title: Covalent antithrombin-heparin effect on thrombin-thrombomodulin and activated protein C reaction with factor V/Va.
abstract: Thrombomodulin (TM), which variably contains a chondroitin sulfate (+/-CS), forms an anticoagulant complex with thrombin (IIa). IIa-TM(+/-CS) converts protein C (PC) into activated PC (APC), which then inactivates activated factors V (FVa) and VIII (FVIIIa). This reduces prothrombinase and tenase complexes that generate IIa. Heparin (H) increases the rate of IIa-TM inhibition by antithrombin (AT) and enhances FV cleavage by APC. Our novel covalent AT-H (ATH) product, has superior anticoagulant activity compared to AT + unfractionated H (UFH). We studied mechanisms by which ATH versus AT + UFH inhibits IIa-TM(+/-CS), and ATH influences on APC cleavage of FV/FVa compared to UFH. Findings would determine how these reactions moderate ATH's overall effects as an anticoagulant. Discontinuous second order rate inhibition assays of IIa-TM(+/-CS) inhibition by AT + UFH or ATH were performed in presence or absence of human umbilical vein endothelial cells (HUVECs). FV/FVa cleavage by APC in the presence of UFH or ATH was analysed by Western blots. ATH increased IIa-TM(+/-CS) inhibition to a greater degree than AT + UFH, both on plastic and HUVEC surfaces. Unlike UFH, ATH did not accelerate FV cleavage by APC, but ATH did enhance FVa cleavage relative to UFH. Increased IIa-TM inhibition by ATH downregulates PC activation. However, ATH does accelerate downstream inactivation of FVa, which increases its potency for IIa generation inhibition compared to UFH. This trend holds true in the presence of APC's cofactor, protein S. Overall, ATH may have a balanced function towards inhibiting or accelerating PC pathway activities.
authors.affiliation: David Braley Research Institute, Hamilton, Ontario, Canada.
authors.forename: Maria Christina
authors.initials: MC
authors.lastname: Van Walderveen
authors.forename: Leslie Roy
authors.initials: LR
authors.lastname: Berry
authors.forename: Helen Mary
authors.initials: HM
authors.lastname: Atkinson
authors.forename: Anthony Kam Chuen
authors.initials: AK
authors.lastname: Chan
mesh_terms: D000925:Anticoagulants / Q000627:therapeutic use; D000991:Antithrombins / Q000138:chemical synthesis / Q000494:pharmacology* / Q000627:therapeutic use; D001777:Blood Coagulation / Q000187:drug effects; D002478:Cells, Cultured; D002809:Chondroitin Sulfates / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D004789:Enzyme Activation / Q000187:drug effects; D005165:Factor V / Q000378:metabolism; D006493:Heparin / Q000138:chemical synthesis / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D011485:Protein Binding; D011486:Protein C / Q000378:metabolism; D011516:Prothrombin / Q000378:metabolism; D013917:Thrombin / Q000037:antagonists & inhibitors*; D018180:Thrombomodulin / Q000378:metabolism
chemical_list: D000925:Anticoagulants; D000991:Antithrombins; D011486:Protein C; D018180:Thrombomodulin; D005165:Factor V; D011516:Prothrombin; C025337:Factor IIa; D006493:Heparin; D002809:Chondroitin Sulfates; D013917:Thrombin