In-vivo detection of white adipose tissue browning: a multimodality imaging approach

Abstract

Detection and differentiation of brown fat in humans poses several challenges, as this tissue is sparse and often mixed with white adipose tissue. Non-invasive detection of beige fat represents an even greater challenge as this tissue is structurally and functionally more like white fat than brown fat. Here we used positron emission tomography with 18F-fluorodeoxyglucose, computed tomography, xenon-enhanced computed tomography, and dynamic contrast-enhanced ultrasound, to non-invasively detect functional and structural changes associated with the browning process of inguinal white fat, induced in mice by chronic stimulation with the β3-adrenergic receptor agonist CL-316243. These studies reveal a very heterogeneous increase in baseline tissue radiodensity and xenon-enhanced radiodensity, indicative of both an increase in adipocytes water and protein content as well as tissue perfusion, mostly in regions that showed enhanced norepinephrine-stimulated perfusion before CL-316243 treatment. No statistically significant increase in 18F-fluorodeoxyglucose uptake or norepinephrine-stimulated tissue perfusion were observed in the mice after the CL-316243 treatment. The increase in tissue-water content and perfusion, along with the negligible increase in the tissue glucose uptake and norepinephrine-stimulated perfusion deserve more attention, especially considering the potential metabolic role that this tissue may play in whole body metabolism.

White adipose tissue uptake on 18F FDG PET/CT: A case report

“…White adipose tissue can be found under the dermis, intramuscular and between viscera [4] , beige adipose tissue is a subtype of WAT and can be found in subcutaneous deposits of WAT [1] . White adipose tissue main function is to store energy, while brown adipose tissue is much more vascularized and regulates temperature [ 2 , 4 ]. Recent studies have found that beige adipocytes also play a role in regulating temperature but only when exposed to cold or certain substances [3] .…”

“…It is well known that in some instances, BAT can be metabolically active which can be considered a normal variant, while WAT is metabolically inactive showing little to no glucose uptake during an FDG PET/CT study [ 4 , 5 ]. Regarding beige adipose tissue it has only been detected in mice after chronic stimulation within the inguinal regions with several modalities that have included FDG PET/CT, Xenon-enhanced CT and contrast-enhanced ultrasound [2] .…”

“…Brown adipose tissue can have uptake on 18 F 2-fluoro-2-deoxyglucose (FDG) positron emission tomography/computer tomography (PET/CT) but white adipose tissue in normal conditions does not, meaning it is metabolically inactive [4] . As to beige adipose tissue it has only been metabolically active after chronic stimulation in mice [2] . In some instances, there has been an abnormal uptake on FDG PET/CT on WAT that has been associated to high-dose corticosteroid use [ 4 , 5 ].…”