Histological validation of fast macromolecular proton fraction mapping as a quantitative myelin imaging method in the cuprizone demyelination model

Marina Yu Khodanovich,Vasily L Yarnykh,Alexander V Romashchenko,Tatyana G Tolstikova,Lilia R Mustafina,Andrey E Akulov,Nikolay M Nemirovich-Danchenko,Valentina Yu Glazacheva,Irina V Sorokina

doi:10.1038/srep46686

Abstract

Cuprizone-induced demyelination in mice is a frequently used model in preclinical multiple sclerosis research. A recent quantitative clinically-targeted MRI method, fast macromolecular proton fraction (MPF) mapping demonstrated a promise as a myelin biomarker in human and animal studies with a particular advantage of sensitivity to both white matter (WM) and gray matter (GM) demyelination. This study aimed to histologically validate the capability of MPF mapping to quantify myelin loss in brain tissues using the cuprizone demyelination model. Whole-brain MPF maps were obtained in vivo on an 11.7T animal MRI scanner from 7 cuprizone-treated and 7 control С57BL/6 mice using the fast single-point synthetic-reference method. Brain sections were histologically stained with Luxol Fast Blue (LFB) for myelin quantification. Significant (p < 0.05) demyelination in cuprizone-treated animals was found according to both LFB staining and MPF in all anatomical structures (corpus callosum, anterior commissure, internal capsule, thalamus, caudoputamen, and cortex). MPF strongly correlated with quantitative histology in all animals (r = 0.95, p < 0.001) as well as in treatment and control groups taken separately (r = 0.96, p = 0.002 and r = 0.93, p = 0.007, respectively). Close agreement between histological myelin staining and MPF suggests that fast MPF mapping enables robust and accurate quantitative assessment of demyelination in both WM and GM.

Highlights

Cuprizone-induced demyelination in mice is a frequently used model in preclinical multiple sclerosis research
Macromolecular proton fraction (MPF) is a biophysical parameter defined within the two-pool model of magnetization transfer (MT)[1] that describes the amount of macromolecular protons characterized by solid-like nuclear magnetic resonance (NMR) spin dynamics and involved into magnetization exchange with free water protons in biological systems
A visible reduction in the optical density on Luxol Fast Blue (LFB) stained brain sections of mice treated with cuprizone can be appreciated in both white matter (WM) and gray matter (GM) structures (Fig. 1)

Summary

Introduction

Cuprizone-induced demyelination in mice is a frequently used model in preclinical multiple sclerosis research. Include Z-spectroscopic imaging based on the analysis of signal dependence on the offset frequency and power of an off-resonance saturation pulse[14,15] and on-resonance techniques based on the analysis of bi-exponential longitudinal relaxation[16,17] These methods allow measurements of several parameters of the two-pool model including MPF and require collection of multiple image sets that results in time-consuming data acquisition rendering them inapplicable in clinics. An alternative fast method allowing whole-brain MPF mapping based on a single MT-weighted image, reference image, and a T1 map was recently proposed[18] This technique was tested in multiple sclerosis (MS)[19] and mild traumatic brain injury[20] studies and demonstrated a promise as a robust clinically-targeted myelin imaging approach. The overall goal of this study was to validate the fast synthetic-reference MPF mapping method using quantitative histology in the murine cuprizone demyelination model

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