Activated Brown Adipose Tissue and Its Relationship to Adiposity and Metabolic Markers (P21-073-19)

Abstract

ObjectivesTo explore potential relationships between PET/CT imaging characteristics of cold-activated brown adipose tissue (BAT), measures of adiposity and metabolic markers in young men. MethodsWe conducted a post-hoc analysis of a study designed to compare magnetic resonance imaging (MRI) techniques to the reference standard, PET/CT, in characterizing BAT. A total of 25 healthy male participants ages 18–24 and body mass index (BMI) ranging from 19.4 to 35.9 Kg/m2 were included in the study. A physical exam and fasting lab draw were performed, including measurement of hemoglobin A1c (HbA1c), lipid panel, thyroid function tests, leptin, adiponectin, FGF-21 and IL-6. Body composition was measured using dual energy X-ray absorptiometry (DXA). An individualized cooling protocol was utilized to activate BAT. Subjects were wrapped in a water-infused suit (CritiCool® System, Mennen Medical, Israel) and cooled to achieve non-shivering thermogenesis prior to imaging. Measures of cold-activated BAT, including mean standardized uptake value adjusted for lean mass (SUVlean mean), maximum SUV (SUVlean max), total BAT activity, and BAT volume were determined from PET/CT images. Pearson’s and Spearman’s rank correlations were employed to relate measures of active BAT to adiposity and metabolic parameters. ResultsThere was an inverse relationship between fasting serum glucose and BAT volume (r = −0.40, P = 0.048). In addition, a positive correlation was observed for serum fibroblast growth factor 21 (FGF-21) and SUVlean max (r = 0.45, P = 0.04). Marginally significant inverse relationships were noted between fasting glucose and total BAT activity (r = −0.39, P = 0.05) and leptin and SUVlean mean (r = −0.42, P = 0.05). However, no significant correlations were noted for measures of BAT activity or volume and other indicators of adiposity or glucose metabolism. ConclusionsData from this exploratory study suggest that BAT volume and activity may be inversely associated with fasting glucose in healthy young men. BAT activity was also correlated with an insulin sensitizer, FGF-21, suggesting BAT may lower glucose levels via an FGF-21 dependent pathway. Further studies are needed to clarify the potential mechanisms by which active BAT may impact glucose metabolism and the relationship between BAT and adiposity. Funding SourcesNIDDK.