Nicotine Addiction Linked to Genetics of Metabolism
September 12, 2012

Smoking Study Highlights Nuanced Role of Genetics in Nicotine Addiction and Cessation

Connie K. Ho for — Your Universe Online

As everyone knows, smoking kills. According to the Centers for Disease Control and Prevention (CDC), smoking can lead to cancer, heart disease, lung disease and stroke. Armed with this understanding of the deadly effects of smoking, scientists have increasingly looked into the habit itself and how individuals can be successful in smoking cessation programs.

Researchers from McGill University in Canada recently looked at how genetics can influence individuals´ addictions, specifically how genes can help predict the brain´s response to smoking.

Previous research has shown that people who have strong reactions to smoking cues, including the sight of cigarettes and smokers, are less likely to be able to kick the habit themselves. In general, such smoking cues are related to cigarette use and relapse in dropping the habit.

The current study, conducted by the Montreal Neurological Institute and Hospital (a.k.a. The Neuro) at McGill University, demonstrated that individuals whose genes can metabolize nicotine quickly can respond more adeptly to smoking cues than those who have slower nicotine metabolism.

"The finding that nicotine metabolism rate has an impact on the brain's response to smoking cues supports our hypothesis that individuals with fast nicotine metabolism would have a greater brain response to smoking cues because of close coupling in everyday life between exposure to cigarettes and surges in blood nicotine concentration,” explained clinician-scientist Dr. Alain Dagher, lead investigator at The Neuro.

“In other words they learn to associate cigarette smoking with the nicotine surge."

Differences in the gene that codes for the liver gene enzyme can provide quicker or slower nicotine metabolism as well as manage the level of nicotine that affects the brain. To better understand the participants´ nicotine metabolism rates and the enzyme genotype, the researchers screened smokers between 18 and 35 years of age who smoked 5 to 25 cigarettes a day for at least two years.

They then tracked the subjects´ brain reaction to visual smoking cues using functional MRIs which allowed them to determine which subjects had the slowest and fastest nicotine metabolism rates.

The scientists found that fast nicotine metabolizers were able to respond more quickly to visual smoking cues than individuals who had slow metabolism in areas that were related to memory, motivation and reward.

"In contrast, individuals with slow metabolism rates, who have relatively constant nicotine blood levels throughout the day, are less likely to develop conditioned responses to cues. For them, smoking is not associated with brief nicotine surges, so they are smoking for other reasons. Possibilities include maintenance of constant brain nicotine levels for cognitive enhancement (i.e., improved attention, memory), or relief of stress or anxiety," continued Dagher in the statement.

The researchers believe that the study´s findings show that smoking cessation programs can be tailored to fit individual genetic structures and different types of smokers. One possible way of adapting smoking cessation programs is to measure the rate of nicotine metabolism along with the therapeutic decision-making process. The scientists believe that individuals with slow nicotine metabolism need different, more targeted strategies for smoking cessation compared to people who have faster nicotine metabolism.