Search PubMed⌕ Search

Biomedical subjects

J Vermylen

Publications and source records attributed to J Vermylen.

At least 73 records · Page 4Linked to original sources
PubMed1997

A technique to investigate mural thrombus formation in small arteries and veins: I. Comparative morphometric and histological analysis.

Numerous clinically relevant animal models exist for thrombosis studies. Few of these are suitable for both arteries and veins. In this investigation, an established venous thrombosis model was adapted through minimal technical adjustments to allow also the study of arterial thrombosis. A standardized subintimal crush injury was performed to carotid arteries or femoral veins of hamsters. Thrombus volumes were then quantified by direct morphometric measurements from serial microscopic sections or by on-line image analysis of light intensity changes from transilluminated vessels. The platelet-rich mural thrombus, which was established within minutes of the trauma, disintegrated during the observation period. The life cycle of the thrombus was different in arteries and veins, but significant linear correlation (p < 0.01) was found in both types of vessel between thrombus volumes measured by the two techniques. The model can consequently be used for comparative in vivo thrombosis studies in small (approximately 1-mm) arteries and veins.

Animals↗
PubMed1997

A technique to investigate microvascular mural thrombus formation in arteries and veins: II. Effects of aspirin, heparin, r-hirudin, and G-4120.

After a standardized trauma to carotid arteries or femoral veins of hamsters, the antithrombotic effects of two antiplatelet agents (aspirin and the glycoprotein IIb/IIIa antagonist G4120) and two anticoagulants (heparin and the direct thrombin inhibitor r-hirudin) were studied in vivo. The thrombus area volume was assessed by image analysis of the transilluminated experimental vessels. Heparin, r-hirudin, and G-4120 demonstrated a dose-dependent complete inhibition of arterial and venous thrombosis. In contrast, the antithrombotic effect of aspirin was only partial in both vessel types. A significant correlation between activated partial thromboplastin time (aPTT) at the end of the experiments and the antithrombotic effect was observed with the anticoagulant agents. However, only r-hirudin inhibited thrombus formation at a therapeutical prolongation of aPTT, while heparin required supratherapeutical amounts to achieve the same inhibition. The data confirm that the inhibition of aspirin, heparin, r-hirudin, and G-4120 on the formation of platelet-rich thrombi is independent of the blood flow rate.

Animals↗
PubMed1997

Recirculated normal platelets adhere to surfaces coated with plasma from patients with immune thrombocytopenia.

Immune thrombocytopenic purpura (ITP) patients have characteristic anti-platelet antibodies in their circulation. To assess the interaction between such antibodies adhering on to a non-physiological surface and human platelets, normal anticoagulated blood was perfused over ITP patient plasma-coated surfaces in a parallel plate flow chamber. At 300 s-1, platelet adhesion to patient plasma-coated glass coverslips (24.0 +/- 10%) was significantly higher than the adhesion to normal plasma-coated surfaces (9.8 +/- 7%). When perfused at 1300 s-1, the adhesion to patient plasma-(5.1 +/- 1.3%) and to normal plasma-(2.5 +/- 1.2%) coated coverslips were significantly weaker. Furthermore, patient platelet binding depended on simultaneous contributions by antibodies and fibrinogen present on the plasma-coated surface, since adherence was antagonized both by normal immunoglobulins added to the perfusate, as well as by the anti-GPIIb/IIIa monoclonal antibody 16N7C2, which competes with fibrinogen for binding to its receptor on the platelet. Accordingly, platelet adhesion was only observed to coverslips coated with the plasma but not the serum of ITP patients. Hence, perfusion of normal platelets over surfaces coated with ITP patient plasma enables a functional assessment of the presence in this plasma of anti-platelet antibodies.

Adult↗
PubMed1997

Factor VIII inhibitors in previously treated haemophilia A patients with a double virus-inactivated plasma derived factor VIII concentrate.

Antibodies to factor VIII (inhibitors) are usually produced at the beginning of treatment with factor VIII and are rare in multitransfused patients. Such antibodies are deemed to be patient-related, as supported by the description of a number of associated risk factors. However, a second category of inhibitors has recently been identified, namely antibodies occurring in multitransfused patients as a result of exposure to a particular factor VIII concentrate. A first outbreak of product-related inhibitors was recently described. The present paper describes the second well-documented occurrence of such inhibitors. Eight out of 140 multitransfused patients with severe haemophilia A developed an inhibitor to factor VIII shortly after changing treatment to a double-virus inactivated plasma-derived factor VIII concentrate. In addition to solvent-detergent treatment, this concentrate was pasteurised at 63 degrees C for 10 hours. Exposure to the pasteurised product before inhibitor detection ranged from 9 to 45 days. Inhibitor titers varied between 2.2 and 60 Bethesda Units and recovery of transfused factor VIII ranged from 0.21 to 0.68 (expressed as i.u./dl factor VIII rise per i.u./kg administered). In contrast to usual inhibitors in haemophilia A patients, these product-related inhibitors showed complex inhibition kinetics. They were found specific for the factor VIII light chain. The inhibitors gradually declined when exposure to the pasteurised product was stopped, despite further treatment with other factor VIII concentrates. The present data stress the importance of carefully monitored clinical studies, both in previously treated and previously untreated patients, before introduction of a new or modified clotting factor concentrate.

Adolescent↗
PubMed1997

Hepatitis G viral RNA in serum and in peripheral blood mononuclear cells and its relation to HCV-RNA in patients with clotting disorders.

The hepatitis G virus (HGV) has recently been identified as a new member of the Flaviviridae family. Infection by this virus is thought to be associated with blood borne hepatitis. In this study, the presence of HCV- and HGV-RNAs in serum or plasma (175 patients) and in peripheral blood mononuclear cells (PBMC) (133 patients) was investigated in patients with clotting disorders using a sensitive reverse transcriptase polymerase chain reaction (RT-PCR). HGV-RNA was detected in serum of 26 patients (14.8%). In apparently healthy blood donors, serum HGV-RNA was detected in 4 of 358 individuals investigated (1.12%). Ninety two percent of the 26 serum HGV-RNA positive patients had coinfection with the hepatitis C virus (HCV), especially with HCV genotype 1b, the most common genotype in Belgium. Of these coinfected patients, 15 (62.5%) showed elevated serum ALT levels. Two patients who were solely infected with HGV had normal serum ALT.HGV-RNA in PBMC was found in 18 patients, of whom 3 were negative for serum HGV-RNA. As in case of HCV, HGV-RNA in PBMC is preferentially sensitive to interferon treatment. Nevertheless, rapid reappearance of HGV-RNA in PBMC was observed after cessation of treatment. In one patient, persistent serum ALT elevation seems to be associated with continued HGV viremia, despite the disappearance of serum HCV-RNA.

Adolescent↗
PubMed1997

Restricted epitope specificity of anti-FVIII antibodies that appeared during a recent outbreak of inhibitors.

We recently described an outbreak of anti-factor VIII (FVIII) antibodies in a population of haemophilia A patients non-responsive to FVIII (1). To find out what part of the FVIII molecule had been altered, we purified specific anti-FVIII antibodies from the plasma of the five patients showing high titres of inhibitors. An average of 100 micrograms antibodies per ml of initial plasma was recovered by immunoadsorption on insolubilised FVIII. The antibodies followed the normal isotypic distribution, including the presence of specific IgG2 antibodies; the relative increase in IgG4 that is usually observed in patients with long-standing inhibitors, was not present. The regions of FVIII to which human antibodies bound were determined by a competition assay using a panel of murine monoclonal antibodies: two major regions were identified, one located in the A2 heavy chain domain, and the other made of determinants of both the A3 and C2 light chain domains. Affinity-purified antibodies inhibited the function of FVIII as determined in a chromogenic assay. However, variations existed in the affinities with which antibodies bound to soluble FVIII. This study shows that the immunogenicity of two particular regions of FVIII has been altered. A screening for alterations located in these two regions should possibly be included in the preclinical evaluation of FVIII concentrates.

Animals↗
PubMed1997

The clinical value of duplex surveillance following internal carotid artery reconstruction.

BACKGROUND: The purpose of this retrospective analysis was to evaluate the benefit of a yearly duplex ultrasonography of both the reconstructed and the contralateral internal carotid artery (ICA). METHODS: From 1985 to 1994, 1210 unilateral, primary ICA reconstructions were performed. Although these patients received yearly invitations, duplex follow-up was not available in 114 patients (9%). RESULTS: At 5 years a stenosis of 50% or more was found in 9% and at 10 years in 14% of patients. During the follow-up period 20 patients developed a stenosis of 80-99%. Ten patients had a redo-procedure. The others remained asymptomatic, even though one patient developed an occlusion. A stroke occurred in 96 patients. 58 of these had no significant stenoses. 57% of all patients had no significant contralateral lesion at the time of the first procedure. In only 4% of these a contralateral CAE was performed during the follow-up. CONCLUSIONS: In view of the above data, we would conclude that the clinical benefit of duplex surveillance is doubtful.

Adult↗
PubMed1996

Neutralizing antiidiotypic antibodies to factor VIII inhibitors after desensitization in patients with hemophilia A.

Hemophilia A patients producing antibodies towards FVIII are usually treated with infusions of high doses of FVIII in an attempt to "desensitize" them. To examine the mechanisms by which such desensitization operates, sequential plasma samples of two unrelated inhibitor patients were analyzed for anti-FVIII and antiidiotypic antibodies before and during infusions of high doses of FVIII. Anti-FVIII antibodies were separated from antiidiotypic antibodies by immunoaffinity chromatography before analysis. We show in the present study that the concentration of anti-FVIII antibodies did not change during a successful desensitization and that antibodies maintained their capacity to inhibit the procoagulant function of FVIII, even though the number of Bethesda units in plasma was reduced to undetectable levels. Using a competition assay with mAbs, we further show that the specificity of human antibodies did not vary significantly during therapy. Finally, we show that the treatment elicited antiidiotypic antibodies, which neutralized the inhibitory capacity of anti-FVIII antibodies. Inhibitor antibodies can therefore not be accurately evaluated in plasma, as their function appears to be neutralized by antiidiotypic antibodies. These findings could have implications for the design of new therapies for hemophilia A patients with inhibitors.

Adolescent↗
PubMed1996

Cutaneous pathology in primary erythermalgia.

Primary or idiopathic erythermalgia is characterized by recurrent, red, warm, and painful lower extremities. It arises at young age and persists throughout life because no treatment is available. We report the cutaneous pathology of affected skin lesions of three patients with primary erythermalgia. Biopsy specimens showed a mild perivascular mononuclear infiltrate, thickened blood vessel basement membranes, abundant perivascular edema, and moderate endothelial swelling. The thickened basal membrane of the blood vessels showed a laminar structure, and abundant perivascular edema and moderate endothelial cell swelling were evident. These histopathologic findings in primary erythermalgia appear to be nonspecific but allow diagnostic differentiation from erythromelalgia in which fibromuscular intimal proliferation and occlusive thrombi in the endarteriolar capillaries are apparent and from erythermalgia secondary to vasculitis. Histopathologic examination of affected skin lesions in patients with red, congested, warm, and painful burning extremities is a valuable tool in the diagnostic process.

Adolescent↗
PubMed1996

Dose-responses to inducers and inhibitors of platelet aggregation analysed via a micro-method.

The ex vivo study of platelet function in small experimental animals treated with anti-platelet drugs is restricted by the limited availability of platelet-rich plasma (PRP). To circumvent this obstacle, a micro-method for platelet aggregation was developed that enables ED50 measurements for various inducers of platelet aggregation. Fifty microliters of human, hamster, or rabbit PRP was mixed with agonist in each well of a microtiter plate, and shaken at 900 rpm at 37 degrees C for intervals up to 5 min. After stopping the aggregation with formaldehyde in PBS, light scattering was measured vs platelet-poor plasma (PPP) at 620 nm. Thus, aggregation in human PRP by ADP (t = 2 min) occurred with an ED50 = 1.8 microM, whereas the collagen (t = 3 min; ED50 = 2 micrograms/ml) and AA (t = 1 min; ED50 = 0.3 microM) induced aggregation occurred at those concentrations that induce aggregation in classical aggregometry. Likewise, aggregation was inhibited by the anti-GPIIb/IIIa antibody MA-16N7C2 and by the GPIIb/IIIa antagonists G4120 or MK-852. In comparison with human PRP, hamster (ED50 = 0.8 microM at t = 2 min) and rabbit (ED50 = 5 microM at t = 4 min) platelet aggregation by ADP occurred with comparable sensitivities, whereas the aggregation of rabbit platelets by collagen (ED50 = 15 micrograms/ml at t = 3 min) appeared to be slightly less sensitive and subject to large interindividual variations. The method was applied to measure plasma levels of a GPIIb/IIIa antagonist following injection into hamsters.

Adenosine Diphosphate↗
PubMed1996

Selective embolization of a superior gluteal artery pseudoaneurysm associated with von Willebrand's disease.

We report the case of an iliopsoas hematoma caused by an iliolumbar branch pseudoaneurysm, following a relatively minor blunt pelvic trauma. Laboratory investigation revealed an as yet undiagnosed von Willebrand's disease. The pseudoaneurysm was successfully embolized superselectively and the hematoma, causing femoral neuropathy, was subsequently drained surgically without major bleeding.

Adolescent↗
PubMed1996

Neointima formation in injured hamster carotid artery is effectively prevented by the combination G4120 and quinapril.

The prevention of neointima formation by the tissue selective angiotensin converting enzyme (ACE) inhibitor quinapril and by the combination quinapril/G4120 (a platelet alpha Ub beta 3 and smooth muscle cell alpha v beta 3 antagonist) was investigated in a hamster carotid artery injury model. Quinapril at 10 mg/kg/day reduced neointima formation by about 45%, 1 and 2 weeks after injury to the artery, i.e. significantly better than the non-tissue selective ACE inhibitor captopril at 100 mg/kg/day. Quinapril did not decrease the early smooth muscle cell (SMC) proliferation in the media, but in agreement with its inhibition of the carotid artery ACE activity by 62%, SMC proliferation was reduced by 70% in the newly forming intima. To improve the inhibition of early medial SMC proliferation, quinapril (10 mg/kg/day) was complemented with G4120 (100 micrograms/kg/h). This combined treatment reduced the proliferation of medial SMCs to about 50% throughout the first week following injury, whereas intima SMC proliferation was reduced by 70% throughout treatment. Accordingly, the drug combination reduced neointima formation more potently than each drug separately by 70%. The disruption of medial elastic laminae, observed in the control and G4120 treated group, was consistently reduced when G4120 was complemented with quinapril. Thus, the present study shows in a hamster model of carotid artery injury, that combining drugs that prevent SMC migration and proliferation via different modes of action can lead to the effective prevention of neointima formation.

Analysis of Variance↗
PubMed1996

Biochemical activity, pharmacokinetics and tolerability of tepoxalin, a cyclooxygenase/5-lipoxygenase inhibitor, in man.

Tepoxalin, a novel inhibitor of cyclooxygenase (CO) and 5-lipoxygenase (5-LO), was investigated for biochemical activity and pharmacokinetics in two studies. Study I was a 4-period, double-blind, randomized, single rising dose using 2 alternating panels (A, B) with interspersed placebo design (A: 25, 100, 400 mg, B: 50, 200, 800 mg p.o.). Study II was a 3-panel, randomized, placebo-controlled, double-blind, multiple dose study (A: 100 mg, B: 200 mg, C: 400 mg). In both studies, CO inhibition was assessed by generation of serum thromboxane (TxB2), 5-LO activity by LTB4 production ex vivo in Caionophore-stimulated blood. Plasma drug concentrations were assayed by HPLC for tepoxalin and its identified acid metabolite. It was found in both studies that at all dose levels the TxB2 generation was markedly suppressed (> 95% 2 h postdose). In study I, at 2 h postdose, % inhibition of LTB4 biosynthesis was marginal for the 3 lower doses but significant at 200 (14%), 400 (25%) and 800 mg (43%). In study II, the only significant inhibition occurred at the 400 mg dose at 6 h postdose on day 1 (17%) and on day 8 at 4, 6 and 8 h postdose (32, 42 and 32% respectively). In both studies and at all doses, plasma concentrations of tepoxalin varied widely between subjects. Linearity between plasma concentrations and dose could not be ascertained, and correlation between drug plasma levels and effect on LTB4 synthesis was poor. Single doses up to 800 mg and multiple doses up to 400 mg of tepoxalin were generally well tolerated.

Adult↗
PubMed1995

Thrombolytic therapy of peripheral arterial occlusion with recombinant staphylokinase.

BACKGROUND: Recombinant staphylokinase (STAR) induces fibrin-specific coronary artery recanalization in patients with evolving myocardial infarction. The present pilot study evaluates its thrombolytic efficacy, safety, fibrin specificity, and immunogenicity in patients with peripheral arterial occlusive disease. METHODS AND RESULTS: Thirty patients (37 to 86 years of age) with angiographically documented thromboembolic peripheral arterial occlusion of recent origin (21 +/- 5.5 days, mean +/- SEM) were treated with heparin and intra-arterial STAR given as a 1-mg bolus followed by a 0.5-mg/h infusion in 20 patients or as a 2-mg bolus followed by a 1-mg/h infusion in 10 subsequent patients. With 7.0 +/- 0.7 mg STAR infused over 8.7 +/- 1.0 hours, recanalization was complete in 25 patients, partial in 2, and absent in 3. Two major hemorrhagic complications occurred: one fatal hemorrhagic stroke and one hypovolemic shock caused by bleeding at the angiographic puncture site. Administration of STAR did not induce fibrinogen breakdown or a significant prolongation of template bleeding time. STAR-neutralizing activity and anti-STAR IgG were low at baseline, increased markedly from the second week on, and remained elevated for several months. CONCLUSIONS: Intra-arterial administration of STAR restores vessel patency in patients with peripheral arterial occlusion in the absence of fibrinogen degradation.

Female↗
PubMed1995

Factor VIII gene inversions in severe hemophilia A: results of an international consortium study.

Twenty-two molecular diagnostic laboratories from 14 countries participated in a consortium study to estimate the impact of Factor VIII gene inversions in severe hemophilia A. A total of 2,093 patients with severe hemophilia A were studied; of those, 740 (35%) had a type 1 (distal) factor VIII inversion, and 140 (7%) showed a type 2 (proximal) inversion. In 25 cases, the molecular analysis showed additional abnormal or polymorphic patterns. Ninety-eight percent of 532 mothers of patients with inversions were carriers of the abnormal factor VIII gene; when only mothers of nonfamilial cases were studied, 9 de novo inversions in maternal germ cells were observed among 225 cases (approximately 1 de novo maternal origin of the inversion in 25 mothers of sporadic cases). When the maternal grandparental origin was examined, the inversions occurred de novo in male germ cells in 69 cases and female germ cells in 1 case. The presence of factor VIII inversions is not a major predisposing factor for the development of factor VIII inhibitors; however, slightly more patients with severe hemophilia A and factor VIII inversions develop inhibitors (130 of 642 [20%]) than patients with severe hemophilia A without inversions (131 of 821 [16%]).

Blotting, Southern↗
PubMed1995

Promotion of binding of von Willebrand factor to platelet glycoprotein Ib by dimers of ristocetin.

In the absence of high shear forces, the in vitro binding of human von Willebrand factor (vWF) to its platelet receptor glycoprotein Ib (GPIb) can be promoted by two well-characterized mediators, botrocetin and ristocetin. Using purified vWF and GPIb, we have investigated the mechanisms by which ristocetin mediates this binding. Specific binding of vWF monomers to GPIb occurred with a 1:1 stoichiometry, but high-affinity binding required the participation of two ristocetin dimers. Binding was strongly dependent on pH and inhibited by low poly-L-lysine concentrations, indicating ristocetin-dependent charge neutralization during the interaction. With increasing ristocetin concentrations, vWF binding depended progressively less on the involvement of its A1 loop, which is compatible with a model in which the two ristocetin dimers bridge the vWF-GPIb complex on secondary sites. In agreement with this model, the ristocetin-dimer-promoted stabilization of vWF on GPIb was abolished by low concentrations of poly(Pro-Gly-Pro), which is known to complex ristocetin dimers. Mechanistic analysis of the inhibition of vWF binding by the recombinant vWF fragment Leu504-Ser728 (VCL), which covers the entire A1 loop, revealed an affinity of VCL for GPIb comparable with that of the botrocetin-vWF complex for GPIb, and identified a specific but 20-fold lower affinity of VCL in the presence of ristocetin. The proline-rich peptides flanking the vWF A1 loop, Cys474-Val489 and Leu694-Asp709, inhibited vWF binding semispecifically by competitively interfering with the formation of the GPIb-vWF complex rather than by complexation of free ristocetin dimers. In conclusion, ristocetin-promoted binding of vWF to its GPIb receptor results from charge neutralization and interactions involving proline residues in the vicinity of the natural interaction sites present on both GPIb and the A1 domain of vWF.

Amino Acid Sequence↗