Molecular imaging of Cathepsin B proteolytic enzyme activity reflects the Inflammatory component of atherosclerotic pathology and can quantitatively demonstrate the antiatherosclerotic therapeutic effects of atorvastatin and glucosamine

Infl ammation in atherosclerotic plaques causes plaque vulnerability and rupture, leading to thromboembolic complications. Cathepsin B (CatB) proteases secreted by macrophages play a major role in plaque infl ammation. We used a CatB-activatable near-infrared fl uorescence (NIRF) imaging agent to demonstrate the infl ammatory component in mice atheromata and the atherosclerosismodulating effects of atorvastatin or glucosamine treatments. Apolipoprotein E knockout mice (n = 35) were fed normal chow, a Western diet, a Western diet + atorvastatin, a Western diet + glucosamine, or a Western diet + atorvastatin + glucosamine for 14 weeks. Twenty-four hours after the intravenous injection of a CatB-activatable probe, ex vivo NIRF imaging of the aortas and brains was performed, followed by histology. The CatB-related signal, observed in the aortas but not in the cerebral arteries, correlated very well with protease activity and the presence of macrophages on histology. Animals on Western diets could be distinguished from animals on a normal diet. The antiatherosclerotic effects of atorvastatin and glucosamine could be demonstrated, with reduced CatB-related signal compared with untreated animals. Plaque populations were heterogeneous within individuals, with some plaques showing a high and others a lower CatB-related signal. These differences in signal intensity could not be predicted by visual inspection of the plaques but did correlate with histologic evidence of infl ammation in every case. This suggests that vulnerable infl amed plaques can be identifi ed by optical molecular imaging.