General mechanisms of axonal damage and its prevention

Conduction slowing, conduction block and temporal dispersion in demyelinating, dysmyelinating and axonal neuropathies: Electrophysiology meets pathology

Nerve conduction studies are usually the first diagnostic step in peripheral nerve disorders and their results are the basis for planning further investigations. However, there are some commonplaces in the interpretation of electrodiagnostic findings in peripheral neuropathies that, although useful in the everyday practice, may be misleading: (1) conduction block and abnormal temporal dispersion are distinctive features of acquired demyelinating disorders; (2) hereditary neuropathies are characterized by uniform slowing of conduction velocity; (3) axonal neuropathies are simply diagnosed by reduced amplitude of motor and sensory nerve action potentials with normal or slightly slow conduction velocity. In this review, we reappraise the occurrence of uniform and non-uniform conduction velocity slowing, conduction block and temporal dispersion in demyelinating, dysmyelinating and axonal neuropathies attempting, with a translational approach, a correlation between electrophysiological and pathological features as derived from sensory nerve biopsy in patients and animal models. Additionally, we provide some hints to navigate in this complex field.

Evidence of brain target engagement in Parkinson's disease and multiple sclerosis by the investigational nanomedicine, CNM-Au8, in the REPAIR phase 2 clinical trials

BACKGROUND

Impaired brain energy metabolism has been observed in many neurodegenerative diseases, including Parkinson's disease (PD) and multiple sclerosis (MS). In both diseases, mitochondrial dysfunction and energetic impairment can lead to neuronal dysfunction and death. CNM-Au8® is a suspension of faceted, clean-surfaced gold nanocrystals that catalytically improves energetic metabolism in CNS cells, supporting neuroprotection and remyelination as demonstrated in multiple independent preclinical models. The objective of the Phase 2 REPAIR-MS and REPAIR-PD clinical trials was to investigate the effects of CNM-Au8, administered orally once daily for twelve or more weeks, on brain phosphorous-containing energy metabolite levels in participants with diagnoses of relapsing MS or idiopathic PD, respectively.

RESULTS

Brain metabolites were measured using 7-Tesla 31P-MRS in two disease cohorts, 11 participants with stable relapsing MS and 13 participants with PD (n = 24 evaluable post-baseline scans). Compared to pre-treatment baseline, the mean NAD+/NADH ratio in the brain, a measure of energetic capacity, was significantly increased by 10.4% after 12 + weeks of treatment with CNM-Au8 (0.584 units, SD: 1.3; p = 0.037, paired t-test) in prespecified analyses of the combined treatment cohorts. Each disease cohort concordantly demonstrated increases in the NAD+/NADH ratio but did not reach significance individually (p = 0.11 and p = 0.14, PD and MS cohorts, respectively). Significant treatment effects were also observed for secondary and exploratory imaging outcomes, including β-ATP and phosphorylation potential across both cohorts.

CONCLUSIONS

Our results demonstrate brain target engagement of CNM-Au8 as a direct modulator of brain energy metabolism, and support the further investigation of CNM-Au8 as a potential disease modifying drug for PD and MS.

Autonomic Modulation of Atrial Fibrillation

The autonomic nervous system plays a vital role in cardiac arrhythmias, including atrial fibrillation (AF). Therefore, reducing the sympathetic tone via neuromodulation methods may be helpful in AF control. Myocardial ischemia is associated with increased sympathetic tone and incidence of AF. It is an excellent disease model to understand the neural mechanisms of AF and the effects of neuromodulation. This review summarizes the relationship between autonomic nervous system and AF and reviews methods and mechanisms of neuromodulation. This review proposes that noninvasive or minimally invasive neuromodulation methods will be most useful in the future management of AF.

Alterations of Oligodendrocyte and Myelin Energy Metabolism in Multiple Sclerosis

Multiple sclerosis (MS) is a complex autoimmune disease of the central nervous system (CNS), characterized by demyelination and neurodegeneration. Oligodendrocytes play a vital role in maintaining the integrity of myelin, the protective sheath around nerve fibres essential for efficient signal transmission. However, in MS, oligodendrocytes become dysfunctional, leading to myelin damage and axonal degeneration. Emerging evidence suggests that metabolic changes, including mitochondrial dysfunction and alterations in glucose and lipid metabolism, contribute significantly to the pathogenesis of MS. Mitochondrial dysfunction is observed in both immune cells and oligodendrocytes within the CNS of MS patients. Impaired mitochondrial function leads to energy deficits, affecting crucial processes such as impulse transmission and axonal transport, ultimately contributing to neurodegeneration. Moreover, mitochondrial dysfunction is linked to the generation of reactive oxygen species (ROS), exacerbating myelin damage and inflammation. Altered glucose metabolism affects the energy supply required for oligodendrocyte function and myelin synthesis. Dysregulated lipid metabolism results in changes to the composition of myelin, affecting its stability and integrity. Importantly, low levels of polyunsaturated fatty acids in MS are associated with upregulated lipid metabolism and enhanced glucose catabolism. Understanding the intricate relationship between these mechanisms is crucial for developing targeted therapies to preserve myelin and promote neurological recovery in individuals with MS. Addressing these metabolic aspects may offer new insights into potential therapeutic strategies to halt disease progression and improve the quality of life for MS patients.

Dependence of cortical neuronal strength-duration properties on TMS pulse shape

OBJECTIVE

The aim of present study was to explore the effects of different combinations of transcranial magnetic stimulation (TMS) pulse width and pulse shape on cortical strength-duration time constant (SDTC) and rheobase measurements.

METHODS

Resting motor thresholds (RMT) at pulse widths (PW) of 30, 45, 60, 90 and 120 µs and M-ratios of 0.2, 0.1 and 0.025 were determined using figure-of-eight coil with initial posterior-to-anterior induced current. The M-ratio indicates the relative phases of the induced current with lower values signifying a more unidirectional stimulus. Strength-duration time constant (SDTC) and rheobase were estimated for each M-ratio and various PW combinations. Simulations of biophysically realistic cortical neuron models assessed underlying neuronal populations and physiological mechanisms mediating pulse shape effects on strength-duration properties.

RESULTS

The M-ratio exerted significant effect on SDTC (F(2,44) = 4.386, P = 0.021), which was longer for M-ratio of 0.2 (243.4 ± 61.2 µs) compared to 0.025 (186.7 ± 52.5 µs, P = 0.034). Rheobase was significantly smaller when assessed with M-ratio 0.2 compared to 0.025 (P = 0.026). SDTC and rheobase values were most consistent with pulse width sets of 30/45/60/90/120 µs, 30/60/90/120 µs, and 30/60/120 µs. Simulation studies indicated that isolated pyramidal neurons in layers 2/3, 5, and large basket-cells in layer 4 exhibited SDTCs comparable to experimental results. Further, simulation studies indicated that reducing transient Na+ channel conductance increased SDTC with larger increases for higher M-ratios.

CONCLUSIONS

Cortical strength-duration curve properties vary with pulse shape, and the modulating effect of the hyperpolarising pulse phase on cortical axonal transient Na+ conductances could account for these changes, although a shift in the recruited neuronal populations may contribute as well.

SIGNIFICANCE

The dependence of the cortical strength-duration curve properties on the TMS pulse shape and pulse width selection underscores the need for consistent measurement methods across studies and the potential to extract information about pathophysiological processes.

Neuron-oligodendrocyte potassium shuttling at nodes of Ranvier protects against inflammatory demyelination

Multiple sclerosis (MS) is a progressive inflammatory demyelinating disease of the CNS. Increasing evidence suggests that vulnerable neurons in MS exhibit fatal metabolic exhaustion over time, a phenomenon hypothesized to be caused by chronic hyperexcitability. Axonal Kv7 (outward-rectifying) and oligodendroglial Kir4.1 (inward-rectifying) potassium channels have important roles in regulating neuronal excitability at and around the nodes of Ranvier. Here, we studied the spatial and functional relationship between neuronal Kv7 and oligodendroglial Kir4.1 channels and assessed the transcriptional and functional signatures of cortical and retinal projection neurons under physiological and inflammatory demyelinating conditions. We found that both channels became dysregulated in MS and experimental autoimmune encephalomyelitis (EAE), with Kir4.1 channels being chronically downregulated and Kv7 channel subunits being transiently upregulated during inflammatory demyelination. Further, we observed that pharmacological Kv7 channel opening with retigabine reduced neuronal hyperexcitability in human and EAE neurons, improved clinical EAE signs, and rescued neuronal pathology in oligodendrocyte-Kir4.1-deficient (OL-Kir4.1-deficient) mice. In summary, our findings indicate that neuron-OL compensatory interactions promoted resilience through Kv7 and Kir4.1 channels and identify pharmacological activation of nodal Kv7 channels as a neuroprotective strategy against inflammatory demyelination.

Clinical Trials Targeting Secondary Damage after Traumatic Spinal Cord Injury

Spinal cord injury (SCI) often causes loss of sensory and motor function resulting in a significant reduction in quality of life for patients. Currently, no therapies are available that can repair spinal cord tissue. After the primary SCI, an acute inflammatory response induces further tissue damage in a process known as secondary injury. Targeting secondary injury to prevent additional tissue damage during the acute and subacute phases of SCI represents a promising strategy to improve patient outcomes. Here, we review clinical trials of neuroprotective therapeutics expected to mitigate secondary injury, focusing primarily on those in the last decade. The strategies discussed are broadly categorized as acute-phase procedural/surgical interventions, systemically delivered pharmacological agents, and cell-based therapies. In addition, we summarize the potential for combinatorial therapies and considerations.

Multiple sclerosis progression: time for a new mechanism-driven framework

Traditionally, multiple sclerosis has been categorised by distinct clinical descriptors-relapsing-remitting, secondary progressive, and primary progressive-for patient care, research, and regulatory approval of medications. Accumulating evidence suggests that the clinical course of multiple sclerosis is better considered as a continuum, with contributions from concurrent pathophysiological processes that vary across individuals and over time. The apparent evolution to a progressive course reflects a partial shift from predominantly localised acute injury to widespread inflammation and neurodegeneration, coupled with failure of compensatory mechanisms, such as neuroplasticity and remyelination. Ageing increases neural susceptibility to injury and decreases resilience. These observations encourage a new consideration of the course of multiple sclerosis as a spectrum defined by the relative contributions of overlapping pathological and reparative or compensatory processes. New understanding of key mechanisms underlying progression and measures to quantify progressive pathology will potentially have important and beneficial implications for clinical care, treatment targets, and regulatory decision-making.

High cortical iron is associated with the disruption of white matter tracts supporting cognitive function in healthy older adults

Aging is associated with brain iron accumulation, which has been linked to cognitive decline. However, how brain iron affects the structure and function of cognitive brain networks remains unclear. Here, we explored the possibility that iron load in gray matter is associated with disruption of white matter (WM) microstructure within a network supporting cognitive function, in a cohort of 95 cognitively normal older adults (age range: 60-86). Functional magnetic resonance imaging was used to localize a set of brain regions involved in working memory and diffusion tensor imaging based probabilistic tractography was used to identify a network of WM tracts connecting the functionally defined regions. Brain iron concentration within these regions was evaluated using quantitative susceptibility mapping and microstructural properties were assessed within the identified tracts using neurite orientation dispersion and density imaging. Results indicated that high brain iron concentration was associated with low neurite density (ND) within the task-relevant WM network. Further, regional associations were observed such that brain iron in cortical regions was linked with lower ND in neighboring but not distant WM tracts. Our results provide novel evidence suggesting that age-related increases in brain iron concentration are associated with the disruption of WM tracts supporting cognitive function in normal aging.

Live imaging reveals the cellular events downstream of SARM1 activation

SARM1 is an inducible NAD+ hydrolase that triggers axon loss and neuronal cell death in the injured and diseased nervous system. While SARM1 activation and enzyme function are well defined, the cellular events downstream of SARM1 activity but prior to axonal demise are much less well understood. Defects in calcium, mitochondria, ATP, and membrane homeostasis occur in injured axons, but the relationships among these events have been difficult to disentangle because prior studies analyzed large collections of axons in which cellular events occur asynchronously. Here, we used live imaging of mouse sensory neurons with single axon resolution to investigate the cellular events downstream of SARM1 activity. Our studies support a model in which SARM1 NADase activity leads to an ordered sequence of events from loss of cellular ATP, to defects in mitochondrial movement and depolarization, followed by calcium influx, externalization of phosphatidylserine, and loss of membrane permeability prior to catastrophic axonal self-destruction.

Diffusely abnormal white matter in multiple sclerosis

MRI enables detailed in vivo depiction of multiple sclerosis (MS) pathology. Localized areas of MS damage, commonly referred to as lesions, or plaques, have been a focus of clinical and research MRI studies for over four decades. A nonplaque MRI abnormality which is present in at least 25% of MS patients but has received far less attention is diffusely abnormal white matter (DAWM). DAWM has poorly defined boundaries and a signal intensity that is between normal-appearing white matter and classic lesions on proton density and T₂ -weighted images. All clinical phenotypes of MS demonstrate DAWM, including clinically isolated syndrome, where DAWM is associated with higher lesion volume, reduced brain volume, and earlier conversion to MS. Advanced MRI metric abnormalities in DAWM tend to be greater than those in NAWM, but not as severe as focal lesions, with myelin, axons, and water-related changes commonly reported. Histological studies demonstrate a primary lipid abnormality in DAWM, with some axonal damage and lesser involvement of myelin proteins. This review provides an overview of DAWM identification, summarizes in vivo and postmortem observations, and comments on potential pathophysiological mechanisms, which may underlie DAWM in MS. Given the prevalence and potential clinical impact of DAWM, the number of imaging studies focusing on DAWM is insufficient. Characterization of DAWM significance and microstructure would benefit from larger longitudinal and additional quantitative imaging efforts. Revisiting data from previous studies that included proton density and T₂ imaging would enable retrospective DAWM identification and analysis.

Gray matter blood-brain barrier water exchange dynamics are reduced in progressive multiple sclerosis

Background and Purpose

To compare transcapillary wall water exchange, a putative marker of cerebral metabolic health, in brain T₂ white matter (WM) lesions and normal appearing white and gray matter (NAWM and NAGM, respectively) in individuals with progressive multiple sclerosis (PMS) and healthy controls (HC).

Methods

Dynamic‐contrast‐enhanced 7T MRI data were obtained from 19 HC and 23 PMS participants. High‐resolution pharmacokinetic parametric maps representing tissue microvascular and microstructural properties were created by shutter‐speed (SS) paradigm modeling to obtain estimates of blood volume fraction (v_b), water molecule capillary efflux rate constant (k_po), and the water capillary wall permeability surface area product (P_wS ≡ v_b*k_po). Linear regression models were used to investigate differences in (i) k_po and P_wS between groups in NAWM and NAGM, and (ii) between WM lesions and NAWM in PMS.

Results

High‐resolution parametric maps were produced to visualize tissue classes and resolve individual WM lesions. Normal‐appearing gray matter k_po and P_wS were significantly decreased in PMS compared to HC (p ≤ .01). Twenty‐one T₂ WM lesions were analyzed in 10 participants with PMS. k_po was significantly decreased in WM lesions compared to PMS NAWM (p < .0001).

Conclusions

Transcapillary water exchange is reduced in PMS NAGM compared to HC and is further reduced in PMS WM lesions, suggesting pathologically impaired brain metabolism. k_po provides a sensitive measure of cerebral metabolic activity and/or coupling, and can be mapped at higher spatial resolution than conventional imaging techniques assessing metabolic activity.

Concurrent axon and myelin destruction differentiates X-linked adrenoleukodystrophy from multiple sclerosis

Cerebral disease manifestation occurs in about two thirds of males with X-linked adrenoleukodystrophy (CALD) and is fatally progressive if left untreated. Early histopathologic studies categorized CALD as an inflammatory demyelinating disease, which led to repeated comparisons to multiple sclerosis (MS). The aim of this study was to revisit the relationship between axonal damage and myelin loss in CALD. We applied novel immunohistochemical tools to investigate axonal damage, myelin loss and myelin repair in autopsy brain tissue of eight CALD and 25 MS patients. We found extensive and severe acute axonal damage in CALD already in prelesional areas defined by microglia loss and relative myelin preservation. In contrast to MS, we did not observe selective phagocytosis of myelin, but a concomitant decay of the entire axon-myelin unit in all CALD lesion stages. Using a novel marker protein for actively remyelinating oligodendrocytes, breast carcinoma-amplified sequence (BCAS) 1, we show that repair pathways are activated in oligodendrocytes in CALD. Regenerating cells, however, were affected by the ongoing disease process. We provide evidence that-in contrast to MS-selective myelin phagocytosis is not characteristic of CALD. On the contrary, our data indicate that acute axonal injury and permanent axonal loss are thus far underestimated features of the disease that must come into focus in our search for biomarkers and novel therapeutic approaches.

Axon-Myelin Unit Blistering as Early Event in MS Normal Appearing White Matter

Objective

Multiple sclerosis (MS) is a chronic neuroinflammatory and neurodegenerative disease of unknown etiology. Although the prevalent view regards a CD4⁺‐lymphocyte autoimmune reaction against myelin at the root of the disease, recent studies propose autoimmunity as a secondary reaction to idiopathic brain damage. To gain knowledge about this possibility we investigated the presence of axonal and myelinic morphological alterations, which could implicate imbalance of axon‐myelin units as primary event in MS pathogenesis.

Methods

Using high resolution imaging histological brain specimens from patients with MS and non‐neurological/non‐MS controls, we explored molecular changes underpinning imbalanced interaction between axon and myelin in normal appearing white matter (NAWM), a region characterized by normal myelination and absent inflammatory activity.

Results

In MS brains, we detected blister‐like swellings formed by myelin detachment from axons, which were substantially less frequently retrieved in non‐neurological/non‐MS controls. Swellings in MS NAWM presented altered glutamate receptor expression, myelin associated glycoprotein (MAG) distribution, and lipid biochemical composition of myelin sheaths. Changes in tethering protein expression, widening of nodes of Ranvier and altered distribution of sodium channels in nodal regions of otherwise normally myelinated axons were also present in MS NAWM. Finally, we demonstrate a significant increase, compared with controls, in citrullinated proteins in myelin of MS cases, pointing toward biochemical modifications that may amplify the immunogenicity of MS myelin.

Interpretation

Collectively, the impaired interaction of myelin and axons potentially leads to myelin disintegration. Conceptually, the ensuing release of (post‐translationally modified) myelin antigens may elicit a subsequent immune attack in MS. ANN NEUROL 2021;89:711–725

Diffusely appearing white matter in multiple sclerosis: Insights from sodium (23Na) MRI

BACKGROUND

In multiple sclerosis (MS), magnetic resonance imaging (MRI) frequently shows ill-defined areas with intermediate signal intensity between the normal appearing white matter (NAWM) and focal T2-hyperintense lesions, termed "diffusely appearing white matter" (DAWM). Even though several advanced MRI techniques have shown the potential to detect and quantify subtle commonly not visible microscopic tissue changes, to date only a few advanced MRI studies investigated DAWM changes in a quantitative manner. The aim of this study was to detect and quantify tissue abnormalities in the DAWM in comparison to focal lesions and the NAWM in MS patients by sodium (²³Na) MRI.

METHODS

²³Na and conventional MRI were performed in 25 MS patients with DAWM (DAWM⁺) and in 25 sex- and age matched MS patients without DAWM (DAWM^-), as well as in ten healthy controls (HC). Mean total sodium concentrations (TSC) were quantified in the DAWM, NAWM, normal appearing grey matter (NAGM) and in focal MS lesions.

RESULTS

In MS DAWM⁺and DAWM^-, TSC values were increased in the NAGM (DAWM⁺: 44.61 ± 4.09 mM; DAWM^-: 45.37 ± 3.8 mM) and in the NAWM (DAWM⁺: 39.85 ± 3.89 mM; DAWM^-: 39.82 ± 4.25 mM) compared to normal grey and white matter in HC (GM 40.87 ± 3.25 mM, WM 35.9 ± 1.81 mM; p < 0.05 for all comparisons). Interestingly, the DAWM showed similar sodium concentrations (39.32 ± 4.59 mM) to the NAWM (39.85 ± 3.89 mM), whereas TSC values in T1 hypointense (46.53 ± 7.87 mM) and T1 isointense (41.99 ± 6.10 mM) lesions were significantly higher than in the DAWM (p < 0.001 and 0.017 respectively).

CONCLUSION

²³Na MRI is confirmed as a sensitive marker of even subtle tissue abnormalities. DAWM sodium levels are increased and comparable to the abnormalities in NAWM, suggesting pathological changes less severe than in focal lesions comparable to what is expected in the NAWM.

Current Methods of Magnetic Resonance for Noninvasive Assessment of Molecular Aspects of Pathoetiology in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease with expanding axonal and neuronal degeneration in the central nervous system leading to motoric dysfunctions, psychical disability, and cognitive impairment during MS progression. The exact cascade of pathological processes (inflammation, demyelination, excitotoxicity, diffuse neuro-axonal degeneration, oxidative and metabolic stress, etc.) causing MS onset is still not fully understood, although several accompanying biomarkers are particularly suitable for the detection of early subclinical changes. Magnetic resonance (MR) methods are generally considered to be the most sensitive diagnostic tools. Their advantages include their noninvasive nature and their ability to image tissue in vivo. In particular, MR spectroscopy (proton 1H and phosphorus 31P MRS) is a powerful analytical tool for the detection and analysis of biomedically relevant metabolites, amino acids, and bioelements, and thus for providing information about neuro-axonal degradation, demyelination, reactive gliosis, mitochondrial and neurotransmitter failure, cellular energetic and membrane alternation, and the imbalance of magnesium homeostasis in specific tissues. Furthermore, the MR relaxometry-based detection of accumulated biogenic iron in the brain tissue is useful in disease evaluation. The early description and understanding of the developing pathological process might be critical for establishing clinically effective MS-modifying therapies.

Mechanisms of small nerve fiber pathology

Small fiber pathology is increasingly recognized as a potential contributor to neuropathic pain in different clinical syndromes, however, the underlying mechanisms leading to nociceptor sensitization and degeneration are unclear. With the diversity in clinical pain phenotypes and etiology of small fiber pathology, individual mechanisms are assumed, but are not yet fully understood. The thinly-myelinated Aδ- and unmyelinated C-nerve fibers are mainly affected and clinically require special small fiber test methods to capture functional, morphological, and electrophysiological alterations. Several methods have been established and implemented in clinical practice in the last years. In parallel, experimental and in vitro test systems have been developed allowing important insights into the molecular mechanisms underlying nociceptor sensitization and degeneration as main hallmarks of small fiber pathology. In our narrative review, we focus on these methods and current knowledge, and provide a synopsis of the achievements made so far in this exciting field.

The electrophysiology of axonal neuropathies: More than just evidence of axonal loss

It is common belief that axonal neuropathies are characterized by simple axonal degeneration and loss and that the electrophysiological correlates are just reduced compound muscle action potential and sensory nerve action potential amplitudes with normal or slightly slow conduction velocity. However, axonal autoimmune neuropathies with involvement of the nodal region and axonal neuropathies due to energy restriction such as occurring in nerve ischemia, thiamine deficiency, critical illness, and mitochondrial disorders present conduction failure that can be either reversible with prompt recovery or progress to axonal degeneration with poor outcome. Moreover autoimmune axonal neuropathies due to nodal voltage gated sodium channels dysfunction/disruption may show slowing of conduction velocity, even in the demyelinating range, possibly due to prolongation of the depolarization time required to reach the threshold for action potential regeneration at subsequent nodes. These observations widen the spectrum of the electrophysiological features in some axonal neuropathies, should be taken into account to avoid misdiagnoses and for correct prognostication, and should stimulate the quest of timely targeted treatments that can eventually halt the progression from conduction failure to axonal degeneration.

Apoptosis in Autoimmunological Diseases, with Particular Consideration of Molecular Aspects of Psoriasis

Apoptosis is a natural physiological process involving programmed cell death. Thanks to this process, it is possible to maintain the homeostasis of the body and the immune system. Dysfunctions of this mechanism lead to development of autoimmune diseases such as psoriasis; these diseases are chronic and treatment is extremely difficult. In psoriasis (a skin disease), apoptosis disorders are manifested by keratinocyte proliferation dysfunction. Autoimmune diseases coexisting with psoriasis include multiple sclerosis, autoimmune thyroid disease, and diabetes, but the common pathogenesis of these diseases is not fully understood. Given the heterogenous nature and chronic and recurrent course of psoriasis, the selection of an effective therapeutic strategy is still a problem. This literature review was focused on the process of apoptosis as a factor in the development of autoimmune diseases, with particular emphasis on psoriasis. The work also includes a review of therapeutic methods of psoriasis based on the latest literature.

New insights in the mechanisms of impaired redox signaling and its interplay with inflammation and immunity in multiple sclerosis

Multiple sclerosis (MS) is an autoimmune neurological disease characterized by chronic inflammation of the central nervous system (CNS), leading to demyelination and axonal damage and resulting in a range of physical, mental or even psychiatric symptoms. Key role of oxidative stress (OS) in the pathogenesis of MS has been suggested, as indicated by the biochemical analysis of cerebrospinal fluid and blood samples, tissue homogenates, and animal models of multiple sclerosis. OS causes demyelination and neurodegeneration directly, by oxidation of lipids, proteins and DNA but also indirectly, by inducing a dysregulation of the immunity and favoring the state of pro-inflammatory response. In this review, we discuss the interrelated mechanisms of the impaired redox signaling, of which the most important are inflammation-induced production of free radicals by activated immune cells and growth factors, release of iron from myelin sheath during demyelination and mitochondrial dysfunction and consequent energy failure and impaired oxidative phosphorylation. Review also provides an overview of the interplay between inflammation, immunity and OS in MS. Finally, this review also points out new potential targets in MS regarding attenuation of OS and inflammatory response in MS.

The Na+/Ca2+ exchangers in demyelinating diseases

Intracellular [Na⁺]_i and [Ca²⁺]_i imbalance significantly contribute to neuro-axonal dysfunctions and maladaptive myelin repair or remyelination failure in chronic inflammatory demyelinating diseases such as multiple sclerosis. Progress in recent years has led to significant advances in understanding how [Ca²⁺]_i signaling network drive degeneration or remyelination of demyelinated axons. The Na⁺/Ca²⁺ exchangers (NCXs), a transmembrane protein family including three members encoded by ncx1, ncx2, and ncx3 genes, are emerging important regulators of [Na⁺]_i and [Ca²⁺]_i both in neurons and glial cells. Here we review recent advance highlighting the role of NCX exchangers in axons and myelin-forming cells, i.e. oligodendrocytes, which represent the major targets of the aberrant inflammatory attack in multiple sclerosis. The contribution of NCX subtypes to axonal pathology and myelin synthesis will be discussed. Although a definitive understanding of mechanisms regulating axonal pathology and remyelination failure in chronic demyelinating diseases is still lacking and requires further investigation, current knowledge suggest that NCX activity plays a crucial role in these processes. Defining the relative contributions of each NCX transporter in axon pathology and myelinating glia will constitute not only a major advance in understanding in detail the intricate mechanism of neurodegeneration and remyelination failure in demyelinating diseases but also will help to identify neuroprotective or remyelinating strategies targeting selective NCX exchangers as a means of treating MS.

The Neuroprotective Effects of Melatonin: Possible Role in the Pathophysiology of Neuropsychiatric Disease

Melatonin is a hormone that is secreted by the pineal gland. To date, melatonin is known to regulate the sleep cycle by controlling the circadian rhythm. However, recent advances in neuroscience and molecular biology have led to the discovery of new actions and effects of melatonin. In recent studies, melatonin was shown to have antioxidant activity and, possibly, to affect the development of Alzheimer's disease (AD). In addition, melatonin has neuroprotective effects and affects neuroplasticity, thus indicating potential antidepressant properties. In the present review, the new functions of melatonin are summarized and a therapeutic target for the development of new drugs based on the mechanism of action of melatonin is proposed.

Mechanisms of Neurodegeneration and Axonal Dysfunction in Progressive Multiple Sclerosis

Multiple Sclerosis (MS) is a major cause of neurological disability, which increases predominantly during disease progression as a result of cortical and grey matter structures involvement. The gradual accumulation of disability characteristic of the disease seems to also result from a different set of mechanisms, including in particular immune reactions confined to the Central Nervous System such as: (a) B-cell dysregulation, (b) CD8⁺ T cells causing demyelination or axonal/neuronal damage, and (c) microglial cell activation associated with neuritic transection found in cortical demyelinating lesions. Other potential drivers of neurodegeneration are generation of oxygen and nitrogen reactive species, and mitochondrial damage, inducing impaired energy production, and intra-axonal accumulation of Ca²⁺, which in turn activates a variety of catabolic enzymes ultimately leading to progressive proteolytic degradation of cytoskeleton proteins. Loss of axon energy provided by oligodendrocytes determines further axonal degeneration and neuronal loss. Clearly, these different mechanisms are not mutually exclusive and could act in combination. Given the multifactorial pathophysiology of progressive MS, many potential therapeutic targets could be investigated in the future. This remains however, an objective that has yet to be undertaken.

Role of axon resealing in retrograde neuronal death and regeneration after spinal cord injury

Spinal cord injury leads to persistent behavioral deficits because mammalian central nervous system axons fail to regenerate. A neuron's response to axon injury results from a complex interplay of neuron-intrinsic and environmental factors. The contribution of axotomy to the death of neurons in spinal cord injury is controversial because very remote axotomy is unlikely to result in neuronal death, whereas death of neurons near an injury may reflect environmental factors such as ischemia and inflammation. In lampreys, axotomy due to spinal cord injury results in delayed apoptosis of spinal-projecting neurons in the brain, beyond the extent of these environmental factors. This retrograde apoptosis correlates with delayed resealing of the axon, and can be reversed by inducing rapid membrane resealing with polyethylene glycol. Studies in mammals also suggest that polyethylene glycol may be neuroprotective, although the mechanism(s) remain unclear. This review examines the early, mechanical, responses to axon injury in both mammals and lampreys, and the potential of polyethylene glycol to reduce injury-induced pathology. Identifying the mechanisms underlying a neuron's response to axotomy will potentially reveal new therapeutic targets to enhance regeneration and functional recovery in humans with spinal cord injury.

Time is spine: a review of translational advances in spinal cord injury

Acute traumatic spinal cord injury (SCI) is a devastating event with far-reaching physical, emotional, and economic consequences for patients, families, and society at large. Timely delivery of specialized care has reduced mortality; however, long-term neurological recovery continues to be limited. In recent years, a number of exciting neuroprotective and regenerative strategies have emerged and have come under active investigation in clinical trials, and several more are coming down the translational pipeline. Among ongoing trials are RISCIS (riluzole), INSPIRE (Neuro-Spinal Scaffold), MASC (minocycline), and SPRING (VX-210). Microstructural MRI techniques have improved our ability to image the injured spinal cord at high resolution. This innovation, combined with serum and cerebrospinal fluid (CSF) analysis, holds the promise of providing a quantitative biomarker readout of spinal cord neural tissue injury, which may improve prognostication and facilitate stratification of patients for enrollment into clinical trials. Given evidence of the effectiveness of early surgical decompression and growing recognition of the concept that "time is spine," infrastructural changes at a systems level are being implemented in many regions around the world to provide a streamlined process for transfer of patients with acute SCI to a specialized unit. With the continued aging of the population, central cord syndrome is soon expected to become the most common form of acute traumatic SCI; characterization of the pathophysiology, natural history, and optimal treatment of these injuries is hence a key public health priority. Collaborative international efforts have led to the development of clinical practice guidelines for traumatic SCI based on robust evaluation of current evidence. The current article provides an in-depth review of progress in SCI, covering the above areas.

Cnidarian peptide neurotoxins: a new source of various ion channel modulators or blockers against central nervous systems disease

Cnidaria provide the largest source of bioactive peptides for new drug development. The venoms contain enzymes, potent pore-forming toxins and neurotoxins. The neurotoxins can immobilize predators rapidly when discharged via modifying sodium-channel-gating or blocking the potassium channel during the repolarization stage. Most cnidarian neurotoxins remain conserved under the strong influence of negative selection. Neuroactive peptides targeting the central nervous system through affinity with ion channels could provide insight leading to drug treatment of neurological diseases, which arise from ion channel dysfunctions. Although marine resources offer thousands of possible peptides, only one peptide derived from Cnidaria: ShK-186, also named dalazatide, has reached the pharmaceutical market. This review focuses on neuroprotective agents derived from cnidarian neurotoxic peptides.

Erythropoietin Upregulates Brain Hemoglobin Expression and Supports Neuronal Mitochondrial Activity

Multiple sclerosis (MS) is a neuro-inflammatory and demyelinating disease. Downregulation of neuronal mitochondrial gene expression and activity have been reported in several studies of MS. We have previously shown that hemoglobin-β (Hbb) signals to the nucleus of neurons and upregulates H3K4me3, a histone mark involved in regulating cellular metabolism and differentiation. The present study was undertaken to evaluate the effect of erythropoietin (EPO) on the upregulation of hemoglobin and mitochondrial-associated neuroprotection. We found that administering EPO (5000 IU/kg intraperitoneally) to mice upregulated brain Hbb expression, levels of H3K4me3, expression of mitochondrial complex III, complex V, and mitochondrial respiration. We also found that the neuronal mitochondrial metabolite N-acetylaspartate (NAA), a marker of neuronal mitochondrial activity, was increased with EPO treatment. Further, we measured the effects of EPO on preventing mitochondrial deficits in the cuprizone toxic demyelinating mouse model of MS. We found that EPO prevented cuprizone-mediated decreases in Hbb, complex III, and NAA. Our data suggest that EPO mediated regulation of Hbb supports neuronal energetics and may provide neuroprotection in MS and other neurodegenerative diseases where a dysfunction of mitochondria contributes to disease.

Multiple mechanisms of dimethyl fumarate in amyloid β-induced neurotoxicity in human neuronal cells

Alzheimer disease (AD) is characterized by a complex heterogeneity of pathological changes, and any therapeutic approach categorically requires a multi-targeted way. It has been demonstrated that together with the hallmarks of the disease such as neurofibrillary tangles and senile plaques, oxidative and inflammatory stress covered an important role. Dimethyl fumarate (DMF) is an orally bioavailable methyl ester of fumaric acid and activator of Nrf2 with potential neuroprotective and immunomodulating activities. Therefore, the aim of the present work was to evaluate the potential beneficial effects of DMF, compared with its active metabolite monomethyl fumarate (MMF) (both at 30 μM) in an in vitro Alzheimer's model using SH-SY5Y human neuroblastoma cell lines stimulated with amyloid-beta (Aβ). Moreover, the effect of DMF, compared with MMF, was evaluate by an ex vivo model using organotypic hippocampal slice cultures stimulated with Aβ1-42 (1 μg/ml), to better understand its action in a pathological setting. In both models, DMF pre-treatment (30 μM) preserved cellular viability from Aβ stimulation, reducing tau hyper-phosphorylation, much more efficiently then MMF (30 μM). Moreover, DMF was able to induce an activation of manganese superoxide dismutase (MnSOD) and heme-oxygenase-1 (HO-1), decreasing the severity of oxidative stress. Our results showed important multi-protective effects of DMF pre-treatment from Aβ stimulation both in in vitro and ex vivo models, highlighting an Nrf2/NF-κB-dependent mechanism, which could provide a valuable support to the therapies for neurodegenerative diseases today.

Pathophysiology of primary open-angle glaucoma from a neuroinflammatory and neurotoxicity perspective: a review of the literature

PURPOSE

Glaucoma is the leading cause of blindness in humans, affecting 2% of the population. This disorder can be classified into various types including primary, secondary, glaucoma with angle closure and with open angle. The prevalence of distinct types of glaucoma differs for each particular region of the world. One of the most common types of this disease is primary open-angle glaucoma (POAG), which is a complex inherited disorder characterized by progressive retinal ganglion cell death, optic nerve head excavation and visual field loss. Nowadays, POAG is considered an optic neuropathy, while intraocular pressure is proposed to play a fundamental role in its pathophysiology and especially in optic disk damage. However, the exact mechanism of optic nerve head damage remains a topic of debate. This literature review aims to bring together the information on the pathophysiology of primary open-angle glaucoma, particularly focusing on neuroinflammatory mechanisms leading to the death of the retinal ganglion cell.

METHODS

A literature search was done on PubMed using key words including primary open-angle glaucoma, retinal ganglion cells, Müller cells, glutamate, glial cells, ischemia, hypoxia, exitotoxicity, neuroinflammation, axotomy and neurotrophic factors. The literature was reviewed to collect the information published about the pathophysiologic mechanisms of RGC death in the POAG, from a neuroinflammatory and neurotoxicity perspective.

RESULTS

Proposed mechanisms for glaucomatous damage are a result of pressure in RGC followed by ischemia, hypoxia of the ONH, and consequently death due to glutamate-induced excitotoxicity, deprivation of energy and oxygen, increase in levels of inflammatory mediators and alteration of trophic factors flow. These events lead to blockage of anterograde and retrograde axonal transport with ensuing axotomy and eventually blindness.

CONCLUSIONS

The damage to ganglion cells and eventually glaucomatous injury can occur via various mechanisms including baric trauma, ischemia and impact of metabolic toxins, which triggers an inflammatory process and secondary degeneration in the ONH.

Retrograde interferon-gamma signaling induces major histocompatibility class I expression in human-induced pluripotent stem cell-derived neurons

Objective

Injury-associated axon-intrinsic signals are thought to underlie pathogenesis and progression in many neuroinflammatory and neurodegenerative diseases, including multiple sclerosis (MS). Retrograde interferon gamma (IFN γ) signals are known to induce expression of major histocompatibility class I (MHC I) genes in murine axons, thereby increasing the susceptibility of these axons to attack by antigen-specific CD8⁺ T cells. We sought to determine whether the same is true in human neurons.

Methods

A novel microisolation chamber design was used to physically isolate and manipulate axons from human skin fibroblast-derived induced pluripotent stem cell (iPSC)-derived neuron-enriched neural aggregates. Fluorescent retrobeads were used to assess the fraction of neurons with projections to the distal chamber. Axons were treated with IFN γ for 72 h and expression of MHC class I and antigen presentation genes were evaluated by RT-PCR and immunofluorescence.

Results

Human iPSC-derived neural stem cells maintained as 3D aggregate cultures in the cell body chamber of polymer microisolation chambers extended dense axonal projections into the fluidically isolated distal chamber. Treatment of these axons with IFN γ resulted in upregulation of MHC class I and antigen processing genes in the neuron cell bodies. IFN γ-induced MHC class I molecules were also anterogradely transported into the distal axon.

Interpretation

These results provide conclusive evidence that human axons are competent to express MHC class I molecules, suggesting that inflammatory factors enriched in demyelinated lesions may render axons vulnerable to attack by autoreactive CD8⁺ T cells in patients with MS. Future work will be aimed at identifying pathogenic anti-axonal T cells in these patients.

Metabolic defects in multiple sclerosis

Brain injuries in multiple sclerosis (MS) involve immunopathological, structural and metabolic defects on myelin sheath, oligodendrocytes (OLs), axons and neurons suggesting that different cellular mechanisms ultimately result in the formation of MS plaques, demyelination, inflammation and brain damage. Bioenergetics, oxygen and ion metabolism dominate the metabolic and biochemical pathways that maintain neuronal viability and impulse transmission which directly or indirectly point to mitochondrial integrity and adenosine triphosphate (ATP) availability indicating the involvement of mitochondria in the pathogenesis of MS. Loss of myelin proteins including myelin basic protein (MBP), proteolipid protein (PLP), myelin associated glycoprotein (MAG), myelin oligodendrocyte glycoproetin (MOG), 2, 3,-cyclic nucleotide phosphodiestarase (CNPase); microglia and microphage activation, oligodendrocyte apoptosis as well as expression of inducible nitric oxide synthase (i-NOS) and myeloperoxidase activities have been implicated in a subset of Balo's type and relapsing remitting MS (RRMS) lesions indicating the involvement of metabolic defects and oxidative stress in MS. Here, we provide an insighting review of defects in cellular metabolism including energy, oxygen and metal metabolism in MS as well as the relevance of animal models of MS in understanding the molecular, biochemical and cellular mechanisms of MS pathogenesis. Additionally, we also discussed the potential for mitochondrial targets and antioxidant protection for therapeutic benefits in MS.

Amiloride does not protect retinal nerve fibre layer thickness in optic neuritis in a phase 2 randomised controlled trial

BACKGROUND

Recent basic and clinical evidence suggests amiloride may be neuroprotective in multiple sclerosis (MS) through the blockade of the acid sensing ion channel (ASIC).

OBJECTIVE

To examine the neuroprotective efficacy of amiloride in acute optic neuritis (ON).

METHODS

A total of 48 patients were recruited to a phase 2, double blind, single site, randomised controlled trial. Scanning laser polarimetry (GDx) at 6 months was the primary outcome measure and optical coherence tomography (OCT) and visual and electrophysiological measures were secondary outcome measures. Participants aged 18-55 years, ≤28 days of onset of first episode unilateral ON, were randomised to amiloride (10 mg daily for 5 months) or placebo ( clinicaltrials.gov , NCT 01802489).

RESULTS

Intention-to-treat (ITT) cohort consisted of 43 patients; 23 placebo and 20 amiloride. No significant drug-related adverse events occurred. No significant differences were found in GDx ( p = 0.840). Visual evoked potentials (VEP) were significantly prolonged in the amiloride group compared to placebo ( p = 0.004). All other secondary outcome measures showed no significant difference. Baseline analysis of OCT data demonstrated a significant pre-randomisation thinning of ganglion cell layer.

CONCLUSION

Amiloride has not demonstrated any neuroprotective benefit within this trial paradigm, but future neuroprotective trials in ON should target the window of opportunity to maximise potential neuroprotective benefit.

Experimental autoimmune encephalomyelitis from a tissue energy perspective

Increasing evidence suggests a key role for tissue energy failure in the pathophysiology of multiple sclerosis (MS). Studies in experimental autoimmune encephalomyelitis (EAE), a commonly used model of MS, have been instrumental in illuminating the mechanisms that may be involved in compromising energy production. In this article, we review recent advances in EAE research focussing on factors that conspire to impair tissue energy metabolism, such as tissue hypoxia, mitochondrial dysfunction, production of reactive oxygen/nitrogen species, and sodium dysregulation, which are directly affected by energy insufficiency, and promote cellular damage. A greater understanding of how inflammation affects tissue energy balance may lead to novel and effective therapeutic strategies that ultimately will benefit not only people affected by MS but also people affected by the wide range of other neurological disorders in which neuroinflammation plays an important role.

Brain sodium MRI in human epilepsy: Disturbances of ionic homeostasis reflect the organization of pathological regions

In light of technical advancements supporting exploration of MR signals other than ¹H, sodium (²³Na) has received attention as a marker of ionic homeostasis and cell viability. Here, we evaluate for the first time the possibility that ²³Na-MRI is sensitive to pathological processes occurring in human epilepsy. A normative sample of 27 controls was used to normalize regions of interest (ROIs) from 1424 unique brain locales on quantitative ²³Na-MRI and high-resolution ¹H-MPRAGE images. ROIs were based on intracerebral electrodes in ten patients undergoing epileptic network mapping. The stereo-EEG gold standard was used to define regions as belonging to primarily epileptogenic, secondarily irritative and to non-involved regions. Estimates of total sodium concentration (TSC) on ²³Na-MRI and cerebrospinal fluid (CSF) on ¹H imaging were extracted for each patient ROI, and normalized against the same region in controls. ROIs with disproportionate CSF contributions (Z_CSF≥1.96) were excluded. TSC levels were found to be elevated in patients relative to controls except in one patient, who suffered non-convulsive seizures during the scan, in whom we found reduced TSC levels. In the remaining patients, an ANOVA (F₁₁₀₀= 12.37, p<0.0001) revealed a highly significant effect of clinically-defined zones (F₁₁₀₀= 11.13, p<0.0001), with higher normalized TSC in the epileptogenic zone relative to both secondarily irritative (F₁₁₀₀= 11, p=0.0009) and non-involved regions (F₁₁₀₀= 17.8, p<0.0001). We provide the first non-invasive, in vivo evidence of a chronic TSC elevation alongside Z_CSF levels within the normative range, associated with the epileptogenic region even during the interictal period in human epilepsy, and the possibility of reduced TSC levels due to seizure. In line with modified homeostatic mechanisms in epilepsy - including altered mechanisms underlying ionic gating, clearance and exchange - we provide the first indication of ²³Na-MRI as an assay of altered sodium concentrations occurring in epilepsy associated with the organization of clinically relevant divisions of pathological cortex.

Pharmacological Approaches to the Management of Secondary Progressive Multiple Sclerosis

It is well recognised that the majority of the impact of multiple sclerosis (MS), both personal and societal, arises in the progressive phase where disability accumulates inexorably. As such, progressive MS (PMS) has been the target of pharmacological therapies for many years. However, there are no current licensed treatments for PMS. This stands in marked contrast to relapsing remitting MS (RRMS) where trials have resulted in numerous licensed therapies. PMS has proven to be a more difficult challenge compared to RRMS and this review focuses on secondary progressive MS (SPMS), where relapses occur before the onset of gradual, irreversible disability, and not primary progressive MS where disability accumulation occurs without prior relapses. Although there are similarities between the two forms, in both cases pinpointing when PMS starts is difficult in a condition in which disability can vary from day to day. There is also an overlap between the pathology of relapsing and progressive MS and this has contributed to the lack of well-defined outcomes, both surrogates and clinically relevant outcomes in PMS. In this review, we used the search term 'randomised controlled clinical drug trials in secondary progressive MS' in publications since 1988 together with recently completed trials where results were available. We found 34 trials involving 21 different molecules, of which 38% were successful in reaching their primary outcome. In general, the trials were well designed (e.g. double blind) with sample sizes ranging from 35 to 1949 subjects. The majority were parallel group, but there were also multi-arm and multidose trials as well as the more recent use of adaptive designs. The disability outcome most commonly used was the Expanded Disability Status Scale (EDSS) in all phases, but also magnetic resonance imaging (MRI)-measured brain atrophy has been utilised as a surrogate endpoint in phase II studies. The majority of the treatments tested in SPMS over the years were initially successful in RRMS. This has a number of implications in terms of targeting SPMS, but principally implies that the optimal strategy to target SPMS is to utilise the prodrome of relapses to initiate a therapy that will aim to both prevent progression and slow its accumulation. This approach is in agreement with the early targeting of MS but requires treatments that are both effective and safe if it is to be used before disability is a major problem. Recent successes will hopefully result in the first licensed therapy for PMS and enable us to test this approach.

Progressive multiple sclerosis: from pathogenic mechanisms to treatment

During the past decades, better understanding of relapsing-remitting multiple sclerosis disease mechanisms have led to the development of several disease-modifying therapies, reducing relapse rates and severity, through immune system modulation or suppression. In contrast, current therapeutic options for progressive multiple sclerosis remain comparatively disappointing and challenging. One possible explanation is a lack of understanding of pathogenic mechanisms driving progressive multiple sclerosis. Furthermore, diagnosis is usually retrospective, based on history of gradual neurological worsening with or without occasional relapses, minor remissions or plateaus. In addition, imaging methods as well as biomarkers are not well established. Magnetic resonance imaging studies in progressive multiple sclerosis show decreased blood-brain barrier permeability, probably reflecting compartmentalization of inflammation behind a relatively intact blood-brain barrier. Interestingly, a spectrum of inflammatory cell types infiltrates the leptomeninges during subpial cortical demyelination. Indeed, recent magnetic resonance imaging studies show leptomeningeal contrast enhancement in subjects with progressive multiple sclerosis, possibly representing an in vivo marker of inflammation associated to subpial demyelination. Treatments for progressive disease depend on underlying mechanisms causing central nervous system damage. Immunity sheltered behind an intact blood-brain barrier, energy failure, and membrane channel dysfunction may be key processes in progressive disease. Interfering with these mechanisms may provide neuroprotection and prevent disability progression, while potentially restoring activity and conduction along damaged axons by repairing myelin. Although most previous clinical trials in progressive multiple sclerosis have yielded disappointing results, important lessons have been learnt, improving the design of novel ones. This review discusses mechanisms involved in progressive multiple sclerosis, correlations between histopathology and magnetic resonance imaging studies, along with possible new therapeutic approaches.

Adenosine Triphosphate Metabolism Measured by Phosphorus Magnetic Resonance Spectroscopy: A Potential Biomarker for Multiple Sclerosis Severity

BACKGROUND/AIMS

Phosphorus magnetic resonance spectroscopy (31P-MRS) has previously shown abnormal changes in energy metabolites in the brain of multiple sclerosis (MS) patients. However, the relationship between these energy metabolites - particularly adenosine triphosphate (ATP) - and the disease severity remains unclear. The objective of this study was to determine whether measuring ATP metabolites can help to predict disease severity in MS patients.

METHODS

31P-MRS at 3 tesla was performed in 9 relapsing remitting (RRMS), 9 secondary progressive MS patients (SPMS), and 10 age-matched healthy controls. ATP metabolites (expressed as %) in normally appearing white matter of the centrum semiovale were compared between patients and healthy controls. The relationship between Expanded Disability Status Scale (EDSS) and ATP metabolites was evaluated.

RESULTS

RRMS and SPMS patients had higher phosphocreatine (PCr) and lower phosphodiesters than healthy controls. In addition, RRMS patients had higher β-ATP% than SPMS patients. β-ATP% was negatively correlated with EDSS in all patients.

CONCLUSION

Our findings suggest a defective PCr metabolism in both patient groups, and a higher state of energy production in RRMS that might reflect a compensatory mechanism in face of the increased needs. The correlation of β-ATP with EDSS makes it a candidate biomarker for assessing MS disease severity.

Transient upregulation of Nav1.6 expression in the genu of corpus callosum following middle cerebral artery occlusion in the rats

Focal ischemic stroke can lead to brain damage and cause human disability and death. Increased excitatory transmission and reduced neuronal inhibition are important pathological alterations in the cerebral ischemia, which can induce abnormal brain excitability. Nav1.6 is a key determinant of neuronal excitability in the nervous system. Here we investigate the expression of Nav1.6 at protein and mRNA levels in the rats subjected to middle cerebral artery occlusion (MCAO). Nav1.6 expression at mRNA levels in the ischemic and contralateral hemispheres of MCAO rats were persistently decreased at 6h, 12h and 24h after reperfusion compared to the sham-operated rats. However, a prominent, dynamic increase of Nav1.6 immunoreactivity in reactive astrocytes was observed in the genu of corpus callosum (GCC) of MCAO rats in the acute phase, reaching the peak at 6h after reperfusion, rapidly dropping at 12h and 24h after reperfusion. Furthermore, the upregulation of Nav1.6 expression was strongly correlated with the severity of reactive astrogliosis. Collectively, these findings suggest that this upregulated astrocytic sodium channel expression in the GCC of MCAO rats may contribute to the functional roles of reactive astrocytes in response to brain ischemia.

Dysregulation of energy metabolism in multiple sclerosis measured in vivo with diffusion-weighted spectroscopy

Objective:

We employed diffusion-weighted magnetic resonance spectroscopy (DW-MRS), which allows to measure in vivo the diffusion properties of metabolites, to explore the functional neuro-axonal damage and the ongoing energetic dysregulation in multiple sclerosis (MS).

Methods:

Twenty-five patients with MS and 18 healthy controls (HC) underwent conventional magnetic resonance imaging (MRI) and DW-MRS. The apparent diffusion coefficient (ADC) of total N-acetyl-aspartate (tNAA) and creatine–phosphocreatine (tCr) were measured in the parietal normal-appearing white matter (NAWM) and in the thalamic grey matter (TGM). Multiple regressions were used to compare metabolite ADCs between groups and to explore clinical correlations.

Results:

In patients compared with HCs, we found a reduction in ADC(tNAA) in the TGM, reflecting functional and structural neuro-axonal damage, and in ADC(tCr) in both NAWM and TGM, possibly reflecting a reduction in energy supply in neurons and glial cells. Metabolite ADCs did not correlate with tissue atrophy, lesional volume or metabolite concentrations, while in TGM metabolite ADCs correlated with clinical scores.

Conclusion:

DW-MRS showed a reduction in tCr diffusivity in the normal-appearing brain of patients with MS, which might reflect a state of ongoing energy dysregulation affecting neurons and/or glial cells. Reversing this energy dysregulation before neuro-axonal degeneration arises may become a key objective in future neuroprotective strategies.

Elevated intracellular Na+ concentrations in developing spinal neurons

Over 25 years ago it was first reported that intracellular chloride levels (Cl^-_in ) were higher in developing neurons than in maturity. This finding has had significant implications for understanding the excitability of developing networks and recognizing the underlying causes of hyperexcitability associated with disease and neural injury. While there is some evidence that intracellular sodium levels (Na⁺_in ) change during the development of non-neural cells, it has largely been assumed that Na⁺_in is the same in developing and mature neurons. Here, using the sodium indicator SBFI, we test this idea and find that Na⁺_in is significantly higher in embryonic spinal motoneurons and interneurons than in maturity. We find that Na⁺_in reaches ~ 60 mM in mid-embryonic development and is then reduced to ~ 30 mM in late embryonic development. By retrogradely labeling motoneurons with SBFI we can reliably follow Na⁺_in levels in vitro for hours. Bursts of spiking activity, and blocking voltage-gated sodium channels did not influence observed motoneuron sodium levels. On the other hand, Na⁺_in was reduced by blocking the Na⁺ -K⁺ -2Cl^- cotransporter NKCC1, and was highly sensitive to changes in external Na⁺ and a blocker of the Na⁺ /K⁺ ATPase. Our findings suggest that the Na⁺ gradient is weaker in embryonic neuronal development and strengthens in maturity in a manner similar to that of Cl^- .

Axonal Excitability in Amyotrophic Lateral Sclerosis : Axonal Excitability in ALS

Axonal excitability testing provides in vivo assessment of axonal ion channel function and membrane potential. Excitability techniques have provided insights into the pathophysiological mechanisms underlying the development of neurodegeneration and clinical features of amyotrophic lateral sclerosis (ALS) and related neuromuscular disorders. Specifically, abnormalities of Na+ and K+ conductances contribute to development of membrane hyperexcitability in ALS, thereby leading to symptom generation of muscle cramps and fasciculations, in addition to promoting a neurodegenerative cascade via Ca2+-mediated processes. Modulation of axonal ion channel function in ALS has resulted in significant symptomatic improvement that has been accompanied by stabilization of axonal excitability parameters. Separately, axonal ion channel dysfunction evolves with disease progression and correlates with survival, thereby serving as a potential therapeutic biomarker in ALS. The present review provides an overview of axonal excitability techniques and the physiological mechanisms underlying membrane excitability, with a focus on the role of axonal ion channel dysfunction in motor neuron disease and related neuromuscular diseases.

A painful neuropathy-associated Nav1.7 mutant leads to time-dependent degeneration of small-diameter axons associated with intracellular Ca2+ dysregulation and decrease in ATP levels

Small fiber neuropathy is a painful sensory nervous system disorder characterized by damage to unmyelinated C- and thinly myelinated Aδ- nerve fibers, clinically manifested by burning pain in the distal extremities and dysautonomia. The clinical onset in adulthood suggests a time-dependent process. The mechanisms that underlie nerve fiber injury in small fiber neuropathy are incompletely understood, although roles for energetic stress have been suggested. In the present study, we report time-dependent degeneration of neurites from dorsal root ganglia neurons in culture expressing small fiber neuropathy-associated G856D mutant Nav1.7 channels and demonstrate a time-dependent increase in intracellular calcium levels [Ca2+]i and reactive oxygen species, together with a decrease in ATP levels. Together with a previous clinical report of burning pain in the feet and hands associated with reduced levels of Na+/K+-ATPase in humans with high altitude sickness, the present results link energetic stress and reactive oxygen species production with the development of a painful neuropathy that preferentially affects small-diameter axons.

Neuroprotection by central nervous system remyelination: Molecular, cellular, and functional considerations

Oligodendrocytes and their myelin sheaths play an intricate role in axonal health and function. The prevalence of white matter pathology in a wide variety of central nervous system disorders has gained attention in recent years. Remyelination has therefore become a major target of therapeutic research, with the aim of protecting axons from further damage. The axon-myelin unit is elaborate, and demyelination causes profound changes in axonal molecular domains, signal transmission, and metabolism. Remyelination is known to restore some of these changes, but many of its outcomes remain unknown. Understanding how different aspects of the axon-myelin unit are restored by remyelination is important for making effective, targeted therapeutics for white matter dysfunction. Additionally, understanding how subtle deficits relate to axonal function during demyelination and remyelination may provide clues into the impact of myelin on neuronal circuits. In this review, we discuss the current knowledge of the neuroprotective effects of remyelination, as well as gaps in our knowledge. Finally, we propose systems with unique myelin profiles that may serve as useful models for investigating remyelination efficacy. © 2016 Wiley Periodicals, Inc.

Lamotrigine attenuates cerebral ischemia-induced cognitive impairment and decreases β-amyloid and phosphorylated tau in the hippocampus in rats

Lamotrigine (LTG) has shown benefits in animal models of cerebral ischemia, but the mechanism involved was not fully studied. This study was carried out to examine the effects of LTG on cognitive dysfunction, β-amyloid1-42 accumulation, and tau protein hyperphosphorylation in the hippocampus of ischemic rats. Transient ischemic stroke was induced by middle cerebral artery occlusion. The Morris water maze test was used to evaluate the cognitive function of rats. We found that LTG significantly attenuated ischemia-induced cognitive deficits and decreased neuronal injury in the hippocampal CA1 zone. Moreover, LTG reduced β-amyloid1-42 and phosphorylated tau (AT8) in the hippocampus after ischemia. These results suggested that the cognition-protective effects of LTG after cerebral ischemia might involve inhibition of toxic β-amyloid accumulation and tau hyperphosphorylation in the hippocampus.

In vivo imaging reveals rapid astrocyte depletion and axon damage in a model of neuromyelitis optica-related pathology

Objective

Neuromyelitis optica (NMO) is an autoimmune disease of the central nervous system, which resembles multiple sclerosis (MS). NMO differs from MS, however, in the distribution and histology of neuroinflammatory lesions and shows a more aggressive clinical course. Moreover, the majority of NMO patients carry immunoglobulin G autoantibodies against aquaporin‐4 (AQP4), an astrocytic water channel. Antibodies against AQP4 can damage astrocytes by complement, but NMO histopathology also shows demyelination, and — importantly—axon injury, which may determine permanent deficits following NMO relapses. The dynamics of astrocyte injury in NMO and the mechanisms by which toxicity spreads to axons are not understood.

Methods

Here, we establish in vivo imaging of the spinal cord, one of the main sites of NMO pathology, as a powerful tool to study the formation of experimental NMO‐related lesions caused by human AQP4 antibodies in mice.

Results

We found that human AQP4 antibodies caused acute astrocyte depletion with initial oligodendrocyte survival. Within 2 hours of antibody application, we observed secondary axon injury in the form of progressive swellings. Astrocyte toxicity and axon damage were dependent on AQP4 antibody titer and complement, specifically C1q.

Interpretation

In vivo imaging of the spinal cord reveals the swift development of NMO‐related acute axon injury after AQP4 antibody‐mediated astrocyte depletion. This approach will be useful in studying the mechanisms underlying the spread of NMO pathology beyond astrocytes, as well as in evaluating potential neuroprotective interventions. Ann Neurol 2016;79:794–805