YM150, An Oral Direct Factor Xa Inhibitor: Combination with Aspirin or Clopidogrel In Arteriovenous Shunt Thrombosis In Rats

YM150, an oral direct factor Xa inhibitor, is currently in clinical development for the prevention of venous thromboembolism in patients undergoing orthopedic surgery, prevention of stroke in patients with atrial fibrillation, and prevention of ischemic events after recent acute coronary syndrome (ACS). The antiplatelet agents aspirin or clopidogrel will likely be co-prescribed with YM150 in ACS. Here, we report the effects of YM150 in combination with aspirin or clopidogrel on thrombus formation, bleeding, platelet aggregation, and coagulation in rats.

The antithrombotic effect was estimated in a rat arteriovenous shunt model. The shunt was formed by attaching a polyethylene tube containing a silk thread to the carotid artery and the contralateral carotid vein. Blood was allowed to circulate in this shunt for 15 min, and then the silk thread was withdrawn from the tube to assess the thrombus weight. YM150, aspirin, or clopidogrel was orally administered 0.5, 1, or 2 h before shunt formation, respectively. At the same time as shunt formation, an incision was made at the sole of the left foot using a template bleeding device (Surgicutt®) to measure bleeding time. To avoid interference with the thrombosis model, blood samples to assess platelet aggregation and prothrombin time were obtained from separate animals at the same time point as shunt formation in the thrombus study. Platelet aggregation was induced using 10 μg/mL of collagen and 5 μM of adenosine 5`-diphosphate (ADP) to assess the effects of aspirin and clopidogrel, respectively.

YM150 alone inhibited thrombus formation, with significance at 10 mg/kg and more (P < 0.05). Respective thrombus weights in the control, 3, 10, and 30 mg/kg groups of YM150 were 4.8, 3.6, 2.4, and 2.0 mg. Aspirin alone inhibited thrombus formation, with significance at 100 mg/kg and more (P < 0.01). Respective thrombus weights in the control, 30, 100, and 300 mg/kg group of aspirin were 6.2, 4.2, 2.8, and 1.5 mg. Clopidogrel alone inhibited thrombus formation, with significance at 1 mg/kg and more (P < 0.01). Respective thrombus weights in the control, 0.3, 1, and 3 mg/kg group of clopidogrel were 4.8, 3.6, 2.9, and 1.3 mg. When administered concomitantly with 100 mg/kg of aspirin, YM150 (3, 10, 30 mg/kg) further inhibited thrombogenesis, with significance at 30 mg/kg of YM150 (P < 0.05) and thrombus weights of 2.4, 1.5, and 1.3 mg, respectively. When administered concomitantly with 1 mg/kg of clopidogrel, YM150 (3, 10, 30 mg/kg) further inhibited thrombogenesis, with significance at 30 mg/kg of YM150 (P < 0.05) and thrombus weights of 3.0, 2.0, and 1.5 mg, respectively. Collagen-induced platelet aggregation was reduced to 16.7% of the control level by 100 mg/kg of aspirin, and ADP-induced platelet aggregation was reduced to 74.4% of the control level by 1 mg/kg of clopidogrel. These effects were not changed in the presence of YM150. Prothrombin time and bleeding time were not prolonged by any of the agents alone, and further, these parameters were not affected by combined use of YM150 with either aspirin or clopidogrel.

The thrombosis study suggests that both the platelet aggregation and coagulation cascade participate in thrombus formation in this model since both antiplatelet agents and the anticoagulant YM150 were effective. Thus, the thrombosis induced in this model can be considered similar to arterial thrombosis in humans where both platelets and fibrin are involved. Taken together, YM150 is a promising antithrombotic agent that augments the effects of antiplatelet agents against arterial thrombosis without increasing bleeding risk.

Iwatsuki:Astellas Phama Inc.: Employment. Sakata:Astellas Phama Inc.: Employment. Moritani:Astellas Phama Inc.: Employment.