A multiple end-point approach to evaluation of cytotoxicity and genotoxicity of erythrosine (FD and C Red No. 3) in a V79 hepatocyte-mediated mutation assay

Gastrointestinal toxicity following sub-acute exposure of erythrosine in rats: biochemical, oxidative stress, DNA damage and histopathological studies

Erythrosine, a synthetic food dye, has been controversial due to its potential health risks. This study examines the effect of erythrosine on activity of antioxidative enzymes, oxidative stress indices, DNA damage through comet assay, and histopathological changes on stomach, intestine, and colon over a period of 28 days in rats. Twenty-four rats were randomly divided into four groups (n = 6). The first is the control group and then one each for three doses of erythrosine based on acceptable daily intake (¼ ADI, ½ ADI, and ADI, 0.1 mg/kg body weight). The results revealed that with increasing dosages the activity of catalase decreased in stomach and intestine but in colon, the catalase activity increased. Superoxide dismutase and glutathione-S-transferase activity decreased in dose-dependent manner in all three tissues. While, in stomach and intestine, the acetylcholinesterase activity showed increment in ¼ ADI dose group and then declined in ½ ADI and ADI dose-administered rats. The oxidative stress indicators showed elevated levels of lipid peroxidation, hydrogen peroxide concentration, and lactate dehydrogenase activity suggesting heightened free radical activity and potential oxidative damage. The comet test was used to evaluate DNA damage, revealing substantial damage in the erythrosine administered groups. Histopathological examination showed inflammatory infiltration and other degenerative changes in gastrointestinal tract, highlighting the dye's adverse effects. The research underscores the need for a comprehensive reevaluation of the safety and toxicity of food dyes like erythrosine, especially considering the inconsistencies in existing studies regarding the dye's safety.

Assessment of synthetic food dye erythrosine induced cytotoxicity, genotoxicity, biochemical and molecular alterations in Allium cepa root meristematic cells: insights from in silico study

Background

Synthetic food dyes are being exponentially used in food products and scarce studies regarding their toxicities and safety raise concern. Erythrosine is one of the synthetic food dyes being used in jams, fig, pineapple marmalades, dairy products, soft drinks, pickles, relishes, smoked fish, cheese, ketchup, maraschino cherries and a variety of other foods.

Methodology

In this study the cyto-genotoxic effect of erythrosine was evaluated, using root meristematic cells of Allium cepa for the cellular and molecular alternations at concentrations 0.1, 0.25, 0.5 and 1 mg/mL.

Results

The results revealed a significant decrease of 57.81% in the mitotic index after 96 h at the 0.1 mg/mL concentration. In biochemical analysis, the malondialdehyde content increased significantly (5.47-fold), while proline content, catalase activity and superoxide dismutase activity decreased gradually in a concentration-dependent manner showing a maximum decrease of 78.11%, 64.68% and 61.73% respectively at the highest concentration after 96 h duration. The comet assay revealed increased DNA damage with increasing concentration and attenuated total reflectance- Fourier transform infrared spectroscopy (ATR-FTIR) analysis showed significant alterations in biomolecules as indicated by multivariate analysis, i.e. Principal Component Analysis (PCA). Furthermore, molecular docking demonstrated a strong binding energy (Gbest = -11.46 kcal/mol) and an inhibition constant (Ki) of 3.96 nM between erythrosine and the DNA minor groove.

Conclusion

The present study's findings revealed the cytotoxic and genotoxic potential of erythrosine on A. cepa root cells. Further, the study also proposed the usefulness of A. cepa as a model system for studying the toxicity of food additives.

Evaluation of potential genotoxicity of five food dyes using the somatic mutation and recombination test

In this study, different concentrations of five food dyes (amaranth, patent blue, carminic acid, indigotine and erythrosine) have been evaluated for genotoxicity in the Somatic Mutation and Recombination Test (SMART) of Drosophila melanogaster. Standard cross was used in the experiment. Larvae including two linked recessive wing hair mutations were chronically fed at different concentrations of the test compounds in standard Drosophila Instant Medium. Feeding ended with pupation of the surviving larvae. Wings of the emerging adult flies were scored for the presence of spots of mutant cells which can result from either somatic mutation or somatic recombination. For the evaluation of genotoxic effects, the frequencies of spots per wing in the treated series were compared to the control group, which was distilled water. The present study shows that carminic acid and indigotine demonstrated negative results while erythrosine demonstrated inconclusive results. In addition 25 mg mL(-1) concentration of patent blue and 12.5, 25 and 50 mg mL(-1) concentrations of amaranth demonstrated positive results in the SMART.

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Cytogenetic evaluation and DNA interaction studies of the food colorants amaranth, erythrosine and tartrazine

Food coloring agents, amaranth, erythrosine and tartrazine have been tested at 0.02-8mM in human peripheral blood cells in vitro, in order to investigate their genotoxic, cytotoxic and cytostatic potential. Amaranth at the highest concentration (8mM) demonstrates high genotoxicity, cytostaticity and cytotoxicity. The frequency of SCEs/cell was increased 1.7 times over the control level. Additionally, erythrosine at 8, 4 and 2mM shows a high cytotoxicity and cytostaticity. Finally, tartrazine seems to be toxic at 8 and 4mM. No signs of genotoxicity were observed. Reversely, tartrazine showed cytotoxicity at 1 and 2mM. Furthermore, spectroscopic titration studies for the interaction of these food additives with DNA showed that these dyes bind to calf thymus DNA and distinct isosbestic points are observed clearly suggesting binding of the dyes to DNA. Additionally DNA electrophoretic mobility experiments showed that these colorants are obviously capable for strong binding to linear dsDNA causing its degradation. PCR amplification of all DNA fragments (which previously were pre-treated with three different concentrations of the colorants, extracted from agarose gel after separation and then purified), seems to be attenuated with a manner dye concentration-dependent reflecting in a delayed electrophoretic mobility due to the possible binding of some molecules of the dyes. Evaluation of the data and curves were obtained after quantitative and qualitative analysis of the lanes of the gel by an analyzer computer program. Our results indicate that these food colorants had a toxic potential to human lymphocytes in vitro and it seems that they bind directly to DNA.

Assessment of genotoxicity of 14 chemical agents used in dental practice: Ability to induce chromosome aberrations in Syrian hamster embryo cells

To assess the genotoxicity of 14 chemical agents used as locally applied agents in dental practice, the ability of these agents to elicit chromosome aberrations was examined using Syrian hamster embryo (SHE) cells. Chromosome aberrations in SHE cells were induced by treatment with three of eight chemical agents used as endodontic medicaments, i.e. ethylenediaminetetraacetic acid (EDTA), formocresol (a mixture of formalin and tricresol), and sodium arsenite. The other five chemical agents, i.e. chloramphenicol, p-chlorophenol, p-phenolsulfonic acid, sodium hypochlorite, and tetracycline hydrochloride exhibited a negative response for chromosome aberrations. Assessment of three dyes used for disclosing dental plaque showed chromosome aberrations induced by basic fuchsin but not by acid fuchsin and erythrosine B. Three local anesthetics, lidocaine hydrochloride, prilocaine hydrochloride, and procaine hydrochloride, were negative for chromosome aberrations. Among the ten chemical agents that exhibited a negative response in the assay, p-chlorophenol, sodium hypochlorite, and erythrosine B induced chromosome aberrations in SHE cells when treated in the presence of exogenous metabolic activation. The percentages of cells with polyploidy or endoreduplication were enhanced by formocresol, sodium arsenite, p-chlorophenol, p-phenolsulfonic acid, sodium hypochlorite, erythrosine B, prilocaine hydrochloride, and procaine hydrochloride in the absence or presence of exogenous metabolic activation. Our results indicate that the chemical agents that had a positive response in the present study are potentially genotoxic to mammalian cells.

The application of in vitro data in the derivation of the acceptable daily intake of food additives

The acceptable daily intake (ADI) for food additives is commonly derived from the NOAEL (no-observed-adverse-effect level) in long-term animal in vivo studies. To derive an ADI a safety or uncertainty factor (commonly 100) is applied to the NOAEL in the most sensitive test species. The 100-fold safety factor is considered to be the product of both species and inter-individual differences in toxicokinetics and toxicodynamics. Although in vitro data have previously been considered during the risk assessment of food additives, they have generally had no direct influence on the calculation of ADI values. In this review 18 food additives are evaluated for the availability of in vitro toxicity data which might be used for the derivation of a specific data-derived uncertainty factor. For the majority of the food additives reviewed, additional in vitro tests have been conducted which supplement and support the short- and long-term in vivo toxicity studies. However, it was recognized that these in vitro studies could not be used in isolation to derive an ADI; only when sufficient in vivo mechanistic data are available can such information be used in a regulatory context. Additional short-term studies are proposed for the food additives which, if conducted, would provide data that could then be used for the calculation of data-derived uncertainty factors.

Comparison of HepG2 feeder cells generated by exposure to gamma-rays, X-rays, UV-C light or mitomycin C for ability to activate 7,12-dimethylbenz[a]anthracene in a cell-mediated Chinese hamster V79/HGPRT mutation assay

The cell-mediated Chinese hamster V79/HGPRT mutagenicity assay is an established in vitro testing method. Although gamma-irradiated human HepG2 hepatoma cells have been used recently for chemical activation, an alternative is now needed due to scheduled retirement of the available gamma-source. X-irradiation, 254 nm UV-C light and mitomycin C were examined as possible HepG2 mitotic inhibitors, and treated cells compared for activation of 7, 12-dimethylbenz[a]anthracene (DMBA). In colony-forming assays, V79 and HepG2 cells differed in sensitivity to DMBA, with V79 survival declining sharply between 1-2.5 microM (LD50=1.75 microM) while HepG2 survival decreased gradually, beginning at 0.01 microM DMBA (LD50=0.045 microM). When HepG2 feeder cells generated by each method were included in V79/HGPRT mutation assays, activation of 1 microM DMBA was found to vary according to the mitotic inhibitor used, with mutation frequencies decreasing in the order 4000 rads gamma-rays>25 microg/ml mitomycin C>4000 rads X-rays>25 J/m2 UV-C light. Only assays containing gamma-irradiated HepG2 cells generated an increase (2-3-fold) in mutation frequency when DMBA exposure was extended from 24 to 48 h. The effect of HepG2 preincubation with either Aroclor 1254 or DMBA on feeder cell activation of DMBA was also assessed using concentrations of Aroclor 1254 (10 microg/ml) or DMBA (1.0 microM) which were found to produce optimum induction of ethoxyresorufin-O-deethylase (EROD) activity (3.1-fold and 2-fold increases, respectively). Compared to results obtained with uninduced HepG2 cells, assays incorporating HepG2 cells activated by either Aroclor 1254 or DMBA produced slightly increased V79/HGPRT mutation frequencies after 24 h of exposure to mutagen; however, a 48 h incubation with mutagen in the presence of HepG2 preincubated with either Aroclor 1254 or DMBA resulted in higher mutation frequencies regardless of the mitotic inhibitor treatment. EROD activity was also induced 1.4-fold following exposure of HepG2 cells to mitomycin C alone. Although gamma-irradiation remains the treatment of choice for producing metabolically active HepG2 feeder cells, comparison of the alternatives tested suggests that mitomycin C would be a convenient and suitable replacement.

In vitro investigation of toxaphene genotoxicity in S. typhimurium and Chinese hamster V79 lung fibroblasts

The polychlorinated pesticide toxaphene has been identified as a persistent environmental contaminant and is of particular concern in the Great Lakes and Arctic regions of Canada. Inconsistencies in published in vitro genotoxicology studies have hindered risk assessments of toxaphene exposure. When toxaphene mutagenicity was re-evaluated in the Ames Salmonella/microsome assay at 10-10,000 microg/plate, a dose-dependent increase in His revertants occurred in all five strains of S. typhimurium tested (TA97, TA98, TA100, TA102 and TA104) with higher mutation frequencies observed in the absence of S9 metabolic activation. However, the mutagenic potential of toxaphene was relatively low with concentrations greater than 500 microg/plate required to induce mutation. Toxaphene genotoxicity was also examined in a mammalian system using Chinese hamster V79 lung fibroblasts with metabolic activation provided by human HepG2 hepatoma cells. Genotoxicity of 1-10 microg/ml toxaphene was examined by measuring the frequency of sister chromatid exchange (SCE) and mutation induction at the hypoxanthine guanine phosphoribosyl transferase (HGPRT) gene locus. Although small increases in SCE were observed at toxic concentrations of toxaphene approaching the LD50 (10 microg/ml), they were not found to be statistically significant relative to control. Toxaphene was also unable to induce HGPRT mutagenesis at the concentrations tested. These results show that while toxaphene is a weak, direct-acting mutagen in the Ames Salmonella Test, convincing evidence of dose-dependent SCE induction and mutagenicity at the HGPRT gene locus could not be demonstrated in V79 cells.

An assessment of the in vivo clastogenicity of erythrosine

In an investigation of the in vivo clastogenic potential of the food colouring erythrosine (ER), male B6C3F1 mice were treated by ip injection at doses of 50, 100 and 200 mg/kg, repeated 24 hr apart. Signs of toxicity were observed at the highest dose of ER administered. The three cytogenetic endpoints analysed were sister chromatid exchanges (SCEs) in peripheral blood lymphocytes (PBLs), micronuclei in bone marrow polychromatic erythrocytes (PCEs), and micronuclei in peripheral blood reticulocytes (PBRs). SCE frequencies in PBLs were 4.13, 4.58, 4.33 and 4.60 SCE/cell at 0, 50, 100 and 200 mg ER/kg, respectively. At the same doses, the frequencies of micronucleated PCEs were 3.5, 3.2, 2.0 and 2.5/1000 PCEs. Micronuclei in PBRs ranged from 1.2 to 3.6 and from 1.4 to 3.0/1000 PBRs in control and treated mice, respectively. These results indicate that ER is inactive as a clastogen in mouse blood and marrow cells. This result supports the hypothesis of a non-genotoxic mechanism for ER carcinogenicity.

Cytotoxic and genotoxic properties of tert.-butyl-p-quinone (TBQ) in an in vitro assay system with Chinese hamster V79 cells and in strain D7 of Saccharomyces cerevisiae

tert.-Butyl-p-quinone (TBQ), a major metabolite of the phenolic antioxidant tert.-butyl-4-hydroxyanisole (BHA), was examined for cytotoxic and genotoxic properties in an in vitro assay system with Chinese hamster V79 cells and in diploid strain D7 of Saccharomyces cerevisiae. TBQ was prepared from BHA by oxidative demethylation with sodium nitrite at low pH. Spectroscopic analyses identified the crystalline reaction product as TBQ with a purity close to 100%. Cytotoxicity of TBQ was determined by cloning efficiency in the absence of hepatocyte activation. TBQ reduced colony size of V79 cells at 0.4 micrograms/ml, prevented growth of 50% of the cells at 0.6 micrograms/ml, and was lethal to 100% of the cells at concentrations above 1.0 micrograms/ml. TBQ was 6-7 times more cytotoxic to V79 cells than TBHQ, a related BHA metabolite, and 100 times more cytotoxic than BHA. At dose levels of 0.2, 0.4 and 0.6 micrograms/ml of medium, TBQ did not increase significantly the frequency of sister-chromatid exchanges (SCE) in V79 cells and did not consistently increase the frequency of mutation to thioguanine resistance (TGR) at the hgprt gene locus either alone or with activation by rat hepatocytes. Incubation with TBQ for 4 h at pH 3.6 without activation resulted in only small increases in the frequency of gene conversion and reverse mutation in strain D7 of Saccharomyces cerevisiae. However, exposure to TBQ alone in growth medium for 24 h, produced inconsistent results. From these studies it was concluded that TBQ was cytotoxic but not genotoxic to V79 cells; and may be weakly genotoxic to strain D7 of S. cerevisiae.

Evaluation of genotoxicity of tert.-butylhydroquinone in an hepatocyte-mediated assay with V79 Chinese hamster lung cells and in strain D7 of Saccharomyces cerevisiae

tert.-Butylhydroquinone (TBHQ) has been reported to be genotoxic in some short-term assays but non-genotoxic in others. We have examined cytotoxicity and genotoxicity of TBHQ, a principal metabolite of the phenolic antioxidant 2(3)-tert.-butyl-4-hydroxyanisole (BHA), in an hepatocyte-mediated assay with V79 Chinese hamster lung cells including both sister-chromatid exchange (SCE) and thioguanine-resistance (TGR) endpoints. The ability of BHA and of TBHQ to elicit a genotoxic response in Saccharomyces cerevisiae strain D7 was also investigated. In V79 cytotoxicity tests, TBHQ without hepatocytes produced a 50% reduction in colony formation at 4.2 micrograms/ml and was lethal to 100% of the cells at concentrations above 5 micrograms/ml. At partially cytotoxic dose levels, (0.17-3.4 micrograms/ml of medium), TBHQ sometimes increased significantly the frequency of SCE. TBHQ also produced sporadic statistically significant increases in the mutation frequency at the HGPRTase (TGR) gene locus when tested alone or with activation by rat or hamster hepatocytes. Mitotic gene conversion and reverse mutation were not induced in strain D7 of Saccharomyces cerevisiae by exposure to BHA or to TBHQ for 4 h at concentrations as high as 200 micrograms/ml for BHA or 500 micrograms/ml for TBHQ, either alone or with activation by rat-liver S9. Incubation of the yeast cells with BHA or TBHQ for 24 h in growth medium without activation also did not induce genotoxic activity. The slight and sporadic response to TBHQ in the V79 test system may indicate weak genotoxicity which is sensitive to slight differences in test conditions. The classification and test strategies adopted for compounds such as TBHQ could have important implications for regulatory decisions and for the validation of short-term tests.

Genotoxicity of 1-nitronaphthalene in Chinese hamster V79 cells

1-Nitronaphthalene (1-NN) has been identified in the U.S. National Toxicology Program as a non-carcinogen showing some evidence of in vitro genotoxicity. We tested this compound in Chinese hamster V79 cells at 20-80 micrograms/ml with two endpoints: sister-chromatid exchange (SCE) and thioguanine resistance (TGR), with 5 repeat experiments. The SCE values in the presence of rat or hamster hepatocytes were consistently above the 95% and usually the 99% upper confidence limits for the corresponding control. Without hepatocyte activation, the control upper confidence limits were not exceeded except in one experiment in which the control SCE value was unusually low. TGR was scored both as proportion of plates with mutant colonies and as number of mutant colonies per plate. In 2 of 5 experiments, these values exceeded control 95% or 99% upper confidence limits; on the other hand, these values were substantially lower than those of the positive controls, dimethylbenz[a]anthracene (2.6 micrograms/ml) with activation and ethyl methanesulfonate (155 microgram/ml), which is direct-acting. For TGR, activation of 1-NN by either rat or hamster hepatocytes produced inconsistent results. Overall we would consider this compound to be a weak genotoxin, to which a cancer bioassay would be expected to be relatively insensitive.

Multigeneration study of FD & C Red No. 3 (erythrosine) in Sprague-Dawley rats

Sprague-Dawley rats received dietary admixtures containing 0.0, 0.25, 1.0 or 4.0% FD & C Red No. 3 (25 rats/sex/group) in a three-generation reproduction study. Each generation was bred twice and breeders for subsequent generations were selected after weaning of the second mating from each generation. There were no compound-related adverse effects on reproductive indices and no gross anomalies were observed. The body weights of parents and pups were significantly reduced (P less than 0.05) in all generations at the 4.0% dietary concentration. Maternal body-weight gain during gestation was frequently reduced in the 1.0 and 4.0% groups. The conservative no-observed-adverse-effect level established in this study was 0.25% (approximately 149 and 255 mg/kg body weight/day for males and females, respectively).

Evaluation of genotoxicity of N-nitrosodibenzylamine in Chinese hamster V79 cells and in Salmonella

Health concerns have arisen due to the formation of N-nitrosodibenzylamine (NDBzA; CAS No. 5336-53-8) in pork processed in a new type of rubber netting. In view of the potent carcinogenicity of related nitrosamines (e.g. N-nitroso-n-dibutylamine and N-nitrosodiethylamine), NDBzA was evaluated for genotoxicity in vitro in both Chinese hamster V79 cells and in Salmonella. In V79 cells, concentrations up to 25 micrograms/ml were tested with and without activation by rat or hamster hepatocytes. Significant elevation of SCE frequency was seen only at 25 micrograms/ml in the presence of uninduced hamster hepatocytes. Mutation to 6-thioguanine resistance was observed at 25 micrograms/ml, in the absence of hepatocytes and in the presence of induced (Aroclor 1254) or uninduced hamster hepatocytes, but not with rat hepatocytes. With uninduced rat hepatocytes, a small but significant (p less than 0.05) increase in the mutation frequency was seen with 10 micrograms/ml NDBzA. In the Salmonella assay, using a pre-incubation protocol and concentrations up to 1000 micrograms/ml, NDBzA was negative in strain TA98, and in TA100 with rat S9, but was positive at the highest dose in TA100 with hamster S9, and more strongly with Aroclor 1254-induced hamster S9. When activated by uninduced rat or hamster hepatocytes, as opposed to S9, NDBzA was negative with all tester strains. Hamster hepatocytes activated more than rat in the V79 studies, and hamster S9 was more strongly activating in the Salmonella assay. These results indicate that NDBzA is weakly mutagenic to both Salmonella and V79 cells.

Comparative genotoxicity of 3 procarcinogens in V79 cells as related to glutathione S-transferase activity of hepatocytes from untreated rats and those fed 2% butylated hydroxyanisole

When 7,12-dimethylbenz[a]anthracene (DMBA) and aflatoxin B1 (AFB1) were activated by hepatocytes from Fischer 344 rats fed a diet containing 2% butylated hydroxyanisole (BHA), frequencies of mutation to 6-thioguanine resistance (TGR) at the HGPRTase gene locus and to ouabain resistance (OuR) at the Na+,K(+)-ATPase gene locus in V79 cells were 30-70% less than those obtained with hepatocytes from untreated controls. A difference in the mutation frequency did not occur when dimethylnitrosamine (DMN) was activated by BHA induced- rather than control-hepatocytes. Analysis of hepatocytes from rats fed 2% BHA showed a small (1.5-fold), but significant, increase in glutathione levels over that in the controls but no change in activity of cytochrome P450. Cytosolic glutathione S-transferase (GST) activity was increased 2-3-fold in hepatocytes from rats fed the 2% BHA diet. These results suggest that mutagenic response to DMBA and AFB1 is reduced, at least in part, because of BHA-induction of hepatocyte GST activity; while activation of DMN can occur by pathway(s) unaffected by BHA-induction of these liver enzymes. In contrast to mutation frequencies, significant differences between BHA- and control-activation in the production of sister-chromatid exchange (SCE) and micronucleus formation (MN) were not detected with any of the genotoxins. It was concluded that the mechanism(s) by which SCE and MN occur are likely unrelated to the capacity of BHA to induced activity of hepatic enzymes, e.g. the GSH S-transferases, that directly or indirectly affect mutation end-points.

A statistical evaluation of the reproducibility of micronucleus, sister-chromatid exchange, thioguanine-resistance and ouabain-resistance assays in V79 cells exposed to ethyl methanesulfonate and 7,12-dimethylbenz[a]anthracene

In contrast to the "validation" of short-term in vitro genotoxicity assays by concordance with the rodent cancer bioassay, the present report describes the multiple replication of 4 short-term tests with V79 cells (micronucleus assay, MN; sister-chromatid exchange, SCE; ouabain resistance. OUR; and thioguanine resistance, TGR) within the same assay system following exposure to each of two genotoxins, ethyl methanesulfonate (direct acting) and 7,12-dimethylbenz[a]anthracene (indirect acting). Reproducibility, proportion of genotoxins correctly identified, and proportion of non-genotoxins correctly identified by each test were each determined statistically. Decision rules were formulated to declare a positive response in each assay, and overall accuracy of each was determined. Statistical analysis of the data, obtained under standardized test conditions, showed that for these two chemicals SCE identified 100% of genotoxins and 86% of non-genotoxins, with overall accuracy of prediction of 93%; TGR identified 98% of genotoxins and 74% of non-genotoxins, with overall accuracy of 86%; MN identified 78% of genotoxins and 84% of non-genotoxins, with overall accuracy of 81%; while OUR indicated 100% of genotoxins, but only 50% of non-genotoxins, and only 76% overall accuracy. The results suggested that the best overall accuracy of classification with the V79 assay system could be achieved by measurement of SCE in combination with thioguanine resistance.

Validity of in vitro testing

In summary, the extent of toxicity studies which can be carried out with bound residues of nitroimidazole drugs will be dictated by the availability and the amount of residues that can be produced. For evaluating their toxicity the use of the Salmonella assay, which has been proven to be sensitive for the parent drugs, is proposed. Furthermore, it is suggested that the toxicity of bound residues for in vivo effects should be investigated in cells of target tissues, such as the epithelial cells of the gastrointestinal tract. Nuclear aberration and sister chromatid exchange assays in this tissue would be good candidates for evaluation. It should be pointed out also that an examination of the literature for genotoxic effects of nitroimidazole drugs reveals an apparent contradiction, especially in the context of genotoxicity testing strategy discussed above. It appears first that these drugs are potent mutagens in vitro in microbial systems (Salmonella and yeast). However, they are not active in mammalian cells in vitro, in both mutation and chromosomal aberration assays, as well as in vivo, in assays such as the dominant lethal test and the micronucleus assay. Thus, it may be of interest to speculate that, although these drugs are in vitro mutagens, they may not be in vivo mutagens in mammals. Their tumorigenic effects, which have been detected at high doses in rodents, may, therefore, be due to other than genotoxic activity. To resolve this conflict, reassessment of genotoxicity of these drugs in vivo would be a worthwhile pursuit. In addition, such seeming discrepancies would also argue strongly for toxicity screening to be conducted in a battery of complementary short-term in vitro and in vivo tests. This would help insure the likelihood of detection of at least some meaningful biological activity, which would serve to flag chemicals warranting further testing.

Evaluation of the genotoxicity of domoic acid in a hepatocyte-mediated assay with V79 Chinese hamster lung cells

Domoic acid, a recognized neurotoxin derived from contaminated samples of the blue mussel (Mytilus edulis L.), was analyzed for mutagenicity at 2 loci and for 2 cytogenetic parameters in a hepatocyte-mediated assay with V79 Chinese hamster lung fibroblasts. Genetic end-points measured were: mutation to 6-thioguanine resistance at the HGPRTase locus; mutation to ouabain resistance at the Na+,K+-ATPase locus; sister-chromatid exchange (SCE) and micronucleus frequency (MN). None of these genetic end-points was significantly affected by exposure to domoic acid at dose levels of 27.2 and 54.4 micrograms/ml with or without activation by freshly isolated rat liver hepatocytes. It was concluded that, within the limits of the test system employed, domoic acid was non-genotoxic to V79 cells.