Lytic and mechanical stability of clots composed of fibrin and blood vessel wall components

Abstract

BackgroundProteases expressed in atherosclerotic plaque lesions generate collagen fragments, release glycosaminoglycans (chondroitin sulfate [CS] and dermatan sulfate [DS]) and expose extracellular matrix (ECM) proteins (e.g. decorin) at sites of fibrin formation.ObjectiveHere we address the effect of these vessel wall components on the lysis of fibrin by the tissue plasminogen activator (tPA)/plasminogen system and on the mechanical stability of clots.Methods and resultsMMP-8-digested collagen fragments, isolated CS, DS, glycosylated decorin and its core protein were used to prepare mixed matrices with fibrin (additives present at a 50-fold lower mass concentration than fibrinogen). Scanning electron microscopy (SEM) showed that the presence of ECM components resulted in a coarse fibrin structure, most pronounced for glycosylated decorin causing an increase in the median fiber diameter from 85 to 187 nm. Rheological measurements indicated that these structural alterations were coupled to decreased shear resistance (1.8-fold lower shear stress needed for gel/fluid transition of the clots containing glycosylated decorin) and rigidity (reduction of the storage modulus from 54.3 to 33.2 Pa). The lytic susceptibility of the modified fibrin structures was increased. The time to 50% lysis by plasmin was reduced approximately 2-fold for all investigated ECM components (apart from the core protein of decorin which produced a moderate reduction of the lysis time by 25%), whereas fibrin-dependent plasminogen activation by tPA was inhibited by up to 30%.ConclusionECM components compromise the chemical and mechanical stability of fibrin as a result of changes in its ultrastructure.

Fibrin Formation, Structure and Properties

“…In addition, the complex mechanical behavior of fibrin is important for the interaction between cells and extracellular matrix (Wen and Janmey 2013). Since mechanical stress makes fibrin more resistant to fibrinolysis (Varju et al 2011; Bucay et al 2015), fibrin elasticity may be a significant determinant of susceptibility of clots and thrombi to enzymatic lysis (Rottenberger et al 2013; Longstaff et al 2013). …”

Fibrin mechanical properties and their structural origins

“…Since mechanical stress makes fibrin more resistant to fibrinolysis [64, 65], fibrin elasticity may be a significant determinant of susceptibility of clots and thrombi to endogenous or exogenous thrombolytics. For example, fibrin formed in the presence of the vessel wall components displayed a reduced stiffness associated with increased susceptibility to enzymatic lysis [66]. On the contrary, the addition of histone-DNA complexes to fibrin (mimicking their interaction in the neutrophil extracellular traps at the site of inflammation/thrombosis) results in an increased fibrin rigidity and slower fibrinolysis [67].…”

Neutrophil extracellular traps in thrombi retrieved during interventional treatment of ischemic arterial diseases

“…Tissue damage in ischemic cardiovascular disease is often a consequence of embolization from unstable thrombi [18], whereas the clinical outcome of the interventional or lytic treatment in AIS, CAD and PAD is also affected by the structural phenotype of fibrin, the primary matrix of thrombi [19]. The structural features of fibrin are greatly modified in the presence of NET or extracellular matrix components and this modification determines the mechanical and lytic stability of thrombi [15,20,21]. These facts justify the growing interest in investigating thrombus composition [22,23], but very few data are available concerning the fibrin structure in relation to the cellular and NET content of thrombi in the clinical setting of AIS.…”