Molecular Hybrid Positron Emission Tomography/Computed Tomography Imaging of Cardiac Angiotensin II Type 1 Receptors

Division of Nuclear Medicine, Russell H. Morgan Department of Radiology, Johns Hopkins University, Baltimore, Maryland.
Journal of the American College of Cardiology (Impact Factor: 15.34). 11/2012; 60(24). DOI: 10.1016/j.jacc.2012.09.023
Source: PubMed

ABSTRACT OBJECTIVES: The goal of this study was to explore the feasibility of targeted imaging of the angiotensin II type 1 receptor (AT1R) in cardiac tissue, using clinical hybrid positron emission tomography/computed tomography (PET/CT). BACKGROUND: AT1R is an attractive imaging target due to its key role in various cardiac pathologies, including post-infarct left ventricular remodeling. METHODS: Using the novel AT1R ligand [(11)C]-KR31173, dynamic PET/CT was performed in young farm pigs under healthy conditions (n = 4) and 3 to 4 weeks after experimental myocardial infarction (n = 5). Ex vivo validation was carried out by immunohistochemistry and polymerase chain reaction. First-in-man application was performed in 4 healthy volunteers at baseline and under AT1R blocking. RESULTS: In healthy pigs, myocardial KR31173 retention was detectable, regionally homogeneous, and specific for AT1R, as confirmed by blocking experiments. Metabolism in plasma was low (85 ± 2% of intact tracer after 60 min). After myocardial infarction, KR31173 retention, corrected for regional perfusion, revealed AT1R up-regulation in the infarct area relative to remote myocardium, whereas retention was elevated in both regions when compared with myocardium of healthy controls (8.7 ± 0.8% and 7.1 ± 0.3%/min vs. 5.8 ± 0.4%/min for infarct and remote, respectively, vs. healthy controls; p < 0.01 each). Postmortem analysis confirmed AT1R up-regulation in remote and infarct tissue. First-in-man application was safe, and showed detectable and specific myocardial KR31173 retention, albeit at a lower level than pigs (left ventricular average retention: 1.2 ± 0.1%/min vs. 4.4 ± 1.2%/min for humans vs. pigs; p = 0.04). CONCLUSIONS: Noninvasive imaging of cardiac AT1R expression is feasible using clinical PET/CT technology. Results provide a rationale for broader clinical testing of AT1R-targeted molecular imaging.

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Sep 9, 2014