Researchers are reporting progress toward what would be a dream come true for many Americans: a vaccine to prevent obesity.

The target of this vaccine is ghrelin, a recently discovered hormone that decreases energy expenditure and fat breakdown. Scientists at the Scripps Research Institute in California reported in this week’s issue of the Proceedings of the National Academy of Sciences that they have developed a way to make the immune system produce antibodies that attack ghrelin, and that rats given the vaccine ate normally but lost weight.

“We have enabled the immune system to recognize a molecule that it ordinarily won’t recognize,” explained study author Kim D. Janda, a professor of chemistry at Scripps.

The immune system thus produced antibodies that bound to and deactivated ghrelin, just as vaccines against diseases caused by bacteria or viruses bind to and inactivate them.

Mice given shots of the vaccine ate just as much as untreated mice but had “about a 20 or 30 percent reduction in weight gain,” Janda said.

However, the mice were fed low-fat, low-energy diets. It’s not certain that a ghrelin vaccine would be effective against the burger-rich, high-fat diet that many Americans eat, the researchers noted.

This is not the only effort to develop a vaccine against ghrelin, the Scripps researchers added. Cytos, a Swiss-based biotechnology company, is already testing a different vaccine in humans. It works in a different way than the Scripps vaccine, by preventing the uptake of ghrelin by the brain.

A lot of basic work must be done before the Scripps obesity vaccine will be tried in humans, Janda said. “We’re going to look at some different flavors of antibodies, see how they work, and then try them in animals,” he said.

Caution will be the byword, Janda said. “We want to do real basic work and make sure we do all our homework before we look at it in humans,” he stressed. “We could do it quickly, but it’s prudent to know exactly what’s going on.”

His best guess is that a first human trial is “about two years” away. The Scripps group is looking to link up with a major pharmaceutical company to help develop a usable vaccine, Janda said.

It’s too early to say how such a vaccine would be given, he said. “It depends on what kind of vaccine it is,” Janda said. “It could be given just once or it could be multiple shots.”

And shots might not even be necessary. There could be an oral vaccine, of the same type as developed for polio and other disease, Janda said.

Dr. David E. Cummings, an associate professor of medicine at the University of Washington, did early work showing that ghrelin levels rise before each meal. He said the new study goes a long way toward showing that a ghrelin vaccine could reduce weight gain.

The one doubt about ghrelin has been whether its removal would affect weight gain, Cummings said. The weight loss in animals bred to lack the ghrelin gene has been “very subtle,” he said, raising doubts about the value of an attack on ghrelin.

“The potential value of this study is that it answers the question, ‘What if you remove ghrelin from an adult animal?’ ” Cummings said. “This paper shows that it does affect weight.”

Source: British Diabetes Foundation