Lack of Correlation between Levels of Osteocalcin and Bone Alkaline Phosphatase in Healthy Control and Postmenopausal Osteoporotic Women

Abstract

The determination of bone alkaline phosphatase (bAP) by IRMA and the measure of intact osteocalcin (BGP) and/or different fragments by IRMA and/or RIA are new commercially available methods for the evaluation of osteoblast activity. The aim of this work was to study the possible correlation among serum bAP and levels of BGP measured by two different methods: an IRMA which only detects intact-BGP and a RIA which detects intact-BGP and carboxyterminal fragments (C-terminal BGP) in healthy post-menopausal control women and in a group of patients with post-menopausal osteoporosis. Serum samples from 42 consecutive osteoporotic postmenopausal women, aged 62 ± 11 years, between 39 - 76, and 14 control women age matched, were drawn after an overnight fasting. Levels of total alkaline phosphatase (AP), bAP, intact BGP, and intact BGP and carboxy terminal fragments were measured. In both groups we found a significant linear correlation between the levels of AP and bAP (r = 0.79, p < 0.001) and intact-BGP and C-terminal BGP (r = 0.97, p < 0.001), but surprisingly we did not find a significant linear correlation between AP or bAP levels and BGP measured in any of the two methods. These results suggest that AP release from osteoblast vesicles and BGP synthesis in these cells are not necessarily simultaneous, reflecting different stages of osteoblast activity.

Key words

Alkaline Phosphatase - Osteocalcin