Summary
A single-site mutant of prouPA (M5) spared haemostatic fibrin during thrombolysis
in dogs. Zymograms of plasma from these dogs showed an unusual inhibitor complex with
C1-inhibitor (C1I). Purified C1I added to human plasma enhanced the fibrinspecificity
of M5. In the present study, the effect of recombinant human C1I (recC1I) on high-dose
M5 and tPA were compared using fluorescein-labeled standardised clots in a plasma
milieu. The shortest time to complete clot lysis (maximum rate) was first determined.
This was ∼65% per hour for both activators. By contrast, their top fibrin-specific
lysis rate (<20% fibrinogen depletion) was less than half maximum (25–30% per hour).
Adding recC1I (250–750 μg/ml) did not affect fibrinolysis, but prevented fibrinogenolysis
and plasminogen depletion by M5, raising its fibrin-specific lysis rate to the maximum.
With tPA, the recC1I modestly attenuated fibrinogenolysis, raising its fibrin-specific
rate to about half the maximum. Consistent with this, the t½ inhibition by C1I was ∼90 min for tPA compared with ∼10 min for tcM5. The t½ of C1I for plasmin was ∼2 min. Zymograms of plasma after clot lysis indicated that
recC1I prevented non-specific tcM5 generation from M5, as evidenced by suppression
of tcM5:C1I complexes. In conclusion, recC1I raised the fibrin-specificity of M5 in
plasma so that a maximum lysis rate could be achieved without fibrinogenolysis. The
inhibition by C1I of nonspecific but not fibrin-dependent plasminogen activation could
not be duplicated by other serpins. The findings provide a potential means to optimize
both the efficacy and safety of thrombolysis.
Keywords
Fibrinolysis - fibrin-specificity - recC1-inhibitor - mutant ProuPA
