Activated Factor XI is Increased in Plasma in Response to Surgical Trauma but not to Recombinant Activated FVII-Induced Thrombin Formation

Abstract

Aim: Feedback activation of factor XI (FXI) by thrombin is believed to play a critical role in the amplification phase of thrombin generation and to contribute to thrombosis development and hemostasis. However, the activation of FXI by thrombin has been shown in vitro to require a cofactor. In this study, the role of thrombin in activated FXI (FXIa) formation in vivo is investigated. Methods: The study population comprised probands in whom coagulation activation was triggered by low-dose (15 µg/kg) recombinant activated factor VII (rFVIIa, n =89), of whom 34 with (VTE+) and 45 without a history of venous thromboembolism (VTE−), and patients undergoing major orthopedic surgeries ( n =45). FXIa was quantified via an enzyme capture assay using a monoclonal FXI-specific antibody. Thrombin formation was monitored using an oligonucleotide-based enzyme capture assay and the thrombin activation markers prothrombin fragment 1＋2 (F1＋2) and thrombin–antithrombin complex (TAT). Results: In the rFVIIa cohort, FXIa and thrombin remained below their lower limit of quantification of 3.48 and 1.06 pmol/L, respectively. By contrast, during the surgeries, median FXIa levels increased from 3.69 pmol/L pre-operatively to 9.41 pmol/L mid-operatively ( P =4·10 −4 ) and remained significantly elevated 24 h thereafter, with 9.38 pmol/L ( P =0.001). Peak levels of F1+2 were comparable in the VTE+, VTE−, and surgery cohort (235, 268, and 253 pmol/L), whereas peak TAT levels were higher in the surgery cohort (53.1, 33.9, and 147.6 pmol/L). Conclusions: Under in vivo conditions, the activation of FXI requires specific local features that are present at the wounded site including potential cofactors of thrombin.

Ex Vivo Modeling of the PC (Protein C) Pathway Using Endothelial Cells and Plasma: A Personalized Approach

“…Free thrombin and APC were measured using highly sensitive OECAs that were initially described by Müller et al 16,17 and applied in other studies. 10,11,[18][19][20][21][22] In brief, Maxisorp Fluoronunc microtiter modules (Nunc A/S, Roskilde, Denmark) were coated with 10 µg/mL of bovine serum albumin (BSA)-biotin (100 µL/well). After incubation at 4 °C overnight, wells were washed, and a solution of 10 µg/mL streptavidin was added and incubated for 1 hour at RT.…”

The Endothelium Modulates the Prothrombotic Phenotype of Factor V Leiden: Evidence from an Ex Vivo Model

“…12,13 The most interesting finding in these studies was the observation that the anticoagulant APC response to thrombin formation was significantly increased in asymptomatic FVL carriers in comparison to those with a history of VTE. 13,14 Potential explanations of this observation include alterations of plasmatic and/or endothelial components of the PC system that might modulate thrombin and APC formation rates. Among the plasmatic variables are, besides levels of involved pro-and anticoagulant proteins, other influencing factors of APC resistance 15 and APC inactivation kinetics, the latter since elevated APC inhibitor levels have been associated with an increased thrombotic risk.…”

“…12,13 The most interesting finding in these studies was the observation that the anticoagulant APC response to thrombin formation was significantly increased in asymptomatic FVL carriers in comparison to those with a history of VTE. 13,14…”