Safrole-DNA adducts in tissues from esophageal cancer patients: clues to areca-related esophageal carcinogenesis

Epidemiological studies have demonstrated that areca quid chewing can be an independent risk factor for developing esophageal cancer. However, no studies are available to elucidate the mechanisms of how areca induces carcinogenesis in the esophagus. Since the areca nut in Taiwan contains a high concentration of safrole, a well-known carcinogenic agent, we analyzed safrole-DNA adducts by the 32P-postlabelling method in tissue specimens from esophageal cancer patients. In total, we evaluated 47 patients with esophageal cancer (16 areca chewers and 31 non-chewers) who underwent esophagectomy at the National Taiwan University Hospital between 1996 and 2002. Of the individuals with a history of habitual areca chewing (14 cigarette smokers and two non-smokers), one of the tumor tissue samples and five of the normal esophageal mucosa samples were positive for safrole-DNA adducts. All patients positive for safrole-DNA adducts were also cigarette smokers. Such adducts could not be found in patients who did not chew areca, irrespective of their habits of alcohol consumption or cigarette smoking (p<0.001, comparing the areca chewers with non-chewers). The genotoxicity of safrole was also tested in vitro in three esophageal cell lines and four cultures of primary esophageal keratinocytes. In two of the esophageal keratinocyte cultures, adduct formation was increased by treatment with safrole after induction of cytochrome P450 by 3-methyl-cholanthrene. This paper provides the first observation of how areca induces esophageal carcinogenesis, i.e., through the genotoxicity of safrole, a component of the areca juice.     

Safrole-DNA adducts in human peripheral blood--an association with areca quid chewing and CYP2E1 polymorphisms

It has been recently demonstrated that safrole (4-allyl-1,2-methylenedioxybenzene)-DNA adducts are present in oral cancer tissue from patients who have chewed areca quid (AQ) containing high concentration of safrole. In this study, the presence of safrole-DNA adducts in peripheral white blood cells from 88 subjects with a known AQ chewing history and 161 matched controls were studied with the aim of identifying the adducts as a biomarker for safrole exposure. This study also analyzed the correlation between the level of safrole-DNA adducts and polymorphism of the CYP2E1 gene, alone and in combination with the GST M1 and GST T1-deletion polymorphisms. The results demonstrated the presence of safrole-DNA adducts in 83 (94.32%) of the DNA samples from subjects with current AQ chewing history and 21 (13.04%) of the control samples without known AQ chewing habit ( [Formula: see text] ). Individuals with at least one CYP2E1 c2 allele had a significant higher frequency of safrole-DNA adducts (odds ratio (OR), 4.00; 95% confidence interval (CI), 1.03-15.53) than those with the CYP2E1 c1c1 genotype while chewing less than 20 areca quids per day. In conclusion, this study demonstrates the presence of safrole-DNA adducts in peripheral blood lymphocytes (PBL), and the presence of these safrole-DNA adducts is correlated with AQ chewing. In addition, the CYP2E1 would seem to play an important role in the modulation of safrole-DNA adduct formation.     

Clastogenic effect for cigarette smoking but not areca quid chewing as measured by micronuclei in exfoliated buccal mucosal cells

The objective of this study was to use the micronuclei from exfoliated buccal mucosal cells to investigate the clastogenic effects of areca quid chewing and cigarette smoking, as well as the interaction between the two. The study population was selected from residents of seven villages recruited for a community-cohort study. A total of 141 subjects were recruited based on the regular consumption of cigarettes and betel quid. Salient personal characteristics were collected from interview using a specially designed questionnaire. Micronuclei were scored on Feulgen/fast green-stained smear preparations of exfoliated cells obtained by scraping the surface of the buccal mucosa. There was no significant interaction between the chewing of betel nut and cigarette smoking. Heavy smoking was positively associated with MN frequency, with areca quid chewing negatively associated. A significant positive trend was demonstrated for the relationship between MN frequency and either daily cigarette consumption or cumulative smoking pack-years. By contrast, negative trends were demonstrated for the analogous relationships with areca quid chewing. These results indicate that heavy smoking, but not areca quid chewing, increases MN formation. These findings suggest that the carcinogenesis of the oral cancers induced by areca quid chewing in Taiwan may be through a pathway other than genotoxicity.     

Areca users in combination with tobacco and alcohol use are associated with younger age of diagnosed esophageal cancer in Taiwanese men

Background

Whether the habitual use of substances (tobacco, alcohol, or areca nut (seed of the Areca palm)) can affect the age of esophageal squamous cell carcinoma (ESCC) presentation has rarely been examined.

Methods

The study subjects were those who were males and the first time to be diagnosed as ESCC (ICD-9 150) and who visited any of three medical centers in Taiwan between 2000 and 2009. A standardized questionnaire was used to collect substance uses and other variables.

Results

Mean age (±SD) at presentation of ESCC was 59.2 (±11.3) years in a total of 668 cases. After adjusting for other covariates, alcohol drinkers were 3.58 years younger to have ESCC than non-drinkers (p = 0.002). A similar result was found among areca chewers, who were 6.34 years younger to have ESCC than non-chewers (p<0.0001), but not among cigarette smokers (p = 0.10). When compared to the group using 0–1 substances, subjects using both cigarettes and alcohol were nearly 3 years younger to contract ESCC. Furthermore, those who use areca plus another substance were 7–8 years younger. Subjects using all three substances had the greatest age difference, 9.20 years younger (p<0.0001), compared to the comparison group.

Conclusion

Our findings suggest that habitually consuming tobacco, alcohol, and areca nut can influence the age-onset of ESCC. Since the development of ESCC is insidious and life-threatening, our observation is worthy to be reconfirmed in the large-scale and long-term follow-up prospective cohort studies to recommend the screening strategy of this disease.     

The Role of Physical Activity in Harm Reduction among Betel Quid Chewers from a Prospective Cohort of 419,378 Individuals

ObjectiveTo assess the benefits of regular exercise in reducing harms associated with betel quid (BQ) chewing.MethodsThe study cohort, 419,378 individuals, participated in a medical screening program between 1994 and 2008, with 38,324 male and 1,495 female chewers, who consumed 5–15 quids of BQ a day. Physical activity of each individual, based on “MET-hour/week”, was classified as “inactive” or “active”, where activity started from a daily 15 minutes/day or more of brisk walking (≥3.75 MET-hour/week). Hazard ratios for mortality and remaining years in life expectancy were calculated.ResultsNearly one fifth (18.7%) of men, but only 0.7% of women were chewers. Chewers had a 10-fold increase in oral cancer risk; and a 2-3-fold increase in mortality from lung, esophagus and liver cancer, cardiovascular disease, and diabetes, with doubling of all-cause mortality. More than half of chewers were physically inactive (59%). Physical activity was beneficial for chewers, with a reduction of all-cause mortality by 19%. Inactive chewers had their lifespan shortened by 6.3 years, compared to non-chewers, but being active, chewers improved their health by gaining 2.5 years. The improvement, however, fell short of offsetting the harms from chewing.ConclusionsChewers had serious health consequences, but being physically active, chewers could mitigate some of these adverse effects, and extend life expectancy by 2.5 years and reduce mortality by one fifth. Encouraging exercise, in addition to quitting chewing, remains the best advice for 1.5 million chewers in Taiwan.     

Epidemiology of areca (betel) nut use in the mariana islands: Findings from the University of Guam/University of Hawai`i cancer center partnership program

BackgroundAreca (betel) nut is considered a Group 1 human carcinogen shown to be associated with other chronic diseases in addition to cancer. This paper describes the areca (betel) nut chewing trend in Guam, and health behaviors of chewers in Guam and Saipan.MethodsThe areca (betel) nut module in the Guam Behavioral Risk Factor Surveillance Survey was used to calculate the 5-year (2011–2015) chewing trend. To assess the association between areca (betel) nut chewing and health risks in the Mariana Islands, a cross-section of 300 chewers, ≥18 years old, were recruited from households in Guam and Saipan. Self-reported socio-demographics, oral health behaviors, chronic disease status, diet, and physical activity were collected. Anthropometry was measured. Only areca (betel) nut-specific and demographic information were collected from youth chewers in the household.ResultsThe 5-year areca (betel) nut chewing prevalence in Guam was 11% and increased among Non-Chamorros, primarily other Micronesians, from 2011 (7%) to 2015 (13%). In the household survey, most adult chewers (46%) preferred areca nut with betel leaf, slaked lime, and tobacco. Most youth chewers (48%) preferred areca nut only. Common adult chronic conditions included diabetes (14%), hypertension (26%), and obesity (58%).ConclusionThe 5-year areca (betel) nut chewing prevalence in Guam is comparable to the world estimate (10–20%), though rising among Non-Chamorros. Adult and youth chewers may be at an increased risk for oral cancer. Adult chewers have an increased risk of other chronic health conditions. Cancer prevention and intervention strategies should incorporate all aspects of health.     

Tobacco,alcohol and tea drinking as risk factors for esophageal cancer: A case–control study from Mumbai,India

Esophageal cancer is a relatively rare form of cancer, but some world areas have a markedly higher incidence than others: China, Iceland, India, Japan and United Kingdom, appear to have a higher incidence, as well as the region around the Caspian Sea. In India the incidence rates vary across the country. Despite higher incidence rate, there are only few studies from the Indian subcontinent. This study conducted at Tata Memorial hospital, Mumbai, India, included 442 cases of esophageal cancer and 1628 hospital controls. Data was collected on chewing, smoking, alcohol habits and dietary habits. The results indicated a moderate 1.1 times excess risk for chewers of pan (betel-leaf) with tobacco, 1.8-fold excess risk for bidi smokers and 2-fold for cigarette smokers, and 1.8-fold excess risk for alcohol drinkers. There was a clear dose–response relationship in those with the habits. Among the beverages, tea drinking, common in India, showed a 4-fold excess risk for esophageal cancer. However fresh-fish showed a 20% reduction in risk for esophageal cancer. Besides several other risk factors, these may be studied in the Indian set-up which has a heterogeneous population with a varied life-style and dietary habits. This could give indicators for prevention.     

Substance Use (Alcohol,Areca Nut and Cigarette) Is Associated with Poor Prognosis of Esophageal Squamous Cell Carcinoma

Background

Few studies have reported the association between lifestyle factors and prognosis of esophageal squamous cell carcinoma (ESCC) and among these, the effects of habitual areca nut chewing have never been examined.

Methodology/Principal Findings

Data from 718 pathology-proven ESCC patients recruited in a multicenter hospital-based case-control study between 2000 and 2008 in Taiwan were analyzed. Clinical and lifestyle information were obtained by chart review and questionnaire survey. Death was confirmed using the National Death Index. The mean age at diagnosis was 59.8 years and 506 (70.5%) patients presented with stage III or IV diseases. The overall 1- and 5-year survival rates were 41.8% and 9.75% respectively. In addition to clinical stage, habitual alcohol drinking was found to be the strongest predictor for ESCC survival, followed by areca chewing and smoking. Compared with non-users, patients who regularly used all three substances (alcohol, areca nut, and cigarette) had 1.52 times the risk of early death (adjusted hazard ratio = 1.52, 95% CI = 1.02–2.27, p = 0.04). In addition, the more the number of substances used, the worse the prognosis of ESCC (adjusted p for trend = 0.01).

Conclusions/Significance

Our study found that indulgence in more substances is a significant predictor of ESCC survival. Further mechanistic studies are necessary to elucidate how these substances lead to an adverse outcome.     

Accumulation of mitochondrial DNA deletions in human oral tissues -- effects of betel quid chewing and oral cancer

Accumulation of mitochondrial DNA (mtDNA) mutations in human tissues has been associated with intrinsic aging and environmental insult. Recently, mtDNA mutations have been detected in various tumors, including head and neck tumors. However, the factors affecting the occurrence and accumulation of mtDNA deletions in tumor tissues are poorly understood. In Taiwan, betel quid chewing is a major risk factor for oral cancer. Using polymerase chain reaction (PCR) techniques, we examined large-scale deletions of mtDNA in 53 pairs of tumor and non-tumor oral tissues from the patients with or without betel quid chewing history. The results revealed that irrespective of the history of betel quid chewing, the incidences of the 4977bp deletion and other deletions of mtDNA were lower in the tumor portion as compared with the non-tumor portion. The average proportions of the 4977bp deleted mtDNA in the tumor tissues of the betel quid chewers and non-betel quid chewers were 13- and 5-fold, respectively, lower than those in the corresponding non-tumor tissues. Moreover, the average proportion of 4977bp deleted mtDNA was significantly higher (P<0.05) in the non-tumor oral tissues of the patients with betel quid chewing history than that of the patients without the history of betel quid chewing. These results suggest that betel quid chewing may increase mtDNA mutation in human oral tissues and that accumulation of mtDNA deletions and subsequent cytoplasmic segregation of these mutations during cell division could be an important contributor to the early phase of oral carcinogenesis.     

Environmental heavy metal as a potential risk factor for the progression of oral potentially malignant disorders in central Taiwan

ObjectiveOral cancer (OC) is a leading cause of death from cancer in men between the ages of 25 and 44 years in Taiwan. The overall 5-year survival rates for the four OC stages (I–IV) in Taiwan are approximately 70%, 30%, 20%, and 10%, respectively, indicating the importance of the early diagnosis of oral potentially malignant disorders (OPMDs). Previous studies indicated an association between the OC incidence and certain environmental heavy metal concentrations. If these associations do exist for OC, they may also be observed for OPMD. The purpose of this study is to explore the association between the development of OPMD to OC and environmental heavy metals. Oral submucous fibrosis (OSF) and oral leukoplakia (OL) are two major types of OPMD in Taiwan.Materials and methodsA retrospective cohort study was conducted by Changhua Christian Hospital, the sole medical center in Changhua County, where 2725 male adult patients diagnosed with either OSF or OL between 2000 and 2014 were recruited. Data were analyzed by Cox regression and adjusted for smoking and betel-quid chewing.Results and discussionOPMD patients who resided in areas with high nickel concentrations (polluted levels) exhibited hazard ratios of 1.8–2 for OC relative to those who lived in areas with low nickel levels (P < 0.01). Meanwhile, smokers with OPMDs had a hazard ratio of 2.8–2.9 relative to non-smokers. Betel-quid chewers had a 2.2–2.3 hazard ratio relative to non-chewers. Smoking, betel-quid chewing, and environmental nickel exposure are associated with an increased risk of OC development in OPMD patients. This study provides valuable findings on the environmental effects of heavy metals on human health. Enhanced surveillance of the condition of OPMD patients who have been exposed to high nickel concentrations may be crucial for OC prevention.     

Genotoxicity of tobacco smoke and tobacco smoke condensate: a review

This report reviews the literature on the genotoxicity of mainstream tobacco smoke and cigarette smoke condensate (CSC) published since 1985. CSC is genotoxic in nearly all systems in which it has been tested, with the base/neutral fractions being the most mutagenic. In rodents, cigarette smoke induces sister chromatid exchanges (SCEs) and micronuclei in bone marrow and lung cells. In humans, newborns of smoking mothers have elevated frequencies of HPRT mutants, translocations, and DNA strand breaks. Sperm of smokers have elevated frequencies of aneuploidy, DNA adducts, strand breaks, and oxidative damage. Smoking also produces mutagenic cervical mucus, micronuclei in cervical epithelial cells, and genotoxic amniotic fluid. These data suggest that tobacco smoke may be a human germ-cell mutagen. Tobacco smoke produces mutagenic urine, and it is a human somatic-cell mutagen, producing HPRT mutations, SCEs, microsatellite instability, and DNA damage in a variety of tissues. Of the 11 organ sites at which smoking causes cancer in humans, smoking-associated genotoxic effects have been found in all eight that have been examined thus far: oral/nasal, esophagus, pharynx/larynx, lung, pancreas, myeoloid organs, bladder/ureter, uterine cervix. Lung tumors of smokers contain a high frequency and unique spectrum of TP53 and KRAS mutations, reflective of the PAH (and possibly other) compounds in the smoke. Further studies are needed to clarify the modulation of the genotoxicity of tobacco smoke by various genetic polymorphisms. These data support a model of tobacco smoke carcinogenesis in which the components of tobacco smoke induce mutations that accumulate in a field of tissue that, through selection, drive the carcinogenic process. Most of the data reviewed here are from studies of human smokers. Thus, their relevance to humans cannot be denied, and their explanatory powers not easily dismissed. Tobacco smoke is now the most extreme example of a systemic human mutagen.     

CD44 Gene Polymorphisms and Environmental Factors on Oral Cancer Susceptibility in Taiwan

Background

Oral squamous cell carcinoma (OSCC) is the fourth leading cause of male cancer death in Taiwan. Exposure to environmental carcinogens is the primary risk factor for developing OSCC. CD44, a well-known tumor marker, plays a crucial role in tumor cell differentiation, invasion, and metastasis. This study investigated CD44 single-nucleotide polymorphisms (SNPs) with environmental risk factors to determine OSCC susceptibility and clinicopathological characteristics.

Methodology/Principal Findings

Real-time polymerase chain reaction (PCR) was used to analyze 6 SNPs of CD44 in 599 patients with oral cancer and 561 cancer-free controls. We determined that the CD44 rs187115 polymorphism carriers with the genotype AG, GG, or AG+GG were associated with oral cancer susceptibility. Among 731 smokers, CD44 polymorphisms carriers with the betel-nut chewing habit had a 10.30–37.63-fold greater risk of having oral cancer compared to CD44 wild-type (WT) carriers without the betel-nut chewing habit. Among 552 betel-nut chewers, CD44 polymorphisms carriers who smoked had a 4.23–16.11-fold greater risk of having oral cancer compared to those who carried the WT but did not smoke. Finally, we also observed that the stage III and IV oral cancer patients had higher frequencies of CD44 rs187115 polymorphisms with the variant genotype (AG+GG) compared with the wild-type (WT) carriers.

Conclusion

Our results suggest that gene–environment interactions between the CD44 polymorphisms and betel quid chewing and tobacco smoking increase the susceptibility to oral cancer development. Patients with CD44 rs187115 variant genotypes (AG+GG) were correlated with a higher risk of oral cancer development, and these patients may possess greater chemoresistance to advanced- to late-stage oral cancer than WT carriers do. The CD44 rs187115 polymorphism has potential predictive significance in oral carcinogenesis and also may be applied as factors to predict the clinical stage in OSCC patients.     

A comparative biomonitoring study of populations residing in regions with low and high risk of lung cancer using the chromosome aberration and the micronucleus tests

Chromosome aberration (CA) and micronucleus (MN) tests were performed in peripheral blood lymphocytes from people residing in two districts of Chiang Mai, Thailand, a high-risk area, Saraphi (n=107), where the lung cancer incidence is three-fold higher than in a low-risk area, Chom Thong (n=118). The percentage of cells with CAs was significantly lower in the Saraphi population than in the Chom Thong population (0.47+/-0.91 versus 1.04+/-1.18, P=0.0001) as was the percentage of CAs (0.49+/-0.91 versus 1.08+/-1.21, P<0.0001) and the mitotic indices (1.25+/-0.44 versus 1.33+/-0.33, P=0.025). The frequency of MN in binucleated (BN) cells, however, was significantly higher in the Saraphi population (12.01+/-3.57 versus 9.99+/-3.11, P<0.0001) as was the percentage of BN cells with MN (1.14+/-0.31 versus 0.93+/-0.23, P<0.0001). There was no difference in the nuclear division indices (1.49+/-0.07 versus 1.47+/-0.11, P=0.1759) between the two populations. With regard to the effect of confounding factors, it was found that cigarette smoking influenced both CA and MN frequencies, and that the chewing of fermented tea leaves or betel nuts affected CA and sex affected MN frequencies. An increasing of CA and MN frequencies were seen in smokers and chewers over non-smokers and non-chewers, with CA frequencies being higher in Chom Thong smokers and chewers and MN frequency being higher in Saraphi smokers. However, pesticide exposure and alcohol consumption had no impact on CA and MN frequencies. Due to the conflicting results obtained in the two tests, we cannot make a clear statement regarding the potential effects of the environmental exposures in the two study populations.     

Areca (betel) nut chewing practices of adults and health behaviors of their children in the Freely Associated States,Micronesia: Findings from the Children’s Healthy Living (CHL) Program

BackgroundChewing areca (betel) nut has been deemed carcinogenic. The practice has become a public health concern in Micronesia. The Children's Healthy Living (CHL) Program included an areca (betel) nut questionnaire in a survey of household characteristics in the Freely Associated States (FAS). This paper describes areca (betel) nut chewing practices of adults and the health behaviors of their children.MethodsA cross-section of 1200 children (2–8 year-olds) and their caregivers in Chuuk, Kosrae, Pohnpei, Republic of Palau, Republic of the Marshall Islands (RMI), and Yap were recruited. Socio-demographics, adult areca (betel) nut chewing practices, and other health behaviors of children and adults were assessed. Child anthropometric measurements were collected to estimate weight status.ResultsThe FAS areca (betel) nut chewing prevalence was 42%, ranging from 3% (RMI) to 94% (Yap). Among chewers, 84% added tobacco, 97% added slaked lime, 85% added betel leaf, and 24% mixed the components with alcohol. Among FAS children, 95% practiced daily teeth-brushing and 53% visited the dentist annually. Compared to non-chewing households, areca (betel) nut chewing households were more likely to have very young children enrolled, more highly educated adults, and members that used tobacco and alcohol.ConclusionThe FAS areca (betel) nut chewing prevalence (42%) is above the world prevalence of 10–20%, with wide variability across the islands. The oral health findings in this study may inform future oral cancer prevention programs or policies. Regular monitoring of areca (betel) nut use is needed to measure the impact of such programs or policies.     

The involvement of reactive oxygen species in oral cancers of betel quid/tobacco chewers

Most biological reactions, including carcinogenesis, are complex processes involving thousands of compounds, their metabolites and intermediates. The separation of events which form part of a direct chain leading to neoplastic transformation from those which are mere by-products is a herculean task. In this study, we focused on the pros and cons of reactive oxygen species (ROS) being involved in the development of oral cancer among chewers of tobacco and areca nuts. The results revealed that bursts of ROS generation occur at different stages of carcinogenesis, and are caused by different mechanisms. This observation may have considerable practical implications. Different strategies will be required in the administration of chemopreventive agents in order to trap ROS formed in the alkaline (due to the addition of slaked lime) chewing mixture within the saliva of a chewer, to scavenge ROS within mucosal cells exposed to an array of tobacco- or areca nut-related carcinogens or tumour promoters, and to inhibit the action of ROS released from ROS-generating white cells during lymphocytic infiltration of the oral mucosa at a precancerous stage. The remission of oral leukoplakias following the administration of vitamin A (200,000 IU/week) or vitamin A (100,000 IU/week) plus beta-carotene (180 mg/week) for 6 months, the inhibition of new leukoplakias during this trial period, and the reduction of micronucleated oral mucosal cells in chewers treated with beta-carotene or vitamin A are indeed promising results. However, a better understanding of the role of ROS in various stages of carcinogenesis will provide the basis for selection of the proper chemopreventive agents and the design of a treatment regime which may either prevent the formation of precancerous lesions, induce their remission, or inhibit the progression of precancerous lesions into malignant cancers.     

DNA adducts in human placenta exposed to ambient environment and passive cigarette smoke during pregnancy

BACKGROUND: The risk of human diseases and abnormal development under the relatively reduced toxic environmental exposure conditions of passive cigarette smoke and urban pollution is emerging as significant. To assess the genotoxic potential of such exposure, we analyzed the DNA adducts of polynuclear aromatic hydrocarbons (PAH), a proven marker of genotoxicity, in human placental DNA samples of pregnancies monitored for passive cigarette smoke exposure. METHODS: Maternal exposure to active and passive cigarette smoke was evaluated by verbal disclosure and urinary nicotine and cotinine measurements. PAH-DNA adducts were assayed by ELISA using a polyclonal antibody against benzo[alpha]pyrene-diol-epoxide-DNA in placental DNA. Birth weights of infants were recorded in these monitored pregnancies. RESULTS: Urinary nicotine and cotinine values were reduced in the passive smoke-exposed group compared to smokers and similar to those in the nonsmoker ambient exposure group. PAH-DNA and nicotine/cotinine values were not correlated with birth weight of the infant. PAH-DNA adducts were present in approximately 25% of samples exposed to passive cigarette smoke and ambient environment. CONCLUSIONS: The study has revealed that a subpopulation of humans is predisposed to accumulating PAH adducts independent of high levels of PAH sources (e.g., maternal cigarette smoke exposure). Because DNA adducts promote genomic changes, it is likely that this subpopulation is susceptible to diverse changes in the genome that may influence human development.     

Sister chromatid exchanges in the peripheral blood of cigarette smokers and in lung cancer patients; and the effect of chemotherapy

Summary Peripheral blood sister chromatid exchange (SCE) rates in chronic cigarette smokers and in subjects with cancer do not differ from those in healthy nonsmokers. SCE patterns were normal in 69 chronic cigarette smokers, including 62 patients with untreated lung cancer. In three chronic smokers with lung cancer, high SCE levels were related to recent intravenous chemotherapy.Presented in part at the 15th Annual Somatic Cell Genetics Conference, Norfolk, Virginia, November 10–12, 1976 (Hollander et al., 1977)     

The role of DNA adducts in smoking-related carcinogenesis

Epidemiological studies indicate a close association between smoking and cancer. Biological activity of many chemical carcinogens and of their metabolites is induced by covalent binding of their reactive derivatives to DNA, which consequently causes mutations in critical genes. Carcinogen-DNA adducts formed by exposure to tobacco smoke have a key role in the initiation of various types of cancer including lung cancer. Presence of tobacco smoke-related carcinogen-DNA adducts in various tissues of smokers proves the DNA damaging effect of smoking. DNA adducts are important biomarkers for the biomonitoring of human genotoxic exposures to tobacco smoke. The paper gives a short overview on the role of smoking-related DNA adducts in carcinogenesis.     

Base damage,local sequence context and TP53 mutation hotspots: a molecular dynamics study of benzo[a]pyrene induced DNA distortion and mutability

The mutational pattern for the TP53 tumour suppressor gene in lung tumours differs to other cancer types by having a higher frequency of G:C>T:A transversions. The aetiology of this differing mutation pattern is still unknown. Benzo[a]pyrene,diol epoxide (BPDE) is a potent cigarette smoke carcinogen that forms guanine adducts at TP53 CpG mutation hotspot sites including codons 157, 158, 245, 248 and 273. We performed molecular modelling of BPDE-adducted TP53 duplex sequences to determine the degree of local distortion caused by adducts which could influence the ability of nucleotide excision repair. We show that BPDE adducted codon 157 has greater structural distortion than other TP53 G:C>T:A hotspot sites and that sequence context more distal to adjacent bases must influence local distortion. Using TP53 trinucleotide mutation signatures for lung cancer in smokers and non-smokers we further show that codons 157 and 273 have the highest mutation probability in smokers. Combining this information with adduct structural data we predict that G:C>T:A mutations at codon 157 in lung tumours of smokers are predominantly caused by BPDE. Our results provide insight into how different DNA sequence contexts show variability in DNA distortion at mutagen adduct sites that could compromise DNA repair at well characterized cancer related mutation hotspots.     

Genotoxicity of environmental tobacco smoke: a review

Environmental tobacco smoke (ETS), or second-hand smoke, is a widespread contaminant of indoor air in environments where smoking is not prohibited. It is a significant source of exposure to a large number of substances known to be hazardous to human health. Numerous expert panels have concluded that there is sufficient evidence to classify involuntary smoking (or passive smoking) as carcinogenic to humans. According to the recent evaluation by the International Agency for Research on Cancer, involuntary smoking causes lung cancer in never-smokers with an excess risk in the order of 20% for women and 30% for men. The present paper reviews studies on genotoxicity and related endpoints carried out on ETS since the mid-1980s. The evidence from in vitro studies demonstrates induction of DNA strand breaks, formation of DNA adducts, mutagenicity in bacterial assays and cytogenetic effects. In vivo experiments in rodents have shown that exposure to tobacco smoke, whole-body exposure to mainstream smoke (MS), sidestream smoke (SS), or their mixture, causes DNA single strand breaks, aromatic adducts and oxidative damage to DNA, chromosome aberrations and micronuclei. Genotoxicity of transplacental exposure to ETS has also been reported. Review of human biomarker studies conducted among non-smokers with involuntary exposure to tobacco smoke indicates presence of DNA adducts, urinary metabolites of carcinogens, urinary mutagenicity, SCEs and hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene mutations (in newborns exposed through involuntary smoking of the mother). Studies on human lung cancer from smokers and never-smokers involuntarily exposed to tobacco smoke suggest occurrence of similar kinds of genetic alterations in both groups. In conclusion, these overwhelming data are compatible with the current knowledge on the mechanisms of carcinogenesis of tobacco-related cancers, occurring not only in smokers but with a high biological plausibility also in involuntary smokers.