Multimodality molecular imaging identifies proteolytic and osteogenic activities in early aortic valve disease

Circulation. 2007 Jan 23;115(3):377-86. doi: 10.1161/CIRCULATIONAHA.106.654913. Epub 2007 Jan 15.


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.

Methods and 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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Aortic Valve Stenosis / pathology
  • Aortic Valve Stenosis / physiopathology*
  • Apolipoproteins E / genetics
  • Apolipoproteins E / physiology
  • Atherosclerosis / pathology
  • Atherosclerosis / physiopathology*
  • Calcinosis / pathology
  • Calcinosis / physiopathology
  • Calcium / metabolism
  • Endothelium, Vascular / pathology
  • Endothelium, Vascular / physiopathology
  • Enzyme Activation / physiology
  • Fibroblasts / pathology
  • Fibroblasts / physiology
  • Gene Expression Profiling
  • Hypercholesterolemia / pathology
  • Hypercholesterolemia / physiopathology
  • Macrophage Activation / physiology
  • Macrophages / pathology
  • Macrophages / physiology
  • Magnetic Resonance Imaging / methods*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Osteoblasts / pathology
  • Osteoblasts / physiology
  • Osteogenesis / physiology*
  • Peptide Hydrolases / physiology*
  • Predictive Value of Tests
  • Spectroscopy, Near-Infrared / methods*


  • Apolipoproteins E
  • Peptide Hydrolases
  • Calcium