CONTACT ACTIVATION OF THE PLASMA COAGULATION CASCADE - III - BIOPHYSICAL ASPECTS OF THROMBIN-BINDING ANTICOAGULANTS

A biophysical model linking fibrin polymerization kinetics (following release from a thrombin-fibrinogen complex), coagulation time, and com petitive inhibition of thrombin illustrates the utility of thrombin-bi nding Ligands as anticoagulants in blood collection applications. The resulting mathematical relationship connecting fibrinogen, ligand, and thrombin concentrations was tested against experimentally observed an ticoagulation of whole, platelet-poor porcine plasma induced by short, single-stranded DNA oligonucleotides originally found to bind thrombi n by screening combinatorial libraries. The thrombin-fibrinogen dissoc iation constant K-s served as the single adjustable parameter in a lea st-squares fitting of the model to experimental anticoagulation data. Best-fit K-s values corroborated mu M values measured in plasma-free s ystems, and application of the model to a ligand challenge to the intr insic pathway of plasma coagulation corroborated nM endogenous thrombi n concentrations measured in porcine blood activated by endotoxin insu lt in vivo. The model fit to data suggests that only about 20% convers ion of blood fibrinogen to fibrin is required to coagulate (gel) porci ne plasma. This prediction is consistent with the common clinical labo ratory observation of latent fibrin formation in ''serum'' separated f rom blood before fibrinogen is fully converted to fibrin. It was concl uded that the thrombin-binding anticoagulation model was a reasonable simulation of the situation in which an initial bolus of either exogen ous or endogenous thrombin is rapidly partitioned between fibrinogen-b ound and ligand-bound forms with little or no additional free thrombin created over time. (C) 1998 John Wiley & Sons, Inc.