Thalidomide Increases Human
Hepatic Cytochrome P450
3A Enzymes by Direct Activation of the Pregnane X Receptor
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Abstract
Heterotropic cooperativity of human
cytochrome P450 (P450) 3A4/3A5
by the teratogen thalidomide was recently demonstrated by H. Yamazaki
et al. ((2013) Chem. Res. Toxicol. 26, 486−489) using the model substrate
midazolam in various <i>in vitro</i> and <i>in vivo</i> models. Chimeric mice with humanized liver also displayed enhanced
midazolam clearance upon pretreatment with orally administered thalidomide,
presumably because of human P450 3A induction. In the current study,
we further investigated the regulation of human hepatic drug metabolizing
enzymes. Thalidomide enhanced levels of P450 3A4 and 2B6 mRNA, protein
expression, and/or oxidation activity in human hepatocytes, indirectly
suggesting the activation of upstream transcription factors involved
in detoxication, e.g., the nuclear receptors pregnane X receptor (PXR)
and constitutive androstane receptor (CAR). A key event after ligand
binding is an alteration of nuclear receptor conformation and recruitment
of coregulator proteins that alter chromatin accessibility of target
genes. To investigate direct engagement and functional alteration
of PXR and CAR by thalidomide, we utilized a peptide microarray with
154 coregulator-derived nuclear receptor-interaction motifs and coregulator
and nuclear receptor boxes, which serves as a sensor for nuclear receptor
conformation and activity status as a function of ligand. Thalidomide
and its human proximate metabolite 5-hydroxythalidomide displayed
significant modulation of coregulator interaction with PXR and CAR
ligand-binding domains, similar to established agonists for these
receptors. These results collectively suggest that thalidomide acts
as a ligand for PXR and CAR and causes enzyme induction leading to
increased P450 enzyme activity. The possibilities of drug interactions
during thalidomide therapy in humans require further evaluation