Abstract 16926: Intravascular Near Infrared Fluorescence Molecular Imaging Identifies Macrophages in vivo in Thrombosis-Prone Plaques
Sudden luminal thrombosis from atherosclerotic plaque disruption leads to acute myocardial infarction. However, the inflammatory process driving plaque destabilization is incompletely understood in vivo. We investigated plaque macrophage distribution prior to triggered thrombosis using a novel near-infrared fluorescence (NIRF) macrophage targeted nanoparticle, CLIO-CyAm7, and intravascular 2D NIRF imaging. We hypothesized that CLIO-CyAm7 would illuminate macrophages in vivo in thrombosis-prone plaques.
High-cholesterol diet and balloon injury at week 2 produced aortic atherosclerosis in rabbits (n=13). CLIO-CyAm7 (2.5mg Fe/kg) was injected 24 hrs before imaging. Intravascular ultrasound (IVUS) and 2D NIRF imaging assessed baseline plaque structure and inflammation prior to 48 hrs of thrombosis triggering using Russell’s viper venom and histamine. IVUS was repeated to identify thrombi in vivo. After sacrifice, fluorescence microscopy (FM), Carstairs’ staining for fibrin and RAM-11 immunostaining for macrophages were performed. In vivo NIRF signal was quantified as peak target-to-background ratio (TBR), the ratio of atheroma signal to uninjured aorta (MATLAB). FM data were analyzed in the superficial 100μm region of each atheroma (ImageJ).
In vivo IVUS and Carstairs’ staining identified thrombosis in 8 of 13 rabbits. On FM, CLIO-CyAm7 primarily colocalized with macrophages at the intimal-luminal border, particularly at plaque shoulders. Atheroma showed a 30-fold higher CLIO-CyAm7 signal compared to the uninjured aorta (percent positive area 1.3±1.1% vs. 0.04±0.07%, p<0.0001). Importantly, plaques with luminal thrombosis showed 50% significantly higher CLIO-CyAm7 macrophage accumulation versus undisrupted atheroma (1.6±1.1% vs. 1.1±1.1%, p=0.05). CLIO-CyAm7-based in vivo intravascular NIRF-IVUS imaging visualized macrophage-rich atheromata, demonstrating significantly higher NIRF peak TBR than normal segments (2.9±1.9 vs. 1.5±0.6, p=0.001).
Plaques with increased CLIO-CyAm7 macrophage uptake preferentially thrombose under triggering conditions. CLIO-CyAm7 enables intravascular NIRF molecular imaging of macrophage-rich plaques in coronary-sized arteries in vivo, through blood.
- © 2013 by American Heart Association, Inc.