title: The effect of antithrombin III-independent thrombin inhibitors and heparin on fibrin accretion onto fibrin-coated polyethylene.
abstract: Prosthetic vascular grafts become coated with a layer of fibrin that contributes to graft thrombosis and occlusion. We compared the effect of antithrombin III-independent inhibitors of thrombin with heparin for their ability to prevent fibrin accretion onto a model of a vascular graft formed in vitro by coating polyethylene tubing with thrombin bound to a layer of polymerized fibrin. Equivalent antithrombin concentrations of heparin, D-Phe-Pro-Arg CH2Cl (PPACK), recombinant hirudin (r-hirudin), and Hirulog-1 were added to barium chloride-absorbed plasma containing radiolabelled fibrinogen. Whereas, PPACK and r-hirudin persistently inhibited fibrin accretion, the inhibition by heparin was transient. Hirulog-1 had no effect on early fibrin accretion and was actually associated with enhanced accretion at 30 min (control 11.7 +/- 2.0 micrograms fibrin/cm2; Hirulog-1, 18.4 +/- 3.5 micrograms fibrin/cm2, p < 0.001). Both Hirulog-1 and r-hirudin displaced radiolabelled thrombin from the fibrin surface. Whereas hirudin-thrombin complexes are stable, Hirulog-1 produces only transient inhibition of the displaced thrombin thereby accounting for the enhanced fibrin accretion with this anticoagulant. These studies show that the antithrombin III-independent inhibitors, r-hirudin and PPACK, are more effective inhibitors of fibrin accretion onto fibrin-coated polyethylene than heparin or Hirulog-1. In addition, they emphasize the importance of determining the ability of anticoagulants to displace thrombin from fibrin and to form stable thrombin-inhibitor complexes; lack of stability of thrombin-inhibitor complexes must be countered by levels of anticoagulant that are adequate to maintain its effectiveness.
authors.affiliation: Department of Pathology, McMaster University, Hamilton, Ontario, Canada.
authors.forename: F D
authors.initials: FD
authors.lastname: Rubens
authors.forename: J I
authors.initials: JI
authors.lastname: Weitz
authors.forename: J L
authors.initials: JL
authors.lastname: Brash
authors.forename: R L
authors.initials: RL
authors.lastname: Kinlough-Rathbone
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000737:chemistry / Q000494:pharmacology; D000595:Amino Acid Sequence; D000990:Antithrombin III / Q000378:metabolism; D001807:Blood Vessel Prosthesis / Q000009:adverse effects; D005337:Fibrin / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology*; D006629:Hirudins / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000494:pharmacology; D011095:Polyethylenes; D011994:Recombinant Proteins / Q000494:pharmacology; D013499:Surface Properties; D013917:Thrombin / Q000037:antagonists & inhibitors*; D013927:Thrombosis / Q000517:prevention & control
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D006629:Hirudins; D010446:Peptide Fragments; D011095:Polyethylenes; D011994:Recombinant Proteins; D000990:Antithrombin III; D005337:Fibrin; D006493:Heparin; D013917:Thrombin; C040308:phenylalanyl-prolyl-arginine-chloromethyl ketone; C074619:bivalirudin