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Biomedical subjects

A Bezeaud

Publications and source records attributed to A Bezeaud.

At least 37 records · Page 2Linked to original sources
PubMed1993

[Prognostic value of pre- and postoperative alpha-fetoprotein in the follow-up of patients with surgically-treated hepatocellular carcinoma].

A percentage ranging from 60 to 80% of hepatocarcinomas are associated with increased levels of alphafetoprotein (AFP). In the three years following surgical resection there was a 80% possibility of recidivation. The aims of the present study were: a) to evaluate the significance of preoperative AFP assay as a prognostic index of recidivation; b) to evaluate the importance of repeated assays during the postoperative period in order to ensure an early diagnosis of recidivation. Between 1982 and 1989, 62 patients underwent surgery for hepatocarcinoma. Thirty-one patients who had undergone so-called curative surgery were periodically controlled for a period varying between 6 and 55 months, and were included in the present study. The remaining 32 patients were excluded for the following reasons: palliative surgery, postoperative death, postoperative complications unrelated to tumoral recidivation. In all cases AFP assay was carried out preoperatively, one month after surgery, and then every six months. Recidivation was always confirmed on the basis of tomodensitometric and arteriographic data. Before surgery out of a group of 30 patients, 11 showed normal AFP levels (below 20 mg/ml), while 19 had levels between 49 and 7350 mg/ml. Twenty-three patients (74%) reported one case of recidivation during the period between 6 and 40 months. Among the 11 patients who had showed normal preoperative AFP levels, 5 had a recidivation between 12 and 36 months, and 3 of these showed high AFP levels. In 18 out of the 19 patients (90%) with high preoperative AFP levels recidivation was diagnosed between 4 and 40 months following surgery; 4 of these were not associated with a rise in AFP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Prothrombin Salakta: substitution of glutamic acid-466 by alanine reduces the fibrinogen clotting activity and the esterase activity.

Structural studies on a hereditary abnormal prothrombin, prothrombin Salakta, have been performed to identify the difference responsible for its reduced fibrinogen clotting activity and its reduced esterase activity. Amino acid composition and sequence analyses of a peptide isolated from a lysylendopeptidase digest of the abnormal thrombin indicated that Glu-466 had been replaced by Ala. This amino acid substitution can result from a single nucleotide change in the codon for Glu-466 (GAG----GCG). The model building and the molecular dynamics simulation of thrombin Salakta suggest that the Glu-466----Ala substitution would change the proper conformation around the substrate binding site containing Trp-468, which is a unique surface loop on the thrombin molecule. This is the experimental and theoretical evidence supporting the role of the surface loop containing Trp-468 for the proper conformation of the substrate binding site.

Alanine↗
PubMed1991

Effect of the hirudin carboxy-terminal peptide 54-65 on the interaction of thrombin with platelets.

The carboxy-terminal region of hirudin (residues 54-65) has previously been shown to inhibit thrombin clotting activity without binding to the catalytic site of the enzyme. In the present study, the effect of hirudin 54-65 on thrombin interaction with specified platelet proteins has been investigated. Hirudin 54-65 was found to inhibit thrombin-induced platelet aggregation and secretion in a dose-dependent manner. Substitution of either Phe56, Glu57, Ile59, Pro60 or Leu64 showed that these residues were critical for inhibition of thrombin-induced platelet activation whereas sulfation of Tyr63 increased the inhibitory potency of the peptide. Hydrolysis of glycoprotein V, a platelet membrane substrate for thrombin, was only partially inhibited by hirudin 54-65. Although hirudin 54-65 did not decrease the amount of thrombin bound to platelets during cross-linking experiments, it was found to inhibit the specific binding of thrombin to platelet glycoprotein Ib. Since the carboxy-terminal region of hirudin has previously been reported to bind near the trypsin-catalyzed beta cleavage site, we have analyzed the consequences of alpha to beta-thrombin conversion on both thrombin-hirudin 54-65 interaction and thrombin activity toward platelets. The beta cleavage induced a decrease in the affinity of thrombin for both glycoprotein Ib and hirudin 54-65. Altogether, our results indicate that thrombin recognition sites for hirudin 54-65 and platelet membrane glycoprotein Ib share common structures located near the beta cleavage site at Arg 73 on the thrombin B chain.

Amino Acid Sequence↗
PubMed1991

An acquired antithrombin autoantibody directed toward the catalytic center of the enzyme.

Antibody inhibitors against human thrombin are rare and have remained poorly characterized. We report the case of a 40-yr-old patient who developed a potent thrombin inhibitor revealed by mild bleeding symptoms and marked prolongation of most laboratory clotting times. After two years of evolution, he died from cerebral hemorrhage. The inhibitor, a polyclonal IgG, was associated with hematological and immunological criteria of autoimmune disorder. Antithrombin IgG was isolated from the patient's plasma by protein A- and thrombin-affinity chromatography. Fab fragments inhibited amidolytic activity of alpha thrombin, and thrombin-thrombomodulin catalyzed protein C activation with a Ki of approximately 10(-8) M in a noncompetitive manner. Alpha to gamma conversion of thrombin resulted in a moderate loss of affinity for the inhibitor. Upon complex formation of thrombin with staphylocoagulase or alpha 2-macroglobulin (alpha 2M), inhibition was decreased by two orders of magnitude and acquired an apparent competitive character. In Western blot experiments, the antibody reacted with active alpha-thrombin, did not react with chloromethylketone-inhibited thrombin and reacted with a lower affinity with iPr2P-thrombin. The inhibitor did not block thrombin binding to benzamidine-, heparin-, or fibrin-Sepharose, but displaced proflavin from its complex with thrombin. Taken together, these results indicate that the patient's autoantibody recognized a conformational structure which includes, at least in part, the apolar binding site adjacent to the catalytic site of thrombin.

Adult↗
PubMed1989

Evaluation of five hepatitis delta virus marker assays for detection of antigen and antibody.

Five commercially available assays for hepatitis delta (HD) virus markers were compared for sensitivity, specificity, and reproducibility: three assays for antibody (anti-HD), provided by Diagnostics Pasteur, Organon Teknika, and Abbott Laboratories, and two assays for antigen (HD Ag), from Pasteur and Organon Teknika. The assay from Organon Teknika is the less sensitive assay for anti-HD detection. Although the sensitivities of the Pasteur and Abbott assays for anti-HD detection are similar, the use of Abbott reagents is hampered by the lack of specificity when HD Ag is present. The greater sensitivity for HD Ag detection is obtained with Organon assay.

Antigens, Viral↗
PubMed1988

Enzymic and nonenzymic properties of human beta-thrombin.

Autolysis or tryptic hydrolysis converts human alpha-thrombin to its beta-derivative and subsequently to gamma-thrombin. Human beta-thrombin was obtained by tryptic digestion of alpha-thrombin and isolated by BioRex chromatography. The kinetic parameters for human alpha- and beta-thrombins with H-D-phenylalanyl-L-pipecolyl-L-arginine-para-nitroanilide were similar, as well as the rate of inactivation by tosyl-lysine chloromethyl ketone. By contrast, the rate of inactivation by diisopropyl fluorophosphate was reduced by half, and the inhibition constant for benzamidine was increased 2.5-fold. Moreover, the beta cleavages induced a drastic reduction in reactivity toward protein C, affinity for thrombomodulin, and fibrinogen clotting activity. Unlike alpha-thrombin, beta-thrombin was not protected from inhibition by diisopropyl fluorophosphate in the presence of fibrinogen and failed to bind to fibrin-Sepharose. Our results indicate that the beta cleavages induce multiple defects in the functions of human thrombin. Although the three catalytic residues remain in an active configuration, subtle changes are induced in the microenvironment of the active serine. However, the drastic reduction of fibrinogen clotting activity should rather be ascribed to major alterations observed in both the fibrinopeptide groove and the fibrin recognition site. These observations provide further evidence for a double-site mechanism in the interaction of fibrinogen with thrombin.

Blood Coagulation↗
PubMed1988

Functional characterization of thrombin Salakta: an abnormal thrombin derived from a human prothrombin variant.

The genetic variant prothrombin Salakta has been described in a patient presenting with a normal level of prothrombin antigen but reduced prothrombin activity. Initial studies indicated that factor Xa-catalyzed cleavages proceed normally but lead to the production of a thrombin molecule with an altered enzymatic activity. To characterize the functional abnormality of thrombin Salakta more precisely, it was purified by chromatography on heparin-Sepharose and diethylaminoethyl-Sephadex. The purified variant does not differ from normal thrombin by size, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and is 93.1% +/- 7.6% active by titration with p-nitrophenyl-p'-guanidinobenzoate. Its activity, however, is altered to various extents toward the following substrates: H-D-phenylalanyl-L-pipecolyl-L-arginine paranitroanilide (S 2238), fibrinogen, factor V, protein C, and antithrombin III. The Michaelis constant (Km) of thrombin Salakta for S 2238 is higher (12.2 +/- 3.3 mumol/L) than normal (2.8 +/- 0.7 mumol/L), whereas the turnover number (Kcat) is normal (84.4 +/- 6.6 s-1 v 85.9 +/- 14.0 s-1 for normal thrombin). The interaction of thrombin Salakta with benzamidine is also altered as evidenced by an increased inhibition constant (Ki = 3.5 mmol/L v 0.28 mmol/L for normal thrombin). The inability of fibrinogen to act as a competitor in the inactivation of thrombin Salakta by diisopropylfluorophosphate clearly indicates that fibrinogen binding to the fibrinopeptide groove is drastically impaired. In contrast, interactions involving sites remote from the active site such as those with fibrin and thrombomodulin are only slightly impaired. These results indicate that thrombin Salakta exhibits a specific pattern of functional alterations different from those reported for other variants. The structural defect seems to affect essentially the primary substrate binding site and to a lesser extent recognition site(s) remote from the catalytic site such as those for fibrin and thrombomodulin.

Catalysis↗
PubMed1987

[Hereditary protein S deficiency and recurrent venous thrombosis. Study of a family].

Hereditary protein S deficiency was detected in three subjects belonging to three generations of one single family. The deficiency was heterozygous and was associated with recurrent venous thromboembolism in two of the subjects affected. Plasma analysis by two-dimensional immunoelectrophoresis showed that the protein S fraction bound to C4b-binding protein was quantitatively normal, whereas the free protein S fraction was much reduced. Since it has been well established that only free protein S intervenes in the regulation of blood coagulation, any quantitative deficiency, even moderate, in protein S resulting in redistribution of its free and bound fractions will have major functional repercussions.

Adult↗
PubMed1987

[Protein C, protein S].

Protein C is a potent inhibitor of blood coagulation, and, in addition, appears to be a profibrinolytic agent. In a first step, protein C must be converted to a serine protease. This activation is catalyzed by a complex formed between thrombin and thrombomodulin, an endothelial cell surface protein. Activated protein C exhibits its anticoagulant activity through the proteolytic inactivation of two blood coagulation cofactors, factors Va and VIIIa. This reaction requires phospholipids, originating from platelets or endothelial cells, and a cofactor protein, protein S. Protein S enhances the binding of activated protein C to phospholipids. In addition, activated protein C stimulates fibrinolysis, through the inactivation of the tissue plasminogen activator (tPA) inhibitor. An isolated constitutional, quantitative or qualitative, protein C or protein S deficiency increases the risk of thrombosis, the clinical features are different in the rare cases of homozygous protein C deficiency (neonatal purpura fulminans) or in the heterozygous patients (recurrent venous thrombosis in young adults). Acquired deficiency in protein C and S had been observed in liver disease, during vitamin K antagonists or L-Asparaginase treatment, and in disseminated intravascular coagulation.

Animals↗
PubMed1986

Effect of L-asparaginase therapy for acute lymphoblastic leukemia on plasma vitamin K-dependent coagulation factors and inhibitors.

Vitamin K-dependent proteins were measured sequentially by immunoassay in eight patients with acute lymphoblastic leukemia receiving L-asparaginase (1000 U/kg/day) for 10 days as induction therapy, in combination with vincristine or vindesine, daunorubicin, cyclophosphamide, and prednisone. The level of each protein was significantly decreased during L-asparaginase therapy, but both the time course of change and the severity of decrease differed among the proteins. The decrease in protein C, factor IX, and factor X was observed earlier than the decrease in protein S and factor II. In the first days of L-asparaginase therapy the protein C level was significantly lower than those of the other vitamin K-dependent proteins. The transient imbalance in the levels of plasma vitamin K-dependent proteins observed in the first days of treatment may contribute to the risk of thrombosis associated with L-asparaginase therapy.

Adolescent↗
PubMed1986

[Occurrence of increased alpha-fetoprotein in non-neoplastic hepatopathies of alcoholic or non-alcoholic origin].

In order to improve the evaluation of the frequency of alpha-fetoprotein reappearance in non-neoplastic liver disease, we assayed serum alpha-fetoprotein in 251 patients: 134 chronic alcoholics including 7 HBs Ag positive patients, 113 of whom had cirrhosis and 117 patients with chronic active hepatitis, 56 of whom were HBs Ag positive. None of these patients had any signs of hepatocellular carcinoma. Alpha-fetoprotein values above the upper normal limit (much greater than 20 ng/ml) were compared with the type of the liver disease, the serum aminotransferase activity, the usual hepatitis B-virus markers assayed by standard radioimmunology and, in 70 patients, with the results of the HBV-DNA hybridization in the liver. Abnormal alpha-fetoprotein levels were found in only 6.3 p. 100 of patients with HBs Ag negative alcoholic disease and in 17 p. 100 of patients with chronic active hepatitis, without any statistical difference concerning the presence of HBs Ag or not. Alpha-fetoprotein was more often abnormal in subjects who had hypertransaminasemia. For given values of transaminases no statistical relationship between serum alpha-fetoprotein levels and the presence of HBs Ag was observed.

Adult↗
PubMed1985

Interaction of human alpha-thrombin and gamma-thrombin with antithrombin III, protein C and thrombomodulin.

Conversion of human alpha-thrombin to gamma-thrombin by limited proteolysis resulted in a decrease in the inactivation rate of the enzyme by antithrombin III. The second-order rate constants were similar but significantly different: 11 +/- 1.7 X 10(3) and 7 +/- 0.5 X 10(3) M-1 s-1 for alpha- and gamma-thrombin respectively. This difference is probably related to a slight change in reactivity of the catalytic site, rather than to a structural alteration of the recognition site for antithrombin III. The rate of protein C activation, measured in the absence of thrombomodulin, was greatly reduced by conversion of alpha-thrombin to gamma-thrombin. In addition, gamma-thrombin failed to displace alpha-thrombin from its complex with thrombomodulin, as demonstrated by measuring either the rate of protein C activation by thrombin-thrombomodulin, or the fibrinogen clotting activity of thrombin-thrombomodulin, in the presence of competing diisopropylphospho-thrombin. It is concluded that the recognition sites involved in protein-C-thrombin and thrombomodulin-thrombin interactions are both dramatically affected by the loss of peptide material occurring during the conversion of alpha-thrombin to gamma-thrombin and/or by the resulting conformational changes.

Animals↗
PubMed1985

[General mechanisms of coagulation and their physiological inhibition. II. The regulation of coagulation by physiological inhibitors].

Inopportune coagulation of blood in vessels is prevented by defense mechanisms, in which plasma inhibitors play an important role. The inhibitors are glycoproteins and belong to two different groups, according to their mechanism of action. The first group consists of the inhibitors of serine proteases, which form inactive complexes with various coagulation enzymes; it includes antithrombin III, heparin cofactor II, alpha 2-macroglobulin, alpha 1-antitrypsin and C1S-inhibitor. The second group includes protein C and its cofactor, protein S. Protein C, activated by thrombin complexed with a protein cofactor present on the endothelial cell surface (thrombomodulin), is responsible for the proteolytic degradation of two coagulation cofactors (Va and VIII: Ca). The clinical importance of both antithrombin III, protein C and protein S is attested by the strong association between recurrent venous thromboembolic manifestations and inherited deficiencies of one or the other of these proteins.

Antithrombin III↗
PubMed1985

[General mechanisms of coagulation and their physiological inhibition. I. General mechanisms of blood coagulation].

Blood coagulation results from a sequence of enzymatic reactions, which involve 12 plasma proteins (coagulation factors), platelets, a tissue lipoprotein (tissue factor), vascular components and calcium ions. These reactions are induced by vascular lesions, and are promoted by blood contact with sub-endothelial structures and by the release of tissue factor into the circulation; they result in the formation of an hemostatic plug constituted of platelets and fibrin. The enzymatic reactions consist of proteolytic reactions, in which zymogens are converted to proteinases. These reactions are accelerated by both proteins-proteins interactions and by proteins-membrane surface (vascular wall, platelets) interactions, responsible for the amplification of the activation process, and its localization at the site of injury. The coagulation process is regulated by positive and negative feed-backs and by physiological inhibitors.

Animals↗