Molecular Imaging of Matrix Metalloproteinase in Atherosclerotic Lesions. Resolution With Dietary Modification and Statin Therapy

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.