PB1212 - Effect of PAI-1 on clot structure and fibrinolysis

Background: Excessive blood clotting can lead to heart attacks and strokes because they can restrict blood flow to downstream organs; these blood clots must be resolved through a process known as fibrinolysis. Tissue plasminogen activator (tPA) triggers the enzymatic process of fibrinolysis. Cancer patients, obese people, and pregnant women all have an increased risk for excessive clotting partly linked to elevated plasminogen activator inhibitor type-1 (PAI-1), which down-regulates fibrinolysis as it inhibits tPA function.

Aims: Here, we studied the biochemical and structural changes that result in altered fibrinolysis from varying PAI-1 levels.

Methods: We used a turbidimetric assay that allowed us to track clot formation and lysis with increasing concentrations of PAI-1 to represent different physiological conditions. Confocal and scanning electron microscopy was utilized to visualize the fibers and network. One-way ANOVA tests were performed to compare clot behavior and structures.

Results: As expected, we observed a slower rate of lysis (p < 0.0001) and delayed time to 50% lysis (p < 0.0001) with increasing PAI-1 concentrations. Interestingly, we observed a slower rate of clot formation (p < 0.0001) and increase in maximum optical density (p < 0.0001) with increasing PAI-1 concentrations. This led us to believe there was both a biochemical and structural change because of exogenously added PAI-1. Confocal microscopy identified no change in network density but an increase in pore size (p < 0.001), while scanning electron microscopy (SEM) revealed fewer, thicker fibers (p < 0.001) for increasing PAI-1 levels.

Conclusion(s): We propose PAI-1 impairs fibrinolysis through both a structural and enzymatic influence. These results on the impact of PAI-1 can aid in the development of better clot degradation agents. Furthermore, this work highlights the need for careful observation of PAI-1 levels in at-risk patients.