Multimodal Imaging with NanoGd Reveals Spatiotemporal Features of Neuroinflammation after Experimental Stroke.

Violaine Hubert,Arindam Dey,Chantal Watrin,Thomas Vorup‐Jensen,Patrice Marche,Camille Amaz,Fréderic Lerouge,Yves Berthezène,Jean‐Christophe Comte,Olivier Pascual,Szilvia Karpati,Fabien Chauveau,Stéphane Parola,Marlène Wiart,Emmanuel Brun,Chloé Dumot,Naura Chounlamountri,Ines Hristovska,Sarah Benkeder

doi:10.1002/advs.202101433

Abstract

The purpose of this study is to propose and validate a preclinical in vivo magnetic resonance imaging (MRI) tool to monitor neuroinflammation following ischemic stroke, based on injection of a novel multimodal nanoprobe, NanoGd, specifically designed for internalization by phagocytic cells. First, it is verified that NanoGd is efficiently internalized by microglia in vitro. In vivo MRI coupled with intravenous injection of NanoGd in a permanent middle cerebral artery occlusion mouse model results in hypointense signals in the ischemic lesion. In these mice, longitudinal two‐photon intravital microscopy shows NanoGd internalization by activated CX3CR1‐GFP/+ cells. Ex vivo analysis, including phase contrast imaging with synchrotron X‐ray, histochemistry, and transmission electron microscopy corroborate NanoGd accumulation within the ischemic lesion and uptake by immune phagocytic cells. Taken together, these results confirm the potential of NanoGd‐enhanced MRI as an imaging biomarker of neuroinflammation at the subacute stage of ischemic stroke. As far as it is known, this work is the first to decipher the working mechanism of MR signals induced by a nanoparticle passively targeted at phagocytic cells by performing intravital microscopy back‐to‐back with MRI. Furthermore, using a gadolinium‐based rather than an iron‐based contrast agent raises future perspectives for the development of molecular imaging with emerging computed tomography technologies.

Highlights

Ischemic stroke is a devastating neurological condition and the second cause of death in Western countries
We assessed the production of proinflammatory cytokines interleukine-6 (IL-6) and tumor-necrosis factor-α (TNFα) by microglial cultures exposed to NanoGd
To understand the biological substrates of MR hypointense signals, we examined NanoGd fate in the 6 mice of group I, in 2 sessions of intravital two-photon microscopy (Figure 2)

Summary

Introduction

Ischemic stroke is a devastating neurological condition and the second cause of death in Western countries. Neuroinflammation is a major component of stroke pathophysiology, often associated with impaired outcome.[1] It is well established that phagocytic cells, including tissueresident microglia and blood-borne recruited macrophages, are the main cellular mediators of inflammation initiation and continuation following stroke. They may contribute to tissue damage early in the acute phase of stroke and are potential therapeutic targets.[2,3]. The gold-standard for imaging immune cells in vivo in preclinical settings is intravital two-photon microscopy coupled with the use of transgenic mouse lines and/or fluorescent dyes.[4] Two-photon microscopy has been used to investigate the dynamics of brain immune cells and their interaction with the neural environment in several

Objectives

Results

Discussion

Conclusion