Assessment of inflammation with a very small iron-oxide particle in a murine model of reperfused myocardial infarction

Purpose To investigate a very small iron-oxide particle (VSOP) in a mouse model of acute ischemia-reperfusion to access the mechanism of such particles in areas of myocardial inflammation. Materials and Methods Animals were injected with VSOP at several time points, in a mouse model of acute myocardial infarction (MI), before and after MI. MRI was used to localize areas of VSOP enhancement, evaluate VSOP areas extension, and determine the related T2* values. Histology, electron microscopy, macrophage counting, and Evan's Blue staining were also performed. Results We found that areas of VSOP uptake decreased from 1 to 8 days post-MI while the related T2* values increased. T2* and VSOP areas, defined from MRI data, correlated well between 1 and 3 days post-MI but not at 7 days after injection. Histological analysis and electron microscopy showed colocalization of macrophages with areas of VSOP staining. However, there was no correlation between number of macrophages and the extension of the VSOP areas achieved by MR. We found that only areas of increased permeability (assessed by Evan's Blue staining) showed colocalization of macrophages and VSOP uptake. Conclusion This study demonstrates that VSOP allows the assessment of myocardial inflammation associated with increased permeability during infarct healing in a mouse model of ischemia-reperfusion. J. Magn. Reson. Imaging 2014;39:598-608. (c) 2013 Wiley Periodicals, Inc.