Investigating the two regimes of fibrin clot lysis: an experimental and computational approach

It has been observed in vitro that complete clot lysis is generally preceded by a period of latency during which the degradation seems to be inefficient. However, this latency was merely notified but not yet quantitatively discussed. In our experiments we observed that the lysis ubiquitously occurred in two distinct regimes, a slow and a fast lysis regime. We quantified extensively the duration of these regimes for a wide spectrum of experimental conditions and found that on average the slow regime lasts longer than the fast one, meaning that during most of the process the lysis is ineffective. We proposed a computational model in which the two regimes result from a spatially constrained kinetic of clot lysis: first the biochemical reactions take place at the outer core of the fibrin fibers composing the clot, then in the bulk resulting in the observed fast lysis regime. This simple hypothesis appeared to be sufficient to reproduce with a great accuracy the lysis profiles obtained experimentally. Our results shed light on new insights regarding the dynamical aspects of the lysis of fibrin rich clots in a context where the timing is so critical for patient treatment and outcome. SignificanceWhile the interplay between the main components of the fibrinolytic system is well understood, some dynamical aspects of the fibrinolysis remain unclear. Notably, we observe that in vitro fibrin rich clots undergo a slow and inefficient phase of degradation when subject to endogenous fibrinolysis. In fact, it turns out that a large part of the lysis process operates in this slow regime. To explain this observation, we proposed a computational model in which the properties of the binding of the proteins change during the lysis. First plasminogen and tissue plasminogen activator bind at the surface of the fibers, resulting in a slow lysis, then in the bulk of the fibers thus speeding up the degradation of the clot..