Visualization of von Willebrand Factor Multimers by Enzyme-Conjugated Secondary Antibodies

A method for visualization of the multimeric forms of von Willebrand Factor (vWF) in plasma and platelets is described. The method is based upon: 1) Separation of the vWF multimers by SDS-agarose electrophoresis, 2) Subsequent blotting of the vWF multimers onto nitrocellulose, 3) Immunolocalization and visualization of the vWF pattern by the sequential incubation of the blot with a) primary vWF antiserum, b) peroxidase- or beta-galactosidase-conjugated secondary antibodies and a relevant chromogenic substrate.

Binding of Various Thrombin Fractions to Fibrin and the Influence of AT-III on Their Adsorption

Human thrombin with high affinity for fibrin was obtained by subjecting purified thrombin to affinity chromatography on Sepharose insolubilized fibrin monomers, after addition of a radioiodinated subsample of thrombin, molar ratio 1:600. As judged by radioprofiling of the electrophoretic distribution of high-affinity thrombin on 10 per cent polyacrylamide gel containing urea/SDS, the preparation consisted of 70 per cent a-thrombin, 28 per cent β-thrombin and only 2 per cent γ-thrombin. Although a-thrombin was bound more strongly to insolubilized fibrin monomers than the other subfractions, complete separation of the individual components could not be achieved.

High-affinity thrombin was employed for studies on thrombin adsorption to polymerized fibrin, assuming equal behaviour of labelled and unlabelled thrombin.

o avoid passive entrapment of thrombin within the fibrin meshwork at physiological pH, ionic strength and calcium concentration, the optimal fibrinogen concentration was found to be 2.94 umol/1. During such conditions, adsorption of thrombin to polymerized fibrin did not exceed 65 per cent of added thrombin, despite an increasing availability of fibrin-related thrombin binding domains obtained by reducing the thrombin concentration.

Adsorption of thrombin to polymerized fibrin increased by 25 per cent when the ionic strength was reduced to 0.05 mol/1. These findings suggest the presence of thrombin subfractions with different affinities for polymerized fibrin.

Aggregates of high-affinity thrombin formed during its preparation by affinity chromatography, but were prevented by adding polyethylene glycol (m.w. 6,000, final conc. 6.6 g/1). Such aggregates were not inactivated by AT-III, but could still adsorb to polymerized fibrin.

In its monomeric form fibrin-adsorbed thrombin was inactivated by AT-III and could then be extruded from the clot upon syneresis and retraction, but a small fraction remained attached to polymerized fibrin, exhibiting minor amidolytic activity.

A New Dysfibrinogenemia: Fibrinogen Oslo IV

A family with dysfibrinogenemia is described. The abnormal fibrinogen occurred in three successive generations indicating a dominant hereditary pattern. Thrombin and reptilase times were about twice the normal value. This was shown to be caused by a polymerization defect, fibrinopeptide release being normal. Platelet aggregation was undisturbed, indicating normal platelet-fibrinogen binding. The bleeding time was normal and there was no bleeding tendency. However, an obscure recurrent pulmonary ailment may, or may not, be related to the dysfibrinogenemia. The abnormal fibrinogen was tentatively termed Oslo IV.

Cross-Linked αsγt-Chain Hybrids in Plasma Clots Studied by 1D- and 2D Electrophoresis and Western Blotting

Fibrinogen and fibrin related chains in reduced human plasma as well as the bonds interlinking partially cross-linked fibrin from plasma clots have been studied by means of 1D- and 2D electrophoresis and Western blotting. Immunovisualization of reduced plasma or partially cross-linked fibrin with monoclonal antibodies specific for the α-chains or the γ-chains have shown that several bands represent material belonging to both chains. In order to decide whether these bands constitute αγ-chain hybrids or superimposed α- and γ-chain dimers, the cross-linked material was separated according to both isoelectric point (pI) and molecular weight (MW) using Pharmacia’s Multiphor II system. Western blotting of the second dimension gels revealed that partially cross-linked fibrin contains αsγt-chain hybrids and γ- polymers, in addition to the well-known γ-dimers and α-polymers. The main αsγt-chain hybrid has a pI between that of the α- and the γ-chains, a MW of about 200 kDa and contains Aα-chains with intact fibrinopeptide A (FPA). It was also observed that soluble fibrinogen/fibrin complexes as well as partially cross-linked fibrin contain degraded α-dimers with MWs close to the γ-dimers. These findings demonstrate that factor XIII-catalyzed cross-linking of fibrin is a more complex phenomenon than earlier recognized.

Identification of Platelet Antigens by Monoclonal Antibodies Using Crossed Immunoelectrophoresis with Immunoblotting of the Monoclonal Antibody

A method is described for the identification of antigens by monoclonal antibodies. This is applicable whenever precipitating antibodies to the same antigens from a different species are available. The method is based upon: 1) Separation and immunoprécipitation of cellular proteins with a polyspecific antiserum in crossed immunoelectrophoresis in the presence of the non-denaturing detergent Triton X-100 and the monoclonal antibody. 2) Coprecipitation of the monoclonal antibody with its antigen. 3) Subsequent passive transfer of the monoclonal antibody in the antibody-antigen complex onto a nitrocellulose membrane. 4) Visualization of the blotted antibody using an enzyme-linked secondary antibody and a chromogenic substrate. 5) Identification of the corresponding antigen by comparisons to the immunoprecipitate pattern of the original immunoplate. To test this method we have analyzed the detection of the antigens recognized by six previously described monoclonal antibodies against platelet membrane proteins and von Willebrand factor. Specific immunoblots were obtained in each case using small amounts of monoclonal antibodies. Thus, the technique provides an alternative when epitopes are denatured by SDS, and avoids the use of radioactively labelled monoclonal antibodies.

Persistently Elevated Levels of von Willebrand Factor Antigen in HIV Infection

Levels of circulating von Willebrand factor (vWf) antigen are thought to reflect endothelial involvement in various disorders. In the present study we found markedly elevated plasma levels of vWf in HIV-infected patients demonstrated on both cross-sectional and longitudinal testing. Notably, we found that a persistent rise in vWf antigen was associated with progression of HIV-related disease. This elevation of vWf antigen represented functionally normal vWf as evaluated by plasma FVIII, ristocetin cofactor assay and vWf multimer analyses. While HIV-infected patients showed enhanced platelet activation, platelets did not contribute substantially to the increased vWf levels. The high vWf levels were significantly correlated with high viral load, and during HAART, the pronounced decline in HIV RNA levels was accompanied by a corresponding decrease in vWf. The persistent elevation of functionally normal vWf during HIV infection, most probably reflecting a persistent endothelial cell activation, may have an important role in the pathogenesis of HIV infection.

Effects of two differently heparin-coated extracorporeal circuits on markers for brain and myocardial dysfunction

Objective: The two most commonly used heparin-coated systems for cardiopulmonary bypass (CPB) are the Carmeda Bio-Active Surface (CBAS) (Medtronic, Minneapolis, MN, USA) and the Duraflo II coating (Baxter Healthcare, Irvine, CA, USA). The two surfaces are technically unequal and previous experimental studies have demonstrated disparities in effects on the immune system and blood cells. However, little is known concerning the influence of the two surfaces on markers for brain and myocardial dysfunction.

Methods: Forty patients undergoing elective, primary coronary bypass grafting with CPB were prospectively randomized to either the CBAS system or the Duraflo II circuit. During and after CPB, biological markers for brain dysfunction and myocardial injury were analysed.

Results: Both markers for brain dysfunction S-100B and neuron-specific enolase (NSE) increased significantly during CPB ( p =0.01). The elevation during bypass correlated significantly with the duration of CPB ( r = 0.39 and r= 0.38, respectively, both p< 0.02). NSE was somewhat more elevated in the Duraflo II group at the end of CPB ( p =0.01) and 5 h after CPB ( p= 0.02); for S-100B, there were no intergroup differences. Also, the markers related to myocardial injury, myoglobin and creatine kinase (CK-MB) mass increased during CPB ( p= 0.01), while elevation of troponin-I occurred 5 h after CPB ( p= 0.01). There were no statistically significant intergroup differences. No significant correlation was seen between the release of cardiac markers and the duration of CPB. The clinical course was similar in both groups.

Conclusions: Except for a slightly higher elevation of NSE at the end of CPB and 5 h after CPB in the Duraflo II group, there were no significant differences between the CBAS group and the Duraflo II group concerning markers for brain and myocardial dysfunction.

The ethanol gelation test and thrombosis

Intravascular fibrin formation takes place during thrombus formation or by activation of coagulation in circulating blood. Incorporation of fibrin in thrombi may be detected by usine 125I-labelled fibrinogen. Soluble fibrin may be present during thrombophilic states or during thromboembolic complications and diseminated intravascular coagulation (DIC) and may be detected and quantitated by various techniques such as N-terminal amino acid analysi, chromatographic procedures and so-called paracoagulation test, using ethanol or protamine sulfate. Finally, transformation of fibrinogen to fibrin may be indirectly assayed by quantitation of fibrinopeptide A released, by immunological technique. For routine purposes and especially in emergency situation, rapid and simple tests are required. In these circumstances, only the paracoagulation tests are at hand. Below, the present situation with regard to the ethanol gelation test (EGT) is outlined.

Glycoprotein IIb-IIIa on platelet-derived microparticles, and microparticle structures studied by electron microscopy, confocal laser microscopy and crossed radio-immunoelectrophoresis

Shedding of microparticles from the platelet surface is usually associated with exposure of platelet procoagulant activity. Platelet-derived microparticles have been detected in blood in various disease states. In vitro, platelet stimulation with a number of different agonists results in formation of microparticles. In the present study, microparticles induced by platelet stimulation by calcium ionophore or by membrane incorporation of the terminal complement complex C5b-9 were studied using electron microscopy, confocal laser microscopy, flow cytometry and radio-immunoelectrophoresis. When studied by electron microscopy, microparticle morphology was found to be dependent upon the induction method. Platelet stimulation with the calcium ionophore resulted in smaller, more homogeneous and electron dense microparticles than those induced by insertion of the terminal complement complex. With flow cytometry and confocal laser immunofluorescence microscopy, microparticle GPIIb-IIIa was demonstrated using a FITC-conjugated antibody to GPIIIa. Surface-bound GPIIb-IIIa was demonstrated on the microparticles by immunoelectron microscopy. Crossed immunoelectrophoresis of detergent-solubilized microparticles visualized a very prominent GPIIb-IIIa immunoprecipitate arc, and binding of [(125)1]fibrinogen to microparticle GPIIb-IIIa was demonstrated by radio-immunoelectrophoresis. This suggests that the activated GPIIb-IIIa complex is preserved intact during the shedding of microparticles from the platelet surface.

Children with acute lymphoblastic leukaemia have high plasma levels of total homocysteine at time of diagnosis

OBJECTIVE

Cancer can induce venous thromboembolic complications for various reasons. As part of a greater study, acquired and congenital prothrombotic risk factors were investigated in children with leukaemia or non-Hodgkin's lymphoma and compared with similar investigations in children with congenital heart defects.

MATERIAL AND METHODS

Blood samples were taken from 60 children with newly diagnosed leukaemia or lymphoma and 133 children with congenital heart defects in the course of a scheduled cardiac catheterization. When children with cancer were in remission, analyses of acquired prothrombotic risk factors were repeated. Children with cancer were observed for symptoms of thromboembolism throughout their treatment period.

RESULTS

Total homocysteine levels were significantly raised in children with cancer (median value 10.0 micromol/L) as compared with the levels in children with congenital heart diseases (5.0 micromol/L) (p<0.001), while children with acute lymphoblastic leukaemia had the highest values. The median level of lipoprotein(a) was slightly increased in children with newly diagnosed leukaemia or lymphoma (105 mg/L versus 100 mg/L, p<0.001), and levels of coagulation inhibitors were higher (p<0.001). Total homocysteine levels normalized when children attained remission of cancer disease. Two children had symptoms of acute thrombosis.

CONCLUSIONS

Raised concentrations of total homocysteine were frequent in children with newly diagnosed cancer, but this normalized when the children were in remission. The clinical significance of our observations and the impact on venous thromboembolism have yet to be defined.

Pattern of acute drug poisoning in Oslo

All 1742 admissions occasioned by acute drug poisoning to a medical ward in Oslo during the periods 1958--60, 1963--65, 1966--69 and 1970--73 have been reviewed. The number of admissions per annum in these periods was 99, 119, 128 and 144, respectively. Because the hospital situation and number of inhabitants in the city remained fairly constant from 1958 to 1973, the increasing figures were assumed to reflect a corresponding increase in the incidence of acute drug poisoning in Oslo. The incidence was estimated to be within the range of 1--2 per 1000 inhabitants per annum. No female predominance was noted except for the age group under 30 years. The occurrence of barbiturate poisonings decreased markedly during the peroids studied, whereas those due to non-barbiturate hypnotics, tranquillizers and tricyclic antidepressants showed a proportionate increase. Slightly less than one fourth of the females and half of the males had taken alcohol. More males (43%) than females (13%) also were alcoholics. A suicidal intention was, however, found more frequently among females (70%) than males (43%). The hospital mortality was approximately 1 %. No death was associated with tricyclic antidepressants, which in the last study period had been ingested by approximately 10% of all patients.

New biomarkers in an acute model of live Escherichia coli-induced sepsis in pigs

We developed a live Escherichia coli model of acute sepsis in pigs with emphasize on biomarkers reflecting the early inflammatory response of sepsis. Healthy pigs, 25-35 kg, were challenged intravenously (IV) (n = 12) or intrapulmonary (n = 6) with live E. coli and observed for 3 and 5 h respectively. Control pigs received culture medium (n = 6 + 3). Haemodynamic parameters and a broad panel of inflammatory mediators were measured. The dose of bacteria was carefully titrated to obtain a condition resembling the early phase of human septic shock. The IV group displayed a pro-inflammatory response [significant increase in tumour necrosis factor-alpha, interleukin (IL)-6 and IL-8] and an early anti-inflammatory response (significant increase in IL-10). For the first time, we demonstrate a significant increase in IL-12 and matrix metalloproteinase-9 (MMP) early in pig sepsis. Coagulation was activated (significant increase in thrombin-antithrombin complexes) and there was a significant decrease in the serum proteins suggesting capillary leakage. Haemodynamic parameters reflected a septic condition with significant decrease in systemic blood pressure, increases in heart rate, pulmonary artery pressure and base deficit. None of these changes was observed in the control group. Interleukin-1beta and vascular endothelial growth factor increased in both groups. Nitric oxide measurements suggested an initial pulmonary vascular endothelial inflammatory response. The intrapulmonary group, which did not resemble septic condition, showed a substantial increase in MMP-9. In this porcine model of sepsis, IL-12 and MMP-9 were detected for the first time. These biomarkers may have an impact in the understanding and future treatment of sepsis.

Syndecan-1 plasma levels during coronary artery bypass surgery with and without cardiopulmonary bypass

The glycocalyx covering the endothelium is shed during ischemia and reperfusion. The shedding is accompanied by increased levels of the glycocalyx component syndecan-1 in the circulation. Our aim was to compare plasma levels of syndecan-1 in patients undergoing coronary artery bypass grafting (CABG), with or without the use of cardiopulmonary bypass (CPB). Syndecan-1 plasma concentrations were measured in patients undergoing CABG on-pump (n = 22) or off-pump (n = 22). The syndecan-1 concentration increased significantly from 29.5 ± 4.6 ng/mL at baseline to 98.7 ± 9.8 ng/mL (p < 0.01) after the start of CPB or 30 minutes after the induction of anesthesia in the off-pump group. There were no significant differences in peak syndecan-1 plasma concentrations between on-pump and off-pump patients. Plasma levels of syndecan-1 increased significantly during CABG, with or without the use of CPB. There were no significant differences in syndecan-1 concentrations in the two groups.

Clopidogrel increases expression of chemokines in peripheral blood mononuclear cells in patients with coronary artery disease: results of a double-blind placebo-controlled study

BACKGROUND

Chemokines and platelet activation are both important in atherogenesis. Platelet inhibitors are widely used in coronary artery disease (CAD), and we hypothesized that the platelet inhibitor clopidogrel could modify chemokines in CAD patients.

OBJECTIVES

We sought to investigate the effect of clopidogrel on the expression of chemokines and chemokine receptors in peripheral blood mononuclear cells (PBMC) in CAD patients.

PATIENTS/METHODS

Thirty-seven patients with stable angina were randomized to clopidogrel (n = 18) or placebo (n = 19). PBMC, blood platelets and plasma were collected at baseline and after 7-10 days in the patients, and in 10 healthy controls. mRNA levels of chemokines and chemokine receptors in PBMC were analyzed by ribonuclease protection assays and real-time reverse transcriptase polymerase chain reaction. Platelet activation was studied by flow cytometry.

RESULTS

(i) At baseline, the gene expression of the regulated on activation normally T-cell expressed and secreted (RANTES) chemokines and macrophage inflammatory peptide (MIP)-1beta in PBMC, the expression of CD62P and CD63 on platelets and the levels of platelet-derived microparticles (PMP) were elevated in angina patients comparing healthy controls; (ii) markers of platelet activation were either reduced (CD63) or unchanged (CD62P, PMP, beta-thromboglobulin) during clopidogrel therapy; (iii) in contrast, clopidogrel significantly up-regulated the gene expression of RANTES and MIP-1beta in PBMC, while no changes were found in the placebo group; (iv) a stable adenosine 5'-diphosphate metabolite attenuated the release of MIP-1beta, but not of RANTES, from activated PBMC in vitro.

CONCLUSIONS

Even if we do not argue against a beneficial role for clopidogrel in CAD, our findings may suggest potential inflammatory effects of clopidogrel in CAD.

Effects of platelets and platelet-derived material on the activated partial thromboplastin time (Cephotest) coagulation test

OBJECTIVE

The Cephotest is an activated partial thromboplastin time (APTT) test used to measure the activity of the intrinsic pathway of coagulation. To perform this test, blood is usually centrifuged to obtain plasma that is almost without erythrocytes and leucocytes and with only a minimal amount of platelets.

MATERIAL AND METHODS

In the present experiments blood was centrifuged at different speeds to produce either platelet-poor plasma (PPP) or platelet-rich plasma (PRP). PPP and PRP obtained from the same whole blood samples from each of several persons were tested in pairs using the standard Cephotest reagent to observe the consequences of Cephotest being performed on plasma containing platelets. The same procedure was used with a Cephotest reagent with a reduced concentration of phosphatidylserine. In succeeding experiments the PRP was preincubated with SFLLRN or Ca-ionophore to activate the platelets, a procedure also known to produce platelet-derived microparticles. PPP and PRP were compared by thrombin time and reptilase time tests to find out at which stage platelets might influence the Cephotest.

RESULTS

The results showed that the platelets did influence Cephotest when using both the regular reagent and the phospholipid-reduced agent. When using the regular reagent, PRP showed a tendency towards a longer APTT than PPP. It is suggested that this was caused by platelets consuming some of the first traces of thrombin generated.

CONCLUSIONS

When using the phospholipid-reduced reagent, PRP showed a shorter APTT than PPP, probably because the platelets contributed phosphatidylserine to the system. When the platelets were activated before testing, their effects on the tests were increased. Microparticles that formed during platelet activation may have contributed to these effects.

Acquired haemophilia: management of bleeds and immune therapy to eradicate autoantibodies

Acquired haemophilia is a rare, but often severe bleeding disorder caused by autoantibodies against a coagulation factor, usually factor VIII (FVIII). Between 1997 and 2004 we observed 14 patients (mean age of 78 years) with acquired haemophilia. The aim of the present study was to investigate the effect of activated prothrombin complex concentrate (aPCC) for bleeds and the response to corticosteroids and cyclophosphamide to eradicate the offending autoantibodies. The most common clinical presentations were severe profuse bruising (12) and haematuria (5). Ten patients were classified as idiopathic. At the time of diagnosis all patients had a very low FVIII level, and one patient also showed factor IX < 1%. High levels of antibodies to FVIII varying from 10 to 1340 Bethesda units (BU) and prolonged activated partial thromboplastin time were disclosed in all patients. Eight severe bleeds were treated with aPCC (FEIBA) at a dosage of 70 IU kg(-1) every 8 h until haemostasis. Ten patients received corticosteroids and cyclophosphamide as immunomodulatory therapy. Effective haemostasis was achieved in all bleeds after aPCC. Ten of 11 patients responded either completely or partially to the immunomodulatory regime within 6 months. Five patients achieved complete response (CR) whereas partial responses were seen in five patients. The anti-CD20 monoclonal antibody rituximab was given to two patients in conventional doses and a CR was seen in one patient. aPCC is effective in treating acute bleeds in patients with acquired haemophilia with high inhibitor levels. The combination of oral corticosteroids and cyclophosphamide seems to be effective to eradicate the inhibitor.

Clinical implications of red blood cell and platelet storage lesions: an overview

Both red blood cells and platelets undergo lesions upon storage which affect their function and possibly their clinical outcome. Some of these lesions are reversible, others not. Improved additive solutions and leukocyte depletion can delay the appearance of storage lesions. In addition, cellular apoptosis leads to numerous mitochondrial and surface changes during storage which have the potential to induce immune suppression by tuning down the innate immune system. This overview highlights some laboratory and clinical aspects of red cell and platelet storage lesions.

Improved preservation of coagulation factors after pre-storage leukocyte depletion of whole blood

Plasma and red blood cell quality are affected both by citrate concentration and the levels of extracellular leukocyte and platelet derived substances, accumulated during storage of blood. The effect of leukocyte filtration on the storage stability of whole blood was therefore studied in blood collected in standard CPD and 0.5CPD (CPD with half strength citrate concentration). A total of 52 units, 12 of them with reduced citrate concentration, were leukocyte-filtered with Pall( whole blood filter (WBF1 or 3). No differences in leukocyte or platelet reduction were observed with the two citrate concentrations. However, with 0.5CPD a significantly longer filtration time and increased complement activation was observed. The effect of pre-storage leukocyte filtration on the plasma quality of whole blood was therefore only studied with standard CPDA1 anticoagulant solution (normal strength citrate concentration). Leukocyte filtration did not affect the von Willebrand factor concentration, while a small reduction (7%, p=0.04) in factor VIII (FVIII) concentration was observed. During storage, however, FVIII decreased more slowly in the filtered than in the unfiltered product, and, from day two, the FVIII content was significantly higher in the filtered product (46% versus 30% at 28 days, p<0.001). Factor V (FV) demonstrated a 16% reduction (p<0.001) upon filtration, followed by an additional 8% in the next 24 h and only a 4% reduction the next 27 days, while unfiltered products demonstrated a continuous reduction to 26% at 28 days. While the beta-thromboglobulin (beta-TG) concentration significantly increased (from 836 to 2483 IU/ml, p<0.001) during leukocyte filtration, no further increase was observed during storage. In contrast, unfiltered products demonstrated an increase to 5762 IU/ml (p<0.001) at 14 days, followed by a slight, not significant, reduction. This indicates platelet activation during filtration and explains a parallel reduction in FV. Filtration induced no increase in prothrombin fragment 1+2, while a slight increase was observed in some unfiltered products after 28 days of storage.Pre-storage leukocyte depletion thus improves the coagulation factor content of plasma in stored whole blood.

Successful thrombolysis by prolonged low-dose alteplase in catheter-directed infusion

Catheter-directed thrombolysis is a sophisticated method in the treatment of thromboembolism with maximum effect on the thrombus and minimal systemic effect. The consequences are enhanced local thrombolysis and a reduction in general bleeding tendency, compared with systemic thrombolysis. At our institution, two children had successful thrombolysis by prolonged continuous catheter-directed low-dose alteplase. The first patient, a boy with Fontan physiology, was successfully treated for a massive pulmonary thromboembolism by catheter-directed very low-dose alteplase for five days. The second patient, who suffered from relapsing nephrotic syndrome, achieved satisfactory thrombolysis of an arterial leg thrombosis after four days of continuous catheter-directed low-dose alteplase.

CONCLUSION

Although catheter-directed thrombolysis seems to be a valuable method in thrombolytic therapy, there is a lack of evidence-based recommendations concerning dosage, effect of bolus, simultaneous anticoagulation and duration of treatment for children.