May 30, 2014

By Medical Discovery News

While they are some of the largest bears on earth, Grizzly bears aren’t usually accused of being fat. Regardless, these animals are helping scientists discover new and better treatments for human obesity and diabetes.

Grizzlies spend the late summers consuming more than 50,000 calories per day. As a comparison, a moderately active 50-year-old human female is recommended 2,300. Grizzlies then hibernate for up to seven months, relying on the pounds of stored fat they accumulated before winter. While hibernating, bears do not eat, urinate, or defecate. 

Scientists wondered if all the weight and fat bears gain results in diabetes like it does in humans. Overweight people face an increased risk of type 2 diabetes, in which the body does not make enough of the hormone insulin or cells do not respond to it. Insulin helps move a type of sugar called glucose from the blood into cells, where it is used for energy and as a precursor for other molecules the body needs. If sugar levels in the blood remain elevated and the body doesn’t have enough insulin, cells are starved for energy, leading to damaged eyes, kidneys, nerves, and hearts. 

Interestingly, Grizzly bears can actually control their insulin responsiveness. When they are the fattest, they are most sensitive to insulin, thereby keeping their blood sugar levels healthy. Soon after going into hibernation, they switch to complete insulin resistance, meaning they develop type 2 diabetes. But unlike humans, their blood sugar levels remain normal. When they awaken in the spring, their insulin responsiveness is restored. Bears do this not so much to regulate their blood sugar levels as to regulate their storage and utilization of fat. So how do bears control their insulin responsiveness? And could it lead to new treatments for type 2 diabetes in humans?

PTEN is a protein that regulates cells’ sensitivity to insulin. Scientists know exactly when Grizzlies increase or decrease PTEN activity, they just don’t know how. People with a PTEN mutation have a metabolism similar to Grizzlies’.  These people have an increased risk of obesity and cancer but a decreased risk of developing type 2 diabetes because they are more sensitive to insulin.

Grizzlies have also evolved to the ability to accumulate large amounts of fat only in their adipose tissue, just below the skin so it doesn’t interfere with the rest of their bodies. In humans, on the other hand, fat can accumulate in many places like the liver, in muscles, and around other internal organs, which are all highly unhealthy places to keep fat. Bears can also have elevated levels of cholesterol without the serious consequences of cardiovascular disease.

During hibernation, the Grizzly bears’ kidneys shut down. But despite the high levels of toxins that accumulate in the blood without working kidneys, they don’t die or even suffer from it like a human would. When they wake up, their kidney function is restored with no permanent damage.

After millions of years of evolution, Grizzly bears and other animals have developed solutions for biological challenges humans still face. Studying them is a new approach that has the potential to create treatments for many human conditions.

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