Table 1.
Products of bone turnover in serum and urine, tissue of origin, and remarks
| Tissue | Comments | |
|---|---|---|
| Bone formation | ||
| Bone-specific alkaline phosphatase (BAP) | Bone1,2 | Membrane-bound enzyme on the osteoblast1,2 In children BAP predominates (over alkaline phosphatase) due to skeletal growth1 |
| Osteocalcin (OC) | Bone1,2, dentin2 | Synthesized by the osteoblast1,2 Incorporated into bone matrix and a fraction is released to the circulation2 |
| Bone resorption | ||
| Deoxypyridinoline (DPD) | Bone, dentin1,5 | Cross-link in collagen1 Degradation product of mature collagen1 Not metabolized in liver4,5 Not influenced by food intake1,5 |
| Pyridinoline (PYD) | Bone, cartilage (tendon, blood vessels)1,5 | Cross-link in collagen1 Degradation product of mature collagen1 Not metabolized in liver4,5 Not influenced by food intake1,5 |
| Carboxyterminal cross-linked telopeptide of type I collagen (CTX-I) | Bone, skin1,2 | Degradation product of collagen1 Influenced by food intake1 |
| Hydroxylysine (HYL) | Collagen6 | Posttranslational modification of collagen6 May be glycosylated6 Not re-utilized for collagen biosynthesis3,6 |
| Galactosyl-hydroxylysine (GAL-HYL) | Skeletal collagens1,7 (also in cartilage and skin but to a much lower extent because partly processed to GLC-GAL-HYL2,7) | Posttranslational modification of collagen6,7 Degradation product of mature collagen7 Not metabolized in liver1,2,4,6 Not influenced by food intake1,7 |
| Glucosyl-galactosyl-hydroxylysine (GLC-GAL-HYL) | Collagens of soft tissue1 (derives to a minor extent from bone) | Posttranslational modification of collagen6 Degradation product of mature collagen Not metabolized in liver1,2,4,6 Not influenced by food intake1 |
| Hydroxyproline (HYP) | Bone, cartilage, soft tissue, skin1 | Degradation product of mature collagen6 Product of posttranslational hydroxylation of proline in the procollagen chain6 Extensive metabolism in liver3,6 Re-utilized for collagen synthesis1 Reflects both formation and resorption1 Influenced by food intake1 |