Objective This study aimed to validate xenon‐enhanced computed tomography (XECT) for the detection of brown adipose tissue (BAT) and to use XECT to assess differences in BAT distribution and perfusion between lean, obese, and diabetic nonhuman primates (NHPs). Methods Whole‐body XECT imaging was performed in anesthetized rhesus and vervet monkeys during adrenergic stimulation of BAT thermogenesis. In XECT images, BAT was identified as fat tissue that, during xenon inhalation, underwent significant radiodensity enhancement compared with subcutaneous fat. To measure BAT blood flow, BAT radiodensity enhancement was measured over time on the six computed tomography scans acquired during xenon inhalation. Postmortem immunohistochemical staining was used to confirm imaging findings. Results XECT was able to correctly identify all BAT depots that were confirmed at necropsy, enabling construction of the first comprehensive anatomical map of BAT in NHPs. A significant decrease in BAT perfusion was found in diabetic animals compared with obese animals and healthy animals, as well as absence of axillary BAT and significant reduction of supraclavicular BAT in diabetic animals compared with obese and lean animals. Conclusions The use of XECT in NHP models of obesity and diabetes allows the analysis of the impact of metabolic status on BAT mass and perfusion.

Background Brown adipose tissue (BAT) is a fat tissue found in most mammals that helps regulate energy balance and core body temperature through a sympathetic process known as non-shivering thermogenesis. BAT activity is commonly detected and quantified in [18F]FDG positron emission tomography/computed tomography (PET/CT) scans, and radiotracer uptake in BAT during adrenergic stimulation is often used as a surrogate measure for identifying thermogenic activity in the tissue. BAT thermogenesis is believed to be contingent upon the expression of the protein UCP1, but conflicting results have been reported in the literature concerning [18F]FDG uptake within BAT of mice with and without UCP1. Differences in animal handling techniques such as feeding status, type of anesthetic, type of BAT stimulation, and estrogen levels were identified as possible confounding variables for [18F]FDG uptake. In this study, we aimed to assess differences in BAT [18F]FDG uptake between wild-type and UCP1-knockout mice using a protocol that minimizes possible variations in BAT stimulation caused by different stress responses to mouse handling. Results [18F]FDG PET/CT scans were run on mice that were anesthetized with pentobarbital after stimulation of non-shivering thermogenesis by norepinephrine. While in wild-type mice [18F]FDG uptake in BAT increased significantly with norepinephrine stimulation of BAT, there was no consistent change in [18F]FDG uptake in BAT of mice lacking UCP1. Conclusions [18F]FDG uptake within adrenergically stimulated BAT of wild-type and UCP1-knockout mice can significantly vary such that an [18F]FDG uptake threshold cannot be used to differentiate wild-type from UCP1-knockout mice. However, while an increase in BAT [18F]FDG uptake during adrenergic stimulation is consistently observed in wild-type mice, in UCP1-knockout mice [18F]FDG uptake in BAT seems to be independent of β3-adrenergic stimulation of non-shivering thermogenesis.

Background Brown adipose tissue (BAT) is a fat tissue found in most mammals that helps regulate energy balance and core body temperature through a sympathetic process known as non-shivering thermogenesis. BAT activity is commonly detected and quantified in [18F]FDG positron emission tomography/computed tomography (PET/CT) scans, and radiotracer uptake in BAT during adrenergic stimulation is often used as a surrogate measure for identifying thermogenic activity in the tissue. BAT thermogenesis is believed to be contingent upon the expression of the protein UCP1, but conflicting results have been reported in the literature concerning [18F]FDG uptake within BAT of mice with and without UCP1. Differences in animal handling techniques such as feeding status, type of anesthetic, type of BAT stimulation, and estrogen levels were identified as possible confounding variables for [18F]FDG uptake. In this study, we aimed to assess differences in BAT [18F]FDG uptake between wildtype and UCP1-knockout mice using a protocol that minimizes possible variations in BAT stimulation caused by different stress responses to mouse handling.Results [18F]FDG PET/CT scans were ran on mice that were anesthetized with pentobarbital after stimulation of non-shivering thermogenesis by norepinephrine. While in wild type mice [18F]FDG uptake in BAT increased significantly with norepinephrine stimulation of BAT, there was no consistent change in [18F]FDG uptake in BAT of mice lacking UCP1. Conclusions [18F]FDG uptake within adrenergically stimulated BAT of wildtype and UCP1-knockout mice can significantly vary such that an [18F]FDG uptake threshold cannot be used to differentiate wildtype from UCP1-knockout mice. However, while an increase in BAT [18F]FDG uptake during adrenergic stimulation is consistently observed in wild type mice, in UCP1-knockout mice [18F]FDG uptake in BAT seems to be is independent of β3 adrenergic stimulation of non-shivering thermogenesis.

Brown adipose tissue (BAT) is a fat tissue specialized in heat production (non-shivering thermogenesis) and used by mammals to defend core body temperature when exposed to cold. Several studies have shown that during non-shivering thermogenesis the increase in BAT oxygen demand is met by a local and specific increase in tissue’s blood flow. While the vasculature of BAT has been extensively studied postmortem in rodents using histology, optical and CT imaging techniques, vasculature changes during stimulation of non-shivering thermogenesis have never been directly detected in vivo. Here, by using computed tomography (CT) angiography with gold nanoparticles we investigate, non-invasively, changes in BAT vasculature during adrenergic stimulation of non-shivering thermogenesis by norepinephrine, a vasoconstrictor known to mediate brown fat heat production, and by CL 316,243, a specific β3-adrenergic agonist also known to elicit BAT thermogenesis in rodents. We found that while CL 316,243 causes local vasodilation in BAT, with little impact on the rest of the vasculature throughout the body, norepinephrine leads to local vasodilation in addition to peripheral vasoconstriction. As a result, a significantly greater relative increase in BAT perfusion is observed following the injection of NE compared to CL. This study demonstrates the use of in vivo CT angiography as an effective tool in assessing vascular reactivity in BAT both qualitatively and quantitatively in preclinical studies.