4-Aminopyridine promotes functional recovery and remyelination in acute peripheral nerve injury

Pharmacological management of secondary chronic spinal cord injury: a systematic review

INTRODUCTION

Spinal cord injury (SCI) may bring lifelong consequences for affected patients and a high financial burden to the health care system.

SOURCE OF DATA

Published peer-reviewed scientific articles identified from EMBASE, Google Scholar, PubMed and Scopus.

AREAS OF AGREEMENT

Surgery and blood pressure management are the main targets in acute SCI to avoid secondary damage.

AREAS OF CONTROVERSY

The management of secondary chronic SCI is challenging, with unpredictable outcomes.

GROWING POINTS

Given the lack of consensus on pharmacological therapy for acute and secondary chronic SCI, the present study analyses the currently available drugs and treatment options to manage secondary chronic SCI.

AREAS TIMELY FOR DEVELOPING RESEARCH

Different approaches exist for the pharmacological management of secondary chronic SCI. One of the most investigated drugs, 4-aminopyridine, improves central motor conduction and shows improvement in neurological signs. Positive results in different areas have been observed in patients receiving the anti-spastic drugs tizanidine and baclofen or Granulocyte colony-stimulating factor. Growth hormone showed only minimal or no significant effects, and the therapy of secondary chronic SCI with riluzole has been poorly researched to date.

Myelinated peripheral axons are more vulnerable to mechanical trauma in a model of enlarged axonal diameters

The velocity of axonal impulse propagation is facilitated by myelination and axonal diameters. Both parameters are frequently impaired in peripheral nerve disorders, but it is not known if the diameters of myelinated axons affect the liability to injury or the efficiency of functional recovery. Mice lacking the adaxonal myelin protein chemokine-like factor-like MARVEL-transmembrane domain-containing family member-6 (CMTM6) specifically from Schwann cells (SCs) display appropriate myelination but increased diameters of peripheral axons. Here we subjected Cmtm6-cKo mice as a model of enlarged axonal diameters to a mild sciatic nerve compression injury that causes temporarily reduced axonal diameters but otherwise comparatively moderate pathology of the axon/myelin-unit. Notably, both of these pathological features were worsened in Cmtm6-cKo compared to genotype-control mice early post-injury. The increase of axonal diameters caused by CMTM6-deficiency thus does not override their injury-dependent decrease. Accordingly, we did not detect signs of improved regeneration or functional recovery after nerve compression in Cmtm6-cKo mice; depleting CMTM6 in SCs is thus not a promising strategy toward enhanced recovery after nerve injury. Conversely, the exacerbated axonal damage in Cmtm6-cKo nerves early post-injury coincided with both enhanced immune response including foamy macrophages and SCs and transiently reduced grip strength. Our observations support the concept that larger peripheral axons are particularly susceptible toward mechanical trauma.

4-Aminopyridine in pediatric traumatic spinal cord injury: A case report

CONTEXT

Spinal cord injury (SCI) presents significant challenges due to its debilitating nature and potential complications. While few medications have shown efficacy in improving neurological recovery, 4-Aminopyridine (4-AP), a voltage-gated potassium channel blocker, has been used clinically off-label to improve neurologic function in adults with spinal cord-related paralysis. However, evidence regarding its safety and effectiveness in the pediatric population remains scarce, as it is approved for use in older patients.

FINDINGS

This manuscript reports the case of a pediatric patient who sustained a traumatic cervical SCI. Initial neurological assessment indicated a C1 motor complete SCI. Surgical intervention for bullet removal and spinal fusion was carried out, followed by comprehensive inpatient rehabilitation.

CONCLUSION/CLINICAL RELEVANCE

4-AP was introduced three months post-injury and was well-tolerated without obvious adverse effects. Notably, he exhibited neurological and functional improvement after four months of 4-AP use, though his improvement followed the expected trajectory of recovery. To date, this case represents the first case of 4-AP administration in a pediatric SCI patient, and therefore these findings contribute valuable clinical insight. By documenting the clinical trajectory of this case, this manuscript suggests 4-AP may be safe for use in pediatric patients.

Progression of axonal excitability abnormalities with increasing clinical severity of diabetic peripheral neuropathy

OBJECTIVE

Diabetic peripheral neuropathy (DPN) is a frequent complication for persons with type 2 diabetes. Previous studies have failed to demonstrate any significant impact of treatment for DPN. The present study assessed the role of axonal ion channel dysfunction in DPN and explored the hypothesis that there may be a progressive change in ion channel abnormalities that varied with disease stage.

METHODS

Neurophysiological studies were conducted using axonal excitability techniques, a clinical method of assessing ion channel dysfunction. Studies were conducted in 178 persons with type 2 diabetes, with participants allocated into four groups according to clinical severity of neuropathy, assessed using the Total Neuropathy Grade.

RESULTS

Analysis of excitability data demonstrated a progressive and stepwise reduction in two parameters that are related to the activity of Kv1.1 channels, namely superexcitability and depolarizing threshold electrotonus at 10-20 ms (p < 0.001), and mathematical modelling of axonal excitability findings supported progressive upregulation of Kv1.1 conductances with increasing greater disease severity.

CONCLUSION

The findings are consistent with a progressive upregulation of juxtaparanodal Kv1.1 conductances with increasing clinical severity of diabetic peripheral neuropathy.

SIGNIFICANCE

From a translational perspective, the study suggests that blockade of Kv1.1 channels using 4-aminopyridine derivatives such as fampridine may be a potential treatment for DPN.

Differentiated mesenchymal stem cells-derived exosomes immobilized in decellularized sciatic nerve hydrogels for peripheral nerve repair

Peripheral nerve injury (PNI) and the limitations of current treatments often result in incomplete sensory and motor function recovery, which significantly impact the patient's quality of life. While exosomes (Exo) derived from stem cells and Schwann cells have shown promise on promoting PNI repair following systemic administration or intraneural injection, achieving effective local and sustained Exo delivery holds promise to treat local PNI and remains challenging. In this study, we developed Exo-loaded decellularized porcine nerve hydrogels (DNH) for PNI repair. We successfully isolated Exo from differentiated human adipose-derived mesenchymal stem cells (hADMSC) with a Schwann cell-like phenotype (denoted as dExo). These dExo were further combined with polyethylenimine (PEI), and DNH to create polyplex hydrogels (dExo-loaded pDNH). At a PEI content of 0.1%, pDNH showed cytocompatibility for hADMSCs and supported neurite outgrowth of dorsal root ganglions. The sustained release of dExos from dExo-loaded pDNH persisted for at least 21 days both in vitro and in vivo. When applied around injured nerves in a mouse sciatic nerve crush injury model, the dExo-loaded pDNH group significantly improved sensory and motor function recovery and enhanced remyelination compared to dExo and pDNH only groups, highlighting the synergistic regenerative effects. Interestingly, we observed a negative correlation between the number of colony-stimulating factor-1 receptor (CSF-1R) positive cells and the extent of PNI regeneration at the 21-day post-surgery stage. Subsequent in vitro experiments demonstrated the potential involvement of the CSF-1/CSF-1R axis in Schwann cells and macrophage interaction, with dExo effectively downregulating CSF-1/CSF-1R signaling.

EBP50 is a key molecule for the Schwann cell-axon interaction in peripheral nerves

Peripheral nerve injury disrupts the Schwann cell-axon interaction and the cellular communication between them. The peripheral nervous system has immense potential for regeneration extensively due to the innate plastic potential of Schwann cells (SCs) that allows SCs to interact with the injured axons and exert specific repair functions essential for peripheral nerve regeneration. In this study, we show that EBP50 is essential for the repair function of SCs and regeneration following nerve injury. The increased expression of EBP50 in the injured sciatic nerve of control mice suggested a significant role in regeneration. The ablation of EBP50 in mice resulted in delayed nerve repair, recovery of behavioral function, and remyelination following nerve injury. EBP50 deficiency led to deficits in SC functions, including proliferation, migration, cytoskeleton dynamics, and axon interactions. The adeno-associated virus (AAV)-mediated local expression of EBP50 improved SCs migration, functional recovery, and remyelination. ErbB2-related proteins were not differentially expressed in EBP50-deficient sciatic nerves following injury. EBP50 binds and stabilizes ErbB2 and activates the repair functions to promote regeneration. Thus, we identified EBP50 as a potent SC protein that can enhance the regeneration and functional recovery driven by NRG1-ErbB2 signaling, as well as a novel regeneration modulator capable of potential therapeutic effects.

Retinal ganglion cell repopulation for vision restoration in optic neuropathy: a roadmap from the RReSTORe Consortium

Retinal ganglion cell (RGC) death in glaucoma and other optic neuropathies results in irreversible vision loss due to the mammalian central nervous system's limited regenerative capacity. RGC repopulation is a promising therapeutic approach to reverse vision loss from optic neuropathies if the newly introduced neurons can reestablish functional retinal and thalamic circuits. In theory, RGCs might be repopulated through the transplantation of stem cell-derived neurons or via the induction of endogenous transdifferentiation. The RGC Repopulation, Stem Cell Transplantation, and Optic Nerve Regeneration (RReSTORe) Consortium was established to address the challenges associated with the therapeutic repair of the visual pathway in optic neuropathy. In 2022, the RReSTORe Consortium initiated ongoing international collaborative discussions to advance the RGC repopulation field and has identified five critical areas of focus: (1) RGC development and differentiation, (2) Transplantation methods and models, (3) RGC survival, maturation, and host interactions, (4) Inner retinal wiring, and (5) Eye-to-brain connectivity. Here, we discuss the most pertinent questions and challenges that exist on the path to clinical translation and suggest experimental directions to propel this work going forward. Using these five subtopic discussion groups (SDGs) as a framework, we suggest multidisciplinary approaches to restore the diseased visual pathway by leveraging groundbreaking insights from developmental neuroscience, stem cell biology, molecular biology, optical imaging, animal models of optic neuropathy, immunology & immunotolerance, neuropathology & neuroprotection, materials science & biomedical engineering, and regenerative neuroscience. While significant hurdles remain, the RReSTORe Consortium's efforts provide a comprehensive roadmap for advancing the RGC repopulation field and hold potential for transformative progress in restoring vision in patients suffering from optic neuropathies.

Sciatic nerve injury regeneration in adult male rats using gelatin methacrylate (GelMA)/poly(2-ethy-2-oxazoline) (PEtOx) hydrogel containing 4-aminopyridine (4-AP)

One of the most important parts of the body is the peripheral nervous system, and any injuries in this system may result in potentially lethal consequences or severe side effects. The peripheral nervous system may not rehabilitate the harmed regions following disabling disorders, which reduce the quality of life of patients. Fortunately, in recent years, hydrogels have been proposed as exogenous alternatives to bridge damaged nerve stumps to create a useful microenvironment for advancing nerve recovery. However, hydrogel-based medicine in the therapy of peripheral nerve injury still needs a lot of improvement. In this study, GelMA/PEtOx hydrogel was used for the first time to deliver 4-Aminopyridine (4-AP) small molecules. 4-AP is a broad-spectrum potassium channel blocker, which has been demonstrated to increase neuromuscular function in patients with various demyelinating disorders. The prepared hydrogel showed a porosity of 92.2 ± 2.6% after 20 min, swelling ratio of 456.01 ± 2.0% after 180 min, weight loss of 81.7 ± 3.1% after 2 weeks, and good blood compatibility as well as sustainable drug release. MTT analysis was performed to assess the cell viability of the hydrogel and proved that the hydrogel is an appropriate substrate for the survival of cells. In vivo studies were performed for functional analysis and the sciatic functional index (SFI) as well as hot plate latency results showed that the use of GelMA/PEtOx+4-AP hydrogel enhances the regeneration compared to the GelMA/PEtOx hydrogel and the control group.

Effects of 4-Aminopyridine on Combined Nerve and Muscle Injury and Bone Loss

PURPOSE

Musculoskeletal injuries are common, and peripheral nerve injury (PNI) causes significant muscle and bone loss within weeks. After PNI, 4-aminopyridine (4-AP) improves functional recovery and muscle atrophy. However, it is unknown whether 4-AP has any effect on isolated traumatic muscle injury and PNI-induced bone loss.

METHODS

A standardized crush injury was performed on the sciatic nerve and muscles in mice, and the mice were assigned to receive normal saline or 4-AP treatment daily for 21 days. The postinjury motor and sensory function recovery was assessed, injured muscles were processed for histomorphometry, and the tibial bone was scanned for bone density.

RESULTS

4-Aminopyridine significantly accelerated the postinjury motor and sensory function recovery, improved muscle histomorphometry, increased muscle satellite cell numbers, and shifted muscle fiber types after combined nerve and muscle injury. Importantly, the 4-AP treatment significantly reduced PNI-induced bone loss. In contrast, in the case of isolated muscle injury, 4-AP had no effect on functional recovery and bone density, but it improved muscle-specific histomorphometry to a limited extent.

CONCLUSIONS

These findings demonstrate the potential beneficial effects of 4-AP on the recovery of muscle morphology and bone density after combined muscle and nerve injury.

CLINICAL RELEVANCE

Nerve injuries frequently involve muscle and result in rapid muscle and bone atrophy. In this scenario, 4-AP, in addition to accelerating nerve functional recovery, might work as an adjunctive agent to improve the recovery of injured muscle and attenuate PNI-induced bone loss.

Phenytoin Decreases Pain-like Behaviors and Improves Opioid Analgesia in a Rat Model of Neuropathic Pain

Neuropathic pain remains a clinical challenge due to its complex and not yet fully understood pathomechanism, which result in limited analgesic effectiveness of the management offered, particularly for patients with acute, refractory neuropathic pain states. In addition to the introduction of several modern therapeutic approaches, such as neuromodulation or novel anti-neuropathic drugs, significant efforts have been made in the repurposing of well-known substances such as phenytoin. Although its main mechanism of action occurs at sodium channels in excitable and non-excitable cells and is well documented, how the drug affects the disturbed neuropathic interactions at the spinal cord level and how it influences morphine-induced analgesia have not been clarified, both being crucial from a clinical perspective. We demonstrated that single and repeated systemic administrations of phenytoin decreased tactile and thermal hypersensitivity in an animal model of neuropathic pain. Importantly, we observed an increase in the antinociceptive effect on thermal stimuli with repeated administrations of phenytoin. This is the first study to report that phenytoin improves morphine-induced antinociceptive effects and influences microglia/macrophage activity at the spinal cord and dorsal root ganglion levels in a neuropathic pain model. Our findings support the hypothesis that phenytoin may represent an effective strategy for neuropathic pain management in clinical practice, particularly when combination with opioids is needed.

Functional recovery and muscle atrophy in pre-clinical models of peripheral nerve transection and gap-grafting in mice: effects of 4-aminopyridine

We recently demonstrated a repurposing beneficial effect of 4-aminopyridine (4-AP), a potassium channel blocker, on functional recovery and muscle atrophy after sciatic nerve crush injury in rodents. However, this effect of 4-AP is unknown in nerve transection, gap, and grafting models. To evaluate and compare the functional recovery, nerve morphology, and muscle atrophy, we used a novel stepwise nerve transection with gluing (STG), as well as 7-mm irreparable nerve gap (G-7/0) and 7-mm isografting in 5-mm gap (G-5/7) models in the absence and presence of 4-AP treatment. Following surgery, sciatic functional index was determined weekly to evaluate the direct in vivo global motor functional recovery. After 12 weeks, nerves were processed for whole-mount immunofluorescence imaging, and tibialis anterior muscles were harvested for wet weight and quantitative histomorphological analyses for muscle fiber cross-sectional area and minimal Feret’s diameter. Average post-injury sciatic functional index values in STG and G-5/7 models were significantly greater than those in the G-7/0 model. 4-AP did not affect the sciatic functional index recovery in any model. Compared to STG, nerve imaging revealed more misdirected axons and distorted nerve architecture with isografting. While muscle weight, cross-sectional area, and minimal Feret’s diameter were significantly smaller in G-7/0 model compared with STG and G-5/7, 4-AP treatment significantly increased right TA muscle mass, cross-sectional area, and minimal Feret’s diameter in G-7/0 model. These findings demonstrate that functional recovery and muscle atrophy after peripheral nerve injury are directly related to the intervening nerve gap, and 4-AP exerts differential effects on functional recovery and muscle atrophy.

4-Aminopyridine Induces Nerve Growth Factor to Improve Skin Wound Healing and Tissue Regeneration

The discovery of ways to enhance skin wound healing is of great importance due to the frequency of skin lesions. We discovered that 4-aminopyridine (4-AP), a potassium channel blocker approved by the FDA for improving walking ability in multiple sclerosis, greatly enhances skin wound healing. Benefits included faster wound closure, restoration of normal-appearing skin architecture, and reinnervation. Hair follicle neogenesis within the healed wounds was increased, both histologically and by analysis of K15 and K17 expression. 4-AP increased levels of vimentin (fibroblasts) and alpha-smooth muscle actin (α-SMA, collagen-producing myofibroblasts) in the healed dermis. 4-AP also increased neuronal regeneration with increased numbers of axons and S100⁺ Schwann cells (SCs), and increased expression of SRY-Box Transcription Factor 10 (SOX10). Treatment also increased levels of transforming growth factor-β (TGF-β), substance P, and nerve growth factor (NGF), important promoters of wound healing. In vitro studies demonstrated that 4-AP induced nerve growth factor and enhanced proliferation and migration of human keratinocytes. Thus, 4-AP enhanced many of the key attributes of successful wound healing and offers a promising new approach to enhance skin wound healing and tissue regeneration.

The Armadillo as a Model for Leprosy Nerve Function Impairment: Preventative and Therapeutic Interventions

Mycobacterium leprae infection of peripheral nerves and the subsequent nerve function impairment (NFI), especially in response to reactional episodes, are hallmarks of leprosy. Improved treatments for M. leprae-induced nerve injury are needed, as most if not all of the disability and stigma associated with leprosy arises from the direct or indirect effects of NFI. Nine-banded armadillos (Dasypus novemcinctus), like humans, exhibit the full clinical spectrum of leprosy and extensive involvement of the peripheral nerves. In this study, state-of-the-art technology was used to compare nerve function between uninfected and M. leprae-infected armadillos. Motor nerve conduction velocity (MNCV) and compound muscle action potential (cMAP), which measure changes in the rate of impulse conduction velocity and amplitude, revealed a progression of impairment that was directly correlated with the duration of M. leprae infection and enabled development of an objective nerve impairment scoring system. Ultrasonography accompanied by color Doppler imaging detected enlargement of the M. leprae-infected nerves and increased vascularity, possibly due to inflammation. Assessment of epidermal nerve fiber density (ENFD), which shows a length-dependent innervation in armadillos that is similar to humans, identified small fiber degeneration early after M. leprae infection. Staining for neuromuscular junction (NMJ) integrity, which is an indicator of signal transduction efficiency into skeletal muscle, discerned a markedly lower number and structural integrity of NMJ in M. leprae-infected armadillo footpads. These tools for assessing nerve injury were used to monitor the effects of intervention therapy. Two potential neuro-protective drugs, ethoxyquin (EQ) and 4-aminopyridine (4-AP), were tested for their ability to ameliorate peripheral nerve injury in M. leprae-infected armadillos. 4-AP treatment improved MNCV, cMAP, and EFND compared to untreated animals, while EQ had less effect. These results support the armadillo as a model for M. leprae-induced peripheral nerve injury that can provide insights toward the understanding of NFI progression and contribute to the preclinical investigation of the safety and efficacy of neuro-preventive and neuro-therapeutic interventions for leprosy.

Acute axon damage and demyelination are mitigated by 4-aminopyridine (4-AP) therapy after experimental traumatic brain injury

Damage to long axons in white matter tracts is a major pathology in closed head traumatic brain injury (TBI). Acute TBI treatments are needed that protect against axon damage and promote recovery of axon function to prevent long term symptoms and neurodegeneration. Our prior characterization of axon damage and demyelination after TBI led us to examine repurposing of 4-aminopyridine (4-AP), an FDA-approved inhibitor of voltage-gated potassium (Kv) channels. 4-AP is currently indicated to provide symptomatic relief for patients with chronic stage multiple sclerosis, which involves axon damage and demyelination. We tested clinically relevant dosage of 4-AP as an acute treatment for experimental TBI and found multiple benefits in corpus callosum axons. This randomized, controlled pre-clinical study focused on the first week after TBI, when axons are particularly vulnerable. 4-AP treatment initiated one day post-injury dramatically reduced axon damage detected by intra-axonal fluorescence accumulations in Thy1-YFP mice of both sexes. Detailed electron microscopy in C57BL/6 mice showed that 4-AP reduced pathological features of mitochondrial swelling, cytoskeletal disruption, and demyelination at 7 days post-injury. Furthermore, 4-AP improved the molecular organization of axon nodal regions by restoring disrupted paranode domains and reducing Kv1.2 channel dispersion. 4-AP treatment did not resolve deficits in action potential conduction across the corpus callosum, based on ex vivo electrophysiological recordings at 7 days post-TBI. Thus, this first study of 4-AP effects on axon damage in the acute period demonstrates a significant decrease in multiple pathological hallmarks of axon damage after experimental TBI.

A Novel Standardized Peripheral Nerve Transection Method and a Novel Digital Pressure Sensor Device Construction for Peripheral Nerve Crush Injury

Peripheral nerve injury (PNI) is common in all walks of life, and the most common PNIs are nerve crush and nerve transection. While optimal functional recovery after crush injury occurs over weeks, functional recovery after nerve transection with microsurgical repair and grafting is poor, and associated with permanent disability. The gold-standard treatment for nerve transection injury is microsurgical tensionless end-to-end suture repair. Since it is unethical to do experimental PNI studies in humans, it is therefore indispensable to have a simple, reliable, and reproducible pre-clinical animal model for successful evaluation of the efficacy of a novel treatment strategy. The objective of this article is two-fold: (A) To present a novel standardized peripheral nerve transection method in mice, using fibrin glue for modeling peripheral nerve transection injury, with reproducible gap distance between the severed nerve ends, and (B) to document the step-wise description of constructing a pressure sensor device for crush injury pressure measurements. We have successfully established a novel nerve transection model in mice using fibrin glue, and demonstrated that this transection method decreases surgical difficulties and variability by avoiding microsurgical manipulations on the nerve, ensuring the reproducibility and reliability of this animal model. Although it is quite impossible to exactly mimic the pathophysiological changes seen in nerve transection with sutures, we hope that the close resemblance of our novel pre-clinical model with gold-standard suturing can be easily reproduced by any lab, and that the data generated by this method significantly contributes to better understanding of nerve pathophysiology, molecular mechanisms of nerve regeneration, and the development of novel strategies for optimal functional recovery. In case of peripheral nerve crush injury, current methods rely on inter-device and operator precision to limit the variation with applied pressure. While the inability to accurately quantify the crush pressure may result in reduced reproducibility between animals and studies, there is no documentation of a pressure monitoring device that can be readily used for real-time pressure measurements. To address this deficit, we constructed a novel portable device comprised of an Arduino UNO microcontroller board and force sensitive resistor (FSR) capable of reporting the real-time pressure applied to a nerve. This novel digital pressure sensor device is cheap, easy to construct and assemble, and we believe that this device will be useful for any lab performing nerve crush injury in rodents.

Novel roles of phentolamine in protecting axon myelination, muscle atrophy, and functional recovery following nerve injury

Incomplete functional recovery after peripheral nerve injury (PNI) often results in devastating physical disabilities in human patients. Despite improved progress in surgical and non-surgical approaches, achieving complete functional recovery following PNI remains a challenge. This study demonstrates that phentolamine may hold a significant promise in treating nerve injuries and denervation induced muscle atrophy following PNI. In a sciatic nerve crush injury mouse model, we found that phentolamine treatment enhanced motor and functional recovery, protected axon myelination, and attenuated injury-induced muscle atrophy in mice at 14 days post-injury (dpi) compared to saline treatment. In the soleus of phentolamine treated animals, we observed the downregulation of phosphorylated signal transducer and activator of transcription factor 3 (p-STAT3) as well as muscle atrophy-related genes Myogenin, muscle ring finger 1 (MuRF-1), and Forkhead box O proteins (FoxO1, FoxO3). Our results show that both nerve and muscle recovery are integral components of phentolamine treatment-induced global functional recovery in mice at 14 dpi. Moreover, phentolamine treatment improved locomotor functional recovery in the mice after spinal cord crush (SCC) injury. The fact that phentolamine is an FDA approved non-selective alpha-adrenergic blocker, clinically prescribed for oral anesthesia reversal, hypertension, and erectile dysfunction makes this drug a promising candidate for repurposing in restoring behavioral recovery following PNI and SCC injuries, axonal neuropathy, and muscle wasting disorders.

Peripheral Nerve Injury Treatments and Advances: One Health Perspective

Peripheral nerve injuries (PNI) can have several etiologies, such as trauma and iatrogenic interventions, that can lead to the loss of structure and/or function impairment. These changes can cause partial or complete loss of motor and sensory functions, physical disability, and neuropathic pain, which in turn can affect the quality of life. This review aims to revisit the concepts associated with the PNI and the anatomy of the peripheral nerve is detailed to explain the different types of injury. Then, some of the available therapeutic strategies are explained, including surgical methods, pharmacological therapies, and the use of cell-based therapies alone or in combination with biomaterials in the form of tube guides. Nevertheless, even with the various available treatments, it is difficult to achieve a perfect outcome with complete functional recovery. This review aims to enhance the importance of new therapies, especially in severe lesions, to overcome limitations and achieve better outcomes. The urge for new approaches and the understanding of the different methods to evaluate nerve regeneration is fundamental from a One Health perspective. In vitro models followed by in vivo models are very important to be able to translate the achievements to human medicine.

A Controlled Clinical Study of Intensive Neurorehabilitation in Post-Surgical Dogs with Severe Acute Intervertebral Disc Extrusion

Simple Summary

This study explores the potential intensive neurorehabilitation plasticity effects in post-surgical paraplegic dogs with severe acute intervertebral disc extrusion aiming to achieve ambulatory status. The intensive neurorehabilitation protocol translated in 99.4% (167/168) of recovery in deep pain perception-positive dogs and 58.5% (55/94) in deep pain perception-negative dogs. There was 37.3% (22/59) spinal reflex locomotion, obtained within a maximum period of 3 months. Thus, intensive neurorehabilitation may be a useful approach for this population of dogs, avoiding future euthanasia and promoting an estimated time window of 3 months to recover.

Abstract

This retrospective controlled clinical study aimed to verify if intensive neurorehabilitation (INR) could improve ambulation faster than spontaneous recovery or conventional physiotherapy and provide a possible therapeutic approach in post-surgical paraplegic deep pain perception-positive (DPP⁺) (with absent/decreased flexor reflex) and DPP-negative (DDP⁻) dogs, with acute intervertebral disc extrusion. A large cohort of T10-L3 Spinal Cord Injury (SCI) dogs (n = 367) were divided into a study group (SG) (n = 262) and a control group (CG) (n = 105). The SG was based on prospective clinical cases, and the CG was created by retrospective medical records. All SG dogs performed an INR protocol by the hospitalization regime based on locomotor training, electrical stimulation, and, for DPP⁻, a combination with pharmacological management. All were monitored throughout the process, and measuring the outcome for DPP⁺ was performed by OFS and, for the DPP⁻, by the new Functional Neurorehabilitation Scale (FNRS-DPP⁻). In the SG, DPP⁺ dogs had an ambulation rate of 99.4% (n = 167) and, in DPP⁻, of 58.5% (n = 55). Moreover, in DPP⁺, there was a strong statistically significant difference between groups regarding ambulation (p < 0.001). The same significant difference was verified in the DPP^– dogs (p = 0.007). Furthermore, a tendency toward a significant statistical difference (p = 0.058) regarding DPP recovery was demonstrated between groups. Of the 59 dogs that did not recover DPP, 22 dogs achieved spinal reflex locomotion (SRL), 37.2% within a maximum of 3 months. The progressive myelomalacia cases were 14.9% (14/94). Therefore, although it is difficult to assess the contribution of INR for recovery, the results suggested that ambulation success may be improved, mainly regarding time.

Functional Neurorehabilitation in Dogs with an Incomplete Recovery 3 Months following Intervertebral Disc Surgery: A Case Series

Simple Summary

A non-invasive neurorehabilitation multimodal protocol (NRMP) may be applicable to chronic T3-L3 dogs 3 months after undergoing surgery for acute Intervertebral Disc Disease (IVDD) Hansen type I; this protocol has been shown to be safe, feasible, and potentially effective at improving ambulation in both open field score (OFS) 0 and OFS 1 dogs. The specific sample population criteria limit the number of dogs included, mainly due to owners withdrawing over time. Thus, the present case series study aimed to demonstrate that an NRMP could contribute to a functional treatment possibly based on synaptic and anatomic reorganization of the spinal cord.

Abstract

This case series study aimed to evaluate the safety, feasibility, and positive outcome of the neurorehabilitation multimodal protocol (NRMP) in 16 chronic post-surgical IVDD Hansen type I dogs, with OFS 0/DPP− (n = 9) and OFS 1/DPP+ (n = 7). All were enrolled in the NRMP for a maximum of 90 days and were clinically discharged after achieving ambulation. The NRMP was based on locomotor training, functional electrical stimulation, transcutaneous electrical spinal cord stimulation, and 4-aminopyridine (4-AP) pharmacological management. In the Deep Pain Perception (DPP)+ dogs, 100% recovered ambulation within a mean period of 47 days, reaching OFS ≥11, which suggests that a longer period of time is needed for recovery. At follow-up, all dogs presented a positive evolution with voluntary micturition. Of the DPP− dogs admitted, all achieved a flexion/extension locomotor pattern within 30 days, and after starting the 4-AP, two dogs were discharged at outcome day 45, with 78% obtaining Spinal Reflex Locomotion (SRL) and automatic micturition within a mean period of 62 days. At follow-up, all dogs maintained their neurological status. After the NRMP, ambulatory status was achieved in 88% (14/16) of dogs, without concurrent events. Thus, an NRMP may be an important therapeutic option to reduce the need for euthanasia in the clinical setting.

Phase IIB Randomized Trial on the Use of 4-Aminopyridine in Guillain-Barré Syndrome

OBJECTIVE

To determine the safety and efficacy of orally delivered 4-aminopyridine (4-AP) in persons with Guillain-Barré Syndrome (GBS) >6 months from initial diagnosis.

DESIGN

A randomized, double-blind, placebo-controlled, crossover study.

SETTING

Tertiary care clinical outpatient program.

PARTICIPANTS

Nineteen participants enrolled (14 male, 5 female; N=19), neurologic impairment secondary to GBS and functional loss on the FIM motor score (stable for ≥12mo) and >3.0 but <5.0 on the American Spinal Injury motor scale. Twelve participants (mean age, 59y; range, 23-77y) completed the study.

INTERVENTIONS

A 4-AP dose-escalation study with 8 weeks in each period with a 3-week washout period, followed by 3 months open-label follow-up.

MAIN OUTCOME MEASURES

FIM motor score was the primary outcome measure; also evaluated were the American Spinal Injury motor strength score (all limbs), handheld dynamometer, 6-minute walk test, Medical Outcomes Study 12-Item Short Form, Center for Epidemiological Studies Depression scale, Positive and Negative Affect Schedule, pain, GBS disability scale, Jepsen-Taylor Hand Function Test, Minnesota Manual Dexterity Test and Minnesota Rate of Manipulation Test, Get Up and Go Test, McGill Pain Inventory, Craig Handicap Assessment and Reporting Technique, and participant self-evaluation.

RESULTS

Seven participants discontinued the study prematurely: 3 because of adverse events, 3 because of travel difficulties or relocation, and 1 because of pretreatment laboratory abnormalities. After removing 3 participants with maximum FIM scores, 4-AP arm trended superior to placebo (P=.065). Patients subjectively could always tell when they were on the active agent usually by tingling sensations or a sense of wellness. No statistically significant differences were found for other outcome measures although there were strong trends.

CONCLUSIONS

This study demonstrates the safety of 4-AP in the patient population with GBS as the predominate goal of the study. A trend toward improved function after treatment was noted with most patients electing to stay on the medication after the trial.

(4-Aminopyridine)-PLGA-PEG as a Novel Thermosensitive and Locally Injectable Treatment for Acute Peripheral Nerve Injury

Traumatic peripheral nerve injury (TPNI) represents a major medical problem that results in loss of motor and sensory function, and in severe cases, limb paralysis and amputation. To date, there are no effective treatments beyond surgery in selective cases. In repurposing studies, we found that daily systemic administration of the FDA-approved drug 4-aminopyridine (4-AP) enhanced functional recovery after acute peripheral nerve injury. This study was aimed at constructing a novel local delivery system of 4-AP using thermogelling polymers. We optimized a thermosensitive (4-AP)-poly(lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG-PLGA) block copolymer formulation. (4-AP)-PLGA-PEG exhibited controlled release of 4-AP both in vitro and in vivo for approximately 3 weeks, with clinically relevant safe serum levels in animals. Rheological investigation showed that (4-AP)-PLGA-PEG underwent a solution to gel transition at 32 °C, a physiologically relevant temperature, allowing us to administer it to an injured limb while subsequently forming an in situ gel. A single local administration of (4-AP)-PLGA-PEG remarkably enhanced motor and sensory functional recovery on post-sciatic nerve crush injury days 1, 3, 7, 14, and 21. Moreover, immunohistochemical studies of injured nerves treated with (4-AP)-PLGA-PEG demonstrated an increased expression of neurofilament heavy chain (NF-H) and myelin protein zero (MPZ) proteins, two major markers of nerve regeneration. These findings demonstrate that (4-AP)-PLGA-PEG may be a promising long-acting local therapeutic agent in TPNI, for which no pharmacologic treatment exists.

4-Aminopyridine: A Single-Dose Diagnostic Agent to Differentiate Axonal Continuity in Nerve Injuries

INTRODUCTION

Traumatic peripheral nerve injuries (TPNIs) are increasingly prevalent in battlefield trauma, and the functional recovery with TPNIs depends on axonal continuity. Although the physical examination is the main tool for clinical diagnosis with diagnostic work up, there is no diagnostic tool available to differentiate nerve injuries based on axonal continuity. Therefore, treatment often relies on "watchful waiting," and this leads to muscle weakness and further reduces the chances of functional recovery. 4-aminopyridine (4-AP) is clinically used in multiple sclerosis patients for walking performance improvement. Preliminary results in conscious mice suggested a diagnostic role of 4-AP in distinguishing axonal continuity. In this study, we thought to evaluate the diagnostic potential of 4-AP on the axonal continuity in unawake/sedated animals.

MATERIALS AND METHODS

Rat sciatic nerve crush and transection injuries were used in this study. Briefly, rats were anesthetized with isoflurane and mechanically ventilated with oxygen-balanced vaporized isoflurane. Sciatic nerve and triceps surae muscles were exposed by blunt dissection, and a stimulating electrode was placed under a sciatic nerve proximal to the crush injury. A force transducer measured muscle tension response to electrical stimulation of sciatic nerve. Muscle response was measured before crush, after crush, and 30 minutes after systemic 4-AP (150 µg/kg) or local (4-AP)-poly(lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG) treatment.

RESULTS

We found that both crush and transection injuries in sciatic nerve completely abolished muscle response to electrical stimulation. Single dose of systemic 4-AP and local (4-AP)-PLGA-PEG treatment with crush injury significantly restored muscle responses to electrical stimulation after 30 minutes of administration. However, systemic 4-AP treatment had no effect on muscle response after nerve transection. These results clearly demonstrate that 4-AP can restore nerve conduction and produce muscle response within minutes of administration only when there is a nerve continuity, even in the sedated animal.

CONCLUSIONS

We conclude that 4-AP could be a promising diagnostic agent in differentiating TPNI based on axonal continuity.

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.

Biopolymer-nanotube nerve guidance conduit drug delivery for peripheral nerve regeneration: In vivo structural and functional assessment

Peripheral nerve injuries account for roughly 3% of all trauma patients with over 900,000 repair procedures annually in the US. Of all extremity peripheral nerve injuries, 51% require nerve repair with a transected gap. The current gold-standard treatment for peripheral nerve injuries, autograft repair, has several shortcomings. Engineered constructs are currently only suitable for short gaps or small diameter nerves. Here, we investigate novel nerve guidance conduits with aligned microchannel porosity that deliver sustained-release of neurogenic 4-aminopyridine (4-AP) for peripheral nerve regeneration in a critical-size (15 mm) rat sciatic nerve transection model. The results of functional walking track analysis, morphometric evaluations of myelin development, and histological assessments of various markers confirmed the equivalency of our drug-conduit with autograft controls. Repaired nerves showed formation of thick myelin, presence of S100 and neurofilament markers, and promising functional recovery. The conduit's aligned microchannel architecture may play a vital role in physically guiding axons for distal target reinnervation, while the sustained release of 4-AP may increase nerve conduction, and in turn synaptic neurotransmitter release and upregulation of critical Schwann cell neurotrophic factors. Overall, our nerve construct design facilitates efficient and efficacious peripheral nerve regeneration via a drug delivery system that is feasible for clinical applications.

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Nerve guidance conduit platform with tunable scaffold properties for repair and regeneration of large-gap nerve injuries.

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Sustained 4-aminopyridine release amplifies neurotrophic factor release by Schwann cells to promote axon regeneration.

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Longitudinally aligned scaffold pores and controllable physicochemical properties provide guidance for axon regeneration.

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Critical-size rat sciatic nerve defect healing both structurally and functionally resembled autograft control treatment.

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Innovative and transformative scaffold technology imbued with structural and functional features for tissue regeneration.

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Scaffold enable tailorable release profiles for small molecules proteins and electrical stimulation for tissue regeneration.

Addressing the Need of a Translational Approach in Peripheral Neuropathy Research: Morphology Meets Function

Peripheral neuropathies (PNs) are a type of common disease that hampers the quality of life of affected people. Treatment, in most cases, is just symptomatic and often ineffective. To improve drug discovery in this field, preclinical evidence is warranted. In vivo rodent models allow a multiparametric approach to test new therapeutic strategies, since they can allow pathogenetic and morphological studies different from the clinical setting. However, human readouts are warranted to promptly translate data from the bench to the bedside. A feasible solution would be neurophysiology, performed similarly at both sides. We describe a simple protocol that reproduces the standard clinical protocol of a neurophysiology hospital department. We devised the optimal montage for sensory and motor recordings (neurography) in mice, and we also implemented F wave testing and a short electromyography (EMG) protocol at rest. We challenged this algorithm by comparing control animals (BALB/c mice) with a model of mild neuropathy to grasp even subtle changes. The neurophysiological results were confirmed with neuropathology. The treatment group showed all expected alterations. Moreover, the neurophysiology matched the neuropathological analyses. Therefore, our protocol can be suggested to promptly translate data from the bench to the bedside and vice versa.

The effects of 4-aminopyridine and methylprednisolone on recovery of the facial nerve crush injury

OBJECTIVE

4-Aminopyridine (4-AP) is a potassium channel blocker that enhances nerve excitability. In this study, rat models that have facial nerve crush injury (FNCI) were grouped and treated with methylprednisolone (MP), 4-AP, and a combination of these two drugs. Electrophysiologic and histopathologic outcomes of these groups will be compared with a control group.

MATERIALS AND METHODS

Thirty healthy male Wistar rats (mean weight of 265 g) were used in this study. The rats were randomly divided into five groups with six subjects in each: Group 1 (sham group), Group 2 (control group), Group 3 (MP group), Group 4 (4-aminopyridine group), and Group 5 (4-AP + MP group). All groups except the sham group underwent crush injury to the right facial nerve. Electrophysiologic and histologic recovery was recorded three weeks postoperatively.

RESULTS

The 4-AP group and the combined group had a more significant recovery at Nerve Excitability Thresholds (NET) at the end of three weeks. The methylprednisolone group and the control group had a minimal recovery of NET. Histologically, when compared with the control group, the combined group was the only group that had significant recovery at all three of axonal degeneration, axon diameter, and myelin thickness.

CONCLUSION

In this experimental study, we demonstrated that a combination treatment of 4-AP and MP is more effective in the recovery of peripheric FNCI than in the no-treatment control group and in the 4-AP- or MP-alone groups. Moreover, our results suggested that 4-AP can be a potent alternative to MP in the treatment of the FNCI.

LEVEL OF EVIDENCE

N/A.

Aminopiridines in the treatment of multiple sclerosis and other neurological disorders

Symptomatic treatment has a great relevance for the management of patients with neurologic diseases, since it reduces disease burden and improves quality of life. Aminopyridines (APs) are a group of potassium (K+) channel blocking agents that exert their activity both at central nervous system level and on neuromuscular junction. This review describes the use of APs for the symptomatic treatment of neurological conditions. We will describe trials leading to the approval of the extended-release 4-aminopyridine for MS and evidence in support of the use in other neurological diseases.

Intra and inter: Alterations in functional brain resting-state networks after peripheral nerve injury

INTRODUCTION

Numerous treatments suggest that brain plasticity changes after peripheral nerve injury (PNI), and most studies examining functional magnetic resonance imaging focused on abnormal changes in specific brain regions. However, it is the large-scale interaction of neuronal networks instead of isolated brain regions contributed to the functional recovery after PNI. In the present study, we examined the intra- and internetworks alterations between the related functional resting-state networks (RSNs) in a sciatic nerve injury rat model.

METHODS

Ninety-six female rats were divided into a control and model group. Unilateral sciatic nerve transection and direct anastomosis were performed in the latter group. We used an independent component analysis (ICA) algorithm to observe the changes in RSNs and assessed functional connectivity between different networks using the functional networks connectivity (FNC) toolbox.

RESULTS

Six RSNs related to PNI were identified, including the basal ganglia network (BGN), sensorimotor network (SMN), salience network (SN), interoceptive network (IN), cerebellar network (CN), and default mode network (DMN). The model group showed significant changes in whole-brain FC changes within these resting-state networks (RSNs), but four of these RSNs exhibited a conspicuous decrease. The interalterations performed that significantly decreased FNC existed between the BGN and SMN, BGN and IN, and BGN and DMN (p < .05, corrected). A significant increase in FNC existed between DMN and CN and between CN and SN (p < .05, corrected).

CONCLUSION

The results showed the large-scale functional reorganization at the network level after PNI. This evidence reveals new implications to the pathophysiological mechanisms in brain plasticity of PNI.

Green Tea Polyphenols Promote Functional Recovery from Peripheral Nerve Injury in Rats

Background

Peripheral nerve injury (PNI) is a common and progressive disorder with sensory and motor deficits in the peripheral nervous system (PNS). Treatment is difficult, with unfavorable prognosis. Green tea polyphenols (GTPs) exert neuroprotective effects on regeneration of the central nervous system (CNS). However, the effects of GTPs on functional recovery of the PNS have not been fully characterized. Consequently, the present study investigated the effects of GTPs on nerve regeneration of rats with PNI.

Material/Methods

The model of PNI was established in rats by sciatic nerve injury (SNI). Adult male Wistar rats with SNI were randomly divided into a vehicle group and a GTPs group. The compound muscle action potential (CMAP) of rat sciatic nerves (SN) was measured using the CM6240 physiological signal acquisition and processing system. The wet weight of the triceps muscle was determined using an analytical balance. The number of myelinated nerve fibers was counted under an optical microscope. Ultrastructure of the regenerated nerves in SN was observed by transmission electron microscopy. The mRNA and protein expression of nerve growth factor (NGF), growth-associated protein-43 (GAP-43), neurofilament 200 (NF200), and myelin-associated glycoprotein (MAG) in SN stumps were measured by real-time quantification PCR (RT-qPCR) and Western blot, respectively.

Results

In rats with SNI, GTPs relieved the adhesion between nerve anastomosis and surrounding tissues, and significantly increased nerve conduction velocity, wet weight of the triceps muscle, and development and axonal regeneration of myelinated nerve fibers. Moreover, GTPs promoted the mRNA and protein expressions of NGF, GAP-43, NF200, and MAG in SN stumps.

Conclusions

GTPs promotes nerve regeneration in rats with SNI.

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.

3D Printing and Bioprinting Nerve Conduits for Neural Tissue Engineering

Fabrication of nerve conduits for perfectly repairing or replacing damaged peripheral nerve is an urgent demand worldwide, but it is also a formidable clinical challenge. In the last decade, with the rapid development of manufacture technologies, 3D printing and bioprinting have been becoming remarkable stars in the field of neural engineering. In this review, we explore that the biomaterial inks (hydrogels, thermoplastic, and thermoset polyesters and composite) and bioinks have been selected for 3D printing and bioprinting of peripheral nerve conduits. This review covers 3D manufacturing technologies, including extrusion printing, inkjet printing, stereolithography, and bioprinting with inclusion of cells, bioactive molecules, and drugs. Finally, an outlook on the future directions of 3D printing and 4D printing in customizable nerve therapies is presented.

Innervation: the missing link for biofabricated tissues and organs

Innervation plays a pivotal role as a driver of tissue and organ development as well as a means for their functional control and modulation. Therefore, innervation should be carefully considered throughout the process of biofabrication of engineered tissues and organs. Unfortunately, innervation has generally been overlooked in most non-neural tissue engineering applications, in part due to the intrinsic complexity of building organs containing heterogeneous native cell types and structures. To achieve proper innervation of engineered tissues and organs, specific host axon populations typically need to be precisely driven to appropriate location(s) within the construct, often over long distances. As such, neural tissue engineering and/or axon guidance strategies should be a necessary adjunct to most organogenesis endeavors across multiple tissue and organ systems. To address this challenge, our team is actively building axon-based "living scaffolds" that may physically wire in during organ development in bioreactors and/or serve as a substrate to effectively drive targeted long-distance growth and integration of host axons after implantation. This article reviews the neuroanatomy and the role of innervation in the functional regulation of cardiac, skeletal, and smooth muscle tissue and highlights potential strategies to promote innervation of biofabricated engineered muscles, as well as the use of "living scaffolds" in this endeavor for both in vitro and in vivo applications. We assert that innervation should be included as a necessary component for tissue and organ biofabrication, and that strategies to orchestrate host axonal integration are advantageous to ensure proper function, tolerance, assimilation, and bio-regulation with the recipient post-implant.

White matter structure and myelin-related gene expression alterations with experience in adult rats

White matter (WM) plasticity during adulthood is a recently described phenomenon by which experience can shape brain structure. It has been observed in humans using diffusion tensor imaging (DTI) and myelination has been suggested as a possible mechanism. Here, we set out to identify molecular and cellular changes associated with WM plasticity measured by DTI. We combined DTI, immunohistochemistry and mRNA expression analysis and examined the effects of somatosensory experience in adult rats. First, we observed experience-induced DTI differences in WM and in grey matter structure. C-Fos mRNA expression, a marker of cortical activity, in the barrel cortex correlated with the MRI WM metrics, indicating that molecular correlates of cortical activity relate to macroscale measures of WM structure. Analysis of myelin-related genes revealed higher myelin basic protein (MBP) mRNA expression. Higher MBP protein expression was also found via immunohistochemistry in WM. Finally, unbiased RNA sequencing analysis identified 134 differentially expressed genes encoding proteins involved in functions related to cell proliferation and differentiation, regulation of myelination and neuronal activity modulation. In conclusion, macroscale measures of WM plasticity are supported by both molecular and cellular evidence and confirm that myelination is one of the underlying mechanisms.

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.

Repair strategies for injured peripheral nerve: Review

Compromised functional regains in about half of the patients following surgical nerve repair pose a serious socioeconomic burden to the society. Although surgical strategies such as end-to-end neurorrhaphy, nerve grafting and nerve transfer are widely applied in distal injuries leading to optimal recovery; however in proximal nerve defects functional outcomes remain unsatisfactory. Biomedical engineering approaches unite the efforts of the surgeons, engineers and biologists to develop regeneration facilitating structures such as extracellular matrix based supportive polymers and tubular nerve guidance channels. Such polymeric structures provide neurotrophic support from injured nerve stumps, retard the fibrous tissue infiltration and guide regenerating axons to appropriate targets. The development and application of nerve guidance conduits (NGCs) to treat nerve gap injuries offer clinically relevant and feasible solutions. Enhanced understanding of the nerve regeneration processes and advances in NGCs design, polymers and fabrication strategies have led to developing modern NGCs with superior regeneration-conducive capacities. Current review focuses on the advances in surgical and engineering approaches to treat peripheral nerve injuries. We suggest the incorporation of endothelial cell growth promoting cues and factors into the NGC interior for its possible enhancement effects on the axonal regeneration process that may result in substantial functional outcomes.

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.

Human equivalent dose of oral 4-aminopyridine differentiates nerve crush injury from transection injury and improves post-injury function in mice

4-Aminopyridine (4-AP), an FDA-approved drug for the symptomatic treatment of multiple sclerosis, is used to improve neuromuscular function in patients with diverse demyelinating disorders. We recently demonstrated that local, transdermal or injectable forms of 4-AP improve myelination, nerve conduction velocity, muscle atrophy, and motor function after traumatic peripheral nerve injury in mice. While oral 4-AP is most commonly used in the clinic, it is unknown whether human equivalent oral doses of 4-AP have effects on traumatic peripheral nerve injury differentiation, myelination, muscle atrophy, functional recovery, and post-injury inflammatory processes in animals. Mice with sciatic nerve crush or denervation injury received oral or intraperitoneal 4-AP (10 μg) or vehicle alone and were examined for pharmacokinetics, motor function, muscle mass, intrinsic muscle force, nerve morphological and gene expression profiles. 4-AP showed linear pharmacokinetics and the maximum plasma 4-AP concentrations were proportional to 4-AP dose. Acute single dose of oral 4-AP administration induced a rapid transient improvement in motor function that was different in traumatic peripheral nerve injury with or without nerve continuity, chronic daily oral 4-AP treatment significantly enhanced post crush injury motor function recovery and this effect was associated with improved myelination, muscle mass, and ex vivo muscle force. Polymerase chain reaction array analysis with crushed nerve revealed significant alterations in gene involved in axonal inflammation and regeneration. These findings provide convincing evidence that regardless of the route of administration, 4-AP can acutely differentiate traumatic peripheral nerve injury with or without nerve continuity and can enhance in vivo functional recovery with better preservation of myelin sheaths, muscle mass, and muscle force. 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.

Current Status of Therapeutic Approaches against Peripheral Nerve Injuries: A Detailed Story from Injury to Recovery

Peripheral nerve injury is a complex condition with a variety of signs and symptoms such as numbness, tingling, jabbing, throbbing, burning or sharp pain. Peripheral nerves are fragile in nature and can easily get damaged due to acute compression or trauma which may lead to the sensory and motor functions deficits and even lifelong disability. After lesion, the neuronal cell body becomes disconnected from the axon's distal portion to the injury site leading to the axonal degeneration and dismantlement of neuromuscular junctions of targeted muscles. In spite of extensive research on this aspect, complete functional recovery still remains a challenge to be resolved. This review highlights detailed pathophysiological events after an injury to a peripheral nerve and the associated factors that can either hinder or promote the regenerative machinery. In addition, it throws light on the available therapeutic strategies including supporting therapies, surgical and non-surgical interventions to ameliorate the axonal regeneration, neuronal survival, and reinnervation of peripheral targets. Despite the availability of various treatment options, we are still lacking the optimal treatments for a perfect and complete functional regain. The need for the present age is to discover or design such potent compounds that would be able to execute the complete functional retrieval. In this regard, plant-derived compounds are getting more attention and several recent reports validate their remedial effects. A plethora of plants and plant-derived phytochemicals have been suggested with curative effects against a number of diseases in general and neuronal injury in particular. They can be a ray of hope for the suffering individuals.

Peripheral nerve injury and myelination: Potential therapeutic strategies

Traumatic peripheral nerve injury represents a major clinical and public health problem that often leads to significant functional impairment and permanent disability. Despite modern diagnostic procedures and advanced microsurgical techniques, functional recovery after peripheral nerve repair is often unsatisfactory. Therefore, there is an unmet need for new therapeutic or adjunctive strategies to promote the functional recovery in nerve injury patients. In contrast to the central nervous system, Schwann cells in the peripheral nervous system play a pivotal role in several aspects of nerve repair such as degeneration, remyelination, and axonal growth. Several non-surgical approaches, including pharmacological, electrical, cell-based, and laser therapies, have been employed to promote myelination and enhance functional recovery after peripheral nerve injury. This review will succinctly discuss the potential therapeutic strategies in the context of myelination following peripheral neurotrauma.

4-Aminopyridine as a Single Agent Diagnostic and Treatment for Severe Nerve Crush Injury

BACKGROUND

Traumatic peripheral nerve injury (TPI) is a major medical problem without effective treatment options. There is no way to diagnose or treat an incomplete injury and delays contribute to morbidity. We examined 4-aminopyridine (4-AP), a potassium-channel blocker as a possible treatment for TPI.

METHODS

We used standard mouse models of TPI with functional outcomes including sciatic-functional-index, sensory indices, and electrodiagnostics; in addition to standard immunohistochemical, and electron microscopic correlates of axon and myelin morphology.

RESULTS

Sustained early 4-AP administration increased the speed and extent of behavioral recovery too rapidly to be explained by axonal regeneration. 4-AP also enhanced recovery of nerve conduction velocity, promoted remyelination, and increased axonal area post-injury. 4-AP treatment also enabled the rapid distinction between incomplete and complete nerve lesions.

CONCLUSION

4-AP singularly provides both a new potential therapy to promote durable recovery and remyelination in acute peripheral nerve injury and a means of identifying lesions in which this therapy would be most likely to be of value. The ability to distinguish injuries that may respond to extended therapy without intervention can offer benefit to wounded soldiers.

4-Aminopyridine attenuates muscle atrophy after sciatic nerve crush injury in mice

INTRODUCTION

We recently demonstrated the beneficial effects of 4-aminopyridine (4-AP), a potassium channel blocker, in enhancing remyelination and recovery of nerve conduction velocity and motor function after sciatic nerve crush injury in mice. Although muscle atrophy occurs very rapidly after nerve injury, the effect of 4-AP on muscle atrophy and intrinsic muscle contractile function is largely unknown.

METHODS

Mice were assigned to sciatic nerve crush injury and no-injury groups and were followed for 3, 7, and 14 days with/without 4-AP or saline treatment. Morphological, functional, and transcriptional properties of skeletal muscle were assessed.

RESULTS

In addition to improving in vivo function, 4-AP significantly reduced muscle atrophy with increased muscle fiber diameter and contractile force. Reduced muscle atrophy was associated with attenuated expression of atrophy-related genes and increased expression of proliferating stem cells.

DISCUSSION

These findings provide new insights into the potential therapeutic benefits of 4-AP against nerve injury-induced muscle atrophy and dysfunction. Muscle Nerve 60: 192-201, 2019.

Pharmacological Attenuation of Electrical Effects in a Model of Compression Neuropathy

BACKGROUND

Peripheral nerve compression and entrapment can be debilitating. Using a validated animal model of peripheral nerve compression, we examined the utility of 2 drugs approved for other uses in humans, 4-aminopyridine (4-AP) and erythropoietin (EPO), as treatments for surgically induced ischemia and as adjuvants to surgical decompression.

METHODS

Peripheral nerve compression was induced in wild-type mice by placing an inert silicone sleeve around the sciatic nerve. Decompression surgery was performed at 6 weeks with mice receiving 4-AP, EPO, or saline solution either during and after compression or only after decompression. A nerve conduction study and morphometric analyses were performed to compare the extent of the injury and the efficacy of the therapies, and the findings were subjected to statistical analysis.

RESULTS

During peripheral nerve compression, there was a progressive decline in nerve conduction velocity compared with that in sham-treatment animals, in which nerve conduction velocity remained normal (∼55 m/s). Mice treated with 4-AP or EPO during the compression phase had significantly smaller declines in nerve conduction velocity and increased plateau nerve conduction velocities compared with untreated controls (animals that received saline solution). Histomorphometric analyses of newly decompressed nerves (i.e., nerves that underwent decompression on the day that the mouse was sacrificed) revealed that both treated groups had significantly greater proportions of large (>5-µm) axons than the untreated controls. Following surgical decompression, all animals recovered to a normal baseline nerve conduction velocity by day 15; however, treatment significantly accelerated improvement (in both the 4-AP and the EPO group), even when it was only started after decompression. Histomorphometric analyses at 7 and 15 days following surgical decompression revealed significantly increased myelin thickness and significantly greater proportions of large axons among the treated animals.

CONCLUSIONS

Both the 4-AP and the EPO-treated group demonstrated improvements in tissue architectural and electrodiagnostic measurements, both during and after peripheral nerve compression, compared with untreated mice.

CLINICAL RELEVANCE

Peripheral nerve decompression is one of the most commonly performed procedures in orthopaedic surgery. We believe that there is reason for some optimism about the translation of our findings to the clinical setting. Our findings in this murine model suggest that 4-AP and EPO may lessen the effects of nerve entrapment and that the use of these agents after decompression may speed and perhaps otherwise optimize recovery after surgery.

Aligned microchannel polymer-nanotube composites for peripheral nerve regeneration: Small molecule drug delivery

Peripheral nerve injury accounts for roughly 2.8% of all trauma patients with an annual cost of 7 billion USD in the U.S. alone. Current treatment options rely on surgical intervention with the use of an autograft, despite associated shortcomings. Engineered nerve guidance conduits, stem cell therapies, and transient electrical stimulation have reported to increase speeds of functional recovery. As an alternative to the conduction effects of electrical stimulation, we have designed and optimized a nerve guidance conduit with aligned microchannels for the sustained release of a small molecule drug that promotes nerve impulse conduction. A biodegradable chitosan structure reinforced with drug-loaded halloysite nanotubes (HNT) was formed into a foam-like conduit with interconnected, longitudinally-aligned pores with an average pore size of 59.3 ± 14.2 μm. The aligned composite with HNTs produced anisotropic mechanical behavior with a Young's modulus of 0.33 ± 0.1 MPa, very similar to that of native peripheral nerve. This manuscript reports on the sustained delivery of 4-Aminopyridine (4AP, molecular weight 94.1146 g/mol), a potassium-channel blocker as a growth factor alternative to enhance the rate of nerve regeneration. The conduit formulation released a total of 30 ± 2% of the encapsulated 4AP in the first 7 days. Human Schwann cells showed elevated expression of key proteins such as nerve growth factor, myelin protein zero, and brain derived neurotrophic factor in a 4AP dose dependent manner. Preliminary in vivo studies in a critical-sized sciatic nerve defect in Wistar rats confirmed conduit suturability and strength to withstand ambulatory forces over 4 weeks of their implantation. Histological evaluations suggest conduit biocompatibility and Schwann cell infiltration and organization within the conduit and lumen. These nerve guidance conduits and 4AP sustained delivery may serve as an attractive strategy for nerve repair and regeneration.

Effects of 4-aminopyridine on attention and executive functions of patients with multiple sclerosis: Randomized, double-blind, placebo-controlled clinical trial. Preliminary report

BACKGROUND

A high percentage of patients with multiple sclerosis present cognitive alterations. Because 4-aminopyridine improves nerve conduction and efficient synaptic connection could improve cognitive dysfunction.

OBJECTIVE

To evaluate the efficacy on cognitive performance and safety of 4-aminopyridine administered to patients with relapsing-remitting multiple sclerosis.

METHODS

A randomized, double-blind, placebo controlled clinical trial was conducted in patients with relapsing-remitting multiple sclerosis diagnosis according to the McDonald criteria. At the beginning and at the end of the treatment different tests were used to assess cognitive performance. Subsequently, patients were randomized 1:1 to receive treatment or placebo. A bootstrap-t test was proposed to test the effectiveness of cognitive performance, considering a p-value < 0.05 as statistically significant.

RESULTS

Twenty-four patients were recruited of which 21 completed the trial, 11 with 4-aminopyridine and 10 with placebo treatment. No significant differences between groups in the initial assessments were observed. In terms of efficacy, the experimental group achieved significantly higher scores in attention span, verbal fluency, planning and graphics and constructive motion.

CONCLUSIONS

4-aminopyridine proved to be an effective treatment on cognitive aspects in patients with relapsing-remitting multiple sclerosis. Drug doses were shown to be safe with mild to moderate adverse events (ClinicalTrials.gov number, NCT02280096).

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.

Restoring Axonal Function with 4-Aminopyridine: Clinical Efficacy in Multiple Sclerosis and Beyond

The oral potassium channel blocker 4-aminopyridine has been used in various neurological conditions for decades. Numerous case reports and studies have supported its clinical efficacy in ameliorating the clinical presentation of certain neurological disorders. However, its short half-life, erratic drug levels, and safety-related dose restrictions limited its use as a self-compounded drug in clinical practice. This changed with the introduction of a prolonged-release formulation, which was successfully tested in patients with multiple sclerosis. It was fully approved by the US FDA in January 2010 but initially received only conditional approval from the European Medicines Agency (EMA) in July 2011. After additional clinical studies, this conditional approval was changed to unrestricted approval in August 2017. This article reviews and discusses these recent studies and places aminopyridines and their clinical utility into the context of a broader spectrum of neurological disorders, where clinical efficacy has been suggested. In 2010, prolonged-release 4-aminopyridine became the first drug specifically licensed to improve walking in patients with multiple sclerosis. About one-third of patients across disease courses benefit from this treatment. In addition, various reports indicate clinical efficacy beyond multiple sclerosis, which may broaden its use in clinical practice.

The effects of paranodal myelin damage on action potential depend on axonal structure

Biophysical computational models of axons provide an important tool for quantifying the effects of injury and disease on signal conduction characteristics. Several studies have used generic models to study the average behavior of healthy and injured axons; however, few studies have included the effects of normal structural variation on the simulated axon's response to injury. The effects of variations in physiological characteristics on axonal function were mapped by altering the structure of the nodal, paranodal, and juxtaparanodal regions across reported values in three different caliber axons (1, 2, and 5.7 μm). Myelin detachment and retraction were simulated to quantify the effects of each injury mechanism on signal conduction. Conduction velocity was most affected by axonal fiber diameter (89%), while membrane potential amplitude was most affected by nodal length (86%) in healthy axons. Postinjury axonal functionality was most affected by myelin detachment in the paranodal and juxtaparanodal regions when retraction and detachment were modeled simultaneously. The efficacy of simulated potassium channel blockers on restoring membrane potential and velocity varied with axonal caliber and injury type. The structural characteristics of axons affect their functional response to myelin retraction and detachment and their subsequent response to potassium channel blocker treatment.

Sodium-dependent Vitamin C transporter 2 deficiency impairs myelination and remyelination after injury: Roles of collagen and demethylation

Peripheral nerve myelination involves rapid production of tightly bound lipid layers requiring cholesterol biosynthesis and myelin protein expression, but also a collagen-containing extracellular matrix providing mechanical stability. In previous studies, we showed a function of ascorbic acid in peripheral nerve myelination and extracellular matrix formation in adult mice. Here, we sought the mechanism of action of ascorbic acid in peripheral nerve myelination using different paradigms of myelination in vivo and in vitro. We found impaired myelination and reduced collagen expression in Sodium-dependent Vitamin C Transporter 2 heterozygous mice (SVCT2^+/- ) during peripheral nerve development and after peripheral nerve injury. In dorsal root ganglion (DRG) explant cultures, hypo-myelination could be rescued by precoating with different collagen types. The activity of the ascorbic acid-dependent demethylating Ten-eleven-translocation (Tet) enzymes was reduced in ascorbic acid deprived and SVCT2^+/- DRG cultures. Further, in ascorbic acid-deprived DRG cultures, methylation of a CpG island in the collagen alpha1 (IV) and alpha2 (IV) bidirectional promoter region was increased compared to wild-type and ascorbic acid treated controls. Taken together, these results provide further evidence for the function of ascorbic acid in myelination and extracellular matrix formation in peripheral nerves and suggest a putative molecular mechanism of ascorbic acid function in Tet-dependent demethylation of collagen promoters.

4-Aminopyridine promotes functional recovery and remyelination in acute peripheral nerve injury

Traumatic peripheral nerve damage is a major medical problem without effective treatment options. In repurposing studies on 4-aminopyridine (4-AP), a potassium channel blocker that provides symptomatic relief in some chronic neurological afflictions, we discovered this agent offers significant promise as a small molecule regenerative agent for acute traumatic nerve injury. We found, in a mouse model of sciatic crush injury, that sustained early 4-AP administration increased the speed and extent of behavioral recovery too rapidly to be explained by axonal regeneration. Further studies demonstrated that 4-AP also enhanced recovery of nerve conduction velocity, promoted remyelination, and increased axonal area post-injury. We additionally found that 4-AP treatment enables distinction between incomplete and complete lesions more rapidly than existing approaches, thereby potentially addressing the critical challenge of more effectively distinguishing injured individuals who may require mutually exclusive treatment approaches. Thus, 4-AP singularly provides both a new potential therapy to promote durable recovery and remyelination in acute peripheral nerve injury and a means of identifying lesions in which this therapy would be most likely to be of value.