Dennis K. Galanakis

Transient Intermediates in the Thrombin Activation of Fibrinogen EVIDENCE FOR ONLY THE desAA SPECIES

The structure of a fibrin gel depends on the nature of the fibrinogen activation products produced by thrombin and the physical condition under which assembly occurs. Two different structures of the intermediate fibrin protofibril have been proposed, the production of which requires different extents of fibrinopeptide A (FpA) cleavage from fibrinogen. The fibrin activation intermediates must be stable since time is required for the intermediates to diffuse to growing protofibrils. The classic Hall-Slayter model requires cleavage of both FpAs to form a desAA intermediate. The Hunziker model requires cleavage of only one FpA to form an AdesA intermediate. Electrophoretic quasi elastic light scattering has been used to show the time-dependent production of the relevant fibrinogen activation intermediates that includes desAA but not AdesA.

The dimeric Aα chain composition of dysfibrinogenemic molecules with mutations at Aα 16

Abstract In the last stage of fibrinogen synthesis, two Aα-Bβ-γ half-molecules are disulfide linked in their N-terminal regions to form a dimeric fibrinogen molecule. It is not known whether intracellular hepatocyte assembly of fibrinogen half-molecules occurs randomly or is a directed process. One analysis based on partitioning of coagulable components of fibrinogen from a heterozygous dysfibrinogenemic subject having a mutation at the thrombin cleavage site (Fibrinogen Louisville, Aα16 R→H), suggested that only homodimeric molecules containing two normal fibrinopeptides A (FPA, FPA) or two abnormal fibrinopeptides A (FPA ★ , FPA ★ ) were present in plasma, implying that fibrinogen dimer assembly is directed. The same type of analyses on Fibrinogen Birmingham (Aα16 R→H) indicated that there were heterodimers as well as homodimers, suggesting that fibrinogen dimer assembly is random. To examine this question more directly, the composition of fibrinogen molecules from seven dysfibrinogenemic families with either R→C (four) or R→H (three) Aα16 mutations was determined. Following treatment with Atroxin to release normal FPA from fibrinogen, N-terminal disulfide knot (‘N-DSK’) cleavage fragments were prepared and subsequently separated by SDS-PAGE to resolve ‘N-DSK’ components with two FPA ★ s (N-DSK homodimer), one FPA ★ (des A N-DSK heterodimer), or no FPAs (des AA N-DSK homodimer). Fibrinogen from subjects whose molecules contained both normal and abnormal Aα chains, yielded a heterodimeric des A N-DSK derivative, as well as smaller amounts of homodimeric N-DSK and des AA N-DSK. These results indicate that when both types of Aα chain are produced, both Aα chain alleles are expressed and the resulting fibrinogen dimers are assembled randomly.

Case Report: Treatment of an Intracranial Arteriovenous Malformation in a Patient With Complicated Hemophilia

The authors describe a young man with hemophilia complicated by chronic hepatic dysfunction, hypodysfibrinogenemia, and immune thrombocytopenia that resulted in a complex coagulopathy. The patient had a ruptured occipital arteriovenous malformation. The malformation was managed by temporary correction of the coagulopathy using cryoprecipitate, platelet transfusions, and plasmapheresis with fresh frozen plasma replacement. The patient underwent staged preoperative embolization followed by surgical excision of the lesion. Hemostasis was acceptable during the neurointerventional and subsequent surgical management, and no complications of coagulopathy occurred. Plasmapheresis may provide effective preparation for patients with hemophilia and complex coagulation abnormalities who require neurosurgical intervention.

Antifibrinogen IgG, fibrinogen, and Clq complexes circulating in a hypodysfibrinogenemic proband. Isolation, stoichiometry, and partial characterization.

Abstract: Circulating antifibrinogen antibodies have been reported in rare afibrinogenemic propositi, apparently occurring following fibrinogen replacement therapy, but immune complexes have not been described. In this report we describe circulating immune complexes formed by a monoclonal antifibrinogen IgG in a heterozygous hypodysfibrinogenemic (Aα 16 Arg → Cys) proband. Estimated by partial protein sequence and by other analyses, each immune complex consisted of one fibrin(ogen), one C1q, and 3–4 IgG molecules. The complexes were cryoprecipitable, a property also displayed by mixtures of proband IgG and normal fibrinogen. Indicating that both D and E domains were necessary for this behavior, cryoprecipitability was abolished by preincubation of the isolated IgG with either isolated normal fibrinogen fragment D100 or E. Consistent with the crossreactivity of the IgG with normal and mutant fibrinogen, the results suggest that the primary epitope resides on a D‐E locus on the fibrin polymer formed by normal and abnormal molecules containing the uncleaved (or mutant) peptide A.