Modulation of oestrogen receptor signalling by association with the activated dioxin receptor

Benzo(a)pyrene attenuates the pattern-recognition-receptor induced proinflammatory phenotype of murine macrophages by inducing IL-10 expression in an aryl hydrocarbon receptor-dependent manner

Polycyclic aromatic hydrocarbons such as benzo(a)pyrene (BaP) are environmental contaminants known to be immunosuppressive. Most effects of BaP towards immune cells are thought to be mediated through activation of the aryl hydrocarbon receptor (AhR). The AhR is a ligand-activated transcription factor, which plays a critical modulatory role in various cells during immune response. Macrophages are key players in innate immunity against intracellular bacteria and are discussed to be a target of AhR-mediated immune regulation. However, so far there is only incomplete knowledge about the effects of BaP on activated macrophages and whether these effects are AhR-dependent in each case. Using murine bone marrow-derived macrophages (BMMs) stimulated with heat-killed salmonellae as a source of different pathogen-associated molecular patterns (PAMPs) for stimulation of different pattern recognition receptors (PRRs) as an in-vitro model, we studied the immunomodulatory effects of low-dose BaP exposure. PRR-activated BMMs produced nitric oxide (NO) and a spectrum of proinflammatory cytokines, i.e. tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-12 but also the anti-inflammatory cytokine IL-10. While BaP exposure suppressed the production of proinflammatory cytokines, the secretion of IL-10 was augmented. Moreover, BaP exposure increased the expression of major histocompatibility complex class II (MHC-II), CD14, Fcγ receptor I (FcγRI/CD64), or CD86, enhanced NO production and phagocytosis what may be beneficial for phagocytosis and killing of microbial pathogens. Of note, without PRR activation low-dose BaP exposure has little influence on the macrophage phenotype. BMMs from AhR-deficient (Ahr^-/-) mice were widely refractory to BaP-induced modulation of cytokine production, surface marker expression, and functional properties in response to PAMPs stimulation, indicating that these effects are dependent on AhR. In summary, these data suggest that induction of AhR-mediated signalling pathways by BaP may attenuate the proinflammatory phenotype of PRR-activated BMMs, while activating IL-10-mediated anti-inflammatory properties but also enhancing uptake and killing of pathogens as well as antigen presentation. Together these features imply a favourable role of BaP exposure for macrophage functions in an ongoing immune response. However, the strong induction of IL-10 may lead to defective pathogen clearance and subsequently to chronic persistent infection. This concept suggests an inhibitory rather than a supporting influence of environmental BaP on immunity to infection or cancer and also emphasises the important regulatory role of AhR in immunity and inflammation.

Peripubertal serum dioxin concentrations and subsequent sperm methylome profiles of young Russian adults

BACKGROUND

The association of exposure to endocrine disrupting chemicals in the peripubertal period with subsequent sperm DNA methylation is unknown.

OBJECTIVE

We examined the association of peripubertal serum 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) concentrations with whole-genome bisulfite sequencing (WGBS) of sperm collected in young adulthood.

METHODS

The Russian Children's Study is a prospective cohort of 516 boys who were enrolled at 8-9 years of age and provided semen samples at 18-19 years of age. WGBS of sperm was conducted to identify differentially methylated regions (DMR) between highest (n = 4) and lowest (n = 4) peripubertal TCDD groups.

RESULTS

We found 52 DMRs that distinguished lowest and highest peripubertal serum TCDD concentrations. One of the top scoring networks, "Cellular Assembly and Organization, Cellular Function and Maintenance, Carbohydrate Metabolism", identified estrogen receptor alpha as its central regulator.

CONCLUSION

Findings from our limited sample size suggest that peripubertal environmental exposures are associated with sperm DNA methylation in young adults.

Aryl hydrocarbon receptor (AhR) a possible target for the treatment of skin disease

Aryl hydrocarbon receptor (AhR) is a transcription factor expressed in all skin cells type. It responds to exogenous and endogenous chemicals by inducing/repressing the expression of several genes with toxic or protective effects in a wide range of species and tissues. In healthy skin, AhR signalling contributes to keratinocytes differentiation, skin barrier function, skin pigmentation, and mediates oxidative stress. In the last years, some studies have shown that AhR seems to be involved in the pathogenesis of some skin diseases, even if the currently available data are contradictory. Indeed, while the blocking the AhR signalling activity could prevent or treat skin cancer, the AhR activation seems to be advantageous for the treatment of inflammatory skin diseases. Therefore, for its multifaceted role in skin diseases, AhR seems to be an attractive therapeutic target. Indeed, recently some molecules have been identified for the prevention of skin cancer and the treatment of inflammatory skin diseases.

Put "gender glasses" on the effects of phenolic compounds on cardiovascular function and diseases

INTRODUCTION

The influence of sex and gender is particularly relevant in cardiovascular diseases (CVD) as well as in several aspects of drug pharmacodynamics and pharmacokinetics. Anatomical and physiological differences between the sexes may influence the activity of many drugs, including the possibility of their interaction with other drugs, bioactive compounds, foods and beverages. Phenolic compounds could interact with our organism at organ, cellular, and molecular levels triggering a preventive action against chronic diseases, including CVD.

RESULTS

This article will review the role of sex on the activity of these bioactive molecules, considering the existence of sex differences in oxidative stress. It describes the pharmacokinetics of phenolic compounds, their effects on vessels, on cardiovascular system, and during development, including the role of nuclear receptors and microbiota.

CONCLUSIONS

Although there is a large gap between the knowledge of the sex differences in the phenolic compounds' activity and safety, and the urgent need for more research, available data underlie the possibility that plant-derived phenolic compounds could differently influence the health of male and female subjects.

Expression of Xenobiotic Biomarkers CYP1 Family in Preputial Tissue of Patients with Hypospadias and Phimosis and Its Association with DNA Methylation Level of SRD5A2 Minimal Promoter

Several epidemiological studies have suggested that the incidence of male reproductive organ malformations, including hypospadias or cryptorchidism, has increased due to fetal-stage exposure to environmental pollutants. However, the association of chemical exposure with the expression of target regulatory genes in the tissues of patients has not yet been reported. Because experimental approaches or clinical trials in human studies are limited, especially those using fetal and/or infants, it is difficult to obtain clear physiological evidence of mechanisms underlying male reproductive malformations. Thus, the lack of physiological evidence makes this issue controversial. We analyzed preputial tissues from patients with hypospadias (n = 23) and phimosis (n = 16). The atypical CYP1 family genes, CYP1A1 and CYP1B1, are potential biomarkers of environmental chemical exposure. We then compared the expression levels of CYP1A1 and CYP1B1 between hypospadias and phimosis samples by quantitative RT-PCR analysis. The mRNA expression levels of SRD5A2 and AR also were measured, because the androgen-related genes involved in the onset of disorders of male reproductive system. A significantly higher CYP1B1 expression level and a lower AR expression level were observed in the hypospadias groups than in the phimosis group. Positive correlations (P < 0.001) between the mRNA expression levels of the CYP1 family and SRD5A2 were found in patients with hypospadias but not in those with phimosis. Moreover, the methylation levels of the four genes were determined by bisulfite genomic sequencing. Although the SRD5A2 promoter region showed moderate methylation, no methylation was detected in CYP1A1, CYP1B1, or AR. There was no significant difference in SRD5A2 promoter methylation level between hypospadias and phimosis patients. Negative correlations were found between the methylation level of SRD5A2, especially at the - 221 Sp1 site, and the CYP1 family mRNA expression levels (CYP1A1, p = 0.002; CYP1B1, p = 0.007) in hypospadias patients, but not in phimosis patients. The significant positive association of mRNA expression level and the negative association of methylation level of the SRD5A2 gene with the mRNA expression levels of CYP1 family genes in the preputial tissue seem to indicate the chemical exposure of patients with hypospadias.

High AHR expression in breast tumors correlates with expression of genes from several signaling pathways namely inflammation and endogenous tryptophan metabolism

Increasing epidemiological and animal experimental data provide substantial support for the role of aryl hydrocarbon receptor (AhR) in mammary tumorigenesis. The effects of AhR have been clearly demonstrated in rodent models of breast carcinogenesis and in several established human breast cancer cell lines following exposure to AhR ligands or AhR overexpression. However, relatively little is known about the role of AhR in human breast cancers. AhR has always been considered to be a regulator of toxic and carcinogenic responses to environmental contaminants such as TCDD (dioxin) and benzo[a]pyrene (BaP). The aim of this study was to identify the type of breast tumors (ERα-positive or ERα-negative) that express AHR and how AhR affects human tumorigenesis. The levels of AHR, AHR nuclear translocator (ARNT) and AHR repressor (AHRR) mRNA expression were analyzed in a cohort of 439 breast tumors, demonstrating a weak association between high AHR expression and age greater than fifty years and ERα-negative status, and HR-/ERBB2 breast cancer subtypes. AHRR mRNA expression was associated with metastasis-free survival, while AHR mRNA expression was not. Immunohistochemistry revealed the presence of AhR protein in both tumor cells (nucleus and/or cytoplasm) and the tumor microenvironment (including endothelial cells and lymphocytes). High AHR expression was correlated with high expression of several genes involved in signaling pathways related to inflammation (IL1B, IL6, TNF, IL8 and CXCR4), metabolism (IDO1 and TDO2 from the kynurenine pathway), invasion (MMP1, MMP2 and PLAU), and IGF signaling (IGF2R, IGF1R and TGFB1). Two well-known ligands for AHR (TCDD and BaP) induced mRNA expression of IL1B and IL6 in an ERα-negative breast tumor cell line. The breast cancer ER status likely influences AhR activity involved in these signaling pathways. The mechanisms involved in AhR activation and target gene expression in breast cancers are also discussed.

Dioxin Exposure Alters Molecular and Morphological Responses to Thyroid Hormone in Xenopus laevis Cultured Cells and Prometamorphic Tadpoles

Amphibian metamorphosis is driven by thyroid hormone (TH). We used prometamorphic tadpoles and a cell line of the African clawed frog (Xenopus laevis) to examine immediate effects of dioxin exposure on TH. Gene expression patterns suggest cross-talk between the thyroid hormone receptor (TR) and aryl hydrocarbon receptor (AHR) signaling pathways. In XLK-WG cells, expression of Cytochrome P450 1A6 (cyp1A6), an AHR target, was induced 1000-fold by 100 nM TCDD (2, 3, 7, 8 tetrachlorodibenzo-p-dioxin). Krüppel-Like Factor 9 (klf9), the first gene induced in a cascade of TH responses tied to metamorphosis, was upregulated over 5-fold by 50 nM triiodothyronine (T3) and 2-fold by dioxin. Co-exposure to T3 and TCDD boosted both responses, further inducing cyp1A6 by 75% and klf9 about 60%. Additional canonical targets of each receptor, including trβa and trβb (TR) and udpgt1a (AHR) responded similarly. Induction of TH targets by TCDD in XLK-WG cells predicts that exposure could speed metamorphosis. We tested this hypothesis in two remodeling events: tail resorption and hind limb growth. Resorption of ex vivo cultured tails was accelerated by 10 nM T3, while a modest increase in resorption by 100 nM TCDD lacked statistical significance. Hind limbs doubled in length over four days following 1 nM T3 treatment, but limb length was unaffected by 100 nM TCDD. TCDD co-exposure reduced the T3 effect by nearly 40%, despite TCDD induction of klf9 in whole tadpoles, alone or with T3. These results suggest that tissue-specific TCDD effects limit or reverse the increased metamorphosis rate predicted by klf9 induction.

Quaking Deficiency Amplifies Inflammation in Experimental Endotoxemia via the Aryl Hydrocarbon Receptor/Signal Transducer and Activator of Transcription 1-NF-κB Pathway

Macrophages, characterized by considerable diversity and plasticity, play a crucial role in a broad spectrum of biological processes, including inflammation. However, the molecular mechanisms underlying the diverse phenotypes of macrophages are not well defined. Here, we show that the RNA-binding protein, quaking (QKI), dynamically modulates macrophage polarization states. After lipopolysaccharide (LPS) stimulation, QKI-silenced RAW 264.7 cells displayed a pro-inflammatory M1 phenotype characterized by increased expression of iNOS, TNF-α, and IL-6 and decreased expression of anti-inflammatory factors, such as IL-10, found in inflammatory zone (Fizz1), and chitinase-like 3 (Chil3 or Ym1). By contrast, QKI5 overexpression led to a suppressive phenotype resembling M2 macrophages, even under M1 differentiation conditions. Moreover, myeloid-specific QKI-deficient mice tended to be more susceptible to LPS-induced endotoxic shock, while the exogenous transfer of macrophages overexpressing QKI5 exerted a significant improving effect. This improvement corresponded to a higher proportion of M2 macrophages, in line with elevated levels of IL-10, and a decrease in levels of pro-inflammatory mediators, such as IL-6, TNF-α, and IL-1β. Further mechanistic studies disclosed that QKI was a potent inhibitor of the nuclear factor-kappa B (NF-κB) pathway, suppressing p65 expression and phosphorylation. Strikingly, reduced expression of the aryl hydrocarbon receptor (Ahr) and reduced phosphorylation of signal transducer and activator of transcription 1 in QKI-deficient cells failed to restrain the transcriptional activity of NF-κB and NRL pyrin domain containing 3 (NLRP3) activation, while restoring QKI expression skewed the above M1-like response toward an anti-inflammatory M2 state. Taken together, these findings suggest a role for QKI in restraining overt innate immune responses by regulating the Ahr/STAT1–NF-κB pathway.

Evaluation of the effect of the new methoxy-stilbenes on expression of receptors and enzymes involved in estrogen synthesis in cancer breast cells

Our previous study showed that the new synthetic methoxy-stilbenes, 3,4,2'-trimethoxy-trans-stilbene (3MS), 3,4,2',4'-tetramethoxy-trans-stilbene (4MS), and 3,4,2',4',6'-pentamethoxy-trans-stilbene (5MS), modulate the constitutive expression of enzymes and receptors involved in estrogen metabolism in breast immortalized epithelial MCF10 cells. In this study, we evaluated the effect of 3MS, 4MS, and 5MS in comparison to resveratrol activity in MCF7 estrogen-dependent and MDA-MB-231 estrogen-independent breast cancer cell lines. 3MS similarly to resveratrol reduced the expression of estrogen receptor α in MCF7 cells. However, in these cells, 5MS reduced the most CYP19, the gene encoding aromatase, at mRNA transcript level. In contrast, in the MDA-MB-231 cells, the most efficient inhibitor of CYP19 expression was 3MS, reducing the level of its protein by ~ 25%. This stilbene also inhibited the aromatase activity in a recombinant protein system with IC₅₀ value ~ 85 µM. Treatment with the methoxy-stilbenes reduced the level of estradiol in culture medium. The most significant reduction was exerted by 3MS. None of the tested stilbenes including resveratrol changed significantly the expression of AhR, although CYP1A1 protein level was slightly reduced in MDA-MB-231 cells, while CYP1B1 expression was increased in these cells as a result of treatment with 3MS, but only at the transcript level. Overall, these results show weak or moderate effect of the new methoxy-stilbenes on the expression of key proteins involved in estrogens metabolism in cancer breast cells. However, the reduced CYP19 expression and activity upon 3MS treatment in metastatic MDA-MB-231 cells require the further studies.

Nuclear transport of the human aryl hydrocarbon receptor and subsequent gene induction relies on its residue histidine 291

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor involved in the metabolism of physiological substances and xenobiotics, representing an interesting target in both toxicology and pharmacology. In this study, we investigated the ligand-dependent conjunction of nuclear import of the human AHR in living cells and target gene induction. Our findings strengthen the theory that the AHR triggers a precisely defined and rapid reaction upon binding to endogenous ligands, while the xenobiotic β-naphthoflavone only induces rather unspecific and slow effects. To better illuminate the ligand-mediated responses of the human AHR, we applied site-directed mutagenesis and identified histidine 291 as key residue for AHR functionality, essential for both nuclear import and target gene induction. Contrary, replacing histidine at position 291 by alanine did not affect nucleo-cytoplasmic shuttling, showing that permanent endogenous import and ligand-induced import of the AHR into the nucleus are two independent and differently regulated processes. Combining these observations with our structural investigations using a homology model of the AHR-PAS B domain, we suggest a dual role of histidine 291: (1) a major role for shaping the ligand binding site including direct interactions with ligands and, (2) an essential role for the conformational dynamics of a PAS B loop, which most likely influences the association of the AHR with the AHR nuclear translocator through interference with their protein-protein interface.

Effects of environmental pollutants on signaling pathways in rat pituitary GH3 adenoma cells

An increased rate of acromegaly was reported in industrialized areas, suggesting an involvement of environmental pollutants in the pathogenesis and behavior of GH-secreting pituitary adenomas. Based on these premises, the aim of the study was to evaluate the effects of some widely diffused pollutants (i.e. benzene, BZ; bis(2-ethylhexyl) phthalate, DEHP and polychlorinated biphenyls, PCB) on growth hormone secretion, the somatostatin and estrogenic pathways, viability and proliferation of rat GH-producing pituitary adenoma (GH3) cells. All the pollutants induced a statistically significant increase in GH secretion and interfered with cell signaling. They all modulated the expression of SSTR2 and ZAC1, involved in the somatostatin signaling, and the expression of the transcription factor FOXA1, involved in the estrogen receptor signaling. Moreover, all the pollutants increased the expression of the CYP1A1, suggesting AHR pathway activation. None of the pollutants impacted on cell proliferation or viability. Present data demonstrate that exposure to different pollutants, used at in vivo relevant concentrations, plays an important role in the behavior of GH3 pituitary adenoma cells, by increasing GH secretion and modulating several cellular signaling pathways. These observations support a possible influence of different pollutants in vivo on the GH-adenoma aggressiveness and biological behavior.

Adipose Tissue as a Site of Toxin Accumulation

We examine the role of adipose tissue, typically considered an energy storage site, as a potential site of toxicant accumulation. Although the production of most persistent organic pollutants (POPs) was banned years ago, these toxicants persist in the environment due to their resistance to biodegradation and widespread distribution in various environmental forms (e.g., vapor, sediment, and water). As a result, human exposure to these toxicants is inevitable. Largely due to their lipophilicity, POPs bioaccumulate in adipose tissue, resulting in greater body burdens of these environmental toxicants with obesity. POPs of major concern include polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and furans (PCDDs/PCDFs), and polybrominated biphenyls and diphenyl ethers (PBBs/PBDEs), among other organic compounds. In this review, we (i) highlight the physical characteristics of toxicants that enable them to partition into and remain stored in adipose tissue, (ii) discuss the specific mechanisms of action by which these toxicants act to influence adipocyte function, and (iii) review associations between POP exposures and the development of obesity and diabetes. An area of controversy relates to the relative potential beneficial versus hazardous health effects of toxicant sequestration in adipose tissue. © 2017 American Physiological Society. Compr Physiol 7:1085-1135, 2017.

In vitro observations and in silico predictions of xenoestrogen mixture effects in T47D-based receptor transactivation and proliferation assays

Within endocrine disruptor research, evaluation and interpretation of mixture effects and the predictive value for downstream responses still warrant more in-depth investigations. We used an estrogen receptor (ER)-mediated reporter gene assay (ER-CALUX®) and a cell proliferation assay (WST-1 assay), both based on the T47D breast cancer cell line, to test mixtures of heterogeneous xenoestrogens. Observed concentration-response curves were compared to those predicted by the concepts of concentration addition (CA), generalized concentration addition (GCA), and a novel full logistic model (FLM). CA performed better regarding mixture potency (EC50 values), whereas GCA was superior in predicting mixture efficacy (maximal response). In comparison, FLM proved to be highly suitable for in silico mixture effect prediction, combining advantages of both CA and GCA. The inter-assay comparison revealed that ER activation is not necessarily predictive for induction of cell proliferation. The results support the use of models like CA, GCA, or FLM in mixture effect evaluation. However, we conclude that reliable estimations regarding the disruptive potential of mixtures of endocrine active substances require an integrative approach considering more than one assay/endpoint to avoid misinterpretations. The formazan-based WST-1 proliferation assay might be a possible alternative to commonly used proliferation assays in endocrine disrupter research.

Characterizing combined effects of antiestrogenic chemicals on vitellogenin production in rainbow trout (Oncorhynchus mykiss) hepatocytes

Fish are exposed to a complex mixture of endocrine disrupting compounds (EDC), some of which display antiestrogenic activity leading to suppression of estrogen receptor (ER)- mediated reproductive processes. Although the main mode of action (MoA) of these antiestrogens is to directly interfere with natural ligand binding of the ER, several other MoA have been proposed. The aim of the present study was to characterize single and combined antiestrogenic effects of the aryl hydrocarbon receptor (AhR)-agonist β-naphthoflavone (BNF) and ER-antagonist 4-hydroxytamoxifen (OHT) on vitellogenin (Vtg) protein using primary rainbow trout (Oncorhynchus mykiss) hepatocytes. Supporting transcriptional analysis of ER-responsive genes (estrogen receptor-α (er-α), vitellogenin-1 (vtg-1), eggshell zona radiata protein (zrp)) and AhR-mediated genes (aryl hydrocarbon receptor-2β, cytochrome p450-1a (cyp1a)) was performed by qPCR to characterize the antiestrogenic influence on ER- and AhR-mediated responses. Data demonstrated that both BNF and OHT significantly reduced 17β-estradiol (E2)-induced Vtg protein expression in a concentration responsive manner, whereas exposure to a mixture of these produced an additive antiestrogenic effect. The results observed at the protein level were further supported by transcriptional analysis of ER-responsive genes (er-α, vtg-1, zrp), where only E2-induced vtg-1 gene expression was significantly decreased by OHT and the mixture of OHT and BNF. E2-induced er-α and zrp gene expression was not markedly altered. The significant reduction of E2-induced vtg-1 gene expression by OHT suggested that the antiestrogenic effect of this compound may be associated with ER signaling pathway. Specific genes involved in putative AhR-ER cross-talk were also investigated, however none were directly associated with the compound anti-estrogenic MoA. Although the MoA of the single compounds and mixture were not completely characterized, the present study enhanced our knowledge of the combined toxicity mediated by antiestrogens acting through different MoA.

Estrogen Receptor β as a Prognostic Marker of Tumor Progression in Colorectal Cancer with Familial Adenomatous Polyposis and Sporadic Polyps

The incidence of colorectal cancer (CRC) is lower in women than in men, and sex steroids can be considered contributing factors because oral contraception usage and estrogen replacement therapy are associated with decreased risk. Conversely, colorectal polyp development in familial adenomatous polyposis (FAP) begins during puberty. The objectives were to evaluate the relationship between the expression of these hormone receptors and adenoma-carcinoma progression, CRC stage and overall survival. We studied 120 A.C. Camargo Cancer Center patients diagnosed with either FAP-associated or spontaneous adenomatous polyps or CRC to determine the immunohistochemical expression levels of estrogen receptor (ER)-α, ER-β and the progesterone and androgen receptors (480 analyses). The ER-β expression levels differed between the groups: the group with FAP polyps had lower ER-β expression than that of the sporadic polyp group. With transformation of the sporadic polyps to cancer, there was a considerable decrease in ER-β expression (from 90% with strong expression to 80% with absent or weak expression) (p < 0.001). The ER-β expression was lower in T3/T4 tumors than in T1/T2 tumors (p = 0.015). The 5-year overall survival of CRC patients positively expressing ER-β exceeded that of patients without detectable expression levels (74.8% vs. 44.3%, respectively; p = 0.035). There was no significant expression of the androgen or progesterone receptor or ER-α among the groups. Differences in ER-β expression represent a potential mechanism through which estrogen might alter the susceptibility to colon cancer, thereby confirming the possibility of a protective role of estrogen against colorectal carcinogenesis.

Effects of the aryl hydrocarbon receptor agonist 3-methylcholanthrene on the 17β-estradiol regulated mRNA transcriptome of the rat uterus

Polycyclic aromatic hydrocarbons (PAHs) are products of incomplete combustion of organic compounds, abundant in exhaust fumes and cigarette smoke. They act by binding to the aryl hydrocarbon receptor (AHR) which induces expression of phase 1 and phase 2 enzymes in the liver. PAH induced AHR activation may also lead to adverse effects by modulating other pathways, for example estrogen receptor (ER) signaling in the female reproductive tract. We have investigated the effects of the PAH 3-methylcholanthrene (3-MC) on 17β-estradiol (E2) dependent signaling in the uterus of ovariectomized rats to characterize the cross talk between AHR and ER on an mRNA transcriptome wide scale. A standard three day uterotrophic assay was performed in young adult Lewis rats. Treatment induced effects were analyzed using histology, immunohistochemistry and gene expression analysis by microarray and qPCR. 3-MC shows broad E2 antagonistic effects on uterine mRNA transcription of the vast majority of E2 regulated genes, significantly altering prostaglandin biosynthesis, complement activation, coagulation pathways and other inflammatory response pathways. The regulation of ER expression in the uterus, but not the regulation of E2 metabolism in the liver, was identified as a potentially important factor in mediating this general antiestrogenic effect. The regulation of prostaglandin biosynthesis by E2 is important for inflammation-like events during pregnancy including the initiation of birth. Our results suggest that adverse effects of PAHs on prostaglandin related pathways are likely caused by the interference with E2 signaling, specifically by inhibiting the E2 mediated downregulation of PGF2α. Characterization of the generalized antagonistic effect of 3-MC on E2 dependent signaling in the rat uterus thus contributes to a better understanding of molecular mechanisms of the toxicity of PAHs in female reproductive organs.

A Molecular Mechanism To Switch the Aryl Hydrocarbon Receptor from a Transcription Factor to an E3 Ubiquitin Ligase

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that is known as a mediator of toxic responses. Recently, it was shown that the AhR has dual functions. Besides being a transcription factor, it also possesses an intrinsic E3 ubiquitin ligase function that targets, e.g., the steroid receptors for proteasomal degradation. The aim of this study was to identify the molecular switch that determines whether the AhR acts as a transcription factor or an E3 ubiquitin ligase. To do this, we used the breast cancer cell line MCF7, which expresses a functional estrogen receptor alpha (ERα) signaling pathway. Our data suggest that aryl hydrocarbon receptor nuclear translocator (ARNT) plays an important role in the modulation of the dual functions of the AhR. ARNT knockdown dramatically impaired the transcriptional activation properties of the ligand-activated AhR but did not affect its E3 ubiquitin ligase function. The availability of ARNT itself is modulated by another basic helix-loop-helix (bHLH)-Per-ARNT-SIM (PAS) protein, the repressor of AhR function (AhRR). MCF7 cells overexpressing the AhRR showed lower ERα protein levels, reduced responsiveness to estradiol, and reduced growth rates. Importantly, when these cells were used to produce estrogen-dependent xenograft tumors in SCID mice, we also observed lower ERα protein levels and a reduced tumor mass, implying a tumor-suppressive-like function of the AhR in MCF7 xenograft tumors.

Endocrine disrupting chemicals in mixture and obesity, diabetes and related metabolic disorders

Obesity and associated metabolic disorders represent a major societal challenge in health and quality of life with large psychological consequences in addition to physical disabilities. They are also one of the leading causes of morbidity and mortality. Although, different etiologic factors including excessive food intake and reduced physical activity have been well identified, they cannot explain the kinetics of epidemic evolution of obesity and diabetes with prevalence rates reaching pandemic proportions. Interestingly, convincing data have shown that environmental pollutants, specifically those endowed with endocrine disrupting activities, could contribute to the etiology of these multifactorial metabolic disorders. Within this review, we will recapitulate characteristics of endocrine disruption. We will demonstrate that metabolic disorders could originate from endocrine disruption with a particular focus on convincing data from the literature. Eventually, we will present how handling an original mouse model of chronic exposition to a mixture of pollutants allowed demonstrating that a mixture of pollutants each at doses beyond their active dose could induce substantial deleterious effects on several metabolic end-points. This proof-of-concept study, as well as other studies on mixtures of pollutants, stresses the needs for revisiting the current threshold model used in risk assessment which does not take into account potential effects of mixtures containing pollutants at environmental doses, e.g., the real life exposure. Certainly, more studies are necessary to better determine the nature of the chemicals to which humans are exposed and at which level, and their health impact. As well, research studies on substitute products are essential to identify harmless molecules.

Spermatogenesis disruption by dioxins: Epigenetic reprograming and windows of susceptibility

Dioxins are a group of highly persistent chemicals that are generated as by-products of industrial and natural processes. Reduction in sperm counts is among the most sensitive endpoints of dioxin toxicity. The exact mechanism by which dioxins reduce sperm counts is not known. Recent data implicate the role of epididymal factors rather than disruption of spermatogenesis. Studies reviewed here demonstrate that dioxins induce the transfer of environmental conditions to the next generation via male germline following exposures during the window of epigenetic reprogramming of primordial germ cells. Increased incidence of birth defects in offspring of male veterans exposed to dioxin containing, Agent Orange, suggest that dioxins may induce epigenomic changes in male germ cells of adults during spermatogenesis. This is supported by recent animal data that show that environmental conditions can cause epigenetic dysregulation in sperm in the context of specific windows of epigenetic reprogramming during spermatogenesis.

The association of peripubertal serum concentrations of organochlorine chemicals and blood lead with growth and pubertal development in a longitudinal cohort of boys: a review of published results from the Russian Children's Study

Organochlorine chemicals and lead are environmental exposures that have endocrine disrupting properties (EDCs) which interfere with many aspects of hormone action. Childhood and adolescence are windows of susceptibility for adverse health effects of EDCs. Our ongoing study, the Russian Children's Study (RCS), is one of the few longitudinal studies investigating the impact of EDCs on growth and puberty in boys. It is conducted in the historically contaminated city of Chapaevsk, in the Samara region. The study focuses on evaluating the associations of persistent organochlorine chemicals and lead with growth and pubertal timing. At enrollment in 2003-2005, we collected blood from 516 boys at ages 8-9 years to measure dioxins, furans, polychlorinated biphenyls (PCBs), chlorinated pesticides and lead. At enrollment and at annual visits through the ages of 18-19 years, a physician performed physical examinations that included pubertal staging and testicular volume measurements. We review the history of Chapaevsk as a research site and summarize published RCS data on the association of peripubertal serum concentrations of organochlorines and blood lead levels with growth, pubertal onset and sexual maturity. Overall, we found that persistent organochlorines and lead negatively affected growth during puberty. Our results also suggest that total toxic equivalents (TEQs), dioxin-like compounds, organochlorine pesticides and lead may delay, while nondioxin-like-PCBs may advance, the timing of male puberty. These findings promoted remediation programs in Chapaevsk, with improvement in health indicators, resulting in Chapaevsk being designated a member of the World Health Organization (WHO) network "Healthy Cities" in 2015.

Review on crosstalk and common mechanisms of endocrine disruptors: Scaffolding to improve PBPK/PD model of EDC mixture

Endocrine disruptor compounds (EDCs) are environment chemicals that cause harmful effects through multiple mechanisms, interfering with hormone system resulting in alteration of homeostasis, reproduction and developmental effect. Many of these EDCs have concurrent exposure with crosstalk and common mechanisms which may lead to dynamic interactions. To carry out risk assessment of EDCs' mixture, it is important to know the detailed toxic pathway, crosstalk of receptor and other factors like critical window of exposure. In this review, we summarize the major mechanism of actions of EDCs with the different/same target organs interfering with the same/different class of hormone by altering their synthesis, metabolism, binding and cellular action. To show the impact of EDCs on life stage development, a case study on female fertility affecting germ cell is illustrated. Based on this summarized discussion, major groups of EDCs are classified based on their target organ, mode of action and potential risk. Finally, a conceptual model of pharmacodynamic interaction is proposed to integrate the crosstalk and common mechanisms that modulate estrogen into the predictive mixture dosimetry model with dynamic interaction of mixture. This review will provide new insight for EDCs' risk assessment and can be used to develop next generation PBPK/PD models for EDCs' mixture analysis.

Canonical and non-canonical aryl hydrocarbon receptor signaling pathways

Decades of research on the Aryl hydrocarbon Receptor (AhR) has unveiled its involvement in the toxicity of halogenated and polycyclic aromatic hydrocarbons, and a myriad of normal physiological processes. The molecular dissection of AhR biology has centered on a canonical signaling pathway in an effort to mechanistically reconcile the diverse pathophysiological effects of exposure to environmental pollutants. As a consequence, we now know that canonical signaling can explain many but not all of the AhR-mediated effects. Here we describe recent findings that point to non-canonical signaling pathways, and focus on a novel AhR interaction with the Krüppel-like Factor 6 protein responsible for previously un-recognized epigenetic changes in the chromatin affecting gene expression.

A Possible Association of Diindolylmethane with Pulmonary Embolism and Deep Venous Thrombosis

Introduction. 3,3'-Diindolylmethane is available as a supplement in the United States for "cancer prevention" and "augmentation of physical fitness." A derivative of indole-3-carbinol found in plants, diindolylmethane, binds to receptors associated with the sex steroid pathways and has unclear effects on estrogen and androgen physiology. We present a patient who had been taking diindolylmethane and developed right lower extremity deep venous thrombosis and bilateral pulmonary embolism. Case Presentation. A 65-year-old man presented with swelling, erythema, and warmth of his right lower extremity for three to four weeks. He had been taking diindolylmethane one tablet daily for three to four months. Risk factors for venous thromboembolism included tobacco use, personal history of possible pulmonary embolism, body mass index, and age. Imaging studies found extensive deep venous thrombosis in his right lower extremity and bilateral pulmonary embolism with probable right middle lobe infarction. Follow-up imaging showed chronic deep venous thrombosis in his right lower extremity. Discussion. As suggested in this single case, patients who take diindolylmethane may be at greater risk for venous thromboembolism. Further reports and studies are necessary in order to elucidate this possible association. Clinicians should question patients about supplements in the setting of venous thromboembolism.

Effects of Postnatal Exposure to a Mixture of Polychlorinated Biphenyls, p,p′-dichlorodiphenyltrichloroethane, and p-p′-dichlorodiphenyldichloroethene in Prepubertal and Adult Female Sprague-Dawley Rats

The postnatal period is a critical phase of development and a time during which humans are exposed to higher levels of persistent organic pollutants (POPs), than during subsequent periods of life. There is a paucity of information describing effects of postnatal exposure to environmentally relevant mixtures of POPs, such as polychlorinated biphenyls (PCBs), p,p′-dichlorodiphenyltrichloroethane (DDT), and p,p′-dichlorodiphenyldichloroethene (DDE). To provide data useful for the risk assessment of postnatal exposure to POPs, mixtures containing 19 PCBs, DDT, and DDE were prepared according to their concentrations previously measured in the milk of Canadian women, and dose-response effects were tested on the proliferation of MCF7-E3 cells in vitro, and in vivo experiments. Female neonates were exposed by gavage at postnatal days (PNDs) 1, 5, 10, 15, and 20 with dosages equivalent to 10, 100, and 1000 times the estimated human exposure level over the first 24 days of life. The MCF7-E3 cells showed a 227% increase in the AlamarBlue proliferation index, suggesting estrogen-like properties of the mixture, but this was not confirmed in vivo, given the absence of uterotrophic effects at PND21. An increase (511%) in hepatic ethoxyresorufin- o-deethylase activity at the dose 100 × was the most sensitive endpoint among those measured at PND21 (organ weight, mammary gland and ovarian morphometry, hepatic enzyme inductions, serum thyroxine and pituitary hormones). In liver samples from older female rats (previously involved in a mammary tumor study [Desaulniers et al., Toxicol. Sci. 75:468–480, 2001]), hepatic metabolism of 14C-estradiol-17 β (E2) at PND55 to PND62 was significantly higher in the 1000 × compared to the control group, but hepatic detoxification enzyme activities had already returned to control values. The production of hepatic 2-hydroxy-E2 decreased, whereas that of estrone increased with age. In conclusion, the smallest dose of the mixture to induce significant effects was 100×, and mixture-induced changes in the hepatic metabolism of estrogens might be a sensitive indicator of persistent effects.

Epidemiology of Uterine Fibroids: From Menarche to Menopause

Uterine leiomyomata (UL) have a substantial impact on women's health, but relatively few studies have identified opportunities for primary prevention of these neoplasms. Most established risk factors are not modifiable, including premenopausal age, African ancestry, age at menarche, and childbearing history. The main challenge in studying UL is that a large proportion of tumors are asymptomatic. Herein, we review the epidemiology of UL from published studies to date. We highlight the advantages of ultrasound screening studies and the ways in which their innovative methods have helped clarify the etiology of disease. We conclude with a discussion of promising new hypotheses.

Induction of expression of aryl hydrocarbon receptor-dependent genes in human HepaRG cell line modified by shRNA and treated with β-naphthoflavone

The aryl hydrocarbon receptor (AhR) mediates a variety of biological responses to ubiquitous environmental pollutants. In this study, the effects of administration of β-naphthoflavone (BNF), a potent AhR ligand, on the expression of AhR-dependent genes were examined by microarray and qPCR analysis in both, differentiated and undifferentiated HepaRG cell lines. To prove that BNF-induced changes of investigated genes were indeed AhR-dependent, we knock down the expression of AhR by stable transfection of HepaRG cells with shRNA. Regardless of genetical identity, our results clearly demonstrate different expression profiles of AhR-dependent genes between differentiated and undifferentiated HepaRG cells. Genes involved in metabolism of xenobiotics constitute only minute fraction of all genes regulated by AhR in HepaRG cells. Participation of AhR in induction of expression of genes associated with regulation of apoptosis or involved in cell proliferation as well as AhR-dependent inhibition of genes connected to cell adhesion could support suggestion of involvement of AhR not only in initiation but also in progression of carcinogenesis. Among the AhR-dependent genes known to be involved in metabolism of xenobiotics, cytochromes P4501A1 and 1B1 belong to the most inducible by BNF. On the contrary, expression of GSTA1 and GSTA2 was significantly inhibited after BNF treatment of HepaRG cells. Among the AhR-dependent genes that are not involved in metabolism of xenobiotics SERPINB2, STC2, ARL4C, and TIPARP belong to the most inducible by BNF. Our results imply involvement of Ah receptor in regulation of CYP19A1, the gene-encoding aromatase, and an enzyme responsible for a key step in the biosynthesis of estrogens.

Dimethyl-Benz(a)anthracene: A mammary carcinogen and a neuroendocrine disruptor

Polycyclic Aromatic Hydrocarbons (PAHs) are potent carcinogens. Among these, dimethylbenz(a)anthracene (DMBA) is well known for its capacity to induce mammary carcinomas in female Sprague-Dawley (SD) rats. Ovariectomy suppresses the susceptibility of this model to DMBA, thus suggesting that the inducible action of the carcinogen depends on ovarian hormones. The promotion of DMBA-induced adenocarcinoma is accompanied by a series of neuroendocrine disruptions of both Hypothalamo-Pituitary-Gonadal (HPG) and Hypothalamo-Pituitary-Adrenal (HPA) axes and of the secretion of melatonin during the latency period of 2 months that precedes the occurrence of the first mammary tumor. The present review analyses the various neuroendocrine disruptions that occur along the HPG and the HPA axes, and the marked inhibitory effect of the carcinogen on melatonin secretion. The possible relationships between the neuroendocrine disruptions, which essentially consist in an increased pre-ovulatory secretion of 17β-estradiol and prolactin, associated with a marked reduction of melatonin secretion, and the decrease in gene expression of the receptors for aryl-hydrocarbons receptor (AhR) and 17β-estradiol (ERα; ERβ) are also discussed.

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Polycyclic Aromatic Hydrocarbons influence promotion of breast tumorigenesis.

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Dimethylbenz(a)anthracene (DMBA) alters neuroendocrine axes and melatonin secretion.

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DMBA modulates the activity of aryl hydrocarbon and 17β-estradiol receptors.

ERβ-Dependent Direct Suppression of Human and Murine Th17 Cells and Treatment of Established Central Nervous System Autoimmunity by a Neurosteroid

Multiple sclerosis (MS), an autoimmune disease of the CNS, is mediated by autoreactive Th cells. A previous study showed that the neurosteroid dehydroepiandrosterone (DHEA), when administered preclinically, could suppress progression of relapsing-remitting experimental autoimmune encephalomyelitis (EAE). However, the effects of DHEA on human or murine pathogenic immune cells, such as Th17, were unknown. In addition, effects of this neurosteroid on symptomatic disease, as well as the receptors involved, had not been investigated. In this study, we show that DHEA suppressed peripheral responses from patients with MS and reversed established paralysis and CNS inflammation in four different EAE models, including the 2D2 TCR-transgenic mouse model. DHEA directly inhibited human and murine Th17 cells, inducing IL-10-producing regulatory T cells. Administration of DHEA in symptomatic mice induced regulatory CD4(+) T cells that were suppressive in an IL-10-dependent manner. Expression of the estrogen receptor β by CD4(+) T cells was necessary for DHEA-mediated EAE amelioration, as well as for direct downregulation of Th17 responses. TGF-β1 as well as aryl hydrocarbon receptor activation was necessary for the expansion of IL-10-producing T cells by DHEA. Thus, our studies demonstrate that compounds that inhibit pathogenic Th17 responses and expand functional regulatory cells could serve as therapeutic agents for autoimmune diseases, such as MS.

The Q-rich/PST domain of the AHR regulates both ligand-induced nuclear transport and nucleocytoplasmic shuttling

The aryl hydrocarbon receptor (AHR) shuttles continuously between cytoplasm and nucleus, unless ligand-binding triggers association with the AHR nuclear translocator (ARNT) and subsequent binding to cognate DNA motifs. We have now identified Val 647 as mandatory residue for export from the nucleus and AHR-function. This residue prevents inactivation of the receptor as a consequence of nuclear sequestration via constitutive import. Concomitantly mutants lacking this residue are exclusively localised in the nucleus. Although ligands accelerate nuclear import transiently, stable nuclear transition depends on a motif adjacent to Val 647 that comprises residues 650-661. Together, this defined region within the Q-rich domain regulates intracellular trafficking of the AHR in context of both nucleocytoplasmic shuttling and receptor activation. Nuclear export therefore depends on the previously characterised N-terminal NES and the newly identified motif that includes V647. Nucleocytoplasmic distribution of full-length human AHR is further affected by a section of the PST domain that shows sequence similarities with nuclear export signals. In concert, these motifs maintain a predominant cytoplasmic compartmentalisation, receptive for ligand binding.

Balancing intestinal and systemic inflammation through cell type-specific expression of the aryl hydrocarbon receptor repressor

As a sensor of polyaromatic chemicals the aryl hydrocarbon receptor (AhR) exerts an important role in immune regulation besides its requirement for xenobiotic metabolism. Transcriptional activation of AhR target genes is counterregulated by the AhR repressor (AhRR) but the exact function of the AhRR in vivo is currently unknown. We here show that the AhRR is predominantly expressed in immune cells of the skin and intestine, different from other AhR target genes. Whereas AhRR antagonizes the anti-inflammatory function of the AhR in the context of systemic endotoxin shock, AhR and AhRR act in concert to dampen intestinal inflammation. Specifically, AhRR contributes to the maintenance of colonic intraepithelial lymphocytes and prevents excessive IL-1β production and Th17/Tc17 differentiation. In contrast, the AhRR enhances IFN-γ-production by effector T cells in the inflamed gut. Our findings highlight the physiologic importance of cell-type specific balancing of AhR/AhRR expression in response to microbial, nutritional and other environmental stimuli.

ERβ in CD4+ T Cells Is Crucial for Ligand-Mediated Suppression of Central Nervous System Autoimmunity

The development of therapies for multiple sclerosis targeting pathogenic T cell responses remains imperative. Previous studies have shown that estrogen receptor (ER) β ligands could inhibit experimental autoimmune encephalomyelitis. However, the effects of ERβ-specific ligands on human or murine pathogenic immune cells, such as Th17, were not investigated. In this article, we show that the synthetic ERβ-specific ligand 4-(2-phenyl-5,7-bis[trifluoromethyl]pyrazolo[1,5-a]pyrimidin-3-yl)phenol (PHTPP) reversed established paralysis and CNS inflammation, characterized by a dramatic suppression of pathogenic Th responses as well as induction of IL-10-producing regulatory CD4(+) T cell subsets in vivo. Moreover, administration of PHTPP in symptomatic mice induced regulatory CD4(+) T cells that were suppressive in vivo. PHTPP-mediated experimental autoimmune encephalomyelitis amelioration was canceled in mice with ERβ-deficient CD4(+) T cells only, indicating that expression of ERβ by these cells is crucial for the observed therapeutic effect. Importantly, synthetic ERβ-specific ligands acting directly on CD4(+) T cells suppressed human and mouse Th17 cells, downregulating Th17 cell signature gene expression and expanding IL-10-producing T cells among them. TGF-β1 and aryl hydrocarbon receptor activation enhanced the ERβ ligand-mediated expansion of IL-10-producing T cells among Th17 cells. In addition, these ERβ-specific ligands promoted the induction and maintenance of Foxp3(+) T regulatory cells, as well as their in vitro suppressive function. Thus, ERβ-specific ligands targeting pathogenic Th17 cells and inducing functional regulatory cells represent a promising subset of therapeutic agents for multiple sclerosis.

Cross-Talk in the Female Rat Mammary Gland: Influence of Aryl Hydrocarbon Receptor on Estrogen Receptor Signaling

BACKGROUND

Cross-talk between the aryl hydrocarbon receptor (AHR) and the estrogen receptor (ER) plays a major role in signaling processes in female reproductive organs.

OBJECTIVES

We investigated the influence of the AHR ligand 3-methylcholanthrene (3-MC) on ER-mediated signaling in mammary gland tissue of ovariectomized (ovx) rats.

METHODS

After 14 days of hormonal decline, ovx rats were treated for 3 days with 4 μg/kg 17β-estradiol (E2), 15 mg/kg 8-prenylnaringenin (8-PN), 15 mg/kg 3-MC, or a combination of these compounds (E2 + 3-MC, 8-PN + 3-MC). Whole-mount preparations of the mammary gland were used to count terminal end buds (TEBs). Protein expression studies (immunohistochemistry, immunofluorescence), a cDNA microarray, pathway analyses, and quantitative real-time polymerase chain reaction (qPCR) were performed to evaluate the interaction between AHR- and ER-mediated signaling pathways.

RESULTS

E2 treatment increased the number of TEBs and the levels of Ki-67 protein and progesterone receptor (PR); this treatment also changed the expression of 325 genes by more than 1.5-fold. Although 3-MC treatment alone had marginal impact on gene or protein expression, when rats were co-treated with 3-MC and E2, 3-MC strongly inhibited E2-induced TEB development, protein synthesis, and the expression of nearly half of E2-induced genes. This inhibitory effect of 3-MC was partially mirrored when 8-PN was used as an ER ligand. The anti-estrogenicity of ligand-activated AHR was at least partly due to decreased protein levels of ERα in ductal epithelial cells.

CONCLUSION

Our data show transcriptome-wide anti-estrogenic properties of ligand-activated AHR on ER-mediated processes in the mammary gland, thereby contributing an explanation for the chemopreventive and endocrine-disrupting potential of AHR ligands.

CITATION

Helle J, Bader MI, Keiler AM, Zierau O, Vollmer G, Chittur SV, Tenniswood M, Kretzschmar G. 2016. Cross-talk in the female rat mammary gland: influence of aryl hydrocarbon receptor on estrogen receptor signaling. Environ Health Perspect 124:601-610; http://dx.doi.org/10.1289/ehp.1509680.

The metabolite 3,4,3',4'-tetrachloroazobenzene (TCAB) exerts a higher ecotoxicity than the parent compounds 3,4-dichloroaniline (3,4-DCA) and propanil

3,4,3',4'-tetrachloroazobenzene (TCAB) is not commercially manufactured but formed as an unwanted by-product in the manufacturing of 3,4-dichloroaniline (3,4-DCA) or metabolized from the degradation of chloranilide herbicides, like propanil. While a considerable amount of research has been done concerning the toxicological and ecotoxicological effects of propanil and 3,4-DCA, limited information is available on TCAB. Our study examined the toxicity of TCAB in comparison to its parent compounds propanil and 3,4-DCA, using a battery of bioassays including in vitro with aryl hydrocarbon receptor (AhR) mediated activity by the 7-ethoxyresorufin-O-deethylase (EROD) assay and micro-EROD, endocrine-disrupting activity with chemically activated luciferase gene expression (CALUX) as well as in vivo with fish embryo toxicity (FET) assays with Danio rerio. Moreover, the quantitative structure activity response (QSAR) concepts were applied to simulate the binding affinity of TCAB to certain human receptors. It was shown that TCAB has a strong binding affinity to the AhR in EROD and micro-EROD induction assay, with the toxic equivalency factor (TEF) of 8.7×10(-4) and 1.2×10(-5), respectively. TCAB presented to be a weak endocrine disrupting compound with a value of estradiol equivalence factor (EEF) of 6.4×10(-9) and dihydrotestosterone equivalency factor (DEF) of 1.1×10(-10). No acute lethal effects of TCAB were discovered in FET test after 96h of exposure. Major sub-lethal effects detected were heart oedema, yolk malformation, as well as absence of blood flow and tail deformation. QSAR modelling suggested an elevated risk to environment, particularly with respect to binding to the AhR. An adverse effect potentially triggering ERβ, mineralocorticoid, glucocorticoid and progesterone receptor activities might be expected. Altogether, the results obtained suggest that TCAB exerts a higher toxicity than both propanil and 3,4-DCA. This should be considered when assessing the impact of these compounds for the environment and also for regulatory decisions.

Mitochondrial-targeted aryl hydrocarbon receptor and the impact of 2,3,7,8-tetrachlorodibenzo-p-dioxin on cellular respiration and the mitochondrial proteome

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor within the Per-Arnt-Sim (PAS) domain superfamily. Exposure to the most potent AHR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is associated with various pathological effects including metabolic syndrome. While research over the last several years has demonstrated a role for oxidative stress and metabolic dysfunction in AHR-dependent TCDD-induced toxicity, the role of the mitochondria in this process has not been fully explored. Our previous research suggested that a portion of the cellular pool of AHR could be found in the mitochondria (mitoAHR). Using a protease protection assay with digitonin extraction, we have now shown that this mitoAHR is localized to the inter-membrane space (IMS) of the organelle. TCDD exposure induced a degradation of mitoAHR similar to that of cytosolic AHR. Furthermore, siRNA-mediated knockdown revealed that translocase of outer-mitochondrial membrane 20 (TOMM20) was involved in the import of AHR into the mitochondria. In addition, TCDD altered cellular respiration in an AHR-dependent manner to maintain respiratory efficiency as measured by oxygen consumption rate (OCR). Stable isotope labeling by amino acids in cell culture (SILAC) identified a battery of proteins within the mitochondrial proteome influenced by TCDD in an AHR-dependent manner. Among these, 17 proteins with fold changes≥2 are associated with various metabolic pathways, suggesting a role of mitochondrial retrograde signaling in TCDD-mediated pathologies. Collectively, these studies suggest that mitoAHR is localized to the IMS and AHR-dependent TCDD-induced toxicity, including metabolic dysfunction, wasting syndrome, and hepatic steatosis, involves mitochondrial dysfunction.

Regulation of vitellogenin (vtg1) and estrogen receptor (er) gene expression in zebrafish (Danio rerio) following the administration of Cd²⁺ and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

We evaluated the individual and joint estrogenic effects of cadmium (Cd(2+)) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the zebrafish liver (ZFL) cell line, zebrafish embryo, larvae and the liver of adult zebrafish. The mRNA expression of vtg1 was inhibited by Cd(2+), but unaffected by TCDD in ZFL cells. Similar changes in the mRNA levels of ERα, ERβ1, ERβ2 and GPER (G protein coupled estrogen receptor) in ZFL cells were also observed. Deletion mutants of vtg1 gene promoters were constructed to investigate transcriptional regulation, and we found that all of the constructs failed to respond to TCDD or Cd(2+). However, after co-transfection with a vtg1 promoter-luciferase construct to the ERα, ERβ1, ERβ2 and GPER expression vectors, decreased luciferase activity was observed in the ERα co-transfection group after treatment with Cd(2+), suggesting that ERα participates in vtg1 transcriptional regulation and is affected by Cd(2+). Differences in the regulation of the mRNA levels of these genes were also observed between different developmental stages and between the livers of male and female zebrafish.

Metabolic and redox barriers in the skin exposed to drugs and xenobiotics

INTRODUCTION

Growing exposure of human skin to environmental and occupational hazards, to numerous skin care/beauty products, and to topical drugs led to a biomedical concern regarding sustainability of cutaneous chemical defence that is essential for protection against intoxication. Since skin is the largest extra-hepatic drug/xenobiotic metabolising organ where redox-dependent metabolic pathways prevail, in this review, publications on metabolic processes leading to redox imbalance (oxidative stress) and its autocrine/endocrine impact to cutaneous drug/xenobiotic metabolism were scrutinised.

AREAS COVERED

Chemical and photo-chemical skin barriers contain metabolic and redox compartments: their protective and homeostatic functions. The review will examine the striking similarity of adaptive responses to exogenous chemical/photo-chemical stressors and endogenous toxins in cutaneous metabolic and redox system; the role(s) of xenobiotics/drugs and phase II enzymes in the endogenous antioxidant defence and maintenance of redox balance; redox regulation of interactions between metabolic and inflammatory responses in skin cells; skin diseases sharing metabolic and redox problems (contact dermatitis, lupus erythematosus, and vitiligo)

EXPERT OPINION

Due to exceptional the redox dependence of cutaneous metabolic pathways and interaction of redox active metabolites/exogenous antioxidants with drug/xenobiotic metabolism, metabolic tests of topical xenobiotics/drugs should be combined with appropriate redox analyses and performed on 3D human skin models.

Aryl Hydrocarbon Receptor Plays Protective Roles against High Fat Diet (HFD)-induced Hepatic Steatosis and the Subsequent Lipotoxicity via Direct Transcriptional Regulation of Socs3 Gene Expression

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor regulating the expression of genes involved in xenobiotic response. Recent studies have suggested that AhR plays essential roles not only in xenobiotic detoxification but also energy metabolism. Thus, in this study, we studied the roles of AhR in lipid metabolism. Under high fat diet (HFD) challenge, liver-specific AhR knock-out (AhR LKO) mice exhibited severe steatosis, inflammation, and injury in the liver. Gene expression analysis and biochemical study revealed thatde novolipogenesis activity was significantly increased in AhR LKO mice. In contrast, induction of suppressor of cytokine signal 3 (Socs3) expression by HFD was attenuated in the livers of AhR LKO mice. Rescue of theSocs3gene in the liver of AhR LKO mice cancelled the HFD-induced hepatic lipotoxicities. Promoter analysis established Socs3 as novel transcriptional target of AhR. These results indicated that AhR plays a protective role against HFD-induced hepatic steatosis and the subsequent lipotoxicity effects, such as inflammation, and that the mechanism of protection involves the direct transcriptional regulation ofSocs3expression by AhR.

Redox Control of Multidrug Resistance and Its Possible Modulation by Antioxidants

Clinical efficacy of anticancer chemotherapies is dramatically hampered by multidrug resistance (MDR) dependent on inherited traits, acquired defence against toxins, and adaptive mechanisms mounting in tumours. There is overwhelming evidence that molecular events leading to MDR are regulated by redox mechanisms. For example, chemotherapeutics which overrun the first obstacle of redox-regulated cellular uptake channels (MDR1, MDR2, and MDR3) induce a concerted action of phase I/II metabolic enzymes with a temporal redox-regulated axis. This results in rapid metabolic transformation and elimination of a toxin. This metabolic axis is tightly interconnected with the inducible Nrf2-linked pathway, a key switch-on mechanism for upregulation of endogenous antioxidant enzymes and detoxifying systems. As a result, chemotherapeutics and cytotoxic by-products of their metabolism (ROS, hydroperoxides, and aldehydes) are inactivated and MDR occurs. On the other hand, tumour cells are capable of mounting an adaptive antioxidant response against ROS produced by chemotherapeutics and host immune cells. The multiple redox-dependent mechanisms involved in MDR prompted suggesting redox-active drugs (antioxidants and prooxidants) or inhibitors of inducible antioxidant defence as a novel approach to diminish MDR. Pitfalls and progress in this direction are discussed.

The emerging role of aryl hydrocarbon receptor in the activation and differentiation of Th17 cells

The aryl hydrocarbon receptor (AHR) is a cytoplasmic transcription factor, which plays an essential role in the xenobiotic metabolism in a wide variety of cells. The AHR gene is evolutionarily conserved and it has a central role not only in the differentiation and maturation of many tissues, but also in the toxicological metabolism of the cell by the activation of metabolizing enzymes. Several lines of evidence support that both AHR agonists and antagonists have profound immunological effects; and recently, the AHR has been implicated in antibacterial host defense. According to recent studies, the AHR is essential for the differentiation and activation of T helper 17 (Th17) cells. It is well known that Th17 cells have a central role in the development of inflammation, which is crucial in the defense against pathogens. In addition, Th17 cells play a major role in the pathogenesis of several autoimmune diseases such as rheumatoid arthritis. Therefore, the AHR may provide connection between the environmental chemicals, the immune regulation, and autoimmunity. In the present review, we summarize the role of the AHR in the Th17 cell functions.