Statins Promote Cardiac Infarct Healing by Modulating Endothelial Barrier Function Revealed by Contrast-Enhanced Magnetic Resonance Imaging.

OBJECTIVE: The endothelium has a crucial role in wound healing, acting as a barrier to control transit of leukocytes. Endothelial barrier function is impaired in atherosclerosis preceding myocardial infarction (MI). Besides lowering lipids, statins modulate endothelial function. Here, we noninvasively tested whether statins affect permeability at the inflammatory (day 3) and the reparative (day 7) phase of infarct healing post-MI using contrast-enhanced cardiac magnetic resonance imaging (MRI). APPROACH AND RESULTS: Noninvasive permeability mapping by MRI after MI in C57BL/6, atherosclerotic ApoE-/-, and statin-treated ApoE-/- mice was correlated to subsequent left ventricular outcome by structural and functional cardiac MRI. Ex vivo histology, flow cytometry, and quantitative polymerase chain reaction were performed on infarct regions. Increased vascular permeability at ApoE-/- infarcts was observed compared with C57BL/6 infarcts, predicting enhanced left ventricular dilation at day 21 post-MI by MRI volumetry. Statin treatment improved vascular barrier function at ApoE-/- infarcts, indicated by reduced permeability. The infarcted tissue of ApoE-/- mice 3 days post-MI displayed an unbalanced Vegfa(vascular endothelial growth factor A)/Angpt1 (angiopoetin-1) expression ratio (explaining leakage-prone vessels), associated with higher amounts of CD45+ leukocytes and inflammatory LY6Chi monocytes. Statins reversed the unbalanced Vegfa/Angpt1 expression, normalizing endothelial barrier function at the infarct and blocking the augmented recruitment of inflammatory leukocytes in statin-treated ApoE-/- mice. CONCLUSIONS: Statins lowered permeability and reduced the transit of unfavorable inflammatory leukocytes into the infarcted tissue, consequently improving left ventricular outcome.

Multiparametric MRI analysis for the evaluation of MR-guided high intensity focused ultrasound tumor treatment.

For the clinical application of high intensity focused ultrasound (HIFU) for thermal ablation of malignant tumors, accurate treatment evaluation is of key importance. In this study, we have employed a multiparametric MRI protocol, consisting of quantitative T1, T2, ADC, amide proton transfer (APT), T1ρ and DCE-MRI measurements, to evaluate MR-guided HIFU treatment of subcutaneous tumors in rats. K-means clustering using all different combinations of the endogenous contrast MRI parameters (feature vectors) was performed to segment the multiparametric data into tissue populations with similar MR parameter values. The optimal feature vector for identification of the extent of non-viable tumor tissue after HIFU treatment was determined by quantitative comparison between clustering-derived and histology-derived non-viable tumor fractions. The highest one-to-one correspondence between these clustering-based and histology-based non-viable tumor fractions was observed for the feature vector {ADC, APT-weighted signal} (R(2) to line of identity (R(2)y=x) = 0.92) and the strongest agreement was seen 3 days after HIFU (R(2)y=x = 0.97). To compare the multiparametric MRI analysis results with conventional HIFU monitoring and evaluation methods, the histology-derived non-viable tumor fractions were also quantitatively compared with non-perfused tumor fractions (derived from the level of contrast enhancement in the DCE-MRI measurements) and 240 CEM tumor fractions (i.e. thermal dose > 240 cumulative equivalent minutes at 43 °C). The correlation between histology-derived non-viable tumor fractions directly after HIFU and the 240 CEM fractions was high, but not significant. The non-perfused fractions overestimated the extent of non-viable tumor tissue directly after HIFU, whereas an underestimation was observed 3 days after HIFU. In conclusion, we have shown that a multiparametric MR analysis, especially based on the ADC and the APT-weighted signal, can potentially be used to determine the extent of non-viable tumor tissue 3 days after HIFU treatment. We expect that this method can be incorporated in the current clinical workflow of MR-HIFU ablation therapies.

Evaluation of 111In-labeled EPep and FibPep as tracers for fibrin SPECT imaging.

Fibrin targeting is an attractive strategy for nuclear imaging of thrombosis, atherosclerosis and cancer. Recently, FibPep, an (111)In-labeled fibrin-binding peptide, was established as a tracer for fibrin SPECT imaging and was reported to allow sensitive detection of minute thrombi in mice using SPECT. In this study, we developed EPep, a novel (111)In-labeled fibrin-binding peptide containing the fibrin-binding domain of the clinically verified EP-2104R peptide, and sought to compare the potential of EPep and FibPep as tracers for fibrin SPECT imaging. In vitro, both EPep and FibPep showed high stability in serum, but were less stable in liver and kidney homogenate assays. Both peptide probes displayed comparable affinities toward human and mouse derived fibrin (Kd ≈ 1 µM), and similarly to FibPep, EPep showed fast blood clearance, low nontarget uptake and high thrombus uptake (6.8 ± 1.2% ID g(-1)) in a mouse carotid artery thrombosis model. Furthermore, EPep showed a similar affinity toward rat derived fibrin (Kd ≈ 1 µM), displayed high thrombus uptake in a rat carotid artery thrombosis model (0.74 ± 0.39% ID g(-1)), and allowed sensitive detection of thrombosis in rats using SPECT. In contrast, FibPep displayed a significantly lower affinity toward rat derived fibrin (Kd ≈ 14 µM) and low uptake in rat thrombi (0.06 ± 0.02% ID g(-1)) and did not allow clear visualization of carotid artery thrombosis in rats using SPECT. These results were confirmed ex vivo by autoradiography, which showed a 7-fold higher ratio of activity in the thrombus over the contralateral carotid artery for EPep in comparison to FibPep. These findings suggest that the FibPep binding fibrin epitope is not fully homologous between humans and rats, and that preclinical rat models of disease should not be employed to gauge the clinical potential of FibPep. In conclusion, both peptides showed approximately similar metabolic stability and affinity toward human and mouse derived fibrin, and displayed high thrombus uptake in a mouse carotid artery thrombosis model. Therefore, both EPep and FibPep are promising fibrin targeted tracers for translation into clinical settings to serve as novel tools for molecular imaging of fibrin.