Characterization of rat thrombin-activatable fibrinolysis inhibitor (TAFI)--a comparative study assessing the biological equivalence of rat, murine and human TAFI.

Background and objectives: Activated thrombin-activatable fibrinolysis inhibitor (TAFIa) attenuates fibrinolysis. Although rat models to study the role of TAFI are available, the biochemical properties of rat TAFI are not well investigated and immunologic tools are lacking. Therefore, we have characterized recombinant rat TAFI-6His and compared its properties with those of human TAFI as well as of murine TAFI-V5-6His. Methods and results: TAFI from all three species is activatable by the thrombin-thrombomodulin complex, generating a highly unstable protein (TAFIa). Half-lives at 37 degrees C are 8.5 +/- 0.6 min, 3.4 +/- 0.4 min and 2.2 +/- 0.2 min for human, rat and murine TAFIa, respectively. The 50% clot lysis times are 6 +/- 1 min for TAFI-depleted rat plasma and 137 +/- 34 min, 62 +/- 9 min and 50 +/- 8 min when TAFI-depleted rat plasma is supplemented with 0.02 U of human, rat or murine TAFIa, respectively, which correlates with their half-lives. Upon incubation with the thrombin-thrombomodulin complex, the 36-kDa fragment of rat and murine TAFI is not cleaved into 25-kDa and 11-kDa fragments. Upon incubation of rat TAFI and murine TAFI with plasmin, a 32-kDa fragment is formed due to cleavage at Arg147, in contrast to the formation of a 36-kDa fragment for human TAFI. Concomitantly, activity levels upon plasmin incubation are drastically reduced for rat and murine TAFI. Conclusions: Recombinant human, rat and murine TAFI have similar but not identical biochemical characteristics, suggesting a similar role during fibrinolysis in vivo.