Fibrinogen Marburg a new genetic variant of fibrinogen

Thrombosis in Inherited Fibrinogen Disorders

Although inherited fibrinogen disorders (IFD) are primarily considered to be bleeding disorders, they are associated with a higher thrombotic complication risk than defects in other clotting factors. Managing IFD patients with thrombosis is challenging as anticoagulant treatment may exacerbate the underlying bleeding risk which can be life-threatening. Due to the low prevalence of IFD, there is little information on pathophysiology or optimal treatment of thrombosis in these patients. We searched the literature for cases of thrombosis among IFD patients and identified a total of 128 patient reports. In approximately half of the cases, thromboses were spontaneous, while in the others trauma, surgery, and parturition contributed to the risk. The true mechanism(s) of thrombosis in IFD patients remain to be elucidated. A variety of anticoagulant treatments have been used in the treatment or prevention of thrombosis, sometimes with concurrent fibrinogen replacement therapy. There is no definite evidence that fibrinogen supplementation increases the risk of thrombosis, and it may potentially be effective in the treatment and prevention of both thrombosis and hemorrhage in IFD patients.

Fibrinogen splice variation and cross-linking: Effects on fibrin structure/function and role of fibrinogen γ' as thrombomobulin II

Fibrin is an important matrix protein that provides the backbone to the blood clot, promoting tissue repair and wound healing. Its precursor fibrinogen is one of the most heterogeneous proteins, with an estimated 1 million different forms due to alterations in glycosylation, oxidation, single nucleotide polymorphisms, splice variation and other variations. Furthermore, ligation by transglutaminase factor XIII (cross-linking) adds to the complexity of the fibrin network. The structure and function of the fibrin network is in part determined by this natural variation in the fibrinogen molecule, with major effects from splice variation and cross-linking. This mini-review will discuss the direct effects of fibrinogen αEC and fibrinogen γ' splice variation on clot structure and function and also discuss the additional role of fibrinogen γ' as thrombomodulin II. Furthermore, the effects of cross-linking on clot function will be described. Splice variation and cross-linking are major determinants of the structure and function of fibrin and may therefore impact on diseases affecting bleeding, thrombosis and tissue repair.

α-α Cross-links increase fibrin fiber elasticity and stiffness

Fibrin fibers, which are ~100 nm in diameter, are the major structural component of a blood clot. The mechanical properties of single fibrin fibers determine the behavior of a blood clot and, thus, have a critical influence on heart attacks, strokes, and embolisms. Cross-linking is thought to fortify blood clots; though, the role of α-α cross-links in fibrin fiber assembly and their effect on the mechanical properties of single fibrin fibers are poorly understood. To address this knowledge gap, we used a combined fluorescence and atomic force microscope technique to determine the stiffness (modulus), extensibility, and elasticity of individual, uncross-linked, exclusively α-α cross-linked (γQ398N/Q399N/K406R fibrinogen variant), and completely cross-linked fibrin fibers. Exclusive α-α cross-linking results in 2.5× stiffer and 1.5× more elastic fibers, whereas full cross-linking results in 3.75× stiffer, 1.2× more elastic, but 1.2× less extensible fibers, as compared to uncross-linked fibers. On the basis of these results and data from the literature, we propose a model in which the α-C region plays a significant role in inter- and intralinking of fibrin molecules and protofibrils, endowing fibrin fibers with increased stiffness and elasticity.

Biophysical characterization of fibrinogen Caracas I with an Aα-chain truncation at Aα-466 Ser

Fibrinogen Caracas I is a dysfibrinogenemia with a mild bleeding tendency; a novel nonsense mutation, in the gene coding the Aalpha-chain, identified in this study as G4731T, giving rise to a new stop codon at Aalpha-Glu 467. Fibrinogen from two family members, the mother and sister of the propositus, both heterozygous for the mutation were studied, analyzing clots made from both plasma and purified fibrinogen. Clot structure and properties were characterized by turbidity, permeation, scanning electron microscopy and rheological studies. Permeation through Caracas I plasma clots was decreased, consistent with the decreased final turbidity. As shown by scanning electron microscopy, plasma clots from the patients were composed of very thin fibers, with increased fibrin density and reduced pore size. Viscoelastic measurements revealed that fibrinogen Caracas I plasma clots were much stiffer and less subject to compaction. These results demonstrate a key role of the carboxyl-terminal alpha chains of fibrin in lateral aggregation during polymerization and reinforce the utility of studying plasma clots. It is important to point out that the biophysical studies with fibrinogen purified by two different methods yielded contradictory results, which can be accounted for by selective purification of certain molecular species as seen by two-dimensional electrophoresis.

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.

Clinical disorders of fibrinolysis: a critical review

Much progress has recently been made in understanding the biochemistry and physiology of endogenous fibrinolysis. As a result, a better understanding of the mechanisms and clinical consequences of disordered fibrinolysis has emerged. Increased fibrinolytic activity is an uncommon but important cause of hemorrhagic disease. Congenital disorders of fibrinolysis which cause bleeding include increased plasma plasminogen activator activity and deficiency of alpha-2 antiplasmin. Acquired disorders associated with increased fibrinolytic activity and bleeding include liver cirrhosis, amyloidosis, acute promyelocytic leukemia, some solid tumors, and certain snake envenomation syndromes. Increased fibrinolysis is important to recognize because epsilon-aminocaproic acid (EACA) may be required to prevent or control bleeding. Diminished fibrinolytic activity has been associated with a variety of thrombotic disorders, but a direct cause-and-effect relationship has yet to be established. Congenital abnormalities of fibrinolysis associated with thrombosis include plasminogen deficiency, decreased endothelial generation of plasminogen activator activity, and certain abnormal fibrinogens. Thrombosis in these disorders is effectively managed with warfarin. Diminished fibrinolysis has also been reported in "idiopathic" venous thrombosis, oral contraceptive-induced and post-operative venous thrombosis, coronary artery disease, cerebrovascular disease, systemic lupus erythematosus, and thrombotic thrombocytopenic purpura, but the significance of abnormal fibrinolysis in these disorders is uncertain. Large, prospective studies of fibrinolytic variables as risk factors for vascular and thrombotic disease are needed to determine whether pharmacologic augmentation of impaired fibrinolysis could be useful in the prevention or treatment of these disorders.

The fibrinolytic system in man

The fibrinolytic system comprises a proenzyme, plasminogen, which can be activated to the active enzyme plasmin, that will degrade fibrin by different types of plasminogen activators. Inhibition of fibrinolysis may occur at the level of plasmin or at the level of the activators. Fibrinolysis in human blood seems to be regulated by specific molecular interactions between these components. In plasma, normally no systemic plasminogen activation occurs. When fibrin is formed, small amounts of plasminogen activator and plasminogen adsorb to the fibrin, and plasmin is generated in situ. The formed plasmin, which remains transiently complexed to fibrin, is only slowly inactivated by alpha 2-antiplasmin, while plasmin, which is released from digested fibrin, is rapidly and irreversibly neutralized. The fibrinolytic process, thus, seems to be triggered by and confined to fibrin. Thrombus formation may occur as the result of insufficient activation of the fibrinolytic system and (or) the presence of excess inhibitors, while excessive activation and/or deficiency of inhibitors might cause excessive plasmin formation and a bleeding tendency. Evidence obtained in animal models suggests that tissue-type plasminogen activator, obtained by recombinant DNA technology, may constitute a specific clot-selective thrombolytic agent with higher specific activity and fewer side effects than those currently in use.

Fibrinogen Logroño. A new case of congenital dysfibrinogenemia

An abnormal fibrinogen was discovered in a 9-year-old male subject without history of hemorrhagic diathesis. Coagulation time, prothrombin time and Reptilase time were prolonged. The thrombin time was corrected using increasing concentrations of normal plasma and bovine thrombin; there was a partial correction at pH 6.5 and ionic strength 0.05. A study of the family showed that the mother and a brother of the propositus presented the same abnormalities. Analysis of the purified fibrinogen showed normal fibrinopeptide release and normal levels of sialic acid and hexosamines. However, coagulation index, polymerization of fibrin monomers, isoelectric point and sedimentation coefficient were abnormal. In view of the abnormalities described and by comparison with the data reported in the literature, we believe that this should be considered a new variant of the fibrinogen molecule and we have designated it 'fibrinogen Logroño'.

An abnormal fibrinogen (Copenhagen II) with increased sialic acid content associated with thrombotic tendency and normal liver function

An increased sialic acid content of the fibrinogen molecule is found in foetal fibrinogen and as an acquired disorder in hepatic disease. A qualitatively abnormal fibrinogen was detected in the plasma of a 25-year-old man with a thrombotic tendency. The purified fibrinogen had a significantly increased content of sialic acid, an abnormal fibrin monomer polymerization, and a changed mobility in crossed affinity-immunoelectrophoresis using immobilized helix pomatia lectin. The patient had no biochemical or clinical signs of liver disease. The occurrence of a thrombotic tendency and an increased fibrinogen sialic acid content without signs of liver disease may represent a new variant of congenital dysfibrinogenaemia.

A new type of congenital dysfibrinogenaemia with defective fibrin lysis--Dusard syndrome: possible relation to thrombosis

Congenital dysfibrinogenaemia is described in three members of a family presenting with recurrent thrombosis and in two other young members not yet affected. An abnormality in the polymerization of fibrin monomers was noted. In addition, the pathological fibrin clots were found to be less sensitive to degradation by a post venous occlusion euglobulin solution than normal fibrin. After fibrin clot incubation with lys-plasminogen at different concentrations, the biological activity of plasminogen in patient fibrin clot on S 2251 after SK-addition, was less than that observed with normal fibrin. It is speculated that defective in vivo thrombolysis might explain the recurrent thrombosis observed in this family. This finding represents a new concept in understanding thromboembolic diseases.

Fibrinogen Copenhagen; an abnormal fibrinogen with defective polymerization and release of fibrinopeptide A, but normal adsorption of plasminogen

A qualitatively abnormal fibrinogen was detected in the plasma of a 53 year old woman with severe arterial thrombotic disease. The concentrations of plasma fibrinogen and serum fibrinogen related material were normal. The abnormal fibrinogen was electrophoretically normal. The defects detected were an abnormality of polymerization of fibrin monomers and a decreased rate of release of fibrinopeptide A. The absorption of radiolabelled partially degraded plasminogen on to fibrin prepared from purified fibrinogen Copenhagen was normal.

Dysfibrinogenaemia characterized by abnormal fibrin monomer polymerization and normal fibrinopeptide A release

Routine testing on plasma from a patient due to undergo a coronary artery bypass graft operation revealed a prolonged thrombin clotting time associated with a normal plasma fibrinogen level when this was determined by a method not dependent upon the rate of fibrin formation. Fibrinogen purified from the patient's plasma by precipitation with beta-alanine also gave a prolonged thrombin time and this confirmed the presence of a dysfibrinogenaemia. Increasing calcium chloride concentration, addition of protamine sulphate and decreasing ionic strength all produced a partial correction of the clotting defect. Addition of normal plasma to patient's plasma failed to correct the prolonged thrombin clotting time and a pH dependence of the defect was also observed. Kinetic studies of fibrinopeptide release, using a specific radioimmunoassay, demonstrated no delay in the release of patient fibrinopeptide A. The functional defect was localized as an abnormality in the polymerization of fibrin monomers by studying fibrin monomers prepared and isolated from plasma and from purified fibrinogen solution. An electrophoretic examination of the patient's fibrinogen using both agarose and polyacrylamide gels failed to demonstrate any alteration in mobility or any structural defect associated with the polypeptide chains A alpha, B beta and gamma. All seven of the living siblings of the propositus and also his daughter showed no abnormality in any clotting assay. However, because the propositus did not suffer from liver disease it has been assumed that the abnormality is genetic in origin.