Shot of Natural Hormone Might Burn Fat Away

Posted October 7th, 2011 at 7:30 pm (UTC-4)
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The leaner mouse with functional brown fat (left) dissipates considerable amounts of energy as heat. The orexin-deficient mouse (right) stores energy as fat instead of burning it. (Image by Peter Allen, UCSB)

The leaner mouse with functional brown fat (left) dissipates considerable amounts of energy as heat. The orexin-deficient mouse (right) stores energy as fat instead of burning it. (Image by Peter Allen, UCSB)

An injection of a hormone produced naturally in the brain might help a person lose weight, without having to cut down on what they eat.

That’s the finding of U.S. researchers at the Sanford-Burnham Medical Research Institute in Florida.

The discovery could provide a new way to treat obesity and other metabolic disorders.

The hormone – orexin – appears to trigger so-called “good” fat to battle “bad” fat.

The fat we typically think of as body fat is called white fat. But we also have another form of fat known as brown fat and, unlike white fat, brown fat does more than just store fat.  According to researchers, it actually burns fat.

Brown fat is full of blood vessels and mitochondria, which is why it’s brown. This fat tissue is apparently very good at turning our calories into energy.

The researchers discovered that orexin activates calorie-burning brown fat in mice and that a deficiency of this hormone could be associated with obesity.

To investigate further, they acquired mice which were genetically engineered to lack orexin.  These mice weighed more than their non-engineered friends even though they actually ate less, which suggests overconsumption was not the cause their obesity.

The researchers found that these orexin-deficient mice, when fed a high-fat diet, were unable to properly convert the extra calories into heat the way normal mice do.  Instead, that energy wound up being stored as fat.

Probing further into the mice’s brown fat, the team discovered that brown fat in the orexin-free mice didn’t develop properly at the embryonic stage, and that this shortage had lasting effects on the creatures’ energy expenditure and weight, even in adulthood.

Furthermore, once the genetically-engineered mice were given some orexin, their offspring’s brown fat developed properly before birth and continued to be active into adulthood.

The team also found that adding orexin to stem cells in a laboratory dish caused them to specialize into brown fat cells, which created even more of a fat-burning engine.

“Without orexin, the mice are permanently programmed to be obese,” says Dr. Devanjan Sikder, senior study author. “With it, brown fat is activated and they burn more calories.”

Further study on mice shows that diet dependent obesity – the most common form of obesity – can be resolved by an injection of orexin, without having to reduce calorie intake.

While most current weight loss products tend to be aimed at reducing a person’s appetite, the researchers believe a therapy based on orexin could launch a new class of fat-fighting drugs.

“This is very exciting and illustrates a shift in paradigm of anti-obesity therapeutics,” says Sikder.

Encouraged by the findings, the researchers look forward to their next step – clinical trials.

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Rick Pantaleo
Rick Pantaleo maintains the Science World blog and writes stories for VOA’s web and radio on a variety of science, technology and health topics. He also occasionally appears on various VOA programs to talk about the latest scientific news. Rick joined VOA in 1992 after a 20 year career in commercial broadcasting.

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