Inflammation imaging of atherosclerosis in Apo-E-deficient mice using a ^99mTc-labeled dual-domain cytokine ligand

Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) play a critical role in initiating and accelerating atherosclerosis. This study evaluated the imaging properties of ^99mTc-TNFR2-Fc-IL-1RA (^99mTc-TFI), a dual-domain cytokine radioligand that targets TNF-α and IL-1β pathways, in assessing atherosclerosis development in apolipoprotein-E-deficient (ApoE^-/-) mice. Methods: The feasibility and specificity of detecting atherosclerosis with ^99mTc-TFI SPECT imaging were investigated in ApoE^-/- and ApoE^+/+ mice. Fifty-four ApoE^-/- mice were fed either an atherogenic diet (AGD) or a normal diet (ND) beginning at 5weeks of age. Eighteen Apo-E wild-type (ApoE^+/+) mice were fed an ND. Two groups of ApoE^-/- mice (n=12 each group) on AGD and ND were imaged three times with ^99mTc-TFI and a high-resolution SPECT system at 20-25, 30-40, and 48-52 weeks to study the evolution of atherosclerotic plaque. Results: Focal radioactive accumulations in the aortic arch region were observed in the ApoE^-/- mice (n=12) on AGD but not in the ApoE^+/+ mice on ND (n=10). Apo-E^-/- mice on ND (n=11) exhibited lower radioactive uptake than ApoE^-/- mice on AGD (P<0.05). Co-injection of an excess of cold ligand with ^99mTc-TFI resulted in significant reduction of ^99mTc-TFI uptake in the ApoE^-/- mice on AGD. Longitudinal studies showed that ^99mTc-TFI uptake in the aortas of ApoE^-/- mice progressively increased from 20 to 48weeks. Real-time PCR assays demonstrated that atherosclerotic aortas expressed significantly higher IL-1β and TNF-α than the aortas from wild-type controls. Conclusions: Atherosclerotic plaques were detected by ^99mTc-TFI imaging in ApoE^-/- mice. ^99mTc-TFI is promising for specific detection of inflammatory response in atherosclerotic plaques.