Evidence for the existence of distinct nitroreductases in Salmonella typhimurium: roles in mutagenesis.

Previous studies on the mutagenicity of nitroheterocyclics and nitrated polycyclic aromatic hydrocarbons had indicted the probable existence in Salmonella typhimurium of a multiplicity of nitroreductase activities of varying specificities which are required for the expression of the mutagenicity of nitro-containing chemicals. In the present study evidence is presented that these activities reside in different gene products: (a) strains totally lacking in the nitroreductase which recognizes niridazole and related substances are not mutagenized by this group of chemicals and yet they are fully responsive to the mutagenic action of dinitropyrenes; (b) double mutants which have lost both types of specificities can be constructed. Finally, the presence of a third type of nitroreductase with a specificity for 4-nitroquinoline-1-oxide is implied by the finding that the nitroreductase-deficient strains described herein retain full sensitivity to the mutagenic action of this chemical.

Cigarette smoking may yield nitroarenes.

Cigarette smoke condensates are readily nitrated to mutagenic substances exhibiting the properties expected of nitroarenes. In addition, nitroarenes also appear to be generated during the smoking of cigarettes enriched with nitrates.

Potent mutagenic activity of nitropyrenes on Chinese hamster lung cells with diphtheria toxin resistance as a selective marker.

Nitropyrenes, which are highly mutagenic in the Salmonella assay, were shown also to be potent mutagens on Chinese hamster lung cells without metabolic activation when resistance to diphtheria toxin was used as a selective marker. Among nitropyrenes tested, 1,8- and 1,6-dinitropyrenes were the most mutagenic, and 1,3-dinitro- and 1,3,6-trinitropyrenes were less active, but showed still much higher mutagenic activity than methyl methanesulfonate or N-methyl-N-nitrosourea. 1-Nitropyrene and 1,3,6,8-tetranitropyrene did not induce diphtheria toxin-resistant mutants at concentrations of up to 20 micrograms/ml.

An evaluation of tests using DNA repair-deficient bacteria for predicting genotoxicity and carcinogenicity. A report of the U.S. EPA's Gene-TOX Program.

The detection of DNA-damaging agents by repair-deficient bacterial assays is based on the differential inhibition of growth of repair-proficient and repair-deficient bacterial pairs. The various methodologies used are described and recommendations are made for their improved use. In a survey of the literature through April 1979, 91 of 276 papers evaluated contained usable data, resulting in an analysis of 611 compounds that had been assayed in 1 or more of 55 pairs of repair-proficient and repair-deficient strains.

Frameshift mutations: relative roles of simple intercalation and of adduct formation.

The contribution of "simple" intercalation and of adduct formation on the expression of frameshift mutations in Salmonella typhimurium was investigated using 9-aminoacridine and derivatives capable of either only intercalating between DNA base pairs or of forming adducts with DNA as well. For a chemical capable of intercalating as well as of forming an adduct, only a small portion of the frameshift mutagenicity is due to "simple" intercalation. Analogs only able to induce frameshift mutations as a result of intercalation generally display only a fraction (approx.

Nitrated fluorene derivatives are potent frameshift mutagens.

Nitrated derivatives if fluorene are potent frameshift-type mutagens. A reduction of the nitro function is required for the expression of mutagenicity. Hydroxylamines are the presumed key intermediates, which following esterification to electrophiles are capable of forming adducts with cellular DNA.

The extraordinary mutagenicity of nitropyrenes in bacteria.

Nitropyrenes cause frameshift mutations in Salmonella typhimurium. This activity which is restricted to frameshift mutations is unusual in several respects: (a) Nitropyrenes, as a class, are the most mutagenic chemicals reported in the literature; (b) The mutagenicity depends upon the formation of adducts between DNA and nitropyrene metabolites; (c) The penultimate intermediates responsible for mutagenic activity (hydroxylamines) are not obtained in all instances by reduction of the nitro function by the "classical" nitroreductase (the one that acts on nitrofurans and other simple nitrated polycyclic aromatic hydrocarbons) but by another nitroreductase which appears to be specific for higher nitrated polycyclic aromatic hydrocarbons; (d) The mutagenicity of nitropyrenes is enhanced when resting rather than growing bacterial cultures are used.

Effect of genotype on mutagenicity of niridazole in nitroreductase-deficient bacteria.

The mutagenicity of niridazole for Salmonella typhimurium depends upon the enzymic reduction of the nitro function. The response of niridazole nitroreductase-deficient bacteria to niridazole is reduced to 4.4 and 0.

4-Nitroquinoline-1-oxide: factors determining its mutagenicity in bacteria.

In bacteria, 4-nitroquinoline-1-oxide (NQO) causes primarily mutations of the base-substitution type although frameshift mutations are also induced. The adducts formed are presumably recognized by error-prone DNA repair enzymes as evidenced by the much greater activity in plasmid pKM101-bearing tester strains. Although reduction of the nitro group appears to be required for mutagenic activity, this reduction is not catalyzed by the nitroreductase required for the demonstration of the mutagenicity in bacteria of other nitro-containing mutagens (nitrofurans, 2-nitronaphthalene, nitrofluorenes).

Structural basis of the mutagenicity in bacteria of nitrated naphthalene and derivatives.

While 2-nitronaphthalene was a weak direct-acting base-substitution mutagen (1.4 revertants/nanomole) for Salmonella typhimurium, the analogous nitronaphthalic acid anhydride and imides were moderate frameshift mutagens (approximately 20 rev/nanomole in strain TA98). Although imide derivatives are efficient DNA intercalators, mutagenicity data indicate that the bulk of the frameshift activity is derived from adduct formation between hydroxylamine intermediates and DNA.

Evidence for the existence of a family of bacterial nitroreductases capable of activating nitrated polycyclics to mutagens.

A derivative of Salmonella typhimurium TA98 which does not respond to the potent mutagenicity of 1,8-dinitropyrene is described. This novel strain also shows a lack of response to the mutagenic action of 1,3-dinitropyrene and a greatly reduced response to 1,6-dinitropyrene and 1-nitropyrene. The responses to 1,3,6-trinitropyrene and 1,3,6,8-tetranitropyrene are affected to a much lesser extent.

An evaluation of the Escherichia coli WP2 and WP2 uvrA reverse mutation assay.

The methodology and status of the Escherichia coli WP2 reverse mutation system as it applies to chemical screening were reviewed using the available published literature. 163 documents were reviewed by the Working Group. These included abstracts, research articles, review articles and publicly available contract and grant final reports.

Non-mutagenic genotoxicants: novobiocin and nalidixic acid, 2 inhibitors of DNA gyrase.

The antimicrobial agents nalidixic acid and novobiocin, both inhibitors of DNA gyrase, preferentially inhibit the growth of DNA repair-deficient Escherichia coli, Salmonella typhimurium and Bacillus subtilis. On the other hand, these agents exhibit no demonstrable mutagenicity for S. typhimurium and E.

Nitropyrenes: isolation, identificaton, and reduction of mutagenic impurities in carbon black and toners.

Extracts of selected xerographic toners and copies were found to be mutagenic in the Salmonella assay. The activity was independent of the xerographic hardware and process and was traced to nitropyrenes present as impurities in the carbon black, the toner colorant. Manufacturing process changes resulted in a substantial reduction of the nitropyrene content of the carbon black and thus in the mutagenicity of the corresponding toners.

A bactericidal activity of microsomal preparations.

Exposure of suspension of Salmonella typhimurium tester strains TA1535, TA1537 and TA98 to mouse hepatic post-mitochondrial supernatants (S9) resulted in appreciable loss of bacterial viability. This lethal activity was destroyed by heating at 56 degrees C for 30 min. The toxic component of the S9 has not been identified.

The E. coli Pol A-1 assay: a quantitative procedure for diffusible and non-diffusible chemicals.

A procedure is described for determining the preferential killing of DNA repair-deficient E. coli. Dilute suspensions of DNA repair-proficient and -deficient bacteria are exposed to a graded series of test chemical concentrations.

Activation of polycyclic aromatic hydrocarbons to mutagens by singlet oxygen: an enhancing effect of atmospheric pollutants?

Chrysene and 3-methylcholanthrene are transformed to direct-acting mutagens by photodynamically generated singlet oxygen. In view of the presence of this species of oxygen in the polluted atmosphere, the possible conversion of environmental polycyclic aromatic hydrocarbons to mutagens and to potential direct-acting ('ultimate') carcinogens deserves consideration.

A new mutagenic and genotoxic response of the flame retardant tris(2,3-dibromopropyl)phosphate. Activation by singlet oxygen.

Illumination of tris (2,3-dibromopropyl)phosphate with visible light in the presence of riboflavin resulted in the formation of a stable product with greatly enhanced genetic and DNA-modifying activities. Because illumination of riboflavin results in the formation of short-lived singlet oxygen, it is assumed that the mutagenic and genotoxic chemical results from a reaction between the flame retardant and singlet oxygen. Since the polluted urban atmosphere is conducive to the generation of this species of oxygen, the present results may, therefore, be relevant to an assessment of the health hazard posed by such an environment.