Dronedarone reduces arterial thrombus formation

Dronedarone has been associated with a reduced number of first hospitalisation due to acute coronary syndromes. Whether this is only due to the reduction in ventricular heart rate and blood pressure or whether other effects of dronedarone may be involved is currently elusive. This study was designed to investigate the role of dronedarone in arterial thrombus formation. C57Bl/6 mice were treated with dronedarone and arterial thrombosis was investigated using a mouse photochemical injury model. Dronedarone inhibited carotid artery thrombus formation in vivo (P?<?0.05). Thrombin- and collagen-induced platelet aggregation was impaired in dronedarone-treated mice (P?<?0.05), and expression of plasminogen activator inhibitor-1 (PAI1), an inhibitor of the fibrinolytic system, was reduced in the arterial wall (P?<?0.05). In contrast, the level of tissue factor (TF), the main trigger of the coagulation cascade, and that of its physiological inhibitor, TF pathway inhibitor, did not differ. Similarly, coagulation times as measured by prothrombin time and activated partial thromboplastin time were comparable between the two groups. Dronedarone inhibits thrombus formation in vivo through inhibition of platelet aggregation and PAI1 expression. This effect occurs within the range of dronedarone concentrations measured in patients, and may represent a beneficial pleiotropic effect of this drug.     

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

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

Upper gastrointestinal complications induced by anti-platelet agents

Low-dose aspirin and thienopyridine are associated with gastrointestinal (GI) complications such as petechiae, erosion, ulcer, bleeding, and perforation. The incidence of GI bleeding in aspirin study groups was 0.82 % in the hypertension optimal treatment (HOT) study and 0.76 % in the primary prevention project (PPP) study. On the other hand, the incidence of GI bleeding by endoscopic evaluation was higher than in an observational study. In a study of 187 patients receiving low-dose aspirin for prevention of cardiovascular disease, the prevalence of endoscopically detected GI ulcers was 11 % (95 % CI 6.3–15.1 %). Several risk factors for GI bleeding (history of peptic ulcer or GI bleeding, high aspirin dose, concomitant use of non-steroidal anti-inflammatory drugs and anti-platelet agents, advanced age and Helicobacter pylori infection) were reported for patients receiving aspirin. Prevention strategies for GI complications induced by anti-platelet agents are treatment with proton pump inhibitors, histamine-2 receptor antagonists, prostaglandin analogs, prostaglandin inducers and H. pylori eradication therapy. Further investigation is necessary to identify the strategies which are suitable for Japan.     

Gorog Thrombosis Test: analysis of factors influencing occlusive thrombus formation.

We used the Gorog Thrombosis Test to analyze the factors influencing the occlusion time, which represents platelet activation and subsequent occlusive thrombus formation, in 132 healthy Japanese volunteers (116 men, 16 women; mean age, 45.0 +/- 12.0 years). The Gorog Thrombosis Test was designed to evaluate platelet aggregation and thrombolytic activity under a high shear stress condition (175 dynes/cm) in a native blood sample in vitro. The mean +/- SD occlusion time was 154.8 +/- 64.7 s (men, 153.4 +/- 64.2 s and women, 165.4 +/- 56.5 s). The occlusion time was inversely correlated with von Willebrand factor ristocetin cofactor activity (VWF:Rco) (r = -0.242, P = 0.0055) and von Willebrand factor antigen (r = -0.230, P = 0.0080). The mean occlusion time in the group with VWF:Rco of at least 170% (137 s) was significantly shorter than that in the group with VWF:Rco less than 170% (156 s, P < 0.05). Platelet counts, other coagulation markers and smoking showed no significant correlations with occlusion time. Red blood cells (r = -0.177, P = 0.0365), hemoglobin (r = -0.191, P = 0.0245) and hematocrit (r = -0.182, P = 0.0329) also showed inverse correlations with the occlusion time. This report is the first to clearly demonstrate the role of von Willebrand factor in the formation of occlusive thrombi in the Gorog Thrombosis Test.     

Hirudin interruption of heparin-resistant arterial thrombus formation in baboons

To determine the role of thrombin in high blood flow, platelet-dependent thrombotic and hemostatic processes we measured the relative antithrombotic and antihemostatic effects in baboons of hirudin, a highly potent and specific antithrombin, and compared the effects of heparin, an antithrombin III-dependent inhibitor of thrombin. Thrombus formation was determined in vivo using three relevant models (homologous endarterectomized aorta, collagen-coated tubing, and Dacron vascular graft) by measuring: (1) platelet deposition, using gamma camera imaging of 111In-platelets; (2) fibrin deposition, as assessed by the incorporation of circulating 125I-fibrinogen; and (3) occlusion. The continuous intravenous infusion of 1, 5, and 20 nmol/kg per minute of recombinant hirudin (desulfatohirudin) maintained constant plasma levels of 0.16 +/- 0.03, 0.79 +/- 0.44, and 3.3 +/- 0.77 mumol/mL, respectively. Hirudin interrupted platelet and fibrin deposition in a dose-dependent manner that was profound at the highest dose for all three thrombogenic surfaces and significant at the lowest dose for thrombus formation on endarterectomized aorta. Thrombotic occlusion was prevented by all doses studied. In contrast, heparin did not inhibit either platelet or fibrin deposition when administered at a dose that maximally prolonged clotting times (100 U/kg) (P greater than .1), and only intermediate effects were produced at 10-fold that dose (1,000 U/kg). Moreover, heparin did not prevent occlusion of the test segments. Hirudin inhibited platelet hemostatic function in concert with its antithrombotic effects (bleeding times were prolonged by the intermediate and higher doses). By comparison, intravenous heparin failed to affect the bleeding time at the 100 U/kg dose (P greater than .5), and only minimally prolonged the bleeding time at the 1,000 U/kg dose (P less than .05). We conclude that platelet-dependent thrombotic and hemostatic processes are thrombin-mediated and that the biologic antithrombin hirudin produces a potent, dose-dependent inhibition of arterial thrombus formation that greatly exceeds the minimal antithrombotic effects produced by heparin.     

Simultaneous subacute stent thrombosis of two sirolimus-eluting stents in a patient treated by ReoPro, thrombus aspiration and triple anti-platelet agents

Effective anti-platelet treatment has a key role in the prevention of stent thrombosis in the drug-eluting stent (DES) era. However, despite of the use of anti-platelet agents, stent thrombosis occurs in approximately 1% of patients, with an increased likelihood of occurrence in high-risk patients or complex lesion subset of patients [1-4]. According to the previous report, triple anti-platelet therapy (aspirin+clopidogrel+cilostazol) seemed to be more effective in preventing thrombotic complications after stenting than dual anti-platelet agent [5]. But, in this report, we present a patient with subacute stent thrombosis (ST) involving two different arteries simultaneously under the use of triple anti-platelet regimen.     

Targeting shear gradient activated von Willebrand factor by the novel single-chain antibody A1 reduces occlusive thrombus formation in vitro

Intraluminal thrombus formation precipitates conditions such as acute myocardial infarction and disturbs local blood flow resulting in areas of rapidly changing blood flow velocities and steep gradients of blood shear rate. Shear rate gradients are known to be pro-thrombotic with an important role for the shear-sensitive plasma protein von Willebrand factor (VWF). Here, we developed a single-chain antibody (scFv) that targets a shear gradient specific conformation of VWF to specifically inhibit platelet adhesion at sites of shear rate gradients (SRG) but not in areas of constant shear. Microfluidic flow channels with stenotic segments were used to create SRG during blood perfusion. VWF-GPIbα interactions were increased at sites of SRG compared to constant shear rate of matched magnitude. The scFv-A1 specifically reduced VWF-GPIbα binding and thrombus formation at sites of SRG but did not block platelet deposition and aggregation under constant shear rate in upstream sections of the channels. Significantly, the scFv A1 attenuated platelet aggregation only in the later stages of thrombus formation. In the absence of shear, direct binding of scFv-A1 to VWF could not be detected and scFVA1 did not inhibit ristocetin induced platelet agglutination. We have exploited the pro-aggregatory effects of SRG on VWF dependent platelet aggregation and developed the shear gradient-sensitive scFv-A1 antibody that inhibits platelet aggregation exclusively at sites of SRG. The lack of VWF inhibition in non-stenosed vessel segments places scFV-A1 in an entirely new class of anti-platelet therapy for selective blockade of pathological thrombus formation while maintaining normal hemostasis.     

The effects of PPAR-gamma ligand pioglitazone on platelet aggregation and arterial thrombus formation

BACKGROUND: It has been suggested that peroxisome proliferator-activated receptor (PPAR)-gamma ligands reduce the development of atherosclerosis and myocardial ischemia-reperfusion injury; both of these phenomena are associated with platelet activation. We postulated that PPAR-gamma activation would inhibit platelet activation and intra-arterial thrombus formation. METHODS AND RESULTS: Sprague-Dawley rats were fed chow mixed with pioglitazone (1 or 10 mg/kg/day) for 7 to 10 days. A filter soaked in 30% FeCl(3) was applied around the abdominal aorta to study the patterns of arterial thrombogenesis. The aortic blood flow was continuously monitored using an ultrasonic Doppler flow probe. ADP and arachidonic acid-induced platelet aggregation and the expression of constitutive nitric oxide synthase (cNOS) and thrombomodulin in aorta were measured. Pioglitazone feeding delayed the time to occlusive thrombus formation by 40% (P<0.01 vs. control, n=9) without affecting the weight of the thrombus. ADP- as well as arachidonic acid-induced platelet aggregation was also inhibited by pioglitazone feeding (P<0.01 vs. control, n=9). Pioglitazone feeding also upregulated the aortic expression of cNOS and thrombomodulin; both are considered important factors in platelet aggregation and thrombus formation in vivo. The effect of a high dose (10 mg/kg/day) of pioglitazone was not more potent than that of a low dose (1 mg/kg/day). CONCLUSION: These results indicate that pioglitazone administration decreases platelet aggregation and delays intra-arterial thrombus formation in rats, at least partially, by an increase in the expression of cNOS and thrombomodulin.     

Inhibition of thrombus formation by activated recombinant protein C in a primate model of arterial thrombosis

Activated protein C (APC) is an antithrombotic enzyme. The therapeutic potential of infused human recombinant APC (rAPC) was studied in a primate model of platelet-dependent thrombosis. Eight baboons with chronic femoral arteriovenous shunts received rAPC infusions for 1 hour. The shunts were extended with 5-cm long, 4-mm-i.d. thrombogenic Dacron graft segments for the time of infusion. The plasma level of the enzyme, the blood flow in the shunt, and the deposition of indium-111-labeled platelets and iodine-125 fibrinogen on the graft were measured. The influence of rAPC infused at doses of 0.25 and 1.0 mg/kg-hr was compared with the effects of control infusions of saline. Five of eight control grafts occluded within 60 minutes, whereas there was no change in the blood flow during rAPC infusion. Deposition of platelets was inhibited by 13 +/- 10% and by 42 +/- 13% (mean +/- SEM) after 30 minutes of infusion at the two doses, which gave rise to circulating rAPC plasma concentrations of 0.4 and 1.9 mg/l, respectively. Both doses significantly inhibited fibrin deposition in the graft. Circulating plasma markers of thrombus formation and of fibrinolysis did not increase significantly during rAPC infusion; measurements of bleeding time were also within normal limits. Thus, rAPC, like human plasma-derived APC, inhibited thrombus formation without impairing primary hemostasis.     

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文章综述了以阿司匹林为代表、临床常用的几种抗血小板药物在卒中防治方面的循证医学证据。在此基础上比较了中国、美国及欧洲关于卒中二级预防抗血小板治疗的指南推荐,并就抗血小板药物临床常见的胃肠道及颅内出血不良反应和临床规范应用策略做了阐述。