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1.
The induction of mutation by certain nitrosamidines and nitrosamides has been quantitated utilizing the hypoxanthine--guanine phosphoribosyl transferase (HGPRT) locus in Chinese hamster ovary cells. Dose--response relationships for cytotoxicity and mutagenicity are presented for N-methyl-N-nitrosourea (MNU), N-ethyl-N-nitrosourea (ENU), N-butyl-N-nitrosourea (BNU), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG). Based on the concentration of each agent required to kill 90% of the cells, the following order of cytotoxicity was observed: MNNG greater than ENNG greater than MNU greater than ENU greater than BNU. This is the same order of potency as observed for mutation induction per unit concentration of mutagen. 相似文献
2.
Low molecular weight alkylating carcinogens, such as nitroso compounds, alkylate guanine of DNA to 7-alkylguanine, but the amount of this product correlates poorly with tumour induction. Loveless postulated that a minor product of alkylation, O-(6)-alkylguanine, may be responsible for mutagenesis and carcinogenesis. He showed that methyl methanesulphonate (MMS) does not produce O-(6)-methylguanine from deoxyguanosine, and in the present study it failed to induce thymic lymphomas or pulmonary adenomas in inbred Swiss mice. Loveless gave evidence that ethyl methanesulphonate (EMS), methylnitrosourea (MNU) and ethylnitrosourea (ENU) did produce O-(6)-alkylguanine, and all three induced pulmonary adenomas in the present study. It has also been shown that both of the alkylnitrosoureas induced thymic lymphomas but ethyl methanesulphonate did not. 相似文献
3.
EM9 is a mutagen-sensitive CHO cell whose phenotype resembles that of normal CHO cells exposed to 3-aminobenzamide, an inhibitor of poly(ADP-ribose) synthesis. This phenotype suggested that EM9 might be defective in poly(ADP-ribose) metabolism, but we now cannot find any abnormality in the synthesis or in the degradation of poly(ADP-ribose) in permeabilized EM9 cells. Thus the effects of 3-aminobenzamide on wild-type cells may be due to the inhibition of processes other than poly(ADP-ribose) synthesis. 3-Aminobenzamide enhances the cytotoxicity of EMS toward EM9 and control cells to the same degree. 相似文献
4.
Suspension cultures of Chinese hamster ovary (CHO) cells were exposed to methyl methanesulfonate (MMS) or methylnitrosourea (MNU) and assayed for mutation induction (6-thioguanine resistance) and for specific DNA adducts. DNA methylation at the 1-, 3- and 7-positions of adenine, the 3-, O6- and 7-positions of guanine, and phosphate was detected in cultures exposed to MMS, while MNU produced 3- and 7-methyladenine, 3-methylcytosine, 3-, O6- and 7-methylguanine, O4-methylthymidine and methylated phosphodiesters. When mutations induced by MMS and MNU were compared by linear correlation analysis with levels of each of these adducts, only O6-methylguanine displayed a strong correlation with mutations (r = 0.879, p less than 0.001). The relationship between O6-methylguanine and induced mutations in CHO cells is similar to that previously reported in CHO cells for O6-ethylguanine and mutations (Heflich et al., 1982) and indicates that alkylation-induced mutations at the HGPRT locus in CHO cells are primarily associated with O6-alkylguanine formation. 相似文献
6.
Published data on mutations induced by ionizing radiation and 6 monofunctional alkylating agents, namely EMS, MMS, ENNG, MNNG, ENU and MNU, in different cell lines (Chinese hamster ovary, Chinese hamster lung V79, mouse lymphoma L5178 and human cells) were analysed so that radiation-equivalent chemical (REC) values could be calculated.REC values thus obtained for a given alkylating agent with different cell lines fall within a narrow range suggesting its validation in cultured mammalian cell systems including human. 相似文献
7.
The effects of altering the cell growth rate (physiological state) and DNA repair capacity (genetic state) on susceptibility to inactivation and mutagenesis by ethyl methanesulfonate (EMS) were studied in 4 strains of E. coli. Logarithmic and stationary phase cells of the polymerase I deficient mutant, P 3478 polA, a recombination deficient mutant, DZ 417 recA, and the respective parental strains, W 3110pol+ and AB 253 rec+, were exposed to EMS and the surviving fraction and mutant frequency determined. At the same EMS concentration both mutants were more susceptible to inactivation than the parental strains. In all 4 strains, log phase cells were more sensitive to inactivation than stationary cells. The surviving fraction of stationary cells exceeded log cells by a factor of 18 for polA, 6 for recA, and about 2 for the parental strains. In all strains, except recA, log phase cells exhibited higher spontaneous mutant frequencies than stationary phase cells. At the same concentration of EMS, survivors of both polA and recA showed more than 10-fold higher induced frequencies than the wild types. However, at the same survival levels the repair deficient mutants exhibited induced mutant frequencies comparable to the repair proficient strains. There was no significant effect of growth phase on EMS induced mutability in recA or the parental strains. In marked contrast, the polymerase I deficient mutant shows both a higher spontaneous frequency and a greater than 10-fold higher EMS induced mutant frequency in log phase cultures compared to stationary phase cultures. Our results support the hypothesis that cellular susceptibility to alkylating agents is influenced by both the genetic capability for repair and the particular physiological state of the cell. 相似文献
8.
Mutation induction and cell killing produced by selected alkylsulfates and alkanesulfonates have been quantitated using the Chinese hamster ovary/hypoxanthine--guanine phosphoribosyl transferase (CHO/HGPRT) system. Dose--response relationships of cytotoxicity and mutagenicity are presented for two alkylsulfates [dimethylsulfate (DMS), diethylsulfate (DES)] and three alkyl alkanesulfonates [methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS), and isopropyl methanesulfonate (iPMS)]. Under the experimental conditions employed, cytotoxicity decreased with the size of the alkyl group. DMS was more toxic than DES, and MMS was more toxic than EMS and iPMS. All agents produced linear dose--response of mutation induction: DMS was more mutagenic than DES, and MMS was more mutagenic than EMS and iPMS based on mutants induced per unit mutagen concentration. However, the following relative mutagenic potency was observed when comparisons were made at 10% survival: DES greater than DMS; EMS greater than MMS greater than iPMS. 相似文献
9.
To compare the size of micronuclei induced by clastogens and by spindle poisons, bone-marrow smears were prepared 24 h after a single intraperitoneal injection of triethylenemelamine (TEM) (0.3 mg/kg) or vincristine (VCR) (0.125 mg/kg) into male mice. 100 micronucleated erythrocytes (MNEs) were randomly selected from each group and photomicrographed. Diameters of the cytoplasm ( D) and the micronucleus ( d) of each MNE were measured on the photographs. Relatively large micronuclei ( d? D/4) were frequent (74%) in the VCR-treated group, and infrequent (2%) in the TEM-treated group. The frequencies of MNEs resulting in d? D/4 were determined for several other mutagens. All clastogens tested could be classified as TEM type, and all spindle poisons as VCR type.These findings indicate that it is possible to analyze the action site of micronucleus-inducing agents on the basis of the relative sizes of micronuclei. 相似文献
10.
When V79 cells are exposed to a single low dose of MNNG or MNU they acquire resistance to the mutagenic or to the clastogenic effect of the agents. Here the effect of MNNG pretreatment on mutagenesis (6-thioguanine resistance) and aberration formation in cells challenged with various mutagens/clastogens is reported. MNNG-adapted cells were resistant to the mutagenic effects of MNU and, to a lower extent, of EMS. No mutagenic adaptation was observed when MNNG-pretreated cells were challenged with MMS, ENU, MMC or UV. Cells pretreated with a dose of MNNG which makes them resistant to the clastogenic effect of this compound were also resistant to the clastogenic activity of other methylating agents (MNU, MMS), but not so with respect to ethylating agents (EMS, ENU). Cycloheximide abolished the aberration-reducing effect of pretreatment. However, when given before the challenge dose of MNNG, MNU or MMS, it drastically enhanced the aberration frequency in both pretreated and non-pretreated cells. No significant enhancement of aberration frequency by cycloheximide was found for ethylating agents. The results indicate that clastogenic adaptation is due to inducible cellular functions. It is concluded that mutagenic and clastogenic adaptation are probably caused by different adaptive repair pathways. 相似文献
11.
Host-mediated assays have been developed to allow determination of the mutagenic potential of promutagens and procarcinogens which require metabolic activation to exert their effects on indicator organisms. We report here the development of the host-(mouse)-mediated CHO/HGPRT system using the procarcinogen dimethylnitrosamine (DMN) as a model agent. Using a 2--h treatment time, we observed a linear dose-response relationship up to 250 mg of DMN per kg body weight. At 100 and 500 mg/kg DMN, mutation induction increased with time up to at least 6 h. DMN was not mutagenic when tested in vitro. Athymic (nude) mice, their phenotypically normal littermates, or BALB/c mice of both sexes were found to be suitable as hosts. A time- and dose-dependency of induced mutation frequency by a direct-acting agent, ethyl methanesulfonate (EMS), was observed in both the in vitro and the host-mediated assays. 相似文献
12.
The dose-rate effects of ethyl methanesulfonate (EMS) on the survival and induction of mutations in Chinese hamster Don cells were investigated. The most effective time of exposure to EMS for reducing the surviving fraction of cells was 4 h, shorter and longer exposure times being less effective. The threshold or minimal concentration of EMS giving a surviving fraction of 0.5 was 0.05 mg/ml. The minimal effective time of exposure to EMS for cell death was 1 h. Corrected survival curves showed that longer exposure times at lower dose rates of EMS had less cytotoxic effect than shorter exposure times at higher dose rates.After exposure of Don cells to various doses of EMS for various times, the frequencies of mutations resistant to 6-thioguanine (6TG) were measured. An exposure time of 4 h produced a lower mutation frequency than shorter or longer exposure times that resulted in the same surviving fraction of cells. An exposure time of 20 h produced the highest induced mutation frequency.This system using cultured Chinese hamster cells should be useful as a sensitive procedure for detecting the mutagenic actions of chemicals. 相似文献
13.
Whether resistance to purine analogues 8-azaguanine (AG) and 6-thioguanine (TG) in mammalian cells is due to gene mutation or to epigenetic changes was investigated by an ethyl methanesulfonate (EMS) dose-dependent induced “resistance” to these analogues in two near-diploid (2N) and one tetraploid (4N) Chinese hamster ovary (CHO) cells. EMS produced higher cell killing in 2N than in 4N cells. In the 2N cells, EMS-induced mutations to TG (1.7 μg/ml) resistance increased approximately as a linear function of the dose from 0–400 μg/ml. However, EMS was ineffective in inducing such mutation in the 4N cells. These observations are consistent with the notion that the induced TG resistance arose as a result of mutation at the gene or chromosome level. In each cell type, both the “observed” spontaneous and the EMS-induced frequency to purine analogue resistance decreased with increasing concentration of purine analogues. However, among the “resistant” clones a high proportion of those selected at 1.2 and 3.0 μg/ml of AG, a small portion selected at 7.5 μg/ml of AG, and virtually none at 1.7 and 6.0 μg/ml of TG are capable of growth in medium containing aminopterin (10 μM). This suggests that, under less stringent selective conditions, some resistant variants were being selected through mechanisms not yet defined. 相似文献
14.
Sensitivity to the monofunctional alkylating agent methyl methanesulfonate (MMS) has been tested as a selection technique to isolate mutant strains which can provide insights into the genetic control of DNA replication, DNA repair and recombination in the complex eucaryote, Drosophila melanogaster. The successful isolation of an X-linked MMS-sensitive strain, muts, has suggested that mutagen sensitivity is a feasible methodology for the selection of mutant strains of Drosophila which will be useful in the genetic and biochemical analysis of these cellular functions. Preliminary characterization of this mutant strain indicates that: ( A) it is extremely sensitive to killing by MMS; ( B) it is more mutable by MMS than the parent wildtype strain; and ( C) it appears to possess mutator gene activity. 相似文献
17.
The indirect mutagen cyclophosphamide was tested in human whole blood cultures with respect to chromosome-breaking activities and suppression of mitotic indices after activation by liver perfusion and crude liver homogenates with and without cofactors. Both methods produced nearly the same effects, with the exception of liver homogenate without cofactors which had only weak metabolic activities. 相似文献
18.
It is known that UV, X-rays, MMC and MMS are not mutagenic for H. influenzae, whereas HZ, EMS and MNNG are potent mutagens for this bacterium. All of these agents, however, are known to be both mutagenic and able to induce prophage in E. coli. We report here that all the agents except HZ induce prophage in H. influenzae, and EMS even induces in the recombination-defective recl mutant, which is non-inducible by UV, MMC, MNNG and MMS. MMS did not cause single-strand breaks or gaps in DNA synthesized after treatment of H. influenzae, but EMS and MNNG produced them. EMS caused more breaks in DNA synthesized before treatment than in that synthesized after treatment. On the other hand we did observe such breaks or gaps induced in E. coli in DNA synthesized posttreatment by EMS as well as by MMS and MNNG, at comparable survival levels. 相似文献
19.
The induction of mutations by the alkylating agent ethyl methanesulfonate (EMS) was determined with Chinese hamster ovary cells maintained in serum-free medium to arrest DNA synthesis and cell division. The arrested cultures were treated with EMS and maintained in serum-free medium for various time intervals post-treatment before serum containing medium was added to initiate DNA synthesis and cell division. The concentration-dependent increase in 6-thioguanine-resistant mutants in the arrested cultures was similar to that found with exponentially dividing cultures when serum was added to the arrested cultures immediately after the EMS treatment; the time course of phenotypic expression was also similar with both cultures. In addition, maintenance of the arrested cultures in serum-free medium for up to 18 days post-treatment resulted in no change in the mutant frequency. This suggests that the mutagenic damage is not removed in these arrested cultures. Furthermore, maintenance of the arrested state for increasing time intervals before serum addition results in decreases in the time necessary for maximum phenotypic expression. Cultures maintained in serum-free medium for 16 days after mutation treatment show complete expression of the mutations with no need for subculture. This last result suggests that the mutagenic damage induced by EMS in Chinese hamster ovary cells is not removed and that this damage results in both the induction and expression of mutation in the absence of DNA replication. 相似文献
20.
328 X-linked recessive lethal mutations induced in late spermatids by hycanthone methanesulfonate were tested for coverage by duplications that comprised, in total, about 24% of the euchromatic X chromosome; 78 lethals appeared to be covered. Crossover localization tests of a random sample of 38 non-covered lethals revealed 4 chromosomes carrying a lethal within a duplicated segment. Lethals localized to a particular region were crossed to reference deficiencies and single-locus mutations, and inter se, to ascertain their genetic extent. The proportion of multi-locus deletions among these 78 covered and 4 non-covered lethals was 3/48, 1/10 and 13/24 for the distal, medial and proximal regions, respectively. A storage period of 9 days did not noticeably influence these proportions. In the sample of 38 non-covered lethals, and among 17 of the covered single-site lethals, 4 cases of strong crossover suppression were detected. Comparison of these results with data obtained with other mutagens suggests that induction of multi-locus deletions, and possibly of other types of chromosome rearrangement, could in part depend on other mechanisms than those acting in the formation of translocations and chromosome loss. For the purpose of mutagen testing, these findings imply that, in Drosophila, results in the regular genetic tests for chromosome breakage events do not always accurately predict the capacity of a mutagen to induce multi-locus deletions. This is of importance since transmissible multi-locus deletions have been considered a significant source of genetic damage in man. 相似文献
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