Conclusion
We demonstrated that TSPO-PET/CLI reflected UCP1 expression in iBAT imaging better than [18F]FDG-PET/CLI under the various conditions. Considering convenience and cost, TSPO-CLI could be used as an alternative TSPO-PET technique for iBAT imaging.
Methods
UCP1 ThermoMouse was used to monitor UCP1 expression. Western blotting and immunohistochemistry were performed to measure the level of protein expression. [18F]fm-PBR28-d 2 and [18F]FDG were used as radioactive probes for iBAT imaging. PET images were acquired with SimPET, and optical images were acquired with IVIS 100.
Results
UCP1 ThermoMouse showed that UCP1 and TSPO expressions were correlated in iBAT. In both PET and CLI, the TSPO-targeting probe [18F]fm-PBR28-d 2 was superior to [18F]FDG for acquiring iBAT images. The high molar activity of the probe was essential for CLI and PET imaging. We tested the feasibility of TSPO-targeting probe under cold exposure by imaging with TSPO-PET/CLI. Both signals of iBAT were clearly increased after cold stimulation. Under prolonged isoflurane anesthesia, TSPO-targeting images showed higher signals from iBAT in the short-term than in long-term groups.