Fish cell lines as a tool in aquatic toxicology

Isolation and characterisation of two epithelial-like cell lines from the gills of Chrysophrys auratus (Australasian snapper) and Oncorhynchus tshawytscha (Chinook salmon) and their use in aquatic toxicology

In vitro gill models are becoming increasingly important in aquatic toxicology, yet the fish gill invitrome is underrepresented, encompassing approximately 0.1% of extant species. Here, we describe the establishment and characterisation of two gill-derived, epithelial-like cell lines isolated from fish species of significant importance to New Zealand: Chrysophrys auratus (Australasian snapper) and Oncorhynchus tshawytscha (Chinook salmon). Designated CAgill1PFR (Chrysophrys auratus, gill 1, Plant & Food Research) and OTgill1PFR (Oncorhynchus tshawytscha, gill 1, Plant & Food Research), these cell lines have each been passaged greater than each 70 times over several years and are considered spontaneously immortalised. Both cell lines required serum for growth and exhibited differential responses to basal media formulations. CAgill1PFR was sensitive to low temperatures (4 °C) but replicated at high temperatures (30 °C), whereas OTgill1PFR was sensitive to high temperatures but remained viable at low temperatures, mirroring the natural environment of their host species. Immunostaining revealed expression of epithelial cell markers cytokeratin and E-cadherin, alongside positivity for the mesenchymal cell marker, vimentin. CAgill1PFR was more sensitive to the environmental toxin 3,4 dichloroaniline than OTgill1PFR through measurements of metabolic activity, membrane integrity, and lysosomal function. Furthermore, CAgill1PFR produced less CYP1A activity, indicative of ongoing biotransformation processes, in response to beta-naphthoflavone than OTgill1PFR. These cell lines expand the toolbox of resources and emphasise the need for species-specific aquatic toxicology research.

Cytotoxicity of Prymnesium parvum extracts and prymnesin analogs on epithelial fish gill cells RTgill-W1 and the human colon cell line HCEC-1CT

Harmful algal blooms kill fish populations worldwide, as exemplified by the haptophyte microalga Prymnesium parvum. The suspected causative agents are prymnesins, categorized as A-, B-, and C-types based on backbone carbon atoms. Impacts of P. parvum extracts and purified prymnesins were tested on the epithelial rainbow trout fish gill cell line RTgill-W1 and on the human colon epithelial cells HCEC-1CT. Cytotoxic potencies ranked A > C > B-type with concentrations spanning from low (A- and C-type) to middle (B-type) nM ranges. Although RTgill-W1 cells were about twofold more sensitive than HCEC-1CT, the cytotoxicity of prymnesins is not limited to fish gills. Both cell lines responded rapidly to prymnesins; with EC50 values for B-types in RTgill-W1 cells of 110 ± 11 nM and 41.5 ± 0.6 nM after incubations times of 3 and 24 h. Results of fluorescence imaging and measured lytic effects suggest plasma membrane interactions. Postulating an osmotic imbalance as mechanisms of toxicity, incubations with prymnesins in media lacking either Cl-, Na+, or Ca2+ were performed. Cl- removal reduced morphometric rearrangements observed in RTgill-W1 and cytotoxicity in HCEC-1CT cells. Ca2+-free medium in RTgill-W1 cells exacerbated effects on the cell nuclei. Prymnesin composition of different P. parvum strains showed that analog composition within one type scarcely influenced the cytotoxic potential, while analog type potentially dictate potency. Overall, A-type prymnesins were the most potent ones in both cell lines followed by the C-types, and lastly B-types. Disturbance of Ca2+ and Cl- ionoregulation may be integral to prymnesin toxicity.

Distinguishing between ante factum and post factum properties of animal cell lines and demonstrating their use in grouping ray-finned fish cell lines into invitromes

In this review, animal cell lines are considered to have two classes of attributes: "before-the-fact" (ante factum) and "after-the-fact" (post factum) properties. Fish cell lines from Actinopterygii (ray-finned fishes) are used to illustrate this distinction and to demonstrate how these properties can be used in various ways to categorize cell lines into groups or invitromes. Before-the-fact properties are set at initiation and are properties of the sample and species from which the cell line arose and of the scientist(s) who developed the cell line. On the basis of the Actinopterygii sample, invitromes exist for embryos, larvae, juveniles, adults, and spawning fish, and for most solid organs but rarely for biological fluids. For species, invitromes exist for only a small fraction of the Actinopterygii total. As to their development, scientists from around the world have contributed to invitromes. By contrast, after-the-fact properties are limitless and become apparent during development, characterization, use, and storage of the cell line. For ray-finned invitromes, cell lines appear to acquire immortality during development, are characterized poorly for differentiation potential, have numerous uses, and are stored formally only sporadically. As an example of applying these principles to a specific organ, the skeletal muscle invitrome is used. For ante factum properties, the cell lines are mainly from trunk muscle of economically important fish from 11 orders, 15 families, 19 genera, and 21 species of ray-finned fishes. For post factum properties, fibroblast-like and myogenic cell lines have been described but epithelial-like FHM is most widely used and curated. Considering cell lines by their before- and after-the-fact properties should facilitate integration of new cell lines into the literature and help incorporate the discipline of cell biology into other research areas, particularly the natural history of fishes.

Development and characterization of a new gill cell line from the striped catfish, Pangasianodon hypophthalmus (Sauvage, 1878)

Cell lines as an in vitro model developed from different target organs of fish find their use in virus susceptibility, cytotoxicity, gene expression studies. The striped catfish, Pangasianodon hypophthalmus, is one of the main species in aquaculture, especially in Southeast Asian countries like Thailand, Indonesia, China, India, Bangladesh, and Vietnam. The present study reports the development of a new permanent cell line from the gills of P. hypophthalmus designated as PHG and its application in toxicological research. Leibovitz's L-15 cell culture medium supplemented with 15% fetal bovine serum (FBS) was used to maintain cell line PHG. The morphology of the PHG cell line was observed fibroblastic-like. PHG cells grew well at varying temperatures ranging from 24 to 30 °C with an optimum temperature of 28 °C. The PHG cell line was characterized using a sequence of mitochondrial cytochrome C oxidase subunit I, which authenticated the species of origin of the cell line. The cell line was transfected with a pEGFP-C1 plasmid, and the transfection reporter gene was successfully expressed 48 h post-transfection with 9% transfection efficiency. The toxicity assessment of two organophosphate pesticides, chlorpyrifos, and malathion using the PHG cell line revealed that the two organophosphate pesticides were cytotoxic to the cell line at varying concentrations.

Assessing Fish Immunotoxicity by Means of In Vitro Assays: Are We There Yet?

There is growing awareness that a range of environmental chemicals target the immune system of fish and may compromise the resistance towards infectious pathogens. Existing concepts to assess chemical hazards to fish, however, do not consider immunotoxicity. Over recent years, the application of in vitro assays for ecotoxicological hazard assessment has gained momentum, what leads to the question whether in vitro assays using piscine immune cells might be suitable to evaluate immunotoxic potentials of environmental chemicals to fish. In vitro systems using primary immune cells or immune cells lines have been established from a wide array of fish species and basically from all immune tissues, and in principal these assays should be able to detect chemical impacts on diverse immune functions. In fact, in vitro assays were found to be a valuable tool in investigating the mechanisms and modes of action through which environmental agents interfere with immune cell functions. However, at the current state of knowledge the usefulness of these assays for immunotoxicity screening in the context of chemical hazard assessment appears questionable. This is mainly due to a lack of assay standardization, and an insufficient knowledge of assay performance with respect to false positive or false negative signals for the different toxicant groups and different immune functions. Also the predictivity of the in vitro immunotoxicity assays for the in vivo immunotoxic response of fishes is uncertain. In conclusion, the currently available database is too limited to support the routine application of piscine in vitro assays as screening tool for assessing immunotoxic potentials of environmental chemicals to fish.

Unknown Extracellular and Bioactive Metabolites of the Genus Alexandrium: A Review of Overlooked Toxins

Various species of Alexandrium can produce a number of bioactive compounds, e.g., paralytic shellfish toxins (PSTs), spirolides, gymnodimines, goniodomins, and also uncharacterised bioactive extracellular compounds (BECs). The latter metabolites are released into the environment and affect a large range of organisms (from protists to fishes and mammalian cell lines). These compounds mediate allelochemical interactions, have anti-grazing and anti-parasitic activities, and have a potentially strong structuring role for the dynamic of Alexandrium blooms. In many studies evaluating the effects of Alexandrium on marine organisms, only the classical toxins were reported and the involvement of BECs was not considered. A lack of information on the presence/absence of BECs in experimental strains is likely the cause of contrasting results in the literature that render impossible a distinction between PSTs and BECs effects. We review the knowledge on Alexandrium BEC, (i.e., producing species, target cells, physiological effects, detection methods and molecular candidates). Overall, we highlight the need to identify the nature of Alexandrium BECs and urge further research on the chemical interactions according to their ecological importance in the planktonic chemical warfare and due to their potential collateral damage to a wide range of organisms.

New Conceptual Toxicokinetic Model to Assess Synergistic Mixture Effects between the Aromatic Hydrocarbon β-Naphthoflavone and the Azole Nocodazole on the CYP1A Biomarker in a Fish Cell Line

Toxicokinetic interactions with catabolic cytochrome P450 (CYP) enzymes can inhibit chemical elimination pathways and cause synergistic mixture effects. We have created a mathematical bottom-up model for a synergistic mixture effect where we fit a multidimensional function to a given data set using an auxiliary nonadditive approach. The toxicokinetic model is based on the data from a previous study on a fish cell line, where the CYP1A enzyme activity was measured over time after exposure to various combinations of the aromatic hydrocarbon β-naphthoflavone and the azole nocodazole. To describe the toxicokinetic mechanism in this pathway and how that affects the CYP1A biomarker, the model uses ordinary differential equations. Local sensitivity and identifiability analyses revealed that all the 10 parameters estimated in the model were identified uniquely while fitting the model to the data for measuring the CYP1A enzyme activity. The model has a good prediction power and is a promising tool to test the synergistic toxicokinetic interactions between different chemicals.

Cytotoxicity Assays with Fish Cells as an Alternative to the Acute Lethality Test with Fish

In ecotoxicology, in vitro assays with fish cells are currently applied for mechanistic studies, bioanalytical purposes and toxicity screening. This paper discusses the potential of cytotoxicity assays with fish cells to reduce, refine or replace acute lethality tests using fish. Basal cytotoxicity data obtained with fish cell lines or fish primary cell cultures show a reasonable to good correlation with lethality data from acute toxicity tests, with the exception of compounds that exert a specific mode of toxic action. Basal cytotoxicity data from fish cell lines also correlate well with cytotoxicity data from mammalian cell lines. However, both the piscine and mammalian in vitro assays are clearly less sensitive than the fish test. Therefore, in vivo LC50 values (concentrations of the test compounds that are lethal to 50% of the fish in the experiment within 96 hours) currently cannot be predicted from in vitro values. This in vitro-in vivo difference in sensitivity appears to be true for both fish cell lines and mammalian cell lines. Given the good in vitro-in vivo correlation in toxicity ranking, together with the clear-cut difference in sensitivity, the role of cytotoxicity assays in a tiered alternative testing strategy could be in priority setting in relation to toxic hazard and in the toxicity classification of chemicals and environmental samples.

A comprehensive review on chromium induced alterations in fresh water fishes

Chromium is considered as one of the most common ubiquitous pollutants in the aquatic environment, but the pure metallic form is absent naturally. There are three oxidation states in case of Chromium viz., Cr (II), Cr (III), Cr (VI). Among which Cr (II) is most unstable. Cr (III) and Cr (VI) are the stable oxidation state of Chromium in the environment. Being one of the commonly used metals Chromium and its particulates enter the aquatic medium through effluents discharged from different industries like textiles, tanneries, electroplating workshops, ore mining, dyeing, printing-photographic and medical industries. Among these, hexavalent chromium is considered as the most toxic form because it readily passes cellular membranes and then reduced to trivalent form. This trivalent chromium combines with several macromolecules including genetic material inside the cytosol, and is ultimately exposes the toxic and mutagenic alterations due of chromium toxicity. Chromium is taken up either through gastrointestinal tract or respiratory tract. The amount varies depending upon the medium and the form of chromium. In this review, an attempt has been made to accumulate the mammoth available data regarding impact of chromium on fresh water fishes into a systematic representation. The main objective of the review is to provide a future guideline for the scientific community and public officials involved in health risk assessment and management ensuring a better environmental condition for human health.

Cytotoxicity and alterations at transcriptional level caused by metals on fish erythrocytes in vitro

The in vitro use of fish erythrocytes to test the toxicity of aquatic pollutants could be a valuable alternative to fish bioassays but has received little attention. In this study, erythrocytes from marine gilthead sea bream (Sparus aurata L.) and European sea bass (Dicentrarchus labrax L.) specimens were exposed for 24 h to Cd, Hg, Pb and As and the resulting cytotoxicity was evaluated. Exposure to metals produced a dose-dependent reduction in the viability, and mercury showed the highest toxicity followed by MeHg, Cd, As and Pb. Moreover, fish erythrocytes incubated with each one of the metals exhibited alteration in gene expression profile of metallothionein, superoxide dismutase, catalase, peroxiredoxin, glutathione reductase, heat shock proteins 70 and 90, Bcl2-associated X protein and calpain1 indicating cellular protection, stress and apoptosis death as well as oxidative stress. This study points to the benefits for evaluating the toxicological mechanisms of marine pollution using fish erythrocytes in vitro.

In vitro immunotoxicological effects of heavy metals on European sea bass (Dicentrarchus labrax L.) head-kidney leucocytes

The knowledge about the direct effects of heavy metals on fish leucocytes is still limited. We investigate the in vitro effects of heavy metals (Cd, Hg, Pb or As) on oxidative stress, viability and innate immune parameters of head-kidney leucocytes (HKLs) from European sea bass (Dicentrarchus labrax). Production of free oxygen radicals was induced by Cd, Hg and As, mainly after 30 min of exposure. Cd and Hg promoted both apoptosis and necrosis cell death while Pb and As did only apoptosis, in all cases in a concentration-dependent manner. Moreover, expression of genes related to oxidative stress and apoptosis was significantly induced by Hg and Pb but down-regulated by As. In addition, the expression of the metallothionein A gene was up-regulated by Cd and Pb exposure though this transcript, as well as the heat shock protein 70, was down-regulated by Hg. Cd, methylmercury (MeHg) and As reduced the phagocytic ability, whereas Hg and Pb increased it. Interestingly, all the heavy metals decreased the phagocytic capacity (the number of ingested particles per cell). Leucocyte respiratory burst changed depending on the metal exposure, usually in a time- and dose-manner. Interestingly, the expression of immune-related genes was slightly affected by Cd, MeHg, As or Pb being Hg the form producing the greatest alterations, which included down-regulation of immunoglobulin M and hepcidin, as well as the up-regulation of interleukin-1 beta mRNA levels. This study provides an in vitro approach for elucidating the heavy metals toxicity, and particularly the immunotoxicity, in fish leucocytes.

Development and characterization of a cell line WAF from freshwater shark Wallago attu

A new epithelial cell line, WAF was developed from caudal fin of freshwater shark, Wallago attu. The cell line was optimally maintained at 28 °C in Leibovitz-15 (L-15) medium supplemented with 20 % fetal bovine serum. The cell line was characterized by various cytogenetic and molecular markers. The cytogenetic analysis revealed a diploid count of 86 chromosomes at different passages. The origin of the cell lines was confirmed by the amplification of 547 and 654 bp sequences of 16S rRNA and cytochrome oxidase subunit I genes of mitochondrial DNA, respectively. WAF cells were characterized for their growth characteristics at different temperature and serum concentration. Epithelial morphology of the cell line was confirmed using immunocytochemistry. Further cell plating efficiency, transfection efficiency and viability of cryopreserved WAF cells was also determined. Cytotoxicity and genotoxicity assessment of cadmium salts on WAF cells by MTT, NR and comet assay illustrated the utility of this cell line as an in vitro model for aquatic toxicological studies. The cell line will be further useful for studying oxidative stress markers against aquatic pollutants.

Fish as research tools: alternatives to in vivo experiments

The use of fish in scientific research is increasing worldwide, due to both the rapid expansion of the fish farming industry and growing awareness of questions concerning the humane use of mammalian models in basic research and chemical testing. As fish are lower on the evolutionary scale than mammals, they are considered to be less sentient. Fish models are providing researchers, and those concerned with animal welfare, with opportunities for adhering to the Three Rs principles of refinement, reduction and replacement. However, it should be kept in mind that fish should also be covered by the principles of the Three Rs. Indeed, various studies have shown that fish are capable of nociception, and of experiencing pain in a manner analogous to that in mammals. Thus, emphasis needs to be placed on the development of alternatives that replace, as much as possible, the use of all living vertebrate animals, including fish. This review gives the first comprehensive and critical overview of the existing alternatives for live fish experimental studies. The alternative methods described range from cell and tissue cultures, organ and perfusion models, and embryonic models, to in silico computer and mathematical models. This article aspires to guide scientists in the adoption of the correct alternative methods in their research, and, whenever possible, to reduce the use of live fish.

The use of fish-derived cell lines for investigation of environmental contaminants

This unit describes protocols for growing salmonid cell lines and using them in in vitro toxicology studies. Cell viability of cultures is assessed with three indicator dyes: alamar blue for metabolic activity, CFDA-AM for membrane integrity, and neutral red for lysosomal activity. These protocols are essential tools for investigating environmental toxicity at the cellular level.

Establishment, characterization of a new cell line from heart of half smooth tongue sole (Cynoglossus semilaevis)

A new cell line was established from the heart of a cultured marine fish, half smooth tongue sole (Cynoglossus semilaevis), designated as CSH (Cynoglossus semilaevis heart cell line). The CSH cells grow over 400 days in minimum essential medium (MEM) supplemented with 10% fetal bovine serum (FBS) and 2 ng/ml basic fibroblast growth factor (bFGF). The suitable temperature for the cell growth was 24-30°C with the optimum growth at 24°C and a reduced growth at 12 and 30°C. FBS and bFGF concentration were the two important components for CSH cells proliferation. Twenty percent FBS in the medium was found to be the optimum concentration and bFGF promoted the growth of CSH cells. The double time of the cells at 24°C was determined to 73.39 h. Chromosome analysis revealed that 44% of the cells maintained a normal diploid chromosome number (2n=42) in the CSH cells at Passage 58. The fluorescent signals were observed in CSH after the cells were transfected with green fluorescent protein (GFP) reporter plasmids. CSH cells showed the cytopathic effect (CPE) after infection with lymphosystis disease virus (LCDV). Moreover, the LCDV particles can be observed in the cytoplasm of virus-infected cells by electron microscopy, and a segment of MCP gene for major capsid protein of LCDV was found by PCR amplification DNA of virus-infected cells.

Insulin regulates the expression of several metabolism-related genes in the liver and primary hepatocytes of rainbow trout (Oncorhynchus mykiss)

Rainbow trout have a limited ability to use dietary carbohydrates efficiently and are considered to be glucose intolerant. Administration of carbohydrates results in persistent hyperglycemia and impairs post-prandial down regulation of gluconeogenesis despite normal insulin secretion. Since gluconeogenic genes are mainly under insulin control, we put forward the hypothesis that the transcriptional function of insulin as a whole may be impaired in the trout liver. In order to test this hypothesis, we performed intraperitoneal administration of bovine insulin to fasted rainbow trout and also subjected rainbow trout primary hepatocytes to insulin and/or glucose stimulation. We demonstrate that insulin was able to activate Akt, a key element in the insulin signaling pathway, and to regulate hepatic metabolism-related target genes both in vivo and in vitro. In the same way as in mammals, insulin decreased mRNA expression of gluconeogenic genes, including glucose 6-phosphatase (G6Pase),fructose 1,6-bisphosphatase (FBPase) and phosphoenolpyruvate carboxykinase (PEPCK). Insulin also limited the expression of carnitine palmitoyltransferase 1 (CPT1), a limiting enzyme of fatty acid β-oxidation. In vitro studies revealed that, as in mammals,glucose is an important regulator of some insulin target genes such as the glycolytic enzyme pyruvate kinase (PK) and the lipogenic enzyme fatty acid synthase (FAS). Interestingly, glucose also stimulates expression of glucokinase (GK), which has no equivalent in mammals. This study demonstrates that insulin possesses the intrinsic ability to regulate hepatic gene expression in rainbow trout, suggesting that other hormonal or metabolic factors may counteract some of the post-prandial actions of insulin.

Analysis of the effects diclofenac has on Japanese medaka (Oryzias latipes) using real-time PCR

The expression levels of cytochrome P450 1A, p53 and vitellogenin were investigated in three different tissues of male medaka fish after exposure to diclofenac that is one of the main concerns among pharmaceuticals frequently found in sewage treatment plant (STP) effluents. The results showed that cytochrome P450 1A, p53 and vitellogenin were highly expressed in tissue-specific gene expression patterns after exposure to 8 mg/l and 1 microg/l of diclofenac. These elevated expression levels of three biomarkers suggested that diclofenac has potential to cause cellular toxicity, p53-related genotoxicity and estrogenic effects. It is also noteworthy that diclofenac has the potential to cause these effects even at an environmentally relevant concentration of diclofenac, 1 microg/l.

The improvement of in vitro cytotoxicity testing for the assessment of acute toxicity in fish

The use of fish cell line cytotoxicity tests as alternatives to acute lethality tests with fish is hampered by the clearly lower sensitivity of the fish cell line tests. Recently, it has been shown that this is not a unique feature of fish cells. In fact, the sensitivity of mammalian and human cell lines toward the cytotoxic actions of chemicals, in general, is comparable to that of fish cell lines. Reviewing some of our recent investigations, the objective of this paper is to show that the sensitivity of in vitro cytotoxicity testing and the correspondence between in vitro cytotoxic and acute fish toxic concentrations (LC50) can be increased, if: a) inhibition of cell growth instead of cell death is used as the endpoint; and b) the bioavailable free cytotoxic concentration (ECu50) of chemicals in vitro, instead of the nominal cytotoxic concentration (EC50), is used as the measure of cytotoxic potency. Based on these results, a pragmatic in vitro testing strategy for estimating the minimal aquatic toxic potency of chemicals is proposed.

In vitro toxicity of antimicrobials on RTG-2 and RTL-W1 fish cell lines

This study proposed a battery of endpoints based on in vitro fish cell lines. Two fish cell lines and four toxicity endpoints are considered. The tetracycline (TC), oxytetracycline (OTC), sulfachlorpyridazine (SCP), and septrin(®) (ST) were selected as model antimicrobials and chlorpyrifos as positive control. EROD was induced by septrin(®) (formulation containing sulfamethoxazole and trimethoprim) at concentrations higher than 20mg/L, but inhibited by tetracycline, oxytetracycline and chlorpyrifos. Dose dependent inhibition responses were observed for β-galactosidase (β-Gal) activity in cells exposed to septrin(®), tetracycline or oxytetracycline. The EROD EC50s ranged between 2.29×10(-2)mg/L (chlorpyrifos) and 167.63mg/L (tetracycline). The β-Gal EC50s ranged between 22.1 (septrin(®)) and 84.59mg/L (tetracycline). Data suggest that in vitro testing using a battery of endpoints can be a cost-effective solution for screening the toxicity of antimicrobials on fish. The absence of in vitro effects at concentrations well above those expected/measured in the environment may replace the need for conducting acute lethality tests on fish.

Use of the single cell gel electrophoresis/comet assay for detecting DNA damage in aquatic (marine and freshwater) animals

The comet assay is a rapid, sensitive and inexpensive method for measuring DNA strand breaks. The comet assay has advantages over other DNA damage methods, such as sister chromatid exchange, alkali elution and micronucleus assay, because of its high sensitivity and that DNA strand breaks are determined in individual cells. This review describes a number of studies that used the comet assay to determine DNA strand breaks in aquatic animals exposed to genotoxicants both in vitro and in vivo, including assessment of DNA damage in aquatic animals collected from contaminated sites. One difficulty of using the comet assay in environmental work is that of comparing results from studies that used different methods, such as empirical scoring or comet tail lengths. There seems to be a consensus in more recent studies to use both the intensity of the tail and the length of the tail, i.e. DNA tail moment, percentage of DNA in the tail. The comet assay has been used to assess DNA repair and apoptosis in aquatic animals and modifications of the comet assay have allowed the detection of specific DNA lesions. There have been some recent studies to link DNA strand breaks in aquatic animals to effects on the immune system, reproduction, growth, and population dynamics. Further work is required before the comet assay can be used as a standard bio-indicator in aquatic environments, including standardization of methods (such as ASTM method E2186-02a) and measurements.

Genotoxicity of the Kishon River, Israel: the application of an in vitro cellular assay

The alkaline comet assay, a sensitive method for DNA strand breaks and alkali labile site detection in individual cells, was employed here as an ecotoxicological monitoring tool for evaluation of genotoxicity in the Kishon River, Israel. This river, the most polluted river in Israel, has recently elicited major public concern with regard to cancer incidences in people who have dived there over many years. Five water samples were collected every odd month throughout the year 2001, from four localities. The comet assay was employed on fish hepatoma cell line RTH-149. Cells were exposed for 2h, in triplicate, to Kishon water: medium (1:1) samples that were pre-adjusted for pH and salinity percentage levels. Three DNA damage parameters (comet percentages, score of damage, and cumulative tail lengths of the comet), revealed significantly higher genotoxic values in Kishon water-treated cells as compared with the controls (up to 2.4, 3.2, and 3.6-fold, respectively). Part of the sampling sites revealed higher genotoxicity than other polluted sites. The results of this study demonstrate that the comet assay with RTH-149 cells can be successfully applied to a variety of aquatic samples revealing freshwater, marine and estuary conditions. The method found to be fast, sensitive, and suitable for monitoring programs.

Detection of DNA damage in two cell lines from rainbow trout, RTG-2 and RTL-W1, using the comet assay

Screening methods to indicate the genotoxic potential of individual chemicals or environmental mixtures rely mainly on short-term bacterial tests. Differences in the genotoxic response of prokaryotic and eukaryotic cells necessitate the development of nonbacterial screening assays. A promising approach for this purpose could be the comet (single-cell gel electrophoresis) assay performed with fish cells in vitro. In the present study, we evaluated the comet assay with two different fish cell lines from rainbow trout (Oncorhyhnchus mykiss), the fibroblast-like RTG-2 cell line established from gonad tissue, and the epitheloid RTL-W1 cell line established from liver tissue. The cells were exposed in vitro during 2 hr to the genotoxins, 4-nitroquinoline-1-oxide (NQO), and benzo(a)pyrene (BaP), as well as to environmental samples. The LOEC values for NQO were similar in both cell lines, whereas for BaP, the RTL-W1 cells were found to be more sensitive than the RTG-2 cells. The slopes of the concentration-response curves of the two test compounds differed between the two cell lines, with RTG-2 cells showing a steeper slope for NQO, and RTL-W1 cells showing a steeper slope for BaP. When exposed to environmental samples from a remediation site, the RTL-W1 cell line, but not the RTG-2 cell line, indicated a genotoxic potential of the samples. The differences in the genotoxic response pattern of the two cell lines could be only partly explained in relation to metabolic enzymes, cytochrome P4501A, glutathione-S-transferase, and xenobiotic reductase. The findings of this study demonstrate that the comet assay with fish cell lines is suitable as in vitro screening assay in environmental genotoxicity testing, but the choice of test cell line may be critical.

Toxicological Evaluation of Surface-water Samples in Sensitised Cultured Fish Cells Compared with the Microtox® Method

A previously described neutral red uptake-inhibition assay on cultured fathead minnow (FHM) fish cells revealed a good correlation with fish toxicity data. The assay was made more sensitive by reducing the number of cells, by using a longer treatment period, and by simultaneous treatment of the cells with sodium dodecyl sulphate and L-buthionine ( S,R)-sulphoximine. The fluorimetrically quantified protein content was then used as the endpoint. The results were compared with toxicity data obtained by the Microtox® method with the bacterium, Vibrio fischeri. A series of 82 surface-water samples were investigated. Cell quantity-dependent and sample concentration-dependent reductions in total protein content were observed. In all, 32 samples were toxic in the FHM assay. Of the seven samples that were shown to be toxic in the Microtox assay, only three were also toxic in FHM cells. No linear relationship was found for the toxicity results obtained with the two methods. Further research to explain the significance of the many positive responses and to identify possible confounding factors will increase the reliability of the sensitised FHM cell assay.