|WASHINGTON: Scientists have designed a new effective nicotine vaccine which they believe could help smokers and even drug addicts quit.
"This study provides new hope that one could make a nicotine vaccine that succeeds in clinical trials," said Kim Janda from The Scripps Research Institute (TSRI).
Nicotine vaccines train the body to see nicotine as a foreign invader. To prompt this immune response, scientists have tried attaching nicotine derivatives called haptens to a larger carrier protein used in other approved vaccines.
The body reacts to the vaccine by creating antibodies to bind specifically to nicotine molecules. When a person later uses tobacco, the anti-nicotine antibodies stop the nicotine molecules from entering the central nervous system and ever reaching the brain.
Though a vaccine would not be a silver bullet - there would still be withdrawal symptoms - a person may be less motivated to relapse because the brain's reward system could no longer react to nicotine, researchers said.
The problem with the previous nicotine vaccine, which only worked in 30 per cent of patients, was that it did not single out the most common form of nicotine for attack.
Nicotine has two forms that look like mirror images of each other - one is a "right-handed" version and one is a "left-handed" version. Even though 99 per cent of the nicotine found in tobacco is the left-handed version, the previous vaccine elicited antibodies against both.
Janda believes that was a waste of immune response. The researchers elicited a more robust antibody response by creating a vaccine from only left-handed nicotine haptens.
They prepared haptens as a 50-50 mixture and as pure right-handed or pure left-handed versions of nicotine, so they could use the two versions together or separately.
They tested both versions and the 50-50 mix in rat models, injecting the rats three times over 42 days. This series of "booster" shots gave the animals' immune systems a chance to create an effective number of antibodies to respond to nicotine.
The researchers analysed blood from the three experimental groups and found that the left-handed hapten elicited a much more effective immune response.
Compared with the right-handed hapten vaccine, the left-handed hapten vaccine prompted the body to create four times as many antibodies against left-handed nicotine molecules.
The 50-50 mix was only 60 per cent as effective as the pure left-handed version.
"This shows that future vaccines should target that left-handed version," said Jonathan Lockner, research associate in the Janda lab and first author of the new paper.
"There might even be more effective haptens out there," said Lockner. The study was published in the Journal of Medicinal Chemistry.