Biomedical subjects

G Escolar

Publications and source records attributed to G Escolar.

187 records · Page 11Linked to original sources

PubMedDate not supplied

Preparations of synthetic phospholipids promote procoagulant activity on damaged vessels: studies under flow conditions.

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.

Animals↗

PubMedDate not supplied

Digital image analysis of platelet-extracellular matrix interactions: studies in von Willebrand disease patients and aspirin-treated donors.

We have developed an automated image analysis method which provides en face morphometric evaluation of platelet interactions with coverslips coated with extracellular matrices. This procedure gives also additional information on the intensity of platelet-surface interactions in the same specimens. To standardize the method, anticoagulated human blood was flowed at 800 s-1 during 10 min at 37 degrees C through a parallel perfusion chamber in which extracellular matrix (ECM)-coated coverslips were placed. The sensitivity of the new method was tested in similar studies performed in patients with von Willebrand disease or treated with aspirin (500 mg/day). The extent of platelet deposition on the ECMs was evaluated by both standard and new morphometric procedures. Coverslips were successively embedded in resin and processed for cross-sectional analysis and results were compared with those provided by the new automated procedure. A good correlation was found between results of covered surface obtained by both methods (r = 0.86; p < 0.005). Results from perfusions performed with blood from patients with platelet defects confirmed the correspondence of grey levels in the digitized images with the heights of groups of interacting platelets calculated from cross sections. The new automated method, in only one stage, allows a reliable evaluation of the global interaction of platelets with the ECM and effectively detected qualitative modifications in platelet-platelet interactions in patients with known platelet defects. The method described could be applied to the evaluation of the interactions of platelets with purified components of the subendothelium.

Aspirin↗

PubMedDate not supplied

Fibrinogen receptors do not undergo spontaneous redistribution on surface-activated platelets.

Studies with fibrinogen coupled to colloidal fibrinogen-gold (Fgn/Au) have suggested that fibrinogen receptors glycoprotein IIb-IIIa (GPIIb-IIIa) on human platelets may undergo spontaneous reorganization and centralization during surface activation. The present study has examined that hypothesis. Platelets were allowed to spread on grids for 20 minutes, just as in previous studies, but they were fixed before, rather than after, exposure to Fgn/Au or latex spherules. A monoclonal antibody to GPIIb-IIIa was also employed. Control experiments demonstrated that Fgn/Au and latex move toward the central zones and into channels of the open canalicular system on surface-activated platelets treated in the usual manner. However, when surface-activated platelets were fixed after spreading and before exposure to ligand, Fgn/Au particles and latex sperules were evenly dispersed over the entire cell membrane. Immunogold staining of GPIIb-IIIa also revealed edge-to-edge localization of the GPIIb-IIIa receptors on surface-activated cells. The findings are consistent with the concept that fibrinogen receptors do not undergo spontaneous reorganization on surface-activated platelets.

Antibodies, Monoclonal↗

PubMedDate not supplied

Platelet adhesion to exposed endothelial cell extracellular matrixes is influenced by the method of preparation.

The relative thrombogenicity of extracellular matrixes (ECMs) produced by cultured human umbilical endothelial cells (ECs) was studied under flow conditions. ECMs were prepared using a number of physical and chemical methods, and their reactivity toward platelets was morphometrically evaluated. von Willebrand factor (vWF), fibronectin (FN), and 13-hydroxy-9-cis,11-trans-octadecadienoic acid (13-HODE) were also determined. We found that platelet adhesion to ECMs differed significantly, both quantitatively and qualitatively, with the method of ECM preparation. Mechanically prepared ECM exposed a less thrombogenic surface compared with ECM prepared by chemical methods (platelet-covered surface of 20% and 50%, respectively). Evaluation of the ECM components vWF, FN, and 13-HODE showed significant changes, both in their concentrations and distribution patterns, depending on the method of ECM preparation. The decrease measured in the levels of ECM-associated vWF (from 108 to 9.2 ng/10(4) cells) and the minor changes observed in the distribution pattern of subendothelial FN did not appear to be sufficient to explain the altered platelet adhesion observed in our model. This suggests that the amount of 13-HODE probably associated to the remaining ECs present in the mechanically exposed ECM could be one factor that specifically contributed to the nonthrombogenic state of these preparations. We conclude that the degree of ECM reactivity toward platelets is dependent on the method of ECM preparation and that this is related to the removal of specific EC/ECM components that modulate their thromboresistant/thrombogenic properties. This fact should be taken into account when ECMs produced by cultured ECs are used in platelet adhesion studies.

Antithrombins↗

PubMedDate not supplied

Effect of anticoagulants on activation of polymorphonuclear leukocytes induced by shear stress.

We analyzed how actin polymerization, CD11b expression and homotypic aggregation could be used as markers to study leukocyte activation. Leukocytes were obtained from blood anticoagulated with: citrate, unfractioned heparin (UH) and low molecular weight heparin (LMWH). Flow cytometry was used to study actin polymerization and expression of CD11b after leukocyte exposure to shear stress. Leukocyte aggregation was microscopically assessed. Shear increased both actin polymerization and expression of CD11b in citrated blood (100.1±7.1 vs. 85.8±8.5 p< 0.05 and 53.5±3.5 vs. 20.7±5.1; p< 0.005 respectively). These parameters remained unmodified in UH samples. Using both anticoagulants together, we observed increase in CD11b expression induced by shear stress (59.3±2.1 vs. 25.1±11.0; p< 0,05). LMWH samples showed higher basal levels of actin polymerization and CD11b expression than citrated samples (237±40.8, vs. 85.8±8.5 p< 0.05 and 47.8±2.6, vs. 20.7±5.1; p< 0.005) but no changes induced by shear were observed. When LMWH was used in combination with citrate we observed a decrease in basal activation and significant modifications in CD11b expression induced by shear stress (80.0±4.1 vs. 50.4±2.7). Leukocyte aggregation was modified by UH at basal levels and by LMWH after shear stress. These results indicate that exposure to shear stress results in leukocyte activation. The choice of anticoagulant is a crucial factor in studies of leukocyte function.

Journal Article↗

PubMedDate not supplied

Relationship between gastric levels and antiulcerogenic activity of zinc.

The relationship between the absorption of an organic zinc salt, zinc acexamate, and its antiulcerogenic activity in a model of cold-restraint stress was studied. Serum and gastric levels of zinc, as well as its antiulcerogenic effect, were determined after oral or intravenous administration of zinc acexamate. Cytochemical and X-ray microanalysis techniques were also applied. In the rats subjected to cold-restraint stress, gastric levels of zinc correlated with the antiulcerogenic effect observed after administration of zinc acexamate. However, it was not possible to establish a relationship between serum levels and the pharmacologic effect of zinc. Our results in animals subjected to regular diet indicate that the antiulcerogenic effect exhibited by zinc compounds could be associated with the presence of zinc at different levels of gastric tissue.

Administration, Oral↗

PubMedDate not supplied

Inhibition of fibrin deposition on the subendothelium by a monoclonal antibody to polymorphonuclear leukocyte integrin CD11b. Studies in a flow system.

BACKGROUND AND OBJECTIVE: The development of prothrombotic and procoagulant states may be regulated by direct platelet-leukocyte contact mediated by membrane receptors. We have investigated the role of CD11b integrin in polymorphonuclear leukocytes (PMN) on fibrin formation and platelet reactivity with vascular subendothelium. METHODS: Studies were carried out following a well-established perfusion model, employing either citrated blood, where fibrin formation is blocked, or blood anticoagulated with low molecular weight heparin, which allows thrombin and fibrin formation. Isolated PMN or platelets were treated with specific monoclonal antibodies to CD11b or to CD62P, respectively, and incorporated in reconstituted blood. RESULTS: Treatment of PMN with anti-CD11b significantly decreased the percentage of surface covered with a thick layer (> 5 microns) of fibrin (34.8 +/- 3.3% vs 53.3 +/- 4.9% in control, p < 0.05); it also reduced the average height of fibrin layer and the number of adherent leukocytes (7.9 +/- 1.2 microns vs 10.6 +/- 1.4 microns in control, p < 0.05; and 87 +/- 8 PMN/mm2 vs 186 +/- 25 PMN/mm2 in control, p < 0.05) respectively. Treatment of PMN with CD11b did not significantly affect the attachment of platelets onto the subendothelium when using citrated blood, though a slight decrease in platelet adhesion was observed in the heparinized samples. Treatment of platelets with anti-CD62P did not significantly modify any of the parameters studied. INTERPRETATION AND CONCLUSIONS: Our results indicate that PMN have a role in promoting fibrin deposition under flow conditions, through the participation of CD11b integrin. Under our experimental conditions, this effect does not seem to be influenced by CD62P expressed on activated platelets.

Animals↗