Lesion remyelinating activity of GSK239512 versus placebo in patients with relapsing-remitting multiple sclerosis: a randomised, single-blind, phase II study

Circulating myeloid-derived suppressor cell load and disease severity are associated to an enhanced oligodendroglial production in a murine model of multiple sclerosis

Multiple sclerosis (MS) is a highly heterogeneous immune-mediated demyelinating disease. Myelin restoration is essential to prevent disability progression in MS patients. However, remyelinating therapies are failing in clinical trials, in part, due to the lack of biomarkers that classify the differing endogenous regenerative capacities of enrolled patients. In the experimental autoimmune encephalomyelitis (EAE) MS model, circulating monocytic myeloid-derived suppressor cells (M-MDSCs) are associated to milder disease courses, better recovery and less degree of tissue damage. Here, we show that disease severity affects the gradient of oligodendrocyte precursor cells (OPCs) present in mixed active-inactive lesions of MS patients, along with a positive correlation between M-MDSC density and OPC abundance. EAE disease severity negatively influences the density of total and newly generated OPCs found associated to the demyelinated lesions. In addition, disease severity also impacts the abundance of newly generated oligodendrocytes throughout the EAE disease course. Interestingly, circulating M-MDSCs at EAE onset and peak of the disease are directly associated to a higher density of newly generated oligodendrocytes in the demyelinated lesions. Our results set the basis for further studies on M-MDSCs as a promising new biomarker that identify a CNS prone to new oligodendrocyte generation in response to an inflammatory insult.

Interventions promoting remyelination in multiple sclerosis: a systematic review of clinical trials

OBJECTIVES

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) characterized by demyelination and axonal damage. Current therapies primarily manage symptoms and slow disease progression but do not achieve remyelination. This systematic review evaluates the efficacy and safety of remyelination-promoting interventions in MS, focusing on clinical trials utilizing outcome measures validated in prior studies as indicators of remyelination.

METHODS

A comprehensive search of PubMed, Embase, Web of Science, and Cochrane Library was conducted in May 2024. Clinical trials assessing interventions with potential remyelinating properties were included. Data extraction followed standardized forms, and study quality was evaluated using ROBINS-I for non-randomized trials and RoB 2.0 for RCTs. Remyelination was assessed using Magnetization Transfer Ratio (MTR), Visual Evoked Potentials (VEPs), Myelin Water Fraction (MWF), Diffusion Tensor Imaging (DTI), and Optical Coherence Tomography (OCT).

RESULTS

From 1,615 screened records, 25 studies met the inclusion criteria and were analyzed. Across the 3341 participants, 17 interventions were evaluated. Most studies demonstrated a moderate risk of bias, yet all interventions, except one, were generally safe and well tolerated. Notably, rHIgM22, L-T3, opicinumab, clemastine fumarate, phenonytoin, domperidone, GSK239512, human fetal neural precursor cells (hfNPCs), and low-intensity repetitive transcranial magnetic stimulation (LI-rTMS) exhibited remyelination potential. Additionally, disease-modifying therapies (DMTs) such as Ocrelizumab, Fingolimod, and Natalizumab showed promising effects.

DISCUSSION

Although several interventions demonstrated remyelination potential, limitations such as small sample sizes, short follow-up periods, and lack of standardized clinical endpoints validating remyelination's functional impact, highlight the need for robust clinical trial designs, advanced biomarkers, and combination therapies integrating remyelination, neuroprotection, and immunomodulation to improve MS treatment outcomes.

Progressive multiple sclerosis: Evaluating current therapies and exploring future treatment strategies

Progressive forms of multiple sclerosis (MS) include primary progressive MS (PPMS) and secondary progressive MS (SPMS). Unlike relapsing-remitting MS (RRMS), progressive MS is recognized by relentless progression with accumulating disability, rare to no relapses nor new activity on MRIs. Clinically, neurologic worsening in MS can occur in the relapsing-remitting (RRMS) phase of disease due to incomplete recovery from neuroinflammatory relapses. However, a progressive disease course is the dominant factor related to accumulating disability. There is persistent central nervous system (CNS) compartmentalized inflammation, mitochondrial dysfunction and altered immune responses. Unlike in RRMS, the efficacy of disease modifying agents (DMA) in progressive MS has been limited, highlighting the need for novel therapeutic approaches that address both inflammation and neurodegeneration. This article explores current management of progressive MS, and future directions in targeting the unique pathophysiology of this complex disease.

Targeting Oligodendrocyte Dynamics and Remyelination: Emerging Therapies and Personalized Approaches in Multiple Sclerosis Management

Multiple sclerosis (MS) is a progressive autoimmune condition that primarily affects young people and is characterized by demyelination and neurodegeneration of the central nervous system (CNS). This in-depth review explores the complex involvement of oligodendrocytes, the primary myelin- producing cells in the CNS, in the pathophysiology of MS. It discusses the biochemical processes and signalling pathways required for oligodendrocytes to function and remain alive, as well as how they might fail and cause demyelination to occur. We investigate developing therapeutic options that target remyelination, a fundamental component of MS treatment. Remyelination approaches promote the survival and differentiation of oligodendrocyte precursor cells (OPCs), restoring myelin sheaths. This improves nerve fibre function and may prevent MS from worsening. We examine crucial parameters influencing remyelination success, such as OPC density, ageing, and signalling pathway regulation (e.g., Retinoid X receptor, LINGO-1, Notch). The review also examines existing neuroprotective and antiinflammatory medications being studied to see if they can assist oligodendrocytes in surviving and reducing the severity of MS symptoms. The review focuses on medicines that target the myelin metabolism in oligodendrocytes. Altering oligodendrocyte metabolism has been linked to reversing demyelination and improving MS patient outcomes through various mechanisms. We also explore potential breakthroughs, including innovative antisense technologies, deep brain stimulation, and the impact of gut health and exercise on MS development. The article discusses the possibility of personalized medicine in MS therapy, emphasizing the importance of specific medicines based on individual molecular profiles. The study emphasizes the need for reliable biomarkers and improved imaging tools for monitoring disease progression and therapy response. Finally, this review focuses on the importance of oligodendrocytes in MS and the potential for remyelination therapy. It also underlines the importance of continued research to develop more effective treatment regimens, taking into account the complexities of MS pathology and the different factors that influence disease progression and treatment.

Remyelinating Drugs at a Crossroad: How to Improve Clinical Efficacy and Drug Screenings

Axons wrapped around the myelin sheath enable fast transmission of neuronal signals in the Central Nervous System (CNS). Unfortunately, myelin can be damaged by injury, viral infection, and inflammatory and neurodegenerative diseases. Remyelination is a spontaneous process that can restore nerve conductivity and thus movement and cognition after a demyelination event. Cumulative evidence indicates that remyelination can be pharmacologically stimulated, either by targeting natural inhibitors of Oligodendrocyte Precursor Cells (OPCs) differentiation or by reactivating quiescent Neural Stem Cells (qNSCs) proliferation and differentiation in myelinating Oligodendrocytes (OLs). Although promising results were obtained in animal models for demyelination diseases, none of the compounds identified have passed all the clinical stages. The significant number of patients who could benefit from remyelination therapies reinforces the urgent need to reassess drug selection approaches and develop strategies that effectively promote remyelination. Integrating Artificial Intelligence (AI)-driven technologies with patient-derived cell-based assays and organoid models is expected to lead to novel strategies and drug screening pipelines to achieve this goal. In this review, we explore the current literature on these technologies and their potential to enhance the identification of more effective drugs for clinical use in CNS remyelination therapies.

The Study of Remyelinating Therapies in Multiple Sclerosis: Visual Outcomes as a Window Into Repair

INTRODUCTION

Amelioration of disability in multiple sclerosis requires the development of complementary therapies that target neurodegeneration and promote repair. Remyelination is a promising neuroprotective strategy that may protect axons from damage and subsequent neurodegeneration.

METHODS

A review of key literature plus additional targeted search of PubMed and Google Scholar was conducted.

RESULTS

There has been a rapid expansion of clinical trials studying putative remyelinating candidates, but further growth of the field is limited by the lack of consensus on key aspects of trial design. We have not yet defined the ideal study population, duration of therapy, or the appropriate outcome measures to detect remyelination in humans. The varied natural history of multiple sclerosis, coupled with the short time frame of phase II clinical trials, requires that we develop and validate biomarkers of remyelination that can serve as surrogate endpoints in clinical trials.

CONCLUSIONS

We propose that the visual system may be the most well-suited and validated model for the study potential remyelinating agents. In this review, we discuss the pathophysiology of demyelination and summarize the current clinical trial landscape of remyelinating agents. We present some of the challenges in the study of remyelinating agents and discuss current potential biomarkers of remyelination and repair, emphasizing both established and emerging visual outcome measures.

Feasibility study to assess lesion repair in relapsing-remitting multiple sclerosis: A randomized controlled pilot clinical trial of domperidone add-on treatment

BACKGROUND

Identification of therapies to promote repair in multiple sclerosis is challenged by the lack of an accepted trial model and associated outcome measures. The goal of this study was to determine the feasibility of a new trial model that enrolls disease modifying therapy (DMT)-treated relapsing-remitting multiple sclerosis (RRMS) participants who have enhancing lesions on clinically indicated brain MRI, and to explore estimates of lesion repair using MRI.

METHODS

This was a single site randomized controlled clinical trial. Recruitment took place between November 2015 and January 2019, with final follow-up in February 2019. DMT-treated RRMS participants aged 18-60 years with at least one gadolinium-enhancing lesion on clinically indicated brain MRI were included. Participants were randomized 2:1 to oral domperidone add-on 10-mg three times daily for 16 weeks or no add-on treatment (control). The primary outcomes were feasibility of the model pre-defined as recruitment of 24 participants within 36 months with a 79 % completion rate, and MRI outcomes of lesion repair measured at 16 and 32 weeks using texture analysis, magnetization transfer imaging (MTI), and diffusion tensor imaging (DTI). The impact of domperidone on serum prolactin at 6 and 16 weeks was also evaluated.

RESULTS

Of 237 RRMS participants screened, 17 (14 women) were randomized: 12 to domperidone add-on and 5 to control. All completed the study. Median (range) age was 38.9 (26.7-55.9) years; EDSS was 1.5 (1.0-3.5); and disease duration was 12.9 (2.9-23.3) years. Both groups showed improvement in MRI texture and diffusion fractional anisotropy (FA) at 32 weeks, and the domperidone group demonstrated additional recovery at 16 weeks in both texture and FA. There was no significant group difference in any MRI outcome. Of the 12 domperidone participants, 7 had ≥4x higher serum prolactin than normal. There were no serious adverse events.

CONCLUSION

The recruitment target was not met and therefore the trial model was not feasible despite a full completion rate. The imaging techniques performed well, especially MRI texture analysis, suggesting the sample size being sufficient for estimating lesion repair. The main challenge of this trial model may be recruiting gadolinium-enhancing lesions in DMT-treated RRMS participants. Prolactin is safe and may hold promise as a remyelination therapy.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02493049.

Discovery of Novel Steroid-Based Histamine H3 Receptor Antagonists/Inverse Agonists

Steroid-based histamine H3 receptor antagonists (d-homoazasteroids) were designed by combining distinct structural elements of HTS hit molecules. They were characterized, and several of them displayed remarkably high affinity for H3 receptors with antagonist/inverse agonist features. Especially, the 17a-aza-d-homolactam chemotype demonstrated excellent H3R activity together with significant in vivo H3 antagonism. Optimization of the chemotype was initiated with special emphasis on the elimination of the hERG and muscarinic affinity. Additionally, ligand-based SAR considerations and molecular docking studies were performed to predict binding modes of the molecules. The most promising compounds (XXI, XXVIII, and XX) showed practically no muscarinic and hERG affinity. They showed antagonist/inverse agonist property in the in vitro functional tests that was apparent in the rat in vivo dipsogenia test. They were considerably stable in human and rat liver microsomes and provided significant in vivo potency in the place recognition and novel object recognition cognitive paradigms.

Remyelination in the Central Nervous System

The inability of the mammalian central nervous system (CNS) to undergo spontaneous regeneration has long been regarded as a central tenet of neurobiology. However, while this is largely true of the neuronal elements of the adult mammalian CNS, save for discrete populations of granule neurons, the same is not true of its glial elements. In particular, the loss of oligodendrocytes, which results in demyelination, triggers a spontaneous and often highly efficient regenerative response, remyelination, in which new oligodendrocytes are generated and myelin sheaths are restored to denuded axons. Yet remyelination in humans is not without limitation, and a variety of demyelinating conditions are associated with sustained and disabling myelin loss. In this work, we will (1) review the biology of remyelination, including the cells and signals involved; (2) describe when remyelination occurs and when and why it fails, including the consequences of its failure; and (3) discuss approaches for therapeutically enhancing remyelination in demyelinating diseases of both children and adults, both by stimulating endogenous oligodendrocyte progenitor cells and by transplanting these cells into demyelinated brain.

Visual outcome measures in clinical trials of remyelinating drugs

One of the most promising approaches to delay, prevent or reverse disability progression in multiple sclerosis (MS) is to enhance endogenous remyelination and limit axonal degeneration. In clinical trials of remyelinating drugs, there is a need for reliable, sensitive and clinically relevant outcome measures. The visual pathway, which is frequently affected by MS, provides a unique model system to evaluate remyelination of acute and chronic MS lesions in vivo and non-invasively. In this review, we discuss the different measures that have been used and scrutinise visual outcome measure selection in current and future remyelination trials.

An update on the role of magnetic resonance imaging in predicting and monitoring multiple sclerosis progression

INTRODUCTION

While magnetic resonance imaging (MRI) is established in diagnosing and monitoring disease activity in multiple sclerosis (MS), its utility in predicting and monitoring disease progression is less clear.

AREAS COVERED

The authors consider changing concepts in the phenotypic classification of MS, including progression independent of relapses; pathological processes underpinning progression; advances in MRI measures to assess them; how well MRI features explain and predict clinical outcomes, including models that assess disease effects on neural networks, and the potential role for machine learning.

EXPERT OPINION

Relapsing-remitting and progressive MS have evolved from being viewed as mutually exclusive to having considerable overlap. Progression is likely the consequence of several pathological elements, each important in building more holistic prognostic models beyond conventional phenotypes. MRI is well placed to assess pathogenic processes underpinning progression, but we need to bridge the gap between MRI measures and clinical outcomes. Mapping pathological effects on specific neural networks may help and machine learning methods may be able to optimize predictive markers while identifying new, or previously overlooked, clinically relevant features. The ever-increasing ability to measure features on MRI raises the dilemma of what to measure and when, and the challenge of translating research methods into clinically useable tools.

Multiple Sclerosis Pathogenesis and Updates in Targeted Therapeutic Approaches

PURPOSE OF REVIEW

In this review, we provide a comprehensive update on current scientific advances and emerging therapeutic approaches in the field of multiple sclerosis.

RECENT FINDINGS

Multiple sclerosis (MS) is a common disorder characterized by inflammation and degeneration within the central nervous system (CNS). MS is the leading cause of non-traumatic disability in the young adult population. Through ongoing research, an improved understanding of the disease underlying mechanisms and contributing factors has been achieved. As a result, therapeutic advancements and interventions have been developed specifically targeting the inflammatory components that influence disease outcome. Recently, a new type of immunomodulatory treatment, known as Bruton tyrosine kinase (BTK) inhibitors, has surfaced as a promising tool to combat disease outcomes. Additionally, there is a renewed interested in Epstein-Barr virus (EBV) as a major potentiator of MS. Current research efforts are focused on addressing the gaps in our understanding of the pathogenesis of MS, particularly with respect to non-inflammatory drivers. Significant and compelling evidence suggests that the pathogenesis of MS is complex and requires a comprehensive, multilevel intervention strategy. This review aims to provide an overview of MS pathophysiology and highlights the most recent advances in disease-modifying therapies and other therapeutic interventions.

Neuronal activity and remyelination: new insights into the molecular mechanisms and therapeutic advancements

This article reviews the role of neuronal activity in myelin regeneration and the related neural signaling pathways. The article points out that neuronal activity can stimulate the formation and regeneration of myelin, significantly improve its conduction speed and neural signal processing ability, maintain axonal integrity, and support axonal nutrition. However, myelin damage is common in various clinical diseases such as multiple sclerosis, stroke, dementia, and schizophrenia. Although myelin regeneration exists in these diseases, it is often incomplete and cannot promote functional recovery. Therefore, seeking other ways to improve myelin regeneration in clinical trials in recent years is of great significance. Research has shown that controlling neuronal excitability may become a new intervention method for the clinical treatment of demyelinating diseases. The article discusses the latest research progress of neuronal activity on myelin regeneration, including direct or indirect stimulation methods, and the related neural signaling pathways, including glutamatergic, GABAergic, cholinergic, histaminergic, purinergic and voltage-gated ion channel signaling pathways, revealing that seeking treatment strategies to promote myelin regeneration through precise regulation of neuronal activity has broad prospects.

An update on combination therapies for multiple sclerosis: where are we now?

INTRODUCTION

In theory, combination of two agents, which are suboptimal when given individually, may result in a significant increase in therapeutic effect. Combination therapies have proven particularly effective against infections such as HIV, cancer, and also chronic autoimmune diseases such as rheumatoid arthritis.

AREAS COVERED

The authors review the literature, searching for randomized placebo-controlled or comparative, double-blind or investigator-blinded clinical trials, not including open label clinical trials, of treatment of multiple sclerosis (MS) with combination therapy or add-on therapy, including trials of induction therapy, trials for prevention of disease activity or worsening, amelioration of adverse effects, and treatment of relapses, and trials to increase remyelination.

EXPERT OPINION

Combination of two platform therapies (Interferon-beta or glatiramer acetate) was without additional effect. Clinical trials with add-on, often applying repurposed drugs (e.g. simvastatin, atorvastatin, minocycline, estriol, cyclophosphamide, azathioprine, albuterol, vitamin D), have been negative, apart from monthly methylprednisolone that, however, had low tolerability. Combination therapy for neuroprotection/remyelination showed some interesting results, though we are still awaiting results of phase III trials. The results of combination of anti-inflammatory therapies have in general been disappointing. In the future, combination of new effective neuroprotective/remyelinating drugs and highly effective anti-inflammatory treatments may benefit people with MS.

Remyelination in animal models of multiple sclerosis: finding the elusive grail of regeneration

Remyelination biology and the therapeutic potential of restoring myelin sheaths to prevent neurodegeneration and disability in multiple sclerosis (MS) has made considerable gains over the past decade with many regeneration strategies undergoing tested in MS clinical trials. Animal models used to investigate oligodendroglial responses and regeneration of myelin vary considerably in the mechanism of demyelination, involvement of inflammatory cells, neurodegeneration and capacity for remyelination. The investigation of remyelination in the context of aging and an inflammatory environment are of considerable interest for the potential translation to progressive multiple sclerosis. Here we review how remyelination is assessed in mouse models of demyelination, differences and advantages of these models, therapeutic strategies that have emerged and current pro-remyelination clinical trials.

Inflammation in multiple sclerosis: consequences for remyelination and disease progression

Despite the large number of immunomodulatory or immunosuppressive treatments available to treat relapsing-remitting multiple sclerosis (MS), treatment of the progressive phase of the disease has not yet been achieved. This lack of successful treatment approaches is caused by our poor understanding of the mechanisms driving disease progression. Emerging concepts suggest that a combination of persisting focal and diffuse inflammation within the CNS and a gradual failure of compensatory mechanisms, including remyelination, result in disease progression. Therefore, promotion of remyelination presents a promising intervention approach. However, despite our increasing knowledge regarding the cellular and molecular mechanisms regulating remyelination in animal models, therapeutic increases in remyelination remain an unmet need in MS, which suggests that mechanisms of remyelination and remyelination failure differ fundamentally between humans and demyelinating animal models. New and emerging technologies now allow us to investigate the cellular and molecular mechanisms underlying remyelination failure in human tissue samples in an unprecedented way. The aim of this Review is to summarize our current knowledge regarding mechanisms of remyelination and remyelination failure in MS and in animal models of the disease, identify open questions, challenge existing concepts, and discuss strategies to overcome the translational roadblock in the field of remyelination-promoting therapies.

Therapeutical growth in oligodendroglial fate induction via transdifferentiation of stem cells for neuroregenerative therapy

The merits of stem cell therapy and research are undisputed due to their widespread usage in the treatment of neurodegenerative diseases and demyelinating disorders. Cell replacement therapy especially revolves around stem cells and their induction into different cell lineages both adult and progenitor - belonging to each germ layer, prior to transplantation or disease modeling studies. The nervous system is abundant in glial cells and among these are oligodendrocytes capable of myelinating new-born neurons and remyelination of axons with lost or damaged myelin sheath. But demyelinating diseases generate tremendous deficit between myelin loss and recovery. To compensate for this loss, analyze the defects in remyelination mechanisms as well as to trigger full recovery in such patients mesenchymal stem cells (MSCs) have been induced to transdifferentiate into oligodendrocytes. But such experiments are riddled with problems like prolonged, tenuous and complicated protocols that stretch longer than the time taken for the spread of demyelination-associated after-effects. This review delves into such protocols and the combinations of different molecules and factors that have been recruited to derive bona fide oligodendrocytes from in vitro differentiation of embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) and MSCs with special focus on MSC-derived oligodendrocytes.

Updates and advances in multiple sclerosis neurotherapeutics

The multiple sclerosis (MS) neurotherapeutic landscape is rapidly evolving. New disease-modifying therapies (DMTs) with improved efficacy and safety, in addition to an expanding pipeline of agents with novel mechanisms, provide more options for patients with MS. While treatment of MS neuroinflammation is well tailored in the existing DMT armamentarium, concerted efforts are currently underway for identifying neuropathological targets and drug discovery for progressive MS. There is also ongoing research to develop agents for remyelination and neuroprotection. Further insights are needed to guide DMT initiation and sequencing as well as to determine the role of autologous stem cell transplantation in relapsing and progressive MS. This review provides a summary of these updates.

Enhancers of Human and Rodent Oligodendrocyte Formation Predominantly Induce Cholesterol Precursor Accumulation

Regeneration of myelin in the central nervous system is being pursued as a potential therapeutic approach for multiple sclerosis. Several labs have reported small molecules that promote oligodendrocyte formation and remyelination in vivo. Recently, we reported that many such molecules function by inhibiting a narrow window of enzymes in the cholesterol biosynthesis pathway. Here we describe a new high-throughput screen of 1,836 bioactive molecules and a thorough re-analysis of more than 60 molecules previously identified as promoting oligodendrocyte formation from human, rat, or mouse oligodendrocyte progenitor cells. These studies highlight that an overwhelming fraction of validated screening hits, including several molecules being evaluated clinically for remyelination, inhibit cholesterol pathway enzymes like emopamil-binding protein (EBP). To rationalize these findings, we suggest a model that relies on the high druggability of sterol-metabolizing enzymes and the ability of cationic amphiphiles to mimic the transition state of EBP. These studies further establish cholesterol pathway inhibition as a dominant mechanism among screening hits that enhance human, rat, or mouse oligodendrocyte formation.

Evidence for oligodendrocyte progenitor cell heterogeneity in the adult mouse brain

Oligodendrocyte progenitor cells (OPCs) account for approximately 5% of the adult brain and have been historically studied for their role in myelination. In the adult brain, OPCs maintain their proliferative capacity and ability to differentiate into oligodendrocytes throughout adulthood, even though relatively few mature oligodendrocytes are produced post-developmental myelination. Recent work has begun to demonstrate that OPCs likely perform multiple functions in both homeostasis and disease and can significantly impact behavioral phenotypes such as food intake and depressive symptoms. However, the exact mechanisms through which OPCs might influence brain function remain unclear. The first step in further exploration of OPC function is to profile the transcriptional repertoire and assess the heterogeneity of adult OPCs. In this work, we demonstrate that adult OPCs are transcriptionally diverse and separate into two distinct populations in the homeostatic brain. These two groups show distinct transcriptional signatures and enrichment of biological processes unique to individual OPC populations. We have validated these OPC populations using multiple methods, including multiplex RNA in situ hybridization and RNA flow cytometry. This study provides an important resource that profiles the transcriptome of adult OPCs and will provide a toolbox for further investigation into novel OPC functions.

Revisiting Preclinical Observations of Several Histamine H3 Receptor Antagonists/Inverse Agonists in Cognitive Impairment, Anxiety, Depression, and Sleep-Wake Cycle Disorder

A relationship appears to exist between dysfunction of brain histamine (HA) and various neuropsychiatric brain disorders. The possible involvement of brain HA in neuropathology has gained attention recently, and its role in many (patho)physiological brain functions including memory, cognition, and sleep-wake cycle paved the way for further research on the etiology of several brain disorders. Histamine H3 receptor (H3R) evidenced in the brains of rodents and humans remains of special interest, given its unique position as a pre- and postsynaptic receptor, controlling the synthesis and release of HA as well as different other neurotransmitters in different brain regions, respectively. Despite several disappointing outcomes for several H3R antagonists/inverse agonists in clinical studies addressing their effectiveness in Alzheimer's disease (AD), Parkinson's disease (PD), and schizophrenia (SCH), numerous H3R antagonists/inverse agonists showed great potentials in modulating memory and cognition, mood, and sleep-wake cycle, thus suggesting its potential role in neurocognitive and neurodegenerative diseases such as AD, PD, SCH, narcolepsy, and major depression in preclinical rodent models. In this review, we present preclinical applications of selected H3R antagonists/inverse agonists and their pharmacological effects on cognitive impairment, anxiety, depression, and sleep-wake cycle disorders. Collectively, the current review highlights the behavioral impact of developments of H3R antagonists/inverse agonists, aiming to further encourage researchers in the preclinical drug development field to profile the potential therapeutic role of novel antagonists/inverse agonists targeting histamine H3Rs.

Progression in multiple sclerosis - a long-term problem

PURPOSE OF REVIEW

Disability progression in multiple sclerosis (MS) is strongly linked to central nervous system (CNS)-specific pathological processes that occur throughout all disease stages, but that become clinically evident in later phases of the disease. We here discuss current views and concepts for targeting progressive MS.

RECENT FINDINGS

Detailed clinical assessment of MS patients has identified an even closer entanglement of relapse-remitting and progressive disease, leading to novel concepts such as 'progression independent of relapse activity'. Evolving clinical concepts together with a focus on molecular (neurofilament light chain) and imaging (paramagnetic rim lesions) biomarkers might specifically identify patients at risk of developing progressive MS considerably earlier than before. A multitude of novel treatment approaches focus either on direct neuroaxonal protection or myelin regeneration or on beneficially modulating CNS-intrinsic or innate immune inflammation. Although some long-awaited trials have recently been unsuccessful, important lessons could still be drawn from novel trial designs providing frameworks for future clinical studies.

SUMMARY

Targeting progressive disease biology and repairing established damage is the current central challenge in the field of MS. Especially, the compartmentalized adaptive and innate CNS inflammation is an attractive target for novel approaches, probably as a combinatory approach together with neuroprotective or myelin regenerating strategies.

Myelin water imaging in relapsing multiple sclerosis treated with ocrelizumab and interferon beta-1a

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2-Year change in MS myelin water fraction favored ocrelizumab over interferon.

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Matched healthy controls showed no change in myelin water fraction over 2 years.

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Ocrelizumab appears to protect against demyelination in MS white matter and lesions.

Background

Myelin water imaging is a magnetic resonance imaging (MRI) technique that quantifies myelin damage and repair in multiple sclerosis (MS) via the myelin water fraction (MWF).

Objective

In this substudy of a phase 3 therapeutic trial, OPERA II, MWF was assessed in relapsing MS participants assigned to interferon beta-1a (IFNb-1a) or ocrelizumab (OCR) during a two-year double-blind period (DBP) followed by a two-year open label extension (OLE) with ocrelizumab treatment.

Methods

MWF in normal appearing white matter (NAWM), including both whole brain NAWM and 5 white matter structures, and chronic lesions, was assessed in 29 OCR and 26 IFNb-1a treated participants at weeks 0, 24, 48 and 96 (DBP), and weeks 144 and 192 (OLE), and in white matter for 23 healthy control participants at weeks 0, 48 and 96.

Results

Linear mixed-effects models of data from baseline to week 96 showed a difference in the change in MWF over time favouring ocrelizumab in all NAWM regions. At week 192, lesion MWF was lower for participants originally randomised to IFNb-1a compared to those originally randomised to OCR. Controls showed no change in MWF over 96 weeks in any region.

Conclusion

Ocrelizumab appears to protect against demyelination in MS NAWM and chronic lesions and may allow for a more permissive micro environment for remyelination to occur in focal and diffusely damaged tissue.

Current status of neuroprotective and neuroregenerative strategies in multiple sclerosis: A systematic review

BACKGROUND

Immune-mediated demyelination and consequent degeneration of oligodendrocytes and axons are hallmark features of multiple sclerosis (MS). Remyelination declines in progressive MS, causing permanent axonal loss and irreversible disabilities. Strategies aimed at enhancing remyelination are critical to attenuate disease progression.

OBJECTIVE

We systematically reviewed recent advances in neuroprotective and regenerative therapies for MS, covering preclinical and clinical studies.

METHODS

We searched three biomedical databases using defined keywords. Two authors independently reviewed articles for inclusion based on pre-specified criteria. The data were extracted from each study and assessed for risk of bias.

RESULTS

Our search identified 7351 studies from 2014 to 2020, of which 221 met the defined criteria. These studies reported 262 interventions, wherein 92% were evaluated in animal models. These interventions comprised protein, RNA, lipid and cellular biologics, small molecules, inorganic compounds, and dietary and physiological interventions. Small molecules were the most highly represented strategy, followed by antibody therapies and stem cell transplantation.

CONCLUSION

While significant strides have been made to develop regenerative treatments for MS, the current evidence illustrates a skewed representation of the types of strategies that advance to clinical trials. Further examination is thus required to address current barriers to implementing experimental treatments in clinical settings.

Imaging Histamine H3 Receptors with Positron Emission Tomography

Positron emission tomography (PET) provides a unique tool to study the biochemistry of the human brain in vivo. By using PET probes that are binding selectively to certain receptor subtypes, brain PET allows the quantification of receptor levels in various brain areas of human subjects. This approach has the potential to reveal abnormal receptor expressions that may contribute to the physiopathology of some psychiatric and neurological disorders. This approach also has the potential to assist in the drug development process by determining receptor occupancy in vivo allowing selection of proper drug dosage to produce therapeutic effects. Several PET tracers have been developed for histamine H3 receptors (H3R). However, despite the potential of PET to elucidate the role of H3R in vivo, only limited work has been conducted so far. This article reviews the work that has been done in this area. Notably, we will cover the limitations of the first-generation PET radioligand for H3R and present the advantages of novel radioligands that promise an explosion of clinical PET research on the role of H3R in vivo.

Kinetics of myelin breakdown products: A labeling study in patients with progressive multiple sclerosis

The majority of disease modifying therapies for multiple sclerosis (MS) reduce inflammation, but do no’t target remyelination. Development of remyelinating therapies will benefit from a method to quantify myelin kinetics in patients with MS. We labeled myelin in vivo with deuterium, and modeled kinetics of myelin breakdown products β‐galactosylceramide (β‐GalC) and N‐Octadecanoyl‐sulfatide (NO‐Sulf). Five patients with MS received 120 ml 70% D₂O daily for 70 days and were compared with six healthy subjects who previously received the same procedure. Mass spectrometry and compartmental modeling were used to quantify the turnover rate of β‐GalC and NO‐Sulf in cerebrospinal fluid (CSF). Turnover rate constants of the fractions of β‐GalC and NO‐Sulf with non‐negligible turnover were 0.00186 and 0.00714, respectively, in both healthy subjects and patients with MS. The turnover half‐life of β‐GalC and NO‐Sulf was calculated as 373 days and 96.5 days, respectively. The effect of MS on the NO‐Sulf (49.4% lower fraction with non‐negligible turnover) was more pronounced compared to the effect on β‐GalC turnover (18.3% lower fraction with non‐negligible turnover). Kinetics of myelin breakdown products in the CSF are different in patients with MS compared with healthy subjects. This may be caused by slower myelin production in these patients, by a higher level of degradation of a more stable component of myelin, or, most likely, by a combination of these two processes. Labeling myelin breakdown products is a useful method that can be used to quantify myelin turnover in patients with progressive MS and can therefore be used in proof‐of‐concept studies with remyelination therapies.

Remyelination: what are the prospects for regenerative therapies in multiple sclerosis?

Multiple sclerosis (MS) involves the immune system attacking the myelin sheaths surrounding axons and is a major cause of disability in working-age adults. Various approved therapies now provide reasonably good control over MS neuroinflammation, but none have a pronounced impact on the neurodegeneration associated with the disease. One prominent approach to fulfilling the unmet need for neuroprotective therapies, is the search for agents that promote 'remyelination', namely the generation of new oligodendrocytes that can form replacement myelin sheaths around denuded axons. In this article, I discuss some emerging targets for remyelinating therapies, mainly being pursued by recently formed small companies translating academic findings.

Ethanol effects on cerebellar myelination in a postnatal mouse model of fetal alcohol spectrum disorders

Fetal alcohol spectrum disorders (FASD) are alarmingly common, result in significant personal and societal loss, and there are no effective treatments for these disorders. Cerebellar neuropathology is common in FASD and can cause impaired cognitive and motor function. The current study evaluates the effects of ethanol on oligodendrocyte-lineage cells, as well as molecules that modulate oligodendrocyte differentiation and function in the cerebellum in a postnatal mouse model of FASD. Neonatal mice were treated with ethanol from P4-P9 (postnatal day), the cerebellum was isolated at P10, and mRNAs encoding oligodendrocyte-associated molecules were quantitated by qRT-PCR. Our studies demonstrated that ethanol significantly reduced the expression of markers for multiple stages of oligodendrocyte maturation, including oligodendrocyte precursor cells, pre-myelinating oligodendrocytes, and mature myelinating oligodendrocytes. Additionally, we determined that ethanol significantly decreased the expression of molecules that play critical roles in oligodendrocyte differentiation. Interestingly, we also observed that ethanol significantly reduced the expression of myelin-associated inhibitors, which may act as a compensatory mechanism to ethanol toxicity. Furthermore, we demonstrate that ethanol alters the expression of a variety of molecules important in oligodendrocyte function and myelination. Collectively, our studies increase our understanding of specific mechanisms by which ethanol modulates myelination in the developing cerebellum, and potentially identify novel targets for FASD therapy.

Guided rational design with scaffold hopping leading to novel histamine H3 receptor ligands

During the past decades, histamine H₃ receptors have received widespread attention in pharmaceutical research due to their involvement in pathophysiology of several diseases such as neurodegenerative disorders. In this context, blocking of these receptors is of paramount importance in progression of such diseases. In the current investigation, novel histamine H₃ receptor ligands were designed by exploiting scaffold-hopping drug-design strategy. We inspected the designed molecules in terms of ADME properties, drug-likeness, as well as toxicity profiles. Additionally molecular docking and dynamics simulation studies were performed to predict binding mode and binding free energy calculations, respectively. Among the designed structures, we selected compound d2 and its demethylated derivative as examples for synthesis and affinity measurement. In vitro binding assays of the synthesized molecules demonstrated that d2 has lower binding affinity (K_i = 2.61 μM) in radioligand displacement assay to hH₃R than that of demethylated form (K_i = 12.53 μM). The newly designed compounds avoid of any toxicity predictors resulted from extended in silico and experimental studies, can offer another scaffold for histamine H₃R antagonists for further structure-activity relationship studies.

Safety and efficacy of bexarotene in patients with relapsing-remitting multiple sclerosis (CCMR One): a randomised, double-blind, placebo-controlled, parallel-group, phase 2a study

BACKGROUND

Progressive disability in multiple sclerosis occurs because CNS axons degenerate as a late consequence of demyelination. In animals, retinoic acid receptor RXR-gamma agonists promote remyelination. We aimed to assess the safety and efficacy of a non-selective retinoid X receptor agonist in promoting remyelination in people with multiple sclerosis.

METHODS

This randomised, double-blind, placebo-controlled, parallel-group, phase 2a trial (CCMR One) recruited patients with relapsing-remitting multiple sclerosis from two centres in the UK. Eligible participants were aged 18-50 years and had been receiving dimethyl fumarate for at least 6 months. Via a web-based system run by an independent statistician, participants were randomly assigned (1:1), by probability-weighted minimisation using four binary factors, to receive 300 mg/m2 of body surface area per day of oral bexarotene or oral placebo for 6 months. Participants, investigators, and outcome assessors were masked to treatment allocation. MRI scans were done at baseline and at 6 months. The primary safety outcome was the number of adverse events and withdrawals attributable to bexarotene. The primary efficacy outcome was the patient-level change in mean lesional magnetisation transfer ratio between baseline and month 6 for lesions that had a baseline magnetisation transfer ratio less than the within-patient median. We analysed the primary safety outcome in the safety population, which comprised participants who received at least one dose of their allocated treatment. We analysed the primary efficacy outcome in the intention-to-treat population, which comprised all patients who completed the study. This study is registered in the ISRCTN Registry, 14265371, and has been completed.

FINDINGS

Between Jan 17, 2017, and May 17, 2019, 52 participants were randomly assigned to receive either bexarotene (n=26) or placebo (n=26). Participants who received bexarotene had a higher mean number of adverse events (6·12 [SD 3·09]; 159 events in total) than did participants who received placebo (1·63 [SD 1·50]; 39 events in total). All bexarotene-treated participants had at least one adverse event, which included central hypothyroidism (n=26 vs none on placebo), hypertriglyceridaemia (n=24 vs none on placebo), rash (n=13 vs one on placebo), and neutropenia (n=10 vs none on placebo). Five (19%) participants on bexarotene and two (8%) on placebo discontinued the study drug due to adverse events. One episode of cholecystitis in a placebo-treated participant was the only serious adverse event. The change in mean lesional magnetisation transfer ratio was not different between the bexarotene group (0·25 percentage units [pu; SD 0·98]) and the placebo group (0·09 pu [0·84]; adjusted bexarotene-placebo difference 0·16 pu, 95% CI -0·39 to 0·71; p=0·55).

INTERPRETATION

We do not recommend the use of bexarotene to treat patients with multiple sclerosis because of its poor tolerability and negative primary efficacy outcome. However, statistically significant effects were seen in some exploratory MRI and electrophysiological analyses, suggesting that other retinoid X receptor agonists might have small biological effects that could be investigated in further studies.

FUNDING

Multiple Sclerosis Society of the United Kingdom.

The Histamine and Multiple Sclerosis Alliance: Pleiotropic Actions and Functional Validation

Multiple sclerosis (MS) is a disease with a resilient inflammatory component caused by accumulation into the CNS of inflammatory infiltrates and macrophage/microglia contributing to severe demyelination and neurodegeneration. While the causes are still in part unclear, key pathogenic mechanisms are the direct loss of myelin-producing cells and/or their impairment caused by the immune system. Proposed etiology includes genetic and environmental factors triggered by viral infections. Although several diagnostic methods and new treatments are under development, there is no curative but only palliative care against the relapsing-remitting or progressive forms of MS. In recent times, there has been a boost of awareness on the role of histamine signaling in physiological and pathological functions of the nervous system. Particularly in MS, evidence is raising that histamine might be directly implicated in the disease by acting at different cellular and molecular levels. For instance, constitutively active histamine regulates the differentiation of oligodendrocyte precursors, thus playing a central role in the remyelination process; histamine reduces the ability of myelin-autoreactive T cells to adhere to inflamed brain vessels, a crucial step in the development of MS; histamine levels are found increased in the cerebrospinal fluid of MS patients. The aim of the present work is to present further proofs about the alliance of histamine with MS and to introduce the most recent and innovative histamine paradigms for therapy. We will report on how a long-standing molecule with previously recognized immunomodulatory and neuroprotective functions, histamine, might still provide a renewed and far-reaching role in MS.

Premyelinating Oligodendrocytes: Mechanisms Underlying Cell Survival and Integration

In the central nervous system, oligodendrocytes produce myelin sheaths that enwrap neuronal axons to provide trophic support and increase conduction velocity. New oligodendrocytes are produced throughout life through a process referred to as oligodendrogenesis. Oligodendrogenesis consists of three canonical stages: the oligodendrocyte precursor cell (OPC), the premyelinating oligodendrocyte (preOL), and the mature oligodendrocyte (OL). However, the generation of oligodendrocytes is inherently an inefficient process. Following precursor differentiation, a majority of premyelinating oligodendrocytes are lost, likely due to apoptosis. If premyelinating oligodendrocytes progress through this survival checkpoint, they generate new myelinating oligodendrocytes in a process we have termed integration. In this review, we will explore the intrinsic and extrinsic signaling pathways that influence preOL survival and integration by examining the intrinsic apoptotic pathways, metabolic demands, and the interactions between neurons, astrocytes, microglia, and premyelinating oligodendrocytes. Additionally, we will discuss similarities between the maturation of newly generated neurons and premyelinating oligodendrocytes. Finally, we will consider how increasing survival and integration of preOLs has the potential to increase remyelination in multiple sclerosis. Deepening our understanding of premyelinating oligodendrocyte biology may open the door for new treatments for demyelinating disease and will help paint a clearer picture of how new oligodendrocytes are produced throughout life to facilitate brain function.

Remyelination therapies for multiple sclerosis: optimizing translation from animal models into clinical trials

Introduction: Multiple sclerosis (MS) is the most common inflammatory disease of the central nervous system (CNS). Demyelination, the main pathology in MS, contributes to clinical symptoms and long-term neurological deficits if left untreated. Remyelination, the natural repair of damaged myelin by cells of the oligodendrocyte lineage, occurs in MS, but eventually fails in most patients as they age. Encouraging timely remyelination can restore axon conduction and minimize deficits.Areas covered: We discuss and correlate human MS pathology with animal models, propose methods to deplete resident oligodendrocyte progenitor cells (OPCs) to determine whether mature oligodendrocytes support remyelination, and review remyelinating agents, mechanisms of action, and available clinical trial data.Expert opinion: The heterogeneity of human MS may limit successful translation of many candidate remyelinating agents; some patients lack the biological targets necessary to leverage current approaches. Development of therapeutics for remyelination has concentrated almost exclusively on mobilization of innate OPCs. However, mature oligodendrocytes appear an important contributor to remyelination in humans. Limiting the contribution of OPC mediated repair in models of MS would allow the evaluation of remyelination-promoting agents on mature oligodendrocytes. Among remyelinating reagents reviewed, only rHIgM22 targets both OPCs and mature oligodendrocytes.

Failed, Interrupted, or Inconclusive Trials on Neuroprotective and Neuroregenerative Treatment Strategies in Multiple Sclerosis: Update 2015-2020

In the recent past, a plethora of drugs have been approved for the treatment of multiple sclerosis (MS). These therapeutics are mainly confined to immunomodulatory or immunosuppressive strategies but do not sufficiently address remyelination and neuroprotection. However, several neuroregenerative agents have shown potential in pre-clinical research and entered Phase I to III clinical trials. Although none of these compounds have yet proceeded to approval, understanding the causes of failure can broaden our knowledge about neuroprotection and neuroregeneration in MS. Moreover, most of the investigated approaches are characterised by consistent mechanisms of action and proved convincing efficacy in animal studies. Therefore, learning from their failure will help us to enforce the translation of findings acquired in pre-clinical studies into clinical application. Here, we summarise trials on MS treatment published since 2015 that have either failed or were interrupted due to a lack of efficacy, adverse events, or for other reasons. We further outline the rationale underlying these drugs and analyse the background of failure to gather new insights into MS pathophysiology and optimise future study designs. For conciseness, this review focuses on agents promoting remyelination and medications with primarily neuroprotective properties or unconventional approaches. Failed clinical trials that pursue immunomodulation are presented in a separate article.

Current and emerging disease-modulatory therapies and treatment targets for multiple sclerosis

The treatment of multiple sclerosis (MS), the most common chronic inflammatory, demyelinating and neurodegenerative disease of the central nervous system (CNS), continues to transform. In recent years, a number of novel and increasingly effective disease-modulatory therapies (DMTs) have been approved, including oral fumarates and selective sphingosine 1-phosphate modulators, as well as cell-depleting therapies such as cladribine, anti-CD20 and anti-CD52 monoclonals. Amongst DMTs in clinical development, inhibitors of Bruton's tyrosine kinase represent an entirely new emerging drug class in MS, with three different drugs entering phase III trials. However, important remaining fields of improvement comprise tracking of long-term benefit-risk with existing DMTs and exploration of novel treatment targets relating to brain inherent disease processes underlying the progressive neurodegenerative aspect of MS, which accumulating evidence suggests start already early in the disease process. The aim here is to review current therapeutic options in relation to an improved understanding of the immunopathogenesis of MS, also highlighting examples where controlled trials have not generated the desired results. An additional aim is to review emerging therapies undergoing clinical development, including agents that interfere with disease processes believed to be important for neurodegeneration or aiming to enhance reparative responses. Notably, early trials now have shown initial evidence of enhanced remyelination both with small molecule compounds and biologicals. Finally, accumulating evidence from clinical trials and post-marketing real-world patient populations, which underscore the importance of early high effective therapy whilst maintaining acceptable tolerability, is discussed.

A review of possible therapies for multiple sclerosis

Multiple sclerosis (MS) is an autoimmune chronic inflammatory disease of the central nervous system with a wide range of symptoms, like executive function defect, cognitive dysfunction, blurred vision, decreased sensation, spasticity, fatigue, and other symptoms. This neurological disease is characterized by the destruction of the blood-brain barrier, loss of myelin, and damage to neurons. It is the result of immune cells crossing the blood-brain barrier into the central nervous system and attacking self-antigens. Heretofore, many treatments proved that they can retard the progression of the disease even though there is no cure. Therefore, treatments aimed at improving patients' quality of life and reducing adverse drug reactions and costs are essential. In this review, the treatment approaches to alleviate the progress of MS include the following: pharmacotherapy, antibody therapy, cell therapy, gene therapy, and surgery. The current treatment methods of MS are described in terms of the prevention of myelin shedding, the promotion of myelin regeneration, and the protection of neurons.

Chronic Demyelination and Axonal Degeneration in Multiple Sclerosis: Pathogenesis and Therapeutic Implications

PURPOSE OF REVIEW

Multiple sclerosis (MS) is the most common demyelinating disease of the central nervous system (CNS). Inflammatory attacks in MS lead to both demyelination and axonal damage. However, due to incomplete remyelination most MS lesions remain chronically demyelinated. In parallel, there is axonal degeneration in the CNS of MS patients, contributing to progressive disability. There are currently no approved therapies that adequately restore myelin or protect axons from degeneration. In this review, we will discuss the pathophysiology of axonal loss and chronic demyelination in MS and how understanding this pathophysiology is leading to the development of new MS therapeutics.

RECENT FINDINGS

Ongoing research into the function of oligodendrocytes and myelin has revealed the importance of their relationship with neuronal health. Demyelination in MS leads to a number of pathophysiologic changes contributing to axonal generation. Among these are mitochondrial dysfunction, persistent neuroinflammation, and the effects of reactive oxygen and nitrogen species. With this information, we review currently approved and investigational therapies designed to restore lost or damaged myelin and protect against neuronal degeneration. The development of therapies to restore lost myelin and protect neurons is a promising avenue of investigation for the benefit of patients with MS.

Oligodendrocyte Development and Regenerative Therapeutics in Multiple Sclerosis

Myelination by oligodendrocytes (OLs) is an important biological process essential for central nervous system (CNS) development and functions. Oligodendroglial lineage cells undergo several morphological and molecular changes at different stages of their lineage progression into myelinating OLs. The transition steps of the oligodendrocyte progenitor cells (OPCs) to myelinating oligodendrocytes are defined by a specific pattern of regulated gene expression, which is under the control of coordinated signaling pathways. Any abnormal development, loss or failure of oligodendrocytes to myelinate axons can lead to several neurodegenerative diseases like multiple sclerosis (MS). MS is characterized by inflammation and demyelination, and current treatments target only the immune component of the disease, but have little impact on remyelination. Recently, several pharmacological compounds enhancing remyelination have been identified and some of them are in clinical trials. Here, we will review the current knowledge on oligodendrocyte differentiation, myelination and remyelination. We will focus on MS as a pathological condition, the most common chronic inflammatory demyelinating disease of the CNS in young adults.

The Current Challenges for Drug Discovery in CNS Remyelination

The myelin sheath wraps around axons, allowing saltatory currents to be transmitted along neurons. Several genetic, viral, or environmental factors can damage the central nervous system (CNS) myelin sheath during life. Unless the myelin sheath is repaired, these insults will lead to neurodegeneration. Remyelination occurs spontaneously upon myelin injury in healthy individuals but can fail in several demyelination pathologies or as a consequence of aging. Thus, pharmacological intervention that promotes CNS remyelination could have a major impact on patient’s lives by delaying or even preventing neurodegeneration. Drugs promoting CNS remyelination in animal models have been identified recently, mostly as a result of repurposing phenotypical screening campaigns that used novel oligodendrocyte cellular models. Although none of these have as yet arrived in the clinic, promising candidates are on the way. Many questions remain. Among the most relevant is the question if there is a time window when remyelination drugs should be administrated and why adult remyelination fails in many neurodegenerative pathologies. Moreover, a significant challenge in the field is how to reconstitute the oligodendrocyte/axon interaction environment representative of healthy as well as disease microenvironments in drug screening campaigns, so that drugs can be screened in the most appropriate disease-relevant conditions. Here we will provide an overview of how the field of in vitro models developed over recent years and recent biological findings about how oligodendrocytes mature after reactivation of their staminal niche. These data have posed novel questions and opened new views about how the adult brain is repaired after myelin injury and we will discuss how these new findings might change future drug screening campaigns for CNS regenerative drugs.

Interaction between Neurons and the Oligodendroglial Lineage in Multiple Sclerosis and Its Preclinical Models

Multiple sclerosis (MS) is a complex central nervous system inflammatory disease leading to demyelination and associated functional deficits. Though endogenous remyelination exists, it is only partial and, with time, patients can enter a progressive phase of the disease, with neurodegeneration as a hallmark. Though major therapeutic advances have been made, with immunotherapies reducing relapse rate during the inflammatory phase of MS, there is presently no therapy available which significantly impacts disease progression. Remyelination has been shown to favor neuroprotection, and it is thus of major importance to better understand remyelination mechanisms in order to promote them and hence preserve neurons. A crucial point is how this process is regulated through the neuronal crosstalk with the oligodendroglial lineage. In this review, we present the current knowledge on neuron interaction with the oligodendroglial lineage, in physiological context as well as in MS and its experimental models. We further discuss the therapeutic possibilities resulting from this research field, which might allow to support remyelination and neuroprotection and thus limit MS progression.

Novel compounds with dual S1P receptor agonist and histamine H3 receptor antagonist activities act protective in a mouse model of multiple sclerosis

The sphingosine 1-phosphate (S1P) receptor 1 (S1P₁) has emerged as a therapeutic target for the treatment of multiple sclerosis (MS). Fingolimod (FTY720) is the first functional antagonist of S1P₁ that has been approved for oral treatment of MS. Previously, we have developed novel butterfly derivatives of FTY720 that acted similar to FTY720 in reducing disease symptoms in a mouse model of experimental autoimmune encephalomyelitis (EAE). In this study, we have synthesized a piperidine derivative of the oxazolo-oxazole compounds, denoted ST-1505, and its ring-opened analogue ST-1478, and characterised their in-vitro and in-vivo functions. Notably, the 3-piperidinopropyloxy moiety resembles a structural motif of pitolisant, a drug with histamine H₃R antagonistic/inverse agonist activity approved for the treatment of narcolepsy. Both novel compounds exerted H₃R affinities, and in addition, ST-1505 was characterised as a dual S1P₁₊₃ agonist, whereas ST-1478 was a dual S1P₁₊₅ agonist. Both multitargeting compounds were also active in mice and reduced the lymphocyte numbers as well as diminished disease symptoms in the mouse model of MS. The effect of ST-1478 was dependent on SK-2 activity suggesting that it is a prodrug like FTY720, but with a more selective S1P receptor activation profile, whereas ST-1505 is a fully active drug even in the absence of SK-2. In summary, these data suggest that the well soluble piperidine derivatives ST-1505 and ST-1478 hold promise as novel drugs for the treatment of MS and other autoimmune or inflammatory diseases, and by their H₃R antagonist potency, they might additionally improve cognitive impairment during disease.

Promoting remyelination in multiple sclerosis

The greatest unmet need in multiple sclerosis (MS) are treatments that delay, prevent or reverse progression. One of the most tractable strategies to achieve this is to therapeutically enhance endogenous remyelination; doing so restores nerve conduction and prevents neurodegeneration. The biology of remyelination-centred on the activation, migration, proliferation and differentiation of oligodendrocyte progenitors-has been increasingly clearly defined and druggable targets have now been identified in preclinical work leading to early phase clinical trials. With some phase 2 studies reporting efficacy, the prospect of licensed remyelinating treatments in MS looks increasingly likely. However, there remain many unanswered questions and recent research has revealed a further dimension of complexity to this process that has refined our view of the barriers to remyelination in humans. In this review, we describe the process of remyelination, why this fails in MS, and the latest research that has given new insights into this process. We also discuss the translation of this research into clinical trials, highlighting the treatments that have been tested to date, and the different methods of detecting remyelination in people.

Advances in the Treatment of Multiple Sclerosis

Multiple sclerosis is a relatively common, immune-mediated neurologic disease of the central nervous system that can cause significant disability and lead to reduced quality of life. There are several currently approved disease-modifying therapies, and more in the pipeline being developed and tested. As the field learns more about the pathophysiology and natural course of the disease, the treatment approaches are also being investigated. This article reviews data on available treatments along with a discussion of future treatment targets under investigation.

Sphingosine-1-Phosphate Receptor Modulators and Oligodendroglial Cells: Beyond Immunomodulation

Multiple sclerosis (MS) is an autoimmune inflammatory disease characterized by demyelination, axonal loss, and synaptic impairment in the central nervous system (CNS). The available therapies aim to reduce the severity of the pathology during the early inflammatory stages, but they are not effective in the chronic stage of the disease. In this phase, failure in endogenous remyelination is associated with the impairment of oligodendrocytes progenitor cells (OPCs) to migrate and differentiate into mature myelinating oligodendrocytes. Therefore, stimulating differentiation of OPCs into myelinating oligodendrocytes has become one of the main goals of new therapeutic approaches for MS. Different disease-modifying therapies targeting sphingosine-1-phosphate receptors (S1PRs) have been approved or are being developed to treat MS. Besides their immunomodulatory effects, growing evidence suggests that targeting S1PRs modulates mechanisms beyond immunomodulation, such as remyelination. In this context, this review focuses on the current understanding of S1PR modulators and their direct effect on OPCs and oligodendrocytes.

Anacardic acid induces IL-33 and promotes remyelination in CNS

Given the known neuroreparative actions of IL-33 in experimental models of central nervous system (CNS) injury, we predicted that compounds which induce IL-33 are likely to promote remyelination. We found anacardic acid as a candidate molecule to serve as a therapeutic agent to promote remyelination. Addition of anacardic acid to cultured oligodendrocyte precursor cells (OPCs) rapidly increased expression of myelin genes and myelin proteins, suggesting a direct induction of genes involved in myelination by anacardic acid. Also, when added to OPCs, anacardic acid resulted in the induction of IL-33. In vivo, treatment of with anacardic acid in doses which ranged from 0.025 mg/kg to 2.5 mg/kg, improved pathologic scores in experimental allergic encephalitis (EAE) and in the cuprizone model of demyelination/remyelination. Electron microscopic studies performed in mice fed with cuprizone and treated with anacardic acid showed lower g-ratio scores when compared to controls, suggesting increased remyelination of axons. In EAE, improvement in paralytic scores was seen when the drug was given prior to or following the onset of paralytic signs. In EAE and in the cuprizone model, areas of myelin loss, which are likely to remyelinate, was associated with a greater recruitment of IL-33-expressing OPCs in mice which received anacardic acid when compared to controls.

Mast cells and angiogenesis in multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease, characterized by multiple demyelination of axons in both white and gray matter in the Central Nervous System (CNS). There is increasing evidence to support the notion that angiogenesis and chronic inflammation are mutually related. Different immune cells, including monocytes-macrophages, lymphocytes, neutrophils, mast cells (MCs) and dendritic cells are able to secrete an array of angiogenic cytokines, which promote growth, migration, and activation of endothelial cells. MCs play various roles in MS pathogenesis, influencing the innate immune response in peripheral tissues and in CNS. The aim of this review article is to discuss the role of MCs in MS pathogenesis with particular reference to the involvement of these inflammatory cells in the angiogenic processes occurring during MS.

Remyelination in multiple sclerosis: from basic science to clinical translation

The treatment of multiple sclerosis has been transformed by the successful development of immunotherapies that efficiently reduce disease activity and related clinical relapses during the relapsing-remitting phase of the disease. However, the prevention of disability progression, which is due to axonal and neuronal damage and loss, has yet to be achieved and is therapeutically challenging, particularly during the progressive phase of the disease. One strategy to counteract neurodegeneration is to promote neuroprotection by enhancing myelin regeneration, hence restoring nerve conduction and metabolic support to the axon. Animal studies have provided targets for interventions to improve brain and spinal cord remyelination, paving the way for the translation of this research to humans. From these initial and promising forays, further problems have emerged, including questions on how best to design these clinical trials and appropriately measure the outcomes. Solving these problems will need additional work before efficacious pro-remyelination therapies will be ready for people with multiple sclerosis, but there is a real sense of hope that researchers are getting closer to a successful therapy.

White matter alterations in Williams syndrome related to behavioral and motor impairments

Myelin is the electrical insulator surrounding the neuronal axon that makes up the white matter (WM) of the brain. It helps increase axonal conduction velocity (CV) by inducing saltatory conduction. Damage to the myelin sheath and WM is associated with many neurological and psychiatric disorders. Decreasing myelin deficits, and thus improving axonal conduction, has the potential to serve as a therapeutic mechanism for reducing the severity of some of these disorders. Myelin deficits have been previously linked to abnormalities in social behavior, suggesting an interplay between brain connectivity and sociability. This review focuses on Williams syndrome (WS), a genetic disorder characterized by neurocognitive characteristics and motor abnormalities, mainly known for its hypersociability characteristic. We discuss fundamental aspects of WM in WS and how its alterations can affect motor abilities and social behavior. Overall, findings regarding changes in myelin genes and alterations in WM structure in WS suggest new targets for drug therapy aimed at improving conduction properties and altering brain-activity synchronization in this disorder.