Platelet CD40 ligand and bleeding during P2Y12 inhibitor treatment in acute coronary syndrome

Antiplatelet therapy through inhibition of the adenosine diphosphate (ADP)/P2Y12 pathway is commonly used in the treatment of acute coronary syndrome (ACS). Although efficient in preventing platelet activation and thrombus formation, it increases the risk of bleeding complications. In patients with ACS receiving platelet aggregation inhibitors, that is, P2Y12 blockers (n = 923), we investigated the relationship between plasma and platelet‐associated CD40L levels and bleeding events (n = 71). Treatment with P2Y12 inhibitors in patients with ACS did not affect plasma‐soluble CD40L levels, but decreased platelet CD40L surface expression (pCD40L) and platelet‐released CD40L (rCD40L) levels in response to stimulation as compared to healthy controls. In vitro inhibition of the ADP pathway in healthy control platelets reduced both pCD40L and rCD40L levels. In a multivariable analysis, the reduced pCD40L level observed in ACS patients was significantly associated with the risk of bleeding occurrence (adjusted odds ratio = 0.15; 95% confidence interval = 0.034‐0.67). P2Y12 inhibitor‐treated (ticagrelor) mice exhibited a 2.5‐fold increase in tail bleeding duration compared with controls. A significant reduction in bleeding duration was observed on CD40L(+/+) but not CD40L(−/−) platelet infusion. In addition, CD40L blockade in P2Y12 inhibitor–treated blood samples from a healthy human reduced thrombus growth over immobilized collagen under arterial flow. In conclusion, measurement of pCD40L may offer a novel approach to assessing bleeding risk in patients with ACS who are being treated with P2Y12 inhibitors.