Constitutive androstane receptor (CAR) mediates dieldrin-induced liver tumorigenesis in mouse.

Dieldrin has been shown to induce liver tumors selectively in mice. Although the exact mechanism is not fully understood, previous studies from our laboratory and others have shown that dieldrin induced liver tumors in mice through a non-genotoxic mechanism acting on tumor promotion stage. Two studies were performed to examine the role of nuclear receptor activation as a possible mode of action (MOA) for dieldrin-induced mouse liver tumors. In the initial study, male C57BL/6 mice (6- to 8-week old) were treated with dieldrin in diet (10 ppm) for 7, 14, and 28 days. Phenobarbital (PB), beta-naphthoflavone (BNF) and Di (2-ethylhexyl) phthalate (DEHP) were included as positive controls in this study for evaluating the involvement of CAR (constitutive androstane receptor), AhR (aryl hydrocarbon receptor) or PPARα (peroxisome proliferator activated receptor alpha) in the MOA of dieldrin hepatocarcinogenesis. A significant increase in hepatocyte DNA synthesis (BrdU incorporation) was seen in treated mice compared with the untreated controls. Analysis of the expression of the nuclear receptor responsive genes revealed that dieldrin induced a significant increase in the expression of genes specific to CAR activation (Cyp2b10, up to 400- to 2700-fold) and PXR activation (Cyp3a11, up to 5- to 11-fold) over untreated controls. The AhR target genes Cyp1a1 and Cyp1a2 were also slightly induced (2.0- to 3.7-fold and 1.7- to 2.8-fold, respectively). PPARα activation was not seen in the liver following dieldrin treatment. In addition, consistent with previous studies in our lab, treatment with dieldrin produced significant elevation in the hepatic oxidative stress. In a subsequent study using CAR, PXR, and CAR/PXR knockout mice, we confirmed that the dieldrin-induced liver effects in mouse were only mediated by the activation of CAR receptor. Based on these findings, we propose that dieldrin induced liver tumors in mice through a nuclear receptor CAR-mediated mode of action. The previously observed oxidative stress/damage may be an associated or modifying factor in the process of dieldrin-induced liver tumor formation subsequent to the CAR activation.

CRISPR-Cas9-Mutated Pregnane X Receptor (pxr) Retains Pregnenolone-induced Expression of cyp3a65 in Zebrafish (Danio rerio) Larvae.

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.

Interindividual variation in the cytochrome P4501A response to 2,3,7,8-tetrachlorodibenzo-p-dioxin in herring gull embryo hepatocytes.

Exposure to dioxin-like compounds is consistently associated with concentration-dependent induction of cytochrome P4501A (CYP1A) enzymes in primary cultures of avian hepatocytes. We have previously demonstrated that the median effective concentration (EC50) for induction of this response is predictive of in vivo sensitivity to dioxin-like compounds in birds. We investigated sources of interindividual variation in the CYP1A response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in wild herring gulls and considered how this variation may complicate dioxin sensitivity estimates based on the CYP1A bioassay. Concentration-dependent effects of TCDD on CYP1A mRNA expression were characterized in 55 hepatocyte cultures prepared from individual herring gull embryos. A large degree of variability was observed among the hepatocyte culture preparations. For example, 1) basal CYP1A4 and CYP1A5 mRNA expression varied by 20- and 126-fold, respectively, among individuals, and 2) exposure to TCDD induced CYP1A4 mRNA expression by 57-fold in the most responsive sample but did not significantly induce CYP1A4 mRNA expression above baseline values in 42% of hepatocyte culture preparations. Environmental and genetic factors contributing to the observed variability are discussed. Despite the large amount of interindividual variation, we conclude that reproducible EC50-based estimates of species sensitivity can be obtained from the CYP1A cell culture bioassay when samples are collected from relatively uncontaminated colonies. Environ Toxicol Chem 2019;38:660-670. © 2019 SETAC.

Systematic developmental neurotoxicity assessment of a representative PAH Superfund mixture using zebrafish.

Superfund sites often consist of complex mixtures of polycyclic aromatic hydrocarbons (PAHs). It is widely recognized that PAHs pose risks to human and environmental health, but the risks posed by exposure to PAH mixtures are unclear. We constructed an environmentally relevant PAH mixture with the top 10 most prevalent PAHs (SM10) from a Superfund site derived from environmental passive sampling data. Using the zebrafish model, we measured body burden at 48 hours post fertilization (hpf) and evaluated the developmental and neurotoxicity of SM10 and the 10 individual constituents at 24 hours post fertilization (hpf) and 5 days post fertilization (dpf). Zebrafish embryos were exposed from 6 to 120 hpf to (1) the SM10 mixture, (2) a variety of individual PAHs: pyrene, fluoranthene, retene, benzo[a]anthracene, chrysene, naphthalene, acenaphthene, phenanthrene, fluorene, and 2-methylnaphthalene. We demonstrated that SM10 and only 3 of the individual PAHs were developmentally toxic. Subsequently, we constructed and exposed developing zebrafish to two sub-mixtures: SM3 (comprised of 3 of the developmentally toxicity PAHs) and SM7 (7 non-developmentally toxic PAHs). We found that the SM3 toxicity profile was similar to SM10, and SM7 unexpectedly elicited developmental toxicity unlike that seen with its individual components. The results demonstrated that the overall developmental toxicity in the mixtures could be explained using the general concentration addition model. To determine if exposures activated the AHR pathway, spatial expression of CYP1A was evaluated in the 10 individual PAHs and the 3 mixtures at 5 dpf. Results showed activation of AHR in the liver and vasculature for the mixtures and some individual PAHs. Embryos exposed to SM10 during development and raised in chemical-free water into adulthood exhibited decreased learning and responses to startle stimulus indicating that developmental SM10 exposures affect neurobehavior. Collectively, these results exemplify the utility of zebrafish to investigate the developmental and neurotoxicity of complex mixtures.

Ligand characterization of CYP4B1 isoforms modified for high-level expression in Escherichia coli and HepG2 cells.

Human CYP4B1, a cytochrome P450 monooxygenase predominantly expressed in the lung, inefficiently metabolizes classical CYP4B1 substrates, such as the naturally occurring furan pro-toxin 4-ipomeanol (4-IPO). Highly active animal forms of the enzyme convert 4-IPO to reactive alkylating metabolite(s) that bind(s) to cellular macromolecules. By substitution of 13 amino acids, we restored the enzymatic activity of human CYP4B1 toward 4-IPO and this modified cDNA is potentially valuable as a suicide gene for adoptive T-cell therapies. In order to find novel pro-toxins, we tested numerous furan analogs in in vitro cell culture cytotoxicity assays by expressing the wild-type rabbit and variants of human CYP4B1 in human liver-derived HepG2 cells. To evaluate the CYP4B1 substrate specificities and furan analog catalysis, we optimized the N-terminal sequence of the CYP4B1 variants by modification/truncation and established their heterologous expression in Escherichia coli (yielding 70 and 800 nmol·l-1 of recombinant human and rabbit enzyme, respectively). Finally, spectral binding affinities and oxidative metabolism of the furan analogs by the purified recombinant CYP4B1 variants were analyzed: the naturally occurring perilla ketone was found to be the tightest binder to CYP4B1, but also the analog that was most extensively metabolized by oxidative processes to numerous non-reactive reaction products.

Regulation of Cytochrome P450 2B10 (CYP2B10) Expression in Liver by Peroxisome Proliferator-activated Receptor-ß/δ Modulation of SP1 Promoter Occupancy.

Alcoholic liver disease is a pathological condition caused by overconsumption of alcohol. Because of the high morbidity and mortality associated with this disease, there remains a need to elucidate the molecular mechanisms underlying its etiology and to develop new treatments. Because peroxisome proliferator-activated receptor-ß/δ (PPARß/δ) modulates ethanol-induced hepatic effects, the present study examined alterations in gene expression that may contribute to this disease. Chronic ethanol treatment causes increased hepatic CYP2B10 expression inPparß/δ+/+ mice but not in Pparß/δ-/- mice. Nuclear and cytosolic localization of the constitutive androstane receptor (CAR), a transcription factor known to regulate Cyp2b10 expression, was not different between genotypes. PPARγ co-activator 1α, a co-activator of both CAR and PPARß/δ, was up-regulated in Pparß/δ+/+ liver following ethanol exposure, but not in Pparß/δ-/- liver. Functional mapping of the Cyp2b10 promoter and ChIP assays revealed that PPARß/δ-dependent modulation of SP1 promoter occupancy up-regulated Cyp2b10 expression in response to ethanol. These results suggest that PPARß/δ regulates Cyp2b10 expression indirectly by modulating SP1 and PPARγ co-activator 1α expression and/or activity independent of CAR activity. Ligand activation of PPARß/δ attenuates ethanol-induced Cyp2b10 expression in Pparß/δ+/+ liver but not in Pparß/δ-/- liver. Strikingly, Cyp2b10 suppression by ligand activation of PPARß/δ following ethanol treatment occurred in hepatocytes and was mediated by paracrine signaling from Kupffer cells. Combined, results from the present study demonstrate a novel regulatory role of PPARß/δ in modulating CYP2B10 that may contribute to the etiology of alcoholic liver disease.

Higher gene expression of CYP1A2, 2B1 and 2D2 in the brain of female compared with male rats.

Cytochrome P450 (CYP) in the brain plays an essential role in the local metabolism of various compounds, including clinically used drugs, toxins, and endogenous substances. In the present study, we compared the expression profiles of mRNAs for several CYP subtypes in the brain between male and female rats. The expression of CYP1A2, CYP2B1, and CYP2D2 in females was significantly higher than that in males. On the other hand, the expression level of the other CYP subtypes examined in the male brain was similar to that in the female brain. These results strongly suggest that marked gender differences exist in the expression profiles of some CYP subtypes in rat brain.

Comparative study of CYP2B1/2 induction and the transport of bilirubin and taurocholate in rat hepatocyte-mono- and hepatocyte-Kupffer cell co-cultures.

INTRODUCTION: Hepatocyte-Kupffer cell (KC) co-cultures represent a promising approach for in vitro modeling of complex interactions between parenchymal and non-parenchymal cells in the liver, responsible for drug-induced liver injury (DILI). In this study we aimed to compare hepatocyte monocultures with hepatocyte-KC co-cultures regarding some basic liver functions associated with the chemical defense system. These pathways involve transporters and enzymes the function of which is highly sensitive towards hepatotoxic events. METHODS: CYP2B1/2 induction and the biliary and sinusoidal elimination of bilirubin (B) and taurocholate (TC) were studied in rat hepatocyte sandwich cultures compared with rat hepatocyte-KC sandwich co-cultures of 1:0, 6:1, 2:1 and 1:1 cell combinations representing the physiologic and pathologic conditions of the liver. RESULTS: KCs decreased phenobarbital inducibility of CYP2B1/2 in a cell ratio dependent manner and activation of KCs by lipopolisacharide (LPS) amplified this effect. Similarly, KCs decreased the transport of B and its glucuronides (BG) in both sinusoidal and canalicular directions resulting in its intracellular accumulation. In contrast, the uptake and the efflux of TC were greater in the co-cultures than in the hepatocyte monocultures. Immuno-labelling of sodium-dependent taurocholate transporter (Ntcp) revealed increased expression of the transporter in the presence of KCs. DISCUSSION: Here we presented that KCs have a direct impact on some hepatocyte functions suggesting that the co-culture model may be more suitable for drug related hepatotoxicity studies than hepatocyte monocultures.

Sex- and isoform-specific mechanism of neuroprotection by transgenic expression of P450 epoxygenase in vascular endothelium.

OBJECTIVE: Cytochrome P450 epoxygenases (CYP) metabolize arachidonic acid to epoxyeicosatrienoic acids (EETs), which exhibit vasodilatory, anti-inflammatory and neuroprotective actions in experimental cerebral ischemia. We evaluated the effect of endothelial-specific CYP overexpression on cerebral blood flow, inflammatory cytokine expression and tissue infarction after focal cerebral ischemia in transgenic mice. APPROACH AND RESULTS: Male and female wild-type and transgenic mice overexpressing either human CYP2J2 or CYP2C8 epoxygenases in vascular endothelium under control of the Tie2 promoter (Tie2-CYP2J2 and Tie2-CYP2C8) were subjected to 60-min middle cerebral artery occlusion (MCAO). Microvascular cortical perfusion was monitored during vascular occlusion and reperfusion using laser-Doppler flowmetry and optical imaging. Infarct size and inflammatory cytokines were measured at 24h of reperfusion by TTC and real-time quantitative PCR, respectively. Infarct size was significantly reduced in both Tie2-CYP2J2 and Tie2-CYP2C8 transgenic male mice compared to corresponding WT male mice (n=10 per group, p<0.05). Tie2-CYP2J2, but not Tie2-CYP2C8 male mice maintained higher blood flow during MCAO; however, both Tie2-CYP2J2 and Tie2-CYP2C8 had lower inflammatory cytokine expression after ischemia compared to corresponding WT males (n=10 per group for CBF and n=3 for cytokines, p<0.05). In females, a reduction in infarct was observed in the caudate-putamen, but not in the cortex or hemisphere as a whole and no differences were observed in blood flow between female transgenic and WT mice (n=10 per group). CONCLUSIONS: Overexpression of CYP epoxygenases in vascular endothelial cells protects against experimental cerebral ischemia in male mice. The mechanism of protection is in part linked to enhanced blood flow and suppression of inflammation, and is both sex- and CYP isoform-specific.

Toxicity and cytochrome P450 1A mRNA induction by 6-formylindolo[3,2-b]carbazole (FICZ) in chicken and Japanese quail embryos.

The tryptophan derivative formylindolo[3,2-b]carbazole (FICZ) binds with high ligand affinity to the aryl hydrocarbon receptor (AHR) and is readily degraded by AHR-regulated cytochrome P450 family 1 (CYP1) enzymes. Whether in vivo exposure to FICZ can result in toxic effects has not been examined and the main objective of this study was to determine if FICZ is embryotoxic in birds. We examined toxicity and CYP1 mRNA induction of FICZ in embryos from chicken (Gallus domesticus) and Japanese quail (Coturnix japonica) exposed to FICZ (2-200µgkg(-1)) by yolk and air sac injections. FICZ caused liver toxicity, embryo mortality, and CYP1A4 and CYP1A5 induction in both species with similar potency. This is in stark contrast to the very large difference in sensitivity of these species to halogenated AHR agonists. We also exposed chicken embryos to a low dose of FICZ (4µgkg(-1)) in combination with a CYP inhibitor, ketoconazole (KCZ). The mixture of FICZ and KCZ was lethal while FICZ alone had no effect at 4µgkg(-1). Furthermore, mixed exposure to FICZ and KCZ caused stronger and more long-lasting hepatic CYP1A4 induction than exposure to each compound alone. These findings indicate reduced biotransformation of FICZ by co-treatment with KCZ as a cause for the enhanced effects although additive AHR activation is also possible. To conclude, FICZ is toxic to bird embryos and it seems reasonable that the toxicity by FICZ involves AHR activation. However, the molecular targets and biological events leading to hepatic damage and mortality are unknown.

Developmental toxicity, EROD, and CYP1A mRNA expression in zebrafish embryos exposed to dioxin-like PCB126.

Dioxin-like PCB126 is a persistent organic pollutant that causes a range of syndromes including developmental toxicity. Dioxins have a high affinity for aryl hydrocarbon receptor (AhR) and induce cytochrome P4501A (CYP1A). However, the role of CYP1A activity in developmental toxicity is less clear. To better understand dioxin induced developmental toxicity, we exposed zebrafish (Danio rerio) embryos to PCB126 at concentrations of 0, 16, 32, 64, and 128 µg L(-1) from 3-h post-fertilization (hpf) to 168 hpf. The embryonic survival rate decreased at 144 and 168 hpf. The fry at 96 hpf displayed gross developmental malformations, including pericardial and yolk sac edema, spinal curvature, abnormal lower jaw growth, and non-inflated swim bladder. The pericardial and yolk sac edema rate significantly increased and the heart rate declined from 96 hpf compared with the controls. PCB126 did not alter the hatching rate. To elucidate the mechanism of PCB126-induced developmental toxicity, we conducted ethoxyresorufin-O-deethylase (EROD) in vivo assay to determine CYP1A enzyme activity, and real-time PCR to study the induction of CYP1A mRNA gene expression in embryo/larval zebrafish at 24, 72, 96, and 132 hpf. In vivo EROD activity was induced by PCB126 at 16 µg L(-1) concentration as early as 72 hpf but significant increases were observed only in zebrafish exposed to 64 and 128 µg L(-1) doses (p < 0.005) at 72, 96, and 132 hpf. Induction of CYP1A mRNA expression was significantly upregulated in zebrafish exposed to 32 and 64 µg L(-1) at 24, 72, 96, and 132 hpf. Overall, the severe pericardial and yolk sac edema and reduced heart rate suggest that heart defects are a sensitive endpoint, and the general trend of dose-dependent increase in EROD activity and induction of CYP1A mRNA gene expression provide evidence that the developmental toxicity of PCB126 to zebrafish embryos is mediated by activation of AhR.

Alternative Multiorgan Initiation-Promotion Assay for Chemical Carcinogenesis in the Wistar Rat.

The medium-term multiorgan initiation-promotion chemical bioassay (diethylnitrosamine, methyl-nitrosourea, butyl-hydroxybutylnitrosamine, dihydroxypropylnitrosamine, dimethylhydrazine [DMBDD]) with the Fischer 344 rat was proposed as an alternative to the conventional 2-year carcinogenesis bioassay for regulatory purposes. The acronym DMBDD stands for the names of five genotoxic agents used for initiation of multiorgan carcinogenesis. The Brazilian Agency for the Environment officially recognized a variation of this assay (DMBDDb) as a valid method to assess the carcinogenic potential of agrochemicals. Different from the original protocol, this DMBDDb is 30-week long, uses Wistar rats and two positive control groups exposed to carcinogenesis promoters sodium phenobarbital (PB) or 2-acetylaminofluorene (2-AAF). This report presents the experience of an academic laboratory with the DMBDDb assay and contributes to the establishment of this alternative DMBDD bioassay in a different rat strain. Frequent lesions observed in positive groups to evaluate the promoting potential of pesticides and the immunohistochemical expressions of liver cytochrome P450 (CYP) 2B1/2B2 and CYP1A2 enzymes were assessed. Commonly affected organs were liver, kidney, intestines, urinary bladder, and thyroid. PB promoting activity was less evident than that of 2-AAF, especially in males. This study provides a repository of characteristic lesions occurring in positive control animals submitted to a modified alternative 2-stage multiorgan protocol for carcinogenesis in Wistar rat.

Expression of hepatic cytochrome P450s and UDP-glucuronosyltransferases in PXR and CAR double humanized mice treated with rifampicin.

Nuclear receptor humanized mice models have been developed to predict regulation of drug metabolizing enzyme by xenobiotics. However, limited information is available concerning xenobiotic-induced regulation of drug metabolizing enzymes in multiple nuclear receptor humanized mice. The present study investigated the hepatic regulation of cytochrome P450s (CYPs) and UDP-glucuronosyltransferases (UGTs) in the pregnane X receptor (PXR) and the constitutive androstane receptor double humanized mice treated with rifampicin (RIF; 10mg/kg) for 4 days. RIF increased hepatic microsomal protein and total CYP contents, and CYP reductase activity in the humanized mice, but not in normal mice. Moreover, hepatic induction of Cyp2b10, Cyp2c, and Cyp3a11 were observed only in the RIF-treated humanized mice, suggesting that the humanized mice are sensitive to RIF with respect to the regulation of the hepatic CYP system. Hepatic UGT activities using estradiol, serotonin, and mefenamic acid, but not chenodeoxycholic acid as substrates, increased in the RIF-treated humanized mice, and the glucuronidation activities of estradiol and chenodeoxycholic acid increased in RIF-treated normal mice. These results raise the possibility that a PXR-independent mechanism may be involved in hepatic regulation of UGTs by RIF.

In vivo induction of CYP in mice by carbamazepine is independent on PXR.

BACKGROUND: The antiepileptic drug carbamazepine (CBZ) is a typical inducer of cytochrome P450 (CYP) 3A and 2C in the clinic. It is considered a strong constitutive androstane receptor activator, however both CBZ and its main metabolite CBZ 10, 11-epoxide have been reported to be pregnane X receptor (PXR) activators whose maximal efficacy and potency are comparable with the human PXR ligand rifampicin. It is unknown whether or not PXR plays a substantially important role in in vivo induction of CYP by CBZ administration. METHODS: In this study, wild type and Pxr-/- mice were administered with CBZ for 5 days. Serum and liver samples were collected and subjected to hepatotoxicity assessment and CYP induction analysis. RESULTS: CYP2b, 2c and 3a were induced similarly in terms of transcription level, enzyme activity and protein abundance in both wild type and Pxr-/- mice. Inductive profile of CYPs in mice by CBZ administration accorded with those reported in rats, but differed from clinically reported data. CONCLUSIONS: These data suggest that in vivo induction of CYP in mice by multiple administration of CBZ is independent of PXR. Knowledge of the featured CYP induction profile in mice helps us understand species related CYP induction profiles among rodents and humans resulting from administration of CBZ.

Permanent uncoupling of male-specific CYP2C11 transcription/translation by perinatal glutamate.

Perinatal exposure of rats and mice to the typically reported 4mg/g bd wt dose of monosodium glutamate (MSG) results in a complete block in GH secretion as well as obesity, growth retardation and a profound suppression of several cytochrome P450s, including CYP2C11, the predominant male-specific isoform--all irreversible effects. In contrast, we have found that a lower dose of the food additive, 2mg/g bd wt on alternate days for the first 9days of life results in a transient neonatal depletion of plasma GH, a subsequent permanent overexpression of CYP2C11 as well as subnormal (mini) GH pulse amplitudes in an otherwise normal adult masculine episodic GH profile. The overexpressed CYP2C11 was characterized by a 250% increase in mRNA, but only a 40 to 50% increase in CYP2C11 protein and its catalytic activity. Using freshly isolated hepatocytes as well as primary cultures exposed to the masculine-like episodic GH profile, we observed normal induction, activation, nuclear translocation and binding to the CYP2C11 promoter of the GH-dependent signal transducers required for CYP2C11 transcription. The disproportionately lower expression levels of CYP2C11 protein were associated with dramatically high expression levels of an aberrant, presumably nontranslated CYP2C11 mRNA, a 200% increase in CYP2C11 ubiquitination and a 70-80% decline in miRNAs associated, at normal levels, with a suppression of CYP2C expression. Whereas the GH-responsiveness of CYP2C7 and CYP2C6 as well as albumin was normal in the MSG-derived hepatocytes, the abnormal expression of CYP2C11 was permanent and irreversible.

Identification and functional characterization of novel feline cytochrome P450 2A.

1. Cytochrome P450s are the major metabolizing enzymes for xenobiotics in humans and other mammals. Although the domestic cat Felis catus, an obligate carnivore, is the most common companion animal, the properties of cytochrome P450 subfamilies are largely unknown. 2. We newly identified the feline CYP2A13, which consists of 494 deduced amino acids, showing the highest identity to CYP2As of dogs, followed by those of pigs, cattle and humans. 3. The feline CYP2A13 transcript and protein were expressed almost exclusively in the liver without particular sex-dependent differences. 4. The feline CYP2A13 protein heterogeneously expressed in Escherichia coli showed metabolic activity similar to those of human and canine CYP2As for coumarin, 7-ethoxycoumarin and nicotine. 5. The results indicate the importance of CYP2A13 in systemic metabolism of xenobiotics in cats.

Impact of Herbal Medicines like Nigella sativa, Trigonella foenum-graecum, and Ferula asafoetida, on Cytochrome P450 2C11 Gene Expression in Rat Liver.

AIM: Combined use of herbs and drugs may result in clinically important herb-drug interactions. The majorities of these interactions are thought to be metabolism-based and involve induction or inhibition of cytochrome P450 (CYP). The current study was designed to investigate the effect of some commonly used herbs on rat CYP2C11 gene expression and metabolic activity. METHODS: Wistar rats were treated for 7 days with increasing doses of 3 herbs; Nigella sativa, Trigonella foenum-graecum, and Ferula asafoetida. Thereafter, CYP2C11 mRNA and protein levels were determined by real-time polymerase chain reaction (RT-PCR) and western blot analyses, respectively. In vitro metabolic activity of CYP2C11 was performed on rat hepatic microsomes using tolbutamide as specific substrate. RESULTS: Our results showed that all the 3 herbs significantly inhibited the mRNA and protein expression levels of CYP2C11 in a dose-dependent manner. Furthermore, the in vitro enzyme metabolic activity study showed a significant decrease in the formation of 4-hyroxy-tolbutamide, a tolbutamide metabolite, at the higher doses. The inhibitory effects of the investigated herbs on rat CYP2C11 was in the order: Nigella Sativa > Trigonella foenum-graecum > Ferula asafoetida. CONCLUSIONS: The 3 herbs are strong inhibitor of CYP2C11 expression, which can lead to an undesirable pharmacological effect of clinically used CYP2C11 substrate drugs with a low therapeutic index.

Ontogeny of the major xenobiotic-metabolizing enzymes expression and the dietary lipids modulatory effect in the rat dimethylbenz(a)anthracene-induced breast cancer model.

Breast cancer is the most common malignancy in women worldwide. Environmental factors such as xenobiotic exposure and lifestyle and nutrition play a key role in its etiology. This study was designed to evaluate the age-related changes in the expression of major xenobiotic-metabolizing enzymes (XMEs) in the rat liver and the mammary gland in the dimethylbenz(a)anthracene-induced breast cancer model. The influence of dietary lipids on the ontogeny of XMEs was also evaluated. mRNA and protein levels of phase I (CYP1A1, CYP1A2, and CYP1B1) and phase II (NAD(P)H:quinone acceptor oxidoreductase 1 and GSTP1) enzymes were analyzed, as well as their regulation by AhR and Nrf2, respectively. Results showed differences in the phase I enzymes expression, whereas little changes were obtained in phase II. High corn oil and olive oil diets differentially influenced the expression of age-related changes, suggesting that the different susceptibility to xenobiotic exposure depending upon the age may be modulated by dietary factors.

Evaluation of Aroclor 1260 exposure in a mouse model of diet-induced obesity and non-alcoholic fatty liver disease.

Polychlorinated biphenyls (PCBs) are persistent organic pollutants associated with non-alcoholic fatty liver disease (NAFLD) in epidemiologic studies. The purpose of this study was to evaluate the hepatic effects of a PCB mixture, Aroclor 1260, whose composition mimics human bioaccumulation patterns, in a mouse model of diet-induced obesity (DIO). Male C57Bl/6J mice were fed control diet or 42% high fat diet (HFD) and exposed to Aroclor 1260 (20mg/kg or 200mg/kg in corn oil) for 12weeks. A glucose tolerance test was performed; plasma/tissues were obtained at necropsy for measurements of adipocytokine levels, histology, and gene expression. Aroclor 1260 exposure was associated with decreased body fat in HFD-fed mice but had no effect on blood glucose/lipid levels. Paradoxically, Aroclor 1260+HFD co-exposed mice demonstrated increased hepatic inflammatory foci at both doses while the degree of steatosis did not change. Serum cytokines, ALT levels and hepatic expression of IL-6 and TNFα were increased only at 20mg/kg, suggesting an inhibition of pro-inflammatory cytokine production at the 200mg/kg exposure. Aroclor 1260 induced hepatic expression of cytochrome P450s including Cyp3a11 (Pregnane-Xenobiotic Receptor target) and Cyp2b10 (constitutive androstane receptor target) but Cyp2b10 inducibility was diminished with HFD-feeding. Cyp1a2 (aryl hydrocarbon Receptor target) was induced only at 200mg/kg. In summary, Aroclor 1260 worsened hepatic and systemic inflammation in DIO. The results indicated a bimodal response of PCB-diet interactions in the context of inflammation which could potentially be explained by xenobiotic receptor activation. Thus, PCB exposure may be a relevant "second hit" in the transformation of steatosis to steatohepatitis.

Clofibric acid induces hepatic CYP 2B1/2 via constitutive androstane receptor not via peroxisome proliferator activated receptor alpha in rat.

Peroxisome proliferator activated receptor α (PPARα) ligands, fibrates used to control hyperlipidemia. We demonstrated CYP2B induction by clofibric acid (CFA) however, the mechanism was not clear. In this study, HepG2 cells transfected with expression plasmid of mouse constitutive androstane receptor (CAR) or PPARα were treated with CFA, phenobarbital (PB) or TCPOBOP. Luciferase assays showed that CFA increased CYP2B1 transcription to the same level as PB, or TCPOBOP in HepG2 transfected with mouse CAR But failed to induce it in PPARα transfected cells. CYP2B expressions were increased with PB or CFA in Wistar female rats (having normal levels of CAR) but not in Wistar Kyoto female rats (having low levels of CAR). The induction of CYP2B by PB or CFA was comparable to nuclear CAR levels. CAR nuclear translocation was induced by CFA in both rat strains. This indicates that fibrates can activate CAR and that fibrates-insulin sensitization effect may occur through CAR, while hypolipidemic effect may operate through PPARα.