The relationship between the fibrinogen D domain self-association/cross-linking site (gammaXL) and the fibrinogen Dusart abnormality (Aalpha R554C-albumin): clues to thrombophilia in the "Dusart syndrome"

Erythrocyte Fraction in Thrombi Is Increased with Serum Iron by Influencing Fibrin Networks via Oxidative Stress

Objective

This study investigated whether the erythrocyte fraction in thrombi would be increased with serum iron via oxidative stress.

Methods

This study retrospectively enrolled patients with acute ischemic stroke treated using endovascular treatment in a single stroke center from October to December 2019. We examined the relationship between serum iron and erythrocyte-rich thrombi and the correlation of serum iron and the erythrocyte fraction in thrombi using clinical samples. Experiments in vivo and in vitro were performed to investigate the influence of oxidative stress on the correlation between serum iron concentration and erythrocyte fraction in thrombi.

Results

We found from the clinical samples that serum iron concentration was related to erythrocyte-rich thrombi and positively associated with the erythrocyte fraction in thrombi in vivo. Further, the tightness of the fibrin networks regulating the erythrocyte fraction in thrombi was increased with serum iron concentration in vivo. Additionally, the oxidative stress level was increased with serum iron concentration in vivo. Moreover, we found that the tightness of the fibrin networks increased with higher oxidative stress levels in vitro. Lastly, experiments in vivo with inhibiting oxidative stress showed that the erythrocyte fraction in thrombi and the tightness of fibrin networks significantly increased in the iron group than those in the iron with oxidative stress inhibitor group and control group.

Conclusions

Oxidative stress played a role in the process that the erythrocyte fraction in thrombi was increased with serum iron by influencing fibrin networks.

Development of a mesoscopic framework spanning nanoscale protofibril dynamics to macro-scale fibrin clot formation

Thrombi form a micro-scale fibrin network consisting of an interlinked structure of nanoscale protofibrils, resulting in haemostasis. It is theorized that the mechanical effect of the fibrin clot is caused by the polymeric protofibrils between crosslinks, or to their dynamics on a nanoscale order. Despite a number of studies, however, it is still unknown, how the nanoscale protofibril dynamics affect the formation of the macro-scale fibrin clot and thus its mechanical properties. A mesoscopic framework would be useful to tackle this multi-scale problem, but it has not yet been established. We thus propose a minimal mesoscopic model for protofibrils based on Brownian dynamics, and performed numerical simulations of protofibril aggregation. We also performed stretch tests of polymeric protofibrils to quantify the elasticity of fibrin clots. Our model results successfully captured the conformational properties of aggregated protofibrils, e.g., strain-hardening response. Furthermore, the results suggest that the bending stiffness of individual protofibrils increases to resist extension.

New method for determining fibrinogen and FDP threshold criteria by artificial intelligence in cases of massive hemorrhage during delivery

AIM

To investigate the feasibility of a novel method using artificial intelligence (AI), in which the fibrinogen criterion was determined by the quantitative relation between the distributions of fibrin/fibrinogen degradation products (FDPs) and fibrinogen.

METHODS

A dataset of 154 deliveries comprising more than 2000 g of blood lost due to hemorrhage, excluding disseminated intravascular coagulation (DIC), among patients from eight national perinatal centers in Japan from 2011 to 2015 were obtained. The fibrinogen threshold criterion was identified by using the function that best fit the distributions of FDP as determined by AI. FDP production was described by differential equations using a dataset containing fibrinogen levels less than the fibrinogen criterion and solved numerically.

RESULTS

A fibrinogen level of 237 mg/dL as the threshold criterion was obtained. The FDP threshold criteria were 2.0 and 8.5 mg/dL for no coagulopathy and a failed coagulation system, respectively.

CONCLUSION

The fibrinogen threshold criterion for patients with massive hemorrhage excluding DIC at delivery were obtained by selecting the functions that best fit the distributions of FDP data by using AI.

Fibrinogen αC domain: Its importance in physiopathology

ABSTRACT

Fibrinogen, involved in coagulation, is a soluble protein composed of two sets of disulfide-bridged Aα, Bβ, and γ-chains. In this review, we present the clinical implications of the αC domain of the molecule in Alzheimer's disease, hereditary renal amyloidosis and a number of thrombotic and hemorrhagic disorders. In Alzheimer's disease, amyloid beta peptide (Aβ) is increased and binds to the αC domain of normal fibrinogen, triggering increased fibrin(ogen) deposition in patients' brain parenchyma. In hereditary renal amyloidosis, fibrinogen is abnormal, with mutations located in the fibrinogen αC domain. The mutant αC domain derived from fibrinogen degradation folds incorrectly so that, in time, aggregates form, leading to amyloid deposits in the kidneys. In these patients, no thrombotic tendency has been observed. Abnormal fibrinogens with either a point mutation in the αC domain or a frameshift mutation resulting in absence of a part of the αC domain are often associated with either thrombotic events or bleeding. Mutation of an amino acid into cysteine (as in fibrinogens Dusart and Caracas V) or a frameshift mutation yielding an unpaired cysteine in the αC domain is often responsible for thrombotic events. Covalent binding of albumin to the unpaired cysteine via a disulphide bridge leads to decreased accessibility to the fibrinolytic enzymes, hence formation of poorly degradable fibrin clots, which explains the high incidence of thrombosis. In contrast, anomalies due to a frameshift mutation in the αC connector of the molecule, provoking deletion of a great part of the αC domain, are associated with bleeding.

VLITL is a major cross-β-sheet signal for fibrinogen Aα-chain frameshift variants

The first case of hereditary fibrinogen Aα-chain amyloidosis was recognized >20 years ago, but disease mechanisms still remain unknown. Here we report detailed clinical and proteomics studies of a French kindred with a novel amyloidogenic fibrinogen Aα-chain frameshift variant, Phe521Leufs, causing a severe familial form of renal amyloidosis. Next, we focused our investigations to elucidate the molecular basis that render this Aα-chain variant amyloidogenic. We show that a 49-mer peptide derived from the C-terminal part of the Phe521Leufs chain is deposited as fibrils in the patient's kidneys, establishing that only a small portion of Phe521Leufs directly contributes to amyloid formation in vivo. In silico analysis indicated that this 49-mer Aα-chain peptide contained a motif (VLITL), with a high intrinsic propensity for β-aggregation at residues 44 to 48 of human renal fibrils. To experimentally verify the amyloid propensity of VLITL, we generated synthetic Phe521Leufs-derived peptides and compared their capacity for fibril formation in vitro with that of their VLITL-deleted counterparts. We show that VLITL forms typical amyloid fibrils in vitro and is a major signal for cross-β-sheet self-association of the 49-mer Phe521Leufs peptide identified in vivo, whereas its absence abrogates fibril formation. This study provides compelling evidence that VLITL confers amyloidogenic properties to Aα-chain frameshift variants, yielding a previously unknown molecular basis for the pathogenesis of Aα-chain amyloidosis.

Study on the influence of oxidative stress on the fibrillization of fibrinogen

Human fibrinogen is an important coagulation factor as well as an independent predictor of coronary heart disease and stroke. Analysis of dysfibrinogens may provide useful information and help us to understand the molecular defects in fibrin polymerization. In the present study, we investigated the influence of oxidative stress of fibrinogen induced by H2O2 on the polymerization state of fibrin. UV absorbance spectroscopy, circular dichroism, ζ-potential, dynamic light scattering and steady shear viscosity were all employed to study the influence of oxidative stress on the molecular structure, the surface charges, and the size and shape of fibrinogen molecules. The fibrin morphology obtained was imaged and investigated using atomic force microscopy. The results demonstrated that the cross-linking, branching and height distribution of formed fibrin will be influenced by the oxidative stress of fibrinogen. This study presents new insights into the aggregation behaviour of fibrinogen and will be helpful to understand the formation mechanism of thrombosis under oxidative stress.

Fibrin clot structure in patients with congenital dysfibrinogenaemia

The clinical phenotype of patients with congenital dysfibrinogenaemia is highly heterogeneous, from absence of symptoms to mild bleeding, or thrombosis. A few mutations are associated with a specific phenotype, but generally the clinical course is not predictable. We investigated whether fibrin clot properties are correlated with the patient's phenotype and/or genotype. Ex vivo plasma fibrin clot characteristics, including turbidity, fibrinolysis, clot permeability and fibrin fibre density assessed by laser scanner confocal microscopy were investigated in 24 genotyped patients with congenital dysfibrinogenaemia compared to normal pool plasma. Compared to normal pool plasma, the patients were characterised by slower fibrin polymerisation (lag time, 345.10 ± 22.98 vs. 166.00s), thinner fibrin fibres (maximum absorbance, 0.15 ± 0.01 vs. 0.31), prolonged clot lysis time (23.72 ± 0.97 vs. 20.32 min) and larger clot pore size (21.5×10(-9) ± 4.48×10(-9) vs. 7.96×10(-9)cm(2)). Laser scanning confocal microscopy images confirmed disorganised fibrin networks in all patients. Patients with tendency to bleed showed an increased permeability compared to asymptomatic patients (p=0.01) and to patients with a thrombotic history (p=0.02) while patients with thrombotic history had a tendency to have a prolonged clot lysis time. Fibrin clot properties were similar among hotspot mutations. Further studies including a larger number of patients are needed to evaluate whether analysis of permeability and clot lysis time may help to distinguish the clinical phenotype in these patients and to assess differences according to the genotype.

MetAmyl: a METa-predictor for AMYLoid proteins

The aggregation of proteins or peptides in amyloid fibrils is associated with a number of clinical disorders, including Alzheimer's, Huntington's and prion diseases, medullary thyroid cancer, renal and cardiac amyloidosis. Despite extensive studies, the molecular mechanisms underlying the initiation of fibril formation remain largely unknown. Several lines of evidence revealed that short amino-acid segments (hot spots), located in amyloid precursor proteins act as seeds for fibril elongation. Therefore, hot spots are potential targets for diagnostic/therapeutic applications, and a current challenge in bioinformatics is the development of methods to accurately predict hot spots from protein sequences. In this paper, we combined existing methods into a meta-predictor for hot spots prediction, called MetAmyl for METapredictor for AMYLoid proteins. MetAmyl is based on a logistic regression model that aims at weighting predictions from a set of popular algorithms, statistically selected as being the most informative and complementary predictors. We evaluated the performances of MetAmyl through a large scale comparative study based on three independent datasets and thus demonstrated its ability to differentiate between amyloidogenic and non-amyloidogenic polypeptides. Compared to 9 other methods, MetAmyl provides significant improvement in prediction on studied datasets. We further show that MetAmyl is efficient to highlight the effect of point mutations involved in human amyloidosis, so we suggest this program should be a useful complementary tool for the diagnosis of these diseases.

Fibrinogen Guarenas, an abnormal fibrinogen with an Aalpha-chain truncation due to a nonsense mutation at Aalpha 467 Glu (GAA)-->stop (TAA)

Fibrinogen Guarenas is a dysfibrinogenemia with a nonsense mutation at G4731T that causes an Aalpha-chain truncation at Ser 466. This abnormal fibrinogen is associated with a bleeding diathesis, severe in the proposita and mild in one brother, even though the fibrinogen levels in plasma are normal. All other family members are asymptomatic. Fibrinogens from the proposita and one family member, the mother of the proposita, both heterozygous for the mutation, were studied. Turbidity curves of fibrin polymerization showed that the lateral association of protofibrils was impaired and the maximum rate of polymerization was slightly diminished. The binding of albumin to fibrinogen was increased compared to control due to the presence of a free sulfhydryl group because of the missing disulphide bridge between Aalpha-Cys 442-472 in the mutated molecules. The abnormal fibrinogen formed much less alpha-polymer, and gamma-dimer formation was delayed compared to the control. Plasminogen activation by t-PA in the presence of fibrin was decreased. When Guarenas clots were perfused with fibrinolytic enzymes, clot degradation was retarded. Clot structure studied by confocal 3D microscopy showed that the fibrin network was dense, made up of thin and highly branched fibers, which accounted for the decreased flow rates by buffer permeation and increased rigidity of the fibrin clots, measured using a torsion pendulum. It seems that the increased clot rigidity, decreased porosity, hypofibrinolysis and t-PA induced fibrinolysis, by itself are not necessarily associated with thrombotic disorders in dysfibrinogenemia.

In vitro fibrin clot formation and fibrinolysis using heterozygous plasma fibrinogen from γAsn319, Asp320 deletion dysfibrinogen, Otsu I

INTRODUCTION

We have reported a heterozygous dysfibrinogenemia, fibrinogen Otsu I, caused by the deletion of gammaAsn319 and gammaAsp320, which was originally identified in the dysfibrinogen Vlissingen/Frankfurt IV (V/FIV) associated with thrombosis. Unlike the V/FIV family, the Otsu propositus showed no thrombotic tendencies. To analyze the relationship between thrombosis and the heterozygous plasma variant fibrinogen, we used purified plasma fibrinogen from the Otsu patient and compared it with a normal control.

MATERIALS AND METHODS

Thrombin-induced fibrin clot formation and clot structure were observed by fibrin polymerization and scanning electron microscopy, respectively. For in vitro observation of fibrinolysis, plasmin generation and clot lysis assays were performed by the addition of tissue type plasminogen activation (tPA) and plasminogen.

RESULTS AND CONCLUSIONS

Polymerization of Otsu was markedly impaired, while fibrin fibers were much thicker and the density of the bundles of fibrin fibers was less and porous compared with normal. Lysis of the Otsu clot was not significantly different from normal when a tPA and plasminogen mixture was overlaid onto the clots. For Otsu, the penetration of the tPA/plasminogen mixture into the clot was much faster than normal and the protection against plasmin cleavage was impaired; however, tPA-induced plasmin activation of the Otsu fibrin was slower than that of normal fibrin, resulting in a clot lysis of Otsu similar to normal.

Fibrinogen and fibrin structure and functions

Fibrinogen molecules are comprised of two sets of disulfide-bridged Aalpha-, Bbeta-, and gamma-chains. Each molecule contains two outer D domains connected to a central E domain by a coiled-coil segment. Fibrin is formed after thrombin cleavage of fibrinopeptide A (FPA) from fibrinogen Aalpha-chains, thus initiating fibrin polymerization. Double-stranded fibrils form through end-to-middle domain (D:E) associations, and concomitant lateral fibril associations and branching create a clot network. Fibrin assembly facilitates intermolecular antiparallel C-terminal alignment of gamma-chain pairs, which are then covalently 'cross-linked' by factor XIII ('plasma protransglutaminase') or XIIIa to form 'gamma-dimers'. In addition to its primary role of providing scaffolding for the intravascular thrombus and also accounting for important clot viscoelastic properties, fibrin(ogen) participates in other biologic functions involving unique binding sites, some of which become exposed as a consequence of fibrin formation. This review provides details about fibrinogen and fibrin structure, and correlates this information with biological functions that include: (i) suppression of plasma factor XIII-mediated cross-linking activity in blood by binding the factor XIII A2B2 complex. (ii) Non-substrate thrombin binding to fibrin, termed antithrombin I (AT-I), which down-regulates thrombin generation in clotting blood. (iii) Tissue-type plasminogen activator (tPA)-stimulated plasminogen activation by fibrin that results from formation of a ternary tPA-plasminogen-fibrin complex. Binding of inhibitors such as alpha2-antiplasmin, plasminogen activator inhibitor-2, lipoprotein(a), or histidine-rich glycoprotein, impairs plasminogen activation. (iv) Enhanced interactions with the extracellular matrix by binding of fibronectin to fibrin(ogen). (v) Molecular and cellular interactions of fibrin beta15-42. This sequence binds to heparin and mediates platelet and endothelial cell spreading, fibroblast proliferation, and capillary tube formation. Interactions between beta15-42 and vascular endothelial (VE)-cadherin, an endothelial cell receptor, also promote capillary tube formation and angiogenesis. These activities are enhanced by binding of growth factors like fibroblast growth factor-2 (FGF-2) and vascular endothelial growth factor (VEGF), and cytokines like interleukin (IL)-1. (vi) Fibrinogen binding to the platelet alpha(IIb)beta3 receptor, which is important for incorporating platelets into a developing thrombus. (vii) Leukocyte binding to fibrin(ogen) via integrin alpha(M)beta2 (Mac-1), which is a high affinity receptor on stimulated monocytes and neutrophils.

Pediatric thrombosis

Although thrombosis is less frequent in children than in adults, it represents a significant source of morbidity and mortality. Multiple factors. both genetic and acquired. contribute to the development of thrombosis in chiidren. Thrombosis in a child warrants investigation of potential underlying prothrombotic conditions. The risk of thrombosis in children with heterozygous deficiencies is not clearly defined, but it appears that children who are heterozygous for more than one risk factor or who have a combination of inherited and acquired defects are at higher risk for thrombosis. Treatment of thrombosis primarily involves a rapidly acting anticoaguiant such as heparin or LMWH to prevent extension, and long-term anticoagulation with warfarin may be instituted to prevent recurrence. Thrombolytic therapy with recombinant tissue plasminogen activator also appears to be safe and effective in children. Prospective and multicenter studies are still needed to clarify the contribution of specific prothrombotic disorders to childhood TE so that evidence-based treatment recommendations can be made.

Structure and function of human fibrinogen inferred from dysfibrinogens

Fibrinogen is a 340-kDa plasma protein that is composed of two identical molecular halves, each consisting of three non-identical subunit polypeptides designated as A alpha, B beta- and gamma-chains held together by multiple disulfide bonds. Fibrinogen has a trinodular structure, i.e., one central E domain comprizing the amino-terminal regions of paired individual three polypeptides, and two identical outer D domains. These three nodules are linked by two coiled-coil regions [1,2]. After activation with thrombin, a tripeptide segment consisting of Gly-Pro-Arg is exposed at the amino-terminus of each alpha-chain residing at the center of the E domain and combines with its complementary binding site, called the 'a' site, residing in the carboxyl-terminal region of the gamma-chain in the outer D domain of another molecule. By crystallographic analysis [3], the alpha-amino group of alpha Gly-1 is shown to be juxtaposed between the carboxyl group of gamma Asp-364 and the carboxyamide of Gln-329 in the 'a' site. Half molecule-staggered, double-stranded fibrin protofibrils are thus formed [4,5]. Upon abutment of two adjacent D domains on the same strand, D-D self association takes place involving Arg-275, Tyr-280 and Ser-300 of the gamma-chain on the surface of the abutting two D domains [3]. Thereafter, carboxyl-terminal regions of the fibrin a-chains are thought to be untethered and interact with those of other protofibrils leading to the formation of thick fibrin bundles and interwoven networks after appropriate branching [6-9]. Although many enigmas still remain regarding the mechanisms of these molecular interactions, fibrin assembly proceeds in a highly ordered fashion. In my talk, I would like to discuss these molecular interactions of fibrinogen and fibrin based on the up-date data provided by analyses of normal as well as hereditary dysfibrinogens, particularly in the latter by introducing representative molecules at each step of fibrin clot formation.

Fibrinogen and fibrin are anti-adhesive for keratinocytes: a mechanism for fibrin eschar slough during wound repair

During cutaneous wound repair the epidermis avoids the fibrin-rich clot; rather it migrates down the collagen-rich dermal wound margin and over fibronectin-rich granulation tissue. The mechanism(s) underlying keratinocyte movement in this precise pathway has not been previously addressed. Here we demonstrate that cultured human keratinocytes do not express functional fibrinogen/fibrin receptors, specifically alpha v beta 3. Biologic modifiers known to induce integrin expression or activation did not induce adhesion to fibrin, fibrinogen, or its fragments. Epidermal explant outgrowth and single epidermal cell migration failed to occur on either fibrin or fibrinogen. Surprisingly, fibrin and fibrinogen mixed at physiologic molar ratios with fibronectin abrogated keratinocyte attachment to fibronectin. Keratinocytes transduced with the beta 3 integrin subunit cDNA, expressed alpha v beta 3 on their surface and attached to and spread on fibrinogen and fibrin. beta-gal cDNA-transduced keratinocytes did not demonstrate this activity. Furthermore, beta 3 cDNA-transduced keratinocyte adhesion to fibrin was inhibited by LM609 monoclonal antibody to alpha v beta 3 in a concentration-dependent fashion. From these data, we conclude that normal human keratinocytes cannot interact with fibrinogen and its derivatives due to the lack of alpha v beta 3. Thus, fibrinogen and fibrin are authentic anti-adhesive for keratinocytes. This may be a fundamental reason why the migrating epidermis dissects the fibrin eschar from wounds.

Hereditary disorders of fibrinogen

Fibrinogen, a 340-kDa plasma protein, is composed of two identical molecular halves each consisting of three non-identical A alpha-, B beta- and gamma-chain subunits held together by multiple disulfide bonds. Fibrinogen is shown to have a trinodular structure; that is, one central nodule, the E domain, and two identical outer nodules, the D-domains, linked by two coiled-coil regions. After activation with thrombin, a pair of binding sites comprising Gly-Pro-Arg is exposed in the central nodule and combines with its complementary binding site a in the outer nodule of another molecules. By using crystallographic analysis, the alpha-amino group of alpha Gly-1 is shown to be juxtaposed between gamma Asp-364 and gamma Asp-330, and guanidino group of alpha Arg-3 between the carboxyl group of gamma Asp-364 and gamma Gln-329 in the a site. Half molecule-staggered, double-stranded protofibrils are thus formed. Upon abutment of two adjacent D domains on the same strand, D-D self association takes place involving Arg-275, Tyr-280, and Ser-300 of the gamma-chain on the surface of the abutting two D domains. Thereafter, carboxyl-terminal regions of the alpha-chains are untethered and interact with those of other protofibrils leading to the formation of thick fibrin bundles and networks. Although many enigmas still remain concerning the exact mechanisms of these molecular interactions, fibrin assembly proceeds in a highly ordered fashion. In this review, these molecular interactions of fibrinogen and fibrin are discussed on the basis of the data provided by hereditary dysfibrinogens on introducing representative molecules at each step of fibrin clot formation.

Aberrant fibrin formation and cross-linking of fibrinogen Nieuwegein, a variant with a shortened Aalpha-chain, alters endothelial capillary tube formation

A congenital dysfibrinogenemia, fibrinogen(Nieuwegein), was discovered in a young man without any thromboembolic complications or bleeding. A homozygous insertion of a single nucleotide (C) in codon Aalpha 453 (Pro) introduced a stop codon at position 454, which resulted in the deletion of the carboxyl-terminal segment Aalpha 454-610. The ensuing unpaired cysteine at Aalpha 442 generated fibrinogen-albumin complexes of different molecular weights. The molecular abnormalities of fibrinogen(Nieuwegein) led to a delayed clotting and a fibrin network with a low turbidity. Electron microscopy confirmed that thin fibrin bundles were organized in a fine network. The use of fibrinogen(Nieuwegein)-derived fibrin (fibrin(Nieuwegein)) in an in vitro angiogenesis model resulted in a strong reduction of tube formation. The ingrowth of human microvascular endothelial cells (hMVEC) was independent of alpha(v)beta(3), indicating that the reduced ingrowth is not due to the absence of the RGD-adhesion site at position Aalpha 572-574. Rather, the altered structure of fibrin(Nieuwegein) is the cause, since partial normalization of the fibrin network by lowering the pH during polymerization resulted in an increased tube formation. Whereas factor XIIIa further decreased the ingrowth of hMVEC in fibrin(Nieuwegein), tissue transglutaminase (TG), which is released in areas of vessel injury, did not. This is in line with the absence of the cross-linking site for TG in the alpha-chains of fibrinogen(Nieuwegein). In conclusion, this newly discovered congenital dysfibrinogenemia has a delayed clotting time and leads to the formation of an altered fibrin structure, which could not be cross-linked by TG and which is less supportive for ingrowth of endothelial cells.

Identification and characterization of novel tPA- and plasminogen-binding sites within fibrin(ogen) alpha C-domains

Molecular defects in the alphaC-domains of some abnormal fibrinogens have been associated with impaired fibrin-mediated activation of plasminogen (Pg) by its activator tPA, suggesting the involvement of these domains in fibrinolysis. To test this suggestion, we expressed in E. coli the alphaC-fragment (residues Aalpha221-610) corresponding to the entire alphaC-domain as well as its NH(2)- and COOH-terminal halves (residues Aalpha221-391 and Aalpha392-610) and tested their effects on activation of Pg and their interaction with Pg and tPA. When the activation was monitored by cleavage of a chromogenic substrate with newly formed plasmin, the reaction was much more efficient in the presence of the alphaC-fragment. This stimulation was abolished upon digestion of the alphaC-fragment with plasmin. In surface plasmon resonance experiments, both tPA and Pg bound to the immobilized alphaC-fragment with K(d)s of 33 and 32 nM, respectively. Similar results were obtained by ELISA. This binding occurred via independent sites since saturating amounts of Pg did not prevent binding of tPA and vice versa. Both sites were localized in the COOH-terminal half of the alphaC-domain since the Aalpha392-610 fragment bound both tPA and Pg and was an effective stimulator whereas Aalpha221-391 was inactive. These results indicate that the fibrinogen alphaC-domains contain novel high-affinity tPA- and Pg-binding sites that play an important role in the regulation of fibrinolysis.

End-linked homodimers in fibrinogen Osaka VI with a Bβ-chain extension lead to fragile clot structure

The authors have identified a 12-residue carboxyl-terminal extension of Lys-Ser-Pro-Met-Arg-Arg-Phe-Leu-Leu-Phe-Cys-Met in a dysfibrinogen derived from a woman heterozygotic for this abnormality and associated with severe bleeding. This extension is due to a T-to-A mutation that creates AAG encoding Lys at the stop (TAG) codon, thus translating 36 base pairs in the noncoding region of the Bβ gene. The extra Cys residues appear to be involved in 1 or 2 disulfide bonds between 2 adjacent abnormal fibrinogen molecules, forming a fibrinogen homodimer as indicated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Indeed, about half of the fibrinogen molecules exist as end-linked dimers oriented in parallel or with an angle, as observed by transmission electron microscopy. These end-linked dimers may well alter the conformations of D and DD regions on fibrin assembly, leading to increased fiber branching at their sites in the growing protofibrils. By scanning electron microscopy, the Osaka VI fibrin network appears to have a lacelike structure composed of highly branched, thinner fibers than the normal fibrin architecture. Such fibrin networks may be easily damaged to form large pores when fluids are allowed to pass through the gels. The fragility of Osaka VI fibrin clots, further confirmed by permeation and compaction studies, may account for the massive bleeding observed in this patient.

End-linked homodimers in fibrinogen Osaka VI with a Bβ-chain extension lead to fragile clot structure

The authors have identified a 12-residue carboxyl-terminal extension of Lys-Ser-Pro-Met-Arg-Arg-Phe-Leu-Leu-Phe-Cys-Met in a dysfibrinogen derived from a woman heterozygotic for this abnormality and associated with severe bleeding. This extension is due to a T-to-A mutation that creates AAG encoding Lys at the stop (TAG) codon, thus translating 36 base pairs in the noncoding region of the Bβ gene. The extra Cys residues appear to be involved in 1 or 2 disulfide bonds between 2 adjacent abnormal fibrinogen molecules, forming a fibrinogen homodimer as indicated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Indeed, about half of the fibrinogen molecules exist as end-linked dimers oriented in parallel or with an angle, as observed by transmission electron microscopy. These end-linked dimers may well alter the conformations of D and DD regions on fibrin assembly, leading to increased fiber branching at their sites in the growing protofibrils. By scanning electron microscopy, the Osaka VI fibrin network appears to have a lacelike structure composed of highly branched, thinner fibers than the normal fibrin architecture. Such fibrin networks may be easily damaged to form large pores when fluids are allowed to pass through the gels. The fragility of Osaka VI fibrin clots, further confirmed by permeation and compaction studies, may account for the massive bleeding observed in this patient.

Familial thrombophilia associated with fibrinogen Paris V: Dusart syndrome

We report on a family with a history of venous thromboembolism associated with fibrinogen Paris V (fibrinogen A-Arg554→Cys). Ten members experienced thrombotic events, including 4 with fatal pulmonary emboli. Pulmonary embolism was the presenting feature in 4. Those with the mutation and a history of thrombosis had somewhat higher fibrinogen concentrations than those with the mutation and no thrombosis (294 ± 70 mg/dL vs 217 ± 37 mg/dL, respectively). The Paris V mutation consistently caused a prolongation of the reptilase time, and fibrin clots containing the abnormal fibrinogen were more translucent than normal clots. Given the early onset of symptoms and the initial presentation with pulmonary embolism in some family members, it was justifiable to offer prophylactic anticoagulation with warfarin to carriers of the mutation. Fibrinogen Paris V has now been reported in 4 apparently unrelated families, indicating that it is a relatively common cause of dysfibrinogenemia-associated thrombosis.

Familial thrombophilia associated with fibrinogen Paris V: Dusart syndrome

We report on a family with a history of venous thromboembolism associated with fibrinogen Paris V (fibrinogen A-Arg554→Cys). Ten members experienced thrombotic events, including 4 with fatal pulmonary emboli. Pulmonary embolism was the presenting feature in 4. Those with the mutation and a history of thrombosis had somewhat higher fibrinogen concentrations than those with the mutation and no thrombosis (294 ± 70 mg/dL vs 217 ± 37 mg/dL, respectively). The Paris V mutation consistently caused a prolongation of the reptilase time, and fibrin clots containing the abnormal fibrinogen were more translucent than normal clots. Given the early onset of symptoms and the initial presentation with pulmonary embolism in some family members, it was justifiable to offer prophylactic anticoagulation with warfarin to carriers of the mutation. Fibrinogen Paris V has now been reported in 4 apparently unrelated families, indicating that it is a relatively common cause of dysfibrinogenemia-associated thrombosis.

Ligneous conjunctivitis: biochemical evidence for hypofibrinolysis

Ligneous conjunctivitis (LC) is a rare disease of unknown etiology characterized by the growth of "woody" plaques on ocular and extraocular mucosa. These lesions are comprised of fibrin and both direct and indirect evidence implicates hypofibrinolysis as the primary defect in LC. To further elucidate the pathophysiology of LC we investigated the biochemical aspects of ligneous lesions with respect to the fibrinolytic system. Ligneous lesions were obtained from the right eye of a 15 year-old female patient with longstanding LC since age 2.5 year. Ligneous conjunctivitis in this patient has exhibited a chronic recurrent coarse and has involved multiple muscosal sites. Samples analyzed included an abundant mucoid thread from the conjunctival fornix and the ligneous plaque attached to the inferior tarsus. Samples were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to characterize protein profiles and by a variety of zymographic methods to visualize fibrinolytic enzymes. We found that mucoid and ligneous samples were distinct entities. Specifically, ligneous samples contained polypeptides with electrophoretic profiles characteristic of intact fibrin, and were replete in fibrin-bound tissue plasminogen activator (t-PA). Despite the presence of ample t-PA, ligneous samples were essentially devoid of fibrinolytic activity. In contrast, neither proteins nor t-PA could be detected in mucoid samples when fractionated by 7.5-15% SDS-PAGE or analyzed by fibrin zymography, respectively. Despite the absence of t-PA, mucoid samples were replete in fibrinolytic activity. This activity was plasminogen independent, heterogenous and inhibited by PMSF. Degradation profiles suggested that this activity represented in part alpha-chymotrypsin, consistent with this patient's treatment regime, as well as plasmin, elastase and an unidentified neutrophil-derived activity. Interestingly, ligneous samples contained both latent and activated forms of matrix metalloproteinase-9 (MMP-9), whereas mucoid samples contained predominantly activated forms of MMP-9. LC is characterized by defective fibrinolysis, despite the presence of ample t-PA and intact fibrin, and by an abundant mucoid thread which binds both endogenous and exogenous enzymes including serine protease(s) and collagenase(s). The implications of these results with respect to a role for exuberant mucus production or abnormal mucins in the development of a relative mucosal-site specific plasmin(ogen) deficiency is discussed.

Fibrinogen Niigata With Impaired Fibrin Assembly: An Inherited Dysfibrinogen With a Bβ Asn-160 to Ser Substitution Associated With Extra Glycosylation at Bβ Asn-158

A novel BβAsn-160 (TAA) to Ser (TGA) substitution has been identified in fibrinogen Niigata derived from a 64-year-old asymptomatic woman, who is heterozygotic for this abnormality. The mutation creates an Asn-X-Ser–type glycosylation sequence, and a partially sialylated biantennary oligosaccharide was linked to the BβAsn-158 residue. The functional abnormality was attributed to delayed lateral association of normally formed double-stranded protofibrils based on normal cross-linking of fibrin γ-chains and tissue-type plasminogen activator-catalyzed plasmin generation by polymerizing fibrin monomers. Enzymatic removal of all the N-linked oligosaccharides from fibrinogen Niigata accelerated fibrin monomer polymerization that reached the level of untreated normal fibrin monomers, but the thrombin time was prolonged from 18.2 seconds to 113 seconds (normal: 11.2 seconds to 8.9 seconds). By scanning electron micrographic analysis, Niigata fibrin fibers were found to be more curvilinear than normal fibrin fibers. After deglycosylation, Niigata fibers became straight being similar to untreated normal fibrin fibers, whereas normal deglycosylated fibrin appeared to be less-branched than untreated normal or deglycosylated Niigata fibrin. Although normal and Niigata fibrins were similar to each other in permeation and compaction studies, deglycosylated normal and Niigata fibrins had much higher permeability and compaction values, indicating that deglycosylation had brought about the formation of more porous networks. The enzymatic deglycosylation necessitates an Asn to Asp change at position Bβ-158 that is responsible for reducing the fiber thickness because of either local repulsive forces or steric hindrance in the coiled-coil region.

Fibrinogen Niigata With Impaired Fibrin Assembly: An Inherited Dysfibrinogen With a Bβ Asn-160 to Ser Substitution Associated With Extra Glycosylation at Bβ Asn-158

A novel BβAsn-160 (TAA) to Ser (TGA) substitution has been identified in fibrinogen Niigata derived from a 64-year-old asymptomatic woman, who is heterozygotic for this abnormality. The mutation creates an Asn-X-Ser–type glycosylation sequence, and a partially sialylated biantennary oligosaccharide was linked to the BβAsn-158 residue. The functional abnormality was attributed to delayed lateral association of normally formed double-stranded protofibrils based on normal cross-linking of fibrin γ-chains and tissue-type plasminogen activator-catalyzed plasmin generation by polymerizing fibrin monomers. Enzymatic removal of all the N-linked oligosaccharides from fibrinogen Niigata accelerated fibrin monomer polymerization that reached the level of untreated normal fibrin monomers, but the thrombin time was prolonged from 18.2 seconds to 113 seconds (normal: 11.2 seconds to 8.9 seconds). By scanning electron micrographic analysis, Niigata fibrin fibers were found to be more curvilinear than normal fibrin fibers. After deglycosylation, Niigata fibers became straight being similar to untreated normal fibrin fibers, whereas normal deglycosylated fibrin appeared to be less-branched than untreated normal or deglycosylated Niigata fibrin. Although normal and Niigata fibrins were similar to each other in permeation and compaction studies, deglycosylated normal and Niigata fibrins had much higher permeability and compaction values, indicating that deglycosylation had brought about the formation of more porous networks. The enzymatic deglycosylation necessitates an Asn to Asp change at position Bβ-158 that is responsible for reducing the fiber thickness because of either local repulsive forces or steric hindrance in the coiled-coil region.

Plasmin degradation of fibrin coatings on synthetic polymer substrates

The goal of this research was to evaluate the in vitro stability of fibrin coatings on polymeric materials in the presence of plasmin. Factor XIIIa-crosslinked and noncrosslinked fibrin layers were coated on three different polyurethane substrates: Corethane, Tegaderm, and a biodegradable polyurethane, PCL/HDI/Phe. Degradation assays indicated that crosslinking the fibrin coatings enhanced the stability of the coatings on both Tegaderm and PCL/HDI/Phe; however, the persistence of the coating on the woven Corethane was not influenced by crosslinking. Degradation assay results also showed that the fibrin coating on the Corethane was significantly less stable than the fibrin coatings on the Tegaderm and PCL/HDI/Phe films. The chromogenic substrate assay data showed crosslinking did not affect the specific plasmin activity on the coatings; therefore, the increased stability resulting from crosslinking was not achieved through a reduction of fibrinolysis. The plasmin activity on the coated Corethane samples was much greater than that on either of the coated flat wound dressing materials. The large surface area of Corethane, a porous woven vascular graft material, may have had a direct influence on the fibrinolysis of its coatings by providing a large number of tissue-type plasminogen activator (tPA) binding sites. A thin, crosslinked, fibrin-coated polyurethane provides a theoretically attractive biomaterial for use in a wound dressing application and should be subject to ongoing research.

Factor XIIIa Cross-Linking of the Marburg Fibrin: Formation of αm·γn-Heteromultimers and the α-Chain–Linked Albumin·γ Complex, and Disturbed Protofibril Assembly Resulting in Acquisition of Plasmin Resistance Relevant to Thrombophila

The truncated Aα-chain of fibrinogen Marburg is partly linked with albumin by a disulfide bond. Based on the recovery of the first six amino acid residues assigned to the subunit polypeptides of fibrinogen (the Aα-and γ-chains) and albumin, 0.33 mol of albumin was estimated to be linked to 1 mol of the Marburg fibrinogen. When the Marburg fibrinogen was clotted with thrombin-factor XIIIa-Ca2+, various αmγnheteromultimers were produced, and part of the albumin was cross-linked to the γ-chain. Acid-solubilized Marburg fibrin monomer failed to form large aggregates that could be detected by monitoring turbidity at A350, but it was able to enhance tissue-type plasminogen-activator–catalyzed plasmin generation, though not as avidly as the normal control, indicating that the double-stranded protofibrils had, to some extent, been constructed. This idea seems to be supported by normal factor XIIIa–catalyzed cross-linking of the fibrin γ-chains. However, the cross-linked Marburg fibrin, being apparently fragile and translucent, was highly resistant against plasmin, and its subunit components were considerably retained for 48 hours as noted by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Although the exact mechanisms are still unclear, the albumin-incorporated factor XIIIa–cross-linked Marburg fibrin seems to have undergone a critical structural alteration(s) to acquire resistance against plasmin. This aquisition of plasmin resistance may be contributed to the postoperative pelvic vein thrombosis and recurrent pulmonary embolisms in the patient after caesarian section for her first delivery at the age of 20 years.

Factor XIIIa Cross-Linking of the Marburg Fibrin: Formation of αm·γn-Heteromultimers and the α-Chain–Linked Albumin·γ Complex, and Disturbed Protofibril Assembly Resulting in Acquisition of Plasmin Resistance Relevant to Thrombophila

The truncated Aα-chain of fibrinogen Marburg is partly linked with albumin by a disulfide bond. Based on the recovery of the first six amino acid residues assigned to the subunit polypeptides of fibrinogen (the Aα-and γ-chains) and albumin, 0.33 mol of albumin was estimated to be linked to 1 mol of the Marburg fibrinogen. When the Marburg fibrinogen was clotted with thrombin-factor XIIIa-Ca2+, various αmγnheteromultimers were produced, and part of the albumin was cross-linked to the γ-chain. Acid-solubilized Marburg fibrin monomer failed to form large aggregates that could be detected by monitoring turbidity at A350, but it was able to enhance tissue-type plasminogen-activator–catalyzed plasmin generation, though not as avidly as the normal control, indicating that the double-stranded protofibrils had, to some extent, been constructed. This idea seems to be supported by normal factor XIIIa–catalyzed cross-linking of the fibrin γ-chains. However, the cross-linked Marburg fibrin, being apparently fragile and translucent, was highly resistant against plasmin, and its subunit components were considerably retained for 48 hours as noted by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Although the exact mechanisms are still unclear, the albumin-incorporated factor XIIIa–cross-linked Marburg fibrin seems to have undergone a critical structural alteration(s) to acquire resistance against plasmin. This aquisition of plasmin resistance may be contributed to the postoperative pelvic vein thrombosis and recurrent pulmonary embolisms in the patient after caesarian section for her first delivery at the age of 20 years.

Human fibroblasts bind directly to fibrinogen at RGD sites through integrin alpha(v)beta3

Fibroblast migration into the blood clot initially filling a wound requires close interaction between fibroblasts and the matrix of the fibrin clot. However, very little is known about the specific receptor-ligand interactions that mediate fibroblast attachment to fibrin. Using an attachment assay developed to measure even relatively weak interactions, we demonstrate here that normal human dermal fibroblasts can attach to substrates coated with fibrinogen, fibrin, or the fibrinogen breakdown product I-9D. Fibroblast attachment to these ligands did not require the presence of fibronectin on the cell surface or as a component of the substrate. Cells treated with cycloheximide and monensin, to limit the synthesis and secretion of endogenous fibronectin, attached as well as untreated cells. The synthetic peptide GRGDS inhibited adhesion to fibrinogen, fibrin, and fibrinogen I-9D by about 60%, while the control peptide GRGES had no substantial effect. We conclude that attachment to these ligands is mediated at least partially by direct interactions between the substrates and one specific receptor, the integrin alpha(v)beta3. Affinity chromatography demonstrated that alpha(v)beta3 from detergent lysates of fibroblasts bound to a fibrinogen matrix and was eluted with EDTA. Furthermore, antibodies against the alpha(v)beta3 complex or against the alpha(v) subunit inhibited fibroblast attachment to fibrinogen and fibrin by 50-70%. An inhibitory antibody against the integrin beta1 subunit had no effect. The observation that integrin antagonists could not produce complete inhibition suggests that there may be other fibroblast cell surface proteins that can bind directly to fibrinogen.