Possible involvement of pregnane X receptor–enhanced CYP24 expression in drug-induced osteomalacia
Jean Marc Pascussi, … , Patrick Maurel, Marie Josè Vilarem
Jean Marc Pascussi, … , Patrick Maurel, Marie Josè Vilarem
Published January 3, 2005
Citation Information: J Clin Invest. 2005;115(1):177-186. https://doi.org/10.1172/JCI21867.
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Article Endocrinology

Possible involvement of pregnane X receptor–enhanced CYP24 expression in drug-induced osteomalacia

Abstract

Vitamin D controls calcium homeostasis and the development and maintenance of bones through vitamin D receptor activation. Prolonged therapy with rifampicin or phenobarbital has been shown to cause vitamin D deficiency or osteomalacia, particularly in patients with marginal vitamin D stores. However, the molecular mechanism of this process is unknown. Here we show that these drugs lead to the upregulation of 25-hydroxyvitamin D3-24-hydroxylase (CYP24) gene expression through the activation of the nuclear receptor pregnane X receptor (PXR; NR1I2). CYP24 is a mitochondrial enzyme responsible for inactivating vitamin D metabolites. CYP24 mRNA is upregulated in vivo in mice by pregnenolone 16α-carbonitrile and dexamethasone, 2 murine PXR agonists, and in vitro in human hepatocytes by rifampicin and hyperforin, 2 human PXR agonists. Moreover, rifampicin increased 24-hydroxylase activity in these cells, while, in vivo in mice, pregnenolone 16α-carbonitrile increased the plasma concentration of 24,25-dihydroxyvitamin D3. Transfection of PXR in human embryonic kidney cells resulted in rifampicin-mediated induction of CYP24 mRNA. Analysis of the human CYP24 promoter showed that PXR transactivates the sequence between –326 and –142. We demonstrated that PXR binds to and transactivates the 2 proximal vitamin D–responsive elements of the human CYP24 promoter. These data suggest that xenobiotics and drugs can modulate CYP24 gene expression and alter vitamin D3 hormonal activity and calcium homeostasis through the activation of PXR.

Authors

Jean Marc Pascussi, Agnes Robert, Minh Nguyen, Odile Walrant-Debray, Michèle Garabedian, Pascal Martin, Thierry Pineau, Jean Saric, Fréderic Navarro, Patrick Maurel, Marie Josè Vilarem

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Effect of 1α,25(OH)2D3, rifampicin, hyperforin, carbamazepine, and pheno...
Effect of 1α,25(OH)2D3, rifampicin, hyperforin, carbamazepine, and phenobarbital on CYP24, CYP2R1, CYP27B, CYP27A, VDR, and CYP3A4 mRNAs in human hepatocytes. Human hepatocytes were cultured for 48 hours in the absence (UT) or presence of the indicated compounds: 50 nM 1α,25(OH)2D3 (VD3), 20 μM rifampicin (RIF), 2 μM hyperforin (HP), 20 μM carbamazepine (CARBA), or 500 μM phenobarbital (PB). Total RNA was isolated using TRIZOL reagent. One microgram of total RNA was reverse-transcribed, and CYP3A4, CYP24, CYP2R1, CYP27B, CYP27A, VDR, and GAPDH mRNAs were quantified by real-time RT-PCR analysis using the LightCycler apparatus (Roche Diagnostics Corp.). Data presented are means ± SE (from 5 different cultures from 5 different liver donors) of the ratio of mRNA levels in treated cells to corresponding levels in untreated cells, normalized with respect to GAPDH mRNA levels, which themselves exhibited no significant variation. Statistically significant inductions compared with those in untreated cells are marked with asterisks: *P < 0.05 and **P < 0.01.