Molecular Imaging of Matrix Metalloproteinase in Atherosclerotic Lesions

Objectives This study sought to evaluate the feasibility of noninvasive detection of matrix metalloproteinase (MMP) activity in experimental atherosclerosis using technetium-99m-labeled broad matrix metalloproteinase inhibitor (MPI) and to determine the effect of dietary modification and statin treatment on MMP activity. Background The MMP activity in atherosclerotic lesions contributes to the vulnerability of atherosclerotic plaques to rupture. Methods Atherosclerosis was produced in 34 New Zealand White rabbits by balloon de-endotheliazation of the abdominal aorta and a high-cholesterol diet. In addition, 12 unmanipulated rabbits were used as controls and 3 for blood clearance characteristics. In vivo micro-single-photon emission computed tomography (SPECT) imaging was performed after radiolabeled MPI administration. Subsequently, aortas were explanted to quantitatively measure percent injected dose per gram (%ID/g) MPI uptake. Histological and immunohistochemical characterization was performed and the extent of MMP activity was determined by gel zymography or enzyme-linked immunosorbent assays. Results The MPI uptake in atherosclerotic lesions (n=18) was clearly visualized by micro-SPECT imaging; MPI uptake was markedly reduced by administration of unlabeled MPI before the radiotracer (n=4). The MPI uptake was also significantly reduced after diet withdrawal (n=6) and fluvastatin treatment (n=6); no uptake was observed in normal control rabbits ( n=12). The %ID/g MPI uptake (0.10 +/- 0.03%) in the atherosclerotic lesions was significantly higher than the uptake in control aorta (0.016 +/- 0.004%, p < 0.0001). Uptake in fluvastatin (0.056 +/- 0.011%, p < 0.0005) and diet withdrawal groups (0.043 +/- 0.011%, p < 0.0001) was lower than the untreated group. The MPI uptake correlated with immunohistochemically verified macrophage infiltration (r = 0.643, p < 0.0001), and MMP-2 (r = 0.542, p < 0.0001) or MMP-9 (r = 0.578, p < 0.0001) expression in plaques. Conclusions The present data show the feasibility of noninvasive detection of MMP activity in atherosclerotic plaques, and confirm that dietary modification and statin therapy reduce MMP activity. (J Am Coll Cardiol 2008; 52: 1847-57) (c) 2008 by the American College of Cardiology Foundation