Novel role of platelets in mediating inflammatory responses and ventricular rupture or remodeling following myocardial infarction.

OBJECTIVE The goal of this study was to investigate the role of platelets in systemic and cardiac inflammatory responses and the development of postinfarct ventricular complications, as well as the efficacy of antiplatelet interventions. METHODS AND RESULTS Using a mouse myocardial infarction (MI) model, we determined platelet accumulation and severity of inflammation within the infarcted myocardium by immunohistochemistry and biochemical assays, analyzed peripheral blood platelet-leukocyte conjugation using flow cytometry, and tested antiplatelet interventions, including thienopyridines and platelet depletion. Platelets accumulated within the infarcted region early post-MI and colocalized with inflammatory cells. MI evoked early increase in circulating platelet-leukocyte conjugation mediated by P-selectin/P-selectin glycoprotein ligand-1. Antiplatelet interventions inhibited platelet-leukocyte conjugation in peripheral blood, inflammatory infiltration, content of matrix metalloproteinases or plasminogen activation, and expression of inflammatory mediators in the infarcted myocardium (all P<0.05) and lowered rupture incidence (P<0.01). Clopidogrel therapy alleviated the extent of chronic ventricular dilatation by serial echocardiography. CONCLUSIONS Platelets play a pivotal role in promoting systemic and cardiac inflammatory responses post-MI. Platelets accumulate within the infarcted myocardium, contributing to regional inflammation, ventricular remodeling, and rupture. Antiplatelet therapy reduces the severity of inflammation and risk of post-MI complications, demonstrating a previously unrecognized protective action.