Circulating myeloid-related protein-8/14 is related to thromboxane-dependent platelet activation in patients with acute coronary syndrome, with and without ongoing low-dose aspirin treatment.

Background-Platelet activation is involved in acute coronary syndromes (ACS). Incomplete suppression by low-dose aspirin treatment of thromboxane (TX) metabolite excretion (urinary 11-dehydro-TXB2) is predictive of vascular events in high-risk patients. Myeloid-related protein (MRP)-8/14 is a heterodimer secreted on activation of platelets, monocytes, and neutrophils, regulating inflammation and predicting cardiovascular events. Among platelet transcripts, MRP-14 has emerged as a powerful predictor of ACS. Methods and Results-We enrolled 68 stable ischemic heart disease (IHD) and 63 ACS patients, undergoing coronary angiography, to evaluate whether MRP-8/14 release in the circulation is related to TX-dependent platelet activation in ACS and IHD patients and to residual TX biosynthesis in low-dose aspirin-treated ACS patients. In ACS patients, plasma MRP-8/14 and urinary 11-dehydro-TXB2 levels were linearly correlated (r=0.651, P<0.001) but significantly higher than those in IHD patients (P=0.012, P=0.044) only among subjects not receiving aspirin. In aspirin-treated ACS patients, MRP-8/14 and 11-dehydro-TXB2 were lower versus those not receiving aspirin (P<0.001) and still significantly correlated (r=0.528, P<0.001). Higher 11-dehydro-TXB2 significantly predicted higher MRP-8/14 in both all ACS patients and ACS receiving aspirin (P<0.001, adj R-2=0.463 and adj R-2=0.497) after multivariable adjustment. Conversely, plasma MRP-8/14 (P<0.001) and higher urinary 8-iso-prostaglandin F-2 alpha (P=0.050) levels were significant predictors of residual, on-aspirin, TX biosynthesis in ACS (adjusted R-2=0.384). Conclusions-Circulating MRP-8/14 is associated with TX-dependent platelet activation in ACS, even during low-dose aspirin treatment, suggesting a contribution of residual TX to MRP-8/14 shedding, which may further amplify platelet activation. Circulating MRP-8/14 may be a target to test different antiplatelet strategies in ACS.