Abstract Number: PB0189
Meeting: ISTH 2022 Congress
Background: We previously reported that a mathematical model of coagulation predicted low normal levels (50%-75%) of factor V (FV) enhance thrombin generation in hemophilia A (Link, JTH, 18, 2020). The study suggested that FV and FVIII compete for cleavage by FXa during the initiation of coagulation.
Aims: To test the hypothesis that substrate competition for FXa is responsible for enhanced thrombin generation in hemophilia A plasma with low amounts of FV.
Methods: 1) A purified system of FV, FVIII, FXa and phospholipids examined the biochemical feasibility of the substrate competition mechanism, wherein the generation of FVIIIa was the output. 2) Tissue factor (TF) initiated thrombin generation was measured in synthetic plasma containing the zymogens and co-factors of the extrinsic pathway and anticoagulants (ATIII, +/-TFPI) at varying levels of FV (25%-150%). 3) A mixture study of FVIII-deficient (5%) human plasma with normal FV and immunodepleted of FV was performed using calibrated automated thrombography (CAT). 4) CAT initiated with 1 or 5 pM TF was used to measure thrombin generation in 75 severe to mild hemophilia A plasmas. Prothrombin, FV, FVIII, total TFPI, and TFPIα levels were measured in these plasma samples and Pearson correlation coefficients were calculated against thrombin generation metrics.
Results: In the purified system, there was an inverse relationship between FV concentration and the amount of FVIIIa generated, indicating competition for FXa between the two substrates. In both synthetic and human plasma, there was an inverse relationship between FV concentration and thrombin generation metrics (Fig. 1). There was negative correlation between FV concentrations and these thrombin generation metrics in hemophilia A plasmas (p < 0.01).
Conclusion(s): Four different biochemical systems support the hypothesis that low normal levels (50%-75%) of FV enhance thrombin generation in hemophilia A plasma. These experiments support the substrate competition mechanism for FXa predicted by our mathematical model.
To cite this abstract in AMA style:Monroe D, Baird C, Peterson J, Fogelson A, Leiderman K, Sindi S, Stobb M, Mast A, Manco-Johnson M, Neeves K. Low normal levels of factor V enhance thrombin generation in hemophilia A [abstract]. https://abstracts.isth.org/abstract/low-normal-levels-of-factor-v-enhance-thrombin-generation-in-hemophilia-a/. Accessed October 1, 2023.
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