Ultra-high field MRI enables the in vivo quantification of the efficacy of candidate promyelinating molecules in the cuprizone mouse model
Isaac Mawusi Adanyeguh1, Emilie Poirion1, Daniel GarcĂ­a-Lorenzo2, Marie-Stephane Aigrot1, Brahim Nait-Oumesmar1, Boris Zalc1, Alexandra Petiet1,2, and Bruno Stankoff1,3

1Inserm U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Brain and Spine Institute, ICM, F-75013, Paris, France, Paris, France, 2Center for NeuroImaging Research (CENIR), Brain and Spine Institute, 75013 Paris, France, Paris, France, 3AP-HP, Saint Antoine Hospital, Department of Neurology, 184 bd Faubourg Saint Antoine, 75012 Paris, Paris, France

Synopsis

Endogenous remyelination can potentially restore rapid axonal-conduction and confer neuroprotection in chronic demyelinating diseases such as multiple sclerosis. We used T2 mapping to evaluate the ability of two candidate pharmacological agents to promote remyelination in cuprizone-demyelinated mice. Demyelination was associated with increase in signal intensity and T2 values in the corpus callosum and external capsules. T2 values showed spontaneous recovery after discontinuation of cuprizone treatment, an effect accelerated following administration of the two compounds tested. This study confirms that in vivo MRI can be used to select pharmacological agents for their therapeutic potential on remyelination.

Purpose

Loss of myelin is a major pathological hallmark of multiple-sclerosis (MS) lesions. Remyelination is a regenerative process that can restore saltatory conduction and protect axons from degeneration.1 There is a crucial need for the development of potential drugs that could enhance and/or accelerate remyelination in patients with MS. The aim of this study was to assess the ability of ultra-high field MRI to quantify the effect of candidate pro-myelinating compounds on spontaneous remyelination in the cuprizone mouse model.

Methods

Cuprizone ingestion induces oligodendrocyte cell death in mice, and demyelination that predominates in the corpus callosum also affects cerebellar peduncles, external capsules, and grey matter.2,3,4 We hypothesized that 11.7 T MRI could evaluate in vivo the efficacy of candidate molecules on remyelination in white matter. The tocopherol derivative, TFA-12, previously shown to promote oligodendrocyte regeneration in EAE and lysolecithin-demyelinated mouse models of MS5 and a novel candidate molecule that promotes oligodendrocyte differentiation were evaluated. We focused on the caudal corpus callosum (CC), rostral corpus callosum (RC) and the external capsule (EC) since we have previously shown that MRI was sensitive enough to capture demyelination and remyelination in these regions.6

a) Mouse Model: Eighteen C57BL6 female mice (8 weeks old) were fed 0.2% cuprizone for 12 weeks. The animals were then divided into three groups and fed normal chow afterwards. The TFA-12 group (n = 5) was given intra-peritoneal injection of 0.39 mg/kg TFA-12 daily. The second group (n = 7) was treated daily with intra-peritoneal injection of the novel candidate drug. The control group (n = 6) received daily dose of saline solution.

b) MRI Experiment: All images were acquired on an 11.7 T MRI system (Bruker Biospec 117/16 USR, 750 mT/m gradients, PV5.1) using a CryoprobeTM as previously described.6 The animals were imaged before and after being fed cuprizone (pre-visit and day 0 respectively), and then 15, 30 and 45 days whilst being fed normal chow and receiving treatment. T2-weighted brain images were acquired with 2D RARE sequence (TR = 6000 ms, TE = 40 ms, resolution = 60 x 60 μm2, slice thickness = 220 μm) to follow the demyelination. Parametric T2 maps were obtained from a MSME sequence (TR = 5500 ms, TE = 15-120 ms/15 ms increments, matrix = 128 x 128, resolution = 100 x 100 μm2, slice thickness = 200 μm). The quantitative values obtained from T2 maps compared to visual assessment of T2-weighted images make T2 mapping an important quantitative tool to evaluate changes in brain structure.

c) Data extraction and analysis: T2 values were calculated from a regression fit function from the multi-echo sequence using the Paravision 5.1 image sequence analysis. Using anatomical landmarks, regions of interest were manually drawn on 3 consecutive slices and averaged to get the T2 values in the CC, RC and EC. Analysis of variance (ANOVA) was used to test for significance (p < 0.05) with step-down Bonferroni correction.

Results and Discussion

T2 RARE images showed prominent hyper-intensities in the CC (Fig 1b), RC (Fig 1d, red arrow), and EC (Fig 1d, green arrow) after cuprizone diet compared to the pre-cuprizone condition (Fig 1a and 1c), characteristic of demyelination.

The parametric T2 maps showed an increase in the T2 values after 12 weeks of being fed cuprizone diet. After cessation of cuprizone administration, the T2 values began decreasing, with an accelerated recovery in the EC on day 15 for both treatments and on day 30 for the novel agent (p < 0.05). This suggests that the pro-myelinating drugs have the potential to accelerate recovery from demyelination.

Comparing the successive time-points within each group, we observed that when compared to day 0, the decrease in T2 values was significant as soon as day 15 and remained significant up to day 45 in the treatments groups (p < 0.05), whilst in the control group, it was only significant in RC and EC from day 30 (p < 0.05). This further supports that the pharmacological agents accelerate the recovery process.

Conclusion

Ultra-high field MRI had the sensitivity to quantify in vivo the impact of two candidate compounds for enhancing myelin repair. This technique might be used for the preclinical selection of candidate promyelinating drugs before their translation into early phase clinical trials.

Acknowledgements

Program “Investissements d’avenir” ANR-10-IAIHU-06. Ile-de-France Region (DIM Cerveau et Pensée).

References

1. Irvine KA, Blakemore WF. Remyelination protects axons from demyelination-associated axon degeneration. Brain 2008;131:1464 -1477.

2. Cammer W. The neurotoxicant, cuprizone, retards the differentiation of oligodendrocytes in vitro. J Neurol Sci. 1999;168(2):116-120.

3. Benardais K, Kotsiari A, Skuljec J, et al. Cuprizone [bis(cyclohexylidenehydrazide)] is selectively toxic for mature oligodendrocytes. Neurotox Res. 2013; 24(2):244-250.

4. Ransohoff RM. Animal models of multiple sclerosis: the good, the bad and the bottom line. Nat Neurosci. 2012;15(8):1074-1077.

5. Blanchard B, Heurtaux T, Garcia C, et al. Tocopherol Derivative TFA-12 promotes myelin repair in experimental models of multiple sclerosis. J Neurosci. 2013;33(28):11633-1642.

6. Petiet A, Aigrot MS, Stankoff B. Gray matter demyelination and remyelination detected with multimodal quantitative analysis at 11.7T in a mouse model of multiple sclerosis. ISMRM proceedings 2014.

Figures

Figure 1: T2-weighted images showing demyelination in the CC (b), RC (d, red arrow) and EC (d, green arrow) of mice after 12 weeks of being fed 0.2% cuprizone diet.

Figure 2: Comparing parametric T2 values of controls to the treated groups. Error bars represent standard error of means (SEM). * p < 0.05 (green * represent significant difference between control and novel agent).



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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