Tris(2,3-dibromopropyl) phosphate: mutagenicity of a widely used flame retardant.

Tris(2,3-dibromopropyl) phosphate, a widely used flame-retardant additive for textiles, is mutagenic to histidine-requiring strains of Salmonella typhimurium. Extracts of fabrics treated with this compound are also capable of inducing mutations in these bacterial strains.

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. Nitropyrenes are potent frameshift mutagens, and possible mechanisms for their biological action are discussed.

Enhanced metabolism and mutagenesis of nitrosopyrrolidine in liver fractions isolated from chronic ethanol-consuming hamsters.

The effect of chronic ethanol consumption on the ability of isolated liver fractions to metabolize the carcinogen N-nitrosopyrrolidine (NPY) was examined. Microsomal fractions of treated animals exhibited increased rates of alpha-hydroxylation of NPY. Similar increases in the specific activities of aniline hydroxylase, reduced nicotinamide adenine dinucleotide phosphate cytochrome c reductase, and the specific content of cytochrome P-450 were also observed. In contrast, no differences in the specific activities of benzo(a)pyrene hydroxylase or glucose-6-phosphatase were observed. Liver postmitochondrial supernatants from ethanol-consuming animals were able to produce 5 times more mutants than did control preparations. It is concluded that alpha-hydroxylation of NPY is probably the mechanism by which NPY is converted to a mutagen and that this pathway can be induced by ethanol.

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.

Pathways for the mutagenesis of 1-nitropyrene and dinitropyrenes in the human hepatoma cell line HepG2.

The mutagenicity, metabolism, DNA adduction and induction of unscheduled DNA synthesis (UDS) of 1-nitropyrene and 1,8-dinitropyrene were investigated in the human hepatoma cell line HepG2. Previous results had demonstrated that 1-nitropyrene was both mutagenic at the hgprt locus and induced UDS in these cells. In the present study, we find that the dinitropyrenes, although highly mutagenic in Salmonella typhimurium, are not mutagenic and do not induce UDS in the HepG2. Although the rate of 1,8-dinitropyrene nitroreduction was less than that of 1-nitropyrene nitroreduction, this did not explain the lack of mutagenicity and UDS induction by the dinitropyrenes. Therefore, it is proposed that the arylhydroxylamine O-esterificase is not expressed in these cells. Since cytochrome P450-mediated C-oxidation is the predominant metabolic pathway in vivo, we sought to determine if an increase in the ratio of cytochrome P450-mediated C-oxidation over nitroreduction would result in increased or decreased DNA adducts in the HepG2. The administration of 2.5 microM 3-methylcholanthrene to the HepG2 increased the ratio of C-oxidation/nitroreduction from 2.8 +/- 1.9 to 50.4 +/- 46.1. This was accompanied by a decrease in the C8-guanyl adduct of 1-nitropyrene (via nitroreduction) from 18.7 +/- 7.0 to 4.8 +/- 1.7 fmoles/micrograms DNA, without any further increase in other 1-nitropyrene DNA adducts. These results suggest that the cytochrome P450-mediated metabolism of 1-nitropyrene to epoxides, phenols, and dihydrodiols is not an activation pathway in the HepG2 cells, and may explain the weak carcinogenicity of 1-nitropyrene in vivo, where cytochrome P450-mediated C-oxidation predominates.

Detection of mutagenic activity in the urines of anesthesiologists: a preliminary report.

While halothane was without mutagenic activity in the Salmonella mutagenicity assay, even in the presence of microsomal fractions, the urines of anesthesiologists induced mutations of the base-substitution type.

Differential antimutagenicity of WR-1065 added after irradiation in L5178Y cell lines.

The purpose of this study was to determine the antimutagenicity of WR-1065 added after irradiation of cells of cell lines differing in their ability to rejoin radiation-induced DNA double-strand breaks (DSBs). The postirradiation antimutagenicity of WR-1065 at the thymidine kinase locus was demonstrated for L5178Y (LY)-S1 cells that are deficient in repair of DNA DSBs. Less postirradiation antimutagenicity of WR-1065 was observed in LY-R16 and LY-SR1 cells, which are relatively efficient in DSB repair. Postirradiation treatment with WR-1065 had only a small stimulatory effect on DSB rejoining. A 3-h incubation of irradiated LY cells with WR-1065 caused slight changes in the distribution of cells in the phases of the cell cycle that differed between LY-S1 and LY-SR1 cells. Both LY-S1 and LY-SR1 cells were protected against the cytotoxic and mutagenic effects of radiation when WR-1065 was present 30 min before and during the irradiation. We conclude that the differential postirradiation effects of WR-1065 in the LY-S1 and LY-SR1 cells are not caused by differences in cellular uptake of the radioprotector or in its radical scavenging activity. Possible mechanisms for the postirradiation antimutagenicity of WR-1065 are discussed.

Genetic activity of allyl chloride.

Allyl chloride (3-chloroprene) is mutagenic for Salmonella typhimurium and it induces gene conversions in Saccharomyces cerevisiae. It also displays DNA-modifying activity for E. coli. This is in contrast to a recent study which reported its lack of genetic activity for Salmonella typhimurium.

Mutagenicity of the phenacetin metabolites: N-hydroxy-p-phenetidine and nitrosophenetol in S. typhimurium TA100 and derivatives deficient in nitroreductase or O-acetylase: probes for testing intrabacterial metabolic activation.

Two mutagenic metabolites of phenacetin, p-nitrosophenetol and N-hydroxy-p-phenetidine, were tested in S. typhimurium strains TA100, its nitroreductase-deficient derivative TA100NR, and O-acetylase-deficient strains TA100 Tn5-1,8-DNP1011 and -DNP1012 in the presence or absence of an exogenous metabolic activation system. The results indicate that bacterial nitroreductase(s) and O-acetylase(s), shown to be involved in the conversion of certain nitroarenes, are not required for the intrabacterial activation of the two phenacetin metabolites to bacterial mutagens. In view of the low reactivity of nitrosoarenes towards nucleophiles at neutrality, the mechanism by which they exert such a high mutagenic effect in S. typhimurium strains remains to be clarified, but is discussed.

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 basis of the insensitivity of Salmonella typhimurium strain TA98/1,8-DNP6 to the mutagenic action of nitroarenes.

Salmonella typhimurium tester strain TA98/1,8-DNP6 is resistant to the mutagenicity of 1,8-dinitropyrene because it lacks an esterification enzyme which is needed for the formation of the ultimate mutagen, presumably the corresponding hydroxamic acid ester. This enzyme does not appear to be required for the activation of all nitroarenes and arylamines, as some of these are fully active in TA98/1,8-DNP. It is suggested that these form electrophilic arylnitrenium ions nonenzymatically from nitroso- and N-hydroxylamino-arenes intermediates. The esterification enzyme appears to be a transacetylase. An assay using 2-aminofluorene as the acetyl acceptor is described. Derivatives of S. typhimurium TA100 also lacking this enzyme were obtained by Tn5-mediated mutagenesis.

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). The reduction of the nitro group appears to be catalyzed by a different nitroreductase. The mutagenicity of the non-carcinogenic 3-methyl-4-nitroquinoline-1-oxide (meNQO) may be related to this newly recognized nitroreductase. It is proposed, further, that the ultimate mutagenic intermediates derived from NQO and MeNQO differ.

Apparent absence of recombinogenic activity of nitropyrenes for yeast.

Nitropyrenes have been shown to be potent bacterial and mammalian mutagens. However, they failed to induce any recombinogenic activity in Saccharomyces cerevisiae D4 even at elevated concentrations and following extended periods of exposure. A plausible explanation for this lack of activity is the absence or the lack of activation of the enzyme required for the activation of nitropyrenes in this test system under the experimental (aerobic) conditions employed.

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. Evidence in support of this mechanism is obtained by the use of tester strains having a functional uvrB gene product or lacking specific nitroreductases. The mutagenic potency of nitrated fluorenes increases upon successive addition of nitro groups reaching a peak at the trisubstituted state. Addition of a 4th nitro group leads to decreased activity.

Carcinogenic N-hydroxylaminopurine derivatives do not act as base analog mutagens in Salmonella typhimurium.

N-Hydroxylaminopurines are highly mutagenic for growing as well as resting Salmonella typhimurium strain TA100 and to a lesser extent for strain TA98. Aminopurines, under similar conditions, are not mutagenic. N-Methylhydroxylaminopurine, under similar conditions, exhibits only minimal activity. The results are taken to indicate that unlike non-hydroxylated aminopurines, N-hydroxylaminopurines exert their mutagenicity not by acting as base analogs but by direct covalent binding with DNA-guanine.

Mutagenicity of nitropyrenes for Escherichia coli: requirement for increased cellular permeability.

Nitropyrenes are mutagenic to E. coli strains that have increased permeabilities to large molecules and carry plasmid pKM101.

Phenotypic instability of Salmonella typhimurium tester strains: an example of a plasmid-enhanced genetic drift?

Strains derived from Salmonella typhimurium LT-2, which are used as tester strains in mutagenicity assays, show significant changes in biochemical phenotypes. The presence of plasmid pKM101 in these strains greatly increases both the frequency of these shifts as well as the spectrum of phenotypes involved. It is suggested that in plasmid-free strains these variations reflect the effects of endogeneously induced mutations which are amplified in the absence of a functional uvrB gene product. In plasmid-containing strains this genetic drift may be promoted further by the pKM101-coded error-prone DNA repair system. The observation of a plasmid-mediated genetic drift lends support to the suggestion that transposons may contribute to the carcinogenic process.

The chemical activation of non-mutagenic nitrated polycyclic aromatic hydrocarbons to mutagens.

Nitrated polycyclic aromatic hydrocarbons, including carcinogens, may be non-mutagenic in microorganisms because bacterial nitroreductases are unable to reduce their nitro function to proximate mutagenic hydroxylamines. This reduction of the nitro moiety can be accomplished chemically in situ using zinc dust. The procedure, which is compatible with the Salmonella mutagenicity assay, was used to generate mutagens from chemicals which otherwise are non-mutagenic even in the presence of microsomal preparations.

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. coli even when tested under conditions designed to take the metabolic properties of these agents into consideration. Novobiocin and nalidixic acid are widely used in animal and human medicine and further studies to assess their genetic and carcinogenic potentials appear to be in order.

Activation of a procarcinogen to a mutagen by cell-free extracts of anaerobic bacteria.

The Salmonella mutagenicity assay can be coupled to cell-free preparations derived from anaerobic bacteria (Clostridium perfringens and Bacteroides fragilis) to activate a procarcinogen to a mutagen. This activity is destroyed by heating and by digestion with pronase and it is sensitive to oxygen. These findings indicate that the Salmonella mutagenicity assay can be adapted to the study of the role of anaerobes in the activation of carcinogens.