[Use of standard for quantitation of adhesion of polynuclear neutrophils by flow cytometry]

Adherence receptors are essential for heterotypic (endothelial cell, platelet) polymorphonuclear neutrophil (PMN) interaction. Determination of their expression level give information about activation state and functionality of PMN. Use of flow cytometry associated with an immunolabeling standard, represented by beads coated by a determined amount of immunoglobulins (Qifikit, Dako), allows analysis of specific antibody binding capacity and gives information about antigen density. Using this methodology, the exploration of surface adherence receptors, L-selectin (CD62L) and b2-integrins (CD11a-c/CD18) from PMN unstimulated and incubated with pro-inflammatory stimuli, formyl-methionyl-leucyl-phenylalanine (fMLP) and tumor necrosis factor a (TNFa), allows, on the one hand, the establishment of basal expression values on resting PNN and on the other hand, the study of PNN reactivity. This method of quantification can be applied to clinical studies as adherence receptor deficiency syndromes or inflammatory, infectious and vascular diseases.

Monovalent binding of autoantibodies to beta2-glycoprotein I, detected using surface plasmon resonance at low antigen density

The precise mechanism of interaction between autoantibodies and beta2-glycoprotein I (beta2GPI) and the experimental conditions to be used for their detection are still under debate. Until now, these interactions have been studied under static conditions. We have investigated the interactions of purified IgG from 25 lupus anticoagulant-positive patients with immobilized beta2GPI under flow conditions by real-time analysis based on surface plasmon resonance technology. Sensor chips were coated with purified human beta2GPI coupled to dextran via amino groups at low densities (1.4, 1.8 or 2. 4 ng beta2GPI/mm2). Four patients' IgG displayed efficient binding and had the highest so-called antiphospholipid IgG levels by enzyme-linked immunosorbent assay (ELISA) and the highest absorbance values in an anti- beta2GPI ELISA at a beta2GPI density reported to be around 12 ng/mm2. Binding of antibodies to the beta2GPI sensor chips proved to be dependent upon the IgG concentration and beta2GPI density and was inhibited by a rabbit antibody against beta2GPI. Similar association and dissociation profiles were observed for the four efficient binders. The fast rate of dissociation limited the binding of autoantibodies to beta2GPI and was highly suggestive of a monovalent association, confirmed by binding of Fab fragments under similar experimental conditions. In conclusion, monovalent binding of low-affinity antibodies to beta2GPI immobilized at a density as low as 1.8 ng/mm2 could be detected using surface plasmon resonance.

Recombinant hirudin anticoagulation for aortic valve replacement in heparin-induced thrombocytopenia

PURPOSE

To report the case of a patient with HIT that received a prolonged infusion of r-hirudin (lepirudin; Refludan; Hoechst, France) before, during and after cardiopulmonary bypass (CPB) for aortic surgery. Although administration of r-hirudin for CPB anticoagulation has previously been reported, many questions persist concerning the best therapeutic regimen for CPB anticoagulation as well as the time of onset and the doses for postoperative anticoagulation.

CLINICAL FEATURES

A 65-yr-old man was admitted for surgery of aortic stenosis after an episode of acute pulmonary edema complicated by deep venous thrombosis in the context of documented HIT. The patient received r-hirudin for 13 dy before surgery at doses (0.4 mg x kg(-1) bolus followed by 0.15 mg x kg(-1) x hr(-1) continuous infusion) that maintained activated partial thromboplastin time (aPTT) ratios between 2 and 2.5. Anticoagulation for CPB was performed with r-hirudin given as 0.1 mg x kg(-1) i.v. bolus and 0.2 mg kg(-1) in the CPB priming volume. Anticoagulation during CPB was monitored with the whole blood activated coagulation time and ecarin clotting time (ECT) performed in the operating room with values corresponding to r-hirudin concentrations >5 microg x ml(-1) during CPB. Anticoagulation during CPB was uneventful. Two bleeding episodes, related to the r-hirudin regimen and necessitating allogeneic blood transfusion, occurred after surgery.

CONCLUSION

This case report confirms previous experience of the use of r-hirudin for anticoagulation during CPB and provides additional information in the context of prolonged r-hirudin infusion before and after CPB.

[Antiplatelet agents and their therapeutic use]

Antiplatelet agents have a well established effect against thrombosis complicating atherosclerosis. Drugs currently in use in France are: aspirin and flurbiprofen, inhibiting thromboxane synthesis; ticlopidine and clopidogrel, inhibiting platelet activation by adenosine diphosphate; dipyridamole, inhibiting platelet activation through adenosine; abciximab, acting on the mechanism of aggregation. Their molecular and cellular pharmacology is in agreement with the clinical effects and the guidelines for practical use. These drugs have in common that they carry a risk of hemorrhage, albeit low but difficult to cope with in case of invasive procedures. There is no antidote. They also have specific contraindications. No laboratory tests aimed at assessing their effect on primary haemostasis are proved of any clinical value.

[Improvement in prevention of venous thromboembolism in medical environment. Mission impossible?]

PURPOSE

In France, low molecular weight heparins are widely used for prophylaxis of venous thromboembolism. This practice is not based on strong evidence supporting the use of this technique, thus leading to important difficulties in defining accurate guidelines. Improvement in the prophylaxis must focus on the process leading to prescription or non-prescription. Our primary objective was to identify and describe this process. We also analyzed the causes for dysfunction and implemented corrective actions.

METHODS

Basic tools and methods specific to improvement of quality were used including: flow charting for process description, causes-effect diagram for updating and analysis of dysfunction, weighted vote for decisions regarding corrective actions, and agenda and designation of leaders for the implementation of corrective actions.

RESULTS

The theoretical process beginning with the recognition of a risk and ending with the adequate treatment or prevention of this risk was demonstrated. The most important dysfunction was the lack of epidemiological and clinical trials. Key corrective actions were the following: standardization of practices where evidence was available; if not, collaborative efforts to collect valid epidemiological data through multicenter surveys and clinical trials; systematic appraisal of the quality of published data; assessment of the risk for venous thromboembolism during hospitalization. To achieve real improvement in practice, priority was given to repeated measures of the risk for thromboembolism. The use of low molecular weight heparins has been so wide however, that it has led to some difficulties. We must draw lessons from this experience.

CONCLUSION

Improvement of quality in terms of healthcare is not only based on auditing the practices or modifying the defective processes, but also on our ability not to use new drugs before fully assessing their validity.

Both kinetic data and epitope mapping provide clues for understanding the anti-coagulant effect of five murine monoclonal antibodies to human beta2-glycoprotein I

The interaction between five murine monoclonal antibodies (mAb) and beta2-glycoprotein I (beta2GPI) in the absence of phospholipids was studied using surface plasmon resonance-based biosensor technology. Two separate epitope regions were confirmed for the five mAb but epitopes of two mAb were shown to be overlapping but not identical. The characteristics of binding on both immobilized beta2GPI, using different chemistries of coupling to a dextran matrix and antibody surfaces prepared by two strategies of immobilization, were compared. Binding was strongly influenced by the orientation of the immobilized partner, and the five mAb showed heterogeneity in their binding to immobilized and soluble beta2GPI. The observed stoichiometries of mAb-beta2GPI complexes and the detailed analysis of the kinetics of the association and dissociation phases of the interactions with soluble and immobilized beta2GPI revealed differences in the dissociation rate constants, resulting in a 10-fold higher affinity for immobilized beta2GPI compared to soluble beta2GPI for four out of five mAb. This suggests bivalent binding of these mAb to immobilized beta2GPI. In addition, the kinetic data helped explain the differing anti-coagulant properties of these mAb.

Heparin-induced thrombocytopenia in France, 1980-1998

Due to the extensive use of unfractionated heparins in France, there is considerable experience with heparin-induced thrombocytopenia (HIT). It is recommended that platelet counts be performed twice a week for three weeks when patients are treated with any form of heparin. A drop in platelet counts can, however, occur not only in HIT patients but also for other unrelated reasons. For diagnosing HIT, all laboratories in France use platelet aggregometry inspite of poor sensitivity. Both false positive and false negative results are obtained. The serotonin release test is not used in France. The ELISA test for HIT does not always correlate with the platelet aggregation test and many patients with a positive ELISA test do not necessarily have other evidence for HIT. This is especially true in patients following cardiopulmonary bypass surgery. None of the available laboratory tests reliably identify patients with HIT. Patients with HIT should not be managed with low-molecular-weight heparins, but danaparoid, argatroban and ancrod are viable options. Also, recombinant hirudin has been employed. All have advantages and disadvantages. At present, the diagnosis and management of patients with HIT remains difficult and properly designed clinical studies are needed to obtain answers to several open questions.

[New thrombolytic agents in myocardial infarction]

Myocardial infarction is the result of thrombotic coronary artery occlusion. Although present-day thrombolytics have major value by increasing the frequency of reopening of arteries responsible for myocardial infarction, by preserving myocardial function and, thereby, significantly reduce mortality. Nevertheless, they are subject to the following limitations: 1) excellent arterial partency is only obtained in 50% of cases: 2) reocclusion occurs in 5 to 10% of cases; 3) severe complications such as cerebral haemorrhage are observed in about 0.5% of cases. Therefore, the search to improve thrombolytic agents is intense. This article reports the recent advances in concept and production of new thrombolytic agents. The most recent results concern the production of mutants of T-PA (tissue plasmogen activator). Of these mutants, the reteplase (r-PA) has already received authorization for its commercialisation. Other t-PA mutants under development (phase 3) include TNK-t-PA and lanoteplase. Over the last few years, there has been renewed interest in staphylokinase. The results of the initial clinical trials with this agent have also been reported. Paradoxically, the mode of action of thrombolytic agents has an inherent pro-thrombotic effect. This explains some of the interest for anti-thrombotic agents as an adjuvant treatment of thrombolysis. The initial results of the association of thrombolytics with new glycoprotein IIb/IIIa platelet inhibitors and anti-thrombin agents are reported.

[Vascular disease and cellular activation: exploration of cell adhesion phenotype by quantitative flow cytometry]

The pathogenesis of atheromatous and/or thrombotic vascular diseases involves rheological parameters, soluble mediators and cellular agents. The many studies that have tried to establish correlations between plasma factors, shear stress and the risk of ischemia have left some questions unanswered. Current exploration methods are now focusing on the determining role of cells. Activated cells express adhesion molecules on their membranes, which allow to communicate in a homo- or heterotypical manner. Quantifying adherence molecules on the surface of platelets, leukocytes and endothelial cells provides an assessment of the "adhesive phenotypical profile". Quantitative cytometry, using beads coated with a known amount of immunoglobulins as calibrators, is perfectly suited, through its multiple parameter analyses and the specificity provided by monoclonal antibodies, for the quantification of membrane antigens. Measuring the adhesive profile on the surface of cells that are implicated in vascular disease makes it possible to correlate that phenotype to the ischemic risk in such diversified pathologies or circumstances as intermittent angor, myocardial infarction, angioplasty, insulin-dependent diabetes or pre-eclampsia. In addition, that quantification permits monitoring the action of new therapeutical agents targeting adherence molecules.

[Heparin-induced thrombopenia]

Heparin-induced thrombocytopenia remains a topical subject for at least two reasons. The first reason is the increasing prescription of low molecular weight heparins (LMWH) rather than unfractionated heparins, with limited laboratory surveillance, raising the question concerning the need for twice-weekly platelet counts, according to the recommendations of the Vidal drug directory. The second reason is the recent release onto the market of two products, danaparoid (Orgaran) and lepirudin (Refludin) for this precise indication of heparin-induced thrombocytopenia. These products greatly facilitate the management of this complication. Many basic research teams are trying to optimize the detection of heparin-dependent antibodies and to more clearly elucidate the mechanism of this particular thrombocytopenia, which carries a risk of very severe thrombotic complications when the diagnosis is delayed.

[Prevention of venous thrombosis: role of heparins]

Prevention of venous thromboembolism is of major importance because deep vein thrombosis is an economic burden. To prevent pulmonary embolism, whether fatal or not, and the postphlebitic syndrome, virtually all patients' level of risk should be assessed in order to provide adequate prophylactic measures against venous thromboembolism. Non-pharmacological, pharmacological or combined modalities can reduce the frequency of venous thrombosis. Evidence-based guidelines are available for most situations in surgical patients. However, in medical patients there are fewer data and there are wide variations of opinion. Systematic reviews should be performed and updated to obtain practice guidelines. Cost and effectiveness as well as patients' preferences should be taken into account. Randomized control trials are ongoing: low-molecular-weight heparins are being evaluated in general medical patients; other forms of prophylaxis or combined methods are also being investigated.

[Prophylaxis of venous thromboembolism in medical patients: from medical decision tools to the use of low molecular weight heparin]

In France, low molecular weight heparins are largely used for prophylaxis of venous thromboembolic disease in medical patients. Although clinical trials show their efficacy in some particular clinical situations, there is no consensus about their use in non-surgical patients. A consequence is a wide disparity of prophylaxis of venous thromboembolic disease regimens: such a situation was observed during a practice survey in two medical units of the general hospital of Lunéville. So, prior assessment for pharmacists and physicians was carried out to determine tools which guide decision-making. These comprise clinical practice guidelines, a record card which allows the scoring of risk for venous thromboembolic disease and a clinical algorithm leading to the appropriate prescription according to the risk and the haematological results. A second concomitant practice survey was organized in the same two units in order to measure the appropriateness of the decision-making tools in medical practice. The four-month study included 108 medical patients. The process was successful because: (1) validated practices are improved, particularly in respect of biological monitoring during treatment, and (2) the disparity of therapeutic strategies is highly reduced, the clinical practice guidelines being followed in 81 per cent of all cases. Despite the lack of consensus, heightened awareness of the attendant risk in many medical conditions allows appropriate prophylactic measures to be taken. These measures need decision-making tools that are easy to use and that improve heparin prescribing and thus healthcare quality.

Assessment of deep vein thrombosis prophylaxis in surgical patients: a study conducted at Nancy University Hospital, France

OBJECTIVE

This retrospective evaluation aimed to assess the adequacy of prophylaxis against thromboembolism prescribed to surgical patients at the authors' institution, and to compare it with generally accepted published guidelines. Aspects considered were indications for prophylaxis, regimens used and monitoring.

METHODS

Eleven units (nine surgical and two surgical intensive care) took part in the survey on a voluntary basis. The clinical audit system used involved developing a set of criteria based on existing guidelines, comparing observed practice with those recommendations, analysing the factors underlying any deviation and developing corrective measures.

RESULTS

When the medical records of 117 patients hospitalized in October 1995 were examined, prophylaxis against deep vein thrombosis was documented in 86 (low molecular weight heparin in 85, dextran in one). No associated physical preventative measures were recorded. Indications and dosage were appropriately handled in 90.7% and 75.2% of patients, respectively. Ninety-five cases were outside the reference criteria: 74 for excluded surgical indications, 13 which involved laparoscopy, and eight in which spinal or epidural anaesthesia was administered. Platelet count was performed in 73.8% of cases before prophylactic treatment, and in 23.10% during its course. Anti-Xa activity was measured in 0.4% of cases. Analysis of causes showed that guidelines were not complied with either because of lack of organization, or because of disagreement with them.

DISCUSSION

In this study, indications for prophylaxis were well established and heparin dosages used were not fundamentally flawed. The weak point in practice was a failure to carry out platelet counts, particularly during the course of treatment. Appropriate corrective action consists of disseminating guidelines and relevant information, and using a preoperative checklist to assess thromboembolic risk.

CONCLUSION

Physicians agree that opportunities to improve preventative practices exist, and that the quality improvement programme should be pursued.

Meta-analysis of the risk of venous thrombosis in individuals with antiphospholipid antibodies without underlying autoimmune disease or previous thrombosis

Patients with systemic lupus erythematosus (SLE) and antiphospholipid antibodies (aPL) are at a greater risk for venous thromboembolism (VTE) than SLE patients without these antibodies. For patients without SLE there is a controversy about the risk associated with these antibodies and about their prognostic significance. We reviewed the degree of evidence and describe the odds ratio for VTE associated with aPL, namely the lupus anticoagulant (LA) and anticardiolipin antibodies (aCL), in patients without SLE. The study was a meta-analysis of seven observational studies of risk for antiphospholipid associated venous thromboembolism (VTE), excluding SLE patients. The strategies to identify published research included a computerized literature search and the review of citations in primarily relevant articles for the period 1983 to 1997. A summary of study characteristics and a critical appraisal of study quality were done. Summary odds ratios were obtained conducted using a random and a fixed effects-model. The overall odds ratio for aCL associated VTE obtained by fixed-effects model was 1.56 (95% CI, 1.10-2.24) and 1.64 (95% CI, 0.93-2.89) by random-effects model. The heterogeneity of these results appeared to be due in part to the detection limit of the aCL assay: the odds ratio was 3.21 (95% CI, 1.11-9.28) with both models when high titres only were considered. The overall odds ratio for LA associated VTE was 11.1 (95% CI, 3.81-32.3). In conclusion meta-analysis of the risk for antiphospholipid associated thrombosis demonstrated a higher risk in patients with the LA than in other patients. This risk was also higher than in patients with aCL even when high titres only were considered.

Immunopurification of human beta2-glycorprotein I with a monoclonal antibody selected for its binding kinetics using a surface plasmon resonance biosensor

The beta2-glycoprotein I (beta2GPI)-binding properties of five murine monoclonal antibodies immobilized as capture antibodies were studied using surface plasmon resonance detection. The monoclonal antibody with the fastest dissociation kinetics (6F3) was selected for the development of an immunoaffinity chromatography procedure, assuming that its behaviour would be similar in both systems since the covalent coupling chemistries involved amino groups in both cases. Under our experimental conditions of a fast one-step procedure, beta2GPI was purified to homogeneity from human plasma with a yield of about 50%. Beta2GPI was eluted under fairly mild conditions, either at low pH or at high pH. The immunoadsorbent was used five times without any apparent loss of binding capacity. The immunopurified protein showed similar binding to cardiolipin-coated polystyrene wells as beta2GPI purified by conventional methods. However, differences in the pattern of immunoreactivity in relation to the purification procedure were observed by surface plasmon resonance using the monoclonal antibody with the highest association kinetics (9G1) immobilized on the sensor surface.

Antibodies against phospholipids and beta 2-glycoprotein I increase the risk of recurrent venous thromboembolism in patients without systemic lupus erythematosus

We studied the prognostic significance of antiphospholipid antibodies for recurrence of venous thromboembolism (VTE), in 71 patients admitted for acute VTE (deep-vein thrombosis or pulmonary embolism) in a single internal medicine unit. Lupus anticoagulant (LA), antibodies directed against beta 2-glycoprotein I (beta 2GPI) and antibodies against both beta 2GPI and a mixture of phospholipids (cardiolipin, phosphatidylserine and phosphatidic acid) (APAs) were measured. The patients were followed-up (mean 4.9 years) to determine the time to the next VTE. We found LA in nine patients, anti-beta 2GPI antibodies in seven patients and APAs in six patients. The cumulative risk of recurring VTE was higher in patients with beta 2GPI-binding antibodies (hazard ratio 12.6, 95% CI 1.5-104.9; p = 0.0029). The risk associated with APAs was 11.5 (95% CI 1.3-98.9; p = 0.0049) and that for LA was 3.7 (95% CI 0.9-15.6; p = 0.055). The risk of VTE recurring was higher both in patients with antibodies directed against beta 2GPI, and in patients with antibodies directed against beta 2GPI and a mixture of phospholipids, than in patients without these antibodies.