Comparison of BMIPP-SPECT/CT to 18FDG-PET/CT for Imaging Brown or Browning Fat in a Preclinical Model

Figure 1. Representative sagittal 18FDG-PET/CT of a CL-316,243 treated (a) and vehicle control (b) mouse and 125I-BMIPP-SPECT/CT of a CL-316,243 (c) and vehicle (d) mouse (n = 5). The classical interscapular fat pad is circled in image (a), cardiac uptake is indicated with orange arrows in (a,d), and prevertebral and anterior abdominal fat uptake indicated with yellow arrows in (c). Extensive hepatic, gastrointestinal, and mediastinal background uptake was seen with BMIPP but not FDG.

Figure 2. Autoradiography of 125I-BMIPP in bilateral BAT depots of vehicle treated control (a) and CL-316,243 treated (b) mice. The area of each BAT pad is delineated by the dashed perimeters. Scalebar is represented in digital light units (DLU)/mm2.

Figure 3. Basal metabolic rate from selected fat pads in CL-316,243 treated and vehicle mice. CL-316,243 treatment increased the metabolic rate significantly in all fat pads, n = 5 for all groups (* indicates p < 0.05, *** p < 0.001).

Figure 4. Histology demonstrates increased brown phenotype in mice treated with CL-316,243. 20× Representative H&E stained sections from control (a) and treated (b) gWAT, control (c) and treated (d) iWAT, and control (e) and treated (f) BAT. Note the increased multilocular adipocytes in treated gWAT and iWAT compared to control and decreased lipid droplet size in treated versus control BAT.

Figure 5. Relative quantification (RQ) of assayed genes. Values were normalized to mRNA expression in gWAT of vehicle mice. Data are reported as the mean expression value with 95% CI in vehicle (n = 5) and CL-316,243 treated mice (n = 4). RQ is shown on a logarithmic scale.

Figure 6. Imaging study protocol schematic. Mice were randomized to treatment with CL-316,243 or vehicle control injections with normal saline. Dual energy X-ray absorptiometry (DEXA) was performed on Days one and eight to assess body fat composition. 18FDG-PET/CT was performed on Day seven and BMIPP-SPECT/CT on Day eight. Animals were sacrificed after SPECT/CT for autoradiography.

Figure 7. Examples of ROIs on an 18FDG-PET/CT in (a) classical interscapular BAT, (b) inguinal WAT, and (c) gonadal WAT. Yellow arrows indicate spherical ROIs positioned within the iWAT and gWAT depots in (b,c).