Genotoxicity of coke-oven and urban air particulate matter in in vitro acellular assays coupled with 32P-postlabeling and HPLC analysis of DNA adducts

Impact of Air Pollution on the Health of the Population in Parts of the Czech Republic

Thirty years ago, Northern Bohemia in the Czech Republic was one of the most air polluted areas in Europe. After political changes, the Czech government put forward a research program to determine if air pollution is really affecting human health. This program, later called the "Teplice Program", was initiated in collaboration with scientists from the United States Environmental Protection Agency (US EPA). This cooperation made possible the use of methods on the contemporary level. The very high concentrations of sulphur dioxide (SO2), particulate matter of 10 micrometers or less (PM10), and polycyclic aromatic hydrocarbons (PAHs) present in the air showed, for the first time, the impact of air pollutants on the health of the population in mining districts: adverse pregnancy outcomes, the impact of air pollution on sperm morphology, learning disabilities in children, and respiratory morbidity in preschool children. A surprising result came from the distribution of the sources of pollution: 70% of PM10 pollution came from local heating and not from power plants as expected. Thanks to this result, the Czech government supported changes in local heating from brown coal to natural gas. This change substantially decreased SO2 and PM10 pollution and affected mortality, especially cardiovascular mortality.

A novel use of neural network model to determine the effects of multibiomarker on early health damage among Chinese steel workers

Coke-oven workers are exposed to many kinds of pollutants that can cause health damage even lead to carcinogenesis. Therefore, it is critical to identify biomarkers that predict early health damage in these exposed individuals in molecular epidemiological studies. We applied an artificial neural network (ANN) model to the identification of such predictors in a study of coke-oven workers. The study included 330 steel-factory workers who were exposed to different levels of polycyclic aromatic hydrocarbons (PAHs) in the workplace and their levels of early health damage were determined by cytokinesis-block micronuclei (CMN), heat shock protein 70 (Hsp70) expression, benzo(a)pyrene diolepoxide-albumin adduct (BPDE-AA), and olive tail moment (OTM). The ANN model was built to predict the early health damage index, and the receiver operating characteristic (ROC) curve was used to illustrate the judged criteria and the ANN model. Trend Chi-square modeling was also performed. We found that there were 55 subjects with early health damage among 330 workers based on the multibiomarker criteria using the 95 percentile of the control group as the cut-off value, while there were 22-35 positive subjects if screening by any single biomarker. The Cochran-Armitage trend test for these findings were statistically significant (Z = 3.21, P = 0.0013). Six variables were selected to simulate the ANN model. The area under ROC (AUROC) was 0.726 ± 0.037 (P < 0.001), and the predictors included workplace, cholesterol, waistline, and others. Therefore, collective using CMN frequency, Hsp70 level, BPDE-AA level, and OTM with equal weights to make an initial screening test for early health damage in coke-oven workers is feasible and superior to any single biomarker. The determinants of the effects of multibiomarker on early health damage screening can be identified by the ANN model and ROC curve method.

Aryl hydrocarbon receptor and estrogen receptor ligand activity of organic extracts from road dust and diesel exhaust particulates

A wide variety of contaminants derived from diesel and gasoline engines, tire, asphalt, and natural organic compounds is found in road dust. Polycyclic aromatic compounds (PACs) are the important toxic targets among various contents in road dust and diesel exhaust particulates (DEPs), and endocrine-disrupting activity of PACs was suggested. In the present study, aryl hydrocarbon receptor (AhR) ligand activity was confirmed in the extract of both road dust and DEPs. In the separation of the extracts for both road dust and DEPs with reversed-phase HPLC, it was found that polar fractions contributed to significant AhR ligand activity in both a mouse hepatoma (H1L1) cell system and a yeast system. Furthermore, the contribution of these polar fractions was higher in DEPs than in road dust, probably because of the greater concentration of oxy-PAHs in DEPs than in road dust. The contribution of contaminants associated with the polar region to AhR ligand activity was also evident following the separation of road dust with normal-phase HPLC. Additionally, remarkable estrogen receptor (ER) ligand activity was detected in the highly polar region separated with normal-phase HPLC. It is suggested that many unknown AhR or ER ligand active compounds are contained in the polar region.

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.

Genotoxicity of airborne particulate matter: the role of cell-particle interaction and of substances with adduct-forming and oxidizing capacity

Exposure to particulate matter (PM) is associated with several health effects including lung cancer. However, the mechanisms of particle-induced carcinogenesis are not fully understood. The main aim of this study was to investigate the genotoxicity of PM in relation to particle-cell interactions and to study the effect of removal of DNA-damaging substances by extraction of PM with different solvents. Genotoxicity was analyzed by means of the comet assay after exposure of cultured human fibroblasts to urban dust particles (SRM 1649). It was found that PM induced DNA damage in a dose-dependent manner and that cells interacting with PM suffered more DNA single-strand breaks relative to other cells. The genotoxicity of PM was significantly reduced after extraction with dichloromethane (DCM), dimethyl sulfoxide (DMSO) and water, but not with acetone and hexane. However, the insoluble particle core still induced DNA single-strand breaks. The extracts were further investigated in cell-free systems. Analysis of aromatic DNA adducts with 32P-HPLC showed that the DMSO and DCM extracts contained most of the DNA-reactive polyaromatic compounds (PACs). Further, the formation of 8-oxo-2'-deoxyguanosine (8-oxodG) upon incubation of the extracts with 2'-deoxyguanosine (dG) showed that the water extract contained most of the oxidizing substances. Thus, the genotoxicity of PM was caused both by adduct-forming PACs and oxidizing substances as well as the insoluble particle-core. This study showed that all these factors together contribute to explaining the mechanisms of PM genotoxicity.

Oxidant mechanisms in response to ambient air particles

The toxic effects of air pollution are widely documented. In recent years, however, there has been an increasing interest in the study of the health effects of particulate matter (PM), a previously unexplored constituent of urban air pollution. Exposure to increased levels of PM of respirable size is strongly and consistently associated with increased cardiopulmonary morbidity and mortality. Conversely, improved air quality appears to correlate with decreased mortality. Particulate matter is a mixture of inorganic and organic components that vary in size, origin, and composition. The mechanisms of PM health effects are still poorly understood. However, studies in cellular and animal models suggest a variety of possible mechanisms including direct effects of particle components on the intracellular sources of reactive oxygen species (ROS), indirect effects due to pro-inflammatory mediators released from PM-stimulated macrophages, and neural stimulation after particle deposition in the lungs. The involvement of ROS in each one of these possible pathways is discussed.

DNA adduct formation by 7H-dibenzo[c,g]carbazole and its tissue- and organ-specific derivatives in Chinese hamster V79 cell lines stably expressing cytochrome P450 enzymes

The cytochrome P4501A subfamily (CYP1A) is involved in the metabolic activation of 7H-dibenzo[c,g]carbazole (DBC) and its tissue- and organ-specific derivatives, N-methyldibenzo[c,g]carbazole (MeDBC)and 5,9-dimethyldibenzo[c,g]carbazole (diMeDBC). In this study, we have evaluated the relationship between the tissue specificity and (32)P-postlabeled adduct patterns produced by these compounds by using a panel of Chinese hamster V79 cell lines stably expressing human CYP1A1 and CYP1A2 and/or N-acetyltransferase. Treatment of the parental cell lines V79MZ and V79NH, which are devoid of any CYP activity, with DBC and its derivatives did not result in detectable adducts. The highest DNA adduct levels were found in CYP1A1-expressing V79MZh1A1 cells after DBC and MeDBC treatment (24.5 +/- 7.2 and 16.2 +/- 3.6 adducts/10(8) nucleotides, respectively). Exposure of this cell line to DBC resulted in five distinct spots, while six spots with different chromatographic mobilities were detected in MeDBC-treated cells. DiMeDBC produced only very low levels of DNA adducts in V79MZh1A1 cells. DBC and MeDBC formed relatively low levels of DNA adducts in CYP1A2-expressing V79MZh1A2 cells (0.7 +/- 0.2 and 2.1 +/- 1.2 adducts/10(8) nucleotides, respectively). DBC formed three weak spots and MeDBC five spots in V79MZh1A2 cells, and all the spots had different chromatographic mobilities. In contrast, diMeDBC did not induce any DNA adducts in these cells, although diMeDBC induced a significant dose-dependent increase in micronucleus frequency under similar treatment conditions (r = 0.76; P < 0.001). The significant increase in DNA damage in the Comet assay following incubation of exposed cells with a repair-specific endonuclease (Fpg protein) suggests that base modifications such as 8-oxodG or Fapy-adducts might be responsible for the genotoxicity of diMeDBC in V79MZh1A2 cells. The similarities between the DNA adduct patterns produced by DBC and MeDBC in V79MZh1A1 and V79MZh1A2 cells suggest that biotransformation mediated via CYP1A1 and CYP1A2 might depend on a PAH-type pathway involving the aromatic ring system.

Biological activities of organic compounds adsorbed onto ambient air particles: comparison between the cities of Teplice and Prague during the summer and winter seasons 2000-2001

The capital of the Czech Republic, Prague, appears today to be one of the most polluted residential areas in the country, whereas air pollution in the Northern Bohemia region (the former "Black Triangle Region") has substantially decreased during the last decade, especially with respect to the gaseous pollutant SO(2). This study evaluated the biological activities of complex mixtures of organic compounds adsorbed onto ambient air particles (PM10) collected during the summer and winter seasons of 2000-2001 at three monitoring sites--Teplice (TP), Prague-Smíchov (PRG-SM) (city centre) and Prague-Libus (PRG-LB) (suburban area). The following short-term in vitro assays with strikingly different endpoints were used: a bacterial mutagenicity test using the Salmonella typhimurium tester strain TA98 and YG1041, an acellular assay (CT DNA) combined with 32P-postlabelling to evaluate DNA adduct-forming potency and the chick embryotoxicity screening test (CHEST). The results of the mutagenicity test with the YG1041 strain, the acellular genotoxicity (DNA adducts) and the embryotoxicity tests responded to the amount of eight carcinogenic polycyclic aromatic hydrocarbons (PAHs) analysed in the EOM (dichloromethane extractable organic matter) samples tested. Nevertheless, the biological effects of the EOM did not differ between locations. The highest biological activity of the ambient air in terms of organic compounds associated with particles (per unit volume of air) was seen in the Prague city centre during both summer and winter seasons. At this location, B[a]P concentration ranged from 0.1 to 8.9 ng/m(3) (mean 0.3 and 3.6 ng/m(3) for summer and winter seasons, respectively), 13 PAHs ranged from 11 to 343 ng/m(3) (mean 52 and 160 ng/m(3) for summer and winter seasons, respectively). Generally, using in vitro tests, higher ambient air activity was found in the winter season as compared with the summer season at all three monitoring sites (TA98 +S9, approximately 4-fold; YG1041 -S9, approximately 5-fold; YG1041 +S9, approximately 8-fold; CT DNA +S9, approximately 10-fold; CHEST, approximately 10-fold; B[a]P, carcinogenic PAHs and total PAHs analysed, more than 10-fold). The different proportions of individual PAHs found in the summer and winter samples suggested traffic as a major emission source in the summer and, additionally, residential heating in the winter season at all three monitoring sites. The DNA adduct patterns resulting from the in vitro acellular assay also demonstrated similar major emission sources at all three locations. The study shows that particle-bound carcinogenic-PAH concentrations may be taken as an index for the biologically active (mutagenic, genotoxic, embryotoxic) components in air particulate samples. Therefore, high-quality monitoring data of carcinogenic PAHs may be useful for epidemiological studies of the impact of air pollution on the health of the population and for helping decision makers to improve our environment.

DNA-adducts and atherosclerosis: a study of accidental and sudden death males in the Czech Republic

Atherosclerosis and carcinogenesis may share some common mechanisms of the genotoxic action of exogenous compounds, such as polycyclic aromatic hydrocarbons (PAHs). The main objective of this study was to test the hypothesis that "bulky" aromatic DNA-adducts in smooth muscle cells (SMCs) of thoracic aortas taken at autopsy from sudden and accidental death male subjects, aged between 30 and 60 years (N=133), are associated with the stage of atherosclerosis. The subjects with severe atherosclerotic damage were treated as "Cases" (N=66). The subjects meeting diagnostic criteria for slight and moderate total atherosclerotic body damage were treated as "Controls" (N=67). An additional objective of the study was to evaluate the effect of known atherogenic risk factors and possible modifiers of atherosclerotic changes, such as age, smoking, plasma lipid and antioxidant vitamin levels and some genetic susceptibility markers, e.g. polymorphisms of GSTM1, GSTT1, NAT2, CYP1A1 or apolipoprotein E (APO E) genes. We found significantly higher DNA-adduct levels in "Cases" as compared with "Controls" (2.11+/-1.07 adducts/10(8) nucleotides versus 1.49+/-0.55 adducts/10(8) nucleotides, P<0.001). "Cases" were significantly older and had elevated heart weight and plasma cholesterol levels and a higher frequency of overweight subjects as compared with "Controls". No significant differences in DNA-adduct levels between smokers and non-smokers within either group were detected. Multivariate logistic regression revealed that the "bulky" aromatic DNA-adducts, which are the most likely related to environmental exposure to genotoxic chemicals, remain a statistically significant predictor of the stage of atherosclerosis (OR=3.76, 95% CI=1.54-9.18, P=0.004) even after adjustment for age, smoking, obesity, heart weight and genetic susceptibility markers (GSTT1 and CYP1A1-MspI polymorphisms) that were also significant predictors. The fact that the "bulky" aromatic DNA-adduct levels predict the progression of atherosclerosis independently of smoking indicates that the formation of atherosclerotic plaques may also be initiated by environmental exposures other than tobacco smoke.

The effect of dibenzo[a,1]pyrene and benzo[a]pyrene on human diploid lung fibroblasts: the induction of DNA adducts, expression of p53 and p21(WAF1) proteins and cell cycle distribution

Polycyclic aromatic hydrocarbons (PAHs) present in ambient air are considered as potential human carcinogens, but the detailed mechanism of action is still unknown. Our aim was to study the in vitro effect of exposure to dibenzo[a,l]pyrene (DB[a,l]P), the most potent carcinogenic PAH ever tested, and benzo[a]pyrene (B[a]P) in a normal human diploid lung fibroblast cells (HEL) using multiple endpoints. DNA adduct levels were measured by 32P-postlabelling, the expression of p53 and p21(WAF1) proteins by western blotting and the cell cycle distribution by flow cytometry. For both PAHs, the DNA adduct formation was proportional to the time of exposure and dependent on the stage of cell growth in culture. DNA binding was detectable even at the lowest concentration used (24h exposure, 0.01 microM for both PAHs). The highest DNA adduct levels were observed after 24h of exposure in near-confluent cells (>90% of cells at G0/G1 phase), but DNA damage induced by DB[a,l]P was approximately 8-10 times higher at a concentration one order of magnitude lower as compared with B[a]P (for B[a]P at 1 microM and for DB[a,l]P at 0.1 microM: 237+/-107 and 2360+/-798 adducts/10(8) nucleotides, respectively). The induction of p53 and p21(WAF1) protein occurred subsequent to the induction of DNA adducts. The DNA adduct levels correlated with both p53 (R=0.832, P<0.001 and R=0.859, P<0.001, for DB[a,l]P and B[a]P, respectively) and p21(WAF1) levels (R=0.808, P<0.001 and R=0.797, P=0.001, for DB[a,l]P and B[a]P, respectively), regardless of the PAH exposure and the phase of cell growth. The results showed that a detectable increase of p53 and p21(WAF1) proteins (> or = 1.5-fold as compared with controls) requires a minimal DNA adduct level of approximately 200-250 adducts/10(8) nucleotides for both PAHs tested and suggest that the level of adducts rather than their structure triggers the p53 and p21(WAF1) responses. The cell cycle was altered after 12-16h of treatment, and after 24h of exposure to 0.1 microM DB[a,l]P in growing cells, there was approximately 24% increase in S phase cells accompanied by a decrease in G1 and G2/mitosis (G2/M) cells. Cell treatment with 1.0 microM B[a]P resulted in more subtle alterations. We conclude that DB[a,l]P, and to a lesser degree B[a]P, are able to induce DNA adducts as well as p53 and p21(WAF1) without eliciting G1 or G2/M arrests but rather an S phase delay/arrest. Whether the S phase delay observed in our study is beneficial for the survival of the cells remains to be further established.

Genotoxicity of urban air pollutants in the Czech Republic. Part I. Bacterial mutagenic potencies of organic compounds adsorbed on PM10 particulates

As part of a long-term program to investigate the impact of air pollution on the health of a population in a polluted region in Northern Bohemia, mutagenicity of extractable organic matter (EOM) from air particles PM10 was investigated by the means of Salmonella typhimurium indicator strains TA98 and YG1041 using the Ames plate incorporation assay. The air samples were collected in both the polluted and the control districts during the summers and winters of 1993-1994. In the polluted district, the collection was repeated during the winter of 1996-1997. The crude extracts from filters pooled according to the locality and the season were fractionated by acid-base partitioning into acid, base, and neutral fractions. The neutral fractions were further fractionated by silica gel column chromatography into five subfractions. The induction of revertants with the crude extracts was higher in winter samples than in summer samples. Both indirect-acting and direct-acting mutagenicity were observed. The indirect mutagenic potency of aromatic subfractions containing polycyclic aromatic hydrocarbons (PAHs) was generally low. The mutagenic potency detected with TA98 was more distinct only in the winter sample 1993-1994 from the polluted area, where the aromatic subfraction accounted for 23% of total mutagenicity. In both strains, the highest direct-acting mutagenicity was found in slightly polar fractions containing nitro-PAHs. The mutagenic potency detected with YG1041 was about two orders of magnitude higher than that detected with TA98. No substantial locational- or time-related variances in the mutagenic potencies of EOM, or in the spectrum of chemical components identified in individual fractions were found. The polluted district, in comparison to the control district, was found to have higher amounts of EOM, carcinogenic PAHs and mutagenicity of air particles (rev/m(3)). The fractionating process, combined with the bacterial mutagenicity test, confirmed that nitro-derivatives are the most important contributors to the bacterial mutagenicity of air particles. However, this study did not fulfill the expectancy to bring substantially new, clear-cut information on the composition and the biological activity of air pollution in both districts.

Genotoxicity and embryotoxicity of urban air particulate matter collected during winter and summer period in two different districts of the Czech Republic

This study is the in vitro part of a long-term program to investigate the impact of air pollution on the health of a population in a polluted region of Northern Bohemia. In order to assess the possible health risks associated with a complex mixture of hundreds of organic compounds adsorbed to air particles, we used a biomarker-directed fractionation procedure to evaluate biological activities of different chemical compound classes. The extractable organic compounds from the air particles collected in both the polluted and the control districts during the summers and winters of 1993-1994 were investigated. The principal aim of this study was to compare the DNA binding activities of those compound classes using an in vitro acellular assay coupled with 32P-postlabeling and an embryotoxicity assay using Chick Embryotoxicity Screening Test (CHEST). In both assays, the highest activity was due to the neutral fractions from which the aromatic subfractions containing mainly polycyclic aromatic hydrocarbons (PAHs) and their methyl-derivates were the most active for both localities and seasons. A good correlation between the levels of DNA adduct formation using S9 metabolic activation and the ED50 for all different complex mixtures of organic compounds was observed (r=0.773, p<0.001). DNA adduct maps and high performance liquid chromatography (HPLC) profiles were similar for samples from both districts and seasons. The major DNA adducts resulting from the crude extracts were identical to those derived from aromatic fractions. The DNA adducts tentatively identified constituted about 50% of the total adducts formed by the crude extracts following S9-metabolic activation. Our results confirmed the similarities of the major ubiquitous emission sources of organic compounds in both districts. This is the first report in which the biological activities of complex mixtures in short-term assays with remarkably different endpoints such as DNA adduct formation and embryotoxicity have been compared.