Gestational and pregnane X receptor-mediated regulation of placental ATP-binding cassette drug transporters in mice

[Quantitative assessment of breast cancer resistance protein during pregnancy in rabbits]

Breast cancer resistance protein (BCRP,ABCG2) is an efflux transporter protein that transports various substrates from the cell to the extracellular space or organ cavities. The aim of this study was a complex assessment of the amount of BCRP during pregnancy in rabbits. The amount of BCRP in samples of the rabbit jejunum, liver, kidney, cerebral cortex, and placenta was determined by enzyme immunoassay, and in human hepatocellular carcinoma (HepG2) cells by the Western blot. To study the mechanisms involved in control of the dynamic BCRP levels during pregnancy, serum concentrations of sex hormones were investigated by radioimmunoassay and relative amounts of constitutive androstane receptor (CAR) and pregnane X receptor (PXR) in these organs were evaluated using the Western blot method. The putative role of CAR and PXR in regulation of the BCRP level by progesterone was evaluated in vitro experiments on HepG2 cells. It was found that amount of BCRP in the jejunum of pregnant rabbits was higher than in the placenta, liver, kidneys, and cerebral cortex. An increase in the amount of BCRP in the liver of rabbits was noted on the 21st day of pregnancy and a tendency to the increase was also detected on the 28th day; in the kidney and cerebral cortex increased BCRP levels were detected on the 28th day and 14th day of pregnancy, respectively, as compared with non-pregnant females. In vitro experiments with HepG2 cells have shown that the increase in the BCRP level is determined by the activating effect of progesterone on PXR.

Transcription factor-mediated regulation of the BCRP/ABCG2 efflux transporter: a review across tissues and species

Introduction: The breast cancer resistance protein (BCRP/ABCG2) is a member of the ATP-binding cassette superfamily of transporters. Using the energy garnered from the hydrolysis of ATP, BCRP actively removes drugs and endogenous molecules from the cell. With broad expression across the liver, kidney, brain, placenta, testes, and small intestines, BCRP can impact the pharmacokinetics and pharmacodynamics of xenobiotics.Areas covered: The purpose of this review is to summarize the transcriptional signaling pathways that regulate BCRP expression across various tissues and mammalian species. We will cover the endobiotic- and xenobiotic-activated transcription factors that regulate the expression and activity of BCRP. These include the estrogen receptor, progesterone receptor, peroxisome proliferator-activated receptor, constitutive androstane receptor, pregnane X receptor, nuclear factor e2-related factor 2, and aryl hydrocarbon receptor.Expert opinion: Key transcription factors regulate BCRP expression and function in response to hormones and xenobiotics. Understanding this regulation provides an opportunity to improve pharmacotherapeutic outcomes by enhancing the efficacy and reducing the toxicity of drugs that are substrates of this efflux transporter.

An update on expression and function of P-gp/ABCB1 and BCRP/ABCG2 in the placenta and fetus

INTRODUCTION

P-glycoprotein (P-gp)/ABCB1 and breast cancer resistance protein (BCRP)/ABCG2 are highly expressed in the placenta and fetus throughout gestation and can modulate exposure and toxicity of drugs and xenobiotics to the vulnerable fetus during the sensitive times of growth and development. We aim to provide an update on current knowledge on placental and fetal expressions of the two transporters in different species, and to provide insight on interpreting transporter expression and fetal exposure relative to the concept of fraction of drug transported. Areas covered: Comprehensive literature review through PubMed (primarily from July 2010 to February 2018) on P-gp and BCRP expression and function in the placenta and fetus of primarily human, mouse, rat, and guinea pig. Expert opinion: While there are many commonalities in the expression and function of P-gp and BCRP in the placenta and fetal tissues across species, there are distinct differences in expression levels and temporal changes. Further studies are needed to quantify protein abundance of these transporters and functionally assess their activities at various gestational stages. Combining the knowledge of interspecies differences and the concept of fraction of drug transported, we may better predict the magnitude of impact these transporters have on fetal drug exposure.

Effects of polymorphisms in NR1I2, CYP3A4, and ABC transporters on the steady-state plasma trough concentrations of bosutinib in Japanese patient with chronic myeloid leukemia

We investigated the effects of polymorphisms in NR1I2 (7635A>G, 8055C>T), CYP3A4 (20230G>A), ABCB1 (1199G>A, 1236C>T, 2677G>T/A, 3435C>T), and ABCG2 (421C>A) on the mean plasma trough concentrations (C₀) of bosutinib at the steady-state in 30 Japanese patients with chronic myeloid leukemia. Bosutinib C₀ values were monitored using high-performance liquid chromatography. The median coefficient of variation (CV) value of the bosutinib C₀ for one patient (intrapatient) during bosutinib therapy was 25.9% (range: 7.66-44.24%). During bosutinib therapy, 17 of 30 patients received 300 mg/day bosutinib. The interpatient CV value for the bosutinib C₀ after administration of 300 mg/day was 45.0%. There were no significant differences in the bosutinib C₀ between genotypes for ABCB1, ABCG2, and CYP3A4 polymorphisms. However, the bosutinib C₀ in patients with the NR1I2 7635G/G or 8055T/T genotype was significantly lower than those in patients with the 7635A allele or 8055C allele, respectively (P = 0.050 and 0.022, respectively). In addition, the bosutinib C₀ in patients with both NR1I2 7635G/G and 8055T/T genotypes was significantly lower than those in patients with other genotypes (P = 0.022). Because patients with the NR1I2 7635G/G or 8055T/T genotype may have increased activity of pregnane X receptor-regulated genes and thereafter higher intestinal expression of CYP3A4 and ABC efflux drug transporters, these patients may have a lower bosutinib C₀. Therefore, information on the NR1I2 genotype may be useful for achieving optimal systemic exposure of bosutinib.

The Role of PXR Genotype and Transporter Expression in the Placental Transport of Lopinavir in Mice

Lopinavir (LPV), an antiretroviral protease inhibitor frequently prescribed in HIV-positive pregnancies, is a substrate of Abcb1 and Abcc2. As differences in placental expression of these transporters were seen in Pregnane X Receptor (PXR) −/− mice, we examined the impact of placental transporter expression and fetal PXR genotype on the fetal accumulation of LPV. PXR +/− dams bearing PXR +/+, PXR +/−, and PXR −/− fetuses were generated by mating PXR +/− female mice with PXR +/− males. On gestational day 17, dams were administered 10 mg/kg LPV (i.v.) and sacrificed 30 min post injection. Concentrations of LPV in maternal plasma and fetal tissue were measured by LC-MS/MS, and transporter expression was determined by quantitative RT-PCR. As compared to the PXR +/+ fetal units, placental expression of Abcb1a, Abcc2, and Abcg2 mRNA were two- to three-fold higher in PXR −/− fetuses (p < 0.05). Two-fold higher fetal:maternal LPV concentration ratios were also seen in the PXR +/+ as compared to the PXR −/− fetuses (p < 0.05), and this significantly correlated to the placental expression of Abcb1a (r = 0.495; p < 0.005). Individual differences in the expression of placental transporters due to genetic or environmental factors can impact fetal exposure to their substrates.

Placental ABC Transporters: Biological Impact and Pharmaceutical Significance

The human placenta fulfills a variety of essential functions during prenatal life. Several ABC transporters are expressed in the human placenta, where they play a role in the transport of endogenous compounds and may protect the fetus from exogenous compounds such as therapeutic agents, drugs of abuse, and other xenobiotics. To date, considerable progress has been made toward understanding ABC transporters in the placenta. Recent studies on the expression and functional activities are discussed. This review discusses the placental expression and functional roles of several members of ABC transporter subfamilies B, C, and G including MDR1/P-glycoprotein, the MRPs, and BCRP, respectively. Since placental ABC transporters modulate fetal exposure to various compounds, an understanding of their functional and regulatory mechanisms will lead to more optimal medication use when necessary in pregnancy.

SMS regulates the expression and function of P-gp and MRP2 in Caco-2 cells

Sphingomyelin synthase (SMS) has two isoforms of SMS1 and SMS2, the last enzyme involved in the biosynthesis of sphingomyelin (SM), and has impact on the expression of membrane proteins. In the present study, we explored the potential effects of SMS on drug transporters, a special family of membrane proteins in human intestinal epithelial Caco-2 cells. The specific knockdown of SMS1 or SMS2 with siRNA in Caco-2 cells substantially decreased the expression and function of P-glycoprotein (P-gp) and multidrug resistance protein 2 (MRP2) rather than other drug transporters MRP1, MRP3, PEPT1, OATP2B1, and BCRP. In the SMS1 stable overexpressed Caco-2 cell line, the expression levels of P-gp and MRP2 and transcription factor pregnane X receptor (PXR) were upregulated and the phosphorylation levels of signaling pathways janus protein tyrosine kinase 2 (JAK-2) and extracellular signal-regulated kinases (ERK) were also evidently increased; however, the upregulated mRNA expression levels of PXR, P-gp, and MRP2 were diminished by inhibiting the phosphorylation of ERK and JAK-2. Furthermore, the SMS1 overexpression in Caco-2 cells altered the expression levels of ERM proteins ezrin and moesin, which are closely connected to the function of drug transporters. In conclusion, we herein demonstrate for the first time that in Caco-2 cells SMS regulates the expression and function of drug transporters P-gp and MRP2, and their regulator PXR is mediated by phosphorylated ERK and JAK-2 signaling pathways.

Nuclear receptors in regulation of biotransformation enzymes and drug transporters in the placental barrier

Over the past 20 years, the toxicological and protective roles of the placental barrier with respect to drug detoxification and transporter-controlled protection of the fetus have been intensively examined. Several cytochrome P450 enzymes are expressed in placental trophoblast at different stages of pregnancy, though only a few of these have functional activity to metabolize xenobiotics. Drug transporters such as P-glycoprotein/MDR1 or breast cancer resistance protein (BCRP) are highly expressed in the placenta, and their functional activities have been demonstrated in the placenta both in vitro and in vivo. In addition, several studies have reported on ligand-activated transcription factors and nuclear receptors referred to as "xenosensors" in the placenta. The xenosensors control transcriptional regulation of both xenobiotic-metabolizing enzymes and drug transporters in different organs. Their ligands include toxic compounds and environmental pollutants, drugs, as well as herbal, dietary or vitamin supplements. Nevertheless, it remains debatable whether the placental barrier adapts to toxic injuries coming either from maternal medication or environmental contamination and whether the placenta contains a mechanism to respond dynamically in protecting the developing fetus. In the present paper, we summarize current knowledge about the activity and expression of major ligand-activated transcriptional mechanisms involved in biotransformation enzymes and transporters regulation in human placenta. In particular, we highlight the emerging roles of aryl hydrocarbon (AHR), vitamin D (VDR), glucocorticoid (GR) and pregnane X (PXR) receptors in that regulation. We show that the placenta constitute a unique metabolizing organ with significant overlap of exogenous and endogenous compounds metabolism controlled by nuclear receptors.

Nuclear-receptor-mediated regulation of drug- and bile-acid-transporter proteins in gut and liver

Adverse drug events (ADEs) are a common cause of patient morbidity and mortality and are classically thought to result, in part, from variation in expression and activity of hepatic enzymes of drug metabolism. It is now known that alterations in the expression of genes that encode drug- and bile-acid-transporter proteins in both the gut and liver play a previously unrecognized role in determining patient drug response and eventual clinical outcome. Four nuclear receptor (NR) superfamily members, including pregnane X receptor (PXR, NR1I2), constitutive androstane receptor (NR1I3), farnesoid X receptor (NR1H4), and vitamin D receptor (NR1I1), play pivotal roles in drug- and bile-acid-activated programs of gene expression to coordinately regulate drug- and bile-acid transport activity in the intestine and liver. This review focuses on the NR-mediated gene activation of drug and bile-acid transporters in these tissues as well as the possible underlying molecular mechanisms.

PXR and NF-κB correlate with the inducing effects of IL-1β and TNF-α on ABCG2 expression in breast cancer cell lines

In this study we aimed to evaluate PXR and ABCG2 gene expression patterns and NF-κB activity induced by proinflammatory cytokines in different breast normal and carcinoma cells. The effects of proinflammatory cytokines on ABCG2 and PXR mRNA expression were studied using real-time PCR. Western blot analysis used for evaluating the protein levels of ABCG2, PXR and the active form of NF-κB (p65 in nuclear protein extract). Significant inductions in the ABCG2 and PXR mRNA and protein levels and NF-κB activity, were observed in MCF7, BT-474, CAL51, 184A1 and HBL100 cells, upon treatment with 50 ng/ml of IL-1β and TNF-α. On the contrary significant reduction of the ABCG2 and PXR mRNA and protein levels and NF-κB activity, were observed in MDA-MB-435 cell line. In conclusion, IL-1β and TNF-α induced ABCG2 and PXR expression and NF-κB activity in some breast cancer and normal cell lines. Similar patterns of induction and reduction in PXR and ABCG2 genes and NF-κB activity suggest a probable relationship between ABCG2, PXR and NF-κB.