Abstract 1311: P2Y1 Receptor Deficiency or Pharmacological Blockade Protects Mice from Ferric Chloride-Induced Vena Cava Thrombosis
Platelet ADP receptors are known to play important roles in thrombosis and hemostasis. To explore the involvement of P2Y1 receptors in venous thrombosis, we determined the antithrombotic efficacy of P2Y1 receptor deficiency or blockade with a potent and selective antagonist in a mouse model of vena cava thrombosis. Topical application of ferric chloride (FeCl3, 2.5–10%) on the vena cava induced graded severity of thrombosis. Compared to wild-type mice, P2Y1 deficient mice were protected against thrombosis induced by 3.5% and 5% FeCl3, with 66% and 60% reduction in thrombus size, respectively (p<0.01). Similar levels of protection were observed in C57BL/6 mice treated with a potent and selective P2Y1 receptor antagonist, MRS-2500, at a dose of 2 mg/kg, i.v. (64% and 60% reduction in thrombus size compared to vehicle with 3.5% and 5% FeCl3, respectively, p<0.01). A parallel study was conducted in C57BL/6 mice using clopidogrel, a potent and selective irreversible inhibitor of the P2Y12 receptor. Clopidogrel dose-dependently inhibited vena cava thrombus formation, matching the efficacy of P2Y1 inhibition, at a dose of 1 mg/kg clopidogrel, p.o. against 3.5% FeCl3 and 3 mg/kg against 5% FeCl3. Tail bleeding time was used to monitor effects on hemostasis during inhibition of P2Y1 and P2Y12 receptors. Bleeding time was moderately but significantly prolonged in P2Y1 deficient mice and in wild-type mice treated with MRS-2500 (2 mg/kg, i.v.). Clopidogrel produced a dose-dependent effect on tail bleeding time with maximum prolongation observed at 30 mg/kg. Ex vivo inhibition of 10 μM ADP-induced platelet aggregation was used to assess antiplatelet effects. With P2Y1 inhibition platelet function tracked well with antithrombotic activity and bleeding liability. In contrast, the antiplatelet activity of clopidogrel mirrored its dose-related effect on bleeding time, but was not a sensitive measure of antithrombotic activity. Given the strong antithrombotic efficacy and moderate bleeding diathesis associated with P2Y1 receptor deficiency or blockade, therapeutic inhibition of the P2Y1 receptor may be a reasonable therapeutic strategy to treat and prevent both arterial and venous thrombosis.