Serum intact molecule of bone Gla-protein in patients with abnormal bone and calcium metabolism

A circulating level of bone Gla-protein (BGP) has been estimated one of the most promising markers for bone turnover in patients with metabolic bone diseases. Although previous bone histomorphometric studies have revealed that serum BGP levels are mainly related to osteoblastic bone formation, multiple immunoreactive forms of BGP present in uremic sera are attributed to both osteoclastic bone resorption and decreased renal metabolism itself. Chromatography and cross-reactivity tests showed that an immunoradiometric assay (IRMA) for BGP specifically recognizes intact molecules of BGP and excludes BGP fragments found in uremic sera. Serum levels of BGP determined by IRMA were found significantly higher than those determined by radioimmnoassay. Elevated serum BGP levels determined by IRMA in primary hyperparathyroidism decreased and returned within the reference range more than 1 year following successful parathyroidectomy. Intermittent oral administration of high dose of 1,25 (OH)₂D₃ enhanced elevated serum BGP levels determined by IRMA which significantly increased from the initial levels at week 4 and at week 8, afterwards gradually returning to the basal levels at week 16. In addition, similar treatment effects were observed in serum prcollagen type I c-terminal peptide (P1CP), a marker for bone matrix formation. In conclusion, the measurement of serum BGP concentration utilizing IRMA, which specifically recognizes intact whole molecules of BGP, is useful to assess bone turnover and treatment effects in metabolic bone diseases, particularly in hyperparathyroidism.