Influence of different factors on the induction of chromosome malsegregation in Saccharomyces cerevisiae D61.M by bavistan and assessment of its genotoxic property in the Ames test and in Saccharomyces cerevisiae D7

Lack of in vivo mutagenicity of carbendazim in the liver and glandular stomach of MutaMice

BACKGROUND

Carbendazim (methyl 2-benzimidazolecarbamate, CASRN: 10605-21-7) exhibits spindle poisoning effects and is widely used as a fungicide. With respect to genotoxicity, carbendazim is deemed to be non-mutagenic in vitro, but it causes indicative DNA damage in vivo and chromosome aberrations in vitro and in vivo. In this study, we examined the mutagenicity of carbendazim in vivo.

RESULTS

MutaMice were treated with carbendazim orally at doses of 0 (corn oil), 250, 500, and 1,000 mg/kg/day once a day for 28 days. A lacZ assay was used to determine the mutant frequency (MF) in the liver and glandular stomach of mice. MutaMice were administered up to the maximum dose recommended by the Organization for Economic Co-operation and Development Test Guidelines for Chemicals No. 488 (OECD TG488). The lacZ MFs in the liver and glandular stomach of carbendazim-treated animals were not significantly different from those in the negative control animals. In contrast, positive control animals exhibited a significant increase in MFs in both the liver and glandular stomach.

CONCLUSIONS

Carbendazim is non-mutagenic in the liver and glandular stomach of MutaMice following oral treatment.

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.

Constituents of aromatic plants: II. Estragole

Estragole (ES) is a natural constituent of a number of plants (e.g. tarragon, sweet basil and sweet fennel) and their essential oils have been widely used in foodstuffs as flavouring agents. Several studies with oral, i.p. or s.c. administration to CD-1 and B6C3F1 mice have shown the carcinogenicity of ES. The 1-hydroxy metabolites are stronger hepatocarcinogens than the parent compound. Controversial results are reported for the mutagenicity of ES. However, the formation of hepatic DNA adducts in vivo and in vitro by metabolites of ES has been demonstrated.

Induction of chromosome loss in Saccharomyces cerevisiae strain D61.M by selected benzimidazole compounds

Twenty-two benzimidazole compounds were tested for induction of chromosome loss (CHRL) in the diploid yeast Saccharomyces cerevisiae strain D61.M. Six compounds tested positive for CHRL induction: mebendazole, albendazole, RS-9237-000, fenbendazole, 2-benzimidazolylacetonitrile, and thiabendazole. Mebendazole, albendazole, RS-9237-000, and fenbendazole were strongly positive only after modified testing media were used to enhance solubility. The compounds that tested negative for CHRL were 2-phenylbenzimidazole, 2-(2-pyridyl)benzimidazole, benzimidazole, 2-aminobenzimidazole, 2-amino-5,6-dimethylbenzimidazole, 2-(aminomethyl)benzimidazole dihydrochloride hydrate, 5,6-dimethylbenzimidazole, 2-guanidinobenzimidazole, 2-methylbenzimidazole, 2-(methylmercapto) benzimidazole, 1-methyl-2-phenylbenzimidazole, 2-benzimidazolylurea, RS-65255-000, oxibendazole, and RS-95005-000. One chemical, cambendazole, tested negative or only marginally positive. Modified testing medium was also used to enhance the solubility of 2-phenylbenzimidazole, oxibendazole, and RS-95005-000. Because no toxicity was observed with oxibendazole or RS-95005-000, the negative results obtained with these two compounds could not be considered definitive.

Effects of benzofuran and seven benzofuran derivatives including four carbamate insecticides in the in vitro porcine brain tubulin assembly assay and description of a new approach for the evaluation of the test data

The influence of benzofuran and 7 benzofuran derivatives, including the carbamate insecticides benfuracarb, carbofuran, carbosulfan, and furathiocarb, on the in vitro assembly kinetics of porcine brain tubulin was investigated. A new approach to the evaluation of the raw data was made based on polynomial regression and the calculation of a polynomial function of the 11th degree fitting the raw data. By this procedure it is possible to calculate the parameters defining the shape of the absorbance curves and more parameters than those used so far can be included in the analysis of substance effects. In detail, the following curve parameters of the dependence of optical absorption on time were included in the evaluation of the substances of interest: the difference between maximum and minimum absorbance as a measure for the polymerization degree, the coordinates of the turning point of the curve, the slope of the tangent at the turning point which represents the maximum reaction velocity, the mean slope between the points with 10% absorbance increase and 90% absorbance increase and the duration of the lag phase. Out of the eight compounds tested, only the carbamate insecticides had distinct effects on the in vitro polymerization of tubulin, whereas benzofuran and the three 2,3-dihydro-2,2-dimethylbenzofuran derivatives without a carbamate function were inactive. Benfuracarb, carbofuran, carbosulfan, and furathiocarb led to a dose-dependent reduction of the polymerization degree of tubulin as well as to reduction of the maximum and mean reaction velocities. The strongest effects were obtained with furathiocarb and benfuracarb.

Genotoxicity of dithiocarbamates and their metabolites

Dithiocarbamate fungicides are widely used in agriculture for protection of vegetable crops and seeds. The mutagenicity spectra of ziram, thiram, zineb S-65 and ETU were determined by employing a battery of test systems included the bacterium Salmonella typhimurium (strains TA98, TA100, TA102, TA104, TA1535, TA1538), the yeast Saccharomyces cerevisiae (strain D61.M) and the shallot Allium ascalonicum somatic cells. Plate incorporation assay with S. typhimurium demonstrated direct mutagenicity of ziram in TA100 and thiram in TA100 and TA98 whereas zineb S-65 and ETU were ineffective. Tests for mitotic chromosome malsegregation in S. cerevisiae D61.M gave positive results with thiram, zineb S-69 and ETU. In shallot somatic root-tip cells ziram, thiram and ETU induced different genetic damages e.g. mitotic disturbance, polyploidy and micronuclei.

Evaluation of benomyl and carbendazim in the in vivo aneuploidy/micronucleus assay in BDF1 mouse bone marrow

Benomyl and its active metabolite carbendazim were investigated in BDF1 mouse bone marrow to establish whether micronuclei induced by these fungicides are caused by clastogenic or aneugenic events. Micronuclei were evaluated for kinetochores using immunofluorescent antikinetochore antibodies. Kinetochore positive (K+) micronuclei are likely to arise from chromosome loss since they presumably contain intact kinetochores and are indicative of aneuploidy. Conversely, kinetochore negative (K-) micronuclei are mostly likely to contain acentric chromosome fragments arising primarily from clastogenic damage. Benomyl and carbendazim were administered as single oral doses of 0.3, 8.6 or 17.2 mmol/kg (for benomyl, equivalent to 100, 2500 or 5000 mg/kg; for carbendazim, equivalent to 66, 1646 or 3293 mg/kg). Both compounds were positive in the micronucleus test at doses of 8.6 and 17.2 mmol/kg, and an average of 82% (benomyl) and 87% (carbendazim) of the total micronucleated polychromatic erythrocytes were K+. No effects were seen with either fungicide at 0.3 mmol/kg. These results are analogous to findings with known aneugens such as vincristine but are in contrast to results with classical clastogens such as cyclophosphamide. Thus, benomyl and carbendazim induce micronuclei in mouse bone marrow cells primarily through an aneugenic mechanism.

Genotoxicity assay of five pesticides and their mixtures in Saccharomyces cerevisiae D7

Four organophosphorus pesticides (azinphos-methyl, diazinone, dimethoate, and pirimiphos-methyl), and one carbamate (benomyl) were tested for cytotoxicity, reverse mutation and gene conversion in Saccharomyces cerevisiae D7, with and without the S9 metabolic system. Furthermore, two mixtures of the above compounds, namely benomyl + pirimiphos-methyl (6/1 ratio) and dimethoate + diazinone + azinphos-methyl (10/4/6 ratio) were tested in the same experimental model. Azinphos-methyl, benomyl, and pirimiphos-methyl alone did not induce any genotoxic effect, whereas azinphos-methyl and diazinone were active in inducing reversion and gene conversion. The benomyl + pirimiphos-methyl mixture did not show any genotoxic activity. The dimethoate + diazinone + azimphos-methyl mixture was genotoxic, although an antagonistic effect between the components was observed. The addition of S9 post-mitochondrial liver fraction decreased the activity of both single and mixed genotoxic agents.

Evaluation of carbendazim for gene mutations in the Salmonella/Ames plate-incorporation assay: the role of aminophenazine impurities

Benomyl (methyl [1-[(butylamino)carbonyl]-1H-benzimidazol-2- yl]carbamate) and its major metabolite carbendazim (methyl 2-benzimidazolecarbamate) are major agricultural systemic fungicides. These compounds inhibit fungal microtubular function and thereby cause nondisjunction of chromosomes at cell division. Several investigators have proposed that these compounds can also cause gene mutations (base-pair substitutions). In this laboratory, no mutagenic activity was observed with either benomyl (analytical grade) or Benlate (samples tested up to 500 and 1200 micrograms/plate, respectively, the limit of cytotoxicity) in the Salmonella/Ames plate-incorporation test in either base-pair substitution (TA100 and TA1535) or frameshift-sensitive (TA98 and TA1537) strains with or without S9 metabolic activation. However, some carbendazim preparations caused mutations in frameshift-sensitive strains at very high concentrations (> or = 5000 micrograms/plate) with metabolic activation. The mutagenic activity was not due to the major carbendazim metabolite, methyl (5-hydroxy-1H-benzimidazol-2-yl)carbamate (5-OH MBC), since 5-OH MBC was not mutagenic with (up to 20,000 micrograms/plate) or without (up to 16,000 micrograms/plate) activation. Subsequently, two highly mutagenic contaminants, 2,3-diaminophenazine (DAP) and 2-amino-3-hydroxyphenazine (AHP) were detected in mutagenic carbendazim samples. In those samples, DAP and AHP contaminant levels ranged as high as 46.5 and 11.6 ppm, respectively. No evidence of mutagenicity could be detected in preparations in which the DAP content was < 1.8 ppm. The mutagenic activity of these two contaminants was further investigated in strain TA98. Without activation, DAP and AHP were positive at test concentrations as low as 5 and 10 micrograms/plate, respectively. In the presence of S9, mutations were detected at much lower concentrations (beginning at 0.025 and 0.05 microgram/plate, respectively). These results indicate that carbendazim samples containing DAP or AHP at levels as low as 5 or 10 ppm, respectively, would be positive in the Salmonella/Ames test with activation when tested at 5000 micrograms/plate. Purified carbendazim is not mutagenic.

Chromosomal aberrations in cultured human lymphocytes treated with Marshal and its effective ingredient Carbosulfan

The aim of this study was to investigate the ability of Marshal (insecticide/nematocide) and its effective ingredient Carbosulfan to induce chromosomal aberrations (CA) and other chromosomal abnormalities in human peripheral lymphocytes. Carbosulfan induced the formation of CA at all concentrations (10(-6), 5 x 10(-6), 10(-5), 5 x 10(-5) v/v) and treatment times. Marshal significantly induced the formation of CA at the two highest concentrations (10(-5) and 5 x 10(-5) v/v) at all treatment times. The extent of damage was greatest with Carbosulfan.

Analysis of the six additional chemicals for in vitro assays of the European Economic Communities' EEC aneuploidy programme using Saccharomyces cerevisiae D61.M and the in vitro porcine brain tubulin assembly assay

We tested six additional chemicals (acetaldehyde, benomyl, diethylstilboestrol, diethylstilboestrol dipropionate, griseofulvin, and mercaptoethanol) for in vitro systems of the coordinated programme to study aneuploidy induction sponsored by the Commission of the European Communities in two in vitro test systems. Using Saccharomyces cerevisiae D61.M (mitotic chromosomal malsegregation assay), benomyl showed a dose-dependent increase in the frequency of chromosomal malsegregation with a lowest effective dose tested (LEDT) of 30 micrograms/ml (0.1 mM). Diethylstilboestrol (DES) showed solvent-dependent effects. DES dissolved in ethanol induced an increase in chromosomal malsegregation as well as in the frequency of total resistant colonies (mutations and recombinations) with a LEDT around 13 micrograms/ml (0.048 mM). Using dimethylsulfoxide as the solvent, no increases were observed with DES up to 333 micrograms/ml (1.24 mM). Acetaldehyde induced an increase in chromosomal malsegregation with the cold treatment protocol (LEDT: 1.25 microliters/ml (21 mM) and 0.75 microliters/ml (13 mM), respectively) but no increase with the overnight protocol (highest dose tested (HDT): 1.75 microliters/ml; 30 mM). Concerning the frequency of total cycloheximide-resistant colonies (mutations and recombinations) increases were obtained with both protocols. The other three compounds were negative when tested up to toxic doses (survival below 10%), up to the maximum solubility in the solvent used or up to heavy precipitation in the incubation mix. The HDT were 333 micrograms/ml (0.88 mM) for diethylstilboestrol dipropionate, 1,600 micrograms/ml (4.5 mM) for griseofulvin and 0.5 microliters/ml (7 mM) for mercaptoethanol. Concerning effects on porcine brain tubulin assembly in vitro, diethylstilboestrol and griseofulvin inhibited the assembly process. The IC30% (30% inhibition concentration) values were 12.5 microM and 100 microM for DES and griseofulvin, respectively. Mercaptoethanol showed no effects up to 50 mM.

Comparison of chemically induced chromosome loss in a diploid, triploid, and tetraploid strain of Saccharomyces cerevisiae

Triploid and tetraploid strains of Saccharomyces cerevisiae were constructed and the spontaneous loss during mitosis of one, two or three copies of chromosome VII was determined. In one strain, a triploid (VM2) in which expression of the recessive alleles can be observed only after loss of two copies of chromosome VII (3N-2), the spontaneous frequency of chromosome loss was lower than in the diploid D61.M. In another strain, a tetraploid (VM4) that also requires the loss of two copies of chromosome VII for observation (4N-2) of the recessive alleles, the spontaneous frequency was slightly higher than in the diploid D61.M. The spontaneous frequency of other genetic events (that is, mutation, recombination or chromosome breakage) were lower by 2-3 orders of magnitude than in the diploid strain D61.M. Induction of chromosome loss and other genetic events by nocodazole, ethyl acetate, hydroxyurea and ethyl methanesulfonate was determined in D61.M, VM2, and VM4, and the results were compared. Nocodazole and ethyl acetate induced chromosome loss in both the triploid and the tetraploid strains at lower concentrations than required in the diploid. These compounds also induced elevated frequencies of other genetic events in both the triploid and the tetraploid strains but not in the diploid. Hydroxyurea induced elevated frequencies of chromosome loss in the diploid and the tetraploid. Frequencies of chromosome loss in the triploid treated with hydroxyurea, although elevated, are based on observation of very few colonies of the correct phenotype. Ethyl methanesulfonate failed to induce chromosome loss in any of the three strains. Hydroxyurea and ethyl methanesulfonate did, however, induce very high frequencies of other genetic events.

The detection of chemically induced chromosomal malsegregation in Saccharomyces cerevisiae D61.M: a literature survey (1984-1990)

Our objective is to summarize the published data obtained with a recently developed tester strain suitable for the detection of chromosomal malsegregation in yeast. Results from 25 papers were reviewed in which numerical data for 111 chemicals tested in Saccharomyces cerevisiae D61.M are reported (a total of 316 independent tests; 279 acceptable, 37 not meeting our criteria). Of the 111 compounds analyzed 43 compounds are positive for chromosomal malsegregation, 56 compounds are negative and 12 compounds do not meet our criteria for acceptance (inconclusive). Of the 43 compounds judged positive 5 (acetone, acetonitrile, benzonitrile, ethylacetate and propionitrile) were only positive using a cold interruption protocol. Recommendations are made for standardization of methods and protocols for screening purposes. Finally, a comparison with in vitro tubulin assembly data using mammalian tubulin is presented.

Reevaluation of the 9 compounds reported conclusive positive in yeast Saccharomyces cerevisiae aneuploidy test systems by the Gene-Tox Program using strain D61.M of Saccharomyces cerevisiae

The state of aneuploidy test methodology was appraised by the U.S. Environmental Protection Agency in 1986 in analyzing published data. In Saccharomyces cerevisiae 9 chemicals were reported to be conclusive positive for aneuploidy induction in either mitotic or meiotic cells. We reevaluated these 9 chemicals using Saccharomyces cerevisiae D61.M, a strain that detects mitotic chromosome malsegregation. Acetone (lowest effective dose (LED): 40 microliters/ml), bavistan (LED: 5 micrograms/ml), benomyl (LED: 30 micrograms/ml) and oncodazole (LED: 4 micrograms/ml) induced a dose-dependent increase in the frequencies of chromosomal malsegregation. Ethyl methanesulfonate (EMS; highest tested dose (HTD): 1000 micrograms/ml) and methyl methanesulfonate (MMS; HTD: 100 micrograms/ml) did not induce malsegregation but were both potent inducers of other genetic events, detected by an increase in the frequencies of cyhR cells. No increases in both endpoints (malsegregation and other genetic events) were observed after treatment of S. cerevisiae D61.M with cyclophosphamide (CP; HTD: 16 mg/ml) in the absence of S9, p-D,L-fluorophenylalanine (p-FPA; HTD: 250 micrograms/ml) and phorbol-12-myristate-13-acetate (TPA; HTD: 50 micrograms/ml). A marginal increase in the frequency of mitotic chromosome malsegregation was obtained with cyclophosphamide in the presence of S9. Thus our test results largely disagree with those previously published by various authors and taken as conclusive by EPA. We interpret the discrepancies to be due to lack of properly controlled testing (e.g., no check for multiple mutational events). Only with a careful test design it is possible to discriminate between chemicals inducing only chromosome loss and no other genetic effects (e.g., acetone, oncodazole), chemicals inducing a variety of genetic damage but no chromosome loss (e.g., EMS, MMS) and chemicals inducing neither chromosome loss nor other genetic events in yeast (e.g., TPA, p-FPA).