Environment and cancer: who are susceptible?

Frog decline, frog malformations, and a comparison of frog and human health

The decline in frog populations and the increase in the frequency of frog malformations are discussed. Topics considered for analysis include chytridiomycosis, retinoids, UV-B radiation, chemical contaminants, environmental threats, introduced invasive species and predation, unsustainable use, and enigmatic decline. Care must be taken to distinguish between hypotheses, laboratory experiments, and the findings in feral frog populations. Clearly, the causes of population decline and malformations are heterogeneous. The subject of frogs and humans is addressed under three subheadings: the importance of frogs to human societies, medical implications of frog studies, and a comparison of frog and human disease factors.

Status of chromosome breaks and gaps in breast cancer. a follow-up study

Genetic susceptibility and environmental factors are believed to be responsible for chromosomal instabilities and higher incidence of breast cancer. We conducted a follow-up study to find the levels of chromosome breaks and gaps in 20 premenopausal women with breast cancer before surgery, 1 month after surgery, and 3 years after surgery with respect to 20 age- and gender-matched controls. The mean level of chromosome breaks and gaps was found to be significantly higher (P<0.001) in breast cancer patients (before surgery) as compared with the controls. The chromosome breaks and gaps after 1 month of surgery were observed significantly decreased (P<0.005) when compared with that of patients before the surgery. Further significant increase in chromosome breaks and gaps was found after 3 years of surgery as compared with both the patients after 1 month of surgery (P<0.05) and controls (P<0.005). The significant increase in chromosome breaks and gaps in breast cancer patients (before surgery) may be due to the effects of genetic susceptibility to environmental carcinogens and endogenous factors. However, the decrease in this level after 1 month of surgery may be due to the removal of cancerous tissues, which in turn removes the effect of mutagens and clastogenic factors. Further increase in chromosome breaks and gaps after 3 years of surgery may be due to the long-term effects of therapeutic agents and genetic susceptibility to environmental carcinogens in the patients. The study furthermore suggests that the high level of chromosome breaks and gaps after 3 years of surgery may be a risk factor for the development of secondary tumor in patients.

DNA adduct levels and DNA repair polymorphisms in traffic-exposed workers and a general population sample

Peripheral blood DNA adducts have been considered an acceptable surrogate for target tissues and possibly predictive of cancer risk. A group of 114 workers exposed to traffic pollution and a random sample of 100 residents were drawn from the EPIC cohort in Florence, a population recently shown to present increased DNA adduct levels (Palli et al., Int J Cancer 2000;87:444-51). DNA bulky adducts and 3 DNA repair gene polymorphisms were analyzed in peripheral leukocytes donated at enrollment, by using (32)P-postlabeling and PCR methods, respectively. Adduct levels were significantly higher for traffic workers among never smokers (p = 0.03) and light current smokers (p = 0.003). In both groups, urban residents tended to show higher levels than those living in suburban areas, and a seasonal trend emerged with adduct levels being highest in summer and lowest in winter. Traffic workers with at least 1 variant allele for XPD-Lys751Gln polymorphism had significantly higher levels in comparison to workers with 2 common alleles (p = 0.02). A multivariate analysis (after adjustment for age, season, area of residence, smoking, XPD-Lys751Gln genotype and antioxidant intake) showed a significant 2-fold association between occupational exposure and higher levels of adducts (odds ratio 2.1; 95% confidence interval 1.1-4.2), in agreement with recent pooled estimates of increased lung cancer risk for similar job titles. Our results suggest that traffic workers and the general population in Florence are exposed to high levels of genotoxic agents related to vehicle emissions. Photochemical pollution in warmer months might be responsible for the seasonal trend of genotoxic damage in this Mediterranean urbanized area.

Expression of ras (p21) protein in plasma from exposed workers and from patients with lung disease

Oncogenes are involved with the regulation of cellular proliferation and thus could be important in the development of many cancers. Cells transformed in culture by ras genes can be activated either by the introduction of specific point mutations or by overexpression of the normal proto-oncogene. The ras genes encode a protein of 189 amino acids (molecular mass 21 kDa) designated as p21. ras p21 proteins are contained in all eukaryotic cells on the inner surface of the plasma membrane. We measured ras p21 proteins in lung cancer patients, patients with chronic obstructive pulmonary disease (COPD) and workers exposed to emissions from petrochemical plants and 1,3-butadiene and 1,3-butadiene/styrene. Proteins were separated by gel electrophoresis, transferred to a nitrocellulose membrane by Western blotting and detected by chemiluminescence. A monoclonal pan-ras antibody was used as the primary antibody. Optical densities of the peak area of the protein bands were calculated and values which were two standard deviations above negative control means were considered positive. Many of the cancer patients and some of the COPD patients gave positive responses, whilst exposed worker groups did not show statistically significant increases by comparison with the controls. Thus, an increase in ras oncoproteins could be a biomarker for cancer or the disease state in general, but it cannot be ruled out that it is a biomarker for exposure since many of the individuals examined were smokers exposed to cigarette smoke.

DNA repair activity of 8-oxoguanine DNA glycosylase 1 (OGG1) in human lymphocytes is not dependent on genetic polymorphism Ser326/Cys326

8-oxoguanine DNA glycosylase 1 (OGG1) is a DNA repair enzyme that excises 7,8-dihydro-8-oxoguanine (8oxoG) from DNA. Since 8oxoG is a highly mispairing lesion, decreased OGG1 expression level could lead to a higher background mutation frequency and could possibly increase the cancer risk of an individual under oxidative stress. In order to analyse the natural variation of OGG1, we measured the DNA repair activity in human lymphocytes of healthy individuals by means of an 8oxoG-containing oligonucleotide assay. The data obtained revealed a two fold interindividual variation of OGG1 activity in lymphocytes. There was no difference in OGG1 activity due to gender and smoking behaviour. Transcriptional analyses of OGG1 showed the expression of two isoforms, 1a and b, in lymphocytes. Structural analysis of the human OGG1 (hOGG1) gene revealed a Ser326/Cys326 polymorphism in the Caucasian population with allele frequencies of 75% for Ser326 and 25% for Cys326. This polymorphism was not associated with altered OGG1 activity. The described routine test system for measuring OGG1 activity in cryopreserved lymphocytes provided highly reproducible results and is a useful tool for risk assessment associated with alterations in the repair of oxidative DNA damage.

Childhood acute lymphoblastic leukemia: genetic determinants of susceptibility and disease outcome

The origin of acute lymphoblastic leukemia (ALL), the most common pediatric cancer, can be explained by a combination of genetic factors and environmental exposure. The environmental toxicants to which an individual is exposed are biotransformed and eliminated from the body after metabolic conversion mediated by Phase I and Phase II xenobiotic-metabolizing enzymes. Phase I enzymes catalyze hydroxylation, reduction and oxidation reactions of xenobiotics (carcinogens/drugs), often converting them into more active or toxic compounds. Phase II enzymes catalyze conjugation reactions (glucuronidation, acetylation, methylation), thereby converting the metabolites into non-reactive, water-soluble products that are eliminated from the organism. The genetic polymorphism underlying the variation in enzyme activity can modify susceptibility to diverse adult cancers, probably by influencing the activation and removal of toxicants or drugs. Here we present an overview of the role of genetic variants of certain Phase I and Phase II enzymes in the development of childhood ALL, a good model for such studies because of its short latency period. The genetic contribution to the development of ALL is examined by association studies that analyze the loci of Phase I enzymes (cytochrome P-450, myeloperoxidase) and Phase II enzymes (quinone-oxidoreductase, glutathione-S-transferase, N-acetyltransferase). The loci of the enzyme variants CYPlA1, CYP2E1, NQO1, GSTM1, GSTP1, NAT2 are associated with disease development, and evidence of gene-gene interactions has emerged as well. Despite the improvements in treatment, resistant cases of ALL remain a leading cause of cancer-related death in children. Although the underlying mechanism of drug resistance is not well understood, differences in the capacity of ALL patients to process drugs and environmental carcinogens could play a role by modifying the risk of recurrent malignancy, as well as the response to therapy. Therefore, polymorphic genes encoding carcinogen- and drug-metabolizing enzymes may not only increase the risk of ALL but also influence the risk of relapse in patients. We found that the prognosis of patients with CYPlA1 and NQO1 variants was worse than that of patients who lack these variants. We conclude that genotyping ALL patients for functional polymorphisms of candidate genes can become an important tool in predicting disease outcome.

Diet and cancer prevention

Research from several sources provides strong evidence that vegetables, fruits, and whole grains, dietary fibre, certain micronutrients, some fatty acids and physical activity protect against some cancers. In contrast, other factors, such as obesity, alcohol, some fatty acids and food preparation methods may increase risks. Unravelling the multitude of plausible mechanisms for the effects of dietary factors on cancer risk will likely necessitate that nutrition research moves beyond traditional epidemiological and metabolic studies. Nutritional sciences must build on recent advances in molecular biology and genetics to move the discipline from being largely 'observational' to focusing on 'cause and effect'. Such basic research is fundamental to cancer prevention strategies that incorporate effective dietary interventions for target populations.

Therapy related leukemias: susceptibility, prevention and treatment

Acute leukemia is the most frequent therapy-related malignancy. Together with the increasing use of chemo- and radiotherapy, individual predisposing factors play a key role. Most of secondary leukemias can be divided in two well-defined groups: those secondary to the use of alkylating agents and those associated to topoisomerase inhibitors. Leukemias induced by alkylating agents usually follow a long period of latency from the primary tumour and present as myelodysplasia with unbalanced chromosomal aberrations. These frequently include deletions of chromosome 13 and loss of the entire or of part of chomosomes 5 or 7. The loss of the coding regions for tumor suppressor genes from hematopoietic progenitor cells is a particularly unfavourable event, since the remaining allele becomes susceptible to inactivating mutations leading to the leukemic transformation. The tumorigenic action of topoisomerase inhibitors is on the other hand due to the formation of multiple DNA strand breaks, resolved by chromosomal translocations. Among these, chromosome 11, band q23, where the myeloid-lymphoid leukemia (MLL) gene is located, is often involved. Frequent partners are chromosomes 9, 19 and 4 in the t(9;11), t(19;11) and t(4;11) translocations. Younger age, a mean period of latency of 2 years and monocytic subtypes are characteristic features of this type of leukemia. Among patients at risk for secondary leukemia, those with Hodgkin's disease are the most extensively studied, with the major impact of alkylating agents included in the chemotherapy schedule. The same is true for non-Hodgkin's lymphoma, while in multiple myeloma and acute lymphoblastic leukemia determinants are the dose of melphalan and of epypodophyllotoxin, respectively. Patients with breast, ovarian and testicular neoplasms are also at risk, in particular if trated with the association of alkylating agents and topoisomerase II inhibitors. According to the EBMT registry, in patients with lymphoma treated with high-dose therapy and autologous stem cell transplantation the cumulative risk of inducing leukemia at 5 years is 2.6%. Among treatment options, supportive therapy is indicated in older patients, while allogeneic stem cell transplantation, related or matched-unrelated, is feasible in younger patients. These data indicate the need for the identification of predisposing factors for secondary leukemia. In particular, frequent follow-up of patients at high-risk should be performed and any peripheral blood cytopenia should be considered suspicious. Whenever possible, the exclusion of drugs known to be leukemogenic from the treatment schedules should be considered, especially in young patients.

A "two-hit" model of cystogenesis in autosomal dominant polycystic kidney disease?

An intriguing feature of autosomal dominant polycystic kidney disease (ADPKD) is the focal and sporadic nature of individual cyst formation. Typically, only a few renal cysts are detectable in an affected individual during the first two decades of life. By the fifth decade, however, hundreds to thousands of renal cysts can be found in most patients. Additionally, significant intra-familial variability of ADPKD has been well documented. Taken together, these findings suggest that factor(s) in addition to the germline mutation of a polycystic kidney disease gene might be required for individual cyst formation. Indeed, recent studies have provided compelling evidence in support of a "two-hit" model of cystogenesis in ADPKD. In this model, inactivation of both copies of a polycystic kidney disease gene by germline and somatic mutations within an epithelial cell provides growth advantages for it to proliferate clonally into a cyst. This article highlights key findings of these recent studies and discusses the controversies and implications of the "two-hit" model in ADPKD.

Induction of cytochrome P4501A1

Cytochrome P4501A1 is a substrate-inducible microsomal enzyme that oxygenates polycyclic aromatic hydrocarbons, such as the carcinogen benzo(a)pyrene, as the initial step in their metabolic processing to water-soluble derivatives. Enzyme induction reflects increased transcription of the cognate CYP1A1 gene. The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin is the most potent known cytochrome P4501A1 inducer. Two regulatory proteins, the aromatic (aryl) hydrocarbon receptor (AhR) and the AhR nuclear translocator (Arnt), mediate induction. AhR and Arnt are prototypical members of the basic helix-loop-helix/Per-Arnt-Sim class of transcription factors. Mechanistic analyses of cytochrome P4501A1 induction provide insights into ligand-dependent mammalian gene expression, basic helix-loop-helix/Per-Arnt-Sim protein function, and dioxin action; such studies also impact public health issues concerned with molecular epidemiology, carcinogenesis, and risk assessment.

The search for cancer risk factors: when can we stop looking?

In recent decades, countless cohort, case-control, and ecologic studies have been conducted in the search for cancer risk factors. On the basis of knowledge gained from these studies, various influential commentaries have endeavored to classify the extent to which the total cancer burden is attributable to general categories of risk, such as diet, tobacco, sun exposure, and others. These commentaries have led to the conventional wisdom that most of the cancer burden is caused by environmental factors and relatively little is directly attributable to genetic susceptibility. In the face of the apparent knowledge that the cancer burden is essentially fully "explainable" on the basis of known environmental risks, this article addresses the conceptual and empirical basis of the continued search for new risk factors. It proposes that the extent of the aggregation of cancer within individuals in the population--that is, the occurrence of second primary cancers--is a crucial statistic in this context. A study of the incidence of second primary melanoma suggests that the bulk of the risk variation in this disease cannot be explained by known risk factors. The implications of these ideas for research strategy and for public health policy are discussed.

Increased DNA alterations in atherosclerotic lesions of individuals lacking the GSTM1 genotype

Reduced glutathione (GSH) plays a critical role as an intracellular defense system providing detoxification of a broad spectrum of reactive species and their excretion as water-soluble conjugates. Conjugation of GSH with electrophiles is catalyzed by GSH S-transferases (GST), which constitute a broad family of phase II isoenzymes. Two of the GST encoding genes, GSTM1 (mu) and GSTT1 (theta), have a null genotype due to their homozygous deletion that results in lack of active protein. Polymorphisms within GSTT1 and especially GSTM1 have often been associated with cancer in various organs as well as with elevated levels of DNA adducts in various cell types. We recently demonstrated that DNA adducts are consistently detectable in smooth muscle cells (SMC) of human abdominal aorta affected by atherosclerotic lesions. Here we provide evidence that levels of adducts to SMC DNA from atherosclerotic lesions are consistently increased in individuals having the null GSTM1 genotype, whereas no association was established with the GSTT1 polymorphism. The influence of GSTM1 deletion was better expressed in never-smokers and ex-smokers than in current smokers. These findings bear relevance to the epidemiology of atherosclerosis and suggest that metabolic polymorphisms may contribute to the interindividual variability in susceptibility not only to carcinogens, but also to DNA binding atherogens.

p53 tumor suppressor gene: at the crossroads of molecular carcinogenesis, molecular epidemiology, and human risk assessment

The molecular archaeology of the mutation spectra of tumor suppressor genes generates hypotheses concerning the etiology and molecular pathogenesis of human cancer. The spectrum of somatic mutations in the p53 gene implicates environmental carcinogens and both endogenous agents and processes in the etiology of human cancer.

Nutrition, genetics, and risks of cancer

Dietary patterns, nutrients, and other constituents of food are major components of the environmental influences that contribute to risk for cancer, and the study of interactions between nutritional and genetic factors is a new and important area or research. This review describes the concepts and principles underlying this area of study and types of relationships between nutritional and genetic factors, and it provides examples of specific diet-gene interactions that are of current interest, with an emphasis on implications for cancer prevention and public health. Polymorphisms exist in the genes for the activating and conjugating metabolizing enzymes, and the induction of metabolizing enzyme activity by nutritional factors may result in either the activation of a carcinogen or the detoxification of a reactive intermediate metabolite. The relationship between the methylenetetrahydrofolate reductase gene and dietary folate is an example of a diet-gene interaction that involves a polymorphism in a vitamin metabolism gene, and the presence of the variant appears to influence both risk for cancer and folate requirements. Diet-gene interactions likely contribute considerably to the observed inter-individual variations in cancer risk in response to exposures to the nutritional factors that have the potential to promote or protect against cancer. Insights into mechanisms by which nutritional factors affect the process of carcinogenesis are provided by knowledge of the targeted gene function and enzyme activity. Increased knowledge in this area will allow a more refined approach to reducing risk for cancer, with diet interventions targeted toward individuals and subgroups that are genetically susceptible and responsive to the effects of nutritional factors.

Evaluation of radioinduced damage and repair capacity in blood lymphocytes of breast cancer patients

Genetic damage caused by ionizing radiation and repair capacity of blood lymphocytes from 3 breast cancer patients and 3 healthy donors were investigated using the comet assay. The comets were analyzed by two parameters: comet tail length and visual classification. Blood samples from the donors were irradiated in vitro with a 60Co source at a dose rate of 0.722 Gy/min, with a dose range of 0.2 to 4.0 Gy and analyzed immediately after the procedure and 3 and 24 h later. The basal level of damage and the radioinduced damage were higher in lymphocytes from breast cancer patients than in lymphocytes from healthy donors. The radioinduced damage showed that the two groups had a similar response when analyzed immediately after the irradiations. Therefore, while the healthy donors presented a considerable reduction of damage after 3 h, the patients had a higher residual damage even 24 h after exposure. The repair capacity of blood lymphocytes from the patients was slower than that of lymphocytes from healthy donors. The possible influence of age, disease stage and mutations in the BRCA1 and BRCA2 genes are discussed. Both parameters adopted proved to be sensitive and reproducible: the dose-response curves for DNA migration can be used not only for the analysis of cellular response but also for monitoring therapeutic interventions. Lymphocytes from the breast cancer patients presented an initial radiosensitivity similar to that of healthy subjects but a deficient repair mechanism made them more vulnerable to the genotoxic action of ionizing radiation. However, since lymphocytes from only 3 patients and 3 normal subjects were analyzed in the present paper, additional donors will be necessary for a more accurate evaluation.

Genetic polymorphisms of cytochrome P450 2A6 in a case-control study on lung cancer in a French population

Cytochrome P450 2A6 (CYP2A6) is involved in the C-oxidation of nicotine and in the metabolic activation of tobacco nitrosamines. Recent data have suggested that CYP2A6 genetic polymorphisms might play a role in tobacco dependence and consumption as well as in lung cancer risk. However, the previously published studies were based on a genotyping method that overestimated the frequencies of deficient alleles, leading to misclassification for the CYP2A6 genotype. In this study, we genotyped DNA from 244 lung cancer patients and from 250 control subjects for CYP2A6 (wild-type allele CYP2A6*1, and two deficient alleles: CYP2A6*2, and CYP2A6*4, the latter corresponding to a deletion of the gene) using a more specific procedure. In this Caucasian population, we found neither a relation between genetically impaired nicotine metabolism and cigarette consumption, nor any modification of lung cancer risk related to the presence of defective CYP2A6 alleles (odds ratio = 1.1, 95% confidence interval = 0.7-1.9).

Genetic epidemiology of multistage carcinogenesis

It is commonly believed that cancer is a multistage, polygenic disease. Even though conceptually appealing, the evidence supporting the multistage theory remains limited. Most known tumor suppresser genes are associated with monogenic dominant cancers following a two-hit pathway. We review results from a recent twin study on 90000 individuals that give support to the multistage theory. Statistically significant heritability estimates were shown for cancers of the colorectum (35%), breast (27%), and prostate (42%). These estimates are much higher than those obtained from family studies in which parents and offspring, or sibs are compared. The difference can be accounted for by the involvement of many genes. A polygenic cancer would show small effects in family studies but large effects in twin studies. We present calculations on the decrease in familial risks when the number of genes involved increases or when the penetrance decreases. We test the apparent number of stages involved in the main cancers from the Swedish Family-Cancer Database. The logarithms of the slopes suggest large differences in the apparent numbers of mutations involved in different cancers. The number of mutations required appears to be less in familial breast cancer compared to sporadic breast cancer. Study designs for gene identification should be revised to accommodate polygenic cancers.

Gender difference in DNA adduct levels among nonsmoking lung cancer patients

Lung cancer is the leading cause of cancer mortality in Taiwanese women. Cigarette smoking cannot explain the high lung cancer mortality in this population because less than 10% of women in Taiwan are smokers. Therefore, environmental factors other than smoking may play an important role in lung cancer development in female nonsmokers. The purpose of this study was to elucidate the role of environmental carcinogen exposure in lung cancer development in Taiwanese female nonsmokers, based on DNA adduct formation. We collected nontumorous lung tissues resected from 62 nonsmoking lung cancer patients and 20 noncancer controls to investigate whether differences in susceptibility to DNA adduct formation exist between men and women. (32)P-postlabeling and ELISA (enzyme-linked immunosorbent assay) with polyclonal antibody against BPDE (7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene)-DNA adduct were used to evaluate DNA adduct levels in lung tissues of study subjects. Our data showed that the DNA adduct levels of lung cancer patients determined by both assays were significantly higher than those of noncancer controls (P = 0.0001 for (32)P-postlabeling; P = 0.01 for ELISA). Moreover, DNA adduct levels in females were markedly greater than those in males (P = 0.014 for (32)P-postlabeling; P = 0.001 for ELISA). The difference in DNA adduct levels could not be explained by genetic polymorphisms of cytochrome P-4501A1 (CYP1A1) or glutathione S-transferase (GSTM1), as determined by polymerase chain reaction and restriction fragment length polymorphism. These results demonstrate that lung cancer patients have a higher susceptibility to DNA damage than that of noncancer controls. In addition, differences in susceptibility to DNA damage derived from environmental carcinogen exposure were observed between male and female nonsmokers. In conclusion, high susceptibility to DNA damage in females may partially explain the high mortality rate of lung cancer in nonsmoking Taiwanese women.

Hydrocarbon deposition and soil microflora as affected by highway traffic

The proximity of a busy highway (90,000 vehicles/day) increased the amount of polycyclic aromatic hydrocarbons (PAHs) in soil at the depth of 5-15 cm from 106 ng/g as a grassland background to 3095 ng/g dry soil at the highway verge (a sum of 10 PAH species). The PAH concentration was related to the distance from the source and exhibited a biphasic character, which is interpreted in terms of bimodal distribution of the exhaust microparticles with different rates of deposition. Similarly, the tendency of benz(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, and indeno(1,2,3-cd)pyrene to decrease their proportion with distance from the highway, in contrast to phenanthrene, fluoranthene, pyrene, benzo(a)pyrene, and benzo(g,h,i)perylene, was attributed to their prevalent localisation on the heavier particle fraction. The abundance of bacteria (8.33 x background) and fungi (3.17 x background) close to the highway is thought to be a consequence of hydrocarbon deposition from the traffic that serves as a significant energetic input into the soil. The elevated concentrations of hydrocarbon substrates, as indicated by PAHs, increased both the absolute and relative numbers of the microbial degraders of diesel fuel, biphenyl, naphthalene, and pyrene. Their maximum numbers at 0.5-1.5 m from the pavement reached 1.3 x 10(4), 1.2 x 10(5), 1.1 x 10(4), and 6.6 x 10(3) colony-forming units (CFU) or infection units per gramme dry soil, respectively. On the other hand, the number of anthracene degraders (1.1 x 10(3) CFU per g dry soil) remained close to the detection limit of the enumeration technique used (0.1-0.2 x 10(3) per g dry soil), consistently with the absence of anthracene and higher linear PAHs in the investigated soil samples. The amounts of persisting PAHs justify artificial inoculation with effective degrader strains in the vicinity of motorways.

From genotype to phenotype: buffering mechanisms and the storage of genetic information

DNA sequence variation is abundant in wild populations. While molecular biologists use genetically homogeneous strains of model organisms to avoid this variation, evolutionary biologists embrace genetic variation as the material of evolution since heritable differences in fitness drive evolutionary change. Yet, the relationship between the phenotypic variation affecting fitness and the genotypic variation producing it is complex. Genetic buffering mechanisms modify this relationship by concealing the effects of genetic and environmental variation on phenotype. Genetic buffering allows the build-up and storage of genetic variation in phenotypically normal populations. When buffering breaks down, thresholds governing the expression of previously silent variation are crossed. At these thresholds, phenotypic differences suddenly appear and are available for selection. Thus, buffering mechanisms modulate evolution and regulate a balance between evolutionary stasis and change. Recent work provides a glimpse of the molecular details governing some types of genetic buffering.

Genetic susceptibility to childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer. The origin of this disease can be explained by a combination of genetic susceptibility factors and environmental exposures. For the purpose of our study it can be considered as a complex disease, caused by the "carcinogenic" effect of the environment modified by a series of genes. In population, these genes tend to occur in allelic forms representing functional polymorphisms thus explaining inter-individual variability in cancer susceptibility. The latter can be evaluated more realistically in childhood ALL than in sporadic cancers of the adult because of its relatively short latency period. We asked therefore, the question about the role of genes controlling the efficiency of xenobiotics metabolism in childhood leukemogenesis. Xenobiotics (drugs and carcinogens) are excreted from the body after metabolic conversion by enzymes mediating oxidation activation (Phase I) and conjugation detoxificaton (Phase II). Functional variants of these enzymes, resulting from known DNA polymorphisms in the corresponding genes, were shown to influence the risk to a variety of solid tumours in adults. A case-control study on ALL patients and healthy controls in a French-Canadian population was carried out by examining the loci of Phase I, CYP1A1 and CYP2D6, as well as Phase II enzymes, GSTM1, GSTT1, NAT1 and NAT2. The NAT2 slow-acetylator, CYP1A1*2A and GSTM1 null genotypes were shown to be significant risk determinants of ALL (OR=1.6, 1.8 and 1.8, respectively), whereas, polymorphisms in CYP2D6 and GSTT1 genes did not seem to play an important role in the aetiology of ALL. Interestingly, the risk associated with NAT2 slow-acetylators was most apparent among males homozygous for NAT1*4 (OR=3.3) whereas girls carrying the CYP1A1*4 allele were significantly underrepresented in the patient group (OR=0.2). These findings point to a gender-specific effect of DNA variants which, at least in part, may explain why ALL is more prevalent among boys. To assess gene-gene interactions, NAT2 slow-acetylators were considered together with GSTM1 null genotypes and CYP1A1*2A alleles. The combined presence of two risk-elevating genotypes appeared to confer an increased risk of ALL among the carriers (OR=2.6). This risk was increased further (OR=3.3) when all three genotypes occurred in the same individuals indicating that the combination of susceptibility variants is more predictive of risk then either of them independently. The association of leukemogenesis in children with metabolising gene variants suggests causal relation to environmental exposures.

Diet, metabolic polymorphisms and dna adducts: the EPIC-Italy cross-sectional study

DNA adducts in peripheral leukocytes are considered a reliable indicator of internal dose exposure to genotoxic agents and, possibly, of cancer risk. We investigated their association with diet and other individual characteristics in healthy adults. The prospective study EPIC-Italy, a section of a larger European project, enrolled 47,749 men and women, aged 35-64 years, in 5 centres: all provided individual information about dietary and life-style habits and a blood sample. In a cross-sectional study, approximately 100 volunteers were randomly selected from each of the three main geographical study areas (Northern, Central and Southern Italy). DNA adducts and four polymorphic metabolic genotypes were determined in peripheral leukocytes by using (32)P-postlabelling technique and PCR methods. Among 309 subjects (153 men), 72.8% had detectable levels of DNA adducts (mean: 8.1 +/- 0.6 per 10(9) nucleotides). Strong negative associations emerged with the reported frequency of consumption of fresh fruit and vegetables, olive oil, and the intake of antioxidants. DNA adducts were higher in subjects with GSTT1 null genotype (p = 0.05). Significant differences between study centres emerged in multivariate analyses (mean levels: 11.0, 10.0, 7.2, 6.5 and 5.2 for Florence, Naples, Turin, Varese and Ragusa, respectively). A possible opposite seasonal variation was found according to latitude: adduct levels tended to be lower in winter in Florence and the southern centres, and during summer in the two northern centres. Frequent consumption of fresh fruit and vegetables is associated with reduced levels of DNA adducts, possibly contributing to the role of diet in modulating cancer risk.

P53 mutations, polymorphisms, and haplotypes in Pakistani ethnic groups and breast cancer patients

Inactivation of the p53 gene has been found to be associated with the pathogenesis of several neoplasias. Three biallelic polymorphisms in the p53 gene have been linked to predisposition to the development of various malignancies. These include a 16-bp duplication in intron 3 and BstU I and Msp I restriction fragment length polymorphisms (RFLPs) in exon 4 and intron 6, respectively. The prevalence of these polymorphisms was studied in breast cancer patients and nine major ethnic groups of Pakistan. Differences in allele frequencies for all three polymorphisms were observed among the various ethnic groups and breast cancer patients. The absence of the 16-bp duplication was common among the northern ethnic groups, being highest in the Hazara (0.90). The Msp I A1 allele frequency in the southern Makrani population was significantly higher in comparison with the other ethnic groups. In the cancer patients, the absence of the 16-bp duplication in combination with the BstU I Pro and absence of Msp I restriction site were the most frequent. In these patients, ten substitution mutations were found in the p53 gene, seven of which have been reported previously for breast cancer. The remaining three mutations have been found in other malignancies, but not in carcinoma of the breast.

Case-parents design for gene-environment interaction

The scientific and public health implications of gene-environment interaction warrant that the most powerful study designs and methods of analysis be used. Because traditional case-control designs, which use nonrelated subjects, have demonstrated the need for large samples to detect interactions, alternative study designs may be worthwhile, such as sampling diseased cases and their parents. If the transmission of particular alleles from parents to their diseased child appears to be distorted from Mendelian expectation, then this suggests an etiologic association of the alleles with disease; if the frequency of transmission differs between exposed and nonexposed cases, then gene-environment interaction is suggested. We present likelihood-based methods to assess interaction, as well as an extension of the transmission/disequilibrium test (TDT). For these statistical tests, we also derive methods to compute sample size and power. Comparisons of sample size requirements between the case-parents design and the case-control design indicate that the case-parents design can be more powerful to detect gene-environment interactions, particularly when the disease susceptible allele is rare. Also, one of the derived likelihood methods, based on additive effects of alleles, tended to be the most robust in terms of power for a broad range of genetic mechanisms, and so may be useful for broad applications to assess gene-environment interactions.

The t(1;12)(q21;p13) translocation of human acute myeloblastic leukemia results in a TEL-ARNT fusion

The TEL/ETV6 gene is located at 12p13 and encodes a member of the ETS family of transcription factors. Translocated ETS leukemia (TEL) is frequently involved in chromosomal translocations in human malignancies, usually resulting in the expression of fusion proteins between the amino-terminal part of TEL and either unrelated transcription factors or protein tyrosine kinases. We have characterized a t(1;12)(q21;p13) translocation in an acute myeloblastic leukemia (AML-M2). At the protein level, the untranslocated TEL copy and, as a result of the t(1;12) translocation, a fusion protein between TEL and essentially all of aryl hydrocarbon receptor nuclear translocator (ARNT) are expressed. The involvement of ARNT in human leukemogenesis has not been previously described. The ARNT protein belongs to a subfamily of the "basic region helix-loop-helix" (bHLH) protein that shares an additional region of similarity called the PAS (Per, ARNT, SIM) domain. ARNT is the central partner of several heterodimeric transcription factors, including those containing the aryl hydrocarbon (dioxin) receptor (AhR) and the hypoxia-inducible factor 1alpha (HIF1alpha). Our results show that the TEL-ARNT fusion protein is the crucial product of the translocation and suggest that interference with the activity of AhR or HIF1alpha can contribute to leukemogenesis.

Cancer risk and low-penetrance susceptibility genes in gene-environment interactions

PURPOSE

To provide a concise review for human cancer risk related to low-penetrance genes and their effects on environmental carcinogen exposure.

METHODS

Citation of relevant and recent references for molecular epidemiology, focusing on lung cancer, ethical issues, and some clinical implications of recent molecular epidemiology studies.

RESULTS

Low-penetrance genes contribute to cancer risk by augmenting the effects of carcinogen exposures. These exposures can be measured in the body through molecular dosimetry (ie, the amount of DNA damage), which reflects a biologically effective dose. The examination of tumors and the mutations within tumor suppressor genes, such as p53, can provide etiologic clues for both exposure and susceptibility. Although many studies have focused on carcinogen metabolism and cancer risk, more recent studies are considering DNA repair. Also, we are learning that behavior, such as tobacco addiction, also may be genetically controlled.

CONCLUSION

Sporadic cancers are caused by gene(n)-environment(n) interactions rather than a dominant effect by a specific gene, environmental exposure, or gene-environment interaction. New paradigms, where we categorize genes as caretaker or gatekeeper genes, will allow for new hypotheses to be tested and will require advanced methods of analysis. The goal of molecular epidemiology is to develop risk assessment models for individuals, but currently the most achievable goal will be population risk assessment and a better understanding of carcinogenesis.

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.

Role of DNA repair in carcinogen-induced ras mutation

In this contribution we discuss the gene- and cell type-specific repair of miscoding DNA alkylation products as a risk parameter in both mutation induction and malignant transformation by N-nitroso carcinogens. Upon exposure to N-nitroso compounds such as N-methyl-N-nitrosourea (MeNU) or N-ethyl-N-nitrosourea (EtNU), about a dozen different alkylation products are formed in cellular DNA. Among these are O(6)-methylguanine (O(6)-MeGua) and O(6)-ethylguanine (O(6)-EtGua), respectively, which differ only by one CH(2) group in their alkyl residue and, when unrepaired, cause G:C-->A:T transition mutations by anomalous base pairing during DNA replication. We have analyzed the global and gene-specific repair of O(6)-MeGua and O(6)-EtGua in target cell DNA, ras gene mutation frequencies, and tumor incidence, in the model of mammary carcinogenesis induced in 50-day-old female Sprague-Dawley rats by a single application of MeNU or EtNU. Both carcinogens induce histologically indistinguishable mammary adenocarcinomas at high yield. In the target mammary epithelia, O(6)-MeGua is repaired at similar slow rates in both transcriptionally active genes (Ha-ras, beta-actin), silent genes (lgE heavy chain), and in bulk DNA, by the one-step repair protein O(6)-alkylguanine-DNA alkyltransferase (MGMT; low level of expression in the target cells). The slow repair of O(6)-MeGua translates into a high frequency of mutations at the central position of Ha-ras codon 12 (GGA) in MeNU-induced tumors. O(6)-EtGua, however, is removed approximately 20 times faster than O(6)-MeGua selectively from transcribed genes via an MGMT independent, as yet uncharacterized excision mechanism. Accordingly, no Ha-ras codon 12 mutations are found in the EtNU-induced mammary tumors. Neither MeNU- nor EtNU-induced tumors exhibit mutations at codons 13 and 61 of Ha-ras or at codons 12, 13 and 61 of Ki-ras. While a moderate surplus MGMT activity of the target cells - contributed by a bacterial MGMT transgene (ada) - significantly counteracts mammary tumorigenesis in MeNU-exposed rats, this is not the case in the EtNU-treated animals. Differential repair of structurally distinct DNA lesions in transcribed or (temporarily) silent genes thus determines the probability of mutation and, together with cell type-specific and interindividual differences in DNA repair capacity, influences carcinogenic risk.

Molecular epidemiology: on the path to prevention?

Cancer prevention has been the stated goal of molecular cancer epidemiology for the past 17 years. In this review, progress toward that goal is evaluated by using as examples well-studied environmental exposures-i.e., tobacco smoke, polycyclic aromatic hydrocarbons, aflatoxin B(1), benzene, and hepatitis B virus-and their roles in lung, breast, and liver cancers and leukemia. The contributions of molecular epidemiology discussed here include providing evidence that environmental agents pose carcinogenic risks, helping establish the causal roles of environmental factors in cancer, identifying environment-susceptibility interactions and populations at greatest risk, and developing new intervention strategies. Molecular epidemiologic and other data indicate that assessment of carcinogenic risks should address both the range of risk across the population and the risk to subgroups who may be at high risk because of genetic or acquired susceptibilities, including young children. However, for the most part, research results have not yet been effectively translated into risk assessments and preventive health policies. An infrastructure linking scientists, policy makers, and other constituencies is needed to facilitate this process. To extend our knowledge, the second generation of molecular epidemiologic research should include large-scale, collaborative studies incorporating validated biomarkers and automated technologies. An incentive to make the necessary investment is the recognition that prevention of only 20% of cancer in the United States would result in 200000 fewer new cases diagnosed each year and an annual savings of $21.4 billion in direct costs alone.

FHIT gene mutations and single nucleotide polymorphism in Indian oral and cervical squamous cell carcinomas

Genetic alterations at the FHIT (fragile histidine triad) tumor suppressor gene have been found in various human cancers. We have made an attempt to find point mutations of this gene in two different cancers from India, with entirely different etiologic factors: oral cancer (55 samples) caused by chewing tobacco and cervical cancer (43 samples) caused mainly by HPV (human papilloma virus) infection. Analysis of tumor DNA by the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) method was performed on each of FHIT exons 5-9 individually, using exon-flanking primers. Two different mutations were identified in both oral and cervical tumors: one at the second nucleotide 3' to the termination codon (TGA) in exon 9 and the other at the ninth nucleotide upstream to the beginning of exon 9. These results indicate that mutations in the FHIT gene are rare events in these tumors in India (approximately 4%). In addition, we found a single nucleotide FHIT gene polymorphism which is due to T/A replacement at 17 nucleotides upstream to exon 9 where the A allele is 0.6 of the population.

Molecular epidemiology: recent advances and future directions

In 1982 we proposed the concept and a framework for implementing molecular cancer epidemiology. Here, we review progress during the past 17 years in validating and applying this approach to cancer prevention. There have been major advances, notably in the understanding of environment-susceptibility interactions in human cancer. However, a review of major findings to date reveals several urgent research needs to keep pace with the rapid evolution in knowledge of mechanisms in carcinogenesis. Although much valuable progress continues to be made in the study of carcinogens that cause direct DNA damage and are mutagenic, exogenous and endogenous carcinogens can also act by altering gene expression, cell proliferation and differentiation. The mechanisms include aberrant DNA methylation, oxidative damage, effects on metabolism of nitrogen oxide and nitrites, activation of receptors and transcription factors, cyclins and other cell cycle proteins. Sensitive, validated biomarkers are needed to detect these mechanisms in small numbers of cells, tissues or fluids. There is also increasing recognition that individual risk from carcinogen exposure varies as a function of both inherited and acquired factors. Recent advances in genomics, microassay technologies and informatics hold promise for rapid identification of polymorphic variants or changes in expression of genes influencing both response and susceptibility to carcinogens. Another emerging area of molecular epidemiology concerns the role of nutrition and specific dietary factors (including studies on antioxidants, energy metabolism, insulin and various growth factors) and the modulating effect of genetic polymorphisms. Finally, molecular epidemiology has enormous potential in cancer prevention through the early identification of 'at risk' populations and the rapid assessment of intervention efficacy. Its success in fully reaching this potential will depend on the application of validated biomarkers, with adherence to sound epidemiologic and ethical principles.

The United Kingdom Childhood Cancer Study: objectives, materials and methods. UK Childhood Cancer Study Investigators

An investigation into the possible causes of childhood cancer has been carried out throughout England, Scotland and Wales over the period 1991-1998. All children known to be suffering from one or other type of the disease over periods of 4-5 years have been included, and control children matched for sex, age and area of residence have been selected at random from population registers. Information about both groups of children (with and without cancer) has been obtained from parental questionnaires, general practitioners' and hospital records, and from measurement of the extent of exposure to radon gas, terrestrial gamma radiation, and electric and magnetic fields. Samples of blood have also been obtained from the affected children and their parents and stored. Altogether 3,838 children with cancer, including 1,736 with leukaemia, and 7,629 unaffected children have been studied. Detailed accounts are given of the nature of the information obtained in sections describing the general methodology of the study, the measurement of exposure to ionizing and non-ionizing radiation, the classification of solid tumours and leukaemias, and the biological material available for genetic analysis.

Molecular evidence of field cancerization in a patient with 7 tumors of the aerodigestive tract

Exposure of the mucosa of the upper aerodigestive tract to carcinogens can induce genetic changes resulting in various independent clones of neoplastic growth, a concept defined as "field cancerization." The risk of developing multiple tumors in this compartment of the body is well established. We studied 6 distinct tumors of the upper aerodigestive tract of a single patient for loss of heterozygosity (LOH), microsatellite instability (MSI), p53 mutations, and K-ras codon 12 point mutations. We detected a unique pattern of LOH and p53 mutations in all 6 tumors. No tumor showed a K-ras mutation or MSI. The results support the mechanism of "field cancerization" and illustrate the potential power of molecular techniques to elucidate pathogenesis.

Achievements in Understanding and Treatment of Myelodysplastic Syndromes

The myelodysplastic syndromes (MDS) constitute a challenge for the biologist as well as for the treating physician. In Section I, Dr. Willman reviews the current classifications and disease mechanisms involved in this heterogeneous clonal hematopoietic stem cell disorder. A stepwise genetic progression model is proposed in which inherited or acquired genetic lesions promote the acquisition of “secondary” genetic events mainly characterized by gains and losses of specific chromosome regions. The genetic risk to develop MDS is likely multifactorial and dependent on various constellations of risk-producing and -protecting alleles. In Section II Dr. Barrett with Dr. Saunthararajah addresses the immunologic factors that may act as important secondary events in the development of severe pancytopenia. T cells from patients with MDS may suppress autologous erythroid and granulocytic growth in vitro, and T cell suppression by antithymocyte globulin or cyclosporine may significantly improve cytopenia, especially in refractory anemia. Recent studies have also demonstrated an increased vessel density in MDS bone marrow, and a phase II trial of thalidomide showed responses in a subgroup of MDS patients especially in those with low blast counts. In Section III Dr. Hellström-Lindberg presents results of allogeneic and autologous stem cell transplantation (SCT), intensive and low-dose chemotherapy. The results of allogeneic SCT in MDS are slowly improving but are still poor for patients with unfavorable cytogenetics and/or a high score according to the International Prognostic Scoring System. A recently published study of patients between 55-65 years old showed a disease-free survival (DFS) at 3 years of 39%. Consolidation treatment with autologous SCT after intensive chemotherapy may result in long-term DFS in a proportion of patients with high-risk MDS. Low-dose treatment with 5-azacytidine has been shown to significantly prolong the time to leukemic transformation or death in patients with high-risk MSA. Erythropoietin and granulocyte colony-stimulating factor may synergistically improve hemoglobin levels, particularly in sideroblastic anemia. Recent therapeutic advances have made it clear that new biological information may lead to new treatment modalities and, in combination with statistically developed predictive models, help select patients for different therapeutic options.

Effect modification in epidemiologic studies of low-level neurotoxicant exposures and health outcomes

Little attention has been invested in exploring the possibility that the nature or magnitude of a neurotoxicant's health impact on children depends on host characteristics (e.g., sex, age) or contextual factors (e.g., socioeconomic status, other chemical exposures). Such effect modification is a property of a true association, and should be distinguished from confounding. In epidemiologic studies of children, most efforts to identify effect modification have been unsystematic, pursued as part of data analysis rather than of study design. As a result, most samples have insufficient statistical power to characterize effect modification with adequate precision. This may contribute to an inconsistency in results across studies. Failure to assess effect modification adequately may also lead to invalid inferences. If the magnitude of an association between a neurotoxicant exposure and a particular end point varies across strata of a third factor, an estimate that summarizes the association across strata of this factor will be inappropriate, overestimating the association in a stratum in which the association is absent, and underestimating it in a stratum in which it is present. Until such dependencies are identified, our understanding of the mechanism(s) of a compound's neurotoxicity will remain incomplete, as will the knowledge base required to formulate public policy that adequately protects the most sensitive subgroups of the population.

Achievements in Understanding and Treatment of Myelodysplastic Syndromes

The myelodysplastic syndromes (MDS) constitute a challenge for the biologist as well as for the treating physician. In Section I, Dr. Willman reviews the current classifications and disease mechanisms involved in this heterogeneous clonal hematopoietic stem cell disorder. A stepwise genetic progression model is proposed in which inherited or acquired genetic lesions promote the acquisition of “secondary” genetic events mainly characterized by gains and losses of specific chromosome regions. The genetic risk to develop MDS is likely multifactorial and dependent on various constellations of risk-producing and -protecting alleles. In Section II Dr. Barrett with Dr. Saunthararajah addresses the immunologic factors that may act as important secondary events in the development of severe pancytopenia. T cells from patients with MDS may suppress autologous erythroid and granulocytic growth in vitro, and T cell suppression by antithymocyte globulin or cyclosporine may significantly improve cytopenia, especially in refractory anemia. Recent studies have also demonstrated an increased vessel density in MDS bone marrow, and a phase II trial of thalidomide showed responses in a subgroup of MDS patients especially in those with low blast counts. In Section III Dr. Hellström-Lindberg presents results of allogeneic and autologous stem cell transplantation (SCT), intensive and low-dose chemotherapy. The results of allogeneic SCT in MDS are slowly improving but are still poor for patients with unfavorable cytogenetics and/or a high score according to the International Prognostic Scoring System. A recently published study of patients between 55-65 years old showed a disease-free survival (DFS) at 3 years of 39%. Consolidation treatment with autologous SCT after intensive chemotherapy may result in long-term DFS in a proportion of patients with high-risk MDS. Low-dose treatment with 5-azacytidine has been shown to significantly prolong the time to leukemic transformation or death in patients with high-risk MSA. Erythropoietin and granulocyte colony-stimulating factor may synergistically improve hemoglobin levels, particularly in sideroblastic anemia. Recent therapeutic advances have made it clear that new biological information may lead to new treatment modalities and, in combination with statistically developed predictive models, help select patients for different therapeutic options.

A note on the relevance of human population genetic variation and molecular epidemiology to assessing radiation health risk for space travellers

We discuss the relevance to space medicine of studies concerning human genetic variation and consequent variable disease susceptibility or sensitivity between individuals. The size of astronaut and cosmonaut populations is both presently and cumulatively small, and despite the launch of the International Space Station, unlikely to increase by orders of magnitude within the foreseeable future. In addition, astronauts-cosmonauts constitute unrepresentative samples of their national populations. While the context of exposure for the astronaut-cosmonaut group is one unlikely to be replicated elsewhere than in space, aspects of specific exposures may be simulated by events such as occupational radiation exposure or radiation therapy. Hence, population-based studies of genetic susceptibility or sensitivity to disease, especially where it is precipitated by events that may simulate consequences of the space environment, likely will prove of value in assessing long-term health risks.

Genetic and environmental risk factors in the aetiology of illicit drug initiation and subsequent misuse in women

BACKGROUND

Subsequent to initial exposure to the use of a psychoactive substance, psychoactive substance use disorder (PSUD) may or may not develop.

AIMS

To investigate the relationship between the risk factors for initiation and the subsequent misuse of psychoactive substances.

METHOD

The lifetime history of illicit substance use and misuse was obtained by telephone interview with 1934 members of female-female twin pairs. We apply a novel model, which estimates the role of genetic and environmental risk factors that influence initiation and those specific to misuse, to three classes of illicit psychoactive substances.

RESULTS

The individual-specific environment and family environment influenced the probability of initiation, but only individual-specific environment had an impact on the probability of subsequent misuse. Genetic factors which influence the risk of initiation and of misuse were identified.

CONCLUSIONS

Aetiological factors that influence drug initiation and subsequent misuse are correlated but not identical. Family environment is an important determinant of risk for drug experimentation. Two classes of genetic risk factors act on the liability to PSUD: those that influence the probability of initiation and those that influence the risk of misuse.

Polycyclic aromatic hydrocarbon-DNA adducts in cervical smears of smokers and nonsmokers

OBJECTIVES

The aim of this study was to detect polycyclic aromatic hydrocarbon-DNA (PAH-DNA) adducts in single cervical cells collected during a routine Papanicolaou smear and to relate this carcinogen exposure dose marker to smoking habit.

METHODS

An immunohistochemical assay, using a polyclonal antiserum raised against benzo[a]pyrene diol epoxide-DNA adducts, was performed to evaluate PAH-DNA adducts in cervical cells collected from 16 volunteers who smoked at least 20 cigarettes/day and 16 nonsmokers.

RESULTS

The mean adduct level, determined as relative staining intensity by an optical density image analyzer, was significantly higher in smokers compared to nonsmokers (AOD x 1000 +/- SD = 98 +/- 32 and 73 +/- 25, respectively) (P = 0.04).

CONCLUSIONS

These results demonstrate that this immunohistochemical assay, much simpler than other methodologies used to evaluate PAH-DNA adducts in cervical tissue, is sufficiently sensitive for quantitative adduct evaluation in single epithelial cervical cells, as already verified for other exfoliated material. This work thus confirms that tobacco smoke is a risk factor for genotoxic damage generation in cervical cells and indicates a procedure likely adaptable to a large population screening.