Exploiting Glutamine Consumption in Atherosclerotic Lesions by Positron Emission Tomography Tracer (2S,4R)-4- 18 F-Fluoroglutamine Senthil Palani 1 * , Maxwell W. G. Miner 1 , Jenni Virta 1 , Heidi Liljenbäck 1,2 , Olli Eskola 1 , Tiit Örd 3 , Aarthi Ravindran 3 , Minna U. Kaikkonen 3 , Juhani Knuuti 1,4,5 , Xiang-Guo Li 1,5 , Antti Saraste 1,6 and Anne Roivainen 1,2,4,5 * 1 Turku PET Centre, University of Turku, Turku, Finland, 2 Turku Center for Disease Modeling, University of Turku, Turku, Finland, 3 A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland, 4 Turku PET Centre, Turku University Hospital, Turku, Finland, 5 InFLAMES Research Flagship Center, University of Turku, Turku, Finland, 6 Heart Center, Turku University Hospital and University of Turku, Turku, Finland Increased glutamine metabolism by macrophages is associated with development of atherosclerotic lesions. Positron emission tomography/computed tomography (PET/CT) with a glutamine analog (2S,4R)-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. Keywords: atherosclerosis, 18 F-fluoroglutamine, PET/CT, macrophages, inflammation Frontiers in Immunology | www.frontiersin.org January 2022 | Volume 13 | Article 821423 1 Edited by: Nick Devoogdt, Free University of Brussels, Belgium Reviewed by: Alexis Broisat, Institut National de la Sante ´ et de la Recherche Me ´ dicale (INSERM), France Ismaheel Lawal, University of Pretoria, South Africa *Correspondence: Anne Roivainen anne.roivainen@utu.fi Senthil Palani palsen@utu.fi Specialty section: This article was submitted to Inflammation, a section of the journal Frontiers in Immunology Received: 24 November 2021 Accepted: 03 January 2022 Published: 25 January 2022 Citation: Palani S, Miner MWG, Virta J, Liljenbäck H, Eskola O, Örd T, Ravindran A, Kaikkonen MU, Knuuti J, Li X-G, Saraste A and Roivainen A (2022) Exploiting Glutamine Consumption in Atherosclerotic Lesions by Positron Emission Tomography Tracer (2S,4R)-4- 18 F-Fluoroglutamine. Front. Immunol. 13:821423. doi: 10.3389/fimmu.2022.821423 ORIGINAL RESEARCH published: 25 January 2022 doi: 10.3389/fimmu.2022.821423