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Biomedical subjects

J Vermylen

Publications and source records attributed to J Vermylen.

At least 109 records · Page 6Linked to original sources
PubMed1994

Hepatitis C virus-RNAs in plasma and in peripheral blood mononuclear cells of hemophiliacs with chronic hepatitis C: evidence for viral replication in peripheral blood mononuclear cells.

Hemophiliacs who have been exposed to unheated and/or dry heated pooled clotting factor concentrates are at high risk of chronic hepatitis C. Although the mechanism and site of hepatitis C virus (HCV) replication are not yet known, HCV is thought to replicate through a complementary negative RNA strand, as has been shown for flaviviruses. The detection of negative RNA strands has therefore been regarded as a marker of replication. We investigated the prevalence of HCV-RNA and of negative HCV-RNA strands in peripheral blood mononuclear cells (PBMC) and plasma of hemophiliacs. Forty-three of 47 patients studied (91%) had anti-HCV antibodies and in 36 patients HCV-RNA was detectable in PBMC. In one group of 20 patients negative HCV-RNA strands were present in PBMC and 10 of these patients also had negative HCV-RNA strands in plasma. In another group of nine patients HCV-RNA was detected in PBMC, although cDNA synthesis was carried out in the absence of primers. Only in two of these nine patients negative and positive HCV-RNA strands were demonstrated specifically in PBMC using a modified reverse transcription step. If the presence of negative HCV-RNA strands can be considered as marker of viral replication, the findings indicate that HCV can replicate in PBMC. Furthermore, in certain patients it is impossible to use the currently available technique to detect selectively positive or negative HCV-RNA strands.

Adolescent↗
PubMed1994

Hematologic aspects of end-stage renal failure.

Renal dysfunction may give rise to a variety of hematologic disturbances, including anemia, leukocyte dysfunction, and coagulopathy. The anemia of renal failure has been attributed to a relative deficiency of erythropoietin, but absolute deficiencies of iron or folate may also play a role. Other contributing factors include heavy-metal toxicity, blood loss, and a reduction in red cell survival induced by toxic radicals. The treatment of the anemia of renal disease has advanced with the development of recombinant human erythropoietin. At subcutaneous doses of 50-75 IU/kg triweekly in selected patients, normalization of hemoglobin is presently possible. The coagulopathy of renal disease consists of an acquired qualitative platelet defect, best remedied by dialysis but also treated successfully by rHuEPO, cryoprecipitate or DDAVP, and conjugated estrogens. Uremia-induced leukocyte dysfunctions include diminished granulocyte chemotaxis, phagocytosis, and bactericidal activity. Cell-mediated immune defects and hypogammaglobulinemia have also been described. The pathophysiology of the hematologic manifestations of uremia is discussed. Therapeutic recommendations for dealing with anemia, bleeding, and infectious complications of renal failure are described.

Anemia↗
PubMed1994

Pharmacokinetics and pharmacodynamics of MK-383, a selective non-peptide platelet glycoprotein-IIb/IIIa receptor antagonist, in healthy men.

MK-383 (L-tyrosine, N-(n-butylsulfonyl)-O-[4-butyl(4-piperidinyl)], monohydrochloride monohydrate) is a potent and specific platelet fibrinogen receptor antagonist that may be useful in preventing processes that lead to occlusive thrombus formation in the lumen of the blood vessel. Two placebo-controlled phase I trials were completed in 56 healthy volunteers to investigate the safety, tolerability, pharmacokinetics, and pharmacodynamics of MK-383 administered as 1- and 4-hour infusions in the presence and absence of aspirin. When administered to healthy male subjects by constant infusions up to 0.4 microgram/kg/min over 1 hour or up to 0.2 microgram/min over 4 hours, it provided a well-tolerated reversible means of inhibiting platelet function. At infusion rates of 0.25 and 0.15 microgram/kg/min for 1 and 4 hours, respectively, MK-383 extended baseline bleeding time by 2.0- to 2.5-fold and inhibited adenosine diphosphate (ADP)-induced platelet aggregation by at least 80%. The pharmacokinetics of MK-383 include a mean plasma clearance of 329 ml/min, steady-state volume of distribution of 76 L, and half-life of 1.6 hours. The percentage of dose excreted in the urine was 37%. Correlations between MK-383 plasma concentration (C) and inhibition of platelet aggregation were examined by fitting with a sigmoid maximum-effect model. The plasma concentration yielding 50% inhibition (C50) for MK-383 in healthy volunteers is approximately 13 ng/ml, with a Hill coefficient > 5. Based on a naive pooled analysis, an exponential empirical model best describes the MK-383 C-extension of template bleeding time (BTE) relationship. The model indicates that the MK-383 plasma concentration necessary to double BTE is approximately 30 ng/ml (i.e., 2.5-fold greater than the C50 for ADP-induced inhibition of platelet aggregation). The pharmacokinetics of MK-383 was unaffected by pretreatment with 325 mg aspirin 1 day before and 1 hour before infusion. Conversely, aspirin pretreatment reduced C50 and increased bleeding time extension, suggesting that aspirin may have an additive effect with respect to inhibition of platelet function. Based on the putative role of the fibrinogen receptor in thrombotic processes and an acceptable human pharmacokinetic-pharmacodynamic profile, MK-383 should be evaluated in patients with unstable angina.

Analysis of Variance↗
PubMed1994

Rapid clearance of hepatitis C virus RNA in peripheral blood mononuclear cells of patients with clotting disorders and chronic hepatitis C treated with alpha-2b interferon is not a predictor for sustained response to treatment.

Thirteen patients with congenital coagulation disorders and chronic hepatitis C were treated with alpha-interferon (IFN). Serum transaminases (ALT) and hepatitis C virus (HCV)-RNA in plasma and peripheral blood mononuclear cells (PBMC) were followed during and after treatment. During IFN treatment ALT levels normalized in 8/13 patients. In all patients HCV-RNA disappeared from PBMC. In 9/13 HCV-RNA also became undetectable from plasma; in six of these nine this occurred earlier in PBMC than in plasma; in the remaining three the disappearance of HCV-RNA occurred simultaneously in plasma and PBMC. All but two patients relapsed within 3 weeks after cessation of IFN, one relapsed after 6 weeks and one patient remains in remission after 6 months. HCV-RNA reappeared either earlier in plasma (3/12) or simultaneously in plasma and PBMC (9/12). Viral replication in PBMC thus can easily be suppressed by IFN, whereas longer treatment is needed for the eradication of HCV-RNA in plasma. The detection of HCV-RNA in PBMC cannot be used as a prognostic marker for the identification of patients with chronic hepatitis C who will have a sustained response to IFN treatment.

Adult↗
PubMed1994

Optimization of the dilute prothrombin time for the detection of the lupus anticoagulant by use of a recombinant tissue thromboplastin.

The dilute prothrombin time (dPT) is a widely accepted sensitive screening test for the lupus anticoagulant (LA). In general, Simplastin (Organon Teknika), a rabbit brain thromboplastin, diluted 1/500, is used in this test. Recently, human tissue thromboplastin obtained by recombinant DNA technology has become available and we have evaluated the usefulness of one such preparation, Innovin (Dade), for the detection of the LA. dPTs, using several dilutions of Innovin were determined on plasmas from 18 normal individuals and 15 patients with a well-documented LA. The dPT ratios, calculated as the individual result divided by the mean normal, were statistically compared. Innovin in dilutions from 1/100 onwards was found to be significantly more responsive to the LA than Simplastin (P < 0.05). Intra-assay coefficients of variation (CVs) ranged from 1.05% to 14.8% with Innovin, versus 2.7%-24.3% with Simplastin (P < 0.05); inter-assay CVs ranged from 5.6%-11.8% with Innovin, versus 4.2%-33.8% with Simplastin (P < 0.001). Analysis of 316 consecutive plasma samples from non-anticoagulated patients, on which a LA determination was requested, showed a 100% sensitivity and a 96% specificity of the dPT performed with Innovin, as compared to 81% and 93% respectively for the dPT using Simplastin.

Antiphospholipid Syndrome↗
PubMed1994

An echistatin-like Arg-Gly-Asp (RGD)-containing sequence in the heavy chain CDR3 of a murine monoclonal antibody that inhibits human platelet glycoprotein IIb/IIIa function.

We describe the production and biochemical characterization of the first GPIIb/IIIa-inhibiting monoclonal antibody that contains an RGD sequence in the CDR3 region of the heavy chain. Monoclonal antibodies obtained by immunizing mice with human platelets were screened using consecutive ELISAs based on human platelets and immuno-affinity-purified glycoprotein (GP) IIb/IIIa coated on microtitre plates. Out of 30 monoclonal antibodies reacting with GPIIb/IIIa, one, MA-16N7C2, potently inhibited platelet aggregation induced by ADP, thrombin, arachidonic acid, collagen, U46619, adrenaline and platelet-activating factor, whereas ristocetin-induced aggregation was unaffected. MA-16N7C2 (IgG2a) bound approximately 4 times faster to activated than to resting platelets, with a Kdcalc of 6.6nM and of 17.5nM, respectively. Equilibrium binding studies to non-activated platelets showed a Kd of 18.2nM with 41 x 10(3) binding sites per platelet. The antibody recognized GPIIb/IIIa only as a Ca(2+)-dependent complex. MA-16N7C2 blocked fibrinogen and von Willebrand factor binding to GPIIb/IIIa in a competitive manner with a Ki of 8.5nM and 13.2nM, respectively. Sequence analysis revealed a RGD-containing sequence with homology to disintegrins, in the CDR3 region of the heavy chain. That this RGD-containing sequence could be involved in the interaction of the antibody to GPIIb/IIIa was finally indicated by showing that the binding is completely and competitively inhibited by echistatin.

Amino Acid Sequence↗
PubMed1994

Inhibition of integrin function by a cyclic RGD-containing peptide prevents neointima formation.

BACKGROUND: RGD-containing peptides are able to prevent binding of ligands to certain integrins such as alpha IIb beta 3 (glycoprotein IIb/IIIa) and alpha v beta 3 and as such are inhibitors for platelet aggregation and smooth muscle cell migration, both of which are involved in neointima formation. METHODS AND RESULTS: Hamster carotid arteries were damaged, and neointima formation was determined at different time points. G4120, a cyclic RGD-containing peptide, was administered continuously intravenously by an implanted osmotic pump. Neointima formation was inhibited dose dependently. The inhibition was strongest when treatment was started before the vascular injury and continued for the full observation period. Treatment started after the damage and maintained until neointima assessment or started before and stopped earlier was less effective. CONCLUSIONS: Inhibition of integrin function by an RGD-containing peptide results in reduction of the development of a neointima. This effect is due both to an early event, which could be due to inhibition of secretion of PDGF by the platelets with blocked alpha IIb beta 3, and to a late event, possibly by interference with smooth muscle cell alpha v beta 3.

Animals↗
PubMed1994

Review of the hepatitis A epidemics in hemophiliacs in Europe.

A recent increased incidence of hepatitis A in the hemophilia populations of Italy, Germany, Belgium and Ireland was studied. The first well-documented outbreak occurred in Italy, where 51 patients with severe hemophilia contracted hepatitis A between the years 1989 and 1992. A case-control study by Mannucci et al. of the first 29 consecutive cases of hemophilia patients with jaundice led to the conclusion that hepatitis A was transmitted to Italian hemophilia patients by solvent-detergent-treated, ion-exchange-purified concentrate. In a retrospective serologic study of the German epidemic, Brakmann et al. isolated 18 seroconversions in a study group of 195 hemophilia patients over a 5-year period. Although several types of concentrate were used in Germany during this time, all but 1 infected patient received large doses of solvent-detergent, ion-exchange product. It was revealed that the 1 exception had a brother with hemophilia who had received solvent-detergent-prepared concentrate and had developed hepatitis A. Transmission to the study patient was therefore attributed to household contact. The Belgian experience corroborated the findings of the Italian and German investigators: several batches of factor VIII, prepared from plasma of Belgian donors in Lille, France, and Vienna, Austria, appeared to be associated with hepatitis A infection, mainly in hemophilia patients who had received large infusions. An interesting observation in the later (1993) case-control portion of the Belgian study was that hepatitis A virus antibodies were less prevalent in hemophilia patients than in age-matched controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Belgium↗
PubMed1994

High-dose intravenous immunoglobulin treatment of a pregnant patient with an antiphospholipid syndrome: immunological changes associated with a successful outcome.

A patient with a history of habitual abortion, deep venous thrombosis, thrombocytopenia, high titer IgG anticardiolipin antibodies and a clearly positive lupus anticoagulant, was treated during her seventh pregnancy with high-dose intravenous immunoglobulins (IVIg) from the third month onwards. Every month, a daily infusion of 400 mg immunoglobulins per kg body weight was given during five consecutive days. The patient's pregnancy ended preterm with a live birth, delivered by caesarian section because of a placental abruption. The 1070 g (P20-P25) weighing girl was in good health, apart from a bradycardia, due to dysfunction of the atrioventricular conduction. Each treatment with IVIg resulted in a slight reduction of both anticardiolipin antibodies and lupus anticoagulant levels and in an increase in platelet count. During the six-month observation period, a gradual decline in antiphospholipid antibodies and an increase in platelet count was found. The potential role of anti-idiotypic antibodies, present in the IVIg used for treatment, was studied. In vitro, IVIg were able to reduce the binding of the patient's anticardiolipin antibodies to cardiolipin coated microtiter plates. The presence of anti-idiotypic antibodies in IVIg was further documented by affinity chromatography and by realtime biospecific interaction analysis (BIA) on a BIA-core instrument. Affinity purified anticardiolipin antibodies were retarded on a column of insolubilized IVIg and a weak interaction was found between IVIg and affinity purified antiphospholipid antibodies, coupled to the BIA-core biosensor. In addition, the same technology revealed increased levels of anti-antiphospholipid antibodies in the patient's plasma following IVIg therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Is the apparent outbreak of hepatitis A in Belgian hemophiliacs due to a loss of previous passive immunity?

Several reports describing outbreaks of hepatitis A in hemophilia A patients transfused with solvent/detergent-treated factor VIII concentrates have raised concern about possible transmission of hepatitis A by these concentrates. We recently witnessed such an outbreak of hepatitis A in 6 hemophilia A patients; review of the clinical data did not disclose any increased risk factor for community-acquired hepatitis A. A case-control study comparing the prevalence of anti-hepatitis A IgG antibodies in hemophiliacs and age-matched controls showed a lower seroprevalence in hemophiliacs. This might be due to passive protection acquired through transfusion of the previously used immunoglobulin-containing cryoprecipitate. The outbreak of hepatitis A could be explained as a catch-up phenomenon linked to the loss of passive protection with the use of purer factor VIII concentrates.

Adolescent↗
PubMed1993

Synergistic antiplatelet effect of ridogrel, a combined thromboxane receptor antagonist and thromboxane synthase inhibitor, and UDCG-212, a cAMP-phosphodiesterase inhibitor.

Ridogrel, a combined thromboxane receptor antagonist and thromboxane synthase inhibitor (1), inhibits platelet aggregation. Following stimulation with arachidonic acid, cAMP-levels are increased in human platelets preincubated with ridogrel, this is due to the known reorientation of the metabolism of the formed endoperoxides towards adenylate cyclase stimulating prostaglandins. Pretreatment of resting platelets with UDCG-212, a cAMP-phosphodiesterase inhibitor (2), also inhibits platele aggregation induced by arachidonic acid, concomitant with an increase in cAMP levels, due to an inhibition of its breakdown. Under basal conditions, cAMP also is increased. By combining the two drugs, a more than additive action was observed on platelet aggregation and on both resting and stimulated platelet cAMP content. The appropriate combination may result in a more effective antiplatelet strategy.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1993

Anti-factor VIII antibodies of hemophiliac patients are frequently directed towards nonfunctional determinants and do not exhibit isotypic restriction.

A significant proportion of hemophilia A patients receiving transfusions of factor VIII (FVIII) develop a specific antibody response towards FVIII. These antibodies are usually detected by assays in which they inhibit the function of the molecule, such as the Bethesda clotting test. We have prepared anti-FVIII antibodies by specific immunoadsorption from the plasma of four hemophiliacs with stable inhibitor levels. The isotypic distribution of such antibodies was determined and their capacity to bind to insolubilized FVIII was compared with their inhibitory activity in two functional assays, namely, the Bethesda assay and a chromogenic assay. In addition, the FVIII epitope specificity was determined by competition with monoclonal antibodies for the binding to insolubilized FVIII. We show here that (1) anti-FVIII antibodies are not isotypically restricted; thus, a significant proportion of specific IgG2 was found; (2) antibodies are frequently directed towards epitopes of FVIII that are not directly involved in the function of the molecule and therefore escape detection in the Bethesda method or chromogenic assay; and (3) each patient shows a unique pattern of FVIII epitope recognition. We conclude that evaluation of anti-FVIII antibodies by a functional method does not provide an accurate evaluation of the specific antibody response. These findings have important implications for the comparison of the immunogenicity of FVIII molecules produced by different technologies and for the development of methods to control anti-FVIII antibody production.

Adolescent↗