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

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.

Using an animal model to predict the effective human dose for oral multiple sclerosis drugs

The objective of this study was to determine the potential usefulness of an animal model to predict the appropriate dose of newly developed drugs for treating relapsing remitting multiple sclerosis (RRMS). Conversion of the lowest effective dose (LEffD) for mice and rats in the experimental autoimmune encephalomyelitis (EAE) model was used to predict the human effective dose utilizing the body surface area correction factor found in the 2005 US Food and Drug Administration (FDA) Guidance for Industry in selecting safe starting doses for clinical trials. Predictions were also tested by comparison with doses estimated by scaling up the LEffD in the model by the human to animal clearance ratio. Although initial proof-of-concept studies of oral fingolimod tested the efficacy and safety of 1.25 and 5 mg in treating RRMS, the EAE animal model predicted the approved dose of this drug, 0.5 mg daily. This approach would have also provided useful predictions of the approved human oral doses for cladribine, dimethyl fumarate, ozanimod, ponesimod, siponimod, and teriflunomide, drugs developed with more than one supposed mechanism of action. The procedure was not useful for i.v. dosed drugs, including monoclonal antibodies. We maintain that drug development scientists should always examine a simple allometric method to predict the therapeutic effective dose in humans. Then, following clinical studies, we believe that the animal model might be expected to yield useful predictions of other drugs developed to treat the same condition. The methodology may not always be predictive, but the approach is so simple it should be investigated.

Ion Channels as New Attractive Targets to Improve Re-Myelination Processes in the Brain

Multiple sclerosis (MS) is the most demyelinating disease of the central nervous system (CNS) characterized by neuroinflammation. Oligodendrocyte progenitor cells (OPCs) are cycling cells in the developing and adult CNS that, under demyelinating conditions, migrate to the site of lesions and differentiate into mature oligodendrocytes to remyelinate damaged axons. However, this process fails during disease chronicization due to impaired OPC differentiation. Moreover, OPCs are crucial players in neuro-glial communication as they receive synaptic inputs from neurons and express ion channels and neurotransmitter/neuromodulator receptors that control their maturation. Ion channels are recognized as attractive therapeutic targets, and indeed ligand-gated and voltage-gated channels can both be found among the top five pharmaceutical target groups of FDA-approved agents. Their modulation ameliorates some of the symptoms of MS and improves the outcome of related animal models. However, the exact mechanism of action of ion-channel targeting compounds is often still unclear due to the wide expression of these channels on neurons, glia, and infiltrating immune cells. The present review summarizes recent findings in the field to get further insights into physio-pathophysiological processes and possible therapeutic mechanisms of drug actions.

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

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

Neuroprotective Properties of 4-Aminopyridine

As an antagonist of voltage-gated potassium (Kv) channels, 4-aminopyridine (4-AP) is used as symptomatic therapy in several neurologic disorders. The improvement of visual function and motor skills and relieve of fatigue in patients with MS have been attributed to 4-AP. Its prolonged release formulation (fampridine) has been approved for the symptomatic treatment of walking disability in MS. The beneficial effects were explained by the blockade of axonal Kv channels, thereby enhancing conduction along demyelinated axons. However, an increasing body of evidence suggests that 4-AP may have additional properties beyond the symptomatic mode of action. In this review, we summarize preclinical and clinical data on possible neuroprotective features of 4-AP.

K channel blockage with 3,4-diaminopyridine potentiates the effect of L-DOPA on dopamine release in striatal slices prepared from 6-OHDA pre-treated rats

Although L-DOPA revolutionized in the treatment of Parkinson's disease, most patients developed motor complications after several years of treatment. Adjunctive therapy to L-DOPA with drugs related to dopaminergic signaling may reduce its dose without decreasing the therapeutic efficiency and thus ameliorates its adverse effects. It has been shown that 3,4-diaminopyridine (3,4-DAP), a K channel blocker, increased dopamine release from striatal slices by increasing neuronal firing in striatal dopaminergic terminals. The current study investigates whether 3,4-DAP may enhance L-DOPA-induced dopamine (DA) release from striatal slices by increasing neuronal firing in striatal dopaminergic terminals. The effects of L-DOPA and 3,4-DAP on spontaneous DA and DOPAC release were tested in vitro, on acute rat striatal slices prepared from non-treated and 6-hydroxydopamine-pre-treated rats. DA and DOPAC levels were determined by HPLC methods. When 3,4-diaminopyridine was combined with L-DOPA, the observed effect was considerably greater than the increases induced by L-DOPA or 3,4-DAP alone in normoxic and neurodegenerative conditions produced by FeSO4 and 6-hydroxydopamine. Furthermore, L-DOPA plus 3,4-DAP also ameliorated DOPAC levels in neurodegenerative conditions. These data indicate that 3,4 DAP plus L-DOPA activates striatal dopaminergic terminals by increasing the DA release and, thus, could be considered as a promising finding in treatment of acute and chronic injury in dopaminergic neurons.

Protective effects of 4-aminopyridine in experimental optic neuritis and multiple sclerosis

Chronic disability in multiple sclerosis is linked to neuroaxonal degeneration. 4-aminopyridine (4-AP) is used and licensed as a symptomatic treatment to ameliorate ambulatory disability in multiple sclerosis. The presumed mode of action is via blockade of axonal voltage gated potassium channels, thereby enhancing conduction in demyelinated axons. In this study, we provide evidence that in addition to those symptomatic effects, 4-AP can prevent neuroaxonal loss in the CNS. Using in vivo optical coherence tomography imaging, visual function testing and histologic assessment, we observed a reduction in retinal neurodegeneration with 4-AP in models of experimental optic neuritis and optic nerve crush. These effects were not related to an anti-inflammatory mode of action or a direct impact on retinal ganglion cells. Rather, histology and in vitro experiments indicated 4-AP stabilization of myelin and oligodendrocyte precursor cells associated with increased nuclear translocation of the nuclear factor of activated T cells. In experimental optic neuritis, 4-AP potentiated the effects of immunomodulatory treatment with fingolimod. As extended release 4-AP is already licensed for symptomatic multiple sclerosis treatment, we performed a retrospective, multicentre optical coherence tomography study to longitudinally compare retinal neurodegeneration between 52 patients on continuous 4-AP therapy and 51 matched controls. In line with the experimental data, during concurrent 4-AP therapy, degeneration of the macular retinal nerve fibre layer was reduced over 2 years. These results indicate disease-modifying effects of 4-AP beyond symptomatic therapy and provide support for the design of a prospective clinical study using visual function and retinal structure as outcome parameters.

Transdermal delivery of 4-aminopyridine accelerates motor functional recovery and improves nerve morphology following sciatic nerve crush injury in mice

Oral 4-aminopyridine (4-AP) is clinically used for symptomatic relief in multiple sclerosis and we recently demonstrated that systemic 4-AP had previously unknown clinically-relevant effects after traumatic peripheral nerve injury including the promotion of re-myelination, improvement of nerve conductivity, and acceleration of functional recovery. We hypothesized that, instead of oral or injection administration, transdermal 4-AP (TD-4-AP) could also improve functional recovery after traumatic peripheral nerve injury. Mice with surgical traumatic peripheral nerve injury received TD-4AP or vehicle alone and were examined for skin permeability, pharmacokinetics, functional, electrophysiological, and nerve morphological properties. 4-AP showed linear pharmacokinetics and the maximum plasma 4-AP concentrations were proportional to TD-4-AP dose. While a single dose of TD-4-AP administration demonstrated rapid transient improvement in motor function, chronic TD-4-AP treatment significantly improved motor function and nerve conduction and these effects were associated with fewer degenerating axons and thicker myelin sheaths than those from vehicle controls. These findings provide direct evidence for the potential transdermal applicability of 4-AP and demonstrate that 4-AP delivered through the skin can enhance in-vivo functional recovery and nerve conduction while decreasing axonal degeneration. The animal experiments were approved by the University Committee on Animal Research (UCAR) at the University of Rochester (UCAR-2009-019) on March 31, 2017.

The Potassium Channel Kv1.5 Expression Alters During Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is a chronic, inflammatory, neurodegenerative disease with an autoimmune component. It was suggested that potassium channels, which are involved in crucial biological functions may have a role in different diseases, including MS and its animal model, experimental autoimmune encephalomyelitis (EAE). It was shown that voltage-gated potassium channels Kv1.5 are responsible for fine-tuning in the immune physiology and influence proliferation and differentiation in microglia and astrocytes. Here, we explored the cellular distribution of the Kv1.5 channel, together with its transcript and protein expression in the male rat spinal cord during different stages of EAE. Our results reveal a decrease of Kv1.5 transcript and protein level at the peak of disease, where massive infiltration of myeloid cells occurs, together with reactive astrogliosis and demyelination. Also, we revealed that the presence of this channel is not found in infiltrating macrophages/microglia during EAE. It is interesting to note that Kv1.5 channel is expressed only in resting microglia in the naïve animals. Predominant expression of Kv1.5 channel was found in the astrocytes in all experimental groups, while some vimentin⁺ cells, resembling macrophages, are devoid of Kv1.5 expression. Our results point to the possible link between Kv1.5 channel and the pathophysiological processes in EAE.

Silent Free Fall at Disease Onset: A Perspective on Therapeutics for Progressive Multiple Sclerosis

Central nervous system (CNS) degeneration occurs during multiple sclerosis (MS) following several years of reversible autoimmune demyelination. Progressive CNS degeneration appears later during the course of relapsing-remitting MS (RRMS), although it starts insidiously at disease onset. We propose that there is an early subclinical phase also for primary-progressive (PP) MS. Consensus exists that many different cell types are involved during disease onset. Furthermore, the response to the initial damage, which is specific for each individual, would result in distinct pathological pathways that add complexity to the disease and the mechanisms underlying progressive CNS degeneration. Progressive MS is classified as either active or not active, as well as with or without progression. Different forms of progressive MS might reflect distinct or overlapping pathogenetic pathways. Disease mechanisms should be determined for each patient at diagnosis and the time of treatment. Until individualized and time-sensitive treatments that specifically target the molecular mechanisms of the progressive aspect of the disease are identified, combined therapies directed at anti-inflammation, regeneration, and neuroprotection are the most effective for preventing MS progression. This review presents selected therapeutics in support of the overall idea of a multidimensional therapy applied early in the disease. This approach could limit damage and increase CNS repair. By targeting several cellular populations (i.e., microglia, astrocytes, neurons, oligodendrocytes, and lymphocytes) and multiple pathological processes (e.g., inflammation, demyelination, synaptopathy, and excitatory/inhibitory imbalance) progressive MS could be attenuated. Early timing for such multidimensional therapy is proposed as the prerequisite for effectively halting progressive MS.

4-Aminopyridine ameliorates relapsing remitting experimental autoimmune encephalomyelitis in SJL/J mice

We evaluated the effects of a non-specific potassium channel blocker, 4-aminopyridine (4-AP), on chronic experimental autoimmune encephalomyelitis (chEAE) and relapsing remitting EAE (rrEAE) in mice. 4-AP did not affect chEAE, but ameliorated rrEAE, particularly in the relapsing phase. Disease amelioration was confirmed pathologically, and glial fibrillary acidic protein expression was observed to be downregulated in 4-AP-treated mice. In the recall response, a T-cell proliferative response was not inhibited; however, Th1/Th17 polarization was attenuated. 4-AP is currently accepted as an anti-symptomatic drug only in the chronic phase of multiple sclerosis (MS); however, its use in the active phase of MS should be considered.

Suppression of Inflammatory Demyelinaton and Axon Degeneration through Inhibiting Kv3 Channels

The development of neuroprotective and repair strategies for treating progressive multiple sclerosis (MS) requires new insights into axonal injury. 4-aminopyridine (4-AP), a blocker of voltage-gated K⁺ (Kv) channels, is used in symptomatic treatment of progressive MS, but the underlying mechanism remains unclear. Here we report that deleting Kv3.1—the channel with the highest 4-AP sensitivity—reduces clinical signs in experimental autoimmune encephalomyelitis (EAE), a mouse model for MS. In Kv3.1 knockout (KO) mice, EAE lesions in sensory and motor tracts of spinal cord were markedly reduced, and radial astroglia were activated with increased expression of brain derived neurotrophic factor (BDNF). Kv3.3/Kv3.1 and activated BDNF receptors were upregulated in demyelinating axons in EAE and MS lesions. In spinal cord myelin coculture, BDNF treatment promoted myelination, and neuronal firing via altering channel expression. Therefore, suppressing Kv3.1 alters neural circuit activity, which may enhance BNDF signaling and hence protect axons from inflammatory insults.

4-Aminopyridine ameliorates experimental autoimmune neuritis in Lewis rats

We investigated the effect of 4-aminopyridine (4-AP) on experimental autoimmune neuritis (EAN) using a 4-AP-treated group in which 4-AP was administered in the diet, and a control group (n=10 per group). Electrophysiological and pathological assessment was performed in the sciatic nerve. The EAN clinical scores were significantly lower in the 4-AP-treated group than in the control group (p<0.05). The motor conductance velocity two weeks post-immunization was significantly higher in the 4-AP-treated group (p<0.05). Finally, 4-AP did not lead to pathological changes. Thus, 4-AP might be a potential therapeutic agent in demyelinating neuropathy.

Experience with fampridine in clinical practice: analysis of a possible marker of clinical response

PURPOSE OF THE STUDY

Approximately 85% of patients with multiple sclerosis experience reduced mobility, which negatively affects quality of life. Fampridine is the first symptomatic treatment aimed at improving gait. We analyzed effectiveness and tolerance in clinical practice. We also sought a prevalent gait pattern in responders as a potential clinical response marker.

MATERIAL AND METHODS

Six-month prospective study of fampridine in patients with multiple sclerosis. Response was evaluated using the Timed 25-Foot Walk Test (T25FW) and the 12-Item Multiple Sclerosis Walking Scale (MSWS-12). Response was defined as increased gait speed (≥20%) and decreased MSWS-12 score (≥4 points).

RESULTS

Fifty-five patients (67.3% women; mean age, 51.7 [11.1] years) with a baseline Expanded Disability Status Scale (EDSS) score of 5.8. Gait pattern was paraparetic (40%), hemiparetic (21.8%) and ataxic (38.2%). Of all patients, 70.9% demonstrated clinical benefit based on response criteria established, at the 14-d follow-up, 61.8% at 3 months and 45.5% at 6 months. A similar response pattern was observed in the MSWS-12. A significant decrease in the mean (SD) EDSS score was observed in responders at 6 months (6.1 [0.9] vs. 5.64 [0.1], p < 0.05). Adverse effects were recorded in 50.9%, although most were mild-moderate and resolved completely. We did not identify a prevalent gait pattern among responders. After a washout period, some patients received fampridine a second time obtaining response recovery.

CONCLUSIONS

In our patients' cohort, fampridine proved clinical benefit, being safe and well tolerated in most cases. We did not identify a gait pattern that was predictive of clinical response.

CatWalk gait analysis in a rat model of multiple sclerosis

Background

Myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) is a widely used animal model for multiple sclerosis. The characteristic feature of the MOG-EAE model in Brown Norway rats is consistent involvement of the spinal cord resulting in limb paresis. The aim of the study was to investigate whether early subclinical gait abnormalities are present in this animal model and can be detected by CatWalk XT, a fully automated gait analysis system. Furthermore, we investigated the usability of CatWalk system for treatment studies.

Results

Our gait analysis showed no preclinical abnormalities in MOG-EAE animals. Nevertheless, we characterized a combination of gait parameters that display a high predictive capacity in regard to disease onset. Our detailed histopathological analysis of the spinal cord revealed that lesion formation starts in the lumbar region and propagates toward the cervical part of the spinal cord during the disease course. In the treatment study, the stabilization of gait parameters under the treatment with methylprednisolone was detected in CatWalk as well as in traditional EAE-scoring system.

Conclusions

The results from CatWalk test indicate no benefit of lab-intensive automated gait system in EAE-model with chronic-progressive disease course as well as in therapeutic studies with pronounced effect on the severity of clinical symptoms. However, due to its quantitative and objective nature this system may display a refined test to detect small but functional relevant changes in regeneration-orientated studies.

Physiological Dynamics in Demyelinating Diseases: Unraveling Complex Relationships through Computer Modeling

Despite intense research, few treatments are available for most neurological disorders. Demyelinating diseases are no exception. This is perhaps not surprising considering the multifactorial nature of these diseases, which involve complex interactions between immune system cells, glia and neurons. In the case of multiple sclerosis, for example, there is no unanimity among researchers about the cause or even which system or cell type could be ground zero. This situation precludes the development and strategic application of mechanism-based therapies. We will discuss how computational modeling applied to questions at different biological levels can help link together disparate observations and decipher complex mechanisms whose solutions are not amenable to simple reductionism. By making testable predictions and revealing critical gaps in existing knowledge, such models can help direct research and will provide a rigorous framework in which to integrate new data as they are collected. Nowadays, there is no shortage of data; the challenge is to make sense of it all. In that respect, computational modeling is an invaluable tool that could, ultimately, transform how we understand, diagnose, and treat demyelinating diseases.

"Disease modifying nutricals" for multiple sclerosis

The association between vitamin D and multiple sclerosis has (re)-opened new interest in nutrition and natural compounds in the prevention and treatment of this neuroinflammatory disease. The dietary amount and type of fat, probiotics and biologicals, salmon proteoglycans, phytoestrogens and protease inhibitor of soy, sodium chloride and trace elements, and fat soluble vitamins including D, A and E were all considered as disease-modifying nutraceuticals. Studies in experimental autoimmune encephalomyelitis mice suggest that poly-unsaturated fatty acids and their 'inflammation-resolving' metabolites and the gut microflora may reduce auto-aggressive immune cells and reduce progression or risk of relapse, and infection with whipworm eggs may positively change the gut-brain communication. Encouraged by the recent interest in multiple sclerosis-nutrition nature's pharmacy has been searched for novel compounds with anti-inflammatory, immune-modifying and antioxidative properties, the most interesting being the scorpion toxins that inhibit specific potassium channels of T cells and antioxidative compounds including the green tea flavonoid epigallocatechin-3-gallate, curcumin and the mustard oil glycoside from e.g. broccoli and sulforaphane. They mostly also inhibit pro-inflammatory signaling through NF-κB or toll-like receptors and stabilize the blood brain barrier. Disease modifying functions may also complement analgesic and anti-spastic effects of cannabis, its constituents, and of 'endocannabinoid enhancing' drugs or nutricals like inhibitors of fatty acid amide hydrolase. Nutricals will not solve multiple sclerosis therapeutic challenges but possibly support pharmacological interventions or unearth novel structures.