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Large Study Reveals Prevalence, Health Benefits of Brown Fat

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Brown Fat
Credit: Andreas G. Wibmer and Heiko Schöder. Memorial Sloan Kettering Cancer Center, New York

It’s pretty easy to spot differences between the two people on these positron emission tomography (PET) scans. In the scan of the male individual on the left, you see lots of small, dark spots around the neck and shoulders. But you can’t see any on the female on the right. What’s the explanation? Is this a sex difference? No! Brown fat!

This energy-burning type of fat happens to show up as small, dark spots in the neck and shoulder area on PET scan studies. So, as these scans reveal, the individual on the left possesses an abundance of brown fat, while the person on the right has essentially none. This wide range of difference in abundance is true for both men and women.

Researchers’ interest in brown fat began to heat up (sorry about that!) more than a decade ago when it was discovered that certain adults have persistently high levels of brown fat. It’s long been known that babies have brown fat, but it had been thought this fat generally vanished as children grew up. It turns out that adults who hold onto their brown fat are less likely to be overweight than adults who do not. That’s because brown fat actually burns extra calories, instead of storing it in the way the more familiar white fat does.

But are people with more brown fat actually any healthier? After studying about 130,000 PET scans from more than 52,000 people, researchers led by Paul Cohen, The Rockefeller University Hospital, New York, NY, say that the answer is “yes” in certain key areas. In a recent study in the journal Nature Medicine, they found that people with detectable brown fat had a lower incidence of many cardiovascular and metabolic conditions, including type 2 diabetes, congestive heart failure, and high blood pressure.

Studies to explore the health benefits of brown fat have been challenging to do. That’s because brown fat only shows up on PET scans, which measure how much glucose various tissues consume, an indication of their metabolic activity. What’s more, PET scans are quite costly and involve radiation exposure. So, researchers have been reluctant to ask healthy people to undergo a PET scan just to look at brown fat. But a solution occurred to the study’s first author Tobias Becher, who was aware that thousands of patients at nearby Memorial Sloan Kettering Cancer Center were undergoing PET scans each year as part of routine evaluation and care. In fact, cancer doctors often make note of brown fat on PET scans, if only to make sure it’s not mistaken for cancer.

So, the Cohen lab teamed up with Memorial Sloan Kettering Cancer Center radiologists Heiko Schöder and Andreas G. Wibmer to review many thousands of PET scans for the presence of brown fat. And they found it in about one of 10 people.

Next, they looked for health differences between the 10 percent of people with brown fat and the 90 percent who lack it. The differences turned out be striking. Type 2 diabetes was about half as prevalent in folks with detectable brown fat compared to those without. Individuals with brown fat also were less likely to have high cholesterol, high blood pressure, congestive heart failure, and coronary artery disease.

The findings suggest that brown fat may even help to offset the negative health effects of obesity. The researchers found that obese people with brown fat had a health profile that otherwise appeared more similar to individuals who weren’t obese. In fact, the benefits of brown fat were more pronounced in individuals who were overweight or obese than they were in people of normal weight.

Still, the researchers note that people with cancer might tend to show differences in brown fat compared to healthy adults. There’s some evidence also that prevalence may vary across cancer types and stages. The researchers took those variables into account in their studies. It’s also known that women are more likely to have brown fat than men and that the amount of brown fat tends to decline with age. What’s not yet well understood is whether differences in brown fat exist among people of different racial and ethnic backgrounds, and whether specific genetic factors are involved.

So, plenty of questions remain! Researchers not only want to figure out why some adults have so much more brown fat than others, they want to explore whether brown fat produces hormones that may add to its calorie-burning benefits. The hope is that these and other discoveries could eventually lead to new strategies for treating obesity, diabetes, and other metabolic conditions.

Reference:

[1] Brown adipose tissue is associated with cardiometabolic health. Becher T, Palanisamy S, Kramer DJ, Eljalby M, Marx SJ, Wibmer AG, Butler SD, Jiang CS, Vaughan R, Schöder H, Mark A, Cohen P. Nat Med. 2021 Jan;27(1):58-65.

Links:

Paul Cohen (The Rockefeller University, New York, NY)

Heiko Schöder (Memorial Sloan Kettering Cancer Center, NY)

Andreas Wibmer (Memorial Sloan Kettering Cancer Center, NY)

NIH Support: National Center for Advancing Translational Sciences


Can Artificial Cells Take Over for Lost Insulin-Secreting Cells?

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artificial beta cells

Caption: Artificial beta cell, made of a lipid bubble (purple) carrying smaller, insulin-filled vesicles (green). Imaged with cryo-scanning electron microscope (cryo-SEM) and colorized.
Credit: Zhen Gu Lab

People with diabetes have benefited tremendously from advances in monitoring and controlling blood sugar, but they’re still waiting and hoping for a cure. Some of the most exciting possibilities aim to replace the function of the insulin-secreting pancreatic beta cells that is deficient in diabetes. The latest strategy of this kind is called AβCs, short for artificial beta cells.

As you see in the cryo-SEM image above, AβCs are specially designed lipid bubbles, each of which contains hundreds of smaller, ball-like vesicles filled with insulin. The AβCs are engineered to “sense” a rise in blood glucose, triggering biochemical changes in the vesicle and the automatic release of some of its insulin load until blood glucose levels return to normal.

In recent studies of mice with type 1 diabetes, researchers partially supported by NIH found that a single injection of AβCs under the skin could control blood glucose levels for up to five days. With additional optimization and testing, the hope is that people with diabetes may someday be able to receive AβCs through patches that painlessly stick on their skin.


Feed a Virus, Starve a Bacterium?

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Woman eating hot soup in bed

Thinkstock/Stockbyte

Yes, the season of colds and flu is coming. You’ve probably heard the old saying “feed a cold and starve a fever.” But is that sound advice? According to new evidence from mouse studies, there really may be a scientific basis for “feeding” diseases like colds and flu that are caused by viruses, as well as for “starving” certain fever-inducing conditions caused by bacteria.

In the latest work, an NIH-funded research team found that providing nutrition to mice infected with the influenza virus significantly improved their survival. In contrast, the exact opposite proved true in mice infected with Listeria, a fever-inducing bacterium. When researchers forced Listeria-infected mice to consume even a small amount of food, they all died.


Taking a New Look at Artificial Sweeteners

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Packets of artificial sweetenersDiet sodas and other treats sweetened with artificial sweeteners are often viewed as guilt-free pleasures. Because such foods are usually lower in calories than those containing natural sugars, many have considered them a good option for people who are trying to lose weight or keep their blood glucose levels in check. But some surprising new research suggests that artificial sweeteners might actually do the opposite, by changing the microbes living in our intestines [1].

To explore the impact of various kinds of sweeteners on the zillions of microbes living in the human intestine (referred to as the gut microbiome), an Israeli research team first turned to mice. One group of mice was given water that contained one of two natural sugars: glucose or sucrose; the other group received water that contained one of three artificial sweeteners: saccharin (the main ingredient in Sweet’N Low®), sucralose (Splenda®), or aspartame (Equal®, Nutrasweet®). Both groups ate a diet of normal mouse chow.


Protein Machines at Work

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This video shows a molecular view of the reactions that take place inside the pyruvate dehydrogenase complex, a protein machine found in the cell’s powerhouse, the mitochondria. 3D imaging of this machine by high-resolution electron microscopy reveals how the different components essential for the reaction are organized. Watch the flexible arms move inside the protein machine as pyruvate (an essential compound made from glucose) gets converted into acetyl-CoA (a precursor to the cell’s energy supply).

Credit: Jacqueline Milne and Sriram Subramaniam, Laboratory of Cell Biology, National Cancer Institute; Donald Bliss, National Library of Medicine; NIH

References:

Molecular architecture and mechanism of an icosahedral pyruvate dehydrogenase complex: a multifunctional catalytic machine. Milne JL, Shi D, Rosenthal PB, Sunshine JS, Domingo GJ, Wu X, Brooks BR, Perham RN, Henderson R, Subramaniam S. EMBO J. 2002 Nov 1;21(21):5587-98.

Molecular structure of a 9-MDa icosahedral pyruvate dehydrogenase subcomplex containing the E2 and E3 enzymes using cryoelectron microscopy. Milne JL, Wu X, Borgnia MJ, Lengyel JS, Brooks BR, Shi D, Perham RN, Subramaniam S. J Biol Chem. 2006 Feb 17;281(7):4364-70.

Extended polypeptide linkers establish the spatial architecture of a pyruvate dehydrogenase multienzyme complex. Lengyel JS, Stott KM, Wu X, Brooks BR, Balbo A, Schuck P, Perham RN, Subramaniam S, Milne JL. Structure. 2008 Jan;16(1):93-103

 


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