Jack Henkin

Bolus dose response characteristics of single chain urokinase plasminogen activator and tissue plasminogen activator in a dog model of arterial thrombosis

Tissue plasminogen activator (t-PA) and single chain urokinase-plasminogen activator (scu-PA) are relatively fibrin-specific thrombolytic drugs with short plasma half lives of 6-8 minutes. Most treatment regimens with these agents utilize a bolus injection followed by continuous drug infusion, usually combined with anticoagulant therapy. The purpose of this study was to establish the dose-response characteristics for scu-PA and t-PA, when given as a single intravenous bolus injection, in a dog model of arterial thrombosis. Eight groups of 6 dogs each were given one of the following doses of scu-PA (mg/kg): 0.20, 0.50, 1.00, 2.00; or t-PA: 0.05, 0.10, 0.20; or an equivalent amount of saline (control group). All doses were given as a single bolus injection 60 minutes after formation of a totally occlusive femoral artery thrombus. Thrombolysis was measured by monitoring the continuous decrement of 125I activity from a radiolabelled thrombus. Ninety minutes after drug injection, all scu-PA treated dogs showed greater thrombolysis (30%, 45%, 56%, and 67%, respectively) than the control group (15%, p less than 0.01). The 0.10 and 0.20 mg/kg t-PA treated dogs showed greater thrombolysis (35% and 49%, respectively) than the control group (15%, p less than 0.01). Both scu-PA and t-PA caused a partial and dose-dependent decrease in alpha 2-antiplasmin activity but scu-PA caused a greater depletion (72% vs. 18%, respectively, p less than 0.05) at 60 minutes after the highest dose of drug administration. Both drugs showed a longer than expected thrombolytic effect based upon the known half lives. Neither drug caused significant changes in the prothrombin time, activated partial thromboplastin time, thrombin time, hematocrit, platelet count, or fibrin degradation product concentration. Single bolus injections of scu-PA and t-PA produce safe and effective thrombolysis in this dog model of arterial thrombosis.

Enhancement of the thrombolytic efficacy of prourokinase by lys-plasminogen in a dog model of arterial thrombosis

Current findings suggest that the efficacy of thrombolytic therapy may be limited by the availability of active forms of plasminogen at the thrombus site. The purpose of this study was to determine if the systemic administration of 0.5 mg kg-1 glu-plasminogen (glu-plg) or 0.5 mg kg-1 lys-plasminogen (lys-plg) could safely increase the efficacy of a single intravenous bolus injection of 50,000 U kg-1 prourokinase (proUK) in a dog model of arterial thrombosis. Thrombolysis was measured by monitoring the continuous decrement of 125I-gamma emissions from a radiolabeled thrombus. Reflow was evaluated by direct visual examination. Forty dogs (mean wt 10.3 +/- 2 kg) were randomly sorted into 4 groups of 10 each. The dogs in each group were given either saline plus saline, saline plus proUK, glu-plg plus proUK, or lys-plg plus proUK 60 minutes after formation of an occlusive arterial thrombus. Ninety minutes after drug administration the dogs receiving saline plus proUK, glu-plg plus proUK, and the lys-plg plus proUK showed greater thrombolysis (41%, 43%, and 66%, respectively) than the control (saline plus saline) group (15%, P less than 0.01). The lys-plg plus proUK treatment caused greater lysis than the saline plus proUK or the glu-plg plus proUK treatment (P less than 0.05). All of the dogs (10/10) receiving lys-plg plus proUK had patent vessels at the end of the 90 minute monitoring period, whereas only 4/10 and 5/10 vessels were patent in the saline plus proUK and glu-plg plus proUK groups, respectively. None of the dogs in the saline plus saline group had patent vessels. No significant changes were observed in the various coagulation parameters tested for any of the 4 treatment groups. The results show that lys-plg can safely increase the thrombolytic efficacy of proUK.

Enhanced lytic efficacy of multiple bolus injections of tissue plasminogen activator in dogs

The purpose of this study was to compare the lytic efficacy of tissue plasminogen activator (tPA) following different dosing regimens. Radiolabelled clots from dog whole blood were inserted into an extracorporeal jugular loop in anesthetized dogs. Clot size (counts/min) was continuously recorded. tPA was administered as a single 1 min bolus of 0.4 mg/kg, as four multiple bolus injections of 0.1 mg/kg each at 30 min intervals, or as an initial bolus (0.04 mg/kg) followed by a 30 min infusion of 0.36 mg/kg (10%/90%, bolus/infusion). Multiple injections of the same total dose of tPA resulted in 76% and 51% greater clot lysis than single bolus injection or bolus/infusion regimen, respectively, measured 120 min after initial dosing. There were no differences in fibrinogen, plasminogen or alpha-2-antiplasmin between the different treatment groups at 120 min.

The Beneficial Effect of Lys-Plasminogen upon the Thrombolytic Efficacy of Urokinase in a Dog Model of Peripheral Arterial Thrombosis

The efficacy of thrombolytic therapy may be limited by local availability of plasminogen near a poorly perfused thrombus. The purpose of this study was to determine if the local (i.e., clot site) administration of 0.5 mg glu-plasminogen (glu-plg) or 0.5 mg lysplasminogen (lys-plg) could safely increase the thrombolytic efficacy of a 30-min intraarterial injection of 3,500 U kg-1 of two-chain urokinase plasminogen activator (UK) in a dog model of arterial thrombosis. Thrombolysis was measured by monitoring the continuous decrement of 125I-gamma emissions from a radiolabeled thrombus. Reflow was evaluated by a distally placed flowmeter and by direct visual examination. Forty-two dogs (mean weight 10.1 +/- 1.9 kg) were randomly sorted into six groups of 7 each. The dogs in each group were given either saline plus saline (group 1), saline plus UK (group 2), glu-plg plus saline (group 3), glu-plg plus UK (group 4), lys-plg plus saline (group 5), or lys-plg plus UK (group 6) by selective arterial catheterization 60 min after formation of an occlusive thrombus. Ninety minutes following drug administration, all groups which received UK (groups 2, 4, and 6) showed greater lysis (p less than 0.05) than the groups which received only saline or either glu- or lys-plg plus saline. Group 6, which received lys-plg plus UK, showed significantly greater lysis (34 +/- 4%) than both group 2 (23 +/- 2%), which received saline plus UK, and group 4 (19 +/- 3%), which received glu-plg plus UK (p less than 0.05). All dogs (7/7) in group 6 had reflow at 90 min whereas only 3/7 dogs had reflow in both groups 2 and 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Optimizing the bolus/infusion ratio for intravenous administration of urokinase in dogs

The purpose of this study was to determine the optimal bolus/infusion ratio of urokinase (UK) in a dog model of experimental thrombosis. Radiolabelled clots from dog whole blood were inserted into an extracorporeal jugular loop in anesthetized dogs. Clot size (counts/min) was continuously recorded. UK was administered i.v. as a 1 min bolus (100%/0%), 30 min infusion (0%/100%), or as a bolus/infusion combination at ratios of 75%/25%, 50%/50%, or 25%/75%. The total dose of UK in all groups was 20,000 U/kg. A bolus/infusion ratio of 25%/75% produced twice as much lysis as either bolus or infusion alone. There were no statistical differences between the UK-treated groups in reduction of plasma alpha 2-antiplasmin concentration. We conclude that thrombolytic efficacy was increased by the bolus/infusion administration of UK without a concomitant increase in systemic plasminogen to plasmin conversion.

Selective binding of plasmin in the presence of excess plasminogen by certain anionic polystyrene resins

Contact of plasminogen with sulfonate or sulfonyl-glutamate derivatized polystyrene resins has previously been reported to lead to the formation of an active single-chain form of the plasminogen (Kichenin-Martin et al., Thrombosis Research, 52, 469-478, 1988). Attempts to duplicate this finding revealed instead that these polymers selectively adsorb active plasmin and thus remove it even in the presence of a great excess of plasminogen. Under optimum conditions 4.0 mg/mL plasminogen containing 3% plasmin was freed of one half of this contaminant by exposure to 6-9 mg of dry resin per mL in a batch mode. Neither ordinary polystyrene nor Dowex nor Sephadex cation exchange resins displayed these properties. The separation is based on the more rapid binding of plasmin to the active resins and is thus kinetically controlled.

Approach to the patient with venous thromboembolism: Treatment with thrombolytic agents

This article reviews the different thrombolytic agents currently available and the different mechanisms by which they activate the bodys fibrinolytic system. The discussion is confined to the approach to the patient with venous thromboembolism using the different thrombolytic agents. Data are presented supporting the use of thrombolytic therapy and its long-term benefits, especially in patients with pulmonary embolism. A substantial portion of this article is devoted to practical considerations involved in the administration of thrombolytic therapy.

New Developments in Thrombolytic Therapy

Pharmacologic lysis of occlusive, ischemia-producing thrombi has become widely accepted during the past decade. New developments in this field have centered around increasing the efficacy of the known plasminogen activators while employing methods to minimize the risk of hemorrhage and decrease the incidence of rethrombosis. Such methods have included the use of thrombus-directed antibodies linked to plasminogen activators, increased plasminogen (substrate) concentration at the thrombus site, anticoagulant and antiplatelet therapy to prevent thrombus propagation and reformation following lysis, and combination plasminogen activator therapy designed to increase efficacy and safety. These new strategies have been extensively tested in vitro and in a variety of animal models. As we have indicated, extrapolation of such results to human patients cannot be done with confidence. However, the strategies are based on sound rationale and the reported findings should serve as the basis for controlled human trials.