Nicotine metabolism and addiction among adolescent smokers

Nicotine metabolite ratio: Comparison of the three urinary versions to the plasma version and nicotine clearance in three clinical studies

BACKGROUND

Variation in CYP2A6 activity influences tobacco smoking behaviors and smoking-related health outcomes. Plasma Nicotine Metabolite Ratio (NMR) is a robust phenotypic biomarker of CYP2A6 activity and nicotine clearance. In urine, the NMR has been calculated as a ratio of free trans-3'-hydroxycotinine to free cotinine (NMR_F/F), total trans-3'-hydroxycotinine to free cotinine (NMR_T/F), or total trans-3'-hydroxycotinine to total cotinine (NMR_T/T). We evaluated these three urinary NMR versions relative to plasma NMR and nicotine clearance and elucidated mechanisms of discrepancies among them.

METHODS

Baseline plasma and urine biomarker data were available from two smoking cessation clinical trials and one nicotine pharmacokinetic study (total N = 768). NMRs were compared using Pearson correlations, linear regressions and ANOVA analyses. UGT2B10 and UGT2B17 were genotyped.

RESULTS

Urinary NMR_T/F was the most highly related to plasma NMR (R² = 0.70, P <2.2e-16) followed by NMR_F/F (R² = 0.68, P <2.2e-16), while NMR_T/T was less strongly related (R² = 0.60, P <2.2e-16); consistent across study, ethnicity, sex, heaviness of smoking, and analyte analysis. Controlling for cotinine glucuronidation, as a phenotype or UGT2B10 genotype, corrected the NMR_T/T discordance with plasma NMR (P_anova<0.001). Similar findings were obtained for relationships of nicotine clearance with plasma NMR > urinary NMR_T/F > NMR_F/F > NMR_T/T (R² = 0.41 > 0.37 > 0.35 > 0.25 respectively).

CONCLUSION

Urinary NMR_T/F followed by NMR_F/F are the best urinary alternatives to plasma NMR or nicotine clearance. NMR_T/T has the least utility as it is influenced substantially by variation in cotinine glucuronidation.

IMPACT

This work highlighted the variation in urinary NMRs, and identified mechanisms for disparities among them, which facilitates their use in predicting smoking-related outcomes.

The reinforcement threshold and elasticity of demand for nicotine in an adolescent rat model of depression

BACKGROUND

The Food and Drug Administration (FDA) is considering setting a nicotine standard for tobacco products to reduce their addictiveness. Such a standard should account for the apparent greater vulnerability to nicotine addiction in some subpopulations, such as adolescents with depression. The present study examined whether the reinforcement threshold and elasticity of demand (i.e., reinforcing efficacy) for nicotine in a genetic inbred rat model of depression (Flinders Sensitive Line [FSL]) differs from an outbred control strain.

METHODS

Acquisition of nicotine self-administration (NSA) across a wide range of nicotine doses was measured in both FSL and Sprague-Dawley (SD) control adolescent rats. At the highest dose, elasticity of demand was also measured. Nicotine pharmacokinetics was examined to determine whether it might modulate NSA, as it does smoking in humans.

RESULTS

FSL rats acquired self-administration quicker and showed more inelastic demand (greater reinforcing efficacy) than SDs at the highest unit dose. However, there was no strain difference in the reinforcement threshold of nicotine. FSL rats exhibited faster nicotine clearance, larger volume of distribution, and lower plasma and brain nicotine concentrations. However, these differences were not consistently related to strain differences in NSA measures.

CONCLUSION

These findings are consistent with studies showing greater dependence and reinforcing efficacy of cigarettes in smokers with depression and those with relatively fast nicotine metabolism. However, these findings also suggest that a nicotine standard to reduce initiation of tobacco use should be similarly effective in both the general adolescent population and those with depression.

Relating individual differences in nicotine dependence severity to underpinning motivational and pharmacological processes among smokers from vulnerable populations

We examined whether elucidating underpinning smoking motivation and related pharmacological processes enhances understanding of nicotine dependence among smokers from vulnerable populations. Data were obtained between Oct, 2016 and Sept, 2019 from 745 adult smokers with co-morbid psychiatric conditions or socioeconomic disadvantage at University of Vermont, Brown University, Johns Hopkins University. Smoking motivation was assessed using the Cigarette Purchase Task (CPT), a behavioral-economic task that models the relative reinforcing value of smoking under varying monetary constraint. Dependence severity was measured using the Heaviness of Smoking Index (HSI), Fagerström Test for Nicotine Dependence total scores (FTND), and FTND total scores minus items 1 and 4 (FTND_2,3,5,6). We also assessed associations between dependence severity and smoking motivation with nicotine levels and metabolism rate. Principal Component Analysis was used to examine the latent structure of the conventional five CPT indices; bivariate and multivariable modeling was used to test associations. Factor analysis resulted in a two-factor solution, Amplitude (demand unconstrained by price) and Persistence (price sensitivity). CPT latent factors were associated with each dependence-severity measure (ps ≤ 0.0001), with associations stronger for Amplitude than Persistence across each, especially HSI which was exclusively associated with Amplitude_. Amplitude and each dependence measure were associated with nicotine intake (ps ≤ 0.0002); Persistence was not (p = .19). Demand Amplitude more than Persistence appears key to understanding individual differences in dependence severity. Regarding potential application, the results suggest a need for interventions that more effectively target demand Amplitude to make greater headway in reducing smoking in vulnerable populations. Trial Registration:clinicaltrials.gov identifiers: NCT02232737, NCT02250664, NCT02250534.

Measuring e-cigarette addiction among adolescents

BACKGROUND AND OBJECTIVES

With high rates of use and uncertain consequences, valid electronic cigarette (e-cigarette) use frequency and addiction measures for adolescents are needed. This cross-sectional study examined correlations for multiple measures of adolescent e-cigarette use with nicotine exposure quantified with salivary cotinine levels.

METHODS

Adolescents (N=173, age 13-18) who reported past-month e-cigarette use were recruited from the San Francisco Bay Area. Participants self-reported: (1) days of e-cigarette use in a typical month, (2) number of e-cigarette sessions in a typical day (sessions per day; SPD) and the (3) E-Cigarette Addiction Severity Index (EASI). Participants also completed the 10-item Penn State Electronic Cigarette Dependence Index (ECDI), which we examined in full and as a 2-item Heaviness of Vaping Index (HVI; the sum of the ECDI items on use frequency and time to first vaping on wakening). Sessions per month (SPM) were calculated using days per month and SPD. Cotinine levels, SPD and SPM were log-transformed.

RESULTS

Among frequency measures, SPM correlated most strongly with cotinine (r=0.59), followed closely by days per month (r=0.58) and SPD (r=0.57), p<0.001. Among dependence measures, the EASI correlated most strongly with cotinine (r=0.51), closely followed by the ECDI and HVI (r's=0.50), all p's<0.001.

CONCLUSIONS

Adolescents' reports of frequency of e-cigarette use and degree of addiction correlated significantly with cotinine as a biomarker of nicotine exposure. We recommend the EASI and days per month as brief general measures. SPM and the ECDI are more extensive measures that may yield a more nuanced understanding of use.

Status and Future Directions of Preclinical Behavioral Pharmacology in Tobacco Regulatory Science

Behavioral pharmacology is a branch of the experimental analysis of behavior that has had great influence in drug addiction research and policy. This paper provides an overview of recent behavioral pharmacology research in the field of tobacco regulatory science, which provides the scientific foundation for the Food and Drug Administration Center for Tobacco Products (FDA CTP) to set tobacco control policies. The rationale and aims of tobacco regulatory science are provided, including the types of preclinical operant behavioral models it deems important for assessing the abuse liability of tobacco products and their constituents. We then review literature relevant to key regulatory actions being considered by the FDA CTP, including regulations over nicotine and menthol content of cigarettes, and conclude with suggesting some directions for future research. The current era of tobacco regulatory science provides great opportunities for behavioral pharmacologists to address the leading cause of preventable death and disease worldwide.

CYP2A6 metabolism in the development of smoking behaviors in young adults

Cytochrome P450 2A6 (CYP2A6) encodes the enzyme responsible for the majority of nicotine metabolism. Previous studies support that slow metabolizers smoke fewer cigarettes once nicotine dependent but provide conflicting results on the role of CYP2A6 in the development of dependence. By focusing on the critical period of young adulthood, this study examines the relationship of CYP2A6 variation and smoking milestones. A total of 1209 European American young adults enrolled in the Collaborative Study on the Genetics of Alcoholism were genotyped for CYP2A6 variants to calculate a previously well-validated metric that estimates nicotine metabolism. This metric was not associated with the transition from never smoking to smoking initiation nor with the transition from initiation to daily smoking (P > 0.4). But among young adults who had become daily smokers (n = 506), decreased metabolism was associated with increased risk of nicotine dependence (P = 0.03) (defined as Fagerström Test for Nicotine Dependence score ≥4). This finding was replicated in the Collaborative Genetic Study of Nicotine Dependence with 335 young adult daily smokers (P = 0.02). Secondary meta-analysis indicated that slow metabolizers had a 53 percent increased odds (OR = 1.53, 95 percent CI 1.11-2.11, P = 0.009) of developing nicotine dependence compared with normal metabolizers. Furthermore, secondary analyses examining four-level response of time to first cigarette after waking (>60, 31-60, 6-30, ≤5 minutes) demonstrated a robust effect of the metabolism metric in Collaborative Study on the Genetics of Alcoholism (P = 0.03) and Collaborative Genetic Study of Nicotine Dependence (P = 0.004), illustrating the important role of this measure of dependence. These findings highlight the complex role of CYP2A6 variation across different developmental stages of smoking behaviors.

Mixed methods research in tobacco control with youth and young adults: A methodological review of current strategies

INTRODUCTION

Tobacco use among young people is a complex and serious global dilemma that demands innovative and diverse research approaches. The purpose of this methodological review was to examine the current use of mixed methods research in tobacco control with youth and young adult populations and to develop practical recommendations for tobacco control researchers interested in this methodology.

METHODS

Using PubMed, we searched five peer-reviewed journals that publish tobacco control empirical literature for the use of mixed methods research to study young populations, age 12-25 years. Our team analyzed the features of each article in terms of tobacco control topic, population, youth engagement strategies, and several essential elements of mixed methods research.

RESULTS

We identified 23 mixed methods studies published by authors from five different countries reported between 2004 and 2015. These 23 articles examined various topics that included tobacco use behavior, tobacco marketing and branding, and cessation among youth and young adults. The most common mixed methods approach was variations of the concurrent design in which the qualitative and quantitative strands were administered at the same time and given equal priority. This review documented several innovative applications of mixed methods research as well as challenges in the reporting of the complex research designs.

CONCLUSIONS

The use of mixed methods research in tobacco control has great potential for advancing the understanding of complex behavioral and sociocultural issues for all groups, especially youth and young adults.

Menthol disrupts nicotine's psychostimulant properties in an age and sex-dependent manner in C57BL/6J mice

Menthol is a commonly used flavorant in tobacco and e-cigarettes, and could contribute to nicotine sensitivity. To understand how menthol could contribute to nicotine intake and addiction, it is important to determine whether specific mechanisms related to sex and age could underlie behavioral changes induced by menthol-laced nicotinic products. Using a validated paradigm of nicotine-dependent locomotor stimulation, adolescent and adult C57BL/6J mice of both sexes were exposed to nicotine, or nicotine laced with menthol, as their sole source of fluid, and psychostimulant effects were evaluated by recording home cage locomotor activity for ten days. Nicotine and cotinine blood levels were measured following exposure. Results show an interaction between treatment, age, and sex on liquid consumption, indicating that mice responded differently to menthol and nicotine based on their age and sex. Adult male mice greatly increased their nicotine intake when given menthol. In female mice of both age groups, menthol did not have this effect. Despite an increase in nicotine intake promoted by menthol, adult male mice showed a significant decrease in locomotion, suggesting that menthol blunted nicotine-induced psychostimulation. This behavioral response to menthol was not detected in adolescent mice of either sex. These data confirm that menthol is more than a flavorant, and can influence both nicotine intake and its psychostimulant effects. These results suggest that age- and sex-dependent mechanisms could underlie menthol's influence on nicotine intake and that studies including adolescent and adult menthol smokers of both sexes are warranted.

Cardiovascular effects of linalyl acetate in acute nicotine exposure

Backgroud

Smoking is a risk factor for cardiovascular diseases as well as pulmonary dysfunction. In particular, adolescent smoking has been reported to have a higher latent risk for cardiovascular disease. Despite the risk to and vulnerability of adolescents to smoking, the mechanisms underlying the effects of acute nicotine exposure on adolescents remain unknown. This study therefore evaluated the mechanism underlying the effects of linalyl acetate on cardiovascular changes in adolescent rats with acute nicotine exposure.

Methods

Parameters analyzed included heart rate (HR), systolic blood pressure, lactate dehydrogenase (LDH) activity, vascular contractility, and nitric oxide levels.

Results

Compared with nicotine alone, those treated with nicotine plus 10 mg/kg (p = 0.036) and 100 mg/kg (p = 0.023) linalyl acetate showed significant reductions in HR. Moreover, the addition of 1 mg/kg (p = 0.011), 10 mg/kg (p = 0.010), and 100 mg/kg (p = 0.011) linalyl acetate to nicotine resulted in significantly lower LDH activity. Nicotine also showed a slight relaxation effect, followed by a sustained recontraction phase, whereas nicotine plus linalyl acetate or nifedipine showed a constant relaxation effect on contraction of mouse aorta (p < 0.001). Furthermore, nicotine-induced increases in nitrite levels were decreased by treatment with linalyl acetate (p < 0.001).

Conclusions

Taken together, our findings suggest that linalyl acetate treatment resulted in recovery of cell damage and cardiovascular changes caused by acute nicotine-induced cardiovascular disruption. Our evaluation of the influence of acute nicotine provides potential insights into the effects of environmental tobacco smoke and suggests linalyl acetate as an available mitigating agent.

Polydrug use among urban adolescent cigarette smokers

PURPOSE

Adolescent smokers are at increased risk for polydrug use, which is associated with more consequences than use of a single drug. Here we classified subgroups of polydrug use among urban adolescent cigarette-smokers; described the sociodemographic, smoking, and depression correlates; and identified three-year outcomes associated with subgroup membership.

METHODS

Adolescent cigarette smokers (N=176; Mage=16.1; 35% male; 27% white) completed surveys assessing drug use, smoking characteristics, demographics, and depressive symptoms at baseline and 12, 24, and 36months follow-up.

RESULTS

Almost all participants (96%) reported using, on average, two (SD=0.97) substances (including other tobacco products) in addition to cigarettes. Latent class analysis revealed two distinct classes of polydrug users. "Limited Range Use" (84%) class members reported current use of other tobacco, alcohol, and marijuana, as did "Extended Range Use" class members (16%) who also reported current use of "harder drugs" (i.e., cocaine/crack, hallucinogens, ecstasy, and misused prescriptions). The classes did not differ on demographics or baseline likelihood of marijuana (χ2=0.25; p<0.62) or alcohol use (χ2=3.3; p<0.07). At baseline, a larger proportion of Extended Range Use class members reported both smoking the entire cigarette and symptoms of clinical depression. Extended Range Use class membership at baseline predicted higher mean depression scores at 24 and 36months.

CONCLUSION

Adolescent cigarette-smokers who reported extended range use (18%) also reported symptoms of clinical depression at baseline and follow-up. These findings indicate a need for early monitoring of depression symptoms and prevention and cessation interventions targeting this high-risk group.

Nicotine and Tobacco as Substances of Abuse in Children and Adolescents

Nicotine is the primary pharmacologic component of tobacco, and users of tobacco products seek out its effects. The highly addictive nature of nicotine is responsible for its widespread use and difficulty with quitting. This technical report focuses on nicotine and discusses the stages of use in progression to dependence on nicotine-containing products; the physiologic characteristics, neurobiology, metabolism, pharmacogenetics, and health effects of nicotine; and acute nicotine toxicity. Finally, some newer approaches to cessation are noted.

Precision Medicine for Tobacco Dependence: Development and Validation of the Nicotine Metabolite Ratio

Quitting smoking significantly reduces the risk of tobacco-related morbidity and mortality, yet there is a high rate of relapse amongst smokers who try to quit. Phenotypic biomarkers have the potential to improve smoking cessation outcomes by identifying the best available treatment for an individual smoker. In this review, we introduce the nicotine metabolite ratio (NMR) as a reliable and stable phenotypic measure of nicotine metabolism that can guide smoking cessation treatment among smokers who wish to quit. We address how the NMR accounts for sources of variation in nicotine metabolism including genotype and other biological and environmental factors such as estrogen levels, alcohol use, body mass index, or menthol exposure. Then, we highlight clinical trials that validate the NMR as a biomarker to predict therapeutic response to different pharmacotherapies for smoking cessation. Current evidence supports the use of nicotine replacement therapy for slow metabolizers, and non-nicotine treatments such as varenicline for normal metabolizers. Finally, we discuss future research directions to elucidate mechanisms underlying NMR associations with treatment response, and facilitate the implementation of the NMR as biomarker in clinical practice to guide smoking cessation.

Reporting of cigar use among adolescent tobacco smokers

INTRODUCTION

With the changing landscape of tobacco products, the divide between cigarettes and cigars is obscured, so understanding adolescent reporting of cigar use is needed to improve best practices for surveillance, screening, and prevention/intervention. This study examined adolescents' reported cigar use and correlates of use.

METHODS

Participants (N=186) were 13-17year old tobacco users participating in a prospective study of adolescent smoking behaviors. Measurement occurred at baseline and 24-months, and included demographics, nicotine dependence, tobacco use, and quit attempts. Cigar use was assessed as, "have you smoked a cigar in the last 30days" and by brand specific use in the past 30days.

FINDINGS

Cigar use was reported by 51 adolescents (27%), and increased to 76 (41%) when identifying by brand name. African Americans (32%) were more likely to smoke cigars than whites (10%, p<.01), Asian/Pacific Islanders (3%, p=.04), and multiracial participants (24%, p=.05). Cigarette-only users smoked more per day (p=.04) and had higher cotinine levels (p=.05) than cigar users. Number of prior quit attempts (p=.84) did not differ by group. Group differences in addiction were found between cigar users and cigarette only users (p<.01). At 24months, more baseline cigar users were tobacco abstinent than cigarette only users (16% versus 7%, p<0.01, respectively).

CONCLUSIONS

Assessment of brand-specific cigars nearly doubled the reporting among adolescent users. Cigar users differed from cigarette-only users in consumption and likelihood of abstinence at 24-months. For more accurate surveillance and to inform treatment considerations, surveys of adolescent tobacco use should include cigars, including brand names, in the assessment strategy.

Variation in CYP2A6 and tobacco dependence throughout adolescence and in young adult smokers

BACKGROUND

Smoking is influenced by genetic factors including variation in CYP2A6 and CYP2B6, which encode nicotine-metabolizing enzymes. In early adolescence, CYP2A6 slow nicotine metabolism was associated with higher dependence acquisition, but reduced cigarette consumption. Here we extend this work by examining associations of CYP2A6 and CYP2B6 with tobacco dependence acquisition in a larger sample of smokers followed throughout adolescence.

METHODS

White participants from the Nicotine Dependence in Teens cohort that had ever inhaled (n=421) were followed frequently from age 12-18 years. Cox's proportional hazards models compared the risk of ICD-10 tobacco dependence acquisition (score 3+) for CYP2A6 and CYP2B6 metabolism groups. Early smoking experiences, as well as amount smoked at end of follow-up, was also computed. At age 24 (N=162), we assessed concordance between self-reported cigarette consumption and salivary cotinine.

RESULTS

In those who initiated inhalation during follow-up, CYP2A6 slow (vs. normal) metabolizers were at greater risk of dependence (hazards ratio (HR)=2.3; 95% CI=1.1, 4.8); CYP2B6 slow (vs. normal) metabolizers had non-significantly greater risk (HR=1.5; 95% CI=0.8, 2.6). Variation in CYP2A6 or CYP2B6 was not significantly associated with early smoking symptoms or cigarette consumption at end of follow-up. At age 24, neither gene was significantly associated with dependence status. Self-reported consumption was associated with salivary cotinine, a biomarker of tobacco exposure, acquired at age 24 (B=0.37; P<0.001).

CONCLUSIONS

Our findings extend previous work indicating that slow nicotine metabolism mediated by CYP2A6, and perhaps CYP2B6, increases risk for tobacco dependence throughout adolescence.

CYP2A6 Effects on Subjective Reactions to Initial Smoking Attempt

INTRODUCTION

In very novice smokers, CYP2A6 genotypes that reduce nicotine metabolism to an intermediate rate may increase smoking risk, relative to both normal and slow rates. The present study examined the hypothesis that intermediate metabolism variants are associated with greater pleasurable effects of the initial smoking attempt than either normal or slow metabolism variants.

METHODS

Participants were novice smokers (N = 261, 65% female) of European descent. Predicted nicotine metabolic rate based on CYP2A6 diplotypes (CYP2A6 Diplotype Predicted Rate [CDPR]) was partitioned into Normal, Intermediate, and Slow categories using a metabolism metric. Subjective reactions to the initial smoking attempt were assessed by the Pleasurable Smoking Experiences (PSE) scale, which was collected within 3 years of the initial smoking attempt. The effect of CDPR on PSE was tested using a generalized linear model in which CDPR was dummy coded and Intermediate CDPR was the reference condition. Gender was included in the model as a control for higher PSE scores by males.

RESULTS

Lower PSE scores were associated with Normal CDPR, β = -0.34, P = .008, and Slow CDPR, β = -0.52, P = .001, relative to Intermediate CDPR.

CONCLUSIONS

Intermediate CDPR-enhanced pleasurable effects of the initial smoking attempt relative to other CYP2A6 variants. This finding is consistent with the hypothesis that the risk effect of Intermediate CDPR on early smoking is a function of optimal pleasurable effects.

IMPLICATIONS

This study supports our recent hypothesis that CYP2A6 diplotypes that encode intermediate nicotine metabolism rate are associated with enhanced pleasurable events following the initial smoking attempt, compared with diplotypes that encode either normal or slow metabolism. This hypothesis was offered to account for our unexpected previous finding of enhanced smoking risk in very novice smokers associated with intermediate metabolism rate. Our new finding encourages further investigation of time-dependent relations between CYP2A6 effects and smoking motives, and it encourages laboratory study of the mechanisms underlying the initial smoking enhancement in novice smokers associated with intermediate metabolism.

How Menthol Alters Tobacco-Smoking Behavior: A Biological Perspective

Mentholated cigarettes gained popularity in the 1950s and were often marketed as "healthy" cigarettes, attributable to their pleasurable mint flavor and cooling sensation in the mouth, lungs, and throat. While it is clear that nicotine is the primary psychoactive component in tobacco cigarettes, recent work has suggested that menthol may also play a role in exacerbating smoking behavior, despite original health claims. Recent evidence highlights four distinct biological mechanisms that can alter smoking behavior: 1) menthol acts to reduce the initially aversive experiences associated with tobacco smoking; 2) menthol can serve as a highly reinforcing sensory cue when associated with nicotine and promote smoking behavior; 3) menthol's actions on nicotinic acetylcholine receptors may change the reinforcing value of nicotine; and 4) menthol can alter nicotine metabolism, thus increasing nicotine bioavailability. The purpose of this review is to highlight and evaluate potential biological mechanisms by which menthol can alter smoking behavior.

Recruitment of adolescents for a smoking study: use of traditional strategies and social media

Engaging and retaining adolescents in research studies is challenging. Social media offers utility for expanding the sphere of research recruitment. This study examined and compared traditional and Facebook-based recruitment strategies on reach, enrollment, cost, and retention. Substance users aged 13-17 years were recruited through several methods, including social media, a study website, fliers, talks in schools, bus ads, and referrals. Study involvement included a one-time visit and semiannual follow-up surveys. 1265 individuals contacted study personnel; 629 were ineligible; 129 declined; and 200 participants enrolled. Facebook drew the greatest volume but had a high rate of ineligibles. Referrals were the most successful and cost-effective ($7 per enrolled participant); school talks were the least. Recruitment source was unrelated to retention success. Facebook may expand recruitment reach, but had greater financial costs and more ineligible contacts, resulting in fewer enrollees relative to traditional interpersonal recruitment methods. Referrals, though useful for study engagement, did not provide a differential benefit in terms of long-term retention.

Predictors of the nicotine reinforcement threshold, compensation, and elasticity of demand in a rodent model of nicotine reduction policy

BACKGROUND

The FDA is considering reducing the nicotine content in tobacco products as a population-based strategy to reduce tobacco addiction. Research is needed to determine the threshold level of nicotine needed to maintain smoking and the extent of compensatory smoking that could occur during nicotine reduction. Sources of variability in these measures across sub-populations also need to be identified so that policies can take into account the risks and benefits of nicotine reduction in vulnerable populations.

METHODS

The present study examined these issues in a rodent nicotine self-administration model of nicotine reduction policy to characterize individual differences in nicotine reinforcement thresholds, degree of compensation, and elasticity of demand during progressive reduction of the unit nicotine dose. The ability of individual differences in baseline nicotine intake and nicotine pharmacokinetics to predict responses to dose reduction was also examined.

RESULTS

Considerable variability in the reinforcement threshold, compensation, and elasticity of demand was evident. High baseline nicotine intake was not correlated with the reinforcement threshold, but predicted less compensation and less elastic demand. Higher nicotine clearance predicted low reinforcement thresholds, greater compensation, and less elastic demand. Less elastic demand also predicted lower reinforcement thresholds.

CONCLUSIONS

These findings suggest that baseline nicotine intake, nicotine clearance, and the essential value of nicotine (i.e. elasticity of demand) moderate the effects of progressive nicotine reduction in rats and warrant further study in humans. They also suggest that smokers with fast nicotine metabolism may be more vulnerable to the risks of nicotine reduction.

CYP2A6 Longitudinal Effects in Young Smokers

INTRODUCTION

The present study sought to identify time-dependent within-participant effects of CYP2A6 genotypes on smoking frequency and nicotine dependence in young smokers.

METHODS

Predicted nicotine metabolic rate based on CYP2A6 diplotypes (CYP2A6 diplotype predicted rate [CDPR]) was partitioned into Normal, Intermediate, and Slow categories using a metabolism metric. Growth-curve models characterized baseline and longitudinal CDPR effects with data from eight longitudinal assessments during a 6-year period (from approximately age 16-22) in young smokers of European descent (N = 296, 57% female) who had smoked less than 100 cigarettes lifetime at baseline and more than that amount by Year 6. Phenotypes were number of days smoked during the previous 30 days and a youth version of the Nicotine Dependence Syndrome Scale (NDSS). A zero-inflated Poisson growth-curve model was used to account for the preponderance of zero days smoked.

RESULTS

At baseline, Intermediate CDPR was a risk factor relative to both Normal and Slow CDPR for smoking frequency and the NDSS. Slow CDPR was associated with the highest probability of smoking discontinuation at baseline. However, due to CDPR time trend differences, by young adulthood these baseline effects had been reordered such that the greatest risks for smoking frequency and the NDSS were associated with Normal CDPR.

CONCLUSIONS

Reduced metabolism CYP2A6 genotypes are associated with both risk and protective effects in novice smokers. However, differences in the time-by-CDPR effects result in a reordering of genotype effects such that normal metabolism becomes the risk variant by young adulthood, as has been reliably reported in older smokers.

Characteristics of adolescent intermittent and daily smokers

INTRODUCTION

Intermittent smoking is common among adolescent smokers, but little is known about adolescent intermittent smokers (ITS). This study describes a cohort of adolescent ITS and compares them to adolescent daily smokers (DS) for the purpose of providing a more detailed characterization of adolescent ITS, specifically patterns of smoking, level of self-reported addiction, and experience with cessation

METHODS

Participants were 124 ITS and 55 DS. ITS were defined as smoking at least monthly but <30 days per month; and DS as smoking daily. Participants completed demographic, smoking and addiction surveys including the HONC and mFTQ.

RESULTS

ITS started smoking at an older age, smoked fewer cigarettes per day and scored significantly lower on addiction scales, but had similar difficulty to DS in quitting smoking with similar numbers of reported quit attempts. These differences remained after adjusting for years of smoking. ITS were more likely to smoke in social situations, while DS were more likely to smoke when angry. Both groups were equally likely to report smoking when drinking alcohol.

CONCLUSIONS

We documented significant differences in smoking related behaviors between adolescent ITS and DS. Importantly, we also found that, despite low level infrequent smoking, ITS reported difficulty in quitting smoking. Given the risks from light and intermittent smoking, it is essential that we develop a greater understanding of adolescent ITS, including their difficulty in quitting and the contextual factors influencing their smoking, so that we may develop new targeted interventions.

Frequent marijuana use is associated with greater nicotine addiction in adolescent smokers

BACKGROUND

Marijuana and tobacco are the substances used most commonly by adolescents and co-occurring use is common. Use of one substance may potentiate the addictive properties of the other. The current study examined the severity of nicotine addiction among teen smokers as a function of co-occurring marijuana use.

METHODS

Participants were 165 adolescents (13-17 years old) who reported smoking at least 1 cigarette per day (CPD) in the past 30 days. General linear models examined the association of marijuana use with multiple measures of nicotine addiction including the Modified Fagerström Tolerance Questionnaire (mFTQ), Hooked on Nicotine Checklist (HONC), ICD-10, and the Nicotine Dependence Syndrome Scale (NDSS).

RESULTS

The adolescent sample (mean age=16.1 years, SD=0.95) averaged 3.0 CPD (SD=3.0) for 1.98 years (SD=1.5). Most (79.5%) also smoked marijuana in the past 30 days. In models controlling for age, daily smoking status, and years of tobacco smoking, frequency of marijuana use accounted for 25-44% of the variance for all four measures of adolescent nicotine dependence.

CONCLUSIONS

Marijuana use was associated with greater reported nicotine addiction among adolescent smokers. The findings suggest a role of marijuana in potentiating nicotine addiction and underscore the need for treatments that address both smoked substances.

COgnitive-pulmonary disease

Over the past few decades, chronic obstructive lung disease (COPD) has been considered a disease of the lungs, often caused by smoking. Nowadays, COPD is regarded as a systemic disease. Both physical effects and effects on brains, including impaired psychological and cognitive functioning, have been demonstrated. Patients with COPD may have cognitive impairment, either globally or in single cognitive domains, such as information processing, attention and concentration, memory, executive functioning, and self-control. Possible causes are hypoxemia, hypercapnia, exacerbations, and decreased physical activity. Cognitive impairment in these patients may be related to structural brain abnormalities, such as gray-matter pathologic changes and the loss of white matter integrity which can be induced by smoking. Cognitive impairment can have a negative impact on health and daily life and may be associated with widespread consequences for disease management programs. It is important to assess cognitive functioning in patients with COPD in order to optimize patient-oriented treatment and to reduce personal discomfort, hospital admissions, and mortality. This paper will summarize the current knowledge about cognitive impairment as extrapulmonary feature of COPD. Hereby, the impact of smoking on cognitive functioning and the impact of cognitive impairment on smoking behaviour will be examined.

Association between smoking and deaths due to colorectal malignant carcinoma: a national population-based case-control study in China

BACKGROUND

This study explored the association between smoking and colorectal malignant carcinoma (CRC) in the Chinese population at the national level for the first time.

METHODS

In the China Nationwide Retrospective Mortality Survey conducted during 1989-1991, 12,942 CRC cases among 1,136,336 all-cause deaths aged ≥30 years were randomly assigned 25,884 control interviews from 325,255 surviving spouses of all-cause deaths across 103 urban and rural areas.

RESULTS

Compared with non-smokers, smoking significantly increased the risk of CRC-specific mortality by 9.8% (odds ratio (OR)=1.098, 95% confidence interval (CI)=1.046-1.153) adjusted for sex, age, and residence. There were significant dose-response relationships between smoking and CRC, such as smoking years, cigarettes smoked daily, and age at onset of smoking. Long-term heavy smokers aged ≥50 years with ≥30 smoking years and ≥20 cigarettes daily had an excess risk of CRC deaths of 30.2% (OR=1.302, 95% CI=1.214-1.397). The strongest association between these smoking variables, such as long-term heavy smokers (OR=1.604, 95% CI=1.341-1.919), and CRC was observed among rural men.

CONCLUSIONS

Quitting smoking at any time would likely be beneficial to CRC prevention. Long-term heavy smokers and rural men should be viewed as special targets for smoking prevention and cessation programs.

The Genetics, Neurogenetics and Pharmacogenetics of Addiction

Addictions are prevalent psychiatric disorders that confer remarkable personal and social burden. Despite substantial evidence for their moderate, yet robust, heritability (approx. 50%), specific genetic mechanisms underlying their development and maintenance remain unclear. The goal of this selective review is to highlight progress in unveiling the genetic underpinnings of addiction. First, we revisit the basis for heritable variation in addiction before reviewing the most replicable candidate gene findings and emerging signals from genomewide association studies for alcohol, nicotine and cannabis addictions. Second, we survey the modest but growing field of neurogenetics examining how genetic variation influences corticostriatal structure, function, and connectivity to identify neural mechanisms that may underlie associations between genetic variation and addiction. Third, we outline how extant genomic findings are being used to develop and refine pharmacotherapies. Finally, as sample sizes for genetically informed studies of addiction approach critical mass, we posit five exciting possibilities that may propel further discovery (improved phenotyping, rare variant discovery, gene-environment interplay, epigenetics, and novel neuroimaging designs).

Genetic and pharmacokinetic determinants of response to transdermal nicotine in white, black, and Asian nonsmokers

The aim of the study was to examine genetic, pharmacokinetic and demographic factors that influence sensitivity to nicotine in never smokers. Sixty never smokers, balanced for gender and race (Caucasian, Blacks and Asian), wore 7 mg nicotine skin patches for up to 8 hours. Serial plasma nicotine concentrations and subjective and cardiovascular effects were measured, and genetic variation in the CYP2A6 gene, the primary enzyme responsible for nicotine metabolism, was assessed. Nicotine toxicity requiring patch removal developed in 9 subjects and was strongly associated with rate of rise and peak concentrations of plasma nicotine. Toxicity, subjective and cardiovascular effects of nicotine were associated with the presence of reduced function CYP2A6 alleles, presumably reflecting slow nicotine metabolic inactivation. This study has implications for understanding individual differences in responses to nicotine medications, particularly when the latter are used for treating medical conditions in non-smokers, and possibly in vulnerability to developing nicotine dependence.