Dual molecular imaging for targeting metalloproteinase activity and apoptosis in atherosclerosis: Molecular imaging facilitates understanding of pathogenesis

Background: Macrophage apoptosis and MMP activity contribute to vulnerability of atherosclerotic plaques to rupture. By employing molecular imaging techniques, we investigated if apoptosis and MMP release are interlinked. Methods: Atherosclerosis was produced in rabbits receiving high-cholesterol diet (HC), who underwent dual radionuclide imaging with ^99mTc-labeled matrix metalloproteinase inhibitor (MPI) and ¹¹¹In-labeled annexin A5 (AA5) using micro-SPECT/CT. %ID/g MPI and AA5 uptake was measured, followed by histological characterization. Unmanipulated animals were used as disease controls. Correlation between MPI and AA5 uptake was undertaken and relationship confirmed in culture study of activated THP-1 monocytes. Results: MPI and AA5 uptake was best visualized in HC diet animals (n = 6) and reduced significantly after fluvastatin treatment (n = 4) or diet withdrawal (n = 3). %ID/g MPI (.087 ± .018%) and AA5 (.03 ± .01%) uptake was higher in HC than control (n = 6) animals (.014 ± .004%, P < .0001; .0007 ± .0002%, P < .0001), and reduced substantially after diet or statin intervention. There was a significant correlation between MPI and AA5 uptake (r = .62, P < .0001), both correlated with pathologically verified MMP-9 activity, macrophage content, and TUNEL staining. In vitro studies demonstrated MMP-9 release in culture medium from apoptotic THP-1 monocytes. Conclusions: The present study suggests that apoptosis and MMP are interrelated in atherosclerotic lesions and the targeting of more than one molecular candidate is feasible by molecular imaging.