Complex formation between urokinase and plasma protein C inhibitor in vitro and in vivo.
Protein C inhibitor (PCI) and plasminogen activator inhibitor 3 (PAI-3; urinary urokinase inhibitor) are immunologically identical. The role of PCI for urokinase (uPA) inhibition in vivo was investigated. We therefore developed an enzyme-linked immunosorbent assay (ELISA) specific for uPA-PCI complexes: Rabbit anti-PCI IgG was immobilized on a microtiter plate and following incubation with uPA-PCI complex-containing samples, bound uPA-PCI complexes were quantified with a horseradish-peroxidase-linked monoclonal antibody (MoAb) to uPA. Using this assay, time, dose, and heparin-dependent complexes were detected when uPA was incubated with normal plasma or purified urinary PCI, whereas no complexes were measurable using PCI-immunodepleted plasma. Plasma samples (containing 20 mmol/L benzamidine to prevent complex formation ex vivo) from patients undergoing systemic urokinase therapy (1 x 10(6) IU/60 min intravenously [IV]) after myocardial infarction were also studied. uPA present in these plasma samples (up to 1,200 ng/mL) had only 43% to 70% of the specific activity of purified 2-chain uPA, suggesting that a major portion of uPA is complexed to inhibitors. In these plasma samples uPA-PCI complexes were present in a concentration corresponding to 21% to 25% of inactive uPA antigen. These data suggest that at high uPA concentrations, such as during uPA therapy, plasma PCI might contribute significantly to uPA inhibition in vivo.
Geiger
M
M
Department of Medical Physiology, University of Vienna, Austria.
Huber
K
K
Wojta
J
J
Stingl
L
L
Espana
F
F
Griffin
J H
JH
Binder
B R
BR
D004797:Enzyme-Linked Immunosorbent Assay; D006493:Heparin; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D011480:Protease Inhibitors / Q000097:blood / Q000378:metabolism* / Q000652:urine; D011486:Protein C / Q000037:antagonists & inhibitors*; D014568:Urokinase-Type Plasminogen Activator / Q000097:blood / Q000378:metabolism* / Q000627:therapeutic use
D046911:Macromolecular Substances; D011480:Protease Inhibitors; D011486:Protein C; D006493:Heparin; D014568:Urokinase-Type Plasminogen Activator