VPB0638 - Effects of Clot Contraction on Clot Degradation: A Mathematical and Experimental Approach

Background: The administration of tissue plasminogen activator (tPA) drives the enzymatic degradation (fibrinolysis) of fibrin in clots and thrombi. We have previously shown that clot contraction decreases the efficacy of fibrinolysis in experiments mimicking the external administration of tPA to preformed clots.

Aims: To understand how key structural changes (1. volume shrinkage, 2. redistribution of platelets-fibrin to the periphery and erythrocytes to the core of the clot, and 3. fibrin densification, Figure 1A) that occur following clot contraction mechanistically drive the decrease in fibrinolysis of contracted blood clots.

Methods: We used a combination of mathematical modeling and experimental methodologies to characterize the process of external fibrinolysis. A 3D stochastic multiscale model of external fibrinolysis (Figure 1B) was used to determine how the structural changes that occur during the process of clot contraction influence the mechanism(s) of fibrinolysis. Turbidity and confocal microscopy experiments were performed based on modeling predictions using pooled human plasma activated with CaCl2 and thrombin, with external delivery of tPA to initiate lysis.

Results: Our model successfully simulates previous experimental results of reduced fibrinolysis rate in contracted clots compared to uncontracted clots (0.0050 vs 0.022 fraction of fibrin degraded per second, p< 0.001). Analysis of additional model and experimental clot scenarios with varying structural changes indicates that fibrin densification (tight vs. loose) makes the most significant contribution to the rate of fibrinolysis (modeling: 0.0022 vs 0.0069 fraction of fibrin degraded per second, p< 0.0001; experimentally: 0.000042 vs 0.0004 optical density per second, p< 0.001, Figure 1C) when compared to the distribution of components (p < 0.05) and degree of compaction (ns).

Conclusion(s): These results suggest that high fibrin densities caused by clot contraction reduce fibrinolysis because they limit tPA diffusion. Our work has the potential to be used to improve on current therapeutics by optimizing timing and delivery of lytic agents.