Genotoxic effects of a complex mixture adsorbed onto ambient air particles on human cells in vitro; the effects of Vitamins E and C

Oxidative Stress and Apoptosis in Benzo[a]pyrene-Induced Neural Tube Defects

Neural tube defects (NTDs) are among the most common and severe congenital malformations and result from incomplete closure of the neural tube during early development. Maternal exposure to polycyclic aromatic hydrocarbons (PAHs) has been suggested to be a risk factor for NTDs and previous studies imply that the mechanism underlying the association between PAH exposure and NTDs may involve oxidative stress and apoptosis. The objectives of this study were to investigate whether there is a direct effect of maternal benzo[α] pyrene (BaP) exposure on the closure of the neural tube in mice, and to examine the underlying mechanisms by combining animal experiments and human subject studies. We found that intraperitoneal injection of BaP from embryonic day 7 at a dose of 250 mg kg^-1 induced NTDs (13.3% frequency) in ICR mice. BaP exposure significantly increased expression of genes associated with oxidative stress, Cyp1a1, Sod1 and Sod2, while repressing Gpx1. Elevated apoptosis and higher protein expression of cleaved caspase-3 in the neuroepithelium of treated embryos were observed. Pre-treatment with vitamin E, added to food, significantly protected against BaP-induced NTDs (1.4% frequency) (P < 0.05). Vitamin E also partly normalized oxidative stress related gene expression and excess apoptosis in BaP-treated embryos. Examination of human neural tissues revealed that increased levels of protein carbonyl and apoptosis were related with maternal exposure to PAHs and the risk of NTDs. Collectively, these results suggest that BaP exposure could induce NTDs and that this may involve increased oxidative stress and apoptosis, while vitamin E may have a protective effect.

Genotoxic effect of a binary mixture of dicamba- and glyphosate-based commercial herbicide formulations on Rhinella arenarum (Hensel, 1867) (Anura, Bufonidae) late-stage larvae

The acute toxicity of two herbicide formulations, namely, the 57.71 % dicamba (DIC)-based Banvel(®) and the 48 % glyphosate (GLY)-based Credit(®), alone as well as the binary mixture of these herbicides was evaluated on late-stage Rhinella arenarum larvae (stage 36) exposed under laboratory conditions. Mortality was used as an endpoint for determining acute lethal effects, whereas the single-cell gel electrophoresis (SCGE) assay was employed as genotoxic endpoint to study sublethal effects. Lethality studies revealed LC5096 h values of 358.44 and 78.18 mg L(-1) DIC and GLY for Banvel(®) and Credit(®), respectively. SCGE assay revealed, after exposure for 96 h to either 5 and 10 % of the Banvel(®) LC5096 h concentration or 5 and 10 % of the Credit(®) LC5096 h concentration, an equal significant increase of the genetic damage index (GDI) regardless of the concentration of the herbicide assayed. The binary mixtures of 5 % Banvel(®) plus 5 % Credit(®) LC5096 h concentrations and 10 % Banvel(®) plus 10 % Credit(®) LC5096 h concentrations induced equivalent significant increases in the GDI in regard to GDI values from late-stage larvae exposed only to Banvel(®) or Credit(®). This study represents the first experimental evidence of acute lethal and sublethal effects exerted by DIC on the species, as well as the induction of primary DNA breaks by this herbicide in amphibians. Finally, a synergistic effect of the mixture of GLY and DIC on the induction of primary DNA breaks on circulating blood cells of R. arenarum late-stage larvae could be demonstrated.

A co-culture system of human intestinal Caco-2 cells and lymphoblastoid TK6 cells for investigating the genotoxicity of oral compounds

Here, we assessed a co-culture system of intestinal Caco-2 cells and lymphoblastoid TK6 cells for modelling the role of intestinal first-pass effects, i.e. absorption and metabolism, in the genotoxicity of oral drugs and food contaminants. Caco-2 cells were seeded onto semipermeable culture inserts for 21 days until differentiation, and then TK6 cells were added to the basal compartment. After apical loading with mutagenic compounds [methylmethanesulfonate (MMS), benzo[a]-pyrene (BaP) and aflatoxin B1 (AFB1)], comet and micronucleus assays were performed on both cell lines. MMS (10 µg/ml) showed positive results in the micronucleus assays in both cell lines, even though DNA damage was only detected in the Caco-2 cells with the comet assay. At concentrations of 0.5-50 µM, BaP induced dose-dependent comet and micronucleus formation at 24h in Caco-2 cells, but no DNA damage was observed in TK6 cells. Although AFB1 failed to induce comet formation, it resulted in a high level of micronuclei in both cell lines. Treatment of Caco-2 cells with the CYP3A4 inhibitor, ketoconazole, inhibited the AFB1-induced cytotoxicity and micronucleus formation in TK6 cells, suggesting that intestinal metabolism is involved in the AFB1 genotoxic response in TK6 cells. Our results suggest that the Caco-2/TK6 co-culture model is suitable for modelling the role of intestinal biotransformation and transport processes in the genotoxic potential of oral drugs and food contaminants in target blood cells.

Genotoxicity of 7H-dibenzo[c,g]carbazole and its methyl derivatives in human keratinocytes

Differences between tissues in the expression of drug-metabolizing enzymes may substantially contribute to tissue-specificity of chemical carcinogens. To verify this hypothesis, the spontaneously immortalized human keratinocytes HaCaT were used, in order to evaluate the genotoxic potential of 7H-dibenzo[c,g]carbazole (DBC), a known hepatocarcinogen and sarcomagen, and its synthetic tissue-specific derivatives, 5,9-dimethyl-DBC (DiMeDBC) and N-methyl-DBC (N-MeDBC), which manifest specific tropism to the liver and skin, respectively. HaCaT cells mainly express cytochrome P4501A1 (CYP1A1), which is involved in metabolism of DBC and N-MeDBC, but not DiMeDBC [10]. Both DBC and the sarcomagen N-MeDBC induced significant levels of DNA strand-breaks, micronuclei, and DNA adducts followed by the phosphorylation of the p53 protein and histone H2AX in HaCaT cells. In contrast, the specific hepatocarcinogen DiMeDBC was devoid of any significant genotoxic activity in this cell line. Our study demonstrates that the absence of drug-metabolizing enzyme(s) involved in DiMeDBC metabolism may contribute substantially to the tissue-specific genotoxicity of this hepatocarcinogen.

Genotoxicity of 7H-dibenzo[c,g]carbazole and its tissue-specific derivatives in human hepatoma HepG2 cells is related to CYP1A1/1A2 expression

The goal of this study was to investigate the genotoxicity of 7H-dibenzo[c,g]carbazole (DBC), a ubiquitous environmental pollutant, and its methyl derivatives, 5,9-dimethylDBC (DiMeDBC), a strict hepatocarcinogen, and N-methylDBC (N-MeDBC), a specific sarcomagen in human hepatoma HepG2 cells, and to infer potential mechanisms underlying the biological activity of particular carcinogen. All dibenzocarbazoles, regardless the tissue specificity, induced significant DNA strand break levels and micronuclei in HepG2 cells; though a mitotic spindle dysfunction rather than a chromosome breakage was implicated in N-MeDBC-mediated micronucleus formation. While DBC and N-MeDBC produced stable DNA adducts followed with p53 protein phosphorylation at Ser-15, DiMeDBC failed. A significant increase in DNA strand breaks following incubation of exposed cells with a repair-specific endonuclease (Fpg protein) suggested that either oxidative DNA damage or unstable DNA-adducts might underlie DiMeDBC genotoxicity in human hepatoma cells. DiMeDBC and N-MeDBC increased substantially also the amount of CYP1A1/2 expression in HepG2 cells. Pretreatment of cells with substances affecting AhR-mediated CYP1A family of enzymes expression; however, diminished DiMeDBC and N-MeDBC genotoxicity. Our data clearly demonstrated differences in the mechanisms involved in the biological activity of DiMeDBC and N-MeDBC in human hepatoma cells; the genotoxicity of these DBC derivatives is closely related to CYP1A1/2 expression.

Relative contribution of DNA strand breaks and DNA adducts to the genotoxicity of benzo[a]pyrene as a pure compound and in complex mixtures

Polycyclic aromatic hydrocarbons (PAH) produced upon incomplete combustion of organic matter are suspected to be carcinogenic to humans. In the present work, we especially studied the genotoxicity of benzo[a]pyrene (B[a]P), pure or in mixtures, with emphasis placed on the contribution of oxidative stress and alkylation. A comparison was made between the extent of DNA strand breaks as determined by the Comet assay and the number of DNA adducts to the diol epoxide metabolite of B[a]P measured by HPLC-mass spectrometry. HepG2 cultured human hepatocytes were treated with either pure B[a]P or particulate matter extracted from air samples collected in an urban peri-industrial site or in a metallurgic plant. Treatment with pure B[a]P did not induce increase in Comet measurements below a concentration of 1 microM whereas adducts were observed for concentrations as low as 0.025 microM. Very different results were obtained with environmental samples. Increase in the Comet score was observed with both urban and industrial mixtures containing 0.16 microM of B[a]P, especially for samples of urban origin. Comparison with the effect of the reconstituted PAH fraction of the mixtures allowed us to conclude that the induction of strand breaks results from the action of other components of the samples. In addition, a 30% potentialization and a 90% inhibition in the level of DNA adducts with respect to exposure to 0.16 microM pure B[a]P were observed for cells exposed to industrial and urban mixtures, respectively. These results contrast with the 6-fold enhancement in the yield of BPDE adducts in cells exposed to the reconstituted PAH fraction with respect to pure BaP. Altogether, our data emphasize that (i) a combination of analytical approaches is required to assess the genotoxicity of complex mixtures and (ii) risk assessment based on additivity consideration such as toxic equivalent factors may be misleading.

Protective effect of vitamin C towards N-nitrosamine-induced DNA damage in the single-cell gel electrophoresis (SCGE)/HepG2 assay

The aim of this study was to investigate the protective effect of vitamin C towards N-nitrosamine-induced DNA damage in the single-cell gel electrophoresis (SCGE)/HepG2 assay. None of the vitamin C concentrations tested (1-10 microM) in presence or absence of formamidopyrimidine-DNA glycosylase (Fpg enzyme) caused DNA damage per se. HepG2 cells simultaneously treated with vitamin C and N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), N-nitrosodibutylamine (NDBA) or N-nitrosopiperidine (NPIP) reduced the genotoxic effects of the N-nitrosamines in a dose-dependent manner. At concentrations of 1-5 microM vitamin C, the protective effect was higher towards NPYR-induced oxidative DNA damage (78-79%) than against NDMA (39-55%), NDBA (12-14%) and NPIP (3-55%), in presence of Fpg enzyme. However, a concentration of 10 microM vitamin C led to a maximum reduction in NDBA (94%), NPYR (81%), NPIP (80%) and NDMA (61%)-induced oxidative DNA damage, in presence of Fpg enzyme. The greatest protective effect of vitamin C (10 microM) was higher towards NDBA-induced oxidative DNA damage. One feasible mechanism by which vitamin C exerted its protective effect is that may interact with the enzyme systems catalyzing the metabolic activation of the N-nitrosamines, blocking the production of genotoxic intermediates. Vitamin C (10 microM) strongly reduced the coumarin hydroxylase (82%) activity. However, the p-nitrophenol hydroxylase and the ethoxyresorufine O-deethylation activities were slightly and weakly reduced (32-19%), respectively.

Complex mixtures that may contain mutagenic and/or genotoxic components: a need to assess in vivo target-site effect(s) associated with in vitro-positive(s)

A battery of short-term in vitro assays and/or in vivo protocols to evaluate single-agent mutagenicity and/or genotoxicity is available. However, a protocol to assess the effect(s) of complex mixtures in vivo following a positive test finding in vitro remains difficult. Complex interactions may occur in vivo because component pharmacokinetics increases the unpredictability of pharmacodynamic outcomes. The question arises as to whether in vitro mutagenic component(s) of a complex mixture, probably unidentified, reach target organ(s) in vivo at a sufficient concentration. To address the issue of an in vitro positive, standard in vivo chromosome damage assays to test both mixtures and fractions could be conducted but, to assess site-of-contact effects, the alkaline single cell-gel electrophoresis ("comet") assay or DNA reactivity (e.g., (32)P-postlabelling of DNA adducts) might be employed. A newer approach may be the derivation of a "biochemical-cell fingerprint" of potential target sites using infrared microspectroscopy. There is interest in platforms such as gene expression, proteomics, epigenomics or metabolomics as biomarkers of signature genotoxic or non-genotoxic mechanisms. One still needs to address whether a mutagenic and/or genotoxic component reaches a target organ. An approach to track levels of target-organ exposure may be to radio-label components with a short-lived positron-emitting radionuclide. The parent compound retains its physicochemical properties whilst allowing non-invasive in vivo tissue-specific imaging. However, determining target-organ concentration(s) and effect(s) in vivo remains a difficult challenge.

Genotoxicity of air borne particulates assessed by comet and the Salmonella mutagenicity test in Jeddah, Saudi Arabia

Fine airborne respirable particulates less than 10 micrometer (PM10) are considered one of the top environmental public health concerns, since they contain polycyclic aromatic hydrocarbons (PAHs) which are among the major carcinogenic compounds found in urban air. The objective of this study is to assess the genotoxicity of the ambient PM10 collected at 11 urban sites in Jeddah, Saudi Arabia. The PM10 extractable organic matter (EOM) was examined for its genotoxicity by the single cell gel electrophoresis (SCGE) comet assay and the Salmonella mutagenicity (Ames) test .Gas chromatography-mass spectrometry was used to quantify 16 PAH compounds in four sites. Samples from oil refinery and heavy diesel vehicles traffic sites showed significant DNA damage causing comet in 20-44% of the cells with tail moments ranging from 0.5-2.0 compared to samples from petrol driven cars and residential area, with comet in less than 2% of the cells and tail moments of < 0.02. In the Ames test, polluted sites showed indirect mutagenic response and caused 20-56 rev/ m3, mean while residential and reference sites caused 2-15 rev /m3. The genotoxicity of the EOM in both tests directly correlated with the amount of organic particulate and the PAHs concentrations in the air samples. The PAHs concentrations ranged between 0.83 ng/m3 in industrial and heavy diesel vehicles traffic sites to 0.18 ng /m3 in the residential area. Benzo(ghi)pyrene was the major PAH components and at one site it represented 65.4 % of the total PAHs. Samples of the oil refinery site were more genotoxic in the SCGE assay than samples from the heavy diesel vehicles traffic site, despite the fact that both sites contain almost similar amount of PAHs. The opposite was true for the mutagenicity in the Ames test. This could be due to the nature of the EOM in both sites. These findings confirm the genotoxic potency of the PM10 organic extracts to which urban populations are exposed.

Effects of organosulfurs, isothiocyanates and vitamin C towards hydrogen peroxide-induced oxidative DNA damage (strand breaks and oxidized purines/pyrimidines) in human hepatoma cells

The aim of this study was to evaluate the effects of organosulfurs, isothiocyanates and vitamin C towards hydrogen peroxide-induced DNA damage (DNA strand breaks and oxidized purines/pyrimidines) in human hepatoma cells (HepG2), using the Comet assay. Treatment with hydrogen peroxide (H(2)O(2)) increased the levels of DNA strand breaks and oxidized purine and pyrimidine bases, in a concentration and time dependent manner. Organosulfur compounds (OSCs) reduced DNA strand breaks induced by H(2)O(2). In addition, OSCs also decreased the levels of oxidized pyrimidines. However, none of the OSCs tested reduced the levels of oxidized purines. Isothiocyanates compounds (ITCs) and vitamin C showed protective effects towards H(2)O(2)-induced DNA strand breaks and oxidized purine and pyrimidine bases. The results indicate that removal of oxidized purine and pyrimidine bases by ITCs was more efficient than by OSCs and vitamin C. Our findings suggest that OSCs, ITCs and vitamin C could exert their protective effects towards H(2)O(2)-induced DNA strand breaks and oxidative DNA damage by the free radical-scavenging efficiency of these compounds.

Sensitivity of different endpoints for in vitro measurement of genotoxicity of extractable organic matter associated with ambient airborne particles (PM10)

Sensitivity and correlations among three endpoints were evaluated to assess the genotoxic potential of organic complex mixtures in vitro. This study was focused on DNA adduct formation, DNA single strand break induction and tumour suppressor p53 protein up-regulation produced by extractable organic matter (EOM) absorbed on respirable particulate matter PM(10) (particulate matter<10microm) collected in three European cities (Prague, Sofia, Kosice) during winter and summer period. To compare the sensitivity of particular endpoints for in vitro measurement of complex mixture genotoxicity, the metabolically competent human hepatoma cell line Hep G2 was treated with equivalent EOM concentration of 50microg/ml. Cell exposure to EOMs resulted in significant DNA adduct formation and DNA strand break induction, however, a lack of protein p53 up-regulation over the steady-state level was found. While the maximum of DNA strand breaks was determined after 2h cell exposure to EOMs, 24h treatment interval was optimal for DNA adduct determination. No substantial location- and season-related differences in EOM genotoxicity were detected using DNA strand break assessment. In agreement with these results no significant variation in DNA adduct levels were found in relation to the locality and season except for the monitoring site in Prague. The Prague EOM sample collected during summer period produced nearly three-fold lower DNA adduct level in comparison to the winter EOM sample. Comparable results were obtained when the ambient air genotoxicity, based on the concentration of carcinogenic PAHs in cubic meter of air (ng c-PAHs/m(3)), was elicited using either DNA adduct or strand break determination. In general, at least six-fold higher genotoxicity of the winter air in comparison to the summer air was estimated by each particular endpoint. Moreover, the genotoxic potential of winter air revealed by DNA adduct assessment and DNA strand break measurement increased in the same order: Kosice<<Prague<Sofia. Based on these data we suppose that two endpoints DNA breakage and DNA adduction are sensitive in vitro biomarkers for estimation of genotoxic activity of organic complex mixture associated with airborne particles. On the other hand, the measurement of protein p53 up-regulation manifested some limitations; therefore it cannot be used as a reliable endpoint for in vitro genotoxicity assessment.

The relationship between biomarkers of oxidative DNA damage, polycyclic aromatic hydrocarbon DNA adducts, antioxidant status and genetic susceptibility following exposure to environmental air pollution in humans

Polycyclic aromatic hydrocarbons (PAHs) appear to be significant contributors to the genotoxicity and carcinogenicity of air pollution present in the urban environment for humans. Populations exposed to environmental air pollution show increased levels of PAH DNA adducts and it has been postulated that another contributing cause of carcinogenicity by environmental air pollution may be the production of reactive oxygen species following oxidative stress leading to oxidative DNA damage. The antioxidant status as well as the genetic profile of an individual should in theory govern the amount of protection afforded against the deleterious effects associated with exposure to environmental air pollution. In this study we investigated the formation of total PAH (bulky) and B[a]P DNA adducts following exposure of individuals to environmental air pollution in three metropolitan cities and the effect on endogenously derived oxidative DNA damage. Furthermore, the influence of antioxidant status (vitamin levels) and genetic susceptibility of individuals with regard to DNA damage was also investigated. There was no significant correlation for individuals between the levels of vitamin A, vitamin E, vitamin C and folate with M(1)dG and 8-oxodG adducts as well as M(1)dG adducts with total PAH (bulky) or B[a]P DNA adducts. The interesting finding from this study was the significant negative correlation between the level of 8-oxodG adducts and the level of total PAH (bulky) and B[a]P DNA adducts implying that the repair of oxidative DNA damage may be enhanced. This correlation was most significant for those individuals that were non smokers or those unexposed to environmental air pollution. Furthermore the significant inverse correlation between 8-oxodG and B[a]P DNA adducts was confined to individuals carrying the wild type genotype for both the GSTM1 and the GSTT1 gene (separately and interacting). This effect was not observed for individuals carrying the null variant.

Effects of dietary intake of a fungal beta-D-glucan derivative on the level of DNA damage induced in primary rat hepatocytes by various carcinogens

Water-soluble derivative of chitin-glucan complex used in our study, carboxymethyl chitin-glucan (CM-CG), enables oral administration without harmful side-effects, which can occur upon parenteral administration of the insoluble fungal beta-D-glucans. The aim of this study was to determine in ex vivo experiments the effects of dietary CM-CG on the level of DNA lesions in primary rat hepatocytes induced by various indirectly acting carcinogens. Multiorgan carcinogen benzo[a]pyrene (BaP); two hepatocarcinogens, dimethyldibenzocarbazole (diMeDBC) and N-nitrosomorpholine (NMOR); as well as a complex mixture of organic compounds adsorbed on ambient air particles (TP-S) were used for this purpose. The amount of DNA lesions was assessed using the comet assay and the micronucleus test. In addition, the mitotic indexes and the frequencies of necrotic and apoptotic cells were evaluated as well. Our results showed that the diet enriched with CM-CG (200 mg/kg of body weight) during 21 days did not induce any negative effect on DNA nor did the mitotic indexes and the frequencies of necrotic and apoptotic cells differ statistically from the controls. On the other hand, the hepatocytes isolated from CM-CG fed animals were more resistant to the action of all genotoxins used in our study [BaP (5-20 microM), diMeDBC (0.2-2 microM), NMOR (3.4-10.2 mM), TP-S (5-20 microM)]. We can conclude that in addition to the known immunopotentiating activity of beta-D-glucans, they can efficiently inhibit the genotoxicity of carcinogens requiring metabolic activation in rat heptocytes.

Toxicological assessment of ambient and traffic-related particulate matter: a review of recent studies

Particulate air pollution (PM) is an important environmental health risk factor for many different diseases. This is indicated by numerous epidemiological studies on associations between PM exposure and occurrence of acute respiratory infections, lung cancer and chronic respiratory and cardiovascular diseases. The biological mechanisms behind these associations are not fully understood, but the results of in vitro toxicological research have shown that PM induces several types of adverse cellular effects, including cytotoxicity, mutagenicity, DNA damage and stimulation of proinflammatory cytokine production. Because traffic is an important source of PM emission, it seems obvious that traffic intensity has an important impact on both quantitative and qualitative aspects of ambient PM, including its chemical, physical and toxicological characteristics. In this review, the results are summarized of the most recent studies investigating physical and chemical characteristics of ambient and traffic-related PM in relation to its toxicological activity. This evaluation shows that, in general, the smaller PM size fractions (<PM(10)) have the highest toxicity, contain higher concentrations of extractable organic matter (comprising a wide spectrum of chemical substances), and possess a relatively high radical-generating capacity. Also, associations between chemical characteristics and PM toxicity tend to be stronger for the smaller PM size fractions. Most importantly, traffic intensity does not always explain local differences in PM toxicity, and these differences are not necessarily related to PM mass concentrations. This implies that PM regulatory strategies should take PM-size fractions smaller than PM(10) into account. Therefore, future research should aim at establishing the relationship between toxicity of these smaller fractions in relation to their specific sources.

Nature of DNA lesions induced in human hepatoma cells, human colonic cells and human embryonic lung fibroblasts by the antiretroviral drug 3'-azido-3'-deoxythymidine

This study tried to clarify the question if nuclear genotoxicity played a role in 3'-azido-3'-deoxythymidine (AZT) toxicity. We investigated cytotoxic and DNA-damaging effects of AZT on human hepatoma HepG2 and human colonic CaCo-2 cells as well as on human diploid lung fibroblasts HEL. The amount of induced DNA damage was measured by standard alkaline single cell gel electrophoresis (SCGE). The nature of induced DNA lesions was evaluated (1) by modified SCGE, which includes treatment of lysed cells with DNA repair enzymes Endo III and Fpg and enables to recognize oxidized bases of DNA, and (2) by SCGE processed in parallel at pH 13.0 (standard technique) and pH 12.1, which enables to recognize alkali labile DNA lesions and direct DNA strand breaks. Cytotoxicity of AZT was evaluated by the trypan blue exclusion technique. Our findings showed that 3-h treatment of cells with AZT decreased the viability of all cell lines studied. SCGE performed in the presence of DNA repair enzymes proved that AZT induced oxidative lesions to DNA in all cell types. In hepatoma HepG2 cells and embryonic lung fibroblasts HEL the majority of AZT-induced DNA strand breaks were pH-independent, i.e. they were identified at both pH values (12.1 and 13.0). These DNA lesions represented direct DNA breaks. In colonic Caco-2 cells DNA lesions were converted to DNA strand breaks particularly under strong alkaline conditions (pH>13.0), which is characteristic for alkali-labile sites of DNA. DNA strand break rejoining was investigated by the standard comet assay technique during 48 h of post-AZT-treatment in HepG2 and Caco-2 cells. The kinetics of DNA rejoining, considered an indicator of DNA repair, revealed that AZT-induced DNA breaks were repaired in both cell types slowly, though HepG2 cells seemed to be more repair proficient with respect to AZT-induced DNA lesions.

Long-term effects of a standardized complex mixture of urban dust particulate on the metabolic activation of carcinogenic polycyclic aromatic hydrocarbons in human cells in culture

Humans are exposed to complex mixtures of polycyclic aromatic hydrocarbons in the atmosphere. We examined the long term effects of a standard reference material (SRM) 1649a over time on the metabolic activation and DNA adduct formation by two carcinogenic PAHs, benzo[a]pyrene (BP) and dibenzo[a,l]pyrene (DBP) in the human mammary carcinoma derived cell line MCF-7. PAH-DNA adduct analysis, cytochrome P450 (CYP) enzyme activity, CYP1A1 and CYP1B1 protein expression were determined in cells treated with SRM 1649a alone or SRM 1649a with either BP or DBP for 24 to 120 h. Averaging over time, significantly higher levels of DNA adducts were observed in cells treated with BP or DBP alone than in co-treatments with SRM 1649a and BP or DBP. Ethoxyresorufin O-deethylase assay indicated a significant increase in activity in cells treated with BP alone and co-treated with SRM1649a in comparison to other treatment groups. Induction of CYP1A1 and CYP1B1 protein expression was observed by immunoblots in cells treated with BP alone or in co-treatments of SRM 1649a and BP or DBP. These data demonstrate the influence of the components of SRM 1649a in inhibiting the activation of BP or DBP by CYP enzymes in the formation of DNA adducts. It also suggests that the carcinogenic activity of PAH within a complex mixture may vary with composition and activation of the components present in the complex mixture.

Oxidative stress-induced DNA damage by particulate air pollution

Exposure to ambient air particulate matter (PM) is associated with pulmonary and cardiovascular diseases and cancer. The mechanisms of PM-induced health effects are believed to involve inflammation and oxidative stress. The oxidative stress mediated by PM may arise from direct generation of reactive oxygen species from the surface of particles, soluble compounds such as transition metals or organic compounds, altered function of mitochondria or NADPH-oxidase, and activation of inflammatory cells capable of generating ROS and reactive nitrogen species. Resulting oxidative DNA damage may be implicated in cancer risk and may serve as marker for oxidative stress relevant for other ailments caused by particulate air pollution. There is overwhelming evidence from animal experimental models, cell culture experiments, and cell free systems that exposure to diesel exhaust and diesel exhaust particles causes oxidative DNA damage. Similarly, various preparations of ambient air PM induce oxidative DNA damage in in vitro systems, whereas in vivo studies are scarce. Studies with various model/surrogate particle preparations, such as carbon black, suggest that the surface area is the most important determinant of effect for ultrafine particles (diameter less than 100 nm), whereas chemical composition may be more important for larger particles. The knowledge concerning mechanisms of action of PM has prompted the use of markers of oxidative stress and DNA damage for human biomonitoring in relation to ambient air. By means of personal monitoring and biomarkers a few studies have attempted to characterize individual exposure, explore mechanisms and identify significant sources to size fractions of ambient air PM with respect to relevant biological effects. In these studies guanine oxidation in DNA has been correlated with exposure to PM(2.5) and ultrafine particles outdoor and indoor. Oxidative stress-induced DNA damage appears to an important mechanism of action of urban particulate air pollution. Related biomarkers and personal monitoring may be useful tools for risk characterization.

Altered gene expression patterns in MCF-7 cells induced by the urban dust particulate complex mixture standard reference material 1649a

Human exposures to polycyclic aromatic hydrocarbon (PAH) occur in complex mixtures. Here, gene expression patterns were investigated using standard reference material (SRM) 1649a (urban dust). MCF-7 cells were exposed to SRM 1649a alone or SRM 1649a with either benzo[a]pyrene (BP) or dibenzo[a,l]pyrene (DBP) for 24 hours. Global analyses of the gene expression data revealed alterations of 41 RNA transcripts with at least 2-fold change (signal log ratio </= -1 or >/= 1) in response to SRM 1649a exposure. Increase in expression of cytochrome P450 (CYP) genes was observed in response to BP exposure (CYP1A1 and CYP1B1; signal log ratio of 4.7 and 2.5, respectively). An additive induction of CYP1A1 and CYP1B1 was observed with cotreatment of SRM 1649a and BP. On the contrary, no change in gene expression of CYP1A1 and CYP1B1 was observed when the cells were exposed to DBP. Furthermore, to study the effect of complex PAH mixtures on the metabolic activation of carcinogenic PAH to DNA-binding derivatives and to relate this with gene expression studies, PAH-DNA adduct formation was determined. SRM 1649a decreased the total level of BP-DNA adducts in comparison with BP alone. No significant difference in adduct levels was observed in response to either DBP alone or in combination with SRM 1649a. These results provide a transcriptional signature for chemical carcinogen exposure; in addition, they suggest a major factor in carcinogenic activity of PAH within complex mixtures is their ability to promote or inhibit the activation of carcinogenic PAH by the induction of CYP enzymes.

Benzo[a]pyrene, but Not 2,3,7,8-TCDD, Induces G2/M Cell Cycle Arrest, p21CIP1 and p53 Phosphorylation in Human Choriocarcinoma JEG-3 Cells: A Distinct Signaling Pathway

Maternal cigarette smoking is known to disrupt placental growth and function. The polyaromatic hydrocarbon benzo[a]pyrene (BaP) is a major toxicant in cigarette smoke that has been shown to alter placental cell function. This study compared the effects of the benzo[a]pyrene (BaP) with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the prototype ligand for the aryl hydrocarbon (Ah) receptor, on proliferation and cell cycle progression in the human trophoblastic JEG-3 cell line. BaP, but not TCDD, significantly inhibited proliferation in a dose-dependent manner characterized by G2/M cell cycle phase arrest. No evidence of apoptosis was detected following BaP or TCDD exposure. Immunocytochemistry and Western blot analysis showed that BaP induced expression of nuclear p21CIP1 protein, the major inhibitor of cyclin-dependent kinases. In contrast, CDK1 expression, the main G2 cyclin-dependent kinase, was significantly reduced by 50% with a shift in localization from the nucleus to cytoplasm. Although BaP had no effect on total cellular p53 levels, phosphorylation of p53 at serine 15 (p53 ser-15phos) was markedly increased. The presence of Wortmannin, an inhibitor of PI-3 kinases, decreased BaP-induced p53 ser-15phos, as did the presence of the antioxidant vitamin E. In addition, vitamin E suppressed BaP-induced G2/M arrest without altering the level of induced CYP1A1 protein. Thus, the anti-proliferative effect of BaP involves activation of a p53-dependent pathway involving cell cycle arrest at G2/M, providing evidence of oxidative stress and activation of a DNA damage response pathway in JEG-3 cells.

Genotoxicity of environmental air pollution in three European cities: Prague, Košice and Sofia

The genotoxic potential of extractable organic matter (EOM) associated with the respirable particulate matter (PM <10 microm) of atmospheric pollution has been determined in three European cities--Prague (Czech Republic, two monitoring sites, Libus and Smíchov), Kosice (Slovak Republic) and Sofia (Bulgaria) using the alkaline single-cell gel electrophoresis (the comet assay). The EOM samples were extracted by dichloromethane from ambient airborne particles collected daily (24 h intervals) during 3-month sampling periods in winter and summer seasons. The human metabolically competent cell line Hep G2 was used as a test system and benzo[a]pyrene (BaP), a known carcinogen, was applied as a positive control (internal standard) in each electrophoretic run. Two-hour exposure of Hep G2 cells to equivalent EOM concentrations ranging from 5 to 150 microg EOM/ml resulted in a linear dose-dependent increase of DNA migration (r > 0.9, P < 0.01). A less significant dose-response (r = 0.61) was only induced by the EOM sample from the locality Prague-Libus (PRG-LB) in the winter. Generally, a 1.5 to four-fold increase of DNA strand breaks over the background control level was determined in EOM-exposed cells. In order to compare the genotoxic potential of individual EOMs, a mathematical model was used to correct the 'real' data. No substantial location- or season-related differences were found in EOM genotoxicity (EOM microg/ml), except for the EOM sample from Sofia, collected in the summer. This EOM sample induced a nearly two-fold lower level of DNA damage in comparison with other EOMs. On the other hand, clear statistically significant location- and season-related differences (P < 0.001) in ambient air genotoxicity were determined when the EOM quantity per cubic meter of air (microg/m3) was taken into account. In that case, the genotoxicity of winter air pollution was six- to 10-fold higher in comparison with summer air. The air pollution genotoxicity in individual localities rose during the winter season in the order: PRG-LB < Kosice < Prague-Smíchov (PRG-SM) < Sofia, while during the summer season the highest ambient air genotoxicity was revealed in the locality Prague-Smíchov and approximately equal air pollution genotoxicity was determined among localities Prague-Libus, Kosice and Sofia (PRG-LB approximately Kosice approximately Sofia < PRG-SM). The greatest overall air pollution genotoxicity was determined in the locality Sofia during the winter season. In a time course study to evaluate the kinetics of DNA strand break rejoining it was shown that the level of DNA strand breaks in EOM-exposed cells has returned to near the background level within 24 h after the treatment.