PET Shows Nicotine in Smokers’ Brains Despite Vaccine

[[{"type":"media","view_mode":"media_crop","fid":"13937","attributes":{"alt":"PET shows nicotine in smokers' brains","class":"media-image media-image-right","id":"media_crop_1274890203757","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"657","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"margin: 5px; float: right; height: 141px; width: 100px;","title":"","typeof":"foaf:Image"}}]]PET brain images show that researchers are not any closer to developing an effective anti-nicotine vaccine, according to a presentation at the Society of Nuclear Medicine and Molecular Imaging (SNMMI) 2013 annual meeting.

Scientists have been working to develop an anti-nicotine vaccine to inhibit nicotine action, eliminating the pleasure-producing chemical response in the brain. However, the latest attempt is showing mixed success, as evidenced by PET brain scans on smokers who have received the experimental vaccine.

The anti-nicotine immunization introduces an antigen that induces production of antibodies that bind circulating nicotine and prevent it from crossing the blood-brain barrier to produce rewarding effects in smokers. To determine if the vaccine was effective, researchers recruited smokers who smoked more than 10 cigarettes per day. The researchers scanned each subject’s brain twice, as they smoked. The first scan was performed before the smokers were given the experimental vaccine, and the second was done two weeks after they received the last dose. Each scan was done with the patient taking a single puff of a cigarette containing S-nicotine labeled with radioactive C-11.

“Ideally, we want [the vaccine] to decrease amount of nicotine that reaches the brain, but when we compared the immune response across subjects, their antibodies appeared to vary in nicotine-binding properties,” Alexey G. Mukhin, MD, PhD, said in a release. Mukhin is a professor or psychiatry and behavioral science at Duke University. 

The results showed that 10 subjects with the highest vaccine-induced serum capacity to bind nicotine had high-affinity antibodies and experienced a slight but statistically significant decrease in accumulation of nicotine in the brain. Another 10 subject who had intermediate serum nicotine binding capacity and low affinity of antibodies showed the opposite response. They had an increase in nicotine accumulation.

“These results are important because they tell us that we should care about not only the amount of antibody, but the quality of the antibody,” explained Mukhin. “We don’t want to have low-affinity antibodies because that can negate the anti-nicotine effects of the vaccination.”