Endocrine disrupting chemicals, phthalic acid and nonylphenol, activate Pregnane X receptor-mediated transcription

A Review of the Ethnobotanical Use, Chemistry and Pharmacological Activities of Constituents Derived from the Plant Genus Geijera (Rutaceae)

Geijera Schott is a plant genus of the Rutaceae Juss. (rue and citrus) family, comprising six species which are all native to Oceania. Of the plants belonging to this genus, the most significant species that has a customary use is Geijera parviflora, which was used by Indigenous Australians, primarily as a pain reliever. Herein, a comprehensive review of the literature published on the genus Geijera from 1930 to 2023 was conducted. This is the first review for this plant genus, and it highlights the chemical constituents reported to date, together with the range of pharmacological properties described from the various species and different parts of the plant. These properties include anti-inflammatory, anti-microbial, anti-parasitic, insect repellent, analgesic, neuroactive, and anti-cancer activities. Finally, a reflection on some of the important areas for future focused studies of this plant genus is provided.

Regulation of PXR in drug metabolism: chemical and structural perspectives

INTRODUCTION

Pregnane X receptor (PXR) is a master xenobiotic sensor that transcriptionally controls drug metabolism and disposition pathways. PXR activation by pharmaceutical drugs, natural products, environmental toxins, etc. may decrease drug efficacy and increase drug-drug interactions and drug toxicity, indicating a therapeutic value for PXR antagonists. However, PXR's functions in physiological events, such as intestinal inflammation, indicate that PXR activators may be useful in certain disease contexts.

AREAS COVERED

We review the reported roles of PXR in various physiological and pathological processes including drug metabolism, cancer, inflammation, energy metabolism, and endobiotic homeostasis. We then highlight specific cellular and chemical routes that modulate PXR activity and discuss the functional consequences. Databases searched and inclusive dates: PubMed, 1 January 1980 to 10 January 2024.

EXPERT OPINION

Knowledge of PXR's drug metabolism function has helped drug developers produce small molecules without PXR-mediated metabolic liabilities, and further understanding of PXR's cellular functions may offer drug development opportunities in multiple disease settings.

Effects of 4-n-nonylphenol in liver of male and female viviparous fish (Poecilia vivipara)

4-n-Nonylphenol (NP) is one of the most toxic alkylphenols found in the environment. To evaluate the transcriptional effects of NP in the viviparous fish Poecilia vivipara, a hepatic transcriptome and qPCR analysis of genes were carried out. Guppies separated by sex were injected with two doses of NP (15 μg/g and 150 μg/g) or peanut oil (control). After 24 h, analysis of transcriptional level of Aryl Hydrocarbon Receptor (AhR), Estrogen Nuclear Receptor Alpha (ESR1), Pregnane X Receptor (PXR), Cytochromes P450 (CYP1A, CYP2K1 and CYP3A30), Glutathione S-transferase A3 and Mu 3 (GSTa3 and GSTMu3), SRY-Box Transcription Factor 9 (SOX9), Vitellogenin-1 (VIT), ATP Binding Cassette Subfamily C Member 1 (ABCC1), Multidrug Resistance-Associated Protein 2 (MRP2) and UDP Glucuronosyltransferase Family 1 Member A1 (UGT1A1) was evaluated. 205,046 transcripts were assembled and protein prediction resulted in 203,147 predicted peptides. In females, no significant changes were detected in the transcription of some phase I biotransformation and ABC transporter genes. AhR, PXR, GSTa3 and SOX9 genes where higher in the lower dose group (15 μg/g) compared to control. In male fish, no changes were observed in the transcript levels of the nuclear receptors, in endocrine disruption and phase I biotransformation genes. GSTa3 showed lower transcription in fish treated with both doses. ABCC1 was higher in guppies treated with the lower dose while MRP2 showed less transcripts. This short-term and low-dose exposure to NP caused changes that could serve as early indicators of deleterious processes. These results indicate P. vivipara as a good sentinel in biomonitoring programs.

Nuclear Receptor Pathways Mediating the Development of Boar Taint

The nuclear receptors PXR, CAR, and FXR are activated by various ligands and function as transcription factors to control the expression of genes that regulate the synthesis and metabolism of androstenone and skatole. These compounds are produced in entire male pigs and accumulate in the fat to cause the development of a meat quality issue known as boar taint. The extent of this accumulation is influenced by the synthesis and hepatic clearance of androstenone and skatole. For this reason, PXR, CAR, and FXR-mediated signaling pathways have garnered interest as potential targets for specialized treatments designed to reduce the development of boar taint. Recent research has also identified several metabolites produced by gut microbes that act as ligands for these nuclear receptors (e.g., tryptophan metabolites, short-chain fatty acids, bile acids); however, the connection between the gut microbiome and boar taint development is not clear. In this review, we describe the nuclear receptor signaling pathways that regulate the synthesis and metabolism of boar taint compounds and outline the genes involved. We also discuss several microbial-derived metabolites and dietary additives that are known or suspected nuclear receptor ligands and suggest how these compounds could be used to develop novel treatments for boar taint.

High-Resolution Exposomics and Metabolomics Reveals Specific Associations in Cholestatic Liver Diseases

Progress in development of prognostic and therapeutic options for the rare cholestatic liver diseases, primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC), is hampered by limited knowledge of their pathogeneses. In particular, the potential role of hepatotoxic and/or metabolism-altering environmental chemicals in the pathogenesis of these diseases remains relatively unstudied. Moreover, the extent to which metabolic pathways are altered due to ongoing cholestasis and subsequent liver damage or possibly influenced by hepatotoxic chemicals is poorly understood. In this study, we applied a comprehensive exposomics-metabolomics approach to uncover potential pathogenic contributors to PSC and PBC. We used untargeted high-resolution mass spectrometry to characterize a wide range of exogenous chemicals and endogenous metabolites in plasma and tested them for association with disease. Exposome-wide association studies (EWAS) identified environmental chemicals, including pesticides, additives and persistent pollutants, that were associated with PSC and/or PBC, suggesting potential roles for these compounds in disease pathogenesis. Metabolome-wide association studies (MWAS) found disease-associated alterations to amino acid, eicosanoid, lipid, co-factor, nucleotide, mitochondrial and microbial metabolic pathways, many of which were shared between PSC and PBC. Notably, this analysis implicates a potential role of the 5-lipoxygenase pathway in the pathogenesis of these diseases. Finally, EWAS × MWAS network analysis uncovered linkages between environmental agents and disrupted metabolic pathways that provide insight into potential mechanisms for PSC and PBC. Conclusion: This study establishes combined exposomics-metabolomics as a generalizable approach to identify potentially pathogenic environmental agents and enumerate metabolic alterations that may impact PSC and PBC, providing a foundation for diagnostic and therapeutic strategies.

The Intestinal Barrier—Shielding the Body from Nano- and Microparticles in Our Diet

Nano- and microparticles are an implicit part of the human diet. They are unknowingly ingested with our food that contains them as additives or pollutants. However, their impact on human health is not yet understood and controversially discussed. The intestinal epithelial barrier shields our body against exogenous influences, such as commensal bacteria, pathogens, and body-foreign particles and, therefore, protects our body integrity. Breakdown of the intestinal epithelial barrier and aberrant immune responses are key events in the pathogenesis of inflammatory bowel disease (IBD). Epithelial lesions might enable systemic translocation of nano- and microparticles into the system, eventually triggering an excessive immune response. Thus, IBD patients could be particularly vulnerable to adverse health effects caused by the ingestion of synthetic particles with food. The food-additive titanium dioxide (TiO2) serves as a coloring agent in food products and is omnipresent in the Western diet. TiO2 nanoparticles exacerbate intestinal inflammation by activation of innate and adaptive immune response. Because of serious safety concerns, the use of TiO2 as a food additive was recently banned from food production within the European Union. Due to environmental pollution, plastic has entered the human food chain, and plastic microparticles have been evidenced in the drinking water and comestible goods. The impact of plastic ingestion and its resulting consequences on human health is currently the subject of intense research. Focusing on TiO2 and plastic particles in the human diet and their impact on epithelial integrity, gut homeostasis, and intestinal inflammation, this review is addressing contemporary hot topics which are currently attracting a lot of public attention.

The Interface between Cell Signaling Pathways and Pregnane X Receptor

Highly expressed in the enterohepatic system, pregnane X receptor (PXR, NR1I2) is a well-characterized nuclear receptor (NR) that regulates the expression of genes in the liver and intestines that encode key drug metabolizing enzymes and drug transporter proteins in mammals. The net effect of PXR activation is to increase metabolism and clear drugs and xenobiotics from the body, producing a protective effect and mediating clinically significant drug interaction in patients on combination therapy. The complete understanding of PXR biology is thus important for the development of safe and effective therapeutic strategies. Furthermore, PXR activation is now known to specifically transrepress the inflammatory- and nutrient-signaling pathways of gene expression, thereby providing a mechanism for linking these signaling pathways together with enzymatic drug biotransformation pathways in the liver and intestines. Recent research efforts highlight numerous post-translational modifications (PTMs) which significantly influence the biological function of PXR. However, this thrust of research is still in its infancy. In the context of gene-environment interactions, we present a review of the recent literature that implicates PXR PTMs in regulating its clinically relevant biology. We also provide a discussion of how these PTMs likely interface with each other to respond to extracellular cues to appropriately modify PXR activity.

Regulation of PXR Function by Coactivator and Corepressor Proteins: Ligand Binding Is Just the Beginning

The pregnane X receptor (PXR, NR1I2) is a nuclear receptor which exerts its regulatory function by heterodimerization with the retinoid-X-receptor α (RXRα, NR2B1) and binding to the promoter and enhancer regions of diverse target genes. PXR is involved in the regulation of drug metabolism and excretion, metabolic and immunological functions and cancer pathogenesis. PXR activity is strongly regulated by the association with coactivator and corepressor proteins. Coactivator proteins exhibit histone acetyltransferase or histone methyltransferase activity or associate with proteins having one of these activities, thus promoting chromatin decondensation and activation of the gene expression. On the contrary, corepressor proteins promote histone deacetylation and therefore favor chromatin condensation and repression of the gene expression. Several studies pointed to clear cell- and ligand-specific differences in the activation of PXR. In this article, we will review the critical role of coactivator and corepressor proteins as molecular determinants of the specificity of PXR-mediated effects. As already known for other nuclear receptors, understanding the complex mechanism of PXR activation in each cell type and under particular physiological and pathophysiological conditions may lead to the development of selective modulators with therapeutic potential.

Competitive Carboxylate-Silicate Binding at Iron Oxyhydroxide Surfaces

Dissolved silicate ions in wet and dry soils can determine the fate of organic contaminants via competitive binding. While fundamental surface science studies have advanced knowledge of binding in competitive systems, little is still known about the ranges of solution conditions, the time dependence, and the molecular processes controlling competitive silicate-organic binding on minerals. Here we address these issues by describing the competitive adsorption of dissolved silicate and of phthalic acid (PA), a model carboxylate-bearing organic contaminant, onto goethite, a representative natural iron oxyhydroxide nanomineral. Using surface complexation thermodynamic modeling of batch adsorption data and chemometric analyses of vibrational spectra, we find that silicate concentrations representative of natural waters (50-1000 μM) can displace PA bound at goethite surfaces. Below pH ∼8, where PA binds, every bound Si atom removes ∼0.3 PA molecule by competing with reactive singly coordinated hydroxo groups (-OH) on goethite. Long-term (30 days) reaction time and a high silicate concentration (1000 μM) favored silicate polymer formation, and increased silicate while decreasing PA loadings. The multisite complexation model predicted PA and silicate binding in terms of the competition for -OH groups without involving PA/silicate interactions, and in terms of a lowering of outer-Helmholtz potentials of the goethite surface by these anions. The model predicted that silicate binding lowered loadings of PA species, and whose two carboxylate groups are hydrogen- (HB) and metal-bonded (MB) with goethite. Vibrational spectra of dried samples revealed that the loss of water favored greater proportions of MB over HB species, and these coexisted with predominantly monomeric silicate species. These findings underscored the need to develop models for a wider range of organic contaminants in soils exposed to silicate species and undergoing wet-dry cycles.

Prenatal exposure to phthalate esters and its impact on child development

Endocrine disruptive chemicals (EDCs) cause adverse health effects through interaction with endocrine systems. They are classified by chemical structure, effects on specific endocrine systems, their bioaccumulation and/or persistence in the environment, and/or clinically observable effects. In industrial nations, people are exposed to complex mixtures of many different substances all of which may have multiple and deleterious effects upon the individual. The clinical importance of epigenetic changes caused by the action of EDCs during vulnerable phases of development is currently unclear but of particular relevance. Epidemiological studies are criticized because reproducibility is not always guaranteed. Nevertheless, they remain the method of choice for the development and analysis of suitable model systems. Positive associations, despite of sometimes conflicting results, are the key in the selection of factors that can then be analyzed in model systems in an unbiased way. This article reports EDC-caused effects in the fields of growth and metabolism, neurocognitive development and sexual development and reproduction focusing mainly on phthalates and their metabolites. However, research will have to focus on the interactions of different EDCs and their consequences of prenatal and early life exposure.

Endocrine disrupting chemicals (EDCs) and the neuroendocrine system: Beyond estrogen, androgen, and thyroid

Hundreds of anthropogenic chemicals occupy our bodies, a situation that threatens the health of present and future generations. This chapter focuses on endocrine disrupting compounds (EDCs), both naturally occurring and man-made, that affect the neuroendocrine system to adversely impact health, with an emphasis on reproductive and metabolic pathways. The neuroendocrine system is highly sexually dimorphic and essential for maintaining homeostasis and appropriately responding to the environment. Comprising both neural and endocrine components, the neuroendocrine system is hormone sensitive throughout life and touches every organ system in the body. The integrative nature of the neuroendocrine system means that EDCs can have multi-system effects. Additionally, because gonadal hormones are essential for the sex-specific organization of numerous neuroendocrine pathways, endocrine disruption of this programming can lead to permanent deficits. Included in this review is a brief history of the neuroendocrine disruption field and a thorough discussion of the most common and less well understood neuroendocrine disruption modes of action. Also provided are extensive examples of how EDCs are likely contributing to neuroendocrine disorders such as obesity, and evidence that they have the potential for multi-generational effects.

Exposure to endocrine disruptor alkylphenols and the occurrence of endometrial cancer

Exposure to environmental chemicals with oestrogenic effects has been associated with the development of endometrial cancer (EMCa). EMCa has become the most commonly diagnosed cancer of the female genital tract. To further understand the potential association between exposure to environmental endocrine disruptors and the occurrence of EMCa, we performed a case-control study between 2011 and 2014. We aimed to detect and compare concentrations of a known hormone disruptor, alkylphenol, between women diagnosed with either EMCa or uterine leiomyoma, and those who did not have either of these. Subjects were women diagnosed with either EMCa or uterine leiomyoma (LM) and healthy controls. A structured questionnaire was administered to collect information on lifestyle and health status. Gas chromatography/mass spectrometry was used to measure urinary NP and OP concentrations in participants. Multiple regression analysis was used to examine the association between exposure and outcomes. Overall, 397 women were recruited, including 49 with EMCa, 247 with LM, and 101 controls. Among them, 73.6% showed detectable levels of NP and 61.0% showed detectable levels of OP. The EMCa group had a significantly higher NP concentration than the control group. Higher OP concentrations were also found in participants with EMCa than those with LM and controls. In addition, women in the upper tertile of the NP group had a significantly increased risk of EMCa occurrence (odds ratio [95% confidence interval] = 4.47 [1.69-11.84] for EMCa vs. control). The same was found in the group of women with more than the median level of OP (odds ratio [95% confidence interval] = 4.32 [2.01-9.30] for EMCa vs. LM). Stratification of pre- and post-menopausal groups resulted in a similar association. The results show that NP/OP exposure is associated with EMCa. Further investigations and exposure minimisation are suggested.

Nonylphenol induced individual and population fluctuation of Caenorhabditis elegans: Disturbances on developmental and reproductive system

The environmental risks that have arisen from endocrine disruption compounds (EDCs) have become global challenges, especially for persistent bio-accumulated xenobiotic chemicals, such as nonylphenol (NP). In the present study, the population dynamics of Caenorhabditis elegans (C. elegans) were systemically investigated by conducting developmental and reproductive bioassays under the exposure of NP, which has been widely detected in actual aquatic environments. The results revealed that under NP exposure (400 μg L^-1 NP), developmental indictors of C. elegans, including the body length and width were significantly inhibited at different life stages of L1 and L4 larva, and the growth curves were further adversely affected. In addition, abnormalities in reproductive systems were also observed under NP exposure. Such abnormalities obeyed a dose-dependent relationship with NP levels, which were closely related to the delayed spawning time and decreased reproductive rates. Moreover, the results from global genome expression analysis for nematodes revealed that the most significant enriched GO terms could be predominantly responsible for the dysregulation of growth and reproductive system. The population's parameters, including age composition and intrinsic growth rate (r_m d^-1), displayed significant changes, with a suppressed potentiality of population growth. Those data elucidated that NP exhibited a profound impact on the dynamic stability of the population, even with no obvious effect on certain biochemical markers.

Cytotoxicity of nonylphenol on spermatogonial stem cells via phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin pathway

BACKGROUND

With continuous advancement of industrial society, environmental pollution has become more and more serious. There has been an increase in infertility caused by environmental factors. Nonylphenol (NP) is a stable degradation product widely used in daily life and production and has been proven to affect male fertility. However, the underlying mechanisms therein are unclear. Thus, it is necessary to study the effect and mechanism of NP on spermatogonial stem cells (SSCs).

AIM

To investigate the cytotoxic effect of NP on SSCs via the phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway.

METHODS

SSCs were treated with NP at 0, 10, 20 or 30 µmol. MTT assay was performed to evaluate the effect of NP on the proliferation of SSCs. Flow cytometry was conducted to measure SSC apoptosis. The expression of Bad, Bcl-2, cytochrome-c, pro-Caspase 9, SOX-2, OCT-4, Nanog, Nanos3, Stra8, Scp3, GFRα1, CD90, VASA, Nanos2, KIT, PLZF and PI3K/AKT/mTOR-related proteins was observed by western blot, and the mRNA expression of SOX-2, OCT-4 and Nanog was detected by quantitative reverse transcription polymerase chain reaction.

RESULTS

Compared with untreated cells (0 μmol NP), SSCs treated with NP at all concentrations showed a decrease in cell proliferation and expression of Bcl-2, Nanog, OCT-4, SOX-2, Nanos3, Stra8, Scp3, GFRα1, CD90, VASA, Nanos2, KIT, and PLZF (P < 0.05), whereas the expression of Bad, cytochrome-c, and pro-Caspase 9 increased significantly (P < 0.05). We further examined the PI3K/AKT/mTOR pathway and found that the phosphorylation of PI3K, AKT, mTORC1, and S6K was significantly decreased by NP at all concentrations compared to that in untreated SSCs (P < 0.05). NP exerted the greatest effect at 30 μmol among all NP concentrations.

CONCLUSION

NP attenuated the proliferation, differentiation and stemness maintenance of SSCs while promoting apoptosis and oxidative stress. The associated mechanism may be related to the PI3K/AKT/mTOR pathway.

Phase 0 of the Xenobiotic Response: Nuclear Receptors and Other Transcription Factors as a First Step in Protection from Xenobiotics

This mini-review examines the crucial importance of transcription factors as a first line of defense in the detoxication of xenobiotics. Key transcription factors that recognize xenobiotics or xenobiotic-induced stress such as reactive oxygen species (ROS), include AhR, PXR, CAR, MTF, Nrf2, NF-κB, and AP-1. These transcription factors constitute a significant portion of the pathways induced by toxicants as they regulate phase I-III detoxication enzymes and transporters as well as other protective proteins such as heat shock proteins, chaperones, and anti-oxidants. Because they are often the first line of defense and induce phase I-III metabolism, could these transcription factors be considered the phase 0 of xenobiotic response?

Effects of Atrazine and Fenoxaprop-Ethyl on Capacitation and the Acrosomal Reaction in Boar Sperm

Atrazine is a herbicide of the chloro-s-triazine family. It inhibits photosynthesis in plants and is an endocrine disruptor, but its effects on human health are controversial. Fenoxaprop-ethyl, an aryloxy phenoxyalkanoic acid herbicide, inhibits the biosynthesis of fatty acids and provokes depolarization of membranes. The aim of this study is to evaluate the in vitro effects of both herbicides on capacitation, spontaneous acrosome reaction (SAR) and progesterone-induced acrosome reaction (PIAR) in boar sperm. Sperm capacitation is done in TALP-HEPES media for 4 hours. Capacitation and SAR are evaluated immediately; PIAR, 30 minutes later. LC50 for fenoxaprop-ethyl is 60 mM and 40 mM for atrazine. Fenoxaprop-ethyl induces capacitation at 60 mM and SAR at all concentrations, also increases significantly PIAR. Atrazine decreased capacitation whereas increase significantly SAR and PIAR at all concentrations. It seems that fenoxaprop-ethyl and atrazine accelerate the capacitation and the acrosomal reaction, possibly via plasma membrane destabilization.

Effects of nonylphenols on embryonic development and metamorphosis of Xenopus laevis: FETAX and amphibian metamorphosis toxicity test (OECD TG231)

Nonylphenols (NPs) are a group of endocrine-disrupting surfactants that mimic estrogen. To determine the developmental toxicity and thyroid-disrupting effect of NPs, the effects of exposure to nonylphenol (NP), 4-nonylphenol (4-NP), and nonylphenol ethoxylate (NP-12) were examined according to the frog embryo teratogenesis assay-Xenopus (FETAX) and Organization for Economic Co-operation and Development test guidelines 231 (TG231). In FETAX, the LC₅₀ values of NP, 4-NP, and NP-12 were 59.14 mg/L, 10.13 mg/L, and 14.60 mg/L, respectively. At 10.0 mg/L, NP, 4-NP, and NP-12 significantly decreased the total length of tadpoles, and NP and 4-NP increased gut malformation and bent tails. In surviving tadpoles, the EC₅₀ values for malformation of NP, 4-NP, and NP-12 were 4.66, 6.51, and 13.08 mg/L, respectively. The teratogenic indices of NP, 4-NP, and NP-12 were 12.69, 1.56, and 1.08, respectively, suggesting the teratogenic potential of NP and 4-NP. In a range-finder assay for TG231, the 96-h LC₅₀ values of NP, 4-NP, and NP-12 were 2.0, 2.0, and 10.57 mg/L, respectively. When NF stage 51 larvae were exposed for 21 days, larval growth was inhibited by NP, 4-NP, and NP-12 at 0.67, 0.07, and 0.37 mg/L, respectively. 4-NP at 0.07 mg/L accelerated the developmental stage and significantly increased hind limb length, while 0.67 mg/L 4-NP delayed the developmental stage and decreased hind limb length, suggesting a bimodal effect of 4-NP on metamorphosis. NP and NP-12 at test concentrations did not alter the larval stage, but NP-12 at 0.37 mg/L significantly decreased total length and tail length, suggesting growth inhibition in larvae. The total colloid area of thyroid follicles was significantly increased by 0.07 mg/L 4-NP but not by NP and NP-12, suggesting that 4-NP may interfere with thyroid function. Together, the developmental toxicity of NPs was in the following order: 4-NP, NP-12, and NP. 4-NP may alter metamorphosis driven by thyroid hormones in X. laevis.

Widespread epigenetic changes to the enhancer landscape of mouse liver induced by a specific xenobiotic agonist ligand of the nuclear receptor CAR

CAR (Nr1i3), a liver nuclear receptor and xenobiotic sensor, induces drug, steroid and lipid metabolism and dysregulates genes linked to hepatocellular carcinogenesis, but its impact on the liver epigenome is poorly understood. TCPOBOP, a halogenated xenochemical and highly specific CAR agonist ligand, induces localized chromatin opening or closing at several thousand mouse liver genomic regions, discovered as differential DNase-hypersensitive sites (ΔDHS). Active enhancer and promoter histone marks induced by TCPOBOP were enriched at opening DHS and TCPOBOP-inducible genes. Enrichment of CAR binding and CAR motifs was seen at opening DHS and their inducible drug/lipid metabolism gene targets, and at many constitutively open DHS located nearby. TCPOBOP-responsive cell cycle and DNA replication genes co-dependent on MET/EGFR signaling for induction were also enriched for CAR binding. A subset of opening DHS and many closing DHS mapping to TCPOBOP-responsive target genes did not bind CAR, indicating an indirect mechanism for their changes in chromatin accessibility. TCPOBOP-responsive DHS were also enriched for induced binding of RXRA, CEBPA and CEBPB, and for motifs for liver-enriched factors that may contribute to liver-specific transcriptional responses to TCPOBOP exposure. These studies elucidate the enhancer landscape of TCPOBOP-exposed liver and the widespread epigenetic changes that are induced by both direct and indirect mechanisms linked to CAR activation. The global maps of thousands of environmental chemical-induced epigenetic changes described here constitute a rich resource for further research on xenochemical effects on liver chromatin states and the epigenome.

Effects of Vitamin K₂ on the Expression of Genes Involved in Bile Acid Synthesis and Glucose Homeostasis in Mice with Humanized PXR

Pregnane X receptor (PXR) is a nuclear receptor activated by various compounds, including prescribed drugs and dietary ingredients. Ligand-specific activation of PXR alters drug metabolism and affects many other physiological conditions. Species-specific ligand preference is a considerable challenge for studies of PXR function. To increase translational value of the results of mouse studies, humanized mouse model expressing human PXR (hPXR) has been developed. Menaquinone-4 (MK-4), one of vitamin K₂ analogs prescribed in osteoporosis, is a PXR ligand. We hypothesized that MK-4 could modulate the physiological conditions endogenously influenced by PXR, including those that have not been yet properly elucidated. In the present study, we investigated the effects of a single oral treatment with MK-4 on hepatic gene expression in wild-type and hPXR mice by using quantitative RT-PCR and DNA microarray. MK-4 administration altered mRNA levels of genes involved in drug metabolism (Abca3, Cyp2s1, Sult1b1), bile acid synthesis (Cyp7a1, Cyp8b1), and energy homeostasis (Aldoc, Slc2a5). Similar mRNA changes of CYP7A1 and CYP8B1 were observed in human hepatocarcinoma HepG2 cells treated with MK-4. These results suggest that MK-4 may modulate bile acid synthesis. To our knowledge, this is the first report showing the effect of MK-4 in hPXR mice.

Sex differences, endogenous sex-hormone hormones, sex-hormone binding globulin, and exogenous disruptors in diabetes and related metabolic outcomes

In assessing clinical and pathophysiological development of type 2 diabetes (T2D), the critical role of the sex steroids axis is underappreciated, particularly concerning the sex-specific relationships with many relevant cardiometabolic outcomes. In this issue of the Journal of Diabetes, we provide a comprehensive overview of these significant associations of germline variants in the genes governing the sex steroid pathways, plasma levels of steroid hormones, and sex hormone-binding globulin (SHBG) with T2D risk that have been observed in many clinical and high-quality large prospective cohorts of men and women across ethnic populations. Together, this body of evidence indicates that sex steroids and SHBG should be routinely incorporated into clinical characterization of T2D patients, particularly in screening prediabetic patients, such as those with metabolic syndrome, using plasma levels of SHBG. Given that several germline mutations in the SHBG gene have also been directly related to both plasma concentrations of SHBG and clinical manifestation of T2D, targeting signals in the sex steroid axis, particularly SHBG, may have significant utility in the prediction and treatment of T2D. Further, many of the environmental endocrine disrupting chemicals may exert their potential adverse effects on cardiometabolic outcomes via either estrogenic or androgenic signaling pathways, highlighting the importance of using the sex steroids and SHBG as important biochemical markers in both clinical and population studies in studying sex-specific mechanisms in the pathogenesis of T2D and its complications, as well as the need to equitably allocate resources in studying both men and women.

Genetic variations of the xenoreceptors NR1I2 and NR1I3 and their effect on drug disposition and response variability

NR1I2 (PXR) and NR1I3 (CAR) are nuclear receptors that are classified as xenoreceptors. Upon activation by various xenobiotics, including marketed drugs, they regulate the transcription level of major drug-metabolizing enzymes and transporters and facilitate the elimination of xenobiotics from the body. The modulation of the activity of these two xenoreceptors by various ligands is a major source of pharmacokinetic variability of environmental origin. NR1I2 and NR1I3 genetic polymorphisms can affect the pharmacokinetics and therapeutic response to many drugs, such as irinotecan, tacrolimus and atazanavir. This review provides an overview of NR1I2 and NR1I3 pharmacogenetic studies in various therapeutic fields (oncology, immunomodulation and infectiology) and discusses the implementation of NR1I2 and NR1I3 genetic polymorphism testing in the clinical routine.

PXR: More Than Just a Master Xenobiotic Receptor

Pregnane X receptor (PXR) is a nuclear receptor considered to be a master xenobiotic receptor that coordinately regulates the expression of genes encoding drug-metabolizing enzymes and drug transporters to essentially detoxify and eliminate xenobiotics and endotoxins from the body. In the past several years, the function of PXR in the regulation of xenobiotic metabolism has been extensively studied, and the role of PXR as a xenobiotic sensor has been well established. It is now clear, however, that PXR plays many other roles in addition to its xenobiotic-sensing function. For instance, recent studies have discovered previously unidentified roles of PXR in inflammatory response, cell proliferation, and cell migration. PXR also contributes to the dysregulation of these processes in diseases states. These recent discoveries of the role of PXR in the physiologic and pathophysiologic conditions of other cellular processes provides the possibility of novel targets for drug discovery. This review highlights areas of PXR regulation that require further clarification and summarizes the recent progress in our understanding of the nonxenobiotic functions of PXR that can be explored for relevant therapeutic applications.

Epigenetic impact of endocrine disrupting chemicals on lipid homeostasis and atherosclerosis: a pregnane X receptor-centric view

Despite the major advances in developing diagnostic techniques and effective treatments, atherosclerotic cardiovascular disease (CVD) is still the leading cause of mortality and morbidity worldwide. While considerable progress has been achieved to identify gene variations and environmental factors that contribute to CVD, much less is known about the role of "gene-environment interactions" in predisposing individuals to CVD. Our chemical environment has significantly changed in the last few decades, and there are more than 100,000 synthetic chemicals in the market. Recent large-scale human population studies have associated exposure to certain chemicals including many endocrine disrupting chemicals (EDCs) with increased CVD risk, and animal studies have also confirmed that some EDCs can cause aberrant lipid homeostasis and increase atherosclerosis. However, the underlying mechanisms of how exposure to those EDCs influences CVD risk remain elusive. Numerous EDCs can activate the nuclear receptor pregnane X receptor (PXR) that functions as a xenobiotic sensor to regulate host xenobiotic metabolism. Recent studies have demonstrated the novel functions of PXR in lipid homeostasis and atherosclerosis. In addition to directly regulating transcription, PXR has been implicated in the epigenetic regulation of gene transcription. Exposure to many EDCs can also induce epigenetic modifications, but little is known about how the changes relate to the onset or progression of CVD. In this review, we will discuss recent research on PXR and EDCs in the context of CVD and propose that PXR may play a previously unrealized role in EDC-mediated epigenetic modifications that affect lipid homeostasis and atherosclerosis.

The endocrine disrupting alkylphenols and 4,4'-DDT interfere with estrogen conversion and clearance by mouse liver cytosol

Endocrine disrupting chemicals (EDCs) are ubiquitous compounds known for negative impacts on reproductive functions and for increasing cancer risk. EDCs are believed to cause the harmful effects in part through their inappropriate low-affinity binding to steroid receptors and other possible non-receptor mediated paradigms, however there is a need to further elucidate other mechanisms involving the direct and indirect impact of EDCs on reproductive functions. We examined the metabolism of 17β-estradiol (E2) and estrone (E1) by cell-free hepatic cytosol in the presence of alkylphenols (nonylphenol/NP and 4-tert-octylphenol/tOP), Dichlorodiphenyltrichloroethane (4,4'-DDT) and other EDCs. Tandem liquid chromatography mass spectrometry was utilized to quantitatively assess the impact of each EDC on estrogen clearance, inter-conversions and downstream metabolism by mouse liver cytosol. The results revealed that NP and tOP (0.1-3μg/mL) significantly reduced the hepatic cytosol clearance and biotransformation of estrogens with inclination for accumulating E2, the stronger estrogen form, than E1. Alkylphenols also caused up to a 34-fold increase in the E2/E1 ratio possibly by suppressing the hepatic E2→E1 conversion by 17β-hydroxysteroid dehydrogenase (17βHSD) types 2, 4 while displaying a weaker inhibition of E1→E2 conversion by type 1, 17βHSD. On the other hand, the pesticide 4,4'-DDT was a weaker inhibitor of clearance of estrogens by the cytosol preparations when compared to alkylphenols, whereas chemicals such as phthalates and atrazine were ineffective. Our data suggest that exposure to NP, tOP and DDT can indirectly increase the estrogenic load by suppressing the hepatic clearance of estrogens and by elevating the E2/1 ratio and could therefore increase the risk of reproductive lesions.

Review on crosstalk and common mechanisms of endocrine disruptors: Scaffolding to improve PBPK/PD model of EDC mixture

Endocrine disruptor compounds (EDCs) are environment chemicals that cause harmful effects through multiple mechanisms, interfering with hormone system resulting in alteration of homeostasis, reproduction and developmental effect. Many of these EDCs have concurrent exposure with crosstalk and common mechanisms which may lead to dynamic interactions. To carry out risk assessment of EDCs' mixture, it is important to know the detailed toxic pathway, crosstalk of receptor and other factors like critical window of exposure. In this review, we summarize the major mechanism of actions of EDCs with the different/same target organs interfering with the same/different class of hormone by altering their synthesis, metabolism, binding and cellular action. To show the impact of EDCs on life stage development, a case study on female fertility affecting germ cell is illustrated. Based on this summarized discussion, major groups of EDCs are classified based on their target organ, mode of action and potential risk. Finally, a conceptual model of pharmacodynamic interaction is proposed to integrate the crosstalk and common mechanisms that modulate estrogen into the predictive mixture dosimetry model with dynamic interaction of mixture. This review will provide new insight for EDCs' risk assessment and can be used to develop next generation PBPK/PD models for EDCs' mixture analysis.

Pregnane X Receptor (PXR)-Mediated Gene Repression and Cross-Talk of PXR with Other Nuclear Receptors via Coactivator Interactions

Pregnane X receptor is a ligand-activated nuclear receptor (NR) that mainly controls inducible expression of xenobiotics handling genes including biotransformation enzymes and drug transporters. Nowadays it is clear that PXR is also involved in regulation of intermediate metabolism through trans-activation and trans-repression of genes controlling glucose, lipid, cholesterol, bile acid, and bilirubin homeostasis. In these processes PXR cross-talks with other NRs. Accumulating evidence suggests that the cross-talk is often mediated by competing for common coactivators or by disruption of coactivation and activity of other transcription factors by the ligand-activated PXR. In this respect mainly PXR-CAR and PXR-HNF4α interference have been reported and several cytochrome P450 enzymes (such as CYP7A1 and CYP8B1), phase II enzymes (SULT1E1, Gsta2, Ugt1a1), drug and endobiotic transporters (OCT1, Mrp2, Mrp3, Oatp1a, and Oatp4) as well as intermediate metabolism enzymes (PEPCK1 and G6Pase) have been shown as down-regulated genes after PXR activation. In this review, I summarize our current knowledge of PXR-mediated repression and coactivation interference in PXR-controlled gene expression regulation.

Environmental risk factors for inflammatory bowel diseases: Evidence based literature review

AIM: Advances in genetics and immunology have contributed to the current understanding of the pathogenesis of inflammatory bowel diseases (IBD).

METHODS: The current opinion on the pathogenesis of IBD suggests that genetically susceptible individuals develop intolerance to dysregulated gut microflora (dysbiosis) and chronic inflammation develops as a result of environmental insults. Environmental exposures are innumerable with varying effects during the life course of individuals with IBD. Studying the relationship between environmental factors and IBD may provide the missing link to increasing our understanding of the etiology and increased incidence of IBD in recent years with implications for prevention, diagnosis, and treatment. Environmental factors are heterogeneous and genetic predisposition, immune dysregulation, or dysbiosis do not lead to the development of IBD in isolation.

RESULTS: Current challenges in the study of environmental factors and IBD are how to effectively translate promising results from experimental studies to humans in order to develop models that incorporate the complex interactions between the environment, genetics, immunology, and gut microbiota, and limited high quality interventional studies assessing the effect of modifying environmental factors on the natural history and patient outcomes in IBD.

CONCLUSION: This article critically reviews the current evidence on environmental risk factors for IBD and proposes directions for future research.

Inhibition of pregnane X receptor pathway contributes to the cell growth inhibition and apoptosis of anticancer agents in ovarian cancer cells

Epithelial ovarian cancer remains the most devastating gynecologic cancer with drug resistance and rapid recurrence. Pregnane X receptor (PXR) is a nuclear receptor that affects drug metabolism/efflux and drug-drug interaction through control of multiple drug resistance 1 (MDR1), which implies a major role in multidrug resistance, and other genes. We examined whether the inhibition of PXR-mediated pathway using siRNA interference and an antagonist for PXR could influence the paclitaxel and cisplatin cytotoxicity in ovarian cancer cells. PXR agonists, phthalate and pregnenolone had significant positive effects on cytochrome P450 (CYP) 3A4 expression and PXR-mediated transcription through the CYP3A4 promoter, whereas MDR1 expression and PXR-mediated transcription though the MDR1 promoter were significantly increased in the presence of paclitaxel or cisplatin. Downregulation of PXR suppressed the augmented MDR1 expression and PXR-mediated transcription by PXR ligands, and significantly enhanced cell growth inhibition and apoptosis in the presence of paclitaxel or cisplatin. Additionally, ketoconazole, a PXR antagonist, suppressed the augmented MDR1 expression and PXR-mediated transactivation by paclitaxel and cisplatin, and enhanced cell growth inhibition and apoptosis in their presence. In conclusion, inhibition of PXR-mediated pathways could be a novel means of augmenting sensitivity, or overcoming resistance to anticancer agents for ovarian cancer.

Regulation of PXR and CAR by protein-protein interaction and signaling crosstalk

INTRODUCTION

Protein-protein interaction and signaling crosstalk contribute to the regulation of pregnane X receptor (PXR) and constitutive androstane receptor (CAR) and broaden their cellular function.

AREA COVERED

This review covers key historic discoveries and recent advances in our understanding of the broad function of PXR and CAR and their regulation by protein-protein interaction and signaling crosstalk.

EXPERT OPINION

PXR and CAR were first discovered as xenobiotic receptors; however, it is clear that PXR and CAR perform a much broader range of cellular functions through protein-protein interaction and signaling crosstalk, which typically mutually affect the function of all the partners involved. Future research on PXR and CAR should, therefore, look beyond their xenobiotic function.

Possible relationship between endocrine disrupting chemicals and hormone dependent gynecologic cancers

The effects of the natural and synthetic estrogens have been studied for a long time but the data regarding estrogen related chemicals (endocrine disrupting chemicals, EDCs) and their effects on reproductive system are scarce. EDCs are hormone like agents that are readily present in the environment, which may alter the endocrine system of humans and animals. Approximately 800 chemicals are known or suspected to have the potential to function as EDC. Potential role of EDCs on reproductive disease has gained attention in medical literature in recent years. We hypothesize that exposure to low doses of EDCs in a chronic manner could cause hormone dependent genital cancers including ovarian and endometrial cancer. Long term exposure to low concentrations of EDCs may exert potentiation effect with each other and even with endogenous estrogens and could inhibit enzymes responsible for estrogen metabolism. Exposure time to these EDCs is essential as we have seen from Diethylstilbestrol experience. Dose-response curves of EDCs are also unpredictable. Hence mode of action of EDCs are more complex than previously thought. In the light of these controversies lower doses of EDCs in long term exposure is not harmless. Possibility of this relationship and this hypothesis merit further investigation especially through in vivo studies that could better show the realistic environmental exposure. With the confirmation of our hypothesis, possible EDCs could be identified and eliminated from general use as a public health measure.

Novel functions of PXR in cardiometabolic disease

Cardiometabolic disease emerges as a worldwide epidemic and there is urgent need to understand the molecular mechanisms underlying this chronic disease. The chemical environment to which we are exposed has significantly changed in the past few decades and recent research has implicated its contribution to the development of many chronic human diseases. However, the mechanisms of how exposure to chemicals contributes to the development of cardiometabolic disease are poorly understood. Numerous chemicals have been identified as ligands for the pregnane X receptor (PXR), a nuclear receptor functioning as a xenobiotic sensor to coordinately regulate xenobiotic metabolism via transcriptional regulation of xenobiotic-detoxifying enzymes and transporters. In the past decade, the function of PXR in the regulation of xenobiotic metabolism has been extensively studied by many laboratories and the role of PXR as a xenobiotic sensor has been well-established. The identification of PXR as a xenobiotic sensor has provided an important tool for the study of new mechanisms through which xenobiotic exposure impacts human chronic diseases. Recent studies have revealed novel and unexpected roles of PXR in modulating obesity, insulin sensitivity, lipid homeostasis, atherogenesis, and vascular functions. These studies suggest that PXR signaling may contribute significantly to the pathophysiological effects of many known xenobiotics on cardiometabolic disease in humans. The discovery of novel functions of PXR in cardiometabolic disease not only contributes to our understanding of "gene-environment interactions" in predisposing individuals to chronic diseases but also provides strong evidence to inform future risk assessment for relevant chemicals. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

RXRα, PXR and CAR xenobiotic receptors mediate the apoptotic and neurotoxic actions of nonylphenol in mouse hippocampal cells

In the present study, we investigated the role of the retinoid X receptor (RXR), the pregnane X receptor (PXR) and the constitutive androstane receptor (CAR), in the apoptotic and toxic effects of nonylphenol in mouse primary neuronal cell cultures. Our study demonstrated that nonylphenol activated caspase-3 and induced lactate dehydrogenase (LDH) release in hippocampal cells, which was accompanied by an increase in the mRNA expression and protein levels of RXRα, PXR and CAR. Nonylphenol stimulated Rxra, Pxr, and Car mRNA expression. These effects were followed by increase in the protein levels of particular receptors. Immunofluorescence labeling revealed the cellular distribution of RXRα, PXR and CAR in hippocampal neurons in response to nonylphenol, shortening of neurites and cytoplasmic shrinking, as indicated by MAP2 staining. It also showed NP-induced translocation of receptor-specific immunofluorescence from cytoplasm to the nucleus. The use of specific siRNAs demonstrated that Rxra-, Pxr-, and Car-siRNA-transfected cells were less vulnerable to nonylphenol-induced activation of caspase-3 and LDH, thus confirming the key involvement of RXRα/PXR/CAR signaling pathways in the apoptotic and neurotoxic actions of nonylphenol. These new data give prospects for the targeting xenobiotic nuclear receptors to protect the developing nervous system against endocrine disrupting chemicals.

Transcription regulation of nuclear receptor PXR: Role of SUMO-1 modification and NDSM in receptor function

Pregnane & Xenobiotic Receptor (PXR) is one of the 48 members of the nuclear receptor superfamily of ligand-modulated transcription factors. PXR plays an important role in metabolism and elimination of diverse noxious endobiotics and xenobiotics. Like in case of some nuclear receptors its function may also be differentially altered, positively or negatively, by various post-translational modifications. In this context, regulation of PXR function by SUMOylation is the subject of present investigation. Here, we report that human PXR is modified by SUMO-1 resulting in its enhanced transcriptional activity. RT-PCR analysis showed that PXR SUMOylation in presence of rifampicin also enhances the endogenous expression levels of key PXR-regulated genes like CYP3A4, CYP2C9, MDR1 and UGT1A1. In addition, mammalian two-hybrid assay exhibited enhanced interaction between PXR and co-activator SRC-1. EMSA results revealed that SUMOylation has no influence on the DNA binding ability of PXR. In silico analysis suggested that PXR protein contains four putative SUMOylation sites, centered at K108, K129, K160 and K170. In addition to this, we identified the presence of NDSM (Negative charge amino acid Dependent SUMOylation Motif) in PXR. Substitution of all its four putative lysine residues along with NDSM abolished the effect of SUMO-1-mediated transactivation function of PXR. Furthermore, we show that interaction between PXR and E2-conjugation enzyme UBCh9, an important step for implementation of SUMOylation event, was reduced in case of NDSM mutant PXRD115A. Overall, our results suggest that SUMOylation at specific sites on PXR protein are involved in enhancement of transcription function of this receptor.

A food contaminant ochratoxin A suppresses pregnane X receptor (PXR)-mediated CYP3A4 induction in primary cultures of human hepatocytes

Ochratoxin A (OCHA) is a mycotoxin, which can be found in food such as coffee, wine, cereals, meat, nuts. Since it is absorbed via gastrointestinal tract, it is reasonable to anticipate that the liver will be the first organ to which OCHA comes into the contact before systemic circulation. Many xenobiotics are metabolically modified after the passage of the liver to biologically more active substances, sometimes with more harmful activity. Promoting own metabolism is often achieved via transcriptional regulation of biotransformation enzymes through ligand-activated transcription factors. Pregnane X receptor (PXR) belongs to such a group of regulators and it was demonstrated to be activated by many compounds of synthetic as well as natural origin. Our intention was to investigate if OCHA is capable of activating the PXR with consequent induction of PXR-regulated CYP3A4 gene. We found that OCHA does not activate PXR but displays antagonist-like behavior when combined with rifampicin (RIF) in gene reporter assay in human embryonal kidney cells (Hek293T). It was very weak inducer of CYP3A4 mRNA in primary cultures of human hepatocytes and it antagonized RIF-mediated CYP3A4 induction of mRNA as well as protein. In addition, it caused the decline of PXR protein as well as mRNA which was faster than that with actinomycin D, a transcription inhibitor. Since we found that OCHA induced the expression of miR-148a, which was described to regulate PXR expression, we conclude that antagonist-like behavior of OCHA is not due to the antagonism itself but due to the downregulation of PXR gene expression. Herein we provide important findings which bring a piece of puzzle into the understanding of mechanism of toxic action of ochratoxin A.

Intestinal pregnane X receptor links xenobiotic exposure and hypercholesterolemia

Recent studies have associated endocrine-disrupting chemical (EDC) exposure with the increased risk of cardiovascular disease in humans, but the underlying mechanisms responsible for these associations remain elusive. Many EDCs have been implicated in activation of the nuclear receptor pregnane X receptor (PXR), which acts as a xenobiotic sensor to regulate xenobiotic metabolism in the liver and intestine. Here we report an important role of intestinal PXR in linking xenobiotic exposure and hyperlipidemia. We identified tributyl citrate (TBC), one of a large group of Food and Drug Administration-approved plasticizers for pharmaceutical or food applications, as a potent and selective PXR agonist. TBC efficiently activated PXR and induced PXR target gene expression in vitro and in vivo. Interestingly, TBC activated intestinal PXR but did not affect hepatic PXR activity. Exposure to TBC increased plasma total cholesterol and atherogenic low-density lipoprotein cholesterol levels in wild-type mice, but not in PXR-deficient mice. TBC-mediated PXR activation stimulated the expression of an essential cholesterol transporter, Niemann-Pick C1-like 1 (NPC1L1), in the intestine. Promoter analysis revealed a DR-4 type of PXR response element in the human NPC1L1 promoter, and TBC promoted PXR recruitment onto the NPC1L1 promoter. Consistently, TBC treatment significantly increased lipid uptake by human and murine intestinal cells and deficiency of PXR inhibited TBC-elicited lipid uptake. These findings provide critical mechanistic insight for understanding the impact of EDC-mediated PXR activation on lipid homeostasis and demonstrate a potential role of PXR in mediating the adverse effects of EDCs on cardiovascular disease risk in humans.

Exposome in IBD: recent insights in environmental factors that influence the onset and course of IBD

It is generally agreed that environmental factors trigger the onset and cause flares of inflammatory bowel disease. Although we have learned much about genetic susceptibility factors of inflammatory bowel disease in recent years, our knowledge on these environmental factors is limited. The sum of all environmental factors a human is exposed to during lifetime has been termed the exposome. The challenge of investigating the exposome is discussed in this overview. The environmental exposure of a subject causes changes in the intestinal microbiota and subsequently changes the epigenetic imprinting of the mucosa and the associated immune system. Some relevant environmental factors have been investigated in recent years in inflammatory bowel disease and other (auto)inflammatory disease. These factors can be categorized in air pollution, diet, drugs, stress, infections, water pollution, food additives, and lifestyle. Examples from those categories and their potential pathophysiological mechanism are discussed.

Apoptotic and neurotoxic actions of 4-para-nonylphenol are accompanied by activation of retinoid X receptor and impairment of classical estrogen receptor signaling

4-para-Nonylphenol (NP) is a non-ionic surfactant that has widespread and uncontrolled distribution in the environment. Little is known, however, about its actions on neuronal cells during critical developmental periods. This study aimed to investigate the mechanisms underlying the apoptotic and toxic actions of NP on mouse embryonic neuronal cells and the possible interactions of NP with estrogen receptor (ER)- and retinoid X receptor (RXR)-mediated intracellular signaling. Treatment of mouse hippocampal neuronal cell cultures with NP (5 and 10μM) induced apoptotic and neurotoxic effects. The 2 and 7 day-old mouse hippocampal cultures were vulnerable to 5 and 10μM NP, whereas 12 day-old cultures responded only to the highest concentration of NP, thus suggesting an age-dependent action of the chemical on neuronal cells. The use of specific inhibitors did not support the involvement of calpains in NP-induced apoptosis, but indicated caspase-8- and caspase-9-dependent effects of NP. Specific ER antagonists MPP and PHTPP potentiated the NP-induced loss of mitochondrial membrane potential and increase in lactate dehydrogenase (LDH) release whereas, ER agonists PPT and DPN inhibited these effects. RXR antagonist HX531 diminished the NP-evoked loss of mitochondrial membrane potential, the activity of caspase-3 and LDH release. In addition, exposure to NP inhibited ERα- and ERβ-specific immunofluorescence but stimulated RXR-specific immunolabeling in mouse hippocampal cells. In conclusion, our study demonstrated that the apoptotic and toxic actions of NP on neuronal cells in early development is accompanied by an impairment of ER- and stimulation of RXR-mediated signaling pathways. Taking into account NP-induced alterations in mRNA expression levels of particular types of RXRs, we suggest that NP affected mainly RXRα and RXRβ, but not RXRγ signaling.

Modulation of metabolizing enzymes by bisphenol a in human and animal models

Xenobiotics, such as contaminants and drugs, can be converted to potentially toxic reactive metabolites by phase 1 oxidizing enzymes. These metabolites are further detoxified by phase 2 conjugating enzymes and eliminated from cells by phase 3 transporters. Moreover, many of these xenobiotics are also able to induce or inhibit these enzymes, potentially modulating their own toxicity or that of other chemicals. The present review is focused on bisphenol A, a synthetic monomer used for many industrial applications and exhibiting xenoestrogen properties. The impact of this contaminant on all major classes of metabolizing enzymes (i.e., cytochromes P450, glutathione-S-transferases, sulfotransferases, UDP-glucuronyltransferases, and transporters) was reviewed, with a highlight on the modulation of cytochromes P450 involved in steroid metabolism. Interestingly, most of the studies reported in this review show that BPA is able to induce or inhibit metabolizing enzymes at high doses but also at doses compatible with human exposure.

Alkylphenol ethoxylates and alkylphenols--update information on occurrence, fate and toxicity in aquatic environment

Alkylphenols and their precursors, alkylphenol etoxylates, are a group of manmade chemicals used mainly as surfactants in domestic and industrial applications worldwide. It has been well established that they have endocrine disruption activity, hepatotoxic, genotoxic and other negative effects on animal and human health. In spite of the effort to reduce their use, they persist in the environment not only in industrial but also in remote regions, and were detected in the variety of natural matrices including air, water, soil as well as food products, and human blood and urine worldwide. This article summarizes their occurrence, fate in natural conditions, and toxicity including mode of action. A subject of our concern was the aquatic environment as the most important reservoir and target of their deleterious impact.

Using in vitro high throughput screening assays to identify potential endocrine-disrupting chemicals

BACKGROUND

Over the past 20 years, an increased focus on detecting environmental chemicals that pose a risk of adverse effects due to endocrine disruption has driven the creation of the U.S. Environmental Protection Agency (EPA) Endocrine Disruptor Screening Program (EDSP). Thousands of chemicals are subject to the EDSP; thus, processing these chemicals using current test batteries could require millions of dollars and decades. A need for increased throughput and efficiency motivated the development of methods using in vitro high throughput screening (HTS) assays to prioritize chemicals for EDSP Tier 1 screening (T1S).

OBJECTIVE

In this study we used U.S. EPA ToxCast HTS assays for estrogen, androgen, steroidogenic, and thyroid-disrupting mechanisms to classify compounds and compare ToxCast results to in vitro and in vivo data from EDSP T1S assays.

METHOD

We implemented an iterative model that optimized the ability of endocrine-related HTS assays to predict components of EDSP T1S and related results. Balanced accuracy was used as a measure of model performance.

RESULTS

ToxCast estrogen receptor and androgen receptor assays predicted the results of relevant EDSP T1S assays with balanced accuracies of 0.91 (p < 0.001) and 0.92 (p < 0.001), respectively. Uterotrophic and Hershberger assay results were predicted with balanced accuracies of 0.89 (p < 0.001) and 1 (p < 0.001), respectively. Models for steroidogenic and thyroid-related effects could not be developed with the currently published ToxCast data.

CONCLUSIONS

Overall, results suggest that current ToxCast assays can accurately identify chemicals with potential to interact with the estrogenic and androgenic pathways, and could help prioritize chemicals for EDSP T1S assays.

Expressing urine from a gel disposable diaper for biomonitoring using phthalates as an example

The urinary metabolites of phthalates are well-accepted exposure biomarkers for adults and children older than 6 years but are not commonly used for infants owing to non-convenient sampling. In the light of this situation, a novel sampling method based on monitoring the urine expressed from the gel diaper was developed. The urine was expressed from the gel absorbent after mixing the absorbent with CaCl(2) and then collected by a laboratory-made device; the urinary phthalate metabolites were extracted and cleaned using a solid-phase extraction (SPE) column and analyzed with high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry / mass spectrometry. To evaluate the method's feasibility, the following factors were investigated: the proportion of CaCl(2) to gel absorbent, the urination volume variation and the target compounds' deposition bias in the diaper, the matrix blank of the different diaper brands, the storage stabilities and the recoveries of creatinine and phthalate metabolites in the expressed urine. Mono-methyl phthalate, mono-ethyl phthalate, mono-butyl phthalate, mono-benzyl phthalate, mono-2-ethylhexyl phthalate and mono-2-ethyl-5-oxohexyl phthalate were involved. 70-80% of the urine can be expressed from the diaper, and the expressed spiking recoveries and the limit of detection of mono-phthalates ranged from 88.5-115% and 0.21-0.50 ng/ml. The method was applied to measure phthalate metabolites in 65 gel diaper samples from 15 infants, and the pilot data suggests the infants are commonly exposed to phthalates. In summary, the method for monitoring of infant exposure to phthalates is sound and validated, and the potential health effects from the vulnerable infants' exposure to phthalates should be concerned.

Pregnane xenobiotic receptor in cancer pathogenesis and therapeutic response

Pregnane xenobiotic receptor (PXR) is an orphan nuclear receptor that regulates the metabolism of endobiotics and xenobiotics. PXR is promiscuous and unique in that it is activated by a diverse group of xenochemicals, including therapeutic anticancer drugs and naturally-occurring endocrine disruptors. PXR has been predominantly studied to understand its regulatory role in xenobiotic clearance in liver and intestine via induction of drug metabolizing enzymes and drug transporters. PXR, however, is widely expressed and has functional implications in other normal and malignant tissues, including breast, prostate, ovary, endometrium and bone. The differential expression of PXR and its target genes in cancer tissues has been suggested to determine the prognosis of chemotherapeutic outcome. In addition, the emerging evidence points to the implications of PXR in regulating apoptotic and antiapoptotic as well as growth factor signaling that promote tumor proliferation and metastasis. In this review, we highlight the recent progress made in understanding the role of PXR in cancer, discuss the future directions to further understand the mechanistic role of PXR in cancer, and conclude with the need to identify novel selective PXR modulators.

The effect of thermal hydrolysis pretreatment on the anaerobic degradation of nonylphenol and short-chain nonylphenol ethoxylates in digested biosolids

The presence of micropollutants can be a concern for land application of biosolids. Of particular interest are nonylphenol diethoxylate (NP(2)EO), nonylphenol monoethoxylate (NP(1)EO), and nonylphenol (NP), collectively referred to as NPE, which accumulate in anaerobically digested biosolids and are subject to regulation based on the environmental risks associated with them. Because biosolids are a valuable nutrient resource, it is essential that we understand how various treatment processes impact the fate of NPE in biosolids. Thermal hydrolysis (TH) coupled with mesophilic anaerobic digestion (MAD) is an advanced digestion process that destroys pathogens in biosolids and increases methane yields and volatile solids destruction. We investigated the impact of thermal hydrolysis pretreatment on the subsequent biodegradation of NPE in digested biosolids. Biosolids were treated with TH, anaerobic digestion, and aerobic digestion in laboratory-scale reactors, and NPE were analyzed in the influent and effluent of the digesters. NP(2)EO and NP(1)EO have been observed to degrade to the more estrogenic NP under anaerobic conditions; therefore, changes in the ratio of NP:NPE were of interest. The increase in NP:NPE following MAD was 56%; the average increase of this ratio in four sets of TH-MAD samples, however, was only 24.6 ± 3.1%. In addition, TH experiments performed in pure water verified that, during TH, the high temperature and pressure alone did not directly destroy NPE; TH experiments with NP added to sludge also showed that NP was not destroyed by the high temperature and pressure of TH when in a more complex sludge matrix. The post-aerobic digestion phases removed NPE, regardless of whether TH pretreatment occurred. This research indicates that changes in biosolids processing can have impacts beyond just gas production and solids destruction.

Bisphenol A and its analogues activate human pregnane X receptor

BACKGROUND

Bisphenol A (BPA) is a base chemical used extensively in many consumer products. BPA and its analogues are present in environmental and human samples. Many endocrine-disrupting chemicals, including BPA, have been shown to activate the pregnane X receptor (PXR), a nuclear receptor that functions as a master regulator of xenobiotic metabolism. However, the detailed mechanism by which these chemicals activate PXR remains unknown.

OBJECTIVE

We investigated the mechanism by which BPA interacts with and activates PXR and examined selected BPA analogues to determine whether they bind to and activate PXR.

METHODS

Cell-based reporter assays, in silico ligand-PXR docking studies, and site-directed mutagenesis were combined to study the interaction between BPA and PXR. We also investigated the influence of BPA and its analogues on the regulation of PXR target genes in human LS180 cells.

RESULTS

We found that BPA and several of its analogues are potent agonists for human PXR (hPXR) but do not affect mouse PXR activity. We identified key residues within hPXR's ligand-binding pocket that constitute points of interaction with BPA. We also deduced the structural requirements of BPA analogues that activate hPXR. BPA and its analogues can also induce PXR target gene expression in human LS180 cells.

CONCLUSIONS

The present study advances our understanding of the mechanism by which BPA interacts with and activates human PXR. Activation of PXR by BPA may explain some of the adverse effects of BPA in humans.