Significant Increase In Mutation Frequency Research Articles

Induction of mutations by tritiated water and 3H-thymidine in Drosophila melanogaster assayed by the somatic zeste-white eye mutation system

In order to study the mutagenic effect of exposure to tritium, Drosophila melanogaster larvae were treated with tritiated water ( 3H 2O) or tritiated thymidine ( 3H-TdR) during development. Dose rates ranged from 0.0058 to 0.058 rad/h per nucleus for 3H-TdR and from 0.049 to 0.122 rad/h for 3H 2O. Induction of mutations was measured by the appearance of somatic mutations in the eyes of an unstable strain of Drosophila melanogaster. Both substances caused a significant increase in mutation frequency. With the assumption that each mutation observed in this assay is caused by one DNA break, the effectiveness of tritium to create DNA breaks is estimated to be 0.20 breaks per decay for 3H-TdR and 0.27 breaks per decay for 3H 2O.

Chemical and Toxicological Characterization of Residential Oil Burner Emissions: II. Mutagenic, Tumorigenic, and Potential Teratogenic Activity

Extracts of effluents from a modern residential oil burner have been evaluated in several toxicological assay systems. Bacterial mutagens were detected in extracts from both the particulate and vapor phase emissions. Effluents from continuous operation were an order of magnitude less mutagenic than those from cyclic (5 min on, 10 min off) operations. No difference in the yield of bacterial mutagens per gram of fuel burned was found between cyclic operation under low and moderate sooting conditions. On the basis of elution behavior from alumina it appeared that the bacterial mutagens collected from high sooting effluents were more polar than those from low sooting effluent. An extract that was mutagenic in bacteria did not induce a significant increase in mutation frequency to human lymphoblasts. No evidence of tumorigenicity was observed in a limited number of newborn mice after IP injection of effluent extract when compared to historical control data. Putative nonmutagenic teratogens were detected in effluent using an attachment inhibition assay. The level of these agents was reduced in effluents from continuous oil burner operation.

Chemical and toxicological characterization of residential oil burner emissions: II. Mutagenic, tumorigenic, and potential teratogenic activity.

Extracts of effluents from a modern residential oil burner have been evaluated in several toxicological assay systems. Bacterial mutagens were detected in extracts from both the particulate and vapor phase emissions. Effluents from continuous operation were an order of magnitude less mutagenic than those from cyclic (5 min on, 10 min off) operations. No difference in the yield of bacterial mutagens per gram of fuel burned was found between cyclic operation under low and moderate sooting conditions. On the basis of elution behavior from alumina it appeared that the bacterial mutagens collected from high sooting effluents were more polar than those from low sooting effluent. An extract that was mutagenic in bacteria did not induce a significant increase in mutation frequency to human lymphoblasts. No evidence of tumorigenicity was observed in a limited number of newborn mice after IP injection of effluent extract when compared to historical control data. Putative nonmutagenic teratogens were detected in effluent using an attachment inhibition assay. The level of these agents was reduced in effluents from continuous oil burner operation.

The mutagenic potency of 4 agents at the thymidine kinase locus in mouse lymphoma L5178Y cells in vitro: Effects of exposure time

Mutagenic potency at the thymidine kinase (TK) locus in mouse lymphoma L5178Y cells (expressed as induced trifluorothymidine (TFT)-resistant mutants/total dose) was assessed for 4 agents (ethyl methanesulphonate (EMS), benzidine, 1,8-dinitropyrene (1,8-DNP) and ICRF 159) using short (3–4 h) and long (21–24 h) exposure times. The mutagenic potency of EMS was found to be essentially independent of concentration and exposure time when tested over a cytotoxic range consistent with routine testing procedures. Similar results were obtained with benzidine but for both 1,8-DNP and ICRF 159 mutagenic potency was found to be highly dependent on the concentration and exposure time. 1,8-DNP failed to induce any significant increases in mutant frequency when tested at concentrations up to 5 μg/ml using short exposure times, whereas the compound was active at concentrations as low as 0.1 μg/ml when the exposure period was extended to 21 h. Under the latter conditions, however, the molar potency of 1,8-DNP was found to be inversely related to concentration over a range extending from 0.1 to 5 μg/ml. ICRF 159 induced increases in the frequency of TFT-resistant mutants using short or long exposure times. When a short exposure time was used, however, the mutagenic potency of the antitumour agent decreased with increasing concentration between 1 and 500 μg/ml. Although possible explanations can be offered to account for these observations the results illustrate potential problems which may arise in this system when comparing mutagenic potency values for a range of compounds with a view to assessing relative risk.

Inhibition of recovery from potentially lethal damage by chemicals in Chinese hamster V79 A cells.

The inhibition of recovery from potentially lethal damage and the influence of mutation induction by lactate, pyruvate, novobiocin, and nalidixic acid was studied in the stationary phase of Chinese hamster V79 A cells. Lactate and pyruvate were selected to elucidate their possible involvement in the inhibition of recovery from PLD since high levels of lactate and pyruvate accumulate due to increased aerobic and anaerobic glycolysis in tumours. Effects of novobiocin and nalidixic acid were also studied to elucidate the possible role of an enzyme similar to DNA gyrase in the potentially lethal damage recovery of V79 cells. The inhibition of recovery depends on drug concentration and is complete with 20 mM of lactate and pyruvate and 20 microM of nalidixic acid and novobiocin. The chemicals seem to interfere with an early step in the recovery process. Incubation with novobiocin in a post-irradiation period does not change the mutation frequency significantly whereas lactate and pyruvate demonstrate a slight increase. Cells incubated with nalidixic acid showed a significant increase in mutation frequency at 24 h post-irradiation recovery time.

Mutational and recombinational events in carcinogen-modified plasmid DNA: Influence of host-cell repair genes

A plasmid containing the STR operon has been modified in vitro (i) by irradiation with UV light, (ii) by reaction with ethyl methanesulphonate (EMS), (iii) by reaction with N-acetoxy-2-acetylaminofluorene (AcO-AAF), (iv) by reaction with (±) trans-benzo[ a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), and (v) by heating at 70°C to produce apurinic sites. Suitably modified plasmid DNA was then used to transform both repair-proficient and repair-deficient strains of Escherichia coli, and the mutation frequency in the plasmid-encoded rspL + gene measured. The influence of host mutations in the uvrB +, recA +, umuC + and lexA +, genes on the mutation frequency have been investigated. Transformation into a uvrB strain significantly decreased survival and increased the level of mutations observed for UV- and AcO-AAF-modified plasmid DNA, while only a small increase in mutation frequency was seen with EMS-modified DNA and no increase in mutation frequency with plasmid DNA containing apurinic sites. Mutagenesis in UV- and BPDE-modified DNA (and probably also DNA containing apurinic sites) was totally dependent on the recA + gene product, while EMS and AcO-AAF induced mutagenesis was only partially independent on the recA + gene. Transformation of UV- or BPDE-modified DNA into a umuC or lexA strain, on the other hand, showed no change in mutation frequency from that observed with wild-type strain. Pre-irradiation of the wild-type host with UV light before transformation led to a significant increase in mutation frequency for UV- and BPDE-modified plasmid DNA. These results are discussed in terms of mutational or recombinational pathways which may be available to act on modified plasmid DNA, and suggest that the majority of the mutational events measured in this system are due to recombination between homologous regions on the plasmid and chromosomal DNA.

Mutagenicity of anti-trypanosomal drug, Ro 7-1051, in Escherichia coli.

The effect of an anti-trypanosomal drug, Ro 7-1051, on killing, mutation induction and prophage induction activities in Escherichia coli has been investigated. A radiation sensitive strain, NG30(recA-), was more sensitive for killing than the wild type strain, H/r30R, and the another radiation-sensitive strain, Hs30R(uvrA-). The killing effect on Hs30R was almost the same as that on H/r30R. Ro 7-1051 induced mutation (arg-→arg+) in both Hs30R and H/r30R strains, while no significant increase of mutation frequency was detected in NG30 strain. The prophage induction was hardly detected from both E, coli W3110(λ) and W3110(λ ind8) strains. The characteristics of lesion of DNA induced by Ro 7-1051 are discussed.

Sensitivity of Drosophila melanogaster to Low concentration of gaseous mutagens: III. Dose-rate effects.

Sex-linked recessive lethal mutations were induced in D melanogaster males by chronic as well as acute treatments of gaseous 1,2-dibromoethane ranging from 2.3 to 31 ppm.hr. Acute treatments corresponding to each chronic treatment were made by increasing chemical concentration approximately 30 times with a concomitant decrease in exposure period. Germ cell stages sampled, in order of decreasing sensitivity, were spermatocytes, spermatids, and spermatozoa. The most significant finding is that no consistent pattern of difference is observed between acute and chronic exposure for three of the four exposure levels. Only at the highest exposure level (30-31 ppm.hr) was any consistent difference observed between chronic and acute exposure levels. At the higher exposure level in all three germ cell stages the acute exposure showed a significant increase in mutation frequency over the chronic exposure. The greater acute vs chronic mutation frequency for spermatozoa, a metabolically inactive cell stage, leads to the conclusion that the exposure rate effect at high exposure levels is due to systemic factors such as metabolic deactivation or elimination rather than repair of premutational damage in the target cells. The significance of these observations in risk assessment for environmental pollutants is discussed.

Conditions for mutagenesis in the cynanobacterium Aphanocapsa 6714

Conditions for induction of mutants have been studied in the unicellular, blue-green alga, Aphanosapsa 6714. Ethylmethanesulfonate, nitrosomethylurea, an acridine (euflavine) and γ-rays from 60Co induced no significant increase in mutant frequency although they produced classical killing effects. Methyl-nitro-nitrosoguanidine (NTG), at similar lethal doses, led to only a small increase in mutant yields. A useful mutagenic action was obtained only with ultraviolet light. This effect proved to be sensitive to photodependent repair processes, but not to dark excision repair systems. Attempts to adapt enrichment procedures by penicillin selective killing were unsuccessful.

Mutation induction by rodent liver microsomal metabolites of aflatoxins B 1 and G 1 in Neurospora crassa

The mutagenic activities of aflatoxins B 1 and G 1 were studied in the ad-3 test system of Neurospora crassa by treatment of conidia with aflatoxin and liver homogenate for 2 h. No significant increase in the ad-3 mutation frequency over the spontaneous frequency was observed when either aflatoxin or mammalian liver homogenate was omitted from the test system. The ad-3 mutation frequencies increased to between 29 and 87/10 6 survivors, which is a 73- to 217-fold increase over the average spontaneous ad-3 mutation frequency (0.4/10 6 survivors), after conidia of N. crassa were treated with 0.67 mM aflatoxin B 1, hamster liver homogenate, and a NADPH generating system. A 9- to 15-fold increase int eh mutation frequency over the spontaneous mutation frequency was found when 0.67 mM of aflatoxin G 1 instead of aflatoxin B 1 was used in the test system. Treatment of conidia with 0.44 mM aflatoxin B 1 mice liver homogenate and a NADPH generating system caused a small, but significant increase in the ad-3 mutation frequencies. No significant increase in the mutation frequency was found when a single sample of human liver homogenate was used in the test system. These studies show that metabolic activation is necessary for the expression of the mutagenic activity of aflatoxins B 1 and G 1 in N. crassa.

Interactive mutagenicity of sodium nitrite, dimethylamine, methylurea and ethylurea

Groups of mice were treated per os with sodium nitrate either alone or in combination with nitrosatable amino compounds and tested in the most mediated assay. When mice were treated with sodium nitrate in combination with demethylamine a small(4-fold) but significant increase in mutant frequency (MF) was observed. Ethylurea or methylurea in combination with sodium nitrate induced 10- or 850-fold increases in MF, respectively. The response to methylurea was dose-dependent with a 6- and 30- fold increase in MF at 5.4 and 11.5 mg/kg NaNO 2 and a 6-fold increase at 108 mg/kg methylurea. That this response reflected gastric nitrosation was shown by the disappearance of the response if NaNO 2 administration preceded methylurea treatment by 10 min. High MF's were observed if NaNO 2 was administered 10 or 20 min after methylurea.