CHRNA5-A3-B4 genetic variants alter nicotine intake and interact with tobacco use to influence body weight in Alaska Native tobacco users

CHRNA5 rs16969968 and CHRNA3 rs578776 polymorphisms are associated with multiple nicotine dependence phenotypes in Bangladeshi smokers

Background

A recent study has identified the role of CHRNA5-A3-B4 gene cluster variants rs16969968 and rs578776 of nicotinic acetylcholine receptors (nAChRs) on smoking status in Bengali ethnicity. The aim of the current study was to investigate whether these rs16969968-rs578776-rs11072768 single nucleotide polymorphisms (SNPs) of CHRNA5-A3-B4 gene cluster were associated with nicotine dependence (ND) and related phenotypes.

Methods

The Fagerstrom Test for Nicotine Dependence (FTND) and Cigarette Dependence Scale (CDS-12) were used to assess the degree of ND, and genotyping was done using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method on a cohort of 129 male smokers participating in a structured questionnaire-based survey.

Results

Smokers with AA genotype of CHRNA5 rs16969968 SNP were at significantly increased risk of developing ND compared to its wild type variant with odds ratio (ORs) of 1.20 (FTND: 95% CI 0.25–5.37, p = 0.253) and 2.48 (CDS-12: 95% CI 0.46–13.26, p = 0.081), respectively. Conversely, smokers with AA genotype of CHRNA3 rs578776 variant had a strong protective effect against ND development (ORs = 0.27, 95% CI 0.09–0.80, p = 0.076). There was no such link reported in CHRNB4 rs11072768 variant carriers. Similarly, G-A/G-A diplotype of rs16969968_rs578776 variants was discovered to be a protective factor against ND. Moreover, demographic features such as age, occupation and dwelling status were found to be significantly associated with ND.

Conclusion

Taken together, CHRNA5-A3-B4 gene cluster variants rs16969968 and rs578776 as well as specific demographic characteristics regulate ND and related smoking phenotypes in Bangladeshi male smokers. Further studies with large sample sizes are required to substantially validate the significance.

Correlates of the nicotine metabolite ratio in Alaska Native people who smoke cigarettes

Research on nicotine metabolism has primarily focused on white adults. This study examined associations between nicotine metabolism, tobacco use, and demographic characteristics among Alaska Native adults who smoke cigarettes. Participants (N = 244) were Alaska Native adults who smoked and who provided a plasma sample at baseline (70.1%) or follow-up (29.9%) of a randomized controlled trial of a cardiovascular risk behavior intervention. At baseline, participants self-reported age, sex, Alaska Native heritage, cigarettes per day, time to first cigarette upon wakening, menthol use, perceived difficulty staying quit, tobacco withdrawal symptoms, and past-month tobacco product use, binge drinking, and cannabis use. At 3-, 6-, 12-, and 18-month follow-ups, participants self-reported 7-day point prevalence abstinence from smoking. Height and weight were measured to calculate body mass index (BMI). Participants' nicotine metabolite ratio (NMR), calculated as the ratio of plasma cotinine and trans-3' hydroxycotinine, was log-transformed. The sample (52.0% male, age M = 47.0 years [SD = 13.8], 60.3% of Inupiaq heritage) averaged 12.5 cigarettes per day (SD = 10.5); 64.0% smoked within 30 min of wakening. NMR was not significantly associated with age, sex, Alaska Native heritage, BMI, cigarettes per day, time to first cigarette upon wakening, menthol use, perceived difficulty staying quit, past-month dual tobacco product use, withdrawal symptoms, past-month binge drinking, past-month cannabis use, or abstinence from smoking (all p-values > .050). Characteristics that relate to NMR in Alaska Native adults may differ from those typically identified among white adults. Specifically, results may suggest that Alaska Native adults with slower nicotine metabolism do not titrate their nicotine intake when smoking. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Nicotinic acetylcholine gene cluster CHRNA5-A3-B4 variants influence smoking status in a Bangladeshi population

BACKGROUND

Past studies have established the association of CHRNA5-A3-B4 gene cluster variants with various smoking behaviors in different ethnicities, yet no such study has been reported in Bengali ethnicity to date.

METHODS

A case-control study with 129 smokers and 111 non-smokers was conducted and genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method aimed to manifest the association of three SNPs in this gene cluster with smoking status (SS) in a Bangladeshi population.

RESULTS

The non-synonymous CHRNA5 rs1s6969968 and 3'-UTR variant CHRNA3 rs578776 polymorphisms were found to have a strong association with SS. Carriers of polymorphic 'A' allele of rs16969968 showed 1.51-fold more risk of being smokers (adjusted OR = 1.51, 95% CI 0.88-2.57, p = 0.128); whereas, rs578776 polymorphic 'A' allele carriers showed 0.595-fold less risk of being smokers (adjusted OR = 1.51, 95% CI 0.88-2.57, p = 0.006). Comparing smokers and non-smokers, A/A mutant homozygous genotypes of rs578776 and rs16969968 variants pose 0.369-fold (95% CI 0.177-0.77, p = 0.008) and 3.3-fold (95% CI 0.66-16.46, p = 0.14) more risk for positive SS, respectively. No genotypic association for SS was found with intronic variant CHRNB4 rs11072768 (T/G; adjusted OR = 0.827, 95% CI 0.457-1.499, p = 0.532 and G/G; adjusted OR = 0.992, 95% CI 0.455-2.167, p = 0.985). Combination of rs16969968-positive/rs578776-negative polymorphic variants possesses the risk of positive SS in young adults. Furthermore, two new haplotypes (AAT and AAG) were identified in Bangladeshi population and GAG (OR = 0.45, 95% CI 0.25-0.8, p = 0.006) haplotype was found to be a protective factor for SS.

CONCLUSION

Nicotinic acetylcholine gene cluster CHRNA5-A3-B4 variants rs16969968 and rs578776 are associated with SS in a Bangladeshi population. Large-scale studies are warranted to establish this genotype-phenotype correlation.

Perceptions of Smoking and Vaping on Weight Control Among Adult American Indians Who Smoke

Interest in electronic cigarette (EC) use, or vaping, to help control weight is increasing. Many American Indian (AI) populations have a high prevalence of smoking, obesity, and EC use, but their perceptions of EC use for weight control are unknown. In Oklahoma in 2016, 375 AI adults who smoke completed a survey including perceptions about smoking and EC effects on weight control. Only 24% believed that smoking helps control weight, and 8% believed that vaping helps control weight. Perceptions differed by EC use, with ever users more often than never users perceiving that smoking (30% vs 12%, respectively; p < .01) and vaping (10% vs 5%; p = .04) help to control weight. Sex, age group (18-44 years vs 45 + years), education (high school graduate/equivalent vs less than high school), smoking cessation attempt in past year, and likelihood to quit in 6 months were not associated with weight control perceptions for either smoking or vaping. Uncertainty regarding EC effects on weight control was less common among EC ever users compared to never users (41% vs 53%, respectively; p = .04). Most people who did not believe or were uncertain that smoking controls weight also did not believe or were uncertain that vaping controls weight. However, only a minority (29%) of people who believed smoking controls weight also believed that vaping controls weight. Among adult AI who smoke, both smoking and vaping were infrequently perceived as helping to control weight, but such perceptions were reported more frequently among those who ever used ECs.

Pharmacogenomics of Nicotine Metabolism: Novel CYP2A6 and CYP2B6 Genetic Variation Patterns in Alaska Native and American Indian Populations

INTRODUCTION

Alaska Native and American Indian (AN/AI) populations have higher tobacco use prevalence than other ethnic/racial groups. Pharmacogenetic testing to tailor tobacco cessation treatment may improve cessation rates. This study characterized polymorphic variations among AN/AI people in genes associated with metabolism of nicotine and drugs used for tobacco cessation.

METHODS

Recruitment of AN/AI individuals represented six subgroups, five geographic subgroups throughout Alaska and a subgroup comprised of AIs from the lower 48 states living in Alaska. We sequenced the CYP2A6 and CYP2B6 genes to identify known and novel gain, reduced, and loss-of-function alleles, including structural variation (eg, gene deletions, duplications, and hybridizations).

RESULTS

Variant allele frequencies differed substantially between AN/AI subgroups. The gene deletion CYP2A6*4 and reduced function CYP2A6*9 alleles were found at high frequency in Northern/Western subgroups and in Lower 48/Interior subgroups, respectively. The reduced function CYP2B6*6 allele was observed in all subgroups and a novel, predicted reduced function CYP2B6 variant was found at relatively high frequency in the Southeastern subgroup.

CONCLUSIONS

Diverse CYP2A6 and CYP2B6 variation among the subgroups highlight the need for comprehensive pharmacogenetic testing to guide tobacco cessation therapy for AN/AI populations.

IMPLICATIONS

Nicotine metabolism is largely determined by CYP2A6 genotype, and variation in CYP2A6 activity has altered the treatment success in other populations. These findings suggest pharmacogenetic-guided smoking cessation drug treatment could provide benefit to this unique population seeking tobacco cessation therapy.

From genes to treatments: a systematic review of the pharmacogenetics in smoking cessation

Smoking cessation treatment outcomes may be heavily influenced by genetic variations among smokers. Therefore, identifying specific variants that affect response to different pharmacotherapies is of major interest to the field. In the current study, we systematically review all studies published in or after the year 1990 which examined one or more gene-drug interactions for smoking cessation treatment. Out of 644 citations, 46 articles met the inclusion criteria for the systematic review. We summarize evidence on several genetic polymorphisms (CHRNA5-A3-B4, CYP2A6, DBH, CHRNA4, COMT, DRD2, DRD4 and CYP2B6) and their potential moderating pharamacotherarpy effects on patient cessation efficacy rates. These findings are promising and call for further research to demonstrate the effectiveness of genetic testing in personalizing treatment decision-making and improving outcome.

The Value of Biosamples in Smoking Cessation Trials: A Review of Genetic, Metabolomic, and Epigenetic Findings

Introduction

Human genetic research has succeeded in definitively identifying multiple genetic variants associated with risk for nicotine dependence and heavy smoking. To build on these advances, and to aid in reducing the prevalence of smoking and its consequent health harms, the next frontier is to identify genetic predictors of successful smoking cessation and also of the efficacy of smoking cessation treatments ("pharmacogenomics"). More broadly, additional biomarkers that can be quantified from biosamples also promise to aid "Precision Medicine" and the personalization of treatment, both pharmacological and behavioral.

Aims and Methods

To motivate ongoing and future efforts, here we review several compelling genetic and biomarker findings related to smoking cessation and treatment.

Results

These Key results involve genetic variants in the nicotinic receptor subunit gene CHRNA5, variants in the nicotine metabolism gene CYP2A6, and the nicotine metabolite ratio. We also summarize reports of epigenetic changes related to smoking behavior.

Conclusions

The results to date demonstrate the value and utility of data generated from biosamples in clinical treatment trial settings. This article cross-references a companion paper in this issue that provides practical guidance on how to incorporate biosample collection into a planned clinical trial and discusses avenues for harmonizing data and fostering consortium-based, collaborative research on the pharmacogenomics of smoking cessation.

Implications

Evidence is emerging that certain genotypes and biomarkers are associated with smoking cessation success and efficacy of smoking cessation treatments. We review key findings that open potential avenues for personalizing smoking cessation treatment according to an individual's genetic or metabolic profile. These results provide important incentive for smoking cessation researchers to collect biosamples and perform genotyping in research studies and clinical trials.

A Genome-Wide mQTL Analysis in Human Adipose Tissue Identifies Genetic Variants Associated with DNA Methylation, Gene Expression and Metabolic Traits

Little is known about the extent to which interactions between genetics and epigenetics may affect the risk of complex metabolic diseases and/or their intermediary phenotypes. We performed a genome-wide DNA methylation quantitative trait locus (mQTL) analysis in human adipose tissue of 119 men, where 592,794 single nucleotide polymorphisms (SNPs) were related to DNA methylation of 477,891 CpG sites, covering 99% of RefSeq genes. SNPs in significant mQTLs were further related to gene expression in adipose tissue and obesity related traits. We found 101,911 SNP-CpG pairs (mQTLs) in cis and 5,342 SNP-CpG pairs in trans showing significant associations between genotype and DNA methylation in adipose tissue after correction for multiple testing, where cis is defined as distance less than 500 kb between a SNP and CpG site. These mQTLs include reported obesity, lipid and type 2 diabetes loci, e.g. ADCY3/POMC, APOA5, CETP, FADS2, GCKR, SORT1 and LEPR. Significant mQTLs were overrepresented in intergenic regions meanwhile underrepresented in promoter regions and CpG islands. We further identified 635 SNPs in significant cis-mQTLs associated with expression of 86 genes in adipose tissue including CHRNA5, G6PC2, GPX7, RPL27A, THNSL2 and ZFP57. SNPs in significant mQTLs were also associated with body mass index (BMI), lipid traits and glucose and insulin levels in our study cohort and public available consortia data. Importantly, the Causal Inference Test (CIT) demonstrates how genetic variants mediate their effects on metabolic traits (e.g. BMI, cholesterol, high-density lipoprotein (HDL), hemoglobin A1c (HbA1c) and homeostatic model assessment of insulin resistance (HOMA-IR)) via altered DNA methylation in human adipose tissue. This study identifies genome-wide interactions between genetic and epigenetic variation in both cis and trans positions influencing gene expression in adipose tissue and in vivo (dys)metabolic traits associated with the development of obesity and diabetes.

Ion Channels in Obesity: Pathophysiology and Potential Therapeutic Targets

Obesity is a multifactorial disease related to metabolic disorders and associated with genetic determinants. Currently, ion channels activity has been linked to many of these disorders, in addition to the central regulation of food intake, energetic balance, hormone release and response, as well as the adipocyte cell proliferation. Therefore, the objective of this work is to review the current knowledge about the influence of ion channels in obesity development. This review used different sources of literature (Google Scholar, PubMed, Scopus, and Web of Science) to assess the role of ion channels in the pathophysiology of obesity. Ion channels present diverse key functions, such as the maintenance of physiological homeostasis and cell proliferation. Cell biology and pharmacological experimental evidences demonstrate that proliferating cells exhibit ion channel expression, conductance, and electrical properties different from the resting cells. Thereby, a large variety of ion channels has been identified in the pathogenesis of obesity such as potassium, sodium, calcium and chloride channels, nicotinic acetylcholine receptor and transient receptor potential channels. The fundamental involvement of these channels on the generation of obesity leads to the progress in the knowledge about the mechanisms responsible for the obesity pathophysiology, consequently emerging as new targets for pharmacological modulation.

Nicotinic acetylcholine receptors: upregulation, age-related effects and associations with drug use

Nicotinic acetylcholine receptors are ligand-gated ion channels that exogenously bind nicotine. Nicotine produces rewarding effects by interacting with these receptors in the brain's reward system. Unlike other receptors, chronic stimulation by an agonist induces an upregulation of receptor number that is not due to increased gene expression in adults; while upregulation also occurs during development and adolescence there have been some opposing findings regarding a change in corresponding gene expression. These receptors have also been well studied with regard to human genetic associations and, based on evidence suggesting shared genetic liabilities between substance use disorders, numerous studies have pointed to a role for this system in comorbid drug use. This review will focus on upregulation of these receptors in adulthood, adolescence and development, as well as the findings from human genetic association studies which point to different roles for these receptors in risk for initiation and continuation of drug use.

Lack of Associations of CHRNA5-A3-B4 Genetic Variants with Smoking Cessation Treatment Outcomes in Caucasian Smokers despite Associations with Baseline Smoking

CHRNA5-A3-B4 variants, rs16969968, rs588765 and rs578776, are consistently associated with tobacco consumption among smokers, but the association with smoking cessation is less consistent. Among the studies that reported significant associations with cessation, the effects were observed in smokers treated with placebo treatment in some studies and conversely in those receiving active pharmacological therapy (bupropion and nicotine replacement therapies) in others. Thus, it remains unclear whether CHRNA5-A3-B4 is a useful marker for optimizing smoking cessation. Using data from 654 Caucasian smokers treated with placebo, nicotine patch or varenicline, we investigated whether CHRNA5-A3-B4 variants were associated with smoking cessation outcomes, and whether there were significant genotype-by-treatment or haplotype-by-treatment interactions. We observed no significant associations between CHRNA5-A3-B4 variants and smoking cessation, despite replicating previous associations with baseline tobacco consumption. At end of treatment the effect size on smoking cessation in the placebo, patch and varenicline groups for rs16969968 [GG vs. GA+AA] was OR = 0.66 (P = 0.23), OR = 1.01 (P = 0.99), and OR = 1.30 (P = 0.36) respectively, of rs588765 [CC vs. CT+TT] was OR = 0.96 (P = 0.90), OR = 0.84 (P = 0.58), and OR = 0.74 (P = 0.29) respectively, and for rs578776 [GG vs. GA+AA] on smoking cessation was OR = 1.02 (P = 0.95), OR = 0.75 (P = 0.35), and OR = 1.20 (P = 0.51) respectively. Furthermore, we observed no associations with cessation using the CHRNA5-A3-B4 haplotype (constructed using rs16969968 and rs588765), nor did we observe any significant genotype-by-treatment interactions, with or without adjusting for the rate of nicotine metabolism (all P>0.05). We also observed no significant genetic associations with 6 month or 12 month smoking abstinence. In conclusion, we found no association between CHRNA5-A3-B4 variants and smoking cessation rates in this clinical trial; however, as expected, significant associations with baseline tobacco consumption were replicated. Our data suggest that CHRNA5-A3-B4 gene variants do not exhibit a robust association with smoking cessation and are unlikely to be useful for clinically optimizing smoking cessation pharmacotherapy for Caucasian smokers.

Nicotinic receptor modulation to treat alcohol and drug dependence

Alcohol and drug dependence are serious public health problems worldwide. The prevalence of alcohol and drug dependence in the United States and other parts of the world is significant. Given the limitations in the efficacy of current pharmacotherapies to treat these disorders, research in developing alternative pharmacotherapies continues. Preclinical and clinical evidence thus far has indicated that brain nicotinic acetylcholine receptors (nAChRs) are important pharmacological targets for the development of medications to treat alcohol and drug dependence. The nAChRs are a super family of ligand gated ion channels, and are expressed throughout the brain with twelve neuronal nAChR subunits (α2–α10 and β2–β4) identified. Here, we review preclinical and clinical evidence involving a number of nAChR ligands that target different nAChR subtypes in alcohol and nicotine addiction. The important ligands include cytisine, lobeline, mecamylamine, varenicline, sazetidine A and others that target α4β2^* nAChR subtypes as small molecule modulators of the brain nicotinic cholinergic system are also discussed. Taken together, both preclinical and clinical data exist that support nAChR–based ligands as promising therapeutic agents for the treatment of alcohol and drug dependence.

Nicotine Dependence, Nicotine Metabolism, and the Extent of Compensation in Response to Reduced Nicotine Content Cigarettes

INTRODUCTION

The Food and Drug Administration has the authority to regulate tobacco product constituents, including nicotine, to promote public health. Reducing the nicotine content in cigarettes may lead to lower levels of addiction. Smokers however may compensate by smoking more cigarettes and/or smoking more intensely. The objective of this study was to test whether individual differences in the level of nicotine dependence (as measured by the Fagerstrom Test of Cigarette Dependence [FTCD]) and/or the rate of nicotine metabolism influence smoking behavior and exposure to tobacco toxicants when smokers are switched to reduced nicotine content cigarettes (RNC).

METHODS

Data from 51 participants from a previously published clinical trial of RNC were analyzed. Nicotine content of cigarettes was progressively reduced over 6 months and measures of smoking behavior, as well as nicotine metabolites and tobacco smoke toxicant exposure, CYP2A6 and nicotinic CHRNA5-A3-B4 (rs1051730) genotype were measured.

RESULTS

Higher baseline FTCD predicted smoking more cigarettes per day (CPD), higher cotinine and smoke toxicant levels while smoking RNC throughout the study, with no interaction by RNC level. Time to first cigarette (TFC) was associated with differences in compensation. TFC within 10 min was associated with a greater increase in CPD compared to TFC greater than 10 min. Neither rate of nicotine metabolism, nor CYP2A6 or nicotinic receptor genotype, had an effect on the outcome variables of interest.

CONCLUSIONS

FTCD is associated with overall exposure to nicotine and other constituents of tobacco smoke, while a short TFC is associated with an increased compensatory response after switching to RNC.

Association of CHRNA5-A3-B4 SNP rs2036527 with smoking cessation therapy response in African-American smokers

Associations between CHRNA5-A3-B4 variants and smoking behaviors exist; however, the association with smoking abstinence is less understood, particularly that among African Americans. In 1,295 African Americans enrolled in two clinical trials, we investigated the association between CHRNA5-A3-B4 and smoking abstinence. The rs2056527(A) allele was associated with lower abstinence with active pharmacotherapy (during treatment: odds ratio (OR) = 0.42, P < 0.001; end of treatment (EOT): OR = 0.55, P = 0.004), or with nicotine gum alone (during treatment: OR = 0.31, P < 0.001; EOT: OR = 0.51, P = 0.02), but not significantly with bupropion, although similar directions and magnitudes were observed (during treatment: OR = 0.54, P = 0.05; EOT: OR = 0.59, P = 0.08). In addition, the rs588765(T) allele was associated with abstinence with gum during treatment (OR = 2.31, P < 0.01). The SNP rs16969968 occurred at a low frequency and was not consistently associated with abstinence. CHRNA5-A3-B4 variants were not associated with tobacco consumption, and adjustments for smoking behaviors did not alter the associations with smoking abstinence. Together, our data suggest that among African Americans, CHRNA5-A3-B4 variants are not associated with baseline smoking but can influence smoking abstinence during active pharmacotherapy.