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

Background The activity of alpha-2-antiplasmin (2AP), the main fibrinolytic inhibitor, is modified by N- and C-terminal proteolytic cleavages. C-terminal cleavage converts plasminogen-binding 2AP (PB-2AP) 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-2AP into Asn-2AP, which is more quickly crosslinked into fibrin. ObjectivesWe developed two novel enzyme-linked immunosorbent assays (ELISAs) to determine the N-terminal variation of 2AP to test the hypothesis that liver cirrhosis, characterized by increased expression of FAP/APCE, results in increased N-terminal cleavage of 2AP. Patients/Methods2AP 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 2AP was calculated. ResultsCompared with levels (median [interquartile range]) in control individuals, total PB-2AP levels and Met-PB-2AP levels were reduced in cirrhosis patients (27.3 [21.4-41.3] g mL(-1) vs. 56.2 [49.6-62.8] g mL(-1), P<0.001, and 2.7 [1.7-5.5] g mL(-1) vs. 12.1 [11.0-15.3] g 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 2AP 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.