In-vivo detection of white adipose tissue browning: a multimodality imaging approach

Figure 1. Overview of study design. PET (Positron Emission Tomography), CT, and US studies were conducted in the same animals on three different days, both before and after a 4-week treatment with the β3-adrenergic agonists CL-316243, injected intraperitonellay at a dose of 1 mg/kg. For the 18F-FDG-PET/CT studies, mice were fasted overnight for more than 10 h. Norepinephrine-stimulated tissue glucose uptake was then quantified in the inguinal depot, before and after CL-316243 treatment. CT, xenon-enhanced CT, and dynamic contrast-ultrasound scans were performed before and after norepinephrine injection during the same imaging session, both before and after CL-316243 treatment.

Figure 2. (a) 18F-FDG-PET/CT coronal fusion images of the same mouse acquired pre- and post-CL-316243 treatment. A zoom in of the inguinal area (red box) shows a localized increase in glucose uptake in the inguinal fat area; (b) Plots showing a non-statistically significant (p > 0.05, paired t-test) change in standardized uptake values (SUV) measured in the mice pre and post CL-316243 treatment. The plot on the right includes all mice, and the one on the left separates male from females; (c) Plots showing a non-statistically significant (p > 0.05, paired t-test) change in standardized uptake value ratios (SUVR) obtained in the mice pre and post CL-316243 treatment. The plot on the left includes all mice while the one on the right present males and females in black and gray colors, respectively.

Figure 3. (a) CT coronal images acquired from a mouse before CL-316243 treatment showing the inguinal white fat depot adjacent to the inguinal lymph node and the external iliac artery; (b) CT coronal image acquired from the same mouse after CL-316243 treatment, showing an increase in tissue radiodensity near the external iliac artery; (c) Inguinal tissue radiodensity as measured in each mouse before and after CL-316243 treatment. A paired t-test shows a significant (p < 0.0001) increase in tissue radiodensity post CL-316243 treatment; (d) Hematoxylin and eosin staining and immunostaining of UCP1 expression for one mouse that showed significant increase in tissue radiodensity (orange line) and one that did not (green line).

Figure 4. Mean tissue radiodensities obtained from all mice analyzed (p-values are reported for combined male and female mouse data): (a) Mean CT inguinal tissue radiodensities. An increase in CT tissue radiodensity is observed after CL-316243 treatment in all mice. An increase in tissue radiodensity is also observed after NE injection, both in pre and post CL-316243 scans; (b) Mean tissue radiodensities obtained before and after a 7-min xenon inhalation. In all mice tissue radiodensity increased except in one mouse, where tissue radiodensity did not increase after xenon inhalation; (c) Tissue radiodensity values as obtained after xenon inhalation, before and after CL-316243 treatment, and before and after norepinephrine injection. Baseline tissue radiodensity after xenon inhalation increased post CL-316243 treatment, indicating an increase in tissue perfusion. No consistent increase in tissue radiodensity was observed in post-NE scans. In all cases, tissue radiodensity increased post norepinephrine injection, indicating an increase in tissue perfusion after NE.

Figure 5. Selective radiodensity enhancement in region near the external iliac artery observed both before CL-316243 treatment in XECT scan and after CL-316243 treatment in CT scans: (a) A magnified view of the inguinal fat near the right inguinal lymph node for one of the mice showing non enhanced CT images acquired before CL-316243 treatment, before NE injection and before xenon inhalation; (b) A magnified view of the same mouse acquired before CL-316243 treatment, after NE injection and after 7-min xenon inhalation showing a selective enhancement of the fat area adjacent to the external iliac artery; (c) A magnified view of an image acquired on the same mouse after CL-316243 treatment, before NE injection and before xenon inhalation showing also a selective enhancement of the fat area adjacent to the external iliac artery.

Figure 6. Acoustic signal intensity, as function of time, collected over 18 s after microbubble destruction in the inguinal fat depot and in the interscapular BAT of the same mouse. (a) Acoustic signal intensity acquired before CL-316243 treatment from one of the mice showing an increase in signal intensity after NE injection. Fitting parameters were A = 5.0 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}± 0.5 a.u., and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\beta$$\end{document}β = 0.15 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}± 0.04 s−1 before NE injection (adjusted R-square 0.60), and A = 5.5…