Mass Spectrometry Analysis of DNA and Protein Adducts as Biomarkers in Human Exposure to Cigarette Smoking: Acrolein as an Example

Acrolein is a major component in cigarette smoke and a product of endogenous lipid peroxidation. It is difficult to distinguish human exposure to acrolein from exogenous sources versus endogenous causes, as components in cigarette smoke can stimulate lipid peroxidation in vivo. Therefore, analysis of acrolein-induced DNA and protein adducts by the highly accurate, sensitive, and specific mass spectrometry-based methods is vital to estimate the degree of damage by this IARC Group 2A carcinogen. This Perspective reviews the analyses of acrolein-induced DNA and protein adducts in humans by mass spectrometry focusing on samples accessible for biomonitoring, including DNA from leukocytes and oral cells and abundant proteins from blood, i.e., hemoglobin and serum albumin.

DNA adducts as link between in vitro and in vivo carcinogenicity - A case study with benzo[a]pyrene

To reduce the need for animal tests, in vitro assays are often used as alternative methods. To derive toxic doses for higher tier organisms from in vitro assay results, quantitative in vitro-in vivo extrapolation (qIVIVE) based on physiological-based toxicokinetic (PBTK) models is typically the preferred approach. Such PBTK models require many input parameters to address the route from dose to target site concentration. However, respective data is very often not available. Hence, our aim is to call attention to an alternative way to build a link between animal (in vivo) and cell-derived (in vitro) toxicity data. To this end, we selected the carcinogenic chemical benzo[a]pyrene (BaP) for our study. Our approach relates both in vitro assay and in vivo data to a main intermediate marker structure for carcinogenicity on the subcellular level - the BaP-DNA adduct BaP-7,8-dihydrodiol-9,10-epoxide-deoxyguanosine. Thus, BaP dose is directly linked to a measure of the toxicity-initiating event. We used Syrian hamster embryo (SHE) and Balb/c 3T3 cell transformation assay as in vitro data and compared these data to outcomes of in vivo carcinogenicity tests in rodents. In vitro and in vivo DNA adduct levels range within three orders of magnitude. Especially metabolic saturation at higher doses and interspecies variabilities are identified and critically discussed as possible sources of errors in our simplified approach. Finally, our study points out possible routes to overcome limitations of the envisaged approach in order to allow for a reliable qIVIVE in the future.

MP-SeNPs; A Promising Cytokines Suppressor in Benzo[a]pyrene-Induced Mammal Tissue Injury in Rats

<b>Background and Objective:</b> <i>Moringa peregrina</i> (family Moringaceae) is a common flowering plant found in the Arabian Peninsula, Horn of Africa and Southern Sinai, Egypt. The purpose of this study was to investigate the protective activity of MP-SeNPs against BaP-induced mammal tissue injury in rats. <b>Materials and Methods:</b> MP-SeNPs were prepared and characterized in terms of particle size and zeta potential. Furthermore, the IC<sub>50</sub> of MP-SeNPs against the Mcf7 breast carcinoma cell line and LD<sub>50</sub> was evaluated. Adult albino rats weighing approximately 187±10 g was used to assess the lung protective activity of MP-SeNPs (28.7 and 71.75 mg kg<sup>1</sup> b.wt.) against BaP-induced mammal tissue injury in rats. <b>Results:</b> The mean particle size of MP-SeNPs was 134.69±8.24 nm with negative zeta potential of +26.04 with the observed shapes of nano particle was spherical. Also, IC<sub>50</sub> of MP-SeNPs against Mcf7 breast carcinoma cell line = 89.57 μg mL<sup>1</sup> and LD<sub>50</sub> equals and 1435 mg kg<sup>1</sup> b.wt., respectively. The daily oral administration of MP-SeNPs at concentrations of 28.7 and 71.75 mg kg<sup>1</sup> b.wt. for 30 days to rats treated with BaP (20 mg kg<sup>1</sup> b.wt.) resulted in a significant improvement of IL-2, IL-6 and IL-10. Oral administration of MP-SeNPs, on the other hand, increased the levels of SOD, GPx, TNF-α, iNOs and GSH as well as decreased the level of MDA in mammal tissue of BaP-treated rats. Furthermore, MP-SeNPs almost normalized these effects in mammal tissue histoarchitecture and MRI examination. <b>Conclusion:</b> The biochemical, histological and MRI findings incurrent study demonstrated that MP-SeNPs have protective activity against BaP-induced mammal tissue injury in rats.

Urinary polycyclic aromatic hydrocarbon metabolites and mortality in the United States: A prospective analysis

Background

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic compounds associated with chronic disease in epidemiologic studies, though the contribution of PAH exposure on fatal outcomes in the U.S. is largely unknown.

Objectives

We investigated urinary hydroxylated PAH metabolites (OH-PAHs) with all-cause and cause-specific mortality in a representative sample of the U.S. population.

Methods

Study participants were ≥20 years old from the National Health and Nutrition Examination Survey 2001–2014. Concentrations (nmol/L) of eight OH-PAHs from four parent PAHs (naphthalene, fluorene, phenanthrene, pyrene) were measured in spot urine samples at examination. We identified all-cause, cancer-specific, and cardiovascular-specific deaths through 2015 using the National Death Index. We used Cox proportional hazards regression to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between ΣOH-PAHs and mortality endpoints. We assessed potential heterogeneity by age, gender, smoking status, poverty, and race/ethnicity. Additionally, we examined the overall mixture effect using quantile g-computation.

Results

In 9,739 eligible participants, there were 934 all-cause deaths, 159 cancer-specific deaths, and 108 cardiovascular-specific deaths (median 6.75 years follow-up). A log₁₀ increase in ΣOH-PAHs was associated with higher all-cause mortality (HR_adj = 1.39 [95%CI: 1.21, 1.61]), and possibly cancer-specific mortality (HR_adj = 1.15 [95%CI: 0.79, 1.69]), and cardiovascular-specific mortality (HR_adj = 1.49 [95%CI: 0.94, 2.33]). We observed substantial effect modification by age, smoking status, gender, and race/ethnicity across mortality endpoints. Risk of cardiovascular mortality was higher for non-Hispanic blacks and those in poverty, indicating potential disparities. Quantile g-computation joint associations for a simultaneous quartile increase in OH-PAHs were HR_adj = 1.15 [95%CI: 1.02, 1.31], HR_adj = 1.41 [95%CI: 1.05, 1.90], and HR_adj = 0.98 [95%CI: 0.66, 1.47] for all-cause, cancer-specific, and cardiovascular-specific mortalities, respectively.

Discussion

Our results support a role for total PAH exposure in all-cause and cause-specific mortality in the U.S. population.

Daytime Restricted Feeding Modifies the Temporal Expression of CYP1A1 and Attenuated Damage Induced by Benzo[a]pyrene in Rat Liver When Administered before CYP1A1 Acrophase

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that heterodimerizes with the AhR nuclear translocator (ARNT) to modulate CYP1A1 expression, a gene involved in the biotransformation of benzo[a]pyrene (BaP). The AhR pathway shows daily variations under the control of the circadian timing system. Daytime restricted feeding (DRF) entrains the expression of genes involved in the processing of nutrients and xenobiotics to food availability. Therefore, we evaluate if temporal AhR, ARNT, and CYP1A1 hepatic expression in rats are due to light/dark cycles or fasting/feeding cycles promoted by DRF. Our results show that AhR oscillates throughout the 24 h period in DRF and ad libitum feeding rats (ALF), showing maximum expression at the same time points. DRF modified the peak of ARNT expression at ZT5; meanwhile, ALF animals showed a peak of maximum expression at ZT17. An increased expression of CYP1A1 was linked to the meal time in both groups of animals. Although a high CYP1A1 expression has been previously associated with BaP genotoxicity, our results show that, compared with the ALF group, DRF attenuated the BaP-CYP1A1 induction potency, the liver DNA-BaP adducts, the liver concentration of unmetabolized BaP, and the blood aspartate aminotransferase and alanine aminotransferase activities when BaP is administered prior to the acrophase of CYP1A1 expression. These results demonstrate that DRF modifies the ARNT and CYP1A1 expression and protects from BaP toxicity.

Transcriptomic analysis reveals dose-dependent modes of action of benzo(a)pyrene in polar cod (Boreogadus saida)

Polar cod (Boreogadus saida) has been used as a model Arctic species for hazard assessment of environmental stressors such as polycyclic aromatic hydrocarbons (PAHs). However, most of the PAH studies using polar cod rely on targeted biomarker-based analysis thus may not adequately address the complexity of the toxic mechanisms of the stressors. The present study was performed to develop a broad-content transcriptomic platform for polar cod and apply it for understanding the toxic mechanisms of a model PAH, benzo(a)pyrene (BaP). Hepatic transcriptional analysis using a combination of high-density polar cod oligonucleotide microarray and quantitative real-time RT-PCR was conducted to characterize the stress responses in polar cod after 14d repeated dietary exposure to 0.4 (Low) and 20.3 μg/g fish/feeding (High) BaP doses. Bile metabolic analysis was performed to identify the storage of a key BaP hepatic biotransformation product, 3-hydroxybenzo(a)pyrene (3-OH-BaP). The results clearly showed that 3-OH-BaP was detected in the bile of polar cod after both Low and High BaP exposure. Dose-dependent hepatic stress responses were identified, with Low BaP suppressing genes involved in the defense mechanisms and High BaP inducing genes associated with these pathways. The results suggested that activation of the aryl hydrocarbon receptor signaling, induction of oxidative stress, DNA damage and apoptosis were the common modes of action (MoA) of BaP between polar cod or other vertebrates, whereas induction of protein degradation and disturbance of mitochondrial functions were proposed as novel MoAs. Furthermore, conceptual toxicity pathways were proposed for BaP-mediated effects in Arctic fish. The present study has for the first time reported a transcriptome-wide analysis using a polar cod-specific microarray and suggested novel MoAs of BaP. The analytical tools, bioinformatics solutions and mechanistic knowledge generated by this study may facilitate mechanistically-based hazard assessment of environmental stressors in the Arctic using this important fish as a model species.

Correlation between Glyoxal-Induced DNA Cross-Links and Hemoglobin Modifications in Human Blood Measured by Mass Spectrometry

Glyoxal is an oxoaldehyde generated from the degradation of glucose-protein conjugates and from lipid peroxidation in foods and in vivo, and it is also present in the environment (e.g., cigarette smoke). The major endogenous source of glyoxal is glucose autoxidation, and the glyoxal concentrations in plasma are higher in diabetic patients than in nondiabetics. Glyoxal reacts with biomolecules forming covalently modified DNA and protein adducts. We previously developed sensitive and specific assays based on nanoflow liquid chromatography-nanospray ionization tandem mass spectrometry (nanoLC-NSI/MS/MS) for quantification of DNA cross-linked adducts (dG-gx-dC and dG-gx-dA) and for hemoglobin adducts derived from glyoxal. In this study, we isolated and analyzed both leukocyte DNA and hemoglobin from the blood of diabetic patients and compared the adduct levels with those from nondiabetic subjects using the modified assays. The results indicated that the extents of glyoxal-induced hemoglobin modifications on α-Lys-11, α-Arg-92, β-Lys-17, and β-Lys-66 were statistically higher in diabetic patients than nondiabetics and they correlated with HbA1c significantly. Moreover, the levels of dG-gx-dC in leukocyte DNA correlated positively with the extents of globin modification at α-Lys-11 and β-Lys-17, while levels of dG-gx-dA correlated with those at α-Lys-11 and α-Arg-92 in nonsmoking subjects. Comparing the levels and the correlation coefficients of these hemoglobin and DNA adducts including or excluding smokers, it appears that smoking is not a major contributor to glyoxal-induced adduction of hemoglobin and leukocyte DNA. To the best of our knowledge, this is one of the few reports of positive correlation between DNA and protein adducts of the same compound (glyoxal) in the blood from the same subjects. Because of the high abundance of hemoglobin in blood, the results indicate that quantification of glyoxal-modified peptides in hemoglobin might serve as a dosimetry for glyoxal and a practical surrogate biomarker for assessing glyoxal-induced DNA damage and its prevention.

Modulation of CYP1A1 metabolism: From adverse health effects to chemoprevention and therapeutic options

The human cytochrome P450 (CYP) 1A1 gene encodes a monooxygenase that metabolizes multiple exogenous and endogenous substrates. CYP1A1 has become infamous for its oxidative metabolism of benzo[a]pyrene and related polycyclic aromatic hydrocarbons, converting these chemicals into very potent human carcinogens. CYP1A1 expression is mainly controlled by the aryl hydrocarbon receptor (AHR), a transcription factor whose activation is induced by binding of persistent organic pollutants, including polycyclic aromatic hydrocarbons and dioxins. Accordingly, induction of CYP1A1 expression and activity serves as a biomarker of AHR activation and associated xenobiotic metabolism as well as toxicity in diverse animal species and humans. Determination of CYP1A1 activity is integrated into modern toxicological concepts and testing guidelines, emphasizing the tremendous importance of this enzyme for risk assessment and regulation of chemicals. Further, CYP1A1 serves as a molecular target for chemoprevention of chemical carcinogenesis, although present literature is controversial on whether its inhibition or induction exerts beneficial effects. Regarding therapeutic applications, first anti-cancer prodrugs are available, which require a metabolic activation by CYP1A1, and thus enable a specific elimination of CYP1A1-positive tumors. However, the application range of these drugs may be limited due to the frequently observed downregulation of CYP1A1 in various human cancers, probably leading to a reduced metabolism of endogenous AHR ligands and a sustained activation of AHR and associated tumor-promoting responses. We here summarize the current knowledge on CYP1A1 as a key player in the metabolism of exogenous and endogenous substrates and as a promising target molecule for prevention and treatment of human malignancies.

Kinetics of Diol and Hydroxybenzo[a]pyrene Metabolites in Relation to DNA Adduct Formation and Gene Expression in Rats

Benzo[a]pyrene (BaP) is a human carcinogen, but there are no validated biomarkers of exposure and the relationship of carcinogenesis with early biological alterations is not fully documented. This study aimed at better documenting the toxicokinetics of diolBaP and hydroxyBaP metabolites as potential biomarkers of exposure to BaP in relation to DNA adduct formation and gene expression. Rats were intravenously (iv) injected with 40 μmol/kg BaP. BaP and several metabolites were measured in blood, tissues, and excreta collected at frequent intervals over 72 h posttreatment. BaP diol epoxide (BaPDE)-DNA adduct formation and gene expression were assessed in lungs. 3-HydroxyBaP (3-OHBaP) and 4,5-diolBaP were the most abundant measured metabolites, and differences in time courses were apparent between the two metabolites. Over the 0-72 h period, mean proportions of BaP dose recovered in urine as 3-OHBaP and 4,5-diolBaP (±SD) were 0.017 ± 0.003% and 0.1 ± 0.03%. Corresponding values in feces were 1.5 ± 0.5% and 0.42 ± 0.052%. BaPDE-DNA adducts were significantly increased in lungs and a correlation was observed with urinary 3-OHBaP and 4,5-diolBaP. Analysis of gene expression showed a modulation of expression of metabolic genes (Cyp1a1, Cyp1b1, Nqo1, Ahr) and oxidative stress and repair genes (Nrf2, Rad51). However, BaPDE adducts formation did not exhibit any significant correlation with expression of genes, except a negative correlation with Rad51 expression. Similarly, there was no significant correlation between urinary excretion of OHBaP and diolBaP and expression of genes, except for urinary 7-OHBaP excretion, which was negatively correlated with Rad51 expression. Results indicate that concomitant measurements of diolBaP and OHBaP may serve to better assess the extent of exposure as compared to single metabolite measurements, given kinetic differences between metabolites. Further, although some urinary metabolites were correlated with BaPDE adducts, links with gene expression need to be further investigated.

The anticancer drug ellipticine activated with cytochrome P450 mediates DNA damage determining its pharmacological efficiencies: studies with rats, Hepatic Cytochrome P450 Reductase Null (HRN™) mice and pure enzymes

Ellipticine is a DNA-damaging agent acting as a prodrug whose pharmacological efficiencies and genotoxic side effects are dictated by activation with cytochrome P450 (CYP). Over the last decade we have gained extensive experience in using pure enzymes and various animal models that helped to identify CYPs metabolizing ellipticine. In this review we focus on comparison between the in vitro and in vivo studies and show a necessity of both approaches to obtain valid information on CYP enzymes contributing to ellipticine metabolism. Discrepancies were found between the CYP enzymes activating ellipticine to 13-hydroxy- and 12-hydroxyellipticine generating covalent DNA adducts and those detoxifying this drug to 9-hydroxy- and 7-hydroellipticine in vitro and in vivo. In vivo, formation of ellipticine-DNA adducts is dependent not only on expression levels of CYP3A, catalyzing ellipticine activation in vitro, but also on those of CYP1A that oxidize ellipticine in vitro mainly to the detoxification products. The finding showing that cytochrome b5 alters the ratio of ellipticine metabolites generated by CYP1A1/2 and 3A4 explained this paradox. Whereas the detoxification of ellipticine by CYP1A and 3A is either decreased or not changed by cytochrome b5, activation leading to ellipticine-DNA adducts increased considerably. We show that (I) the pharmacological effects of ellipticine mediated by covalent ellipticine-derived DNA adducts are dictated by expression levels of CYP1A, 3A and cytochrome b5, and its own potency to induce these enzymes in tumor tissues, (II) animal models, where levels of CYPs are either knocked out or induced are appropriate to identify CYPs metabolizing ellipticine in vivo, and (III) extrapolation from in vitro data to the situation in vivo is not always possible, confirming the need for these animal models.

Tetrahydroxylated-benzo[a]pyrene isomer analysis after hydrolysis of DNA-adducts isolated from rat and human white blood cells

Since exposure to benzo[a]pyrene is suspected to be associated with several health issues, significant efforts have been made to develop efficient strategies for the assessment of human exposure to this ubiquitous compound. In this context, a method was developed for the analysis of four tetrahydroxylated-benzo[a]pyrene isomers resulting from the hydrolysis of their respective diol-epoxide precursors which are involved in DNA-adduct formation. The analytical sensitivity necessary to reach environmental levels of concentration was obtained by using gas chromatography-tandem mass spectrometry. The recovery determined at the four concentration levels were estimated in average at 83% for benzo[a]pyrene-r-7,t-8,t-9,c-10-tetrahydrotetrol(±), 29% for benzo[a]pyrene-r-7,t-8,t-9,t-10-tetrahydrotetrol(±), and 82% for benzo[a]pyrene-r-7,t-8,C-9,c-10-tetrahydrotetrol(±). The coefficient of determination of the calibration curve was above 0.997 for all the analytes investigated and the limit of quantification ranged from 0.5 to 2 adduct/10(8) nucleotides. The precision was between 5.3% and 22.3%. The suitability of the method was firstly evaluated by the analysis of DNA isolated from white blood cells of rats submitted after controlled exposure to benzo[a]pyrene. The four targeted tetra-OH-benzo[a]pyrenes as well as two unknown isomers were detected in all the treated animals. Benzo[a]pyrene-r-7,t-8,c-9,c-10-tetrahydrotetrol(±) appeared as the most abundant isomer in both treated and control animals followed by benzo[a]pyrene-r-7,t-8,t-9,c-10-tetrahydrotetrol(±). The method was afterwards applied to the analysis of DNA isolated from white blood cells of human volunteers. The results confirmed that this method was sufficiently sensitive to monitor environmental levels of exposure since all the specimens analyzed were above the limit of quantification for benzo[a]pyrene-r-7,t-8,t-9,c-10-tetrahydrotetrol(±) and two of them were positive for benzo[a]pyrene-r-7,t-8,c-9,c-10-tetrahydrotetrol(±), thereby highlighting interspecies differences in the nature of the tetrahydroxylated-benzo[a]pyrene isomers formed. This study confirms the necessity to focus on all the tetrahydroxylated-benzo[a]pyrene isomers, which could be indicators of benzo[a]pyrene-associated toxicity related to an individual's own metabolism, rather than limit to a single form.

Exposure of primary porcine urothelial cells to benzo(a)pyrene: in vitro uptake, intracellular concentration, and biological response

More than 90 % of all bladder cancers are transitional cell carcinomas arising from the cells lining the inside of the hollow organ (uroepithelium). Cell cultures from primary urinary bladder epithelial cells (PUBEC) of pigs were established to assess the uptake, intracellular concentration, and subcellular distribution of the environmental pollutant benzo(a)pyrene (BaP). During treatment of the cells with 0.5 μM BaP for up to 24 h, intracellular concentration of BaP increased without saturation but with marked differences between various PUBEC pools. Analysis of BaP uptake by laser scanning microscopy indicated that BaP is rapidly partitioned into the cell membrane, while only a slight but significant increase in BaP fluorescence intensity was observed in the cytosol and nucleus. Spectrofluorometric quantification of BaP in PUBEC using ex situ calibration revealed a strong accumulation of BaP, leading to intracellular concentrations ranging from 7.28 to 35.70 μM in cells exposed to 0.5 μM BaP and from 29.9 to 406.64 μM in cells exposed to 10 μM BaP. These results were confirmed by gas chromatographic mass spectrometric analysis. Apoptotic cell nuclei were assessed by TUNEL analysis to see whether BaP exposure at the given concentrations results in a toxic effect. While apoptotic cells were barely detectable in control epithelial cells, there was a marked elevation in apoptosis in the BaP-exposed cells. In conclusion, a comprehensive study on uptake and quantification of BaP in epithelial cells from pig bladder is reported for the first time. The study may be helpful in understanding the pattern of BaP uptake and distribution in bladder and its possible implication in bladder cancer development.

Evaluation of DNA adducts, DNA and RNA oxidative lesions, and 3-hydroxybenzo(a)pyrene as biomarkers of DNA damage in lung following intravenous injection of the parent compound in rats

Biomarkers of exposure and effect were assessed in 40 male Sprague-Dawley rats injected intravenously with 40 micromol/kg of benzo(a)pyrene (BaP) to determine which biomarkers are more representative of BaP-induced DNA damage in lung. Lung, liver, blood, and urine were collected at t = 2, 4, 8, 16, 24, 33, 48, 72, and 360 h postdosing. Specific BaP-diol epoxide (BPDE)-DNA adducts, 8-hydroxy-7,8-dihydro-2'-deoxyguanosine (8-OHdGuo), were measured in lung, liver, and mononucleated blood cells by high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS). Urinary 8-OHdGuo and 8-hydroxy-7,8-dihydroguanosine (8-OHGuo) were also determined by HPLC-MS/MS, and urinary 3-hydroxybenzo(a)pyrene was measured by HPLC/fluorescence. Between 2 and 72 h postdosing, BPDE-DNA adducts were significantly increased in lung, liver, and mononucleated blood cells of BaP-treated rats as compared to controls, with the highest levels found in lung. 8-OHdGuo levels also increased in lung of BaP-treated rats with values reaching statistical significance at 2, 8, and 16 h postinjection. No influence of BaP treatment was found on 8-OHdGuo and 8-OHGuo urinary excretions. BPDE-DNA adducts in lung were strongly correlated to urinary 3-OHBaP (r = 0.936 and p < 0.001) and to a lesser extent to blood BPDE-DNA adducts (r = 0.636 and p < 0.001), the latter of which were correlated to each other (r = 0.573 and p = 0.002). Urinary 3-OHBaP and BPDE-DNA adducts in mononucleated blood cells appear as relevant biomarkers of BaP genotoxic exposure and are highly promising for health risk assessment in humans.

Biotransformation of benzo[a]pyrene in Ahr knockout mice is dependent on time and route of exposure

Benzo[a]pyrene (BP) is an ubiquitous environmental pollutant with potent mutagenic and carcinogenic properties. The Ah receptor (Ahr) is important in the metabolic activation of BP and is therefore central to BP-induced carcinogenesis. Although Ahr(-/-) mice are refractory to BP-induced carcinogenesis, higher levels of BP-DNA and -protein adducts were formed in them than in wild-type mice. These results indicated the presence of an Ahr-independent and/or a slower biotransformation of BP in Ahr knockout mice. To address this issue further, we have now performed a time-course experiment, with mice receiving a single oral dose of BP (100 mg/kg). Wild-type mice have an effective clearance of BP metabolites, mainly through 3-hydroxybenzo[a]pyrene and 9-hydroxybenzo[a]pyrene in the feces with reduced levels of DNA and protein adducts in the examined tissues. On the other hand, the Ahr(-/-) mice appear to have a lower metabolic clearance of BP resulting in increased levels of DNA and protein adducts and of unmetabolized BP. In addition, we have performed an administration route experiment and found that skin-exposed Ahr(-/-) mice showed lower levels of protein adducts along with markedly reduced P450 1B1 expression, but only in the exposed area, as compared with the wild-type mice. In addition, the systemic uptake of BP is increased in the Ahr(-/-) mice as compared with the wild-type mice. Hence, the lack of a functional Ah receptor results in an Ahr-independent biotransformation of BP with a slower clearance of BP and higher levels of DNA and protein adducts, but the distribution and levels of BP and BP-protein adducts are clearly dependent on the route of exposure.

DNA adduct kinetics in reproductive tissues of DNA repair proficient and deficient male mice after oral exposure to benzo(a)pyrene

Benzo(a)pyrene (B[a]P) can induce somatic mutations, whereas its potential to induce germ cell mutations is unclear. There is circumstantial evidence that paternal exposure to B[a]P can result in germ cell mutations. Since DNA adducts are thought to be a prerequisite for B[a]P induced mutations, we studied DNA adduct kinetics by (32)P-postlabeling in sperm, testes and lung tissues of male mice after a single exposure to B[a]P (13 mg/kg bw, by gavage). To investigate DNA adduct formation at different stages of spermatogenesis, mice were sacrificed at Day 1, 4, 7, 10, 14, 21, 32, and 42 after exposure. In addition, DNA repair deficient (Xpc(-/-)) mice were used to study the contribution of nucleotide excision repair in DNA damage removal. DNA adducts were detectable with highest levels in lung followed by sperm and testis. Maximum adduct levels in the lung and testis were observed at Day 1 after exposure, while adduct levels in sperm reached maximum levels at approximately 1 week after exposure. Lung tissue and testis of Xpc(-/-) mice contained significantly higher DNA adduct levels compared to wild type (Wt) mice over the entire 42 day observation period (P < 0.05). Differences in adduct half-life between Xpc(-/-) and Wt mice were only observed in testis. In sperm, DNA adduct levels were significantly higher in Xpc(-/-) mice than in Wt mice only at Day 42 after exposure (P = 0.01). These results indicate that spermatogonia and testes are susceptible for the induction of DNA damage and rely on nucleotide excision repair for maintaining their genetic integrity.

Ovarian susceptibility to benzo[a]pyrene: tissue burden of metabolites and DNA adducts in F-344 rats

Exposure to environmental toxicants has been implicated as one of the causative factors for infertility in mammals. The objective of this study was to determine the amount of ingested benzo[a]pyrene (BaP), an environmental toxicant that reaches the reproductive tissues (internal dose) subsequent to a single acute exposure. Toward this end, the concentrations of BaP reactive metabolites and BaP-DNA adducts were measured throughout the course of BaP's residence in the body. Ten-week-old female Fischer-344 rats weighing approximately 220 g were administered 5 mg BaP/kg body weight orally. 1, 7, 14, 2,1 and 28 d post BaP exposure, BaP parent compound and metabolites from plasma, ovaries, and liver tissues were extracted using liquid-liquid extraction. The extracts were analyzed by reverse-phase highperformance liquid chromatography (HPLC). DNA was isolated and analyzed for BaP-induced DNA adducts by (32)P-postlabeling method. The BaP total metabolite concentrations in plasma, ovaries, and liver showed a gradual decrease from d 1 to 28 post BaP administration. The BaP-DNA adducts concentrations in ovaries and liver tissues from the treatment group demonstrated a trend similar to that observed for metabolites. Ovaries showed greater concentrations of DNA adducts compared to liver. However, with an increase in time post cessation of exposure, the adduct concentrations in liver tissue started declining rapidly, from d 1 to 28. For ovaries, the adduct concentrations demonstrated a significant decline from d 1 to 7 and a gradual fall thereafter. A concordance between BaP reactive metabolite levels and adduct concentrations indicates that the bioavailability of reactive metabolites determines the binding with DNA and consequently the formation and persistence of adducts in an acute exposure regimen.

Dietary factors, food contamination and lung cancer risk in Xuanwei, China

BACKGROUND

In rural Xuanwei County, China, the high incidence of lung cancer is attributable largely to burning smoky coal indoors for heating and cooking without adequate ventilation. Such burning generates very high levels of indoor air pollutants, including carcinogenic polycyclic aromatic hydrocarbons, which could contaminate foodstuffs in the home. Thus, residents could be exposed to carcinogenic coal emissions not only via inhalation but also via ingestion of these foodstuffs.

METHODS

A population-based case-control study of 498 lung cancer patients and 498 controls was conducted from 1985 through 1990 in Xuanwei. The interviewer-administered study questionnaire queried the frequency of food items commonly consumed in this region. Overall and sex-specific multiple logistic regression models were constructed to estimate Odds ratios (OR) and 95% confidence intervals (CI) for consumption of these foods.

RESULTS

Intake of rice, green vegetables, mushrooms and fresh meat was associated with an increased risk of lung cancer. In contrast, intake of corn, buckwheat, radishes, peppers, melons, pickled vegetables, and salt-preserved meats was associated with reduced risk. The detrimental effect of ingesting green vegetables (OR, 2.39; 95% CI, 1.28-4.48) is consistent with previous reports.

CONCLUSIONS

These findings suggest that in Xuanwei, food contamination by environmental polycyclic aromatic hydrocarbons may be an important risk factor for lung cancer, and that differential contamination of foods by polycyclic aromatic hydrocarbons possibly explained the different associations with lung cancer risk.

Genotoxicity of organic extracts of house dust from Shanxi, China

Indoor combustion of solid fuel such as coal may generate respirable particles containing polycyclic aromatic hydrocarbons (PAH) that may adhere to settled dust. Dust might therefore present a major source of PAH exposure in humans. This study evaluated the in vitro and in vivo genotoxicity of PAH mixtures extracted from house dust samples. Four dust samples (E1-4) were collected from houses in Shanxi, China, where coal is heavily used for heating and cooking. For comparison, a coal sample was also collected from one of the houses and included in the analyses. The samples were extracted with methylene chloride:acetone (95:5 v/v), dried, and redissolved in appropriate solvents for assessment in genotoxicity assays. Samples were evaluated for their ability to induce point mutations in bacteria and DNA adducts in vivo. DNA adduct levels were analyzed by nuclease P1-enhanced 32P-postlabeling. PAH were quantified using gas chromatography/mass spectrometry. Based on chemical analysis, sample E1 had the highest concentration by sampling area of benzo[a]pyrene (BaP) (181 microg/m2) and total PAH (10100 microg/m2). However, based on the microbial genotoxicity assay, sample E3, with the highest carcinogenic PAH/total PAH ratio (26%), produced the greatest number of revertants. In mice, administration of the extract of coal induced more adducts (9.81 adducts per 10(9) nucleotides) than dust extracts. The results of this study confirm the presence of genotoxic chemicals in residential dust. Inhalation of respirable particles containing similar mixtures of PAH represents a cancer risk for humans.

Single-walled carbon nanotubes: geno- and cytotoxic effects in lung fibroblast V79 cells

With the development of nanotechnology, there is a tremendous growth of the application of nanomaterials, which increases the risk of human exposure to these nanomaterials through inhalation, ingestion, and dermal penetration. Among different types of nanoparticles, single-walled carbon nanotubes (SWCNT) with extremely small size (1 nm in diameter) exhibit extraordinary properties and offer possibilities to create materials with astounding features. Since the release of nanoparticles in an enclosed environment is of great concern, a study of possible genotoxic effects is important. Our previous data showed that pharyngeal aspiration of SWCNT elicited pulmonary effects in C57BL/6 mice that was promoted by a robust, acute inflammatory reaction with early onset resulting in progressive interstitial fibrogenic response and the formation of granulomas. In the present study, the genotoxic potential of SWCNT was evaluated in vitro. The genotoxic effects of nanoparticles were examined using three different test systems: the comet assay and micronucleus (MN) test in a lung fibroblast (V79) cell line, and the Salmonella gene mutation assay in strains YG1024/YG1029. Cytotoxicity tests showed loss of viability in a concentration- and time-dependent manner after exposure of cells to SWCNT. Results from the comet assay demonstrated the induction of DNA damage after only 3 h of incubation with 96 microg/cm2 of SWCNT. The MN test indicated some but not significant micronucleus induction by SWCNT in the V79 cell line at the highest concentrations tested. With two different strains of Salmonella typhimurium, no mutations were found following SWCNT exposure.

Combustion-derived nanoparticles: mechanisms of pulmonary toxicity

1. The general term 'nanoparticle' (NP) is used to define any particle less than 100 nm in at least one dimension and NPs are generally classified as natural, anthropogenic or engineered in origin. Anthropogenic, also referred to as 'ultrafine' particles (UFPs), are predominately combustion derived and are characterized by having an equivalent spherical diameter less than 100 nm. 2. These particles, considered to be 'combustion-derived nanoparticles' (CDNPs), are of toxicological interest given their nanosized dimensions, with properties not displayed by their macroscopic counterparts. 3. The pulmonary deposition efficiency of inhaled UFPs, along with their large surface areas and bound transition metals, is considered important in driving the emerging health effects linked to respiratory toxicity. 4. The toxicology of CDNPs is currently used to predict the health outcomes in humans following exposure to manufactured NPs. Their similar physicochemistry would suggest similar adverse health effects (i.e. pulmonary (and perhaps cardiac) toxicity). As such, it is essential to fully understand CDNP nanotoxicology in order to minimize occupational and environmental exposure.

Impact of multiple genetic polymorphisms on effects of a 4-week blueberry juice intervention on ex vivo induced lymphocytic DNA damage in human volunteers

Consumption of fruits and vegetables has been associated with a decrease in cancer incidence and cardiovascular disease, presumably caused by antioxidants. We designed a human intervention study to assess antioxidative and possible anti-genotoxic properties of fruit-borne antioxidants. We hypothesized that individuals bearing genetic polymorphisms for genes related to quercetin metabolism, benzo[a]pyrene metabolism, oxidative stress and DNA repair differ in their response to DNA protective effects of increased antioxidant intake. In the present study, 168 healthy volunteers consumed a blueberry/apple juice that provided 97 mg quercetin and 16 mg ascorbic acid a day. After a 4-week intervention period, plasma concentrations of quercetin and ascorbic acid and trolox equivalent antioxidant capacity (TEAC) were significantly increased. Further, we found 20% protection (P < 0.01) against ex vivo H(2)O(2)-provoked oxidative DNA damage, measured by comet assay. However, the level of ex vivo induced benzo[a]pyrene-diol-epoxide (BPDE)-DNA adducts was 28% increased upon intervention (P < 0.01). Statistical analysis of 34 biologically relevant genetic polymorphisms revealed that six significantly influenced the outcome of the intervention. Lymphocytes from individuals bearing variant genotype for Cyp1B1 5 seemed to benefit more than wild-types from DNA damage-protecting effects upon intervention. Variants for COMT tended to benefit less or even experienced detrimental effects from intervention. With respect to GSTT1, the effect is ambiguous; variants respond better in terms of intervention-related increase in TEAC, but wild-types benefit more from its protecting effects against oxidative DNA damage. We conclude that genotyping for relevant polymorphisms enables selecting subgroups among the general population that benefit more of DNA damage-modulating effects of micronutrients.

Formation and persistence of DNA adducts of anticancer drug ellipticine in rats

Ellipticine is an antineoplastic agent, whose mode of antitumor and/or toxic side effects is based on DNA intercalation, inhibition of topoisomerase II and formation of DNA adducts mediated by cytochromes P450 and peroxidases. We investigated the formation and persistence of DNA adducts generated in rat, the animal model mimicking the bioactivation of ellipticine in human. Using (32)P-postlabeling, ellipticine-DNA adducts were found in liver, kidney, lung, spleen, heart and brain of female and male rats exposed to ellipticine (4, 40 and 80 mg/kg body weight, i.p.). The two major adducts were identical to the deoxyguanosine adducts generated in DNA by 13-hydroxy- and 12-hydroxyellipticine in vitro as confirmed by HPLC of the isolated adducts. At four post-treatment times (2 days, 2, 10 and 32 weeks) DNA adducts in rats treated with 80 mg/kg of ellipticine were analyzed in each tissue to study their long-term persistence. In all organs maximal adduct levels were found 2 days after administration. At all time points highest total adduct levels were in liver (402 adducts/10(8) nucleotides after 2 days and 3.6 adducts/10(8) nucleotides after 32 weeks), kidney and lung followed by spleen, heart and brain. Total adduct levels decreased over time to 0.8-8.3% of the initial levels till the latest time point and showed a biphasic profile, a rapid loss during the first 2 weeks was followed by a much slower decline till 32 weeks. These results, the first characterization of persistence of ellipticine-DNA adducts in vivo, are necessary to evaluate genotoxic side effects of ellipticine.

Damage effects of dust storm PM2.5 on DNA in alveolar macrophages and lung cells of rats

The aim of the present study was to investigate in vitro toxicological effects of PM2.5 suspensions, their water-soluble fraction and solvent-extractable organics from dust storm on the viability and DNA of rat alveolar macrophages and in vivo toxicological effects of PM2.5 suspensions on DNA of lung cells of rats. PM2.5 samples from dust storm and normal weather were collected in Baotou city, Inner Mongolia Autonomous Region, and Wuwei city, Gansu Province, China, in March, 2004. DNA damage was detected with single cell gel electrophoresis technique and cytotoxicity was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay. The results showed that: (1) In vitro, PM2.5 suspensions, their water-soluble fraction and solvent-extractable organics from both dust storm and normal weather caused a decrease of the cell viability and an increase of DNA damage of rat alveolar macrophages in a dose-response manner; for both Baotou city and Wuwei city, the samples of normal weather showed higher DNA damage than those of dust storm at the highest treated dosage; for both normal weather PM2.5 and dust storm PM2.5, their solvent-extractable organics showed higher DNA damage than the water-soluble fraction. (2) In vivo, PM2.5 from both dust storm and normal weather caused an increase of DNA damage of rat lung cells in a dose-response manner. (3) Baotou city is one of the heavy industrial cities, while Wuwei is one of agricultural cities in Northwest region of China. The effects induced by normal weather samples in Baotou city slightly higher than those in Wuwei city on DNA damage, though there was no significant difference was found between two cities. These results lead to conclusions that dust storm PM2.5 as well as normal weather PM2.5 could lead to DNA damage and the organic compounds and the insoluble particle-core might be the main contributors to DNA damage. Our results suggest that the risk of health effects may be greater during dust storms because dust storm PM2.5 whose airborne mass were much higher. Further studies are needed to determine the components of dust storm particles that may contribute to the particle toxicity.

Determinants of anti-benzo[a]pyrene diol epoxide-DNA adduct formation in lymphomonocytes of the general population

We evaluated determinants of anti-benzo[a]pyrenediolepoxide-(B[a]PDE)-DNA adduct formation (adduct induced by the ultimate carcinogenic metabolite of B[a]P) in lymphomonocytes of subjects environmentally exposed to low doses of polycyclic aromatic hydrocarbons (PAHs) (B[a]P). Our study population consisted of 585 Caucasian subjects, all municipal workers living in North-East Italy and recruited during their periodic check-ups after informed consent. PAH (B[a]P) exposure was assessed by questionnaire. Anti-B[a]PDE-DNA levels were measured by HPLC fluorescence analysis. We found that cigarette smoking (smokers (22%) versus non-smokers, p<0.0001), dietary intake of PAH-rich meals (> or =52 (38%) versus <52 times/year, p<0.0001), and outdoor exposure (> or =4 (19%) versus <4h/day; p=0.0115) significantly influenced adduct levels. Indoor exposure significantly increased the frequency of positive subjects (> or =0.5 adducts/10(8) nucleotides; chi(2) for linear trend, p=0.051). In linear multiple regression analysis the major determinants of increased DNA adduct levels (ln values) were smoking (t=6.362, p<0.0001) and diet (t=4.035, p<0.0001). In this statistical analysis, indoor and outdoor exposure like other factors of PAH exposure had no influence. In non-smokers, the influence of diet (p<0.0001) and high indoor exposure (p=0.016) on anti-B[a]PDE-DNA adduct formation became more evident, but not that of outdoor exposure, as was confirmed by linear multiple regression analysis (diet, t=3.997, p<0.0001 and high indoor exposure, t=2.522, p=0.012). This study indicates that anti-B[a]PDE-DNA adducts can be detected in the general population and are modulated by PAH (B[a]P) exposure not only with smoking - information already known from studies with limited number of subjects - but also with dietary habits and high indoor exposure. In non-smokers, these two factors are the principal determinants of DNA adduct formation. The information provided here seems to be important, since DNA adduct formation in surrogate tissue is an index of genotoxic exposure also in target organs (e.g., lung) and their increase may also be predictive of higher risk for PAH-related cancers.

Bulky DNA adducts as risk indicator of lung cancer in a Danish case-cohort study

Little is known of the predictive value of the levels of DNA adducts in terms of cancer risk. We examined the association between bulky DNA adducts and risk of lung cancer in a population-based cohort, comprising of 25,717 men and 27,972 women aged 50-64 years at entry. We included 245 cases (137 men and 108 women) with lung cancer and a comparison group of 255 individuals (137 men and 118 women), matched on sex, age and smoking duration. Bulky adducts in white blood cells collected at enrollment and stored at -150 degrees C were analyzed by (32)P-postlabeling method, using the butanol enrichment procedure. The median level of bulky DNA adducts was 0.196 adduct/10(8) nucleotides (5-95 percentiles: 0.094-0.595) among current smokers who were later diagnosed with lung cancer and 0.163 adduct/10(8) nucleotides (5-95 percentiles: 0.091-0.455) among current smokers in the comparison group. The smoking adjusted incidence rate ratios (IRR) for lung cancer in relation to one log unit (natural logarithm) difference in adduct levels were 1.22 (95% CI 0.85-1.74), 1.33 (95% CI 0.89-1.98) and 0.76 (95% CI 0.39-1.47) among all, current and former smokers, respectively. Current smokers with bulky DNA adduct levels above the median had a significant higher lung cancer rate than those with adduct levels below the median (IRR = 1.61; 95% CI 1.04-2.49). The results are compatible with previous studies, suggesting a slightly higher risk of lung cancer with higher levels of adducts among smokers. Our results indicate that bulky DNA adducts may have a weak association with lung cancer risk.

Combustion-derived nanoparticles: a review of their toxicology following inhalation exposure

This review considers the molecular toxicology of combustion-derived nanoparticles (CDNP) following inhalation exposure. CDNP originate from a number of sources and in this review we consider diesel soot, welding fume, carbon black and coal fly ash. A substantial literature demonstrates that these pose a hazard to the lungs through their potential to cause oxidative stress, inflammation and cancer; they also have the potential to redistribute to other organs following pulmonary deposition. These different CDNP show considerable heterogeneity in composition and solubility, meaning that oxidative stress may originate from different components depending on the particle under consideration. Key CDNP-associated properties of large surface area and the presence of metals and organics all have the potential to produce oxidative stress. CDNP may also exert genotoxic effects, depending on their composition. CDNP and their components also have the potential to translocate to the brain and also the blood, and thereby reach other targets such as the cardiovascular system, spleen and liver. CDNP therefore can be seen as a group of particulate toxins unified by a common mechanism of injury and properties of translocation which have the potential to mediate a range of adverse effects in the lungs and other organs and warrant further research.

DNA adduct formation by the environmental contaminant 3-nitrobenzanthrone after intratracheal instillation in rats

3-Nitrobenzanthrone (3-NBA) is an environmental pollutant and suspected human carcinogen found in emissions from diesel and gasoline engines and on the surface of ambient air particulate matter; human exposure to 3-NBA is likely to occur primarily via the respiratory tract. In our study female Sprague Dawley rats were treated by intratracheal instillation with a single dose of 0.2 or 2 mg/kg body weight of 3-NBA. Using the butanol enrichment version of the (32)P-postlabeling method, DNA adduct formation by 3-NBA 48 hr after intratracheal administration in different organs (lung, pancreas, kidney, urinary bladder, heart, small intestine and liver) and in blood was investigated. The same adduct pattern consisting of up to 5 DNA adduct spots was detected by thin layer chromatography in all tissues and blood and at both doses. Highest total adduct levels were found in lung and pancreas (350 +/- 139 and 620 +/- 370 adducts per 10(8) nucleotides for the high dose and 39 +/- 18 and 55 +/- 34 adducts per 10(8) nucleotides for the low dose, respectively) followed by kidney, urinary bladder, heart, small intestine and liver. Adduct levels were dose-dependent in all organs (approximately 10-fold difference between doses). It was demonstrated by high performance liquid chromatography (HPLC) that all 5 3-NBA-derived DNA adducts formed in rats after intratracheal instillation are identical to those formed by other routes of application and are, as previously shown, formed from reductive metabolites bound to purine bases. Although total adduct levels in the blood were much lower (41 +/- 27 and 9.5 +/- 1.9 adducts per 10(8) nucleotides for the high and low dose, respectively) than those found in the lung, they were related to dose and to the levels found in lung. These results show that uptake of 3-NBA by the lung induces high levels of specific DNA adducts in several organs of the rat and an identical adduct pattern in DNA from blood. Therefore, 3-NBA-DNA adducts present in the blood are useful biomarkers for exposure to 3-NBA and may help to assess the effective biological dose in humans exposed to it.

DNA adduct formation of benzo[a]pyrene in white blood cells of workers exposed to polycyclic aromatic hydrocarbons

The major DNA adducts of anti-benzo[a]pyrene diolepoxide (BPDE) were determined by high performance liquid chromatography with fluorescence detection (HPLC-FLD) in white blood cells (WBC) of workers exposed to benzo[a]pyrene (B[a]P). In addition, ambient concentrations of B[a]P at the workplace were determined by personal air sampling. Workers in a refractory setting were examined before (n=26) and 3 months after (n = 33) changing the production material (binding pitch). Furthermore, 9 coke oven workers were examined. The change in the production process in the refractory setting led to a decrease in the median of ambient B[a]P concentrations (0.14 to <0.07 microg/m3). The median of BPDE-DNA adduct levels in WBC also decreased from 0.9 adducts/10(8) nucleotides before changing the production material to <0.5 adducts/10(8) nucleotides 3 months afterwards. The B[a]P concentrations at the workplace for the coke oven workers were found to be significantly higher than in the refractory setting. However, BPDE-DNA adduct concentrations in coke oven workers and refractory setting workers showed no significant difference, which was probably due to the low number of studied subjects in the coke-oven setting. No significant differences could be observed for BPDE-DNA adduct levels between current smokers (n=21) and non-smokers (n=14; p = 0.93) from both plants. In addition, no correlation between B[a]P concentrations in the air and DNA adduct levels in refractory workers and in coke oven workers could be found (r = -0.03, p = 0.87). Because of the missing correlation between personal air sampling and BPDE-DNA adduct levels in WBC, the results may indicate that their formation is either influenced by other routes of exposure to B[a]P (e.g., skin absorption, dietary habits) or interindividual differences in their formation and repair.

Differential gene expression in human peripheral blood mononuclear cells induced by cigarette smoke and its constituents

In current molecular epidemiology studies, a wide range of methods are used to monitor early biological effects after exposure to xenobiotic agents. Gene expression profiling is considered a promising tool that may provide more sensitive, mechanism-based biomarkers. As a first step toward obtaining information on the applicability of gene expression profiles as a biomarker for early biological effects of carcinogen exposure, we conducted in vitro studies on human peripheral blood mononuclear cells (PBMC). We used cigarette smoke condensate (CSC) and a selection of its genotoxic constituents as model agents, applying cDNA microarray technology to investigate modulated gene expression. In independent experiments using cells from several donors, quiescent PBMC were exposed for 18 h, followed by gene expression analyses on a microarray containing 600 toxicologically relevant genes. The search for candidate biomarker genes was binomial: first we looked for genes responding similarly to all agents; second, for agent-specific genes. Many genes were significantly deregulated by all compounds, but as the direction of deregulation frequently differed per agent, they are not useful as generic biomarkers. Cigarette smoke condensate modulated the expression of many more genes than any of its constituents, with the largest effect in SERPINB2. The affected genes are involved in immune or stress responses, but surprisingly no genes involved in DNA damage response were modulated, and only a few in DNA repair. In conclusion, several genes have been identified as potential biomarkers for population studies on early biological effects caused by cigarette smoke exposure, but no genes were identified that represent a generic biomarker.

Protection by quercetin and quercetin-rich fruit juice against induction of oxidative DNA damage and formation of BPDE-DNA adducts in human lymphocytes

Flavonoids are claimed to protect against cardiovascular disease, certain forms of cancer and ageing, possibly by preventing initial DNA damage. Therefore, we investigated the protective effects of the flavonoid quercetin against the formation of oxidative DNA damage and bulky DNA adducts in human lymphocytes, both in vitro and ex vivo. First, human lymphocytes were pre-incubated with various concentrations of quercetin, followed by incubation with hydrogen peroxide; protection against oxidative DNA damage was evaluated by use of the single-cell gel electrophoresis (Comet) assay. Second, quercetin-treated human lymphocytes were challenged by treatment with benzo(a)pyrene (B(a)P), and BPDE-DNA adduct formation was measured by (32)P-postlabelling. Third, in a pilot study, lymphocytes from female volunteers who consumed a quercetin-rich blueberry/apple juice mixture for four weeks, were treated ex vivo with an effective dose of H(2)O(2) and benzo(a)pyrene, respectively, at three different time points, i.e. before (t=0 weeks), during (t=2 weeks) and after (t=4 weeks) the intervention. Results in vitro: a significant dose-dependent protection by quercetin against both the formation of oxidative DNA damage (p<0.01) and of BPDE-DNA adducts (p<0.05) was observed. Results in vivo: four weeks of juice intervention led to a significant increase in the total antioxidant capacity of plasma, as reflected by the increase of the TEAC value from 773 microM trolox equivalent at t=0 to 855 microM at t=4 weeks (p=0.04) and an increase in plasma quercetin content from 5.0 to 10.6 nM (p=0.03). After intervention, the level of oxidative damage upon ex vivo exposure to H(2)O(2) was non-significantly (p=0.07) decreased by 41%, and the BPDE-DNA adduct level induced ex vivo was non-significantly decreased by 11%. The combination of our findings in vitro and ex vivo provides evidence that quercetin is able to protect against chemically induced DNA damage in human lymphocytes, which may underlie its suggested anticarcinogenic properties.

Inflammatory and genotoxic effects of diesel particles in vitro and in vivo

Recent studies have identified an indirect genotoxicity pathway involving inflammation as one of the mechanisms underlying the carcinogenic effects of air pollution/diesel exhaust particles (DEP). We investigated the short-term effects of DEP on markers of inflammation and genotoxicity in vitro and in vivo. DEP induced an increase in the mRNA level of pro-inflammatory cytokines and a higher level of DNA strand breaks in the human lung epithelial cell line A549 in vitro. For the in vivo study, mice were exposed by inhalation to 20 or 80 mg/m3 DEP either as a single 90-min exposure or as four repeated 90-min exposures (5 or 20 mg/m3) and the effects in broncho-alveolar lavage (BAL) cells and/or lung tissue were characterized. Inhalation of DEP induced a dose-dependent inflammatory response with infiltration of macrophages and neutrophils and elevated gene expression of IL-6 in the lungs of mice. The inflammatory response was accompanied by DNA strand breaks in BAL cells and oxidative DNA damage and increased levels of bulky DNA adducts in lung tissue, the latter indicative of direct genotoxicity. The effect of a large single dose of DEP was more pronounced and sustained on IL-6 expression and oxidative DNA damage in the lung tissue than the effect of the same dose administered over four days, whereas the reverse pattern was seen in BAL cells. Our results suggest that the effects of DEP depend on the rate of delivery of the particle dose. The mutation frequency (MF), after DEP exposure, was determined using the transgenic Muta Mouse and a similar exposure regimen. No increase was observed in MF in lung tissue 28-days after exposure. In conclusion, short-term exposure to DEP resulted in DNA strand breaks in BAL cells, oxidative DNA damage and DNA adducts in lungs; and suggested that DNA damage in part is a consequence of inflammatory processes. The response was not associated with increased MF, indicating that the host defence mechanisms were sufficient to counteract the adverse effects of inflammation. Thus, there may be thresholds for the inflammation-associated genotoxic effects of DEP inhalation.

A critical evaluation of DNA adducts as biological markers for human exposure to polycyclic aromatic compounds

The causative role of polycyclic aromatic hydrocarbons (PAH) in human carcinogenesis is undisputed. Measurements of PAH-DNA adduct levels in easily accessible white blood cells therefore represent useful early endpoints in exposure intervention or chemoprevention studies. The successful applicability of DNA adducts as early endpoints depends on several criteria: i. adduct levels in easily accessible surrogate tissues should reflect adduct levels in target-tissues, ii. toxicokinetics and the temporal relevance should be properly defined. iii. sources of interand intra-individual variability must be known and controllable, and finally iv. adduct analyses must have advantages as compared to other markers of PAHexposure. In general, higher DNA adduct levels or a higher proportion of subjects with detectable DNA adduct levels were found in exposed individuals as compared with nonexposed subjects, but saturation may occur at high exposures. Furthermore, DNA adduct levels varied according to changes in exposure, for example smoking cessation resulted in lower DNA adduct levels and adduct levels paralleled seasonal variations of air-pollution. Intraindividual variation during continuous exposure was low over a short period of time (weeks), but varied significantly when longer time periods (months) were investigated. Inter-individual variation is currently only partly explained by genetic polymorphisms in genes involved in PAH-metabolism and deserves further investigation. DNA adduct measurements may have three advantages over traditional exposure assessment: i. they can smooth the extreme variability in exposure which is typical for environmental toxicants and may integrate exposure over a longer period of time. Therefore, DNA adduct assessment may reduce the monitoring effort. ii. biological monitoring of DNA adducts accounts for all exposure routes. iii. DNA adducts may account for inter-individual differences in uptake, elimination, distribution, metabolism and repair amongst exposed individuals. In conclusion, there is now a sufficiently large scientific basis to justify the application of DNA adduct measurements as biomarkers in exposure assessment and intervention studies. Their use in risk-assessment, however, requires further investigation.

Modified immunoenriched (32)P-HPLC assay for the detection of O(4)-ethylthymidine in human biomonitoring studies

Increased excretion of ethylated DNA bases has been reported in the urine of cigarette smokers. To study DNA ethylation in the target organs of smokers, an immunoenriched (32)P-postlabeling assay for O(4)-ethylthymidine (O(4)-etT) was developed. O(4)-etT-3'-monophosphate (O(4)-etT-3'P) was synthesized, purified, and characterized by LC-MS, ESI-MS, and NMR. DNA was enzymatically digested to 2'-deoxynucleoside-3'-monophosphate followed by immunoprecipitation of O(4)-etT-3'P using specific monoclonal antibodies. The immunoconjugate was washed by filtration, and O(4)-etT-3'P was recovered by ethanol treatment. The enriched O(4)-etT-3'P was labeled with [gamma-(32)P]ATP in the presence of T4-polynucleotide kinase at pH 6.8 to yield its 5'-labeled monophosphate and was subsequently resolved on RP-HPLC and detected with online detection of radioactivity. Adduct recovery was >80%, and the detection limit was approximately 500 amol. To further validate the method, O(4)-etT levels were determined in calf thymus DNA treated with N-ethyl-N-nitrosourea, and a dose-dependent formation of O(4)-etT was observed. Furthermore, O(4)-etT was found to be present in the cells obtained from the lower respiratory tract by sputum induction of two out of four smokers but not in three nonsmokers. O(4)-etT is a poorly repaired promutagenic DNA lesion; thus, it could be of potential use for biomonitoring smoking-related DNA damage. Our improved assay was found to be sufficiently sensitive and specific to detect O(4)-etT in surrogate cells from cigarette smoke exposed humans.

Metabolism, bioavailability, and toxicokinetics of benzo(alpha)pyrene in F-344 rats following oral administration

The objective of this study was to evaluate the bioavailability of Benzo(a)pyrene [B(a)p], subsequent to oral exposure. Eight-week-old F-344 rats were dosed orally with 100 mg/kg body weight B(a)p and sacrificed at 0, 0.5, 1.0, 2.0, 4.0. 8.0, 24, 48 and 72 hours post exposure. Blood, liver, reproductive tissues, urine and fecal samples were collected at necropsy and were analyzed for parent B(a)p and metabolites by HPLC with fluorescence detection. Peak levels of B(a)p in plasma occurred 8 hours after exposure (67%) followed by a gradual decrease. Liver retained 10% of the administered B(a)p up to 24 hours following, which the levels dropped during the remaining time periods studied. Twenty-four hours after administration, 45% of the dose was excreted in feces and urine. Metabolite levels in plasma peaked at 24 hours (10%) and decreased to 1% at 72 hours. In the liver, metabolite levels were higher at 8 hours (10%) but were only 3% at 72 hours. Benzo(a)pyrene levels increased after 24 hours in the reproductive organs and constituted 10% of the administered dose at 72 hours. Blood showed high levels of 7,8-diol than 9,10 and 4,5-diols which were high in liver and reproductive organs. Compared to diols, the hydroxy metabolites were detected at high levels in urine and fecal samples. Among the aqueous phase metabolites, glucuronides were at higher levels compared to glutathiones and sulfates. The slow release of unmetabolized B(a)p from reproductive organs and the presence of reactive metabolites in these organs is a matter of concern as they could interfere with gonadal steroid synthesis and release and its regulatory role in gamete production, maturation and function of male animals in a continuous exposure paradigm.