Complex formation between urokinase and plasma protein C inhibitor in vitro and in vivo

Blood. 1989 Aug 1;74(2):722-8.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Enzyme-Linked Immunosorbent Assay
  • Heparin
  • Humans
  • Kinetics
  • Macromolecular Substances
  • Protease Inhibitors / blood
  • Protease Inhibitors / metabolism*
  • Protease Inhibitors / urine
  • Protein C / antagonists & inhibitors*
  • Urokinase-Type Plasminogen Activator / blood
  • Urokinase-Type Plasminogen Activator / metabolism*
  • Urokinase-Type Plasminogen Activator / therapeutic use

Substances

  • Macromolecular Substances
  • Protease Inhibitors
  • Protein C
  • Heparin
  • Urokinase-Type Plasminogen Activator