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Washed Platelets (washed + platelet)
Selected Abstracts4-Thio-deoxyuridylate-modified thrombin aptamer and its inhibitory effect on fibrin clot formation, platelet aggregation and thrombus growth on subendothelial matrixJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2008S. MENDELBOUM RAVIV Summary.,Background:,The consensus thrombin aptamer C15-mer is a single-stranded DNA of 15 nucleotides [d(GGTTGGTGTGGTTGG)] that was identified by the selection of thrombin-binding molecules from a large combinatorial library of oligonucleotides. It is capable of inhibiting thrombin at nanomolar concentrations through binding to a specific region within thrombin exosite 1. As has been shown in our earlier studies, the 4-thio-deoxyuridylate (s4dU)-containing oligonucleotides have high affinity for a number of proteins, due to the reduced hydrophilic character of the modified oligonucleotide. Methods:,Three different analogs of the original thrombin-inhibiting sequence, in which some of the thymidylate residues were replaced by 4-thio-deoxyuridylates, were synthesized. The inhibitory effect of modified aptamers was tested on thrombin-catalyzed fibrin clot formation and fibrinopeptide A release from fibrinogen, thrombin-induced platelet aggregation/secretion, and the formation of thrombus on coverslips coated with human collagen type III, thrombin-treated fibrinogen or subendothelial matrix of human microvascular endothelial cells. Results:,As compared with the C15-mer, the analog with the sequence GG(s4dU)TGG(s4dU)G(s4dU)GGT(s4dU)GG (UC15-mer) showed a 2-fold increased inhibition of thrombin-catalyzed fibrin clot formation, fibrinopeptide A release, platelet aggregation and secretion in human plasma and thrombus formation on thrombin-treated fibrinogen surfaces under flow conditions. Concerning the inhibition of thrombin-induced fibrin formation from purified fibrinogen and activation of washed platelets, UC15-mer was 3-fold and twelve-fold more effective than C15-mer, respectively. Conclusion:,The replacement of four thymidylate residues in C15-mer by 4-thio-deoxyuridylate resulted in a new thrombin aptamer with increased anticoagulant and antithrombotic properties. [source] The P2Y1 receptor plays an essential role in the platelet shape change induced by collagen when TxA2 formation is preventedJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 6 2004P. Mangin Summary., ADP and TxA2 are secondary agonists which play an important role as cofactors when platelets are activated by agonists such as collagen or thrombin. The aim of the present study was to characterize the role of the ADP receptor P2Y1 in collagen-induced activation of washed platelets. Inhibition of P2Y1 alone with the selective antagonist MRS2179 prolonged the lag phase preceding aggregation in response to low or high concentrations of fibrillar collagen, without affecting the maximum amplitude of aggregation or secretion. A combination of MRS2179 and aspirin resulted in complete inhibition of platelet shape change at low and high collagen concentrations, together with a profound decrease in aggregation and secretion. Scanning electron microscopy showed that these platelets had conserved the discoid morphology typical of the resting state. A lack of shape change was also observed in aspirin-treated P2Y1 - and G,q -deficient mouse platelets and in ,-storage pool-deficient platelets from Fawn Hooded rats. In contrast, when the second ADP receptor P2Y12 was inhibited with AR-C69931MX, aspirin-treated platelets were still able to change shape and displayed only a moderate decrease in aggregation and secretion. In conclusion, this study provides evidence that collagen requires not only the TxA2 receptor Tp,, but also P2Y1, to induce platelet shape change. [source] Antistreptokinase platelet-activating antibodies are common and heterogeneousJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 5 2003V. Regnault Summary.,Background:,Platelet activation by antistreptokinase (SK) antibodies could impair the clinical effect of SK administration. Objective:,To better describe anti-SK antibodies with particular emphasis on procoagulant activities as a result of platelet activation. Patients and methods:,Sera were collected from 146 patients with coronary artery disease: non-SK-treated, 95 from mainland France, 31 from French Polynesia; 20 patients from mainland in year 2 after SK treatment. Serum-induced SK-dependent platelet activation resulting in procoagulant activities was assessed with washed platelets from five donors representative of the known patterns of reactivities to IgG. Results:,Concentrations (2,5252 µg mL,1) and fibrinolytic neutralization titres (< 10 to >,1280) were found in the expected wide range and correlated (, = 0.66, P < 0.0001). Platelet activation was detected with 145 samples, but varied in intensity and pattern (depending on the donors), although there was no systematic hierarchy; it was presumably due to IgG (inhibited by an IgG Fc receptor-blocking antibody and recovered in the IgG fraction) and only partially affected by aspirin. Marked platelet activation could be detected in samples with concentration as low as 2 µg mL,1, and/or no detectable neutralizing titers. The way of immunization to SK was not found to influence the functional profile of antibodies. Conclusion:,Anti-SK platelet-activating antibodies are widespread, heterogeneous, poorly predictable on the basis of their antifibrinolytic effect and strong enough to trigger procoagulant activities. Their clinical relevance should be formally assessed, using patients' own platelets for detection owing to the variation of platelet reactivity. [source] Platelet CD62 expression and PDGFAB secretion in patients undergoing PTCA and treatment with abciximabBRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Issue 6 2001J. Graff Aims, To investigate a correlation of the platelet activation marker CD62 and secretion of the growth factor PDGF from platelets in coronary patients under therapy with the GPIIb/IIIa-inhibitor abciximab. Methods, Flow cytometric assessment of fibrinogen binding (GPIIb/IIIa-binding site) and CD62 expression, as well as PDGF release of human platelets (immunoassay) and platelet aggregation with 20 µm ADP and 2 µg ml,1 collagen were evaluated in nine patients with stable coronary artery disease. Patients were undergoing elective balloon angioplasty and were treated with aspirin (100 mg day,1), heparin (ACT < 220 s) and abciximab (bolus and infusion over 12 h). Blood samples were obtained before initiation of abciximab therapy (under aspirin and heparin) (I), 3 h after angioplasty under abciximab (II) and 12 h after termination of abciximab infusion (III). Results, Compared with sample I before abciximab therapy, fibrinogen binding was reduced to 37% (± 34 s.d., P < 0.05) (II) and 55% (± 40 s.d., P < 0.05) (III). Reduced fibrinogen binding also led to a significant reduction of the aggregation response to ADP (down to 37% ± 20) and collagen (down to 0%). Mean fluorescence intensity of CD62-expression was 78 units (± 20 s.d.) (I), 72 units (± 14 s.d.) (II) and 64 units (± 12 s.d., P < 0.05) (III). PDGF release from isolated, washed platelets was 99 (± 33 s.d.) ng/109 platelets at (I), 82 (± 31 s.d.) ng/109 platelets and 96 (± 30 s.d.) ng/109 platelets. Conclusions, The results indicate that despite a strong reduction of GPIIb/IIIa-binding and platelet aggregation, CD62 as a marker of platelet secretion and the secretion product PDGF were only slightly reduced under abciximab treatment. No direct correlation between CD62 expression and PDGF release could be demonstrated. [source] | ||||||||||