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PubMed1990

The polymerization and thrombin-binding properties of des-(B beta 1-42)-fibrin.

Multiple factors affect the thrombin-catalyzed conversion of fibrinogen to fibrin, including: fibrinopeptide (FPA and FPB) release leading to exposure of two types of polymerization domains ("A" and "B," respectively) in the central portion of the molecule, and exposure of a noncatalytic "secondary" thrombin-binding site in fibrin. Fibrinogen containing the FPA sequence but lacking the B beta 1-42 sequence ("des-(B beta 1-42)-fibrinogen"), was compared to native fibrinogen (containing both FPA and FPB) to investigate the role played by B beta 1-42 in the polymerization of alpha-fibrin (i.e. fibrin lacking FPA), to compare reptilase and thrombin cleavage of FPA from fibrinogen, and to explore the location and function of the secondary thrombin-binding site. Electron microscopy of evolving polymer structures (mu, 0.14; pH 7.4) plus turbidity measurements, showed that early thin fibril formation as well as subsequent lateral fibril associations were impaired in des-(B beta 1-42)-alpha-fibrin, thus indicating that the B beta 1-42 sequence contributes to the A polymerization site. Reptilase-activated des-(B beta 1-42)-alpha-fibrin polymerized even more slowly than thrombin-activated des-(B beta 1-42)-alpha-fibrin, differences that disappeared when repolymerization of preformed fibrin monomers was carried out. Since existing data indicate that thrombin releases FPA in a concerted manner, resulting in relatively rapid evolution of fully functional divalent alpha-fibrin monomers, it can be inferred that delayed fibrin assembly of reptilase fibrin is due to slower formation of divalent alpha-fibrin monomers. Thrombin-activated des-(B beta 1-42)-alpha-fibrin polymerized more rapidly at low ionic strength (mu, 0.04) than did native alpha,beta-fibrin, a reversal of their behavior at physiological ionic strength (mu, 0.14). Concomitant measurement of FPA release revealed modest slowing of release at low ionic strength from des-(B beta 1-42)-fibrinogen (t1/2, 36.5 versus 21.5 min) and marked slowing from native fibrinogen (t1/2, 138 versus 22.2 min). This behavior correlated with increased thrombin binding to native alpha,beta-fibrin at low ionic strength, coupled with weak thrombin binding to des-(B beta 1-42)-alpha-fibrin, and indicates that secondary thrombin binding plays an important role in regulating thrombin diffusion and catalytic activity. Des-(B beta 1-42)-fibrinogen lacks or has a markedly defective secondary thrombin-binding site, from which we conclude that the B beta 15-42 sequence in fibrin plays a major role in forming or providing this site.

Batroxobin↗
PubMed1985

Regulation of plasma factor XIII binding to fibrin in vitro.

The binding of plasma factor XIII to fibrinogen or fibrin that has been chemically or enzymatically induced to polymerize was studied. Factor XIII binding was assayed using a 3H-putrescine incorporation assay and an 125I-plasma factor XIII binding assay. More than 80% of the native and radiolabeled plasma factor XIII was bound to fibrin I formed by reptilase in EDTA, citrate, or heparin anticoagulated plasma. Plasma factor XIII and 125I-factor XIII was bound (89.6% to 92.5%) to fibrin II formed by thrombin in either citrate or EDTA anticoagulated plasma. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of 125I-plasma factor XIII bound to fibrin I or fibrin II formed by reptilase or thrombin in the presence of EDTA demonstrated the b2-subunit remained bound to the a-chains or thrombin-cleaved a-chains. In the presence of calcium chloride and thrombin, the b2-subunit dissociated and factor XIIIa was bound. Protamine sulfate caused fibrinogen polymerization in the absence of divalent cations and reduced both plasma factor XIII and immunologic fibrinogen levels. Fibrinogen polymerized by protamine sulfate bound plasma factor XIII and the a2-subunit of 125I-platelet factor XIII. Plasma factor XIII was also bound to sonicated non-cross-linked fibrin II in either normal plasma or afibrinogenemic plasma. Plasma levels of several coagulation proteins were unchanged after the addition of reptilase, protamine sulfate, or sonicated fibrin to plasma. These results demonstrate that a specific binding site for the a2-subunit of plasma factor XIII is present on polymerized fibrinogen, fibrin I, and fibrin II. Furthermore, the presence of divalent cations, thrombin-cleavage of plasma factor XIII, and release of fibrinopeptides A or B are not required for plasma factor XIII binding to polymerized fibrinogen and fibrin.

Antithrombins↗
PubMed1986

Effect of hydroxyethyl starch on the structure of thrombin- and reptilase-induced fibrin gels.

The effect of hydroxyethyl starch (HES), a complex polysaccharide colloid plasma expander, on the structure of fibrin gels was studied turbidimetrically. HES at concentrations as low as 2.5 mg/ml shortened the lag phase of turbidity increase and caused increased fibrin fiber mass/length ratios in both purified fibrin and plasma systems. For purified fibrin gels clotted with thrombin the mass/length ratio increased in a linear fashion from 2.6 to 6.1 X 10(12) daltons/cm as HES increased from 0 to 15 mg/ml. Fiber mass/length ratios for purified fibrin gels clotted with reptilase increased from 1.1 to 6.4 X 10(12) daltons/cm over the same HES concentration range. The addition of 5 mmol/L calcium to either system produced additional increases in fiber size. In 1:10 dilutions of plasma, HES shortened the lag phase, enhanced the rate of turbidity increase, and increased the final gel turbidity. The fiber mass/length ratio for plasma gels clotted with thrombin increased from 0.3 to 1.7 X 10(12) daltons/cm as HES increased from 0 to 20 mg/ml. For plasma gels clotted with reptilase, the fiber mass/length ratio increased from 1.5 to 2.4 X 10(12) daltons/cm over the same HES concentration range. The effects of HES are comparable to those of dextran at concentrations less than 5 mg/ml and can be explained on the basis of HES-enhanced lateral association of fibrin fibers during polymerization.

Batroxobin↗
PubMed1989

Effect of glycosaminoglycans on thrombin- and atroxin-induced fibrin assembly and structure.

This study was performed to quantitate the impact of several glycosaminoglycans (GAG) on fibrin assembly and structure. Gel formation was monitored as the increase in optical density at 633 nm subsequent to thrombin (2 NIH u/ml) or atroxin (0.10 mg/ml) addition to solutions of buffered fibrinogen (1 mg/ml) or plasma. Gel absorbance was measured as a function of wavelength (400 to 800 nm) and gel fiber diameter and mass/length ratio (mu) were calculated. Chondroitin sulfate A (CSA) shortened the lag phase, enhanced the maximal rate of turbidity increase, and increased the final gel turbidity of fibrin gels formed by thrombin or atroxin. CSA (16 mg/ml) increased fiber mu from 1.3 to 3.1 x 10(13) dalton/cm and fiber radius from 6.0 to 8.6 x 10(-6) cm in thrombin-induced gels. Mu increased from 0.7 to 2.7 x 10(13) dalton/cm and fiber radius from 4 to 7.8 x 10(-6) cm for atroxin-induced gels. Above 16 mg/ml, CSA caused fibrinogen precipitation in purified solutions but not in plasma. CSA inhibited thrombin-induced plasma clotting of plasma but effects in atroxin-mediated plasma gels paralleled those seen in purified solutions. Chondroitin sulfate B (CSB)-induced changes in fibrin were similar but slightly less dramatic than those seen with CSA. Mu increased from 0.9 to 2.0 x 10(13) dalton/cm for atroxin-induced fibrin gels and from 0.8 to 2.3 x 10(13) dalton/cm for atroxin-induced gels. Low molecular weight heparin (Mr = 5100) slowed fibrin assembly and reduced fiber size by 50% in thrombin-induced gels. Changes in mu of atroxin-induced gels were much less pronounced (less than 20%).(ABSTRACT TRUNCATED AT 250 WORDS)

Batroxobin↗
PubMed1989

[Therapeutic effect of defibrase in chronic glomerulonephritis with chronic renal failure].

When chronic glomerulonephritis (CGN) proceeds to chronic renal failure (CRF), there are decline of fibrinolytic activity and deposition of fibrin in glomeruli with resulting thromboembolic lesions. 46 CGN patients with complicating CRF were thus treated with defibrase made from viper venom. Defibrase in a dose of 0.025 unit/kg dissolved in 250 ml 10% glucose was infused slowly once every 3 days in a total of 6 times. After the treatment, BUN and serum creatinine levels decreased, creatinine cleance improved and the clinical manifestations of uremia alleviated or disappeared. In some patients there were increase of hemoglobin concentration and decrease of urinary protein excretion. Hypertension was controlled in 17 out of 20 patients treated in combination with captopril. Level of plasma fibrinogen was significantly reduced after defibrase administration, but the reduction was not related to the therapeutic effect. Urinary output was increased in most of the patients, being related to the therapeutic effect. The authors are of the opinion that renal function may be improved in CGN patients after defibrase treatment due probably to elimination of fibrin deposition and resolution of thromboembolic lesions in glomeruli. However, a suitable dose has to be determined as there is no effective way to monitor the most dreaded complication of defibrase therapy bleeding.

Adolescent↗
PubMed1988

[Effect of fibronectin on fibrinogen conversion into fibrin].

The effects of fibronectin on fibrinogen clotting induced by thrombin or reptilase and on fibrin monomer polymerization in a pure system in the absence of factor XIIIa were studied. It was shown that within a broad range of concentrations and molar ratios of the mixed proteins, fibronectin does not alter significantly the fibrinogen clotting time either under thrombin or under reptilase action. The effect of fibronectin on the fibrin self-assembly consists in a slight acceleration of this process, whose degree is directly dependent on the fibronectin/fibrin monomer molar ratio as well as on the absolute fibrin monomer content at a constant molar ratio. The stimulating effect of fibronectin is amplified by Ca2+. The experimental results suggest that fibronectin can noncovalently bind the fibrin monomer and/or intermediate polymers in the non-enzymatic phase of fibrinogen conversion to fibrin.

Batroxobin↗
PubMed1987

Comparison of the thrombolytic efficacy of defibrase and urokinase on canine coronary artery thrombosis and the mechanism of urokinase-induced hemorrhage.

The thrombolytic efficacy of defibrase (DF) and urokinase (UK) was evaluated and compared in a canine model in which left circumflex coronary artery (LCX) thrombus formation was initiated by electrical stimulation (150 UA, DC) of the arterial intimal surface via an implanted copper wire electrode. Forty-eight mongrel dogs were equally divided into 8 groups: six groups for both intravenous (iv) and intracoronary (ic) infusion of DF, UK and normal saline 30 min after complete obstruction by a LCX thrombus, the remaining two groups for iv infusion DF and UK 360 min after occlusion. Results showed that in the control groups no LCX recanalization after infusion occurred, but all the treated groups recanalized when drug infusion started 30 min after occlusion. Thrombus wet weight and infarct size were much higher in the control group. No significant differences were found between treated groups except that the recanalizing speed was fastest by ic UK with the highest occurrence rate of reperfusion arrhythmia. For 6-hour-old thrombi, DF was more effective than UK for recanalization. Thrombus wet weight and infarct size were lower in the recanalized dogs. Both agents reduced plasma plasminogen and fibrinogen significantly but serious incision bleeding was only found in the UK group. In order to study the mechanism underlying UK-induced hemorrhage, we observed the influences of UK and DF on blood coagulation factors in another 12 dogs. Results showed that DF only reduced factor 1 while UK additionally reduced coagulation factors 2, 7, 8 and 10, indicating that the non-selective depletive effect on coagulation factors may be one of the mechanisms of UK-induced hemorrhage. We conclude that both DF and UK can lyse fresh coronary thrombi, DF was more effective than UK on lysing older thrombi, considering its convenient use and less frequency of side effects, DF is therefore considered a more promising agent clinically.

Animals↗
PubMed1987

The impact of delayed fibrinopeptide-A release on fibrin structure. Studies of an abnormal fibrinogen.

The impact of delayed fibrinopeptide-A release on polymerization and structure of fibrin gels was studied utilizing a heterozygously transmitted variant fibrinogen. An arginine to histidine substitution at position 16 of the alpha chain of the abnormal fibrinogen delayed release of an abnormal fibrinopeptide-A (A) by thrombin and completely blocked release of A by reptilase. When clotted with thrombin, patient fibrin formed more slowly than normal fibrin, but clottability was normal and gel fiber mass/length ratios were decreased less than 10%. Gels formed with reptilase clotted slowly, demonstrated reduced clottability, but had normal fiber mass/length ratios. Reptilase clotted the normal but not the variant component of the patient fibrinogen. Thrombin-induced cleavage of fibrinopeptide-B prior to A occurred in these experiments, but polymerization of this species beyond trimers has been reported to be minimal under the conditions used. With time, A is removed by thrombin resulting in the slow production of normal fibrin monomer from the abnormal component. These monomers subsequently polymerize. The minimal change in gel fiber size caused by slow A release implies that fibrin fiber size is primarily a function of ionic environment and not of the sequence of peptide release.

Arginine↗
PubMed1979

The effect of prophylaxis with low dose heparin on blood coagulation parameters. A double blind study in connection with transvesical prostatectomy.

Heparin was administered subcutaneously 5.000 IU twice daily using a double blind method to ten of twenty-one patients undergoing transvesical prostatectomy. Platelet count, APTT, throbin time, Reptilase time, Normotest, fibrinogen, Factor-VIII, ethanol gelation test, antithrombin III, fibrinolytic degradation products, alpha1-antitrypsin and alpha2-macroglobulin were studied pre- and postoperatively up to the 10th postoperative day. Statistical analysis of parameters of blood coagulation and fibrinolysis showed no significant difference between the two groups. The mechanism by which low dose heparin exerts its thromboprophylactic effect could not be elucidated from the study of the investigated parameters. The laboratory data gave no indication to a possible increased risk of postoperative hemorrhage.

Aged↗
PubMedDate not supplied

Therapeutic defibrinogenation in peripheral vascular disease.

Despite considerable uncontrolled clinical data implying a beneficial effect of defibrinogenation in peripheral vascular disease, this is not supported by double blind placebo controlled trials. A hypothetical explanation for this discrepancy is developed from experimental studies suggesting that in the absence of adequate shear forces defibrinogenation might induce occlusion of the impaired microcirculation and therefore can lead to an aggravation of tissue hypoxia.

Ancrod↗