Antithrombotic effect of GYKI-14766 in a canine model of arterial and venous rethrombosis: a comparison with heparin

American College of Veterinary Emergency and Critical Care (ACVECC) Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE) guidelines: Small animal

OBJECTIVES

To systematically review available evidence and establish guidelines related to the risk of developing thrombosis and the management of small animals with antithrombotics.

DESIGN

Standardized, systematic evaluation of the literature (identified by searching Medline via PubMed and CAB abstracts) was carried out in 5 domains (Defining populations at risk; Defining rational therapeutic use; Defining evidence-based protocols; Refining and monitoring antithrombotic therapies; and Discontinuing antithrombotic therapies). Evidence evaluation was carried out using Population, Intervention, Comparison, Outcome generated within each domain questions to address specific aims. This was followed by categorization of relevant articles according to level of evidence and quality (Good, Fair, or Poor). Synthesis of these data led to the development of a series of statements. Consensus on the final guidelines was achieved via Delphi-style surveys. Draft recommendations were presented at 2 international veterinary conferences and made available for community assessment, review, and comment prior to final revisions and publication.

SETTINGS

Academic and referral veterinary medical centers.

RESULTS

Over 500 studies were reviewed in detail. Worksheets from all 5 domains generated 59 statements with 83 guideline recommendations that were refined during 3 rounds of Delphi surveys. A high degree of consensus was reached across all guideline recommendations.

CONCLUSIONS

Overall, systematic evidence evaluations yielded more than 80 recommendations for the treatment of small animals with or at risk of developing thrombosis. Numerous significant knowledge gaps were highlighted by the evidence reviews undertaken, indicating the need for substantial additional research in this field.

Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE): Domain 2-Defining rational therapeutic usage

OBJECTIVES

To systematically review available evidence to determine when small animals at risk of thrombosis should be treated with antiplatelet agents and anticoagulants, which antiplatelet and anticoagulant agents are most effective, and when multimodal therapy is indicated.

DESIGN

Standardized, systematic evaluation of the literature, categorization of relevant articles according to level of evidence (LOE) and quality (Good, Fair, or Poor), and development of consensus on conclusions via a Delphi-style survey for application of the concepts to clinical practice. Draft recommendations were presented at 2 international veterinary conferences and made available for community assessment, review, and comment prior to final revisions and publication.

SETTINGS

Academic and referral veterinary medical centers.

RESULTS

Databases searched included Medline via PubMed and CAB abstracts. Twelve Population Intervention Comparison Outcome questions were devised and generated corresponding worksheets investigating indications for use of antithrombotic drugs in small animals. Seventy-eight studies were reviewed in detail. Most studies assessed were experimentally controlled laboratory studies in companion animals (56 LOE 3) with smaller numbers of LOE 2 (1), LOE 4 (5), LOE 5 (6), and LOE 6 (4) studies assessed. Only 5 randomized controlled clinical trials were identified (LOE 1, Good-Fair). The 12 worksheets generated 21 guidelines with 17 guideline statements that were refined during 3 rounds of Delphi surveys. A high degree of consensus was reached across all guideline recommendations during the Delphi process.

CONCLUSIONS

Overall, systematic evidence evaluations generated 2 strong recommendations, 19 weak recommendations (formulated as suggestions), 9 situations where the evidence was insufficient to make strong recommendations, and 8 situations where no relevant evidence was retrieved to aid guideline generation. Numerous significant knowledge gaps were highlighted by the evidence reviews undertaken, indicating the need for substantial additional research in this field.

Design, green synthesis and pharmacological evaluation of novel 5,6-diaryl-1,2,4-triazines bearing 3-morpholinoethylamine moiety as potential antithrombotic agents (.)

The aim of this research work was to investigate a series of novel 5,6-diaryl-1,2,4-triazines (3a-3q) containing 3-morpholinoethylamine side chain, and to address their antiplatelet activity by in vitro, ex vivo and in vivo methods. All compounds were synthesized by environment benign route and their structures were unambiguously confirmed by spectral data. Compounds (3l) and (3m) were confirmed by their single crystal X-ray structures. Out of all the synthesized compounds, 10 were found to be more potent in vitro than aspirin; six of them were found to be prominent in ex vivo assays and one compound (3d) was found to have the most promising antithrombotic profile in vivo. Moreover, compound (3d) demonstrated less ulcerogenicity in rats as compared to aspirin. The selectivity of the most promising compound (3d) for COX-1 and COX-2 enzymes was determined with the help of molecular docking studies and the results were correlated with the biological activity.

Hirudin and s18886 maintain luminal patency after thrombolysis with alfimeprase

BACKGROUND

An optimal strategy to improve reperfusion in patients with arterial occlusions is a recognized clinical need. We hypothesized that hirudin (thrombin inhibitor) and S18886 [S18, thromboxane A(2) receptor (TP) antagonist] would improve blood flow and reperfusion rates after thrombolysis with the direct-acting fibrinolytic enzyme alfimeprase.

METHODS

In anesthetized beagles, carotid artery thrombosis was induced by electrolytic endothelial injury. After 30 minutes of occlusion, animals were administered vehicle, hirudin, and/or S18. Carotid artery blood flow was monitored for 90 minutes after the infusion of alfimeprase or recombinant tissue plasminogen activator (rt-PA).

RESULTS

The onset to reperfusion was more rapid in animals treated with alfimeprase than in those treated with rt-PA. All the animals treated with hirudin + S18 + alfimeprase maintained vessel patency, and all vehicle-treated animals reoccluded. In animals treated with hirudin + S18 + alfimeprase, time to reocclusion and total reflow time after thrombolysis were longer compared with vehicle-treated animals. The quality and quantity of blood flow were most improved in animals treated with hirudin + S18 + alfimeprase. There were no significant differences in time to reocclusion, total reflow time, and quality and quantity of blood flow between vehicle + rt-PA-treated animals and hirudin + S18 + rt-PA-treated animals.

CONCLUSIONS

Dual antithrombotic therapy with hirudin and S18 improves reperfusion after thrombolysis with alfimeprase but not rt-PA.

Effect of thrombolysis on myocardial injury: recombinant tissue plasminogen activator vs. alfimeprase

Plasmin-dependent thrombolytic agents are potentially prothrombotic and proinflammatory. Alfimeprase, a zinc-containing metalloproteinase, degrades fibrin directly and achieves thrombolysis independent of plasmin formation. This study examines the hypothesis that thrombolysis in the absence of plasmin generation results in improved myocardial salvage on reperfusion. The thrombolytic effects of recombinant tissue plasminogen activator [rt-PA; 0.022 mg/kg, 1/10 of which was administered as a loading dose; the rest (9/10) was infused over 60 min by intracoronary (ic) administration] or alfimeprase (0.5 mg/kg over 1 min ic) were evaluated in a canine model of arterial thrombosis involving electrolytic injury of the left circumflex (LCX) coronary artery. Both agents induced thrombolysis, with onset of reperfusion being more rapid after alfimeprase compared with rt-PA (1.5 ± 0.6 vs. 10.1 ± 2.1 min). In the absence of adjunctive therapy, time to reocclusion after alfimeprase was 3.2 ± 0.5 min compared with 77.5 ± 31.9 min with rt-PA. The glycoprotein IIb/IIIa platelet receptor antagonist CRL-42796 prolonged reperfusion time after thrombolysis with alfimeprase or rt-PA. The effect of each lytic agent on myocardial infarct size was examined in a separate group of dogs subjected to 60 min of LCX coronary artery ligation and 4 h of reperfusion. Myocardial infarct size, expressed as percentage of the risk region, was larger (32.16 ± 3.95%) after rt-PA compared with alfimeprase (19.85 ± 3.61%) or that of the saline control group (18.46 ± 3.34%). rt-PA in contrast to alfimeprase, a direct-acting fibrinolytic agent, is associated with an increase in myocyte reperfusion injury.

Glycoprotein IIb/IIIa receptor antagonist (2S)-2-[(2-Naphthyl-sulfonyl)amino]-3-[[2-([4-(4-piperidinyl)-2-[2-(4-piperidinyl)ethyl] butanoyl]amino)acetyl]amino]propanoic acid dihydrochloride (CRL42796), in combination with aspirin and/or enoxaparin, prevents coronary artery rethrombosis after successful thrombolytic treatment by recombinant tissue plasminogen activator

The antithrombotic effect of the glycoprotein IIb/IIIa (GPIIb/IIIa) antagonist (2S)-2-[(2-naphthyl-sulfonyl)amino]-3-[[2-([4-(4-piperidinyl)-2-[2-(4-piperidinyl)ethyl] butanoyl]amino)acetyl]amino] propanoic acid dihydrochloride (CRL42796), administered alone, or in combination with aspirin, and/or enoxaparin, was examined in a canine left circumflex (LCX) coronary artery rethrombosis model. The electrolytic induction of arterial thrombosis was followed by intracoronary recombinant tissue plasminogen activator administration to achieve thrombolysis, and the adjunctive therapy was initiated 15 min earlier and maintained for 4 h. Thirty-five purpose-bred beagle dogs were randomized to receive one of the following treatments: group 0 (n = 6, placebo); group 1 (n = 6, CRL42796 15 microg/kg i.v. loading dose followed by 0.31 microg/kg/min i.v. infusion), group 2 (n = 6, aspirin 7 mg/kg, administered orally, at -47, -23, -17 h before entry into the experimental protocol); group 3 (n = 6, aspirin + CRL42796); group 4 (n = 6, aspirin + enoxaparin 0.6 microg/kg i.v. loading dose followed by 6.0 microg/kg/min i.v. infusion); and group 5 (n = 5, aspirin + CRL42796 + enoxaparin). The incidence of LCX reocclusion was as follows: group 0, 6/6; group 1, 3/6; group 2, 5/6; group 3, 2/6; group 4, 2/6; and group 5, 0/5. Aspirin pretreatment increased the tongue-bleeding time, whereas the addition of CRL42796 or enoxaparin did not prolong bleeding time to a further degree. However, the combination of the three drugs did increase bleeding time significantly, from 173.9 +/- 19.8 to 620.0 +/- 98.7 s. In conclusion, low-dose CRL42796 together with aspirin and enoxaparin prevented coronary artery rethrombosis, although bleeding time was prolonged. The latter may be of concern in the clinical use of combination therapy.

Blockade of the thrombin receptor protease-activated receptor-1 with a small-molecule antagonist prevents thrombus formation and vascular occlusion in nonhuman primates

Although it is well recognized that human platelet responses to alpha-thrombin are mediated by the protease-activated receptors PAR-1 and PAR-4, their role and relative importance in platelet-dependent human disease has not yet been elucidated. Because the expression profile of PARs in platelets from nonprimates differs from humans, we used cynomolgus monkeys to evaluate the role of PAR-1 in thrombosis. Based on reverse transcription-polymerase chain reaction, PAR expression in platelets from cynomolgus monkeys consisted primarily of PAR-1 and PAR-4, thereby mirroring the profile of human platelets. We probed the role of PAR-1 in a primate model of vascular injury-induced thrombosis with the selective PAR-1 antagonist (alpha S)-N-[(1S)-3-amino-1-[[(phenylmethyl)amino]carbonyl]propyl]-alpha-[[[[[1-(2,6-dichlorophenyl)methyl]-3-(1-pyrrolidinylmethyl)-1H-indazol-6-yl]amino]carbonyl]amino]-3,4-difluorobenzenepropanamide (RWJ-58259). After pretreatment with RWJ-58259 or vehicle, both carotid arteries of anesthetized monkeys were electrolytically injured and blood flow was monitored for 60 min. Time to occlusion was significantly extended after RWJ-58259 administration (27 +/- 3 to 53 +/- 8 min; p < 0.048). Vessels from three of the five treated animals remained patent. Ex vivo platelet aggregation measurements indicated complete PAR-1 inhibition, as well as an operational PAR-4 response. Immunohistochemical staining of mural thrombi with antibodies to the platelet marker CD61 and fibrinogen indicated that RWJ-58259 significantly reduced thrombus platelet deposition. Drug treatment had no effect on key hematological or coagulation parameters. Our results provide direct evidence that PAR-1 is the primary receptor that mediates alpha-thrombin's prothrombotic actions in primates and suggest that PAR-1 antagonists may have potential for the treatment of thrombotic disorders in humans.

An endovascular model of carotid stenosis for the evaluation of thrombolysis and angioplasty

PURPOSE

To develop a porcine carotid artery thrombosis model using a novel stent-graft device to evaluate the efficacy of thrombolytic therapy and angioplasty procedures.

METHODS

An endovascular device made from a tapered polytetrafluoroethylene graft inverted in a self-expanding nitinol stent was delivered to bilateral carotid arteries via a right femoral approach in 16 pigs. Carotid thrombotic occlusion ensued from flow stasis created by the intrastent stenosis. Via selective carotid catheterization from a femoral approach, urokinase (250,000 IU) was pulse-sprayed in one carotid artery while a control saline solution was infused in the contralateral vessel; delivery times were 1 hour, 8 hours, 3 days, or 6 days after carotid occlusion (4 animals per time period). After thrombolysis, balloon angioplasty was performed to maintain carotid patency. Arteriography and intravascular ultrasound were used to evaluate the efficacy of thrombolysis. Light microscopy was used for histological analysis of the thrombus.

RESULTS

Carotid artery occlusion occurred in 15+/-8 minutes after stent-graft placement in all animals. Urokinase was effective in recanalizing all occluded arteries in the 1-hour, 4-hour, and 3-day groups (100%) but was effective in only 2 of 4 animals in the 6-day group (p < 0.05). Overall thrombolytic efficacy was 78%+/-7%. Control saline solution showed no thrombolytic effect (p < 0.001). Angioplasty successfully restored normal luminal diameter in all fully lysed arteries (100%). Histological analysis showed fibrin-predominant thrombus with a varying degree of platelet deposition.

CONCLUSIONS

This endovascular approach, which creates a carotid stenosis using this novel stent-graft device, is reliable in producing carotid thrombosis. In our model, thrombolytic therapy was effective in restoring luminal patency, and the intraluminal stenosis is amenable to balloon angioplasty. The model is useful for the evaluation of antithrombotic therapy and adjunctive endovascular interventions.

Antithrombotic properties of RWJ-50353, a potent and novel thrombin inhibitor

The antithrombotic, anticoagulant, and kinetic properties of RWJ-50353, a novel, reversible, active-site-directed thrombin inhibitor, were evaluated. RWJ-50353 inhibited the catalytic activity of human alpha-thrombin with a K(i) of 0.19+/-0.02 nM. It showed a 16-fold selectivity relative to inhibition of trypsin and at least 330-fold selectivity relative to inhibition of other biologically important serine proteases. In a gel-filtered platelet preparation, RWJ-50353 inhibited alpha-thrombin-induced aggregation with an IC(50) of 32+/-6 nM. In a canine arteriovenous shunt antithrombotic model, RWJ-50353 demonstrated a significant dose-related (0.1-1.0 mg/kg, i.v.) reduction in thrombus formation with 50% inhibition (ID(50)) obtained at 0.46+/-0.1 mg/kg. In a rabbit deep vein thrombosis model, RWJ-50353 dose-dependently (0.1-1. 0 mg/kg, i.v.) reduced thrombus formation with an ID(50) of 0.25+/-0. 03 mg/kg. The antithrombotic activity in both of these models was associated with only mild prolongations in bleeding time and coagulation parameters. These results demonstrate that RWJ-50353 is a potent, selective thrombin inhibitor that is an effective antithrombotic agent after intravenous administration in models of arterial and venous thrombosis and may be useful in the management of various thrombotic disorders.

Antithrombotic effects of BCH 2763, a new direct thrombin inhibitor, in a canine model of venous thrombosis

Deep venous thrombosis (DVT) is a common cardiovascular disease, resulting in significant mortality each year in the United States. Direct thrombin inhibitors represent a new class of drugs that could potentially be better than conventional antithrombotic therapy based on indirect inhibition of coagulation factors with heparin and warfarin. BCH 2763 is a potent, selective bifunctional thrombin inhibitor that blocks both the active catalytic site and the anion binding exosite. The objective of this study is to test the antithrombotic efficacy of BCH 2763 in a canine model of DVT induced through electrolytic injury to the femoral vein. BCH 2763 was administered at three dose levels: 0.125 mg/kg bolus followed by 10 microg/kg/min IV infusion (low-dose; n = 5), 0.25 mg/kg bolus followed by 20 microg/kg/min infusion (mid-dose; n = 5), and 0.75 mg/kg bolus followed by 60 microg/kg/min (high-dose; n = 5). The control group (n = 5) received a 5-ml intravenous bolus of saline followed by a 1 mL/kg/h infusion. The parameters evaluated were changes in activated partial thromboplastin time (aPTT), thrombin time (TT), prothrombin time (PT), time to formation of an occlusive thrombus in the femoral vein, and the amount of venous blood flow delivered over the course of the experiment. There were significant dose-dependent increases in aPTT, TT, and PT in the BCH 2763-treated animals compared with the control group. The time to formation of an occlusive thrombus in the control group averaged 69.6 +/- 9 minutes. Treatment with BCH 2763 prolonged the time to occlusion to 126.4 +/- 13 minutes in the low-dose group, 155.4 +/- 17 minutes in the mid-dose group, and 229 +/- 7 minutes in the high-dose group (80% remained patent for the duration of the study), which were all significantly greater than the controls. Femoral venous blood flow was significantly greater in the mid-dose (51 +/- 8%) and the high-dose (70 +/- 6%) groups compared with the control vessels (22 +/- 3%). In conclusion, the results of this study indicate that BCH 2763 is an effective intravenous antithrombotic agent in the canine electrolytic injury model of venous thrombosis.

Effects of Intravenous Enoxaparin and Intravenous Inogatran in an Electrolytic Injury Model of Venous Thrombosis in the Dog

The objective of this study was to compare the effectiveness of the low molecular weight heparin, enoxaparin (Lovenox((R))), and inogatran (a direct thrombin inhibitor) in a canine electrolytic injury model of venous thrombosis. Effectiveness was defined as the ability of either drug to prolong the following parameters: activated partial thromboplastin time (aPTT), thrombin time (TT), prothrombin time (PT), and time to formation of an occlusive thrombus in the vein. There were 5 dogs and 10 vessels for each group (the right and left femoral veins were used in each dog to measure time to occlusion). Dogs were randomly assigned to one of six groups: (1) saline controls; (2) low-dose inogatran (0.075 mg/kg IV bolus followed by a 5 µg/kg/min infusion); (3) mid-dose inogatran (0.25 mg/kg IV bolus followed by a 20 µg/kg/min infusion); (4) high-dose inogatran (0.75 mg/kg IV bolus followed by a 50 µg/kg/min infusion); (5) low-dose enoxaparin (100 units/kg IV bolus followed by a 50 U/kg/h infusion); and (6) high-dose enoxaparin (200 U/kg IV bolus followed by a 100 U/kg/h infusion). Administration of inogatran resulted in dose-dependent increases in aPTT, TT, and PT, and administration of enoxaparin resulted in dose-dependent increases in aPTT and TT. There were no changes in hemodynamics. The time to occlusion in the control group averaged 81.7 +/- 9.9 minutes compared with 141.8 +/- 12.7, 185.8 +/- 17.6, and 226.9 +/- 8.8 minutes with the low, mid, and high doses of inogatran, and 131 +/- 20.3, and 183.0 +/- 19.0 minutes with the low and high doses of enoxaparin. Bleeding times were elevated by inogatran and enoxaparin, but no appreciable differences were detected between the two compounds. In summary, the direct thrombin inhibitor inogatran, administered intravenously, was as effective as the low molecular weight heparin enoxaparin in a canine model of venous thrombosis induced by electrolytic injury, supporting the conclusion that direct antithrombins may prove useful for prevention and treatment of deep venous thrombosis.