In vitro experiments have revealed that DMF, as well as its primary metabolite monomethyl fumarate (MMF), can exert immunomodulatory effects on T-cell subsets as well as on antigen-presenting cells,[93, 94] and experiments in EAE have demonstrated that DMF is effective in
both preventive check details and therapeutic applications, albeit marginal in chronic EAE, promoting myelin and axonal preservation and reducing astrocyte activation.[95, 96] It has been speculated that part of the effect of DMF could be mediated through modulation of microglia phenotype. Histological studies demonstrated that, during the acute phase of EAE, Mac-3-positive cells (microglia and macrophages) are significantly reduced in the spinal cord of DMF-treated animals. Such an observation is also supported by in vitro studies in which pre-treatment with DMF can inhibit LPS-induced activation of microglial cells by reducing
the expression of NO, TNF-α, IL-1β and IL-6, possibly through an inhibition of the extracellular-signal regulated kinase pathway and an activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. While in vitro data prompted the hypothesis that DMF and MMF could affect microglia activation through Nrf2, Target Selective Inhibitor high throughput screening a pathway involved in the expression of proteins critical in the detoxification of reactive oxygen and reactive nitrogen species,[97, 98] this has not been demonstrated in vivo. Indeed, although Linker et al. showed
that Nrf2 is required for the therapeutic effect of DMF, double-labelling these of Nrf2 with a marker for microglia did not reveal an increase of its expression in those cells after DMF treatment in EAE-affected mice. Further in vitro and in vivo studies are needed to dissect the pathways through which DMF promote an alternative neuroprotective phenotype in microglia. Mesenchymal stem cells (MSC) are currently being investigated as an alternative therapeutic approach for MS. The potential therapeutic use of MSC for neurodegenerative diseases was originally considered as related to their possible regenerative function through their ability to differentiate into mesodermal tissues and perhaps into other embryonic lineages. However, recent observations have indicated that, upon systemic administration, most MSC are rapidly entrapped in the lungs, and only a few engraft into injured CNS, where they display negligible transdifferentiation capacity.[100-102] In vitro studies demonstrating that MSC can modulate several effector functions of cells of both the adaptive and innate immune systems introduced the possibility that MSC might be effective in EAE. Indeed, Zappia et al.