DNA adduct formation in mammalian cell cultures by polycyclic aromatic hydrocarbons (PAH) and nitro-PAH in coke oven emission extract

Classifying polycyclic aromatic hydrocarbons by carcinogenic potency using in vitro biosignatures

One of the most difficult challenges for risk assessment is evaluation of chemicals that predominately co-occur in mixtures like polycyclic aromatic hydrocarbons (PAHs). We previously developed a classification model in which systems biology data collected from mice short-term after chemical exposure accurately predict tumor outcome. The present study demonstrates translation of this approach into a human in vitro model in which chemical-specific bioactivity profiles from 3D human bronchial epithelial cells (HBEC) classify PAHs by carcinogenic potency. Gene expression profiles were analyzed from HBEC exposed to carcinogenic and non-carcinogenic PAHs and classification accuracies were identified for individual pathway-based gene sets. Posterior probabilities of best performing gene sets were combined via Bayesian integration resulting in a classifier with four gene sets, including aryl hydrocarbon receptor signaling, regulation of epithelial mesenchymal transition, regulation of angiogenesis, and cell cycle G2-M. In addition, transcriptional benchmark dose modeling of benzo[a]pyrene (BAP) showed that the most sensitive gene sets to BAP regulation were largely dissimilar from those that best classified PAH carcinogenicity challenging current assumptions that BAP carcinogenicity (and subsequent mode of action) is reflective of overall PAH carcinogenicity. These results illustrate utility of using systems toxicology approaches to analyze global gene expression towards carcinogenic hazard assessment.

Vertical distribution of polycyclic aromatic hydrocarbons in the brackish sea water column: ex situ experiment

Background

Oil spills can cause severe damage within a marine ecosystem. Following a spill, the soluble fraction of polycyclic aromatic hydrocarbons is rapidly released into the water column. These remain dissolved in seawater over an extended period of time, even should the insoluble fraction be removed. The vertical distribution of the aromatic hydrocarbon component and how these become transferred is poorly understood in brackish waters. This study examines the vertical distribution of polycyclic aromatic hydrocarbons having been released from a controlled film of spilled oil onto the surface of brackish water.

Methods

The study was undertaken under controlled conditions so as to minimize the variability of environmental factors such as temperature and hydrodynamics. The distribution of polycyclic aromatic hydrocarbons was measured in the dissolved and suspended phases throughout the 1 m water column with different intensity of water sampling: 1, 2, 4, 7, 72, 120, 336, 504 and 984 h.

Results

The total concentration of polycyclic aromatic hydrocarbons ranged from 19.01 to 214.85 ng L^–1 in the dissolved phase and from 5.14 to 63.92 ng L^–1 in the suspended phase. These hydrocarbons were released immediately following a controlled spill attaining 214.9 ng L^–1 in the dissolved phase and 54.4 ng L^–1 in the suspended phase near the cylinder bottom after 1–2 h. The 2–3 ring polycyclic aromatic hydrocarbons dominated in the dissolved phase (60–80%), whereas the greater amount of 4–6 ring polycyclic aromatic hydrocarbons (55–90%) occurred in the suspended phase. A relatively low negative correlation (r_S = –0.41) was determined between the concentration of phenanthrene and suspended matter, whereas a high negative correlation (r =  − 0.79) was found between the concentration of pyrene and suspended matter. Despite the differences in the relationships between the concentration ratio and amount of suspended matter the obtained regressions allow roughly to predict the concentration of polycyclic aromatic hydrocarbons.

Physico-chemical characterization and in vitro inflammatory and oxidative potency of atmospheric particles collected in Dakar city's (Senegal)

Exposure to atmospheric pollutants has been recognized as a major risk factor of respiratory and cardiovascular diseases. Fine particles (PM_2.5) and a coarser fraction (PM_>2.5) sampled at an urban site in Dakar (HLM), characterized by high road traffic emissions, were compared with particles sampled at a rural area, Toubab Dialaw located about 40 km from Dakar. The physicochemical characteristics of samples revealed that PMs differ for their physical (surface area) and chemical properties (in terms of CHN, metals, ions, paraffins, VOCs and PAHs) that were 65-75% higher in urban samples. Moreover the fine PMs contain higher amounts of anthropogenic related pollutants than the PM_>2.5 one. These differences are sustained by the ratios reported for the analysed PAHs which suggest as predominant primary emission sources vehicle exhausts at urban site and biomass combustion at the rural site. The inflammatory response and the oxidative damages were evaluated in BEAS-2B cells by the quantification of 4 selected inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-8) and of total carbonylated proteins and the oxidative DNA adduct 8-OHdG after 8 or 24 h exposure. In accordance with the different sources and different physical and chemical properties, the inflammatory response and the oxidative damages were found higher in bronchial cells exposed to urban PMs. These data confirm the importance, also for West African countries, to evaluate the correlation between PM physico-chemical properties and potential biological impacts.

PAHs and PCBs accumulated by SPMD-based virtual organisms and feral fish in Three Gorges Reservoir, China

Polycyclic aromatic hydrocarbon (PAHs) and polychlorinated biphenyls (PCBs) accumulated by semipermeable membrane device (SPMD)-based virtual organisms (VOs) and local feral fish were studied in Three Gorges Reservoir (TGR), China. VOs were deployed at seven sites in TGR for two periods in 2009 and 5 species of fish with different living habitats and feeding habits collected in the same periods from two counties in TGR. The concentration and profile of PAHs and PCBs in fish were quite different from those in VOs. Most high-molecular-weight-PAHs were detected in VOs, while they were undetected in fish. Most PCBs were undetected in VOs, while most of them were detected in fish. Low-molecular-weight-PAHs were predominant contaminants of PAHs and non-dioxin-like-PCBs were the main PCBs in fish. The levels of PAHs and PCBs in the few fish samples were low and were not of concern based on chemical contaminant limits of non-carcinogenic effect.

Induction of c-Jun by air particulate matter (PM₁₀) of Mexico city: Participation of polycyclic aromatic hydrocarbons

The carcinogenic potential of urban particulate matter (PM) has been partly attributed to polycyclic aromatic hydrocarbons (PAHs) content, which activates the aryl hydrocarbon receptor (AhR). Here we report the effect of PM with an aerodynamic size of 10 μm (PM10) on the induction of AhR pathway in A549 cells, evaluating its downstream targets CYP1B1, IL-6, IL-8 and c-Jun. Significant increases in CYP1B1 protein and enzyme activity; IL-6 and IL-8 secretion and c-Jun protein were found in response to PM10. The formation of PAH-DNA adducts was also detected. The involvement of AhR pathway was confirmed with Resveratrol as AhR antagonist, which reversed CYP1B1 and c-Jun induction. Nevertheless, in IL-6 and IL-8 secretion, the Resveratrol was ineffective, suggesting an effect independent of this pathway. Considering the role of c-Jun in oncogenesis, its induction by PM may be contributing to its carcinogenic potential through induction of AhR pathway by PAHs present in PM10.

Microsatellite DNA mutations in double-crested cormorants (Phalacrocorax auritus) associated with exposure to PAH-containing industrial air pollution

Hamilton Harbour, Ontario, Canada is one of the most polluted sites on the Great Lakes, and is subject to substantial airborne pollution due to emissions from both heavy industry and intense vehicle traffic. Mutagenic Polycyclic aromatic hydrocarbons (PAHs) are present at very high concentrations in the air and sediment of Hamilton Harbour. We used five variable DNA microsatellites to screen for mutations in 97 families of Double-crested Cormorants (Phalacrocorax auritus) from three wild colonies, two in Hamilton Harbour and one in cleaner northeastern Lake Erie. Mutations were identified in all five microsatellites at low frequencies, with the majority of mutations found in chicks from the Hamilton Harbour site closest to industrial sources of PAH contamination. Microsatellite mutation rates were 6-fold higher at the Hamilton Harbour site closest to the industrial sources of PAH contamination than the other Hamilton Harbour site, and both were higher than the reference colony. A Phase I metabolite of the PAH benzo[a]pyrene identified by LC-MS/MS in bile and liver from Hamilton Harbour cormorant chicks suggests that these cormorants are exposed to and metabolizing PAHs, highlighting their potential to have caused the observed mutations.

PAH distribution and mass fluxes in the Three Gorges Reservoir after impoundment of the Three Gorges Dam

Mass fluxes of polycyclic aromatic hydrocarbons (PAHs) were calculated for the Three Gorges Reservoir (TGR) in China, based on concentration and discharge data from the Yangtze River. Virtual Organisms (VOs) have been applied during four campaigns in 2008, 2009 (twice) and 2011 at sampling sites distributed from Chongqing to Maoping. The total PAH mass fluxes ranged from 110 to 2,160 mg s(-1). Highest loads were determined at Chongqing with a decreasing trend towards Maoping in all four sampling campaigns. PAH remediation capacity of the TGR was found to be high as the mass flux reduced by more than half from upstream to downstream. Responsible processes are thought to be adsorption of PAH to suspended particles, dilution and degradation. Furthermore, the dependence of PAH concentration upon water depth was investigated at Maoping in front of the Three Gorges Dam. Although considerable differences could be revealed, there was no trend observable. Sampling of water with self-packed filter cartridges confirmed more homogenous PAH depth distribution. Moreover, PAH content of suspended particles was estimated from water concentrations gathered by VOs based on a water-particle separation model and subsequently compared to PAH concentration measured in water and in filter cartridges. It could be shown that the modeled data predicts the concentration caused by particle-bound PAHs to be about 6 times lower than PAHs dissolved in water. Besides, the model estimates the proportions of 5- and 6-ring PAHs being higher than in water phase.

Environmental nitration processes enhance the mutagenic potency of aromatic compounds

This work is an attempt to establish if aromatic nitration processes are always associated with an increase of genotoxicity. We determined the mutagenic and genotoxic effects of Benzene (B), Nitrobenzene (NB), Phenol (P), 2-Nitrophenol (2-NP), 2,4-Dinitrophenol (2,4-DNP), Pyrene (Py), 1-Nitropyrene (1-NPy), 1,3-Dinitropyrene (1,3-DNPy), 1,6-Dinitropyrene (1,6-DNPy), and 1,8-Dinitropyrene (1,8-DNPy). The mutagenic activities were evaluated with umuC test in presence and in absence of metabolic activation with S9 mix. Then, we used both cytokinesis-blocked micronucleus (CBMN) assay, in combination with fluorescent in situ hybridization (FISH) of human pan-centromeric DNA probes on human lymphocytes in order to evaluate the genotoxic effects. Analysis of all results shows that nitro polycyclic aromatic hydrocarbons (PAHs) are definitely environmental genotoxic/mutagenic hazards and confirms that environmental aromatic nitration reactions lead to an increase in genotoxicity and mutagenicity properties. Particularly 1-NPy and 1,8-DNPy can be considered as human potential carcinogens. They seem to be significant markers of the genotoxicity, mutagenicity, and potential carcinogenicity of complex PAHs mixtures present in traffic emission and industrial environment. In prevention of environmental carcinogenic risk 1-NPy and 1,8-DNPy must therefore be systematically analyzed in environmental complex mixtures in association with combined umuC test, CBMN assay, and FISH on cultured human lymphocytes. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2012.

Origin of ultrafast excited state dynamics of 1-nitropyrene

Time-resolved emission measurements in subpicosecond time domain have been carried out for 1-nitropyrene in different solvents to understand the mechanism for the observed ultrafast decay of its first excited singlet state. Excited-state dynamics of 1-nitropyrene is found to be independent of the solvent viscosity. This result contradicts the proposition in the literature (J. Phys. Chem. A 2007, 111, 552) that the ultrafast decay in 1-nitropyrene is due to the large amplitude torsional motion of the nitro group around the pyrene moiety. Excited-state dynamics of 1-nitropyrene in solvents with different dielectric constants shows that excited-state lifetime suddenly increases after a certain value of the dielectric constant. Detailed quantum chemical calculations have been carried out to understand the process that is responsible for the observed effect of the dielectric constant on the excited-state dynamics of 1-nitropyrene. It is seen that the excited-state lifetime and the singlet-triplet energy gap follow similar variation with the dielectric constant of the medium. Such a correlation between the excited-state lifetime and the singlet-triplet energy gap supports the fact that the observed ultrafast decay for 1-nitropyrene is due to an efficient intersystem crossing rather than to the torsional motion of the nitro group as proposed in the literature.

Oxidative stress and air pollution exposure

Air pollution is associated with increased cardiovascular and pulmonary morbidity and mortality. The mechanisms of air pollution-induced health effects involve oxidative stress and inflammation. As a matter of fact, particulate matter (PM), especially fine (PM(2.5), PM < 2.5 μm) and ultrafine (PM(0.1), PM < 0.1 μm) particles, ozone, nitrogen oxides, and transition metals, are potent oxidants or able to generate reactive oxygen species (ROS). Oxidative stress can trigger redox-sensitive pathways that lead to different biological processes such as inflammation and cell death. However, it does appear that the susceptibility of target organ to oxidative injury also depends upon its ability to upregulate protective scavenging systems. As vehicular traffic is known to importantly contribute to PM exposure, its intensity and quality must be strongly relevant determinants of the qualitative characteristics of PM spread in the atmosphere. Change in the composition of this PM is likely to modify its health impact.

Organic extracts of urban air pollution particulate matter (PM2.5)-induced genotoxicity and oxidative stress in human lung bronchial epithelial cells (BEAS-2B cells)

Traffic is a major source of particulate matter (PM), and ultrafine particulates and traffic intensity probably contribute significantly to PM-related health effects. As a strong relationship between air pollution and motor vehicle-originated pollutants has been shown to exist, air pollution genotoxicity studies of urban cities are steadily increasing. In Korea, the death rate caused by lung cancer is the most rapidly increased cancer death rate in the past 10 years. In this study, genotoxicity of PM2.5 (<2.5μm in aerodynamic diameter particles) collected from the traffic area in Suwon City, Korea, was studied using cultured human lung bronchial epithelial cells (BEAS-2B) as a model system for the potential inhalation health effects. Organic extract of PM2.5 (CE) generated significant DNA breakage and micronucleus formation in a dose-dependent manner (1μg/cm(3)-50μg/cm(3)). In the acid-base-neutral fractionation of PM2.5, neutral samples including the aliphatic (F3), aromatic (F4) and slightly polar (F5) fractions generated significant DNA breakage and micronucleus formation. These genotoxic effects were significantly blocked by scavenging agents [superoxide dismutase (SOD), sodium selenite (SS), mannitol (M), catalase (CAT)]. In addition, in the modified Comet assay using endonucleases (FPG and ENDOIII), CE and its fractions (F3, F4, and F5) increased DNA breakage compared with control groups, indicating that CE and fractions of PM2.5 induced oxidative DNA damage. These results clearly suggest that PM2.5 collected in the Suwon traffic area has genotoxic effects and that reactive oxygen species may play a distinct role in these effects. In addition, aliphatic/chlorinated hydrocarbons, PAH/alkylderivatives, and nitro-PAH/ketones/quinones may be important causative agents of the genotoxic effects.

Production of polycyclic aromatic hydrocarbon metabolites from a peroxynitrite/iron(III) porphyrin biomimetic model and their mutagenicities

Some polycyclic aromatic hydrocarbons (PAHs) are typical promutagens that require metabolic activation to exhibit their mutagenicities and carcinogenicities. The metabolites of three PAHs, pyrene (PY), fluoranthene (FLU), and benzo[a]pyrene (BaP), produced from the peroxynitrite/T(p-Cl)PPFeCl(peroxynitrite/(chloride)iron(III)tetrakis(p-chlorophenyl)porphyrin) system, have been identified with high-performance liquid chromatography coupled with electron spray ionization tandem mass spectrometry. The results demonstrated that three major metabolites were the quinone group, OH group, and nitro group. In the Ames test, all three PAH metabolites became mutagenic without using the enzymatic activating system, whereas their parents did not show positive results. Cell transformation assay indicated that 1,3-nitro-BaP and BaP metabolites produced from this biomimetic system have more serious effects in inducing cancer than the BaP parent.

Temporal variation of nitro-polycyclic aromatic hydrocarbons in PM10 and PM2.5 collected in Northern Mexico City

With the aim to determine the presence of individual nitro-PAH contained in particles in the atmosphere of Mexico City, a monitoring campaign for particulate matter (PM(10) and PM(2.5)) was carried out in Northern Mexico City, from April 2006 to February 2007. The PM(10) annual median concentration was 65.2μgm(-3) associated to 7.6μgm(-3) of solvent-extractable organic matter (SEOM) corresponding to 11.4% of the PM(10) concentration and 38.6μgm(-3) with 5.9μgm(-3) SEOM corresponding to 15.2% for PM(2.5). PM concentration and SEOM varied with the season and the particle size. The quantification of nitro-polycyclic aromatic hydrocarbons (nitro-PAH) was developed through the standards addition method under two schemes: reference standard with and without matrix, the former giving the best results. The recovery percentages varied with the extraction method within the 52 to 97% range depending on each nitro-PAH. The determination of the latter was effected with and without sample purification, also termed fractioning, giving similar results. 8 nitro-PAH were quantified, and their sum ranged from 111 to 819pgm(-3) for PM(10) and from 58 to 383pgm(-3) for PM(2.5), depending on the season. The greatest concentration was for 9-Nitroanthracene in PM(10) and PM(2.5), detected during the cold-dry season, with a median (10th-90th percentiles) concentration in 235pgm(-3) (66-449pgm(-3)) for PM(10) and 73pgm(-3) (18-117pgm(-3)) for PM(2.5). The correlation among mass concentrations of the nitro-PAH and criteria pollutants was statistically significant for some nitro-PAH with PM(10), SEOM in PM(10), SEOM in PM(2.5), NO(X), NO(2) and CO, suggesting either sources, primary or secondary origin. The measured concentrations of nitro-PAH were higher than those reported in other countries, but lower than those from Chinese cities. Knowledge of nitro-PAH atmospheric concentrations can aid during the surveillance of diseases (cardiovascular and cancer risk) associated with these exposures.

Identification of estrogen-like effects and biologically active compounds in river water using bioassays and chemical analysis

The Nackdong River is the longest river in South Korea and passes through major cities that have several industrial complexes, including chemical, electric, and petrochemical complexes, and municipal characteristics such as apartment complexes. Along the river, the Gumi region has an electric industrial complex and an apartment complex that may be possible point sources of xenoestrogens such as phenolic compounds. To identify the causative chemicals for estrogenic activity in the river water of this region, bioassay-directed chemical analysis was performed. All samples from six sampling sites (an upstream point: S1; hot spot points: S2-1, S2-2, and S2-3; and downstream points: S3, and S4) showed estrogenic activity in the E-screen assay, with bio-EEQs (17beta-E(2)-equivalent quantities) ranging from 25.35-677.15 pg/L. Samples from S2-2, the sampling point downstream of the junction of stream water, and domestic and industrial wastewater, contained the highest estrogenic activity. Since the bio-EEQ of the organic acid fraction (F2) of the S2-2 sample had the highest activity (823.25 pg-EEQ/L) and F2 may contain phenolic compounds, GC-MS analyses for phenolic xenoestrogens were conducted with the organic acid fractions of the river water samples. Six estrogenic phenolic chemicals, 4-NP, BPA, 4-t-OP, 4-t-BP, 4-n-OP, and 4-n-HTP, were detected, with the highest concentrations (I-EEQ) found in S2-2 (231.80 pg/L). Among these phenolic chemicals, 4-NP was the most potent estrogen (bio-EEF; 8.12 x1 0(-5)) and acted as a full agonist. Furthermore, 4-NP was present at levels (2.0 microg/L in S2-2) that can induce VTG induction in fish (>1 microg/L). In addition, we confirmed that river water (S2-2) significantly increased serum VTG levels in crucian carp (Carassius auratus) in a fish exposure experiment under laboratory conditions. Therefore, phenolic xenoestrogens, especially 4-NP, may be the main causative compounds responsible for the estrogenic effect on the Nackdong River.

Identification of estrogenic and antiestrogenic activities of respirable diesel exhaust particles by bioassay-directed fractionation

Bioassay-directed fractionation was performed to identify causative chemical groups of DEPs with estrogenic and antiestrogenic activities. Bioassay-directed fractionation consists of a cell bioassay (E-SCREEN) in conjunction with acid-base partitioning (F1 and F2) and silica gel column fractionation of neutral fractions (F3-F7). Crude extract (CE) of DEPs in dichloromethane (DCM) exhibited both estrogenic and antiestrogenic activity. Estrogenic activity of CE and some fractions (F1, F2, F3, F5 and F6) was induced through estrogen receptor (ER)-mediated pathways. In particular, the acid polar fraction (F2) of DEPs, which contains phenols, induced high levels of estrogenic activity compared to other fractions. The estrogenic activity of F2 (610.80 pg-bio-EEQ/g-DEPs) was higher than that of the total estrogenic activity of CE (222.22 pg-bio-EEQ/g-DEPs). This result indicates that the estrogenic activity induced by causative estrogenic fraction (F2) may be antagonized by unidentified chemicals in DEPs. On the other hand, non-polar fractions (F3 and F4) of DEPs include aliphatic and chlorinated hydrocarbon, polyaromatic hydrocarbons, and their alkyl derivatives, which play an important role in the antiestrogenic activity of DEPs. In particular, F4, which contains PAH and its derivatives, showed the highest antiestrogenic activity. Since in our previous study, dibenzo(a, h)anthracene and chrysene were identified in F4, and these chemicals have antiestrogenic activity, we assume that these chemicals are the major causative chemicals with antiestrogenic activity in DEPs. In contrast to the estrogenic activity of DEPs, antiestrogenic activity of CE was stronger than that of antiestrogenic fractions (F3 and F4) at non-cytotoxic concentrations, indicating that additive or synergistic effects by unidentified chemicals contained in DEPs occurred.

The 32P-postlabeling assay for DNA adducts

32P-postlabeling analysis is an ultrasensitive method for the detection and quantitation of carcinogen-DNA adducts. It consists of four principal steps: (i) enzymatic digestion of DNA to nucleoside 3'-monophosphates; (ii) enrichment of the adduct fraction of the DNA digest; (iii) 5'-labeling of the adducts by transfer of 32P-orthophosphate from [gamma-32P]ATP mediated by polynucleotide kinase (PNK); (iv) chromatographic or electrophoretic separation of the labeled adducts or modified nucleotides and quantitation by measurement of their radioactive decay. The assay requires only microgram quantities of DNA and is capable of detecting adducts at frequencies as low as 1 in 10(10) nt, making it applicable to the detection of events resulting from environmental exposures, or experiments using physiological concentrations of agents. It has a wide range of applications in human, animal and in vitro studies, and can be used for a wide variety of classes of compound and for the detection of adducts formed by complex mixtures. This protocol can be completed in 3 d.

Temporal variation in the genotoxic potential of urban air particulate matter

The main aim of this study was to compare the genotoxic potential of organic extracts from urban air particles collected in three different sampling periods in the center of Prague (Czech Republic). For this purpose, we analyzed the DNA adduct forming activity of extractable organic matter (EOM) from urban air particles <10 microm (PM10) in the human hepatoma cell line HepG2. DNA adducts were analyzed by (32)P-postlabelling with nuclease P1 enrichment. PM10 concentrations were 36.9 microg/m(3), 62.6mug/m(3) and 39.0 microg/m(3), in summer 2000, winter 2001 and winter 2005, respectively. The corresponding EOM contents were 5.0 microg/m(3) (13.9% of PM10), 14.9 microg/m(3) (23.8%) and 6.7 microg/m(3) (17.2%). The total DNA adduct levels induced by 10 microg EOM/ml were 4.7, 19.5 and 37.2 adducts/10(8) nucleotides in summer 2000, winter 2001 and winter 2005, respectively. However, when the EOM quantities per cubic meter of air were taken into consideration, the summer sample exhibited a 10-fold lower genotoxicity than did those of winter, while the difference between the winter samples was not significant: 23.4 in summer 2000, 291 in winter 2001 and 249 in winter 2005 (in relative units). Although the PM10 concentration in air and the EOM content in particles in winter 2005 were significantly lower than in winter 2001, the genotoxic potential of the ambient air in these samples was almost equal. There were significant positive correlations between the B[a]P and c-PAH content in EOM from various sampling periods and the total DNA adduct levels detected in the EOM-treated samples. These findings support the hypothesis that the B[a]P and c-PAH content in EOM is the most important factor that determines its genotoxic potential. Thus, estimating the genotoxic potential of the ambient air and predicting health risk should be based mainly on the c-PAH concentration and the biological activity of the extracts, while the mass of particles and the EOM content do not seem to be crucial determinants of ambient air genotoxicity.

The potent protective effect of wild ginseng (Panax ginseng C.A. Meyer) against benzo[alpha]pyrene-induced toxicity through metabolic regulation of CYP1A1 and GSTs

Wild Panax ginseng C.A. Meyer (WG) is a well-known medicinal herb. In this study, the protective effects of a water extract from the root of WG on benzo[alpha]pyrene (BP)-induced hepatotoxicity and the mechanism of these effects were investigated for the first time. The effects of WG on liver toxicities induced by BP were assessed by blood biochemical and histopathological analyses. BP caused severe liver injury in rats, as indicated by elevated plasma ALT, AST and LPO levels. Pretreatment with WG for 4 weeks completely abrogated increases in the ALT, AST and LPO levels when challenged with BP. Reductions in GSH content and GST activity by BP were reversed by WG. These protective effects of WG against BP-induced toxicity were consistent with the results of histopathological examinations. We next examined the effects of WG on the gene expression of the enzymes that metabolize BP in H4IIE cells. CYP1A1 mRNA and protein expression were increased by BP. WG moderately inhibited BP-induced CYP1A1 gene expression. Moreover, GSTA2, GSTA3 and GSTM2 gene expressions were significantly increased by WG through the Nrf2/antioxidant responsive element pathway for enzyme induction. In summary, WG is efficacious in protecting against BP-induced hepatotoxicity as results of metabolic regulations through both the inhibition of metabolic enzyme activation and the enhancement of electrophilic detoxification, implying that WG should be considered a potential chemopreventive agent.

In vitro genotoxicity of PAH mixtures and organic extract from urban air particles part II: human cell lines

Principal aims of this study were at first, to find a relevant human derived cell line to investigate the genotoxic potential of PAH-containing complex mixtures and second, to use this cell system for the analysis of DNA adduct forming activity of organic compounds bound onto PM10 particles. Particles were collected by high volume air samplers during summer and winter periods in three European cities (Prague, Kosice, and Sofia), representing different levels of air pollution. The genotoxic potential of extractable organic matter (EOM) was compared with the genotoxic potential of individual carcinogenic polycyclic aromatic hydrocarbons (c-PAHs) as well as their artificial mixtures. Metabolically competent human hepatoma HepG2 cells, confluent cultures of human diploid lung fibroblasts (HEL), and the human monocytic leukemia cell line THP-1 were used as models. DNA adducts were analyzed by (32)P-postlabeling. The total DNA adduct levels induced in HepG2 cells after exposure to EOMs were higher than in HEL cells treated under the same conditions (15-190 versus 2-15adducts/10(8) nucleotides, in HepG2 and HEL cells, respectively). THP-1 cells exhibited the lowest DNA adduct forming activity induced by EOMs (1.5-3.7adducts/10(8) nucleotides). A direct correlation between total DNA adduct levels and c-PAH content in EOM was found for all EOMs in HepG2 cells incubated with 50microg EOM/ml (R=0.88; p=0.0192). This correlation was even slightly stronger when B[a]P content in EOMs and B[a]P-like adduct spots were analyzed (R=0.90; p=0.016). As THP-1 cells possess a limited metabolic capacity for most c-PAHs to form DNA reactive intermediates and are also more susceptible to toxic effects of PAHs and various EOM components, this cell line seemed to be an inappropriate system for genotoxicity studies of PAH-containing complex mixtures. The seasonal variability of genotoxic potential of extracts was stronger than variability among the three localities studied. In HepG2 cells, the highest DNA adduct levels were induced by EOM collected in Prague in the winter period, followed by Sofia and Kosice. However, in the summer sampling period, the order was quite opposite: Kosice>Sofia>Prague. When the EOM content per m(3) of air was taken into consideration in order to compare real exposures of humans to genotoxic compounds in all three localities, extracts from respirable dust particles collected in Sofia exhibited the highest genotoxicity regardless of the sampling period. The results indicate that most of DNA adducts detected in cells incubated with EOMs have their origin in low concentrations of c-PAHs representing 0.03-0.17% of EOM total mass. Finally, our results suggest that HepG2 cells have a metabolic capacity for PAHs similar to human hepatocytes and represent therefore the best in vitro model for investigating the genotoxic potential of complex mixtures containing PAHs among the three cell lines tested in this study.

In vitro genotoxicity of PAH mixtures and organic extract from urban air particles part I: acellular assay

Acellular assay of calf thymus DNA+/-rat liver microsomal S9 fraction coupled with (32)P-postlabelling was used to study the genotoxic potential of organic compounds bound onto PM10 particles collected in three European cities-Prague (CZ), Kosice (SK) and Sofia (BG) during summer and winter periods. B[a]P alone induced DNA adduct levels ranging from 4.8 to 768 adducts/10(8) nucleotides in the concentration dependent manner. However, a mixture of 8 c-PAHs with equimolar doses of B[a]P induced 3.7-757 adducts/10(8) nucleotides, thus suggesting the inhibition of DNA adduct forming activity by interaction among various PAHs. Comparison of DNA adduct levels induced by various EOMs indicates higher variability among seasons than among localities. DNA adduct levels for Prague collection site varied from 19 to 166 adducts/10(8) nucleotides, for Kosice from 22 to 85 and for Sofia from 6 to 144 adducts/10(8) nucleotides. Bioactivation with S9 microsomal fraction caused 2- to 7-fold increase in DNA adduct levels compared to -S9 samples, suggesting a crucial role of indirectly acting genotoxic EOM components, such as PAHs. We have demonstrated for the first time a significant positive correlation between B[a]P content in EOMs and total DNA adduct levels detected in the EOM treated samples (R=0.83; p=0.04). These results suggest that B[a]P content in EOM is an important factor for the total genotoxic potential of EOM and/or B[a]P is a good indicator of the presence of other genotoxic compounds causing DNA adducts. Even stronger correlation between the content of genotoxic compounds in EOMs and total DNA adduct levels detected (R=0.94; p=0.005) was found when eight c-PAHs were taken into the consideration. Our findings support a hypothesis that a relatively limited number of EOM components is responsible for a major part of its genotoxicity detectable as DNA adducts by (32)P-postlabelling.

Immunization with soot from a non-combustion process provokes formation of antibodies against polycyclic aromatic hydrocarbons

The emission of soot during combustion processes used in transportation, manufacturing, and power generation is of increasing concern because of its serious adverse health effects. In particular, the ability to modulate the immune system has recently been established. In the present investigation, an artificial soot sample that was prepared by fragmentation of acetylene in a laser-induced plasma was used as an antigen for the immunization of a rabbit. A highly sensitive competition curve in an indirect competitive ELISA using a benzo[a]pyrene-BSA conjugate as a coating antigen could be constructed for benzo[a]pyrene with an IC50 of 2.94 mug/l (11.65 nmol/l). In contrast to the high affinity, the soot antiserum dilution (antibody titer) of 1:750 was rather low. The cross-reactivity was tested with 16 parent polycyclic aromatic hydrocarbons, 7 nitrated polycyclic aromatics, and 3 methylated, hydroxylated or butyric acid derivatives. The results obtained suggest that the vertebrate immune system can respond to an immunization with soot by the generation of high affinity IgG class antibodies against polycyclic aromatics. It is likely that antibodies are raised against the molecular structures which form the framework of the soot particles and not against adsorbed and extractable polyaromatic compounds. The experiments suggest that if soot is considered a T-independent antigen, the isotype switch, essentially from IgM to IgG, could have been caused by co-inoculation with a T-dependent antigen, i.e., mycobacteria contained in Freunds complete adjuvant. However, at the cellular level the mechanism remains to be uncovered.

Antiestrogenic effects of marijuana smoke condensate and cannabinoid compounds

The antiestrogenic effects of marijuana smoke condensate (MSC) and three major cannabinoids, ie., delta9-tetrahydrocannabinol (THC), cannabidiol (CBD), and cannabinol (CBN), were evaluated using in vitro bioassays, viz., the human breast cancer cell proliferation assay, the recombinant human estrogen receptor (ER) competitive binding assay, and the reporter gene assay. The inhibitory effects on estrogen were also examined using the ethoxyresorufin-O-deethylase (EROD) assay, the aromatase assay, and the 17beta-estradiol (E2) metabolism assay. The results showed that MSC induced the antiestrogenic effect via the ER-mediated pathway, while THC, CBD, and CBN did not have any antiestrogenic activity. This suggests that the combined effects of the marijuana smoke components are responsible for the antiestrogenicity of marijuana use. In addition, MSC induced the CYP1A activity and the E2 metabolism, but inhibited the aromatase activity, suggesting that the antiestrogenic activity of MSC is also related to the indirect ER-dependent pathway, as a result of the depletion of the in situ E2 level available to bind to the ER. In conclusion, pyrogenic products including polycyclic aromatic hydrocarbons (PAHs) in the non-polar fraction, which is the most biologically active fraction among the seven fractions of MSC, might be responsible for the antiestrogenic effect.

Modulation of gene expression and DNA adduct formation in HepG2 cells by polycyclic aromatic hydrocarbons with different carcinogenic potencies

Polycyclic aromatic hydrocarbons (PAHs) can occur in relatively high concentrations in the air, and many PAHs are known or suspected carcinogens. In order to better understand differences in carcinogenic potency between PAHs, we investigated modulation of gene expression in human HepG2 cells after 6 h incubation with varying doses of benzo[a]pyrene (B[a]P), benzo[b]fluoranthene (B[b]F), fluoranthene (FA), dibenzo[a,h]anthracene (DB[a,h]A), 1-methylphenanthrene (1-MPA) or dibenzo[a,l]pyrene (DB[a,l]P), by using cDNA microarrays containing 600 toxicologically relevant genes. Furthermore, DNA adduct levels induced by the compounds were assessed with (32)P-post-labeling, and carcinogenic potency was determined by literature study. All tested PAHs, except 1-MPA, induced gene expression changes in HepG2 cells, although generally no dose-response relationship could be detected. Clustering and principal component analysis showed that gene expression changes were compound specific, since for each compound all concentrations grouped together. Furthermore, it showed that the six PAHs can be divided into three groups, first FA and 1-MPA, second B[a]P, B[b]F and DB[a,h]A, and third DB[a,l]P. This grouping corresponds with the carcinogenic potencies of the individual compounds. Many of the modulated genes are involved in biological pathways like apoptosis, cholesterol biosynthesis and fatty acid synthesis. The order of DNA adduct levels induced by the PAHs was: B[a]P >> DB[a,l]P > B[b]F > DB[a,h]A > 1-MPA >/= FA. When comparing the expression change of individual genes with DNA adduct levels, carcinogenic potency or Ah-receptor antagonicity (the last two were taken from literature), several highly correlated genes were found, of which CYP1A1, PRKCA, SLC22A3, NFKB1A, CYP1A2 and CYP2D6 correlated with all parameters. Our data indicate that discrimination of high and low carcinogenic PAHs by gene expression profiling is feasible. Also, the carcinogenic PAHs induce several pathways that were not affected by the least carcinogenic PAHs.

Identification of mammalian cell genotoxins in respirable diesel exhaust particles by bioassay-directed chemical analysis

A bioassay-directed chemical analysis which consists of mammalian cell bioassays (comet assay, CBMN assay and EROD-microbioassay) in conjunction with analytical measurements was performed to identify the most biologically active compounds of the diesel exhaust particulate matters (DEPs) on mutagenic activity. These bioassay systems were suitable to estimate the mammalian genotoxic potentials of pollutants present in low concentrations in limited environmental samples, as is the case with DEPEs. The results from mutagenic assay showed that the aromatic and slightly polar fraction of DEPs induced chromosomal damage and DNA breakage in a non-cytotoxic dose. It was also revealed that indirect-acting mutagens may mainly contribute to the mutagenic effect of aromatic fraction via the enzyme metabolism system. In the aromatic fraction, several indirect-acting mutagenic PAHs such as dibenzo(a,h)anthracene, chrysene, and 1,2-benzanthracene were detected by GC-MS and the complex mixture effect of this fraction was quantified in terms of its biological-TCDD equivalent concentration (bio-TEQ) which was 32.82 bio-TEQ ng/g-DEPs by EROD-microbioassay. Conclusively, we confirmed that indirect-acting mutagens contained in aromatic fraction may be important causatives of the genotoxicity of extracts of DEPs by integrating the results obtained from a mammalian cell bioassay-directed fractionation.

Development of an analytical method for polycyclic aromatic hydrocarbons and their derivatives

The possibilities of utilising pressurised liquid extraction for five nitro-polycyclic aromatic hydrocarbons from an inert matrix are shown. Different extraction temperatures and pressures were tested. The highest recoveries were obtained at extraction pressure 14 MPa and temperature 100 C. Separation of non-polar, aromatic and polar fractions by the silica gel column chromatography is shown. n-Hexane, cyclohexane and dichloromethane as a solvent were tested. The best separations of monitored fractions were obtained, when extract was dissolved in cyclohexane. Non-polar and aromatic fractions eluted together when the extract was dissolved in dichloromethane.

DNA adduct formation by the environmental contaminant 3-nitrobenzanthrone in V79 cells expressing human cytochrome P450 enzymes

Diesel exhaust is known to induce tumours in animals. Of the compounds found in diesel exhaust 3-nitrobenzanthrone (3-NBA) is particularly a powerful mutagen. Recently we showed that 3-NBA is genotoxic in vivo in rats by forming specific DNA adducts derived from nitroreduction. In this study a panel of genetically engineered V79 Chinese hamster cell lines expressing various human cytochrome P450 (CYP) enzymes (CYP1A1, CYP3A4) and/or human NADPH:CYP oxidoreductase (CYPOR) was used to identify CYP enzymes involved in the metabolic activation of 3-NBA. We analyzed the formation of specific DNA adducts by 32P-postlabelling after exposing cells to 1 microM 3-NBA. A similar pattern with a total of four distinct 3-NBA-DNA adducts was found in all cells, identical to those detected previously in DNA from rats treated with 3-NBA in vivo. Total adduct levels ranged from 75 to 132 using nuclease P1 and from 103 to 220 adducts per 10(8) nucleotides, using butanol enrichment. Comparison of DNA binding between different V79MZ derived cells revealed that human CYPOR and CYP3A4 were involved in the metabolic activation of 3-NBA. Furthermore, dose-dependent high adduct levels were detected after exposure to 0.01, 0.1 or 1 microM 3-NBA in the subclone V79NH which exhibits high activities of nitroreductase and N,O-acetyltransferase. Our results suggest that nitroreduction is the major pathway in the human bioactivation of 3-NBA. Moreover, acetylation of the initially formed N-hydroxy arylamine intermediates may contribute to the high genotoxic potential of 3-NBA.

Effects of fractions of traffic particulate matter on TH2-cytokines, IgE levels, and bronchial hyperresponsiveness in mice

In recent decades an increased prevalence of allergic conditions has been observed in developed countries. Although lifestyles, exposure to infection, and diet are all likely important factors, many studies have also shown a strong link between industrialization and allergy. The aim of this study was to investigate which extract fractions from traffic particulate matter (TPM, collected in a tunnel in Prague) have the greatest impact on different inflammatory and immunological parameters, such as cytokine production, levels of immunoglobulin E (IgE) antibodies, and bronchial hyperresponsiveness (BHR) in mice, when the extracts are used together with birch pollen for immunization. BP2 mice were immunized with birch pollen and different fractions of TPM (fractions 1-8). They were provoked intranasally with a mixture of pollen and TPM or pollen alone before they were challenged with methacholine. The BHR was evaluated in a whole-body plethysmograph. Th2 cytokines and fibronectin concentrations were measured, and differential cell counts were performed in the bronchioalveolar lavage (BAL) fluid. Sera were collected for determination of antibody titers. The highest titers of IgE and the highest BHR were found in the positive control mice (immunized and provoked with a mixture of pollen and TPM), followed by mice immunized with pollen and fraction 2 (which contains organic acids). Fraction 2 also induced the highest number of eosinophils and increased levels of interleukin 5 (IL-5) in the BAL fluid. The highest levels of IL-5, in BAL fluid and sera, were obtained in mice immunized with fraction 6 (moderately polar compounds), a somewhat surprising result since those mice did not produce any IgE, did not have any eosinophils in their BAL, or showed almost no BHR. Our data demonstrate that fractions 2 (organic acids) and 7 (highly polar compounds) seem to contain potential adjuvants stimulating the IL-5 production, the IgE synthesis, the eosinophil recruitment, and the bronchial hyperreactivity. Further characterization at the molecular level is now necessary to be able to identify the exact nature of those potential adjuvants. This will be of help in the future to improve the quality of the urban air aerosol.

Cytochrome P450 (CYP1A) induction and DNA adducts in a rat hepatoma cell line (Fao), exposed to environmentally relevant concentrations of organic compounds, singly and in combinations

Cytochrome P4501A (CYP1A) induction and DNA adduct formation were evaluated in the rat hepatoma cell line Fao, as biomarkers of exposure to organic compounds. Cells were exposed to environmentally relevant concentrations of benzo[a]pyrene (B[a]P) or 3,3',4,4'-tetrachlorobiphenyl (TCB), and to combinations of B[a]P and TCB. Both B[a]P and TCB induced CYP1A proteins in a concentration-dependent relationship, up to concentrations of 10 and 1 μM, respectively, detected by Western blotting. DNA adducts, analyzed by (32)P-postlabeling, were found at the highest concentrations of B[a]P (1 and 10 μM). No adducts were found in cells exposed to 0.1 μM TCB alone. The cotreatment of TCB and B[a]P indicated an increase in DNA adduct formation, compared with B[a]P, but no further induction of CYP1A protein compared with TCB alone. This study suggests that Western blotting and (32)P-postlabeling might be suitable methods for detecting CYP1A protein induction and DNA adducts, respectively, after exposure to environmentally relevant concentrations of organic compounds.

Relating repair susceptibility of carcinogen-damaged DNA with structural distortion and thermodynamic stability

A key issue in the nucleotide excision repair (NER) of bulky carcinogen-DNA adducts is the ability of the NER machinery to recognize and repair certain adducts while failing to repair others. Unrepaired adducts can survive to cause mutations that initiate the carcinogenic process. Benzo[c]phenanthrene (B[c]Ph), a representative fjord region polycyclic aromatic hydrocarbon, can be metabolically activated to the enantiomeric benzo[c]phenanthrene diol epoxides (B[c]PhDEs), (+)-(1S,2R,3R,4S)-3,4- dihydroxy-1,2-epoxy-1,2,3,4-tetrahydrobenzo[c]phenanthrene and the corresponding (-)-(1R,2S,3S,4R) isomer. These react predominantly with adenine residues in DNA to produce the stereoisomeric 1R (+)- and 1S (-)-trans-anti-B[c]Ph-N6-dA adducts. Duplexes containing the 1R (+) or 1S (-) B[c]Ph-dA adduct in codon 61 of the human N-ras mutational hotspot sequence CA*A, with B[c]Ph modification at A*, are not repaired by the human NER system. However, the analogous stereoisomeric DNA adducts of the bay region benzo[a]pyrene diol epoxide (B[a]PDE), 10S (+)- and 10R (-)-trans-anti-B[a]P-N6-dA, are repaired in the same base sequence. In order to elucidate structural and thermodynamic origins of this phenomenon, we have carried out a 2 ns molecular dynamics simulation for the 1R (+)- and 1S (-)-trans-anti-B[c]Ph-N6-dA adducts in an 11mer duplex containing the human N-ras codon 61 sequence, and compared these results with our previous study of the B[a]P-dA adducts in the same sequence. The molecular mechanics Poisson- Boltzmann surface area (MM-PBSA) method was applied to calculate the free energies of the pair of stereoisomeric B[c]Ph-dA adducts, and a detailed structural analysis was carried out. The different repair susceptibilities of the B[a]P-dA adducts and the B[c]Ph-dA adducts can be attributed to different degrees of distortion, stemming from combined effects of differences in the quality of Watson-Crick hydrogen bonding, unwinding, stretching and helix backbone perturbations. These differences are due to the different intrinsic topologies of the rigid, planar bay region adducts versus the twisted, sterically hindered fjord region adducts.

Retinal pigment epithelial cell DNA is damaged by exposure to benzo[a]pyrene, a constituent of cigarette smoke

This study examined the effect of exogenous benzo[ a ]pyrene (BaP), an important constituent of cigarette smoke, on cultured bovine retinal pigment epithelial (RPE) cells. Evidence is presented for its metabolic conversion into benzo[ a ]pyrene diol epoxide (BPDE) and the consequent formation of potentially cytotoxic nucleobase adducts in DNA. Cultured RPE cells were treated with BaP at concentrations in the range of 0-100 microM. The presence of BaP was found to cause inhibition of cell growth and replication. BaP induced the expression of a phase I drug metabolizing enzyme which was identified as cytochrome P450 1A1 (CYP 1A1) by RT-PCR and by Western blotting. Coincident with the increased expression of CYP 1A1, covalent adducts between the mutagenic metabolite BPDE and DNA could be detected within RPE cells by immunocytochemical staining. Additional support for their formation was afforded by nuclease P1 enhanced (32)P-postlabelling assays on cellular DNA. Single-cell gel electrophoresis (comet) assays showed that exposure of RPE cells to BaP rendered them markedly more susceptible to DNA damage induced by broad band UVB or blue light laser irradiation. In the case of UVB, this is consistent with the photosensitization of DNA cleavage by nucleobase adducts of BPDE. Collectively, these findings imply that BaP has a significant impact on RPE cell pathophysiology and suggest mechanisms whereby exposure to cigarette smoke might cause RPE dysfunction and cell death, thus possibly contributing to degenerative disorders of the retina.

Evading the proofreading machinery of a replicative DNA polymerase: induction of a mutation by an environmental carcinogen

DNA replication fidelity is dictated by DNA polymerase enzymes and associated proteins. When the template DNA is damaged by a carcinogen, the fidelity of DNA replication is sometimes compromized, allowing mispaired bases to persist and be incorporated into the DNA, resulting in a mutation. A key question in chemical carcinogenesis by metabolically activated polycyclic aromatic hydrocarbons (PAHs) is the nature of the interactions between the carcinogen-damaged DNA and the replicating polymerase protein that permits the mutagenic misincorporation to occur. PAHs are environmental carcinogens that, upon metabolic activation, can react with DNA to form bulky covalently linked combination molecules known as carcinogen-DNA adducts. Benzo[a]pyrene (BP) is a common PAH found in a wide range of material ingested by humans, including cigarette smoke, car exhaust, broiled meats and fish, and as a contaminant in other foods. BP is metabolically activated into several highly reactive intermediates, including the highly tumorigenic (+)-anti-benzo[a]pyrene diol epoxide (BPDE). The primary product of the reaction of (+)-anti-BPDE with DNA, the (+)-trans-anti-benzo[a]pyrene diol epoxide-N(2)-dG ((+)-ta-[BP]G) adduct, is the most mutagenic BP adduct in mammalian systems and primarily causes G-to-T transversion mutations, resulting from the mismatch of adenine with BP-damaged guanine during replication. In order to elucidate the structural characteristics and interactions between the DNA polymerase and carcinogen-damaged DNA that allow a misincorporation opposite a DNA lesion, we have modeled a (+)-ta-[BP]G adduct at a primer-template junction within the replicative phage T7 DNA polymerase containing an incoming dATP, the nucleotide most commonly mismatched with the (+)-ta-[BP]G adduct during replication. A one nanosecond molecular dynamics simulation, using AMBER 5.0, has been carried out, and the resultant trajectory analyzed. The modeling and simulation have revealed that a (+)-ta-[BP]G:A mismatch can be accommodated stably in the active site so that the fidelity mechanisms of the polymerase are evaded and the polymerase accepts the incoming mutagenic base. In this structure, the modified guanine base is in the syn conformation, with the BP moiety positioned in the major groove, without interfering with the normal protein-DNA interactions required for faithful polymerase function. This structure is stabilized by a hydrogen bond between the modified guanine base and dATP partner, hydrophobic interactions between the BP moiety and the polymerase, a hydrogen bond between the modified guanine base and the polymerase, and several hydrogen bonds between the BP moiety and polymerase side-chains. Moreover, the G:A mismatch in this system closely resembles the size and shape of a normal Watson-Crick pair. These features reveal how the polymerase proofreading machinery may be evaded in the presence of a mutagenic carcinogen-damaged DNA, so that a mismatch can be accommodated readily, allowing bypass of the adduct by the replicative T7 DNA polymerase.

Accelerated DNA adduct formation in the lung of the Nrf2 knockout mouse exposed to diesel exhaust

Diesel exhaust (DE) has been recognized as a noxious mutagen and/or carcinogen, because its components can form DNA adducts. Mechanisms governing the susceptibility to DE and the efficiency of such DNA adduct formation require clarification. The transcription factor Nrf2 is essential for inducible and/or constitutive expression of a group of detoxification and antioxidant enzymes, and we hypothesized that the nrf2 gene knockout mouse might serve as an excellent model system for analyzing DE toxicity. To address this hypothesis, lungs from nrf2(-/-) and nrf2(+/-) mice were examined for the production of xenobiotic-DNA adducts after exposure to DE (3 mg/m(3) suspended particulate matter) for 4 weeks. Whereas the relative adduct levels (RAL) were significantly increased in the lungs of both nrf2(+/-) and nrf2(-/-) mice upon exposure to DE, the increase of RAL in the lungs from nrf2(-/-) mice exposed to DE were approximately 2.3-fold higher than that of nrf2(+/-) mice exposed to DE. In contrast, cytochrome P4501A1 mRNA levels in the nrf2(-/-) mouse lungs were similar to those in the nrf2(+/-) mouse lungs even after exposure to DE, suggesting that suppressed activity of phase II drug-metabolizing enzymes is important in giving rise to the increased level of DNA adducts in the Nrf2-null mutant mouse subjected to DE. Importantly, severe hyperplasia and accumulation of the oxidative DNA adduct 8-hydroxydeoxyguanosine were observed in the bronchial epidermis of nrf2(-/-) mice following DE exposure. These results demonstrate the increased susceptibility of the nrf2 germ line mutant mouse to DE exposure and indicate the nrf2 gene knockout mouse may represent a valuable model for the assessment of respiratory DE toxicity.

Effects of chronic exposure to coal in wild rodents (Ctenomys torquatus) evaluated by multiple methods and tissues

Rio Grande do Sul (RS) coal is low quality and typically obtained by strip mining. In a recent study concerning 2 years of biomonitoring in coal regions, we demonstrated the genotoxicity of coal and related products on blood cells of native rodents, from RS, Brazil. With the goal of studying the variations in the effects of RS coal on different tissues of the same rodent, we utilized, besides the single cell gel (SCG) and micronucleus (MN) assay on blood, histological analyses and SCG assay of bone marrow, spleen, kidney, liver and lung cells, and MN assay of bone marrow and spleen cells. In addition, to identify agents that can potentially influence the results, concentrations of several heavy metals were analyzed in livers and in soil, and the total concentration of hydrocarbons in the soil was determined. Rodents exposed to coal were captured at two different sites, Butiá and Candiota, in RS. Reference animals were obtained from Pelotas, where there is no coal mining. This report provides chemical and biological data from coal regions, indicating the possible association between Zn, Ni, Pb and hydrocarbons in the induction of DNA damage (e.g. single strand-breaks and alkali-labile sites) determined by the alkaline SCG assay in cells from Ctenomys torquatus. The results of the present SCG study indicate that coal and by-products not only induce DNA damage in blood cells, but also in other tissue cells, mainly liver, kidney and lung. Neither the MN assay nor histopathological observations showed significant differences; these analyses may be useful under circumstances where genotoxicity is higher. In conclusion we believe that the in vivo genotoxicity of coal can be biomonitored by the SCG assay, and our studies suggest that wild rodents, such as C. torquatus are useful for monitoring genotoxic damage by both methods, the SCG assay and the MN test.

Genotoxicity of urban air pollutants in the Czech Republic. Part II. DNA adduct formation in mammalian cells by extractable organic matter

The study was aimed at determining the genotoxic potential of extractable organic matter (EOM) from ambient air particles PM10 (<10 micrometer) using mammalian cells in culture as test system. Air samples were collected in the course of summer and winter periods in two regions of the Czech Republic representing low and high levels of air pollution, the districts of industrial Teplice and rural Prachatice, respectively. EOM was fractionated by acid-base partitioning and silica gel column chromatography. Aliquots of fractions were incubated with cultured hepatocytes derived from male rats or Chinese hamster lung V79NH cells expressing nitroreductase activity but virtually no cytochrome P450 activity. DNA adduct levels were analyzed by 32P-postlabeling using butanol extraction for adduct enrichment. In hepatocytes, crude extracts caused the formation of substantial amounts of DNA reactive material being detectable in a broad diagonal radioactive zone (DRZ) in the chromatograms. Highest DNA adduct levels were found in the aromatic fractions and slightly polar fractions which contain most of the polycyclic aromatic hydrocarbons (PAH) and nitro-substituted PAH (nitro-PAH), respectively, comprising 75-90% of total adducts. This partitioning was independent of the sampling period and locality. In agreement with the higher average ambient air concentrations of PAH in the winter than the summer, 3-4-fold higher DNA adduct levels were detected in extracts sampled in the winter. Calculated on the basis of EOM/m(3), DNA adduct levels of samples collected in winter period were 10-fold higher than those collected in the summer period and 2-fold higher in Teplice than in Prachatice. Pretreatment of hepatocytes with 2,3,7,8-tetrachlorodibenzo-p-dioxin decreased DNA binding by 50-75%. In contrast to the findings in hepatocytes, in V79NH cells about 80% of the DNA adducts were caused by material in the slightly polar fractions appearing as distinct spots in the radiochromatograms. Seasonal variation of DNA adducts in V79NH cells was greater than variation between localities. Our results suggest that PAH as well as nitro-PAH are the main contributors to the genotoxicity of EOM derived from both industrial and rural areas. The results, furthermore, indicate that analysis of DNA adducts in mammalian cells in culture offers a suitable method for monitoring the genotoxicity of complex mixtures of environmental chemicals.