Antithrombotic effects of PAR1 and PAR4 antagonists evaluated under flow and static conditions

Thromb Res. 2014 Jan;133(1):66-72. doi: 10.1016/j.thromres.2013.10.037. Epub 2013 Oct 31.


Introduction: Thrombin-mediated activation of human platelets involves the G-protein-coupled protease-activated receptors PAR1 and PAR4. Inhibition of PAR1 and/or PAR4 is thought to modulate platelet activation and subsequent procoagulant reactions. However, the antithrombotic effects of PAR1 and PAR4 antagonism have not been fully elucidated, particularly under flow conditions.

Materials and methods: A microchip-based flow chamber system was used to evaluate the influence of SCH79797 (PAR1 antagonist) and YD-3 (PAR4 antagonist) on thrombus formation mediated by collagen and tissue thromboplastin at shear rates simulating those experienced in small- to medium-sized arteries (600s(-1)) and large arteries and small veins (240s(-1)).

Results: At a shear rate of 600s(-1), SCH79797 (10μM) efficiently reduced fibrin-rich platelet thrombi and significantly delayed occlusion of the flow chamber capillary (1.44 fold of control; P<0.001). The inhibitory activity of SCH79797 was diminished at 240s(-1). YD-3 (20μM) had no significant effect at either shear rate. The antithrombotic effects of SCH79797 were significantly augmented when combined with aspirin and AR-C66096 (P2Y12 antagonist), but not with YD-3. In contrast, no significant inhibition of tissue factor-induced clot formation under static conditions was observed in blood treated with SCH79797 and YD-3, although thrombin generation in platelet-rich plasma was weakly delayed by these antagonists.

Conclusions: Our results suggest that the antithrombotic activities of PAR1 and/or PAR4 antagonism is influenced by shear conditions as well as by combined platelet inhibition with aspirin and a P2Y12-antagonist.

Keywords: ACS; ADP; AP; ASP; AU; AUC; CFT; CT; CTI; ETP; Flow chamber; GP; LT; MCF; OT; PAR; PH; PPP; PRP; Platelet; Protease-activated receptor; T-TAS; TF; TG; TTP; TXA(2); Thrombin; Thrombus formation; activating peptide; acute coronary syndrome; adenosine 5’-diphosphate; aggregation units; area under the aggregation curve; aspirin; clot formation time; clotting time; corn trypsin inhibitor; endogenous thrombin generation potential; glycoprotein; lag time; maximum clot firmness; occlusion time; peak height; platelet-poor plasma; platelet-rich plasma; protease-activated receptor; r-TF; recombinant tissue factor; thrombin generation; thromboxane A(2); time to peak; tissue factor; total thrombus-formation analysis system.

MeSH terms

  • Fibrinolytic Agents / pharmacology*
  • Humans
  • Microscopy, Confocal
  • Platelet Activation / drug effects*
  • Platelet Aggregation / drug effects*
  • Platelet Aggregation Inhibitors / pharmacology
  • Receptor, PAR-1 / antagonists & inhibitors*
  • Receptor, PAR-1 / metabolism
  • Receptors, Thrombin / antagonists & inhibitors*
  • Receptors, Thrombin / metabolism


  • Fibrinolytic Agents
  • Platelet Aggregation Inhibitors
  • Receptor, PAR-1
  • Receptors, Thrombin
  • protease-activated receptor 4