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Secretion of osteocalcin and its propeptide from human osteoblastic cells: dissociation of the secretory patterns of osteocalcin and its propeptide.

Authors
  • Hosoda, K
  • Kanzaki, S
  • Eguchi, H
  • Kiyoki, M
  • Yamaji, T
  • Koshihara, Y
  • Shiraki, M
  • Seino, Y
Type
Published Article
Journal
Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research
Publication Date
May 01, 1993
Volume
8
Issue
5
Pages
553–565
Identifiers
PMID: 8511982
Source
Medline
License
Unknown

Abstract

Specific immunoassay systems for intact human osteocalcin (I-OC) and its 26-residue propeptide have been newly developed to assess their usefulness as biochemical markers of bone metabolism. Using human cultured osteoblastic periosteal cells, we monitored 24 h secretion of these molecules from the osteoblastic cells and also examined the deposition of Ca, P, and I-OC on the extracellular matrix. At day 5, both I-OC and its propeptide were secreted by osteoblastic cells in a concentration-dependent manner by treatment with 1,25-(OH)2D3. This propeptide was not detected in the serum of adult subjects but was detected in the serum of normal children, which confirmed this in vitro result of propeptide secretion. The secretion of I-OC into medium transiently decreased at day 11, when the rapid accumulation of I-OC, Ca, and P, namely mineralization, was observed on the extracellular matrix of osteoblastic cells, although secretion of the propeptide constantly increased throughout the culture period. Therefore, the ratio of the amount of propeptide to I-OC in the supernatant markedly increased when mineralization started. These data demonstrate the superior specificity of propeptide as a marker of osteoblastic function in vitro compared with I-OC and that monitoring the changes in propeptide to I-OC ratios in the culture supernatant may be useful for predicting the timing of mineralization on the extracellular matrix of osteoblastic cells.

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