Mutation Research/Genetic Toxicology最新文献

The present study gives a comprehensive update of all umu genotoxicity assay results published so far. The available data of 486 chemicals investigated with the umu test are compared with the Ames test (274 compounds) as well as rodent carcinogenicity data (179 compounds). On the whole, there is good agreement between the umu test and the Ames test results, with a concordance of about 90%. The umu test was able to detect 86% of the Ames mutagens, while the Ames test (using at least 5 strains) detected 97% of the umu positive compounds. The elimination of TA102 from the set of Ames tester strains reduced the percentage of detectable umu genotoxins from 97 to 86%. The agreement between carcinogenesis and umu response was 65%, which is comparable to earlier studies concerning rodent carcinogenesis and Salmonella mutagenesis. The present compilation of umu results provides a database that can be used for the comparison of the SOS-inducing activity of chemicals and their mutagenicity, respectively, carcinogenicity. The results presented here clearly demonstrate that a chemical which induces the expression of the umu operon can be regarded a rodent carcinogen with a high degree of certainty (93%).

In a collaborative study organized under the JEMS MMS, nine mouse lymphoma assay (MLA) ‘unique positive’ NTP rodent carcinogens were re-evaluated by an in vitro chromosomal aberration assay using Chinese hamster lung fibroblast cells (CHL/IU). Six of nine chemicals induced chromosomal aberrations; bromodichloromethane, chlorendic acid and isophorone induced structural aberrations, and chlorodibromomethane, pentachloromethane and 1,1,1,2-tetrachloroethane induced numerical aberrations (polyploidy). These six chemicals, therefore, are not uniquely positive in the MLA. The difference between the NTP results and ours might be due to the use of diffent cell lines and protocols, and in some cases, to different interpretations of polyploidy. The remaining three chemicals, ebzykl acetate, cinnamyl anthranilate and trichloroethylene, were negative in this study.

The genotoxic environmental contaminant 1-nitropyrene is metabolised in mammalian systems by pathways more complex than the straightforward nitroreduction which accounts for most of its biological activity in bacteria. In order to evaluate the role of O-acetyltransferase (OAT) activity in generation of genotoxic intermediates from 1-nitropyrene, the mutagenecity of the major primary oxidised metabolites of 1-nitropyrene was characterised in the Ames Salmonella typhimurium plate incorporation assay with strain TA98, and with variants of TA98 deficient (TA98/1,8-DNP₆) or enhanced (YG1024) in O-acetyltransferase. 1-Nitropyren-3-ol was more mutagenic in the absence than in the presence of S9, while 1-nitropyren-4-ol, 1-nitropyren-6-ol and 1-nitropyren-8-ol required S9 for maximum expression of mutagenicity. 1-Nitropyren-4-ol (176 rev/nmol without S9, 467 rev/nmol with S9 in TA98) and 1-nitropyren-6-ol (13 rev/nmol without and the S9-dependent mutagenicity of all the compounds studied was enhanced in the OAT-overproducing strain and much diminished (though not always entirely lost) in the OAT-deficient strain, showing that OAT amplifies expression of the genotoxicity of these compounds. 1-Acetamidopyren-6-ol required both S9 and OAT activity in order to exhibit any mutagenicity; this finding strongly implicates N-hydroxylation followed by O-esterification, as opposed to further S9-catalyzed ring oxidation, as a major route of activation for urinary metabolites of 1-nitropyrene.

The Salmonella sulA-test is a newly developed colorimetric assay to detect genotoxins. This technique is based on the ability of DNA-damaging agents to induce the sulA gene, one of the SOS response genes. A constructed plasmid, pEM1968, carrying a fused sulA′::′lacZ was introduced into Salmonella typhimurium TA1538. Monitoring sulA gene expression was performed by assaying the ß-galactosidase activity in the transformed strain S. typhimurium TA1538/pEM1968. A simple, fast and sensitive liquid incubation procedure has been developed after optimization of the S9 mix composition and ß-galactosidase assay. The SOS-inducing potency (SOSIP, μM⁻¹) was defined as the slopes of the non-linear dose-response relationships. Twenty-one chemicals with different modes of action were examined for a preliminary evaluation of the test. Nineteen chemicals were genotoxic in the Salmonella sulA-test. The SOSIP ranged from 1.2 · 10⁻⁴ μM⁻¹ (ethyl methanesulfonate) to 419.9 μM⁻¹ (bleomycin). Sodium azide and 5-fluoroucil were not genotoxic. Frameshift, base-pair and oxidative genotoxins were detected by the tester strain. The calculated SOSIP and the minimum concentrations detected (MCD) in the Salmonella sulA-test were compared to the reported values obtained with two similar assays: the SOS Chromotest and umu-test. The SOSIP values of 12 compounds were the highest in this new assay. Five chemicals tested in the Salmonella sulA-test gave similar SOSIP values with those of one of the two other tests. ICR-191 had the highest SOSIP with the SOS Chromotest and 3-methylchloranthrene showed the highest SOSIP with the umu-test. Similarly, the lowest MCD values were found for 12 compounds in the Salmonella sulA-test. Four compounds had close MCD values in this assay and one of the two other techniques. The SOS Chromotest remained the most sensitive assay for cisplatin and ICR 191. The umu-test was the technique of choice for 3-methylchloranthrene.

The L5178Y tk^+/− mouse lymphoma assay (MLA) has been in use for more than 15 years as a tool for evaluating the mutagenic potential of various agents. As with other genetic toxicology test systems, one criterion for a positive response has been the requirement of at least a 2-fold increase in mutant frequency (MF) as compared to the respective MF of the solvent controls. More recently, an actual specific increase in MF has been proposed as a criterion for determining a positive response in the MLA; however, this may not be appropriate for laboratories with a low, yet stable, background MF. The twofold rule criterion was evaluated in our laboratory with 66 compounds. The mutagenic status of these compounds was previously determined in other test systems and at one or more laboratories, including Lilly Research Laboratories. The results of this evaluation demonstrate that the twofold rule is an effective method for identifying mutagenic agents in the MLA at LRL where a lower, yet acceptable, background mutation frequency is the norm. A small number of compounds (6) yielded results discordant with the literature; however, these compounds have been previously found to be either difficult to detect in genotoxic assays or to show specific sensitivity in the MLA.

Various stress conditions including exposure to low-dose radiation and low concentrations of chemical mutagens can induce an adaptive response to subsequent radiation-induced chromosome damage. In this study, the effect of pretreatment of rabbit lymphocytes with zinc or copper salts on radiation-induced chromosome damage was investigated. Pretreatment of rabbit peripheral lymphocytes with Zn (50 μM in vitro or 100 μmol/g body weight in vivo) resulted in resistance to γ radiation (2.0 Gy)-induced chromosome aberrations such as dicentrics plus centric rings and cells with chromosome aberrations. On the other hand, pretreatment with Cu (50 μM in vitro) did not show any protective effect on radiation-induced chromosome damage in rabbit lymphocytes. However, the concentration of metallothionein increased in activated lymphocytes 24 h after in vitro pretreatment with both Zn and Cu. In addition, γ-radiation-induced calf thymus DNA damage could be prevented directly by the addition of Zn-metallothionein in the cell-free system. These results suggest that the induction of zinc-metallothionein synthesis may act as one of the defensive mechanisms to the induction of cytogenetic adaptive response to ionizing radiation while copper-metallothionein did not show any radioprotective effect.

Methyl eugenol, is a commercially used fruit fly attractant and a suspected carcinogen. Several phenylpropenes, including methyl eugenol and the known carcinogen safrole, score negative in the Salmonella assay but score positive in the yeast DEL assay that selects for intrachromosomal recombination events in the yeast Saccharomyces cerevisiae. In an attempt to dissociate the beneficial properties of methyl eugenol from its genotoxic properties, saturated or fluorinated analogs were evaluated for their ability to induce intrachromosomal (DEL) recombination in yeast. Field tests have previously shown that all of the analogs used have appreciable properties as fruit fly attractants. The analogs 1,2-dimethoxy-4-ethylbenzene, 1,2-dimethoxy-4-(2-fluoro-2-propenyl)benzene, 1,2-dimethoxy-4-(2-fluoroethyl)benzene and 1,2-dimethoxy-4-(3-fluoro-2-propenyl)benzene all showed reduced toxicity and reduced recombinagenicity in yeast compared to methyl eugenol. These results confirm the validity of fluorination and/or removal of the 2-propenyl moiety in reducing the toxicity and recombinagenicity of methyl eugenol derivatives.

In this paper we report the results of a study to determine the frequencies of spontaneous micronucleated erythrocytes (MNE) in peripheral blood of 35 mammalian species. The main goal was to find mammals with a high spontaneous frequency of MNE that could, therefore, be good candidates for biomonitoring genotoxic agents in their natural habitat. We obtained 187 peripheral blood samples, but in 13 of the species we could only sample one individual. A wide range in the number of MNE ($\text{1}\text{434}\text{to}\text{0}\text{40 000}$ erythrocytes) was observed. Since the number of individuals per species is not high enough, this results should be cautiously considered. The cat, mouse, giraffe, pig, opossum and capuchin monkey seem to be suitable species for biomonitoring for genotoxic events.