Abstract 1799: Molecular Imaging Identifies Inflammation and Precalcification in Aortic Valve Disease
Background Aortic stenosis is a frequent indication for valve replacement, however, underlying molecular and cellular mechanisms remain obscure. Visualizing and understanding function of specific cell populations in subclinical valve lesions in vivo may predict the future risk and identify therapeutic targets for prevention of this disease.
Methods and Results To test the hypotheses 1) that aortic stenosis shares a similar pathogenesis to atherosclerosis and 2) that multimodality molecular imaging can detect early changes in aortic valve disease, we employed in vivo near-infrared fluorescence (NIRF) imaging agents for endothelial cell and macrophage activation, and proteolytic and osteogenic activity in aortic valves of cholesterol-fed apoE-deficient mice (apoE−/−, 30 weeks old, n=25). ApoE−/− mice with no probe injection (n=10) and wild-type mice (n=5) served as controls. Valve leaflets of apoE−/− mice contained macrophages and were thicker than wild-type mice (p< 0.001). Fluorescence reflectance imaging detected uptake of macrophage-targeted magnetofluorescent nanoparticles (24 h post-injection) in apoE−/− valves that was negligible in controls (p< 0.01). Valvular macrophages showed proteolytic activity (gelatinases MMP-2/9 and cathepsin B) visualized by activatable probes using NIRF microscopy. MRI enhanced with VCAM-1 targeted nanoparticles detected ex vivo endothelial activation in valve commissures - the regions of highest mechanical stress. Inflamed valves exhibited osteogenic activity visualized by OsteoSense, a bisphosphonate-derivatized agent, using high-resolution laser scanning fluorescence microscopy. Osteogenic NIRF signals further colocalized with immunoreactive osteopontin and osteocalcin despite no evidence of calcium deposits (von Kossa staining), suggesting that OsteoSense detected valvular precalcification. Notably, the aortic wall contained prominent calcification. Quantitative image analysis correlated NIRF signals with immunoreactive VCAM-1, macrophages, and cathepsin B (R2=0.784; 0.879; 0.858, p<0.001).
Conclusion Multimodality molecular imaging can visualize endothelial cell activation, inflammation, and proteolytic and osteogenic activity in early aortic valve disease.