Inhibition of endothelial cell-mediated generation of activated protein C by direct and antithrombin-dependent thrombin inhibitors

• Published in: Blood coagulation & fibrinolysis Vol. 14; no. 2; pp. 139 - 146
• Main Authors: Linder, Rikard, Frebelius, Siw, Jansson, Katarina, Swedenborg, Jesper
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA Lippincott Williams & Wilkins, Inc 01-02-2003; The Scientist
• Subjects: Antithrombins - pharmacology; Azetidines; Benzylamines; Biological and medical sciences; Blood. Blood coagulation. Reticuloendothelial system; Dose-Response Relationship, Drug; Endothelium, Vascular - cytology; Endothelium, Vascular - drug effects; Endothelium, Vascular - metabolism; Flow Cytometry; Glycine - analogs & derivatives; Glycine - pharmacology; Heparin - pharmacology; Hirudins - pharmacology; Humans; Medical sciences; Medicin och hälsovetenskap; Pharmacology. Drug treatments; Piperidines - pharmacology; Protein C - metabolism; Thrombin - antagonists & inhibitors; Thrombin - physiology; Thrombomodulin - physiology; Human; thrombin; Serine endopeptidases; Enzyme; endothelial cell; Pharmacology; thrombin inhibitor; Antithrombin; Peptidases; Hydrolases; Inhibitor; Thrombomodulin; Protein C (activated); activated protein C
• ISSN: 0957-5235; 1473-5733
• DOI: 10.1097/00001721-200302000-00004

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.