Markers Of Procoagulant Activity Research Articles

Blood cell activation as an indicator of prothrombogenesis in polycythemia vera: Case control study

BACKGROUND: Polycythemia vera (PV) is a chronic myeloproliferative stem cell disease usually combined with JAK2 mutation. Active JAK2 mutation directly promote platelets and granulocytes activation and indirectly initiate endothelial activation. Such interactions can provoke endothelial injury with subsequent release of procoagulant factors. The aim of this study was to understand of this study is to understand the pathophysiology of increased thrombosis in PV in terms of the effect of JAK2V617F gene mutation in relation to the intensity of the neutrophil CD11b and platelet CD62P. SUBJECTS AND METHODS: A group of 53 patients was examined comprised 30 PV patients and 23 with secondary polycythemia. In parallel, 30 aged- and sex-matched, nonsmokers healthy volunteers served as a control group. Hemoglobin level, packed cell volume, white and red blood cells count, mean corpuscular volume, and platelet count were estimated for all the 83 participants. Flow cytometry for the detection of neutrophil CD11b and platelet CD62P were done for all the participants; whereas quantitative polymerase chain reaction technique for the assessment of JAK2 mutation rate was done for the 30 PV patients only. RESULTS: We were able to detect significantly higher neutrophil CD11b and platelet CD62P expressions in PV patients. Within PV, JAK2 mutation rate was significantly higher in those with a history of thrombosis. A positive relationship was demonstrated between the JAK2 mutation rate and each of CD11b and CD62P. CONCLUSION: There is an overexpression of neutrophil CD11b and platelets CD62P in patients with PV which can be considered as a marker of procoagulant activity in blood cells. Active JAK2 mutation directly promote platelets and granulocytes activation and indirectly initiate endothelial activation and in turn endothelium into a proadhesive and procoagulant surface.

Real-time analysis of platelet aggregation and procoagulant activity during thrombus formation in vivo

The exact mechanism of blood vessel thrombus formation remains to be defined. Here, we introduce a new approach to probe thrombus formation in blood vessels of living animals using intravital microscopy in green fluorescent protein (GFP)-transgenic mice to simultaneously monitor platelet aggregation and procoagulant activity. To this end, GFP-expressing platelets and annexin A5 labeled with a fluorescent dye were employed to visualize and analyze platelet aggregation and markers of procoagulant activity (platelet surface phosphatidylserine (PS)). Laser-induced thrombi increased and then decreased in size with time in vessels of living animals, whereas platelet surface PS initiated at the site of injury and then penetrated into the thrombus. PS-positive platelets were predominantly localized in the center of the thrombus, as was fibrin generation. The experimental system proposed here is a valuable tool not only for investigating mechanisms of thrombus formation but also to assess the efficacy of antithrombotic drugs within the vasculature.

Platelet microparticles are heterogeneous and highly dependent on the activation mechanism: Studies using a new digital flow cytometer

Platelet-derived microparticles (MPs) are believed to play an important role in coagulation and inflammatory disorders. Unfortunately, MP size renders them difficult to study and analyze by conventional flow cytometry. We analyzed and characterized platelet-derived MPs, using antibodies against the major surface glycoproteins (GP), the platelet activation antigen P-selectin (CD62P), and a marker of procoagulant activity (phosphatidylserine exposure). MPs were generated by exposure of platelets to thrombin receptor activating peptide (TRAP) or ionophore. Both agonists induced significant microvesiculation of platelets, and the resulting MPs were analyzed by a new digital flow cytometer: Becton-Dickinson FACSAria. Membrane GPs were equally well represented in MPs generated by either reagent. In contrast, P-selectin was more intensely expressed in TRAP-MPs, while phosphatidylserine (PS) expression was markedly increased in ionophore-MPs. Two distinct populations of TRAP-MPs (one PS-positive and another PS-negative) were apparent. The latter characteristic facilitated sorting of MPs according to their PS exposure. The data presented herein show a significant improvement in the methodology applied until now to the characterization of MPs. The ability to characterize and sort MP subpopulations may help to resolve their contributions to normal and pathological functions.

PAR-1 genotype influences platelet aggregation and procoagulant responses in patients with coronary artery disease prior to and during clopidogrel therapy

Genetic variations of the protease-activated receptor-1 (PAR-1) have been associated with platelet receptor density and linked to thrombin receptor-activating peptide (TRAP)-induced phenotypes of platelet aggregation and P-selectin expression. We investigated whether the PAR-1 intervening sequence-14 A > T dimorphism influences platelet procoagulant activity. We also determined whether the P2Y12 antagonist clopidogrel could offset any observed functional polymorphism of the PAR-1 receptor by inhibiting P2Y12-mediated amplification of TRAP-induced responses. We studied 54 patients listed for elective percutaneous coronary intervention assessing TRAP-induced platelet aggregation and markers of procoagulant activity. Platelet responses were measured at baseline, 4 h post clopidogrel 300 mg, and 10 and 28 days following clopidogrel 75 mg daily. Each patient was genotyped for the PAR-1 intervening sequence-14 A/T dimorphism. Increased platelet aggregation and procoagulant responses were observed with PAR-1 A allele homozygotes. Clopidogrel significantly inhibited these platelet responses regardless of PAR-1 genotype, but did not offset the hyper-reactivity associated with the A/A homozygotes. We conclude that a common sequence variation within the PAR-1 gene influences TRAP-induced platelet procoagulant activity as well as aggregation. Higher platelet reactivity associated with PAR-1 IVSn–14 A allele homozygotes persists despite clopidogrel therapy. These individuals may be at higher risk of thromboembolic events and may require additional anti-platelet medication.

Relationship between hypercoagulable state and erythrocyte phosphatidylserine exposure in splenectomized haemoglobin E/beta-thalassaemic patients.

Small pulmonary arterial thromboses can occur following splenectomy of patients with haemoglobin E/beta-thalassaemia (Hb E/beta-thal). We compared plasma markers of coagulation activation in vivo and red blood cell (RBC) markers of procoagulant activity in 15 Hb E/beta-thal patients who were not splenectomized (NS), 15 who had been splenectomized (S), and 15 normal controls (NC). Levels of plasma thrombin-antithrombin III complex (TAT) were significantly higher in the S group than in either the NS or the NC groups, and levels of prothrombin fragment 1.2 (F 1.2) were significantly higher in the S than in the NC group. Diluted Russell's viper venom clotting times were significantly shorter when RBCs from group S patients were added to the assay compared with RBCs from the NC group. Phosphatidylserine (PS) expression (% of annexin V-positive RBCs) on the outer leaflet of RBC membrane of both 'larger'- and 'smaller'-sized RBCs was significantly higher for the S than the NC group. The RBC PS expression of the S and the NS groups, respectively, accounted for 25 x 3% (P = 0 x 174) and 6.3% (P = 0 x 675) of the variation in plasma TAT levels. Our findings indicated that, when compared with NC, splenectomized patients with Hb E/beta-thal were in a chronic low-grade hypercoagulable state associated with increased numbers of circulating PS exposed RBCs. This condition may have a role in the risk of these patients for pulmonary arterial thromboses.

No Association of Plasma Prothrombin Concentration or the G20210A Mutation with Incident Cardiovascular Disease

Prothrombin is a key factor in blood clotting, a process intimately involved in thrombotic disease. We assessed prothrombin levels and G20210A genotype in a case-control study within the Cardiovascular Health Study. Cases included angina, myocardial infarction, stroke, and the presence of MRI-detectable infarcts (n approximately 250 each). Population-based controls free of clinical cardiovascular disease (CVD) (n approximately 500) and a subset free of clinical and subclinical CVD (n approximately 250) were used for comparison. The 20210 A allele, frequency 2.9%, was associated with higher mean prothrombin levels: 166.3 vs. 139.5 microg/ml (P <0.001). Significant correlates of prothrombin included gender, plasma lipids, other vitamin K-dependent proteins, and inflammatory markers, but not race, smoking, hypertension, diabetes, measures of subclinical CVD, or markers of procoagulant activity. Compared to controls, neither genotype nor prothrombin level was associated with any CVD case group. We conclude that, in the elderly, neither prothrombin level nor 20210 genotype were associated with either CVD risk factors or events. This is consistent with the lack of association of prothrombin levels with measures of underlying CVD or procoagulant markers.

Usefulness of fibrinogenolytic and procoagulant markers during thrombolytic therapy in predicting clinical outcomes in acute myocardial infarction

Thrombin activity is increased in the setting of acute myocardial infarction (AMI) and has been shown to increase further after the administration of thrombolytic therapy for acute infarction. This increase in thrombin activity may play an important role in the 15% to 25% rate of failure to achieve initial reperfusion and in the 5% to 15% rate of early reocclusion after initially successful thrombolysis. To investigate potential mechanisms of thrombin formation in vivo, to understand better the balance of coagulation and fibrinolysis during treatment with recombinant tissue-type plasminogen activator (rt-PA), and to investigate the role of hemostatic markers as predictors of clinical events, we measured 3 markers of procoagulant activity: fibrinopeptide A (FPA), thrombin-antithrombin III complexes (TAT), and prothrombin fragment 1.2 (F1.2), and a marker of fibrinogenolytic activity (Bβ1–42) in patients enrolled in the Thrombolysis in Myocardial Infarction (TIMI)-5 study. This trial was a randomized, dose-ranging, pilot trial of hirudin versus heparin as adjunctive antithrombotic therapy with rt-PA administered to patients with AMI. Correlation of markers at 1 hour with clinical outcomes revealed that increased FPA and TAT levels were associated with increased mortality and TIMI grades 0, 1, or 2 flow at 90 minutes; increased F1.2 levels were associated with TIMI grade 0 or 1 flow at 90 minutes; and increased levels of all 3 procoagulant markers were associated with hemorrhagic events. Late (12 to 24 hours) increases in F1.2, TAT, and Bβ1–42 may be predictive of recurrent ischemia. These results suggest that selected markers of procoagulant and fibrinogenolytic activity may be useful in predicting clinical outcomes in patients treated with thrombolytic therapy for AMI.