C1272F: a novel type 2A von Willebrand's disease mutation in A1 domain; its clinical significance

Most mutations identified in 2A VWD patients are localized in the A2 domain, although missense substitutions have also been recognized in the A1 domain. We describe a novel heterozygous missense mutation in the A1 domain of VWF gene responsible for type 2A phenotype. Analysis of the complete exon 28 was carried out in a patient and his mother with life-long histories of moderate to severe bleeding and laboratory data of type 2A VWD. The analysis of exon 28 of VWF gene showed a 3815 G → T transversion resulting in C1272F mutation. It is probably associated with a group I mechanism according to patients' clinical symptoms, and, in the case of the propositus, the lack of clinical response to treatment with desmopressin. The mutation was not found in 100 normal alleles. This substitution affected the normal S-S bound between C1272 and C1458, which is involved in A1 loop structure, altering the normal multimerization and function of VWF. The VWFpp/VWF:Ag ratio in the propositus and his mother was >3, suggesting a shortened survival of VWF. We believe it is important to report the complete clinical phenotype corresponding to the new mutation to increase the knowledge in the clinical field.

von Willebrand's disease diagnosis and laboratory issues

SUMMARY

In this paper, the recent developments in the diagnosis and laboratory issues of von Willebrand's disease (VWD) are presented. Dr. Castaman reviews the functional tests available for the diagnosis of VWD and their pathophysiological significance, focusing on which tests are best used in the diagnosis and classification of VWD. Dr Montgomery reviews an emerging issue that is accelerated clearance of von Willebrand factor (VWF) occurring in some variants of VWD. This phenotype can be suspected by the presence of an increased ratio between the VWF propeptide and the VWF antigen. These patients have typically a robust, but short-lived increase of FVIII and VWF after desmopressin. Dr Meschengieser reviews the determinants of bleeding after surgery in patients with VWD, emphasizing the role of bleeding history in predicting this risk.

Patients' perceptions regarding oral anticoagulation therapy and its effect on quality of life

OBJECTIVE

Anticoagulation clinics have improved the time spent within therapeutic range and decreased hemorrhagic complications and costs in chronic oral anticoagulation. Whether these benefits correlate to patients' quality of life (QOL) remains to be determined. The impact of patients' perceptions about anticoagulation on QOL has not been evaluated. The objective of this study was to evaluate prospectively patients' perceptions and quality of life in patients chronically anticoagulated.

RESEARCH DESIGN AND METHODS

A cross-sectional study was designed to investigate the prevalence of positive and negative perceptions about oral anticoagulation therapy (OAT) and to identify vulnerable groups. Patients anonymously completed the SF-36 survey and a questionnaire that focused on patients' perceptions of protection from thrombotic complications or fear of haemorrhage due to the anticoagulation. We related those perceptions to the General Health SF-36 score, to the patient's characteristics, the absolute bleeding risk (i.e. intended International Normalized Ratio [INR]), duration of therapy and medical attention.

RESULTS

One thousand patients were included and 905 questionnaires evaluated. Most patients felt protected and better since the beginning of therapy (71.5% and 61.5%, respectively). Patient characteristics associated with negative perceptions were; female sex (Odds Ratio [OR] 1.58, 95% Confidence Interval [CI] 1.06-2.36, p = 0.01); patients with less than 1 year of therapy (OR 2.16, 95% CI 1.34-3.48, p = 0.006); those not satisfied with medical attention (OR 2.86, 95% CI 1.53-5.18, p = 0.0001); and those that modified their lifestyle (OR 2.75, 95% CI 1.49-4.91, p = 0.0002). Patients with a lower bleeding risk (INR 2.0-3.0) had more negative perceptions than those with a higher risk. Patients with negative perceptions achieved the lowest score in the SF-36 survey. Haemorrhages did not affect patients' perception or QOL.

CONCLUSIONS

Patients' perceptions correlated with QOL. We were able to identify patient characteristics associated with poor QOL and thus the group of patients whose negative perceptions most warranted special attention from their clinicians.

von Willebrand disease: laboratory aspects of diagnosis and treatment

von Willebrand disease is the most common inherited bleeding disorder in humans. VWD can be classified into three major types, designated Types 1, 2 and 3; Type 2 can be further separated into subtypes 2A, 2B, 2M and 2N. The diagnosis of VWD requires a personal and family history of bleeding and confirmation by laboratory analysis. Although Types 2 and 3 are relatively straightforward to diagnose, there may be a risk of overdiagnosis of Type 1 because of an overlap within the normal range. We also report on the clinical profile and diagnosis of VWD in a South American cohort of patients and on the in vitro characteristics of some factor concentrates available for treatment of VWD.

Effects of lopap on human endothelial cells and platelets

Severe consumption coagulopathy has been detected in rats after Lopap (a prothrombin activator from Lonomia obliqua caterpillar bristles) infusion and in humans after accidental contact with L. obliqua bristles. However, platelet count and antithrombin (AT) levels were only modestly affected, suggesting that a different form of blood coagulation activation may be involved in this hemorrhagic syndrome. Here we describe that Lopap had no effect on aggregation of washed human platelets induced by several agonists, suggesting that it might not impair platelet function in vivo. AT was able to inhibit the amidolytic activity of thrombin generated by incubation of Lopap with prothrombin in a purified system, which may be different from that generated by the prothrombinase complex in vivo. The surface expression of both ICAM-1 and E-selectin but not of VCAM-1 was upregulated by Lopap in cultured HUVEC, suggesting that it may behave differently from other mediators, such as thrombin and tumor necrosis factor-alpha.

Recurrent haemoperitoneum in a mild von Willebrand's disease combined with a storage pool deficit

Haemoperitoneum secondary to haemorrhagic corpus luteum has been described in severe bleeding disorders such as afibrinogenaemia, type 3 von Willebrand's disease and patients under oral anticoagulation. We have studied one patient who presented three episodes of severe bleeding at ovulation, requiring surgery twice, with the diagnosis of mild von Willebrand's disease and mild storage pool deficiency. Mild von Willebrand's disease (associated with other thrombopathies or coagulopathies) should be considered in this pathology, although physicians would prefer to find a severe haemorrhagic disorder as the underlying condition in these cases.

Effect of nitric oxide on megakaryocyte growth induced by thrombopoietin

The present study investigated the effect of nitric oxide (NO) on megakaryocyte (Mk) proliferation induced by thrombopoietin (TPO). Low-density mononuclear cells (MNCs) and CD34+ cells from human bone marrow (BM) were cultured in liquid medium in the presence of sodium nitroprusside (SNP) or (Z)-1-[2-(aminoethyl)-N-(2-ammonioethyl) amino] diazen-1-ium-1, 2-diolate (DETA/NO) and then stimulated with TPO. Mk number decreased in both NO donors, as identified by flow cytometry 11 to 13 days after TPO stimulation. Nitrite, cyanide, or the carrier molecule DETA failed to reproduce the inhibition caused by NO donors. When CD34+ cells were treated with DETA/NO, the inhibition of Mk growth was even more pronounced than that in MNCs. Failure of the guanosine 3',5'-cyclic monophosphate (cGMP) analog 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP) to inhibit Mk proliferation suggests that cGMP is not involved in Mk suppression mediated by NO. On the other hand, DNA analysis by flow cytometry showed that apoptosis of CD34+ cells and Mks seemed to be at least one of the mechanisms associated with the cytotoxic DETA/NO effect. Stimulation of MNCs or CD34+ cells with tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) increased endogenous NO levels and suppressed Mk growth. Treatment with NO synthesis inhibitors such as L -N(G)-monomethyl arginine (L -NMMA) or L -N(G)-nitroarginine methyl ester hydrochloride (L -NAME) partially reversed Mk growth inhibition induced by TNF-alpha and IFN-gamma, although increased NO levels returned to normal values. The results presented here strongly indicate that NO regulates the growth of Mks induced by TPO by a direct effect on both progenitors and mature Mks.

Clinical features and laboratory patterns in a cohort of consecutive Argentinian patients with von Willebrand's disease

BACKGROUND AND OBJECTIVES

von Willebrand's disease (vWD) is a bleeding disorder with variable clinical expression. Our aim was to classify patients with vWD and to determine the phenotype in their relatives.

DESIGN AND METHODS

The types and subtypes, blood group frequency and its relevance, bleeding sites, response to the desmopressin (DDAVP) test, transfusion requirements and clinical features in type 1 and 2A families were determined in 1,885 patients.

RESULTS

Our findings were: type 1: 91%, type 2A: 3.1%, severe vWD: 1.3%; type 2N: 1.6%; type low intraplatelet: 2.7%; combined 1+ 2N: 0.3%. Blood group O prevalence was 70.5%. Bleeding and transfusion requirements were not correlated to blood groups. The most frequent symptoms were: ecchymoses-hematomas and epistaxis and, in females over 13 years, also menorrhagia. Normal levels of factor VIII:C were found in 38.4% of the patients. DDAVP was infused in 567 patients with a good response in 80.6%. About 9% of our patients needed transfusion therapy. The diagnosis of von Willebrand's disease is more likely in subjects belonging to families with type 2A disease than in members of families with type 1 vWD in spite of these being symptomatic.

INTERPRETATION AND CONCLUSIONS

These observations provide a good strategy to identify, classify and treat vWD patients without performing molecular assays.

Circulating platelet/polymorphonuclear leukocyte mixed-cell aggregates in patients with mechanical heart valve replacement

There is convincing evidence that cell adhesion plays an important role in cardiovascular pathology and is frequently associated to "in vivo" cellular activation. This study involves patients with mechanical heart valve replacement (MHVR patients) who have increased platelet polymorphonuclear leukocyte (PMN) reactivity. Dual-color cytometry was used to determine the expression of adhesive molecules on cellular surfaces, platelet, and PMN-bound fibrinogen as well as the presence of circulating platelet/PMN mixed-cell aggregates (MCA) in 55 MHVR patients, 49 control patients under oral anticoagulant therapy, and 22 healthy volunteers. The results demonstrated that (a) PMN from MHVR patients showed an increased PMN-bound fibrinogen (mean +/- SEM: 1,420 +/- 169 anti-fibrinogen fluorescence intensity, P= 0.0012), when compared to controls (mean +/- SEM: 747 +/- 32 anti-fibrinogen fluorescence intensity) and healthy volunteers (mean +/- SEM: 692 +/- 25 anti-fibrinogen fluorescence intensity; (b) platelet activation in MHVR patients was evidenced by the higher expression of CD62P (mean +/- SEM: 128 +/- 19 anti-CD62P fluorescence intensity, P = 0.003) compared to controls (mean +/- SEM: 65 +/- 15 and 50 +/- 10 anti CD62P fluorescence intensity) and by increased levels of platelet-bound fibrinogen (mean +/- SEM: 625 +/- 20 anti-fibrinogen fluorescence intensity, P = 0.0043 versus 496 +/- 45 and 480 +/- 30 for control patients and for healthy volunteers, respectively); and (c) the proportion of MCA in MHVR patients (15 +/- 2%) was significantly higher (P = 0.009) compared to controls (7 + 1%) and healthy volunteers (6 +/- 2%). The results indicate that the presence of stable circulating MCA represents another marker of "in vivo" PMN activation in MHVR patients.

An ELISA system to detect anti-factor VIII antibodies without interference by lupus anticoagulants. Preliminary data in hemophilia A patients

BACKGROUND AND OBJECTIVES

Difficulties in identifying the coexistence of neutralizing anti-factor VIII antibodies (anti-fVIII) and lupus anticoagulant (LA) are mainly due to the interference of LA on anti-fVIII assays. Our aim was to reveal the presence of anti-fVIII using a system that is not affected by LA.

DESIGN AND METHODS

We developed an enzyme-linked immunosorbent assay (ELISA) method that uses phospholipid-free recombinant factor VIII as the antigen. A monoclonal anti-fVIII was tested as a positive control, excluding non-specific binding by using two unrelated monoclonal antibodies. The ELISA was performed on hemophilic plasmas with anti-fVIII and negative LA (n=12) or without inhibitors (n=12). Two hemophilic plasmas with LA and presumably anti-fVIII were also assayed. Positive LA (n=12) and normal (n=10) plasmas were tested as negative controls.

RESULTS

All (12/12) plasmas with anti-fVIII and 5/12 hemophilic plasmas without inhibitors were positive; LA and normal plasma controls were negative.

INTERPRETATION AND CONCLUSIONS

Results presented here show that LA does not interfere with the anti-fVIII ELISA: However, the assay detects both neutralizing and non-neutralizing anti-fVIII antibodies, therefore a neutralizing effect must be confirmed through functional tests.

Effect of thrombopoietin and granulocyte colony-stimulating factor on platelets and polymorphonuclear leukocytes

Thrombopoietin (TPO) and granulocyte colony-stimulating factor (G-CSF) may be administered together in aplastic patients. We evaluated the effect of both cytokines alone or combined on platelets and polymorphonuclear leukocytes (PMN) functional responses. TPO, G-CSF, or the combination of both cytokines, induced neither platelet nor PMN activation. TPO but not G-CSF synergized with threshold ADP concentrations to induce maximal aggregation and ATP release. The synergistic effect of TPO with ADP was not modified by the presence of G-CSF. Flow cytometry studies have shown that thrombin-induced loss of GPIb from platelet surface was significantly increased by pretreatment of platelets with TPO, G-CSF, or both cytokines. P-selectin expression induced by thrombin was augmented by TPO, but not by G-CSF. Coincubation of the cells with TPO and G-CSF did not modify the values obtained with TPO alone. Expression of CD11b on PMN surface was augmented by G-CSF or fMLP. G-CSF-treated PMN increased the effect of fMLP on CD11b expression. TPO did not modify either basal levels of CD11b or the increased expression induced by G-CSF or fMLP. Incubation of PMN with both cytokines showed no differences compared to G-CSF alone. Platelet-PMN aggregates induced by thrombin in whole blood were augmented by TPO. G-CSF alone neither synergized with thrombin nor changed the results observed with TPO. These data show that in vitro functional responses of platelets, or PMN induced by TPO or G-CSF alone, were neither further increased nor inhibited by treatment of the cells with both cytokines.

[Present and future of oral anticoagulants]

The number of patients under oral anticoagulant therapy has markedly increased lately, mainly due to those with chronic atrial fibrillation. Progress has been made in the control of oral anticoagulation because sensitive and calibrated commercial reagents for prothrombin time have become available. But bleeding is still a problem in these patients. In our experience, the intensity and the duration of the anticoagulant therapy are the most important risk factors for bleeding. The deviation of INR (International Normalized Ratio) can also be associated with higher risk for bleeding. The limitations of oral anticoagulant therapy include frequent laboratory controls for dose adjustment, drug interactions, narrow therapeutic range and the high variability in patient response. These limitations prompted the development of new antithrombotic agents. A number of low molecular weight active site inhibitors of thrombin are being developed and one of them is orally bioavailable, and could become an alternative to vitamin K antagonists.

Bleeding risk factors in chronic oral anticoagulation with acenocoumarol

We studied major bleeding complications, death related to hemorrhage, and tried to identify predisposing factors for bleeding in outpatients treated with acenocoumarol. We evaluated 811 outpatients attending a specialized anticoagulant therapy unit. The intended INR range was 3.5-4.5 for mechanical heart valve replacement (N= 384) and 2.0-3.0 for other indications (N= 427). The variability of INR for the total follow-up and the 2 months before the hemorrhage was calculated. The total follow-up was 1,963.26 years with 27,321 control tests. We observed 47 major bleeding episodes, including 2 fatal (central nervous system hemorrhages), in 37 patients. 49.5% of the patients had underlying diseases. The rate of major and fatal hemorrhage was 2.39 and 0.10 episodes per 100 patients year, respectively. Hemorrhagic complications were more frequently observed in patients with a more intense intended range (8.2% in the INR 3.5-4.5 group vs. 1.5% in the 2.0-3.0 INR group). The risk of major bleeding increased in patients with an achieved INR higher than 6 and in those with higher INR variability during follow-up. The estimated probability of bleeding also increased with time: it was 0.102% at 78 months, and at the beginning of therapy it was 0.006% and 0.007% at 1 and 4 months, respectively. The intensity of anticoagulation and the deviation of the INR from the target are the most important risk factors for bleeding in patients taking acenocoumarol. Monitoring the variability of INR can help identifying patients predisposed to bleeding. However, the screening for underlying disease should always be performed.

Anticoagulation in pregnant women with mechanical heart valve prostheses

OBJECTIVE

To evaluate the outcome of pregnancy in women with mechanical heart valve prostheses in relation to the anticoagulant treatment used in the first trimester and the incidence of thrombotic and bleeding complications.

METHODS

92 pregnancies in 59 women were followed between 1986 and 1997. In 31 pregnancies, oral anticoagulants were discontinued when pregnancy was diagnosed and subcutaneous heparin was started (12 500 U every 12 hours) adjusted to prolong the adjusted partial thromboplastin time to twice the control level. In the second trimester oral anticoagulants were resumed but changed to heparin again 15 days before the expected delivery date. In 61 pregnancies oral anticoagulants were continued during the first trimester. The same regimen of heparin was used for delivery.

RESULTS

Abortion or fetal losses were similar (p = 0. 5717) in women exposed to oral anticoagulants in the first trimester (13/61; 25%) compared with those who received adjusted subcutaneous heparin (6/31; 19%). Embolic episodes were more common (p = 0.0029) in women who received heparin (4.92%) compared with those on oral anticoagulants (0.33%). Embolic episodes were cerebral and transient. No valve thromboses were observed. No malformations appeared in the 71 newborns, except for one case of hydrocephalus. There were no maternal deaths secondary to thrombotic complications. The only death was the result of major bleeding after the delivery of a premature stillborn.

CONCLUSIONS

Oral anticoagulants seem to be safer for the mother than adjusted subcutaneous heparin. Heparin does not offer a clear advantage over oral anticoagulation in the pregnancy outcome.

Binding of von Willebrand factor to collagen by flow cytometry

We developed a new method for the detection of large von Willebrand factor (vWf) multimers binding to collagen and for the determination of vWf antigen (vWf:Ag) using flow cytometry. Collagen is coated on to polystyrene beads, allowing detection of found large vWf multimers. In addition, rabbit antibody against vWf is coated on to the beads allowing detection of all vWf:Ag. In plasma samples from healthy persons and patients (with type 1, 2A, 2N, or severe von Willebrand disease or hemophilia), 4 different assays were performed: vWf:Ag by immunoelectrophoresis; vWf ristocetin cofactor (vWf:RCof); CBA; and vWf:Ag based on an enzyme-linked immunosorbent assay using polystyrene beads. We assayed the flow cytometric method using 2 bead sizes. The optimal bead size was 3.136 microns. The results of CBA and vWf:Ag closely correlated with those of vWf:RCof and vWf:Ag (immunoelectrophoresis), respectively, and showed a low limit of detection. Interassay variance of cytometric methods was lower than interassay variance of traditional assays. In addition, we used the new assays to monitor desmopressin therapy.

Requirement of a plasma fraction for the loss of large von Willebrand factor multimers induced by high wall shear rate

The perfusion of serum, citrated whole blood and citrated plasma, through a simple tube system resulted in a significant loss of large von Willebrand factor (vWf) multimers, without decrease in antigen levels. Maximum loss of large multimers was observed at a shear rate of 15,000 s-1 for 15 min. Heparin, aprotinin, soybean trypsin inhibitor, phenylmethylsulphonylfluoride, N-ethylmaleimide, leupeptin or calpain inhibitor peptide could not prevent the loss of large vWf multimers in citrated plasma. The addition of EDTA calcium salt partially prevented it, and it was totally prevented by EDTA without calcium. Perfusion of purified vWf did not induce the loss of large multimers, but this did happen after the addition of either whole serum or a plasma fraction. The activity of this plasma fraction disappeared at pH < 6.8. Besides, we have found that the binding to subendothelium of purified vWf diluted in dialyzed serum was lower at pH 7.2 than at pH 6.0. Chromatographic studies demonstrated that the loss of large vWf multimers, induced by high shear rates, involves a plasma substance(s) of molecular weight larger than 200 kD; calpain and granulocyte or cysteine proteases do not seem to be this plasma substance(s).

Low-intensity oral anticoagulation plus low-dose aspirin versus high-intensity oral anticoagulation alone: a randomized trial in patients with mechanical prosthetic heart valves

BACKGROUND

Mechanical heart valve replacement requires lifelong anticoagulant treatment. Aspirin has proved useful in further reducing thromboembolic events when added to oral anticoagulants. However, increased (gastrointestinal) bleeding was observed at the doses previously tested for this combination in heart valve prostheses.

METHODS

We performed a prospective randomized trial to compare the combination of low-intensity oral anticoagulants (international normalized ratio 2.5 to 3.5) plus aspirin (100 mg/day) (arm A) versus high-intensity oral anticoagulants alone (arm B) (international normalized ratio 3.5 to 4.5). Arm A included 258 patients and arm B 245 patients. The two groups were comparable for all baseline characteristics.

RESULTS

The outcomes of the study were embolism, valve thrombosis, and major hemorrhage. The median follow-up was 23 months. The two treatments offered similar antithrombotic protection. The incidence of embolic episodes was 1.32 per 100 patient-years (95% confidence interval 0.53 to 2.7) for arm A and 1.48 per 100 patient-years (95% confidence interval 0.59 to 3.03) for arm B. Major hemorrhage occurred in 1.13 per 100 patient-years (95% confidence interval 0.41 to 2.45) for arm A and 2.33 per 100 patient-years (95% confidence interval 1.17 to 4.14) for arm B. Gastrointestinal bleeding was not increased by this combined reduced dose of aspirin and coumarin.

Anti-factor VIII inhibitors and lupus anticoagulants in haemophilia A patients

In a study of 170 haemophilia A patients, 43 were found to have an inhibitory effect; seven had anti-factor VIII inhibitors (a-fVIII)(A), 18 had lupus anticoagulants (LAs) with a strong (B: 12) or weak (C: 6) time-dependent effect and 18 had no time-dependent LAs (D). The a-fVIII showed a neutralizing effect only against factor VIII and negative diluted Russell viper venom time (dRVVT). The LAs were diagnosed by dRVVT; the Staclot LA agreed with the dRVVT. During the study, three patients changed from an a-fVIII to an LA pattern; they also modified their clinical response. Our prevalence of a-fVIII was low (4%) and we found 21% of LA, with a high (50%) prevalence of time-dependent inhibition. This pattern raises the possibility of the coexistence of LA and a-fVIII, stressing the need to develop specific tests to identify a-fVIII and LA.

Differential formation of a bioactive antiaggregating substance (BAS) by layers of the vein wall

Human umbilical veins were analyzed with and without endothelium in order to study the ability of endothelial cells and subendothelium to release a bioactive anti-aggregating substance (BAS: MW > 30kDa) independent of prostacyclin (PGI(2)). To evaluate the role of the subendothelium, the endothelial cells were removed by rubbing on filter paper for 1 min. We performed a histopathological study of the vessels using hematoxylin and eosine, and stained for elastic tissue fibers in order to confirm the presence of endothelium. The supernatant from incubated vascular rings was partially purified by Sephadex G-50 to rule out PGI(2). The void volume fractions were collected and the anti-aggregating activity was tested on platelet aggregation induced by arachidonic acid, ADP, collagen and epinephrine. We observed that the activity was taking place with the use of the intact endothelium while there was no activity in the denuded vein. These observations could help to explain the well known antithrombotic properties of vascular endothelium.

Enhanced response to chemotactic activation of polymorphonuclear leukocytes from patients with heart valve replacement

Artificial surfaces activate blood components. Since anticoagulant and antiplatelet therapy fail to abolish thromboembolic complications in patients with mechanical heart valve replacement (MHVR), other mechanisms might contribute to switch on a thrombotic event. We therefore investigated the reactivity to chemotactic activation of PMN from patients with MHVR. PMN responses were analyzed in 3 groups: 130 patients with MHVR and oral anticoagulant therapy, with or without aspirin, 57 patients on a comparable antithrombotic regimen, but without MHVR and 50 healthy subjects. In vitro studies showed that the release of cathepsin G and elastase from fMLP-stimulated PMN was significantly higher in the MHVR group, the leukocyte content of alpha 1-antitrypsin (an inhibitor of both enzymes) being similar in all three groups. CD11b expression after stimulation with fMLP was also significantly higher on PMN from MHVR patients than from control patients or healthy volunteers, while PMN CD11b basal expression was similar in all three groups. This increased PMN response in vitro in the absence of an obvious activation in vivo, may reflect a modified reactivity of circulating PMN passing through the artificial valves. Increased reactivity to local stimuli might allow PMN to participate in thrombus formation, despite conventional antithrombotic therapy.

Platelet aggregation inhibition by mononuclear leukocytes

In this study we have investigated the effect of human mononuclear leukocytes (ML) on platelet aggregation. The results obtained demonstrated that coincubation of platelets with nonstimulated ML decreased platelet aggregation induced by collagen or thrombin in a concentration-dependent manner. The inhibitory effect increased with the incubation period of the cells, reaching a plateau at 5 minutes. T and non-T enriched ML suspensions exerted an inhibitory effect similar to the total population of ML. Supernatants from ML or mixed cell suspensions also diminished platelet aggregation. 6-keto PGF1 alpha concentration in the supernatants was less than 10 pg/ml. Hemoglobin, L-arginine and cytochrome C did not modify the antiaggregating activity of ML, whereas superoxide dismutase potentiated the inhibition of aggregation mediated by ML. The inhibitory effect was not modified by monoclonal antibody (MoAb) against the lymphocyte function-associated antigen 1, alpha subunit (LFA-1 alpha) or by a MoAb directed against P-selectin. Our results demonstrated that ML inhibited platelet aggregation, at least partially, by the release of a soluble factor(s) distinct of prostacyclin or nitric oxide. Surface adhesion molecules seem also not to be involved.

Behavior of diluted activated partial thromboplastin time in pregnant women with a lupus anticoagulant

The present study was developed to verify whether a reduction in phospholipid concentration could increase the activated partial thromboplastin time (APTT) sensitivity to detect lupus anticoagulant (LA) during pregnancy. The authors studied 38 pregnant women (10 normal subjects and 28 patients with associated clinical complications) and 40 nonpregnant control subjects. Tests to detect LA, including APTT, platelet neutralization procedure (standard APTT), the kaolin clotting time, the diluted Russell viper venom test neutralized by lysed platelets, and factor assays, were performed. Positive results were found in 5 of 28 pregnant women with associated clinical complications. The APTT, using three different phospholipid concentrations (standard and more diluted cephalin), was performed on plasma samples and on its 1:1 mixture with normal plasma. The behavior of standard and diluted APTT was similar in negative LA pregnant women and nonpregnant control subjects. The mean values showed nonsignificant differences. Four of five pregnant women with positive LA findings had a prolonged APTT, which was not corrected by the addition of normal plasma using standard conditions. When diluted phospholipids were used, only one of them had a prolonged APTT that was corrected by the addition of normal plasma. Therefore, the highest sensitivity (80%) and specificity (100%) of the APTT to detect LA in pregnant women were obtained using the standard conditions.

A simple enzyme-immunoassay test for von Willebrand factor binding in human arterial subendothelium

In order to determine the binding of vWF, subendothelium from everted human umbilical arteries was perfused with dialysed serum containing different concentrations of purified vWF using an annular perfusion chamber at a wall shear rate of 1100 sec-1 for 30 min. After perfusion, control (not perfused) and perfused vessel segments were washed and incubated with a diluted rabbit antibody against human vWF. Then the nonbound anti-vWF from both samples were used to determine indirectly vWF by EIA. Although in our experiments normal vWF serum concentrations were not enough to exert vWF binding, a substantial binding could be attained with vWF levels around 2.5 U/ml. To estimate the pre-existing subendothelial vWF amount, three different experiments were developed: a) diluted IgG from a nonimmunized rabbit, b) a diluted rabbit antibody to human vWF, c) PBS-BSA. After washing, vessel segments were incubated with rabbit antibody to human vWF. After incubation, the nonbound anti-vWF was used to determine indirectly vWF by EIA. The results obtained showed that the amount of pre-existing vWF was approximately 1.1x10(-3) U vWF/cm2 subendothelium.

Visualization of platelet glycoproteins Ib and IIIa by immunoenzymatic stain using avidin-biotin peroxidase complex

A method is described here for the identification and quantitation of antigens by monoclonal antibodies. This method is based upon 1) separation (crossed-immunoelectrophoresis) and immunoprecipitation (rocket immunoelectrophoresis and crossed immunoelectrophoresis) of glycoproteins Ib and IIIa with a polyspecific antiserum; 2) binding of the non precipitating monoclonal antibody to glycoproteins precipitated by the rabbit antibody; 3) visualization of the monoclonal antibody with secondary biotinylated antibody and after addition of avidin biotin peroxidase complex, the peroxidase activity is detected by 4-Cl-1-naphtol. By this technique, the agarose gel plate could be stained directly and this allowed us to eliminate electrophoretic transblotting and radioactive compounds.

Interferon-gamma enhances PAF-acether production by stimulated human polymorphonuclear leucocytes

Human polymorphonuclear leucocytes (PMN) stimulated with either immune complexes (IC), phorbol myristate acetate (PMA) or N-formyl-methionyl-leucyl-phenylalanine (FMLP) generate platelet-activating factor (PAF-acether). The present study demonstrates that treatment of PMN with recombinant human interferon-gamma (IFN-gamma) significantly enhanced the production of PAF-acether by stimulated cells, in a concentration-dependent mode. On the contrary, alpha and beta IFN were completely unable to increase PAF-acether synthesis by stimulated PMN. The significance of these results is discussed.

Inhibition of human platelet activation by polymorphonuclear leukocytes

1. The effect of unstimulated human polymorphonuclear leukocytes (PMNs) on platelet activation was examined. 2. Human platelet aggregation and adenosine 5'-triphosphate (ATP) release induced by collagen (1-2 micrograms ml-1); thrombin (0.01-0.02 u ml-1) or arachidonic acid (AA) (0.1-0.2 mM) were markedly inhibited when conducted in the presence of unstimulated PMNs. 3. Platelet inhibition induced by PMNs was dependent on the number of PMNs and on the incubation time of the mixed cell suspension. 4. Platelet inhibition was not reversed in time when PMNs were depleted from the mixed-cell suspension. 5. PMN-mediated platelet-inhibition was not mediated by AA metabolites, oxygen reactive intermediates, nitric oxide or proteases. 6. The factor(s) accounting for the platelet inhibition mediated by PMNs are not yet characterized.

Effect of acenocoumarine on the breast-fed infant

Apart from teratogenic phenomena and the potential risk of maternal or neonatal peripartum haemorrhage, the use of oral anticoagulants during pregnancy poses an additional hazard: the risk of transferring some anticoagulant activity to the nursing infant through breast milk. We analysed the coagulation status of seven full term breast-fed neonates whose mothers were under chronic anticoagulant therapy with acenocoumarine as thromboembolic prophylaxis following cardiac valve replacement. Prothrombin Times (PT) observed in neonates were significantly higher than the corresponding maternal values. Data were subsequently compared with those obtained from a control group comprising forty-two full term neonates nursed by non-anticoagulated mothers: coagulation profiles again showed no signs of any noticeable antivitamin K effect. Our results indicate that mothers given acenocoumarine at therapeutic doses may safely breast-feed their infants: anticoagulant activity in breast milk seems to be negligible as assessed by neonates PT.

The influence of sex and different segments of thoracic aorta on bioactive aortic substance (BAS) and prostacyclin (PGI2) synthesis

BAS is a protein generated by aortic rings isolated from rats. Our previous results clearly established that BAS inhibits platelet aggregation and modifies vascular tone. We have now examined the effect of separated segments of thoracic aorta and the effect of sex on the release of the BAS and PGI2. We evaluated three different segments of thoracic aorta: A = aortic arch, B = the upper segment and C = the lowest segment of the thoracic aorta. We measured the release of BAS and PGI2 from them. The BAS production increased in the first segment (A) when compared with the other two (B and C), whilst PGI2 production was the same along the thoracic aorta. On the other hand female and male thoracic aorta produced the same levels of BAS and 6-keto PGF1 cm.

Hormonal regulation on bioactive aortic substance (BAS) production

Rat's vessel wall releases a protein named BAS (Bioactive Aortic Substance) whose antiaggregating effect on platelets and inotropy vascular properties have been already described. In this work we have investigated the effects of pregnancy, gonadectomy and gonadectomy with hormonal treatment on the BAS production from rat aortic rings. BAS production in pregnancy and ovariectomized rats was markedly decreased compared to normal rats. Return to normal values was obtained after estradiol treatment in ovariectomized rats. Castration resulted in an increased of BAS production which was suppressed by testosterone treatment.