Conclusion
These data show that [18F]FEPPA can detect BAT and newly formed beige fat under non-stimulated, thermoneutral conditions and that uptake after stimulation is linked to mitochondrial expression as opposed to activation.
Methods
Female Balb/c mice (n = 5) were treated for 7 days with the β3 adrenergic agonist CL-316,243 to induce the browning of inguinal WAT (beige fat). Animals were imaged longitudinally with [18F]FDG and [18F]FEPPA and uptake in interscapular BAT and inguinal WAT assessed. The browning of inguinal WAT was confirmed using H&E and immunohistochemical detection of UCP-1 and TSPO.
Results
Repeated dosing with β3-adrenergic agonist CL-316,243 caused a significant increase in [18F]FDG uptake in both interscapular BAT and inguinal WAT associated with the increased metabolic activity of brown and beige adipocytes respectively. [18F]FEPPA uptake was likewise increased in inguinal WAT but showed no increase in BAT uptake due to stimulation over the same time course. Furthermore, inguinal WAT uptake was unaffected by pharmacological blockade, indicating that [18F]FEPPA uptake is associated with the expression of mitochondria in BAT and beige adipocytes and independent of activation.