[Rapid centrifugation for routine coagulation testing]

Routine coagulation assays are performed with platelet-poor plasma obtained after centrifugation of whole citrated blood. Usually clinical laboratories centrifuge blood from 2,000 to 2,500 g for 15-30 minutes. Thirty two blood samples routinely submitted to coagulation tests, were assayed for the prothrombin time, activated partial thromboplastin time, and fibrinogen level, in order to compare results obtained using 2 types of centrifugation : centrifugation at 2,500 g for 15 minutes and rapid centrifugation on StatSpin Express 2 at 4,440 g for 2 minutes. A good correlation was observed for the prothrombin time, activated partial thromboplastin time, and fibrinogen levels being respectively 1,009, 0,908 and 1. We concluded that rapid centrifugation at 4,440 g for 2 minutes does not modify results and contributes, by decreasing duration of the pre-analytical variable to reduce the completion time of these tests.

Quantitative gene expression in Budd-Chiari syndrome: a molecular approach to the pathogenesis of the disease

BACKGROUND

Budd-Chiari syndrome (BCS) is associated with parenchymal changes leading to major architecture remodelling. In order to gain further insight into the pathogenesis of BCS, we investigated expression of a set of genes involved in the course of chronic liver diseases.

METHODS

Quantitative expression of 35 selected genes involved in extracellular matrix regulation, growth factors, and angiogenesis was investigated in 13 cases of BCS and compared with 10 normal livers and 13 cirrhosis cases by real time reverse transcription-polymerase chain reaction. Differential gene expression was considered significant for genes showing at least a twofold variation, with p < 0.05.

RESULTS

Expression of 14 genes was significantly increased in BCS versus normal liver, with the highest increase in superior cervical ganglion 10 (SCG10) gene. BCS cases were classified according to their evolution and morphological pattern as either acute or chronic in six and seven cases, respectively. Unsupervised hierarchical clustering of acute and chronic BCS cases on the basis of similarity in gene expression pattern led to distinction between the two groups. Expression of three genes was significantly different in acute versus chronic BCS (increase in matrix metalloproteinase 7 and SCG10, decrease in thrombospondin-1 for chronic BCS). Seventeen and 10 genes, mainly involved in extracellular matrix and vascular remodelling, were significantly deregulated in acute BCS versus normal liver and cirrhosis, respectively.

CONCLUSION

These results show that BCS cases display a specific gene expression profile that is different from that of normal liver and cirrhosis; the molecular configuration of BCS can be readily distinguished by its evolution and morphological pattern.

A critical role for Gly25 in the B chain of human thrombin

We have recently identified (Akhavan S et al., Thromb Haemost 2000; 84: 989-97) a patient with a mild bleeding diathesis associated to an homozygous mutation in the thrombin B chain (Gly25Ser, chymotrypsinogen numbering, i.e. position 330 in human prothrombin numbering). Transient transfection of wild-type prothrombin (FII-WT) and mutant prothrombin (designated FII-G25(330)S) cDNA in COS-7 cells showed a mild reduction (50%) in FII-G25(330)S production. Recombinant proteins, stably expressed in Chinese hamster ovary cells, were isolated and activated by Taipan snake or Echis carinatus venoms. We show that the G25(330)S mutation results in a decrease in the rate of prothrombin proteolytic activation. The mutation also significantly decreases (i) the catalytic activity of thrombin with a 9-fold reduction in catalytic efficiency of the mutant toward S-2238; (ii) the interaction with benzamidine; (iii) the rate of inhibition by TLCK and antithrombin; and (iv) the rate of hydrolysis of macromolecular substrates (fibrinogen, protein C). In contrast, exosite I does not appear to be affected by the molecular defect. These results, together with molecular modeling and dynamics, indicate that Gly25(330) is important for proper expression and probably proper folding of prothrombin, and also plays a critical role in both the alignment of the catalytic triad and the flexibility of one of the activation segments of prothrombin.

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.

Cause of portal or hepatic venous thrombosis in adults: the role of multiple concurrent factors

According to a recent hypothesis, venous thrombosis results from the concurrence of several factors. This hypothesis was assessed in patients with portal or hepatic venous thrombosis by simultaneously investigating most of the currently identified prothrombotic disorders, local precipitating factors, and other risk factors such as oral contraceptive use. Patients with a tumorous obstruction and patients with cirrhosis with portal vein thrombosis were excluded. The prothrombotic disorders that were investigated included classical and occult myeloproliferative disorders; antiphospholipid syndrome; protein C; protein S and antithrombin deficiency; factor V Leiden; factor II; and methylene-tetrahydrofolate-reductase gene mutations. We found 1 or several prothrombotic disorders and a local precipitating factor in 26 and 10 of the 36 patients with portal vein thrombosis, respectively; and in 28 and none of the 32 patients with hepatic vein thrombosis, respectively. We found a combination of prothrombotic disorders in 5 and 9 patients with portal and hepatic vein thrombosis, respectively, whereas such a combination is expected in less than 1% of asymptomatic subjects. Of the 10 patients with a local precipitating factor, 8 had a prothrombotic disorder. Of the 13 patients who use oral contraceptives, 10 had a prothrombotic disorder. We conclude that portal or hepatic venous thrombosis should be regarded as an index for 1 or several prothrombotic disorders, whether or not local precipitating factors or oral contraceptive use are found. Concurrence of prothrombotic disorders is more common than expected. Extensive investigation of prothrombotic disorders and anticoagulation should be considered in patients with portal or hepatic venous thrombosis.

Inhibition of thrombin-catalyzed factor V activation by bothrojaracin

We have previously identified and characterized a potent and specific thrombin inhibitor, isolated from Bothrops jararaca, named bothrojaracin. Bothrojaracin interacts with the two positively charged recognition sites of thrombin referred to as exosite 1 and exosite 2, whereas it does not interact with the thrombin active site. Consequently, bothrojaracin inhibits thrombin-induced fibrinogen to fibrin conversion and platelet activation, without inhibition of thrombin-catalyzed cleavage of small synthetic substrates. In the present study, we show that bothrojaracin exerts an anticoagulant effect in plasma, illustrated by the prolongation of the aPTT. Using purified proteins, we observed that the anticoagulant effect of bothrojaracin was not only due to the inhibition of fibrinogen to fibrin conversion, but in addition to the inhibition of factor V activation by thrombin. Bothrojaracin decreased the rate of thrombin-catalyzed proteolysis of factor V and concurrently the generation of factor Va cofactor activity measured in a prothrombinase assay. We compared the effect of bothrojaracin with that of ligands binding specifically exosite 1 (hirudin C-terminal peptide SH54-65) or exosite 2 (heparin, prothrombin fragment 2). SH54-65 delayed thrombin catalyzed factor V activation whereas heparin or prothrombin fragment 2 did not. The thrombin derivatives beta- and gamma-thrombin, which are defective in their exosite 1, but present with a normally exposed exosite 2, had a reduced capacity to activate factor V, which was not further impaired by the exosite 2 ligands, bothrojaracin, heparin or prothrombin fragment 2. Altogether, our results provide further insight into the anticoagulant effect of bothrojaracin showing that it is a potent inhibitor of the feedback activation of factor V by thrombin, and thus of the up-regulation of its own production by thrombin. Inhibition of thrombin-catalyzed factor V activation by bothrojaracin is mainly mediated through the interaction of the inhibitor with thrombin exosite 1, whereas contribution of the interaction with exosite 2 does not appear to play a direct role in factor V recognition by thrombin.

Sickle cell disease: relation between procoagulant activity of red blood cells from different phenotypes and in vivo blood coagulation activation

In the present study we examined if, among other mechanisms, the abnormal exposure of phosphatidylserine at the surface of sickle red blood cells (RBCs) contributes to the hypercoagulability which characterizes homozygous sickle cell disease (SCD). The question was addressed by comparison of the procoagulant properties of RBCs from subjects with various phenotypes (SS, SC and AS) that differ in clinical presentation. As previously reported, SS-RBCs accelerated the prothrombin activation by factor Xa, by decreasing the Km of the reaction compared to normal RBCs. SC-RBCs and AS-RBCs also promoted prothrombin activation although their procoagulant properties were milder compared to SS-RBCs. A significant increase of the thrombin-antithrombin complexes was observed in SS subjects. Prothrombin fragment 1+2 (F1+2) was elevated in half of the SS subjects, but the difference with controls did not reach significance. Elevated levels of thrombin-antithrombin complexes were observed in a number of SC (4/11) and AS (3/12) subjects, but the difference with controls was not significant. A significant correlation was observed between the plasma levels of thrombin-antithrombin complexes in the subjects with SS, AS and AA phenotypes, and the procoagulant properties of RBCs. Our results strongly suggest that the procoagulant properties which characterize SS-RBCs also affect SC-RBCs and AS-RBCs, and that exposure of phosphatidylserine by RBCs contributes to the hypercoagulable state observed in SCD.

Polymorphism in exon 10 of the human coagulation factor V gene in a population at risk for sickle cell disease

In Caucasians, the R506Q mutation in exon 10 of the factor V gene (FV Leiden) confers an increased risk of thromboembolism. We have scanned this region of the gene for possible mutations in 450 subjects from populations at risk for sickle cell disease (SCD). The R506Q mutation was absent in subjects from sub-Saharan Africa, whereas its allelic frequency was 2.5% in the West Indies. Only one other substitution with no functional consequences in vitro (R485K) was found (32.4% allelic frequency) in sub-Saharan Africa. Thus, we found no mutations in exon 10 of the FV gene constituting an additional risk factor for thrombosis in SCD in sub-Saharan Africa. This suggests that the putative selective advantage conferred by R506Q does not exist in these populations, unless R485K has functional consequences in vivo. If further suggests that R506Q in American Africans is of Caucasian origin. Our data are the first to document ethnic variations in the frequency of the R485K polymorphism.

Increased procoagulant activity of red blood cells from patients with homozygous sickle cell disease and beta-thalassemia

It has recently been proved that, in vitro, red blood cells (RBCs) from patients with homozygous beta-thalassemia behave as procoagulant cells. The procoagulant activity of beta-thalassemia RBCs might be the result of an increased exposure of procoagulant phospholipids (i.e. phosphatidylserine) in the outer leaflet of the membrane. In order to test this hypothesis, we compared the catalytic properties of RBCs of patients with beta-thalassemia and homozygous sickle cell disease (SS-RBCs) with that of controls. The catalytic parameters (Km, kcat) of prothrombin activation by factor Xa were determined both in the absence and in the presence of RBCs. The turn-over number (kcat) of the reaction was not modified by normal, SS- or beta-thalassemia RBCs. The Km was lower in the presence of normal RBCs (mean value: 9.1 microM) than in the absence of cells (26 microM). The Km measured in the presence of either SS-RBCs (mean value: 1.6 microM) or beta-thalassemia RBCs (mean value: 1.5 microM) was significantly lower compared to normal RBCs (p < 0.001). No significant difference was observed between SS-RBCs and beta-thalassemia RBCs. Annexin V, a protein with high affinity and specificity for anionic phospholipids, inhibited the procoagulant activity of both SS-RBCs and beta-thalassemia RBCs, in a dose-dependent manner. More than 95% inhibition was achieved at nanomolar concentrations of annexin V. These results indicate that the procoagulant activity of both beta-thalassemia RBCs and SS-RBCs may be fully ascribed to an abnormal exposure of phosphatidylserine at the outer surface of the red cells.

Specific measurement of hypocarboxylated prothrombin in plasma or serum and application to the diagnosis of hepatocellular carcinoma

An enzyme-linked immunosorbent assay (ELISA) was developed for measuring human hypocarboxyprothrombin, a protein induced by vitamin K antagonists (PIV KA-II). A specific monoclonal antibody (P1-2-B9) was prepared and used for coating a microELISA plate, and revelation proceeded with a rabbit polyclonal anti-human prothrombin antibody-peroxidase conjugate. This assay allowed the measurement of PIVKA-II at concentrations ranging from 2 to 200 ng/ml, with an intraassay coefficient of variation of less than 5.2% and an interassay coefficient of variation of less than 7.4%. This assay permits the direct evaluation of PIVKA-II in citrated plasma as well as in serum. The concentration of PIVKA-II is expressed in nanograms per milliliter. It offers specific measurement of PIVKA-II without any cross-reactivity from native prothrombin: the specificity for PIVKA-II respective to prothrombin is > 10(5). No reactivity was observed with other vitamin K-dependent proteins, whether fully active or decarboxylated. Complementary studies have demonstrated that the monoclonal antibody used was preferentially directed to 3 to 6 Gla hypocarboxylated prothrombin. PIVKA-II concentration was below 2.4 ng/ml in normal individuals (n = 59). In 61 patients given dicoumarol for more than 90 days (receiving a stable therapy), the measured concentrations of PIVKA-II ranged from 750 to 13,400 ng/ml. Combined with the assay of alpha-fetoprotein (AFP), measurement of PIVKA-II in patients with liver diseases introduces a complementary exploration for hepatocellular carcinoma (HCC). In a study in 59 patients with HCC, the assay sensitivity was 49.1% for PIVKA-II, 47.5% for AFP, and 71% for both markers combined.

Functional consequences of the Ser334-->Pro mutation in a human factor X variant (factor XMarseille)

A factor X molecular variant was identified in a 55-year-old woman at a routine preoperative coagulation screening. Plasma factor X antigen was normal, whereas factor X activity was decreased when factor X was activated by either the extrinsic pathway (21%), the intrinsic pathway (21%) or the factor X activator from Russell viper venom, RVV-X (26%). Factor XMarseille was isolated from plasma by immunoaffinity chromatography and compared with normal factor X purified by the same method. Activation of factor XMarseille by factor IXa or by RVV-X in a purified system showed that the rate of cleavage was decreased, whereas once produced, factor XaMarseille had a normal catalytic efficiency for either the peptide substrate S-2765 (D-Arg-Gly-Arg-NH-Np) or prothrombin. The rate of inhibition of factor XaMarseille by antithrombin III was also normal. Defective proteolysis of factor XMarseille by factor IXa or by RVV-X was the consequence of a threefold decrease in the kcat for the activation of factor XMarseille while the Km of RVV-X or factor IXa for factor X was normal. We have determined the molecular basis of the defect in the factor XMarseille gene by amplification of all eight exons, single-strand conformational polymorphism analysis of the amplified exons and subsequent sequence analysis. The patient was homozygous for a T-->C mutation in exon VIII, resulting in the substitution of Ser334 by proline. From comparison of three-dimensional models of various serine proteases, it appears that Ser334 is located within a surface-exposed variable region of factor X. This observation suggests that the Ser334-->Pro mutation either is responsible for a misalignment of the active sites of specific factor X activators in close proximity to the cleavage site, or that the Ser-->Pro mutation alters the spatial orientation of the cleavage site by nonlocal modifications of factor X structure.

Thrombin specificity

A model of thrombin interaction with distinct substrates or ligands has been derived from the crystallographic studies of thrombin-inhibitors complexes, and buttressed by functional studies with mutant thrombins, thrombin proteolytic derivatives or antibodies against thrombin. The unique specificity of thrombin for its substrates and ligands may be ascribed to multiple interactions with both the active site cleft and exosite(s) distinct from the active site. Two prominent insertion loops around Trp 50 and Trp 148 project over the active site cleft and play an important role in the substrates selection. Several substrates (fibrinogen, thrombin receptor, heparin cofactor II) or ligands (thrombomodulin, glycoprotein Ib) interact with a large exosite located on the surface of the loop segment 65-76, mainly constituted of basic amino acids, designated anion binding exosite 1. Interaction with these various macromolecules appears to involve a limited number of residues within the large exosite 1. It is conceivable that exosite 1 contains distinct subsites, although most of them may overlap. A second basic exosite (anion binding exosite 2) is located close to the carboxy-terminal B chain helix. Exosite 2 interacts with heparin, the chondroitin sulfate moiety of thrombomodulin and prothrombin activation fragment 2. Interaction of ligands with either exosite 1 or exosite 2 leads to conformational changes of the thrombin molecule, that may be important determinants of thrombin specificity. Whether exosite 2 cooperates with exosite 1 for thrombin interaction with fibrin(ogen) or the thrombin receptor remains to be determined.

Hepatitis B virus precore mutations and HBeAg negative reactivation of chronic hepatitis B after interferon therapy

The objective of this study was to look for HBV precore mutations in three patients with chronic active hepatitis B who developed HBV-DNA-positive/HBeAg-negative reactivation after HBe seroconversion induced by interferon therapy. Direct sequencing of polymerase chain reaction products was performed on serum collected before and after HBe seroconversion. In two patients precore sequence showed only wild-type HBV before and after interferon therapy. In one patient, precore sequence showed only wild-type HBV before interferon therapy and a mixed infection by wild-type HBV and precore mutant viruses (1858 and 1896 nucleotide mutations) after treatment. The presence of HBeAg/anti-HBe immune complexes was found after HBe seroconversion in all cases. Our results suggest that: 1) precore mutations are not always found in patients with chronic hepatitis B who develop HBV DNA-positive/HBeAg-negative reactivation; and 2) HBeAg negativity, despite the presence of wild-type HBV, might be due to HBeAg/anti-HBe immune complexes. We speculate that the production of these immune complexes may be favored by interferon therapy.

Low frequency of precore hepatitis B virus mutants in anti-hepatitis B e-positive reactivation after loss of hepatitis B e antigen in patients with chronic hepatitis B

The objective of this study was to evaluate the role of hepatitis B virus (HBV) precore mutations in patients with anti-HBe-positive chronic hepatitis B with or without previous known HBe antigen (HBeAg) viremic phase, and to assess the potential implication of precore mutants in HBeAg-negative reactivation after loss of HBeAg. Nineteen patients were studied: 7 had a previous HBeAg-positive phase and had spontaneous or therapeutically induced loss of HBeAg (group A); 12 had no previous HBeAg-positive phase (group B). Direct sequencing of PCR products was performed on serum collected during the anti-HBe-positive phase in the two groups. In group A, precore sequencing showed that 5 patients were infected by wild-type virus, 1 patient was infected with a precore mutant, and 1 patient was found to be infected by a mixture of wild-type and precore mutant viruses. In group B, precore sequencing showed that only 1 patient was infected with wild-type virus and that 11 were infected with precore mutants. In a few patients, the presence of HBeAg within immune complexes may explain HBeAg negativity. In conclusion, our results show that, in patients with anti-HBe-positive chronic hepatitis B: (1) precore mutations creating a stop codon are more frequently found in those without known previous HBeAg positivity; (2) after loss of HBeAg, the patients who have anti-HBe-positive reactivation are infected by wild-type virus, which suggests that reactivation is not related to precore mutations; (3) HBeAg negativity may be caused by immune complexes formation.

Limited proteolysis of human alpha-thrombin by urokinase yields a non-clotting enzyme

Limited proteolysis of human alpha-thrombin by various proteases has been efficiently used to demonstrate the importance of two insertion loops located on the surface of this molecule. In the present study, we demonstrate that two-chain urokinase (tcu-PA) specifically cleaves the B chain of alpha-thrombin giving rise to a transient derivative, consisting of two non-covalently linked subunits. Although the thrombin derivative conserves its activity towards the synthetic substrate S-2238 (Km = 8.4 microM and kcat = 145 s-1 versus respectively 4.5 microM and 149 s-1 for alpha-thrombin), most of its coagulant activity is lost (140 NIH u/mg versus 3000 NIH u/mg) and its ability to activate platelets is considerably reduced (threshold for full platelet aggregation 2.5 nM versus 0.25 nM). The thrombin fragments were separated by HPLC and after reduction and S-carboxyamidemethylation were digested with a lysylendopeptidase; the resulting peptides were separated by HPLC and sequenced. One fragment corresponded to B chain fragment 1-73 and the second to B chain fragment 74-259 covalently linked to the A chain, indicating that tcu-PA cleaves selectively the peptide bond Arg 73-Asn 74 in the B chain. The proteolytic derivative obtained, designated beta u-thrombin, is therefore identical to the transient proteolytic derivative, beta 1-thrombin, produced by trypsin. Prolonged incubation with tcu-PA resulted in further conversion in a derivative analogous to gamma t-thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of the abnormal vitamin K-dependent gamma-carboxylation process in human hepatocellular carcinomas

BACKGROUND

An important marker for hepatocellular carcinoma is the presence of des-gamma-carboxy (abnormal) prothrombin. However, the molecular basis for the reduced carboxylation of prothrombin is unknown.

METHODS

Two groups of patients were defined according to the absence (Group I, n = 7) or presence (Group II, n = 8) of des-gamma-carboxy prothrombin. The enzymatic activity of gamma-carboxylase and the total microsomal prothrombin concentration were determined in all tumors. The kinetic parameters for the synthetic peptide Phe-Leu-Glu-Glu-Leu (FLEEL) were measured in eight tumors. The gamma-carboxylase mRNA expression was evaluated by Northern blot analysis in 12 of 15 tumors. In addition, the total vitamin K content (K1, K1 epoxide, and menaquinones 4-10) in 10 tumors was investigated by high performance liquid chromatography.

RESULTS

Concentrations of menaquinones 4-10 were normal in the nontumorous part of the liver but significantly decreased (P = 0.02) in all the tumors (Groups I and II). This decrease was more severe in Group II (P = 0.02). The tumors in Group I had normal or increased gamma-carboxylase activity and increased mRNA expression (P < 0.02) as compared with their nontumorous counterparts. The tumors in Group II were heterogeneous. Five tumors displayed low gamma-carboxylase activity, associated with low mRNA expression in two, whereas two others had high gamma-carboxylase activity and mRNA expression. The concentration of FLEEL at half-maximal velocity was normal in all the tumors examined (Groups I and II), and a relation was found between the level of expression of gamma-carboxylase and the maximal velocity for FLEEL carboxylation in the tumors in Group II (r = 0.98; P < 0.01). The microsomal content of normal prothrombin was within normal limits in all tumors (Groups I and II).

CONCLUSIONS

Tumor vitamin K content has a critical role in the synthesis of des-gamma-carboxy prothrombin. Furthermore, the gamma-carboxylase defect, which is observed in some secreting tumors, is the result of the defective gene expression of a normal enzyme and not the consequence of the presence of a competitive inhibitor. It is possible that a 75% reduction in gamma-carboxylase gene expression could take a part in the secretion of des-gamma-carboxy prothrombin, but this mechanism is not predominant.

Prevalence of hepatitis C virus infection in asymptomatic anti-HIV1 negative pregnant women and their children

The prevalence of hepatitis C virus (HCV) infection was studied prospectively in pregnant women in France and their children by detection of anti-HCV with second-generation ELISA (ELISA2). In ELISA2-positive women, anti-HCV was detected with second- and third-generation RIBA (RIBA2 and RIBA3) and serum HCV RNA was detected with PCR. Among 670 women, anti-HIV1-negative, 26 (3.9%) were positive with ELISA2. RIBA2 was positive in 13 and HCV RNA was found in 10. Ten ELISA2-positive women had a further evaluation with assessment of HCV infection in their children. Among the 10 children born to the index pregnancy, only one was positive with ELISA2 and RIBA2 but negative with RIBA3 and PCR; the nine other children were ELISA2, RIBA2, RIBA3, and PCR negative. All 26 siblings (2-16 years old), of whom 14 were born to PCR-positive mothers, were ELISA2 and RIBA2 negative. We conclude that among anti-HIV1-negative pregnant women with normal serum ALT levels, the prevalence of HCV infection is relatively high but the risk for mother-to-infant transmission of HCV seems to be low.

Late-fibrin(ogen) fragment E modulates human alpha-thrombin specificity

Fibrinogen contains at least two independent sites having demonstrable affinity for alpha-thrombin. One of these two sites, located in the fibrin E domain, binds to structures within the anion-binding exosite of alpha-thrombin. Taking advantage of its solubility, we have used late-fibrin(ogen) fragment E in competition experiments to examine its effect on alpha-thrombin specificity. We show that fragment E modulates alpha-thrombin enzymic activity towards small synthetic substrates, suggesting that fibrin-thrombin interaction might induce subtle changes in the conformation near the catalytic center of the enzyme. In addition, fragment E behaved as a competitive inhibitor of alpha-thrombin-catalyzed fibrinopeptide-A cleavage (Ki = 5.2 +/- 1.3 microM), indicating that alpha-thrombin interaction with the fibrin moiety of fibrinogen makes a major contribution to the efficacy of fibrinogen hydrolysis. Fragment E inhibited alpha-thrombin-induced serotonin release by platelets (concentration required to obtain 50% inhibition, IC50 = 10 microM) and alpha-thrombin binding to GPIb. Fragment E competitively inhibited alpha-thrombin binding to thrombomodulin (Ki = 18.3 +/- 0.8 microM) but did not inhibit protein-C activation in the absence of thrombomodulin. The data are consistent with the proposal that fibrin, platelet GPIb and thrombomodulin bind to overlapping, but probably non-identical sites, while protein C binds to an independent site on alpha-thrombin.

[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)

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.

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.

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.

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.

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.

[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.

Multivariate analysis of prognostic factors in fulminant hepatitis B

We assessed prognostic factors in 115 patients with serologically defined fulminant hepatitis B. The diagnosis in each case was based on the finding of IgM antibody to the hepatitis B core antigen in serum. Multivariate analysis showed that factor V level (p less than 0.001), patient's age (p = 0.001), absence of detectable HBsAg by radioimmunoassay (p = 0.06) and serum alpha-fetoprotein concentration (p = 0.07) were independent predictors of survival. The survival rate in the 21 patients in whom HBsAg was not detected was 47%, which was significantly higher than the survival rate of 17% observed in the 94 HBsAg-positive patients (p = 0.006). In patients with fulminant hepatitis B, the absence of HBsAg in serum as detected by radioimmunoassay has an independent, favorable prognostic value.

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.

[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.

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.

[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.

Quantitation of prothrombin activation products in human urine

Urine samples obtained from 37 normal individuals have been screened for the presence of prothrombin activation products using radioimmunoassays developed for fragment 1, fragment 2 and prothrombin derivatives bearing the thrombin region. The cross-reacting materials detected in urine were isolated by affinity chromatography on insolubilized antibodies, and analysed by SDS polyacrylamide gel electrophoresis. The only prothrombin derivatives detected were fragment 1 (37/37) and fragment 2 (22/37). The mean values of daily urinary fragment 1 and fragment 2 excretion were respectively 13.4 nM and 1.5 nM. The excretion of prothrombin derivatives has been quantitated in 14 normal pregnant women, during the third trimester of gestation. The mean values of urinary excretion were 47.2 nM per day for fragment 1 (P less than 0.005) and 6.4 nM per day for fragment 2 (P less than 0.05). The significant increase in fragment 1 and fragment 2 excretion observed in a condition known to be associated with the so-called hypercoagulable state suggest that the measurement of prothrombin derivatives in urine could be a useful tool for the non-invasive detection of thromboembolic diseases or prethrombotic states.

Prothrombin Salakta: an abnormal prothrombin characterized by a defect in the active site of thrombin

An abnormal prothrombin has been detected in a 17 yr-old female originating from Tunisia. There was no history of excessive bleeding. Prothrombin time and activated partial thromboplastin time were moderately prolonged. Prothrombin activity was 15-18% when measured using either the classical one-stage and two-stage assays, or assays with Echis carinatus venom or staphylocoagulase, whereas prothrombin antigen was 100%. In keeping with current nomenclature practices, the abnormal molecule has been designated prothrombin Salakta. The electrophoretic behaviour and calcium binding properties of the abnormal prothrombin did not differ significantly from normal, as assessed by crossed immunoelectrophoresis. Prothrombin Salakta was isolated by chromatography on DEAE-Sephadex and Dextran sulphate sepharose. Electrophoretic migration of purified prothrombin Salakta on SDS polyacrylamide gels or alkaline disc gels was normal. Upon activation by either bovine factor Xa or Echis carinatus venom, thrombin activity produced by prothrombin Salakta was only 15% of normal, even when the incubation period was prolonged for 24 hours. The pattern of factor Xa-catalyzed proteolysis of prothrombin Salakta, investigated by SDS polyacrylamide gel electrophoresis, was found to be normal. These results indicated that prothrombin Salakta was characterized by a defective thrombin enzymatic activity. Thrombin Salakta was therefore isolated by heparin-sepharose chromatography. Affinity for heparin and molecular weight of thrombin Salakta were found to be normal. Biological activity of thrombin Salakta, determined by clotting assay, was 535 u/mg versus 3 200 u/mg for normal thrombin. Amidolytic activity of thrombin Salakta parallelled its clotting activity, suggesting that the defect resides either in the catalytic site or in the residues adjacent to the catalytic site and implicated as contact residues, rather than in the fibrinogen recognition site.

Anti-spectrin in sera containing smooth muscle autoantibodies from patients with chronic active hepatitis

Sera from patients with chronic active hepatitis containing anti-smooth muscle autoantibodies (SMA) react against rabbit muscle actin as well as human red cell spectrin. These anti-spectrin antibodies recognize the same antigen as rabbit anti-human spectrin antibodies and are not involved in the staining pattern given by SMA-containing sera tested with smooth muscle sections. These anti-spectrin antibodies probably recognize an antigenic structure common to both spectrin and another as yet undetermined molecule (which however is not likely to be myosin).

Congenital deficiency of blood clotting factors II, VII, IX, and X

A patient congenitally deficient in factors II, VII, IX, and X has been further investigated after a follow-up of 15 yr. At birth, these factors, when determined by clotting assays, were undetectable. Following therapy with vitamin K1, the clotting activity of these factors rose but never exceeded 18% of normal. Immunologic assays revealed much higher levels of these factors than did clotting assays, thus suggesting that the vitamin-K-dependent factors were present in abnormal forms. Two-dimensional crossed immunoelectrophoresis showed that at least two forms of prothrombin were present in the patient's plasma. One form was similar to normal prothrombin; the other had the same mobility as acarboxyprothrombin. In addition, the majority of this fast-migrating peak was not adsorbable onto insoluble barium salts. These observations suggested that some molecules of the patient's prothrombin lacked the normal complement of gamma-carboxyglutamic acid residues. This observation was confirmed by a specific assay for gamma-carboxyglutamate. Since malabsorption of vitamin K, warfarin intoxication, and hepatic dysfunction were excluded as causes of this patient's syndrome, this rare congenital abnormality could represent either a defective gamma-carboxylation mechanism within the hepatocyte or faulty vitamin K transport.

The mechanism of activation of human prothrombin by an activator isolated from Dispholidus typus venom

Purified human prothrombin was activated, both in the absence and in the presence of thrombin inhibitors (diisopropylfluorophosphate or hirudin), by a coagulant principle isolated from Dispholidus typus venom. The process of activation was monitored by sodium dodecyl sulfate polyacrylamide gel electrophoresis. In the absence of thrombin inhibitor, prolonged incubation of prothrombin with the purified venom yielded thrombin, fragment 1 (F 1) and fragment 2 (F 2). In the presence of diisopropylfluorophosphate, which in the experimental conditions used inhibited only partially the thrombin generated activity, products obtained upon activation of prothrombin by venom were F 1 and a two-chain, disulfide-bridged protein of 58 000 daltons called meizothrombin (des F 1). In the presence of hirudin, which fully inhibited thrombin generated activity, prothrombin activation by the venom did not liberate any fragment, but prothrombin was converted to a derivative composed of two disulfide-bridged polypeptide chains of 48 000 and 37 000 daltons, called meizothrombin. These results are similar to those reported by others when studying the process of prothrombin activation by Echis carinatus venom and allow to conclude that Dispholidus typus venom cleaves a bond linking the A and B chains of thrombin, converting prothrombin into meizothrombin. This enzyme is then responsible for the cleavage of the bond linking F 1 and F 2 and the bond linking F2 the A chain of thrombin.