Recombinant nematode anticoagulant protein c2, an inhibitor of tissue factor/factor VIIa, attenuates coagulation and the interleukin-10 response in human endotoxemia.

The tissue factor-factor (F)VIIa complex (TF/FVIIa) is responsible for the initiation of blood coagulation under both physiological and pathological conditions. Recombinant nematode anticoagulant protein c2 (rNAPc2) is a potent inhibitor of TF/FVIIa, mechanistically distinct from tissue factor pathway inhibitor. The first aim of this study was to elucidate the pharmacokinetics and pharmacodynamics of a single intravenous (i.v.) dose of rNAPc2. The second aim was to study its effect on endotoxin-induced coagulation and inflammation. Initially, rNAPc2 was administered to healthy volunteers in three different doses. There were no safety concerns and the pharmacokinetics were consistent with previous studies, in which rNAPc2 was administered subcutaneously. rNAPc2 elicited a dose-dependent reduction of the endogenous thrombin potential and a selective prolongation of prothrombin time. Subsequently, the effect on endotoxin-induced coagulation and inflammation was studied. The administration of rNAPc2 completely blocked the endotoxin-induced thrombin generation, as measured by plasma prothrombin fragment F1+2. The endotoxin-induced effect on fibrinolytic parameters such as plasmin-antiplasmin complexes and plasminogen activator inhibitor type 1 was not affected by rNAPc2. The administration of rNAPc2 attenuated the endotoxin-induced rise in interleukin (IL)-10, without affecting the rise in other cytokines. In conclusion, rNAPc2 is a potent inhibitor of TF/FVIIa, which was well tolerated and could safely be used intravenously in this Phase I study in healthy male volunteers. A single i.v. dose rNAPc2 completely blocked endotoxin-induced thrombin generation without affecting the fibrinolytic response. In addition, rNAPc2 attenuated the endotoxin-induced rise in IL-10, without affecting the rises in other cytokines.

Dose-response study of recombinant factor VIIa/tissue factor inhibitor recombinant nematode anticoagulant protein c2 in prevention of postoperative venous thromboembolism in patients undergoing total knee replacement.

BACKGROUND: With the best prophylactics now available, venous thromboembolism after total knee replacement remains substantial (25% to 27%). Recombinant nematode anticoagulant protein c2 (rNAPc2) is a potent inhibitor of factor VIIa/tissue factor complex that has the potential to reduce this risk. The present study was performed to determine an efficacious and safe dose of rNAPc2 for prevention of venous thromboembolism after elective, unilateral total knee replacement. METHODS AND RESULTS: This open-label, sequential dose-ranging study was conducted in 11 centers in Canada, Europe, and the United States. Five regimens were tested. Injections were administered subcutaneously on the day of surgery (day 1) and days 3, 5, and optionally, day 7. Primary efficacy outcome was a composite of overall deep vein thrombosis based on mandatory unilateral venography (day 7+/-2) and confirmed symptomatic venous thromboembolism recorded

Ability of recombinant factor VIIa to generate thrombin during inhibition of tissue factor in human subjects.

BACKGROUND: In view of the central role of the tissue factor-factor VIIa pathway in the initiation of blood coagulation, novel therapeutic strategies aimed at inhibiting this catalytic complex are currently being evaluated. A limitation of this new class of anticoagulants may be the lack of an appropriate strategy to reverse the effect if a bleeding event occurs. The aim of this study was to investigate the in vivo potential of recombinant factor VIIa (rVIIa) to induce thrombin generation in healthy subjects pretreated with recombinant nematode anticoagulant protein c2, a specific inhibitor of the tissue factor-factor VIIa complex, in a double-blind randomized crossover study. METHODS AND RESULTS: Administration of nematode anticoagulant protein c2 (3.5 microgram/kg) caused a prolongation of the prothrombin time from 13.7+/-0.6 to 16.9+/-1.2 seconds. The subsequent injection of rVIIa (90 microgram/kg) resulted in an immediate and complete correction of the prothrombin time and a marked generation of thrombin, reflected by increased levels of prothrombin activation fragment F1+2 and thrombin-antithrombin complexes from 0.75+/-0.64 to 3.29+/-6.3 nmol/L and from 2.4+/-0.6 to 10.7+/-3.9 microgram/mL, respectively. Factor X and IX activation peptides showed a 3.5-fold and a 3.8-fold increase, respectively, after the administration of rVIIa in the presence of nematode anticoagulant protein c2. CONCLUSIONS: During treatment with an inhibitor of the tissue factor-factor VIIa complex, the infusion of rVIIa resulted in thrombin generation. Our results indicate that rVIIa may be a good candidate as an antidote for inhibitors of tissue factor.

Antithrombotic efficacy of a recombinant nematode anticoagulant peptide (rNAP5) in canine models of thrombosis after single subcutaneous administration.

We describe the antithrombotic effects of recombinant nematode anticoagulant peptide (rNAP5), a selective and direct factor Xa inhibitor, after a single s.c. administration in canine models of arterial and venous thrombosis. The systemic anticoagulant effects of rNAP5 were evaluated initially in conscious dogs after s.c. dosing (0.03, 0.1 and 0.3 mg/kg) that resulted in a dose-dependent increase in the activated clotting time and the activated partial thromboplastin time. The antithrombotic effects of rNAP5 were evaluated in anesthetized dogs where saline or rNAP5 (0.03, 0.1 and 0.3 mg/kg s.c.) was administered 1 hr before the left circumflex coronary artery was subjected to electrolytic injury. In the saline group (n = 10), the left circumflex artery occluded in 79 +/- 9 min, and 5 of 10 animals progressed to sudden death due to ventricular fibrillation. rNAP5 significantly prolonged the time to occlusion in the 0.03 mg/kg (163 +/- 62 min) and 0.1 mg/kg (327 +/- 62) treatment groups (n = 6). In the 0.3 mg/kg group (n = 5), all of the injured vessels remained patent for 8 hr. There was a dose-dependent reduction in the thrombus mass in the rNAP5-treated animals as compared with controls, as well as a lower mortality rate. rNAP5, in the doses of 0.03 and 0.1 mg/kg, did not alter the bleeding time, whereas 0.3 mg/kg produced a 5-fold increase. In a separate study, we evaluated the efficacy of rNAP5 (0.1 mg/kg) in the prevention of carotid artery and jugular vein thrombosis. In response to endothelial injury, the carotid artery and jugular vein in the saline group (n = 6) occluded in 142 +/- 16 and 100 +/- 11 min, respectively, compared with rNAP5, which maintained vessel patency in the carotid artery (6/6) and jugular vein (5/6) and significantly decreased the thrombus weights. The results demonstrate that rNAP5 has antithrombotic efficacy in canine models of arterial and venous thrombosis after a single s.c. administration.

Orally effective CVS-1123 prevents coronary artery thrombosis in the conscious dog.

BACKGROUND: We examined the oral efficacy of a direct thrombin inhibitor, CVS-1123 [(CH3CH2CH2)(2)-CH-CO-Asp (OCH3)-Pro-Arg-CHO; MW, 575]. The object was to determine whether thrombin inhibition could reduce the incidence of occlusive coronary artery thrombosis in response to arterial wall injury. METHODS AND RESULTS: Arterial wall injury was induced in conscious dogs by a 150-muA anodal current applied to the intimal surface of the circumflex coronary artery 30 minutes after oral CVS-1123 (20 mg/kg every 8 hours for three doses; n = 11) or placebo containing diluent (n = 10). Dogs were monitored for 8 hours and at 24 hours. The coronary artery remained patent for 24 hours in 8 of 11 CVS-1123-treated dogs. All dogs (n = 10) in the placebo group developed a sustained, occlusive arterial thrombus. Two hours after the initial oral dose, the plasma CVS-1123 concentration was 13 +/- 1 microgram/mL, reaching a maximum of 15 +/- 1 micrograms/mL after the second dose and 4.4 +/- 0.5 micrograms/mL at 24 hours. Ex vivo platelet aggregation to gamma-thrombin was inhibited and activated partial thromboplastin time was increased after treatment with CVS-1123 (P < .05). CONCLUSIONS: The direct thrombin inhibitor CVS-1123 is effective after oral administration in reducing the incidence of primary thrombus formation in an experimental model of arterial wall injury. Thrombin-specific inhibitors, such as CVS-1123, may be alternative antithrombotic agents in clinical settings in which heparin-associated thrombosis is a complicating factor or when long-term anticoagulation is required.

The role of CD11/CD18 integrins in the reverse passive Arthus reaction in rat dermal tissue.

The CD11/CD18 leukocyte integrins are necessary for tissue localization of neutrophils, an early requisite event in inflammation. We have analyzed the contribution of CD11a/CD18 and CD11b/CD18 to local neutrophil accumulation and tissue injury in the reverse passive Arthus reaction in the rat dermis. Experimental groups comprised animals that received an intravenous infusion of (1) recombinant neutrophil inhibitory factor (NIF), a hookworm-derived antagonist of CD11b/CD18; (2) monoclonal antibody to CD11a/CD18 (TA-3); (3) a combination of these agents; (4) a monoclonal antibody to CD18 (WT.3); or (5) saline. Administration of recombinant NIF or anti-CD11a/CD18 monoclonal antibody alone produced a slight reduction in neutrophil accumulation but did not affect edema formation. In contrast, a combination of these antagonists yielded a significant reduction in neutrophil accumulation and a modest reduction in edema, equivalent to levels observed with either anti-CD18 antibodies or animals that were rendered neutropenic. These results indicate that neutrophil infiltration in rat dermal tissue in the reverse passive Arthus reaction is dependent predominantly on the leukocyte integrins CD11a/CD18 and CD11b/CD18 and that either of these integrins is sufficient for neutrophil trafficking in this inflammatory setting.

Neutrophil inhibitory factor is neuroprotective after focal ischemia in rats.

We tested the neuroprotective potential of neutrophil inhibitory factor (rNIF), a novel 41-kd recombinant glycoprotein derived from a hookworm, in a model of focal cerebral ischemia in the rat. Male Wistar rats were assigned to treatment with rNIF and vehicle. Middle cerebral artery occlusion (MCAO) for 2 hours was induced by insertion of an intraluminal suture. Infusion of the drug was initiated at the onset of reperfusion. Infarct volume was determined 48 hours after reperfusion. Neutrophils were measured within the ischemic tissue by myeloperoxidase (MPO) staining. Treatment with rNIF resulted in a 48% reduction in cerebral infarction compared with control animals (p < 0.01). Neutrophil accumulation in the ischemic brains of rNIF-treated rats was reduced significantly (p < 0.01) compared with control animals. The number of neutrophils within the infarcted tissue correlated positively with the size of the area of infarction (p < 0.001, r = 0.6) within representative cerebral coronal sections. We demonstrated a significant neuroprotective effect of rNIF with continuous treatment for 48 hours following 2 hours of MCAO. The neuroprotective effect was correlated with a reduced number of neutrophils within the ischemic tissue. These results demonstrate potential therapeutic properties of rNIF in the management of stroke.

Prevention of thrombosis and rethrombosis and enhancement of the thrombolytic actions of recombinant tissue-type plasminogen activator in the canine heart by DMP728, a glycoprotein IIb/IIIa antagonist.

1. We studied DMP728, a non-peptide glycoprotein (GP) IIb/IIIa receptor antagonist, for prevention of coronary artery thrombosis or rethrombosis in a chronic canine model subjected to arterial injury. 2. In protocol I, DMP728 (1.0 mg kg-1, i.v., n = 8) or saline (n = 8) was administered and a 150 microA anodal current was applied to the intimal surface of the left circumflex coronary artery (LCX). Dogs were monitored for 6 h and again on each of 5 subsequent days. 3. Ex vivo platelet aggregation was inhibited but returned to baseline 1 day after drug administration. Thrombus weight was reduced (saline, 20.7 +/- 5.0 mg; DMP728 1.7 +/- 0.4 mg; P < 0.05), as was infarct size [saline, 27.5 +/- 4.3; DMP728, 1.6 +/- 0.7 (per cent left ventricle); P < 0.05]. All control animals died by day 3, while all but one of the treated dogs survived the entire protocol (P < 0.05). 4. In protocol II, an LCX thrombus was induced and thrombolytic therapy was initiated 30 min later. DMP728 (1.0 mg kg-1, i.v., n = 8) or saline (n = 8) was administered 5 min after recombinant tissue-type plasminogen activator infusion had begun. The incidence of reocclusion was reduced by DMP728 (saline, 4/8; DMP728, 1/8). One day after thrombolysis, 7/8 DMP728-treated animals were alive compared with 1/8 in the control group (P = 0.01). 5. DMP728 inhibited ex vivo platelet aggregation, prevented primary and secondary occlusive thrombus formation, reduced thrombus weight and infarct size and increased survival in a chronic canine model of coronary artery thrombus formation. DMP728 is an effective anti-platelet intervention when used as the singular adjunctive agent in association with thrombolytic therapy.

Chimeric 7E3 prevents carotid artery thrombosis in cynomolgus monkeys.

BACKGROUND AND PURPOSE: We compared the current antithrombotic strategy of antiplatelet therapy with aspirin, and anticoagulant therapy with heparin, with a specific genetically engineered chimeric antibody (c7E3 Fab) directed against the human glycoprotein IIb/IIIa receptor in an animal model of arterial thrombosis. METHODS: Anesthetized cynomolgus monkeys (Macaca fascicularis) were instrumented for monitoring of arterial blood pressure, heart rate, and carotid artery flow velocity. Animals were treated with saline (n = 6), aspirin (25 mg PO daily for 3 days; n = 6), heparin (100 U/kg i.v. plus infusion adjusted to maintain activated partial thromboplastin time at 2 to 3 times baseline; n = 6), aspirin plus heparin (as administered separately, n = 6), or c7E3 Fab (0.10 mg/kg i.v., n = 7; 0.15 mg/kg i.v., n = 6; 0.20 mg/kg i.v., n = 6; 0.25 mg/kg i.v., n = 6). Thrombus formation via anodal electrolytic stimulation (100 microA) to the intimal surface of the right carotid artery was initiated 15 minutes after drug administration and continued for 180 minutes. Electrolytic injury to the left carotid artery began 210 minutes after drug administration and continued for 180 minutes. Whole blood cell counts, glycoprotein IIb/IIIa receptor blockade, ex vivo platelet aggregation, template bleeding time, and activated partial thromboplastin time were assessed at various time points throughout the experimental protocol. RESULTS: Hemodynamic and hematologic parameters were comparable among groups at baseline. Treatment with c7E3 Fab inhibited ex vivo platelet aggregation, increased bleeding time, decreased thrombus weight, and increased time to occlusion in a dose-dependent manner in both vessels. Treatment with aspirin, heparin, or the combination of aspirin plus heparin was ineffective for the prevention of carotid artery thrombosis in this model. CONCLUSIONS: Inhibition of the platelet glycoprotein IIb/IIIa receptor with c7E3 Fab was found to be safe and effective for the prevention of primary thrombus formation, whereas treatment with either aspirin or heparin or the combination of the two agents failed to protect against occlusive thrombus formation in cynomolgus monkeys.

Nitroglycerin inhibits experimental thrombosis and reocclusion after thrombolysis.

Nitroglycerin inhibits platelet aggregation in vitro, but its effect on thrombosis and platelet function in vivo is controversial. This study assessed the effect of nitroglycerin on primary thrombus formation in response to vessel wall injury and secondary thrombus formation, or rethrombosis, after lysis of an existing thrombus. In the first protocol the right carotid artery was instrumented with a flow probe, stenosis, an anodal electrode, and a proximal infusion line. A 300 microA anodal current was used to induce endothelial injury and subsequent thrombotic occlusion of the vessel. Anisoylated plasminogen streptokinase activator complex (APSAC; 0.05 U/kg intraarterially) was injected proximal to the thrombus 30 minutes after occlusion. After APSAC, nitroglycerin (1 microgram/kg/min intraarterially, n = 7) or vehicle (n = 6) was infused proximal to the thrombus for 3 hours. Reocclusion occurred in two of seven nitroglycerin-treated dogs and six of six vehicle-treated dogs (p < 0.05). In the second protocol both carotid arteries were instrumented as described previously. Anodal current (300 microA, 180 minutes) was applied to the right carotid (n = 12) artery to determine control times to occlusion. The left carotid artery served as the test vessel, receiving either nitroglycerin (1 microgram/kg/min intraarterially, n = 6) or trimethaphan (0.05 mg/kg/hr intraarterially, n = 6). Trimethaphan was used to produce controlled hypotension to match the approximately 10% decrease in mean arterial blood pressure that was observed during nitroglycerin infusion. Control arteries and those treated with trimethaphan formed occlusive thrombi in all instances. Nitroglycerin infusion resulted in a lower incidence of occlusion (1 of 6; p < 0.05 vs control value) and inhibited ex vivo platelet aggregation to adenosine diphosphate and arachidonic acid (p < 0.05). Local infusion of nitroglycerin reduced the formation of primary thrombi, independent of the hypotensive effect of the drug, and exerted systemic effects on platelet aggregation. Furthermore, platelet inhibition with nitroglycerin reduced the incidence of secondary thrombus formation (rethrombosis) after thrombolysis. The results suggest that a potential benefit of nitroglycerin therapy may be derived from its ability to inhibit thrombotic events in patients with unstable angina or myocardial infarction.

Antithrombotic effects of DMP 728, a platelet GPIIb/IIIa receptor antagonist, in a canine model of arterial thrombosis.

The platelet glycoprotein IIb/IIIa receptor (GPIIb/IIIa, fibrinogen receptor) represents the final common pathway for platelet aggregation. Inhibition of GPIIb/IIIa with antibodies or peptides containing the RGD sequence has been reported to prevent arterial thrombosis. We examined DMP 728 [(cyclic[D-2-amino-butyryl-N2-methyl-L-arginyl-glycyl-L-aspartyl-3-(a min o- methyl-benzoic acid], methanesulfonic acid salt], a cyclic peptidomimetic, GPIIb/IIIa receptor antagonist, for prevention of thrombosis and rethrombosis in a canine model of carotid artery thrombosis. Dogs were anesthetized, and both carotid arteries were instrumented with an electrode, a flow probe, and a stenosis. A 300-microA current was applied to the intimal surface in the right carotid artery (RCA, control) through the electrode; time to occlusive thrombus formation and thrombus mass was noted. The RCA served as the control vessel; the left carotid artery (LCA) served as the test vessel after DMP 728 administration (0.1 or 1. mg/kg, intravenously, i.v.). As compared with controls, occlusive thrombus formation was reduced by both doses of DMP 728 (control 100% n = 12; 0.1 mg/kg i.v. 17%, p < 0.05, n = 6; 1.0 mg/kg i.v. 0%, p < 0.05, n = 6), time to occlusion was increased (p < 0.05), and thrombus weight was reduced (p < 0.05). Ex vivo platelet aggregation was inhibited in all groups. In a second group of animals, a carotid artery thrombus was formed and lysed with anisoylated plasminogen activator complex (APSAC; 0.05 U/kg intraarterially, i.a.) with or without DMP 728.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of rethrombosis after coronary thrombolysis in a chronic canine model. I. Adjunctive therapy with monoclonal antibody 7E3 F(ab')2 fragment.

We examined the efficacy of the monoclonal antibody (MoAb) 7E3 F(ab')2 fragment, an inhibitor of the platelet glycoprotein (GP)IIb/IIIa receptor, to prevent coronary artery rethrombosis after successful thrombolysis with rt-PA. The circumflex coronary artery of anesthetized dogs was instrumented with a flow probe, an electrode, and a stenosis. After recovery from the surgical procedure, the animals were reanesthetized on post-operative day 9, and vessel wall injury was induced with current applied to the intimal surface of the circumflex coronary artery. The resulting occlusive thrombus was aged for 30 min, and recombinant tissue plasminogen activator (rt-PA) was administered. The animals were allocated to receive either placebo or a single dose of 7E3 [0.8 mg/kg intravenous (i.v.) bolus] as the sole adjunctive agent. Ex vivo platelet function and coronary artery blood flow velocity were recorded on each of 5 consecutive days. Reocclusion and mortality were reduced significantly in animals treated with 7E3 as compared with the placebo-treated group. Significant inhibition of ex vivo platelet aggregation persisted for 48 h after a single injection of 7E3. The MoAb 7E3 F(ab')2 fragment is effective as the sole adjunctive agent with rt-PA for prevention of rethrombosis. The present study is unique in that it examined the efficacy of GPIIb/IIIa inhibition in an experimental model for an extended time, demonstrating the duration of antiplatelet therapy required to prevent rethrombosis after thrombolysis.

Prevention of rethrombosis after coronary thrombolysis in a chronic canine model. II. Adjunctive therapy with r-hirudin.

We examined the effectiveness of the direct-acting thrombin inhibitor, recombinant hirudin (r-hirudin), for prevention of coronary rethrombosis after thrombolysis with recombinant tissue plasminogen activator (rt-PA) in a canine model of coronary artery thrombosis. The reocclusion rate of 15-30% associated with thrombolytic therapy emphasizes the need for adjunctive therapy to prevent rethrombosis. We studied r-hirudin for its potential to prevent reocclusion in a model of coronary artery thrombosis/thrombolysis. The circumflex coronary arteries of anesthetized dogs were instrumented with a flow probe, an intraluminal electrode, and a ligature stenosis. The dogs were reanesthetized on the ninth postoperative day, and intimal injury was induced with an anodal current. After occlusive thrombus formation, tissue plasminogen activator (rt-PA) was administered. The animals were allocated to receive either placebo, r-hirudin [5 mg/kg intravenously (i.v.) bolus, 2 mg/kg/h i.v., for 3.5 h] or r-hirudin (5 mg/kg i.v., bolus, 1 mg/kg/h i.v., for 12 h). Neither aspirin nor heparin was used. Ex vivo platelet function and coronary artery blood flow velocity were recorded on each of 5 consecutive days. Infarct size and residual thrombus weight were determined at the end of the protocol. r-Hirudin infusion (3.5 and 12 h) provided little benefit over rt-PA alone. Ex vivo platelet aggregation was not affected by r-hirudin. Little improvement in the incidence of reocclusion and mortality in a model of coronary artery thrombosis/thrombolysis resulted from adjunctive treatment with r-hirudin.

Purification and characterization of platelet aggregation inhibitors from snake venoms.

Proteins that inhibit glycoprotein (GP) IIb/IIIa mediated platelet aggregation have been purified from the venom of two snake species. A small platelet aggregation inhibitor (p1.AI), multisquamatin (Mr = 5,700), was purified from Echis multisquamatus venom by hydrophobic interaction HPLC and two steps on C18 reverse phase HPLC. A larger p1.AI, contortrostatin (Mr = 15,000), was purified by a similar HPLC procedure from the venom of Agkistrodon contortrix contortrix. Both p1.AIs inhibit ADP-induced human, canine and rabbit platelet aggregation using platelet rich plasma (PRP). Multisquamatin has an IC50 of 97 nM, 281 nM and 333 nM for human, canine and rabbit PRP, respectively. Contortrostatin has an IC50 of 49 nM, 120 nM and 1,150 nM for human, canine and rabbit PRP, respectively. In a competitive binding assay using 125I-7E3 (a monoclonal antibody to GPIIb/IIIa that inhibits platelet aggregation) both contortrostatin and multisquamatin demonstrated GPIIb/IIIa specific binding to human and canine platelets. The IC50 for contortrostatin displacement of 7E3 binding to human and canine GPIIb-/IIIa is 27 nM and 16 nM, respectively and for multisquamatin it is 3 nM and 63 nM, respectively. Our results indicate that both p1.AIs inhibit platelet aggregation by binding with high affinity to GPIIb/IIIa.

Prevention of experimental carotid artery thrombosis by applaggin.

Applaggin, an inhibitor of platelet aggregation via binding to the glycoprotein IIb/IIIa receptor, was examined in an anesthetized canine model of arterial thrombosis formation secondary to arterial wall injury. Both carotid arteries were isolated and instrumented with flow probes, intravascular anodal electrodes and adjustable constrictors. The right carotid artery was injured initially and served as the control response to vessel wall injury in each animal, whereas the left carotid was injured after applaggin administration (1.0 mg/kg, i.v.). Arterial occlusion in the control vessel occurred in each of seven animals. Time for occlusive thrombus development was 125.6 +/- 15.2 min. One of the seven left carotid arteries occluded after applaggin. Thrombus weight was greater in control vessels (44.2 +/- 7.0 mg) vs. thrombus weight after applaggin (11.2 +/- 2.4 mg). Cyclic flow variations occurred in all control arteries before development of an occlusive thrombus. In contrast, cyclic flow variations were observed only in two of seven vessels injured after applaggin. One of the latter vessels developed an occlusive thrombus. Platelet counts, heart rate and blood pressure were unaltered over the course of the experimental protocol. Ex vivo platelet aggregation to arachidonic acid was examined before and after applaggin administration. Platelet-rich plasma from animals having initial normal baseline aggregation no longer aggregated 30 min after administration of applaggin. Aggregation returned to normal within 3 hr. Applaggin binds to stimulated and unstimulated platelets and two classes of binding sites were identified. The results demonstrate that applaggin possesses an antithrombotic effect in the experimental model of canine carotid artery thrombosis.

Thromboxane antagonism in experimental canine carotid artery thrombosis.

BACKGROUND AND PURPOSE: The two objectives of this study were to assess the potential of BAY U 3405 to prevent arterial thrombosis in response to vessel wall injury and to determine the ability of BAY U 3405 to prevent thrombotic reocclusion after thrombolysis with anisoylated plasminogen streptokinase activator complex. METHODS: Dogs were instrumented with a carotid flow probe, stimulating electrode, and a stenosis. Current (150 microA) was applied to the intimal surface of the right carotid artery, and time to occlusive thrombus formation was noted. BAY U 3405 was administered, and the procedure for thrombus formation was repeated for the left carotid artery. RESULTS: BAY U 3405 administration prevented occlusive arterial thrombosis formation. Ex vivo platelet aggregation was inhibited, bleeding time increased, and thrombus weight reduced after BAY U 3405 treatment. In a second group, thrombi were formed initially in both carotid arteries, BAY U 3405 was administered as before, and anisoylated plasminogen streptokinase activator complex was infused in the right carotid artery proximal to the occlusive thrombus. BAY U 3405 did not alter the incidence of rethrombosis compared with the lytic agent alone. CONCLUSIONS: BAY U 3405 prevented primary arterial thrombosis, corresponding to inhibition of platelet aggregation, and increased bleeding times. BAY U 3405, however, did not prevent rethrombosis after successful thrombolysis with anisoylated plasminogen streptokinase activator complex, despite the fact that platelet reactivity was inhibited. The data are consistent with the concept that the residual thrombus represents a more effective thrombogenic stimulus as compared with arterial wall injury alone and that the mechanisms associated with primary versus secondary thrombus formation may require separate therapeutic approaches.

Platelet GPIIb/IIIa receptor inhibition by SC-49992 prevents thrombosis and rethrombosis in the canine carotid artery.

OBJECTIVE: Platelet glycoprotein IIb/IIIa (GPIIb/IIIa) receptors represent the final common pathway for aggregation. GPIIb/IIIa inhibition with antibodies or RGD peptides prevents arterial thrombosis. The present study examined the ability of SC-49992 (SC), a GPIIb/IIIa receptor antagonist, to prevent thrombosis in a canine model of carotid artery thrombosis. METHODS: Both carotid arteries of anaesthetised dogs were instrumented with Doppler probes. A 300 microA current was applied to the intimal surface of the right carotid artery via an intraluminal electrode; time to occlusive thrombus formation was noted. SC (30 and 60 micrograms/.kg-1 x min-1, intravenously) or saline was infused for 240 min. The procedure for thrombus formation was repeated after 60 min of drug infusion for the left carotid artery. RESULTS: SC did not alter heart rate or blood pressure. Frequency of occlusive thrombus formation was reduced or prevented in a dose dependent manner (control = 100%, n = 12; SC 30 micrograms = 50%, n = 6; SC 60 micrograms = 0%, n = 6; p < 0.05). SC resulted in a reduction in thrombus weight (p < 0.05) v control. Ex vivo platelet aggregation to ADP and arachidonic acid was inhibited. Platelet reactivity remained inhibited 60 min after cessation of SC infusion. In a second group of animals, a carotid artery thrombus was formed and lysed with administration of anisoylated plasminogen streptokinase activator complex (0.05 U.kg-1). SC (60 micrograms.kg-1 x min-1, intravenously, n = 6) or saline (n = 6) was infused for 240 min. In dogs receiving saline there was an 83% rate of rethrombosis; none of the SC treated animals had reocclusion after recanalisation (p < 0.05). CONCLUSIONS: SC-49992 inhibits ex vivo platelet aggregation, prevents occlusive thrombus formation in a canine model of arterial thrombosis, and prevents rethrombosis after thrombolysis. The data are consistent with results obtained with murine monoclonal antibodies directed against the platelet GPIIb/IIIa receptor.

Autonomic mechanisms in heart rate variability after isoproterenol-induced myocardial damage in rats.

The effect of isoproterenol-induced myocardial damage on heart rate variability was examined in conscious, unrestrained, male, Sprague-Dawley rats. We used power spectrum analysis of beat-to-beat heart rate to study the levels and interaction of sympathetic and parasympathetic neural influences on the heart. One day after isoproterenol (80 mg/kg s.c.), mean heart rate was significantly elevated when compared to controls (isoproterenol 413.9 b.p.m. +/- 7.7 S.E.M.; saline 368.8 b.p.m. +/- 12.8 S.E.M.; P less than 0.05), even though the low frequency and respiratory components of the power spectrum were not different between the two groups. By contrast, a week after isoproterenol administration, heart rate was normal; however, variability in low frequency and respiratory areas of the power spectrum was significantly increased suggesting an abnormal sympathovagal balance. An imbalance in autonomic regulation of cardiac automaticity could account for the 27% incidence of arrhythmias in rats given isoproterenol. These results indicate that autonomic responses associated with isoproterenol-induced myocardial ischemia differ from those in human and in animal models of myocardial infarction.