Assessment of metabolic capabilities of PLHC-1 and RTL-W1 fish liver cell lines

Delayed clearance of the pro-carcinogen benzo[a]pyrene in PLHC-1 cells when co-exposed to the antifungal drug clotrimazole and effects on the CYP1A biomarker

Cytochrome P450 1 A (CYP1A) is a key enzyme in the metabolism of the polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (BaP) in animals, and a biomarker for environmental PAH exposure. The common antimycotic imidazole drug clotrimazole (CLO) has been detected in the aquatic environment and likely co-exists with BaP. Like BaP, CLO can bind to CYP1A enzymes and can act as a CYP1A inhibitor. Co-exposure of BaP with CLO significantly delayed BaP elimination in a fish liver cell line (PLHC-1). Intracellular BaP concentration was 2.4 times higher after 6 h in co-exposed cells, compared to cells exposed to BaP alone. Higher BaP concentrations in cells co-exposed to CLO positively correlated with CLO dose, indicating CLO-mediated delays in BaP clearance. After 24 h, BaP was undetectable irrespective of CLO co-exposure. In contrast, intracellular CLO concentrations remained constant over the 72 h experimental period. Co-exposure of BaP with CLO caused synergistic and time-dependent increases on the CYP1A biomarker both on CYP1A mRNA levels and on CYP1A enzyme activity, in accordance with an apparent delayed BaP elimination in the presence of CLO. These results indicate a toxicokinetic interaction between BaP and CLO on the CYP1A enzyme that delays metabolic clearance of BaP.

Comparative toxicity of beach mesoplastics from South Spain: An in vitro approach

Plastics, particularly mesoplastics, dominate beach debris and act as carriers of hazardous chemicals, either initially present in plastics or absorbed from the surrounding environment. In this study, mesoplastics were collected from five beaches in the southern region of Spain to investigate their potential impact on marine life. In vitro assays employing fish liver cells (PLHC-1) were conducted to evaluate the toxicity of methanolic extracts derived from intact mesoplastics and after simulated photodegradation. LC-MS analysis of the methanolic extracts revealed the presence of organophosphate esters, phthalates, and phthalate alternatives. The extracts from photodegraded plastics generally showed higher cytotoxicity, ability to generate reactive oxygen species (ROS), and genotoxicity (micronuclei formation) than those from intact mesoplastics. All the extracts induced EROD activity in PLHC-1 cells, indicating the presence of significant amounts of CYP1A inducers in beach mesoplastics. Thus, mesoplastics contain chemicals able to induce cytotoxicity and genotoxicity in PLHC-1 cells, and further photodegradation of mesoplastics facilitates the release of additional chemicals, increasing the overall toxicity. This work also highlights the usefulness of cell-based assays to better define the risks of plastic pollution.

Bioconcentration Assessment of Three Cationic Surfactants in Permanent Fish Cell Lines

Cationic surfactants are used in many industrial processes and in consumer products with concurrent release into the aquatic environment, where they may accumulate in aquatic organisms to regulatoryly relevant thresholds. Here, we aimed to better understand the bioconcentration behavior of three selected cationic surfactants, namely N,N-dimethyldecylamine (T10), N-methyldodecylamine (S12), and N,N,N-trimethyltetradecylammonium cation (Q14), in the cells of fish liver (RTL-W1) and gill (RTgill-W1) cell lines. We conducted full mass balances for bioconcentration tests with the cell cultures, in which the medium, the cell surface, the cells themselves, and the plastic compartment were sampled and quantified for each surfactant by HPLC MS/MS. Accumulation in/to cells correlated with the surfactants' alkyl chain lengths and their membrane lipid-water partitioning coefficient, DMLW. Cell-derived bioconcentration factors (BCF) of T10 and S12 were within a factor of 3.5 to in vivo BCF obtained from the literature, while the cell-derived BCF values for Q14 were >100 times higher than the in vivo BCF. From our experiments, rainbow trout cell lines appear as a suitable conservative in vitro screening method for bioconcentration assessment of cationic surfactants and are promising for further testing.

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

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

Investigating the bioaccumulation potential of anionic organic compounds using a permanent rainbow trout liver cell line

Permanent rainbow trout (Oncorhynchus mykiss) cell lines represent potential in vitro alternatives to experiments with fish. We here developed a method to assess the bioaccumulation potential of anionic organic compounds in fish, using the rainbow trout liver-derived RTL-W1 cell line. Based on the availability of high quality in vivo bioconcentration (BCF) and biomagnification (BMF) data and the substances' charge state at physiological pH, four anionic compounds were selected: pentachlorophenol (PCP), diclofenac (DCF), tecloftalam (TT) and benzotriazol-tert-butyl-hydroxyl-phenyl propanoic acid (BHPP). The fish cell line acute toxicity assay (OECD TG249) was used to derive effective concentrations 50 % and non-toxic exposure concentrations to determine exposure concentrations for bioaccumulation experiments. Bioaccumulation experiments were performed over 48 h with a total of six time points, at which cell, medium and plastic fractions were sampled and measured using high resolution tandem mass spectrometry after online solid phase extraction. Observed cell internal concentrations were over-predicted by KOW-derived predictions while pH-dependent octanol-water partitioning (DOW) and membrane lipid-water partitioning (DMLW) gave better predictions of cell internal concentrations. Measured medium and cell internal concentrations at steady state were used to calculate RTL-W1-based BCF, which were compared to DOW- or DMLW-based model approaches and in vivo data. With the exception of PCP, the cell-derived BCF best compared to DOW-based model predictions, which were higher than predictions based on DMLW. All methods predicted the in vivo BCF for diclofenac well. For PCP, the cell-derived BCF was lowest although all BCF predictions underestimated the in vivo BCF by ≥ 1 order of magnitude. The RTL-W1 cells, and all other prediction methods, largely overestimated in vivo BMF, which were available for PCP, TT and BHPP. We conclude that the RTL-W1 cell line can supplement BCF predictions for anionic compounds. For BMF estimations, however, in vitro-in vivo extrapolations need adaptation or a multiple cell line approach.

Effects of perfluoroalkyl substances (PFASs) and benzo[a]pyrene (BaP) co-exposure on phase I biotransformation in rainbow trout (Oncorhynchus mykiss)

The presence of perfluoroalkyl substances (PFASs) in the environment, especially in aquatic ecosystems, continues to be a significant concern for human and environmental health. Previous studies have suggested that several PFASs do not undergo biotransformation due to their chemical stability, yet perfluorooctanesulfonic acid (PFOS)- and perfluorooctanoic acid (PFOA)-exposed organisms have presented altered activity of important biotransformation pathways. Given the fundamental role of biotransformation in biological organisms and the significant distribution of PFAS in aquatic environments, the present study investigated the influence of PFOA and PFOS on phase I biotransformation enzymes in vitro using the rainbow trout liver RTL-W1 cell line and in vivo using juvenile rainbow trout. Cells and fish were exposed and co-exposed to environmentally relevant concentrations of PFOA, PFOS, and benzo[a]pyrene (BaP), for 72 h and 10 days, respectively, prior to measurements of cytotoxicity and biotransformation ability through measurements of CYP1A1-, CYP1A2-, and CYP3A4-like activities. Our results indicate that exposure to PFAS-BaP binary mixtures altered CYP1A-like activity in vivo; however, those alterations were not observed in vitro. Similarly, while BaP did not significantly induce CYP3A4 in vivo, exposure to the PFAS led to significantly lower enzymatic activity relative to basal levels. These observations may have implications for organisms simultaneously exposed to PFASs and other environmental pollutants for which biotransformation is necessary, especially in detoxification mechanisms. Furthermore, the interference with biotransformation pathways could potentially predispose exposed organisms to a compromised physiology, which may increase their vulnerability to other stressors and erode their survival fitness.

Optimisation of an automated high-throughput micronucleus (HiTMiN) assay to measure genotoxicity of environmental contaminants

Anthropogenic contaminants can have a variety of adverse effects on exposed organisms, including genotoxicity in the form of DNA damage. One of the most commonly used methods to evaluate genotoxicity in exposed organisms is the micronucleus (MN) assay. It provides an efficient assessment of chromosomal impairment due to either chromosomal rupture or mis-segregation during mitosis. However, evaluating chromosomal damage in the MN assay through manual microscopy is a highly time-consuming and somewhat subjective process. High-throughput evaluation with automated image analysis could reduce subjectivity and increase accuracy and throughput. In this study, we optimised and streamlined the HiTMiN assay, adapting the MN assay to a miniaturised, 96-well plate format with reduced steps, and applied it to both primary cells from green turtle fibroblasts (GT12s-p) and a freshwater fish hepatoma cell line (PLHC-1). Image analysis using both commercial (Columbus) and freely available (CellProfiler) software automated the scoring of MN, with improved precision and drastically reduced time compared to manual scoring and other available protocols. The assay was validated through exposure to two inorganic (chromium and cobalt) and one organic (the herbicide metolachlor) compounds, which are genotoxicants of concern in the marine environment. All compounds tested induced MN formation below cytotoxic concentrations. The HiTMiN assay presented here greatly increases the suitability of the MN assay as a quick, affordable, sensitive and accurate assay to measure genotoxicity of environmental samples in different cell lines.

Reduced biotransformation of polycyclic aromatic hydrocarbons (PAHs) in pollution-adapted Gulf killifish (Fundulus grandis)

Anthropogenic pollution represents a significant source of selection, potentially leading to the emergence of evolutionary adaptations in chronically exposed organisms. A recent example of this scenario corresponds to Gulf killifish (Fundulus grandis) populations inhabiting the Houston Ship Channel (HSC), Texas, USA, which have been documented to have adapted to this heavily contaminated environment. Although not fully elucidated, one particularly important aspect of their adaptation involves the reduced inducibility of the aryl hydrocarbon receptor (AhR) and, potentially, the alteration of major biotransformation pathways. In the present study, we employed a modified Organization for Economic Cooperation and Development (OECD) 319-B test guideline to explore population and sex-related differences in the hepatic biotransformation of six polycyclic aromatic hydrocarbons (PAHs) in F. grandis populations with different exposure histories. Pollution-adapted F. grandis showed significantly lower hepatic clearance of PAHs than non-adapted fish, especially for high molecular weight PAHs (chrysene, benzo[k]fluoranthene, and benzo[a]pyrene), with pollution-adapted females presenting the lowest clearance. The characterization of different phase I biotransformation enzymes revealed that the basal activity of CYP1A, fundamental in the biotransformation of PAHs, was significantly lower in pollution-adapted fish, especially in females, which showed the lowest activity. Contrarily, basal CYP2C9-like activity was significantly higher in pollution-adapted fish. These results demonstrate the importance of exposure and evolutionary histories in shaping organisms' responses to pollution and provide significant evidence of sex-specific biotransformation differences in F. grandis populations.

Toxicity assessment of Lemna solid waste dumpsite (Calabar, Nigeria) using different extraction methods and toxicological responses of PLHC-1 cells

In the present study, we have investigated the effects of three (elutriate, polar and non-polar) different soil extraction methods from the Lemna solid waste dumpsite (Calabar, Nigeria) on the biotransformation, antioxidant and cellular defense responses of PLHC-1 cell line. Following a 48 h exposure period to different concentrations of each extract, the PLHC-1 cells were evaluated for enzymatic activities - glutathione peroxidase (Gpx), glutathione reductase (Gr), glutathione S-transferase (Gst), 7-ethoxy-, pentoxy-, and benzyloxyresorufin O-deethylase (EROD, PROD and BROD) and mRNA expressions for catalase (cat), gpx, gst, cyp1a, cyp3a, mammalian target of rapamycin (mtor), nuclear factor erythroid 2-related factor 2 (nrf2) and Kelch-like erythroid cell-derived protein (keap-1). Overall, our results showed parameter-, extract- and concentration-specific increases in transcripts and functional product levels for biotransformation, antioxidant and cellular defense/cytoprotective responses, compared with control. These responses were mostly characterized by a biphasic pattern of effects by either, increasing at low concentration, and thereafter decrease, as the concentration increases or vice versa, depending on the extract type. These observations paralleled soil contaminants (organics and inorganics) burden from the dumpsite. Principal component analysis (PCA) showed that cells treated with the non-polar extract produced more pronounced effects on the measured toxicological responses, compared with the polar and elutriate extracts. Thus, our data highlight peculiar risks to cells exposed to each soil extract, indicating complex and multiple chemical interactions with diverse functional groups that contaminants may have in mixture scenarios. Given the limitations and cost implications of contaminants analysis for the numerous soil- or sediment-bound compounds, we propose that this approach represents an analytical benchmark and endpoints for assessing the risk of complex environmental matrices such as soil and sediments, for ecotoxicological monitoring programs.

Prymnesium parvum differentially triggers sublethal fish antioxidant responses in vitro among salinity and nutrient conditions

Significant fish kills have been attributed to Prymnesium parvum in coastal and inland waters around the world. However, specific mechanisms responsible for adverse outcomes resulting from this harmful algal bloom (HAB) species remain unclear, though the gill has previously been identified as an important target organ. In the present study, an in vitro approach was used to examine cytotoxicity and antioxidant responses in fish liver (Hepa-E1 and PLHC-1) and gill (G1B and RTgill-W1) cell lines, following exposure to P. parvum grown at different salinities and nutrient concentrations, which can influence the magnitude of acute toxicity. Cultures from high salinity compromised survival of hepatic cell lines exposed to high dilutions, whereas no significant cytotoxicity was observed for gill cell lines. With respect to control groups, catalase showed significant activity in both gill cell lines, especially RTgill-W1, following exposure to high salinity cultures. High levels of superoxide dismutase were measured in Hepa-E1 cells exposed to all experimental treatment combinations and in RTgill-W1 cells following exposure to high salinity conditions, with respect to non-exposed cells Glutathione peroxidase activity was also detected at significant levels in Hepa-E1 cells after exposure to cultures from high salinity and the low salinity X low nutrients. Slight GPx increases were only observed in PLHC-1 and G1B exposed to P. parvum grown at high salinity. These results suggest that: 1. specific combinations of salinity and nutrient levels may contribute to production and potency of P. parvum toxins resulting in sub-lethal effects, and 2. sub-lethal responses are more prominent than cytotoxicity, and that oxidative stress may be a significant adverse effect of toxins produced by P. parvum.

Applicability of in vitro methods in evaluating the biotransformation of polycyclic aromatic hydrocarbons (PAHs) in fish: Advances and challenges

The biotransformation of polycyclic aromatic hydrocarbons (PAHs) and the biochemical mechanisms involved in such process continue to be intensively studied in the fields of environmental science and toxicology. The investigation of PAH biotransformation in fish is fundamental to understand how piscine species cope with PAH exposure, as these compounds are ubiquitous in aquatic ecosystems and impact different levels of biological organization. New approaches are continuously developed in the field of ecotoxicology, allowing live animal testing to be combined with and, in some cases, replaced with novel in vitro systems. Many in vitro techniques have been developed and effectively applied in the investigation of the biochemical pathways driving the biotransformation of PAH in fish. In vitro experimentation has been fundamental in the advancement of not only understanding PAH-mediated toxicity, but also in highlighting suitable cell-based models for such investigations. Therefore, the present review highlights the value and applicability of in vitro systems for PAH biotransformation studies, and provides up-to-date information on the use of in vitro fish models in the evaluation of PAH biotransformation, common biomarkers, and challenges encountered when developing and applying such systems.

Applicability of a human cell co-culture model to evaluate antioxidant responses triggered by chemical mixtures in fish and oyster homogenates

The accumulation of chemical compounds in fish tissue represents significant health concerns for seafood consumers, but little is known about the risks to human health associated with such substances. The identification of adverse biological responses upon exposure to contaminants has been facilitated by the development of in vitro systems resembling the human dietary pathway. The present study explores the applicability of an organotypic co-culture system, using intestinal (Caco-2) and hepatic (HepaRG) cell lines, to provide insight into the toxicity of chemical mixtures found in commercially available seafood. Chemical extractions were conducted utilizing fish and oyster standard reference material (SRM) from the U.S. National Institute of Standards and Technology (NIST). Cells were seeded in monoculture and co-culture systems and exposed to SRM extracts before measurements of cytotoxicity and antioxidant responses. Exposure to oyster extracts led to significant cell mortality in monocultures. HepaRG cells in monoculture expressed lower levels of glutathione peroxidase and superoxide dismutase than HepaRG cells in co-culture, upon exposure to both oyster and fish extracts. These observations illustrate the importance of organotypic co-culture models to explore biological responses that could be otherwise difficult to evaluate in monocultures, and the adverse effects associated with the consumption of contaminated seafood.

Development of three-dimensional (3D) spheroid cultures of the continuous rainbow trout liver cell line RTL-W1

In vitro experimental systems based on continuous piscine cell lines can be used as an alternative to animal tests for obtaining qualitative and quantitative information on the possible fate and effect of chemicals in fish. However, their capability to reproduce complex metabolic processes and toxic responses as they occur in vivo is limited due to the lack of organ-specific tissue architecture and functions. Here we introduce a three-dimensional (3D) in vitro experimental system based on spheroidal aggregate cultures (spheroids) of the continuous rainbow trout liver cell line RTL-W1 and provide a first description of their structural and functional properties including growth, viability/longevity, metabolic activity, ultrastructure and cytochrome P450 1A (CYP1A) expression determined by bright-field, multi-photon fluorescence and transmission electron microscopy as well as RT-qPCR analysis. Our results show that RTL-W1 cells in 3D spheroids (ø ~ 150 µm) (including those in the interior) were viable, metabolically active and had higher basal and β-naphthoflavone-induced CYP1A expression levels than conventional 2D cell cultures. Furthermore, they displayed ultrastructural characteristics similar to differentiated hepatocytes. The available evidence suggests that 3D RTL-W1 spheroids may have enhanced hepatotypic functions and be a superior in vitro model to assess hepatic biotransformation, bioaccumulation and chronic toxicity compared to conventional cell monolayer cultures.

Xenobiotic metabolism in the fish hepatic cell lines Hepa-E1 and RTH-149, and the gill cell lines RTgill-W1 and G1B: Biomarkers of CYP450 activity and oxidative stress

The use of fish cell cultures has proven to be an effective tool in the study of environmental and aquatic toxicology. Valuable information can be obtained from comparisons between cell lines from different species and organs. In the present study, specific chemicals were used and biomarkers (e.g. 7-Ethoxyresorufin-O-deethylase (EROD) activity and reactive oxygen species (ROS)) were measured to assess the metabolic capabilities and cytotoxicity of the fish hepatic cell lines Hepa-E1 and RTH-149, and the fish gill cell lines RTgill-W1 and G1B. These cell lines were exposed to β-naphthoflavone (BNF) and benzo[a]pyrene (BaP), the pharmaceutical tamoxifen (TMX), and the organic peroxide tert-butylhydroperoxide (tBHP). Cytotoxicity in gill cell lines was significantly higher than in hepatic cells, with BNF and TMX being the most toxic compounds. CYP1-like associated activity, measured through EROD activity, was only detected in hepatic cells; Hepa-E1 cells showed the highest activity after exposure to both BNF and BaP. Significantly higher levels of CYP3A-like activity were also observed in Hepa-E1 cells exposed to TMX, while gill cell lines presented the lowest levels. Measurements of ROS and antioxidant enzymes indicated that peroxide levels were higher in gill cell lines in general. However, levels of superoxide were significantly higher in RTH-149 cells, where no distinctive increase of superoxide-related antioxidants was observed. The present study demonstrates the importance of selecting adequate cell lines in measuring specific metabolic parameters and provides strong evidence for the fish hepatocarcinoma Hepa-E1 cells to be an excellent alternative in assessing metabolism of xenobiotics, and in expanding the applicability of fish cell lines for in vitro studies.

Biotransformation of Benzo[ a]pyrene by Three Rainbow Trout ( Onchorhynchus mykiss) Cell Lines and Extrapolation To Derive a Fish Bioconcentration Factor

Permanent fish cell lines constitute a promising complement or substitute for fish in the environmental risk assessment of chemicals. We demonstrate the potential of a set of cell lines originating from rainbow trout ( Oncorhynchus mykiss) to aid in the prediction of chemical bioaccumulation in fish, using benzo[ a]pyrene (BaP) as a model chemical. We selected three cell lines from different tissues to more fully account for whole-body biotransformation in vivo: the RTL-W1 cell line, representing the liver as major site of biotransformation, and the RTgill-W1 (gill) and RTgutGC (intestine) cell lines, as important environment-organism interfaces, which likely influence chemical uptake. All three cell lines were found to effectively biotransform BaP. However, rates of in vitro clearance differed, with the RTL-W1 cell line being most efficient, followed by RTgutGC. Co-exposures with α-naphthoflavone as potent inhibitor of biotransformation, assessment of CYP1A catalytic activity, and the progression of cellular toxicity upon prolonged BaP exposure revealed that BaP is handled differently in the RTgill-W1 compared to the other two cell lines. Application of the cell-line-derived in vitro clearance rates into a physiology-based toxicokinetic model predicted a BaP bioconcentration factor (BCF) of 909-1057 compared to 920 reported for rainbow trout in vivo.

A 3D fish liver model for aquatic toxicology: Morphological changes and Cyp1a induction in PLHC-1 microtissues after repeated benzo(a)pyrene exposures

To identify the potential environmental impacts of aquatic pollutants, rapid and sensitive screening tools are needed to assess adaptive and toxic responses. This study characterizes a novel fish liver microtissue model, produced with the cell line PLHC-1, as an in vitro aquatic toxicity testing platform. These 3D microtissues remain viable and stable throughout the 8-day testing period and relative to 2D monolayers, show increased basal expression of the xenobiotic metabolizing enzyme cytochrome P450 1A (Cyp1a). To evaluate pulsed, low-dose exposures at environmentally relevant concentrations, microtissue responsiveness to the model toxicant benzo(a)pyrene was assessed after single and repeated exposures for determination of both immediate and persistent effects. Significant induction of Cyp1a gene and protein expression was detected after a single 24h exposure to as little as 1nM benzo(a)pyrene, and after a 24h recovery period, Cyp1a expression declined in a dose-dependent manner. However, cell death continued to increase during the recovery period and alterations in microtissue architecture occurred at higher concentrations. To evaluate a pulsed or repeated exposure scenario, microtissues were exposed to benzo(a)pyrene, allowed to recover, then exposed a second time for 24h. Following pre-exposure to benzo(a)pyrene, cyp1a expression remained equally inducible and the pattern and level of Cyp1a protein response to a second exposure were comparable. However, pre-exposure to 1μM or 5μM of benzo(a)pyrene resulted in increased cell death, greater disruption of microtissue architecture, and alterations in cell morphology. Together, this study demonstrates the capabilities of this PLHC-1 microtissue model for sensitive assessment of liver toxicants over time and following single and repeated exposures.

Combining different assays and chemical analysis to characterize the genotoxicity of waters impacted by textile discharges

Waters receiving textile discharges can exhibit genotoxic and mutagenic activity, which has been related to the presence of dyes and aromatic amines as synthesis precursors or byproducts. The aim of this study was to identify dyes and aromatic amines in water samples impacted by textile discharges, and to evaluate the genotoxic responses of these samples using the Salmonella/microsome assay in strains TA98 and YG1041, and the Fpg-modified comet assay in the RTL-W1 fish cell line. The genotoxicity of river samples downstream of the discharge was greater than the upstream samples in both of the Ames tests. The Fpg-modified comet assay detected similar levels of DNA damage in the upstream and downstream samples. Mutagenicity was not detected with TA98, except for the Quilombo River samples, but when YG1041 was used as the tester strain mutagenicity was detected for all sites with a very different profile in upstream sites relative to the other sites. The mutagenic response strongly indicated that aromatic amines or dyes were contributing to the mutagenic activity downstream. The impact of textile discharges was also confirmed by chemical analysis, because the highest concentrations of azo dyes and aromatic amines were detected in the river downstream. This study shows the value of combining assays measuring complementary endpoints to better characterize the mutagenicity of environmental samples, with the advantage that this approach provides an indication of what classes of compounds are responsible for the effect. Environ. Mol. Mutagen. 57:559-571, 2016. © 2016 Wiley Periodicals, Inc.

BFCOD activity in fish cell lines and zebrafish embryos and its modulation by chemical ligands of human aryl hydrocarbon and nuclear receptors

Assessment of exposure and effect of fish to pharmaceuticals that contaminate aquatic environment is a current major issue in ecotoxicology and there is a need to develop specific biological marker to achieve this goal. Benzyloxy-4-trifluoromethylcoumarin-O-debenzyloxylase (BFCOD) enzymatic activity has been commonly used to monitor CYP3A activity in fish. In this study, we assessed the capacity of a panel of toxicologically relevant chemicals to modulate BFCOD activity in fish, by using in vitro and in vivo bioassays based on fish liver cell lines (PLHC-1, ZFL, RTL-W1) and zebrafish embryos, respectively. Basal BFCOD activity was detectable in all biological models and was differently modulated by chemicals. Ligands of human androgens, glucocorticoids, or pregnanes X receptors (i.e., dexamethasone, RU486, rifampicin, SR12813, T0901317, clotrimazole, ketoconazole, testosterone, and dihydrotestosterone) moderately increased or inhibited BFCOD activity, with some variations between the models. No common feature could be drawn by regards to their capacity to bind to these receptors, which contrasts with their known effect on mammalian CYP3A. In contrast, dioxins and polycyclic aromatic hydrocarbons (PAHs) strongly induced BFCOD activity (up to 30-fold) in a time- and concentration-dependent manner, both in vitro in all cell lines and in vivo in zebrafish embryos. These effects were AhR dependent as indicated by suppression of induced BFCOD by the AhR pathway inhibitors 8-methoxypsoralen and α-naphthoflavone. Altogether our result further question the relevance of using liver BFCOD activity as a biomarker of fish exposure to CYP3A-active compounds such as pharmaceuticals.

Alteration of cellular lipids and lipid metabolism markers in RTL-W1 cells exposed to model endocrine disrupters

This work investigates the suitability of the rainbow trout liver cell line (RTL-W1) as an in-vitro model to study the ability of model endocrine disrupters, namely TBT, TPT, 4-NP, BPA and DEHP, to act as metabolic disrupters by altering cellular lipids and markers of lipid metabolism. Among the tested compounds, BPA and DEHP significantly increased the intracellular accumulation of triacylglycerols (TAGs), while all the compounds -apart from TPT-, altered membrane lipids - phosphatidylcholines (PCs) and plasmalogen PCs - indicating a strong interaction of the toxicants with cell membranes and cell signaling. RTL-W1 expressed a number of genes involved in lipid metabolism that were modulated by exposure to BPA, TBT and TPT (up-regulation of FATP1 and FAS) and 4-NP and DEHP (down-regulation of FAS and LPL). Multiple and complex modes of action of these chemicals were observed in RTL-W1 cells, both in terms of expression of genes related to lipid metabolism and alteration of cellular lipids. Although further characterization is needed, this might be a useful model for the detection of chemicals leading to steatosis or other diseases associated with lipid metabolism in fish.

Exposure to runoff from coal-tar-sealed pavement induces genotoxicity and impairment of DNA repair capacity in the RTL-W1 fish liver cell line

Coal-tar-based (CTB) sealcoat, frequently applied to parking lots and driveways in North America, contains elevated concentrations of polycyclic aromatic hydrocarbons (PAHs) and related compounds. The RTL-W1 fish liver cell line was used to investigate two endpoints (genotoxicity and DNA-repair-capacity impairment) associated with exposure to runoff from asphalt pavement with CTB sealcoat or with an asphalt-based sealcoat hypothesized to contain about 7% CTB sealcoat (AS-blend). Genotoxic potential was assessed by the Formamido pyrimidine glycosylase (Fpg)-modified comet assay for 1:10 and 1:100 dilutions of runoff samples collected from 5 h to 36 d following sealcoat application. DNA-repair capacity was assessed by the base excision repair comet assay for 1:10 dilution of samples collected 26 h and 36 d following application. Both assays were run with and without co-exposure to ultraviolet-A radiation (UVA). With co-exposure to UVA, genotoxic effects were significant for both dilutions of CTB runoff for three of four sample times, and for some samples of AS-blend runoff. Base excision repair was significantly impaired for CTB runoff both with and without UVA exposure, and for AS-blend runoff only in the absence of UVA. This study is the first to investigate the effects of exposure to the complex mixture of chemicals in coal tar on DNA repair capacity. The results indicate that co-exposure to runoff from CT-sealcoated pavement and UVA as much as a month after sealcoat application has the potential to cause genotoxicity and impair DNA repair capacity.

Cytotoxicity of binary mixtures of human pharmaceuticals in a fish cell line: approaches for non-monotonic concentration-response relationships

Predicting the effects of mixtures of environmental micropollutants is a priority research area. In this study, the cytotoxicity of ten pharmaceuticals to the rainbow trout cell line RTG-2 was determined using the neutral red uptake assay. Fluoxetine (FL), propranolol (PPN), and diclofenac (DCF) were selected for further study as binary mixtures. Biphasic concentration-response relationships were observed in cells exposed to FL and PPN. In the case of PPN, microscopic examination revealed lysosomal swelling indicative of direct uptake and accumulation of the compound. Three equations describing non-monotonic concentration-response relationships were evaluated and one was found to consistently provide more accurate estimates of the median and 10% effect concentrations compared with a sigmoidal concentration-response model. Predictive modeling of the effects of binary mixtures of FL, PPN, and DCF was undertaken using an implementation of the concentration addition (CA) conceptual model incorporating non-monotonic concentration-response relationships. The cytotoxicity of the all three binary combinations could be adequately predicted using CA, suggesting that the toxic mode of action in RTG-2 cells is unrelated to the therapeutic mode of action of these compounds. The approach presented here is widely applicable to the study of mixture toxicity in cases where non-monotonic concentration-response relationships are observed.

In vitro exposure to copper influences lipid metabolism in hepatocytes from grass carp (Ctenopharyngodon idellus)

In the present study, three different copper (Cu) concentrations (control, 10 and 100 lM, respectively) and three incubation times (24, 48 and 96 h) were chosen to assess in vitro effect of Cu on lipid metabolism in hepatocytes of grass carp Ctenopharyngodon idellus. Increased glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and carnitine palmitoyltransferase I activities were observed in hepatocytes with increasing Cu concentration and exposure duration. Cu decreased mRNA levels of several lipogenic and lipolytic genes at 24 h. However, at 48 h, Cu down-regulated the process of lipogenesis but up-regulated that of lipolysis. The Cudriven up-regulation of lipolytic genes was maintained after 96 h and accompanied by a decreased intracellular triglyceride accumulation, while no effect on lipogenic genes was shown. Thus, 96-h Cu exposure induced lipid depletion, possibly due to the upregulation of lipolysis. Although in this process, lipogenesis might be up-regulated, it was not enough to compensate lipid consumption. Our study represents the first approach to concentration- and time-dependent in vitro effects of Cu on lipid metabolism of fish hepatocytes and provides new insights into Cu toxicity in fish at both enzymatic and molecular levels.

Transgenic (cyp19a1b-GFP) zebrafish embryos as a tool for assessing combined effects of oestrogenic chemicals

Endocrine disrupting chemicals and especially oestrogen receptor (ER) agonists have been extensively studied over the years due to their potential effects on sexual development and reproduction in vertebrates, notably fish. As ER agonists can exist as complex mixtures in the aquatic environment, evaluating the impact of combined exposure on oestrogenic effects has become increasingly important. Use of predictive models such as concentration addition (CA) and independent action (IA) has allowed assessment of combined estrogenic effects of complex multi-compound mixtures of ER agonists in various fish in vitro and in vivo experimental models. The present work makes use of a transgenic zebrafish strain, tg(cyp19a1b-GFP), which expresses the green fluorescent protein (GFP) under the control of the cyp19a1b (brain aromatase or aromatase B) gene to determine the oestrogenic potency of ER agonists alone or in mixtures. In these studies, tg(cyp19a1b-GFP) zebrafish embryos were exposed for four days (from one to five days post fertilization) to five different oestrogenic chemicals; 17α-ethinylestradiol (EE2), 17β-estradiol (E2), estrone (E1), bisphenol A (BPA) and 4-tert-octylphenol (OP), and three mixtures of up to four of these compounds. The mixture of BPA, OP and E2 was also tested with primary cultures of rainbow trout hepatocytes by analysing the ER-mediated induction of the oestrogenic biomarker vitellogenin in order to compare the performance of the two methods for assessing oestrogenic effects of complex mixtures. The three tested mixtures were predominantly acting in an additive manner on the expression of GFP. Additivity was indicated by the overlap of the 95% confidence interval of the concentration response curves for the observed data with the CA and IA prediction models, and model deviation ratios within a factor of two for a majority of the mixture concentrations. However, minor deviations determined as more than additive effects for the mixture of EE2, E1 and E2 and less than additive effects for the mixture of BPA, OP, EE2 and E1 were observed at the higher mixture concentrations tested. The successful prediction of additivity by CA and IA in tg(cyp19a1b-GFP) zebrafish embryos and deviations at high mixture concentrations seemed to correspond well to results obtained in the rainbow trout hepatocyte assay. The present results clearly show the usefulness of combining predictive modelling and use of in vitro bioassays for rapid screening of oestrogenic effects of complex mixtures and environmental samples.

Interactions of pharmaceuticals and other xenobiotics on key detoxification mechanisms and cytoskeleton in Poeciliopsis lucida hepatocellular carcinoma, PLHC-1 cell line

Fish are exposed to chemicals, including pharmaceuticals, in their natural habitat. This study focuses on effects of chemicals, including nine classes of pharmaceuticals, on key detoxification mechanisms in a fish liver cell-line (PLHC-1). Chemical interactions were investigated on efflux pumps, P-glycoprotein (Pgp) and multidrug resistance associated proteins (MRP1/MRP2), and on biotransformation enzymes, cytochrome P450 (CYP1A/CYP3A). Diclofenac and troleandomycin inhibited efflux activities, whereas ethinylestradiol activated efflux function. Exposure to troleandomycin and β-naphthoflavone induced MRP2 mRNA levels, but no effects were seen on MRP1 or Pgp expressions. Inhibition of CYP1A activities were seen in cells exposed to α-naphthoflavone, β-naphthoflavone, clotrimazole, nocodazole, ketoconazole, omeprazole, ethinylestradiol, lithocholic acid, rifampicin and troleandomycin. Exposure to fulvestrant, clotrimazole and nocodazole resulted in induction of CYP1A mRNA levels. Although, exposure to nocodazole resulted in disassembled microtubules. A CYP3A-like cDNA sequence was isolated from PLHC-1, but basal expression and activities were low and the gene was not responsive to prototypical CYP3A inducers. Exposure to ibuprofen, lithocholic acid and omeprazole resulted in fragmentation of microtubules. This study revealed multiple interactions on key detoxification systems, which illustrates the importance of study effects on regulation combined with functional studies to provide a better picture of the dynamics of the chemical defense system.

Gene-TEQ--a standardized comparative assessment of effects in the comet assay using genotoxicity equivalents

Existing methods for the comparison of genotoxic effects in the comet assay bear considerable disadvantages such as the problem to link information about concentration dependence and severity of effects. Moreover, given the lack of standardized protocols and the use of various standards, it may be extremely difficult to compare different studies. In order to provide a method for standardized comparative assessment of genotoxic effects, the concept of genotoxicity equivalents (Gene-TEQ) was developed. As potential reference compounds for genotoxic effects, three directly acting (N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), methyl-methanesulfonate, and N-methyl-N-nitrosourea) and three indirectly acting (cyclophosphamide, dimethylnitrosamine, and 4-nitroquinoline-oxide) genotoxic substances were compared with respect to their cytotoxic (neutral red) and genotoxic (comet assay) concentration-response profiles in the permanent fish cell line RTL-W1. For further comparison, two sediment extracts from the upper Danube River were investigated as environmental samples. Based on the results of cytotoxicity and genotoxicity testing, MNNG was selected as the reference compound. At several exposure levels and durations, genotoxic effects of both the other pure substances and the environmental samples were calculated as percentages of the maximum MNNG effect and related to the absolute MNNG effect (EC values). Thus, genotoxicity equivalent factors (Gene-TEQs) relative to MNNG could be calculated. Gene-TEQs can easily be applied to pure substances, mixtures and field samples to provide information about their toxicity relative to the reference compound. Furthermore, the Gene-TEQ concept allows a direct comparison of environmental samples from different laboratories.

Steroid catabolism in marine and freshwater fish

Steroids play important roles in regulating many physiological functions in marine and freshwater fish. Levels of active steroid in blood and tissues are determined by the balance between synthetic and catabolic processes. This review examines what is known about pathways of catabolism of steroids, primarily sex steroids, in marine and freshwater fish. Cytochrome P450 (P450) isoforms present in hepatic microsomes catalyze steroid hydroxylation to metabolites with lower or no activity at estrogen or androgen receptors. Important pathways of steroid catabolism to readily excreted metabolites are glucuronidation and sulfonation of hydroxyl groups. Estradiol, testosterone, DHEA and hydroxylated metabolites of these and other steroids readily form glucuronide and sulfate conjugates in those fish species where these pathways have been examined. Little is known, however, of the structure and function of the UDP-glucuronosyltransferase (UGT) and sulfotransferase (SULT) enzymes involved in steroid conjugation in fish. Glucuronide and sulfate conjugates of steroids may be transported into and out of cells by organic anion transporter proteins and multi-drug resistance proteins, and there is growing evidence that these proteins play important roles in steroid conjugate transport and elimination. Induction or inhibition of any of these pathways by environmental chemicals can result in alteration of the natural balance of steroid hormones and could lead to disruption of the endocrine system. Recent studies in this area are presented, with particular focus on phase II (conjugative) pathways.