title: Inhibition of endothelial cell-mediated generation of activated protein C by direct and antithrombin-dependent thrombin inhibitors.
abstract: The present study investigated the effect of the thrombin inhibitors antithrombin (AT) (with and without unfractionated heparin or low molecular weight heparin), hirudin, inogatran and melagatran on thrombin-thrombomodulin-mediated generation of activated protein C (APC), in solution and on endothelial cells. Sequential incubation with thrombin, thrombin inhibitors and protein C was followed by measurement of APC by an amidolytic assay. The approximate concentrations resulting in 50% inhibition of endothelial cell-mediated APC generation for AT, AT-unfractionated heparin, AT-low molecular weight heparin, hirudin, melagatran and inogatran were 200, 4, 9, 1, 8 and 60 nmol/l, respectively. The normal plasma level of AT is 2800 nmol/l and relevant therapeutic concentrations from clinical trials are 200 nmol/l for hirudin, 500 nmol/l for melagatran and 1000 nmol/l for inogatran. The present study indicates that clinically relevant concentrations of the tested thrombin inhibitors interfere with endothelial-mediated APC generation, which may offer an explanation for the lack of a dose-response effect in clinical trials with thrombin inhibitors.
authors.affiliation: Department of Cardiology, Karolinska Hospital, Stockholm, Sweden and Department of Surgical Sciences, Karolinska Institutet, Stockholm, Sweden. rikard.linder@medks.ki.se
authors.forename: Rikard
authors.initials: R
authors.lastname: Linder
authors.forename: Siw
authors.initials: S
authors.lastname: Frebelius
authors.forename: Katarina
authors.initials: K
authors.lastname: Jansson
authors.forename: Jesper
authors.initials: J
authors.lastname: Swedenborg
mesh_terms: D000991:Antithrombins / Q000494:pharmacology*; D001384:Azetidines; D001596:Benzylamines; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005434:Flow Cytometry; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D006629:Hirudins / Q000494:pharmacology; D006801:Humans; D010880:Piperidines / Q000494:pharmacology; D011486:Protein C / Q000378:metabolism*; D013917:Thrombin / Q000037:antagonists & inhibitors* / Q000502:physiology; D018180:Thrombomodulin / Q000502:physiology
chemical_list: D000991:Antithrombins; D001384:Azetidines; D001596:Benzylamines; D006629:Hirudins; D010880:Piperidines; D011486:Protein C; D018180:Thrombomodulin; C109573:melagatran; C099871:inogatran; D006493:Heparin; D013917:Thrombin; D005998:Glycine