The interplay between tamoxifen and endoxifen plasma concentrations and coagulation parameters in patients with primary breast cancer

Background: Tamoxifen is an effective treatment for primary breast cancer but increases the risk for venous thromboembolism. Tamoxifen decreases anticoagulant proteins, including antithrombin (AT), protein C (PC) and tissue factor (TF) pathway inhibitor, and enhances thrombin generation (TG). However, the relation between plasma concentrations of both tamoxifen and its active metabolite endoxifen and coagulation remains unknown. Methods: Tamoxifen and endoxifen were measured in 141 patients from the prospective open-label intervention TOTAM-study after 3 months (m) and 6 m of tamoxifen treatment. Levels of AT and PC, the procoagulant TF, and TG parameters were determined at both timepoints if samples were available (n = 53–135 per analysis). Levels of coagulation proteins and TG parameters were correlated and compared between: 1) quartiles of tamoxifen and endoxifen levels, and 2) 3 m and 6 m of treatment. Results: At 3 m, levels of AT, PC, TF and TG parameters were not associated with tamoxifen nor endoxifen levels. At 6 m, median TF levels were lower in patients in the 3rd (56.6 [33] pg/mL), and 4th (50.1 [19] pg/mL) endoxifen quartiles compared to the 1st (lowest) quartile (76 [69] pg/mL) (P=0.027 and P=0.018, respectively), but no differences in anticoagulant proteins or TG parameters were observed. An increase in circulating TF levels (3 m: 46.0 [15] versus 6 m: 54.4 [39] pg/mL, P &lt; 0.001) and TG parameters was observed at the 6 m treatment timepoint, while AT and PC levels remained stable.Conclusions: Our results indicate that higher tamoxifen and endoxifen levels are not correlated with an increased procoagulant state, suggesting tamoxifen dose escalation does not further promote hypercoagulability.</p

Functional expression of the human coagulation factor IX using heterologous signal peptide and propeptide sequences in mammalian cell line

Thrombosis and Hemostasi

Engineered factor Xa variants retain procoagulant activity independent of direct factor Xa inhibitors

The absence of an adequate reversal strategy to prevent and stop potential life-threatening bleeding complications is a major drawback to the clinical use of the direct oral inhibitors of blood coagulation factor Xa. Here we show that specific modifications of the substrate-binding aromatic S4 subpocket within the factor Xa active site disrupt high-affinity engagement of the direct factor Xa inhibitors. These modifications either entail amino-acid substitution of S4 subsite residues Tyr99 and/or Phe174 (chymotrypsinogen numbering), or extension of the 99-loop that borders the S4 subsite. The latter modifications led to the engineering of a factor Xa variant that is able to support coagulation in human plasma spiked with (supra-)physiological concentrations of direct factor Xa inhibitors. As such, this factor Xa variant has the potential to be employed to bypass the direct factor Xa inhibitor-mediated anticoagulation in patients that require restoration of blood coagulation.A major drawback in the clinical use of the oral anticoagulants that directly inhibit factor Xa in order to prevent blood clot formation is the potential for life threatening bleeding events. Here the authors describe factor Xa variants that are refractory to inhibition by these anticoagulants and could serve as rescue agents in treated patients

Venom factor V from the common brown snake escapes hemostatic regulation through procoagulant adaptations

Venomous snakes produce an array of toxic compounds, including procoagulants to defend themselves and incapacitate prey. The Australian snake Pseudonaja textilis has a venom-derived prothrombin activator homologous to coagulation factors V (FV) and Xa (FXa). Here we show that the FV component (pt-FV) has unique biologic properties that subvert the normal regulatory restraints intended to restrict an unregulated procoagulant response. Unlike human FV, recombinant pt-FV is constitutively active and does not require proteolytic processing to function. Sequence comparisons show that it has shed a large portion of the central B-domain, including residues that stabilize the inactive procofactor state. Remarkably, pt-FV functions in the absence of anionic membranes as it binds snake-FXa with high affinity in solution. Furthermore, despite cleavage in the heavy chain, pt-FV is functionally resistant to activated protein C, an anticoagulant. We speculate this stability is the result of noncovalent interactions and/or a unique disulfide bond in pt-FV linking the heavy and light chains. Taken together, these findings provide a biochemical rationale for the strong procoagulant nature of venom prothrombinase. Furthermore, they illustrate how regulatory mechanisms designed to limit the hemostatic response can be uncoupled to provide a sustained, disseminated procoagulant stimulus for use as a biologic toxin

Clinical relevance of brown snake (Pseudonaja spp) factor V escaping hemostatic regulation (letter)

Despite the work by Bos et al. reported in Blood and by other researchers on the structure and function of the procoagulant molecules, the pathophysiology of venom-induced consumption coagulopathy (VICC) associated with human envenoming by these snakes remains unclear. Although it would appear that the presence of a factor Va–like toxin in brown snake (Pseudonaja spp) venom that is impervious to regulation by the hemostatic system provides a potent biologic weapon against prey and in human envenoming, clinical research does not fully support this

Objectives and Design of BLEEDS: A Cohort Study to Identify New Risk Factors and Predictors for Major Bleeding during Treatment with Vitamin K Antagonists

<div><p>Background</p><p>Risk scores for patients who are at high risk for major bleeding complications during treatment with vitamin K antagonists (VKAs) do not perform that well. BLEEDS was initiated to search for new biomarkers that predict bleeding in these patients.</p><p>Objectives</p><p>To describe the outline and objectives of BLEEDS and to examine whether the study population is generalizable to other VKA treated populations.</p><p>Methods</p><p>A cohort was created consisting of all patients starting VKA treatment at three Dutch anticoagulation clinics between January-2012 and July-2014. We stored leftover plasma and DNA following analysis of the INR.</p><p>Results</p><p>Of 16,706 eligible patients, 16,570 (99%) were included in BLEEDS and plasma was stored from 13,779 patients (83%). Patients had a mean age of 70 years (SD 14), 8713 were male (53%). The most common VKA indications were atrial fibrillation (10,876 patients, 66%) and venous thrombosis (3920 patients, 24%). 326 Major bleeds occurred during 17,613 years of follow-up (incidence rate 1.85/100 person years, 95%CI 1.66–2.06). The risk for major bleeding was highest in the initial three months of VKA treatment and increased when the international normalized ratio increased. These results and characteristics are in concordance with results from other VKA treated populations.</p><p>Conclusion</p><p>BLEEDS is generalizable to other VKA treated populations and will permit innovative and unbiased research of biomarkers that may predict major bleeding during VKA treatment.</p></div

Number of bleeding events stratified by area.

<p>Number of bleeding events stratified by area.</p

Time in therapeutic range per day after starting VKA treatment.

<p>Time in therapeutic range per day after starting VKA treatment.</p

Incidence rates of bleeding events stratified by time since start of VKA treatment.

<p>Incidence rates of bleeding events stratified by time since start of VKA treatment.</p