PB1075 - APC Response Rates in Factor V Leiden Carriers Correlate with Thrombotic Risk Independent from Endothelial Properties: Results from an Endothelial Cell-based Ex Vivo Model of the Protein C Pathway

Tuesday, June 27, 2023

18:30 – 19:30 ET

Room: Exhibition

Presenting Author(s)

Nadine Schwarz, MS

PhD Student
Institute of Experimental Haematology and Transfusion Medicine, University Hospital Bonn
Bonn, Nordrhein-Westfalen, Germany

Co-Author(s)

JM

Jens Müller

Scientific Director
Institute of Experimental Haematology and Transfusion Medicine, University Hospital Bonn
Bonn, Nordrhein-Westfalen, Germany
Hannah L. McRae

PhD Student
Institute of Experimental Hematology and Transfusion Medicine, University Hospital Bonn
Bonn, Nordrhein-Westfalen, Germany
Johannes Oldenburg, MD (he/him/his)

Professor, Chairman and Director
University Clinic Bonn AöR, Institute of Experimental Haematology and Transfusion Medicine, Bonn, Germany
Bonn, Nordrhein-Westfalen, Germany
BP

Bernd Pötzsch

Professor
Institute of Experimental Haematology and Transfusion Medicine, University Hospital Bonn
Bonn, Nordrhein-Westfalen, Germany
HR

Heiko Rühl

Senior researcher
Institute of Experimental Haematology and Transfusion Medicine, University Hospital Bonn
Bonn, Nordrhein-Westfalen, Germany

Background: Clinical expressivity of the thrombophilic factor V Leiden (FVL) mutation is highly variable. Recently we have shown that asymptomatic FVL carriers respond to in vivo coagulation activation with higher activated PC (APC) formation rates than those with a history of venous thromboembolism (VTE).

Aims: To investigate potential modulating factors of the APC response in an ex vivo model of the PC pathway using endothelial colony forming cells (ECFCs) and autologous plasma.

Methods: ECFCs were isolated from FVL carriers with/without VTE (VTE+/VTE-, n=7 each) and healthy controls (n=5). Overlaid with defibrinated plasma, thrombin formation was initiated by addition of tissue factor (1 pmol/L) and thrombin/APC formation was measured over time using oligonucleotide-based enzyme capture assays (OECAs). Additionally, ECFC-dependent APC formation was measured in HEPES buffer containing thrombin and PC. Thrombomodulin and endothelial protein C receptor (EPCR) expression were quantified in cell-ELISAs. Inactivation kinetics of exogenously added APC were monitored in plasma by OECA.

Results: With comparable thrombin formation rates, APC formation rates in plasma were significantly higher in FVL VTE- compared to FVL VTE+ subjects (P=0.022) and healthy controls (P=0.006) as indicated by a higher ratio between the area under the curve (AUC) of APC generation to thrombin AUC (Figure 1). APC formation in the purified system, APC inactivation kinetics, thrombomodulin expression as well as plasma levels of PC, free protein S, antithrombin, coagulation factors II, V, VII, VIII, IX, X, XI, and soluble thrombomodulin/EPCR did not differ significantly between cohorts. EPCR expression was lower in FVL VTE+ patients than in healthy controls (P=0.031) but not compared to FVL VTE- subjects (Figure 2).

Conclusion(s): The observation of increased APC formation rates in asymptomatic FVL carriers in the ex vivo model further strengthens previous in vivo observations. Endothelial-related factors do not appear to modulate the extent of the APC response.