Fumaric acid esters exert neuroprotective effects in neuroinflammation via activation of the Nrf2 antioxidant pathway

Abstract

Inflammation and oxidative stress are thought to promote tissue damage in multiple sclerosis. Thus, novel therapeutics enhancing cellular resistance to free radicals could prove useful for multiple sclerosis treatment. BG00012 is an oral formulation of dimethylfumarate. In a phase II multiple sclerosis trial, BG00012 demonstrated beneficial effects on relapse rate and magnetic resonance imaging markers indicative of inflammation as well as axonal destruction. First we have studied effects of dimethylfumarate on the disease course, central nervous system, tissue integrity and the molecular mechanism of action in an animal model of chronic multiple sclerosis: myelin oligodendrocyte glycoprotein induced experimental autoimmune encephalomyelitis in C57BL/6 mice. In the chronic phase of experimental autoimmune encephalomyelitis, preventive or therapeutic application of dimethylfumarate ameliorated the disease course and improved preservation of myelin, axons and neurons. In vitro, the application of fumarates increased murine neuronal survival and protected human or rodent astrocytes against oxidative stress. Application of dimethylfumarate led to stabilization of the transcription factor nuclear factor (erythroid-derived 2)-related factor 2, activation of nuclear factor (erythroid-derived 2)-related factor 2-dependent transcriptional activity and accumulation of NADP(H) quinoline oxidoreductase-1 as a prototypical target gene. Furthermore, the immediate metabolite of dimethylfumarate, monomethylfumarate, leads to direct modification of the inhibitor of nuclear factor (erythroid-derived 2)-related factor 2, Kelch-like ECH-associated protein 1, at cysteine residue 151. In turn, increased levels of nuclear factor (erythroid-derived 2)-related factor 2 and reduced protein nitrosylation were detected in the central nervous sytem of dimethylfumarate-treated mice. Nuclear factor (erythroid-derived 2)-related factor 2 was also upregulated in the spinal cord of autopsy specimens from untreated patients with multiple sclerosis. In dimethylfumarate-treated mice suffering from experimental autoimmune encephalomyelitis, increased immunoreactivity for nuclear factor (erythroid-derived 2)-related factor 2 was detected by confocal microscopy in neurons of the motor cortex and the brainstem as well as in oligodendrocytes and astrocytes. In mice deficient for nuclear factor (erythroid-derived 2)-related factor 2 on the same genetic background, the dimethylfumarate mediated beneficial effects on clinical course, axon preservation and astrocyte activation were almost completely abolished thus proving the functional relevance of this transcription factor for the neuroprotective mechanism of action. We conclude that the ability of dimethylfumarate to activate nuclear factor (erythroid-derived 2)-related factor 2 may offer a novel cytoprotective modality that further augments the natural antioxidant responses in multiple sclerosis tissue and is not yet targeted by other multiple sclerosis therapies.

Effects of fumarates on inflammatory human astrocyte responses and oligodendrocyte differentiation

“…In the cuprizone model, mice receiving DMF displayed reduced demyelination,20 a result that has been suggested to be due to reduced microglia activation. These results were similar to EAE results, which demonstrated reduced demyelination associated with reduced immune cell infiltration, astrocyte activation, and increased cytoprotection 2. In MS patients, DMF treatment significantly increased brain magnetization transfer ratio, suggesting increases in myelin density 21.…”

“…To date, direct comparisons of fumarates on human and murine glial cells have not been performed. In addition, the biological role(s) of the active metabolite of DMF treatment has been controversial, with evidence supporting that both MMF2, 29 and DMF9, 16 modulate anti‐inflammatory and antioxidant effects. Although the debate against DMF has been widely attributed to previous reports citing the inability to measure biologically significant concentrations in the brain and periphery, a recent report has shown that DMF is indeed present in the CNS following oral administration 16…”

“…Interestingly, MMF (10 μmol/L) also increased IL‐6 production by murine astrocytes, an observation that has also been previously observed in human fetal microglia9; this effect was not observed for the other chemokines that were measured, suggesting that this effect was restricted to IL‐6, a highly pleiotropic cytokine, but not reflective of an astrocyte in a heightened proinflammatory state. Reductions in astrocyte chemokine and cytokine secretion may contribute to the reduced leukocyte infiltration and activation seen in vivo in animals treated with DMF 2, 20, 33. Furthermore, since CXCL10 is known to inhibit of OPC differentiation,24 DMF may impact CNS remyelination indirectly through the astrocyte.…”

“…Dimethyl fumarate (DMF) (Tecfidera ® ) is an orally available drug that has emerged as an effective therapy for the treatment of relapsing‐remitting multiple sclerosis (RRMS) 1. The therapeutic mechanism of action for DMF has been attributed to both immunosuppression and induction of antioxidant pathways 2, 3, 4. The induction of antioxidant response element (ARE) genes by DMF is attributed to the activation of the Nrf2 transcription factor that leads to subsequent reductions in oxidative stress and increased neuroprotection in vivo 2, 5.…”

“…The therapeutic mechanism of action for DMF has been attributed to both immunosuppression and induction of antioxidant pathways 2, 3, 4. The induction of antioxidant response element (ARE) genes by DMF is attributed to the activation of the Nrf2 transcription factor that leads to subsequent reductions in oxidative stress and increased neuroprotection in vivo 2, 5. The induction of Nrf2 is achieved through glutathione depletion as well as direct binding of fumaric acid esters to the Nrf2 repressor KEAP1 3, 6, 7.…”