NBQX treatment improves mitochondrial function and reduces oxidative events after spinal cord injury

AMPA receptors play an important role in the biological consequences of spinal cord injury: Implications for AMPA receptor modulators for therapeutic benefit

Spinal cord injury (SCI) afflicts millions of individuals globally. There are few therapies available to patients. Ascending and descending excitatory glutamatergic neural circuits in the central nervous system are disrupted by SCI, making α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) a potential therapeutic drug target. Emerging research in preclinical models highlights the involvement of AMPARs in vital processes following SCI including breathing, pain, inflammation, bladder control, and motor function. However, there are no clinical trial data reported in this patient population to date. No work on the role of AMPA receptors in sexual dysfunction after SCI has been disclosed. Compounds with selective antagonist and potentiating effects on AMPA receptors have benefit in animal models of SCI, with antagonists generally showing protective effects early after injury and potentiators (ampakines) producing improved breathing and bladder function. The role of AMPARs in pathophysiology and recovery after SCI depends upon the time post injury, and the timing of AMPAR augmentation or antagonism. The roles of inflammation, synaptic plasticity, sensitization, neurotrophic factors, and neuroprotection are considered in this context. The data summarized and discussed in this paper document proof of principle and strongly encourage additional studies on AMPARs as novel gateways to therapeutic benefit for patients suffering from SCI. The availability of both AMPAR antagonists such as perampanel and AMPAR allosteric modulators (i.e., ampakines) such as CX1739, that have been safely administered to humans, provides an expedited means of clinical inquiry for possible therapeutic advances.

Perspectives in the Cell-Based Therapies of Various Aspects of the Spinal Cord Injury-Associated Pathologies: Lessons from the Animal Models

Traumatic injury of the spinal cord (SCI) is a devastating neurological condition often leading to severe dysfunctions, therefore an improvement in clinical treatment for SCI patients is urgently needed. The potential benefits of transplantation of various cell types into the injured spinal cord have been intensively investigated in preclinical SCI models and clinical trials. Despite the many challenges that are still ahead, cell transplantation alone or in combination with other factors, such as artificial matrices, seems to be the most promising perspective. Here, we reviewed recent advances in cell-based experimental strategies supporting or restoring the function of the injured spinal cord with a particular focus on the regenerative mechanisms that could define their clinical translation.

Trehalose Augments Neuron Survival and Improves Recovery from Spinal Cord Injury via mTOR-Independent Activation of Autophagy

Spinal cord injury (SCI) is a major cause of irreversible nerve injury and leads to serious tissue loss and neurological dysfunction. Thorough investigation of cellular mechanisms, such as autophagy, is crucial for developing novel and effective therapeutics. We administered trehalose, an mTOR-independent autophagy agonist, in SCI rats suffering from moderate compression injury to elucidate the relationship between autophagy and SCI and evaluate trehalose's therapeutic potential. 60 rats were divided into 4 groups and were treated with either control vehicle, trehalose, chloroquine, or trehalose + chloroquine 2 weeks prior to administration of moderate spinal cord crush injury. 20 additional sham rats were treated with control vehicle. H&E staining, Nissl staining, western blot, and immunofluorescence studies were conducted to examine nerve morphology and quantify autophagy and mitochondrial-dependent apoptosis at various time points after surgery. Functional recovery was assessed over a period of 4 weeks after surgery. Trehalose promotes autophagosome recruitment via an mTOR-independent pathway, enhances autophagy flux in neurons, inhibits apoptosis via the intrinsic mitochondria-dependent pathway, reduces lesion cavity expansion, decreases neuron loss, and ultimately improves functional recovery following SCI (all p < 0.05). Furthermore, these effects were diminished upon administration of chloroquine, an autophagy flux inhibitor, indicating that trehalose's beneficial effects were due largely to activation of autophagy. This study presents new evidence that autophagy plays a critical neuroprotective and neuroregenerative role in SCI, and that mTOR-independent activation of autophagy with trehalose leads to improved outcomes. Thus, trehalose has great translational potential as a novel therapeutic agent after SCI.

The Roles of Superoxide on At-Level Spinal Cord Injury Pain in Rats

Background: In the present study, we examined superoxide-mediated excitatory nociceptive transmission on at-level neuropathic pain following spinal thoracic 10 contusion injury (SCI) in male Sprague Dawley rats. Methods: Mechanical sensitivity at body trunk, neuronal firing activity, and expression of superoxide marker/ionotropic glutamate receptors (iGluRs)/CamKII were measured in the T7/8 dorsal horn, respectively. Results: Topical treatment of superoxide donor t-BOOH (0.4 mg/kg) increased neuronal firing rates and pCamKII expression in the naïve group, whereas superoxide scavenger Tempol (1 mg/kg) and non-specific ROS scavenger PBN (3 mg/kg) decreased firing rates in the SCI group (* p < 0.05). SCI showed increases of iGluRs-mediated neuronal firing rates and pCamKII expression (* p < 0.05); however, t-BOOH treatment did not show significant changes in the naïve group. The mechanical sensitivity at the body trunk in the SCI group (6.2 ± 0.5) was attenuated by CamKII inhibitor KN-93 (50 μg, 3.9 ± 0.4) or Tempol (1 mg, 4 ± 0.4) treatment (* p < 0.05). In addition, the level of superoxide marker Dhet showed significant increase in SCI rats compared to the sham group (11.7 ± 1.7 vs. 6.6 ± 1.5, * p < 0.05). Conclusions: Superoxide and the pCamKII pathway contribute to chronic at-level neuropathic pain without involvement of iGluRs following SCI.

Imaging mass spectrometry reveals loss of polyunsaturated cardiolipins in the cortical contusion, hippocampus, and thalamus after traumatic brain injury

Traumatic brain injury (TBI) leads to changes in ion fluxes, alterations in mitochondrial function, and increased generation of reactive oxygen species, resulting in secondary tissue damage. Mitochondria play important signaling roles in coordination of multiple metabolic platforms in addition to their well-known role in bioenergetics. Mitochondrial signaling strongly depends on cardiolipin (CL), a mitochondria-specific structurally unusual anionic phospholipid containing four fatty acyl chains. While our previous reports indicated that CL is selectively oxidized and presents itself as a target for the redox therapy following TBI, the topography of changes of CL in the injured brain remained to be defined. Here, we present a matrix-assisted laser desorption/ionization imaging study which reports regio-specific changes in CL, in a controlled cortical impact model of TBI in rats. Matrix-assisted laser desorption/ionization imaging revealed that TBI caused early decreases in CL in the contusional cortex, ipsilateral hippocampus, and thalamus with the most highly unsaturated CL species being most susceptible to loss. Phosphatidylinositol was the only other lipid species that exhibited a significant decrease, albeit to a lesser extent than CL. Signals for other lipids remained unchanged. This is the first study evaluating the spatial distribution of CL loss after acute brain injury. We propose that the CL loss may constitute an upstream mechanism for CL-driven signaling in different brain regions as an early response mechanism and may also underlie the bioenergetic changes that occur in hippocampal, cortical, and thalamic mitochondria after TBI.

Mitochondrial Division Inhibitor 1 Ameliorates Mitochondrial Injury, Apoptosis, and Motor Dysfunction After Acute Spinal Cord Injury in Rats

Mitochondrial division inhibitor 1 (Mdivi-1) is the most effective pharmacological inhibitor of mitochondrial fission. Spinal cord injury (SCI) is a common and serious trauma, which lacks efficient treatment. This study aimed to detect the role of Mdivi-1 in neuronal injury and its underlying mechanism after acute SCI (ASCI) in rats. Western blot analysis showed that Bax levels on the mitochondrial outer membrane, and release of cytochrome C (cytC) and apoptosis-inducing factor (AIF) from the mitochondria began to increase significantly at 4 h after ASCI, then peaked at 16 h, and declined significantly from 16 to 24 h. However, the mitochondrial levels of Bcl-2 increased significantly at 2 h, peaked at 4 h, and subsequently significantly decreased from 4 to 24 h after ASCI. In addition, Mdivi-1(1.2 mg/kg) significantly suppressed the translocation of dynamin-related protein 1 (Drp1) and Bax to the mitochondria, mitochondrial depolarization, decrease of ATP and reduced Glutathione, increase of the Malondialdehyde, cytC release, and AIF translocation at 16 h and 3 days after ASCI, and also inhibited the caspase-3 activation and decrease of the percentage of apoptotic cells at 16 h, 3 and 10 days, further, ameliorated the motor dysfunction greatly from 3 to 10 days after ASCI in rats. This neuroprotective effect was dose-dependent. However, Mdivi-1(1.2 mg/kg) had no effects on the translocation of Bcl-2 and fission protein 1 on the mitochondria, and did not affect the expression of total Drp1 at 16 h after ASCI. Our experimental findings indicated that Mdivi-1 can protect rats against ASCI, and that its underlying mechanism may be associated with inhibition of Drp1 translocation to the mitochondria, alleviation of mitochondrial dysfunction and oxidative stress, and suppression of caspase-dependent and -independent apoptosis.

Valproic acid protects motor neuron death by inhibiting oxidative stress and endoplasmic reticulum stress-mediated cytochrome C release after spinal cord injury

Both oxidative stress and endoplasmic reticulum (ER) stress are known to contribute to secondary injury, ultimately leading to cell death after spinal cord injury (SCI). Here, we showed that valproic acid (VPA) reduced cell death of motor neurons by inhibiting cytochrome c release mediated by oxidative stress and ER stress after SCI. After SCI, rats were immediately injected with VPA (300 mg/kg) subcutaneously and further injected every 12 h for an indicated time period. Motor neuron cell death at an early time after SCI was significantly attenuated by VPA treatment. Superoxide anion (O2-) production and inducible NO synthase (iNOS) expression linked to oxidative stress was increased after injury, which was inhibited by VPA. In addition, VPA inhibited c-Jun N-terminal kinase (JNK) activation, which was activated and peaked at an early time after SCI. Furthermore, JNK activation and c-Jun phosphorylation were inhibited by a broad-spectrum reactive oxygen species (ROS) scavenger, Mn (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP), indicating that ROS including O2- increased after SCI probably contribute to JNK activation. VPA also inhibited cytochrome c release and caspase-9 activation, which was significantly inhibited by SP600125, a JNK inhibitor. The levels of phosphorylated Bim and Mcl-1, which are known as downstream targets of JNK, were significantly reduced by SP600125. On the other hand, VPA treatment inhibited ER stress-induced caspase-12 activation, which is activated in motor neurons after SCI. In addition, VPA increased the Bcl-2/Bax ratio and inhibited CHOP expression. Taken together, our results suggest that cell death of motor neurons after SCI is mediated through oxidative stress and ER stress-mediated cytochrome c release and VPA-inhibited cytochrome c release by attenuating ROS-induced JNK activation followed by Mcl-1 and Bim phosphorylation and ER stress-coupled CHOP expression.

Inhibition of NADPH oxidase activation in oligodendrocytes reduces cytotoxicity following trauma

Spinal cord injury is a debilitating neurological disorder that initiates a cascade of cellular events that result in a period of secondary damage that can last for months after the initial trauma. The ensuing outcome of these prolonged cellular perturbations is the induction of neuronal and glial cell death through excitotoxic mechanisms and subsequent free radical production. We have previously shown that astrocytes can directly induce oligodendrocyte death following trauma, but the mechanisms regulating this process within the oligodendrocyte remain unclear. Here we provide evidence demonstrating that astrocytes directly regulate oligodendrocyte death after trauma by inducing activation of NADPH oxidase within oligodendrocytes. Spinal cord injury resulted in a significant increase in oxidative damage which correlated with elevated expression of the gp91 phox subunit of the NADPH oxidase enzyme. Immunohistochemical analysis confirmed the presence of gp91 phox in oligodendrocytes in vitro and at 1 week following spinal cord injury. Exposure of oligodendrocytes to media from injured astrocytes resulted in an increase in oligodendrocyte NADPH oxidase activity. Inhibition of NADPH oxidase activation was sufficient to attenuate oligodendrocyte death in vitro and at 1 week following spinal cord injury, suggesting that excitotoxicity of oligodendrocytes after trauma is dependent on the intrinsic activation of the NADPH oxidase enzyme. Acute administration of the NADPH oxidase inhibitor apocynin and the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate channel blocker 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione significantly improved locomotor behavior and preserved descending axon fibers following spinal cord injury. These studies lead to a better understanding of oligodendrocyte death after trauma and identify potential therapeutic targets in disorders involving demyelination and oligodendrocyte death.

Topiramate treatment is neuroprotective and reduces oligodendrocyte loss after cervical spinal cord injury

Excess glutamate release and associated neurotoxicity contributes to cell death after spinal cord injury (SCI). Indeed, delayed administration of glutamate receptor antagonists after SCI in rodents improves tissue sparing and functional recovery. Despite their therapeutic potential, most glutamate receptor antagonists have detrimental side effects and have largely failed clinical trials. Topiramate is an AMPA-specific, glutamate receptor antagonists that is FDA-approved to treat CNS disorders. In the current study we tested whether topiramate treatment is neuroprotective after cervical contusion injury in rats. We report that topiramate, delivered 15-minutes after SCI, increases tissue sparing and preserves oligodendrocytes and neurons when compared to vehicle treatment. In addition, topiramate is more effective than the AMPA-receptor antagonist, NBQX. To the best of our knowledge, this is the first report documenting a neuroprotective effect of topiramate treatment after spinal cord injury.

Reduction in expression of the astrocyte glutamate transporter, GLT1, worsens functional and histological outcomes following traumatic spinal cord injury

The astrocyte glutamate transporter, GLT1, is responsible for the vast majority of glutamate uptake in the adult central nervous system (CNS), thereby regulating extracellular glutamate homeostasis and preventing excitotoxicity. Glutamate dysregulation plays a central role in outcome following traumatic spinal cord injury (SCI). To determine the role of GLT1 in secondary cell loss following SCI, mice heterozygous for the GLT1 astrocyte glutamate transporter (GLT1+/-) and wild-type mice received thoracic crush SCI. Compared with wild-type controls, GLT1+/- mice had an attenuated recovery in hindlimb motor function, increased lesion size, and decreased tissue sparing. GLT1+/- mice showed a decrease in intraspinal GLT1 protein and functional glutamate uptake compared with wild-type mice, accompanied by increased apoptosis and neuronal loss following crush injury. These results suggest that astrocyte GLT1 plays a role in limiting secondary cell death following SCI, and also show that compromise of key astrocyte functions has significant effects on outcome following traumatic CNS injury. These findings also suggest that increasing intraspinal GLT1 expression may represent a therapeutically relevant target for SCI treatment.

Spatial and temporal changes in promoter activity of the astrocyte glutamate transporter GLT1 following traumatic spinal cord injury

After traumatic spinal cord injury (SCI), there is an opportunity for preserving function by attenuating secondary cell loss. Astrocytes play crucial roles in the adult CNS and are responsible for the vast majority of glutamate buffering, potentially preventing excitotoxic loss of neurons and oligodendrocytes. We examined spatial and temporal changes in gene expression of the major astrocyte glutamate transporter GLT1 following moderate thoracic contusion SCI using transgenic BAC-GLT1-eGFP promoter reporter mice. In dorsal column white matter, total intensity of GLT1-eGFP expression per region was significantly reduced following SCI at both lesion epicenter and at rostral and caudal areas where no tissue loss occurred. This regional decrease in GLT1 expression was due to significant loss of GLT1-eGFP(+) cells, partially accounted for by apoptosis of eGFP(+) /GFAP(+) astrocytes in both white and gray matter. There were also decreased numbers of GLT1-eGFP-expressing cells in multiple gray matter regions following injury; nevertheless, there was sustained or even increased regional GLT1-eGFP expression in gray matter as a result of up-regulation in astrocytes that continued to express GLT1-eGFP. Although there were increased numbers of GFAP(+) cells both at the lesion site and in surrounding intact spinal cord following SCI, the majority of proliferating Ki67(+) /GFAP(+) astrocytes did not express GLT1-eGFP. These findings demonstrate that spatial and temporal alterations in GLT1 expression observed after SCI result from both astrocyte death and gene expression changes in surviving astrocytes. Results also suggest that following SCI a significant portion of astrocytes lacks GLT1 expression, possibly compromising the important role of astrocytes in glutamate homeostasis.

NMDA receptor blockage with 2-amino-5-phosphonovaleric acid improves oxidative stress after spinal cord trauma in rats

STUDY DESIGN

2-amino-5-phosphonovaleric acid (APV) is an N-methyl-D-aspartate (NMDA) receptor blocker and has neuroprotective properties. This study is aimed at evaluating the effect of APV treatment on oxidative status after spinal cord injury (SCI).

METHODS

The experiment was carried out on the following five groups: Group 1: sham operated, non-traumatized; Group 2: with injured spinal cord, no treatment; Group 3: with SCI, injected with 100 microg kg(-1) APV; Group 4: with SCI, injected with 200 microg kg(-1) APV; and Group 5: with SCI, injected with 400 microg kg(-1) APV. SCI was inflicted by epidural compression with a cerebral vascular clip after T9-11 laminectomy. The experiments were completed after 12 h of trauma. Spinal cords were excised for evaluation of superoxide dismutase (SOD), catalase, reduced glutathione (GSH) and malonyldialdehyde (MDA) levels.

RESULTS

After SCI, SOD and GSH levels decreased and the MDA level increased significantly. APV treatment decreased the MDA level and increased SOD, catalase and GSH levels. The maximum decrease in MDA was detected in the group treated with 100 microg kg(-1) APV compared with the other groups. The GSH level was significantly increased in the group treated with 200 microg kg(-1) APV. The SOD level was significantly increased in the group treated with 200 microg kg(-1) APV.

CONCLUSION

The results of this study have shown that APV treatment creates a dose-dependent antioxidant effect in rats with SCI and may be used for the treatment of SCIs.

The efficacy of intratechal administration of a very low dose potirelin after acute spinal cord injury

BACKGROUND AND OBJECT

The objective of this study was to determine the effect of a very low dose protirelin in cerebrospinal fluid (CSF) glucose, magnesium and lactate levels after spinal cord trauma (SCT) in rabbits. We also aimed to evaluate whether this very low dose might induce analeptic effect.

MATERIAL AND METHODS

Twenty rabbits were divided equally into two groups: group I (n=10) was the control group, suffered from SCT but received only saline after SCT. Group II (n=10) (treatment group), received a very low dose of 0.05 mg/kg thyrotropin releasing hormone (TRH), analogue protirelin intratechally after SCT. The basal CSF glucose, magnesium and lactate levels were recorded in both groups. CSF lactate, glucose and magnesium contents were recorded at the same time (an hour before and after) SCT. Serum thyroid stimulating hormone (TSH), freetriiodothyronine (FT3) and freethyroxine (FT4) were measured in all rabbits before and after SCT.

RESULTS

Before spinal cord trauma, there were not any significant differences in glucose, lactate and magnesium levels between group I and II whereas, after spinal cord trauma in group II, the significant suppression in elevation of lactate and glucose depletion (p<0.05) were observed while no significant suppression was observed in magnesium level (p>0.05) as compared with group I (Table 3). In respect of serum TSH levels, there were not any significant differences between two groups before and after SCT.

CONCLUSIONS

This study showed that intratechal TRH has no analeptic effect on serum TSH, FT3 and FT4 levels but can attenuate the increase of lactate levels following spinal cord trauma. No significant decrease in magnesium level and also suppression of glucose decline in group II, may be related to the neuroprotective effects of TRH.

Systemic administration of PEP-1-SOD1 fusion protein improves functional recovery by inhibition of neuronal cell death after spinal cord injury

Spinal cord injury (SCI) produces excessive levels of reactive oxygen species (ROS) that induce apoptosis of neurons. Cu,Zn-superoxide dismutase (SOD1) is a key antioxidant enzyme that detoxifies intracellular ROS, thereby protecting cells from oxidative damage. PEP-1 is a peptide carrier capable of delivering full-length native peptides or proteins into cells. In the study described here, we fused a human SOD1 gene with PEP-1 in a bacterial expression vector to produce a genetic in-frame PEP-1-SOD1 fusion protein; we then investigated the neuroprotective effect of the fusion protein after SCI. The expressed and purified PEP-1-SOD1 was efficiently delivered into cultured cells and spinal cords in vivo, and the delivered fusion protein was biologically active. Systemic administration of PEP-1-SOD1 significantly decreased levels of ROS and protein carbonylation and nitration in spinal motor neurons after injury. PEP-1-SOD1 treatment also significantly inhibited mitochondrial cytochrome c release and activation of caspase-9 and caspase-3 in spinal cords after injury. Furthermore, PEP-1-SOD1 treatment significantly reduced ROS-induced apoptosis of motor neurons and improved functional recovery after SCI. These results suggest that PEP-1-SOD1 may provide a novel strategy for the therapeutic delivery of antioxidant enzymes that protect neurons from ROS after SCI.

The neuroprotective potential of phase II enzyme inducer on motor neuron survival in traumatic spinal cord injury in vitro

(1) Phase II enzyme inducer is a kind of compound which can promote the expression of antioxidative enzymes through nuclear factor erythroid 2-related factor 2 (Nrf2) activation. Recently, it has been reported that these compounds show neuroprotective effect via combating oxidative stress. The purpose of this study is to determine whether phase II enzyme inducers have neuroprotective effects on traumatic spinal cord injury. (2) An organotypic spinal cord culture system was used, Phase II enzyme inducers were added to culture medium for 1 week, motor neurons were counted by SMI-32 staining, glutamate, Nrf2, and Heme oxygenase-1(HO-1) mRNA were tested. (3) This study showed motor neuron loss within 1 week in culture. After 1 week in culture, the system was stable. Moreover, Glutamate was increased when in culture 48 h and decreased after 1 week in culture. There was no significant change between 1 and 4 weeks in culture. Necrotic motor neuron and damaged mitochondrial were observed in culture 48 h. Furthermore, phase II enzyme inducers: tert-butyhydroquinone (t-BHQ), 3H-1,2-dithiole-3-thione (D3T), and 5,6-dihydrocyclopenta-1,2-dithiole-3-thione (CPDT) were shown to promote motor neuron survival after dissection, it was due to increasing Nrf2 and HO-1 mRNA expression and protecting mitochondrial not due to decreasing glutamate level. (4) The loss of motor neuron due to dissection can mimic severe traumatic spinal cord injury. These results demonstrate that glutamate excitotoxicity and the damage of mitochondrial is possibly involve in motor neuron death after traumatic spinal cord injury and phase II enzyme inducers show neuroprotective potential on motor neuron survival in traumatic spinal cord injury in vitro.

Caspase-3 activity is reduced after spinal cord injury in mice lacking dynorphin: differential effects on glia and neurons

Dynorphins are endogenous opioid peptide products of the prodynorphin gene. An extensive literature suggests that dynorphins have deleterious effects on CNS injury outcome. We thus examined whether a deficiency of dynorphin would protect against tissue damage after spinal cord injury (SCI), and if individual cell types would be specifically affected. Wild-type and prodynorphin(-/-) mice received a moderate contusion injury at 10th thoracic vertebrae (T10). Caspase-3 activity at the injury site was significantly decreased in tissue homogenates from prodynorphin(-/-) mice after 4 h. We examined frozen sections at 4 h post-injury by immunostaining for active caspase-3. At 3-4 mm rostral or caudal to the injury, >90% of all neurons, astrocytes and oligodendrocytes expressed active caspase-3 in both wild-type and knockout mice. At 6-7 mm, there were fewer caspase-3(+) oligodendrocytes and astrocytes than at 3-4 mm. Importantly, caspase-3 activation was significantly lower in prodynorphin(-/-) oligodendrocytes and astrocytes, as compared with wild-type mice. In contrast, while caspase-3 expression in neurons also declined with further distance from the injury, there was no effect of genotype. Radioimmunoassay showed that dynorphin A(1-17) was regionally increased in wild-type injured versus sham-injured tissues, although levels of the prodynorphin processing product Arg(6)-Leu-enkephalin were unchanged. Our results indicate that dynorphin peptides affect the extent of post-injury caspase-3 activation, and that glia are especially sensitive to these effects. By promoting caspase-3 activation, dynorphin peptides likely increase the probability of glial apoptosis after SCI. While normally beneficial, our findings suggest that prodynorphin or its peptide products become maladaptive following SCI and contribute to secondary injury.

Temporal characterization of mitochondrial bioenergetics after spinal cord injury

Mitochondrial dysfunction following spinal cord injury (SCI) may be critical for the development of secondary pathophysiology and neuronal cell death. Previous studies have demonstrated a loss of mitochondrial bioenergetics at 24 h following SCI. To begin to understand the evolution and study the contribution of mitochondrial dysfunction in pathophysiology of SCI, we investigated mitochondrial bioenergetics in the mid-thoracic region at 6, 12, and 24 h following contusion SCI. It is widely accepted that increased free radical generation plays a critical role in neuronal damage after SCI. Hence, to ascertain the role of free radicals in SCI-induced mitochondrial dysfunction, markers for oxidative damage, including nitrotyrosine (3-NT), lipid peroxidation byproduct (4-hydroxynonenal [HNE]), and protein oxidation (protein carbonyls) were quantified in the same samples of isolated mitochondria during the 24-h time course. The results demonstrate that a significant decline in mitochondrial function begins to occur 12 h post-injury and persists for a least 24 h following SCI. Furthermore, there was a progressive increase in mitochondrial oxidative damage that preceded the loss of mitochondrial bioenergetics, suggesting that free radical damage may be a major mitochondrial secondary injury process. Based on the present results, the temporal profile of mitochondrial dysfunction indicates that interventions targeting mitochondrial oxidative damage and dysfunction may serve as a beneficial pharmacological treatment for acute SCI.

Manganese superoxide dismutase induced by TNF-beta is regulated transcriptionally by NF-kappaB after spinal cord injury in rats

Antioxidant enzymes including superoxide dismutase (SOD) may play a role in the mechanism by which cells counteract the deleterious effects of reactive oxygen species (ROS) after spinal cord injury (SCI). Cu/Zn and MnSOD are especially potent scavengers of superoxide anion and likely serve important cytoprotective roles against cellular damage. We investigated expression of SOD after SCI to address its role during the early stages of injury. MnSOD activity was increased 4 h after SCI and persisted at elevated levels up to 24-48 h; by contrast, Cu/ZnSOD activity was not changed. RT-PCR and Western blot analyses showed increased levels of MnSOD mRNA and protein, respectively, by 4 h and reached maximum levels by 24-48 h. Double immunostaining revealed that MnSOD protein was localized within neurons and oligodendrocytes. Tumor necrosis factor-alpha (TNF-alpha) was administered locally into uninjured spinal cords to examine potential mechanisms for MnSOD induction after injury. TNF-alpha administered exogenously increased MnSOD expression in uninjured spinal cords. Western blot and immunostaining also revealed that a transcription factor, NF-kappaB, was activated and translocated into the nuclei of neurons and oligodendrocytes. By contrast, administration of neutralizing antibody against TNF-alpha into injured spinal cords attenuated the increase in MnSOD expression and activation of NF-kappaB. Double immunostaining revealed that MnSOD was co-localized with NF-kappaB in neurons and oligodendrocytes after SCI. These results suggest that TNF-alpha may be an inducer of NF-kappaB activation and MnSOD expression after SCI and that MnSOD expression induced by TNF-alpha is likely mediated through activation of NF-kappaB.

The Mitochondrial Uncoupling Agent 2,4-Dinitrophenol Improves Mitochondrial Function, Attenuates Oxidative Damage, and Increases White Matter Sparing in the Contused Spinal Cord

The purpose of this study was to investigate the potential neuroprotective efficacy of the mitochondrial uncoupler 2,4-dinitrophenol (DNP) in rats following a mild to moderate spinal cord contusion injury. Animals received intraperitoneal injections of vehicle (DMSO) or 5 mg/mL of DNP prior to injury. Twenty-four hours following surgery, mitochondrial function was assessed in mitochondria isolated from spinal cord synaptosomes. In addition, synaptosomes were used to measure indicators of reactive oxygen species formation, lipid peroxidation, and protein oxidation. Relative to vehicle-treated animals, pretreatment with DNP maintained mitochondrial bioenergetics and significantly decreased reactive oxygen species levels, lipid peroxidation, and protein carbonyl content following spinal cord injury. Furthermore, pretreatment with DNP significantly increased the amount of remaining white matter at the injury epicenter 6 weeks after injury. These results indicate that treatment with mitochondrial uncoupling agents may provide a novel approach for the treatment of secondary injury following spinal cord contusion.

The Role of Excitotoxicity in Secondary Mechanisms of Spinal Cord Injury: A Review with an Emphasis on the Implications for White Matter Degeneration

Following an initial impact after spinal cord injury (SCI), there is a cascade of downstream events termed 'secondary injury', which culminate in progressive degenerative events in the spinal cord. These secondary injury mechanisms include, but are not limited to, ischemia, inflammation, free radical-induced cell death, glutamate excitotoxicity, cytoskeletal degradation and induction of extrinsic and intrinsic apoptotic pathways. There is emerging evidence that glutamate excitotoxicity plays a key role not only in neuronal cell death but also in delayed posttraumatic spinal cord white matter degeneration. Importantly however, the differences in cellular composition and expression of specific types of glutamate receptors in grey versus white matter require a compartmentalized approach to understand the mechanisms of secondary injury after SCI. This review examines mechanisms of secondary white matter injury with particular emphasis on glutamate excitotoxicity and the potential link of this mechanism to apoptosis. Recent studies have provided new insights into the mechanisms of glutamate release and its potential targets, as well as the downstream pathways associated with glutamate receptor activation in specific types of cells. Evidence from molecular and functional expression of glutamatergic AMPA receptors in white matter glia (and possibly axons), the protective effects of AMPA/kainate antagonists in posttraumatic white matter axonal function, and the vulnerability of oligodendrocytes to excitotoxic cell death suggest that glutamate excitotoxicity is associated with oligodendrocyte apoptosis. The latter mechanism appears key to glutamatergic white matter degeneration after SCI and may represent an attractive therapeutic target.