Effect of high-dose 1.25 dihydroxyvitamin D3 on remyelination in the cuprizone model

Vitamin D supplementation is increasingly recommended to patients with multiple sclerosis (MS). To study the effect of high-dose vitamin D on remyelination, female C57Bl/6 mice were demyelinated with dietary 0.2% cuprizone for 7 weeks. The mice received intraperitoneal injections of 1.25-dihydroxyvitamin D3 (calcitriol) or placebo (vehicle) injections twice a week, from week 6, throughout week 9. Mice that received calcitriol had initially increased demyelination (p = 0.021), astrocytosis (p = 0.043), and microglia activation. However, levels of astrocytosis and microglia activation dropped below those of the placebo group during the remyelination phase. There was a significant increase in myelination in the calcitriol group throughout the remyelination phase (p = 0.041), while the remyelination in the placebo group was not significant (p = 0.317). After 3 weeks of remyelination, the calcitriol group had more myelin than the placebo group (p = 0.001). The calcitriol group had a higher density of NOGO-A positive cells throughout the remyelination phase, and the number of NOGO-A positive cells was significantly higher in the calcitriol group at one week of remyelination (p = 0.019). There were no significant differences in extent of T-lymphocyte infiltration. High-dose calcitriol seems to be safe regarding remyelination. Our results indicate that this treatment could actually promote the repair process, possibly through a stimulating effect on oligodendrocyte maturation and astrocyte activation. The potential of calcitriol to stimulate the remyelination process should be investigated further in functional studies.