Journal of Thrombosis and Haemostasis最新文献

Endothelial cells deliver a vital contribution to the maintenance of hemostasis by constituting an anatomical as well as functional barrier between the blood and the rest of the body. Apart from the physical barrier function, endothelial cells maintain the hemostatic equilibrium by their pro- and anticoagulant functions. An important part of their procoagulant contribution is the production of von Willebrand factor (VWF), which is a carrier protein for coagulation factor VIII and facilitates the formation of a platelet plug. Thus, VWF is indispensable for both primary and secondary hemostasis, which is exemplified by the bleeding disorder von Willebrand disease that results from qualitative or quantitative deficiencies in VWF. A cellular model that was found to accurately reflect the endothelium and its secretory organelles are endothelial colony-forming cells, which can be readily isolated from peripheral blood and constitute a robust ex vivo model to investigate the donor's endothelial cell function. This review summarizes some of the valuable insights on biology of VWF and pathogenic mechanisms of von Willebrand disease that have been made possible using studies with endothelial colony-forming cells derived from patients with bleeding disorders.

Background: A paucity of data exists to support the use of factor (F)Xa inhibitors in severely obese patients with a weight of ≥150 kg or body mass index (BMI) of ≥50 kg/m².

Objectives: The purpose of this study was to evaluate whether FXa inhibitors are as safe and effective as warfarin for the treatment of atrial fibrillation (AF) and/or venous thromboembolism (VTE) in individuals with a BMI of ≥50 kg/m² and/or weight of ≥150 kg.

Methods: This was a multicenter retrospective cohort study of severely obese adult patients with AF and/or VTE treated with a FXa inhibitor or warfarin. The primary effectiveness outcome was composite odds of stroke, systemic embolism, or VTE; the primary safety outcome was odds of major bleeding. Secondary outcomes included incidence of stroke or systemic embolism, VTE, major bleeding, clinically relevant nonmajor bleeding, all-cause mortality, change in anticoagulation, and total number of hospital encounters. Outcomes were assessed for 12 months following initiation of study drug.

Results: A total of 1736 patients were included. The mean weight and BMI of the overall cohort were 164.4 kg and 54.6 kg/m², respectively. There was no difference in odds of stroke, systemic embolism or VTE (odds ratio, 1.005; 95% CI, 0.6-1.68), or major bleeding (odds ratio, 0.9; 95% CI, 0.47-1.7) between groups.

Conclusion: These data suggest that apixaban and rivaroxaban are safe and effective alternatives to warfarin for the treatment of AF and/or VTE in individuals with a BMI of ≥50 kg/m² and/or weight of ≥150 kg.

Background: Protein S (PS) is an anticoagulant that functions as a cofactor for activated protein C and the tissue factor pathway inhibitor. PS deficiency is a risk factor for venous thromboembolism. PS activity is commonly measured using clot-based assays involving fibrin and thrombin production, but improvements are needed.

Objectives: To develop a new assay for measuring plasma PS activity by quantifying the amount of activated coagulation factor (F)V cleaved by activated protein C.

Methods: We designed a recombinant, modified FV (FVm) that mimicked FVa. We analyzed 160 purposively selected plasma samples from the Biobank of the National Cerebral and Cardiovascular Center.

Results: The assay using mixed normal and PS-deficient plasma detected FVm cleavage in a PS concentration-dependent manner. The correlation between PS activity, measured using the FVm cleavage assay, and free PS antigen levels was relatively weak. We then sequenced all exons of PROS1 from 47 subjects with <60% activity in either the FVm cleavage assay or the clot-based assay. Nonsynonymous variants were identified in 12 of 24 subjects with <60% activity in both assays and in 2 of 7 subjects with <60% activity in the FVm cleavage assay alone. No variants were identified in 16 subjects with <60% activity in the clot-based assay alone. Unlike the clot-based assay, the FVm cleavage assay was not affected by the presence of rivaroxaban in the plasma.

Conclusion: An assay using the FVm substrate may be less susceptible to interference and provide a more accurate evaluation of plasma PS activity than clot-based assays.

Background: Almost half of severe hemophilia A (HA) cases are caused by an intron 22 inversion (Int22Inv) mutation, which truncates the 26-exon F8 messenger RNA (mRNA) after exon 22. Another F8 transcript, F8_B, is initiated from within F8-intron-22. F8_B mRNA consists of a short exon spliced to exons 23 to 26 and is expressed in multiple human cell types. It has been hypothesized that Int22Inv patients have self-tolerance to partial factor (F)VIII proteins expressed from these 2 transcripts. FVIII is expressed in endothelial cells, primarily in the liver and lungs. Several studies have reported FVIII expression in other cell types, although this has been controversial.

Objectives: To determine if partial FVIII proteins are expressed from intron 22-inverted and/or F8_B mRNA and if FVIII is expressed in nonendothelial cells.

Methods: A panel of FVIII-specific antibodies was validated and employed to label FVIII in cells and tissues and for immunoprecipitation followed by western blots and mass spectrometry proteomics analysis.

Results: Immunofluorescent staining localized FVIII to endothelial cells in liver sections from non-HA but not HA-Int22Inv dogs. Neither FVIII nor FVIII_B was detected in human peripheral blood mononuclear cells, B cell or T cell lines, or cell lines expanded from peripheral blood mononuclear cells, whereas FVIII antigen and activity were readily detected in primary nonhemophilic liver sinusoidal endothelial cells.

Conclusion: If FVIII is expressed in nonendothelial cells or if partial FVIII proteins are expressed in HA-Int22Inv, the concentrations are below the detection limits of these sensitive assays. Our results argue against promotion of immune tolerance through expression of partial FVIII proteins in Int-22Inv patients.