Preclinical evaluation of the antithrombotic potential of the most commonly prescribed antiplatelets

Abstract

Myocardial infarctions and stroke are the leading causes of death in developed countries, and often result from arterial thrombus formation triggered by the rupture of an advanced atherosclerotic plaque. Plasma levels of cholesterol are correlated with risk of cardiovascular disease. In addition, platelets have a predominant role in the formation of arterial thrombi. Thus, lipid-lowering drugs, such as atorvastatin, are used in combination with antiplatelet agents, such as acetylsalicylic acid (ASA) and clopidogrel, to prevent and treat cardiovascular disease. In the studies described in this thesis, we measured the antiplatelet effects of atorvastatin, ASA and clopidogrel in mice. We discovered that atorvastatin attenuates platelet activation via protease-activated receptor 4 (PAR4, thrombin receptor) signaling in a nitric oxide (NO)-independent manner. We evaluated the antiplatelet effects of all three medications in vitro. Furthermore, we measured the antithrombotic potential of these three medications in vivo in a murine arterial thrombosis model. We first demonstrated that the sensitivity of the laser injury thrombosis model is improved by measuring platelet activation markers (platelet aggregation, degranulation and phosphatidylserine (PS) exposure). Using this modified laser injury thrombosis model, we found that neither atorvastatin nor ASA reduces thrombus volume, however both delayed in vivo platelet activation. Moreover, we showed that in the context of co-administration with clopidogrel (which is the standard-of-care), ASA at 10 mg is more effective at reducing in vivo thrombosis than ASA at 40 mg. This supports the notion that high doses of ASA offset the partial inhibitory effect of P2Y12 antagonists by interfering with prostacyclin (PGI2) formation. In conclusion, our results support PAR4 signaling as a target for developing new antiplatelets and advocate for ASA dose adjustment in standard-of-care therapeutic strategies that use both ASA and P2Y12 antagonists. Our findings will help guide and improve future pharmaceutical intervention strategies for arterial thrombosis patients.