Summary
The role of plasma α2-antiplasmin (α2-AP) in the fibrinspecificity of clot lysis by recombinant single-chain urokinase-type
plasminogen activator (rscu-PA) and in the conversion of rscu-PA to its two-chain
derivative (rtcu-PA, urokinase) was investigated in an in vitro human plasma clot
lysis system. Fifty % lysis in 2 h of a 0.1 ml 125l-fibrin labeled human plasma clot immersed in 0.5 ml normal human plasma was obtained
with 1.4 ± 0.15 µg/ml rscu-PA (mean ± SD, n = 8). This was associated with degradation
of 23 ± 7% of fibrinogen and generation of 0.20 ± 0.09 µg/ml rtcu-PA. In α2-AP-depleted plasrna 50% clot lysis in 2 h required 2-fold less rscu-PA which was
associated with 3-fold more extensive fibrinogen degradation and 2-fold more rtcu-PA
generation. Fifty % lysis in? h, of a 0.1 ml α2-AP-depleted plasma clot, subriersed in 0.5 ml normal plasma, was obtained with 0.80
± 0.05 µg/ml rscu-PA (n = 3, p <0.001 vs normal clot) and was associated with 17 ±
6% fibrinogen breakdown (p : 0.22 vs normal clot) and 0.08 ± 0.02 µg/ml rtcu-PA generation
(p < 0.05 vs normal clot). In α2-AP-depleted plasma the equipotent rscu-PA concentration was 4-fold lower than in
normal plasma and was associated with 3-fold more fibrinogen degradation and a similar
extent of rtcu-PA generation
Thus, α2-AP in plasma contributes significantly to the fibrinspecificity of rscu-PA, primarily
via prevention of conversion in plasma of rscu-PA to rtcu-PA. Clot associated α2-AP increases the resistance of the clot to lysis with rscu-PA, but plays an only
minor role in the fibrin-specificity of clot lysis in normal plasma.
