Indoleamine 2,3-dioxygenase-1, a Novel Therapeutic Target for Post-Vascular Injury Thrombosis in CKD

BACKGROUND

CKD, characterized by retained uremic solutes, is a strong and independent risk factor for thrombosis after vascular procedures . Urem ic solutes such as indoxyl sulfate (IS) and kynurenine (Kyn) mediate prothrombotic effect through tissue factor (TF). IS and Kyn biogenesis depends on multiple enzymes, with therapeutic implications unexplored. We examined the role of indoleamine 2,3-dioxygenase-1 (IDO-1), a rate-limiting enzyme of kynurenine biogenesis, in CKD-associated thrombosis after vascular injury.

METHODS

IDO-1 expression in mice and human vessels was examined. IDO-1-/- mice, IDO-1 inhibitors, an adenine-induced CKD, and carotid artery injury models were used.

RESULTS

Both global IDO-1-/- CKD mice and IDO-1 inhibitor in wild-type CKD mice showed reduced blood Kyn levels, TF expression in their arteries, and thrombogenicity compared with respective controls. Several advanced IDO-1 inhibitors downregulated TF expression in primary human aortic vascular smooth muscle cells specifically in response to uremic serum. Further mechanistic probing of arteries from an IS-specific mouse model, and CKD mice, showed upregulation of IDO-1 protein, which was due to inhibition of its polyubiquitination and degradation by IS in vascular smooth muscle cells. In two cohorts of patients with advanced CKD, blood IDO-1 activity was significantly higher in sera of study participants who subsequently developed thrombosis after endovascular interventions or vascular surgery.

CONCLUSION

Leveraging genetic and pharmacologic manipulation in experimental models and data from human studies implicate IS as an inducer of IDO-1 and a perpetuator of the thrombotic milieu and supports IDO-1 as an antithrombotic target in CKD.

NADPH Oxidases Are Required for Full Platelet Activation In Vitro and Thrombosis In Vivo but Dispensable for Plasma Coagulation and Hemostasis

OBJECTIVE

Using 3KO (triple NOX [NADPH oxidase] knockout) mice (ie, NOX1-/-/NOX2-/-/NOX4-/-), we aimed to clarify the role of this family of enzymes in the regulation of platelets in vitro and hemostasis in vivo. Approach and Results: 3KO mice displayed significantly reduced platelet superoxide radical generation, which was associated with impaired platelet aggregation, adhesion, and thrombus formation in response to the key agonists collagen and thrombin. A comparison with single-gene knockouts suggested that the phenotype of 3KO platelets is the combination of the effects of the genetic deletion of NOX1 and NOX2, while NOX4 does not show any significant function in platelet regulation. 3KO platelets displayed significantly higher levels of cGMP-a negative platelet regulator that activates PKG (protein kinase G). The inhibition of PKG substantially but only partially rescued the defective phenotype of 3KO platelets, which are responsive to both collagen and thrombin in the presence of the PKG inhibitors KT5823 or Rp-8-pCPT-cGMPs, but not in the presence of the NOS (NO synthase) inhibitor L-NG-monomethyl arginine. In vivo, triple NOX deficiency protected against ferric chloride-driven carotid artery thrombosis and experimental pulmonary embolism, while hemostasis tested in a tail-tip transection assay was not affected. Procoagulatory activity of platelets (ie, phosphatidylserine surface exposure) and the coagulation cascade in platelet-free plasma were normal.

CONCLUSIONS

This study indicates that inhibiting NOXs has strong antithrombotic effects partially caused by increased intracellular cGMP but spares hemostasis. NOXs are, therefore, pharmacotherapeutic targets to develop new antithrombotic drugs without bleeding side effects.

Targeting Thymidine Phosphorylase With Tipiracil Hydrochloride Attenuates Thrombosis Without Increasing Risk of Bleeding in Mice

OBJECTIVE

Current antiplatelet medications increase the risk of bleeding, which leads to a clear clinical need in developing novel mechanism-based antiplatelet drugs. TYMP (Thymidine phosphorylase), a cytoplasm protein that is highly expressed in platelets, facilitates multiple agonist-induced platelet activation, and enhances thrombosis. Tipiracil hydrochloride (TPI), a selective TYMP inhibitor, has been approved by the Food and Drug Administration for clinical use. We tested the hypothesis that TPI is a safe antithrombotic medication. Approach and Results: By coexpression of TYMP and Lyn, GST (glutathione S-transferase) tagged Lyn-SH3 domain or Lyn-SH2 domain, we showed the direct evidence that TYMP binds to Lyn through both SH3 and SH2 domains, and TPI diminished the binding. TYMP deficiency significantly inhibits thrombosis in vivo in both sexes. Pretreatment of platelets with TPI rapidly inhibited collagen- and ADP-induced platelet aggregation. Under either normal or hyperlipidemic conditions, treating wild-type mice with TPI via intraperitoneal injection, intravenous injection, or gavage feeding dramatically inhibited thrombosis without inducing significant bleeding. Even at high doses, TPI has a lower bleeding side effect compared with aspirin and clopidogrel. Intravenous delivery of TPI alone or combined with tissue plasminogen activator dramatically inhibited thrombosis. Dual administration of a very low dose of aspirin and TPI, which had no antithrombotic effects when used alone, significantly inhibited thrombosis without disturbing hemostasis.

CONCLUSIONS

This study demonstrated that inhibition of TYMP, a cytoplasmic protein, attenuated multiple signaling pathways that mediate platelet activation, aggregation, and thrombosis. TPI can be used as a novel antithrombotic medication without the increase in risk of bleeding.

Lipid Receptor GPR31 (G-Protein-Coupled Receptor 31) Regulates Platelet Reactivity and Thrombosis Without Affecting Hemostasis

OBJECTIVE

12-LOX (12-lipoxygenase) produces a number of bioactive lipids including 12(S)-HETE that are involved in inflammation and platelet reactivity. The GPR31 (G-protein-coupled receptor 31) is the proposed receptor of 12(S)-HETE; however, it is not known whether the 12(S)-HETE-GPR31 signaling axis serves to enhance or inhibit platelet activity. Approach and Results: Using pepducin technology and biochemical approaches, we provide evidence that 12(S)-HETE-GPR31 signals through Gi to enhance PAR (protease-activated receptor)-4-mediated platelet activation and arterial thrombosis using both human platelets and mouse carotid artery injury models. 12(S)-HETE suppressed AC (adenylyl cyclase) activity through GPR31 and resulted in Rap1 (Ras-related protein 1) and p38 activation and low but detectable calcium flux but did not induce platelet aggregation. A GPR31 third intracellular (i3) loop-derived pepducin, GPR310 (G-protein-coupled receptor 310), significantly inhibited platelet aggregation in response to thrombin, collagen, and PAR4 agonist, AYPGKF, in human and mouse platelets but relative sparing of PAR1 agonist SFLLRN in human platelets. GPR310 treatment gave a highly significant 80% protection (P=0.0018) against ferric chloride-induced carotid artery injury in mice by extending occlusion time, without any effect on tail bleeding. PAR4-mediated dense granule secretion and calcium flux were both attenuated by GPR310. Consistent with these results, GPR310 inhibited 12(S)-HETE-mediated and PAR4-mediated Rap1-GTP and RASA3 translocation to the plasma membrane and attenuated PAR4-Akt and ERK activation. GPR310 caused a right shift in thrombin-mediated human platelet aggregation, comparable to the effects of inhibition of the Gi-coupled P2Y12 receptor. Co-immunoprecipitation studies revealed that GPR31 and PAR4 form a heterodimeric complex in recombinant systems.

CONCLUSIONS

The 12-LOX product 12(S)-HETE stimulates GPR31-Gi-signaling pathways, which enhance thrombin-PAR4 platelet activation and arterial thrombosis in human platelets and mouse models. Suppression of this bioactive lipid pathway, as exemplified by a GPR31 pepducin antagonist, may provide beneficial protective effects against platelet aggregation and arterial thrombosis with minimal effect on hemostasis.

Orally administered heparins prevent arterial thrombosis in a rat model

Our previous studies demonstrated that orally administered heparins prevent thrombosis in a rat jugular vein thrombosis model, where bovine unfractionated heparin (UFH) and the low molecular weight heparin tinzaparin reduced thrombotic incidence by 50% at 7.5 and 0.1 mg/kg, respectively. Our objectives were to determine if similar antithrombotic effects of oral heparin could be observed in an arterial thrombosis model. In this model, filter paper soaked in 30% ferric chloride was applied to the exposed rat carotid artery. A flowmeter recorded blood flow over a 60 min period determining time when the thrombus began forming (TTB) and time till occlusion (TTO). Immediately following, the thrombus was removed, dried and weighed 24 h later. Bovine UFH (7.5 mg/kg), tinzaparin (0.1 mg/kg) or saline was administered by stomach tube at 2, 5 and 25 h prior to thrombus initiation. TTB was significantly increased when UFH was given at 5 and 25 h but not 2 h prior, and when tinzaparin was given at 5 but not 2 or 25 h prior compared to rats given oral saline. TTO was significantly increased for both UFH and tinzaparin when given 5 and 25 h but not 2 h prior (one-way ANOVA). There was no difference in TTO and TTB between UFH and tinzaparin treated groups. A trend in reduction in thrombus weight was observed for UFH at 5 and 25 h prior and tinzaparin at 5 h prior to thrombus initiation (one-way ANOVA). Although no significant changes were observed in activated partial thromboplastin times, Heptest or anti-Xa activity from plasma of heparin treated rats, endothelial heparin concentrations were significantly greater than controls for UFH at 5 h and for tinzaparin at 2, 5, and 24 h. Thus, heparins administered by the oral route are effective antithrombotic agents in arterial as well as venous models.

Intraoperative sonography during carotid endarterectomy: normal appearance and spectrum of complications

Carotid endarterectomy is a commonly performed procedure for prevention of stroke related to carotid stenosis. Intraoperative sonography is used to identify potentially correctable technical defects during carotid endarterectomy. The main risk of endarterectomy is perioperative stroke, and great effort has been put into trying to reduce this risk through various surgical techniques and evaluation of the surgical bed. Postoperative carotid thrombosis, or thombo-embolization from the arterectomy site, remains a common cause of perioperative stroke and is often related to technical defects in the arterial reconstruction procedure. Re-exploration and repair of any imperfections have the potential to improve outcomes. Intraoperative imaging can identify potentially occult lesions, provide the option for correction, and thus reduce chance of stroke. Familiarity with the spectrum of intraoperative sonographic findings helps correctly identify residual intimal dissection flaps, plaque, thrombi, and stenosis, which may require immediate surgical revision. Our objective is to illustrate the spectrum of intraoperative findings and their importance.

Simplagrin, a platelet aggregation inhibitor from Simulium nigrimanum salivary glands specifically binds to the Von Willebrand factor receptor in collagen and inhibits carotid thrombus formation in vivo

BACKGROUND

Among the several challenges faced by bloodsucking arthropods, the vertebrate hemostatic response against blood loss represents an important barrier to efficient blood feeding. Here we report the first inhibitor of collagen-induced platelet aggregation derived from the salivary glands of a black fly (Simulium nigrimanum), named Simplagrin.

METHODS AND FINDINGS

Simplagrin was expressed in mammalian cells and purified by affinity-and size-exclusion chromatography. Light-scattering studies showed that Simplagrin has an elongated monomeric form with a hydrodynamic radius of 5.6 nm. Simplagrin binds to collagen (type I-VI) with high affinity (2-15 nM), and this interaction does not involve any significant conformational change as determined by circular dichroism spectroscopy. Simplagrin-collagen interaction is both entropically and enthalpically driven with a large negative ΔG, indicating that this interaction is favorable and occurs spontaneously. Simplagrin specifically inhibits von Willebrand factor interaction with collagen type III and completely blocks platelet adhesion to collagen under flow conditions at high shear rates; however, Simplagrin failed to block glycoprotein VI and Iα2β1 interaction to collagen. Simplagrin binds to RGQOGVMGF peptide with an affinity (K(D) 11 nM) similar to that of Simplagrin for collagen. Furthermore, Simplagrin prevents laser-induced carotid thrombus formation in vivo without significant bleeding in mice and could be useful as an antithrombotic agent in thrombosis related disease.

CONCLUSION

Our results support the orthology of the Aegyptin clade in bloodsucking Nematocera and the hypothesis of a faster evolutionary rate of salivary function of proteins from blood feeding arthropods.

Hyperglycemia accelerates arterial thrombus formation and attenuates the antithrombotic response to endotoxin in mice

Recent human studies reveal that hyperglycemia induces procoagulant and antifibrinolytic effects in blood that may contribute to a greater risk of arterial thrombosis, but the direct relationship between high blood glucose levels and thrombosis has not yet been investigated. We performed a number of experiments to clarify whether hyperglycemia was causally related to arterial thrombosis and whether the combined stimulus of hyperglycemia and inflammation would enhance the thrombotic effect. In a model of ferric-chloride-induced carotid artery thrombosis, hyperglycemia did not influence the time to occlusion in mice pretreated with streptozotocin, but the rate of thrombus formation was accelerated. This effect was associated with increased thrombin generation and could not be explained by changes in vessel-wall tissue factor activity. The prothrombotic effect of hyperglycemia was assessed in a separate experiment, showing that collagen/thrombin-induced platelet procoagulant activity was increased in hyperglycemic mice. The effect of inflammation was studied by injecting a low dose of endotoxin that caused a systemic inflammatory state after 24 h (increased plasma levels of tumor necrosis factor alpha, interleukin-6 and monocyte chemotactic protein 1 in diabetic and nondiabetic mice) associated with a mild delay in thrombus formation. This reduced rate of thrombus formation was attenuated by hyperglycemia. Together, these data establish a discrete but clear contribution of hyperglycemia in experimental arterial thrombosis.

Platelet aggregometry and receptor binding to predict the magnitude of antithrombotic and bleeding time effects of clopidogrel in rabbits

Target levels of ex vivo inhibition of platelet aggregation (IPA) induced by adenosine diphosphate (ADP) that produce clinically relevant effects of clopidogrel, a P2Y12 antagonist, are unclear. We examined standard and modified IPA and P2Y12 receptor occupancy as predictors of antithrombotic (% thrombus weight reduction) and bleeding time (BT, fold-increase over control) effects of clopidogrel in rabbit models of carotid artery thrombosis and cuticle bleeding, respectively. Standard and modified IPA with 20 microM ADP were measured in the absence and presence of partial P2Y1 blockade, respectively. Clopidogrel maximally produced standard IPA of 57% +/- 5%, antithrombotic effect of 85% +/- 1%, BT increase of 6.0 +/- 0.4-fold and P2Y12 receptor occupancy of 87% +/- 5%. Surprisingly, a clopidogrel dose that produced a low standard IPA of 17% +/- 4% and P2Y12 receptor occupancy of 39% +/- 5% achieved a significant antithrombotic activity of 55% +/- 2% with a moderate increase in BT of 2.0 +/- 0.1-fold. This underestimation of clopidogrel efficacy by standard IPA was improved by measuring either modified IPA or P2Y12 receptor occupancy. These results suggest that in clopidogrel-treated rabbits, low standard IPA is associated with significant antithrombotic effects. Moreover, modified IPA and P2Y12 receptor occupancy appear to better predict the magnitude of clopidogrel's efficacy compared with standard IPA, which may be a better predictor of BT.

Heme oxygenase-1 inducer hemin prevents vascular thrombosis

Hemin is a heme oxygenase-1 (HO-1) inducer which provides endogenous carbon monoxide known for playing roles in cell proliferation, inflammation or aggregation process. The objective of the current study was to examine the effect of prophylactic treatment with hemin in a thrombosis vascular model. Three groups of Wistar rats, control (n = 6), hemin (n = 6) and hemin + HO-1 inhibitor (n = 6), were used for this study. Hemin-treated animals received hemin (50 mg/kg/d; I.P.) for seven days and HO-1 inhibitor group received hemin at the same dose and SnPP IX (60 mg/kg/d; I.P.). All animals were exposed to electric stimulation of the left carotid according to Kawasaki's procedure to induce reproducible thrombus formation. The hemin treatment did not induce blood pressure disturbance. Effects of hemin on vascular thrombosis were quantified by histopathology and its influence on haemostasis was assessed by measuring prothrombin time (PT), activated partial thromboplastin time (APTT) and blood parameters at the end of treatment. The HO-1 mRNA and protein level variation were also checked out. Results showed that chronic treatment with hemin significantly (p < 0.01) reduced the vascular occlusion degree when compared to control and hemin SnPP groups with 7.2 +/- 4.6 vs. 71.1 +/- 14.7 and 74.0 +/- 8.8%, respectively. Moreover, we observed significant (p < 0.05) perturbations of blood parameters in hemin-treated and hemin-SnPP treated rats. Interestingly, hemin treatment did not significantly increase both PT and APTT. Finally, the HO-1 mRNA and protein levels were increased in hemin-treated carotid artery. In conclusion, hemin by inducing HO-1 expression may be a preventive agent against clinical disorders associated to an increased risk of thrombosis events and may limit haemorrhagic risks.

Technical Limitations of Carotid Filter Embolic Protection Devices

Improved carotid artery stenting (CAS) results are credited to the development of embolic protection devices (EPDs). Reported are outcomes and technical failures of two classes of EPDs: distal balloon occlusion and distal filtration. We present a retrospective review of 206 CAS procedures from April 2001-September 2005. Filters (AccuNet, Angioguard, Filterwire, or Emboshield) were used in 98 cases (48%), distal balloon occlusion (PercuSurge) in 94 (46%), and no protection in 14. Data include demographics and procedural records. Mean age was 70 years (76% men, 24% women). At 30 days, there were no deaths, no myocardial infarctions, two major ipsilateral strokes (1%), two minor posterior strokes (1%), four transient ischemic attacks (2%), and one major access site complication (0.5%). Major neurologic events were equally divided between balloon occlusion and filters. Mean balloon occlusion time was 12 min, with only two patients (2%) manifesting reversible neurologic intolerance during flow arrest. In the last 100 cases, filter devices were preferentially used due to preserved antegrade flow. However, 11 cases (11%) necessitated intraoperative switching to balloon occlusion because of either extreme tortuosity or severe stenosis of the target lesion precluding passage of the filter element. CAS-specific equipment has improved procedural results. Despite theoretic advantages of filter EPDs, up to 10% of lesions are either too narrow or tortuous to allow safe passage of the filter element. Switching to a distal balloon occlusion system, which is well tolerated, may be preferred to unprotected predilation. Practitioners of CAS should be versed in both.

[Effects of procyanidin oligomers on experimental thrombosis in rats]

The study was aimed to investigate the potential effect of procyanidins (PC) as a antithrombotic agent and its mechanism. 48 male SD rats were randomized into 6 groups, which include 8 rats each. Group A was normal control, group B was model control (no treatment), group C was group treated with aspirin [10mg/(kg x d)], groups D, E and F were treated with low, medial and high dose [100, 200 and 400 mg/(kg x d)] of PC respectively. In accordance with Kurz's protocols, rat's model of thrombosis of common carotid artery was contructed with FeCl(3), but for goup A 0.9% of normal saline was used for 20 minutes. The thromboxane B2 (TXB(2)), 6-Keto-PGF1alpha and GMP-140 contents in plasma were measured. The results showed that compared with the normal control group, the contents of TXB(2) and GMP-140 in plasma markedly increased in all of PC groups and aspirin group, and the contents of 6-Keto-PGF1alpha in plasma decreased. Compared with the model group, the contents of TXB(2) and GMP-140 in plasma markedly decreased in all of PC groups and aspirin group, and the contents of 6-Keto-PGF1alpha in plasma increased. Compared with the aspirin group, the contents of TXB(2) and GMP-140 in plasma reduced in all of PC groups and the contents of 6-Keto-PGF1alpha in plasma increased which was obvious in PC 400 mg/(kg x d) group. It is concluded that PC shows obvious anti-thrombosis effect, its mechanism closely correlates with inhibition of platelet activation and aggregation as well as protecting vasoendothelial cells. Antithrombosis of PC shows significant dose-dependence. The effect of the PC 400 mg/(kg x d) surpass the aspirin, but there is no significant difference between the PC 200 mg/(kg x d) and aspirin. This study provides experimental basis for clinical prevention and treatment of thrombosis.

Antithrombotic and antiplatelet activities of Korean red ginseng extract

The antithrombotic and antiplatelet activities of Korean red ginseng extract (KRGE) were examined on rat carotid artery thrombosis in vivo and platelet aggregation in vitro and ex vivo. The KRGE significantly prevented rat carotid arterial thrombosis in vivo in a dose-dependent manner. Administration of the KRGE to rats significantly inhibited adenosine diphosphate (ADP)- and collagen-induced platelet aggregation ex vivo, although it failed to prolong coagulation times such as activated partial thromboplastin and prothrombin time indicating that the antithrombotic effect of the red ginseng may be due to its antiplatelet aggregation rather than anticoagulation effect. In line with the above observations, the red ginseng inhibited the U46619-, arachidonic acid-, collagen- and thrombin-induced rabbit platelet aggregations in vitro in a concentration-dependent manner, with IC(50) values of 390 +/- 15, 485 +/- 19, 387 +/- 11 and 335 +/- 15 microg/ml, respectively. Consistently, serotonin secretion was also inhibited by ginseng in the same pattern. These results suggest that the red ginseng has a potent antithrombotic effect in vivo, which may be due to the antiplatelet rather than the anticoagulation activity, and the red ginseng intake may be beneficial for individuals with high risks of thrombotic and cardiovascular diseases.

Antiplatelet and antithrombotic activities of Korean Red Ginseng

The antiplatelet and antithrombotic activities of Korean Red Ginseng (KRG) were examined on rat carotid artery thrombosis in vivo, and platelet aggregation in vitro and ex vivo. Administration of KRG to rats not only prevented carotid artery thrombosis in vivo in a dose-dependent manner, but also significantly inhibited ADP- and collagen-induced platelet aggregation ex vivo, while failed to prolong coagulation times such as activated partial thromboplastin time (APTT) and prothrombin time (PT), indicating the antithrombotic effect of KRG might be due to its antiplatelet aggregation rather than anticoagulation effect. In line with the above observations, KRG inhibited U46619-, arachidonic acid-, collagen- and thrombin-induced rabbit platelet aggregation in vitro in a concentration-dependent manner, with IC50 values of 620 +/- 12, 823 +/- 22, 722 + 21 and 650 +/- 14 microg/mL, respectively. Accordingly, KRG also inhibited various agonists-induced platelet serotonin secretions as it suppressed platelet aggregation. These results suggest that KRG has a potent antithrombotic effect in vivo, which may be due to antiplatelet rather than anticoagulation activity, and KRG intake may be beneficial to the individuals with high risks of thrombotic and cardiovascular diseases.

Preclinical evaluation of S18886 in an experimental model of coronary arterial thrombosis

The specific thromboxane receptor antagonist, S18886, was evaluated for prevention of coronary arterial thrombosis and myocardial ischemia-reperfusion in anesthetized canines. For the primary thrombosis study in left circumflex (LCX) coronary artery, 26 dogs were randomized to receive either vehicle (n = 7) or intravenous S18886 (0.3 mg/kg, n = 6; 1.0 mg/kg, n = 6; and 3.0 mg/kg, n = 7). The respective times to occlusion after S18886 were as follows: 56.8 +/- 9.3, 83.5 +/- 14.9, and 92.4 +/- 15.7 minutes compared to 43.3 +/- 8.2 minutes after vehicle. S18886 caused a minimal increase in tongue bleeding time and a significant decrease in ex vivo platelet aggregation to arachidonic acid or U46619. Another 37 dogs were randomized to receive placebo (n = 12), clopidogrel 1.0 mg/kg p.o. QDX3 (n = 9), clopidogrel + S18886 0.3 (n = 9) or 1.0 (n = 7) mg/kg intravenous. Clopidogrel produced a 50% reduction in adenosine diphosphate-induced platelet aggregation and a slight increase in the time to occlusion. However, clopidogrel + S18886 1.0 mg/kg prevented occlusive thrombus formation in most of the coronary vessels over 6 hours. S18886 did not alter myocardial infarct size in the ischemia-reperfusion model. In conclusion, S18886 alone caused a dose-dependent prolongation in the time to primary occlusive coronary artery thrombosis, whereas S18886 + clopidogrel displayed effective in preventing occlusive thrombus formation with only a moderate increase of tongue-bleeding time.

Distinct antithrombotic consequences of platelet glycoprotein Ibalpha and VI deficiency in a mouse model of arterial thrombosis

BACKGROUND

Collagen and von Willebrand factor (VWF) are considered essential to initiate platelet deposition at sites of vascular injury, but their respective roles remain to be elucidated.

METHODS

We used a model of carotid artery thrombosis induced by a ferric chloride injury to compare the time to first occlusion and occlusion rate at 25 min postinjury in mice lacking the collagen receptor, glycoprotein (GP) VI, or the ligand-binding domain of the VWF receptor, GP Ibalpha.

RESULTS

In normal mice used as controls (n = 12), a complete obstruction of blood flow developed within 8.05 +/- 0.47 min (mean +/- SEM), and the occlusion rate was 100%. The results were variable in 26 GP VI(-/-) mice. The artery never occluded in eight mice, but the time to first occlusion in the remaining 18 (8.36 +/- 0.27 min) was not different from normal (P = 0.556). Nonetheless, the occlusion rate was 42%, because in seven mice the occluded artery reopened and stayed patent at 25 min. In contrast, the artery never occluded in 12 mice lacking GP Ibalpha. In ex vivo perfusion experiments, GP VI(-/-) platelets failed to form thrombi onto collagen type I fibrils, but formed thrombi of normal size when exposed to endothelial or fibroblast extracellular matrix.

CONCLUSIONS

Absence of GP Ibalpha function has a more profound antithrombotic effect in vivo than absence of the GP VI-dependent pathway of collagen-induced adhesion/activation. Components of the extracellular matrix may elicit a thrombogenic response in the absence of GP VI but not GP Ibalpha.

Detection of microembolic signals with transcranial Doppler ultrasound

Detection of microembolic signals (MES) with transcranial Doppler was introduced in the late 1980s; several animal and in vitro models reported a high sensitivity and specificity with this technique. Monitoring for MES in various patient groups has provided valuable insights on stroke pathophysiology, although its clinical value remains a matter of debate. Diagnosis of imminent occlusion of the internal carotid artery following carotid endarterectomy, selection of high-risk patients with asymptomatic carotid disease, and evaluation of drug efficacy constitute potential applications of this technique.

Adaptation of the Folts and electrolytic methods of arterial thrombosis for the study of anti-thrombotic molecules in small animals

INTRODUCTION

Animal preparations of arterial thrombosis play a crucial role in the discovery and validation of novel drug targets in vivo, aiding in the selection of new drugs for clinical evaluation. The Folts and electrolytic methods of arterial thrombosis are two of the most commonly used techniques to investigate drugs with novel anti-thrombotic potential. However, these techniques often involved the use of large animals such as dogs, and their application to small animals was limited. The aim of the present study was to adapt the Folts and electrolytic methods previously described in large animals to create highly reproducible, quantitative models of arterial thrombosis in mice, rats and rabbits.

METHODS

Carotid artery blood flow was measured in anaesthetised mice, rats and rabbits. In the Folts-like method, a silk suture was tied around one carotid artery distal to a flow probe and tightened to cause a concentric stenosis sufficient to decrease blood flow by 50%. Intimal damage was induced by pinching the artery at the site of stenosis using forceps. The sequential formation and mechanical dislodgement of the resultant platelet-rich occlusive thrombus caused cyclic carotid artery flow reductions. In the electrolytic method in mice, a platinum hook electrode was placed distal to a flow probe on one carotid artery. The artery was clamped distally to the electrode to cause stasis and an electrical current (4 mA for 1.25 min) was applied before clamp release. This induced vascular injury resulting in occlusive thrombus (platelet- and fibrin-rich) formation.

CONCLUSION

The Folts-like method of arterial thrombosis was successfully adapted for use in mice, rats and rabbits, and the electrolytic technique for use in mice. Compared with larger animals, these methods are highly reproducible and ideal for pre-clinical, cost-effective, low-cost routine screening of novel anti-thrombotic drugs.

Thrombin-free Fibrin Coating on Small Caliber Vascular Prostheses Has High Antithrombogenicity in Rabbit Model

Fibrin coatings on prosthetic vascular graft, which are conventionally produced by fibrinogen and thrombin, are expected to improve antithrombogenicity and healing characteristics. Thrombin is one of the factors of blood coagulation cascade; however, it has a possibility to play a negative role in the graft antithrombogenicity. The purpose of this study was to evaluate the performance of our new grafts, thrombin-free fibrin-coated small caliber vascular prostheses. Knitted polyester fabric vascular prostheses 2 mm in internal diameter were coated with fibrin coating with thrombin (Graft I) or without thrombin (Graft II). Both grafts were implanted in bilateral common carotid arteries of 35 Japanese white rabbits, with Graft I in one side and Graft II in the contralateral side. Graft patency, histology, thrombin activity, and platelet deposition were compared between both grafts on postoperative days (PODs) 1, 3, 7, 10, 14, 30, and 60. Both grafts were patent without thrombus or stenosis at each end point (maximal period, POD 60). Macro- and microscopic findings revealed that no obvious difference was observed between both grafts. Before graft implantation, thrombin activities in Grafts I and II were 0.711 +/- 0.086 and 0.009 +/- 0.007 optical density at 405 nm, respectively. Thrombin activity of Graft II was significantly less than that of Graft I in every period after graft implantation, and platelet deposition of Graft II was significantly less than that of Graft I until POD 30. Thrombin-free fibrin-coated vascular prostheses have superior performance of antithrombogenicity to conventional fibrin-coated vascular prostheses with thrombin.

Proteasome inhibitor prevents experimental arterial thrombosis in renovascular hypertensive rats

Recent studies indicate that highly selective proteasome inhibitors can be useful in prevention of some cardiovascular events. Here we demonstrate that proteasome inhibitor, Z-Ile-Glu (Ot-Bu) Ala-Leucinal (PSI), is active in the prevention of platelet-dependent arterial thrombosis induced in renovascular hypertensive rats (two-kidney, one clip Goldblatt model, and 2K1C, n=5). The administration of PSI intravenously at a single dose of 0.3 mg/kg before induction of arterial thrombosis markedly increased carotid final flow rate, as compared to control (vehicle) group (10.36 +/- 1.8 ml/min and 1.2 +/- 1.2 ml/min, respectively), significantly decreased the wet (1.23 +/- 0.23 mg and 4.1 +/- 0.94 mg, respectively), and dry (0.46 +/- 0.145 mg and 1.46 +/- 0.39, respectively) thrombus weight, and completely prevented arterial occlusion. Moreover, platelets from PSI - treated thrombotic 2K1C rats, showed in response to collagen a significant inhibition of aggregation in the whole blood (10.26 +/- 0.6 ohms vs. 15.51 +/- 0.91 ohms in the control group). In contrast, collagen-induced platelet aggregation was not inhibited in vitro, after pre-treatment of the blood with PSI at the concentration of 10 microM that effectively inhibited the 20S proteasome activity in platelets, indicating that ex vivo anti-aggregatory effect of PSI proceeds through an indirect mechanism not associated with suppression of 20S proteasome activity in platelets. In conclusion, our in vivo findings demonstrate that proteasome inhibitor, Z-Ile-Glu(Ot-Bu)Ala-Leucinal, prevents the development of arterial thrombosis in renovascular hypertensive rats and effectively suppresses platelet aggregation by an indirect mechanism. Thus the data provide a new insight into the potential role for the proteasome-dependent pathway in cardiovascular events.

Inhibition and reversal of platelet-rich arterial thrombus in vivo: direct vs. indirect factor Xa inhibition

BACKGROUND/OBJECTIVE

The efficacy of a direct factor (F)Xa inhibitor, ZK-807834, was compared with indirect inhibition by enoxaparin for inhibition and deaggregation of acute platelet-rich thrombi in a well-characterized porcine carotid injury model.

METHODS

A crush injury was performed on a randomly chosen carotid artery and the thrombus allowed to propagate for 30 min. Pigs then received intravenous drug for 35 min: ZK-807834-Dose 1 (40 microg kg(-1) bolus + 1.5 microg kg(-1) min(-1) infusion, n=6); ZK-807834-Dose 2 (20 microg kg(-1) bolus + 0.75 microg kg(-1) min(-1) infusion; n=6); enoxaparin (1 mg kg(-1) bolus; n=6); or saline (n=6). Five minutes after drug initiation, the contralateral artery was injured. Thrombus size was monitored by scintillation detection of autologous 111In-platelets.

RESULTS

The prothrombin time ratio was 2.2 +/- 0.1; 1.4 +/- 0.3; 1.2 +/- 0.9 and 1.1 +/- 0.2, respectively. ZK-807834-Dose 1 significantly inhibited carotid platelet deposition (525 +/- 226 x 10(6) cm(-2); P = 0.008), whereas ZK-807834-Dose 2 (2325 +/- 768) and enoxaparin (1236 +/- 383) were not different from saline (2776 +/- 642). Thrombus deaggregation was greatest for animals receiving ZK-807834-Dose 1 (473 +/- 185). Neither ZK-807834-Dose 2 (1588 +/- 480) nor enoxaparin (1618 +/- 686) was different from saline control (2222 +/- 598).

CONCLUSIONS

Direct FXa inhibition with ZK-807834, at a prothrombin time ratio of 2.2, effectively inhibits thrombosis and promptly deaggregates thrombi induced by arterial injury. In contrast, indirect FXa inhibition with enoxaparin was ineffective.

Effect of trans-resveratrol on the thrombogenicity and atherogenicity in apolipoprotein E-deficient and low-density lipoprotein receptor-deficient mice

Resveratrol is one of the major polyphenolics in red wine that has been shown to exert the preventive effects against cardiovascular diseases. The effect of trans-resveratrol (t-RES) administered as an ingredient of the diet on the atherothrombotic tendency was assessed in genetically hypercholesterolemic mice after laser-induced damage on endothelium. Mice lacking both apolipoprotein E and low-density lipoprotein receptor (apoE-/-/LDLR-/-) were fed with a high-fat diet with or without t-RES (9.6 and 96 mg/kg diet) for 8 weeks. The atherosclerotic tendency was morphometrically analyzed in their aortae. The thrombotic tendency was determined by inducing thrombus by the irradiation of a helium-neon laser on carotid arteries of these mice with injection of Evans blue. Atherosclerotic area and thrombus size were evaluated by image analyzing in a computer system. Even though the plasma concentrations of lipids (total cholesterol and triacylglycerol) did not change in the control and t-RES groups, a significant decrease (approximately 30%) in the formation of atheroma was observed in the aortae of the t-RES group. The size of laser-induced thrombus that mostly consisted of platelet aggregates was significantly reduced (approximately 25%) in the t-RES group compared with that in the control group. Thus, t-RES orally administrated with a high-fat diet in apoE-/-/LDLR-/- mice significantly suppressed atherosclerosis in their aortae and reduced the laser-induced thrombosis in their carotid arteries.

Antiplatelet properties of a novel, non-NO-based soluble guanylate cyclase activator, BAY 41-2272

Nitric oxide (NO) plays an important role in cardiovascular homeostasis, particularly in the regulation of vascular tone and the reactivity of platelets and circulating cells. Soluble guanylate cyclase (sGC) acts as the principal biological target for NO and catalyses the formation of the intracellular second messenger cyclic GMP (cGMP); activation of this enzyme is thought to be responsible for the majority of cardiovascular actions of NO. In the present study, we have evaluated the antiplatelet effects of a novel non-NO-based sGC activator, BAY 41-2272, in vitro and in vivo. BAY 41-2272 produced a marked inhibition of platelet aggregation in washed platelets with a potency (IC(50) approximately 100 nM) some threefold less than the NO donor S-nitrosoglutathione. BAY 41-2272 also prevented aggregation in platelet-rich plasma (PRP), albeit with a much lower potency. Both NO and prostacyclin exhibited synergistic activity with BAY 41-2272 to inhibit platelet aggregation. In vivo, at doses of BAY 41-2272 that significantly reduced blood pressure, the compound had little effect on FeCl(3)-induced thrombosis. These data confirm that intraplatelet sGC activation results in inhibition of aggregation and suggests that novel non-NO-based sGC activators, which possess both hypotensive and antiplatelet activities, may be useful as therapeutic agents.

Recombinant activated factor VII decreases bleeding without increasing arterial thrombosis in rabbits

PURPOSE

To compare the effects of recombinant activated factor VII (rFVIIa) and platelet-rich plasma (PRP) in an experimental model of bleeding and arterial thrombosis.

METHODS

The Folts model was used in 60 rabbits. After anesthesia, the carotid artery was exposed and a 75% stenosis was induced. A compression injury of the artery triggered a series of cyclic flow reductions (CFRs). After counting baseline CFRs, animals were assigned randomly to one of four groups (n = 15 in each): control, PRP, rFVIIa and placebo. Control animals received 10 mL.kg(-1) of saline while 10 mL.kg(-1) of a hydroxyethyl starch solution (200,000/6%/0.5) were infused in the three other groups. CFRs were measured again, followed by treatment with PRP, rFVIIa or placebo and by a final measurement of CFRs. At the end of each observation period, an ear immersion bleeding time (BT) was measured and a blood sample was drawn for the evaluation of hematological variables. Microvascular bleeding was evaluated at the end of the experiment in grams of blood shed from liver and spleen sections. Results are presented as median (range).

RESULTS

rFVIIa shortened the BT and decreased microvascular bleeding as compared with placebo [60 (35-100) sec vs 110 (50-140) sec, P = 0.0019 and 9 (4-24) g vs 17 (5-28) g, P = 0.002, respectively]. rFVIIa did not increase CFRs [3(0-9) vs |(0-5), P = 0.11].

CONCLUSION

rFVIIa led to a decrease in BT and microvascular bleeding but did not significantly affect arterial thrombosis in rabbits.

Antibody blockade or mutation of the fibrinogen gamma-chain C-terminus is more effective in inhibiting murine arterial thrombus formation than complete absence of fibrinogen

An elevated plasma fibrinogen level is a risk factor for thrombotic cardiovascular disease, but which of fibrinogen's functions is responsible for the increased risk is unknown. To define better the contribution of fibrinogen to large vessel thrombus formation, we studied carotid artery thrombosis in wild-type mice, mice lacking fibrinogen (fbg-/-), mice treated with 7E9 (a blocking antibody to the fibrinogen gamma-chain C-terminus), and mice expressing a mutant fibrinogen (gamma delta 5) that lacks the gamma-chain platelet-binding motif QADGV. In control mice, thrombus formation resulted in occlusion in 8 +/- 2 minutes (mean +/- SD). In fbg-/- mice, thrombi grew to large sizes, but then they abruptly embolized, confirming previous observations by others in an arteriolar thrombus model. In contrast, mice treated with 7E9 and gamma delta 5 mice developed only small, nonoclusive mural thrombi and embolization was limited. These findings reveal that a fibrinogen antibody, 7E9, or a fibrinogen mutant retaining clotting function, can limit thrombus formation more effectively than the complete absence of fibrinogen. We hypothesize that the smaller thrombi in these animals result from the ability of fibrin to bind and sequester thrombin and/or the ability of the altered fibrinogen molecules, which cannot recruit platelets, to bind to and passivate the surface.

Prevention of thrombosis following deep arterial injury in rats by bovine activated protein C requiring co-administration of bovine protein S

The antithrombotic effect of bovine activated protein C (bAPC) given with or without bovine protein S (bPS) was investigated in a rat model of deep arterial injury. A segment of the left common carotid artery was isolated between vascular clamps and opened longitudinally. An endarterectomy was performed and the arteriotomy was closed with a running suture, whereafter the vessel was reperfused by removing the clamps. The antithrombotic effect (vascular patency rates 31 minutes after reperfusion) and the arteriotomy bleeding were measured. Ten treatment groups each containing 10 rats and a control group of 20 animals were in a blind random fashion given intravenous bolus injections of increasing doses of activated protein C, with or without co-administration of protein S. The groups received either bAPC alone (0.8, 0.4, 0.2 or 0.1 mg/kg), bAPC (0.8, 0.4, 0.2, 0.1 or 0.05 mg/kg) combined with bPS (0.6 mg/kg), or bPS alone (0.6 mg/kg) whereas the control group received vehicle only. Administered alone, bAPC or bPS had no antithrombotic effect, regardless of dosage. In contrast, all groups that were treated with bAPC in combination with bPS demonstrated a significant antithrombotic effect, as compared to controls. Neither bAPC, bPS, nor the combination of bAPC and bPS increased the arteriotomy bleeding significantly compared to controls. In vitro clotting assays using bAPC or bPS alone yielded only minor prolongation of clotting time, whereas bAPC combined with bPS prolonged the clotting time considerably, demonstrating the dependence on the APC-cofactor activity of bPS for expression of anticoagulant activity by bAPC. In conclusion, our study shows the in vivo significance of protein S as a cofactor to activated protein C, and that potent anti-thrombotic effect can be achieved by low doses of bAPC combined with bPS, without producing hemorrhagic side effects.

Prevention of carotid artery thrombosis after oral administration of the glycoprotein IIb/IIIa antagonist CRL42796

This study investigates the effect of the glycoprotein IIb/IIIa receptor antagonist CRL42796 in a canine model of carotid artery thrombosis. Both carotid arteries developed occlusive thrombosis in each of the five control animals (time to occlusion: right carotid artery, 92.6 minutes; left carotid artery, 89.0 minutes). A single oral dose of CRL42796 (3 mg/kg) prevented occlusive thrombosis in 4 of 6 vessels and increased time to thrombosis, albeit not significantly (right carotid artery, 134.1 minutes; left carotid artery, 145.0 minutes). When the initial dose of CRL42796 was followed by a second oral dose (3 mg/kg) 2 hours later, 10 of 10 carotid arteries remained patent throughout the period of electrolytic injury. CRL42796 reduced thrombus weight in both treatment protocols. Ex vivo platelet aggregation with arachidonic acid (AA) or adenosine diphosphate (ADP) was reduced at 120, 240, and 360 minutes after two doses of CRL42796. A single oral dose reduced ADP-induced responses at 240 and 360 minutes, but significant effects were not observed with AA. Bleeding time increased 360 minutes after two oral doses of CRL42796, but not at 120 minutes. Bleeding time was unchanged with the single dose of CRL42796. The results demonstrate that oral administration of CRL42796 prevents carotid artery thrombosis in response to deep vessel wall injury and may have potential value to be characterized in extended preclinical and clinical study.

Low-molecular-weight heparin (dalteparin) effectively prevents thrombosis in a rat model of deep arterial injury

Unfractionated heparin is often used to prevent thrombosis in microvascular surgery, but a major drawback of heparin therapy is increased bleeding. Low-molecular-weight heparins prevent venous thrombosis as effectively as heparin and have better bioavailability and a longer plasma half-life, which explains the increased use of low-molecular-weight heparins as substitutes for heparin in clinical practice. However, the ability of low-molecular-weight heparins to prevent arterial thrombosis has been debated. In this study, the authors compared the antithrombotic and antihemostatic effects of heparin and the low-molecular-weight heparin dalteparin in a rat model of arterial thrombosis. A segment of the left common carotid artery was isolated between vascular clamps and opened longitudinally. An endarterectomy was performed and the arteriotomy was closed with a running suture. The antithrombotic effect (vascular patency 31 minutes after reperfusion) and the surgical bleeding were measured. Groups of 10 rats were treated in a blind, random fashion with intravenous injection of one of the following substances 1 minute before clamp release. Three groups received a bolus of heparin (20, 60, or 180 IU anti-factor Xa/kg), three groups received dalteparin (60, 180, or 540 IU anti-factor Xa/kg), and one group was treated with vehicle (saline). Heparin 180 IU/kg produced a distinct antithrombotic effect compared with the control group (p = 0.03), but it also significantly increased the surgical bleeding to 2.0 g compared with 1.5 g in the control group (medians, p = 0.01). Dalteparin 180 and 540 IU/kg also produced a powerful antithrombotic effect (p = 0.01 and p = 0.03, respectively). In contrast to heparin, 180 IU/kg dalteparin did not increase the surgical bleeding (median, 1.5 g; p = 0.37 versus controls). Dalteparin 540 IU/kg increased the median surgical bleeding to 2.6 g (p = 0.06 versus controls). The nonsignificant difference may be explained by the great interindividual variation of surgical bleeding in the high-dose dalteparin group. Dalteparin prevented arterial thrombosis as effectively as unfractionated heparin. In contrast to heparin, dalteparin did not increase the surgical bleeding, which indicates that dalteparin instead of heparin can be used to prevent thrombosis in microvascular surgery.

LB30057, an orally effective direct thrombin inhibitor, prevents arterial and venous thrombosis in rats and dogs

The anti-thrombotic effects of LB30057, a direct thrombin inhibitor, were evaluated with in vivo rat and dog thrombosis models. In rats, 1 mg/kg of LB30057 inhibited half of the clot formations in the inferior vena cava at 5 minutes after intravenous application. When measured at 2 hours after oral application, 100 mg/kg prevented approximately half of the clot formations in the inferior vena cava and 50 mg/kg prolonged the mean occlusion time from 15.6 +/- 1.3 minutes to 47.2 +/- 8.3 minutes in the carotid artery. In dogs, the formation of thrombus in the jugular vein was reduced to half at a dose range of 20-30 mg/kg at 6 hours after oral application. In addition, the LB30057 dosage required to reduce venous clot formation by approximately 80-90% in dogs was only about 10% of that required for the same reduction in rats. This is probably due to the variation in its time-dependent blood concentration profiles in each species; for example, the plasma half-life of LB71350 in dogs was longer than that in rats (153.0 +/- 3.0 vs. 129.7 +/- 12.7 min at 30 mg/kg, i.v., respectively). AUC, T(max), C(max), and BA in dogs were 59, 8.9, 9.17, and 13.3 times higher than those in rats at oral 30 mg/kg, respectively. Taken together, these results suggest that LB30057 administered orally is effective in the prevention of arterial and venous thrombosis in rats and dogs. It therefore represents a good lead compound for investigations to discover a new, orally available, therapeutic agent for treating thrombotic diseases.

[Per and early postoperative use of low molecular weight heparin in carotid surgery]

The goal of this study was to evaluate per and postoperative use of nadroparin during carotid surgery with mortality and neurologic morbidity as primary end points. From January 1995 to December 1999, 237 procedures were performed on 215 patients for isolated carotid surgery; 57% were symptomatic. Surgery was performed under general anesthesia. Before clamping, patients received an intravenous bolus of 70 UI/kg of nadroparin. Shunting was used in 40% of patients. Postoperatively, from the 6(th) hour, nadroparin was given subcutaneously, 2,850 UI or 3,800 UI every 12 hours depending on the patient weight (less or more than 70 kg). The only biologic surveillance was platelet count twice a week. Antiplatelet drugs were given at day 2. Completion Duplex scan was performed before day 30. Seven postoperative ischemic strokes (3 non disabling) occurred including one fatal stroke. Another patient died at day 25 from inaugural duodenal bleeding due to pancreas cancer. The 30 days stroke or death rate was 3.37% (5.92% in symptomatic; 0% in asymptomatic). No hemorrhagic stroke occurred. Four patients were reoperated for cervical hematoma (1.68%). No thrombocytopenia occurred. Duplex scan, performed on 235 operated carotid arteries, showed 2 asymptomatic carotid thromboses. No other cardiovascular complication was found on clinical data. These results are comparable to published literature data in prospective as well as retrospective studies. Per and postoperative use of nadroparin in carotid surgery gave results similar to previously published reports in terms of mortality, neurologic morbidity and hematoma. Its easy use, needing only 2 injections a day and platelet count, with a reduction of the risk of heparin-induced thrombocytopenia make the use of nadroparin very attractive during the perioperative period.

Local expression of C-type natriuretic peptide suppresses inflammation, eliminates shear stress-induced thrombosis, and prevents neointima formation through enhanced nitric oxide production in rabbit injured carotid arteries

We previously observed that adenovirus-mediated expression of C-type natriuretic peptide (CNP) markedly inhibits neointima formation after balloon injury in rat carotid arteries, suggesting that CNP has multiple effects over its modest inhibitory effect on cellular proliferation. We hypothesized that local expression of CNP might have antithrombotic and antiinflammatory effects. Balloon-injured rabbit carotid arteries were infected with an adenovirus expressing human CNP (AdCNP), human tissue factor pathway inhibitor (AdTFPI), or bacterial beta-galactosidase (AdLacZ) or infused with saline. Seven days later, shear stress-induced thrombosis was evaluated by cyclic flow variation (CFV), reflecting recurrent cycles of thrombus formation and dislodgment. CFV was observed in all AdLacZ-infected and saline-infused arteries but not in arteries infected with AdCNP or AdTFPI even in the presence of epinephrine. Injury increased the expressions of intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) and infiltration of macrophages. However, these effects were markedly reduced in AdCNP-treated arteries but not in AdTFPI-infected ones. In AdCNP-infected arteries, injury-induced expression of inducible NO synthase (iNOS) was enhanced, leading to increased NO generation. Interestingly, when the enhanced NO production was inhibited, neither inhibitory effect was observed, and suppression of neointima formation by CNP was canceled. Our study demonstrates that overexpression of CNP shows antithrombotic and antiinflammatory effects and reduces neointima formation mainly through enhanced NO production.

Prevention of experimental carotid and coronary artery thrombosis by the glycoprotein IIb/IIIa receptor antagonist CRL42796

1. The antithrombotic effect of the glycoprotein IIb/IIIa receptor antagonist, CRL42796, was examined in canine models of carotid and coronary artery thrombosis. 2. In the carotid artery thrombosis model, occlusion occurred in all control vessels (time to thrombosis 47.6+/-8.9 min). After treatment with low dose CRL42796 (15 microg kg(-1) loading dose +0.31 microg kg(-1) min(-1) i.v.), two of five vessels occluded. Time to thrombosis increased significantly to 155.2+/-23.1 min. When the drug infusion was increased (0.69 microg kg(-1) min(-1)), each of five vessels remained patent. 3. Ex vivo platelet aggregation in response to arachidonic acid (AA) and ADP was examined in platelet rich plasma (PRP) prepared from citrate or heparin anticoagulated blood. CRL42796 reduced platelet reactivity at low and high doses in PRP from citrate anticoagulated blood. However, in PRP from heparin anticoagulated blood, only the higher infusion dose produced a significant reduction in ex vivo platelet responses. 4. A combination of oral aspirin (4.6 mg kg(-1) -41, -17 h) and the low infusion dose of CRL42796 did not produce an additional benefit beyond that provided by CRL42796 alone. 5. Coronary artery thrombosis was inhibited in four of five vessels treated with the lower infusion dose of CRL42796 and in five of five vessels treated with the higher infusion. Time to thrombosis increased with both doses (Control, 90.8+/-10.4 min; low dose, 165.8+/-14.2 min; high dose, >180.0+/-0 min). 6. The results indicate that CRL42796 is an effective in vivo antithrombotic agent against experimentally-induced carotid and coronary artery thrombosis.

[Experimental study on anti-thrombus effect of different extracts from Semen Persicae]

OBJECTIVE

To observe the effects of anti-thrombus of different extracts from Semen Persicae and provide experimental basis for finding and defining effective fraction of Semen Persicae.

METHODS

The effects of different extracts from Semen Persicae on clotting time in mice, pulmonary embolism in mice and electro-irritate thrombosis in rats were observed.

RESULT

Ethyl acetate extract from Semen Persicae could prolong clotting time in mice, markedly relieve respiratory difficult due to pulmonary embolism in mice induced by ADP-Na, obviously retard the generation of thrombosis induced by electrical injury of carotid artery in rats.

CONCLUSION

Ethyl acetate extract from Semen Persicae possesses evidently anti-thrombotic effect.

Intimatan prevents arterial and venous thrombosis in a canine model of deep vessel wall injury

Resistance of fibrin-bound thrombin to inactivation by the heparin/antithrombin III complex is considered a limitation in the use of heparin as an antithrombotic agent. Intimatan (dermatan 4,6-di-O-sulfate) is a heparin cofactor II agonist that inhibits both free and bound forms of thrombin. The present study examines the hypothesis that Intimatan prevents thrombotic occlusion in response to vascular wall injury in a canine model of carotid artery/jugular vein thrombosis. The left carotid artery and right jugular vein served as vehicle-treated control vessels, whereas the right carotid artery and left jugular vein were subjected to electrolytic injury after administration of Intimatan (9 mg/kg bolus + 300 microg/kg/min infusion, i.v.) or dalteparin (Fragmin) (400 IU/kg, s.c.). Intimatan significantly increased time to carotid artery (226.0 +/- 14.0 min) and jugular vein (240.0 +/- 0.0 min) thrombosis, compared with control vessels (carotid artery, 87.1 +/- 7.9 min; jugular vein, 60.6 +/- 7.4 min). Vessel patency was maintained in eight of eight jugular veins and seven of eight carotid arteries during treatment with Intimatan. Dalteparin significantly increased time to carotid artery thrombosis (122.1 +/- 17.5 min) compared with control (64.3 +/- 8.2 min), but did not change the time to thrombosis in the jugular vein. Only one carotid artery remained patent at the end of the dalteparin protocol. The two drugs produced minimal increases in bleeding times, and Intimatan increased the activated partial thromboplastin time above that observed with dalteparin. The results demonstrate that Intimatan is effective in preventing occlusive arterial and venous thrombosis in an experimental model of deep vascular wall injury.

Long-term inhibition of nitric oxide synthesis increases arterial thrombogenecity in rat carotid artery

Reduced activity of endothelial nitric oxide (NO) may be involved in thrombus formation on atherosclerotic plaques, a major cause of acute coronary syndrome. However, mechanisms of such increase in arterial thrombogenecity have not been fully understood. We previously reported that long-term inhibition of NO synthesis by administration of N(G)-nitro-L-arginine methyl ester (L-NAME) causes hypertension and activates vascular tissue angiotensin-converting enzyme (ACE) activity. We used this model to investigate the mechanism by which long-term impairment of NO activity increases arterial thrombogenecity. We observed cyclic flow variations (CFVs), a reliable marker of platelet thrombi, after the production of stenosis of the carotid artery in rats treated with L-NAME for 4 wk. The thrombin antagonist argatroban suppressed the CFVs. The CFVs were detected in rats receiving L-NAME plus hydralazine but not in rats receiving L-NAME plus an ACE inhibitor (imidapril). Treatment with the ACE inhibitor imidapril, but not with hydralazine, prevented L-NAME-induced increases in carotid arterial ACE activity and attenuated tissue factor expression. These results suggest that long-term inhibition of endothelial NO synthesis may increase arterial thrombogenecity at least in part through angiotensin II-induced induction of tissue factor and the resultant thrombin generation. These data provide a new insight as to how endothelial NO exhibits antithrombogenic properties of the endothelium.

A human antibody that inhibits factor IX/IXa function potently inhibits arterial thrombosis without increasing bleeding

10C12, a human antibody F(ab')2, which specifically binds to the gamma-carboxyglutamic acid domain of factor IX/factor IXa (F.IX/IXa), interferes with all known coagulation processes in which F.IX/IXa is involved. In a rabbit model of carotid artery injury, intravenous administration of 10C12 or heparin decreased thrombosis dose dependently. The dose that resulted in a 90% reduction of thrombus mass (ED90) was a 30-microg/kg bolus of 10C12 or a 100-U/kg bolus plus 1.0 U x kg(-1) x min(-1) infusion of heparin. Heparin, at and below the ED90, significantly prolonged coagulation times and cuticle bleeding times. In contrast, 10C12 had no effect on coagulation or bleeding times at doses up to 4 times the ED90. To further evaluate the effect of 10C12 on bleeding, it was compared with heparin in a novel model of blood loss. At the ED90 of heparin, blood loss induced by a standardized injury to the vasculature of the rabbit tibia increased to more than 2 times that of saline controls. In contrast, the dose of 10C12 required to produce a similar increase in blood loss was more than 30 times the ED90. The antithrombotic potency and relative safety of this fully human antibody suggests that it may have therapeutic value for treatment of thrombotic disorders.

Heparin cofactor II inhibits arterial thrombosis after endothelial injury

Heparin cofactor II (HCII) is a plasma protein that inhibits thrombin rapidly in the presence of dermatan sulfate, heparan sulfate, or heparin. HCII has been proposed to regulate coagulation or to participate in processes such as inflammation, atherosclerosis, and wound repair. To investigate the physiologic function of HCII, about 2 kb of the mouse HCII gene, encoding the N-terminal half of the protein, was deleted by homologous recombination in embryonic stem cells. Crosses of F1 HCII(+/-) animals produced HCII(-/-) offspring at the expected mendelian frequency. Biochemical assays confirmed the absence of dermatan sulfate-dependent thrombin inhibition in the plasma of HCII(-/-) animals. Crosses of HCII(-/-) animals produced litters similar in size to those obtained from heterozygous matings. At 1 year of age, HCII-deficient animals were grossly indistinguishable from their wild-type littermates in weight and survival, and they did not appear to have spontaneous thrombosis or other morphologic abnormalities. In comparison with wild-type animals, however, they demonstrated a significantly shorter time to thrombotic occlusion of the carotid artery after photochemically induced endothelial cell injury. This abnormality was corrected by infusion of purified HCII but not ovalbumin. These observations suggest that HCII might inhibit thrombosis in the arterial circulation.

Recombinant annexin II modulates impaired fibrinolytic activity in vitro and in rat carotid artery

Fibrinolytic activity has been reported to be decreased in atherosclerosis. Recently, annexin II was identified as a coreceptor on endothelial cells for plasminogen and tissue plasminogen activator. In this study, we examined whether recombinant annexin II (rAN II) protein can modulate fibrinolytic activity on vascular endothelium in vitro and in vivo. The effect of rAN II on human umbilical vein endothelial cells (HUVECs) was measured. Addition of a fluorescent plasmin substrate revealed that HUVECs treated with rAN II exhibited significantly more plasmin generation than those treated with BSA. Moreover, rAN II treatment of HUVECs restored plasmin generation impaired by plasminogen activator inhibitor-1 or homocysteine pretreatment. In a rat carotid artery thrombus model, the patency of thrombosed carotid arteries was significantly enhanced by rAN II injection, in contrast to BSA injection, without systemic blood coagulation dysregulation. We found that rAN II enhanced plasmin generation on vascular endothelium in vitro and reduced thrombus formation in vivo, and concluded that enhancement of endothelial fibrinolytic activity by annexin II could modulate the hypercoagulable state of atherosclerosis. Further study of rAN II in vitro and in vivo may lead to the establishment of novel therapeutic approaches to thrombogenic vascular disease.

The effect of aspirin and prostaglandin E(1) on the patency of microvascular anastomosis in the rats

The purpose of this study was to evaluate the effect of oral prostaglandin E(1)(PGE(1)) on the patency of the microvascular anastomosis of the carotid artery in rat. A total of 48 rats were used, and divided into three groups. The first group (A) was used as a control with no medical agent being used after anastomosis, the second group (B) was medicated with aspirin, and the third group (C) was medicated with oral PGE(1). In each group, four rats were sacrificed serially on every post-operative 3, 5, 10 and 15 days after arterial anastomosis. Patency and histologic evaluations at the anastomotic site were observed. The results revealed that the PGE(1) therapied group showed highest patency rate (100%), lesser formation of mural thrombosis, and also minimal changes in the intimal hyperplasia and medial fibrosis. From these findings, we could conclude that PGE(1) has superior effect on maintaining the patency after microvascular surgery.

The antithrombotic efficacy of AT-1459, a novel, direct thrombin inhibitor, in rat models of venous and arterial thrombosis

The antithrombotic efficacy of AT-1459, a novel, direct thrombin inhibitor (Ki = 4.9 nM) was evaluated in rat models of venous thrombosis combined with a bleeding time test and arterial thrombosis. After drugs were given by i. v. bolus injection plus a continuous infusion, the ID50, (a dose that exhibits 50% inhibition of thrombus formation over each vehicle group) values of AT-1459, argatroban, and dalteparin were 0.04 mg/kg plus 0.04 mg/kg/h, 0.1 mg/kg plus 0.4 mg/ kg/h, and 13.0 IU/kg plus 26.0 IU/kg/h, respectively, in the venous thrombosis study. The BT2 (a dose that causes 2-fold prolongation of bleeding time over each vehicle group) values of AT-1459, argatroban, and dalteparin were 0.9 mg/kg plus 0.9 mg/kg/h, 1.0 mg/kg plus 0.6 mg/kg/h, and 345.5 IU/kg plus 691.0 IU/kg/h in the rat tail transection model. The ratios of BT2/ID50 of AT-1459, argatroban, and dalteparin were 22.5, 10.0, and 26.6, respectively. In a rat model of arterial thrombosis induced by topical FeCl2 application, intravenous administration of AT-1459, argatroban, and dalteparin improved the vessel patency significantly (P < 0.01) at 0.6 mg/kg plus 0.6 mg/kg/h, 0.6 mg/kg plus 2.4 mg/kg/h, and 300 IU/kg plus 600 IU/kg/h, respectively. The oral antithrombotic effect of AT-1459 lasted for 6 after administering 30 mg/kg and improved the vessel patency significantly 1 h after administering the same dose in venous and arterial thrombosis models, respectively, with a rapid onset of action. Warfarin also inhibited thrombus weight and improved the vessel patency significantly after oral administration of 0.3 mg/kg for three consecutive days in the same study. The antithrombotic and hemorrhagic effects of all drugs studied were correlated with plasma concentration or clotting times. These results suggest that AT-1459 may be clinically useful as an orally available antithrombotic agent for the prevention of venous and arterial thrombosis.

[Application of clexane in reconstructive surgery of the aorta arch vessels for the arterial thrombosis prophylaxis]

Results of treatment of 114 patients for ten-year period, operated on for diseases of extracranial vessels, were adduced. Up to 1998 after performance of reconstructive operation as anticoagulant heparin was used in 80 patients and in last time--low-molecular heparin clexane in 34. After operation all patients survived. An ischemic insult occurred in 2-3 days after the operation in 2(2.5%) patients, while application of heparin, in 5--positive changes of the disease course were absent, in 19(23.75%)--postoperative hemorrhagic complications occurred. When clexane was administered in 2(5.9%) patients the cerebral hemodynamics improvement was not noted, complications in the early and late postoperative periods were absent. In term of observation up to 5 years good results was noted in 21(62.3%) patient, fair--in 9 (27.2%). In late postoperative period the brain hemodynamics improvement was not noted in 2 (5.9%) patients. Application of clexane for the arterial thrombosis prophylaxis is clinically substantiated and permits to reduce significantly the risk of the complications occurrence, which are observed with usage of heparin.

Inhibition of arterial thrombosis by a soluble tissue factor mutant and active site-blocked factors IXa and Xa in the guinea pig

The substrate recognition region of tissue factor contains two residues, Lys165 and Lys166, which are important for macromolecular substrate activation by the tissue factor:factor VIIa complex. Replacement of these two residues with alanine in a soluble version of human tissue factor resulted in a mutant, hTFAA, which can bind factor VIIa but forms an enzymatically inactive complex. We found that hTFAA inhibits the activity of guinea pig factor VIIa, allowing us to evaluate hTFAA's effects on thrombosis and hemostasis in a guinea pig model of recurrent arterial thrombosis. In addition to heparin, the effects of hTFAA were compared to active site inhibited factor IXa (F.IXai) and factor Xa (F.Xai). We found that hTFAA, F.IXai and F.Xai were potent antithrombotics and may possess a decreased risk of hemorrhage when compared to unfractionated heparin. When administered at a dose that inhibited thrombosis by about 90%, hTFAA neither affected cuticle bleeding nor the activated partial thromboplastin time, and had only a modest effect on the prothrombin time. At equi-efficacious doses, F.IXai, F.Xai and heparin prolonged bleeding times by 20% (p >0.5), 50% (p <0.05) and 100% (p <0.01), respectively. In summary, our study demonstrates that, unlike heparin, specific inhibitors of factors VIIa, IXa and Xa can produce antithrombotic effects without or with only minimally disturbing normal hemostasis. The results further suggest that factor VIIa and factor IXa are especially promising targets for antithrombotic drug development.

Prevention of arterial thrombosis by intravenously administered platelet P2T receptor antagonist AR-C69931MX in a canine model

P2Y1, P2X1, and P2T receptors mediate ADP-induced platelet aggregation. The antithrombotic effects of AR-C69931MX (N6-[2-methylthio)ethyl]-2-[3,3,3-trifluoropropylthio]-5'-adenylic acid, monoanhydride with dichloromethylenebiphosphonic acid), a selective P2T platelet receptor antagonist, was assessed in a canine model of arterial thrombosis. Placebo or AR-C69931MX (4.0 microg/kg/min for 6 h) pretreatment was administered as an intravenous infusion beginning 15 min before inducing vessel wall injury. A 300-microA anodal current was applied to the intima of the carotid artery for 180 min or discontinued 30 min after cessation of blood flow due to thrombus formation. Each of five control animals developed occlusive thrombi within 3 h after induction of vessel wall injury. In contrast, carotid artery blood flow in five of six AR-C69931MX-treated animals was maintained for the duration of the protocol. Ex vivo platelet aggregation in response to adenosine diphosphate was inhibited at the first measurement time point of 75 min after the start of drug infusion and remained inhibited during drug administration. Bleeding time values were increased in the drug-treated group. Values for both the ex vivo platelet aggregation and the bleeding times returned to control values shortly after discontinuation of AR-C69931MX. The results indicate that AR-C69931MX antagonizes the ex vivo and in vivo aggregatory actions of ADP, and displays a rapid onset and offset of action with the ability to prevent occlusive arterial thrombus formation. AR-C69931MX may be suitable for the management of patients who require short-term modulation of platelet function.

Inhibition of arterial thrombosis by a peptide ligand of the thrombin receptor

Thrombin plays an important role in promoting arterial thrombosis by platelet activation and by catalyzing fibrin formation. Use of thrombin inhibitors that block both the platelet-activating and fibrin formation properties of thrombin are associated with hemostasis. This problem might be overcome by developing agents that block only the platelet-activating property of thrombin. Because the platelet-activating property of thrombin is mediated by the thrombin receptor, antagonists of the thrombin receptor might be efficacious and potentially safer with regard to bleeding complications. We investigated whether a peptide ligand (AFLARAA) of the thrombin receptor that blocked alpha-thrombin and thrombin receptor activating peptide-induced platelet aggregation could inhibit thrombosis. A partially occlusive thrombus was generated by application of electric current in rabbit carotid artery. In control animals, the artery was completely occluded within 42+/-12 min after the current was discontinued. When the thrombin receptor activating peptide antagonist was given (100 micromol/kg as an IV bolus followed by 900 micromol/kg infusion for a period of 180 min) starting at the time the current was stopped, blood flow remained patent throughout the infusion period and for an additional 60 min after the infusion was stopped. The antithrombotic effect of the antagonist peptide was not associated with increased bleeding tendency, as judged by the amount of blood adsorbed by a gauze pad placed in a surgical incision extending to the muscle tissue and by a standard template bleeding time. These results indicate that thrombin receptor antagonist peptides can be used as antithrombotic agents.

Transcranial Doppler-directed Dextran-40 therapy is a cost-effective method of preventing carotid thrombosis after carotid endarterectomy

OBJECTIVES

perioperative stroke reduces the clinical effectiveness of carotid endarterectomy (CEA). Postoperative thrombotic stroke may be reduced in incidence by the use of transcranial Doppler-directed Dextran-40 therapy. This programme requires the purchase of additional equipment and employment of more staff. This study examined whether this additional financial outlay was cost-effective in terms of saving expenditure by preventing postoperative thrombotic stroke.

MATERIALS AND METHODS

data was collected prospectively on a series of 600 consecutive CEAs. The costs of the monitoring programme were analysed over 1- and 5-year periods. Formulae were derived allowing other units to calculate whether this technique will be cost-effective for them.

RESULTS

after the introduction of TCD monitoring the postoperative thrombotic stroke rate fell from 2.7% to 0% (8 strokes prevented). Our local unit cost for the treatment of stroke was 25,702 pounds. After allowing for the additional costs of the monitoring programme, we calculate that postoperative TCD has saved 171,393 pounds.

CONCLUSIONS

postoperative TCD monitoring is a clinically effective and also cost-effective method of reducing the stroke rate associated with CEA. For units performing more than 50 CEAs per year who experience occasional postoperative carotid thrombosis, its introduction should be considered.

Correlation between the in vivo efficacy of GPIIb/IIIa receptor antagonists (m7E3, MK-383 and DMP-728) and ex vivo platelet inhibition

In vivo antithrombotic efficacy of GPIIb/IIIa receptor antagonists (m7E3, MK-383 and DMP-728) was studied with respect to their ex vivo platelet inhibition in heparinized platelet-rich plasma (hPRP) and citrated platelet-rich plasma (cPRP) using a canine model of carotid artery thrombosis. For each drug group (n = 6), the right carotid artery was used as control vessel and resulting occlusive thrombus was kept in situ to examine the direct thrombolytic efficacy of the antagonists. Thirty minutes after occlusion of control vessel, a low or high dose of each antagonist was administered and the left carotid artery was used as test vessel. All control vessels occluded within 86-96 min in response to electrolytic injury. The incidence of occlusion with lower doses of m7E3, DMP-728, and MK-383 was 100, 33 and 100%, respectively; corresponding times to occlusion were 174, 220 and 118 min. Lower doses inhibited ADP- or AA-induced platelet aggregation in cPRP (>80%). Incidence of occlusion with high doses of m7E3, DMP-728 and MK-383 was 33, 0 and 0%, respectively; corresponding times to occlusion were 209, >240 and >240 min. Higher doses inhibited aggregation in cPRP (>80%), but only partially in hPRP (45-66%). Dose-dependent prolongation of bleeding time occurred with all antagonists. None of the antagonists lyzed preformed thrombi in control vessels. The results indicate that ex vivo platelet aggregation conducted in hPRP, as opposed to conventional cPRP, provides a better assessment of the in vivo efficacy of GPIIb/IIIa receptor antagonists.

Transcranial Doppler directed dextran therapy in the prevention of carotid thrombosis: three hour monitoring is as effective as six hours

BACKGROUND

Six hours' monitoring by transcranial Doppler (TCD) has been successful in directing Dextran therapy in patients at high risk of thrombotic stroke after carotid endarterectomy (CEA).

OBJECTIVES

Is 3 h of routine monitoring as effective as 6 h in the prevention of early postoperative thrombotic stroke?

DESIGN

Prospective, consecutive study in all patients with an accessible cranial window.

METHODS

One hundred and sixty-six patients undergoing CEA underwent 3 h of postoperative monitoring by TCD. Any patient with > 25 emboli detected in any 10 min period or those with emboli that distorted the arterial waveform were commenced on an incremental infusion of dextran 40.

RESULTS

The majority of patients destined to embolise will do so within the first 2 postoperative hours. Dextran therapy was instituted in nine patients (5%) and rapidly controlled this phase of embolisation although the dose had to be increased in three (33%). No patient suffered a postoperative carotid thrombosis but one suffered a minor stroke on day 5 and was found to have profuse embolisation on TCD; high dose dextran therapy was again instituted, the embolus count rate fell rapidly and he made a good recovery thereafter. Overall, the death and disabling stroke rate was 1.2% and the death/any stroke rate was 2.4%.

CONCLUSION

Three hours of postoperative TCD monitoring is as effective as 6 h in the prevention of postoperative carotid thrombosis.

Vitronectin inhibits the thrombotic response to arterial injury in mice

Vitronectin (VN) binds to plasminogen activator inhibitor-1 (PAI-1) and integrins and may play an important role in the vascular response to injury by regulating fibrinolysis and cell migration. However, the role of VN in the earliest response to vascular injury, thrombosis, is not well characterized. The purpose of this study was to test the hypothesis that variation in vitronectin expression alters the thrombotic response to arterial injury in mice. Ferric chloride (FeCl3) injury was used to induce platelet-rich thrombi in mouse carotid arteries. Wild-type (VN +/+, n = 14) and VN-deficient (VN -/-, n = 15) mice, matched for age and gender, were studied. Time to occlusion after FeCl3 injury was determined by application of a Doppler flowprobe to the carotid artery. Occlusion times of VN -/- mice were significantly shorter than those of VN +/+ mice (6.0 +/- 1.2 minutes v 17.8 +/- 2.3 minutes, respectively, P < .001). Histologic analysis of injured arterial segments showed that thrombi from VN +/+ and VN -/- mice consisted of dense platelet aggregates. In vitro studies of murine VN +/+ and VN -/- platelets showed no significant differences in ADP-induced aggregation, but a trend towards increased thrombin-induced aggregation in VN -/- platelets. Purified, denatured VN inhibited thrombin-induced platelet aggregation, whereas native VN did not. Thrombin times of plasma from VN -/- mice (20.5 +/- 2.1 seconds, n = 4) were significantly shorter than those of VN +/+ mice (34.2 +/- 6.7 seconds, n = 4, P < .01), and the addition of purified VN to VN -/- plasma prolonged the thrombin time into the normal range, suggesting that VN inhibits thrombin-fibrinogen interactions. PAI-1-deficient mice (n = 6) did not demonstrate significantly enhanced arterial thrombosis compared with wild-type mice (n = 6), excluding a potential indirect antithrombin function of VN mediated by interactions with PAI-1 as an explanation for the accelerated thrombosis observed in VN -/- mice. These results suggest that vitronectin plays a previously unappreciated antithrombotic role at sites of arterial injury and that this activity may be mediated, at least in part, by inhibiting platelet-platelet interactions and/or thrombin procoagulant activity.