Increased N-terminal cleavage of alpha-2-antiplasmin in patients with liver cirrhosis

Abstract

Summary: Background: The activity of alpha-2-antiplasmin (α2AP), the main fibrinolytic inhibitor, is modified by N- and C-terminal proteolytic cleavages. C-terminal cleavage converts plasminogen-binding α2AP (PB-α2AP) into a non-plasminogen-binding derivative. N-terminal cleavage by antiplasmin-cleaving enzyme (APCE), a soluble, circulating derivative of fibroblast activation protein (FAP), turns native Met-α2AP into Asn-α2AP, which is more quickly crosslinked into fibrin. Objectives: We developed two novel enzyme-linked immunosorbent assays (ELISAs) to determine the N-terminal variation of α2AP to test the hypothesis that liver cirrhosis, characterized by increased expression of FAP/APCE, results in increased N-terminal cleavage of α2AP. Patients/Methods: α2AP and FAP/APCE antigen levels were measured in the plasma samples of 75 patients with cirrhosis with different severities and 30 healthy control individuals. The percentage of N-terminal cleavage of α2AP was calculated. Results: Compared with levels (median [interquartile range]) in control individuals, total PB-α2AP levels and Met-PB-α2AP levels were reduced in cirrhosis patients (27.3 [21.4-41.3] μg mL-1 vs. 56.2 [49.6-62.8] μg mL-1, P < 0.001, and 2.7 [1.7-5.5] μg mL-1 vs. 12.1 [11.0-15.3] μg mL-1, P < 0.001, respectively). Interestingly, the percentage of N-terminal cleavage was increased in the patients (87.8 [85.0-91.6]% vs. 77.2 [72.2-79.8]% in controls, P < 0.001), as well as the plasma FAP/APCE levels (166 [60-550] ng mL-1 in patients vs. 107 [67-157] ng mL-1 in controls, P < 0.001). Additionally, all variables significantly correlated with the severity of disease. Conclusions: Using our novel ELISAs we found increased N-terminal cleavage of α2AP in liver cirrhosis patients, which correlated with the severity of disease and is likely to have reflected the increased FAP/APCE levels in these patients. © 2013 International Society on Thrombosis and Haemostasis.