Blockade of protein C activation reduces microvascular surgical blood loss (original) (raw)
Related papers
Circulation, 1990
Activated protein C (APC) is an antithrombotic enzyme. The therapeutic potential of infused human recombinant APC (rAPC) was studied in a primate model of platelet-dependent thrombosis. Eight baboons with chronic femoral arteriovenous shunts received rAPC infusions for 1 hour. The shunts were extended with 5-cm long, 4-mm-i.d. thrombogenic Dacron graft segments for the time of infusion. The plasma level of the enzyme, the blood flow in the shunt, and the deposition of indium-ill-labeled platelets and iodine-125 fibrinogen on the graft were measured. The influence of rAPC infused at doses of 0.25 and 1.0 mg/kg-hr was compared with the effects of control infusions of saline. Five of eight control grafts occluded within 60 minutes, whereas there was no change in the blood flow during rAPC infusion. Deposition of platelets was inhibited by 13±10% and by 42±13% (mean±SEM) after 30 minutes of infusion at the two doses, which gave rise to circulating rAPC plasma concentrations of 0.4 and 1.9 mg/l, respectively. Both doses significantly inhibited fibrin deposition in the graft. Circulating plasma markers of thrombus formation and of fibrinolysis did not increase significantly during rAPC infusion; measurements of bleeding time were also within normal limits. Thus, rAPC, like human plasma-derived APC, inhibited thrombus formation without impairing primary hemostasis. (Circulation 1990;82:578-585) A ctivated protein C (APC) is an antithrombotic serine protease. It is generated from vitamin K-dependent plasma protein C (PC) by the catalytic complex of thrombin and thrombomodulin.' PC circulates in blood at a plasma level of 4 mg/1.2 APC acts by inhibiting thrombin formation by means of enzymatic cleavage and destruction of coagulation factors Va and VIIa, thus providing negative feedback regulation of coagulation.3 The physiological importance of APC is shown by clinical observations that 1) the incidence of heterozygous PC deficiency is higher in patients with thrombophilia (4%)4.5 than among healthy individuals (0.4%)6; 2) there is a pos-From the Committee on Vascular Biology and the
Inhibition of platelet-dependent thrombus formation by human activated protein C in a primate model
Blood, 1989
The in vivo antithrombotic properties of human plasma activated protein C (APC), a natural anticoagulant enzyme, were investigated in a baboon model of thrombus formation on prosthetic vascular grafts. Infusion of 0.25 to 1.1 mg/kg/h purified, human, APC inhibited blood clotting, as measured by the activated partial thromboplastin time (APTT), and reduced vascular graft platelet deposition by 40% to 70%, as determined by the real-time scintillation camera imaging of 111In-labeled platelet deposition. APC infusion also preserved graft patency. Hemostatic plug formation remained normal, as measured by the template bleeding times. These results suggest that APC administration may produce immediate antithrombotic effects under arterial flow conditions.
Activated protein C inhibits thrombus formation in a system with flowing blood
British Journal of Haematology, 1996
We studied the effect of increasing concentrations of protein C (PC) and activated protein C (APC) on haemostasis in an in vitro thrombosis model. Blood from healthy donors was anticoagulated with citrate-phosphatedextrose (final citrate concentration 19 mM) or a low molecular weight heparin (LMWH, 20 IU/ml). Enzymatically denuded rabbit aorta segments were exposed to flowing blood for 10 min in an annular perfusion chamber. PC and APC were added to the perfusate immediately prior to exposure. In citrated blood at a shear rate of 800/s, PC and APC induced a statistically significant decrease in platelet deposit at 16 ¹ g/ml and 32 ¹ g/ml. In perfusions performed with blood anticoagulated with LMWH, there was no effect on platelet deposition at 16 and 32 ¹ g/ml either at shear rates of 300/s or 800/s. Addition of PC showed no effect on fibrin deposition at a shear rate of 300/s; in contrast, a nonstatistically significant 40% reduction was seen at a shear rate of 800/s, compared to controls. Addition of APC caused a 100% reduction in fibrin formation at 16 and 32 ¹ g/ml at both shear rates studied. PC and APC inhibited platelet deposition on the exposed subendothelial surface, in a dosedependent manner. Effects of PC and APC on platelet function might be mediated through inhibition of thrombin generation at the platelet microenvironment.
Antithrombotic effects of thrombin-induced activation of endogenous protein C in primates
Journal of Clinical Investigation, 1993
The effects on thrombosis and hemostasis of thrombin-induced activation of endogenous protein C (PC) were evaluated in baboons. Thrombosis was induced by placing into arteriovenous shunts a segment of Dacron vascular graft, which generated arterial platelet-rich thrombus, followed by an expansion region of low-shear blood flow, which in turn accumulated fibrinrich venous-type thrombus. Thrombosis was quantified by "'In-platelet imaging and '25I-fibrinogen accumulation. Intravenous infusion of a-thrombin, 1-2 U/kg-min for 1 h, increased baseline activated PC levels (-5 ng/ml) to 250-500 ng/ml (P < 0.01). The lower thrombin dose, which did not deplete circulating platelets, fibrinogen, or PC, reduced arterial graft platelet deposition by 48% (P < 0.05), and platelet and fibrin incorporation into venous-type thrombus by > 85% (P < 0.01). Thrombin infusion prolonged the activated partial thromboplastin clotting time, elevated fibrinopeptide A (FPA), thrombin-antithrombin III complex (T:AT III), and fibrin D-dimer plasma levels (P < 0.01), but did not affect bleeding times. Thrombin's antithrombotic effects were blocked by infusing a monoclonal antibody (HPC4) which prevented PC activation in vivo, caused shunt occlusion, increased the consumption of platelets and fibrinogen, elevated plasma FPA and T:AT III levels, and reduced factor VIII (but not factor V) procoagulant activity (P < 0.05). We conclude that activated PC is a physiologic inhibitor of thrombosis, and that activation of endogenous PC may represent a novel and effective antithrombotic strategy.
Antithrombotic effects of combining activated protein C and urokinase in nonhuman primates
Circulation, 1991
Background. We have determined in vivo the relative antithrombotic efficacy and hemostatic safety of combining low-dose activated protein C (APC) and urokinase (urinary plasminogen activator, u-PA), two natural proteins that regulate thrombogenesis. Methods and Results. To model acute thrombotic responses of native blood under conditions of arterial flow, thrombogenic segments of Dacron vascular graft (VG) were incorporated into chronic exteriorized femoral arteriovenous (AV) access shunts in baboons. Thrombus formation on VG was determined by measuring 1) the deposition of autologous`lIn platelets using real-time scintillation camera imaging, 2) the accumulation of 125I fibrin, 3) segment patency by Doppler flow analysis, and 4) blood tests for thrombosis, including plasma concentrations of platelet factor 4, ,8-thromboglobulin, fibrinopeptide A (FPA), and D-dimer. Treatments consisting of low-dose and intermediate-dose APC (0.07 or 0.25 mg/kg hr), u-PA (25,000 or 50,000 IU/kg hr), or the combination were administered for 1 hour by continuous intravenous infusion. In untreated controls, platelets and fibrin accumulated rapidly, reaching plateau values at 1 hour of 15.1+3.8x i09 platelets and 7.8+2.2 mg fibrin. Although the low-dose APC or u-PA alone did not decrease either platelet or fibrin deposition significantly, this combination moderately reduced both platelet and fibrin accumulation (7.3 ±2.6x 109 platelets, p<0.05; 3.9±0.6 mg fibrin, p<0.05). Furthermore, intermediate-dose APC or u-PA reduced thrombus formation by half when administered alone (p<0.001 for both platelet and fibrin deposition), and the combination markedly interrupted the accumulation of platelets (3.0+1.0X 109 platelets, p <0.001) and fibrin (13+0.6 mg fibrin, p <0.001). During active treatments, all VG segments remained patent. Hemostatic plug forming capability, as measured by template bleeding times, remained normal during all experiments (p>0.05). The T;% clearance time for APC activity was not affected by the concurrent administration of u-PA. u-PA alone increased the plasma levels of D-dimer, FPA, and, interestingly, APC, implying that during pharmacological activation of the fibnrnolytic system, thrombin activity was released, and the protein C pathway was activated. Conclusions. A combination of intermediate-dose APC and u-PA produce substantial and efficient antithrombotic effects without impairing hemostatic function. (Circulation 1991; 84:2454-2462) T wo physiological serine proteasesactivated protein C (APC) and plasminexhibit potent antithrombotic effects, as evidenced by the capacity of APC to interrupt platelet-dependent thrombus formation in nonhuman primate models of From the Committee on Vascular Biology and the
Cardiopulmonary bypass and activation of antithrombotic plasma protein C
The Journal of Thoracic and Cardiovascular Surgery, 1999
We hypothesized that antithrombotic plasma-activated protein C plays a defensive antithrombotic role during coronary ischemia and postischemic reperfusion. We evaluated protein C activation during cardiopulmonary bypass and coronary reperfusion in 20 patients undergoing coronary bypass surgery. During cardiopulmonary bypass and during the 10 minutes after aortic unclamping, the plasma levels of protein C (mean +/- standard error of the mean) decreased from 123% +/- 7% to 74% +/- 5% of normal mean. In contrast, the levels of activated protein C in plasma increased from 122% +/- 8% to 159% +/- 21%, and the activated protein C/protein C ratio increased from 1.04 +/- 0.08 to 2.29 +/- 0. 31 (P =.006, 2-tailed Wilcoxon signed rank test). Patients were stratified on the basis of the increase in activated protein C in the coronary sinus plasma at 10 minutes after reperfusion by means of the arbitrary value of 1.5 for the activated protein C/protein C ratio. Within 24 hours, the patients with low increases in activated protein C (ratio < 1.5, n = 8) had a significantly (P <.05) lower cardiac output and mean pulmonary artery pressure, as well as a higher systemic vascular resistance, than patients (n = 11) with high increases in activated protein C (ratio > 1.5). The rapid increase in activated protein C during the first 10 minutes after aortic unclamping indicated protein C activation in the reperfused vascular beds. The antithrombotic protein C pathway was significantly activated during cardiopulmonary bypass mainly during the minutes after aortic unclamping in the ischemic vascular beds. Suboptimal protein C activation during ischemia may impair the postischemic recovery of human heart and circulation.
Activation of protein C and hemodynamic recovery after coronary artery bypass surgery
The Journal of Thoracic and Cardiovascular Surgery, 2007
Objectives: Activated protein C is a physiologic anticoagulant that is activated by thrombin and upregulated during coronary artery bypass grafting. We studied the balance between thrombin generation and activated protein C levels during coronary artery bypass grafting and hypothesized that protein C activation during reperfusion is associated with hemodynamic recovery or postoperative myocardial damage.
Thrombosis Research, 1984
On both oral and intramuscular administration, the anabolic steroid stanozolol was found to increase protein C antigen concentrations in circulating blood. In fourteen healthy young volunteers (who received stanozolol orally, dose 10 mg/day) the average increase was 1.5-1.6 times the normal concentrations after 3-6 weeks' treatment and was accompanied by more moderate increases in the other vitamin K-deoendent factors II, IX and X to 1.4, 1.4 and 1.2 times their normal concentration respectively. However, there was no change in factor VII. In sixteen elderly surgical patients, intramuscular injection (50 mg) one day prior to surgery induced a moderate increase within 24 hours (to 1.11 times the pretreatment concentration) and seven days after operation (to 1.19 times), and reduced the postoperative fall in protein C. Stanozolol administration seems to be a promising pharmacological method for increasing anticoagulant protein C levels in congenital and acquired deficiencies.