Soluble cathepsin-L: a marker of bone resorption and bone density?

We sought to evaluate cathepsin L serum levels in the peripheral blood of patients with low bone density. Blood samples from 60 patients (32 osteoporotic, 28 osteopenic) and 16 healthy controls were taken and quantitative measurements of cathepsin L were performed with the use of a commercially available enzyme-linked immunosorbent assay. Dual x-ray absorptionometry measurements and serum levels of alkaline phosphatase, bone-specific alkaline phosphatase, osteocalcin, parathyroid hormone, sexual hormones, and N -terminal crosslinks of type I collagen were examined. Group comparisons between patients with osteoporosis and controls showed significant differences with respect to cathepsin L ( t = -2.839; df = 29; P =.008). Osteoporosis treatment decreased the serum level of cathespsin L in a statistically significant fashion ( P =.002). These results suggest that the serum level of cathepsin L can serve as a marker of bone resorption and bone density.