Case-control study of the D2 dopamine receptor gene and smoking status in lung cancer patients

"Genetic influences impacting nicotine use and abuse during adolescence: insights from human and rodent studies"

Nicotine use continues to be a major public health concern, with an alarming recent rise in electronic cigarette consumption. Heritability estimates of nicotine use and abuse range from 40-80%, providing strong evidence that genetic factors impact nicotine addiction-relevant phenotypes. Although nicotine use during adolescence is a key factor in the development of addiction, it remains unclear how genetic factors impact adolescent nicotine use and abuse. This review will discuss studies investigating genetic factors impacting nicotine use during adolescence. Evidence from both rodent and human studies will be summarized and integrated when possible. Human adolescent studies have largely included candidate gene studies for genes identified in adult populations, such as genes involved in nicotine metabolism, nicotinic acetylcholine receptor signaling, dopaminergic signaling, and other neurotransmitter signaling systems. Alternatively, rodent studies have largely taken a discovery-based approach identifying strain differences in adolescent nicotine addiction-relevant behaviors. Here, we aim to answer the following three questions by integrating human and rodent findings: 1) Are there genetic variants that uniquely impact nicotine use during adolescence? 2) Are there genetic variants that impact both adolescent and adult nicotine use? and 3) Do genetic factors in adolescence significantly impact long-term consequences of adolescent nicotine use? Determining answers for these three questions will be critical for the development of preventative measures and treatments for adolescent nicotine use and addiction.

Trace Amines and Their Receptors

Trace amines are endogenous compounds classically regarded as comprising β-phenylethyalmine, p-tyramine, tryptamine, p-octopamine, and some of their metabolites. They are also abundant in common foodstuffs and can be produced and degraded by the constitutive microbiota. The ability to use trace amines has arisen at least twice during evolution, with distinct receptor families present in invertebrates and vertebrates. The term "trace amine" was coined to reflect the low tissue levels in mammals; however, invertebrates have relatively high levels where they function like mammalian adrenergic systems, involved in "fight-or-flight" responses. Vertebrates express a family of receptors termed trace amine-associated receptors (TAARs). Humans possess six functional isoforms (TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9), whereas some fish species express over 100. With the exception of TAAR1, TAARs are expressed in olfactory epithelium neurons, where they detect diverse ethological signals including predators, spoiled food, migratory cues, and pheromones. Outside the olfactory system, TAAR1 is the most thoroughly studied and has both central and peripheral roles. In the brain, TAAR1 acts as a rheostat of dopaminergic, glutamatergic, and serotonergic neurotransmission and has been identified as a novel therapeutic target for schizophrenia, depression, and addiction. In the periphery, TAAR1 regulates nutrient-induced hormone secretion, suggesting its potential as a novel therapeutic target for diabetes and obesity. TAAR1 may also regulate immune responses by regulating leukocyte differentiation and activation. This article provides a comprehensive review of the current state of knowledge of the evolution, physiologic functions, pharmacology, molecular mechanisms, and therapeutic potential of trace amines and their receptors in vertebrates and invertebrates.

The dopamine D2 receptor mediates approach-avoidance tendencies in smokers

Dopamine D2 receptors (DRD2) have been strongly implicated in reward processing of natural stimuli and drugs. Using the approach-avoidance task (AAT), we recently demonstrated that smokers show an increased approach-bias toward smoking-related cues but not toward naturally rewarding stimuli. Here, we examined the contribution of the DRD2 Taq1B polymorphism to smokers' and non-smokers' responsivity toward smoking versus naturally rewarding stimuli in the AAT. Smokers carrying the minor B1 allele of the DRD2 Taq1B polymorphism showed reduced approach behavior for food-related pictures compared to non-smokers with the same allele. In the group of smokers, a higher approach-bias toward smoking-related compared to food-related pictures was found in carriers of the B1 allele. This pattern was not evident in smokers homozygous for the B2 allele. In addition, smokers with the B1 allele reported fewer attempts to quit smoking relative to smokers homozygous for the B2 allele. This is the first study demonstrating that behavioral shifts in response to smoking relative to natural rewards in smokers are mediated by the DRD2 Taq1B polymorphism. Our results indicate a reduced natural-reward brain reactivity in smokers with a genetically determined decrease in dopaminergic activity (i.e., reduction of DRD2 availability). It remains to be determined whether this pattern might be related to a different outcome after psychological cessation interventions, i.e., AAT modification paradigms, in smokers.

Transcriptomics and methylomics in chronic periodontitis with tobacco use: a pilot study

Background

Accumulating evidence suggests that tobacco smoking affects the susceptibility to and severity of chronic periodontitis. Epigenetics may explain the role of smoking in the development and progress of periodontal disease. In this study, we performed transcriptomic and methylomic analyses of non-periodontitis and periodontitis-affected gingival tissues according to smoking status.

Methods

Human gingival tissues were obtained from 20 patients, including non-smokers with and without periodontitis (n = 5 per group) and smokers with and without periodontitis (n = 5 per group). Total RNA and genomic DNA were isolated, and their quality was validated according to strict standards. The Illumina NextSeq500 sequencing system was used to generate transcriptome and methylome datasets.

Results

Comprehensive analysis, including between-group correlation, differential gene expression, DNA methylation, gene set enrichment, and protein-protein interaction, indicated that smoking may change the transcription and methylation states of extracellular matrix (ECM) organization-related genes, which exacerbated the periodontal condition.

Conclusions

Our results suggest that smoking-related changes in DNA methylation patterns and subsequent alterations in the expression of genes coding for ECM components may be causally related to the increased susceptibility to periodontitis in smokers as they could influence ECM organization, which in turn may have an effect on disease characteristics.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-017-0381-z) contains supplementary material, which is available to authorized users.

Evaluation of a Novel Difficulty of Smoking Cessation Phenotype Based on Number of Quit Attempts

Background

Numerous studies have sought to identify genes that influence the ability to quit smoking, but none found any that are consistently associated with smoking cessation.

Methods

We developed a novel difficulty of quitting smoking phenotype based on the extremes of the number of quit attempts needed to achieve successful abstinence: Easy quitters were defined as having achieved long-term (>1 year) abstinence after their first quit attempt and difficult quitters as having reported 10 or more quit attempts. We conducted a two-stage study to determine if this phenotype could be useful for identifying single nucleotide polymorphisms (SNPs) that influence smoking cessation. In stage 1, 82 SNPs in 26 genes involved in nicotine signaling and metabolism were genotyped in 1357 easy quitters and 1321 difficult quitters from Cancer Prevention Study 3 (CPS-3). In stage 2, the 11 SNPs associated with difficult quitting in stage 1 (p < .1) were genotyped in an independent sample of 1300 easy quitters and 1299 difficult quitters from CPS-3.

Results

Three of 11 SNPs (HTR1B rs6298, NR4A2 rs834829, and CYP2A65 rs8192729) were significantly associated with the difficult quitting phenotype in stage 2 (p < .05). In addition, a polygenic risk score based on the 11 SNPs identified in stage 1 was significantly associated with the difficult quitting phenotype in stage 2 (odds ratio = 1.08, 95% confidence interval: 1.03-1.14 per quintile, p trend = 4.5×10-3).

Conclusions

Using a novel difficulty of quitting phenotype, three gene variants and a polygenic risk score based on 11 SNPs were found to be significantly associated with smoking cessation.

Implications

Our results provide evidence that a difficulty of quitting smoking phenotype based on the extremes of number of quit attempts could be a useful tool for identifying genetic variants that influence difficulty of smoking cessation. Knowledge of these genetic variants will indicate biological pathways that could be targeted for the development of novel smoking cessation aids and could be used to determine which smokers are most likely to benefit from such smoking cessation aids.

The significant association of Taq1A genotypes in DRD2/ANKK1 with smoking cessation in a large-scale meta-analysis of Caucasian populations

Although a number of studies have analyzed the relation between the DRD2/ANKK1 gene Taq1A polymorphism and smoking cessation, the results remain controversial. The primary objective of the present study was to determine whether this variant indeed has any effect on smoking cessation. The A1-dominant model that considers A1/* (*=A1 or A2) and A2/A2 as two genotypes and compares their frequencies in current and former smokers was applied. A total of 22 studies with 11,075 subjects were included in the meta-analyses. Considering the potential influence of between-study heterogeneity, we conducted stratified meta-analyses with the Comprehensive Meta-Analysis statistical software (version 2.0). Results based on either cross-sectional or longitudinal studies consistently showed a statistically significant association between Taq1A A1/* genotypes and smoking cessation. Further, a more significant association of the variant with smoking cessation was detected when both types of studies were combined. However, there was marginal evidence of heterogeneity among studies (I(2)=33.9%; P=0.06). By excluding other ethnicities and subjects with cancer, the meta-analysis on the basis of 9487 Caucasians demonstrated that Taq1A A1/* genotypes indeed were significantly associated with smoking cessation under both the fixed- and random-effects models (pooled OR 1.22; 95% CI 1.11-1.34; P=3.9 × 10(-5) for both models). No evidence of between-study heterogeneity or publication bias was observed. Thus, we conclude that the polymorphism of Taq1A has an important role in the process of abstaining from smoking, and smokers carrying A2/A2 genotype have a higher likelihood of smoking cessation than those who carry A1/A1 or A1/A2.

Molecular Genetic Testing in Pain and Addiction: Facts, Fiction and Clinical Utility

The Brain Reward Cascade (BRC) is an interaction of neurotransmitters and their respective genes to control the amount of dopamine released within the brain. Any variations within this pathway, whether genetic or environmental (epigenetic), may result in addictive behaviors as well as altered pain tolerance. While there are many studies claiming a genetic association with addiction and other behavioral infractions, defined as Reward Deficiency Syndrome (RDS), not all are scientifically accurate and in some case just wrong. Albeit our bias, we discuss herein the facts and fictions behind molecular genetic testing in RDS (including pain and addiction) and the significance behind the development of the Genetic Addiction Risk Score (GARSPREDX™), the first test to accurately predict one's genetic risk for RDS.

A review of pharmacogenetic studies of substance-related disorders

BACKGROUND

Substance-related disorders (SRDs) are a major cause of morbidity and mortality worldwide. Family, twin, and adoption studies have demonstrated the substantial heritability of SRDs. To determine the impact of genetic variation on risk for SRD and the response to treatment, researchers have conducted a number of secondary data analyses and quasi-experimental studies that target one or more candidate gene variants.

METHODS

This review examines studies in which candidate polymorphisms were examined as mediator variables to identify pharmacogenetic effects on subjective responses to drug administration or cues or outcomes of medication trials for SRDs. Efforts to use a meta-analytic approach to quantify these effects are premature because the number of available studies using similar methods and outcomes is limited, so the present review is qualitative.

RESULTS

Findings from these studies provide preliminary evidence of clinically relevant pharmacogenetic effects. However, independent replication of these findings has been sparse.

CONCLUSIONS

Although this growing body of literature has produced conflicting results, improved statistical controls may help to clarify the findings. Additionally, the use of empirically derived sub-phenotypes (i.e., which serve to differentiate distinct groups of affected individuals) may also help to identify genetic mediators of pharmacologic response in relation to SRDs. The identification of genetic mediators can inform clinical care both by identifying risk factors for SRDs and predicting adverse events and therapeutic outcomes associated with specific pharmacotherapies.

Effects of Interaction Between Dopamine D2 Receptor and Monoamine Oxidase A Genes on Smoking Status in Young Men

Although the effect of gene-gene interaction on nicotine-dopamine metabolism for smoking behavior has been reported, polymorphisms of dopamine D2 receptor (DRD2) and monoamine oxidase A (MAOA) have not been simultaneously examined among smokers. In this study, 481 young Taiwanese men completed a self-report questionnaire on smoking status, and data were obtained on polymorphisms of DRD2 rs1800497, DRD2 rs1079597, MAOA rs309850, and MAOA rs1137070, urinary nicotine, and urinary cotinine. In a comparison of 261 current smokers and 220 never smokers, odds ratios (ORs) for the development of smoking in all genotypes were not statistically significant. Among smokers with DRD2 rs1079597 GG//MAOA rs309850 3-repeat, the OR of heavier smoking was 2.67 times higher (95% confidence interval [CI]: [1.08, 6.59], p = .031) and the score on the Fagerstrom test for nicotine dependence was higher (4.26 vs. 2.83) than in those with DRD2 rs1079597 AA//MAOA rs309850 3-repeat. Adjusted urinary cotinine concentration was significantly different between those two groups (median value: 95.83 ng/μl vs. 133.24 ng/μl, respectively, p = .045). These findings suggest that the interaction of DRD2 rs1079597 and MAOA rs309850 3-repeat affects smoking intensity in young Taiwanese men.

Molecular Genetic Testing in Reward Deficiency Syndrome (RDS): Facts and Fiction

Background

The Brain Reward Cascade (BRC) is an interaction of neurotransmitters and their respective genes to control the amount of dopamine released within the brain. Any variations within this pathway, whether genetic or environmental (epigenetic), may result in addictive behaviors or RDS, which was coined to define addictive behaviors and their genetic components.

Methods

To carry out this review we searched a number of important databases including: Filtered: Cochrane Systematic reviews; DARE; Pubmed Central Clinical Quaries; National Guideline Clearinghouse and unfiltered resources: PsychINFO; ACP PIER; PsychSage; Pubmed/Medline. The major search terms included: dopamine agonist therapy for Addiction; dopamine agonist therapy for Reward dependence; dopamine antagonistic therapy for addiction; dopamine antagonistic therapy for reward dependence and neurogenetics of RDS.

Results

While there are many studies claiming a genetic association with RDS behavior, not all are scientifically accurate.

Conclusion

Albeit our bias, this Clinical Pearl discusses the facts and fictions behind molecular genetic testing in RDS and the significance behind the development of the Genetic Addiction Risk Score (GARS_PREDX™), the first test to accurately predict one’s genetic risk for RDS.

Updated findings of the association and functional studies of DRD2/ANKK1 variants with addictions

Both nicotine and alcohol addictions are severe public health hazards worldwide. Various twin and family studies have demonstrated that genetic factors contribute to vulnerability to these addictions; however, the susceptibility genes and the variants underlying them remain largely unknown. Of susceptibility genes investigated for addictions, DRD2 has received much attention. Considering new evidence supporting the association of DRD2 and its adjacent gene ankyrin repeat and kinase domain containing 1 (ANKK1) with various addictions, in this paper, we provide an updated view of the involvement of variants in DRD2 and ANKK1 in the etiology of nicotine dependence (ND) and alcohol dependence (AD) based on linkage, association, and molecular studies. This evidence shows that both genes are significantly associated with addictions; however the association with ANKK1 appears to be stronger. Thus, both more replication studies in independent samples and functional studies of some of these variants are warranted.

Association of dopamine receptor D2 TaqI A polymorphism and cannabis use disorder in Lagos, Nigeria

TaqI A polymorphism (rs1800497) has been linked to many substance use disorders but there is a shortage of data on cannabis use disorder. Nigeria has a huge burden of cannabis use disorder, prompting our investigation of the relation between cannabis use disorder and the TaqI A polymorphism among males in Lagos, Nigeria. We recruited 106 males with cannabis use disorder based on International Classification of Diseases, version 10 (ICD-10) and 98 cannabis-naive males for the study. Cannabis use disorder was assessed using the Severity of Dependence Scale (SDS) and Cannabis Use Disorder Identification Test (CUDIT). Genotyping was done using the Restriction Fragment Length Polymorphism (RFLP). The frequency of the A1 allele was higher among the cannabis users (57.8%) compared with the nonusers (42.2%). The genotype distribution was found to be in Hardy-Weinberg equilibrium in both populations. The homozygous A1 genotype alone contributed 11.8% to the variance in the SDS scores. However, both A1/A1 and A1/A2 genotypes contributed to the variance in the CUDIT scores (10.2% and 5.1%, respectively). In conclusion, the distribution of the A1 allele among the general population in this study correlates with the previously reported findings in a southwestern Nigerian population. We also found that carrying an A1 allele appears to be a significant predictor of cannabis use disorder. The result suggests that carrying just a single allele of the A1 is enough to predict cannabis abuse, as shown by the allele association with CUDIT scores. However, double A1 alleles seem to be necessary for the prediction of dependence.

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.

Multivariate analysis of dopaminergic gene variants as risk factors of heroin dependence

BACKGROUND

Heroin dependence is a debilitating psychiatric disorder with complex inheritance. Since the dopaminergic system has a key role in rewarding mechanism of the brain, which is directly or indirectly targeted by most drugs of abuse, we focus on the effects and interactions among dopaminergic gene variants.

OBJECTIVE

To study the potential association between allelic variants of dopamine D2 receptor (DRD2), ANKK1 (ankyrin repeat and kinase domain containing 1), dopamine D4 receptor (DRD4), catechol-O-methyl transferase (COMT) and dopamine transporter (SLC6A3) genes and heroin dependence in Hungarian patients.

METHODS

303 heroin dependent subjects and 555 healthy controls were genotyped for 7 single nucleotide polymorphisms (SNPs) rs4680 of the COMT gene; rs1079597 and rs1800498 of the DRD2 gene; rs1800497 of the ANKK1 gene; rs1800955, rs936462 and rs747302 of the DRD4 gene. Four variable number of tandem repeats (VNTRs) were also genotyped: 120 bp duplication and 48 bp VNTR in exon 3 of DRD4 and 40 bp VNTR and intron 8 VNTR of SLC6A3. We also perform a multivariate analysis of associations using Bayesian networks in Bayesian multilevel analysis (BN-BMLA).

FINDINGS AND CONCLUSIONS

In single marker analysis the TaqIA (rs1800497) and TaqIB (rs1079597) variants were associated with heroin dependence. Moreover, -521 C/T SNP (rs1800955) of the DRD4 gene showed nominal association with a possible protective effect of the C allele. After applying the Bonferroni correction TaqIB was still significant suggesting that the minor (A) allele of the TaqIB SNP is a risk component in the genetic background of heroin dependence. The findings of the additional multiple marker analysis are consistent with the results of the single marker analysis, but this method was able to reveal an indirect effect of a promoter polymorphism (rs936462) of the DRD4 gene and this effect is mediated through the -521 C/T (rs1800955) polymorphism in the promoter.

The Impact of Cigarette Quitting during Pregnancy on Other Prenatal Health Behaviors

Several economic studies have evaluated the effects of cigarette smoking and quitting on other health behaviors such as alcohol use and weight gain. However, there is little research that evaluates the effects of cigarette quitting during pregnancy on other health behaviors such as caloric intake, alcohol consumption, multivitamin use, and caffeine intake. In this paper, we evaluate these effects and employ a genetic variant that predicts cigarette quitting to aid in identification. We find some evidence that cigarette quitting during pregnancy may increase multivitamin use and caloric intake and reduce caffeine consumption.

Effects of nicotine on emotional distraction of attentional orienting: evidence of possible moderation by dopamine type 2 receptor genotype

INTRODUCTION

Growing evidence suggests that attentional bias to, and distraction by, emotional stimuli may moderate affective states and motivation for nicotine and other drug use.

METHODS

The present study assessed the effects of nicotine and dopamine receptor genotype on distraction by emotional pictures, during a modified spatial attention task, in 46 overnight-deprived smokers.

RESULTS

Relative to placebo, 14mg nicotine patch produced shorter overall reaction times (RTs) and individuals with two dopamine type 2 receptor (DRD2) A2 alleles exhibited the greatest RT benefit from nicotine following emotionally negative pictures after the longest cue-target delay (800ms), but benefitted least from nicotine following positive pictures after the shortest delay (400ms). In contrast, at the shortest delay, A1 carriers did not benefit from nicotine following emotionally negative pictures but did following positive ones.

CONCLUSIONS

These genetic differences in the effects of nicotine on attention immediately following emotionally positive versus negative stimuli may reflect differential excitatory and inhibitory transmitter processes related to approach (reward) and avoidance (punishment) sensitivities of dopamine-related neural networks that support positive and negative affect.

A prospective study of the effects of the DRD2/ANKK1 TaqIA polymorphism and impulsivity on smoking initiation

This study tested whether DRD2/ANKK1 TaqIA genotype predicted smoking initiation and subsequent use, and effects were mediated by sensation seeking and negative urgency. Between 2009 and 2012, college never smokers (n = 387) completed six assessments over 15 months; those who reported smoking were classified as initiators. Logistic regression indicated that the A1 allele was associated with initiation (p = .003). This effect was partially mediated by sensation seeking and negative urgency. Effects were stronger in Asian Americans. Findings have implications for improving prevention by including elements focused on urges to seek positive or negative reinforcement. Limitations and future directions are discussed.

Exploring the relationships between tobacco smoking and schizophrenia in first-degree relatives

Up to 90% of individuals with schizophrenia suffer from nicotine dependence. Both schizophrenia and nicotine consumption have strong genetic components, which may overlap. The relationship between schizophrenia and nicotine dependence remains unclear, due in part to confounding factors. Studies of the relationship between nicotine consumption and milder schizophrenia-related phenotypes, such as schizotypy, in first-degree relatives of individuals with schizophrenia could help to better understand the relationship between smoking and schizophrenia while avoiding such confounders. We assessed the proportion of smokers, their level of nicotine dependence and their level of schizotypy in a sample of 98 first-degree relatives of schizophrenic subjects and 110 healthy controls. Partial correlation analysis was used to assess the relationship between schizotypal dimensions and smoking dependence. The prevalence of smoking and nicotine dependence levels were higher in the relatives than in the healthy control group. We found no relationship between nicotine dependence and the magnitude of schizotypal features in either group. Our results support the hypothesis that the relationship between schizophrenia and smoking is largely mediated by common familial factors, which may be genetic.

The TaqIA RFLP is associated with attenuated intervention-induced body weight loss and increased carbohydrate intake in post-menopausal obese women

INTRODUCTION

Polymorphisms of the dopamine receptor D2 (DRD2) gene have been associated with obesity phenotypes. Our aim was to examine if the genotype of TaqIA Restriction Fragment Length Polymorphism (RFPL) was related to an attenuated weight loss response or to changes in energy expenditure (EE) and food preference before and after weight loss. methods: Obese post-menopausal women (age=57.1 ± 4.6 yr, weight=85.4 ± 15.4 kg and BMI=32.8 ± 4.5 kg/m(2)) were genotyped for TaqIA (n=127) by using PCR-RFLP analysis and categorized as possessing at least one copy of the A1 allele (A1(+)) or no copy (A1(-)). Women were randomized into two groups, caloric restriction (CR) and caloric restriction+resistance training (CRRT) and in this study were further classified as follows: A1(+)CR, A1(+)CRRT, A1-(-)CR and (-)A1(-)CRRT. Body composition, total daily EE, physical activity EE, Resting EE (REE), and energy intake were obtained at baseline and post-intervention using DXA, doubly-labeled water, indirect calorimetry, and 3-day dietary records, respectively.

RESULTS

Overall, all of the anthropometric variables and REE significantly decreased post-intervention (p<0.001). Women in the CRRT group lost significantly more fat mass (FM) than the CR women (p<0.05). There were significant time by group by allele interactions for attenuated body weight (BW), BMI, and FM loss for A1(+) (vs. A1(-)) in CRRT (p<0.05) and for increased % carbohydrate intake (p<0.01).

CONCLUSION

TaqIA genotype was associated with body weight loss post-intervention; more specifically, carriers of the A1 allele lost significantly less BW and FM than the A1(-) and had increased carbohydrate intake in the CRRT group.

Tobacco-specific nitrosamine exposures in smokers and nonsmokers exposed to cigarette or waterpipe tobacco smoke

INTRODUCTION

The causal relationship between tobacco smoking and a variety of cancers is attributable to the carcinogens that smokers inhale, including tobacco-specific nitrosamines (TSNAs). We aimed to assess the exposure to TSNAs in waterpipe smokers (WPS), cigarette smokers (CS), and nonsmoking females exposed to tobacco smoke.

METHODS

We measured 2 metabolites, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronides (NNAl-Gluc) in the urine of males who were either current CS or WPS, and their wives exposed to either cigarette or waterpipe smoke in a sample of 46 subjects from rural Egypt.

RESULTS

Of the 24 current male smokers, 54.2% were exclusive CS and 45.8% were exclusive WPS. Among wives, 59.1% reported exposure to cigarette smoke and 40.9% to waterpipe smoke. The geometric mean of urinary NNAL was 0.19 ± 0.60 pmol/ml urine (range 0.005-2.58) in the total sample. Significantly higher levels of NNAL were observed among male smokers of either cigarettes or waterpipe (0.89 ± 0.53 pmol/ml, range 0.78-2.58 in CS and 0.21-1.71 in WPS) compared with nonsmoking wives (0.04 ± 0.18 pmol/ml, range 0.01-0.60 in CS wives, 0.05-0.23 in WPS wives, p = .000). Among males, CS had significantly higher levels of NNAL compared with WPS (1.22 vs. 0.62; p = .007). However, no significant difference was detected in NNAL levels between wives exposed to cigarette smoke or waterpipe smoke.

CONCLUSIONS

Cigarette smokers levels of NNAL were higher than WPS levels in males. Exposure to tobacco smoke was evident in wives of both CS and WPS. Among WPS, NNAL tended to increase with increasing numbers of hagars smoked/day.

Smoking and body weight: evidence using genetic instruments

Several studies have evaluated whether the high and rising obesity rates over the past three decades may be due to the declining smoking rates. There is mixed evidence across studies - some find negative smoking effects and positive cigarette cost effects on body weight, while others find opposite effects. This study applies a unique approach to identify the smoking effects on body weight and to evaluate the heterogeneity in these effects across the body mass index (BMI) distribution by utilizing genetic instruments for smoking. Using a data sample of 1057 mothers from Norway, the study finds heterogeneous effects of cigarette smoking on BMI - smoking increases BMI at low/moderate BMI levels and decreases BMI at high BMI levels. The study highlights the potential advantages and challenges of employing genetic instrumental variables to identify behavior effects including the importance of qualifying the instruments and the need for large samples.

Generational association studies of dopaminergic genes in reward deficiency syndrome (RDS) subjects: selecting appropriate phenotypes for reward dependence behaviors

Abnormal behaviors involving dopaminergic gene polymorphisms often reflect an insufficiency of usual feelings of satisfaction, or Reward Deficiency Syndrome (RDS). RDS results from a dysfunction in the "brain reward cascade," a complex interaction among neurotransmitters (primarily dopaminergic and opioidergic). Individuals with a family history of alcoholism or other addictions may be born with a deficiency in the ability to produce or use these neurotransmitters. Exposure to prolonged periods of stress and alcohol or other substances also can lead to a corruption of the brain reward cascade function. We evaluated the potential association of four variants of dopaminergic candidate genes in RDS (dopamine D1 receptor gene [DRD1]; dopamine D2 receptor gene [DRD2]; dopamine transporter gene [DAT1]; dopamine beta-hydroxylase gene [DBH]).

METHODOLOGY

We genotyped an experimental group of 55 subjects derived from up to five generations of two independent multiple-affected families compared to rigorously screened control subjects (e.g., N = 30 super controls for DRD2 gene polymorphisms). Data related to RDS behaviors were collected on these subjects plus 13 deceased family members.

RESULTS

Among the genotyped family members, the DRD2 Taq1 and the DAT1 10/10 alleles were significantly (at least p < 0.015) more often found in the RDS families vs. controls. The TaqA1 allele occurred in 100% of Family A individuals (N = 32) and 47.8% of Family B subjects (11 of 23). No significant differences were found between the experimental and control positive rates for the other variants.

CONCLUSIONS

Although our sample size was limited, and linkage analysis is necessary, the results support the putative role of dopaminergic polymorphisms in RDS behaviors. This study shows the importance of a nonspecific RDS phenotype and informs an understanding of how evaluating single subset behaviors of RDS may lead to spurious results. Utilization of a nonspecific "reward" phenotype may be a paradigm shift in future association and linkage studies involving dopaminergic polymorphisms and other neurotransmitter gene candidates.

Can the chronic administration of the combination of buprenorphine and naloxone block dopaminergic activity causing anti-reward and relapse potential?

Opiate addiction is associated with many adverse health and social harms, fatal overdose, infectious disease transmission, elevated health care costs, public disorder, and crime. Although community-based addiction treatment programs continue to reduce the harms of opiate addiction with narcotic substitution therapy such as methadone maintenance, there remains a need to find a substance that not only blocks opiate-type receptors (mu, delta, etc.) but also provides agonistic activity; hence, the impetus arose for the development of a combination of narcotic antagonism and mu receptor agonist therapy. After three decades of extensive research, the federal Drug Abuse Treatment Act 2000 (DATA) opened a window of opportunity for patients with addiction disorders by providing increased access to options for treatment. DATA allows physicians who complete a brief specialty-training course to become certified to prescribe buprenorphine and buprenorphine/naloxone (Subutex, Suboxone) for treatment of patients with opioid dependence. Clinical studies indicate that buprenorphine maintenance is as effective as methadone maintenance in retaining patients in substance abuse treatment and in reducing illicit opioid use. With that stated, we must consider the long-term benefits or potential toxicity attributed to Subutex or Suboxone. We describe a mechanism whereby chronic blockade of opiate receptors, in spite of only partial opiate agonist action, may ultimately block dopaminergic activity causing anti-reward and relapse potential. While the direct comparison is not as yet available, toxicity to buprenorphine can be found in the scientific literature. In considering our cautionary note in this commentary, we are cognizant that, to date, this is what we have available, and until such a time when the real magic bullet is discovered, we will have to endure. However, more than anything else this commentary should at least encourage the development of thoughtful new strategies to target the specific brain regions responsible for relapse prevention.

GENES AS INSTRUMENTS FOR STUDYING RISK BEHAVIOR EFFECTS: AN APPLICATION TO MATERNAL SMOKING AND OROFACIAL CLEFTS

This study uses instrumental variable (IV) models with genetic instruments to assess the effects of maternal smoking on the child's risk of orofacial clefts (OFC), a common birth defect. The study uses genotypic variants in neurotransmitter and detoxification genes relateded to smoking as instruments for cigarette smoking before and during pregnancy. Conditional maximum likelihood and two-stage IV probit models are used to estimate the IV model. The data are from a population-level sample of affected and unaffected children in Norway. The selected genetic instruments generally fit the IV assumptions but may be considered "weak" in predicting cigarette smoking. We find that smoking before and during pregnancy increases OFC risk substantially under the IV model (by about 4-5 times at the sample average smoking rate). This effect is greater than that found with classical analytic models. This may be because the usual models are not able to consider self-selection into smoking based on unobserved confounders, or it may to some degree reflect limitations of the instruments. Inference based on weak-instrument robust confidence bounds is consistent with standard inference. Genetic instruments may provide a valuable approach to estimate the "causal" effects of risk behaviors with genetic-predisposing factors (such as smoking) on health and socioeconomic outcomes.

Dopamine polymorphisms and depressive symptoms predict foods intake. Results from a nationally representative sample

Depression and variation in dopamine related genes have both independently been associated with food consumption. Depressive symptoms could synergistically interact with genetic variation to influence food intake. We examined the interaction between high depressive symptoms and functional polymorphisms of dopamine transporter (SLC6A3), monoamine oxidase A (MAOA), dopamine receptor D2 (DRD2) and dopamine receptor D4 (DRD4) on intake of high-calorie sweet, high-calorie non-sweet, and low-calorie foods in the National Longitudinal Study of Adolescent Health (Add Health). Multivariate linear regression analyses were used to examine main effects of gene and depression symptoms and their interaction (genotype-by-high depression symptoms) on food categories. Applying a false discovery rate criterion for multiple comparisons indicated a statistically significant interaction for females with high depressive symptoms and the SLC6A3 gene, such that those with the SLC6A3 10/10 allele reported greater intake of high-calorie sweet foods than their counterparts high in depressive symptoms with the SLC6A3 any 9 allele (LS mean 10/10 allele=2.5, SE=.13; LS mean any 9 allele=1.8, SE=.13, p<.05). These findings highlight that the relationship between depression and food intake may vary as a function of genetic polymorphism. Further research is needed to confirm these findings.

Tridimensional personalities and polymorphism of dopamine D2 receptor among heroin addicts

BACKGROUND

Drug addiction is a multifactorial disorder. Researchers have posited that an individual's inherited behavioral propensity or temperament contributes to the disorder by shaping a personality strongly linked with the risk of drug abuse. Further, they hypothesize that the polymorphism of dopamine D2 receptor increases the susceptibility to and severity of addiction. We, therefore, investigated possible associations between dopamine D2 receptor (DRD2) and personality traits among intravenous heroin addicts.

METHODS

We assessed 93 intravenous heroin addicts and controls using Diagnostic and Statistical Manual, Fourth Edition (DSM-IV) and the Tridimensional Personality Questionnaire (TPQ). We confirmed drug-dependence status using a questionnaire based on DSM-IV criteria. We extracted DNA from the subjects' whole blood and genotyped it for DRD2 allelic variants.

RESULTS

Genotype analysis showed a significantly higher frequency for the TaqIA polymorphism among the addicts (69.9%) compared to control subjects (42.6%; Fisher's exact χ(2), p < .05). We observed no significant differences for other variants between the addicts and controls. The addicts had higher scores for novelty seeking (NS) and harm avoidance (HA) personality traits but lower scores for reward dependence (RD) when compared to control subjects.

LIMITATION

The environmental cues are different for the addicts, and the healthy university students we used as controls. We recommend that researchers employ a gene-environment interaction approach to study factors associated with addictive behaviors in future studies.

CONCLUSION

Taq1A may be implicated for an increased vulnerability to addiction. Screening of this marker might be useful for identifying individuals at risk of addiction.

Population-based case-control study of DRD2 gene polymorphisms and alcoholism

Several independent lines of evidence for genetic contributions to vulnerability to alcoholism exist. Dopamine is thought to play a major role in the mechanism of reward and reinforcement in response to alcohol. D2 dopamine receptor (DRD2) gene has been among the stronger candidate genes implicated in alcoholism. In this study, alcohol use was assessed in 196 randomly selected Kota individuals of Nilgiri Hills, South India. Six DRD2 SNPs were assessed in 81 individuals with alcoholism and 151 controls to evaluate the association between single nucleotide polymorphisms (SNPs) and alcoholism. Of the three models (dominant, recessive, and additive) tested for association between alcoholism and DRD2 SNPs, only the additive model shows association for three loci (rs1116313, TaqID, and rs2734835). Of six studied polymorphisms, five are in strong linkage disequilibrium forming onesingle haplotype block. Though the global haplotype analysis with these five SNPs was not significant, haplotype analysis using all six SNPs yielded a global P value of .033, even after adjusting for age. These findings support the importance of dopamine receptor gene polymorphisms in alcoholism. Further studies to replicate these findings in different populations are needed to confirm these results.

Genetic variation in three candidate genes and nicotine dependence, withdrawal and smoking cessation in hospitalized patients

AIMS

This study evaluates the relationship of six polymorphisms found in the CHRNA3, DRD2 and COMT genes with nicotine dependence, the ability to quit smoking and the occurrence of withdrawal symptoms after short-term use of nicotine patch in hospitalized patients.

MATERIALS & METHODS

The study included 233 participants from a double-blind, placebo-controlled trial of nicotine patch substitution with a 6-month follow-up period. Nicotine dependence was assessed by the Fagerström Test for Nicotine Dependence (FTND) questionnaire, withdrawal symptoms by the Minnesota Nicotine Withdrawal Scale questionnaire and smoking cessation by self-reported abstinence at 1 week, 1 month and 6 months after treatment.

RESULTS

After correcting for multiple testing, three polymorphisms in the DRD2 gene (Taq1A, Taq1B and Pro319Pro) were significantly associated with nicotine dependence (p = 0.018, p = 0.048 and p = 0.006, respectively). Using a cutoff point for the FTND score, the CHRNA3 Tyr215Tyr (rs1051730) polymorphism was also associated with nicotine dependence (p = 0.037 and p = 0.074 after correction for multiple testing). No association of any of the studied polymorphisms was observed with either smoking cessation or the occurrence of withdrawal symptoms.

CONCLUSION

This study confirms the reported association of the CHRNA3 locus with nicotine dependence and shows the involvement of two independent DRD2 polymorphisms in nicotine dependence.

Brief communication: Allelic and haplotypic structure at the DRD2 locus among five North Indian caste populations

The dopamine D2 receptor (DRD2) gene, with its known human-specific derived alleles that can facilitate haplotype reconstruction, presents an important locus for anthropological studies. The three sites (TaqIA, TaqIB, and TaqID) of the DRD2 gene are widely studied in various world populations. However, no work has been previously published on DRD2 gene polymorphisms among North Indian populations. Thus, the present study attempts to understand the genetic structure of North Indian upper caste populations using the allele and haplotype frequencies and distribution patterns of the three TaqI sites of the DRD2 gene. Two hundred forty-six blood samples were collected from five upper caste populations of Himachal Pradesh (Brahmin, Rajput and Jat) and Delhi (Aggarwal and Sindhi), and analysis was performed using standard protocols. All three sites were found to be polymorphic in all five of the studied populations. Uniform allele frequency distribution patterns, low heterozygosity values, the sharing of five common haplotypes, and the absence of two of the eight possible haplotypes observed in this study suggest a genetic proximity among the selected populations. The results also indicate a major genetic contribution from Eurasia to North Indian upper castes, apart from the common genetic unity of Indian populations. The study also demonstrates a greater genetic inflow among North Indian caste populations than is observed among South Indian caste and tribal populations.

Orexin and leptin are associated with nicotine craving: a link between smoking, appetite and reward

OBJECTIVE

Preclinical data suggest modulating effects of both orexin/hypocretin and leptin on dopaminergic transmission in mesolimbic reward pathways. This indicates a possible role of both peptides in reward function and motivation, and thus in addictive diseases. The aim of this study was to examine the possible association between orexin and leptin, and nicotine craving in smokers in a clinical case-control study under standardized conditions.

METHODS

We compared orexin and leptin, ACTH and cortisol plasma concentrations (RIA) between tobacco smokers (n=60) during early nicotine withdrawal and healthy controls (n=64). Motivational aspects of nicotine craving were additionally assessed in the smoking participants using the Questionnaire of Smoking Urges (QSU).

RESULTS

As main results we detected a significant negative correlation between orexin plasma concentration and nicotine craving (r=-0.28; p<.05), and a positive association between craving and leptin plasma concentration (r=0.29; p<.05).

CONCLUSIONS

Our results show an association between craving for nicotine and plasma concentrations of orexin and leptin suggesting that both peptides interfere with the dopaminergic transmission during nicotine withdrawal in a bidirectional manner and, thus, modulate craving for nicotine.

Pharmacogenetics of drug dependence: role of gene variations in susceptibility and treatment

Drug dependency is a highly prevalent mental health disorder that imposes a significant burden on those directly affected, health care systems, and society in general. There is substantial heritability in the susceptibility to drug addiction, which indicates that there are genetic risk factors. Variation in the human genome is abundant and can directly affect drug dependency phenotypes, for example, by altering the function of a gene product or by altering gene expression. Pharmacogenetic studies can assess the effects of genetic variation on the risk for a particular phenotype (e.g., being an alcoholic). In addition, pharmacogenetic variability in treatment efficacy and adverse reactions can be investigated to identify particular genetic variants associated with altered responses. This review highlights examples of genetic variations that are important in the development and maintenance of specific drug dependencies as well as those that affect the response to treatment.

Genetic diagnostics of functional variants of the human dopamine D2 receptor gene

INTRODUCTION

The importance of dopamine D2 receptors (DRD2) for central nervous dopaminergic signalling makes variants in the DRD2 gene potential modulators of the risk or course of various behavioural, psychiatric or neurologic diseases (e.g. addiction, schizophrenia, Parkinson's disease). We developed Pyrosequencing genetic screening assays for single nucleotide polymorphisms spanning the whole range of the DRD2 gene locus up to the functionally related ankyrin repeat and kinase domain containing 1 gene (ANKK1) located at approximately 10 kb downstream of DRD2.

METHODS

Assays for 11 genetic variants with reported functional association were developed in DNA samples from 300 unrelated healthy Caucasians and validated by independent conventional sequencing.

RESULTS

In all DNA samples the DRD2/ANKK1 genetic variants were identified correctly as verified by the control samples. The observed frequencies of homozygous, heterozygous and noncarriers of the minor alleles were in agreement with the Hardy-Weinberg equilibrium. Observed minor allele frequencies were DRD2 rs12364283T>C: 6.5%, rs1799978A>G: 4.8%, rs1799732C del: 14.2%, rs4648317C>T: 12.8%, rs1079597G>A: 13.8%, rs1076560G>T: 14.5%, rs1800496C>T: 0.2%, rs1801028C>G: 3.0%, rs6275C>T: 32.7%, rs6277C>T: 53.0% and ANKK1 rs1800497C>T: 17.5%.

CONCLUSION

The presently developed Pyrosequencing assays are provided to facilitate further research toward personalized approaches to pathophysiological conditions involving behavioural, psychiatric and neurologic disorders including addiction, schizophrenia and Parkinson's disease.

Common and unique biological pathways associated with smoking initiation/progression, nicotine dependence, and smoking cessation

Twin and family studies reveal a significant genetic contribution to the risk of smoking initiation and progression (SI/P), nicotine dependence (ND), and smoking cessation (SC). Further, numerous genes have been implicated in these smoking-related behaviors, especially for ND. However, no study has presented a comprehensive and systematic view of the genetic factors associated with these important smoking-related phenotypes. By reviewing the literature on these behaviors, we identified 16, 99, and 75 genes that have been associated with SI/P, ND, and SC, respectively. We then determined whether these genes were enriched in pathways important in the neuronal and brain functions underlying addiction. We identified 9, 21, and 13 pathways enriched in the genes associated with SI/P, ND, and SC, respectively. Among these pathways, four were common to all of the three phenotypes, that is, calcium signaling, cAMP-mediated signaling, dopamine receptor signaling, and G-protein-coupled receptor signaling. Further, we found that serotonin receptor signaling and tryptophan metabolism pathways were shared by SI/P and ND, tight junction signaling pathway was shared by SI/P and SC, and gap junction, neurotrophin/TRK signaling, synaptic long-term potentiation, and tyrosine metabolism were shared between ND and SC. Together, these findings show significant genetic overlap among these three related phenotypes. Although identification of susceptibility genes for smoking-related behaviors is still in an early stage, the approach used in this study has the potential to overcome the hurdles caused by factors such as genetic heterogeneity and small sample size, and thus should yield greater insights into the genetic mechanisms underlying these complex phenotypes.

The D2 dopamine receptor gene and nicotine dependence among bladder cancer patients and controls

Multiple twin, family, and genetic studies have rendered substantial evidence supporting an association between hereditary factors and smoking initiation and maintenance. To investigate further the relationships between the DRD2 genotypes, cigarette use and nicotine dependence, we examined the prevalence of polymorphisms in the TaqIA (A1 and A2) and the TaqIB (B1 and B2) alleles among a series of 608 non-Hispanic White bladder cancer patients and 608 matched controls. Among ever-smoking controls, A1 and B1 genotypes exhibited a greater smoking intensity and were significantly younger at the age of initiation than A2A2 or B2B2 genotypes (two-sided P < 0.05). Among former smoking cases, persons with the A1 genotypes exhibited significantly higher mean pack-years and years of smoking, and were younger at the age of initiation than were persons with the A2A2 genotype (two-sided P < 0.05). Additionally, current smokers with the A1 genotypes reported fewer quit attempts than those with the A2A2 genotype (two-sided P < 0.01). The present study suggests that the DRD2 alleles A1 and B1 confer greater vulnerability to tobacco use.

Influences of polymorphic variants of DRD2 and SLC6A3 genes, and their combinations on smoking in Polish population

BACKGROUND

Polymorphisms in dopaminergic genes may influence cigarette smoking by their potential impact on dopamine reward pathway function. A1 allele of DRD2 gene is associated with a reduced dopamine D2 receptor density, and it has been hypothesised that A1 carriers are more vulnerable to smoking. In turn, the 9-repeat allele of dopamine transporter gene (SLC6A3) has been associated with a substantial reduction in dopamine transporter, what might result in the higher level of dopamine in the synaptic cleft, and thereby protective role of this allele from smoking. In the present study we investigated whether polymorphic variants of DRD2 and SLC6A3 genes and their combinations are associated with the smoking habit in the Polish population.

METHODS

Genotyping for TaqIA polymorphism of DRD2 and SLC6A3 VNTR polymorphism was performed in 150 ever-smokers and 158 never-smokers. The association between the smoking status and smoking phenotypes (related to the number of cigarettes smoked daily and age of starting regular smoking), and genotype/genotype combinations was expressed by ORs together with 95% CI. Alpha level of 0.05, with Bonferroni correction whenever appropriate, was used for statistical significance.

RESULTS

At the used alpha levels no association between DRD2 and SLC6A3 genotypes and smoking status was found. However, A1 allele carriers reported longer abstinence periods on quitting attempts than non-carriers (p = 0.049). The ORs for heavier smoking were 0.38 (0.17-0.88), p = 0.023, and 0.39 (0.17-0.88), p = 0.021 in carriers compared to non-carriers of A1 or *9 allele, respectively, and the OR for this smoking phenotype was 8.68 (2.47-30.46), p = 0.0005 for the A1-/9- genotype combination, relatively to the A1+/9+. Carriers of *9 allele of SLC6A3 had over twice a lower risk to start smoking before the age of 20 years compared to non-carriers (sex-adjusted OR = 0.44; 95% CI: 0.22-0.89; p = 0.0017), and subjects with A1-/9- genotype combination had a higher risk for staring regular smoking before the age of 20 years in comparison to subjects with A1+/9+ genotype combination (sex-adjusted OR = 3.79; 95% CI:1.03-13.90; p = 0.003).

CONCLUSION

Polymorphic variants of DRD2 and SLC6A3 genes may influence some aspects of the smoking behavior, including age of starting regular smoking, the level of cigarette consumption, and periods of abstinence. Further large sample studies are needed to verify this hypothesis.

Nicotine dependence: biology, behavior, and treatment

Despite great advances in the understanding and treatment of nicotine dependence, close to 21% of adults in the United States continue to smoke. Tobacco use is the single greatest cause of premature and preventable death in the United States. This article reviews the epidemiology, assessment, neurobiology, genetic etiology, and treatment of nicotine dependence. Enhanced understanding of these dimensions of nicotine dependence may help to advance progress toward lowering the prevalence rate of tobacco use in the U.S. and lowering the rate of tobacco-related morbidity and mortality.

Neurotransmission-related genetic polymorphisms, negative affectivity traits, and gender predict tobacco abstinence symptoms across 44 days with and without nicotine patch

Genetic and personality trait moderators of tobacco abstinence-symptom trajectories were assessed in a highly controlled study. Based on evidence suggesting their importance in stress reactivity and smoking, moderators studied were serotonin transporter gene (5-HTTLPR) and dopamine D2 receptor gene (DRD2) polymorphisms and personality traits related to negative affect (NA). Smokers were randomly assigned to quit smoking with nicotine or placebo patches. Financial incentives resulted in 80% verified abstinence across the 44-day study. Individuals with 1 or 2 short alleles of 5-HTTLPR (S carriers) experienced larger increases in NA symptoms than did those without a short allele. Nicotine replacement therapy (NRT) alleviated anxiety only in S carriers. NRT reduced NA to a greater extent in DRD2 A1 carriers than in A2A2 individuals during the 1st 2 weeks of treatment (when on the 21-mg patch); however, A1 carriers experienced a renewal of NA symptoms when switched to the 7-mg patch and when off the patch, while A2A2 individuals continued to benefit from NRT. The results suggest that the effects of genotype and treatment may vary across different durations of abstinence, treatment doses, and genotypes.

Cancer prevention: from 1727 to milestones of the past 100 years

The rich, multidisciplinary history of cancer prevention recounted here begins with surgical and workplace recommendations of the 1700s and ends with 2009 results of the enormous (35,535 men) Selenium and Vitamin E [prostate] Cancer Prevention Trial (SELECT). This history comprises a fascinating array of chemopreventive, vaccine, surgical, and behavioral science research, both preclinical and clinical. Preclinical milestones of cancer prevention include the 1913 and 1916 mouse studies by Lathrop and Loeb of cancer development associated with pregnancy or cancer prevention through castration (oophorectomy), preventing chemically induced mouse carcinogenesis as early as 1929, energy restriction studies in the 1940s, the 1950s discoveries and later molecular characterizations of field cancerization and multistep carcinogenesis, and the effects of angiogenesis inhibition in genetically engineered mice reported in 2009. The extraordinary panoply of clinical research includes numerous large and smaller chemoprevention studies of nutritional supplements, other dietary approaches, a Bacillus Calmette-Guérin trial in 1976, molecular-targeted agents, and agents to prevent infection-related cancers such as hepatitis B virus vaccine to prevent liver cancer in 1984. Clinical surgical prevention includes removal of intraepithelial neoplasia detected by screening (including Pap testing developed in 1929 and culposcopy for cervical premalignancy and colonoscopy and polypectomy to prevent colorectal cancer begun in the 1960s) and prophylactic surgeries, such as in Lynch syndrome patients begun in 1977. Behavioral studies include smoking cessation and control beginning in the 1950s, obesity control rooted in studies of 1841, and genetic-counseling and cancer-survivorship studies. This history of pioneering events may help in better understanding who we are and what we want to achieve as cancer prevention researchers and practitioners.

Interactions between genotype and depressive symptoms on obesity

Depression and Genetic variation in serotonin and monoamine transmission have both been associated with body mass index (BMI), but their interaction effects are not well understood. We examined the interaction between depressive symptoms and functional polymorphisms of serotonin transporter (SLC6A4) and monoamine oxidase A (MAOA) on categories of BMI. Participants were from the National Longitudinal Study of Adolescent Health. Multiple logistic regression was used to investigate interactions between candidate genes and depression on risk of obesity (BMI > or = 30) or overweight + obese combined (BMI > or = 25). Males with an MAOA active allele with high depressive symptoms were at decreased risk of obesity (OR 0.22; 95% CI 0.06-0.78) and overweight + obesity (OR 0.48; 95% CI 0.26-0.89). No similar effect was observed among females. These findings highlight that the obesity-depression relationship may vary as a function of gender and genetic polymorphism, and suggest the need for further study.

The impact of genetic variation in DRD2 and SLC6A3 on smoking cessation in a cohort of participants 1 year after enrollment in a lung cancer screening study

Smoking cessation strategies continue to have disappointing results. By determining the interindividual genetic differences that influence smoking behaviors, we may be able to develop tailored strategies that increase the likelihood of successful cessation. This study attempts to determine genetic influences on the relationship between the dopamine pathway and smoking cessation by examining associations with a variable number tandem repeat variation in SLC6A3 and the DRD2 variants TaqIA (A2 vs. A1), TaqIB (B2 vs. B1), C957T (C vs. T), and -141C Ins/Del (C vs. Del). Baseline smokers in the Pittsburgh Lung Screening Study who provided information on smoking status 1 year later were evaluated. We frequency-matched those who were not abstinent at 1 year to those who were abstinent at 1 year by gender, decade of age, and time of enrollment (3-month intervals) in a 3:1 ratio (N = 881). Logistic regression was used to identify the effect of genotype on abstinence at 1 year. In a model containing the matching variables and other genotypes, DRD2 TaqIA was significantly associated with being abstinent at 1 year (P = 0.01). Compared to participants who were homozygous for the TaqIA major allele (A2A2), participants who carried at least one minor allele (A1) were less likely to quit (Odds Ratio: 0.47, 95% CI: 0.24-0.94). The other dopamine receptor genotypes and the SLC6A3 genotype were not associated with smoking status at 1 year. The association between DRD2 TaqIA and smoking cessation supports the hypothesis that genetic variation in the dopamine pathway influences smoking cessation.

Genetics of dopamine receptors and drug addiction: a comprehensive review

Drug dependence is a chronic, relapsing disorder in which compulsive drug-seeking and drug-taking behaviours persist despite serious negative consequences. Addictive substances, such as opioids, ethanol, psychostimulants and nicotine, induce pleasant states or relieve distress, effects that contribute to their recreational use. Dopamine is critically involved in drug addiction processes. However, the role of the various dopaminergic receptor subtypes has been difficult to delineate. Here, we will review the information collected implicating the receptors of the D1 family (DRD1 and DRD5) and of the D2 family (DRD2, DRD3 and DRD4) in drug addiction. We will summarize the distribution of these receptors in the brain, the preclinical experiments carried out with pharmacological and transgenic approaches and the genetic studies carried out linking genetic variants of these receptors to drug addiction phenotypes. A meta-analysis of the studies carried out evaluating DRD2 and alcohol dependence is also provided, which indicates a significant association. Overall, this review indicates that different aspects of the addiction phenotype are critically influenced by dopaminergic receptors and that variants of those genes seem to influence some addiction phenotypes in humans.

5HTT polymorphisms are associated with job stress in Japanese workers

Recently, the number of workers who suffer from job stress was increasing in Japan because of a prolonged recession, increasing number of elderly workers, and structural reorganization of companies. On the other hand, polymorphism associated with depression or alcoholism was detected. Relationship between job stress and these polymorphisms were investigated. Brief job stress questionnaire was assessed for 243 employees who worked at a manufacturing company and a local hospital in Japan (mean age 40.8 years). Alcohol consumption and smoking habit were assessed as lifestyle factors. DNA samples were prepared to detect polymorphisms of 5HTT, aldehyde dehydrogenase 2 (ALDH2), D2 dopamine receptor (DRD2), and cytochrome p450 2A6 (CYP2A6) genes. The level of depressed mood by job stress was significantly higher among carriers of two short alleles of the 5HTT regulatory region compared with carriers of one or two long alleles (Mann-Whitney U, p<0.05). In a logistic regression analysis, the s/s allele of the 5HTT had a tendency to be a risk of depressed mood. When subjects had high supervisor's support, depressed mood was significantly lower irrespective of 5HTT polymorphism. Job stress may elicit biological responses that contribute to depressed mood in relation to 5HTT polymorphism.

Association of the DRD2 gene Taq1A polymorphism and smoking behavior: a meta-analysis and new data

INTRODUCTION

Many studies have investigated the association of the dopamine type-2 receptor (DRD2) Taq1A polymorphism with tobacco use and cigarette smoking behaviors, but findings remain equivocal. There is a biological basis for considering that this association differs by sex, and differences in subpopulations might explain some of the contradictory evidence.

METHODS

Our a priori hypothesis was that the association of the DRD2 Taq1A polymorphism with smoking behavior would be more prominent in females than males. We therefore investigated the strength of evidence for an association between the DRD2 Taq1A polymorphism and smoking behavior in a large sample of females and used meta-analytic techniques to synthesize existing published data and explore the role of sex in explaining any heterogeneity between studies.

RESULTS

We did not observe any strong evidence of association between the DRD2 Taq1A polymorphism and smoking behavior, including smoking initiation, smoking persistence, and smoking rate, either in our female sample or in our meta-analysis of 29 studies, comprising 28 published studies and the data from the present study. Metaregression suggested an association between the proportion of male participants in a study and the individual study effect size, indicating a larger effect size with a greater proportion of male participants for smoking initiation and smoking persistence. This effect did not appear to be due to the inclusion of the data from the present study.

DISCUSSION

Available evidence does not support an association between the DRD2 Taq1A polymorphism and smoking behavior. Contrary to our a priori hypothesis, we found evidence of a stronger association in males than in females.

Gene-environment interactions across development: Exploring DRD2 genotype and prenatal smoking effects on self-regulation

Genetic factors dynamically interact with both pre- and postnatal environmental influences to shape development. Considerable attention has been devoted to gene-environment interactions (G x E) on important outcomes (A. Caspi & T. E. Moffitt, 2006). It is also important to consider the possibility that these G x E effects may vary across development, particularly for constructs like self-regulation that emerge slowly, depend on brain regions that change qualitatively in different developmental periods, and thus may be manifested differently. To illustrate one approach to exploring such developmental patterns, the relation between variation in the TaqIA polymorphism, related to D2 dopamine receptor expression and availability, and prenatal exposure to tobacco was examined in two exploratory studies. First, in 4-week-old neonates, genotype-exposure interactions were observed for attention and irritable reactivity, but not for stress dysregulation. Second, in preschool children, genotype was related to Preschool Trail Making Test (K. A. Espy and M. F. Cwik, 2004) task performance on conditions requiring executive control; children with both the A1+ genotype and a history of prenatal tobacco exposure displayed disproportionately poor performance. Despite study limitations, these results illustrate the importance of examining the interplay between genetic and prenatal environmental factors across development.

Multiple genetic tests for susceptibility to smoking do not outperform simple family history

AIMS

To evaluate the utility of using predictive genetic screening of the population for susceptibility to smoking.

METHODS

The results of meta-analyses of genetic association studies of smoking behaviour were used to create simulated data sets using Monte Carlo methods. The ability of the genetic tests to screen for smoking was assessed using receiver operator characteristic curve analysis. The result was compared to prediction using simple family history information. To identify the circumstances in which predictive genetic testing would potentially justify screening we simulated tests using larger numbers of alleles (10, 15 and 20) that varied in prevalence from 10 to 50% and in strength of association [relative risks (RRs) of 1.2-2.1].

RESULTS

A test based on the RRs and prevalence of five susceptibility alleles derived from meta-analyses of genetic association studies of smoking performed similarly to chance and no better than the prediction based on simple family history. Increasing the number of alleles from five to 20 improved the predictive ability of genetic screening only modestly when using genes with the effect sizes reported to date.

CONCLUSIONS

This panel of genetic tests would be unsuitable for population screening. This situation is unlikely to be improved upon by screening based on more genetic tests. Given the similarity with associations found for other polygenic conditions, our results also suggest that using multiple genes to screen the general population for genetic susceptibility to polygenic disorders will be of limited utility.

Activation instead of blocking mesolimbic dopaminergic reward circuitry is a preferred modality in the long term treatment of reward deficiency syndrome (RDS): a commentary

Background and hypothesis

Based on neurochemical and genetic evidence, we suggest that both prevention and treatment of multiple addictions, such as dependence to alcohol, nicotine and glucose, should involve a biphasic approach. Thus, acute treatment should consist of preferential blocking of postsynaptic Nucleus Accumbens (NAc) dopamine receptors (D1-D5), whereas long term activation of the mesolimbic dopaminergic system should involve activation and/or release of Dopamine (DA) at the NAc site. Failure to do so will result in abnormal mood, behavior and potential suicide ideation. Individuals possessing a paucity of serotonergic and/or dopaminergic receptors, and an increased rate of synaptic DA catabolism due to high catabolic genotype of the COMT gene, are predisposed to self-medicating any substance or behavior that will activate DA release, including alcohol, opiates, psychostimulants, nicotine, gambling, sex, and even excessive internet gaming. Acute utilization of these substances and/or stimulatory behaviors induces a feeling of well being. Unfortunately, sustained and prolonged abuse leads to a toxic" pseudo feeling" of well being resulting in tolerance and disease or discomfort. Thus, a reduced number of DA receptors, due to carrying the DRD2 A1 allelic genotype, results in excessive craving behavior; whereas a normal or sufficient amount of DA receptors results in low craving behavior. In terms of preventing substance abuse, one goal would be to induce a proliferation of DA D2 receptors in genetically prone individuals. While in vivo experiments using a typical D2 receptor agonist induce down regulation, experiments in vitro have shown that constant stimulation of the DA receptor system via a known D2 agonist results in significant proliferation of D2 receptors in spite of genetic antecedents. In essence, D2 receptor stimulation signals negative feedback mechanisms in the mesolimbic system to induce mRNA expression causing proliferation of D2 receptors.

Proposal and conclusion

The authors propose that D2 receptor stimulation can be accomplished via the use of Synapatmine™, a natural but therapeutic nutraceutical formulation that potentially induces DA release, causing the same induction of D2-directed mRNA and thus proliferation of D2 receptors in the human. This proliferation of D2 receptors in turn will induce the attenuation of craving behavior. In fact as mentioned earlier, this model has been proven in research showing DNA-directed compensatory overexpression (a form of gene therapy) of the DRD2 receptors, resulting in a significant reduction in alcohol craving behavior in alcohol preferring rodents. Utilizing natural dopaminergic repletion therapy to promote long term dopaminergic activation will ultimately lead to a common, safe and effective modality to treat Reward Deficiency Syndrome (RDS) behaviors including Substance Use Disorders (SUD), Attention Deficit Hyperactivity Disorder (ADHD), Obesity and other reward deficient aberrant behaviors. This concept is further supported by the more comprehensive understanding of the role of dopamine in the NAc as a "wanting" messenger in the meso-limbic DA system.