ABSTRACT
Table 9.1 Biochemical markers for bone remodelling and abbreviations. The markers with the best performance characteristics in osteoporosis are in bold type
FORMATION Serum - Osteocalcin (OC) - Total and bone alkaline phosphatase (bone ALP) - Procollagen type I C-and N propeptides {PICP and PINP)
RESORPTION Plasma/serum - tartrate-resistant acid phosphatase (TRACP 5b) - free pyridinoline (free PYD) and deoxypyridinoline (free DPD) - C-terminal cross-linking telopeptide of type I collagen generated by MMPs (CTX-MMP) - N-terminal (S-NTX) and C-terminal (S-CTX) crosslinking telopeptide of type I collagen
Urine - free pyridinoline (PYD) and deoxypyridinoline (DPD) - N-terminal (U-NTX) and C-terminal (U-CTX) crosslinking telopeptide of type I collagen
calcium hydroxyproline (-Hyp) Galactosylhydroxylysine Type I collagen helicoidal peptide 620-633
- Urinary osteocalcin fragments
B O N E M A R K E R S 159
B a c k g r o u n d . Osteocalcin is the most abundant non-collagenous protein of bone matrix. It consists of 49 amino acid residues, three of which are a 7-carboxylated glutamic acid. Although most newly synthesized osteocalcin is captured by the bone matrix, a small fraction is released into the blood where it can be detected by immunoassays and it is currently considered a specific bone formation marker |2-5|. Circulating osteocalcin is constituted of different immunoreactive forms, including the intact molecule, but also various fragments |6,7|. It has been shown that the majority of circulating fragments arises from the in vivo degradation of the intact molecule and thus also reflects bone formation |7|. However, some of these fragments can also be released from degradation of the bone matrix, are resistant to glomeral filtration and accumulate in urine |6|. The characterization of such fragments and the development of a specific immunoassay for their detection would provide the basis for new, highly specific bone resorption markers which may offer additional information to that provided by collagen-related fragments.
