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Background: The contribution of fibrinogen (FBN) to hemostasis acting on platelet aggregation and clot formation is well established. It has been suggested that FBN-coated liposomes could be useful in restoring hemostasis. In the present study, we evaluated the modifications induced by multilamellar raw liposomes (MLV) or fibrinogen-coated liposomes (MLV-FBN) on hemostatic parameters., Materials and Methods: Different experimental settings using whole blood or thrombocytopenic blood were used. Thromboelastometry, aggregation studies, platelet function analyzer (PFA-100(®)) tests and studies under flow conditions were applied to detect the effect of MLV-FBN on hemostatic parameters., Results: The presence of MLV-FBN in whole blood modified its viscoelastic properties, prolonging clot formation time (CFT) (226.5 ± 26.1 mm versus 124.1 ± 9.4 mm; P < 0.01) but reducing clot firmness (45.4 ± 1.8 mm versus 35.5 ± 2.3 mm; P < 0.05). Under thrombocytopenic conditions, FIBTEM analysis revealed that MLV-FBN shortened clotting time (CT) compared to MLV (153.3 ± 2.8 s versus 128.0 ± 4.6 s; P < 0.05). Addition of either liposome decreased fibrin formation on the subendothelium (MLV 8.1% ± 4.7% and MLV-FBN 0.8% ± 0.5% versus control 36.4% ± 6.7%; P < 0.01), whereas only MLV-FBN significantly reduced fibrin deposition in thrombocytopenic blood (14.4% ± 6.3% versus control 34.5% ± 5.2%; P < 0.05). MLV-FBN inhibited aggregation induced by arachidonic acid (52.1% ± 8.1% versus 88.0% ± 2.1% in control; P < 0.01) and ristocetin (40.3% ± 8.8% versus 94.3% ± 1.1%; P < 0.005), but it did not modify closure times in PFA-100(®) studies. In perfusion experiments using whole blood, MLV and MLV-FBN decreased the covered surface (13.25% ± 2.4% and 9.85% ± 2.41%, respectively, versus control 22.0% ± 2.0%; P < 0.01) and the percentage of large aggregates (8.4% ± 2.3% and 3.3% ± 1.01%, respectively, versus control 14.6% ± 1.8%; P < 0.01)., Conclusion: Our results reveal that, in addition to the main contribution of fibrinogen to hemostasis, MLV-FBN inhibits platelet-mediated hemostasis and coagulation mechanisms. more...

Background: The possibility of developing synthetic platelet substitutes that could promote hemostasis with prolonged shelf-life and increased safety is an appealing one., Study Design and Methods: Preparations containing synthetic phospholipids were incorporated into blood samples (1.15 mg/mL) in which platelets and white cell counts had been experimentally reduced by a filtration procedure. Vesicles containing phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), or combinations of PC and PE and of PC and PS were tested in this system. Blood was recirculated (10 min; shear rate, 250/sec) through a perfusion chamber containing vascular segments. The ability of the various phospholipid preparations to promote fibrin formation on the damaged subendothelium was evaluated morphometrically and expressed as the percentage of fibrin coverage. Generation of thrombin in the system was monitored through the measurement of prothrombin fragments 1 and 2., Results: Vesicles containing PC, PI, PE:PC (1:1), or PS:PC (1:3) increased fibrin deposition on the subendothelium (64.5 +/- 9.8%, 32.7 +/- 6.3%, 58.3 +/- 6.5%, and 46.6 +/- 15.2%, respectively; p < 0.01 vs. 11.5 +/- 1.2% in thrombocytopenic blood). Vesicles containing PE, PS, or PS:PC (3:1) did not show procoagulant effect., Conclusion: Synthetic phospholipid preparations promote a local procoagulant activity at sites of vascular damage when they are incorporated into thrombocytopenic blood maintained under flow conditions. more...

Background: Evaluation of the hemostatic effectiveness of platelet transfusions is difficult. Perfusion methods have been employed to test the quality and function of platelet concentrates, allowing differentiation between platelet-platelet and platelet-surface interactions., Study Design and Methods: A study was performed to investigate platelet adhesive and cohesive properties as well as the formation of fibrin when aliquots of platelet concentrates were added to thrombocytopenic blood. Blood previously anticoagulated with low-molecular-weight heparin (20 U/mL) underwent platelet and white cell reduction by filtration. Perfusates were prepared by adding to filtered blood platelets obtained from standard concentrates (stored for 1, 3, and 5 days). The final platelet count in these perfusates was standardized at 80,000 per microL. After perfusions, platelet-subendothelium interaction and fibrin formation were analyzed morphometrically. Results were always compared with those obtained in unfiltered blood (> 150,000 platelets/microL)., Results: A slight impairment in the ability of stored platelets to interact with the subendothelium was noticed during the storage period. However, the presence of fibrin was significantly greater than that observed in studies with unfiltered blood (Day 1 = 23.48 +/- 9.43%*; Day 3 = 26.99 +/- 6.74%*; Day 5 = 17.95 +/- 9.06% vs. unfiltered blood = 12.60 +/- 3.08%; *p < 0.05). The lower platelet counts (80,000/microL) in the perfusates containing platelets from concentrates could account for the reduced platelet-subendothelium interactions, but they cannot explain the increments in fibrin formation., Conclusion: While the preparation and storage of platelets have a detrimental effect on platelet adhesiveness, such procedures can positively influence the platelet procoagulant activity necessary to platelet hemostasis. more...