CYP2A6 associates with respiratory disease risk and younger age of diagnosis: a phenome-wide association Mendelian Randomization study.

CYP2A6, a genetically variable enzyme, inactivates nicotine, activates carcinogens, and metabolizes many pharmaceuticals. Variation in CYP2A6 influences smoking behaviors and tobacco-related disease risk. This phenome-wide association study examined associations between a reconstructed version of our weighted genetic risk score (wGRS) for CYP2A6 activity with diseases in the UK Biobank (N = 395 887). Causal effects of phenotypic CYP2A6 activity (measured as the nicotine metabolite ratio: 3'-hydroxycotinine/cotinine) on the phenome-wide significant (PWS) signals were then estimated in two-sample Mendelian Randomization using the wGRS as the instrument. Time-to-diagnosis age was compared between faster versus slower CYP2A6 metabolizers for the PWS signals in survival analyses. In the total sample, six PWS signals were identified: two lung cancers and four obstructive respiratory diseases PheCodes, where faster CYP2A6 activity was associated with greater disease risk (Ps < 1 × 10-6). A significant CYP2A6-by-smoking status interaction was found (Psinteraction < 0.05); in current smokers, the same six PWS signals were found as identified in the total group, whereas no PWS signals were found in former or never smokers. In the total sample and current smokers, CYP2A6 activity causal estimates on the six PWS signals were significant in Mendelian Randomization (Ps < 5 × 10-5). Additionally, faster CYP2A6 metabolizer status was associated with younger age of disease diagnosis for the six PWS signals (Ps < 5 × 10-4, in current smokers). These findings support a role for faster CYP2A6 activity as a causal risk factor for lung cancers and obstructive respiratory diseases among current smokers, and a younger onset of these diseases. This research utilized the UK Biobank Resource.

Fine-mapping the CYP2A6 regional association with nicotine metabolism among African American smokers.

The nicotine metabolite ratio (NMR; 3'hydroxycotinine/cotinine) is a stable biomarker for CYP2A6 enzyme activity and nicotine clearance, with demonstrated clinical utility in personalizing smoking cessation treatment. Common genetic variation in the CYP2A6 region is strongly associated with NMR in smokers. Here, we investigated this regional association in more detail. We evaluated the association of CYP2A6 single-nucleotide polymorphisms (SNPs) and * alleles with NMR among African American smokers (N = 953) from two clinical trials of smoking cessation. Stepwise conditional analysis and Bayesian fine-mapping were undertaken. Putative causal variants were incorporated into an existing African ancestry-specific genetic risk score (GRS) for NMR, and the performance of the updated GRS was evaluated in both African American (n = 953) and European ancestry smokers (n = 933) from these clinical trials. Five independent associations with NMR in the CYP2A6 region were identified using stepwise conditional analysis, including the deletion variant CYP2A6*4 (beta = -0.90, p = 1.55 × 10-11). Six putative causal variants were identified using Bayesian fine-mapping (posterior probability, PP = 0.67), with the top causal configuration including CYP2A6*4, rs116670633, CYP2A6*9, rs28399451, rs8192720, and rs10853742 (PP = 0.09). Incorporating these putative causal variants into an existing ancestry-specific GRS resulted in comparable prediction of NMR within African American smokers, and improved trans-ancestry portability of the GRS to European smokers. Our findings suggest that both * alleles and SNPs underlie the association of the CYP2A6 region with NMR among African American smokers, identify a shortlist of variants that may causally influence nicotine clearance, and suggest that portability of GRSs across populations can be improved through inclusion of putative causal variants.

Smoking, tobacco dependence, and neurometabolites in the dorsal anterior cingulate cortex.

Cigarette smoking has a major impact on global health and morbidity, and positron emission tomographic research has provided evidence for reduced inflammation in the human brain associated with cigarette smoking. Given the consequences of inflammatory dysfunction for health, the question of whether cigarette smoking affects neuroinflammation warrants further investigation. The goal of this project therefore was to validate and extend evidence of hypoinflammation related to smoking, and to examine the potential contribution of inflammation to clinical features of smoking. Using magnetic resonance spectroscopy, we measured levels of neurometabolites that are putative neuroinflammatory markers. N-acetyl compounds (N-acetylaspartate + N-acetylaspartylglutamate), glutamate, creatine, choline-compounds (phosphocholine + glycerophosphocholine), and myo-inositol, have all been linked to neuroinflammation, but they have not been examined as such with respect to smoking. We tested whether people who smoke cigarettes have brain levels of these metabolites consistent with decreased neuroinflammation, and whether clinical features of smoking are associated with levels of these metabolites. The dorsal anterior cingulate cortex was chosen as the region-of-interest because of previous evidence linking it to smoking and related states. Fifty-four adults who smoked daily maintained overnight smoking abstinence before testing and were compared with 37 nonsmoking participants. Among the smoking participants, we tested for associations of metabolite levels with tobacco dependence, smoking history, craving, and withdrawal. Levels of N-acetyl compounds and glutamate were higher, whereas levels of creatine and choline compounds were lower in the smoking group as compared with the nonsmoking group. In the smoking group, glutamate and creatine levels correlated negatively with tobacco dependence, and creatine correlated negatively with lifetime smoking, but none of the metabolite levels correlated with craving or withdrawal. The findings indicate a link between smoking and a hypoinflammatory state in the brain, specifically in the dorsal anterior cingulate cortex. Smoking may thereby increase vulnerability to infection and brain injury.

Identification of Sociodemographic, Clinical, and Genetic Factors to Aid Alaska Native and American Indian People to Successfully Quit Smoking.

INTRODUCTION: Alaska Native and American Indian (ANAI) people have a smoking prevalence of 23%. Nicotine metabolite ratio (NMR) and genetic testing may enable tailored selection of tobacco cessation medication. AIMS AND METHODS: The purpose of this study was to evaluate the relative contributions of NMR, cessation medication, demographics, and tobacco use history to cessation. Participants were recruited into an observational cohort study consisting of a baseline visit prior to their quit date and 6-week follow-up. Demographic and tobacco use surveys and blood, urine, and breath samples were collected at each visit. Electronic health records were queried for cessation medications. NMR was categorized into slow or normal nicotine metabolism phenotypes (<0.31 and ≥ 0.31, respectively). The main outcome was cessation at 6 weeks. Analyses consisted of descriptive statistics, medication and phenotype concordance, and estimates of relative risk (RR) of quitting. RESULTS: We enrolled 151 ANAI adults who smoked cigarettes daily. Two-thirds had normal nicotine metabolism phenotype. Retrospective medication and phenotype concordance was 39%. The overall quit rate was 25%. No demographic factors or tobacco use history were associated with quit success. Varenicline and bupropion increased the likelihood of quitting (RR = 2.93 [1.42, 6.03] and RR = 2.52 [1.12, 5.64], respectively) compared to nicotine replacement therapy. Non-optimal medication and phenotype concordance decreased likelihood of quit success (RR = 0.44 [0.22, 0.91]) compared to optimal concordance. CONCLUSIONS: This exploratory study found associations between quit success and tobacco cessation medication as well as medication and phenotype concordance. Additional research is needed to assess use of NMR for treatment selection among ANAI people. IMPLICATIONS: These results broadly support additional community-engaged research to improve medication and phenotype concordance in tribal health settings. Such future research on implementing meditcation and phenotype concordance holds promise to improve expectations, quit success, and health outcomes amongst individuals attempting to quit smoking.

Genotyping, characterization, and imputation of known and novel CYP2A6 structural variants using SNP array data.

CYP2A6 metabolically inactivates nicotine. Faster CYP2A6 activity is associated with heavier smoking and higher lung cancer risk. The CYP2A6 gene is polymorphic, including functional structural variants (SV) such as gene deletions (CYP2A6*4), duplications (CYP2A6*1 × 2), and hybrids with the CYP2A7 pseudogene (CYP2A6*12, CYP2A6*34). SVs are challenging to genotype due to their complex genetic architecture. Our aims were to develop a reliable protocol for SV genotyping, functionally phenotype known and novel SVs, and investigate the feasibility of CYP2A6 SV imputation from SNP array data in two ancestry populations. European- (EUR; n = 935) and African- (AFR; n = 964) ancestry individuals from smoking cessation trials were genotyped for SNPs using an Illumina array and for CYP2A6 SVs using Taqman copy number (CN) assays. SV-specific PCR amplification and Sanger sequencing was used to characterize a novel SV. Individuals with SVs were phenotyped using the nicotine metabolite ratio, a biomarker of CYP2A6 activity. SV diplotype and SNP array data were integrated and phased to generate ancestry-specific SV reference panels. Leave-one-out cross-validation was used to investigate the feasibility of CYP2A6 SV imputation. A minimal protocol requiring three Taqman CN assays for CYP2A6 SV genotyping was developed and known SV associations with activity were replicated. The first domain swap CYP2A6-CYP2A7 hybrid SV, CYP2A6*53, was identified, sequenced, and associated with lower CYP2A6 activity. In both EURs and AFRs, most SV alleles were identified using imputation (>70% and >60%, respectively); importantly, false positive rates were <1%. These results confirm that CYP2A6 SV imputation can identify most SV alleles, including a novel SV.

The humanised CYP2C19 transgenic mouse exhibits cerebellar atrophy and movement impairment reminiscent of ataxia.

AIMS: CYP2C19 transgenic mouse expresses the human CYP2C19 gene in the liver and developing brain, and it exhibits altered neurodevelopment associated with impairments in emotionality and locomotion. Because the validation of new animal models is essential for the understanding of the aetiology and pathophysiology of movement disorders, the objective was to characterise motoric phenotype in CYP2C19 transgenic mice and to investigate its validity as a new animal model of ataxia. METHODS: The rotarod, paw-print and beam-walking tests were utilised to characterise the motoric phenotype. The volumes of 20 brain regions in CYP2C19 transgenic and wild-type mice were quantified by 9.4T gadolinium-enhanced post-mortem structural neuroimaging. Antioxidative enzymatic activity was quantified biochemically. Dopaminergic alterations were characterised by chromatographic quantification of concentrations of dopamine and its metabolites and by subsequent immunohistochemical analyses. The beam-walking test was repeated after the treatment with dopamine receptor antagonists ecopipam and raclopride. RESULTS: CYP2C19 transgenic mice exhibit abnormal, unilateral ataxia-like gait, clasping reflex and 5.6-fold more paw-slips in the beam-walking test; the motoric phenotype was more pronounced in youth. Transgenic mice exhibited a profound reduction of 12% in cerebellar volume and a moderate reduction of 4% in hippocampal volume; both regions exhibited an increased antioxidative enzyme activity. CYP2C19 mice were hyperdopaminergic; however, the motoric impairment was not ameliorated by dopamine receptor antagonists, and there was no alteration in the number of midbrain dopaminergic neurons in CYP2C19 mice. CONCLUSIONS: Humanised CYP2C19 transgenic mice exhibit altered gait and functional motoric impairments; this phenotype is likely caused by an aberrant cerebellar development.

Bayesian regularization to predict neuropsychiatric adverse events in smoking cessation with pharmacotherapy.

BACKGROUND: Research on risk factors for neuropsychiatric adverse events (NAEs) in smoking cessation with pharmacotherapy is scarce. We aimed to identify predictors and develop a prediction model for risk of NAEs in smoking cessation with medications using Bayesian regularization. METHODS: Bayesian regularization was implemented by applying two shrinkage priors, Horseshoe and Laplace, to generalized linear mixed models on data from 1203 patients treated with nicotine patch, varenicline or placebo. Two predictor models were considered to separate summary scores and item scores in the psychosocial instruments. The summary score model had 19 predictors or 26 dummy variables and the item score model 51 predictors or 58 dummy variables. A total of 18 models were investigated. RESULTS: An item score model with Horseshoe prior and 7 degrees of freedom was selected as the final model upon model comparison and assessment. At baseline, smokers reporting more abnormal dreams or nightmares had 16% greater odds of experiencing NAEs during treatment (regularized odds ratio (rOR) = 1.16, 95% credible interval (CrI) = 0.95 - 1.56, posterior probability P(rOR > 1) = 0.90) while those with more severe sleep problems had 9% greater odds (rOR = 1.09, 95% CrI = 0.95 - 1.37, P(rOR > 1) = 0.85). The prouder a person felt one week before baseline resulted in 13% smaller odds of having NAEs (rOR = 0.87, 95% CrI = 0.71 - 1.02, P(rOR < 1) = 0.94). Odds of NAEs were comparable across treatment groups. The final model did not perform well in the test set. CONCLUSIONS: Worse sleep-related symptoms reported at baseline resulted in 85%-90% probability of being more likely to experience NAEs during smoking cessation with pharmacotherapy. Treatment for sleep disturbance should be incorporated in smoking cessation program for smokers with sleep disturbance at baseline. Bayesian regularization with Horseshoe prior permits including more predictors in a regression model when there is a low number of events per variable.

Influence of CYP2A6 Genetic Variation, Nicotine Dependence Severity, and Treatment on Smoking Cessation Success.

INTRODUCTION: Genetic variation in Cytochrome P450 2A6 (CYP2A6), the major nicotine metabolizing enzyme, is associated with nicotine dependence and smoking cessation. Nicotine dependence severity also predicts smoking cessation. Our goals were to determine how CYP2A6 variation and nicotine dependence alter smoking cessation, and whether dependence could refine CYP2A6-based treatment recommendations. AIMS AND METHODS: Adult smokers treated for 12 weeks with placebo, nicotine patch, or varenicline (NCT01314001) were grouped as CYP2A6 normal (n = 567) or slow (n = 432) nicotine metabolizers based on a CYP2A6 weighted genetic risk score. Fagerström test for nicotine dependence scores were measured at baseline and biochemically verified smoking cessation was assessed at end of treatment. RESULTS: Dependence neither mediated nor moderated an association between CYP2A6 variation and smoking cessation overall, within any treatment arm, or after stratifying by ancestry (n = 591 European, n = 408 African ancestry) or sex (n = 444 women, n = 555 men). In within-treatment analyses, the mediation effect odds ratio (OR) ranged from 0.95 to 1.00 and the bias-corrected 95% confidence interval contained 1. Moderation (i.e. interaction) effect ORs ranged from 0.88 to 1.61 (p = .397-.828). For CYP2A6 normal metabolizers, quit rates on varenicline were similar for those with high (41.1%) and low (43.4%) dependence, while quit rates were lower for those with high versus low dependence on both patch (16.5 vs. 29.7%) and placebo (8.9 vs. 18.5%). CYP2A6 slow metabolizers with high versus low dependence had lower quit rates in all three treatment arms. CONCLUSIONS: Although nicotine dependence severity neither mediated nor moderated CYP2A6 associations with smoking cessation, incorporating information on dependence may optimize the choice of smoking cessation treatment aid in CYP2A6 normal and slow metabolizers. IMPLICATIONS: Variation in CYP2A6 and nicotine dependence severity alter smoking cessation success. Our findings suggest that while nicotine dependence severity is unlikely to mediate or moderate CYP2A6 associations with cessation, incorporating patient information on both CYP2A6 and nicotine dependence severity may lead to improved smoking cessation strategies.

Relationships Between the Nicotine Metabolite Ratio (NMR) and Laboratory Assessments of Smoking Reinforcement and Craving Among Adults in a Smoking Cessation Trial.

INTRODUCTION: People who metabolize nicotine more quickly are generally less successful at quitting smoking. However, the mechanisms that link individual differences in the nicotine metabolite ratio (NMR), a phenotypic biomarker of the rate of nicotine clearance, to smoking outcomes are unclear. We tested the hypotheses that higher NMR is associated with greater smoking reinforcement, general craving, and cue-induced cigarette craving in a treatment-seeking sample. METHODS: Participants were 252 adults who smoke cigarettes enrolled in a randomized controlled smoking cessation trial (NCT03262662) conducted in Buffalo, New York, USA. Participants completed the Choice Behavior Under Cued Conditions (CBUCC) paradigm, a laboratory choice procedure, ~1 week before the first cessation treatment visit, at which time a saliva sample was collected for NMR assessment. On each CBUCC trial, participants reported cigarette craving during cue presentation (cigarette, water) and spent $0.01-0.25 for a chance (5%-95%) to sample the cue (1 puff, sip), providing measures of smoking reinforcement (spending for cigarettes vs. water), general cigarette craving (averaged across cigarette and water cues), and cue-specific craving (cigarette craving during cigarette vs. water cues). RESULTS: As observed in prior work, the NMR was significantly higher among white and female participants. As expected, both spending and cigarette craving were significantly greater on cigarette compared to water trials. However, contrary to our hypotheses, higher NMR was not associated with greater smoking reinforcement, general craving, or cue-specific craving. CONCLUSIONS: The present data do not support that smoking reinforcement or craving are related to nicotine metabolism among individuals seeking to quit smoking. IMPLICATIONS: Though greater smoking reinforcement, general craving, and cue-specific craving are hypothesized to be linked to faster nicotine metabolism, there was no evidence of such relationships in the present sample of adults seeking to quit smoking. Further research, including replication and consideration of alternate hypotheses, is warranted to elucidate the mechanisms by which the NMR is related to smoking cessation.

Can Treatment Support Mitigate Nicotine Metabolism-Based Disparities in Smoking Abstinence? Secondary Analysis of the Helping HAND 4 Trial.

INTRODUCTION: The nicotine metabolite ratio (NMR), a biomarker of CYP2A6-mediated nicotine metabolism, predicts the efficacy of nicotine replacement therapy (NRT), with fast metabolizers benefiting less than slow metabolizers. Whether treatment support to optimize NRT use (henceforth "treatment support") modifies this pharmacogenetic relationship is unknown. METHODS: Hospitalized adult daily smokers were assigned to one of two post-discharge smoking cessation interventions offering NRT and counseling: (1) Transitional Tobacco Care Management, which delivered enhanced treatment support via free combination NRT at discharge and automated counseling, and (2) a quitline-based approach representing usual care (UC). The primary outcome was biochemically verified 7-day point prevalence abstinence 6 months after discharge. Secondary outcomes were the use of NRT and counseling during the 3-month intervention period. Logistic regression models tested for interactions between NMR and intervention, controlling for sex, race, alcohol use, and BMI. RESULTS: Participants (N = 321) were classified as slow (n = 80) or fast (n = 241) metabolizers relative to the first quartile of NMR (0.012-0.219 vs. 0.221-3.455, respectively). Under UC, fast (vs. slow) metabolizers had lower odds of abstinence at 6 months (aOR 0.35, 95% CI 0.13-0.95) and similar odds of NRT and counseling use. Compared to UC, enhanced treatment support increased abstinence (aOR 2.13, 95% CI 0.98-4.64) and use of combination NRT (aOR 4.62, 95% CI 2.57-8.31) in fast metabolizers, while reducing abstinence in slow metabolizers (aOR 0.21, 95% CI 0.05-0.87; NMR-by-intervention interaction p = .004). CONCLUSIONS: Treatment support increased abstinence and optimal use of NRT among fast nicotine metabolizers, thereby mitigating the gap in abstinence between fast and slow metabolizers. IMPLICATIONS: In this secondary analysis of two smoking cessation interventions for recently hospitalized smokers, fast nicotine metabolizers quit at lower rates than slow metabolizers, but providing fast metabolizers with enhanced treatment support doubled the odds of quitting in this group and mitigated the disparity in abstinence between fast and slow metabolizers. If validated, these findings could lead to personalized approaches to smoking cessation treatment that improve outcomes by targeting treatment support to those who need it most.

Behavioral and pharmacokinetic assessment of nicotine e-cigarette inhalation in female rats.

INTRODUCTION: Nicotine and tobacco use remain high both globally and in the USA, contributing to large healthcare expenditures. With a rise in e-cigarette use, it is important to have clinically relevant models of inhaled nicotine exposure. This study aims to extend prior preclinical nicotine inhalation animal data to females and provide both behavior and serum pharmacokinetics. METHODS: We tested two inhalation doses of nicotine (24 mg/ml and 59 mg/ml) and compared these to injected doses (0.4 mg/kg and 1 mg/kg). In addition, we assessed locomotor behavior after the same doses. Blood was collected at 10- and 120-minutes post-administration. We assessed nicotine and cotinine serum concentrations by LC-MS/MS. RESULTS: showed that while nicotine serum concentrations for the respective high and low-dose administrations were similar between both routes of administration, the route had differential effects on locomotor behavior. Inhaled nicotine showed a dose-dependent decrease in locomotor activity while injected doses showed the opposite trend. CONCLUSIONS: Our results indicate that the route of administration is an important factor when establishing preclinical models of nicotine exposures. Given that the overall use of e-cigarettes in vulnerable populations is on the rise, our study provides important behavioral and pharmacokinetic information to advance our currently limited understanding of the effects of nicotine vapor exposure. IMPLICATIONS: This study highlights behavioral differences between different routes of administration of similar doses of nicotine. Using a low and high dose of nicotine, we found that nicotine serum concentrations were similar between the different routes of administration. Our results indicate that different routes of administration have opposing effects on locomotor activity. These findings provide important implications for future behavioral models.

Exploring Potential for a Personalized Medicine Approach to Smoking Cessation With an American Indian Tribe.

INTRODUCTION: A potential precision medicine approach to smoking cessation is tailoring pharmacotherapy to a biomarker known as the nicotine metabolite ratio (NMR). Little is known about the potential impact and acceptability of this approach for American Indian (AI) persons. AIMS AND METHODS: Tribal-academic collaboration was formed and during 2019-2020 AI adults who smoke(N = 54) were recruited to (1) examine correlations between NMR, dependence, and smoking exposure; (2) assess the extent to which pharmacotherapy preference aligned with NMR-informed recommendations; (3) explore acceptability of NMR-informed pharmacotherapy selection. Participants provided samples for assessment of salivary NMR and urinary total nicotine equivalents (TNE) and completed a questionnaire that assessed cigarettes per day (CPD), Fagerstrom Test for Cigarette Dependence (FTCD), pharmacotherapy preference, and perceptions of NMR-informed pharmacotherapy selection. RESULTS: Significant positive correlations were observed between NMR and FTCD (r = 0.29;p = .0383) and its abbreviated version Heaviness of Smoking Index (HIS) (r = 0.28;p =.0426). Post-hoc analyses suggest that relationships between dependence and NMR were driven by time to first cigarette. Nonsignificant, but directionally consistent, relationships were observed between NMR and CPD (r = 0.21; p =0.1436) and TNE (r = 0.24;p = .2906). Most participants preferred nicotine replacement therapy (71%) over varenicline (29%) and preference for pharmacotherapy matched NMR-based recommendations in 54% of participants. NMR-informed pharmacotherapy selection was supported by 62% of participants. CONCLUSION: In a sample of AI adults who smoke, NMR was related to cigarette dependence and about one-half of participants' pharmacotherapy preference matched their NMR-informed recommendation. There was lower acceptability of NMR-informed approach in this sample of AI adults than prior studies among white or black/African American people who smoke. IMPLICATIONS: Relationships between NMR, dependence, and self-preference for pharmacotherapy suggest that NMR-informed pharmacotherapy selection may have potential for enhancing smoking quitting success in this Tribe. Lower acceptability of NMR-informed pharmacotherapy in this Tribe suggests that this approach may not be equitably utilized. Future work could include identifying community-driven solutions to mitigate precision medicine concerns.

Accuracy and applications of sequencing and genotyping approaches for CYP2A6 and homologous genes.

OBJECTIVES: We evaluated multiple genotyping/sequencing approaches in a homologous region of chromosome 19, and investigated associations of two common 3'-UTR CYP2A6 variants with activity in vivo. METHODS: Individuals (n = 1704) of European and African ancestry were phenotyped for the nicotine metabolite ratio (NMR), an index of CYP2A6 activity, and genotyped/sequenced using deep amplicon exon sequencing, SNP array, genotype imputation and targeted capture sequencing. Amplicon exon sequencing was the gold standard to which other methods were compared within-individual for CYP2A6, CYP2A7, CYP2A13, and CYP2B6 exons to identify highly discordant positions. Linear regression models evaluated the association of CYP2A6*1B and rs8192733 genotypes (coded additively) with logNMR. RESULTS: All approaches were ≤2.6% discordant with the gold standard; discordant calls were concentrated at few positions. Fifteen positions were discordant in >10% of individuals, with 12 appearing in regions of high identity between homologous genes (e.g. CYP2A6 and CYP2A7). For six, allele frequencies in our study and online databases were discrepant, suggesting errors in online sources. In the European-ancestry group (n = 935), CYP2A6*1B and rs8192733 were associated with logNMR (P < 0.001). A combined model found main effects of both variants on increasing logNMR. Similar trends were found in those of African ancestry (n = 506). CONCLUSION: Multiple genotyping/sequencing approaches used in this chromosome 19 region contain genotyping/sequencing errors, as do online databases. Gene-specific primers and SNP array probes must consider gene homology; short-read sequencing of related genes in a single reaction should be avoided. Using improved sequencing approaches, we characterized two gain-of-function 3'-UTR variants, including the relatively understudied rs8192733.

Genome-wide association meta-analysis of nicotine metabolism and cigarette consumption measures in smokers of European descent.

Smoking behaviors, including amount smoked, smoking cessation, and tobacco-related diseases, are altered by the rate of nicotine clearance. Nicotine clearance can be estimated using the nicotine metabolite ratio (NMR) (ratio of 3'hydroxycotinine/cotinine), but only in current smokers. Advancing the genomics of this highly heritable biomarker of CYP2A6, the main metabolic enzyme for nicotine, will also enable investigation of never and former smokers. We performed the largest genome-wide association study (GWAS) to date of the NMR in European ancestry current smokers (n = 5185), found 1255 genome-wide significant variants, and replicated the chromosome 19 locus. Fine-mapping of chromosome 19 revealed 13 putatively causal variants, with nine of these being highly putatively causal and mapping to CYP2A6, MAP3K10, ADCK4, and CYP2B6. We also identified a putatively causal variant on chromosome 4 mapping to TMPRSS11E and demonstrated an association between TMPRSS11E variation and a UGT2B17 activity phenotype. Together the 14 putatively causal SNPs explained ~38% of NMR variation, a substantial increase from the ~20 to 30% previously explained. Our additional GWASs of nicotine intake biomarkers showed that cotinine and smoking intensity (cotinine/cigarettes per day (CPD)) shared chromosome 19 and chromosome 4 loci with the NMR, and that cotinine and a more accurate biomarker, cotinine + 3'hydroxycotinine, shared a chromosome 15 locus near CHRNA5 with CPD and Pack-Years (i.e., cumulative exposure). Understanding the genetic factors influencing smoking-related traits facilitates epidemiological studies of smoking and disease, as well as assists in optimizing smoking cessation support, which in turn will reduce the enormous personal and societal costs associated with smoking.

Stability of Varenicline Concentration in Saliva Over 21 Days at Three Storage Temperatures.

INTRODUCTION: Varenicline is the most efficacious drug for smoking cessation; saliva varenicline concentrations can be useful for the evaluation of adherence in smoking cessation trials. Saliva is a useful noninvasive matrix for mail-in specimen collection, if stable. We investigated the stability of varenicline in saliva at different storage temperatures simulating the time it takes to mail in a sample. METHODS: We evaluated the concentrations of varenicline, nicotine, cotinine, 3'-hydroxycotinine, and 3'-hydroxycotinine/cotinine (3HC/COT) ratio in quality control saliva samples (and after repeated freezing and thawing), and in smokers' saliva samples, stored for up to 21 days at room temperature (~25°C), 4°C, and -80°C. RESULTS: In saliva quality control samples, concentrations of varenicline, nicotine, cotinine, 3'-hydroxycotinine, and 3HC/COT remained unchanged and showed little within-sample variation (CV ≤ 5.5%) for up to 21 days at the three storage temperatures; they were also not altered after three thaw-freeze cycles. In smokers' saliva, a significant main effect of storage duration, but not temperature, was observed for varenicline, cotinine, and 3'-hydroxycotinine, but not for nicotine or the 3HC/COT ratio. However, these changes were within analytical (i.e., equipment) variation resulting in little within-sample variation (CV ≤ 5.8%) for all analytes in smokers' saliva. CONCLUSIONS: Varenicline, the other analytes, and the 3HC/COT ratio remained stable in saliva during storage for 21 days at all temperatures tested and after repeated freezing and thawing with only minor changes in concentration over time. These findings support the potential use of mail-in approach for saliva samples in varenicline smoking cessation clinical trials. IMPLICATIONS: Assessing saliva varenicline concentrations can be useful for the evaluation of adherence in smoking cessation trials. Saliva is a noninvasive matrix suitable for mail-in specimen collection. This is the first investigation of stability of varenicline in saliva. Varenicline, nicotine, cotinine, 3'-hydroxycotinine, and 3HC/COT were stable in saliva for up to 21 days at room temperature (~25°C), 4°C, and -80°C, supporting the use of a mail-in approach for saliva specimen in smoking cessation trials.

Evaluating Treatment Mechanisms of Varenicline: Mediation by Affect and Craving.

INTRODUCTION: Negative reinforcement models posit that relapse to cigarette smoking is driven in part by changes in affect and craving during the quit attempt. Varenicline may aid cessation by attenuating these changes; however, this mediational pathway has not been formally evaluated in placebo-controlled trials. Thus, trajectories of negative affect (NA), positive affect (PA), and craving were tested as mediators of the effect of varenicline on smoking cessation. AIMS AND METHODS: Secondary data analysis was conducted on 828 adults assigned to either varenicline or placebo in a randomized controlled trial for smoking cessation (NCT01314001). Self-reported NA, PA, and craving were assessed 1-week pre-quit, on the target quit day (TQD), and 1 and 4 weeks post-TQD. RESULTS: Across time, NA peaked 1-week post-quit, PA did not change, and craving declined. Less steep rises in NA (indirect effect 95% CI: .01 to .30) and lower mean craving at 1-week post-quit (CI: .06 to .50) were mediators of the relationship between varenicline and higher cessation rates at the end of treatment. PA was associated with cessation but was not a significant mediator. CONCLUSIONS: These results partially support the hypothesis that varenicline improves smoking cessation rates by attenuating changes in specific psychological processes and supported NA and craving as plausible treatment mechanisms of varenicline. IMPLICATIONS: The present research provides the first evidence from a placebo-controlled randomized clinical trial that varenicline's efficacy is due, in part, to post-quit attenuation of NA and craving. Reducing NA across the quit attempt and craving early into the attempt may be important treatment mechanisms for effective interventions. Furthermore, post-quit NA, PA, and craving were all associated with relapse and represent treatment targets for future intervention development.

Effect of Varenicline Added to Counseling on Smoking Cessation Among African American Daily Smokers: The Kick It at Swope IV Randomized Clinical Trial.

Importance: African American smokers have among the highest rates of tobacco-attributable morbidity and mortality in the US, and effective treatment is needed for all smoking levels. Objectives: To evaluate the efficacy of varenicline vs placebo among African American adults who are light, moderate, and heavy daily smokers. Design, Setting, and Participants: The Kick It at Swope IV (KIS-IV) trial was a randomized, double-blind, placebo-controlled clinical trial conducted at a federally qualified health center in Kansas City. A total of 500 African American adults who were daily smokers of all smoking levels were enrolled from June 2015 to December 2017; final follow-up was completed in June 2018. Interventions: Participants were provided 6 sessions of culturally relevant individualized counseling and were randomized (in a 3:2 ratio) to receive varenicline (1 mg twice daily; n = 300) or placebo (n = 200) for 12 weeks. Randomization was stratified by sex and smoking level (1-10 cigarettes/d [light smokers] or >10 cigarettes/d [moderate to heavy smokers]). Main Outcomes and Measures: The primary outcome was salivary cotinine-verified 7-day point prevalence smoking abstinence at week 26. The secondary outcome was 7-day point prevalence smoking abstinence at week 12, with subgroup analyses for light smokers (1-10 cigarettes/d) and moderate to heavy smokers (>10 cigarettes/d). Results: Among 500 participants who were randomized and completed the baseline visit (mean age, 52 years; 262 [52%] women; 260 [52%] light smokers; 429 [86%] menthol users), 441 (88%) completed the trial. Treating those lost to follow-up as smokers, participants receiving varenicline were significantly more likely than those receiving placebo to be abstinent at week 26 (15.7% vs 6.5%; difference, 9.2% [95% CI, 3.8%-14.5%]; odds ratio [OR], 2.7 [95% CI, 1.4-5.1]; P = .002). The varenicline group also demonstrated greater abstinence than the placebo group at the end of treatment week 12 (18.7% vs 7.0%; difference, 11.7% [95% CI, 6.0%-17.7%]; OR, 3.0 [95% CI, 1.7-5.6]; P < .001). Smoking abstinence at week 12 was significantly greater for individuals receiving varenicline compared with placebo among light smokers (22.1% vs 8.5%; difference, 13.6% [95% CI, 5.2%-22.0%]; OR, 3.0 [95% CI, 1.4-6.7]; P = .004) and among moderate to heavy smokers (15.1% vs 5.3%; difference, 9.8% [95% CI, 2.4%-17.2%]; OR, 3.1 [95% CI, 1.1-8.6]; P = .02), with no significant smoking level × treatment interaction (P = .96). Medication adverse events were generally comparable between treatment groups, with nausea reported more frequently in the varenicline group (163 of 293 [55.6%]) than the placebo group (90 of 196 [45.9%]). Conclusions and Relevance: Among African American adults who are daily smokers, varenicline added to counseling resulted in a statistically significant improvement in the rates of 7-day point prevalence smoking abstinence at week 26 compared with counseling and placebo. The findings support the use of varenicline in addition to counseling for tobacco use treatment among African American adults who are daily smokers. Trial Registration: ClinicalTrials.gov Identifier: NCT02360631.

Dissecting the genetic overlap of smoking behaviors, lung cancer, and chronic obstructive pulmonary disease: A focus on nicotinic receptors and nicotine metabolizing enzyme.

Smoking is a major contributor to lung cancer and chronic obstructive pulmonary disease (COPD). Two of the strongest genetic associations of smoking-related phenotypes are the chromosomal regions 15q25.1, encompassing the nicotinic acetylcholine receptor subunit genes CHRNA5-CHRNA3-CHRNB4, and 19q13.2, encompassing the nicotine metabolizing gene CYP2A6. In this study, we examined genetic relations between cigarettes smoked per day, smoking cessation, lung cancer, and COPD. Data consisted of genome-wide association study summary results. Genetic correlations were estimated using linkage disequilibrium score regression software. For each pair of outcomes, z-score-z-score (ZZ) plots were generated. Overall, heavier smoking and decreased smoking cessation showed positive genetic associations with increased lung cancer and COPD risk. The chromosomal region 19q13.2, however, showed a different correlational pattern. For example, the effect allele-C of the sentinel SNP (rs56113850) within CYP2A6 was associated with an increased risk of heavier smoking (z-score = 19.2; p = 1.10 × 10-81 ), lung cancer (z-score = 8.91; p = 5.02 × 10-19 ), and COPD (z-score = 4.04; p = 5.40 × 10-5 ). Surprisingly, this allele-C (rs56113850) was associated with increased smoking cessation (z-score = -8.17; p = 2.52 × 10-26 ). This inverse relationship highlights the need for additional investigation to determine how CYP2A6 variation could increase smoking cessation while also increasing the risk of lung cancer and COPD likely through increased cigarettes smoked per day.

Effect of race and glucuronidation rates on the relationship between nicotine metabolite ratio and nicotine clearance.

OBJECTIVES: To investigate if the nicotine metabolite ratio (NMR, the ratio of nicotine metabolites 3'-hydroxycotinine/cotinine) is a reliable phenotypic biomarker for nicotine clearance across races, and as a function of differences in the rate of nicotine, cotinine and 3'-hydroxycotinine glucuronidation and UGT genotypes. METHODS: Participants [Caucasians (Whites), African Americans (Blacks) and Asian-Americans (Asians)] received an oral solution of deuterium-labeled nicotine and its metabolite cotinine. Plasma and saliva concentrations of nicotine and cotinine were used to determine oral clearances. Rates of glucuronidation were assessed from urine glucuronide/parent ratios, and UGT2B10 and UGT2B17 genotypes from DNA. RESULTS: Among the 227 participants, 96 (42%) were White, 67 (30%) Asian and 64 (28%) Black. Compared to the other two races, Whites had higher nicotine and cotinine total oral clearance, Blacks had lower nicotine and cotinine glucuronidation rates and Asians had lower 3'-hydroxycotinine glucuronidation rates. A strong positive correlation (correlations coefficients 0.77-0.84; P < 0.001) between NMR and nicotine oral clearance was found for all three races, and NMR remained a strong predictor for the nicotine oral clearance while adjusting for race, sex and age. Neither the metabolite glucuronidation ratios nor the UGT genotypes had significant effects on the ability of NMR to predict nicotine oral clearance. CONCLUSION: NMR appears to be a reliable phenotypic biomarker for nicotine clearance across races, glucuronidation phenotypes and genotypes. Racial differences in the relationships between NMR, smoking behaviors and addiction are unlikely to be related to an inadequate estimation of nicotine clearance on the basis of NMR.

Sex Differences in the Association of Cigarette Craving With Insula Structure.

BACKGROUND: Cigarette craving, which can negatively impact smoking cessation, is reportedly stronger in women than in men when they initiate abstinence from smoking. Identifying approaches to counteract craving in people of different sexes may facilitate the development of personalized treatments for Tobacco Use Disorder, which disproportionately affects women. Because cigarette craving is associated with nicotine dependence and structure of the insula, this study addressed whether a person's sex influences these associations. METHODS: The research participants (n = 99, 48 women) reported daily cigarette smoking and provided self-reports of nicotine dependence. After overnight abstinence from smoking, they underwent structural magnetic resonance imaging scanning to determine cortical thickness of the left and right anterior circular insular sulcus, and self-rated their cigarette craving before and after their first cigarette of the day. RESULTS: Women reported stronger craving than men irrespective of smoking condition (i.e., pre- and post-smoking) (P = .048), and smoking reduced craving irrespective of sex (P < .001). A 3-way interaction of sex, smoking condition, and right anterior circular insular sulcus thickness on craving (P = .033) reflected a negative association of cortical thickness with pre-smoking craving in women only (P = .012). No effects of cortical thickness in the left anterior circular insular sulcus were detected. Nicotine dependence was positively associated with craving (P < .001) across groups and sessions, with no sex differences in this association. CONCLUSIONS: A negative association of right anterior insula thickness with craving in women only suggests that this region may be a relevant therapeutic target for brain-based smoking cessation interventions in women.