Riluzole prevents ischemic spinal cord injury caused by aortic crossclamping

Riluzole treatment modulates KCC2 and EAAT-2 receptor expression and Ca2+ accumulation following ventral root avulsion injury

Avulsion injury results in motoneuron death due to the increased excitotoxicity developing in the affected spinal segments. This study focused on possible short and long term molecular and receptor expression alterations which are thought to be linked to the excitotoxic events in the ventral horn with or without the anti-excitotoxic riluzole treatment. In our experimental model the left lumbar 4 and 5 (L4, 5) ventral roots of the spinal cord were avulsed. Treated animals received riluzole for 2 weeks. Riluzole is a compound that acts to block voltage-activated Na⁺ and Ca²⁺ channels. In control animals the L4, 5 ventral roots were avulsed without riluzole treatment. Expression of astrocytic EAAT-2 and that of KCC2 in motoneurons on the affected side of the L4 spinal segment were detected after the injury by confocal and dSTORM imaging, intracellular Ca²⁺ levels in motoneurons were quantified by electron microscopy. The KCC2 labeling in the lateral and ventrolateral parts of the L4 ventral horn was weaker compared with the medial part of L4 ventral horn in both groups. Riluzole treatment dramatically enhanced motoneuron survival but was not able to prevent the down-regulation of KCC2 expression in injured motoneurons. In contrast, riluzole successfully obviated the increase of intracellular calcium level and the decrease of EAAT-2 expression in astrocytes compared with untreated injured animals. We conclude that KCC2 may not be an essential component for survival of injured motoneurons and riluzole is able to modulate the intracellular level of calcium and expression of EAAT-2.

A mechanistic overview of spinal cord injury, oxidative DNA damage repair and neuroprotective therapies

Despite substantial development in medical treatment strategies scientists are struggling to find a cure against spinal cord injury (SCI) which causes long term disability and paralysis. The prime rationale behind it is the enlargement of primary lesion due to an initial trauma to the spinal cord which spreads to the neighbouring spinal tissues It begins from the time of traumatic event happened and extends to hours and even days. It further causes series of biological and functional alterations such as inflammation, excitotoxicity and ischemia, and promotes secondary lesion to the cord which worsens the life of individuals affected by SCI. Oxidative DNA damage is a stern consequence of oxidative stress linked with secondary injury causes oxidative base alterations and strand breaks, which provokes cell death in neurons. It is implausible to stop primary damage however it is credible to halt the secondary lesion and improve the quality of the patient's life to some extent. Therefore it is crucial to understand the hidden perspectives of cell and molecular biology affecting the pathophysiology of SCI. Thus the focus of the review is to connect the missing links and shed light on the oxidative DNA damages and the functional repair mechanisms, as a consequence of the injury in neurons. The review will also probe the significance of neuroprotective strategies in the present scenario. HIGHLIGHTSSpinal cord injury, a pernicious condition, causes excitotoxicity and ischemia, ultimately leading to cell death.Oxidative DNA damage is a consequence of oxidative stress linked with secondary injury, provoking cell death in neurons.Base excision repair (BER) is one of the major repair pathways that plays a crucial role in repairing oxidative DNA damages.Neuroprotective therapies curbing SCI and boosting BER include the usage of pharmacological drugs and other approaches.

Spinal Stroke: Outcome Attenuation by Erythropoietin and Carbamylated Erythropoietin and Its Prediction by Sphingosine-1-Phosphate Serum Levels in Mice

Spinal strokes may be associated with tremendous spinal cord injury. Erythropoietin (EPO) improves the neurological outcome of animals after spinal cord ischemia (SCI) and its effects on ischemia-induced endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) are considered possible molecular mechanisms. Furthermore, sphingosin-1-phosphate (S1P) is suggested to correlate with SCI. In this study, the effect of recombinant human EPO (rhEPO) and carbamylated EPO (cEPO-Fc) on the outcome of mice after SCI and a prognostic value of S1P were investigated. SCI was induced in 12-month-old male mice by thoracic aortal cross-clamping after administration of rhEPO, cEPO-Fc, or a control. The locomotory behavior of mice was evaluated by the Basso mouse scale and S1P serum levels were measured by liquid chromatography-tandem mass spectrometry. The spinal cord was examined histologically and the expressions of key UPR proteins (ATF6, PERK, and IRE1a, caspase-12) were analyzed utilizing immunohistochemistry and real-time quantitative polymerase chain reaction. RhEPO and cEPO-Fc significantly improved outcomes after SCI. The expression of caspase-12 significantly increased in the control group within the first 24 h of reperfusion. Animals with better locomotory behavior had significantly higher serum levels of S1P. Our data indicate that rhEPO and cEPO-Fc have protective effects on the clinical outcome and neuronal tissue of mice after SCI and that the ER is involved in the molecular mechanisms. Moreover, serum S1P may predict the severity of impairment after SCI.

Histological Findings After Aortic Cross-Clamping in Preclinical Animal Models

Spinal cord ischemic injury and paralysis are devastating complications after open surgical repair of thoracoabdominal aortic aneurysms. Preclinical models have been developed to simulate the clinical paradigm to better understand the neuropathophysiology and develop therapeutic treatment. Neuropathological findings in the preclinical models have not been comprehensively examined before. This systematic review studies the past 40 years of the histological findings after open surgical repair in preclinical models. Our main finding is that damage is predominantly in the grey matter of the spinal cord, although white matter damage in the spinal cord is also reported. Future research needs to examine the neuropathological findings in preclinical models after endovascular repair, a newer type of surgical repair used to treat aortic aneurysms.

Delayed Onset Muscle Soreness (DOMS): The Repeated Bout Effect and Chemotherapy-Induced Axonopathy May Help Explain the Dying-Back Mechanism in Amyotrophic Lateral Sclerosis and Other Neurodegenerative Diseases

Delayed onset muscle soreness (DOMS) is hypothesized to be caused by glutamate excitotoxicity-induced acute compression axonopathy of the sensory afferents in the muscle spindle. Degeneration of the same sensory afferents is implicated in the disease onset and progression of amyotrophic lateral sclerosis (ALS). A series of “silent” acute compression proprioceptive axonopathies with underlying genetic/environmental factors, damaging eccentric contractions and the non-resolving neuroinflammatory process of aging could lead to ALS disease progression. Since the sensory terminals in the muscle spindle could not regenerate from the micro-damage in ALS, unlike in DOMS, the induced protective microcircuits and their long-term functional plasticity (the equivalent of the repeated bout effect in DOMS) will be dysfunctional. The acute stress invoking osteocalcin, bradykinin, COX1, COX2, GDNF, PGE2, NGF, glutamate and N-methyl-D-aspartate (NMDA) receptors are suggested to be the critical signalers of this theory. The repeated bout effect of DOMS and the dysfunctional microcircuits in ALS are suggested to involve several dimensions of memory and learning, like pain memory, inflammation, working and episodic memory. The spatial encoding of these memory dimensions is compromised in ALS due to blunt position sense from the degenerating proprioceptive axon terminals of the affected muscle spindles. Dysfunctional microcircuits progressively and irreversibly interfere with postural control, with motor command and locomotor circuits, deplete the neuroenergetic system, and ultimately interfere with life-sustaining central pattern generators in ALS. The activated NMDA receptor is suggested to serve the “gate control” function in DOMS and ALS in line with the gate control theory of pain. Circumvention of muscle spindle-loading could be a choice of exercise therapy in muscle spindle-affected neurodegenerative diseases.

Safety and efficacy of riluzole in patients undergoing decompressive surgery for degenerative cervical myelopathy (CSM-Protect): a multicentre, double-blind, placebo-controlled, randomised, phase 3 trial

BACKGROUND

Degenerative cervical myelopathy represents the most common form of non-traumatic spinal cord injury. This trial investigated whether riluzole enhances outcomes in patients undergoing decompression surgery for degenerative cervical myelopathy.

METHODS

This multicentre, double-blind, placebo-controlled, randomised, phase 3 trial was done at 16 university-affiliated centres in Canada and the USA. Patients with moderate-to-severe degenerative cervical myelopathy aged 18-80 years, who had a modified Japanese Orthopaedic Association (mJOA) score of 8-14, were eligible. Patients were randomly assigned (1:1) to receive either oral riluzole (50 mg twice a day for 14 days before surgery and then for 28 days after surgery) or placebo. Randomisation was done using permuted blocks stratified by study site. Patients, physicians, and outcome assessors remained masked to treatment group allocation. The primary endpoint was change in mJOA score from baseline to 6 months in the intention-to-treat (ITT) population, defined as all individuals who underwent randomisation and surgical decompression. Adverse events were analysed in the modified intention-to-treat (mITT) population, defined as all patients who underwent randomisation, including those who did not ultimately undergo surgical decompression. This study is registered with ClinicalTrials.gov, NCT01257828.

FINDINGS

From Jan 31, 2012, to May 16, 2017, 408 patients were screened. Of those screened, 300 were eligible (mITT population); 290 patients underwent decompression surgery (ITT population) and received either riluzole (n=141) or placebo (n=149). There was no difference between the riluzole and placebo groups in the primary endpoint of change in mJOA score at 6-month follow-up: 2·45 points (95% CI 2·08 to 2·82 points) versus 2·83 points (2·47 to 3·19), difference -0·38 points (-0·90 to 0·13; p=0·14). The most common adverse events were neck or arm or shoulder pain, arm paraesthesia, dysphagia, and worsening of myelopathy. There were 43 serious adverse events in 33 (22%) of 147 patients in the riluzole group and 34 serious adverse events in 29 (19%) of 153 patients in the placebo group. The most frequent severe adverse events were osteoarthrosis of non-spinal joints, worsening of myelopathy, and wound complications.

INTERPRETATION

In this trial, adjuvant treatment for 6 weeks perioperatively with riluzole did not improve functional recovery beyond decompressive surgery in patients with moderate-to-severe degenerative cervical myelopathy. Whether riluzole has other benefits in this patient population merits further study.

FUNDING

AOSpine North America.

The Impact of Riluzole on Neurobehavioral Outcomes in Preclinical Models of Traumatic and Nontraumatic Spinal Cord Injury: Results From a Systematic Review of the Literature

STUDY DESIGN

Systematic review.

OBJECTIVE

To evaluate the impact of riluzole on neurobehavioral outcomes in preclinical models of nontraumatic and traumatic spinal cord injury (SCI).

METHODS

An extensive search of the literature was conducted in Medline, EMBASE, and Medline in Process. Studies were included if they evaluated the impact of riluzole on neurobehavioral outcomes in preclinical models of nontraumatic and traumatic SCI. Extensive data were extracted from relevant studies, including sample characteristics, injury model, outcomes assessed, timing of evaluation, and main results. The SYRCLE checklist was used to assess various sources of bias.

RESULTS

The search yielded a total of 3180 unique citations. A total of 16 studies were deemed relevant and were summarized in this review. Sample sizes ranged from 14 to 90, and injury models included traumatic SCI (n = 9), degenerative cervical myelopathy (n = 2), and spinal cord-ischemia (n = 5). The most commonly assessed outcome measures were BBB (Basso, Beattie, Besnahan) locomotor score and von Frey filament testing. In general, rats treated with riluzole exhibited significantly higher BBB locomotor scores than controls. Furthermore, riluzole significantly increased withdrawal thresholds to innocuous stimuli and tail flick latency following application of radiant heat stimuli. Finally, rats treated with riluzole achieved superior results on many components of gait assessment.

CONCLUSION

In preclinical models of traumatic and nontraumatic SCI, riluzole significantly improves locomotor scores, gait function, and neuropathic pain. This review provides the background information necessary to interpret the results of clinical trials on the impact of riluzole in traumatic and nontraumatic SCI.

Degenerative cervical myelopathy - update and future directions

Degenerative cervical myelopathy (DCM) is the leading cause of spinal cord dysfunction in adults worldwide. DCM encompasses various acquired (age-related) and congenital pathologies related to degeneration of the cervical spinal column, including hypertrophy and/or calcification of the ligaments, intervertebral discs and osseous tissues. These pathologies narrow the spinal canal, leading to chronic spinal cord compression and disability. Owing to the ageing population, rates of DCM are increasing. Expeditious diagnosis and treatment of DCM are needed to avoid permanent disability. Over the past 10 years, advances in basic science and in translational and clinical research have improved our understanding of the pathophysiology of DCM and helped delineate evidence-based practices for diagnosis and treatment. Surgical decompression is recommended for moderate and severe DCM; the best strategy for mild myelopathy remains unclear. Next-generation quantitative microstructural MRI and neurophysiological recordings promise to enable quantification of spinal cord tissue damage and help predict clinical outcomes. Here, we provide a comprehensive, evidence-based review of DCM, including its definition, epidemiology, pathophysiology, clinical presentation, diagnosis and differential diagnosis, and non-operative and operative management. With this Review, we aim to equip physicians across broad disciplines with the knowledge necessary to make a timely diagnosis of DCM, recognize the clinical features that influence management and identify when urgent surgical intervention is warranted.

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

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

Effectiveness assessment of riluzole in the prevention of oxaliplatin-induced peripheral neuropathy: RILUZOX-01: protocol of a randomised, parallel, controlled, double-blind and multicentre study by the UNICANCER-AFSOS Supportive Care intergroup

INTRODUCTION

Most patients (>70%) experience acute neuropathic symptoms shortly after oxaliplatin infusions. These symptoms are not always resolved between infusions. Overall, 30%-50% of patients suffer from chronic oxaliplatin-induced peripheral neuropathy (OIPN). This cumulative and dose-dependent sensory neuropathy limits compliance or results in oxaliplatin-based chemotherapies to be substituted with less neurotoxic agents. These treatment changes impair clinical outcomes, and may be associated with comorbidities, such as distress, depression and anxiety. Currently, no drug used to prevent or treat OIPN is sufficiently effective to be used routinely in clinical practice. There is, thus, an unmet therapeutic need to reduce the intensity of and/or prevent OIPN. We hypothesised that riluzole would be an excellent candidate to address this public health issue. Riluzole is approved for treating amyotrophic lateral sclerosis. In animals, there is a beneficial effect on sensorimotor and pain disorders, as well as related comorbidities, after repeated administration of oxaliplatin. In humans, riluzole has shown neuroprotective, anxiolytic and antidepressive effects.

METHODS AND ANALYSIS

RILUZOX-01 trial was designed as a randomised, controlled, double-blind study to evaluate the efficacy of riluzole to prevent OIPN. Patients with colorectal cancer and initiating adjuvant oxaliplatin-based chemotherapy are eligible. Patients (n=210) will be randomly assigned to either riluzole or placebo, concomitantly with chemotherapy. The primary endpoint is the change in OIPN intensity, assessed by the sensory scale of the QLQ-CIPN20, after six 2-week cycles of chemotherapy. Secondary endpoints include incidence and severity of neuropathy, grade of sensory neuropathy, intensity and features of neuropathic pain, health-related quality of life, disease-free survival, overall survival and safety.

ETHICS AND DESSIMINATION

The study was approved by a French ethics committee (ref:39/18_1, 'Comité de Protection des Personnes' Ouest-IV, France) and plans to start enroling patients in September 2019. The trial is registered in EudraCT and clinicaltrials.gov.

TRIAL REGISTRATION NUMBER

N°2017-002320-25; NCT03722680.

Targeting the TREK-1 potassium channel via riluzole to eliminate the neuropathic and depressive-like effects of oxaliplatin

Neurotoxicity remains the most common adverse effect of oxaliplatin, limiting its clinical use. In the present study, we developed a mouse model of chronic oxaliplatin-induced neuropathy, which mimics both sensory and motor deficits observed in patients, in a clinically relevant time course. Repeated oxaliplatin administration in mice induced both cephalic and extracephalic long lasting mechanical and cold hypersensitivity after the first injection as well as delayed sensorimotor deficits and a depression-like phenotype. Using this model, we report that riluzole prevents both sensory and motor deficits induced by oxaliplatin as well as the depression-like phenotype induced by cumulative chemotherapeutic drug doses. All the beneficial effects are due to riluzole action on the TREK-1 potassium channel, which plays a central role in its therapeutic action. Riluzole has no negative effect on oxaliplatin antiproliferative capacity in human colorectal cancer cells and on its anticancer effect in a mouse model of colorectal cancer. Moreover, riluzole decreases human colorectal cancer cell line viability in vitro and inhibits polyp development in vivo. The present data in mice may support the need to clinically test riluzole in oxaliplatin-treated cancer patients and state for the important role of the TREK-1 channel in pain perception.

Combining neuroprotective agents: effect of riluzole and magnesium in a rat model of thoracic spinal cord injury

BACKGROUND CONTEXT

Damage to the spinal cord can result in irreversible impairments or complete loss of motor, sensory, and autonomic functions. Riluzole and magnesium have been widely investigated as neuroprotective agents in animal models of spinal cord injury. As these drugs protect the injured spinal cord through different mechanisms, we aimed to investigate if their neuroprotective efficacy could be cumulative.

PURPOSE

This study aimed to investigate the neuroprotective efficacy of combined administration of riluzole and magnesium chloride in a contusive model of thoracic spinal cord injury.

STUDY DESIGN

An in vivo experiment was set using female Wistar Han rats that underwent a thoracic spinal cord contusion (T8) using a weight drop method. An hour after injury, animals were randomly distributed to receive (1) saline, (2) riluzole (2.50 mg/kg), (3) magnesium chloride (24.18 mg/kg) in a polyethylene glycol formulation, or (4) a combined treatment (riluzole and magnesium). Subsequent treatments were given in four intraperitoneal injections (spaced 12 hours apart).

METHODS

The Basso, Beattie, and Bresnahan locomotor rating scale, an activity box test, and a swimming test were used to evaluate behavioral recovery over a 4-week period. Histologic analysis of the spinal cords was performed to measure the extent and volume of the lesion, axonal preservation, serotonergic and glutamatergic fiber sparing, motor neuron survival, and inflammation.

RESULTS

Our results show that only the riluzole treatment significantly improved behavioral recovery up to 4 weeks after injury when compared with saline controls (6.2±1.8), with animals achieving weight-supported stepping (9.1±1.2). Riluzole also promoted tissue sparing with significant differences achieved from 200 to 600 µm (caudally to the lesion epicenter), and reduced lesion volume, with animals presenting a significantly smaller lesion (3.23±0.26 mm(3)) when compared with the saline-treated group (4.74±0.80 mm(3)), representing a 32% decrease in lesion volume. Riluzole treatment induced significant axonal preservation, as well as serotonergic fiber sparing, caudally to the injury epicenter.

CONCLUSIONS

Our results suggest that the combined treatment, although simultaneously targeting two excitotoxic-related mechanisms, did not further improve behavioral and histologic outcome when compared with riluzole given alone.

Riluzole as a neuroprotective drug for spinal cord injury: from bench to bedside

Spinal cord injury (SCI) is a devastating event resulting in permanent loss of neurological function. To date, effective therapies for SCI have not been established. With recent progress in neurobiology, however, there is hope that drug administration could improve outcomes after SCI. Riluzole is a benzothiazole anticonvulsant with neuroprotective effects. It has been approved by the U.S. Food and Drug Administration as a safe and well-tolerated treatment for patients with amyotrophic lateral sclerosis. The mechanism of action of riluzole involves the inhibition of pathologic glutamatergic transmission in synapses of neurons via sodium channel blockade. There is convincing evidence that riluzole diminishes neurological tissue destruction and promotes functional recovery in animal SCI models. Based on these results, a phase I/IIa clinical trial with riluzole was conducted for patients with SCI between 2010 and 2011. This trial demonstrated significant improvement in neurological outcomes and showed it to be a safe drug with no serious adverse effects. Currently, an international, multi-center clinical trial (Riluzole in Acute Spinal Cord Injury Study: RISCIS) in phase II/III is in progress with riluzole for patients with SCI (clinicaltrials.gov, registration number NCT01597518). This article reviews the pharmacology and neuroprotective mechanisms of riluzole, and focuses on existing preclinical evidence, and emerging clinical data in the treatment of SCI.

Pharmacology of riluzole in acute spinal cord injury

OBJECT

The aim of this paper was to characterize individual and population pharmacokinetics of enterally administered riluzole in a Phase 1 clinical trial of riluzole as a neuroprotective agent in adults 18-70 years old with acute spinal cord injury (SCI).

METHODS

Thirty-five individuals with acute SCI, American Spinal Injury Association Impairment Scale Grades A-C, neurological levels from C-4 to T-12, who were enrolled in the Phase 1 clinical trial sponsored by the North American Clinical Trials Network for Treatment of Spinal Cord Injury, received 50 mg riluzole twice daily for 28 doses. The first dose was administered at a mean of 8.7 ± 2.2 hours postinjury. Trough plasma samples were collected within 1 hour predose, and peak plasma samples were collected 2 hours postdose on Days 3 and 14 of treatment. Riluzole concentrations were quantified by high-performance liquid chromatography assay. The data were analyzed for individual and population pharmacokinetics using basic structural and covariate models. The pharmacokinetic measures studied were the peak concentration (C(max)), trough concentration (C(min)), systemic exposure (AUC(0-12)), clearance (CL/F), and volume of distribution (V_F) normalized by the bioavailability (F).

RESULTS

The C(max) and AUC(0-12) achieved in SCI patients were lower than those in ALS patients on the same dose basis, due to a higher CL and larger V. The pharmacokinetics of riluzole (C(max), C(min), AUC(0-12), CL, and V) changed during the acute and subacute phases of SCI during the 14 days of therapy. It was consistently observed in patients at all clinical sites that C(max), C(min), and AUC(0-12) (128.9 ng/ml, 45.6 ng/ml, and 982.0 ng × hr/ml, respectively) were significantly higher on Day 3 than on Day 14 (76.5 ng/ml, 19.1 ng/ml, and 521.0 ng × hr/ml, respectively). These changes resulted from lower CL (49.5 vs 106.2 L/hour) and smaller V (557.1 vs 1297.9/L) on Day 3. No fluid imbalance or cytochrome P 1A2 induction due to concomitant medications was identified during the treatment course to account for such increases in V and CL, respectively. Possible mechanisms underlying these changes are discussed.

CONCLUSIONS

This is the first report of clinical pharmacokinetics of riluzole in patients with SCI. The C(max) and AUC(0-12) achieved in SCI patients were lower than those in ALS patients on the same dose basis, due to a higher clearance and larger volume of distribution in SCI patients. The finding in SCI patients of an increase in the clearance and distribution of riluzole between the 3rd and 14th days after SCI, with a lower plasma concentration of riluzole on the 14th day, stresses the importance of monitoring changes in drug metabolism after SCI in interpreting the safety and efficacy of therapeutic drugs that are used in clinical trials in SCI. Clinical trial registration no.: NCT00876889.

A human TREK-1/HEK cell line: a highly efficient screening tool for drug development in neurological diseases

TREK-1 potassium channels are involved in a number of physiopathological processes such as neuroprotection, pain and depression. Molecules able to open or to block these channels can be clinically important. Having a cell model for screening such molecules is of particular interest. Here, we describe the development of the first available cell line that constituvely expresses the TREK-1 channel. The TREK-1 channel expressed by the h-TREK-1/HEK cell line has conserved all its modulation properties. It is opened by stretch, pH, polyunsaturated fatty acids and by the neuroprotective molecule, riluzole and it is blocked by spadin or fluoxetine. We also demonstrate that the h-TREK-1/HEK cell line is protected against ischemia by using the oxygen-glucose deprivation model.

Chemical priming for spinal cord injury: a review of the literature part II-potential therapeutics

INTRODUCTION

Spinal cord injury is a complex cascade of reactions secondary to the initial mechanical trauma that puts into action the innate properties of the injured cells, the circulatory, inflammatory, and chemical status around them, into a non-permissive and destructive environment for neuronal function and regeneration. Priming means putting a cell, in a state of "arousal" towards better function. Priming can be mechanical as trauma is known to enhance activity in cells.

MATERIALS AND METHODS

A comprehensive review of the literature was performed to better understand the possible chemical primers used for spinal cord injuries.

CONCLUSIONS

Taken together, many studies have shown various promising results using the substances outlined herein for treating SCI.

Baicalein and wogonin are activators of rat TREK-2 two-pore domain K+ channel

AIM

Earlier studies have shown that TREK-1 and TREK-2 (TREKs), members of the two-pore domain K(+) (K(2P)) channel family that are highly expressed under pathological conditions, are activated by neuroprotective agents. Baicalein and wogonin, oriental flavonoids originating from the root of the medicinal herb Scutellaria baicalensis, are known to have beneficial effects for neuroprotection. However, little is known about the effects of baicalein and wogonin on ion channels including TREKs. We investigated whether baicalein and wogonin modulate the TREK-2 channel, which has been less studied than TREK-1.

METHODS

Single-channel recordings were performed in COS-7 cells transfected with rat TREK-2 and analyzed baicalein- or wogonin-induced channel activity.

RESULTS

We found that baicalein and wogonin activated the TREK-2 current by increasing the opening frequency (channel activity: from 0.05 ± 0.01 to 0.17 ± 0.06 in baicalein treatment and from 0.03 ± 0.01 to 0.29 ± 0.09 in wogonin treatment, P < 0.05), while leaving the single-channel conductance and mean open time unchanged. Baicalein continuously activated TREK-2, whereas wogonin transiently activated TREK-2. Application of baicalein and wogonin activated TREK-2 in both cell attached and excised patches, suggesting that baicalein and wogonin may modulate TREK-2 either directly or indirectly with different mechanisms.

CONCLUSION

These results suggest that baicalein- and wogonin-induced TREK-2 activation help set the resting membrane potential of cells exposed to pathological conditions and thus may give beneficial effects in neuroprotection.

Increased survival and reinnervation of cervical motoneurons by riluzole after avulsion of the C7 ventral root

Although adult motoneurons do not die if their axons are injured at some distance from the cell body, they are unable to survive injury caused by ventral root avulsion. Some of the injured motoneurons can be rescued if the ventral root is re-inserted into the spinal cord. Brachial plexus injuries that involve the complete or partial avulsion of one or more cervical ventral roots can be treated successfully only if satisfactory numbers of motoneurons remain alive following such an injury at the time of reconstructive surgery. Here we investigated the various strategies that could be used to rescue injured rat cervical motoneurons. The seventh cervical ventral root (C7) was avulsed and various therapeutic approaches were applied to induce motoneuronal survival and regeneration. Avulsion of the root without reimplantation resulted in very low numbers of surviving motoneurons (65 ± 8 SEM), while treatment of the injured motoneurons with riluzole resulted in high numbers of surviving motoneurons (637 ± 26 SEM). When the C7 ventral root was reimplanted or a peripheral nerve implant was used to guide the regenerating axons to a muscle, considerable numbers of motoneurons regenerated their axons (211 ± 15 SEM and 274 ± 28 SEM, respectively). Much greater numbers of axons regenerated when reimplantation was followed by riluzole treatment (573 ± 9 SEM). These results show that injured adult motoneurons can be rescued by riluzole treatment, even if they cannot regenerate their axons. Reinnervation of the peripheral targets can also be further improved with riluzole treatment.

Resveratrol improves neuron protection and functional recovery in rat model of spinal cord injury

Researches on the pathology of spinal cord injury (SCI) have been recently focused on oxidative radicals stress and inflammation associated neuronal apoptosis. Resveratrol, a natural phenolic compound, has been extensively studied and shown a wide variety of health beneficial effects, including prevention of cardiovascular diseases and cancer and neuroprotective activities. However, the study of its potential role in neuroprotection and underlying mechanism in SCI model has been limited. In this study, we investigated the effect of resveratrol on neurologic functions and histopathologic changes after SCI and the mechanism underlying its neuroprotective effects. First, neuronal function after SCI was evaluated with Basso Beattle Bresnahan locomotor rating scale (BBB) and the result showed that injured animals treated with resveratrol showed a significant increase in BBB scores. Further, histopathological alternations were evaluated with HE and Nissl staining, showing a restored neural morphology and an increase of the number of neurons after resveratrol administration. To explore the underlying mechanism, anti-oxidation effect of resveratrol was assessed by measuring superoxide dismutase (SOD) activity and malondialdehyde (MDA) level after SCI. Resveratrol treatment reversed the decrease of SOD activity and increase of MDA level caused by SCI, suggesting its anti-oxidation role in response to the injury. In addition, resveratrol treatment suppressed immunoreactivity and expression of inflammatory cytokines including IL-1β, IL-10, TNF-α, and myeloperoxidase (MPO) after SCI, suggesting an anti-inflammation effect of resveratrol. Finally, resveratrol treatment inhibited injury-induced apoptosis as assessed by electrical microscopy and TUNEL staining and affected the expression level of apoptosis-related gene Bax, Bcl-2 and caspase-3, which indicated its anti-apoptosis role after SCI. Our data suggest that resveratrol significantly promotes the recovery of rat dorsal neuronal function after SCI, and this effect is related to its characteristics of anti-oxidation, anti-inflammation and anti-apoptosis.

Evaluation of the systemic use of riluzole in post-traumatic facial nerve regeneration: experimental study in rabbits

CONCLUSIONS

Riluzole promoted increase and/or preservation of axon density in the animals treated with this drug as compared to the control group; it did not increase the mean diameter of facial nerve fibres as compared to the non-treated group; and it did not provide a better functional motor recovery than in the control group.

OBJECTIVE

Traumatic peripheral facial paralysis is a frequent affection. In incomplete nerve injuries, systemic drugs acting on regeneration may decrease the patient's period of morbidity. This study aimed to determine the effect of the drug riluzole on regeneration of the facial nerve of rabbits submitted to post-traumatic facial paralysis.

MATERIALS AND METHODS

Eighteen rabbits were submitted to compression of the facial nerve and divided into control (A) and treated (B) groups. The animals were sacrificed 4 weeks after the injury and their nerves were studied regarding density of myelinated axons and measure of external axon diameters.

RESULTS

Partial functional recovery was observed within 2 weeks and complete recovery 5 weeks after injury. Mean neural density was 12,679.7 axons/mm2 (SD+/-237.5) in group A, and 19,073.8 axons/mm2 (SD+/-3549.9) in group B. Group A presented less than two-thirds the density of group B. There was no statistical difference in axon diameters between the studied groups.

Delayed riluzole treatment is able to rescue injured rat spinal motoneurons

The effect of delayed 2-amino-6-trifluoromethoxy-benzothiazole (riluzole) treatment on injured motoneurons was studied. The L4 ventral root of adult rats was avulsed and reimplanted into the spinal cord. Immediately after the operation or with a delay of 5, 10, 14 or 16 days animals were treated with riluzole (n=5 in each group) while another four animals remained untreated. Three months after the operation the fluorescent dye Fast Blue was applied to the proximal end of the cut ventral ramus of the L4 spinal nerve to retrogradely label reinnervating neurons. Three days later the spinal cords were processed for counting the retrogradely labeled cells and choline acetyltransferase immunohistochemistry was performed to reveal the cholinergic cells in the spinal cords. In untreated animals there were 20.4+/-1.6 (+/-S.E.M.) retrogradely labeled neurons while in animals treated with riluzole immediately or 5 and 10 days after ventral root avulsion the number of labeled motoneurons ranged between 763+/-36 and 815+/-50 (S.E.M.). Riluzole treatment starting at 14 and 16 days after injury resulted in significantly lower number of reinnervating motoneurons (67+/-4 and 52+/-3 S.E.M., respectively). Thus, riluzole dramatically enhanced the survival and reinnervating capacity of injured motoneurons not only when treatment started immediately after injury but also in cases when riluzole treatment was delayed for up to 10 days. These results suggest that motoneurons destined to die after ventral root avulsion are programmed to survive for some time after injury and riluzole is able to rescue them during this period of time.

The Effects of L-Arginine on Neurological Function, Histopathology, and Expression of Hypoxia-Inducible Factor-1 Alpha following Spinal Cord Ischemia in Rats

The aim of this study was to investigate the effects of L-arginine (L-Arg) on neurological function, histopathology, and expression of hypoxia-inducible factor-1 alpha (HIF-1alpha) following spinal cord ischemia in rats, and the interaction between therapy with the nitric oxide donor L-Arg and up-regulation of the expression of HIF-1alpha. Thirty Wistar rats weighing between 200 and 250 g were divided into three groups, each containing 10 rats: group 1, sham operation; group 2, untreated ischemia-reperfusion (I-R); group 3, I-R plus L-Arg treatment. Spinal cord ischemia was applied for 20 min. There were no significant differences in mean arterial pressures, temperatures, and blood gas levels among the groups. In group 2, malondialdehyde values were significantly increased compared with groups 1 and 3. The rats with aortic occlusion in group 2 had paraplegia or paraparesis. In group 3, all animals were neurologically intact. In group 3, spinal motor neurons did not decrease significantly, and little proliferation of microglia was observed compared with those in group 2. In group 2, spinal motor neurons in ventral gray matter decreased significantly compared with those in groups 1 and 3. HIF-1alpha-positive immunostaining was mildly detected in group 2 animals. The expression of immunoreactive cells was intensely increased in spinal cord tissue from I-R/L-Arg rats. In conclusion, our findings suggest that HIF-1alpha-positive immunostaining may be critical factors in the pathophysiology of inflammatory spinal cord injury induced by I-R. Nitric oxide may play an important role in the immunohistochemical expression of these molecules, and the neuroprotective benefit of L-Arg may be attributed to preventing neural cell necrosis.

Alpha-Linolenic acid and riluzole treatment confer cerebral protection and improve survival after focal brain ischemia

We investigated here the effects of alpha-linolenic acid and riluzole, both activators of the 2P-domain K+ channel family TREK/TRAAK, in a model of focal ischemia clinically relevant to stroke, not only assessing neuronal protection, but also long term survival. Moreover, all the drug treatments were initiated post-ischemia. Mice were subjected to transient middle cerebral artery occlusion (1 h) and reperfusion according to the intraluminal filament model. Drugs were injected into the jugular vein according to three protocols: (i) a single dose of 4 mg/kg riluzole or 500 nmol/kg alpha-linolenic acid at different reperfusion time; (ii) a three-day therapy (a single dose of 2 mg/kg riluzole and 250 nmol/kg alpha-linolenic acid given 1-2, 48 and 72 h after reperfusion); (iii) a three-week therapy (a single dose of 2 mg/kg riluzole and 250 nmol/kg alpha-linolenic acid given once a week during three weeks after reperfusion. A combined treatment with 2mg/kg riluzole+250 nmol/kg alpha-linolenic acid injected 2 h after reperfusion was also tested. A single dose of riluzole (4 mg/kg) or alpha-linolenic acid (500 nmol/kg) injected up to 3 h after reperfusion reduced drastically the stroke volume by 75% and 86%, respectively. Neurological deficits 24 h after ischemia were significantly improved by alpha-linolenic acid500 or riluzole4 with a neurological score of 1.8 as compared with 2.5 observed in vehicle-treated mice. Alpha-linolenic acid- and riluzole treatment were associated with a reduction in cytopathological features of cell injury, including DNA fragmentation and Bax expression in the cortex and the caudate putamen. With regard to the survival rate at 30 days, the best protections were obtained with the alpha-linolenic acid-injection in the three-week therapy as well as with a single dose of the combined treatment (2 mg/kg riluzole+250 nmol/kg alpha-linolenic acid). Palmitic acid, a saturated fatty acid that does not activate the 2P-domain K-channel TREK/TRAAK family, did not provide any neuroprotection. Taken together, these data suggest that the TREK/TRAAK K-channel family may be a promising target for neuroprotection, and that riluzole and alpha-linolenic acid could be of therapeutic value against focal ischemia/reperfusion injury to the brain.

MK-801 improves neurological and histological outcomes after spinal cord ischemia induced by transient aortic cross-clipping in rats

BACKGROUND

Glutamergic excitotoxicity has been shown to play a deleterious role in the pathophysiology of ischemic spinal cord injury (ISCI). The aim of this study was to investigate the neuroprotective effect of a single dose of MK-801, an antiexcitotoxic drug, in a rat model of ISCI.

METHODS

Ischemic spinal cord injury was induced for 17 minutes in Sprague-Dawley rats using direct aortic arch, just proximal to the left common carotid artery, plus left subclavian artery cross-clamping through a left-sided limited thoracotomy. Study groups were as follows: control group (n = 8) receiving only vehicle and experimental group (n = 8) receiving a single dose of MK-801 (1 mg/kg IV) 10 minutes before aortic clamping. Neurological examination was performed at 6 hours, 24 hours, and daily up to 96 hours. Rats were sacrifice at methylprenisolone socium succinate 96 hours, and spinal cords were removed for histopathology.

RESULTS

All the control rats had severe permanent neurological deficits after ISCI, whereas the MK-801-treated rats had statistically (P < .05) better neurological outcome and good recovery. Histopathology revealed severe neuronal necrosis in the lumbar gray matter of control rats, whereas MK-801-treated rats showed mild injury.

CONCLUSION

These results demonstrate that combined temporary clipping of the aortic arch (just proximal to the left common carotid artery) plus left subclavian artery for 17 minutes reproduces reliable paraplegia, and a single dose of MK-801 given before ISCI provides significant neuroprotection.

Inhibition of the cloned delayed rectifier K+ channels, Kv1.5 and Kv3.1, by riluzole

The action of riluzole, a neuroprotective drug, on cloned delayed rectifier K+ channels (Kv1.5 and Kv3.1) was examined using the whole-cell patch-clamp technique. Riluzole reversibly inhibited Kv1.5 currents in a concentration-dependent manner with an IC50 of 39.69+/-2.37 microM. G-protein inhibitors (pertussis toxin and GDPbetaS) did not prevent this inhibition of riluzole on Kv1.5. No voltage-dependent inhibition by riluzole was found over the voltage range in which channels are fully activated. Riluzole shifted the steady-state inactivation curves of Kv1.5 in a hyperpolarizing direction in a concentration-dependent manner. It accelerated the deactivation kinetics of Kv1.5 in a concentration dependent-manner, but had no effect on the steady-state activation curve. Riluzole exhibited a use-independent inhibition of Kv1.5. The effects of riluzole on Kv3.1, the Shaw-type K+ channel were also examined. Riluzole caused a concentration-dependent inhibition of Kv3.1 currents with an IC50 of 120.98+/-9.74 microM and also shifted the steady-state inactivation curve of Kv3.1 in the hyperpolarizing direction. Thus, riluzole inhibits both Kv1.5 and Kv3.1 currents in a concentration-dependent manner and interacts directly with Kv1.5 by preferentially binding to the inactivated and to the closed states of the channel.

Neuroprotection of adult rat dorsal root ganglion neurons by combined hypothermia and alkalinization against prolonged ischemia

Ischemia and ischemia-induced secondary events, such as acidosis and excessive activation of receptors by amino acids, trigger neuron death. The isolation and dissociation of dorsal root ganglion (DRG) involves time during which the neurons are ischemic due to being densely packed within the intact DRG and surrounded by a connective tissue coat. Thus, the longer the time between killing the host animal and when the DRG are dissociated, the longer the neurons are ischemic and exposed to ischemia-induced secondary causes of neuron death. It is well established that hypothermia and alkalinization each separately protect neurons from ischemia and ischemia-induced secondary causes of neuron death, but there are no data on the neuroprotection provided by simultaneous hypothermia and alkalinization. The present experiments were designed to determine the combination of hypothermic and alkaline conditions that yield the largest number of viable neurons dissociated from intact DRG maintained ischemic for up to 4 h. Hypothermia (20 degrees C>15 degrees C>37 degrees C) and alkalinization (pH 9.3>pH 8.3>pH 7.4) increased the yield of viable neurons compared with the yield from DRG maintained under physiological conditions. Hypothermia and alkalinization combined (20 degrees C/pH 9.3) provided the greatest neuroprotection with a yield of viable neurons after 1 h of ischemia 2.5-fold larger than that from DRG maintained under physiological conditions (37 degrees C/pH 7.6). Over 4 h of ischemia, the yield of viable neurons from DRG maintained under both hypothermic/alkaline and physiological conditions decreased in a linear manner, but those at 20 degrees C/pH 9.3 had a 4.5-fold greater yield of viable neurons than those at 37 degrees C/pH 7.6. Thus, combined hypothermia and alkalinization provide significantly greater protection against ischemia and ischemia-induced secondary causes of neuron death than either alone.

TREK-1, a K+ channel involved in neuroprotection and general anesthesia

TREK-1 is a two-pore-domain background potassium channel expressed throughout the central nervous system. It is opened by polyunsaturated fatty acids and lysophospholipids. It is inhibited by neurotransmitters that produce an increase in intracellular cAMP and by those that activate the Gq protein pathway. TREK-1 is also activated by volatile anesthetics and has been suggested to be an important target in the action of these drugs. Using mice with a disrupted TREK-1 gene, we now show that TREK-1 has an important role in neuroprotection against epilepsy and brain and spinal chord ischemia. Trek1-/- mice display an increased sensitivity to ischemia and epilepsy. Neuroprotection by polyunsaturated fatty acids, which is impressive in Trek1+/+ mice, disappears in Trek1-/- mice indicating a central role of TREK-1 in this process. Trek1-/- mice are also resistant to anesthesia by volatile anesthetics. TREK-1 emerges as a potential innovative target for developing new therapeutic agents for neurology and anesthesiology.

Protective effect of D-003 on experimental spinal cord ischemia in rabbits

D-003 is a natural mixture of long chain aliphatic acids isolated and purified from sugar cane wax. It possesses antiplatelet and antithrombotic effects as well as decreases plasma and serum levels of thromboxane B(2) (TxB(2)), meanwhile significantly and markedly raises prostacyclin (PgI(2)) levels in rats. This study was undertaken to investigate the effects of D-003 on spinal cord injury in rabbits. New Zealand rabbits were treated during 10 days with D-003 (25 and 200 mg kg(-1)) and ASA (2 mg kg(-1)) before spinal cord ischemia. Animals were subjected to 20 min of aortic occlusion and 24h of reperfusion. Clinical symptoms and histopathological changes of spinal cord were observed. The PgI(2) levels in thoracic aorta were quantified by bioassay. D-003 (25 and 200 mg kg(-1)) significantly increased the mean scores reached 4h after reperfusion, although no dose relation was observed. Twenty-four hours after reperfusion, no deaths occurred in both sham and D-003 treated groups, meanwhile in positive controls and ASA the mortality rate was 38.5% and 7.69% respectively. In addition, 100% of sham, 69% and 77% of rabbits treated with D-003 at 25 and 200 mg kg(-1), respectively, did not show histopathological changes. By the contrary, 100% of positive control animals showed severe damage and ASA-treated rabbits showed only a partial protection. Animals treated with both doses of D-003 showed PgI(2) levels significantly larger than those of positive and negative controls, an effect dose-related, while ASA 2 mg kg(-1) did not change PgI(2) values. The increase of PgI(2) levels achieved in the D-003 treated animals could be an important mechanism in the protection against the spinal cord ischemia.

Ischémie médullaire

Traditional data and recent advances in the field of spinal cord ischemia are reviewed, with special attention to clinical and radiological features, as well as underlying etiology, outcome, and pathophysiology. Acute spinal cord ischemia includes arterial and venous infarction and global ischemia resulting from cardiac arrest or severe hypotension. MRI has become the technique of choice for the imaging diagnosis of spinal cord infarction. Correlation of clinical and MRI data has allowed diagnosis of clinical syndromes due to small infarcts in the central or peripheral arterial territory of the spinal cord. Diffusion-weighted MR imaging may increase the sensitivity and specificity for diagnosis of acute spinal cord infarction. Diagnosis of venous spinal cord infarction remains difficult. As for global ischemia, neuropathological studies demonstrated a great sensitivity of spinal cord to ischemia, with selective vulnerability of lumbosacral neurons. Chronic spinal cord ischemia results in a syndrome of progressive myelopathy. The cause is usually an arteriovenous malformation. Most often, diagnosis may be suspected on MRI, leading to diagnostic, and eventually therapeutic, spinal angiography.

The use of the potassium channel activator riluzole to test whether potassium channels mediate the capacity of isoflurane to produce immobility

Inhaled anesthetics produce immobility during noxious stimulation, primarily by actions on the spinal cord. In this study, we examined whether activation of potassium channels of the KCNK subfamily alters volatile anesthetic potency. We measured the change in isoflurane minimum alveolar anesthetic concentration (MAC) during 4-h intrathecal or IV infusions of the nonspecific KCNK activator riluzole in 54 Sprague-Dawley rats. IV or intrathecal infusions of riluzole doses that did not result in permanent injury or death equally decreased isoflurane MAC. We conclude that although riluzole exhibited anesthetic effects, the similar dose response from IV or intrathecal infusion suggests systemic absorption and actions in the brain rather than the spinal cord.

IMPLICATIONS

Riluzole, a drug that activates potassium channels and decreases glutamatergic neurotransmission, primarily acts on supraspinal sites to produce immobility in response to noxious stimuli. This finding does not support the hypothesis that potassium channels mediate the capacity of inhaled anesthetics to produce immobility in the face of noxious stimulation.

Linolenic acid prevents neuronal cell death and paraplegia after transient spinal cord ischemia in rats

PURPOSE

Spinal cord ischemia is a devastating complication of thoracic and thoracoabdominal aortic surgery. Recent studies have suggested a neuroprotective effect of polyunsaturated fatty acids against cerebral ischemia. We investigated the effect of linolenic acid (LIN) in a rat model of spinal cord ischemia.

METHODS

Rats were subjected to cross-clamping of the aortic arch and left subclavian artery for 14 minutes. Groups were as follows: sham operation (n = 15); ischemia (n = 15), receiving only vehicle; LIN A (n = 15), receiving LIN before clamping; and LIN B (n = 15), receiving LIN at onset of reperfusion. Neurologic status was assessed daily for 7 days. Spinal cords were harvested for histopathologic analysis, TUNEL staining, and immunohistochemistry for Bax, heat shock protein 70 (HSP70), and nuclear factor-kappaB.

RESULTS

Ischemic rats had severe and definitive paraplegia. LIN-treated rats had significantly better neurologic function. Histopathologic analysis disclosed severe neuronal necrosis in the lumbar gray matter of ischemic rats, whereas most of the LIN-treated rats sustained mild to moderate injury. LIN reduced the loss of motor neurons at 7 days (LIN A, 17 +/- 6, and LIN B, 15 +/- 7, versus ischemia, 6 +/- 2 per section; P <.05). LIN prevented apoptotic neuronal cell death, Bax immunoreactivity of the pro-apoptotic protein Bax, and the nuclear transcription factor NF-kappaB. Nuclear HSP70 immunoreactivity was noted exclusively in motor neurons from LIN-treated rats and not in motor neurons from ischemic rats.

CONCLUSION

These results suggest that LIN can induce protection against ischemia in the spinal cord, thereby preventing both necrosis and apoptosis of motor neurons.

Early ischemic preconditioning without hypotension prevents spinal cord injury caused by descending thoracic aortic occlusion

OBJECTIVE

Postoperative neurologic deficits after thoracic aortic reconstruction vary widely. Our previous study showed that delayed ischemic preconditioning could prevent spinal cord injury caused by occlusion of the descending thoracic aorta in pigs. We investigated early ischemic preconditioning in the same model.

METHODS

Twenty-eight pigs were divided into 4 groups: group 1 (n = 6) underwent a sham operation, group 2 (n = 6) underwent aortic occlusion for 20 minutes, group 3 (n = 8) underwent aortic occlusion for 35 minutes, and group 4 (n = 8) underwent aortic occlusion for 20 minutes and underwent aortic occlusion 80 minutes later without hypotension for 35 minutes. Aortic occlusion was accomplished by using 2 balloon occlusion catheters placed fluoroscopically at T6 to T8 above the diaphragm and at the aortic bifurcation. Neurologic evaluation was performed by an independent observer according to the Tarlov scale (0-4). The lower thoracic and lumbar spinal cords were harvested at 120 hours and examined histologically with hematoxylin-and-eosin stain. Histologic results (number of neurons and grade of inflammation) were scored (0-4) and were similarly analyzed. Statistical analysis was by means of the Kruskal-Wallis test.

RESULTS

Group 4 had a better neurologic outcome at 24, 48, and 120 hours in comparison with group 3 (P <.001). The histologic changes were proportional to the neurologic test scores, with the more severe and extensive gray matter damage in animals of group 3 (number of neurons, P <.001; grade of inflammation, P <.001).

CONCLUSION

Early ischemic preconditioning without hypotension protects against spinal cord injury after aortic occlusion, as confirmed by using the Tarlov score and histopathology.

Secondary injury mechanisms of spinal cord trauma: a novel therapeutic approach for the management of secondary pathophysiology with the sodium channel blocker riluzole

Traumatic spinal cord injury is a consequence of a primary mechanical insult and a sequence of progressive secondary pathophysiological events that confound efforts to mitigate neurological deficits. Pharmacotherapy aimed at reducing the secondary injury is limited by a narrow therapeutic window. Thus, novel drug strategies must target early pathological mechanisms in order to realize the promise of efficacy for this form of neurotrauma. Research has shown that an accumulation of intracellular sodium as a result of trauma-induced perturbation of voltage-sensitive sodium channel activity is a key early mechanism in the secondary injury cascade. As such, voltage-sensitive sodium channels are an important therapeutic target for the treatment of spinal cord trauma. This review describes the evolution of acute spinal cord injury and provides a rationale for the clinical utility of sodium channel blockers, particularly riluzole, in the management of spinal cord trauma.

Reduction of spinal cord injury with pentobarbital and hypothermia in a rabbit model

OBJECTIVES

to evaluate the effects of hypothermia and pentobarbital on spinal cord ischaemia induced in a rabbit model.

MATERIALS AND METHODS

thirty-two rabbits, allocated into four equal groups, had the infrarenal aorta clamped distal to the left renal artery and above the iliac bifurcation for 40 min. Groups 3 and 4 had infusion of 15 mg/kg of pentobarbital intravenously for 5 min, 15 min before the cross-clamping. Groups 2 and 4 had infusion of 20 ml of Ringer's lactate (LR) solution at 3 degrees C for 3 min during aortic cross clamp into the isolated aortic segment. Group 1 was untreated and served as control. Postoperative functions of spinal cord were assessed.

RESULTS

paraplegia occurred in all rabbits in Group 1, in one in each of Groups 2 and 3, whereas no paraplegia was observed in Group 4. In addition 2 and 3 animals of Groups 2 and 3, respectively revealed varying degree of neurological disturbances, whereas all animals of Group 4 had normal function. This difference between Groups 2, 3, and 4 vs Group 1 was significant (p<0.002). So was the difference between Groups 2 and 4 (p=0.03), whereas the difference between Groups 3 and 4 was not significant.

CONCLUSIONS

hypothermia and pentobarbital was more effective than hypothermia alone for prevention of spinal cord ischaemia in a rabbit model.

Modulation of recombinant and native neuronal SK channels by the neuroprotective drug riluzole

Small conductance, Ca(2+)-activated K(+) channels (SK channels) regulate neuronal excitability. We used patch clamp to study the actions of the neuroprotective drug riluzole on recombinant SK2 channels expressed in HEK293 cells and native SK channels underlying the afterhyperpolarization current (I(AHP)) in cultured hippocampal neurons. External riluzole activated whole-cell SK2 channel currents in HEK293 cells dialyzed with a Ca(2+)-free intracellular solution. When applied to the intracellular aspect of the membrane of giant inside-out patches, riluzole enhanced the membrane current activated by 100 nM Ca(2+) in a reversible and concentration-dependent manner; 30 microM riluzole applied to the intracellular aspect of the patches sensitized the channels to activation by Ca(2+), resulting in a leftward shift of the Ca(2+) activation curve. Riluzole also enhanced the I(AHP) and reduced the spontaneous action potential frequency in chemically stimulated neurons. Modulation of SK channel activity by riluzole may contribute to its cellular, behavioral, and clinical effects.

A potent protective role of lysophospholipids against global cerebral ischemia and glutamate excitotoxicity in neuronal cultures

Lysophospholipids (LPLs) are important intermediates in the synthesis and degradation of membrane phospholipids. Here we show that certain LPLs, particularly lysophosphatidylcholine and lysophosphatidylinositol, prevent neuronal death both in an in vivo model of transient global ischemia and in an in vitro model of excitotoxicity using primary cultures of cerebellar granule cells exposed to high extracellular concentrations of glutamate (20-40 micromol/L). The intravenous injection of lysophosphatidylcholine or lysophosphatidylinositol at a concentration of 200 nmol/kg induced a survival of CA1 pyramidal neurons as high as approximately 95%, even when the treatment was started 30 minutes after 15-minute global ischemia. In contrast, lysophosphatidic acid induced no protection. This work also provides evidence that a pretreatment with lysophosphatidylcholine or lysophosphatidylinositol (200 nmol/kg) injected as long as 3 days before a severe 6-minute ischemia provided a potent tolerance against neurodegeneration. Neuroprotection was also observed in in vitro experiments with LPLs. Taken together, in vivo and in vitro data suggest a potential therapeutic use of LPLs as antiischemic compounds. The potential role of 2P-domain K+ channels as targets of LPLs in this potent neuroprotective effect is discussed.

Tetramethylpyrazine attenuates spinal cord ischemic injury due to aortic cross-clamping in rabbits

BACKGROUND

Lower limb paralysis occurs in 11% of patients after surgical procedure of thoracic or thoracoabdominal aneurysms and is an unpredictable and distressful complication. The aim of this study was to investigate the effects of tetramethylpyrazine (TMP), an intravenous drug made from traditional Chinese herbs, on the neurologic outcome and histopathology after transient spinal cord ischemia in rabbits.

METHODS

Forty-five male New Zealand white rabbits were anesthetized with isoflurane and spinal cord ischemia was induced for 20 min by infrarenal aortic occlusion. Animals were randomly allocated to one of five groups (n = 8 each). Group C received no pharmacologic intervention. Group P received intravenous infusion of 30 mg x kg(-1) TMP within 30 min before aortic occlusion. Group T1, Group T2 and Group T3 received intravenous infusion of 15, 30 and 60 mg x kg(-1) TMP respectively within 30 min after reperfusion. In the sham group (n = 5), the animals underwent the same procedures as the control group except infrarental aortic unocclusion. Neurologic status was scored by using the Tarlov criteria (in which 4 is normal and 0 is paraplegia) at 4 h, 8 h, 12 h, 24 h, and 48 h after reperfusion. All animals were sacrificed at 48 h after reperfusion and the spinal cords (L5) were removed immediately for histopathologic study.

RESULTS

All animals in the control group became paraplegic. Neurologic status and histopathology (48 h) in the Groups P, T2 and T3 were significantly better than those in the control group (P < 0.05). There was a strong correlation between the final neurologic scores and the number of normal neurons in the anterior spinal cord (r = 0.776, P < 0.01).

CONCLUSION

Tetramethylpyrazine significantly reduces neurologic injury related to spinal cord ischemia and reperfusion after aortic occlusion within a certain range of dose.

Reduction of ischemic spinal cord injury by dextrorphan: comparison of several methods of administration

OBJECTIVES

We investigated the effect of dextrorphan, an N -methyl-D -aspartate receptor antagonist, on the reduction of ischemic spinal cord injury and the safe clamping time after various methods of administration.

METHODS

Spinal cord ischemia was induced in New Zealand White rabbits by infrarenal aortic clamping and animals were divided into 5 groups. Group A (n = 15) received simple clamping. Groups B (n = 20) and C (n = 35) received dextrorphan pretreatment (10 mg/kg), followed by continuous intravenous or intra-aortic infusion (1 mg/min), respectively. Group D (n = 25) received the same dextrorphan pretreatment and bolus intra-aortic injection at clamping (1 mg per minute of clamping time). Group E (n = 15) received bolus intrathecal injection of dextrorphan (0.2 mg/kg). Each dextrorphan-treated group had a small group of control animals (n = 5). The neurologic status was assessed by the Johnson score (5 = normal, 0 = paraplegic) 48 hours after unclamping, and animals were put to death for histopathologic examination.

RESULTS

All dextrorphan-treated groups showed better neurologic function than the respective control animals (P <.001 vs groups B, C, and D; P =.014 vs group E). The order of efficacy of dextrorphan (as revealed by the average of neurologic status) was as follows: group C > group D (P =.017, after 50 minutes of clamping), group D > group B (P =.014, after 45 minutes of clamping), and group B > group E (P <.001, after 40 minutes of clamping). Histopathologic findings did not necessarily correspond with hind-limb neurologic function.

CONCLUSIONS

Dextrorphan reduced the physical findings associated with ischemic spinal cord injury, and continuous intra-aortic infusion prolonged the safe clamping time significantly more than delivery by other routes.

Insulin-like growth factor 1 prevents neuronal cell death and paraplegia in the rabbit model of spinal cord ischemia

OBJECTIVE

Insulin-like growth factor 1 has been shown to be cytoprotective against ischemia-reperfusion injury in various organs. However, spinal cord protection by insulin-like growth factor 1 has not been tested. We have therefore examined the effect of insulin-like growth factor 1 on neuronal cell death and motor function after spinal cord ischemia.

METHODS

Japanese white rabbits were subjected to spinal cord ischemia by clamping the abdominal aorta for 15 minutes. Insulin-like growth factor 1 (0.3 mg/kg) at a dose equipotent to insulin (0.3 IU/kg) in lowering blood glucose level or the control (phosphate-buffered saline solution as a vehicle) was administered intravenously 30 minutes before the aortic clamp.

RESULTS

Hind-limb motor function had recovered normally 48 hours after the operation in all the rabbits (n = 8) treated with insulin-like growth factor 1. In contrast, all the control-treated (n = 8) and all but one of the insulin-treated (n = 6) rabbits had deteriorated to paraplegia by 48 hours after the operation. Histopathologic sections in the involved spinal cord segment showed that a significantly (P <.0001) greater number of motor neuron cells were preserved in the rabbits treated with insulin-like growth factor 1 (17.9 +/- 4.8 per section) than in those treated with the control (8.0 +/- 2.1). Although insulin was equipotent to insulin-like growth factor 1 in preserving the number of motor neuron cells (18.5 +/- 2.7), the percentage of motor neuron cells positive for terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate-biotin nick-end labeling were significantly (P <.01) smaller in the rabbits treated with insulin-like growth factor 1 (6.0 +/- 4.6) compared with those treated with the control (54.6 +/- 33.8) and insulin (26.2 +/- 11.7). Immunohistochemical studies revealed that insulin-like growth factor 1 increased expression of the antiapoptotic Bcl-xL protein and inhibited expression of the proapoptotic Bax protein in motor neuron cells 24 and 48 hours after the operation. In contrast, expression of only Bax was increased after the operation in other groups of rabbits subjected to spinal cord ischemia.

CONCLUSIONS

These results suggest that insulin-like growth factor 1, but not insulin with a conventional dose, protects motor neuron cells from ischemic spinal cord injury associated with differential regulation of Bcl-xL and Bax protein.

Pharmacological modulation of SK3 channels

Small-conductance, calcium-activated K+ channels (SK channels) are voltage-insensitive channels that have been identified molecularly within the last few years. As SK channels play a fundamental role in most excitable cells and participate in afterhyperpolarization (AHP) and spike-frequency adaptation, pharmacological modulation of SK channels may be of significant clinical importance. Here we report the functional expression of SK3 in HEK293 and demonstrate a broad pharmacological profile for these channels. Brain slice studies commonly employ 4-aminopyridine (4-AP) to block voltage-dependent K+ channels or a methyl derivative of bicuculline, a blocker of gamma-aminobutyric acid (GABA)-gated Cl- channels, in order to investigate the role of various synapses in specialized neural networks. However, in this study both 4-AP and bicuculline are shown to inhibit SK3 channels (IC50 values of 512 microM and 6 microM, respectively) at concentrations lower than those used for brain slice recordings. Riluzole, a potent neuroprotective drug with anti-ischemic, anticonvulsant and sedative effects currently used in the treatment of amyotrophic lateral sclerosis, activates SK3 channels at concentrations of 3 microM and above. Amitriptyline, a tricyclic antidepressive widely used clinically, inhibits SK3 channels with an IC50 of 39.1 +/- 10 microM (n=6).

Hyperbaric oxygen therapy given 30 minutes after spinal cord ischemia attenuates selective motor neuron death in rabbits

OBJECTIVE

Spinal cord ischemia sometimes causes paraplegia because the spinal motor neuron cells are vulnerable to ischemia. Although various protective remedies for spinal cord injury have been reported, there have been few established clinical methods. Although hyperbaric oxygen (HBO) has been used clinically as a treatment for ischemia, the reason for its effectiveness is still uncertain because sufficient experimental data are lacking.

DESIGN

Prospective, randomized, controlled study.

SETTING

Experimental animal research laboratory in a university research center.

SUBJECTS

Twenty-three Japanese white rabbits, weighing 2-3 kg.

INTERVENTIONS

A modified rabbit spinal cord ischemia model of infrarenal aortic occlusion for 15 mins was employed. Rabbits were randomly assigned to four groups; the rabbits in group A did not undergo ischemic insults (n = 5). The rabbits in groups B and C underwent ischemic insult for 15 mins, followed by 1 hr of HBO treatment at 3 atm absolute with 100% oxygen at 30 mins (n = 6) or 6 hrs (n = 7) after reperfusion, respectively. The rabbits in group D underwent ischemic insult for 15 mins without HBO treatment (n = 5).

MEASUREMENTS AND MAIN RESULTS

We observed neurologic functions for 14 days. The sections of the spinal cords were stained with hematoxylin and eosin, and the number of spinal motor neurons in ventral region was counted by light microscopy. All rabbits in groups A and B could stand, whereas all rabbits in groups C and D showed irreversible paraplegia on days 2 and 14 after reperfusion. Spinal motor neurons in ventral gray matter in groups C and D decreased significantly compared with those in groups A and B.

CONCLUSIONS

HBO therapy shortly after ischemic insult had protective effects against ischemic spinal cord damage. However, delayed treatment with HBO did not change the prognosis.

The effect of riluzole treatment in rats on the survival of injured adult and grafted embryonic motoneurons

The effect of riluzole on the survival of injured motoneurons was studied. The L4 ventral root was avulsed and reimplanted into the spinal cord. Immediately after the operation, 4 animals were treated with riluzole for 3 weeks while another 4 animals received no treatment after the operation. Three months later the fluorescent dyes, Fast Blue and Diamidino Yellow, were applied to the cut ventral ramus of the L4 spinal nerve, for retrograde labelling of neurons. Three days later, the spinal cords were processed to reveal the retrograde-labelled cells. In untreated animals, there were 20 +/- 2.1 labelled neurons (+/- SEM), while in animals treated with riluzole there were 723 +/- 26. Thus, treatment with riluzole dramatically enhanced the survival of injured motoneurons. In another series of experiments, after avulsion of the L4 ventral root and its reinsertion, embryonic spinal cord pieces were grafted into the host cord. Five animals received riluzole treatment and 4 were left untreated. In the untreated animals, 125 +/- 5.1 retrograde-labelled cells of both graft and host origin were detected. In rats treated with riluzole, 645 +/- 35.7 retrograde-labelled cells were seen and almost all of these were of host origin. Thus, treatment with riluzole enhanced the survival of injured host motoneurons, and by doing so, (i) reduced the ability of grafted neurons to extend their axons into the reimplanted L4 ventral root, and (ii) reduced the survival of the grafted cells.

Pharmacologic neuroprotection in experimental spinal cord ischemia: a systematic review

Various surgical procedures may cause temporary interruption of spinal cord blood supply and may result in irreversible ischemic injury and neurological deficits. The cascade of events that leads to neuronal death following ischemia may be amenable to pharmacological manipulations that aim to increase the tolerable duration of ischemia. Many agents have been evaluated in experimental spinal cord ischemia (SCI). In order to investigate whether an agent is available that justifies clinical evaluation, the literature on pharmacological neuroprotection in experimental SCI was systematically reviewed to assess the neuroprotective efficacy of the various agents. In addition, the strength of the evidence for neuroprotection was investigated by analyzing the methodology. The authors used a systematic review to conduct this evaluation. The included studies were analyzed for neuroprotection and methodology. In order to be able to compare the various agents for neuroprotective efficacy, relative risks and confidence intervals were calculated from the data in the results sections. A total of 103 studies were included. Seventy-nine different agents were tested. Only 14 of the agents tested did not afford protection at all. A large variation was observed in the experimental models to produce SCI. This variation limited comparison of the individual agents. In 48 studies involving 31 single agents, the relative risks and confidence intervals could be calculated. An analysis of the methodology revealed poor temperature management and lack of statistical power in the majority of the 103 studies. The results suggest that numerous agents may protect the spinal cord from transient ischemia. However, poor temperature management and lack of statistical power severely weakened the evidence. Consequently, clinical evaluation of pharmacological neuroprotection in surgical procedures that carry a risk of ischemic spinal cord damage is not justified on the basis of this study.

Prevention of ischemic spinal cord injury: comparative effects of magnesium sulfate and riluzole

PURPOSE

Excitotoxic mechanisms have been implicated in the pathophysiology of spinal cord ischemic injury induced by aortic cross-clamping. We investigated the effects of the anti-excitotoxic drugs magnesium sulfate (MgSO(4)) and riluzole in a rabbit model of spinal cord ischemia.

METHOD

The infrarenal aorta of New Zealand albino white rabbits (n = 68) was occluded for 40 minutes. Experimental groups included: a control group, which received only vehicle (n = 17); group A (n = 17), which received riluzole (8 mg/kg) before clamping; group B (n = 17), which received MgSO(4) (100 mg/kg) before clamping; and group C (n = 17), which received riluzole (8 mg/kg) and MgSO(4) (100 mg/kg) before clamping. Five additional rabbits had the same operation, but did not undergo aortic clamping (sham operation). The neurological status of the rabbits was assessed at 24 hours, 48 hours, and then daily for as long as 120 hours by using a modified Tarlov scale. The rabbits were killed at 24 hours (n = 3 per group), 48 hours (n = 4 per group), and 120 hours (n = 10 per group) postoperatively. Spinal cords were harvested for histopathologic and immunohistochemistry examinations for microtubule-associated protein-2 (MAP-2), a cytoskeletal protein specific from neurons.

RESULTS

No major adverse effect was observed with either riluzole or MgSO(4). All control rabbits became severely paraplegic. All riluzole-treated and MgSO(4)-treated animals had a better neurological status than control animals. Typical morphological changes characteristic of neuronal necrosis in the gray matter of control animals was demonstrated by means of the histopathological examination, whereas riluzole or magnesium prevented or attenuated necrotic phenomenons. Moreover, MAP-2 immunoreactivity was completely lost in control rabbits, whereas it was preserved, either completely or partially, in rabbits treated with riluzole or magnesium. Riluzole was more effective than MgSO(4) in preventing paraplegia caused by motor neuron injury (P <.01 ). Riluzole and MgSO(4) had no additive neuroprotective effect.

CONCLUSION

These results demonstrate that riluzole and, to a lesser extent, MgSO(4) may afford significant spinal cord protection in a setting of severe ischemia and may, therefore, be considered for clinical use during "high-risk" operations on the thoracic and thoracoabdominal aorta.