Comparisons on chemically-induced mutagenicity among four bacterial strains, Salmonella typhimurium TA102 and TA2638, and Escherichia coli WP2/pKM101 and WP2 uvrA/pKM101: collaborative study I

Mutagenesis induced by 12 quinolone antibacterial agents in Escherichia coli WP2uvrA/pKM101

The mutagenic potential of 12 quinolone antibacterial agents (quinolones) was examined at concentrations of 3.91-1000 ng/plate with or without S9 mix in Escherichia coli WP2uvrA/pKM101. All quinolones showed mutagenic potential in the strain: the maximum numbers of revertant colonies were observed at 7.81 ng/plate for clinafloxacin and sitafloxacin; 15.63 ng/plate for ciprofloxacin, gatifloxacin, grepafloxacin, levofloxacin, moxifloxacin, and trovafloxacin; and 31.25-500 ng/plate for enoxacin, lomefloxacin, norfloxacin and ofloxacin. The numbers for all quinolones were comparable between the groups with and without S9 mix. In all quinolones, bactericidal effects were observed at one or two higher concentrations than their mutagenic concentrations except for enoxacin without S9 mix. From these results, the WP2uvrA/pKM101 strain is proved to be highly sensitive to quinolones.

Mutation spectra of chemical mutagens determined by Lac+ reversion assay with Escherichia coli WP3101P-WP3106P tester strains

We previously reported the development of mutation-specific Escherichia coli B tester strains WP3101 to WP3106 from strain WP2uvrA. In this study we constructed their pKM101-containing derivatives WP3101P to WP3106P, and further isolated their rfa derivatives WP4101-WP4106 and WP4101P-WP4106P. The six kinds of F' plasmids (lacI-, lacZ-, proAB+), each of which carries a different lacZ allele, contained in the above strains were originally derived from E. coli K-12 strains CC101-CC106. All the tester strains show Lac- and Trp- phenotype. Assays for transitions and transversions are based upon Lac+ reversion of a specific mutation located within the lacZ gene on an F' plasmid. The trpE65(ochre) allele in the same strains enables them to be used for Trp+ reversion assays as well. In the present paper, we evaluated the sensitivity, specificity, and usefulness of the newly developed tester strains. Strains WP3101P-WP3106P were highly sensitive to determine mutational profile of heterocyclic amines with S9 mix-mediated metabolic activation and most of the oxidative mutagens and free radical generators tested. Every type of base-pair substitutions induced by 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) or 5-diazouracil were detected in strains WP3101P-WP3106P, while A:T-->C:G and G:C-->A:T mutations induced by MeIQ, and A:T-->C:G, G:C-->A:T, and G:C-->C:G by 5-diazouracil were not detected in pKM101-free tester strains. In pKM101-carrying strains, cumene hydroperoxide induced all types of base substitutions, while formaldehyde preferentially induced G:C-->T:A transversions. Phenazine methosulfate induced predominantly G:C-->A:T transitions and G:C-->T:A transversions, while H2O2 induced predominantly G:C-->T:A and A:T-->T:A transversions. Introduction of the rfa mutation considerably enhanced sensitivity to bulky mutagens such as polycyclic aromatic compounds. All six possible base substitutions induced by 9, 10-dimethyl-1,2-benzanthracene (DMBA) were detected in tester strains WP4101P-WP4106P. In conclusion, our tester strains WP3101P-WP3106P and WP4101P-WP4106P permitted rapid and simple detection of specific mutations induced by variety of mutagens.

Comparisons of chemically-induced mutation among four bacterial strains, Salmonella typhimurium TA102 and TA2638, and Escherichia coli WP2/pKM101 and WP2 uvrA/pKM101: collaborative study III and evaluation of the usefulness of these strains

Over the past 5 years, a large collaborative study of chemically-induced mutation has been performed using the four bacterial strains Salmonella typhimurium TA102 and TA2638 and Escherichia coli WP2/pKM101 and WP2 uvrA/pKM101 in order to compare the specific spectrum of response to chemicals and to evaluate the usefulness (sensitivity) of each strain. Following the two collaborative studies to test the chemicals in category 1, chemicals previously judged as positive only in E. coli WP2 strains and derivatives of these chemicals, and category 2, oxidative agents or crosslinking agents, 22 compounds of category 3 consisting of 10 nonmutagenic carcinogens and another 12 chemicals were selected in this study. Twenty participating laboratories tested each compound in the same method as previous reports. In the group of nonmutagenic carcinogens, no chemical induced revertant colonies of any strain tested. In the group of other chemicals, response to the chemicals was similar in TA102 and WP2 uvrA/pKM101. Overall, in the three collaborative studies, a total of 79 compounds were tested. No difference in qualitative response to the four strains was observed for 71% (56/79) of the test chemicals. The combination of strains providing the greatest number of positive responses was WP2 uvrA/pKM101 with TA102; 84% (66/79) of the test chemicals elicited the same qualitative response in these two strains. Therefore, it is suggested that WP2 uvrA/pKM101 and TA102 can be included as a part of the standard tester strains for detection of mutagenic activity of chemicals.

Mutagenicity of p-aminophenol in E. coli WP2uvrA/pKM101 and its relevance to oxidative DNA damage

It was recently reported that p-aminophenol (p-AP) induces DNA cleavage in mouse lymphoma cells, CHO cells and human lymphoblastoid cells. The mutagenicity of p-AP has not, however, been detected by reverse mutation assays. The purpose of this study was to assess the mutagenicity of p-AP by reverse mutation assay using Escherichia coli WP2uvrA/pKM101, which has a spectrum for detecting mutations different from those of other strains in the family with an AT base pair at the mutation site and has higher sensitivity to certain oxidative mutagens as compared to other strains. We found that p-AP was mutagenic to E. coli WP2uvrA/pKM101. The mutagenic activity of this compound was suppressed with the addition of dimethylsulfoxide or catalase, suggesting the involvement of active oxygen species in the mutagenic process induced by p-AP. To further elucidate the underlying mechanism, we used isolated DNA for the following experiments. It was revealed, by gel electrophoretic analysis, that p-AP induced DNA cleavage in the presence of Fe(III). However, p-AP alone did not induce this cleavage. Formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine by p-AP in calf thymus DNA was also detected in the presence of Fe(III) by HPLC with an electrochemical detector. ESR-spin trapping experiments using DMPO detected the production of hydroxyl radical (.OH) in the solution of p-AP with Fe(III). Both p-AP mediated DNA damages and .OH production by p-AP in the presence of Fe(III) were completely inhibited by .OH scavengers (ethanol, mannitol, sodium formate, dimethylsulfoxide) and catalase. These results suggest that .OH derived from the reaction between H2O2 and Fe(III) (Fenton reaction) participates in the oxidative DNA damage. Accordingly, the same mechanism might be working in E. coli WP2uvrA/pKM101 during induction of the mutation by p-AP.

A dietary toxicity/oncogenicity study of tributyl phosphate in the rat

Tri-n-butyl phosphate (TBP, CAS No. 126-73-8), an industrial chemical, was administered in the diet at concentrations of 0, 200, 700 and 3000 ppm to groups of 50 male and 50 female Sprague-Dawley rats for 2 years. Body weights and food consumption were measured weekly for the first 13 weeks and monthly thereafter. Hematology was performed at 12, 18 and 24 months; urinalyses were performed at 3 weeks and 3, 6, 12 and 18 months. All surviving animals were euthanized after 24 months of treatment. Macroscopic postmortem examinations were performed on all animals; complete histopathological evaluation was performed on control and high dose animals; target organs were examined in all dose groups. Significant decreases in body weight gain occurred in males and females receiving the 3000 ppm concentration and a slight decrease in weight gain occurred in females receiving the 700 ppm concentration. The only clinical sign attributed to TBP was an increased incidence of red discoloration of the urine in some high-dose males. Survival, hematology and urinalysis parameters were unaffected by treatment at any concentration. A dose-related increase in the incidence and severity of urinary bladder hyperplasia and the incidence of urinary bladder papillomas was evident in male and female rats receiving the 700 and 3000 ppm concentrations. Transitional cell carcinomas were present in six of 49 males and two of 50 females and a squamous cell carcinoma was present in one of 49 males in the group which received 3000 ppm. The oncogenic effects showed a clear threshold of 700 ppm in the diet. The NOEL (no observable effect level) for chronic toxicity was 200 ppm. Mean intake of TBP was 9 and 12 mg/kg/day for males and females, respectively, receiving 200 ppm; 33 and 42 mg/kg/day for males and females, respectively, receiving 700 ppm, and 143 and 182 mg/kg/day for males and females, respectively, receiving 3000 ppm. TBP was negative in genotoxicity tests, suggesting that the tumors are induced by nongenotoxic mechanisms.

Comparisons on chemically-induced mutation among four bacterial strains, Salmonella typhimurium TA102 and TA2638, and Escherichia coli WP2/pKM101 and WP2 uvrA/pKM101: collaborative study II

A collaborative study of chemically-induced mutation was performed using the four bacterial strains Salmonella typhimurium TA102 and TA2638, and Escherichia coli WP2/pKM101 and WP2 uvrA/pKM101, used in the previous successive studies in order to compare the specific spectrum of response to chemicals among the four strains and to determine the usefulness (sensitivity) of each strain. Twenty-two laboratories participated in this study. Following the previous study, 28 compounds were selected consisting of oxidative agents or crosslinking agents. These compounds were tested for mutagenicity using the plate incorporation method with or without metabolic activation. The tests were performed in two laboratories per chemical. The number of chemicals which showed positive results were 18, 17, 16 and 14 with WP2 uvrA/pKM101, TA2638, TA102 and WP2/pKM101, respectively. In all four strains 19/28 chemicals (68%) were either positive or negative while the remaining 9 chemicals showed a heterogeneous response. With TA102 and TA2638 89% (25/28) of the test chemicals showed the same response, while 75-79% (21-22/28) showed the same response in these two S. typhimurium strains and in WP2 uvrA/pKM101. In conclusion, WP2/pKM101 strain showed the least sensitivity to the chemicals used. Among the other three strains, WP2 uvrA/pKM101 was the most sensitive strain, although the difference in the number of chemicals which showed positive results was minor. Concerning the spectrum of response to chemicals, it is apparent that TA102 and TA2638 have almost the same sensitivity, but some chemicals induce different responses between the two S. typhimurium strains and WP2 uvrA/pKM101.