VACCINES designed to help people give up smoking or kick a cocaine habit are already undergoing trials. And soon the first ever vaccine designed to help people lose weight will join them.
The vaccine tricks the body into making antibodies that neutralise ghrelin, a hormone released into the bloodstream by cells lining the stomach. When it reaches the brain, ghrelin triggers feelings of hunger.
But if it is intercepted by antibodies in the bloodstream, the hormone cannot activate the usual 鈥渇eed me鈥� signal. 鈥淲e want to reduce the feeling of hunger,鈥� says Claudine Blaser of Cytos Biotechnology of Zurich, Switzerland, the company developing the vaccine. 鈥淎s far as we know, it鈥檚 the only vaccine approach for obesity.鈥�
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Mice given the vaccine put on 15 per cent less weight on a high-fat diet than unvaccinated animals. Now Cytos is planning to test different doses of the vaccine, code-named CYT009-GhrQb, on 112 volunteers, the company announced last week.
Not everyone is convinced the vaccine will work. Appetite researcher Steven Bloom at Imperial College London says that contrary to what one might expect, obese people have low levels of ghrelin anyway, so reducing levels of the hormone still further is unlikely to influence appetite.
David Cummings of the University of Washington in Seattle, another appetite researcher, agrees that the vaccine itself might not help people lose weight. But because weight loss by almost any means increases ghrelin levels, he thinks the vaccine might help people keep their weight down after shedding the pounds by means such as dieting or exercise.
Then there is the question of safety. Bloom questions whether it is wise to make the immune system target the body鈥檚 appetite signalling system. There is a risk of knocking out an entire neurofeedback loop, he points out.
But Blaser says that trials of similar vaccines show that antibody levels fall by a half within about 50 days of the initial vaccination. So the effect should be reversible, unless regular booster jabs are given. And the approach is certainly less drastic than surgical methods such as stomach stapling.
Other companies are trying to block ghrelin using a more traditional approach. Noxxon Pharma of Berlin, Germany, hopes next year to test Speigelmer, a small-molecule drug designed to mop up ghrelin in blood. Patients would have to take pills regularly, whereas those given the vaccine would need only an occasional booster. But Noxxon argues that a pill would allow better fine-tuning of appetite over time.
Targeting ghrelin is just one of many strategies being pursued by companies eager to get a slice of the vast market for anti-obesity drugs. For instance, Rimonabant, developed by the French company Sanofi-Aventis, blocks CB1, a cannabinoid receptor in the brain that triggers hunger when activated. Sanofi hopes for approval from the US Food and Drug Administration next year.
Meanwhile, Bloom at Imperial says he has an ace up his sleeve. He has been exploring the use of a hormone called oxyntomodulin, which in the body does the opposite of ghrelin, reducing appetite after a meal. A clinical trial of oxyntomodulin has already been completed, and the results will be published soon, Bloom says.
