Molecular Imaging of Interstitial Alterations in Remodeling Myocardium After Myocardial Infarction

Objectives: The purpose of this study was to evaluate interstitial alterations in myocardial remodeling using a radiolabeled Cy5.5-RGD imaging peptide (CRIP) that targets myofibroblasts. Background: Collagen deposition and interstitial fibrosis contribute to cardiac remodeling and heart failure after myocardial infarction (MI). Evaluation of myofibroblastic proliferation should provide indirect evidence of the extent of fibrosis. Methods: Of 46 Swiss-Webster mice, MI was induced in 41 by coronary artery occlusion, and 5 were unmanipulated. Of the 41 mice, 6, 6, and 5 received intravenous technitium-99m labeled CRIP for micro-single-photon emission computed tomography imaging 2, 4, and 12 weeks after MI, respectively; 8 received captopril or captopril with losartan up to 4 weeks after MI. Scrambled CRIP was used 4 weeks after MI in 6 mice; the remaining 10 of 46 mice received unradiolabeled CRIP for histologic characterization. Results: Maximum CRIP uptake was observed in the infarct area; quantitative uptake (percent injected dose/g) was highest at 2 weeks (2.75 ± 0.46%), followed by 4 (2.26 ± 0.09%) and 12 (1.74 ± 0.24%) weeks compared with that in unmanipulated mice (0.59 ± 0.19%). Uptake was higher at 12 weeks in the remote areas. CRIP uptake was histologically traced to myofibroblasts. Captopril alone (1.78 ± 0.31%) and with losartan (1.13 ± 0.28%) significantly reduced tracer uptake; scrambled CRIP uptake in infarct area (0.74 ± 0.17%) was similar to CRIP uptake in normal myocardium. Conclusions: Radiolabeled CRIP allows for noninvasive visualization of interstitial alterations during cardiac remodeling, and is responsive to antiangiotensin treatment. If proven clinically feasible, such a strategy would help identify post-MI patients likely to develop heart failure.