Influence of Fibrin Network Conformation and Fibrin Fiber Diameter on Fibrinolysis Speed

Abstract

Abstract-Abnormal fibrin architecture is thought to be a determinant factor of hypofibrinolysis. However, because of the lack of structural knowledge of the process of fibrin digestion, relationships between fibrin architecture and hypofibrinolysis remain controversial. To elucidate further structural and dynamic changes occurring during fibrinolysis, cross-linked plasma fibrin was labeled with colloidal gold particles, and fibrinolysis was followed by confocal microscopy. Morphological changes were characterized at fibrin network and fiber levels. The observation of a progressive disaggregation of the fibrin fibers emphasizes that fibrinolysis proceeds by transverse cutting rather than by progressive cleavage uniformly around the fiber. Plasma fibrin clots with a tight fibrin conformation made of thin fibers were dissolved at a slower rate than those with a loose fibrin conformation made of thicker (coarse) fibers, although the overall fibrin content remained constant. Unexpectedly, thin fibers were cleaved at a faster rate than thick ones. A dynamic study of FITC-recombinant tissue plasminogen activator distribution within the fibrin matrix during the course of fibrinolysis showed that the binding front was broader in coarse fibrin clots and moved more rapidly than that of fine plasma fibrin clots. These dynamic and structural approaches to fibrin digestion at the network and the fiber levels reveal aspects of the physical process of clot lysis. Furthermore, these results provide a clear explanation for the hypofibrinolysis related to a defective fibrin architecture as described in venous thromboembolism and in premature coronary artery disease. Key Words: fibrin Ⅲ fibrinolysis Ⅲ confocal microscopy T he fibrin matrix has a much more complicated role than that of providing the scaffolding of the thrombus or being the target of fibrinolysis. Abnormal fibrin structure in vitro has been related to in vivo premature coronary artery disease in young patients and to severe venous thromboembolic disease in patients with dysfibrinogenemias. 1,2 In those situations, an abnormal fibrin matrix made up of abnormally thin fibers has been shown to promote hypofibrinolysis and embolization. Although much is known about the molecular basis of fibrinolysis, relationships between fibrin conformation and fibrinolysis need to be clarified.Fibrin actively regulates its self-dissolution through numerous interactions with fibrinolytic and antifibrinolytic components. Activation of plasminogen by tissue plasminogen activator (tPA) that is initiated on the conversion of fibrinogen into fibrin is a critical step that is affected by fibrin structure. The theory of a decrease of plasminogen binding to fibrin 3 has been strengthened from observations showing that clots with a fine fibrin (tight) conformation display a slower lysis rate than those with a coarse fibrin (loose) conformation. 2,4,5 So far, neither a molecular nor a structural basis has been detected for these differences. Moreover, a recent report demonstrates that under othe...

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

“…Cross-linking of fibronectin to fibrin has been shown to have no effect on clot rigidity, however those clots were denser, with smaller pores [37]. A more recent study by Ramanathan et al, in a purified system in the absence of FXIII, showed that fibronectin increases the initial rate of fibrin polymerisation, leading to the formation of denser clots [38], thought to be more resistant to fibrinolysis [39].…”

“…Ligation of thrombospondin-1 within the fibrin clot was found to reduce the lag-time and lead to the formation of denser clots containing thinner fibres, in a dose-dependent manner [41], rendering them more resistant to fibrinolysis [39].…”

The influence of type 2 diabetes on fibrin structure and function

“…Assessment of the structure of the fibrin clot itself in relation to atherothrombotic disease development has revealed its structure to be heterogeneous, being influenced by genetic and environmental factors [14]. Clinical studies have reported an association between clot structure and the development of premature coronary heart disease [15]; patients suffering a myocardial infarction before the age of 45 years formed clots with a denser, less permeable structure than healthy control subjects [15], a structural change that may contribute to atherothrombotic risk by increasing resistance to fibrinolysis [16].…”

“…Analysis of the structure of the fibrin clot in relation to diabetes has revealed that fibrin clots formed from the plasma of subjects with type 1 diabetes have a denser structure, with smaller intrinsic pores than those formed by healthy control subjects [17,18], a feature that has been shown to enhance a clot's resistance to fibrinolysis [16,19]. However, the mechanism(s) by which fibrin clot structure is altered in type 1 diabetes are unclear.…”

The clinical relevance of altered fibrinogen packaging in the presence of 17β-estradiol and progesterone

“…Although individual thinner fibers lyse more easily [30] a dense network of thin fibrin fibers are more resilient to lysis than thick fibers arranged in a more dispersed configuration, regardless of the quantity of the lytic agent [31]. Since both hormones decrease the 22 fibrin fiber diameter it could be assumed that in turn this would decrease the local enhancement and acceleration of fibrinolysis [31]. However, turbidimetric analysis indicated that both 17β-Estradiol and Progesterone decreased the CLT, although only significantly for 17β-Estradiol at concentrations between 140 -300 pg.mL -1 .…”