Mutant of Bacterium paracoli 5099 with an altered DNA: identification as a Flavobacterium.

A difference in the base composition of the DNA of Bacterium paracoli 5099 and of a "mutant" (No. 1975) derived from it was found. This is in accordance with the finding of others. However, biochemical tests revealed that the "mutant" was a Flavobacterium, whereas the parent strain belonged to a species of Escherichia. The base composition of the DNA of the "mutant" is similar to that reported for the DNA of Flavobacterium.

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.

Evaluation of the mutagenicity and DNA-modifying activity of carcinogens and noncarcinogens in microbial systems.

The mutagenicity of 99 chemicals was determined in a standard Salmonella typhimurium assay with the use of strains TA1535 and TA1538; the DNA-modifying capacity was determined with normal and DNA polymerase-deficient Escherichia coli strains. The following categories of chemicals were studied: alkylating agents (15); nitrosamines, hydrazines, and related substances (8); heterocyclics (10); aromatic amines (36); polycyclic aromatic hydrocarbons (11); amides, ureas, and acylating agents (7); antimetabolites (5); inorganics (4); and promoters (3). Of the substances studied, 21 were known noncarcinogens, 21 were ultimate carcinogens, and 45 were procarcinogens. Of the noncarcinogens, 35, 30, and 25% were positive in the Salmonella, E. coli, and both systems, respectively. All of the ultimate carcinogens were detectable as mutagens of DNA-modifying agents; 79, 100, and 79% gave positive tests in the Salmonella, E. coli, and both systems, respectively. Of the procarcinogens 72% were identifiable by these procedures: 52, 67, and 48% in the Salmonella, E. coli, and both assays, respectively. A tabulation of the combined data for ultimate carcinogens and procarcinogens indicates that 77% of the carcinogens gave positive results: 61, 74, and 59% in the Salmonella, E. coli, and both assays, respectively. We suggest that, for prescreening procedures with microbial assays, S. typhimurium strains TA98 and TA100 be included and the standard E. coli DNA polymerase-deficient assay be run in tandem with the Salmonella mutagenicity assay. When the standard E. coli DNA polymerase-deficient assay does not give interpretable results because of the lack of zones of growth inhibition, a modified assay with the use of liquid suspension should be performed.

Mutagenicity of metronidazole: presence of several active metabolites in human urine.

Mutagenic activity was found in the urine of 10 patients given therapeutic dosages of metronidazole orally or per vagina. Paper chromatographic separation revealed that mutagenicity in the urine was associated with unmodified metronidazole and at least four of its known urinary metabolites. Activity was also recovered in a region of the chromatogram heretofore not assigned to a metronidazole metabolite.

Mutagenic activity of chemical carcinogens and related compounds in the intraperitoneal host-mediated assay.

The mutagenic activities of 79 carcinogens, noncarcinogens, and structurally related compounds toward Salmonella typhimurium strains TA1530, TA1535, and TA1538 and toward Saccharomyces cerevisiae D3 were investigated in the intraperitoneal host-mediated assay. Fewer than half of the carcinogens were mutagenic toward the Salmonella strains. The insensitivity of the system was most marked with the aromatic amine and polycyclic hydrocarbon procarcinogens. Under the test conditions, fewer than 10% of the carcinogens showed clear mutagenic activity toward S. cerevisiae D3. However, none of the noncarcinogens was significantly mutagenic toward either S. typhimurium or S. cerevisiae D3. Overall, the intraperitoneal host-mediated assay does not seem suitable for routine preliminary screening of large numbers of potential carcinogens. The median lethal doses to mice of 46 compounds were determined.

Mutagenicity of azathioprine.

Azathioprine (6-[(1-methyl-4-nitroimidazol-5-yl)thio]purine; lmuran) is mutagenic for Salmonella typhirmuium. Demonstration of this mutagenic effect requires a period of anaerobic incubation of the bacteria with the test agent.

Light-induced mutagenicity of neutral red (3-amino-7-dimethylamino-2-methylphenazine hydrochloride).

Illumination of Salmonella typhimurium in the presence of neutral red (3-amino-7-dimethylamino-2-methylphenazine hydrochloride) results in mutations of the base substitution type.

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 0.19% that exhibited by the enzyme-proficient parent strain when the deficiency is the result of a base substitution and frame-shift mutation, respectively. The results are taken to indicate that the residual activity (4.4%) seen in the strain with a base substitution mutation reflects the activity of an enzyme with an amino acid substitution, while the basal level (0.19%) of activity indicates the action of a different nitroreductase with a low specificity for niridazole.

Mutagenicity, unscheduled DNA synthesis, and metabolism of 1-nitropyrene in the human hepatoma cell line HepG2.

The cell line HepG2 is derived from a well differentiated human hepatoblastoma, which retains many of the morphological characteristics of liver parenchymal cells. These cells at passages greater than 95 were found to metabolically activate carcinogens to genotoxic metabolites. The addition of 6.8 microM 1-methyl-3-nitro-1-nitrosoguanidine, 5.3 microM 4-nitroquinoline-N-oxide, and 4-20.3 microM 1-nitropyrene resulted in the induction of mutations at the HGPRT locus as determined by 6-thioguanine resistance. This is the first description of the induction of mutations in these cells. Additionally, unscheduled DNA synthesis in the presence of 4 mM hydroxyurea was increased by 9% with 5.3 microM 4-nitroquinoline-N-oxide, 57% with 13.6 microM 1-methyl-3-nitro-1-nitrosoguanidine, and 300% with 8.2 microM 1-nitropyrene. High performance liquid chromatographic analysis of metabolites formed following incubation of HepG2 with either [3H]-1-nitropyrene or [14C]benzo(a)pyrene demonstrate the occurrence of arene oxidation as well as nitroreduction.

Further observations on the photooxidation of DNA in the presence of riboflavin.

Illumination of DNA in the presence of riboflavin results in an increase in buoyant density and a decrease in the temperature of the thermal helix-coil transition (Tm). The increase in buoyant density is maintained even after thermal denaturation, which indicates that it reflects a chemical alteration of a DNA base (presumably guanine). beta-Carotene, a quencher of singlet oxygen, inhibits the increase in buoyant density but it prevents only partially the decrease in Tm. This is taken as an indication that the photo-induced alteration of the DNA structure is due to more than one reaction. Illumination of DNA in the presence of methylene blue also causes an increase in buoyant density , but this increase is not retained upon thermal denaturation.

The photodynamic modification of DNA by hematoporphyrin.

Illumination (white light: 300-750 nm) of DNA in the presence of hematoporphyrin (less than or equal to 5-10 (-4) M) results in selective degradation of the guanine moiety. DNA so illuminated exhibits physical chemical properties (lowered sedimentation coefficients, lower temperatures of helix-coil transitions, increased buoyant density values) consistent with single-chain scissions (and the generation of single-stranded regions) which presumably are secondary to the photodegradation of the guanine residue. Illumination of DNA in the presence of low levels of hematoporphyrin (greater than or equal to 2.5 - 10 (-4) M) results in a biopolymer exhibiting all of the physical properties described above with the exception of a lowered sedimentation coefficient; on the contrary such DNA is aggregated. Of the four usual deoxynucleosides irradiated in the presence of hematoporphyrin, only deoxyguanosine is destroyed.

Natural history of neonatal colonization with group B streptococci.

Thirteen percent of the newborns in our study group were colonized with group B streptococci on day 3. This colonization rate appeared constant during the first two weeks of life and then decreased to 5%. Of the babies colonized on day 3, 59% and 91% were culture-negative on days 14 and 42, respectively. Sixty-five percent of the babies carrying group B streptococci on day 14 acquired this microorganism following discharge (day 3). Babies colonized with staphylococci or Escherichia coli were found to have decreased probability of colonization with group B streptococci.

The carcinogenic potential of cocaine.

Analysis of cocaine by CASE, an expert system, results in the prediction that cocaine is a rodent carcinogen. In view of the widespread exposure to cocaine this is cause for alarm, especially as in utero exposure has been widely documented and the developing human fetus is at an increased risk of transplacental cancer induction.

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.

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.

Mutagenicity of halogenated alkanes and their derivatives.

The ability of a series of haloalkanes, haloethanols and haloacetaldehydes to induce mutations in Salmonella typhrimurium and preferentially to inhibit the growth of DNA polymerase-deficient E. coli (pol A(+)/pol A(-)) was investigated. For the haloalkanes investigated, the order of reactivities towards the E. coli pol A(+)/pol A(-), was: 1,1,2,2-tetrabromoethane > 1,1-dibromoethane > 1,1,2,2-tetrachlorethane > 1,2-dibromoethane = 1,5 dibromopentane > 1,2-dibromo-2-methylpropane > 1-bromo-2-chloroethane > 1,2-dichloroethane. In the standard Salmonella mutagenicity assay the order of these substances was 1,2-dibromoethane = 1,5-dibromopentane > 1,2-dibromo-2-methylpropane >/= 1-bromo-2-chloroethane > 1,1,2,2-tetrachloroethane = 1,1-dibromoethane > 1,2-dichloroethane. 1,1,2,2-Tetrabromoethane was negative in the standard assay but strongly mutagenic when tested in suspension. It would appear that the discrepancy between the two procedures is due to the fact that bactericidal mutagens cannot be scored reliably in the standard Salmonella assay. The order of reactivity of 2-haloethanols in E. coli pol. A(+)/pol A(-), was 2-iodo > 2-bromo-> 2-chloroethanol. In the Salmonella assay the order was 2-bromo-> 2 iodo- >2-chloro-ethanol. 2-Fluoroethanol and ethanol were devoid of activity in both assays. For the 2-haloacetaldehydes the reactivities in the E. coli system were 2-bromoethylacetate > 2-bromoacetaldehyde = acetaldehyde > 2-chloroacetaldehyde while in the Salmonella system the order was 2-bromoethylacetate > 2-chloroacetaldehyde. Acetaldehyde had minimal activity, while 2-bromoacetaldehyde was without activity but strongly bactericidal.

Estimating the extent of the health hazard posed by high-production volume chemicals.

We used structure-activity relationship modeling to estimate the number of toxic chemicals among the high-production volume (HPV) group. We selected 200 chemicals from among the HPV chemical list and predicted the potential of each for its ability to induce a variety of adverse effects including genotoxicity, carcinogenicity, developmental, and systemic toxicity. We found a significantly less than expected proportion of toxic chemicals among the HPV sample when compared to a reference set of 10,000 chemicals representative of the universe of chemicals.

Carcinogenicity predictions for a group of 30 chemicals undergoing rodent cancer bioassays based on rules derived from subchronic organ toxicities.

Rodent carcinogenicities for a group of 30 chemicals which form the subject of the Second NIEHS Predictive-Toxicology Evaluation Experiment are predicted based on their subchronic organ toxicities. Predictions are made by rules learned by the rule learning (RL) induction program.

A dichotomy in the lipophilicity of natural estrogens, xenoestrogens, and phytoestrogens.

Using two independent analyses, it is demonstrated that natural (e.g., estradiol) and some xenoestrogens (e.g., methoxychlor metabolite) are characterized by a lipophilic region that is absent in nonestrogens as well as in phytoestrogens. It is suggested that this lipophilic region affects binding to specific receptors and may, in fact, differentiate harmful from beneficial estrogens.

Prediction of the carcinogenicity of a second group of organic chemicals undergoing carcinogenicity testing.

Twenty-four organic compounds currently undergoing testing within cancer bioassays under the aegis of the U.S. National Toxicology Program (NTP) were submitted to the computer automated structure evaluation (CASE) and multiple computer automated structure evaluation (MULTICASE) system for predictions of activity. Individual predictions resulting from the NTP combined rodent, NTP mouse, Carcinogenic Potency Database (CPDB) combined rodent, and CPDB mouse databases were combined using Bayes' theorem to yield an overall probability of rodent carcinogenicity. Based upon an arbitrary probability cut-off of 0.50, nine compounds were predicted to be rodent carcinogens. The predicted carcinogens are chloroprene, 1-chloro-2-propanol, codeine, emodin, furfuryl alcohol, isobutyraldehyde, primaclone, sodium xylenesulfonate, and t-butylhydroquinone.