Comparative Anticoagulant Effects of Recombinant Thrombomodulin, Antithrombin, and Unfractionated Heparin, Hematological Implications
Authors: Siddiqui Zafar , Fareed Jaweed , Aggarwal Parul , Iqbal Omer , Hoppensteadt Debra , Abro Schuharazad 
Published: November 2023

Introduction

Unfractionated heparin (UFH), antithrombin (AT), and recombinant thrombomodulin (RT) are three distinct anticoagulant/antithrombotic agents with different targets in the hemostatic process. Currently, a recombinant version of thrombomodulin, ART‐123 (Recomodulin) is undergoing clinical trials for treatment of sepsis‐associated coagulopathy. RT is a novel, recombinant and soluble human thrombomodulin with thrombin inhibiting and protein C stimulating activities. In comparison to UFH and AT, this agent has 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 RT, UFH, and AT.

Materials and Methods

Porcine UFH was obtained from Medefil Inc. (Glendale Heights, IL) with a specific activity of 175 U/mg, and a working concentration of 100 ug/mL was made in sterile saline. AT was obtained from Baxter Healthcare Corporation (Deerfield, IL), and a working concentration of 100 U/mL was made in sterile saline. RT was obtained from Asahi Kasei Pharma (Japan), and a working concentration of 100 ug/mL was made in sterile saline. The effect of RT, 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 (AIPA) (arachidonic acid, ADP, collagen, thrombin, and epinephrine) was measured in platelet rich plasma collected from healthy donors.

Results

In comparison to AT and UFH, RT did not produce any anticoagulant effects in either the TEG or the ACT tests at a concentration of 1.25 ug/mL. At higher concentrations of 2.5 and 5.0 ug/mL, the relative anticoagulant effects of RT were much weaker in comparison to AT and UFH. In the TEG profile at 5.0 ug/mL, the AT and UFH produced complete anticoagulation. However, RT 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 > RT. In the AIPA studies, while UFH produced a mild increase in the aggregation profile of some of the agonists, AT and RT 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 RT 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 RT is a much weaker anticoagulant in comparison to UFH and AT and at therapeutic concentrations, it does not produce any measurable anticoagulant effects. At supratherapeutic concentrations of > 2.5 ug/mL, RT exhibits weaker anticoagulant effects which are unlikely to contribute to any hemostatic deficit resulting in potential bleeding complications.