Hormonal regulation of CYP1A expression

The shared pathoetiological effects of particulate air pollution and the social environment on fetal-placental development

Exposure to particulate air pollution and socioeconomic risk factors are shown to be independently associated with adverse pregnancy outcomes; however, their confounding relationship is an epidemiological challenge that requires understanding of their shared etiologic pathways affecting fetal-placental development. The purpose of this paper is to explore the etiological mechanisms associated with exposure to particulate air pollution in contributing to adverse pregnancy outcomes and how these mechanisms intersect with those related to socioeconomic status. Here we review the role of oxidative stress, inflammation and endocrine modification in the pathoetiology of deficient deep placentation and detail how the physical and social environments can act alone and collectively to mediate the established pathology linked to a spectrum of adverse pregnancy outcomes. We review the experimental and epidemiological literature showing that diet/nutrition, smoking, and psychosocial stress share similar pathways with that of particulate air pollution exposure to potentially exasperate the negative effects of either insult alone. Therefore, socially patterned risk factors often treated as nuisance parameters should be explored as potential effect modifiers that may operate at multiple levels of social geography. The degree to which deleterious exposures can be ameliorated or exacerbated via community-level social and environmental characteristics needs further exploration.

The role of androgens in experimental rodent mammary carcinogenesis

Breast cancer is currently the most frequent, fatal cancer of women in western countries. While estrogens have a widely understood involvement in breast cancer, a significant but not yet fully understood role for androgens has also been suggested. The principal androgen, testosterone, is the obligate steroidal precursor of estradiol, but can equally be metabolized into dihydrotestosterone, a more potent, pure androgen. Both androgens exert their distinctive biological effects via the androgen receptor, which is coexpressed with estrogen receptor alpha in 80 to 90% of breast cancers. The hormonal control of breast development and pathology has been examined experimentally through the use of animal models, notably mice and rats. This review summarizes the data from experimental rodent models on the effects of androgens in experimental breast cancer, aiming to address the importance of androgens and the androgen receptor in the origins and pathogenesis of breast cancers, as well as to discuss potential biomarker and therapeutic opportunities arising from novel insights based on the experimental research.

SIN3A, generally regarded as a transcriptional repressor, is required for induction of gene transcription by the aryl hydrocarbon receptor

CYP1A1 bioactivates several procarcinogens and detoxifies several xenobiotic compounds. Transcription of CYP1A1 is highly induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) via the aryl hydrocarbon receptor. We recently described an RNAi high throughput screening performed in the Hepa-1 mouse hepatoma cell line, which revealed that SIN3A is necessary for the induction of CYP1A1-dependent ethoxyresorufin-o-deethylase (EROD) enzymatic activity by TCDD. In the current studies, we sought to provide insight into the role of SIN3A in this process, particularly because studies on SIN3A have usually focused on its repressive activity on transcription. We report that ectopic expression of human SIN3A in Hepa-1 cells enhanced EROD induction by TCDD and efficiently rescued TCDD induction of EROD activity in cells treated with an siRNA to mouse SIN3A, thus validating a role for SIN3A in CYP1A1 induction. We demonstrate that SIN3A is required for TCDD induction of the CYP1A1 protein in Hepa-1 cells but not for expression of the aryl hydrocarbon receptor protein. In addition, siRNAs for SIN3A decreased TCDD-mediated induction of CYP1A1 mRNA and EROD activity in human hepatoma cell line Hep3B. We establish that TCDD treatment of Hepa-1 cells rapidly increases the degree of SIN3A binding to both the proximal promoter and enhancer of the Cyp1a1 gene and demonstrate that increased binding to the promoter also occurs in human Hep3B, HepG2, and MCF-7 cells. These studies establish that SIN3A physically interacts with the CYP1A1 gene and extends the transcriptional role of SIN3A to a gene that is very rapidly and dramatically induced.

Benzo[a]pyrene modulates the biotransformation, DNA damage and cortisol level of red sea bream challenged with lipopolysaccharide

In animals, biotransformation and the immune system interact with each other, however, knowledge of the toxic mechanism of benzo[a]pyrene (BaP) on these two systems is not well known. The present study investigated the toxic effects of BaP on the biotransformation system, cortisol level and DNA integrity of red sea bream (Pagrus major). The results showed that cortisol level was induced under the challenge of lipopolysaccharide (LPS). Short-term exposure (96 h) of BaP at environmental concentration significantly increased the cortisol level, hepatic EROD activity and CYP1A1 mRNA expression. When P. major was exposed to BaP for 14 d followed by LPS challenge this increased the cortisol level, EROD activity and hepatic DNA damage except CYP1A1 mRNA expression. Combined with our previous data, which showed that BaP exposure can modulate the immunologic response in P. major challenged with LPS, a hypothetical adverse outcome pathway of BaP on fish was suggested.

Cytochrome P450 enzyme regulation by glucocorticoids and consequences in terms of drug interaction

INTRODUCTION

Due to their multiple effects, glucocorticoids (GCs) have versatile medical uses. They can regulate many xenobiotic-metabolizing enzymes of the cytochrome P450 (CYP) superfamily, and thus, influence pharmacotherapy.

AREAS COVERED

The aim of this paper is to summarize the molecular effects of GCs on CYP as well as the available clinical evidence on drug-drug interactions (DDIs) between GCs and other drugs in which GCs influence the metabolism of other medicines through modifying CYP activity. We used the factographic database DRUGDEX® along with bibliographic searches.

EXPERT OPINION

Most of the literature reported CYP3A4 induction by GCs, but this was not proved in all research. As the conclusions on these DDIs are conflicting, there are several issues to be considered like the dosage of GCs, the length of GCs treatment and concomitant therapy, all of which can have an additive inducing effect. Further, in designing a DDI study, crossover studies are preferred. A literature search of the abovementioned information resources provided dissimilar results.

Gender matters: estrogen receptor alpha (ERα) and histone deacetylase (HDAC) 1 and 2 control the gender-specific transcriptional regulation of human uridine diphosphate glucuronosyltransferases genes (UGT1A)

BACKGROUND & AIMS

Gender influences incidence, progression, and therapy of hepatogastrointestinal diseases. The aim of this study was to elucidate the molecular mechanism of gender-specific UDP-glucuronosyltransferases (UGT1A) regulation, representing important hepatogastrointestinal detoxification enzymes for xenobiotics, drugs, and endobiotics.

METHODS

UGT1A-gene activation was studied by reporter gene experiments and estrogen receptor alpha (ESR1/ERα) co-transfection using KYSE70- and HepG2 cells (male origin), and SW403 cells (female origin). Cell lines, and humanized transgenic UGT1A (htgUGT1A) mice (female/male) were treated with the ERα inhibitor tamoxifen. UGT1A mRNA expression was analyzed by TaqMan PCR, the recruitment of ERα, histone deacetylases (HDAC), and the aryl hydrocarbon receptor (AhR) by chromatin immunoprecipitation (ChIP), and ERα expression in gastrointestinal mouse tissues by Western blot and immunofluorescence.

RESULTS

In KYSE70 cells (male), UGT1A gene expression was induced 5-10 fold, and inhibited in the presence of ERα by 55-77%. In SW403 (female) cells, absent inducibility was restored after tamoxifen treatment. In the jejunum and colon of tgUGT1A mice, UGT1A induction that was exclusively detected in male mice could be restored in female mice after tamoxifen pre-treatment. ChIP assays demonstrated the recruitment of ERα and HDACs to the xenobiotic response elements of UGT1A promoters during gene repression. Western blot showed higher ERα expression in the female jejunum and colon.

CONCLUSIONS

We show gender-specific transcriptional control of UGT1A genes in jejunum and colon, which is repressed by ERα and the recruitment of HDCAs to the UGT1A promoter sequence in females. A molecular mechanism controlling gender-specific drug metabolism and its therapeutic reversal is demonstrated.

Dexamethasone accelerates degradation of aryl hydrocarbon receptor (AHR) and suppresses CYP1A1 induction in placental JEG-3 cell line

The JEG-3 choriocarcinoma cell line has been proposed as a model cell line of human placental trophoblast for induction studies via aryl hydrocarbon receptor (AHR). We examined whether glucocorticoid dexamethasone influences AHR-mediated induction of CYP1A1 enzyme in the JEG-3 cell line. We found that dexamethasone dose- and time-dependently suppresses CYP1A1 transactivation in gene reporter assays, CYP1A1 mRNA induction, and upregulation of 7-ethoxyresorufin-O-deethylase (EROD) activity by 3-methylcholanthrene (MC) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in JEG-3 cells. Co-transfection of JEG-3 cells with glucocorticoid receptor (GR) expression construct and treatment with dexamethasone abolished the effect of MC on CYP1A1 promoter construct in transient transfection gene reporter assays. RU486, a GR antagonist, suppressed the effect of dexamethasone on MC-induced transactivation of AHR responsive reporter constructs. We also found that dexamethasone stimulates both ligand-dependent and ligand-independent degradation of AHR but not of aryl hydrocarbon receptor nuclear translocator (ARNT) protein in JEG-3 cells. In experiments with proteasome inhibitors MG132 and bortezomib, we found that the degradation is not sensitive to proteasome inhibition in JEG-3. We can conclude that dexamethasone suppresses AHR-mediated CYP1A1 induction in JEG-3 cells through the unique mechanism of AHR-GR crosstalk, which involves accelerated degradation of AHR.

Genome-wide RNAi high-throughput screen identifies proteins necessary for the AHR-dependent induction of CYP1A1 by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The aryl hydrocarbon receptor (AHR) has a plethora of physiological roles, and upon dysregulation, carcinogenesis can occur. One target gene of AHR encodes the xenobiotic and drug-metabolizing enzyme CYP1A1, which is inducible by the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) via the AHR. An siRNA library targeted against over 5600 gene candidates in the druggable genome was used to transfect mouse Hepa-1 cells, which were then treated with TCDD, and subsequently assayed for CYP1A1-dependent ethoxyresorufin-o-deethylase (EROD) activity. Following redundant siRNA activity (RSA) statistical analysis, we identified 93 hits that reduced EROD activity with a p value ≤ .005 and substantiated 39 of these as positive hits in a secondary screening using endoribonuclease-prepared siRNAs (esiRNAs). Twelve of the corresponding gene products were subsequently confirmed to be necessary for the induction of CYP1A1 messenger RNA by TCDD. None of the candidates were deficient in aryl hydrocarbon nuclear translocator expression. However 6 gene products including UBE2i, RAB40C, CRYGD, DCTN4, RBM5, and RAD50 are required for the expression of AHR as well as for induction of CYP1A1. We also found 2 gene products, ARMC8 and TCF20, to be required for the induction of CYP1A1, but our data are ambiguous as to whether they are required for the expression of AHR. In contrast, SIN3A, PDC, TMEM5, and CD9 are not required for AHR expression but are required for the induction of CYP1A1, implicating a direct role in Cyp1a1 transcription. Our methods, although applied to Cyp1a1, could be modified for identifying proteins that regulate other inducible genes.

Metabolism of the environmental toxicant benzo(a)pyrene by subcellular fractions of human ovary

Knowledge of the ability of the female reproductive system to metabolize environmental chemicals is critical not only from the standpoint of toxicity but also from infertility risk assessment. Benzo(a)pyrene (BaP) is a toxicant that is released into the environment from automobile exhausts, cigarette smoke, burning of refuse, industrial emissions, and hazardous waste sites. In exposed animals, BaP becomes activated to reactive metabolites that interfere with target organ function and as a consequence cause toxicity. Studies on animal models conducted in our laboratories and those of others have shown that BaP possess endocrine disrupting properties. Thus, this chemical has the potential to cause infertility and cancers in the female genital tract. An understanding of BaP metabolism in the female reproductive system will be of importance in the diagnosis and management of female fertility as well as cancers in the reproductive tissues. Therefore, the objective of our study was to examine the metabolism of BaP by human ovarian subcellular fractions. Human ovary samples (eight individuals) were obtained from postoperative tissue removed from subjects with uterine tumors. Subcellular fractions (nuclear, cytosolic, mitochondrial, and microsomal) were prepared by differential centrifugation. BaP (1 μM and 3 μM) was individually incubated with individual subcellular fractions for 15 min and the products were analyzed by high-performance liquid chromatography. Among the different fractions tested, microsomal BaP metabolism was higher than the rest of the fractions. The BaP metabolites identified were as follows: BaP-9,10-diol, BaP-4,5-diol, BaP-7,8-diol, 9(OH) BaP, 3(OH) BaP, BaP-1,6-dione, BaP-3,6-dione, and BaP-6,12-dione. Of interest was the presence of DNA-reactive metabolites such as BaP-3,6-dione, BaP-6,12-dione, and BaP 7,8-diol, which have been implicated in the causation of infertility and cancer. Our results indicate that women who are exposed to BaP via cigarette smoke, occupational settings, and diet are more likely at a larger risk of this toxicant-induced infertility and cancer than others.

GFP transgenic medaka (Oryzias latipes) under the inducible cyp1a promoter provide a sensitive and convenient biological indicator for the presence of TCDD and other persistent organic chemicals

Persistent organic pollutants (POPs) are resistant to environmental degradation and can cause multitude of health problems. Cytochrome P450 1A (Cyp1a) is often up-regulated by POPs through the activation of aryl hydrocarbon receptor (AhR) pathway and is thus usually used as a biomarker for xenobiotics exposure. To develop a convenient in vivo tool to monitor xenobiotic contamination in the water, we have established GFP transgenic medaka using the inducible cyp1a promoter, Tg(cyp1a:gfp). Here we tested Tg(cyp1a:gfp) medaka at three different stages, prehatching embryos, newly hatched fry and adult with 2,3,7,8-tetrachlorodiebnzo-p-dioxin (TCDD), a dioxin. While GFP induction was observed in all three stages, newly hatched fry were the most sensitive with the lowest observed effective concentration of 0.005 nM or 16.1 ng/L. The highly sensitive organs included the kidney, liver and intestine. With high concentrations of TCDD, several other organs such as the olfactory pit, tail fin, gills, lateral line neuromast cells and blood vessels also showed GFP expression. In addition, Tg(cyp1a:gfp) medaka fry also responded to two other AhR agonists, 3-methylcholanthrene and benzo[a]pyrene, for GFP induction, but no significant GFP induction was observed towards several other chemicals tested, indicating the specificity of this transgenic line. The GFP inducibility of Tg(cyp1a:gfp) medaka at both fry and adult stages may be useful for development of high-throughput assays as well as online water monitoring system to detect xenobiotic toxicity.

Pelargonidin activates the AhR and induces CYP1A1 in primary human hepatocytes and human cancer cell lines HepG2 and LS174T

We examined the effects of anthocyanidins (cyanidin, delphinidin, malvidin, peonidin, petunidin, pelargonidin) on the aryl hydrocarbon receptor (AhR)-CYP1A1 signaling pathway in human hepatocytes, hepatic HepG2 and intestinal LS174T cancer cells. AhR-dependent reporter gene expression in transfected HepG2 cells was increased by pelargonidin in a concentration-dependent manner at 24h. Similarly, pelargonidin induced the expression of CYP1A1 mRNA up to 5-fold in HepG2 and LS174T cells relative to the induction by 5 nM 2,3,7,8-tetrachlorodibenzodioxin (TCDD), the most potent activator of AhR. CYP1A1 and CYP1A2 mRNAs were also increased by pelargonidin in three primary human hepatocytes cultures (approximately 5% of TCDD potency) and the increase in CYP1A1 protein in HepG2 and LS174T cells was comparable to the increase in catalytic activity of CYP1A1 enzyme. Ligand binding analysis demonstrated that pelargonidin was a weak ligand of AhR. Enzyme kinetic analyses using human liver microsomes revealed inhibition of CYP1A1 activity by delphinidin (IC50 78 μM) and pelargonidin (IC50 33 μM). Overall, although most anthocyanidins had no effects on AhR-CYP1A1 signaling, pelargonidin can bind to and activate the AhR and AhR-dependent gene expression, and pelargonidin and delphinidin inhibit the CYP1A1 catalytic activity.

The synthetic progestin levonorgestrel is a potent androgen in the three-spined stickleback (Gasterosteus aculeatus)

The use of progestins has resulted in contamination of aquatic environments and some progestins have in experimental studies been shown to impair reproduction in fish and amphibians at low ng L(-1) concentrations. The mechanisms underlying their reproductive toxicity are largely unknown. Some progestins, such as levonorgestrel (LNG), exert androgenic effects in mammals by activating the androgen receptor (AR). Male three-spined stickleback (Gasterosteus aculeatus) kidneys produce spiggin, a gluelike glycoprotein used in nest building, and its production is directly governed by androgens. Spiggin is normally absent in females but its production in female kidneys can be induced by AR agonists. Spiggin serves as the best known biomarker for androgens in fish. We exposed adult female sticklebacks to LNG at 5.5, 40, and 358 ng L(-1) for 21 days. Androgenic effects were found at LNG concentrations ≥40 ng L(-1) including induction of spiggin transcription, kidney hypertrophy, and suppressed liver vitellogenin transcription. These are the first in vivo quantitative data showing that LNG is a potent androgen in fish supporting the contention that androgenic effects of certain progestins contribute to their reproductive toxicity.

Cytochrome P4501A mRNA and protein induction in striped bass (Morone saxatilis)

The striped bass (Morone saxatilis) supports a valuable recreational fishery and is among the most important piscivorous fish of the San Francisco Estuary. This species has suffered a significant decline in numbers over the past decades, and there is indication that contaminants are important contributors. Polycyclic aromatic hydrocarbons (PAHs) and polyhalogenated aromatic hydrocarbons (PHAHs) including PCBs and dioxins are widespread in the estuary, they typically bioaccumulate through trophic levels, reaching highest levels in top predators and are known to affect the fish health and development. The aim of this study was to investigate the dynamics of cytochrome P4501A (Cyp1a) induction simultaneously at different levels of biological organization (RNA transcription and protein synthesis) as a biomarker of exposure to PAHs and PHAHs. We utilized β-naphthoflavone (BNF) as a model PAH to induce Cyp1a responses in juvenile striped bass in both dose-response and time-response assessments and determined Cyp1a mRNA and protein levels. Significant responses were measured in both systems at 10 mg ΒΝF kg⁻¹, a concentration used for time-response studies. Messenger RNA levels peaked at 6 h post-injection, while protein levels increased progressively with time, significantly peaking at 96 h post-injection; both remaining elevated throughout the duration of the test (8 days). Our data suggest that rapid induction of gene transcription following exposure and subsequent cumulative protein synthesis could provide a useful means of identifying temporal variants in exposure to Cyp1a inducers in Morone saxatilis. The potential application of this combined Cyp1a gene and protein biomarker in this species for field studies is discussed.

Cross-species comparisons of transcriptomic alterations in human and rat primary hepatocytes exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

A toxicogenomics approach was used to qualitatively and quantitatively compare the gene expression changes in human and rat primary hepatocytes exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Hepatocytes from five individual rats and five individual humans were exposed for 24 h to 11 concentrations of TCDD ranging from 0.00001 to 100nM and a vehicle control. Gene expression changes were analyzed using whole-genome microarrays containing 13,002 orthologs. Significant changes in expression of individual orthologs at any concentration (fold change [FC] ± 1.5 and false discovery rate < 0.05) were higher in the rat (1547) compared with human hepatocytes (475). Only 158 differentially expressed orthologs were common between rats and humans. Enrichment analysis was performed on the differentially expressed orthologs in each species with 49 and 34 enriched human and rat pathways, respectively. Only 12 enriched pathways were shared between the two species. The results demonstrate significant cross-species differences in expression at both the gene and pathway level. Benchmark dose analysis of gene expression changes showed an average 18-fold cross-species difference in potency among differentially expressed orthologs with the rat more sensitive than the human. Similar cross-species differences in potency were observed for signaling pathways. Using the maximum FC in gene expression as a measure of efficacy, the human hepatocytes showed on average a 20% lower efficacy among the individual orthologs showing differential expression. The results provide evidence for divergent cross-species gene expression changes in response to TCDD and are consistent with epidemiological and clinical evidence showing humans to be less sensitive to TCDD-induced hepatotoxicity.

Exactly the same but different: promiscuity and diversity in the molecular mechanisms of action of the aryl hydrocarbon (dioxin) receptor

The Ah receptor (AhR) is a ligand-dependent transcription factor that mediates a wide range of biological and toxicological effects that result from exposure to a structurally diverse variety of synthetic and naturally occurring chemicals. Although the overall mechanism of action of the AhR has been extensively studied and involves a classical nuclear receptor mechanism of action (i.e., ligand-dependent nuclear localization, protein heterodimerization, binding of liganded receptor as a protein complex to its specific DNA recognition sequence and activation of gene expression), details of the exact molecular events that result in most AhR-dependent biochemical, physiological, and toxicological effects are generally lacking. Ongoing research efforts continue to describe an ever-expanding list of ligand-, species-, and tissue-specific spectrum of AhR-dependent biological and toxicological effects that seemingly add even more complexity to the mechanism. However, at the same time, these studies are also identifying and characterizing new pathways and molecular mechanisms by which the AhR exerts its actions and plays key modulatory roles in both endogenous developmental and physiological pathways and response to exogenous chemicals. Here we provide an overview of the classical and nonclassical mechanisms that can contribute to the differential sensitivity and diversity in responses observed in humans and other species following ligand-dependent activation of the AhR signal transduction pathway.

Transcriptional profiling of human liver identifies sex-biased genes associated with polygenic dyslipidemia and coronary artery disease

Sex-differences in human liver gene expression were characterized on a genome-wide scale using a large liver sample collection, allowing for detection of small expression differences with high statistical power. 1,249 sex-biased genes were identified, 70% showing higher expression in females. Chromosomal bias was apparent, with female-biased genes enriched on chrX and male-biased genes enriched on chrY and chr19, where 11 male-biased zinc-finger KRAB-repressor domain genes are distributed in six clusters. Top biological functions and diseases significantly enriched in sex-biased genes include transcription, chromatin organization and modification, sexual reproduction, lipid metabolism and cardiovascular disease. Notably, sex-biased genes are enriched at loci associated with polygenic dyslipidemia and coronary artery disease in genome-wide association studies. Moreover, of the 8 sex-biased genes at these loci, 4 have been directly linked to monogenic disorders of lipid metabolism and show an expression profile in females (elevated expression of ABCA1, APOA5 and LDLR; reduced expression of LIPC) that is consistent with the lower female risk of coronary artery disease. Female-biased expression was also observed for CYP7A1, which is activated by drugs used to treat hypercholesterolemia. Several sex-biased drug-metabolizing enzyme genes were identified, including members of the CYP, UGT, GPX and ALDH families. Half of 879 mouse orthologs, including many genes of lipid metabolism and homeostasis, show growth hormone-regulated sex-biased expression in mouse liver, suggesting growth hormone might play a similar regulatory role in human liver. Finally, the evolutionary rate of protein coding regions for human-mouse orthologs, revealed by dN/dS ratio, is significantly higher for genes showing the same sex-bias in both species than for non-sex-biased genes. These findings establish that human hepatic sex differences are widespread and affect diverse cell metabolic processes, and may help explain sex differences in lipid profiles associated with sex differential risk of coronary artery disease.

Regulation of drug-metabolizing cytochrome P450 enzymes by glucocorticoids

The regulation of drug-metabolizing cytochrome P450 enzymes (CYP) is a complex process involving multiple mechanisms. Among them, transcriptional regulation through ligand-activated nuclear receptors is the crucial mechanism involved in hormone-controlled and xenobiotic-induced expression of drug-metabolizing CYPs. In this article, we focus, in detail, on the role of the glucocorticoid receptor (GR) in the transcriptional regulation of human drug-metabolizing CYP enzymes and the mechanisms of the regulation. There are at least three distinct transcriptional mechanisms by which GR controls the expression of CYPs: 1) direct binding of GR to a specific gene-promoter sequence called the glucocorticoid responsive element (GRE); 2) indirect binding of GR in the form of a multiprotein complex to gene promoters without a direct contact between GR and promoter DNA; and 3) up- or downregulation of other CYP transcriptional regulators or nuclear receptors (i.e., transcriptional regulatory cross-talk). However, due to the general effect of glucocorticoids on numerous cellular pathways and functions, the net transcriptional effect of glucocorticoids on drug-metabolizing enzymes is usually a combination of several mechanisms. Since synthetic glucocorticoids are widely prescribed in human pharmacotherapy for the treatment of many diseases, comprehensive understanding of the transcriptional regulation of drug-metabolizing CYPs via GR with respect to glucocorticoid therapy or glucocorticoid hormonal status will aid in the development of efficient individualized pharmacotherapy without drug-drug interactions.

Molecular mechanisms of cold-induced CYP1A activation in rat liver microsomes

Cytochrome P4501A (the CYP1A1 and CYP1A2 enzymes) is known to metabolize anthropogenic xenobiotics to carcinogenic and mutagenic compounds. CYP1A1 transcriptional activation is regulated via the aryl hydrocarbon receptor (AhR)-dependent signal transduction pathway. CYP1A2 activation may occur through the AhR-dependent or AhR-independent signal transduction pathways. We used male Wistar rats to explore possible mechanisms of CYP1A activation induced by exposure to cold and the effects of the protein-tyrosine kinase inhibitors genistein, herbimycin A, and geldanamycin on the properties of hepatic CYP1A1 and CYP1A2 proteins following exposure to cold and to classic CYP1A inducers. The molecular mechanisms of cold-induced CYP1A1 and CYP1A2 activation are different. The CYP1A2 activation apparently occurs at the post-transcriptional level. The CYP1A1 activation, whether caused by exposure to cold or by classic CYP1A inducers, is AhR-dependent and occurs at the transcriptional level. Protein tyrosine kinase inhibitors have no effect on benzo(a)pyrene-induced CYP1A expression but alter cold-induced CYP1A1 activity and the CYP1A1 mRNA level. Thus, treatment with herbimycin A or geldanamycin leads to an increase in CYP1A1 activity, while treatment with genistein increases CYP1A1 mRNA expression and decreases CYP1A2 activity. These data elucidate the molecular mechanisms of cold-induced CYP1A activation and the role of protein kinases in the regulation of CYP1A during exposure to cold. Our results can also help identify the differences between the molecular mechanisms underlying the effects of the classic CYP1A inducers and the effects of cooling.

Role of xenobiotic metabolism in cancer: involvement of transcriptional and miRNA regulation of P450s

Cytochrome P450 enzymes (P450s) are important targets in cancer, due to their role in xenobiotic metabolism. Since P450s are the "bridges" between the environment and our body, their function can be linked in many ways to carcinogenesis: they activate dietary and environmental components to ultimate carcinogens (i), the cancer tissue maintains its drug resistance with altered expression of P450s (ii), P450s metabolize (sometimes activate) drugs used for cancer treatment (iii) and they are potential targets for anticancer therapy (iiii). These highly polymorphic enzymes are regulated at multiple molecular levels. Regulation is as important as genetic difference in the existing individual variability in P450 activity. In this review, examples of the transcriptional (DNA methylation, histone modification, modulation by xenosensors) and post-transcriptional (miRNA) regulation will be presented and thereby introduce potential molecular targets at which the metabolism of anticancer drugs, the elimination of cancerogenes or the progress of carcinogenesis could be affected.

Constitutive expression of drug metabolizing enzymes and related transcription factors in cattle testis and their modulation by illicit steroids

In veterinary species, little information about extrahepatic drug metabolism is actually available. Therefore, the presence of foremost drug metabolizing enzymes (DMEs) and related transcription factors mRNAs was initially investigated in cattle testis; then, their possible modulation following the in vivo exposure to illicit growth promoters (GPs), which represent a major issue in cattle farming, was explored. All target genes were expressed in cattle testis, albeit to a lower extent compared to liver ones; furthermore, illicit protocols containing dexamethasone and 17β-oestradiol significantly up-regulated cytochrome P450 1A1, 2E1, oestrogen receptor-α and peroxisome proliferator-activated receptor-α mRNA levels. Overall, the constitutive expression of foremost DMEs and related transcription factors was demonstrated for the first time in cattle testis and illicit GPs were shown to affect pre-transcriptionally some of them, with possible consequences upon testicular xenobiotic drug metabolism.

Effect of seawater transfer on CYP1A gene expression in rainbow trout gills

During the transfer of rainbow trout from freshwater to seawater, the gills have to switch from an ion-absorption epithelium to an ion-secretion epithelium in order to maintain equilibrium of their hydromineral balance. After a change to ambient salinity, several gill modifications have already been demonstrated, including ion transporters. In order to identify new branchial mechanisms implicated in seawater acclimation, we carried out an extensive analysis of gene expression in gills using microarray technology. This strategy allowed us to show that CYP1A gene expression was up-regulated in the gills after salinity transfer. This increase was confirmed by real-time reverse transcription PCR. Furthermore, measurements of CYP1A enzyme activity (EROD) showed a significant increase after transfer to seawater. Immunohistochemistry analysis in the gills revealed that cells with a higher expression of CYP1A protein were principally pillar cells and those in the primary lamellae not in contact with the external medium. The results of this study suggest for the first time that CYP1A may be implicated in the seawater acclimation of the gills of rainbow trout.