Purpose: Endothelial cell adhesion molecules such as ICAM-1 are up-regulated in early inflammation in atherosclerotic disease. We hypothesize that fluorescence imaging of ICAM-1 expression in atherosclerosis may serve as a new method to probe the development of inflammatory pathology in vivo.
Methods: To test this hypothesis, we prospectively imaged the development of inflammatory atherosclerotic lesions in ApoE-/- mice fed high fat diet (HFD) using an anti-human ICAM-1 single domain antibody (sdAb) tagged with near infrared red fluorophore (NIRF) Cy5.5. At the 4th month, a subset of ApoE-/- and C57Bl/6 mice were treated with Lipitor (25mg/kg/day), while the mice were continuously fed with HFD. Control animals remained normally increasing body weight, but ApoE-/- shown progressively reduction of body weight four months after experiment.
Anti-ICAM-1 single domain antibody sd-11-4-Cy5.5 was intravenously injected inHFD-fed ApoE-/- and C57Bl/6 mice, and whole-body imaging was performed before and 24, 48 and 72 hours post-injection. using a time-domain imaging instrument. This procedure was repeated each month for 4 months following the start of HFD.
Results: Fluorescence imaging showed that (1) anti-ICAM-1 antibody accumulated in the thoracic region of ApoE-/- mice but not in C57Bl/6 mice in time-dependent fashion; (2) the anti-ICAM antibody was localized in the heart-aorta region of ApoE -/- mice. In time resolved 3D fluorescence images after perfusion, heart-aorta ex vivo fluorescence signal analyses revealed that ApoE-/- group has significantly higher fluorescence signal than the control group. Immunohistochemistry of frozen heart-aorta sections showed that extensive colocalization of Cy5.5 with large atherosclerosis lesions in ApoE-/- mice but not in control mice. (3) There was a significant fluorescence signals reduction in Lipitor-treated compared to non-treated ApoE-/- animals. Comparative study with commercial anti-ICAM-1 antibody (mAb ICAM-1) was also performed.
Conclusion: Combining all of these, we can conclude that it is feasible to image atherosclerosis plaque in vivo using fluorescence imaging technique and monitor therapy with NIRF-labeled sd-11-4 specifically targeted to ICAM-1.