The myeloperoxidase product, hypochlorous acid, reduces thrombus formation under flow and attenuates clot retraction and fibrinolysis in human blood

Hypochlorite (HOCl), a strong oxidant and antimicrobial agent, has been proposed to be associated with hemostatic abnormalities during inflammatory response. However, its complex impact on hemostasis is not completely understood. In this report we studied the effect of clinically relevant (micromolar) HOCl concentrations on thrombus formation under flow, kinetics of platelet-fibrin clot formation, its architecture, retraction, and lysis. We found that HOCl (up to 500 µM) did not affect kinetics of coagulation measured in whole blood. HOCl (500-1000 µM) markedly diminished thrombus formation under flow. Clot retraction rate was reduced by HOCl dose-dependently (50-500 µM). HOCl (125-500 µM) inhibited fibrinolysis in whole blood and in platelet-depleted plasma, dose-dependently. Activity of plasmin was reduced by HOCl at concentrations started from 500 µM. HOCl (up to 500 µM) did not reduce plasminogen binding to fibrin under flow. HOCl (125-500 µM) modulated architecture of fibrin- and platelet-fibrin clots towards structures made of thin and densely packed fibers. Exposure of pure fibrinogen to HOCl (10-1000 µM) resulted in formation of dityrosine and was associated with altered fibrin structure derived from such modified fibrinogen. HOCl-altered fibrin net structure was not related with modulation of platelet procoagulant response, thrombin generation, and factor XIII activity. We conclude that, in human blood, clinically relevant HOCl concentrations may inhibit thrombus formation under flow, clot retraction and fibrinolysis. Fibrinolysis and clot retraction seem to be the most sensitive to HOCl-evoked inhibition. HOCl-modified fibrinogen and altered clot structure associated with it are likely to be primary sources of attenuated fibrinolysis.

[Evaluation of haemostasis in children treated with valproic acid]

Coagulation parameters were determined in children with valproic acid mono- and valproic acid-lamotrigin combination therapy.

PATIENTS, METHODS

Monotherapy group (n = 22; mean age: 10.5 years) was compared to combination therapy (n = 7; 12.9 years) and a control group (n = 22; 8.7 years). The following parameters were measured: aggregation and ATP-release in whole blood (ADP: 20 μmol/l, collagen: 1 μg/ml, thrombin: 0.5 U/ml), PFA-100® closure times (CT), blood cell counts, global tests, VWF:Ag, VWF:CBA, factors VIII and XIII as well as fibrinogen. Bleeding symptoms were evaluated by using a questionnaire.

RESULTS

For ADP- and collagen-induced aggregation as well as for ATP release no significant differences between the groups were detected. The combined therapy group showed significantly prolonged CT. Von Willebrand disease was not detected in any of the patients. The platelet count was significantly decreased in the monotherapy group. In six children a mild bleeding tendency was observed, mostly epistaxis.

CONCLUSION

A clinically relevant influence of valproic acid on haemostasis was found only in few cases. However, before surgical procedures an extended coagulation diagnostics is recommended in patients with valproic acid therapy.

Residual iliofemoral thrombosis in a 31-year-old woman on oral contraceptives possessing heterozygous factor V Leiden, factor XIII Val34Leu allele and alpha-fibrinogen Thr312Ala allele: case report

We present the case of a 31-year-old woman on oral contraceptives with a 3-year history of iliofemoral thrombosis resistant to recanalization despite satisfactory anticoagulation therapy and absence of concomitant diseases. Thrombophilia screening revealed heterozygous factor V Leiden mutation. We also detected the presence of factor XIII (FXIII) Leu34 allele and alpha-chain fibrinogen 312Ala allele, which are known to adversely affect fibrin clot structure and lysis. It might be speculated that the presence of 3 polymorphisms in this patient could contribute to proximal thrombosis resistant to treatment. We postulate that determination of FXIII and alpha-fibrinogen polymorphisms can be useful in the evaluation of some young patients with deep vein thrombosis.

The effect of acetaldehyde on human plasma factor XIII function

The effect of acetaldehyde on the transglutaminase activity in pooled normal human plasma has been investigated. In this study, 0.05, 0.2, and 0.7 ml of pooled human plasma were preincubated for 30 min. at room temperature with buffer or acetaldehyde at final concentrations of 40.6, 22.4, and 11.2 mM before being utilized for Factor XIIIa assay with fibrinogen and thrombin which had been preheated at 40 degrees C to destroy endogenous Factor XIII/XIIIa activity. At all concentrations of acetaldehyde and all concentrations of plasma-containing Factor XIII which were employed, prolongation of both clotting time and stabilization time was observed. The 11.2 mM acetaldehyde is within the range of daily acetaldehyde production to be predicted in severe alcoholics as a consequence of imbibing alcohol. The stabilization times measured for Factor XIIIa activity appear to be the most sensitive to acetaldehyde compared to acetaldehyde effects on thrombin, Factor Xa, and fibrinogen studied earlier in this laboratory, as well as Factors II, VII, and X.

Purification and properties of a coagulant thrombin-like enzyme from the venom of Bothrops leucurus

A thrombin-like enzyme from Bothrops leucurus venom, named leucurobin (leuc), was purified by gel filtration, affinity and ion exchange chromatographies. Physicochemical studies indicated that the purified enzyme is a 35 kDa monomeric glycoprotein on SDS-PAGE under reducing conditions, which decreased to 29 kDa after deglycosylation with N-glycosidase F (PNGase F). The amino acid sequence of leuc was determined by automated sequencing of the intact native protein and peptides produced by digestion of the S-pyridyl-ethylated protein with trypsin. The protein sequence exhibits significant similarities with other serine proteases reported from snake venoms, and contains two potential sites of N-linked glycosylation. The proteinase split off fibrinopeptide A (FPA) rapidly from human fibrinogen; however, only negligible traces of fibrinopeptide B (FPB) were observed. In addition, the enzyme released the N-terminal peptide (Mr=4572) containing the first 42 residues from the Bbeta-chain. Leuc could neither activate factor XIII nor release kinins from heat-treated bovine plasma. Its specific clotting activity was equivalent to 198 NIH thrombin U/mg on human fibrinogen. Kinetic properties of leuc were determined using representative chromogenic substrates. The enzyme evoked the gyroxin syndrome when injected into the tail veins of mice at levels of 0.143 microg/g mouse. The inhibitory effects of PMSF and benzamidine on the amidolytic activity suggest that leuc is a serine proteinase, and inhibition by beta-mercaptoethanol revealed the important role of the disulfide bonds in the stabilization of the native structure. Antibothropic serum, SBTI and EDTA had little or no effect on its amidolytic activity. However, the clotting effect of the enzyme was strongly inhibited by antibothropic serum. A Dixon plot showed that the hydrolysis of Bz-L-Arg-pNA by leuc was competitively inhibited by benzamidine (Ki=1.61+/-0.25 mM).

Coagulation factor XIII reduces postoperative bleeding after coronary surgery with extracorporeal circulation

BACKGROUND

One cause of diffuse bleeding after cardiac operations may be a low plasma concentration of coagulation Factor XIII, which is essential for coagulation but is not covered by standard coagulation monitoring.

PATIENTS AND METHODS

In a prospective, randomized, double blinded study, 2500 units, 1250 units, and a placebo were administered in groups of 25 patients each, immediately after administration of protamine. Postoperative amount of blood loss and blood transfusion was recorded.

RESULTS

Patients were not statistically different with respect to the course of plasma levels of Factor XIII until administration of the study drug. In all groups Factor XIII fell from preoperative normal values to subnormal values after extracorporeal circulation. After administration of the study drug, Factor XIII increased to 71 %, 85 %, 103 % in the placebo, 1250 units, and 2500 units group, respectively, and these differences were statistically significant ( p < 0.05). Postoperative blood loss was lowest in the 2500 units group and highest in the placebo group, however this was not significantly different. There was also no significant difference in the amount of blood transfusion. After differentiating all patients according to their post medication Factor XIII level into two groups with levels of < 70 % and > or = 70 %, postoperative blood loss was found to be significantly higher in the < 70 % group as was the amount of blood transfusions.

CONCLUSIONS

Factor XIII administration reduces postoperative blood loss and the extent of blood transfusion after coronary surgery, however administration is only helpful if plasma levels are below the normal value. Measurement of plasma levels is recommended before Factor XIII substitution.

Valproate induces reversible factor XIII deficiency with risk of perioperative bleeding

The antiepileptic drug valproic acid (VPA) induces subclinical changes in both the intrinsic and extrinsic coagulation system. However, fatal bleeding is very rare. This study reports a 39-year-old patient who underwent selective amygdalohippocampectomy because of drug-resistant temporal lobe epilepsy. Preoperatively, the patient was on a combined therapy with VPA and topiramate, and routine coagulation laboratory parameters were entirely normal. Epilepsy surgery was immediately followed by severe intracranial bleeding events which promped repeated craniectomy. Extensive laboratory analyses revealed a factor XIII activity level of 17%, indicating factor XIII deficiency confirmed by a reduced XIIIA-antigen. After termination of treatment with VPA, factor XIII levels returned to normal. Control examinations after 9 and 24 months showed normal range values for all coagulation parameters, including factor XIII, platelet function, and von Willebrand factor. To our knowledge, this case is the first description of a well-documented, clinically relevant transient factor XIII-deficiency syndrome related to VPA treatment.

Characterization of a thrombin-like enzyme from the venom of Trimeresurus jerdonii

From the venom of Trimeresurus jerdonii, a distinct thrombin-like enzyme, called jerdonobin, was purified by DEAE A-25 ion-exchange chromatography, Sephadex G-75 gel filtration, and fast protein liquid chromatography (FPLC). SDS-PAGE analysis of this enzyme shows that it consists of a single polypeptide chain with a molecular weight of 38,000. The NH(2)-terminal amino acid sequence of jerdonobin has great homology with venom thrombin-like enzymes documented. Jerdonobin is able to hydrolyze several chromogenic substrates. The enzyme directly clots fibrinogen with an activity of 217 NIH units/mg. The fibrinopeptides released, identified by HPLC, consisted of fibrinopeptide A and a small amount of fibrinopepide B. The activities of the enzyme were inhibited by phenylmethylsulfonyl fluoride (PMSF) and p-nitrophenyl-p-guanidinobenzoate (NPGB). However, metal chelator (EDTA) had no effect on it, indicating it is venom serine protease.

Effect of Tween 20 on freeze-thawing- and agitation-induced aggregation of recombinant human factor XIII

Agitation- and freeze-thawing-induced aggregation of recombinant human factor XIII (rFXIII) is due to interfacial adsorption and denaturation at the air-liquid and ice-liquid interfaces. The aggregation pathway proceeds through soluble aggregates to formation of insoluble aggregates regardless of the denaturing stimuli. A nonionic surfactant, polyoxyethylene sorbitan monolaurate (Tween 20), greatly reduces the rate of formation of insoluble aggregates as a function of surfactant concentration, thereby stabilizing native rFXIII. Maximum protection occurs at concentrations close to the critical micelle concentration (cmc), independent of initial protein concentration. To study the mechanistic aspects of the surfactant-induced stabilization, a series of spectroscopic studies were conducted. Electron paramagnetic resonance spectroscopy indicates that binding is not occurring between Tween 20 and either the native state or a folding intermediate state of rFXIII. Further, circular dichroism spectroscopy suggests that Tween 20 does not prevent the secondary structural changes induced upon guanidinium hydrochloride-induced unfolding. Taken together, these results imply that Tween 20 protects rFXIII against freeze-thawing- and agitation-induced aggregation primarily by competing with stress-induced soluble aggregates for interfaces, inhibiting subsequent transition to insoluble aggregates.

Factor XIII deficiency: pathogenic mechanisms and clinical significance

Congenital factor XIII deficiency is a rare disease, but has provided valuable information on the physiological role of factor XIII and the benefit of factor XIII replacement therapy. It could be shown that not only homozygous patients but also heterozygotes are at risk for bleeding complications. Acquired factor XIII deficiency, however, is much more common, and preliminary studies suggest a lack of factor XIII to be an important feature of various diseases. In acute states and severe hemorrhages, replacement therapy with factor XIII concentrates is recommended. Recent progress in assay methods and future clinical studies should help to evaluate the therapeutic potential of factor XIII.

Domain structure, stability and domain-domain interactions in recombinant factor XIII

The process of heat denaturation of recombinant factor XIII (rFXIII), as well as its C-terminal 24 kDA and 12 kDa elastase-produced fragments starting at Ser514 and Thr628, respectively, was investigated in a wide range of conditions by fluorescence, CD and differential scanning calorimetry (DSC). It was found that the intact protein melts in two distinct temperature regions reflecting unfolding of different parts of the molecule with different stability. The less stable structures unfold in a low temperature transition with a tm of 69 degrees C or lower depending on conditions. Unfolding of the more stable structures was observed at extremely high temperatures, tm > 110 degrees C at acidic pH < 3.5 and tm = 90 degrees C at pH 8.6 with 2 M GdmCL. Thermodynamic analysis of the low and high temperature DSC-obtained heat absorption peaks indicated unambiguously that the first represents melting of three thermolabile independently folded domains while two thermostable domains melt in the second one giving a total of five domains in each a subunit of rFXIII. Both 24 kDa and 12 kDa fragments exhibited a sigmoidal spectral transition at comparatively high temperature where the thermolabile structures are already denatured, indicating that two thermostable domains are formed by the C-terminal portion of rFXIII and correspond to the two beta-barrels revealed by crystallography. The remaining 56 kDa portion forms three thermolabile domains, one of which corresponds to the N-terminal beta-sandwich and the other two to the catalytic core. Fast accessible surface calculations of the X-ray model of rFXIII confirmed the presence of two structural subdomains in the core region with the boundary at residue 332. The thermolabile domains appear to interact with each other intra- and/or intermolecularly resulting in dimerization the a subunits. At acidic pH, where all domains became destabilized but still remained folded, interdomainial interactions seemed to be abolished, resulting in the reversible dissociation of the dimer as revealed by ultracentrifugation analysis.

Alpha-thrombin-catalyzed activation of human platelet factor XIII: relationship between proteolysis and factor XIIIa activity

The kinetics of activation of platelet factor XIII, an a-subunit dimer, were characterized by determining rate constants for activation peptide (AP) release, generation of activity, and exposure of the active-site thiol group. The specificity constant (kappacat/Km) for alpha-thrombin-catalyzed AP release, 1.2 x 10(5) M-1s-1, was found to be similar to that for AP release from the tetramer plasma factor XIII (a2b2) [Janus, T.J., Lewis, S. D., Lorand, L., & Shafer, J. A. (1983) Biochemistry 22, 6269-6272], implying that the b subunits of plasma factor XIII do not hinder alpha-thrombin-catalyzed cleavage of AP from the a subunit. Platelet factor XIIIa activity was generated at a rate approximately twice the rate of AP release. This difference in rates was shown to be consistent with a reaction pathway for activation of platelet factor XIII wherein full factor XIIIa activity is generated when one AP is removed from the dimeric zymogen so that removal of the second AP has no detectable effect on catalytic activity. In accord with this conclusion, the rate constant for exposure of the active-site thiol group, as measured by the incorporation of [1-14C]-iodoacetamide, was about twice that observed for the removal of AP.(ABSTRACT TRUNCATED AT 250 WORDS)