Thrombocytopenia and the neglected megakaryocyte.
Explore the source record for details and available documents.
HIV Infections↗
Biomedical subjects
J J Sixma
Publications and source records attributed to J J Sixma.
The ideal anti-thrombotic drug.
An ideal antithrombotic drug should inhibit thrombosis without affecting hemostasis. It should have a long half life. It should be absorbed after oral administration; it should be safe and it should have a wide therapeutic range. These criteria are discussed using new antithrombotics as examples.
Administration, Oral↗
Inhibition of platelet adhesion to fibrin(ogen) in flowing whole blood by Arg-Gly-Asp and fibrinogen gamma-chain carboxy terminal peptides.
We have employed synthetic peptides with sequences corresponding to the integrin receptor-recognition regions of fibrinogen as inhibitors of platelet aggregation and adhesion to fibrinogen- and fibrin-coated surfaces in flowing whole blood, using a rectangular perfusion chamber at wall shear rates of 300 s-1 and 1,300 s-1. D-RGDW caused substantial inhibition of platelet aggregation and adhesion to fibrinogen and fibrin at both shear rates, although it was least effective at blocking platelet adhesion to fibrin at 300 s-1. RGDS was a weaker inhibitor, and produced a biphasic dose-response curve; SDRG was inactive. HHLGGAKQAGDV partially inhibited platelet aggregation and adhesion to fibrin(ogen) at both shear rates. These results support the identification of an RGD-specific receptor, most likely the platelet integrin glycoprotein IIb:IIIa, as the primary receptor responsible for platelet:fibrin(ogen) adhesive interactions under flow conditions, and indicate that platelet adhesion to surface bound fibrin(ogen) is stabilized by multivalent receptor-ligand contacts.
Amino Acid Sequence↗
Antiphospholipid antibody positive sera enhance endothelial cell procoagulant activity--studies in a thrombosis model.
The effect of sera and IgG from 12 patients with systemic lupus erythematosus (SLE) on the endothelial cell (EC) procoagulant activity (PCA) was investigated in an in vitro thrombosis model. Six of the 12 SLE sera contained antiphospholipid antibodies (aPL). EC were stimulated for 8 h at 37 degrees C with or without 50 pM tumor necrosis factor (TNF) in culture medium containing 20% patient or control serum. Then the endothelial cell matrix (ECM) was isolated and subsequently exposed in a perfusion chamber to circulating normal whole blood, anticoagulated with low molecular weight heparin (LMWH). The PCA of the ECM was determined as the amount of generated fibrinopeptide A (FPA) in samples taken before and after perfusion. Furthermore, cross sections were made of the perfused matrix and analyzed for platelet adhesion and aggregate formation. All six aPL containing sera induced a small, but significant increase of ECM procoagulant activity. When added in combination with a low dose of TNF (50 pM), a synergistic enhancement of ECM procoagulant activity was found. The FPA generation was increased to 150-614% from the values obtained after stimulation with TNF and control serum. Also a shift towards the formation of larger platelet thrombi was observed. After stimulation with TNF and patient serum the surface of ECM covered with large aggregates (greater than 5 microns) was increased by 124-329% compared to the results obtained after stimulation with control serum and TNF. When patient sera were depleted from IgG the effects were strongly decreased.(ABSTRACT TRUNCATED AT 250 WORDS)
Antibodies↗
Role of plasma viscosity in platelet adhesion.
Platelet adhesion to the vessel wall is initiated by transport of blood platelets from the bulk flow to the wall. The process of diffusion and convection of the platelets is affected by rheological conditions such as well shear rate, red blood cell (RBC) deformability, and viscosity of the medium. To study the effect of plasma viscosity on platelet adhesion, perfusion experiments with a rectangular perfusion chamber were performed. Reconstituted blood, consisting of washed platelets and washed RBCs, was circulated through this chamber for 5 minutes at a wall shear rate of 300 s-1. Different albumin concentrations were made, to obtain different medium viscosities (0.89 to 1.85 mPa.s). Platelet adhesion decreased with increasing medium viscosity up to viscosities of 0.95 mPa.s, but increased with medium viscosity above this value. Instead of human albumin solution, different plasma viscosities were obtained by dilution of Waldenström plasma with buffer. Plasma was depleted of fibronectin, which gave a final plasma viscosity of 2.0 mPa.s, and was dialyzed against HEPES buffer and subsequently diluted with the dialysis buffer in different fractions (0.89 to 2.00 mPa.s). Perfusions were performed over a purified von Willebrand factor coating on glass, or over an endothelial cell matrix, preincubated with von Willebrand factor. With both surfaces, platelet adhesion was dependent on the plasma viscosity in a similar way: at low plasma viscosities, adhesion was decreased with increasing plasma viscosity, while at higher plasma viscosities, adhesion increased with plasma viscosity. Adhesion values at higher plasma viscosity or at higher human albumin concentrations could be explained by effects of the medium on the rigidity of the RBCs, since platelet adhesion is known to be increased by enhanced RBC rigidity. Effects of the medium on the deformability of the RBCs were measured separately with the laser diffraction method. These experiments confirmed that presence of human albumin or plasma in the measuring suspension increased the rigidity of RBCs. To prevent influence of the medium on the RBCs in perfusion experiments, the RBCs were fixated with glutaraldehyde. Perfusion experiments with fixated RBCs in plasma over a von Willebrand factor preincubated endothelial cell matrix, showed a consequent decrease in adhesion with increasing plasma viscosity, according to the diffusion theories, whereas the increase of adhesion at high plasma viscosities was lacking. This suggests that the latter effect was entirely due to increased transport of platelets by more rigid RBCs.
Blood Viscosity↗
Platelet adhesion to laminin: role of Ca2+ and Mg2+ ions, shear rate, and platelet membrane glycoproteins.
The adhesion of platelets to purified laminin under flow conditions was investigated. Adhesion to laminin was strongly dependent on the presence of divalent cations. In the absence of cations platelet adhesion (8% coverage in 5 minutes) was maximal at a shear rate of 100/s and no adhesion could be detected at shear rates above 800/s. In the presence of 0.8 mmol/L Mg2+ and 2 mmol/L Ca2+ platelet adhesion reached its maximum (30% coverage) around 800/s. At 1,800/s platelets still adhered to purified laminin (coverage of 6%). Antibodies against the E8 domain of laminin and antibodies against the alpha 6 and beta 1 chains of platelet membrane glycoprotein very late activation antigen-6 (VLA-6), completely inhibited adhesion. No inhibition was found with antibodies against glycoprotein IIb:IIIa, against the alpha 2 chain of VLA-2, and against the alpha 5 chain of VLA-5. Fibronectin and von Willebrand factor were not involved in laminin-dependent adhesion. Anti-VLA-6 partly inhibited platelet adhesion to the extracellular matrix of endothelial cells at shear rates below 800/s. Preincubation of the matrices with antilaminin E8 antibodies did not influence the adhesion. These results show that purified laminin supports platelet adhesion and that the presence of VLA-6 is important for platelet adhesion under flow conditions. The protein in the matrix with which VLA-6 interacts is currently unknown.
Adsorption↗
In vivo experiments indicate that relatively high platelet deposition in von Willebrand's disease 'Vicenza' is caused by normal platelet-VWF levels rather than by high VWF-multimers in plasma.
Von Willebrand's disease (vWD) 'Vicenza' is characterized by low plasma von Willebrand Factor antigen (vWF:Ag) and very low levels of Ristocetin Cofactor activity (RiCof). The hemorrhagic tendency in vWD 'Vicenza' is, however, mild and bleeding times in this rare vWD-subtype are only slightly prolonged (1). Larger than normal multimers of plasma-vWF and normal levels of platelet-vWF have both been suggested to compensate the defects that are normally present in vWD. To elucidate the mechanisms involved, whole blood of four patients with vWD 'Vicenza' was circulated through a rectangular perfusion chamber (2) with fibrillar collagen as adhesive surface. Under these conditions, both plasma and platelet vWF participate to platelet adhesion. Compared to perfusion results with blood of normal donors, platelet adhesion of 'Vicenza' patients was decreased. However, the Vicenza defect was less than was observed in parallel experiments with blood of vWD type 1 subtype platelet-low patients and blood of a severe vWD patient. Adhesion was not increased in perfusions with only plasma of the 'Vicenza' vWD-patients. Equal vWF:Ag concentrations of normal multimeric composition were just as effective as the high multimeric 'Vicenza' vWF. Therefore, the abnormal plasma-vWF in 'Vicenza' patients does not cause the relatively high adhesion obtained with whole blood. In contrast, platelets of vWD 'Vicenza' patients resuspended in human albumine solution (HAS) showed far better adhesion than (vWF-poor) platelets of a patient with severe vWD. The values were at least comparable and tended to be higher than those obtained with normal platelets or with platelets of patients with vWD type I subtype platelet normal.(ABSTRACT TRUNCATED AT 250 WORDS)
Biopolymers↗
Identification of a 33-Kd protein associated with the alpha-granule membrane (GMP-33) that is expressed on the surface of activated platelets.
To identify antigens on the platelet plasma membrane that are exposed after activation, we developed a monoclonal antibody (MoAb) designated RUU-SP 1.77. The RUU-SP 1.77 antigen is present on the membrane of resting platelets at a basal level and is strongly expressed on the plasma membrane after thrombin activation. Freshly fixed platelets bound 4,150 +/- 1,935 (mean +/- SD) RUU-SP 1.77 molecules per platelet; on fixed thrombin-stimulated platelets the number of binding sites was upregulated to 19,050 +/- 5,120 (kd 4.5 +/- 0.8 nmol/L). MoAb RUU-SP 1.77 recognized a major protein of 33 Kd and a minor 28-Kd protein, both under nonreduced and reduced conditions. Immunoelectron microscopic studies showed the presence of the protein associated with the membrane of alpha-granules. Due to the localization associated with the alpha-granule membrane, we have designated it GMP-33 (granule membrane protein with a molecular weight of 33 Kd). Based on structural properties, we conclude that GMP-33 is a protein associated with the alpha-granule membrane that has not been described before.
Antibodies, Monoclonal↗
Effects of mefenamic acid on menstrual hemostasis in essential menorrhagia.
Prostaglandin synthesis inhibitors decrease menstrual blood loss by 30% to 50% in patients with essential menorrhagia. To obtain insight into their mechanism of action, we measured menstrual blood loss in menorrhagic women, who were receiving mefenamic acid (500 mg, three times daily) (n = 6) or placebo (n = 5) in a double-blind way. In addition we studied the morphology of early menstrual hemostasis. The subjects' uteri were extirpated in the first 24 hours of menstruation, and light and electron microscopy were used to perform morphologic and morphometric studies. In the group treated with mefenamic acid mean menstrual blood loss was decreased by 40%. In uteri of the women treated with mefenamic acid hemostatic plugs were further transformed, and fewer vessels without a plug were observed than in uteri of the group receiving placebo. These data suggest that mefenamic acid may act through an improvement of platelet aggregation and degranulation and through increased vasoconstriction.
Adult↗
Thrombogenicity and procoagulant activity of human mesothelial cells.
Cell seeding may decrease the thrombogenicity of implanted vascular grafts, but its application is hampered by the limited availability of autologous endothelial cells. We studied the interaction of alternate cells, human peritoneal mesothelial cells, with whole blood in a flow chamber. When citrated blood was perfused over mesothelial cells, platelet adhesion was seen on the intercellular matrix but not on the cells themselves. Perfusions with blood anticoagulated with low-molecular-weight heparin resulted in fibrin formation at the surface of mesothelial cells but not at the surface of human umbilical venous endothelial cells. At shear rates of 200 sec-1 fibrin deposition on the mesothelial cell surface increased during the first 5 minutes to 5.7 +/- 1.06 micrograms fibrin per square centimeter, whereafter these values stabilized. The procoagulant activity of cultured mesothelial cells was higher than that of peritoneal membrane studied ex vivo. However, cultured mesothelial cells incubated with polyclonal antibodies against tissue factor showed a significant decrease in procoagulant activity. We conclude that human peritoneal mesothelial cells may be used for cell seeding procedures, provided that their tissue factor expression can be controlled.
Blood Coagulation Factors↗
Nitric oxide functions as an inhibitor of platelet adhesion under flow conditions.
BACKGROUND: Nitric oxide (NO) has been identified as endothelium-derived relaxing factor (EDRF), which, in addition to its relaxant effects on vascular smooth muscle cells, is also a potent inhibitor of platelet aggregation. An inhibitory role on platelet adhesion has been suggested from experiments with washed platelets under static conditions. We have determined whether endothelium-derived and exogenous NO also regulates platelet adhesion in whole blood under flow conditions. METHODS AND RESULTS: The effect of endothelium-derived NO was studied by the addition of specific inhibitors of NO production, L-N-monomethyl arginine (L-NMMA) and N-iminoethyl-L-ornithine (L-NIO), to a perfusion system in which both endothelial cells and their matrices were present. A concentration-dependent increase in platelet adhesion to the matrix was found with a maximum inhibition at a concentration of 2 mM L-NMMA and 0.1 mM L-NIO. The effect was dependent on the presence of endothelial cells, because no increase in platelet adhesion was observed in their absence. The effect of exogenous NO was tested in a specially devised perfusion system in which the NO was introduced at the site of adhesion by means of a porous membrane on which an extracellular matrix of endothelial cells was present. Inhibition of platelet adhesion by NO was found at all shear rates tested and after all perfusion periods. CONCLUSIONS: These results demonstrate that NO is a potent inhibitor of platelet adhesion under flow conditions and thereby contributes to the regulatory role of vascular endothelial cells on platelet-vessel wall interaction.
Animals↗
Menorrhagia. Current drug treatment concepts.
Since menorrhagia occurs in 9 to 14% of populations of healthy women, many general practitioners will encounter menorrhagia-related problems. Menorrhagia is difficult to objectify and the choice of treatment between the available drugs is not always an easy one. In this survey, the available knowledge on menorrhagia diagnosis, underlying pathophysiology and treatment, especially medicinal treatment, are discussed. Overall, a practical approach is emphasised. The desire for contraception as well as the underlying cause of menorrhagia determine the drug of choice in the treatment of menorrhagia. If contraception is desired, oral combination contraceptives and continuously dosed progestogens, orally or as a medicated intrauterine device (IUD), are the first choice drugs for essential menorrhagia, and for fibroid- and bleeding disorder-associated menorrhagia. If no contraception is desired, the first choice treatments are drugs that need to be administered only during menstruation, such as prostaglandin synthesis inhibitors or antifibrinolytics. Of these, antifibrinolytics reduce menstrual blood loss to the greatest extent, whereas prostaglandin synthesis inhibitors have the lowest incidence of side effects. Prostaglandin synthesis inhibitors also have the extra advantage of diminishing dysmenorrhoea. There is no place for ergometrine in the treatment of menorrhagia. No studies are available as yet on the combination of various drug treatment modalities, although such an evaluation would be desirable.
Female↗
Treatment of uremic anemia with recombinant erythropoietin also reduces the defects in platelet adhesion and aggregation caused by uremic plasma.
In the present study, uremic patients on chronic maintenance hemodialysis were treated with recombinant erythropoietin. Before and after 20 weeks of treatment, platelet adhesion and aggregation were studied with perfusions over a sprayed collagen surface and over matrix of cultured endothelial cells with high tissue factor activity. The influence of the erythropoietin induced raise in hematocrit on platelet transport and adhesion was excluded by performing the perfusions at a standard red blood cell concentration. The present study clearly demonstrates that erythropoietin treatment improves platelet adhesion and aggregation in addition to and independent of its effect on the hematocrit. Studies with control platelets resuspended in plasma of untreated patients showed that a uremic plasma factor reduced adhesion and thrombin- and collagen-dependent aggregation. Patient platelets resuspended in control plasma showed no defects. After erythropoietin treatment, the plasma-induced inhibition of adhesion and aggregation had almost completely disappeared from patient plasma. The beneficial effect of the erythropoietin treatment on uremic hemostasis is therefore twofold. The increase of the red blood cell mass improves transport of platelets, and thus adhesion to the vessel wall. The intrinsic defect due to the presence of an inhibitory toxin in uremic plasma is, in large part, corrected. Improved neutralization of uremic toxins by red blood cells or less production of toxins by better oxygenated tissue might play a role in the observed phenomena.
Adult↗
Biochemical characterization of PECAM-1 (CD31 antigen) on human platelets.
The platelet plasma membrane expresses several membrane glycoproteins with a high molecular weight. In this study we have investigated the properties of the CD31 antigen on platelets and endothelial cells using the monoclonal antibody (MoAb) RUU-PL 7E8. Comparative studies revealed that the CD31 antigen, PECAM-1 and endoCAM are the same protein. The CD31 antigen was immunoprecipitated with a molecular mass of 125 kDa nonreduced and 135 kDa reduced from Nonidet-P40 lysates of surface labeled human platelets. The relative position in two-dimensional nonreduced/reduced SDS-PAGE and IEF-PAGE, compared to other glycoproteins of similar molecular weight, was elucidated. The position of the CD31 antigen was clearly distinct from the position of the platelet membrane glycoproteins Ia, Ib, IIa, IIb, IIIa and the granule membrane protein GMP-140. Native resting platelets bound 7,760 +/- 1,670 molecules/platelet, whereas thrombin-stimulated platelets bound 14,500 +/- 3,790 molecules/platelet. Immunoelectron microscopy revealed the presence of the CD31 antigen on the membrane of both resting and thrombin-activated platelets. Immunofluorescence studies showed the presence of the CD31 antigen in the membrane of endothelial cells on sites of cell-cell contact, suggesting that the CD31 antigen might be involved in cell-cell interaction. In functional studies, MoAb RUU-PL 7E8 did not inhibit platelet aggregation, platelet adherence to the extracellular matrix of endothelial cells and purified collagen fibrils under flow conditions, nor was any influence found on endothelial cell detachment and growth.
Antibodies, Monoclonal↗
Identification of risk factors for bleeding during treatment of acute venous thromboembolism with heparin or low molecular weight heparin.
In a prospective double-blind trial, we treated 194 patients with acute venous thromboembolism with heparin or low molecular weight heparin (LMWH; Fragmin). To evaluate the most important prognostic factors for bleeding, the presenting clinical features of the patients, the patients' anticoagulant responses, and the doses of the drugs were analyzed using univariate and multivariate regression analyses. No significant differences in clinical risk factors associated with bleeding were observed between heparin and LMWH. The univariate analyses ranked the parameters in the following order of importance: World Health Organization (WHO) performance status, history of bleeding tendency, cardiopulmonary resuscitation, recent trauma or surgery, leukocyte counts, platelet counts, duration of symptoms, and body surface area. Patients with WHO grade 4 had an eightfold increase in risk of bleeding as compared with WHO grade 1. Assessment of the individual contribution of each variable using multivariate regression analysis showed that the WHO performance status was the most important independent factor predicting major bleeding. A history of a bleeding tendency, recent trauma or surgery, and body surface area were also independent risk factors. The risk of bleeding was influenced by two factors related to the treatment, the patient's anticoagulant response as measured with the anti-Xa assay and the dose of the drug expressed as U/24 h/m2. An increased risk of bleeding was only observed at mean anti-Xa levels greater than 0.8 U/mL for both drugs. Significantly more major bleedings occurred in patients treated with high doses of the drugs, an observation that was independent of the concomitant anti-Xa levels. It should be considered whether choosing an appropriate initial dose adapted to the patient's body surface area and clinical risk factors can improve the efficacy to safety ratio of heparin treatment.
Dose-Response Relationship, Drug↗
Ascorbic acid increases the thrombogenicity of cellular matrices.
We have studied the influence of ascorbate on extracellular matrix formation in cultured human endothelial cells, smooth muscle cells and fibroblasts and measured the influence of the changed composition of their isolated extracellular matrices on their affinity for platelets. When endothelial cells were grown for a week in the presence of ascorbate, no influence on proline incorporation in their extracellular matrix was found. In accordance, no influence on platelet adhesion or aggregate formation on these matrices was detected. When smooth muscle cells were cultured in the presence of ascorbate, a strong increase in the amount of collagen types I and III in the extracellular matrix was found. When these matrices were perfused with whole blood, a significant enhanced increase in aggregate formation was observed. No influence was seen on the total coverage of the matrix with platelets. When fibroblasts were grown in the presence of ascorbate, no significant increase in proline incorporation in their matrix was measured. However, an increased adhesion of platelets was seen to the matrices at lower shear rates. We conclude that ascorbate feeding has a significant effect on endogenous deposited matrices of smooth muscle cells and fibroblasts, and that the changed composition had profound effects on platelet interaction with these matrices.
Ascorbic Acid↗
Activation of the coagulation mechanism on tumor necrosis factor-stimulated cultured endothelial cells and their extracellular matrix. The role of flow and factor IX/IXa.
Infusion of tumor necrosis factor (TNF) into tumor-bearing mice led to intravascular clot formation with fibrin deposition in microvessels in the tumor bed in close association with the vessel wall, which could be prevented by active site-blocked factor IXa (IXai). This observation prompted us to examine the role of the intrinsic system in activation of the coagulation mechanism on TNF-stimulated human endothelial cell monolayers and endothelial-derived matrix during exposure to purified coagulation factors or flowing blood. Treatment of endothelial cells in intact monolayers with TNF induced expression of the procoagulant cofactor tissue factor (TF) in a dose-dependent manner, and after removal of the cells, TF was present in the matrix. TNF-treated endothelial cell monolayers exposed to blood anticoagulated with low molecular weight heparin induced activation of coagulation. Addition of IXai blocked the procoagulant response on TNF-treated endothelial cells, and consistent with this, the presence of factor IX/VIIIa enhanced endothelial TF/factor VII(a) factor X activation over a wide range of cytokine concentrations (0-600 pM). When TF-dependent factor X activation on endothelial cells was compared with preparations of subendothelium, the extracellular matrix was 10-20 times more effective. IXai blocked TF/factor VII(a) mediated activated coagulation on matrix, but only at lower concentration of TNF (less than 50 pM). Similarly, enhancement of factor Xa formation on matrix by factors IX/VIIIa was most evident at lower TNF concentrations. When anticoagulated whole blood flowing with a shear of 300 s-1 was exposed to matrices from TNF-treated endothelial cells, but not matrices from control cells, fibrinopeptide A (FPA) generation, fibrin deposition, and platelet aggregate formation were observed. FPA generation could be prevented by a blocking antibody to TF and by active site-blocked factor Xa (Xai) over a wide range of TNF concentrations (0-600 pM), whereas IXai only blocked FPA generation at lower TNF concentrations (less than 50 pM). Activation of coagulation on matrix from TNF-stimulated endothelial cells was dependent on the presence of platelets, indicating the important role of platelets in propagating the reactions leading to fibrin formation. These observations demonstrate the potential of cytokine-stimulated endothelium and their matrix to activate coagulation and suggest the importance of the intrinsic system in factor Xa formation on cellular surfaces.
Animals↗
Effect of deletion of the A1 domain of von Willebrand factor on its binding to heparin, collagen and platelets in the presence of ristocetin.
In order to study the functional importance of the collagen, heparin and glycoprotein-Ib-binding domain, we deleted the A1 domain of von Willebrand factor (vWF), corresponding to residues 478-716, by oligonucleotide-directed mutagenesis. The resulting delta A1-vWF cDNA was expressed in COS-1 monkey kidney cells and compared to wild-type vWF. The higher-molecular-mass multimers were decreased in delta A1 recombinant von Willebrand factor (delta A1-rvWF) compared to plasma vWF and rvWF. The reactivity of delta A1-rvWF and rvWF with monoclonal antibodies directed against the collagen-binding domain (residues 969-992), the vessel-wall-binding domain, and the binding site for glycoprotein IIb-IIIa on platelets was identical. The interaction with vWF of the monoclonal antibody directed against the glycoprotein Ib binding domain was abolished for delta A1-rvWF, and similar to plasma vWF for rvWF. The binding of factor VIII to delta A1-rvWF and rvWF was similar. delta A1-rvWF and rvWF bound similarly to collagen, but the binding of delta A1-rvWF to heparin and to platelets in the presence of ristocetin were abolished. These data indicate that the heparin-binding site in the A1 domain is essential. There is no second binding domain for glycoprotein Ib outside the A1 domain. The collagen-binding domain in the A1 domain is either not active or its action can be compensated by the second collagen-binding domain.
Animals↗