Background: Elevated levels of coagulation factors (F) II (FII), FV, FVII, FIX, FX, and FXI have often been related with coronary heart disease, ischemic stroke, and venous thrombosis (VT). However... Show moreBackground: Elevated levels of coagulation factors (F) II (FII), FV, FVII, FIX, FX, and FXI have often been related with coronary heart disease, ischemic stroke, and venous thrombosis (VT). However, there are few studies on their associations with all-cause mortality. Objective: We explored whether elevated levels of FII, FV, FVII, FIX, FX, and FXI are associated with an increased risk of death in patients who had VT and in individuals from the general population.Methods: We followed 1919 patients with previous VT and 2800 age-and sex -matched community controls in whom coagulation factor levels were measured. A high coagulation factor was defined as the >90th percentile of normal in the controls. Cox regression analyses were adjusted for age and sex and for being a patient with VT or being a control subject.Results: The median age at time of enrolment was 48 years for both patients and controls, and slightly more women than men were followed. Over a median follow-up of 6.1 years for patients and 5.0 years for controls, there were 79 and 60 deaths in patient and controls respectively. There was no association of FII, FV, FVII, FIX, FX, and FXI with all-cause mortality in patients or in control individuals.Conclusions: Elevated levels of FII, FV, FVII, FIX, FX, and FXI levels may not be associated with an increased risk of all-cause mortality. Only for cardiac death, an association with high FX and FXI was found, which confirms the findings of previous studies, but numbers were small. Show less
Maag, A.; Rein, N. van; Schuijt, T.J.; Kopatz, W.F.; Kruijswijk, D.; Thomassen, S.; ... ; van't Veer, C. 2021
Objective: Plasma thrombin generation (TG) provides important information on coagulation status; however, current TG output parameters do not predict major bleeding of patients on anticoagulants.... Show moreObjective: Plasma thrombin generation (TG) provides important information on coagulation status; however, current TG output parameters do not predict major bleeding of patients on anticoagulants. We recently reported that factor V (FV) activation by factor X (FX)a contributes importantly to the initiation phase of TG. Here we investigated how this pathway varies in the normal population and whether FXa-mediated activation of FV is associated with major bleeding in patients on anticoagulant therapy. Approach: We employed TIX-5, a specific inhibitor of FV activation by FXa, to estimate the contribution of FXa-mediated FV activation to tissue factor (TF)-initiated TG. Results: We show that the contribution of this pathway to plasma TG varies considerably in the normal population, as measured by the time needed to form the first traces of thrombin (TG lag time; mean prolongation by TIX-5 40%, range 0%-116%). Comparing patients on vitamin K antagonists (VKA) of the BLEED study (263 patients with and 538 patients without major bleeding), showed a marked prolongation in the median TG lag time in the presence of TIX-5 in cases (12.83 versus 11.00 minutes, P = 0.0030), while the TG lag time without TIX-5 only showed a minor although significant difference (5.83 vs. 5.67 minutes, P = 0.0198). The TIX-5 sensitivity (lag time + TIX-5/lag time + vehicle) in the upper quartile was associated with a 1.62-fold (95% confidence interval 1.04-2.52) increased risk of major bleeding compared to the lowest quartile. Conclusion: A greater dependence on FXa-mediated activation of FV of TG is associated with increased risk of major bleeding during VKA therapy. Show less
Objective: The Australian snake venom ptFV (Pseudonaja textilis venom-derived factor V) variant retains cofactor function despite APC (activated protein C)-dependent proteolysis. Here, we aimed to... Show moreObjective: The Australian snake venom ptFV (Pseudonaja textilis venom-derived factor V) variant retains cofactor function despite APC (activated protein C)-dependent proteolysis. Here, we aimed to unravel the mechanistic principles by determining the role of the absent Arg306 cleavage site that is required for the inactivation of FVa (mammalian factor Va). Approach and Results: Our findings show that in contrast to human FVa, APC-catalyzed proteolysis of ptFVa at Arg306 and Lys507 does not abrogate ptFVa cofactor function. Remarkably, the structural integrity of APC-proteolyzed ptFVa is maintained indicating that stable noncovalent interactions prevent A2-domain dissociation. Using Molecular Dynamics simulations, we uncovered key regions located in the A1 and A2 domain that may be at the basis of this remarkable characteristic. Conclusions: Taken together, we report a completely novel role for uniquely adapted regions in ptFVa that prevent A2 domain dissociation. As such, these results challenge our current understanding by which strict regulatory mechanisms control FVa activity. Show less
Maag, A.; Sharma, P.; Schuijt, T.J.; Kopatz, W.F.; Kruijswijk, D.; Marquart, J.A.; ... ; Veer, C. van 't 2021
Background The prothrombinase complex consists of factors Xa (FXa) and Va (FVa) on an anionic phospholipid surface and converts prothrombin into thrombin. Both coagulation factors require... Show moreBackground The prothrombinase complex consists of factors Xa (FXa) and Va (FVa) on an anionic phospholipid surface and converts prothrombin into thrombin. Both coagulation factors require activation before complex assembly. We recently identified TIX-5, a unique anticoagulant tick protein that specifically inhibits FXa-mediated activation of FV. Because TIX-5 inhibited thrombin generation in blood plasma, it was concluded that FV activation by FXa contributes importantly to coagulation.Objective We aimed to unravel the structure-function relationships of TIX-5.Method We used a structure model generated based on homology with the allergen Der F7.Results Tick inhibitor of factor Xa toward FV was predicted to consist of a single rod formed by several beta sheets wrapped around a central C-terminal alpha helix. By mutagenesis we could show that two hydrophobic loops at one end of the rod mediate the phospholipid binding of TIX-5. On the other end of the rod an FV interaction region was identified on one side, whereas on the other side an EGK sequence was identified that could potentially form a pseudosubstrate of FXa. All three interaction sites were important for the anticoagulant properties of TIX-5 in a tissue factor-initiated thrombin generation assay as well as in the inhibition of FV activation by FXa in a purified system.Conclusion The structure-function properties of TIX-5 are in perfect agreement with a protein that inhibits the FXa-mediated activation on a phospholipid surface. The present elucidation of the mechanism of action of TIX-5 will aid in deciphering the processes involved in the initiation phase of blood coagulation. Show less
The venom of the Australian brown snake Pseudonaja textilis contains a prothrombinase-like initiator of blood coagulation, which has evolved into a potent weapon through several gainof-function... Show moreThe venom of the Australian brown snake Pseudonaja textilis contains a prothrombinase-like initiator of blood coagulation, which has evolved into a potent weapon through several gainof-function adaptations. Here we examined the functional implications of a disulfide bond exclusively found in the factor (F)Va-like cofactor component, ptFV. We found that this remarkable structural feature is not required for the procoagulant properties of ptFV. The nearly identical liver-derived plasma ptFV that lacks this disulfide link displayed a similar procoagulant profile. Whether the unique disulfide bond imposes conformational constraints essential to other aspects of the venom FV life cycle remains to be determined. Show less
