Showing papers in "Mutation Research\/reviews in Genetic Toxicology in 1981"

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

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

Mammalian in vivo and in vitro cytogenetic assays: a report of the U.S. EPA's gene-tox program.

Abstract: This report presents an assessment made by the U.S. Environmental Protection Agency Gene-Tox Program's Work Group on mammalian cytogenetics of the clastogenic effects of chemicals in in vivo and in vitro mammalian cell assays. This assessment is based on information provided by the Environmental Mutagen Information Center, Oak Ridge National Laboratory, with the proviso that the experimental protocol used in these papers was adjudged to be acceptable by standards outlined by the Work Group. Some data were accepted as "qualitative only" because the protocol used was fairly close to that proposed as suitable. Using these criteria, 177 papers were selected for review. 6 assays were reviewed: bone marrow (32 papers, 31 chemicals), spermatogonial (10 papers, 10 chemicals), spermatocyte (25 papers, 25 chemicals), oocyte or early embryo (18 papers, 19 chemicals), in vitro cell culture (30 papers, 66 chemicals), and leukocyte (66 papers, 53 chemicals). Each assay was considered separately, and comparisons were then made between them for their similarities or differences in producing a positive or negative clastogenic effect of a particular chemical or chemical class. A large proportion of the available cytogenetic data was not suitable for inclusion in the final data base because of poor experimental design or unsatisfactory reporting of the information. It was not possible to recommend any one assay for determining potential clastogenicity because each had its own particular advantages and limitations and provided unique information. For demonstrating in vivo effects, the bone-marrow assay is probably the simplest and most economical. If only in vitro exposures were considered, leukocytes or cultured mammalian cell lines would be suitable. However, there are advantages to using leukocytes because they are a synchronous population, at least through their cell division, and because of the ready availability of human cells. In general, there was good agreement between clastogenicity and carcinogenicity.

Genetic toxicity of some important epoxides

Abstract: In various biological systems, 1,2-epoxides are able to cause biological effects with genetic mechanisms: point mutations, deletions, chromosomal aberrations, gene conversion, crossing-over, cancer and virus (prophage) induction. Dose—response curves are linear, or should be interpreted to have a linear component that predominates at low doses or concentrations. In forward mutation systems the effectiveness is related to the dose in the target cells and to the chemical reactivity. By applying experimentally determined correction factors for difunctionality (in the case of diepoxides or monoepoxides with a reactive substituent such as a carbonyl group), genetic risks may be estimated by a unitary approach, valid for epoxides in general, if not for all alkylating agents. The use of this approach, to calculate type-II errors in negative carcinogenicity tests, indicates that no data presently available support a conclusion that certain epoxides are non-mutagenic or non-carcinogenic, i.e. are less effective than expected from reactivity data. Determination of the rad-equivalence of genetic risks, i.e. the use of corresponding risks from a unit dose of ionizing radiation as a standard, indicates that the risks associated with Threshold Limit Values for epoxides in work environments in Western countries are 1–2 orders of magnitude higher than permissible risks for radiological workers.

The use of Chinese hamster ovary cells to quantify specific locus mutation and to determine mutagenicity of chemicals. A report of the gene-tox program.

Abstract: The GENE-TOX Group on Specific Gene Mutations in Chinese Hamster Ovary (CHO) Cells has evaluated the use of mutational systems in these cells for identification of mutagenic chemicals from 261 references in the file of the Environmental Mutagen Information Center, Oak Ridge National Laboratory by February, 1979; 68 references were found to be relevant to the stated task. After establishing that the end-point of mutational measurement occurs at a specific locus and the determinations are quantifiable and reproducible, data from 21 references were found to fulfill such requirements. Among them, 14 were concerned with chemically-induced mutations to resistance to a purine analogue, 6-thioguanine, which selects for variants deficient in the enzyme hypoxanthine—guanine phosphoribosyl transferase (HGPRT). This mutational system is referred to as the CHO/HGPRT assay. Studies with other genetic markers offer promise for the development of quantitative specific genemutational assays, but these studies have not advanced thoroughly enough to assess their value. Several lines of genetic, physiological and biochemical evidence support the premise that the CHO/HGPRT system fulfills the criteria for measurement of specific gene mutations using CHO-K1-BH4 subclone and other appropriate CHO subclones. Based largely on published information, this Work Group has suggested a protocol for testing of chemical agents with consideration of the following: cells, media, culture conditions and their quality control, treatment with test compounds with and without an exogenous metabolic activation system, estimation of cytoxicity (cloning efficiency), optimum expression and selection of the mutant phenotype, calculation of mutation frequency, positive and negative controls, vehicles or solvents, spontaneous mutation frequency, dosage selection and number of doses, and collection of raw data. For interpretation of the mutagenesis data, this Work Group recommends various ways of presenting data, numerous criteria for acceptability of data, the need to use appropriate statistical procedures for data evaluation, and a potential applicability of results to hazard evaluation. Evaluation of test performances with 18 chemicals revealed that the correlation between mutagenicity in CHO/HGPRT assay and animal mutagenicity and carcinogenicity is high. Since the number of chemicals tested was small and 17 of the 18 compounds were direct-acting agents, the utility of the system for identification of various classes of potential mutagens and carcinogens cannot be adequately assessed until more chemical classes, especially promutagens, are tested. However, the assay has a sound genetic and biochemical basis for quantifying specific locus mutation reproducibly. The fact that CHO cells are also useful for determination of chemically-induced chromosome aberration and sister-chromatid exchange adds an additional strength to the assay. Future research should address the possible improvement of procedures for phenotypic expression and application for testing gaseous and volatile liquids, as well as such problems as appropriate metabolic activation system(s) and effective statistical procedures common to perhaps all short-term cellular assays. Recent rapid development of mutagen test systems like the CHO/HGPRT assay calls for a need to update and evaluate the data base generated.

On the mutagenicity of nitroimidazoles.

Abstract: Regarding mutagenicity, metronidazole is one of the best-investigated compounds of the nitroimidazoles. This drug is mutagenic on bacteria, especially if base-pair tester strains are used and bacterial nitroreductases are present. The serum levels attained in man after intake of this drug are sufficient to cause mutations in bacteria. Furthermore, interaction with and binding to DNA occurs under anaerobic conditions and sometimes DNA breaks are observed. However, metronidazole does not show mutagenic activity in mammalian cells in vitro; the micronucleus test is negative and chromosome aberrations are only found under anaerobic conditions. With microbial systems the mutagenicity of 47 nitroimidazoles has been investigated. Only 4 compounds were always negative in the applied test systems. Because with base-pair tester strains mutagenicity was assessed, this class of compounds should be regarded as a base-pair mutagen. In fungi, some compounds (e.g. ZK 26173 and azathioprine) are potent mutagens, whilst with most investigated nitroimidazoles only a weak or no mutagenic activity could be detected. Somewhat similar observations have been made in tests with Drosophila melanogaster, a test for gene mutations in mammalian cells, the micronucleus test, cytogenic tests and the dominant lethal test. The reduction products of metronidazole, misonidazole and 1-methyl-2-nitro-5-vinylimidazole, cause DNA damage if the nitro group is reduced in the presence of DNA. Reduction products are formed by microbes in the gut or by mammalian cells under anaerobic conditions. No teratological effect due to metronidazole or most other nitroimidazoles has been observed. Metronidazole is carcinogenic in mice and rats, and dimetridazole in rats. Up to the present, no carcinogenic effects have been observed in man. Azathioprine is probably carcinogenic for man. It is unlikely that the therapeutic applications of the presently used nitroimidazoles, except for azathioprine, will cause an increase in the tumor incidence in man or will cause other genotoxic effects, although such effects cannot be excluded with certainty.

Carcinogenicity, mutagenicity and teratogenicity of nickel.

Abstract: Nickel is widely used in the metallurgical industry, and although not released extensively into the environment, may represent a hazard to human health. Owing to their low absorption from the gastrointestinal tract, nickel compounds, except nickel carbonyl, are essentially non-toxic after ingestion. Epidemiological investigations and experimental studies have demonstrated that certain nickel compounds are extremely potent carcinogens after inhalation, but also that the carcinogenic risk is limited to conditions of occupational exposure. The relatively small number of mutagenicity studies performed up to now do not yet allow definite conclusions as to whether nickel is mutagenic. Nickel can cross the placenta and has embryotoxic and teratogenic properties. The principal hazard of nickel to man, beside its carcinogenicity, however, is its ability to provoke reactions of sensitization.

Bacterial systems for carcinogenicity testing

Abstract: During the past 30 years, bacterial test systems have been extensively refined in their ability to detect not only mutagenic agents but, in many cases, carcinogenic ones as well. Since many carcinogens are known to be activated within the mammalian body, major improvements in bacterial test systems were made when representative parts of mammalian metabolism were included as part of the test protocol. Presently, systems of great simplicity and convenience are available for the efficient detection of gene mutations, lysogenic induction of prophages, and differential DNA repair. These qualities render bacterial systems potentially useful in distinguishing between carcinogens and non-carcinogens, in characterizing induced mutation spectra, and possibly in quantifying mutagenic potency that may be used to predict tumor-initiating potency. Sensitive strains of Salmonella typhimurium, Escherichia coli and Bacillus subtilis with altered DNA-repair capacities have been constructed which accurately identify many carcinogens. Comparative studies have shown that techniques using these strains can be standardized to some extent and that the majority of carcinogens are active in all adequately sensitive genetic systems. Because of this redundancy, it may be sufficient to employ only one standardized set of tester strains and methodology. However, several classes of known carcinogens are undetected or underestimated when assayed in standard testing procedures. Some of these chemicals can be efficiently recognized as mutagens upon varying the methodology, the genetic endpoint, or the mammalian activation system. Thus, to modify and adjust the experimental protocol to the particular type of chemical under study and to calibrate the system with appropriate carcinogenic and non-carcinogenic reference compounds is advisable. It is noteworthy that chemical carcinogens which probably act by non-genotoxic mechanisms thus far remain undetected in bacterial tests. Newly developed systems which measure specific types of genetic events, such as transpositions of DNA segments and derepression of genes, presently are being tested for their ability to detect such carcinogens. A final matter of growing concern is the increasing number of environmental chemicals that are found to be mutagenic in bacteria but for which information about carcinogenic activity in vivo is insufficient. The possible use of bacteria for quantifying mutagenic potency and extrapolating this information to tumor-initiating potency can be envisaged in three ways: (i) direct extrapolation from standard in vitro tests, (ii) indirect extrapolation making use of an in vitro/in vivo comparison of induced effects (the parallelogram method) as devised by Sobels [138] on the basis of identical dose (to DNA), and (iii) host-mediated assays to assess mutagenic potency of carcinogens in selected organs of mammals. As pertains to the first possibility, direct quantitative assessments with those tester strains which are of use in the primary identification phase appears attractive for practical reasons, but presents the following problems: The specific response of genetic endpoints and the exclusive use of repair-deficient tester strains may lead to misinterpretations of induced mutation spectra and to gross underestimations or overestimations of actual mutagenic potency in the corresponding wild-types. On the other hand, in bacteria there are hints that the mutagenic activity of certain classes of chemical carcinogens correlates with their chemical reactivity (with DNA or with model nucleophiles) and that the relative degree of mutagenicity is similar in bacteria and in eukaryotic mutation system. It would appear that the “indirect extrapolation” (item ii above), combined with host-mediated assays, can be of certain value. More systematic studies are needed to determine the most representative genetic endpoints and genetic backgrounds of the tester strains; the feasibility of such quantitative comparisons when using monofunctional alkylating agents are facilitated by the knowledge of DNA adducts potentially responsible for both mutation and tumor-initiation. However, inconsistencies in the pattern of mutagenic response of bacteria to the action of aromatic amines and polycyclic hydrocarbons indicate that the universal role of bacteria as predictive, quantitative indicators of the tumor-initiating potential of chemicals is still uncertain.

Carcinogens and carcinogenesis enhancers

Abstract: The concept that chemical agents may lead to enhancement of carcinogenesis, rather than to its complete induction, is explored to explain the inexact correlation between carcinogen prescreening tests and the results of whole animal bioassays. It is suggested that carcinogenesis-enhancing agents are non-genotoxic chemicals which are positive in animal carcinogenesis bioassays. The importance of understanding the mechanisms of action of carcinogenesis-enhancing agents is emphasized.

Mutagenesis in mammalian cells

Abstract: Chemical mutagenesis in animal cells is a complex process. Whereas some chemicals are mutagenic in their original form, others such as the nitrosamines and polycyclic hydrocarbon carcinogens are mutagenic only when enzymatically activated. The active form, or ultimate carcinogen, can interact with proteins and nucleic acids, altering amino acids and producing modified bases in DNA. The modified bases do not usually constitute mutations as produced. Instead they are acted on by the DNA enzymes of the cell, which repair most damaged bases but occasionally insert incorrect base sequences at or near the sites of damage. The frequency at which mutant animal cells are recovered depends upon the selection conditions in culture, upon whether the mutation selected is in a gene present in single or multiple active copies, and upon whether expression is dominant or recessive. Many studies depend on selecting for 8-azaguanine- or 6-thioguanine-resistant mutants, which are due to mutations in the HGPRT locus present in a single active copy on the X-chromosome. Other widely used systems depend on selecting for ouabain resistance, which is dominant and results from a change in the sodium/potassium ATPase activity, or on selecting for thymidine kinase mutants in heterozygous Tk+/Tk- mouse cells. Many other types of mutation including nutritional markers are recessive and express only in cells carrying a single active gene copy, as is sometimes the case in established cell lines. The types of base damage causing mutations have been identified in very few cases only, and little is known about the enzymatic mechanisms of mutagenesis. However, chemical mutagenesis in cultured animal cells provide a practical way of testing chemicals and radiations for mutagenicity directly in animal cells, and much has been learned about the mutagenicity of various carcinogenic substances. To date, there is reasonable qualitative agreement between these results and those obtained in the widely used liver microsome-activated bacterial mutagenesis test systems.

Epidemiological studies into the possible carcinogenicity of hair dyes

Abstract: As emphasized by Wynder et al. (1963): “With too broad a definition of an occupation, increased risks for specific job categories can be overlooked. On the other hand, with rather restrictive definitions, it becomes unlikely that any study of limited size will yield significant results.”. It follows that duration and intensity of exposure to hair dyes are difficult to determine and the latent period of a possible carcinogenesis is correspondingly difficult to define. It is against this background that investigators have worked. With the exception of Wynder et al. (1963), Cole et al. (1972) and Kinlen et al. (1977), most authors have restricted themselves to brief communications of nonsignificant results. Statistical significance is interpreted in most cases to be P > 0.005, which according to chance must occur in about 5% of the cases. Without specific information on habits like tobacco smoking, it is impossible to decide whether any increase in cancer among barbers and others associated with haircare is occupational or attributable to life-style. From the present review, it seems possible to summarize the following conclusions: Urinary bladder. In their analysis of 300 male and 50 female cases of bladder carcinoma, Wynder et al. (1963) found 4 male hairdressers (all smokers) and 1 female beautician (non-smoker) among the carcinoma patients. No haircare professionals were present in the control group. Howe et al. (1977) analysed 522 cases and observed a significantly increased use of hair dyes among male patients, although accompanied by a strong cigarette association for both sexes. Dunham et al. (1968) found an inconclusive risk for barbers of 5 : 1 among 564 cases and 527 control patients. Anthony and Thomas (1970), reporting on 287 male and 39 female cases, saw a nonsignificant cancer excess of 4 : 1 for hairdressers. Cole et al. (1972) found no excess for barbers. Neutel et al. (1978) contacted 50 pairs of women in a study of bladder tumours and found 18 cases using hair dyes and 19 controls. Their study showed a seemingly protective effect of hair dressing with P Lung. Garfinkel et al. (1977) found a slightly elevated but not significant ratio (P > 0.005) for 3450 cancer deaths, 24 of which were among female beauticians, hairdressers, and cosmeticians with a 6-fold excess in lung cancer, and Menck et al. (1977) found a similar, 2-fold risk. Neither study gave information on smoking habits. Larynx. Viadana et al. (1976) reported an increased number of 10 barbers among 17 714 patients, 76% of whom had cancer, admitted to a cancer hospital. Adjustments were made for smoking but not for alcohol consumption. Breast. In a careful analysis Kinlen et al. (1977) found no difference in the use of hair dyes between 191 breast cancer patients and controls. Working with a smaller sample size of 129 cases, Shore et al. (1979) found an association between the self-reported use of hair dyes and breast cancer beyond the age of 50. The authors expressed a need for further validation of their results. Stavraky et al. (1979) on the basis of a still smaller sample of 85 cases found no support for an association between hair dyes and breast or endometrial uterine cancer but expected to extend their study. Finally, Nasca et al. (1980) have reported on interviews by telephone of 118 breast cancer patients and 233 controls selected by telephone dialling. Among a total of 24 women, they found increased risk of breast cancer among women with a history of benign breast disease and hair dye use. The authors admitted that additional studies were needed before the nature of the associations reported could be determined. General statistics. Data from England, Wales, and the United States provide no substantial evidence to suggest a higher cancer incidence among hairdressers. Detailed analysis of Danish data shows considerable structural changes among the occupations concerned so that further data will be necessary. So far, there is no support for the assumption of any carcinogenic effect on selected organs.