COMPLEX-FORMATION BETWEEN PROTEIN-C INHIBITOR AND TISSUE-PLASMINOGEN ACTIVATOR DURING THROMBOLYTIC THERAPY - EVIDENCE OF ACTIVATION OF PROTEIN-C PATHWAY
F. Espana et al., COMPLEX-FORMATION BETWEEN PROTEIN-C INHIBITOR AND TISSUE-PLASMINOGEN ACTIVATOR DURING THROMBOLYTIC THERAPY - EVIDENCE OF ACTIVATION OF PROTEIN-C PATHWAY, Fibrinolysis, 7(5), 1993, pp. 308-315
Protein C inhibitor (PCI) is a heparin-dependent serine protease inhib
itor which, in vitro, inhibits activated protein C (APC), urokinase (u
-PA) and tissue plasminogen activator (t-PA), plasma kallikrein (KK),
thrombin and factors Xa and Xla. We have previously shown in vivo comp
lexes of PCI with APC, u-PA and KK. Here we study the contribution of
PCI to the inhibition of t-PA both in vitro and in vivo. PCI complexed
to t-PA (t-PA:PCI) was measured by a sandwich ELISA using antibodies
directed against each protein in the complex. The formation of t-PA:PC
I complexes paralleled the inhibition of t-PA amidolytic activity by P
CI in a purified system. In the plasma milieu, after incubation of 8 m
ug/mL t-PA (final concentration) with human plasma for 2 h at 37-degre
es-C, in the presence of heparin, the residual t-PA activity was about
38% and plasma contained 0.56 mug/mL t-PA:PCI complexes. To study com
plex formation in vivo, human plasma samples from patients (n=5) with
myocardial infarction were analyzed following infusion of 100 mg recom
binant t-PA for 2.5 h (10% initial bolus; 40% by a 20min infusion, and
50% by a 2-h infusion). Maximum peak values of t-PA:PCI complexes wer
e measured immediately after the second and third t-PA doses, ranging
from 16 to 135 ng/mL. In contrast, during t-PA infusion the level of c
omplexes of t-PA with plasminogen activator inhibitor-I (t-PA:PAI-1) i
ncreased only slightly, from 2.4+/-1.5 to 7.2+/-4.6 ng/mL, and reached
a maximum mean value of 17.2+/-20.6 ng/mL 2h post-infusion. PCI antig
en decreased during t-PA infusion from 80%+/-16% to 71%+/-7%. Protein
C antigen levels decreased during t-PA infusion, with the subsequent a
ppearance of complexes between APC and PCI (APC:PCI), and free protein
S gradually declined during infusion, reaching levels of 69% of the b
asal value 2h post-infusion. These data show that in vivo interaction
of PCI and t-PA exists, which in turn support the view that PCI may pl
ay a role in the regulation of the fibrinolysis pathway. They also sho
w that thrombolytic therapy with t-PA produces activation and a subseq
uent decrease in protein C antigen levels as well as in free protein S
levels.