OC 67.2 - Personalized Assessment of the Protein C Pathway Using Endothelial Colony Forming Cells

Background: The endothelium provides an anticoagulatory and anti-inflammatory system by promoting the formation of activated protein C (APC). Mutations such as factor V Leiden (FVL) or inflammatory signaling can affect the protein C (PC) pathway and modulate hemostasis and host defence.

Aims: Aim of this study was to establish an assay system using human plasma and endothelial colony forming cells (ECFCs), allowing personalized assessment of the PC pathway.

Methods: Citrated, defibrinated plasma was added to ECFCs, which were cultivated from peripheral blood mononuclear cells, in 24-well microtiter plates and coagulation was initiated by the 1 pM tissue factor. Thrombin and subsequent APC generation was quantified over time using corresponding oligonucleotide-based enzyme capture assays (OECAs) after quenching the reaction using the reversible thrombin inhibitor argatroban. By treating ECFCs with cytokines, inflammatory stimulation was assessed. FVL carriers and non-carriers (n=3 each) were studied using the established ex vivo system.

Results: Similar thrombin and APC formation rates in normal pooled plasma were measured in the presence of ECFCs and human umbilical vein endothelial cells (HUVECs). Under inflammatory stimulation by treating ECFCs with 1 ng/mL interleukin 1 beta, peak APC formation was decreased (1.12 ± 0.04 nmol/L versus 3.66 ± 0.13 nmol/L, P = 7·10-9). As evidenced by a higher ratio between the area under curve (AUC) of APC generation and that of thrombin, thrombin-dependent APC generation was significantly higher in FVL carriers compared to non-carriers (0.085 ± 0.014 versus 0.03 ± 0.019, P = 6·10-4).

Conclusion(s): The established ex vivo model was shown to be suitable for measuring plasma thrombin and APC formation on ECFCs and to detect inter-individual differences. Therefore, the assay system allows for personalized assessment of the PC pathway. It might contribute to further explanation of mechanisms modulating the thrombogenicity in inflammatory states, or of FVL and other mutations affecting the PC pathway.