Abstract
Vitamin D3 is critical for the regulation of calcium and phosphate homeostasis. In some individuals, mineral homeostasis can be disrupted by long-term therapy with certain antiepileptic drugs and the antimicrobial agent rifampin, resulting in drug-induced osteomalacia, which is attributed to vitamin D deficiency. We now report a novel CYP3A4-dependent pathway, the 4-hydroxylation of 25-hydroxyvitamin D3 (25OHD3), the induction of which may contribute to drug-induced vitamin D deficiency. The metabolism of 25OHD3 was fully characterized in vitro. CYP3A4 was the predominant source of 25OHD3 hydroxylation by human liver microsomes, with the formation of 4β,25-dihydroxyvitamin D3 [4β,25(OH)2D3] dominating (Vmax/Km = 0.85 ml · min−1 · nmol enzyme−1). 4β,25(OH)2D3 was found in human plasma at concentrations comparable to that of 1α,25-dihydroxyvitamin D3, and its formation rate in a panel of human liver microsomes was strongly correlated with CYP3A4 content and midazolam hydroxylation activity. Formation of 4β,25(OH)2D3 in primary human hepatocytes was induced by rifampin and inhibited by CYP3A4-specific inhibitors. Short-term treatment of healthy volunteers (n = 6) with rifampin selectively induced CYP3A4-dependent 4β,25(OH)2D3, but not CYP24A1-dependent 24R,25-dihydroxyvitamin D3 formation, and altered systemic mineral homeostasis. Our results suggest that CYP3A4-dependent 25OHD3 metabolism may play an important role in the regulation of vitamin D3 in vivo and in the etiology of drug-induced osteomalacia.
Footnotes
This work was supported by the National Institutes of Health National Institute of General Medical Sciences [Grants R01-GM063666, P01-GM032165]; National Institutes of Health National Institute of Environmental Health Sciences [Grant P30-ES07033]; and National Institutes of Health National Institute of National Center for Research Resources [Grant GUL1-RR025014].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
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The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
ABBREVIATIONS:
- 25OHD3
- 25-hydroxyvitamin D3
- 1α,25(OH)2D3
- 1α,25-dihydroxyvitamin D3
- PXR
- pregnane X receptor
- DHB
- 6′,7′-dihydroxybergamottin
- KTZ
- ketoconazole
- 24R,25(OH)2D3
- 24R,25-dihydroxyvitamin D3
- PTAD
- 4-phenyl-1,2,4-triazoline-3,5-dione
- 23R,25(OH)2D3
- 23R,25-dihydroxyvitamin D3
- 24S,25(OH)2D3
- 24R,25-dihydroxyvitamin D3
- 25,26(OH)2D3
- 25,26-dihydroxyvitamin D3
- 23S,25(OH)2D3
- 23S,25-dihydroxyvitamin D3
- 1α,25(OH)2-3-epi-D3
- 1α,25-dihydroxy-3-epi-vitamin D3
- HLM
- human liver microsome(s)
- 4,25(OH2)D3
- 4,25-dihydroxyvitamin D3
- 4α,25(OH)2D3
- 4α,25-dihydroxyvitamin D3
- 4β,25(OH)2D3
- 4β,25-dihydroxyvitamin D3
- LLE
- liquid-liquid extraction
- LC
- liquid chromatography
- MS/MS
- tandem mass spectrometry
- HPLC
- high-performance liquid chromatography
- MRM
- multiple reaction monitoring
- GC
- gas chromatography
- MS
- electron impact mass spectrometry
- MDZ
- midazolam
- DMSO
- dimethyl sulfoxide.
- Received October 13, 2011.
- Accepted December 28, 2011.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics
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