Differential contribution of genetic variation in multiple brain nicotinic cholinergic receptors to nicotine dependence: recent progress and emerging open questions

"Weeding out" violence? Translational perspectives on the neuropsychobiological links between cannabis and aggression

Recent shifts in societal attitudes towards cannabis have led to a dramatic increase in consumption rates in many Western countries, particularly among young people. This trend has shed light on a significant link between cannabis use disorder (CUD) and pathological reactive aggression, a condition involving disproportionate aggressive and violent reactions to minor provocations. The discourse on the connection between cannabis use and aggression is frequently enmeshed in political and legal discussions, leading to a polarized understanding of the causative relationship between cannabis use and aggression. However, integrative analyses from both human and animal research indicate a complex, bidirectional interplay between cannabis misuse and pathological aggression. On the one hand, emerging research reveals a shared genetic and environmental predisposition for both cannabis use and aggression, suggesting a common underlying biological mechanism. On the other hand, there is evidence that cannabis consumption can lead to violent behaviors while also being used as a self-medication strategy to mitigate the negative emotions associated with pathological reactive aggression. This suggests that the coexistence of pathological aggression and CUD may result from overlapping vulnerabilities, potentially creating a self-perpetuating cycle where each condition exacerbates the other, escalating into externalizing and violent behaviors. This article aims to synthesize existing research on the intricate connections between these issues and propose a theoretical model to explain the neurobiological mechanisms underpinning this complex relationship.

Candidate gene-environment interactions in substance abuse: A systematic review

BACKGROUND

The abuse of psychogenic drugs can lead to multiple health-related problems. Genetic and environmental vulnerabilities are factors in the emergence of substance use disorders. Empirical evidence regarding the gene-environment interaction in substance use is mixed. Summaries of the latest findings from a candidate gene approach will be useful for revealing the significance of particular gene contributions. Thus, we aim to identify different gene-environment interactions in patterns of substance use and investigate whether any effects trend notably across different genders and races.

METHODS

We reviewed published studies, until March 1, 2022, on substance use for candidate gene-environment interaction. Basic demographics of the included studies, target genes, environmental factors, main findings, patterns of gene-environment interaction, and other relevant information were collected and summarized.

RESULTS

Among a total of 44 studies, 38 demonstrated at least one significant interaction effect. About 61.5% of studies on the 5-HTTLPR gene, 100% on the MAOA gene, 42.9% on the DRD2 gene, 50% on the DRD4 gene, 50% on the DAT gene, 80% on the CRHR1 gene, 100% on the OPRM1 gene, 100% on the GABRA1 gene, and 50% on the CHRNA gene had a significant gene-environment interaction effect. The diathesis-stress model represents a dominant interaction pattern (89.5%) in the studies with a significant interaction effect; the remaining significant effect on substance use is found in the differential susceptibility model. The social push and swing model were not reported in the included studies.

CONCLUSION

The gene-environment interaction research on substance use behavior is methodologically multidimensional, which causes difficulty in conducting pooled analysis, or stated differently-making it hard to identify single sources of significant influence over maladaptive patterns of drug taking. In decreasing the heterogeneity and facilitating future pooled analysis, researchers must (1) replicate the existing studies with consistent study designs and measures, (2) conduct power calculations to report gene-environment correlations, (3) control for covariates, and (4) generate theory-based hypotheses with factorial based experiments when designing future studies.

Understanding the habenula: A major node in circuits regulating emotion and motivation

Over the last decade, the understanding of the habenula has rapidly advanced from being an understudied brain area with the Latin name 'habena" meaning "little rein", to being considered a "major rein" in the control of key monoaminergic brain centers. This ancient brain structure is a strategic node in the information flow from fronto-limbic brain areas to brainstem nuclei. As such, it plays a crucial role in regulating emotional, motivational, and cognitive behaviors and has been implicated in several neuropsychiatric disorders, including depression and addiction. This review will summarize recent findings on the medial (MHb) and lateral (LHb) habenula, their topographical projections, cell types, and functions. Additionally, we will discuss contemporary efforts that have uncovered novel molecular pathways and synaptic mechanisms with a focus on MHb-Interpeduncular nucleus (IPN) synapses. Finally, we will explore the potential interplay between the habenula's cholinergic and non-cholinergic components in coordinating related emotional and motivational behaviors, raising the possibility that these two pathways work together to provide balanced roles in reward prediction and aversion, rather than functioning independently.

Association between the ACE-I/D polymorphism and nicotine dependence amongst patients with lung cancer

The biologically active peptide angiotensin II is cleaved from angiotensinogen by the renin and the angiotensin-converting enzyme (ACE), an enzymatic cascade known as the renin-angiotensin system (RAS). RAS may be important in the etiology of nicotine dependence by influencing dopaminergic signaling. In the present study, the association between an insertion/deletion (I/D) polymorphism of ACE and nicotine dependence amongst patients with lung cancer was assessed. To date, several studies have shown the relevance of this polymorphic variant in both nicotine dependence and lung cancer. However, the present study is the first to address the potential role of the ACE-I/D polymorphism in nicotine dependence among patients with lung cancer. Genotyping was performed in 305 patients with lung cancer (males/females, 214/91). Significantly more male smokers had the ACE-I allele compared with male non-smokers (44.9 vs. 20.0%; P<0.05). The risk of smoking was ~5-fold higher for males with the ACE-I allele (ACE-II homozygous and ACE-ID heterozygous) vs. ACE-DD homozygous (odds ratio, 5.47; 95% confidence interval, 1.4-21.9; P=0.016). The pack-year smoking history in a subgroup of females with squamous cell carcinoma carrying the ACE-I allele was significantly lower compared with ACE-DD (37.1±14.1 vs. 57.0±29.1; F=4.5; P=0.046). The ACE-I/D polymorphism accounted for 17.6% of the smoking severity in this patient group (β, -0.42; multiple R² change, 0.176; P=0.046). These results suggest that the ACE-I/D polymorphism contributes to the risk of nicotine dependence and smoking severity in lung cancer patients in a sex-specific manner.

Genetic susceptibility to nicotine addiction: Advances and shortcomings in our understanding of the CHRNA5/A3/B4 gene cluster contribution

Over the last decade, robust human genetic findings have been instrumental in elucidating the heritable basis of nicotine addiction (NA). They highlight coding and synonymous polymorphisms in a cluster on chromosome 15, encompassing the CHRNA5, CHRNA3 and CHRNB4 genes, coding for three subunits of the nicotinic acetylcholine receptor (nAChR). They have inspired an important number of preclinical studies, and will hopefully lead to the definition of novel drug targets for treating NA. Here, we review these candidate gene and genome-wide association studies (GWAS) and their direct implication in human brain function and NA-related phenotypes. We continue with a description of preclinical work in transgenic rodents that has led to a mechanistic understanding of several of the genetic hits. We also highlight important issues with regards to CHRNA3 and CHRNB4 where we are still lacking a dissection of their role in NA, including even in preclinical models. We further emphasize the use of human induced pluripotent stem cell-derived models for the analysis of synonymous and intronic variants on a human genomic background. Finally, we indicate potential avenues to further our understanding of the role of this human genetic variation. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.

Profound alteration in reward processing due to a human polymorphism in CHRNA5: a role in alcohol dependence and feeding behavior

Human genetic variation in the nicotinic receptor gene cluster CHRNA5/A3/B4, in particular the non-synonymous and frequent CHRNA5 variant rs16969968 (α5SNP), has an important consequence on smoking behavior in humans. A number of genetic association studies have additionally implicated the CHRNA5 gene in addictions to other drugs, and also body mass index (BMI). Here, we model the α5SNP, in a transgenic rat line, and establish its role in alcohol dependence, and feeding behavior. Rats expressing the α5SNP consume more alcohol, and exhibit increased relapse to alcohol seeking after abstinence. This high-relapsing phenotype is reflected in altered activity in the insula, linked to interoception, as established using c-Fos immunostaining. Similarly, relapse to food seeking is increased in the transgenic group, while a nicotine treatment reduces relapse in both transgenic and control rats. These findings point to a general role of this human polymorphism in reward processing, and multiple addictions other than smoking. This could pave the way for the use of medication targeting the nicotinic receptor in the treatment of alcohol use and eating disorders, and comorbid conditions in smokers.

Not all smokers appear to seek nicotine for the same reasons: implications for preclinical research in nicotine dependence

Tobacco use leads to 6 million deaths every year due to severe long-lasting diseases. The main component of tobacco, nicotine, is recognized as one of the most addictive drugs, making smoking cessation difficult, even when 70 percent of smokers wish to do so. Clinical and preclinical studies have demonstrated consistently that nicotine seeking is a complex behavior involving various psychopharmacological mechanisms. Evidence supports that the population of smokers is heterogeneous, particularly as regards the breadth of motives that determine the urge to smoke. Here, we review converging psychological, genetic and neurobiological data from clinical and preclinical studies supporting that the mechanisms controlling nicotine seeking may vary from individual to individual. It appears timely that basic neuroscience integrates this heterogeneity to refine our understanding of the neurobiology of nicotine seeking, as tremendous progress has been made in modeling the various psychopharmacological mechanisms driving nicotine seeking in rodents. For a better understanding of the mechanisms that drive nicotine seeking, we emphasize the need for individual-based research strategies in which nicotine seeking, and eventually treatment efficacy, are determined while taking into account individual variations in the mechanisms of nicotine seeking.

The effects of high glucose exposure on global gene expression and DNA methylation in human pancreatic islets

BACKGROUND

Type 2 diabetes (T2D) is a complex disease characterised by chronic hyperglycaemia. The effects of elevated glucose on global gene expression in combination with DNA methylation patterns have not yet been studied in human pancreatic islets. Our aim was to study the impact of 48 h exposure to high (19 mM) versus control (5.6 mM) glucose levels on glucose-stimulated insulin secretion, gene expression and DNA methylation in human pancreatic islets.

RESULTS

While islets kept at 5.6 mM glucose secreted significantly more insulin in response to short term glucose-stimulation (p = 0.0067), islets exposed to high glucose for 48 h were desensitised and unresponsive to short term glucose-stimulation with respect to insulin secretion (p = 0.32). Moreover, the exposure of human islets to 19 mM glucose resulted in significantly altered expression of eight genes (FDR<5%), with five of these (GLRA1, RASD1, VAC14, SLCO5A1, CHRNA5) also exhibiting changes in DNA methylation (p < 0.05). A gene set enrichment analysis of the expression data showed significant enrichment of e.g. TGF-beta signalling pathway, Notch signalling pathway and SNARE interactions in vesicular transport; these pathways are of relevance for islet function and possibly also diabetes. We also found increased DNA methylation of CpG sites annotated to PDX1 in human islets exposed to 19 mM glucose for 48 h. Finally, we could functionally validate a role for Glra1 in insulin secretion.

CONCLUSION

Our data demonstrate that high glucose levels affect human pancreatic islet gene expression and several of these genes also exhibit epigenetic changes. This might contribute to the impaired insulin secretion seen in T2D.

Genetic variation in CHRNA7 and CHRFAM7A is associated with nicotine dependence and response to varenicline treatment

The role of nicotinic acetylcholine receptors (nAChR) in nicotine dependence (ND) is well established; CHRNA7, encoding the α7 subunit, has a still uncertain role in ND, although it is implicated in a wide range of neuropsychiatric conditions. CHRFAM7A, a hybrid gene containing a partial duplication of CHRNA7, is possibly involved in modulating α7 nAChR function. The aim of this study was to investigate the role of CHRNA7 and CHRFAM7A genetic variants in ND and to test the hypothesis that α7 nAChR variation may modulate the efficacy of varenicline treatment in smoking cessation. We assessed CHRNA7 and CHRFAM7A copy number, CHRFAM7A exon 6 ∆2 bp polymorphism, and sequence variants in the CHRNA7 proximal promoter in an Italian sample of 408 treatment-seeking smokers. We conducted case-control and quantitative association analyses using two smoking measures (cigarettes per day, CPD, and Fagerström Test for Nicotine Dependence, FTND). Next, driven by the hypothesis that varenicline may exert some of its therapeutic effects through activation of α7 nAChRs, we restricted the analysis to a subgroup of 142 smokers who received varenicline treatment. The CHRNA7 promoter variant rs28531779 showed association with both smoking quantitative measures (FNTD p = 0.026, β = 0.89, 95% CI 0.11-1.67; CPD p = 0.006, β = 4.82 95% CI 1.42-8.22). Moreover, in the varenicline-treated subgroup we observed association of CHRFAM7A copy number with 6 months smoking abstinence (p = 0.035, OR = 3.18, 95% CI = 1.09-9.30). Thus, our study points to a possible role of genetic variation in CHRNA7 and CHRFAM7A in tobacco addiction mechanisms and response to varenicline treatment.

The α3β4 nAChR partial agonist AT-1001 attenuates stress-induced reinstatement of nicotine seeking in a rat model of relapse and induces minimal withdrawal in dependent rats

The strong reinforcing effects of nicotine and the negative symptoms such as anxiety experienced during a quit attempt often lead to relapse and low success rates for smoking cessation. Treatments that not only block the reinforcing effects of nicotine but also attenuate the motivation to relapse are needed to improve cessation rates. Recent genetic and preclinical studies have highlighted the involvement of the α3, β4, and α5 nicotinic acetylcholine receptor (nAChR) subunits and the α3β4 nAChR subtype in nicotine dependence and withdrawal. However, the involvement of these nAChR in relapse is not fully understood. We previously reported that the α3β4 nAChR partial agonist AT-1001 selectively decreases nicotine self-administration in rats without affecting food responding. In the present experiments, we examined the efficacy of AT-1001 in attenuating reinstatement of nicotine-seeking behavior in a model of stress-induced relapse. Rats extinguished from nicotine self-administration were treated with the pharmacological stressor yohimbine prior to AT-1001 treatment and reinstatement testing. We also examined whether AT-1001 produced any withdrawal-related effects when administered to nicotine-dependent rats. We found that AT-1001 dose-dependently reduced yohimbine stress-induced reinstatement of nicotine seeking. When administered to nicotine-dependent rats at the dose that significantly blocked nicotine reinstatement, AT-1001 elicited minimal somatic withdrawal signs in comparison to the nicotinic antagonist mecamylamine, which is known to produce robust withdrawal. Our data suggest that α3β4 nAChR-targeted compounds may be a promising approach for nicotine addiction treatment because they can not only block nicotine's reinforcing effects, but also decrease motivation to relapse without producing significant withdrawal effects.

Associations of rare nicotinic cholinergic receptor gene variants to nicotine and alcohol dependence

Nicotine's rewarding effects are mediated through distinct subunits of nAChRs, encoded by different nicotinic cholinergic receptor (CHRN) genes and expressed in discrete regions in the brain. In the present study, we aimed to test the associations between rare variants at CHRN genes and nicotine dependence (ND), and alcohol dependence (AD). A total of 26,498 subjects with nine different neuropsychiatric disorders in 15 independent cohorts, which were genotyped on Illumina, Affymetrix, or PERLEGEN microarray platforms, were analyzed. Associations between rare variants (minor allele frequency (MAF) <0.05) at CHRN genes and nicotine dependence, and alcohol dependence were tested. The mRNA expression of all Chrn genes in whole mouse brain and 10 specific brain areas was investigated. All CHRN genes except the muscle-type CHRNB1, including eight genomic regions containing 11 neuronal CHRN genes and three genomic regions containing four muscle-type CHRN genes, were significantly associated with ND, and/or AD. All of these genes were expressed in the mouse brain. We conclude that CHRNs are associated with ND (mainly) and AD, supporting the hypothesis that the full catalog of ND/AD risk genes may contain most neuronal nAChRs-encoding genes. © 2016 Wiley Periodicals, Inc.

Alterations in alpha5* nicotinic acetylcholine receptors result in midbrain- and hippocampus-dependent behavioural and neural impairments

RATIONALE

Evidence links alterations in α5-containing nicotinic receptors (α5*-nAChRs) to nicotine addiction. Notably, the rs16969968 polymorphism in the α5 gene (α5SNP) increases the risk for heavy smoking and impairs nicotine-rewarding properties in mice. Additional work is needed to understand how native and polymorphic α5*-nAChRs contribute to processes associated with the risk for nicotine addiction.

OBJECTIVES

We aimed at understanding the contribution of α5*-nAChRs to endophenotypes like increased responses to novelty and anxiety, known to promote vulnerability to addiction, and to the response of the dopamine and serotonin systems to nicotine.

METHODS

Behavioural phenotypes were investigated in mice lacking the α5 gene (α5(-/-)). Nicotine injections were performed to test the consequences of nicotine exposure on the phenotypes identified. Dopamine and serotonin signalling were assessed using in vivo microdialysis and electrophysiology. We used lentiviral vectors to compare the consequences of re-expressing either the α5 wild-type allele or the α5SNP in specific brain areas of α5(-/-) mice.

RESULTS

α5(-/-) mice did not exhibit high responses to novelty but showed decreased novelty-induced rearing behaviour together with high anxiety. Exposure to high doses of nicotine rescued these phenotypes. We identified altered spontaneous and nicotine-elicited serotonin and dopamine activity in α5(-/-) mice. Re-expression of α5 in the ventral tegmental area and hippocampus rescued rearing and anxiety levels in α5(-/-) mice, respectively. When expressing the α5SNP instead, this resulted in a knockout-like phenotype for both behaviours.

CONCLUSIONS

We propose that altered α5*-nAChR cholinergic signalling contributes to emotional/behavioural impairments that may be alleviated by nicotine consumption.

Genetic variants associated with physical and mental characteristics of the elite athletes in the Polish population

The aim of the study was to assess whether selected genetic variants are associated with elite athlete performance in a group of 413 elite athletes and 451 sedentary controls. Polymorphisms in ACE, ACTN3, AGT, NRF-2, PGC1A, PPARG, and TFAM implicated in physical performance traits were analyzed. Additionally, polymorphisms in CHRNB3 and FAAH coding for proteins modulating activity of brain's emotion centers were included. The results of univariate analyses indicated that the elite athletic performance is associated with four polymorphisms: ACE (rs4341, P = 0.0095), NRF-2 (rs12594956, P = 0.011), TFAM (rs2306604, P = 0.049), and FAAH (rs324420, P = 0.0041). The multivariate analysis adjusted for age and gender confirmed this association. The higher number of ACE D alleles (P = 0.0021) and the presence of NRF-2 rs12594956 A allele (P = 0.0067) are positive predictors, whereas TFAM rs2306604 GG genotype (P = 0.031) and FAAH rs324420 AA genotype (P = 0.0084) negatively affect the elite athletic performance. The CHRNB3 variant (rs4950, G allele) is significantly more frequent in the endurance athletes compared with the power ones (P = 0.025). Multivariate analysis demonstrated that the presence of rs4950 G allele contributes to endurance performance (P = 0.0047). Our results suggest that genetic inheritance of psychological traits should be taken into consideration while trying to decipher a genetic profile of top athletic performance.

CHRNA5/A3/B4 Variant rs3743078 and Nicotine-Related Phenotypes: Indirect Effects Through Nicotine Craving

OBJECTIVE

Nicotine craving is considered an important element in the persistence of cigarette smoking, but little is known about the role of craving in the widely recognized association between variants mapped to the neuronal nicotinic acetylcholine receptor (CHRN) genes on chromosome 15 and nicotine phenotypes.

METHOD

The associations between CHRNA5-CHRNA3-CHRNB4 variants and cigarettes per day (CPD), the Fagerström Test for Nicotine Dependence (FTND), and craving were analyzed in data from 662 lifetime smokers from an Israeli adult Jewish household sample. Indirect effects of genotype on nicotine phenotypes through craving were formally tested using regression and bootstrapping procedures.

RESULTS

At CHRNA3, allele G of rs3743078 was associated with increased craving, CPD, and FTND scores: Participants with one or two copies of the G allele had, on average, higher scores on the craving scale (p = .0025), more cigarettes smoked (p = .0057), and higher scores on the FTND (p =.0024). With craving in the model, variant rs3743078 showed a significant indirect effect through craving on CPD (p = .0026) and on FTND score (p = .0024). A sizeable proportion of the total rs3743078 effect on CPD (56.4%) and FTND (65.2%) was indirect through craving.

CONCLUSIONS

These results suggest that nicotine craving may play a central role in nicotine use disorders and may have utility as a therapeutic target.

Scientific overview: 2013 BBC plenary symposium on tobacco addiction

Nicotine dependence plays a critical role in addiction to tobacco products, and thus contributes to a variety of devastating tobacco-related diseases (SGR 2014). Annual costs associated with smoking in the US are estimated to be between $289 and $333 billion. Effective interventions for nicotine dependence, especially in smokers, are a critical barrier to the eradication of tobacco-related diseases. This overview highlights research presented at the Plenary Symposium of Behavior, Biology and Chemistry: Translational Research in Addiction Conference (BBC), hosted by the UT Health Science Center San Antonio, on March 9-10, 2013. The Plenary Symposium focused on tobacco addiction, and covered topics ranging from basic science to national policy. As in previous years, the meeting brought together globally-renowned scientists, graduate student recruits, and young scientists from underrepresented populations in Texas and other states with the goal of fostering interest in drug addiction research in young generations.

Significant associations of CHRNA2 and CHRNA6 with nicotine dependence in European American and African American populations

The direct physiological effects that promote nicotine dependence (ND) are mediated by nicotinic acetylcholine receptors (nAChRs). In line with the genetic and pharmacological basis of addiction, many previous studies have revealed significant associations between variants in the nAChR subunit genes and various measures of ND in different ethnic samples. In this study, we first examined the association of variants in nAChR subunits α2 (CHRNA2) and α6 (CHRNA6) genes on chromosome 8 with ND using a family sample consisting of 1,730 European Americans (EAs) from 495 families and 1,892 African Americans (AAs) from 424 families (defined as the discovery family sample). ND was assessed by two standard quantitative measures: smoking quantity (SQ) and the Fagerström Test for ND (FTND). We found nominal associations for all seven tested SNPs of the genes with at least one ND measure in the EA sample and for two SNPs in CHRNA2 in the AA sample. Of these, associations of SNPs rs3735757 with FTND (P = 0.0068) and rs2472553 with both ND measures (with a P value of 0.0043 and 0.00086 for SQ and FTND, respectively) continued to be significant in the EA sample even after correction for multiple tests. Further, we found several haplotypes that were significantly associated with ND in the EA sample in CHRNA6 and in the both EA and AA samples in CHRNA2. To confirm the associations of the two genes with ND, we conducted a replication study with an independent case-control sample from the SAGE study, which showed a significant association of the two genes with ND, although the significantly associated SNPs were not always the same in the two samples. Together, these findings indicate that both CHRNA2 and CHRNA6 play a significant role in the etiology of ND in AA and EA smokers. Further replication in additional independent samples is warranted.

Physiological effects of cigarette smoking in the limbic system revealed by 3 tesla magnetic resonance spectroscopy

Several studies and recent models of effects of nicotine, the main addictive and psychoactive component in tobacco, point to action of the drug on the limbic system during maintenance of addiction, either direct or indirect via projections from the ventral tegmental area. The objective of this study was to demonstrate physiological effects of cigarette smoking on the hippocampus and the grey matter of the dorsal anterior cingulate cortex in the human brain with regard to addiction and withdrawal. This aim was achieved by group comparisons of results of magnetic resonance spectroscopy between non-smokers, smokers and smokers during withdrawal. 12 smokers and 12 non-smokers were measured with single voxel proton magnetic resonance spectroscopy for total N-acetyl aspartate, glutamate and glutamine, choline-containing compounds, myo-inositol and total creatine in the right and the left hippocampus and in the right and the left dorsal anterior cingulate cortex. Smokers were examined twice, first during regular cigarette smoking and second on the third day of nicotine withdrawal. The ratios to total creatine were used for better reliability. In our study, Glx/tCr was significantly increased and tCho/tCr was significantly decreased in the left cingulate cortex in smokers compared to non-smokers (p = 0.01, both). Six out of seven smokers showed normalization of the Glx/tCr in the left cingulate cortex during withdrawal. Although these results are preliminary due to the small sample size, our results confirm the assumption that cigarette smoking interferes directly or indirectly with the glutamate circuit in the dorsal anterior cingulate cortex.

Familial aggregation of tobacco use behaviors among Amish men

INTRODUCTION

Tobacco use is a complex behavior. The Old Order Amish community offers unique advantages for the study of tobacco use because of homogenous ancestral background, sociocultural similarity, sex-specific social norms regarding tobacco use, and large family size. Tobacco use in the Old Order Amish community is almost exclusively confined to males.

METHODS

We examined characteristics of tobacco use and familial aggregation among 1,216 Amish males from cross-sectional prospectively collected data. Outcomes examined included ever using tobacco regularly, current use, quantity of use, duration of use, and frequency of use.

RESULTS

Sixteen percent of Amish men were current tobacco users, with the majority reporting cigar use only. Higher rates of tobacco use were found among sons of fathers who smoked compared with sons of fathers who did not smoke (46% vs. 22%, p < .001) as well as among brothers of index cases who smoked compared with brothers of index cases who did not smoke (61% vs. 29%, p < .001). After controlling for shared household effects and age, heritability accounted for 66% of the variance in ever smoking regularly (p = .045).

CONCLUSIONS

The familial patterns of tobacco use observed among Amish men highlight the important role of family in propagating tobacco use and support the usefulness of this population for future genetic studies of nicotine addiction.

1H-Nuclear magnetic resonance-based metabolomic analysis of brain in mice with nicotine treatment

Background

Nicotine is rapidly absorbed from cigarette smoke and therefore induces a number of chronic illnesses with the widespread use of tobacco products. Studies have shown a few cerebral metabolites modified by nicotine; however, endogenous metabolic profiling in brain has not been well explored.

Results

H NMR-based on metabonomics was applied to investigate the endogenous metabolic profiling of brain hippocampus, nucleus acumens (NAc), prefrontal cortex (PFC) and striatum. We found that nicotine significantly increased CPP in mice, and some specific cerebral metabolites differentially changed in nicotine-treated mice. These modified metabolites included glutamate, acetylcholine, tryptamine, glucose, lactate, creatine, 3-hydroxybutyrate and nicotinamide-adenine dinucleotide (NAD), which was closely associated with neurotransmitter and energy source. Additionally, glutathione and taurine in hippocampus and striatum, phosphocholine in PFC and glycerol in NAc were significantly modified by nicotine, implying the dysregulation of anti-oxidative stress response and membrane metabolism.

Conclusions

Nicotine induces significant metabonomic alterations in brain, which are involved in neurotransmitter disturbance, energy metabolism dysregulation, anti-oxidation and membrane function disruptions, as well as amino acid metabolism imbalance. These findings provide a new insight into rewarding effects of nicotine and the underlying mechanism.

The association between CHRN genetic variants and dizziness at first inhalation of cigarette smoke

Numerous single nucleotide polymorphisms (SNPs) in multiple nicotinic receptor genes (CHRN) are associated with smoking. However few studies have examined the association between CHRN SNPs and subjective responses to smoking in adolescents which may relate to sustained smoking, such as dizziness at first inhalation. The objective of this study was to investigate the association between 61 SNPs in eight CHRN genes (CHRNA3, CHRNA4, CHRNA5, CHRNA6, CHRNA7, CHRNB2, CHRNB3, CHRNB4) and dizziness at first inhalation. Data were available from a longitudinal cohort investigation of 1293 students 12-13year-old at baseline. Students completed self-report questionnaires at school every 3months for 5years during secondary school, and a mailed questionnaire three years later. DNA extracted from blood or saliva was genotyped for 61 CHRN SNPs selected using a gene tagging approach. Associations were modeled using logistic regression controlling for sex, race and age at first cigarette. Complete data were available for 356 of 475 participants (75%) who initiated smoking. The minor alleles of three SNPs in CHRNA6 (rs7812298, rs2304297, rs7828365) were associated with a decreased probability of dizziness (OR(95% CI)=0.54 (0.36, 0.81), 0.59 (0.40, 0.86) and 0.58 (0.36, 0.95), respectively), while one SNP in each of three other genes (rs3743077 (CHRNA3), rs755204 (CHRNA4), rs7178176 (CHRNA7)) was associated with an increased probability of dizziness (OR(95% CI)=1.40 (1.02, 1.90), 1.85 (1.05, 3.27) and 1.51 (1.06, 2.15), respectively). Thus, several SNPs located in CHRN genes are associated with dizziness at first inhalation, a smoking initiation phenotype that may relate to sustained smoking.

Distinct loci in the CHRNA5/CHRNA3/CHRNB4 gene cluster are associated with onset of regular smoking

Neuronal nicotinic acetylcholine receptor (nAChR) genes (CHRNA5/CHRNA3/CHRNB4) have been reproducibly associated with nicotine dependence, smoking behaviors, and lung cancer risk. Of the few reports that have focused on early smoking behaviors, association results have been mixed. This meta-analysis examines early smoking phenotypes and SNPs in the gene cluster to determine: (1) whether the most robust association signal in this region (rs16969968) for other smoking behaviors is also associated with early behaviors, and/or (2) if additional statistically independent signals are important in early smoking. We focused on two phenotypes: age of tobacco initiation (AOI) and age of first regular tobacco use (AOS). This study included 56,034 subjects (41 groups) spanning nine countries and evaluated five SNPs including rs1948, rs16969968, rs578776, rs588765, and rs684513. Each dataset was analyzed using a centrally generated script. Meta-analyses were conducted from summary statistics. AOS yielded significant associations with SNPs rs578776 (beta = 0.02, P = 0.004), rs1948 (beta = 0.023, P = 0.018), and rs684513 (beta = 0.032, P = 0.017), indicating protective effects. There were no significant associations for the AOI phenotype. Importantly, rs16969968, the most replicated signal in this region for nicotine dependence, cigarettes per day, and cotinine levels, was not associated with AOI (P = 0.59) or AOS (P = 0.92). These results provide important insight into the complexity of smoking behavior phenotypes, and suggest that association signals in the CHRNA5/A3/B4 gene cluster affecting early smoking behaviors may be different from those affecting the mature nicotine dependence phenotype.

Nicotinic receptor gene variants interact with attention deficient hyperactive disorder symptoms to predict smoking trajectories from early adolescence to adulthood

OBJECTIVE

To examine the association of single nucleotide polymorphisms (SNPs) of the CHRNB3 (rs13280604) and CHRNA6 (rs892413) nicotinic acetylcholine receptor (nAChR) genes and symptoms of attention deficit hyperactivity disorder (ADHD) in predicting smoking patterns from early adolescence to adulthood.

METHOD

A longitudinal cohort of 1137 unrelated youths from the National Longitudinal Study of Adolescent Health provided responses to four surveys from Waves I to IV, and a genetic sample in Wave III. Growth mixture modeling was used to identify smoking patterns and to assess the effects of the two SNPs and ADHD symptoms on cigarette use over time.

RESULTS

There were significant main effects of ADHD symptoms and CHRNA6 variants in predicting the number of cigarettes smoked and the pattern of use over time, respectively. There were no main effects of the CHRNB3 variants. However, a significant CHRNB3 variant×ADHD symptom interaction was observed, such that individuals with elevated ADHD symptoms and a particular CHRNB3 variant were at increased risk of cigarette use over time.

CONCLUSIONS

These findings demonstrate that a SNP in a nicotinic receptor gene may interact with ADHD symptoms to link with increased cigarette use across adolescence and young adulthood. Unique associations between specific variants and patterns of ADHD symptoms were identified which may be useful for targeting prevention efforts to individuals at greatest risk for cigarette smoking.

Effect of neuronal nicotinic acetylcholine receptor genes (CHRN) on longitudinal cigarettes per day in adolescents and young adults

INTRODUCTION

Few studies have sought to identify specific genetic markers associated with cigarettes per day (CPD) during adolescence and young adulthood, the period of greatest vulnerability for the development of nicotine dependence.

METHODS

We used a longitudinal design to investigate the effect of neuronal nicotinic acetylcholine receptor (CHRN) subunit genes on CPD from 15 to 21 years of age in young smokers of European descent (N = 439, 59% female). The number of CPD typically smoked during the previous 30 days was self-reported. Single nucleotide polymorphisms (SNPs) from CHRN genes were genotyped using DNA extracted from saliva samples collected at the 5-year assessment. Mixed-model analyses of SNP effects were computed across age at the time of assessment using log-transformed CPD as the phenotype. Data from the 1000 Genomes Project were used to clarify the architecture of CHRN genes to inform SNP selection and interpretation of results.

RESULTS

CPD was associated with a CHRNB3A6 region tagged by rs2304297, with CHRNA5A3B4 haplotype C (tagged by rs569207), and with the CHRNA2 SNP rs2271920, ps < .004. The reliability of single-SNP associations was supported by the correspondence between a more extensive set of SNP signals and the underlying genetic architecture. The 3 signals identified in this study appear to make independent contributions to CPD, and their combined effect accounts for 5.5% of the variance in log-transformed CPD.

CONCLUSIONS

Level of CPD during adolescence and young adulthood is associated with CHRNB3A6, CHRNA5A3B4, and CHRNA2.

Polygenic risk and the developmental progression to heavy, persistent smoking and nicotine dependence: evidence from a 4-decade longitudinal study

IMPORTANCE

Genome-wide hypothesis-free discovery methods have identified loci that are associated with heavy smoking in adulthood. Research is needed to understand developmental processes that link newly discovered genetic risks with adult heavy smoking.

OBJECTIVE

To test how genetic risks discovered in genome-wide association studies of adult smoking influence the developmental progression of smoking behavior from initiation through conversion to daily smoking, progression to heavy smoking, nicotine dependence, and struggles with cessation.

DESIGN

A 38-year, prospective, longitudinal study of a representative birth cohort.

SETTING

The Dunedin Multidisciplinary Health and Development Study of New Zealand.

PARTICIPANTS

The study included 1037 male and female participants.

EXPOSURE

We assessed genetic risk with a multilocus genetic risk score. The genetic risk score was composed of single-nucleotide polymorphisms identified in 3 meta-analyses of genome-wide association studies of smoking quantity phenotypes.

MAIN OUTCOMES AND MEASURES

Smoking initiation, conversion to daily smoking, progression to heavy smoking, nicotine dependence (Fagerström Test of Nicotine Dependence), and cessation difficulties were evaluated at 8 assessments spanning the ages of 11 to 38 years.

RESULTS

Genetic risk score was unrelated to smoking initiation. However, individuals at higher genetic risk were more likely to convert to daily smoking as teenagers, progressed more rapidly from smoking initiation to heavy smoking, persisted longer in smoking heavily, developed nicotine dependence more frequently, were more reliant on smoking to cope with stress, and were more likely to fail in their cessation attempts. Further analysis revealed that 2 adolescent developmental phenotypes-early conversion to daily smoking and rapid progression to heavy smoking-mediated associations between the genetic risk score and mature phenotypes of persistent heavy smoking, nicotine dependence, and cessation failure. The genetic risk score predicted smoking risk over and above family history.

CONCLUSIONS AND RELEVANCE

Initiatives that disrupt the developmental progression of smoking behavior among adolescents may mitigate genetic risks for developing adult smoking problems. Future genetic research may maximize discovery potential by focusing on smoking behavior soon after smoking initiation and by studying young smokers.

Why have tobacco control policies stalled? Using genetic moderation to examine policy impacts

BACKGROUND

Research has shown that tobacco control policies have helped produce the dramatic decline in use over the decades following the 1964 surgeon general's report. However, prevalence rates have stagnated during the past two decades in the US, even with large tobacco taxes and expansions of clean air laws. The observed differences in tobacco control policy effectiveness and why policies do not help all smokers are largely unexplained.

OBJECTIVE

The aim of this study was to determine the importance of genetics in explaining response to tobacco taxation policy by testing the potential of gene-policy interaction in determining adult tobacco use.

METHODS

A moderated regression analysis framework was used to test interactive effects between genotype and tobacco policy in predicting tobacco use. Cross sectional data of US adults from the National Health and Nutrition Examination Survey (NHANES) linked with genotype and geocodes were used to identify tobacco use phenotypes, state-level taxation rates, and variation in the nicotinic acetylcholine receptor (CHRNA6) genotype. Tobacco use phenotypes included current use, number of cigarettes smoked per day, and blood serum cotinine measurements.

RESULTS

Variation in the nicotinic acetylcholine receptor was found to moderate the influence of tobacco taxation on multiple measures of tobacco use. Individuals with the protective G/G polymorphism (51% of the sample) responded to taxation while others had no response. The estimated differences in response by genotype were C/C genotype: b = -0.016 se = 0.018; G/C genotype: b = 0.014 se = 0.017; G/G genotype: b = -0.071 se 0.029.

CONCLUSIONS

This study provides novel evidence of "gene-policy" interaction and suggests a genetic mechanism for the large differences in response to tobacco policies. The inability for these policies to reduce use for individuals with specific genotypes suggests alternative methods may be needed to further reduce use.

Direct-to-consumer genetic testing for addiction susceptibility: a premature commercialisation of doubtful validity and value

Genetic research on addiction liability and pharmacogenetic research on treatments for addiction have identified some genetic variants associated with disease risk and treatment. Genetic testing for addiction liability and treatment response has not been used widely in clinical practice because most of the genes identified only modestly predict addiction risk or treatment response. However, many of these genetic tests have been commercialized prematurely and are available direct to the consumer (DTC). The easy availability of DTC tests for addiction liability and lack of regulation over their use raises a number of ethical concerns. Of paramount concern is the limited predictive power and clinical utility of these tests. Many DTC testing companies do not provide the consumer with the necessary genetic counselling to assist them in interpreting and acting on their test results. They may also engage in misleading marketing to entice consumers to purchase their products. Consumers' genetic information may be vulnerable to misuse by third parties, as there are limited standards to protect the privacy of the genetic information. Non-consensual testing and inappropriate testing of minors may also occur. The United States Food and Drug Administration plans to regulate DTC genetic tests. Based on the ethical concerns we discuss below, we believe there is a strong case for regulation of DTC genetic tests for addiction liability and treatment response. We argue that until this occurs, these tests have more potential to cause harm than to contribute to improved prevention and treatment of addiction.

Externalizing behaviors are associated with SNPs in the CHRNA5/CHRNA3/CHRNB4 gene cluster

There is strong evidence for shared genetic factors contributing to childhood externalizing disorders and substance abuse. Externalizing disorders often precede early substance experimentation, leading to the idea that individuals inherit a genetic vulnerability to generalized disinhibitory psychopathology. Genetic variation in the CHRNA5/CHRNA3/CHRNB4 gene cluster has been associated with early substance experimentation, nicotine dependence, and other drug behaviors. This study examines whether the CHRNA5/CHRNA3/CHRNB4 locus is correlated also with externalizing behaviors in three independent longitudinally assessed adolescent samples. We developed a common externalizing behavior phenotype from the available measures in the three samples, and tested for association with 10 SNPs in the gene cluster. Significant results were detected in two of the samples, including rs8040868, which remained significant after controlling for smoking quantity. These results expand on previous work focused mainly on drug behaviors, and support the hypothesis that variation in the CHRNA5/CHRNA3/CHRNB4 locus is associated with early externalizing behaviors.

The CHRNA5/A3/B4 gene cluster and tobacco, alcohol, cannabis, inhalants and other substance use initiation: replication and new findings using mixture analyses

Multiple studies have provided evidence for genetic associations between single nucleotide polymorphisms (SNPs) located on the CHRNA5/A3/B4 gene cluster and various phenotypes related to Nicotine Dependence (Greenbaum et al. 2009). Only a few studies have investigated other substances of abuse. The current study has two aims, (1) to extend previous findings by focusing on associations between the CHRNA5/A3/B4 gene cluster and age of initiation of several different substances, and (2) to investigate heterogeneity in age of initiation across the different substances. All analyses were conducted with a subset of the Add Health study with available genetic data. The first aim was met by modeling onset of tobacco, alcohol, cannabis, inhalants, and other substance use using survival mixture analysis (SMA). Ten SNPs in CHRNA5/A3/B4 were used to predict phenotypic differences in the risk of onset, and differences between users and non-users. The survival models aim at investigating differences in the risk of initiation across the 5-18 age range for each phenotype separately. Significant or marginally significant genetic effects were found for all phenotypes. The genetic effects were mainly related to the risk of initiation and to a lesser extent to discriminating between users and non-users. To address the second goal, the survival analyses were complemented by a latent class analysis that modeled all phenotypes jointly. One of the ten SNPs was found to predict differences between the early and late onset classes. Taken together, our study provides evidence for a general role of the CHRNA5/A3/B4 gene cluster in substance use initiation that is not limited to nicotine and alcohol.

Pharmacogenetics of smoking cessation: role of nicotine target and metabolism genes

Many smokers attempt to quit smoking but few are successful in the long term. The heritability of nicotine addiction and smoking relapse have been documented, and research is focused on identifying specific genetic influences on the ability to quit smoking and response to specific medications. Research in genetically modified cell lines and mice has identified nicotine acetylcholine receptor subtypes that mediate the pharmacological and behavioral effects of nicotine sensitivity and withdrawal. Human genetic association studies have identified single nucleotide polymorphisms (SNPs) in genes encoding nicotine acetylcholine receptor subunits and nicotine metabolizing enzymes that influence smoking cessation phenotypes. There is initial promising evidence for a role in smoking cessation for SNPs in the β2 and α5/α3/β4 nAChR subunit genes; however, effects are small and not consistently replicated. There are reproducible and clinically significant associations of genotypic and phenotypic measures of CYP2A6 enzyme activity and nicotine metabolic rate with smoking cessation as well as response to nicotine replacement therapies and bupropion. Prospective clinical trials to identify associations of genetic variants and gene-gene interactions on smoking cessation are needed to generate the evidence base for both medication development and targeted therapy approaches based on genotype.

Low concentrations of nicotine differentially desensitize nicotinic acetylcholine receptors that include α5 or α6 subunits and that mediate synaptosomal neurotransmitter release

Desensitization is a complex property of nicotinic acetylcholine receptors (nAChR). Several subtypes of nAChR have high sensitivity to nicotine and mediate effects of nicotine at concentrations found in blood of tobacco smokers. Desensitization of some of these receptor subtypes has been studied in model systems, however, other subtypes have been difficult to express heterologously in native forms. In addition, model systems may not have the same accessory molecules and post-translational modifications found in native populations. We have used wild-type and subunit null mutant mice to study desensitization properties of the high sensitivity α4β2-nAChRs including those that have α5 subunits at both GABAergic and dopaminergic nerve terminals. In addition, we have studied the desensitization of one subtype of α6β2-nAChRs at dopaminergic terminals using α4 subunit null mutant mice. Exposure to low nicotine concentrations, leads to rapid, but partial desensitization of activity mediated by these receptors. α4β2-nAChRs including α5 subunits show faster rates of recovery from desensitization than α4β2-nAChRs without α5. Inclusion of the α5 subunit significantly shifts the concentration response for desensitization to higher values, indicating that receptors with α5 subunits are less desensitized by a 10-min exposure to low concentrations of nicotine. Receptors with α6 subunits appear to desensitize to a lesser degree than those with α4 subunits, indicating that α6β2-nAChRs are somewhat resistant to desensitization by nicotine. These results highlight the importance of studying various receptor subtypes in native systems and how they may differentially respond to nicotine and to nicotinic drugs.

Relationship between CYP2A6 and CHRNA5-CHRNA3-CHRNB4 variation and smoking behaviors and lung cancer risk

Genetic variations in the CYP2A6 nicotine metabolic gene and the CHRNA5-CHRNA3-CHRNB4 (CHRNA5-A3-B4) nicotinic gene cluster have been independently associated with lung cancer. With genotype data from ever-smokers of European ancestry (417 lung cancer patients and 443 control subjects), we investigated the relative and combined associations of polymorphisms in these two genes with smoking behavior and lung cancer risk. Kruskal-Wallis tests were used to compare smoking variables among the different genotype groups, and odds ratios (ORs) for cancer risk were estimated using logistic regression analysis. All statistical tests were two-sided. Cigarette consumption (P < .001) and nicotine dependence (P = .036) were the highest in the combined CYP2A6 normal metabolizers and CHRNA5-A3-B4 AA (tag single-nucleotide polymorphism rs1051730 G>A) risk group. The combined risk group also exhibited the greatest lung cancer risk (OR = 2.03; 95% confidence interval [CI] = 1.21 to 3.40), which was even higher among those who smoked 20 or fewer cigarettes per day (OR = 3.03; 95% CI = 1.38 to 6.66). Variation in CYP2A6 and CHRNA5-A3-B4 was independently and additively associated with increased cigarette consumption, nicotine dependence, and lung cancer risk. CYP2A6 and CHRNA5-A3-B4 appear to be more strongly associated with smoking behaviors and lung cancer risk, respectively.

The galanin receptor 1 gene associates with tobacco craving in smokers seeking cessation treatment

Craving for tobacco is a major challenge for people with nicotine dependence (ND) who try to quit smoking. Galanin (GAL) and its receptors (GALRs) can alter addiction-related behaviors and are therefore good candidates for modulators of behavioral parameters associated with smoking. We performed a genetic association study in 486 subjects (432 European American, EA) recruited for smoking cessation trials. Twenty-six candidate genes for ND-related phenotypes were selected based on the literature. Subjects were assessed using the Minnesota Withdrawal Scale (MWS), which included a specific item for craving, the Fagerström Scale of Nicotine Dependence (FTND), and other ND-related instruments. One single-nucleotide polymorphism (SNP) in GALR1, rs2717162, significantly associated with severity of craving in EA samples (p=6.48 × 10(-6)) and in the combined sample (p=9.23 × 10(-6)). Individuals with TT and TC genotypes had significantly higher craving scores than CC subjects. We also observed that SNPs in the CHRNA5 locus, rs16969968 and rs684513, which have been associated with ND-related phenotypes in previous studies, were nominally associated with FTND scores, although these results did not meet Bonferroni-adjusted criteria for experiment-wide significance. Our findings suggest that variation at GALR1 associates with differences in the severity of past craving for tobacco among smokers motivated to quit. Taken together with preclinical evidence, these results, if replicated, suggest that GAL and GALRs may be useful therapeutic targets for the pharmacological treatment of ND. Our results also confirm previously reported associations between variation at CHRNA5 and ND.

Association of the calcyon neuron-specific vesicular protein gene (CALY) with adolescent smoking initiation in China and California

Although previous investigations have indicated a role for genetic factors in smoking initiation, the underlying genetic mechanisms are still unknown. In 2,339 adolescents from a Chinese Han population in the Wuhan Smoking Prevention Trial (Wuhan, China, 1998-1999), the authors explored the association of 57 genes in the dopamine pathway with smoking initiation. Using a conservative approach for declaring significance, positive findings were further examined in an independent sample of 603 Caucasian adolescents followed for up to 10 years as part of the Children's Health Study (Southern California, 1993-2009). The authors identified 1 single nucleotide polymorphism (rs2298122) in the calcyon neuron-specific vesicular protein gene (CALY) that was positively associated with smoking initiation in females (odds ratio = 2.21, 95% confidence interval: 1.49, 3.27; P = 8.4 × 10(-5)) in the Wuhan Smoking Prevention Trial cohort, and they replicated the association in females from the Children's Health Study cohort (hazard rate ratio = 2.05, 95% confidence interval: 1.27, 3.31; P = 0.003). These results suggest that the CALY gene may influence smoking initiation in adolescents, although the potential roles of underlying psychological characteristics that may be components of the smoking-initiation phenotype, such as impulsivity or novelty-seeking, remain to be explored.

CHRNB2 promoter region: association with subjective effects to nicotine and gene expression differences

Smoking behavior is a complex, which includes multiple stages in the progression from experimentation to continued use and dependence. The experience of subjective effects, such as dizziness, euphoria, heart pounding, nausea and high, have been associated with varying degrees of persistence and subsequent abuse/dependence of marijuana, cocaine, tobacco and alcohol (Grant et al. 2005, Wagner & Anthony 2002). Previous studies have reported associations between neuronal nicotinic receptor (CHRN) genes and subjective effects to nicotine. We sought to replicate and expand this work by examining eight single nucleotide polymorphisms (SNPs) in a sample of adult smokers (n = 316) who reported subjective effects following cigarette smoking in a controlled laboratory environment. Two SNPs each in the CHRNB2, CHRNB3, CHRNA6 and CHRNA4 genes were examined. A significant association was found between two SNPs and physical effects reported after smoking the first experimental cigarette. SNP rs2072658 is upstream of CHRNB2 (P-value = 0.0046) and rs2229959 is a synonymous change in exon 5 of CHRNA4 (P value = 0.0051). We also examined possible functional relevance of SNP rs2072658 using an in vitro gene expression assay. These studies provided evidence that the minor allele of rs2072658 may lead to decreased gene expression, using two separate cell lines, P19 and SH-SY5Y (18% P < 0.001 and 26% P < 0.001 respectively). The human genetic study and functional assays suggest that variation in the promoter region of CHRNB2 gene may be important in mediating levels of expression of the β2 nicotinic receptor subunit, which may be associated with variation in subjective response to nicotine.

Why do young women smoke? VII COMT as a risk modifying gene for Nicotine dependence - role of gene-gene interaction, personality, and environmental factors

OBJECTIVES

Catechol-O-methyltransferase (COMT) may be a risk modifying gene for Nicotine dependence (ND) rather than a direct susceptibility gene for this phenotype. Brain nicotinic cholinergic receptors modulate dopaminergic transmission, and several variants within the neighboring CHRNA5-CHRNA3 genes have been associated with ND. Therefore, it is biologically reasonable to study the interactive contribution of COMT and the CHRNA5 and CHRNA3 genes to ND.

METHODS

Using a case-control sample of 90 young, Israeli, Jewish female smokers (FTND ≥ 4) and 108 controls (FTND = 0 during heaviest period of smoking), we studied association with ND of 8 COMT tagging SNPs, their interaction with tagging CHRNA5-A3 SNPs and the role of background, personality, and environmental factors.

RESULTS

None of the COMT SNPs were associated directly with ND. In pairwise interaction analysis of SNPs from the two loci (COMT SNP-CHRNA5-CHRNA3 SNP), the interaction of intronic COMT SNP, rs9332377, with CHRNA3 3'UTR SNP rs660652 was significantly associated with ND (p = 0.0005), withstanding correction for multiple testing.

CONCLUSION

Addition of the genetic interaction variable into a model of non-genetic ND predictors [parental smoking, novelty seeking (NS), and lifetime history of trauma], substantially increases the percentage of ND variance explained by the model, as well as the percentage of cases correctly identified by it.

Multiple cholinergic nicotinic receptor genes affect nicotine dependence risk in African and European Americans

Several independent studies show that the chromosome 15q25.1 region, which contains the CHRNA5-CHRNA3-CHRNB4 gene cluster, harbors variants strongly associated with nicotine dependence, other smoking behaviors, lung cancer and chronic obstructive pulmonary disease. We investigated whether variants in other cholinergic nicotinic receptor subunit (CHRN) genes affect the risk of nicotine dependence in a new sample of African Americans (AAs) (N = 710). We also analyzed this AA sample together with a European American (EA) sample (N = 2062, 1608 of which have been previously studied), allowing for differing effects in the two populations. Cases are current nicotine-dependent smokers and controls are non-dependent smokers. Variants in or near CHRND-CHRNG, CHRNA7 and CHRNA10 show modest association with nicotine dependence risk in the AA sample. In addition, CHRNA4, CHRNB3-CHRNA6 and CHRNB1 show association in at least one population. CHRNG and CHRNA4 harbor single nucleotide polymorphisms (SNPs) that have opposite directions of effect in the two populations. In each of the population samples, these loci substantially increase the trait variation explained, although no loci meet Bonferroni-corrected significance in the AA sample alone. The trait variation explained by three key associated SNPs in CHRNA5-CHRNA3-CHRNB4 is 1.9% in EAs and also 1.9% in AAs; this increases to 4.5% in EAs and 7.3% in AAs when we add six variants representing associations at other CHRN genes. Multiple nicotinic receptor subunit genes outside chromosome 15q25 are likely to be important in the biological processes and development of nicotine dependence, and some of these risks may be shared across diverse populations.

From smoking to lung cancer: the CHRNA5/A3/B4 connection

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that modulate key physiological processes ranging from neurotransmission to cancer signaling. These receptors are activated by the neurotransmitter, acetylcholine, and the tobacco alkaloid, nicotine. Recently, the gene cluster encoding the alpha3, alpha5 and beta4 nAChR subunits received heightened interest after a succession of linkage analyses and association studies identified multiple single-nucleotide polymorphisms in these genes that are associated with an increased risk for nicotine dependence and lung cancer. It is not clear whether the risk for lung cancer is direct or an effect of nicotine dependence, as evidence for both scenarios exist. In this study, we summarize the body of work implicating nAChRs in the pathogenesis of lung cancer, with special focus on the clustered nAChR subunits and their emerging role in this disease state.

A transcriptional regulatory element critical for CHRNB4 promoter activity in vivo

Genome-wide association studies have underscored the importance of the clustered neuronal nicotinic acetylcholine receptor (nAChR) subunit genes with respect to nicotine dependence as well as lung cancer susceptibility. CHRNB4, which encodes the nAChR β4 subunit, plays a major role in the molecular mechanisms that govern nicotine withdrawal. Thus, elucidating how expression of the β4 gene is regulated is critical for understanding the pathophysiology of nicotine addiction. We previously identified a CA box regulatory element, (5'-CCACCCCT-3') critical for β4 promoter activity in vitro. We further demonstrated that a 2.3-kb fragment of the β4 promoter region containing the 5'-CCACCCCT-3' regulatory element in the β4 gene promoter (CA box) is capable of directing cell-type specific expression of a reporter gene to a myriad of brain regions that endogenously express the β4 gene. To test the hypothesis that the CA box is critical for β4 promoter activity in vivo, transgenic animals expressing a mutant form of the β4 promoter were generated. Reporter gene expression was not detected in any tissue or cell type at embryonic day 18.5 (ED 18.5). Similarly, we observed drastically reduced reporter gene expression at postnatal day 30 (PD30) when compared to wild type (WT) transgenic animals. Finally, we demonstrated that CA box mutation results in decreased interaction of the transcription factor Sp1 with the mutant β4 promoter. Taken together these results demonstrate that the CA box is critical for β4 promoter activity in vivo.

Nicotine addiction and nicotinic receptors: lessons from genetically modified mice

The past decades have seen a revolution in our understanding of brain diseases and in particular of drug addiction. This has been largely due to the identification of neurotransmitter receptors and the development of animal models, which together have enabled the investigation of brain functions from the molecular to the cognitive level. Tobacco smoking, the principal - yet avoidable - cause of lung cancer is associated with nicotine addiction. Recent studies in mice involving deletion and replacement of nicotinic acetylcholine receptor subunits have begun to identify the molecular mechanisms underlying nicotine addiction and might offer new therapeutic strategies to treat this addiction.

The nicotinic acetylcholine receptor CHRNA5/A3/B4 gene cluster: dual role in nicotine addiction and lung cancer

More than 1 billion people around the world smoke, with 10 million cigarettes sold every minute. Cigarettes contain thousands of harmful chemicals including the psychoactive compound, nicotine. Nicotine addiction is initiated by the binding of nicotine to nicotinic acetylcholine receptors, ligand-gated cation channels activated by the endogenous neurotransmitter, acetylcholine. These receptors serve as prototypes for all ligand-gated ion channels and have been extensively studied in an attempt to elucidate their role in nicotine addiction. Many of these studies have focused on heteromeric nicotinic acetylcholine receptors containing α4 and β2 subunits and homomeric nicotinic acetylcholine receptors containing the α7 subunit, two of the most abundant subtypes expressed in the brain. Recently however, a series of linkage analyses, candidate-gene analyses and genome-wide association studies have brought attention to three other members of the nicotinic acetylcholine receptor family: the α5, α3 and β4 subunits. The genes encoding these subunits lie in a genomic cluster that contains variants associated with increased risk for several diseases including nicotine dependence and lung cancer. The underlying mechanisms for these associations have not yet been elucidated but decades of research on the nicotinic receptor gene family as well as emerging data provide insight on how these receptors may function in pathological states. Here, we review this body of work, focusing on the clustered nicotinic acetylcholine receptor genes and evaluating their role in nicotine addiction and lung cancer.

Nicotine: alcohol reward interactions

It is well established that the continued intake of drugs of abuse is reinforcing-that is repeated consumption increases preference. This has been shown in some studies to extend to other drugs of abuse; use of one increases preference for another. In particular, the present review deals with the interaction of nicotine and alcohol as it has been shown that smoking is a risk factor for alcoholism and alcohol use is a risk factor to become a smoker. The review discusses changes in the brain caused by chronic nicotine and chronic alcohol intake to approach the possible mechanisms by which one drug increases the preference for another. Chronic nicotine administration was shown to affect nicotine receptors in the brain, affecting not only receptor levels and distribution, but also receptor subunit composition, thus affecting affinity to nicotine. Other receptor systems are also affected among others catecholamine, glutamate, GABA levels and opiate and cannabinoid receptors. In addition to receptor systems and transmitters, there are endocrine, metabolic and neuropeptide changes as well induced by nicotine. Similarly chronic alcohol intake results in changes in the brain, in multiple receptors, transmitters and peptides as discussed in this overview and also illustrated in the tables. The changes are sex and age-dependent-some changes in males are different from those in females and in general adolescents are more sensitive to drug effects than adults. Although nicotine and alcohol interact-not all the changes induced by the combined intake of both are additive-some are opposing. These opposing effects include those on locomotion, acetylcholine metabolism, nicotine binding, opiate peptides, glutamate transporters and endocannabinoid content among others. The two compounds lower the negative withdrawal symptoms of each other which may contribute to the increase in preference, but the mechanism by which preference increases-most likely consists of multiple components that are not clear at the present time. As the details of induced changes of nicotine and alcohol differ, it is likely that the mechanisms of increasing nicotine preference may not be identical to that of increasing alcohol preference. Stimulation of preference of yet other drugs may again be different -representing one aspect of drug specificity of reward mechanisms.