Phenobarbital suppresses vitamin D3 25-hydroxylase expression: A potential new mechanism for drug-induced osteomalacia

https://doi.org/10.1016/j.bbrc.2007.03.177Get rights and content

Abstract

Prolonged therapy with phenobarbital may cause vitamin D deficiency or osteomalacia. In the current study, we propose a novel mechanism for drug-induced osteomalacia involving impaired bioactivation of vitamin D3 due to decreased 25-hydroxylation of vitamin D3 in liver. The present data, using the pig as model, demonstrate direct effects by phenobarbital on the expression of CYP27A1 and CYP2D25, two important 25-hydroxylases. Treatment by phenobarbital markedly reduced the rate of 25-hydroxylation by primary hepatocytes and suppressed the cellular CYP27A1 mRNA levels. The rate of 25-hydroxylation by two different purified 25-hydroxylases, microsomal CYP2D25, and mitochondrial CYP27A1, respectively, was dose-dependently inhibited by phenobarbital. Reporter assay experiments in liver-derived HepG2 cells revealed a marked PXR-mediated transcriptional downregulation of the CYP2D25 promoter. In addition, the data indicate that phenobarbital might affect the mRNA stability of CYP2D25. Taken together, the data suggest that vitamin D3 25-hydroxylation may be suppressed by phenobarbital. A downregulation of 25-hydroxylation by phenobarbital may explain, at least in part, the increased risk of osteomalacia, bone loss, and fractures in long-term phenobarbital therapy.

Section snippets

Materials and methods

Materials. The expression plasmid for the human retinoid X receptor α (RXRα) was a kind gift from Dr. Ronald M. Evans, Howard Hughes Medical Institute, The Salk Institute for Biological Studies, San Diego, CA. The expression plasmids for the human pregnane X receptor (PXR) and constitutive androstane receptor (CAR) and the empty vector pCR3 were gifts from Dr. Masahiko Negishi, Laboratory of Reproductive and Developmental Toxicology, NIEHS, NIH, Research Triangle Park, NC. 1α-Hydroxyvitamin D3

Phenobarbital inhibits vitamin D3 25-hydroxylase activity in primary hepatocytes

Primary porcine hepatocytes treated with phenobarbital (1.5 mM) for 48 h were incubated with 1α-hydroxyvitamin D3. HPLC analysis of the cell culture medium showed that phenobarbital inhibited the rate of 25-hydroxylation by about 70% (Table 1).

Effects of phenobarbital on the expression of CYP2D25 and CYP27A1 mRNA in primary hepatocytes

Experiments were carried out to study the effects of phenobarbital on mRNA levels of two hepatic 25-hydroxylases, the microsomal CYP2D25 and mitochondrial CYP27A1. The isolated hepatocytes were separately treated with phenobarbital for 6, 12, or 48 h and RNA

Acknowledgments

This work was supported by the Swedish Research Council-Medicine (project 03X-218) and the Novo Nordisk Foundation.

References (23)

  • Y. Ohyama et al.

    Eight cytochrome P450s catalyze vitamin D metabolism

    Front. Biosci.

    (2004)
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