The search is on for drugs that could turn white fat into brown fat, the “good fat,” the fat that generates heat and thereby favors weight reduction. Although the search has started briskly—it has already identified promising drug targets—it is racing toward a formidable hurdle: efficacy testing.
At present, there is no simple, safe, and inexpensive means of testing the activity of brown fat. The standard means of testing involves positron emission tomography coupled with computer tomography (PET/CT). It is not only expensive and inconvenient, particularly for large groups of test subjects, it also exposes people to radiation.
A better alternative has been suggested by scientists based at the University of Bonn. These scientists, led by Prof. Dr. Alexander Pfeifer, have reported that they found a potential serum biomarker for brown adipose tissue (BAT) activity. They summarized their work April 27 in the journal Nature Communications, in an article entitled, “Exosomal MicroRNA miR-92a Concentration in Serum Reflects Human Brown Fat Activity.”
“Here we show that brown adipocytes release exosomes and that BAT activation increases exosome release,” wrote the article’s authors. “Profiling miRNAs in exosomes released from brown adipocytes, and in exosomes isolated from mouse serum, we show that levels of miRNAs change after BAT activation in vitro and in vivo.”
Dr. Pfeifer noted that microRNAs (miRNAs) are known to be responsible for the regulation of genes. He also indicated that his team showed for the first time that brown fat cells deliver these miRNAs into the blood by packaging into so-called exosomes, which “can be seen as little packages that are delivered by the brown fat cells through the circulation.” However, Prof. Pfeiffer added, “to whom the packages are delivered is yet unknown.”
Many miRNAs were investigated during the investigation. It turned out that miR-92a, which is present in human and mice, is related to brown fat activity. “[Serum] concentrations of exosomal miR-92a inversely correlate with human BAT activity measured by 18F-FDG PET/CT in two unique and independent cohorts comprising 41 healthy individuals,” explained the study’s authors. “Thus, exosomal miR-92a represents a potential serum biomarker for BAT activity in mice and humans.”
“miR-92a seems to be a promising biomarker to test new drugs in the field of weight reduction or transition from white-to-brown fat in humans,” asserted Prof. Pfeifer. “This promising biomarker should be tested in larger cohorts.” This new method might enable advances in obesity research and related fields.