von Willebrand factor multimer composition is modified following oral methionine load in women with thrombosis, but not in healthy women

Prospective study of hemostatic alterations in children with acute lymphoblastic leukemia

In a group of newly diagnosed acute lymphocytic leukemia (ALL) children we evaluated a number of hemostatic and inflammatory markers at diagnosis and at different time points during chemotherapy for the remission induction to identify alterations in the plasma levels of prothrombotic markers before and during the course of chemotherapy. The following plasma markers were evaluated: thrombin-antithrombin complex (TAT), D-Dimer, plasminogen activator inhibitor 1 (PAI-1), antithrombin, fibrinogen, von Willebrand factor (VWF) antigen and high molecular weight VWF (HMW-VWF) multimers, P-selectin, tumor necrosis factor alpha (TNF-alpha), and interleukin 6 (IL-6). Plasma samples were collected at the following time points: at T0 (baseline) and T1 (+24 days of therapy), T2 (+36 days therapy), and T3 (+64 days therapy). The results show that, at diagnosis, ALL children presented with laboratory signs of increased thrombin generation and fibrin formation (i.e. high TAT and D-dimer levels), fibrinolysis inhibition (i.e. high PAI-1 level), endothelial activation (i.e., high HMW-VWF and soluble P-selectin levels) and inflammation (i.e. high TNF-alpha and IL-6 levels). After starting induction therapy, the thrombin generation markers and inflammatory cytokines significantly decreased. To the opposite, PAI-1 and P-selectin significantly increased, suggesting an insult by chemotherapy on the vascular endothelium. These effects were more evident during steroid administration. Symptomatic venous thromboembolism (VTE) episodes developed in two cases during induction therapy, which did not allow the evaluation of the predictive value for VTE of laboratory markers.

Cleavage of von Willebrand factor by ADAMTS-13 in vitro: effect of temperature and barium ions on the proteolysis kinetics

The multimeric size of von Willebrand factor (VWF) is regulated by the specific cleaving metalloprotease, ADAMTS-13. Laboratory assays for ADAMTS-13 are useful for identifying severe protease-deficient activity. ADAMTS-13 activity is currently assayed by prolonged dialysis of plasma at 37 degrees C in low-ionic-strength denaturing buffer. We investigated the effect of temperature and divalent cation supplementation on the kinetics of VWF proteolysis by ADAMTS-13 in vitro. Proteolysis was monitored for 24 h at 37, 22, and 4 degrees C, in the presence or absence of barium ions, by measuring the binding of VWF to collagen. Complete VWF proteolysis was observed at 37 degrees C in the presence of BaCl2, while about 25% VWF still bound to collagen when BaCl2 supplementation was omitted. Proteolysis kinetics at 22 and 4 degrees C was slower but complete, even in the absence of added barium. A subphysiological temperature might influence the proteolysis kinetics by determining minor variations of the ADAMTS-13 structure, or further modification of the VWF substrate. We describe a simple procedure to analyse the kinetics of VWF proteolysis that is suitable for routine diagnostic use. Furthermore, we offer new insight into the biochemistry of ADAMTS-13.