The detection and evaluation of aneugenic chemicals

Effect of cell treatment procedures on in vitro genotoxicity assessment

So far, the majority of in vitro toxicological experiments are conducted after an acute 24 h treatment that does not represent a realistic human chemical exposure. Recently, new in vitro approaches have been proposed to study the chemical toxicological effect over several days in order to be more predictive of a representative exposure scenario. In this study, we investigated the genotoxic potential of chemicals (direct or bioactived clastogen, aneugen and apoptotic inducer) with the γH2AX and pH3 biomarkers, in the human liver-derived HepaRP cell line. We used different treatment durations, with or without a three-day recovery stage (release period), before genotoxicity measurement. Data were analysed with the Benchmark Dose approach. We observed that the detection of clastogenic compounds (notably for DNA damaging agents) was more sensitive after three days of repeated treatment compared to one or three treatments over 24 h. In contrast, aneugenic chemicals were detected as genotoxic in a similar manner whether after a 24 h exposure or a three-day repeated treatment. Globally, the release period decreases the genotoxicity measurement substantially. For DNA damaging agents, after high concentration treatments, γH2AX induction was always observed after a three-day release period. In contrast, for DNA topoisomerase inhibitors, no effect could be observed after the release period. In conclusion, in the HepaRP cell line, there are some important differences between a one-day acute and a three-day repeated treatment protocol, indicating that different cell treatment procedures may differentiate chemical genotoxic mechanisms of action more efficiently.

Towards prevention of aneuploidy-associated cellular senescence and aging: more questions than answers?

The aim of this review is to discuss how aneuploidy contributes to the aging process, and to identify plausible strategies for its prevention. After an overview of mechanisms leading to aneuploidy and the major features of cellular senescence, we discuss the link between (i) aneuploidy and cellular senescence; (ii) aneuploidy and aging; and (iii) cellular senescence and aging. We also consider (i) interactions between aneuploidy, micronuclei, cellular senescence and aging, (ii) the potential of nutritional treatments to prevent aneuploidy-associated senescence and aging, and (iii) knowledge and technological gaps. Evidence for a causal link between aneuploidy, senescence and aging is emerging. In vitro, aneuploidy accompanies the entry into cellular senescence and can itself induce senescence. How aneuploidy contributes in vivo to cellular senescence is less clear. Several routes depending on aneuploidy and/or senescence converge towards chronic inflammation, the major driver of unhealthy aging. Aneuploidy can induce the pro-inflammatory Senescence Associated Secretory Phenotype (SASP), either directly or as a result of micronucleus (MN) induction leading to leakage of DNA into the cytoplasm and triggering of the cGAS-STING pathway of innate immune response. A major difficulty in understanding the impact of aneuploidy on senescence and aging in vivo, results from the heterogeneity of cellular senescence in different tissues at the cytological and molecular level. Due to this complexity, there is at the present time no biomarker or biomarker combination characteristic for all types of senescent cells. In conclusion, a deeper understanding of the critical role aneuploidy plays in cellular senescence and aging is essential to devise practical strategies to protect human populations from aneuploidy-associated pathologies. We discuss emerging evidence, based on in vitro and in vivo studies, that adequate amounts of specific micronutrients are essential for prevention of aneuploidy in humans and that precise nutritional intervention may be essential to help avoid the scourge of aneuploidy-driven diseases.

Exploring graphene-based materials' genotoxicity: inputs of a screening method

Graphene-based materials (GBMs) are promising nanomaterials, and several innovations depend on their use. However, the assessment of their potential hazard must be carefully explored before entering any market. GBMs are indeed well-known to induce various biological impacts, including oxidative stress, which can potentially lead to DNA damage. Genotoxicity is a major endpoint for hazard assessment and has been explored for GBMs, but the available literature shows conflicting results. In this study, we assessed the genotoxicity of 13 various GBMs, one carbon black and one amorphous silica through a DNA damage response assay (using a human respiratory cell model, BEAS-2B). Concurrently, oxidative stress was assessed through a ROS production quantification (DCFH-DA assay using a murine macrophage model, RAW 264.7). We also performed a full physicochemical characterization of our samples to explore potential structure-activity relationships involving genotoxicity. We observed that surface oxidation appears linked to genotoxicity response and were able to distinguish several groups within our studied GBMs showing different genotoxicity results. Our findings highlight the necessity to individually consider each nanoform of GBMs since the tested samples showed various results and modes of action. We propose this study as a genotoxicity assessment using a high-throughput screening method and suggest few hypotheses concerning the genotoxicity mode of action of GBMs.

HepGentox: a novel promising HepG2 reportergene-assay for the detection of genotoxic substances in complex mixtures

BACKGROUND

In risk assessment, genotoxicity is a key factor to determine the safety for the consumer. Most in vitro genotoxicity assays were developed for the assessment of pure substances. However, in recent years more attention has been given to complex mixtures, where usually low amounts of a substance are present. For high-throughput screening, a toxicologically sensitive assay should be used, covering a broad range of genotoxic substances and detecting them at low concentrations. HepG2 cells have been recommended as one of the prime candidates for genotoxicity testing, as they are p53 competent, less prone towards cytotoxic effects and tend to have some metabolic activity.

METHODS

A HepG2 liver cell line was characterized for its suitability for genotoxicity assessment. For this, a luciferase based reporter gene assay revolving around the p53 pathway was validated for the analysis of pure substances and of complex mixtures. Further, the cell's capability to detect genotoxins correctly with and without an exogenous metabolizing system, namely rat liver S9, was assessed.

RESULTS

The assay proved to have a high toxicological sensitivity (87.5%) and specificity (94%). Further, the endogenous metabolizing system of the HepG2 cells was able to detect some genotoxins, which are known to depend on an enzymatic system. When complex mixtures were added this did not lead to any adverse effects concerning the assays performance and cytotoxicity was not an issue.

DISCUSSION

The HepGentox proved to have a high toxicological sensitivity and specificity for the tested substances, with similar or even lower lowest effective concentration (LEC) values, compared to other regulatory mammalian assays. This combines some important aspects in one test system, while also being less time and material consuming and covering several genotoxicity endpoints. As the assay performs well with and without an exogenous metabolizing system, no animal liver fractions have to be used, which application is discussed controversially and is considered to be expensive and laborious in sample testing. Because of this, the HepGentox is suitable for a cost-efficient first screening approach to obtain important information with human cells for further approaches, with a relatively fast and easy method. Therefore, the HepGentox is a promising assay to detect genotoxic substances correctly in complex mixtures even at low concentrations, with the potential for a high throughput application. In a nutshell, as part of an in vitro bioassay test battery, this assay could provide valuable information for complex mixtures.

Chromosomal Instability in Farmers Exposed to Pesticides: High Prevalence of Clonal and Non-Clonal Chromosomal Alterations

Introduction

An important economic activity in Colombia is agricultural production and farmers are frequently exposed to pesticides. Occupational exposure to pesticides is associated with an increased incidence of various diseases, including cancer, Parkinson’s disease, Alzheimer’s disease, reproductive disorders, and birth defects. However, although high genotoxicity is associated with these chemicals, information about the type and frequency of specific chromosomal alterations (CAs) and the level of chromosomal instability (CIN) induced by exposure to pesticides is scarce or absent.

Methods

In this study, CAs and CIN were assessed in peripheral blood lymphocytes (PBLs) from five farmers occupationally exposed to pesticides and from five unexposed individuals using GTG-banding and molecular cytogenetic analysis.

Results

A significant increase in clonal and non-clonal chromosomal alterations was observed in pesticide-exposed individuals compared with unexposed individuals (510±12,2 vs 73±5,7, respectively; p<0.008). Among all CAs, monosomies and deletions were more frequently observed in the exposed group. Also, a high frequency of fragilities was observed in the exposed group.

Conclusion

Together, these findings suggest that exposure to pesticides could be associated with CIN in PBLs and indicate the need for the establishment of educational programs on safety precautions when handling pesticides, such as wearing gloves, masks and boots, changing clothes and maintaining proper hygiene, among others. Further evaluation in other similar studies that include a greater number of individuals exposed to pesticides is necessary.

Targets and mechanisms of chemically induced aneuploidy. Part 1 of the report of the 2017 IWGT workgroup on assessing the risk of aneugens for carcinogenesis and hereditary diseases

An aneuploidy workgroup was established as part of the 7th International Workshops on Genotoxicity Testing. The workgroup conducted a review of the scientific literature on the biological mechanisms of aneuploidy in mammalian cells and methods used to detect chemical aneugens. In addition, the current regulatory framework was discussed, with the objective to arrive at consensus statements on the ramifications of exposure to chemical aneugens for human health risk assessment. As part of these efforts, the workgroup explored the use of adverse outcome pathways (AOPs) to document mechanisms of chemically induced aneuploidy in mammalian somatic cells. The group worked on two molecular initiating events (MIEs), tubulin binding and binding to the catalytic domain of aurora kinase B, which result in several adverse outcomes, including aneuploidy. The workgroup agreed that the AOP framework provides a useful approach to link evidence for MIEs with aneuploidy on a cellular level. The evidence linking chemically induced aneuploidy with carcinogenicity and hereditary disease was also reviewed and is presented in two companion papers. In addition, the group came to the consensus that the current regulatory test batteries, while not ideal, are sufficient for the identification of aneugens and human risk assessment. While it is obvious that there are many different MIEs that could lead to the induction of aneuploidy, the most commonly observed mechanisms involving chemical aneugens are related to tubulin binding and, to a lesser extent, inhibition of mitotic kinases. The comprehensive review presented here should help with the identification and risk management of aneugenic agents.

Assessment of the performance of the TGx-DDI biomarker to detect DNA damage-inducing agents using quantitative RT-PCR in TK6 cells

Gene expression biomarkers are now available for application in the identification of genotoxic hazards. The TGx-DDI transcriptomic biomarker can accurately distinguish DNA damage-inducing (DDI) from non-DDI exposures based on changes in the expression of 64 biomarker genes. The 64 genes were previously derived from whole transcriptome DNA microarray profiles of 28 reference agents (14 DDI and 14 non-DDI) after 4 h treatments of TK6 human lymphoblastoid cells. To broaden the applicability of TGx-DDI, we tested the biomarker using quantitative RT-PCR (qPCR), which is accessible to most molecular biology laboratories. First, we selectively profiled the expression of the 64 biomarker genes using TaqMan qPCR assays in 96-well arrays after exposing TK6 cells to the 28 reference agents for 4 h. To evaluate the classification capability of the qPCR profiles, we used the reference qPCR signature to classify 24 external validation chemicals using two different methods-a combination of three statistical analyses and an alternative, the Running Fisher test. The qPCR results for the reference set were comparable to the original microarray biomarker; 27 of the 28 reference agents (96%) were accurately classified. Moreover, the two classification approaches supported the conservation of TGx-DDI classification capability using qPCR; the combination of the two approaches accurately classified 21 of the 24 external validation chemicals, demonstrating 100% sensitivity, 81% specificity, and 91% balanced accuracy. This study demonstrates that qPCR can be used when applying the TGx-DDI biomarker and will improve the accessibility of TGx-DDI for genotoxicity screening. Environ. Mol. Mutagen. 60: 122-133, 2019. © 2018 Her Majesty the Queen in Right of Canada Environmental and Molecular Mutagenesis.

Risks of aneuploidy induction from chemical exposure: Twenty years of collaborative research in Europe from basic science to regulatory implications

Although Theodor Boveri linked abnormal chromosome numbers and disease more than a century ago, an in-depth understanding of the impact of mitotic and meiotic chromosome segregation errors on cell proliferation and diseases is still lacking. This review reflects on the efforts and results of a large European research network that, from the 1980's until 2004, focused on protection against aneuploidy-inducing factors and tackled the following problems: 1) the origin and consequences of chromosome imbalance in somatic and germ cells; 2) aneuploidy as a result of environmental factors; 3) dose-effect relationships; 4) the need for validated assays to identify aneugenic factors and classify them according to their modes of action; 5) the need for reliable, quantitative data suitable for regulating exposure and preventing aneuploidy induction; 6) the need for mechanistic insight into the consequences of aneuploidy for human health. This activity brought together a consortium of experts from basic science and applied genetic toxicology to prepare the basis for defining guidelines and to encourage regulatory activities for the prevention of induced aneuploidy. Major strengths of the EU research programmes on aneuploidy were having a valuable scientific approach based on well-selected compounds and accurate methods that allow the determination of precise dose-effect relationships, reproducibility and inter-laboratory comparisons. The work was conducted by experienced scientists stimulated by a fascination with the complex scientific issues surrounding aneuploidy; a key strength was asking the right questions at the right time. The strength of the data permitted evaluation at the regulatory level. Finally, the entire enterprise benefited from a solid partnership under the lead of an inspired and stimulating coordinator. The research programme elucidated the major modes of action of aneugens, developed scientifically sound assays to assess aneugens in different tissues, and achieved the international validation of relevant assays with the goal of protecting human populations from aneugenic chemicals. The role of aneuploidy in tumorigenesis will require additional research, and the study of effects of exposure to multiple agents should become a priority. It is hoped that these reflections will stimulate the implementation of aneuploidy testing in national and OECD guidelines.

The influence of exogenous metabolism on the specificity of in vitro mammalian genotoxicity tests

A two-part study was designed to determine whether the inclusion of the rodent liver 'S9' exogenous metabolic activating system contributes to the generation of misleading positive results by the regulator-required in vitro mammalian genotoxicity tests. The mono-oxygenase enzymes in S9 produce direct-acting DNA-reactive electrophiles, and are included in in vitro genotoxicity tests to enhance the detection of substances which only become genotoxic following metabolism. However, as the S9 system lacks 'detoxifying' phase 2 factors it was hypothesised that increased chemical metabolism per se may lead to an increase in irrelevant S9 test outcomes in safety assessment. To test this, 89 compounds with positive or negative carcinogenicity data were identified, which produced negative Ames test data (+/- S9), and only produced positive in vitro mammalian test data in the presence of S9. This allowed a determination of whether or not misleading predictions of carcinogenicity by the in vitro mammalian tests were more or less prevalent in the presence of S9. A subset of these compounds was then tested with and without S9 in the GADD45a-GFP genotoxicity test, in order to determine whether misleading in vitro mammalian positive results were generally more prevalent with S9, or reflected particular tests' liabilities. This study suggests that the use of S9 metabolic activation in in vitro genotoxicity tests does not increase the prevalence of misleading positive results in in vitro mammalian genotoxicity assays, at least amongst Ames negative compounds.

Occurrence and Comparative Toxicity of Haloacetaldehyde Disinfection Byproducts in Drinking Water

The introduction of drinking water disinfection greatly reduced waterborne diseases. However, the reaction between disinfectants and natural organic matter in the source water leads to an unintended consequence, the formation of drinking water disinfection byproducts (DBPs). The haloacetaldehydes (HALs) are the third largest group by weight of identified DBPs in drinking water. The primary objective of this study was to analyze the occurrence and comparative toxicity of the emerging HAL DBPs. A new HAL DBP, iodoacetaldehyde (IAL) was identified. This study provided the first systematic, quantitative comparison of HAL toxicity in Chinese hamster ovary cells. The rank order of HAL cytotoxicity is tribromoacetaldehyde (TBAL) ≈ chloroacetaldehyde (CAL) > dibromoacetaldehyde (DBAL) ≈ bromochloroacetaldehyde (BCAL) ≈ dibromochloroacetaldehyde (DBCAL) > IAL > bromoacetaldehyde (BAL) ≈ bromodichloroacetaldehyde (BDCAL) > dichloroacetaldehyde (DCAL) > trichloroacetaldehyde (TCAL). The HALs were highly cytotoxic compared to other DBP chemical classes. The rank order of HAL genotoxicity is DBAL > CAL ≈ DBCAL > TBAL ≈ BAL > BDCAL>BCAL ≈ DCAL>IAL. TCAL was not genotoxic. Because of their toxicity and abundance, further research is needed to investigate their mode of action to protect the public health and the environment.

The in vitro micronucleus assay and kinetochore staining: methodology and criteria for the accurate assessment of genotoxicity and cytotoxicity

The in vitro micronucleus assay is currently one of the most commonly used test systems for the study of genotoxic effects of chemicals. It is considered the preferred method for measuring chromosome damage as it allows the determination of both chromosomal loss and breakage. The type of chromosomal damage induced can be distinguished by using the kinetochore or pan-centromeric staining using molecular probes that label the centromeric regions of chromosomes allowing the determination of aneugenic (chromosome loss) or clastogenic (chromosome breakage) agents. In this chapter, we provide a description of the basic principles and methods of the in vitro micronucleus assay with detailed explanations of the scoring criteria for the genotoxicity and cytotoxicity end-points by manual or automated analysis.

Numerical chromosome disorders in the common marmoset (Callithrix jacchus)--comparison between two captive colonies

BACKGROUND

Chromosomal analyses were performed for marmosets from two colonies - Deutsches Primatenzentrum (DPZ) and Biomedical Primate Research Centre (BPRC). Chlorine-based disinfectants are used in DPZ; no chemical disinfection is applied in BPRC.

METHODS

The rates of chromosomal non-disjunction, polyploidy and endoreduplication were investigated after G-banding.

RESULTS

For DPZ monkeys, the mean rates of non-disjunction were 7.6% for bone marrow and 11.3% for lymphocytes. The polyploidy level was 2.5% in bone marrow and 0.8% in blood. Frequency of endoreduplication in bone marrow and in leucocytes was 0.5% and 0.8%, respectively. For BPRC, the rate of non-disjunction in leucocytes (1.3%) was significantly lower than that for DPZ; the polyploidy rate (0.2%) in blood was lower than that in DPZ; endoreduplication was not observed.

CONCLUSION

The levels of chromosomal disorders are elevated for DPZ colony. We suggest that the increased rate of chromosomal disorders in DPZ marmosets can be related to the chemical disinfection of their environment.

Comparison of in vitro micronucleus and gene mutation assay results for p53-competent versus p53-deficient human lymphoblastoid cells

The high frequency of false or irrelevant positive results in in vitro mammalian cell genotoxicity tests is a critical concern for regulators. Here, we tested whether such results may be due to the mammalian cells used in the tests being deficient in p53, which is involved in the maintenance of genomic stability. We compared the in vitro responses of two human lymphoblastoid cell lines derived from the same progenitor cell-p53-competent (TK6) and p53-deficient (WTK-1) cells-in a micronucleus (MN) test and a thymidine kinase gene (TK) mutation assay. We tested 14 chemicals including three mutagens and 11 clastogens and spindle poisons. The three mutagens evoked clear positive responses in both assays in both cell lines. The responses to the clastogens and spindle poisons, on the other hand, depended on the assay endpoint and/or the cell line. Most of clastogens and spindle poisons were positive in the MN test in both cell lines. In the TK mutation assay, on the other hand, WTK-1 cells but not TK6 cells detected spindle poisons, which may have been due to the disturbance of the spindle checkpoint and lack of apoptosis in the p53-deficient cells. Some chemicals that induced chromosome aberrations in rodent cells were negative in both TK6 and WTK-1 cells, indicating that a species-specific factor rather than p53 status was associated with the response. In conclusion, the p53 status did not seriously influence the MN test results but it did influence the TK mutation assay results.

Reflections on the development of micronucleus assays

These are personal reflections on the development of methods to use micronuclei as a measure of genetic damage and their use in research and in toxicology by four people who have been intimately involved with this work, a personal rather than a comprehensive history. About 6000 papers have been published using such methods in many tissues in vivo or in cultured cells of many organisms from plants to humans, but the majority of the work has been on mammalian erythrocytes and human lymphocytes, the areas in which we have worked primarily. Although this is by no means a complete history, those working in the field may be interested in some of the personal events that lie behind the development and acceptance of methods that are now standard.

Toxicity, biomarkers, genotoxicity, and carcinogenicity of trichloroethylene and its metabolites: a review

Trichloroethylene (TCE) is a prevalent occupational and environmental contaminant that has been reported to cause a variety of toxic effects. This article reviews toxicity, mutagenicity, and carcinogenicity caused by the exposure of TCE and its metabolites in the living system as well as on their (TCE and its metabolites) toxicity biomarkers.

In vitro genotoxic assessment of xenobiotic diacylglycerols in an in vitro micronucleus assay

Xenobiotic diacylglycerols (DG) may induce pathological disorders by causing abnormal chromosomal segregation, which could be aneuploid. In this study, seven xenobiotic-diacylglycerols (four of drug origin and three of pesticide origin) were evaluated for their ability to induce aneuploidy in mammalian cultures using in vitro cytokinesis blocked micronucleus (CBMN) assay coupled with kinetochore labeling and interphase fluorescent in situ hybridization. Out of seven xeno-DGs, two (ibuprofen-DG and fenbufen-DG) induced statistically significant (P < 0.001) and dose-dependent increase in micronucleus induction, but this apparent micronucleus induction was very weak in case of fenbufen-DG. These MN were produced predominantly by aneugenic and clastogenic mechanisms, respectively, confirmed by immunofluorescent labeling of kinetochores. Fluorescent in situ hybridization analysis revealed that ibuprofen-DG induced significantly higher nondisjunction for chromosomes 10, 17, and 18. Other xenobiotic diacylglycerols (indomethacin-DG, salicylic acid-DG, 4-(2-methyl-4-chlorophenoxy) butanoic acid-DG (MCPB-DG), 2-(2-methyl-4-chlorophenoxy) propanoic acid-DG (MCPP-DG) and 2-(4-dichlorophenoxy)-butanoic acid-DG (2,4 DB-DG) did not induce micronuclei, but the concentrations tested did not reach levels that caused the marked growth suppression typically required for testing for regulatory testing purposes. However, the levels of growth suppression achieved were similar to that seen with ibuprofen-DG, which was positive. This study shows that xeno-DGs, which have been neglected in the past for their possible link to any pathological disorders, need serious assessment of their mutagenic potential.

Fifty years of cytogenetics: a parallel view of the evolution of cytogenetics and genotoxicology

A parallelism exists between human cytogenetics and cytogenetic toxicology. The breakthroughs, mostly coming from and used in clinical genetics, are widely used in genetic toxicology. The birth of human cytogenetics occurred in 1956 when it was published that the diploid number of chromosomes in humans is 46. The first stage in chromosome-induced mutagenesis began in 1938 when Sax published the effects of X-rays on the chromosomes of Drosophila. In 1959, the cytogenetic anomalies for Down, Klinefelter, and Turner syndromes were described, and parallelly in 1960, the first publication on chromosomal aberrations in man caused by ionizing radiation appeared. The cytogenetic analysis of chromosomal aberrations in cell cultures is considered one of the primary methods to evaluate induced mutagenesis. At the end of the 1960s, banding techniques allowed chromosomes to be individually identified, in parallel, the sister chromatid exchange analysis technology was described. Another milestone in the history of induced mutagenesis was the discovery that mutagenic agents were able to alter chromosomal division and segregation in gonads inducing meiotic nondisjunction. Here we review new approaches and applications such as biological dosimetry, translocation scoring using FISH, and micronucleus test. Chromosomal aberrations and micronucleus test are now effective cytogenetic biomarkers of early effect used as cancer predictors. Human cytogenetics has proven to be effective over its 50-year lifespan and, although each new technique that has appeared seemed to announce its end, the fact is that the current state of cytogenetics is in reality a collection of techniques that, while common, are cheap, fast, and wide-ranging. Therefore, in genotoxicology, they continue to be useful to identify mutagenic agents as well as to evaluate and analyze exposed populations.

ECVAM retrospective validation of in vitro micronucleus test (MNT)

In the past decade several studies comparing the in vitro chromosome aberration test (CAT) and the in vitro micronucleus test (MNT) were performed. A high correlation was observed in each of the studies (>85%); however, no formal validation for the micronucleus in vitro assay had been carried out. Therefore, a working group was established by the European Centre for the Validation of Alternative Methods (ECVAM) to perform a retrospective validation of the existing data, in order to evaluate the validity of the in vitro MNT on the basis of the modular validation approach. The primary focus of this retrospective validation was on the evaluation of the potential of the in vitro MNT as alternative to the standard in vitro CAT. The working group evaluated, in a first step, the available published data and came to the conclusion that two studies [German ring trial, von der Hude, W., Kalweit, S., Engelhardt, G. et al. (2000) In-vitro micronucleus assay with Chinese hamster V79 cells: results of a collaborative study with 26 chemicals. Mutat. Res., 468, 137–163, and SFTG International Collaborative Study, Lorge, E., Thybaud, V., Aardema, M., Oliver, J., Wataka, A., Lorenzon, G. and Marzin, D. (2006) SFTG International Collaborative Study on in-vitro micronucleus test I. General conditions and overall conclusions of the study. Mutat. Res., 607, 13–36] met the criteria for a retrospective validation according to the criteria previously defined by the working group. These two studies were evaluated in depth (including the reanalysis of raw data) and provided the information required for assessing the reliability (reproducibility) of the test. For the assessment of the concordance between the in vitro MNT and the in vitro CAT, additional published data were considered. Based on this retrospective validation, the ECVAM Validation Management Team concluded that the in vitro MNT is reliable and relevant and can therefore be used as an alternative method to the in vitro CAT. Following peer review, these conclusions were formally endorsed by the ECVAM Scientific Advisory Committee.

Do oestrogens induce chromosome specific aneuploidy in vitro, similar to the pattern of aneuploidy seen in breast cancer?

The study was concerned with investigating the specific effects of non-DNA reactive oestrogens at low "biologically relevant" doses and the causative role they may play in breast cancer through inducing aneuploidy. A review of previous studies identified a non-random pattern of aneuploidy seen in breast cancers. This information was used to select those chromosomes that undergo copy number changes in breast cancer and chromosomes that appear stable. A panel of centromeric specific probes were selected and centromeric specific fluorescence in situ hybridisation (FISH) was carried out on the human lymphoblastoid cell line, AHH-1, which had been pre-treated with the chemical aneugens 17-beta oestradiol, diethylstilbestrol (DES) and bisphenol-A (BP-A). The results suggest that oestrogens may play a causative role in breast cancer by inducing a specific pattern of aneuploidy similar to that seen in breast carcinomas. 17-beta oestradiol appears to induce changes most similar to those seen in breast tumours, BP-A induces the same pattern but at a lower frequency and DES appears to be less chromosome specific in its act.

Acrylamide effects on kinesin-related proteins of the mitotic/meiotic spindle

The microtubule (MT) motor protein kinesin is a vital component of cells and organs expressing acrylamide (ACR) toxicity. As a mechanism of its potential carcinogenicity, we determined whether kinesins involved in cell division are inhibited by ACR similar to neuronal kinesin [Sickles, D.W., Brady, S.T., Testino, A.R., Friedman, M.A., and Wrenn, R.A. (1996). Direct effect of the neurotoxicant acrylamide on kinesin-based microtubule motility. Journal of Neuroscience Research 46, 7-17.] Kinesin-related genes were isolated from rat testes [Navolanic, P.M., and Sperry, A.O. (2000). Identification of isoforms of a mitotic motor in mammalian spermatogenesis. Biology of Reproduction 62, 1360-1369.], their kinesin-like proteins expressed in bacteria using recombinant DNA techniques and the effects of ACR, glycidamide (GLY) and propionamide (a non-neurotoxic metabolite) on the function of two of the identified kinesin motors were tested. KIFC5A MT bundling activity, required for mitotic spindle formation, was measured in an MT-binding assay. Both ACR and GLY caused a similar concentration-dependent reduction in the binding of MT; concentrations of 100 microM ACR or GLY reduced its activity by 60%. KRP2 MT disassembling activity was assayed using the quantity of tubulin disassembled from taxol-stabilized MT. Both ACR and GLY inhibited KRP2-induced MT disassembly. GLY was substantially more potent; significant reductions of 60% were achieved by 500 microM, a comparable inhibition by ACR required a 5 mM concentration. Propionamide had no significant effect on either kinesin, except KRP2 at 10 mM. This is the first report of ACR inhibition of a mitotic/meiotic motor protein. ACR (or GLY) inhibition of kinesin may be an alternative mechanism to DNA adduction in the production of cell division defects and potential carcinogenicity. We conclude that ACR may act on multiple kinesin family members and produce toxicities in organs highly dependent on microtubule-based functions.

Impact of diuron on aneuploidy and hemocyte parameters in Pacific oyster, Crassostrea gigas

Diuron is a substituted urea herbicide used for agricultural and nonagricultural weed control. Its widespread use and relatively slow breakdown led us to analyze its influence on aneuploidy level (lowered chromosome number in a percentage of somatic cells) and hemocyte parameters in Pacific oysters, Crassostrea gigas. Adult oysters were subjected to two diuron concentrations (300 ng L(-1) and 3 microg L(-1)) for 11 weeks. Significantly higher aneuploidy level was observed in diuron-treated oysters compared with the control. Furthermore, the observed impact on aneuploidy persisted to the next generation as offspring exhibited significantly higher aneuploidy levels when their parents had been exposed to diuron. Significant increases in hemocyte parameters (cell mortality, phagocytosis, granulocyte percentage, reactive oxygen species, and lysosome presence) of the adults were also observed after 4 weeks of diuron exposure. The effects observed on oyster aneuploidy level and hemocyte parameters could have serious environmental and practical consequences.

Number of centromeric signals in micronuclei and mechanisms of aneuploidy

Genome instability or changes in chromosome structure and number are important facets of oncogenesis. Aneuploidy is a major cause of human reproductive failure and plays a large role in cancer. It is therefore important that any increase in its frequency due to occupational exposure to mutagens and carcinogens should be recognized and controlled. In recent years, the cytokinesis-block micronucleus assay has emerged as a biomarker of chromosome/genome damage relevant to cancer. Fluorescent in situ hybridisation using human pancentromeric DNA probes discriminates between the presence of acentric chromosomal fragments and whole chromosomes in binucleated micronucleated lymphocytes. The separated analysis of centromeric micronuclei may improve the sensitivity of the micronucleus assay in detecting genotoxic effects and chromosome instability. Our previous findings suggest that aneugenic events leading to micronuclei (MN) containing a single centromere (C1+MN) and two or more centromeres (Cx+MN) may arise through different pathways. Chromosome migration impairment would lead to increased C1+MN frequency whereas centrosome amplification would induce Cx+MN with three or more centromeric signals. Additional studies that target cellular defects on the centrosome (microtubule nucleation, organization of the spindle poles, cell cycle progression) are required to better understand aneuploid cell production.

High-specificity and high-sensitivity genotoxicity assessment in a human cell line: Validation of the GreenScreen HC GADD45a-GFP genotoxicity assay

The battery of genetic toxicity tests required by most regulatory authorities includes both bacterial and mammalian cell assays and identifies practically all genotoxic carcinogens. However, the relatively high specificity of the Salmonella mutagenicity assay (Ames test) is offset by the low specificity of the established mammalian cell assays, which leads to difficulties in the interpretation of the biological relevance of results. This paper describes a new high-throughput assay that links the regulation of the human GADD45a gene to the production of Green Fluorescent Protein (GFP). A study of 75 well-characterised genotoxic and non-genotoxic compounds with diverse mechanisms of DNA-damage induction (including aneugens) reveals that the assay responds positively to all classes of genotoxic damage with both high specificity and high sensitivity. The current micro-well assay format does not include metabolic activation, but a separate low-throughput protocol demonstrates a successful proof-of-principle for an S9 metabolic activation assay with the model pro-mutagen cyclophosphamide. The test should be of value both as a tool in the selection of candidate compounds for further development, where additional data may be required because of conflicting information from the in vitro test battery, or in product development areas where the use of animals is to be discontinued. As a microplate assay however, it has the qualities of high throughput and low compound use that will facilitate its application in early screening for genotoxic liability.

SFTG international collaborative study on in vitro micronucleus test

This study on the in vitro micronucleus assay, comprising 11 laboratories using human lymphocytes, was coordinated by an organizing committee supported by the SFTG (the French branch of the European Environmental Mutagen Society). Nine coded substances were assessed for their ability to induce micronuclei in human lymphocytes in vitro, mitomycin C being used as a positive control. Cultures were exposed to the test substances for a short (early or late) time or for a long time, followed by a short or long recovery period, in the presence of cytochalasin B. Each chemical was evaluated, generally in two laboratories, using three treatment schedules at least twice. The data were assessed for acceptability, and then classified as negative, positive or equivocal. Two of seven genotoxic compounds, namely colchicine and bleomycin, clearly induced micronuclei. Reproducible results were difficult to obtain for some substances, which tended to be those acting at specific stages of the cell cycle. Cytosine arabinoside, diethylstilboestrol and 5-fluorouracil were classified as equivocal. Urethane and thiabendazole were classified as negative. The two presumed non-genotoxic compounds, mannitol and clofibrate, did not induce micronuclei. Repeat testing, exposing cells at both an early and late time after mitogenic stimulation, was needed to detect substances classified as equivocal. These results show the importance of achieving sufficient inhibition of nuclear division to avoid the possibility of missing an effect. The evaluation of micronuclei in mononucleated as well as binucleated cells was particularly useful to detect aneugens. There were no false positive results using lymphocytes, indicating a high specificity. It is concluded that the clastogenic or aneugenic potential in vitro of the substances tested was correctly identified in this study, but that refining the protocol to take into account factors such as the stages of the cell cycle exposed to the compound, or the duration of recovery would be likely to improve the sensitivity of detection using lymphocytes.

SFTG international collaborative study on in vitro micronucleus test I. General conditions and overall conclusions of the study

This study, coordinated by the SFTG (French branch of European Environmental Mutagen Society), included 38 participants from Europe, Japan and America. Clastogens (bleomycin, urethane), including base and nucleoside analogs (5-fluorouracil and cytosine arabinoside), aneugens and/or polyploidy inducers (colchicine, diethylstilboestrol, griseofulvin and thiabendazole), as well as non-genotoxic compounds (mannitol and clofibrate), were tested. Four cell types were used, i.e. human lymphocytes in the presence of cytochalasin B and CHO, CHL and L5178Y cell lines, in the presence or absence of cytochalasin B, with various treatment-recovery schedules. Mitomycin C was used as a positive control for all cell types. Mannitol and clofibrate were consistently negative in all cell types and with all treatment-recovery conditions. Urethane, known to induce questionable clastogenicity, was not found as positive. Bleomycin and mitomycin C were found positive in all treatment-recovery conditions. The base and nucleoside analogs were less easy to detect, especially 5-fluorouracil due to the interference with cytotoxicity, while cytosine arabinoside was detected in all cell types depending on the treatment-recovery schedule. Aneugens (colchicine, diethylstilboestrol and griseofulvin) were all detected in all cell types. In this study, the optimal detection was ensured when a short treatment followed by a long recovery was associated with a long continuous treatment without recovery. There was no impact of the presence or absence of cytochalasin B on the detection of micronucleated cells on cell lines. Scoring micronucleated cells in both mononucleated and binucleated cells when using cytochalasin B was confirmed to be useful for the detection and the identification of aneugens. In conclusion, these results, together with previously published validation studies, provide a useful contribution to the optimisation of a study protocol for the detection of both clastogens and aneugens in the in vitro micronucleus test.

Personal and Occupational Exposure to Organic Solvents and Risk of Non-Hodgkin’s Lymphoma (NHL) in Women (United States)

OBJECTIVES

The authors assessed whether home and occupational exposure to organic solvents is associated with risk of NHL in women.

METHODS

A population-based, incidence case-control study was conducted in upstate New York, involving 376 NHL cases and 463 population controls selected from the Medicare beneficiary files and State driver's license records. Exposure information was obtained by telephone interview. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using an unconditional logistic regression model, adjusting for a number of risk factors for NHL.

RESULTS

Overall, history of exposure to organic solvents was not associated with the risk of NHL. A statistically significant increase in risk associated with occupational exposure was observed only for the subjects whose first exposure occurred before 1970 (OR=1.87, 95% CI 1.03-3.40). When occupational and home exposures to paint thinners/turpentine were combined and analyzed together, the risk of NHL associated with any exposure, compared to no exposure at either job or home, was a statistically significantly increased (OR=1.46, 95% CI: 1.05-2.03). This observation was more pronounced for B-cell lymphoma and for low-grade lymphoma with ORs of 1.52 (95 CI: 1.08-2.14) and 2.20 (95% CI; 1.42-3.41), respectively.

CONCLUSIONS

The results of this case-control study do support of a major role of organic solvents in the development of NHL among women currently living in the US. However, relatively intensive exposure in past occupations and use of paint thinners/turpentine may deserve further investigation.

Pesticides and the induction of aneuploidy in human sperm

Pesticides are some of the most frequently released toxic chemicals into the environment. Exposure to them has been associated with reproductive dysfunction, but the knowledge of the genotoxic risks of these substances is still limited. In vitro and in vivo, many pesticides are shown to induce aneuploidy. Analysis of sperm chromosomes by fluorescence in situ hybridization (FISH) with chromosome-specific probes has obtained increasing popularity in genetic toxicology. Sperm-FISH studies on men exposed to pesticides have yielded conflicting results: in men exposed to multiple pesticides during spraying no increased disomy frequencies in sperm were observed, although one study reported an increased rate of sex chromosome nullisomy. In contrast the two studies conducted in pesticide factories showed increased frequencies of sperm aneuploidy in exposed men compared to controls. The available data indicates that at least some of the commonly used pesticides are capable of inducing aneuploidy in human sperm when the exposure level is high enough.

Evaluation of the ability of a battery of three in vitro genotoxicity tests to discriminate rodent carcinogens and non-carcinogens I. Sensitivity, specificity and relative predictivity

The performance of a battery of three of the most commonly used in vitro genotoxicity tests--Ames+mouse lymphoma assay (MLA)+in vitro micronucleus (MN) or chromosomal aberrations (CA) test--has been evaluated for its ability to discriminate rodent carcinogens and non-carcinogens, from a large database of over 700 chemicals compiled from the CPDB ("Gold"), NTP, IARC and other publications. We re-evaluated many (113 MLA and 30 CA) previously published genotoxicity results in order to categorise the performance of these assays using the response categories we established. The sensitivity of the three-test battery was high. Of the 553 carcinogens for which there were valid genotoxicity data, 93% of the rodent carcinogens evaluated in at least one assay gave positive results in at least one of the three tests. Combinations of two and three test systems had greater sensitivity than individual tests resulting in sensitivities of around 90% or more, depending on test combination. Only 19 carcinogens (out of 206 tested in all three tests, considering CA and MN as alternatives) gave consistently negative results in a full three-test battery. Most were either carcinogenic via a non-genotoxic mechanism (liver enzyme inducers, peroxisome proliferators, hormonal carcinogens) considered not necessarily relevant for humans, or were extremely weak (presumed) genotoxic carcinogens (e.g. N-nitrosodiphenylamine). Two carcinogens (5-chloro-o-toluidine, 1,1,2,2-tetrachloroethane) may have a genotoxic element to their carcinogenicity and may have been expected to produce positive results somewhere in the battery. We identified 183 chemicals that were non-carcinogenic after testing in both male and female rats and mice. There were genotoxicity data on 177 of these. The specificity of the Ames test was reasonable (73.9%), but all mammalian cell tests had very low specificity (i.e. below 45%), and this declined to extremely low levels in combinations of two and three test systems. When all three tests were performed, 75-95% of non-carcinogens gave positive (i.e. false positive) results in at least one test in the battery. The extremely low specificity highlights the importance of understanding the mechanism by which genotoxicity may be induced (whether it is relevant for the whole animal or human) and using weight of evidence approaches to assess the carcinogenic risk from a positive genotoxicity signal. It also highlights deficiencies in the current prediction from and understanding of such in vitro results for the in vivo situation. It may even signal the need for either a reassessment of the conditions and criteria for positive results (cytotoxicity, solubility, etc.) or the development and use of a completely new set of in vitro tests (e.g. mutation in transgenic cell lines, systems with inherent metabolic activity avoiding the use of S9, measurement of genetic changes in more cancer-relevant genes or hotspots of genes, etc.). It was very difficult to assess the performance of the in vitro MN test, particularly in combination with other assays, because the published database for this assay is relatively small at this time. The specificity values for the in vitro MN assay may improve if data from a larger proportion of the known non-carcinogens becomes available, and a larger published database of results with the MN assay is urgently needed if this test is to be appreciated for regulatory use. However, specificity levels of <50% will still be unacceptable. Despite these issues, by adopting a relative predictivity (RP) measure (ratio of real:false results), it was possible to establish that positive results in all three tests indicate the chemical is greater than three times more likely to be a rodent carcinogen than a non-carcinogen. Likewise, negative results in all three tests indicate the chemical is greater than two times more likely to be a rodent non-carcinogen than a carcinogen. This RP measure is considered a useful tool for industry to assess the likelihood of a chemical possessing carcinogenic potential from batteries of positive or negative results.

Veterinary pharmacovigilance. Part 6. Predictability of adverse reactions in animals from laboratory toxicology studies

Toxicological studies are conducted on constituents of veterinary medicinal products for a number of reasons. Aside from being a requirement of legislation, they are carried out for predictive purposes in the assessment of user safety or for the determination of consumer safety, for example, in the elaboration of maximum residue limits or tolerances. Alternatively, the results of toxicology studies may be available as they have been generated for registration of the drug for human medicinal purposes. This paper examines if the results of such studies have any predictive value for adverse reactions, which might occur during clinical use in animals. A number of adverse reactions, notably the Type A (toxicology or pharmacology dependent) should be predictable from these laboratory studies. However, as with human pharmaceutical products, they have less utility in predicting Type-B reactions (idiosyncratic in nature).

A comparison of genotoxicity between three common heterocyclic amines and acrylamide

Heterocyclic amines (HCAs), a group of genotoxic compounds formed during the heating of proteinaceous food items, have been known since the late 1970s. However, the genotoxic effect of these compounds in the low dose region has not yet been thoroughly studied. Here we used a sensitive flow cytometer-based micronucleus assay in mice to determine the frequency of micronucleated erythrocytes (fMPCE) of the three common HCAs, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), in the low dose region. We especially looked for any deviation from linearity of the dose-response curves. Male Balb/C mice were intra peritoneally injected with different doses of either PhIP (0-36 mg/kg b.w.), MeIQx (0-90 mg/kg b.w.) or IQ (0-40 mg/kg b.w.). In the case of PhIP, we found a significant dose-response relationship, while MeIQx and IQ did not display an increased fMPCE level. This flow cytometer method allows for determination of the DNA content of micronuclei. All three HCAs tested here yielded a low DNA content of micronuclei, indicating that they do not possess aneugenic effects. A comparison between the HCAs and acrylamide (AA), another heat induced genotoxic compound, revealed that the slope of the dose-response curve is about 10 times steeper for PhIP than AA. In spite of this, AA probably constitutes a higher human risk than HCAs since the intake is about a 100- to 1000-fold higher than the intake of HCAs.

Cytogenetic Consequences of Vinblastine Treatment in Mouse Bone Marrow

BACKGROUND

Vinblastine (VBL), a vinca alkaloid, has very often been included in different cancer chemotherapeutic treatment regimens. Chemotherapy cures certain cancers and, at least, increases the life expectancy of cancer patients. However, in cancer survivors, a second malignancy frequently occurs after chemotherapy, which warrants detailed genotoxicity testing of the chemotherapeutic agents. The available genotoxicity test reports on VBL are self-contradictory and inconclusive. Thus, following a suitable experimental protocol, it is necessary to test the cytogenetic consequences of VBL treatment in mammals.

METHODS

Swiss mice received 1 of 3 different doses of VBL (0.5, 1.0 and 1.5 mg/kg body weight) as a single intraperitoneal injection. The cytogenetic toxicity of VBL was assessed from the induced aberrant metaphases, chromosomal aberrations (CAs) excluding gaps and the mitotic index (MI) 24 h after treatment, and micronuclei (MN) 30 h after treatment.

RESULTS

All 3 doses of VBL induced statistically significant (p < or = 0.01) percentages of aberrant metaphases and CAs, but there was no significant change in the MI. The induced percentage of aberrant metaphases and CAs were decreased with the increase in the dose of VBL. On the other hand, there was a dose-dependent and significant (p < or = 0.01) increase in MN induction.

CONCLUSIONS

The results of this study indicate the clastogenic potential of VBL in the mouse bone marrow. In the present study, the induction of numerous relatively large-sized MN by VBL is in agreement with the reported aneugenic action of the drug. Although VBL is cytotoxic and is a spindle poison, the mechanism(s) involved in bringing about its clastogenic effects is yet to be elucidated.

Chromosome malsegregation induced by the rodent carcinogens acetamide, pyridine and diethanolamine in Drosophila melanogaster females

The effect of the rodent carcinogens acetamide (AC), pyridine (PY) and diethanolamine (DEA) on meiotic chromosome segregation was assessed in 4-day-old Drosophila melanogaster females. After oral treatment with 0.05, 0.1, 0.2 and 0.3% PY; 0.5, 1, 1.5, 2 and 4% AC; or 5, 10, 20, 40 and 80% DEA, the females were mated to 7-day-old males and three 24h broods were obtained to sample cells exposed mainly as mature oocytes (brood I), and nearly mature oocytes (brood II) with an increasing proportion of early oocytes (brood III). Viability was not affected at the two (PY) or three (AC, DEA) lowest concentrations, decreasing thereafter. PY increased the frequency of nondisjunction exclusively in brood II suggesting its interaction with specific targets. AC and DEA (the most active of the three) induced similar frequencies of nondisjunction in all broods suggesting unspecific cell division perturbations probably due to toxicity. No clear dose effect relationships were observed.

Effect of the dithiocarbamate pesticide zineb and its commercial formulation, the azzurro. V. Abnormalities induced in the spindle apparatus of transformed and non-transformed mammalian cell lines

Abnormalities induced in the mitotic spindle by zineb and azzurro (1.0-25.0 micro g/ml, 24h) were evaluated in Chinese hamster ovary (CHO) and HeLa cells, and in non-transformed human fibroblasts (NTHF). Spindles were stained with FITC-conjugated anti-beta tubulin. Treatment with 10.0 micro g/ml of zineb induced complete inhibition of cell viability in NTHF cells while 10.0 micro g/ml of azzurro decreased cell growth down to 62%. Higher doses of both compounds induced cell death. In HeLa and CHO cells, 15.0 micro g/ml of zineb and 10.0-15.0 micro g/ml of azzurro decreased viability, whereas 25.0 micro g/ml of both compounds was cytotoxic. A significantly decreased mitotic index (MI) was observed in NTHF treated with 5.0 micro g/ml zineb or azzurro, whereas 10.0 micro g/ml of both chemicals were necessary to induce the same phenomenon in HeLa and CHO cells. Treatment with 1.0-5.0 micro g/ml of zineb or azzurro induced a dose-dependent increase of degenerated spindles in NTHF and the number of degenerated or multipolar spindles in HeLa and CHO cells increased in a dose-dependent manner with 1.0-10.0 micro g/ml zineb and azzurro. Although zineb and azzurro were able to induce mitotic spindle abnormalities in all cell types, non-transformed cells were less resistant than immortalized cells.

Using CTLL-2 and CTLL-2 bcl2 cells to avoid interference by apoptosis in the in vitro micronucleus test

In vitro assays for chromosome aberrations (i.e., in vitro micronucleus and in vitro metaphase analysis tests) frequently produce false-positive or exaggerated-positive results. Our previous work suggested that apoptosis interferes with these tests, producing misleading results. These previous studies were conducted by performing the in vitro micronucleus test in CTLL-2 cells and a CTLL-2 cell derivative stably transfected with the apoptosis inhibitor gene bcl2. In the present study, these previous observations were extended by examining micronucleus induction with a larger number of compounds in both CTLL-2 and CTLL-2 bcl2 cells and measuring apoptosis with annexin V-FITC. Both cell lines were treated with different classes of compounds that were anticipated to be exclusively apoptosis inducers, or compounds known to be clastogens or aneugens, some of which were anticipated to be both genotoxic and apoptotic. We were able to confirm that compounds that are only apoptogenic induced micronuclei in CTLL-2 but not CTLL-2 bcl2 cells, indicating that the positive responses are due to apoptosis in CTLL-2 cells. Some genotoxins (clastogens and aneugens) did not produce apoptosis by the annexin V assay and gave similar responses in CTLL-2 and CTLL-2 bcl2 cells. Finally, higher responses were induced in CTLL-2 cells compared to CTLL-2 bcl2 cells that were treated with aneugens or clastogens that were also apoptosis inducers, suggesting that the greater response in CTLL-2 cells is a consequence of both genotoxicity and apoptosis. Finally, it was demonstrated that just eliminating CTLL-2 cells having three or more micronuclei from scoring was not adequate for correctly evaluating agents that only produce apoptosis. The results indicate that coupling the in vitro micronucleus test in both CTLL-2 and CTLL-2 bcl2 cells with the measurement of apoptosis is able to distinguish the genotoxic effects of a test compound from its apoptotic potential and is able to avoid interference from apoptosis in the in vitro micronucleus test. These observations may provide the basis for a useful genotoxicity assay.

The rodent carcinogens 1,4-dioxane and thiourea induce meiotic non-disjunction in Drosophila melanogaster females

The ability of the rodent carcinogens 1,4-dioxane (DX) and thiourea (TU) to induce meiotic non-disjunction (ND) was assessed in 3- and 6-day-old Drosophila melanogaster females. The chemicals were administered orally and three 24 h and one 48 h broods were obtained after mating, to sample oocytes treated in increasingly earlier stages of development. The broods represent mainly mature oocytes (brood I), nearly mature oocytes (brood II), early oocytes (brood III) and very early oocytes (brood IV). The toxicity of DX increased with dose (1% (not toxic), 1.5, 2, 3, 3.5%) as well as a reduction in fecundity which was moderate. Induction of ND in mature oocytes was positive with 2, 3 and 3.5% concentrations and was not related to dose. In immature oocytes it was also positive though already at the lowest concentration tested (1%), suggesting a sensitivity higher than that of mature oocytes. TU at 0.10-10%, did not affect viability, but since fecundity was seriously impaired at high doses, ND was not assessed beyond the 1.5% concentration. TU also induced ND in mature and in immature oocytes; neither a threshold nor a dose effect was detected. The response of mature oocytes was lower than that of immature oocytes. TU induced increases of ND in the earliest cells tested in a more consistent fashion than DX. The data clearly show that both chemicals induced ND in mature oocytes and in the three subsets in which immature oocytes were fractionated. Though toxicity may play a significant unspecific role in the induction of chromosome malsegregation by DX and TU, the induction of ND at low doses, moderately toxic to the oocytes, suggests that the interaction with specific targets contributed to the results obtained.

Effect of hydroquinone on meiotic segregation in Drosophila melanogaster females

The induction of sex chromosomes meiotic nondisjunction (ND) by hydroquinone (HQ) given orally was investigated in Drosophila melanogaster 2-7, 8-22, 24, 48, 72 and 96 h-old females. ND was assessed by a system where exceptional females (XXY) and only 1/4 of the expected regular progeny are viable. Oocytes were treated at different stages of development. 4% HQ tested only in 72 h-old females induced ND in oocytes sampled in brood I (mostly mature oocytes at metaphase I). 6% HQ increased ND in brood I of 8-22 h-old females, while other broods, (including cells treated at early prophase) were also affected in older flies, the highest significance being attained in the 48 h-old series. Newly hatched females (2-7 h-old) were refractory to the treatment, though oocytes sampled in the first three subcultures are comparable to cells showing enhancement of ND in series run with older females. Toxicity of 2, 4 and 6% HQ increased with concentration and females' age: (a) 2% was not toxic; (b) 4% was toxic only to 72 h-old females; (c) 6% was increasingly toxic to females 24, 48 and 72 h-old. The results indicate that age plays a significant role on both chromosomal segregation and toxicity and suggest that in Drosophila HQ is metabolized to its reactive species. The lack of toxic and aneugenic effect in very young females could reflect a more efficient detoxification due to the known high specific activity of glutathione-S-transferase (GST) after eclosion. The decline in GST activity around day 2 of adult life coincides with the high effect of HQ in 48 h-old females.

Induction of micronuclei in vitro by organochlorine compounds in beluga whale skin fibroblasts

Beluga whales (Delphinapterus leucas) inhabiting the St. Lawrence estuary are highly contaminated with environmental pollutants and have a high incidence of cancer. Environmental contaminants may be partly responsible for the high cancer incidence observed in this population. DNA damage plays an important role in the development of cancer. The micronuclei (MN) assay was used to test the genotoxic potential of organochlorine (OC) pesticides with and without external metabolic factor in skin fibroblasts of an Arctic beluga whale. Toxaphene, chlordane and p,p'-DDT induced significant (p<0. 05) concentration-response increases of micronucleated cells (MNCs). Statistically significant increases in MNCs, ranging from 1.7- to 5-folds when compared to control cultures, were observed for 0.05, 0. 5, 5 and 10 microg/ml toxaphene, 2, 5 and 10 microg/ml chlordane and 10 and 15 microg/ml p,p'-DDT. Presence of exogeneous metabolic factor (S9) completely abolished the MN induction potency of chlordane and p,p'-DDT, and toxaphene induced MN formation at higher concentrations (0.5 microg/ml) than without S9 mix. The ecotoxicological significance of MN induction by low concentrations of toxaphene is unknown and do not imply that toxaphene is involved in the etiology of cancer in St. Lawrence beluga whales. However, because of the known genotoxicity of toxaphene and the long lifespan of beluga whales, it cannot be excluded that toxaphene may pose a long-term genetic hazard to the more contaminated whales of this population.

Spindle disturbances induced by benzo[a]pyrene and 7, 12-dimethylbenz[a]anthracene in a Chinese hamster cell line (V79-MZ) and the stability of the numerical chromosome aberrations that follow

We previously reported that benzo[a]pyrene (BP) and 7, 12-dimethylbenz[a]anthracene (DMBA) induce aneuploidy and polyploidy, respectively, in the Chinese hamster cell line V79-MZ in the absence of S9 mix. In the present study we investigated the effect of BP and DMBA on the mitotic spindle. BP caused incomplete spindle formation and DMBA inhibited spindle formation completely. The combined results indicate that incomplete spindles caused by BP resulted in aneuploidy, and the absence of spindle formation caused by DMBA resulted in polyploidy. The induced polyploidy was stable for several serial passages in fresh medium. BP and DMBA induced different chromosome number distributions. After BP treatment, the normal distribution of chromosome number was restored in 4 days. After DMBA treatment, on the other hand, a tetraploid peak was maintained for 2 months following an initial transient broad distribution of chromosome number after 1 day. The results suggest that different mechanisms were involved in the induction of numerical aberrations by BP and DMBA. Furthermore the induction of numerical aberrations by BP and DMBA was reproducible over 5 months of passages. In four clones tested, the frequency of cells with the modal chromosome number in control cultures gradually decreased from 82% on the average just after cloning to 62% 5 months later. BP and DMBA induced characteristic ploidy changes following succeeding cell passages for up to 5 months, indicating that the ability to respond to BP and DMBA was stable for that period of time. Because these findings were specific to V79-MZ cells, this cell line might be a good tool for studying chemicals that induce numerical chromosome aberrations.

Genetics of oocyte ageing

OBJECTIVES

Correlations between parental age, aneuploidy in germ cells and recent findings on aetiological factors in mammalian trisomy formation are reviewed.

METHODS

Data from observations in human oocytes, molecular studies on the origin of extra chromosomes in trisomies, experiments in a mouse model system, and transgenic approaches are shown.

RESULTS

Errors in chromosome segregation are most frequent in meiosis I of oogenesis in mammals and predominantly predispose specific chromosomes and susceptible chiasmate configurations to maternal age-related nondisjunction. Studies on spindle structure, cell cycle and chromosome behaviour in oocytes of the CBA/Ca mouse used as a model for the maternal age-effect suggest that hormonal homeostasis and size of the follicle pool influence the quality, maturation competence and spindle size of the mammalian oocyte. Predisposition to errors in chromosome segregation are critically dependent on altered cell cycles. Compromised protein synthesis and mitochondrial function affect maturation kinetics and spindle formation, and cause untimely segregation of chromosomes (predivision), mimicking an aged phenotype.

CONCLUSIONS

Altered cell cycles and untimely resolution of chiasmata but also nondisjunction of late segregating homologues caused by asynchrony in cytoplasmic and nuclear maturation appear to be causal to errors in chromosome segregation with advanced maternal age. Oocytes appear to lack checkpoints guarding against untimely chromosome segregation. Genes and exposures affecting pool size, hormonal homeostasis and interactions between oocytes and their somatic compartment and thus quality of follicles and oocytes have the potential to critically influence chromosome distribution in female meiosis and affect fertility in humans and other mammals.

Cytogenetic consequences after occupational exposure to antineoplastic drugs

Cytogenetic monitoring was carried out on a group of 38 nurses who reconstitute antineoplastic drugs in order to determine the extent of chromosomal damage. Genotoxic activities of antineoplastic drugs are studied by chromosome aberration assay, micronucleus assay, sister chromatid exchange (SCE) frequency high frequency cells (HFC) analysis, and mitotic activity of peripheral lymphocytes. Results confirmed that occupational exposure to a mixture of antineoplastic drugs may cause genome damages. The results of this study show that biomonitoring after exposure to a mixture of antineoplastic drugs which express clastogenic and aneugenic activity should involve a battery of cytogenetic methods.

Cytogenetic monitoring of pesticide sprayers

The induction of chromosome aberrations, micronuclei, and sister-chromatid exchanges (SCEs) was examined in cultured lymphocytes of 27 vineyard growers exposed to pesticides. Cytogenetic examinations were performed during the prespraying period, a month after spraying, and at the end of the spraying season. For comparison purposes, the same cytogenetic monitoring program was applied to two control groups. The first consisted of 15 individuals from a nearby town, and the second consisted of 20 volunteers living 200 km from the vine-growing area (reference control group). A positive, though low statistically significant (P < 0.017) difference in the yield of unstable chromosomal aberrations in exposed sprayers was observed compared with both control groups during the prespraying period. The mean group value of micronuclei in exposed workers averaged 5.41 per 1000 binucleated cells, with individual means ranging from 0 to 15. In both control groups, the yield of micronuclei averaged 5.09 per 1000 binucleated cells, with individual means ranging from 1 to 10. No statistically significant (P < 0.5) differences in yield of micronuclei were found in exposed subjects compared with both control groups. Significant individual variation (F = 14.09, P < 0.000) in SCE frequency was observed in exposed subjects, as well as in both control groups (F = 14.09, P < 0.000). A month after spraying, the average incidence of unstable aberrations in pesticide sprayers was 0.22%, and the yield of micronuclei averaged 17.78 per 1000 binucleated cells, with individual means ranging from 7 to 28. The incidence of micronuclei a month after spraying in exposed subjects was elevated (statistically significant at P < 0.01) in comparison with the prespraying period, while the difference in the yield of chromosomal aberrations in exposed subjects was insignificant (P < 0.5). At the end of the spraying season, the average incidence of unstable aberrations in exposed subjects was 0.79%, and the yield of micronuclei averaged 39.92 micronuclei per 1000 binucleated cells, with individual means ranging from 21 to 62. The appearance of more than one micronucleus per binucleated cell was related to the results on chromosome aberrations. The frequencies of chromosomal aberrations and micronuclei were significantly higher (P < 0.001, P < 0.000) in the exposed group than in their matched control groups. The yield of micronuclei in pesticide sprayers at the end of the season was higher than expected with respect to chromosomal aberration frequency, which provides some evidence that some of the micronuclei are induced by the spindle-inhibiting effects of pesticides. A statistically significant (P < 0.003) difference in micronuclei in the first control group was observed compared with the reference control group at the end of the spraying season. With respect to the incidence of micronuclei in the control group in the vine-growing area, a poor but positive correlation (r = 0.074, P < 0.104) with duration of the spraying season was found, which is probably due to airborne pesticides in the vine-growing area. SCE frequencies of the workers' lymphocytes were not significantly changed due to the exposure. The yield of aberrations as well as that of micronuclei in exposed subjects correlated positively (r = 16, P = 0.016) with duration of exposure.

Chromosomal mutations and chromosome loss measured in a new human-hamster hybrid cell line, ALC: studies with colcemid, ultraviolet irradiation, and 137Cs gamma-rays

Small mutations, megabase deletions, and aneuploidy are involved in carcinogenesis and genetic defects, so it is important to be able to quantify these mutations and understand mechanisms of their creation. We have previously quantified a spectrum of mutations, including megabase deletions, in human chromosome 11, the sole human chromosome in a hamster-human hybrid cell line AL. S1- mutants have lost expression of a human cell surface antigen, S1, which is encoded by the M1C1 gene at 11p13 so that mutants can be detected via a complement-mediated cytotoxicity assay in which S1+ cells are killed and S1- cells survive. But loss of genes located on the tip of the short arm of 11 (11p15.5) is lethal to the AL hybrid, so that mutants that have lost the entire chromosome 11 die and escape detection. To circumvent this, we fused AL with Chinese hamster ovary (CHO) cells to produce a new hybrid, ALC, in which the requirement for maintaining 11p15.5 is relieved, allowing us to detect mutations events involving loss of 11p15.5. We evaluated the usefulness of this hybrid by conducting mutagenesis studies with colcemid, 137Cs gamma-radiation and UV 254 nm light. Colcemid induced 1000 more S1- mutants per unit dose in ALC than in AL; the increase for UV 254 nm light was only two-fold; and the increase for 137Cs gamma-rays was 12-fold. The increase in S1- mutant fraction in ALC cells treated with colcemid and 137Cs gamma-rays were largely due to chromosome loss and 11p deletions often containing a breakpoint within the centromeric region.

Research on the mechanisms of action of aneugenic chemicals and regulatory approaches for their control in the European Communities

The European Communities have developed a wide range of regulatory instruments for the control of chemical products sold and used within its geographical area. An important part of the testing requirements for most chemicals within the European Communities is the preparation of an information package on the potential mutogen properties of each chemical. Currently, no test requirements specify a unique test for aneugenic activity, although current methods such as in vitro cytogenetic and bone marrow micronucleus assays provide some useful indirect information on aneugenic activity. During the past 15 years the European Communities supported a series of collaborative research projects that have investigated the mechanisms by which chemicals induce aneuploidy and developmental studies of test methods for the detection of aneugenic chemicals. These projects led to the development of in vitro methods for the detection and quantification of induced nondisjunction and chromosome loss and the measurement of aneuploidy in rodent bone marrow. The European Communities projects have demonstrated the aneugenic potential of a diverse range of chemicals and their potential role in inherited disease and tumour induction. However, regulatory guidelines have yet to be modified to take advantage of the methods developed for the detection and evaluation of aneugenic chemicals.