Neuroprotection and secondary damage following spinal cord injury: concepts and methods

MicroRNA-219 Inhibits Proliferation and Induces Differentiation of Oligodendrocyte Precursor Cells after Contusion Spinal Cord Injury in Rats

MicroRNA-219 (miR-219) regulates the proliferation and differentiation of oligodendrocyte precursor cells (OPCs) during central nervous system (CNS) development. OPCs only differentiate into oligodendrocytes (OLs) in the healthy CNS, but can generate astrocytes (As) after injury. We hypothesized that miR-219 may modulate OPC proliferation and differentiation in a cervical C5 contusion spinal cord injury (SCI) model. After injury, we observed a decrease in the miR-219 level and quantity of OLs and an increase in the number of OPCs and As. Silencing of miR-219 by its antagomir in vivo produced similar results, but of greater magnitude. Overexpression of miR-219 by its agomir in vivo increased the number of OLs and suppressed generation of OPCs and As. Luxol fast blue staining confirmed that SCI caused demyelination and that the extent of demyelination was attenuated by miR-219 overexpression, but aggravated by miR-219 reduction. Monocarboxylate transporter 1 (MCT-1) may be implicated in the regulation of OPC proliferation and differentiation mediated by miR-219 following contusion SCI. Collectively, our data suggest that miR-219 may mediate SCI-induced OPC proliferation and differentiation, and MCT-1 may participate in this process as a target of miR-219.

Axonal degeneration and demyelination following traumatic spinal cord injury: A systematic review and meta-analysis

The pathophysiology of spinal cord injury (SCI) related processes of axonal degeneration and demyelination are poorly understood. The present systematic review and meta-analysis were performed such to establish quantitative results of animal studies regarding the role of injury severity, SCI models and level of injury on the pathophysiology of axon and myelin sheath degeneration. 39 related articles were included in the analysis. The compiled data showed that the total number of axons, number of myelinated axons, myelin sheath thickness, axonal conduction velocity, and internode length steadily decreased as time elapsed from the injury (P_{for trend}<0.0001). The rate of axonal retrograde degeneration was affected by SCI model and severity of the injury. Axonal degeneration was higher in injuries of the thoracic region. The SCI model and the site of the injury also affected axonal retrograde degeneration. The number of myelinated axons in the caudal region of the injury was significantly higher than the lesion site and the rostral region. The findings of the present meta-analysis show that the pathophysiology of axons and myelin sheath differ in various phases of SCI and are affected by multiple factors related to the injury.

Lysophosphatidic acid receptor type 2 activation contributes to secondary damage after spinal cord injury in mice

Lysophosphatidic acid (LPA) is an extracellular lipid mediator involved in many physiological functions by signaling through six known G-protein-coupled receptors (LPA₁-LPA₆). In the central nervous system (CNS), LPA mediates a wide range of effects, including neural progenitor cell physiology, astrocyte and microglia activation, neuronal cell death, axonal retraction, and contributions to pain, schizophrenia and hydrocephalus. We recently reported that LPA-LPA₁ signaling mediates functional deficits and myelin loss after spinal cord injury (SCI). Here, we provide clear evidence on the deleterious contribution of another LPA receptor, LPA₂, to myelin loss after SCI. We found that LPA₂ is constitutively expressed in the spinal cord parenchyma and its transcripts were up-regulated after contusion injury, in part, by microglial cells. We also found that the demyelinating lesion triggered by intraspinal injection of LPA into the undamaged spinal cord was markedly reduced in the lack of LPA₂. Similarly, LPA₂ deficient mice showed enhanced motor skills and myelin sparing after SCI. To gain insights into the detrimental actions of LPA₂ in spinal cord we performed cell culture studies. These experiments revealed that, similar to LPA₁, activation of microglia LPA₂ led to oligodendrocyte cell death. Moreover, we also found that the cytotoxic effects underlaying microglial LPA-LPA₂ axis were mediated by the release of purines by microglia and the activation of P₂X₇ receptor on oligodendrocytes. Overall, this study provides new mechanistic insights into how LPA contributes to SCI physiopathology, and suggest that targeting LPA₂ could be a novel therapeutic approach for the treatment of acute SCI.

CNB-001 reduces paraplegia in rabbits following spinal cord ischemia

Spinal cord ischemia associated with trauma and surgical procedures including thoraco-abdominal aortic aneurysm repair and thoracic endovascular aortic repair results in devastating clinical deficits in patients. Because spinal cord ischemia is inadequately treated, we studied the effects of [4-((1E)-2-(5-(4-hydroxy-3-methoxystyryl-)-1-phenyl-1H-pyrazoyl-3-yl) vinyl)-2-methoxy-phenol)] (CNB-001), a novel curcumin-based compound, in a rabbit SCI model. CNB-001 is known to inhibit human 5-lipoxygenase and 15-lipoxygenase and reduce the ischemia-induced inflammatory response. Moreover, CNB-001 can reduce the level of oxidative stress markers and potentiate brain-derived neurotrophic factor and brain-derived neurotrophic factor receptor signaling. The Tarlov scale and quantal analysis technique results revealed that CNB-001 administered as an intravenous dose (bolus) 30 minutes prior to spinal cord ischemia improved the behaviors of female New Zealand White rabbits. The improvements were similar to those produced by the uncompetitive N-methyl-D-aspartate receptor antagonist memantine. At 48 hours after aortic occlusion, there was a 42.7% increase (P < 0.05) in tolerated ischemia duration (n = 14) for rabbits treated with CNB-001 (n = 16), and a 72.3% increase for rabbits treated with the positive control memantine (P < 0.05) (n = 23) compared to vehicle-treated ischemic rabbits (n = 22). CNB-001 is a potential important novel treatment for spinal cord ischemia induced by aortic occlusion. All experiments were approved by the CSMC Institutional Animal Care and Use Committee (IACUC #4311) on November 1, 2012.

Bioactive Lipids in Inflammation After Central Nervous System Injury

Despite the progress made over the last decades to understand the mechanisms underlying tissue damage and neurological deficits after neurotrauma, there are currently no effective treatments in the clinic. It is well accepted that the inflammatory response in the CNS after injury exacerbates tissue loss and functional impairments. Unfortunately, the use of potent anti-inflammatory drugs, such as methylprednisolone, fails to promote therapeutic recovery and also gives rise to several undesirable side effects related to immunosuppression. The injury-induced inflammatory response is complex, and understanding the mechanisms that regulate this inflammation is therefore crucial in the quest to develop effective treatments. Bioactive lipids have emerged as potent molecules in controlling the initiation, coordination, and resolution of inflammation and in promoting tissue repair and recovery of homeostasis. These bioactive lipids are produced by cells involved in the inflammatory response, and their defective synthesis leads to persistent chronic inflammation, tissue damage, and fibrosis. The present chapter discusses recent evidence for the role of some of these bioactive lipids, in particular, eicosanoid and pro-resolving lipid mediators, in the regulation of inflammation after neurotrauma and highlights the therapeutic potential of some of these lipids in enhancing neurological outcomes after CNS injuries.

Inosine - a Multifunctional Treatment for Complications of Neurologic Injury

Spinal cord injury (SCI) caused by trauma or disease leads to motor and sensory abnormalities that depend on the level, severity and duration of the lesion. The most obvious consequence of SCI is paralysis affecting lower and upper limbs. SCI also leads to loss of bladder and bowel control, both of which have a deleterious, life-long impact on the social, psychological, functional, medical and economic well being of affected individuals. Currently, there is neither a cure for SCI nor is there adequate management of its consequences. Although medications provide symptomatic relief for the complications of SCI including muscle spasms, lower urinary tract dysfunction and hyperreflexic bowel, strategies for repair of spinal injuries and recovery of normal limb and organ function are still to be realized. In this review, we discuss experimental evidence supporting the use of the naturally occurring purine nucleoside inosine to improve the devastating sequelae of SCI. Evidence suggests inosine is a safe, novel agent with multifunctional properties that is effective in treating complications of SCI and other neuropathies.

Systemic administration of epothilone D improves functional recovery of walking after rat spinal cord contusion injury

Central nervous system (CNS) injuries cause permanent impairments of sensorimotor functions as mature neurons fail to regenerate their severed axons. The poor intrinsic growth capacity of adult CNS neurons and the formation of an inhibitory lesion scar are key impediments to axon regeneration. Systemic administration of the microtubule stabilizing agent epothilone B promotes axon regeneration and recovery of motor function by activating the intrinsic axonal growth machinery and by reducing the inhibitory fibrotic lesion scar. Thus, epothilones hold clinical promise as potential therapeutics for spinal cord injury. Here we tested the efficacy of epothilone D, an epothilone B analog with a superior safety profile. By using liquid chromatography and mass spectrometry (LC/MS), we found adequate CNS penetration and distribution of epothilone D after systemic administration, confirming the suitability of the drug for non-invasive CNS treatment. Systemic administration of epothilone D reduced inhibitory fibrotic scarring, promoted regrowth of injured raphespinal fibers and improved walking function after mid-thoracic spinal cord contusion injury in adult rats. These results confirm that systemic administration of epothilones is a valuable therapeutic strategy for CNS regeneration and repair after injury and provides a further advance for potential clinical translation.

[Icariin alleviates lipid peroxidation after spinal cord injury in rats]

OBJECTIVE

To assess the effects of intragastric administration of icariin on lipid peroxidation after spinal cord injury in rats.

METHODS

Seventy-two healthy adult male SD rats were randomized equally into icariin group, control group and sham-operated group. In the control and icariin groups, spinal cord injury was induced using modified Allen's method, and the rats in the sham-operated group underwent laminotomy without damaging the spinal cord. Immediately after the surgery, the rats in icariin group were subjected to intragastric administration of icariin (100 mg/kg), and those in the control and sham-operated groups received an equal volume of saline in the same manner once a day. At 24 h after the operation, malondialdehyde (MDA) content was detected using thiobarbituric acid method, superoxide dismutase (SOD) activity was measured with xanthine oxidase method, and the water content in the spinal cord was measured using dry-wet weight method. At 48 h after the operation, the ultrastructure of the spinal cord was observed with transmission electron microscopy and scored using Kaptanoglu scoring method. The motor function of the rats was assessed using BBB scoring at 7, 14, 21 and 28 days after the operation.

RESULTS

At 24 h after the operation, MDA content was significantly higher in the control group and icariin group than in the sham-operated group, and was significantly lower in icariin group than in the control group (P<0.05); SOD activity was significantly higher in icariin group than in the control group, and was both significantly lower than that in the sham-operated group (P<0.05). At 48 h after operation, the water content and ultrastructure score of the spinal cord were the highest in sham-operated group (P<0.05), and were significantly lower in icariin group than in the control group (P<0.05). At all the time points of measurement, the BBB scores were significantly lower in the control and icariin groups than in the sham-operated group (P<0.05), and were significantly higher in icariin group than in the control group (P<0.05).

CONCLUSION

Icariin can significantly reduce MDA content, increase SOD activity, and ameliorate lipid peroxidation, spinal cord edema, and histopathological damage of the spinal cord to improve motor function of rats with spinal cord injury.

Activity-Based Physical Rehabilitation with Adjuvant Testosterone to Promote Neuromuscular Recovery after Spinal Cord Injury

Neuromuscular impairment and reduced musculoskeletal integrity are hallmarks of spinal cord injury (SCI) that hinder locomotor recovery. These impairments are precipitated by the neurological insult and resulting disuse, which has stimulated interest in activity-based physical rehabilitation therapies (ABTs) that promote neuromuscular plasticity after SCI. However, ABT efficacy declines as SCI severity increases. Additionally, many men with SCI exhibit low testosterone, which may exacerbate neuromusculoskeletal impairment. Incorporating testosterone adjuvant to ABTs may improve musculoskeletal recovery and neuroplasticity because androgens attenuate muscle loss and the slow-to-fast muscle fiber-type transition after SCI, in a manner independent from mechanical strain, and promote motoneuron survival. These neuromusculoskeletal benefits are promising, although testosterone alone produces only limited functional improvement in rodent SCI models. In this review, we discuss the (1) molecular deficits underlying muscle loss after SCI; (2) independent influences of testosterone and locomotor training on neuromuscular function and musculoskeletal integrity post-SCI; (3) hormonal and molecular mechanisms underlying the therapeutic efficacy of these strategies; and (4) evidence supporting a multimodal strategy involving ABT with adjuvant testosterone, as a potential means to promote more comprehensive neuromusculoskeletal recovery than either strategy alone.

Carbonyl scavengers as pharmacotherapies in degenerative disease: Hydralazine repurposing and challenges in clinical translation

During cellular metabolism, spontaneous oxidative damage to unsaturated lipids generates many electrophilic carbonyl compounds that readily attack cell macromolecules, forming adducts that are potential drivers of tissue dysfunction. Since such damage is heightened in many degenerative conditions, researchers have assessed the efficacy of nucleophilic carbonyl-trapping drugs in animal models of such disorders, anticipating that they will protect tissues by intercepting toxic lipid-derived electrophiles (LDEs) within cells. This Commentary explores recent animal evidence for carbonyl scavenger efficacy in two disparate yet significant conditions known to involve LDE production, namely spinal cord injury (SCI) and alcoholic liver disease (ALD). Primary emphasis is placed on studies that utilised hydralazine, a clinically-approved "broad-spectrum" scavenger known to trap multiple LDEs. In addition to reviewing recent studies of hydralazine efficacy in animal SCI and ALD models, the Commentary reviews new insights concerning novel lifespan- and healthspan-extending properties of hydralazine obtained during studies in model invertebrate organisms, since the mechanisms involved seem of likely benefit during the treatment of degenerative disease. Finally, noting that human translation of the histoprotective properties of hydralazine have been limited, the final section of the Commentary will address two obstacles that hamper clinical translation of LDE-trapping therapies while also suggesting potential strategies for overcoming these problems.

Repeatability of a Dislocation Spinal Cord Injury Model in a Rat-A High-Speed Biomechanical Analysis

Dislocation is the most common, and severe, spinal cord injury (SCI) mechanism in humans, yet there are few preclinical models. While dislocation in the rat model has been shown to produce unique outcomes, like other closed column models it exhibits higher outcome variability. Refinement of the dislocation model will enhance the testing of neuroprotective strategies, further biomechanical understanding, and guide therapeutic decisions. The overall objective of this study is to improve biomechanical repeatability of a dislocation SCI model in the rat, through the following specific aims: (i) design new injury clamps that pivot and self-align to the vertebrae; (ii) measure intervertebral kinematics during injury using the existing and redesigned clamps; and (iii) compare relative motion at the vertebrae-clamp interface to determine which clamps provide the most rigid connection. Novel clamps that pivot and self-align were developed based on the quantitative rat vertebral anatomy. A dislocation injury was produced in 34 rats at C4/C5 using either the existing or redesigned clamps, and a high-speed X-ray device recorded the kinematics. Relative motion between the caudal clamp and C5 was significantly greater in the existing clamps compared to the redesigned clamps in dorsoventral translation and sagittal rotation. This study demonstrates that relative motions can be of magnitudes that likely affect injury outcomes. We recommend such biomechanical analyses be applied to other SCI models when repeatability is an issue. For this dislocation model, the results show the importance of using clamps that pivot and self-align to the vertebrae.

Therapeutic time window of anti-high mobility group box-1 antibody administration in mouse model of spinal cord injury

Spinal cord injury (SCI) is a devastating neurologic disorder that often leads to permanent disability, and there is no effective treatment for it. High mobility group box-1 (HMGB1) is a damage-associated molecular protein that triggers sterile inflammation upon injuries. We have previously shown that two administrations of neutralizing monoclonal antibody (mAb) against HMGB1 (immediately after (0 h) and 6 h after) SCI dramatically improves functional recovery after SCI in mice. However, when considering clinical application, 0 h after SCI is not practical. Therefore, in this study, we examined the therapeutic time window of the mAb administration. Injection at 3 h after SCI significantly improved the functional recovery comparably to injection immediately after SCI, while injection at 6 h was less effective, and injection at 9 or 12 h had no therapeutic effect. We also found beneficial effects of injection at 3 h after injury on blood-spinal cord barrier maintenance, inflammatory-related gene expression and preservation of the damaged spinal cord tissue. Taken together, our results suggest that a single administration of anti-HMGB1 mAb within a proper time window could be a novel and potential therapeutic strategy for SCI.

Stress-Activated Protein Kinases in Spinal Cord Injury: Focus on Roles of p38

Spinal cord injury (SCI) consists of three phases-acute, secondary, and chronic damages-and limiting the development of secondary damage possibly improves functional recovery after SCI. A major component of the secondary phase of SCI is regarded as inflammation-triggered events: induction of cytokines, edema, microglial activation, apoptosis of cells including oligodendrocytes and neurons, demyelination, formation of the astrocytic scar, and so on. Two major stress-activated protein kinases (SAPKs)-c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK)-are activated in various types of cells in response to cellular stresses such as apoptotic stimuli and inflammatory waves. In animal models of SCI, inhibition of either JNK or p38 has been shown to promote neuroprotection-associated functional recovery. Here, we provide an overview on the roles of SAPKs in SCI and, in particular, the pathological role of p38 will be discussed as a promising target for therapeutic intervention in SCI.

Can injured adult CNS axons regenerate by recapitulating development?

In the adult mammalian central nervous system (CNS), neurons typically fail to regenerate their axons after injury. During development, by contrast, neurons extend axons effectively. A variety of intracellular mechanisms mediate this difference, including changes in gene expression, the ability to form a growth cone, differences in mitochondrial function/axonal transport and the efficacy of synaptic transmission. In turn, these intracellular processes are linked to extracellular differences between the developing and adult CNS. During development, the extracellular environment directs axon growth and circuit formation. In adulthood, by contrast, extracellular factors, such as myelin and the extracellular matrix, restrict axon growth. Here, we discuss whether the reactivation of developmental processes can elicit axon regeneration in the injured CNS.