Bone cytokines and renal osteodystrophy in peritoneal dialysis patients

Bone turnover is regulated by local concentrations of cytokines such as osteoprotegerin (OPG) and receptor activator of nuclear factor kappaB ligand (RANKL). It is not known whether these cytokines can predict renal osteodystrophy in peritoneal dialysis (PD) patients. We measured serum levels of OPG, RANKL, intact parathyroid hormone (iPTH), calcium, phosphorus, and biologic parameters of bone turnover [carboxy-terminal propeptide of type I procollagen (PICP) and beta-crosslaps (betaCL)] in 21 PD patients and 42 healthy subjects matched for age and sex, who served as controls. Bone mineral density (BMD) was also evaluated (Z-scores) in the PD patients. Circulating levels of OPG were significantly higher in PD patients than in healthy subjects (p < 0.001). Mean levels of RANKL did not differ from normal. However, RANKL levels were increased in the group of patients with iPTH levels above 322 pg/mL. Biologic parameters of bone turnover (PICP and betaCL) were significantly increased in PD patients (p < 0.001). We found a positive correlation between serum levels of betaCL and iPTH. At several skeletal sites, betaCL also correlated with the BMD Z-score. No correlations were observed between OPG, RANKL, PICP, betaCL, CaxP, or time on dialysis. Circulating levels of OPG and RANKL do not reflect bone status in PD patients. The value of betaCL is a good marker of bone resorption that correlates with iPTH and BMD.