C-C motif chemokine ligand 3 is associated with atherosclerotic plaque vulnerability and increased risk of mortality

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Abstract Background and Purpose Chemokines play a crucial role in the inflammatory process underlying atherosclerotic plaque formation, progression and subsequent cardiovascular events. However, the specific role of C-C motif chemokine ligand 3 (CCL3) in atherosclerosis remains largely unexplored. This study aims to explore associations between intra-plaque levels of CCL3 and plaque vulnerability as well as to investigate the prognostic role of circulating CCL3 levels in patients undergoing carotid endarterectomy. Methods The CCL3 protein expression was measured using a proximity extension assay in 207 human carotid plaques and 558 plasma samples from patients undergoing carotid endarterectomy, all enrolled in the Carotid Plaque Imaging Project (CPIP) cohort. Protein expression is quantified as normalized protein expression (NPX), an arbitrary unit on a log2-scale. Plaque components and extracellular matrix including smooth muscle cells, macrophages, neutral lipids, intraplaque hemorrhage, collagen (by histology), and matrix metalloproteinases (assessed biochemically), were quantified. Plaque vulnerability index was calculated as the sum percentage of plaque areas stained for lipids, macrophages and hemorrhage, divided by the sum percentage of smooth muscle cells and collagen. Patients were followed up to 10.2 years to record cardiovascular events and mortality. Results Plaque and circulating levels of CCL3 were higher in symptomatic patients compared to asymptomatic patients (plaque, median NPX (interquartile range, IQR): 18.2 (17.4–19.1) vs 17.2 (16.4–18.0), P<0.001; plasma, median NPX (IQR): 1.78 (1.42–2.21) vs 1.56 (1.28–1.97), P<0.001). Plaque levels of CCL3 showed positive correlations with neutral lipids, macrophages, intraplaque hemorrhage, plaque vulnerability index and matrix metalloproteinases including MMP1, MMP2, MMP9, MMP10 and TIMP1, but inversely with smooth muscle cells. Among 511 patients with complete follow-up and circulating CCL3 measures, 144 (28.2%) patients developed cardiovascular events and 123 (24.1%) patients died. Elevated circulating CCL3 levels were associated with increased risk of cardiovascular events (hazard ratio (HR) per standard deviation (SD) = 1.40, 95% CI 1.06–1.84) and mortality (HR per SD=1.77, 95% CI 1.34–2.33), respectively. Higher levels of circulating CCL3 remained independently associated with an increased risk of mortality (HR per SD=1.50, 95% CI 1.09–2.04) even after adjustment for potential confounders. Conclusions Plaque levels of CCL3 are associated with plaque vulnerability features. Circulating levels of CCL3 predict higher risk of cardiovascular events and mortality among carotid endarterectomy patients.