FLICKING a metabolic switch could help obese people burn off excess fat, say
researchers in Italy.
Saverio Cinti and his colleagues at the University of Ancona have managed to
transform normal fat cells in rats into a different type that burns energy to
produce heat, instead of storing it. They hope that similar drugs could be
developed to help people lose weight.
Body fat, or adipose tissue, is actually a complex organ, composed of two
different types of fat cell. White adipose tissue mainly stores fat. Brown
adipose tissue, however, keeps the body warm by releasing the energy stored in
fat as heat.
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The ratio of white to brown fat is influenced by the environment. People who
work outdoors in cold climes have more brown fat. What鈥檚 more, if you keep a rat
at 4 掳C for a few days, it develops more brown fat, Cinti told the joint
meeting of the Association for the Study of Obesity and the Nutrition Society in
London last week. Once a rat is returned to normal temperatures, the effect is
reversed.
快猫短视频s have long known that drugs called beta-3 adrenoreceptor agonists
can alter the ratio of fat cells, but thought new brown fat cells might be
replacing existing white fat cells. Now Cinti and his colleagues have shown that
a beta-3 agonist called CL 316243 actually transforms mature white fat cells
into brown fat cells鈥攁 remarkable example of cell plasticity.
In rats given CL 316243, Cinti found that the white cells took on the
appearance of brown cells and developed many more mitochondria, the powerhouses
of cells. What鈥檚 more, they also started to make a protein called UCP-1.
In most cells, mitochondria use the energy they liberate to make ATP, the
fuel that drives chemical reactions in living organisms. But in brown fat cells,
UCP-1 鈥渦ncouples鈥� this process, forcing the cells to release energy as heat.
Previous studies have shown that beta-3 agonists can help obese mice to lose
weight. There鈥檚 no reason why the approach should not work in humans, Cinti
says. 鈥淧otentially, the adipose organ of all humans has the possibility of
transforming into brown fat.鈥� However, a treatment for people is some way off,
he adds, as no one has yet developed a safe drug.
One problem is that the beta-3 receptors of rodents have a very different
structure to those of humans. Drugs companies are now trying to develop
compounds that activate the human receptor, says Steve Smith of SmithKline
Beecham. 鈥淭he beauty of beta-3 agonists is that all the weight loss occurs from
fat and not muscle.鈥�