Thrombin-induced platelet activation and its inhibition by anticoagulants with different modes of action.
Thrombin-induced platelet activation involves cleavage of protease-activated receptors (PARs) 1 and 4, and interaction, via glycoprotein (Gp)Ibalpha, with the platelet GpIb/IX/V complex. This study investigated inhibition of platelet activation by thrombin inhibitors with different modes of action: two reversible direct thrombin inhibitors, melagatran and inogatran; hirudin, a tightly binding direct thrombin inhibitor; and two indirect thrombin inhibitors, heparin and dalteparin. Up-regulation of P-selectin (CD62P) and PAR-1 cleavage was measured in human whole blood, by flow cytometry. The thrombin concentration that induced 50% of maximum (EC50 ) PAR-1 cleavage was 0.028 nmol/l, while that of platelet activation (CD62P) was over two-fold higher (0.64 nmol/l). The EC50 of a PAR-1-independent component, defined as a further activating effect of thrombin on top of the maximum PAR-1-activating peptide (AP) effect, was 3.2 nmol/l. All anticoagulants were concentration-dependent inhibitors of thrombin-induced platelet activation and PAR-1 cleavage, but none inhibited PAR-1-AP or PAR-4-AP induced activation. Melagatran and inogatran were more potent inhibitors of CD62P up-regulation than of PAR-1 cleavage; conversely, hirudin, heparin and dalteparin were more potent inhibitors of PAR-1 cleavage.Thus, reversible direct thrombin inhibitors, such as melagatran, are potent inhibitors of thrombin-induced platelet activation, acting mainly by inhibition of a PAR-1-independent component.
Nylander
Sven
S
Cell Biology and Biochemistry, Preclinical R&D, AstraZeneca R&D Mölndal, Sweden. sven.nylander@astrazeneca.com
Mattsson
Christer
C
D000328:Adult; D000925:Anticoagulants / Q000494:pharmacology*; D001384:Azetidines; D001596:Benzylamines; D017985:Dalteparin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D006629:Hirudins / Q000494:pharmacology; D006801:Humans; D008297:Male; D019007:P-Selectin / Q000097:blood / Q000187:drug effects / Q000378:metabolism; D010880:Piperidines / Q000494:pharmacology; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000187:drug effects / Q000378:metabolism; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin / Q000097:blood / Q000187:drug effects / Q000378:metabolism; D013223:Statistics as Topic; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*
D000925:Anticoagulants; D001384:Azetidines; D001596:Benzylamines; D006629:Hirudins; D019007:P-Selectin; D010880:Piperidines; D010975:Platelet Aggregation Inhibitors; D019038:Platelet Glycoprotein GPIb-IX Complex; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin; C109573:melagatran; C099871:inogatran; D006493:Heparin; D013917:Thrombin; C112908:protease-activated receptor 4; D017985:Dalteparin; D005998:Glycine