Microtubules-interfering agents restrict aryl hydrocarbon receptor-mediated CYP1A2 induction in primary cultures of human hepatocytes via c-jun-N-terminal kinase and glucocorticoid receptor

Transcriptional and Epigenetic Consequences of DMSO Treatment on HepaRG Cells

Dimethyl sulfoxide (DMSO) is used to sustain or favor hepatocyte differentiation in vitro. Thus, DMSO is used in the differentiation protocol of the HepaRG cells that present the closest drug-metabolizing enzyme activities to primary human hepatocytes in culture. The aim of our study is to clarify its influence on liver-specific gene expression. For that purpose, we performed a large-scale analysis (gene expression and histone modification) to determine the global role of DMSO exposure during the differentiation process of the HepaRG cells. The addition of DMSO drives the upregulation of genes mainly regulated by PXR and PPARα whereas genes not affected by this addition are regulated by HNF1α, HNF4α, and PPARα. DMSO-differentiated-HepaRG cells show a differential expression for genes regulated by histone acetylation, while differentiated-HepaRG cells without DMSO show gene signatures associated with histone deacetylases. In addition, we observed an interplay between cytoskeleton organization and EMC remodeling with hepatocyte maturation.

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the proteome of porcine granulosa cells

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a toxic man-made chemical compound contaminating the environment. The exposure of living organisms to TCDD may result in numerous disorders, including reproductive pathologies. By employing two-dimensional fluorescence difference gel electrophoresis we aimed to identify proteins potentially involved in the mechanism of TCDD action and toxicity in porcine granulosa cells. The porcine granulosa cells were treated with TCDD (100 nM) for 3, 12 or 24 h, and afterwards, cytoplasmic proteins were isolated and labeled with cyanines. Next, samples were separated by isoelectric focusing and SDS-PAGE. Proteins of interest were identified by MALDI-TOF/TOF MS analysis. A total of 75 differentially expressed protein spots (p < 0.05 and fold change ≥2.0) were found in granulosa cells treated with TCDD. After 3, 12 and 24 h of TCDD treatment, we were able to identify 29, 34 and 12 spots, respectively. Functional analysis showed that cytoskeletal proteins formed the largest class of proteins significantly affected by TCDD in all time points. We also demonstrated that most of the identified proteins were associated with the "structural constituent of cytoskeleton" and "chaperone binding" Gene Ontology categories. Based on the analysis of the porcine granulosa cell proteome, we demonstrated that TCDD may affect the ovarian follicle fate by the rearrangement of the cytoskeleton and extracellular matrix as well as the modulation of proteins important for the cellular response to stress. The results of the current study present an extended insight into the TCDD mechanism of action in porcine granulosa cells, providing new directions for future functional studies.

In Vivo Toxicity of Solasonine and Its Effects on cyp450 Family Gene Expression in the Livers of Male Mice from Four Strains

Solasonine was reported to inhibit tumour cell growth in several different models. The in vivo toxicity of solasonine, the effects of genetic background on its toxicity, and its possible roles in regulating the expression of cyp450 family genes were still unclear and required characterisation. Here, Horn’s assays were performed on male mice from four different strains, and the expression of cyp450 family genes in their livers was examined by RT-PCR and ELISA. Mice treated by intraperitoneal injection with high levels of solasonine showed immediate post-excitatory depression, intraperitoneal tissue adhesion, and dissolving of cells in the liver. Furthermore, these four mouse strains showed different toxicological sensitivity to solasonine. The strains, in decreasing order of LD50 value, rescuing speed of body weight, and more severe pathological symptoms, were KM, ICR, C57BL/6, and BALB/c. Interestingly, more cyp450 genes were downregulated at the mRNA and/or protein level in the livers of male mice from C57BL/6 or BALB/c strains than those from KM or ICR strains. These results suggest that (1) Solasonine has hepatic toxicity and downregulates cyp450 genes expression at transcriptional and/or post-transcriptional levels; (2) Genetic background is an important factor which can affect the in vivo toxicity; (3) Downregulation of cyp450 gene expression in the liver may be a clue to help understand whether or not a given strain is sensitive to solasonine; (4) Influences on the expression of cyp450 genes should be considered when using solasonine alone, or in combination with other drugs.

Assessment of endocrine disruption potential of essential oils of culinary herbs and spices involving glucocorticoid, androgen and vitamin D receptors

Essential oils (EOs) of culinary herbs and spices are consumed on a daily basis. They are multicomponent mixtures of compounds with already demonstrated biological activities. Taking into account regular dietary intake and the chemical composition of EOs, they may be considered as candidates for endocrine-disrupting entities. Therefore, we examined the effects of 31 EOs of culinary herbs and spices on transcriptional activities of glucocorticoid receptor (GR), androgen receptor (AR) and vitamin D receptor (VDR). Using reporter gene assays in stably transfected cell lines, weak anti-androgen and anti-glucocorticoid activity was observed for EO of vanilla and nutmeg, respectively. Moderate augmentation of calcitriol-dependent VDR activity was caused by EOs of ginger, thyme, coriander and lemongrass. Mixed anti-glucocorticoid and VDR-stimulatory activities were displayed by EOs of turmeric, oregano, dill, caraway, verveine and spearmint. The remaining 19 EOs were inactive against all receptors under investigation. Analyses of GR, AR and VDR target genes by means of RT-PCR confirmed the VDR-stimulatory effects, but could not confirm the anti-glucocorticoid and anti-androgen effects of EOs. In conclusion, although we observed minor effects of several EOs on transcriptional activities of GR, AR and VDR, the toxicological significance of these effects is very low. Hence, 31 EOs of culinary herbs and spices may be considered safe, in terms of endocrine disruption involving receptors GR, AR and VDR.

The comparative effects of diethyldithiocarbamate-copper complex with established proteasome inhibitors on expression levels of CYP1A2/3A4 and their master regulators, aryl hydrocarbon and pregnane X receptor in primary cultures of human hepatocytes

In the recent years, a therapeutic potential of disulfiram (Antabuse) complex with copper, as an anticancer drug, was recognized towards several cancer cell lines. The proteasome was suggested as one of the cellular targets for this compound. As the therapeutic use of diethyldithiocarbamate-copper complex (CuET) is expected to increase, it is of great interest to know whether this compound may be the source of drug-drug interactions via the induction of biotransformation enzymes, especially cytochromes P450 (CYPs). To this purpose, we examined the effect of CuET and compared it with typical inducers (rifampicin and dioxin) of CYPs and with well-established proteasome inhibitors (MG132 and bortezomib). Diethyldithiocarbamate-copper complex revealed inconsistent and rather modulatory effect on the expression of CYP1A2 and CYP3A4 in several cultures of human hepatocytes. Moreover, it was able to cause neither ubiquitin accumulation nor significant and dose-dependent inhibition of proteasome activity. It had no effect on essential transcription factors involved in regulation of selected CYPs, aryl hydrocarbon (AhR) nor pregnane X receptor (PXR). However, the AhR protein was increased in majority of examined hepatocyte cultures. The main finding of this study is that: (i) disulfiram-copper complex is not the cause of drug-drug interactions via CYP1A2/3A4 induction; (ii) proteasome inhibitors may have different impact on studied parameters in given in vitro system.

Long-term culture and cryopreservation does not affect the stability and functionality of human embryonic stem cell-derived hepatocyte-like cells

Human embryonic stem cells (hESCs) are predicted to be an unlimited source of hepatocytes which can pave the way for applications such as cell replacement therapies or as a model of human development or even to predict the hepatotoxicity of drug compounds. We have optimized a 23-d differentiation protocol to generate hepatocyte-like cells (HLCs) from hESCs, obtaining a relatively pure population which expresses the major hepatic markers and is functional and mature. The stability of the HLCs in terms of hepato-specific marker expression and functionality was found to be intact even after an extended period of in vitro culture and cryopreservation. The hESC-derived HLCs have shown the capability to display sensitivity and an alteration in the level of CYP enzyme upon drug induction. This illustrates the potential of such assays in predicting the hepatotoxicity of a drug compound leading to advancement of pharmacology.

Mixture effects between different azoles and β-naphthoflavone on the CYP1A biomarker in a fish cell line

The cytochrome P450 1A (CYP1A) biomarker response was studied in the Poeciliopsis lucida hepatocellular carcinoma (PLHC-1) cell line, which represents a good model for studies on aryl hydrocarbon receptor (AhR) - CYP1A signaling. The PLHC-1 cells were exposed to the prototypical CYP1A inducer and AhR agonist β-naphthoflavone (BNF) in combination with different azoles. Two imidazoles (clotrimazole and prochloraz) and two benzimidazoles (nocodazole and omeprazole) were used. Exposure to clotrimazole, prochloraz and nocodazole resulted in 2-4 fold induction of the CYP1A-mediated ethoxyresorufin-O-deethylase (EROD) activities at 24 and 48h, whereas exposure to the omeprazole for 48h had no effect on the EROD activity. Clotrimazole, nocodazole and prochloraz also acted as inhibitors of EROD activities in situ in PLHC-1 cells (IC50=1.3-7.7μM), whereas omeprazole had no effect on this activity (IC50=72μM). Exposure to 10μM prochloraz resulted in 3-fold induction of CYP1A mRNA and exposure to 10μM nocodazole resulted in 16-fold induction of CYP1A mRNA levels at 24h compared to controls. In the mixture experiments, more-than-additive mixture effects between BNF and the azoles clotrimazole, prochloraz and nocodazole on EROD activities were evident, with nocodazole showing the strongest mixture effect. The presence of nocodazole increased the response to BNF up to 200-fold on CYP1A mRNA and up to 16-fold on EROD activities and prolonged the effect of BNF exposure on EROD activities by 24h or longer. This suggests that azoles that are inhibitors and/or competing substrates for the CYP1A enzymes can cause increased sensitivity to exposures to chemicals that depend on CYP1A metabolism for their elimination in situations of mixed chemical exposures. The results also suggest that the EROD biomarker response can be significantly affected in azole-contaminated areas. The responsiveness of the EROD biomarker to BNF exposure was studied in PLHC-1 that had been pre-treated with nocodazole for 5 or 24h at concentrations that are known to disassemble microtubules at 24h in these cells. Pre-treatment of PLHC-1 cells with nocodazole for either 5 or 24h had no effect on the responsiveness to BNF exposure, which implies that the EROD activity can be induced in cells with disassembled microtubules.

Collagen density regulates xenobiotic and hypoxic response of mammary epithelial cells

Breast density, where collagen I is the dominant component, is a significant breast cancer risk factor. Cell surface integrins interact with collagen, activate focal adhesion kinase (FAK), and downstream cell signals associated with xenobiotics (AhR, ARNT) and hypoxia (HIF-1α, ARNT). We examined if mammary cells cultured in high density (HD) or low density (LD) collagen gels affected xenobiotic or hypoxic responses. ARNT production was significantly reduced by HD culture and in response to a FAK inhibitor. Consistent with a decrease in ARNT, AhR and HIF-1α reporter activation and VEGF production was lower in HD compared to LD. However, P450 production was enhanced in HD and induced by AhR and HIF-1α agonists, possibly in response to increased NF-κB activaton. Thus, collagen density differentially regulates downstream cell signals of AhR and HIF-1α by modulating the activity of FAK, the release of NF-κB transcriptional factors, and the levels of ARNT.

Enantiospecific effects of ketoconazole on aryl hydrocarbon receptor

Azole antifungal ketoconazole (KET) was demonstrated to activate aryl hydrocarbon receptor (AhR). Since clinically used KET is a racemic mixture of two cis-enantiomers (2R,4S)-(+)-KET and (2S,4R)-(-)-KET, we examined the effects of KET enantiomers on AhR signaling pathway. (+)-KET dose-dependently activated AhR in human gene reporter cell line AZ-AHR, and displayed 5-20× higher agonist activity (efficacy), as compared to (-)-KET; both enantiomers were AhR antagonists with equal potency (IC50). Consistently, (+)-KET strongly induced CYP1A1 mRNA and protein in human HepG2 cells, while (-)-KET exerted less than 10% of (+)-KET activity. In primary human hepatocytes, both enantiomers preferentially induced CYP1A2 over CYP1A1 mRNA and protein, and the potency of (+)-KET was slightly higher as compared to (-)-KET. Ligand binding assay with guinea pig liver cytosols revealed that both (+)-KET and (-)-KET are weak ligands of AhR that displaced [3H]-TCDD with comparable potency. Similarly, both enantiomers weakly transformed AhR to DNA-binding form with similar potency, as showed by EMSA, in guinea pig liver cytosolic extracts and nuclear extracts from mouse Hepa-1 cells. We also examined effects of KET on glucocorticoid receptor (GR), a regulator of AhR activity. Both KET enantiomers antagonized GR with similar potency, as revealed by gene reporter assay in AZ-GR cell line and down-regulation of tyrosine aminotransferase mRNA in human hepatocytes. Finally, we demonstrate enantiospecific antifungal activities of KET enantiomers in six Candida spp. strains. In conclusion, the significance of current study is providing the first evidence of enatiospecific effects of cis-enantiomers of ketoconazole on AhR-CYP1A pathway.

Interactions of pharmaceuticals and other xenobiotics on key detoxification mechanisms and cytoskeleton in Poeciliopsis lucida hepatocellular carcinoma, PLHC-1 cell line

Fish are exposed to chemicals, including pharmaceuticals, in their natural habitat. This study focuses on effects of chemicals, including nine classes of pharmaceuticals, on key detoxification mechanisms in a fish liver cell-line (PLHC-1). Chemical interactions were investigated on efflux pumps, P-glycoprotein (Pgp) and multidrug resistance associated proteins (MRP1/MRP2), and on biotransformation enzymes, cytochrome P450 (CYP1A/CYP3A). Diclofenac and troleandomycin inhibited efflux activities, whereas ethinylestradiol activated efflux function. Exposure to troleandomycin and β-naphthoflavone induced MRP2 mRNA levels, but no effects were seen on MRP1 or Pgp expressions. Inhibition of CYP1A activities were seen in cells exposed to α-naphthoflavone, β-naphthoflavone, clotrimazole, nocodazole, ketoconazole, omeprazole, ethinylestradiol, lithocholic acid, rifampicin and troleandomycin. Exposure to fulvestrant, clotrimazole and nocodazole resulted in induction of CYP1A mRNA levels. Although, exposure to nocodazole resulted in disassembled microtubules. A CYP3A-like cDNA sequence was isolated from PLHC-1, but basal expression and activities were low and the gene was not responsive to prototypical CYP3A inducers. Exposure to ibuprofen, lithocholic acid and omeprazole resulted in fragmentation of microtubules. This study revealed multiple interactions on key detoxification systems, which illustrates the importance of study effects on regulation combined with functional studies to provide a better picture of the dynamics of the chemical defense system.

Valproate activates ERK signaling pathway in primary human hepatocytes

AIM

Valproic acid (VPA) is a widely-used anticonvulsant and mood-stabilizing agent. VPA is also known to inhibit histone deacetylases (HDACs) affecting the expression of numerous genes.

METHODS

In the present study, we examined the effect of VPA on the extracellular signal-related kinase (ERK, p42/p44) pathway (Ras-Raf-MEK-ERK) belonging to the mitogen-activated protein kinases (MAPKs) pathways in primary human hepatocytes. In the liver, the pathway is associated with progression of hepatocellular carcinoma.

RESULTS

We found that VPA in a therapeutically relevant concentration (500 µM) activates the ERK pathway, as indicated by increased ERK Thr202/Tyr204 phosphorylation. Interestingly, a prototype HDAC inhibitor, trichostatin A, also activated ERK phosphorylation in primary human hepatocytes. These data suggest that HDAC inhibition might be the primary stimulus for ERK pathway activation in primary human hepatocytes. Notably, U0126, a MEK1 inhibitor, was ineffective in inhibiting ERK pathway activation, likely due to its metabolic deactivation in metabolically competent primary human hepatocytes.

CONCLUSION

We conclude that VPA activates the ERK pathway in primary human hepatocytes.

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.

The interplay between tubulins and P450 cytochromes during Plasmodium berghei invasion of Anopheles gambiae midgut

Background

Plasmodium infection increases the oxidative stress inside the mosquito, leading to a significant alteration on transcription of Anopheles gambiae detoxification genes. Among these detoxification genes several P450 cytochromes and tubulins were differently expressed, suggesting their involvement in the mosquito's response to parasite invasion. P450 cytochromes are usually involved in the metabolism and detoxification of several compounds, but are also regulated by several pathogens, including malaria parasite. Tubulins are extremely important as components of the cytoskeleton, which rearrangement functions as a response to malaria parasite invasion.

Methodology/Principal Findings

Gene silencing methods were used to uncover the effects of cytochrome P450 reductase, tubulinA and tubulinB silencing on the A. gambiae response to Plasmodium berghei invasion. The role of tubulins in counter infection processes was also investigated by inhibiting their effect. Colchicine, vinblastine and paclitaxel, three different tubulin inhibitors were injected into A. gambiae mosquitoes. Twenty-four hours post injection these mosquitoes were infected with P. berghei through a blood meal from infected CD1 mice. Cytochrome P450 gene expression was measured using RT-qPCR to detect differences in cytochrome expression between silenced, inhibited and control mosquitoes. Results showed that cytochrome P450 reductase silencing, as well as tubulin (A and B) silencing and inhibition affected the efficiency of Plasmodium infection. Silencing and inhibition also affected the expression levels of cytochromes P450.

Conclusions

Our results suggest the existence of a relationship between tubulins and P450 cytochromes during A. gambiae immune response to P. berghei invasion. One of the P450 cytochromes in this study, CYP6Z2, stands out as the potential link in this association. Further work is needed to fully understand the role of tubulin genes in the response to Plasmodium infection.

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.

Effects of interleukin-6 (IL-6) and an anti-IL-6 monoclonal antibody on drug-metabolizing enzymes in human hepatocyte culture

The cytokine-mediated suppression of hepatic drug-metabolizing enzymes by inflammatory disease and the relief of this suppression by successful disease treatment have recently become an issue in the development of drug interaction labels for new biological products. This study examined the effects of the inflammatory cytokine interleukin-6 (IL-6) on drug-metabolizing enzymes in human hepatocyte culture and the abrogation of these effects by a monoclonal antibody directed against IL-6. Treatment of human hepatocytes with IL-6 (n = 9 donors) revealed pan-suppression of mRNA of 10 major cytochrome P450 isoenzymes, but with EC(50) values that differed by isoenzyme. Some EC(50) values were above the range of clinically relevant serum concentrations of IL-6. Marker activities for CYP1A2 and CYP3A4 enzyme were similarly suppressed by IL-6 in both freshly isolated and cryopreserved hepatocytes. IL-6 suppressed induction of CYP1A2 enzyme activity by omeprazole and CYP3A4 enzyme activity by rifampicin but only at supraphysiological concentrations of IL-6. Glycosylated and nonglycosylated IL-6 did not significantly differ in their ability to suppress CYP1A2 and CYP3A4 enzyme activity. A monoclonal antibody directed against IL-6 abolished or partially blocked IL-6-mediated suppression of CYP1A2 and CYP3A4 enzyme activity, respectively. These data indicate that experimentation with IL-6 and anti-IL-6 monoclonal antibodies in human hepatocyte primary culture can quantitatively measure cytochrome P450 suppression and desuppression and determine EC(50) values for IL-6 against individual cytochrome P450 isoenzymes. However, the complex biology of inflammatory disease may not allow for quantitative in vitro-in vivo extrapolation of these simple in vitro data.

Human and rat primary hepatocyte CYP1A1 and 1A2 induction with 2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzofuran, and 2,3,4,7,8-pentachlorodibenzofuran

The concentration dose response for aryl hydrocarbon receptor (AHR)-mediated CYP1A1 and CYP1A2 messenger RNA (mRNA) induction and enzyme activity was determined in primary cultures of rat and human hepatocytes for 2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3,4,7,8-pentachlorodibenzofuran, and 2,3,7,8-tetrachlorodibenzofuran. Eleven different congener concentrations from 0.00001 to 100 nM were used, thus spanning seven orders of magnitude. The Hill model was used to obtain values of EC(x) and maximal response from the individual data sets. No-observed effect concentration values were derived using several statistical methods including Dunnett's test, the Welch-Aspin test, and step-down bilinear regression. Thresholds were estimated using baseline projection methods and a "hockey stick" fitting method. Human hepatocytes were less responsive and less sensitive with respect to CYP1A1 activity and mRNA induction than rats. On the other hand, the human CYP1A2 response was more robust than the response in rats but generally less sensitive. These data allow an evaluation of relative species sensitivities for developing interspecies toxicodynamic adjustment factors, for assessing AHR activation thresholds, and for evaluating relative congener potencies. Overall, these data support the position that humans are less sensitive than rats to these AHR-dependent end points and support the use of a data-derived adjustment factor of 1.0 or less for extrapolating between rats and humans.

Interplay between cholesterol and drug metabolism

Cholesterol biosynthetic and metabolic pathways contain several branching points towards physiologically active molecules, such as coenzyme Q, vitamin D, glucocorticoid and steroid hormones, oxysterols, or bile acids. Sophisticated regulatory mechanisms are involved in maintenance of the homeostasis of not only cholesterol but also other cholesterogenic molecules. In addition to endogenous cues, cholesterol homeostasis needs to accommodate also to exogenous cues that are imported into the body, such as chemicals and medications. Steroid and nuclear receptors together with sterol regulatory element-binding protein (SREBP) mediate the fine tuning of biosynthetic and metabolic routes as well as transports of cholesterol and its derivatives. Similarly, drug/xenobiotic metabolism is the subject to the feedback regulation of cytochrome P450 enzymes and transporters. The regulatory mechanisms that maintain the homeostasis of cholesterogenic molecules and are involved in drug metabolism share similarities. Cholesterol and cholesterogenic compounds (bile acids, glucocorticoids, vitamin D, etc.) regulate the xenosensor signaling in drug-mediated induction of the major drug-metabolizing cytochrome P450 enzymes. The key cellular receptors, pregnane X receptor (PXR), constitutive androstane receptor (CAR), vitamin D receptor (VDR), and glucocorticoid receptor (GR) provide a functional cross-talk between the pathways maintaining cholesterol homeostasis and controlling the expression of drug-metabolizing enzymes. These receptors serve as metabolic sensors, resulting in a coordinate regulation of cholesterogenic compounds metabolism and of the defense against xenobiotic and endobiotic toxicity. Herein we present a comprehensive review of functional interactions between cholesterol homeostasis and drug metabolism involving the main nuclear and steroid receptors.

Comparative effects of microtubules disruption on glucocorticoid receptor functions in proliferating and quiescent cells

We have recently demonstrated that the alkaloid colchicine (COL) inhibits glucocorticoid receptor (GR) transcriptional activity. In addition, we described proteasome-mediated degradation of GR in COL-treated HeLa cells. While these effects were previously attributed to cell cycle arrest in G2/M phase, this explanation is not applicable for nonproliferating cells such as human hepatocytes (HH). In the current study, we compared COL-mediated microtubule disruption and cell cycle arrest with selected GR functions in HeLa cells and HH as models of proliferating and quiescent cells, respectively. Microtubule disruption led to irreversible decrease in GR binding capacity and protein level in HeLa cells. None of the parameters was restored 24 hours after COL withdrawal. In contrast, dexamethasone (DEX) binding was increased in HH at the beginning of the treatment, with following transient activation of extracellular signal-regulated kinase (ERK). The findings of these investigations emphasize the GR-signaling differences between primary and transformed cells.

Beta tubulin affects the aryl hydrocarbon receptor function via an Arnt-mediated mechanism

We have been studying the requirement for the aryl hydrocarbon receptor nuclear translocator (Arnt)-dependent DNA complex formation, which precedes the activation of gene transcription. Using DEAE chromatography, we have obtained a Sf9 insect fraction F5 that is highly enriched with beta-tubulin. F5 inhibits the formation of the AhR gel shift complex and this inhibition is sensitive to protease, suggesting that proteins that are present in this F5 fraction are responsible for the inhibition. Additional experiments have revealed that this inhibition is less pronounced in the presence of anti-beta-tubulin IgG and beta-tubulin enriched fraction from pig brain also inhibits the AhR gel shift formation. Sf9 beta-tubulin interacts with Arnt and suppresses the binding of the AhR/Arnt heterodimer to its corresponding enhancer. Human beta4-tubulin, which shares high sequence identity with Sf9 beta-tubulin, suppresses the AhR-dependent luciferase expression by reducing the nuclear Arnt content and retaining Arnt in the cytoplasm. Fluorescence studies using the GFP fusion of human beta4-tubulin have revealed that beta4-tubulin prevents the localization of Arnt in Sf9 cells. Here we have provided evidence suggesting that beta-tubulin may regulate the physiological content of Arnt.

Effects of dinuclear copper(II) complexes with 6-(benzylamino)purine derivatives on AhR and PXR dependent expression of cytochromes P450 CYP1A2 and CYP3A4 genes in primary cultures of human hepatocytes

A series of dinuclear copper(II) complexes of the compositions [Cu(2)(micro-L(n))(2)(micro-Cl)(2)Cl(2)] (1, 2), [Cu(2)(micro-L(n))(4)Cl(2)]Cl(2).2H(2)O (3, 4) and [Cu(2)(micro-L(n))(4)(ClO(4))(2)](ClO(4))(2).xSolv (5, 6; xSolv=4MeOH for 5 and 2EtOH for 6), involving 6-(benzylamino)purine derivatives (L(n)), have been evaluated with the aim to determine their possible drug interactions and their capability to induce the expression of major drug-metabolizing cytochromes P450. The above-mentioned complexes have been chosen based on the fact that substantial both in vitro (cytotoxicity, SOD-mimic) and in vivo (antidiabetic) biological activity has been found for them. As models, primary cultures of human hepatocytes and human hepatoma cells HepG2 transiently transfected with a plasmid containing dioxin-responsive element fused to the luciferase reporter gene (DRE-LUC) have been chosen. It has been found that the tested complexes 1-6 did not significantly induce the expression of CYP1A2 and CYP3A4 mRNAs in the concentration range of 0.1-10.0microM, in three different primary human hepatocyte cultures after 24h of the treatment. On the other hand, the model inducers, i.e. 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) and rifampicin, significantly increased the levels of CYP1A2 and CYP3A4 mRNAs in all cultures. In addition, compounds 1-6 did not transactivate DRE-LUC in transiently transfected HepG2, while TCDD strongly induced luciferase activity after 24h of incubation. Based on the obtained results, it may be concluded that the studied dinuclear copper(II) complexes 1-6 possess very low toxicological potential to cause drug interactions in terms of transcriptional activation of the major human cytochromes P450.

Catechol-o-methyltransferase expression and 2-methoxyestradiol affect microtubule dynamics and modify steroid receptor signaling in leiomyoma cells

Context

Development of optimal medicinal treatments of uterine leiomyomas represents a significant challenge. 2-Methoxyestradiol (2ME) is an endogenous estrogen metabolite formed by sequential action of CYP450s and catechol-O-methyltransferase (COMT). Our previous study demonstrated that 2ME is a potent antiproliferative, proapoptotic, antiangiogenic, and collagen synthesis inhibitor in human leiomyomas cells (huLM).

Objectives

Our objectives were to investigate whether COMT expression, by the virtue of 2ME formation, affects the growth of huLM, and to explore the cellular and molecular mechanisms whereby COMT expression or treatment with 2ME affect these cells.

Results

Our data demonstrated that E₂-induced proliferation was less pronounced in cells over-expressing COMT or treated with 2ME (500 nM). This effect on cell proliferation was associated with microtubules stabilization and diminution of estrogen receptor α (ERα) and progesterone receptor (PR) transcriptional activities, due to shifts in their subcellular localization and sequestration in the cytoplasm. In addition, COMT over expression or treatment with 2ME reduced the expression of hypoxia-inducible factor -1α (HIF-1 α) and the basal level as well as TNF-α-induced aromatase (CYP19) expression.

Conclusions

COMT over expression or treatment with 2ME stabilize microtubules, ameliorates E₂-induced proliferation, inhibits ERα and PR signaling, and reduces HIF-1 α and CYP19 expression in human uterine leiomyoma cells. Thus, microtubules are a candidate target for treatment of uterine leiomyomas. In addition, the naturally occurring microtubule-targeting agent 2ME represents a potential new therapeutic for uterine leiomyomas.

Dexamethasone controls aryl hydrocarbon receptor (AhR)-mediated CYP1A1 and CYP1A2 expression and activity in primary cultures of human hepatocytes

CYP1A1 and CYP1A2 genes encode members of the cytochrome P450 superfamily of enzymes primarily involved in xenobiotic and drug metabolism. In this paper we examined the effects of synthetic glucocorticoid dexamethasone (DEX) on aryl hydrocarbon receptor (AhR)-mediated regulation of CYP1A1 and CYP1A2 genes and their enzymatic activity in primary cultures of human hepatocytes obtained from 17 donors and prepared in 3 countries. Dexamethasone significantly reduced both basal and inducible CYP1A1/2 ethoxyresorufin-O-deethylase (EROD) activities by more than 75 and 50%, respectively. Glucocorticoid receptor (GR) antagonist RU486 abolished this effect suggesting the involvement of GR in the process. In contrast, dexamethasone significantly augmented transcriptional activation of CYP1A2 mRNA but not CYP1A1 gene by prototype AhR ligands 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3-methylcholanthrene (3MC). Dexamethasone had no effect on basal and TCDD-inducible levels of CYP1As proteins; however, it reduced the levels of AhR and GRalpha mRNAs and AhR protein levels. In addition, using RT(2) Profiler PCR Array, we found the effect of dexamethasone on the expression of several co-activators of AhR and GR nuclear receptors in the primary human hepatocytes. We conclude that dexamethasone controls CYP1A1 and CYP1A2 expression and activity in human hepatocytes via multiple mechanisms, which remain to be elucidated.

Role of mitogen-activated protein kinases in aryl hydrocarbon receptor signaling

Human populations are increasingly exposed to a number of environmental pollutants such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls and dioxins. These compounds are activators of the aryl hydrocarbon receptor (AhR) that controls the expression of many genes including those for detoxification enzymes. The regulatory mechanisms of AhR are multi-factorial and include phosphorylation by various protein kinases. Significant progress in the research of mitogen-activated protein kinases (MAPKs) has been achieved in the last decade. Isolated reports have been published on the role of MAPKs in AhR functions and vice versa, with activation of MAPKs by AhR ligands. This mini-review summarizes current knowledge on the mutual interactions between MAPKs and AhR. The majority of studies has been done on cancer-derived cell lines that have impaired cell cycle regulation and lacks the complete detoxification apparatus. We emphasize the importance of the future studies that should be done on non-transformed cells to distinguish the role of MAPKs in cancer and normal cells. Primary cultures of human or rodent hepatocytes that are equipped with a fully functional biotransformation battery or xenobiotics-metabolizing extra-hepatic tissues should be the models of choice, as the results in our experiments confirm.