Role of orphan nuclear receptors in the regulation of drug-metabolising enzymes

AhR, PXR and CAR: From Xenobiotic Receptors to Metabolic Sensors

Traditionally, xenobiotic receptors are known for their role in chemical sensing and detoxification, as receptor activation regulates the expression of various key enzymes and receptors. However, recent studies have highlighted that xenobiotic receptors also play a key role in the regulation of lipid metabolism and therefore function also as metabolic sensors. Since dyslipidemia is a major risk factor for various cardiometabolic diseases, like atherosclerosis and non-alcoholic fatty liver disease, it is of major importance to understand the molecular mechanisms that are regulated by xenobiotic receptors. In this review, three major xenobiotic receptors will be discussed, being the aryl hydrocarbon receptor (AhR), pregnane X receptor (PXR) and the constitutive androstane receptor (CAR). Specifically, this review will focus on recent insights into the metabolic functions of these receptors, especially in the field of lipid metabolism and the associated dyslipidemia.

Resveratrol protects against cadmium-induced cerebrum toxicity through modifications of the cytochrome P450 enzyme system in microsomes

BACKGROUND

Cadmium (Cd), known as a vital contaminant in the environment, penetrates the blood-brain barrier and accumulates in the cerebrum. Acute toxicosis of Cd, which leads to lethal cerebral edema, intracellular accumulation and cellular dysfunction, remains to be illuminated with regard to the exact molecular mechanism of cerebral toxicity. Resveratrol (RES), present in the edible portions of numerous plants, is a simply acquirable and correspondingly less toxic natural compound with neuroprotective potential, which provides some theoretical bases for antagonizing Cd-induced cerebral toxicity.

RESULTS

This work was executed to research the protective effects of RES against Cd-induced toxicity in chicken cerebrum. Markedly, these lesions were increased in the Cd group, which also exhibited a thinner cortex, reduced granule cells, vacuolar degeneration, and an enlarged medullary space in the cerebrum. Furthermore, Cd induced CYP450 enzyme metabolism disorders by disrupting the nuclear xenobiotic receptor response (NXRs), enabling the cerebrum to reduce the ability to metabolize exogenous substances, eventually leading to Cd accumulation. Meanwhile, accumulated Cd promoted oxidative damage and synergistically promoted the damage to neurons and glial cells.

CONCLUSION

RES initiated NXRs (especially for aromatic receptor and pregnancy alkane X receptor), decreasing the expression of CYP450 genes, changing the content of CYP450, maintaining CYP450 enzyme normal activities, and exerting antagonistic action against the Cd-induced abnormal response of nuclear receptors. These results suggest that the cerebrum toxicity caused by Cd was reduced by pretreatment with RES. © 2023 Society of Chemical Industry.

Phenobarbital in Nuclear Receptor Activation: An Update

Phenobarbital (PB) is a commonly prescribed anti-epileptic drug that can also benefit newborns from hyperbilirubinemia. Being the first drug demonstrating hepatic induction of cytochrome P450 (CYP), PB has since been broadly used as a model compound to study xenobiotic-induced drug metabolism and clearance. Mechanistically, PB-mediated CYP induction is linked to a number of nuclear receptors, such as the constitutive androstane receptor (CAR), pregnane X receptor (PXR), and estrogen receptor α, with CAR being the predominant regulator. Unlike prototypical agonistic ligands, PB-mediated activation of CAR does not involve direct binding with the receptor. Instead, dephosphorylation of threonine 38 in the DNA-binding domain of CAR was delineated as a key signaling event underlying PB-mediated indirect activation of CAR. Further studies revealed that such phosphorylation sites appear to be highly conserved among most human nuclear receptors. Interestingly, while PB is a pan-CAR activator in both animals and humans, PB activates human but not mouse PXR. The species-specific role of PB in gene regulation is a key determinant of its implication in xenobiotic metabolism, drug-drug interactions, energy homeostasis, and cell proliferation. In this review, we summarize the recent progress in our understanding of PB-provoked transactivation of nuclear receptors with a focus on CAR and PXR. SIGNIFICANCE STATEMENT: Extensive studies using PB as a research tool have significantly advanced our understanding of the molecular basis underlying nuclear receptor-mediated drug metabolism, drug-drug interactions, energy homeostasis, and cell proliferation. In particular, CAR has been established as a cell signaling-regulated nuclear receptor in addition to ligand-dependent functionality. This mini-review highlights the mechanisms by which PB transactivates CAR and PXR.

Clinical Relevance of the Constitutive Androstane Receptor

Constitutive androstane receptor (CAR) (NR1I3), a xenobiotic receptor, has long been considered a master mediator of drug disposition and detoxification. Accumulating evidence indicates that CAR also participates in various physiologic and pathophysiological pathways regulating the homeostasis of glucose, lipid, and bile acids, and contributing to cell proliferation, tissue regeneration and repair, as well as cancer development. The expression and activity of CAR can be regulated by various factors, including small molecular modulators, CAR interaction with other transcription factors, and naturally occurring genetic variants. Given that the influence of CAR has extended beyond the realm of drug metabolism and disposition and has expanded into a potential modulator of human diseases, growing efforts have centered on understanding its clinical relevance and impact on human pathophysiology. This review highlights the current information available regarding the contribution of CAR to various metabolic disorders and cancers and ponders the possible challenges that might arise from pursuing CAR as a potential therapeutic target for these diseases. SIGNIFICANCE STATEMENT: The growing importance of the constitutive androstane receptor (CAR) in glucose and lipid metabolism as well as its potential implication in cell proliferation emphasizes a need to keenly understand the biological function and clinical impact of CAR. This minireview captures the clinical relevance of CAR by highlighting its role in metabolic disorders and cancer development.

Targeting CAR and Nrf2 improves cyclophosphamide bioactivation while reducing doxorubicin-induced cardiotoxicity in triple-negative breast cancer treatment

Cyclophosphamide (CPA) and doxorubicin (DOX) are key components of chemotherapy for triple-negative breast cancer (TNBC), although suboptimal outcomes are commonly associated with drug resistance and/or intolerable side effects. Through an approach combining high-throughput screening and chemical modification, we developed CN06 as a dual activator of the constitutive androstane receptor (CAR) and nuclear factor erythroid 2-related factor 2 (Nrf2). CN06 enhances CAR-induced bioactivation of CPA (a prodrug) by provoking hepatic expression of CYP2B6, while repressing DOX-induced cytotoxicity in cardiomyocytes in vitro via stimulating Nrf2-antioxidant signaling. Utilizing a multicellular coculture model incorporating human primary hepatocytes, TNBC cells, and cardiomyocytes, we show that CN06 increased CPA/DOX-mediated TNBC cell death via CAR-dependent CYP2B6 induction and subsequent conversion of CPA to its active metabolite 4-hydroxy-CPA, while protecting against DOX-induced cardiotoxicity by selectively activating Nrf2-antioxidant signaling in cardiomyocytes but not in TNBC cells. Furthermore, CN06 preserves the viability and function of human iPSC-derived cardiomyocytes by modulating antioxidant defenses, decreasing apoptosis, and enhancing the kinetics of contraction and relaxation. Collectively, our findings identify CAR and Nrf2 as potentially novel combined therapeutic targets whereby CN06 holds the potential to improve the efficacy/toxicity ratio of CPA/DOX-containing chemotherapy.

Human constitutive androstane receptor represses liver cancer development and hepatoma cell proliferation by inhibiting erythropoietin signaling

The constitutive androstane receptor (CAR) is a nuclear receptor that plays a crucial role in regulating xenobiotic metabolism and detoxification, energy homeostasis, and cell proliferation by modulating the transcription of numerous target genes. CAR activation has been established as the mode of action by which phenobarbital-like nongenotoxic carcinogens promote liver tumor formation in rodents. This paradigm, however, appears to be unrelated to the function of human CAR (hCAR) in hepatocellular carcinoma (HCC), which remains poorly understood. Here, we show that hCAR expression is significantly lower in HCC than that in adjacent nontumor tissues and, importantly, reduced hCAR expression is associated with a worse HCC prognosis. We also show overexpression of hCAR in human hepatoma cells (HepG2 and Hep3B) profoundly suppressed cell proliferation, cell cycle progression, soft-agar colony formation, and the growth of xenografts in nude mice. RNA-Seq analysis revealed that the expression of erythropoietin (EPO), a pleiotropic growth factor, was markedly repressed by hCAR in hepatoma cells. Addition of recombinant EPO in HepG2 cells partially rescued hCAR-suppressed cell viability. Mechanistically, we showed that overexpressing hCAR repressed mitogenic EPO-EPO receptor signaling through dephosphorylation of signal transducer and activator of transcription 3, AKT, and extracellular signal-regulated kinase 1/2. Furthermore, we found that hCAR downregulates EPO expression by repressing the expression and activity of hepatocyte nuclear factor 4 alpha, a key transcription factor regulating EPO expression. Collectively, our results suggest that hCAR plays a tumor suppressive role in HCC development, which differs from that of rodent CAR and offers insight into the hCAR-hepatocyte nuclear factor 4 alpha-EPO axis in human liver tumorigenesis.

Genome-wide transcriptional response of the causal soybean sudden death syndrome pathogen Fusarium virguliforme to a succinate dehydrogenase inhibitor fluopyram

BACKGROUND

Succinate dehydrogenase inhibitors (SDHIs) have been widely used to manage plant diseases caused by phytopathogenic fungi. Although attention to and use of SDHI fungicides has recently increased, molecular responses of fungal pathogens to SDHIs have often not been investigated. A SDHI fungicide, fluopyram, has been used as a soybean seed treatment and has displayed effective control of Fusarium virguliforme, one of the causal agents of soybean sudden death syndrome. To examine genome-wide gene expression of F. virguliforme to fluopyram, RNA-seq analysis was conducted on two field strains of F. virguliforme with differing SDHI fungicide sensitivity in the absence and presence of fluopyram.

RESULTS

The analysis indicated that several xenobiotic detoxification-related genes, such as those of deoxygenase, transferases and transporters, were highly induced by fluopyram. Among the genes, four ATP-binding cassette (ABC) transporters were characterized by the yeast expression system. The results revealed that expression of three ABCG transporters was associated with reduced sensitivity to multiple fungicides including fluopyram. In addition, heterologous expression of a major facilitator superfamily (MFS) transporter that was highly expressed in the fluopyram-insensitive F. virguliforme strain in the yeast system conferred decreased sensitivity to fluopyram.

CONCLUSION

This study demonstrated that xenobiotic detoxification-related genes were highly upregulated in response to fluopyram, and expression of ABC or MFS transporter genes was associated with reduced sensitivity to the SDHI fungicide. This is the first transcriptomic analysis of the fungal species response to fluopyram and the finding will help elucidate the molecular mechanisms of SDHI resistance. © 2021 Society of Chemical Industry.

Short-term exposure to pharmaceuticals negatively impacts marine flatfish species: Histological, biochemical and molecular clues for an integrated ecosystem risk assessment

The marine habitat and its biodiversity can be impacted by released pharmaceuticals. The short-term (7 days) effect of 3 commonly used drugs - warfarin, dexamethasone and imidazole - on Senegalese sole (Solea senegalensis) juveniles was investigated. Occurrence of hemorrhages, histopathological alterations, antioxidant status, activity of antioxidant enzymes and expression of genes involved in the xenobiotic response (pxr, abcb1 and cyp1a), were evaluated. The results showed a time and drug-dependent effect. Warfarin exposure induced hemorrhages, hepatocyte vacuolar degeneration, and altered the activity of glutathione peroxidase (GPx) and the expression of all the studied genes. Dexamethasone exposure increased liver glycogen content, altered antioxidant status, GPx and superoxide dismutase activities, as well as abcb1 and cyp1a expression. Imidazole induced hepatocyte vacuolar degeneration and ballooning, and altered the antioxidant status and expression of the tested genes. The present work anticipates a deeper impact of pharmaceuticals on the aquatic environment than previously reported, thus underlining the urgent need for an integrated risk assessment.

Polymorphisms at CYP enzymes, NR1I2 and NR1I3 in association with virologic response to antiretroviral therapy in Brazilian HIV-positive individuals

Virologic failure of antiretroviral therapy (ART) may be explained by single nucleotide polymorphisms (SNPs) in drug absorption and metabolism genes. Here, we characterized the associations between polymorphisms in cytochrome P450 enzymes' genes CYP2B6 and CYP3A4/A5, nuclear receptor genes NR1I2/3, and initial ART efficacy among 203 HIV-positive individuals from Rio de Janeiro. Association between SNPs and virologic control was evaluated after 6 and 12 months of follow-up using Cox regression models. The SNP rs2307424 (NR1I3) was associated with increased virologic response after 12 months of treatment, while rs1523127 (NR1I2), rs3003596, and rs2502815 (NR1I3) were associated with decreased response. Increased virologic response after 12 months (_adjHR = 1.54; p = 0.02) was also observed among carriers of the NR1I3 haplotype rs2502815G-rs3003596A-rs2307424A versus the reference haplotype G-A-G. Our results suggest that NR1I2 and NR1I3 variants are associated with virologic responses to ART among Brazilians.

Identifying CAR Modulators Utilizing a Reporter Gene Assay

The constitutive androstane receptor (CAR, NR1I3) controls the transcription of numerous hepatic drug metabolizing enzymes and transporters. There are two possible methods of activation for CAR, direct ligand binding and a ligand-independent method, which makes this a unique nuclear receptor. Both mechanisms require the translocation of CAR from the cytoplasm into the nucleus. Interestingly, CAR is constitutively active and spontaneously localized in the nucleus of most immortalized cell lines. This creates an important challenge in most in vitro assay models because immortalized cells cannot be used without inhibiting the high basal activity. In this book chapter, we go into detail of how to perform quantitative high-throughput screens to identify human CAR modulators through the employment of a double stable cell line. Using this line, we can identify activators, as well as deactivators, of the challenging nuclear receptor, CAR.

The role of pregnane X receptor (PXR) in substance metabolism

As a member of the nuclear receptor (NR) superfamily, pregnane X receptor (PXR; NR1I2) is a ligand-activated transcription factor that plays a crucial role in the metabolism of xenobiotics and endobiotics in mammals. The tissue distribution of PXR is parallel to its function with high expression in the liver and small intestine and moderate expression in the kidney, stomach, skin, and blood-brain barrier, which are organs and tissues in frequent contact with xenobiotics. PXR was first recognized as an exogenous substance receptor regulating metabolizing enzymes and transporters and functioning in detoxification and drug metabolism in the liver. However, further research revealed that PXR acts as an equally important endogenous substance receptor in the metabolism and homeostasis of endogenous substances. In this review, we summarized the functions of PXR in metabolism of different substances such as glucose, lipid, bile acid, vitamin, minerals, and endocrines, and also included insights of the application of PXR ligands (drugs) in specific diseases.

Evaluation of human relevance of Nicofluprole-induced rat thyroid disruption

Nicofluprole is a novel insecticide of the phenylpyrazole class conferring selective antagonistic activity on insect GABA receptors. After repeated daily dietary administration to Wistar rats for 28/90 days, Nicofluprole induced increases in thyroid (and liver) weight, associated with histopathology changes. Nicofluprole did not inhibit thyroid peroxydase nor sodium/iodide symporter, two key players in the biosynthesis of thyroid hormones, indicating the absence of a direct thyroid effect. The results seen in rats suggested a mode of action of Nicofluprole driven by the molecular initiating event of CAR/PXR nuclear receptor activation in livers, with key events of increases in liver weight and hypertrophy, decreasing circulatory thyroid hormones, a compensatory increase in TSH release and follicular cell hypertrophy. To explore the relevance of these changes to humans, well established in vitro rat and human sandwich-cultured hepatocytes were exposed to Nicofluprole up to 7 days. A concentration-dependent CYP3A induction (PXR-activation), an increase in T4-glucuronoconjugation accompanied by UGT1A/2B inductions was observed in rat but not in human hepatocytes. The inductions seen with Nicofluprole in rat (in vivo and in vitro in hepatocytes) that were absent in human hepatocytes represent another example of species-selectivity of nuclear CAR/PXR receptor activators. Importantly, the different pattern observed in rat and human models demonstrate that Nicofluprole-related thyroid effects observed in the rat are with no human relevance.

Targeting Xenobiotic Nuclear Receptors PXR and CAR to Prevent Cobicistat Hepatotoxicity

Liver-related diseases including drug-induced liver injury are becoming increasingly prominent in AIDS patients. Cobicistat (COBI) is the backbone of multiple regimens for antiretroviral therapy. The current work investigated the mechanisms of adverse drug-drug interactions associated with COBI that lead to liver damage. For individuals co-infected with HIV and tuberculosis (TB), the World Health Organization recommends the initiation of TB treatment followed by antiretroviral therapy. Rifampicin (RIF), a first line anti-TB drug, is a human specific activator of pregnane X receptor (PXR). Using PXR-humanized mice, we found that RIF-mediated PXR activation potentiates COBI hepatotoxicity. In contrast, rifabutin, a PXR-neutral analog of RIF, has no impact on COBI hepatotoxicity. Because of the crosstalk between PXR and the constitutive androstane receptor (CAR), the role of CAR in COBI hepatotoxicity was also investigated. Similar to PXR, ligand-dependent activation of CAR also potentiates COBI hepatotoxicity. Our further studies illustrated that PXR and CAR modulate COBI hepatotoxicity through the CYP3A4-dependent pathways. In summary, the current work determined PXR and CAR as key modulators of COBI hepatotoxicity. Given the fact that many prescription drugs and herbal supplements can activate PXR and CAR, these two receptors should be considered as targets to prevent COBI hepatotoxicity in the clinic.

Arsenic: Various species with different effects on cytochrome P450 regulation in humans

Arsenic is well-recognized as one of the most hazardous elements which is characterized by its omnipresence throughout the environment in various chemical forms. From the simple inorganic arsenite (iAsIII) and arsenate (iAsV) molecules, a multitude of more complex organic species are biologically produced through a process of metabolic transformation with biomethylation being the core of this process. Because of their differential toxicity, speciation of arsenic-based compounds is necessary for assessing health risks posed by exposure to individual species or co-exposure to several species. In this regard, exposure assessment is another pivotal factor that includes identification of the potential sources as well as routes of exposure. Identification of arsenic impact on different physiological organ systems, through understanding its behavior in the human body that leads to homeostatic derangements, is the key for developing strategies to mitigate its toxicity. Metabolic machinery is one of the sophisticated body systems targeted by arsenic. The prominent role of cytochrome P450 enzymes (CYPs) in the metabolism of both endobiotics and xenobiotics necessitates paying a great deal of attention to the possible effects of arsenic compounds on this superfamily of enzymes. Here we highlight the toxicologically relevant arsenic species with a detailed description of the different environmental sources as well as the possible routes of human exposure to these species. We also summarize the reported findings of experimental investigations evaluating the influence of various arsenicals on different members of CYP superfamily using human-based models.

Rifampicin Induces Gene, Protein, and Activity of P-Glycoprotein (ABCB1) in Human Precision-Cut Intestinal Slices

P-glycoprotein (ABCB1), an ATP-binding cassette efflux transporter, limits intestinal absorption of its substrates and is a common site of drug–drug interactions. Drug-mediated induction of intestinal ABCB1 is a clinically relevant phenomenon associated with significantly decreased drug bioavailability. Currently, there are no well-established human models for evaluating its induction, so drug regulatory authorities provide no recommendations for in vitro/ex vivo testing drugs’ ABCB1-inducing activity. Human precision-cut intestinal slices (hPCISs) contain cells in their natural environment and express physiological levels of nuclear factors required for ABCB1 induction. We found that hPCISs incubated in William’s Medium E for 48 h maintained intact morphology, ATP content, and ABCB1 efflux activity. Here, we asked whether rifampicin (a model ligand of pregnane X receptor, PXR), at 30 μM, induces functional expression of ABCB1 in hPCISs over 24- and 48-h incubation (the time to allow complete induction to occur). Rifampicin significantly increased gene expression, protein levels, and efflux activity of ABCB1. Moreover, we described dynamic changes in ABCB1 transcript levels in hPCISs over 48 h incubation. We also observed that peaks of induction are achieved among donors at different times, and the extent of ABCB1 gene induction is proportional to PXR mRNA levels in the intestine. In conclusion, we showed that hPCISs incubated in conditions comparable to those used for inhibition studies can be used to evaluate drugs’ ABCB1-inducing potency in the human intestine. Thus, hPCISs may be valuable experimental tools that can be prospectively used in complex experimental evaluation of drug–drug interactions.

Biochemical and molecular responses of the Mediterranean mussel (Mytilus galloprovincialis) to short-term exposure to three commonly prescribed drugs

Pharmaceuticals represent a group of emerging contaminants. The short-term effect (3 and 7 days) of warfarin (1 and 10 mg L^-1), dexamethasone (0.392 and 3.92 mg L^-1) and imidazole (0.013 and 0.13 mg L^-1) exposure was evaluated on mussels (Mytilus galloprovincialis). Total antioxidant status, glutathione reductase, glutathione peroxidase (GPx) and superoxide dismutase enzyme activities, and the expression of genes involved in the xenobiotic response (ATP binding cassette subfamily B member 1 (abcb1) and several nuclear receptor family J (nr1j) isoforms), were evaluated. All nr1j isoforms are suggested to be the xenobiotic receptor orthologs of the NR1I family. All drugs increased GPx activity and altered the expression of particular nr1j isoforms. Dexamethasone exposure also decreased abcb1 expression. These findings raised some concerns regarding the release of these pharmaceuticals into the aquatic environment. Thus, further studies might be needed to perform an accurate environmental risk assessment of these 3 poorly studied drugs.

Overexpression of three P450 genes is responsible for resistance to novel pyrimidine amines in Magnaporthe oryzae

BACKGROUND

A series of pyrimidine amine derivatives has been synthesized by modifying the pyrimidine ring group of diflumetorim-a mitochondrial complex I inhibiting fungicide. One derivative, code number SYP-34773, is investigated in this study involving Magnaporthe oryzae, the causal agent of rice blast, which is the most devastating disease in rice. The response, resistance profile and mechanism of M. oryzae to SYP-34773 were investigated, which provides or provide?? important data for the registration and rational use of pyrimidine amines.

RESULTS

SYP-34773 showed greater control efficacy than fungicide isoprothiolane in the field. The baseline sensitivity was established at a mean 50% effective concentration (EC₅₀ ) of 0.08 μg ml^-1 . Four stable SYP-34773-resistant isolates with reduced sensitivity were generated from one (S118) of ten sensitive isolates with a resistance factor of EC₅₀ ranging from 7.00 to 15.00. Conidia production and pathogenicity were similar to that of S118, although there was a significant decrease in mycelial growth and conidial germination in resistant isolates. Positive cross-resistance was observed between SYP-34773 and diflumetorim; and the SYP-34773-resistant isolates were still sensitive to isoprothiolane, carbendazim, fluazinam, azoxystrobin, or prochloraz. RNA-Seq analyses revealed three cytochrome P450 genes were upregulated in the resistant isolate under the treatment with SYP-34773, as confirmed by quantitative real-time PCR. The SYP-34773 content was significantly reduced in the resistant isolate when compared with the parental isolate.

CONCLUSION

The study demonstrated that SYP-34773 exhibits high activity against M. oryzae. Overexpression of three cytochrome P450 genes has an important role in the resistance of M. oryzae to novel pyrimidine amines. © 2020 Society of Chemical Industry.

Constitutive Androstane Receptor: A Peripheral and a Neurovascular Stress or Environmental Sensor

Xenobiotic nuclear receptors (NR) are intracellular players involved in an increasing number of physiological processes. Examined and characterized in peripheral organs where they govern metabolic, transport and detoxification mechanisms, accumulating data suggest a functional expression of specific NR at the neurovascular unit (NVU). Here, we focus on the Constitutive Androstane Receptor (CAR), expressed in detoxifying organs such as the liver, intestines and kidneys. By direct and indirect activation, CAR is implicated in hepatic detoxification of xenobiotics, environmental contaminants, and endogenous molecules (bilirubin, bile acids). Importantly, CAR participates in physiological stress adaptation responses, hormonal and energy homeostasis due to glucose and lipid sensing. We next analyze the emerging evidence supporting a role of CAR in NVU cells including the blood-brain barrier (BBB), a key vascular interface regulating communications between the brain and the periphery. We address the emerging concept of how CAR may regulate specific P450 cytochromes at the NVU and the associated relevance to brain diseases. A clear understanding of how CAR engages during pathological conditions could enable new mechanistic, and perhaps pharmacological, entry-points within a peripheral-brain axis.

Pharmaceutical Excipients and Drug Metabolism: A Mini-Review

Conclusions from previously reported articles have revealed that many commonly used pharmaceutical excipients, known to be pharmacologically inert, show effects on drug transporters and/or metabolic enzymes. Thus, the pharmacokinetics (absorption, distribution, metabolism and elimination) of active pharmaceutical ingredients are possibly altered because of their transport and metabolism modulation from the incorporated excipients. The aim of this review is to present studies on the interaction of various commonly-used excipients on pre-systemic metabolism by CYP450 enzymes. Excipients such as surfactants, polymers, fatty acids and solvents are discussed. Based on all the reported outcomes, the most potent inhibitors were found to be surfactants and the least effective were organic solvents. However, there are many factors that can influence the inhibition of CYP450, for instance type of excipient, concentration of excipient, type of CYP450 isoenzyme, incubation condition, etc. Such evidence will be very useful in dosage form design, so that the right formulation can be designed to maximize drug bioavailability, especially for poorly bioavailable drugs.

Vasodilation activity of dipfluzine metabolites in isolated rat basilar arteries and their underlying mechanisms

Identifying the metabolites of a drug has become an indispensable task in the development of new drugs. Dipfluzine (Dip) is a promising candidate for the treatment of cerebral vascular diseases and has 5 metabolites (M1∼M5) in rat urine and liver microsomes, but their biological activity is still unknown. Because selective cerebral vasodilation is a main role of Dip, we investigated the vasodilation of Dip and its 5 metabolites in isolated Sprague-Dawley (SD) male rat basilar arteries preconstricted with high-K⁺ or 5-HT. The results showed that only M1 possessed concentration-dependent inhibitory activity on the vasoconstriction of arteries with or without the endothelium, and M1 has a more potent vasodilatory effect than Dip on both contraction models. Like Dip, the vasodilatory mechanisms of M1 may be not only related to receptor-operated and voltage-dependent calcium ion channels of smooth muscle cells but also to the release of NO and EDHF from endothelial cells and the opening of Ca²⁺-activated K⁺ channels and ATP-sensitive potassium ion channels. Unlike Dip, the vasodilation mechanism of M1 is also related to the opening of voltage-sensitive K⁺ channel. Together with more selectivity to non-VDCC than Dip, this may partially explain why M1 has stronger vasodilatory effects than Dip. The mechanisms of vasodilation of Dip and M1 may result from the combined action of these or other factors, especially blocking non-endothelium dependent non-VDCC and endothelium dependent IK_Ca channels. These results point to the possibility that M1 provides synergism for the clinical use of Dip, which may inform the synthesis of new drugs.

HIV-1 Sanctuary Sites-the Role of Membrane-Associated Drug Transporters and Drug Metabolic Enzymes

Despite significant advances in the treatment of human immunodeficiency virus-1 (HIV) infection with highly active antiretroviral drug therapy, the persistence of the virus in cellular and anatomic reservoirs is a major obstacle preventing total HIV eradication. Viral persistence could result from a variety of contributing factors including, but not limited to, non-adherence to treatment and adverse drug reactions, latently infected cells carrying replication-competent virus, drug-drug interactions, and inadequate antiretroviral drug (ARV) concentrations reached in several anatomic sites such as the brain, testis, and gut-associated lymphoid tissues. The distribution of ARVs at specific sites of infection is primarily dependent on drug physicochemical properties and drug plasma protein binding, as well as drug efflux, influx, and metabolic processes. A thorough understanding of the functional roles of drug transporters and metabolic enzymes in the disposition of ARVs in immune cell types and tissues that are characterized as HIV reservoirs and sanctuaries is critical to overcome the challenge of suboptimal drug distribution at sites of persistent HIV infection. This review summarizes the current knowledge related to the expression and function of drug transporters and metabolic enzymes in HIV cellular and anatomic reservoirs, and their potential contribution to drug-drug interactions and insufficient drug concentration at these sites.

Non-alcoholic Fatty Liver Disease and Alcohol-Related Liver Disease: Two Intertwined Entities

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide, with a prevalence of 25-30%. Since its first description in 1980, NAFLD has been conceived as a different entity from alcohol-related fatty liver disease (ALD), despite that, both diseases have an overlap in the pathophysiology, share genetic-epigenetic factors, and frequently coexist. Both entities are characterized by a broad spectrum of histological features ranging from isolated steatosis to steatohepatitis and cirrhosis. Distinction between NAFLD and ALD is based on the amount of consumed alcohol, which has been arbitrarily established. In this context, a proposal of positive criteria for NAFLD diagnosis not considering exclusion of alcohol consumption as a prerequisite criterion for diagnosis had emerged, recognizing the possibility of a dual etiology of fatty liver in some individuals. The impact of moderate alcohol use on the severity of NAFLD is ill-defined. Some studies suggest protective effects in moderate doses, but current evidence shows that there is no safe threshold for alcohol consumption for NAFLD. In fact, given the synergistic effect between alcohol consumption, obesity, and metabolic dysfunction, it is likely that alcohol use serves as a significant risk factor for the progression of liver disease in NAFLD and metabolic syndrome. This also affects the incidence of hepatocellular carcinoma. In this review, we summarize the overlapping pathophysiology of NAFLD and ALD, the current data on alcohol consumption in patients with NAFLD, and the effects of metabolic dysfunction and overweight in ALD.

Mutation of a single amino acid of pregnane X receptor switches an antagonist to agonist by altering AF-2 helix positioning

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.

Population pharmacokinetics of cyclosporine in Chinese children receiving hematopoietic stem cell transplantation

Cyclosporine (CsA) is characterized by a narrow therapeutic window and high interindividual pharmacokinetic variability, particularly in juvenile patients. The aims of this study were to build a population pharmacokinetic model of CsA in Chinese children with hematopathy who received allogeneic hematopoietic stem cell transplantation (allo-HSCT) and to identify covariates affecting CsA pharmacokinetics. A total of 86 Chinese children aged 8.4 ± 3.8 years (range 1.1–16.8 years) who received allo-HSCT were enrolled. Whole blood samples were collected before allo-HSCT. Genotyping was performed using an Agena MassARRAY system. A total of 1010 trough plasma concentration values of CsA and clinical data were collected. The population pharmacokinetic model of CsA was constructed using nonlinear mixed-effects modeling (NONMEM) software. The stability and performance of the final model were validated using bootstrapping and normalized prediction distribution errors. We showed that a one-compartment model with first-order elimination adequately described the pharmacokinetics of CsA. The typical values for clearance (CL) and volume of distribution (V) were 42.3 L/h and 3100 L, respectively. Body weight, postoperative days, CYP3A4*1 G genotype, estimated glomerular filtration rate and coadministration of triazole antifungal drugs were identified as significant covariates for CL. Weight and postoperative days were significant covariates for the V of CsA. Our model can be adopted to optimize the CsA dosing regimen for Chinese children with hematopathy receiving allo-HSCT.

Strategies for developing pregnane X receptor antagonists: Implications from metabolism to cancer

Pregnane X receptor (PXR) is a ligand-activated nuclear receptor (NR) that was originally identified as a master regulator of xenobiotic detoxification. It regulates the expression of drug-metabolizing enzymes and transporters to control the degradation and excretion of endobiotics and xenobiotics, including therapeutic agents. The metabolism and disposition of drugs might compromise their efficacy and possibly cause drug toxicity and/or drug resistance. Because many drugs can promiscuously bind and activate PXR, PXR antagonists might have therapeutic value in preventing and overcoming drug-induced PXR-mediated drug toxicity and drug resistance. Furthermore, PXR is now known to have broader cellular functions, including the regulation of cell proliferation, and glucose and lipid metabolism. Thus, PXR might be involved in human diseases such as cancer and metabolic diseases. The importance of PXR antagonists is discussed in the context of the role of PXR in xenobiotic sensing and other disease-related pathways. This review focuses on the development of PXR antagonists, which has been hampered by the promiscuity of PXR ligand binding. However, substantial progress has been made in recent years, suggesting that it is feasible to develop selective PXR antagonists. We discuss the current status, challenges, and strategies in developing selective PXR antagonists. The strategies are based on the molecular mechanisms of antagonism in related NRs that can be applied to the design of PXR antagonists, primarily driven by structural information.

Herb-Drug Interactions and Hepatotoxicity

BACKGROUND

In recent times, herbals or phytomedicines have become very popular due to their global acceptance as a complementary and alternative remedy. While modern drugs are commercially available only after laboratory validations, clinical trials, as well as approval from drug regulatory authorities, majority of the marketed herbal products lack such scientific evidence of efficacy and safety. This results in herb or herb-drug interaction induced unfavorable clinical outcomes without crucial documentation on their temporal relations and concomitant use.

METHODS

An online literature search for peer-reviewed articles was conducted on the PubMed, Europe PMC, Medline and Google Scholar portals, using the phrases: complementary & alternative medicine, traditional Chinese medicine, herb-drug interaction, mechanisms of herb-drug interaction, herb-induced toxicity, herbal hepatotoxicity and causality, traditional medicine, viral hepatitis, etc.

Results

The retrieved data showed that globally, patients are attracted to herbal remedies with the misconception that these are completely safe and therefore, use them simultaneously with prescription drugs. Notably, there exists a potential risk of herb-drug interactions leading to some adverse side effects, including hepatotoxicity. The toxicological effect of a drug or herb is due to the inhibition of drug metabolizing enzymes (e.g., cytochrome P450), including interactions with certain prescription drugs through various mechanisms. Several cases of hepatotoxicity due to use of herbals in viral hepatitis-related liver diseases have been recently reported. However, limited experimental data and clinical evidence on herbal pharmacokinetics hamper the evaluation and reporting of adverse reactions and the underlying mechanisms.

CONCLUSION

Herb-drug interaction related morbidity is thus an emerging serious public health issue with broad implications for clinicians, pharmaceutical industries and health authorities. Nonetheless, despite increasing recognition of herb-drug interaction, a standard system for interaction prediction and evaluation is still nonexistent. This review article discusses the herb-drug interactions related hepatotoxicity and underlying mechanisms, including drug metabolizing enzymes and their regulation.

The Role of Xenobiotic Receptors on Hepatic Glycolipid Metabolism

Background:

PXR (Pregnane X Receptor) and CAR (Constitutive Androstane Receptor) are termed as xenobiotic receptors, which are known as core factors in regulation of the transcription of metabolic enzymes and drug transporters. However, accumulating evidence has shown that PXR and CAR exert their effects on energy metabolism through the regulation of gluconeogenesis, lipogenesis and β-oxidation. Therefore, in this review, we are trying to summary recent advances to show how xenobiotic receptors regulate energy metabolism.

Methods:

A structured search of databases has been performed by using focused review topics. According to conceptual framework, the main idea of research literature was summarized and presented.

Results:

For introduction of each receptor, the general introduction and the critical functions in hepatic glucose and lipid metabolism have been included. Recent important studies have shown that CAR acts as a negative regulator of lipogenesis, gluconeogenesis and β -oxidation. PXR activation induces lipogenesis, inhibits gluconeogenesis and inhabits β-oxidation.

Conclusion:

In this review, the importance of xenobiotic receptors in hepatic glucose and lipid metabolism has been confirmed. Therefore, PXR and CAR may become new therapeutic targets for metabolic syndrome, including obesity and diabetes. However, further research is required to promote the clinical application of this new energy metabolism function of xenobiotic receptors.

Endocrine disrupting chemicals: Impact on human health, wildlife and the environment

Endocrine disrupting chemicals are a group of pollutants that can affect the endocrine system and lead to diseases and dysfunctions across the lifespan of organisms. They are omnipresent. They are in the air we breathe, in the food we eat and in the water we drink. They can be found in our everyday lives through personal care products, household cleaning products, furniture and in children's toys. Every year, hundreds of new chemicals are produced and released onto the market without being tested, and they reach our bodies through everyday products. Permanent exposure to those chemicals may intensify or even become the main cause for the development of diseases such as type 2 diabetes, obesity, cardiovascular diseases and certain types of cancer. In recent years, legislation and regulations have been implemented, which aim to control the release of potentially adverse endocrine disrupting chemicals, often invoking the precautionary principle. The objective of this review is to provide an overview of research on environmental aspects of endocrine disrupting chemicals and their effects on human health, based on evidence from animal and human studies. Emphasis is given to three ubiquitous and persistent groups of chemicals, polychlorinated biphenyls, polybrominated diphenyl ethers and organochlorine pesticides, and on two non-persistent, but ubiquitous, bisphenol A and phthalates. Some selected historical cases are also presented and successful cases of regulation and legislation described. These led to a decrease in exposure and consequent minimization of the effects of these compounds. Recommendations from experts on this field, World Health Organization, scientific reports and from the Endocrine Society are included.

Drug discovery technologies to identify and characterize modulators of the pregnane X receptor and the constitutive androstane receptor

The pregnane X receptor (PXR) and the constitutive androstane receptor (CAR) are ligand-activated nuclear receptors (NRs) that are notorious for their role in drug metabolism, causing unintended drug-drug interactions and decreasing drug efficacy. They control the xenobiotic detoxification system by regulating the expression of an array of drug-metabolizing enzymes and transporters that excrete exogenous chemicals and maintain homeostasis of endogenous metabolites. Much effort has been invested in recognizing potential drugs for clinical use that can activate PXR and CAR to enhance the expression of their target genes, and in identifying PXR and CAR inhibitors that can be used as co-therapeutics to prevent adverse effects. Here, we present current technologies and assays used in the quest to characterize PXR and CAR modulators, which range from biochemical to cell-based and animal models.

The responses of Oncorhynchus mykiss coping with BDE-47 stress via PXR-mediated detoxification and Nrf2-mediated antioxidation system

The low brominated polybrominated diphenyl ether (PBDE) 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) is ubiquitous in the marine environment. To elucidate the stress response and possible mechanisms underlying BDE-47, the rainbow trout fish Oncorhynchus mykiss were selected and orally fed bait with BDE-47 concentrations of 50 ng/g and 500 ng/g. BDE-47 was found to be mainly accumulated in head kidney and caused lipid peroxidation after prolonged exposure. We studied the detoxification system genes pregnane X receptor (PXR) and downstream genes (cytochrome 3 A, CYP3 A; glutathione S-transferase, GST) and their corresponding enzyme activity and found that the above indicators in the treatment groups increased first and then decreased with time, while the 500 ng/g group showed more significant changes. Further, the antioxidant system gene expression levels of the NF-E2-related factor 2 (Nrf2) and downstream genes (superoxide dismutase, SOD; catalase, CAT) were found significantly up-regulated with concentration and time. The change in the enzyme activity of SOD and CAT showed the same tendency as that of indicators of detoxifying system. The results showed that BDE-47 can accumulated in head kidney and caused activate and fast increase of genes and enzymes of detoxification and antioxidant system in the short-term and then damage the response systems in longer times. After Pearson correlation analysis, the Integrated Biomarker Response (IBR) Index was established with malondialdehyde (MDA) content; PXR, Nrf2, SOD, and CAT gene expression; and CYP3 A, GST, and CAT enzymatic activity, which were significantly related to BDE-47 bioaccumulation (P < 0.5). The IBR value can indicate the ecotoxicological responses of the head kidney to different BDE-47 concentrations exposure, but the high activity of the antioxidant system might obscure the damage of the detoxification system.

Gancao (Glycyrrhizae Radix) provides the main contribution to Shaoyao-Gancao decoction on enhancements of CYP3A4 and MDR1 expression via pregnane X receptor pathway in vitro

BACKGROUND

Chinese herbal formula Shaoyao Gancao decoction (SGD) is often used as an adjuvant with chemotherapeutic agents to treat cancer. Due to the herb-drug interactions, the alternations of drug metabolic enzyme and drug transporters induced by SGD deserve to be explored. We aimed to investigate the effect of SGD on the pregnane X receptor (PXR)-mediated transcriptional regulation of cytochrome P450 3A4 (CYP3A4) and drug transporter multidrug resistance protein 1 (MDR1) in vitro. Besides, we assessed the contribution of constituent herbs to SGD on the regulation of CYP3A4 and MDR1.

METHODS

The dual luciferase reporter gene system containing the hPXR expression plasmid and the reporter gene plasmid of CYP3A4 or MDR1 was co-transfected to HepG2 and Caco2 cells. Luciferase activities were determined using a Dual-luciferase reporter assay kit. The gene expression of CYP3A4 and MDR1 in the hPXR-transfected LS174T cells were assessed by real-time qPCR. Finally, the contribution of constituent herbs from SGD was evaluated.

RESULTS

SGD, Shaoyao and Gancao concentration-dependently increased promoter activities of CYP3A4 and MDR1 in vitro. Moreover, SGD, Shaoyao and Gancao up-regulated CYP3A4 and MDR1 mRNA in hPXR-transfected LS174T cells. As the herbal constituent of SGD, Gancao possesses significantly higher levels of metabolic enzyme and drug transporters compared with Shaoyao.

CONCLUSION

SGD tends to enhance CYP3A4 and MDR1 expression via PXR pathway, especially Gancao provides the main contribution. This study highlights a potential in vitro mechanism for SGD on the regulation of drug metabolic enzymes and drug transporters.

Constitutive androstane receptor weakens the induction of panaxytriol on CYP3A4 by repressing the activation of pregnane X receptor

Nuclear receptors pregnane X receptor (PXR; NR1I2) and constitutive androstane receptor (CAR; NR1I3) play a vital role in regulating CYP3A4. Our previous studies have demonstrated that panaxytriol (PXT) upregulates the expression of CYP3A4 via the PXR regulatory pathway. This study aimed to explore how CAR mediates the regulation of CYP3A4 in the presence of PXT using HepG2 cell, hCAR-overexpressing HepG2 cell and hCAR-silenced HepG2 cell models. In HepG2 cells, PXT induced the expression of CYP3A4 in a concentration-dependent manner (10-80 μM) and the high concentration of PXT (80 μM) upregulated the expression of CAR. The concentrations of PXT (10-40 μM) had no impact on the expression of CAR, but could significantly induce the expression of CYP2B6 target gene by activating CAR. The dual-luciferase reporter gene assay also showed that CAR-mediated CYP3A4 luciferase activity can be promoted by 80 μM of PXT (1.54-fold), while 5, 10, 20, and 40 μM of PXT had no influence on CAR-mediated CYP3A4 luciferase activity. In hCAR-overexpressing HepG2 cells, PXT concentrations (10-40 μM) that significantly induced PXR and CYP3A4 in HepG2 cells had no impact on the expression of CYP3A4, CAR and PXR, whereas a high concentration of PXT (80 µM) could weakly induce the mRNA and protein levels of CAR and CYP3A4. Moreover, the expression of PXR and CYP3A4 in hCAR-silenced HepG2 cells was markedly elevated compared with the blank control or with normal HepG2 cells treated with 10-80 μM of PXT. In conclusion, CAR significantly weakens the ability of PXT to induce CYP3A4 expression by repressing the activation of PXR. There may be a cross-talk mechanism between PXR and CAR on the regulation of CYP3A4 in the presence of PXT. Additionally, a high concentration of PXT (80 μM) induced CYP3A4 via the CAR regulatory pathway.

Drug-drug interactions among drugs prescribed for nontuberculous mycobacterial infection and epilepsy: A case report

WHAT IS KNOWN AND OBJECTIVE

Multi-drug combinations often make chemotherapy difficult owing to drug-drug interactions (DDIs). We report a rare and difficult-to-treat case due to DDIs between drugs for Mycobacterium avium complex (MAC) infection and antiepileptic drugs.

CASE DESCRIPTION

A 70-year-old Japanese woman was diagnosed as having pulmonary MAC disease. She had a history of symptomatic epilepsy, which was successfully treated with phenytoin and phenobarbital. Serum phenytoin concentrations increased upon the initiation of MAC infection treatment.

WHAT IS NEW AND CONCLUSION

We evaluated DDIs and adjusted the dosage of drugs by monitoring the serum drug level.

Human relevance of follicular thyroid tumors in rodents caused by non-genotoxic substances

Chronic stimulation of the thyroid gland of rodents by TSH leads to thyroid follicular hyperplasia and subsequently to thyroid follicular adenomas and carcinomas. However, the interpretations of rodent thyroid tumors are contradictory. The U.S. Food and Drug Administration (FDA) concluded that findings with drugs that lead to increased levels of thyroid-stimulating hormone (TSH) in rats are not relevant to humans, whereas the U.S. Environmental Protection Agency (US EPA) concluded that chemicals that produce rodent thyroid tumors may pose a carcinogenic hazard for humans although the thyroid of rodents appears to be more sensitive to a carcinogenic stimulus than that of humans. Meanwhile, based on the CLP Criteria of the European Chemicals Agency (ECHA), rodent thyroid tumors caused by the induction of uridine-diphosphate-glucuronosyl transferases (UDGT) were assessed as not relevant to humans. To clarify these discrepant positions, the function and regulation of the thyroid gland are described and the types of thyroid tumors and the causes of their development in humans and animals are examined. Based on these data and the evidence that so far, except radiation, no chemical is known to increase the incidence of thyroid tumors in humans, it is concluded that rodent thyroid tumors resulting from continuous stimulation of the thyroid gland by increased TSH levels are not relevant to humans. Consequently, compounds that induce such tumors do not warrant classification as carcinogenic.

A Xenobiotic Detoxification Pathway through Transcriptional Regulation in Filamentous Fungi

Fungi are known to utilize transcriptional regulation of genes that encode efflux transporters to detoxify xenobiotics; however, to date it is unknown how fungi transcriptionally regulate and coordinate different phases of detoxification system (phase I, modification; phase II, conjugation; and phase III, secretion). Here we present evidence of an evolutionary convergence between the fungal and mammalian lineages, whereby xenobiotic detoxification genes (phase I coding for cytochrome P450 monooxygenases [CYP450s] and phase III coding for ATP-binding cassette [ABC] efflux transporters) are transcriptionally regulated by structurally unrelated proteins. Following next-generation RNA sequencing (RNA-seq) analyses of a filamentous fungus, Sclerotinia homoeocarpa, the causal agent of dollar spot on turfgrasses, a multidrug resistant (MDR) field strain was found to overexpress phase I and III genes, coding for CYP450s and ABC transporters for xenobiotic detoxification. Furthermore, there was confirmation of a gain-of-function mutation of the fungus-specific transcription factor S. homoeocarpa XDR1 (ShXDR1), which is responsible for constitutive and induced overexpression of the phase I and III genes, resulting in resistance to multiple classes of fungicidal chemicals. This fungal pathogen detoxifies xenobiotics through coordinated transcriptional control of CYP450s, biotransforming xenobiotics with different substrate specificities and ABC transporters, excreting a broad spectrum of xenobiotics or biotransformed metabolites. A Botrytis cinerea strain harboring the mutated ShXDR1 showed increased expression of phase I (BcCYP65) and III (BcatrD) genes, resulting in resistance to fungicides. This indicates the regulatory system is conserved in filamentous fungi. This molecular genetic mechanism for xenobiotic detoxification in fungi holds potential for facilitating discovery of new antifungal drugs and further studies of convergent and divergent evolution of xenobiotic detoxification in eukaryote lineages.IMPORTANCE Emerging multidrug resistance (MDR) in pathogenic filamentous fungi is a significant threat to human health and agricultural production. Understanding mechanisms of MDR is essential to combating fungal pathogens; however, there is still limited information on MDR mechanisms conferred by xenobiotic detoxification. Here, we report for the first time that overexpression of phase I drug-metabolizing monooxygenases (cytochrome P450s) and phase III ATP-binding cassette efflux transporters is regulated by a gain-of-function mutation in the fungus-specific transcription factor in the MDR strains of the filamentous plant-pathogenic fungus Sclerotinia homoeocarpa This study establishes a novel molecular mechanism of MDR through the xenobiotic detoxification pathway in filamentous fungi, which may facilitate the discovery of new antifungal drugs to control pathogenic fungi.

Population pharmacokinetics of valproic acid in epileptic children: Effects of clinical and genetic factors

Valproic acid (VPA) is a first-line anti-epileptic drug that is used in the treatment of generalized and partial seizures. Gene variants had been proved to influence the pharmacokinetics (PK) of VPA and contribute to its inter-individual variability (IIV). The aim of this study was to systematically investigate the effects of candidate gene variants (CYPs, UGTs, ABC transporters, and nuclear receptors) on VPA PK in Chinese children with epilepsy. A total of 1065 VPA serum trough concentrations at steady state were collected from 264 epileptic pediatric patients aged 3 months to 16 years. The population pharmacokinetic (PPK) model was developed using a nonlinear mixed effects modelling (NONMEM) approach. For the final PPK model, the oral clearance (CL/F) of VPA was estimated to be 0.259 L/h with IIV of 13.3%. The estimates generated by NONMEM indicated that the VPA CL/F was significantly influenced by patient body weight (increased by an exponent of 0.662), co-administration with carbamazepine (increased CL/F by 22%), and daily dose of VPA (increased by an exponent of 0.22). CL/F in patients with the LEPR rs1137101 variant (668 AG and GG genotypes) was much lower than in patients with the AA genotype (17.8% and 22.6% lower, respectively). However, none of the CYPs or UGTs gene variants was found to influence the PK of VPA in this study. Evaluation by bootstrap and normalized prediction distribution error (NPDE) showed that the final model was stable. The predictive performance was evaluated by goodness-of-fit (GOF) plots and visual predictive checks (VPC), and the results indicated satisfactory precision. Our model suggests a correlation between VPA CL/F and LEPR rs1137101 variants, which might be beneficial in the context of individual dose optimization.

A current structural perspective on PXR and CAR in drug metabolism

INTRODUCTION

Pregnane X receptor (PXR) and the constitutive androstane receptor (CAR) are two members of the nuclear receptor superfamily that play major roles in the expression of various drug metabolism enzymes and are known for their ligand promiscuity. As with other nuclear receptors, PXR and CAR are each composed of a ligand-binding domain (LBD) and a DNA-binding domain (DBD) connected by a hinge region. Areas covered: This review focuses on the information obtained over the last 15+ years from X-ray crystallography studies of the structure of PXR and CAR. Areas of focus include the mobility of each structure, based on temperature factors (B factors); multimeric interactions; the binding of coregulators and ligands; and how the crystal structures were obtained. The first use of hydrogen-deuterium exchange coupled with mass spectroscopy (HDX-MS) to study compound-protein interactions in the PXR-LBD is also addressed. Expert opinion: X-ray crystallography studies have provided us with an excellent understanding of how the LBDs of each receptor function; however, many questions remain concerning the structure of these receptors. Future research should focus on determining the co-crystal structure of an antagonist bound to PXR and on studying the structural aspects of the full-length CAR and PXR proteins.

The Roles of Xenobiotic Receptors: Beyond Chemical Disposition

Over the past 20 years, the ability of the xenobiotic receptors to coordinate an array of drug-metabolizing enzymes and transporters in response to endogenous and exogenous stimuli has been extensively characterized and well documented. The constitutive androstane receptor (CAR) and the pregnane X receptor (PXR) are the xenobiotic receptors that have received the most attention since they regulate the expression of numerous proteins important to drug metabolism and clearance and formulate a central defensive mechanism to protect the body against xenobiotic challenges. However, accumulating evidence has shown that these xenobiotic sensors also control many cellular processes outside of their traditional realms of xenobiotic metabolism and disposition, including physiologic and/or pathophysiologic responses in energy homeostasis, cell proliferation, inflammation, tissue injury and repair, immune response, and cancer development. This review will highlight recent advances in studying the noncanonical functions of xenobiotic receptors with a particular focus placed on the roles of CAR and PXR in energy homeostasis and cancer development.

Therapeutic opportunities for alcoholic steatohepatitis and nonalcoholic steatohepatitis: exploiting similarities and differences in pathogenesis

Alcoholic steatohepatitis (ASH) and nonalcoholic steatohepatitis (NASH) are among the most frequent causes of chronic liver disease in the United States. Although the two entities are triggered by different etiologies - chronic alcohol consumption (ASH) and obesity-associated lipotoxicity (NASH) - they share overlapping histological and clinical features owing to common pathogenic mechanisms. These pathogenic processes include altered hepatocyte lipid metabolism, organelle dysfunction (i.e., ER stress), hepatocyte apoptosis, innate immune system activation, and hepatic stellate cell activation. Nonetheless, there are several disease-specific molecular signaling pathways, such as differential pathway activation downstream of TLR4 (MyD88-dependence in NASH versus MyD88-independence in ASH), inflammasome activation and IL-1β signaling in ASH, insulin resistance and lipotoxicity in NASH, and dysregulation of different microRNAs, which clearly highlight that ASH and NASH are two distinct biological entities. Both pathogenic similarities and differences have therapeutic implications. In this Review, we discuss these pathogenic mechanisms and their therapeutic implications for each disease, focusing on both shared and distinct targets.

Pregnane X receptor (PXR) signaling in seabream primary hepatocytes exposed to extracts of seawater samples collected from polycyclic aromatic hydrocarbons (PAHs)-contaminated coastal areas

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants damaging to the marine environment and the wildlife. Herein, we investigated the effects of extracts from coastal seawaters (central Adriatic sea, Italy), showing high concentrations of PAHs, on pregnane X receptor (PXR)-transcriptional regulation of the cytochrome P450 3A (CYP3A) gene using seabream primary hepatocytes. The results show that concentrated extracts of seawater with original ΣPAH concentrations above the putative threshold of 30 ng L^-1 increased expression of PXR and its main target gene, CYP3A. Similar results were observed for LXR and its target gene SREBP-1c suggesting pathway cross-talk. These data are further supported by the finding of multiple PXR and LXR response elements in the putative promoters of their target genes. Overall, our data indicate the capacity of seawater extracts, containing environmentally relevant levels of PAHs, to affect multiple pathways, including lipid and cholesterol metabolism.

Simvastatin modulates gene expression of key receptors in zebrafish embryos

Nuclear receptors (NR) are involved in the regulation of several metabolic processes and it is well known that these constituents may be modulated by different chemicals classes, including pharmaceuticals that may activate or antagonize NR. In mammals, some pharmaceuticals modulate the transcription of pregnane X receptor, Pxr, peroxisome proliferator activated receptor, Ppars, and aryl hydrocarbon receptor, Ahr, affecting mRNA expression of genes belonging to various regulatory pathways, including lipid metabolism and detoxification mechanisms. The aim of this study was to determine the effects of simvastatin (SIM), an anticholesterolemic drug, on selected NR and AhR mRNA transcription levels during zebrafish early development. Embryos were collected at different development stages (0, 2, 6, 14, 24, 48, and 72 hr post fertilization (hpf)) and mRNA of all target NR was detected at all time points. Embryos (1 and 24 hpf) were exposed to different concentrations of SIM (5 or 50 μg/L) in two differing assays with varying exposure times (2 or 80 hr). The transcription levels of ahr2, raraa, rarab, rarga, pparαa, pparβ1, pparγ, pxr, rxraa, rxrab, rxrbb, rxrga, rxrgb, as well as levels of cholesterol (Chol) were measured after exposure. SIM exerted no marked effect on Chol levels, and depending upon exposure duration mRNA levels of NR and AhR either increased or decreased. After 2 hr SIM treatment in 24 hpf embryos, transcription of ppars, pxr, and ahr was up-regulated, while after 80 hr mRNA levels of pxr and ahr were decreased with no marked changes in ppars. Data demonstrate that SIM produced alterations in gene expression of NR which are involved in varying physiological functions and that may disturb regulation of different physiological processes which might impair fish survival and ecosystems regeneration.

3D cell clusters combined with a bioreactor system to enhance the drug metabolism activities of C3A hepatoma cell lines

Since clinical drugs need to be approved for their liver metabolism efficiency before commercialization, a powerful in vitro drug-screening platform is imperative and indispensable for the clinical medicine and pharmaceutical industries. An essential issue in the development of drug screening platforms is choosing cell candidates that mimic and perform cell/tissue functions of normal hepatic tissues in vivo. In this study, we developed a self-designed bioreactor system to provide and mimic an appropriate environment for systematic cell expansion, micro-tissue formation, and increased cellular cytochrome P450 (CYP) enzymatic activities. Since CYP3A4 is the most plentiful and crucial enzyme in drug metabolism among liver CYP superfamily members, we demonstrated that micro-tissue formation under three-dimensional dynamic conditions could enhance cellular CYP3A4 enzymatic activity, maintain cell viability, and preserve adhesive abilities. Furthermore, Ca-alginate scaffolds used in this study can be completely removed by a non-toxic chelating reagent (EDTA solution), and the functional micro-tissues can be collected by slow-speed centrifugation. In conclusion, these micro-tissues are advantageous and show great potential in in vitro drug metabolizing assays.

Nuclear receptor function in skin health and disease: therapeutic opportunities in the orphan and adopted receptor classes

The skin forms a vital barrier between an organism's external environment, providing protection from pathogens and numerous physical and chemical threats. Moreover, the intact barrier is essential to prevent water and electrolyte loss without which terrestrial life could not be maintained. Accordingly, acute disruption of the skin through physical or chemical trauma needs to be repaired timely and efficiently as sustained skin pathologies ranging from mild irritations and inflammation through to malignancy impact considerably on morbidity and mortality. The Nuclear Hormone Receptor Family of transcriptional regulators has proven to be highly valuable targets for addressing a range of pathologies, including metabolic syndrome and cancer. Indeed members of the classic endocrine sub-group, such as the glucocorticoid, retinoid, and Vitamin D receptors, represent mainstay treatment strategies for numerous inflammatory skin disorders, though side effects from prolonged use are common. Emerging evidence has now highlighted important functional roles for nuclear receptors belonging to the adopted and orphan subgroups in skin physiology and patho-physiology. This review will focus on these subgroups and explore the current evidence that suggests these nuclear receptor hold great promise as future stand-alone or complementary drug targets in treating common skin diseases and maintaining skin homeostasis.

Danio rerio embryos on Prozac - Effects on the detoxification mechanism and embryo development

In the past decade the presence of psychopharmaceuticals, including fluoxetine (FLU), in the aquatic environment has been associated with the increasing trend in human consumption of these substances. Aquatic organisms are usually exposed to chronic low doses and, therefore, risk assessments should evaluate the effects of these compounds in non-target organisms. Teleost fish possess an array of active defence mechanisms to cope with the deleterious effects of xenobiotics. These include ABC transporters, phase I and II of cellular detoxification and oxidative stress enzymes. Hence, the present study aimed at characterising the effect of FLU on embryo development of the model teleost zebrafish (Danio rerio) concomitantly with changes in the detoxification mechanisms during early developmental phases. Embryos were exposed to different concentrations of FLU (0.0015, 0.05, 0.1, 0.5 and 0.8μM) for 80hours post fertilization. Development was screened and the impact in the transcription of key genes, i.e., abcb4, abcc1, abcc2, abcg2, cyp1a, cyp3a65, gst, sod, cat, ahr, pxr, pparα, pparβ, pparγ, rxraa, rxrab, rxrbb, rxrga, rxrgb, raraa, rarab, rarga evaluated. In addition, accumulation assays were performed to measure the activity of ABC proteins and antioxidant enzymes (CAT and Cu/ZnSOD) after exposure to FLU. Embryo development was disrupted at the lowest FLU concentration tested (0.0015μM), which is in the range of concentrations found in WWTP effluents. Embryos exposed to higher concentrations of FLU decreased Cu/Zn SOD, and increased CAT (0.0015 and 0.5μM) enzymatic activity. Exposure to higher concentrations of FLU decreased the expression of most genes belonging to the detoxification system and upregulated cat at 0.0015μM of FLU. Most of the tested concentrations downregulated pparα, pparβ, pparγ, and raraa, rxraa, rxrab, rxrbb rxrgb and ahr gene expression while pxr was significantly up regulated at all tested concentrations. In conclusion, this study shows that FLU can impact zebrafish embryo development, at concentrations found in effluents of WWTPs, concomitantly with changes in antioxidant enzymes, and the transcription of key genes involved in detoxification and development. These finding raises additional concerns supporting the need to monitor the presence of this compound in aquatic reservoirs.

Systems Toxicology of Male Reproductive Development: Profiling 774 Chemicals for Molecular Targets and Adverse Outcomes

BACKGROUND

Trends in male reproductive health have been reported for increased rates of testicular germ cell tumors, low semen quality, cryptorchidism, and hypospadias, which have been associated with prenatal environmental chemical exposure based on human and animal studies.

OBJECTIVE

In the present study we aimed to identify significant correlations between environmental chemicals, molecular targets, and adverse outcomes across a broad chemical landscape with emphasis on developmental toxicity of the male reproductive system.

METHODS

We used U.S. EPA's animal study database (ToxRefDB) and a comprehensive literature analysis to identify 774 chemicals that have been evaluated for adverse effects on male reproductive parameters, and then used U.S. EPA's in vitro high-throughput screening (HTS) database (ToxCastDB) to profile their bioactivity across approximately 800 molecular and cellular features.

RESULTS

A phenotypic hierarchy of testicular atrophy, sperm effects, tumors, and malformations, a composite resembling the human testicular dysgenesis syndrome (TDS) hypothesis, was observed in 281 chemicals. A subset of 54 chemicals with male developmental consequences had in vitro bioactivity on molecular targets that could be condensed into 156 gene annotations in a bipartite network.

CONCLUSION

Computational modeling of available in vivo and in vitro data for chemicals that produce adverse effects on male reproductive end points revealed a phenotypic hierarchy across animal studies consistent with the human TDS hypothesis. We confirmed the known role of estrogen and androgen signaling pathways in rodent TDS, and importantly, broadened the list of molecular targets to include retinoic acid signaling, vascular remodeling proteins, G-protein coupled receptors (GPCRs), and cytochrome P450s.

CITATION

Leung MC, Phuong J, Baker NC, Sipes NS, Klinefelter GR, Martin MT, McLaurin KW, Setzer RW, Darney SP, Judson RS, Knudsen TB. 2016. Systems toxicology of male reproductive development: profiling 774 chemicals for molecular targets and adverse outcomes. Environ Health Perspect 124:1050-1061; http://dx.doi.org/10.1289/ehp.1510385.

Evaluation of a New Molecular Entity as a Victim of Metabolic Drug-Drug Interactions-an Industry Perspective

Under the guidance of the International Consortium for Innovation and Quality in Pharmaceutical Development (IQ), scientists from 20 pharmaceutical companies formed a Victim Drug-Drug Interactions Working Group. This working group has conducted a review of the literature and the practices of each company on the approaches to clearance pathway identification (fCL), estimation of fractional contribution of metabolizing enzyme toward metabolism (fm), along with modeling and simulation-aided strategy in predicting the victim drug-drug interaction (DDI) liability due to modulation of drug metabolizing enzymes. Presented in this perspective are the recommendations from this working group on: 1) strategic and experimental approaches to identify fCL and fm, 2) whether those assessments may be quantitative for certain enzymes (e.g., cytochrome P450, P450, and limited uridine diphosphoglucuronosyltransferase, UGT enzymes) or qualitative (for most of other drug metabolism enzymes), and the impact due to the lack of quantitative information on the latter. Multiple decision trees are presented with stepwise approaches to identify specific enzymes that are involved in the metabolism of a given drug and to aid the prediction and risk assessment of drug as a victim in DDI. Modeling and simulation approaches are also discussed to better predict DDI risk in humans. Variability and parameter sensitivity analysis were emphasized when applying modeling and simulation to capture the differences within the population used and to characterize the parameters that have the most influence on the prediction outcome.

Reduction of hyperbilirubinemia with hypericum extract (St. John's Wort) in a patient with Crigler-Najjar syndrome type II

AIMS

Crigler-Najjar syndrome (CN) type II is a congenital disease with unconjugated hyperbilirubinemia due to a deficiency of uridine 5'-diphospho-glucuronosyltransferase 1A1. Since the currently proposed treatment with phenobarbital is associated with adverse reactions, we investigated the effect of hypericum extract.

METHODS

Repetitive determination of total serum bilirubin in a female with CN type II before, during and after daily treatment with 900 mg hypericum extract on two occasions for 8 weeks. Confirmation of the enzyme-inducing effect of hypericum using the cytochrome P450 3A4 probe drug i.v. midazolam.

RESULTS

Hypericum reduced midazolam exposure by 42% and the total serum bilirubin concentration by 30 to 35%.

CONCLUSIONS

Hypericum extract is a potential alternative to phenobarbital in patients with CN type II.