Fig. 3.

Protease-activatable near-infrared fluorescent (NIRF) imaging to allow the visualization of vulnerable plaques in the aorta of a mouse. In the areas positive for cathepsin K (CatK) immunohistochemical staining (A, ×20, red-colored regions), the fluorescence activation of the intravenously-injected imaging agent⁵⁹ by the CatK cleavage activity is evident in NIRF microscopy imaging of cryosections of the aortic atheromata in an ApoEknock-out mouse fed on a Western diet (B, ×20); the co-localization is illustrated by the yellow arrowheads. Higher magnification (C, ×40) reveals the derangement of undulated elastic fibers (red arrow), suggesting matrix disorganization. A stable portion of the artery without CatK activity or elastin degradation is indicated by the blue arrow. Taken together, these results suggest that molecular optical imaging can reflect matrix-disorganizing protease activity, allowing identification of rupture-prone inflammatory plaques.