Simultaneous Assessment of Cardiac Inflammation and Extracellular Matrix Remodeling after Myocardial Infarction

Optimal healing of the myocardium following myocardial infarction (MI) requires a suitable degree of inflammation and its timely resolution, together with a well-orchestrated deposition and degradation of extracellular matrix (ECM) proteins.

MI and SHAM-operated animals were imaged at 3,7,14 and 21 days with 3T magnetic resonance imaging (MRI) using a ¹⁹F/¹H surface coil. Mice were injected with ¹⁹F-perfluorocarbon (PFC) nanoparticles to study inflammatory cell recruitment, and with a gadolinium-based elastin-binding contrast agent (Gd-ESMA) to evaluate elastin content. ¹⁹F MRI signal co-localized with infarction areas, as confirmed by late-gadolinium enhancement, and was highest 7days post-MI, correlating with macrophage content (MAC-3 immunohistochemistry) (ρ=0.89,P<0.0001). ¹⁹F quantification with in vivo (MRI) and ex vivo nuclear magnetic resonance (NMR) spectroscopy correlated linearly (ρ=0.58,P=0.020). T₁ mapping after Gd-ESMA injection showed increased relaxation rate (R₁) in the infarcted regions and was significantly higher at 21days compared with 7days post-MI (R₁[s^-1]:21days=2.8 [IQR,2.69-3.30] vs 7days=2.3 [IQR,2.12-2.5], P<0.05), which agreed with an increased tropoelastin content (ρ=0.89, P<0.0001). The predictive value of each contrast agent for beneficial remodeling was evaluated in a longitudinal proof-of-principle study. Neither R₁ nor ¹⁹F at day 7 were significant predictors for beneficial remodeling (P=0.68;P=0.062). However, the combination of both measurements (R₁<2.34Hz and 0.55≤¹⁹F≤1.85) resulted in an odds ratio of 30.0 (CI95%:1.41-638.15;P=0.029) for favorable post-MI remodeling.

Multinuclear ¹H/¹⁹F MRI allows the simultaneous assessment of inflammation and elastin remodeling in a murine MI model. The interplay of these biological processes affects cardiac outcome and may have potential for improved diagnosis and personalized treatment.