Factor IX and deep vein thrombosis

Markers of Hereditary Thrombophilia with Unclear Significance

Thrombophilia leads to an increased risk of venous thromboembolism. Widely accepted risk factors for thrombophilia comprise deficiencies of protein C, protein S, and antithrombin, as well as the factor V "Leiden" mutation, the prothrombin G20210A mutation, dysfibrinogenemia, and, albeit less conclusive, increased levels of factor VIII. Besides these established markers of thrombophilia, risk factors of unclear significance have been described in the literature. These inherited risk factors include deficiencies or loss-of-activity of the activity of ADAMTS13, heparin cofactor II, plasminogen, tissue factor pathway inhibitor (TFPI), thrombomodulin, protein Z (PZ), as well as PZ-dependent protease inhibitor. On the other hand, thrombophilia has been linked to the gain-of-activity, or elevated levels, of α2-antiplasmin, angiotensin-converting enzyme, coagulation factors IX (FIX) and XI (FXI), fibrinogen, homocysteine, lipoprotein(a), plasminogen activator inhibitor-1 (PAI-1), and thrombin-activatable fibrinolysis inhibitor (TAFI). With respect to the molecular interactions that may influence the thrombotic risk, more complex mechanisms have been described for endothelial protein C receptor (EPCR) and factor XIII (FXIII) Val34Leu. With focus on the risk for venous thrombosis, the present review aims to give an overview on the current knowledge on the significance of the aforementioned markers for thrombophilia screening. According to the current knowledge, there appears to be weak evidence for a potential impact of EPCR, FIX, FXI, FXIII Val34Leu, fibrinogen, homocysteine, PAI-1, PZ, TAFI, and TFPI on the thrombotic risk.

The Intrinsic Pathway of Coagulation as a Target for Antithrombotic Therapy

Plasma coagulation in the activated partial thromboplastin time assay is initiated by sequential activation of coagulation factors XII, XI, and IX. While this series of proteolytic reactions is not an accurate model for hemostasis in vivo, there is mounting evidence that factor XI and factor XII contribute to thrombosis, and that inhibiting them can produce an antithrombotic effect with a small effect on hemostasis. This article discusses the contributions of components of the intrinsic pathway to thrombosis in animal models and humans, and results of early clinical trials of drugs targeting factors IX, XI, and XII.

Prophylactic efficacy of BeneFIX vs Alprolix in hemophilia B mice

FIX binds tightly to collagen IV. Furthermore, a FIX mutant, FIXK5R, which binds better than wild-type FIX to collagen IV, provides better hemostasis than wild-type FIX, long after both are undetectable in the plasma. There is also credible evidence of extravascular FIX. Here, we use the saphenous vein bleeding model to compare the efficacy of recombinant FIXFc (Alprolix) and wild-type FIX (BeneFIX) in hemophilia B mice 7 days postinfusion. Although the terminal half-life of Alprolix is significantly longer than that of BeneFIX, at equal doses Alprolix is not better at controlling bleeding 7 days postinfusion, presumably because of the extravascular FIX. Both BeneFIX and Alprolix exhibit a linear response in clotting efficacy up to 150 IU/kg, where they appear to saturate an extravascular compartment, because there is no additional prophylactic benefit from higher doses. A robust pool of extravascular FIX is clearly observed surrounding blood vessels, localized to the same region as collagen IV, in 2 representative human tissues: liver and skeletal muscle. We see no increased risk for thrombosis at 250 IU/kg FIX at 6 hours postinfusion. In summary, 7 days postinfusion into hemophilia B mice, BeneFIX and Alprolix are hemostatically indistinguishable despite the latter's increased half-life. We predict that doses of FIX ∼3 times higher than the currently recommended 40 to 50 IU/kg will, because of FIX's large extravascular compartment, efficiently prolong prophylactic hemostasis without thrombotic risk.

Causality relationships between coagulation factors in type 2 diabetes mellitus: path analysis approach

BACKGROUND

Type 2 diabetic mellitus patients are amongst the most susceptible groups to vascular abnormalities, which predominantly lead to myocardial disease. The hypercoagulable state has been widely studied by researchers as being the major suspicious mechanism facilitating the consecutive chain of molecular events leading to these complications. However, there is no consensus on the definition of the hypercoagulable state with respect to coagulation quantities, their interrelations and basic factor(s) initiating this pathogenic event, by which the prognosis of myocardial complications could be determined.

METHODS

Path analysis was used to study the interactions between coagulation factors as well as other factors beyond coagulation factors in relation with pathogenic events in both diabetics and healthy subjects. In the present work, coagulation factors of 40 healthy and 40 type 2 diabetics were determined experimentally. The data were then analyzed using SPSS and AMOS software. Multivariate regression analysis was done to draw path diagrams.

RESULTS

Our results show that FII, as the main cause for hypercoagulable state, is directly induced by FX and FVIII in normal individuals and by FX, FXI, FV and VWF cofactors in diabetic patients.

CONCLUSION

In general, our findings showed complicated relationship between coagulation factors and their effects either separately or combined.