Visualization of Activated Fibroblasts in Heart Failure with Preserved Ejection Fraction with [ 18 F]AlF-NOTA-FAPI-04 PET/CT Imaging.

During the pathogenesis of heart failure with preserved ejection fraction (HFpEF), fibroblasts are activated and express the fibroblast activation protein (FAP). Targeted imaging of FAP can qualitatively and quantitatively assess the fibroblast activity. This study aimed to use [ ¹⁸ F]AlF-NOTA-FAPI-04 (AlF = aluminum fluoride; NOTA = 1,4,7-triazacyclononane-1,4,7-triacetic acid; FAPI = FAP inhibitor) positron emission tomography/computed tomography (PET/CT) imaging to detect activated fibroblasts in a rat HFpEF model. The rat HfpEF model was established by feeding a high-fat diet plus l-NAME ( N ^ω -nitro-l-arginine methyl ester) for 10 weeks. Blood pressure, echocardiography, and [ ¹⁸ F]AlF-NOTA-FAPI-04 PET/CT were used to assess the progression of HfpEF. The biodistribution of [ ¹⁸ F]AlF-NOTA-FAPI-04 in healthy rats was obtained. Cardiac tissue sections were also analyzed using Masson's, hematoxylin and eosin (H&E), and FAP immunohistochemistry (IHC) staining. The echocardiography and blood pressure data indicated that the rat HfpEF model was successfully established. [ ¹⁸ F]AlF-NOTA-FAPI-04 PET/CT imaging showed obvious radiotracer accumulation in the left ventricular wall of the HfpEF rats from the seventh week. A biodistribution test showed that the tracer was cleared mainly via renal and intestinal excretion. Percentage of injected dose per gram tissue (% ID) of the heart and its surrounding organs was lower in normal rats, which was conducive to image analysis. Masson's and H&E stainings showed large areas of vascular and interstitial fibrosis in the HfpEF rat hearts. IHC staining also confirmed the presence of FAP-positive cardiac fibroblasts of the HfpEF rat hearts, with a good correlation with FAPI PET. Thus, [ ¹⁸ F]AlF-NOTA-FAPI-04 PET/CT is a promising and non-invasive method to assess the progression of fibrosis in HfpEF to facilitate the clinical management.