Dimethyl Fumarate Reduces Microglia Functional Response to Tissue Damage and Favors Brain Iron Homeostasis

Nrf2 activators for the treatment of rare iron overload diseases: From bench to bedside

Iron overload and related oxidative damage are seen in many rare diseases, due to mutation of iron homeostasis-related genes. As a core regulator on cellular antioxidant reaction, Nrf2 can also decrease systemic and cellular iron levels by regulating iron-related genes and pathways, making Nrf2 activators very good candidates for the treatment of iron overload disorders. Successful examples include the clinical use of omaveloxolone for Friedreich's Ataxia and dimethyl fumarate for relapsing-remitting multiple sclerosis. Despite these uses, the therapeutic potentials of Nrf2 activators for iron overload disorders may be overlooked in clinical practice. Therefore, this study talks about the potential use, possible mechanisms, and precautions of Nrf2 activators in treating rare iron overload diseases. In addition, a combination therapy with Nrf2 activators and iron chelators is proposed for clinical reference, aiming to facilitate the clinical use of Nrf2 activators for more iron overload disorders.

Ferritin nanocage-enabled detection of pathological tau in living human retinal cells

Tauopathies, including Alzheimer's disease and Frontotemporal Dementia, are debilitating neurodegenerative disorders marked by cognitive decline. Despite extensive research, achieving effective treatments and significant symptom management remains challenging. Accurate diagnosis is crucial for developing effective therapeutic strategies, with hyperphosphorylated protein units and tau oligomers serving as reliable biomarkers for these conditions. This study introduces a novel approach using nanotechnology to enhance the diagnostic process for tauopathies. We developed humanized ferritin nanocages, a novel nanoscale delivery system, designed to encapsulate and transport a tau-specific fluorophore, BT1, into human retinal cells for detecting neurofibrillary tangles in retinal tissue, a key marker of tauopathies. The delivery of BT1 into living cells was successfully achieved through these nanocages, demonstrating efficient encapsulation and delivery into retinal cells derived from human induced pluripotent stem cells. Our experiments confirmed the colocalization of BT1 with pathological forms of tau in living retinal cells, highlighting the method's potential in identifying tauopathies. Using ferritin nanocages for BT1 delivery represents a significant contribution to nanobiotechnology, particularly in neurodegenerative disease diagnostics. This method offers a promising tool for the early detection of tau tangles in retinal tissue, with significant implications for improving the diagnosis and management of tauopathies. This study exemplifies the integration of nanotechnology with biomedical science, expanding the frontiers of nanomedicine and diagnostic techniques.

Dimethyl fumarate improves cognitive impairment and neuroinflammation in mice with Alzheimer's disease

BACKGROUND

Neuroinflammation substantially contributes to the pathology of Alzheimer's disease (AD), the most common form of dementia. Studies have reported that nuclear factor erythroid 2-related factor 2 (Nrf2) attenuates neuroinflammation in the mouse models of neurodegenerative diseases, however, the detailed mechanism remains unclear.

METHODS

The effects of dimethyl fumarate (DMF), a clinically used drug to activate the Nrf2 pathway, on neuroinflammation were analyzed in primary astrocytes and AppNL-G-F (App-KI) mice. The cognitive function and behavior of DMF-administrated App-KI mice were evaluated. For the gene expression analysis, microglia and astrocytes were directly isolated from the mouse cerebral cortex by magnetic-activated cell sorting, followed by quantitative PCR.

RESULTS

DMF treatment activated some Nrf2 target genes and inhibited the expression of proinflammatory markers in primary astrocytes. Moreover, chronic oral administration of DMF attenuated neuroinflammation, particularly in astrocytes, and reversed cognitive dysfunction presumably by activating the Nrf2-dependent pathway in App-KI mice. Furthermore, DMF administration inhibited the expression of STAT3/C3 and C3 receptor in astrocytes and microglia isolated from App-KI mice, respectively, suggesting that the astrocyte-microglia crosstalk is involved in neuroinflammation in mice with AD.

CONCLUSION

The activation of astrocytic Nrf2 signaling confers neuroprotection in mice with AD by controlling neuroinflammation, particularly by regulating astrocytic C3-STAT3 signaling. Furthermore, our study has implications for the repositioning of DMF as a drug for AD treatment.

Microglia at the Tripartite Synapse during Postnatal Development: Implications for Autism Spectrum Disorders and Schizophrenia

Synapses are the fundamental structures of neural circuits that control brain functions and behavioral and cognitive processes. Synapses undergo formation, maturation, and elimination mainly during postnatal development via a complex interplay with neighboring astrocytes and microglia that, by shaping neural connectivity, may have a crucial role in the strengthening and weakening of synaptic functions, that is, the functional plasticity of synapses. Indeed, an increasing number of studies have unveiled the roles of microglia and astrocytes in synapse formation, maturation, and elimination as well as in regulating synaptic function. Over the past 15 years, the mechanisms underlying the microglia- and astrocytes-dependent regulation of synaptic plasticity have been thoroughly studied, and researchers have reported that the disruption of these glial cells in early postnatal development may underlie the cause of synaptic dysfunction that leads to neurodevelopmental disorders such as autism spectrum disorder (ASD) and schizophrenia.

Neuroglial components of brain lesions may provide new therapeutic strategies for multiple sclerosis

Multiple sclerosis (MS) is a chronic autoimmune and demyelinating disease of the central nervous system (CNS) which leads to focal demyelinated lesions in the brain and spinal cord. Failure of remyelination contributes to chronic disability in young adults. Characterization of events occurring during the demyelination and remyelination processes and those of which subsequently limit remyelination or contribute to demyelination can provide the possibility of new therapies development for MS. Most of the currently available therapies and investigations modulate immune responses and mediators. Since most therapeutic strategies have unsatisfied outcomes, developing new therapies that enhance brain lesion repair is a priority. A close look at cellular and chemical components of MS lesions will pave the way to a better understanding of lesions pathology and will provide possible opportunities for repair strategies and targeted pharmacotherapy. This review summarizes the lesion components and features, particularly the detrimental elements, and discusses the possibility of suggesting new potential targets as therapies for demyelinating diseases like MS.

Central nervous system demyelinating diseases: glial cells at the hub of pathology

Inflammatory demyelinating diseases (IDDs) are among the main causes of inflammatory and neurodegenerative injury of the central nervous system (CNS) in young adult patients. Of these, multiple sclerosis (MS) is the most frequent and studied, as it affects about a million people in the USA alone. The understanding of the mechanisms underlying their pathology has been advancing, although there are still no highly effective disease-modifying treatments for the progressive symptoms and disability in the late stages of disease. Among these mechanisms, the action of glial cells upon lesion and regeneration has become a prominent research topic, helped not only by the discovery of glia as targets of autoantibodies, but also by their role on CNS homeostasis and neuroinflammation. In the present article, we discuss the participation of glial cells in IDDs, as well as their association with demyelination and synaptic dysfunction throughout the course of the disease and in experimental models, with a focus on MS phenotypes. Further, we discuss the involvement of microglia and astrocytes in lesion formation and organization, remyelination, synaptic induction and pruning through different signaling pathways. We argue that evidence of the several glia-mediated mechanisms in the course of CNS demyelinating diseases supports glial cells as viable targets for therapy development.

Discovery of blood-brain barrier permeant amine-functionalized aurones as inhibitors of activated microglia

Sulfuretin, a naturally occurring aurone is reported to inhibit macrophage and microglia activation. A series of aurones incorporating basic amines and lipophilic functionalities at ring A and/or ring B were synthesized to improve upon present sulfuretin activity towards targeting brain microglia while overcoming the blood-brain barrier (BBB). Evaluation of the ability of the aurones to inhibit lipopolysaccharide (LPS)-stimulated nitric oxide (NO) secretion by murine BV-2 microglia has identified several inhibitors showing significant NO reduction at 1 to 10 µM. Potent inhibitors were represented by aurones with bulky, planar moieties at ring A (3f) or at ring B (1e and 1f) and having a pendant piperidine at ring B (1a, 2a, 2b, and 3f). The active aurones inhibited the BV-2 microglia polarizing towards the M1 state as indicated by attenuation of IL-1β and TNF-α secretions in LPS-activated microglia but did not induce the microglia towards the M2 state. The aurones 2a, 2b, and 1f showed high passive BBB permeability in the parallel artificial membrane permeability assay (PAMPA) owing to their optimal lipophilicities. 2a, being non-cell toxic, BBB permeant and potent, represents a new lead for the development of aurones as inhibitors of activated microglia.

Human iPSC-Derived Cortical Neurons Display Homeostatic Plasticity

Maintaining the excitability of neurons and circuits is fundamental for healthy brain functions. The global compensatory increase in excitatory synaptic strength, in response to decreased activity, is one of the main homeostatic mechanisms responsible for such regulation. This type of plasticity has been extensively characterized in rodents in vivo and in vitro, but few data exist on human neurons maturation. We have generated an in vitro cortical model system, based on differentiated human-induced pluripotent stem cells, chronically treated with tetrodotoxin, to investigate homeostatic plasticity at different developmental stages. Our findings highlight the presence of homeostatic plasticity in human cortical networks and show that the changes in synaptic strength are due to both pre- and post-synaptic mechanisms. Pre-synaptic plasticity involves the potentiation of neurotransmitter release machinery, associated to an increase in synaptic vesicle proteins expression. At the post-synaptic level, we report an increase in the expression of post-synaptic density proteins, involved in glutamatergic receptor anchoring. These results extend our understanding of neuronal homeostasis and reveal the developmental regulation of its expression in human cortical networks. Since induced pluripotent stem cell-derived neurons can be obtained from patients with neurodevelopmental and neurodegenerative diseases, our platform offers a versatile model for assessing human neural plasticity under physiological and pathological conditions.

Neuroinflammation in Friedreich's Ataxia

Friedreich's ataxia (FRDA) is a rare genetic disorder caused by mutations in the gene frataxin, encoding for a mitochondrial protein involved in iron handling and in the biogenesis of iron-sulphur clusters, and leading to progressive nervous system damage. Although the overt manifestations of FRDA in the nervous system are mainly observed in the neurons, alterations in non-neuronal cells may also contribute to the pathogenesis of the disease, as recently suggested for other neurodegenerative disorders. In FRDA, the involvement of glial cells can be ascribed to direct effects caused by frataxin loss, eliciting different aberrant mechanisms. Iron accumulation, mitochondria dysfunction, and reactive species overproduction, mechanisms identified as etiopathogenic in neurons in FRDA, can similarly affect glial cells, leading them to assume phenotypes that can concur to and exacerbate neuron loss. Recent findings obtained in FRDA patients and cellular and animal models of the disease have suggested that neuroinflammation can accompany and contribute to the neuropathology. In this review article, we discuss evidence about the involvement of neuroinflammatory-related mechanisms in models of FRDA and provide clues for the modulation of glial-related mechanisms as a possible strategy to improve disease features.

Dimethyl fumarate decreases short-term but not long-term inflammation in a focal EAE model of neuroinflammation

Background

Dimethyl fumarate (DMF) is an oral immunomodulatory drug used in the treatment of autoimmune diseases. Here, we sought to study whether the effect of DMF can be detected using positron emission tomography (PET) targeting the 18-kDa translocator protein (TSPO) in the focal delayed-type hypersensitivity rat model of multiple sclerosis (fDTH-EAE). The rats were treated orally twice daily from lesion activation (day 0) with either vehicle (tap water with 0.08% Methocel, 200 µL; control group n = 4 (3 after week four)) or 15 mg/kg DMF (n = 4) in 0.08% aqueous Methocel (200 µL) for 8 weeks. The animals were imaged by PET using the TSPO tracer [¹⁸F]GE-180 in weeks 0, 1, 2, 4, 8, and 18 following lesion activation, and the non-displaceable binding potential (BP_ND) was calculated. Immunohistochemical staining for Iba1, CD4, and CD8 was performed in week 18, and in separate cohorts of animals, following 2 or 4 weeks of treatment.

Results

Using the fDTH-EAE model, DMF reduced the [¹⁸F]GE-180 BP_ND in the DMF-treated animals compared to control animals after 1 week of treatment (two-tailed unpaired t test, p = 0.031), but not in weeks 2, 4, 8, or 18 when imaged in vivo by PET. Immunostaining for Iba1 showed that DMF had no effect on the perilesional volume or the core lesion volume after 2 or 4 weeks of treatment, or at 18 weeks. However, the optical density (OD) measurements of CD4⁺ staining showed reduced OD in the lesions of the treated rats.

Conclusions

DMF reduced the microglial activation in the fDTH-EAE model after 1 week of treatment, as detected by PET imaging of the TSPO ligand [¹⁸F]GE-180. However, over an extended time course, reduced microglial activation was not observed using [¹⁸F]GE-180 or by immunohistochemistry for Iba1⁺ microglia/macrophages. Additionally, DMF did affect the infiltration of CD4⁺ and CD8⁺ T-lymphocytes at the fDTH-EAE lesion.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-022-00878-y.

In a focal rat DTH-EAE model of neuroinflammation, dimethyl fumarate decreases the uptake of TSPO PET tracer [18F]GE-180 in the short term.

Long-term [¹⁸F]GE-180 follow-up did not indicate a treatment effect.

Decreased neuroinflammation, CD4⁺ T cell infiltration, and CD8⁺ T cell infiltration were detected using immunohistochemistry.

Mechanism-based criteria to improve therapeutic outcomes in progressive multiple sclerosis

In contrast to the multiple disease-modifying therapies that are available for relapsing-remitting multiple sclerosis (MS), the therapeutic options for progressive MS (PMS) are limited. Recent advances in our understanding of the neuroimmunology of PMS, including the mechanisms that drive slowly expanding lesions, have fuelled optimism for improved treatment of this condition. In this Review, we highlight the commonly observed neuropathology of PMS and discuss the associated mechanisms of CNS injury. We then apply this knowledge to formulate criteria for therapeutic efficacy in PMS, beginning with the need for early treatment owing to the substantial neuropathology that is already present at the initial clinical presentation. Other requirements include: antagonism of neuroaxonal injury mediators such as pro-inflammatory microglia and lymphocytes; remediation of oxidative stress resulting from iron deposition and mitochondrial dysfunction; and promotion of neuroprotection through remyelination. We consider whether current disease-modifying therapies for relapsing-remitting MS meet the criteria for successful therapeutics in PMS and suggest that the evidence favours the early introduction of sphingosine 1-phosphate receptor modulators. Finally, we weigh up emerging medications, including repurposed generic medications and Bruton's tyrosine kinase inhibitors, against these fundamental criteria. In this new therapeutic era in PMS, success depends collectively on understanding disease mechanisms, drug characteristics (including brain penetration) and rational use.

Antibiotics Treatment Modulates Microglia-Synapses Interaction

‘Dysbiosis’ of the adult gut microbiota, in response to challenges such as infection, altered diet, stress, and antibiotics treatment has been recently linked to pathological alteration of brain function and behavior. Moreover, gut microbiota composition constantly controls microglia maturation, as revealed by morphological observations and gene expression analysis. However, it is unclear whether microglia functional properties and crosstalk with neurons, known to shape and modulate synaptic development and function, are influenced by the gut microbiota. Here, we investigated how antibiotic-mediated alteration of the gut microbiota influences microglial and neuronal functions in adult mice hippocampus. Hippocampal microglia from adult mice treated with oral antibiotics exhibited increased microglia density, altered basal patrolling activity, and impaired process rearrangement in response to damage. Patch clamp recordings at CA3-CA1 synapses revealed that antibiotics treatment alters neuronal functions, reducing spontaneous postsynaptic glutamatergic currents and decreasing synaptic connectivity, without reducing dendritic spines density. Antibiotics treatment was unable to modulate synaptic function in CX3CR1-deficient mice, pointing to an involvement of microglia–neuron crosstalk through the CX3CL1/CX3CR1 axis in the effect of dysbiosis on neuronal functions. Together, our findings show that antibiotic alteration of gut microbiota impairs synaptic efficacy, suggesting that CX3CL1/CX3CR1 signaling supporting microglia is a major player in in the gut–brain axis, and in particular in the gut microbiota-to-neuron communication pathway.

Dimethyl fumarate does not mitigate cognitive decline and β-amyloidosis in female APPPS1 mice

INTRODUCTION

Alzheimer's disease (AD) is the leading cause of dementia and a major global health issue. Currently, only limited treatment options are available to patients. One possibility to expand the treatment repertoire is repurposing of existing drugs such as dimethyl fumarate (DMF). DMF is approved for treatment of multiple sclerosis and previous animal studies have suggested that DMF may also have a beneficial effect for the treatment of AD.

METHODS

We used an APPPS1 transgenic model of senile β-amyloidosis and treated female mice orally with DMF in two treatment paradigms (pre and post onset). We quantified learning and memory parameters, β-amyloidosis, and neuroinflammation to determine the potential of DMF as AD therapeutics.

RESULTS

Treatment with DMF had no influence on water maze performance, β-amyloid accumulation, plaque formation, microglia activation, and recruitment of immune cells to the brain. Compared to vehicle-treated animals, oral DMF treatment could not halt or retard disease progression in the mice.

DISCUSSION

Our results do not favour the use of DMF as treatment for AD. While our results stand in contrast to previous findings in other models, they emphasize the importance of animal model selection and suggest further studies to elucidate the mechanisms leading to conflicting results.

Exploring the Use of Dimethyl Fumarate as Microglia Modulator for Neurodegenerative Diseases Treatment

The maintenance of redox homeostasis in the brain is critical for the prevention of the development of neurodegenerative diseases. Drugs acting on brain redox balance can be promising for the treatment of neurodegeneration. For more than four decades, dimethyl fumarate (DMF) and other derivatives of fumaric acid ester compounds have been shown to mitigate a number of pathological mechanisms associated with psoriasis and relapsing forms of multiple sclerosis (MS). Recently, DMF has been shown to exert a neuroprotective effect on the central nervous system (CNS), possibly through the modulation of microglia detrimental actions, observed also in multiple brain injuries. In addition to the hypothesis that DMF is linked to the activation of NRF2 and NF-kB transcription factors, the neuroprotective action of DMF may be mediated by the activation of the glutathione (GSH) antioxidant pathway and the regulation of brain iron homeostasis. This review will focus on the role of DMF as an antioxidant modulator in microglia processes and on its mechanisms of action in the modulation of different pathways to attenuate neurodegenerative disease progression.

Molecular Effects of FDA-Approved Multiple Sclerosis Drugs on Glial Cells and Neurons of the Central Nervous System

Multiple sclerosis (MS) is characterized by peripheral and central inflammatory features, as well as demyelination and neurodegeneration. The available Food and Drug Administration (FDA)-approved drugs for MS have been designed to suppress the peripheral immune system. In addition, however, the effects of these drugs may be partially attributed to their influence on glial cells and neurons of the central nervous system (CNS). We here describe the molecular effects of the traditional and more recent FDA-approved MS drugs Fingolimod, Dimethyl Fumarate, Glatiramer Acetate, Interferon-β, Teriflunomide, Laquinimod, Natalizumab, Alemtuzumab and Ocrelizumab on microglia, astrocytes, neurons and oligodendrocytes. Furthermore, we point to a possible common molecular effect of these drugs, namely a key role for NFκB signaling, causing a switch from pro-inflammatory microglia and astrocytes to anti-inflammatory phenotypes of these CNS cell types that recently emerged as central players in MS pathogenesis. This notion argues for the need to further explore the molecular mechanisms underlying MS drug action.

Fingolimod and Dimethyl-Fumarate-Derived Lymphopenia is not Associated with Short-Term Treatment Response and Risk of Infections in a Real-Life MS Population

BACKGROUND

The association between treatment-related lymphopenia in multiple sclerosis, drug efficacy and the risk of infections is not yet fully understood.

OBJECTIVE

The objective of this study was to assess whether lymphopenia is associated with short-term treatment response and infection rate in a real-life multiple sclerosis population treated with fingolimod and dimethyl-fumarate. We assessed the associations between baseline absolute lymphocyte count and the lymphocyte mean percentage decrease at 6 and 12 months with treatment response and the occurrence of adverse events over 12 months in the entire cohort of patients and in the two treatment groups separately.

METHODS

This is a retrospective observational real-world study of patients with multiple sclerosis treated with fingolimod and dimethyl-fumarate at the MS Center of the University of Genoa between 2011 and 2018. Patients with at least 12 months of follow-up were eligible if [1] they had an Expanded Disability Status Scale assessment at baseline and 12 months after treatment onset, [2] they had undergone brain magnetic resonance imaging at baseline and after 12 months, and [3] absolute lymphocyte counts were available at baseline, 6 and 12 months. Patients shifting from dimethyl-fumarate to fingolimod or vice versa were excluded from the analysis.

RESULTS

In total, 137 and 75 patients treated with fingolimod and dimethyl-fumarate, respectively, were included in the analysis. At 12 months, fingolimod-treated patients were more likely to experience grade II and grade III lymphopenia compared with dimethyl-fumarate patients (p < 0.001, χ2 = 94) and had a higher lymphocyte mean percentage decrease (p < 0.001, U = 540). A higher number of previous therapies and a lower baseline absolute lymphocyte count were predictors of lymphopenia at 6 months (p = 0.047, odds ratio = 1.60 and p = 0.014, odds ratio = 1.1) and 12 months (p = 0.003, odds ratio = 1.97 and p = 0.023, odds ratio = 1.1). In fingolimod-treated patients only, female sex and a higher Expanded Disability Status Scale score were predictors of lymphopenia at 12 months (p = 0.006, odds ratio = 7.58 and p = 0.03, odds ratio = 1.56). Neither absolute lymphocyte count at 6 and 12 months nor the mean percentage decrease at 6 and 12 months predicted No Evidence of Disease Activity (NEDA-3) status at 1 year, the occurrence of relapses, disease activity on MRI or disability progression.

CONCLUSIONS

Our findings suggest that peripheral blood lymphocyte changes are not associated with short-term treatment response and with the rate of infections during fingolimod and dimethyl-fumarate treatment in real-world patients. Higher treatment exposure and a lower baseline absolute lymphocyte count are risk factors for lymphopenia development during fingolimod and dimethyl-fumarate therapy.