Determination of atmospheric nitrobenzanthrones by high-performance liquid chromatography with chemiluminescence detection

Fluorescence Enhancement of Ethanolic Solution of Nitroarenes and Its Analytical Application

When ethanolic solutions of 1-nitropyrene (1-NP) and 3-nitrobenzanthorone (3-NBA) were irradiated with intense light, which they absorb, for several minutes, the fluorescence characteristics of the solutions were significantly changed. After such preliminary irradiation, the fluorescence intensity of 1-NP increased immediately by a factor of 10⁴ with a blue shift of 100 nm and that of 3-NBA 700 with a red shift of 10 nm. The findings were applied to high performance liquid chromatography with a fluorescence detector so that the two nitroarenes could be quantitatively analyzed by preliminary irradiation of their solutions before measurements. The calibration curves were linearly drawn over the concentration range from 1.0 × 10^-9 to 1.0 × 10^-7 M for 1-NP and 1.0 × 10^-8 to 1.0 × 10^-6 M for 3-NBA and the limits of detection were 2.3 pg for 1-NP and 28 pg for 3-NBA. From the results, fluorescence enhancement was found to be very effective for determining nitroarenes, being practically non-fluorescent and very important in environmental health-risk assessment, easily and sensitively. The mechanism of the fluorescence enhancement of 1-NP and 3-NBA was also discussed.

Occurrence of the potent mutagens 2- nitrobenzanthrone and 3-nitrobenzanthrone in fine airborne particles

Polycyclic aromatic compounds (PACs) are known due to their mutagenic activity. Among them, 2-nitrobenzanthrone (2-NBA) and 3-nitrobenzanthrone (3-NBA) are considered as two of the most potent mutagens found in atmospheric particles. In the present study 2-NBA, 3-NBA and selected PAHs and Nitro-PAHs were determined in fine particle samples (PM 2.5) collected in a bus station and an outdoor site. The fuel used by buses was a diesel-biodiesel (96:4) blend and light-duty vehicles run with any ethanol-to-gasoline proportion. The concentrations of 2-NBA and 3-NBA were, on average, under 14.8 µg g⁻¹ and 4.39 µg g⁻¹, respectively. In order to access the main sources and formation routes of these compounds, we performed ternary correlations and multivariate statistical analyses. The main sources for the studied compounds in the bus station were diesel/biodiesel exhaust followed by floor resuspension. In the coastal site, vehicular emission, photochemical formation and wood combustion were the main sources for 2-NBA and 3-NBA as well as the other PACs. Incremental lifetime cancer risk (ILCR) were calculated for both places, which presented low values, showing low cancer risk incidence although the ILCR values for the bus station were around 2.5 times higher than the ILCR from the coastal site.

Vibrational and electronic spectra of 2-nitrobenzanthrone: An experimental and computational study

The environmental pollutant 2-nitrobenzanthrone (2-NBA) poses human health hazards, and is formed by atmospheric reactions of NOX gases with atmospheric particulates. Though its mutagenic effects have been studied in biological systems, its comprehensive spectroscopic experimental data are scarce. Thus, vibrational and optical spectroscopic analysis (UV-Vis, and fluorescence) of 2-NBA was studied using both experimental and density functional theory employing B3LYP method with 6-311+G(d,p) basis set. The scaled theoretical vibrational frequencies show good agreement to experiment to within ~5 cm(-1) and <20 cm(-1) for frequencies <1800 cm(-1) and 2700-3200 cm(-1), respectively. In addition, predictions of the DFT frequencies below 1800 cm(-1) yield an overall root mean square (RMS) of ±20.1 and ±20.6 cm(-1) for benzanthrone and 2-NBA, respectively. On the basis of normal coordinate analysis complete assignments of harmonic experimental infrared and Raman bands are made. The influence of the nitro group substitution upon the benzanthrone structure and symmetric CH vibrations, and electronic spectra is noted. This study is useful for the development of spectroscopy-mutagenicity relationships in nitrated polycyclic aromatic hydrocarbons.

The molecular properties of nitrobenzanthrone isomers and their mutagenic activities

The mutagenic activity of five mono-substituted nitrobenzanthrones (NBA) has been determined in the Ames assay (Takamura-Enya et al., 2006). In the present study, a theoretical investigation of the electronic properties of all mono-substituted NBA isomers and their relation to mutagenic activity are presented. Equilibrium geometries, vertical ionization potentials (VIP), vertical electron affinities (VEA), relative energies, dipole moments and electronic dipole polarizabilities, and the IR and Raman spectra of NBA isomers calculated by Density Functional Theory (DFT) methods are presented. The position of the nitro group affects the spectral features of the IR and Raman spectra of the NBA isomers. The results show that a good linear relationship exists between the summation of Raman activities (∑ARaman) over all the 3N-6 vibrational modes and the mutagenic activity of the NBA isomers in Salmonella typhimurium strains. The spectroscopic results suggest that the unknown mutagenic activities of 4-NBA, 5-NBA, 6-NBA, 8-NBA and 10-NBA are predicted to follow the order 4-NBA>10-NBA>5-NBA>8-NBA>6-NBA.

Development of a two-dimensional high-performance liquid chromatography system coupled with on-line reduction as a new efficient analytical method of 3-nitrobenzanthrone, a potential human carcinogen

3-Nitrobenzanthrone (3-NBA) is an extremely strong mutagen and carcinogen in rats inducing squamous cell carcinoma and adenocarcinoma. We developed a new sensitive analytical method, a two-dimensional HPLC system coupled with on-line reduction, to quantify non-fluorescent 3-NBA as fluorescent 3-aminobenzanthrone (3-ABA). The two-dimensional HPLC system consisted of reversed-phase HPLC and normal-phase HPLC, which were connected with a switch valve. 3-NBA was purified by reversed-phase HPLC and reduced to 3-ABA with a catalyst column, packed with alumina coated with platinum, in ethanol. An alcoholic solvent is necessary for reduction of 3-NBA, but 3-ABA is not fluorescent in the alcoholic solvent. Therefore, 3-ABA was separated from alcohol and impurities by normal-phase HPLC and detected with a fluorescence detector. Extracts from surface soil, airborne particles, classified airborne particles, and incinerator dust were applied to the two-dimensional HPLC system after clean-up with a silica gel column. 3-NBA, detected as 3-ABA, in the extracts was found as a single peak on the chromatograms without any interfering peaks. 3-NBA was detected in 4 incinerator dust samples (n=5). When classified airborne particles, that is, those <1.1, 1.1-2.0, 2.0-3.3, 3.3-7.0, and >7.0 μm in size, were applied to the two-dimensional HPLC system after purified using a silica gel column, 3-NBA was detected in those particles with particle sizes <1.1 and 1.1-2.0 μm and the particle-size distribution ratios were 84% and 16%, respectively. This is the first report on the particle-size distribution of 3-NBA in airborne particles and the detection of 3-NBA in incinerator dust.

Mutagenic potential of nitrenium ions of nitrobenzanthrones: correlation between theory and experiment

The mutagenic activity of nine substituted nitrobenzanthrone (NBA) derivatives was recently established in the Ames assay and ranged from near inactivity to extremely high mutagenic activity (Takamura-Enya et al. 2006: Mutagenesis 21:399-404). Using thermochemical and molecular modeling techniques, the activation pathway of these NBA derivatives, namely 1-nitro-, 2-nitro-, 3-nitro-, 9-nitro-, 11-nitro-, 1,9-dinitro-, 3,9-dinitro-, 3,11-dinitro-, and 3,9,11-trinitrobenzanthrone, and the formation of the corresponding aryl-nitrenium ions, were investigated using density functional theory calculations. The calculated properties of the NBA derivatives were systematically compared with their bacterial mutagenic potency. Accommodation of the ligand substrates into the binding pocket of the bacterial nitroreductases was not sterically inhibited for the NBAs. Moreover, electron affinities, water elimination energies, esterification, and solvolysis energies did not reveal any possible links with the observed mutagenic potency of the NBAs. However, a strong negative linear correlation was found when the relative energies of the nitrenium ions of the mono and disubstituted NBAs were plotted against the logarithm of the mutagenic potency of the NBAs found in the different Salmonella typhimurium strains. Therefore, our data clearly indicate that the stability of the nitrenium ions is one critical determinant of the mutagenic potency of NBAs in Salmonella tester strains.

Genotoxicity of 3-nitrobenzanthrone and 3-aminobenzanthrone in MutaMouse and lung epithelial cells derived from MutaMouse

FE1 lung epithelial cells derived from MutaMouse are a new model system to provide in vitro mutagenicity data with the potential to predict the outcome of an in vivo MutaMouse test. 3-Nitrobenzanthrone (3-NBA) is a potent mutagen and suspected human carcinogen identified in diesel exhaust and urban air pollution. We investigated the mutagenicity and DNA binding of 3-NBA and its main metabolite 3-aminobenzanthrone (3-ABA) in vitro and in vivo in the MutaMouse assay. Mice were treated with 3-NBA or 3-ABA (0, 2 or 5 mg/kg body weight/day) by gavage for 28 days and 28 days later lacZ mutant frequency (MF) was determined in liver, lung and bone marrow. For both compounds, dose-related increases in MF were seen in liver and bone marrow, but not in lung; mutagenic activity was approximately 2-fold lower for 3-ABA than for 3-NBA. With 3-NBA, highest DNA adduct levels (measured by (32)P-post-labelling) were found in liver (approximately 230 adducts per 10(8) nucleotides) with levels 20- to 40-fold lower in bone marrow and lung. With 3-ABA, DNA adduct levels were again highest in the liver, but approximately 4-fold lower than for 3-NBA. FE1 cells were exposed to up to 10 microg/ml 3-NBA or 3-ABA for 6 h with or without exogenous activation (S9) and harvested after 3 days. For 3-NBA, there was a dose-related increase in MF both with and without S9 mix, which was >10 times higher than observed in vivo. At the highest concentration of 3-ABA (10 microg/ml), we found only around a 2-fold increase in MF relative to controls. DNA adduct formation in FE1 cells was dose-dependent for both compounds, but 10- to 20-fold higher for 3-NBA compared to 3-ABA. Collectively, our data indicate that MutaMouse FE1 cells are well suited for cost-effective testing of suspected mutagens with different metabolic activation pathways as a guide for subsequent in vivo MutaMouse testing.

Mutagenicity and DNA adduct formation of PAH, nitro-PAH, and oxy-PAH fractions of atmospheric particulate matter from São Paulo, Brazil

Urban particulate matter (UPM) contributes to lung cancer incidence. Here, we have studied the mutagenic activity and DNA adduct-forming ability of fractionated UPM extractable organic matter (EOM). UPM was collected with a high-volume sampler in June 2004 at two sites, one at street level adjacent to a roadway and the other inside a park within the urban area of the city of São Paulo, Brazil. UPM was extracted using dichloromethane, and the resulting EOM was separated by HPLC to obtain PAH, nitro-PAH, and oxy-PAH fractions which were tested for mutagenicity with the Salmonella strains TA98 and YG1041 with and without S9 metabolic activation. The PAH fraction from both sites showed negligible mutagenic activity in both strains. The highest mutagenic activity was found for the nitro-PAH fraction using YG1041 without metabolic activation; however, results were comparable for both sites. The nitro-PAH and oxy-PAH fractions were incubated with calf thymus DNA under reductive conditions appropriate for the activation of nitro aromatic compounds, then DNA adduct patterns and levels were determined with thin-layer chromatography (TLC) 32P-postlabeling method using two enrichment procedures-nuclease P1 digestion and butanol extraction. Reductively activated fractions from both sites produced diagonal radioactive zones (DRZ) of putative aromatic DNA adducts on thin layer plates with both enrichment procedures. No such DRZ were observed in control experiments using fractions from unexposed filters or from incubations without activating system. Total adduct levels produced by the nitro-PAH fractions were similar for both sites ranging from 30 to 45 adducts per 10(8) normal nucleotides. In contrast, the DNA binding of reductively activated oxy-PAH fractions was three times higher and the adduct pattern consisted of multiple discrete spots along the diagonal line on the thin layer plates. However, DNA adduct levels were not significantly different between the sampling sites. Both samples presented the same levels of mutagenic activity. The response in the Salmonella assay was typical of nitroaromatics. Although, more mutagenic activity was related to the nitro-PAH fraction in the Salmonella assay, the oxy-PAH fractions showed the highest DNA adduct levels. More studies are needed to elucidate the nature of the genotoxicants occurring in São Paulo atmospheric samples.

Structural identification of DNA adducts derived from 3-nitrobenzanthrone, a potent carcinogen present in the atmosphere

3-Nitrobenzanthrone is a powerful bacterial mutagen and carcinogen to mammals. To obtain precise information on DNA-adduct formation by 3-nitrobenzanthrone, a number of DNA adducts, including N-(2'-deoxyguanosin-8-yl)-3-aminobenzanthrone (13 a), 2-(2'-deoxyguanosin-N2-yl)-3-aminobenzanthrone (14 a), N-(2'-deoxyadenosin-8-yl)-3-aminobenzanthrone (15 a), 2-(2'-deoxyadenosin-N6-yl)-3-aminobenzanthrone (16 a), and their N-acetylated counterparts 13 b, 14 b, 15 b, and 16 b were synthesized by palladium-catalyzed aryl amination of the corresponding nucleoside and bromobenzanthrone derivatives. Among these DNA adducts, DNA adducts 13 a, 13 b, 14 a, 14 b, and 16 a were identified in the reaction mixture of nucleosides (2'-deoxyguanosine, 2'-deoxyadenosine, or DNA) with N-acetoxy-3-aminobenzanthrone or N-acetyl-N-acetoxy-3-aminobenzanthrone, both of which are recognized as activated metabolites of 3-nitrobenzanthrone. The formation of these multiple DNA adducts may help explain the potent mutacarcinogenicity of 3-nitrobenzanthrone.

The environmental carcinogen 3-nitrobenzanthrone and its main metabolite 3-aminobenzanthrone enhance formation of reactive oxygen intermediates in human A549 lung epithelial cells

The environmental contaminant 3-nitrobenzanthrone (3-NBA) is highly mutagenic and a suspected human carcinogen. We aimed to evaluate whether 3-NBA is able to deregulate critical steps in cell cycle control and apoptosis in human lung epithelial A549 cells. Increased intracellular Ca(2+) and caspase activities were detected upon 3-NBA exposure. As shown by cell cycle analysis, an increased number of S-phase cells was observed after 24 h of treatment with 3-NBA. Furthermore, 3-NBA was shown to inhibit cell proliferation when added to subconfluent cell cultures. The main metabolite of 3-NBA, 3-ABA, induced statistically significant increases in tail moment as judged by alkaline comet assay. The potential of 3-NBA and 3-ABA to enhance the production of reactive oxygen species (ROS) was demonstrated by flow cytometry using 2',7'-dichlorofluorescein-diacetate (DCFH-DA). The enzyme inhibitors allopurinol, dicumarol, resveratrol and SKF525A were used to assess the impact of metabolic conversion on 3-NBA-mediated ROS production. Resveratrol decreased dichlorofluorescein (DCF) fluorescence by 50%, suggesting a role for CYP1A1 in 3-NBA-mediated ROS production. Mitochondrial ROS production was significantly attenuated (20% reduction) by addition of rotenone (complex I inhibition) and thenoyltrifluoroacetone (TTFA, complex II inhibition). Taken together, the results of the present study provide evidence for a genotoxic potential of 3-ABA in human epithelial lung cells. Moreover, both compounds lead to increased intracellular ROS and create an environment favorable to DNA damage and the promotion of cancer.

Development of analytical methods for polycyclic aromatic hydrocarbons (PAHs) in airborne particulates: a review

In the present work, the different sample collection, pretreatment and analytical methods for polycyclic aromatic hydrocarbons (PAHs) in airborne particulates is systematacially reviewed, and the applications of these pretreatment and analytical methods for PAHs are compared in detail. Some comments on the future expectation are also presented.

Mutagenic activities and physicochemical properties of selected nitrobenzanthrones

Mutagenic activity of nine nitro derivatives of benzanthrone, namely 1-nitro-, 2-nitro-, 3-nitro-, 9-nitro-, 11-nitro-, 1,9-dinitro-, 3,9-dinitro-, 3,11-dinitro- and 3,9,11-trinitrobenzanthrone were tested with Salmonella strains TA98, TA100, YG1021 and YG1024 in both the presence and absence of an S9 mix. Each compound exhibited mutagenic activity with all the strains. Among these nine isomers, 3-nitrobenzantrone exhibited the most mutagenic activity with all the strains without the S9 mix. The mutagenic activities of the dinitro and trinitro derivatives of benzanthrone were lower than that of the 3-nitro derivative; this is evident from the mutagenic activity of nitrated polyaromatic hydrocarbons (PAH), which is generally enhanced with an increase in nitration. The physicochemical properties of nitrated benzanthrone (reduction potential, hydrophobicity and orientation of nitro groups to the aromatic ring) demonstrated that mononitrated benzanthrone exhibits a lower reduction potential than mononitroPAHs such as 1-nitropyrene and 3-nitrofluoranthene, but was almost equivalent to that of dinitroPAH. Moreover, the mutagenic activity of mononitrobenzanthrones clearly depend on the reduction potential of each compound; however, this tendency was not observed in polynitrobenzanthrones, probably because the reduction of the nitro groups to amino groups of polynitrated benzanthrone might be predominant without a sufficient formation of corresponding hydroxyamines. These results suggest that aromatic compounds that contain keto groups, when nitrated, may act as potentially powerful direct-acting mutagens.

Analysis of nitrated polycyclic aromatic hydrocarbons

Many nitrated polycyclic aromatic hydrocarbons (NPAH) that are present in low concentrations in the environment and in emission sources have been shown to be mutagenic and/or carcinogenic. This paper reviews the current methods of analysis of these compounds with the emphasis on NPAH measurements in ambient particulate matter samples.

3-Nitrobenzanthrone, a potential human cancer hazard in diesel exhaust and urban air pollution: a review of the evidence

Epidemiological studies have shown that exposure to diesel exhaust and urban air pollution is associated with an increased risk of lung cancer. 3-Nitrobenzanthrone [3-nitro-7H-benz[de]anthracen-7-one (3-NBA)] is an extremely potent mutagen and suspected human carcinogen identified in diesel exhaust and ambient air particulate matter. The main metabolite of 3-NBA, 3-aminobenzanthrone (3-ABA), was found in the urine of salt mine workers occupationally exposed to diesel emissions, indicating that human exposure to 3-NBA due to diesel emissions can be significant and is detectable. There is clear evidence that 3-NBA is a genotoxic mutagen forming DNA adducts after metabolic activation through simple reduction of the nitro group. Several human enzymes have been shown to activate 3-NBA and its metabolites in vitro and in cells to form electrophilic arylnitrenium and rearranged carbenium ions, leading to the formation of purine adducts at the C8 and N2 position of guanine and at the C8 and N6 position of adenine. The predominant DNA adducts in vivo, 2-(2'-deoxyguanosin-N2-yl)-3-aminobenzanthrone and N-(2'-deoxyguanosin-8-yl)-3-aminobenzanthrone are also the most persistent adducts in target tissue in rodents, and are most probably responsible for the induction of GC-->TA transversion mutations observed in vivo. It is concluded that these adducts not only represent premutagenic lesions in DNA but are of primary importance for the initiation of the carcinogenic process and subsequent tumour formation in target tissue. Indeed, 3-NBA is carcinogenic in rats after intratracheal instillation, inducing mainly squamous cell carcinoma in lung. The intention of this article is to provide a critical review on the potential genotoxic effects of 3-NBA on human health. However, in general, there is a need for more mechanistic studies that relate 3-NBA to all processes that are considered to orchestrate tumour development and of studies on the ability of particles to promote 3-NBA genotoxicity. Because of its widespread environmental presence, 3-NBA may represent not only an occupational health hazard but also a hazard for larger sections of the general population. For an accurate risk assessment more epidemiological studies on 3-NBA-exposed individuals and a broader monitoring of environmental levels of 3-NBA are required.

Direct-acting mutagenicity of extracts of coal burning-derived particulates and contribution of nitropolycyclic aromatic hydrocarbons

Benzene-ethanol extracts from particulates produced by coal burning were separated into four fractions by silica-gel column chromatography using n-hexane (240 ml), n-hexane-dichloromethane (3:1, v/v) (200 ml), dichloromethane (200 ml) and methanol (450 ml), as the corresponding eluents. The mutagenicity of each fraction was assayed by the Ames test using the Salmonellatyphimurium YG1024 strain. The nitropolycyclic aromatic hydrocarbons (NPAHs) of each fraction were assayed by high-performance liquid chromatography with chemiluminescence detection. The highest activity was observed in the n-hexane-dichloromethane fraction (Fr. 2). The mutagenic contribution of this fraction was 69.9% of the total of the four fractions. Ten of 11 NPAHs detected were in Fr. 2 and one (1-nitropyrene) was most concentrated in Fr. 3. Among the NPAHs examined, 3-nitrobenzanthrone made the largest mutagenic contribution. This is the first report of detection of 3-nitrobenzanthrone in coal burning-derived particulates.