Scientists may be onto a tantalizing breakthrough in the treatment of obesity: a vaccine against fat. And no, this is no joke. The same principle that has made vaccines effective against infectious disease for centuries may apply to the inhibition of a hormone called ghrelin that encourages weight gain.

A team of researchers at the Scripps Research Institute in California have developed a vaccine that prevents rats from getting fat, according to a report published in the Proceedings of the National Academy of Sciences. The scientists say their work offers clues that could lead to human treatments.

They hope eventually to come up with a cure for the obesity epidemic, a serious and growing problem for millions of people worldwide. Obesity contributes to a range of health problems including heart disease, various cancers, Type 2 diabetes, stroke, arthritis and depression.

Pharmaceutical approaches to control body weight have been largely unsuccessful and several, including the drugs fenfluamine and ephedrine, have been banned by the US Food and Drug Administration.

Antidote for Yo-Yo Dieting?

Kim Janda, PhD, and colleagues developed three vaccinations against ghrelin, a hormone that stimulates hunger and facilitates the storage of sugar as fat. They then administered the vaccines to laboratory rats.

"While food intake was unchanged in all testing groups, those who were given the most effective vaccines gained the least amount of weight," said Dr. Janda, who is a professor of chemistry at Scripps Research, a member of the Skaggs Institute for Chemical Biology, and director of the Worm Institute of Research and Medicine.

"To have an impact on appetite and weight gain, ghrelin first has to move from the bloodstream into the brain -- where, over long periods, it stimulates the retention of a level of stored energy as fat. Our study is the first published evidence proving that preventing ghrelin from reaching the central nervous system can produce a desired reduction in weight gain."

The vaccine triggered the rats' immune systems to produce antibodies against the ghrelin, according to the researchers. It appeared to affect the ability of ghrelin to slow down metabolism as well as to store fat.

This finding may be especially important to stop what is commonly known as "yo-yo dieting," the cycle of repeatedly losing and regaining weight experienced by many dieters, the scientists suggested.

Turning Point

The ultimate goal is to develop a vaccine to aid weight loss in humans, Dr. Janda said. In 2003 to 2004, approximately 66 percent of all American adults 20 years of age or older were overweight or obese, according to the National Health and Nutrition Examination Survey. Almost 80 percent of American men aged 40 to 59 were categorized as overweight in a 2006 study published by the Journal of the American Medical Association. About 1 billion people worldwide are overweight or obese, based on recent reports from the World Health Organization.

"We're not claiming that our study answers the question of obesity treatment once and for all," said Dr. Janda. "What we are saying -- and what our study confirms -- is that [a vaccine against ghrelin] looks like a serious workable solution to the problem. And while much more research is needed to understand the full therapeutic potential of immunopharmacotherapy in combating obesity, these initial results are extremely positive. Right now it appears that active vaccination against ghrelin is one avenue that can slow weight gain and fat build-up in the body."

This study could mark a turning point in the treatment of obesity by confirming the effectiveness of immunopharmacotherapy to combat this serious and growing global problem, the scientists maintained. Immunopharmacotherapy engages the immune system, specifically antibodies, to bind to selected targets, directing the body's own immune response against them.

This approach is being tested in a number of other areas including drug addiction, especially addiction to cocaine and nicotine.