Neuropeptide Y and markers of osteoblast activity in dialysis patients: a cross-sectional study.

In mice, neuropeptide Y (NPY) decreases bone turnover by means of a parathyroid hormone-independent effect on osteoblast activity. Cross-sectional study. We studied the relationship between levels of NPY and biomarkers of osteoblast activity in 161 nondiabetic patients with end-stage renal disease (131 patients, hemodialysis; 30 patients, continuous ambulatory peritoneal dialysis). We performed an analysis of demographic and clinical variables associated with NPY as a dependent variable and a second analysis testing the association of NPY (as an independent variable) with markers of osteoblast activity. Peritoneal dialysis as treatment modality (beta = 0.37; P < 0.001) and longer duration of dialysis therapy (beta = 0.24; P < 0.01) were independently related to plasma NPY. NPY level was related inversely (P < 0.001) to serum alkaline phosphatase and bone alkaline phosphatase levels (P = 0.01). The NPY-alkaline phosphatase link was confirmed in a multiple regression analysis adjusting for a series of potential confounders, including parathyroid hormone. In a categorical analysis in which the study population was divided according to NPY quartiles, the proportion of patients with low alkaline phosphatase levels was lowest in the first 2 NPY quartiles (26%) and highest in NPY quartile 4 (80%; P < 0.001), and this association held true in a multiple logistic regression analysis, indicating that the risk of low alkaline phosphatase level increases in parallel with NPY level. The hypothesis generated by this cross-sectional study needs to be confirmed in cohort studies. The inverse relationships between levels of NPY and biomarkers of bone turnover support the hypothesis that NPY may be implicated in low bone turnover in dialysis patients by a central parathyroid-independent mechanism.