Magnetic Resonance Imaging In The Cuprizone-Induced Demyelination Model

Background: The cuprizone-induced demyelination model provides a useful system for preclinical testing of novel molecules aimed at promoting remyelination and repair in MS patients. Longitudinal magnetic resonance imaging (MRI) analysis in cuprizone fed animals provides an advantage over terminal histopathological analysis because it allows for repeated monitoring of changes in myelin and inflammation over time. To establish the MRI parameters needed for future longitudinal efficacy studies, here we describe results from a detailed time-course experiment including histological confirmation during both the demyelination and remyelination phases of the model.

Objectives: Establish MRI parameters to allow for longitudinal monitoring of cuprizone-induced changes in myelin and inflammation in the corpus callosum (CC).

Methods: Mice were fed 0.2% cuprizone diet for 4 wks and then returned to normal chow.  Animals were imaged at 2, 3, and 4 wks while on cuprizone diet and then at 1, 2, 3, and 5 wks after returning to normal diet. MRI was conducted on a 9.4T Bruker scanner.  A Bruker volume coil transmit and a four channel phased array coil receive system was used for image acquisition. T2-weighted (T2w) RARE and magnetization transfer (MTR) MRI were used to evaluate inflammation and myelin, respectively.  After imaging, mice were euthanized and brains collected for histological analysis of the CC.

Results: T2-weighted signal intensity started to increase after 3 wks on cuprizone and reached a maximum of ~160% of control levels by wk 4. Histological analysis confirmed a dramatic increase in inflammation, as measured by an increase in IBA1 immunoreactive (IR) microglia (>8000%) in the CC after 4 weeks of cuprizone diet. There was also a 17% decrease in MTR during the demyelination phase corresponding to an 80% reduction in proteolipid protein (PLP) IR and 60% decrease in CC1-IR oligodendrocytes. Returning mice to normal diet resulted in a gradual decrease in T2w intensity and corresponding reduction in IBA1 immunroeactivity, but neither measure returned to control levels. In contrast, MTR and PLP-IR slowly returned to baseline levels during the 5 wks on normal chow. 

Conclusions: This study demonstrates that cuprizone-induced changes in myelin and inflammation measured histologically can be detected and monitored using serial MR. These data will enable future longitudinal efficacy studies testing novel therapeutics with the potential to promote remyelination and repair of the CNS.