Researchers at Joslin Diabetes Center have shown that while a type of "good" fat
found in the body can be activated by cold temperatures, it is not able to be
activated by the drug ephedrine.
The finding, published in
PNAS
USA Early Edition, may lead to drugs or other methods aimed at activating the
good fat, known as brown fat. When activated, brown fat burns calories and can
help in the battle against
obesity.
"We
propose that agents that work similarly to cold in activating brown fat
specifically can provide promising approaches to fighting obesity while
minimizing other side effects," said Aaron Cypess, M.D., Ph.D., an assistant
investigator and staff physician at Joslin and lead author of the paper.
"At the same time, we now know that ephedrine is not the way to do it,"
he added.
Brown fat is found in humans naturally and consumes calories
to generate heat. Prior studies had shown that brown fat can be activated by
cold exposure in a process called non-shivering thermogenesis.
Researchers have been working for years to find ways to activate brown
fat.
Ephedrine, a decongestant and bronchodilator, has been used as a
weight loss drug because it increases the number of calories burned. However,
there are side effects.
In this study, the Joslin team tested 10 study
subjects in three ways. They were each separately given injections of ephedrine,
given injections of saline as a control, and made to wear "cooling vests" that
had water cooled to 57 degrees pumped into them. After each intervention, the
brown fat activity was measured using PET/CT scans.
The researchers
found that brown fat activity was the same following both the ephedrine and
saline injections. However, after the subjects wore the cooling vests for two
hours, their brown fat activity was stimulated significantly.
Both
interventions - ephedrine injections and the wearing of the cooling vests - did
result in the same number of calories being burned, Dr. Cypess noted.
"But we found that ephedrine was not using brown fat to do it," he said.
"This is the first time it has been found that ephedrine does not turn on brown
fat."
Both interventions had other effects on the sympathetic nervous
system - which activates the fight or flight response - such as increased blood
pressure, but those associated with brown fat activation were fewer, the study
showed.
"Mild cold exposure stimulates (brown fat) energy expenditure
with fewer other systemic effects, suggesting that cold activates specific
sympathetic pathways," the paper concludes. "Agents that mimic cold activation
of (brown fat) could provide a promising approach to treating obesity while
minimizing systemic effects."
As a result of the findings, drug
companies may find it easier to come up with agents that stimulate brown fat to
help people lose weight, Dr. Cypess said.
One method may be simply to
design cooling vests that people can wear to help them lose weight. A future
study will have subjects wear the vests for several weeks to see what happens,
Dr. Cypess said.
"Will they get the same health benefits they would have
seen with several weeks of exercise? That's the billion dollar question."
The findings should also be of interest to heart researchers interested
in the mechanisms of activation of the sympathetic nervous system, he added.
http://www.medicalnewstoday.com/releases/246251.php
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