Search

© 2018 Elsevier B.V. Toxicity of dioxin-like compounds (DLCs), such as polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls, is largely mediated via aryl hydrocarbon receptor (AhR) activation. AhR-mediated gene expression can be tissue-specific; however, the inducibility of AhR in the lungs, a major target of DLCs, remains poorly characterized. In this study, we developed relative effective potencies (REPs) for a series of DLCs in both rodent (MLE-12, RLE-6TN) and human (A549, BEAS-2B) lung and bronchial epithelial cell models, using expression of both canonical (CYP1A1, CYP1B1) and less well characterized (TIPARP, AHRR, ALDH3A1) AhR target genes. The use of rat, murine and human cell lines allowed us to determine both species-specific differences in sensitivity of responses to DLCs in lung cellular models and deviations from established WHO toxic equivalency factor values (TEF) values. Finally, expression of selected AhR target genes was determined in vivo, using lung tissues of female rats exposed to a single oral dose of DLCs and compared with the obtained in vitro data. All cell models were highly sensitive to DLCs, with murine MLE-12 cells being the most sensitive and human A549 cells being the least sensitive. Interestingly, we observed that four AhR target genes were more sensitive than CYP1A1 in lung cell models (CYP1B1, AHRR, TIPARP and/or ALDH3A1). We found some deviations, with strikingly low REPs for polychlorinated biphenyls PCBs 105, 167, 169 and 189 in rat RLE-6TN cells-derived REPs for a series of 20 DLCs evaluated in this study, as compared with WHO TEF values. For other DLCs, including PCBs 126, 118 and 156, REPs were generally in good accordance with WHO TEF values. This conclusion was supported by in vivo data obtained in rat lung tissue. However, we found that human lung REPs for 2,3,4,7,8-pentachlorodibenzofuran and PCB 126 were much lower than the respective rat lung REPs. Furthermore, PCBs 118 and 156 were almost inactive in these h

Polar fractions of a sediment extract of the industrial area of Bitterfeld, Germany, have been subjected for effect-directed identification of mutagens using the Ames fluctuation assay with TA98. Mutagenicity could be well recovered in several secondary and tertiary fractions. Dinitropyrenes and 3-nitrobenzanthrone could be confirmed to contribute great shares of the observed mutagenicity. In addition, a multitude of polar polycyclic aromatic compounds has been tentatively identified in mutagenic fractions including nitro-PAHs, azaarenes, ketones, quinones, hydroxy-compounds, lactones and carboxylic acids although their contribution to mutagenicity could not be quantified due to a lack of standards. Diagnostic Salmonella strains YG1024 and YG1041 were applied to confirm the contribution of nitro-aromatic compounds. We suggest the inclusion of dinitropyrenes and 3-nitrobenzanthrone into sediment monitoring in order to minimize the mutagenic risk to aquatic organisms and to human health.

Sediment extracts from three polluted sites of the river Elbe basin were fractionated using a novel online fractionation procedure. Resulting fractions were screened for mutagenic, aryl hydrocarbon receptor (AhR)-mediated, transthyretin (TTR)- binding, and estrogenic activities and their potency to inhibit gap junctional intercellular communication (GJIC) to compare toxicity patterns and identify priority fractions. Additionally, more than 200 compounds and compound classes were identified using GCMS/ MS, LC-MS/MS, and HPLC-DAD methods. For all investigated end points, major activities were found in polar fractions, which are defined here as fractions containing dominantly compounds with at least one polar functional group. Nonpolar PAH fractions contributed to mutagenic and AhR-mediated activities while inhibition of GJIC and estrogenic and TTR-binding activities were exclusively observed in the polar fractions. Known mutagens in polar fractions included nitro- and dinitro-PAHs, azaarenes, and keto-PAHs, while parent and monomethylated PAHs such as benzo[a]pyrene and benzofluoranthenes were identified in nonpolar fractions. Additionally, for one sample, high AhR-mediated activities were determined in one fraction characterized by PCDD/Fs, PCBs, and PCNs. Estrone, 17β-estradiol, 9H-benz[de]anthracen-7-one, and 4-nonylphenol were identified as possible estrogenic and TTR-binding compounds. Thus, not only nonpolar compounds such as PAHs, PCBs, and PCDD/Fs but also the less characterized and investigated more polar substances should be considered as potent mutagenic, estrogenic, AhR-inducing, TTR-binding, and GJIC-inhibiting components for future studies. © 2011 American Chemical Society.

The toxic equivalency concept used for the risk assessment of polychlorinated biphenyls (PCBs) is based on the aryl hydrocarbon receptor (AhR)-mediated toxicity of coplanar dioxin-like (DL) PCBs. Most PCBs in the environment, however, are non-dioxin-like (NDL) PCBs that cannot adopt a coplanar structure required for AhR activation. For NDL-PCBs, no generally accepted risk concept is available because their toxicity is insufficiently characterized. Here,we systematically determined in vitro toxicity profiles for 24 PCBs regarding 10 different mechanisms of action. Prior to testing, NDL-PCB standards were purified to remove traces of DL compounds. All NDL-PCBs antagonized androgen receptor activation and inhibited gap junctional intercellular communication (GJIC). Lower chlorinated NDL-PCBswereweak estrogen receptor (ER) agonists,whereas higher chlorinated NDL-PCBs were weak ER antagonists. Several NDL-PCBs inhibited estradiol-sulfotransferase activity and bound to transthyretin (TTR) but with much weaker potencies than reported for hydroxylated PCB metabolites. AhR-mediated expression of uridine-glucuronyl transferase isozyme UGT1A6 was induced by DL-PCBs only. Hierarchical cluster analysis of the toxicity profiles yielded three separate clusters of NDL-PCBs and a fourth cluster of reference DL-PCBs. Due to small differences in relative potency among congeners, the highly abundant indicator PCBs 28, 52, 101, 118, 138, 153, and 180 also contributed most to the antiandrogenic, (anti)estrogenic, antithyroidal, tumorpromoting, and neurotoxic potencies calculated for PCB mixtures reported in human samples, whereas the most potent AhRactivating DL-PCB-126 contributed at maximum 0.2% to any of these calculated potencies. PCB-168 is recommended as an additional indicator congener, given its relatively high abundance and antiandrogenic, TTR-binding, and GJIC-inhibiting potencies. © The Author 2011. Published by Oxford University Press on behalf of the Society of Toxicology. A

Sediment extracts from three polluted sites of the river Elbe basin were fractionated using a novel online fractionation procedure. Resulting fractions were screened for mutagenic, aryl hydrocarbon receptor (AhR)-mediated, transthyretin (TTR)-binding, and estrogenic activities and their potency to inhibit gap junctional intercellular communication (GJIC) to compare toxicity patterns and identify priority fractions. Additionally, more than 200 compounds and compound classes were identified using GC-MS/MS, LC-MS/MS, and HPLC-DAD methods. For all investigated end points, major activities were found in polar fractions, which are defined here as fractions containing dominantly compounds with at least one polar functional group. Nonpolar PAH fractions contributed to mutagenic and AhR-mediated activities while inhibition of GJIC and estrogenic and TTR-binding activities were exclusively observed in the polar fractions. Known mutagens in polar fractions included nitro- and dinitro-PAHs, azaarenes, and keto-PAHs, while parent and monomethylated PAHs such as benzo[a]pyrene and benzofluoranthenes were identified in nonpolar fractions. Additionally, for one sample, high AhR-mediated activities were determined in one fraction characterized by PCDD/Fs, PCBs, and PCNs. Estrone, 17ß-estradiol, 9H-benz[de]anthracen-7-one, and 4-nonylphenol were identified as possible estrogenic and TTR-binding compounds. Thus, not only nonpolar compounds such as PAHs, PCBs, and PCDD/Fs but also the less characterized and investigated more polar substances should be considered as potent mutagenic, estrogenic, AhR-inducing, TTR-binding, and GJIC-inhibiting components for future studies.

Multiple stressor scenarios, as they are relevant in many watersheds, call for approaches extending beyond conventional chemical-focused approaches. The present study, investigated the fish population, represented by chub (Leuciscus cephalus), in the Býlina River (Czech Republic), which is impacted by various pollution sources and might pose a risk on the fish population. To confirm or reject this hypothesis, examined was whether there exists an association between abundance of chub and exposure to toxic chemicals as well as natural stressors, represented by parasites, and whether health-related suborganismal traits, namely, organ indices, tissue histopathology, and immune parameters, would help in revealing relationships between stressor impact and population status. Toxic pressure was assessed by the toxic unit approach, which gives an integrative estimate of toxic effect concentrations and by measuring the biomarkers cytochrome P4501A and vitellogenin, which indicate exposure to bioavailable arylhydrocarbon- or estrogen receptor ligands. Parasite pressure was estimated by determining abundance and species composition of ecto- and endoparasites of chub. Chubabundance was high upstream in the Bilina, low to zero in the middle stretches, and increased again downstream. Toxic pressure increased in the downstream direction, while parasite intensity decreased in this direction. Health status of chub did not differ clearly between up-, middle-, and downstream sites. Thus, it appears that neither toxic pressure nor parasite pressure nor their combination translates into a change of chub health status. By using varied assessment tools, this study provides evidence against a presumed causative role of toxicants impairing the fish ecological status of the Býlina River.

no abstract

Due to the production and use of a multitude of chemicals in modern society, waters, sediments, soils and biota may be contaminated with numerous known and unknown chemicals that may cause adverse effects on ecosystems and human health. Effect-directed analysis (EDA), combining biotesting, fractionation and chemical analysis, helps to identify hazardous compounds in complex environmental mixtures. Confirmation of tentatively identified toxicants will help to avoid artefacts and to establish reliable cause-effect relationships. A tiered approach to confirmation is suggested in the present paper. The first tier focuses on the analytical confirmation of tentatively identified structures. If straightforward confirmation with neat standards for GC-MS or LC-MS is not available, it is suggested that a lines-of-evidence approach is used that combines spectral library information with computer-based structure generation and prediction of retention behaviour in different chromatographic systems using quantitative structure-retention relationships (QSRR). In the second tier, the identified toxicants need to be confirmed as being the cause of the measured effects. Candidate components of toxic fractions may be selected based, for example, on structural alerts. Quantitative effect confirmation is based on joint effect models. Joint effect prediction on the basis of full concentration-response plots and careful selection of the appropriate model are suggested as a means to improve confirmation quality. Confirmation according to the Toxicity Identification Evaluation (TIE) concept of the US EPA and novel tools of hazard identification help to confirm the relevance of identified compounds to populations and communities under realistic exposure conditions. Promising tools include bioavailability-directed extraction and dosing techniques, biomarker approaches and the concept of pollution-induced community tolerance (PICT).

Ku-dependent nonhomologous end joining (NHEJ) is a double-strand break repair process conserved in all branches of cellular life but has not previously been implicated in the DNA metabolic processes of viruses. We identified Ku homologs in Corndog and Omega, two related mycobacteriophages of Mycobacterium smegmatis. These proteins formed homodimers and bound DNA ends in a manner identical to other Ku's and stimulated joining of ends by the host NHEJ DNA ligase (LigD). Omega and Corndog are unusual in having short 4 base cos ends that would not be expected to self-anneal and would therefore require NHEJ during phage genome circularization. Consistently, M. smegmatis LigD null strains are entirely and selectively unable to support infection by Corndog or Omega, with concomitant failure of genome circularization. These results establish a new paradigm for sequestration of the host cell NHEJ process by bacteriophage and provide a framework for understanding similar transactions in eukaryotic viral infections. © 2006 Elsevier Inc. All rights reserved.

A group of heterocyclic aromatic compounds, dinaphthofurans (DNFs), recently have been identified as potentially significant contaminants in freshwater sediments. In the present study, a battery of in vitro assays was used for detection of toxic effects of DNFs that are potentially associated with endocrine disruption and tumor promotion. Dinaphthofurans were found to act as relatively potent inducers of aryl hydrocarbon receptor (AhR)–mediated activity in the chemical-activated luciferase reporter gene expression DR-CALUX assay. The relative AhR-inducing potencies of DNFs were similar or even higher than relative potencies of unsubstituted polycyclic aromatic hydrocarbons (PAHs), with dinaphtho[1,2-b;2′3′-d]furan being the most potent AhR agonist. Two compounds, dinaphtho[2,1-b;2′3′-d]furan and dinaphtho[1,2-b;1′2′-d]furan, induced estrogen receptor (ER)–mediated activity in the estrogen receptor–mediated CALUX (the ER-CALUX) assay. Two types of potential tumor-promoting effects of DNFs were investigated, using in vitro bioassays for detection of inhibition of gap-junctional intercellular communication and detection of a release from contact inhibition. Although the acute inhibition of gap-junctional intercellular communication was not observed, all six tested DNFs were able to release rat liver epithelial WB-F344 cells from contact inhibition at concentrations as low as 100 nM. In summary, the present study indicated that DNFs can exert multiple biological effects in vitro, including induction of the AhR-mediated activity, release of cells from contact inhibition, and induction of ER-mediated activity.