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D Collen

Publications and source records attributed to D Collen.

At least 343 records · Page 19Linked to original sources
PubMed1992

Stimulation by retinoids of tissue-type plasminogen activator secretion in cultured human endothelial cells: relations of structure to effect.

Retinoic acid induces tissue-type plasminogen activator (t-PA) but not plasminogen activator inhibitor-1 (PAI-1) expression in cultured human umbilical vein endothelial cells (HUVEC). To further investigate the relation between the structure of the retinoids and their ability to induce t-PA synthesis in vitro, 11 analogues were studied in HUVEC culture. The retinoid analogues were classified into one of three groups according to their t-PA-inducing potential. Group 1 showed little induction (0.9- to 1.9-fold after 48 h) at concentrations between 10(-8) and 10(-6) M. Group 2, which includes all-trans-retinoic acid, induced t-PA threefold to fivefold at 10(-6) M but had little effect at 10(-8) M (less than threefold). Group 3, which comprises arotinoid acid (RO-13-7410) and RO-13-6307, induced t-PA antigen secretion fivefold at 10(-8) M. The retinoids of groups 2 and 3 had a terminal carboxyl group and alkyl substitution of the lipophylic head of the retinoid skeleton. The group 3 retinoids also contained an aromatic ring. The t-PA-inducing activity of these third-generation retinoids correlates to some extent with other activities, including regression of papilloma, keratinization in vivo, and clonal inhibition of tumor cell lines in vitro. Some of the retinoids caused a small but significant (up to 1.5-fold at 24 h) increase in PAI-1 antigen secretion. The group 3 retinoids appear to be sufficiently potent inducers of t-PA secretion to warrant further investigation in in vivo animal models.

Cell Survival↗
PubMed1992

Comparative copper coil-induced thrombogenicity of the internal mammary, left anterior descending coronary, and popliteal arteries in dogs.

The internal mammary artery (IMA) is the graft of choice for coronary artery bypass surgery because of its resistance to atherosclerosis. Studies to elucidate the mechanism of this phenomenon have focused on vasoactive properties of the vessel wall; however, low thrombogenicity might also contribute to the protection of the IMA against atherosclerosis. To test this hypothesis, copper coils 3 mm long were introduced in 14 heparinized dogs into both the IMA and the left anterior descending coronary artery (LAD) (n = 7) or into both the IMA and the popliteal artery (POP) (n = 7). Arterial patency was monitored angiographically at 15-minute intervals for 4 hours. Occlusion occurred in all LADs and POPs and in 10 of the 14 IMAs. Spontaneous reflow after occlusion occurred in all IMAs and was followed by cyclic reocclusion and reflow in two animals. Short periods of reflow followed by reocclusion occurred in two of the seven LADs and three of the seven POPs. The patency status, categorized as persistent occlusion, reflow followed by reocclusion, reflow without reocclusion, or persistent patency, was significantly different between IMA and LAD (p less than 0.02) and between IMA and POP (p less than 0.04) but not between LAD and POP. Patent arteries at the end of the 4-hour period were observed in all of the 14 IMAs versus none of the seven LADs and two of the seven POPs (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiography↗
PubMed1992

Antithrombotic effect of a monoclonal antibody against tissue factor in a rabbit model of platelet-mediated arterial thrombosis.

Activation of the coagulation system by contact of circulating blood with tissue factor, a component of the extrinsic blood coagulation pathway that is produced in the vessel wall, may represent a pathway for the initiation of thrombosis in atherosclerotic vessels. This hypothesis was tested in vivo in a rabbit femoral artery eversion (inside-out) graft model, in which the adventitia, with its tissue factor, was exposed to circulating blood. Intra-arterial infusion of a neutralizing monoclonal antibody against tissue factor (D3) at a rate of 12 mg/kg over 15 minutes prevented thrombosis of a 7-8-mm eversion graft within a 2-hour observation period in four of five rabbits, whereas with a control antibody infusion (MA-15C5), occlusion occurred within 2 hours in five of six rabbits. In vitro immersion before reinsertion of the arterial segment in a solution containing 2 mg/ml of the control antibody for 30 minutes was associated with occlusion in all six rabbits, whereas pretreatment with D3 was associated with persistent patency in three of nine rabbits. Stepwise logistic-regression analysis of the results with perfusion status as the dependent variable and type of antibody (D3 or MA-15C5), application method (infusion versus immersion), and graft segment length as independent variables yielded a significant difference in frequency of occlusion with the two antibodies (p = 0.016). It is concluded that exposure of tissue factor to flowing blood may constitute a trigger mechanism for platelet-mediated arterial thrombosis.

Animals↗
PubMed1992

Plasma fibrinopeptide A levels in patients with acute myocardial infarction treated with alteplase. Correlation with concomitant heparin, coronary artery patency, and recurrent ischemia. The European Cooperative Study Group.

BACKGROUND: Fibrin generation during and after therapy with alteplase may depend on the level of concomitant anticoagulation. The hypothesis that fibrinopeptide A (FPA) levels, as markers of ongoing in vivo fibrin formation, correlate with the angiographic and clinical outcome of thrombolysis is tested. METHODS AND RESULTS: Serial plasma FPA levels were determined in 334 patients of the randomized European Cooperative Study Group trial comparing heparin versus placebo plus alteplase and aspirin in patients with acute myocardial infarction. Median FPA levels (with the 10th to 90th percentiles) were 21 ng/ml (2-390 ng/ml) before treatment in placebo-allocated patients (n = 166) and increased to 49 (15-580), 34 (4-320), 27 (2-240), 29 (2-430), and 30 (3-390) ng/ml after 0.75, 3, 12, 24, and 36 hours, respectively. In heparin-allocated patients (n = 168), median baseline FPA values were 18 ng/ml (2-210 ng/ml) and decreased to 6 (1-110), 5 (1-75), 5 (1-60), 7 (1-100), and 10 (1-170) ng/ml at corresponding time points (p less than 0.0001 for the difference at each time point). Adequate anticoagulation, defined as no activated partial thromboplastin time value below twice the pretreatment value at 3, 12, 24, and 36 hours after initiation of treatment, was obtained in 48 patients assigned to heparin. It was associated with normal median FPA levels (less than or equal to 4 ng/ml) at all time points compared with 12 (2-80), 16 (2-240), and 15 (2-240) ng/ml at 12, 24, and 36 hours, respectively, in heparin-assigned but inadequately anticoagulated patients (n = 102, p less than 0.001 for each time point). In the heparin-treated group, median FPA values tended to be lower at all time points in patients with patent vessels than in patients with occluded arteries, but the difference was significant only at 24 hours (p = 0.04). FPA levels did not correlate with clinically apparent recurrent ischemia or with left ventricular thrombosis on two-dimensional echocardiography. CONCLUSIONS: During and after thrombolytic therapy with alteplase, the enhanced fibrin generation is suppressed by sustained concomitant anticoagulation with intravenous heparin. Adequate anticoagulation warrants individual titration of the heparin dose. High plasma FPA levels 24 hours after alteplase therapy are specific but insensitive markers of vessel occlusion in anticoagulated patients. They do not correlate with clinical outcome.

Coronary Vessels↗
PubMed1992

Comparative antithrombotic effects of heparin, recombinant hirudin and argatroban in a hamster femoral vein platelet-rich mural thrombosis model.

The antithrombotic properties of bolus i.v. injections of heparin, of recombinant hirudin (r-hirudin) or of the synthetic competitive thrombin inhibitor Argatroban were investigated in a quantitative hamster femoral vein platelet-rich mural thrombosis model. Heparin at a dose of 100 U/kg prolonged the activated partial thromboplastin time from 26 +/- 15 to 177 +/- 45 sec (P = .001), but did not significantly inhibit platelet-rich thrombus formation (7 +/- 44% inhibition, P = NS vs. placebo). However, 400 U/kg of heparin produced total inhibition of thrombus formation (101 +/- 14+, P less than .06 vs. control). R-hirudin and argatroban inhibited thrombus formation in a dose-dependent manner: 50% inhibition was obtained with 1.4 mg/kg for r-hirudin and with 2.0 mg/kg for Argatroban. A linear correlation was observed between the percentage of inhibition of thrombus formation vs. Activated partial thromboplastin time (r = 0.57, P = .003 for r-hirudin and r = 0.66, P = .002 for Argatroban). These results suggest that thrombin plays a pivotal role in platelet-rich mural thrombus formation, that this small animal model may be useful for investigation of the pharmacodynamics of synthetic thrombin inhibitors and that platelet-rich thrombus formation is inhibited effectively by heparin, r-hirudin and Argatroban. However, r-hirudin and Argatroban cause less profound changes in the coagulant function at doses that inhibit platelet-rich thrombus formation than heparin.

Animals↗
PubMed1991

Enhancement of clot lysis in vitro and in vivo with a bispecific monoclonal antibody directed against human fibrin and against urokinase-type plasminogen activator.

A hybrid hybridoma (FU1-74), secreting a bispecific monoclonal antibody (bs mAb), was obtained by fusion of a murine hybridoma secreting a monoclonal antibody (mAb) specific for human fibrin with a murine hybridoma secreting a mAb against urokinase-type plasminogen activator (u-PA). The bs mAb (MA-FU1-74), purified to homogeneity from mouse ascitic fluid, migrated as a single band with apparent Mr 150,000 on nonreduced SDS-PAGE and had an affinity for both human fibrin (Ka = 2 x 10(7) M-1) and for u-PA (Ka = 10(8) M-1) comparable to that of the mAbs obtained from the respective parental hybridomas. MA-FU1-74 did not influence the enzymatic activity of two-chain u-PA (tcu-PA) towards plasminogen or towards a chromogenic substrate. The complex of MA-FU1-74 with recombinant single chain u-PA (rscu-PA) or with tcu-PA (urokinase) enhanced the fibrinolytic potency of the plasminogen activator towards clotted human plasma 20-fold and 5-fold, respectively. In a hamster pulmonary embolism model, the rscu-PA/MA-FU1-74 complex had a 13- to 17-fold increased thrombolytic potency (percent lysis per mg/kg u-PA administered) relative to that of rscu-PA. The specific thrombolytic activity (percent lysis per microgram/ml steady state plasma level of u-PA antigen) of the complex was, however, not significantly different from that of rscu-PA. The complex of rscu-PA with the parental anti-u-PA mAb (MA-UK1-3) had only a 2-fold enhanced thrombolytic potency relative to that of rscu-PA and had a 5-fold decreased specific thrombolytic activity. The plasma clearance rates of the complexes of rscu-PA with both MA-FU1-74 and MA-UK1-3 were about 10-fold lower than that of rscu-PA. In a rabbit jugular vein thrombosis model, the rscu-PA/MA-FU1-74 complex had a 4-fold enhanced thrombolytic potency, an unchanged specific thrombolytic activity and 20-fold reduced plasma clearance. In both animal models, the rscu-PA/MA-FU1-74 complex did not cause more extensive systemic activation of the fibrinolytic system than rscu-PA. It is concluded that the bispecific anti-fibrin/anti-u-PA mAb MA-FU1-74 targets u-PA to the fibrin clot, resulting in a significantly enhanced thrombolytic potency of the plasminogen activator.

Amino Acid Sequence↗
PubMed1991

Effect of retinoic acid on the synthesis of tissue-type plasminogen activator and plasminogen activator inhibitor-1 in human endothelial cells.

The synthesis of plasminogen activators and inhibitors in endothelial cells is highly regulated by hormones, drugs and growth factors. The present study evaluates the effect of retinoic acid on the synthesis of tissue-type plasminogen activator (t-PA) and of plasminogen activator inhibitor-1 (PAI-1) by cultured human umbilical vein endothelial cells (HUVEC). Retinoic acid produced a time- and concentration-dependent increase in the secretion of t-PA-related antigen but not of PAI-1 related antigen into the culture medium. A maximal sevenfold increase of t-PA antigen after 24 h was observed with 10 microM and a half-maximal increase with 0.1 microM retinoic acid. Retinoic acid induced a time-dependent increase of the t-PA mRNA, with a maximum at 8 h and returning to normal at 24 h. The protein kinase inhibitor H7 decreased the t-PA antigen induced by both retinoic acid and phorbol 12-myristate 13-acetate. These results suggest that treatment of HUVEC with retinoic acid increases t-PA production by a pathway which, at some level, involves protein kinases. Thus, retinoic acid induces t-PA synthesis in the absence of altered PAI-1 synthesis, which may enhance the fibrinolytic potential of the endothelium.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1991

Characterization of a chimeric plasminogen activator consisting of a single-chain Fv fragment derived from a fibrin fragment D-dimer-specific antibody and a truncated single-chain urokinase.

An Mr 57,000 single-chain chimeric plasminogen activator, K12G0S32, consisting of a variable region fragment (Fv) derived from the fibrin fragment D-dimer-specific monoclonal antibody MA-15C5 and of a 33-kDa (amino acids Ala132 to Leu411) recombinant single-chain urokinase-type plasminogen activator (rscu-PA-33k) was studied. K12G0S32, secreted by infected Spodoptera frugiperda insect cells at a rate of 1.5 micrograms/10(6) cells/48 h, was purified to homogeneity by ion-exchange chromatography and gel filtration. It was obtained essentially as a single-chain molecule with a Ka = 5.5 x 10(9) M-1 for immobilized fragment D-dimer, similar to that of MA-15C5. The specific activity of both its single-chain and two-chain forms on fibrin plates was 100,000 IU/mg of urokinase-type plasminogen activator (u-PA) equivalent. Activation of plasminogen by two-chain K12G0S32 obeyed Michaelis-Menten kinetics with Km = 2.9 +/- 0.6 microM and a k2 = 3.7 +/- 0.6 s-1 (mean +/- S.D.; n = 3), as compared to Km = 12 microM and k2 = 4.8 s-1 for rtcu-PA-32k (recombinant low Mr two-chain u-PA consisting of amino acids Leu144 to Leu411). Single-chain K12G0S32 induced a dose- and time-dependent lysis of a 125I-fibrin-labeled human plasma clot immersed in citrated human plasma; 50% lysis in 2 h was obtained with 0.70 +/- 0.07 micrograms/ml (mean +/- S.D.; n = 5), as compared with 8.8 +/- 0.1 micrograms/ml for rscu-PA-32k (recombinant low Mr single-chain u-PA consisting of amino acids Leu144 to Leu411) (mean +/- S.D.; n = 3). With two-chain K12G0S32, 50% clot lysis in 2 h required 0.25 +/- 0.03 micrograms/ml (mean +/- S.D.; n = 3), as compared with only 0.62 +/- 0.04 micrograms/ml (mean +/- S.D.; n = 2) for rtcu-PA-32k. These results indicate that low Mr single-chain u-PA can be targeted to a fibrin clot with a single-chain Fv fragment of a fibrin-specific antibody, resulting in a 13-fold increase of the fibrinolytic potency of the single-chain form and a 2.5-fold increase of the potency of the two-chain form.

Amides↗
PubMed1991

Comparative fibrinolytic properties of staphylokinase and streptokinase in animal models of venous thrombosis.

The thrombolytic and pharmacokinetic properties of staphylokinase were compared with those of streptokinase in hamsters with a pulmonary embolus produced from human plasma or from hamster plasma, and in rabbits with a jugular vein blood clot produced from rabbit blood. In both models, a continuous intravenous infusion of staphylokinase and streptokinase over 60 min in hamsters or over 4 h in rabbits, induced dose-dependent progressive clot lysis in the absence of significant systemic activation of the fibrinolytic system. The results of thrombolytic potency (clot lysis at 30 min after the end of the infusion, in percent, versus dose administered, in mg/kg) were fitted with an exponentially transformed sigmoidal function (formula: see text) and the maximal percent clot lysis (c), the maximal rate of lysis (z = 1/4 ac.eb) and the dose at which the maximal rate of lysis is achieved (b) were determined. In hamsters with a pulmonary embolus produced from human plasma, streptokinase had a somewhat higher thrombolytic potency than staphylokinase, as revealed by a higher z value (2,100 +/- 1,100% lysis per mg/kg streptokinase administered versus 1,100 +/- 330% lysis per mg/kg for staphylokinase). In hamsters with a pulmonary embolus produced from hamster plasma, staphylokinase had a somewhat higher thrombolytic potency than streptokinase (z = 1,600 +/- 440 versus 1,200 +/- 370% lysis per mg/kg). Staphylokinase had a higher thrombolytic potency than streptokinase in rabbits,as revealed by a higher z-value (950 +/- 350% lysis per mg/kg staphylokinase administered versus 330 +/- 39% lysis per mg/kg for streptokinase) and a lower b-value (0.035 +/- 0.010 mg/kg staphylokinase versus 0.091 +/- 0.008 mg/kg for streptokinase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Characterization of a recombinant single-chain molecule comprising the variable domains of a monoclonal antibody specific for human fibrin fragment D-dimer.

A recombinant single-chain molecule, scFv-K12G0, containing the variable domains of the monoclonal antibody MA-15C5, specific for fragment D-dimer of human cross-linked fibrin, was constructed and expressed in Spodoptera frugiperda, Sf9, insect cells. The Arg108 carboxyl-terminal amino acid of the variable domain of the light-chain of the antibody was connected through a synthetic Ala-Gly-Gln-Gly-Ser-Ser-Val peptide linker with the Gln1 amino-terminal amino acid of the variable domain of its heavy chain. scFv-K12G0 was secreted by the infected Sf9 cells at a rate of 10 micrograms/10(6) cells within 48 h, resulting in conditioned medium with a maximal concentration of 15 mg of scFv-K12G0/liter. The molecule, purified to homogeneity by ion exchange chromatography and gel filtration, migrated as a single Mr band on reduced sodium dodecyl sulfate-gel electrophoresis. It bound to immobilized fragment D-dimer with an affinity constant of 4.0 x 10(9) M-1 (2.0 x 10(10) M-1 for intact MA-15C5). Clearing of scFv-K12G0 from the circulation in rabbits occurred with an initial half-life (t1/2 alpha) of 10 min and a clearance of 5.1 ml min-1, as compared to 90 min and 210 ml min-1 for intact MA-15C5. Nephrectomy resulted in a prolongation of t1/2 alpha to 110 min, suggesting that the rapid clearance of scFv-K12G0 occurs primarily via the kidney, presumably by glomerular filtration. The results indicate that the single-chain recombinant molecule scFv-K12G0 is secreted in functionally intact form and suggest that it may be useful for targeting of radioisotopes or plasminogen activators to blood clots in vivo.

Amino Acid Sequence↗
PubMed1991

Hemorrhagic events during therapy with recombinant tissue-type plasminogen activator, heparin, and aspirin for acute myocardial infarction. Results of the Thrombolysis in Myocardial Infarction (TIMI), Phase II Trial.

OBJECTIVES: To assess the effects of invasive procedures, hemostatic and clinical variables, the timing of beta-blocker therapy, and the doses of recombinant plasminogen activator (rt-PA) on hemorrhagic events. DESIGN: A multicenter, randomized, controlled trial. SETTING: Hospitals participating in the Thrombolysis in Myocardial Infarction, Phase II trial (TIMI II). INTERVENTIONS: Patients received rt-PA, heparin, and aspirin. The total dose of rt-PA was 150 mg for the first 520 patients and 100 mg for the remaining 2819 patients. Patients were randomly assigned to an invasive strategy (coronary arteriography with percutaneous angioplasty [if feasible] done routinely 18 to 48 hours after the start of thrombolytic therapy) or to a conservative strategy (coronary arteriography done for recurrent spontaneous or exercise-induced ischemia). Eligible patients were also randomly assigned to either immediate intravenous or deferred beta-blocker therapy. MEASUREMENTS: Patients were monitored for hemorrhagic events during hospitalization. MAIN RESULTS: In patients on the 100-mg rt-PA regimen, major and minor hemorrhagic events were more common among those assigned to the invasive than among those assigned to the conservative strategy (18.5% versus 12.8%, P less than 0.001). Major or minor hemorrhagic events were associated with the extent of fibrinogen breakdown, peak rt-PA levels, thrombocytopenia, prolongation of the activated partial thromboplastin time (APTT) to more than 90 seconds, weight of 70 kg or less, female gender, and physical signs of cardiac decompensation. Immediate intravenous beta-blocker therapy had no important effect on hemorrhagic events when compared with delayed beta-blocker therapy. Intracranial hemorrhages were more frequent among patients treated with the 150-mg rt-PA dose than with the 100-mg rt-PA dose (2.1% versus 0.5%, P less than 0.001). The extent of the plasmin-mediated hemostatic defect was also greater in patients receiving the 150-mg dose. CONCLUSIONS: Increased morbidity due to hemorrhagic complications is associated with an invasive management strategy in patients with acute myocardial infarction. Our findings show the complex interaction of several factors in the occurrence of hemorrhagic events during thrombolytic therapy.

Aspirin↗
PubMed1991

Effect of chemical conjugation of recombinant single-chain urokinase-type plasminogen activator with monoclonal antiplatelet antibodies on platelet aggregation and on plasma clot lysis in vitro and in vivo.

The murine monoclonal antiplatelet antibodies MA-TSPI-1 (directed against human thrombospondin) and MA-PMI-2, MA-PMI-1, and MA-LIBS-1 (directed against ligand-induced binding sites [LIBS] on human platelet glycoprotein IIb/IIIa) were conjugated with recombinant single-chain urokinase-type plasminogen activator (rscu-PA) using the cross-linking reagent N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP). The conjugates (rscu-PA/MA-TSPI-1, rscu-PA/MA-PMI-2, rscu-PA/MA-PMI-1, and rscu-PA/MA-LIBS-1), purified by immunoadsorption and gel filtration, were obtained with recoveries of 34% to 45%, with an average stoichiometry of 1.6 to 1.8 IgG molecules per rscu-PA molecule, and with unaltered specific activities and affinities. Preincubation of human platelet-rich plasma with rscu-PA/MA-PMI-2, rscu-PA/MA-PMI-1, or unconjugated rscu-PA resulted in partial inhibition of ADP-induced aggregation; 25% inhibition was obtained with 63 micrograms/mL rscu-PA and with 6 micrograms u-PA/mL rscu-PA/MA-PMI-2 or 1.2 micrograms u-PA/mL rscu-PA/MA-PMI-1. In an in vitro system composed of a 125I-fibrin-labeled platelet-rich human plasma clot immersed in normal human plasma, the conjugates had threefold to greater than 15-fold less fibrinolytic potency than unconjugated rscu-PA. The thrombolytic potency of rscu-PA/MA-PMI-1 and rscu-PA/MA-LIBS-1 was compared with that of rscu-PA and that of a control conjugate rscu-PA/MA-1C8 in a pulmonary embolism model in the hamster, using clots prepared from platelet-poor or platelet-rich human plasma. Lysis was measured 30 minutes after the end of a 60-minute intravenous infusion of the thrombolytic agents. rscu-PA, rscu-PA/MA-PMI-1, rscu-PA/MA-LIBS-1, as well as rscu-PA/MA-1C8 had comparable thrombolytic potencies (percent lysis per dose administered) towards platelet-poor human plasma clots. In contrast, the thrombolytic potency of rscu-PA/MA-PMI-1 and of rscu-PA/MA-LIBS-1 towards platelet-rich clots was 2.3- to 3-fold higher than that of rscu-PA (P less than .005) and fivefold to sevenfold higher than that of the control conjugate (P less than .01).

Adenosine Diphosphate↗
PubMed1991

Comparative thrombolytic properties of bolus injections and continuous infusions of a chimeric (t-PA/u-PA) plasminogen activator in a hamster pulmonary embolism model.

The recombinant chimeric plasminogen activator, rt-PA-delta FE/scu-PA-e, consisting of amino acids 1 to 3 and 87 to 274 of tissue-type plasminogen activator (t-PA) and amino acids 138 to 411 of single-chain urokinase-type plasminogen activator (scu-PA), has a markedly increased thrombolytic potency following its continuous intravenous infusion in animal models of venous thrombosis (Collen et al, Circulation, in press). In the present study, the thrombolytic potencies of intravenous bolus injections of rt-PA-delta FE/scu-PA-e, of recombinant t-PA (rt-PA), and of recombinant scu-PA (rscu-PA), given alone or in combination, were compared with those of intravenous infusions in a hamster pulmonary embolism model. Dose-dependent clot lysis was obtained in the absence of systemic activation of the fibrinolytic system and fibrinogen breakdown. In bolus injection experiments, the maximal rate of clot lysis, expressed in percent clot lysis per milligrams per kilogram compound administered, was 120 +/- 10 for rt-PA, 54 +/- 8 for rscu-PA, and 2,100 +/- 500 for rt-PA-delta FE/scu-PA-e (P less than .01 v rt-PA or rscu-PA). Comparative results with continuous infusion over 1 hour were 270 +/- 64, 99 +/- 18, and 1,500 +/- 250 (P less than .01 v rt-PA or rscu-PA) percent lysis per mg/kg compound infused for rt-PA, rscu-PA, and rt-PA-delta FE/scu-PA-e, respectively. Thus, rt-PA and rscu-PA are more potent when administered as an infusion than as a bolus, whereas rt-PA-delta FE/scu-PA-e is at least as potent when administered as a bolus. Combined bolus injections of rt-PA and rscu-PA had a 2.2-fold synergistic effect on clot lysis, but no synergism was observed with combined bolus injections or with combined infusions of rt-PA and rt-PA-delta FE/scu-PA-e, or of rscu-PA and rt-PA-delta FE/scu-PA-e. The present study thus shows that rt-PA-delta FE/scu-PA-e is much more potent for clot lysis than rt-PA or rscu-PA when administered as a bolus injection, but no synergistic interaction is observed between the chimera and either rt-PA or rscu-PA.

Animals↗
PubMed1991

On the mechanism of fibrin-specific plasminogen activation by staphylokinase.

The mechanism of plasminogen activation by recombinant staphylokinase was studied both in the absence and in the presence of fibrin, in purified systems, and in human plasma. Staphylokinase, like streptokinase, forms a stoichiometric complex with plasminogen that activates plasminogen following Michaelis-Menten kinetics with Km = 7.0 microM and k2 = 1.5 s-1. In purified systems, alpha 2-antiplasmin inhibits the plasminogen-staphylokinase complex with k1(app) = 2.7 +/- 0.30 x 10(6) M-1 s-1 (mean +/- S.D., n = 12), but not the plasminogen-streptokinase complex. Addition of 6-aminohexanoic acid induces a concentration-dependent reduction of k1(app) to 2.0 +/- 0.17 x 10(4) M-1 s-1 (mean +/- S.D., n = 5) at concentrations greater than or equal to 30 mM, with a 50% reduction at a 6-aminohexanoic acid concentration of 60 microM. Staphylokinase does not bind to fibrin, and fibrin stimulates the initial rate of plasminogen activation by staphylokinase only 4-fold. Staphylokinase induces a dose-dependent lysis of a 0.12-ml 125I-fibrin-labeled human plasma clot submersed in 0.5 ml of citrated human plasma; 50% lysis in 2 h is obtained with 17 nM staphylokinase and is associated with only 5% plasma fibrinogen degradation. Corresponding values for streptokinase are 68 nM and more than 90% fibrinogen degradation. In the absence of a fibrin clot, 50% fibrinogen degradation in human plasma in 2 h requires 790 nM staphylokinase, but only 4.4 nM streptokinase. These results suggest the following mechanism for relatively fibrin-specific clot lysis with staphylokinase in a plasma milieu. In plasma in the absence of fibrin, the plasminogen-staphylokinase complex is rapidly neutralized by alpha 2-antiplasmin, thus preventing systemic plasminogen activation. In the presence of fibrin, the lysine-binding sites of the plasminogen-staphylokinase complex are occupied and inhibition by alpha 2-antiplasmin is retarded, thus allowing preferential plasminogen activation at the fibrin surface.

Antifibrinolytic Agents↗