Induction of sister chromatid exchanges in the central mudminnow following in vivo exposure to mutagenic agents

Assessment of genotoxicity in gonads, liver and gills of zebrafish (Danio rerio) by use of the comet assay and micronucleus test after in vivo exposure to methyl methanesulfonate

Since generative tissues are a link between the generations, the detection of genetic damage in testis and ovary of fish is conductive to elucidating the relationship between genotoxicity and impairment of reproduction. In the current study, exposure of zebrafish to methyl methanesulfonate over two weeks caused concentration dependent genotoxic effects in gonads, liver and gills using the alkaline comet assay. Likewise, the micronucleus frequency was elevated in all of these organs. Thus, the comet assay and the micronucleus test proved appropriate for the detection of genotoxicity in primary male and female gonad cells and histological sections of the gonads from zebrafish, respectively.

Genotoxic effects in the Eastern mudminnow (Umbra pygmaea L.) after exposure to Rhine water, as assessed by use of the SCE and Comet assays: A comparison between 1978 and 2005

Surface water used for drinking-water preparation requires continuous monitoring for the presence of toxic compounds. For monitoring of genotoxic compounds fish models have been developed, such as the Eastern mudminnow (Umbra pygmaea L.) because of its clearly visible 22 meta-centric chromosomes. It was demonstrated in the late seventies that Rhine water was able to induce chromosome aberrations and sister chromatid exchange in this fish species. Although in vitro mutagenicity studies of the RIWA (Rhine Water Works, The Netherlands) have shown that the genotoxicity of the river Rhine steadily decreased during the last decades, there is still concern about the presence of some residual mutagenicity. In addition, in most studies the water samples have been tested only in in vitro test systems such as the Salmonella-microsome test. For this reason, and in order to be able to make a comparison with the water quality 27 years ago, a study was performed with the same experimental design as before in order to measure the effect of Rhine water on the induction of SCE in the Eastern mudminnow. As a new test system the single cell gel electrophoresis assay (Comet assay) was performed. Fish were exposed to Rhine water or to groundwater for 3 and 11 days in flow-through aquaria. Fish exposed for 11 days to Rhine water had a significantly higher number of SCE and an increased comet tail-length compared with control fish exposed to groundwater. After exposure for three days to Rhine water there was no difference in SCE and a slightly increased comet tail-length compared with the control. It was concluded that genotoxins are still present in the river Rhine, but that the genotoxic potential has markedly decreased compared with 27 years ago. Furthermore, the Comet assay appears to be a sensitive assay to measure the genotoxic potential of surface waters in fish.

River water genotoxicity evaluation using micronucleus assay in fish erythrocytes

The quality of Caí river water (Rio Grande do Sul State) in an area under the influence of a petrochemical complex was studied using the micronucleus assay in erythrocytes from peripheral blood of the fathead minnow Pimephales promelas. This cytogenetic in vivo assay was performed to evaluate the effects of petrochemical effluents on the stream. Organisms were exposed to samples collected at four sites, during an 11-month period. Three different exposure periods were used (7, 14, and 21 days) to evaluate their influence in genotoxic detection. The 14-day exposure period was most effective in detecting genotoxicity in samples from this area. The presence of substances with clastogenic and/or aneugenic potential could be detected at the different sites analyzed. This in vivo assay allowed the detection of genotoxicity in the area studied, indicating the potential for environmental genotoxicity monitoring.

Micronuclei induced in erythrocytes of Cyprinus carpio (teleostei, pisces) by X-rays and colchicine

In the present work the induction of micronuclei in erythrocytes of Cyprinus carpio treated with X-rays and colchicine is studied for the evaluation of mutagenic effects of both clastogenic and mitoclastic (spindle poisoning) agents in this system. Three different experiments were performed treating groups of laboratory-reproduced animals with (1) single doses of X-rays (0.1, 0.5 and 2Gy); (2) a single i.p. injection of colchicine at the concentrations: 1.6x10(-2), 8x10(-2), 0.4 and 2mg/kg b.w. so as to mimic an acute exposure to the agent and (3) six repeated i.p. injections of the first three concentrations of colchicine, over a period of 18 days, so as to mimic a chronic exposure. Repeated blood samplings were performed by cardiac puncture over a period of about 2 months after the treatment and micronucleus frequencies were determined at multiple times on the same individuals after mutagen exposure. A dose-dependent increase in the micronucleus frequency was observed in irradiated fish and a peak value detected at 21 days. Slight increases of micronucleus frequencies were also observed in both colchicine experiments only for the highest concentrations at the earliest sampling time. Higher concentrations of colchicine clearly showed a lethal effect. According to the present data the micronucleus frequency induced by the highest colchicine dose is comparable to that observed after 0.1Gy of X-ray irradiation.

Micronuclei and other nuclear lesions as genotoxicity indicators in rainbow trout Oncorhynchus mykiss

The induction of micronuclei and other nuclear abnormalities in renal erythrocytes of rainbow trout Oncorhynchus mykiss by six genotoxic compounds is evaluated. Colchicine, mitomycin, cyclophosphamide, acrylamide, methyl-methanesulfonate, and N-ethyl-N-nitrosourea were intraperitoneally injected in trout. Our results show that cyclophosphamide induces the formation of micronuclei and also the other nuclear abnormalities; N-ethyl-N-nitrosourea, acrylamide, and colchicine induce only micronuclei; mitomycin-C induces only other nuclear abnormalities but not micronuclei. Methyl-methanesulfonate does not induce nuclear abnormalities in rainbow trout at the dose assayed in this work. The possible genotoxic origin for the different nuclear abnormalities is discussed.

Induction of sister chromatid exchanges and chromosome aberrations in vivo in Etroplus suratensis (Bloch) following exposure to organophosphorus pesticides

The genotoxic potential of methyl parathion and phosphamidon, two commercial formulations of organophosphorus pesticides, was evaluated through induction of sister chromatid exchanges (SCE) and chromosome aberrations in fish gill tissues. Fishes exposed to the medium containing 0.05, 0.1 and 0.2 ppm of methyl parathion or 0.5, 1.0, and 2.0 ppm of phosphamidon for a duration of 96 h revealed significant increase in the number of SCE and chromosome aberrations against control values. This demonstrates the feasibility of the fish in vivo system in detecting genotoxic potential of pollutants.

Development of genotoxicity assay systems that use aquatic organisms

Our aim is to develop and evaluate monitoring systems that use aquatic organisms to assess the genotoxicity of water in the field and in the laboratory. In a field study, we have shown that the micronucleus assay is applicable to freshwater and marine fishes and that gill cells are more sensitive than hematopoietic cells to micronucleus-inducing agents. Gill cells from Carassius sp. (Funa) and Zacco platypus (Oikawa) collected upstream on the Tomio River (Nara, Japan), tended to have lower micronucleus frequencies than gill cells from fish collected at the midstream of the river. Leiognathus nuchalis (Hiiragi) and Ditrema temmincki (Umitanago), small marine fishes collected periodically at Mochimune Harbor (Shizuoka, Japan), showed seasonal differences in the frequencies of micronucleated gill cells and erythrocytes; they were highest in summer. For laboratory studies, we developed a method for analyzing chromosomal aberrations and micronuclei using Rhodeus ocellatus ocellatus (rose bitterling) embryos. One day after artificial insemination (gastrula stage), we observed structural chromosomal aberrations and micronuclei in the cells of embryos grown in water containing trichloroethylene. Although more work is needed to fully assess their sensitivity, these assays show promise as a means of detecting environmental genotoxins.

Micronuclei and fluctuating asymmetry in brown trout (Salmo trutta): complementary methods to biomonitor freshwater ecosystems

In this work we measured both micronuclei number in kidney erythrocytes and fluctuating asymmetry in wild brown trout (Salmo trutta), caught in different fluvial ecosystems of Asturias (northern Spain) characterized by different levels of anthropic influence. Brown trout samples from rivers with high anthropic influence possessed significantly higher averages of both micronuclei and fluctuating asymmetry than brown trout samples from less anthropic-influenced rivers. These findings demonstrated the sensitivity of the micronucleus test in kidney erythrocytes to biomonitor freshwater ecosystems. The positive association found between micronuclei average and fluctuating asymmetry at the populational level suggests that fluctuating asymmetry tests could be potential indicators of environmental threat. Variation of fish asymmetry with ageing indicates that fluctuating asymmetry surveys of wild populations should be carried out in trouts of the same age class.

Development of an in vivo genotoxicity assay using the marine worm Platynereis dumerilii (Polychaeta: Nereidae)

An in vivo genotoxicity test system has been developed using the embryo-larval stages of the marine annelid, Platynereis dumerilii (Polychaeta: Nereidae). This species is representative of an ecologically important group of marine invertebrates, it is amenable to laboratory culture and has a well defined and stable karyotype (2n=28) which is suitable for the analysis of a range of cytogenetic endpoints, including chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs). An evaluation of the cell cycle kinetics using the embryo-larval stages allowed selection of exposure times for cytogenetic work. Subsequently, 12-h-old embryos were exposed to reference mutagens, dissolved in sea water, in the presence of 5-bromodeoxyuridine (BrdU) for 12 h (SCE analysis) or 8 h (CA analysis) at 15 +/- 1 degree C, by which time they had reached the first larval stage (20-24h). Dose response-relationships for cytotoxicity, SCEs and CAs were observed for both direct acting mutagens (methyl methanesulfonate, mitomycin C) and mutagens which require metabolic activation (cyclophosphamide, benzo[a]pyrene). The sensitivity of the embryo-larval stages of P. dumerilii to both direct and indirect acting mutagens, their suitability for laboratory culture, together with the presence of a good karyotype and chromosome morphology for cytogenetic analyses, makes this species a potentially valuable in vivo model for marine genotoxicity testing.

Sister-chromatid exchange: second report of the Gene-Tox Program

This paper reviews the ability of a number of chemicals to induce sister-chromatid exchanges (SCEs). The SCE data for animal cells in vivo and in vitro, and human cells in vitro are presented in 6 tables according to their relative effectiveness. A seventh table summarizes what is known about the effects of specific chemicals on SCEs for humans exposed in vivo. The data support the concept that SCEs provide a useful indication of exposure, although the mechanism and biological significance of SCE formation still remain to be elucidated.

Genotoxic, carcinogenic, and teratogenic hazards in the marine environment, with special reference to the Mediterranean Sea

Genotoxic, carcinogenic, and teratogenic hazards arising out of pollution in the marine environment are discussed in this article, with special reference to the situation in the Mediterranean area. A number of chemical compounds or complex mixtures relevant to marine pollution, either natural or of anthropogenic origin, are tentatively listed, along with protective factors which may play a counteracting role in the same environment. Harmful substances tend to undergo interactions and transformations in seawater, sediments, and marine biota, due to physical, chemical, microbial, or light-mediated mechanisms. Bioaccumulation phenomena in marine organisms may result from food-chain biomagnification processes or from concentration of pollutants by filter feeders. A variety of sources can account for marine pollution by genotoxic, carcinogenic, and teratogenic compounds, but there is a relative paucity of analytical data concerning the Mediterranean. Metabolic transformations of xenobiotics occur in all marine organisms, the biochemical mechanisms in fish being comparable to those which have been extensively investigated in mammals. Induction of metabolic pathways, and especially of the mixed-function oxygenase system, represents the earliest warning signal of exposure to pollutants. Occurrence of neoplastic diseases is documented by experimental and field studies in marine vertebrates as well as in invertebrates. The association with local pollution phenomena has been recognized in several studies, but other etiopathogenetic factors may be also involved, and in some cases tumors have been reported to be unrelated to chemical pollution. Genotoxic agents have been detected by means of suitable techniques in seawater, sediments, and marine organisms. Several studies have investigated the presence of carcinogen-DNA adducts, DNA damage and repair processes, and cytogenetic alterations, such as chromosomal aberrations, sister-chromatid exchanges, and micronuclei, in tissues of marine organisms. However, monitoring of these end-points under field conditions encounters some limitations and problems. Even more fragmentary is the information on teratogenic effects in marine organisms, although interesting test systems have been set up. On the whole, a quite extensive database on all these toxicological issues is already available in the literature, but further studies are warranted for an adequate assessment of genotoxic, carcinogenic, and teratogenic hazards, and possibly counteracting factors in the marine environment, and specifically in the Mediterranean Sea.

Persistence of micronuclei in the marine mussel, Mytilus galloprovincialis, after treatment with mitomycin C

The frequency of micronuclei induced by mitomycin C (MMC) in cells of the gill tissue of the marine mussel, Mytilus galloprovincialis Lmk., was determined over a long period (up to 40-52 days) following treatment. Two doses of MMC (0.5 X 10(-7) and 10(-7) M) were tested at 13 degrees C and 23 degrees C, temperatures representative of the winter and summer thermic conditions of the Mediterranean Sea. In all cases, the frequency of micronuclei was significantly increased by MMC and declined after treatment until it reached a plateau level, significantly higher than the control value. This persisted for a very long time. The frequency of micronuclei induced by a second treatment with MMC performed on the 28th day, did not differ significantly from that produced by the first treatment at the same dose. Temperature did not influence the pattern of the described phenomena to a significant extent. The reason for the persistence of an increased frequency of micronuclei is discussed, and a system is proposed for evaluating the genotoxicity of water pollutants present long before sampling.

DNA repair synthesis in cultured fish and human cells exposed to fish S9-activated aromatic hydrocarbons

Unscheduled DNA repair synthesis was measured autoradiographically in cultured rainbow trout gonad (RTG) and human fibroblast (HF) cells following exposure to aflatoxin B1 (AFB1), 3,4-benzopyrene (BP), 1,2,5,6-dibenzanthracene (DBA), 1,2-benzanthracene (BA) and pyrene (PY) activated with S9 prepared from rainbow trout liver. S9 from rainbow trout injected with Arochlor 1254 or an oil extract was compared with S9 from Fischer rats injected with Arochlor 1254 for the ability to activate AFB1 and cause DNA repair in RTG and HF cells. All three types of S9 activated AFB1, but the measured DNA repair response was greater in the HF cells. A significant grain count response was found following exposure of HF cells to fish S9-activated BP. Using assay conditions which enhance fish cell grain counts, a significant level of DNA repair was also found in RTG cells exposed to fish S9-activated BP. Marginal but statistically significant amounts of DNA repair were elicited in HF and RTG cells exposed to rainbow trout S9-activated BA and DBA, but no response was detected following PY exposure. Fish S9 was found to be able to activate a series of polycyclic aromatic hydrocarbons (PAH) and cause DNA repair synthesis in both fish and mammalian cells. The magnitude of the repair response roughly parallels the carcinogenic potential of the PAHs. These results elicit trans species and phyla comparisons which help to validate fish as models for aquatic carcinogenesis research, and also demonstrate PAH DNA-damaging effects on fish DNA, adding further credence for studying the effects of these chemicals on aquatic organisms.

Induction of sister-chromatid exchanges and chromosomal aberrations in hematopoietic tissue of a marine fish following in vivo exposure to genotoxic carcinogens

The development of procedures to assess genetic damage in fish exposed in situ to point sources of aquatic pollution can be expected to contribute to the evaluation of the role of genotoxic contaminants in epizootic neoplasia in fish populations. To this end methods have been developed for assessing the in vivo induction of chromosomal aberrations (CAs) and sister-chromatid exchanges (SCEs) in tissues of a marine teleost, the oyster toadfish, which may be applicable to other species. An alternative to the solid tissue and squash techniques for metaphase preparation permits the resolution of more than 100 SCEs/metaphase in toadfish kidney cells, which have moderately large chromosomes (0.122 pg DNA/chromosome). The bleeding of toadfish which have been injected with 5-bromodeoxyuridine (BrdUrd) and the subsequent use of hematopoietic tissue (kidney) for cytogenetic analysis was shown to increase the metaphase yield and provide a more predictable production of second-division metaphases required for SCE analysis. With these methods linear dose-dependent increases in chromatid-type exchange CAs and SCEs were obtained with i.p. exposure to ethyl methanesulfonate (EMS) and cyclophosphamide (CP). The doses required to double the observed control SCE frequencies (least effective doses) were 170 mg/kg for EMS and 7.4 mg/kg for CP. which are comparable to those reported for rodent bone marrow assays. A BrdUrd-sensitive site for chromatid breakage was observed on a pair of apparently homologous acrocentric chromosomes for the toadfish.

A new micronucleus test using peripheral blood erythrocytes of the newt Pleurodeles waltl to detect mutagens in fresh-water pollution

A model micronucleus test system using peripheral blood erythrocytes from larvae of Pleurodeles waltl is described. The most suitable larval stage for testing chemical treatments was determined. Larvae were reared in water containing one of the 4 compounds: benzo[a]pyrene (BaP), ethyl methanesulphonate (EMS), diethyl sulphate (DES) and N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG). Response curves as a function of treatment duration over a period of 16 days were plotted for 3 different concentrations of the 4 compounds in order to optimize conditions for a low dose micronucleus test. This model can be used as a monitoring system for the detection of fresh water pollution and can also be employed for clastogen screening of chemical compounds. The test is sensitive, reliable and easy to use.

Clastogenic effects of five carcinogenic-mutagenic chemicals on the cells of the common carp, Cyprinus carpio L

The cytogenetic effects of various i.p. treatments with five carcinogenic-mutagenic chemicals and three doses for each (aflatoxin B1, Aroclor 1254, benzidine, benzo[a]pyrene and 20-methylcholanthrene), were investigated in the cells of the common carp, Cyprinus carpio. Injection with distilled water and corn oil served as the two control groups. For detecting cytogenetic damage we used two test systems, chromosomal aberrations (CA) in kidney cells and micronucleated erythrocytes (M). At 48 hr after treatment with the chemicals under investigation, the frequencies of CA and M were clearly increased in a dose-response manner compared to the control groups.

Some factors affecting optimal differential staining of sister-chromatids in vivo in the fish Nothobranchius rachowi

In the past few years, routine studies of SCE induction in vivo in fish have been hampered by unreliable SCD techniques. This paper presents a number of modifications of the SCD technique in vivo in Nothobranchius rachowi. Major improvements were obtained by BrdU incorporation from aqueous solutions, short intervals between preparation and staining of slides and post-treatment with HCl. These improvements resulted in a highly reliable SCD procedure in Nothobranchius with a low level base-line SCE frequency (0.90 SCE/metaphase, 0.059 SCE/chromosome). Further research is now directed at gathering additional data on base-line SCE frequencies, establishing the sensitivity of the assay for aqueous solutions of known mutagens, and defining an experimental set-up for optimal statistical evaluation.

Carcinogenic-mutagenic chemicals induced chromosomal aberrations in the kidney cells of three cyprinids

In vivo kidney cells of three cyprinids (common carp, tench and grass carp) were used to study chromosomal aberrations (CA) after i.p. administration and direct effects of five well known carcinogenic-mutagenic chemicals (aflatoxin B1, Aroclor 1254, benzidine, benzo[a]pyrene and 20-methyl-cholanthrene). Injections with distilled water and corn oil served as the two control groups. The induction rate of CA in the cells of the fish species exposed to the chemicals tested for 48 hr clearly shows not only an increase in the CA frequency in a dose-response manner above the control, but also a species response dependency. The results show that the in vivo CA method in the fish system proved to be an excellent means to detect or investigate water-borne or internally administered carcinogenic-mutagenic agents.

Comparison of DNA-repair synthesis, chromosome aberrations and induction of micronuclei in cultured human fibroblast, Chinese hamster ovary and central mudminnow (Umbra limi) cells exposed to chemical mutagens

In mammalian cells it has previously been observed that low DNA-repair activity is correlated with high chromosome-aberration frequency. Since fish cells typically express comparatively low amounts of DNA repair, the chromosome aberration test holds potential as a sensitive fish genotoxicity assay. A comparison of in vitro DNA-repair activity showed HF greater than CHO greater than Ul-H = Ul-F following exposure to MNNG and 4NQO. Although peak chromosome-aberration frequency varied CHO greater than Ul-H greater than HF, at comparable mutagen concentrations the relationship was Ul-H greater than HF greater than CHO following 4NQO exposure and Ul-H greater than HF = CHO after MNNG exposure. Analyzing for chromosome aberrations at high mutagen concentrations was not possible due to mitotic inhibition/toxicity which varied according to the mutagen and cell line. Micronuclei frequency varied CHO greater than Ul-H greater than HF = Ul-F. In CHO and Ul-H, a 10-15-fold increase over controls compares with only a 2-3-fold increase for HF and Ul-F. These differences are likely related, in part, to the cell-division rate of each line and the coincident repair of the damaged DNA. Reasons for the lack of negative correlation between DNA repair and chromosomal damage in fish cells are discussed.

Sister chromatid exchange analysis in cultured peripheral blood leukocytes of the coldwater marine fish, Pacific staghorn sculpin (Leptocottus armatus): a feasible system for assessing genotoxic marine pollutants

The genotoxicity of environmental contaminants and test compounds to aquatic and marine fish has primarily been assessed by in vivo techniques that require sacrifice of the test organism for analysis. The major objective of this research was to develop an in vitro sister chromatid exchange (SCE) assay which would utilize cultured peripheral blood leukocytes (PBLs) of a coldwater marine fish species. Use of PBLs in cytogenetic genotoxicity tests has several advantages, the major one being that the experimental fish need not be sacrificed for sample collection. In addition, this nondestructive method of tissue collection permits the investigator to take multiple samples from a single individual and thereby allows the use of an individual as its own control and to monitor its SCE frequency over time. A suitable in vitro culture method for fish PBLs was a prerequisite for cytogenetic analysis of this tissue. The in vitro culture conditions necessary to provide a sufficient number of dividing cells for performance of the SCE assay were established in our laboratory for the PBLs of the Pacific staghorn sculpin (Leptocottus armatus), a common bottom-dwelling Puget Sound fish. The major components of this culture system are heparinized whole blood, fetal bovine serum-supplemented enriched tissue culture medium (RPMI 1640), purified protein derivative of tuberculin as a mitogen, and an incubation temperature of 13.5 degrees C. This in vitro PBL culture system is unique because it involves cultured blood cells from a coldwater marine fish species. Using this culture method, SCE induction was investigated in Pacific staghorn sculpin PBLs which had been exposed in vitro to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a known direct-acting inducer of SCEs. Cultured cells exposed in vitro responded to MNNG in a dose-related manner in regard to SCE induction, and the frequency of "outlier" cells increased at the higher concentrations of MNNG. With further development, this technique may be adaptable for use with in vivo genotoxicity studies and provide information concerning the induction and persistence of chemically induced SCEs in fish. This PBL/SCE assay may also be a feasible assessment tool for detecting exposure of marine fish to genotoxic environmental contaminants in laboratory and field situations.

In vivo induction of sister-chromatid exchange in Umbra limi by the insecticides endrin, chlordane, diazinon and guthion

Central mudminnows, Umbra limi, were exposed to the insecticides endrin, chlordane, diazinon and guthion at concentrations of 5.4 X 10(-12) M to 5.4 X 10(-9) M in the aquaria water. Endrin, chlordane and diazinon caused significant increase in the frequencies of SCE. The results of these tests in part are in contrast to previous work which did not find endrin to be mutagenic. Our results suggest that the in vivo SCE test is an efficacious method of detecting mutagenic pesticides in water.

Induction of chromosomal aberrations in fish Boleophthalmus dissumieri after exposure in vivo to mitomycin C and heavy metals mercury, selenium and chromium

The possibilities were explored of using fish as a cytogenetic model in vivo for the detection of potential mutagens. Boleophthalmus dussumieri (2n = 46, fairly large acrocentric chromosomes), an edible mud-skipper and a widely occurring Goby along the Bombay coast, was chosen as the test species after screening 20 species of fish locally available. I.m. injections of mitomycin C in the dose range of 0.5-2.0 mg/kg body weight resulted in a significant increase in the frequency of aberrations per metaphase compared with the control. A dose-response effect was also evident. The types of aberration observed included chromatid and isochromatid breaks, fragments, rings, exchanges and unclassified markers. A significant increase in the number of gaps was also observed. Clastogenic effects of metals such as Hg, Se and Cr in the form of phenyl mercuric acetate, selenium dioxide and sodium dichromate following direct (i.m. injections) and indirect (dissolved in the aquarial water) exposures were studied. A marked enhancement was noticed in the aberration frequency at most of the dose levels tested. Spontaneous chromosomal aberrations in this species were rather rare and occurred at a rate close to zero. If developed along proper lines, fish could be a useful biological model for studying the teratogenic, carcinogenic and mutagenic effects of environmental chemicals.

The killifish Nothobranchius rachowi, a new animal in genetic toxicology

Nothobranchius rachowi, a tropical fish that belongs to the family of the Cyprinodontidae, is introduced as a new animal for genetic toxicological studies. The karyotype of N. rachowi consists of 16 large chromosomes. This species can be used for studies on chromosomal aberrations as well as for observations on sister-chromatid exchanges (SCEs). Exposure to 120 mg ethyl methanesulphonate per litre water induced 0.66 SCEs per chromosome, whereas the spontaneous frequency amounted to 0.10 SCEs per chromosome. A comparative study with Umbra pygmaea indicated that the sensitivity for this kind of mutagen is the same in both species. After exposure of N. rachowi to 50 mg cyclophosphamide per litre of water, 0.35 SCEs per chromosome were induced, showing that promutagens could be detected. It is postulated that N. rachowi can be used for screening both pure compounds and surface water for genotoxic potential. An advantage of N. rachowi over Umbra spp. is that the former species is more likely to breed under laboratory conditions.

Elevated sister chromatid exchange rate in lymphocytes of the European eel (Anguilla anguilla) with cauliflower tumor

Sister chromatid exchange (SCE) frequency and chromosomal aberration were studied in cultured lymphocytes from the European eel (Anguilla anguilla) with cauliflower tumors. SCE was significantly increased in the affected fishes compared with normal controls, whereas chromosomal aberration did not. In comparison to normal cells, the lymphocytes responding to phytohemagglutinin M (PHA-M) in cultures from tumorous eels showed no evidence of cell cycle retardation. A possible mechanism for elevation of SCE and the significance of this finding relation to the etiology were discussed.

Anaphase aberrations: a measure of genotoxicity in mutagen-treated fish cells

Rainbow trout gonad cells (RTG-2) were cultured for various lengths of time in the presence of several classes of known mutagenic chemicals and several related compounds that possessed no known mutagenic/carcinogenic activity. During the course of exposure the cells were examined for the presence of abnormalities in the chromosome arrangement of anaphase figures during mitosis. Untreated and solvent-treated (dimethylsulfoxide-treated) cells exhibited a background abnormality rate of 12% with only minor chromosomal defects being observed. This was also true for those cells exposed to naphthol and anthracene, two chemicals with no proven mutagenic or carcinogenic activity. Conversely, significant increases in the frequency of anaphase aberrations were produced in cells treated with N-methyl-N'-nitro-N-nitrosoguanidine, benzo(a)pyrene, 9-aminoacridine and mitomycin-C. These abnormalities were also far more complex and extensive than those observed in the control and nonmutagen-treated cells. Many species of fish have extremely small and numerous chromosomes, making resolution of chromosome defects such as sister chromatid exchange and deletions more difficult than in most mammalian diploid cells, which generally have larger and fewer chromosomes. Examination of cells during anaphase eliminates the need to observe each chromosome separately as well as the need to produce well-spread metaphase chromosomes. Since the sensitivity of anaphase aberrations to known mutagenic/carcinogenic compounds appears to be quite high in trout cells and since hundreds of suitable cells are available for analysis, this may be an appropriate alternative or addition to some of the more standard chromosome macrolesion tests developed in mammalian systems.

Sister-chromatid exchanges: a report of the GENE-TOX program

The effects of a number of chemicals on sister-chromatid exchange (SCE) frequencies in in vivo and in vitro systems are reviewed. Standardized protocols for future SCE testing in important systems, as well as for evaluation of test results, are presented. Data reported thus far suggest that SCE analysis may prove useful, especially at a secondary level, as a test of mutagenic carcinogens. Strengths and limitations of SCE analysis are summarized as a guide for future evaluation and use of this procedure.

Induction of sister-chromatid exchanges in fish exposed to Rhine water

The induction was studied of sister-chromatid exchanges in gill and testis of fish exposed to Rhine water. The eastern mudminnow, Umbra pygmaea, was chosen because the usefulness of this species with a karyotype of 22 large chromosomes had been demonstrated in cytogenetic mutagenicity testing. Fish exposed to Rhine water for 3 and 11 days showed a 2-fold and 3-fold higher SCE rate resp., compared with fish exposed to ground water of drinking water quality. There was no difference in SCE rate between gill and testicular cells before and after exposure. GLC/MS analysis indicated that different classes of chemical compounds may be involved in the cytogenetic effects found in fish. The mudminnow has proved to be a useful fish species for biological monitoring of mutagens in polluted waters. The SCE test may be a suitable test system to prescreen their mutagenic potential.

The effects of short- and long-term exposure of chick embryos to neutral red on the frequency of sister-chromatid exchange

The chick embryo was used to study the effects of neutral red (NR) on the frequency of sister-chromatid exchange (SCE) in specific tissues exposed to this mutagen for short and long periods as development proceeded. In short-term trials, aqueous NR at doses of 10, 25 and 100 micrograms was injected in 3-day and 6-day embryos. In each case, embryos were also treated with 5-bromodeoxyuridine (BrdU) for a 24-h period (two cell cycles) and harvested at 4 days and 7 days, resp. A long-term exposure (about 8 cell cycles) was achieved by exposing embryos to NR from day 3 to day 7 of incubation. At a NR dose of 25 micrograms, the chronic exposure resulted in a doubling of the rate of SCE (11.4/cell) over that observed in embryos exposed for only 24 h at either days 3-4 (6.0/cell) or days 6-7 (6.0/cell). At 100 micrograms of NR, the same relationship held with SCE rates of 14.2/cell for the chronic exposure versus rates of 8.0/cell (3-4 days) and 6.9/cell (6-7 days). At 10 micrograms of NR, no such accumulation of SCE occurred upon long-term treatment. These results show an enhanced SCE response upon growth of embryonic cells in the presence of NR for several days. This may be the result of the persistence of past lesions with the addition of more lesions upon continued exposure to NR.

Tissue-specific induction of sister chromatid exchanges by ehtyl carbamate in mice

Sister chromatid exchange (SCE) techniques were used to analyze the genetic effects of ethyl carbamate (urethane) in cultured mouse-bone marrow cells, and in several different mouse tissues in vivo. Ethyl carbamate concentrations up to 5.0 mg/ml were ineffective in causing a significant elevation of SCE in vitro. After in vivo drug administration, bone marrow, liver and spermatogonial cells all revealed significant dose-related increases in SCE. Baseline and relative incremental levels of SCE were somatic vs germ tissue-specific. Regenerating liver cells exhibited significantly greater absolute SCE values than all other tissues examined. Marrow cells revealed intermediate values, while germ cells were the least sensitive in SCE responsiveness. Spermatogonia required a fourfold higher dose, over that effective in somatic tissues, to promote an approximate doubling of the baseline SCE level. In vivo SCE analysis affords sensitive risk assessments for different tissues. Thus, this approach; should be generally useful for studying compounds with questionable mutagenic potential, and/or those exerting target organ specificities of related biological activity (eg, toxicity, carcinogenesis).

Sister chromatid exchange studies in human fibroblast-rat hepatocyte co-cultures: a new in vitro system to study SCEs

To approximate better the metabolic reactions that take place in vivo yet maintain the simplicity and reproducibility of in vitro systems, we have developed a co-culture system making use of freshly isolated rat hepatocytes and confluent human fibroblasts for the study of SCE induction by genotoxic agents. Hepatocytes were obtained from male rats by reverse collagenase perfusion and plated over low-passage male human fibroblasts. Preliminary studies demonstrated that although the number of hepatocytes plated was not critical, the best attachment to, and coverage of, the fibroblasts occurred when between 10 x 10(6) and 20 x 10(6) hepatocytes were plated/100 mm tissue culture dish. Results with the promutagen cyclophosphamide showed that the hepatocytes could metabolize the compound and deliver active moieties to the fibroblasts resulting in a linear dose-dependent increase in SCE frequencies. Control fibroblast cultures lacking hepatocytes displayed no increase in SEC frequencies. Control fibroblast cultures lacking hepatocytes displayed no increase in SEC frequencies following cyclophosphamide administration.