Piperine activates human pregnane X receptor to induce the expression of cytochrome P450 3A4 and multidrug resistance protein 1

Diindolylmethane, a naturally occurring compound, induces CYP3A4 and MDR1 gene expression by activating human PXR

Activation of human pregnane X receptor (hPXR)-regulated expression of cytochrome P450 3A4 (CYP3A4) and multidrug resistance protein 1 (MDR1) plays an important role in mediating adverse drug interactions. Given the common use of natural products as part of adjunct human health behavior, there is a growing concern about natural products for their potential to induce undesired drug interactions through the activation of hPXR-regulated CYP3A4 and MDR1. Here, we studied whether 3,3'-diindolylmethane (DIM), a natural health supplement, could induce hPXR-mediated regulation of CYP3A4 and MDR1 in human hepatocytes and intestinal cells. DIM, at its physiologically relevant concentrations, not only induced hPXR transactivation of CYP3A4 promoter activity but also induced gene expression of CYP3A4 and MDR1. DIM decreased intracellular accumulation of MDR1 substrate rhodamine 123, suggesting that DIM induces the functional expression of MDR1. Pharmacologic inhibition or genetic knockdown of hPXR resulted in attenuation of DIM induced CYP3A4 and MDR1 gene expression, suggesting that DIM induces CYP3A4 and MDR1 in an hPXR-dependent manner. Together, these results support our conclusion that DIM induces hPXR-regulated CYP3A4 and MDR1 gene expression. The inductive effects of DIM on CYP3A4 and MDR1 expression caution the use of DIM in conjunction with other medications metabolized and transported via CYP3A4 and MDR1, respectively.

Thiazide-like diuretic drug metolazone activates human pregnane X receptor to induce cytochrome 3A4 and multidrug-resistance protein 1

Human pregnane X receptor (hPXR) regulates the expression of drug-metabolizing enzyme cytochrome P450 3A4 (CYP3A4) and drug transporters such as multidrug-resistance protein 1 (MDR1). PXR can be modulated by small molecules, including Federal Drug Administration (FDA)-approved drugs, thus altering drug metabolism and causing drug-drug interactions. To determine the role of FDA-approved drugs in PXR-mediated regulation of drug metabolism and clearance, we screened 1481 FDA-approved small-molecule drugs by using a luciferase reporter assay in HEK293T cells and identified the diuretic drug metolazone as an activator of hPXR. Our data showed that metolazone activated hPXR-mediated expression of CYP3A4 and MDR1 in human hepatocytes and intestine cells and increased CYP3A4 promoter activity in various cell lines. Mammalian two-hybrid assays showed that hPXR recruits its co-activator SRC-1 upon metolazone binding in HepG2 cells, explaining the mechanism of hPXR activation. To understand the role of other commonly-used diuretics in hPXR activation and the structure-activity relationship of metolazone, thiazide and non-thiazide diuretics drugs were also tested but only metolazone activates hPXR. To understand the molecular mechanism, docking studies and mutational analysis were carried out and showed that metolazone binds in the ligand-binding pocket and interacts with mostly hydrophobic amino acid residues. This is the first report showing that metolazone activates hPXR. Because activation of hPXR might cause drug-drug interactions, metolazone should be used with caution for drug treatment in patients undergoing combination therapy.

Pregnane X receptor and drug-induced liver injury

INTRODUCTION

The liver plays a central role in transforming and clearing foreign substances. The continuous exposure of the liver to xenobiotics sometimes leads to impaired liver function, referred to as drug-induced liver injury (DILI). The pregnane X receptor (PXR) tightly regulates the expression of genes in the hepatic drug-clearance system and its undesired activation plays a role in DILI.

AREAS COVERED

This review focuses on the recent progress in understanding PXR-mediated DILI and highlights the efforts made to assess and manage PXR-mediated DILI during drug development.

EXPERT OPINION

Future efforts are needed to further elucidate the mechanisms of PXR-mediated liver injury, including the epigenetic regulation and polymorphisms of PXR. Novel in vitro models containing functional PXR could improve our ability to predict and assess DILI during drug development. PXR inhibitors may provide chemical tools to validate the potential of PXR as a therapeutic target and to develop drugs to be used in the clinic to manage PXR-mediated DILI.

ABC transporters in fish species: a review

ATP-binding cassette (ABC) proteins were first recognized for their role in multidrug resistance (MDR) in chemotherapeutic treatments, which is a major impediment for the successful treatment of many forms of malignant tumors in humans. These proteins, highly conserved throughout vertebrate species, were later related to cellular detoxification and accounted as responsible for protecting aquatic organisms from xenobiotic insults in the so-called multixenobiotic resistance mechanism (MXR). In recent years, research on these proteins in aquatic species has highlighted their importance in the detoxification mechanisms in fish thus it is necessary to continue these studies. Several transporters have been pointed out as relevant in the ecotoxicological context associated to the transport of xenobiotics, such as P-glycoproteins (Pgps), multidrug-resistance-associated proteins (MRPs 1-5) and breast cancer resistance associated protein (BCRP). In mammals, several nuclear receptors have been identified as mediators of phase I and II metabolizing enzymes and ABC transporters. In aquatic species, knowledge on co-regulation of the detoxification mechanism is scarce and needs to be addressed. The interaction of emergent contaminants that can act as chemosensitizers, with ABC transporters in aquatic organisms can compromise detoxification processes and have population effects and should be studied in more detail. This review intends to summarize the recent advances in research on MXR mechanisms in fish species, focusing in (1) regulation and functioning of ABC proteins; (2) cooperation with phase I and II biotransformation enzymes; and (3) ecotoxicological relevance and information on emergent pollutants with ability to modulate ABC transporters expression and activity. Several lines of evidence are clearly suggesting the important role of these transporters in detoxification mechanisms and must be further investigated in fish to underlay the mechanism to consider their use as biomarkers in environmental monitoring.

Stability of the human pregnane X receptor is regulated by E3 ligase UBR5 and serine/threonine kinase DYRK2

The hPXR (human pregnane X receptor), a major chemical toxin sensor, is a ligand-induced transcription factor activated by various xenobiotics and toxins, resulting in the transcriptional up-regulation of detoxifying enzymes. To date, little is known about the upstream regulation of hPXR. Using MS analysis and a kinome-wide siRNA screen, we report that the E3 ligase UBR5 (ubiquitin protein ligase E3 component n-recognin 5) and DYRK2 (dual-specificity tyrosine-phosphorylation-regulated kinase 2) regulate hPXR stability. UBR5 knockdown resulted in accumulation of cellular hPXR and a concomitant increase in hPXR activity, whereas the rescue of UBR5 knockdown decreased the cellular hPXR level and activity. Importantly, UBR5 exerted its effect in concert with the serine/threonine kinase DYRK2, as the knockdown of DYRK2 phenocopied UBR5 knockdown. hPXR was shown to be a substrate for DYRK2, and DYRK2-dependent phosphorylation of hPXR facilitated its subsequent ubiquitination by UBR5. This is the first report of the post-translational regulation of hPXR via phosphorylation-facilitated ubiquitination by DYRK2 and UBR5. The results of the present study reveal the role of the ubiquitin-proteasomal pathway in modulating hPXR activity and indicate that pharmacological inhibitors of the ubiquitin-proteasomal pathway that regulate hPXR stability may negatively affect treatment outcome from unintended hPXR-mediated drug-drug interactions.