Cathepsin K in treatment monitoring following intravenous zoledronic acid.

Cathepsin K (CatK) is mainly expressed by osteoclasts and plays an important role in bone resorption. As CatK is expressed and secreted by osteoclasts during active bone resorption, it may be a useful and specific biochemical marker of osteoclastic activity. Therefore, CatK serum levels were studied for monitoring the treatment of females with postmenopausal osteoporosis by zoledronic acid. The serum CatK levels were determined in nine postmenopausal females before and after 3, 6 and 12 months of treatment. The levels were significantly reduced after 3 and 6 months (P<0.05), whereas they returned to baseline after 1 year. Taken together, the serum level of CatK may be suitable for monitoring anti-osteoporotic therapy in association with treatment response.