O-176 - ANALYSIS AND INTERPRETATION OF PATHOPHYSIOLOGIC MECHANISMS ASSOCIATED WITH THE DEVELOPMENT AND PROGRESSION OF THORACIC AORTIC ANEURYSMS THROUGH MOLECULAR IMAGING IN MURINE MODELS

TOPIC:
Other
AUTHORS:
Anaya-Ayala J.E. (Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Universidad Nacional Autonoma de Mexico ~ Mexico City ~ Mexico) , Verduzco-Vazquez A. (Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Universidad Nacional Autonoma de Mexico ~ Mexico City ~ Mexico) , Medina L.A. (Instituto Nacional de Cancerologia, Universidad Nacional Autonoma de Mexic ~ Mexico City ~ Mexico) , Marquina-Castillo B. (Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Universidad Nacional Autonoma de Mexico ~ Mexico City ~ Mexico) , Juan A. (Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Universidad Nacional Autonoma de Mexico ~ Mexico City ~ Mexico) , Bravo-Reyna C. (Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Universidad Nacional Autonoma de Mexico ~ Mexico City ~ Mexico) , Martinez-Martinez R. (Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Universidad Nacional Autonoma de Mexico ~ Mexico City ~ Mexico) , Bolanos-De-La Torre J. (Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Universidad Nacional Autonoma de Mexico ~ Mexico City ~ Mexico) , Hinojosa C.A. (Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Universidad Nacional Autonoma de Mexico ~ Mexico City ~ Mexico)
Introduction:
The pathogenesis and progression of aortic aneurysms (AA) are complex processes, and these remain not fully understood. Studies in aneurysmal aortic wall in human tissue and animal models have demonstrated an increased mural presence of macrophages and neovascularization (1, 2). Integrin αVβ3 and 18F Fluoro-2-Deoxi-D-glucose (FDG) are known molecular markers for angiogenesis and inflammation respectively (2). We aim to study and compare the Integrin αVβ3 expression with Gallium-68(68Ga)-labeled Arg-Gly-Asp (RGD), and inflammation with FDG using MicroPositron Emission Tomography (PET) in a Murine model of Thoracic Aortic Aneurysms (Aneurysms) and healthy aortic tissue (controls). Additionally, we evaluated post mortem tissue at 6 months in the same models and compared the expression with immunofluorescence for Integrin αVβ3, and Immunohistochemistry to identify CD-68 for macrophages as an inflammatory marker.
Methods:
A total of eight specimens of Wistar rat with Calcium Chloride (0.8 M CaCl), experimentally induced Thoracic Aortic Aneurysms were evaluated. (3) The equipment utilized for the evaluation was an Albira microPET/CT unit (Bruker, Spain), and accesses were obtained in one of the caudal veins for radiomarkers infusion. The PET uptake and activity were expressed as median value with interquartile range and the Mann-Whitney U test was employed to analyse and compare the chemically induced-site (Aneurysm) and intact aortic tissue (Control) in the same specimens. Immunofluorescence using specific antibody (Integrin av/b3 Antibody (23C6) Alexa Fluor 546: sc-7312AF546 Santa Cruz Biotechnology), the tissues were evaluated with a confocal microscope obtaining the mean intensity of fluorescence. The immunohistochemistry was evaluated using specific antibodies: CD-31 for the endothelium and with CD-68 for macrophages as an inflammation marker. Statistical analysis was performed with GraphPad Prism 8.0 software.
Results:
An overall focal increased PET uptake was observed in the thoracic aortic lesions compared to control regions. The median standard uptake value (SUV) of 68Ga-RGD in the chemically induced-injury site (aneurysm) was 0.0125, while the uptake in the intact site (control) was 0.0003 (p value=0.0006) during a mean follow up period of 37 days. The median SUV for FDG of aneurysm was 0.15 while the control median was 0.02 (p value= 0.0286) at 28 days. (Figure 1 A, B). Immunohistochemical studies identified MMP-9-positive macrophages in the intima/media See panel in Figure 2. Fluorescence microscopy of the collected samples also confirmed the accumulation of Integrin αVβ3 in the intima/media in comparison with control tissue. These patterns were found and confirmed in ex-vivo human aortic tissue.
Conclusion:
We found significant differences of Integrin αVβ3 and FDG expression uptakes using microPET imaging in chemically induced thoracic aortic aneurysms compared with the intact aortic tissue within 4 to 6 weeks of vessel injury in the murine model. The analyses of immunofluorescence and immunohistochemistry confirmed these differences at six months of follow up. Studies with nuclear imaging may assist in the molecular characterization of pathophysiologic processes in animal models, and this knowledge might be translated into well-designed clinical research studies in human patients with aortic aneurysms for the determination of risk prediction of complications, including rupture. (4, 5)
References:
1. Paik DC, Fu C, Bhattacharya J, Tilson MD. Ongoing angiogenesis in blood vessels of the abdominal aortic aneurysm. Exp Mol Med. 2004;36(6):524-33 2. Kitagawa T, Kosuge H, Chang E, James ML, Yamamoto T, Shen B, Chin FT, Gambhir SS, Dalman RL, McConnell MV. Integrin-targeted molecular imaging of experimental abdominal aortic aneurysms by (18)F-labeled Arg-Gly-Asp positron-emission tomography. Circ Cardiovasc Imaging. 2013;6(6):950-6. 3. Anaya-Ayala JE, Medina LA, Martinez-Martinez R, Rosas-Rios C, Hinojosa CA. Contrast Enhanced Computed Tomography Angiography Protocol for the Assessment of Thoracic Aortic Diameters in a Murine Model. Arteriosclerosis, Thrombosis, and Vascular Biology. 2020;40:A441. 4. Bell M, Gandhi R, Shawer H, Tsoumpas C, Bailey MA. Imaging Biological Pathways in Abdominal Aortic Aneurysms Using Positron Emission Tomography. Arterioscler Thromb Vasc Biol. 2021;41(5):1596-1606. 5. Sokol J, Nguyen PK. Risk prediction for abdominal aortic aneurysm: One size does not necessarily fit all. J Nucl Cardiol. 2022 Feb 16.
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