Molecular epidemiology in cancer risk assessment and prevention: recent progress and avenues for future research

Biomarkers of genotoxic damage in pulmonary alveolar macrophages: a review

DNA damage is one of the primary mechanisms underlying cancer and other chronic degenerative diseases. Early evaluation of this damage in the affected cells and tissues is crucial for understanding pathogenesis and implementing effective prevention strategies. However, isolating target cells from affected organs, such as the lungs, can be challenging. Therefore, an alternative approach is to evaluate genotoxic damage in surrogate cells. Pulmonary alveolar macrophages are ideally suited for this purpose because they are in close contact with the target cells of the bronchial and alveolar epithelium, share the exact mechanisms and levels of exposure, and are easily recoverable in large numbers. This review comprehensively lists all studies using alveolar macrophages as surrogate cells to show genotoxic lung damage in humans or laboratory animals. These investigations provide fundamental information on the mechanisms of DNA damage in the lung and allow for better assessment and management of risk following exposure to inhalable genotoxic agents. Furthermore, they may be a valuable tool in cancer chemoprevention, helping the right choice of agents for clinical trials.

Literature review and evaluation of biomarkers, matrices and analytical methods for chemicals selected in the research program Human Biomonitoring for the European Union (HBM4EU)

Humans are potentially exposed to a large amount of chemicals present in the environment and in the workplace. In the European Human Biomonitoring initiative (Human Biomonitoring for the European Union = HBM4EU), acrylamide, mycotoxins (aflatoxin B1, deoxynivalenol, fumonisin B1), diisocyanates (4,4'-methylenediphenyl diisocyanate, 2,4- and 2,6-toluene diisocyanate), and pyrethroids were included among the prioritized chemicals of concern for human health. For the present literature review, the analytical methods used in worldwide biomonitoring studies for these compounds were collected and presented in comprehensive tables, including the following parameter: determined biomarker, matrix, sample amount, work-up procedure, available laboratory quality assurance and quality assessment information, analytical techniques, and limit of detection. Based on the data presented in these tables, the most suitable methods were recommended. According to the paradigm of biomonitoring, the information about two different biomarkers of exposure was evaluated: a) internal dose = parent compounds and metabolites in urine and blood; and b) the biologically effective = dose measured as blood protein adducts. Urine was the preferred matrix used for deoxynivalenol, fumonisin B1, and pyrethroids (biomarkers of internal dose). Markers of the biological effective dose were determined as hemoglobin adducts for diisocyanates and acrylamide, and as serum-albumin-adducts of aflatoxin B1 and diisocyanates. The analyses and quantitation of the protein adducts in blood or the metabolites in urine were mostly performed with LC-MS/MS or GC-MS in the presence of isotope-labeled internal standards. This review also addresses the critical aspects of the application, use and selection of biomarkers. For future biomonitoring studies, a more comprehensive approach is discussed to broaden the selection of compounds.

Lymphocyte-based challenge DNA-repair assays for personalized health risk assessment

Combinations of genetic and environmental factors are responsible for the development of many human diseases, such as cancer, as demonstrated using various biomarkers. Within this scenario, DNA repair holds a gate-keeper position which determines outcomes after appearance of DNA damage and, therefore, adverse cellular consequences, e.g., initiation of carcinogenesis. DNA repair deficiency and some of the subsequent events can be validated from studies using live cells from cancer patients. However, these deficiencies/events are difficult to demonstrate in live cells from normal individuals because individual variations in DNA repair capacities (DRC) are too low to be measured easily. Such lack of information has been hindering progress in developing personalized disease prevention and intervention protocols, especially among exposed populations. However, using a variety of challenge assays as biomarkers, variations in individual's DRC can be amplified in live cells and be determined. Furthermore, evidence indicates that DRC are not only inherited but can also be modified by environmental factors (e.g., nutritional status and exposure to genotoxic substances). Using these challenge assays, e.g., in live lymphocytes, individual's DRC can be holistically and functionally determined as well as quantitated. With the more precise information, assessment of health risk can be better determined on an individual rather than on a population basis. This review provides a succinct summary on the development and application of recent challenge assays in lymphocytes which can provide measurements of individuals' DRC, and on the latest data for more precise disease prevention and intervention.

A CRISPR/Cas9-based method for targeted DNA methylation enables cancer initiation in B lymphocytes

Targeted DNA methylation is important for understanding transcriptional modulation and epigenetic diseases. Although CRISPR-Cas9 has potential for this purpose, it has not yet been successfully used to efficiently introduce DNA methylation and induce epigenetic diseases. We herein developed a new system that enables the replacement of an unmethylated promoter with a methylated promoter through microhomology-mediated end joining-based knock-in. We successfully introduced an approximately 100% DNA methylation ratio at the cancer-associated gene SP3 in HEK293 cells. Moreover, engineered SP3 promoter hypermethylation led to transcriptional suppression in human B lymphocytes and induced B-cell lymphoma. Our system provides a promising framework for targeted DNA methylation and cancer initiation through epimutations.

The Molecular Mechanisms of Adaptive Response Related to Environmental Stress

The exposure of living organisms to environmental stress triggers defensive responses resulting in the activation of protective processes. Whenever the exposure occurs at low doses, defensive effects overwhelm the adverse effects of the exposure; this adaptive situation is referred to as “hormesis”. Environmental, physical, and nutritional hormetins lead to the stimulation and strengthening of the maintenance and repair systems in cells and tissues. Exercise, heat, and irradiation are examples of physical hormetins, which activate heat shock-, DNA repair-, and anti-oxidative-stress responses. The health promoting effect of many bio-actives in fruits and vegetables can be seen as the effect of mildly toxic compounds triggering this adaptive stimulus. Numerous studies indicate that living organisms possess the ability to adapt to adverse environmental conditions, as exemplified by the fact that DNA damage and gene expression profiling in populations living in the environment with high levels of air pollution do not correspond to the concentrations of pollutants. The molecular mechanisms of the hormetic response include modulation of (a) transcription factor Nrf2 activating the synthesis of glutathione and the subsequent protection of the cell; (b) DNA methylation; and (c) microRNA. These findings provide evidence that hormesis is a toxicological event, occurring at low exposure doses to environmental stressors, having the benefit for the maintenance of a healthy status.

Gene expression of Aspergillus flavus strains on a cheese model system to control aflatoxin production

The expression of genes associated with aflatoxin biosynthesis by different Aspergillus flavus strains growing on a cheese model system has not been studied. To control aflatoxin biosynthesis, it would be useful to understand the changes in gene expression during cheesemaking and relate those changes to toxin production. The objective of this study was to evaluate the effects of pH, water activity, and temperature on the expression of 2 regulatory genes (aflR and aflS) and 1 structural gene (aflP) involved in aflatoxin biosynthesis, using 3 aflatoxigenic A. flavus strains growing on a cheese-based medium and reverse-transcription real-time PCR. The gene expression patterns were influenced by A. flavus strain and environmental conditions. The structural gene aflP and the regulatory genes aflR and aflS showed similar expression patterns in each A. flavus strain, but we also observed inter-strain differences. We observed the highest expression levels at 6 and 9 d of incubation by A. flavus strains CQ8 and CQ103, and saw a decrease in the days following. Strain CQ7 showed the lowest expression of these genes. We observed the highest expression levels of these genes at pH 5.5, water activity 0.95, and 20 to 25°C; strain CQ103 showed a different pattern for the aflS gene, with maximum expression at pH 6.0 on d 6 of incubation. For the 3 strains, we found a strong correlation between the relative expression of the aflR and aflS genes and the concentration of aflatoxins under conditions that simulated cheese ripening. Control strategies to avoid aflatoxin contamination during cheesemaking could use the detection of regulatory gene expression.

Incorporating Transgenerational Epigenetic Inheritance into Ecological Risk Assessment Frameworks

Chronic exposure to environmental contaminants can induce heritable "transgenerational" modifications to organisms, potentially affecting future ecosystem health and functionality. Incorporating transgenerational epigenetic heritability into risk assessment procedures has been previously suggested. However, a critical review of existing literature yielded numerous studies claiming transgenerational impacts, with little compelling evidence. Therefore, contaminant-induced epigenetic inheritance may be less common than is reported in the literature. We identified a need for multigeneration epigenetic studies that extend beyond what could be deemed "direct exposure" to F1 and F2 gametes and also include subsequent multiple nonexposed generations to adequately evaluate transgenerational recovery times. Also, increased experimental replication is required to account for the highly variable nature of epigenetic responses and apparent irreproducibility of current studies. Further, epigenetic end points need to be correlated with observable detrimental organism changes before a need for risk management can be properly determined. We suggest that epigenetic-based contaminant studies include concentrations lower than current "EC_10-20" or "Lowest Observable Effect Concentrations" for the organism's most sensitive phenotypic end point, as higher concentrations are likely already regulated. Finally, we propose a regulatory framework and optimal experimental design that enables transgenerational epigenetic effects to be assessed and incorporated into conventional ecotoxicological testing.

Effect of temperature and water activity on gene expression and aflatoxin biosynthesis in Aspergillus flavus on almond medium

Almonds are among the commodities at risk of aflatoxin contamination by Aspergillus flavus. Temperature and water activity are the two key determinants in pre and post-harvest environments influencing both the rate of fungal spoilage and aflatoxin production. Varying the combination of these parameters can completely inhibit or fully activate the biosynthesis of aflatoxin, so it is fundamental to know which combinations can control or be conducive to aflatoxin contamination. Little information is available about the influence of these parameters on aflatoxin production on almonds. The objective of this study was to determine the influence of different combinations of temperature (20 °C, 28 °C, and 37 °C) and water activity (0.90, 0.93, 0.96, 0.99 aw) on growth, aflatoxin B1 (AFB1) production and expression of the two regulatory genes, aflR and aflS, and two structural genes, aflD and aflO, of the aflatoxin biosynthetic cluster in A. flavus grown on an almond medium solidified with agar. Maximum accumulation of fungal biomass and AFB1 production was obtained at 28 °C and 0.96 aw; no fungal growth and AFB1 production were observed at 20 °C at the driest tested conditions (0.90 and 0.93 aw). At 20° and 37 °C AFB1 production was 70-90% lower or completely suppressed, depending on aw. Reverse transcriptase quantitative PCR showed that the two regulatory genes (aflR and aflS) were highly expressed at maximum (28 °C) and minimum (20 °C and 37 °C) AFB1 production. Conversely the two structural genes (aflD and aflO) were highly expressed only at maximum AFB1 production (28 °C and 0.96-0.99 aw). It seems that temperature acts as a key factor influencing aflatoxin production which is strictly correlated to the induction of expression of structural biosynthesis genes (aflD and aflO), but not to that of aflatoxin regulatory genes (aflR and aflS), whose functional products are most likely subordinated to other regulatory processes acting at post-translational level. The results of this study are useful to select conditions that could be used in the almond processing chain to suppress aflatoxin production in this important product.

Causes of genome instability: the effect of low dose chemical exposures in modern society

Genome instability is a prerequisite for the development of cancer. It occurs when genome maintenance systems fail to safeguard the genome's integrity, whether as a consequence of inherited defects or induced via exposure to environmental agents (chemicals, biological agents and radiation). Thus, genome instability can be defined as an enhanced tendency for the genome to acquire mutations; ranging from changes to the nucleotide sequence to chromosomal gain, rearrangements or loss. This review raises the hypothesis that in addition to known human carcinogens, exposure to low dose of other chemicals present in our modern society could contribute to carcinogenesis by indirectly affecting genome stability. The selected chemicals with their mechanisms of action proposed to indirectly contribute to genome instability are: heavy metals (DNA repair, epigenetic modification, DNA damage signaling, telomere length), acrylamide (DNA repair, chromosome segregation), bisphenol A (epigenetic modification, DNA damage signaling, mitochondrial function, chromosome segregation), benomyl (chromosome segregation), quinones (epigenetic modification) and nano-sized particles (epigenetic pathways, mitochondrial function, chromosome segregation, telomere length). The purpose of this review is to describe the crucial aspects of genome instability, to outline the ways in which environmental chemicals can affect this cancer hallmark and to identify candidate chemicals for further study. The overall aim is to make scientists aware of the increasing need to unravel the underlying mechanisms via which chemicals at low doses can induce genome instability and thus promote carcinogenesis.

Biomarkers of tobacco smoke exposure

Diseases and death caused by exposure to tobacco smoke have become the single most serious preventable public health concern. Thus, biomarkers that can monitor tobacco exposure and health effects can play a critical role in tobacco product regulation and public health policy. Biomarkers of exposure to tobacco toxicants are well established and have been used in population studies to establish public policy regarding exposure to second-hand smoke, an example being the nicotine metabolite cotinine, which can be measured in urine. Biomarkers of biological response to tobacco smoking range from those indicative of inflammation to mRNA and microRNA patterns related to tobacco use and/or disease state. Biomarkers identifying individuals with an increased risk for a pathological response to tobacco have also been described. The challenge for any novel technology or biomarker is its translation to clinical and/or regulatory application, a process that requires first technical validation of the assay and then careful consideration of the context the biomarker assay may be used in the regulatory setting. Nonetheless, the current efforts to investigate new biomarker of tobacco smoke exposure promise to offer powerful new tools in addressing the health hazards of tobacco product use. This review will examine such biomarkers, albeit with a focus on those related to cigarette smoking.

Multimedia fate and source apportionment of polycyclic aromatic hydrocarbons in a coking industry city in Northern China

A steady state Level III fate model was established and applied to quantify source-receptor relationship in a coking industry city in Northern China. The local emission inventory of PAHs, as the model input, was acquired based on energy consumption and emission factors. The model estimations were validated by measured data and indicated remarkable variations in the paired isomeric ratios. When a rectification factor, based on the receptor-to-source ratio, was calculated by the fate model, the quantitatively verified molecular diagnostic ratios provided reasonable results of local PAH emission sources. Due to the local ban and measures on small scale coking activities implemented from the beginning of 2004, the model calculations indicated that the local emission amount of PAHs in 2009 decreased considerably compared to that in 2003.

Improving the environmental quality component of the County Health Rankings model

OBJECTIVES

We examined the association between environmental quality measures and health outcomes by using the County Health Rankings data, and tested whether a revised environmental quality measure for 1 state could improve the models.

METHODS

We conducted state-by-state, county-level linear regression analyses to determine how often the model's 4 health determinants (social and economic factors, health behaviors, clinical care, and physical environment) were associated with mortality and morbidity outcomes. We then developed a revised measure of environmental quality for West Virginia, and tested whether the revised measure was superior to the original measure.

RESULTS

Measures of social and economic conditions, and health behaviors, were related to health outcomes in 58% to 88% of state models; measures of environmental quality were related to outcomes in 0% to 8% of models. In West Virginia, the original measure of environmental quality was unrelated to any of the 8 health outcome measures, but the revised measure was significantly related to all 8.

CONCLUSIONS

The County Health Rankings model underestimates the impact of the physical environment on public health outcomes. Suggestions for other data sources that may contribute to improved measurement of the physical environment are provided.

Environmental pollution effects on reproductive health - clinical-epidemiological study in southern Italy

This study aims to address the clinical, statistical and Epidemiological Relationship Between Birth Defects and Environmental Pollution, in the Campania Region and in Salerno.

OBJECTIVES

WE EXAMINED FOUR GROUPS OF SUBJECTS AS FOLLOWS: a sample of pregnant women living in Salerno, a sample of pregnant women living in highly polluted areas, a sample of controls, pregnant women and residents out of the Campania Region, considered in unpolluted areas (Foggia) and in the Salerno area.

METHODOLOGIES

a toxicological and genetic analysis was conducted on patients examined.

CONCLUSIONS

there is an epidemiological link between environmental pollution and reproductive health in the Salerno area. Experimentally there are the first evidences of endocrine disruptors by the PCB. It has been inferred an overexpression of the mir-191 as a marker of pollution by dioxin-like compounds. Socially, correct information of populations at risk is necessary and a possible preventive and ongoing medical care must be ensured.

Combined exposure to X-irradiation followed by N-ethyl-N-nitrosourea treatment alters the frequency and spectrum of Ikaros point mutations in murine T-cell lymphoma

Ionizing radiation is a well-known carcinogen, but its potency may be influenced by other environmental carcinogens, which is of practical importance in the assessment of risk. Data are scarce, however, on the combined effect of radiation with other environmental carcinogens and the underlying mechanisms involved. We studied the mode and mechanism of the carcinogenic effect of radiation in combination with N-ethyl-N-nitrosourea (ENU) using doses approximately equal to the corresponding thresholds. B6C3F1 mice exposed to fractionated X-irradiation (Kaplan's method) followed by ENU developed T-cell lymphomas in a dose-dependent manner. Radiation doses above an apparent threshold acted synergistically with ENU to promote lymphoma development, whereas radiation doses below that threshold antagonized lymphoma development. Ikaros, which regulates the commitment and differentiation of lymphoid lineage cells, is a critical tumor suppressor gene frequently altered in both human and mouse lymphomas and shows distinct mutation spectra between X-ray- and ENU-induced lymphomas. In the synergistically induced lymphomas, we observed a low frequency of LOH and an inordinate increase of Ikaros base substitutions characteristic of ENU-induced point mutations, G:C to A:T at non-CpG, A:T to G:C, G:C to T:A and A:T to T:A. This suggests that radiation doses above an apparent threshold activate the ENU mutagenic pathway. This is the first report on the carcinogenic mechanism elicited by combined exposure to carcinogens below and above threshold doses based on the mutation spectrum of the causative gene. These findings constitute a basis for assessing human cancer risk following exposure to multiple carcinogens.

Is it time to advance the chemoprevention of environmental carcinogenesis with microdosing trials?

This perspective on Jubert et al. (beginning on page [1015] in this issue of the journal) discusses the use of microdosing with environmental carcinogens to accelerate the evaluation and optimization of chemopreventive interventions. The need for chemoprevention of environmental carcinogenesis is considered, as are the structure of microdosing, or phase 0, trials, technologies required to conduct microdose studies in this context, and ethical concerns. We also reflect on what microdosing studies have taught us to date.

Epigenetics and environmental chemicals

PURPOSE OF REVIEW

Epigenetics investigates heritable changes in gene expression occurring without changes in DNA sequence. Several epigenetic mechanisms, including DNA methylation, histone modifications, and microRNA expression, can change genome function under exogenous influence. Here, we review current evidence indicating that epigenetic alterations mediate toxicity from environmental chemicals.

RECENT FINDINGS

In-vitro, animal, and human investigations have identified several classes of environmental chemicals that modify epigenetic marks, including metals (cadmium, arsenic, nickel, chromium, and methylmercury), peroxisome proliferators (trichloroethylene, dichloroacetic acid, and TCA), air pollutants (particulate matter, black carbon, and benzene), and endocrine-disrupting/reproductive toxicants (diethylstilbestrol, bisphenol A, persistent organic pollutants, and dioxin). Most studies conducted so far have been centered on DNA methylation, whereas only a few investigations have studied environmental chemicals in relation to histone modifications and microRNA.

SUMMARY

For several exposures, it has been proved that chemicals can alter epigenetic marks, and that the same or similar epigenetic alterations can be found in patients with the disease of concern or in diseased tissues. Future prospective investigations are needed to determine whether exposed individuals develop epigenetic alterations over time and, in turn, which such alterations increase the risk of disease. Also, further research is needed to determine whether environmental epigenetic changes are transmitted transgenerationally.

Biomarkers of induced active and passive smoking damage

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

Genetic polymorphisms and benzene metabolism in humans exposed to a wide range of air concentrations

Using generalized linear models with natural-spline smoothing functions, we detected effects of specific xenobiotic metabolizing genes and gene-environment interactions on levels of benzene metabolites in 250 benzene-exposed and 136 control workers in Tianjin, China (for all individuals, the median exposure was 0.512 p.p.m. and the 10th and 90th percentiles were 0.002 and 6.40 p.p.m., respectively). We investigated five urinary metabolites (E,E-muconic acid, S-phenylmercapturic acid, phenol, catechol, and hydroquinone) and nine polymorphisms in seven genes coding for key enzymes in benzene metabolism in humans {cytochrome P450 2E1 [CYP2E1, rs2031920], NAD(P)H: quinone oxidoreductase [NQO1, rs1800566 and rs4986998], microsomal epoxide hydrolase [EPHX1, rs1051740 and rs2234922], glutathione-S-transferases [GSTT1, GSTM1 and GSTP1(rs947894)] and myeloperoxidase [MPO, rs2333227]}. After adjusting for covariates, including sex, age, and smoking status, NQO1*2 (rs1800566) affected all five metabolites, CYP2E1 (rs2031920) affected most metabolites but not catechol, EPHX1 (rs1051740 or rs2234922) affected catechol and S-phenylmercapturic acid, and GSTT1 and GSTM1 affected S-phenylmercapturic acid. Significant interactions were also detected between benzene exposure and all four genes and between smoking status and NQO1*2 and EPHX1 (rs1051740). No significant effects were detected for GSTP1 or MPO. Results generally support prior associations between benzene hematotoxicity and specific gene mutations, confirm earlier evidence that GSTT1 affects production of S-phenylmercapturic acid, and provide additional evidence that genetic polymorphisms in NQO1*2, CYP2E1, and EPHX1 (rs1051740 or rs2234922) affect metabolism of benzene in the human liver.

Role of metabolism and viruses in aflatoxin-induced liver cancer

The use of biomarkers in molecular epidemiology studies for identifying stages in the progression of development of the health effects of environmental agents has the potential for providing important information for critical regulatory, clinical and public health problems. Investigations of aflatoxins probably represent one of the most extensive data sets in the field and this work may serve as a template for future studies of other environmental agents. The aflatoxins are naturally occurring mycotoxins found on foods such as corn, peanuts, various other nuts and cottonseed and they have been demonstrated to be carcinogenic in many experimental models. As a result of nearly 30 years of study, experimental data and epidemiological studies in human populations, aflatoxin B(1) was classified as carcinogenic to humans by the International Agency for Research on Cancer. The long-term goal of the research described herein is the application of biomarkers to the development of preventative interventions for use in human populations at high-risk for cancer. Several of the aflatoxin-specific biomarkers have been validated in epidemiological studies and are now being used as intermediate biomarkers in prevention studies. The development of these aflatoxin biomarkers has been based upon the knowledge of the biochemistry and toxicology of aflatoxins gleaned from both experimental and human studies. These biomarkers have subsequently been utilized in experimental models to provide data on the modulation of these markers under different situations of disease risk. This systematic approach provides encouragement for preventive interventions and should serve as a template for the development, validation and application of other chemical-specific biomarkers to cancer or other chronic diseases.

Environmental and chemical carcinogenesis

People are continuously exposed exogenously to varying amounts of chemicals that have been shown to have carcinogenic or mutagenic properties in experimental systems. Exposure can occur exogenously when these agents are present in food, air or water, and also endogenously when they are products of metabolism or pathophysiologic states such as inflammation. It has been estimated that exposure to environmental chemical carcinogens may contribute significantly to the causation of a sizable fraction, perhaps a majority, of human cancers, when exposures are related to "life-style" factors such as diet, tobacco use, etc. This chapter summarizes several aspects of environmental chemical carcinogenesis that have been extensively studied and illustrates the power of mechanistic investigation combined with molecular epidemiologic approaches in establishing causative linkages between environmental exposures and increased cancer risks. A causative relationship between exposure to aflatoxin, a strongly carcinogenic mold-produced contaminant of dietary staples in Asia and Africa, and elevated risk for primary liver cancer has been demonstrated through the application of well-validated biomarkers in molecular epidemiology. These studies have also identified a striking synergistic interaction between aflatoxin and hepatitis B virus infection in elevating liver cancer risk. Use of tobacco products provides a clear example of cancer causation by a life-style factor involving carcinogen exposure. Tobacco carcinogens and their DNA adducts are central to cancer induction by tobacco products, and the contribution of specific tobacco carcinogens (e.g. PAH and NNK) to tobacco-induced lung cancer, can be evaluated by a weight of evidence approach. Factors considered include presence in tobacco products, carcinogenicity in laboratory animals, human uptake, metabolism and adduct formation, possible role in causing molecular changes in oncogenes or suppressor genes, and other relevant data. This approach can be applied to evaluation of other environmental carcinogens, and the evaluations would be markedly facilitated by prospective epidemiologic studies incorporating phenotypic carcinogen-specific biomarkers. Heterocyclic amines represent an important class of carcinogens in foods. They are mutagens and carcinogens at numerous organ sites in experimental animals, are produced when meats are heated above 180 degrees C for long periods. Four of these compounds can consistently be identified in well-done meat products from the North American diet, and although a causal linkage has not been established, a majority of epidemiology studies have linked consumption of well-done meat products to cancer of the colon, breast and stomach. Studies employing molecular biomarkers suggest that individuals may differ in their susceptibility to these carcinogens, and genetic polymorphisms may contribute to this variability. Heterocyclic amines, like most other chemical carcinogens, are not carcinogenic per se but must be metabolized by a family of cytochrome P450 enzymes to chemically reactive electrophiles prior to reacting with DNA to initiate a carcinogenic response. These same cytochrome P450 enzymes--as well as enzymes that act on the metabolic products of the cytochromes P450 (e.g. glucuronyl transferase, glutathione S-transferase and others)--also metabolize chemicals by inactivation pathways, and the relative amounts of activation and detoxification will determine whether a chemical is carcinogenic. Because both genetic and environmental factors influence the levels of enzymes that metabolically activate and detoxify chemicals, they can also influence carcinogenic risk. Many of the phenotypes of cancer cells can be the result of mutations, i.e., changes in the nucleotide sequence of DNA that accumulate as tumors progress. These can arise as a result of DNA damage or by the incorporation of non-complementary nucleotides during DNA synthetic processes. Based upon the disparity between the infrequency of spontaneous mutations and the large numbers of mutations reported in human tumors, it has been postulated that cancers must exhibit a mutator phenotype, which would represent an early event in cancer progression. A mutator phenotype could be generated by mutations in genes that normally function to guarantee genetic stability. These mutations presumably arise via DNA damage by environmental or endogenous agents, but it remains to be determined whether the acquisition of a mutator phenotype is a necessary event during tumor progression.

Locating gene-environment interaction: at the intersections of genetics and public health

Over the past two decades, the applications of genetic and genomic technologies have begun to transform research questions and practices within epidemiology and toxicology, the "core sciences" of public health (Annu. Rev. Public Health 21 (2000) 1). These technologies provide new models and techniques for studying genetic traits, environmental exposures, and gene-environment interaction in the production of human health and illness. This paper explores the consequences of emergent genetic and genomic approaches, their ongoing redefinitions of both genetic and environmental "risks", and their potential implications for public health practice. The central argument of the paper is that the increasing focus on gene-environment interaction directs scientific, biomedical, and public health attention both inward, to the gene/genome, and outward, to particular places. In so doing, studies of gene-environment interaction create a challenging and productive tension-at the same time that bodies are being geneticized (Am. J. Law Med. 17 (1992) 15), they also are emphatically emplaced, located where social and cultural practices come to matter. This tension, this simultaneous movement outward and inward, towards the gene and towards the environment, into the body and into place, opens up a vista into the processes through which culture and biology form a locally and historically situated dialectic (Encounters With Aging: Mythologies of Menopause in Japan and North America, University of California Press, Berkeley, CA, 1993) and raises important questions about the production of health and illness.

Food mutagens

Several lines of evidence indicate that diet and dietary behaviors can contribute to human cancer risk. One way that this occurs is through the ingestion of food mutagens. Sporadic cancers result from a gene-environment interactions where the environment includes endogenous and exogenous exposures. In this article, we define environment as dietary exposures in the context of gene-environment interactions. Food mutagens cause different types of DNA damage: nucleotide alterations and gross chromosomal aberrations. Most mutagens begin their action at the DNA level by forming carcinogen-DNA adducts, which result from the covalent binding of a carcinogen or part of a carcinogen to a nucleotide. However the effect of food mutagens in carcinogenesis can be modified by heritable traits, namely, low-penetrant genes that affect mutagen exposure of DNA through metabolic activation and detoxification or cellular responses to DNA damage through DNA repair mechanisms or cell death. There are some clearly identified (e.g., aflatoxin) and suspected (e.g., N-nitrosamines, polycyclic aromatic hydrocarbons or heterocyclic amines) food mutagens. The target organs for these agents are numerous, but there is target-organ specificity for each. Mutagenesis however is not the only pathway that links dietary exposures and cancers. There is growing evidence that epigenetic factors, including changes in the DNA methylation pattern, are causing cancer and can be modified by dietary components. Also DNA damage may be indirect by triggering oxidative DNA damage. When considering the human diet, it should be recognized that foods contain both mutagens and components that decrease cancer risk such as antioxidants. Thus nutritionally related cancers ultimately develop from an imbalance of carcinogenesis and anticarcinogenesis. The best way to assess nutritional risks is through biomarkers, but there is no single biomarker that has been sufficiently validated. Although panels of biomarkers would be the most appropriate, their use as a reflection of target-organ risk remains to be determined. Also even when new biomarkers are developed, their application in target organs is problematic because tissues are not readily available. For now most biomarkers are used in surrogate tissues (e.g., blood, urine, oral cavity cells) that presumably reflect biological effects in target organs. This article reviews the role of food mutagens in mutagenesis and carcinogenesis and how their effects are modified by heritable traits and discusses how to identify and evaluate the effects of food mutagens.

Micronuclei in cervical smears and peripheral blood lymphocytes from women with and without cervical uterine cancer

Cervical cancer represents the second most common malignant neoplasia in women world-wide. In Mexico, cervical cancer is the most common female malignancy. It has been recently seen an increased frequencies of micronuclei (MN) lymphocytes and cervical epithelial cells of cervical cancer patients. The aim of this hospital-based unmatched case-control study was to investigate the association between progressive stages in development of cervical cancer and frequency of micronucleated cells in the cervical epithelium and peripheral lymphocytes of 40 women, grouped by disease stage. Women at the Obstetrics and Gynecology Hospital of the Instituto Mexicano del Seguro Social (IMSS) in Monterrey, Mexico were diagnosed and classified on the bases of the Papanicolaou (PAP) smear and colposcopy/biopsy into control, low-grade squamous intraepithelial lesions (LGSIL), high-grade squamous intraepithelial lesions (HGSIL), and invasive groups. Analysis of the MN data in both cell types revealed (a) homogeneity among women within each of the four groups with regard to MN frequency, (b) in general, a correlation between MN frequency and grade of cervical lesion, and (c) a positive linear trend between the MN frequency and increased cervical cancer risk. In conclusion, we suggest that MN are a useful biomarker of cancer risk. Nonetheless, these results should be validated by other researchers.

Sister chromatid exchange in patients with joint prostheses

The evaluation of sister chromatid exchanges (SCE) is used to establish the cytogenic damage in subjects exposed to toxic substances. The test is considered to be 1 of the most sensitive and accurate indicators of damage and responds to toxic chemicals at low doses. We evaluated the incidence of SCE in peripheral lymphocytes of patients with articular prostheses. Subjects with prostheses made of titanium-aluminium-vanadium alloys presented a significantly higher SCE number than the control population (6.3+/-2.3 vs 4.4+/-1.3; P = .0128), whereas subjects with prostheses made of chrome-cobalt alloy or mixed prostheses presented a higher SCE value than the controls but not significantly different. The presence of high-frequency cells was alarming only in 5 patients, 4 of whom had titanium alloy prostheses, whereas none belonged to the control group. The number of SCE was not affected by the presence of bone-cement used in prosthesis fixation or by the implant duration. The indication of possible cytogenic damage in patients with titanium alloy prostheses that emerged from this study should be considered carefully, even though the sample population was small.

Quantitation of benzo[a]pyrene-DNA adducts by postlabeling with 14C-acetic anhydride and accelerator mass spectrometry

Quantitation of carcinogen-DNA adducts provides an estimate of the biologically effective dose of a chemical carcinogen reaching the target tissue. In order to improve exposure-assessment and cancer risk estimates, we are developing an ultrasensitive procedure for the detection of carcinogen-DNA adducts. The method is based upon postlabeling of carcinogen-DNA adducts by acetylation with 14C-acetic anhydride combined with quantitation of 14C by accelerator mass spectrometry (AMS). For this purpose, adducts of benzo[a]pyrene-r-7,t-8-dihydrodiol-t-9,10-epoxide (BPDE) with DNA and deoxyguanosine (dG) were synthesized. The most promutagenic adduct of BPDE, 7R,8S,9R-trihydroxy-10S-(N(2)-deoxyguanosyl)-7,8,9, 10-tetrahydrobenzo[a]pyrene (BPdG), was HPLC purified and structurally characterized. Postlabeling of the BPdG adduct with acetic anhydride yielded a major product with a greater than 60% yield. The postlabeled adduct was identified by liquid chromatography-mass spectrometry as pentakis(acetyl) BPdG (AcBPdG). Postlabeling of the BPdG adduct with 14C-acetic anhydride yielded a major product coeluting with an AcBPdG standard. Quantitation of the 14C-postlabeled adduct by AMS promises to allow detection of attomolar amounts of adducts. The method is now being optimized and validated for use in human samples.

Carcinogen-DNA adducts as tools in risk assessment

Genotoxic chemicals are known to react with DNA either directly or after metabolic activation to form adducts, a step thought to be relevant with respect to chemical carcinogenesis. Evaluation of cancer risk due to exposure to chemicals requires information about the internal dose which depends on individual variation in rates of metabolic activation and detoxification. The presence and the amount of specific DNA adducts provide a good indication of chemical exposure and genetic damage resulting from exposure to carcinogens and account for some of the factors affecting individual susceptibility to cancer. Analysis of DNA adducts requires that the sensitivity of the methods be sufficiently high to allow the detection of about 1 adduct/109 normal nucleotides. Most suitable methods are based on 32P-postlabelling, immunoassays or physico-chemical techniques such as HPLC coupled to synchronous fluorescence spectroscopy or gas chromatography-mass spectrometry. These methods have been used to assess human exposure to a variety of chemical carcinogens including polycyclic aromatic hydrocarbons, aromatic amines, heterocyclic aromatic amines or aflatoxins. In some instances, the use of DNA-adducts has given accurate estimates of risk.

Studies on biomarkers in cancer etiology and prevention: a summary and challenge of 20 years of interdisciplinary research

Sensitive, specific methods have been developed that allow quantitative measurements of the metabolites of carcinogen metabolites and of DNA and protein adducts in humans exposed occupationally, environmentally and endogenously to genotoxic agents. The interrelationship between exposure to carcinogens, host risk factors and the responses of biomarkers has been examined in cross-sectional, ecological and case-control studies which provided new insights into the causes of cancer and the mechanisms of carcinogenesis. The identification of hitherto unknown DNA-reactive chemicals formed in the human body from dietary precursors and of carcinogenic components of complex mixtures has increased the possibility of establishing causal relationships in etiology. The identification of individuals and subgroups heavily exposed to carcinogens has led to the development of measures for avoiding or decreasing exposure to carcinogenic risk factors. New, ultrasensitive methods for measuring DNA adducts allow the quantification and structural elucidation of specific DNA damage in humans arising from oxidative stress and lipid peroxidation (LPO), which have been found to be the driving forces in several human malignancies. Background DNA damage in "unexposed" individuals has been shown unequivocally to be due to LPO products, and a significant interindividual variation in adduct levels has been shown in individuals with comparable exposure to carcinogens. Thus, pharmacogenetic variants with higher susceptibility to carcinogenic insults, due to genetic polymorphism in xenobiotic-metabolizing enzymes, have been characterized by a combination of genotyping and measurements of macromolecular adducts. Dosimetry has been used in human studies to evaluate the efficacy of interventions with chemopreventive agents like ascorbic acid, dietary phenols and green tea. Advances in the application of selected biomarkers in human studies are reviewed and illustrated by examples from the author's research conducted during the past two decades.

Negative binomial additive models

The generalized additive model is extended to handle negative binomial responses. The extension is complicated by the fact that the negative binomial distribution has two parameters and is not in the exponential family. The methodology is applied to data involving DNA adduct counts and smoking variables among ex-smokers with lung cancer. A more detailed investigation is made of the parametric relationship between the number of adducts and years since quitting while retaining a smooth relationship between adducts and the other covariates.

Determination of heterocyclic aromatic amines in meat extracts by liquid chromatography-ion-trap atmospheric pressure chemical ionization mass spectrometry

When protein-rich foods are processed under normal cooking conditions, heterocyclic aromatic amines (HAAs) can be generated at a few parts per billion level. In this work, we have analyzed the HAAs present in a lyophilized meat extract by means of a simplified solid-phase extraction procedure. All the analytes were collected in a single extract with recoveries in the range of 45.6-75.2%, so the analysis time has been greatly reduced. Problems derived from the less exhaustive purification of the extract have been solved by using MS(ion trap) detection. The RSD for quantification ranged from 2.1% to 5.1% for run-to-run precision and from 5.2% to 11% for day-to-day precision. The limits of detection for standard solutions ranged from 20 to 150 pg injected. For the meat extract analyzed limits of detection from 0.9 to 11.2 ng g(-1) were obtained. Results of the quantification are in agreement with those obtained using different clean-up procedures.

Early age at smoking initiation and tobacco carcinogen DNA damage in the lung

BACKGROUND

DNA adducts formed as a consequence of exposure to tobacco smoke may be involved in carcinogenesis, and their presence may indicate a high risk of lung cancer. To determine whether DNA adducts can be used as a "dosimeter" for cancer risk, we measured the adduct levels in nontumorous lung tissue and blood mononuclear cells from patients with lung cancer, and we collected data from the patients on their history of smoking.

METHODS

We used the 32P-postlabeling assay to measure aromatic hydrophobic DNA adducts in nontumorous lung tissue from 143 patients and in blood mononuclear cells from 54 of these patients. From the smoking histories, we identified exposure variables associated with increased DNA adduct levels by use of multivariate analyses with negative binomial regression models. RESULTS/ CONCLUSIONS: We found statistically significant interactions for variables of current and former smoking and for other smoking variables (e.g., pack-years [number of packs smoked per day x years of smoking] or years smoked), indicating that the impact of smoking variables on DNA adduct levels may be different in current and former smokers. Consequently, our analyses indicate that models for current and former smokers should be considered separately. In current smokers, recent smoking intensity (cigarettes smoked per day) was the most important variable. In former smokers, age at smoking initiation was inversely associated with DNA adduct levels. A highly statistically significant correlation (r=.77 [Spearman's correlation]; two sided P<.001) was observed between DNA adduct levels in blood mononuclear cells and lung tissue.

IMPLICATIONS

Our results in former smokers suggest that smoking during adolescence may produce physiologic changes that lead to increased DNA adduct persistence or that young smokers may be markedly susceptible to DNA adduct formation and have higher adduct burdens after they quit smoking than those who started smoking later in life.

Evaluation of different clean-up procedures for the analysis of heterocyclic aromatic amines in a lyophilized meat extract

Along with other mutagenic and carcinogenic contaminants in foods such as aflatoxins, and polycyclic aromatic hydrocarbons, heterocyclic aromatic amines (HAAs) have received considerable attention in recent years. A major drawback in the analysis of HAAs in foods is their very low level of concentration (0.1 50 ng g-1) as well as matrix interferences. Solid-phase extraction (SPE), forming an integral part of chromatographic analysis, is one of the procedures currently used for the extraction and purification of HAAs in food samples. In this paper a comparative study of several SPE procedures for HAAs determination was performed. Recoveries of the heterocyclic amines in the analysis of both a simple matrix such as a standard methanolic solution and a contaminated meat extract were established. HAAs were determined by HPLC analysis with photodiode-array detection (DAD) of the purified extracts, and the adequacy of different clean-up procedures for the analysis of a contaminated meat extract was discussed.

Biological effect markers for exposure to carcinogenic compound and their relevance for risk assessment

In this review data are summarized on biomarkers that are used for biological effect monitoring of human populations exposed to genotoxic carcinogens. The biomarkers are DNA and protein adducts and cytogenetic effects. Most of these biomarkers are relevant for the process of carcinogenesis. Emphasis is on providing information on the properties of the biomarkers and on their relevance for predicting cancer risk. Overviews are presented of: (1) studies on effects of exposure in target tissues of human origin obtained by surgical biopsies or autopsies, (2) epidemiological studies on healthy (cancer-free) individuals, correlating the putative occupational, lifestyle or environmental exposure with increased levels of biomarkers in blood cells, and (3) studies with animal models on the relation between biomarkers and cancer. Finally, on the basis of epidemiological data the possibilities were explored to use biomarker data to estimate the risk of death due to cancer. For several biomarkers the increment of the cancer mortality risk was calculated on the basis of a lifetime doubling of the biomarker level.

Carcinogen DNA and protein adducts as biomarkers of human exposure in environmental cancer epidemiology

Carcinogen DNA and protein adducts promise to provide a more objective measure of human exposure to environmental carcinogens than can be obtained by questionnaire data or environmental measurements. The adducts represent an integration of exposure, absorption, distribution, metabolism, DNA repair, and cell turnover, and thus provide a measure of biologically effective dose; the fact that DNA adducts are involved in the carcinogenic process means such a measure may be more relevant than exposure measures based on ambient levels of a given carcinogen. This approach has been successfully applied to situations where accurate questionnaire data on exposure are difficult to obtain (e.g., for the dietary carcinogens aflatoxins and heterocyclic amines, aromatic amine exposure via environmental tobacco smoke, etc.). Despite the promise of carcinogen DNA and protein adducts, there are a number of issues that must be addressed, including sensitivity, specificity, temporal relationship between exposure and disease, and their mechanistic role in the process of carcinogenesis. This information is a necessary prerequisite to the successful application of these biomarkers into appropriately designed epidemiological studies.

Assessment of vinyl chloride-induced DNA damage in lymphocytes of plastic industry workers using a single-cell gel electrophoresis technique

DNA damage and the formation of stable carcinogen-DNA adducts are considered critical events in the initiation of the carcinogenic process. This study was carried out to assess whether exposure of plastics industry workers to the vinyl chloride monomer (VCM) for different periods of time would cause DNA damage, using the single-cell gel electrophoresis (SCGE) technique. Levels of DNA damage was assessed by both extent of DNA migration and numbers of DNA damaged spots in the peripheral blood lymphocytes from 32 plastics workers with different periods of exposure to VCM; they were evaluated by comparison with a group of non-exposed individuals. It was found that plastics workers who were exposed to VCM for different periods of time showed significantly increased levels of DNA damage compared with the non-exposed subjects. There was a significant correlation between the severity of DNA damage and duration of exposure. However, no significant correlation was found between the age of all subjects and DNA damage. Concentrations of VCM in the air inside the factory were found to be significantly higher than values in non-exposed areas, despite being lower than the threshold limit value (TLV). Our results encourage the application of SCGE as a sensitive, simple, fast and useful technique in the regular health screening of workers occupationally exposed to VCM (even at concentrations below the TLV) to assess the possibility of any DNA damage.

Air pollution exposure-DNA adduct dosimetry in humans and rodents: evidence for non-linearity at high doses

The impact of air pollution exposure on the level of total DNA adducts in human white blood cells (WBCs) was evaluated in two populations in the Czech Republic and compared to the exposure-DNA adduct relationship in other populations in the US and China in human lung cells and rodent lung tissue. The human populations examined were exposed to respirable particles (< 2.5 microm) (PM2.5) in urban, rural, and occupational settings where the particles originated from coal and petroleum fuel combustion, coke production, and other coal-tar aerosols (e.g., used in aluminum production). These particles contain carcinogenic polycyclic aromatic hydrocarbons (PAHs) that are known to form DNA adducts through covalent binding. Personal exposure to PM2.5 and PAHs were measured prior to collection of blood samples for DNA adduct analysis by 32P-postlabeling. Coke oven workers (n = 76), in 10 job categories on the top and side of a coke oven in Ostrava, CZ, were studied and compared to a different population exposed to environmental levels of PAHs from air pollution in Teplice, CZ. Personal exposures to airborne particles ranged from < 1 to more than 15,000 microg/m3 and carcinogenic PAHs exposure ranged from < 5 to > 200,000 ng/m3. At low to moderate environmental exposures to carcinogenic PAHs, DNA adduct levels in the WBCs were significantly correlated with exposure. However, at the higher occupational levels found on the coke oven, the exposure-DNA adduct relationship became non-linear. Under these high exposure conditions, the relative DNA adduct level per unit of exposure (DNA-binding potency) was significantly lower than measured at environmental exposures. This finding is consistent with observations in lung cells from bronchoalveolar lavage of humans exposed to a wide range of PAH. This same high exposure-dose non-linearity was also observed in lung DNA from rats exposed by inhalation to a coal-tar pitch aerosol. DNA adduct levels in all these cases show evidence of a form of non-linearity at high doses that has been described by Lutz (W.K. Lutz, Dose-response relationship and low dose extrapolation in chemical carcinogenesis, Carcinogenesis, 11 (1990) 1243-1247) as a superlinear dose response. This superlinear response may be due to saturation of metabolic activation enzymes, induction of either DNA repair processes or detoxification enzymes, or other mechanisms. Regardless of the mechanism, this decrease in the DNA-binding potency at moderate to high doses of PAH has important implications for dose-response extrapolation in risk assessment.

Molecular epidemiology in environmental health: the potential of tumor suppressor gene p53 as a biomarker

One of the challenges in environmental health is to attribute a certain health effect to a specific environmental exposure and to establish a cause-effect relationship. Molecular epidemiology offers a new approach to addressing these challenges. Mutations in the tumor suppressor gene p53 can shed light on past environmental exposure, and carcinogenic agents and doses can be distinguished on the basis of mutational spectra and frequency. Mutations in p53 have successfully been used to establish links between dietary aflatoxin exposure and liver cancer, exposure to ultraviolet light and skin cancer, smoking and cancers of the lung and bladder, and vinyl chloride exposure and liver cancer. In lung cancer, carcinogens from tobacco smoke have been shown to form adducts with DNA. The location of these adducts correlates with those positions in the p53 gene that are mutated in lung cancer, confirming a direct etiologic link between exposure and disease. Recent investigations have also explored the use of p53 as a susceptibility marker for cancer. Furthermore, studies in genetic toxicology have taken advantage of animals transgenic for p53 to screen for carcinogens in vivo. In this review, we summarize recent developments in p53 biomarker research and illustrate applications to environmental health.

Human biomonitoring: research goals and needs

Epidemiological studies have taken advantage of a number of strategies to monitor human populations for mortality, incidence, and exposure to hazardous environmental agents. These studies have been compromised by the lack of individual exposure assessment data that precisely quantified internal dose. As methods improve in analytical chemistry and molecular biology, direct biological monitoring of exposed populations is possible. Biomarkers have been developed and validated in exposed populations that quantify individual exposure, susceptibility, and early markers of health effects and can be used to study relationships between exposures and environmentally induced diseases. This paper provides background on the state of the art of human populations monitoring and, through a series of case studies, provides examples of novel biomarkers of exposure, susceptibility, and effect that highlight new opportunities for biomonitoring. Prevention of human disease due to environmental contaminants can be accomplished by implementing strategies such as those discussed to monitor exposure and early health effects in human populations.

Human biomonitoring: research goals and needs

Epidemiological studies have taken advantage of a number of strategies to monitor human populations for mortality, incidence, and exposure to hazardous environmental agents. These studies have been compromised by the lack of individual exposure assessment data that precisely quantified internal dose. As methods improve in analytical chemistry and molecular biology, direct biological monitoring of exposed populations is possible. Biomarkers have been developed and validated in exposed populations that quantify individual exposure, susceptibility, and early markers of health effects and can be used to study relationships between exposures and environmentally induced diseases. This paper provides background on the state of the art of human populations monitoring and, through a series of case studies, provides examples of novel biomarkers of exposure, susceptibility, and effect that highlight new opportunities for biomonitoring. Prevention of human disease due to environmental contaminants can be accomplished by implementing strategies such as those discussed to monitor exposure and early health effects in human populations.

Molecular epidemiology and human risk monitoring

Molecular epidemiologic research involves the identification of relations between previous exposure to some putative causative agent and subsequent biological effects in a cluster of individuals in populations. There is intensive current research in the field of molecular epidemiology, and this research has a direct impact on risk assessment processes. Many of the challenges facing risk assessors today can be addressed by research focused on developing a better understanding of (a) exposure characteristics or assessment, (b) the relationship between exposure and dose, and (c) the ultimate exposure/dose effect response relationship. Results from this research can be used to design and implement preventive interventions in at risk populations. Thus, the application of research in exposure assessment and molecular epidemiology to risk assessment and preventive interventions makes this a core program for public health.

Early biochemical markers of effects: enzyme induction, oncogene activation and markers of oxidative damage

Experimental carcinogenicity studies focus on identification of single carcinogens. Humans, however, appear exposed to a variety of low doses of carcinogens. Furthermore, few chemical entities are carcinogenic or toxic per se, but require metabolic activation to form ultimate carcinogens or toxins. In contrast to experimental animals, humans show considerable difference in genetic properties. In that situation it is particularly important to estimate individual capability for metabolic activation. To an increasing extent, activation includes formation of toxic oxygen metabolites. Particular targets for activated species are DNA and lipids; in particular low-density lipoproteins (LDL). Modifications of DNA are important for initiating the multistep process of carcinogenesis, in particular if oncogenes are activated or if tumor supressor genes are inactivated. Such DNA modification can be identical regardless of the reactive specimens being a xenobiotic or an oxygen species. Modification of LDL can start the process of atherosclerosis by transforming macrophages into foam cells, deposited as fatty streaks in the arterial wall. Biomarkers for activation capacity of xenobiotics include the use of prototype substrates and molecular techniques to determine genetic polymorphisms. Oxidative DNA modification can be measured from urinary excretion of oxidatively modified deoxynucleosides, particularly guanosine. Future efforts have to include individual measurements in order to improve the 'resolution' of molecular epidemiological approaches.

The use of in vitro DNA adduct formation to estimate the genotoxicity of residues at contaminated sites

Genotoxic carcinogens such as polycyclic aromatic hydrocarbons (PAHs) covalently bind to the bases in DNA to form adducts. The formation of DNA adducts is significant with respect to chemical carcinogenesis. Many contaminated sites contain quantities of carcinogens such as PAHs, and the evaluation of the genotoxicity of these soils has important implications for human risk assessment. DNA adducts can be formed using an in vitro system incorporating extracts from contaminated soils. The 32P-postlabelling assay is a sensitive technique for the detection of DNA adducts from complex mixtures of environmental carcinogens. These techniques have been used to form and detect DNA adducts using soils from a number of coal gasworks sites. The results show that the extent of adduct formation depends partially on the petroleum hydrocarbon content of samples, but also on other undetermined factors related to composition. While environmental weathering has been shown to effect the PAH composition of samples, this is not an important factor in controlling the genotoxicity of samples as estimated by DNA adduct formation.