Brain Imaging in Tobacco Smokers During a Quit Attempt

Overview

The proposed study will help fill gaps in existing research by determining if nicotine-dependent cigarette smokers show changes in α7 nicotinic acetylcholine receptor (nAChR) availability when compared to matched historical controls using positron emission tomography (PET) imaging and the radioactive ligand \[18F\]-ASEM (3-(1,4-diazabicyclo\[3.2.2\]nonan-4-yl)-6 \[18F\]fluorodibenzo\[b,d\]thiophene 5,5-dioxide), an α7 nAChR antagonist. The study will also explore whether α7 nAChR availability influences clinically relevant measures of tobacco abstinence (e.g., withdrawal and craving, cognitive impairment), self-reported cigarettes per day, and time to relapse during an 8-day quit attempt during which smokers can receive escalating payments contingent upon providing objective evidence (breath CO and urinary cotinine) of smoking abstinence.

The primary objective of this basic clinical research study is to examine the role of the alpha7-nicotinic acetylcholine receptors (nAChRs) in tobacco use disorder. nAChRs are the primary site of action for nicotine (the main psychoactive component of tobacco). The most common types of nAChRs are heteromeric nAChRs containing beta2 subunits and homomeric nAChRs, which contain only alpha7 subunits. It is currently unknown if or how chronic tobacco use affects alpha7 nAChR in humans. The investigators' working hypothesis is brain alpha7 nAChR density associated with chronic nicotine exposure and the development of tobacco use disorder may be influence severity of tobacco craving and withdrawal during early smoking abstinence. Proposed group sample sizes are 18 tobacco smokers (accrual) and 18 nonsmokers (drawn from historical and contemporary controls in ongoing studies). Media-recruited male and female heavy smokers will be assessed for study inclusion/exclusion criteria using a structured diagnostic interview and a standard battery of instruments, as well as a medical exam to determine general health. Study candidates also provide breath and urine samples to determine biomarkers of tobacco use (breath carbon oxide and urinary cotinine levels), other drug use (breath alcohol and urine toxicology) and for females a pregnancy test. To ensure there are a sufficient number of subjects, 60 subjects will be screened for study eligibility and assessed for matching criteria (age, race and sex). Groups (smokers vs. non-smokers) will include equal numbers of males and females. In addition, male and female smokers will be matched for tobacco use disorder severity using symptom counts (DSM 5). Eligible subjects will be enrolled in an outpatient protocol completed at the Behavioral Pharmacology Research Unit (BPRU) at the Johns Hopkins Bayview Medical Center, and at the Johns Hopkins Hospital (JHH) PET imaging Center. Abstinent smokers (as verified by CO and cotinine, see below) will complete an magnetic resonance imaging (MRI) scan and a PET scan with the alpha-7 nAChR radiotracer \[18F\]-ASEM. Matched historical controls will have completed the MRI and PET scans previously. Tobacco users will receive contingency management incentive payments for verified smoking abstinence (Intervention 2, behavioral counseling). Smokers will continue in the study after the PET scan and complete an 8-day practice quit attempt. To evaluate smoking abstinence and lapse behavior, smokers will be asked to complete study six visits with a practice quit attempt. Smoker will receive the incentive intervention for smoking abstinence. At each visit, smokers will provide carbon monoxide (CO) and urine samples, and complete assessment instruments to self-report on daily symptoms of nicotine withdrawal and craving, and number of cigarettes smoked. The incentive intervention is a validated, established intervention for smoking cessation. At each visit, smokers will receive escalating incentive payments contingent upon provision of samples that meet study defined abstinence criteria. The incentive earning schedule starts at $9 on day 1 of abstinence and increases by $1.50 for each day of verified abstinence to $19.50 on day 8. To boost the incentive for abstinence, provision of samples that meet bonus abstinence (cotinine \<100 ng/ml day 8) results additional $10 or $20 bonus payments. The incentive earnings schedule includes allowance for a slip, and a reset contingency to allow smokers to retry the quit attempt and complete the study. This incentive earnings schedule with resets is of high magnitude to reinforce abstinence, and increase participant retainment. The number of days in the quit attempt (8) yields a sufficient sample to examine both withdrawal and biomarkers (CO and cotinine) to quantify number of days in which use of any nicotine occurred vs. days participants were compliant in maintaining abstinence. These data will be utilized to explore the relationship of alpha7-nAChR availability to these clinically meaningful measures of tobacco use and abstinence.