Received for publication December 20, 2006.
Revised March 23, 2007.
Accepted for publication March 23, 2007.

Valproic Acid induces CYP3A4 and MDR1 genes expression by activation of Constitutive Androstane Receptor and Pregnane X Receptor pathways

Abstract

In our study, we tested the hypothesis whether valproic acid (VPA) in therapeutic concentrations has potential to affect expression CYP3A4 and MDR1 via constitutive androstane receptor (CAR) and pregnane X receptor (PXR) pathways. Interaction of VPA with CAR and PXR nuclear receptors was studied employing luciferase reporter assays, real time RT-PCR, EMSA, and analysis of CYP3A4 catalytic activity. Using transient transfection reporter assays in HepG2 cells, VPA was recognized to activate CYP3A4 promoter via CAR and PXR pathways. By contrast, significant effect of VPA on MDR1 promoter activation was observed only in CAR co-transfected HepG2 cells. These data well correlated with up-regulation of CYP3A4 and MDR1 mRNAs analyzed by real time RT-PCR in cells transfected with expression vectors encoding CAR or PXR and treated with VPA. Additionally, VPA significantly up-regulated CYP3A4 mRNA in primary hepatocytes and augmented the effect of rifampicin. EMSA experiments showed VPA-mediated augmentation of CAR/RXR heterodimer binding to DR3 and DR4 responsive elements of CYP3A4 and MDR1 genes, respectively. Finally, analysis of specific CYP3A4 catalytic activity revealed its significant increase in VPA-treated LS174T cells transfected with PXR. In conclusion, we provide novel insight into mechanism, by which VPA affect gene expression of CYP3A4 and MDR1 genes. Our results demonstrate that VPA has potential to up-regulate CYP3A4 and MDR1 through direct activation of CAR and/or PXR pathways. Furthermore, we suggest that VPA synergistically augments the effect of rifampicin in transactivation of CYP3A4 in primary human hepatocytes.

Key words: ABC transporters, CAR, CYP3A, enzyme induction, hepatocytes, nuclear receptors, PXR, SXR, transcriptional regulation, transporters

This article has been cited by other articles:

				A. Gupta, G. M. Mugundu, P. B. Desai, K. E. Thummel, and J. D. Unadkat Intestinal Human Colon Adenocarcinoma Cell Line LS180 Is an Excellent Model to Study Pregnane X Receptor, but Not Constitutive Androstane Receptor, Mediated CYP3A4 and Multidrug Resistance Transporter 1 Induction: Studies with Anti-Human Immunodeficiency Virus Protease Inhibitors Drug Metab. Dispos., June 1, 2008; 36(6): 1172 - 1180. [Abstract] [Full Text] [PDF]

				L. Svecova, R. Vrzal, L. Burysek, E. Anzenbacherova, L. Cerveny, J. Grim, F. Trejtnar, J. Kunes, M. Pour, F. Staud, et al. Azole Antimycotics Differentially Affect Rifampicin-Induced Pregnane X Receptor-Mediated CYP3A4 Gene Expression Drug Metab. Dispos., February 1, 2008; 36(2): 339 - 348. [Abstract] [Full Text] [PDF]