CYP2A6 genetic polymorphisms and correlation with smoking status in Brazilians

Accuracy and applications of sequencing and genotyping approaches for CYP2A6 and homologous genes

OBJECTIVES

We evaluated multiple genotyping/sequencing approaches in a homologous region of chromosome 19, and investigated associations of two common 3'-UTR CYP2A6 variants with activity in vivo.

METHODS

Individuals (n = 1704) of European and African ancestry were phenotyped for the nicotine metabolite ratio (NMR), an index of CYP2A6 activity, and genotyped/sequenced using deep amplicon exon sequencing, SNP array, genotype imputation and targeted capture sequencing. Amplicon exon sequencing was the gold standard to which other methods were compared within-individual for CYP2A6, CYP2A7, CYP2A13, and CYP2B6 exons to identify highly discordant positions. Linear regression models evaluated the association of CYP2A6*1B and rs8192733 genotypes (coded additively) with logNMR.

RESULTS

All approaches were ≤2.6% discordant with the gold standard; discordant calls were concentrated at few positions. Fifteen positions were discordant in >10% of individuals, with 12 appearing in regions of high identity between homologous genes (e.g. CYP2A6 and CYP2A7). For six, allele frequencies in our study and online databases were discrepant, suggesting errors in online sources. In the European-ancestry group (n = 935), CYP2A6*1B and rs8192733 were associated with logNMR (P < 0.001). A combined model found main effects of both variants on increasing logNMR. Similar trends were found in those of African ancestry (n = 506).

CONCLUSION

Multiple genotyping/sequencing approaches used in this chromosome 19 region contain genotyping/sequencing errors, as do online databases. Gene-specific primers and SNP array probes must consider gene homology; short-read sequencing of related genes in a single reaction should be avoided. Using improved sequencing approaches, we characterized two gain-of-function 3'-UTR variants, including the relatively understudied rs8192733.

Association of genetic polymorphisms CYP2A6*2 rs1801272 and CYP2A6*9 rs28399433 with tobacco-induced lung Cancer: case-control study in an Egyptian population

Background

Several studies have reported the role of CYP2A6 genetic polymorphisms in smoking and lung cancer risk with some contradictory results in different populations. The purpose of the current study is to assess the contribution of the CYP2A6*2 rs1801272 and CYP2A6*9 rs28399433 gene polymorphisms and tobacco smoking in the risk of lung cancer in an Egyptian population.

Methods

A case-control study was conducted on 150 lung cancer cases and 150 controls. All subjects were subjected to blood sampling for Extraction of genomic DNA and Genotyping of the CYP2A6 gene SNPs (CYP2A6*2 (1799 T > A) rs1801272 and CYP2A6*9 (− 48 T > G) rs28399433 by Real time PCR.

Results

AC and CC genotypes were detected in CYP2A6*9; and AT genotype in CYP2A6*2. The frequency of CYP2A6*2 and CYP2A6*9 were 0.7% and 3.7% respectively in the studied Egyptian population. All cancer cases with slow metabolizer variants were NSCLC. Non-smokers represented 71.4% of the CYP2A6 variants. There was no statistical significant association between risk of lung cancer, smoking habits, heaviness of smoking and the different polymorphisms of CYP2A6 genotypes.

Conclusion

The frequency of slow metabolizers CYP2A6*2 and CYP2A6*9 are poor in the studied Egyptian population. Our findings did not suggest any association between CYP2A6 genotypes and risk of lung cancer.

Distribution of polymorphic variants of CYP2A6 and their involvement in nicotine addiction

Tobacco consumption has become a major public health issue, which has motivated studies to identify and understand the biological processes involved in the smoking behavior for prevention and smoking cessation treatments. CYP2A6 has been identified as the main gene that codifies the enzyme that metabolizes nicotine. Many alleles have been identified after the discovery of CYP2A6, suggesting a wide interethnic variability and a diverse smoking behavior of the allele carrying individuals. The main purpose of this review is to update and highlight the effects of the CYP2A6 gene variability related to tobacco consumption reported from diverse human populations. The review further aims to consider CYP2A6 in future studies as a possible genetic marker for the prevention and treatment of nicotine addiction. Therefore, we analyzed several population studies and their importance at addressing and characterizing a population using specific parameters. Our efforts may contribute to a personalized system for detecting, preventing and treating populations at a higher risk of smoking to avoid diseases related to tobacco consumption.

Does ethnic ancestry play a role in smoking?

The higher proportion of smokers among Black people in Brazil has been attributed to socioeconomic disparities, but genetic factors could also contribute for this finding. This study aimed at investigating associations between smoking status with genetically defined ethnic ancestry and socioeconomic features in Brazilians. Blood samples were collected from 448 volunteers (66.7% male; age: 37.1 ± 11.4 years) classified as current smokers (CS: 60.9%), former smokers (FS: 8.9%) and never smokers (NS: 30.1%). Individual interethnic admixtures were determined using a 48 insertion-deletion polymorphisms ancestry-informative-marker panel. CS showed a lower amount of European ancestry than NS (0.837 ± 0.243 X 0.883 ± 0.194, p ≤ 0.05) and FS (0.837 ± 0.243 X 0.864 ± 0.230, p ≤ 0.05), and a higher proportion of African Sub-Saharan ancestry than FS (0.128 ± 0.222 X 0.07 ± 0.174, p ≤ 0.05) and NS (0.128 ± 0.222 X 0.085 ± 0.178, p ≤ 0.05). NS reported a higher number of years in school than CS (11.2 ± 3.7 X 8.9 ± 3.8, p ≤ 0.001). CS were less common in economic Class A (30%) and more common in Class B (56.8%). In multivariate analysis, only lower number of school years and lower economic class were associated with higher chances for CS. The use of genetic molecular markers for characterizing ethnic background confirmed that socioeconomic disparities are the main determinants of higher smoking rates among Blacks in Brazil.

Genetic polymorphisms in the Cytochrome P450 family and squamous cell carcinoma of the oral cavity, pharynx and larynx

Objective:To analyze the genetic polymorphisms of the cytochrome P450 family and their relationship with squamous cell carcinoma of the oral cavity, pharynx and larynx.Methods: We present a narrative literature review, conducted in Pubmed, Lilacs and Cochrane Databases of articles published in the last five years correlating genetic polymorphisms of the cytochrome P450 family and cancer risk in different populations worldwide.Results: We initially found 65 articles and, after selection criteria, 20 case-control studies with various populations worldwide were eligible. The most studied polymorphisms were those of CYP2E1 and CYP1A1 subfamilies. There is little about the other subfamilies. The association found between polymorphisms and cancer risk amounted to a countless number of variables, amongst them: population, selection methods, racial factors and different modes of exposure to carcinogens, genotyping methods, and nomenclature of the polymorphisms.Conclusion: so far, there is no proven link between genetic polymorphisms of cytochrome P450 family and squamous cell carcinoma of the oral cavity, pharynx and larynx relationship.

CYP2A6 deletion polymorphism is associated with decreased susceptibility of lung cancer in Asian smokers: a meta-analysis

Cytochrome P450 2A6 (CYP2A6) is an enzyme involved in the metabolism of some tobacco carcinogens, which is an important risk factor of lung cancer. Among CYP2A6 allelic variants, CYP2A6*4 presents a whole gene deletion that accounts for the majority of poor metabolizer. In this study, a meta-analysis was performed to assess the association between CYP2A6*4 and risk of lung cancer. Literature searches were conducted to identify peer-reviewed manuscripts published up to December 20, 2012. Pooled odds ratios (ORs) and 95 % confidence intervals (95 % CIs) were calculated in a fixed-effects model and a random-effects model when appropriate. Eight eligible studies with 3,203 lung cancer cases and 2,839 controls were included in this study. Overall, no significant association was observed in CYP2A6*4 with the risk of lung cancer under any genetic model for all samples after correction. However, subgroup analysis showed that significant associations were observed in Asian with pooled OR (95 %CI) of 0.761 (0.672-0.861) for allele comparison, 0.769 (0.668-0.886) for dominant model, and 0.522 (0.359-0.760) for recessive model. Furthermore, after stratifying Asian samples according to smoking status, significant associations were only observed in smokers with pooled OR (95 %CI) of 0.713 (0.607-0.838) for allele comparison, 0.720 (0.596-0.869) for dominant model, and 0.444 (0.275-0.715) for recessive model. This meta-analysis suggests that the CYP2A6*4 polymorphism was associated with susceptibility of lung cancer for smokers in Asian. The whole gene deletion of CYP2A6 might decrease the risk of tobacco-related lung cancer in Asian.

Association of CYP2A6*4 with susceptibility of lung cancer: a meta-analysis

OBJECTIVES

To assess the association between the variant of Cytochrome P450 2A6 whole gene deletion (CYP2A6*4) polymorphism and risk of lung cancer.

METHODS

Two investigators independently searched the PubMed, Elsevier, EMBASE, Web of Science, Wiley Online Library and Chinese National Knowledge Infrastructure (CNKI). Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) for CYP2A6*4 and lung cancer were calculated in a fixed-effects model (the Mantel-Haenszel method) and a random-effects model (the DerSimonian and Laird method) when appropriate.

RESULTS

This meta-analysis included seven eligible studies, which included 2524 lung cancer cases and 2258 controls (cancer-free). Overall, CYP2A6*4 was associated with the risk of lung cancer (allele*4 vs. allele non-*4, pooled OR  = 0.826, 95% CI  = 0.725-0.941, P-value  = 0.004). When stratifying for population, significant association was observed in Asian (additive model, pooled OR  = 0.794, 95% CI  = 0.694-0.909, P-value  = 0.001; dominant model, pooled OR  = 0.827, 95% CI  = 0.709-0.965, P-value  = 0.016; recessive model (pooled OR  = 0.444, 95% CI  = 0.293-0.675, P-value <0.0001). In the overall analysis, a comparably significant decrease in the frequency of *4/*4 genotype was detected between cases and controls in Asian while no *4/*4 genotype was detected in Caucasian in collected data.

CONCLUSION

This meta-analysis suggests that the CYP2A6*4 polymorphism is associated with susceptibility of lung cancer in Asian. The whole gene deletion of CYP2A6 may decrease the risk of lung cancer in Asian samples.

Application of the buccal micronucleus cytome assay and analysis of PON1Gln192Arg and CYP2A6*9(-48T>G) polymorphisms in tobacco farmers

Tobacco is a major Brazilian cash crop. Tobacco farmers apply large amounts of pesticides to control insect growth. Workers come into contact with green tobacco leaves during the tobacco harvest and absorb nicotine through the skin. In the present study, micronucleus frequency, cell death, and the frequency of basal cells were measured in tobacco farmers using the buccal micronucleus cytome assay (BMCyt), in parallel with measurement of blood butyrylcholinesterase (BChE) and nicotine levels. Polymorphisms in PONIGln192Arg and CYP2A6*9(-48T>G) were evaluated to verify the relationship between genetic susceptibility and the measured biomarkers. Peripheral blood and buccal cell samples were collected from 106 agricultural workers, at two different crop times (during pesticide application and leaf harvest), as well as 53 unexposed controls. BMCyt showed statistically significant increases in micronuclei, nuclear buds, and binucleated cells among exposed subjects in differentiated cells, and in micronuclei in basal cells. In addition, the exposed group showed higher values for condensed chromatin, karyorrhectic, pyknotic, and karyolitic cells, indicative of cell death, and an increase in the frequency of basal cells compared to the unexposed control group. A slight difference in mutagenicity using the BMCyt assay was found between the two different sampling times (pesticide application and leaf harvest), with higher micronucleus frequencies during pesticide application. Elevated cotinine levels were observed during the leaf harvest compared to the unexposed controls, while BChE level was similar among the farmers and controls. PONIGln192Arg and CYP2A6*9(-48T>G) polymorphisms were associated with DNA damage induced by pesticides and cell death.

Genotoxic biomonitoring of tobacco farmers: Biomarkers of exposure, of early biological effects and of susceptibility

Tobacco farming presents several hazards to those who cultivate and harvest the plant. The genotoxic and mutagenic effects in tobacco farmers were investigated. In order to verify the relationship between genetic susceptibility and biomarkers GSTT1, GSTM1, GSTP1, CYP2A6, PON, OGG1, RAD51, XRCC1, and XRCC4 genes polymorphism were evaluated. Oxidative stress markers and trace elements content were determined. Peripheral blood cells samples were collected from 111 agricultural workers during pesticides application and leaf harvest, and 56 non-exposed subjects. Results show that farmers are exposed to mixture of substances with genotoxic and cytotoxic potential. Only GSTM1 null and CYP2A6*9 showed significant associations with cytokinesis-blocked micronuclei assay results. In pesticide application an increase in trace elements content was observed. The results indicated that exposure to pesticides and nicotine can influence antioxidant enzymes activity. Our study drives the attention once more to the need for occupational training on safe work environment for farm workers.

Associations of various gene polymorphisms with toxicity in colorectal cancer patients receiving oral uracil and tegafur plus leucovorin: a prospective study

BACKGROUND

To assess the predictive value of polymorphism in nine genes, primarily thymidylate synthase (TS) and orotate phosphoribosyltransferase (OPRT), which relates to 5-fluorouracil (5-FU) metabolism, for toxicity in patients treated with oral uracil/tegafur (UFT) plus leucovorin (LV).

PATIENTS AND METHODS

We treated 99 patients with stage II or III colorectal carcinoma with oral UFT + LV. Germline DNA from patients was genotyped for 5-FU and folate metabolism-relating genes. CYP2A6, tegafur-activating enzyme, and uridine diphosphate-glucuronosyltransferase 1A1 genetic variation were also assessed. Toxicity was graded by the National Cancer Institute Common Toxicity Criteria, version 2.0.

RESULTS

The multivariate logistic regression revealed that OPRT 638G>C polymorphism was associated with grade 3 diarrhea [odds ratio (OR) 19.84 for patients with the C/C homozygous type compared with patients with wild type, P = 0.014] and polymorphisms of UGT1A1 were associated with hyperbilirubinemia (OR 38.76 for homozygotes and double heterozygotes of *6 or *28 compared with wild type, P = 0.0008). No relationships were observed between TS polymorphisms and any toxicity.

CONCLUSIONS

OPRT polymorphism predicts toxicity, especially grade 3 or greater diarrhea to oral UFT + LV adjuvant chemotherapy, whereas TS does not, in our study cohort. UGT1A1 polymorphism seems to be a risk factor for hyperbilirubinemia due to UFT+LV.

In vivo evaluation of CYP2A6 and xanthine oxidase enzyme activities in the Serbian population

PURPOSE

The main aim of the study was to investigate the distribution of cytochrome P450 2A6 (CYP2A6) and xanthine oxidase (XO) enzyme activities in the Serbian population. Secondly, we tested the influence of genetics (CYP2A6 polymorphism), sex, and cigarette smoking on both enzymes.

METHODS

One hundred forty healthy Serbian volunteers were genotyped for common CYP2A6 alleles. In 100 of them, CYP2A6 and XO activities were determined by the urinary 17U/17X and 1U/(1U + 1X) ratios, respectively, after oral administration of 100 mg caffeine as a probe.

RESULTS

A 21-fold variation in the 17U/17X ratio was observed (range: 0.49-10.28, mean = 1.65, 95% CI: 1.49-1.83). The urinary 1U/(1U + 1X) ratios displayed four-fold variation, ranging from 0.17 to 0.71 (mean = 0.43, 95% CI: 0.41-0.45). CYP2A6 alleles *1A, *1B1, *9, *4 and *1B1x2 were found with frequencies of 0.579, 0.307, 0.082, 0.029, and 0.004 respectively. CYP2A6*5 was not detected. CYP2A6 genotype influenced interindividual variability in CYP2A6 enzyme activity (P = 0.04). Cigarette smoking inhibited CYP2A6 enzyme activity (P = 0.02), but had no effect on activity of XO (P = 0.16).There was no significant difference between men and women in terms of CYP2A6 or XO activity.

CONCLUSIONS

Serbs displayed interindividual variations in CYP2A6 activity. CYP2A6 genotype and cigarette smoking, but not sex, influenced CYP2A6 enzyme activity. Unimodal distribution of XO enzyme activity in Serbs implies the absence of subjects with low enzyme activity in this population. XO activity is not influenced by sex or cigarette smoking.

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

AIMS

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.

MATERIALS & METHODS

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.

RESULTS

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.

CONCLUSION

As new variants are discovered, the relationships between CYP2A6 genotype, nicotine metabolism, smoking behaviors and tobacco-related cancer risk will be further clarified.

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.

Identification of novel CYP2A6*1B variants: the CYP2A6*1B allele is associated with faster in vivo nicotine metabolism

Cytochrome P450 2A6 (CYP2A6) is the human enzyme responsible for the majority of nicotine's metabolism. CYP2A6 genetic variants contribute to the interindividual and interethnic variation in nicotine metabolism. We examined the association between the CYP2A6*1B variant and nicotine's in vivo metabolism. Intravenous infusions of deuterium-labeled nicotine were administered to 292 volunteers, 163 of whom were White and did not have common CYP2A6 variants, other than CYP2A6*1B. We discovered three novel CYP2A6*1B variants in the 3'-flanking region of the gene that can confound genotyping assays. We found significant differences between CYP2A6*1A/*1A, CYP2A6*1A/*1B, and CYP2A6*1B/*1B groups in total nicotine clearance (17.2+/-5.2, 19.0+/-6.4, and 20.4+/-5.9, P<0.02), non-renal nicotine clearance (16.4+/-5.0, 18.5+/-6.2, and 19.8+/-5.7, P<0.01), and the plasma trans-3'-hydroxycotinine/cotinine ratio (0.26+/-0.1, 0.26+/-0.1, and 0.34+/-0.1, P<0.001). There were also differences in total nicotine (29.4+/-12.9, 25.8+/-0.12.9, and 22.4+/-12.4, P<0.01), cotinine (29.2+/-8.1, 32.2+/-9.1, and 33.0+/-6.6, P<0.01) and trans-3'-hydroxycotinine (32.4+/-9.1, 34.2+/-12.3, and 41.3+/-11.3, P<0.001) excreted in the urine. We report evidence that CYP2A6*1B genotype is associated with faster nicotine clearance in vivo, which will be important to future CYP2A6 genotype association studies.

CYP2A6 and CYP2E1 polymorphisms in a Brazilian population living in Rio de Janeiro

Cytochrome P450 (CYP) is a superfamily of enzymes involved in the metabolism of endogenous compounds and xenobiotics. CYP2A6 catalyzes the oxidation of nicotine and the activation of carcinogens such as aflatoxin B1 and nitrosamines. CYP2E1 metabolizes ethanol and other low-molecular weight compounds and can also activate nitrosamines. The CYP2A6 and CYP2E1 genes are polymorphic, altering their catalytic activities and susceptibility to cancer and other diseases. A number of polymorphisms described are ethnic-dependent. In the present study, we determined the genotype and allele frequencies of the main CYP2A6 and CYP2E1 polymorphisms in a group of 289 volunteers recruited at the Central Laboratory of Hospital Universitário Pedro Ernesto. They had been residing in the city of Rio de Janeiro for at least 6 months and were divided into two groups according to skin color (white and non-white). The alleles were determined by allele specific PCR (CYP2A6) or by PCR-RFLP (CYP2E1). The frequencies of the CYP2A6*1B and CYP2A6*2 alleles were 0.29 and 0.02 for white individuals and 0.24 and 0.01 for non-white individuals, respectively. The CYP2A6*5 allele was not found in the population studied. Regarding the CYP2E1*5B allele, we found a frequency of 0.07 in white individuals, which was statistically different (P < 0.05) from that present in non-white individuals (0.03). CYP2E1*6 allele frequency was the same (0.08) in both groups. The frequencies of CYP2A6*1B, CYP2A6*2 and CYP2E1*6 alleles in Brazilians are similar to those found in Caucasians and African-Americans, but the frequency of the CYP2E1*5B allele is higher in Brazilians.

CYP2A6, MAOA, DBH, DRD4, and 5HT2A genotypes, smoking behaviour and cotinine levels in 1518 UK adolescents

OBJECTIVES

Smoking is a major cause of death and often initiates in adolescence. Mutations in CYP2A6 slow metabolism of nicotine to cotinine. Haploinsufficiency in adults is associated with lower cigarette consumption, lower cotinine level and higher quit rates. Other genes are also implicated in smoking behaviour. We explored smoking behaviour and cotinine levels in relation to genotypes in adolescents.

METHODS

1518 subjects from the Ten Towns Heart Health Study were genotyped for CYP2A6 alleles *1A, *1B, *2, *4, *5, *9 and *12 to classify predicted nicotine metabolism rate. DBH(rs77905), MAOA(rs1801291+VNTR), DRD4(VNTR) and 5HT2A(rs6313) were also studied. Smoking status was established by questionnaire and salivary cotinine measurement at 13-15 and 18 years.

RESULTS

No significant associations were identified for DBH, MAOA, DRD4 and 5HT2A markers, with smoking status or cotinine level at either age. At age 18, haploinsufficiency (HI) for CYP2A6 was associated with a higher odds of being a current smoker compared with the *1B carriers (WT1B) (OR = 2.23 (1.16, 4.27) for current versus ex); *1A homozygotes (WT1A) were also at slightly higher risk (OR = 1.44 (1.01, 2.06)). Partial haploinsufficiency (PHI) was not associated with being a current smoker. There were no significant associations at age 13-15. PHI and HI were associated with higher cotinine levels amongst smokers at both 13-15 and at 18 years compared with WT1B and WT1A groups.

CONCLUSIONS

CYP2A6 haploinsufficiency increases likelihood of continuing smoking in teenagers. We hypothesize an explanatory 'occupancy' model to explain why haploinsufficiency results in faster progression to nicotine dependence, but lower subsequent consumption.

Métodos para abandono do tabagismo e tratamento da dependência da nicotina

O tabagismo está relacionado a 30% das mortes por câncer. É fator de risco para desenvolver carcinomas do aparelho respiratório, esôfago, estômago, pâncreas, cérvix uterina, rim e bexiga. A nicotina induz tolerância e dependência pela ação nas vias dopaminérgicas centrais, levando às sensações de prazer e recompensa mediadas pelo sistema límbico. É estimulante do sistema nervoso central (SNC), aumenta o estado de alerta e reduz o apetite. A diminuição de 50% no consumo da nicotina pode desencadear sintomas de abstinência nos indivíduos dependentes: ansiedade, irritabilidade, distúrbios do sono, aumento do apetite, alterações cognitivas e fissura pelo cigarro. O aconselhamento médico é fundamental para o sucesso no abandono do fumo. A farmacoterapia da dependência de nicotina divide-se em: primeira linha (bupropiona e terapia de reposição da nicotina), e segunda linha (clonidina e nortriptilina). A bupropiona é um antidepressivo não-tricíclico que age inibindo a recaptação de dopamina, cujas contra-indicações são: epilepsia, distúrbios alimentares, hipertensão arterial não-controlada, abstinência recente do álcool e uso de inibidores da monoaminoxidase (MAO). A terapia de reposição de nicotina pode ser feita com adesivos e gomas de mascar. Os efeitos da acupuntura no abandono do fumo ainda não estão completamente esclarecidos. As estratégias de interrupção abrupta ou redução gradual do fumo têm a mesma probabilidade de sucesso.

Methods for smoking cessation and treatment of nicotine dependence

Smoking is related to 30% of cancer deaths. It is a risk factor for respiratory tract, esophagus, stomach, pancreas, uterine cervix, kidney and bladder carcinomas. Nicotine induces tolerance and addiction by acting on the central dopaminergic pathways, thus leading to pleasure and reward sensations within the limbic system. It stimulates the central nervous system (CNS), enhances alertness and reduces the appetite. A 50% reduction of nicotine consumption may trigger withdrawal symptoms in addicted individuals: anxiety, anger, sleep disorders, hunger, cognitive dysfunction and cigarette craving. Medical advice is the cornerstone of smoking cessation. Pharmacotherapy of nicotine addiction comprises first-line (bupropion and nicotine replacement therapy) and second-line (clonidine and nortriptyline) drugs. Bupropion is a non-tricyclic antidepressant that inhibits dopamine uptake, whose contraindications are: epilepsy, eating disorders, uncontrolled hypertension, recent alcohol abstinence and current therapy with MAO inhibitors. Nicotine replacement therapy can be done with patches or gums. Counseling groups and behavioral interventions are efficacious. The effects of acupuncture on smoking cessation are not fully elucidated. Prompt smoking cessation or gradual reduction strategies have similar success rates.

Association of CYP2A6*1B genetic variant with the amount of smoking in French adults from the Stanislas cohort

This study was designed in order to investigate the influence of the genetic polymorphism of CYP2A6 on the amount of smoking. In all, 463 French adults included in the Stanislas cohort were studied and underwent two examinations at 5 years distance (t0 and t(+5) years). Information on their smoking habits was collected. They were genotyped by RFLP for the CYP2A6*1A, CYP2A6*1B and CYP2A6*4 alleles. CYP2A6*1B and CYP2A6*4 allele frequencies were 32 and 4%, respectively. The subjects carrying the CYP2A6*1B allele oxidize nicotine to cotinine faster than subjects with the CYP2A6*1A allele. The number of cigarettes smoked per day was significantly higher in the CYP2A6*1B/*1B group as compared to the CYP2A6*1A/*1A group (P = 0.01 at t0; P = 0.001 t(+5) years), with a larger increase in their daily cigarettes consumption over the 5-year period (P = 0.006). No significant difference in the smoking status was observed according to the CYP2A6 genotype. These data suggest that the CYP2A6*1B is associated with the number of cigarettes smoked per day.