Exploiting Glutamine Consumption in Atherosclerotic Lesions by Positron Emission Tomography Tracer (2S,4R)-4-18F-Fluoroglutamine
Senthil Palani, Maxwell W. G. Miner, Jenni Virta, Heidi Liljenbäck, Olli Eskola, Tiit Örd, Aarthi Ravindran, Minna U. Kaikkonen, Juhani Knuuti, Xiang‐Guo Li, Antti Saraste, Anne Roivainen
Abstract
Increased glutamine metabolism by macrophages is associated with development of atherosclerotic lesions. Positron emission tomography/computed tomography (PET/CT) with a glutamine analog (2S,4 R )-4- 18 F-fluoroglutamine ( 18 F-FGln) allows quantification of glutamine consumption in vivo . Here, we investigated uptake of 18 F-FGln by atherosclerotic lesions in mice and compared the results with those obtained using the glucose analog 2-deoxy-2- 18 F-fluoro- D -glucose ( 18 F-FDG). Uptake of 18 F-FGln and 18 F-FDG by healthy control mice (C57BL/6JRj) and atherosclerotic low-density lipoprotein receptor-deficient mice expressing only apolipoprotein B100 (LDLR −/− ApoB 100/100 ) was investigated. The mice were injected intravenously with 18 F-FGln or 18 F-FDG for in vivo PET/CT imaging. After sacrifice at 70 minutes post-injection, tracer uptake was analyzed by gamma counting of excised tissues and by autoradiography of aorta cryosections, together with histological and immunohistochemical analyses. We found that myocardial uptake of 18 F-FGln was low. PET/CT detected lesions in the aortic arch, with a target-to-background ratio (SUV max , aortic arch/SUV mean , blood) of 1.95 ± 0.42 (mean ± standard deviation). Gamma counting revealed that aortic uptake of 18 F-FGln by LDLR −/− ApoB 100/100 mice (standardized uptake value [SUV], 0.35 ± 0.06) was significantly higher than that by healthy controls (0.20 ± 0.08, P = 0.03). More detailed analysis by autoradiography revealed that the plaque-to-healthy vessel wall ratio of 18 F-FGln (2.90 ± 0.42) was significantly higher than that of 18 F-FDG (1.93 ± 0.22, P = 0.004). Immunohistochemical staining confirmed that 18 F-FGln uptake in plaques co-localized with glutamine transporter SLC7A7-positive macrophages. Collectively these data show that the 18 F-FGln PET tracer detects inflamed atherosclerotic lesions. Thus, exploiting glutamine consumption using 18 F-FGln PET may have translational relevance for studying atherosclerotic inflammation.