Benzo[a]pyrene diol-epoxide DNA adducts and levels of polycyclic aromatic hydrocarbons in autoptic samples from human lungs

Deciphering the dynamic code: DNA recognition by transcription factors in the ever-changing genome

Transcription factors (TFs) intricately navigate the vast genomic landscape to locate and bind specific DNA sequences for the regulation of gene expression programs. These interactions occur within a dynamic cellular environment, where both DNA and TF proteins experience continual chemical and structural perturbations, including epigenetic modifications, DNA damage, mechanical stress, and post-translational modifications (PTMs). While many of these factors impact TF-DNA binding interactions, understanding their effects remains challenging and incomplete. This review explores the existing literature on these dynamic changes and their potential impact on TF-DNA interactions.

Impact of phenanthrene co-administration on the toxicokinetics of benzo[a]pyrene in humans. UPLC-accelerator mass spectrometry following oral microdosing

Current risk assessments for environmental carcinogens rely on animal studies utilizing doses orders of magnitude higher than actual human exposures. Epidemiological studies of people with high exposures (e.g., occupational) are of value, but rely on uncertain exposure data. In addition, exposures are typically not to a single chemical but to mixtures, such as polycyclic aromatic hydrocarbons (PAHs). The extremely high sensitivity of accelerator mass spectrometry (AMS) allows for dosing humans with known carcinogens with de minimus risk. In this study UPLC-AMS was used to assess the toxicokinetics of [14C]-benzo[a]pyrene ([14C]-BaP) when dosed alone or in a binary mixture with phenanthrene (Phe). Plasma was collected for 48 h following a dose of [14C]-BaP (50 ng, 5.4 nCi) or the same dose of [14C]-BaP plus Phe (1250 ng). Following the binary mixture, Cmax of [14C]-BaP significantly decreased (4.4-fold) whereas the volume of distribution (Vd) increased (2-fold). Further, the toxicokinetics of twelve [14C]-BaP metabolites provided evidence of little change in the metabolite profile of [14C]-BaP and the pattern was overall reduction consistent with reduced absorption (decrease in Cmax). Although Phe was shown to be a competitive inhibitor of the major hepatic cytochrome P-450 (CYP) responsible for metabolism of [14C]-BaP, CYP1A2, the high inhibition constant (Ki) and lack of any increase in unmetabolized [14C]-BaP in plasma makes this mechanism unlikely to be responsible. Rather, co-administration of Phe reduces the absorption of [14C]-BaP through a mechanism yet to be determined. This is the first study to provide evidence that, at actual environmental levels of exposure, the toxicokinetics of [14C]-BaP in humans is markedly altered by the presence of a second PAH, Phe, a common component of environmental PAH mixtures.

Benzo[a]pyrene (BaP) metabolites predominant in human plasma following escalating oral micro-dosing with [14C]-BaP

Benzo[a]pyrene (BaP) is formed by incomplete combustion of organic materials (petroleum, coal, tobacco, etc.). BaP is designated by the International Agency for Research on Cancer as a group 1 known human carcinogen; a classification supported by numerous studies in preclinical models and epidemiology studies of exposed populations. Risk assessment relies on toxicokinetic and cancer studies in rodents at doses 5-6 orders of magnitude greater than average human uptake. Using a dose-response design at environmentally relevant concentrations, this study follows uptake, metabolism, and elimination of [¹⁴C]-BaP in human plasma by employing UPLC - accelerator mass spectrometry (UPLC-AMS). Volunteers were administered 25, 50, 100, and 250 ng (2.7-27 nCi) of [¹⁴C]-BaP (with interceding minimum 3-week washout periods) with quantification of parent [¹⁴C]-BaP and metabolites in plasma measured over 48 h. [¹⁴C]-BaP median T_max was 30 min with C_max and area under the curve (AUC) approximating dose-dependency. Marked inter-individual variability in plasma pharmacokinetics following a 250 ng dose was seen with 7 volunteers as measured by the C_max (8.99 ± 7.08 ng × mL^-1) and AUC_0-48hr (68.6 ± 64.0 fg × hr^-1 × mL^-1). Approximately 3-6% of the [¹⁴C] recovered (AUC_{0-48 hr}) was parent compound, demonstrating extensive metabolism following oral dosing. Metabolite profiles showed that, even at the earliest time-point (30 min), a substantial percentage of [¹⁴C] in plasma was polar BaP metabolites. The best fit modeling approach identified non-compartmental apparent volume of distribution of BaP as significantly increasing as a function of dose (p = 0.004). Bay region tetrols and dihydrodiols predominated, suggesting not only was there extensive first pass metabolism but also potentially bioactivation. AMS enables the study of environmental carcinogens in humans with de minimus risk, allowing for important testing and validation of physiologically based pharmacokinetic models derived from animal data, risk assessment, and the interpretation of data from high-risk occupationally exposed populations.

Sex Differences in Embryonic Gonad Transcriptomes and Benzo[a]pyrene Metabolite Levels After Transplacental Exposure

Polycyclic aromatic hydrocarbons like benzo[a]pyrene (BaP) are generated during incomplete combustion of organic materials. Prior research has demonstrated that BaP is a prenatal ovarian toxicant and carcinogen. However, the metabolic pathways active in the embryo and its developing gonads and the mechanisms by which prenatal exposure to BaP predisposes to ovarian tumors later in life remain to be fully elucidated. To address these data gaps, we orally dosed pregnant female mice with BaP from embryonic day (E) 6.5 to E11.5 (0, 0.2, or 2 mg/kg/day) for metabolite measurement or E9.5 to E11.5 (0 or 3.33 mg/kg/day) for embryonic gonad RNA sequencing. Embryos were harvested at E13.5 for both experiments. The sum of BaP metabolite concentrations increased significantly with dose in the embryos and placentas, and concentrations were significantly higher in female than male embryos and in embryos than placentas. RNA sequencing revealed that enzymes involved in metabolic activation of BaP are expressed at moderate to high levels in embryonic gonads and that greater transcriptomic changes occurred in the ovaries in response to BaP than in the testes. We identified 490 differentially expressed genes (DEGs) with false discovery rate P-values < 0.05 when comparing BaP-exposed to control ovaries but no statistically significant DEGs between BaP-exposed and control testes. Genes related to monocyte/macrophage recruitment and activity, prolactin family genes, and several keratin genes were among the most upregulated genes in the BaP-exposed ovaries. Results show that developing ovaries are more sensitive than testes to prenatal BaP exposure, which may be related to higher concentrations of BaP metabolites in female embryos.

Patterns of carbon-bound exogenous compounds in lung cancer patients and association with disease pathophysiology

Asymptomatic anthracosis is the accumulation of black carbon particles in adult human lungs. It is a common occurrence, but the pathophysiological significance of anthracosis is debatable. Using in situ high mass resolution matrix-assisted laser desorption/ionization (MALDI) fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry imaging analysis, we discovered noxious carbon-bound exogenous compounds, such as polycyclic aromatic hydrocarbons (PAHs), tobacco-specific nitrosamines, or aromatic amines, in a series of 330 lung cancer patients in highly variable and unique patterns. The characteristic nature of carbon-bound exogenous compound had a strong association with patient outcome, tumor progression, the tumor immune microenvironment, PD-L1 expression, and DNA damage. Spatial correlation network analyses revealed substantial differences in the metabolome of tumor cells compared to tumor stroma depending on carbon-bound exogenous compounds. Overall, the bioactive pool of exogenous compounds is associated with several changes in lung cancer pathophysiology and correlates with patient outcome. Given the high prevalence of anthracosis in the lungs of adult humans, future work should investigate the role of carbon-bound exogenous compounds in lung carcinogenesis and lung cancer therapy.

Organ and tissue-specific distribution of selected polycyclic aromatic hydrocarbons (PAHs) in ApoE-KO mouse

Polycyclic aromatic hydrocarbons (PAHs) are one of the most prevalent classes of environmental pollutants resulting from the incomplete combustion of hydrocarbons. Exposure to PAHs is implicated in the pathogenesis of the cardiovascular disease, pulmonary disease, and even cancer. However, little is known about organ- and tissue-specific distribution patterns of PAHs in animals at macro-tissue and microscopic levels. Here, by combining GC-MS and single-molecule fluorescence microscopy (SMFM), we revealed the distribution characteristics of four different PAHs (phenanthrene (Phe), pyrene (Pyr), perylene (Per), and benzo[a]pyrene (BaP)) in atherosclerosis model mice (ApoE-KO mice) at macro-tissue and micro-region level after long-term oral exposure. Average PAH concentrations detected by GC-MS in seven tissues ranged from 6.44 to 441 ng/g. The gastrointestinal tract, epididymal fat pat, and lung accumulated higher levels of PAHs, whereas relatively lower PAH residuals were found in the liver, brain, and kidney. Correlation analysis showed that PAHs with higher molecular weight (r: -0.972 to -0.746), Log K_ow (r: -0.984 to -0.746) and lower water solubility (r: 0.720 to 0.994) were less prone to bioaccumulate. For the first time, SMFM demonstrated a distinct heterogeneous distribution of Per in the tissue slices. More interestingly, we observed many micro-cluster regions, namely hotspots, showed much higher Per fluorescent intensity than the other common regions. In the area of atherosclerotic plaque, the Per hotspots were colocalized with the micro-regions with the most severe inflammatory response. The hotspots with very high enrichment in PAHs were likely to stimulate the local inflammation and cause excessive damage of the aorta, which resulted in a significant increase of the relative area of atherosclerosis lesion and aggravated atherosclerosis, as observed in PAH exposed mice.

A look beyond the priority: A systematic review of the genotoxic, mutagenic, and carcinogenic endpoints of non-priority PAHs

Knowledge of the toxic potential of polycyclic aromatic hydrocarbons (PAHs) has increased over time. Much of this knowledge is about the 16 United States - Environmental Protection Agency (US - EPA) priority PAHs; however, there are other US - EPA non-priority PAHs in the environment, whose toxic potential is underestimated. We conducted a systematic review of in vitro, in vivo, and in silico studies to assess the genotoxicity, mutagenicity, and carcinogenicity of 13 US - EPA non-priority parental PAHs present in the environment. Electronic databases, such as Science Direct, PubMed, Scopus, Google Scholar, and Web of Science, were used to search for research with selected terms without time restrictions. After analysis, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol, 249 articles, published between 1946 and 2020, were selected and the quality assessment of these studies was performed. The results showed that 5-methylchrysene (5-MC), 7,12-dimethylbenz[a]anthracene (7,12-DMBA), cyclopenta[cd]pyrene (CPP), and dibenzo[al]pyrene (Db[al]P) were the most studied PAHs. Moreover, 5-MC, 7,12-DMBA, benz[j]aceanthrylene (B[j]A), CPP, anthanthrene (ANT), dibenzo[ae]pyrene (Db[ae]P), and Db[al]P have been reported to cause mutagenic effects and have been being associated with a risk of carcinogenicity. Retene (RET) and benzo[c]fluorene (B[c]F), the least studied compounds, showed evidence of a strong influence on the mutagenicity and carcinogenicity endpoints. Overall, this systematic review provided evidence of the genotoxic, mutagenic, and carcinogenic endpoints of US - EPA non-priority PAHs. However, further studies are needed to improve the future protocols of environmental analysis and risk assessment in severely exposed populations.

Mode of action-based risk assessment of genotoxic carcinogens

The risk assessment of chemical carcinogens is one major task in toxicology. Even though exposure has been mitigated effectively during the last decades, low levels of carcinogenic substances in food and at the workplace are still present and often not completely avoidable. The distinction between genotoxic and non-genotoxic carcinogens has traditionally been regarded as particularly relevant for risk assessment, with the assumption of the existence of no-effect concentrations (threshold levels) in case of the latter group. In contrast, genotoxic carcinogens, their metabolic precursors and DNA reactive metabolites are considered to represent risk factors at all concentrations since even one or a few DNA lesions may in principle result in mutations and, thus, increase tumour risk. Within the current document, an updated risk evaluation for genotoxic carcinogens is proposed, based on mechanistic knowledge regarding the substance (group) under investigation, and taking into account recent improvements in analytical techniques used to quantify DNA lesions and mutations as well as "omics" approaches. Furthermore, wherever possible and appropriate, special attention is given to the integration of background levels of the same or comparable DNA lesions. Within part A, fundamental considerations highlight the terms hazard and risk with respect to DNA reactivity of genotoxic agents, as compared to non-genotoxic agents. Also, current methodologies used in genetic toxicology as well as in dosimetry of exposure are described. Special focus is given on the elucidation of modes of action (MOA) and on the relation between DNA damage and cancer risk. Part B addresses specific examples of genotoxic carcinogens, including those humans are exposed to exogenously and endogenously, such as formaldehyde, acetaldehyde and the corresponding alcohols as well as some alkylating agents, ethylene oxide, and acrylamide, but also examples resulting from exogenous sources like aflatoxin B1, allylalkoxybenzenes, 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline (MeIQx), benzo[a]pyrene and pyrrolizidine alkaloids. Additionally, special attention is given to some carcinogenic metal compounds, which are considered indirect genotoxins, by accelerating mutagenicity via interactions with the cellular response to DNA damage even at low exposure conditions. Part C finally encompasses conclusions and perspectives, suggesting a refined strategy for the assessment of the carcinogenic risk associated with an exposure to genotoxic compounds and addressing research needs.

Toxicokinetics of benzo[a]pyrene in humans: Extensive metabolism as determined by UPLC-accelerator mass spectrometry following oral micro-dosing

Benzo[a]pyrene (BaP), is a known human carcinogen (International Agency for Research on Cancer (IARC) class 1). The remarkable sensitivity (zepto-attomole ¹⁴C in biological samples) of accelerator mass spectrometry (AMS) makes possible, with de minimus risk, pharmacokinetic (PK) analysis following [¹⁴C]-BaP micro-dosing of humans. A 46 ng (5 nCi) dose was given thrice to 5 volunteers with minimum 2 weeks between dosing and plasma collected over 72 h. [¹⁴C]-BaP_eq PK analysis gave plasma T_max and C_max values of 1.25 h and 29-82 fg/mL, respectively. PK parameters were assessed by non- compartment and compartment models. Intervals between dosing ranged from 20 to 420 days and had little impact on intra-individual variation. DNA, extracted from peripheral blood mononuclear cells (PBMCs) of 4 volunteers, showed measurable levels (LOD ~ 0.5 adducts/10¹¹ nucleotides) in two individuals 2-3 h post-dose, approximately three orders of magnitude lower than smokers or occupationally-exposed individuals. Little or no DNA binding was detectable at 48-72 h. In volunteers the allelic variants CYP1B1^*1/*⁎1, ^*1/*3 or ^*3/*3 and GSTM1^*0/0 or ^*1 had no impact on [¹⁴C]-BaP_eq PK or DNA adduction with this very limited sample. Plasma metabolites over 72 h from two individuals (one CYP1B1^*1/*1 and one CYP1B1^*3/*3) were analyzed by UPLC-AMS. In both individuals, parent [¹⁴C]-BaP was a minor constituent even at the earliest time points and metabolite profiles markedly distinct. AMS, coupled with UPLC, could be used in humans to enhance the accuracy of pharmacokinetics, toxicokinetics and risk assessment of environmental carcinogens.

BPDE-induced genotoxicity: relationship between DNA adducts, mutagenicity in the in vitro PIG-A assay, and the transcriptional response to DNA damage in TK6 cells

Benzo[a]pyrene is a known human carcinogen. As underlying mechanism, the induction of stable DNA adducts and mutations have been repeatedly demonstrated. Also, the activation of cellular stress response on the transcriptional level has been described. Nevertheless, the interrelationship between these different events is less well understood, especially at low, for human exposure relevant concentrations. Within the present study, we applied the reactive metabolite benzo[a]pyrene diolepoxide (BPDE) in the nanomolar, non-cytotoxic concentration range in human TK6 cells and quantified the induction and repair of stable DNA adducts at the N²-position of guanine by HPLC with fluorescence detection. Significant levels of DNA lesions were detected even at the lowest concentration of 10 nM BPDE, with a linear increase up to 50 nM. Relative repair was similar at all damage levels, reaching about 30% after 8 h and 60% after 24 h. Mutation frequencies were quantified as GPI-deficient cells by the recently established in vitro PIG-A mutagenicity assay. Again, a linear dose–response-relationship in the before-mentioned concentration range was observed, also when plotting the number of GPI-deficient cells against the number of DNA adducts. Furthermore, we explored the time- and concentration-dependent DNA damage response on the transcriptional level via a high-throughput RT-qPCR technique by quantifying the impact of BPDE on the transcription of 95 genes comprising DNA damage response, DNA repair factors, oxidative stress response, cell cycle arrest, cell proliferation, and apoptosis. As expected, BPDE activated DNA damage signaling, p53 and AP-1 dependent signaling, oxidative stress response, and apoptosis. However, in contrast to DNA adducts and mutations, the onset of the transcriptional DNA damage response was restricted to higher concentrations, indicating that its respective activations require a certain level of DNA lesions. Altogether, the results indicate that in case of BPDE, DNA lesions and mutations were correlated at all concentrations, suggesting that repair is not complete even at low levels of DNA damage. Considering the ongoing discussion on potential thresholds also for genotoxic carcinogens, the results are of major relevance, both with respect to basic research as well as to risk assessment of chemical carcinogens.

Comparison of toxicogenomics and traditional approaches to inform mode of action and points of departure in human health risk assessment of benzo[a]pyrene in drinking water

Toxicogenomics is proposed to be a useful tool in human health risk assessment. However, a systematic comparison of traditional risk assessment approaches with those applying toxicogenomics has never been done. We conducted a case study to evaluate the utility of toxicogenomics in the risk assessment of benzo[a]pyrene (BaP), a well-studied carcinogen, for drinking water exposures. Our study was intended to compare methodologies, not to evaluate drinking water safety. We compared traditional (RA1), genomics-informed (RA2) and genomics-only (RA3) approaches. RA2 and RA3 applied toxicogenomics data from human cell cultures and mice exposed to BaP to determine if these data could provide insight into BaP's mode of action (MOA) and derive tissue-specific points of departure (POD). Our global gene expression analysis supported that BaP is genotoxic in mice and allowed the development of a detailed MOA. Toxicogenomics analysis in human lymphoblastoid TK6 cells demonstrated a high degree of consistency in perturbed pathways with animal tissues. Quantitatively, the PODs for traditional and transcriptional approaches were similar (liver 1.2 vs. 1.0 mg/kg-bw/day; lungs 0.8 vs. 3.7 mg/kg-bw/day; forestomach 0.5 vs. 7.4 mg/kg-bw/day). RA3, which applied toxicogenomics in the absence of apical toxicology data, demonstrates that this approach provides useful information in data-poor situations. Overall, our study supports the use of toxicogenomics as a relatively fast and cost-effective tool for hazard identification, preliminary evaluation of potential carcinogens, and carcinogenic potency, in addition to identifying current limitations and practical questions for future work.

Systems approaches evaluating the perturbation of xenobiotic metabolism in response to cigarette smoke exposure in nasal and bronchial tissues

Capturing the effects of exposure in a specific target organ is a major challenge in risk assessment. Exposure to cigarette smoke (CS) implicates the field of tissue injury in the lung as well as nasal and airway epithelia. Xenobiotic metabolism in particular becomes an attractive tool for chemical risk assessment because of its responsiveness against toxic compounds, including those present in CS. This study describes an efficient integration from transcriptomic data to quantitative measures, which reflect the responses against xenobiotics that are captured in a biological network model. We show here that our novel systems approach can quantify the perturbation in the network model of xenobiotic metabolism. We further show that this approach efficiently compares the perturbation upon CS exposure in bronchial and nasal epithelial cells in vivo samples obtained from smokers. Our observation suggests the xenobiotic responses in the bronchial and nasal epithelial cells of smokers were similar to those observed in their respective organotypic models exposed to CS. Furthermore, the results suggest that nasal tissue is a reliable surrogate to measure xenobiotic responses in bronchial tissue.

Polycyclic aromatic hydrocarbons in lung tissue of patients with pulmonary cancer from Romania. Influence according as demographic status and ABO phenotypes

The lung is a target organ for the toxic effects of several chemical agents, including natural products, industrial chemicals, environmental agents, and occasionally, drugs. The assessment of PAHs in the lungs of patients with pulmonary cancer is important because these pollutants have mutagenic, carcinogenic and endocrine-disrupting properties. This study included 31 histological confirmed lung cancer cases diagnosed consecutively at the Clinical Hospital of Pneumology (Iasi, Romania) from 2008 to 2009. Analyses were carried out using an accelerated solvent extraction technique and HPLC with a fluorescence detector. Fifteen PAHs were detected in all analyzed samples with non-carcinogenic compounds significantly elevated (45.57 ng g(-1) wet tissue) against carcinogenic compounds (6.12 ng g(-1) wet tissue). The mean ± SD lung tissue level of benzo(a)anthracene (3.57 ± 4.64 ng g(-1) wet tissue), a carcinogenic PAH, was found to be significantly higher (p<0.05) in patients from urban areas compared with the level (1.22 ± 1.45 ng g(-1) wet tissue) in patients from rural areas. Similarly, the levels of non-carcinogenic acenaphtene (8.95 ± 13.32 ng g(-1) wet tissue), fluoranthrene (5.31 ± 5.40 ng g(-1) wet tissue) and anthracene (4.83 ± 7.57 ng g(-1) wet tissue) were also detected to be higher (p<0.05) in the urban group compared to the levels for the rural group (1.46 ± 2.34, 1.83 ± 2.50 and 1.89 ± 3.79 ng g(-1) wet tissue, respectively). High concentrations of PAHs, especially carcinogenic PAHs, such as benzo(a)pyrene, benzo(a)anthracene, benzo(b)fluoranthrene, and benzo(k)fluoranthrene, were observed in lung tissue samples collected from subjects with A and O blood types.

Biomarkers of induced active and passive smoking damage

In addition to the well-known link between smoking and lung cancer, large epidemiological studies have shown a relationship between smoking and cancers of the nose, oral cavity, oropharynx, larynx, esophagus, pancreas, bladder, kidney, stomach, liver, colon and cervix, as well as myeloid leukemia. Epidemiological evidence has reported a direct link between exposure of non-smokers to environmental tobacco smoke and disease, most notably, lung cancer. Much evidence demonstrates that carcinogenic-DNA adducts are useful markers of tobacco smoke exposure, providing an integrated measurement of carcinogen intake, metabolic activation, and delivery to the DNA in target tissues. Monitoring accessible surrogate tissues, such as white blood cells or bronchoalveolar lavage (BAL) cells, also provides a means of investigating passive and active tobacco exposure in healthy individuals and cancer patients. Levels of DNA adducts measured in many tissues of smokers are significantly higher than in non-smokers. While some studies have demonstrated an association between carcinogenic DNA adducts and cancer in current smokers, no association has been observed in ex or never smokers. The role of genetic susceptibility in the development of smoking related-cancer is essential. In order to establish whether smoking-related DNA adducts are biomarkers of tobacco smoke exposure and/or its carcinogenic activity we summarized all data that associated tobacco smoke exposure and smoking-related DNA adducts both in controls and/or in cancer cases and studies where the effect of genetic polymorphisms involved in the activation and deactivation of carcinogens were also evaluated. In the future we hope we will be able to screen for lung cancer susceptibility by using specific biomarkers and that subjects of compared groups can be stratified for multiple potential modulators of biomarkers, taking into account various confounding factors.

Blood levels of polycyclic aromatic hydrocarbons in children of Lucknow, India

Polycyclic aromatic hydrocarbons (PAHs) are compounds with two or more fused benzene rings produced by incomplete combustion of organic substances involved in natural and anthropogenic processes. Children are exposed to these compounds through inhalation, dietary ingestion, and, also, soil at the playground. It has been well established that PAHs have carcinogenic, mutagenic, and teratogenic effects. Considering possible health risks due to PAHs exposure among children, the present study was carried out in collaboration with the Pediatrics Department, King George's Medical University (KGMU), Lucknow, to determine its exposure in children by estimating blood PAHs levels. Due to the variable composition of PAHs mixtures emitted from different environmental sources, any single compound or metabolite may not be representative of all exposure conditions. For these reasons, the measurement of blood PAHs levels as a possible biomarker, especially of the EPA (Environmental Protection Agency, USA) priority list, has been proposed. Acenaphthylene, anthracene, phenanthrene, fluoranthene, naphthalene, pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, and benzo(a)pyrene were determined by HPLC-FD/UV. On the basis of the individual compound, the median (50th percentile) of naphthalene (19 ppb) was highest, however, benzo(a)pyrene (4.0 ppb) level was found to be lowest among all detected PAHs. The median level of total noncarcinogenic PAHs (113.55 ppb) was higher than the total carcinogenic PAHs (32.35 ppb) in blood samples of children. A significant correlation was found between period of time spent in the surrounding breathing zone of the cooking place and total noncarcinogenic PAHs (p < 0.05), while the blood carcinogenic PAHs level in children was found to be associated with lower status of their families (p < 0.05). It is speculated that there may be chances of health hazards through exposure to PAHs, those not yet declared hazardous and present at higher concentrations in the Indian environment. Further study with a larger sample size and accompanying environmental data is desired to validate the findings of this pilot study and strengthen the database of PAHs exposure in India.

Maternal smoking during pregnancy specifically reduces human fetal desert hedgehog gene expression during testis development

CONTEXT

Maternal cigarette smoking during gestation increases cryptorchidism and hypospadias and reduces testis size and fertility in sons by unknown mechanisms.

OBJECTIVE

The objective of the study was to determine whether maternal smoking is linked with changes in male human fetal endocrinology, testis gene expression, and liver concentrations of cigarette smoke chemicals.

DESIGN

This was an observational study of the male fetus, comparing pregnancies during which the mothers either did or did not smoke.

SETTING

The study was conducted at the universities of Aberdeen, Glasgow, and Nottingham and Macaulay Institute (Aberdeen).

PATIENTS/PARTICIPANTS

Testes, blood, and livers were collected from 69 morphologically normal human male fetuses of women undergoing elective termination of normal second-trimester pregnancies.

MAIN OUTCOME MEASURES

Testosterone, human chorionic gonadotropin, LH, and cotinine; expression of 30 reproductive/developmental genes; liver concentrations of 16 polycyclic aromatic hydrocarbons; and Leydig, Sertoli. and germ cell numbers were determined.

RESULTS

There were no significant differences in fetal size, testis weight, cell numbers, seminiferous tubule diameter, or circulating LH and testosterone. Fetuses from smoking mothers had smoking range cotinine levels and liver concentrations of polycyclic aromatic hydrocarbons that were significant predictors of maternal smoking (P < 0.001). Only the Sertoli cell-specific gene, desert hedgehog (DHH), was significantly altered by maternal smoking (reduced 1.8-fold, P = 0.013).

CONCLUSIONS

The consequences of reduced DHH signaling in men and mice are consistent with epidemiology for effects of gestational maternal smoking on sons. Given the absence of other observed effects of maternal smoking, we concluded that reduced DHH is part of a mechanism linking maternal gestational smoking with impaired reproductive development in male offspring.

Blood levels of polycyclic aromatic hydrocarbons in children and their association with oxidative stress indices: an Indian perspective

BACKGROUND

Polycyclic aromatic hydrocarbons (PAHs), some ubiquitous environmental contaminants are capable to cause oxidative stress, during its metabolism. It is believed that many diseases that have a common origin in oxidative stress begin in childhood. Considering oxidative stress evolved during PAHs metabolism as one main mechanism responsible for health hazards related to PAHs exposure in children, we biomonitored blood PAHs levels in connection with redox status among children of Lucknow (India).

METHODS

The study consisted of children (n = 50) who visited to the Pediatrics Department (KGMU) Lucknow for usual health check-up camp over the study period (August 2005-July 2006). Blood samples were drawn and levels of acenaphthylene, anthracene, phenanthrene, fluoranthene, naphthalene, pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene and benzo(a)pyrene were determined by HPLC-FD/UV. Malondialdehyde (MDA), glutathione (GSH) levels, catalase (CAT) and superoxide dismutase (SOD) activity were also determined to evaluate redox status.

RESULTS

Significantly elevated carcinogenic blood PAHs levels (125.55 +/- 26.99ppb, p < 0.05) were found in rural children compared to children from urban region (23.96 +/- 13.46). Results revealed that remoteness between residence and highway/traffic, significantly influences the blood levels of carcinogenic PAHs. There were significant correlations between total PAHs and MDA (r = 0.82, p < 0.001), carcinogenic PAHs and SOD activity (r = 0.35, p < 0.01), Total PAHs and blood GSH level (r = - 0.49, p < 0.01) and carcinogenic PAHs and CAT activity (r = 0.42, p < 0.01). Blood MDA level was also found correlated with increasing body mass index (BMI) (r = 0.29, p < 0.05).

CONCLUSION

Our results showed blood PAHs levels in children significantly correlated with oxidative stress and altered antioxidant status. It supports our hypothesis that the children exposed to high PAHs level will suffer more to oxidative stress that may lead to possible health risks. Additional studies with large sample size are considered necessary to strengthen the database and also to explore the PAHs associated health risks in children.

Quantifying potential health impacts of cadmium in cigarettes on smoker risk of lung cancer: a portfolio-of-mechanisms approach

This article introduces an approach to estimating the uncertain potential effects on lung cancer risk of removing a particular constituent, cadmium (Cd), from cigarette smoke, given the useful but incomplete scientific information available about its modes of action. The approach considers normal cell proliferation; DNA repair inhibition in normal cells affected by initiating events; proliferation, promotion, and progression of initiated cells; and death or sparing of initiated and malignant cells as they are further transformed to become fully tumorigenic. Rather than estimating unmeasured model parameters by curve fitting to epidemiological or animal experimental tumor data, we attempt rough estimates of parameters based on their biological interpretations and comparison to corresponding genetic polymorphism data. The resulting parameter estimates are admittedly uncertain and approximate, but they suggest a portfolio approach to estimating impacts of removing Cd that gives usefully robust conclusions. This approach views Cd as creating a portfolio of uncertain health impacts that can be expressed as biologically independent relative risk factors having clear mechanistic interpretations. Because Cd can act through many distinct biological mechanisms, it appears likely (subjective probability greater than 40%) that removing Cd from cigarette smoke would reduce smoker risks of lung cancer by at least 10%, although it is possible (consistent with what is known) that the true effect could be much larger or smaller. Conservative estimates and assumptions made in this calculation suggest that the true impact could be greater for some smokers. This conclusion appears to be robust to many scientific uncertainties about Cd and smoking effects.

Estimating preventable fractions of disease caused by a specified biological mechanism: PAHs in smoking lung cancers as an example

Epidemiology textbooks often interpret population attributable fractions based on 2 x 2 tables or logistic regression models of exposure-response associations as preventable fractions, i.e., as fractions of illnesses in a population that would be prevented if exposure were removed. In general, this causal interpretation is not correct, since statistical association need not indicate causation; moreover, it does not identify how much risk would be prevented by removing specific constituents of complex exposures. This article introduces and illustrates an approach to calculating useful bounds on preventable fractions, having valid causal interpretations, from the types of partial but useful molecular epidemiological and biological information often available in practice. The method applies probabilistic risk assessment concepts from systems reliability analysis, together with bounding constraints for the relationship between event probabilities and causation (such as that the probability that exposure X causes response Y cannot exceed the probability that exposure X precedes response Y, or the probability that both X and Y occur) to bound the contribution to causation from specific causal pathways. We illustrate the approach by estimating an upper bound on the contribution to lung cancer risk made by a specific, much-discussed causal pathway that links smoking to a polycyclic aromatic hydrocarbon (PAH) (specifically, benzo(a)pyrene diol epoxide-DNA) adducts at hot spot codons at p53 in lung cells. The result is a surprisingly small preventable fraction (of perhaps 7% or less) for this pathway, suggesting that it will be important to consider other mechanisms and non-PAH constituents of tobacco smoke in designing less risky tobacco-based products.

An approach to investigating the importance of high potency polycyclic aromatic hydrocarbons (PAHs) in the induction of lung cancer by air pollution

Evidence suggests that people living in urban areas have an increased risk of lung cancer due to higher levels of air pollution in these areas. Benzo[a]pyrene (B[a]P) is currently used as the main indicator of carcinogenic polycyclic aromatic hydrocarbons (PAHs) in air pollution, but there is concern that B[a]P may not be the ideal surrogate of choice for PAH mixtures since higher potency PAHs have recently been identified which could potentially contribute more and variably to the overall carcinogenicity. Dibenzo[a,h]anthracene (DBA) and dibenzo[a,l]pyrene (DB[a,l]P) are estimated to have carcinogenic potencies 10 or more times greater than B[a]P but data on their presence and formation in the environment are limited. Several occupational and environmental PAH biomonitoring studies are reviewed here, with particular focus on the specific exposure groups, study design, sample tissue, in particular the use of nasal tissues, and biomarkers used in each study. Consideration of these data is then used to propose a novel biomonitoring approach to evaluate exposure, uptake and the role of high potency PAHs in air pollution-related lung cancer. This is based upon an occupational study examining specific DNA adducts for DBA and DB[a,l]P in nasal cells to evaluate the extent to which these high potency PAHs might contribute to the increased risk of developing lung cancer from air pollution.

Benzo(a)pyrene Diolepoxide (BPDE)-DNA Adduct Levels in Leukocytes of Smokers in Relation to Polymorphism of CYP1A1, GSTM1, GSTP1, GSTT1, and mEH

Benzo(a)pyrene [B(a)P] diolepoxide (BPDE)-DNA adducts were measured in the leukocytes of 41 healthy smokers using high-performance liquid chromatography coupled with a fluorimetric detector. The correlation between exposure to B(a)P through smoking and BPDE-DNA adduct levels was poor (r = 0.31), although subjects in the high exposure group [B(a)P &gt; 50 ng/d] had a slightly higher level of adducts compared with the less exposed group (mean ± SE, 1.70 ± 0.3 versus 1.09 ± 0.1; P = 0.057). We studied the effect on BPDE-DNA adducts of individual variations in genes controlling B(a)P metabolism, classifying subjects in “low-risk” and “high-risk” genotypes for smoking-related B(a)P DNA damage. The high-risk group included subjects characterized by a combination of increased B(a)P activation [cytochrome P450 1A1 (CYP1A1) MspI and/or exon 7 Ile462Val allele variants and microsomal epoxide hydrolase (mEH) fast activity] and decreased deactivation ability [presence of glutathione S-transferase M1 (GSTM1) null allele and wild-type glutathione S-transferase P1 (GSTP1)]. The low-risk group included smokers with lower B(a)P activation (wild-type CYP1A1, low or intermediate mEH activity) and higher deactivation capacity (active GSTM1, GSTP1 Ile105Val allele). Subjects in the low-risk group had lower levels of BPDE-DNA adducts compared with subjects in the high-risk genotype group; this difference was significant using two markers (CYP1A1 and GSTM1, median ± SD, 0.77 ± 1.16 versus 1.89 ± 0.39; P = 0.03) or three markers (CYP1A1, GSTM1, and GSTP1, median ± SD, 0.66 ± 0.93 versus 1.43 ± 1.17; P = 0.013). The discrimination between groups was reduced when including mEH as an additional marker (P = 0.085). In conclusion, CYP1A1, GSTM1, and GSTP1 genotyping seems to be a risk predictor of BPDE-DNA adduct formation in leukocytes.

Reduction of androgen receptor expression by benzo[a]pyrene and 7,8-dihydro-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene in human lung cells

5Alpha-dihydrotestosterone significantly increased cell growth of lung adenocarcinoma cell line H1355. Benzo[alpha]pyrene (BaP) was a pulmonary carcinogen found in cigarette smoke. Treatment with 1microM BaP tremendously reduced constitutive androgen receptor (AR) expression, as determined with Western immunoblotting and the real-time RT-PCR assay, as well as testosterone-induced AR protein levels in H1355 cells. Similarly, 1microM BaP significantly reduced AR mRNA levels in human bronchial epithelial cells BEAS-2B. Although BaP, 2,3,7,8-tetrachlorodibenzo-p-dixin and polychlorinated biphenyl 126 activated aryl hydrocarbon receptor (AhR), which subsequently induced cytochrome P4501A1 (CYP1A1) and P4501B1 (CYP1B1) expression in H1355 cells, unexpectedly, neither TCDD nor PCB126 reduced AR expression. Antagonizing AhR activation and cytochrome P4501 activity with alpha-naphthoflavone, or inhibiting CYP1B1 activity with 2,4,3',5'-tetramethoxystilbene, however, prevented BaP-induced AR reduction. Furthermore, 7,8-dihydro-9,10-epoxy-7,8,9,10-tetrahydrobenzo[alpha]pyrene, a BaP carcinogenic metabolite catalyzed by CYP1A1 and CYP1B1, significantly reduced AR expression in H1355 cells and human lung fibroblasts WI-38. This was the first study that reports that BaP and BPDE reduced endogenous AR expression. These data suggest that metabolically activated BaP may disrupt androgen function by reducing AR levels in androgen-responsive organs.

Effects of fluoranthene, a polycyclic aromatic hydrocarbon, on cAMP-dependent anion secretion in human airway epithelia

The human respiratory tract is constantly exposed to polycyclic aromatic hydrocarbons (PAHs) through inhalation of atmospheric pollutants. We examined the effects of three PAHs (benzo[a]pyrene, anthracene, and fluoranthene) on the airway ion transport, which is essential for lung defense and normal airway function, using human airway epithelia (Calu-3). These three PAHs had no significant effect on the basal short-circuit current (I(sc)). However, fluoranthene (1-100 microM) applied in the apical compartment potentiated I(sc) in response to cAMP-related agents (isoproterenol, forskolin, and 8-bromo-cAMP). The effects of fluoranthene were unaffected by ellipticine, a PAH receptor antagonist. Estimation of the anionic composition of I(sc) revealed that isoproterenol increased both HCO(3)(-) and Cl(-) transport in the control, whereas it potentiated only Cl(-) transport in the presence of fluoranthene. The fluoranthene-induced modulations of these anion transporters were counteracted by charybdotoxin (ChTx, a hIK-1 channel blocker). Fluoranthene gradually augmented the ChTx-sensitive K(+) current (I(K)) across the basolateral membrane, accompanied by a sustained increase in the cytosolic Ca(2+) concentration ([Ca(2+)](i)). In the presence of fluoranthene, however, a much larger hIK-1-dependent I(K) was identified by the application of 8-bromo-cAMP without concomitant elevation of [Ca(2+)](i). These results suggest that fluoranthene switches from cAMP-dependent HCO(3)(-) secretion to Cl(-) secretion through the hIK-1 channel, whose sensitivity to protein kinase A may be up-regulated by the sustained [Ca(2+)](i) elevation produced by this chemical.

Analysis of DNA and protein adducts of benzo[a]pyrene in human tissues using structure-specific methods

We review studies which investigate the presence, using structure-specific analytical methods, of DNA or protein adducts of the carcinogen benzo[a]pyrene (BaP) in human tissues. The analytical methods include high performance liquid chromatography with fluorescence detection and gas chromatography-mass spectrometry. Although, for DNA detection these methods are somewhat less sensitive than non-specific techniques such as 32P-postlabeling and immunoassay, they have the distinct advantage of providing reliable structural information. In order to achieve adequate sensitivity, these methods often require the use of fairly large amounts of DNA (>100 microg) or protein (50-100mg). Most studies reviewed here measured tetraols released from DNA or protein by hydrolysis of adducts derived from (7R,8S)-dihydroxy-(9S,10R)-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE), a major ultimate carcinogen of BaP. BPDE-DNA adducts were detected in 39% of 705 samples analyzed. BPDE-protein adducts were found in 59% of 772 samples. There was no single exposure situation that led to an overwhelming presence of detectable adducts. For example, BPDE-DNA adducts were detected in 45% of smokers, 33% of former smokers, 52% of non-smokers, 39% of occupationally exposed individuals, and 34% of environmentally exposed people. Adduct levels were influenced by polymorphisms in carcinogen metabolizing genes such as GSTM1, the presence of which was frequently protective. The relatively high occurrence of non-detectable adducts may result from low levels of BaP exposure and host factors such as genetic polymorphisms. Our analysis demonstrates that the presence of BaP adducts in human tissues cannot be assumed, even in situations where exposure to BaP is relatively high.

DNA adduct burden and tobacco carcinogenesis

DNA adducts associated with tobacco smoking could provide a marker of biologically effective dose of tobacco carcinogens and improve individual cancer risk prediction. A significant number of clinical and epidemiologic studies have reported associations of increased DNA adduct levels with the occurrence of the prevalent tobacco related cancers including cancer of the lung, head and neck, and bladder. The inducibility of DNA adducts following in vitro treatments using blood lymphocytes also appears to be a risk factor in the development of lung and head and neck cancer. Corroborative evidence pointing to the importance of DNA adducts in tobacco carcinogenesis include numerous studies showing associations of tobacco smoke exposure with the induction of DNA adducts in humans in vivo. Further effort is necessary, however, to more fully characterize the dose-response relationship between smoking and DNA adducts in exposed target and surrogate tissues. The relationship between gene polymorphisms thought to modify tobacco-related cancer risk and DNA adduct levels is complex. Results of some DNA adduct studies (both in vitro and in vivo) appear inconsistent with the epidemiologic findings. This is evident for polymorphisms involving both carcinogen metabolism (e.g. GSTP1) and DNA repair (e.g. XRCC1). Molecular studies of human tumors suggest associations of p53 mutation with DNA adducts and have revealed correlations of DNA adduct levels with somatic alterations (e.g. 3p21 LOH) that are thought to occur at the very earliest stages of tobacco carcinogenesis. More research is needed to assess the relationship between endogenous sources of DNA adducts and tobacco smoke exposure and the relative oncogenic effects of chemically stable versus unstable DNA adducts. Many potentially fruitful new avenues of cancer research are emerging that integrate DNA adduct analyses with assessments of smoking, genetics, diet and ambient air quality. These investigations aim to understand the multifactorial nature of interindividual variability in response to tobacco carcinogens. As these trends continue a variety of innovative study designs and approaches will become important in human populations.

Molecular epidemiology of smoking and lung cancer

Lung cancer is the single most common cause of death, and almost all of it is due to tobacco smoking. Before the widespread use of cigarettes in this century, lung cancer was a rare illness. Tobacco smoke is a complex mixture of numerous mutagens and carcinogens. Over the last 40 years, the type of cigarettes most frequently used has been changing, namely the increased use of low tar and nicotine cigarettes. This has been accompanied by an increased risk of lung cancer due to a smokers' need to maintain blood nicotine levels, which in turn causes the need for smoking more cigarettes per day and deeper inhalation. This phenomena has led to the increasing rates of lung adenocarcinoma, compared to squamous cell carcinoma. It also probably explains, in part, the greater risk of lung cancer in women compared to men (in addition to some biological differences). The study of lung cancer involves many types of biomarkers, including those that measure exposure, the biologically effective dose and harm. The use of these has allowed us to understand many parts of lung carcinogenesis. Genetic susceptibilities play a large role in lung cancer risk. They govern smoking behavior (affecting dopamine reward mechanisms due to nicotine and nicotine metabolism), carcinogen metabolism and detoxification, DNA repair, cell cycle control and other cellular responses. The need for the study of lung cancer is highlighted by the need to improve cessation rates and reduce exposure among persons who cannot quit smoking, for better prevention strategies for former smokers and an understanding of environmental tobacco smoke risk.

Tobacco smoking, harm reduction, and biomarkers

The only known way to reduce cancer risk in smokers is complete cessation, but many smokers are unable or unwilling to quit. Consequently, tobacco companies are now marketing products that purport to reduce carcinogen exposure, with the implication that such products provide a safer way to smoke. Moreover, researchers are exploring ways to reduce the amount of cigarette smoke carcinogens to which the smokers are exposed. Although these methods are, in theory beneficial, it is possible that the perceived availability of "safe" ways to smoke will cause some former smokers to resume smoking and some current smokers to delay quitting. Thus, the extent of exposure reduction and the impact on public health of these methods need to be considered carefully. However, risk reduction and its relation to exposure are not simple to estimate. The way people smoke and the way they respond to carcinogen exposure are both highly variable, as evidenced by the previous history of smokers who switched to light, or low-tar cigarettes. This can actually increase risk in some smokers. The evaluation of exposure reduction will therefore need to be multidisciplinary and include in vitro cell culture studies, animal studies, human clinical studies, and epidemiologic studies. Biomarkers will be critical for rapidly evaluating the effects of new strategies or products to reduce exposure to tobacco smoke carcinogens. No single biomarker will likely satisfy our assessment needs, and so a panel of biomarkers should be used that includes biomarkers of exposure, biologically effective dose, and potential harm. In addition, usefulness of new products will need to be tested in people of different susceptibilities (i.e., who vary in behavior, sex, age, genetics, and prior tobacco use). Even if the new products are shown to be effective at reducing lung carcinogens, they should not be used alone but rather be incorporated into a comprehensive tobacco control program.

Biomonitoring of tobacco smoke carcinogenicity by dosimetry of DNA adducts and genotyping and phenotyping of biotransformational enzymes: a review on polycyclic aromatic hydrocarbons

In this review article, we summarize the data on tobacco smoke carcinogenicity in relation to DNA adduct dosimetry and genotyping and phenotyping of biotransformational enzymes. A major class of carcinogens, polycyclic aromatic hydrocarbons, present in substantial quantities in tobacco smoke, is discussed. The historical background and an overview of the metabolic pathways are given. The epidemiological and biological data in particular on dosimetry of the representative DNA adducts and genotyping and phenotyping of the respective activating and detoxifying enzymes are presented. The salient findings are highlighted, the uncertainties are underlined and, finally, recommendations for future research are made.

Different levels of Schistosoma mansoni infection increased the mutagenicity of benzo(a)pyrene, the activity of aryl hydrocarbon hydroxylase and the formation of hepatic microsomal hydrogen peroxide

The present study investigates the influence of different levels of Schistosoma mansoni infection (60, 120, 180, 300, 600 cercariae per mice) after 33 days on the activity of aryl hydrocarbon hydroxylase (AHH) and the formation of hepatic hydrogen peroxide (H(2)O(2)) during the metabolic activation of benzo(a)pyrene [B(a)p]. Also, it shows the mutagenic effect of B(a)p at different levels of S. mansoni infection using Salmonella typhimurium TA 98 and TA 102 as a tester strains. High levels of H(2)O(2) production (222 nmol/mg protein) and AHH activity (240 pmol 3-OH B(a)p per mg protein) were seen at 300 cercariae per mice. Increasing histidine revertant colonies at TA98 and TA102 were detected at different levels of S. mansoni infection. These data clearly demonstrate that S. mansoni infection changes the mutagenicity of B(a)p, AHH activity, as well as enhancing the formation of hepatic H(2)O(2) generated during the metabolic activation of B(a)p in infected mice.

Tobacco-related diseases. Is there a role for antioxidant micronutrient supplementation?

It is clear that smoking causes an increase in free radicals, reactive nitrogen and oxygen species (RNS and ROS, respectively), and that cigarette smoking is associated with increases in the incidence and severity of several diseases including atherosclerosis, cancer, and chronic obstructive lung disease. Although there is still no unequivocal evidence that oxidative stress is a contributor to these diseases or that an increased intake of antioxidant nutrients is beneficial, the observation that smokers have lower circulating levels of some of these nutrients, raises concern. This article discusses the possible links between the observed oxidant-induced damage related to tobacco smoking, effects on cellular mechanisms, and their potential involvement in the causation and enhancement of disease processes.

Levels of 8-hydroxydeoxyguanosine as a marker of DNA damage in human leukocytes

We measured 8-hydroxy-2-deoxyguanosine (8-OHdG) levels in human leukocytes from healthy donors to evaluate oxidative DNA damage and its correlation with smoking, physical exercise, and alcohol consumption. A significant increase in oxidative DNA damage was induced by cigarette smoke, with the mean level of 8-OHdG being significantly higher in smokers (33.1 +/- 10.6 per 10(6) 2-deoxyguanosine (dG) [mean +/- SE], n = 16) compared with nonsmokers (15.3 +/- 1.8 per 10(6) dG, n = 31) and former smokers (17.8 +/- 1.5 per 10(6) dG, n = 9). The highest values were observed after smoking more than 10 cigarettes per day (41.8 +/- 17.1 per 10(6) dG, n = 9). A large interindividual variation in 8-OHdG levels was observed in all analyzed groups. We also observed a correlation between 8-OHdG levels and age in nonsmokers and former smokers. Neither frequency of physical exercise nor alcohol drinking significantly modified 8-OHdG levels in leukocytes.