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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.

Adult↗

Fibrinogen and albumin deficiencies associated with packed red blood cell transfusions.

Fibrinogen content was determined for each of 50 units of citrate-dextrose-phosphate (CPD)-preserved whole blood, packed red blood cells reconstituted with 250 ml. of saline, and packed red cells reconstituted with 250 ml. of purified plasma protein fraction (PPF). The total protein and albumin were measured, by electrophoresis, on each of 10 units of the three varieties of blood. The fibrinogen content of the two types of reconstituted cells was significantly lower than that of whole blood. Although the total protein/albumin content of whole blood and PPF-reconstituted red cells was similar, saline-reconstituted cells were markedly deficient in both total protein and albumin. Low fibrinogen and platelet levels subsequent to transfusion with reconstituted packed red cells can lead to an erroneous diagnosis of disseminated intravascular coagulation. Administration of large quantities of saline-reconstituted packed cells could be an etiologic factor in postoperative interstitial pulmonary edema.

Adult↗

The effect of hypofibrinogenemia with batroxobin on rat Masugi nephritis.

The effect of hypofibrinogenemia with batroxobin on proliferative glomerular lesions of Masugi nephritis was examined in the rat. Batroxobin-treated rats had a relatively low level of plasma fibrinogen and a reduction in glomerular fibrin deposition. Mean nuclear counts in the outer cortical glomeruli were less in the batroxobin-treated group than in the untreated group on the 7th day. However, the difference in the overall severity of the glomerular histologic lesions between the two groups was not significant. Continual injections of the same dosage of batroxobin failed to maintain hypofibrinogenemia, possibly due to the antibody formation. These results suggest that relatively low plasma levels of fibrinogen are obviously not effective enough to prevent the development of the proliferative lesions in rat Masugi nephritis.

Afibrinogenemia↗

Cryoprecipitate. Patterns of use.

The type of coagulation factors and proteins in cryoprecipitate determine the appropriate indications for its use. To determine the pattern of use at a tertiary care medical center, we performed a retrospective audit of cryoprecipitate utilization. A total of 51 patients received 88 pools of cryoprecipitate. In 39 patients, cryoprecipitate was transfused for appropriate indications: hypofibrinogenemia (n = 19), tissue plasminogen activator reversal (n = 1), management of massive transfusion (n = 7), correction of uremic bleeding (n = 2), and for making fibrin sealant (n = 10). Overall, these patients used approximately 80% of the cryoprecipitate transfused. In 12 other patients, cryoprecipitate was transfused inappropriately to attempt reversal of the anticoagulant effects of warfarin therapy (n = 6), to treat impaired surgical hemostasis in the absence of hypofibrinogenemia (n = 4), and to treat hepatic coagulopathy with multiple factor deficiencies (n = 2). The patterns of misuse, involving 24% of all cryoprecipitate orders, suggest a widespread misunderstanding and need for focused education about the coagulation factors and proteins present in cryoprecipitate and appropriate indications for its use.

Adult↗

Elevated fibrinogen in an acute phase reaction prolongs the reptilase time but typically not the thrombin time.

The effects of elevated fibrinogen on thrombin and reptilase times have not been well documented. High fibrinogen levels are common (38% of specimens submitted to our coagulation laboratory). Among 102 patients in the present study, an endogenously elevated fibrinogen level was significantly associated, as follows, with prolonged reptilase times: 1 (4%) of 28 with normal fibrinogen levels, 6 (20%) of 30 with levels in the 400 to 700 mg/dL (4.0-7.0 g/L) range, 10 (34%) of 29 with levels in the 700 to 1,000 mg/dL (7.0-10.0 g/L) range, and 7 (47%) of 15 with fibrinogen levels greater than 1,000 mg/dL (10.0 g/L). This association was independent of patient age and fibrin degradation product titer. In contrast, thrombin time was not altered notably by elevated fibrinogen levels. In 4 patients studied further, the prolonged clotting times could be corrected or nearly corrected by adding calcium chloride or albumin, whereas no such corrections were demonstrable in samples from several hereditary dysfibrinogenemia control subjects. An elevated fibrinogen level is common and is associated with reptilase time prolongations. For patients with prolonged reptilase times, a fibrinogen assay is suggested before establishing a diagnosis of dysfibrinogenemia.

Acute-Phase Reaction↗

Structural alterations in hereditary dysfibrinogens.

Dysfibrinogens can be grossly divided in two groups: (1) defective thrombin-catalyzed conversion of fibrinogen molecules to fibrin monomers, and (2) defective fibrin polymerization due to structural alterations in polymerization sites, that include "A" and "a" sites, end-to-end D:D abutment surfaces, and lateral association sites involving the carboxyl terminal region of the fibrin alpha-chain. Recently, a number of mutations in the fibrinogen genes have been identified, and many of these encode changes that occur in regions of fibrinogen that have been elucidated by high-resolution structural studies. Here we focus on the structure-function relationships of fibrinogen that can be inferred from studies involving these abnormal molecules.

Afibrinogenemia↗

Mutant fibrinogen cleared from the endoplasmic reticulum via endoplasmic reticulum-associated protein degradation and autophagy: an explanation for liver disease.

The endoplasmic reticulum (ER) quality control processes recognize and remove aberrant proteins from the secretory pathway. Several variants of the plasma protein fibrinogen are recognized as aberrant and degraded by ER-associated protein degradation (ERAD), thus leading to hypofibrinogenemia. A subset of patients with hypofibrinogenemia exhibit hepatic ER accumulation of the variant fibrinogens and develop liver cirrhosis. One such variant named Aguadilla has a substitution of Arg375 to Trp in the gamma-chain. To understand the cellular mechanisms behind clearance of the aberrant Aguadilla gamma-chain, we expressed the mutant gammaD domain in yeast and found that it was cleared from the ER via ERAD. In addition, we discovered that when ERAD was saturated, aggregated Aguadilla gammaD accumulated within the ER while a soluble form of the polypeptide transited the secretory pathway to the trans-Golgi network where it was targeted to the vacuole for degradation. Examination of Aguadilla gammaD in an autophagy-deficient yeast strain showed stabilization of the aggregated ER form, indicating that these aggregates are normally cleared from the ER via the autophagic pathway. These findings have clinical relevance in the understanding of and treatment for ER storage diseases.

Afibrinogenemia↗