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Biomedical subjects

Jef Arnout

Publications and source records attributed to Jef Arnout.

11 recordsLinked to original sources
PubMed2006

Angiogenesis enhances factor IX delivery and persistence from retrievable human bioengineered muscle implants.

Human muscle progenitor cells transduced with lentiviral vectors secreted high levels of blood clotting factor IX (FIX). When bioengineered into postmitotic myofibers as human bioartificial muscles (HBAMs) and subcutaneously implanted into immunodeficient mice, they secreted FIX into the circulation for >3 months. The HBAM-derived FIX was biologically active, consistent with the cells' ability to conduct the necessary posttranslational modifications. These bioengineered muscle implants are retrievable, an inherent safety feature that distinguishes this "reversible" gene therapy approach from most other gene therapy strategies. When myofibers were bioengineered from human myoblasts expressing FIX and vascular endothelial growth factor, circulating FIX levels were increased and maintained long term within the therapeutic range, consistent with the generation of a vascular network around the HBAM. The present study implicates an important role for angiogenesis in the efficient delivery of therapeutic proteins using tissue engineered stem cell-based gene therapies.

Animals↗
PubMed2005

Thrombophilia in mice expressing a tissue factor variant lacking its transmembrane and cytosolic domain.

Mice with a targeted truncation in the gene encoding tissue factor of blood coagulation (TF) to eliminate the cytosolic domain and carrying a neo(R) cassette in intron 5 unexpectedly displayed severe spontaneous thrombosis in various vascular beds. Thrombosis was observed in heterozygous TF(+/neo) mice, causing death of over 50% of adults within 36 weeks of birth, and fulminantly exacerbating in pregnant females. Homozygous TF(neo/neo) mice were more severely affected and died within 7 weeks after birth. These TF(neo) mice primarily synthesized a mutant mRNA aberrantly spliced from exon 5 to neo(R), encoding an apparently non-vesicle-binding soluble TF lacking both the transmembrane and cytosolic domain, but still capable of blood coagulation induction. This severe thrombotic phenotype associated with the presence of a non-anchored soluble TF variant underscores the recently recognized significance of circulating TF for thrombus formation and development.

Animals↗
PubMed2005

The Belgian Improvement Study on Oral Anticoagulation Therapy: a randomized clinical trial.

AIMS: In Belgium, general practitioners (GPs) mainly manage oral anticoagulation therapy. To improve the quality of oral anticoagulation management by GPs and to compare different models and interventions, a randomized clinical trial was performed. METHODS AND RESULTS: Stratified randomization divided 66 GP-practices into four groups. A 6-month retrospective analysis assessed the baseline quality. In the prospective study, each group received education on oral anticoagulation, anticoagulation files, and patient information booklets (groups A, B, C, and D). Group B additionally received feedback every 2 months on their anticoagulation performance; group C determined the international normalized ratio (INR) with a CoaguChek device in the doctor's office or at the patient's home; and group D received Dawn AC computer assisted advice for adapting oral anticoagulation. For the different groups, the time spent in target INR range (Rosendaal's method) and adverse events related to anticoagulation were determined and compared with the same quality indicators at baseline. There was a significant increase in per cent of time within 0.5 INR from target, from 49.5% at baseline to 60% after implementing the different interventions. However, neither the per cent in target range nor the event rates differed among the four groups. CONCLUSION: The interventions significantly improved the quality of management of oral anticoagulation by Belgian GPs, mainly as a result of an education and support programme.

Administration, Oral↗
PubMed2005

Heparin influences human platelet behavior in cardiac surgery with or without cardiopulmonary bypass.

The objective was to investigate whether the platelet dysfunction in cardiac surgery is caused by hemodilution or by shear stress due to cardiopulmonary bypass (CPB). Platelet count and function were prospectively analyzed in two groups of patients undergoing cardiac surgery either with or without CPB (n = 40). In the first study (n = 20; 10 patients with and 10 without CPB), platelet counts were assessed at seven time points. In the second study (n = 20; 10 patients with and 10 without CPB), platelet function was studied with platelet aggregometry at different points during surgery: (a) after induction of anesthesia; (b) after sternotomy; and (c) 1 h after heparin. In the first study, the CPB group showed a significant decrease in platelet count starting after sternotomy (230 +/- 34 vs. 182 +/- 25, P < 0.05) and a maximum decrease at day 1 postoperative (96 +/- 34, P < 0.05). A similar observation was made in the non-CBP group. In the second study, a significant decrease of ADP (54 +/- 13% vs. 38 +/- 9%, P < 0.05), AA (76 +/- 16% vs. 22 +/- 14%, P < 0.05), and Collagen (66 +/- 13% vs. 37 +/- 11%, P < 0.05) induced platelet aggregation was observed at MOMENT d compared to the beginning of surgery in the CPB group. In the non-CBP group a significant decrease was observed in AA-induced platelet aggregation at MOMENT d (83% +/- 4 vs. 44% +/- 14, P < 0.05). The reduction in platelet count is similar with or without cardiopulmonary bypass and is due to pure hemodilution. Platelet function reduces significantly after heparin administration. Hemodilution and predominantly heparin are the causes of platelet dysfunction after cardiac surgery.

Anticoagulants↗
PubMed2005

Plasma glycocalicin as a source of GPIbalpha in the von Willebrand factor ristocetin cofactor ELISA.

We have previously demonstrated that the von Willebrand factor ristocetin cofactor activity (VWF:RCo), used in the diagnosis of vonWillebrand disease (VWD), can be accurately determined via ELISA by measuring the ristocetin-induced binding of VWF to a captured recombinant fragment of GPIbalpha (rfGPIbalpha, AA 1-289) (Vanhoorelbeke et al., Thromb Haemost 2000; 83: 107-13). This ELISA is more reliable than the currently used platelet agglutination test. Normal plasma contains relatively high concentrations of glycocalicin, a proteolytic fragment of GPIbalpha. We therefore studied whether non-purified plasma glycocalicin can replace rfGPIbalpha in our ELISA. Of 42 anti-GPIbalpha monoclonal antibodies (MAbs) capable of binding plasma glycocalicin, only one MAb captured glycocalicin in a spatial orientation exposing the VWF-binding site in glycocalicin, allowing a specific and dose-dependent ristocetin-mediated VWF-binding. Intra- and interassay variability were comparable with those for the rfGPIbalpha based VWF:RCo ELISA. The VWF:RCo activity of plasma from 33 normal individuals, 19 type 1, 16 type 2A, 9 type 2B, 8 type 2M and 7 type 3VWD patients was determined with this ELISA and allowed a clear identification of VWD patients. Furthermore, determination of the VWF:RCo/VWF:Ag ratio resulted in the discrimination between type 1 and type 2 VWD patients. Results for the glycocalicin based and the rfGPIbalpha based VWF:RCo ELISAs were in good agreement (r=0.943). There was also a good correlation between the glycocalicin based ELISA and the standard platelet agglutination test (r=0.963). In conclusion, to diagnose VWD, a VWF:RCo ELISA based on antibody immobilized plasma glycocalicin can be performed reliably.

Diagnosis, Differential↗
PubMed2005

Quality assessment of oral anticoagulation in Belgium, as practiced by a group of general practitioners.

OBJECTIVE: In Belgium oral anticoagulation therapy is mainly supervised by general practitioners (GPs). This study aims to evaluate the quality of management of oral anticoagulation by Belgian GPs and to verify the relation between time in range and a set of potentially influencing co-variables. METHODS: In a retrospective cross-sectional study, involving 66 GP-practices, the INR-values obtained over a 6-month period were analysed. All INR-values were determined by a single clinical laboratory and additional medical information was provided by the GPs. Linear mixed models have been used to model the patient-specific percentage INR in target as a function of different co-variables. RESULTS: 737 patients were included in the study. Patients who underwent a surgical intervention with an interruption of the anticoagulation during the study were excluded. Patients were only included after the initial starting-up period. 5890 INR-values were obtained. A total of 92,566 days of therapy was evaluated. 50% of the day values were within 0.5 INR-units from target (and 66% within 0.75 INR-units from target). In a multiple regression model, a significant relation between the percentage of time in range and the target INR (2.5 or 3.5) and the gender of the patient was shown. The incidence rate for major bleeding was 5.5/100 patient years (and 3.5/100 patient years for thrombo-embolic events). CONCLUSION: The quality of management of oral anticoagulation by the GPs in Belgium is suboptimal. It is unknown whether interventions such as guidelines, feedback, point-of-care monitoring and computer-assisted anticoagulation monitoring could improve the results.

Aged↗
PubMed2005

Understanding the antiphospholipid syndrome and its treatment.

The antiphospholipid syndrome (APS) is a clinicopathologic disorder characterized by the persistent presence of anticardiolipin antibodies, lupus anticoagulants, or both in the plasma of patients with arterial or venous thrombosis or obstetric complications. The antiphospholipid antibodies involved in this syndrome have a relatively weak affinity for phospholipid-binding proteins such as b(2) glycoprotein I and prothrombin. In certain conditions they form bivalent antibody-protein complexes that bind with a relatively high affinity to negatively charged phospholipid surfaces. Evidence is accumulating for a pathogenetic role of antiphospholipid antibodies via interference with surface-mediated anticoagulant and procoagulant processes. The syndrome is characterized by the recurrence of thrombotic and obstetric complications. Retrospective studies have suggested that patients with APS and thrombosis need a high-intensity anticoagulant treatment. A few small prospective studies support treatment with a targeted INR of 2 to 3.

Antibodies, Antiphospholipid↗
PubMed2003

Dimers of beta 2-glycoprotein I increase platelet deposition to collagen via interaction with phospholipids and the apolipoprotein E receptor 2'.

Patients with prolonged clotting times caused by lupus anticoagulant (LAC) are at risk for thrombosis. This paradoxal association is not understood. LAC is frequently caused by anti-beta2-glycoprotein I (beta 2GPI) antibodies. Antibody-induced dimerization of beta 2GPI increases the affinity of beta 2GPI for phospholipids, explaining the observed prolonged clotting times. We constructed dimers of beta 2GPI that mimic effects of beta 2GPI-anti-beta 2GPI antibody complexes, and we studied their effects on platelet adhesion and thrombus formation in a flow system. Dimeric beta 2GPI increased platelet adhesion to collagen by 150% and increased the number of large aggregates. We also observed increased platelet adhesion to collagen when whole blood was spiked with patient-derived polyclonal anti-beta 2GPI or some, but not all, monoclonal anti-beta 2GPI antibodies with LAC activity. These effects could be abrogated by inhibition of thromboxane synthesis. A LAC-positive monoclonal anti-beta 2GPI antibody, which did not affect platelet adhesion, prevented the induced increase in platelet adhesion by beta 2GPI dimers. Furthermore, increased platelet adhesion disappeared after preincubation with receptor-associated protein, a universal inhibitor of interaction of ligands with members of the low density lipoprotein receptor family. Using co-immunoprecipitation, it was shown that dimeric beta 2GPI can interact with apolipoprotein E receptor 2 (apoER2'), a member of the low density lipoprotein receptor family present on platelets. These results demonstrate that dimeric beta 2GPI induces increased platelet adhesion and thrombus formation, which depends on activation via apoER2'.

Antibodies, Monoclonal↗
PubMed2002

Thrombogenicity of beta 2-glycoprotein I-dependent antiphospholipid antibodies in a photochemically induced thrombosis model in the hamster.

We previously showed that beta(2)-glycoprotein I (beta(2)GPI)-dependent lupus anticoagulants (LAs) form bivalent antigen-antibody complexes with high affinity for phospholipids; these complexes are responsible for their in vitro anticoagulant effect. We now studied the role of these bivalent complexes in arterial thrombosis in the hamster. Three monoclonal antibodies (mAbs) raised against human beta(2)GPI were selected on the basis of their cross-reactivity with hamster beta(2)GPI. Two of these, one with LA activity, 5H2, and one with only anticardiolipin properties, 11E8, were infused at 0 to 10 mg/kg prior to photochemically induced vessel damage. 5H2 promoted thrombus formation dose dependently, raising the thrombus size from 6.0 arbitrary units (AU) in controls (n = 9) to 65.0 AU in the high-dose group (10 mg/kg, n = 6, P =.007). The LA(-) mAb 11E8 and mAb 27A8, reactive with human beta(2)GPI exclusively, did not significantly promote thrombus formation. In a second set of experiments, intact mAb 5H2 was compared to its fragments. Intact mAb 5H2 at 3.3 mg/kg and the equimolar dose of F(ab')(2) fragments (2.2 mg/kg) promoted thrombus formation equally well (55.8 AU, n = 8 and 62.5 AU, n = 7, respectively); mAb 5H2-derived Fab' fragments were inactive. Immunohistochemical analysis showed platelet-rich thrombi, with 5H2 or its F(ab')(2) fragments mainly bound to individual platelets. Our results indicate that bivalent immune complex formation plays an important role in the genesis of arterial thrombosis by certain antiphospholipid antibodies. Cellular activation via the Fc portion of these immune complexes, however, is not essential, because F(ab')(2) fragments of 5H2 still promote thrombus formation.

Adenosine Diphosphate↗