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Suppression of the expression of the CYP2B1/2 gene by retinoic acids

H Yamada1, T Yamaguchi, K Oguri

  • 1Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan.

Biochemical and Biophysical Research Communications
|October 12, 2000
PubMed

Insights

Retinoic acids (RAs) significantly suppress phenobarbital-mediated CYP2B induction in rat hepatocytes. 9-cis-retinoic acid is more potent than all-trans-retinoic acid, suggesting a key role for RA formation in CYP2B regulation.

Area of Science:

  • Pharmacology
  • Hepatology
  • Molecular Biology

Background:

  • Cytochrome P450 enzymes, specifically CYP2B1/2, are crucial for drug metabolism.
  • Phenobarbital (PB) is a known inducer of CYP2B enzymes.
  • Constitutive Androstane Receptor (CAR) and Retinoid X Receptors (RXRs) are key regulators of xenobiotic metabolism.

Purpose of the Study:

  • To investigate the effects of 5alpha-androsten-3alpha-ol (ASE) and retinoic acids (RAs) on phenobarbital-induced CYP2B expression.
  • To elucidate the role of specific RA isomers and precursors in CYP2B regulation.
  • To understand the mechanism by which RAs influence CYP2B induction via CAR and RXR signaling.

Main Methods:

  • Primary rat hepatocyte cultures were used to examine gene expression.
  • Phenobarbital was administered to induce CYP2B1 and CYP2B2.
  • Dose-response effects of ASE, 9-cis-RA, all-trans-RA, 9-cis-retinal, all-trans-retinol, and all-trans-retinal on CYP2B induction were assessed.

Main Results:

  • Both 9-cis-RA and all-trans-RA significantly suppressed PB-mediated CYP2B1/2 induction.
  • 9-cis-RA demonstrated a more potent suppressive effect at lower concentrations compared to all-trans-RA.
  • Suppression was also observed with 9-cis-retinal, but not with all-trans-retinol or all-trans-retinal.
  • ASE showed no suppressive effect on PB-mediated CYP2B induction.

Conclusions:

  • ASE, an inverse agonist of CAR, does not significantly contribute to CYP2B suppression.
  • 9-cis-RA suppresses CYP2B induction by potentially decreasing the availability of ligand-free RXRs for CAR dimerization.
  • Enzymes involved in RA synthesis play a critical role in the regulatory mechanisms of CYP2B.

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