B N
authors.initials: BN
authors.lastname: Bouma
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001777:Blood Coagulation; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology*; D015949:Factor IXa / Q000378:metabolism; D015944:Factor VIIIa / Q000378:metabolism; D006801:Humans; D010446:Peptide Fragments / Q000032:analysis; D010477:Perfusion; D011486:Protein C / Q000502:physiology; D017293:Protein S / Q000037:antagonists & inhibitors / Q000276:immunology / Q000502:physiology*; D011516:Prothrombin / Q000032:analysis / Q000378:metabolism*; D012212:Rheology; D013925:Thromboplastin / Q000502:physiology; D013997:Time Factors
chemical_list: D000911:Antibodies, Monoclonal; D010446:Peptide Fragments; D011486:Protein C; D017293:Protein S; C045879:prothrombin fragment 1.2; D015944:Factor VIIIa; D011516:Prothrombin; D013925:Thromboplastin; D015949:Factor IXa