Influence of fibrinogen on fibrin polymerization. Ultracentrifugation studies

During the transformation of fibrinogen to fibrin, excess fibrinogen suppresses further polymerization of fibrin, thereby enabling the nascent fibrin to be transported in a soluble form in blood. The question of possible complex formation between fibrin and fibrinogen was addressed by analyzing fibrin/fibrinogen (1:20, mol/mol) mixtures in the presence of calcium ions in stable linear sucrose density gradients by ultracentrifugation at 37 degrees C. During the period of ultracentrifugation in independent experiments, 40% of desAA-fibrin and 30% of desAABB-fibrin, respectively, precipitated without the participation of fibrinogen. The desAABB-fibrin, recovered in the gradient fractions, appeared as high-molecular-weight polymers (22 S), whereas the recovered desAA-fibrin exhibited only a slight increase in molecular weight (9 S) compared to fibrinogen (8 S). In contrast to this finding, both types of fibrin were totally recovered in gradient fractions provided that fibrinogen was present in the gradient at a uniform concentration of 2 mg/ml. In addition, the presence of fibrinogen but not human serum albumin reduced the size of desAABB-fibrin polymers (17 S). However, stable fibrin-fibrinogen complexes could not be demonstrated, since cosedimentation of differently labelled desAABB-fibrin and fibrinogen was not detectable. These studies suggest a specific but weak interaction of the solubilizing fibrinogen with the soluble fibrin polymers as demonstrated by a rapid exchange of both macromolecules.     

Quasielastic light-scattering studies on human fibrinogen and fibrin. II. Fibrin polymerization

The shape of fibrin intermediate polymers as well as the rate of fibrinogen polymerization was studied using diffusion measured by quasielastic light scattering. After their length distribution was narrowed by gel filtration, the polymers yielded translational and rotational diffusion coefficients of 0.37 ± 0.05 × 10^?7 cm² sec^?1 and 142 ± 32 sec^?1, respectively. Theoretical considerations indicated the polymers to be rigid rods. The rate of polymerization of fibrinogen monitored by diffusion paralleled that provided by simulataneous intensity measurements. Both monitors indicated polymerization occurs most rapidly at 30°C.     

The conversion of fibrinogen to fibrin. XIII. Dissolution of fibrin and inhibition of clotting by various neutral salts

1. Fibrin clots prepared in the absence of calcium can be dissolved in solutions of lithium chloride and bromide and sodium bromide and iodide, as well as of guanidine hydrochloride and urea. These salts do not denature fibrinogen under the same conditions of concentration, temperature, and time. Sedimentation experiments on the fibrin solutions show in each case a single sharp peak with a sedimentation constant close to that of fibrinogen. 2. At lower concentrations, these salts inhibit the clotting of fibrinogen by thrombin, but in the case of lithium bromide and sodium iodide, at least, allow an intermediate polymer to accumulate whose sedimentation constant is close to that of the polymer observed in systems inhibited by hexamethylene glycol or urea.     

Effect of fibronectin on fibrinogen conversion into fibrin

The effects of fibronectin on fibrinogen clotting induced by thrombin or reptilase and on fibrin monomer polymerization in a pure system in the absence of factor XIIIa were studied. It was shown that within a broad range of concentrations and molar ratios of the mixed proteins, fibronectin does not alter significantly the fibrinogen clotting time either under thrombin or under reptilase action. The effect of fibronectin on the fibrin self-assembly consists in a slight acceleration of this process, whose degree is directly dependent on the fibronectin/fibrin monomer molar ratio as well as on the absolute fibrin monomer content at a constant molar ratio. The stimulating effect of fibronectin is amplified by Ca2+. The experimental results suggest that fibronectin can noncovalently bind the fibrin monomer and/or intermediate polymers in the non-enzymatic phase of fibrinogen conversion to fibrin.     

The conversion of fibrinogen to fibrin at the surface of curliated Escherichia coli bacteria leads to the generation of proinflammatory fibrinopeptides

The inflammatory response to bacterial infection is the result of a complex interplay between bacterial products and host effector systems, such as the immune and complement systems. Here we show that Escherichia coli bacteria expressing fibrous surface proteins, known as curli, assemble and activate factors of the human coagulation cascade at their surface. As a result of this interaction, fibrinogen is converted to fibrin and fibrinogen-derived peptides, termed fibrinopeptides, are generated. The molecular mechanisms behind the bacteria-induced formation of fibrinopeptides were investigated and shown to be triggered by the activation of the contact system, also known as the kallikrein/kinin system or the intrinsic pathway of coagulation. Samples containing fibrinopeptides generated by the interaction between bacteria and plasma were injected into animals and the inflammatory response was monitored. We found that this treatment provoked an infiltration of white blood cells, and the induction of the proinflammatory cytokine MCP-1 at the inflamed site. Our results therefore demonstrate that activation of the coagulation system at the bacterial surface contributes to the pathophysiology of bacterial infectious diseases.