Cathepsin K predicts femoral neck bone mineral density change in nonosteoporotic peri- and early postmenopausal women

Objective: Cathepsin K is a cysteine protease that plays an essential role in organic bone matrix degradation. The aim of our study was to seek correlation of serum cathepsin K levels and a change in bone mineral density (BMD) over a 3-year period in a population of healthy nonosteoporotic women. The secondary end points were the correlations of serum cathepsin K with cross-sectional BMD and with other serum bone turnover markers and age. Design: In 43 healthy women aged 42 to 57 years, blood samples for determination of cathepsin K, osteocalcin, bone alkaline phosphatase, C-terminal cross-linking telopeptide of type I collagen, osteoprotegerin, and nuclear factor kappa B ligand were collected at the time of the first BMD measurement. BMD measurements were repeated after 3 years. Results: We found a moderate negative correlation of serum cathepsin K levels with change in femoral neck BMD, but none with change in spinal BMD. There were no significant correlations between cross-sectional BMD of the spine or femoral neck and serum levels of cathepsin K. Serum levels of cathepsin K were not significantly correlated with any bone turnover markers studied or with age. Conclusions: Serum cathepsin K does not seem to represent a surrogate for bone turnover markers used at present, but it might be useful as a predictor of cortical bone loss.