Plasma osteoprotegerin is associated with mortality in hemodialysis patients

Abstract

Expression of bone proteins resulting from transdifferentiation of vascular smooth muscle cells into osteoblasts suggests that vascular calcifications are a bioactive process. Regulating molecules such as osteoprotegerin (OPG) and receptor activator of NF-κB ligand (RANKL) could play a key role in bone-vascular calcification imbalance. This study investigated the contribution of these proteins as well as mineral metabolism disorders in hemodialysis (HD) patient outcome. A total of 185 HD patients were followed up prospectively for 2 yr. In addition to clinical characteristics, mineral metabolism markers as well as OPG and soluble RANKL (sRANKL) were measured at baseline. After 2 yr, survival rates were described with Kaplan-Meier and compared with Cox regression analyses; 50 patients died (27 from cardiovascular diseases). Calcium, phosphate, and calcium x phosphate product were not associated with mortality. Both hyperparathyroidism (parathyroid hormone ≥300 pg/ml) and hypoparathyroidism (parathyroid hormone <150 pg/ml) were poorly associated with all-cause and cardiovascular mortality. By contrast, elevated OPG levels predicted all-cause (relative risk [RR] 2.67; 95% confidence interval [CI] 1.32 to 5.41; P = 0.006) and cardiovascular mortality (RR 3.15; 95% CI 1.14 to 8.69; P = 0.03). Low levels of sRANKL were associated with a protective effect for all-cause mortality (RR 0.45; 95% CI 0.21 to 0.94; P = 0.03). The association of OPG with all-cause mortality was stronger in patients with C-reactive protein ≥12.52 mg/L. In this condition, both highest (RR 5.68; 95% CI 1.48 to 22.73; P = 0.01) and lowest tertiles (RR 5.37; 95% CI 147 to 1968; P = 0.01) significantly predicted poor outcome. These results show that regulating-bone molecules, especially OPG, are strong predictors of mortality in HD patients, suggesting that OPG is a vascular risk factor, in particular in patients who have high C-reactive protein levels. OPG determination therefore should be added to the biologic follow-up of these patients. Copyright © 2006 by the American Society of Nephrology.