Effects of several dioxin-like compounds on estrogen metabolism in the malignant MCF-7 and nontumorigenic MCF-10A human mammary epithelial cell lines

Effects of xenobiotics on CYP1 enzyme-mediated biotransformation and bioactivation of estradiol

Endogenous estradiol (E2) exerts diverse physiological and pharmacological activities, commonly used for hormone replacement therapy. However, prolonged and excessive exposure to E2 potentially increases estrogenic cancer risk. Reportedly, CYP1 enzyme-mediated biotransformation of E2 is largely concerned with its balance between detoxification and carcinogenic pathways. Among the three key CYP1 enzymes (CYP1A1, CYP1A2, and CYP1B1), CYP1A1 and CYP1A2 mainly catalyze the formation of nontoxic 2-hydroxyestradiol (2-OH-E2), while CYP1B1 specifically catalyzes the formation of genotoxic 4-hydroxyestradiol (4-OH-E2). 4-OH-E2 can be further metabolized to electrophilic quinone intermediates accompanied by the generation of reactive oxygen species (ROS), triggering DNA damage. Since abnormal alterations in CYP1 activities can greatly affect the bioactivation process of E2, regulatory effects of xenobiotics on CYP1s are essential for E2-associated cancer development. To date, thousands of natural and synthetic compounds have been found to show potential inhibition and/or induction actions on the three CYP1 members. Generally, these chemicals share similar planar polycyclic skeletons, the structural motifs and substituent groups of which are important for their inhibitory/inductive efficiency and selectivity toward CYP1 enzymes. This review comprehensively summarizes these known inhibitors and/or inductors of E2-metabolizing CYP1s based on chemical categories and discusses their structure-activity relationships, which would contribute to better understanding of the correlation between xenobiotic-regulated CYP1 activities and estrogenic cancer susceptibility.

Interindividual variation contributes to differential PCB 126 induced gene expression in primary breast epithelial cells and tissues

PCB 126 is a pervasive, dioxin-like chemical pollutant which can activate the aryl hydrocarbon receptor (AhR). Despite being banned from the market, PCB 126 can be detected in breast milk to this day. The extent to which interindividual variation impacts the adverse responses to this chemical in the breast tissue remains unclear. This study aimed to investigate the impact of 3 nM PCB 126 on gene expression in a panel of genetically diverse benign human breast epithelial cell (HBEC) cultures and patient derived breast tissues. Six patient derived HBEC cultures were treated with 3 nM PCB 126. RNAseq was used to interrogate the impact of exposure on differential gene expression. Gene expression changes from the top critical pathways were confirmed via qRT-PCR in a larger panel of benign patient derived HBEC cultures, as well as in patient-derived breast tissue explant cultures. RNAseq analysis of HBEC cultures revealed a signature of 144 genes significantly altered by 3 nM PCB 126 treatment. Confirmation of 8 targets using a panel of 12 HBEC cultures and commercially available breast cell lines demonstrated that while the induction of canonical downstream target gene, CYP1A1, was consistent across our primary HBECs, other genes including AREG, S100A8, IL1A, IL1B, MMP7, and CCL28 exhibited significant variability across individuals. The dependence on the activity of the aryl hydrocarbon receptor was confirmed using inhibitors. PCB 126 can induce significant and consistent changes in gene expression associated with xenobiotic metabolism in benign breast epithelial cells. Although the induction of most genes was reliant on the AhR, significant variability was noted between genes and individuals. These data suggest that there is a bifurcation of the pathway following AhR activation that contributes to the variation in interindividual responses.

Human Family 1-4 cytochrome P450 enzymes involved in the metabolic activation of xenobiotic and physiological chemicals: an update

This is an overview of the metabolic activation of drugs, natural products, physiological compounds, and general chemicals by the catalytic activity of cytochrome P450 enzymes belonging to Families 1-4. The data were collected from > 5152 references. The total number of data entries of reactions catalyzed by P450s Families 1-4 was 7696 of which 1121 (~ 15%) were defined as bioactivation reactions of different degrees. The data were divided into groups of General Chemicals, Drugs, Natural Products, and Physiological Compounds, presented in tabular form. The metabolism and bioactivation of selected examples of each group are discussed. In most of the cases, the metabolites are directly toxic chemicals reacting with cell macromolecules, but in some cases the metabolites formed are not direct toxicants but participate as substrates in succeeding metabolic reactions (e.g., conjugation reactions), the products of which are final toxicants. We identified a high level of activation for three groups of compounds (General Chemicals, Drugs, and Natural Products) yielding activated metabolites and the generally low participation of Physiological Compounds in bioactivation reactions. In the group of General Chemicals, P450 enzymes 1A1, 1A2, and 1B1 dominate in the formation of activated metabolites. Drugs are mostly activated by the enzyme P450 3A4, and Natural Products by P450s 1A2, 2E1, and 3A4. Physiological Compounds showed no clearly dominant enzyme, but the highest numbers of activations are attributed to P450 1A, 1B1, and 3A enzymes. The results thus show, perhaps not surprisingly, that Physiological Compounds are infrequent substrates in bioactivation reactions catalyzed by P450 enzyme Families 1-4, with the exception of estrogens and arachidonic acid. The results thus provide information on the enzymes that activate specific groups of chemicals to toxic metabolites.

Assessing anti-estrogenic effects of AHR ligands in primary human and rat endometrial epithelial cells

Unopposed estrogenic action in the uterus can lead to the development of endometrial cancer in both humans and rats. Aryl hydrocarbon receptor (AHR) activation gives rise to anti-estrogenic actions and may consequently reduce the development of endometrial cancer. In this study, the anti-estrogenic potential of the AHR ligands 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and DELAQ, a metabolite of the pharmaceutical laquinimod, was assessed in in primary human and rat endometrial epithelial cells (EECs) with and without co-exposure to endogenous hormones. In human EECs, estradiol and progesterone did not affect AHR gene expression, but in rat EECs, progesterone decreased Ahre xpression (1.4-fold). In accordance, AHR-mediated induction of Cyp1a1/1b1 expression by DELAQ and TCDD decreased in hormone-treated rat EECs. DELAQ was 22-fold more potent than TCDD in human EECs in inducing CYP1A1/1B1 gene expression, while DELAQ was approximately 16-33-fold less potent than TCDD in rat EECs. In human EECs, 10 nM DELAQ decreased estradiol-induced expression of growth-regulated estrogen receptor binding 1 (GREB1) by 1.8-fold. In rat EECs, both DELAQ and TCDD did not affect the expression of estradiol-induced genes. This study shows that AHR ligand DELAQ, but not TCDD, causes anti-estrogenic effects in primary human EECs. Furthermore, although AHR-mediated CYP1A1/1B1/Cyp1a1/1b1 induction by DELAQ and TCDD was stronger in rat EECs than human EECs, this did not result in apparent anti-estrogenic effects in the rat cells. This study shows that primary human and rat endometrial cells respond differently towards hormones and AHR ligands. This should be considered in human risk assessment based on rodent studies.

Risk of breast cancer and adipose tissue concentrations of polychlorinated biphenyls and organochlorine pesticides: a hospital-based case-control study in Chinese women

Polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), and dichlorodiphenyldichloroethylene (DDE) are suspected to be associated with breast cancer risk, but the results are controversial. This study was performed to evaluate the associations between adipose tissue PCB, DDT, and DDE concentrations and breast cancer risk. Two hundred and nine pathologically diagnosed breast cancer cases and 165 controls were recruited from three local hospitals in Shantou city, China, from 2014 to 2016. Concentrations of 7 PCB congeners, p,p'-DDT, and p,p'-DDE were measured in adipose tissues obtained from the breast for cases and the breast/abdomen for controls during surgery. Clinicopathologic information and demographic characteristics were collected from medical records. PCBs, p,p'-DDT, and p,p'-DDE concentrations in adipose tissues were compared between cases and controls. Multivariate logistic regression model was used to analyze the risk of breast cancer by PCBs, p,p'-DDT, and p,p'-DDE concentrations in adipose tissues. Breast cancer cases have relatively higher menarche age, higher breastfeeding and postmenopausal proportion than controls. Levels of PCB-52, PCB-101, PCB-118, PCB-138, PCB-153, PCB-180, total PCBs (∑PCBs), and p,p'-DDE were relatively higher in breast cancer cases than controls. Breast cancer risk was increased in the third tertile of PCB-101, PCB-118, PCB-138, PCB-153, PCB-180, ∑PCBs, and p,p'-DDE as compared with the first tertile in both adjusted and unadjusted logistic regression models (odds ratios [ORs] were from 1.58 to 7.88); and increased linearly across categories of PCB-118 and p,p'-DDE in unadjusted model, and PCB-118 and PCB-153 in the adjusted model with trend (all P < 0.01). While breast cancer risk was declined in the second tertile of PCB-28, PCB-52, and PCB-101 in both unadjusted and adjusted models, also second tertile of p,p'-DDT and third tertile of PCB-28 in the adjusted models. This study suggests associations between the exposure of PCBs, p,p'-DDT, and p,p'-DDE and breast cancer risk. Based on adjusted models, PCB-118, PCB-138, PCB-153, PCB-180, ∑PCBs, and p,p'-DDE exposures increase breast cancer risk at current exposure levels, despite existing inconsistent even inverse results in PCB-28, PCB-52, PCB-101, and p,p'-DDT. More epidemiological studies are still needed to verify these findings in different populations.

Laser irradiation affects the biological identity and cellular uptake of plasmonic nanoparticles

The biological identity of nanoparticles (NPs) is defined by a protein layer formed on their surface, called protein corona (PC), once they meet the biological milieu. Any change in the PC composition may influence the biological fate of NPs. The PC composition is strongly dependent on several parameters including the physicochemical properties of NPs, and biological and environmental factors. As one of the main features of plasmonic NPs is their capacity to induce local heating by laser irradiation, we hypothesized that laser irradiation may change the biological identity of NPs and therefore alter their biological fate. To test this hypothesis, here we investigated the effects of either simultaneous or sequential laser irradiation on the conformations of a few proteins selected from two main categories of plasma proteins (i.e. human serum albumin and human fibrinogen) on the surfaces of gold nanorods (AuNRs). The outcomes revealed a significant role of laser irradiation on conformational changes of fibrinogen compared to albumin. Moreover, the effects of plasmonic heating - at various times - on the achieved corona composition from interactions of AuNRs and human plasma with various concentrations were monitored. Consequently, the cellular uptake of the corona coated AuNRs was measured in two cell types: malignant (MCF-7) and normal (MCF-10A) breast cell lines. The results demonstrated a substantial reduction in the cellular uptake of AuNRs in response to an increase in the laser irradiation time, especially in MCF-10A. Our results may pave the way for a mechanistic understanding of the biological identity of plasmonic NPs which in turn can help their safe and efficient clinical translations.

Modulation of estrogen synthesis and metabolism by phytoestrogens in vitro and the implications for women's health

Phytoestrogens are increasingly used as dietary supplements due to their suggested health promoting properties, but also by women for breast enhancement and relief of menopausal symptoms. Generally, phytoestrogens are considered to exert estrogenic activity via estrogen receptors (ERs), but they may also affect estrogen synthesis and metabolism locally in breast, endometrial and ovarian tissues. Considering that accurate regulation of local hormone levels is crucial for normal physiology, it is not surprising that interference with hormonal synthesis and metabolism is associated with a wide variety of women's health problems, varying from altered menstrual cycle to hormone-dependent cancers. Yet, studies on phytoestrogens have mainly focused on ER-mediated effects of soy-derived phytoestrogens, with less attention paid to steroid synthesis and metabolism or other phytoestrogens. This review aims to evaluate the potential of phytoestrogens to modulate local estrogen levels and the implications for women's health. For that, an overview is provided of the effects of commonly used phytoestrogens, i.e. 8-prenylnaringenin, biochanin A, daidzein, genistein, naringenin, resveratrol and quercetin, on estrogen synthesizing and metabolizing enzymes in vitro. The potential implications for women's health are assessed by comparing the in vitro effect concentrations with blood concentrations that can be found after intake of these phytoestrogens. Based on this evaluation, it can be concluded that high-dose supplements with phytoestrogens might affect breast and endometrial health or fertility in women via the modulation of steroid hormone levels. However, more data regarding the tissue levels of phytoestrogens and effect data from dedicated, tissue-specific assays are needed for a better understanding of potential risks. At least until more certainty regarding the safety has been established, especially young women would better avoid using supplements containing high doses of phytoestrogens.

Hop (Humulus lupulus L.) Extract and 6-Prenylnaringenin Induce P450 1A1 Catalyzed Estrogen 2-Hydroxylation

Humulus lupulus L. (hops) is a popular botanical dietary supplement used by women as a sleep aid and for postmenopausal symptom relief. In addition to its efficacy for menopausal symptoms, hops can also modulate the chemical estrogen carcinogenesis pathway and potentially protect women from breast cancer. In the present study, an enriched hop extract and the key bioactive compounds [6-prenylnarigenin (6-PN), 8-prenylnarigenin (8-PN), isoxanthohumol (IX), and xanthohumol (XH)] were tested for their effects on estrogen metabolism in breast cells (MCF-10A and MCF-7). The methoxyestrones (2-/4-MeOE₁) were analyzed as biomarkers for the nontoxic P450 1A1 catalyzed 2-hydroxylation and the genotoxic P450 1B1 catalyzed 4-hydroxylation pathways, respectively. The results indicated that the hop extract and 6-PN preferentially induced the 2-hydroxylation pathway in both cell lines. 8-PN only showed slight up-regulation of metabolism in MCF-7 cells, whereas IX and XH did not have significant effects in either cell line. To further explore the influence of hops and its bioactive marker compounds on P450 1A1/1B1, mRNA expression and ethoxyresorufin O-dealkylase (EROD) activity were measured. The results correlated with the metabolism data and showed that hop extract and 6-PN preferentially enhanced P450 1A1 mRNA expression and increased P450 1A1/1B1 activity. The aryl hydrocarbon receptor (AhR) activation by the isolated compounds was tested using xenobiotic response element (XRE) luciferase construct transfected cells. 6-PN was found to be an AhR agonist that significantly induced XRE activation and inhibited 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced XRE activity. 6-PN mediated induction of EROD activity was also inhibited by the AhR antagonist CH223191. These data show that the hop extract and 6-PN preferentially enhance the nontoxic estrogen 2-hydroxylation pathway through AhR mediated up-regulation of P450 1A1, which further emphasizes the importance of standardization of botanical extracts to multiple chemical markers for both safety and desired bioactivity.

Evaluation of relative effect potencies (REPs) for dioxin-like compounds to derive systemic or human-specific TEFs to improve human risk assessment

Toxic equivalency factors (TEFs) are generally applied for estimating human risk of dioxins and dioxin-like compounds using systemic (e.g., blood) levels, even though these TEFs are established based on intake doses in rodent studies. This review shows that systemic relative effect potencies (REPs) can deviate substantially from intake REPs, but are similar to in vitro-derived REPs. Interestingly, the in vitro REPs for 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (HpCDD) and 2,3,4,7,8-pentachlorodibenzofuran (4-PeCDF) are up to one order of magnitude higher than their in vivo REPs and WHO-TEFs, based on oral intake. In addition, clear species-differences in in vitro REPs were apparent for some congeners. Especially the human-derived REP for polychlorinated biphenyl 126 is one to two orders of magnitude lower than rodent REPs and its current WHO-TEF. Next, suggested adapted systemic or human-specific TEFs for these congeners were applied to calculate changes in systemic TEQ concentrations in studies from the USA, Germany and Japan and compared with either the JECFA TDI or USEPA RfD of TCDD. Overall, the effect of such TEF changes for these three congeners on total TEQ roughly balances each other out in the general population. However, results may be different for situations in which a specific group of congeners dominates. For those congeners that show a distinct deviation between either intake and systemic REPs or between rodent- and human-based in vitro REPs, we propose that especially REPs derived from human-based in vitro models are weighted more heavily in establishing systemic or human-specific TEF values to improve human health risk assessment.

Biphenyl urea derivatives as selective CYP1B1 inhibitors

Herein, we report the discovery of ‘biphenyl ureas’ as selective CYP1B1 inhibitors.

Endocrine disruption of oestrogen action and female reproductive tract cancers

Endocrine disrupting chemicals (EDC) are ubiquitous and persistent compounds that have the capacity to interfere with normal endocrine homoeostasis. The female reproductive tract is exquisitely sensitive to the action of sex steroids, and oestrogens play a key role in normal reproductive function. Malignancies of the female reproductive tract are the fourth most common cancer in women, with endometrial cancer accounting for most cases. Established risk factors for development of endometrial cancer include high BMI and exposure to oestrogens or synthetic compounds such as tamoxifen. Studies on cell and animal models have provided evidence that many EDC can bind oestrogen receptors and highlighted early life exposure as a window of risk for adverse lifelong effects on the reproductive system. The most robust evidence for a link between early life exposure to EDC and adverse reproductive health has come from studies on women who were exposed in utero to diethylstilbestrol. Demonstration that EDC can alter expression of members of the HOX gene cluster highlights one pathway that might be vulnerable to their actions. In summary, evidence for a direct link between EDC exposure and cancers of the reproductive system is currently incomplete. It will be challenging to attribute causality to any single EDC when exposure and development of malignancy may be separated by many years and influenced by lifestyle factors such as diet (a source of phytoestrogens) and adiposity. This review considers some of the evidence collected to date.

Differential relative effect potencies of some dioxin-like compounds in human peripheral blood lymphocytes and murine splenic cells

Human risk assessment for dioxin-like compounds is typically based on the concentration measured in blood serum multiplied by their assigned toxic equivalency factor (TEF). Consequently, the actual value of the TEF is very important for accurate human risk assessment. In this study we investigated the effect potencies of three polychlorinated dibenzo-p-dioxins (PCDDs), six polychlorinated dibenzofurans (PCDFs) and 10 polychlorinated biphenyls (PCBs) relative to the reference congener 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) in in vitro exposed primary human peripheral blood lymphocytes (PBLs) and mouse splenic cells. REPs were determined based on cytochrome P450 (CYP) 1A1, 1B1 and aryl hydrocarbon receptor repressor (AhRR) gene expression as well as CYP1A1 activity in human PBLs and Cyp1a1 gene expression in murine splenic cells. Estimated median human REPs for 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (1234678-HpCDD), 2,3,4,7,8,-pentachlorodibenzofuran (23478-PeCDF), 1,2,3,4,7,8-hexachlorodibenzofuran (123478-HxCDF) and 1,2,3,4,7,8,9-heptachlorodibenzofuran (1234789-HpCDF) were with 0.1, 1.1, 1 and 0.09, respectively, significantly higher compared to those estimated for mouse with REPs of 0.05, 0.45, 0.09 and 0.04, respectively. Opposite to these results, the estimated median human REP of 3,3',4,4',5-pentachlorobiphenyl (PCB 126), was with 0.001 30-fold lower compared to the mouse REP of 0.03. Furthermore, human REPs for 1234678-HpCDD, 23478-PeCDF, 123478-HxCDF, 1234789-HpCDF and PCB 126 were all outside the ± half log uncertainty range that is taken into account in the WHO-assigned TEFs. Together, these data show congener- and species-specific differences in REPs for some, but not all dioxin-like congeners tested. This suggests that, more emphasis should be placed on human-tissue derived REPs in the establishment of a TEF for human risk assessment.

Phytoestrogens in menopausal supplements induce ER-dependent cell proliferation and overcome breast cancer treatment in an in vitro breast cancer model

Breast cancer treatment by the aromatase inhibitor Letrozole (LET) or Selective Estrogen Receptor Modulator Tamoxifen (TAM) can result in the onset of menopausal symptoms. Women often try to relieve these symptoms by taking menopausal supplements containing high levels of phytoestrogens. However, little is known about the potential interaction between these supplements and breast cancer treatment, especially aromatase inhibitors. In this study, interaction of phytoestrogens with the estrogen receptor alpha and TAM action was determined in an ER-reporter gene assay (BG1Luc4E2 cells) and human breast epithelial tumor cells (MCF-7). Potential interactions with aromatase activity and LET were determined in human adrenocorticocarcinoma H295R cells. We also used the previously described H295R/MCF-7 co-culture model to study interactions with steroidogenesis and tumor cell proliferation. In this model, genistein (GEN), 8-prenylnaringenin (8PN) and four commercially available menopausal supplements all induced ER-dependent tumor cell proliferation, which could not be prevented by physiologically relevant LET and 4OH-TAM concentrations. Differences in relative effect potencies between the H295R/MCF-7 co-culture model and ER-activation in BG1Luc4E2 cells, were due to the effects of the phytoestrogens on steroidogenesis. All tested supplements and GEN induced aromatase activity, while 8PN was a strong aromatase inhibitor. Steroidogenic profiles upon GEN and 8PN exposure indicated a strong inhibitory effect on steroidogenesis in H295R cells and H295R/MCF-7 co-cultures. Based on our in vitro data we suggest that menopausal supplement intake during breast cancer treatment should better be avoided, at least until more certainty regarding the safety of supplemental use in breast cancer patients can be provided.

Effects of Developmental Exposure to Mixtures of Environmental Contaminants on the Hepatic Metabolism of Estradiol-17β in Immature Female Sprague Dawley Rats

Exposure to environmental contaminants induces the activation of cytochrome P450s (CYP) which lead to the hydroxylation of contaminants and endogenous hormones such as estrogens. The hydroxylation of estrogens forms catecholestrogens (CEs), one of them being the mutagenic 4-hydroxyestradiol-17β (4−OH−E2). Catecholestrogens are transformed by catechol -o-methyltransferases (COMTs) into nonreactive methoxyestrogens. To investigate the hepatic metabolism of estradiol-17β in female offspring at postnatal day (PND) 21, pregnant rats were dosed daily from gestation day 1 until PND 21 with 2 dose levels of organochlorine pesticides (OCPs; 0.019 or 1.9 mg/kg per d), methylmercury (MeHg; 0.02 or 2 mg/kg per d), polychlorinated biphenyls (PCBs; 0.011 or 1.1 mg/kg per d), or a mixture (M; 0.05 or 5 mg/kg per d) including all 3 groups of chemicals. Concentrations of organochlorines in the mixture M were based on their proportions in serum of the Canadian Arctic population. The messenger RNA (mRNA) expressions of CYP and COMT were analyzed by quantitative reverse transcriptase–polymerase chain reaction (qRT-PCR). High-performance thin layer chromatography and phosphor imaging were used to measure the transformation of 14C substrates into estrogen metabolites. The low-dose treatments or the MeHg groups had no effect. The high-dose OCP, PCB, and M group increased the production of 2-OH-E2 and 6α-OH-E2, while only the PCB and M groups increased the 2-OH-CE/methoxyestrogen ratio. In all groups, the cytosolic COMT activity exceeded the microsomal production rate of 4-OH-E2. Although the M treatment included the PCB and OCP mixtures, it did not modify the estrogen metabolism more than did the PCB mixture alone. This endocrine disruption information contributes to our understanding of chemical interactions in the toxicology of chemical mixtures.

Relative imbalances in the expression of catechol-O-methyltransferase and cytochrome P450 in breast cancer tissue and their association with breast carcinoma

OBJECTIVE

To investigate the expression levels of genes encoding phase I and phase II estradiol-metabolizing enzymes, and their association with breast cancer risk in Chinese women.

METHODS

The mRNA expression levels of cytochrome P450 (CYP) 1A1, 1B1 and 3A4 and catechol-O-methyltransferase (COMT) were examined in the breast tumor tissues, matched adjacent non-tumor tissues and the tissues with benign breast disease (BBD) by fluorescent quantitative real-time PCR.

RESULTS

Compared to BBD tissue, the mRNA expression of CYP1A1, CYP1B1 and CYP3A4 significantly reduced by 81.8%, 77.5%, and 85.6%, respectively, in the breast tumor tissue and by 27.2%, 38.8%, and 51.3%, respectively, in the adjacent non-tumor tissue in average (p<0.0001). COMT mRNA was 6.9 and 6.4 fold higher in the breast tumor and match non-tumor tissue (p<0.0001) than in the BBD, respectively. The level of COMT detected in pre-menopausal group and lymph nodal stage N1-N2 group was lower than that in post-menopausal group (p=0.0292) and N0 group (p=0.0389), respectively.

CONCLUSION

Significantly deceased expression of estradiol-metabolizing enzymes might result in the excess exposure of intratumoural E2, which could be one of the important risk factors for breast cancer. Significantly elevated COMT expression suggested that COMT could play a key role in breast tumor formation.

Differential effects of a complex organochlorine mixture on the proliferation of breast cancer cell lines

Organochlorine compounds (OCs) are a group of persistent chemicals that accumulate in fatty tissues with age. Although OCs has been tested individually for their capacity to induce breast cancer cell proliferation, few studies examined the effect of complex mixtures that comprise compounds frequently detected in the serum of women. We constituted such an OC mixture containing 15 different components in environmentally relevant proportions and assessed its proliferative effects in four breast cancer cell lines (MCF-7, T47D, CAMA-1, MDAMB231) and in non-cancerous CV-1 cells. We also determined the capacity of the mixture to modulate cell cycle stage of breast cancer cells and to induce estrogenic and antiandrogenic effects using gene reporter assays. We observed that low concentrations of the mixture (100 × 10(3) and 50 × 10(3) dilutions) stimulated the proliferation of MCF-7 cells while higher concentrations (10 × 10(3) and 5 × 10(3) dilutions) had the opposite effect. In contrast, the mixture inhibited the proliferation of non-hormone-dependent cell lines. The mixture significantly increased the number of MCF-7 cells entering the S phase, an effect that was blocked by the antiestrogen ICI 182,780. Low concentrations of the mixture also caused an increase in CAMA-1 cell proliferation but only in the presence estradiol and dihydrotestosterone (p<0.05 at the 50 × 10(3) dilution). DDT analogs and polychlorinated biphenyls all had the capacity to stimulate the proliferation of CAMA-1 cells in the presence of sex steroids. Reporter gene assays further revealed that the mixture and several of its constituents (DDT analogs, aldrin, dieldrin, β-hexachlorocyclohexane, toxaphene) induced estrogenic effects, whereas the mixture and several components (DDT analogs, aldrin, dieldrin and PCBs) inhibited the androgen signaling pathway. Our results indicate that the complex OC mixture increases the proliferation of MCF-7 cells due to its estrogenic potential. The proliferative effect of the mixture on CAMA-1 cells in the presence of sex steroids appears mostly due to the antiandrogenic properties of p,p'-DDE, a major constituent of the mixture. Other mixtures of contaminants that include emerging compounds of interest such as brominated flame retardants and perfluoroalkyl compounds should be tested for their capacity to induce breast cancer cell proliferation.

Health effects from long-range transported contaminants in Arctic top predators: An integrated review based on studies of polar bears and relevant model species

The aim of this review is to provide a thorough overview of the health effects from the complexed biomagnified mixture of long-range transported industrial organochlorines (OCs), polybrominated diphenyl ethers (PBDEs), perfluorinated compounds (PFCs) and mercury (Hg) on polar bear (Ursus maritimus) health. Multiple scientific studies of polar bears indicate negative relationships between exposure to these contaminants and health parameters; however, these are all of a correlative nature and do not represent true cause-and-effects. Therefore, information from controlled studies of farmed Norwegian Arctic foxes (Vulpes lagopus) and housed East and West Greenland sledge dogs (Canis familiaris) were included as supportive weight of evidence in the clarification of contaminant exposure and health effects in polar bears. The review showed that hormone and vitamin concentrations, liver, kidney and thyroid gland morphology as well as reproductive and immune systems of polar bears are likely to be influenced by contaminant exposure. Furthermore, exclusively based on polar bear contaminant studies, bone density reduction and neurochemical disruption and DNA hypomethylation of the brain stem seemed to occur. The range of tissue concentration, at which these alterations were observed in polar bears, were ca. 1-70,000 ng/g lw for OCs (blood plasma concentrations of some PCB metabolites even higher), ca. 1-1000 ng/g lw for PBDEs and for PFCs and Hg 114-3052 ng/g ww and 0.1-50 microg/g ww, respectively. Similar concentrations were found in farmed foxes and housed sledge dogs while the lack of dose response designs did not allow an estimation of threshold levels for oral exposure and accumulated tissue concentrations. Nor was it possible to pinpoint a specific group of contaminants being more important than others nor analyze their interactions. For East Greenland polar bears the corresponding daily SigmaOC and SigmaPBDE oral exposure was estimated to be 35 and 0.34 microg/kg body weight, respectively. Furthermore, PFC concentrations, at which population effect levels could occur, are likely to be reached around year 2012 for the East Greenland polar bear subpopulation if current increasing temporal trends continue. Such proposed reproductive population effects were supported by physiological based pharmacokinetic (PBPK) modelling of critical body residues (CBR) with risk quotients >or=1 for SigmaPCB, dieldrin, SigmaPFC and SigmaOHC (organohalogen contaminant). The estimated daily TEQ for East Greenland polar bears and East Greenland sledge dogs were 32-281-folds above WHO SigmaTEQ guidelines for humans. Compared to human tolerable daily intake (TDI), these were exceeded for PCBs, dieldrin, chlordanes and SigmaHCH in East Greenland polar bears. Comparisons like these should be done with caution, but together with the CBR modelling and T-score estimations, these were the only available tools for polar bear risk evaluation. In conclusion, polar bears seem to be susceptible to contaminant induced stress that may have an overall sub-clinical impact on their health and population status via impacts on their immune and reproductive systems.

Divergent transcriptomic responses to aryl hydrocarbon receptor agonists between rat and human primary hepatocytes

Toxicogenomics has great potential for enhancing our understanding of environmental chemical toxicity, hopefully leading to better informed human health risk assessments. This study employed toxicogenomic technology to reveal species differences in response to two prototypical aryl hydrocarbon receptor (AHR) agonists 2,3,7,8-tetrachlorodibenzo-p-dioxin and the polychlorinated biphenyl (PCB) congener PCB 126. Dose-responses of primary cultures of rat and human hepatocytes were determined using species-specific microarrays sharing over 4000 gene orthologs. Forty-seven human and 79 rat genes satisfied dose-response criteria for both chemicals and were subjected to further analysis including the calculation of the 50% effective concentration and the relative potency (REP) of PCB 126 for each gene. Only five responsive orthologous genes were shared between the two species; yet, the geometric mean of the REPs for all rat and human modeled responsive genes were 0.06 (95% confidence interval [CI]; 0.03-0.1) and 0.002 (95% CI; 0.001-0.005), respectively, suggesting broad species differences in the initial events that follow AHR activation but precede toxicity. This indicates that there are species differences in both the specific genes that responded and the agonist potency and REP for those genes. This observed insensitivity of human cells to PCB 126 is consistent with more traditional measurements of AHR activation (i.e., cytochrome P450 1A1 enzyme activity) and suggests that the species difference in PCB 126 sensitivity is likely due to certain aspects of AHR function. That a species divergence also exists in this expanded AHR-regulated gene repertoire is a novel finding and should help when extrapolating animal data to humans.

Bioaccumulation of polychlorinated biphenyls in the eel (Anguilla anguilla) at the Camargue Nature Reserve - France

Fish consumption is a potential source of human exposure to pollutants. Here, we study residue levels of PCBs in the eel, Anguilla anguilla, from the Nature Camargue Reserve in southern France. Chromatographic analysis (GC-ECD) found seventy identifiable congeners, among which, 10 are considered as dioxin-like PCBs, such as the non-ortho PCB 81 and the mono-ortho chlorobiphenyls PCB105, 114, 118, 123, 156, 157, 167, 170, 180. Toxic Equivalents (TEQ, WHO 2005 TEF-Toxic Equivalent Factors) varied among sites with a maximum in eels from Mornès (29.6pgg(-1) dry weight). Indicator PCBs (28, 52, 101, 118, 138, 153 and 180) were 22% and 29% of the total PCBs in livers and muscles respectively. Greater homogeneous bioaccumulation in muscle than that in liver suggests an increase risk for humans due to fish consumption.

Greenland sledge dogs (Canis familiaris) develop liver lesions when exposed to a chronic and dietary low dose of an environmental organohalogen cocktail

We assessed the relationship between exposure to organohalogen polluted minke whale (Balaenoptera acutorostrata) blubber and liver morphology and function in a generational controlled study of 28 Greenland sledge dogs (Canis familiaris). The prevalence of portal fibrosis, mild bile duct hyperplasia, and vascular leukocyte infiltrations was significantly higher in the exposed group (all Chi-square: p<0.05). In case of granulomas, the frequency was significantly highest in the bitches (P generation) while the prevalence of portal fibrosis was highest in the F generation (pups) (both Chi-square: p<0.05). No significant difference between exposed and controls was found for bile acid, ALAT, and ALKP, while ASAT and LDH were significantly highest in the control group (both ANOVA: p<0.05). We therefore suggest that a daily intake of 50-200g environmentally organohalogen polluted minke whale blubber can cause liver lesions in Greenland sledge dogs. It is reasonable to infer that other apex predators such as polar bears (Ursus maritimus) and humans may suffer from similar impacts.

The 2005 World Health Organization reevaluation of human and Mammalian toxic equivalency factors for dioxins and dioxin-like compounds

In June 2005, a World Health Organization (WHO)-International Programme on Chemical Safety expert meeting was held in Geneva during which the toxic equivalency factors (TEFs) for dioxin-like compounds, including some polychlorinated biphenyls (PCBs), were reevaluated. For this reevaluation process, the refined TEF database recently published by Haws et al. (2006, Toxicol. Sci. 89, 4-30) was used as a starting point. Decisions about a TEF value were made based on a combination of unweighted relative effect potency (REP) distributions from this database, expert judgment, and point estimates. Previous TEFs were assigned in increments of 0.01, 0.05, 0.1, etc., but for this reevaluation, it was decided to use half order of magnitude increments on a logarithmic scale of 0.03, 0.1, 0.3, etc. Changes were decided by the expert panel for 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) (TEF = 0.3), 1,2,3,7,8-pentachlorodibenzofuran (PeCDF) (TEF = 0.03), octachlorodibenzo-p-dioxin and octachlorodibenzofuran (TEFs = 0.0003), 3,4,4',5-tetrachlorbiphenyl (PCB 81) (TEF = 0.0003), 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169) (TEF = 0.03), and a single TEF value (0.00003) for all relevant mono-ortho-substituted PCBs. Additivity, an important prerequisite of the TEF concept was again confirmed by results from recent in vivo mixture studies. Some experimental evidence shows that non-dioxin-like aryl hydrocarbon receptor agonists/antagonists are able to impact the overall toxic potency of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds, and this needs to be investigated further. Certain individual and groups of compounds were identified for possible future inclusion in the TEF concept, including 3,4,4'-TCB (PCB 37), polybrominated dibenzo-p-dioxins and dibenzofurans, mixed polyhalogenated dibenzo-p-dioxins and dibenzofurans, polyhalogenated naphthalenes, and polybrominated biphenyls. Concern was expressed about direct application of the TEF/total toxic equivalency (TEQ) approach to abiotic matrices, such as soil, sediment, etc., for direct application in human risk assessment. This is problematic as the present TEF scheme and TEQ methodology are primarily intended for estimating exposure and risks via oral ingestion (e.g., by dietary intake). A number of future approaches to determine alternative or additional TEFs were also identified. These included the use of a probabilistic methodology to determine TEFs that better describe the associated levels of uncertainty and "systemic" TEFs for blood and adipose tissue and TEQ for body burden.

Body burdens of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls and their relations to estrogen metabolism in pregnant women

Polychlorinated dibenzo-p-dioxins (PCDDs, dioxins), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) are environmental endocrine disruptors that have half-lives of 7-10 years in the human body and have toxicities that probably include carcinogenesis. A high ratio of 4-hydroxyl estradiol (4-OH-E2) to 2-hydroxyl estradiol (2-OH-E2) has been suggested as a potential biomarker for estrogen-dependent neoplasms. In this cohort study of maternal-fetal pairs, we examined the relationship of PCDD/PCDF and PCB exposure to levels of estrogen metabolites in the sera of 50 pregnant women 25-34 years of age from central Taiwan. Maternal blood was collected during the third trimester, and the placenta was collected at delivery. We measured 17 dioxin congeners, 12 dioxin-like PCBs, and 6 indicator PCBs in placenta using gas chromatography coupled with high-resolution mass spectrometry. Estrogen metabolites in maternal serum were analyzed by liquid chromatography tandem mass spectrometry. The ratio of 4-OH-E2:2-OH-E2 decreased with increasing exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (beta=-0.124, p=0.004 by the general linear regression model, R=0.4). Meanwhile, serum levels of 4-OH-E2 increased with increasing concentrations of high-chlorinated PCDFs (i.e., 1,2,3,4,6,7,8-hepta-CDF: beta=0.454, p=0.03, R=0.30). Altered estrogen catabolism might be associated with body burdens of PCDDs/PCDFs. Our study suggests that exposure to PCDDs/PCDFs significantly affects estrogen metabolism. Therefore, PCDD/PCDF exposure must be considered when using the OH-E2 ratio as a breast cancer marker.

Do organohalogen contaminants contribute to histopathology in liver from East Greenland polar bears (Ursus maritimus)?

In East Greenland polar bears (Ursus maritimus), anthropogenic organohalogen compounds (OHCs) (e.g., polychlorinated biphenyls, dichlorodiphenyltrichloroethane, and polybrominated diphenyl ethers) contributed to renal lesions and are believed to reduce bone mineral density. Because OHCs are also hepatotoxic, we investigated liver histology of 32 subadult, 24 adult female, and 23 adult male East Greenland polar bears sampled during 1999-2002. Light microscopic changes consisted of nuclear displacement from the normal central cytoplasmic location in parenchymal cells, mononuclear cell infiltrations (mainly portally and as lipid granulomas), mild bile duct proliferation accompanied by fibrosis, and fat accumulation in hepatocytes and pluripotent Ito cells. Lipid accumulation in Ito cells and bile duct hyperplasia accompanied by portal fibrosis were correlated to age, whereas no changes were associated with either sex or season (summer vs. winter). For adult females, hepatocytic intracellular fat increased significantly with concentrations of the sum of hexachlorocyclohexanes, as was the case for lipid granulomas and hexachlorobenzene in adult males. Based on these relationships and the nature of the chronic inflammation, we suggest that these findings were caused by aging and long-term exposure to OHCs. Therefore, these changes may be used as biomarkers for OHC exposure in wildlife and humans. To our knowledge, this is the first time liver histology has been evaluated in relation to OHC concentrations in a mammalian wildlife species, and the information is important to future polar bear conservation strategies and health assessments of humans relying on OHC-contaminated food resources.

Impact of polychlorinated biphenyls contamination on estrogenic activity in human male serum

Polychlorinated biphenyls (PCBs) are thought to cause numerous adverse health effects, but their impact on estrogen signaling is still not fully understood. In the present study, we used the ER-CALUX bioassay to determine estrogenic/antiestrogenic activities of the prevalent PCB congeners and PCB mixtures isolated from human male serum. The samples were collected from residents of an area with an extensive environmental contamination from a former PCB production site as well as from a neighboring background region in eastern Slovakia. We found that the lower-chlorinated PCBs were estrogenic, whereas the prevalent higher-chlorinated PCB congeners 138, 153, 170, 180, 187, 194, 199, and 203, as well as major PCB metabolites, behaved as antiestrogens. Coplanar PCBs had no direct effect on estrogen receptor (ER) activation in this in vitro model. In human male serum samples, high levels of PCBs were associated with a decreased ER-mediated activity and an increased dioxin-like activity, as determined by the DR-CALUX assay. 17beta-Estradiol (E2) was responsible for a major part of estrogenic activity identified in total serum extracts. Significant negative correlations were found between dioxin-like activity, as well as mRNA levels of cytochromes P450 1A1 and 1B1 in lymphocytes, and total estrogenic activity. For sample fractions containing only persistent organic pollutants (POPs), the increased frequency of antiestrogenic samples was associated with a higher sum of PCBs. This suggests that the prevalent non-dioxin-like PCBs were responsible for the weak antiestrogenic activity of some POPs fractions. Our data also suggest that it might be important to pay attention to direct effects of PCBs on steroid hormone levels in heavily exposed subjects.

Plasma Protein Level Changes in Waste Incineration Workers Exposed to 2,3,7,8-Tetrachlorodibenzo-p-dioxin

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is a chemical compound which is known to induce severe reproductive and developmental problems, immune system damage, and interference with regulatory hormones. To characterize changes in the expression of plasma proteins caused by exposure to TCDD, we analyzed plasma samples from workers at municipal incinerators using two-dimensional gel electrophoresis (2-DE). Proteins exhibiting differences in expression were identified by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) and electrospray ionization quadrupole (ESI-Q) TOF mass spectrometry. One newly expressed protein was identified as the adrenomedulin binding protein (AMBP). Seven overexpressed proteins were identified in this study, and the most overexpressed protein was identified as alpha-fetoprotein (AFP). In addition, we cultured HepG2 cells in the presence of TCDD, to determine the effects of TCDD on the AFP and albumin expression in mRNA and protein levels, via RT-PCR and Western blotting, respectively. TCDD treatment resulted in an increase in the mRNA and protein expression levels of AFP, but reduced albumin expression. According to our results, exposure to TCDD may induce liver disease or cancer, and the proteins identified in this study could help reveal the mechanisms underlying TCDD toxicity.

Enlarged clitoris in wild polar bears (Ursus maritimus) can be misdiagnosed as pseudohermaphroditism

A 23-year-old female polar bear (Ursus maritimus) killed in an Inuit hunt in East Greenland on July 9, 1999 had a significantly enlarged clitoris resembling, in size, form and colour, those of previously reported 'pseudohermaphroditic' polar bears from Svalbard. It has been suggested that an enzyme defect (21-hydroxylase deficiency), androgen producing tumour or high exposure to organochlorines during the foetal stage or early development could be the reason for the supposed pseudohermaphroditism observed for Svalbard bears. Except for the enlarged clitoris, all dimensions of the external and internal reproductive organs of the present were similar to a reference group of 23 normal adult female polar bears from East Greenland collected in 1999-2002. The aberrant bear was a female genotype, and macroscopic examination of her internal reproductive organs indicated that she was reproductively functional. A histological examination of the clitoral enlargement in the present East Greenland specimen allows a first-time histological evaluation of the earlier macroscopic field diagnosis from Svalbard. This examination revealed intense chronic ulcerative and perivascular clitoriditis similar to "acral lick dermatitis" frequently seen in domestic dogs (i.e., we did not find any signs of pseudohermaphroditic hyperplasia of clitoral tissue due to androgenic or antiestrogenic endocrine disruption). The levels of organohalogens and TEQ values were lower than concentration thresholds of toxicological risk. It is hence possible that the previously reported adult female polar bear pseudohermaphrodites from Svalbard are in fact misdiagnoses. Therefore, future studies examining pseudohermaphroditism in wildlife should consider that certain occurrences are natural events, e.g., enlarged clitoris in the present East Greenland polar bear. Furthermore, caution should be exercised in suggesting linkages of such inflammatory abnormalities with correlations to anthropogenic pollutant exposures.

The case for taking account of metabolism when testing for potential endocrine disruptors in vitro

Legislation in the USA, Europe and Japan will require that chemicals are tested for their ability to disrupt the hormonal systems of mammals. Such chemicals are known as endocrine disruptors (EDs), and will require extensive testing as part of the new European Union Registration, Evaluation and Authorisation of Chemicals (REACH) system for the risk assessment of chemicals. Both in vivo and in vitro tests are proposed for this purpose, and there has been much discussion and action concerning the development and validation of such tests. However, to date, little interest has been shown in incorporating metabolism into in vitro tests for EDs, in sharp contrast to other areas of toxicity testing, such as genotoxicity, and, ironically, such in vitro tests are criticised for not modelling in vivo metabolism. This is despite the existence of much information showing that endogenous and exogenous steroids are extensively metabolised by Phase I and Phase II enzymes both in the liver and in hormonally active tissues. Such metabolism can lead to the activation or detoxification of steroids and EDs. The absence of metabolism from these tests could give rise to false-positive data (due to lack of detoxification) or false-negative data (lack of activation). This paper aims to explain why in vitro assays for EDs should incorporate mammalian metabolising systems. The background to ED testing, the test methods available, and the role of mammalian metabolism in the activation and detoxification of both endogenous and exogenous steroids, are described. The available types of metabolising systems are compared, and the potential problems in incorporating metabolising systems into in vitro tests for EDs, and how these might be overcome, are discussed. It is recommended that there should be: a) an assessment of the intrinsic metabolising capacity of cell systems used in tests for EDs; b) an investigation into the relevance of using the prostaglandin H synthase system for metabolising EDs; and c) a feasibility study into the generation of genetically engineered mammalian cell lines expressing specific metabolising enzymes, which could also be used to detect EDs.

Effects of zearalenone on mRNA expression and activity of cytochrome P450 1A1 and 1B1 in MCF-7 cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a ubiquitous pollutant and promoter of carcinogenesis with both estrogenic and antiestrogenic effects in mammal epithelium. Zearalenone (ZEA) is a naturally occurring estrogenic contaminant of moldy feeds and is present in high concentrations in dairy products and cereals. Numerous studies describe a possible correlation between xenoestrogens and breast cancer risk. A potential mechanism for the etiology of breast cancer involves altered cytochrome P450 (CYP) enzymes. Since cocontamination of multiple compounds in our environmental and occupational circumstances likely happens and since few studies have addressed the molecular consequences of combinations of contaminants, we decided to investigate the effects of ZEA on basal and TCDD-induced mRNA expression and enzymic activity of CYP1A1 and CYP1B1 in human breast cancer MCF-7 cells. CYP1A1 enzyme activity was measured by the CYP1A1-referential activity assay, ethoxyresorufin O-deethylase (EROD), in MCF-7 cells. To investigate CYP1B1 activity, we employed the microsomal EROD assay prepared from baculovirus-infected insect cells expressing human cDNA CYP1B1. Reverse transcription-polymerase chain reaction was used to detect mRNA expression of CYP1A1 and CYP1B1 in MCF-7 cells. The results demonstrated that 10nM TCDD could readily induce a significant increase in the enzyme activity and mRNA expression of CYP1A1 in MCF-7 cells and 5 nM estradiol (E2) significantly reduced both basal and TCDD-induced activity and mRNA expression in MCF-7 cells. The same pattern was observed with 50nM ZEA. The estrogen receptor antagonist 4-hydroxytamoxifen could attenuate these inhibitive effects of both E2 and ZEA. Interestingly, Both E2 and ZEA could promote basal and TCDD-induced CYP1B1 activity but with no effect on CYP1B1 mRNA expression. These results suggest that the effect of ZEA on the TCDD-induced CYP1A1 activity and gene expression involved the estrogen receptor pathway and that the increase in the CYP1B1/CYP1A1 ratio underlying the basal or TCDD-treated condition might constitute one of the mechanisms underlying the synergic carcinogenic action of these compounds.