title: Interactions of heparin and a covalently-linked antithrombin-heparin complex with components of the fibrinolytic system.
abstract: Unfractionated heparin (UFH) is used as an adjunct during thrombolytic therapy. However, its use is associated with limitations, such as the inability to inhibit surface bound coagulation factors. We have developed a covalent conjugate of antithrombin (AT) and heparin (ATH) with superior anticoagulant properties compared with UFH. Advantages of ATH include enhanced inhibition of surface-bound coagulation enzymes and the ability to reduce the overall size and mass of clots in vivo. The interactions of UFH or ATH with the components of the fibrinolytic pathway are not well understood. Our study utilised discontinuous second order rate constant (k₂) assays to compare the rates of inhibition of free and fibrin-associated plasmin by AT+UFH vs ATH. Additionally, we evaluated the effects of AT+UFH and ATH on plasmin generation in the presence of fibrin. The k₂ values for inhibition of plasmin were 5.74 ± 0.28 x 10⁶ M⁻¹ min⁻¹ and 6.39 ± 0.59 x 10⁶ M⁻¹ min⁻¹ for AT+UFH and ATH, respectively. In the presence of fibrin, the k₂ values decreased to 1.45 ± 0.10 x 10⁶ M⁻¹ min⁻¹ and 3.07 ± 0.19 x 10⁶ M⁻¹ min⁻¹ for AT+UFH and ATH, respectively. Therefore, protection of plasmin by fibrin was observed for both inhibitors; however, ATH demonstrated superior inhibition of fibrin-associated plasmin. Rates of plasmin generation were also decreased by both inhibitors, with ATH causing the greatest reduction (approx. 38-fold). Nonetheless, rates of plasmin inhibition were 2-3 orders of magnitude lower than for thrombin, and in a plasma-based clot lysis assay ATH significantly inhibited clot formation but had little impact on clot lysis. Cumulatively, these data may indicate that, relative to coagulant enzymes, the fibrinolytic system is spared from inhibition by both AT+UFH and ATH, limiting reduction in fibrinolytic potential during anticoagulant therapy.
authors.affiliation: Dr. Anthony K. C. Chan, Thrombosis and Atherosclerosis Research Institute (TaARI), DBCVSRI, Hamilton General Hospital, 237 Barton Street East, Hamilton, Ontario, Canada, L8L 2X2, Tel: 905 521 2100 (Ext. 40719), Fax: 905 577 1427, E-mail: akchan@mcmaster.ca.
authors.forename: Ankush
authors.initials: A
authors.lastname: Chander
authors.forename: Helen M
authors.initials: HM
authors.lastname: Atkinson
authors.forename: Ivan
authors.initials: I
authors.lastname: Stevic
authors.forename: Leslie R
authors.initials: LR
authors.lastname: Berry
authors.forename: Paul Y
authors.initials: PY
authors.lastname: Kim
authors.forename: Anthony K C
authors.initials: AK
authors.lastname: Chan
mesh_terms: D000991:Antithrombins / Q000008:administration & dosage* / Q000009:adverse effects / Q000138:chemical synthesis; D002478:Cells, Cultured; D005337:Fibrin / Q000378:metabolism; D005341:Fibrinolysin / Q000378:metabolism; D005342:Fibrinolysis / Q000187:drug effects* / Q000502:physiology; D006493:Heparin / Q000008:administration & dosage* / Q000009:adverse effects / Q000138:chemical synthesis; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D046912:Multiprotein Complexes / Q000008:administration & dosage* / Q000009:adverse effects / Q000138:chemical synthesis; D011485:Protein Binding / Q000187:drug effects; D011516:Prothrombin / Q000378:metabolism; D015912:Thrombolytic Therapy
chemical_list: D000991:Antithrombins; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D011516:Prothrombin; D005337:Fibrin; C025337:Factor IIa; D006493:Heparin; D005341:Fibrinolysin
keywords: Fibrinolysis; antithrombin; antithrombin-heparin covalent complex; heparin; plasmin generation