The effect of SLC6A3 variable number of tandem repeats and methylation levels on individual susceptibility to start tobacco smoking and on the ability of smokers to quit smoking.

OBJECTIVE: Nicotine acts through the dopamine pathway in the brain affecting reward processing through cigarette consumption. Thus, both genetic and epigenetic factors related to dopamine metabolism may influence individual's smoking behavior. MATERIALS AND METHODS: We studied variations of two variable numbers of tandem repeats (VNTRs), 40 and 30 bp in length, in SLC6A3 gene together with six DNA methylation sites located in a first intron of the gene in relation to several smoking-related phenotypes in a study population consisting of 1230 Whites of Russian origin. RESULTS: Both the 5R allele of 30 bp VNTR and the 9R allele of 40 bp VNTR in SLC6A3 were associated with a reduced risk to tobacco smoking [odds ratio (OR) 0.53, 95% confidence interval (CI) 0.37-0.75; OR 0.62, 95% CI 0.43-0.88]. Although the carriers of 9R allele also had high Fagerström test for nicotine dependence scores (OR 1.65, 95% CI 1.04-2.60), they were still more likely to succeed in smoking cessation (OR 0.59, 95% CI 0.40-0.88). Also, current smokers had more than 2.5-fold likelihood to have increased SLC6A3 methylation levels than former smokers (OR 2.72, 95% CI 1.63-4.53). CONCLUSION: The SLC6A3 5R of 30 bp and 9R of 40 bp VNTR variants may lead to a reduced risk to start smoking through decreased dopamine availability, and can also affect the success in subsequent smoking cessation attempts. Moreover, the elevated mean methylation values in the first intron of SLC6A3 may be related to nicotine dependence via a more active dopamine transporter.

The genotypes and methylation of MAO genes as factors behind smoking behavior.

OBJECTIVE: Smoking dependence is the main cause for tobacco-related illnesses. The addiction-causing substance in tobacco, nicotine, acts through the dopamine pathway in the brain, causing several pleasurable experiences through cigarette smoking. Thus, both genetic and epigenetic factors related to dopamine metabolism may play an important role in influencing an individual's smoking behavior. MATERIALS AND METHODS: We studied the 1460 C/T variation and the variable number tandem repeat polymorphism in the MAOA gene and A/G variation in intron 13 in the MAOB gene together with four DNA methylation sites in both of these genes in relation to several smoking-related phenotypes in a study population of 1230 Whites of Russian origin. RESULTS: The genotypes studied were found to be associated with smoking status in women; the MAOB G variant allele was more prevalent in female smokers than nonsmokers [odds ratio (OR): 2.16, 95% confidence interval (CI): 1.08-4.33], whereas a reverse relation was observed for the MAOA 1460 T-variant allele (OR: 0.44, 95% CI: 0.21-0.91) and variable number tandem repeat low-activity alleles (OR: 0.49, 95% CI: 0.24-0.98). Moreover, the mean methylation values of the CpG sites studied in the MAOA gene were related to smoking behavior in women. Similarly, several methylation patterns in the MAOB gene were associated with a smoking history, with each CpG site showing a remarkable sex dependence. CONCLUSION: Smoking behavior seems to be related to the genetic and epigenetic profile of MAO genes, with considerable individual and sex-related differences.

Effect of genotype and methylation of CYP2D6 on smoking behaviour.

OBJECTIVE: Cigarette smoking is one of the most influential environmental factors affecting the DNA methylation patterns. The addiction-causing substance of tobacco smoke, nicotine, has also shown the potential to alter DNA methylation patterns. However, genetics has a strong influence on DNA methylation patterns, which in turn may affect an individual's smoking behaviour. MATERIALS AND METHODS: We studied eight functional gene variants of one of the most important drug-metabolizing enzymes, CYP2D6, in relation to smoking behaviour in our well-characterized study population consisting of 1230 Whites of Russian origin. In addition, potential associations between methylation levels in a CpG island in the CYP2D6 gene and sex, age, different smoking-related phenotypes and CYP2D6 genotypes were studied. RESULTS: Both age and sex were found to be associated with the methylation level of the CYP2D6 gene. The CYP2D6 methylation pattern also showed high genotype dependence; compared with the extensive metabolizer genotype, the poor metabolizer genotype occurred notably more frequently with higher methylation status (odds ratio 5.05, 95% confidence interval 2.14-11.90). Moreover, higher methylation levels were found to be related inversely to heavier smoking (odds ratio 0.56, 95% confidence interval 0.35-0.91). We also found associations between the CYP2D6 genotype and smoking habits; the poor metabolizer genotype tended to decrease the risk of becoming a heavy smoker compared with the extensive metabolizers, whereas the ultrarapid metabolism-related genotypes tended to increase the risk. CONCLUSION: The CYP2D6-related metabolic capacity seems to be related to cigarette consumption both through genetic and through epigenetic mechanisms.

Association of genes of protease-antiprotease balance pathway to lung function and emphysema subtypes.

BACKGROUND: The imbalance between proteases and antiproteases has been proposed to participate to the pathogenesis of chronic obstructive pulmonary disease (COPD) and emphysema. Gene level variation in different metalloproteinases, metalloproteinase inhibitors, and cytokines affecting them may contribute to this imbalance and destruction of the lung parenchyma. We investigated whether polymorphisms in selected protease-antiprotease balance pathway genes predispose to different emphysema subtypes (centrilobular, paraseptal, panlobular, and bullae) and airflow limitation among Finnish construction workers. METHODS: Eleven single nucleotide polymorphisms (SNPs) from seven genes (GC: rs7041 and rs4588; MMP1: rs1799750; MMP9: rs3918242; MMP12: rs652438; TIMP2: rs2277698; TNF: rs1799724 and rs1800629; TGFB1: rs1800469, rs1800470, and rs2241718) were analyzed from 951 clinically and radiologically characterized construction workers. The genotype and haplotype data was compared to different emphysematous signs confirmed with high resolution computed tomography (HRCT), forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and maximal expiratory flow at 50% of FVC (MEF50) by using linear and logistic regression analyses, adjusted for potential confounders. RESULTS: The TIMP2 rs2277698 SNP was associated with overall (p = 0.022) and paraseptal (p = 0.010) emphysema, as well as with FEV1/FVC ratio (p = 0.035) and MEF50 (p = 0.008). The TGFB1 rs2241718 and MMP9 rs3918242 SNPs were associated with centrilobular emphysema (p = 0.022 and p = 0.008), and the TNF rs1800629 SNP with paraseptal emphysema (p = 0.017). In stratified analysis, individuals with at least one TIMP2 rs2277698 or TNF rs1800629 variant allele were found to be at around two-fold risk for pathological paraseptal changes (OR 1.94, 95% CI 1.14-3.30; OR 2.10, 95% CI 1.24-3.56). On the contrary, the risk for pathological centrilobular changes was halved for individuals with at least one MMP9 rs3918242 (OR 0.51, 95% CI 0.30-0.86) or TGFB1 rs2241718 (OR 0.53, 95% CI 0.30-0.90) variant allele, or TGFB1 rs1800469-rs1800470 AT-haplotype (OR 0.55, 95% CI 0.33-0.93). MEF50, in turn, was significantly reduced among individuals with at least one TIMP2 rs2277698 variant allele (p = 0.011). CONCLUSION: Our findings strengthen the hypothesis of the importance of protease-antiprotease balance in pathogenesis of emphysema and shed light on the aetiology of different emphysema subtypes by associating MMP9 and TGFB1 to centrilobular emphysema, and TIMP2 and TNF to paraseptal emphysema and/or airflow obstruction.

SERPINE2 haplotype as a risk factor for panlobular type of emphysema.

BACKGROUND: SERPINE2 (serpin peptidase inhibitor, clade E, member 2) has previously been identified as a positional candidate gene for chronic obstructive pulmonary disease (COPD) and has subsequently been associated to COPD and emphysema in several populations. We aimed to further examine the role of SERPINE2 polymorphisms in the development of pulmonary emphysema and different emphysema subtypes. METHODS: Four single nucleotide polymorphisms (SNPs) in SERPINE2 were analyzed from 951 clinically and radiologically examined Finnish construction workers. The genotype and haplotype data was compared to different emphysematous signs confirmed with high-resolution computed tomography (HRCT), forced vital capacity (FVC), forced expiratory volume in one second (FEV1), diffusing capacity (DLCO), and specific diffusing capacity (DLCO/VA). RESULTS: Three of the studied SERPINE2 SNPs (rs729631, rs975278, and rs6748795) were found to be in tight linkage disequilibrium. Therefore, only one of these SNPs (rs729631) was included in the subsequent analyses, in addition to the rs840088 SNP which was in moderate linkage with the other three studied SNPs. The rs729631 SNP showed a significant association with panlobular emphysema (p = 0.003). In further analysis, the variant allele of the rs729631 SNP was found to pose over two-fold risk (OR 2.22, 95% CI 1.05-4.72) for overall panlobular changes and over four-fold risk (OR 4.37, 95% CI 1.61-11.86) for pathological panlobular changes. A haplotype consisting of variant alleles of both rs729631 and rs840088 SNPs was found to pose an almost four-fold risk for overall panlobular (OR 3.72, 95% CI 1.56-8.90) and subnormal (OR 3.98, 95% CI 1.55-10.20) emphysema. CONCLUSIONS: Our results support the previously found association between SERPINE2 polymorphisms and pulmonary emphysema. As a novel finding, our study suggests that the SERPINE2 gene may in particular be involved in the development of panlobular changes, i.e., the same type of changes that are involved in alpha-1-antitrypsin (AAT) -deficiency.