The influence of direct and antithrombin-dependent thrombin inhibitors on the procoagulant and anticoagulant effects of thrombin.
BACKGROUND
Clinical trials evaluating direct thrombin inhibitors in unstable coronary artery disease (CAD) have been disappointing. The hypothesis tested in the present study was that these agents may inhibit the anticoagulant effect of thrombin to a further extent than the procoagulant effect of thrombin.


METHODS
We studied both reversible and irreversible thrombin inhibitors and compared the effects of each inhibitor on activated protein C (APC) generation vs. the effect on fibrinopeptide A (FPA) generation. A mixture of protein C, thrombin inhibitor, fibrinogen, fibrin polymerisation blocker and thrombin was incubated with thrombomodulin (TM)-expressing human saphenous vein endothelial cells (HSVECs). The inhibitors investigated were melagatran, inogatran, hirudin, hirugen, D-Phe-D-Pro-D-arginyl chloromethyl ketone (PPACK), and antithrombin (AT) alone or in combination with unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH).


RESULTS
All agents, except hirugen, inhibited APC and FPA generation in a dose-dependent manner. FPA inhibition/APC inhibition ratios, based on IC50 for inogatran, melagatran, hirudin, PPACK, AT, AT-UFH and AT-LMWH were 1.73, 0.85, 0.55, 2.1, 0.5, 0.65 and 3.1 respectively.


CONCLUSIONS
All agents, except hirugen, inhibited APC and FPA generation approximately to a similar extent. Thus, it can be inferred that the poor efficacy of thrombin inhibitors in recent clinical trials in patients with unstable CAD is unlikely to be a consequence of their effects on the protein C system.
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000925:Anticoagulants / Q000037:antagonists & inhibitors / Q000378:metabolism; D001384:Azetidines; D001596:Benzylamines; D002986:Clinical Trials as Topic; D003029:Coagulants / Q000037:antagonists & inhibitors / Q000378:metabolism; D003324:Coronary Artery Disease / Q000188:drug therapy; D005344:Fibrinopeptide A / Q000187:drug effects*; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006629:Hirudins / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D010446:Peptide Fragments / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011486:Protein C / Q000187:drug effects*; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism
D000590:Amino Acid Chloromethyl Ketones; D000925:Anticoagulants; D001384:Azetidines; D001596:Benzylamines; D003029:Coagulants; D006629:Hirudins; D010446:Peptide Fragments; D010880:Piperidines; D011486:Protein C; C062510:hirugen; D005344:Fibrinopeptide A; C109573:melagatran; C099871:inogatran; D013917:Thrombin; C040308:phenylalanyl-prolyl-arginine-chloromethyl ketone; D005998:Glycine