2-Nitrofluorene and related compounds: prevalence and biological effects

Conformation-dependent lesion bypass of bulky arylamine-dG adducts generated from 2-nitrofluorene in epigenetic sequence contexts

Sequence context influences structural characteristics and repair of DNA adducts, but there is limited information on how epigenetic modulation affects conformational heterogeneity and bypass of DNA lesions. Lesions derived from the environmental pollutant 2-nitrofluorene have been extensively studied as chemical carcinogenesis models; they adopt a sequence-dependent mix of two significant conformers: major groove binding (B) and base-displaced stacked (S). We report a conformation-dependent bypass of the N-(2'-deoxyguanosin-8-yl)-7-fluoro-2-aminofluorene (dG-FAF) lesion in epigenetic sequence contexts (d[5'-CTTCTC#G*NCCTCATTC-3'], where C# is C or 5-methylcytosine (5mC), G* is G or G-FAF, and N is A, T, C or G). FAF-modified sequences with a 3' flanking pyrimidine were better bypassed when the 5' base was 5mC, whereas sequences with a 3' purine exhibited the opposite effect. The conformational basis behind these variations differed; for -CG*C- and -CG*T-, bypass appeared to be inversely correlated with population of the duplex-destabilizing S conformer. On the other hand, the connection between conformation and a decrease in bypass for flanking purines in the 5mC sequences relative to C was more complex. It could be related to the emergence of a disruptive non-S/B conformation. The present work provides novel conformational insight into how 5mC influences the bypass efficiency of bulky DNA damage.

Oxygenated and Nitrated Polycyclic Aromatic Hydrocarbons: Sources, Quantification, Incidence, Toxicity, and Fate in Soil—A Review Study

The genotoxicity, mutagenesis, and carcinogenic effects of polycyclic aromatic hydrocarbon (PAH) derivatives may exceed the parent PAHs. However, their influence on the soil environment has not been explored to a large extent. Oxygenated polycyclic aromatic hydrocarbons (OPAHs) and nitrated polycyclic aromatic hydrocarbons (NPAHs) are typical polar substituted compounds. We offer a review of the literature on the sources, quantification, incidence, toxicity, and transport of these compounds in soil. Although their environmental concentrations are lower than those of their parent compounds, they exert higher toxicity. Both types of substances are basically related to carcinogenesis. OPAHs are not enzymatically activated and can generate reactive oxygen species in biological cells, while NPAHs have been shown to be mutagenic, genotoxic, and cytotoxic. These compounds are largely derived from the transformation of PAHs, but they behave differently in soil because of their higher molecular weight and dissimilar adsorption mechanisms. Therefore, specialized knowledge of model derivatives is required. We also made recommendations for future directions based on existing research. It is expected that the review will trigger scientific discussions and provide a research basis for further study on PAH derivatives in the soil environment.

Incorporation of Metabolic Activation in the HPTLC-SOS-Umu-C Bioassay to Detect Low Levels of Genotoxic Chemicals in Food Contact Materials

The safety evaluation of food contact materials requires excluding mutagenicity and genotoxicity in migrates. Testing the migrates using in vitro bioassays has been proposed to address this challenge. To be fit for that purpose, bioassays must be capable of detecting very low, safety relevant concentrations of DNA-damaging substances. There is currently no bioassay compatible with such qualifications. High-performance thin-layer chromatography (HPTLC), coupled with the planar SOS Umu-C (p-Umu-C) bioassay, was suggested as a promising rapid test (~6 h) to detect the presence of low levels of mutagens/genotoxins in complex mixtures. The current study aimed at incorporating metabolic activation in this assay and testing it with a set of standard mutagens (4-nitroquinoline-N-oxide, aflatoxin B1, mitomycin C, benzo(a)pyrene, N-ethyl nitrourea, 2-nitrofluorene, 7,12-dimethylbenzanthracene, 2-aminoanthracene and methyl methanesulfonate). An effective bioactivation protocol was developed. All tested mutagens could be detected at low concentrations (0.016 to 230 ng/band, according to substances). The calculated limits of biological detection were found to be up to 1400-fold lower than those obtained with the Ames assay. These limits are lower than the values calculated to ensure a negligeable carcinogenic risk of 10^-5. They are all compatible with the threshold of toxicological concern for chemicals with alerts for mutagenicity (150 ng/person). They cannot be achieved by any other currently available test procedures. The p-Umu-C bioassay may become instrumental in the genotoxicity testing of complex mixtures such as food packaging, foods, and environmental samples.

Direct Comparison of the Lowest Effect Concentrations of Mutagenic Reference Substances in Two Ames Test Formats

The Ames assay is the standard assay for identifying DNA-reactive genotoxic substances. Multiple formats are available and the correct choice of an assay protocol is essential for achieving optimal performance, including fit for purpose detection limits and required screening capacity. In the present study, a comparison of those parameters between two commonly used formats, the standard pre-incubation Ames test and the liquid-based Ames MPF™, was performed. For that purpose, twenty-one substances with various modes of action were chosen and tested for their lowest effect concentrations (LEC) with both tests. In addition, two sources of rat liver homogenate S9 fraction, Aroclor 1254-induced and phenobarbital/β-naphthoflavone induced, were compared in the Ames MPF™. Overall, the standard pre-incubation Ames and the Ames MPF™ assay showed high concordance (>90%) for mutagenic vs. non-mutagenic compound classification. The LEC values of the Ames MPF™ format were lower for 17 of the 21 of the selected test substances. The S9 source had no impact on the test results. This leads to the conclusion that the liquid-based Ames MPF™ assay format provides screening advantages when low concentrations are relevant, such as in the testing of complex mixtures.

The presence of nitroarenes formed by secondary atmospheric processes in the Japanese freshwater environment

In this study, the concentrations and distributions of nitrated polycyclic aromatic hydrocarbons (NPAHs) were characterized in the freshwater environment of a Japanese city. While the NPAHs were few in number, they were found in pg/L concentrations and the specific isomers suggested the deposition of NPAHs formed via the atmospheric transformation of PAHs. The absence of NPAHs formed via primary combustion processes such as automobile exhaust, suggests that improvements in emission standards are being reflected in the environment, though the NPAHs formed by secondary atmospheric processes are still a significant ecotoxicological threat. The stability of the NPAHs was also examined in spiked freshwater matrices. There was a significant decrease in spiked NPAHs over this period, suggesting that they were either being sorbed or transformed and are therefore not long lived in the freshwater environment. This indicates that the NPAHs found in freshwater samples are from recent deposition.

Repair-Resistant DNA Lesions

The eukaryotic global genomic nucleotide excision repair (GG-NER) pathway is the major mechanism that removes most bulky and some nonbulky lesions from cellular DNA. There is growing evidence that certain DNA lesions are repaired slowly or are entirely resistant to repair in cells, tissues, and in cell extract model assay systems. It is well established that the eukaryotic DNA lesion-sensing proteins do not detect the damaged nucleotide, but recognize the distortions/destabilizations in the native DNA structure caused by the damaged nucleotides. In this article, the nature of the structural features of certain bulky DNA lesions that render them resistant to NER, or cause them to be repaired slowly, is compared to that of those that are good-to-excellent NER substrates. Understanding the structural features that distinguish NER-resistant DNA lesions from good NER substrates may be useful for interpreting the biological significance of biomarkers of exposure of human populations to genotoxic environmental chemicals. NER-resistant lesions can survive to replication and cause mutations that can initiate cancer and other diseases. Furthermore, NER diminishes the efficacy of certain chemotherapeutic drugs, and the design of more potent pharmaceuticals that resist repair can be advanced through a better understanding of the structural properties of DNA lesions that engender repair-resistance.

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) in the environment - A review

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) are derivatives of PAHs with at least one nitro-functional group (-NO₂) on the aromatic ring. The toxic effects of several nitro-PAHs are more pronounced than those of PAHs. Some nitro-PAHs are classified as possible or probable human carcinogens by the International Agency for Research on Cancer. Nitro-PAHs are released into the environment from combustion of carbonaceous materials (e.g. fossil fuels, biomass, waste) and post-emission transformation of PAHs. Most studies on nitro-PAHs are about air (gas-phase and particulate matter), therefore less is known about the occurrence, concentrations, transport and fate of nitro-PAHs in soils, aquatic environment and biota. Studies on partition and exchange of nitro-PAHs between adjacent environmental compartments are also sparse. The concentrations of nitro-PAHs cannot easily be predicted from the intensity of anthropogenic activity or easily related to those of PAHs. This is because anthropogenic source strengths of nitro-PAHs are different from those of PAHs, and also nitro-PAHs have additional sources (formed by photochemical conversion of PAHs). The fate and transport of nitro-PAHs could be considerably different from their related PAHs because of their higher molecular weights and considerably different sorption mechanisms. Hence, specific knowledge on nitro-PAHs is required. Regulations on nitro-PAHs are also lacking. We present an extensive review of published literature on the sources, formation, physico-chemical properties, methods of determination, occurrence, concentration, transport, fate, (eco)toxicological and adverse health effects of nitro-PAHs. We also make suggestions and recommendations about data needs, and future research directions on nitro-PAHs. It is expected that this review will stimulate scientific discussion and provide the basis for further research and regulations on nitro-PAHs.

FTIR analysis and evaluation of carcinogenic and mutagenic risks of nitro-polycyclic aromatic hydrocarbons in PM1.0

Nitro-polycyclic aromatic hydrocarbons (NPAHs) represent a group of organic compounds of significant interest due to their presence in airborne particulates of urban centers, wide distribution in the environment, and mutagenic and carcinogenic properties. These compounds, associated with atmospheric particles of size < 1 μm, have been reported as a major risk to human health. This study aims at identifying the spectral features of NPAHs (1-nitropyrene, 2-nitrofluorene, and 6-nitrochrysene) in emissivity and transmittance spectra of samples of particulate matter < 1 μm (PM1.0) using infrared spectrometry. Carcinogenic and mutagenic risks of the studied NPAHs associated with PM1.0 samples were also determined for two sampling sites: Canoas and Sapucaia do Sul. The results showed that NPAH standard spectra can effectively identify NPAHs in PM1.0 samples. The transmittance and emissivity sample spectra showed broader bands and lower relative intensity than the standard NPAH spectra. The carcinogenic risk and the total mutagenic risk were calculated using the toxic equivalent factors and mutagenic potency factors, respectively. Canoas showed the highest total carcinogenic risk, while Sapucaia do Sul had the highest mutagenic risk. The seasonal analysis suggested that in the study area the ambient air is more toxic during the cold periods. These findings might of significant importance for the decision and policy making authorities.

Structural and dynamic characterization of polymerase κ's minor groove lesion processing reveals how adduct topology impacts fidelity

DNA lesion bypass polymerases process different lesions with varying fidelities, but the structural, dynamic, and mechanistic origins of this phenomenon remain poorly understood. Human DNA polymerase κ (Polκ), a member of the Y family of lesion bypass polymerases, is specialized to bypass bulky DNA minor groove lesions in a predominantly error-free manner, by housing them in its unique gap. We have investigated the role of the unique Polκ gap and N-clasp structural features in the fidelity of minor groove lesion processing with extensive molecular modeling and molecular dynamics simulations to pinpoint their functioning in lesion bypass. Here we consider the N²-dG covalent adduct derived from the carcinogenic aromatic amine, 2-acetylaminofluorene (dG-N²-AAF), that is produced via the combustion of kerosene and diesel fuel. Our simulations reveal how the spacious gap directionally accommodates the lesion aromatic ring system as it transits through the stages of incorporation of the predominant correct partner dCTP opposite the damaged guanine, with preservation of local active site organization for nucleotidyl transfer. Furthermore, flexibility in Polκ’s N-clasp facilitates the significant misincorporation of dTTP opposite dG-N²-AAF via wobble pairing. Notably, we show that N-clasp flexibility depends on lesion topology, being markedly reduced in the case of the benzo[a]pyrene-derived major adduct to N²-dG, whose bypass by Polκ is nearly error-free. Thus, our studies reveal how Polκ’s unique structural and dynamic properties can regulate its bypass fidelity of polycyclic aromatic lesions and how the fidelity is impacted by lesion structures.

The effect of environmental pollutants and food processing on the development of antibiotic resistance

AIM

The purpose of this study was to determine how various compounds known to be positive mutagens, contribute to the development of mutations leading to ciprofloxacin resistance in Salmonella enterica subsp. enterica serotype Typhimurium. The molecular mechanism of ciprofloxacin resistance in treated strains was investigated.

METHODS

A modified version of the incorporation plate test was used for quantitative determination of ciprofloxacin resistant mutants and for assessment of the mutation frequency induced by the positive mutagens in different concentrations. An AS-PCR-RFLP for monitoring of gyrA mutations was applied.

RESULTS

Mutation frequency, expressed as number of antibiotic resistant colonies per 10(8) viable cells, was much higher after exposure of bacterial cells to 3-(5-nitro-2-furyl) acrylic acid and 2-nitrofluorene. All isolated cultures retain decreased susceptibility to antibiotic after multiple passages in antibiotic-free medium. 2-nitrofluorene was the best inducer of mutations in gyrA and in regulation genes affecting suppression of synthesis of outer membrane porins. 3-(5-nitro-2-furyl) acrylic acid gives rise to overproduction of efflux pump.

CONCLUSIONS

The data suggest that antibiotic resistance may not be only a consequence of misuse of antibiotics. A polluted environment as well as food processing could contribute to this unwanted process.

Absorption of nitro-polycyclic aromatic hydrocarbons by biomembrane models: effect of the medium lipophilicity

To demonstrate the relationship between the structure of nitro-polycyclic aromatic hydrocarbons and their effect on biomembranes, we have investigated the influence of three structurally different nitro-polycyclic aromatic hydrocarbons, 2-nitrofluorene, 2,7-dinitrofluorene and 3-nitrofluoranthene, on the thermotropic behavior of dimyristoylphosphatidylcholine multilamellar vesicles, used as biomembrane models, by means of differential scanning calorimetry. The obtained results indicate that the studied nitro-polycyclic aromatic hydrocarbons affected the thermotropic behavior of multilamellar vesicles to various extents, modifying the pretransition and the main phase transition peaks and shifting them to lower temperatures. The effect of the aqueous and lipophilic medium on the absorption process of these compounds by the biomembrane models has been also investigated revealing that the process is hindered by the aqueous medium but strongly allowed by the lipophilic medium.

Human arylamine N-acetyltransferase 1: in vitro and intracellular inactivation by nitrosoarene metabolites of toxic and carcinogenic arylamines

Arylamines (ArNH 2) are common environmental contaminants, some of which are confirmed risk factors for cancer. Biotransformation of the amino group of arylamines involves competing pathways of oxidation and N-acetylation. Nitrosoarenes, which are products of the oxidation pathway, are electrophiles that react with cellular thiols to form sulfinamide adducts. The arylamine N-acetyltransferases, NAT1 and NAT2, catalyze N-acetylation of arylamines and play central roles in their detoxification. We hypothesized that 4-nitrosobiphenyl (4-NO-BP) and 2-nitrosofluorene (2-NO-F), which are nitroso metabolites of arylamines that are readily N-acetylated by NAT1, would be potent inactivators of NAT1 and that nitrosobenzene (NO-B) and 2-nitrosotoluene (2-NO-T), which are nitroso metabolites of arylamines that are less readily acetylated by NAT1, would be less effective inactivators. The second order rate constants for inactivation of NAT1 by 4-NO-BP and 2-NO-F were 59200 and 34500 M (-1) s (-1), respectively; the values for NO-B and 2-NO-T were 25 and 23 M (-1) s (-1). Densitometry quantification and comparisons of specific activities with those of homogeneous recombinant NAT1 showed that NAT1 constitutes approximately 0.002% of cytosolic protein in HeLa cells. Treatment of HeLa cells with 4-NO-BP (2.5 microM) for 1 h caused a 40% reduction in NAT1 activity, and 4-NO-BP (10 microM) caused a 50% loss of NAT1 activity within 30 min without affecting either glyceraldehyde 3-phosphate dehydrogenase (GAPDH) or glutathione reductase (GR) activities. 2-NO-F (1 microM) inhibited HeLa cell NAT1 activity by 36% in 1 h, and a 10 microM concentration of 2-NO-F reduced NAT1 activity by 70% in 30 min without inhibiting GAPDH or GR. Mass spectrometric analysis of NAT1 from HeLa cells in which NAT1 was overexpressed showed that treatment of the cells with 4-NO-BP resulted in sulfinamide adduct formation. These results indicated that exposure to low concentrations of nitrosoarenes may lead to a loss of NAT1 activity, thereby compromising a critical detoxification process.

Tumorigenicity and genotoxicity of an environmental pollutant 2,7-dinitrofluorene after systemic administration at a low dose level to female rats

Environmental pollution with nitroaromatic compounds may pose health hazards. We have examined the tumorigenicity in female Sprague-Dawley rats of 2,7-dinitrofluorene (2,7-diNF) and 9-oxo-2,7-diNF administered by intraperitoneal (i.p.) and oral routes at 10 micromol/kg body weight, 3 times per week for 4 weeks. After i.p. treatment, the estimated median latency for the combined malignant and benign mammary tumors was decreased in 2,7-diNF- (p = 0.003) or 9-oxo-2,7-diNF-treated (p = 0.007), relative to vehicle-treated rats (42 or 64 vs. 80 weeks, respectively), whereas after oral dosing, there were no significant differences. At 90 weeks, the malignant mammary tumor incidence in 2,7-diNF-, 9-oxo-2,7-diNF- and vehicle-i.p. treated rats was 44 (p = 0.02 vs. vehicle-treated), 25 and 6%, respectively. Liver and mammary gland DNA was analyzed by HPLC combined with electrospray tandem mass spectrometry for the presence of a deoxyguanosine (dG-2,7-diNF) adduct and a deoxyadenosine (dA-2,7-diNF) adduct derived from 2,7-diNF, and a deoxyguanosine (dG-9-oxo-2,7-diNF) adduct derived from 9-oxo-2,7-diNF. Both dG-2,7-diNF and dA-2,7-diNF were detected in DNA of 2,7-diNF-treated rats, whereas only very low levels of dG-9-oxo-2,7-diNF were detected in DNA of 9-oxo-2,7-diNF-treated rats. After i.p. treatment, the dA-2,7-diNF level was higher (p < 0.01) in the mammary gland than liver (13.6 vs. 7.8 adducts/10(8) nucleotides). In the mammary gland, the dG-2,7-diNF level was higher (p < 0.05) after i.p. than oral dosing and also higher (p < 0.05) than in the liver (36 vs. 8.6 and vs. 9.1 adducts/10(8) nucleotides, respectively). The preferential display of carcinogenicity and genotoxicity in the mammary gland by low doses of 2,7-diNF signifies its potential relevance for environmental breast cancer.

Examination of the long-range effects of aminofluorene-induced conformational heterogeneity and its relevance to the mechanism of translesional DNA synthesis

Adduct-induced conformational heterogeneity complicates the understanding of how DNA adducts exert mutation. A case in point is the N-deacetylated AF lesion [N-(2'-deoxyguanosin-8-yl)-2-aminofluorene], the major adduct derived from the strong liver carcinogen N-acetyl-2-aminofluorene. Three conformational families have been previously characterized and are dependent on the positioning of the aminofluorene rings: B is in the "B-DNA" major groove, S is "stacked" into the helix with base-displacement, and W is "wedged" into the minor groove. Here, we conducted (19)F NMR, CD, T(m), and modeling experiments at various primer positions with respect to a template modified by a fluorine tagged AF-adduct (FAF). In the first set, the FAF-G was paired with C and in the second set it was paired with A. The FAF-G:C oligonucleotides were found to preferentially adopt the B or S-conformers while the FAF-G:A mismatch ones preferred the B and W-conformers. The conformational preferences of both series were dependent on temperature and complementary strand length; the largest differences in conformation were displayed at lower temperatures. The CD and T(m) results are in general agreement with the NMR data. Molecular modeling indicated that the aminofluorene moiety in the minor groove of the W-conformer would impose a steric clash with the tight-packing amino acid residues on the DNA binding area of the Bacillus fragment (BF), a replicative DNA polymerase. In the case of the B-type conformer, the carcinogenic moiety resides in the solvent-exposed major groove throughout the replication/translocation process. The present dynamic NMR results, combined with previous primer extension kinetic data by Miller & Grollman, support a model in which adduct-induced conformational heterogeneities at positions remote from the replication fork affect polymerase function through a long-range DNA-protein interaction.

Site-specific incorporation of N-(deoxyguanosin-8-yl)-2-acetylaminofluorene (dG-AAF) into oligonucleotides using modified 'ultra-mild' DNA synthesis

Aromatic amino and nitro compounds are potent carcinogens found in the environment that exert their toxic effects by reacting with DNA following metabolic activation. One important adduct is N-(deoxyguanosin-8-yl)-2-acetylaminofluorene (dG-AAF), which has been extensively used in studies of the mechanisms of DNA repair and mutagenesis. Despite the importance of dG-AAF adducts in DNA, an efficient method for its incorporation into DNA using solid-phase synthesis is still missing. We report the development of a modified 'ultra-mild' DNA synthesis protocol that allows the incorporation of dG-AAF into oligonucleotides of any length accessible by solid-phase DNA synthesis with high efficiency and independent of sequence context. Key to this endeavor was the development of improved deprotection conditions (10% diisopropylamine in methanol supplemented with 0.25 M of beta-mercaptoethanol) designed to remove protecting groups of commercially available 'ultra-mild' phosphoramidite building blocks without compromising the integrity of the exquisitely base-labile acetyl group at N8 of dG-AAF. We demonstrate the suitability of these oligonucleotides in the nucleotide excision repair reaction. Our synthetic approach should facilitate comprehensive studies of the mechanisms of repair and mutagenesis induced by dG-AAF adducts in DNA and should be of general use for the incorporation of base-labile functionalities into DNA.

Estrogenic activity of an environmental pollutant, 2-nitrofluorene, after metabolic activation by rat liver microsomes

In this study, the metabolic activation of 2-nitrofluorene (NF) to estrogenic compounds was examined. NF was negative in estrogen reporter assays using estrogen-responsive yeast and human breast cancer cell line MCF-7. However, the compound exhibited estrogenic activity after incubation with liver microsomes of 3-methylcholanthrene-treated rats in the presence of NADPH. Minor estrogenic activity was observed when liver microsomes of untreated or phenobarbital-treated rats were used instead of those from 3-methylcholanthrene-treated rats. When the compound was incubated with the liver microsomes of 3-methylcholanthrene-treated rats in the presence of NADPH, 7-hydroxy-2-nitrofluorene (7-OH-NF) was formed as a major metabolite. However, little of the metabolite was formed by liver microsomes of untreated or phenobarbital-treated rats. Rat recombinant cytochrome P450 1A1 exhibited a significant oxidase activity toward NF, affording 7-OH-NF. Liver microsomes of phenobarbital-treated rats also enhanced oxidase activity toward NF. In this case, 9-hydroxy-2-nitrofluorene was formed. 7-OH-NF exhibited a significant estrogenic activity, while the activity of 9-hydroxy-2-nitrofluorene was much lower. These results suggest that the estrogenic activity of NF was due to formation of the 7-hydroxylated metabolite by liver microsomes.

Metabolism of 2-nitrofluorene, an environmental pollutant, by liver preparations of sea bream, Pagrus major

1. The in vitro metabolism of 2-nitrofluorene (NF), an environmental pollutant, was examined in fish, focusing on nitro-reduction followed by N-acylation and hydroxylation. 2. When NF was incubated with liver microsomes or cytosol of sea bream, Pagrus major, in the presence of NADPH or 2-hydroxypyrimidine, 2-aminofluorene (AF) was formed. 3. When AF was incubated with liver cytosol in the presence of acetyl-CoA or N-formyl-L-kynurenine, 2-acetylaminofluorene (AAF) or 2-formylaminofluorene (FAF) was formed, respectively. AAF and FAF thus formed were deacylated to the parent AF by the liver preparations. 4. AF, AAF and FAF were oxidized to 7-hydroxy or 5-hydroxy derivatives by the liver microsomes. 5. Nitro-reduction, N-acylation and ring-hydroxylation of NF and the metabolites were also observed in rat liver preparations. These activities in sea bream livers were lower than those of rat liver. However, the order of magnitude of these activities in fish was the same as in rat. 6. It is suggested that NF is effectively reduced to AF by the cytochrome P450 system or aldehyde oxidase, and the acylated metabolites, AAF and FAF, generated by arylamine acetyltransferase and formamidase were hydroxylated by the cytochrome P450 system in fish in the same way as in rat. Further, the acetylamino and formylamino derivatives were interconverted via amino derivatives in the fish.

Chromatographic methods for carcinogenic/mutagenic nitropolycyclic aromatic hydrocarbons

Nitropolycyclic aromatic hydrocarbons (NPAHs), which are known to be carcinogenic and/or mutagenic, are considered to be one of the air pollutants that cause lung cancer. In the last two decades, a number of sensitive and selective methods have been developed for the determination of NPAHs and related compounds in environmental and biological samples. This paper describes the state of the art of the methods and applications.

Potent carcinogenicity of 2,7-dinitrofluorene, an environmental pollutant, for the mammary gland of female Sprague-Dawley rats

Nitrofluorene compounds are environmental pollutants chiefly from incomplete combustion. This study examined carcinogenicities after one intramammary injection of 2-nitrofluorene (2-NF), 2, 7-dinitrofluorene (2,7-diNF) or dimethyl sulfoxide (DMSO) (solvent control) to 30-day-old and of 2-NF, 9-OH-2-NF, 9-oxo-2-NF, 2,7-diNF, 9-oxo-2,7-diNF, 2,5-dinitrofluorene, 9-oxo-2,4,7-trinitrofluorene, N-OH-2-acetylaminofluorene (N-OH-2-AAF) (carcinogen control) or DMSO to 50-day-old female Sprague-Dawley rats. In 30- and 50-day-old rats 6 and 8 glands/rat, respectively, were injected with 2.04 micromol of compound in 50 microliter/gland of DMSO. Whereas all compounds including DMSO yielded combined malignant and benign mammary tumor incidences of 33-87% by week 82 after injection, 2,7-diNF produced 100 and 93% incidences significantly (P < 0.001) sooner than did DMSO, i.e. by weeks 23-49 and 18-48 after treatment of 30- and 50-day-old rats, respectively. Rats treated with 2,7-diNF and 9-oxo-2,7-diNF had significantly (P < 0.0001) and marginally (P = 0. 0536) more mammary tumors, respectively, than DMSO-treated rats. In 2,7-diNF-treated rats, the ratio of malignant to benign mammary tumors was 5.4, whereas in all other groups it was <0.5. N-OH-2-AAF, a potent tumorigen when applied to the mammary gland as a solid or in suspension, did not yield the expected tumorigenicity here. The contrasting tumorigenic potencies of 2,7-diNF and N-OH-2-AAF may have been prompted by differences in their solubilities in DMSO. Thus, the poorly soluble 2,7-diNF was slowly absorbed from the injection sites since residues (up to 0.9% of the dose injected) were recovered even after 45 weeks. The data indicate prolonged exposure of the mammary gland to 2,7-diNF and suggest that contamination of the environment with 2,7-diNF, even at low levels, poses substantial carcinogenic risk.

Formation and persistence of DNA adducts during and after a long-term administration of 2-nitrofluorene

2-Nitrofluorene (NF) is an environmental pollutant. Our previous studies have shown that NF is a carcinogen, primarily targeting the liver, kidney and forestomach in rats. NF-induced DNA adducts were also shown higher levels in the tumor-targeting tissues compared to non-tumor targeting organs. The present study was aimed to observe the kinetics of DNA adduct formation and persistence during the process of NF-induced tumor formation. NF was supplemented in diet at three dose levels and was fed to rats continuously for up to 11 months. DNA adduct formation in the liver, kidney, spleen and stomach of rats after different period (10 days and 11 months) of NF administration was analyzed with 32P-HPLC techniques. DNA adduct persistence in the liver was also assessed after the withdrawal of NF administration. Four major NF-DNA adducts (adducts A, B, C and D) were found in the liver and kidney. DNA adduct D showed high level in the forestomach mucosa after 10 days of NF feeding while adducts A and C were undetectable. DNA adduct C and D co-migrated with C3-(deoxyguanosin-N2-yl)-2-acetylaminofluorene (dG-N2-AAF) and N-(deoxyguanosin-8-yl)-2-aminofluorene (dG-C8-AF), respectively, by 32P-HPLC co-chromatography. DNA adducts A and B constituted the major part (>80%) of NF-DNA adducts after a long period (11 months) of NF feeding. The four NF-DNA adducts showed different recovery from different enrichment procedures, i.e., nuclease P1 or butanol treatment. Three out of the four NF-DNA adducts were still detectable in the rat liver after 11 months on the basal diet. In conclusion, four major DNA adducts are induced by NF oral administration. Among those, one is identified as dG-N2-AAF and another one as dG-C8-AF. The four NF-DNA adducts showed different kinetics of formation and persistence, which may play different roles in NF-induced tumor formation.

Mitogenic short-term effects on hepatocytes and adrenocortical cells: phenobarbital and reserpine compared to carcinogenic and non-carcinogenic fluorene derivatives

The adrenal cortex has a low physiologic cell renewal and shows only a moderate cell replication even after contralateral adrenalectomy. Although rather unsusceptible to the malignancy-inducing action of carcinogens, a single oral dose of various tumorigenic xenobiotics induced an additive mitotic response of adrenocortical cells studied after 48 h. Presently we report on three different response patterns in rats. First, a selective mitostimulation of the zona glomerulosa occured after reserpine associated with a loss of body weight, thymus and liver weight. These are unspecific stress effects and occur also after exogenous ACTH. Second, hepatomitogenic and liver-enlarging congeners, e.g. fluorene (FEN), fluorenone (FON) and 4-benzoyl-FON, but also the genotoxic 2-acetylaminofluorene (2-AAF) and 2,4,7-trinitro-FON induced a selective mitotic response of the zona fasciculata (ZF). After the lowest effective dose of FEN or FON the afore-mentioned effects occured simultaneously, but were absent in the high dose group (only studied with fluorene). The 2-benzyl and 2-benzoyl-substituted derivatives were ineffective at all. Third, a bizonal response was found only after phenobarbital (PB) or the lowest effective FEN dose. The preventive action of a low PB dose on the 2-AAF-induced ZF response indicates a modified metabolism. We conclude that the rapid mitotic ZF response is an endogenously mediated net effect of interactions between metabolic and various adaptive mechanisms. The latter are reported to be activated in a stressor-dependent manner and converge in the adrenals. In this way the early mitotic ZF response could reflect indirectly 'specific' proliferation-prone properties of xenobiotics.

Preneoplastic lesions, DNA adduct formation and mutagenicity of 5-, 7- and 9-hydroxy-2-nitrofluorene, metabolites of the air pollutant 2-nitrofluorene

The metabolites of 2-nitrofluorene (NF), 5-, 7- and 9-OH-2-nitrofluorene (OH-NF) were compared for their genotoxicity. Seventy-two hours after intraperitoneal administration of these substances individually to rats (100 mg/kg body wt.), DNA adducts in liver tissue were analyzed with 32P-TLC and 32P-HPLC. An in vivo liver model was used to test the initiating capacity of the said substances for the formation of preneoplastic lesions. 5-OH-NF showed low capacity to induce DNA adduct formation and low potential as initiator to induce preneoplastic lesions-foci/nodules in the liver of rats. Both 7- and 9-OH-NF induced DNA adducts and preneoplastic liver lesions but with smaller quantities compared to NF. It seems that 7- and 9-OH-NF can not be considered as detoxification products of NF. In general, the initiating capacity of these substances for the formation of preneoplastic lesions has a good correlation with their potency to form DNA adducts.

Derivatives of 2-nitrofluorene cause changes of human sperm motility

The effects on human sperm motility characteristics of 2-nitrofluorene and selected derivatives were studied in vitro, using computer aided sperm analysis (Cellsoft). Substances to be tested were dissolved in acetone and added to separated spermatozoa in culture media to final concentrations of 100 and 1000 microM. Aliquots were removed immediately (< 5 min.) and 24 hr after the addition and tested for sperm motility characteristics. Four of the substances tested; 2,4,7-trinitrofluoren-9-one (2,4,7-tNFO), 2,5-diaminofluorene (2,5-dAF), 7-hydroxy-2-nitrofluorene (7-OH-NF) and 2,7-diaminofluorene (2,7-dAF) showed strong detrimental effects on the sperm motility. Slight detrimental effects were also recorded using 2-nitrofluorene and 2,5-dinitrofluorene (2,5-dNF). Weak stimulatory effects were obtained using 2-acetoamidofluorene (AAF) and 2,7-dinitrofluorene (2,7-dNF). No significant effects were seen with 5-hydroxy-2-nitrofluorene (5-OH-NF), 2-aminofluorene (AF), 2-aminofluoren-9-one (AFO), 2-amino-9-hydroxyfluorene (9-OH-AF) or 9-hydroxy-2-nitrofluorene (9-OH-NF). The mechanism behind this effect is not known but it could be speculated that these lipophilic substances interact with the membranes or the cellular respiration.

Genetic toxicity of 2-acetylaminofluorene, 2-aminofluorene and some of their metabolites and model metabolites

2-Acetylaminofluorene and 2-aminofluorene are among the most intensively studied of all chemical mutagens and carcinogens. Fundamental research findings concerning the metabolism of 2-acetylaminofluorene to electrophilic derivatives, the interaction of these derivatives with DNA, and the carcinogenic and mutagenic responses that are associated with the resulting DNA damage have formed the foundation upon which much of genetic toxicity testing is based. The parent compounds and their proximate and ultimate mutagenic and carcinogenic derivatives have been evaluated in a variety of prokaryotic and eukaryotic assays for mutagenesis and DNA damage. The reactive derivatives are active in virtually all systems, while 2-acetylaminofluorene and 2-aminofluorene are active in most systems that provide adequate metabolic activation. Knowledge of the structures of the DNA adducts formed by 2-acetylaminofluorene and 2-aminofluorene, the effects of the adducts on DNA conformation and synthesis, adduct distribution in tissues, cells and DNA, and adduct repair have been used to develop hypotheses to understand the genotoxic and carcinogenic effects of these compounds. Molecular analysis of mutations produced in cell-free, bacterial, in vitro mammalian, and intact animal systems have recently been used to extend these hypotheses.

In vivo metabolism and genotoxic effects of nitrated polycyclic aromatic hydrocarbons

During incomplete combustion of organic matter, nitro-polycyclic aromatic hydrocarbons (nitro-PAHs), are formed in a reaction that is catalyzed by a low pH. 2-Nitrofluorene (NF), a marker for nitro-PAHs, is metabolized in vivo by two different routes. After inhalation, potent mutagenic metabolites, hydroxylated nitrofluorenes (OH-NFs), are formed. The metabolites are distributed by systemic circulation. After oral administration, NF is reduced to the corresponding amine, a reaction mediated by the intestinal microflora. This metabolite is acetylated to 2-acetylaminofluorene (AAF), a potent carcinogen. Further ring-hydroxylation of AAF leads to detoxification and excretion. Induction of cytochrome P450s affects the metabolism, and more OH-NFs are formed. As a consequence, more mutagenic metabolites are found in the circulation. OH-NFs are excreted in the bile as, in terms of mutagenicity, totally harmless glucuronide conjugates. When these conjugates are excreted via the bile, intestinal beta-glucuronidase can liberate direct-acting mutagens in the intestine. Thus, inhalation of NF can lead to formation of potent mutagens in the intestine. NF is a direct-acting mutagen in bacterial assays and an initiator and promoter of the carcinogenic process, and gives rise to DNA adduct formation in laboratory animals.

Review of the genotoxicity of nitrogen oxides

Nitrogen oxides (NOx) are formed in combustion processes and are major pollutants in urban air. Relatively few studies on the genotoxicity of NO2 and NO have been performed. These studies indicate that NO2 is genotoxic in vitro, but the effect of NO seems to be very slight. One in vivo study showed chromosome aberrations and mutations in lung cells after inhalation of NO2 (and NO), but tests for chromosome aberrations in lymphocytes and spermatocytes or micronuclei in bone marrow were negative after inhalation of NO2. Based on present studies, there is no clear evidence of a carcinogenic potential of NO2, although lung adenomas were induced in the susceptible strain A/J mouse. The primary metabolites of NOx are nitrite and nitrate. Nitrate seems to be devoid of genotoxic properties, but nitrite is genotoxic in vitro, and there are also positive in vivo results. Cancer studies have been mainly negative. However, carcinogenic nitrosamines have been shown to be formed in vivo after inhalation of NO2. Nitrogen oxides are key components in atmospheric smog formation, which may lead to secondary effects. Strongly mutagenic nitro-PAH compounds are easily formed, and mutagenic reaction products may be formed photochemically from alkenes.

Mutagenicity of nitro- and amino-substituted carbazoles in Salmonella typhimurium. I. Monosubstituted derivatives of 9H-carbazole

Mononitro, monoamino and monoacetamido carbazoles were assayed for mutagenicity in Salmonella typhimurium strains TA1535, TA1538, TA1537, TA1977, TA98 and TA100, with and without the addition of S9 from phenobarbital-induced rat liver. The role of bacterial metabolism of the nitro group was also studied using the additional strains TA98NR and TA98/1,8DNP6. None of the compounds was active in TA1535, while only 2-nitrocarbazole and 3-nitrocarbazole presented a weak mutagenicity towards its pKM101 derivative, TA100. All four nitrocarbazole isomers were mutagenic for TA1538 and TA98, their activities decreasing in the order: 2-nitrocarbazole approximately 3-nitrocarbazole > 1-nitrocarbazole > 4-nitrocarbazole. Direct-acting mutagenicities for TA1537 were lower than for TA1538, but varied in the same order. Nitro reduction was an important step of metabolic activation of nitrocarbazoles, as indicated by the dramatic reduction of activity with TA98NR, as compared to TA98. Results obtained with TA98/1,8DNP6 showed that O-acetyltransferase was only partly required for the expression of mutagenic potency of these compounds. 2-Aminocarbazole was a weak direct-acting mutagen for TA1538 and TA98. Its activity was strongly increased in the presence of S9 mix, while 3-aminocarbazole became active in these conditions. The acetamido derivatives were consistently less mutagenic than their parent amines. These results show that nitrocarbazoles and aminocarbazoles behave as reactive frameshift mutagens, acting mainly through the formation of esterified hydroxylamines. The very low activity of 4-nitrocarbazole might be related to an orientation of the nitro group perpendicular to the aromatic ring.

Human sperm motility is affected by plasticizers and diesel particle extracts

In order to test various drugs and possibly hazardous compounds on living cells in vitro a system with human spermatozoa was employed. A population of human spermatozoa was transferred into a defined medium by a swim-up procedure or by separation on a Percoll gradient. Such a population is rather homogenous with respect to motility characteristics and was found to be useful for this purpose. Different modes of response were recorded, indicating various effect mechanisms. Effects of various phthalates used as plastic softeners in the production of medical equipment, and extracts from diesel particulate material were recorded. All these compounds interfered with sperm motility in a dose-response fashion. Immediate effects of phthalates were modest, but upon prolonged exposure effects became more evident. Sperm motility was more affected by diethyl-hexyl and dibutyl phthalates. Significant effects were noted for the different phthalates with regard both to percent motility and to some of the various qualities of motility, such as velocity, linearity and amplitude of the track. Thus, the pattern of response considering the motion variables was not the same with the different phthalates. With regard to the effects on sperm motion di-n-octyl phthalate seemed to be the least toxic, followed by dibutyl phthalate. The initial effects of diesel particulate extracts were moderate and mainly restricted to percent motile sperm but upon exposure for 18 hr the effects became more pronounced for all the movement variables.

Dietary pesticides (99.99% all natural)

The toxicological significance of exposures to synthetic chemicals is examined in the context of exposures to naturally occurring chemicals. We calculate that 99.99% (by weight) of the pesticides in the American diet are chemicals that plants produce to defend themselves. Only 52 natural pesticides have been tested in high-dose animal cancer tests, and about half (27) are rodent carcinogens; these 27 are shown to be present in many common foods. We conclude that natural and synthetic chemicals are equally likely to be positive in animal cancer tests. We also conclude that at the low doses of most human exposures the comparative hazards of synthetic pesticide residues are insignificant.

A comparative study of mutagenic and SOS-inducing activity of biphenyls, phenanthrenequinones and fluorenones

A total of 23 chemicals--biphenyls, phenanthrenequinones and fluorenones--were tested for mutagenicity towards Salmonella typhimurium strains TA1538, TA1535 and TA98. SOS-inducing activity of the same chemicals was studied in terms of the SOS-inducing potency in Escherichia coli PQ37, using an automated instrument controlled by a dedicated computer program for the SOS Chromotest. Of the 23 chemicals studied 14 induced His+ revertants in S. typhimurium TA1538 hisD305 (-1 frameshift); none induced His+ reversions in TA1535 (base-pair substitution). The mutagenicity of the chemicals in S. typhimurium TA98 (pKM 101) was lower than in TA1538. There was a close correlation between mutagenicity and SOS-inducing activity of fluorenones and phenanthrenequinones. None of the biphenyls tested induced SOS response and this property does not depend upon the mutagenic activity of the chemicals. SOS Chromotest is particularly valid in detecting chemicals which give rise to base-pair substitutions through SOS induction. If positive results are obtained, the Salmonella assay may be omitted. However, this test cannot replace the Ames test especially for the primary screening of mutagenicity of chemicals with unknown structure.

Genotoxicity of benzo[a]pyrene, 2-nitrofluorene and airborne particulates in the DNA-repair host-mediated assay

The genotoxic activity of benzo[a]pyrene (BAP), 2-nitrofluorene (NF) and airborne particulate matter was evaluated in the DNA-repair host-mediated assay after intraperitoneal or intratracheal administration. Dimethylnitrosamine (DMNA), used as a positive control, showed a genotoxic effect after both intraperitoneal and intratracheal administration, the strongest effect being found in liver, followed by lungs and kidneys, whereas a weak effect was observed in the spleen. In general no difference in genotoxicity was found between the 2 administration routes used. For BAP, although clearly positive in vitro, a moderate dose-dependent effect was found only in the liver after intraperitoneal administration. NF, which was positive in vitro both with and without a metabolizing system, produced no genotoxic effect in any of the organs tested after intraperitoneal administration. Extracts of airborne particulate matter which were genotoxic in vitro failed to cause a genotoxic effect in vivo by either route of administration. Possible explanations for the differences between the data obtained in vitro and in vivo are discussed.