Osteocalcin Expression by Circulating Endothelial Progenitor Cells in Patients With Coronary Atherosclerosis

ObjectivesThis study was designed to test whether patients with coronary atherosclerosis have increases in circulating endothelial progenitor cells (EPCs) expressing an osteogenic phenotype.BackgroundIncreasing evidence indicates a link between bone and the vasculature, and bone marrow and circulating osteogenic cells have been identified by staining for the osteoblastic marker, osteocalcin (OCN). Endothelial progenitor cells contribute to vascular repair, but repair of vascular injury may result in calcification. Using cell surface markers (CD34, CD133, kinase insert domain receptor [KDR]) to identify EPCs, we examined whether patients with coronary atherosclerosis had increases in the percentage of EPCs expressing OCN.MethodsWe studied 72 patients undergoing invasive coronary assessment: control patients (normal coronary arteries and no endothelial dysfunction, n = 21) versus 2 groups with coronary atherosclerosis—early coronary atherosclerosis (normal coronary arteries but with endothelial dysfunction, n = 22) and late coronary atherosclerosis (severe, multivessel coronary artery disease, n = 29). Peripheral blood mononuclear cells were analyzed using flow cytometry.ResultsCompared with control patients, patients with early or late coronary atherosclerosis had significant increases (∼2-fold) in the percentage of CD34+/KDR+ and CD34+/CD133+/KDR+ cells costaining for OCN. Even larger increases were noted in the early and late coronary atherosclerosis patients in the percentage of CD34+/CD133−/KDR+ cells costaining for OCN (5- and 2-fold, p < 0.001 and 0.05, respectively).ConclusionsA higher percentage of EPCs express OCN in patients with coronary atherosclerosis compared with subjects with normal endothelial function and no structural coronary artery disease. These findings have potential implications for the mechanisms of vascular calcification and for the development of novel markers for coronary atherosclerosis.