Vaccine Lets Rats Pig Out, Stay Svelte

Scientists at Scripps Research Institute in La Jolla have developed an experimental anti-obesity vaccine that allowed rats to feast on dry pet chow without getting fat.

The vaccine reduced levels of ghrelin, a hormone found in mammals that regulates the consumption and storage of fat, according to their study, which was published today in the Proceedings of the National Academy of Sciences.

The rats received up to four shots over nine weeks.

The vaccine appeared to be long-acting: One week in a rat’s life is the equivalent of one year for humans, the researchers said.

The experiment opens the possibility of a vaccine that could one day help people lose weight.

Since the discovery of the hormone in 1999, scientists have been searching for a drug that would block ghrelin to help reduce weight.

In the published study, vaccinated rats were allowed to eat regular rat food for 13 weeks.

A control group of rats received an inactive form of the vaccine.

The rats that received the active vaccine ate as much food as the rats in the control group.

But by the end of the experiment, vaccinated rats weighed 20% to 30% less.

Scripps chemist Kim D. Janda, one of the study’s authors, said the results were a surprise because ghrelin had been thought to work by regulating appetite.

Instead, ghrelin apparently altered the rats’ metabolism, Janda said, so that vaccinated rats accumulated less fat and more muscle.

The vaccine worked by tricking the rats’ immune system into attacking the body’s naturally produced ghrelin.

The vaccine was made of ghrelin to which scientists had attached a sea-mollusk protein.

The immune system interpreted both the mollusk protein and ghrelin as foreign, destroying them.

Some researchers were not convinced the vaccine had long-term promise.

In previous experiments, mice incapable of producing ghrelin became just as fat as normal mice.

Yuxiang Sun, a ghrelin researcher at Baylor College of Medicine in Houston who was not connected with the current study, said that eating was such a basic human function that it seemed unlikely that a single hormone could govern appetite, fat storage and weight gain.

Dr. David Cummings, a professor of medicine at the University of Washington in Seattle, said that the number of animals in the study -- 17 -- was very small, and that much larger studies were needed to confirm the results.

But he said he thought the experiment provided strong evidence of the role ghrelin played in weight gain.