title: Effect of high- and low-molecular-weight heparins on thrombin-thrombomodulin interaction and protein C activation.
abstract: BACKGROUND
  Thrombin-thrombomodulin (TM) interaction, which is critical for accelerating the protein C anticoagulant pathway, involves the heparin-like domain of TM. This study was aimed at investigating the possible effect of heparin on thrombin-TM binding and protein C activation.
  
  
  RESULTS
  The affinity of thrombin-TM interaction was studied by a functional method, based on the ability of thrombin-TM adduct to activate protein C, and by evaluation of the binding of thrombin to immobilized TM. Both experimental approaches showed that the affinity of thrombin-TM interaction was decreased by micromolar heparin concentrations. Heparin had no significant effect when a recombinant TM form, lacking the chondroitin sulfate moiety, was used. Furthermore, it was also shown that the inhibitory effect of heparin was directly proportional to the heparin molecular mass (molecular weight range, 3 to 16 kDa), which suggests that the effect was mediated by formation of electrostatic bonds between heparin and thrombin.
  
  
  CONCLUSIONS
  These results indicate that heparin at therapeutic concentrations reduces the affinity of thrombin for TM and the rate of protein C activation. The magnitude of this effect is proportionally linked to the molecular mass of heparin.
authors.affiliation: Hemostasis Research Center, Department of Internal Medicine, Catholic University, Rome, Italy.
authors.forename: R
authors.initials: R
authors.lastname: De Cristofaro
authors.forename: E
authors.initials: E
authors.lastname: De Candia
authors.forename: R
authors.initials: R
authors.lastname: Landolfi
mesh_terms: D000925:Anticoagulants / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006493:Heparin / Q000494:pharmacology*; D006495:Heparin, Low-Molecular-Weight / Q000494:pharmacology*; D006801:Humans; D008970:Molecular Weight; D011486:Protein C / Q000378:metabolism*; D013917:Thrombin / Q000378:metabolism*; D013925:Thromboplastin / Q000378:metabolism*
chemical_list: D000925:Anticoagulants; D006495:Heparin, Low-Molecular-Weight; D011486:Protein C; D006493:Heparin; D013925:Thromboplastin; D013917:Thrombin