Irisin is a newly discovered factor that is secreted by skeletal muscle and plays an important role in the homeostasis and metabolism of energy balance. This study used irisin radiolabeled with (125)I and small-animal SPECT/CT imaging to investigate the metabolic elimination and distribution of irisin in vivo. Irisin was labeled with (125)I using the Iodogen method. Small-animal SPECT/CT imaging was performed on C57/B16 mice at 15, 30, 60, 120, and 240 min after receiving a tail vein injection, and the radioactive distribution in the organs of mice was determined at 15, 60, and 120 min. Small-animal SPECT/CT imaging revealed the highest level of radioactivity in the gallbladder followed by the liver and kidney. Radioactivity decreased gradually with time in all organs. The radioactive distribution in the mice organs also showed that the highest %ID/g was in the gallbladder followed by the kidney and liver, and decreased gradually with time. The radioactivity in the gastric system reached its highest level at 60 min. Finally, our study showed the metabolic clearance of (125)I-irisin is achieved primarily through the hepatobiliary and renal system and provided the basis for the clinical application of irisin.
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