Comparative Anticoagulant Effects of Recombinant Thrombomodulin, Antithrombin, and Unfractionated Heparin, Hematological Implications

Introduction: Unfractionated heparin (UFH), antithrombin (AT), and recombinant thrombomodulin (RT) represent two distinct anticoagulant/antithrombotic agents with different targets in the hemostatic process to produce their therapeutic effects. Both of these agents are widely used in various hematologic indications in mono and poly therapeutic approaches. Currently, a recombinant version of thrombomodulin, ART-123 (Recomodulin) is undergoing clinical trials to validate its efficacy in sepsis-associated coagulopathy. Recomodulin is a novel, recombinant and soluble thrombomodulin, and is a human protein with both thrombin inhibiting and protein C stimulating activities. In comparison to both UFH and AT, this agent has relatively weaker anticoagulant activities related to bleeding risk at therapeutic concentrations of ≤ 1.25 ug/mL. Supratherapeutic concentrations of this agent may occur in some patients with renal dysfunction. The purpose of this study is to compare the anticoagulant and platelet modulatory effects of ART-123, UFH, and AT.

Materials and Methods: UFH of porcine origin was obtained from Medefil Inc. (Glendale Heights, IL) in powdered form with a specific activity of 175 U/mg. A working concentrations of this agent was made at 100 ug/mL in sterile saline. AT was commercially obtained from Baxter Healthcare Corporation (Deerfield, IL). A working concentration of AT was prepared at 100 U/mL in sterile saline. Recomodulin was commercially obtained and was manufactured by Asahi Kasei Pharma (Japan). A working concentration of Recomodulin at 100 ug/mL was prepared in sterile saline. The effect of Recomodulin, AT, and UFH on the glass activated clotting time and thromboelastographic (TEG) profile was measured at concentrations of 0-5 ug/mL. Global anticoagulant assays including PT, APTT, and TT were also measured in citrated whole blood and retrieved plasma. The effect of these drugs on agonist induced platelet aggregation (arachidonic acid, ADP, collagen, thrombin, and epinephrine) was measured in platelet rich plasma collected from healthy donors.

Results: In comparison to both AT and UFH, Recomodulin did not produce any anticoagulant effects in either the TEG or the ACT tests at concentrations of 1.25 ug/mL. At higher concentrations of 2.5 and 5.0 ug/mL, the relative anticoagulant effects of Recomodulin were much weaker in comparison to both AT and UFH. In the TEG profile at 5.0 ug/mL, both the AT and UFH produced complete anticoagulation. However, Recomodulin did not produce a complete anticoagulation at 2.5 and 5.0 ug/mL. In the whole blood global clotting assays, all agents produced a concentration-dependent anticoagulant effect following the order UFH > AT > Recomodulin. In the platelet aggregation studies, while heparin produced a mild increase in the aggregation profile of some of the agonists, AT and Recomodulin did not produce any effects at concentrations of up to 10 ug/ml and 5 U/ml for all of the agonists except thrombin.

Conclusion: The circulating levels of Recomodulin for the management of sepsis-associated coagulopathy range from 0.5-1.5 ug/mL. The therapeutic levels of UFH for similar indications range from 1.5-5.0 ug/mL (0.25-1.0 U/mL), whereas the circulating AT levels may range from 1-2.5 U/mL. The results from this study suggest that Recomodulin is a much weaker anticoagulant in comparison to both UFH and AT and at therapeutic concentrations, it does not produce any measurable anticoagulant effects. At supratherapeutic concentrations of > 2.5 ug/mL, Recomodulin exhibits weaker anticoagulant effects which are unlikely to contribute to any hemostatic deficit resulting in potential bleeding complications.