Algal fucoidan, unlike heparin, has thrombolytic activity in a murine arterial thrombosis model

Thrombolytic effects of fucoidans were investigated in the FeCl3-induced arterial thrombus mouse model and compared with heparin and tissue plasminogen activator (t-PA). Thrombosis model was made by applying 5% FeCl3 on the carotid artery of a Balb/c mouse. Twenty minutes after complete occlusion, a couple of test agents including fucoidan were infused into each mouse group with various doses intravenously, before measuring the time to reperfusion. The occluded arteries were reperfused 37.5 ± 12.4 min after administration of unfractionated fucoidan from Undaria pinnatifida sporophylls (UPS-UF) with a dose of 100 mg/kg. In the mice given either a low-molecular-weight UPS fucoidan or fucoidan source from Fucus vesiculosus (FV-UF), reperfusion was delayed at 55.0 ± 8.0 min with a higher reperfusion effective dose (RED) of 1 g/kg or at 63.3 ± 7.2 at RED of 200 mg/kg, respectively. In the control mice given t-PA of 15 mg/kg, reperfusion occurred at 24.8 ± 6.5 min after administration. In contrast, reperfusion was not observed in the occluded mice given heparin (P < 0.001) in the range of 60-1000 mg/kg. Minimal injection of fucoidan in addition to a given t-PA-enabled restoration of blood flow in the blocked artery without reocclusion at 17.2 ± 2.3 min postinjection (P < 0.002). In conclusion, algal fucoidan has both thrombolytic activity and a stimulatory effect on the thrombolytic activity of t-PA in a dose-dependent manner at an arterial thrombosis model.     

Antithrombotic activity of orally administered low molecular weight heparin (Logiparin) in a rat model

Previous studies in rats demonstrated that orally administered, unfractionated bovine lung heparin is absorbed and has a dose-dependent antithrombotic effect. The objective of this study was to determine if an oral low molecular weight heparin had a similar antithrombotic effect in the same model. Thrombosis was induced in rats by application of 10% formalin in 65% methanol to the exposed jugular vein. Immediately following, saline, unfractionated heparin (3.3-60 mg/kg) or the low molecular weight heparin, Logiparin (0.025-15 mg/kg; 20-30 rats per group) was placed in the stomach and 4 h later the jugular vein was inspected for a thrombus. Compared to saline, oral Logiparin reduced the incidence of thrombosis at all doses with a dose-dependent effect suggested. A significant increase was observed in the activated partial thromboplastin time and in plasma heparin concentrations, determined by Accuclot Heptest and anti-factor Xa chromogenic assay for rats given oral Logiparin versus saline. A dose-dependent increase in plasma heparin concentration was observed when estimated by the anti-Xa chromogenic assay. Heparin was recovered in 9% of aortic endothelial samples when > or = 0.8 mg/kg Logiparin was administered. A 50% reduction in thrombosis was observed at 0.1 mg/kg for oral Logiparin versus 7.5 mg/kg for unfractionated bovine lung heparin indicating that oral Logiparin is an effective antithrombotic agent at doses lower than unfractionated heparin. Orally administered low molecular weight heparin may be useful for the prevention and treatment of thrombosis.     

Conjunctive enhancement of enzymatic thrombolysis and prevention of thrombotic reocclusion with the selective factor Xa inhibitor, tick anticoagulant peptide. Comparison to hirudin and heparin in a canine model of acute coronary artery thrombosis.

BACKGROUND. Effective thrombolytic recanalization of an occluded coronary vessel is often limited by acute thrombotic reocclusion, which has galvanized the search for effective adjunctive or conjunctive antithrombotic agents. METHODS AND RESULTS. Recombinant versions of tick anticoagulant peptide (rTAP) and hirudin (rHIR) are highly selective and potent polypeptide inhibitors of factor Xa and thrombin, respectively. The comparative antithrombotic efficacies of rTAP, rHIR, and heparin, administered conjunctively with recombinant tissue-type plasminogen activator (rt-PA), on thrombolytic reperfusion and reocclusion, were determined in a canine model of occlusive coronary artery thrombosis with a superimposed critical stenosis. In this model, a platelet-rich occlusive thrombus was formed after damage to the intimal surface of the left circumflex coronary artery induced by electrolytic injury. Fifteen minutes after occlusion, the dogs received a systemic intravenous administration of either saline (control), heparin (200 units/kg bolus + 2 units/kg/min, heparin (HEP) 200 or 100 units/kg bolus + 1 unit/kg/min, HEP 100), rHIR (50 or 100 micrograms/kg/min, rHIR 50 or 100, respectively), or rTAP (100 micrograms/kg/min, rTAP 100) followed 15 minutes later by rt-PA (100 micrograms/kg bolus + 10 micrograms/kg/min over 90 minutes). Infusions of the conjunctive agents were discontinued 60 minutes after termination of rt-PA. The incidence and time (mean +/- SEM) to thrombolytic reperfusion were determined for control (five of 12; 68.0 +/- 7.8 minutes), HEP 100 (six of eight; 40.1 +/- 8.3 minutes), HEP 200 (six of eight; 39.8 +/- 9.5 minutes), rHIR 50 (six of eight; 51.7 +/- 14.6 minutes), rHIR 100 (eight of eight; 19.5 +/- 4.2 minutes), and rTAP 100 (eight of eight; 22.8 +/- 10.0 minutes). The incidence and time to reocclusion after rt-PA were determined for control (four of five; 45.7 +/- 12.5 minutes), HEP 100 (four of six; 18.2 +/- 10.7 minutes), HEP 200 (five of six; 26.2 +/- 20.7 minutes), rHIR 50 (four of six; 47.3 +/- 21.6 minutes), rHIR 100 (six of eight; 89.8 +/- 5.9 minutes), and rTAP 100 (three of eight; 54.0 +/- 16.3 minutes). All of the dogs that reoccluded in the rHIR 100 group did so after termination of the inhibitor infusion, whereas two of the three dogs in the rTAP 100 group that reoccluded did so during the inhibitor infusion. Coronary artery blood flow was characterized by intermittent periods of reocclusion and recanalization in all groups except rTAP 100. CONCLUSIONS. The potent antithrombotic effects of rTAP in this model directly implicate de novo thrombin formation as a major source of thrombin activity within the highly thrombogenic residual thrombus. These findings suggest that direct inhibition of prothrombinase activity may be an effective strategy in the development of a new class of conjunctive agents.     

Individual and combined effects of a thromboxane receptor antagonist and different antithrombotic agents in a rat microcirculatory thrombosis model.

The antithrombotic effect of a thromboxane A2 receptor antagonist (HN-11501:5-[2-(4-chlorophenylsulfonylamino)-ethyl]-2-thienylox y-acetic acid) alone and in combination with other antithrombotic agents has been studied in an experimental thrombosis model in which laser lesions are used to induce a defined thrombosis in rat mesenteric venules. The thromboxane receptor antagonist showed a significant and dose-dependent antithrombotic effect if given orally. The strongest additive thrombosis-inhibiting effect was observed after oral administration of HN-11501 at a dose of 2.5 mg/kg together with an intravenous infusion of 1 microgram/kg/h of a prostacyclin analogue (cicaprost). An additive antithrombotic effect was also observed after oral application of 2.5 mg/kg of HN-11501 and intravenous injection of 0.2 mg/kg of a low molecular weight heparin (Fraxiparine). The combination of 2.5 mg/kg of HN-11501 orally with an intravenous injection of 0.1 mg/kg molsidomine also had a significant additive effect. No significant additive effect was observed when 2.5 mg/kg of HN-11501 and 10 mg/kg of acetylsalicylic acid were orally administered simultaneously.     

Heparin requirement in tissue-type plasminogen activator-induced experimental coronary thrombolysis: comparison with urokinase-induced coronary thrombolysis

The requirement of heparin in experimental coronary thrombolysis induced by tissue-type plasminogen activator (t-PA) was studied in closed-chest dogs with one hour old coronary thrombi and compared with that in urokinase (UK)-induced coronary thrombolysis. Animals were divided into 5 treatment groups as follows: group 1 received intracoronary t-PA alone (1,000 IU/kg/min; n = 5), and if thrombolysis was not induced within 40 to 50 min, dogs then received an intravenous injection of heparin (300 U/kg) plus intracoronary t-PA; group 2 received intravenous heparin at first, and if thrombolysis was not induced within 10 min, dogs subsequently received intracoronary t-PA (n = 5); group 3 also received intravenous heparin at first, and if thrombolysis was not induced within 10 min, dogs subsequently received t-PA but intravenously, as compared with the groups administered by the intracoronary route (n = 6); group 4 received intracoronary UK alone (1,000 IU/kg/min; n = 6); group 5 received intravenous heparin at first, and if thrombolysis was not induced within 10 min, dogs subsequently received intracoronary UK (n = 5). Thrombolysis was confirmed angiographically. In group I, coronary thrombolysis could not be induced within 44 +/- 4 min by intracoronary t-PA alone, but it occurred in 8 +/- 4 min when administered in combination with heparin in all dogs. Heparin alone failed to elicit reperfusion within 10 min in group 2, 3 and 5. t-PA, however, induced successful reperfusion in 16 +/- 5 min (group 2) and in 23 +/- 6 min (group 3), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reocclusion after thrombolysis: a problem solved by hirudin?

The effect of recombinant hirudin (r-hir), unfractionated heparin (UFH) and acetylsalicylic acid (ASA) on the incidence of reocclusion after thrombolysis with plasminogen activator (rt-PA) was evaluated in anaesthetized rabbits. Formation of a platelet rich thrombus was achieved by implantation of a copper coil into the iliac artery. The occluded artery was recanalized in six of ten animals by intravenous administration of rt-PA given as a bolus injection of 0.1 mg/kg followed by infusion of 0.5 mg/kg/h. Within 1 h after termination of rt-PA infusion rethrombosis was observed in 100% of recanalized vessels. The incidence of reocclusion was diminished by r-hir in a dose-dependent manner to 50% after infusion of 0.05 mg/kg/h and to 25% after 0.1 mg/kg/h. No effect on APTT was detectable in this dosage after 3 h infusion. UFH in a dosage increasing APTT two-fold (35 U/kg/h) did not reduce the reocclusion rate. 100 U/kg/h UFH increased APTT to greater than 3 min and reduced reocclusion rates to 50%. ASA showed a minor effect on the incidence of restenosis whereas the combination of 0.1 mg/kg/h r-hir plus bolus injection of 10 mg/kg ASA led to a further reduction in reocclusion rates to only 11% and an increase in reperfusion rates from 60 to 90%. Our experiments indicate that the combination of plasminogen activator with r-hir may be a useful approach for the prophylaxis of early reocclusion.     

Comparative thrombolytic properties of tissue-type plasminogen activator (t-PA), single-chain urokinase-type plasminogen activator (u-PA) and K1K2Pu (a t-PA/u-PA chimera) in a combined arterial and venous thrombosis model in the dog.

The chimeric molecule K1K2Pu, comprising the two kringle domains (K1 and K2) of tissue-type plasminogen activator (t-PA) and the COOH-terminal region with the serine protease domain (Pu) of urokinase-type plasminogen activator (u-PA), was previously shown to have a 5- to 10-fold reduced clearance rate with maintained specific thrombolytic activity, resulting in an increased thrombolytic potency in animal models of venous and arterial thrombosis. To document the thrombolytic potential of K1K2Pu, the thrombolytic potency and fibrin specificity were studied in a combined platelet-rich arterial eversion graft thrombosis and venous whole blood clot model in heparinized dogs (100 U/kg bolus and 50 U/kg per h infusion). Dose-response effects of bolus injections of K1K2Pu (0.032 to 0.25 mg/kg) were compared with those of recombinant t-PA (rt-PA) and of recombinant single chain u-PA (rscu-PA) (0.25 to 1.0 mg/kg each) in groups of five or six dogs, each given heparin with or without the thromboxane synthase inhibitor/prostaglandin endoperoxide receptor antagonist ridogrel. Heparin and ridogrel in the absence of a thrombolytic agent did not produce arterial reflow or venous clot lysis in five dogs. Addition of K1K2Pu, rt-PA or rscu-PA resulted in a dose-dependent induction of arterial reflow and of venous clot lysis in the absence of systemic fibrinolytic activation and fibrinogen breakdown. Consistent arterial reflow required 0.063 mg/kg of K1K2Pu and 0.5 mg/kg of rt-PA or of rscu-PA. The thrombolytic potency for venous clot lysis, expressed as percent lysis per mg compound administered per kg body weight, was (mean +/- SEM) 750 +/- 160 for K1K2Pu, 68 +/- 17 for rscu-PA (p less than 0.001 vs. K1K2Pu) and 110 +/- 29 for rt-PA (p less than 0.001 vs. K1K2Pu). The plasma clearance rates were significantly lower for K1K2Pu than for rscu-PA and rt-PA. In the absence of ridogrel, arterial reflow was significantly slower and was followed by cyclic reocclusion and reflow; however, venous clot lysis was unaffected. Template bleeding times were not significantly altered in the absence but were markedly prolonged in the presence of ridogrel. These results confirm and establish that, when given as a bolus injection, K1K2Pu has an approximately 10-fold higher thrombolytic potency for arterial and venous thrombolysis than does rt-PA or rscu-PA. Thrombolysis with K1K2Pu is obtained in the absence of systemic fibrinolytic activation and fibrinogen breakdown. These properties suggest that K1K2Pu offers potential for thrombolytic therapy by bolus administration in patients with thromboembolic disease.     

Acceleration of recombinant tissue-type plasminogen activator-induced thrombolysis and prevention of reocclusion by the combination of heparin and the Arg-Gly-Asp-containing peptide bitistatin in a canine model of coronary thrombosis

The effect of tissue-type plasminogen activator (t-PA) alone or in combination with heparin, the Arg-Gly-Asp-containing peptide bitistatin, or both heparin and bitistatin was evaluated on thrombolysis time and acute reocclusion in a canine model of coronary thrombosis. Thrombus formation was elicited by electrolytic injury with a needle electrode to the endothelial surface of the circumflex coronary artery in the open-chest, anesthetized dog in the presence of a flow-limiting critical stenosis. Thirty minutes after spontaneous coronary artery occlusion, t-PA (1 mg/kg i.v. over 90 minutes) was administered. Group 1 was given t-PA alone; reperfusion occurred at 78.2 +/- 5.6 minutes with a reperfusion incidence of 60% (6/10). Group 2 received t-PA plus heparin (100 units/kg plus 50 units/kg/hr); reperfusion occurred at 61.9 +/- 9.1 minutes with a reperfusion incidence of 90% (9/10). Group 3 received t-PA plus heparin plus bitistatin (30 micrograms/kg plus 3 micrograms/kg/min); reperfusion occurred at 47.3 +/- 7.6 minutes (p less than 0.05 versus group 1) with a reperfusion incidence of 90% (9/10). Group 4 received t-PA plus bitistatin, and reperfusion occurred at 51.8 +/- 8.5 minutes; however, the reperfusion incidence was only 60% (6/10). In groups 1, 2, and 4, acute reocclusion occurred in more than 80% of the reperfused dogs, whereas in group 3 reocclusion occurred in 22% (2/9) of the reperfused dogs (p less than 0.05 versus group 1). The dose of heparin used in this study increased activated partial thromboplastin times 1.5-2.0-fold over control.(ABSTRACT TRUNCATED AT 250 WORDS)     

New heparin dosing recommendations for patients with acute coronary syndromes

Despite major innovations in antithrombotic and antiplatelet therapy, unfractionated intravenous heparin is widely used to treat acute coronary syndromes. Recommendations for unfractionated heparin dosing in acute myocardial infarction and unstable angina have been issued in two recent American College of Cardiology/American Heart Association guidelines. An initial heparin bolus of 60 U/kg (maximum, 4000 U) followed by a 12-U/kg/h infusion (maximum 1000 U/h) is recommended with alteplase for ST-elevation myocardial infarction. When intravenous heparin is administered for myocardial infarction with non-ST elevation and unstable angina, an initial bolus of 60 to 70 U/kg (maximum, 5000 U) followed by a 12- to 15-U/kg/h infusion is recommended. The goal is to achieve an activated partial thromboplastin time of 50 to 70 seconds. Here, we review these new dosing regimens and explain the rationale for their use. We also review the risk of bleeding with heparin, especially when administered concurrently with aspirin, thrombolytic agents, and glycoprotein IIb/IIIa antagonists, and the relationship between activated partial thromboplastin time and cardiac events.     

Arachidonic acid metabolites, ADP and thrombin modulate occlusive thrombus formation over extensive arterial injury in the rat

Platelet-dependent occlusive thrombosis at sites of deep vessel wall injury elicited by electrical stimulation of rat carotid arteries was significantly reduced by thromboxane A2 (TXA2) synthetase inhibition and/or TXA2/prostaglandin endoperoxide receptor antagonism (ridogrel 1.25 mg/kg i.v.; dazoxiben 5 mg/kg i.v.; sulotroban 20 mg/kg i.v.), by inhibition of ADP-dependent platelet responses (ticlopidine 3 x 200 mg/kg orally) and by anticoagulation (heparin 250 U/kg i.v.; warfarin 1.25 mg/kg i.p.). This points to an involvement of arachidonic acid metabolites, ADP and thrombin as modulators of the thrombotic process. The antithrombotic effect of ridogrel (IC50 = 0.22 mg/kg i.v.) was abolished by cyclooxygenase inhibition (suprofen 5 mg/kg i.v.) but enhanced by cAMP phosphodiesterase inhibition (HL 725 6 micrograms/kg/min i.v.), demonstrating the importance of platelet inhibitory prostanoids such as PGD2, and prostacyclin formed after TXA2 synthetase inhibition. High doses of ridogrel (1.25 mg/kg i.v.) producing additional TXA2/prostaglandin endoperoxide receptor antagonism were more effective than lower doses (0.16 mg/kg i.v.) providing TXA2 synthetase inhibition alone. The antithrombotic effect of ridogrel, when combined with ticlopidine or heparin, exceeded that of the single compounds, pointing to interactions between arachidonic acid metabolites, ADP and thrombin in the formation of occlusive thrombosis at sites of arterial injury.     

Thrombolytic, antiplatelet, and antithrombotic agents

The relative efficacy and safety of individual thrombolytic agents, administered alone and with antiplatelet and antithrombotic drugs, in the treatment of acute myocardial infarction are presented. The clinical benefits and risks of treatment choices are discussed in relation to the mechanisms of the formation and prevention of thrombus and thrombolysis. It is concluded that streptokinase, tissue plasminogen activator (t-PA), and anisoylated plasminogen-streptokinase activator complex (APSAC) significantly reduce mortality and improve left ventricular function equally, despite differences in the rate at which they achieve vascular patency, their durations of action, and the extent to which their use is associated with adverse events. The questions of how best to minimize reocclusion/reinfarction, bleeding, and stroke are discussed, with particular focus on the beneficial use of aspirin and the unresolved issue of how best to use heparin.     

Rapid and sustained coronary artery recanalization with combined bolus injection of recombinant tissue-type plasminogen activator and monoclonal antiplatelet GPIIb/IIIa antibody in a canine preparation

The effects of bolus injections of recombinant single-chain tissue-type plasminogen activator (rt-PA) and of F(ab')2 fragments of a murine monoclonal antibody (7E3) against the human platelet GPIIb/IIIa receptor [7E3-F(ab')2] on coronary arterial thrombolysis and reocclusion was studied in a canine preparation of coronary artery thrombosis superimposed on high-grade stenosis. Bolus intravenous injections of rt-PA at a dose of 0.45 mg/kg, repeated at 15 min intervals until reperfusion occurred (maximum of four injections) caused reperfusion in five of seven dogs within 100 min (33 +/- 15 min, mean +/- SD). Reperfusion was rapidly followed (generally within 10 min) by reocclusion and then by periods of cyclical reflow and reocclusion. A single intravenous injection of 7E3-F(ab')2 alone at 0.8 mg/kg caused reperfusion within 100 min in two of six dogs (19 and 37 min) without subsequent reocclusion. Single bolus injections of different amounts (0.1 to 0.8 mg/kg) of 7E3-F(ab')2 were then combined with bolus injections of 0.45 mg/kg of rt-PA. Stable reperfusion without reocclusion was accomplished with 0.8 or 0.6 mg/kg 7E3-F(ab')2 and a single injection of 0.45 mg/kg rt-PA within 6 +/- 3 min (n = 6, p less than .01) and 8 +/- 5 min (n = 5, p less than .02), respectively. None of these animals suffered reocclusion of the coronary artery. Lower doses (0.1 to 0.2 mg/kg) of 7E3-F(ab')2 did not significantly shorten the time to reperfusion and did not prevent reocclusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impairment by Heparin of Primary Haemostasis and Platelet [14C]5-Hydroxytryptamine Release

Heparin was administered to 34 normal subjects by intravenous injection (100 u/kg) and the template bleeding time was significantly increased both 10 min and 120 min following injection. Before heparin the bleeding time was 5.3±1.0 min (mean±1 SD); 10 min after injection it was 9.8±5.6 min ( P <0.001); and 120 min after injection it was 7.2±3.9 min ( P <0.001). Increases in the bleeding time were unrelated to changes in platelet count, and independent of heparin's effect on plasma coagulation. In blood drawn 10 min and 120 min following heparin injection, there was significantly less [¹⁴C]5-HT released from platelet-rich plasma (PRP) in response to collagen, 0.41 mM epinephrine and 8 μM ADP, although in vitro addition of heparin (0.1 u/ml, 0.5 u/ml and 2.5 u/ml) to baseline PRP of three subjects did not depress [¹⁴C]5-HT release. Our experiments suggest that intravenous administration of a therapeutic dose of heparin can cause a significant reversible impairment of platelet haemostatic properties, possibly by an indirect mechanism.     

Evaluation of the antithrombotic effects of pentoxifylline, acetylsalicylic acid and low molecular weight heparin in the laser model of thrombosis]

Antithrombotic effects of different agents including acetylsalicylic acid (Asprocol/Polfa PL/), pentoxifylline (Agapurin/Spofa CS/) and low molecular weight heparin (Antixarin B. Braun, Melsungen, FRG) were studied in the laser-induced rat thrombosis model. The investigations were carried out on male Wistar rats weighing 200-300 g. Thrombus formation was induced in small mesenteric arteries 25-30 microns; using argon laser. An interference contrast system based on a Leitz Orthoplan microscope for the evaluation of thrombus formation was used. The number of laser injuries needed to induce a defined thrombus proved to be a useful way to quantitate the results in this thrombosis mode. All agents showed dose dependent antithrombotic effect in our laser model. Acetylsalicylic acid (ASA) 2 hours after oral administration markedly inhibited thrombus formation in minimal dose 50 mg/kg, pentoxifylline in dose 10 mg/kg 30 min after i.v. injection and low molecular weight heparin (Antixarin) in dose 0.1 mg/kg, 2 hours, after s.c. injection. Antithrombotic effect of administration of minimal effective doses of ASA (orally) and pentoxifylline (i.v.) lasted longer than 4 hours but less then 6 hours. LMW heparin (Antixarin) in minimal effective dose 0.1 mg/kg after s.c. injection inhibited thrombus formation in small mesenteric vessels for more than 12 hours but less than 24 hours.     

Antithrombotic efficacy of a novel murine antihuman factor IX antibody in rats.

A murine antihuman factor IX monoclonal antibody (BC2) has been generated and evaluated for its capacity to prolong the activated partial thromboplastin time (aPTT) in vitro and ex vivo and to prevent arterial thrombosis in a rat model in vivo. BC2 extended aPTT to a maximum of 60 to 80 seconds at 100 to 1000 nmol/L in vitro (rat and human plasma, respectively) and ex vivo (rat) after dosing of rats up to 6 mg/kg in vivo. BC2, administered as bolus (1 to 6 mg/kg) followed by infusion (0.3 to 2 mg x kg(-1) x h(-1)), dose-dependently prevented thrombosis of an injured rat carotid artery (FeCl(3)-patch model), increased time to artery occlusion, and reduced incidence of vessel occlusion. BC2 efficacy in preventing arterial thrombosis exceeded that of heparin (bolus 15 to 120 U/kg followed by infusion 0.5 to 4.0 U x kg(-1) x min(-1)), whereas the latter rendered the blood incoagulable (aPTT>1000 seconds). BC2 demonstrated complete antithrombotic efficacy also as a single bolus given either as prevessel or postvessel injury as evidenced by reduction of thrombus mass (from 4.18+/-0.49 to 1.80 +/-0.3 mg, P<0.001), increasing vessel patency time (from 14.9+/-0.9 minutes to 58.3+/-1.7 minutes, P<0.001) and decreasing incidence of vessel occlusion from 100% to 0% in vehicle- versus BC2-treated rats, respectively. BC2 (3 mg/kg, IV) administered in a single bolus resulted in 50% reduction in thrombus mass (P<0.01), extended vessel patency time (P<0.001), extended aPTT only 4-fold, and had no effect on blood loss via a tail surgical wound; heparin, at doses that reduced thrombus mass to a similar extent, extended aPTT beyond 1000 seconds (over 500-fold) and increased blood loss from 1.8+/-0.7 to 3.3 +/-0.6 mL (P<0.001). These data suggest that BC2 may provide enhanced therapeutic efficacy in humans at lesser interference with blood hemostasis than heparin.     

Role of thrombin and thromboxane A2 in reocclusion following coronary thrombolysis with tissue-type plasminogen activator.

Reocclusion of the coronary artery occurs after thrombolytic therapy of acute myocardial infarction despite routine use of the anticoagulant heparin. However, heparin is inhibited by platelet activation, which is greatly enhanced in this setting. Consequently, it is unclear whether thrombin induces acute reocclusion. To address this possibility, we examined the effect of argatroban [MCI9038, (2R,4R)-4-methyl-1-[N alpha-(3-methyl-1,2,3,4-tetrahydro-8- quinolinesulfonyl)-L-arginyl]-2-piperidinecarboxylic acid], a specific thrombin inhibitor, on the response to tissue-type plasminogen activator in a closed-chest canine model of coronary thrombosis. MCI9038 prolonged the thrombin time and shortened the time to reperfusion (28 +/- 2 min vs. 59 +/- 7 min in controls; mean +/- SEM, n = 5, P less than 0.01). At the highest dose, 2.5 mg/kg per hr, complete reocclusion was prevented in four of the five experimental animals, whereas reocclusion occurred in all five controls. However, reperfusion was complicated by cycles of decrease flow, which were abolished by the thromboxane A2 antagonist, GR32191. GR32191 at 1 mg/kg combined with MCI9038 at 0.5 mg/kg per hr prevented reocclusion, whereas, at these doses, either drug alone was without effect. In addition, thromboxane A2 biosynthesis, determined as excretion of its metabolite 2,3-dinor-thromboxane B2, was increased after reperfusion at all doses of MCI9038. These data demonstrate that thrombin impairs thrombolysis induced by tissue-type plasminogen activator in vivo and induces acute reocclusion. Furthermore, the response to thrombin inhibition may be impaired by continued formation of thromboxane A2.     

Adjunctive Therapy with an Antithrombotic Drug Can Prevent Reocclusion and Induce Residual Thrombus Reduction After Percutaneous Transcatheter Angioplasty of the Thrombotic Lesions

Acute reocclusion after successful angioplasty is a severe complication. The preventive effects of heparin, the synthetic antithrombin, argtroban, and the defibrinogenating agent batroxobin on reocclusion after balloon angioplasty of thrombotic occlusions were evaluated in canine iliac arteries. After the 2-hour-old thrombus was evaluated by angiography and angioscopy, percutaneous transcatheter angioplasty (PTA) was performed on the thrombotic stenosis. We used one of the three agents, heparin (100 U/kg), the antithrombin argatroban (0.3 mg/kg), or the defibrinogenating agent batroxobin (0.3 U/kg). Then angioscopy and angiography were performed before, just after, and 2 hours after PTA. After PTA, angiography revealed a marked reduction in percent stenosis in all groups (from 88 ± 8% to 24 ± 4% in the heparin group, from 79 ± 7% to 26 + 11% in the argatroban group and from 89 ± 12% to 32 ± 7% in the batroxobin group). At 2 hours after PTA, angiography demonstrated a greater reduction in percent stenosis with argatroban (from 26 ± 11% to 9 ± 3%) and batroxobin (from 32 ± 7% to 10 ± 8%), and maintenance of percent stenosis reduced by PTA with heparin (from 24 ± 5% to 28 ± 9%) when compared with the significant reversal of percent obstruction in the control side. Angioscopic visualization also demonstrated a similar trend. These results show that these antithrombotic drugs have a preventive effect on reocclusion after balloon angioplasty for thrombotic obstruction.     

Lysis of plasminogen activator-resistant platelet-rich coronary artery thrombus with combined bolus injection of recombinant tissue-type plasminogen activator and antiplatelet GPIIb/IIIa antibody

Resistance of coronary occlusive thrombus to thrombolytic therapy, found in some patients with acute myocardial infarction, may be due to the presence of platelet-rich coronary clot. Reperfusion therapy in such patients may require the development and evaluation of alternative strategies in animal models. Therefore, platelet-rich coronary artery thrombus was developed by excision, eversion (inside out) and reanastomosis of a 1 cm segment of the left circumflex coronary artery in anesthetized dogs maintained on heparin antiocoagulation. Blood flow was restored in 25 of 27 dogs. Thrombotic occlusion of the everted segment graft with primarily platelet-rich thrombus or thrombus containing platelet-rich and erythrocyte-rich zones, persisting for at least 30 min, occurred within 4.5 +/- 3.5 min (mean +/- SD) in 20 of these 25 dogs. In 5 of these 20 dogs (group I, control), stable occlusion, as monitored with an ultrasound flow probe and coronary angiography, was maintained during a 2 h observation period. In group II (n = 5), intravenous bolus injections of recombinant tissue-type plasminogen activator (rt-PA) at a dose of 0.45 mg/kg body weight at four 15 min intervals did not cause reperfusion in four dogs and produced cyclic reperfusion and reocclusion in one dog. In group III (n = 5), a single intravenous bolus injection of 0.8 mg/kg of the F(ab')2 fragment of a murine monoclonal antibody (7E3) against the human platelet GPIIb/IIIa receptor [7E3-F(ab')2] produced stable reperfusion in two of the five dogs, whereas occlusion persisted in the other three. In group IV (n = 5), injection of 7E3-F(ab')2 (0.8 mg/kg) followed by rt-PA (0.45 mg/kg) caused stable reperfusion without reocclusion in all dogs (p less than 0.05 versus rt-PA alone and p less than 0.01 versus control). This study confirms that platelet-rich occlusive coronary thrombus is very resistant to lysis with intravenous rt-PA. However, this resistance may be overcome by the combined use of a reduced dose of rt-PA and the antiplatelet GPIIb/IIIa receptor antibody 7E3. The results indicate that platelet-rich thrombus resistant to thrombolytic agents may be dispersed pharmacologically without resort to mechanical recanalization. The present dog model may be useful in investigating specific strategies for the dispersion of resistant platelet-rich coronary thrombus.     

Combination reperfusion therapy with abciximab and reduced dose reteplase: results from TIMI 14. The Thrombolysis in Myocardial Infarction (TIMI) 14 Investigators.

Aims Abciximab has previously been shown to enhance thrombolysis and improve myocardial perfusion when combined with reduced doses of alteplase. The purpose of the reteplase phase of TIMI 14 was to evaluate the effects of abciximab when used in combination with a reduced dose of reteplase for ST-elevation myocardial infarction. Methods and Results Patients (n=299) with ST-elevation myocardial infarction were treated with aspirin and randomized to a control arm with standard dose reteplase (10+10 U given 30 min apart) or abciximab (bolus of 0.25 mg. kg(-1)and 12-h infusion of 0.125 microg. kg(-1). min(-1)) in combination with reduced doses of reteplase (5+5 U or 10+5 U). Control patients received standard weight-adjusted heparin (bolus of 70 U. kg(-1); infusion of 15 U. kg(-1). h(-1)), while each of the combination arms with abciximab and reduced dose reteplase received either low dose heparin (bolus of 60 U. kg(-1); infusion of 7 U. kg(-1). h(-1)) or very low dose heparin (bolus of 30 U. kg(-1); infusion of 4 U. kg(-1). h(-1)). The rate of TIMI 3 flow at 90 min was 70% for patients treated with 10+10 U of reteplase alone (n=87), 73% for those treated with 5+5 U of reteplase with abciximab (n=88), and 77% for those treated with 10+5 U of reteplase with abciximab (n=75). Complete (>/=70%) ST resolution at 90 min was seen in 56% of patients receiving a reduced dose of reteplase in combination with abciximab compared with 48% of patients receiving reteplase alone.Conclusions Reduced doses of reteplase when administered in combination with abciximab were associated with higher TIMI 3 flow rates than reported previously for reduced doses of reteplase without abciximab and were at least as high as for full dose reteplase alone Copyright 2000 The European Society of Cardiology.