The Clotting Trigger Is an Important Determinant for the Coagulation Pathway In Vivo or In Vitro—Inference from Data Review

Abstract

Blood coagulation comprises a series of enzymatic reactions leading to thrombin generation and fibrin formation. This process is commonly illustrated in a waterfall-like manner, referred to as the coagulation cascade. In vivo, this “cascade” is initiated through the tissue factor (TF) pathway, once subendothelial TF is exposed and bound to coagulation factor VII (FVII) in blood. In vitro, a diminutive concentration of recombinant TF (rTF) is used as a clotting trigger in various global hemostasis assays such as the calibrated automated thrombogram, methods that assess fibrin turbidity and fibrin viscoelasticity tests such as rotational thromboelastometry. These assays aim to mimic in vivo global coagulation, and are useful in assessing hyper-/hypocoagulable disorders or monitoring therapies with hemostatic agents. An excess of rTF, a sufficient amount of negatively charged surfaces, various concentrations of exogenous thrombin, recombinant activated FVII, or recombinant activated FIXa are also used to initiate activation of specific sub-processes of the coagulation cascade in vitro. These approaches offer important information on certain specific coagulation pathways, while alterations in pro-/anticoagulants not participating in these pathways remain undetectable by these methods. Reviewing available data, we sought to enhance our knowledge of how choice of clotting trigger affects the outcome of hemostasis assays, and address the call for further investigations on this topic.

Inhibitory role of recombinant neorudin on canine coronary artery thrombosis

“…At the beginning of the intrinsic coagulation cascade, coagulant factor XI was activated, 23 which hydrolyzed neorudin to hirudin, a known thrombin inhibitor 12 . However, tissue cutting wound activated the extrinsic coagulation pathway and coagulant factor XI was almost not activated in this process 24 . Therefore, little neorudin was converted to hirudin and the increase of the bleeding time and bleeding volume of cutting wound was lower in high dose group of neorudin than LMWH group at the similar thrombus inhibiting action.…”

Fibrin Network Porosity and Endo-/Exogenous Thrombin Cross-talk

“…47 A significant correlation between the values of Darcy constant (Ks) and "drug" concentrations was observed in the samples containing rivaroxaban greater than 30 μg/L, but not in those 30 μg/L (equivalent to assay limit of detection). According to the known concepts of the "coagulation cascade," [39][40][41] we hypothesize that fibrin formation in this case was affected not only by exogenous thrombin but also by endogenous thrombin produced from a "positive feedback loop" action by the added thrombin. The "positive feedback loop" action involves FX activities; the effects of rivaroxaban on fibrin network porosity was therefore detectable.…”

“…It is commonly accepted that the coagulation cascade in vivo is initiated by activation of the TF pathway once subendothelial TF is exposed to FVII forming a TF-FVII complex, or by activation of the contact pathway once negatively charged surfaces come into contact with factor XII. [39][40][41] Via the TF pathway, FVII within the TF-FVII complex is converted into FVIIa, which in sequence yields activation of FX and FIX, followed by a series of enzymatic reactions that lead toward thrombin burst and fibrin (network) formation. [39][40][41] This coagulation process is well mimicked by the CAT measurement using rTF (plus PPL) as the clotting trigger.…”

“…[39][40][41] Via the TF pathway, FVII within the TF-FVII complex is converted into FVIIa, which in sequence yields activation of FX and FIX, followed by a series of enzymatic reactions that lead toward thrombin burst and fibrin (network) formation. [39][40][41] This coagulation process is well mimicked by the CAT measurement using rTF (plus PPL) as the clotting trigger. 41 To render the assay of fibrin network porosity more relevant, our group was the first to modify the original protocol by replacing purified thrombin with rTF (plus PPL).…”

“…[39][40][41] This coagulation process is well mimicked by the CAT measurement using rTF (plus PPL) as the clotting trigger. 41 To render the assay of fibrin network porosity more relevant, our group was the first to modify the original protocol by replacing purified thrombin with rTF (plus PPL). Using this modified clotting trigger, we performed studies in vitro, examining NPP samples spiked with a thrombin inhibitor (melagatran, argatroban, bivalirudin, or lepirudin), a factor Xa inhibitor (fondaparinux, apixaban, or rivaroxaban), or a vitamin K antagonist (warfarin).…”