A new vaccine helps rats stay svelte no matter what they eat, a study has found. The findings represent the first published animal research on an "obesity vaccine." Meanwhile, a Swiss company is testing a related vaccine on people.
Obesity is a major challenge for the pharmaceutical industry. But some progress has been made. Since the early 1990s, scientists have managed to identify naturally occurring molecules that control energy expenditure, satiation, and other elements that govern weight gain and loss. One of these, the hormone ghrelin, was identified 7 years ago and is produced in the stomach (ScienceNOW, 10 November 2005). Rodents given ghrelin eat more and gain weight. Puzzlingly, however, mice that lack ghrelin don't eat less: They have normal appetites, although they burn excess fat.
Choosing the hormone as their target, chemical biologist Kim Janda of the Scripps Research Institute in San Diego, California, and colleagues at Scripps and Osaka City University in Japan, crafted three antighrelin vaccines. Each was designed to recognize and inactivate different parts of the hormone. The team immunized 14 male rats with one of the three vaccines; three others got a placebo. The rats received five shots over 12 weeks.
During the study, all rats ate similar amounts of food. But each day, recipients of two of the antighrelin vaccines gained less than a third of the weight put on by the other animals, the team reports online this week in Proceedings of the National Academy of Sciences. Janda speculates that the vaccine is speeding up metabolism, somehow allowing the rats to burn extra fat. Still, he cautions, "I'm not going to say this is going to be a drug of the future," although it could "point us in the right direction." Janda has applied for a patent on the vaccine and next plans to test it on obese animals.
The vaccine is a "very novel approach for the treatment of obesity," says Matthias Tschöp, an obesity researcher at the University of Cincinnati in Ohio. But he notes that obesity is probably far more complex in humans than in rats, so targeting just one molecule is "highly unlikely" to work in people. In addition, blocking ghrelin might cause side effects; Tschöp and others have found that the hormone may be involved in learning and memory.
Whether ghrelin proves a good target for human obesity may become clear soon. Cytos, a biotechnology company outside of Zurich, Switzerland, is testing a different antighrelin vaccine in a clinical trial of 112 obese humans; results, says Martin Bachmann, Cytos's chief scientific officer, will be available in November.