Abstract
Lipophilic bile acids are suggested to be involved in the endogenous expression of CYP3A4 in human and experimental animals as ligands of nuclear receptors. To verify the nuclear receptor specificity, the bile acid-mediated induction of CYP3A4 has been studied in vitro and in vivo in the present study. Lithocholic acid (LCA) strongly enhanced the activities of the CYP3A4 reporter gene, which contained multiple nuclear receptor binding elements, in both HepG2 and LS174T cells. The introduction of small interfering RNA for human vitamin D receptor (VDR), but not for human pregnane X receptor, reduced the LCA-induced activation of the reporter gene in these cells, suggesting the major role of VDR in the LCA induction of CYP3A4. Consistently, oral administration of LCA (100 mg/kg/day for 3 days) increased Cyp3a protein levels in the intestine but not in the liver, where a negligible level of VDR mRNA is detected. The selective role of VDR was tested in mice with the adenoviral overexpression of the receptor. Oral administration of LCA had no clear influence on the CYP3A4 reporter activity in the liver of control mice. In mice with the adenovirally expressed VDR, LCA treatment (100 or 400 mg/kg/day for 3 days) resulted in the enhanced reporter activities and increased levels of Cyp3a proteins in the liver. These results indicate the selective involvement of VDR, but not pregnane X receptor, in the LCA-mediated induction of both human and mouse CYP3As in vivo.
Footnotes
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This study was supported by a Grant-in-Aid from the Ministry of Education, Culture, Sports, Sciences and Technology, the Ministry of Health, Labor, and Welfare of Japan and Comprehensive Research and Education Center for Planning of Drug Development and Clinical Education, Tohoku University 21st Century “Center of Excellence” Program.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.108.021501.
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ABBREVIATIONS: RIF, rifampicin; PXR, pregnane X receptor; VDR, vitamin D receptor; RXR, retinoid X receptor; FXR, farnesoid X receptor; CA, cholic acid; CDCA, chenodeoxycholic acid; LCA, lithocholic acid; UDCA, ursodeoxycholic acid; h, human; siRNA, small interfering RNA; VD3, 1α,25-dihydroxyvitamin D3; PCR, polymerase chain reaction; TCID50, 50% titer culture infectious dose; MOI, multiplicity of infection; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; DMSO, dimethyl sulfoxide.
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↵1 Current affiliation: Tohoku Pharmaceutical University, Sendai, Miyagi, Japan.
- Received March 14, 2008.
- Accepted July 18, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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