Regulation of CYP3A4 and CYP2B6 expression by liver X receptor agonists.

The liver X receptor (LXR) agonists, 24(S),25-epoxycholesterol and T0901317, were previously shown to be capable of inducing CYP3A expression in primary cultured rodent hepatocytes through activation of the pregnane X receptor (PXR). In this study, the abilities of these two LXR agonists to regulate CYP3A4 and CYP2B6 mRNA expression in primary cultures of human hepatocytes were evaluated. Treatment with 10 or 30 microM of the endogenous oxysterol, 24(S),25-epoxycholesterol, had no effect on CYP3A4 mRNA content in five preparations of primary cultured human hepatocytes, while 30 microM 24(S),25-epoxycholesterol treatment increased CYP2B6 mRNA content by approximately two-fold. By comparison, treatment with the synthetic LXR agonist, T0901317, potently increased CYP3A4 and CYP2B6 mRNA levels in the human hepatocyte cultures, producing multi-fold increases at 10nM. Using a HepG2-based transactivation assay, T0901317 activated human PXR with an EC(50) approximately 20nM, which was more than 10-fold lower than that of the potent PXR ligand, SR-12813, while treatment with 24(S),25-epoxycholesterol failed to induce reporter expression in this assay. Therefore, while 24(S),25-epoxycholesterol-mediated PXR activation and CYP3A induction does not appear to be conserved from rodent to human, T0901317 is among the most potent known activators of human PXR.

[1]  S. Kliewer,et al.  Structural requirements of ligands for the oxysterol liver X receptors LXRalpha and LXRbeta. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[2]  L. Moore,et al.  St. John's wort induces hepatic drug metabolism through activation of the pregnane X receptor. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[3]  B. Goodwin,et al.  The orphan human pregnane X receptor mediates the transcriptional activation of CYP3A4 by rifampicin through a distal enhancer module. , 1999, Molecular pharmacology.

[4]  B. M. Forman,et al.  Identification of an endogenous ligand that activates pregnane X receptor-mediated sterol clearance , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[5]  J. Gustafsson,et al.  LXR deficiency and cholesterol feeding affect the expression and phenobarbital-mediated induction of cytochromes P450 in mouse liver Published, JLR Papers in Press, June 1, 2005. DOI 10.1194/jlr.M400453-JLR200 , 2005, Journal of Lipid Research.

[6]  Zhe Zhang,et al.  Key regulatory oxysterols in liver: analysis as delta4-3-ketone derivatives by HPLC and response to physiological perturbations. , 2001, Journal of lipid research.

[7]  Bert W O'Malley,et al.  Coregulator function: a key to understanding tissue specificity of selective receptor modulators. , 2004, Endocrine reviews.

[8]  T. Kocarek,et al.  CYP3A induction by liver x receptor ligands in primary cultured rat and mouse hepatocytes is mediated by the pregnane X receptor. , 2004, Drug metabolism and disposition: the biological fate of chemicals.

[9]  L. Moore,et al.  Pharmacophore analysis of the nuclear oxysterol receptor LXRalpha. , 2001, Journal of medicinal chemistry.

[10]  D. Mangelsdorf,et al.  Role of LXRs in control of lipogenesis. , 2000, Genes & development.

[11]  Timothy M Willson,et al.  Crystal structure of the PXR-T1317 complex provides a scaffold to examine the potential for receptor antagonism. , 2007, Bioorganic & medicinal chemistry.

[12]  J. Nelson,et al.  Biosynthesis of 24,25-epoxycholesterol from squalene 2,3;22,23-dioxide. , 1981, The Journal of biological chemistry.

[13]  L. Moore,et al.  The Pregnane X Receptor: A Promiscuous Xenobiotic Receptor That Has Diverged during Evolution , 2000 .

[14]  S. Kliewer,et al.  Identification of bile acid precursors as endogenous ligands for the nuclear xenobiotic pregnane X receptor , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[15]  D. Kipnis,et al.  Pregnane X receptor (PXR) activation: A mechanism for neuroprotection in a mouse model of Niemann–Pick C disease , 2006, Proceedings of the National Academy of Sciences.

[16]  L. Moore,et al.  Regulation of the human CYP2B6 gene by the nuclear pregnane X receptor. , 2001, Molecular pharmacology.

[17]  J. Pascussi,et al.  Expression of CYP3A4, CYP2B6, andCYP2C9 Is Regulated by the Vitamin D Receptor Pathway in Primary Human Hepatocytes* , 2002, The Journal of Biological Chemistry.

[18]  N. Mitro,et al.  T0901317 is a potent PXR ligand: Implications for the biology ascribed to LXR , 2007, FEBS letters.

[19]  C. Smith,et al.  Differential Regulation of Hepatic CYP2B6 and CYP3A4 Genes by Constitutive Androstane Receptor but Not Pregnane X Receptor , 2006, Journal of Pharmacology and Experimental Therapeutics.

[20]  D. Mangelsdorf,et al.  Liver X receptor signaling pathways in cardiovascular disease. , 2003, Molecular endocrinology.

[21]  L. Moore,et al.  Identification of a Novel Human Constitutive Androstane Receptor (CAR) Agonist and Its Use in the Identification of CAR Target Genes* , 2003, The Journal of Biological Chemistry.