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8 Enhanced thrombolysis in vivo by a specific factor XIIIa inhibitor
4
SESSION 2: Experimental Thrombolysis II
7
RECOMBINANT ACTIVATED PROTEIN C PREVENTS OCCLUSION IN AN ARTERIO-VENOUS SHUNT
~&&LJ~~~
!Z&Y ODDenheirneh RichardIialgw ad
IIntegrate\ Genetics, Inc., Framingham, MA. and zEG&G Mason Research Institute, Worcester, MA. USA. Protein C, a vitamin K-dependent protein, plays a key role in inhibiting the clotting cascade. Protein C has also been implicated in fibinolysis by its binding to PAI-1, a plasminogen activator inhibitor. Imbalances in this regulatory pathway can shift the hemostatic balance towards a thrombotic state as demonstrated in protein C deficient patients who are prone to recurrent thromboses. We performed primate studies to determine the pharmacokinetics of recombinant protein C zymogen (rPC) and recombinant activated protein C (rAPC), and their efficacy in preventing thrombosis in an arterio-venous shunt. In cynomologous monkeys (Macaca fasicularts) bolus intravenous injections of both protein C zymogen &d activated protein C showed typical biphasic clearance with values of 5.2 and 82.5 hours for the alpha and
8
ENHANCED THROMBOLYSISINVIVO BY A SPECIFIC FACTOR XIIIa INHIBITOR. L.R. Bush, P.A. Friedman, M.J. Mellott*, S.M. Kanovsky*, and A.M. Stern* Merck Sharp 6 Dohme, West Point, PA 19486 Factor XIIIa (FXIIIa) catalyzes crosslinking reactions of fibrin, increasing its mechanical stability and resistance to lysis. We evaluated the ability of L-722,151 (L72), a FXIIIa inhibitor to enhance the thrombolytic effects of streptokinase (SK) or tissue plasminogen activator (t-PA) in a canine model of femoral artery (FA) thrombolysis. Copper coils were inserted into FAs of anesthetized dogs with an 8F catheter and guidewire via the left carotid artery. FA blood flow (FABFGas measured with Doppler flow probes to monitor the time of occlusion and lysis and to quantify the extent of FABF restoration after lysis. L72 or vehicle was administered as a bolus and continuous IV infusion (1 mg/kg plus
Fibmolysis 8 Longman
(1988) 2, Supp. I, 4-6 Group UK Ltd 1988
beta phases of the rPC and 7.6 and 109 minutes for the alpha and beta phases of rAPC. The efficacy of rAPC protein was demonstrated in a baboon (&& attub&) model. Percutaneous catheters were inserted in the femoral artery and femoral vein and connected with silastic tubing. A knitted Dacron vascular graft was preclotted and placed into this shunt, and the flowrate monitored via a Transonic 1OlD blood flowmeter. Placebo treated animals showed a 50-7096 reduction in flow within 30 minutes. Animals treated with X5Opg/kg body weight of rAPC showed no reduction in flowrate for at least 60 minutes while identical concentrations of rPC were similar to placebo. At concentrations of rAPC known to be effective in preventing occlusion of the shunt, no detectable increase in PTT was measured. Heparin administered as a bolus IV dose of 100 IU/kg body weight was also effective in maintaining flowrate, but did exhibit a greater than 3 fold increase in PIT. We conclude that rPC and rAPC exhibit typical pharmacokinetic behavior and that rAPC but not rPC is effective in preventing thrombosis in a baboon arterio-venous shunt.
0.1 mg/kg/min) 5 min before coil insertion and continued for 2 hr. Infusion of t-PA or SK was initiated 30 minutes after FA occlusion and continued for 60 or 90 min, respectively. In vehicle-treated dogs, the times to lysis (TTL) by 0.5 (n=6) and 1.0 mg/kg (n=4) t-PA were 53+7 and 20+6 minutes (x+SEM). Thirty min after lysis FAEF was 10+7% 2nd 91+5% of control levels, respectively.In six LIZ-treated dogs, 0.5 mg/kg of t-PA induced lysis in 25+4 min; 30 min after lysis, FABF was 73+12X. WiTh IV SK (500 U/kg/min), the TTLTs did not differ between control and L72-treated dogs, but maximum FABF after lysis was higher in L72-treated dogs (72+ 8% vs. 24+5%). Re-occlusion after thrombolysis, which was-common in vehicle-treated dogs, was prevented by L72. Thus, FXIIIa inhibition enhances thrombolysis by SK and t-PA in vivo.
SESSION 2: Experimental Thrombolysis II
7
RECOMBINANT ACTIVATED PROTEIN C PREVENTS OCCLUSION IN AN ARTERIO-VENOUS SHUNT
~&&LJ~~~
!Z&Y ODDenheirneh RichardIialgw ad
IIntegrate\ Genetics, Inc., Framingham, MA. and zEG&G Mason Research Institute, Worcester, MA. USA. Protein C, a vitamin K-dependent protein, plays a key role in inhibiting the clotting cascade. Protein C has also been implicated in fibinolysis by its binding to PAI-1, a plasminogen activator inhibitor. Imbalances in this regulatory pathway can shift the hemostatic balance towards a thrombotic state as demonstrated in protein C deficient patients who are prone to recurrent thromboses. We performed primate studies to determine the pharmacokinetics of recombinant protein C zymogen (rPC) and recombinant activated protein C (rAPC), and their efficacy in preventing thrombosis in an arterio-venous shunt. In cynomologous monkeys (Macaca fasicularts) bolus intravenous injections of both protein C zymogen &d activated protein C showed typical biphasic clearance with values of 5.2 and 82.5 hours for the alpha and
8
ENHANCED THROMBOLYSISINVIVO BY A SPECIFIC FACTOR XIIIa INHIBITOR. L.R. Bush, P.A. Friedman, M.J. Mellott*, S.M. Kanovsky*, and A.M. Stern* Merck Sharp 6 Dohme, West Point, PA 19486 Factor XIIIa (FXIIIa) catalyzes crosslinking reactions of fibrin, increasing its mechanical stability and resistance to lysis. We evaluated the ability of L-722,151 (L72), a FXIIIa inhibitor to enhance the thrombolytic effects of streptokinase (SK) or tissue plasminogen activator (t-PA) in a canine model of femoral artery (FA) thrombolysis. Copper coils were inserted into FAs of anesthetized dogs with an 8F catheter and guidewire via the left carotid artery. FA blood flow (FABFGas measured with Doppler flow probes to monitor the time of occlusion and lysis and to quantify the extent of FABF restoration after lysis. L72 or vehicle was administered as a bolus and continuous IV infusion (1 mg/kg plus
Fibmolysis 8 Longman
(1988) 2, Supp. I, 4-6 Group UK Ltd 1988
beta phases of the rPC and 7.6 and 109 minutes for the alpha and beta phases of rAPC. The efficacy of rAPC protein was demonstrated in a baboon (&& attub&) model. Percutaneous catheters were inserted in the femoral artery and femoral vein and connected with silastic tubing. A knitted Dacron vascular graft was preclotted and placed into this shunt, and the flowrate monitored via a Transonic 1OlD blood flowmeter. Placebo treated animals showed a 50-7096 reduction in flow within 30 minutes. Animals treated with X5Opg/kg body weight of rAPC showed no reduction in flowrate for at least 60 minutes while identical concentrations of rPC were similar to placebo. At concentrations of rAPC known to be effective in preventing occlusion of the shunt, no detectable increase in PTT was measured. Heparin administered as a bolus IV dose of 100 IU/kg body weight was also effective in maintaining flowrate, but did exhibit a greater than 3 fold increase in PIT. We conclude that rPC and rAPC exhibit typical pharmacokinetic behavior and that rAPC but not rPC is effective in preventing thrombosis in a baboon arterio-venous shunt.
0.1 mg/kg/min) 5 min before coil insertion and continued for 2 hr. Infusion of t-PA or SK was initiated 30 minutes after FA occlusion and continued for 60 or 90 min, respectively. In vehicle-treated dogs, the times to lysis (TTL) by 0.5 (n=6) and 1.0 mg/kg (n=4) t-PA were 53+7 and 20+6 minutes (x+SEM). Thirty min after lysis FAEF was 10+7% 2nd 91+5% of control levels, respectively.In six LIZ-treated dogs, 0.5 mg/kg of t-PA induced lysis in 25+4 min; 30 min after lysis, FABF was 73+12X. WiTh IV SK (500 U/kg/min), the TTLTs did not differ between control and L72-treated dogs, but maximum FABF after lysis was higher in L72-treated dogs (72+ 8% vs. 24+5%). Re-occlusion after thrombolysis, which was-common in vehicle-treated dogs, was prevented by L72. Thus, FXIIIa inhibition enhances thrombolysis by SK and t-PA in vivo.