Scientist Cellphire Therapeutics, Inc Rockville, Maryland, United States
Background: A human lyophilized platelet derived hemostatic, Thrombosomes®, are currently in phase 2 trials in thrombocytopenic bleeding patients. A prerequisite to the assessment of Thrombosomes® as a potential hemostatic agent to quell bleeding associated with CABG surgery is compatibility with heparin:protamine. Herein we investigated heparin:protamine treatment’s impact on Thrombosomes® hemostatic potential, in vitro.
Aims: Investigate Thrombosomes®’ ability to generate thrombin in the presence of pharmacologic concentrations of heparin:protamine.
Methods: A prophylactic level of heparin, 0.1 U/mL plasma, was combined with 5 and 50 K/µL Thrombosomes® and assayed using a Thrombin Generation Assay (TGA). A therapeutic level of heparin, 0.8 U/mL plasma, was tested without reversal and with 0.5-, 1-, and 1.5-times the recommended reversal dose of protamine (4, 8, or 12 µg/mL, respectively) along with 10, 25, or 50 K/µL Thrombosomes® using a TGA and activated clotting time (ACT) measurements.
Results: Thrombosomes® at 5 and 50 K/µL returned peak thrombin production to normal in 0.1 U/mL heparin (Figure 1A). Thrombosomes® at 10 to 50 K/µL was unable to return peak thrombin generation when 0.8 U/mL heparin and 4 ug/mL protamine (1/2 P). (Figure 1B, C). However, reversal of heparin with recommended (P) and excess (3/2 P) doses of protamine resulted in thrombin generation potential of Thrombosomes® similar to when no heparin was added (Figure 1C). There is a trend towards lower ACT with higher concentrations of Thrombosomes® in the sample groups containing excess heparin (Figure 2).
Conclusion(s): Thrombosomes® restored hemostasis at prophylactic heparin dose. Thrombosomes® retain thrombin generation potential at therapeutic dose of heparin:protamine, and accelerated clotting in a dose dependent manner. These results support the assessment of Thrombosomes® for their potential use in CABG surgery and other clinical applications wherein heparin has been given and reversed by protamine. Future work to confirm Thrombosomes® usage in animal models where heparin-protamine complexation is planned.
