Vascular calcification is a common finding in atherosclerosis and a serious problem in diabetic and uremic patients. Because of the correlation of hyperphosphatemia and vascular calcification, the ability of extracellular inorganic phosphate levels to regulate human aortic smooth muscle cell (HSMC) culture mineralization in vitro was examined. HSMCs cultured in media containing normal physiological levels of inorganic phosphate (1.4 mmol/L) did not mineralize. In contrast, HSMCs cultured in media containing phosphate levels comparable to those seen in hyperphosphatemic individuals (>1.4 mmol/L) showed dose-dependent increases in mineral deposition. Mechanistic studies revealed that elevated phosphate treatment of HSMCs also enhanced the expression of the osteoblastic differentiation markers osteocalcin and Cbfa-1. The effects of elevated phosphate on HSMCs were mediated by a sodium-dependent phosphate cotransporter (NPC), as indicated by the ability of the specific NPC inhibitor phosphonoformic acid, to dose dependently inhibit phosphate-induced calcium deposition as well as osteocalcin and Cbfa-1 gene expression. With the use of polymerase chain reaction and Northern blot analyses, the NPC in HSMCs was identified as Pit-1 (Glvr-1), a member of the novel type III NPCs. These data suggest that elevated phosphate may directly stimulate HSMCs to undergo phenotypic changes that predispose to calcification and offer a novel explanation of the phenomenon of vascular calcification under hyperphosphatemic conditions. The full text of this article is available at http://www.circresaha.org.

Background-Osteoprotegerin (OPG) is a secretory glycoprotein that belongs to the tumor necrosis factor receptor family.OPG-deficient mice develop severe osteoporosis and medial arterial calcification of the aorta and renal arteries. OPG immunoreactivity was demonstrated in the normal blood vessels and in early atherosclerotic lesions. A recent clinical study suggests that there is a significant correlation between elevated serum OPG levels and cardiovascular mortality. We examined whether serum OPG levels are associated with the progression of coronary artery disease (CAD). Methods and Results-Serum OPG levels were examined in 201 patients who underwent coronary angiography because of stable chest pain. The number of diseased vessels was used to represent the severity of CAD. Serum OPG levels were measured by ELISA and were significantly greater in patients with significant stenosis of the coronary arteries than in those without stenosis. As the severity of CAD increased, there was a significant increase in serum OPG levels. Serum OPG levels were 0.94Ϯ0. 1 Recently, it has been demonstrated that OPG is produced by a variety of tissues, including the cardiovascular system (heart, arteries, veins), lung, kidney, and immune tissues, as well as bone, 1,2 and that the expression and production of OPG are regulated by various cytokines and hormones. 3 It has been shown that OPGdeficient mice develop severe osteoporosis and medial arterial calcification of the aorta and renal arteries, 4 and that the development of osteoporosis and arterial calcification was completely prevented by restoration of the gene. 5 OPG is also expressed in vascular cells such as coronary smooth muscle cells and endothelial cells in vitro. 6 In endothelial cells, OPG has been demonstrated to act as an anti-apoptotic factor. 7 Moreover, OPG immunoreactivity was demonstrated not only in the nondiseased vessel wall, but also in early atherosclerotic lesions in human tissues. 8 These findings suggest that OPG may play an important role in the development of vascular disease. A recent clinical study reported that there is a significant correlation between elevated serum OPG levels and cardiovascular mortality, 9 suggesting that OPG may contribute to the progression of coronary artery disease (CAD). In this study, we assessed the severity of CAD by coronary angiography and examined whether serum OPG levels are associated with the progression of CAD. Methods PatientsThe present study involved 201 patients who underwent coronary angiography. All patients fulfilled the criteria of stable chest pain and/or signs of myocardial ischemia on exercise electrocardiography for clinical indication for cardiac catheterization. Patients with an acute coronary syndrome were excluded. At the time of a physical examination, blood pressure, body mass index (BMI), and a hematological and biochemical profile were determined. Age and history of cigarette use were assessed through an interview preceding the physical examination. Ninety-six subjects were receiving antian...