Contribution of nitropyrene to the mutagenic activity of coal fly ash

Reactive oxygen species-mediated cellular genotoxic stress is involved in 1-nitropyrene-induced trophoblast cycle arrest and fetal growth restriction

1-nitropyrene (1-NP) is a key component of diesel exhaust-sourced fine particulate matter (PM2.5). Our recent study demonstrated that gestational 1-NP exposure caused placental proliferation inhibition and fetal intrauterine growth restriction (IUGR). This study aimed to investigate the role of genotoxic stress on 1-NP-induced placental proliferation inhibition and fetal IUGR. Human trophoblasts were exposed to 1-NP (10 μM). Growth index was reduced and PCNA was downregulated in 1-NP-exposed placental trophoblasts. More than 90% of 1-NP-exposed trophoblasts were arrested in either G0/G1 or G2/M phases. CDK1 and cyclin B, two G2/M cycle-related proteins, and CDK2, a G0/G1 cycle-related protein, were reduced in 1-NP-exposed trophoblasts. Phosphorylated Rb, a downstream molecule of CDK2, was inhibited in 1-NP-exposed trophoblasts. Moreover, DNA double-strand break was observed and γ-H2AX, another indicator of DNA double-strand break, was upregulated in 1-NP-exposed trophoblasts. Phosphorylated ATM, a key molecule of genotoxic stress, and its downstream molecule Chk2 were elevated. By contrast, Cdc25A, a downstream target of Chk2, was reduced in 1-NP-exposed trophoblasts. Phenyl-N-t-butylnitrone (PBN), a free radical scavenger, inhibited 1-NP-induced genotoxic stress and trophoblast cycle arrest. Animal experiment showed that N-acetylcysteine (NAC), an antioxidant, rescued 1-NP-induced placental proliferation inhibition and fetal IUGR in mice. These results provide evidence that reactive oxygen species (ROS)-mediated cellular genotoxic stress partially contributes to 1-NP-induced placental proliferation inhibition and fetal IUGR.

Gestational 1-nitropyrene exposure causes fetal growth restriction through disturbing placental vascularity and proliferation

1-Nitropyrene (1-NP) is a widely distributed pollutant in the environment and is best known for its mutagenicity and carcinogenicity. In this study, we evaluated the effects of 1-NP exposure in different gestational stages on the pregnant outcomes. Pregnant mice were administered with 1-NP by gavage daily in early (GD1-GD6), middle (GD7-GD12) or late pregnancy (GD13-GD17), respectively. We found that gestational 1-NP exposure had no effect on implantation sites per litter, preterm delivery and fetal death. Interestingly, mice exposed to 1-NP in late pregnancy showed a significant reduction in fetal weight and crown-rump length. Correspondingly, placental weight and diameter were markedly reduced in dams exposed to 1-NP in late pregnancy. Additional experiment showed maternal 1-NP exposure in late pregnancy reduced blood sinusoid area of placental labyrinthine region in a dose-dependent manner. Although gestational 1-NP exposure had little effect on placental cell apoptosis, as determined by the TUNEL assay, the rate of Ki67-positive cell, a marker of cell proliferation, was reduced in placental labyrinthine region of mice exposed to 1-NP in late pregnancy. These findings provide evidence that gestational 1-NP exposure induces fetal growth restriction in a stage-dependent manner. Placenta is a toxic target in the process of 1-NP-induced fetal growth restriction.

Linking Ah receptor mediated effects of sediments and impacts on fish to key pollutants in the Yangtze Three Gorges Reservoir, China - A comprehensive perspective

The Three Gorges Reservoir (TGR), created in consequence of the Yangtze River's impoundment by the Three Gorges Dam, faces numerous anthropogenic impacts that challenge its unique ecosystem. Organic pollutants, particularly aryl hydrocarbon receptor (AhR) agonists, have been widely detected in the Yangtze River, but only little research was yet done on AhR-mediated activities. Hence, in order to assess effects of organic pollution, with particular focus on AhR-mediated activities, several sites in the TGR area were examined applying the "triad approach". It combines chemical analysis, in vitro, in vivo and in situ investigations to a holistic assessment. Sediments and the benthic fish species Pelteobagrus vachellii were sampled in 2011/2012, respectively, to identify relevant endpoints. Sediment was tested in vitro with the ethoxyresorufin-O-deethylase (EROD) induction assay, and in vivo with the Fish Embryo Toxicity Test and Sediment Contact Assay with Danio rerio. Activities of phase I (EROD) and phase II (glutathione-S-transferase) biotransformation enzymes, pollutant metabolites and histopathological alterations were studied in situ in P. vachellii. EROD induction was tested in vitro and in situ to evaluate possible relationships. Two sites, near Chongqing and Kaixian city, were identified as regional hot-spots and further investigated in 2013. The sediments induced in the in vitro/in vivo bioassays AhR-mediated activities and embryotoxic/teratogenic effects - particularly on the cardiovascular system. These endpoints could be significantly correlated to each other and respective chemical data. However, particle-bound pollutants showed only low bioavailability. The in situ investigations suggested a rather poor condition of P. vachellii, with histopathological alterations in liver and excretory kidney. Fish from Chongqing city exhibited significant hepatic EROD induction and obvious parasitic infestations. The polycyclic aromatic hydrocarbon (PAH) metabolite 1-hydroxypyrene was detected in bile of fish from all sites. All endpoints in combination with the chemical data suggest a pivotal role of PAHs in the observed ecotoxicological impacts.

Magnetic graphene composites as both an adsorbent for sample enrichment and a MALDI-TOF MS matrix for the detection of nitropolycyclic aromatic hydrocarbons in PM2.5

Magnetic graphene composites were synthesized and applied for MALDI-TOFMS analysis of 3 nitropolycyclic aromatic hydrocarbons in PM_2.5.

Laser desorption/ionization time-of-flight mass spectrometry of nitrated polycyclic aromatic hydrocarbons

Mass spectra of four nitrated polycyclic aromatic hydrocarbons (nitro-PAHs), 9-nitroanthracene, 1-nitropyrene, 2-nitro-9-fluorenone, and 2-nitrofluorene, have been investigated using single-step laser desorption/ionization time-of-flight mass spectrometry. Pulsed UV radiation at 266 or 213 nm was used for desorption and ionization of solid samples deposited on an aluminum probe. The positive molecular ion which was observed for each nitro-PAH was of greater relative intensity when 213 nm radiation was used. A strong [M - NO]+ peak was observed in all spectra, and an intense NO+ signal accompanied the [M - NO]+ signal when 213 nm was used but was only weakly present when 266 nm was used. Comparison of the various spectra suggests that nitro-PAHs undergo an excited state nitro-nitrite rearrangement, followed by loss of NO. Multiphoton ionization of the NO fragment appears to be the principal route of formation of NO+ during laser desorption/ionization when 213 nm radiation is used. The presence of the carbonyl group in 2-nitro-9-fluorenone leads to unique and prominent fragments involving losses of CO from the carbonyl bridge.

Evaluation of exposure reducing measures on parameters of genetic risk in a population occupationally exposed to coal fly ash

In a previous study we found increased SCE frequencies in peripheral blood lymphocytes (PBLs) of workers occupationally exposed in a coal fly ash processing industry, as compared to a non-exposed control population. Shortly after this study, measures were taken in this plant to reduce fly ash levels. The objective of the present study, conducted 2 years later in the same plants, was to evaluate the effect of these measures with respect to genotoxic risk. A group of 18 male workers of the coal fly ash processing industry agreed to participate in the study. The control population consisted of 18 male workers from a flour processing industry, who were matched for age and smoking behavior. In contrast to our previous study, no increased SCE frequencies were found in PBLs of workers potentially exposed to coal fly ash when compared to the control group (mean SCEs: 6.4 +/- 1.2 and 7.0 +/- 0.9, respectively). In addition, no differences were observed between the exposed and control groups for frequencies of gene mutations at the hypoxanthine guanine phosphoribosyltransferase (hprt) locus in PBLs, for micronucleus frequencies using the cytokinesis block method, or for urinary mutagen excretion measured with Salmonella typhimurium tester strains TA98 and TA97 with and without metabolic activation. In smokers, however, SCE frequencies in PBLs were significantly increased in comparison to non-smokers (7.1 +/- 1.1 vs. 6.1 +/- 0.5; P < 0.005), as was 24-h urinary mutagen excretion measured with strain TA98 with S9 mix (2373 +/- 1870 vs. 156 +/- 211; P < 0.001) and with TA98 with S9 mix and beta-glucuronidase/arylsulfatase (2361 +/- 1958 vs. 538 +/- 396; P < 0.005). In addition, hprt variant frequencies in PBLs were higher in smokers than in non-smokers (15.0 +/- 23.5 x 10(-6)6 vs. 2.6 +/- 2.8 x 10(-6); P < 0.05). No differences were observed for micronucleus induction between smokers and non-smokers. It is concluded that the protective measures taken in the coal fly ash processing plant appear to have been sufficient, since an effect of exposure to coal fly ash on parameters of genetic risk was not found any longer.

Bioassay-directed fractionation of mutagenic PAH atmospheric photooxidation products and ambient particulate extracts

Simulated atmospheric gas-phase reactions of naphthalene, fluorene and phenanthrene have been carried out in an environmental chamber with bioassay-directed chemical analysis of the reaction products. Nitro-PAH were found to be the most significant mutagens formed from the reactions of naphthalene and fluorene. The mutagram (bar graph of mutagenic activity versus HPLC fraction) of the phenanthrene reaction products closely resembled that of an ambient air particulate extract with the most mutagenic activity being in a fraction more polar than that in which the nitro-PAH elute. Nitrophenanthrene lactones (nitro-6H-dibenzo[b,d]pyran-6-ones) were found to account for the observed activity of this polar fraction of the phenanthrene reaction products. It has been shown that the utilization of an environmental chamber with a known PAH-starting material and the ability to produce sufficient product for isomer-specific identifications of mutagens is a promising complement to bioassay-directed fractionation of ambient air particulate extracts.

The effect of extraction solvent on the mutagenicity of airborne particles

Two different solvents (acetone and dichloromethane) were compared for their efficacy in extraction of mutagenic compounds from airborne particulate samples. Their mutagenicity was examined with Salmonella typhimurium TA98 in presence or absence of S9 mix. The total mutagenic activity of the acetone extract was 1.8-7.0-fold that of the dichloromethane extract. The content of 1-nitropyrene, 1,6-dinitropyrene, dibenzo[a,h]anthracene and indo[1,2,3-c,d]pyrene in acetone extracts of airborne particulate samples was 3.8-, 3.6-, 6.6- and 1135-fold that of dichloromethane extracts, respectively. 1,8-Dinitropyrene, benzo[a]pyrene, chrysene, benzo[a]fluoranthene, benzo [a] anthracene, and benzo[g,h,i]perylene were found in the acetone extract, but were negative in the dichloromethane extract under the same conditions. However, the amount of pyrene in the dichloromethane extract was much higher than in the acetone extract. These results indicate that the extraction efficacy of 1-nitropyrene, dinitropyrenes and benzo[a]pyrene is higher with acetone than with dichloromethane. This may be the reason why acetone is the most effective solvent in extraction of mutagens from airborne particulate samples.

Genotoxicity of coal fly ash, assessed in vitro in Salmonella typhimurium and human lymphocytes, and in vivo in an occupationally exposed population

Fly ash as a product of coal combustion is known to contain various mutagenic substances, but genotoxic properties, especially of the particular (larger-size) fly ash fraction which is electrostatically precipitated (ESP) in the energy plant, have hardly been investigated. While smaller-size fly ash particles escape through the stack during powder coal combustion, the ESP fraction is collected and used for the manufacturing, for instance according to the Lytag process, of secondary products which can serve several construction purposes. Since fly ash as well as fly ash products are generally introduced into the human environment, a study of possible genotoxic effects to human DNA is indicated. Mutagenic properties of ESP fly ash, as well as of the Lytag product, were investigated by means of the Salmonella microsome assay. The capacity to cause human chromosome damage of both ESP fly ash and Lytag dust was studied in vitro by application of the sister-chromatid exchange (SCE) test using human lymphocytes. Furthermore, effects of ESP fly ash/Lytag dust on the incidence of SCE in peripheral lymphocytes in vivo were measured in an occupationally exposed, male population, using individually matched employees from a flour-processing industry as the control population. It is demonstrated that ultrasonically treated DMSO extracts of ESP fly ash are slightly mutagenic to Salmonella tester strains TA97 and TA102. Lytag dust is effective in inducing reversions in all tester strains. Furthermore, it appeared that both compounds significantly increase the SCE frequency of human lymphocytes after incubation in vitro in comparison to non-exposed cells. Also, peripheral lymphocytes of the occupationally exposed population show a considerably higher incidence of SCE than the control population. Major disturbing factors in assessing the effects of occupational exposure to fly ash/Lytag dust on lymphocyte SCE frequency appeared to be smoking behavior and alcohol consumption. It is concluded that exposure to fly ash from powder coal combustion implies a moderate genotoxic risk to man.

The effects of 1,6-dinitropyrene on spindle morphology in transformed human cells

The effects of 1,6-dinitropyrene (1,6-DNP) on the fidelity of cell division were studied in the transformed human fibroblast cell line MRC5VA. Over a dose range of 0.1-10 micrograms/ml of 1.6-DNP, we observed significant increases in the levels of abnormal division stages, associated with damage to the spindle apparatus of the cell. Qualitative changes in spindle morphology and a quantitative decrease in pole-to-pole spindle length were also observed with increasing doses of 1.6-DNP. Such changes in the size and morphology of the spindle corresponded with an accumulation of cells blocked at metaphase. The presence of catalase did not modify the response, suggesting that the effects on the spindle apparatus and cell division were not caused by the generation of radicals but by the direct action of 1.6-DNP.

Genotoxic effects of fly ash in bacteria, mammalian cells and animals

The increasing use of fossil fuels has raised concerns about possible deleterious health effects of the final combustion product, fly ash. Seven ash samples from coal sources obtained from Battelle Columbus Laboratories were evaluated in the Salmonella/mammalian microsome mutagenicity assay to determine their mutagenic potential. While dimethyl sulfoxide extracts of five samples showed no mutagenicity, sample 102 caused an increase in the number of revertants per plate over controls in TA100 and TA98 with activation by liver homogenate (2-fold and 2.4-fold, respectively), and without (2-fold and 6-fold). This ash was thus evaluated in whole animal studies. Animals treated by inhalation or oral gavage were assayed for the presence of mutagens in the urine, micronuclei in polychromatic erythrocytes, and chromosomal aberrations in metaphase bone marrow cells. Those animals treated by inhalation were also examined for local damage in the lung. The assay for mutagens in the urine was negative as shown by the Ames assay with TA100 and TA98 and there was no increase in micronuclei or in metaphase aberrations. Histological sections from the animals treated by inhalation did not show the presence of particles, macrophage infiltrations and generalized lung damage. We tested the same fly ash with an in vitro cell transformation assay with the cell line Balb/c 3T3 subclone A31-1-13. Although there was not an increase in Type III foci, there was a dose-dependent increase of Type II foci in the treated cells over the controls. In one assay, there was approximately a 14-fold increase in Type II foci in the highest dose (2 mg/ml) compared to the solvent control. One other ash sample induced cell transformation without being markedly cytotoxic, while a third sample was highly toxic but did not induce transformation.

The clastogenic activity of 1,6-dinitropyrene in peripheral human lymphocytes

The ability of 1,6-dinitropyrene to induce chromosome damage in peripheral human lymphocyte cultures has been demonstrated. Low levels of clastogenic activity were detected following 3-h treatments with 1,6-dinitropyrene in the presence of a rat-liver cytosol fraction. The clastogenic activity reached a peak at a concentration of 1.25 micrograms/ml of 1,6-dinitropyrene after which the frequency of aberrations decreased. This unusual genotoxic dose response is similar to that found previously in yeast and rat-liver cells. The fact that a positive result was obtained using human lymphocytes shows that, in the presence of the appropriate activation system, dinitropyrene is genotoxic in human cells.

Mutagenic activity of nitro-substituted cyclopenta-fused polycyclic aromatic hydrocarbons towards Salmonella typhimurium

Cyclopenta-fused isomers of pyrene and benz[a]anthracene, nitrated on the etheno bridge, were synthesized and tested in the Ames plate-incorporation assay. Since enzymatic reduction, if it occurs in these compounds, would form arylhydroxylamines which in turn would form highly stabilized arylnitrenium ions, we hoped to test the hypothesis that the direct-acting mutagenic activity of nitroPAH is correlated with the degree of stabilization of the electrophilic intermediate. We found that these compounds are mutagenic (1-9 rev/nmole in Salmonella typhimurium TA98) and do not require S9 activation. However, this activity is substantially lower than that of other nitroPAH of comparable size such as 1-nitropyrene (250-300 rev/nmole). The reasons for this comparative lack of activity are discussed with reference to current theories regarding structure-activity relationships of nitroPAH.

Correlation of nitroaromatic compounds with the mutagenic activity of coal fly ash

Stack-collected fly-ash particles from a commercial pulverized-coal power plant were extracted with 60/40 w/w benzene-methanol to remove as much of the organic fraction as possible. The extract was sequentially fractionated on a series of high-performance liquid chromatography columns, and the Salmonella bacterial mutagenicity assay using both normal and nitroreductase-deficient strains was used to localize the most mutagenic fractions. Selected fractions were analyzed by a variety of techniques, including gas chromatography with dual-flame ionization and thermionic nitrogen-phosphorus detectors, gas chromatography-mass spectrometry, direct-probe low-resolution or low-voltage mass spectrometry, and high-resolution mass spectrometry. Mutagenicity data indicated that nitroorganic compounds were the primary mutagens in all samples submitted for chemical analysis. A series of homologous alkylated nitrophenanthrenes appear to be important mutagens in one major fraction, while alkylated nitrofluorenones appear to be the dominant mutagens in a second major fraction. No nitro compounds were identified in a third major fraction. In addition to the nitro compounds, substantial amounts of fluorenones were also found, although these are not believed to contribute to the direct-acting mutagenic activity of the samples.

Toxicity and DNA damage induced by 1-nitropyrene and its derivatives in Chinese hamster lung fibroblasts

1-Nitropyrene and its chemically synthesised derivatives were investigated for their cytotoxicity and ability to induce DNA-strand breaks in Chinese hamster lung fibroblasts. Both 1-nitrosopyrene (0.25-60 micrograms/ml) and 1-aminopyrene (0.25-25 micrograms/ml) were cytotoxic, and induced the formation of DNA lesions, which were measured as DNA single-strand breaks after sedimentation in alkaline sucrose-density gradients. Higher doses of 1-aminopyrene (25-60 micrograms/ml) inhibited the formation of DNA single-strand breaks. 1-Nitropyrene was not toxic (0.25-60 micrograms/ml) and induced low levels of detectable DNA strand breaks, whilst N-acetyl-1-aminopyrene was inactive. The post-mitochondrial supernatant fraction of Aroclor-induced rat-liver containing 4 mM NADPH (S9 mix) did not promote the activation of 1-nitropyrene. In fact DNA strand breaks induced by either 1-nitropyrene or 1-nitrosopyrene was abolished in the presence of S9 mix. The 1-nitropyrene reduced intermediate, N-hydroxy-1-aminopyrene was synthesised by the reduction of 1-nitrosopyrene with ascorbic acid. In the presence of ascorbic acid, 1-nitrosopyrene caused a 5-fold increase in the number of DNA single-strand breaks when compared to cells treated with 1-nitrosopyrene alone. The results are discussed in terms of the metabolic activation of 1-nitropyrene and 1-aminopyrene in Chinese hamster lung cells.

Ubiquitous occurrence of 2-nitrofluoranthene and 2-nitropyrene in air

Several nitrated polycyclic aromatic hydrocarbons (nitro-PAH) are direct-acting mutagens and/or carcinogens, and are important constituents of combustion emissions and ambient air. These nitro-PAH are emitted from various combustion sources including gasoline and diesel engine exhaust, aluminium smelting effluent, coal fly ash, wood smoke, and cigarette smoke condensates. Of these, diesel engine exhaust is the best characterized, more than 50 nitrated polycyclic aromatic compounds having been identified by Paputa-Peck et al., including 1-nitropyrene (1-NP) as the single most abundant nitro-PAH. However, nitro-PAH may also be formed during source-receptor transport by atmospheric reactions of adsorbed or gas-phase PAH with oxides of nitrogen, nitric acid and other atmospherically important species such as the OH radical. Evidence for the atmospheric formation of nitro-PAH has come only recently, from observations that 2-nitropyrene (2-NP) and 2-nitrofluoranthene (2-NF) neither of which has been reported to be emitted from combustion sources, are among the major nitro-PAH present in ambient air. We present here data from several locations which demonstrate that these two atmospherically formed nitro-PAH are ubiquitous in tropospheric ambient air.

Identification and quantification of highly mutagenic nitroacetoxypyrenes and nitrohydroxypyrenes in diesel-exhaust particles

Heavy-duty diesel-exhaust particles were collected, extracted and fractionated into diethyl ether-soluble neutral, acidic and basic fractions. The mutagenicity of these fractions was measured with Salmonella typhimurium strains TA100, TA98, TA98NR and TA98/1,8-DNP6 in the presence and absence of a 9000 X g post-mitochondrial supernatant from Aroclor-induced rat liver (S9 mix). The neutral and acidic fractions showed high mutagenicity with TA98 in the absence of S9 mix, the acidic fraction having the highest specific activity. In the absence of S9 mix, the mutagenicity of crude, neutral and acidic fractions was greater in TA98 than in TA98NR and TA98/1,8-DNP6. Chemically-synthesized nitroacetoxypyrenes and nitrohydroxypyrenes were fractionated into the neutral and acidic fractions, respectively. These nitroarenes were purified by high-performance liquid chromatography and their mutagenicity was measured with the 4 strains. With TA98 in the absence of S9 mix, 1-nitro-3-acetoxypyrene, 1-nitro-6/8-acetoxypyrene, 1-nitro-3-hydroxypyrene, 1-nitro-6/8-hydroxypyrene induced 16 700, 336, 992, 94 His+ revertants per plate per nmole, respectively. In the absence of S9 mix, the level of mutagenicity of these nitroarenes was highest in TA98, lowest in TA98/1,8-DNP6 and intermediate in TA98NR. The neutral and acidic fractions of diesel-exhaust particles were analyzed by gas chromatography-mass spectrometry and gas chromatography-mass fragmentography. The neutral fraction was found to contain nitroacetoxypyrenes, 1-nitropyrene, 1,6-dinitropyrene, while nitrohydroxypyrenes were detected in the acidic fraction. The amounts of 1-nitro-3-acetoxypyrene, 1-nitropyrene, 1,6-dinitropyrene and 1-nitro-3-hydroxypyrene were 6.3, 62, 0.81, and 70 ng per mg of crude extract, and accounted for 12, 3.6, 8.0, and 9.0%, respectively, of mutagenicity of the crude extract in TA98 in the absence of S9 mix.

Mutagenicity in Salmonella of nitroorganic compounds in extracts of fly ash from a lignite-fired atmospheric fluidized-bed combustor

The mutagenicity of a benzene/methanol extract of fly ash from an atmospheric fluidized-bed combustor burning Beulah, N.D., lignite was tested in Salmonella. Six strains were used, including three that were mutants in a nitroreductase gene locus. The numbers of revertants from his- to his+ as a function of the amount of fly ash extracted were determined. The results showed that the major mutagens in the crude extract were nitro compounds, from the fact that reversion rates in the nitroreductase-deficient strains were significantly lower than in the parent strains from which they were derived. The responses of the three parental strains, TA1538, TA98, and TA100, were quite similar; thus no conclusions could be made about frameshift versus base-substitution mutagens. Mutagenicity of 15 fractions of the extract was also tested, and one major peak of activity was detected. This activity eluted from a high-performance liquid chromatograph outside the range of retention times associated with mononitroaromatics. No further identification of specific nitroorganic compounds has been made.