Environmental and chemical carcinogenesis

Cancer genetic association studies in the genome-wide age

Genome-wide association studies of hundreds of thousands of SNPs have led to a deluge of studies of genetic variation in cancer and other common diseases. Large case-control and cohort studies have identified novel SNPs as markers of cancer risk. Genome-wide association study SNP data have also advanced understanding of population-specific genetic variation. While studies of risk profiles, combinations of SNPs that may increase cancer risk, are not yet clinically applicable, future, large-scale studies will make individualized cancer screening and prevention possible.

Targeting cytochrome P450 CYP1B1 with a therapeutic cancer vaccine

The role that the immune system plays in limiting tumor formation and growth is becoming increasingly clear and passive immunotherapeutic approaches, such as the use of monoclonal antibodies, are now being successfully applied in clinical practice. Active immunization against tumors, however, has not yet been shown to have the same level of clinical efficacy. Two important reasons for this lack of efficacy have to do with the antigens being targeted, as well as the immunization approaches that have been tested. This review will highlight some of the requirements thought to be important for the successful development of an active immunization approach, with a focus on the ongoing development efforts for a novel agent targeting the cytochrome P450 family member, CYP1B1.

Role of exhaled breath biomarkers in environmental health science

As a discipline of public health, environmental health science is the study of the linkage from environmental pollution sources to eventual adverse health outcome. This progression may be divided into two components, (1) "exposure assessment," which deals with the source terms, environmental transport, human exposure routes, and internal dose, and (2) "health effects," which deals with metabolism, cell damage, DNA changes, pathology, and onset of disease. The primary goal of understanding the linkage from source to health outcome is to provide the most effective and efficient environmental intervention methods to reduce health risk to the population. Biomarker measurements address an individual response to a common external environmental stressor. Biomarkers are substances within an individual and are subdivided into chemical markers, exogenous metabolites, endogenous response chemicals, and complex adducts (e.g., proteins, DNA). Standard biomarker measurements are performed in blood, urine, or other biological media such as adipose tissue and lavage fluid. In general, sample collection is invasive, requires medical personnel and a controlled environment, and generates infectious waste. Exploiting exhaled breath as an alternative or supplement to established biomarker measurements is attractive primarily because it allows a simpler collection procedure in the field for numerous individuals. Furthermore, because breath is a gas-phase matrix, volatile biomarkers become more readily accessible to analysis. This article describes successful environmental health applications of exhaled breath and proposes future research directions from the perspective of U.S. Environmental Protection Agency (EPA) human exposure research.

Gamma-aminobutyric acid, a potential tumor suppressor for small airway-derived lung adenocarcinoma

Pulmonary adenocarcinoma (PAC) is the leading type of lung cancer in smokers and non-smokers that arises in most cases from small airway epithelial cells. PAC has a high mortality due to its aggressive behavior and resistance to cancer therapeutics. We have shown previously that the proliferation of human PAC cells NCI-H322 and immortalized human small airway epithelial cells HPL1D is stimulated by cyclic adenosine monophosphate (cAMP)/protein kinase A-dependent phosphorylation of cyclic adenosine monophosphate response element-binding (CREB) protein and transactivation of the epidermal growth factor receptor and that this pathway is activated by beta-1-adrenoreceptors (beta(1)-ARs) and the non-genomic estrogen receptor beta. Our current in vitro studies with HPL1D and NCI-H322 cells showed that signaling via the gamma-amino butyric acid receptor (GABA(B)R) strongly inhibited base level and isoproterenol-induced cAMP, p-CREB, cyclic adenosine monophosphate response element-luciferase activity and p-extracellular regulated kinase-1 (ERK1)/2 and effectively blocked DNA synthesis and cell migration. The inhibitory effects of gamma-amino butyric acid (GABA) were disinhibited by the GABA(B)R antagonist CGP-35348 or GABA(B)R knockdown. Immunohistochemical investigation of hamster lungs showed significant underexpression of GABA in animals with small airway-derived PACs induced by the nicotine-derived carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). These findings suggest that GABA may have tumor suppressor function in small airway epithelia and the PACs derived from them and that downregulation of GABA by NNK may contribute to the development of this cancer in smokers. Our findings suggest that marker-guided treatment with GABA or a GABA(B)R agonist of individuals with downregulated pulmonary GABA may provide a novel targeted approach for the prevention of PAC in smokers.

Emerging contaminants in car interiors: evaluating the impact of airborne PBDEs and PBDD/Fs

Air samples from automobile cabins were collected and analyzed for polybrominated diphenyl ethers (PBDEs), polybrominated dibenzofurans (PBDFs), and polybrominated dibenzo-p-dioxins (PBDDs). The concentration of total PBDEs (sigmaPBDE; sum of 19 congeners) varied from 0.4 to 2644 pg m(-3), with a median of 201 pg m(-3), while BDE 47, 99, and 209 collectively accounted for 70 +/- 30% of sigmaPBDE concentrations. Multiple linear regression analysis revealed that sigmaPBDE concentration was significantly influenced by vehicle's age and interior temperature. More specifically, sigmaPBDE decreased over time and increased with the rise of temperature. The daily inhalation intake of PBDEs during commuting was estimated to range from 0.5 to 2909 pg day(-1) (median 221 pg day(-1)) and contributed 29% of the overall daily exposure to PBDEs via inhalation. When excluding BDE 209, a lower contribution was calculated for this source (18%), but this was still comparable with residential exposure (22%). The levels of PBDD/Fs were generally below the limits of detection and only in one case were hepta-BDFs positively detected at a concentration of 61 pg m(-3). This study demonstrates that car interiors, especially when new, contain high levels of airborne PBDEs and represent a potential route of human exposure via inhalation.

Neurotransmission and cancer: implications for prevention and therapy

Published evidence compiled in this review supports the hypothesis that the development, progression, and responsiveness to prevention and therapy of the most common human cancers is strongly influenced, if not entirely orchestrated, by an imbalance in stimulatory and inhibitory neurotransmission. The neurotransmitters acetylcholine, adrenaline, and noradrenaline of the autonomic nervous system act as powerful upstream regulators that orchestrate numerous cell and tissue functions, by releasing growth factors, angiogenesis factors and metastasis factors, arachidonic acid, proinflammatory cytokines, and local neurotransmitters from cancer cells and their microenvironment. In addition, they modulate proliferation, apoptosis, angiogenesis, and metastasis of cancer directly by intracellular signaling downstream of neurotransmitter receptors. Nicotine and the tobacco-specific nitrosamines have the documented ability to hyperstimulate neurotransmission by both branches of the autonomic nervous system. The expression and function of these neurotransmitter pathways are cell type specific. Lifestyle, diet, diseases, stress, and pharmacological treatments modulate the expression and responsiveness of neurotransmitter pathways. Current preclinical testing systems fail to incorporate the modulating effects of neurotransmission on the responsiveness to anticancer agents and should be amended accordingly. The neurotransmitter gamma-aminobutyric acid has a strong inhibitory function on sympathicus-driven cancers whereas stimulators of cyclic adenosine monophosphate/protein kinase A signaling have strong inhibitory function on parasympathicus-driven cancers. Marker-guided restoration of the physiological balance in stimulatory and inhibitory neurotransmission represents a promising and hitherto neglected strategy for the prevention and therapy of neurotransmitter-responsive cancers.

Airborne concentrations of volatile organic compounds in neonatal incubators

OBJECTIVE

To identify and quantify airborne volatile organic compounds (VOCs) inside neonatal incubators during various modes of operation within the neonatal intensive care unit (NICU) environment.

STUDY DESIGN

Air samples were taken from 10 unoccupied incubators in four operational settings along with ambient air samples using air sampling canisters. The samples were analyzed following EPA TO-15 using a Tekmar AutoCan interfaced to Agilent 6890 Gas Chromatograph with a 5973 Mass Spectrometer calibrated for 60 EPA TO-15 method target compounds. Non-target compounds were tentatively identified using mass spectral interpretation and with a mass spectral library created by National Institute for Standards and Technology.

RESULT

Two non-target compounds, 2-heptanone and n-butyl acetate, were found at elevated concentrations inside the incubators compared with ambient room air samples. Increase in temperature and addition of humidity produced further increased concentrations of these compounds. Their identities were verified by mass spectra and relative retention times using authentic standards. They were quantified using vinyl acetate and 2-hexanone as surrogate standards.

CONCLUSION

The emission pattern of these two compounds and background measurements indicate that they originate inside the incubator. There is evidence that exposure to some VOCs may adversely impact the fetal and developing infants' health. Currently, as there is no definitive information available on the effects of acute or chronic low-level exposure to these compounds in neonates, future studies evaluating the health effects of neonatal exposure to these VOCs are needed.

Protective interventions to prevent aflatoxin-induced carcinogenesis in developing countries

The public health impact of aflatoxin exposure is pervasive in economically developing countries; consequently, we need to design intervention strategies for prevention that are practicable for these high-risk populations. The adverse health consequences of aflatoxins in populations are quite varied, eliciting acute effects, such as rapid death, and chronic outcomes, such as hepatocellular carcinoma. Furthermore, a number of epidemiological studies describe a variety of general adverse health effects associated with aflatoxin, such as impaired growth in children. Thus, the magnitude of the problem is disseminated across the entire spectrum of age, gender, and health status in the population. The aflatoxins multiplicatively increase the risk of liver cancer in people chronically infected with hepatitis B virus (HBV), which illustrates the deleterious impact that even low toxin levels in the diet can pose for human health. Thus other aflatoxin interactions, which likely contribute to the disease burden, still remain to be identified. Therefore, many diverse and appropriate strategies for disease prevention are needed to decrease the incidence of aflatoxin carcinogenesis in developing countries.

Precancerous carcinogenesis of human breast epithelial cells by chronic exposure to benzo[a]pyrene

To understand carcinogenesis of human breast epithelial cells induced by chronic exposure to environmental pollutants, we studied biological and molecular changes in progression of cellular carcinogenesis induced by accumulated exposures to the potent environmental carcinogen benzo[a]pyrene (B[a]P). Increasing exposures of human breast epithelial MCF10A cells to B[a]P at picomolar concentrations resulted in cellular transformation from a noncancerous stage to precancerous substages, in which cells acquired the cancerous abilities of a reduced dependence on growth factors, anchorage-independent growth, and disruption in acini formation on reconstituted basement membranes. Using cDNA microarrays, we detected seven upregulated genes related to human cancers in B[a]P-transformed MCF10A cells. Using this model, we verified that green tea catechin significantly (P < 0.05) suppressed B[a]P-induced carcinogenesis. Our studies indicate that this cellular model may serve as a cost-efficient, in vitro system, mimicking the chronic carcinogenesis of breast cells that likely occurs in early stages of carcinogenesis in vivo, to identify agents that inhibit cellular carcinogenesis.

The application of normal, SV40 T-antigen-immortalised and tumour-derived oral keratinocytes, under serum-free conditions, to the study of the probability of cancer progression as a result of environmental exposure to chemicals

In vitro models are currently not considered to be suitable replacements for animals in experiments to assess the multiple factors that underlie the development of cancer as a result of environmental exposure to chemicals. An evaluation was conducted on the potential use of normal keratinocytes, the SV40 T-antigen-immortalised keratinocyte cell line, SVpgC2a, and the carcinoma cell line, SqCC/Y1, alone and in combination, and under standardised serum-free culture conditions, to study oral cancer progression. In addition, features considered to be central to cancer development as a result of environmental exposure to chemicals, were analysed. Genomic expression, and enzymatic and functional data from the cell lines reflected many aspects of the transition of normal tissue epithelium, via dysplasia, to full malignancy. The composite cell line model develops aberrances in proliferation, terminal differentiation and apoptosis, in a similar manner to oral cancer progression in vivo. Transcript and protein profiling links aberrations in multiple gene ontologies, molecular networks and tumour biomarker genes (some proposed previously, and some new) in oral carcinoma development. Typical specific changes include the loss of tumour-suppressor p53 function and of sensitivity to retinoids. Environmental agents associated with the aetiology of oral cancer differ in their requirements for metabolic activation, and cause toxic effects to cells in both the normal and the transformed states. The results suggest that the model might be useful for studies on the sensitivity of cells to chemicals at different stages of cancer progression, including many aspects of the integrated roles of cytotoxicity and genotoxicity. Overall, the properties of the SVpgC2a and SqCC/Y1 cell lines, relative to normal epithelial cells in monolayer or organotypic culture, support their potential applicability to mechanistic studies on cancer risk factors, including, in particular, the definition of critical toxicity effects and dose-effect relationships.

Characterization and distribution of PAHs in surface sediments of Daliao River, China

The concentrations of 16 priority pollutant PAHs in the samples of Daliao River were analyzed by a method based on Soxhlet extraction, solid-phase extraction clean-up and high performance liquid chromatography-programmable fluorescence/ultra violet detection. The total concentrations of PAHs in Daliao River ranged from 267.9 ng/g to 9,212 ng/g. The highest concentration of PAHs was 9,212 ng/g at the Station 24 (Anshan Railroad Bridge), and the lowest 267.9 ng/g at the Station 19 (Estuary). Compared with the total concentrations of PAHs of rivers in other parts of the world, the degree of contamination of Daliao River by PAHs was moderate to high. Specific compounds or groups of PAHs have been used as molecular markers to differentiate petrogenic and pyrogenic origin. The results showed that the main sources of PAHs in Daliao River were pyrolytic inputs such as combustion of coal, wood and petrogenic chemicals. The data was also compared by mean of two guideline values, an effects range-low (ER-L) and effects range-medium (ER-M), to assess the potential biological effects of the sediment adsorbed PAHs. It showed that the PAHs in some sites of Daliao River would exert adverse biological effects.

Cigarette smoking and adenomatous polyps: a meta-analysis

BACKGROUND & AIMS

Through the past 2 decades, a consistent association between cigarette smoking and colorectal adenomatous polyps, recognized precursor lesions of colorectal cancer, has been shown. We performed a meta-analysis to provide a quantitative pooled risk estimate of the association, focusing on the different characteristics of the study populations, study designs, and clinical feature of the polyps.

METHODS

We performed a comprehensive literature search of studies linking cigarette smoking and adenomas. We used random effects models to evaluate pooled relative risks and performed dose-response, heterogeneity, publication bias, and sensitivity analyses.

RESULTS

Forty-two independent observational studies were included in the analysis. The pooled risk estimates for current, former, and ever smokers in comparison with never smokers were 2.14 (95% confidence interval [CI], 1.86-2.46), 1.47 (95% CI, 1.29-1.67), and 1.82 (95% CI, 1.65-2.00), respectively. The association was stronger for high-risk adenomas than for low-risk adenomas. Studies in which all controls underwent full colonoscopy showed a higher risk compared with studies in which some or all controls underwent partial colon examination.

CONCLUSIONS

This meta-analysis provides strong evidence of the detrimental effect of cigarette smoking on the development of adenomatous polyps. Smoking is important for both formation and aggressiveness of adenomas.

Inflammation and lung cancer: roles of reactive oxygen/nitrogen species

The lung is a highly specialized organ that facilitates uptake of oxygen and release of carbon dioxide. Due to its unique structure providing enormous surface area to outside ambient air, it is vulnerable to numerous pathogens, pollutants, oxidants, gases, and toxicants that are inhaled continuously from air, which makes the lung susceptible to varying degrees of oxidative injury. To combat these unrelenting physical, chemical, and biological insults, the respiratory epithelium is covered with a thin layer of lining fluid containing several antioxidants and surfactants. Inhaled toxic agents stimulate the generation of reactive oxygen/nitrogen species (ROS/RNS), which in turn provoke inflammatory responses resulting in the release of proinflammatory cytokines and chemokines. These subsequently stimulate the influx of polymorphonuclear leukocytes (PMNs) and monocytes into the lung so as to combat the invading pathogens or toxic agents. In addition to the beneficial effects, persistent inhalation of the invading pathogens or toxic agents may result in overwhelming production of ROS/RNS, producing chronic inflammation and lung injury. During inflammation, enhanced ROS/RNS production may induce recurring DNA damage, inhibition of apoptosis, and activation of proto-oncogenes by initiating signal transduction pathways. Therefore, it is conceivable that chronic inflammation-induced production of ROS/RNS in the lung may predispose individuals to lung cancer. This review describes the complex relationship between lung inflammation and carcinogenesis, and highlights the role of ROS/RNS in cancer development.

Etiology of specific molecular alterations in human malignancies

Cancer results from multiple genomic changes that affect DNA and its gene expression. The DNA sequences may be gained, lost or amplified, or translocated into different parts of the genome to form a fusion gene with oncogenic properties. The occurrence of specific chromosomal aberrations may be restricted to only one cancer type and it may be considered a primary carcinogenic event. Furthermore, the aberration profiles may be used to cluster tumors with similar origins. A variety of techniques exist for the detection of specific chromosomal and gene expression changes. However, the etiology of these molecular alterations remains unclear. Here we discuss the roles of Helicobacter pylori and asbestos burden as carcinogens that cause gastric cancer, mesothelioma and lung cancer.

Processing of nonconventional DNA strand break ends

Single-strand breaks (SSBs) are one of the most common forms of genetic damage, arising from attack of DNA by reactive oxygen species or as intended or inadvertent products of normal cellular DNA metabolic events. Recent evidence linking defects in the enzymatic processing of nonconventional DNA SSBs, i.e., lesions incompatible with polymerase or ligase reactions, with inherited neurodegenerative disorders, reveals the importance of SSB repair in disease manifestation. I review herein the major eukaryotic enzymes (with an emphasis on the human proteins) responsible for the "clean-up" of DNA breaks harboring 3'- or 5'-blocking termini, and the cellular and disease ramifications of unrepaired SSB damage.

Application of the adductome approach to assess intertissue DNA damage variations in human lung and esophagus

Methods for determining the differential susceptibility of human organs to DNA damage have not yet been explored to any large extent due to technical constraints. The development of comprehensive analytical approaches by which to detect intertissue variations in DNA damage susceptibility may advance our understanding of the roles of DNA adducts in cancer etiology and as exposure biomarkers at least. A strategy designed for the detection and comparison of multiple DNA adducts from different tissue samples was applied to assess esophageal and peripherally- and centrally-located lung tissue DNA obtained from the same person. This adductome approach utilized LC/ESI-MS/MS analysis methods designed to detect the neutral loss of 2'-deoxyribose from positively ionized 2'-deoxynucleoside adducts transmitting the [M+H](+)>[M+H-116](+) transition over 374 transitions. In the final analyses, adductome maps were produced which facilitated the visualization of putative DNA adducts and their relative levels of occurrence and allowed for comprehensive comparisons between samples, including a calf thymus DNA negative control. The largest putative adducts were distributed similarly across the samples, however, differences in the relative amounts of putative adducts in lung and esophagus tissue were also revealed. The largest-occurring lung tissue DNA putative adducts were 90% similar (n=50), while putative adducts in esophagus tissue DNA were shown to be 80 and 84% similar to central and peripheral lung tissue DNA respectively. Seven DNA adducts, N(2)-ethyl-2'-deoxyguanosine (N(2)-ethyl-dG), 1,N(6)-etheno-2'-deoxyadenosine (varepsilondA), alpha-S- and alpha-R-methyl-gamma-hydroxy-1,N(2)-propano-2'-deoxyguanosine (1,N(2)-PdG(1), 1,N(2)-PdG(2)), 3-(2'-deoxyribosyl)-5,6,7,8-tetrahydro-8-hydroxy-pyrimido[1,2-a]purine-(3H)-one (8-OH-PdG) and the two stereoisomers of 3-(2'-deoxyribosyl)-5,6,7,8-tetrahydro-6-hydroxypyrimido[1,2-a]purine-(3H)-one (6-OH-PdG) were unambiguously detected in all tissue DNA samples by comparison to authentic adduct standards and stable isotope dilution and their identities were matched to putative adducts detected in the adductome maps.

New insights in the formation of deoxynucleoside adducts with the heterocyclic aromatic amines PhIP and IQ by means of ion trap MSn and accurate mass measurement of fragment ions

The formation of adducts by reaction of active metabolites of two heterocyclic aromatic amines (NHOH-PhIP and NHOH-IQ) at nucleophilic sites of deoxynucleosides has been studied by LC-MS(n) analyses of the obtained reaction mixtures. Sequential MS(3) experiments were carried out on an ion trap mass spectrometer to gain extensive structural information on each adduct detected in the first MS step. Attribution of ions was supported by accurate mass measurements performed on an Orbitrap mass analyzer. Particular attention was given to ions diagnostic of the linking between the heterocyclic aromatic amine (HAA) and the deoxynucleoside. By this way, the structures of five adducts have been characterized in this study, among which two are new compounds: dG-N7-IQ and dA-N(6)-IQ. No depurinating adduct was found in the reactions investigated therein. As expected, the C8 and N(2) atoms of dG were found as the most reactive sites of deoxynucleosides, resulting in the formation of two different adducts with IQ and one adduct with PhIP. An unusual non-depurinating dG-N7-IQ adduct has been characterized and a mechanism is proposed for its formation on the basis of the reactivity of arylamines. A dA-N(6)-IQ adduct has been identified for the first time in this work, showing that HAAs can generate DNA adducts with bases other than dG.

High association of human papillomavirus infection with oral cancer: a case-control study

BACKGROUND

The aim of the present study was to determine the association of high-risk human papillomavirus (HR-HPV) in Mexican individuals with oral squamous cell carcinoma (OSCC) and their association with various risk factors.

METHODS

We designed a matched case-control study. Cases were individuals with newly diagnosed OSCC, age- and sex-matched with controls (1:4). Demographic and clinical data were obtained; also a self-administered questionnaire about sexual behavior was included. DNA from oral brushing was purified to amplify HPV-DNA through MY09/MY11 and GP5+/GP6+ primers and subsequently subjected to sequencing. Conditional regression models were built to calculate odds ratios (ORs) and 95% confidence intervals (CI).

RESULTS

Sixty two cases and 248 controls (53.2% males), median age 62 years (Q1-Q3=54-72 years) were included. HPV prevalence was 43.5% in cases and 17.3% in controls (HR-HPV: 37.1% cases, 9.7% controls). The most frequent types in cases were HPV-16 and HPV-18 (55.6 and 18.5%). The presence of HR-HPV was associated with OSCC (OR=6.2; 95% CI: 2.98-12.97) controlling for the most common risk factors. An interaction between smoking and drinking was detected, and family history of cancer was also significant (OR: 3.61; 95% CI=1.44-8.99). Early age at first sexual intercourse and large number of lifetime sexual partners showed an association with HR-HPV (p=0.019 and p=0.033, respectively).

CONCLUSIONS

Oral HR-HPV was strongly associated with OSCC, suggesting that HPV-16 and -18 are risk factors for oral cancer in Mexican patients. A significant association of tobacco and alcohol was confirmed. In addition, family history of cancer was associated with OSCC. The results underline the role of HPV in OSCC and its multifactorial etiology.

Repair kinetics of specific types of nitroso-induced DNA damage using the comet assay in human cells

The comet assay is sensitive and can detect DNA damage frequencies less than 1 in 10(7) bases. We have previously shown that several types of DNA damage associated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a tobacco-specific pro-mutagen, can be investigated with some specificity using this technique. Little is known about their repair. We verified the ability of the comet assay to quantify the repair kinetics of specific types of damage in normal fibroblasts, e.g., dimethylsulfate-induced 7-methylguanines (7-mG) and UVB-induced cyclobutane pyrimidine dimers. The time course, formation and repair, of DNA damage after acute doses of NNK reactive metabolites, were then compared in normal human cells (fibroblasts and lymphocytes) and in cells proficient for activating NNK (U937 and NCI-H23). NNK can be activated in cells into reactive metabolites that can either methylate or pyridyloxobutylate DNA. The 7-mG generated by methylation gave post-treatment patterns that were sufficiently different between cell types to conclude that repair of 7-mG in U937 cells was fast, repair in lymphocytes was slow, and repair in NCI-H23 cells and fibroblasts displayed intermediate rates. Pyridyloxobutylation generated formamidopyrimidine (fapy) glycosylase (fpg)-sensitive sites that could be the fapy form of 7-pyridyloxobutylguanines produced in cells. For this type of adducts, the post-treatment patterns of adduct frequency as a function of time depended even more clearly on the cell type: fibroblasts and NCI-H23 cells showed an initial rapid increase in fpg-sensitive damage frequency that did not occur in lymphocytes and U937 cells. This increase seemed associated with p53 proficiency in fibroblasts. Our results show that repair kinetics can be investigated with the comet assay and that differences between cell types can be observed with that technique. But it seems that pro-mutagen activation and/or the way a type of adducts is formed can affect the quantification of the repair.

Metabolomics

Metabolomics is the systematic identification and quantitation of all metabolites in a given organism or biological sample. The enhanced resolution provided by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS), along with powerful chemometric software, allows the simultaneous determination and comparison of thousands of chemical entities, which has lead to an expansion of small molecule biochemistry studies in bacteria, plants, and mammals. Continued development of these analytical platforms will accelerate the widespread use of metabolomics and allow further integration of small molecules into systems biology. Here, recent studies using metabolomics in xenobiotic metabolism and genetically modified mice are highlighted.

Role of environmental toxins in endemic (Balkan) nephropathy. October 2006, Zagreb, Croatia

An international symposium, held in Zagreb, Croatia, in October 2006, brought together basic scientists and clinical investigators engaged in research on endemic (Balkan) nephropathy, a chronic renal tubulointerstitial disease of previously unknown cause that often is accompanied by upper urinary tract urothelial cancer. Although this disease is endemic in rural areas of Bosnia, Bulgaria, Croatia, Romania, and Serbia, a similar clinical entity occurs throughout Europe, Asia, and North America. Recent advances in the understanding of endemic nephropathy now favor the causative role of aristolochic acid over the ubiquitous mycotoxin known as ochratoxin A. Specifically, aristolactam-DNA adducts have been found in renal tissues and urothelial cancers of affected patients. A "signature" p53 mutation in the upper urothelial cancer associated with this disease provides evidence of long-term exposure to aristolochic acid. In addition, the renal pathophysiology and histopathology observed in endemic nephropathy most closely resemble the entity known as aristolochic acid nephropathy. Public health authorities in countries harboring this disease are encouraged to reduce the potential for dietary exposure to Aristolochia clematitis.

Ocimum sanctumLinn. (Holy Basil) Ethanolic Leaf Extract Protects Against 7,12-Dimethylbenz[a]Anthracene-Induced Genotoxicity, Oxidative Stress, and Imbalance in Xenobiotic-Metabolizing Enzymes

The present study was designed to evaluate the protective effects of ethanolic Ocimum sanctum leaf extract against 7,12-dimethylbenz[a]anthracene (DMBA)-induced genotoxicity, oxidative stress, and imbalance in xenobiotic-metabolizing enzymes. Four different concentrations of ethanolic O. sanctum leaf extract (100, 200, 300, and 400 mg/kg of body weight) were administered to Wistar rats by intragastric intubation for five consecutive days followed by intraperitoneal injection of DMBA (35 mg/kg of body weight) 90 minutes after the final dose of the extract. Administration of DMBA increased bone marrow micronuclei, phase I enzymes, lipid peroxidation, and protein carbonyl formation. This was accompanied by a significant decrease in the activities of phase II detoxification enzymes and antioxidants in the liver, erythrocytes, and bone marrow. Pretreatment with ethanolic O. sanctum leaf extract at a concentration of 300 mg/kg of body weight significantly reduced micronuclei formation and phase I enzymes as well as lipid and protein oxidation with enhanced antioxidant and phase II enzyme activities. The results of the present study suggest that ethanolic O. sanctum leaf extract inhibits DMBA-induced genotoxicity and oxidative stress by modulating xenobiotic-metabolizing enzymes, reducing the extent of lipid and protein oxidation and up-regulating antioxidant defenses.

The surgeon's role in cancer prevention. The model in colorectal carcinoma

Cancer Prevention is an emerging field, capturing the old traditional concept of anticipating the development of a major disease and preventing its full impact by early detection, treatment, or aborting the tumorigenic process by a "molecular vaccine" and alleviating the full impact of the disease. Surgeons are important clinician scientists who can carry this discipline forward and develop its full potential in the clinics and in the community. Advances in molecular biology, genetics, and other technologies have permitted seminal understanding of the carcinogenic pathways and identification of targets and intermediate end points in neoplasia. In this review, we will see that we have the means of preventing significant numbers of colorectal carcinomas (CRC).

Precancerous model of human breast epithelial cells induced by NNK for prevention

Epidemiological investigations have suggested that exposure to tobacco and environmental carcinogens increase the risk of developing human breast cancer. In light of the chronic exposure of human breast tissues to tobacco and environmental carcinogens, we have taken an approach of analyzing cellular changes of immortalized non-cancerous human breast epithelial MCF10A cells during the acquisition of cancerous properties induced by repeated exposure to the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) at a low concentration of 100 pM. We found that accumulated exposures of MCF10A cells to NNK result in progressive development of cellular carcinogenesis from a stage of immortalization to precancerous sub-stages of acquiring a reduced dependence on growth factors and acquiring anchorage-independent growth. Using Matrigel for MCF10A cells to form size-restricted acini, we detected that exposures to NNK resulted in altered acinar conformation. Analysis of gene expression profiles by cDNA microarrays revealed up- and down-regulated genes associated with NNK-induced carcinogenesis. Using this cellular carcinogenesis model as a target system to identify anticancer agents, we detected that grape seed proanthocyanadin extract significantly suppressed NNK-induced carcinogenesis of MCF10A cells. Our studies provide a carcinogenesis-cellular model mimicking the accumulative exposure to carcinogens in the progression of human breast epithelial cells to increasingly acquire cancerous properties, as likely occurs in the development of precancerous human breast cells. Our cellular model also serves as a cost-efficient, in vitro system to identify preventive agents that inhibit human breast cell carcinogenesis induced by chronic exposures to carcinogens.

Smoking, alcohol, and dietary choices: evidence from the Portuguese National Health Survey

BACKGROUND

Unhealthy lifestyle choices tend to cluster, but controversy remains regarding relationships between smoking and dietary habits. The aim of this study was to compare dietary intake and alcohol consumption, according to smoking status, in the Portuguese population.

METHODS

The study sample included all participants in the third Portuguese National Health Survey who were older than 19 years (20,302 women and 17,923 men). Participants were selected from households in the five regions of Portugal (NUTS II classification), using a multi-stage random probability design. Trained interviewers conducted face-to-face interviews in each household and obtained information on social and demographic characteristics, lifestyle and health, smoking, and intakes of selected food and beverages. Age-adjusted and education-adjusted binomial and multinomial logistic regression models were fitted separately for males and females, to estimate the magnitude of the association between smoking and the consumption of various food and beverage groups.

RESULTS

When heavy smokers were compared with non-smokers, the odds ratio (OR) favouring soup consumption was 0.60 (95% Confidence Interval [95%CI]: 0.54-0.68) in males and 0.46 (95% CI: 0.33-0.65) in females. Similar ORs were observed for vegetables (males: OR = 0.56, 95%CI: 0.49-0.64; females: OR = 0.47, 95%CI: 0.32-0.69) and fruit (males: OR = 0.36, 95%CI: 0.31-0.41; females: OR = 0.29, 95%CI: 0.19-0.44). Overall, these food items were consumed at significantly lower levels as cigarette consumption increased. Heavy male smokers, compared to non-smokers, presented lower odds favouring milk consumption (OR = 0.89; 95%CI: 0.67-0.89). When heavy smokers were compared with non-smokers, the ORs favouring wine drinking, among heavy drinkers, were 1.47 (95%CI: 1.27-1.70) in men and 3.97 (95%CI: 2.07-7.61) in women. Similar ORs were observed for beer (males: OR = 3.30; 95%CI: 2.87-3.78; females: OR = 23.1; 95%CI: 12.2-43.6), Port wine (males: OR = 2.21 95%CI: 1.65-2.98; females: OR = 2.85; 95%CI: 0.68-12.1), brandy (males: OR = 3.67 95%CI: 2.98-4.52; females: OR = 13.2; 95%CI: 3.72-46.6) and whisky (males: OR = 3.31; 95%CI: 2.71-4.03; females: OR = 41.4; 95%CI: 18.5-92.5).

CONCLUSION

This study showed that smokers have a higher intake of alcoholic beverages and a lower consumption of food items rich in fibre, antioxidants, or phytochemicals, which are suspected to have beneficial roles in the prevention of multiple chronic diseases.

Effects of the environmental mammary carcinogen 6-nitrochrysene on p53 and p21(Cip1) protein expression and cell cycle regulation in MCF-7 and MCF-10A cells

The environmental pollutant 6-nitrochrysene (6-NC) is a potent mammary carcinogen in rats; it is more potent than numerous classical mammary carcinogens such as benzo[a]pyrene (BaP). The mechanisms that account for the remarkable carcinogenicity of 6-NC remain elusive. Similar to BaP, 6-NC is also known to induce DNA damage in rodents and in human breast tissues. As an initial investigation, we reasoned that DNA damage induced by 6-NC may alter the expression of p53 protein in a manner that differs from other DNA damaging carcinogens (e.g. BaP). Using human breast adenocarcinoma MCF-7 cells and immortalized human mammary epithelial MCF-10A cells, we determined the effects of 6-NC on the expression of p53 protein and its direct downstream target cyclin-dependent kinase inhibitor p21(Cip1) as well as on the cell cycle progression. Western blot analysis demonstrated that treatments of MCF-7 and MCF-10A cells with 6-NC for 12, 24 or 48h did not increase the level of total p53 protein; however, an increase of p21(Cip1) protein and a commitment increase of G(1) phase were observed in MCF-10A cells but not in MCF-7 cells. Further studies using 1,2-dihydroxy-1,2-dihydro-6-hydroxylaminochrysene (1,2-DHD-6-NHOH-C), the putative ultimate genotoxic metabolite of 6-NC, was conducted and showed a significant induction of p53 (p<0.05) in MCF-7 cells; however, this effect was not evident in MCF-10A cells, indicating the varied DNA damage responses between the two cell lines. By contrast to numerous DNA damaging agents such as BaP which is known to stimulate p53 expression, the lack of p53 response by 6-NC imply the lack of protective functions mediated by p53 (e.g. DNA repair machinery) after exposure to 6-NC and this may, in part, account for its remarkable carcinogenicity in the mammary tissue.

Nitrosamines as nicotinic receptor ligands

Nitrosamines are carcinogens formed in the mammalian organism from amine precursors contained in food, beverages, cosmetics and drugs. The potent carcinogen, NNK, and the weaker carcinogen, NNN, are nitrosamines formed from nicotine. Metabolites of the nitrosamines react with DNA to form adducts responsible for genotoxic effects. We have identified NNK as a high affinity agonist for the alpha7 nicotinic acetylcholine receptor (alpha7nAChR) whereas NNN bound with high affinity to epibatidine-sensitive nAChRs. Diethylnitrosamine (DEN) bound to both receptors but with lower affinity. High levels of the alpha7nAChR were expressed in human small cell lung cancer (SCLC) cell lines and in hamster pulmonary neuroendocrine cells (PNECs), which serve as a model for the cell of origin of human SCLC. Exposure of SCLC or PNECs to NNK or nicotine increased expression of the alpha7nAChR and caused influx of Ca(2+), activation of PKC, Raf-1, ERK1/2, and c-myc, resulting in the stimulation of cell proliferation. Signaling via the alpha7nAChR was enhanced when cells were maintained in an environment of 10-15% CO(2) similar to that in the diseased lung. Hamsters with hyperoxia-induced pulmonary fibrosis developed neuroendocrine lung carcinomas similar to human SCLC when treated with NNK, DEN, or nicotine. The development of the NNK-induced tumors was prevented by green tea or theophylline. The beta-adrenergic receptor agonist, isoproterenol or theophylline blocked NNK-induced cell proliferation in vitro. NNK and nicotine-induced hyperactivity of the alpha7nAChR/RAF/ERK1/2 pathway thus appears to play a crucial role in the development of SCLC in smokers and could be targeted for cancer prevention.

Registry-based case-control study of cancer in California firefighters

BACKGROUND

There is no consensus whether firefighters are at increased cancer risk for particular cancers. Previous studies have been small, mostly investigated cancer mortality, and suggested increased risks for brain, bladder, testicular, prostate, thyroid and colo-rectal cancers, leukemia, and melanoma.

METHODS

Records of all male cancers registered in California during 1988-2003 were obtained. Firefighters were identified from occupation and industry text fields. Logistic regression analysis used other cancers as controls.

RESULTS

Of the 804,000 eligible records, 3,659 had firefighting as their occupation. Firefighting was associated with testicular cancer (odds ratio = 1.54, 95% confidence interval: 1.18-2.02), melanoma (1.50, 1.33-1.70), brain cancer (1.35, 1.06-1.72), esophageal cancer (1.48, 1.14-1.91), and prostate cancer (1.22, 1.12-1.33).

CONCLUSIONS

Use of other-cancer controls and lack of an occupational history may have biased relative risks towards the null. However, this study, which contained more firefighter cancers than any previous epidemiologic study, produced evidence supporting some prior hypotheses.

AhR- and c-maf-dependent induction of beta7-integrin expression in human macrophages in response to environmental polycyclic aromatic hydrocarbons

In order to identify molecular targets of environmental polycyclic aromatic hydrocarbons (PAHs), we have analysed regulation of integrin (ITG) expression in PAH-exposed human macrophages. Among ITG subunits, beta7 ITG was found to be markedly up-regulated at both mRNA and protein levels in response to the prototypical PAH benzo(a)pyrene (BP). Knock-down of the transcription factor c-maf, known to control beta7 ITG expression, markedly impaired BP-mediated beta7 ITG induction. Moreover, chromatin immunoprecipitation and electrophoretic mobility shift assays showed BP-triggered binding of c-maf to a specific maf-responsive element found in beta7 ITG promoter. Such a binding, and also beta7 ITG induction, were however abolished in response to chemical inhibition of the aryl hydrocarbon receptor (AhR), to which PAHs bind. Taken together, these data establish beta7 ITG as a new molecular target of PAHs, whose up-regulation by these environmental contaminants most likely requires activation of co-operative pathways involving both AhR and c-maf.

Monitoring repair of DNA damage in cell lines and human peripheral blood mononuclear cells

We introduce a method to follow DNA repair that is suitable for both clinical and laboratory samples. An episomal construct with a unique 8-oxoguanine (8-oxoG) base at a defined position was prepared in vitro using single-stranded phage harboring a 678-bp tract from exons 5 to 9 of the human P53 gene. Mixing curve experiments showed that the real-time PCR method has a linear response to damage, suggesting that it is useful for DNA repair studies. The episomal construct with a unique 8-oxoG base was introduced into AD293 cells or human peripheral blood mononuclear cells, and plasmids were recovered as a function of time. The quantitative real-time PCR assay demonstrated that repair of the 8-oxoG was 80% complete in less than 48 h in AD293 cells. Transfection of small interfering RNAs down-regulated OGG1 expression in AD293 cells and reduced the repair of 8-oxoG to 30%. Transfection of the episome into unstimulated white blood cells showed that 8-oxoG repair had a half-life of 2 to 5h. This method is a rapid, reproducible, and robust way to monitor repair of specific adducts in virtually any cell type.

Workgroup report: base stations and wireless networks-radiofrequency (RF) exposures and health consequences

Radiofrequency (RF) waves have long been used for different types of information exchange via the air waves--wireless Morse code, radio, television, and wireless telephone (i.e., construction and operation of telephones or telephone systems). Increasingly larger numbers of people rely on mobile telephone technology, and health concerns about the associated RF exposure have been raised, particularly because the mobile phone handset operates in close proximity to the human body, and also because large numbers of base station antennas are required to provide widespread availability of service to large populations. The World Health Organization convened an expert workshop to discuss the current state of cellular-telephone health issues, and this article brings together several of the key points that were addressed. The possibility of RF health effects has been investigated in epidemiology studies of cellular telephone users and workers in RF occupations, in experiments with animals exposed to cell-phone RF, and via biophysical consideration of cell-phone RF electric-field intensity and the effect of RF modulation schemes. As summarized here, these separate avenues of scientific investigation provide little support for adverse health effects arising from RF exposure at levels below current international standards. Moreover, radio and television broadcast waves have exposed populations to RF for > 50 years with little evidence of deleterious health consequences. Despite unavoidable uncertainty, current scientific data are consistent with the conclusion that public exposures to permissible RF levels from mobile telephone and base stations are not likely to adversely affect human health.

Variation, "evolution", immortality and genetic instabilities in tumour cells

The pathological characteristics of tumour cells often include variation of their histopathological features (i.e. "degrees of de-differentiation") between cases of the same tumour type and between different foci within individual tumours. Usually, only a few cell lines from tumours are immortal. Currently, somatic mutation, replicative infidelity of DNA and aneuploidy are suggested as alternative mechanisms of genomic disturbance underlying tumours. Nevertheless, apart from Hansemann's ideas of "anaplasia" and "de-differentiation" (proposed in the 1890s), and supposed "evolutionary themes" in cancer cell biology, little has been published concerning how histopathologic variation and immortality in tumour cells might arise. This paper reviews applications of the concepts of "variation" to tumours, including concepts of "evolution" and "cellular Darwinism". It is proposed that combinations of somatic mutation, DNA replicative infidelity and aneuploidy may explain the variabilities in tumours, and provide immortality in occasional tumour cells. A possible model involves (i) an initial somatic mutation causing reduced replicative fidelity of DNA, which could be variable in intensity, and thus give rise to variations between cases; (ii) a phase of replicative infidelity of DNA causing daughter cells lines to develop various abnormalities to different degrees, and hence provide for variation between areas of the same tumour. As a last event (iii) occasional asymmetric chromosomal distributions (aneuploidy) might "refresh" the ability of a daughter cell to replicate DNA faithfully causing them to become immortal. Thus extensively mutant and variable, hyperploid, and occasionally immortal cells might arise.

A comparative study on the antimutagenic properties of aqueous extracts of Aspalathus linearis (rooibos), different Cyclopia spp. (honeybush) and Camellia sinensis teas

Antimutagenic activity of aqueous extracts of the South African herbal teas, Aspalathus linearis (rooibos) and Cyclopia spp. (honeybush) was compared with that of Camellia sinensis (black, oolong and green) teas in the Salmonella mutagenicity assay using aflatoxin B(1) (AFB(1)) and 2-acetylaminofluorene (2-AAF) as mutagens. The present study presents the first investigation on antimutagenic properties of C. subternata, C. genistoides and C. sessiliflora. The herbal teas demonstrated protection against both mutagens in the presence of metabolic activation, with the exception of "unfermented" (green/unoxidised) C. genistoides against 2-AAF, which either protected or enhanced mutagenesis depending on the concentration. Antimutagenic activity of "fermented" (oxidised) rooibos was significantly (P<0.05) less than that of Camellia sinensis teas against AFB(1), while for 2-AAF it was less (P<0.05) than that of black tea and similar (P>0.05) to that of oolong and green teas. Antimutagenic activity of unfermented C. intermedia and C. subternata exhibited a similar protection as fermented rooibos against AFB(1). Against 2-AAF, fermented rooibos exhibited similar protective properties than unfermented C. intermedia and C. sessiliflora. Unfermented rooibos was less effective than the C. sinensis teas and fermented rooibos, but had similar (P>0.05) antimutagenicity to that of fermented C. sessiliflora against AFB(1) and fermented C. subternata against 2-AAF. Fermented C. intermedia and C. genistoides exhibited the lowest protective effect against 2-AAF, while fermented C. intermedia exhibited the lowest protection when utilising AFB(1) as mutagen. Aspalathin and mangiferin, major polyphenols in rooibos and Cyclopia spp., respectively, exhibited weak to moderate protective effects when compared to the major green tea catechin, (-)epigallocatechin gallate (EGCG). Antimutagenic activity of selected herbal tea phenolic compounds indicated that they contribute towards (i) observed antimutagenic activity of the aqueous extracts against both mutagens and (ii) enhancement of the mutagenicity of 2-AAF by unfermented C. genistoides. Antimutagenic activity of the South African herbal teas was mutagen-specific, affected by fermentation and plant material, presumably due to changes and variation in phenolic composition.

Formation and biochemistry of carcinogenic heterocyclic aromatic amines in cooked meats

Heteroyclic aromatic amines (HAAs) are a class of hazardous chemicals that are receiving heightened attention as a risk factor for human cancer. HAAs arise during the cooking of meats, fish, and poultry, and several HAAs also occur in tobacco smoke condensate and diesel exhaust. Many HAAs are carcinogenic and induce tumors at multiple sites in rodents. A number of epidemiologic studies have reported that frequent consumption of well-done cooked meats containing HAAs can result in elevated risks for colon, prostate, and mammary cancers. Moreover, DNA adducts of HAAs have been detected in human tissues, demonstrating that HAAs induce genetic damage even though the concentrations of these compounds in cooked meats are generally in the low parts-per-billion (ppb) range. With recent improvements in sensitivity of mass spectrometry instrumentation, HAAs, their metabolites, and DNA adducts can be detected at trace amounts in biological fluids and tissues of humans. The incorporation of HAA biomarkers in epidemologic studies will help to clarify the role of these dietary genotoxicants in the etiology of human cancer.

An environmental quinoid polycyclic aromatic hydrocarbon, acenaphthenequinone, modulates cyclooxygenase-2 expression through reactive oxygen species generation and nuclear factor kappa B activation in A549 cells

Diesel exhaust particles (DEPs) contain oxygen-containing polycyclic aromatic hydrocarbons (PAHs) called quinoid PAHs. Some quinoid PAHs generate free radicals as they undergo enzymatic and nonenzymatic redox cycling with their corresponding semiquinone radicals. Reactive oxygen species (ROS) produced by these reactions can cause severe oxidative stress connected with inflammatory processing. Although humans and animals are continuously exposed to these chemicals in the environment, little is known about which quinoid PAHs are active. In this study, we estimated the intracellular ROS production and nuclear factor kappa B (NF-kappaB) translocation in A549 cells exposed to isomers of quinoid PAHs having two to four rings. We found that both acenaphthenequinone (AcQ) and 9,10-phenanthrenequinone (PQ) enhanced ROS generation and that AcQ translocated NF-kappaB from the cytosol to the nucleus. However, PQ, which has been reported to induce apoptosis, did not influence NF-kappaB activation. In addition, AcQ induced cyclooxygenase-2 (COX-2) expression which is a key enzyme in the inflammatory processing involved in the activation of NF-kappaB. Upregulation of NF-kappaB and COX-2 expression by AcQ treatment was suppressed by the antioxidant N-acetylcysteine (NAC). These results provide that AcQ might play an important role in human lung inflammatory diseases as an air pollutant.

Mitochondrial dysfunction, persistently elevated levels of reactive oxygen species and radiation-induced genomic instability: a review

Radiation-induced genomic instability (RIGI) challenges the long-standing notion that radiation's effects derive solely from nuclear impact. In RIGI it is the unirradiated progeny that can display phenotypic changes at delayed times after irradiation of the parental cell. RIGI might well provide the driving force behind the development of radiation-induced tumorigenesis as most cancer cells even in pre-neoplastic states display multiple genetic alterations. Thus, understanding RIGI may help elucidate the mechanisms underlying radiation-induced carcinogenesis. One characteristic of clones of genetically unstable cells is that many exhibit persistently increased levels of reactive oxygen species (ROS). Furthermore, oxidants enhance and antioxidants diminish radiation-induced instability. However, much about the mechanisms behind the initiation and perpetuation of RIGI remains unknown and we examine the evidence for the hypothesis that oxidative stress and mitochondrial dysfunction may be involved in perpetuating the unstable phenotype in some cell clones surviving ionizing radiation.

The nicotinic receptor antagonists abolish pathobiologic effects of tobacco-derived nitrosamines on BEP2D cells

Identification of the mechanisms leading to malignant transformation of respiratory cells may prove useful in the prevention and treatment of tobacco-related lung cancer. Nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) can induce tumors both locally and systemically. In addition to the genotoxic effect, they have been shown to affect lung cells due to ligating the nicotinic acetylcholine receptors (nAChRs) expressed on the plasma membrane. In this study, we sought to establish the role for nAChRs in malignant transformation caused by NNK and NNN. We used the BEP2D cells that represent a suitable model for studying the various stages of human bronchial carcinogenesis. We found that these cells express alpha1, alpha3, alpha5, alpha7, alpha9, alpha10, beta1, beta2, and beta4 nAChR subunits that can form high-affinity binding sites for NNK and NNN. Exposure of BEP2D cells to either NNK or NNN in both cases increased their proliferative potential which could be abolished in the presence of nAChR antagonists alpha-bungarotoxin, which worked most effectively against NNK, or mecamylamine, which was most efficient against NNN. The BEP2D cells stimulated with the nitrosamines showed multifold increases of the transcription of the PCNA and Bcl-2 genes by both real-time polymerase chain reaction and in-cell western assays. To gain a mechanistic insight into NNK- and NNN-initiated signaling, we investigated the expression of genes encoding the signal transduction effectors GATA-3, nuclear factor-kappaB, and STAT-1. Experimental results indicated that stimulation of nAChRs with NNK led to activation of all three signal transduction effectors under consideration, whereas NNN predominantly activated GATA-3 and STAT-1. The GATA-3 protein-binding activity induced by NNK and NNN correlated with elevated gene expression. The obtained results support the novel concept of receptor-mediated action of NNK and NNN placing cellular nAChRs in the center of the pathophysiologic loop, and suggest that an nAChR antagonist may serve as a chemopreventive agent.

Formamidopyrimidine adducts are detected using the comet assay in human cells treated with reactive metabolites of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is the most lung-specific of the carcinogens present in tobacco smoke. Its bioactivation in cells leads to a small amount of methylation or pyridyloxobutylation DNA damage. Considering its great sensitivity, the comet assay seems a technique of choice to investigate NNK-related damage. Several strategies were used to impart some specificity to the assay: (1) using analogs that produce a limited variety of DNA lesions, as they mimic either the methylation or the pyridyloxobutylation pathway; (2) using cells with different bioactivation abilities; (3) using alkali conversion and/or enzymes specific for cleaving particular classes of damage; (4) using different lysis conditions to convert a specific class of DNA lesions into enzyme-sensitive lesions. We determined that several NNK-associated lesions can be detected with some specificity with the comet assay. For the methylation pathway, they are AP sites and the more frequent formamidopyrimidine (fapy) adducts. These fapy adducts correspond to N7-methylguanines generated in the cells that were ring-opened during the assay by the lysis solution at pH 10. For the pyridyloxobutylation pathway, alkylphosphotriesters and a roughly equal frequency of fapy sites were detected. By analogy to the methylation damage, these fapy adducts are thought to be the ring-opened form of N7-pyridyloxobutylguanines (N7-pobG). N7-pobG are unstable and this constitutes the first indirect demonstration of their formation in cells. But contrary to N7-m-fapy, the lysis time or pH did not influence the frequency of N7-pob-fapy adducts detected, suggesting that they already exist in the cells and are not related to the experimental conditions. These N7-pob-fapy have a strong mutagenic potential and we think that the comet assay, in spite of its limitations, is a good way to study them considering their low frequency and the inherent instability of the adduct from which they originate.

Induction of the transferrin receptor gene by benzo[a]pyrene in breast cancer MCF-7 cells: potential as a biomarker of PAH exposure

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental DNA-damaging agents regarded as risk factors for human disease, including lung and breast cancer. The biotransformation of PAHs to carcinogenic metabolites is mediated by the aromatic hydrocarbon receptor (AhR), which activates transcription at xenobiotic responsive elements (XREs = 5'-GCGTG-3') found in the promoter regions of genes encoding for detoxifying enzymes, including CYP1A1 and CYP1B1. In this study, we wished to identify novel biomarkers that may be useful in monitoring critical carcinogenic events of the breast induced by PAHs. Using a GeneMAP CancerArray, we analyzed in breast cancer MCF-7 cells the temporal effects of the AhR agonist benzo[a]pyrene (B[a]P), which is a prototype PAH and known environmental carcinogen. Genes upregulated at least threefold by B[a]P and containing potential XREs within their promoter regions included CYP1A1, CYP1B1, paired box gene 3 (PAX3), cortactin (CTTN/EMS1), beta-2-microglobulin (B2M), and transferrin receptor (TfR). The stimulatory effects of B[a]P on expression of these genes were abrogated by cotreatment with the AhR antagonist flavonoid, alpha-napthoflavone (ANF). The TfR gene was selected for further analysis as its promoter region contains two potential XREs and its expression has been shown to be increased in breast cancer cells. Accumulation of TfR mRNA in B[a]P-treated cells was confirmed by quantitative real time PCR. Transient transfection studies indicated that the transcriptional activity of the TfR promoter was stimulated by B[a]P, whereas ANF counteracted this induction. These results indicate that the TfR gene may be a potential biomarker of PAH exposure.

Early manifestations of NNK-induced lung cancer: role of lung immunity in tumor susceptibility

A strong correlation exists between smoking and lung cancer; however, susceptibility to lung cancer among smokers is not uniform. Similarly, mice show differential susceptibility to the tobacco carcinogen nitrosamine 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which produces lung tumors in A/J but not in C3H mice. Host immunity may play a role in the susceptibility to cancer, and cigarette smoke/nicotine suppresses the immune system through activation of nicotinic acetylcholine receptors (nAChRs). Mammalian lungs express alpha7-nAChRs, and NNK is a high-affinity agonist for alpha7-nAChRs. To examine whether NNK differentially modulates lung immunity in susceptible and resistant mouse strains, A/J and C3H mice were treated with NNK and/or immunized with sheep red blood cells. Lung tissues and RNA of treated and untreated animals were analyzed by immunohistochemistry and RT-PCR for alpha7-nAChR and COX-2 expression. Spleen- and the lung-associated lymph node cells from control and immunized animals were assessed for immunologic responses, including anti-sheep red blood cell antibody plaque-forming cells, concanavalin A-induced T-cell proliferation, and the anti-CD3/CD28 antibody-induced rise in intracellular calcium. NNK strongly suppressed these responses in A/J but not in C3H mice. Similar NNK-induced immunologic changes were seen in another pair of carcinogen-sensitive (NGP) and relatively carcinogen-resistant (B10.A) mouse strains. Moreover, NNK stimulates a significantly higher expression of COX-2 and alpha7-nAChRs in A/J than in C3H lungs. These results suggest that the susceptibility to chemical carcinogenesis among various mouse strains might be influenced by their immunologic response to the carcinogen.

Carcinogens induce genome-wide loss of heterozygosity in normal stem cells without persistent chromosomal instability

Widespread losses of heterozygosity (LOH) in human cancer have been thought to result from chromosomal instability caused by mutations affecting DNA repair/genome maintenance. However, the origin of LOH in most tumors is unknown. The present study examined the ability of carcinogenic agents to induce LOH at 53 sites throughout the genome of normal diploid mouse ES cells. Brief exposures to nontoxic levels of methylnitrosourea, diepoxybutane, mitomycin C, hydroxyurea, doxorubicin, and UV light stimulated LOH at all loci at frequencies ranging from 1-8 x 10(-3) per cell (10-123 times higher than in untreated cells). This greatly exceeds the frequencies at which these agents have been reported to induce point mutations and is comparable to the rates of LOH observed in ES cells lacking the gene responsible for Bloom syndrome, an inherited DNA repair defect that results in greatly increased risk of cancer. These results suggest that LOH contributes significantly to the carcinogenicity of a variety of mutagens and raises the possibility that genome-wide LOH observed in some human cancers may reflect prior exposure to genotoxic agents rather than a state of chromosomal instability during the carcinogenic process. Finally, as a practical matter, chemically induced LOH is expected to enhance the recovery of homozygous recessive mutants from phenotype-based genetic screens in mammalian cells.

Biochemical basis of genotoxicity of heterocyclic arylamine food mutagens: Human DNA polymerase eta selectively produces a two-base deletion in copying the N2-guanyl adduct of 2-amino-3-methylimidazo[4,5-f]quinoline but not the C8 adduct at the NarI G3 site

Heterocyclic arylamines are highly mutagenic and cause tumors in animal models. The mutagenicity is attributed to the C8- and N2-G adducts, the latter of which accumulates due to slower repair. The C8- and N 2-G adducts derived from 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) were placed at the G1 and G3 sites of the NarI sequence, in which the G3 site is an established hot spot for frameshift mutation with the model arylamine derivative 2-acetylaminofluorene but G1 is not. Human DNA polymerase (pol) eta extended primers beyond template G-IQ adducts better than did pol kappa and much better than pol iota or delta. In 1-base incorporation studies, pol eta inserted C and A, pol iota inserted T, and pol kappa inserted G. Steady-state kinetic parameters were measured for these dNTPs opposite the C8- and N 2-IQ adducts at both sites, being most favorable for pol eta. Mass spectrometry of pol eta extension products revealed a single major product in each of four cases; with the G1 and G3 C8-IQ adducts, incorporation was largely error-free. With the G3 N 2-IQ adduct, a -2 deletion occurred at the site of the adduct. With the G1 N 2-IQ adduct, the product was error-free at the site opposite the base and then stalled. Thus, the pol eta products yielded frame-shifts with the N 2 but not the C8 IQ adducts. We show a role for pol eta and the complexity of different chemical adducts of IQ, DNA position, and DNA polymerases.

Modification of p53 protein profile by gamma irradiation followed by methyl donor starvation

The possible beneficial radio-protective effects of one-carbon transfer agents namely folate, choline and methionine have been the subject of extensive investigation. Ionizing radiation is known to extensively damage the DNA. One-carbon transfer agents have been proposed to have important role in context of DNA repair via their role in purine and thymidylate synthesis and in DNA methylation. Sufficient dietary availability of one-carbon transfer agents therefore, might have ability to modify radiation effects. In present study modifications in level of tumor suppressor protein p53 by gamma irradiation followed by methyl donor starvation was observed. Experiments showed an increase in nuclear and cytoplasmic p53 protein concentration in liver, spleen and thymus. The overall rise in the level of p53 protein in liver was found to be less than that in spleen and thymus. Moreover significant heterogeneity in the basal level of expression of the p53 protein in liver, spleen and thymus was observed as the level of p53 protein in spleen and thymus was found to be 7-8 fold more than that in liver. Results indicated that radiation stress followed by methyl donor starvation could significantly induce p53 protein in spleen and thymus where there was a dramatic accumulation of p53 following irradiation, while in other tissues, particularly the liver, no such dramatic response was seen. Folate contribution of intestinal bacteria was found to influence p53 protein levels. Our observations indicated a prominent role played by the methyl donors in protecting the cell against harmful effects of ionizing radiation.

Hepatitis B virus x gene and cyanobacterial toxins promote aflatoxin B1-induced hepatotumorigenesis in mice

AIM: To assess the combinative role of aflatoxin B₁ (AFB₁), cyanobacterial toxins (cyanotoxins), and hepatitis B virus (HBV) x gene in hepatotumorigenicity.

METHODS: One-week-old animals carrying HBV x gene and their wild-type littermates were intraperitoneally (ip) injected with either single-dose AFB₁ [6 mg/kg body weight (bw)], repeated-dose cyanotoxins (microcystin-LR or nodularin, 10 μg/kg bw once a week for 15 wk), DMSO (vehicle control) alone, or AFB₁ followed by cyanotoxins a week later, and were sacrificed at 24 and 52 wk post-treatment.

RESULTS: AFB₁ induced liver tumors in 13 of 29 (44.8%) transgenic mice at 52 wk post-treatment, significantly more frequent than in wild-type mice (13.3%). This significant difference was not shown in the 24-wk study. Compared with AFB₁ exposure alone, MC-LR and nodularin yielded approximately 3-fold and 6-fold increases in the incidence of AFB₁-induced liver tumors in wild-type animals at 24 wk, respectively. HBV x gene did not further elevate the risk associated with co-exposure to AFB₁ and cyanotoxins. With the exception of an MC-LR-dosed wild-type mouse, no liver tumor was observed in mice treated with cyanotoxins alone at 24 wk. Neither DMSO-treated transgenic mice nor their wild-type littermates had pathologic alterations relevant to hepatotumorigenesis in even up to 52 wk.

CONCLUSION: HBV x gene and nodularin promote the development of AFB₁-induced liver tumors. Co-exposure to AFB₁ and MC-LR tends to elevate the risk of liver tumors at 24 wk relative to exposure to one of them. The combinative effect of AFB₁, cyanotoxins and HBVx on hepatotumorigenesis is weak at 24 wk.