New research suggests vulnerability to smoking addiction is a genetic trait, a finding that explains why it is so difficult, if not impossible, for some to quit.
The study from the Montreal Neurological Institute and Hospital shows that people with genetically fast nicotine metabolism have a significantly greater brain response to smoking cues than those with slow nicotine metabolism.
Prior studies have found that some people are more responsive to environmental cues that trigger smoking — a trait that predicts decreased success at smoking cessation. This new finding that nicotine metabolism rates affect the brain’s response to smoking may lead the way for tailoring smoking cessation programs based on individual genetics.
In the study, researchers used brain scans to show areas of brain activation in response to smoking cues in people with fast nicotine metabolism (upper row) and slow nicotine metabolism (bottom row). Brain regions are more activated in individuals with fast nicotine metabolism.
Experts have known that smoking cues, such as the sight of cigarettes or smokers, affect smoking behavior and are linked to relapse and cigarette use.
Researchers also are aware that nicotine metabolism, by a liver enzyme, also influences smoking behavior. Variations in the gene that codes for this enzyme determine slow or fast rates of metabolism and therefore, the level of nicotine in the blood that reaches the brain.
In the current study smokers were screened for their nicotine metabolism rates and their enzyme genotype. Participants were aged 18 to 35 and smoked 5 to 25 cigarettes daily for a minimum of 2 years.
People with the slowest and fastest metabolism had their brain response to visual smoking cues measured using functional MRI.
Fast metabolizers had significantly greater response to visual cigarette cues than slow metabolizers in brain areas linked to memory, motivation and reward.
“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 rates 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.
“In other words they learn to associate cigarette smoking with the nicotine surge,” said lead investigator Dr. Alain Dagher.
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.
These reasons may include the desire or need to maintain constant brain nicotine levels for cognitive enhancement (ie, improved attention, memory), or relief of stress or anxiety.
Researchers say that future investigations could focus on improving smoking cessation methods by tailoring treatments for different types of smokers.
Source: McGill University