Using a Radial Diffusion Method to Investigate the Role of Plasmin Degradation of Fibrin in a Physical Model of an Early-phase Wound

Fibrin clot formation, which acts to stabilize a wound following injury, is among the key early aspects of dermal wound healing. This preliminary matrix is eventually degraded via a process known as fibrinolysis and replaced with a collagen-rich matrix that continues to be remodeled to minimize scarring. Disruptions in these carefully coordinated events lead to certain undesirable conditions such as fibrosis and the formation of abnormal scars that are associated with excess amounts of collagen. The hypothesis proposed herein is that the presence of collagen (and potentially other molecules) in an early-phase model of healing alters fibrinolysis and that this effect can be attenuated with mediators of the process. Laboratory in vitro experiments were conducted using agarose-fibrin gel systems with and without collagen to study fibrinolysis caused by plasmin (a serine protease that degrades fibrin) and the effects of aprotinin (a serine protease inhibitor) and bromelain (an extract from pineapple) on fibrin clot breakdown. The extent of fibrinolysis was monitored at various times (0.5, 1, 2, 4, 8, 12, 24, 48, and 72 hours) by measuring the size of rings of fibrinolysis following the diffusion of plasmin. The data obtained at 0.5, 12, and 24-hour time points were considered (because there was no difference found in the data collected for closer intermediates nor for the longer times beyond 24 hours) and were compared using the nonparametric Mann-Whitney U statistical significance test. The results obtained showed aprotinin significantly inhibited fibrinolysis in systems containing collagen, while bromelain improved fibrinolysis. In general, the presence of increasing amounts of collagen in the system decreased the extent of fibrinolysis. These findings support the notion that early-phase deposition of collagen contributes to disrupted fibrinolysis, which could lead to impaired healing as well as potentially facilitate control of fibrinolysis.