title: Direct microscopic monitoring of initial and dynamic clot lysis using plasmin or rt-PA in an in vitro flow system.
abstract: BACKGROUND
  Plasmin is a direct-acting thrombolytic agent with a favorable safety profile upon intra-arterial delivery in pre-clinical and phase I studies. However, the thrombolytic efficacy of plasmin, relative to that of rt-PA, remains to be established. We have compared the dynamics of clot lysis with plasmin or rt-PA in an in vitro perfusion system, in which thrombolytic agent is administered locally, allowed to induce lysis for short intervals, then washed with plasma in a re-circulation circuit.
  
  
  METHODS
  Whole blood human clots were prepared in observation chambers, exposed to plasmin or rt-PA at equimolar concentrations (1.2/1.0, 1.8/1.5 and 2.4/2.0 mg/ml) for measured intervals of time, followed by perfusion with human plasma. Clot size was monitored by digital analysis of sequential photographs obtained through an optical microscope.
  
  
  RESULTS
  Plasma perfusion after incubation with thrombolytic agent rapidly removed superficial clot fragments. This initial decrease in clot size was greater with plasmin than with rt-PA when tested at the highest concentrations of agent (0.63 ± 0.11 vs. 0.30 ± 0.11, p=0.001 for clots with non-cross-linked fibrin and 0.53 ± 0.15 vs. 0.14 ± 0.15, p=0.02, for clots with cross-linked-fibrin). Subsequent clot lysis during plasma flow was greater after prior incubation with rt-PA. Longer incubation times of plasmin resulted in larger portions of the clot being washed free. Repeated plasmin incubations and plasma perfusions of a clot successfully induced stepwise reductions in clot size.
  
  
  CONCLUSIONS
  Initial clot lysis is greater with direct exposure using plasmin than rt-PA. During washout and circulation with plasma, rt-PA induced continued clot lysis, while plasmin lysis was curtailed, presumably because of plasmin inhibition.
authors.affiliation: Jožef Stefan Institute, Ljubljana, Slovenia.
authors.forename: Nina
authors.initials: N
authors.lastname: Bizjak
authors.affiliation: Jožef Stefan Institute, Ljubljana, Slovenia.
authors.forename: Franci
authors.initials: F
authors.lastname: Bajd
authors.affiliation: Institute of Physiology, Medical Faculty of Ljubljana, Slovenia.
authors.forename: Jernej
authors.initials: J
authors.lastname: Vidmar
authors.affiliation: Department of Vascular Diseases, University of Ljubljana Medical Center, Slovenia.
authors.forename: Aleš
authors.initials: A
authors.lastname: Blinc
authors.affiliation: Institute of Biomedical Informatics, Medical Faculty of Ljubljana, Slovenia.
authors.forename: Maja Pohar
authors.initials: MP
authors.lastname: Perme
authors.affiliation: Division of Hematology/Medical Oncology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Marder
authors.affiliation: Grifols, Inc., Research Triangle Park, NC, USA.
authors.forename: Valery
authors.initials: V
authors.lastname: Novokhatny
authors.affiliation: Jožef Stefan Institute, Ljubljana, Slovenia; EN-FIST Centre of Excellence, Ljubljana, Slovenia. Electronic address: igor.sersa@ijs.si.
authors.forename: Igor
authors.initials: I
authors.lastname: Serša
mesh_terms: D001777:Blood Coagulation / Q000187:drug effects*; D005341:Fibrinolysin / Q000494:pharmacology*; D005342:Fibrinolysis / Q000187:drug effects*; D005343:Fibrinolytic Agents / Q000494:pharmacology*; D006439:Hemodynamics; D006801:Humans; D066298:In Vitro Techniques; D010958:Plasminogen / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D010959:Tissue Plasminogen Activator / Q000494:pharmacology*
chemical_list: D005343:Fibrinolytic Agents; D011994:Recombinant Proteins; D010958:Plasminogen; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin
keywords: Hemodynamics; Microscopy; Plasmin; Plasminogen activator; Thrombolytic therapy