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J Amiral

Publications and source records attributed to J Amiral.

At least 37 records · Page 2Linked to original sources
PubMed1999

Decision analysis for use of platelet aggregation test, carbon 14-serotonin release assay, and heparin-platelet factor 4 enzyme-linked immunosorbent assay for diagnosis of heparin-induced thrombocytopenia.

The value of the platelet aggregation test, carbon 14-labeled serotonin release assay (SRA), and heparin-platelet factor 4 enzyme-linked immunosorbent assay (H-PF4 ELISA) for the diagnosis of heparin-induced thrombocytopenia was evaluated by studying blood samples from 100 patients with suspected heparin-induced thrombocytopenia, and categorized into 4 clinical groups: unlikely (n = 22), possible (34), probable (36), and definite (8) thrombocytopenia. Results of the platelet aggregation test were positive in 40 of 44 patients with probable or definite heparin-induced thrombocytopenia (sensitivity 91%) and in 5 of 22 unlikely to have heparin-induced thrombocytopenia (specificity 77%). The SRA exhibited sensitivity of 88% and negative predictive value of 81%, close to those values for the platelet aggregation test; specificity and positive predictive value were 100%. The sensitivity of the heparin-PF4 ELISA was 97%, with specificity 86%, and a positive correlation was recorded between the level of antibodies to H-PF4 and clinical score (P = 0.66). When ELISA was used with the platelet aggregation test or SRA, positive predictive value and specificity were 100% when both tests yielded positive results, and negative predictive value was 100% when both tests yielded negative results. A biologic flow chart was designed that presented a choice based on the results of the platelet aggregation test or SRA in association with ELISA, and enabled more accurate and specific identification of heparin-induced thrombocytopenia.

Carbon Radioisotopes↗
PubMed1999

Diagnostic approach of phospholipid-dependent antibodies. State-of-the art lecture.

Recent scientific developments enable to better understand the strong heterogeneity of assay methods for phospholipid (PLP)-dependent antibodies, measured as lupus anticoagulant (LA) or as anti-PLP antibodies (APA). These latter are actually targeted at complexes of beta(2)-glycoprotein I (beta2GPI) and anionic PLP and also react with insolubilized beta2GPI alone in some patients. Although APA present little species specificity for beta2GPI, some of them bind preferentially to complexes of human beta2GPI and PLP. LAs are diagnosed with screening assays (dPT, dRVVT, KCT, APTT); their sensitivity is dependent on the concentration and type of PLPs used. They are either beta2GPI or prothrombin dependent. Based on the antibody-neutralizing capacity of PLP preparations (such as hexagonal phase phosphatidylethanolamine) or their bypassing activity, confirmatory assays enable to confirm LA. LAs and APAs bind to different epitopes on beta2GPI or its complexes with PLP. Major characteristics of APA assays are: the capture antigen (PLPs, beta2GPI source); its optimization and density on micro-ELISA plates; the efficacy of postcoating saturation; the animal serum used for saturation and diluent; the second antibody which must avoid nonspecific interactions; the calibrators proposed and their reference to international standards; the cutoff between the normal and the pathological ranges; the assay sensitivity and overall specificity for APAs. New optimized assays have been developed to meet these criteria. They are designed with PLP-coated plates, saturated first with immunoglobulin-free human serum as a source of beta2GPI, then with goat serum also used in diluent. The cutoff value is determined with at least 200 normal plasma samples (mean + 3 standard deviations or 99th percentiles) and plasma samples from patients without APAs. This approach offers both optimized specificity and sensitivity for testing APAs, along with a good standardization and it helps to measure the true APAs associated with pathology.

Antibodies, Antiphospholipid↗
PubMed1999

Complex association of protein C gene promoter polymorphism with circulating protein C levels and thrombotic risk.

The allele and haplotype frequency of the -1654 C/T and -1641 A/G protein C (PC) gene promoter polymorphisms was determined and analyzed according to circulating PC concentrations in 394 healthy subjects aged 20 to 60 years. The CG haplotype was associated with a lower PC concentration in both homozygous and heterozygous subjects compared with noncarriers. The TA allele had the reverse effect, but only in homozygotes. The distribution of the CG and TA alleles was significantly different in 242 patients, aged 17 to 60 years, with venous thromboembolism. The CG allele increased the risk of thrombosis, with an OR of 1.39 (95% confidence interval (CI), 1.04 to 1.87). The TA allele was protective in subjects aged <45 years, with an OR of 0.68 (95% CI, 0.44 to 1.04). TA was also significantly associated with older age at the first thrombosis. This study confirms the link between the PC gene promoter and circulating PC levels, and suggests a complex effect on the risk of thrombosis.

Adult↗
PubMed1999

Regulation of adhesion molecules during human endotoxemia. No acute effects of aspirin.

Gram-negative septic shock is mediated in part by endotoxin (lipopolysaccharide; LPS), and animal models have shown that blockade of even single adhesion molecules considerably improves survival. Thus interference with the adhesion cascade may provide a useful therapeutic approach in human sepsis. Young healthy men (n = 30) each received a bolus of 4 ng/kg LPS intravenously to study the effects of endotoxemia on adhesion processes in humans and to identify potential targets for pharmacologic intervention. One third of subjects received pretreatment with 1,000 mg aspirin and 1,000 mg paracetamol to study potential antiinflammatory effects of aspirin or effects of antipyresis. Circulating neutrophils dropped by -80% at 67 min after LPS, monocytes by -96% at 90 min, and lymphocytes by -85% at 240 min. L-selectin expression decreased, particularly on monocytes. Circulating (c)E-selectin levels increased by 820%, von Willebrand factor-Ag (vWF), soluble thrombomodulin, circulating (c)P-selectin, circulating intercellular adhesion molecule-1 (cICAM-1), and circulating vascular cell adhesion molecule-1 (cVCAM-1) by a mean of 65 to 98% (p < 0.001 for all), but cL-selectin by only 15%. Urinary excretion of soluble adhesion molecules was negligible. Aspirin had no influence on the LPS-induced changes of adhesion parameters, but paracetamol blunted the relative increase in vWF while having no effects on the other parameters measured. The consistent, profound, and early upregulation of cE-selectin during endotoxemia indicates that cE-selectin may be a better surrogate marker to monitor the activation status of endothelial cells in systemic inflammation than the other markers measured. Although aspirin did not have any antiinflammatory effects in this model, paracetamol lowered the relative increase in vWF.

Acetaminophen↗
PubMed1999

Generation and pathogenicity of anti-platelet factor 4 antibodies: diagnostic implications.

Recent studies have elucidated the target antigens for heparin-dependent antibodies. The major one is generated in the presence of platelet factor 4 (PF4) and heparin at a well-defined concentration that allows formation of heparin-PF4 complexes and induces an alteration of the PF4 molecule. It then exposes neoepitopes, which bind the heparin-dependent antibodies. These antibodies are generated only in some heparin-treated patients, and only a subgroup of them develops thrombocytopenia (HIT) sometimes associated with thrombosis (HITT). The major challenge is to understand how antibodies can be generated and why only some of them are pathogenic. The presence of the IgG isotype at a high concentration is an important factor for developing HIT/HITT. The clinical context, which induces accumulation and activation of platelets at pathological sites, is also important for disease occurrence. The presence of antibodies (mainly the IgG isotype) enhances cell-cell interactions and platelet activation followed by platelet accumulation at these sites. Generation and expression of the autoantigen, HPF4 complexes, is a key feature for triggering antibody binding and pathogenicity. Factors contributing to antibody generation and its persistence, and factors contributing to the expression of the autoantigen triggering the disease development are discussed.

Antibodies↗
PubMed1999

The factor V gene A4070G mutation and the risk of venous thrombosis.

The A4070G polymorphism in exon 13 of the factor V (FV) gene, which replaces His by Arg at position 1299 of the B domain, was recently shown to influence circulating FV levels and to contribute to the activated protein C (APC) resistance phenotype. We examined the impact of this polymorphism in a population of unselected patients with venous thromboembolic disease (VTE). The prevalence of the G4070 (R2) allele was determined in 205 patients and 394 healthy subjects of similar age and sex distribution. Thirty-seven patients (18%) were heterozygous for the R2 allele and 1 (0.5%) was homozygous. Forty-four controls (11.2%) were heterozygous for the R2 allele and 1 (0.2%) was homozygous. Thus, the allelic frequency was significantly higher in the patients with VTE than in the healthy controls, with respective values of 9.5% and 5.8%. The odds ratio was 1.8 (95% CI: 1.1-2.8, p = 0.02), pointing to an increased risk of VTE in carriers of the R2 allele. After excluding subjects with putative or confirmed gene defects (mainly the FV R506Q mutation), the R2 allele was still a risk factor for VTE in the remaining patients, with an odds ratio of 2.0 (95% CI: 1.2-3.5, p = 0.01), demonstrating that this polymorphism is itself a risk factor. This study also confirms that the R2 allele influences APC resistance (APCR) in the absence of the FV R506Q mutation.

Activated Protein C Resistance↗
PubMed1999

Elevated plasma fibrinogen and increased fibrin turnover among healthy women who both smoke and use low-dose oral contraceptives--a preliminary report.

Among users of low-dose oral contraceptives (OC), cardiovascular diseases occur mainly in smokers. The mechanisms by which OC and smoking increase the risk for arterial thrombotic risk have not been adequately explained. Epidemiological evidence suggests that changes in blood coagulation and fibrinolysis may play an important role as determinants of thrombotic events. Therefore, we have investigated the associations of OC and smoking with haemostatic variables among 194 premenopausal healthy women. Fourty women were current users of low-dose OC and 62 women were smokers. After adjustment for age and body mass index, mean values of factor XIIa, factor VII activity and antigen, fibrinogen, D-dimer, global fibrinolytic capacity were significantly higher in OC users than in non-users. Mean levels of PAI activity and t-PA antigen were significantly lower in OC users than in non-users. Smokers had significantly higher mean values of fibrinogen than non-smokers. Two-way analysis of variance showed that the differences in mean levels of fibrinogen and D-dimer between OC users and non users were restricted to smokers. The positive and significant interactions between OC use and smoking in their effects on haemostatic variables were consistent with respect to age and type of OC. These preliminary data suggest that elevated plasma levels of fibrinogen and intravascular fibrin deposition may play a role in the pathogenesis of arterial thrombotic disease among women who are both low-dose OC users and smokers.

Adult↗
PubMed1999

Antigens involved in heparin-induced thrombocytopenia.

Heparin-induced thrombocytopenia (HIT), a common side effect of heparin therapy, can be life-threatening. Following treatment with heparin, platelet factor 4 (PF4) is released into the circulation. Heparin can bind to PF4 to form a reactive antigen on the platelet. The formation of large heparin-PF4 (H-PF4) complexes that can react with HIT antibodies depends on the concentrations of heparin and PF4. Antibodies involved in HIT are usually of the IgG class, but can be IgA or IgM; Fab and Fc fragments are necessary for the activation of platelets. In a minority of cases of HIT, antibodies to H-PF4 are not present, but antibodies to other cytokines have been found. These antibodies frequently react either with interleukin-8 (IL-8) or with neutrophil-activating peptide 2 (NAP-2). Discontinuation of heparin has been the traditional first step in the treatment of HIT. Drugs that inhibit thrombin directly may be necessary in some cases.

Antigens↗
PubMed1998

New insights into the negative regulation of hematopoiesis by chemokine platelet factor 4 and related peptides.

Platelet factor 4 (PF4) has been recognized as an inhibitor of myeloid progenitors. However, the mechanism of action of this chemokine remains poorly understood. The present study was designed to determine its structure/function relationship. A series of peptides overlapping the C-terminal and central regions of PF4 were analyzed in vitro for their action on murine hematopoietic progenitor growth to assess the minimal sequence length required for activity. The peptides p17-58 and p34-58 possessed an increased hematopoietic inhibitory activity when compared with PF4, whereas the shorter peptides p47-58 and p47-70 were equivalent to the native molecule and the peptide p58-70 was inactive. The PF4 functional motif DLQ located in 54-56 was required for the activity of these peptides. The peptide p34-58 impaired to a similar extent the growth of colony-forming unit-megakaryocyte (CFU-MK) as well as burst-forming unit-erythroid (BFU-E) and colony-forming unit-granulocyte-macrophage (CFU-GM), whereas PF4 was more active on CFU-MK. In the experiments using purified murine CD34(+) marrow cells, statistically significant inhibition induced by p34-58 was shown at concentrations of 2.2 nmol/L or greater for progenitors of the three lineages, whereas that induced by PF4 was seen at 130 nmol/L for CFU-MK and 650 nmol/L for CFU-GM and BFU-E, indicating that the p34-58 acts directly on hematopoietic progenitors and its activity is approximately 60- to 300-fold higher than PF4. The p34-58, unlike PF4, lacked affinity for heparin and its inhibitory activity could not be abrogated by the addition of heparin. In addition, an antibody recognizing p34-58 neutralized the activity of p34-58 but not whole PF4 molecule. These results demonstrate that PF4 contains a functional domain in its central region, which is independent of the heparin binding properties, and provide evidence for a model of heparin-dependent and independent pathways of PF4 in inhibiting hematopoiesis.

Amino Acid Sequence↗
PubMed1998

Heparin-induced thrombocytopenia: diagnostic tests and biological mechanisms.

The discovery of the role of PF4 in the development and pathogenicity of heparin-dependent antibodies which trigger heparin-induced thrombocytopenia (HIT), a rare but severe adverse effect of heparin therapy, has allowed us to revisit the diagnosis of this complication and the pathological mechanisms involved. In this review, diagnostic tests available for confirmation or prediction of HIT are analysed, and new diagnostic strategies are discussed. Factors involved in the development of the heparin-dependent immune response in some heparin-treated patients are then presented. Lastly, it is hypothesized that the presence of antibodies is a risk factor for HIT. The mechanisms which contribute to the development of complications and the role of additional risk factors, including the patient's clinical state and the type of heparin used, are discussed (Magnani, 1993).

Anticoagulants↗
PubMed1998

Longitudinal study on activated factors XII and VII levels during normal pregnancy.

Levels of activated factor XII (FXIIa) and VII (FVIIa) were determined in 100 women with uneventful pregnancies. Samples were divided into five study intervals: three during pregnancy, one at delivery and one 3 d postpartum. The median (range) for FXIIa levels were 3.4 ng/ml (1.2-9.1) from 11 to 20 weeks, 4.6 ng/ml (1.4-15.2) from 21 to 30 weeks, 5.4 ng/ml (1.9-14.3) from 31st week to delivery, 5.2 (1.3-11.4) at delivery and 4.3 (1.8-8.5) ng/ml in the postpartum sample. For FVIIa the median and range levels for the five periods were 4.9 (1.7-77.3), 7.2 (2.5-80.4), 11.1 (2.9-90.6), 12.0 (3.1-64.1) and 8.2 (4.0-23.5) ng/ml. Although the increase of FVIIa was higher than that of FXIIa during pregnancy, the overall changes of FXIIa and FVIIa were highly correlated (P<0.0001). At each time period the changes of FVIIa correlated with FVII:C which was not the case with FVII:Ag. These data indicate that during pregnancy both the contact phase and extrinsic pathway are activated.

Adult↗
PubMed1998

High incidence of anti-heparin/platelet factor 4 antibodies after cardiopulmonary bypass surgery.

Fifty-one patients undergoing cardiopulmonary bypass (CPB) were studied on day 0 and day 8 for heparin-induced thrombocytopenia (HIT). The platelet aggregation test (PAT) and tests for anti-heparin-platelet factor 4 (anti-H.PF4), anti-IL8 and anti-neutrophil activating peptide 2 (anti-NAP2) antibodies (Ab) were performed by ELISA. On day 8, 27% of patients were positive for anti-H.PF4Ab. None of these results were found to influence thrombotic complications or platelet counts after CPB. Our results suggest that IgG to H.PF4 may be considered a risk factor, but that additional factors must be required for HIT to develop. We conclude that assays based on platelet activation would be more appropriate for the diagnosis of HIT after CPB.

Adult↗
PubMed1998

Autoantibodies directed against phospholipids or human beta 2-glycoprotein I in HIV-seropositive patients: relationship with endothelial activation and antimalonic dialdehyde antibodies.

BACKGROUND: We investigated the possible role of antiphospholipid (APA) and anti-human 2-glycoprotein I (beta2-GPI) antibodies (Ab) in thrombosis and atherosclerosis in human immunodeficiency (HIV)-positive patients, in whom they seem to be more frequent. METHODS: We measured APA and anti-beta2-GPI Ab in 58 HIV-positive patients together with markers of disease progression, circulating beta2-GPI, plasma lipids, biological markers of endothelial activation and integrity (plasma thrombomodulin, von Willebrand factor, vascular cell adhesion molecule 1) and with antimalonic dialdehyde antibodies (anti-MDA Ab). RESULTS: We found a 41% frequency of IgG APA in the HIV-positive patients. APA IgMs were rarely positive (7%), and anti-beta2-GPI IgGs were positive in 3-4% patients. There was no correlation between APA or anti-beta2-GPI Ab and the presence of opportunistic infections. Although plasma thrombomodulin, von Willebrand factor and vascular cell adhesion molecule 1 were significantly increased in the HIV-positive patients, APA was correlated only with vascular cell adhesion molecule 1, suggesting that APAs are correlated with endothelial activation but not with vascular endothelial lesions. A correlation between APA and anti-MDA IgG was demonstrated using multivariate analysis (r=0.542, P < 0.0001), suggesting a relationship between the targets of these antibodies. Finally, IgG APAs are frequent in HIV infection but are not correlated with biological markers of endothelial injury. CONCLUSION: Our results do not support a role for APA or anti-beta2-GPI in HIV-associated silent vascular endothelial damage. However, the role of these autoantibodies in clinically relevant thrombotic events should be investigated in HIV-positive patients.

Adult↗
PubMed1998

Assay of factor VIII antigen (VIII:CAg) in 294 haemophilia A patients by a new commercial ELISA using monoclonal antibodies.

Monoclonal antibodies (MoAbs 833 and D4H1) directed against human factor VIII (FVIII) have been produced on a large scale to measure VIII:CAg by two-site ELISA (Asserachrom VIII:CAg, Diagnostica Stago). F(ab')2 from MoAb 833 were used for coating and bound VIII:CAg was revealed with MoAb D4H1 coupled to peroxidase. Control plasma (100 VIII:CAg U dL-1 by comparing with the International Standard) was used as reference. The assay sensitivity was 0.1 U dL-1 VIII:CAg. No apparent effect of the plasma proteins was observed provided plasma dilution was > or = 5. Thus this ELISA allowed us to estimate VIII:CAg levels of 0.5 U dL-1 in plasma. Levels of VIII:CAg were similar to those of VIII:C (correlation coefficient r = 0.87) in plasma from normal individuals (32 cases) and in patients with von Willebrand disease of various types (30 cases). Among 294 patients with haemophilia A (HA), 161 had severe HA (VIII:C < 1 U dL-1). Among those patients, 124 were cross-reacting material (CRM) negative with undetectable VIII:CAg and 37 were CRM+ (VIII:CAg 1-31 U dL-1). In 42 patients with moderate HA (VIII:C 1-5 U dL-1), 33 were CRM reduced (VIII:CAg 0.5-8 U dL-1) and nine were CRM+ with a VIII:CAg/VIII:C ratio of 6-91 (mean 34.3). In mild HA (91 cases with VIII:C > or = 6 U dL-1), 29 patients were classified as CRM+ (VIII:C 6-57 U dL-1, VIII:CAg 17-130 U dL-1 and VIII:CAg/VIII:C ratio 1.8-13.7 (mean 4.51)). In 62 CRM reduced patients there was a linear correlation between VIII:C (6-39 U dL-1) and VIII:CAg (2-36 U dL-1) levels (r = 0.88). In conclusion, this sensitive assay allows us to distinguish the quantitative CRM reduced and negative from the qualitative (CRM+) abnormalities in haemophilia A.

Antibodies, Monoclonal↗
PubMed1998

The biological basis of immune heparin-induced thrombocytopenia.

Heparin induced thrombocytopenia (HIT) remains the most severe adverse effect of heparin therapy. Recently, new information has been uncovered regarding the pathogenesis of this disorder. This review summarizes the clinical state, pathogenesis and diagnosis of HIT. It was stimulated by the recent recognition of heparin-platelet factor 4 (H.PF4) complexes as the major target antigen for heparin-dependent antibodies involved in this pathology. The formation of complexes between PF4 and heparin or other glycosaminoglycans, leading in some circumstances to the generation of antigenic structures reactive with HIT antibodies, is analysed. We also discuss how antibodies develop in heparin-exposed patients and why these antibodies can become pathogenic only in some patients, while their presence remains asymptomatic in others. This review also focuses on the mechanisms that could be involved in the development of thrombocytopenia and thrombosis. This new understanding of HIT pathogenesis has permitted the introduction of new tools for retrospective or prospective diagnosis, and may provide new strategies for the avoidance or treatment of HIT and its complications.

Journal Article↗
PubMed1998

Evaluation of a new rapid D-dimer assay for clinically suspected deep venous thrombosis (Liatest D-dimer).

In previous studies, enzyme-linked immunosorbent assays (ELISA) for plasma D-dimer analysis have demonstrated high sensitivity, suggesting their potential usefulness in excluding deep venous thrombosis (DVT). We evaluated the usefulness of a new D-dimer test (Liatest D-dimer) for suspected DVT in a prospective study of patients admitted to the hospital because of recent (not exceeding 1 week before admission) clinical signs. Contrast venography or compression ultrasonography or both were performed within 24 hours of admission. A new quantitative determination of D-dimer concentration using a suspension of microlatex particles coated with specific antibodies was tested. A standard plasma D-dimer ELISA measurement was also performed. Of 464 patients, 276 had a proven DVT (distal, 74; proximal, 202). For a cutoff level of 400 ng/mL, sensitivity of the Liatest method in the diagnosis of overall DVT was 94.6% (95% confidence interval, 92.0%-97.0%), and the specificity was 35% (95% confidence interval, 28%-42%). The sensitivity and negative predictive value were 98.5% and 95.6%, respectively, in the diagnosis of proximal DVT, but only 83.8% and 84.6%, respectively, in the diagnosis of distal DVT. This new rapid Liatest D-dimer assay seems to be highly sensitive and could replace the ELISA method in excluding patients with proximal DVT. Both methods provide lower sensitivity for distal DVT.

Autoanalysis↗
PubMed1998

Tissue factor pathway inhibitor and anti-FXa kinetic profiles of a new low-molecular-mass heparin, Bemiparin, at therapeutic subcutaneous doses.

Low-molecular-mass heparins (LMMHs) exert an anti-FXa effect through antithrombin III (ATIII) and tissue factor pathway inhibitor (TFPI) displaced from endothelium and lipoproteins. This global anti-FXa potency is specific for different compounds. Whether these effects have a similar kinetic and duration is a matter of interest. We compared the kinetic profile of the TFPI effect (total and free) to the anti-FXa amidolytic activity induced by therapeutic subcutaneous doses of a new LMMH, Bemiparin. The overall kinetics of the anti-FXa amidolytic activity and the TFPI effect were different, TFPI achieving a maximal effect earlier than the anti-FXa activity and completely disappearing before it. The anti-FXa amidolytic activity of Bemiparin followed a linear dose-response pattern. Neither total nor free TFPI was directly proportional to the dose. At therapeutic subcutaneous doses, Bemiparin exerted an anti-FXa effect through TFPI during the first 2 h, through both ATIII and TFPI during the following 8 h (range 2-10 h) and through ATIII during the last 8 h (range 10-18 h).

Adult↗