By Marie Ellis
Medical News Today
Brown adipose tissue – also known as brown fat – is a beneficial form of fat that acts as the body’s furnace, burning energy and glucose to make heat. Previous research has shown that obese individuals have less brown fat, and now, researchers may have discovered why: a specific hormone is elevated in obese people, inhibiting brown fat activity and contributing to obesity and diabetes.
The researchers – led by Prof. Gregory Steinberg, of the Michael G. DeGroote School of Medicine and co-director of the Metabolism and Childhood Obesity Research Program at McMaster University in Ontario, Canada – publish their work in the journal Nature Medicine.
They explain that there are two types of serotonin, a chemical created by the body that acts as a neurotransmitter, relaying signals from one area of the brain to another. Though most people are familiar with the type that affects mood and appetite, this type only accounts for 5% of the body’s serotonin.
The other 95% is known as peripheral serotonin, which circulates in the blood, and the researchers say this type reduces brown fat activity. In the first study of its kind, the team has shown that blocking the creation of this type of serotonin results in more active brown fat.
“Our results are quite striking,” says Prof. Steinberg, “and indicate that inhibiting the production of this hormone may be very effective for reversing obesity and related metabolic diseases including diabetes.”
Blocking Tph1 in mice improves brown fat’s ability to burn calories
Prof. Steinberg and his colleagues note that the majority of the body’s serotonin is produced by an enzyme called tryptophan hydroxylase (Tph1).
When they genetically removed or blocked Tph1 in mice that were fed a high-fat diet, the mice experienced an improved ability of their brown fat to burn more calories, protecting them from obesity, fatty liver disease and pre-diabetes.
Co-author Waliul Khan, associate professor at the medical school, notes that our “high-fat western diet” is “an environmental cue that could be causing higher serotonin levels in our body.”
“Too much serotonin is not good,” he adds. “We need a balance. If there is too much, it leads to diabetes, fatty liver and obesity.”
Furthermore, Prof. Steinberg explains that too much peripheral serotonin “acts like the parking brake on your brown fat. You can step on the gas of the brown fat, but it doesn’t go anywhere.”
He adds that inhibiting the peripheral serotonin does not affect the brain’s serotonin or the functioning of the central nervous system, which is in contrast to earlier weight-loss drugs that suppressed appetite by altering brain serotonin levels.
Such drugs were linked to cardiac complications and increased risk of depression and suicide, he says, which is why they are working on “increasing energy expenditure instead of decreasing the appetite, which involves more risks.”
The researchers are now working on a pharmacological “enzyme blocker” that reduces serotonin production by inhibiting Tph1.