A team of scientists at the Scripps Research Institute has synthesized a new nicotine-degrading enzyme and successfully tested it in nicotine-dependent rats. Named NicA2-J1, the engineered enzyme decreased blood nicotine levels and had remarkable efficacy in reducing addiction-like behaviors in the rodents. The results appear in the journal Science Advances.
NicA2-J1 is a version of a natural enzyme produced by Pseudomonas putida, a Gram-negative, rod-shaped bacterium that is found in most soil and water habitats where there is oxygen.
It was modified — to optimize its potency, its staying time in the blood, and other pharmacological properties — by Scripps Research Institute’s Professor Kim Janda and colleagues.
“This is a very exciting approach because it can reduce nicotine dependence without inducing cravings and other severe withdrawal symptoms, and it works in the bloodstream, not the brain, so its side effects should be minimal,” said Dr. Olivier George, co-lead author of the study.
In one set of experiments, rats spent 21 hours of every day, for 12 days, in a chamber where they could press a lever to give themselves an intravenous infusion of nicotine. In this way they learned to self-administer nicotine, and became dependent on it.
After the 12 days the rodents were given access to nicotine only every 48 hours, which led them to experience withdrawal symptoms between access periods, and to escalate their intake — a classic sign of deepening addiction — whenever they regained access.
The animals treated with the highest dose of NicA2-J1 (10 mg/kg) continued to self-administer nicotine when they could, but showed very low blood levels of the molecule compared to controls that did not receive the enzyme.
Signs of nicotine withdrawal, such as susceptibility to pain and aggressive behaviors, were correspondingly reduced during the no-access periods, compared to untreated controls.
“It’s as if they were smoking 20 cigarettes but receiving the nicotine dose of only one or two, so that made their withdrawal process much less severe,” said co-lead author Dr. Marsida Kallupi.
Surprisingly, even the acute effect of NicA2-J1 on the nicotine-taking rats was benign. Typically when an animal is highly nicotine dependent, receiving a drug that suddenly blocks all nicotine activity will trigger withdrawal symptoms right away.
“It’s like quitting ‘cold turkey’ — the subject will feel horrible. However, what’s unique about this enzyme is that it removes enough nicotine to reduce the level of dependence, but leaves enough to keep the animals from going into severe withdrawal,” Dr. George said.
One of the other hallmarks of nicotine dependence is the continuation of nicotine-seeking despite serious adverse consequences — consequences that for human tobacco-smokers include short-term impairments of lung function and physical fitness, plus longer-term risks of cancers, heart disease, stroke, and many other ailments.
The study authors showed that NicA2-J1 could reduce this compulsive motivation for nicotine in the addicted rats.
When each lever-press for nicotine also brought a 30% chance of receiving an electric shock to the feet, the NicA2-J1-treated rats — unlike untreated controls — quickly reduced their lever presses.
The scientists modeled yet another key aspect of nicotine dependence, the susceptibility to relapse after abstinence: they took the rats off nicotine for 10 days, then gave them an injection of nicotine to re-awaken their desire for the drug, and restored access via the lever-presses.
Untreated rats who were primed this way increased their lever presses by a large amount — NicA2-J1 treated rats much less so.
The same beneficial effect of NicA2-J1 was seen when the researchers triggered relapse with a stress-inducing drug, mimicking the way that stress causes relapse in humans.
With such promising results in preclinical tests, the team now hopes to take NicA2-J1 into clinical trials in humans.
Marsida Kallupi et al. 2018. An enzymatic approach reverses nicotine dependence, decreases compulsive-like intake, and prevents relapse. Science Advances 4 (10): eaat4751; doi: 10.1126/sciadv.aat4751