Cigarette smokers have new ally in fighting nicotine addiction, researchers say

ATLANTA (CNN) -- A medication used in the treatment of a skin disease can help smokers who are trying to end their nicotine addiction, Canadian researchers reported Wednesday.

It works by reducing the activity of an enzyme that metabolizes nicotine inside a smoker's body.

The research "opens up an exciting new avenue of treatment" for nicotine addiction, said Dr. Alan I. Lesher, director of the U.S. National Institute on Drug Abuse.

After a cigarette, a smoker has nicotine in his bloodstream. As the nicotine slowly metabolizes, its level in the blood drops. At a certain point, the smoker is often chemically triggered to light another cigarette, researchers at the University of Toronto reported.

Methoxsalen, a compound used to treat psoriasis, slows the metabolism of nicotine. The delay causes nicotine to last longer in the bloodstream, thus postponing the smoker's urge for another cigarette, they said.

Using methoxsalen improves the effectiveness of nicotine-replacement therapy -- often administered by a skin patch or by chewing gum, said the lead researcher, Dr. Edward Sellers of the university.

In the study, when methoxsalen was combined with controlled oral nicotine doses, smokers tested had fewer cigarettes, waited longer intervals between cigarettes and took fewer puffs on each cigarette, the researchers reported in the journal Clinical Pharmacology and Therapeutics.

"The primary pharmacologic function of tobacco smoking is to deliver nicotine to the brain," the journal article said. "Tobacco-dependent smokers try to maintain their (blood) plasma nicotine concentration within a relatively narrow range to avoid toxicity or withdrawal."

An enzyme, CYP2A6, is the chemical key for removing nicotine from the bloodstream, the researchers said. And methoxsalen inhibits CYP2A6.

In earlier studies, researchers found that people with a deficiency in CYP2A6, perhaps because of genetic reasons, are less likely to start smoking and if they do, they smoke less often than people with normal levels of CYP2A6.

"CYP2A6 inhibition appears to be a potential component of a potent, novel treatment for tobacco dependence," the report said.

"As most of the health risks of tobacco use are consequences of exposure to constituents of the smoke other than nicotine, there are considerable potential health benefits of CYP2A6 inhibition," the researchers said.

Lesher of the National Institute on Drug Abuse said a new treatment based on the Canadian research "can help smokers substantially reduce their exposure to the deadly particles of tobacco smoke while they overcome the addiction to nicotine that makes it so hard to quit."

Before methoxsalen can be safely employed for long-term use in battling nicotine addiction, additional study is needed, Sellers said. The drug has not been proven safe for long term use in humans.

The nicotine study was partly financed by the National Institute on Drug Abuse, part of the U.S. National Institutes of Health, and by Nicogen Inc., a Toronto-based private-venture capital company pursuing biopharmaceuticals.

Nicogen's board of directors includes two of the study's researchers -- Sellers, M.D. and Ph.D., and Rachel F. Tyndale, Ph.D. Both are vice presidents of Nicogen, and both are on the faculty of the University of Toronto.

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University of Toronto
Nicogen Inc.
National Institute on Drug Abuse

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