Rosmarinus officinalis L. Leaf Extracts and Their Metabolites Inhibit the Aryl Hydrocarbon Receptor (AhR) Activation In Vitro and in Human Keratinocytes: Potential Impact on Inflammatory Skin Diseases and Skin Cancer.

Aryl hydrocarbon receptor (AhR) activation by environmental agents and microbial metabolites is potentially implicated in a series of skin diseases. Hence, it would be very important to identify natural compounds that could inhibit the AhR activation by ligands of microbial origin as 6-formylindolo[3,2-b]carbazole (FICZ), indirubin (IND) and pityriazepin (PZ) or the prototype ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Five different dry Rosmarinus officinalis L. extracts (ROEs) were assayed for their activities as antagonists of AhR ligand binding with guinea pig cytosol in the presence of [3H]TCDD. The methanolic ROE was further assayed towards CYP1A1 mRNA induction using RT-PCR in human keratinocytes against TCDD, FICZ, PZ, and IND. The isolated metabolites, carnosic acid, carnosol, 7-O-methyl-epi-rosmanol, 4',7-O-dimethylapigenin, and betulinic acid, were assayed for their agonist and antagonist activity in the presence and absence of TCDD using the gel retardation assay (GRA). All assayed ROE extracts showed similar dose-dependent activities with almost complete inhibition of AhR activation by TCDD at 100 ppm. The methanol ROE at 10 ppm showed 99%, 50%, 90%, and 85% inhibition against TCDD, FICZ, IND, and PZ, respectively, in human keratinocytes. Most assayed metabolites exhibited dose-dependent antagonist activity. ROEs inhibit AhR activation by TCDD and by the Malassezia metabolites FICZ, PZ, and IND. Hence, ROE could be useful for the prevention or treatment of skin diseases mediated by activation of AhR.

Using Estrogenic Activity and Nontargeted Chemical Analysis to Identify Contaminants in Sewage Sludge.

Diverse organic compounds, many derived from consumer products, are found in sewage sludge worldwide. Understanding which of these poses the most significant environmental threat following land application can be investigated through a variety of predictive and cell-based toxicological techniques. Nontargeted analysis using high-resolution mass spectrometry with predictive estrogenic activity modeling was performed on sewage sludge samples from 12 wastewater treatment plants in California. Diisobutyl phthalate and dextrorphan were predicted to exhibit estrogenic activity and identified in >75% of sludge samples, signifying their universal presence and persistence. Additionally, the application of an estrogen-responsive cell bioassay revealed reductions in agonistic activity during mesophilic and thermophilic treatment but significant increases in antagonism during thermophilic treatment, which warrants further research. Ten nontarget features were identified (metoprolol, fenofibric acid, erythrohydrobupropion, oleic acid, mestranol, 4'-chlorobiphenyl-2,3-diol, medrysone, scillarenin, sudan I, and N,O-didesmethyltramadol) in treatment set samples and are considered to have influenced the in vitro estrogenic activity observed. The combination of predictive and in vitro estrogenicity with nontargeted analysis has led to confirmation of 12 estrogen-active contaminants in California sewage sludge and has highlighted the importance of evaluating both agonistic and antagonistic responses when evaluating the bioactivity of complex samples.

Identifying Toxicologically Significant Compounds in Urban Wildfire Ash Using In Vitro Bioassays and High-Resolution Mass Spectrometry.

Urban wildfires may generate numerous unidentified chemicals of toxicity concern. Ash samples were collected from burned residences and from an undeveloped upwind reference site, following the Tubbs fire in Sonoma County, California. The solvent extracts of ash samples were analyzed using GC- and LC-high-resolution mass spectrometry (HRMS) and using a suite of in vitro bioassays for their bioactivity toward nuclear receptors [aryl hydrocarbon receptor (AhR), estrogen receptor (ER), and androgen receptor (AR)], their influence on the expression of genetic markers of stress and inflammation [interleukin-8 (IL-8) and cyclooxygenase-2 (COX-2)], and xenobiotic metabolism [cytochrome P4501A1 (CYP1A1)]. Genetic markers (CYP1A1, IL-8, and COX-2) and AhR activity were significantly higher with wildfire samples than in solvent controls, whereas AR and ER activities generally were unaffected or reduced. The bioassay responses of samples from residential areas were not significantly different from the samples from the reference site despite differing chemical compositions. Suspect and nontarget screening was conducted to identify the chemicals responsible for elevated bioactivity using the multiple streams of HRMS data and open-source data analysis workflows. For the bioassay endpoint with the largest available database of pure compound results (AhR), nontarget features statistically related to whole sample bioassay response using Spearman's rank-order correlation coefficients or elastic net regression were significantly more likely (by 10 and 15 times, respectively) to be known AhR agonists than the overall population of compounds tentatively identified by nontarget analysis. The findings suggest that a combination of nontarget analysis, in vitro bioassays, and statistical analysis can identify bioactive compounds in complex mixtures.

A Biomimetic, One-Step Transformation of Simple Indolic Compounds to Malassezia-Related Alkaloids with High AhR Potency and Efficacy.

Malassezia furfur isolates from diseased skin preferentially biosynthesize compounds which are among the most active known aryl-hydrocarbon receptor (AhR) inducers, such as indirubin, tryptanthrin, indolo[3,2-b]carbazole, and 6-formylindolo[3,2-b]carbazole. In our effort to study their production from Malassezia spp., we investigated the role of indole-3-carbaldehyde (I3A), the most abundant metabolite of Malassezia when grown on tryptophan agar, as a possible starting material for the biosynthesis of the alkaloids. Treatment of I3A with H2O2 and use of catalysts like diphenyldiselenide resulted in the simultaneous one-step transformation of I3A to indirubin and tryptanthrin in good yields. The same reaction was first applied on simple indole and then on substituted indoles and indole-3-carbaldehydes, leading to a series of mono- and bisubstituted indirubins and tryptanthrins bearing halogens, alkyl, or carbomethoxy groups. Afterward, they were evaluated for their AhR agonist activity in recombinant human and mouse hepatoma cell lines containing a stably transfected AhR-response luciferase reporter gene. Among them, 3,9-dibromotryptanthrin was found to be equipotent to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) as an AhR agonist, and 3-bromotryptanthrin was 10-times more potent than TCDD in the human HG2L7.5c1 cell line. In contrast, 3,9-dibromotryptanthrin and 3-bromotryptanthrin were ∼4000 and >10,000 times less potent than TCDD in the mouse H1L7.5c3 cell line, respectively, demonstrating that they are species-specific AhR agonists. Involvement of the AhR in the action of 3-bromotryptanthrin was confirmed by the ability of the AhR antagonists CH223191 and SR1 to inhibit 3-bromotryptanthrin-dependent reporter gene induction in human HG2L7.5c1 cells. In conclusion, I3A can be the starting material used by Malassezia for the production of both indirubin and tryptanthrin through an oxidation mechanism, and modification of these compounds can produce some highly potent, efficacious and species-selective AhR agonists.

In Vitro Evaluation of Mitochondrial Function and Estrogen Signaling in Cell Lines Exposed to the Antiseptic Cetylpyridinium Chloride.

BACKGROUND: Quaternary ammonium salts (QUATS), such as cetylpyridinium chloride (CPC) and benzalkonium chloride (BAK), are frequently used in antiseptic formulations, including toothpastes, mouthwashes, lozenges, throat and nasal sprays, and as biocides. Although in a recent ruling, the U.S. Food and Drug Administration (FDA) banned CPC from certain products and requested more data on BAK's efficacy and safety profile, QUATS, in general, and CPC and BAK, in particular, continue to be used in personal health care, food, and pharmaceutical and cleaning industries. OBJECTIVES: We aimed to assess CPC's effects on mitochondrial toxicity and endocrine disruption in vitro. METHOD: Mitochondrial O2 consumption and adenosine triphosphate (ATP) synthesis rates of osteosarcoma cybrid cells were measured before and after CPC and BAK treatment. Antiestrogenic effects of the compounds were measured by a luciferase-based assay using recombinant human breast carcinoma cells (VM7Luc4E2, ERalpha-positive). RESULTS: CPC inhibited both mitochondrial O2 consumption [half maximal inhibitory concentration (IC50): 3.8µM] and ATP synthesis (IC50: 0.9µM), and additional findings supported inhibition of mitochondrial complex 1 as the underlying mechanism for these effects. In addition, CPC showed concentration-dependent antiestrogenic activity half maximal effective concentration [(EC50): 4.5µM)]. BAK, another antimicrobial QUATS that is structurally similar to CPC, and the pesticide rotenone, a known complex 1 inhibitor, also showed mitochondrial inhibitory and antiestrogenic effects. In all three cases, there was overlap of the antiestrogenic activity with the mitochondrial inhibitory activity. CONCLUSIONS: Mitochondrial inhibition in vitro occurred at a CPC concentration that may be relevant to human exposures. The antiestrogenic activity of CPC, BAK, rotenone, and triclosan may be related to their mitochondrial inhibitory activity. Our findings support the need for additional research on the mitochondrial inhibitory and antiestrogenic effects of QUATS, including CPC and BAK. https://doi.org/10.1289/EHP1404.

Use of nuclear receptor luciferase-based bioassays to detect endocrine active chemicals in a biosolids-biochar amended soil.

Biosolids are a potentially valuable source of carbon and nutrients for agricultural soils; however, potential unintended impacts on human health and the environment must be considered. Virtually all biosolids contain trace amounts endocrine-disrupting chemicals derived from human use of pharmaceuticals and personal care products (PPCPs). One potential way to reduce the bioavailability of PPCPs is to co-apply biosolids with biochar to soil, because biochar's chemical (e.g., aromaticity) and physical properties (e.g., surface area) give it a high affinity to bind many organic chemicals in the environment. We developed a soil-specific extraction method and utilized a luciferase-based bioassay (CALUX) to detect endocrine active chemicals in a biosolids-biochar co-amendment soil greenhouse study. Both biochar (walnut shell, 900 °C) and biosolids had positive impacts on carrot and lettuce biomass accumulation over our study period. However, the walnut shell biochar stimulated aryl hydrocarbon receptor activity, suggesting the presence of potential endocrine active chemicals in the biochar. Since the biochar rate tested (100 t ha-1) is above the average agronomic rate (10-20 t ha-1), endocrine effects would not be expected in most environmental applications. The effect of high temperature biochars on endocrine system pathways must be explored further, using both quantitative analytical tools to identify potential endocrine active chemicals and highly sensitive bioanalytical assays such as CALUX to measure the resulting biological activity of such compounds.

Changes in Menidia beryllina Gene Expression and In Vitro Hormone-Receptor Activation After Exposure to Estuarine Waters Near Treated Wastewater Outfalls.

Fishes in estuarine waters are frequently exposed to treated wastewater effluent, among numerous other sources of contaminants, yet the impacts of these anthropogenic chemicals are not well understood in these dynamic and important waterways. Inland silversides (Menidia beryllina) at an early stage of development [12 days posthatch (dph)] were exposed to waters from two estuarine wastewater-treatment outfall locations in a tidal estuary, the Sacramento/San Joaquin Delta (California, USA) that had varied hydrology and input volumes. The genomic response caused by endocrine-disrupting compounds (EDCs) in these waters was determined using quantitative polymerase chain reaction on a suite of hormonally regulated genes. Relative androgenic and estrogenic activities of the waters were measured using CALUX reporter bioassays. The presence of bifenthrin, a pyrethroid pesticide and known EDC, as well as caffeine and the anti-inflammatory pharmaceutical ibuprofen, which were used as markers of wastewater effluent input, were determined using instrumental analysis. Detectable levels of bifenthrin (2.89 ng L(-1)) were found on one of the sampling dates, and caffeine was found on all sampling dates, in water from the Boynton Slough. Neither compound was detected at the Carquinez Strait site, which has a much smaller effluent discharge input volume relative to the receiving water body size compared with Boynton Slough. Water samples from both sites incubated in the CALUX cell line induced estrogenic and androgenic activity in almost all instances, though the estrogenicity was relatively higher than the androgenicity. Changes in the abundance of mRNA transcripts of endocrine-responsive genes and indicators of general chemical stress were observed after a 96-h exposure to waters from both locations. The relative levels of endocrine response, changes in gene transcript abundance, and contaminant concentrations were greater in water from the Boynton Slough site despite those effluents undergoing a more advanced treatment process. The availability of a widely geographically distributed estuarine model species (M. beryllina) now allows for improved assessment of treated effluent impacts across brackish, estuarine, and marine environments.

Development of a recombinant human ovarian (BG1) cell line containing estrogen receptor α and ß for improved detection of estrogenic/antiestrogenic chemicals.

Estrogenic endocrine-disrupting chemicals are found in environmental and biological samples, commercial and consumer products, food, and numerous other sources. Given their ubiquitous nature and potential for adverse effects, a critical need exists for rapidly detecting these chemicals. The authors developed an estrogen-responsive recombinant human ovarian (BG1Luc4E2) cell line recently accepted by the US Environmental Protection Agency (USEPA) and Organisation for Economic Co-operation and Development (OECD) as a bioanalytical method to detect estrogen receptor (ER) agonists/antagonists. Unfortunately, these cells appear to contain only 1 of the 2 known ER isoforms, ERα but not ERß, and the differential ligand selectivity of these ERs indicates that the currently accepted screening method only detects a subset of total estrogenic chemicals. To improve the estrogen screening bioassay, BG1Luc4E2 cells were stably transfected with an ERß expression plasmid and positive clones identified using ERß-selective ligands (genistein and Br-ERß-041). A highly responsive clone (BG1LucERßc9) was identified that exhibited greater sensitivity and responsiveness to ERß-selective ligands than BG1Luc4E2 cells, and quantitative reverse-transcription polymerase chain reaction confirmed the presence of ERß expression in these cells. Screening of pesticides and industrial chemicals identified chemicals that preferentially stimulated ERß-dependent reporter gene expression. Together, these results not only demonstrate the utility of this dual-ER recombinant cell line for detecting a broader range of estrogenic chemicals than the current BG1Luc4E2 cell line, but screening with both cell lines allows identification of ERα- and ERß-selective chemicals.

Development of Species-Specific Ah Receptor-Responsive Third Generation CALUX Cell Lines with Enhanced Responsiveness and Improved Detection Limits.

The Ah receptor (AhR)-responsive CALUX (chemically activated luciferase expression) cell bioassay is commonly used for rapid screening of samples for the presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin), dioxin-like compounds, and AhR agonists/antagonists. By increasing the number of AhR DNA recognition sites (dioxin responsive elements), we previously generated a novel third generation (G3) recombinant AhR-responsive mouse CALUX cell line (H1L7.5c3) with a significantly enhanced response to DLCs compared to existing AhR-CALUX cell bioassays. However, the elevated background luciferase activity of these cells and the absence of comparable G3 cell lines derived from other species have limited their utility for screening purposes. Here, we describe the development and characterization of species-specific G3 recombinant AhR-responsive CALUX cell lines (rat, human, and guinea pig) that exhibit significantly improved limit of detection and dramatically increased TCDD induction response. The low background luciferase activity, low minimal detection limit (0.1 pM TCDD) and enhanced induction response of the rat G3 cell line (H4L7.5c2) over the H1L7.5c3 mouse G3 cells, identifies them as a more optimal cell line for screening purposes. The utility of the new G3 CALUX cell lines were demonstrated by screening sediment extracts and a small chemical compound library for the presence of AhR agonists. The improved limit of detection and increased response of these new G3 CALUX cell lines will facilitate species-specific analysis of DLCs and AhR agonists in samples with low levels of contamination and/or in small sample volumes.

Chemicals having estrogenic activity can be released from some bisphenol A-free, hard and clear, thermoplastic resins.

BACKGROUND: Chemicals that have estrogenic activity (EA) can potentially cause adverse health effects in mammals including humans, sometimes at low doses in fetal through juvenile stages with effects detected in adults. Polycarbonate (PC) thermoplastic resins made from bisphenol A (BPA), a chemical that has EA, are now often avoided in products used by babies. Other BPA-free thermoplastic resins, some hypothesized or advertised to be EA-free, are replacing PC resins used to make reusable hard and clear thermoplastic products such as baby bottles. METHODS: We used two very sensitive and accurate in vitro assays (MCF-7 and BG1Luc human cell lines) to quantify the EA of chemicals leached into ethanol or water/saline extracts of fourteen unstressed or stressed (autoclaving, microwaving, UV radiation) thermoplastic resins. Estrogen receptor (ER)-dependent agonist responses were confirmed by their inhibition with the ER antagonist ICI 182,780. RESULTS: Our data showed that some (4/14) unstressed and stressed BPA-free thermoplastic resins leached chemicals having significant levels of EA, including one polystyrene (PS), and three Tritan™ resins, the latter reportedly EA-free. Exposure to UV radiation in natural sunlight resulted in an increased release of EA from Tritan™ resins. Triphenyl-phosphate (TPP), an additive used to manufacture some thermoplastic resins such as Tritan™, exhibited EA in both MCF-7 and BG1Luc assays. Ten unstressed or stressed glycol-modified polyethylene terephthalate (PETG), cyclic olefin polymer (COP) or copolymer (COC) thermoplastic resins did not release chemicals with detectable EA under any test condition. CONCLUSIONS: This hazard survey study assessed the release of chemicals exhibiting EA as detected by two sensitive, widely used and accepted, human cell line in vitro assays. Four PC replacement resins (Tritan™ and PS) released chemicals having EA. However, ten other PC-replacement resins did not leach chemicals having EA (EA-free-resins). These results indicate that PC-replacement plastic products could be made from EA-free resins (if appropriate EA-free additives are chosen) that maintain advantages of re-usable plastic items (price, weight, shatter resistance) without releasing chemicals having EA that potentially produce adverse health effects on current or future generations.

From 'omics to otoliths: responses of an estuarine fish to endocrine disrupting compounds across biological scales.

Endocrine disrupting chemicals (EDCs) cause physiological abnormalities and population decline in fishes. However, few studies have linked environmental EDC exposures with responses at multiple tiers of the biological hierarchy, including population-level effects. To this end, we undertook a four-tiered investigation in the impacted San Francisco Bay estuary with the Mississippi silverside (Menidia audens), a small pelagic fish. This approach demonstrated links between different EDC sources and fish responses at different levels of biological organization. First we determined that water from a study site primarily impacted by ranch run-off had only estrogenic activity in vitro, while water sampled from a site receiving a combination of urban, limited ranch run-off, and treated wastewater effluent had both estrogenic and androgenic activity. Secondly, at the molecular level we found that fish had higher mRNA levels for estrogen-responsive genes at the site where only estrogenic activity was detected but relatively lower expression levels where both estrogenic and androgenic EDCs were detected. Thirdly, at the organism level, males at the site exposed to both estrogens and androgens had significantly lower mean gonadal somatic indices, significantly higher incidence of severe testicular necrosis and altered somatic growth relative to the site where only estrogens were detected. Finally, at the population level, the sex ratio was significantly skewed towards males at the site with measured androgenic and estrogenic activity. Our results suggest that mixtures of androgenic and estrogenic EDCs have antagonistic and potentially additive effects depending on the biological scale being assessed, and that mixtures containing androgens and estrogens may produce unexpected effects. In summary, evaluating EDC response at multiple tiers is necessary to determine the source of disruption (lowest scale, i.e. cell line) and what the ecological impact will be (largest scale, i.e. sex ratio).

Ginsenosides are novel naturally-occurring aryl hydrocarbon receptor ligands.

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor that mediates many of the biological and toxicological actions of structurally diverse chemicals. In this study, we examined the ability of a series of ginsenosides extracted from ginseng, a traditional Chinese medicine, to bind to and activate/inhibit the AHR and AHR signal transduction. Utilizing a combination of ligand and DNA binding assays, molecular docking and reporter gene analysis, we demonstrated the ability of selected ginsenosides to directly bind to and activate the guinea pig cytosolic AHR, and to stimulate/inhibit AHR-dependent luciferase gene expression in a recombinant guinea pig cell line. Comparative studies revealed significant species differences in the ability of ginsenosides to stimulate AHR-dependent gene expression in guinea pig, rat, mouse and human cell lines. Not only did selected ginsenosides preferentially activate the AHR from one species and not others, mouse cell line was also significantly less responsive to these chemicals than rat and guinea pig cell lines, but the endogenous gene CYP1A1 could still be inducted in mouse cell line. Overall, the ability of these compounds to stimulate AHR signal transduction demonstrated that these ginsenosides are a new class of naturally occurring AHR agonists.

The in vivo estrogenic and in vitro anti-estrogenic activity of permethrin and bifenthrin.

Pyrethroids are highly toxic to fish at parts per billion or parts per trillion concentrations. Their intended mechanism is prolonged sodium channel opening, but recent studies reveal that pyrethroids such as permethrin and bifenthrin also have endocrine activity. Additionally, metabolites may have greater endocrine activity than parent compounds. The authors evaluated the in vivo concentration-dependent ability of bifenthrin and permethrin to induce choriogenin (an estrogen-responsive protein) in Menidia beryllina, a fish species known to reside in pyrethroid-contaminated aquatic habitats. The authors then compared the in vivo response with an in vitro assay--chemical activated luciferase gene expression (CALUX). Juvenile M. beryllina exposed to bifenthrin (1, 10, 100 ng/L), permethrin (0.1, 1, 10 µg/L), and ethinylestradiol (1, 10, 50 ng/L) had significantly higher ng/mL choriogenin (Chg) measured in whole body homogenate than controls. Though Chg expression in fish exposed to ethinylestradiol (EE2) exhibited a traditional sigmoidal concentration response, curves fit to Chg expressed in fish exposed to pyrethroids suggest a unimodal response, decreasing slightly as concentration increases. Whereas the in vivo response indicated that bifenthrin and permethrin or their metabolites act as estrogen agonists, the CALUX assay demonstrated estrogen antagonism by the pyrethroids. The results, supported by evidence from previous studies, suggest that bifenthrin and permethrin, or their metabolites, appear to act as estrogen receptor (ER) agonists in vivo, and that the unmetabolized pyrethroids, particularly bifenthrin, act as an ER antagonists in cultured mammalian cells.

Novel 2-amino-isoflavones exhibit aryl hydrocarbon receptor agonist or antagonist activity in a species/cell-specific context.

The aryl hydrocarbon receptor (AhR) mediates the induction of a variety of xenobiotic metabolism genes. Activation of the AhR occurs through binding to a group of structurally diverse compounds, most notably dioxins, which are exogenous ligands. Isoflavones are part of a family which include some well characterised endogenous AhR ligands. This paper analysed a novel family of these compounds, based on the structure of 2-amino-isoflavone. Initially two luciferase-based cell models, mouse H1L6.1c2 and human HG2L6.1c3, were used to identify whether the compounds had AhR agonistic and/or antagonistic properties. This analysis showed that some of the compounds were weak agonists in mouse and antagonists in human. Further analysis of two of the compounds, Chr-13 and Chr-19, was conducted using quantitative real-time PCR in rat H4IIE and human MCF-7 cells. The results indicated that Chr-13 was an agonist in rat but an antagonist in human cells. Chr-19 was shown to be an agonist in rat but more interestingly, a partial agonist in human. Luciferase induction results not only revealed that subtle differences in the structure of the compound could produce species-specific differences in response but also dictated the ability of the compound to be an AhR agonist or antagonist. Substituted 2-amino-isoflavones represent a novel group of AhR ligands that must differentially interact with the AhR ligand binding domain to produce their species-specific agonist or antagonist activity and future ligand binding analysis and docking studies with these compounds may provide insights into the differential mechanisms of action of structurally similar compounds.

Exactly the same but different: promiscuity and diversity in the molecular mechanisms of action of the aryl hydrocarbon (dioxin) receptor.

The Ah receptor (AhR) is a ligand-dependent transcription factor that mediates a wide range of biological and toxicological effects that result from exposure to a structurally diverse variety of synthetic and naturally occurring chemicals. Although the overall mechanism of action of the AhR has been extensively studied and involves a classical nuclear receptor mechanism of action (i.e., ligand-dependent nuclear localization, protein heterodimerization, binding of liganded receptor as a protein complex to its specific DNA recognition sequence and activation of gene expression), details of the exact molecular events that result in most AhR-dependent biochemical, physiological, and toxicological effects are generally lacking. Ongoing research efforts continue to describe an ever-expanding list of ligand-, species-, and tissue-specific spectrum of AhR-dependent biological and toxicological effects that seemingly add even more complexity to the mechanism. However, at the same time, these studies are also identifying and characterizing new pathways and molecular mechanisms by which the AhR exerts its actions and plays key modulatory roles in both endogenous developmental and physiological pathways and response to exogenous chemicals. Here we provide an overview of the classical and nonclassical mechanisms that can contribute to the differential sensitivity and diversity in responses observed in humans and other species following ligand-dependent activation of the AhR signal transduction pathway.

Third-generation Ah receptor-responsive luciferase reporter plasmids: amplification of dioxin-responsive elements dramatically increases CALUX bioassay sensitivity and responsiveness.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, dioxin) and related dioxin-like chemicals are widespread and persistent environmental contaminants that produce diverse toxic and biological effects through their ability to bind to and activate the Ah receptor (AhR) and AhR-dependent gene expression. The chemically activated luciferase expression (CALUX) system is an AhR-responsive recombinant luciferase reporter gene-based cell bioassay that has been used in combination with chemical extraction and cleanup methods for the relatively rapid and inexpensive detection and relative quantitation of dioxin and dioxin-like chemicals in a wide variety of sample matrices. Although the CALUX bioassay has been validated and used extensively for screening purposes, it has some limitations when screening samples with very low levels of dioxin-like chemicals or when there is only a small amount of sample matrix for analysis. Here, we describe the development of third-generation (G3) CALUX plasmids with increased numbers of dioxin-responsive elements, and stable transfection of these new plasmids into mouse hepatoma (Hepa1c1c7) cells has produced novel amplified G3 CALUX cell bioassays that respond to TCDD with a dramatically increased magnitude of luciferase induction and significantly lower minimal detection limit than existing CALUX-type cell lines. The new G3 CALUX cell lines provide a highly responsive and sensitive bioassay system for the detection and relative quantitation of very low levels of dioxin-like chemicals in sample extracts.

Comparative gene responses to collected ambient particles in vitro: endothelial responses.

Epidemiologic studies associate exposure to ambient particulate matter (APM) with increased cardiovascular mortality. Since both pulmonary inflammation and systemic circulation of ultrafine particles are hypothesized as initiating cardiovascular effects, we examined responses of potential target cells in vitro. Human aortic endothelial cells (HAEC) were exposed to 10 µg/ml fine and ultrafine APM collected in an urban setting in summer 2006 or winter 2007 in the San Joaquin Valley, California. RNA isolated after 3 h was analyzed with high-density oligonucleotide arrays. Summer APM treatment affected genes involved in xenobiotic and oxidoreductase activity, transcription factors, and inflammatory responses in HAEC, while winter APM had a robust xenobiotic but lesser inflammatory response. Real-time polymerase chain reaction analysis confirmed that particulate matter (PM)-treated HAEC increased mRNA levels of xenobiotic response enzymes CYP1A1, ALDH1A3, and TIPARP and cellular stress response transcription factor ATF3. Inflammatory response genes included E-selectin, PTGS2, CXCL-2 (MIP-2α), and CCL-2 (MCP-1). Multiplex protein assays showed secretion of IL-6 and MCP-1 by HAEC. Since induction of CYP1A1 is mediated through the ligand-activated aryl hydrocarbon receptor (AhR), we demonstrated APM induced AhR nuclear translocation by immunofluorescence and Western blotting and activation of the AhR response element using a luciferase reporter construct. Inhibitor studies suggest differential influences of polycyclic aromatic hydrocarbon signaling, ROS-mediated responses and endotoxin alter stress and proinflammatory endothelial cell responses. Our findings demonstrate gene responses correlated with current concepts that systemic inflammation drives cardiovascular effects of particulate air pollution. We also demonstrate a unique pattern of gene responses related to xenobiotic metabolism in PM-exposed HAEC.

Identification of benzothiazole derivatives and polycyclic aromatic hydrocarbons as aryl hydrocarbon receptor agonists present in tire extracts.

Leachate from rubber tire material contains a complex mixture of chemicals previously shown to produce toxic and biological effects in aquatic organisms. The ability of these leachates to induce Ah receptor (AhR)-dependent cytochrome P4501A1 expression in fish indicated the presence of AhR active chemicals, but the responsible chemicals and their direct interaction with the AhR signaling pathway were not examined. Using a combination of AhR-based bioassays, we have demonstrated the ability of tire extract to stimulate both AhR DNA binding and AhR-dependent gene expression and confirmed that the responsible chemicals were metabolically labile. The application of CALUX (chemical-activated luciferase gene expression) cell bioassay-driven toxicant identification evaluation not only revealed that tire extract contained a variety of known AhR-active polycyclic aromatic hydrocarbons but also identified 2-methylthiobenzothiazole and 2-mercaptobenzothiazole as AhR agonists. Analysis of a structurally diverse series of benzothiazoles identified many that could directly stimulate AhR DNA binding and transiently activate the AhR signaling pathway and identified benzothiazoles as a new class of AhR agonists. In addition to these compounds, the relatively high AhR agonist activity of a large number of fractions strongly suggests that tire extract contains a large number of physiochemically diverse AhR agonists whose identities and toxicological/biological significances are unknown.

CH223191 is a ligand-selective antagonist of the Ah (Dioxin) receptor.

The aryl hydrocarbon (dioxin) receptor (AhR) is a ligand-dependent transcription factor that produces a wide range of biological and toxic effects in many species and tissues. Whereas the best-characterized high-affinity ligands include structurally related halogenated aromatic hydrocarbons (HAHs) and polycyclic aromatic hydrocarbons (PAHs), the AhR is promiscuous and can also be activated by structurally diverse exogenous and endogenous chemicals. However, little is known about how these diverse ligands actually bind to and activate the AhR. Utilizing AhR ligand binding, DNA binding, and reporter gene expression assays, we have identified a novel ligand-selective antagonist (CH223191) that preferentially inhibits the ability of some classes of AhR agonists (2,3,7,8-tetrachlorodibenzo-p-dioxin and related HAHs), but not others (PAHs, flavonoids, or indirubin), to bind to and/or activate the AhR and AhR signal transduction. HAH-specific antagonism of AhR-dependent reporter gene expression by CH223191 was observed with mouse, rat, human, and guinea pig cell lines. Ligand- and species-selective antagonism was also observed with the AhR antagonists 3'-methoxy-4'-nitroflavone and 6,2',4',-trimethoxyflavone. Our results suggest that the differences in the binding by various ligands to the AhR contribute to the observed structural diversity of AhR ligands and could contribute in ligand-specific variation in AhR functionality and the toxic and biological effects of various classes of AhR agonists.

Toxicology in the fast lane: application of high-throughput bioassays to detect modulation of key enzymes and receptors.

BACKGROUND: Legislation at state, federal, and international levels is requiring rapid evaluation of the toxicity of numerous chemicals. Whole-animal toxicologic studies cannot yield the necessary throughput in a cost-effective fashion, leading to a critical need for a faster and more cost-effective toxicologic evaluation of xenobiotics. OBJECTIVES: We tested whether mechanistically based screening assays can rapidly provide information on the potential for compounds to affect key enzymes and receptor targets, thus identifying those compounds requiring further in-depth analysis. METHODS: A library of 176 synthetic chemicals was prepared and examined in a high-throughput screening (HTS) manner using nine enzyme-based and five receptor-based bioassays. RESULTS: All the assays have high Z' values, indicating good discrimination among compounds in a reliable fashion, and thus are suitable for HTS assays. On average, three positive hits were obtained per assay. Although we identified compounds that were previously shown to inhibit a particular enzyme class or receptor, we surprisingly discovered that triclosan, a microbiocide present in personal care products, inhibits carboxylesterases and that dichlone, a fungicide, strongly inhibits the ryanodine receptors. CONCLUSIONS: Considering the need to rapidly screen tens of thousands of anthropogenic compounds, our study shows the feasibility of using combined HTS assays as a novel approach toward obtaining toxicologic data on numerous biological end points. The HTS assay approach is very useful to quickly identify potentially hazardous compounds and to prioritize them for further in-depth studies.