Osteocalcin and bone remodelling in Paget's disease of bone, primary hyperparathyroidism, hypercalcaemia of malignancy and involutional osteoporosis

Abstract

We have measured classic markers of bone turnover, serum alkaline phosphatase (sAP), urinary hydroxyproline/creatinine ratio (uOH-Prol/creatinine) and osteocalcin (sBGP), in two bone disorders characterized by an increase in bone remodelling, namely Paget's disease of bone and primary hyperparathyroidism (PHPT) and in two other bone diseases characterized by an increase in bone resorption without the concomitant increase in bone formation, hypercalcaemia of malignancy (HM) and involutional osteoporosis (IO). Serum BGP was increased in patients with Paget's disease of bone (6.7±3.1; n=25; p<0.01) and in PHPT patients (8.3±5.3; n=20; p<0.005) with respect to control patients (4.2±1.2 ng/ml; n = 12). Two subgroups of patients with high and normal levels of sBGP were found in both pathologies. Serum BGP was decreased in HM patients (2.111.7; n=9; p<0.01) and in IO patients (1.9±1.4; n=31; p<0.001). Two subgroups of patients with normal and low sBGP values were found in these two last disorders. A positive linear correlation was found between sBGP and sAP (y=14.6x+73.7; r=0.44; p<0.05) and between sBGP and uOH-Prol/ creatinine (y=0.008x+0.007; r=0.67; p<0.001) in Paget's disease of bone. A similar correlation between sBGP and sAP (y=214x+35.6; r=0.43; p<0.05) and between sBGP and uOH-Prol/creatinine (y=0.0025x+0.023; r=0.70; p<0.01) was previously described by us in PHPT patients. No linear correlation has been found either between sBGP and sAP or between sBGP and uOH-Prol/creatinine in HM and IO patients. Bone formation and resorption are coupled in Paget's disease of bone and PHPT. However, in HM and IO these two processes are uncoupled. The results of the present work suggest that sBGP is a marker of bone turnover and bone BGP could be a factor of coupling in the osseous remodelling activity.

Key Words:

• BGP
• bone Gla-protein