Chronic thrombo-embolic pulmonary hypertension (CTEPH) is a debilitating and potentially fatal sequelae of acute pulmonary embolism. The etiology of CTEPH has not been determined, resulting in a lack of predictive or preventive strategies for CTEPH after acute pulmonary embolism. We speculate that the N-terminus of the fibrin beta chain (residues 15-21) is a potent stimulator of pulmonary endothelial cells and fibroblasts and could be involved in pulmonary vascular scarring in CTEPH. We studied fibrinogen purified from patients with CTEPH to determine the susceptibility of the beta chain N-terminus to lysis by plasmin.
The kinetic patterns of fibrin polymer digestion by plasmin were compared between five CTEPH patients and five healthy volunteers. Non-CROSS-linked fibrin clots (50 ug) were incubated with plasmin (1.25 ug) for various times (0-6 hours) at 37 degrees C. Aliquots from each time point were subjected to SDS-PAGE under reducing conditions, and the gels were western blotted using antibodies specific for the fibrin beta chain N-terminus or stained with Coomassie blue.
Western blotting disclosed that plasmin lysed the fibrin beta chain N-terminus more slowly in CTEPH patients than in controls (see figure). A two way ANOVA of western blot densitometry, considering patient group and digestion time, disclosed a significant persistence of fibrin beta-chains with intact N-termini in the CTEPH group compared to the controls (p = 0.025). Coomassie blue disclosed trends toward resistance of the CTEPH alpha, beta and gamma chains to plasmin-mediated lysis, relative to the controls (p values of 0.12, 0.17 and 0.23, respectively).
These results indicate that fibrin from CTEPH patients may be digested more slowly and perhaps less completely by plasmin, particularly at the N-terminus of the beta chain. This phenomenon may be due to an alteration in the structure or accessibility of its plasmin cleavage site.
Structural variances of fibrinogen, which make it relatively resistant to normal fibrinolysis, may be one of the mechanisms responsible for the development of CTEPH after acute pulmonary embolism.
T.A. Morris, None.