Rapid quantification of inflammation in tissue samples using perfluorocarbon emulsion and fluorine-19 nuclear magnetic resonance

Abstract

Quantification of inflammation in tissue samples can be a time-intensive bottleneck in therapeutic discovery and preclinical endeavors. We describe a versatile and rapid approach to quantitatively assay macrophage burden in intact tissue samples. Perfluorocarbon (PFC) emulsion is injected intravenously, and the emulsion droplets are effectively taken up by monocytes and macrophages. These ‘in situ’ labeled cells participate in inflammatory events in vivo resulting in PFC accumulation at inflammatory loci. Necropsied tissues or intact organs are subjected to conventional fluorine-19 (19F) NMR spectroscopy to quantify the total fluorine content per sample, proportional to the macrophage burden. We applied these methods to a rat model of experimental allergic encephalomyelitis (EAE) exhibiting extensive inflammation and demyelination in the central nervous system (CNS), particularly in the spinal cord. In a cohort of EAE rats, we used 19F NMR to derive an inflammation index (IFI) in intact CNS tissues. Immunohistochemistry was used to confirm intracellular colocalization of the PFC droplets within CNS CD68+ cells having macrophage morphology. The IFI linearly correlated to mRNA levels of CD68 via real-time PCR analysis. This 19F NMR approach can accelerate tissue analysis by at least an order of magnitude compared with histological approaches.

Technical Advance: Monitoring the trafficking of neutrophil granulocytes and monocytes during the course of tissue inflammation by noninvasive 19F MRI

“…3B, left). These results are consistent with previous studies showing that the 19 F label is actively carried by CD11b ϩ myeloid cells into the inflamed area [15,18,23]. Currently, it is yet unclear why the myeloid immune cells locate to the periphery of the plug.…”

Tracking immune cells in vivo using magnetic resonance imaging

“…As these in situ- labelled cells participate in inflammatory events in the body, the result is 19 F accumulation at inflammatory sites. Importantly, the in vivo 19 F MRI signal can be quantified in inflammatory sites, and this signal is linearly proportional to the macrophage burden 52,53 . 19 F labelling in situ has been widely used to visualize inflammation in a large number of preclinical models of human disease, such as IBD 53 (FIG.…”

Perfluorocarbon Nanoparticles for Physiological and Molecular Imaging and Therapy

“…A variety of cell types are capable of being isolated, subjected to PFC NP labeling by endocytosis in vivo, and then reinjected either locally into tissues or systemically where they can be tracked by 19 F MRI. 49, 51, 52, 55, 112–114 Figure 10 shows an example of two distinct PFC labels in endothelial precursor cells that contribute to tumor angiogenesis, and illustrates the opportunity for tracking multiple cell labels simultaneously. In other example, Ahrens and collaborators have mapped acute allograft rejection with 19 F labeled immune cells.…”