High-resolution Imaging of Myeloperoxidase Activity Sensors in Human Cerebrovascular Disease

Peter Caravan,Alexei A. Bogdanov,Youssef Z. Wadghiri,Anita Leporati,Matthew J. Gounis,Mary L. Mazzanti,Aurora Rodríguez-Rodríguez,John P. Weaver,Dung Minh Hoang,Ajay K. Wakhloo

doi:10.1038/s41598-018-25804-y

Abstract

Progress in clinical development of magnetic resonance imaging (MRI) substrate-sensors of enzymatic activity has been slow partly due to the lack of human efficacy data. We report here a strategy that may serve as a shortcut from bench to bedside. We tested ultra high-resolution 7T MRI (µMRI) of human surgical histology sections in a 3-year IRB approved, HIPAA compliant study of surgically clipped brain aneurysms. µMRI was used for assessing the efficacy of MRI substrate-sensors that detect myeloperoxidase activity in inflammation. The efficacy of Gd-5HT-DOTAGA, a novel myeloperoxidase (MPO) imaging agent synthesized by using a highly stable gadolinium (III) chelate was tested both in tissue-like phantoms and in human samples. After treating histology sections with paramagnetic MPO substrate-sensors we observed relaxation time shortening and MPO activity-dependent MR signal enhancement. An increase of normalized MR signal generated by ultra-short echo time MR sequences was corroborated by MPO activity visualization by using a fluorescent MPO substrate. The results of µMRI of MPO activity associated with aneurysmal pathology and immunohistochemistry demonstrated active involvement of neutrophils and neutrophil NETs as a result of pro-inflammatory signalling in the vascular wall and in the perivascular space of brain aneurysms.

Highlights

Magnetic resonance imaging (MRI) provides 3-D structural information about tissue volume as well as detailed physiological and anatomical information for thick tissue sections
In the subluminal regions of the vessel walls we observed the formation of perivascular wall haemorrhages and neutrophil extracellular traps (NETs) suggesting terminal neutrophil activation in the areas of vascular pathology and microthrombosis (Fig. 3B, arrow)
The assessment of MPO activity as opposed to the presence of protein antigen alone was essential for determining whether it would be feasible to further process the samples for μMRI because MR signal depended on the presence of active MPO enzyme

Summary

Introduction

Magnetic resonance imaging (MRI) provides 3-D structural information about tissue volume as well as detailed physiological and anatomical information for thick tissue sections. Ultra-high-resolution MRI using small field-of-view acquisitions, i.e. micro-MRI (μMRI), can be used to obtain microscopic images within whole organs (e.g. MRI biopsy) reflecting differences in water relaxation times in various tissue components[1]. Such μMRI techniques have been used to study the developmental biology of mice[2,3], reveal details of brain structure[4,5], and show anatomical and functional changes of skeletal/connective tissue systems[6,7]. Set forth to find out: (1) whether μMRI of enzyme- dependent vascular wall enhancement is feasible in the very small volumes of histology sections and; (2) whether such MR signal enhancement correlates with the distribution of MPO activity in the tissue

Methods

Results

Conclusion