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Secondhand Smoke Significantly Impacts nAChRs in Smokers and Non-Smokers

May 27, 2011

Secondhand smoke has been found to be the most dangerous aspect of sharing a space, regardless of size, with a smoker, as it can be more toxic than the smoke being inhaled by the smoker. Arthur L. Brody, MD, and colleagues, measured the effects of secondhand smoke on brain α4ß2* nicotinic acetylcholine receptor (nAChR) occupancy via positron emission tomography (PET) scanning and radiotracers. Brody and colleagues compared 11 smokers (smoking a mean of 15.2 cigarettes/day for an average of 13 years) and 13 non-smokers (subjects with >2 years without a cigarette or no history of nicotine dependence). At baseline, the patients documented their smoking history using the Smoker’s Profile Form, and were evaluated with the Fagerström Test for Nicotine Dependence, the Hamilton Depression Rating Scale, and Hamilton Anxiety Rating Scale. A Micro Smokerlyzer was used to assess and verify smoking status (carbon monoxide level 8 ppm for active smokers and 4 ppm for nonsmokers).

At 6 PM two nights before their PET scans, the smokers were required to abstain from smoking, ensuring that nicotine in their systems from cigarettes would not compete with the secondhand smoke breathed during the study. The day before the PET scans, a brief clinical interview was conducted and a carbon monoxide measurement taken. Exhaling a carbon monoxide level of <8 PPM confirmed smoking abstinence. On the day of the PET scan, the patients received a bolus plus continuous infusion of 2-FA, the bolus being equal to the amount infused over 500 minutes. Three hours after the PET scans, subjects sat in the passenger seat of a car next to a smoker in the driver’s seat. Each “driver” smoker smoked a mean of 3.7 cigarettes in order to keep the car’s carbon monoxide level >7 ppm. The secondhand smoke “passengers” were then re-scanned for an hour, and were then allowed to smoke during a 10-minute break. Smoking saturated the α4ß2* nAChRs, allowing the researchers to obtain a measure of non-displaceable radioactivity and determine which radiotracers could then be displaced from the brain.

The researchers administered the Secondhand Smoke Rating Scale, which analyzes the most common symptoms of exposure to secondhand smoke (chest tightness, coughing, eye irritation, heart palpitations, nasal congestion, nose irritation, and runny nose), before and after each subject was exposed to secondhand smoke.

Brody and colleagues found that moderate secondhand smoke exposure caused a mean 19% occupancy of α4ß2* nAChRs in smokers and 18% for non-smokers. The receptor occupancy values for the thalamus, brainstem, and cerebellum were P=.02, P=.01, and P=.01, respectively, for smokers, and P=.002, P=.008, and P=.001, respectively, for non-smokers. Non-smokers were found to have a more significant increase (1.2 to 3.9) in symptom ratings compared to smokers (2.8 to 3.4) on the Secondhand Smoker Rating Scale. The smokers had a 23% increase in craving with secondhand smoke exposure.

Overall, Brody and colleagues found that nicotine inhaled from secondhand smoke crosses the blood brain barrier which results in α4ß2* nAChRs occupancy in non-smokers.

Funding for this research was provided by grant 16RT-0098from the Tobacco-Related Disease Research Program awarded to Dr. Brody, grant R01 DA20872 from the National Institute on Drug Abuseawarded to Dr. Brody, a Veterans Affairs Type I Merit Review Award awarded to Dr. Brody, grant DABT63-00-C-1003 from the Office of National Drug Control Policy awarded to Dr. London, and endowments from the Richard Metzner Chair in Clinical Neuropharmacology awarded to Dr. Brody, the Thomas P. and Katherine K. Pike Chair in Addiction Studies awarded to Dr. London, and the Marjorie Greene Family Trust awarded to Dr. London.

The full paper can be found at http://archpsyc.amaassn.org/cgi/content/full/archgenpsychiatry.2011.51. —Christopher Naccari

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From → Psychiatry

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