Serum Tartrate-Resistant Acid Phosphatase 5b or Amino-Terminal Propeptide of Type I Procollagen for Monitoring Bisphosphonate Therapy in Postmenopausal Osteoporosis?

摘要

Bone markers to monitor the efficacy of antiresorptive therapy of osteoporosis are of great value to clinicians. Considerable decreases in markers can be seen within 3 to 6 months after the start of an efficient treatment, with considerable increases in bone mineral density (BMD) being observed in 1 to 2 years (1)(2)(3). Decreases in marker concentrations reflect the patient’s compliance to treatment and, particularly for bisphosphonate therapy, the intestinal absorption of the drug, which may be poor. By indicating that the treatment is efficacious, biomarkers may also encourage the patient to continue therapy (4). Economic restrictions and the many bone turnover markers available make it challenging to choose the one that best serves these purposes and most reliably predicts fracture prevention. The most important consideration in practice may be to choose a marker that enables the clinician to make a clear distinction between responders and nonresponders to treatment.The amino-terminal propeptide of type I procollagen (PINP) is liberated into the circulation during type I collagen formation, and its serum concentration reflects bone formation rate (5). Because of the coupling between bone resorption and formation, PINP shows promise as a sensitive indicator of the efficacy of antiresorptive therapy (6). Tartrate-resistant acid phosphatase (TRACP), an iron-containing 35-kDa enzyme, is produced in osteoclasts, beginning early in their development. TRACP has several known functions in the osteoclasts from which it is liberated into the circulation in active form (7)(8)(9). In addition to osteoclastic isoform TRACP5b, human serum contains another, differently glycosylated isoform, TRACP5a. Secreted TRACP5b activity, which can be measured specifically with a novel immunoextraction method (10), is believed to reflect bone resorption.We compared serum PINP and TRACP5b as markers for distinguishing between responders and nonresponders to bisphosphonate treatment with alendronate or risedronate. The response …