Estrogen receptor-hijacking by dioxin-like 3,3'4,4',5-pentachlorobiphenyl (PCB126) in salmon hepatocytes involves both receptor activation and receptor protein stability

A bioanalytical approach for assessing the effects of soil extracts from solid waste dumpsite in Calabar (Nigeria) on lipid and estrogenic signaling of fish Poeciliopsis lucida hepatocellular carcinoma-1 cells in vitro and in vivo African catfish (Clarias gariepinus)

In applying bioanalytical approaches, the aim of this study was to determine the toxicity of contaminants derived from a solid waste dumpsite in Calabar (Nigeria), by investigating the alterations of lipid and estrogen signaling pathways in Poeciliopsis lucida hepatocellular carcinoma-1 (PLHC-1) cells and compared to in vivo African catfish (Clarias gariepinus), using polar, nonpolar and elutriate extraction methods. Cells were exposed for 48 hr period to different concentrations of the contaminant extracts. The PLHC-1 cells were evaluated for lipid responses as follows adipoRed assay, retinoid x receptor (rxr), peroxisome proliferator-activated receptor isoforms (ppar-α and γ), estrogen receptor (er-α) and vitellogenin (vtg) transcripts. The lipid signaling activation was also assessed in vivo using C. gariepinus, where hepatic levels of ppar-α were determined at both transcript and functional proteins levels. Data showed variable-, extract type and concentration-specific elevations in mRNA and protein levels for lipidomic and estrogenic effects. These effects were either biphasic at low and high concentrations, depending upon extract type, or concentration-dependent elevations. In general, these toxicological responses may be attributed to soil organic and inorganic contaminants burden previously derived from the dumpsite. Thus, our data demonstrate a unique lipid and endocrine-disruptive chemical (EDC) effects of each soil extract, suggesting multiple and complex contaminant interactions in the environment and biota. Analysis of numerous soil- or sediment-bound contaminants have numerous limitations and cost implications for developing countries. Our approach provides a bioanalytical protocol and endpoints for measuring the metabolic and EDC effects of complex environmental matrices for ecotoxicological assessment and monitoring.

Key Characteristics of Cardiovascular Toxicants

BACKGROUND

The concept of chemical agents having properties that confer potential hazard called key characteristics (KCs) was first developed to identify carcinogenic hazards. Identification of KCs of cardiovascular (CV) toxicants could facilitate the systematic assessment of CV hazards and understanding of assay and data gaps associated with current approaches.

OBJECTIVES

We sought to develop a consensus-based synthesis of scientific evidence on the KCs of chemical and nonchemical agents known to cause CV toxicity along with methods to measure them.

METHODS

An expert working group was convened to discuss mechanisms associated with CV toxicity.

RESULTS

The group identified 12 KCs of CV toxicants, defined as exogenous agents that adversely interfere with function of the CV system. The KCs were organized into those primarily affecting cardiac tissue (numbers 1-4 below), the vascular system (5-7), or both (8-12), as follows: 1) impairs regulation of cardiac excitability, 2) impairs cardiac contractility and relaxation, 3) induces cardiomyocyte injury and death, 4) induces proliferation of valve stroma, 5) impacts endothelial and vascular function, 6) alters hemostasis, 7) causes dyslipidemia, 8) impairs mitochondrial function, 9) modifies autonomic nervous system activity, 10) induces oxidative stress, 11) causes inflammation, and 12) alters hormone signaling.

DISCUSSION

These 12 KCs can be used to help identify pharmaceuticals and environmental pollutants as CV toxicants, as well as to better understand the mechanistic underpinnings of their toxicity. For example, evidence exists that fine particulate matter [PM ≤2.5μm in aerodynamic diameter (PM2.5)] air pollution, arsenic, anthracycline drugs, and other exogenous chemicals possess one or more of the described KCs. In conclusion, the KCs could be used to identify potential CV toxicants and to define a set of test methods to evaluate CV toxicity in a more comprehensive and standardized manner than current approaches. https://doi.org/10.1289/EHP9321.

Associations between functional polychlorinated biphenyls in adipose tissues and prognostic biomarkers of breast cancer patients

BACKGROUND

Exposure to polychlorinated biphenyls (PCBs) has been shown to influence expression of some biomarkers that are predictive/prognostic for breast cancer. Therefore, our study was conducted to further investigating associations of different functional PCBs in adipose tissue with breast cancer prognostic biomarkers.

METHODS

Two hundred and five breast cancer patients were recruited in Shantou, China. Breast adipose tissues were collected during their resection surgery and levels of 7 PCB congeners were analyzed by gas chromatography-mass spectrometry (GC-MS). The PCB congeners were divided into 4 groups according to structure-activity. Socio-demographic, clinical and pathological information were obtained from questionnaire and digital medical records. Odds ratios (ORs) for associations between prognostic biomarkers and PCB levels (tertile 3 [T3], tertile 2 [T2] vs. tertile 1) were estimated from logistic regression models.

RESULTS

Most PCB congeners were detectable, with a highest level (22.06 ng/g lipid) of PCB153. As for estrogenic PCBs, increased PCB52 exposure was positively associated with PR expression (OR_T2 = 2.36, P_trend = 0.054), but higher PCB101 level was negatively associated with HER-2 (OR_T3 = 0.24, P_trend = 0.029) and tumor size (OR = 0.43). Limited dioxin-like PCB138 exposure was positively associated with ER (OR_T2 = 3.23, OR_T3 = 3.77, P_trend = 0.047) but negatively with Top-IIα expression (OR_T2 = 0.35, OR_T3 = 0.28, P_trend = 0.080). Higher PCB153 (CYP inducer) level was negatively associated with ER (OR_T2 = 0.32, OR_T3 = 0.19, P_trend = 0.038) but positively with Ki-67 expression (OR_T2 = 1.43, OR_T3 = 3.60, P_trend = 0.055). Higher neurotoxic PCB28 was positively associated with HER-2 (OR_T3 = 5.43, P_trend = 0.006) and tumor size (OR = 2.37). Moreover, total PCBs exposure was positively associated with VEGF-C (OR_T2 = 76.91, OR_T3 = 97.96, P_trend = 0.041) and tumor metastasis (OR = 2.25).

CONCLUSIONS

Different functional PCB congeners have different associations (both positive and negative) with breast cancer prognostic biomarkers, as well as tumor classification stage. Therefore, the development and aggressiveness of breast cancer may depend upon exposure to specific structure-activity of PCBs.

In vivo effects of PCB-126 and genistein on vitellogenin expression in zebrafish

In this study, the vitellogenin (Vtg) modulation by genistein and polychlorinated biphenyl-126 (PCB-126) exposure in zebrafishes has been investigated. Both PCB-126 and genistein have been identified as aquatic pollutants and can further increase estrogenicity of waterways. Vtg is egg yolk precursor protein release by the hepatocytes during vitellogenesis. This process occurs normally in the hepatocytes in response to the activation with the estrogens such as 17-β-estradiol. Our immunohistochemical findings showed a Vtg expression that increases at 12 h and at 72 h in the liver of treated fishes with both PCB-126 and genistein, individually and in combination. Furthermore, for the first time, also hepatic stellate cells (HSC) in the liver parenchyma were strongly positive for vitellogenin.

Development and Application of a Novel Bioassay System for Dioxin Determination and Aryl Hydrocarbon Receptor Activation Evaluation in Ambient-Air Samples

Airborne persistent toxic substances are associated with health impacts resulting from air pollution, for example, dioxins, dioxin-like polychlorinated biphenyls, and certain polycyclic aromatic hydrocarbons (PAHs), which activate aryl hydrocarbon receptors (AhR) and thereby produce adverse outcomes. Thus, a bioassay for evaluating AhR activation is required for risk assessment of ambient-air samples, and for this purpose, we developed a new and sensitive recombinant mouse hepatoma cell line, CBG2.8D, in which a novel luciferase-reporter plasmid containing two copies of a newly designed dioxin-responsive domain and a minimal promoter derived from a native gene were integrated. The minimal detection limit for 2,3,7,8-tetrachlorodibenzo- p-dioxin with this assay system was 0.1 pM. We used CBG2.8D to determine dioxin levels in 45 ambient-air samples collected in Beijing. The measured bioanalytical equivalent (BEQ) values were closely correlated with the toxic equivalent values obtained from chemical analysis. In haze ambient-air samples, the total activation of aryl hydrocarbon receptors (TAA) was considerably higher than the BEQ of dioxin-rich fractions, according to the results of the cell-based bioassay. Notably, the haze samples contained abundant amounts of PAHs, whose relative toxicity equivalent was correlated with the TAA; this finding suggests that PAHs critically contribute to the AhR-related biological impacts of haze ambient-air samples.

Association of breast adipose tissue levels of polychlorinated biphenyls and breast cancer development in women from Chaoshan, China

Polychlorinated biphenyls (PCBs) are implied to be potential risk factors for breast cancer in wildlife and in in vivo and in vitro studies. Epidemiological studies revealed some individual or groups of PCB congeners associated with breast cancer risk, but consistent conclusions are scarce. This study aimed to explore the association between PCB exposure and breast cancer development. Breast adipose tissues were collected, and seven PCB congeners were analyzed by gas chromatography-mass spectrometry (GC-MS). Demographic characteristics, basic clinical data, and pathological diagnosis information were obtained from medical records. The differences in PCB exposure levels among different groups and indices were compared, and the correlation among PCB congeners was evaluated. The order of congener profile by molar concentration was PCB-153 > PCB-138 > PCB-180 > PCB-118 > PCB-101 > PCB-52 > PCB-28. ∑PCB level differed by occupation and residence and was significantly higher at 55-59-year-old group than at the other age groups. ∑PCB level was higher in postmenopausal than in premenopausal women. Decreasing ∑PCB levels were related with increasing parity among women with progesterone receptor (PR)-positive breast tumors. With increased clinical stage, the ∑PCB level increased significantly. ∑PCB level did not differ by tumor-node-metastasis classification and PR or human epidermal growth factor receptor 2 (HER2) expression but did differ by estrogen receptor (ER) expression (P = 0.04) without a regularly increasing trend in breast adipose tissue. These results suggest a potential association between PCB exposure and breast cancer development. Further in vitro and in vivo studies are needed to confirm these findings and explain the underlying mechanisms. Graphical Abstract Total PCBs level among different clinical stages in breast cancer patients.

Exposure to coplanar PCBs induces endothelial cell inflammation through epigenetic regulation of NF-κB subunit p65

Epigenetic modifications of DNA and histones alter cellular phenotypes without changing genetic codes. Alterations of epigenetic marks can be induced by exposure to environmental pollutants and may contribute to associated disease risks. Here we test the hypothesis that endothelial cell dysfunction induced by exposure to polychlorinated biphenyls (PCBs) is mediated in part though histone modifications. In this study, human vascular endothelial cells were exposed to physiologically relevant concentrations of several PCBs congeners (e.g., PCBs 77, 118, 126 and 153) followed by quantification of inflammatory gene expression and changes of histone methylation. Only exposure to coplanar PCBs 77 and 126 induced the expression of histone H3K9 trimethyl demethylase jumonji domain-containing protein 2B (JMJD2B) and nuclear factor-kappa B (NF-κB) subunit p65, activated NF-κB signaling as evidenced by nuclear translocation of p65, and up-regulated p65 target inflammatory genes, such as interleukin (IL)-6, C-reactive protein (CRP), intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and IL-1α/β. The increased accumulation of JMJD2B in the p65 promoter led to a depletion of H3K9me3 repression mark, which accounts for the observed up-regulation of p65 and associated inflammatory genes. JMJD2B gene knockdown confirmed a critical role for this histone demethylase in mediating PCB-induced inflammation of the vascular endothelium. Finally, it was determined, via chemical inhibition, that PCB-induced up-regulation of JMJD2B was estrogen receptor-alpha (ER-α) dependent. These data suggest that coplanar PCBs may exert endothelial cell toxicity through changes in histone modifications.

Bioaccumulation, biotransformation, and toxicity of BDE-47, 6-OH-BDE-47, and 6-MeO-BDE-47 in early life-stages of zebrafish (Danio rerio)

2,2',4,4'-Tetrabromodiphenyl ether (BDE-47), 6-hydroxy-tetrabromodiphenyl ether (6-OH-BDE-47), and 6-methoxy-tetrabromodiphenyl ether (6-MeO-BDE-47) are the most detected congeners of polybrominated diphenyl ethers (PBDEs), OH-BDEs, and MeO-BDEs, respectively, in aquatic organisms. Although it has been demonstrated that BDE-47 can interfere with certain endocrine functions that are mediated through several nuclear hormone receptors (NRs), most of these findings were from mammalian cell lines exposed in vitro. In the present study, embryos and larvae of zebrafish were exposed to BDE-47, 6-OH-BDE-47, and 6-MeO-BDE-47 to compare their accumulation, biotransformation, and bioconcentration factors (BCF) from 4 to 120 hpf. In addition, effects on expression of genes associated with eight different pathways regulated by NRs were investigated at 120 hpf. 6-MeO-BDE-47 was most bioaccumulated and 6-OH-BDE-47, which was the most potent BDE, was least bioaccumulated. Moreover, the amount of 6-MeO-BDE-47, but not BDE-47, transformed to 6-OH-BDE-47 increased in a time-dependent manner, approximately 0.01%, 0.04%, and 0.08% at 48, 96, and 120 hpf, respectively. Expression of genes regulated by the aryl hydrocarbon receptor (AhR), estrogen receptor (ER), and mineralocorticoid receptor (MR) was affected in larvae exposed to 6-OH-BDE-47, whereas genes regulated by AhR, ER, and the glucocorticoid receptor (GR) were altered in larvae exposed to BDE-47. The greatest effect on expression of genes was observed in larvae exposed to 6-MeO-BDE-47. Specifically, 6-MeO-BDE-47 affected the expression of genes regulated by AhR, ER, AR, GR, and thyroid hormone receptor alpha (TRα). These pathways were mostly down-regulated at 2.5 μM. Taken together, these results demonstrate the importance of usage of an internal dose to assess the toxic effects of PBDEs. BDE-47 and its analogs elicited distinct effects on expression of genes of different hormone receptor-mediated pathways, which have expanded the knowledge of different mechanisms of endocrine disrupting effects in aquatic vertebrates. Because some of these homologues are natural products, assessments of risks of anthropogenic PBDE need to be made against the background of concentrations from naturally occurring products. Even though PBDEs are being phased out as flame retardants, the natural products remain.

Role of AHR, AHRR and ARNT in response to dioxin-like PCBs in Spaurus aurata

The aryl hydrocarbon receptor (AHR) mediates a variety of biological responses to ubiquitous dioxin and PCB dioxin-like. AHR together with ARNT, AHRR, represent a novel basic helix-loop-helix/PAS family of transcriptional regulators. Their interplay may affect the xenobiotic response. The aim of this study was to investigate, by histological, immunohistochemical investigations and western-blot analysis, the expression of AHR, ARNT and AHRR in liver of seabrem (Spaurus aurata) after exposure at different time to dioxin-like PCB126 in order to deep the knowledge about their specific role. The findings showed a significant increase of AHR and ARNT expression in juvenile fishes after 12 h than control group. The induction of AHR and ARNT is also significant at 24 and 72 hours compared to the control group. Furthemore, induction of AHRR expression has proved to increase both 12 h but this induction does not seem significant to 24 and 72 hours. The most important data of this work is that the induction of AHRR, when the action of the toxic persistence substances, as dioxin and PCB-126, it is not enough to reduce AHR signaling and thus its hyperactivation leads to toxic effects in seabrem (Spaurus aurata). All this confirms the importance of AHR ligands as new class of drugs that can be directed against severe disease such as cancer.

Applicability of the TCDD-TEQ approach to predict sublethal embryotoxicity in Fundulus heteroclitus

The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxic equivalent quantity (TCDD-TEQ) approach was used successfully to predict lethal embryotoxicity in salmonids, but its applicability to sublethal effects of mixtures of organohalogenated compounds in other fish species is poorly known. The sublethal toxicity of two dioxin-like compounds (DLCs), 3,3',4,4'-tetrachlorobiphenyl (PCB77) and 2,3,4,7,8-pentachlorodibenzofuran (2,3,4,7,8-PnCDF), two non-dioxin-like (NDL) polychlorinated biphenyls (PCBs), 2,2',5,5'-tetrachlorobiphenyl (PCB52) and 2,3,3',4',6-pentachlorobiphenyl (PCB110), and of Aroclor 1254, a complex commercial mixture of PCBs, was assessed in Fundulus heteroclitus embryos exposed by intravitelline injection. At 16 days post-fertilization, the two DLCs and Aroclor 1254 altered prey capture ability in addition to inducing classical aryl hydrocarbon receptor-mediated responses: ethoxyresorufin-O-deethylase (EROD) induction, craniofacial deformities and reduction in body length. None of these responses was induced by the two NDL PCBs, at doses up to 5400 ng g(-1)wet weight. Dose-response curves for prey capture ability for the 2 DLCs tested were not parallel to that of TCDD, violating a fundamental assumption for relative potency (ReP) estimation. Dose-response curves for EROD induction were parallel for 2,3,4,7,8-PnCDF and TCDD, but the ReP of 2,3,4,7,8-PnCDF for F. heteroclitus was 5-fold higher than the World Health Organization (WHO) fish toxic equivalent factor (TEF) based on embryolethality in salmonids. The chemically derived TCDD-TEQs of Aroclor 1254, calculated using 3,3',4,4',5-pentachlorobiphenyl (PCB126) concentrations and it ReP for F. heteroclitus, overestimated its potency to induce EROD activity possibly due to antagonistic interactions among PCBs. This study highlights the limitations of using TEFs based on salmonid toxicity data alone for risk assessment to other fish species. There is a need to assess the variability of RePs of DLCs in different species for a variety of endpoints and to better understand interactions between DLCs and other toxic chemicals.