Metabolism of 1alpha-hydroxyvitamin D3 by cytochrome P450scc to biologically active 1alpha,20-dihydroxyvitamin D3

J Steroid Biochem Mol Biol. 2008 Dec;112(4-5):213-9. doi: 10.1016/j.jsbmb.2008.10.005. Epub 2008 Oct 21.


Cytochrome P450scc (CYP11A1) metabolizes vitamin D3 to 20-hydroxyvitamin D3 as the major product, with subsequent production of dihydroxy and trihydroxy derivatives. The aim of this study was to determine whether cytochrome P450scc could metabolize 1alpha-hydroxyvitamin D3 and whether products were biologically active. The major product of 1alpha-hydroxyvitamin D3 metabolism by P450scc was identified by mass spectrometry and NMR as 1alpha,20-dihydroxyvitamin D3. Mass spectrometry of minor metabolites revealed the production of another dihydroxyvitamin D3 derivative, two trihydroxy-metabolites made via 1alpha,20-dihydroxyvitamin D3 and a tetrahydroxyvitamin D3 derivative. The Km for 1alpha-hydroxyvitamin D3 determined for P450scc incorporated into phospholipid vesicles was 1.4 mol substrate/mol phospholipid, half that observed for vitamin D3. The kcat was 3.0 mol/min/mol P450scc, 6-fold lower than that for vitamin D3. 1alpha,20-Dihydroxyvitamin D3 inhibited DNA synthesis by human epidermal HaCaT keratinocytes propagated in culture, in a time- and dose-dependent fashion, with a potency similar to that of 1alpha,25-dihydroxyvitamin D3. 1alpha,20-Dihydroxyvitamin D3 (10 microM) enhanced CYP24 mRNA levels in HaCaT keratinocytes but the potency was much lower than that reported for 1alpha,25-dihydroxyvitamin D3. We conclude that the presence of the 1-hydroxyl group in vitamin D3 does not alter the major site of hydroxylation by P450scc which, as for vitamin D3, is at C20. The major product, 1alpha,20-dihydroxyvitamin D3, displays biological activity on keratinocytes and therefore might be useful pharmacologically.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cattle
  • Cell Proliferation / drug effects
  • Cholesterol Side-Chain Cleavage Enzyme / metabolism*
  • Gene Expression / drug effects
  • Humans
  • Hydroxycholecalciferols / biosynthesis*
  • Hydroxycholecalciferols / metabolism*
  • Hydroxycholecalciferols / pharmacology
  • Keratinocytes / cytology
  • Kinetics
  • Nuclear Magnetic Resonance, Biomolecular
  • Steroid Hydroxylases / biosynthesis
  • Vitamin D3 24-Hydroxylase


  • 1alpha,20-dihydroxyvitamin D3
  • Hydroxycholecalciferols
  • Steroid Hydroxylases
  • Vitamin D3 24-Hydroxylase
  • Cholesterol Side-Chain Cleavage Enzyme
  • alfacalcidol