Effects of ADH1C, ALDH2, and CYP2A6 Polymorphisms on Individual Risk of Tobacco-Related Lung Cancer in Male Japanese Smokers


Recent genome-wide association studies have identified several lung cancer susceptibility loci. We previously carried out a replication study in male Japanese smokers that focused on chromosome 5p15 (telomerase reverse transcriptase) and 3q28 (tumor protein p63) (Shimizu et al., Journal of Cancer Therapy, Vol. 2, No. 5, 2011, pp. 690-696). The current study was performed to confirm the association of traditional susceptibility loci [i.e., alcohol dehydrogenase 1C (ADH1C) and aldehyde dehydrogenase 2 (ALDH2)] in 1039 male Japanese smokers (573 lung cancer patients and 466 healthy control subjects) who were previously enrolled in a study to investigate the low odds ratio for lung cancer risk associated with functionally impaired and deletion polymorphisms in cytochrome P450 2A6 (CYP2A6). The minor allele frequency of rs671 in ALDH2 (0.304) was significantly higher in lung cancer cases than in controls (0.226), with an odds ratio of 1.42 [95% confidence interval (CI) of 1.12 - 1.80, p = 0.0033]. No significant association of rs698 in ADH1C with lung cancer risk was found in this population of male Japanese smokers. For light smokers categorized according to the 50th percentile Brinkman index value among the control subjects (620 daily cigarettes × years) and for the CYP2A6*1 wild-type non-carrier sub-population, significantly high odds ratios of 1.98 and 1.68 (95% CI of 1.28 - 3.06, p = 0.0022, and 1.07 - 2.66, p = 0.025), respectively, were observed for rs671 in ALDH2. The present results support the association of ALDH2 loci with lung cancers and suggest a specific effect of ALDH2 loci resulting in a higher risk of lung cancer in light smokers. CYP2A6 polymorphisms, including copy number polymorphisms, may lower the risk of heavy tobacco use-related lung cancer.

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Shimizu, M. , Ishii, Y. , Okubo, M. , Kunitoh, H. , Kamataki, T. and Yamazaki, H. (2013) Effects of ADH1C, ALDH2, and CYP2A6 Polymorphisms on Individual Risk of Tobacco-Related Lung Cancer in Male Japanese Smokers. Journal of Cancer Therapy, 4, 29-35. doi: 10.4236/jct.2013.48A005.

1. Introduction

Cigarette smoking and alcohol consumption affect susceptibility to etiologically complex diseases, including various tumors [1,2]. Polymorphisms of the alcohol-metabolizing enzymes alcohol dehydrogenase 1C (ADH1C) and aldehyde dehydrogenase 2 (ALDH2) influence the risks of various cancers such as those of the esophagus [3], breast [4], pancreas [5], stomach [6], mouth [7], lung [8], and liver [1]. The International Lung Cancer Consortium was established in 2004 and coordinates genotyping activities and ongoing genome-wide association studies (GWAS) [9]. Recent association findings for smokingrelated diseases implicate genetically derived individual differences [10-14]. Several reports from GWAS with respect to lung cancer risk in different ethnic populations have suggested a variety of susceptibility genes, such as telomerase reverse transcriptase (TERT, rs2736100) [15-17] and tumor protein p63 (TP63, rs4488809, rs9816619, or rs10937405) [17,18]. In one of our previous reports [19], we demonstrated that genetic polymorphisms in cytochrome P450 2A6 (CYP2A6) are determinants of smoking behavior and tobacco-related lung cancer risk, particularly for squamous cell and small cell carcinoma, which are known to be associated with cigarette smoking [13] in male Japanese heavy smokers. In addition, significant associations of rs4488809 (TP63) and rs2736100 (TERT) with the risk of lung adenocarcinoma were identified [20]. Some of the single nucleotide polymorphisms (SNPs) found by GWAS have been investigated extensively; however, there have been few reports of the effects of SNPs in combination in a typical population.

We performed further study of the traditional candidate genes for lung cancer risk (i.e., ADH1C and ALDH2) in a population of male Japanese smokers. Herein, we confirm the increased susceptibility to lung cancers associated with ALDH2 SNPs, especially for light smokers. Also, CYP2A6 polymorphisms, including copy number polymorphisms that were not fully studied in GWAS (except for one computer-based special analytical study [18]), were found to be a major influence reducing the risk of heavy tobacco use-related lung cancer.

2. Materials and Methods

2.1. Subjects

This study was approved by the ethics committees of Hokkaido University and Showa Pharmaceutical University. The sample population comprised 1039 unrelated male Japanese smokers (573 case and 466 control subjects) selected from the 1705 participants of our previous study [19,20]. The other 666 subjects could not be included in this study because of genomic DNA sample limitations; there were apparently no differences in demographic factors such as ages and smoking status between case and control groups after exclusion of these subjects. The patient group consisted of 573 men who had received a pathological diagnosis of lung cancer [squamous cell or small cell carcinoma (n = 285) or adenocarcinoma (n = 288)] with a mean (±SD) age of 63.4 ± 9.3 years (range 29 - 86 years). The control group consisted of 466 male smokers with a mean age of 52.2 ± 12.2 years (range 20 - 92 years) without a history of cancer. The age of the lung cancer patients was defined at the time of pathological diagnosis of lung cancer.

Smokers included current and ex-smokers and were defined as individuals who had ever smoked cigarettes with a minimum smoking history of 10 cigarettes per day for at least 1 year. Light and heavy smokers were categorized by the 50th percentile Brinkman index value (daily cigarettes × years) among control subjects and was found to be less than 620 (n = 233) and more than or equal to 620 (n = 233), respectively. Pathological classification of lung cancers was determined by at least three pathologists according to the criteria described in the literature [19].

2.2. Genotyping

Genomic DNA was prepared from peripheral lymphocytes [19]. Genotyping of ADH1C Ile350Val (rs698) [21] and ALDH2 Glu504Lys (rs671) [3] polymorphisms was carried out according to previously described methods. Genotyping of CYP2A6 was carried out by the methods described previously [19,20] with respect to rs5031016 for CYP2A6*7 and rs28399433 for CYP2A6*9 and the wholegene deletion polymorphism of CYP2A6 (CYP2A6*4). CYP2A6 variants were major alleles in control.

2.3. Statistical Analyses

The associations between the genotype distributions and patient status were assessed by odds ratios and 95% confidence intervals (CIs) that were calculated by unconditional logistic regression adjusting for age and cigarette smoking (Brinkman index value), unless otherwise mentioned. A p value less than 0.05 was considered to be statistically significant. Statistical computations were carried out using the statistical software SAS, version 5.1 (SAS Institute, Inc., Cary, NC) or PLINK 1.07 [22].

3. Results

Table 1 shows the association results of polymorphisms in three genes analyzed in terms of lung cancer risk in a

Conflicts of Interest

The authors declare no conflicts of interest.


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