Despite the tremendous public health and financial burden of cigarette smoking, relatively little is understood about brain mechanisms that subserve smoking behavior. This study investigated the effect of lifetime regular smoking on brain processing in a reward guessing task using functional magnetic resonance imaging (fMRI) and a cotwin-control study design in monozygotic (MZ) twin pairs that maximally controls for genetic and family background factors. Young adult (24–34 years) MZ female twin pairs (n=15 pairs), discordant for regular smoking defined using Centers for Disease Control (CDC) criteria as having smoked ≥100 cigarettes lifetime were recruited from an ongoing genetic epidemiological longitudinal study of substance use and psychopathology. We applied hypothesis-driven region of interest and whole brain analyses to investigate the effect of regular smoking on reward processing. Reduced response to reward and punishment in regular compared to never-regular smokers was seen in hypothesis-driven region of interest analysis of bilateral ventral striatum. Whole brain analysis identified bilateral reward-processing regions that showed activation differences in response to winning or losing money but no effect of regular smoking; and frontal/parietal regions, predominantly in the right hemisphere, that showed robust effect of regular smoking but no effect of winning or losing money. Altogether, using a study design that maximally controls for group differences, we found that regular smoking had modest effects on striatal reward processing regions but robust effects on cognitive control/attentional systems.
cigarette smoking; cotwin-control; fMRI
To investigate the relative contribution of genetic and environmental factors on smoking trajectory membership and to test whether individual smoking trajectories represent phenotypic thresholds of increasing genetic risk along a common genetic liability dimension.
Prospective study of a birth cohort of female like-sex twin pairs.
Participants completed diagnostic interview surveys 4 times from adolescence (average age 16) through young adulthood (average age 25).
Female twins who had smoked ≥100 cigarettes lifetime (n=1466 regular smokers).
Number of cigarettes smoked per day during the heaviest period of smoking (2 waves) or during the past 12 months (2 waves).
A 4-trajectory class solution provided the best fit to cigarette consumption data and was characterized by Low (n=564, 38.47%), Moderate (n=366, 24.97%), and High level smokers (n=197, 13.44%), and smokers who increased their smoking from adolescence to young adulthood (n=339, 23.12%). The best genetic model fit was a 3-category model that comprised the Low, a combined Increasing + Moderate, and High trajectories. This trajectory categorization was heritable (72.7%) with no evidence for significant contribution from shared environmental factors.
The way that smoking patterns develop in adolescence has a high level of heritability.
smoking trajectories; twins; heritability
This study investigated the role of genetic and environmental influences on individual differences in brain volumes measured at two time points in normal elderly males from the National Heart, Lung, and Blood Institute Twin Study. The MRI scans were conducted four years apart on 33 monozygotic and 33 dizygotic male twin pairs, aged 68 to 77 years when first scanned. Volumetric measures of total brain and total cerebrospinal fluid were significantly heritable at baseline (over 70%). For both volumes genetic influences at follow-up were entirely accounted for by genetic influences at baseline, suggesting that the same genetic factors influence variability in brain volume at each time of assessment. Variability in 4-year volume change was due to shared and individual-specific environmental influences. There was little evidence for heritable influences on change measures. These results suggest that variation in longitudinal change of some brain volume measures may have different underlying genetic and environmental architecture from variation in repeat cross-sectional measures, which could have implications for intervention strategies for age-related illness associated with brain morphology. The results of this study are discussed in the context of the small sample size and associated limitations of statistical power.
twins; volumetric MRI; longitudinal; aging
Susceptibility to cigarette smoking in tobacco-naive youth is a strong predictor of smoking initiation. Identifying mechanisms that contribute to smoking susceptibility provide information about early targets for smoking prevention. This study investigated whether sensitivity to secondhand smoke exposure (SHSe) contributes to smoking susceptibility.
PARTICIPANTS AND METHODS:
Subjects were high-risk, ethnically diverse 8- to 13-year-old subjects who never smoked and who lived with at least 1 smoker and who participated in a longitudinal SHSe reduction intervention trial. Reactions (eg, feeling dizzy) to SHSe were assessed at baseline, and smoking susceptibility was assessed at baseline and 3 follow-up measurements over 12 months. We examined the SHSe reaction factor structure, association with demographic characteristics, and prediction of longitudinal smoking susceptibility status.
Factor analysis identified “physically unpleasant” and “pleasant” reaction factors. Reported SHSe reactions did not differ across gender or family smoking history. More black preteens reported feeling relaxed and calm, and fewer reported feeling a head rush or buzz compared with non-Hispanic white and Hispanic white counterparts. Longitudinally, 8.5% of subjects tracked along the trajectory for high (versus low) smoking susceptibility. Reporting SHSe as “unpleasant or gross” predicted a 78% reduction in the probability of being assigned to the high–smoking susceptibility trajectory (odds ratio: 0.22 [95% confidence interval: 0.05–0.95]), after covariate adjustment.
Assessment of SHSe sensitivity is a novel approach to the study of cigarette initiation etiology and informs prevention interventions.
secondhand smoke; sensitivity; smoking susceptibility; trajectories; preteens
Hubs integrate and distribute information in powerful ways due to the number and positioning of their contacts in a network. Several resting state functional connectivity MRI reports have implicated regions of the default mode system as brain hubs; we demonstrate that previous degree-based approaches to hub identification may have identified portions of large brain systems rather than critical nodes of brain networks. We utilize two methods to identify hub-like brain regions: 1) finding network nodes that participate in multiple sub-networks of the brain, and 2) finding spatial locations where several systems are represented within a small volume. These methods converge on a distributed set of regions that differ from previous reports on hubs. This work identifies regions that support multiple systems, leading to spatially constrained predictions about brain function that may be tested in terms of lesions, evoked responses, and dynamic patterns of activity.
To investigate the sensitivity to secondhand smoke exposure (SHSe) in preteens age 8 to 13 who have never smoked, and to determine whether SHSe sensitivity predicts smoking susceptibility.
We assessed sensitivity to SHSe using reactions commonly used for assessment of sensitivity to the first smoked cigarette (e.g., feeling dizzy), and investigated the factor structure of these reactions for the purpose of data reduction. We examined the association of each reaction measure and summary score with demographic characteristics and with smoking susceptibility, using logistic regression and ordinal logistic regression.
One factor was identified that captured physical/unpleasant reactions. Older preteens and preteens with more highly educated parents reported fewer reactions to SHSe. More African American preteens reported feeling relaxed or calm compared to all other racial/ethnic groups. Experiencing physical/unpleasant reactions to SHSe predicted lower risk for smoking susceptibility.
This was the first study to extend analytical methodology for sensitivity to active smoking to sensitivity to SHSe in youth who have never smoked. Results suggest a desensitization process with age and lower sensitivity to some reactions in preteens from more highly educated households. Preteens who have more aversive experience s with SHSe tend to be less susceptible to smoking than those who experience fewer aversive reactions. Assessment of sensitivity to SHSe is a novel approach to the study of cigarette use etiology and may contribute to better prediction of smoking initiation.
preteens; secondhand smoke; reactions; sensitivity; smoking susceptibility
Less is known about the effects of secondhand smoke (SHS) on mental health as compared with other medical disorders.
The aims of this study were to examine the following: 1) the association of SHS exposure with childhood attention-deficit/hyperactivity (ADHD) and disruptive disorders; and 2) the association of maternal recall of a child’s SHS exposure and that child’s exposure as measured by bioassay.
Sixty children had their saliva collected and assayed for cotinine when they were 4 years old and again when they were 6 years old. Phone interview data were collected to assess maternal recall of the children’s exposure to SHS at these ages. The children were assessed annually for ADHD and disruptive disorders. Repeated measures analysis of exposure level by child characteristics was performed.
Greater ADHD and conduct disorder severity scores were associated with greater child smoke exposure (ADHD severity, P = .043; conduct disorder severity, P = .035). A large proportion of mothers reported that their children had no exposure to SHS, despite high levels of measured cotinine in the children’s saliva.
An association between SHS exposure and ADHD and conduct disorder symptoms was found. Children and parents may benefit from parent education regarding the deleterious effects of SHS.
secondhand smoke; attention-deficit/hyperactivity disorder; disruptive; preschool; parenting
nicotine metabolism; glucuronidation; twins; heritability
Retrospectively collected data about the development and maintenance of behaviors that impact health are a valuable source of information. Establishing the reliability of retrospective measures is a necessary step in determining the utility of that methodology and in studying behaviors in the context of risk and protective factors.
The goal of this study was to examine the reliability of self-report of a specific health-affecting behavior, tobacco use, and its associated risk and protective factors as examined with a Web-based questionnaire.
Core tobacco use and risk behavior questions in the Lifetime Tobacco Use Questionnaire—a closed, invitation-only, password-controlled, Web-based instrument—were administered at a 2-month test-retest interval to a convenience sample of 1229 respondents aged 18 to 78 years. Tobacco use items, which covered cigarettes, cigars, smokeless tobacco, and pipe tobacco, included frequency of use, amount used, first use, and a pack-years calculation. Risk-related questions included family history of tobacco use, secondhand smoke exposure, alcohol use, and religiosity.
Analyses of test-retest reliability indicated modest (.30 to .49), moderate (.50 to .69), or high (.70 to 1.00) reliability across nearly all questions, with minimal reliability differences in analyses by sex, age, and income grouping. Most measures of tobacco use history showed moderate to high reliability, particularly for age of first use, age of first weekly and first daily smoking, and age at first or only quit attempt. Some measures of family tobacco use history, secondhand smoke exposure, alcohol use, and religiosity also had high test-retest reliability. Reliability was modest for subjective response to first use.
The findings reflect the stability of retrospective recall of tobacco use and risk factor self-report responses in a Web-questionnaire context. Questions that are designed and tested with psychometric scrutiny can yield reliable results in a Web setting.
Tobacco smokers; retrospective studies; psychometrics
Nicotine dependence is substantially heritable. Several regions across the genome have been implicated in containing genes that confer liability to nicotine dependence and variation in individual genes has been associated with nicotine dependence. Smoking cessation measures are also heritable, and measured genetic variation is associated with nicotine dependence treatment efficacy. Despite significant strides in the understanding of the relative contribution of genetic and environmental factors to nicotine dependence and treatment, emergent challenges necessitate interdisciplinary coordinated effort for effective problem solving. These challenges include refinement of the nicotine dependence phenotype, better understanding of the dynamic interplay between genes and environment in nicotine dependence etiology, application and development of molecular and statistical methodology that can adequately address vast amounts of data, and continuous translational cross-talk.
phenotype refinement; genes; environment; comorbidity; pharmacogenetics; transdisciplinary
The objective of this study was to determine whether race/ethnicity was associated with time to smoking initiation and time from first cigarette to onset of DSM-IV nicotine dependence (ND) after adjusting for familial and individual psychosocial risk factors.
Cox proportional hazards models with time-dependent covariates were used to analyze data from 1376 offspring aged 12–33 years from 532 families at high risk for substance use problems due to paternal alcohol problems and 235 low risk families. Fifty-six percent of the sample self-identified as African-American (AA) and 44% were mainly of European descent.
Controlling for covariates, AAs began smoking at older ages (HR=0.58; 95% CI: 0.48–0.70) and had longer times between smoking initiation and onset of ND compared to non-AAs (HR=0.25, 95% CI: 0.16–0.39 for ND onset occurring <18 years and HR=0.49, 95% CI: 0.30–0.80 for ND onsets ≥ age 18). After additionally controlling for number of cigarettes smoked daily, the racial/ethnic effects for onset of ND were attenuated, but remained statistically significant for ND onset <18 (HR=0.34, 95% CI: 0.19–0.61); however, the estimate was no longer significant for later ND onset (HR=0.84, 95% CI: 0.50–1.41).
AA adolescents and young adults initiate smoking at older ages and have longer transition periods between initiation and onset of ND compared to non-AAs, even after controlling for many relevant psychiatric and psychosocial covariates; however, racial/ethnic differences in time to onset of nicotine dependence in late adolescence and young adulthood may be explained by differences in daily quantity smoked.
smoking initiation; nicotine dependence; racial/ethnic differences
We utilized a cohort of 828 treatment seeking self-identified white cigarette smokers (50% female) to rank candidate gene single nucleotide polymorphisms (SNPs) associated with the Fagerström Test for Nicotine Dependence (FTND), a measure of nicotine dependence which assesses quantity of cigarettes smoked and time- and place-dependent characteristics of the respondent’s smoking behavior. 1123 SNPs at 55 autosomal candidate genes, nicotinic acetylcholine receptors and genes involved in dopaminergic function, were tested for association to baseline FTND scores adjusted for age, depression, education, sex and study site. SNP P values were adjusted for the number of transmission models, the number of SNPs tested per candidate gene, and their intragenic correlation. DRD2, SLC6A3 and NR4A2 SNPs with adjusted P values < 0.10 were considered sufficiently noteworthy to justify further genetic, bioinformatic and literature analyses. Each independent signal among the top-ranked SNPs accounted for ~1% of the FTND variance in this sample. The DRD2 SNP appears to represent a novel association with nicotine dependence. The SLC6A3 SNPs have previously been shown to be associated with SLC6A3 transcription or dopamine transporter density in vitro, in vivo and ex vivo. Analysis of SLC6A3 and NR4A2 SNPs identified a statistically significant gene-gene interaction (P=0.001), consistent with in vitro evidence that the NR4A2 protein product (NURR1) regulates SLC6A3 transcription. A community cohort of N=175 multiplex ever smoking pedigrees (N=423 ever smokers) provided nominal evidence for association with the FTND at these top ranked SNPs, uncorrected for multiple comparisons.
dopamine transporter; Fagerström Test for Nicotine Dependence; single nucleotide polymorphism; candidate gene association scan; gene-gene interaction
Motivational models of alcohol use propose that the motivation to consume alcohol is the final common pathway to its use. Both alcohol consumption and drinking motives are influenced by latent genetic factors that partially overlap. This study investigated whether drinking motives mediate the associations between alcohol consumption and 2 single-nucleotide polymorphisms (SNPs) from genes involved in serotonin (TPH2; rs1386496) and dopamine synthesis (DDC; rs3779084). Based on earlier work showing that enhancement and coping motives were heritable in regular smokers but not in nonregular smokers, we hypothesized these motives would mediate the relationships between alcohol consumption and these SNPs in regular smokers.
Drinking motives data were available from 830 young adult female twins (n = 344 regular smokers and n = 486 never/nonregular smokers). We used confirmatory factor analyses to model enhancement, coping, and alcohol consumption factors and to conduct mediation analyses in the regular smoker and never/nonregular smoker groups.
Our hypothesis was partially supported. The relationship between alcohol consumption and rs1386496 was not mediated by drinking motives in either group. However, in the regular smokers, the relationship between alcohol consumption and rs3779084 was mediated by enhancement and coping motives. Carriers of the rs3779084 minor allele who were regular smokers reported more motivation to consume alcohol. Given this pattern of results was absent in the never/nonregular smokers, our results are consistent with a gene × smoking status interaction.
In regular smokers, variability at the locus marked by rs3779084 in the DDC gene appears to index biologically based individual differences in the motivation to consume alcohol to attain or improve a positive affective state or to relieve a negative one. These results could be because of increased sensitivity to the reinforcing effects of alcohol among minor allele carriers who smoke, which might be due to structural or functional differences in mesorticolimic dopamine “reward” circuitry.
Alcohol; Tobacco; Drinking Motives; DDC; TPH2; Mediation
Outcome expectancy is a central construct in models of addiction. Several outcome expectancies associated with smoking cigarettes have been identified, and studies suggest that individual differences in smoking expectancies are related to important aspects of tobacco use, including levels of smoking, nicotine dependence and smoking cessation. In the present study, we used a novel analytic method, exploratory structural equation modeling (ESEM), to quantify smoking expectancies from a subset of items adapted from the Smoking Consequences Questionnaire (SCQ; Brandon and Baker, 1991) and SCQ-Adult (Copeland et al., 1995). In our sample of 1262 monozygotic and dizygotic young adult, female twins who were regular smokers, we quantified six smoking expectancy factors similar to those reported in previous studies. These included Negative Affect Reduction, Boredom Reduction, Weight Control, Taste Manipulation, Craving/Addiction and Stimulation-State Enhancement. We used genetic model-fitting to examine the extent to which individual differences in the expectancies were influenced by latent genetic, shared environmental and non-shared environmental factors. We also examined the validity of the expectancy factors by examining their associations with nicotine dependence (ND) before and after adjusting for comorbid diagnoses of drug dependence and alcohol use disorder. Results of the validity analysis indicated that all of the expectancies were associated with ND after covariate adjustment. Although we lacked the statistical power to distinguish between genetic and shared environmental sources of variance, our results suggest that smoking outcome expectancies aggregate in families, but the majority of variance in these expectancies is due to environmental factors specific to the individual.
Smoking expectancies; Smoking Consequences Questionnaire; Nicotine Dependence; Genetics; Female
Little is known about the relationship between relative body weight and transition from experimentation to regular smoking in young adult women. In the current study, data from 2494 participants in wave 4 of the Missouri Adolescent Female Twin Study (aged 18-29 years) who reported ever smoking a cigarette were analyzed using logistic regression. Body mass index (BMI) at time of interview was categorized according to CDC adult guidelines, and regular smoking was defined as having ever smoked 100 or more cigarettes and having smoked at least once a week for two months in a row. Since the OR’s for the overweight and obese groups did not differ significantly from one another in any model tested, these groups were combined. Forty-five percent of women who had ever smoked had become regular smokers. Testing of interactions between potential covariates and levels of the categorical BMI variable revealed a significant interaction between overweight/obesity and childhood sexual abuse (CSA; p<0.001) associated with regular smoking. Among women reporting CSA, the association between overweight/obesity and having become a regular smoker was negative (n=374; OR=0.48, 95% CI: 0.28-0.81). Both underweight and overweight/obesity were positively associated with transition to regular smoking among women who did not report CSA (n=2076; OR=1.57, 95% CI: 1.05-2.35 and OR=1.73, 95% CI: 1.35-2.20, respectively). These results suggest that experiencing CSA alters the association between BMI and regular smoking in women who have experimented with cigarettes.
Smoking; body mass index; childhood sexual abuse; twins; MOAFTS
Alcohol and tobacco use often co-occur. Human and animal studies indicate that nicotine increases alcohol’s rewarding effects and the motivation to consume it. The aims of this study were to examine whether the factorial architecture of self-reported motivations to consume alcohol differed between regular and nonregular cigarette smokers while taking into account the lifetime history of alcohol dependence and psychopathology, and to estimate the genetic and environmental influences on the motivations.
Using data on 2,189 monozygotic and dizygotic female twins, we examined the factorial structure (item thresholds and factor loadings, means, and variances) of the items from the Drinking Motives Questionnaire (DMQ) in regular and nonregular smokers. Post hoc tests examined the association between the latent drinking motives factors and alcohol dependence in both groups. Twin models were fitted to the latent drinking motives factors, testing for variations in the magnitude of additive genetic, shared, and nonshared environmental influences between the groups.
The 4 DMQ factors (social, conformity, coping, and enhancement) were recovered in both groups, and their measurement structure was consistent across the groups. Regular smokers reported higher levels of coping, enhancement, and social motives while nonregular smokers reported higher conformity motives. Alcohol dependence was associated with higher scores on all motives in both groups; however, in a regression analysis that included all of the motives as predictor variables, only coping was significantly related to alcohol dependence. While twin models revealed evidence for substantially greater genetic influences on enhancement (h2 = 0.40), coping (h2 = 0.35) and social (h2 = 0.37) drinking motives in regular compared to nonregular smokers, the power to statistically distinguish the 2 groups was low.
While the measurement structure of the drinking motive factors appears to be similar across regular and nonregular smokers, regular smokers report more motivation to drink for internal affect-related reasons and to obtain social reward. Of all the motives, coping was the most robust predictor of alcohol dependence in both the regular and the nonregular smokers. Further, genetic influences might play a larger role in drinking motives among regular smokers, which provides tentative evidence for latent genetic × smoking status interactions.
Alcohol; Tobacco; Drinking Motives; Genetic Influences; Alcohol Dependence
The aim of this study was to examine the association between initial subjective effects from cigarettes and the rate of progression from first cigarette to regular smoking. Latent class analysis (LCA) was applied to subjective effects data from 573 offspring of twins ranging in age from 14 to 32 years. LCA revealed four classes: 1) High on both pleasurable and physiological respondeses, 2) Cough only response, 3) High on physiological, low on pleasurable respondses, and 4) High on pleasurable, low on physiological respondses. Classes of responses were then used to predict time from first cigarette to the onset of regular smoking in a Cox proportional hazards model. Time-varying covariates representing relevant psychiatric and psychosocial factors as well as dummy variables representing the offspring-of-twins design were included in the model. Members of classes 1 and 4 transitioned more rapidly to regular smoking than the classes characterized as low on the pleasurable response dimension. Our findings provide evidence that previously reported associations between pleasurable initial experiences and progression to regular smoking hold true as well for the rate at which that transition occurs. Furthermore, the fact that profiles of responses did not fall into global categories of exclusively pleasurable vs. exclusively negative (physiological) responses suggests the importance of considering both dimensions in combination to characterize risk for smoking-related outcomes.
smoking; subjective effects; offspring of twins
Group functional connectivity magnetic resonance imaging (fcMRI) studies have documented reliable changes in human functional brain maturity over development. Here we show that support vector machine-based multivariate pattern analysis extracts sufficient information from fcMRI data to make accurate predictions about individuals’ brain maturity across development. The use of only 5 minutes of resting-state fcMRI data from 238 scans of typically developing volunteers (ages 7 to 30 years) allowed prediction of individual brain maturity as a functional connectivity maturation index. The resultant functional maturation curve accounted for 55% of the sample variance and followed a nonlinear asymptotic growth curve shape. The greatest relative contribution to predicting individual brain maturity was made by the weakening of short-range functional connections between the adult brain’s major functional networks.
Although African Americans (AA) smoke fewer average cigarettes per day (CPD) than European Americans (EA), they carry a disproportionate tobacco related morbidity and mortality burden.
To evaluate ethnic differences in markers of nicotine addiction, including rates of lifetime nicotine dependence (ND) symptoms, current smoking and smoking during pregnancy across different levels of peak lifetime cigarette consumption.
Data from 237 EA (N=118) and AA (N=119) mothers participating in the Missouri Family Study (2003-2005), an ethnically diverse family study of offspring outcomes in high and low risk families, were used to contrast prevalence of ND symptoms and other smoking behaviors between EA and AA women at low (1-10 CPD), moderate (11-19 CPD), and high (≥ 20 CPD) levels of lifetime peak daily cigarette consumption.
Compared with EA smokers, AAs had lower lifetime prevalence of DSM-IV ND (68% v. 54%, p<.05), consumed fewer CPD during their heaviest lifetime consumption (18% EA v. 58% AA smoked ≤ 10 CPD, p<.0001), but did not differ in overall rates of smoking during pregnancy or current smoking. However, stratifying by categories of peak lifetime daily cigarette use, AA mothers who smoked ≤ 10 CPD reported greater lifetime ND symptoms and current smoking than their EA counterparts. In addition, nearly two-thirds of AA mothers in this smoking category smoked during pregnancy and 30% smoked throughout an entire pregnancy. The respective prevalence estimates in EA mothers were 38% and 0%.
Stratifying the sample into categories of lifetime peak daily cigarette use revealed significant ethnic/racial differences in smoking prevalence during pregnancy that were obscured in overall analysis. Substantial public health risks warranting clinical attention exist among light smokers, particularly AA women.
nicotine dependence; light smoker; African American; women; pregnancy
This project studied the convergent validity of current recall of tobacco-related health behaviors, compared with prospective self-report collected earlier at two sites. Cohorts were from the Oregon Research Institute at Eugene (N = 346, collected 19.5 years earlier) and the University of Pittsburgh, Pennsylvania (N = 294, collected 3.9 years earlier). Current recall was examined through computer-assisted interviews with the Lifetime Tobacco Use Questionnaire from 2005 through 2008. Convergent validity estimates demonstrated variability. Validity estimates of some tobacco use measures were significant for Oregon subjects (age at first cigarette, number of cigarettes/day, quit attempts yes/no and number of attempts, and abstinence symptoms at quitting; all P < 0.03). Validity estimates of Pittsburgh subjects’ self-reports of tobacco use and abstinence symptoms were significant (P < 0.001) for all tobacco use and abstinence symptoms and for responses to initial use of tobacco. These findings support the utility of collecting recalled self-report information for reconstructing salient lifetime health behaviors and underscore the need for careful interpretation.
data collection; mental recall; prospective studies; reproducibility of results; retrospective studies; tobacco use disorder
Cytochrome P450 2A6 (CYP2A6) is the human enzyme responsible for the majority of nicotine’s metabolism. CYP2A6 genetic variants contribute to the inter-individual and inter-ethnic variation in nicotine metabolism. We examined the association between the CYP2A6*1B variant and nicotine’s in vivo metabolism.
Intravenous infusions of deuterium-labeled nicotine were administered to 292 volunteers, 163 of whom were White and did not have common CYP2A6 variants, other than CYP2A6*1B.
We discovered three novel CYP2A6*1B variants in the 3′-flanking region of the gene that can confound genotyping assays. We found significant differences between CYP2A6*1A/*1A, CYP2A6*1A/*1B and CYP2A6*1B/*1B groups in total nicotine clearance (17.2±5.2, 19.0±6.4 and 20.4±5.9, P < 0.02), nonrenal nicotine clearance (16.4±5.0, 18.5±6.2 and 19.8±5.7, P < 0.01) and the plasma 3HC/COT ratio (0.26±0.1, 0.26±0.1 and 0.34±0.1, P < 0.001). There were also differences in total nicotine (29.4±12.9, 25.8±0.12.9 and 22.4±12.4, P < 0.01), cotinine (29.2±8.1, 32.2±9.1 and 33.0±6.6, P < 0.01) and trans-3′-hydroxcotinine (32.4±9.1, 34.2±12.3 and 41.3±11.3, P < 0.001) excreted in the urine.
We report evidence that CYP2A6*1B genotype is associated with faster nicotine clearance in vivo, which will be important to future CYP2A6 genotype association studies.
PMID: 17522595 CAMSID: cams1335
Characterizing cotinine pharmacokinetics is a useful way to study nicotine metabolism because the same liver enzyme is primarily responsible for the metabolism of both, and the clearances of nicotine and cotinine are highly correlated. We conducted a whole-genome linkage analysis to search for candidate regions influencing quantitative variation in cotinine pharmacokinetics in a large-scale pharmacokinetic study with 61 families containing 224 healthy adult participants. The strongest linkage signal was identified at 135 cM of chromosome 9 with LOD=2.81 and P=0.0002; two other suggestive linkage peaks appear at 31.4 and 73.5 cM of chromosome 11 with LOD=1.96 (P=0.0013) and 1.94 (P=0.0014). The confidence level of the linkage between the three genome regions and cotinine pharmacokinetics is statistically significant with a genome-wide empirical probability of P=0.029.
pharmacokinetics; nicotine; dependence; linkage analysis
To examine whether Rasch modeling would yield a unidimensional withdrawal sensitivity measure correlating with factors associated with successful smoking cessation.
The psychometric Rasch modeling approach was applied to estimate an underlying latent construct (withdrawal sensitivity) in retrospective responses from 1,644 smokers who reported quitting for three or more months at least once.
Web-based, passcode-controlled self-administered computerized questionnaire.
Randomly selected convenience sample of N=1,644 adult members of an e-mail invitation-only Web panel drawn from consumer databases.
Lifetime Tobacco Use Questionnaire, assessing tobacco use across the lifespan, including demographics and respondent ratings of the severity of withdrawal symptoms experienced in respondents' first and most recent quit attempts lasting three or more months.
Rasch-modeled withdrawal sensitivity was generally unidimensional and was associated with longer periods of smoking cessation. One latent variable accounted for 74% of the variability in symptom scores. Rasch modeling with a single latent factor fit withdrawal symptoms well, except for increased appetite, for which the fit was marginal. Demographic variables of education, gender, and ethnicity were not related to changes in sensitivity. Correlates of greater withdrawal sensitivity in cessation attempts of at least three months included younger age at first quit attempt and indicators of tobacco dependence.
The relationship between tobacco dependence symptoms and Rasch-model withdrawal sensitivity further defines the relationship between sensitivity and dependence. The findings demonstrate the utility of modeling to create an individual-specific sensitivity measure as a tool for exploring the relationships among sensitivity, dependence, and cessation.
Rasch model; withdrawal symptoms; tobacco dependence; nicotine withdrawal; Lifetime Tobacco Use Questionnaire
The ratio of trans-3’hydroxycotinine/cotinine (3HC/COT) is a marker of CYP2A6 activity, an important determinant of nicotine metabolism. This analysis sought to conduct a combined genetic epidemiologic and pharmacogenetic investigation of the 3HC/COT ratio in plasma and urine.
One hundred thirty nine twin pairs (110 monozygotic [MZ] and 29 dizygotic [DZ]) underwent a 30-minute infusion of stable isotope-labeled nicotine and its major metabolite, cotinine, followed by an 8-hour in-hospital stay. Blood and urine samples were taken at regular intervals for analysis of nicotine, cotinine, and metabolites. DNA was genotyped to confirm zygosity and for variation in the gene for the primary nicotine metabolic enzyme, CYP2A6 (variants genotyped: *1B, *1×2, *2, *4, *9, *12). Univariate biometric analyses quantified genetic and environmental influences on each measure in the presence and absence of covariates, including measured CYP2A6 genotype.
There was a substantial amount of variation in the free 3HC/COT ratio in plasma (6 hours post-infusion) attributable to additive genetic influences (67.4%, 95% CI = 55.9–76.2%). The heritability estimate was reduced to 61.0% and 49.4%, respectively, after taking into account the effect of covariates and CYP2A6 genotype. In urine (collected over 8 hours), the estimated amount of variation in the 3HC/COT ratio attributable to additive genetic influences was smaller (47.2%, 95% CI = 0–67.2%) and decreased to 44.6% and 42.0% after accounting for covariates and genotype.
Additive genetic factors are prominent in determining variation in plasma 3HC/COT variation but less so in determining variation in urine 3HC/COT.
pharmacogenetics; nicotine; cotinine; metabolism; CYP2A6; twins; genetics; heritability
Genome-wide model free linkage analysis was conducted for nicotine dependence and tobacco use phenotypes in 607 members of 158 nuclear families consisting of at least two ever smokers (100 or more cigarettes smoked in lifetime). DNA from whole blood was genotyped for 739 autosomal microsatellite polymorphisms with an average inter-marker distance of 4.6 cM. A peak LOD score of 2.7 was observed on chromosome 6 for scores for the Fagerström Test for Nicotine Dependence. Exploratory analyses were conducted to determine whether sequence variation at other loci affected other measures of dependence or tobacco use. Four additional loci with LOD scores of 2.7 or more were associated with alternative measures of nicotine dependence, one with current frequency of use, and one with smoking cessation. Several of the corresponding support intervals were near putative loci reported previously (on chromosomes 6, 7, and 8) while others appear to be novel (on chromosomes 5, 16, and 19).
nicotine; dependence; linkage; genetics; smoking