Showing papers in "Mutation Research in 1984"

A review of the genetic effects of ethyl methanesulfonate.

Abstract: Ethyl methanesulfonate (EMS) is a monofunctional ethylating agent that has been found to be mutagenic in a wide variety of genetic test systems from viruses to mammals. It has also been shown to be carcinogenic in mammals. Alkylation of cellular, nucleophilic sites by EMS occurs via a mixed SN1/SN2 reaction mechanism. While ethylation of DNA occurs principally at nitrogen positions in the bases, because of the partial SN1 character of the reaction, EMS is also able to produce significant levels of alkylation at oxygens such as the O6 of guanine and in the DNA phosphate groups. Genetic data obtained using microorganisms suggest that EMS may produce both GC to AT and AT to GC transition mutations. There is also some evidence that EMS can cause base-pair insertions or deletions as well as more extensive intragenic deletions. In higher organisms, there is clear-cut evidence that EMS is able to break chromosomes, although the mechanisms involved are not well understood. An often cited hypothesis is that DNA bases ethylated by EMS (mostly the N-7 position of guanine) gradually hydrolyze from the deoxyribose on the DNA backbone leaving behind an apurinic (or possibly an apyrimidinic) site that is unstable and can lead to single-strand breakage of the DNA. Data also exist that suggest that ethylation of some chromosomal proteins in mouse spermatids by EMS may be an important factor in causing chromosome breakage.

Genotoxic activity and potency of 135 compounds in the Ames reversion test and in a bacterial DNA-repair test

Abstract: Compounds of various chemical classes were comparatively assayed in the Ames reversion test with his- S typhimurium strains TA1535, TA157 , TA1538, TA98, TA100, and, in part, TA97 , and in a DNA-repair test with trp- E coli strains WP2 (repair-proficient), WP67 (uvrA- polA-) and CM871 (uvrA- recA- lexA-) A liquid micromethod procedure for the assessment of the minimal inhibitory concentration (MIC) of test compounds, using the same reagents as the Ames test, was set up and calibrated in its technical details Other techniques (spot test and treat-and-plate method) were applied to a number of compounds in order to obtain more complete information on their DNA-damaging activity in E coli From a qualitative standpoint, the results obtained in the reversion test and in the DNA-repair test (liquid micromethod) were overlapping for 96 (59 positive and 37 negative) out of 135 compounds (711%) There was disagreement for 39 compounds (289%), 9 of which were positive only in the reversion test (8 requiring metabolic activation and 5 genotoxic in the treat-and-plate method) 30 compounds were positive only in the lethality test, showing a direct DNA-damaging activity, which in half of the cases was completely eliminated by S9 mix Although the experimental protocol intentionally included several compounds already reported as nonmutagenic carcinogens or as noncarcinogenic mutagens, the overall accuracy was 645% for the reversion test and 724% for the DNA-repair test, as evaluated for 75 compounds classified according to their carcinogenic activity Quantitation of results was obtained in the Ames test by relating the net number of revertants to nmoles of compound and in the DNA-repair test by means of a formula relating the difference and ratio of MICs in repair-proficient and -deficient bacteria to nmoles of compound Following these criteria, the genotoxic potency varied over a 45 X 10(7)-fold range among compounds positive in the reversion test and over a 6 X 10(9)-fold range among compounds damaging E coli DNA The genotoxic potencies in the two bacterial systems were correlated within the majority of the chemical classes under scrutiny

Testing of chemicals for genetic activity with Saccharomyces cerevisiae: a report of the U.S. Environmental Protection Agency Gene-Tox Program.

Abstract: The yeast Saccharomyces cerevisiae is a unicellular fungus that can be cultured as a stable haploid or a stable diploid . Diploid cultures can be induced to undergo meiosis in a synchronous fashion under well-defined conditions. Consequently, yeasts can be used to study genetic effects both in mitotic and in meiotic cells. Haploid strains have been used to study the induction of point mutations. In addition to point mutation induction, diploid strains have been used for studying mitotic recombination, which is the expression of the cellular repair activities induced by inflicted damage. Chromosomal malsegregation in mitotic and meiotic cells can also be studied in appropriately marked strains. Yeast has a considerable potential for endogenous activation, provided the tests are performed with appropriate cells. Exogenous activation has been achieved with S9 rodent liver in test tubes as well as in the host-mediated assay, where cells are injected into rodents. Yeast cells can be recovered from various organs and tested for induced genetic effects. The most commonly used genetic end point has been mitotic recombination either as mitotic crossing-over or mitotic gene conversion. A number of different strains are used by different authors. This also applies to haploid strains used for monitoring induction of point mutations. Mitotic chromosome malsegregation has been studied mainly with strain D6 and meiotic malsegregation with strain DIS13 . Data were available on tests with 492 chemicals, of which 249 were positive, as reported in 173 articles or reports. The genetic test/carcinogenicity accuracy was 0.74, based on the carcinogen listing established in the Gene-Tox Program. The yeast tests supplement the bacterial tests for detecting agents that act via radical formation, antibacterial drugs, and other chemicals interfering with chromosome segregation and recombination processes.

Induction of congenital malformations in the offspring of male mice treated with X-rays at pre-meiotic and post-meiotic stages.

Abstract: The induction of congenital malformations among the offspring of male mice treated with X-rays at pre-meiotic and post-meiotic stages has been studied in two experiments. Firstly, animals were exposed to varying doses (108-504 cGy) of X-rays and mated at various time intervals (1-7, 8-14, 15-21 and 64-80 days post-irradiation), so as to sample spermatozoa, spermatids and spermatogonial stem cells. In the second experiment, only treated spermatogonial stem cells were sampled. One group of males was given a single 500-cGy dose, a second group a fractionated dose (500 + 500 cGy, 24 h apart) and a third group was left unexposed. In the first experiment, induced post-implantation dominant lethality increased with dose, and was highest in week 3, in line with the known greater radiosensitivity of the early spermatid stage. Preimplantation loss also increased with dose and was highest in week 3. There was no clear induction of either pre-implantation or post-implantation loss at spermatogonial stem cell stages. There was a clear induction of congenital malformations at post-meiotic stages, the overall incidence being 2.0 +/- 0.32% in the irradiated series and 0.24 +/- 0.17% among the controls. The induction was statistically significant at each dose. At the two highest doses the early spermatids (15-21 days) appeared more sensitive than spermatozoa, and at this stage the incidence of malformations increased with dose. The data from Expt. 1 on the induction of malformations by irradiation of spermatogonial stages were equivocal. In contrast, Expt. 2 showed a statistically significant induction of malformations at both dose levels (2.2 +/- 0.46% after 500 cGy and 3.1 +/- 0.57% after 500 + 500 cGy). The relative sensitivities of male stem cells, post-meiotic stages and mature oocytes to the induction of congenital malformations were reasonably similar to their sensitivities for specific-locus mutations, except that the expected enhancing effect of the fractionation regime used was not seen. Dwarfism and exencephaly were the two most commonly observed malformations in all series.

Formation of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in a model system by heating creatinine, glycine and glucose

Abstract: A mixture of creatinine, glucose and glycine was heated in diethylene glycol containing 14% water for 2 h at 128°C, and the mutagens formed were purified by XAD-2 column chromatography, acid-base partition, Sephadex LH-20 column chromatography, ‘blue cotton’ treatment and HPLC. Two mutagenic substances were isolated by HPLC. The major mutagen was identified by its UV absorption and mass and NMR spectra as 2-amino-3,8-dimethylimidazo[4,5- f ]quinoxaline, which was originally isolated from fried beef. This finding supported the idea that creatinine, amino acids and sugars present in meat are precursors in the formation of the mutagenic imidazoquinoxaline derivative.

Mutagenicity of benzidine and benzidine-congener dyes and selected monoazo dyes in a modified Salmonella assay.

Abstract: We have evaluated the mutagenic activity of a series of diazo compounds derived from benzidine and its congeners o-tolidine, o-dianisidine and 3,3'-dichlorobenzidine as well as several monoazo compounds. The test system used was a modification of the standard Ames Salmonella assay in which FMN, hamster liver S9 and a preincubation step are used to facilitate azo reduction and detection of the resulting mutagenic aromatic amines. All of the benzidine and o-tolidine dyes tested were clearly mutagenic. The o-dianisidine dyes except for Direct Blue 218 were also mutagenic. Direct Blue 218 is a copper complex of the mutagenic o-dianisidine dye Direct Blue 15. Pigment Yellow 12, which is derived from 3,3'-dichlorobenzidine, could not be detected as mutagenic, presumably because of its lack of solubility in the test reaction mixture. Of the monoazo dyes tested, methyl orange was clearly mutagenic, while C.I. Acid Red 26 and Acid Dye (C.I. 16155; often referred to as Ponceau 3R) had marginal to weak mutagenic activity. Several commercial dye samples had greater mutagenic activity with the modified test protocol than did equimolar quantities of their mutagenic aromatic amine reduction products. Investigation of this phenomenon for Direct Black 38 and trypan blue showed that it was due to the presence of mutagenic impurities in these samples. The modified method used appears to be suitable for testing the mutagenicity of azo dyes, and it may also be useful for monitoring the presence of mutagenic or potentially carcinogenic impurities in otherwise nonmutagenic azo dyes.

The role of deoxynucleoside triphosphate pools in the inhibition of DNA-excision repair and replication in human cells by hydroxyurea

Abstract: The effects of hydroxyurea (HU) on the DNA-excision repair process in human cells has been systematically examined. It is demonstrated that HU induces DNA single-strand break accumulation in a dose-dependent fashion in ultraviolet-irradiated and MMS-treated conlfuent but not log-phase fibroblasts and that these breaks are clearly the consequence of the inhibition of HU of the enzyme, ribonucleotide reductase. The breaks form rapidly, are stable for at least 10 h and largely disappera by 20 h. The production of thse DNA-strand breaks is antigonzed by a combined treatment of 10 μM deoxyadenosine, deoxycytidine and deoxyguanosine whereas thymidine potebntiates strand-break formation of low HU concentrations. It is also confirmed that HU, while inhibiting replicative synthesis has no apparent inhibitory effect on unscheduled DNA synthesis (UDS) (UDS) although the increased uptake of labeled DNA precursors into HU-treated cells makes it difficult to assises the actual ouptake effects on the repair-synthetic process. Analysis of the effects of HU on deoxynucleoside triphosphate pool levels and the demonstration of the failure of the HU block to replicative synthesis to be reversed by high (1 mM) concentrations of added deoxynucleosides lend support to the notion of compartmentalized dNTP pools for repair and replication.

Kinetics of micronucleus formation in relation to chromosomal aberrations in mouse bone marrow

Abstract: A simulation analysis of the kinetics of micronucleus formation in polychromatic erythrocytes in mouse bone marrow was performed after a single administration of 3 chemicals — mitomycin C (MMC), 6-mercaptopurine (6-MP) and 1-β- D -arabinofuranosylcytosine (Ara-C) — with different modes of action. The time-response patterns in the incidence of chromosomal aberrations and micronuclei after treatment with each chemical were compared and subjected to the simulation study with 3 parameters. Two of them, the time between the final mitotic metaphase of the erythroid series and nucleus expulsion ( T 1 ), and the duration of the polychromatic erythrocyte (PCE) stage in the bone marrow ( T 2 ), were almost identical for the 3 chemicals. However, the coefficients of formation rate of micronucleated cells resulting from cells with chromosomal aberration(s) ( k ) differed: Ara-C differed from the other two. These results indicate that chromosomal aberrations, especially chromatid breaks and probably gaps, induced by this chemical, effectively contribute to micronucleus formation. The DNA content of micronuclei was also compared to the length of acentric fragments induced by Ara-C and it was found that their distributions were comparable. These findings strongly suggest that chromosomal aberrations induced by chemicals are essential events for the induction of micronuclei in the PCE of bone marrow.

Relationship between cell killing, chromosomal aberrations, sister-chromatid exchanges and point mutations induced by monofunctional alkylating agents in Chinese hamster cells. A correlation with different ethylation products in DNA.

Abstract: Several monofunctional alkylating agents (AA) were compared for their ability to induced chromosomal aberrations, cell killing, sister-chromatid exchanges (SCE) and point mutations in Chinese hamster cells (CHO and V79 cells) The AAs chosen varied in their reaction kinetics as well as their affinity to nucleophilic sites (different s values) AAs with low s values were more mutagenic in comparison to those with high s values, whereas the reverse was true for induction of cytotoxic effects Neither SCEs nor chromosomal aberrations correlated with the induction of point mutations, indicating that different primary DNA lesions and repair pathways are involved in these biological processes Molecular dosimetric studies indicate that O6 alkylation of guanine is the most probable cause of lesions in DNA leading to point mutations following treatment with ethyl methanesulphonate and ethyl nitrosourea

The persistence of micronucleated erythrocytes in the peripheral circulation of normal and splenectomized Fischer 344 rats: implications for cytogenetic screening.

Abstract: Micronucleated erythrocytes are selectively removed from the peripheral circulation of normal rats. Splenectomy prevents this selective removal. In normal rats treated daily for 20 days with 0.2 mg/kg triethylenemelamine (TEM), micronucleated normochromatic (mature) erythrocytes did not accumulate in peripheral blood. In these same animals, the frequencies of micronucleated cells among polychromatic (newly formed) erythrocytes increased from 0.21 to 5.25 per thousand in peripheral blood and from 1.75 to 31.5 per thousand in bone marrow. Since both control and induced frequencies in peripheral blood were approximately 15% of those in bone marrow, the removal appears to be equally efficient for cells containing either spontaneously occurring or clastogen-induced micronuclei. In splenectomized rats treated daily for 11 days with 0.2 mg/kg TEM, the frequency of micronucleated normochromatic erythrocytes (NCEs) in the peripheral blood rose rapidly to 9 times the control value and remained elevated for 50-55 days, indicating a life span approximately equivalent to that of normal erythrocytes. Among splenectomized rats exposed to either 0.15 mg/kg triethylenemelamine, 6.5 mg/kg cyclophosphamide, or 300 mg/kg urethane for periods exceeding the erythrocyte life span, the incidences of micronucleated NCEs in the peripheral blood rose steadily from a control value of 1.0 per thousand to maximum values of 15.0, 12.7 and 8.9 per thousand, respectively. During these extended exposures, the mean frequencies of micronucleated polychromatic erythrocytes (PCEs) in peripheral blood increased from a spontaneous value of 0.9 per thousand to 23.0, 13.0 and 6.6 per thousand, respectively, reflecting the frequencies among PCEs in the bone marrow and approximating the maximum values among NCEs in the peripheral blood. Thus, the frequency of micronucleated erythrocytes in the peripheral blood of splenectomized rats can be used as an index of both acute and cumulative chromosomal damage, while in normal rats the use of peripheral blood for cytogenetic monitoring is restricted by the selective removal of these micronucleated cells.

Assay for gene mutation in a human lymphoblast line, AHH-1, competent for xenobiotic metabolism.

Abstract: A novel quantitative gene-locus mutation assay has been developed using a line of human lymphoblast cells, designated AHH-1, competent in oxidative xenobiotic metabolism. AHH-1 cells are sensitive to the mutagenic action of both chemically reactive mutagens and mutagens which require oxidative metabolism to exert their mutagenicity. These cells are readily mutated by direct exposure to ethyl methanesulfonate, ICR-191, 2-acetoaminofluorene, aflatoxin B1, benzo[a]pyrene (BP), cyclopenta[c, d]pyrene, dimethylnitrosamine, lasiocarpine, and 1-methylphenanthrene.

An evaluation of the l5178y tk+/- mouse lymphoma forward mutation assay using 42 chemicals.

Abstract: The L5178YTK+/- mouse lymphoma assay (MLA) has been utilized in several laboratories as a short-term test for chemical-induced forward mutation in cultured mammalian cells. In order to evaluate several technical modifications to the MLA, 42 chemicals representing 9 chemical classes were tested and the results were compared with those published elsewhere as well as with findings in a genetic toxicology test battery currently used in this laboratory. A positive response for the induction of TK-/- mutants was obtained for 26 chemicals. With the exception of p-aminophenol, all of these compounds were recognized mutagens or carcinogens and were representative of direct-acting and activation-dependent genotoxins. 16 compounds did not induce TK-/- mutants and among these were 5 compounds that were considered to be mutagens or carcinogens. A comparison of the results of this study with those published elsewhere revealed a strong agreement among findings for this test irrespective of minor technical variations. It was concluded that the MLA is a useful system for identifying chemical mutagens in mammalian cells and can serve as a valuable component in a genetic toxicology test battery.

Cytotoxicity, chromosome aberrations and unscheduled DNA synthesis in cultured human diploid fibroblasts induced by sodium fluoride.

Abstract: The effects of exposure of cultured human diploid fibroblasts (JHU-1 cells) to sodium fluoride have been studied with respect to cytotoxicity and induction of chromosome aberrations and unscheduled DNA synthesis (UDS) Cytotoxicity of NaF on JHU-1 cells, as determined by a decrease in colony-forming ability, linearly increased with increasing dose of NaF (50-150 micrograms/ml) or exposure time (1-24 h). Treatment of the cells with 50 micrograms/ml NaF for 24 h resulted in a lethality (approximately 70%) similar to that obtained with 100 micrograms/ml for 12 h. A linear increase in cytotoxicity was observed as a fraction of the product of NaF treatment time and dose. JHU-1 cells treated with 20-50 micrograms/ml NaF for 12 or 24 h were analyzed for chromosome aberrations. A significant increase in the frequency of chromosome aberrations at the chromatid level was observed in treated cells in a dose-dependent manner. For detection of UDS, confluent JHU-1 cells were cultured with medium containing low serum and then exposed to NaF in the presence of 10 mM hydroxyurea. Treatment with 100-400 micrograms NaF/ml for 4-24 h reproducibly elicited UDS in a dose-related fashion as determined by direct scintillation counting of [3H]thymidine incorporated into DNA during repair synthesis. These results suggest that NaF causes DNA damage in human diploid fibroblasts in culture.

Measurement of spontaneous and X-irradiation-induced 6-thioguanine-resistant human blood lymphocytes using a T-cell cloning technique.

Abstract: Lymphocytes separated from human peripheral blood were cultured in vitro, in the presence of 6-thioguanine (TG), to select and clone rate TG-resistant (TG r ) cells present in the circulation in vivo. The incidence of such TG r cells ranged from 0.83 × 10 −5 to 2.53 × 10 −5 (mean 1.48 × 10 −5 ) in healthy individuals aged between 19 and 79 years; did not differ between males and females; but increased significantly with age at rat of 2.4 cells/10 7 lymphocytes/year. Exposure of lymphocytes (G 0 ) in vitro to X-ray doses of upto 200 rad resulted in a dose-dependent increase in TG r cell frequencies. The rates of increase were approximately proportion to the square to the square of the dose and these rates were closely similar to those obtained in cultured skin fibroblasts and suggest that the bulk of these mutations are a consequence of chromosome structural aberrations. The cloned TG r cells are considered to be HPRT − mutants and the mutation frequencies in lymphocytes determined using this cloning technique were compared with the variant frequencies obtained in earlier experiments utilising an autoradiographic technique to detect azaguanine-resistant (AG r ) variant cells. Mutation frequencies with the cloning technique were 10–20-fold lower than variant frequencies with the autoradiographic method.

Structural requirements for the mutagenicity of environmental nitroarenes

Abstract: The nitroarenes comprise a large group of widely distributed environmental agents some of which are extraordinarily mutagenic while others are devoid of such activity. A newly developed computer program has been used to determine which structural features of these molecules might account for this broad spectrum of activities. Using Salmonella mutagenicity data for 53 nitroarenes, 2 fragments associated with activity and 2 deactivating fragments have been identified. The coexistence of an active and a deactivating fragment on the same molecule results in a nitroarene possessing marginal or no mutagenicity. The activity of 47 of 53 nitroarenes was correctly predicted by this procedure. Most of the discrepancies involved hexa- and heptacyclic nitroarenes which were predicted to be active but reported to be inactive. The ‘CASE’ program can be used to predict the mutagenicity of the many untested nitroarenes identified in the ambient environment.

The load of genetic and partially genetic disorders in man I. Congenital anomalies: estimates of detriment in terms of years of life lost and years of impaired life

Abstract: This paper represents an attempt to estimate quantitatively, the detriment associated with spontaneously arising congenital anomalies in man. The system used in the International Classification of Diseases (Chapter XIV, entries 740–759) has been followed to classify the congenital anomalies. Detriment was assessed using estimates of the years of life lost, years of life potentially impaired and years of life actually impaired, as indicators. The data on birth prevalences for the various conditions were derived from several epidemiological surveys carried out in Hungary and from the Hungarian Congenital Malformation Registry. Most of the information on mortality profiles was obtained from the records of the Hungarian Central Statistical Office, Budapest. An overall comparison of the prevalence figures in Hungary with those for the U.S. (this study aimed at complete ascertainment) and for the Canadian province of British Columbia (in this study, ascertainment is believed to be incomplete) showed that, in Hungary, at least certain classes of congenital anomalies, particularly some of the less severe ones, have been under-ascertained. Since detriment estimates are heavily dependent on accurate estimates of birth prevalences, we believe that the estimates of detriment arrived at using the Hungarian data may also be underestimates. In Hungary, the total birth prevalence of all isolated major congenital anomalies is of the order of about 600/104. Our calculations show that these congenital anomalies may cause, per 104 livebirths, about 4800 years of life loss, about 37 000 years of potentially impaired life and about 4500 years of actually impaired life. In these calculations, it has been assumed that the average life-expectancy at live birth for the general population is 70 years. These estimates are considerably higher than those made by Carter for detriment associated with spontaneously arising monogenic disorders.

The SOS-function-inducing activity of chemical mutagens in Escherichia coli.

Abstract: The SOS-function-inducing activities of 42 chemical mutagens were investigated in Escherichia coli K12. The induction of the SOS function was assayed by monitoring the s-galactosidase activity in the sulA::laZ fusion strain PQ37. To correct for the inhibitory effects of test chemicals on mRNA or protein synthesis, the level of the constitutive alkaline phosphatase was assayed in parallel. Most of the mutagens reported to be mutagenic to the Ames' Salmonella tester strains showed the SOS-function-inducing activity. The inducible SOS repair may be responsible for not only base-change mutations but also frameshift mutations. However, 9-aminoacridine, ethidium bromide and 4-nitro-o-phenylenediamine did not induced the SOS function, suggesting that the mutagenesis induced by these mutagens may occur independently of SOS repair. Present results supported the SOS mutagenesis model that error-prone SOS repair plays an important role in mutagenesis induced by most chemical mutagens.

Tradescantia-Micronucleus (Trad-MCN) tests on 140 health-related agents

Abstract: The Tradescantia-Micronucleus (Trad-MCN) test is a simple short-term bioassay for various gaseous and liquid forms of chemical agents, and physical agents such as radiation. 140 agents, directly or indirectly related to human health, were screened for their mutagenicity. Plant cuttings of young inflorescences, in which the pollen mother cells undergo various stages of meiosis, were maintained in nutrient solution for experimentation. Treatments were made either by absorption of the soluble agents through the stem, by diffusion of gaseous agents through the leaves and buds, by exposure to internal/external radiation or by in situ exposure to air pollutants. Micronuclei formed from damaged chromosomes served as the indicators of mutagenicity. Results of 140 agents tested are listed in 9 different categories. (1) Carcinogens/mutagens, (2) common beverages, (3) common chemicals, (4) drugs, (5) pesticides, (6) common household chemicals, (7) radiation and radioisotopes, (8) in situ monitoring, (9) complex environmental mixtures. Out of 140 agents tested, 52 showed positive, 20 showed borderline positive responses and 5 showed strong toxicity. Test results of 41 agents in the present study showed 67% congruity with Ames test results found in the literature.

Sister-chromatid exchange (SCE) report on control subjects in a study of occupationally exposed workers.

Abstract: The range and distribution of Sister-Chromatid Exchange (SCE) scores in 479 control persons were determined. All SCE readings were performed in a single laboratory according to the same protocol and regularly checked by referee readers to assure consistency. A mean SCE per cell value of 9.9 and a 95th percentile of 13.4 were established for this study sample. The range of SCE scores across all non-exposed individuals tested was 5.0-17.5 SCE per cell. Differences in SCE scores were associated with reader, smoking, sex, and, to a small extent, age. Individual test results showed reasonable consistency across the entire control group, but, as with most clinical measurements, care should be taken to avoid placing too much emphasis on a single test result when communicating with an individual. This report on the largest control group studied to date provides necessary normative data for further SCE investigations in occupational settings.

Induction of mutations and chromosome aberrations in lung cells following in vivo exposure of rats to nitrogen oxides

Abstract: In order to investigate the mutagenic effects of nitrogen oxides (NOx), induced mutations and chromosome aberrations were examined using primary lung cells obtained from rats exposed in vivo to NO 2 and NO. Rats were exposed to nitrogen oxide gases at concentrations of 8–27 ppm for 3 h in a stainless steel chamber. Over the range 15–27 ppm, NO 2 significantly increased mutation to ouabain resistance. Over a similar dose range, NO significantly increased mutation only at the highest concentration (27 ppm). Following NO 2 exposure, chromosome aberrations (mainly chromatid type) were induced in chromatid breaks, 2.5–11.6-fold over the control at 8 and 27 ppm, respectively.

Non-mutagenicity of 27 aliphatic acrylate esters in the Salmonella-microsome test.

Abstract: The mutagenicity of 27 acrylate esters was assessed in the Salmonella-microsome assay. Methyl, ethyl, butyl, t-butyl, pentyl, neopentyl, hexyl acrylate and methacrylate and 2-hydroxyethyl methacrylate were tested; furthermore ethanediol, butanediol, pentanediol, neopentanediol, hexanediol and diethyleneglycol diacrylate and dimethacrylate. None of these 27 acrylate esters appeared to be mutagenic in the standard Ames assay with TA1535, TA1537, TA1538, TA98 and TA100, both with and without Aroclor 1254 or phenobarbital-induced S9 mix. A liquid incubation assay of methyl methacrylate, methyl, butyl and hexyl acrylate with TA100 neither gave any indication of a mutagenic activity of these compounds.

Relationship between polarographic reduction potential and mutagenicity of nitroarenes.

Abstract: A series of nitropyrenes and other nitroarenes were reduced electrochemically with a dropping mercury electrode. The half-wave potentials (E1/2) corresponding to the reduction of the various nitro functions mutagenicities exhibited by these chemicals in Salmonella typhimurium strains TA98 and TA1538 was demonstrated. A linear relationship between E1/2 and the calculated energies of the Lowest Unoccupied Molecular Orbital (LUMO) was also established. This indicates that the mutagenicities of nitroarenes can be predicted from calculated LUMO energies.

Genetic damage in CHO cells exposed to enzymically generated active oxygen species.

Abstract: The genetic toxicity of active oxygen species produced during the enzymic oxidation of xanthine has been investigated using Chinese hamster ovary (CHO) cells. Incubation of cells with xanthine plus xanthine oxidase resulted in extensive chromosome breakage and sister-chromatid exchange and gave a small increase in frequency of thioguanine-resistant cells (HGPRT test). Inclusion of superoxide dismutase or catalase in the xanthine/xanthine oxidase system inhibited chromosome breakage, whereas only catalase prevented SCE and mutant induction. It is concluded that hydrogen peroxide is responsible for most of the genetic effects observed in CHO cells exposed to xanthine/xanthine oxidase but that superoxide plays a key role in chromosome breakage.

Mutagenic activity of methyl-substituted tri-and tetracyclic aromatic sulfur heterocycles

Abstract: A number of polycyclic aromatic sulfur heterocycles have been identified in coal-derived products and in shale oils. The mutagenic activity of some of these compounds, including dibenzothiophene, benzo[b]naphtho[1,2-d]thiophene, benzo[b]naphtho[2,1-d]thiophene and benzo[b]naphtho[2,3-d]thiophene have been determined using the Salmonella/microsome mutagenicity test. These compounds demonstrated either very weak or no mutagenic activity. The methyl derivatives of each of these four compounds were assayed for mutagenic activity. Salmonella typhimurium TA98 was used as the tester strain. All assays required a rat-liver homogenate metabolic activator. Five of the methylated derivatives, 1-methylbenzo[b]naphtho[1,2-d]thiophene, 3-methylbenzo[b]naphtho[1,2,-d]thiophene, 1-methylbenzo[b]-naphtho[2,1-d]thiophene, 6-methylbenzo[b]naphtho[2,1-d]thiophene and 4-methylbenzo[b]naphtho[2,3-[d]thiophene demonstrated mutagenic activity. However, activity was observed only at high concentrations of the metabolic activator.

Mutagenicity testing with TA97 and TA102 of 30 DNA-damaging compounds, negative with other Salmonella strains.

Abstract: In a comparative study on 135 compounds of various chemical classes, 30 agents inducing direct nonreparable DNA damage in repair-deficient E. coli failed in reverting strains TA1535, TA1537, TA1538, TA98 and TA100 of S. typhimurium (De Flora et al., 1984b). These compounds were re-assayed in the Ames test using strains TA97 and TA102. A dose-dependent mutagenic response was detected with aminoantipyrine and p-rosaniline in TA97 and with streptomycin and formaldehyde in TA102. p-Rosaniline was the only mutagen requiring metabolic activation. 5 compounds, i.e. o-aminophenol in TA97 and methanol, ethanol, cadmium chloride and cadmium sulfate in TA102, induced a reproducible increase in revertants over controls, but this was less than 2-fold. The remaining 21 chemicals — including amino compounds, aliphatics, aromatics, heterocycles, hydrazine derivatives and inorganics — confirmed their inactivity in the Ames test. Overall data for 135 compounds, comparing the Ames test (7 strains) and the DNA-repair test (3 strains), are re-assessed on the basis of these findings.

Sister-chromatid exchanges in association with occupational exposure to ethylene oxide

Abstract: Sister-chromatid exchange (SCE) frequencies in employees potentially exposed to ethylene oxide (ETO) were compared with those in unexposed control groups. Three worksites where the previous environmental control of ETO was known to have differed were chosen. Within these worksites, subjects were categorized into high potential exposed, low potential exposed and control groups. An additional community control group was obtained. Blood samples for chromosomes studies of peripheral lymphocytes were dawn at several time points over a period of 24 months. The effects on SCE of age, sex, smoking habits and reader variation were considered. Worksites I, II and III, respectively, represented increasing levels of exposure. At Worksite III large differences among groups persisted over 24 months. At Worksite II, the SCEs in the high potential exposed workers were higher than those in the other groups. At no time was the low potential exposed group at Worksite II statistically significantly higher in mean SCE than the worksite controls. No consistent differences among groups were noted in Worksite I.

A pilot experiment for the micronucleus test. The multi-sampling at multi-dose levels method.

Abstract: A pilot experiment was undertaken to find the optimal dose range and sampling time in the micronucleus test; 2 animals per group were used. The chemical was injected at 4 different doses, and smear preparations were made from femoral marrow cells at 5 different sampling times for each dose group. The incidence of micronucleated polychromatic erythrocytes was scored on the preparations stained with acridine orange. When the data were arranged two-dimensionally, the optimal dose and sampling time which could be used for a further full-scale test, could be estimated. In addition, sex differences and the effect of multiple treatment can be estimated using this protocol with minor modifications.

Genetic effects of 5-azacytidine in Saccharomyces cerevisiae.

Abstract: The base analog 5-azacytidine induced a variety of genetic and epigenetic effects in different organisms. It was tested in two diploid strains of the yeast Saccharomyces cerevisiae to study the induction of point mutation, mitotic reciprocal crossing-over, mitotic gene conversion (strain D7) and mitotic aneuploidy (strain D61.M). It was used on cells growing in its presence for 4–5 generations. There was a strong induction of both types of mitotic recombination and point mutation. However, there was no induction of mitotic chromosomal malsegregation under the same conditions.