Effect of Cigarette Smoking on a Marker for Neuroinflammation: A [11C]DAA1106 Positron Emission Tomography Study.

This corrects the article DOI: 10.1038/npp.2017.48.

Effect of Cigarette Smoking on a Marker for Neuroinflammation: A [11C]DAA1106 Positron Emission Tomography Study.

In the brain, microglia continuously scan the surrounding extracellular space in order to respond to damage or infection by becoming activated and participating in neuroinflammation. When activated, microglia increase the expression of translocator protein (TSPO) 18 kDa, thereby making the TSPO expression a marker for neuroinflammation. We used the radiotracer [11C]DAA1106 (a ligand for TSPO) and positron emission tomography (PET) to determine the effect of smoking on availability of this marker for neuroinflammation. Forty-five participants (30 smokers and 15 non-smokers) completed the study and had usable data. Participants underwent a dynamic PET scanning session with bolus injection of [11C]DAA1106 (with smokers in the satiated state) and blood draws during PET scanning to determine TSPO affinity genotype and plasma nicotine levels. Whole-brain standardized uptake values (SUVs) were determined, and analysis of variance was performed, with group (smoker vs non-smoker) and genotype as factors, thereby controlling for genotype. Smokers and non-smokers differed in whole-brain SUVs (P=0.006) owing to smokers having 16.8% lower values than non-smokers. The groups did not differ in injected radiotracer dose or body weight, which were used to calculate SUV. An inverse association was found between whole-brain SUV and reported cigarettes per day (P<0.05), but no significant relationship was found for plasma nicotine. Thus, smokers have less [11C]DAA1106 binding globally than non-smokers, indicating less microglial activation. Study findings are consistent with much prior research demonstrating that smokers have impaired inflammatory functioning compared with non-smokers and that constituents of tobacco smoke other than nicotine affect inflammatory processes.

Nicotinic acetylcholine receptor availability in cigarette smokers: effect of heavy caffeine or marijuana use.

RATIONALE: Upregulation of α4ß2* nicotinic acetylcholine receptors (nAChRs) is one of the most well-established effects of chronic cigarette smoking on the brain. Prior research by our group gave a preliminary indication that cigarette smokers with concomitant use of caffeine or marijuana have altered nAChR availability. OBJECTIVE: We sought to determine if smokers with heavy caffeine or marijuana use have different levels of α4ß2* nAChRs than smokers without these drug usages. METHODS: One hundred and one positron emission tomography (PET) scans, using the radiotracer 2-FA (a ligand for ß2*-containing nAChRs), were obtained from four groups of males: non-smokers without heavy caffeine or marijuana use, smokers without heavy caffeine or marijuana use, smokers with heavy caffeine use (mean four coffee cups per day), and smokers with heavy marijuana use (mean 22 days of use per month). Total distribution volume (Vt/fp) was determined for the brainstem, prefrontal cortex, and thalamus, as a measure of nAChR availability. RESULTS: A significant between-group effect was found, resulting from the heavy caffeine and marijuana groups having the highest Vt/fp values (especially for the brainstem and prefrontal cortex), followed by smokers without such use, followed by non-smokers. Direct between-group comparisons revealed significant differences for Vt/fp values between the smoker groups with and without heavy caffeine or marijuana use. CONCLUSIONS: Smokers with heavy caffeine or marijuana use have higher α4ß2* nAChR availability than smokers without these drug usages. These findings are likely due to increased nicotine exposure but could also be due to an interaction on a cellular/molecular level.

Brain nicotinic acetylcholine receptor availability and response to smoking cessation treatment: a randomized trial.

IMPORTANCE: Cigarette smoking leads to upregulation of nicotinic acetylcholine receptors (nAChRs) in the human brain, including the common α4ß2* nAChR subtype. While subjective aspects of tobacco dependence have been extensively examined as predictors of quitting smoking with treatment, no studies to our knowledge have yet reported the relationship between the extent of pretreatment upregulation of nAChRs and smoking cessation. OBJECTIVE: To determine whether the degree of nAChR upregulation in smokers predicts quitting with a standard course of treatment. DESIGN, SETTING, AND PARTICIPANTS: Eighty-one tobacco-dependent cigarette smokers (volunteer sample) underwent positron emission tomographic (PET) scanning of the brain with the radiotracer 2-FA followed by 10 weeks of double-blind, placebo-controlled treatment with nicotine patch (random assignment). Pretreatment specific binding volume of distribution (VS/fP) on PET images (a value that is proportional to α4ß2* nAChR availability) was determined for 8 brain regions of interest, and participant-reported ratings of nicotine dependence, craving, and self-efficacy were collected. Relationships between these pretreatment measures, treatment type, and outcome were then determined. The study took place at academic PET and clinical research centers. MAIN OUTCOMES AND MEASURES: Posttreatment quit status after treatment, defined as a participant report of 7 or more days of continuous abstinence and an exhaled carbon monoxide level of 3 ppm or less. RESULTS: Smokers with lower pretreatment VS/fP values (a potential marker of less severe nAChR upregulation) across all brain regions studied were more likely to quit smoking (multivariate analysis of covariance, F8,69 = 4.5; P < .001), regardless of treatment group assignment. Furthermore, pretreatment average VS/fP values provided additional predictive power for likelihood of quitting beyond the self-report measures (stepwise binary logistic regression, likelihood ratio χ21 = 19.8; P < .001). CONCLUSIONS AND RELEVANCE: Smokers with less upregulation of available α4ß2* nAChRs have a greater likelihood of quitting with treatment than smokers with more upregulation. In addition, the biological marker studied here provided additional predictive power beyond subjectively rated measures known to be associated with smoking cessation outcome. While the costly, time-consuming PET procedure used here is not likely to be used clinically, simpler methods for examining α4ß2* nAChR upregulation could be tested and applied in the future to help determine which smokers need more intensive and/or lengthier treatment. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01526005.

Treatment for tobacco dependence: effect on brain nicotinic acetylcholine receptor density.

Cigarette smoking leads to upregulation of brain nicotinic acetylcholine receptors (nAChRs), including the common α4ß2* nAChR subtype. Although a substantial percentage of smokers receive treatment for tobacco dependence with counseling and/or medication, the effect of a standard course of these treatments on nAChR upregulation has not yet been reported. In the present study, 48 otherwise healthy smokers underwent positron emission tomography (PET) scanning with the radiotracer 2-FA (for labeling α4ß2* nAChRs) before and after treatment with either cognitive-behavioral therapy, bupropion HCl, or pill placebo. Specific binding volume of distribution (VS/fP), a measure proportional to α4ß2* nAChR density, was determined for regions known to have nAChR upregulation with smoking (prefrontal cortex, brainstem, and cerebellum). In the overall study sample, significant decreases in VS/fP were found for the prefrontal cortex, brainstem, and cerebellum of -20 (±35), -25 (±36), and -25 (±31)%, respectively, which represented movement of VS/fP values toward values found in non-smokers (mean 58.2% normalization of receptor levels). Participants who quit smoking had significantly greater reductions in VS/fP across regions than non-quitters, and correlations were found between reductions in cigarettes per day and decreases in VS/fP for brainstem and cerebellum, but there was no between-group effect of treatment type. Thus, smoking reduction and cessation with commonly used treatments (and pill placebo) lead to decreased α4ß2* nAChR densities across brain regions. Study findings could prove useful in the treatment of smokers by providing encouragement with the knowledge that decreased smoking leads to normalization of specific brain receptors.

Up-regulation of nicotinic acetylcholine receptors in menthol cigarette smokers.

One-third of smokers primarily use menthol cigarettes and usage of these cigarettes leads to elevated serum nicotine levels and more difficulty quitting in standard treatment programmes. Previous brain imaging studies demonstrate that smoking (without regard to cigarette type) leads to up-regulation of ß(2)*-containing nicotinic acetylcholine receptors (nAChRs). We sought to determine if menthol cigarette usage results in greater nAChR up-regulation than non-menthol cigarette usage. Altogether, 114 participants (22 menthol cigarette smokers, 41 non-menthol cigarette smokers and 51 non-smokers) underwent positron emission tomography scanning using the α(4)ß(2)* nAChR radioligand 2-[(18)F]fluoro-A-85380 (2-FA). In comparing menthol to non-menthol cigarette smokers, an overall test of 2-FA total volume of distribution values revealed a significant between-group difference, resulting from menthol smokers having 9-28% higher α(4)ß(2)* nAChR densities than non-menthol smokers across regions. In comparing the entire group of smokers to non-smokers, an overall test revealed a significant between-group difference, resulting from smokers having higher α(4)ß(2)* nAChR levels in all regions studied (36-42%) other than thalamus (3%). Study results demonstrate that menthol smokers have greater up-regulation of nAChRs than non-menthol smokers. This difference is presumably related to higher nicotine exposure in menthol smokers, although other mechanisms for menthol influencing receptor density are possible. These results provide additional information about the severity of menthol cigarette use and may help explain why these smokers have more trouble quitting in standard treatment programmes.