Inhibition by Argatroban, a Specific Thrombin Inhibitor, of Platelet Activation by Fibrin Clot-associated Thrombin

Abstract

SummaryClot-associated thrombin retains amidolytic activity, and is resistant to inhibition by heparin, but not to low molecular weight thrombin inhibitors. We show that clot-associated thrombin induces platelet aggregation, is resistant to heparin:antithrombin III, less so to recombinant hirudin (rHV2Lys47) but not to argatroban, an active-site directed thrombin inhibitor. Fibrin clots prepared with human fibrinogen and thrombin were used to aggregate rabbit washed platelets assessed by single platelet counting, thromboxane B2 (TXB2) immunoassay and scanning electron microscopy. Fibrin clots decreased platelet counts, and released TXB2. Electron microscopy showed platelet aggregates on the clot surface. Argatroban concentration-dependently inhibited such aggregation with IC50s of 21 nM and 13 nM versus aggregation and TXB2 release respectively. The IC50s of Argatroban against fluid-phase thrombin producing similar aggregation were 12 nM (aggregation) and 33 nM (TXB2). rHV2Lys47 was less active against clot-induced aggregation (IC50 = 1.8 nM) than against fluid-phase thrombin (IC50 = 0.06 nM). Heparin had an IC50 of 0.02 mU/ml against aggregation induced by fluid-phase thrombin, but much greater concentrations are required to inhibit clot-induced aggregation (IC50 = 48 mU/ml). These data provide a basis for the superiority of direct-acting thrombin inhibitors over heparin in platelet rich thrombi.

Local Delivery of Argatroban for the Prevention of Restenosis After Coronary Balloon Angioplasty

“…16 The reason that both local delivery and continuous intravenous infusion of argatroban were used in the present study was to inhibit thrombin activity, which may increase immediately after angioplasty before the local delivery of argatroban, because there was a time delay (approximately 10 min) between the first balloon inflation and the local delivery of argatroban (thrombin receptors have been reported to appear on a SMC within a few min after balloon injury 12 ). The present findings, together with the report of Rogasta et al, 13 suggest that direct thrombin inhibition may successfully inhibit cell migration in the initiation of restenosis in human patients.…”

“…The patients were randomly assigned to 2 groups according to consecutive sealed envelopes; the control group (n=35) underwent a conventional method of POBA, and the argatroban group (n=35) had the addition of local delivery of argatroban. The exclusion criteria were (1) more than 80 years old or less than 20 years old, (2) a target lesion in a non-protected left main coronary artery, (3) a total occlusive lesion equal to TIMI 0-1 flow, (4) a severely calcified lesion, (5) a diffuse lesion, (6) a target vessel with severe proximal tortuosity, (7) a lesion that restenosed more than once, (8) a bypass graft vessel, (9) an indication for a new device (eg, directional coronary atherectomy, stent, rotational atherectomy or laser ablation), (10) poor left ventricular function (ejection fraction <40%), (11) patients receiving warfarin, (12) patients receiving an intravenous infusion of heparin, (13) a history of gastrointestinal bleeding, thrombocytopenia, or coagulopathy, (14) a history of stroke within the preceding 3 months, (15) acute myocardial infarction within the previous month, (16) patients undergoing thrombolysis within the past 24 h, (17) pregnancy, and (18) other major illness including renal failure and liver dysfunction. Informed consent was obtained from each patient.…”

“…Argatroban is a direct thrombin inhibitor that has a more potent inhibitory effect on fibrin-or clot-incorporated thrombin than other thrombin inhibitors such as heparin and hirudin. 15, 16 Tomaru et al reported that the local delivery of argatroban using a double-balloon catheter reduced intimal thickening after balloon injury in an experimental study. 17 Accordingly, we conducted a prospective, randomized, controlled clinical trial to assess the effect of the local delivery of argatroban as a direct thrombin inhibitor using a Dispatch™ catheter system 18 (SIMED Life Systems, Inc, Maple Grove, MN, USA) in the prevention of restenosis after percutaneous coronary intervention (PCI).…”

Influence of direct thrombin inhibitor argatroban on coagulation assays in healthy individuals, patients under oral anticoagulation therapy and patients with liver dysfunction

“…This particular thrombin function is inhibited by argatroban [23,24], which has been described to influence clot strength [25]. For melagatran, another direct thrombin inhibitor, thrombin inhibition reduces thrombin-induced platelet activation but not ADP-induced or collagen-induced platelet aggregation [26].…”

Modulating Platelet Function With Selective Thrombin Inhibitors

“…Argatroban is capable of inhi biting platelet aggregation by clot-associated thrombin with either a moderate or no shift to the right of the log dose inhibition curves compared to their activity on aggregation induced by thrombin in solution. Both compounds are active in animal models of platelet-rich throm bosis which are insensitive to heparin [16]. The capacity of these compounds to inhibit pla telet aggregation by clot-bound thrombin could in part account for the superioirty of argatro ban and other direct thrombin inhibitors in experimental thrombosis, and reinforce the poten tial for the use of thrombin inhibitors in the treatment of arterial thrombosis.…”