Serum osteoprotegerin (OPG) in children with primary nephrotic syndrome

A novel cytokine system secreted by osteoblast, osteoprotegerin (OPG) and its ligand (OPGL) regulates osteoclastogenesis. To determine the relation of the serum OPG levels in children with nephrotic syndrome (NS) to the renal disease, we studied 30 patients with NS in comparison with 30 healthy children serving as controls. The study patients were divided into three equal groups: group 1 included newly diagnosed patients who were studied before and after a short course (one month) of steroid therapy for the first time, group 2 included frequent relapsers (FR), and group 3 included infrequent relapsers (IFR). In addition to serum OPG (ELISA), osteocalcin (OC), parathormone (PTH), alkaline phosphatase (ALP), and 24- hour urinary Ca and proteins were measured. The NS patients revealed a significantly lower serum OPG and parameters of bone formation (ALP and OC) and a significantly higher 24- hour urinary Ca than controls. A short course of glucocorticoids therapy for one month resulted in a significant decrease of serum OPG, ALP and OC levels and a significant increase of 24- hour urinary Ca, while serum PTH levels were not significantly affected by this the- rapy; the FR revealed a significantly lower serum level and a significantly higher 24- hour urinary Ca and serum PTH than the IFR. OPG had significant negative correlations with markers of disease activity and severity (ESR, serum cholesterol, 24- hour urinary protein and cumulative steroid dose), PTH and 24- hour urinary Ca. On the other hand, OPG had significant positive correlations with ALP, OC, and serum albumin. Low serum OPG, which is attributed to the renal disease and/or steroid therapy, may be an important factor contributing to bone resorption in NS. Studies of the protective effect of OPG administration against bone loss in NS are warranted.