Application of Europium-Doped Very Small Iron Oxide Nanoparticles to Visualize Neuroinflammation with MRI and Fluorescence Microscopy.

Our recent studies demonstrated that electrostatically stabilized very small superparamagnetic iron oxide particles (VSOPs) are promising MRI probes for detecting various pathological aspects of autoimmunity in the central nervous system (CNS). However, investigation of the precise tissue and cellular distribution of VSOP has been technically limited due to the need to use iron detection methods for VSOP visualization. Therefore, we assessed here the utility of europium (Eu)-doped VSOP as an MRI tool for in vivo investigations in the animal model experimental autoimmune encephalomyelitis (EAE), and as a tool to investigate histopathological processes in the CNS using fluorescence microscopy. We demonstrated that Eu-VSOP display the same properties as VSOP in terms of revealing inflammation-mediated changes by binding to brain endothelium in vitro, and in terms of visualizing brain lesions in EAE in vivo. MRI examinations with Eu-VSOP confirm that at peak disease particles accumulated inside the choroid plexus, and in cerebellar and meningeal lesions. Importantly, Eu-VSOP-based MRI showed for the first time in a longitudinal setup that particles were absent from the choroid plexus in mice during remission of EAE, but accumulated again during subsequent relapse. Within the choroid plexus, Eu-VSOP were associated both with monocytes/macrophages present in the plexus stroma, and associated with epithelial cells. Using Eu-VSOP, we demonstrated for the first time the involvement of the choroid plexus in relapses. Thus, Eu-VSOP have the potential to reveal various aspects of choroid plexus involvement in neuroinflammation, including monocyte recruitment from the blood and alterations of the choroid plexus epithelium.

MR Elastography-Based Assessment of Matrix Remodeling at Lesion Sites Associated With Clinical Severity in a Model of Multiple Sclerosis.

Magnetic resonance imaging (MRI) with gadolinium based contrast agents (GBCA) is routinely used in the clinic to visualize lesions in multiple sclerosis (MS). Although GBCA reveal endothelial permeability, they fail to expose other aspects of lesion formation such as the magnitude of inflammation or tissue changes occurring at sites of blood-brain barrier (BBB) disruption. Moreover, evidence pointing to potential side effects of GBCA has been increasing. Thus, there is an urgent need to develop GBCA-independent imaging tools to monitor pathology in MS. Using MR-elastography (MRE), we previously demonstrated in both MS and the animal model experimental autoimmune encephalomyelitis (EAE) that inflammation was associated with a reduction of brain stiffness. Now, using the relapsing-remitting EAE model, we show that the cerebellum-a region with predominant inflammation in this model-is especially prone to loss of stiffness. We also demonstrate that, contrary to GBCA-MRI, reduction of brain stiffness correlates with clinical disability and is associated with enhanced expression of the extracellular matrix protein fibronectin (FN). Further, we show that FN is largely expressed by activated astrocytes at acute lesions, and reflects the magnitude of tissue remodeling at sites of BBB breakdown. Therefore, MRE could emerge as a safe tool suitable to monitor disease activity in MS.