Hormone may hold key to weight loss

WASHINGTON - Leptin, a hormone that affects weight and appetite, apparently helps wire the brain in ways that might set an animal on a lifetime path to slenderness or obesity, two teams of US researchers have found.

The studies may take doctors a step closer to understanding whether leptin could be manipulated to help overweight people lose weight and keep it off.

The findings may also help explain why the food a person eats when very young, or even what a mother eats while pregnant, affects weight, heart disease and other aspects of metabolism later in life.

In one study, a team at the Howard Hughes Medical Institute and Rockefeller University and at Yale University found that leptin affected both the physical structure and the function of neural circuits in the brain.


When it was discovered in 1994, leptin thrilled scientists because it seemed so basic to obesity and appetite. Overweight rodents fed leptin lost weight and studies quickly showed that some overweight people had unusually low levels of the hormone.

But leptin's effect was not so straightforward in humans, and it became clear that simply injecting obese people with it was not going to make them lose weight.

In a second study, scientists at Oregon Health & Science University found exposure to leptin early in life affected brain structures involved in weight regulation.

Also working with mice, Richard Simerly and colleagues tracked development of neurons in a part of the brain called the arcuate nucleus of the hypothalamus.

Brain circuits there were less developed in mice which were genetically engineered to make no leptin compared to normal mice.

Injecting baby mice with leptin restored normal brain structure.

"We're excited about this finding because it shows how exposure to leptin can directly affect development of brain structures involved in regulating body weight," Simerly said.

"Our findings suggest a link between the developmental actions of leptin and early onset obesity.

"We were shocked by how clear the result was. Leptin plays an important role in brain development, by acting specifically on the clusters of brain cells that regulate food intake."

Scientists Joel Elmquist and Jeffrey Flier said the findings supported the concept that under- and over-nutrition during critical periods of hypothalamic (brain) development could induce long-lasting and potentially irreversible effects into adulthood.

- REUTERS