Risk Of Tobacco-related Cancers Research Articles

Risk of tobacco-related cancers in CDKN2A mutation-positive melanoma families.

1513 Background: Germline mutations in the tumor suppressor gene CDKN2A occur in 5-20% of familial melanoma cases. A single founder mutation, p.Arg112dup, accounts for the majority of CDKN2A mutati...

Smokers' risk perception, socioeconomic status and source of information on cancer

BackgroundIn many countries, the decline in smoking prevalence has coincided with a growing concentration of smoking among people with lower socioeconomic status (SES). This concentration may reflect the social differentiation of risk perceptions. We investigated the factors associated with risk perception and fear of cancer, paying particular attention to SES indicators and health information seeking. MethodologyA cross-sectional telephone survey conducted in France in 2010 (including 826 current smokers aged 18–75) assessing how smokers perceive the risk of smoking-related cancer in terms of daily consumption and duration thresholds. ResultsAmong current smokers, 38% considered that smoking can cause cancer only for a daily consumption higher than their own consumption, and an additional 22% stated that tobacco-related cancer risk only becomes high for a longer smoking duration than their personal one. Predictors of such risk perceptions included low SES, material deprivation and mentioning either the internet or their relatives as one's main source of information on cancer. The same characteristics were also predictive of personal fear of tobacco-related cancer. ConclusionOur results illustrate the challenges faced by prevention campaigns in the internet society, as information found on the web may fuel smokers' risk denial. Anti-tobacco policies should tailor interventions to people with low SES, who may be especially impervious to standard prevention campaigns because of material deprivation, and they should also address and challenge smokers' risk denial beliefs.

Vitamin D and Cancer: Can We Believe the Evidence from Observational Studies?

The article by Afzal et al. in this issue of Clinical Chemistry (1) presents data showing an association of low concentrations of vitamin D with risk of tobacco-related cancers. The authors found that vitamin D was not associated with other types of cancer, that the effect was stronger among smokers, and that it appeared to be independent of levels of tobacco consumption among smokers. Although these data suggest that increasing concentrations of plasma 25-hydroxyvitamin D [25(OH)D],2 especially among smokers, may lead to cancer protection, the data remain suggestive rather than conclusive. Science is rife with examples of promising hypotheses based on observational data that did not hold up under more rigorous randomized controlled trials. An early panacea was β-carotene, which was hypothesized to reduce cancer incidence (2). At the time, it was the exciting new theory and garnered much attention. When tested in randomized controlled trials, however, the promising hypothesis failed to hold up. The Physicians' Health Study, the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) trial, the Beta-Carotene and Retinol Efficacy Trial (CARET), and other trials found no overall effect of β-carotene on cancer (3). Whereas observational analyses can carefully control for many confounders, residual confounding cannot be ruled out. There is a persistent and consistent association of consumption of fruits and vegetables with reduced cancer risk, but it is difficult to break down the food items into individual nutrients that may be causally related. The same has occurred for various other dietary nutrients, including vitamin E, vitamin C, and the B vitamins (4). All had been shown to be related to cancer or cardiovascular disease in observational data, but the results did not hold up to the more rigorous examination of a randomized trial. Vitamin E, in particular, enjoyed widespread public attention and was promoted as akin to a …

Low Plasma 25-Hydroxyvitamin D and Risk of Tobacco-Related Cancer

Tobacco smoke chemicals may influence vitamin D metabolism and function, and conversely vitamin D may modify the carcinogenicity of tobacco smoke chemicals. We tested the hypothesis that lower plasma 25-hydroxyvitamin D [25(OH)D] is associated with a higher risk of tobacco-related cancer in the general population. A prospective population-based cohort of 9791 individuals from the Copenhagen City Heart Study who were free of cancer at baseline was followed from 1981-1983 until December 2008 with 100% complete follow-up. During up to 28 years of follow-up, 1081 participants developed a tobacco-related cancer and 1506 developed other cancers. Decreasing 25(OH)D concentrations, subdivided by clinical categories or by seasonally adjusted percentile categories, were associated with increasing cumulative incidence of tobacco-related cancer (log-rank trend P = 2 × 10(-6) and P = 5 × 10(-9)). Multivariable adjusted hazard ratios of tobacco-related cancer were 1.75 (95% CI, 1.33-2.30) for 25(OH)D <5 vs ≥20 ng/mL, and 2.07 (1.63-2.62) for ≤5th vs >66th percentile. Also, multivariable adjusted hazard ratios for a 50% reduction in 25(OH)D were 1.20 (1.13-1.28) for any tobacco-related cancer, 1.19 (95% CI, 1.09-1.31) for lung cancer, 1.44 (1.19-1.73) for head and neck cancer, 1.28 (1.06-1.54) for bladder cancer, 1.34 (1.04-1.73) for kidney cancer, and 0.95 (0.89-1.01) for other cancers. Lower plasma 25(OH)D was associated with higher risk of tobacco-related cancers, but not with risk of other cancers.

Cytochrome P450 1B1 and 2C9 Genotypes and Risk of Ischemic Vascular Disease, Cancer, and Chronic Obstructive Pulmonary Disease

The aim of this review is to summarize present knowledge of genetic variation in cytochrome P450 1B1 (CYP1B1) and 2C9 (CYP2C9) genes and risk of tobacco-related cancer, female cancer, chronic obstructive pulmonary disease and ischemic vascular disease. The CYP1B1 and CYP2C9 enzymes metabolize polycyclic aromatic hydrocarbons found in tobacco smoke and thereby generate disease-causing metabolites suggested to be important in tobacco-related diseases. Furthermore, CYP1B1 also metabolizes estrogen while CYP2C9 metabolizes arachidonic acid, both creating metabolites potentially important in risk of female cancer or ischemic vascular disease. Genetic variation in genes coding for CYP1B1 and CYP2C9 enzymes have shown altered enzyme activity affecting levels of metabolites and thus potentially risk of disease. So far, however, findings have been inconsistent. Recently, large studies on the association between genetic variation in CYP1B1 and CYP2C9 and risk of disease with considerable statistical power rebutted the hypotheses that these genetic variants affect risk of tobacco-related cancer, female cancer, chronic obstructive pulmonary disease and ischemic vascular disease.

Highlights of This Issue

Although mammographic density is a strong marker of breast cancer risk, it is unclear whether tumors arise specifically within dense breast tissue. Pinto Pereira and colleagues studied 231 British women diagnosed with breast cancer and assessed whether tumor location was related to localized mammographic density 5 years prior to diagnosis. Tumor locations, identified on digitized diagnostic films, were aligned with serial images obtained from the same woman before diagnosis. The authors report that prediagnostic mammographic density was higher in areas that subsequently contained tumors. This work supports a model in which tumors predominantly arise within radiodense breast tissue and suggests that localized mammographic density may be a predictor of subsequent tumor location.To uncover new biomarkers for bladder cancer, Eissa and colleagues retrospectively analyzed the methylation status of the RARβ2 and APC genes in urine samples from bladder cancer patients. The authors report that the methylation of these two genes was higher in cancer patients compared with healthy controls. Methylated RARβ2 and APC were found in all bladder cancer grades and stages. These studies suggest that methylated RARβ2 and APC might represent valuable urinary molecular markers for the early detection of bladder cancer.Previous studies, using serotype-derived blood typing, have shown an association between ABO blood type and gastric cancer. In this study, Nakao and colleagues further explored this association using single-nucleotide polypeptide analysis to evaluate ABO blood genotype and the risks of gastric cancer, atrophic gastritis and Helicobacter pylori infection. They report a significant association between ABO genotype and gastric cancer risk. In addition, the study revealed that ABO genotype may also influence atrophic gastritis prevalence and H. pylori infection.The microsomal epoxide hydrolase enzyme (mEH), encoded by EPHX1, has an established role in the detoxification of smoking-induced oxidative substances. Lee and colleagues explored the association between two EPHX1 polymorphisms and cancer risk in a large Danish population. In these studies, 47,000 individuals were genotyped and divided into groups with predicted fast, intermediate, and slow mEH phenotypes. The authors then evaluated the risks of several cancer diagnoses and found that individuals with predicted intermediate and slow mEH activities were at higher risk of tobacco-related cancers, compared with subjects with fast mEH phenotypes. This work represents one of the largest studies testing the hypothesis that genetically lowered mEH activities are associated with cancer risk.

Characterization of UDP-glucuronosyltransferase 2A1 (UGT2A1) variants and their potential role in tobacco carcinogenesis

To examine UGT2A1 expression in human tissues, determine its glucuronidation activity against tobacco carcinogens, and assess the potential functional role of UGT2A1 missense single nucleotide polymorphisms on UGT2A1 enzyme activity. Reverse transcription polymerase chain reaction and real time polymerase chain reaction were used to assess UGT2A1 gene expression in various human tissues. A glucuronidation assay measured by reverse phase ultra-performance liquid chromatography was used to determine UGT2A1 activity. UGT2A1 was expressed in aerodigestive tract tissues including trachea, larynx, tonsil, lung, and colon; no expression was observed in breast, whole brain, pancreas, prostate, kidney, liver, or esophagus. UGT2A1 exhibited highest expression in the lung, followed by trachea >tonsil >larynx >colon >olfactory tissue. Cell homogenates prepared from wildtype UGT2A1(75Lys308Gly) overexpressing HEK293 cells showed significant glucuronidation activity against a variety of polycyclic aromatic hydrocarbons including, 1-hydroxy-benzo(a)pyrene, benzo(a)pyrene-7,8-diol, and 5-methylchrysene-1,2-diol. No activity was observed in UGT2A1 overexpressing cell homogenate against substrates that form N-glucuronides, such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), nicotine, or N-OH-2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (N-OH PhIP). A significant (P<0.05) decrease (approximately 25%) in glucuronidation activity (Vmax/KM) was observed against all polycyclic aromatic hydrocarbons substrates for the UGT2A1(75Lys308Gly) variant compared with homogenates from wildtype UGT2A1(75Lys308Gly); no activity was observed for cell homogenates overexpressing the UGT2A1 variant for all substrates tested. These data suggest that UGT2A1 is an important detoxification enzyme in the metabolism of polycyclic aromatic hydrocarbons within target tissues for tobacco carcinogens and functional polymorphisms in UGT2A1 may play a role in tobacco-related cancer risk.

Knowledge and Beliefs about Smoking and Cancer among Women in Five European Countries

Lung cancer mortality in women is increasing across Europe, reflecting the alarming increase in smoking prevalence. Understanding women's perception of smoking may help to identify ways to reduce its prevalence and prevent uptake of smoking. The aim of this study was to examine factors associated with knowledge and beliefs about smoking and cancer among European women. A cross-sectional landline telephone survey on health attitudes and knowledge was conducted in five European countries: France, Ireland, Italy, the Czech Republic, and Sweden. A general linear modeling was used to explore the factors related to knowledge and beliefs about smoking and cancer. A total of 5,000 women were interviewed (1,000 women from each country). The mean knowledge and belief scores about smoking and cancer were lower in current smokers than those of never and former smokers (P < 0.05). Women with above-the-median income (P = 0.001) and women who held skilled occupations seemed to be more knowledgeable about tobacco health risks (P < 0.001). The number of friends and family who smoked was inversely associated with knowledge on the harmful effects of tobacco (P = 0.001). Swedish women were the most knowledgeable about tobacco-related cancer risk, whereas in France and Italy, current smokers were less knowledgeable. Knowledge and beliefs about cancer and smoking varied significantly by smoking status. Results emphasize the need to develop health education programs that enhance cancer knowledge among women who currently smoke and are in low socioeconomic groups.

Nicotinic acetylcholine receptor polymorphism, smoking history, and tobacco-related cancer in the general population.

1530 Background: Smokers often develop lung and bladder cancer; however, not all smokers develop these diseases. We examined whether the nicotinic acetylcholine receptor gene (CHRNA3) rs1051730 polymorphism can identify smokers in the general population at genetically high risk of tobacco-related cancer, that is, at higher risk than that explained by detailed smoking history alone. Methods: We genotyped 10,322 participants from the Danish general population, the Copenhagen City Heart Study. Detailed smoking history was obtained and validated at baseline. End-points during the following 18 years were lung and bladder cancer from the Danish cancer registry. Follow-up was 100% complete. Results: Among the 7831 ever smokers, CHRNA3 non-carriers (44%) and homozygotes (11%) had daily tobacco consumption of 16 and 18 g/day (Wilcoxon: p = 0.000004), cumulative tobacco consumption of 28 to 31 packyears (p = 0.001), and smoking inhalation of 72% and 78% (chi- square: p = 0.0002). As expected increasing baseline packyears smoked associated with increasing risk of lung and bladder cancer during the following 18 years (trend-tests: p = 4*10-47 and p = 0.0002); the hazard ratios for lung and bladder cancer in those with baseline > 40 packyears smoked vs. never-smokers were 44 (95% CI:14-105) and 2.9 (1.4-5.9) after multifactorial adjustment including genotype. In addition, CHRNA3 homozygotes vs. non-carriers had hazard ratios for lung and bladder cancer of 1.65 (1.18-2.30) and 1.79 (1.05-3.06) after multifactorial adjustment including detailed smoking history. The highest absolute 10-year risks were 11.4% for lung cancer and 4.4% for bladder cancer for homozygous smokers above 60 years who had smoked > 30 packyears at baseline. Conclusions: The nicotinic acetylcholine receptor rs1051730 polymorphism identifies 11% of smokers in the general population at excessive high risk of tobacco-related cancer, even after considering a full smoking history. No significant financial relationships to disclose.

Abstract 1698: Characterization of the activity and expression of UDP-Glucuronosyltransferase 2A1 variants and potential role in tobacco carcinogenesis

Abstract UDP-glucuronosyltransferases (UGTs) play an important role in the metabolism and excretion of various endogenous and xenobiotic compounds including several carcinogens and chemotherapeutic agents. UGT2A1 is an extra-hepatic member of the UGT2A sub-family that was shown to be expressed in the lung in previous studies. The goal of the present study was to examine UGT2A1 expression in human tissues, assess its glucuronidation activity against exogenous substrates including lung carcinogens, and determine the potential functional role of UGT2A1 polymorphisms on UGT2A1 enzyme activity. Cell homogenates were prepared from HEK293 cells transfected with wild type or variant UGT2A1. Enzyme activity against carcinogens was determined through reverse-phase UPLC. Expression of UGT2A1 was determined by RT-PCR/sequencing, real time PCR (ABI), and western blot using a UGT2A1-specific antibody. In addition to the wild-type UGT2A1*1, two prevalent variants of UGT2A1 were investigated: a variant that causes a lysine to arginine amino acid change at codon 75 (UGT2A1*2), and a variant that causes a glycine to arginine amino acid change at codon 308 (UGT2A1*3). In addition, a newly-identified splice variant isoform lacking exon 3 (allele identified as UGT2A1*1a since it was not yet determined whether this variant was due to a genetic polymorphism or to altered splicing) was also investigated. As determined by RT-PCR and direct sequencing, UGT2A1 was expressed in lung, trachea, larynx, tonsil, mouth, and colon; no expression was observed in breast, whole brain, cerebral cortex or esophageal tissues. Reverse transcription-PCR demonstrated that tissues had variable levels of expression of UGT2A1 and the splice variant encoded by UGT2A1*1a; the UGT2A1*1a encoded variant was expressed in 5 of 6 individual lung specimens and a pooled larynx sample from 10 people. Homogenates of HEK293 cells over-expressing UGT2A1*1 or UGT2A1*2 both exhibited significant activity against 1-naphthol, with a Vmax/KM of 4.0 uL.min−1.ug homogenate protein−1 and 3.5 uL.min−1.ug homogenate protein−1 respectively. No activity was observed for cell homogenates over-expressing the UGT2A1*3 variant or the UGT2A1*1a isoform. A similar pattern of activity was observed for a variety of polycyclic aromatic hydrocarbons (PAHs) including 1-hydroxypyrene, dibenzo(a,l)pyrene-11,12-diol, benzo(a)pyrene-7,8-diol, 5-methylchrysene-1,2-diol, 1-hydroxy (OH)-benzo(a)pyrene, 7-OH-benzo(a)pyrene, and 8-OH-benzo(a)pyrene. No activity was observed against substrates that form N-glucuronides such as NNAL, nicotine or N-OH-PhIP. UGT2A1 is expressed in various target organs for tobacco-induced carcinogenesis and exhibits activity against a variety of PAHs abundant in tobacco smoke. The UGT2A1308Arg variant could play an important role in tobacco-related cancer risk due to a lack of enzyme activity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1698.

CYP2C9 genotype does not affect risk of tobacco-related cancer in the general population

Background: CYP2C9 enzymes are important in the metabolism of procarcinogenic chemicals such as polycyclic aromatic hydrocarbons (PAHs) found in tobacco smoke. Two functional variants in the CYP2C9 gene (CYP2C9*2 and CYP2C9*3) are known to be associated with decreased enzyme activity towards tolbutamide and warfarin, while this has not been investigated for PAHs. We hypothesised that these two variants in the CYP2C9 gene influence risk of tobacco-related cancer. Methods: In a prospective study of the general population ( n = 10 392) with 60 years of follow-up, the Copenhagen City Heart Study, we associated two variants of CYP2C9 (CYP2C9*2 and CYP2C9*3) with risk of tobacco-related cancer and all cancer. All results were re-tested in a cross-sectional study of the general population ( n = 36 856), the Copenhagen General Population Study. Results: We found no association between any of the CYP2C9 genotypes and risk of tobacco-related cancer, individual tobacco-related cancers, or all cancer. For the combined carriers (any CYP2C9*2 or CYP2C9*3 heterozygotes or homozygotes) vs. non-carriers we had 90% statistical power to exclude measures of relative risks below/above 0.8/1.2 and 0.9/1.1 in the Copenhagen City Heart Study and below/above 0.8/1.3 and 0.9/1.1 in the Copenhagen General Population Study for tobacco-related cancer and all cancer, respectively. Conclusion: Genetic variations in CYP2C9 do not affect risk of tobacco-related cancers.

New CYP2A6 gene deletion and conversion variants in a population of Black African descent.

Cytochrome P450 2A6 (CYP2A6) is a human enzyme best known for metabolizing nicotine and nitrosamine precarcinogens. Our aim was to discover and characterize new CYP2A6 alleles in a population of Black African descent. We used cloning, sequencing and genotyping of genomic DNA to discover new variants, and in vivo nicotine pharmacokinetic phenotyping to characterize the functional effect of the new alleles. Four new CYP2A6 alleles, CYP2A6*4G, *4H, *1B4 and *1L, were discovered and characterized in a population of Black African descent. The two new deletion alleles, CYP2A6*4G and *4H, are distinguished by different crossover junctions at 7.9 and 7.8 kb downstream of the CYP2A6 +1ATG start site, respectively; their combined allele frequency is 1.6%. The new gene conversion alleles, CYP2A6*1B4 and CYP2A6*1L, contain 27 and 10 bp of CYP2A7 sequence in the CYP2A6 3 -flanking region, respectively; their combined allele frequency is 7.3%. CYP2A6*4 appears to associate with lower CYP2A6 activity in vivo, while CYP2A6*1L does not; however, CYP2A6*1L confounds genotyping assays that use the 2A6R3 and 2A6R4 primers. As new variants are discovered, the relationships between CYP2A6 genotype, nicotine metabolism, smoking behaviors and tobacco-related cancer risk will be further clarified.

Commentary: A new dawn for genetic epidemiology?

2003;32:1–22. 4 Frayling TM, Timpson NJ, Weedon MN et al. A common variant in the FTO gene is associated with body mass index and predisposes to childhood and adult obesity. Science 2007;316:89–94. 5 Dina C, Meyre D, Gallina S et al. Variation in FTO contributes to childhood obesity and severe adult obesity. Nat Genet 2007;39:724–26. 6 Brennan P, McKay J, Moore L et al. Uncommon CHEK2 mis-sense variant and reduced risk of tobacco-related cancers: case-control study. Hum Mol Genet 2007;16:1–8.

CYP2A6 Polymorphisms and Risk for Tobacco-Related Cancers

Tobacco consumption is the main identifiable risk to cancer, contributing to the majority of tumors in upper aerodigestive tissues. The psychoactive compound responsible for tobacco addiction, nicotine and the potent carcinogens present at high concentrations either in cigarette mainstream smoke or in smokeless tobacco products, 4-(methylnitrosamino)-1-(3-pyridyl)-butanone (NNK) and N-nitrosonornicotine (NNN) can be metabolized by CYP2A6. CYP2A6 is expressed in many aerodigestive tissues with high interindividual variability. The CYP2A6 gene is highly polymorphic and CYP2A6 alleles coding for enzymes with altered expression or metabolic capacity produce alterations in nicotine metabolism in vivo and seem to influence smoking behavior. These polymorphisms may change the rate of NNK and NNN activation and, therefore, may influence cancer risk associated with tobacco consumption. However, to date only a few and inconclusive studies have addressed the risk that a given CYP2A6 polymorphism presents for the development of tobacco-related tumors. Most, but not all, show a reduced risk associated with alleles that result in decreased enzyme activity. The overlapping substrate specificity and tissue expression between CYP2A6 and the highly similar CYP2A13 may add to the conflicting results observed. The intricate regulation of CYP2A6 and the variation of structurally different chemical compounds capable of inhibiting CYP2A enzymes also add to the complexity. Finally, the interaction between polymorphisms of genes that code for CYP2A6, CYP2A13 and other potent carcinogen-metabolizing CYP enzymes may help to determine individuals that are at higher risk of developing tumors associated with tobacco consumption.

Different modes of inhibition of mouse Cyp2a5 and rat CYP2A3 by the food-derived 8-methoxypsoralen

CYP2A enzymes are responsible for nicotine metabolism and for activating tobacco-related carcinogens. Inhibition of CYP2A is a promising approach in chemoprevention, which could lead to a decrease in cigarette consumption and to a reduction in tobacco-related cancer risk. 8-Methoxypsoralen (8-MOP) is a mechanism-based inhibitor of human CYP2A6 and CYP2A13. 8-MOP is also an inhibitor of Cyp2a5, but the mode of this inhibition is unknown. There is no published data on the inhibition of CYP2A3 by 8-MOP. The objective of this work was to investigate the characteristics of 8-MOP inhibition on mouse hepatic Cyp2a5 and rat nasal CYP2A3, in order to determine the best experimental model for chemoprevention studies using 8-MOP. The results show that 8-MOP inhibits CYP2a5 through three different mechanisms: competitive, non-competitive ( K iu = 1.7 μM), and mechanism-based ( K inactivation of 0.17 min –1). By contrast, 8-MOP was able to inhibit CYP2A3-mediated coumarin 7-hydroxylase only in a non-competitive way ( K iu = 0.22 μM). In conclusion, we showed that 8-MOP inhibits Cyp2a5 and CYP2A3 through different mechanisms.

Uncommon CHEK2 mis-sense variant and reduced risk of tobacco-related cancers: case–control study

CHEK2 is a key cell cycle control gene encoding a pluripotent kinase that can cause arrest or apoptosis in response to unrepaired DNA damage. We report a large case-control study of a non-functional variant that had previously been expected to increase cancer rates. Four thousand and fifteen cancer patients (2250 lung, 811 squamous upper aero-digestive and 954 kidney) and 3052 controls in central Europe were genotyped for the mis-sense variant rs17879961 (replacement of T by C), which changes an amino acid (I157T) in an active site of the gene product. The heterozygous (T/C) genotype was associated with a highly significantly lower incidence of lung cancer than the common T/T genotype [relative risk (RR), T/C versus T/T, 0.44, with 95% confidence interval (CI) 0.31-0.63, P < 0.00001] and with a significantly lower incidence of upper aero-digestive cancer (RR 0.44, CI 0.26-0.73, P = 0.001; P = 0.000001 for lung or upper aero-digestive cancer). Protection was significantly greater for squamous than adenomatous lung cancer (P = 0.001). There was an increase of borderline significance in kidney cancer (RR 1.44, CI 0.99-2.00, P = 0.06). This unexpected halving of tobacco-related cancer (since replicated independently) implies much greater absolute risk reduction in smokers than in non-smokers. The mechanism is unknown: perhaps squamous stem cell apoptosis following smoke exposure causes net harm (e.g. by forcing nearby stem cells to divide before they have repaired their own DNA damage from tobacco smoke). If so, reducing the rate of apoptosis by reducing CHEK2 activity could be protective-although not smoking would be far more so.

Folate-related genes and the risk of tobacco-related cancers in Central Europe

Folate has been hypothesized to protect against aero-digestive cancers although the evidence is not yet conclusive due to possible confounding by other dietary factors. Sequence variants in folate pathway were suggested to be associated with plasma folate levels and are unlikely to be confounded by other lifestyle factors. We therefore investigated the effects of key folate genetic variants on the risk of aero-digestive cancers and their potential effect modification by folate intake in a multicenter study in Central Europe. A total of 2250 lung cases, 811 upper aero-digestive tract cases and 2899 controls were recruited with blood samples. The methylenetetrahydrofolate reductase (MTHFR) C677T variant was associated with an increased risk of lung cancer with an odds ratio (OR) for homozygote variant of 1.37 [95% confidence interval (CI) = 1.10-1.71]. The two MTHFR variants were in strong linkage disequilibrium, and 677T-1298A appeared to be the primary haplotype associated with cancer risk. The risk estimates for MTHFR 677T/677T genotype was more prominent among lung cancer patients with young onset (OR = 1.92, 95% CI = 1.12-3.29). When stratified by dietary intake of folate, the effect of the MTHFR 677T variant was more prominent among subjects with low intake of folate: the ORs for 677T/677T genotype among subjects with the lowest decile were 2.60 (95% CI = 1.39-4.88) and 4.14 (95% CI = 1.47-11.7) for lung and upper aero-digestive tract cancer, respectively. In conclusion, we identified a moderate effect of MTHFR C677T on lung cancer risk and a possible effect modification by folate intake that is consistent with the functional data. These results support an important role of folate in protecting against tobacco-related cancers.

Pharmacogenomics of maternal tobacco use: Metabolic gene polymorphisms modify risk of adverse pregnancy outcomes

Epidemiologic studies have linked tobacco-related cancer risk to an altered ability to metabolize carcinogenic or addictive compounds along well-characterized pathways. We hypothesized that maternal(m) or fetal(f) genotypes which alter activity along such pathways may account for varying susceptibility to adverse pregnancy outcomes among smokers, and thus sought to determine the association between functional polymorphisms in CYP1A1, GSTT1, and CYP2A6 and these outcomes. Blinded genotyping was perfomed from prospectively obtained banked DNA samples for known functional allelic variants of CYP1A1(Ile462ValAA>AG/GG), GSTT1(del), and CYP2A6(Lys160HisT>A) in 502 smokers, 502 contols, and their conceptuses. Associations between smoking and genotype in relation to individual and a composite outcome [SGA <10%, fetal loss, preterm birth (PTB), and abruption] and birthweight were evaluated. The overall relative risk of adverse composite outcome among tobacco users (RR1.2, p=.04) was modified in a genotype-specific fashion: increased risk occurred among GSTT1del (RRf1.7, p=.07; RRm1.9, p=.01) while maternal CYP2A6AT trended towards a protective effect (RRm.69, p=.47); CYP1A1AA>AG/GG trended towards modified risk (RRf1.8, p=.27; RRm1.8, p=.10). The overall risk of smoking for SGA (RR1.7, p=.006) was increased with fetal but not maternal GSTT1del (RRf3.4, p=.02). Considering birthweight as a continuous variable after adjustment for gestational age in a linear model, the mean birthweight of tobacco-exposed fetuses with GSTT1del was reduced by 291g (p<.0001), whereas tobacco-exposed fetuses without the GSTT1(del) were unaffected (mean reduction 56g, p=0.22). Metabolic gene polymorphisms alter tobacco-related risk of adverse pregnancy outcomes. The inability to excrete reactive intermediates (GSTT1del), increased ability to form carcinogenic adducts (CYP1A1Ile462Val), or altered nicotine metabolism(CYP2A6Lys160His) may explain varying susceptibility to in utero tobacco exposure.

IMPORTANCE OF UDP-GLUCURONOSYLTRANSFERASE 1A10 (UGT1A10) IN THE DETOXIFICATION OF POLYCYCLIC AROMATIC HYDROCARBONS: DECREASED GLUCURONIDATIVE ACTIVITY OF THE UGT1A10139LYS ISOFORM

UDP-glucuronosyltransferase 1A10 (UGT1A10) is an extrahepatic enzyme expressed in aerodigestive tract tissues that exhibits significant glucuronidation activity against the important procarcinogenic benzo(a)pyrene (BaP) metabolite, BaP-trans-7,8-dihydrodiol (BPD), and the UGT1A10 codon 139 (Glu>Lys) polymorphism was previously implicated in risk for orolaryngeal cancer by Elahi et al. in their 2003 study. To better assess the potential role of UGT1A10 in risk for tobacco-related cancers, the glucuronidation activity of UGT1A10 was compared with that of other known UGT enzymes against selected polycyclic aromatic hydrocarbons, and the effects of the codon 139 polymorphism on UGT1A10 function were examined in vitro. UGT1A10 exhibited considerably more glucuronidation activity as determined by Vmax/Km against 3-hydroxy (OH)-BaP, 7-OH-BaP, 9-OH-BaP, and 1-OH-pyrene than any other UGT1A family member. Although a kinetic comparison using Vmax could not be performed against family 2B UGTs, UGT1A10 exhibited a 1.7- to 254-fold lower Km than active family 2B UGTs against 3-OH-BaP, 7-OH-BaP, and 1-OH-pyrene. A significantly (p < 0.01) higher Vmax/Km was observed for homogenates from wild-type UGT1A10139Glu-overexpressing cells against all four BaP metabolites tested (3-OH-BaP, 7-OH-BaP, 9-OH-BaP, and BPD). A similarly significant (p < 0.05) increase in Vmax/Km was observed for homogenates from wild-type UGT1A10139Glu-overexpressing cells against 1-OH-pyrene. Significant differences in Km were observed for homogenates from wild-type UGT1A10139Glu-overexpressing cells against 1-OH-pyrene (p < 0.05) and 3-OH-BaP (p < 0.01). Reverse transcription-polymerase chain reaction of total lung RNA showed low levels of UGT1A10 expression in human lung tissue. Together, these studies implicate UGT1A10 as an important detoxifier of polycyclic aromatic hydrocarbons in humans and that the UGT1A10 codon 139 polymorphism may be an important determinant in risk for tobacco-related cancers.

Genetic Polymorphism of CYP2A6 and Tobacco-Related Cancer Risk: From the Establishment of Genetically Engineered Salmonella to Large Scale Epidemiology

Most mutagens/carcinogens are metabolically activated by enzymes such as cytochrome P450 to exert their mutagenicity or carcinogenicity. Since the catalytic properties of cytochrome P450 vary among animal species, it was necessary to establish a mutation-detection system carrying human cytochrome P450 to estimate if the chemicals are mutagenic in humans. For this purpose, we introduced genes for human cytochrome P450 together with NADPH-cytochrome P450 reductase to establish humanized Salmonella typhimurium. Using the genetically engineered Salmonella typhimurium, we found that CYP2A6 was involved in the metabolic activation of a variety of nitrosamines such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) contained in tobacco smoke. Analyzing the CYP2A6 gene of subjects who showed a poor metabolic phenotype towards (+)-cis-3,5-dimethyl-2-(3-pyridyl)thiazoline-4-one hydrochloride (SM-12502), we discovered a novel mutant allele (CYP2A6*4C) lacking the whole CYP2A6 gene. Taking these results into account, we hypothesized that the subjects carrying the CYP2A6*4C allele had lower risk to tobacco-related lung cancer. In accordance with our hypothesis, our large scale epidemiological studies clearly indicated that smokers homozygous for the CYP2A6*4C allele showed much smaller odds ratios towards cancer risk. Other mutant alleles reducing the CYP2A6 activity besides the CYP2A6*4C allele also reduced the risk for lung cancer in smokers, particularly squamous cell carcinoma and small cell carcinoma frequently seen in smokers. 8-Methoxypsoralen, an inhibitor of CYP2A6, efficiently prevented the occurrence of adenoma caused by NNK in A/J mice.