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Introduction: Macranthoidin B (MB) is a primary active component of Flos Lonicerae. In Chinese veterinary clinics, Flos Lonicerae is frequently used in combination with florfenicol to prevent and treat infections in livestock and poultry. However, potential interactions between Flos Lonicerae and florfenicol remain unclear. To systematically study these interactions, it is crucial to investigate the individual phytochemicals within Flos Lonicerae. Therefore, MB was selected for this study to assess its effect on the pharmacokinetics of florfenicol in vivo and to explore the underlying mechanisms involved. Methods: Male Sprague-Dawley rats were administered MB (60 mg/kg BW) or sterile water orally for 7 consecutive days. On the 8th day, a single oral dose of florfenicol (25 mg/kg BW) was given. Florfenicol pharmacokinetics were analyzed using ultra-high performance liquid chromatography. The hepatic expression levels of cytochrome P450 (CYP1A2, CYP2C11, CYP3A1), UDPglucuronosyltransferase (UGT1A1), P-glycoprotein (P-gp), and nuclear receptors, including constitutive androstane receptor (CAR), pregnane X receptor (PXR), and retinoid X receptor alpha (RXRa), were quantified via reverse transcription-quantitative polymerase chain reaction and Western blotting (WB). Hepatic CYP1A2 and CYP2C11 activities were measured using a cocktail method. Additionally, the subcellular expression and localization of CAR, PXR, and RXRain hepatocytes was assessed using WB and immunofluorescence staining. Results: MB significantly reduces the AUC(0-8) and MRT(0-8) of florfenicol. MB also markedly upregulates the mRNA and protein expression of hepatic CYP1A2 and CYP2C11, along with their catalytic activities. Substantial upregulation of CAR and PXR proteins occurs in the hepatocyte nucleus, along with significant nuclear colocalization of the transcriptionally active CAR/RXRa and PXR/RXRaheterodimers, indicating MB-induced nuclear translocation of both CAR and PXR. Discussion: These findings suggest that MB-induced alterations in florfenicol pharmacokinetics, particularly its accelerated elimination, may be due to increased expression and activities of CYP1A2 and CYP2C11, with CAR and PXR potentially involved in these regulatory effects. Further investigation is yet needed to fully elucidate the clinical implications of these interactions concerning the efficacy of florfenicol in veterinary medicine. [ABSTRACT FROM AUTHOR]

Thyroid hormone system disrupting compounds are considered potential threats for human and environmental health. Multiple adverse outcome pathways (AOPs) for thyroid hormone system disruption (THSD) are being developed in different taxa. Combining these AOPs results in a cross-species AOP network for THSD which may provide an evidence-based foundation for extrapolating THSD data across vertebrate species and bridging the gap between human and environmental health. This review aimed to advance the description of the taxonomic domain of applicability (tDOA) in the network to improve its utility for cross-species extrapolation. We focused on the molecular initiating events (MIEs) and adverse outcomes (AOs) and evaluated both their plausible domain of applicability (taxa they are likely applicable to) and empirical domain of applicability (where evidence for applicability to various taxa exists) in a THSD context. The evaluation showed that all MIEs in the AOP network are applicable to mammals. With some exceptions, there was evidence of structural conservation across vertebrate taxa and especially for fish and amphibians, and to a lesser extent for birds, empirical evidence was found. Current evidence supports the applicability of impaired neurodevelopment, neurosensory development (eg, vision) and reproduction across vertebrate taxa. The results of this tDOA evaluation are summarized in a conceptual AOP network that helps prioritize (parts of) AOPs for a more detailed evaluation. In conclusion, this review advances the tDOA description of an existing THSD AOP network and serves as a catalog summarizing plausible and empirical evidence on which future cross-species AOP development and tDOA assessment could build. [ABSTRACT FROM AUTHOR]

Induction of drug-metabolizing enzymes and efflux transporters (DMET) through activation of pregnane x receptor (PXR) is the primary factor involved in almost all bioavailability and drug resistance-related problems of anticancer drugs. PXR is a transcriptional regulator of many metabolizing enzymes and efflux transporters proteins like p-glycoprotein (p-gp), multidrug resistant protein 1 and 2 (MRP 1 and 2), and breast cancer resistant protein (BCRP), etc. Several anticancer drugs are potent activators of PXR receptors and can modulate the gene expression of DMET proteins. Involvement of anticancer drugs in transcriptional regulation of DMET can prompt increased metabolism and efflux of their own or other co-administered drugs, which leads to poor site-specific bioavailability and increased drug resistance. In this review, we have discussed several novel strategies to evade drug-induced PXR activation and p-gp efflux including assessment of PXR ligand and p-gp substrate at early stages of drug discovery. Additionally, we have critically discussed the chemical structure and drug delivery-based approaches to avoid PXR binding and inhibit the p-gp activity of the drugs at their target sites. [ABSTRACT FROM AUTHOR]

In fish, the intestine is fundamental for digestion, nutrient absorption, and other functions like osmoregulation, acid-base balance, and excretion of some metabolic products. These functions require a large exchange surface area, which, in turn, favors the absorption of natural and anthropogenic foreign substances (xenobiotics) either dissolved in water or contained in the food. According to their chemical nature, nutrients, ions, and water may cross the intestine epithelium cells' apical and basolateral membranes by passive diffusion or through a wide array of transport proteins and also through endocytosis and exocytosis. In the same way, xenobiotics can cross this barrier by passive diffusion or taking advantage of proteins that transport physiological substrates. The entry of toxic substances is counterbalanced by an active efflux transport mediated by diverse membrane proteins, including the ATP binding cassette (ABC) proteins. Recent advances in structure, molecular properties, and functional studies have shed light on the importance of these proteins in cellular and organismal homeostasis. There is abundant literature on mammalian ABC proteins, while the studies on ABC functions in fish have mainly focused on the liver and, to a minor degree, on the kidney and other organs. Despite their critical importance in normal physiology and as a barrier to prevent xenobiotics incorporation, fish intestine's ABC transporters have received much less attention. All the ABC subfamilies are present in the fish intestine, although their functionality is still scarcely studied. For example, there are few studies of ABC-mediated transport made with polarized intestinal preparations. Thus, only a few works discriminate apical from basolateral transport activity. We briefly describe the main functions of each ABC subfamily reported for mammals and other fish organs to help understand their roles in the fish intestine. Our study considers immunohistochemical, histological, biochemical, molecular, physiological, and toxicological aspects of fish intestinal ABC proteins. We focus on the most extensively studied fish ABC proteins (subfamilies ABCB, ABCC, and ABCG), considering their apical or basolateral location and distribution along the intestine. We also discuss the implication of fish intestinal ABC proteins in the transport of physiological substrates and aquatic pollutants, such as pesticides, cyanotoxins, metals, hydrocarbons, and pharmaceutical products. [ABSTRACT FROM AUTHOR]

Lorlatinib is a potent small-molecule anaplastic lymphoma kinase inhibitor approved for the treatment of patients with nonsmall cell lung cancer. In a drug-drug interaction study in healthy human participants, liver enzyme elevations were observed when a single 100 mg dose of lorlatinib was administered after multiple doses of rifampin, a strong cytochrome P450 (CYP) 3A inducer and a pregnane X receptor (PXR) agonist. A series of in vitro and in vivo studies were conducted to evaluate potential mechanisms for the observed clinical toxicity. To investigate the involvement of CYP3A and/or PXR in the observed liver toxicity, studies were conducted in cynomolgus monkeys administered lorlatinib alone or with coadministration of multiple doses of known CYP3A inducers that are predominantly PXR agonists (rifampin, St. John's wort) or predominantly constitutive androstane receptor agonists (carbamazepine, phenytoin) and a net CYP3A inhibitory PXR agonist (ritonavir). Results from the investigative studies identified cynomolgus monkeys as a pharmacologically relevant nonclinical model, which recapitulated the elevated liver function test results observed in humans. Furthermore, liver toxicity was only observed in this model when lorlatinib was coadministered with strong CYP3A inducers, and the effects were not restricted to, or exclusively dependent upon, a PXR activation mechanism. These results generated mechanistic insights on the liver enzyme elevations observed in the clinical drug-drug interaction study and provided guidance on appropriate product safety label for lorlatinib. [ABSTRACT FROM AUTHOR]

Pregnane X receptor (PXR) is activated by chemicals to transcriptionally regulate drug disposition and possibly decrease drug efficacy and increase resistance, suggesting therapeutic value for PXR antagonists. We previously reported the antagonist SPA70 and its analog SJB7, which unexpectedly is an agonist. Here, we describe another unexpected observation: mutating a single residue (W299A) within the PXR ligand-binding domain converts SPA70 to an agonist. After characterizing wild-type and W299A PXR activity profiles, we used molecular dynamics simulations to reveal that in wild-type PXR, agonists stabilize the activation function 2 (AF-2) helix in an "inward" position, but SPA70 displaces the AF-2. In W299A, however, SPA70 stabilizes the AF-2 "inward", like agonists. We validated our model by predicting the antagonist SJC2 to be a W299A agonist, which was confirmed experimentally. Our work correlates previously unobserved ligand-induced conformational changes to PXR cellular activity and, for the first time, reveals how PXR antagonists work. [ABSTRACT FROM AUTHOR]

Pregnane X receptor (PXR; NR1I2) is a nuclear receptor that regulates transcriptional responses to drug or xenobiotic exposure, including induction of CYP3A transcription, in many vertebrate species. PXR is activated by a wide range of ligands that differ across species, making functional studies on its role in the chemical defensome most relevant when approached in a species-specific manner. Knockout studies in mammals have shown a requirement for PXR in ligand-dependent activation of CYP3A expression or reporter gene activity. Morpholino knockdown of Pxr in zebrafish indicated a similar requirement. Here, we report on the generation of 2 zebrafish lines each carrying a heritable deletion in the pxr coding region, predicted to result in loss of a functional gene product. To our surprise, larvae homozygous for either of the pxr mutant alleles retain their ability to induce cyp3a65 mRNA expression following exposure to the established zebrafish Pxr ligand, pregnenolone. Thus, zebrafish carrying pxr alleles with deletions in either the DNA binding or the ligand-binding domains did not yield a loss-of-function phenotype, suggesting that a compensatory mechanism is responsible for cyp3a65 induction. Alternative possibilities are that Pxr is not required for the induction of selected genes, or that truncated yet functional mutant Pxr is sufficient for the downstream transcriptional effects. It is crucial that we develop a better understanding for the role of Pxr in this important biomedical test species. This study highlights the potential for compensatory mechanisms to avoid deleterious effects arising from gene mutations. [ABSTRACT FROM AUTHOR]

Hepatocellular carcinoma appears as an extremely angiogenic solid tumor marked by apoptosis evasion, dysregulated cell cycle and low sensitivity to chemotherapy. TGF-β, a multifunctional cytokine, plays a pleiotropic role in the tumor microenvironment and has implications in cancer drug resistance. The current study provides novel evidence that TGF-β signaling contributes to drug resistance in liver cancer cells by inducing the expression of xenobiotic nuclear receptor PXR. We observed that PXR increases the expression of drug efflux transporters; therefore, accounting for exacerbated drug resistance. Additionally, anti-apoptotic nature of PXR contributes to TGF-β mediated chemoresistance as seen by procaspase-3 and Mcl-1 cellular levels. TGF-β binding to the TGF-β receptor triggers a complex downstream signaling cascade through a non-canonical SMAD-independent ERK pathway that leads to increased PXR expression. Activated ERK activates ETS1 transcription factor which is a critical regulator of endogenous PXR expression in hepatic cells. Loss of function of ETS1 abrogates the TGF-β induced PXR expression. Together these findings indicate that PXR modulates TGF-β induced resistance to chemotherapy in liver cancer cells. This underscores the need for combinatorial approaches with focus on PXR antagonism to improve drug effectiveness in hepatocellular carcinoma. Abbreviations: HCC: Hepatocellular Carcinoma; FDA: Food and Drug Administration; TGF-β: Transforming growth factor-β; PXR: Pregnane X receptor; CAR: Constitutive androstane receptor; P-gp/ABCB1: P-glycoproteins/ATP-binding cassette transporter subfamily B member 1; MRP1/ABCC1 and MRP2/ABCC2: Multidrug-resistance associated proteins; BCRP/ABCG2: Breast cancer resistant protein; DMEs: Drug-metabolizing enzymes; CFDA: 5,6-carboxyfluorescein diacetate; ETS1: Transcription factor E26 transformation specific sequence 1. [ABSTRACT FROM AUTHOR]

Purpose: Chinese patients have been enrolled in multiple Phase III trials of the poly(ADP-ribose) polymerase (PARP) inhibitor olaparib (Lynparza); however, the pharmacokinetic (PK) profile of olaparib has not been investigated in this population. This two-part, open-label Phase I study was, therefore, carried out to determine the PK and safety profile of olaparib (tablet formulation) in Chinese patients with advanced solid tumours as monotherapy and in combination with paclitaxel (NCT02430311).Methods: The PK profile of olaparib 300 mg (twice daily [bid]; Cohort 1) as monotherapy after a single dose and at steady state, and 100 mg (bid; Cohort 2) as monotherapy (single dose and at steady state) and in combination (at steady state) with weekly paclitaxel (80 mg/m2) was assessed during Part A. Patients could continue to receive treatment (monotherapy, Cohort 1; combination therapy, Cohort 2) in Part B, which assessed safety and tolerability.Results: Twenty and 16 patients were enrolled into Cohorts 1 and 2, respectively. Steady-state olaparib exposure increased slightly less than proportionally with increasing monotherapy dose and inter-patient variability was high. A statistically significant decrease in olaparib exposure was seen when given in combination with paclitaxel. Discontinuation due to adverse events (AEs) was rare and haematological AEs were more common in patients receiving combination treatment.Conclusions: The PK and safety profile of olaparib monotherapy in Chinese patients is consistent with that seen previously in Western and Japanese patients, and the recommended Phase III monotherapy tablet dose (300 mg bid) is suitable for use in this population. [ABSTRACT FROM AUTHOR]

The gut microbiome regulates important host metabolic pathways including xenobiotic metabolism and intermediary metabolism, such as the conversion of primary bile acids (BAs) into secondary BAs. The nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are well-known regulators for xenobiotic biotransformation in liver. However, little is known regarding the potential effects of PXR and CAR on the composition and function of the gut microbiome. To test our hypothesis that activation of PXR and CAR regulates gut microbiota and secondary BA synthesis, 9-week-old male conventional and germ-free mice were orally gavaged with corn oil, PXR agonist PCN (75 mg/kg), or CAR agonist TCPOBOP (3 mg/kg) once daily for 4 days. PCN and TCPOBOP decreased two taxa in the Bifidobacterium genus, which corresponded with decreased gene abundance of the BA-deconjugating enzyme bile salt hydrolase. In liver and small intestinal content of germ-free mice, there was a TCPOBOP-mediated increase in total, primary, and conjugated BAs corresponding with increased Cyp7a1 mRNA. Bifidobacterium, Dorea, Peptociccaceae, Anaeroplasma, and Ruminococcus positively correlated with T-UDCA in LIC, but negatively correlated with T-CDCA in serum. In conclusion, PXR and CAR activation downregulates BA-metabolizing bacteria in the intestine and modulates BA homeostasis in a gut microbiota-dependent manner. [ABSTRACT FROM AUTHOR]

Regulators of biotransformation are of particular interest in pharmacology and toxicology, determining in part the metabolism, disposition, and toxicity of chemicals. The nuclear receptor NR1I2 (pregnane X receptor, PXR) is a prominent xenosensor that regulates the expression of biotransformation enzymes governing elimination of many exogenous as well as endogenous compounds. Zebrafish (Danio rerio) has only one gene locus for pxr, but different genetic variants have been identified in zebrafish. However, the prevalence and significance of these variants are unknown. We hypothesize that sequence variation occurring in the Pxr gene of zebrafish may affect the action and fate of many chemicals in this species, a key model organism in various fields of research, including environmental toxicology. Here, we examine variation in Pxr sequences from four different strains of zebrafish and assess the responses of each Pxr to clotrimazole and butyl-4-aminobenzoate. The Pxr variants differed in both their ability to bind these structurally different ligands and to regulate reporter gene expression in vitro. We infer that the observed sequence variations in zebrafish Pxrs likely affect the response to putative Pxr agonists in vivo and potentially cause strain-specific biotransformation of xenobiotics in zebrafish. Thus, the choice of zebrafish strain could affect the outcome of downstream toxicological studies. [ABSTRACT FROM AUTHOR]

Fipronil (FIP) is widely used across the world as a broad-spectrum phenylpyrazole insecticide and veterinary drug. FIP was the insecticide to act by targeting the γ-aminobutyric acid (GABA) receptor and has favorable selective toxicity towards insects rather than mammals. However, because of accidental exposure, incorrect use of FIP or widespread FIP use leading to the contamination of water and soil, there is increasing evidence that FIP could cause a variety of toxic effects on animals and humans, such as neurotoxic, hepatotoxic, nephrotoxic, reproductive, and cytotoxic effects on vertebrate and invertebrates. In the last decade, oxidative stress has been suggested to be involved in the various toxicities induced by FIP. To date, few reviews have addressed the toxicity of FIP in relation to oxidative stress. The focus of this article is primarily intended to summarize the progress in research associated with oxidative stress as a possible mechanism for FIP-induced toxicity as well as metabolism. The present review reports that studies have been conducted to reveal the generation of reactive oxygen species (ROS) and oxidative stress as a result of FIP treatment and have correlated them with various types of toxicity. Furthermore, the metabolism of FIP was also reviewed, and during this process, various CYP450 enzymes were involved and oxidative stress might occur. The roles of various compounds in protecting against FIP-induced toxicity based on their anti-oxidative effects were also summarized to further understand the role of oxidative stress in FIP-induced toxicity. [ABSTRACT FROM PUBLISHER]

Safety concerns have emerged regarding the potential long-lasting effects due to developmental exposure to xenobiotics. The pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are critical xenobiotic-sensing nuclear receptors that are highly expressed in liver. The goal of this study was to test our hypothesis that neonatal exposure to PXR- or CAR-activators not only acutely but also persistently regulates the expression of drug-processing genes (DPGs). A single dose of the PXR-ligand PCN (75 mg/kg), CAR-ligand TCPOBOP (3 mg/kg), or vehicle (corn oil) was administered intraperitoneally to 3-day-old neonatal wild-type mice. Livers were collected 24h post-dose or from adult mice at 60 days of age, and global gene expression of these mice was determined using Affymetrix Mouse Transcriptome Assay 1.0. In neonatal liver, PCN up-regulated 464 and down-regulated 449 genes, whereas TCPOBOP up-regulated 308 and downregulated 112 genes. In adult liver, there were 15 persistently up-regulated and 22 persistently down-regulated genes following neonatal exposure to PCN, as well as 130 persistently up-regulated and 18 persistently down-regulated genes following neonatal exposure to TCPOBOP. Neonatal exposure to both PCN and TCPOBOP persistently down-regulated multiple Cyp4a members, which are prototypical-target genes of the lipid-sensor PPARα, and this correlated with decreased PPARα-binding to the Cyp4a gene loci. RT-qPCR, western blotting, and enzyme activity assays in livers of wildtype, PXR-null, and CAR-null mice confirmed that the persistent down-regulation of Cyp4a was PXR and CAR dependent. In conclusion, neonatal exposure to PXR- and CAR-activators both acutely and persistently regulates critical genes involved in xenobiotic and lipid metabolism in liver. [ABSTRACT FROM AUTHOR]

Acifluorfen (ACI), a protoporphyrinogen oxidase (PROTOX) inhibitor herbicide, promotes the accumulation of protoporphyrin IX (PPIX), and induces tumors in the rodent liver. Porphyria is a risk factor for liver tumors in humans; however, the specific mechanisms through which ACI induces hepatocarcinogenesis in rodents are unclear. Here, we investigated the mode of action of ACI-induced hepatocarcinogenesis, focusing on constitutive androstane receptor (CAR, NR1I3), which is essential for the development of rodent liver tumors in response to certain cytochrome P450 (CYP) 2B inducers. Dietary treatment with 2500ppmACI for up to 13 weeks increased Cyp2b10 expression in the livers of wild-type (WT)mice, but not in CAR-knockout (CARKO)mice. Microscopically, ACI treatment-induced cytotoxic changes, including hepatocellular necrosis and inflammation, and caused regenerative changes accompanied by prolonged increases in the numbers of proliferating cell nuclear antigen-positive hepatocytes in WTmice. In contrast, these cytotoxic and regenerative changes in hepatocytes were significantly attenuated, but still observed, in CARKO mice. ACI treatment also increased liver PPIX levels similarly in both genotypes; however, no morphological evidence of porphyrin deposition was found in hepatocytes from either genotype. Treatment with 2500ppmACI for 26 weeks after initiation with diethylnitrosamine increased the incidence and multiplicities of altered foci and adenomas in hepatocytes from WT mice; these effects were significantly reduced in CARKO mice. These results indicated that prolonged cytotoxicity in the liver was a key factor for ACI-induced hepatocarcinogenesis, and that CAR played an important role in ACI-induced liver injury and tumor development in mice. [ABSTRACT FROM AUTHOR]

Aim: The goal of our study was to assess the impact of patients' genetic background on their sensitivity to carboplatin/paclitaxel hematotoxicity. Patients & methods: Parameters describing sensitivity to neutropenia and to thrombocytopenia of 201 patients were extracted from a previous pharmacokinetic/pharmacodynamics analysis, in order to assess their association with 52 candidates SNPs in 18 genes. Results: Carriers of a T allele of SLCO1B3-rs4149117 were 19% less sensitive to thrombocytopenia than the homozygotes for the G allele (p = 0.00279). Carriers of two copies of the ATG haplotypes of NR1I2-rs1523130, rs3814055 and rs1523127 were 19% less sensitive to thrombocytopenia than those harboring other haplotypes (p = 0.025). Conclusion: Our results revealed the importance of SLCO1B3 and NR1I2 in the sensitivity to carboplatin/paclitaxel thrombocytopenia. [ABSTRACT FROM AUTHOR]

Developing high-throughput assays to screen marine extracts for bioactive compounds presents both conceptual and technical challenges. One major challenge is to develop assays that have well-grounded ecological and evolutionary rationales. In this review we propose that a specific group of ligand-activated transcription factors are particularly well-suited to act as sensors in such bioassays. More specifically, xenobiotic-activated nuclear receptors (XANRs) regulate transcription of genes involved in xenobiotic detoxification. XANR ligand-binding domains (LBDs) may adaptively evolve to bind those bioactive, and potentially toxic, compounds to which organisms are normally exposed to through their specific diets. A brief overview of the function and taxonomic distribution of both vertebrate and invertebrate XANRs is first provided. Proof-of-concept experiments are then described which confirm that a filter-feeding marine invertebrate XANR LBD is activated by marine bioactive compounds. We speculate that increasing access to marine invertebrate genome sequence data, in combination with the expression of functional recombinant marine invertebrate XANR LBDs, will facilitate the generation of high-throughput bioassays/biosensors of widely differing specificities, but all based on activation of XANR LBDs. Such assays may find application in screening marine extracts for bioactive compounds that could act as drug lead compounds. [ABSTRACT FROM AUTHOR]

High doses of sodium phenobarbital (NaPB), a constitutive androstane receptor (CAR) activator, have been shown to produce hepatocellular tumors in rodents by a mitogenic mode of action (MOA) involving CAR activation. The effect of 1-week dietary treatment with NaPB on liver weight and histopathology, hepatic CYP2B enzyme activity and CYP2B/3A mRNA expression, replicative DNA synthesis and selected genes related to cell proliferation, and functional transcriptomic and metabolomic analyses was studied in male CD-1 mice, Wistar Hannover (WH) rats, and chimeric mice with human hepatocytes. The treatment of chimeric mice with 1000-1500-ppm NaPB resulted in plasma levels around 3-5-fold higher than those observed in human subjects given therapeutic doses of NaPB. NaPB produced dose-dependent increases in hepatic CYP2B activity and CYP2B/3A mRNA levels in all animal models. Integrated functional metabolomic and transcriptomic analyses demonstrated that the responses to NaPB in the human liver were clearly different from those in rodents. Although NaPB produced a dose-dependent increase in hepatocyte replicative DNA synthesis in CD-1 mice and WH rats, no increase in replicative DNA synthesis was observed in human hepatocyte-originated areas of chimeric mice. In addition, treatment with NaPB had no effect on Ki-67, PCNA, GADD45ß, and MDM2 mRNA expression in chimeric mice, whereas significant increases were observed in CD-1 mice and/or WH rats. However, increases in hepatocyte replicative DNA synthesis were observed in chimeric mice both in vivo and in vitro after treatment epidermal growth factor. Thus, although NaPB could activate CAR in both rodent and human hepatocytes, NaPB did not increase replicative DNA synthesis in human hepatocytes of chimeric mice, whereas it was mitogenic to rat and mouse hepatocytes. As human hepatocytes are refractory to the mitogenic effects of NaPB, the MOA for NaPB-induced rodent liver tumor formation is thus not relevant for humans. [ABSTRACT FROM AUTHOR]

The constitutive androstane receptor (CAR) and the pregnane X receptor (PXR) are closely related nuclear receptors involved in drug metabolism and play important roles in the mechanism of phenobarbital (PB)-induced rodent nongenotoxic hepatocarcinogenesis. Here, we have used a humanized CAR/PXR mouse model to examine potential species differences in receptor-dependent mechanisms underlying liver tissue molecular responses to PB. Early and late transcriptomic responses to sustained PB exposure were investigated in liver tissue from double knock-out CAR and PXR (CARKO-PXRKO), double humanized CAR and PXR (CARh-PXRh), and wild-type C57BL/6 mice. Wild-type and CARh-PXRh mouse livers exhibited temporally and quantitatively similar transcriptional responses during 91 days of PB exposure including the sustained induction of the xenobiotic response gene Cyp2b10, the Wnt signaling inhibitor Wisp1, and noncoding RNA biomarkers from the Dlk1-Dio3 locus. Transient induction of DNA replication (Hells, Mcm6, and Esco2) and mitotic genes (Ccnb2, Cdc20, and Cdk1) and the proliferation-related nuclear antigen Mki67 were observed with peak expression occurring between 1 and 7 days PB exposure. All these transcriptional responses were absent in CARKO-PXRKO mouse livers and largely reversible in wild-type and CARh-PXRh mouse livers following 91 days of PB exposure and a subsequent 4-week recovery period. Furthermore, PB-mediated upregulation of the noncoding RNA Meg3, which has recently been associated with cellular pluripotency, exhibited a similar dose response and perivenous hepatocyte-specific localization in both wild-type and CARh-PXRh mice. Thus, mouse livers coexpressing human CAR and PXR support both the xenobiotic metabolizing and the proliferative transcriptional responses following exposure to PB. [ABSTRACT FROM PUBLISHER]

Endocrine-disrupting chemicals (EDC), including phthalates, bisphenol A (BPA), phytoestrogens such as genistein and daidzein, dichlorodiphenyltrichloroethane (DDT), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are associated with a variety of adverse health effects in organisms or progeny by altering the endocrine system. Environmental estrogens, including BPA, phthalates, and phytoestrogens, are the most extensively studied and are considered to mimic the actions of endogenous estrogen, 17β-estradiol (E2). Diverse modes of action of estrogen and estrogen receptors (ERα and ERβ) have been described, but the mode of action of estrogenic EDC is postulated to be more complex and needs to be more clearly elucidated. This review examines the adverse effects of estrogenic EDC on male or female reproductive systems and molecular mechanisms underlying EDC effects that modulate ER-mediated signaling. Mechanisms of action for estrogenic EDC may involve both ER-dependent and ER-independent pathways. Recent findings from systems toxicology of examining estrogenic EDC are also discussed. [ABSTRACT FROM AUTHOR]

The CAR (constitutive androstane receptor; NR1I3) is a critical xenobiotic sensor that regulates xenobiotic metabolism, drug clearance, energy and lipid homoeostasis, cell proliferation and development. Although constitutively active, in hepatocytes CAR is normally held quiescent through a tethering mechanism in the cytosol, anchored to a protein complex that includes several components, including heat-shock protein 90. Release and subsequent nuclear translocation of CAR is triggered through either direct binding to ligand activators such as CITCO {6- (4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde O- (3,4-dichlorobenzyl)oxime} or through indirect chemical activation, such as with PB (phenobarbital). In the present study, we demonstrate that proteasomal inhibition markedly disrupts CAR function, repressing CAR nuclear trafficking, disrupting CAR’s interaction with nuclear co-activators and inhibiting induction of CAR target gene responses in human primary hepatocytes following treatment with either PB or CITCO. Paradoxically, these effects occur following accumulation of ubiquitinated hCAR (human CAR). Furthermore, a non-proteolytic function was indicated by its interaction with a SUG1 (suppressor for Gal1), a subunit of the 26S proteasome. Taken together, these data demonstrate that the proteasome complex functions at multiple levels to regulate the functional biology of hCAR activity. [ABSTRACT FROM AUTHOR]

This review highlights several in vivo studies utilizing non-genotoxic and genotoxic chemical carcinogens, and the mechanisms of their high and low dose carcinogenicities with respect to formation of oxidative stress. Here, we survey the examples and discuss possible mechanisms of hormetic effects with cytochrome P450 inducers, such as phenobarbital, α-benzene hexachloride and 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane. Epigenetic processes differentially can be affected by agents that impinge on oxidative DNA damage, repair, apoptosis, cell proliferation, intracellular communication and cell signaling. Non-genotoxic carcinogens may target nuclear receptors and induce post-translational modifications at the protein level, thereby impacting on the stability or activity of key regulatory proteins, including oncoproteins and tumor suppressor proteins. We further discuss role of oxidative stress focusing on the low dose carcinogenicities of several genotoxic carcinogens such as a hepatocarcinogen contained in seared fish and meat, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, arsenic and its metabolites, and the kidney carcinogen potassium bromate [ABSTRACT FROM AUTHOR]

Xenobiotic compounds undergo a critical range of biotransformations performed by the phase I, II, and III drug-metabolizing enzymes. The oxidation, conjugation, and transportation of potentially harmful xenobiotic and endobiotic compounds achieved by these catalytic systems are significantly regulated, at the gene expression level, by members of the nuclear receptor (NR) family of ligand-modulated transcription factors. Activation of NRs by a variety of endo- and exogenous chemicals are elemental to induction and repression of drug-metabolism pathways. The master xenobiotic sensing NRs, the promiscuous pregnane X receptor and less-promiscuous constitutive androstane receptor are crucial to initial ligand recognition, jump-starting the metabolic process. Other receptors, including farnesoid X receptor, vitamin D receptor, hepatocyte nuclear factor 4 alpha, peroxisome proliferator activated receptor, glucocorticoid receptor, liver X receptor, and RAR-related orphan receptor, are not directly linked to promiscuous xenobiotic binding, but clearly play important roles in the modulation of metabolic gene expression. Crystallographic studies of the ligand-binding domains of nine NRs involved in drug metabolism provide key insights into ligand-based and constitutive activity, coregulator recruitment, and gene regulation. Structures of other, noncanonical transcription factors also shed light on secondary, but important, pathways of control. Pharmacological targeting of some of these nuclear and atypical receptors has been instituted as a means to treat metabolic and developmental disorders and provides a future avenue to be explored for other members of the xenobiotic-sensing NRs. [ABSTRACT FROM AUTHOR]

Adopted orphan nuclear receptor (NR), pregnane X receptor (PXR), plays a central role in the regulation of xeno- and endobiotic metabolism. Since the discovery of the functional role of PXR in 1998, there is evolving evidence for the role of PXR agonists in abrogating metabolic pathophysiology (e.g., cholestasis, hypercholesterolemia, and inflammation). However, more recently, it is clear that PXR is also an important mediator of adverse xeno- (e.g., enhances acetaminophen toxicity) and endobiotic (e.g., hepatic steatosis) metabolic phenotypes. Moreover, in cancer therapeutics, PXR activation can induce drug resistance, and there is growing evidence for tissue-specific enhancement of the malignant phenotype. Thus, in these instances, there may be a role for PXR antagonists. However, as opposed to the discovery efforts for PXR agonists, there are only a few antagonists described. The mode of action of these antagonists (e.g., sulforaphane) remains less clear. Our laboratory efforts have focused on this question. Since the original discovery of azoles analogs as PXR antagonists, we have preliminarily defined an important PXR antagonist pharmacophore and developed less-toxic PXR antagonists. In this review, we describe our published and unpublished findings on recent structure-function studies involving the azole chemical scaffold. Further work in the future is needed to fully define potent, more-selective PXR antagonists that may be useful in clinical application. [ABSTRACT FROM AUTHOR]

The mycotoxin, patulin (PAT), which is frequently found in apples, grapes, oranges, pear, peaches, and in apple juices, has previously been shown to be cytotoxic, genotoxic, and mutagenic. In this study, we have investigated the effect of PAT on mRNA level of pregnane X receptor (PXR), constitutive androstane receptor (CAR), aryl hydrocarbon receptor (AhR), and their corresponding target cytochrome P450s. Using primary cultures of adult human hepatocytes, we evaluated PAT cytotoxicity on hepatocytes after 24 hours of treatment. Real time reverse-transcriptase polymerase chain reaction procedure was employed to determine the effect of PAT on receptors (PXR, CAR, and AhR) and cytochrome (CYP3A4, 2B6, 3A5, 2C9, 1A1, and 1A2) genes. Our results showed that PAT reduced hepatocyte viability. At a noncytotoxic range of PAT concentrations, PAT induced an upregulation of the PXR gene in the three treated hepatocytes cultures, whereas CAR was overexpressed in only 1 treated liver. PXR gene induction was accompanied by the enhancement of CYP2B6, 3A5, 2C9, and 3A4 expression. PAT was also found to induce an overexpression of AhR and CYP1A1 and CYP1A2 mRNA expression. These findings suggested that PAT may activate PXR and/or CAR and AhR. However, further investigations are needed to confirm nuclear receptor activation by PAT and to elucidate the molecular mechanism of PAT action. [ABSTRACT FROM AUTHOR]

Conazoles are fungicides used as agricultural pesticides and pharmaceutical products. We investigated whether a common core of toxicological and transcriptional responses underlies the observed carcinogenic effects of three conazoles: cyproconazole, epoxiconazole, and propiconazole. In studies where mice were fed diets of these conazoles for 30 days, we found a common set of toxicological effects altered by these conazoles: hepatomegaly, hepatocellular hypertrophy, decreased serum cholesterol, decreased hepatic levels of all-trans-retinoic acid, and increased hepatic cell proliferation. Microarray-based transcriptional analysis revealed 330 significantly altered probe sets common to these conazoles, many of which showed strong dose responses for cytochrome P450, glutathione S-transferase, and oxidative stress genes. More detailed analyses identified a subset of 80 altered genes common to the three conazoles that were associated with cancer. Pathways associated with these genes included xenobiotic metabolism, oxidative stress, cell signaling, and cell proliferation. A common TGFα-centric pathway was identified within the 80-gene set, which, in combination with the toxicological and other transcriptomic findings, provides a more refined toxicity profile for these carcinogenic conazoles. [ABSTRACT FROM PUBLISHER]

Ochratoxin A (OTA) is a mycotoxin produced by fungi of two genera: Penicillium and Aspergillus. OTA has been shown to be nephrotoxic, hepatotoxic, teratogenic, and immunotoxic to several species of animals and to cause kidney and liver tumors in mice and rats. Biotransformation of OTA has not been entirely elucidated. Several metabolites have been characterized in vitro and/or in vivo, whereas other metabolites remain to be characterized. At present, data available regarding OTA metabolism and cytochrome inductions concern only rodents or in vitro systems. The aim of the present study was to explore the effect of OTA on mRNA expression of some cytochromes known to be regulated by pregnane X receptor (PXR), constitutive androstane receptor (CAR), and aryl hydrocarbon receptor (AhR), using primary cultures of human hepatocytes. Our results showed that OTA reduced hepatocyte viability in a dose-dependent manner. Using quantitative real-time reverse-transcription polymerase chain reaction, our study showed that treatment of primary cultured human hepatocytes with noncytotoxic increasing concentrations of OTA for 24 hours caused a significant upregulation of CYP3A4, CYP2B6, and, to a lesser extent, CYP3A5 and CYP2C9. PXR mRNA expression increased in only 1 treated liver, whereas CAR mRNA expression was not affected. OTA was found also to induce an overexpression of CYP1A1 and CYP1A2 genes accompanied by an increase in AhR mRNA expression. These findings suggest that OTA could activate PXR and AhR; however, further investigations are needed to confirm nuclear-receptor activation by OTA. [ABSTRACT FROM AUTHOR]

J. Neurochem. (2011) 118, 163-175. Abstract In mammalian systems, pregnane X receptor (PXR) and constitutive androstane receptor (CAR) have been recognized as xenobiotic-sensors which can up-regulate the functional expression of drug transporters, such as P-glycoprotein (P-gp). In the brain, an increase in P-gp expression can further limit drug permeability across the blood-brain barrier (BBB) and potentially reduce CNS pharmacotherapy efficacy. At present, the involvement of human PXR (hPXR) and CAR (hCAR) in the regulation of P-gp expression at the human BBB is unknown. In this study, we investigate the role of hPXR and hCAR in the regulation of P-gp expression using a human cerebral microvessel endothelial cell culture system. We demonstrate that activation of hPXR and hCAR by their respective ligands leads to P-gp induction at both mRNA and protein levels, while pharmacological inhibitors of hPXR and hCAR prevent ligand-mediated P-gp induction. Ligand-induced nuclear translocation of hPXR is observed, although such effect could not be demonstrated for hCAR. Furthermore, down-regulation of hPXR and hCAR proteins using small-interfering RNA decreased P-gp expression. Our findings provide first evidence for P-gp regulation by hPXR and hCAR at the human BBB and suggest insights on how to achieve selective P-gp regulation at this site. [ABSTRACT FROM AUTHOR]

Transgenic animal models are powerful tools for developing a more detailed understanding on the roles of specific genes in biological pathways and systems. Applications of these models have been made within the field of toxicology, most notably for the screening of mutagenic and carcinogenic potential and for the characterization of toxic mechanisms of action. It has long been a goal of research toxicologists to use the data from these models to refine hazard identification and characterization to better inform human health risk assessments. This review provides an overview on the applications of transgenic animal models in the assessment of mutagenicity and carcinogenicity, their use as reporter systems, and as tools for understanding the roles of xenobiotic-metabolizing enzymes and biological receptors in the etiology of chemical toxicity. Perspectives are also shared on the future outlook for these models in toxicology and risk assessment and how transgenic technologies are likely to be an integral tool for toxicity testing in the 21st century. [ABSTRACT FROM AUTHOR]

A primary objective of the lunar laser ranging (LLR) experiment is to provide precise observations of the lunar orbit that contribute to a wide range of science investigations. In particular, time series of the highly accurate measurements of the distance between the Earth and the Moon provide unique information used to determine whether, in accordance with the equivalence principle (EP), these two celestial bodies are falling toward the Sun at the same rate, despite their different masses, compositions, and gravitational self-energies. Thirty-five years since their initiation, analyses of precision laser ranges to the Moon continue to provide increasingly stringent limits on any violation of the EP. Current LLR solutions give (-1.0 ± 1.4) × 10-13 for any possible inequality in the ratios of the gravitational and inertial masses for the Earth and Moon, Δ(MG/MI). This result, in combination with laboratory experiments on the weak equivalence principle, yields a strong equivalence principle (SEP) test of Δ(MG/MI)SEP = (-2.0 ± 2.0) × 10-13. Such an accurate result allows other tests of gravitational theories. The result of the SEP test translates into a value for the corresponding SEP violation parameter η of (4.4 ± 4.5) × 10-4, where η = 4β - γ - 3 and both γ and β are parametrized post-Newtonian (PPN) parameters. Using the recent result for the parameter γ derived from the radiometric tracking data from the Cassini mission, the PPN parameter β (quantifying the nonlinearity of gravitational superposition) is determined to be β - 1 = (1.2 ± 1.1) × 10-4. We also present the history of the LLR effort and describe the technique that is being used. Focusing on the tests of the EP, we discuss the existing data, and characterize the modeling and data analysis techniques. The robustness of the LLR solutions is demonstrated with several different approaches that are presented in the text. We emphasize that near-term improvements in the LLR accuracy will further advance the research on relativistic gravity in the solar system and, most notably, will continue to provide highly accurate tests of the EP. [ABSTRACT FROM AUTHOR]

Nuclear receptors (NRs) are attractive drug targets due to their role in regulation of a wide range of physiologic responses. In addition to providing therapeutic value, many pharmaceutical agents along with environmental chemicals are ligands for NRs and can cause adverse health effects that are directly related to activation of NRs. Identifying the molecular events that produce a toxic response may be confounded by the fact that there is a significant overlap in the biological processes that NRs regulate. Microarrays and other methods for gene expression profiling have served as useful, sensitive tools for discerning the mechanisms by which therapeutics and environmental chemicals invoke toxic effects. The capability to probe thousands of genes simultaneously has made genomics a prime technology for identifying drug targets, biomarkers of exposure/toxicity and key players in the mechanisms of disease. The complex intertwining networks regulated by NRs are hard to probe comprehensively without global approaches and genomics has become a key technology that facilitates our understanding of NR-dependent and -independent events. The future of drug discovery, design and optimization, and risk assessment of chemical toxicants that activate NRs will inevitably involve genomic profiling. This review will focus on genomics studies related to PPAR, CAR, PXR, RXR, LXR, FXR, and AHR. [ABSTRACT FROM AUTHOR]

To characterize the function of constitutive active/androstane receptor (CAR) in aquatic mammals, CAR complementary DNA (cDNA) was cloned from the liver of Baikal seal (Pusa sibirica) from Lake Baikal, Russia, and the messenger RNA (mRNA) expression levels in various tissues/organs of the wild population and the CAR ligand profiles were investigated. The seal CAR cDNA had an open reading frame of 1047 bp encoding 348 amino acids that revealed 74–84% amino acid identities with CARs from rodents and human. The mRNA expression profile of tissues/organs represented that Baikal seal CAR was predominantly expressed in the liver followed by heart and intestine. The expression analysis of hepatic CAR mRNA showed no correlation with expression of cytochrome P450 (CYP) 1A, 1B, 2B, 2C, and 3A-like proteins, indicating that the CAR expression level may not be the sole determinant of the regulation of these CYP expressions in the seal liver. There was no significant correlation between CAR expression and any of the persistent organic pollutants (POPs) levels. Furthermore, we performed an in vitro CAR transactivation assay using MCF-7 cells transfected with Baikal seal CAR expression plasmid and (NR1)3-luciferase reporter gene plasmid. In the transactivation analysis of Baikal seal CAR, neither repression by androstanol and androstenol, nor activation by estrone and estradiol, which are recognized as endogenous ligands for mouse and human CARs, was detected. On the other hand, bile acids such as chenodeoxycholic acid, deoxycholic acid, and lithocholic acid activated the seal CAR as well as mouse CAR. As for exogenous chemicals, the seal CAR was transactivated by a human CAR agonist, 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime), but not by a mouse CAR agonist, (1,4-bis[2-(3,5-dichloropyridyloxy)]benzene). In addition, the seal CAR was also activated by polychlorinated biphenyls (PCBs) (Kanechlor-500, International Union of Pure and Applied Chemistry No. PCB153; 2,2′,4,4′,5,5′-hexachlorobiphenyl and PCB180; 2,2′,3,4,4′,5,5′-heptachlorobiphenyl), and 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p′-DDT) and its metabolite, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p′-DDE). The seal CAR responded more sensitively to PCBs than the mouse CAR. Based on the results of CAR transactivation assay, the lowest observable effect levels of Kanechlor-500, PCB153, PCB180, p,p′-DDT, and p,p′-DDE in Baikal seal were estimated to be 10, 20, 20, 10, and 10 ppm on wet weight basis, respectively. These results suggest that CAR is conserved in diverse mammalian species including seals. Whereas the seal CAR-mediated gene transcription may potentially be a sensitive response to the exposure of certain POPs, the ligand profile of seal CAR may be different from those of other mammalian CARs. This study indicates that CAR-mediated responses may be useful information to assess the ecotoxicological risk of xenobiotics such as POPs in wildlife but the previous results derived from rodent and human CAR may not be applicable to the risk assessment in wild species. [ABSTRACT FROM PUBLISHER]

Xenobiotic metabolism and detoxification is regulated by receptors (e.g., PXR, CAR) whose characterization has contributed significantly to our understanding of drug responses in humans. Technologies facilitating the screening of compounds for receptor interactions provide valuable tools applicable in drug development. Most use in vitro systems or mice humanized for receptors in vivo. In vitro assays are limited by the reporter systems and cell lines chosen and are uninformative about effects in vivo. Humanized mouse models provide novel, exciting ways of understanding the functions of these genes. This article evaluates these technologies and current knowledge on PXR/CAR-mediated regulation of gene expression. [ABSTRACT FROM AUTHOR]

Constitutive androstane receptor (CAR) and pregnane X receptor (PXR) are members of the nuclear receptor superfamily. These transcription factors are predominantly expressed in the liver, where they are activated by structurally diverse compounds, including many drugs and endogenous substances. CAR and PXR regulate the expression of a broad range of genes, which contribute to transcellular transport, bioactivation, and detoxification of numerous xenochemicals and endogenous substances. This article discusses the importance of these receptors for pharmacology and toxicology, emphasizing the role of individual drugs and natural products as agonists, indirect activators, inverse agonists, and antagonists of CAR and PXR. [ABSTRACT FROM AUTHOR]

Hazard identification and risk assessment paradigms depend on the presumption of the similarity of rodents to humans, yet species specific responses, and the extrapolation of high-dose effects to low-dose exposures can affect the estimation of human risk from rodent data. As a consequence, a human relevance framework concept was developed by the International Programme on Chemical Safety (IPCS) and International Life Sciences Institute (ILSI) Risk Science Institute (RSI) with the central tenet being the identification of a mode of action (MOA). To perform a MOA analysis, the key biochemical, cellular, and molecular events need to first be established, and the temporal and dose-dependent concordance of each of the key events in the MOA can then be determined. The key events can be used to bridge species and dose for a given MOA. The next step in the MOA analysis is the assessment of biological plausibility for determining the relevance of the specified MOA in an animal model for human cancer risk based on kinetic and dynamic parameters. Using the framework approach, a MOA in animals could not be defined for metal overload. The MOA for phenobarbital (PB)-like P450 inducers was determined to be unlikely in humans after kinetic and dynamic factors were considered. In contrast, after these factors were considered with reference to estrogen, the conclusion was drawn that estrogen-induced tumors were plausible in humans. Finally, it was concluded that the induction of rodent liver tumors by porphyrogenic compounds followed a cytotoxic MOA, and that liver tumors formed as a result of sustained cytotoxicity and regenerative proliferation are considered relevant for evaluating human cancer risk if appropriate metabolism occurs in the animal models and in humans. [ABSTRACT FROM AUTHOR]

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent developmental toxicant in most vertebrates. However, frogs are relatively insensitive to TCDD toxicity, especially during early life stages. Toxicity of TCDD and related halogenated aromatic hydrocarbons is mediated by the aryl hydrocarbon receptor (AhR), and specific differences in properties of the AhR signaling pathway can underlie in TCDD toxicity in different species. This study investigated the role of AhR in frog TCDD insensitivity, using Xenopus laevis as a model system. X. laevis, a pseudotetraploid species, expresses two distinct AhR1 genes, AhR1α and AhR1β. Sharing 86% amino acid identity, these likely represent distinct genes, both orthologous to mammalian AhR and paralogous to the AhR2 gene(s) in most fish. Both AhR1α and AhR1β exhibit TCDD-dependent binding of cognate DNA sequences, but they bind TCDD with at least 20-fold lower affinity than the mouse AhRb–1 protein, and they are similarly less responsive in TCDD-induced reporter gene induction in conjunction with the mouse CYP1A1 promoter. Furthermore, CYP1A6 and CYP1A7 induction by TCDD in cultured X. laevis A6 cells appears much less responsive than CYP1A induction in cell lines derived from more sensitive animals. Taken together, these data suggest that low affinity binding by X. laevis AhRs plays an important mechanistic role in the insensitivity of frogs to TCDD. An understanding of these molecular mechanisms should aid amphibian ecotoxicology and refine the use of frog embryos as a model [e.g. in FETAX (Frog Embryo Teratogenesis Assay-Xenopus)] for determining developmental toxicity of samples containing dioxin-like compounds. [ABSTRACT FROM AUTHOR]

Purpose: Paclitaxel (Taxol) is an effective agent against a broad range of human cancers. Studies on the metabolism and disposition of paclitaxel have shown that it is primarily eliminated via hepatic metabolism by P450 enzymes (2C8 and 3A4) to essentially inactive metabolites, and that biliary and gut transport by P-glycoprotein (PGP) as well as urinary elimination of the parent compound play relatively minor roles. Recent studies in vitro have shown that paclitaxel treatment increases the level of CYP2C8 and CYP3A4 in human hepatocytes as well as PGP in colon tumor cells. The data suggest that previous paclitaxel exposure may influence metabolism and elimination of subsequent doses. Further, since weekly paclitaxel dose schedules are becoming more common as opposed to the original every 21-day dosing, the likelihood of enzyme induction from previous doses impacting that from subsequent doses is increased. Methods: To study the potential for such sequence-dependent alterations in paclitaxel pharmacokinetics, we carried out pharmacokinetic studies in mouse plasma and tissues following day 1 and days 1 and 5 dosing at 20 mg/kg. Paclitaxel concentrations were determined by a sensitive LC/MS/MS assay out to 16 h post-dosing in plasma, liver, kidney, gut and heart. The effect of paclitaxel treatment on hepatic expression of PGP and P450 isoforms (CYP2C and CYP3A) was determined to elucidate the mechanism by which paclitaxel disposition is altered by previous drug exposure. Results: Pharmacokinetic analysis of the data showed that plasma and tissue AUC values after treatment on day 5 following a dose on day 1 were between 50% and 74% of those determined following a single dose on day 1. The terminal elimination half-life was not different. Activity and protein levels for CYP2C in liver were elevated at 24 and 96 h after paclitaxel dosing. Cremophor EL, a carrier solvent for paclitaxel, also caused elevated CYP2C activity. Neither CYP3A nor PGP levels in liver were altered by paclitaxel or Cremophor EL treatment at the 24-h and 96-h time points. The levels of 6α-OH-paclitaxel in feces were increased on day 5 as opposed to day 1 while paclitaxel levels in feces were unchanged. Conclusions: The results of our studies showed that paclitaxel pharmacokinetics are altered by previous paclitaxel exposure up to 96 h earlier. [ABSTRACT FROM AUTHOR]

This article reports on the awarding of the 1988 Nobel Prize in Physics to physics professors Leon Lederman, Melvin Schwartz and Jack Steinberger, as of January 1989. The Royal Swedish Academy of Sciences awarded them jointly the prize for the neutrino-beam method and the demonstration of the doublet structure of the leptons through the discovery of the muon neutrino. Lederman, Schwartz and Steinberger were teaching in the early 1960 when they conducted the first neutrino-beam experiment. Lederman is now director of the Fermi National Accelerator Laboratory, and Steinberger is a senior physicist at the European Laboratory for Particle Physics and a professor at the Scuola Normale Superiore in Pisa, Italy. Schwartz is president of Digital Pathways, a computer communications firm in California. Not only did the demonstration provide a fundamental piece of information essential to the development of the now standard model of the elementary physics; it also introduced the basic technique for the experimental study of the weak interactions at high energies.

The production, collection and deceleration of antiprotons is reviewed with the aim of establishing guidelines for the design of a simple yet efficient source of stopped antiprotons. A high-energy (20–100 GeV) high-intensity (∼1013 protons/pulse) proton accelerator is needed to produce antiprotons in copious numbers. A “passive” conversion-target consisting of a thin iridium rod embedded in graphite, and a magnetic-horn type lens to collect the antiproton flux from the target represent a good compromise between yield and reliability. To transport the flux to low energy a large-acceptance cooling and deceleration ring working up to an energy equal to one-eighth to one-tenth of the primary proton energy is required. Stochastic cooling (at high energy) and electron cooling (at lower energy) are indispensable for providing low-energy beams of useful density. [ABSTRACT FROM AUTHOR]

Once known exclusively for their role in nutrients absorption, bile acids have emerged as signaling molecules, generated from cholesterol breakdown, acting on several immune cells by activating a variety of receptors including the G protein-coupled bile acid receptor 1 (GPABR1 or TGR5), the Farnesoid-X-receptor (FXR) and, as recently discovered, the retinoid-related orphan receptors (ROR)γt. GPBAR1, FXR, and RORγt are highly expressed in cells of the innate and adaptive immune system (i.e., dendritic cells (DCs), macrophages, innate lymphoid 3 cells (ILC3s), and T helper 17 (Th17) lymphocytes) and plays an important role in regulating intestinal and liver immunity, highlighting a role for various bile acid species in regulating immune responses to intestinal microbial antigens. While primary bile acids are generated from the cholesterol breakdown secondary bile acids, the GPBAR1 ligands, and oxo-bile acids derivatives, the RORγt ligands, are generated by the intestinal microbiota, highlighting the potential of these bile acids in mediating the chemical communication between the intestinal microbiota and the host. Changes in intestinal microbiota, dysbiosis, alter the composition of the bile acid pool, promoting the activation of the immune system and development of chronic inflammation. In this review, we focus on the molecular mechanisms by which an altered bile acid signaling promotes intestinal inflammation. [ABSTRACT FROM AUTHOR]

The farnesoid X receptor (FXR) plays a critical role in the regulation of lipid and bile acid (BA) homeostasis. Hepatic FXR loss results in lipid and BA accumulation, and progression from hepatic steatosis to nonalcoholic steatohepatitis (NASH). This study aimed to evaluate the effects of xanthohumol (XN), a hop-derived compound mitigating metabolic syndrome, on liver damage induced by diet and FXR deficiency in mice. Wild-type (WT) and liver-specific FXR-null mice (FXRLiver−/−) were fed a high-fat diet (HFD) containing XN or the vehicle formation followed by histological characterization, lipid, BA and gene profiling. HFD supplemented with XN resulted in amelioration of hepatic steatosis and decreased BA concentrations in FXRLiver−/− mice, the effect being stronger in male mice. XN induced the constitutive androstane receptor (CAR), pregnane X receptor (PXR) and glucocorticoid receptor (GR) gene expression in the liver of FXRLiver−/− mice. These findings suggest that activation of BA detoxification pathways represents the predominant mechanism for controlling hydrophobic BA concentrations in FXRLiver−/− mice. Collectively, these data indicated sex-dependent relationship between FXR, lipids and BAs, and suggest that XN ameliorates HFD-induced liver dysfunction via FXR-dependent and independent signaling. [ABSTRACT FROM AUTHOR]