Anticoagulant Actions of Recombinant Thrombomodulin and Activated Protein C and Their Neutralization By Factor VIII Inhibitor Bypass Activity (FEIBA)

Introduction:

Thromboelastographic (TEG) analysis represents a global approach to monitor the clotability of the native whole blood. rTM (recombinant Thrombomodulin) is a mild anticoagulant with pleiotropic actions which are modulated through its complexation with thrombin. This agent has been developed for various clinical indications including DIC and related disorders. Activated Protein C (APC) represents an anticoagulant which produces its action by regulating activated factors V and VII and modulates fibrinolysis. A recombinant version of this drug was previously approved for the management of Sepsis and this agent is currently withdrawn from the market. FEIBA (Factor VII Inhibitor Bypass Activity) contains non activated factors II, IX and X and activated factor VII and is currently approved for the management of bleeding in hemophilia patients.

Aim:

The purpose of this study is to compare the relative anticoagulant effects of rTM and APC, employing the thromboelastographic analysis and their neutralization by graded amounts of FEIBA.

Methods:

Citrated Whole Blood samples were supplemented with rTM and APC at a concentration of 3 ug/mL (n=20). TEG analysis was performed on a TEG 5000 system in which clotting was initiated by recalcification of the whole blood and set parameters as R time, K time, MA and Angle were measured. The relative neutralization profiles of the APC and rTM by FEIBA at 1.0, 0.1, and 0.01 U/ml were investigated. All results were analyzed in terms of Means Values and Standard Deviations.

Results:

At 3ug/ml rTM produced a mild anticoagulant effect as evident by its TEG profile in terms of prolongation of R and K times and marked decrease in angle and maximum amplitude. APC at 3 ug/mL produced a relatively stronger anticoagulant effects on all of the parameters in the TEG profile. The supplementation of FEIBA at 0.1 U/mL to the whole blood mixtures containing 3 ug/mL completely neutralized rTM and resulted in the partial neutralization of the anticoagulant effects of APC as shown in Table 1. FEIBA at different dosages of 1.0 U/mL and 0.01 U/mL proportionately neutralized the anticoagulant effects of both of these agents.

Discussion:

These results indicate that on a weight basis, APC is a stronger anticoagulant in comparison to rTM as measured by the thromboelastographic analysis. FEIBA is very effective in the neutralization of the anticoagulant effects of rTM and results in a weaker neutralization of APC in a concentration dependent fashion. FEIBA at a much lower level of less than 0.1 U/mL is effective in neutralizing the effects of rTM. Therefore, this agent can be considered for the neutralization of rTM.

Conclusions:

These studies clearly indicate that on a comparative basis, rTM is a weaker anticoagulant in comparison to APC. Furthermore, FEIBA at a very low level of less than 0.1 U/mL dosage, projected clinical dosage of 5-10 U/kg, may be effective in the neutralization of the anticoagulant effects rTM. These results suggest that FEIBA can be used for the neutralization of such mild anticoagulants as rTM at much lower levels than the proposed dosing for the bleeding control of hemophiliac patients.

Table.

View largeDownload slide

Table.

View largeDownload slide

Close modal