Protein interacts with hormone that quells hunger.

A protein that's especially abundant in the blood of obese people inactivates a hormone that controls hunger, according to a new study.

Animals engineered to lack this hormone, leptin, eat more and gain weight, making the hormone an attractive target for obesity treatments. However, notes Allan Z. Zhao of the University of Pittsburgh, obese people typically produce the same concentration of leptin that thin people do.

Zhao and his colleagues suspected that, in obese people, some substance might prevent leptin from stimulating receptors in the brain that affect appetite. After analyzing rat and human blood, the researchers homed in on C-reactive protein (CRP), a substance that's associated with inflammation and has been found in higher-than-normal concentrations in obese people. From test tube experiments, the team found that CRP binds to leptin and prevents it from reaching its receptors.

In a different experiment, the researchers gave leptin to mice that were engineered not to produce the hormone. As expected, the animals then ate less and lost weight. However, when the scientists administered the hormone along with CRP, leptin had no discernible effect on the rodents' appetites or weight.

Zhao's team suggests in the April Nature Medicine that preventing leptin from interacting with CRP may provide a new way to treat obesity.