Under normal physiological conditions, fat cells store energy. In the cells of brown adipose tissue, or fat, however, energy is dissipated in the form of heat: brown fat therefore acts as a biological heater. Most mammals have this mechanism. In humans it keeps newborns warm, in adults the activation of brown fat is positively correlated with cardio-metabolic health.
“Nowadays, however, we are warm even in winter. This is why the "ovens" we have in our body are almost no longer necessary", explains Prof. Dr. Alexander Pfeifer of the Institute of Pharmacology and Toxicology of the University of Bonn. At least funtil next winter, I say. At the same time, we eat an increasingly energy-rich diet and move much less than our ancestors. These three factors are poison to brown fat cells: They gradually stop functioning and eventually die. On the other hand, the number of severely overweight people in the world continues to increase. “Research groups around the world are looking for fat-burning substances that stimulate brown fat,” explains Pfeifer.
News from brown fat
The group of researchers at the University of Bonn has recently identified a previously never observed function of a well-known molecule, inosine, which is believed to be an effective fat burner.
“It is known that dying cells release a series of messenger molecules that influence the function of neighboring cells,” explains Dr. Birte Niemann from Pfeifer's research group. “We wanted to know if this mechanism also exists in brown fat.”
For this study the researchers observed brown fat cells subjected to severe stress, so that the cells were essentially dying. “We found that they secrete purine inosine in large quantities,” says Niemann. More interesting, however, was how the intact brown fat cells responded to the call for molecular help: they were activated by inosine (or simply by dying cells in their vicinity). The inosine then ignited the furnace inside them. The white fat cells also converted to their brown brethren. Mice fed a high-energy diet and simultaneously treated with inosine remained leaner than control animals and were protected from diabetes.
Okay, it burns fat in mice… And in humans?
“There is a drug developed for clotting disorders, but which also inhibits the inosine transporter,” explains Pfeifer, who is also a member of the transdisciplinary research areas “Life and Health” and “Sustainable Futures” at the University of Bonn. “We gave this fat-burning drug to mice and as a result they consumed more energy.”
And U.S? Interestingly, humans also have an inosine transporter. And in 2-4% of people it is less active due to a genetic variation.
“Our colleagues at the University of Leipzig genetically analyzed 900 individuals,” explains Pfeifer. “Subjects with the less active transporter were significantly leaner on average.” These findings suggest that inosine also regulates thermogenesis in human brown fat cells. Substances that interfere with transporter activity might therefore be suitable for treating obesity. The drug already approved for clotting disorders could serve as a starting point for a new fat-burning drug.
Obviously, even if the drug is already used for other purposes, further human studies are needed to clarify the pharmacological potential of this mechanism. It is clear, however, that a pill alone cannot be the solution to the rampant obesity pandemic in the world and the scientific community agrees on this. Similar assessments have also been made with the recent discovery of a possible "exercise pill” which in the future could completely replace physical activity.
Available therapies are not effective enough at the moment. There are also subjects who do not have a "normal" weight imbalance, and need concrete support with diet and exercise: it is welcome to investigate the role of inosine.
