Molecular Imaging of Matrix Metalloproteinase Expression in Atherosclerotic Plaques of Mice Deficient in Apolipoprotein E or Low-Density-Lipoprotein Receptor

Abstract

Matrix metalloproteinases (MMPs) are expressed in atherosclerotic plaques and play an important role in plaque instability. Methods: Using 99m Tc-labeled broad-spectrum MMP inhibitor (MPI), we performed noninvasive imaging of MMP expression with micro-SPECT/micro-CT in mice deficient in apolipoprotein E (ApoE 2/2 , n 5 14), mice deficient in low-density-lipoprotein receptor (LDLR 2/2 , n 5 14), and C57/BL6 mice as controls (n 5 7). Seven ApoE 2/2 and 7 LDLR 2/2 received a high-cholesterol diet. After in vivo imaging, aortas were explanted, ex vivo images acquired, and the percent injected dose of MPI per gram (%ID/g) determined, followed by histologic characterization of atherosclerotic lesions. Results: MPI uptake was noninvasively visualized in atherosclerotic lesions by micro-SPECT, with confirmation by micro-CT of anatomic location and aortic calcification. %ID/g in each part of the aorta was highest in ApoE 2/2 that were fed a high-cholesterol diet, followed by LDLR 2/2 that were fed a high-cholesterol diet, ApoE 2/2 that were fed normal chow, and LDLR 2/2 that were fed normal chow. The control mice had minimal MPI uptake. A significant correlation was noted between %ID/g and % area positive for macrophages (r 5 0.81, P 5 0.009), MMP-2 (r 5 0.65, P 5 0.013), and MMP-9 (r 5 0.62, P 5 0.008). Conclusion: This study demonstrates the usefulness of molecular imaging for noninvasive assessment of the extent of MMP expression in various transgenic mouse models of atherosclerosis receiving a normal or hyperlipidemic diet. It is conceivable that such a strategy may be translationally developed for identification of unstable atherosclerotic plaques.

Extracellular proteolysis in macrophage migration: Losing grip for a breakthrough

“…In vivo, future insights into the behavior of monocyte/macrophages will require a coordinated effort of technical and biological considerations. Although new technical approaches have been developed to track macrophages [62,82] and detect proteinase expression and activity in situ [66,69,86], a major technical challenge remains the intravital depth imaging limits that hinder resolution and sensitivity.…”

“…In vivo, future insights into the behavior of monocyte/macrophages will require a coordinated effort of technical and biological considerations. Although new technical approaches have been developed to track macrophages [62,82] and detect proteinase expression and activity in situ [66,69,86], a major technical challenge remains the intravital depth imaging limits that hinder resolution and sensitivity.In contrast to lymphocytes which use the protease-independent, amoeboid migration mode [1], macrophages use distinct migration modes, and, in situations where proteolytic activities are required, distinct proteases are used in different environments. Thus, although many questions remain, this research field is a key area whose results would potentially lead to the specific control of macrophage infiltration in determined tissue and the control of pathology.…”

Identification of cholesterol crystals in plaques of atherosclerotic mice using hyperspectral CARS imaging

“…Importantly, we have found that this technique can successfully discriminate lipophilic compounds, in both intra-and extracellular regions, in a label-free manner. We have applied this method to study the structure and chemical makeup of plaques in two atherosclerotic mouse models: the LDL receptor-defi cient (LDLR Ϫ / Ϫ ) mouse and the ApoE-defi cient (ApoE Ϫ / Ϫ ) mouse (37)(38)(39)(40)(41). Our label-free imaging results reveal clusters of macrophage cells as well as needle-shaped and plate-shaped lipid crystal structures within plaque lesions.…”

Molecular Imaging of Vulnerable Coronary Plaque: A Pathophysiologic Perspective

“…MMPs have therefore been considered ideal targets for molecular imaging of vulnerable plaque. In preclinical models of atherosclerosis, 123 I-or 125 I-labeled CGS 27023A, a broad-spectrum MMP inhibitor (32), and RP-805, a 99m Tc-labeled broad-spectrum MMP-inhibiting macrocyclic compound, have been shown to bind to atherosclerotic plaque (33,34).…”