Relative potencies of PAHs and PCBs based on the response of human cells

Benzo[b]naphtho[d]thiophenes and naphthylbenzo[b]thiophenes: Their aryl hydrocarbon receptor-mediated activities and environmental presence

Polycyclic aromatic sulfur heterocyclic compounds (PASHs) belong among ubiquitous environmental pollutants; however, their toxic effects remain poorly understood. Here, we studied the aryl hydrocarbon receptor (AhR)-mediated activity of dibenzothiophene, benzo[b]naphtho[d]thiophenes, and naphthylbenzo[b]thiophenes, as well as their presence in two types of environmental matrices: river sediments collected from both rural and urban areas, and in airborne particulate matter (PM_2.5) sampled in cities with different levels and sources of pollution. Benzo[b]naphtho[2,1-d]thiophene, benzo[b]naphtho[2,3-d]thiophene, 2,2-naphthylbenzo[b]thiophene, and 2,1-naphthylbenzo[b]thiophene were newly identified as efficient AhR agonists in both rat and human AhR-based reporter gene assays, with 2,2-naphthylbenzo[b]thiophene being the most potent compound identified in both species. Benzo[b]naphtho[1,2-d]thiophene and 3,2-naphthylbenzo[b]thiophene elicited AhR-mediated activity only in the rat liver cell model, while dibenzothiophene and 3,1-naphthylbenzo[b]thiophene were inactive in either cell type. Independently of their ability to activate the AhR, benzo[b]naphtho[1,2-d]thiophene, 2,1-naphthylbenzo[b]thiophene, 3,1-naphthylbenzo[b]thiophene, and 3,2-naphthylbenzo[b]thiophene inhibited gap junctional intercellular communication in a model of rat liver epithelial cells. Benzo[b]naphtho[d]thiophenes were dominant PASHs present in both PM_2.5 and sediment samples, with benzo[b]naphtho[2,1-d]thiophene being the most abundant one, followed by benzo[b]naphtho[2,3-d]thiophene. The levels of naphthylbenzo[b]thiophenes were mostly low or below detection limit. Benzo[b]naphtho[2,1-d]thiophene and benzo[b]naphtho[2,3-d]thiophene were identified as the most significant contributors to the AhR-mediated activity in the environmental samples evaluated in this study. Both induced nuclear translocation of the AhR, and they induced CYP1A1 expression in a time-dependent manner, suggesting that their AhR-mediated activity may depend on the rate of their intracellular metabolism. In conclusion, some PASHs could be significant contributors to the overall AhR-mediated toxicity of complex environmental samples suggesting that more attention should be paid to the potential health impacts of this group of environmental pollutants.

How does habitat influence metabolism? Clues from biomarker response and contaminant profile in Tursiops truncatus (Montagu, 1821) subspecies living in parapatry

In western South America (WSA) two subspecies of bottlenose dolphin are recognized: Tursiops truncatus gephyreus, predominantly found in estuaries and river mouths, and Tursiops truncatus truncatus, occurring along the continental shelf. Despite a partial spatial overlap, both subspecies are considered to occupy different habitats and ecological niches. In the present study, chemical analyzes as well as biochemical and molecular biomarkers were used to investigate the influence of niche partitioning over metabolic pathways associated with the detoxification of persistent organic pollutants (POPs), antioxidant metabolism, immune activity and lipid metabolism in Tursiops truncatus subspecies living in parapatry. Overall, the profile and levels of bioaccumulated PCBs, pesticides and PBDEs were similar between groups, with a greater variety of pesticides, such as γ-HCHs, heptachlor, oxychlordane and o,p'DDT, detected in T. truncatus gephyreus. Multivariate analysis of variance (MANOVA) and non-metric multidimensional scaling (NMDS) results indicated that glutathione reductase (GR) and superoxide dismutase (SOD) enzymatic activities were higher in coastal dolphins, as were the mRNA levels of metallothionein 2A (MT2A), interleukin-1α (IL-1α), ceramide synthase 3 (CERS3) and fatty acid elongase (ELOVL4). In parallel, mRNA levels of fatty acid synthase complex 1 (FASN 1) were higher in oceanic dolphins. These findings suggest that, due to their occurrence in coastal habitats, T. truncatus gephyreus is more exposed to environmental pollutants and pathogenic microorganisms. Likewise, niche partitioning may influence lipid biosynthesis, possibly due to differences on feeding habits, reflecting in an enhanced long chain ceramides biosynthesis in T. truncatus gephyreus. Collectively, these data reinforce the need to address habitat specificities in conservation efforts, since distinct groups can be facing different anthropogenic pressures in WSA.

An equivalency iterative algorithm for cancer risk assessment of chemical mixtures with additive effects

To better estimate cumulative cancer risks and avoid the overestimated risk from the linear extrapolation, an equivalency iterative algorithm associated with a carcinogenesis hypothesis was introduced for a mixture of chemicals with the same mode of action (MOA). A lognormal dose-response function was applied for carcinogenic chemicals. Under some circumstances, the repetitive random iterative algorithm could be transformed into the nonrepetitive one. It was also demonstrated that the equivalent value for a lognormal-based equivalency iterative algorithm with the same shape parameter was independent of the operation order. Based on the theorems of the algorithm and Plackett and Hewlett's minimum effective dose assumption, the sum of toxicity-weighted dose for a mixture of chemicals was mathematically derived. Compared to the estimation of risk by the linear extrapolation method (e.g., cancer slope factors), the equivalency iterative algorithm for lognormal functions can avoid overestimated risk significantly, which can help better estimate the cumulative cancer risk for a mixture of chemicals with the same MOA.

Environmental six-ring polycyclic aromatic hydrocarbons are potent inducers of the AhR-dependent signaling in human cells

The toxicities of many environmental polycyclic aromatic hydrocarbons (PAHs), in particular those of high-molecular-weight PAHs (with MW higher than 300), remain poorly characterized. The objective of this study was to evaluate the ability of selected environmentally relevant PAHs with MW 302 (MW302 PAHs) to activate the aryl hydrocarbon receptor (AhR), since this represents a major toxic mode of action of PAHs. A large number of the evaluated compounds exhibited strong AhR-mediated activities, in particular in human models. The studied MW302 PAHs also significantly contributed to the overall calculated AhR activities of complex environmental mixtures, including both defined standard reference materials and collected diesel exhaust particles. The high AhR-mediated activities of representative MW302 PAHs, e.g. naphtho[1,2-k]fluoranthene, corresponded with the modulation of expression of relevant AhR target genes in a human lung cell model, or with the AhR-dependent suppression of cell cycle progression/proliferation in estrogen-sensitive cells. This was in a marked contrast with the limited genotoxicity of the same compound(s). Given the substantial levels of the AhR-activating MW302 PAHs in combustion particles, it seems important to continue to investigate the toxic modes of action of this large group of PAHs associated with airborne particulate matter.

Concentration dependence of human and mouse aryl hydrocarbon receptor responsiveness to polychlorinated biphenyl exposures: Implications for aroclor mixtures

1. Aryl hydrocarbon receptor (AhR) ligands, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs), are endocrine disrupting chemicals associated with nonalcoholic fatty liver disease. This study documents the species-specific differences between mouse (high affinity mAhR) and human AhR (hAhR) activation by PCB congeners and Aroclor mixtures. 2. AhR activation by TCDD or PCBs 77, 81, 114, 114, 126, and 169 was measured using luciferase reporter constructs transfected into either Hepa1c1c7 mouse or HepG2 human liver cell lines. The EC₅₀ values were lower in Hepa1c1c7 cells than HepG2 cells for all compounds tested except PCB 81. The results for TCDD and PCB 126 were validated in primary human and mouse hepatocytes by measuring CYP1A1 gene transcript levels. 3. Because humans are exposed to PCB mixtures, several mixtures (Aroclors 1254; 1260; and 1260 + 0.1% PCB126 each at 10 µg/ml) were then tested. Neither Aroclor 1254 nor Aroclor 1260 increased luciferase activity by the transfected AhR reporter construct. The Aroclor 1260 + 0.1% PCB 126 mixture induced mAhR-mediated transactivation, but not hAhR activation in cell lines. 4. In summary, significant concentration-dependent differences exist between human and mouse AhR activation by PCBs. Relative effect potencies differed, in some cases, from published toxic equivalency factors.

Assessment of the aryl hydrocarbon receptor-mediated activities of polycyclic aromatic hydrocarbons in a human cell-based reporter gene assay

Activation of the aryl hydrocarbon receptor (AhR)-mediated activity is one of key events in toxicity of polycyclic aromatic hydrocarbons (PAHs). Although various classes of AhR ligands may differentially activate human and rodent AhR, there is presently a lack of data on the human AhR-inducing relative potencies (REPs) of PAHs. Here, we focused on estimation of the AhR-mediated activities of a large set of environmental PAHs in human gene reporter AZ-AhR cell line, with an aim to develop the human AhR-based REP values with potential implications for risk assessment of PAHs. The previously identified weakly active PAHs mostly failed to activate the AhR in human cells. The order for REPs of individual PAHs in human cells largely corresponded with the available data from rodent-based experimental systems; nevertheless, we identified differences up to one order of magnitude in REP values of PAHs between human and rodent cells. Higher REP values were found in human cells for some important environmental contaminants or suspected carcinogens, such as indeno[1,2,3-cd]pyrene, benz[a]anthracene or benzo[b]fluoranthene, while lower REP values were determined for methyl-substituted PAHs. Our results also indicate that a different rate of metabolism for individual PAHs in human vs. rodent cells may affect estimation of REP values in human cell-based assay, and potentially alter toxicity of some compounds, such as benzofluoranthenes, in humans. We applied the AZ-AhR assay to evaluation of the AhR-mediated activity of complex mixtures of organic compounds associated with diesel exhaust particles, and we identified the polar compounds present in these mixtures as being particularly highly active in human cells, as compared with rodent cells. The present data suggest that differences may exist between the AhR-mediated potencies of PAHs in human and rodent cells, and that the AhR-mediated effects of polar PAH derivatives and metabolites in human cell models deserve further attention.

Improving the in vitro ethoxyresorufin-O-deethylase (EROD) assay with RTL-W1 by metabolic normalization and use of β-naphthoflavone as the reference substance

The ethoxyresorufin-O-deethylase (EROD) assay is a widely applied method for the evaluation of the dioxin-like activity of single substances and environmental samples. As for most enzyme assays, the specific activity is normally related to total protein contents, the determination of which has clear limitations in high-throughput assays. EROD induction potentials are usually expressed as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents, a substance highly toxic to humans. In order to compensate for these shortcomings, two modifications of the EROD protocol are proposed: (1) EROD activity is normalized to the metabolic activity of the cells as determined by a modified thiazolyl blue tetrazolium (MTT) assay and expressed as metabolic cell equivalents (MCE) based on MTT data rather than to protein contents. Via MCE data, cytotoxicity information can always be reported in parallel to EROD data; with the protocol presented here, MTT and EROD data are collected simultaneously. (2) Among several reference substances tested (2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), β-naphthoflavone and benzo[a]pyrene), β-naphthoflavone proved to be the most suitable reference for the routine in vitro EROD assay, although TCDD has generally been preferred for purely scientific reasons.

Chemical and bioanalytical characterization of dioxins in indoor dust in Hong Kong

In the present work, air-conditioner filter dust samples collected from commercial office, secondary school, shopping mall, electronic factory and manufacturing plant in Hong Kong were collected for 7-ethoxyresorufin O-deethylase (EROD) assay using a hepatoma cell line (H4IIE) and chemical analysis of dioxins including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and PCBs with dioxin-like structure. The result of EROD assay showed that bioassay derived TEQ of 2,3,7,8-TCDD (TEQ(bio)) of dust samples varied from 320 to 730 pg/g. Chemical analyses revealed that chemical derived TEQ of 2,3,7,8-TCDD (TEQ(cal)) of dust samples ranged from 134 to 531 pg/g. In addition, the TEQ(cal) of samples were significantly correlated with TEQ(bio) of samples (R=0.83, P<0.01). The average daily doses (ADDs) of dioxins via indoor dust with the estimated ADDs of dioxins via air and food were compared. The results showed that indoor dust is an important medium of exposure to dioxins.

Construction of a system that simultaneously evaluates CYP1A1 and CYP1A2 induction in a stable human-derived cell line using a dual reporter plasmid

Human CYP1A1 and CYP1A2 genes are in a head-to-head orientation on chromosome 15 and are separated by a 23-kb intergenic space. To our knowledge, this is the first report on a stable cell line that contains the 23-kb full-length regulatory region and is able to simultaneously assess the transcriptional activation of CYP1A1 and CYP1A2 genes. The stable cell line that constitutively expresses the reporter activities was constructed by inserting the dual reporter plasmid containing the 23-kb region between the CYP1A1 and CYP1A2 genes into the chromosome. Transcriptional activation of the CYP1A1 and CYP1A2 genes was measured simultaneously using luciferase (Luc) and secreted alkaline phosphatase (SEAP) activities, respectively. To demonstrate the utility of the stable cell line, CYP1A1/1A2 induction by the majority of compounds previously identified as CYP1A1/1A2 inducers was measured. The results clearly show that all compounds caused induction of reporter activities. In addition to assessing transcriptional activation of the CYP1A1 and CYP1A2 genes by measuring reporter activities, we determined the intrinsic CYP1A1 and CYP1A2 mRNA levels by treating them with the same compounds. The results suggest that this stable cell line may be used to rapidly and accurately predict CYP1A1/1A2 induction.

Aryl hydrocarbon receptor and estrogen receptor ligand activity of organic extracts from road dust and diesel exhaust particulates

A wide variety of contaminants derived from diesel and gasoline engines, tire, asphalt, and natural organic compounds is found in road dust. Polycyclic aromatic compounds (PACs) are the important toxic targets among various contents in road dust and diesel exhaust particulates (DEPs), and endocrine-disrupting activity of PACs was suggested. In the present study, aryl hydrocarbon receptor (AhR) ligand activity was confirmed in the extract of both road dust and DEPs. In the separation of the extracts for both road dust and DEPs with reversed-phase HPLC, it was found that polar fractions contributed to significant AhR ligand activity in both a mouse hepatoma (H1L1) cell system and a yeast system. Furthermore, the contribution of these polar fractions was higher in DEPs than in road dust, probably because of the greater concentration of oxy-PAHs in DEPs than in road dust. The contribution of contaminants associated with the polar region to AhR ligand activity was also evident following the separation of road dust with normal-phase HPLC. Additionally, remarkable estrogen receptor (ER) ligand activity was detected in the highly polar region separated with normal-phase HPLC. It is suggested that many unknown AhR or ER ligand active compounds are contained in the polar region.

Induction of CYP1A1 and CYP1B1 by benzo(k)fluoranthene and benzo(a)pyrene in T-47D human breast cancer cells: roles of PAH interactions and PAH metabolites

The interactions of polycyclic aromatic hydrocarbons (PAH) and cytochromes P450 (CYP) are complex; PAHs are enzyme inducers, substrates, and inhibitors. In T-47D breast cancer cells, exposure to 0.1 to 1 microM benzo(k)fluoranthene (BKF) induced CYP1A1/1B1-catalyzed 17beta-estradiol (E(2)) metabolism, whereas BKF levels greater than 1 muM inhibited E(2) metabolism. Time course studies showed that induction of CYP1-catalyzed E(2) metabolism persisted after the disappearance of BKF or co-exposed benzo(a)pyrene, suggesting that BKF metabolites retaining Ah receptor agonist activity were responsible for prolonged CYP1 induction. BKF metabolites were shown, through the use of ethoxyresorufin O-deethylase and CYP1A1-promoter-luciferase reporter assays to induce CYP1A1/1B1 in T-47D cells. Metabolites formed by oxidation at the C-2/C-3 region of BKF had potencies for CYP1 induction exceeding those of BKF, whereas C-8/C-9 oxidative metabolites were somewhat less potent than BKF. The activities of expressed human CYP1A1 and 1B1 with BKF as substrate were investigated by use of HPLC with fluorescence detection, and by GC/MS. The results showed that both enzymes efficiently catalyzed the formation of 3-, 8-, and 9-OHBKF from BKF. These studies indicate that the inductive effects of PAH metabolites as potent CYP1 inducers are likely to be additional important factors in PAH-CYP interactions that affect metabolism and bioactivation of other PAHs, ultimately modulating PAH toxicity and carcinogenicity.

Reaction of polycyclic aromatic hydrocarbons adsorbed on silica in aqueous chlorine

The reaction of polycyclic aromatic hydrocarbons (PAHs) previously adsorbed on silica gel or diatomaceous earth with sodium hypochlorite was carried out to elucidate their reactivity to aqueous chlorine. It was demonstrated that the PAHs adsorbed on silica reacted more rapidly than the PAHs themselves in water, leading to the formation of many chlorinated and oxidized derivatives. A similar reaction in the presence of potassium bromide was found to preferentially produce corresponding brominated derivatives. These reactions seem to proceed through PAHs adsorbed on the silica surface and halogenating agents, the electrophilicity of which may be raised by the catalytic effect of the silanol group of the silica surface. These findings from the environmental viewpoint suggest that the reaction of hydrophobic compounds adsorbed on sediment cannot be neglected.

Metabolic Enzyme Induction by HepG2 Cells Exposed to Oxygenated and Nonoxygenated Polycyclic Aromatic Hydrocarbons

Oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) such as polycyclic aromatic quinones and polycyclic aromatic ketones as well as polycyclic aromatic hydrocarbons (PAHs) are abundant in the atmospheric environment. In this study, mRNA induction of six metabolic enzymes including P4501A1, 1A2, and 1B1, aldo-keto reductase 1C1 (AKR1C1), NAD(P)H-dependent quinone oxidoreductase 1 (NQO1), and glutathione S-transferase M1 (GSTM1) were examined in detail in human hepatoma (HepG2) cells exposed to environmentally relevant 13 PAHs and seven oxy-PAHs. Most PAHs such as benzo[a]pyrene (B[a]P) showed significant induction of P4501A1 and 1A2 mRNA, while induction by oxy-PAHs such as 5,12-naphthacenequinone (NCQ) and 11H-benzo[b]fluoren-11-one (B[b]FO) occurred less strongly. AKR1C1 mRNA was significantly induced by oxy-PAHs, 11H-benzo[a]fluoren-11-one (B[a]FO), NCQ, cyclopenta[cd]pyren-3(4H)-one (CPPO), and B[b]FO and also by P450s-inducing PAHs such as B[a]P, benzo[k]fluoranthene (B[k]FA), and dibenz[a,h]anthracene (DB[a,h]A). Both chemical-dependent and time-dependent induction patterns of NQO1 mRNA were of the mixed types of P4501A1 and AKR1C1. The tendency for the decrease of GSTM1 mRNA was observed when exposed to PAHs B[a]P and B[k]FA.

Activation of Ah receptor by pure humic acids

Humic substances (HS) are ubiquitous in the environment. However, some studies indicate that HS could induce direct adverse effects on human health and hormone-like effects in fish, amphibians, and invertebrates. In this study we investigated a possible biochemical mechanism of HS toxicity via activation of the aryl hydrocarbon receptor (AhR). AhR mediates the toxic and biological effects of environmental contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), but a number of structurally diverse compounds has also been found to activate AhR. Alkali solutions of humic acids (HA) were prepared, and subsequently, lipophilic compounds (including parts of HA) were extracted by liquid-liquid extraction with hexane/dichloromethane. Organic extract of HA was further treated with sulfuric acid to study the role of possible trace persistent contaminants. In vitro dioxin-like activities of obtained extract and HA solutions have been evaluated using H4IIE.luc cells by determining the ethoxyresorufin-O-deethylase (EROD) activity and induction of AhR-dependent reporter luciferase. Traces of nonpersistent residues in HA with known AhR activity were identified and quantified by GC-MS. Our results show that an alkali solution as well as organic extract of HA were active in both EROD and luciferase assays, while H2SO4-treated extract activity was negligible. Only nonsignificant levels of AhR-inducing contaminants (PAHs and PCBs) were found in the HA samples. Our results indicate that HA or their fragments can elicit significant inductions of AhR-mediated effects in vitro. To our best knowledge, this study is the first in providing direct evidence of dioxin-like effects of HA. Further efforts should focus on detailed characterization of potential toxic effects of various HSs.

Activation of ERK1/2 and p38 kinases by polycyclic aromatic hydrocarbons in rat liver epithelial cells is associated with induction of apoptosis

Deregulation of various signaling pathways, linked either to induction of cell proliferation or to modulation of cellular differentiation and apoptosis, has been proposed to contribute to carcinogenicity of polycyclic aromatic hydrocarbons (PAHs). In the present study, we investigated effects of the PAHs previously shown to induce cell proliferation and/or apoptosis in contact-inhibited rat liver epithelial WB-F344 cells, with an aim to define the role of mitogen-activated protein kinases in both events. We found that only strong genotoxin dibenzo[a,l]pyrene (DBalP) activated extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 kinase, but not c-Jun N-terminal kinases (JNKs), at concentrations inducing both apoptosis and phosphorylation of p53 tumor suppressor at serine 15 residue. In contrast, the PAHs stimulating cell proliferation in WB-F344 cell line had no effect on activation of ERK1/2, p38 or JNKs. Synthetic inhibitors of ERK1/2 activation (U0126) or p38 kinase activity (SB203580) prevented both apoptosis and induction of p53 phosphorylation by DBalP. Pifithrin-alpha, inhibitor of p53 transcriptional activity, prevented induction of apoptosis and activation of ERK1/2 and p38. Taken together, our data suggest that both ERK1/2 and p38 are activated in response to DBalP and that they might be involved in regulation of cellular response to DNA damage induced by DBalP, while neither kinase is involved in the release from contact inhibition induced by PAHs.

Transformation of pyrene in aqueous chlorination in the presence and absence of bromide ion: kinetics, products, and their aryl hydrocarbon receptor-mediated activities

To assess the endocrine-disrupting activity stemming from the presence of pyrene in drinking water, the kinetics of chlorination of pyrene was investigated at room temperature, the products of its aqueous chlorination with and without bromide ion were identified, and their aryl hydrocarbon receptor (AhR)-mediated activities were determined. It was found that the presence of bromide ion greatly promoted the reaction rate of chlorination of pyrene accompanied with the formation of brominated products. While the main product was 1-Cl-pyrene without the addition of bromide ion, di-Br-pyrene and 1-Br-pyrene became the main products in the presence of bromide ion. GC-MS and NMR analysis identified three structures of dibromopyrene in chlorination with the addition of bromide ion as 1,3-di-Br-pyrene, 1,6-di-Br-pyrene, and 1,8-di-Br-pyrene, and their molar ratio was determined to be approximately 0.3:1:1. Finally, 1-Br-pyrene, 1,3-di-Br-pyrene, a mixture of 1,6-di-Br-pyrene and 1,8-di-Br-pyrene (di-Br-pyrene), 1-Cl-pyrene, and a mixture of 1,6-di-Cl-pyrene and 1,8-di-Cl-pyrene (di-Cl-pyrene) were fractionated by HPLC, and their AhR-mediated activities were assessed by a yeast assay. It was found that the effective molar concentrations (or mass concentration) showing half-maximal transcriptional response, EC50, for pyrene, 1-Br-pyrene, 1-Cl-pyrene, di-Cl-pyrene, and di-Br-pyrene were 5632 (1.14), 3089 (0.86), 1942 (0.46), 597.2 (0.21), and 147.3 (0.04) nM (mg/L), respectively.

Modulation of gene expression and DNA adduct formation in HepG2 cells by polycyclic aromatic hydrocarbons with different carcinogenic potencies

Polycyclic aromatic hydrocarbons (PAHs) can occur in relatively high concentrations in the air, and many PAHs are known or suspected carcinogens. In order to better understand differences in carcinogenic potency between PAHs, we investigated modulation of gene expression in human HepG2 cells after 6 h incubation with varying doses of benzo[a]pyrene (B[a]P), benzo[b]fluoranthene (B[b]F), fluoranthene (FA), dibenzo[a,h]anthracene (DB[a,h]A), 1-methylphenanthrene (1-MPA) or dibenzo[a,l]pyrene (DB[a,l]P), by using cDNA microarrays containing 600 toxicologically relevant genes. Furthermore, DNA adduct levels induced by the compounds were assessed with (32)P-post-labeling, and carcinogenic potency was determined by literature study. All tested PAHs, except 1-MPA, induced gene expression changes in HepG2 cells, although generally no dose-response relationship could be detected. Clustering and principal component analysis showed that gene expression changes were compound specific, since for each compound all concentrations grouped together. Furthermore, it showed that the six PAHs can be divided into three groups, first FA and 1-MPA, second B[a]P, B[b]F and DB[a,h]A, and third DB[a,l]P. This grouping corresponds with the carcinogenic potencies of the individual compounds. Many of the modulated genes are involved in biological pathways like apoptosis, cholesterol biosynthesis and fatty acid synthesis. The order of DNA adduct levels induced by the PAHs was: B[a]P >> DB[a,l]P > B[b]F > DB[a,h]A > 1-MPA >/= FA. When comparing the expression change of individual genes with DNA adduct levels, carcinogenic potency or Ah-receptor antagonicity (the last two were taken from literature), several highly correlated genes were found, of which CYP1A1, PRKCA, SLC22A3, NFKB1A, CYP1A2 and CYP2D6 correlated with all parameters. Our data indicate that discrimination of high and low carcinogenic PAHs by gene expression profiling is feasible. Also, the carcinogenic PAHs induce several pathways that were not affected by the least carcinogenic PAHs.

Environmental xenobiotics and nuclear receptors--interactions, effects and in vitro assessment

A group of intracellular nuclear receptors is a protein superfamily including arylhydrocarbon AhR, estrogen ER, androgen AR, thyroid TR and retinoid receptors RAR/RXR as well as molecules with unknown function known as orphan receptors. These proteins play an important role in a wide range of physiological as well as toxicological processes acting as transcription factors (ligand-dependent signalling macromolecules modulating expression of various genes in a positive or negative manner). A large number of environmental pollutants and other xenobiotics negatively affect signaling pathways, in which nuclear receptors are involved, and these modulations were related to important in vivo toxic effects such as immunosuppression, carcinogenesis, reproduction or developmental toxicity, and embryotoxicity. Presented review summarizes current knowledge on major nuclear receptors (AhR, ER, AR, RAR/RXR, TR) and their relationship to known in vivo toxic effects. Special attention is focused on priority organic environmental contaminants and experimental approaches for determination and studies of specific toxicity mechanisms.

Cell-based high-throughput bioassays to assess induction and inhibition of CYP1A enzymes

CYP1A is a subfamily of cytochrome P450 enzymes involved in the metabolism of numerous therapeutic drugs and in the bioactivation of procarcinogens to mutagens. Because of their diverse metabolic capacities, differences in expression of CYP1A enzymes may profoundly influence drug-drug interactions and drug or carcinogen activation and detoxification. Here, we demonstrate that cell-based bioassays are capable of identifying xenobiotics that either alter aryl hydrocarbon receptor (AhR)-mediated CYP1A levels or produce inhibition of enzyme activity. To assess induction, a stable cell line harboring a luciferase reporter driven by multiple dioxin response elements (DREs) was developed. Using this cell line, AhR agonists and antagonists were identified among drugs, dietary agents, and environmental compounds. Of the chemicals examined, the therapeutic agent omeprazole induced reporter gene activity 12.5+/-0.41 fold above control, whereas the phytochemical, chrysin and environmental pollutant, benzanthracene enhanced luciferase activity 3.3+/-0.03 and 28.7+/-1.7 fold above control, respectively. Several natural products, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) prevented TCDD-mediated increases in luciferase expression. For example, the botanical kava inhibited TCDD-mediated induction by 88%. Northern blot analyses of CYP1A1 in HepG2 cells treated with similar agents validated results generated in the stable cell line. The stable cells were further used to identify inhibitors of CYP1A-mediated metabolism. Resveratrol and furafylline exhibited dose-dependent decreases in CYP1A1 and CYP1A2 enzyme activities with IC50 values of 1.89 and 0.79 microM, respectively. In summary, chemicals that possess the ability to alter CYP1A expression or inhibit CYP1A enzyme activities can be rapidly identified with the cell-based bioassays described here.

Regional comparisons of coastal sediment contamination detected by a biomarker (P450 HRGS; EPA Method 4425)

Pollution investigations by the Center for Coastal Monitoring and Assessment of the National Oceanic and Atmospheric Administration (NOAA) have been conducted since 1984 and have incorporated extensive biological and chemical analyses. Since 1993, one of the biological tests utilized in these studies has been the biomarker P450HRGS, which is more recently described as EPA Method 4425. Extracts of sediments are applied to a human cell line with a reporter gene (firefly luciferase) at the CYP1A1 site. Light produced by the extracts is a function of the concentrations and potencies of those compounds with an affinity for Ah-receptor (certain polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and dioxins/ furans). These compounds are carcinogenic and can produce chronic toxicity, and those containing chlorine are persistent and bioaccumulated. Nineteen coastal regions and 1309 samples from the three U.S. coasts have been evaluated as part of the NOAA investigations. The stratified random sampling approach used by NOAA provides estimates of the areas (km2) of each region containing levels of the compounds above thresholds. From analysis of the database, sediments with concentrations at or below 11 microg benzo[a]pyrene equivalents (B[a]PEq)/g would not be expected to produce effects on the benthos. At 32 microg B[a]PEq/g and above there is the potential for impacts on the biota, and above 60 microg/g, the degradation of the benthic community has been observed. Several of the regional surveys found no samples at or above 60 microg B[a]PEq/g, but 60% of the samples from New York Harbor (280 km2) were above this level. Analyses of data from Puget Sound and Chesapeake Bay demonstrate an increase in samples above 32 microg B[a]PEq/g in more populated and industrial regions. Method 4425 serves as both a biomarker, simulating the response of an organism (with CYP1A) exposed to inducing compounds, and as a bioanalytical technique measuring the levels of these chemicals in the samples. A targeted investigation of the distribution of the three important classes of compounds identified by Method 4425 would be more cost-effective by first screening samples by this method before expending substantial funds in the detailed chemical analysis of all samples.

Contrasting effects of coplanar versus non-coplanar PCB congeners on immunomodulation and CYP1A levels (determined using an adapted ELISA method) in the common sea star Asterias rubens L

Biological effects of two structurally contrasting PCB congeners (coplanar 77 and non coplanar 153) were investigated by measuring the induction of CYP1A immunopositive protein (CYP1A IPP) in the pyloric caeca and the production of reactive oxygen species (ROS) by amoebocytes in the common sea star Asterias rubens. CYP1A IPP was quantified using a specially designed ELISA which uses competitive binding between sea stars and trout CYP1A IPPs. Only the coplanar congener had a significant effect on the two considered biological responses. Intensity of the effects was dose-dependent. However, the highest dose of PCB 77 induced a dramatic decrease of ROS production. It is concluded that coplanar PCBs straightforwardly affect key biological processes such as the immune system and mixed-function oxidase (MFO) system.

Relative potency of PAHs and heterocycles as aryl hydrocarbon receptor agonists in fish

The relative potency of polycyclic aromatic compounds as aryl hydrocarbon receptor (AhR) agonists in fish was determined using data on CYP1A induction or AhR binding for 74 polycyclic aromatic hydrocarbons (PAHs) and heterocycles in teleost, avian, or mammalian systems from 18 published papers. Each PAH was assigned a fish potency factor relative to the potency of 2,3,7,8-tetrachlorodibenzo-p-dioxin as an AhR agonist. Two and three ring unsubstituted PAHs were generally inactive in fish, avian, and mammalian systems. Benzo[k]fluoranthene and indeno[1,2,3-cd]pyrene were consistently the most potent PAHs, with fish potency factors of 0.001-0.002. Common structural features associated with higher potency PAHs included 4-6 rings containing fluoranthene or phenanthrene structures with an exposed bay region. These results show that PAHs can have similar potency as many dioxin-like PCBs, and AhR mediated toxicity should be considered in assessing the risks of PAHs in fish.

Differential action of polycyclic aromatic hydrocarbons on endogenous estrogen-responsive genes and on a transfected estrogen-responsive reporter in MCF-7 cells

Polycyclic aromatic hydrocarbons (PAHs) are common environmental pollutants that have been extensively studied for multiple toxicological endpoints in both laboratory animals and humans. The purpose of this study was to investigate the estrogenicity of PAHs in the human breast cancer cell line MCF-7. We investigated 14 PAHs for their ability to bind either the estrogen receptor (ER) or the aryl hydrocarbon receptor (AhR) and to activate target gene expression. PAHs were tested in a human recombinant estrogen receptor (hrER) competitive binding assay, and in both an estrogen response element (ERE)- and xenobiotic response element (XRE)-mediated reporter gene assay. We used quantitative RT-PCR to examine selected PAHs that showed activity in the ERE reporter gene assay for their ability to upregulate estrogen-responsive genes HEM45, progesterone receptor, and pS2, and the aryl hydrocarbon-responsive CYP1A1 gene. None of the 14 PAHs bound the hrER, but five of the PAHs (anthracene, B[a]A, chrysene, B[b]F, and B[a]P) induced ER-reporter activity. This activity was dependent on the metabolism of PAHs in MCF-7 cells via the AhR pathway, which resulted in the formation of metabolites that bound the ER. None of the five PAHs that induced the ER-reporter were found to upregulate estrogen-responsive genes, yet four of the five PAHs induced AhR-dependent CYP1A1 gene expression. In contrast, a metabolite of B[a]P, 3'OH-B[a]P, and a PCB metabolite, 4'OH-2,4,6-BP, did weakly upregulate all three estrogen-responsive genes. Data from these studies indicate that induction of ER-reporter activity alone does not necessarily parallel endogenous gene transcription, and that the reporter gene assay may detect interactions that are not functional in vivo.

Structural changes in gill DNA reveal the effects of contaminants on Puget Sound fish

Structural differences were identified in gill DNA from two groups of English sole collected from Puget Sound, Washington, in October 2000. One group was from the industrialized Duwamish River (DR) in Seattle and the other from relatively clean Quartermaster Harbor (QMH). Chemical markers of sediment contamination [e.g., polynuclear aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs)] established that the DR was substantially more contaminated than QMH. The levels of these chemicals in the sediments of both sites were consistent with levels of cytochrome P450 1A (CYP1A) expression in the gills of English sole from the same sites. Structural differences in gill DNA between the groups were evinced via statistical models of Fourier transform-infrared (FT-IR) spectra. Marked structural damage was found in the gill DNA of the DR fish as reflected in differences in base functional groups (e.g., C-O and NH2) and conformational properties (e.g., arising from perturbations in vertical base stacking interactions). These DNA differences were used to discriminate between the two fish groups through principal components analysis of mean FT-IR spectra. In addition, logistic regression analysis allowed for the development of a "DNA damage index" to assess the effects of contaminants on the gill. The evidence implies that environmental chemicals contribute to the DNA changes in the gill. The damaged DNA is a promising marker for identifying, through gill biopsies, contaminant effects on fish.

Brominated dioxin-like compounds: in vitro assessment in comparison to classical dioxin-like compounds and other polyaromatic compounds

Recently, several countries agreed to adopt the Stockholm convention on persistent organic pollutants (POPs). One future obligation will be to add other POPs as new evidence becomes available. In vitro cell-based bioassays offer a rapid, sensitive, and relatively inexpensive solution to screen possible POP candidates. In the present study, we investigated the aryl hydrocarbon (Ah)-receptor activity of several dioxin-like POPs by using the Micro-EROD (Ethoxy-Resorufin-O-Deethylase) and DR-CALUX (Dioxin-Responsive-Chemical Activated Luciferase gene eXpression) bioassays, which are two state-of-the-art methods. The Micro-EROD system used in our study utilizes a wild-type rat liver cell line (rat liver H4IIEC3/T cells), while the DR-CALUX bioassay consists of a genetically modified rat hepatoma H4IIE cell line that incorporates the firefly luciferase gene coupled to dioxin-responsive elements (DREs) as a reporter gene. In the case of the DR-CALUX bioassay, we used an exposure time of 24 h, whereas we used a 72-h exposure time in the Micro-EROD bioassay. The aim of this study was to compare conventional dioxin-like POPs (such as polychlorinated dibenzodioxins and -furans, PCDD/Fs and coplanar polychlorinated biphenyls, PCBs) with several other classes of possible candidates to be added to the current toxicity equivalent factor (TEF) model in the future. Therefore, this study compares in vitro CYP1A1 (Micro-EROD bioassay) and firefly luciferase induction (DR-CALUX bioassay) in several mixed polyhalogenated dibenzodioxins and -furans (PXDD/Fs; X=Br, Cl, or F), alkyl-substituted polyhalogenated dibenzodioxins and -furans (PMCDD/Fs; M=methyl), polyhalogenated biphenyls (PXBs, X=Br, Cl ), polybrominated diphenyl ethers (PBDEs), pentabromophenols (PBPs), and tetrabromobisphenol-A (TBBP-A). We also evaluate congener-specific relative potencies (REPs) and efficacies (% of TCDD(max)) and discuss the dose-response curves of these compounds, as well as the dioxin-like potency of several other Ah-receptor agonists, such as those of the polyaromatic hydrocarbons (PAHs) and polychlorinated naphthalenes (PCNs). The highest REP values were found for several PXDD/F congeners, followed by some coplanar PXBs, trichlorinated PCDD/Fs, PAHs, PBDE-126, 1-6-HxCN, and some brominated flame retardants (TBBP-A). These in vitro investigations indicate that further research is necessary to evaluate more Ah-receptor agonists for dioxin-like potency.

Activation of the human Ah receptor by aza-polycyclic aromatic hydrocarbons and their halogenated derivatives

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor through which dioxins and carcinogenic polycyclic aromatic hydrocarbons cause altered gene expression and toxicity. Ten aza-polycyclic aromatic hydrocarbons (aza-PAHs), consisting of nitrogen substituted naphthalenes, phenanthrenes, chrysenes, and benzo[a]pyrenes (BaPs), were subjected to analysis of their structure-activity relationships as an AhR ligand by using a yeast AhR signaling assay, in which AhR ligand activity was evaluated as lacZ units. Most of the aza-PAHs showed similar or more potent AhR ligand activities than the corresponding parent PAHs. About a 100-fold increased in ligand activity was observed in 10-azaBaP compared with BaP. Halogen-substitution effects on AhR ligand activity in aza-polycyclic aromatics were also investigated with quinoline, benzo[f]quinoline (BfQ), benzo[h]quinoline (BhQ) and 1,7-phenanthroline (1,7-Phe). Position-specific induction of AhR ligand activity was observed in aza-tricyclic aromatic compounds, BfQ, BhQ, and 1,7-Phe, and the ratio of the ligand activities (lacZ units/microM) of monochlorinated and monobrominated aza-tricyclic aromatic compounds to those of the corresponding parent non-halogenated compounds ranged from 2.2- to 254-fold. Greatest enhancement of ligand activity was observed in 2-brominated BfQ (2-Br-BfQ), and its ligand activity was higher than that of BaP. These results suggest that even monohalogenation markedly enhances AhR ligand activity in aza-PAHs.

Activation of the aryl hydrocarbon receptor by some vegetable constituents determined using in vitro reporter gene assay

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates the biological action of many aromatic environmental pollutants. In this study, we investigated the activation of the AhR by some vegetable constituents using the AhR-based bioassay for dioxins, i.e., the chemical activated luciferase gene expression (CALUX) assay. Ninety-five vegetable constituents, including flavonoids, tannins, saponins, and terpenes, were tested in vitro. Among them, isoflavones such as daidzein, resveratrol having a stilbene structure, and some flavonoids such as naringenin, hesperetin, and baicalein showed AhR activation.

Induction of cytochrome P450 1B1 in MDA-MB-231 human breast cancer cells by non-ortho-substituted polychlorinated biphenyls

The effects of 12 non-ortho-substituted polychlorinated biphenyl (PCB) congeners on the induction of human cytochrome P450 1B1 (CYP1B1), an estradiol 4-hydroxylase, were investigated in MDA-MB-231 breast cancer cells. Three independent quantitative assays were used, in which the rates of estrogen metabolism, the levels of the CYP1B1 and CYP1A1 mRNAs, and luciferase activities under the control of the CYP1B1 promoter were measured. Of the congeners investigated, 3,4,4',5-tetrachlorobiphenyl (PCB 81), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 3,4',5-trichlorobiphenyl (PCB 39) and 3,3',4,5-tetrachlorobiphenyl (PCB 78) were the most potent in each assay, causing four to 10-fold increases in response. Exposure to 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169) resulted in elevated CYP1B1 mRNA and increased CYP1B1-promoter driven luciferase activity, but caused depressed rather than elevated rates of E(2) metabolism due to inhibition of CYP1B1. The relative magnitudes of CYP1B1 induction by the PCB congeners, as determined by the three assays, were in close agreement, with the exception noted for PCB 169. These results indicate that PCB structure-activity relationships for the induction of human CYP1B1 are similar to those observed for human CYP1A1, but differ somewhat from what has been reported for induction of rat CYP1A1.

Application of the luciferase cell culture bioassay for the detection of refined petroleum products

A luciferase cell culture-based bioassay, developed to detect 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like activity of halo-genated and polycyclic aromatic hydrocarbons, was optimized to detect refined petroleum products and to determine their relative inducing potency. Quality control standards from 32 refined products (gasolines and diesels, jet fuels, lubricating oils, fuel oils and weathered products) and three commercial products were evaluated. Induction equivalents (I-EQs) were determined by direct comparison of the EC50 and EC20 values (based on the median and 20% TCDD maximal response, respectively) from dose-response curves for each product to those obtained with TCDD. Most petroleum products were active in the luciferase bioassay, with those products composed of fractions produced later in the distillation process (i.e. fuel oils) inducing higher levels. Additionally, weathering of products reduced their induction potency. Based on the high I-EQ estimates of many products, biological effects associated with exposure may have been previously underestimated using other diagnostic methods.

Biomarkers and bioassays for detecting dioxin-like compounds in the marine environment

The presence of toxic chemical contaminants in some marine organisms, including those consumed by humans, is well known. Monitoring the levels of such contaminants and their geographic and temporal variability is important for assessing and maintaining the safety of seafood and the health of the marine environment. Chemical analyses are sensitive and specific, but can be expensive and provide little information on the actual or potential biological activity of the contaminants. Biologically-based assays can be used to indicate the presence and potential effects of contaminants in marine animals, and therefore, have potential for routine monitoring of the marine environment. Halogenated aromatic hydrocarbons (HAHs) such as chlorinated dioxins, dibenzofurans, and biphenyls comprise a major group of marine contaminants. The most toxic HAHs (dioxin-like compounds) act through an intracellular receptor protein, the aryl hydrocarbon receptor, which is present in humans and many, but not all, marine animals. A toxic equivalency approach based on an understanding of this mechanism provides an integrated measure of the biological potency or activity of HAH mixtures. Biomarkers measured in marine animals indicate their exposure to these chemicals in vivo. Similarly, in vitro biomarker responses measured in cell culture bioassays can be used to assess the concentration of 'dioxin equivalents' in extracts of environmental matrices. Here, I have reviewed the types and relative sensitivities of mechanistically-based, in vitro bioassays for dioxin-like compounds, including assays of receptor-binding, DNA-binding and transcriptional activation of native (CYP1A) or reporter (luciferase) genes. Examples of their use in environmental monitoring are provided. Cell culture bioassays are rapid and inexpensive, and thus have great potential for routine monitoring of marine resources, including seafood. Several such assays exist, or are being developed, for a variety of marine contaminants in addition to the dioxin-like chemicals. A battery of cell culture bioassays might be used to rapidly and sensitively screen seafood for the presence of contaminants of concern, including dioxin-like compounds as well as other contaminants such as natural toxins, hormonally active agents, and heavy metals. Such a battery of mechanism-based, in vitro bioassays could be incorporated into monitoring efforts under recently adopted hazard analysis and critical control point (HACCP) programs.

Activation of the aryl hydrocarbon receptor by methyl yellow and related congeners: structure-activity relationships in halogenated derivatives

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates the biological action of many environmental compounds. Methyl yellow (4-dimethylaminoazobenzene; MY) is a principal azo-dye, and structurally related compounds were subjected to analysis of structure-activity relationships as AhR ligands by using a yeast AhR signaling assay. The effects of halogen-substitution among 23 halogenated MYs on the AhR ligand activity can be summarized as follows: enhancement by halogen-substitution at the ortho-position (2'- and 6'-position), and reduction by substitution at the para-position (4'-position). The greatest enhancement of the ligand activity was observed in 2',6'-dichlorinated MY (13.5-fold of MY), and its AhR ligand activity was very close to that of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the present assay system. In the study of compounds structurally related to MY, benzanilide (BA) showed almost the same AhR ligand activity as azobenzene and trans-stilbene. Furthermore, 4'-chlorobenzanilide, in which the length of the molecule is similar to that of MY, enhanced the AhR ligand activity by ortho(2')-chlorine-substitution, and the AhR ligand activity of 2',4'-dichlorobenzanilide was similar to that of 2'-chloro-MY. These results suggest that the amide bond is equivalent to the -N=N- or -CH=CH- double bond for recognition as the ligand by AhR in 1,2-diphenyl-1,2-ene derivatives.

Combinatorial bio/chemical analysis of dioxin and dioxin-like compounds in waste recycling, feed/food, humans/wildlife and the environment

The present review describes international activities using bioassays/biomarkers in combination with chemical analysis to measure the effects of dioxin and dioxin-like compounds (DLCs) in the environment. The above authors reviewed already the state-of-art bioanalytical detection methods (BDMs) for dioxins and DLCs [Environ Int (2001)]. The aim of this study will be to review applications of these bioassays/biomarkers to evaluate potential dioxins and DLCs. The present literature study lists relative potencies (REPs) of polyhalogenated dibenzo-p-dioxins and -furans (PXDD/Fs; X = Cl, Br, F), their thio analogues polychlorinated dibenzothiophenes (PCDTs) and thianthrens (PCTAs), polyhalogenated biphenyls (PXBs), polychlorinated naphthalenes (PCNs) and other Ah receptor agonists measured by several biodetectors (Tier 3 screening). The authors will discuss some examples of the applications of some of these biodetectors in biomonitoring programmes and recently occurred dioxin crisis in feed/food. The diagnosis of the biopotency of these pollutants in technical processes like thermally treated waste, waste water treatment, landfill leachate treatment, commercial PCB-mixtures, the release into the environment (soil, air and water) and the final intake into wildlife and humans will be reviewed.

Bioanalytical screening methods for dioxins and dioxin-like compounds a review of bioassay/biomarker technology

Determination of environmental pollutants utilizing biodetectors such as bioassays, biomarkers, enzyme immunoassays (EIAs), or other bioanalytical tools is a continuously growing area. The present literature review describes the principles and advantages/limitations of several bioanalytical detection methods (BDMs) for the screening and diagnosis of dioxin and dioxin-like compounds. This study characterizes briefly the family of dioxin and dioxin-like compounds, discusses potential Ah receptor (AhR) ligands and cytochrome P-450 (CYP) 1A1-enzyme-inducing compounds. 'Milestones' in the development of BDMs are summarized and explained in detail for a number of bioanalytical tools that can be used to detect these classes of dioxin-like persistent bioaccumulative toxicants (PBTs). The design of a screening profile with a battery of bioassays/biomarkers coupled with the chemical analysis is evaluated. The relative potencies (REPs) to 2,3,7,8-TCDD for dioxin-like compounds are reviewed for various BDMs and the differences are noted.

In vitro response of fish and mammalian cells to complex mixtures of polychlorinated naphthalenes, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons

In vitro characterization and comparison of responses to different classes of biologically active compounds can increase the utility of bioassays. In this study, the relative potencies (REPs) of mixtures of polychlorinated naphthalenes (PCNs), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs), to induce in vitro ethoxyresorufin-O-deethylase (EROD) in PLHC-1 fish hepatoma cells, H4IIE wild type (H4IIE-wt) rat hepatoma cells, and recombinant H4IIE cells (H4IIE-EROD) were determined. The mixtures were also analyzed by in vitro luciferase assay with recombinant H4IIE cells (H4IIE-luc). Halowaxes 1051, 1014, and 1013 caused significant induction in all three H4IIE assays at concentrations less than 10 mg/l, but did not elicit a significant response in the PLHC-1 assay. Based on H4IIE results, the Halowaxes were estimated to have relative potencies (REPs) of approximately 10(-6)-10(-8) relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Less than 5 mg/l of Aroclors 1242, 1248, 1254; Clophens A60, T64; and Chlorofen induced significant responses in the H4IIE assays, while only Clophens A60 and T64 caused a significant response in the PLHC-1 assay. The efficacy of the Aroclor mixtures was generally insufficient to allow for quantitative REP estimates, but, based on their responses in the H4IIE assays, Clophen A60 and Chlorofen were estimated to have REPs of approximately 10(-6) and 10(-7), respectively. A mixture of 16 priority PAHs caused significant induction in all four cell types and was estimated to have a REP of approximately 10(-4). Overall, the results of this study add to a growing database on the dioxin-like potency of complex mixtures of xenobiotics, and suggested that H4IIE-based in vitro bioassays were more sensitive than PLHC-1 cells for detecting dioxin-like activity in complex mixtures.

Induction of the P450 reporter gene system bioassay by polycyclic aromatic hydrocarbons in Ulsan Bay (South Korea) sediments

Polycyclic aromatic hydrocarbons (PAHs) and induction of the P450 reporter gene system (RGS) for 6- and 16-h exposure periods were determined in organic extracts of Ulsan Bay (South Korea) sediments to assess the utility of this bioassay as a screening tool for PAH contamination. The sum of the concentrations of 23 individual PAHs in 30 sediment samples (sigma PAH) based on GC-MS analysis ranged from 0.05 to 6.1 micrograms/g dry wt. P450 RGS fold induction ranged from 4.0 to 320 micrograms/g based on benzo[a]pyrene toxic equivalents (BaPEq). P450 RGS BaPEq and the 'chemical BaPEq', defined as the sum of the products of individual PAH concentrations and pre-determined toxic equivalency factors, exhibited very strong positive correlations with sigma PAH (r2 > 0.90; P < 0.001). Fold induction did not increase (and in some cases decreased) after the optimal incubation period (6 h) for PAHs, indicating that other compounds known to induce the P450 RGS (e.g. chlorinated organics) were not present at levels effecting significant induction. This was supported by GC-ECD analysis where non-ortho and mono-ortho polychlorinated biphenyls (PCBs) known to be strong P450 RGS inducers were found to be at very low or non-detectable levels in samples with the highest P450 RGS responses. The profound difference in PAH profiles for the two most contaminated sites suggested that this assay is especially sensitive for selected PAHs with greater than four rings. Combined with previous results, the P450 RGS shows promise as a useful screening tool for predicting deleterious biological effects resulting from CYP1A1-inducing, sediment-associated chemicals, particularly high molecular weight PAHs.

Using the metabolism of PAHs in a human cell line to characterize environmental samples

P450 reporter gene system (RGS) is an in vitro assay to detect compounds that activate the Ah receptor and induce cytochrome P450 (CYP1A1). This system utilizes a human cell (101L) stably transfected with a luciferase reporter downstream of human CYP1A1 promoter sequences. When CYP1A1-inducing compounds are present, luciferase is produced as well as endogenous CYP1A1 enzymes. Polycyclic aromatic hydrocarbons (PAHs) are more readily degraded than chlorinated compounds including dioxins, furans, and coplanar polychlorinated biphenyls (PCBs). PAH-induced luciferase production begins to decrease between 6 and 16 h, while chlorinated compounds produce a more sustained response. Individual and mixtures of CYP1A1-inducing compounds were tested at both 6 and 16 h. Extracts of soils containing both PAHs and dioxins were also tested, before and after cleanup to remove PAHs. Results indicate that RGS testing at 6 and 16 h is a promising tool to differentiate between PAHs and chlorinated hydrocarbons often co-occurring in environmental samples.