Characteristics of biochemical markers for bone formation in the elderly

Currently, several promising biochemical markers for bone metabolism have been postulated and expected to be applied to their clinical use. Among these markers, circulating levels of bone Gla-protein (BGP) and carboxyterminal peptide of type I procollagen (P1CP) have been established as non-invasive indices to assess bone turnover, especially bone formation. We investigated age-related effects on serum levels of both peptides and relationships between loss of bone mass and biochemical indices in the elderly. Fasting blood sample were obtained from 330 healthy volunteers to simultaneously measure serum BGP, serum P1CP and serum tartrate-resistant acid phosphatase (TRACP) as a marker for bone resorption. Serum BGP levels were found almost stable throughout life in men with a tendency to decrease in the elderly. Serum P1CP levels linearly decreased towards 50 to 60 years of age in men, followed by its constant increase with aging afterwards. Although a constant increase in serum P1CP levels were noted in women with aging, serum BGP levels were found remarkably elevated during menopausal periods of 50 to 70 years of age, followed by its wide distribution in the elderly. Both serum BGP and P1CP levels were elevated accompanied with age-related decrease in glomerular filtration rates in the elderly. In addition, a bone specific index, TRACP/BGP ratio consolidated the negative correlation between serum TRACP and % changes of bone mineral density (BMD). However, TRACP/P1CP ratio had nothing to do with % change of BMD. In conclusion, loss of bone mass could be predicted by bone specific indices, particularly in elderly women with widely distributed bone turnover. The data in this paper were reported in part in International Coference on Osteoporosis, Kobe, November 1991.