Multimodality molecular imaging identifies proteolytic and osteogenic activities in early aortic valve disease.
BACKGROUND
Visualizing early changes in valvular cell functions in vivo may predict the future risk and identify therapeutic targets for prevention of aortic valve stenosis.


RESULTS
To test the hypotheses that (1) aortic stenosis shares a similar pathogenesis to atherosclerosis and (2) molecular imaging can detect early changes in aortic valve disease, we used in vivo a panel of near-infrared fluorescence imaging agents to map endothelial cells, macrophages, proteolysis, and osteogenesis in aortic valves of hypercholesterolemic apolipoprotein E-deficient mice (30 weeks old, n=30). Apolipoprotein E-deficient mice with no probe injection (n=10) and wild-type mice (n=10) served as controls. Valves of apolipoprotein E-deficient mice contained macrophages, were thicker than wild-type mice (P<0.001), and showed early dysfunction detected by MRI in vivo. Fluorescence imaging detected uptake of macrophage-targeted magnetofluorescent nanoparticles (24 hours after injection) in apolipoprotein E-deficient valves, which was negligible in controls (P<0.01). Valvular macrophages showed proteolytic activity visualized by protease-activatable near-infrared fluorescence probes. Ex vivo magnetic resonance imaging enhanced with vascular cell adhesion molecule-1-targeted nanoparticles detected endothelial activation in valve commissures, the regions of highest mechanical stress. Osteogenic near-infrared fluorescence signals colocalized with alkaline phosphatase activity and expression of osteopontin, osteocalcin, Runx2/Cbfa1, Osterix, and Notch1 despite no evidence of calcium deposits, which suggests ongoing active processes of osteogenesis in inflamed valves. Notably, the aortic wall contained advanced calcification. Quantitative image analysis correlated near-infrared fluorescence signals with immunoreactive vascular cell adhesion molecule-1, macrophages, and cathepsin-B (P<0.001).


CONCLUSIONS
Molecular imaging can detect in vivo the key cellular events in early aortic valve disease, including endothelial cell and macrophage activation, proteolytic activity, and osteogenesis.
Aikawa
Elena
E
Center for Molecular Imaging Research, Massachusetts General Hospital, Harvard Medical School, Charlestown, Mass 02129, USA. eaikawa@partners.org
Nahrendorf
Matthias
M
Sosnovik
David
D
Lok
Vincent M
VM
Jaffer
Farouc A
FA
Aikawa
Masanori
M
Weissleder
Ralph
R
D000818:Animals; D001024:Aortic Valve Stenosis / Q000473:pathology / Q000503:physiopathology*; D001057:Apolipoproteins E / Q000235:genetics / Q000502:physiology; D050197:Atherosclerosis / Q000473:pathology / Q000503:physiopathology*; D002114:Calcinosis / Q000473:pathology / Q000503:physiopathology; D002118:Calcium / Q000378:metabolism; D004730:Endothelium, Vascular / Q000473:pathology / Q000503:physiopathology; D004789:Enzyme Activation / Q000502:physiology; D005347:Fibroblasts / Q000473:pathology / Q000502:physiology; D020869:Gene Expression Profiling; D006937:Hypercholesterolemia / Q000473:pathology / Q000503:physiopathology; D008262:Macrophage Activation / Q000502:physiology; D008264:Macrophages / Q000473:pathology / Q000502:physiology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010006:Osteoblasts / Q000473:pathology / Q000502:physiology; D010012:Osteogenesis / Q000502:physiology*; D010447:Peptide Hydrolases / Q000502:physiology*; D011237:Predictive Value of Tests; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
D001057:Apolipoproteins E; D010447:Peptide Hydrolases; D002118:Calcium