Abstract
BACKGROUND: Apoptosis plays a critical role in the development and progression of atherosclerotic plaques. [18F] fluoride 2-(5-fluoro-pentyl)-2-methylmalonic acid ((18)F-ML-10), a positron emission tomography (PET) radiotracer, selectively targets cells undergoing apoptosis by binding to apoptosis-associated membrane alterations. This study evaluated the efficacy of (18)F-ML-10 PET/computed tomography (CT) in visualizing apoptotic activity in atherosclerotic plaques. METHODS: Apolipoprotein E knockout (ApoE(-/-)) mice were fed a high-fat diet to induce atherosclerosis, and imaged at 20 and 32 weeks, with C57BL/6J (C57) mice serving as controls. (18)F-ML-10 was synthesized using a standard conjugation protocol and subsequently used for the in-vivo PET/CT imaging of the atherosclerotic plaques in this animal model. Oil-red-O staining, hematoxylin and eosin (H&E) staining, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL), and caspase-3 staining were performed to evaluate the deposition of lipids and amount of apoptosis in the lesions where focal intensity was positively correlated with the uptake of (18)F-ML-10. RESULTS: (18)F-ML-10 was synthesized with a high radiochemical purity (>99%), a quick clearance rate, and a favorable biodistribution. In the (18)F-ML-10 PET/CT imaging, the plaque-to-background (P/B) ratio of the ApoE(-/-) mice at 32 weeks was significantly higher than that of the ApoE(-/-) mice at 20 weeks. Specifically, the P/B ratio values of the ApoE(-/-) mice were 2.28±0.20 at 32 weeks, and 1.69±0.22 at 20 weeks (P=0.002, n=5). No plaque was found in the PET images of the control mice. Further, oil-red-O staining revealed a significant increase in lipid deposition in the ApoE(-/-) mice from 20 to 32 weeks, which was consistent with the (18)F-ML-10 PET/CT findings. Immunohistochemically, the apoptosis index (AI) on TUNEL (r=0.950, P<0.001) and the integrated optic density (IOD)/area on caspase-3 staining (r=0.955, P<0.001) were significantly correlated with the P/B ratio of the lesions on (18)F-ML-10 PET/CT in the corresponding area. CONCLUSIONS: The (18)F-ML-10 PET/CT imaging technique enables the visualization of atherosclerotic plaques that are rich in apoptotic cells.