title: Antithrombotic effects of PAR1 and PAR4 antagonists evaluated under flow and static conditions.
abstract: BACKGROUND
  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.
  
  
  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.
authors.affiliation: Research Institute, Fujimori Kogyo Co., Ltd., Yokohama, Kanagawa, Japan; Department of System Biology in Thromboregulation, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan. Electronic address: kazuya-hosokawa@zacros.co.jp.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Hosokawa
authors.affiliation: Research Institute, Fujimori Kogyo Co., Ltd., Yokohama, Kanagawa, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Ohnishi
authors.affiliation: Joint Faculty of Veterinary Medicine, Kagoshima University, Kagoshima, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Miura
authors.affiliation: Research Institute, Fujimori Kogyo Co., Ltd., Yokohama, Kanagawa, Japan.
authors.forename: Hisayo
authors.initials: H
authors.lastname: Sameshima
authors.affiliation: Department of System Biology in Thromboregulation, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Koide
authors.affiliation: Department of Anesthesiology, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA.
authors.forename: Kenichi A
authors.initials: KA
authors.lastname: Tanaka
authors.affiliation: Department of System Biology in Thromboregulation, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
authors.forename: Ikuro
authors.initials: I
authors.lastname: Maruyama
mesh_terms: D005343:Fibrinolytic Agents / Q000494:pharmacology*; D006801:Humans; D018613:Microscopy, Confocal; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D044463:Receptor, PAR-1 / Q000378:metabolism; D018179:Receptors, Thrombin / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D005343:Fibrinolytic Agents; D010975:Platelet Aggregation Inhibitors; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin; C112908:protease-activated receptor 4
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