Researchers
from the Johns Hopkins University
School of Medicine have made a discovery that could eventually treat
obesity in humans.
A recent
trio of studies reported that obesity rates have
doubled in less than 30 years worldwide. In 1980, 5 percent of men and
8 percent of women were obese. By the end of 2008, 10 percent of men and 14
percent of women were obese. This means that worldwide, 343 million men and 458
million women were obese just three years ago. In addition, another 1.5 billion
adults were overweight.
Today,
more than two-thirds of U.S. adults are overweight and more than one-third are
obese.
Sheng Bi,
M.D., study leader and associate professor of psychiatry and behavioral
sciences at the Johns Hopkins University School of Medicine, and a team of
researchers have now found that reducing the expression of a certain protein in
the brains of rats decreases their calorie intake and weight. Also, their fat
was transformed into another type of fat that burns off more energy.
Bi and
his colleagues made this discovery by studying the two types of fat that the
body makes, which are white and brown adipose tissues. White fat stores the
extra calories we eat and is found around the mid-section and other places. It
has one large droplet of lipid, which is a building block for fat like
triglycerides and cholesterol. Brown fat, on the other hand, is a better fat
that has several little droplets of lipid, and each little droplet has its own
power source to allow for heat generation. Brown fat is known for its energy
burning characteristics.
Sheng
wanted to figure out if suppressing the neuropeptide Y (NPY) protein in the
dorsomedial hypothalamus, which is located right above the brain stem and
regulates thirst, hunger, water balance, blood pressure and body temperature,
would reduce body fat in rats. NPY is an appetite-stimulating protein.
In the experiment, Sheng had two groups of rats that
were both fed a regular diet. One group was a control group while the other was
treated with a virus to inhibit NPY expression. Over a five-week period, both
groups were observed, and Sheng found that those with NPY suppression were
eating less.
The
researchers then divided both groups into two, making four groups of rats. One
of the treated groups and one of the control groups were given a regular diet
while the other control group and treated group were given a high-fat diet.
The
results showed that the control group on the regular diet weighed more after 11
weeks than the treated group on the regular diet. As far as the high-fat diet
goes, the suppressed NPY group gained less weight than the control group, which
became obese.
Sheng
explained that the less NPY expressed, the less the rats would eat, thus the
more weight lost. In addition, after the rats died, Sheng checked the fat in the bodies and found that brown fat
had begun to replace white fat. This was confirmed through the observation of
levels of mitochondrial uncoupling protein-1, or UCP-1, "through which
brown fat burns to produce heat." Researchers originally expected to find
white fat, but found signs of brown in the groin area of the rats.
Sheng
believes this occurred due to brown fat stem cells being contained in white fat
tissue. Brown fat is found in infants, but as we age, it fades and is replaced
by white fat. Sheng believes that brown fat may not fade completely, but just
becomes inactive, as we grow older.
Researchers
hope to one day inject brown fat stem cells under the skin in order to burn
white fat, which would lead to weight loss in humans.
"If
we could get the human body to turn 'bad fat' into 'good fat' that burns
calories instead of storing them, we could add a serious new tool to tackle the
obesity epidemic in the United States," said Sheng.
This study was published in Cell
Metabolism.
