Fibrin Derived from Patients with Chronic Thromboembolic Pulmonary Hypertension is Resistant to Lysis

Rationale Although acute pulmonary embolism is epidemiologically associated with chronic thromboembolic pulmonary hypertension, the factors responsible for resistance to thrombolysis and a shift toward vascular remodeling within the pulmonary arteries of patients with chronic thromboembolic pulmonary hypertension are unknown. Objective Determine whether fibrin from patients is more resistant to plasmin-mediated lysis than fibrin from healthy control subjects. Methods Fibrinogen purified from patients and control subjects was used to prepare fibrin clots, which were subsequently digested with plasmin for various periods of time. The degradation of the α-, β-, and γ-chains of fibrin and the appearance of peptide fragments over time were assessed by polyacrylamide gel electrophoresis and Western blotting. Measurements and Main Results Densitometry of Coomassie-stained gels revealed significantly slower cleavage of all three polypeptide chains of fibrin from patients compared with control subjects (p < 0.05). In particular, release of N-terminal fragments from the β-chain of fibrin, which promote cell signaling, cell migration, and angiogenesis, was retarded in patients compared with control subjects (p < 0.01). Conclusions The relative resistance of patient fibrin to plasmin-mediated lysis may be due to alterations in fibrin(ogen) structure affecting accessibility to plasmin cleavage sites. The persistence of structural motifs of fibrin, such as the β-chain N-terminus, within the pulmonary vasculature could promote the transition from acute thromboemboli into chronic obstructive vascular scars.