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PubMed2002

[The relationship of beta-fibrinogen gene polymorphisms and ischaemic cardiocerebral vascular disease].

OBJECTIVE: To analyze the frequency of beta-fibrinogen (beta-Fg) gene -455G/A, -148C/T and 448G/A polymorphism, fibrinogen molecular reactivity and their association with plasma fibrinogen levels in health adults, myocardial infarction and cerebral infarction disease. METHODS: The beta-Fg gene -455G/A, -148C/T and 448G/A polymorphisms were analyzed by restriction fragment length polymorphism (RFLP). Fibrinogen molecular reactivity was analyzed for the conversion kinetics of fibrinogen into fibrin by a computer assistant procedure. Plasma fibrinogen levels were determined by Clauss method. RESULTS: The frequencies of -455A, -148T, 448A allele in health adults were 0.185, 0.194 and 0.192, in myocardial infarction disease 0.295, 0.318 and 0.307, in cerebral infarction disease 0.177, 0.193 and 0.182, respectively. The frequencies of -455A, -148T, 448A alleles in myocardial infarction disease were apparently higher than that of health adults. There were close linkage between -455G, -148C and 448G or -455A, -148T and 448A, the correspondence was over 98%. There are no differences in the plasma fibrinogen levels of the three polymorphisms in two genotype groups. The fibrinogen molecular reactivity was significantly increased in cardiocerebral vascular disease and related with plasma fibrinogen level. CONCLUSION: The three polymorphisms loci are strong linkage disequilibrium. There are no significant differences in the plasma fibrinogen levels of the three polymorphisms in two genotype groups. The frequencies of -455A, -148T, 448A alleles in myocardial infarction disease were apparently higher than that of health adults. It suggest that there was no association between beta-Fg gene -455G/A, -148C/T and 448G/A polymorphisms and plasma fibrinogen levels, but did in myocardial infarction disease. The fibrinogen molecular reactivity was significantly increased in cardiocerebral vascular disease and related with plasma fibrinogen level.

Adult↗
PubMed1991

Baboon fibrinogen adsorption and platelet adhesion to polymeric materials.

The role of fibrinogen in mediating platelet adhesion to polymers exposed to blood plasma was studied by comparison of the effect of plasma dilution on fibrinogen adsorption and platelet adhesion, and by the use of coagulation factor deficient plasmas. Polyetherurethane substrates were first preadsorbed with dilute plasma, then contacted with washed platelets suspended in a modified, apyrase containing Tyrode's buffer. Platelet adhesion was studied under static conditions in Multiwell dishes, and also under shearing conditions using a parallel plate perfusion chamber. Fibrinogen adsorption and platelet adhesion were measured using 125I radiolabeled baboon fibrinogen and 111In radiolabeled baboon platelets, respectively. Surfaces were characterized by electron spectroscopy for chemical analysis (ESCA). When fibrinogen adsorption to Biomer was measured after 2 h contact with a series of dilute plasma solutions under static conditions, a peak in adsorption was observed from 0.26% plasma, i.e., adsorption was greater from 0.26% plasma than from either more or less dilute plasma. A peak in subsequent platelet adhesion to the plasma preadsorbed surfaces, measured after 2 h static incubation with washed platelets, was also observed but occurred on Biomer preadsorbed with 1.0% plasma. When fibrinogen adsorption was measured after 5 min contact under shearing conditions, the fibrinogen adsorption peak occurred on surfaces that had been exposed to 1.0% plasma. A peak in platelet adhesion to these preadsorbed surfaces, measured after 5 min contact with the platelet suspensions under shearing conditions, was observed on Biomer preadsorbed with 0.1% plasma. Shifts between the positions of the peaks in protein adsorption and platelet adhesion occurred on other polymers tested as well. Platelet adhesion was almost completely inhibited when baboon and human plasmas lacking fibrinogen (i.e., serum, heat defibrinogenated plasma, and congenitally afibrinogenemic plasma) were used. Platelet adhesion was restored to near normal when exogenous fibrinogen was added to fibrinogen deficient plasmas. Adhesion was also inhibited completely when a monoclonal antibody directed against the glycoprotein IIb/IIIa complex was added to the platelet suspension. Platelet adhesion to surfaces preadsorbed to von Willebrand factor deficient plasma was the same as to surfaces preadsorbed with normal plasma. While it appears that surface bound fibrinogen does mediate the initial attachment of platelets to Biomer, the observation that the fibrinogen adsorption and platelet adhesion maxima do not coincide exactly also suggests that the degree of subsequent platelet adhesion is dictated not only by the amount of surface bound fibrinogen but also by its conformation.

Adsorption↗
PubMed1986

Expression of fibrinogen receptors during activation and subsequent desensitization of human platelets by epinephrine.

Epinephrine causes platelet aggregation and secretion by interacting with alpha 2-adrenergic receptors on the platelet surface. Platelet aggregation requires the binding of fibrinogen to a specific receptor on the membrane glycoprotein IIb-IIIa complex. Although the IIb-IIIa complex is identifiable on the surface of resting platelets, the fibrinogen receptor is expressed only after platelet activation. The current studies were designed to examine the effect of occupancy of platelet alpha 2-adrenergic receptors by epinephrine on the expression of fibrinogen receptors and on the aggregation of platelets. The ability of epinephrine to induce the expression of fibrinogen receptors was studied under two different conditions: acute stimulation (less than 1 min) and prolonged stimulation (50 to 90 min), the latter of which is associated with a reduction or "desensitization" of the platelet aggregation response. Expression of the fibrinogen receptor was monitored with 125I-fibrinogen as well as with 125I-PAC-1 (PAC-1), a monoclonal antibody that binds to the glycoprotein IIb-IIIa complex only after platelets are activated. Epinephrine caused an immediate increase in PAC-1 and fibrinogen binding that was dependent on occupancy of the alpha 2-receptor by epinephrine and on the presence of extracellular free Ca (KCa = 30 mumol/L). By itself, 1 mmol/L Mg was unable to support induction of the fibrinogen receptor by epinephrine. However, it did decrease the Ca requirement by about two orders of magnitude. Prolonged stimulation of unstirred platelets by epinephrine led to a 70% decrease in the aggregation response when the platelets were subsequently stirred. Despite their decreased aggregation response, desensitized platelets bound PAC-1 and fibrinogen normally, indicating that the loss of aggregation was not due simply to a decrease in fibrinogen receptor expression. Although desensitization was not affected by pretreatment of the platelets with aspirin, it was partially prevented when extracellular Ca was chelated by EDTA during the long incubation with epinephrine. These studies demonstrate that once platelet alpha 2-adrenergic receptors are occupied by epinephrine, extracellular Ca is involved in initiating the aggregation response by supporting the induction of the fibrinogen receptor and the binding of fibrinogen. Furthermore. Ca-dependent reactions subsequent to fibrinogen binding may be necessary for maximal platelet aggregation and are impaired when platelets become desensitized to epinephrine.

Antibodies, Monoclonal↗
PubMed1987

Binding and processing of fibrinogen by rabbit hepatocytes.

We describe a specific fibrinogen-hepatocyte interaction. Rabbit 125I-labeled fibrinogen (125I-FGN) was incubated at 4 degrees C with suspensions of rabbit hepatocytes (approximately 1 X 10(6) cells/ml). Bound ligand was separated from free by centrifugation of cells through oil and quantitated by gamma-scintillation counting. Specific binding, determined by subtraction of nonspecific binding in the presence of 8 mM EDTA from total binding in the presence of 2 mM CaCl2, required 3 h to plateau and represented approximately 70% of total binding. Specific binding was calcium-dependent and was negligible in buffer containing 2 mM MgCl2. Half-maximal saturation occurred at approximately 30 nM 125I-FGN with approximately 480,000 molecules/cell at saturation. Dilution experiments revealed comparable affinities for labeled and unlabeled fibrinogen. Total binding was irreversible as determined by addition of excess unlabeled fibrinogen or EDTA. Specific binding of 25 nM 125I-FGN was inhibited, in a concentration-dependent fashion, by unlabeled fibrinogen or fibrinogen fragment D95 (Mr = 95,000), but not by fibrinogen fragment E or Arg-Gly-Asp-containing peptides. Unlabeled fibrinogen (3.1 microM) completely abolished specific binding, whereas greater than 80% inhibition was achieved with 10 microM fragment D95. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and autoradiography of 125I-FGN bound in the presence of calcium demonstrated disappearance of A alpha chains with formation of products of Mr greater than 200,000; EDTA or unlabeled fibrinogen prevented fibrinogen processing. These data describe a unique fibrinogen-hepatocyte interaction which differs considerably from the platelet-fibrinogen interaction, especially with regard to the processing of the fibrinogen molecule.

Animals↗
PubMed1982

Identification of the fibrinogen receptor on human platelets by photoaffinity labeling.

Fibrinogen binding to receptors on stimulated platelets is a prerequisite for platelet aggregation. In order to identify the platelet fibrinogen receptor, we modified fibrinogen with the photoreactive, heterobifunctional cross-linking reagent methyl 4-azidobenzoimidate (MABI). MABI-fibrinogen was fully clottable and able to support platelet aggregation. To photoaffinity label the fibrinogen receptor, gel-filtered human platelets were incubated at 37 degrees C in the dark with 200 micrograms/ml of MABI-fibrinogen, 10 microM ADP, and 0.5 mM calcium. Irradiation of these platelets with ultraviolet light resulted in the incorporation of MABI-fibrinogen into the platelet surface. Incorporation could be prevented by excess native fibrinogen suggesting that MABI-fibrinogen had interacted with the fibrinogen receptor before photolysis. Examination of the irradiated platelets by sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that the photoactivated MABI-fibrinogen had been incorporated into a 105,000 molecular weight membrane polypeptide that also contained the PlA1 antigen. Thus, this polypeptide has the characteristics of the membrane glycoprotein IIIa. Previous studies have shown that thrombasthenic platelets lack this glycoprotein and fail to bind fibrinogen after stimulation by ADP. Consequently, our data suggest that glycoprotein IIIa constitutes at least one component of the platelet fibrinogen receptor.

Affinity Labels↗
PubMed1982

Kinetic and functional studies of platelets, fibrinogen, and plasminogen in patients with hepatic cirrhosis.

To assess the nature of the hemostatic abnormalities associated with chronic liver disease, we have simultaneously evaluated the kinetic of radiolabeled platelets, fibrinogen, and plasminogen, together wit tests of platelet and fibrinogen function, and coagulation factors in 60 patients with documented, severe but stable cirrhosis of the liver. The mean platelet survival was substantially reduced (5.8 +/- 1.7 days compared with 9.5 +/- 0.6 days in normals, p less than 0.0001) and splenic sequestration of platelets was increased (mean recovery was 47% +/- 18 vs. 65% +/- 5 in normals, p less than 0.0001). Nevertheless the mean platelet count was nearly normal because platelet production was increased nearly twice normal values (mean turnover was 64,000 +/- 33,000 platelets/microliter/day; p less than 0.0001). The mean rate of fibrinogen removal was shortened (p less than 0.0001) and fibrinogen turnover increased about 20% (p = 0.008) while the mean fibrinogen concentration was not different from the results in normal control subjects (p = 0.212). Autologous and homologous fibrinogen disappeared from the circulation at equivalent rates (r = 0.751; p = 0.008), indicating that fibrinogen from cirrhotic patients was not kinetically different from normal fibrinogen. The mean plasminogen survival was significantly shortened (p less than 0.0001), but the mean plasminogen turnover was not increased (p = 0.388). Thus the plasminogen concentration was reduced (p less than 0.0001). For platelets, fibrinogen, and plasminogen, the production rate was the most important determinant of the concentration in the circulation. The administration of heparin to cirrhotic patients improved the survival of fibrinogen but not of platelets. LeVeen valve implantation generally resulted in parallel shortening of both the platelet and fibrinogen survivals and concentrations. Platelet function as assessed by template bleeding time, platelet retention by glass bead columns, and aggregation induced by ADP, epinephrine, and collagen was normal. Fibrinogen determinations by the Clauss and Jacobsson techniques were equivalent, indicating that the ability to polymerize fibrin monomer was not detectably altered. Sixty percent of patients had an abnormal prothrombin time and half that number had a prolonged partial thromboplastin time. Although most patients had a modest decrease in the prothrombin complex coagulation factors, fibrin degradation products were, in general, not elevated in the circulation. The wide range of values observed suggests that a number of different and complex processes may be ongoing in different patients. Overall, the kinetic data suggest that platelets are initially consumed, perhaps on incompletely endothelialized endovascular surfaces in the liver, and that fibrin subsequently forms secondary to local stasis. The absence of increased production of fibrinogen and plasminogen despite shortened survival times reflects the reduced capability of the cirrhotic liver to increase protein synthesis.

Blood Platelets↗
PubMed1995

Regulation of platelet aggregation by post-fibrinogen binding events. Insights provided by dithiothreitol-treated platelets.

A variety of data suggest that fibrinogen binding is necessary but not sufficient for platelet aggregation: post fibrinogen binding events may play an important role. The present study compared fibrinogen binding and platelet aggregation in response to dithiothreitol (DTT) and ADP. DTT induced saturable and specific fibrinogen binding (Kd 0.07 + 0.02 microM, Bmax 15,000 + 3000 molecules/platelet) which supported complete platelet aggregation as determined by single platelet counting. The aggregates were small, however, and more readily dissociated by EDTA than their ADP-treated counterparts, despite quantitatively similar fibrinogen binding. Unlike fibrinogen bound to ADP-stimulated platelets, fibrinogen bound to DTT-treated platelets remained sensitive to dissociation by EDTA over a 3 h time course, retained its ability to support aggregation, even when aggregation was induced 60 min after the initial platelet exposure to fibrinogen, and remained accessible to polyclonal antibodies and plasmin. Confocal scanning laser microscopy showed only a surface clustering of fibrinogen bound to DTT-treated platelets over the 3 h time course compared to rapid fibrinogen clearing from the surface of ADP-stimulated platelets. These data suggest that post fibrinogen binding events involved in the stabilization of fibrinogen binding and/or the redistribution of bound fibrinogen may play important roles in regulating platelet aggregation.

Adenosine Diphosphate↗
PubMed1994

Adenosine diphosphate-induced aggregation of human platelets in flow through tubes: III. Shear and extrinsic fibrinogen-dependent effects.

The effect of shear rate and fibrinogen concentration on adenosine diphosphate-induced aggregation of suspensions of washed human platelets in Poiseuille flow at 23 degrees C was studied using a previously described double infusion technique and resistive particle counter size analysis. Using suspensions of multiple-centrifuged and -washed cells in Tyrodes-albumin [3 x 10(5) microliters-1; (17)] with [fibrinogen] from 0 to 1.2 microM, the rate and extent of aggregation with 0.7 microM ADP in Tyrodes-albumin were measured over a range of mean transit times from 0.2 to 43 s, and at mean tube shear rates, G, = 41.9, 335 and 1,335 s-1. As measured by the decrease in singlet concentration, aggregation at 1.2 microM fibrinogen increased with increasing G up to 1,335 s-1, in contrast to that previously reported in citrated plasma, in which aggregation reached a maximum at G = 335 s-1. Without added fibrinogen, there was no aggregation at G = 41.9 s-1; at G = 335 s-1, there was significant aggregation but with an initial lag time, aggregation increasing further at G = 1,335 s-1. Without added fibrinogen, aggregation was abolished at all G upon incubation with the hexapeptide GRGDSP, but was almost unaffected by addition of an F(ab')2 fragment of an antibody to human fibrinogen. Aggregation in the absence of added fibrinogen was also observed at 37 degrees C. The activation of the multiple-washed platelets was tested using flow cytometry with the fluorescently labelled monoclonal antibodies FITC-PAC1 and FITC-9F9. It was shown that 57% of single cells in unactivated PRT expressed maximal GPIIb-IIIa fibrinogen receptors (MoAb PAC1) and 54% expressed pre-bound fibrinogen (MoAb 9F9), with further increases on ADP activation. However, incubation with GRGDSP and the F(ab')2 fragment did not inhibit the prebound fibrinogen. Moreover, relatively unactivated cells (8% expressing receptor, 14% prebound fibrinogen), prepared from acidified cPRP by single centrifugation with 50 nM of the stable prostacyclin derivative, ZK 36,374, and resuspension in Tyrodes-albumin at 5 x 10(4) microliters-1, aggregated with 2 and 5 microM ADP at G = 335 and 1,335 s-1 in the absence of added fibrinogen. We therefore postulate that a protein such as von Willebrand factor, secreted during platelet isolation or in flow at sufficiently high shear rates, may yield the observed shear-rate dependent aggregation without fibrinogen.

Adenosine Diphosphate↗
PubMed1993

Catabolism of unglycated and naturally glycated forms of rabbit fibrinogen: their interaction with the healthy and deendothelialized aorta wall in normal and diabetic rabbits.

The incidence of nonenzymatic glycation of proteins within the hyperglycemic environment of diabetic plasma is increased compared with that in normal (i.e., nondiabetic) plasma. Whether glycation in vivo alters the behavior of proteins within the circulation is not well understood. Glycated fibrinogen, although not detected in normal rabbit plasma, was isolated from diabetic rabbit plasmas (glucose concentration 12 to 39 mmol/L) and separated from unglycated fibrinogen by boronate chromatography. The yield of glycated fibrinogen, which amounted to 3% to 6% of total fibrinogen, correlated with the content of plasma glucose. Glycated and unglycated fibrinogens facilitated aggregation of normal or diabetic platelets to a similar extent after adding adenosine-5'-diphosphate. Normal platelets stimulated by adenosine-5'-diphosphate bound more iodine 131-glycated fibrinogen than iodine 125-unglycated fibrinogen (p < 0.05), whereas the quantities of glycated and unglycated fibrinogens bound by diabetic platelets were not significantly different. When coinjected intravenously into normal or diabetic rabbits, 131I-glycated fibrinogen was cleared from the circulation faster than 125I-unglycated fibrinogen although the catabolic rates, measured as half-life, were not significantly different. At equilibrium, glycated fibrinogen was distributed significantly more in the extravascular and less in the vascular compartments of the normal and diabetic rabbit compared with the unglycated type. After balloon injury to the aorta in vivo, the unglycated/glycated ratio of radiolabeled fibrinogens associated with the platelet monolayer was 0.94, whereas for the damaged subendothelium the ratio was 1.20 (p < 0.005). We conclude that glycation in vivo changes several metabolic characteristics of fibrinogen in the normal and diabetic rabbit.

Animals↗
PubMed1993

Unusual A alpha 16Arg-->Cys dysfibrinogenaemic family: absence of normal A alpha-chains in fibrinogen from two of four heterozygous siblings.

We describe studies of fibrinogen from an asymptomatic family, Fibrinogen Frankfurt XIII, with the substitution A alpha 16Arg-->Cys. The mother's fibrinogen was normal as assessed by plasma fibrinogen assays but the father and four children were affected. Two affected siblings and their father had thrombin times approximately 20 s longer than controls, fibrinogen of 35-52 mg/dl by clotting assay and normal levels by immunoassay. Measured by HPLC their fibrinogen had decreased amounts of releasable fibrinopeptide A (FpA) relative to normal controls. In addition, their fibrinogen was partly coagulable with batroxobin and fully coagulable with thrombin; consistent with its incomplete FpA release. In contrast, plasma from the other two siblings had thrombin times > 2 min longer than controls, and their fibrinogen was < 10 mg/dl by clotting assay and normal by immunoassay. Their isolated fibrinogen did not release FpA (n = 5) and formed thrombin clots only at cold temperatures indicating formation of desBB fibrin. Assessed by SDS-PAGE, only monomeric fibrinogen was seen in isolated fibrinogen, washed and unreduced plasma immunoprecipitates, non-crosslinked plasma clots or 56 degrees C precipitates. DNA sequencing of PCR products using oligonucleotide primers which flanked sequences coding for A alpha 7Asp to 35Phe, disclosed mutant (C-->T, coding for A alpha 16Cys) and wild type alleles present in both severely affected siblings. It is concluded that circulating fibrinogen contained only mutant FpA. A possible second mutation, not apparent from plasma assays on the mother, is believed to account for the absence of releasable normal FpA in circulating fibrinogen.

Alleles↗
PubMed1995

A new method for the assay of exposed platelet fibrinogen receptor using a chemiluminescent label.

Assay of the platelet fibrinogen-binding receptor glycoprotein (GP) IIb/IIIa is widely performed using 125I-labeled fibrinogen (125I-fibrinogen). We successfully devised a receptor binding assay system with high selectivity and sensitivity using a stable chemiluminescent acridinium derivative-I-labeled fibrinogen (acridinium-fibrinogen). Human fibrinogen is saline was labeled with equimolar acridinium dissolved in dimethylformamide, and allowed to react with gel-filtered human platelets in the presence of ADP. Acridinium-fibrinogen binding to GPIIb/IIIa was assayed by measuring chemiluminescence emitted on addition of 0.1 N NaOH containing 0.06% H2O2 in a luminometer. Non-specific binding was measured in the presence of 10 mM EDTA. Acridinium-fibrinogen binding to human platelets was rapid and reversible, specific and saturable, and dependent on ADP concentrations. Scatchard plot analysis revealed one class of binding sites with Kd of 326 nM and Bmax of 7.8 pmol/10(8) platelets. These values were comparable to the data obtained by using 125I-fibrinogen. Unlabeled fibrinogen, RGDS, and HHLGGAKQAGDV (fibrinogen gamma-chain 400-411) displaced acridinium-fibrinogen from its binding site with Ki values of 322 nM, 9.2 microM and 31.3 microM, respectively. Thus, this binding assay system may be useful in measuring the binding between platelet GPIIb/IIIa and fibrinogen without using a radioisotope.

Acridines↗
PubMed1985

Fibrinogen Manchester. Detection of a heterozygous phenotype in the intraplatelet pool.

Family members heterozygous for the congenitally abnormal fibrinogen designated fibrinogen Manchester, A alpha 16Arg----His, have previously been shown by h.p.l.c. and amino acid analysis to release a variant fibrinopeptide, [His16]fibrinopeptide A, from plasma fibrinogen after the addition of thrombin. The present study was designed to determine if the same abnormal phenotype was also present in the intraplatelet fibrinogen pool. Fresh platelets were washed in buffers containing EDTA until it could be shown that all washable plasma fibrinogen was removed. Normal platelets were then lysed by freezing and thawing to release their intracellular proteins, which were then treated with thrombin. The fibrinopeptides, cleaved from the intraplatelet fibrinogen, could be detected by an optimized h.p.l.c. technique. Quantification of the intraplatelet fibrinogen gave a result (means +/- S.D., n = 5) of 110 +/- 30 and 90 +/- 30 micrograms/10(9) platelets, when determined by h.p.l.c. quantification of fibrinopeptide B content and fibrinogen fragment E radioimmunoassay respectively. Examination of fibrinopeptides released from the platelet fibrinogen from the family with fibrinogen Manchester with the same techniques showed elution peaks in the same positions as both [His16]fibrinopeptide A and normal fibrinopeptide A. The identity of these peaks was further substantiated by analysis of the h.p.l.c. peaks by using specific radioimmunoassay to fibrinopeptide A. Our results therefore demonstrate that platelet fibrinogen expresses the heterozygous A alpha 16His phenotype. This supports the view that the A alpha chains of platelet and plasma fibrinogen are produced from a single genetic locus.

Blood Platelets↗
PubMed1962

Significance of cryoprofibrin in fibrinogen-fibrin conversion.

Fibrinogen altered by thrombin-catalyzed liberation of fibrinopeptide A was found to combine with native fibrinogen to form a cold-precipitable complex we have called "cryoprofibrin." The altered fibrinogen lacking fibrino-peptide A polymerized into fibrin, but not until conditions for equilibrium between its incorporation into both cryoprofibrin and fibrin were satisfied. At equilibrium, the concentration of cryoprofibrin was maintained at a threshold proportional to the concentration of fibrinogen. When the concentration of cryoprofibrin was below threshold, fibrin could be depolymerized and solubilized by fibrinogen with resultant formation of cryoprofibrin. Since threshold concentrations of cryoprofibrin appear necessary for precipitation of fibrin, the concentration of cryoprofibrin in plasma provides a basis for determining intravascular deposition of fibrin. Intravascular deposition of fibrin does not appear to occur normally in rabbits, because the concentration of cryoprofibrin in plasma from normal rabbits is far below the threshold for precipitation of fibrin. The applicability of cryoprofibrin as an indicator of fibrin deposition is demonstrated by the occurrence of levels of cryoprofibrin approaching the threshold for precipitation of fibrin in plasma from endotoxin-treated rabbits. The current concept that the fibrinogen molecule can dissociate into subunits can be used to explain the conversion of fibrinogen to cryoprofibrin. As one possibility, the two residues of fibrinopeptide A contained in fibrinogen may be located on two separate subunits of the molecule; cryoprofibrin is produced when one of these subunits is replaced by a subunit altered by loss of fibrinopeptide A. Recombination of native subunits with subunits altered by loss of A would counter dissociation of cryoprofibrin and inhibit polymerization of subunits lacking fibrinopeptide A. As an alternate mechanism, two residues of A may be liberated concurrently from a single subunit. Cryoprofibrin would then correspond to a fibrinogen molecule, containing a subunit with two residues of A, in combination with an altered molecule containing a subunit lacking two residues of A. Liberation of fibrinopeptide B did not contribute measurably to production of fibrin resulting from limited action of thrombin on rabbit fibrinogen. Both fibrin containing B but not A, and fibrin containing neither B nor A, as is produced by extensive action of thrombin, could be solubilized by fibrinogen. Thrombin, or another enzyme utilizing tosyl-L-arginine methyl ester as substrate, appeared reversibly to inhibit polymerization of fibrin containing fibrinopeptide B. This enzyme and fibrinogen were the only proteins appearing to inhibit polymerization in plasma from normal rabbits.

Arginine↗
PubMed2002

Fibrinogen assembly and crosslinking on a fibrin fragment E template.

There is an ongoing controversy concerning whether crosslinked gamma chains in fibrin are oriented "transversely" between fibril strands or "end-to-end" along fibril strands. From the latter viewpoint, Veklich et al. [Proc Natl Acad Sci (USA) 95: 1438, 1998] observed that fibrinogen fibrils that had been assembled on a fibrin fragment E template, cross-linked with factor XIIIa, and then dissociated in acetic acid solution, were aligned end-to-end. This led to the conclusion that crosslinked gamma chains in fibrin under physiological conditions were also aligned end-to-end. To assess its validity we studied the assembly and organization of fibrinogen molecules on a des AB-fibrin fragment E (E-des AB) or a des A-fibrin fragment E (E-des A) template. We evaluated the roles of E polymerization sites E(A) and E(B), and D association sites gammaXL, Da, Db, betaC and alphaC in this process. E(A):Da interactions caused fibrinogen: E "DED" complexes to form, and markedly enhanced the gamma chain crosslinking rates of fibrinogen or des alphaC-fibrinogen. Fibrinogen crosslinking without added fibrin E was slower, and that of des alphaC-fibrinogen was still slower. These events showed that although alphaC domains promote fibrinogen fibril assembly and crosslinking, they contribute little to increasing the E(A):Da-dependent crosslinking rate. Electron microscopic (STEM) images of E-des AB and fibrinogen plus factor XIIIa showed single-, double-, and multistranded fibrils with interstrand DED complexes aligned side-to-side. This alignment was due to betaC:betaC contacts resulting from D subdomain rearrangements initiated by the E(B):Db interactions, and also occurred in mixtures of des alphaC-fibrinogen with E-des AB. In contrast, a mixture of fibrinogen and E-des A plus XIIIa revealed double-stranded fibrils with interstrand DED complexes in a half-staggered arrangement, an alignment that we attribute to crosslinking of gammaXL sites bridging between fibrils strands. These and other features of E-des A-based fibrinogen fibrils, including interstrand gamma chain bridges and early and extensive lateral fibril strand associations concomitant with accelerated gamma chain crosslinking, indicate that crosslinking of fibrin fibril strands takes place preferentially on transversely positioned gamma chains.

Biopolymers↗
PubMed1993

The polymerization of fibrinogen Dusart (A alpha 554 Arg-->Cys) after removal of carboxy terminal regions of the A alpha-chains.

The six polypeptide chains of normal fibrinogen are covalently linked by interchain disulphide bonds, and there are no free sulphydryl groups. Fibrinogen Dusart is a congenital fibrinogen variant in which A alpha 554 Arg is replaced by Cys; albumin is disulphide linked to these fibrinogen molecules, possibly at A alpha 554 Cys. Functionally, Dusart fibrinogen displays markedly abnormal fibrin polymerization, characterized by delayed lateral fibril association and matrix fibre bundles that are thinner than normal fibrin bundles. These observations are consistent with experiments suggesting that the carboxy terminal region of the A alpha-chain contains a polymerization domain that participates in lateral fibril associations. In order to investigate the location and the effect of albumin binding to Dusart fibrinogen, we examined the fibrinogen by electron microscopy, and compared the polymerization and ultrastructure of fibrin prepared from normal fibrinogen containing intact A alpha-chains (fraction I-2) or plasmin degraded fibrinogen molecules lacking carboxy terminal regions of A alpha-chains (fraction I-9D), with fibrin prepared from Dusart fraction I-2 and I-9D. Most bound albumin was released from Dusart fibrinogen by plasmin degradation involving the A alpha-chains. Nevertheless, we were able to visualize albumin molecules remaining covalently bound to Dusart I-9D as well as to Dusart I-2 fibrinogen, as distinct globular domains situated near the fibrinogen D domain. The presence of albumin in these fractions was confirmed by Western blotting using anti-albumin. Dusart fibrin polymerized much more slowly than normal I-2, as previously reported, whereas polymerization of Dusart I-9D fibrin was faster than Dusart I-2 and nearly the same as normal I-9D fibrin.(ABSTRACT TRUNCATED AT 250 WORDS)

Albumins↗
PubMed1999

Human plasma fibrinogen adsorption and platelet adhesion to polystyrene.

The purpose of this study was to further investigate the role of fibrinogen adsorbed from plasma in mediating platelet adhesion to polymeric biomaterials. Polystyrene was used as a model hydrophobic polymer; i.e., we expected that the role of fibrinogen in platelet adhesion to polystyrene would be representative of other hydrophobic polymers. Platelet adhesion was compared to both the amount and conformation of adsorbed fibrinogen. The strategy was to compare platelet adhesion to surfaces preadsorbed with normal, afibrinogenemic, and fibrinogen-replenished afibrinogenemic plasmas. Platelet adhesion was determined by the lactate dehydrogenase (LDH) method, which was found to be closely correlated with adhesion of 111In-labeled platelets. Fibrinogen adsorption from afibrinogenemic plasma to polystyrene (Immulon I(R)) was low and <10 ng/cm2. Platelet adhesion was absent on surfaces preadsorbed with afibrinogenemic plasma when the residual fibrinogen was low enough (<60 microg/mL). Platelet adhesion was restored on polystyrene preadsorbed with fibrinogen-replenished afibrinogenemic plasma. Addition of even small, subnormal concentrations of fibrinogen to afibrinogenemic plasma greatly increased platelet adhesion. In addition, surface-bound fibrinogen's ability to mediate platelet adhesion was different, depending on the plasma concentration from which fibrinogen was adsorbed. These differences correlated with changes in the binding of a monoclonal antibody that binds to the Aalpha chain RGDS (572-575), suggesting alteration in the conformation or orientation of the adsorbed fibrinogen. Platelet adhesion to polystyrene preadsorbed with blood plasma thus appears to be a strongly bivariate function of adsorbed fibrinogen, responsive to both low amounts and altered states of the adsorbed molecule.

Adsorption↗
PubMed1999

Residence-time dependent changes in fibrinogen adsorbed to polymeric biomaterials.

It has generally been accepted that biomaterials adsorbing the least amount of the plasma protein fibrinogen following exposure to blood will support less platelet adhesion and therefore exhibit less thrombogenicity. Several studies suggest, however, that the conformation or orientation of immobilized fibrinogen rather than the total amount adsorbed plays an important role in determining the blood compatibility of biomaterials. The purpose of this study was to investigate time-dependent functional changes in fibrinogen adsorbed to polytetrafluoroethylene (PTFE), polyethylene (PE), and silicone rubber (SR). Fibrinogen was adsorbed to these materials for 1 min and then allowed to 'reside" on the surfaces for up to 2 h prior to assessing its biological activity. Changes in fibrinogen reactivity were determined by measuring the adhesion of 51Cr-labeled platelets, the binding of a monoclonal antibody (mAb) directed against an important functional region of the fibrinogen molecule (the gamma-chain dodecapeptide sequence 400-411), and the ability of blood plasma to displace previously adsorbed fibrinogen. Platelet adhesion differed among the polymeric materials studied, and PTFE and PE samples exhibited a small decrease in adhesion with increasing fibrinogen residence time. Platelet adhesion to SR was the least among all materials studied and showed no variation with residence time. When using PTFE and SR as substrates, mAb recognition of adsorbed fibrinogen did not change with residence time whereas that on PE decreased slightly. The mAb binding was least to fibrinogen adsorbed to SR, which is in agreement with the platelet adhesion results. Finally, the ability of plasma to displace previously adsorbed fibrinogen decreased dramatically with increasing residence time on all materials. These in vitro studies support the hypothesis that fibrinogen undergoes biologically significant conformational changes upon adsorption to polymeric biomaterials, a phenomenon that may contribute to the hemocompatibility of the materials following implantation in the body.

Adsorption↗
PubMed1992

Postadsorptive transitions in fibrinogen adsorbed to polyurethanes: changes in antibody binding and sodium dodecyl sulfate elutability.

Residence time-dependent changes in fibrinogen after adsorption to six different polyurethanes were examined by measuring polyclonal antifibrinogen binding to the adsorbed protein. The amount of adsorbed fibrinogen that could be eluted by sodium dodecyl sulfate (SDS) was also measured. Baboon fibrinogen was first adsorbed from dilute plasma to the polymers, which were then stored in either buffer or buffered albumin solution prior to testing. Subsequently, the amount of antifibrinogen bound by the adsorbed fibrinogen was measured using a direct enzyme linked immunosorbent assay (ELISA). Alternatively, the surface with the adsorbed fibrinogen was soaked in a 3% SDS solution, and the amount of retained 125I-radiolabeled fibrinogen was measured. With increasing residence time, decreases in both antibody binding and the SDS elutability of the adsorbed fibrinogen occurred, but the rate of change was dependent on the polyurethane to which the fibrinogen was adsorbed. In addition, the antibody binding per unit of adsorbed fibrinogen, when measured immediately after the adsorption step, varied by approximately a factor of 3 among the various polyurethanes. When the protein-coated surfaces were stored in buffered albumin solution rather than buffer, the decrease in the reactivity of fibrinogen with residence time did not occur on some of the surfaces. This study shows that the chemical properties of the adsorbing surface influence the rate at which adsorbed fibrinogen undergoes change. The significance of the polymer-dependent changes in adsorbed fibrinogen with respect to blood reactions with polymers is discussed.

Adsorption↗