The thermoneutral zone in women takes an "arctic" shift compared to men.

Conventionally, women are perceived to feel colder than men, but controlled comparisons are sparse. We measured the response of healthy, lean, young women and men to a range of ambient temperatures typical of the daily environment (17 to 31 °C). The Scholander model of thermoregulation defines the lower critical temperature as threshold of the thermoneutral zone, below which additional heat production is required to defend core body temperature. This parameter can be used to characterize the thermoregulatory phenotypes of endotherms on a spectrum from "arctic" to "tropical." We found that women had a cooler lower critical temperature (mean ± SD: 21.9 ± 1.3 °C vs. 22.9 ± 1.2 °C, P = 0.047), resembling an "arctic" shift compared to men. The more arctic profile of women was predominantly driven by higher insulation associated with more body fat compared to men, countering the lower basal metabolic rate associated with their smaller body size, which typically favors a "tropical" shift. We did not detect sex-based differences in secondary measures of thermoregulation including brown adipose tissue glucose uptake, muscle electrical activity, skin temperatures, cold-induced thermogenesis, or self-reported thermal comfort. In conclusion, the principal contributors to individual differences in human thermoregulation are physical attributes, including body size and composition, which may be partly mediated by sex.

Brown adipose tissue activation in humans increases plasma levels of lipid mediators.

CONTEXT: Activation of brown adipose tissue (BAT) thermogenesis improves insulin sensitivity and is beneficial in obesity. Emerging evidence indicates that BAT activation increases lipid mediators that play autocrine and endocrine roles to regulate metabolism and inflammation. OBJECTIVE: The goal of the study was to determine the relationship between two distinct approaches of BAT activation (cold exposure and mirabegron treatment) with lipid mediators in humans. METHODS: Healthy female subjects (n = 14) were treated with ß3-adrenergic receptor agonist mirabegron (100 mg) daily for 28 days. A subset of female subjects (n = 8) was additionally exposed to cold temperatures (14-16°C) for 2 hours using a cooling vest prior to initiating mirabegron treatment. MAIN OUTCOME MEASURES: A panel of lipid mediators was assessed in plasma using targeted liquid chromatography-tandem mass spectrometry, and their relationship to anthropometric and metabolic parameters was determined. RESULTS: Activation of BAT with cold exposure acutely increased levels of lipoxygenase and cyclooxygenase products, including 12-hydroxyeicosapentaenoic acid (HEPE), 12-hydroxyeicosatetraenoic acid (HETE), 5-HETE, 14-hydroxydocosahexaenoic acid (HDHA), an isomer of maresin 2 (MaR2), 17-HDHA, protectin D1 (PD1), and prostaglandin E2 (PGE2). Mirabegron treatment similarly increased these products acutely, although levels of some mediators were blunted after chronic mirabegron treatment. Selected lipid mediators, including a MaR2 isomer, 17-HDHA, 5-HETE, and 15-HETE, positively correlated with non-esterified fatty acids and negatively correlated with the respiratory quotient, while PD1, 15-HETE, and 5-HETE positively correlated with adiponectin. CONCLUSION: These results indicate that selected lipid mediators may serve as biomarkers of BAT activation.

Standardized In Vitro Models of Human Adipose Tissue Reveal Metabolic Flexibility in Brown Adipocyte Thermogenesis.

Functional human brown and white adipose tissue (BAT and WAT) are vital for thermoregulation and nutritional homeostasis, while obesity and other stressors lead, respectively, to cold intolerance and metabolic disease. Understanding BAT and WAT physiology and dysfunction necessitates clinical trials complemented by mechanistic experiments at the cellular level. These require standardized in vitro models, currently lacking, that establish references for gene expression and function. We generated and characterized a pair of immortalized, clonal human brown (hBA) and white (hWA) preadipocytes derived from the perirenal and subcutaneous depots, respectively, of a 40-year-old male individual. Cells were immortalized with hTERT and confirmed to be of a mesenchymal, nonhematopoietic lineage based on fluorescence-activated cell sorting and DNA barcoding. Functional assessments showed that the hWA and hBA phenocopied primary adipocytes in terms of adrenergic signaling, lipolysis, and thermogenesis. Compared to hWA, hBA were metabolically distinct, with higher rates of glucose uptake and lactate metabolism, and greater basal, maximal, and nonmitochondrial respiration, providing a mechanistic explanation for the association between obesity and BAT dysfunction. The hBA also responded to the stress of maximal respiration by using both endogenous and exogenous fatty acids. In contrast to certain mouse models, hBA adrenergic thermogenesis was mediated by several mechanisms, not principally via uncoupling protein 1 (UCP1). Transcriptomics via RNA-seq were consistent with the functional studies and established a molecular signature for each cell type before and after differentiation. These standardized cells are anticipated to become a common resource for future physiological, pharmacological, and genetic studies of human adipocytes.

m 6 A mRNA Methylation in Brown Adipose Tissue Regulates Systemic Insulin Sensitivity via an Inter-Organ Prostaglandin Signaling Axis.

Brown adipose tissue (BAT) has the capacity to regulate systemic metabolism through the secretion of signaling lipids. N6-methyladenosine (m 6 A) is the most prevalent and abundant post-transcriptional mRNA modification and has been reported to regulate BAT adipogenesis and energy expenditure. In this study, we demonstrate that the absence of m 6 A methyltransferase-like 14 (METTL14), modifies the BAT secretome to initiate inter-organ communication to improve systemic insulin sensitivity. Importantly, these phenotypes are independent of UCP1-mediated energy expenditure and thermogenesis. Using lipidomics, we identified prostaglandin E2 (PGE2) and prostaglandin F2a (PGF2a) as M14 KO -BAT-secreted insulin sensitizers. Notably, circulatory PGE2 and PGF2a levels are inversely correlated with insulin sensitivity in humans. Furthermore, in vivo administration of PGE2 and PGF2a in high-fat diet-induced insulin-resistant obese mice recapitulates the phenotypes of METTL14 deficient animals. PGE2 or PGF2a improves insulin signaling by suppressing the expression of specific AKT phosphatases. Mechanistically, METTL14-mediated m 6 A installation promotes decay of transcripts encoding prostaglandin synthases and their regulators in human and mouse brown adipocytes in a YTHDF2/3-dependent manner. Taken together, these findings reveal a novel biological mechanism through which m 6 A-dependent regulation of BAT secretome regulates systemic insulin sensitivity in mice and humans. Highlights: Mettl14 KO -BAT improves systemic insulin sensitivity via inter-organ communication; PGE2 and PGF2a are BAT-secreted insulin sensitizers and browning inducers;PGE2 and PGF2a sensitize insulin responses through PGE2-EP-pAKT and PGF2a-FP-AKT axis; METTL14-mediated m 6 A installation selectively destabilizes prostaglandin synthases and their regulator transcripts; Targeting METTL14 in BAT has therapeutic potential to enhance systemic insulin sensitivity.

ADRA1A-Gαq signalling potentiates adipocyte thermogenesis through CKB and TNAP.

Noradrenaline (NA) regulates cold-stimulated adipocyte thermogenesis1. Aside from cAMP signalling downstream of ß-adrenergic receptor activation, how NA promotes thermogenic output is still not fully understood. Here, we show that coordinated α1-adrenergic receptor (AR) and ß3-AR signalling induces the expression of thermogenic genes of the futile creatine cycle2,3, and that early B cell factors, oestrogen-related receptors and PGC1α are required for this response in vivo. NA triggers physical and functional coupling between the α1-AR subtype (ADRA1A) and Gαq to promote adipocyte thermogenesis in a manner that is dependent on the effector proteins of the futile creatine cycle, creatine kinase B and tissue-non-specific alkaline phosphatase. Combined Gαq and Gαs signalling selectively in adipocytes promotes a continual rise in whole-body energy expenditure, and creatine kinase B is required for this effect. Thus, the ADRA1A-Gαq-futile creatine cycle axis is a key regulator of facultative and adaptive thermogenesis.

Architecture of the outbred brown fat proteome defines regulators of metabolic physiology.

Brown adipose tissue (BAT) regulates metabolic physiology. However, nearly all mechanistic studies of BAT protein function occur in a single inbred mouse strain, which has limited the understanding of generalizable mechanisms of BAT regulation over physiology. Here, we perform deep quantitative proteomics of BAT across a cohort of 163 genetically defined diversity outbred mice, a model that parallels the genetic and phenotypic variation found in humans. We leverage this diversity to define the functional architecture of the outbred BAT proteome, comprising 10,479 proteins. We assign co-operative functions to 2,578 proteins, enabling systematic discovery of regulators of BAT. We also identify 638 proteins that correlate with protection from, or sensitivity to, at least one parameter of metabolic disease. We use these findings to uncover SFXN5, LETMD1, and ATP1A2 as modulators of BAT thermogenesis or adiposity, and provide OPABAT as a resource for understanding the conserved mechanisms of BAT regulation over metabolic physiology.

Brown adipose tissue-derived MaR2 contributes to cold-induced resolution of inflammation.

Obesity induces chronic inflammation resulting in insulin resistance and metabolic disorders. Cold exposure can improve insulin sensitivity in humans and rodents, but the mechanisms have not been fully elucidated. Here, we find that cold resolves obesity-induced inflammation and insulin resistance and improves glucose tolerance in diet-induced obese mice. The beneficial effects of cold exposure on improving obesity-induced inflammation and insulin resistance depend on brown adipose tissue (BAT) and liver. Using targeted liquid chromatography with tandem mass spectrometry, we discovered that cold and ß3-adrenergic stimulation promote BAT to produce maresin 2 (MaR2), a member of the specialized pro-resolving mediators of bioactive lipids that play a role in the resolution of inflammation. Notably, MaR2 reduces inflammation in obesity in part by targeting macrophages in the liver. Thus, BAT-derived MaR2 could contribute to the beneficial effects of BAT activation in resolving obesity-induced inflammation and may inform therapeutic approaches to combat obesity and its complications.

Activating Human Adipose Tissue with the ß3-Adrenergic Agonist Mirabegron.

An appealing strategy for treatment of metabolic disease in humans is activation of brown adipose tissue (BAT), a thermogenic organ best visualized through 18F-FDG PET/CT. BAT has been activated to varying degrees by mild cold exposure. However, this approach can cause undesirable stress, and there remains no consensus protocol. Here, we describe standardized methods for both acute and chronic activation of BAT using the orally administered ß3-adrenergic receptor (AR) agonist, mirabegron. Acute pharmacological stimulation has enabled quantification of whole-body BAT volume and metabolic activity using PET/CT imaging, and chronic stimulation increases these properties of BAT over time.

Characterization of transcript enrichment and detection bias in single-nucleus RNA-seq for mapping of distinct human adipocyte lineages.

Single-cell RNA sequencing (scRNA-seq) enables molecular characterization of complex biological tissues at high resolution. The requirement of single-cell extraction, however, makes it challenging for profiling tissues such as adipose tissue, for which collection of intact single adipocytes is complicated by their fragile nature. For such tissues, single-nucleus extraction is often much more efficient and therefore single-nucleus RNA sequencing (snRNA-seq) presents an alternative to scRNA-seq. However, nuclear transcripts represent only a fraction of the transcriptome in a single cell, with snRNA-seq marked with inherent transcript enrichment and detection biases. Therefore, snRNA-seq may be inadequate for mapping important transcriptional signatures in adipose tissue. In this study, we compare the transcriptomic landscape of single nuclei isolated from preadipocytes and mature adipocytes across human white and brown adipocyte lineages, with whole-cell transcriptome. We show that snRNA-seq is capable of identifying the broad cell types present in scRNA-seq at all states of adipogenesis. However, we also explore how and why the nuclear transcriptome is biased and limited, as well as how it can be advantageous. We robustly characterize the enrichment of nuclear-localized transcripts and adipogenic regulatory lncRNAs in snRNA-seq, while also providing a detailed understanding for the preferential detection of long genes upon using this technique. To remove such technical detection biases, we propose a normalization strategy for a more accurate comparison of nuclear and cellular data. Finally, we show successful integration of scRNA-seq and snRNA-seq data sets with existing bioinformatic tools. Overall, our results illustrate the applicability of snRNA-seq for the characterization of cellular diversity in the adipose tissue.

Combining a ß3 adrenergic receptor agonist with alpha-lipoic acid reduces inflammation in male mice with diet-induced obesity.

OBJECTIVES: Beta-3 adrenergic receptors (ß3-AR) stimulate lipolysis and thermogenesis in white and brown adipose tissue (WAT and BAT). Obesity increases oxidative stress and inflammation that attenuate AT ß3-AR signaling. The objective of this study was to test the hypothesis that the combination of the ß3-AR agonist CL-316,243 (CL) and the antioxidant alpha-lipoic acid (ALA) would lower inflammation in diet-induced obesity (DIO) and improve ß3-AR function. METHODS: A total of 40 DIO mice were separated into four groups: Control (per os and intraperitoneal [IP] vehicle); CL alone (0.01 mg/kg IP daily); ALA alone (250 mg/kg in drinking water); or ALA+CL combination, all for 5 weeks. RESULTS: Food intake was similar in all groups; however, mice receiving ALA+CL showed improved body composition and inflammation as well as lower body weight (+1.7 g Control vs. -2.5 g ALA+CL [-7%]; p < 0.01) and percentage of body fat (-9%, p < 0.001). Systemic and epididymal WAT inflammation was lower with ALA+CL than all other groups, with enhanced recruitment of epididymal WAT anti-inflammatory CD206+ M2 macrophages. ß3-AR signaling in WAT was enhanced in the combination-treatment group, with higher mRNA and protein levels of thermogenic uncoupling protein 1 and AT lipases. CONCLUSIONS: Chronic treatment with ALA and a ß3-AR agonist reduces DIO-induced inflammation. AT immune modulation could be a therapeutic target in patients with obesity.

The transcriptional co-regulator LDB1 is required for brown adipose function.

OBJECTIVE: Brown adipose tissue (BAT) is critical for thermogenesis and glucose/lipid homeostasis. Exploiting the energy uncoupling capacity of BAT may reveal targets for obesity therapies. This exploitation requires a greater understanding of the transcriptional mechanisms underlying BAT function. One potential regulator of BAT is the transcriptional co-regulator LIM domain-binding protein 1 (LDB1), which acts as a dimerized scaffold, allowing for the assembly of transcriptional complexes. Utilizing a global LDB1 heterozygous mouse model, we recently reported that LDB1 might have novel roles in regulating BAT function. However, direct evidence for the LDB1 regulation of BAT thermogenesis and substrate utilization has not been elucidated. We hypothesize that brown adipocyte-expressed LDB1 is required for BAT function. METHODS: LDB1-deficient primary cells and brown adipocyte cell lines were assessed via qRT-PCR and western blotting for altered mRNA and protein levels to define the brown adipose-specific roles. We conducted chromatin immunoprecipitation with primary BAT tissue and immortalized cell lines. Potential transcriptional partners of LDB1 were revealed by conducting LIM factor surveys via qRT-PCR in mouse and human brown adipocytes. We developed a Ucp1-Cre-driven LDB1-deficiency mouse model, termed Ldb1ΔBAT, to test LDB1 function in vivo. Glucose tolerance and uptake were assessed at thermoneutrality via intraperitoneal glucose challenge and glucose tracer studies. Insulin tolerance was measured at thermoneutrality and after stimulation with cold or the administration of the ß3-adrenergic receptor (ß3-AR) agonist CL316,243. Additionally, we analyzed plasma insulin via ELISA and insulin signaling via western blotting. Lipid metabolism was evaluated via BAT weight, histology, lipid droplet morphometry, and the examination of lipid-associated mRNA. Finally, energy expenditure and cold tolerance were evaluated via indirect calorimetry and cold challenges. RESULTS: Reducing Ldb1 in vitro and in vivo resulted in altered BAT-selective mRNA, including Ucp1, Elovl3, and Dio2. In addition, there was reduced Ucp1 induction in vitro. Impacts on gene expression may be due, in part, to LDB1 occupying Ucp1 upstream regulatory domains. We also identified BAT-expressed LIM-domain factors Lmo2, Lmo4, and Lhx8, which may partner with LDB1 to mediate activity in brown adipocytes. Additionally, we observed LDB1 enrichment in human brown adipose. In vivo analysis revealed LDB1 is required for whole-body glucose and insulin tolerance, in part through reduced glucose uptake into BAT. In Ldb1ΔBAT tissue, we found significant alterations in insulin-signaling effectors. An assessment of brown adipocyte morphology and lipid droplet size revealed larger and more unilocular brown adipocytes in Ldb1ΔBAT mice, particularly after a cold challenge. Alterations in lipid handling were further supported by reductions in mRNA associated with fatty acid oxidation and mitochondrial respiration. Finally, LDB1 is required for energy expenditure and cold tolerance in both male and female mice. CONCLUSIONS: Our findings support LDB1 as a regulator of BAT function. Furthermore, given LDB1 enrichment in human brown adipose, this co-regulator may have conserved roles in human BAT.

ß3-Adrenergic receptors regulate human brown/beige adipocyte lipolysis and thermogenesis.

ß3-Adrenergic receptors (ß3-ARs) are the predominant regulators of rodent brown adipose tissue (BAT) thermogenesis. However, in humans, the physiological relevance of BAT and ß3-AR remains controversial. Herein, using primary human adipocytes from supraclavicular neck fat and immortalized brown/beige adipocytes from deep neck fat from 2 subjects, we demonstrate that the ß3-AR plays a critical role in regulating lipolysis, glycolysis, and thermogenesis. Silencing of the ß3-AR compromised genes essential for thermogenesis, fatty acid metabolism, and mitochondrial mass. Functionally, reduction of ß3-AR lowered agonist-mediated increases in intracellular cAMP, lipolysis, and lipolysis-activated, uncoupling protein 1-mediated thermogenic capacity. Furthermore, mirabegron, a selective human ß3-AR agonist, stimulated BAT lipolysis and thermogenesis, and both processes were lost after silencing ß3-AR expression. This study highlights that ß3-ARs in human brown/beige adipocytes are required to maintain multiple components of the lipolytic and thermogenic cellular machinery and that ß3-AR agonists could be used to achieve metabolic benefit in humans.

Proton MR Spectroscopy Measurements of White and Brown Adipose Tissue in Healthy Humans: Relaxation Parameters and Unsaturated Fatty Acids.

Background Activation of brown adipose tissue (BAT) in rodents increases lipolysis in white adipose tissue (WAT) and improves glucose tolerance. Adult humans can have metabolically active BAT. Implications for diabetes and obesity in humans require a better characterization of BAT in humans. Purpose To study fat depots with localized proton MR spectroscopy relaxometry and to identify differences between WAT and fluorine 18 fluorodeoxyglucose (FDG) PET/CT proven cold-activated BAT in humans. Materials and Methods Participants were consecutively enrolled in this prospective study (ClinicalTrials.gov identifiers: NCT01568671 and NCT01399385) from August 2016 to May 2019. Supraclavicular potential BAT regions were localized with MRI. Proton densities, T1, and T2 were measured with localized MR spectroscopy in potential BAT and in subcutaneous WAT. FDG PET/CT after cold stimulation was used to retrospectively identify active supraclavicular BAT or supraclavicular quiescent adipose tissue (QAT) regions. MR spectroscopy results from BAT and WAT were compared with grouped and paired tests. Results Of 21 healthy participants (mean age, 36 years ± 16 [standard deviation]; 13 men) FDG PET/CT showed active BAT in 24 MR spectroscopy-targeted regions in 16 participants (eight men). Four men had QAT. The T2 for methylene protons was shorter in BAT (mean, 69 msec ± 6, 24 regions) than in WAT (mean, 83 msec ± 3, 18 regions, P < .01) and QAT (mean, 78 msec ± 2, five regions, P < .01). A T2 cut-off value of 76 msec enabled the differentiation of BAT from WAT or QAT with a sensitivity of 85% and a specificity of 95%. Densities of protons adjacent and between double bonds were 33% and 24% lower, respectively, in BAT compared with those in WAT (P = .01 and P = .03, respectively), indicating a lower content of unsaturated and polyunsaturated fatty acids, respectively, in BAT compared with WAT. Conclusion Proton MR spectroscopy showed shorter T2 and lower unsaturated fatty acids in brown adipose tissue (BAT) than that in white adipose tissue in healthy humans. It was feasible to identify BAT with MR spectroscopy without the use of PET/CT or cold stimulation. © RSNA, 2021 See also the editorial by Barker in this issue. Online supplemental material is available for this article.

Reduced brown adipose tissue activity during cold exposure is a metabolic feature of the human thrifty phenotype.

BACKGROUND: We recently demonstrated that thrifty subjects, characterized by a greater decrease in 24 h energy expenditure (24hEE) during short-term fasting, have less capacity for cold-induced thermogenesis (CIT) during 24 h of mild cold exposure. OBJECTIVE: As cold-induced brown adipose tissue activation (CIBA) is a determinant of CIT, we sought to investigate whether thrifty individuals also have reduced CIBA. METHODS: Twenty-four healthy subjects (age: 29.8 ±â€¯9.5y, body fat: 27.3 ±â€¯12.4%, 63% male) were admitted to our clinical research unit and underwent two 24hEE assessments in a whole-room indirect calorimeter during energy balance and fasting conditions at thermoneutrality to quantify their degree of thriftiness. Positron emission tomography/computed tomography scans were performed after exposure to 16 °C for 2 h to quantify peak CIBA. RESULTS: A greater decrease in 24hEE during fasting was associated with lower peak CIBA (r = 0.50, p = 0.01), such that a 100 kcal/day greater reduction in 24hEE related to an average 3.2 g/mL lower peak CIBA. CONCLUSION: Our results indicate that reduced CIBA is a metabolic trait of the thrifty phenotype which might explain reduced CIT capacity and greater predisposition towards weight gain in individuals with a thrifty metabolism.

Identification and characterization of distinct brown adipocyte subtypes in C57BL/6J mice.

Brown adipose tissue (BAT) plays an important role in the regulation of body weight and glucose homeostasis. Although increasing evidence supports white adipose tissue heterogeneity, little is known about heterogeneity within murine BAT. Recently, UCP1 high and low expressing brown adipocytes were identified, but a developmental origin of these subtypes has not been studied. To obtain more insights into brown preadipocyte heterogeneity, we use single-cell RNA sequencing of the BAT stromal vascular fraction of C57/BL6 mice and characterize brown preadipocyte and adipocyte clonal cell lines. Statistical analysis of gene expression profiles from brown preadipocyte and adipocyte clones identify markers distinguishing brown adipocyte subtypes. We confirm the presence of distinct brown adipocyte populations in vivo using the markers EIF5, TCF25, and BIN1. We also demonstrate that loss of Bin1 enhances UCP1 expression and mitochondrial respiration, suggesting that BIN1 marks dormant brown adipocytes. The existence of multiple brown adipocyte subtypes suggests distinct functional properties of BAT depending on its cellular composition, with potentially distinct functions in thermogenesis and the regulation of whole body energy homeostasis.

Sexual Dimorphisms in Adult Human Brown Adipose Tissue.

OBJECTIVE: This study aimed to quantify and compare the amount, activity, and anatomical distribution of cold-activated brown adipose tissue (BAT) in healthy, young, lean women and men. METHODS: BAT volume and 18 F-fluorodeoxyglucose uptake were measured by positron emission tomography and computerized tomography in 12 women and 12 men (BMI 18.5-25 kg/m2 , aged 18-35 years) after 5 hours of exposure to their coldest temperature before overt shivering. RESULTS: Women had a lower detectable BAT volume than men (P = 0.03), but there was no difference after normalizing to body size. The mean BAT glucose uptake and relative distribution of BAT did not differ by sex. 18 F-fluorodeoxyglucose uptake consistent with BAT was observed in superficial dorsocervical adipose tissue of 6 of 12 women but only 1 of 12 men (P = 0.02). This potential BAT depot would pose fewer biopsy risks than other depots. CONCLUSIONS: Despite differences in adiposity and total BAT volume, we found that healthy, lean, young women and men do not differ in the relative amount, glucose uptake, and distribution of BAT. Dorsocervical 18 F-fluorodeoxyglucose uptake was more prevalent in women and may be a remnant of interscapular BAT seen in human newborns. Future studies are needed to discern how BAT contributes to whole-body thermal physiology and body weight regulation in women and men.

Pheochromocytoma and Paraganglioma Patients With Poor Survival Often Show Brown Adipose Tissue Activation.

CONTEXT: Pheochromocytomas/paragangliomas (PPGLs) are neuroendocrine tumors that can secrete norepinephrine (NE). Brown adipose tissue (BAT) activation is mediated through the action of NE on ß-adrenoceptors (ß-ARs). In some malignancies, BAT activation is associated with higher cancer activity. OBJECTIVE: To study the relationship between BAT activation and PPGL clinical outcomes. DESIGN: A retrospective case-control study that included 342 patients with PPGLs who underwent 18F-fluoro-2-deoxy-D-glucose positron emission tomography-computed tomography (18F-FDG PET/CT) imaging at the National Institutes of Health (NIH). We excluded all patients with parasympathetic tumors and those who underwent 18F-FDG PET/CT after PPGL resection. Scans of 205 patients were reviewed by 2 blinded nuclear medicine physicians; 16 patients had BAT activation on 18F-FDG PET/CT [7.80%; age 27.50 (15.00-45.50) years; 10 female/6 male; body mass index [BMI] 24.90 [19.60-25.35] kg/m2). From the remaining 189 patients, we selected 36 matched controls (age 34.4 [25.4-45.5] years; 21 female/15 male; BMI 25.0 [22.0-26.0] kg/m2). PRIMARY OUTCOME MEASURE: Overall survival. RESULTS: The presence of active BAT on 18F-FDG PET/CT was associated with decreased overall survival when compared with the control group (HRz 5.80; 95% CI, 1.05-32.05; P = 0.02). This association remained significant after adjusting for the SDHB mutation. Median plasma NE in the BAT group was higher than the control group [4.65 vs 0.55 times above the upper limit of normal; P < 0.01]. There was a significant association between higher plasma NE levels and mortality in PPGLs in both groups. CONCLUSIONS: Our findings suggest that the detection of BAT activity in PPGL patients is associated with higher mortality. We suggest that BAT activation could either be reflecting or contributing to a state of increased host stress that may predict poor outcome in metastatic PPGL.