Analysis of factor XIa, factor IXa and tissue factor activity in burn patients

The rise of factor X level in blood plasma of patients at severe burn injuries

This work is dedicated to the detection of imbalance between the pro- and anti-coagulant branches of hemostasis at severe burn injuries by evaluating the content or activity of individual clotting factors. To select the targets for accurate diagnostics we measured the concentrations of soluble fibrin monomeric complexes and fibrinogen, levels of total prothrombin, factor X, protein C and antithrombin III, and recorded the time of clotting in activated partial thromboplastin time and prothrombin time tests. Factor X level was increased in 26 % of patients on the first day after the burn and it rose further in 62 % patients on the 14 th day of recovery. Increasing factor X level is assumed to be a risk factor of thrombotic complications. We propose to use it as a marker of predisposition to thrombosis at severe burn injury.

Hypercoagulation and Hypermetabolism of Fibrinogen in Severely Burned Adults

This study investigated changes in plasma fibrinogen metabolism and changes in coagulation in severely burned adults. Ten patients (27 ± 3 years; 91 ± 6 kg) with 51 ± 3% TBSA were consented and enrolled into an institutional review board-approved prospective study. On the study day, stable isotope infusion of 1-13C-phenylalanine and d5-phenylalanine was performed to quantify fibrinogen production and consumption. During the infusion, vital signs were recorded and blood samples were drawn every hour. Coagulation was measured by thromboelastograph (TEG). Ten normal healthy volunteers (37 ± 7 years; 74 ± 4 kg) were included as the control group. Burned adults had elevated heart rates (120 ± 2 vs 73 ± 5 [control] beats/minute), respiration rates (23 ± 2 vs 15 ± 1 breaths/minute), plasma glucose (127 ± 10 vs 89 ± 2 mg/dl), and fibrinogen levels (613 ± 35 vs 239 ± 17 mg/dl); and decreased albumin (1.3 ± 0.2 vs 3.7 ± 0.1 g/dl) and total protein (4.4 ± 0.2 vs 6.8 ± 0.1 g/dl, all P < .05). Fibrinogen breakdown was elevated in the burn group (2.3 ± 0.4 vs. 1.0 ± 0.3 µmol/kg/minute); and fibrinogen synthesis was further enhanced in the burn group (4.4 ± 0.7 vs 0.7 ± 0.2 µmol/kg/minute, both P < .05). Clotting speed (TEG-alpha) and clot strength (TEG-MA) were increased in the burn group (62 ± 4 vs 50 ± 4°, and 76 ± 2 vs 56 ± 2 mm, respectively, both P < .05). Fibrinolysis of TEG-LY60 was accelerated in the burn group (16 ± 6 vs 3 ± 1) and so was the increase in D-dimer level in the burn group (4.5 ± 0.4 vs 1.9 ± 0.3 mg/l, both P < .05). The hypercoagulable state postburn is in part a result of increased fibrinogen synthesis, over and above increased fibrinogen breakdown.

Coagulation factor XI induces Ca2+ response and accelerates cell migration in vascular smooth muscle cells via proteinase-activated receptor 1

Activated coagulation factor XI (FXIa) is a serine proteinase that plays a key role in the intrinsic coagulation pathway. The analysis of FXI-knockout mice has indicated the contribution of FXI to the pathogenesis of atherosclerosis. However, the underlying mechanism remains unknown. We hypothesized that FXIa exerts vascular smooth muscle effects via proteinase-activated receptor 1 (PAR₁). Fura-2 fluorometry revealed that FXIa elicited intracellular Ca²⁺ signal in rat embryo aorta smooth muscle A7r5 cells. The influx of extracellular Ca²⁺ played a greater role in generating Ca²⁺ signal than the Ca²⁺ release from intracellular stores. The FXIa-induced Ca²⁺ signal was abolished by the pretreatment with atopaxar, an antagonist of PAR₁, or 4-amidinophenylmethanesulfonyl fluoride (p-APMSF), an inhibitor of proteinase, while it was also lost in embryonic fibroblasts derived from PAR₁^-/- mice. FXIa cleaved the recombinant protein containing the extracellular region of PAR₁ at the same site (R45/S46) as that of thrombin, a canonical PAR₁ agonist. The FXIa-induced Ca²⁺ influx was inhibited by diltiazem, an L-type Ca²⁺ channel blocker, and by siRNA targeted to Ca_V1.2. The FXIa-induced Ca²⁺ influx was also inhibited by GF109203X and rottlerin, inhibitors of protein kinase C. In a wound healing assay, FXIa increased the rate of cell migration by 2.46-fold of control, which was partly inhibited by atopaxar or diltiazem. In conclusion, FXIa mainly elicits the Ca²⁺ signal via the PAR₁/Ca_V1.2-mediated Ca²⁺ influx and accelerates the migration in vascular smooth muscle cells. The present study provides the first evidence that FXIa exerts a direct cellular effect on vascular smooth muscle.