ristocetin and Thromboembolism

Topics: Binding Sites, Antibody; Blood Platelets; Cell Differentiation; Cell Migration Inhibition; Clot Retraction; Complement Fixation Tests; Gold; Heparin; Humans; Immunoglobulin G; Intradermal Tests; Platelet Aggregation; Platelet Factor 3; Prednisone; Quinidine; Ristocetin; Serotonin; Thrombocytopenia; Thromboembolism; Urea; Valproic Acid

Erythropoietin corrects anemia and improves hemostasis, but on the other hand bears a risk of thrombotic complications. Therefore in the present study an attempt has been made to evaluate bleeding time, platelet functions and some hemostatic and fibrinolytic parameters in relation to blood and platelet serotonin before and after 1, 2, 4, 8 and 12 weeks of treatment. 22 chronically hemodialyzed patients were administered with human recombinant erythropoietin (rHuEPO) in a dose of 2000 IU s.c. 3 times a week. Bleeding time was shortened significantly as early as after 1 week of the therapy, whereas hematocrit and hemoglobin increased after 2 weeks. These changes lasted throughout the study. Only a transient rise in platelet count, collagen-induced platelet aggregation, beta-thromboglobulin and VIII:C activity were observed during therapy relative to baseline values. ADP- and arachidonic acid-induced platelet aggregation seemed to be unaffected by rHuEPO treatment, whereas a gradual and progressive enhancement in platelet aggregation in response to ristocetin was found, starting from the 2nd week of the therapy. It lasted throughout the study and correlated inversely with the bleeding time and positively with a rise in both blood and platelet serotonin. rHuEPO did not alter plasminogen, fibrinogen, platelet factor 4, alpha 2 macroglobulin levels, protein C activity and euglobulin clot lysis time. A decline in protein C and S concentrations and antithrombin III activity observed during the therapy were counterbalanced by a fall in the activity of alpha 2 antiplasmin, C1 esterase inhibitor and plasminogen activator inhibitor. It is concluded that rHuEPO may improve platelet/vessel wall interactions possibly by means of serotonergic mechanisms. A lowered activity of inhibitors of fibrinolysis may be regarded as a protection against a general tendency to thrombosis during rHuEPO therapy.

Topics: Adenosine Diphosphate; Adult; Anemia; Arachidonic Acid; Biomarkers; Bleeding Time; Blood Platelets; Blood Proteins; Erythropoietin; Female; Fibrinolysis; Hematocrit; Hemoglobins; Hemostasis; Humans; Kidney Failure, Chronic; Male; Middle Aged; Platelet Aggregation; Recombinant Proteins; Renal Dialysis; Ristocetin; Serotonin; Thromboembolism; Time Factors

Platelet cross-linking during arterial thrombosis involves von Willebrand Factor (VWF) multimers. Therefore, proteolysis of VWF appears promising to disaggregate platelet-rich thrombi and restore vessel patency in acute thrombotic disorders such as ischemic stroke, acute coronary syndrome, or acute limb ischemia.. Experimental models of thrombotic stroke induced by either intra-arterial thrombin injection or ferric chloride application followed by measurement of cerebral blood flow using a combination of laser Doppler flowmetry and MRI were performed to uncover the effects of NAC on arterial thrombi. To investigate the effect of NAC on larger vessels, we also performed ferric chloride-induced carotid artery thrombosis. In vitro experiments were performed to study the molecular bases of NAC thrombolytic effect, including platelet aggregometry, platelet-rich thrombi lysis assays, thromboelastography (ROTEM), and high-shear VWF string formation using microfluidic devices. We also investigated the putative prohemorrhagic effect of NAC in a mouse model of intracranial hemorrhage induced by in situ collagenase type VII injection.. We demonstrated that intravenous NAC administration promotes lysis of arterial thrombi that are resistant to conventional approaches such as recombinant tissue-type plasminogen activator, direct thrombin inhibitors, and antiplatelet treatments. Through in vitro and in vivo experiments, we provide evidence that the molecular target underlying the thrombolytic effects of NAC is principally the VWF that cross-link platelets in arterial thrombi. Coadministration of NAC and a nonpeptidic GpIIb/IIIa inhibitor further improved its thrombolytic efficacy, essentially by accelerating thrombus dissolution and preventing rethrombosis. Thus, in a new large-vessel thromboembolic stroke model in mice, this cotreatment significantly improved ischemic lesion size and neurological outcome. It is important to note that NAC did not worsen hemorrhagic stroke outcome, suggesting that it exerts thrombolytic effects without significantly impairing normal hemostasis.. We provide evidence that NAC is an effective and safe alternative to currently available antithrombotic agents to restore vessel patency after arterial occlusion.

Topics: Acetylcysteine; Animals; Blood Platelets; Chlorides; Disease Models, Animal; Ferric Compounds; Fibrinolytic Agents; Infarction, Middle Cerebral Artery; Male; Mice; Platelet Aggregation; Ristocetin; Thromboembolism; Thrombosis; Tissue Plasminogen Activator; von Willebrand Factor

This study evaluated platelet function for an extended period of time in patients with a HeartMate II continuous-flow left ventricular assist device (Thoratec Corporation, Pleasanton, Calif) with light transmission aggregometry and investigated the potential role of this test in clinical management.. Twenty-four patients were studied prospectively after implantation. Mean duration of support was 8.5 months. Platelet functions were assessed with light transmission aggregometry induced by thrombin receptor agonist peptide, ristocetin, or arachidonic acid. All patients received an aspirin regimen that was progressively increased until arachidonic acid-triggered platelet aggregation dropped lower than 20%. Plasma levels of von Willebrand factor were also determined when ristocetin-induced platelet agglutination was impaired.. Intensity of platelet aggregation with thrombin receptor agonist peptide was little changed in patients with a HeartMate II relative to control subjects. Aspirin dose greater than 160 mg/d was progressively required in 46% of patients. Ristocetin-induced platelet agglutination was impaired in 4 patients in association with a lack of high molecular weight von Willebrand factor multimers. Three patients had thromboembolic events (12.5%) and 8 (33%) suffered from major bleeding complications.. High platelet reactivity during treatment with aspirin is common in patients with a HeartMate II. Moreover, light transmission aggregometry may detect impaired ristocetin-induced platelet agglutination, enabling dosage of aspirin to be adjusted. Our strategy showed no major improvements in terms of thrombosis rate when compared with published data, although bleeding frequency was somewhat reduced. Benefits of light transmission aggregometry testing need to be assessed in a larger randomized study with a longer follow-up.

Topics: Aged; Arachidonic Acid; Aspirin; Drug Administration Schedule; Drug Monitoring; Female; France; Heart Failure; Heart-Assist Devices; Hemorrhage; Humans; Male; Middle Aged; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Function Tests; Predictive Value of Tests; Prospective Studies; Prosthesis Design; Risk Factors; Ristocetin; Thromboembolism; Time Factors; Treatment Outcome; Ventricular Function, Left