Aspergillus nidulans: systems and results of tests for induction of mitotic segregation and mutation. II. Haploid assay systems and overall response of all systems. A report of the U.S. EPA Gene-Tox Program

Mutagenic effects of a commercial glyphosate-based herbicide formulation on the soil filamentous fungus Aspergillus nidulans depending on the mode of exposure

Glyphosate-based herbicides (GBH) are the most used pesticides worldwide. This widespread dissemination raises the question of non-target effects on a wide range of organisms, including soil micro-organisms. Despite a large body of scientific studies reporting the harmful effects of GBHs, the health and environmental safety of glyphosate and its commercial formulations remains controversial. In particular, contradictory results have been obtained on the possible genotoxicity of these herbicides depending on the organisms or biological systems tested, the modes and durations of exposure and the sensitivity of the detection technique used. We previously showed that the well-characterized soil filamentous fungus Aspergillus nidulans was highly affected by a commercial GBH formulation containing 450 g/L of glyphosate (R450), even when used at doses far below the agricultural application rate. In the present study, we analysed the possible mutagenicity of R450 in A. nidulans by screening for specific mutants after different modes of exposure to the herbicide. R450 was found to exert a mutagenic effect only after repeated exposure during growth on agar-medium, and depending on the metabolic status of the tested strain. The nature of some mutants and their ability to tolerate the herbicide better than did the wild-type strain suggested that their emergence may reflect an adaptive response of the fungus to offset the herbicide effects. The use of a non-selective molecular approach, the quantitative random amplified polymorphic DNA (RAPD-qPCR), showed that R450 could also exert a mutagenic effect after a one-shot overnight exposure during growth in liquid culture. However, this effect was subtle and no longer detectable when the fungus had previously been repeatedly exposed to the herbicide on a solid medium. This indicated an elevation of the sensitivity threshold of A. nidulans to the R450 mutagenicity, and thus confirmed the adaptive capacity of the fungus to the herbicide.

A Novel Strategy to Predict Carcinogenicity of Antiparasitics Based on a Combination of DNA Lesions and Bacterial Mutagenicity Tests

Genotoxicity and carcinogenicity testing of pharmaceuticals prior to commercialization is requested by regulatory agencies. The bacterial mutagenicity test was considered having the highest accuracy of carcinogenic prediction. However, some evidences suggest that it always results in false-positive responses when the bacterial mutagenicity test is used to predict carcinogenicity. Along with major changes made to the International Committee on Harmonization guidance on genotoxicity testing [S2 (R1)], the old data (especially the cytotgenetic data) may not meet current guidelines. This review provides a compendium of retrievable results of genotoxicity and animal carcinogenicity of 136 antiparasitics. Neither genotoxicity nor carcinogenicity data is available for 84 (61.8%), while 52 (38.2%) have been evaluated in at least one genotoxicity or carcinogenicity study, and only 20 (14.7%) in both genotoxicity and carcinogenicity studies. Among 33 antiparasitics with at least one old result in in vitro genotoxicity, 15 (45.5%) are in agreement with the current ICH S2 (R1) guidance for data acceptance. Compared with other genotoxicity assays, the DNA lesions can significantly increase the accuracy of prediction of carcinogenicity. Together, a combination of DNA lesion and bacterial tests is a more accurate way to predict carcinogenicity.

Follow-up actions from positive results of in vitro genetic toxicity testing

Appropriate follow-up actions and decisions are needed when evaluating and interpreting clear positive results obtained in the in vitro assays used in the initial genotoxicity screening battery (i.e., the battery of tests generally required by regulatory authorities) to assist in overall risk-based decision making concerning the potential effects of human exposure to the agent under test. Over the past few years, the International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute (HESI) Project Committee on the Relevance and Follow-up of Positive Results in In Vitro Genetic Toxicity (IVGT) Testing developed a decision process flow chart to be applied in case of clear positive results in vitro. It provides for a variety of different possibilities and allows flexibility in choosing follow-up action(s), depending on the results obtained in the initial battery of assays and available information. The intent of the Review Subgroup was not to provide a prescriptive testing strategy, but rather to reinforce the concept of weighing the totality of the evidence. The Review Subgroup of the IVGT committee highlighted the importance of properly analyzing the existing data, and considering potential confounding factors (e.g., possible interactions with the test systems, presence of impurities, irrelevant metabolism), and chemical modes of action when analyzing and interpreting positive results in the in vitro genotoxicity assays and determining appropriate follow-up testing. The Review Subgroup also examined the characteristics, strengths, and limitations of each of the existing in vitro and in vivo genotoxicity assays to determine their usefulness in any follow-up testing.

Mutagens in contaminated soil: a review

The intentional and accidental discharges of toxic pollutants into the lithosphere results in soil contamination. In some cases (e.g., wood preserving wastes, coal-tar, airborne combustion by-products), the contaminated soil constitutes a genotoxic hazard. This work is a comprehensive review of published information on soil mutagenicity. In total, 1312 assessments of genotoxic activity from 118 works were examined. The majority of the assessments (37.6%) employed the Salmonella mutagenicity test with strains TA98 and/or TA100. An additional 37.6% of the assessments employed a variety of plant species (e.g., Tradescantia clone 4430, Vicia faba, Zea mays, Allium cepa) to assess mutagenic activity. The compiled data on Salmonella mutagenicity indicates significant differences (p<0.0001) in mean potency (revertents per gram dry weight) between industrial, urban, and rural/agricultural sites. Additional analyses showed significant empirical relationships between S9-activated TA98 mutagenicity and soil polycyclic aromatic hydrocarbon (PAH) concentration (r2=0.19 to 0.25, p<0.0001), and between direct-acting TA98 mutagenicity and soil dinitropyrene (DNP) concentration (r2=0.87, p<0.0001). The plant assay data revealed excellent response ranges and significant differences between heavily contaminated, industrial, rural/agricultural, and reference sites, for the anaphase aberration in Allium cepa (direct soil contact) and the waxy locus mutation assay in Zea mays (direct soil contact). The Tradescantia assays appeared to be less responsive, particularly for exposures to aqueous soil leachates. Additional data analyses showed empirical relationships between anaphase aberrations in Allium, or mutations in Arabidopsis, and the 137Cs contamination of soils. Induction of micronuclei in Tradescantia is significantly related to the soil concentration of several metals (e.g., Sb, Cu, Cr, As, Pb, Cd, Ni, Zn). Review of published remediation exercises showed effective removal of genotoxic petrochemical wastes within one year. Remediation of more refractory genotoxic material (e.g., explosives, creosote) frequently showed increases in mutagenic hazard that remained for extended periods. Despite substantial contamination and mutagenic hazards, the risk of adverse effect (e.g., mutation, cancer) in humans or terrestrial biota is difficult to quantify.

Tests for recombinagens in fungi

Three types of mitotic recombination can be studied in Aspergillus nidulans and Saccharomyces cerevisiae: (1) The classical type of reciprocal mitotic crossing-over which can be detected when it occurs between non-sister chromatids at the four-strand stage followed by co-segregation of a crossing-over and a non-crossing-over chromatid in the subsequent mitotic division. Consequently, mitotic crossing-over reflects cellular responses to primary genetic damage in the G2 phase of the cell cycle. (2) Mitotic gene conversion is a unidirectional event of a localized transfer of genetic information between non-sister chromatids which in yeast can extend to segments of up to 18 cM and even beyond 22 cM in Aspergillus nidulans. Mitotic gene conversion can also occur between unreplicated chromatids and lead to the expression of the newly created genotype without any need for a subsequent mitotic cell division. It reflects a cellular response in G1. (3) Mitotic sister-strand gene conversion can be studied in a recently constructed strain with the same technical ease as classical non-sister chromatid gene conversion. It can be induced by chemicals which do not induce mutation in the Salmonella system and non-sister chromatid gene conversion. Mitotic segregation in Saccharomyces cerevisiae results almost exclusively from crossing-over and gene conversion whereas mitotic chromosomal malsegregation contributes only very little. In contrast to this, in Aspergillus nidulans, both processes contribute considerably so that mitotic segregants always have to be tested for their mechanistic origin.

The genotoxicity of industrial wastes and effluents

A review of the literature published on the genotoxicity of industrial wastes and effluents using short-term genetic bioassays is presented in this document. The importance of this task arises from the ubiquity of genotoxic compounds in the environment and the need to identify the sources of contamination so that efforts aimed at control and minimization can be implemented. Of even greater significance is the immediate concern for the welfare of human health and the environment. Subheadings of this document include a description of the genetic bioassays that have been used to test industrial wastes, a compendium of methods commonly used to prepare crude waste samples for bioassay, and a review of the genetic toxicity of wastes and effluents. Wastes and effluents have been grouped according to industrial source. Major categories include chemical and allied products, pulp and paper manufacturing, defense and munitions, petroleum refining, primary metal industries, and miscellaneous industrial manufacturers. Within each industrial category, a synopsis of individual genetic toxicity studies is presented, followed by an interpretation of results on a comprehensive, industry-wide basis. In this evaluation, a discussion of the types and extent of genotoxic damage caused by a particular set of wastes is presented, and potential sources of genotoxic activity are identified. Concluding the document is a commentary, which discloses potential shortcomings in the way in which current legislation protects human heath and the environment from the release of genotoxic substances via industrial wastes and effluents. It also provides an assessment of the genotoxic burden that industrial wastes place on the environment.

Chemical and biological characterization of hazardous industrial waste. II. Eukaryotic bioassay of a wood-preserving bottom sediment

The eukaryotic haploid and diploid forms of Aspergillus nidulans were used to detect gene mutations and various types of chromosome damage, respectively, in the acid, base and neutral fractions of a wood-preserving bottom sediment. The corresponding response to prokaryotic mutagenicity assays and major chemical constituents of the 3 waste fractions were described by Donnelly et al. (1987). The haploid methionine system detected genotoxic compounds in all 3 primary waste fractions without metabolic activation. With metabolic activation, the maximum response observed in the gene mutation assay was induced by the base fraction. In the diploid assay without metabolic activation, the acid fraction induced the maximum number of major chromosome abnormalities, while the base fraction induced the maximum number of minor deletions or insertions. These results appear to reflect the different composition of the waste fractions since each fraction induced a different type of genetic damage in the two bioassays employed. Alternately, because exposure in the diploid assay was during a growth stage, the results may reflect a varying response at different points of the cell division cycle. The results obtained using eukaryotic bioassays indicate that the wood preserving waste contains compound(s) capable of inducing point mutations, chromosome damage, recombination, and compound(s) acting as spindle poisons.

Detection of point-mutation mutagens in Aspergillus nidulans: comparison of methionine suppressors and arginine resistance induction by fungicides

In the present study we describe the effect of 4 fungicides on the induction of point mutations in strains biA1 methG1 (induction of methionine suppressors) and 118 (induction of arginine resistance) of Aspergillus nidulans. Captan, which was used as a known mutagen, Daconil 2787 and Dithane M-45 were effective in inducing these mutations, whereas the fungicide Cercobin caused no significant increase in the induction frequency of the point mutations selected. Actually, a decrease in the frequency of methionine suppressors was observed in relation to those occurring spontaneously. However, this effect could not be considered antimutagenic because the revertants were more sensitive to the fungicide than the biA1 methG1 strain. Although the induction of methionine suppressors was more convenient because it permits the visualization of several morphological types, the 118 strain system also proved to be effective in detecting point-mutation induction.

Chemical carcinogens. A review and analysis of the literature of selected chemicals and the establishment of the Gene-Tox Carcinogen Data Base. A report of the U.S. Environmental Protection Agency Gene-Tox Program

The literature on 506 selected chemicals has been evaluated for evidence that these chemicals induce tumors in experimental animals and this assessment comprises the Gene-Tox Carcinogen Data Base. Three major sources of information were used to create this evaluated data base: all 185 chemicals determined by the International Agency for Research on Cancer to have Sufficient evidence of carcinogenic activity in experimental animals, 28 selected chemicals bioassayed for carcinogenic activity by the National Toxicology Program/National Cancer Institute and found to induce tumors in mice and rats, and 293 selected chemicals which had been evaluated in genetic toxicology and related bioassays as determined from previous Gene-Tox reports. The literature data on the 239 chemicals were analyzed by the Gene-Tox Carcinogenesis Panel in an organized, rational and consistent manner. Criteria were established to assess individual studies employing single chemicals and 4 categories of response were developed: Positive, Negative, Inconclusive (Equivocal) and Inconclusive. After evaluating each of the individual studies on the 293 chemicals, the Panel placed each of the 506 chemicals in an overall classification category based on the strength of the evidence indicating the presence or absence of carcinogenic effects. An 8-category decision scheme was established using a modified version of the International Agency for Research on Cancer approach. This scheme included two categories of Positive (Sufficient and Limited), two categories of Negative (Sufficient and Limited), a category of Equivocal (the evidence of carcinogenicity from well-conducted and well-reported lifetime studies had uncertain significance and was neither clearly positive nor negative), and three categories of Inadequate (the evidence of carcinogenicity was insufficient to make a decision, however, the data suggested a positive or negative indication). Of the 506 chemicals in the Gene-Tox Carcinogen Data Base, 252 were evaluated as Sufficient Positive, 99 as Limited Positive, 40 as Sufficient Negative, 21 as Limited Negative, 1 as Equivocal, 13 as Inadequate with the data suggesting a positive indication, 32 as Inadequate with the data suggesting a negative indication, and 48 Inadequate with the data not suggesting any indication of activity. This data base was analyzed and examined according to chemical class, using a 29 chemical class scheme.(ABSTRACT TRUNCATED AT 400 WORDS)

Systems and results of tests for chemical induction of mitotic malsegregation and aneuploidy in Aspergillus nidulans

In Aspergillus several types of test systems have been developed for detection of chemicals which induce aneuploidy and/or malsegregation of chromosomes. Results from 23 papers were reviewed in which numerical data for 42 chemicals had been reported. The test systems fall into two groups. One group includes all purely genetic tests that detect euploid mitotic segregants from heterozygous diploids and identify these either as products of malsegregation of chromosomes or as products of crossing-over (13 papers, several reviewed in detail previously; Käfer et al. (1982) and Scott et al. (1982)). The other group includes tests that treat haploid or diploid strains and detect aneuploids as unstable abnormally growing segregants which can be identified as specific disomics or trisomics by their characteristic phenotypes. In addition, such tests characterize abnormal segregants from heterozygous diploids by correlating phenotypes with patterns of genetic segregation in spontaneous euploid sectors. This analysis makes it possible to distinguish between induced primary aneuploidy of whole chromosomes and partial tri- or monosomy resulting from chromosome breakage and secondary spontaneous malsegregation (10 papers). Based on results of both types of tests, it is postulated that chemicals which cause increases of euploid malsegregants, but not of crossovers, normally induce aneuploids as primary products (as shown for 7 of the 14 cases). These include compounds which damage spindles or membranes (especially the well-known haploidizing agents) and generally are effective only when growing cells are exposed. (8 chemicals that may belong in this category could not be classified for certain, because information was insufficient.) On the other hand, chemicals which cause increases of all types of euploid segregants (11 cases), mostly induce drastic mutations and aberrations as primary effects and cause spontaneous malsegregation or crossing-over only as secondary events (as demonstrated for radiation-induced abnormals). In addition, a few chemicals were negative, because they increased only crossing-over or showed no increased segregation at all at concentrations which reduced survival or growth rate (9 cases). Recommendations are made for standardization of methods and protocols. New tester strains and specific procedures are outlined which should be useful for conclusive tests of chemicals that may induce aneuploidy.