Gene jabs slim down fat rats

Injections of a fat-regulating hormone help rats to lose weight by turning their fat-storing cells into fat-burning cells, say US and Swiss scientists. Rats injected with a gene that makes the hormone leptin displayed 'substantial weight loss' after just two weeks of therapy, say the researchers. They conclude that their study, published online in the journal Proceedings of the National Academy of Sciences, suggests new ways to treat obesity in people.

Scientists have known for some time that leptin is involved in controlling appetite and body weight - mice bred to have no leptin are severely obese. However, its role in humans is not fully understood: in a few families, obesity has been linked to leptin gene mutations, but many overweight people have normal or high levels of the hormone. In the latest study, researchers based at the Veteran's Affairs Medical Center in Dallas, US, and the University of Geneva Medical School in Switzerland, compared the effects of leptin injections with that of a low-calorie diet. They studied laboratory rats weighing between 280 and 300 grammes, some of which received intravenous injections of the leptin gene, while others followed a restricted diet. The scientists found that after just two weeks, the rats receiving the leptin gene therapy lost almost a third of their total body weight. And in contrast to the restricted diet animals, which had less energy and were constantly searching for food, the rats given the leptin were healthy, active and had a decreased appetite.

When the researchers looked at the fat-storage cells of the rats treated with leptin, they found that instead of containing fat, they were packed with mitochondria: the 'powerhouses' of the cell, which convert nutrients into energy. Lead author Dr Roger Unger said that the cells had a 'very novel' appearance, that had not been seen before. 'The ability to convert fat cells into fat-burning cells may suggest novel therapeutic strategies for obesity' he said. The study also found that the rats treated with leptin did not put weight back on as quickly as the rats fed a restricted diet. But UK expert Dr Andrew Hill, of the Association for the Study of Obesity, cautioned that there was 'an enormous distance' between what the researchers had done and a human treatment for obesity. He added that despite the prospect of scientific quick-fixes for obesity, for most people the only solution was to work hard at maintaining a low weight throughout their life.