Human bone cells in culture metabolize 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3

G. A. Howard, R. T. Turner, D. J. Sherrard, D. J. Baylink

Research output: Contribution to journalArticlepeer-review

190 Scopus citations


Bone c ells respond to 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) for mineral mobilization and contain receptors for 1,25 (OH2)O3. We report here the expression of 25-hydroxyvitamin D3 (25 OH)D3) metabolizing enzymes in primary cultures of human bone cells, as well as in a human osteosarcoma cell line. Human bone cells were obtained by enzyme digestion of the extracellular matrix of bone from iliac crest biopsies from 3 male patients without primary bone disease. These cells were plated (5 x 104/mm2) in medium with 10% fetal calf serum and proliferated to confluence in 10-14 days. At confluence, the medium was replaced with serum-free medium. The cells were preincubated in this serum-free medium for 24 h prior to incubating them 2-4 h with [3H]25(OH)D3 (10-20 nM). The vitamin D metabolites synthesized during this incubation were extracted from the medium and cells with dichloromethane, then separated by chromatography on Sephadex LH-20, followed by high performance liquid chromatography. The cells synthesized 1,25 (OH)2D3 and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) with the specific activities of the 1- and 24-hydroxylases similar in magnitude to those in kidney cells in vitro. The enzymes could be regulated by external perturbations, in that the activity of the 1-hydroxylase was inhibited by preincubation of the cells for 8 h with 1,25(OH)2D3 (10 nM), whereas the 24-hydroxylase was enhanced. Incubation of the cells in a low calcium medium (0.6 mM) depressed the 24-hydroxylase activity. We conclude: normal human bone cells can produce 1,25(OH)2D3 and 24,25(OH)2D3 in vitro in amounts similar to kidney cells, suggesting a physiological significance and this synthesis could account for the increase in osteoclast number in anephric patients with renal osteodystrophy.

Original languageEnglish (US)
Pages (from-to)7738-7740
Number of pages3
JournalJournal of Biological Chemistry
Issue number15
StatePublished - 1981
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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