Enhancement of fibrinolysis by inhibiting enzymatic cleavage of precursor α2-antiplasmin

J Thromb Haemost. 2011 May;9(5):987-96. doi: 10.1111/j.1538-7836.2011.04195.x.


Background and objective: Resistance of thrombi to plasmin digestion depends primarily on the amount of α(2)-antiplasmin (α(2)AP) incorporated within fibrin. Circulating prolyl-specific serine proteinase, antiplasmin-cleaving enzyme (APCE), a homologue of fibroblast activation protein (FAP), cleaves precursor Met-α(2)AP between -Pro12-Asn13- to yield Asn-α(2)AP, which is crosslinked to fibrin approximately 13× more rapidly than Met-α(2)AP and confers resistance to plasmin. We reasoned that an APCE inhibitor might decrease conversion of Met-α(2)AP to Asn-α(2)AP and thereby enhance endogenous fibrinolysis.

Methods and results: We designed and synthesized several APCE inhibitors and assessed each vs. plasma dipeptidyl peptidase IV (DPPIV) and prolyl oligopeptidase (POP), which have amino acid sequence similarity with APCE. Acetyl-Arg-(8-amino-3,6-dioxaoctanoic acid)-D-Ala-L-boroPro selectively inhibited APCE vs. DPPIV, with an apparent K(i) of 5.7 nm vs. 6.1 μm, indicating that an approximately 1000-fold greater inhibitor concentration is required for DPPIV than for APCE. An apparent K(i) of 7.4 nm was found for POP inhibition, which is similar to 5.7 nm for APCE; however, the potential problem of overlapping FAP/APCE and POP inhibition was negated by our finding that normal human plasma lacks POP activity. The inhibitor construct caused a dose-dependent decrease of APCE-mediated Met-α(2)AP cleavage, which ultimately shortened plasminogen activator-induced plasma clot lysis times. Incubation of the inhibitor with human plasma for 22 h did not lessen its APCE inhibitory activity, with its IC(50) value in plasma remaining comparable to that in phosphate buffer.

Conclusion: These data establish that inhibition of APCE might represent a therapeutic approach for enhancing thrombolytic activity.

Publication types

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

MeSH terms

  • Fibrinolysis*
  • Gelatinases / chemistry
  • Humans
  • Inhibitory Concentration 50
  • Kinetics
  • Membrane Proteins / chemistry
  • Peptides / chemistry
  • Protein Precursors / chemistry
  • Serine Endopeptidases / chemistry
  • Solubility
  • Thrombolytic Therapy
  • Time Factors
  • alpha-2-Antiplasmin / chemistry
  • alpha-2-Antiplasmin / metabolism*


  • Membrane Proteins
  • Peptides
  • Protein Precursors
  • alpha-2-Antiplasmin
  • pro-alpha-2-plasmin inhibitor
  • Serine Endopeptidases
  • fibroblast activation protein alpha
  • prolyl oligopeptidase
  • Gelatinases