Relationship Between Changes in Serum Levels of Intact Parathyroid Hormone and Sclerostin After a Single Dose of Zoledronic Acid: Results of a Phase 1 Pharmacokinetic Study

Abstract

Although changes in serum sclerostin levels at 12 months after infusion of zoledronic acid have been reported, the changes in sclerostin levels at earlier time points are poorly understood. We reanalyzed the study data of a previous phase 1 pharmacokinetic study and investigated the correlation between changes in sclerostin levels and relevant factors in calcium metabolism. A total of 24 Japanese female subjects with primary postmenopausal osteoporosis were administered a single 4- or 5-mg dose of zoledronic acid. Serum and urine samples were collected on days 15, 29, 90, 180, and 365 after administration. Serum levels of calcium, phosphate, intact parathyroid hormone (iPTH), and sclerostin were measured. Levels of serum sclerostin were unchanged from baseline on days 15 and 29, but increased significantly on day 90, subsequently decreased significantly on day 180, and returned to baseline levels on day 365. A significant negative correlation was observed between changes in iPTH levels at early time points and sclerostin levels at later time points. This suggests that sclerostin was negatively regulated by iPTH, and the decrease in sclerostin may indicate the start of bone formation during later time points after zoledronic acid injection.

Osteocytic Sclerostin Expression as an Indicator of Altered Bone Turnover

“…The same applies for the relationship between serum iPTH and osseous sclerostin expression, which may be largely driven by altered kidney function. It has also been reported that changes in iPTH occur more quickly than in serum sclerostin, which may, at least in part, explain the different trends in serum iPTH and sclerostin levels [ 46 ]. In addition, based on observations in both our rat study and human study, one may suggest that the changes in serum occur later than in bone tissue.…”