Conduction block in acute and chronic spinal cord injury: different dose-response characteristics for reversal by 4-aminopyridine

4-AP-3-MeOH Promotes Structural and Functional Spontaneous Recovery in the Acute Sciatic Nerve Stretch Injury

Background:

4-AP-3-MeOH, a derivative of 4-aminopyridine, was developed and demonstrated to prevent nerve pulse diffusion due to myelin damage and significantly enhance axonal conduction following nerve injury. Currently, repurposing the existing drug such as 4-AP-3-MeOH to restore motor function is a promising and potential therapy of peripheral nerve injury. However, to evaluate drug effect on sciatic nerve injury is full of challenge.

Methods:

Sciatic functional index was used to determine and measure the walking track in the stretch injury model. Nerve conductivity was performed by electrical stimulation of a nerve and recording the compound muscle action potential. Myelin thickness and regeneration was imaged and measured with transmission electron microscopy (TEM).

Results:

In this study, we developed a sciatic nerve injury model to minimize the spontaneous recovery mechanism and found that 4-AP-3-MeOH not only improved walking ability of the animals but also reduced the sensitivity to thermal stimulus. More interesting, 4-AP-3-MeOH enhanced and recovered electric conductivity of injured nerve; our TEM results indicated that the axon sheath thickness was increased and myelin was regenerated, which was an important evidence to support the recovery of injured nerve conductivity with 4-AP-3-MeOH treatment.

Conclusions:

In summary, our studies suggest that 4-AP-3-MeOH is a viable and promising approach to the therapy of peripheral nerve injury and in support of repurposing the existing drug to restore motor function.

Cognitive Fatigability Interventions in Neurological Conditions: A Systematic Review

INTRODUCTION

Although fatigue is a well-studied concept in neurological disease, cognitive fatigability (CF) is less understood. While most studies measure fatigue using subjective self-report, fewer have measured CF objectively. Given the negative impact of CF on quality-of-life, there is a need for targeted interventions. The objective of this review was to determine which procedural, behavioural and pharmacological treatments for objectively measured CF are available to people living with neurological conditions.

METHODS

In accordance with the PRISMA guidelines, systematic searches for randomized control trials (RCTs), case-controlled studies and case reports/series were conducted across the Ovid Medline, PsycInfo, EMBASE and Cochrane Library databases. English-language articles published between 1980 and February 2019 were considered for eligibility. Included were those that objectively measured CF in individuals with neurological disease/disorder/dysfunction between the ages of 18 and 65 years. Studies were reviewed using a modified Cochrane Data Extraction Template. Risk of bias was assessed using the Cochrane Risk of Bias tool. The review process was facilitated using Covidence software (www.covidence.org). Two authors reviewed articles independently, with a third resolving conflicts regarding article inclusion.

RESULTS

The search identified 450 records. After duplicates were removed and remaining titles/abstracts were screened for eligibility, 28 full-text articles were assessed, and two studies were included in the qualitative synthesis. Studies were a priori divided into those with pharmacological, procedural or behavioural interventions. Two studies met eligibility criteria; both of these included participants with multiple sclerosis. One study utilized a procedural intervention (i.e. transcranial direct current stimulation), while the other utilized a pharmacological intervention (i.e. fampridine-SR). Studies were evaluated for risk of bias, and evidence from both eligible studies was discussed.

CONCLUSION

Despite the positive results of the procedural intervention, the paucity of eligible studies and the nascent nature of the field suggests that more studies are required before firm conclusions can be drawn regarding the amenability of CF to treatment.

TRIAL REGISTRATION

The review was registered with PROSPERO (CRD42019118706).

Parallel Evaluation of Two Potassium Channel Blockers in Restoring Conduction in Mechanical Spinal Cord Injury in Rat

Myelin damage is a hallmark of spinal cord injury (SCI), and potassium channel blocker (PCB) is proven effective to restore axonal conduction and regain neurological function. Aiming to improve this therapy beyond the U.S. Food and Drug Administration-approved 4-aminopyridine (4-AP), we have developed multiple new PCBs, with 4-aminopyridine-3-methanol (4-AP-3-MeOH) being the most potent and effective. The current study evaluated two PCBs, 4-AP-3-MeOH and 4-AP, in parallel in both ex vivo and in vivo rat mechanical SCI models. Specifically, 4-AP-3-MeOH induced significantly greater augmentation of axonal conduction than 4-AP in both acute and chronic injury. 4-AP-3-MeOH had no negative influence on the electrical responsiveness of rescued axons whereas 4-AP-recruited axons displayed a reduced ability to follow multiple stimuli. In addition, 4-AP-3-MeOH can be applied intraperitoneally at a dose that is at least 5 times higher (5 mg/kg) than that of 4-AP (1 mg/kg) in vivo. Further, 5 mg/kg of 4-AP-3-MeOH significantly improved motor function whereas both 4-AP-3-MeOH (1 and 5 mg/kg) and, to a lesser degree, 4-AP (1 mg/kg) alleviated neuropathic pain-like behavior when applied in rats 2 weeks post-SCI. Based on these and other findings, we conclude that 4-AP-3-MeOH appears to be more advantageous over 4-AP in restoring axonal conduction because of the combination of its higher efficacy in enhancing the amplitude of compound action potential, lesser negative effect on axonal responsiveness to multiple stimuli, and wider therapeutic range in both ex vivo and in vivo application. As a result, 4-AP-3-MeOH has emerged as a strong alternative to 4-AP that can complement the effectiveness, and even partially overcome the shortcomings, of 4-AP in the treatment of neurotrauma and degenerative diseases where myelin damage is implicated.

Primary Spinal OPC Culture System from Adult Zebrafish to Study Oligodendrocyte Differentiation In Vitro

Endogenous oligodendrocyte progenitor cells (OPCs) are a promising target to improve functional recovery after spinal cord injury (SCI) by remyelinating denuded, and therefore vulnerable, axons. Demyelination is the result of a primary insult and secondary injury, leading to conduction blocks and long-term degeneration of the axons, which subsequently can lead to the loss of their neurons. In response to SCI, dormant OPCs can be activated and subsequently start to proliferate and differentiate into mature myelinating oligodendrocytes (OLs). Therefore, researchers strive to control OPC responses, and utilize small molecule screening approaches in order to identify mechanisms of OPC activation, proliferation, migration and differentiation. In zebrafish, OPCs remyelinate axons of the optic tract after lysophosphatidylcholine (LPC)-induced demyelination back to full thickness myelin sheaths. In contrast to zebrafish, mammalian OPCs are highly vulnerable to excitotoxic stress, a cause of secondary injury, and remyelination remains insufficient. Generally, injury induced remyelination leads to shorter internodes and thinner myelin sheaths in mammals. In this study, we show that myelin sheaths are lost early after a complete spinal transection injury, but are re-established within 14 days after lesion. We introduce a novel, easy-to-use, inexpensive and highly reproducible OPC culture system based on dormant spinal OPCs from adult zebrafish that enables in vitro analysis. Zebrafish OPCs are robust, can easily be purified with high viability and taken into cell culture. This method enables to examine why zebrafish OPCs remyelinate better than their mammalian counterparts, identify cell intrinsic responses, which could lead to pro-proliferating or pro-differentiating strategies, and to test small molecule approaches. In this methodology paper, we show efficient isolation of OPCs from adult zebrafish spinal cord and describe culture conditions that enable analysis up to 10 days in vitro. Finally, we demonstrate that zebrafish OPCs differentiate into Myelin Basic Protein (MBP)-expressing OLs when co-cultured with human motor neurons differentiated from induced pluripotent stem cells (iPSCs). This shows that the basic mechanisms of oligodendrocyte differentiation are conserved across species and that understanding the regulation of zebrafish OPCs can contribute to the development of new treatments to human diseases.

The effect of Fampridine-SR on cognitive fatigue in a randomized double-blind crossover trial in patients with MS

BACKGROUND

Cognitive fatigue (CF) is a common complaint in persons with MS (PwMS). Fampridine-SR improves ambulation, fatigue and endurance, due to enhancing action potential formation by blocking potassium channels in demyelinated axons. Thus, through this same mechanism, it is hypothesized that Fampridine-SR could improve CF.

OBJECTIVE

To determine if Fampridine-SR objectively improves CF in PwMS.

METHODS

Sixty PwMS of any type with CF, defined as 3 or less correct responses when comparing the last third to the first third on the Paced Auditory Serial Addition Test (PASAT), were recruited from a tertiary care MS clinic in London (ON) Canada. Subjects also had to be between 18 and 64 years of age, inclusive, not had a relapse in the last 60 days or corticosteroids in the last 30 days, EDSS 0.0-7.0, and no other diagnosis that could cause cognitive impairment. A randomized double blind crossover design was used: subjects were randomized to either placebo or Fampridine-SR for 4 weeks, then after at least a one week washout, received the opposite treatment. Subjects were assessed before and after each treatment block. The primary outcome was the PASAT CF score after treatment with Fampridine-SR compared to placebo. T-tests and chi-square were used to compare demographics between the two groups (placebo-Fampridine-SR vs. Fampridine SR-placebo). Treatment effects were assessed using factorial ANOVA, with treatment (Fampridine-SR vs. placebo) and time (before and after treatment) as within-subject variables.

RESULTS

Of the 60 subjects randomized, 48 completed the study; three were removed due to an adverse event while in the treatment arm (one due to relapse while on placebo, one due to urinary retention and one due to dizziness and headache while on Fampridine-SR). The subjects had a mean age of 46.5±10.0 years, education of 13.6±1.9 years, and were diagnosed with MS 10.6±9.6 years ago. The majority were female (46, 76.7%), had relapsing remitting MS (41, 68.3%) with median EDSS of 3.5 (range 1.0-7.0). There were no significant demographic differences between the two groups. The treatment x time interaction within the factorial ANOVA on PASAT CF scores was statistically significant, F(1, 45)=8.28, p=0.006, suggesting there is a difference between the treatments (placebo vs. Fampridine-SR), over the course of the study. An evaluation of the mean scores suggests, however, that subjects saw a greater improvement when they were given the placebo, than when they were given the active medication. Similarly, individuals showed a greater increase in their information processing speed (as measured by the PASAT) over the course of treatment when they were given the placebo, as compared with the active medication F(1,45)=4.17, p=0.047.

CONCLUSION

Although this small pilot study does not suggest that Fampridine-SR results in a statistically significant improvement of CF in MS patients, as compared to placebo, individuals demonstrated an improvement in both information processing speed and CF, suggesting further studies are warranted.

Acrolein-mediated conduction loss is partially restored by K⁺ channel blockers

Acrolein-mediated myelin damage is thought to be a critical mechanism leading to conduction failure following neurotrauma and neurodegenerative diseases. The exposure and activation of juxtaparanodal voltage-gated K(+) channels due to myelin damage leads to conduction block, and K(+) channel blockers have long been studied as a means for restoring axonal conduction in spinal cord injury (SCI) and multiple sclerosis (MS). In this study, we have found that 100 μM K(+) channel blockers 4-aminopyridine-3-methanol (4-AP-3-MeOH), and to a lesser degree 4-aminopyridine (4-AP), can significantly restore compound action potential (CAP) conduction in spinal cord tissue following acrolein-mediated myelin damage using a well-established ex vivo SCI model. In addition, 4-AP-3-MeOH can effectively restore CAP conduction in acrolein-damaged axons with a range of concentrations from 0.1 to 100 μM. We have also shown that while both compounds at 100 μM showed no preference of small- and large-caliber axons when restoring CAP conduction, 4-AP-3-MeOH, unlike 4-AP, is able to augment CAP amplitude while causing little change in axonal responsiveness measured in refractory periods and response to repetitive stimuli. In a prior study, we show that 4-AP-3-MeOH was able to functionally rescue mechanically injured axons. In this investigation, we conclude that 4-AP-3-MeOH is an effective K(+) channel blocker in restoring axonal conduction following both primary (physical) and secondary (chemical) insults. These findings also suggest that 4-AP-3-MeOH is a viable alternative of 4-AP for treating myelin damage and improving function following central nervous system trauma and neurodegenerative diseases.

Molecular mechanisms of acrolein-mediated myelin destruction in CNS trauma and disease

Myelin is a critical component of the nervous system facilitating efficient propagation of electrical signals and thus communication between the central and peripheral nervous systems and the organ systems that they innervate throughout the body. In instances of neurotrauma and neurodegenerative disease, injury to myelin is a prominent pathological feature responsible for conduction deficits, and leaves axons vulnerable to damage from noxious compounds. Although the pathological mechanisms underlying myelin loss have yet to be fully characterized, oxidative stress (OS) appears to play a prominent role. Specifically, acrolein, a neurotoxic aldehyde that is both a product and an instigator of OS, has been observed in studies to elicit demyelination through calcium-independent and -dependent mechanisms and also by affecting glutamate uptake and promoting excitotoxicity. Furthermore, pharmacological scavenging of acrolein has demonstrated a neuroprotective effect in animal disease models, by conserving myelin's structural integrity and alleviating functional deficits. This evidence indicates that acrolein may be a key culprit of myelin damage while acrolein scavenging could potentially be a promising therapeutic approach for patients suffering from nervous system trauma and disease.

Development of dalfampridine, a novel pharmacologic approach for treating walking impairment in multiple sclerosis

Walking impairment is a clinical hallmark of multiple sclerosis (MS). Dalfampridine-ER, an extended-release formulation of dalfampridine (also known by its chemical name, 4-aminopyridine, and its international nonproprietary name, fampridine), was developed to maintain drug plasma levels within a narrow therapeutic window, and assessed for its ability to improve walking in MS. The putative mechanism of action of dalfampridine-ER is restoration of axonal conduction via blockade of the potassium channels that become exposed during axonal demyelination. Two pivotal phase III clinical trials demonstrated that dalfampridine-ER 10-mg tablets administered twice daily improved walking speed and patient-reported perceptions of walking in some patients. Dalfampridine-ER was generally well tolerated, and, at the approved dose, risk of seizure was neither elevated relative to placebo nor higher than the rate in the MS population. Dalfampridine-ER (AMPYRA®) was approved in the United States for the treatment of walking in patients with MS as demonstrated by an increase in walking speed. The use of the dalfampridine-ER is contraindicated in patients with a history of seizure. It is the first pharmacologic therapy for this indication and has been incorporated into clinical management of MS.

4-Aminopyridine for symptomatic treatment of multiple sclerosis: a systematic review

This systematic review summarizes the existing evidence on the effect of 4-aminopyridine (4-AP) as a symptomatic treatment of decreased walking capacity in patients with multiple sclerosis (MS) when administered as an immediate release compound and a slow release compound. It summarizes existing evidence on the basic mechanisms of 4-AP from experimental studies and evidence on the clinical use of the compound. A systematic literature search was conducted of the following databases: PubMed and EMBASE. Thirty-five studies were included in the review divided into 16 experimental studies, two clinical studies with paraclinical endpoints and 17 clinical studies with clinical endpoints. Animal studies show that 4-AP can improve impulse conduction through demyelinated lesions. In patients with MS this translates into improved walking speed and muscle strength of the lower extremities in a subset of patients at a level that is often of clinical relevance. Phase III trials demonstrate approximately 25% increase in walking speed in roughly 40% and improved muscle strength in the lower extremities. Furthermore, 4-AP might have an effect on other domains such as cognition, upper extremity function and bowel and bladder, but this warrants further investigation. Side effects are mainly mild to moderate, consisting primarily of paraesthesia, dizziness, nausea/vomiting, falls/balance disorders, insomnia, urinary tract infections and asthenia. Side effects are worse when administered intravenously and when administered as an immediate release compound. Serious adverse events are rarely seen in the marketed clinical dosages. In conclusion, 4-AP is easy and safe to use. Slow release 4-AP shows more robust clinical effects and a more beneficial side-effect profile than immediate release 4-AP.

Targeting ion channels for the treatment of autoimmune neuroinflammation

Pharmacological targeting of ion channels has long been recognized as an attractive strategy for the treatment of various diseases. Multiple sclerosis (MS) is an autoimmune disorder of the central nervous system with a prominent neurodegenerative component. A multitude of different cell types are involved in the complex pathophysiology of this disorder, including cells of the immune system (e.g. T and B lymphocytes and microglia), the neurovascular unit (e.g. endothelial cells and astrocytes) and the central nervous system (e.g. astrocytes and neurons). The pleiotropic expression and function of ion channels gives rise to the attractive opportunity of targeting different players and pathophysiological aspects of MS by the modulation of ion channel function in a cell-type and context-specific manner. We discuss the emerging knowledge about ion channels in the context of autoimmune neuroinflammation. While some pharmacological targets are at the edge of clinical translation, others have only recently been discovered and are still under investigation. Special focus is given to those candidates that could be attractive novel targets for future therapeutic approaches in neuroimmune autoinflammation.

4-Aminopyridine ameliorates mobility but not disease course in an animal model of multiple sclerosis

Neuropathological changes following demyelination in multiple sclerosis (MS) lead to a reorganization of axolemmal channels that causes conduction changes including conduction failure. Pharmacological modulation of voltage-sensitive potassium channels (K(V)) has been found to improve conduction in experimentally induced demyelination and produces symptomatic improvement in MS patients. Here we used an animal model of autoimmune inflammatory neurodegeneration, namely experimental autoimmune encephalomyelitis (EAE), to test the influence of the K(V)-inhibitor 4-aminopyridine (4-AP) on various disease and immune parameters as well as mobility in MOG₃₅₋₅₅ immunized C57Bl/6 mice. We challenged the hypothesis that 4-AP exerts relevant immunomodulatory or neuroprotective properties. Neither prophylactic nor therapeutic treatment with 4-AP altered disease incidence or disease course of EAE. Histopathological signs of demyelination and neuronal damage as well as MRI imaging of brain volume changes were unaltered. While application of 4-AP significantly reduced the standing outward current of stimulated CD4(+) T cells compared to controls, it failed to impact intracellular calcium concentrations in these cells. Compatibly, KV channel inhibition neither influenced CD4(+) T cell effector functions (proliferation, IL17 or IFNγ production). Importantly however, despite equal disease severity scores 4-AP treated animals showed improved mobility as assessed by 2 independent methods, 1) foot print and 2) rotarod analysis (0.332 ± 0.03, n=7 versus 0.399 ± 0.08, n=14, p<0.001, respectively). Our data suggest that 4-AP while having no apparent immunomodulatory or direct neuroprotective effects, significantly ameliorates conduction abnormalities thereby improving gait and coordination. Improvement of mobility in this experimental model supports trial data and clinical experience with 4-AP in the symptomatic treatment of MS.

Understanding secondary injury

Secondary injury is a term applied to the destructive and self-propagating biological changes in cells and tissues that lead to their dysfunction or death over hours to weeks after the initial insult (the "primary injury"). In most contexts, the initial injury is usually mechanical. The more destructive phase of secondary injury is, however, more responsible for cell death and functional deficits. This subject is described and reviewed differently in the literature. To biomedical researchers, systemic and tissue-level changes such as hemorrhage, edema, and ischemia usually define this subject. To cell and molecular biologists, "secondary injury" refers to a series of predominately molecular events and an increasingly restricted set of aberrant biochemical pathways and products. These biochemical and ionic changes are seen to lead to death of the initially compromised cells and "healthy" cells nearby through necrosis or apoptosis. This latter process is called "bystander damage." These viewpoints have largely dominated the recent literature, especially in studies of the central nervous system (CNS), often without attempts to place the molecular events in the context of progressive systemic and tissue-level changes. Here we provide a more comprehensive and inclusive discussion of this topic.

Spinal cord injury clinical trials translational process, review of past and proposed acute trials with reference to recommended trial guidelines

Within the past few years there has been increasing interest in the translation of experimental therapeutic interventions to improve functional outcomes after spinal cord injury (SCI). The number of reported successes using preclinical animal models has been substantial and this has encouraged the development of several clinical trial programs. We will briefly discuss a desired process for the translation of preclinical therapeutic discoveries, as well as the design and conduct of valid human SCI studies. Past SCI trials are examined and current ongoing human studies are outlined. We identify some of the confounding factors that can influence the accurate interpretation of study outcomes. The discussion here will be restricted to treatment strategies that involve drug administration and cell transplants, not that these are currently the most beneficial treatments, but cell transplants are already being offered to patients without completing a valid clinical trial program.

Acrolein-mediated injury in nervous system trauma and diseases

Acrolein, an α,β-unsaturated aldehyde, is a ubiquitous pollutant that is also produced endogenously through lipid peroxidation. This compound is hundreds of times more reactive than other aldehydes such as 4-hydroxynonenal, is produced at much higher concentrations, and persists in solution for much longer than better known free radicals. It has been implicated in disease states known to involve chronic oxidative stress, particularly spinal cord injury and multiple sclerosis. Acrolein may overwhelm the anti-oxidative systems of any cell by depleting glutathione reserves, preventing glutathione regeneration, and inactivating protective enzymes. On the cellular level, acrolein exposure can cause membrane damage, mitochondrial dysfunction, and myelin disruption. Such pathologies can be exacerbated by increased concentrations or duration of exposure, and can occur in normal tissue incubated with injured spinal cord, showing that acrolein can act as a diffusive agent, spreading secondary injury. Several chemical species are capable of binding and inactivating acrolein. Hydralazine in particular can reduce acrolein concentrations and inhibit acrolein-mediated pathologies in vivo. Acrolein scavenging appears to be a novel effective treatment, which is primed for rapid translation to the clinic.

Treatment of walking impairment in multiple sclerosis with dalfampridine

Potassium channel blockade has long been considered a potential therapeutic strategy for treatment of multiple sclerosis (MS) based on the pathophysiology of demyelinated axons. Dalfampridine, which is also known as fampridine or 4-aminopyridine (4-AP), is the potassium channel blocker that has been studied most extensively in MS and other demyelinating neurologic disorders. An extended-release formulation of dalfampridine was recently approved by the US Food and Drug Administration to improve walking in patients with MS. In randomized, double-blind, placebo-controlled trials, with dalfampridine extended release tablets 10 mg taken twice daily, about 12 h apart, walking speed was improved in approximately one-third of treated patients; in these patients, average walking speed on therapy was about 25% above baseline. This improvement was clinically meaningful as assessed by concurrent measurement of patient-reported severity of walking-related disability. Dalfampridine extended release tablets were generally well tolerated, with a range of adverse effects that appear to be related to increases in central nervous system excitation. There is a dose-dependent increase in the occurrence of seizures at doses higher than the recommended 10 mg twice daily.

Dalfampridine: a brief review of its mechanism of action and efficacy as a treatment to improve walking in patients with multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) can cause progressive walking impairment that contributes to disability, loss of independence, and reduced quality of life. Dalfampridine (4-aminopyridine), a voltage-dependent potassium channel blocker, has been shown to improve walking in patients with MS, as demonstrated by an increase in walking speed.

OBJECTIVE

To summarize knowledge about the mechanism of action of dalfampridine in the context of clinical evidence of walking improvement in MS patients.

METHODS

Although this was not a systematic review, which is the primary limitation of this study, searches of PubMed were performed using relevant search terms to identify studies that examined the mechanism of action related to MS and its effects in patients with MS in clinical trials.

RESULTS

Voltage-gated potassium channels represent a family of related proteins that span cell membranes, open and close in response to changes in the transmembrane potential, and help regulate ionic potassium currents. Action potential conduction deficits in demyelinated axons result in part from the exposure after demyelination of the paranodal and internodal potassium channels that are distributed in the axonal membrane. This exposure leads to abnormal currents across the axonal membrane that can slow action potential conduction, result in conduction failure, or affect the axon's capacity for repetitive discharge. While dalfampridine is a broad-spectrum blocker of voltage-dependent potassium channels at millimolar concentrations, studies have shown improvement in action potential conduction in demyelinated axons at concentrations as low as 1 μM, and therapeutic plasma concentrations (associated with improved walking) are in the range of 0.25 µM. However, no specific potassium channel subtype has yet been characterized with significant sensitivity to dalfampridine in this range, and the effects of the drug at this low concentration appear to be quite selective. Improved conduction translates into clinical benefit as measured by objectively and subjectively assessed walking relative to placebo. Such improvements were observed in approximately one third of patients treated with an extended-release formulation of dalfampridine in clinical trials. These patients who responded to dalfampridine had an average increase in walking speed of approximately 25%, and greater improvements than nonresponders on a self-reported subjective measure of walking.

CONCLUSIONS

The extended-release formulation of dalfampridine has been shown in clinical trials to improve walking speed in approximately one third of MS patients with ambulatory impairment. The putative mechanism of action of dalfampridine is restoration of action potential conduction via blockade of an as yet uncharacterized subset of potassium channels in demyelinated axons.

Dalfampridine in multiple sclerosis: from symptomatic treatment to immunomodulation

Multiple sclerosis (MS) is a neurodegenerative disease that is deemed to affect more than 2.1 million people worldwide, and for which there is no cure. Early symptoms of MS are believed to result from axonal demyelination leading to slowing or blockade of impulse conduction. The blockade of K+ channels has been proven to improve conduction deficiencies secondary to demyelination in patients with MS. Dalfampridine is a K+ channel blocker that was recently approved by FDA for the symptomatic treatment of ambulation hardship in MS. Understanding the mechanisms by which Dalfampridine exerts its therapeutic effects is a complex issue as it blocks a wide variety of K+ channels that are distributed across multiple cell types in the nervous system but also in the immune system, and because of their molecular identities remaining unknown. This review describes Dalfampridine potential roles at the cellular and molecular levels in MS pathogenesis.

Potassium channel blockers as an effective treatment to restore impulse conduction in injured axons

Most axons in the vertebral central nervous system are myelinated by oligodendrocytes. Myelin protects and insulates neuronal processes, enabling the fast, saltatory conduction unique to myelinated axons. Myelin disruption resulting from trauma and biochemical reaction is a common pathological event in spinal cord injury and chronic neurodegenerative diseases. Myelin damage-induced axonal conduction block is considered to be a significant contributor to the devastating neurological deficits resulting from trauma and illness. Potassium channels are believed to play an important role in axonal conduction failure in spinal cord injury and multiple sclerosis. Myelin damage has been shown to unmask potassium channels, creating aberrant potassium currents that inhibit conduction. Potassium channel blockade reduces this ionic leakage and improves conduction. The present review was mainly focused on the development of this technique of restoring axonal conduction and neurological function of demyelinated axons. The drug 4-aminopyridine has recently shown clinical success in treating multiple sclerosis symptoms. Further translational research has also identified several novel potassium channel blockers that may prove effective in restoring axonal conduction.

High doses of 4-aminopyridine improve functionality in chronic complete spinal cord injury patients with MRI evidence of cord continuity

BACKGROUND AND AIMS

Many patients with complete spinal cord injury (SCI) exhibit demyelinated and poorly myelinated nerve fibers traversing the lesion site. Conventional doses of 4-aminopyridine (4-AP, 30 mg/day) have shown to provide no or minor functional improvement in these patients. We undertook this study to test the functional effect of high doses of 4-AP on patients with chronic complete SCI with cord continuity at the site of injury demonstrated by magnetic resonance imaging.

METHODS

Fourteen patients were included in a double-blind, randomized, placebo-controlled trial followed by an open label long-term follow-up. Initially, patients received 4-AP or placebo orally, with 4-AP being increased gradually (5 mg/week) to reach 30 mg/day. For long-term treatment, 4-AP was increased 10 mg periodically according to negative electroencephalogram and blood test abnormalities and minor adverse reactions. Pre-treatment, 12 and 24 weeks of the controlled trial, and 6 and 12 months of open trial evaluations, or with the highest doses reached were obtained.

RESULTS

Three of 12 patients were able to walk with the assistance of orthopedic devices, 1/12 became incomplete (AIS B), 7/12 improved their somatosensory evoked potentials, 5/12 had sensation and control of bladder and anal sphincters, and 4/9 male patients had psychogenic erection.

CONCLUSIONS

Positive changes were seen mainly in patients with cyst (4/5) or atrophy (3/5) of the injury site. Two patients withdrew from the study: one had seizures and one had intolerant adverse reactions. We conclude that high doses of 4-AP in the studied population produced several functional benefits not observed using lower doses.

Ion channel blockers and spinal cord injury

The activation of a delayed secondary cascade of unsatisfactory cellular and molecular responses after a primary mechanical insult to the spinal cord causes the progressive degeneration of this structure. Disturbance of ionic homeostasis is part of the secondary injury process and plays an integral role in the early stage of spinal cord injury (SCI). The secondary pathology of SCI is complex and involves disturbance of the homeostasis of K(+) , Na(+) , and Ca(2+) . The effect of ion channel blockers on chronic SCI has also been proved. In this Mini-Review, we provide a comprehensive summary of the effects of ion channel blockers on the natural responses after SCI. Combination therapy is based on the roles of ions and disturbance of their homeostasis in SCI. The effects of ion channel blockers suggest that they have potential in the treatment of SCI, although the complexity of their effects shows that further knowledge is needed before they can be applied clinically.

Real-time CARS imaging reveals a calpain-dependent pathway for paranodal myelin retraction during high-frequency stimulation

High-frequency electrical stimulation is becoming a promising therapy for neurological disorders, however the response of the central nervous system to stimulation remains poorly understood. The current work investigates the response of myelin to electrical stimulation by laser-scanning coherent anti-Stokes Raman scattering (CARS) imaging of myelin in live spinal tissues in real time. Paranodal myelin retraction at the nodes of Ranvier was observed during 200 Hz electrical stimulation. Retraction was seen to begin minutes after the onset of stimulation and continue for up to 10 min after stimulation was ceased, but was found to reverse after a 2 h recovery period. The myelin retraction resulted in exposure of Kv 1.2 potassium channels visualized by immunofluorescence. Accordingly, treating the stimulated tissue with a potassium channel blocker, 4-aminopyridine, led to the appearance of a shoulder peak in the compound action potential curve. Label-free CARS imaging of myelin coupled with multiphoton fluorescence imaging of immuno-labeled proteins at the nodes of Ranvier revealed that high-frequency stimulation induced paranodal myelin retraction via pathologic calcium influx into axons, calpain activation, and cytoskeleton degradation through spectrin break-down.

Potassium channel blocker, 4-aminopyridine-3-methanol, restores axonal conduction in spinal cord of an animal model of multiple sclerosis

Multiple sclerosis (MS) is a severely debilitating neurodegenerative diseases marked by progressive demyelination and axonal degeneration in the CNS. Although inflammation is the major pathology of MS, the mechanism by which it occurs is not completely clear. The primary symptoms of MS are movement difficulties caused by conduction block resulting from the demyelination of axons. The possible mechanism of functional loss is believed to be the exposure of potassium channels and increase of outward current leading to conduction failure. 4-Aminopyridine (4-AP), a well-known potassium channel blocker, has been shown to enhance conduction in injured and demyelinated axons. However, 4-AP has a narrow therapeutic range in clinical application. Recently, we developed a new fast potassium channel blocker, 4-aminopyridine-3-methanol (4-AP-3-MeOH). This novel 4-AP derivative is capable of restoring impulse conduction in ex vivo injured spinal cord without compromising the ability of axons to follow multiple stimuli. In the current study, we investigated whether 4-AP-3-MeOH can enhance impulse conduction in an animal model of MS. Our results showed that 4-AP-3-MeOH can significantly increase axonal conduction in ex vivo experimental autoimmune encephalomyelitis mouse spinal cord.

Human neural stem cells differentiate and promote locomotor recovery in an early chronic spinal cord injury NOD-scid mouse model

Background

Traumatic spinal cord injury (SCI) results in partial or complete paralysis and is characterized by a loss of neurons and oligodendrocytes, axonal injury, and demyelination/dysmyelination of spared axons. Approximately 1,250,000 individuals have chronic SCI in the U.S.; therefore treatment in the chronic stages is highly clinically relevant. Human neural stem cells (hCNS-SCns) were prospectively isolated based on fluorescence-activated cell sorting for a CD133⁺ and CD24^−/lo population from fetal brain, grown as neurospheres, and lineage restricted to generate neurons, oligodendrocytes and astrocytes. hCNS-SCns have recently been transplanted sub-acutely following spinal cord injury and found to promote improved locomotor recovery. We tested the ability of hCNS-SCns transplanted 30 days post SCI to survive, differentiate, migrate, and promote improved locomotor recovery.

Methods and Findings

hCNS-SCns were transplanted into immunodeficient NOD-scid mice 30 days post spinal cord contusion injury. hCNS-SCns transplanted mice demonstrated significantly improved locomotor recovery compared to vehicle controls using open field locomotor testing and CatWalk gait analysis. Transplanted hCNS-SCns exhibited long-term engraftment, migration, limited proliferation, and differentiation predominantly to oligodendrocytes and neurons. Astrocytic differentiation was rare and mice did not exhibit mechanical allodynia. Furthermore, differentiated hCNS-SCns integrated with the host as demonstrated by co-localization of human cytoplasm with discrete staining for the paranodal marker contactin-associated protein.

Conclusions

The results suggest that hCNS-SCns are capable of surviving, differentiating, and promoting improved locomotor recovery when transplanted into an early chronic injury microenvironment. These data suggest that hCNS-SCns transplantation has efficacy in an early chronic SCI setting and thus expands the “window of opportunity” for intervention.

Novel Potassium Channel Blocker, 4-AP-3-MeOH, Inhibits Fast Potassium Channels and Restores Axonal Conduction in Injured Guinea Pig Spinal Cord White Matter

We have demonstrated that 4-aminopyridine-3-methanol (4-AP-3-MeOH), a 4-aminopyridine derivative, significantly restores axonal conduction in stretched spinal cord white-matter strips and shows no preference in restoring large and small axons. This compound is 10 times more potent when compared with 4-AP and other derivatives in restoring axonal conduction. Unlike 4-AP, 4-AP-3-MeOH can restore axonal conduction without changing axonal electrophysiological properties. In addition, we also have confirmed that 4-AP-3-MeOH is indeed an effective blocker of IA based on patch-clamp studies using guinea pig dorsal root ganglia cells. Furthermore, we have also provided the critical evidence to confirm the unmasking of potassium channels following mechanical injury. Taken together, our data further supports and implicates the role of potassium channels in conduction loss and its therapeutic value as an effective target for intervention to restore function in spinal cord trauma. Furthermore, due to its high potency and possible low side effect of impacting electrophysiological properties, 4-AP-3-MeOH is perhaps the optimal choice in reversing conduction block in spinal cord injury compared with other derivatives previously reported from this group.

Glutamate excitotoxicity inflicts paranodal myelin splitting and retraction

Paranodal myelin damage is observed in white matter injury. However the culprit for such damage remains unknown. By coherent anti-Stokes Raman scattering imaging of myelin sheath in fresh tissues with sub-micron resolution, we observed significant paranodal myelin splitting and retraction following glutamate application both ex vivo and in vivo. Multimodal multiphoton imaging further showed that glutamate application broke axo-glial junctions and exposed juxtaparanodal K⁺ channels, resulting in axonal conduction deficit that was demonstrated by compound action potential measurements. The use of 4-aminopyridine, a broad-spectrum K⁺ channel blocker, effectively recovered both the amplitude and width of compound action potentials. Using CARS imaging as a quantitative readout of nodal length to diameter ratio, the same kind of paranodal myelin retraction was observed with applications of Ca²⁺ ionophore A23187. Moreover, exclusion of Ca²⁺ from the medium or application of calpain inhibitor abolished paranodal myelin retraction during glutamate exposure. Examinations of glutamate receptor agonists and antagonists further showed that the paranodal myelin damage was mediated by NMDA and kainate receptors. These results suggest that an increased level of glutamate in diseased white matter could impair paranodal myelin through receptor-mediated Ca²⁺ overloading and subsequent calpain activation.

N-(4-pyridyl) methyl carbamate inhibits fast potassium currents in guinea pig dorsal root ganglion cells

Axonal demyelination is a critical pathological phenomenon associated with spinal cord injury and multiple sclerosis (MS). Previous studies demonstrated that 4-Aminopyridine, a fast potassium channel blocker, enhances impulse conduction on damaged and/or demyelinated axons, allowing for functional recovery in spinal cord injuries and MS, but with severe therapeutic limitations. To continue to explore the therapeutic value of blocking fast potassium channels while circumventing the side effects of 4-AP, we have developed three novel 4-AP derivatives that enhance impulse conduction in spinal cord trauma. In the current study, we have shown that one of these three derivatives, N-(4-pyridyl) methyl carbamates (MC), significantly inhibits a fast, I(A) like potassium current in guinea pig dorsal root ganglion cells in a whole cell patch clamp configuration. This inhibition of I(A) likely plays a critical role in MC's ability to restore conduction in mechanically injured spinal cord axons and may present a viable alternative to 4-AP for individuals with spinal cord injury or MS. From this, compounds with greater efficacy and perhaps less side effects will likely emerge in the near future, which will greatly enhance the functional restoration and lessen the suffering of SCI and MS patients.

The distribution of tissue damage in the spinal cord is influenced by the contusion velocity

STUDY DESIGN

A rat model of thoracic spinal cord contusion was used to examine the effect of velocity on the primary injury.

OBJECTIVES

The overall objective of this study was to determine the effect of the contusion velocity (slow vs. fast) on damage to the spinal cord immediately following mechanical injury. Secondary objectives were to demarcate between damage in the gray and white matters and to observe damage to the mechanical elements of the neurons (i.e., neurofilaments).

SUMMARY OF BACKGROUND DATA

Although studies have explored the effect of impact velocity on spinal cord damage and functional deficits, no study has addressed regional tissue damage of the primary injury (e.g., between the gray and white matter) as a function of velocity.

METHODS

A modified Spinal Cord Injury Research System generated 1 mm contusions in 24 male, Sprague-Dawley rats (210-320 g) at T10, using slow (3 mm/s) and fast (300 mm/s) velocities. The primary lesion (<2 minutes postinjury) was assessed using hematoxylin and eosin staining for hemorrhage volume and immunostaining for nonphosphorylated heavy neurofilament damage.

RESULTS

The volume of hemorrhage in the white matter was significantly increased following fast impact (fast = 0.61 mm3, slow = 0.24 mm3, P = 0.013) whereas the total hemorrhage volume (fast = 1.51 mm, slow = 1.21 mm, P = 0.22) showed no effect. Complete axonal disruption was evident in the fast injury group around the injury epicenter. A significant increase in nonphosphorylated neurofilament staining (P = 0.013) was observed for fast impacts. Hemorrhage in the gray matter was similar between the slow and fast groups, but an increase in neurofilament dephosphorylation was observed in the gray matter following fast contusion (P = 0.03).

CONCLUSION

We conclude that contusion velocity has an effect on the magnitude of injury within the white matter during spinal cord injury and the amount of neuronal damage in the gray matter. The results of this study demonstrate the importance of including high impact velocity as a variable in models of spinal cord injury.

Control of demyelination for recovery of spinal cord injury

Since loss of oligodendrocytes and consequent demyelination of spared axons severely impair the functional recovery of injured spinal cord, it is reasonably expected that the reduction of oligodendroglial death and enhanced remyelination of demyelinated axons will have a therapeutic potential to treat spinal cord injury. Amelioration of axonal myelination in the injured spinal cord is valuable for recovery of the neural function of incompletely injured patients. Here, this article presents an overview about the pathophysiology and mechanism of axonal demyelination in spinal cord injury and discusses its therapeutic significance in the treatment of spinal cord injury. Moreover, it further introduces the recent strategies to improve the axonal myeliantion to facilitate functional recovery of spinal cord injury.

Carbon monoxide-releasing molecule tricarbonyldichlororuthenium (II) dimer induces concentration-dependent alterations in the electrophysiological properties of axons in mammalian spinal cord

Traumatic spinal cord injury (SCI) typically involves intraparenchymal hemorrhage and a cascade of inflammatory and cytotoxic processes leading to tissue necrosis and apoptosis. A consequence of the hemorrhage is the accumulation of deoxygenated heme proximal and distal to the epicenter of the lesion. The heme oxygenase (HO) system is an endogenous heme degradation system and is upregulated following neurotrauma. The breakdown of heme via HO activity yields the byproducts carbon monoxide (CO), biliverdin, and iron. CO has documented neuromodulatory properties; however, the effects of elevated concentrations of CO on axonal conduction in the spinal cord have not previously been studied. The present study tested the hypothesis that CO causes alterations in the electrophysiological properties of axons within the isolated guinea-pig spinal cord. Ex vivo spinal cord preparations were exposed to 100, 500, and 1000 microM concentrations of the carbon monoxide-releasing molecule (CORM) 2 for 30 min in a double sucrose gap electrophysiological recording system and the compound action potential (CAP) and membrane potential (CMP) were recorded continuously during pretreatment, CORM-2 treatment, and washout (30 min) with Krebs' solution. CAP amplitude and area were significantly (P<0.05) reduced following treatment with 500 and 1000 microM CORM-2 and did not recover during washout. No effect on CMP was observed, however, stimulus-peak latency did increase significantly (P<0.05) following CORM-2 treatment at these concentrations, and a decrease in the amplitude of the second CAP elicited by paired-pulse stimulation was also evident at interpulse intervals of 2 and 4 ms. These results are consistent with a CO-induced alteration in axonal conduction, possibly attributable to modified Na+ channel conductance. They also identify a new mechanism by which post-traumatic hemorrhage contributes to the neurological deficits observed following SCI.

4-Aminopyridine derivatives enhance impulse conduction in guinea-pig spinal cord following traumatic injury

4-Aminopyridine (4-AP), a potassium channel blocker, is capable of restoring conduction in the injured spinal cord. However, the maximal tolerated level of 4-AP in humans is 100 times lower than the optimal dose in in vitro animal studies due to its substantially negative side effects. As an initial step toward the goal of identifying alternative potassium channel blockers with a similar ability of enhancing conduction and with fewer side effects, we have synthesized structurally distinct pyridine-based blockers. Using isolated guinea-pig spinal cord white matter and a double sucrose gap recording device, we have found three pyridine derivatives, N-(4-pyridyl)-methyl carbamate (100 microM), N-(4-pyridyl)-ethyl carbamate (100 microM), and N-(4-pyridyl)-tertbutyl (10 microM) can significantly enhance conduction in spinal cord white matter following stretch. Similar to 4-AP, the derivatives did not preferentially enhance conduction based on axonal caliber. Unlike 4-AP, the derivatives did not change the overall electrical responsiveness of axons to multiple stimuli, indicating the axons recruited by the derivatives conducted in a manner similar to healthy axons. These results demonstrate the ability of novel constructs to serve as an alternative to 4-AP for the purpose of reversing conduction deficits.

Gastric emptying effect by 4-aminopyridine in patients with chronic spinal cord injury

BACKGROUND

4-Aminopyridine (4-AP) given to patients with chronic spinal cord injury (SCI) has shown beneficial effects in some somatic and autonomic functions, although patients often develop dyspeptic symptoms. 4-AP is a potassium-channel blocker capable of altering gastro-pyloric functions as demonstrated experimentally. Our objective was to examine the influence of 4-AP treatment on gastric emptying in patients with chronic SCI.

METHODS

Gastric emptying was measured by the acetaminophen absorption test in 18 patients (9 with cervical and 9 with thoracic injury), and 9 healthy volunteers. Patients received increasing oral doses, 5 mg day(-1) of oral 4-AP (5-30 mg day(-1)), for 12 weeks. Patients were studied before and at the end of the last week of 4-AP treatment, whereas healthy volunteers (without 4-AP treatment) were studied only once. Whole blood samples of 2.5 mL were drawn at 0 (before 1 g of oral acetaminophen) and at 15, 30, 45, 60, 75, 90, 105 and 120 min postdose. Acetaminophen concentration in plasma was determined by high-pressure liquid chromatography.

RESULTS

Treatment with 4-AP significantly delayed stomach emptying in patients with chronic SCI, considering the significant decreasing of acetaminophen absorption (t paired test, p <0.05). This effect did not correlate either to the level or ASIA score of the injury (linear regression correlation analysis, r(2) = 0.003 and 0.015, respectively). No significant differences were observed by comparing data of patients before 4-AP treatment with healthy volunteers.

CONCLUSIONS

4-AP intake in patients with chronic spinal cord injury significantly slowed gastric emptying regardless of level and ASIA score of the injury.

Functional Changes in Genetically Dysmyelinated Spinal Cord Axons ofShivererMice: Role of Juxtaparanodal Kv1 Family K+Channels

Axonal dysfunction after spinal cord injury (SCI) and other types of neurotrauma is associated with demyelination and exposure of juxtaparanodal K+channels. In this study, sucrose gap electrophysiology using selective and nonselective K+channel blockers, confocal immunohistochemistry, and Western blotting were used to study the role of Kv1.1 and Kv1.2 K+channel subunits in dysmyelination-induced spinal cord axonal dysfunction in s hiverer mice, which lack the gene encoding myelin basic protein (MBP) and exhibit incomplete myelin sheath formation on CNS axons. The s hiverer spinal cord axons exhibited smaller amplitude of compound action potentials (CAPs), reduced conduction velocity, reduced excitability, and greater degree of high-frequency conduction failure. The “fast” K+channel blocker 4-aminopyridine, the toxin DTX-I, which targets the Kv1.1 and Kv1.2, but not DTX- K, which has higher selectivity for Kv1.1, increased the amplitude and area of CAPs of shiverer mice spinal cord axons but had insignificant effects in wild-type mice. Confocal immunohistochemistry showed that, unlike wild-type mice, which have a precise juxtaparanodal localization of the Kv1.l and Kv1.2 K+channel subunits, shiverer mouse axons displayed a dispersed distribution of these subunits along the internodes. In contrast, the Kv1.l and Kv1.2 subunits, Na+channels remained highly localized to the nodal regions. Western blotting showed an increased expression of Kv 1.1 and 1.2 in the shiverer mouse spinal cord. These results provide evidence that the neurological deficits associated with myelin deficiency reflect the altered distribution and expression of the K+channel subunits Kv1.l and Kv1.2 along the internodes of spinal cord axons associated with the biophysical consequences caused by alterations in the myelin sheaths.

Dose responses of three 4-aminopyridine derivatives on axonal conduction in spinal cord trauma

To explore novel treatments for enhancing conduction through traumatically injured spinal cord we have synthesized structurally distinct pyridine based compounds; N-(4-pyridyl) methyl carbamate, N-(4-pyridyl) ethyl carbamate, and N-(4-pyridyl) t-butyl carbamate. With the use of a double sucrose gap-recording chamber we perform a dose-response assay to examine the effects of these compounds on axonal conduction following an in vitro stretch injury. The tested compounds significantly enhanced axonal conduction to the stretch injured cord at 1 microM, a dose that coincides with the clinically relevant dose of potassium channel blocker 4-aminopyridine (4-AP). Methyl carbamate enhanced conduction maximally at 100 microM. This is also the most effective concentration of 4-AP in vitro. The other compounds ethyl carbamate and t-butyl carbamate enhanced conduction maximally at lower concentrations of 10 and 1 microM. At higher concentrations each of these compounds continued to increased CAP amplitude, however not significantly. Additionally, two of the compounds ethyl and t-butyl carbamate appear to have negative effects on CAP amplitude when administered at or beyond 100 microM. These compounds demonstrate the possibility that derivatives of 4-AP can retain the ability to increase axonal conduction in the injured spinal cord.

An Appraisal of Ongoing Experimental Procedures in Human Spinal Cord Injury

Clinicians and scientists in the field of spinal cord injury research and medicine are poised to begin translating promising new experimental findings into treatments for people. Advances in experimental regeneration research have led to several transplantation strategies that promote axonal regrowth and partial functional recovery in animal models of injury. In this review, we summarize current knowledge regarding various invasive experimental treatments that have been or are now being applied clinically. Various questions about the timeliness, safety, and benefits of the procedures are under discussion within the spinal cord injury (SCI) research community. We also describe guidelines for carrying out optimal clinical trials and efforts to establish specific international guidelines to translate preclinical treatment strategies into clinical trials in SCI. The clinical trial process and the role that clinical professionals have in advising individuals regarding participation in experimental procedures also is discussed.

Demyelination and Schwann cell responses adjacent to injury epicenter cavities following chronic human spinal cord injury

The natural history of post-traumatic demyelination and myelin repair in the human spinal cord is largely unknown and has remained a matter of speculation. A wealth of experimental studies indicate that mild to moderate contusive injuries to the mammalian spinal cord evolve into a cavity with a preserved rim of white matter in which a population of segmentally demyelinated axons persists. It is believed that such injured axons have abnormal conduction properties. Theoretically, such axons might show improved function if myelin repair occurred. Schwann cells can remyelinate axons affected by multiple sclerosis, but little evidence exists that such repair can occur spontaneously following traumatic human SCI. Therefore, it is important to determine if chronic demyelination is present following human spinal cord injury. There are no previous reports that have conclusively demonstrated demyelination in the human spinal cord following traumatic spinal cord injury using immunohistochemical techniques. Immunohistochemical methods were used to study the distribution of peripheral and central myelin proteins as well as axonal neurofilament at the injury epicenter in 13 postmortem chronically injured human spinal cords 1-22 years following injury. Of these seven could be assessed by our methods. We found that some axonal demyelination can be detected even a decade following human SCI and indirect evidence that invading Schwann cells contributed to restoration of myelin sheaths around some spinal axons.

Setting the stage for functional repair of spinal cord injuries: a cast of thousands

Here we review mechanisms and molecules that necessitate protection and oppose axonal growth in the injured spinal cord, representing not only a cast of villains but also a company of therapeutic targets, many of which have yet to be fully exploited. We next discuss recent progress in the fields of bridging, overcoming conduction block and rehabilitation after spinal cord injury (SCI), where several treatments in each category have entered the spotlight, and some are being tested clinically. Finally, studies that combine treatments targeting different aspects of SCI are reviewed. Although experiments applying some treatments in combination have been completed, auditions for each part in the much-sought combination therapy are ongoing, and performers must demonstrate robust anatomical regeneration and/or significant return of function in animal models before being considered for a lead role.

AIT-082 and methylprednisolone singly, but not in combination, enhance functional and histological improvement after acute spinal cord injury in rats

Extracellular non-adenine based purines are neuroprotective. Preliminary studies indicate that administration of the synthetic purine 4-[[3-(1,6 dihydro-6-oxo-9-purine-9-yl)-1-oxypropyl] amino] benzoic acid (AIT-082, leteprinim potassium) to rats immediately after acute spinal cord injury (SCI), improves functional outcome. The effects of potential new agents are often compared to methylprednisolone (MPSS). We evaluated the effects of AIT-082 and MPSS, separately and in combination, on the functional and morphological outcome of acute SCI in adult rats. After standardized T11-12 spinal cord compression rats were given intraperitoneally one of the following: vehicle (saline); MPSS (30 mg/kg or 60 mg/kg body weight, first dose 15 min after crush); AIT-082 (60 mg/kg body weight daily, first dose 15 min after crush); or AIT-082 plus MPSS. After 1, 3, or 21 days, the rats were perfused for histological analysis. AIT-082 administrations significantly reduced locomotor impairment from 121 days post-operatively. At 1 and 3 days post injury, AIT-082-treatment reduced tissue swelling, tissue loss and astrogliosis at the injured cords but did not alter the extent of hemorrhage and the number of macrophages and/or microglia. MPSS reduced hemorrhage and the number of macrophages and/or microglia, but did not alter astrogliosis. At 21 days, either AIT-082 or MPSS administration improved function and morphology similarly (less tissue loss and astrogliosis). In contrast, administration of AIT-082 and MPSS together abolished the beneficial effects observed when either drug was given individually. These results suggest that MPSS and AIT-082 may exert their beneficial effects through different and potentially antagonistic pathways.

Cellular transplantation strategies for spinal cord injury and translational neurobiology

Basic science advances in spinal cord injury and regeneration research have led to a variety of novel experimental therapeutics designed to promote functionally effective axonal regrowth and sprouting. Among these interventions are cell-based approaches involving transplantation of neural and non-neural tissue elements that have potential for restoring damaged neural pathways or reconstructing intraspinal synaptic circuitries by either regeneration or neuronal/glial replacement. Notably, some of these strategies (e.g., grafts of peripheral nerve tissue, olfactory ensheathing glia, activated macrophages, marrow stromal cells, myelin-forming oligodendrocyte precursors or stem cells, and fetal spinal cord tissue) have already been translated to the clinical arena, whereas others have imminent likelihood of bench-to-bedside application. Although this progress has generated considerable enthusiasm about treating what once was thought to be a totally incurable condition, there are many issues to be considered relative to treatment safety and efficacy. The following review reflects on different experimental applications of intraspinal transplantation with consideration of the underlying pathological, pathophysiological, functional, and neuroplastic responses to spinal trauma that such treatments may target along with related issues of procedural and biological safety. The discussion then moves to an overview of ongoing and completed clinical trials to date. The pros and cons of these endeavors are considered, as well as what has been learned from them. Attention is primarily directed at preclinical animal modeling and the importance of patterning clinical trials, as much as possible, according to laboratory experiences.

Temporal and spatial patterns of Kv1.1 and Kv1.2 protein and gene expression in spinal cord white matter after acute and chronic spinal cord injury in rats: implications for axonal pathophysiology after neurotrauma

After spinal cord injury (SCI), surviving white matter axons display axonal dysfunction associated with demyelination and altered K+ channel activity. To clarify the molecular basis of posttraumatic axonal pathophysiology after SCI, we investigated the changes in expression and distribution of the axonal K+ channel subunits Kv1.1 and Kv1.2 in spinal cord white matter after in vivo SCI in the rat. Using Western blot analysis, we found an increased expression of Kv1.1 and Kv1.2 at 2 and 6 weeks after SCI. By real-time PCR we observed an increase in Kv1.1 and Kv1.2 mRNA levels 1 day after SCI, which persisted until 6 weeks. Confocal immunohistochemistry showed a markedly dispersed labelling of Kv1.1 and Kv1.2 along the injured axons, in contrast to the tight localization of these channels to the juxtaparanodes of noninjured axons. This redistribution of Kv1.1 and Kv1.2 occurred as early as 1 h postinjury along some injured axons, and persisted at 6 weeks postinjury. In parallel with the redistribution of Kv1.1 and 1.2, contactin-associated protein (Caspr), which is normally confined to a paranodal location, also displayed a more diffuse distribution along the injured spinal cord axons. Our results suggest that the increased expression of Kv1.1 and Kv1.2 proteins is transcriptionally regulated. In contrast, the redistribution of the axonal K+ channel subunits occurs very early postinjury and probably reflects a disruption of the juxtaparanodal axonal region due to physical trauma, as shown by altered localization of Caspr.

Effects of 4-aminopyridine on stretched mammalian spinal cord: the role of potassium channels in axonal conduction

Axonal conduction deficit is a major contributor to various degrees of disability after spinal cord injury. 4-aminopyridine (4-AP), a potassium channel blocker, has been shown to restore some conduction and improve neurological function in both animal and human studies. Using a double sucrose-gap recording device, we have examined the effects of 4-AP on isolated guinea pig spinal cord white matter after stretch injury. At a concentration of 100 microM, 4-AP increased the amplitude of the compound action potential by 100% while 1 microM 4-AP increased it by 43%, a larger response than seen following compression injury. The length of affected tissue is suggested as a potential explanation of this differential sensitivity to 4-AP. Plastic sections taken from the injury site revealed severe myelin damage, especially in the paranodal area, which may also partially explain why 4-AP has more effect on conduction after stretch injury than compression. In addition, we have shown that while enhancing conductivity in some axons, 4-AP significantly reduced the overall responsiveness to multiple stimuli, as evidenced by increase of the refractory period in response to dual stimuli and the decreased ability to follow repetitive stimuli. This increased refractoriness may be largely attributed to residual deficits in fibers newly recruited by 4-AP treatment.

Caspase inhibition attenuates transection-induced oligodendrocyte apoptosis in the developing chick spinal cord

A developmental model of spinal cord injury in the embryonic chick was specifically developed to characterize the involvement of caspases in injury-induced oligodendrocyte apoptosis remote from the lesion and the ability of caspase inhibitors to attenuate this process. Developmental apoptosis in the cervical spinal cord increased within the white matter between embryonic days 13 and 18, the period of myelination of this region. Spinal cord transection during this period induced a rapid increase in apoptotic cells in the ventral and lateral white matter over several millimeters caudal to the injury. Immunostaining identified large numbers of these cells as oligodendrocytes. Catalytic activity assays and immunostaining demonstrated caspase-3-like but not caspase-1-like activity to be involved in this apoptotic response. In vivo application of specific caspase inhibitors significantly attenuated transection-induced apoptosis. Thus, we describe a developmental period during which spinal oligodendrocytes exhibited a heightened, caspase-dependent sensitivity to transection-induced apoptosis that is attenuated by caspase inhibition.

Efficacy and safety of 4-aminopyridine in patients with long-term spinal cord injury: a randomized, double-blind, placebo-controlled trial

OBJECTIVES

To study the efficacy and safety of 4-aminopyridine (4-AP), and to document sensorimotor changes after discontinuation of the drug in patients with long-term spinal cord injury.

DESIGN

Randomized, double-blind, placebo-controlled trial.

SETTING

Clinical research unit.

PATIENTS

Twenty-seven patients with long-term spinal cord injury.

INTERVENTION

Patients were randomized to receive either oral 4-AP 5 mg/day, which was increased by 5 mg/week to a maximum dosage of 30 mg/day, or placebo for 12 weeks. They switched to the opposite treatment for the next 12 weeks.

MEASUREMENTS AND MAIN RESULTS

Twenty-five patients finished the study. The results from the first 12 weeks were used to test efficacy. Positive gains in motor function, sensation, and independence occurred more frequently in patients receiving 4-AP (69%) than those receiving placebo (46%). Significant functional improvement was also noted in those treated with 4-AP (chi2, p=0.042). When each evaluation scale was considered separately, significant improvement was seen only in motor function (4-AP 92% vs placebo 46%, Fisher exact test, p=0.03). Persistent effects of the drug were assessed at week 24 in the group that initially received 4-AP. A persistent, significant 4-AP effect was observed in evaluations of sensation and independence (67% and 83% of patients, respectively; Wilcoxon signed rank test, p=0.032 and 0.042, respectively). Fourteen (56%) patients had 26 adverse reactions. One moderate adverse reaction--posterior tibial artery vasospasm--and 25 mild adverse reactions, such as dry mouth, dizziness, nausea, gastritis, oral and peripheral paresthesia, resolved adequately. Six (24%) patients experienced transitory alterations of enzyme levels (alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and creatine kinase) and thrombocytopenia.

CONCLUSION

Patients who received 4-AP showed significant improvement in motor function, and a persistent effect on sensation and independent function occurred. The drug is safe; however, after starting 4-AP therapy, patients must be carefully monitored for the possible occurrence of peripheral vasospasm.