Integrating toxicogenomics into human health risk assessment: lessons learned from the benzo[a]pyrene case study

The use of short-term toxicogenomic tests to predict cancer (or other health effects) offers considerable advantages relative to traditional toxicity testing methods. The advantages include increased throughput, increased mechanistic data, and significantly reduced costs. However, precisely how toxicogenomics data can be used to support human health risk assessment (RA) is unclear. In a companion paper ( Moffat et al. 2014 ), we present a case study evaluating the utility of toxicogenomics in the RA of benzo[a]pyrene (BaP), a known human carcinogen. The case study is meant as a proof-of-principle exercise using a well-established mode of action (MOA) that impacts multiple tissues, which should provide a best case example. We found that toxicogenomics provided rich mechanistic data applicable to hazard identification, dose-response analysis, and quantitative RA of BaP. Based on this work, here we share some useful lessons for both research and RA, and outline our perspective on how toxicogenomics can benefit RA in the short- and long-term. Specifically, we focus on (1) obtaining biologically relevant data that are readily suitable for establishing an MOA for toxicants, (2) examining the human relevance of an MOA from animal testing, and (3) proposing appropriate quantitative values for RA. We describe our envisioned strategy on how toxicogenomics can become a tool in RA, especially when anchored to other short-term toxicity tests (apical endpoints) to increase confidence in the proposed MOA, and emphasize the need for additional studies on other MOAs to define the best practices in the application of toxicogenomics in RA.

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.

Prevalence of occupational exposure to carcinogens among workers of Arabic, Chinese and Vietnamese ancestry in Australia

BACKGROUND

Although job-related diseases result in more deaths per year than job-related injuries, most research concerning ethnic minority workers has concerned accidents and injuries rather than disease-causing exposures such as carcinogens.

METHODS

We conducted a telephone-based cross-sectional survey to estimate the prevalence of occupational exposure to carcinogens among a sample of ethnic minority workers in Australia, and compared their exposure prevalence to that of a sample of the general Australian-born working population ('Australian workers').

RESULTS

One-third of the ethnic minority workers were exposed to at least one carcinogen at work. The likelihood of exposure to carcinogens was not significantly different from that of Australian workers, although the likelihood of exposure to individual carcinogens varied by ethnicity.

CONCLUSION

Knowing the prevalence of exposure to carcinogens in the workplace in different ethnic groups will allow better targeted and informed occupational health and safety measures to be implemented where necessary.

Gene-diet interactions in exposure to heterocyclic aromatic amines and bulky DNA adduct levels in blood leukocytes

Heterocyclic aromatic amines (HAAs), carcinogens produced in meat when cooked at high temperatures, are an emerging biologic explanation for the meat-colorectal cancer relationship. HAAs form DNA adducts; left unrepaired, adducts can induce mutations, which may initiate/promote carcinogenesis. The purpose of this research was to investigate the relationship between dietary HAAs, genetic susceptibility and bulky DNA adduct levels. Least squares regression was used to examine the relationship between dietary HAA exposure and bulky DNA adduct levels in blood measured using (32)P-postlabeling among 99 healthy volunteers. Gene-diet interactions between dietary HAAs and genetic factors relevant to the biotransformation of HAAs and DNA repair were also examined. No main effects of dietary HAAs on bulky DNA adduct levels was found. However, those with the putative NAT1 rapid acetylator phenotype had lower adduct levels than those with the slow acetylator phenotype (P = 0.02). Furthermore, having five or more 'at-risk' genotypes was associated with higher bulky DNA adduct levels (P = 0.03). Gene-diet interactions were observed between NAT1 polymorphisms and dietary HAAs (P < 0.05); among the slow acetylator phenotype, higher intakes of HAAs were associated with an increase in DNA adduct levels compared to lower intakes. This study provides evidence of a biologic relationship between dietary HAAs, genetic susceptibility and bulky DNA adduct formation. However, the lack of a strong main effect of HAAs suggests that dietary HAAs are not a large contributor to bulky DNA adducts in this population; future studies should consider relevant gene-diet interactions to clarify the role of HAAs in carcinogenesis.

Increased pancreas cancer in a bio-technological research laboratory

BACKGROUND

Pancreatic cancer is extremely rare among people under 55 years old. Its prognosis is poor, and the causal background remains almost unresolved. A previous study observed an increased occurrence of pancreatic cancer in workers in a French biochemical laboratory.

METHODS

CASE REPORT

During an approximate 10 year period in a Danish bio-chemical laboratory with about 50 stable employees, four cases of pancreatic cancer have been diagnosed at a mean age of 53 years. Approximately 0.02 cases should be expected if the laboratory employees had experienced the same rate of pancreatic cancer as that observed in the respective general Danish populations.

RESULT

All the four cases had a long-term occupational history of exposure to carcinogens during the early bio-technology period.

CONCLUSIONS

Causal conclusions cannot be made yet, but observation of former and present workers in biotechnological laboratories and their cancer occurrence is warranted.

Malignant skin lesions in Oshogbo, Nigeria

INTRODUCTION

The aim of this study is to retrospectively assess the prevalence of some of skin malignancies in our environment and to provide a data base for creating awareness for prevention and early detection of the diseases in order to reduce morbidity and mortality associated with these skin lesions in our environment.

METHODS

This is a retrospective study of all histologically diagnosed malignant skin lesions which presented at Ladoke Akintola University of Technology Teaching Hospital Osogbo Osun State between January 2006 and December 2010.

RESULTS

Ninety- eight patients presented with skin cancers out of which 60 (61.2%)were males and 38 (38.8%) were females. Malignant melanoma ranked highest followed by squamous cell carcinoma, dermatofibrosarcoma and basal cell carcinoma in that order. Malignant melanoma affects male more than female and it commonly affects lower limbs.

CONCLUSION

Skin malignancies pose a burden to the economy of the country. Efforts should be directed toward prevention, early diagnosis and management in order to abolish or reduce morbidity, as well as mortality associated with late presentation of people in the developing countries.

Mortality after exposure to polychlorinated biphenyls and polychlorinated dibenzofurans: a meta-analysis of two highly exposed cohorts

Both Yucheng and Yusho were events of accidental exposure to highly doses of polychlorinated biphenyls and dibenzofurans in Asian people. Mortality experiences caused by various diseases were reported in both cohorts with similar and dissimilar findings. We thus conducted a meta-analysis of two cohorts to reevaluate the effects of PCBs and PCDFs on major causes of mortalities. Two recently updated Yucheng and Yusho mortality studies were included. For selected diseases, standardized mortality ratios (SMR) and 95% confidence intervals (95% CI) were extracted. Meta-analyses were conducted using a random-effects model only when heterogeneity (I(2)  > 50% and/or p value <0.10 by the Q test) was not found. A total of 1,803 Yucheng subjects (male, N = 830; female, N = 973) with 48,751 person-years of follow-up and 1,664 Yusho subjects (male, N = 860; female, N = 804) with 50,773 person-years are included. An increase in all-cause mortality (pooled SMR=1.2, 95% CI: 1.1-1.3, I(2)  = 0.0%), all cancers (pooled SMR=1.3, 95% CI: 1.1-1.6, I(2)  = 0.0%), lung cancer (pooled SMR=1.7, 95% CI: 1.2-2.3, I(2) =0.0%), heart disease (pooled SMR=1.3, 95% CI: 1.0-1.7, I(2)  = 43.4%) and hepatic disease (pooled SMR=1.9, 95% CI: 1.3-2.8, I(2)  = 0.0%) were found in pooled males. Significant elevation from liver cancer was found in pooled females (pooled SMR=2.0, 95% CI: 1.1-3.6, I(2)  = 0.0%). This meta-analysis of Yucheng and Yusho cohorts showed similar elevation from all cancer, lung cancer, heart disease and hepatic disease mortalities in exposed men. Furthermore, a new finding of elevated liver cancer mortality in exposed women was identified.

Determination of polycyclic aromatic hydrocarbons in dry tea

Twenty-eight different tea samples sold in the United States were evaluated using high-performance liquid chromatography (HPLC) with fluorescence detection (FLD) for their contamination with polycyclic aromatic hydrocarbons (PAHs). Many PAHs exhibit carcinogenic, mutagenic, and teratogenic properties and have been related to several kinds of cancer in man and experimental animals. The presence of PAHs in environmental samples such as water, sediments, and particulate air has been extensively studied, but food samples have received little attention. Eighteen PAHs congeners were analyzed, with percentage recovery higher than 85%. Contamination expressed as the sum of the 18 analyzed PAHs was between 101 and 1337 μg/kg on dry mass and the average contents in all of the 28 examined samples was 300 μg/kg on dry mass. Seven of the congeners were found in all samples with wide ranges of concentrations as follows: fluorene (7-48 μg/kg), anthracene (1-31 μg/kg), pyrene (1-970 μg/kg), benzo(a)anthracene (1-18 μg/kg) chrysene (17-365 μg/kg), benzo(a)pyrene (1-29 μg/kg), and indeno(1,2,3-cd)pyrene (4-119 μg/kg). The two most toxic congeners benzo(a)pyrene and dibenzo(a,h)anthracene were found at high concentrations only in Earl Grey Twinnings, Earl Grey Harney& Sons Fine Teas, and Chai Ultra Spice Black Tea Twinnings. Six PAH congeners are considered as suspected carcinogens (U.S.EPA), formed the basis of the estimation of the toxic equivalent (TEQ), Chai Ultra-Spice Black Tea Twinnings had the highest TEQ (110.9) followed by two grey tea samples, Earl Grey Harney & Sons Fine Tea (57.7) and Earl Grey Twinnings (54.5). Decaffeinated grey teas had the lowest TEQs, decaffeinated Earl Grey Bigelow (9.4) and Green Tea Honey Lemon Decaffeinated Lipton (9.6).

Self-reported Occupational Exposures Relevant for Cancer among 28,000 Offshore Oil Industry Workers Employed between 1965 and 1999

The objective of this study was to examine self-reported frequency of occupational exposure reported by 28,000 Norwegian offshore oil workers in a 1998 survey. Predictors of self-reported exposure frequency were identified to aid future refinements of an expert-based job-exposure-time matrix (JEM). We focus here on reported frequencies for skin contact with oil and diesel; exposure to oil vapor from shaker, to exhaust fumes, vapor from mixing chemicals used for drilling, natural gas, chemicals used for water injection and processing, and to solvent vapor. Exposure frequency was reported by participants as the exposed proportion of the work shift, defined by six categories, in their current or last position offshore (between 1965 and 1999). Binary Poisson regression models with robust variance were used to examine the probabilities of reporting frequent exposure (≥&frac14; vs. <&frac14; of work shift) according to main activity, time period, supervisory position, type of company, type of installation, work schedule, and education. Holding a non-supervisory position, working shifts, being employed in the early period of the offshore industry, and having only compulsory education increased the probability of reporting frequent exposure. The identified predictors and group-level patterns may aid future refinement of the JEM previously developed for the present cohort.

The rhetoric of cancer

BACKGROUND

Research involving the discovery of novel anticancer drugs and treatments hold precedence among the general public. However, investigating the etiology and epidemiology of malignancies can have a significant effect on reducing the prevalence of cancer in society. Understanding risk factors that drive neoplastic development can provide educated individuals the opportunity to avoid such catalysts.

METHODS

Literature searches were conducted on prominent magazine and newspaper sources to analyze the accuracy and relevance the material had toward cancer prevention. Additionally, two professionals involved in oncology were interviewed to gain a more personal view of the population's knowledge on cancer awareness and prevention.

RESULTS

The lack of attention paid to the understanding of cancer and its subsequent prevention has resulted in fundamental misconceptions that facilitate the development of neoplastic growths.

CONCLUSIONS

Addressing the lack of attention paid to cancer awareness and prevention through proper education can have a significant effect on limiting the impact cancer has on society.

Inhibition of tumor growth by U0126 is associated with induction of interferon-γ production

Several MEK1/2 inhibitors have been in clinical trial evaluation for cancer treatment. Interferon-γ (IFN-γ) is a cytokine with multiple biological functions including antitumor activity. Expression of IFN-γ can be induced by liver X receptor (LXR), a ligand-activated transcription factor. However, it remains unknown if the anti-cancer action of MEK1/2 inhibitors is completed, at least in part, by activating IFN-γ expression. In this study, we determined that U0126, a MEK1/2 inhibitor, increased tumor-free and survival rates and decreased growth of inoculated Lewis lung carcinomas in wild type mice. However, the protective effects were substantially attenuated in IFN-γ deficient (IFN-γ-/-) mice. At cellular and molecular levels, MEK1/2 inhibitors increased IFN-γ protein and mRNA expression and activated natural IFN-γ promoter but not the IFN-γ promoters with mutations of the LXR responsive elements (LXREs). MEK1/2 inhibitors also enhanced formation of the LXRE-nuclear protein complexes by inducing LXR expression and nuclear translocation. Similarly, MEK1/2 siRNA inhibited phosphorylation of ERK1/2 by MEK1/2 while activated IFN-γ expression. In contrast, inhibition of LXR expression by siRNA blocked MEK1/2 inhibitors-induced IFN-γ expression. U0126 also inhibited chemicals-induced pulmonary carcinomas, which was associated with increased IFN-γ expression in the lung. Taken together, our study suggests that MEK1/2 inhibitors induce IFN-γ production in an LXR-dependent manner and the induction of IFN-γ expression can partially contribute to the anti-tumorigenic properties of U0126.

Electronic nicotine delivery systems ("e-cigarettes"): review of safety and smoking cessation efficacy

BACKGROUND AND OBJECTIVES

Cigarette smoking is common among cancer patients and is associated with negative outcomes. Electronic nicotine delivery systems ("e-cigarettes") are rapidly growing in popularity and use, but there is limited information on their safety or effectiveness in helping individuals quit smoking.

DATA SOURCES

The authors searched PubMed, Web of Science, and additional sources for published empirical data on safety and use of electronic cigarettes as an aid to quit smoking.

REVIEW METHODS

We conducted a structured search of the current literature up to and including November 2013.

RESULTS

E-cigarettes currently vary widely in their contents and are sometimes inconsistent with labeling. Compared to tobacco cigarettes, available evidence suggests that e-cigarettes are often substantially lower in toxic content, cytotoxicity, associated adverse effects, and secondhand toxicity exposure. Data on the use of e-cigarettes for quitting smoking are suggestive but ultimately inconclusive.

CONCLUSIONS

Clinicians are advised to be aware that the use of e-cigarettes, especially among cigarette smokers, is growing rapidly. These devices are unregulated, of unknown safety, and of uncertain benefit in quitting smoking.

IMPLICATIONS FOR PRACTICE

In the absence of further data or regulation, oncologists are advised to discuss the known and unknown safety and efficacy information on e-cigarettes with interested patients and to encourage patients to first try FDA-approved pharmacotherapies for smoking cessation.

Genetic Modeling of PIM Proteins in Cancer: Proviral Tagging and Cooperation with Oncogenes, Tumor Suppressor Genes, and Carcinogens

The PIM proteins, which were initially discovered as proviral insertion sites in Moloney-murine leukemia virus infection, are a family of highly homologous serine/threonine kinases that have been reported to be overexpressed in hematological malignancies and solid tumors. The PIM proteins have also been associated with metastasis and overall treatment responses and implicated in the regulation of apoptosis, metabolism, the cell cycle, and homing and migration, which makes these proteins interesting targets for anti-cancer drug discovery. The use of retroviral insertional mutagenesis and refined approaches such as complementation tagging has allowed the identification of myc, pim, and a third group of genes (including bmi1 and gfi1) as complementing genes in lymphomagenesis. Moreover, mouse modeling of human cancer has provided an understanding of the molecular pathways that are involved in tumor initiation and progression at the physiological level. In particular, genetically modified mice have allowed researchers to further elucidate the role of each of the Pim isoforms in various tumor types. PIM kinases have been identified as weak oncogenes because experimental overexpression in lymphoid tissue, prostate, and liver induces tumors at a relatively low incidence and with a long latency. However, very strong synergistic tumorigenicity between Pim1/2 and c-Myc and other oncogenes has been observed in lymphoid tissues. Mouse models have also been used to study whether the inhibition of specific PIM isoforms is required to prevent carcinogen-induced sarcomas, indicating that the absence of Pim2 and Pim3 greatly reduces sarcoma growth and bone invasion; the extent of this effect is similar to that observed in the absence of all three isoforms. This review will summarize some of the animal models that have been used to understand the isoform-specific contribution of PIM kinases to tumorigenesis.

Determination of polycyclic aromatic hydrocarbons in roasted coffee

Polycyclic aromatic hydrocarbons (PAHs) are suspected to be carcinogenic and mutagenic. This study describes the presence of PAHs in light, medium and dark roasted coffee including instant and decaffeinated brands. Total PAHs concentration was related to the degree of roasting with light roasted coffee showing the least and dark roasted coffee showing the highest level. Both instant and decaffeinated coffee brand showed lower levels of PAHs. Naphthalene, acenaphthylene, pyrene and chrysene were the most abundant individual isomers. The concentrations ranged from 0 to 561 ng g(-1) for naphthalene, 0 to 512 ng g(-1) for acenaphthylene, 60 to 459 ng g(-1) for pyrene and 56 to 371 ng g(-1) for chrysene. Thus, roasting conditions should be controlled to avoid the formation of PAHs due to their suspected carcinogenic and mutagenic properties.

The future of cancer research: prevention, screening, vaccines, and tumor-specific drug combos

New cancer research strategies have developed very rapidly over the past five years, including extensive DNA sequencing of tumor and normal cells; use of highly sensitive cancer cell detection methods; vaccine development and tumor-specific (designer) drugs. These developments have raised questions about where to concentrate efforts in the near future when establishing clinical trials, particularly important in an age of diminishing resources and during a period when competing strategies for cancer control are likely to overwhelm the opportunities for establishing large, effective clinical trials. In particular, it behooves the research community to be mindful of the inevitable, challenging obligation to responsibly choose between clinical trials that offer the credible hope of incremental advances vs. trials that are less traditional but may have revolutionary outcomes.

Loss of VHL in RCC Reduces Repair and Alters Cellular Response to Benzo[a]pyrene

Mutations of the von Hippel-Lindau (VHL) tumor suppressor gene occur in the majority of sporadic renal-cell carcinomas (RCC). Loss of VHL function is associated with stabilization of hypoxia-inducible factor α (HIFα). We and others demonstrated that there is a two-way interaction between the aryl hydrocarbon receptor, which is an important mediator in the metabolic activation and detoxification of carcinogens, and the HIF1-pathway leading to an increased genetic instability when both pathways are simultaneously activated. The aim of this study was to investigate how environmental carcinogens, such as benzo[a]pyrene (BaP), which can be metabolically activated to BaP-7,8-diOH-9,10-epoxide (BPDE) play a role in the etiology of RCC. We exposed VHL-deficient RCC4 cells, in which HIFα is stabilized regardless of oxygen tension, to 0.1 μM BaP for 18 h. The mutagenic BPDE-DNA adduct levels were increased in HIFα stabilized cells. Using qRT-PCR, we demonstrated that absence of VHL significantly induced the mRNA levels of AhR downstream target CYP1A1. Furthermore, HPLC analysis indicated that loss of VHL increased the concentration of BaP-7,8-dihydroxydiol, the pre-cursor metabolite of BPDE. Interestingly, the capacity to repair BPDE-DNA adducts in the HIFα stabilized RCC4 cells, was markedly reduced. Taken together, these data indicate that loss of VHL affects BaP-mediated genotoxic responses in RCC and decreases repair capacity.

DNA adduct formation of 2-amino-9H-pyrido[2,3-b]indole and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline in mouse liver and extrahepatic tissues during a subchronic feeding study

Tobacco smoking is a risk factor for cancers of the liver and gastrointestinal (GI) tract, but the causal agents responsible for these cancers are uncertain. 2-Amino-9H-pyrido[2,3-b]indole (AαC) is an abundant heterocyclic aromatic amine present in tobacco smoke. AαC is a liver carcinogen and both a transgene mutagen and inducer of aberrant crypt foci in the colon of mice. We hypothesize that AαC may contribute to DNA damage and tumorigenesis in these organs of smokers. The potential of AαC to induce DNA adduct formation in liver, organs of the GI tract, lung, and urinary bladder, which are target organs of cancer in smokers, was examined using the C57BL/6 mouse as an animal model. AαC (400 or 800 ppm) and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) (300 ppm), a liver and colon carcinogen in C57BL/6 mice, were given in the diet for up to 12 weeks. Liquid chromatography/mass spectrometry was employed to measure DNA adducts. The major DNA adducts of both carcinogens were identified as deoxyguanosine-C8 adducts. The levels of formation of AαC- and MeIQ-DNA adducts were similar in liver and extrahepatic tissues when adjusted for dose. The highest levels of adducts occurred in liver, followed by urinary bladder, and then in cecum and colon; lower DNA adduct levels were formed in the lung and pancreas following 12 weeks of feeding. The high levels of AαC adduct formed in liver, GI tract, and bladder of C57BL/6 mice reinforce the notion that AαC may contribute to DNA damage and cancer of these organs in smokers.

Assessing secondhand smoke using biological markers

Secondhand smoke exposure (SHSe) is a known cause of many adverse health effects in adults and children. Increasingly, SHSe assessment is an element of tobacco control research and implementation worldwide. In spite of decades of development of approaches to assess SHSe, there are still unresolved methodological issues; therefore, a multidisciplinary expert meeting was held to catalogue the approaches to assess SHSe and with the goal of providing a set of uniform methods for future use by investigators and thereby facilitate comparisons of findings across studies. The meeting, held at Johns Hopkins, in Baltimore, Maryland, USA, was supported by the Flight Attendant Medical Research Institute (FAMRI). A series of articles were developed to summarise what is known about self-reported, environmental and biological SHSe measurements. Non-smokers inhale toxicants in SHS, which are mainly products of combustion of organic materials and are not specific to tobacco smoke exposure. Biomarkers specific to SHSe are nicotine and its metabolites (e.g., cotinine), and metabolites of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Cotinine is the preferred blood, saliva and urine biomarker for SHSe. Cotinine and nicotine can also be measured in hair and toenails. NNAL (4-[methylnitrosamino]-1-[3-pyridyl]-1-butanol), a metabolite of NNK, can be determined in the urine of SHS-exposed non-smokers. The selection of a particular biomarker of SHSe and the analytic biological medium depends on the scientific or public health question of interest, study design and setting, subjects, and funding. This manuscript summarises the scientific evidence on the use of biomarkers to measure SHSe, analytical methods, biological matrices and their interpretation.

Risk-based indicators of Canadians' exposures to environmental carcinogens

BACKGROUND

Tools for estimating population exposures to environmental carcinogens are required to support evidence-based policies to reduce chronic exposures and associated cancers. Our objective was to develop indicators of population exposure to selected environmental carcinogens that can be easily updated over time, and allow comparisons and prioritization between different carcinogens and exposure pathways.

METHODS

We employed a risk assessment-based approach to produce screening-level estimates of lifetime excess cancer risk for selected substances listed as known carcinogens by the International Agency for Research on Cancer. Estimates of lifetime average daily intake were calculated using population characteristics combined with concentrations (circa 2006) in outdoor air, indoor air, dust, drinking water, and food and beverages from existing monitoring databases or comprehensive literature reviews. Intake estimates were then multiplied by cancer potency factors from Health Canada, the United States Environmental Protection Agency, and the California Office of Environmental Health Hazard Assessment to estimate lifetime excess cancer risks associated with each substance and exposure pathway. Lifetime excess cancer risks in excess of 1 per million people are identified as potential priorities for further attention.

RESULTS

Based on data representing average conditions circa 2006, a total of 18 carcinogen-exposure pathways had potential lifetime excess cancer risks greater than 1 per million, based on varying data quality. Carcinogens with moderate to high data quality and lifetime excess cancer risk greater than 1 per million included benzene, 1,3-butadiene and radon in outdoor air; benzene and radon in indoor air; and arsenic and hexavalent chromium in drinking water. Important data gaps were identified for asbestos, hexavalent chromium and diesel exhaust in outdoor and indoor air, while little data were available to assess risk for substances in dust, food and beverages.

CONCLUSIONS

The ability to track changes in potential population exposures to environmental carcinogens over time, as well as to compare between different substances and exposure pathways, is necessary to support comprehensive, evidence-based prevention policy. We used estimates of lifetime excess cancer risk as indicators that, although based on a number of simplifying assumptions, help to identify important data gaps and prioritize more detailed data collection and exposure assessment needs.

Cigarette smoke metabolically promotes cancer, via autophagy and premature aging in the host stromal microenvironment

Cigarette smoke has been directly implicated in the disease pathogenesis of a plethora of different human cancer subtypes, including breast cancers. The prevailing view is that cigarette smoke acts as a mutagen and DNA damaging agent in normal epithelial cells, driving tumor initiation. However, its potential negative metabolic effects on the normal stromal microenvironment have been largely ignored. Here, we propose a new mechanism by which carcinogen-rich cigarette smoke may promote cancer growth, by metabolically "fertilizing" the host microenvironment. More specifically, we show that cigarette smoke exposure is indeed sufficient to drive the onset of the cancer-associated fibroblast phenotype via the induction of DNA damage, autophagy and mitophagy in the tumor stroma. In turn, cigarette smoke exposure induces premature aging and mitochondrial dysfunction in stromal fibroblasts, leading to the secretion of high-energy mitochondrial fuels, such as L-lactate and ketone bodies. Hence, cigarette smoke induces catabolism in the local microenvironment, directly fueling oxidative mitochondrial metabolism (OXPHOS) in neighboring epithelial cancer cells, actively promoting anabolic tumor growth. Remarkably, these autophagic-senescent fibroblasts increased breast cancer tumor growth in vivo by up to 4-fold. Importantly, we show that cigarette smoke-induced metabolic reprogramming of the fibroblastic stroma occurs independently of tumor neo-angiogenesis. We discuss the possible implications of our current findings for the prevention of aging-associated human diseases and, especially, common epithelial cancers, as we show that cigarette smoke can systemically accelerate aging in the host microenvironment. Finally, our current findings are consistent with the idea that cigarette smoke induces the "reverse Warburg effect," thereby fueling "two-compartment tumor metabolism" and oxidative mitochondrial metabolism in epithelial cancer cells.

Feasibility of identifying the tobacco-related global metabolome in blood by UPLC-QTOF-MS

Metabolomics is likely an ideal tool to assess tobacco smoke exposure and the impact of cigarette smoke on human exposure and health. To assess reproducibility and feasibility of this by UPLC-QTOF-MS, three experiments were designed for the assessment of smokers' blood. Experiment I was an analysis of 8 smokers with 8 replicates. Experiment II was an analysis of 62 pooled quality control (QC) samples from 7 nonsmokers' plasma placed as every tenth sample among a study of 613 samples from 160 smokers. Finally, to examine the feasibility of metabolomic study in assessing smoke exposure, Experiment III consisted of 9 smokers and 10 nonsmokers' serum to evaluate differences in their global metabolome. There was minimal measurement and sample preparation variation in all experiments, although some caution is needed when analyzing specific parts of the chromatogram. When assessing QC samples in the large scale study, QC clustering indicated high stability, reproducibility, and consistency. Finally, in addition to the identification of nicotine metabolites as expected, there was a characteristic profile distinguishing smokers from nonsmokers. Metabolites selected from putative identifications were verified by MS/MS, showing the potential to identify metabolic phenotypes and new metabolites relating to cigarette smoke exposure and toxicity.

Significant variation in the concentration of carcinogenic polycyclic aromatic hydrocarbons in yerba maté samples by brand, batch, and processing method

Drinking maté, common in southern South America, may increase the risk of esophageal squamous cell carcinoma (ESCC). In 2006, we found high but variable polycyclic aromatic hydrocarbon (PAH) content in commercial yerba maté samples from eight Brazilian brands. The PAH content of new samples from the same brands, purchased in 2008, and four brands from a single manufacturer processed in different ways, obtained in 2010, were quantified to determine whether PAH concentration was still high, whether PAH content variation was brand specific, and whether processing method affects PAH content of commercial yerba maté. Concentrations of individual PAHs were quantified using gas chromatography/mass spectrometry with deuterated PAHs as internal standards. Median total PAH concentration was 1500 ng/g (range: 625-3710 ng/g) and 1090 ng/g (621-1990 ng/g) in 2008 and 2010 samples, respectively. Comparing 2006 and 2008 samples, some brands had high PAH concentrations in both years, while PAH concentration changed considerably in others. Benzo[a]pyrene concentrations ranged from 11.9 to 99.3 ng/g and 5.11 to 21.0 ng/g in 2008 and 2010 samples, respectively. The 2010 sample processed without touching smoke had the lowest benzo[a]pyrene content. These results support previous findings of very high total and carcinogenic PAH concentrations in yerba maté, perhaps contributing to the high incidence of ESCC in southern South America. The large PAH content variation by brand, batch, and processing method suggests it may be possible to reduce the content of carcinogenic PAHs in commercial yerba maté, making it a healthier beverage.

Lung carcinogenesis by tobacco smoke

Cigarette smoke is a complex mixture of chemicals including multiple genotoxic lung carcinogens. The classic mechanisms of carcinogen metabolic activation to DNA adducts, leading to miscoding and mutations in critical growth control genes, applies to this mixture but some aspects are difficult to establish because of the complexity of the exposure. This article discusses certain features of this mechanism including the role of nicotine and its receptors; lung carcinogens, co-carcinogens and related substances in cigarette smoke; structurally characterized DNA adducts in the lungs of smokers; the mutational consequences of DNA adduct formation in smokers' lungs; and biomarkers of nicotine and carcinogen uptake as related to lung cancer. While there are still uncertainties which may never be fully resolved, the general mechanisms by which cigarette smoking causes lung cancer are well understood and provide insights relevant to prevention of lung cancer, the number one cancer killer in the world, causing 1.37 million deaths per year.

Gender differences in chemical carcinogenesis in National Toxicology Program 2-year bioassays

Differences in cancer incidences between men and women are often explained by either differences in environmental exposures or by influences of sex hormones. However, there are few studies on intrinsic gender differences in susceptibility to chemical carcinogens. We have analyzed the National Toxicology Program (NTP) database for sex differences in rat responses to chemical carcinogens. We found that the odds that male rat bioassays were assigned a higher level of evidence than female rat bioassays was 1.69 (p < .001). Of 278 carcinogenic chemicals in the database, 201 (72%) exhibited statistical gender differences (p ≤ .05) in at least one nonreproductive organ. One hundred thirty of these 201 chemicals induced gender-specific tumors in male rats and 59 in female rats. Sixty-eight chemicals induced tumors in males but no tumors in females. Less than one third (i.e., 19 chemicals) induced tumors in females but not males. Male-specific tumors included pancreatic and skin tumors, and female-specific tumors included lung tumors. For some tumor sites, these differences in gender susceptibility can be associated with literature data on sex hormone receptor expression. In conclusion, gender-specific tumors were common. The male dominance is in line with recent human data, and the male susceptibility to carcinogens should be further studied.