Direct thrombin inhibitors in cardiovascular medicine

Aptamer-thrombin loaded magnetic microspheres for bio-specific extraction and precise detection of hirudin

Hirudin, that is naturally occurring in leeches (Hirudo medicinalis) and known as the most potent natural inhibitor of thrombin, exerts double-edged effects in clinic application. It can be used as a therapeutic ingredient for cardiovascular disease, while it can be regarded as a toxic polypeptide with bleeding risk. Effective detection of hirudin in biological samples contributes greatly to reasonable therapy. In this study, we proposed a smart adsorbent based on affinity magnetic microspheres, where thrombin was immobilized for capturing hirudin in the animal serum. Aptamer was introduced as a ligand for linking the magnetic agarose microspheres and thrombin, thereby avoiding loss of biological activity of the enzyme to hirudin. Taken recombinant hirudin variant 2-Lys47 (rHV2) as a model, we established a rapid and bio-specific extraction method coupled with liquid chromatography and quadrupole-time-of-flight mass spectrometry (LC-QTOF/MS) for determination of hirudin in the serum. Owing to this strategy, a low limit of detection (LOD) of rHV2 (0.5 nM), a good linearity with correlation coefficient of 0.9975, an acceptable precision with relative standard deviation (RSD) below 3.6% (n = 6) and acceptable recoveries ranging from 85.7% to 90.2% were achieved. Moreover, the functionalized magnetic composite could be reused for at least nine cycles. Our work combined the merits of affinity separation and advanced instrument analysis for hirudin, providing a new vision to precise determination of hirudin in medical and pharmaceutical fields.

Safety and Efficacy of Periprocedural Heparin Plus a Short-Term Infusion of Tirofiban Versus Bivalirudin Monotherapy in Patients Who Underwent Percutaneous Coronary Intervention (from the Intermountain Heart Institute STAIR Observational Registry)

Glycoprotein IIb/IIIa inhibitors, used as a standard intravenous bolus followed by a prolonged infusion for 12 to 18 hours, reduces ischemic complications during percutaneous coronary interventions (PCI) but often at a cost of increased bleeding. Today, when dual oral antiplatelet therapy is routine, heparin use plus short-term (bolus alone or with a <6 hours infusion) glycoprotein IIb/IIIa inhibitors, or bivalirudin monotherapy, have been proposed as potentially superior alternatives. This observational study evaluated the safety and efficacy of heparin plus short-term tirofiban versus bivalirudin monotherapy during PCI. Patients with successful PCI and no cardiogenic shock who were anticoagulated with either of the above regimens were followed for 30-day major bleeding and major adverse cardiovascular events (death, nonfatal myocardial infarction, and urgent target vessel revascularization) at 30 days, 1 year, and long term. A total of 727 patients receiving tirofiban (age = 63 ± 13 years, males = 76%, ACS presentation = 75%, radial access = 51%) and 459 patients receiving bivalirudin, (age = 65 ± 13 years, males = 71%, ACS presentation = 78%, radial access = 18%) were included. Thirty-day major bleeding was 0.7% and 4.1% for tirofiban and bivalirudin, respectively (adjusted odds ratio = 0.17 [0.06, 0.46], p = 0.001). During 30-day, 1-year, and long-term (1.7 ± 0.9 years) follow-up, major adverse cardiovascular events risk did not differ significantly between tirofiban and bivalirudin. However, long-term death was significantly lower in those receiving tirofiban (adjusted hazard ratio = 0.58 [0.34, 1.00], p = 0.05). In conclusion, in this observational study, PCI patients receiving heparin plus short-term tirofiban experienced significantly lower 30-day major bleeding, and improved long-term survival, than those receiving bivalirudin monotherapy.

EP217609, a neutralisable dual-action FIIa/FXa anticoagulant, with antithrombotic effects in arterial thrombosis

EP217609 is a new synthetic parenteral dual-action anticoagulant combining a direct thrombin inhibitor (α-NAPAP analog), an indirect factor Xa inhibitor (fondaparinux analog) and a biotin moiety allowing its neutralisation. EP217609 exhibited similar in vitro anticoagulant properties as its parent compounds. On the basis of dose-response curves, we identified low and moderate doses of EP217609 resulting in similar ex vivo prolongation of the APTT as α-NAPAP analog and comparable ex vivo anti-FXa activity as fondaparinux. The effects of EP217609 were compared to those of its parent compounds used alone or in combination in two models of experimental thrombosis induced by FeCl3 injury of the carotid artery or mechanical injury of atherosclerotic plaques in ApoE-deficient mice. When administered at low doses increasing the APTT by only 1.1 fold, EP217609 significantly reduced the thrombus area in both models as compared to α-NAPAP analog or fondaparinux alone, but not to the combination of these drugs. In contrast, at higher doses increasing the APTT 1.5 times, EP217609 was not superior to either parent compound. Low doses of EP217609 did not prolong the tail bleeding time or increase the volume of blood loss, although a tendency towards an increased blood loss was observed in five out of 12 mice. Finally, the effects of EP217609 could be neutralised in vivo by injection of avidin. The pharmacological profile of EP217609, its performance in arterial thrombosis models and its possible neutralisation make it an interesting molecule and a potential candidate as an antithrombotic drug.

Optical sensing of anticoagulation status: Towards point-of-care coagulation testing

Anticoagulant overdose is associated with major bleeding complications. Rapid coagulation sensing may ensure safe and accurate anticoagulant dosing and reduce bleeding risk. Here, we report the novel use of Laser Speckle Rheology (LSR) for measuring anticoagulation and haemodilution status in whole blood. In the LSR approach, blood from 12 patients and 4 swine was placed in disposable cartridges and time-varying intensity fluctuations of laser speckle patterns were measured to quantify the viscoelastic modulus during clotting. Coagulation parameters, mainly clotting time, clot progression rate (α-angle) and maximum clot stiffness (MA) were derived from the clot viscoelasticity trace and compared with standard Thromboelastography (TEG). To demonstrate the capability for anticoagulation sensing in patients, blood samples from 12 patients treated with warfarin anticoagulant were analyzed. LSR clotting time correlated with prothrombin and activated partial thromboplastin time (r = 0.57-0.77, p<0.04) and all LSR parameters demonstrated good correlation with TEG (r = 0.61-0.87, p<0.04). To further evaluate the dose-dependent sensitivity of LSR parameters, swine blood was spiked with varying concentrations of heparin, argatroban and rivaroxaban or serially diluted with saline. We observed that anticoagulant treatments prolonged LSR clotting time in a dose-dependent manner that correlated closely with TEG (r = 0.99, p<0.01). LSR angle was unaltered by anticoagulation whereas TEG angle presented dose-dependent diminution likely linked to the mechanical manipulation of the clot. In both LSR and TEG, MA was largely unaffected by anticoagulation, and LSR presented a higher sensitivity to increased haemodilution in comparison to TEG (p<0.01). Our results establish that LSR rapidly and accurately measures the response of various anticoagulants, opening the opportunity for routine anticoagulation monitoring at the point-of-care or for patient self-testing.

The Future of Anticoagulation

Anticoagulant agents, such as unfractionated heparin and warfarin, have been in use for roughly 50 years. Over the past decade, injectable agents such as low-molecular-weight heparins, pentasaccharide, and direct thrombin inhibitors have been major advances in preventing and treating thrombosis. Despite these somewhat recent additions, there is still enormous potential to improve on the pharmacokinetic and pharmacodynamic properties of these agents, as well as improve patient outcomes. There are currently a large number of anticoagulant agents (injectable and oral) that could be available for use in the next several years. Many of these new agents have unique mechanisms that may provide practitioners with anticoagulant alternatives. This review gives a detailed analysis of the anticoagulant agents that may add to our armamentarium in the management of thrombosis.

State-of-the-Art Review: The Preclinical and Clinical Pharmacology of Novastan (Argatroban): A Small-Molecule, Direct Thrombin Inhibitor

Because of the unsatisfactory options available for safe and effective antithrombotic therapy, recent, intense research and development efforts have been focused on direct thrombin inhibitors, also known as site-directed thrombin inhibitors. The intravenous agent Novastan (argatroban) is a small-molecule, reversible, direct thrombin inhibitor that is selective for the catalytic site of the thrombin molecule. Argatroban's molecular properties (small molecule; fast, selective, and reversible inhibition of the thrombin catalytic site; and similar in vitro potency for inhibiting both clot-bound and soluble thrombin) offer the potential for significant antithrombotic efficacy with minimal systemic anticoagulant ef fects. Its clinical pharmacologic properties offer the potential for minimal risk of bleeding, very rapid achievement of therapeutic antithrombotic efficacy, predictable dose-response, and rapid restoration of the hemostatic systems to normal upon termination of intravenous infusion. Argatroban is currently approved for clinical use in Japan for the treatment of peripheral arterial occlusive disease. It is in advanced clinical development in North America, South America, and Western Europe for several clinical indications, including (1) adjunctive therapy to thrombolytic agents in the treatment of acute myocardial infarction and (2) antithrombotic therapy for patients with heparin-induced thrombocytopenia and heparin-induced thrombocytopenia and thrombosis syndrome. Key Words: Molecular properties—Novastan (argatroban)—Pharmacology—Thrombin inhibitor.

Heparin is Not Inferior to Bivalirudin in Percutaneous Coronary Intervention-Focusing on the Effect of Glycoprotein IIb/IIIa Inhibitor Use: A Meta-Analysis

Our aim was to compare the efficacy and safety of bivalirudin (Biv) versus heparin (Hep) with or without similar usage rate of glycoprotein IIb/IIIa inhibitors (GPIs) during percutaneous coronary intervention (PCI). The PubMed and EMbase were searched. Randomized trials comparing Biv versus Hep were eligible for inclusion. With imbalanced GPI use, Biv had significantly lower major bleeding (pooled risk ratio [RR], 0.67; 95% confidence interval [CI], 0.54-0.83) without difference in mortality (pooled RR, 0.95; 95% CI, 0.80-1.14). With comparable GPI use, no significant difference was observed in major bleeding (pooled RR, 0.95; 95% CI, 0.82-1.10) and mortality (pooled RR, 1.13; 95% CI, 0.85-1.50). With no GPI use, Biv was associated with numerically higher mortality (pooled RR, 1.17; 95% CI, 0.83-1.65) without significant difference in major bleeding (pooled RR, 0.81; 95% CI, 0.64-1.02). In conclusion, when comparing different anticoagulants during PCI, the effect of GPIs should not be underestimated. Heparin as such was found noninferior to Biv.

An objective comparison between bivalirudin and heparin during peripheral vascular interventions

ABSTRACT 

Patients undergoing percutaneous peripheral interventions are at increased risk for thrombotic complications hence the routine use of periprocedural anticoagulants. There is currently no American College of Cardiology/American Heart Association guidelines for periprocedural anticoagulants use in percutaneous peripheral interventions. Historically, unfractionated heparin has been the most common periprocedural anticoagulant used during percutaneous peripheral interventions. There may be a role for more predictable periprocedural anticoagulants in percutaneous peripheral interventions as has been demonstrated in percutaneous coronary interventions. Our review focuses on the evidence supporting the use of bivalirudin in percutaneous peripheral interventions.

Meta-analysis of randomized clinical trials comparing bivalirudin versus heparin plus glycoprotein IIb/IIIa inhibitors in patients undergoing percutaneous coronary intervention and in patients with ST-segment elevation myocardial infarction

This study sought to investigate the relative safety and efficacy of bivalirudin versus heparin plus glycoprotein (GP) IIb/IIIa inhibitors in patients undergoing percutaneous coronary intervention (PCI) and in those with ST-segment elevation myocardial infarction (STEMI). The safety of bivalirudin in PCI, particularly in patients with STEMI, continues to be debated. We searched the on-line databases for randomized controlled trials of bivalirudin versus heparin plus GP IIb/IIIa inhibitors. Data on study design, inclusion and exclusion criteria, sample characteristics, and clinical outcomes at 30 days were extracted. A total of 19,856 PCI patients included in 7 randomized trials and 5,820 patients with STEMI included in 2 randomized trials were separately analyzed. At 30 days, bivalirudin use in patients undergoing PCI resulted in similar rates of death, myocardial infarction, repeat revascularization, and stent thrombosis. In patients with STEMI, bivalirudin use resulted in decreased cardiac mortality (risk ratio [RR] 0.70, 95% confidence interval [CI] 0.50 to 0.97, p=0.03) compared with heparin plus GP IIb/IIIa inhibitors but an increase in definite stent thrombosis at 30 days (RR 1.88, 95% CI 1.09 to 3.24, p=0.02) driven by an increase in acute stent thrombosis (RR 5.48, 95% CI 2.30 to 13.07, p=0.0001). Bivalirudin use was associated with a decrease in Thrombolysis In Myocardial Infarction (TIMI) major (RR 0.58, 95% CI 0.46 to 0.74, p<0.0001) and TIMI minor (RR 0.55, 95% CI 0.48 to 0.63, p<0.0001) bleeding rates in PCI patients as well as in a subgroup of patients with STEMI. In conclusion, in PCI patients anticoagulation with bivalirudin results in similar ischemic adverse events and a reduction in TIMI major and minor bleeding at 30 days compared with heparin plus GP IIb/IIIa inhibitors. In patients with STEMI, bivalirudin use is associated with a reduction in TIMI major and minor bleeding and fewer deaths from cardiac causes but an increase in acute and 30-day definite stent thrombosis.

Thrombin-targeted liposomes establish a sustained localized anticlotting barrier against acute thrombosis

The goal of the present work was to design and test an acute-use nanoparticle-based antithrombotic agent that exhibits sustained local inhibition of thrombin without requiring a systemic anticoagulant effect to function against acute arterial thrombosis. To demonstrate proof of concept, we functionalized the surface of liposomes with multiple copies of the direct thrombin inhibitor, d-phenylalanyl-l-prolyl-l-arginyl-chloromethyl ketone (PPACK), which exhibits high affinity for thrombin as a free agent but manifests too rapid clearance in vivo to be effective alone. The PPACK-liposomes were formulated as single unilamellar vesicles, with a diameter of 170.78 ± 10.59 nm and a near neutral charge. In vitro models confirmed the inhibitory activity of PPACK-liposomes, demonstrating a KI' of 172.6 nM. In experimental clots in vitro, treatment of formed clots completely abrogated any further clotting upon exposure to human plasma. The liposomes were evaluated in vivo in a model of photochemical-induced carotid artery injury, resulting in significantly prolonged arterial occlusion time over that of controls (69.06 ± 5.65 min for saline treatment, N = 6, 71.33 ± 9.46 min for free PPACK treated; N = 4, 85.75 ± 18.24 min for precursor liposomes; N = 4, 139.75 ± 20.46 min for PPACK-liposomes; P = 0.0049, N = 6). Systemic anticoagulant profiles revealed a rapid return to control levels within 50 min, while still maintaining antithrombin activity at the injury site. The establishment of a potent and long-acting anticoagulant surface over a newly forming clot with the use of thrombin targeted nanoparticles that do not require systemic anticoagulation to be effective offers an alternative site-targeted approach to the management of acute thrombosis.

Bivalirudin in acute coronary syndromes and percutaneous coronary intervention: should we use it?

Major bleeding remains a major risk factor for percutaneous coronary intervention of acute coronary syndromes and is associated with higher morbidity, mortality, prolonged hospital stay and costs. With the recognition that bleeding is an important factor in patient outcomes, the prevention of bleeding has become as important a goal as the prevention of ischaemia. The direct thrombin inhibitor bivalirudin has been shown to reduce ischaemia and importantly, is associated with less bleeding. In this article we review the evidence base that supports the use of bivalirudin across all spectrums of coronary syndromes and percutaneous coronary intervention. An algorithm for the use of bivalirudin in high risk subgroups and coronary syndromes is suggested.

Selective light-triggered release of DNA from gold nanorods switches blood clotting on and off

Blood clotting is a precise cascade engineered to form a clot with temporal and spatial control. Current control of blood clotting is achieved predominantly by anticoagulants and thus inherently one-sided. Here we use a pair of nanorods (NRs) to provide a two-way switch for the blood clotting cascade by utilizing their ability to selectively release species on their surface under two different laser excitations. We selectively trigger release of a thrombin binding aptamer from one nanorod, inhibiting blood clotting and resulting in increased clotting time. We then release the complementary DNA as an antidote from the other NR, reversing the effect of the aptamer and restoring blood clotting. Thus, the nanorod pair acts as an on/off switch. One challenge for nanobiotechnology is the bio-nano interface, where coronas of weakly adsorbed proteins can obscure biomolecular function. We exploit these adsorbed proteins to increase aptamer and antidote loading on the nanorods.

Specificity and selectivity profile of EP217609: a new neutralizable dual-action anticoagulant that targets thrombin and factor Xa

EP217609 is a new dual-action parenteral anticoagulant that combines an indirect factor Xa inhibitor (fondaparinux analog) and a direct thrombin inhibitor (α-NAPAP analog) in a single molecule together with a biotin tag to allow avidin neutralization. EP217609 exhibits an unprecedented pharmacologic profile in showing high bioavailability, long plasma half-life, and potent antithrombotic activity in animals without the complications of thrombin rebound. Here we report the exceptional specificity and selectivity profile of EP217609. EP217609 inhibited thrombin with rapid kinetics (k(on) > 10(7)M(-1)s(-1)), a high affinity (K(I) = 30-40pM), and more than 1000-fold selectivity over other coagulation and fibrinolytic protease targets, comparing favorably with the best direct thrombin inhibitors known. EP217609 bound antithrombin with high affinity (K(D) = 30nM) and activated the serpin to rapidly (k(ass) ∼ 10(6)M(-1)s(-1)) and selectively (> 20-fold) inhibit factor Xa. The dual inhibitor moieties of EP217609 acted largely independently with only modest linkage effects of ligand occupancy of one inhibitor moiety on the potency of the other (∼ 5-fold). In contrast, avidin binding effectively neutralized the potency of both inhibitor moieties (20- to 100-fold). These findings demonstrate the superior anticoagulant efficacy and rapid avidin neutralizability of EP217609 compared with anticoagulants that target thrombin or factor Xa alone.

Animal models of DIC and their relevance to human DIC: a systematic review

Disseminated intravascular coagulation (DIC) is a severe clinical condition with activation of coagulation and fibrinolysis. Its diagnosis is based on the International Society of Thrombosis and Haemostasis (ISTH) scoring system of DIC. Animal models of DIC, used to investigate pathophysiology and evaluate treatments, have not been developed in a standardized way, which impedes comparison between models and translation to the human setting. In the current review of animal models of DIC an overview of species, inducers, and dosing regimens is provided. Diagnostic approaches are compared in the light of the ISTH score and treatments tested in animal models of DIC are summarized. Systematic analysis revealed that the rat is by far the preferred species amongst animal models of DIC and lipopolysaccharides (LPS) the preferred inducer of DIC. An overview of the reporting of ISTH DIC score parameters elucidated that only about 25% of the studies measure all of the four parameters necessary for the implementation the ISTH scoring system. Furthermore, most therapeutic interventions tested in animal models of DIC are administered prophylactically, which may be irrelevant to the clinical setting and could explain why compounds effective in preclinical animal models often fail in clinical trials. It is concluded that Implementation of a scoring system in animal models of DIC may increase the ability to compare DIC amongst animal models and improve the translational aspect of treatment effect.

Stroke prevention treatment of patients with atrial fibrillation: old and new

Atrial fibrillation is the most common cause of cardioembolic ischemic stroke and has a rising prevalence worldwide. Stroke prevention in this condition is poised to take a substantial leap forward with the evolution of new anticoagulant medications, with superior properties compared to vitamin K antagonists. New, safer and more effective chronic therapy is on the horizon. However, many issues surrounding the management of stroke prevention after an acute stroke and during the course of chronic anticoagulant therapy remain to be resolved.

Fondaparinux (Arixtra®), a Safe Alternative for the Treatment of Patients With Heparin-Induced Thrombocytopenia?

Fondaparinux, a pentasaccharide which selectively binds to antithrombin III, has negligible to no cross-reactivity with heparin-induced thrombocytopenia (HIT) antibodies in in vitro studies. The lack of cross-reactivity suggests a potential role in the management of HIT, and indeed, there are several such case reports and small studies. These published data have used both the prophylactic and weight-based treatment doses. However, due to the small possibility of developing HIT with thromboembolic complications while receiving fondaparinux, it is suggested that the appropriate weight-based treatment dose be used. In all these reports, fondaparinux provided adequate anticoagulation, prevented further thromboembolic events, and platelet counts returned to normal. However, there have been a couple of case reports on possible HIT or HIT-like syndrome secondary to fondaparinux use. Conclusion: Fondaparinux is an attractive anticoagulant therapy in patients with HIT. There is still the need for larger randomized trials evaluating the true efficacy, appropriate dose, safe duration of treatment, and the true incidence of HIT associated with fondaparinux.

New classes of anticoagulation and antiplatelet agents: preprocedure management and safety guidelines for imaging-guided intervention

OBJECTIVE

New medications are available for prophylaxis of deep venous thrombosis, the treatment of venous thromboembolism, and also to reduce the risk of acute coronary syndrome and stroke. The purpose of this review is to provide the radiologist a practical and succinct summary of the new anticoagulation and antiplatelet medications and how to manage these medications in patients who are in need of a radiology intervention.

CONCLUSION

This article provides recommendations for preprocedure management of new anticoagulants and antiplatelet agents in patients undergoing radiology intervention.

Impact of bivalirudin on outcomes after percutaneous coronary revascularization with drug-eluting stents

BACKGROUND

The direct thrombin inhibitor bivalirudin has been found to be noninferior to heparin plus planned glycoprotein (GP) IIb/IIIa blockade in the prevention of acute ischemic end points and 1-year mortality after percutaneous coronary intervention (PCI) with bare metal stents. We investigated whether long-term outcomes after bivalirudin use remained comparable to heparin plus GP IIb/IIIa blockade in current clinical practice of drug-eluting stent use.

METHODS

Using the 2004-2005 Cornell Angioplasty Registry, we studied 2504 consecutive patients undergoing urgent or elective PCI with periprocedural use of bivalirudin or heparin plus GP IIb/IIIa platelet inhibitors. Patients presenting with an acute ST-elevation myocardial infarction (MI) < or = 24 hours, thrombolytic therapy < or = 7 days, hemodynamic instability/shock, or renal insufficiency were excluded.

RESULTS

Of the study cohort, 1340 patients (54%) received bivalirudin and 1164 patients (46%) received heparin plus GP IIb/IIIa blockade. The incidence of inhospital mortality (0.3% vs 0.2%, P = .692), MI (6.6% vs 8.1%, P = .191), and combined end point of death, stroke, emergent coronary artery bypass graft/PCI, and MI (6.9% vs 8.3%, P = .199) was similar in the bivalirudin and heparin plus GP IIb/IIIa inhibitor groups. There was a lower incidence of major (0.7% vs 1.9%, P = .012) and minor bleeding (9.6% vs 15.6%, P < .001) in the bivalirudin versus heparin plus GP IIb/IIIa inhibitor group. Mean clinical follow-up was 24.8 +/- 7.7 months. At follow-up, there were 87 (6.5%) deaths in the bivalirudin group versus 42 (3.6%) in the heparin plus GP IIb/IIIa inhibitor group (hazard ratio 1.87, 95% CI 1.30-2.71, P = .001). After a propensity score adjusted multivariate Cox analysis, bivalirudin use was associated with a nonsignificant trend toward increased long-term mortality (hazard ratio 1.45, 95% CI 0.98-2.16, P = .065).

CONCLUSIONS

Compared with heparin plus GP IIb/IIIa inhibition, routine use of bivalirudin as the procedural anticoagulant in contemporary PCI with drug-eluting stents was associated with lower rates of inhospital complications and similar long-term all-cause mortality.

Thiophene-anthranilamides as highly potent and orally available factor Xa inhibitors

There remains a high unmet medical need for a safe oral therapy for thrombotic disorders. The serine protease factor Xa (fXa), with its central role in the coagulation cascade, is among the more promising targets for anticoagulant therapy and has been the subject of intensive drug discovery efforts. Investigation of a hit from high-throughput screening identified a series of thiophene-substituted anthranilamides as potent nonamidine fXa inhibitors. Lead optimization by incorporation of hydrophilic groups led to the discovery of compounds with picomolar inhibitory potency and micromolar in vitro anticoagulant activity. Based on their high potency, selectivity, oral pharmacokinetics, and efficacy in a rat venous stasis model of thrombosis, compounds ZK 814048 (10b), ZK 810388 (13a), and ZK 813039 (17m) were advanced into development.

Bivalirudin in patients with acute coronary syndromes undergoing percutaneous coronary intervention: a subgroup analysis from the Acute Catheterization and Urgent Intervention Triage strategy (ACUITY) trial

BACKGROUND

The aim of this study was to assess anticoagulation with the direct thrombin inhibitor bivalirudin during percutaneous coronary intervention in individuals with moderate and high-risk acute coronary syndromes.

METHODS

13,819 individuals in the Acute Catheterization and Urgent Intervention Triage strategy (ACUITY) trial were prospectively randomly assigned to receive heparin (unfractionated or enoxaparin) plus glycoprotein IIb/IIIa inhibitors, bivalirudin plus glycoprotein IIb/IIIa inhibitors, or bivalirudin alone. Of these individuals, 7789 underwent percutaneous coronary intervention after angiography. The effect of the three regimens on the primary 30-day endpoints of composite ischaemia (death, myocardial infarction, or unplanned revascularisation for ischaemia), major bleeding, and net clinical outcomes (composite ischaemia or major bleeding) was assessed in this subgroup. Analyses were done by intention to treat. This trial is registered with ClinicalTrials.gov, with the number NCT00093158.

FINDINGS

Of the individuals who underwent percutaneous coronary intervention, 2561 received heparin plus glycoprotein IIb/IIIa inhibitors, 2609 received bivalirudin plus glycoprotein IIb/IIIa inhibitors, and 2619 received bivalirudin alone. 26 (0.3%) individuals dropped out or were lost to follow-up. There was no significant difference in the proportion of individuals with composite ischaemia, major bleeding, or net clinical outcomes at 30 days between those who received bivalirudin plus glycoprotein IIb/IIIa inhibitors and those who received heparin plus glycoprotein IIb/IIIa inhibitors (composite ischaemia: 243 [9%] patients vs 210 [8%] patients, p=0.16; major bleeding: 196 [8%] patients vs 174 [7%] patients, p=0.32; net clinical outcomes: 389 [15%] patients vs 341 [13%] patients, p=0.1). Rates of composite ischaemia were much the same in those who received bivalirudin alone and those who received heparin plus glycoprotein IIb/IIIa inhibitors (230 [9%] patients vs 210 [8%] patients, p=0.45); however, there were significantly fewer individuals who experienced major bleeding among those who received bivalirudin alone than among those who received heparin plus glycoprotein IIb/IIIa inhibitors (92 [4%] patients vs 174 [7%] patients, p<0.0001, relative risk 0.52, 95% CI 0.40-0.66), resulting in a trend towards better 30-day net clinical outcomes (303 [12%] patients vs 341 [13%] patients, p=0.057; 0.87, 0.75-1.00).

INTERPRETATION

Substitution of unfractionated heparin or enoxaparin with bivalirudin results in comparable clinical outcomes in patients with moderate and high-risk acute coronary syndromes treated with glycoprotein IIb/IIIa inhibitors in whom percutaneous coronary intervention is done. Anticoagulation with bivalirudin alone suppresses adverse ischaemic events to a similar extent as does heparin plus glycoprotein IIb/IIIa inhibitors, while significantly lowering the risk of major haemorrhagic complications.

A functional clotting assay to monitor the hirudin dosage

Hirudin, a direct thrombin inhibitor, has potential advantages over indirect thrombin inhibitors and is increasingly used in clinical settings. There are, however, large variations in individual responses to this drug and no recognized clinical laboratory tests used to monitor its anticoagulant effects. We evaluated the use of the thromboelastograph, a common clinical coagulation instrument, to monitor the effects of hirudin in vitro. We developed a novel, whole blood clotting assay that utilizes the tissue factor stimulating properties of mercuric ion to measure the anticoagulant potential of therapeutic doses of hirudin. At doses equivalent to those found in the therapeutic range, the thromboelastograph was capable of showing significant changes when compared with control and different concentrations of hirudin (P < 0.05). A linear relationship was observed between increasing concentrations of recombinant hirudin and clotting times. In conclusion, the use of this test system warrants further investigation for monitoring hirudin.

Outcomes of patients with acute coronary syndromes who are treated with bivalirudin during percutaneous coronary intervention: an analysis from the Randomized Evaluation in PCI Linking Angiomax to Reduced Clinical Events (REPLACE-2) trial

BACKGROUND

The REPLACE-2 trial demonstrated that bivalirudin with provisional glycoprotein IIb/IIIa (GPIIb/IIIa) inhibition is not inferior to heparin plus GPIIb/IIIa inhibition in patients undergoing percutaneous coronary intervention. The extent to which this applies to patients with acute coronary syndromes (ACS) is unclear. Therefore, we sought to determine if bivalirudin has similar efficacy in ACS patients as compared with "stable" patients in the REPLACE-2 trial.

METHODS

We analyzed the outcomes of ACS patients compared with stable patients and the outcomes of ACS patients according to whether or not they had received bivalirudin, including the economic costs. The trial enrolled 1351 ACS patients (myocardial infarction within 7 days or unstable angina within 48 hours, but not on ongoing GPIIb/IIIa or heparin therapy) and 4554 stable patients.

RESULTS

Patients with ACS had a similar rate of death or myocardial infarction at 30 days compared to stable patients (7.2% vs 6.7%, P = .51) and death at 1 year (1.6% vs 2.2%, P = .169), but a higher rate of urgent coronary artery bypass graft at 30 days (1.0% vs 0.3%, P = .002). Patients with ACS treated with bivalirudin had a similar rate of 30-day death, myocardial infarction, or urgent revascularization compared with ACS patients treated with heparin and GPIIb/IIIa inhibitors (8.7% vs 8.0%, P = .616) and death at 1 year (1.5% vs 1.8%, P = .701), but a higher rate of revascularization at 6 months (12% vs 8.4%, P = .04). Patients with ACS treated with bivalirudin had less major bleeding than ACS patients treated with heparin and GPIIb/IIIa inhibitors, although this was not statistically significant (2.7% vs 4.5%, P = .07). Mean 30-day costs for patients with ACS were dollar 12415 for those treated with bivalirudin and dollar 12806 for those treated with heparin plus GPIIb/IIIa inhibitors (P = .022).

CONCLUSION

Bivalirudin with provisional GPIIb/IIIa inhibitor use in low-risk ACS patients (not receiving preprocedural GPIIb/IIIa blockade) appears to provide similar protection against death and myocardial infarction as the combination of heparin and GPIIb/IIIa inhibitors, although we observed a higher rate of revascularization at 6 months.

Emerging role of direct thrombin inhibitors in nonvalvular atrial fibrillation: potential and peril

Ximelagatran, an emerging new direct, oral, fixed-dose thrombin inhibitor may offer an attractive alternate to warfarin for patients with nonvalvular atrial fibrillation. The lack of drug-to-drug interactions and need for coagulation monitoring parameters such as international normalized ratio and a short half-life make therapeutic control and withdrawal in the event of bleeding easier. The side-effect profile, including elevation of liver enzymes, may temper the clinical utility of long-term use ximelagatran.

Synthetic heparin derivatives as new anticoagulant drugs

The journey towards a detailed mechanistic understanding of the anticoagulant action of heparin has resulted in synthetic mimetics with improved pharmacodynamic profiles. Inspired by the ternary complex formation of heparin with antithrombin III and thrombin, the active pentasaccharide fondaparinux has been succeeded by several clinical candidates, such as SR123781, that have tailor-made factor Xa and thrombin inhibitory activities combined with less aspecific binding (e.g. binding to platelet factor 4 involved in thrombocytopenia). Novel compounds with both antithrombin III-mediated inhibition of factor Xa and direct thrombin inhibition are emerging. Org42675 is one such compound, balancing dual inhibition of factor Xa and thrombin in one anticoagulant drug, with excellent pharmacokinetic properties and strong inhibitory activity toward clot-bound thrombin.

Ximelagatran: Pharmacology, Pharmacokinetics, and Pharmacodynamics

Thromboembolism is the largest cause of morbidity and mortality in the western world, yet oral anticoagulation is currently available only with vitamin K antagonists--most often, warfarin. Warfarin has been used for treatment of thrombotic disease for about 50 years. However, despite its widespread use, it is associated with several limitations, such as varied patient response, a narrow therapeutic window, numerous drug and food interactions, and need for frequent therapeutic monitoring. In addition, its full anticoagulant effect usually takes at least 4-5 days after the start of therapy or any dosage change, and it has a slow offset of therapy. A new oral anticoagulant, ximelagatran, has considerable advantages compared with warfarin. The agent requires no therapeutic monitoring, has a wide therapeutic window, and is not known to interact with food or drugs. The advantages ximelagatran brings to clinical practice should be a welcome addition to the options for management of thrombotic disease.

Comparison of bivalirudin versus heparin during percutaneous coronary intervention (the Randomized Evaluation of PCI Linking Angiomax to Reduced Clinical Events [REPLACE]-1 trial)

To assess the efficacy of the direct thrombin inhibitor bivalirudin relative to heparin during contemporary coronary intervention, 1,056 patients who underwent elective or urgent revascularization were randomized in a large-scale pilot study to receive heparin (70 U/kg initial bolus) or bivalirudin (0.75 mg/kg bolus, 1.75 mg/kg/hour infusion during the procedure). All patients received aspirin; pretreatment with clopidogrel was encouraged, and glycoprotein (GP) IIb/IIIa blockade was at the physician's discretion. Stents were placed in 85% of patients; 72% received a GP IIb/IIIa inhibitor, and 56% were pretreated with clopidogrel. Activated clotting times were higher among patients randomized to bivalirudin than among those given heparin before device activation (median 359 vs 293 seconds, p <0.001). The composite efficacy end point of death, myocardial infarction, or repeat revascularization before hospital discharge or within 48 hours occurred in 5.6% and 6.9% of patients in the bivalirudin and heparin groups, respectively (p = 0.40). Major bleeding occurred in 2.1% versus 2.7% of patients randomized to bivalirudin or heparin, respectively (p = 0.52). This trial represents the largest prospective dataset of bivalirudin administered concomitantly with planned GP IIb/IIIa blockade and provides evidence of the safety and efficacy of this combined antithrombotic approach.

Direct thrombin inhibitors for anticoagulation

OBJECTIVE

To review the progress in developing direct thrombin inhibitors (DTIs) for anticoagulation within the context of existing anticoagulation therapies.

DATA SOURCES

Searches of MEDLINE (1993-June 2003) were conducted.

STUDY SELECTION AND DATA EXTRACTION

We examined English-language articles, human studies, and relevant animal studies, and obtained additional citations from the references of these articles.

DATA SYNTHESIS

Because of its pivotal role in hemostasis, thrombin is a key therapeutic target in the treatment and prevention of thromboembolic disorders. Conventional anticoagulant therapies, such as warfarin, unfractionated heparin, and low-molecular-weight heparin, exert their pharmacologic action by indirect thrombin inhibition. Although these agents are effective, each has limitations, prompting a search for more effective, specific, better-tolerated, and convenient anticoagulants. The efficacy and safety of factor Xa inhibitors are being investigated. Furthermore, the development of DTIs such as recombinant hirudin (lepirudin), bivalirudin, and argatroban continues. Challenges in the development of DTIs include establishing a binding affinity for thrombin that is not associated with excessive bleeding, attaining high thrombin specificity, achieving inhibition of both unbound and clot-bound thrombin, and producing an effective, fixed-dose oral anticoagulant to improve the practicality of anticoagulation therapy. Ximelagatran, an oral DTI designed to meet these standards, is currently in Phase III clinical trials.

CONCLUSIONS

Significant progress has been made in developing DTIs. The recent emergence of orally administered DTIs may simplify the prevention and treatment of thrombosis.

Local Delivery of Argatroban for the Prevention of Restenosis After Coronary Balloon Angioplasty-A Prospective Randomized Pilot Study-

BACKGROUND

Effective pharmacological prevention of restenosis using the systemic administration of various drugs that were effective for the prevention of restenosis in experimental studies has not been reported. The purpose of this study was to evaluate whether the local delivery of a potent thrombin inhibitor, argatroban, using a local drug delivery device would prevent restenosis after plain old balloon angioplasty (POBA).

METHODS AND RESULTS

Seventy patients with chronic coronary artery disease requiring POBA were randomly assigned to wither the control group (n=35) or the argatroban group (n=35). In the argatroban group, argatroban was administered intravenously for 30 min before the POBA and intracoronarily into the dilated site using a Dispatch catheter immediately after the POBA, followed by a postoperative intravenous infusion for 4 h. The angiographical lesion restenosis and clinical restenosis rates at follow-up were significantly lower in the argatroban group (27% and 14%) than in the control group (56% and 37%; p=0.02 and p=0.03, respectively). There was no major complication during the procedure.

CONCLUSION

The local delivery of argatroban is safe and effective in preventing restenosis after balloon angioplasty.

Prevention of Venous Thromboembolism Following Orthopaedic Surgery

Patients undergoing total hip or total knee replacement are at high risk of venous thromboembolism (VTE), and are therefore considered to be populations well suited for the evaluation and dose optimisation of new anticoagulants. Deep vein thrombosis may lead to life-threatening pulmonary embolism, disabling morbidity in the form of the post-thrombotic syndrome, and risk of recurrent thrombotic events. There is increasing evidence that anticoagulant treatment for the prevention of VTE should be extended from 1 to at least 4 weeks after surgery. Anticoagulation with vitamin K antagonists (such as warfarin), low molecular weight heparin or unfractionated heparin effectively lowers the risk of VTE, but these anticoagulants have limitations such as the need for coagulation monitoring and subsequent dose adjustment (vitamin K antagonists), difficulty of continuing prophylaxis out of hospital because of the requirement for parenteral administration, and risk of heparin-induced thrombocytopenia. The development of new anticoagulants has been pursued with the aim of finding more effective, safer and/or more convenient therapies. Thrombin is a central regulator in the coagulation and inflammation process and several direct thrombin inhibitors (DTIs) with distinct pharmacological profiles, as well as pharmacological differences from the conventional anticoagulants, are currently in clinical use for certain indications or are under development. Clinical experience with parenterally administered DTIs has accumulated since the mid 1990s, although only desirudin (a recombinant hirudin) is currently approved for use in patients undergoing orthopaedic surgery. Two oral DTIs, ximelagatran and dabigatran etexilate, are in clinical development. Dabigatran etexilate has recently been evaluated in phase II clinical trials in patients undergoing total hip replacement. Several large phase III trials have now demonstrated the efficacy and safety of ximelagatran in the prevention of VTE following total hip or knee replacement. Ximelagatran can be used with an oral fixed dose without the need for coagulation monitoring or dose adjustment. Hence, it offers significant potential to facilitate the management of anticoagulation in or out of hospital.

Discovery of 1-(2-Aminomethylphenyl)-3-trifluoromethyl-N- [3-fluoro-2‘-(aminosulfonyl)[1,1‘-biphenyl)]-4-yl]-1H-pyrazole-5-carboxyamide (DPC602), a Potent, Selective, and Orally Bioavailable Factor Xa Inhibitor

Factor Xa, a serine protease, is at the critical juncture between the intrinsic and extrinsic pathways of the coagulation cascade. Inhibition of factor Xa has the potential to provide effective treatment for both venous and arterial thrombosis. We recently described a series of meta-substituted phenylpyrazoles that are highly potent, selective, and orally bioavailable factor Xa inhibitors. In this paper we report our efforts to further optimize the selectivity profile of our factor Xa inhibitors with a series of ortho- and/or para-substituted phenylpyrazole derivatives. The most potent compounds display sub-nanomolar inhibition constants for factor Xa and show greater than 1000-fold selectivity against other serine proteases. These compounds are also effective in a rabbit model of arteriovenous shunt thrombosis. Optimization of this series led to the preclinical development of DPC602, a 2-(aminomethyl)phenylpyrazole analogue, as a highly potent, selective, and orally bioavailable factor Xa inhibitor.

Antithrombotic properties of a direct thrombin inhibitor with a prolonged half-life and AT-mediated factor Xa inhibitory activity

Rebound thrombin generation after successful thrombolysis might be related to (i) too short-term anticoagulant therapy and to (ii) the inability of heparin derivatives to inhibit clot-bound thrombin. To meet these shortcomings, a compound was synthesized, which consists of a pentasaccharide conjugated to a direct thrombin inhibitor. This compound (Org 42675) has a 10 times longer half-life compared with the original half-life of the direct thrombin inhibitor, while the thrombin inhibitory activity is maintained. An extra advantage of this product is the inhibitory activity on thrombin generation via antithrombin III (AT)-mediated factor (F)Xa inhibition. Org 42675 inhibited in vitro clot-bound thrombin with similar activity to the direct thrombin inhibitor argatroban. In experimental models in rats, Org 42675 showed on a molar base similar antithrombotic activity to unfractionated heparin, was more active than argatroban and was more active than fondaparinux sodium (AT-mediated FXa inhibitor) in arterial thrombosis. Finally, Org 42675 was far more active than the three reference compounds in an experimental thrombolysis model in rabbits. These properties of Org 42675, with its FXa and (clot-bound) thrombin inhibitory activity in combination with its long half-life, make this compound a powerful drug that is likely to be effective in the prevention of re-occlusion after successful thrombolysis in man.

Long-lasting antithrombotic effects of a single dose of human recombinant, active site-blocked factor VII: insights into possible mechanism(s) of action

Tissue factor (TF) is important in initiating intravascular thrombosis. We demonstrated that active-site blocked factor VII (FVIIai) inhibits intravascular thrombosis for at least 6 h following a single injection, despite FVIIai plasma half-life was approximately 45 min. The aims of the present study were: (a) to determine the duration of the antithrombotic effects of a single injection of FVIIai; and (b) to assess whether FVIIai prolonged effects can be explained by a slow dissociation rate from TF in the arterial wall. Cyclic flow variations (CFVs), obtained in stenotic rabbit carotid arteries with endothelial injury, were abolished by either FVIIai (100 micro g kg-1 min-1 for 10 min) or hirudin (1 mg kg-1). After CFVs were abolished, carotid blood flow velocity was recorded continuously for 24 h. CFVs restored in all hirudin-treated animals after 2.1 +/- 0.3 h, while they restored in only four of nine FVIIai-treated rabbits in 10.1 +/- 2.2 h. Five animals in this group did not show restoration of CFVs up to 24 h. Immunohistochemistry revealed that FVIIai was still bound to the arterial wall 24 h following its administration, despite at this time FVIIai plasma levels were undetectable. Prothrombin time and partial thromboplastin time did not change significantly. FVIIai exerts potent, long-lasting antithrombotic effects without affecting systemic hemostatic parameters; a possible mechanism is a slow dissociation rate of FVIIai from TF. These proprieties make FVIIai particularly attractive as an antithrombotic intervention.

Alternative methods of anticoagulation for dialysis-dependent patients with heparin-induced thrombocytopenia

Dialysis patients who are continually exposed to heparin are at risk for heparin-induced thrombocytopenia (HIT). Heparin-induced antibodies have been reported to occur in 0-12% of hemodialysis (HD) patients. The diagnosis or suspicion of HIT in this patient population requires careful confirmation of the diagnosis and substitution of heparin with an alternate anticoagulant for dialysis. Alternate agents such as the direct thrombin inhibitors (hirudin and argatroban) are available, but careful dosing and monitoring of the anticoagulant effect are required. Despite careful dosing, hemorrhagic complications have occurred with these agents. Unfortunately there are limited options for treatment of hemorrhagic complications and no specific antidotes are available for the direct thrombin inhibitors. In this report the currently available alternatives to heparin for dialysis, including dosing and monitoring recommendations, are reviewed.

Bivalirudin with planned or provisional abciximab versus low-dose heparin and abciximab during percutaneous coronary revascularization: results of the Comparison of Abciximab Complications with Hirulog for Ischemic Events Trial (CACHET)

BACKGROUND

The direct thrombin inhibitor bivalirudin has previously been associated with better efficacy and lower hemorrhage risk than heparin during balloon angioplasty. This agent has not yet been tested with stenting or in combination with platelet glycoprotein IIb/IIIa antagonists.

METHODS AND RESULTS

In a pilot trial, 268 patients who underwent coronary intervention were randomized in 3 sequential phases to treatment with bivalirudin (with or without abciximab) or the control regimen of low-dose weight-adjusted heparin with abciximab. Patients in the bivalirudin arms received bivalirudin (1.0 mg/kg bolus, infusion of 2.5 mg/kg/h for 4 hours) plus abciximab in phase A, bivalirudin (0.5 mg/kg bolus, infusion of 1.75 mg/kg/h for the procedure duration) plus provisional ("rescue") abciximab in phase B, or bivalirudin (0.75 mg/kg bolus, infusion of 1.75 mg/kg/h for the procedure duration) plus provisional abciximab in phase C. Abciximab was necessitated on a provisional basis in 24% of the patients in the bivalirudin arms of phases B and C. A composite clinical endpoint of death, myocardial infarction, repeat revascularization, or major bleeding by 7 days occurred in 3.3%, 5.9%, 0, and 10.6% of the patients in the bivalirudin phase A, bivalirudin phase B, bivalirudin phase C, and heparin plus planned abciximab arms, respectively (P =.018 for the pooled bivalirudin groups versus the heparin group).

CONCLUSION

Bivalirudin with planned or provisional abciximab may be at least as safe and effective as low-dose heparin plus abciximab during percutaneous coronary intervention.

Thrombin inhibition attenuates neurodegeneration and cerebral edema formation following transient forebrain ischemia

The disturbance of microcirculation following cerebral ischemia leads to an enlargement of cerebral infarct volume. Endogenous thrombin may play a role in this disturbance of microcirculation following cerebral ischemia. Therefore, the inhibition of thrombin may improve neurodegeneration and the accumulation of cerebral edema following cerebral ischemia in gerbils. The effects of thrombin inhibitor (argatroban) on cerebral ischemia were investigated in comparison with thromboxane A2 synthase inhibitor (ozagrel) and cyclooxygenase inhibitor (aspirin) following bilateral common carotid artery occlusion and reperfusion (CCA:O/R) in male Mongolian gerbils. This study consisted of three experiments: (1) morbidity and survival ratio (n=40 for each), (2) histopathology (n=12 for each), and (3) mean arterial blood pressure, local cerebral blood flow (CBF), and cerebral specific gravity (n=8 for each). Argatroban treatment improved survival ratio and stroke index, and decreased ischemically injured cell numbers in cortex and hippocampus and cerebral edema in cortex compared with aspirin and saline, in concert with the fast recovery of local CBF without reactive hyperemia following bilateral CCA:O/R. Ozagrel treatment also improved those factors compared with saline, in concert with the fast recovery of local CBF with reactive hyperemia. Aspirin treatment improved survival ratio and stroke index, and decreased ischemically injured cell numbers in cortex. Thrombin inhibition with argatroban decreases neurodegeneration and cerebral edema following bilateral CCA:O/R in gerbils.

Discovery of 1-[3-(aminomethyl)phenyl]-N-3-fluoro-2'-(methylsulfonyl)-[1,1'-biphenyl]-4-yl]-3-(trifluoromethyl)-1H-pyrazole-5-carboxamide (DPC423), a highly potent, selective, and orally bioavailable inhibitor of blood coagulation factor Xa

Factor Xa (fXa) plays a critical role in the coagulation cascade, serving as the point of convergence of the intrinsic and extrinsic pathways. Together with nonenzymatic cofactor Va and Ca2+ on the phospholipid surface of platelets or endothelial cells, factor Xa forms the prothrombinase complex, which is responsible for the proteolysis of prothrombin to catalytically active thrombin. Thrombin, in turn, catalyzes the cleavage of fibrinogen to fibrin, thus initiating a process that ultimately leads to clot formation. Recently, we reported on a series of isoxazoline and isoxazole monobasic noncovalent inhibitors of factor Xa which show good potency in animal models of thrombosis. In this paper, we wish to report on the optimization of the heterocyclic core, which ultimately led to the discovery of a novel pyrazole SN429 (2b; fXa K(i) = 13 pM). We also report on our efforts to improve the oral bioavailability and pharmacokinetic profile of this series while maintaining subnanomolar potency and in vitro selectivity. This was achieved by replacing the highly basic benzamidine P1 with a less basic benzylamine moiety. Further optimization of the pyrazole core substitution and the biphenyl P4 culminated in the discovery of DPC423 (17h), a highly potent, selective, and orally active factor Xa inhibitor which was chosen for clinical development.

Local treatment with recombinant tissue factor pathway inhibitor reduces the development of intimal hyperplasia in experimental vein grafts

BACKGROUND

Tissue factor (TF)-initiated thrombin generation has been implicated in the development of intimal hyperplasia after arterial injury. An increase in intimal TF expression has been shown to precede the development of intimal hyperplasia in vein grafts. This study examines the effects of local treatment with recombinant human tissue factor pathway inhibitor (rTFPI) in experimental vein grafts.

METHODS

Thirty-six male New Zealand white rabbits underwent bypass grafting of the carotid artery by use of the reversed ipsilateral jugular vein and were divided into four groups. Twenty animals had ex vivo incubation with rTFPI treatment (50 microg x mL(-1); n = 10) or placebo vehicle (control; n = 10). Sixteen animals received both ex vivo incubation and in vivo gel treatment with rTFPI (50 microg. mL(-1); n = 8) or without rTFPI (gel-control; n = 8). After operation, vein grafts were harvested at 3 days for immunohistochemical and Western analyses and at 28 days for histomorphologic study.

RESULTS

Western analysis demonstrated a 6.2-fold reduction in the expression of TF protein with rTFPI treatment in comparison to without rTFPI treatment. CD-18 leukocyte staining was diminished, whereas Tie-2 endothelial staining was increased in all rTFPI-treated vein grafts, compared with control and gel-control vein grafts. Intimal thickness was reduced by 21% with ex vivo rTFPI treatment compared with placebo (69 +/- 4 versus 87 +/- 5 microm; P <.05) and by 30% with the addition of rTFPI in vivo compared with gel-control (60 +/- 4 versus 86 +/- 5 microm; P <.01).

CONCLUSION

Local administration of rTFPI exerts early beneficial effects and limits the development of intimal hyperplasia in vein grafts. Therefore blocking TF-mediated pathway may offer new therapeutic options to reduce vein graft failure.

Antithrombotic effect of LB-30057 (CI-1028), a new synthetic thrombin inhibitor, in a rabbit model of thrombosis: comparison with inogatran

LB-30057 (CI-1028) is a novel, orally bioavailable, direct thrombin inhibitor with a Ki of 0.38 nM against human thrombin. The effects of LB-30057 on thrombus formation and hemostasis were evaluated in a veno-venous shunt model of thrombosis in rabbits, and compared with inogatran, another direct inhibitor of thrombin. Each compound was studied at 5 or 6 different doses with 5 or 6 rabbits in each group. After administration as a bolus i.v. injection followed by continuous infusion, both LB-30057 and inogatran dose-dependently inhibited thrombus formation, which was measured as an increase in time to occlusion (TTO) and a decrease in thrombus weight. Both compounds also improved vena caval blood flow and reduced the overall incidence of thrombotic occlusion. LB-30057 significantly prolonged TTO from 23 +/- 4 min (before dose) to 110 +/- 10 min at the highest dose (0.7 mg/kg + 47 microg/kg/min) (p < 0.001), and reduced thrombus weight from 57 +/- 2 mg to 15 +/- 5 mg (p < 0.001). Occlusive thrombus formed in only one of six rabbits that received the highest dose of LB-30057 (vs. 13/13 in the control group, p < 0.01). At the dose that produced the maximum antithrombotic effect (0.7 mg/kg + 47 microg/kg/min), LB-30057 increased aPTT and bleeding time approximately 2-and 2.5-fold above baseline, respectively. On a gravimetric basis, LB-30057 and inogatran displayed comparable in vivo antithrombotic efficacy. When compared to equally effective anti thrombotic doses of inogatran, LB-30057 caused less prolongation in aPTT, had no effect on PT, and tended to have less of effect on bleeding time. These results indicate that LB-30057 is an effective antithrombotic compound and it appears to have a better benefit/risk profile than inogatran in this experimental model.