The role of reactive nitrogen species in secondary spinal cord injury: formation of nitric oxide, peroxynitrite, and nitrated protein

Nitric oxide synthases: A delicate dance between bone regeneration and neuronal birth

Spinal cord injury (SCI) is a devastating condition resulting from traumatic or nontraumatic injury/chronic disorder. The pathogenesis of SCI necessitates a comprehensive approach, as it involves therapeutic strategies addressing both bone (spine) and neural (spinal cord) damage. This review centers on the pivotal role of nitric oxide (NO) and its synthesizing enzymes, nitric oxide synthases (NOS), in mediating the crosstalk between osteogenesis and neurogenesis. NO's effects are context-dependent, exhibiting a delicate balance between beneficial and detrimental actions. Reduced levels of nitric oxide (NO), primarily derived from endothelial NOS (eNOS), tipically stimulate osteoblast activity and promote neurogenesis by influencing neural stem cell (NSC) migration and differentiation. Conversely, elevated NO levels, predominantly from inducible NOS (iNOS), tipically triggered by inflammation, inhibit both processes through pro-apoptotic mechanisms. Nevertheless, these phenomena are not merely simplistic; they can be influenced by a variety of other factors. We explore the intricate interplay of NO/NOS with key signaling pathways crucial in neurogenesis and osteogenesis, including mechanical stimuli, Wnt, interleukins, BMPs, NF-κB, etc., revealing their influence on neuroinflammation, neurogenesis, and osteoblast differentiation. The temporal and spatial dynamics of NO/NOS activity and the implications for therapeutic intervention have been discussed. Precise modulation of NO levels and NOS isoforms, potentially through targeted therapies manipulating these interacting signaling pathways, emerges as a promising strategy for promoting bone and neural regeneration. This review highlights the critical need for a balanced approach in therapeutic strategies to harness the beneficial effects of NO/NOS while mitigating its detrimental consequences.

Unveiling the effects of Rosa canina oligosaccharide liposome on neuropathic pain and motor dysfunction following spinal cord injury in rats: relevance to its antioxidative effects

Background

Spinal cord injury (SCI) is a leading cause of sensorimotor disorders, impacting millions of people globally. The absence of effective treatments and the side effects of existing medications highlight the need for innovative research into new therapeutic compounds.

Purpose

Given the critical role of oxidative stress in the development of SCI and the antioxidant properties of oligosaccharides in other neurological disorders, this study focuses on the role of oxidative stress in SCI and explores the potential of a novel oligosaccharide nanoformulation derived from Rosa canina (Oligo-L).

Materials and methods

Oligo-L was formulated using soy lecithin as the phospholipid and the characterization included size, zeta potential, morphology, and drug loading efficiency. Then 35 Wistar male rats were divided into five groups of Sham, SCI, and Oligo-L (10 μL intrathecal injection of 15, 30, and 45 mg/mL). An aneurysm clip was used to induce compression injury of the SCI and Oligo-L groups. Sensory-motor functions were evaluated weekly for 4 weeks using tests such as the BBB scale, inclined plane, acetone drop, hot plate, von Frey, and monitoring of weight changes. Additionally, oxidative stress markers and histological changes were examined to evaluate changes in nitrite, glutathione, catalase, and neuronal survival.

Results and discussion

The findings indicated that Oligo-L treatment led to significant improvements in neuropathic pain, and motor function performance and weight of the animals from the first week post-SCI. Oligo-L also enhanced catalase and glutathione levels while reducing serum nitrite levels, contributing to neuronal preservation. Additionally, Oligo-L increased neuronal survival in the both ventral (motor neurons) and dorsal (sensory neurons) horns of the spinal cord.

Conclusion

Overall, Oligo-L, characterized by its beneficial physicochemical properties, showed promising potential as a neuroprotective agent and facilitated the recovery of sensory and motor functions after SCI.

Advancements in Antioxidant-Based Therapeutics for Spinal Cord Injury: A Critical Review of Strategies and Combination Approaches

Spinal cord injury (SCI) initiates a cascade of secondary damage driven by oxidative stress, characterized by the excessive production of reactive oxygen species and other reactive molecules, which exacerbate cellular and tissue damage through the activation of deleterious signaling pathways. This review provides a comprehensive and critical evaluation of recent advancements in antioxidant-based therapeutic strategies for SCI, including natural compounds, RNA-based therapies, stem cell interventions, and biomaterial applications. It emphasizes the limitations of single-regimen approaches, particularly their limited efficacy and suboptimal delivery to injured spinal cord tissue, while highlighting the synergistic potential of combination therapies that integrate multiple modalities to address the multifaceted pathophysiology of SCI. By analyzing emerging trends and current limitations, this review identifies key challenges and proposes future directions, including the refinement of antioxidant delivery systems, the development of multi-targeted approaches, and strategies to overcome the structural complexities of the spinal cord. This work underscores the pressing need for innovative and integrative therapeutic approaches to advance the clinical translation of antioxidant-based interventions and improve outcomes for SCI patients.

Research Progress of Antioxidants in Oxidative Stress Therapy after Spinal Cord Injury

Spinal cord injury (SCI) is a serious problem in the central nervous system resulting in high disability and mortality with complex pathophysiological mechanisms. Oxidative stress is one of the main secondary reactions of SCI, and its main pathophysiological marker is the production of excess reactive oxygen species. The overproduction of reactive oxygen species and insufficient antioxidant capacity lead to the occurrence of oxidative stress and neuroinflammation, and the dysregulation of oxidative stress and neuroinflammation leads to further aggravation of damage. Oxidative stress can initiate a variety of inflammatory and apoptotic pathways, and targeted antioxidant therapy can greatly reduce oxidative stress and reduce neuroinflammation, which has a certain positive effect on rehabilitation and prognosis in SCI. This article reviewed the research on different types of antioxidants and related treatments in SCI, focusing on the mechanisms of oxidative stress.

Models and approaches to comprehend and address glial inflammation following spinal cord injury

Spinal cord injury (SCI) culminates in chronic inflammation and glial scar formation driven by the activation of microglia and astrocytes. Current anti-inflammatory strategies to treat glial activation associated with SCI have several limitations. Existing in vitro and ex vivo models studying molecular mechanisms associated with inflammation focus only on the acute phase. However, the progression of glial cell-derived inflammation over the acute-to-chronic phases has not been assessed. Understanding this progression will help establish a framework for evaluating therapeutic strategies. Additionally, new models could be useful as high-throughput screening (HTS) platforms. This review aims to highlight currently available models and future methods that could facilitate screening of novel therapeutics for SCI.

The Influence of Exercise on Oxidative Stress after Spinal Cord Injury: A Narrative Review

Spinal cord injury (SCI) is an irreversible disease resulting in partial or total loss of sensory and motor function. The pathophysiology of SCI is characterized by an initial primary injury phase followed by a secondary phase in which reactive oxygen species (ROSs) and associated oxidative stress play hallmark roles. Physical exercise is an indispensable means of promoting psychophysical well-being and improving quality of life. It positively influences the neuromuscular, cardiovascular, respiratory, and immune systems. Moreover, exercise may provide a mechanism to regulate the variation and equilibrium between pro-oxidants and antioxidants. After a brief overview of spinal cord anatomy and the different types of spinal cord injury, the purpose of this review is to investigate the evidence regarding the effect of exercise on oxidative stress among individuals with SCI.

Pathophysiology and Therapeutic Approaches for Spinal Cord Injury

Spinal cord injury (SCI) is a disabling condition that disrupts motor, sensory, and autonomic functions. Despite extensive research in the last decades, SCI continues to be a global health priority affecting thousands of individuals every year. The lack of effective therapeutic strategies for patients with SCI reflects its complex pathophysiology that leads to the point of no return in its function repair and regeneration capacity. Recently, however, several studies started to uncover the intricate network of mechanisms involved in SCI leading to the development of new therapeutic approaches. In this work, we present a detailed description of the physiology and anatomy of the spinal cord and the pathophysiology of SCI. Additionally, we provide an overview of different molecular strategies that demonstrate promising potential in the modulation of the secondary injury events that promote neuroprotection or neuroregeneration. We also briefly discuss other emerging therapies, including cell-based therapies, biomaterials, and epidural electric stimulation. A successful therapy might target different pathologic events to control the progression of secondary damage of SCI and promote regeneration leading to functional recovery.

Oxidative DNA Damage in the Pathophysiology of Spinal Cord Injury: Seems Obvious, but Where Is the Evidence?

Oxidative stress occurs at various phases of spinal cord injury (SCI), promoting detrimental processes such as free radical injury of proteins, nucleic acids, lipids, cytoskeleton, and organelles. Oxidative DNA damage is likely a major contributor to the pathogenesis of SCI, as a damaged genome cannot be simply turned over to avert detrimental molecular and cellular outcomes, most notably cell death. Surprisingly, the evidence to support this hypothesis is limited. There is some evidence that oxidative DNA damage is increased following SCI, mainly using comet assays and immunohistochemistry. However, there is great variability in the timing and magnitude of its appearance, likely due to differences in experimental models, measurement techniques, and the rigor of the approach. Evidence indicates that 8-oxodG is most abundant at 1 and 7 days post-injury (dpi), while DNA strand breaks peak at 7 and 28 dpi. The DNA damage response seems to be characterized by upregulation of PCNA and PARP1 but downregulation of APEX1. Significant improvements in the analysis of oxidative DNA damage and repair after SCI, including single-cell analysis at time points representative for each phase post-injury using new methodologies and better reporting, will uncover the role of DNA damage and repair in SCI.

The Glial Cells Respond to Spinal Cord Injury

It is been over 100 years since glial cells were discovered by Virchow. Since then, a great deal of research was carried out to specify these further roles and properties of glial cells in central nervous system (CNS). As it is well-known that glial cells, such as astrocytes, microglia, oligodendrocytes (OLs), and oligodendrocyte progenitor cells (OPCs) play an important role in supporting and enabling the effective nervous system function in CNS. After spinal cord injury (SCI), these glial cells play different roles in SCI and repair. In this review, we will discuss in detail about the role of glial cells in the healthy CNS and how they respond to SCI.

Mitochondrial function in spinal cord injury and regeneration

Many people around the world suffer from some form of paralysis caused by spinal cord injury (SCI), which has an impact on quality and life expectancy. The spinal cord is part of the central nervous system (CNS), which in mammals is unable to regenerate, and to date, there is a lack of full functional recovery therapies for SCI. These injuries start with a rapid and mechanical insult, followed by a secondary phase leading progressively to greater damage. This secondary phase can be potentially modifiable through targeted therapies. The growing literature, derived from mammalian and regenerative model studies, supports a leading role for mitochondria in every cellular response after SCI: mitochondrial dysfunction is the common event of different triggers leading to cell death, cellular metabolism regulates the immune response, mitochondrial number and localization correlate with axon regenerative capacity, while mitochondrial abundance and substrate utilization regulate neural stem progenitor cells self-renewal and differentiation. Herein, we present a comprehensive review of the cellular responses during the secondary phase of SCI, the mitochondrial contribution to each of them, as well as evidence of mitochondrial involvement in spinal cord regeneration, suggesting that a more in-depth study of mitochondrial function and regulation is needed to identify potential targets for SCI therapeutic intervention.

L-Arginine Depletion Improves Spinal Cord Injury via Immunomodulation and Nitric Oxide Reduction

Background: Spinal cord injury (SCI) elicits robust neuroinflammation that eventually exacerbates the initial damage to the spinal cord. L-arginine is critical for the responsiveness of T cells, which are important contributors to neuroinflammation after SCI. Furthermore, L-arginine is the substrate for nitric oxide (NO) production, which is a known inducer of secondary damage. Methods: To accomplish systemic L-arginine depletion, repetitive injections of recombinant arginase-1 (rArg-I) were performed. Functional recovery and histopathological parameters were analyzed. Splenic immune responses were evaluated by flow cytometry. Pro-inflammatory gene expression and nitrite concentrations were measured. Results: We show for the first time that systemic L-arginine depletion improves locomotor recovery. Flow cytometry and immunohistological analysis showed that intraspinal T-cell infiltration was reduced by 65%, and peripheral numbers of Th1 and Th17 cells were suppressed. Moreover, rArg-I treatment reduced the intraspinal NO production by 40%. Histopathological analyses revealed a 37% and 36% decrease in the number of apoptotic neurons and neuron-macrophage/microglia contacts in the spinal cord, respectively. Conclusions: Targeting detrimental T-cell responses and NO-production via rArg-I led to a reduced neuronal cell death and an improved functional recovery. These findings indicate that L-arginine depletion holds promise as a therapeutic strategy after SCI.

Neuroimmune System as a Driving Force for Plasticity Following CNS Injury

Following an injury to the central nervous system (CNS), spontaneous plasticity is observed throughout the neuraxis and affects multiple key circuits. Much of this spontaneous plasticity can elicit beneficial and deleterious functional outcomes, depending on the context of plasticity and circuit affected. Injury-induced activation of the neuroimmune system has been proposed to be a major factor in driving this plasticity, as neuroimmune and inflammatory factors have been shown to influence cellular, synaptic, structural, and anatomical plasticity. Here, we will review the mechanisms through which the neuroimmune system mediates plasticity after CNS injury. Understanding the role of specific neuroimmune factors in driving adaptive and maladaptive plasticity may offer valuable therapeutic insight into how to promote adaptive plasticity and/or diminish maladaptive plasticity, respectively.

Amelioration of spinal cord injury in rats by blocking peroxynitrite/calpain activity

Background

Spinal cord injury (SCI) is one of the leading causes of disability and chronic pain. In SCI-induced pathology, homeostasis of the nitric oxide (NO) metabolome is lost. Major NO metabolites such as S-nitrosoglutathione (GSNO) and peroxynitrite are reported to play pivotal roles in regulating the activities of key cysteine proteases, calpains. While peroxynitrite (a metabolite of NO and superoxide) up regulates the activities of calpains leading to neurodegeneration, GSNO (a metabolite of NO and glutathione) down regulates the activities of calpains leading to neuroprotection. In this study, effect of GSNO on locomotor function and pain threshold and their relationship with the levels of peroxynitrite and the activity of calpain in the injured spinal cord were investigated using a 2-week rat model of contusion SCI.

Results

SCI animals were initially treated with GSNO at 2 h after the injury followed by a once daily dose of GSNO for 14 days. Locomotor function was evaluated by “Basso Beattie and Bresnahan (BBB) locomotor rating scale” and pain by mechanical allodynia. Peroxynitrite level, as expression of 3-nitrotyrosine (3-NT), calpain activity, as the degradation products of calpain substrate alpha II spectrin, and nNOS activity, as the expression phospho nNOS, were measured by western blot analysis. Treatment with GSNO improved locomotor function and mitigated pain. The treatment also reduced the levels of peroxynitrite (3-NT) and decreased activity of calpains. Reduced levels of peroxynitrite resulted from the GSNO-mediated inhibition of aberrant activity of neuronal nitric oxide synthase (nNOS).

Conclusions

The data indicates that higher levels of 3-NT and aberrant activities of nNOS and calpains correlated with SCI pathology and functional deficits. Treatment with GSNO improved locomotor function and mitigated mechanical allodynia acutely post-injury. Because GSNO shows potential to ameliorate experimental SCI, we discuss implications for GSNO therapy in clinical SCI research.

Effects of Dietary Vitamin E Supplementation in Bladder Function and Spasticity during Spinal Cord Injury

Traumatic spinal cord injury (SCI) results in debilitating autonomic dysfunctions, paralysis and significant sensorimotor impairments. A key component of SCI is the generation of free radicals that contributes to the high levels of oxidative stress observed. This study investigates whether dietary supplementation with the antioxidant vitamin E (alpha-tocopherol) improves functional recovery after SCI. Female adult Sprague-Dawley rats were fed either with a normal diet or a dietary regiment supplemented with vitamin E (51 IU/g) for eight weeks. The rats were subsequently exposed either to a contusive SCI or sham operation, and evaluated using standard functional behavior analysis. We report that the rats that consumed the vitamin E-enriched diet showed an accelerated bladder recovery and significant improvements in locomotor function relative to controls, as determined by residual volumes and Basso, Beatie, and Bresnaham BBB scores, respectively. Interestingly, the prophylactic dietary intervention did not preserve neurons in the ventral horn of injured rats, but it significantly increased the numbers of oligodendrocytes. Vitamin E supplementation attenuated the depression of the H-reflex (a typical functional consequence of SCI) while increasing the levels of supraspinal serotonin immunoreactivity. Our findings support the potential complementary use of vitamin E to ameliorate sensory and autonomic dysfunctions associated with spinal cord injury, and identified promising new cellular and functional targets of its neuroprotective effects.

Targeted siRNA delivery reduces nitric oxide mediated cell death after spinal cord injury

BACKGROUND

Traumatic spinal cord injury (SCI) includes the primary insult as well as a sequela of biochemical and cellular cascades that amplifies the initial injury. This degenerative process, known as secondary injury, is often mediated by both reactive oxygen and nitrogen species released from damaged cells. Previous data suggests that dysregulated production of nitric oxide via inducible nitric oxide synthase (iNOS) is detrimental to spinal cord recovery. M1 macrophages have been implicated to overexpress iNOS post-SCI. In this work, we propose to inhibit iNOS expression through small interfering RNA (siRNA) complexed chitosan nanoparticles (NPs) that primarily target M1 macrophages.

METHODS

siRNA conjugated chitosan complexes were fabricated with and without an antibody (Ab) targeting moiety and screened for efficiency to reduce iNOS expression in vitro. Best formulations were subsequently applied in vivo following acute SCI in a rodent model. iNOS expression as well as Bax and Bcl-2 biomarkers were used to assess cell apoptosis within the lesion at 24 h post-injury.

RESULTS

Ab-siRNA conjugated chitosan NPs significantly reduced iNOS expression in vitro in M1 polarized macrophages. Results show high transfection efficiency with low cytotoxicity. Subsequent application of NPs in vivo after SCI demonstrated both a reduction in iNOS expression and cellular apoptosis.

CONCLUSION

Proof of concept indicates that siRNA conjugated chitosan NPs can downregulate iNOS production and inhibit apoptosis following SCI. Our proposed gene silencing method putatively targets M1 macrophages as a means to attenuate secondary injury.

Identifying the Long-Term Role of Inducible Nitric Oxide Synthase after Contusive Spinal Cord Injury Using a Transgenic Mouse Model

Inducible nitric oxide synthase (iNOS) is a potent mediator of oxidative stress during neuroinflammation triggered by neurotrauma or neurodegeneration. We previously demonstrated that acute iNOS inhibition attenuated iNOS levels and promoted neuroprotection and functional recovery after spinal cord injury (SCI). The present study investigated the effects of chronic iNOS ablation after SCI using inos-null mice. iNOS^-/- knockout and wild-type (WT) control mice underwent a moderate thoracic (T8) contusive SCI. Locomotor function was assessed weekly, using the Basso Mouse Scale (BMS), and at the endpoint (six weeks), by footprint analysis. At the endpoint, the volume of preserved white and gray matter, as well as the number of dorsal column axons and perilesional blood vessels rostral to the injury, were quantified. At weeks two and three after SCI, iNOS^-/- mice exhibited a significant locomotor improvement compared to WT controls, although a sustained improvement was not observed during later weeks. At the endpoint, iNOS^-/- mice showed significantly less preserved white and gray matter, as well as fewer dorsal column axons and perilesional blood vessels, compared to WT controls. While short-term antagonism of iNOS provides histological and functional benefits, its long-term ablation after SCI may be deleterious, blocking protective or reparative processes important for angiogenesis and tissue preservation.

Cytokine and Growth Factor Activation In Vivo and In Vitro after Spinal Cord Injury

Spinal cord injury results in a life-disrupting series of deleterious interconnected mechanisms encompassed by the primary and secondary injury. These events are mediated by the upregulation of genes with roles in inflammation, transcription, and signaling proteins. In particular, cytokines and growth factors are signaling proteins that have important roles in the pathophysiology of SCI. The balance between the proinflammatory and anti-inflammatory effects of these molecules plays a critical role in the progression and outcome of the lesion. The excessive inflammatory Th1 and Th17 phenotypes observed after SCI tilt the scale towards a proinflammatory environment, which exacerbates the deleterious mechanisms present after the injury. These mechanisms include the disruption of the spinal cord blood barrier, edema and ion imbalance, in particular intracellular calcium and sodium concentrations, glutamate excitotoxicity, free radicals, and the inflammatory response contributing to the neurodegenerative process which is characterized by demyelination and apoptosis of neuronal tissue.

Propitious Therapeutic Modulators to Prevent Blood-Spinal Cord Barrier Disruption in Spinal Cord Injury

The blood-spinal cord barrier (BSCB) is a specialized protective barrier that regulates the movement of molecules between blood vessels and the spinal cord parenchyma. Analogous to the blood-brain barrier (BBB), the BSCB plays a crucial role in maintaining the homeostasis and internal environmental stability of the central nervous system (CNS). After spinal cord injury (SCI), BSCB disruption leads to inflammatory cell invasion such as neutrophils and macrophages, contributing to permanent neurological disability. In this review, we focus on the major proteins mediating the BSCB disruption or BSCB repair after SCI. This review is composed of three parts. Section 1. SCI and the BSCB of the review describes critical events involved in the pathophysiology of SCI and their correlation with BSCB integrity/disruption. Section 2. Major proteins involved in BSCB disruption in SCI focuses on the actions of matrix metalloproteinases (MMPs), tumor necrosis factor alpha (TNF-α), heme oxygenase-1 (HO-1), angiopoietins (Angs), bradykinin, nitric oxide (NO), and endothelins (ETs) in BSCB disruption and repair. Section 3. Therapeutic approaches discusses the major therapeutic compounds utilized to date for the prevention of BSCB disruption in animal model of SCI through modulation of several proteins.

Panax ginseng Improves Functional Recovery after Contusive Spinal Cord Injury by Regulating the Inflammatory Response in Rats: An In Vivo Study

Spinal cord injury (SCI) results in permanent loss of motor function below the injured site. Neuroinflammatory reaction following SCI can aggravate neural injury and functional impairment. Ginseng is well known to possess anti-inflammatory effects. The present study investigated the neuroprotective effects of Panax ginseng C.A. Mayer (P. ginseng) after SCI. A spinal contusion was made at the T11-12 spinal cord in adult male Sprague-Dawley rats (n = 47) using the NYU impactor. Motor function was assessed using the Basso-Beattie-Bresnahan (BBB) score in P. ginseng (0.1, 0.5, 1, 3, and 5 mg/kg) or vehicle (saline) treated after SCI. We also assessed the protein expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) at the lesion site by western blot and then measured the cavity area using luxol fast blue/cresyl violet staining. P. ginseng treated group in SCI showed a significant improvement in locomotor function after the injury. The protein expression of COX-2 and iNOS at the lesion site and the cavity area were decreased following SCI by P. ginseng treatment. These results suggest that P. ginseng may improve the recovery of motor function after SCI which provides neuroprotection by alleviating posttraumatic inflammatory responses.

Survival of neural stem cell grafts in the lesioned spinal cord is enhanced by a combination of treadmill locomotor training via insulin-like growth factor-1 signaling

Combining cell transplantation with activity-based rehabilitation is a promising therapeutic approach for spinal cord repair. The present study was designed to investigate potential interactions between the transplantation (TP) of neural stem cells (NSCs) obtained at embryonic day 14 and treadmill training (TMT) in promoting locomotor recovery and structural repair in rat contusive injury model. Combination of TMT with NSC TP at 1 week after injury synergistically improved locomotor function. We report here that combining TMT increased the survival of grafted NSCs by >3-fold and >5-fold at 3 and 9 weeks after injury, respectively. The number of surviving NSCs was significantly correlated with the extent of locomotor recovery. NSCs grafted into the injured spinal cord were under cellular stresses induced by reactive nitrogen or oxygen species, which were markedly attenuated by TMT. TMT increased the concentration of insulin-like growth factor-1 (IGF-1) in the CSF. Intrathecal infusion of neutralizing IGF-1 antibodies, but not antibodies against either BDNF or Neurotrophin-3 (NT-3), abolished the enhanced survival of NSC grafts by TMT. The combination of TP and TMT also resulted in tissue sparing, increased myelination, and restoration of serotonergic fiber innervation to the lumbar spinal cord to a larger extent than that induced by either TP or TMT alone. Therefore, we have discovered unanticipated beneficial effects of TMT in modulating the survival of grafted NSCs via IGF-1. Our study identifies a novel neurobiological basis for complementing NSC-based spinal cord repair with activity-based neurorehabilitative approaches.

Hydrogen peroxide administered into the rat spinal cord at the level elevated by contusion spinal cord injury oxidizes proteins, DNA and membrane phospholipids, and induces cell death: attenuation by a metalloporphyrin

We previously demonstrated that hydrogen peroxide concentration ([H2O2]) significantly increases after spinal cord injury (SCI). The present study explored (1) whether SCI-elevated [H2O2] is sufficient to induce oxidation and cell death, (2) if apoptosis is a pathway of H2O2-induced cell death, and (3) whether H2O2-induced oxidation and cell death could be reversed by treatment with the catalytic antioxidant Mn (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP). H2O2 was perfused through a microcannula into the uninjured rat spinal cord to mimic the conditions induced by SCI. Protein and DNA oxidation, membrane phospholipids peroxidation (MLP), cell death and apoptosis were characterized by histochemical and immunohistochemical staining with antibodies against markers of oxidation and apoptosis. Stained cells were quantified in sections of H2O2-, or artificial cerebrospinal fluid (ACSF)-exposed with vehicle-, or MnTBAP-treated groups. Compared with ACSF-exposed animals, SCI-elevated [H2O2] significantly increased intracellular protein and DNA oxidation by threefold and MLP by eightfold in neurons, respectively. H2O2-elevated extracellular malondialdehyde was measured by microdialysis sampling. We demonstrated that SCI-elevated [H2O2] significantly increased extracellular malondialdehyde above pre-injury levels. H2O2 also significantly increased cell loss and the numbers of terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate-(dUTP)-biotin nick end labeling (TUNEL)-positive and active caspase-3-positive neurons by 2.3-, 2.8-, and 5.6-fold compared to ACSF controls, respectively. Our results directly and unequivocally demonstrate that SCI-elevated [H2O2] contributes to post-SCI MLP, protein, and DNA oxidation to induce cell death. Therefore, we conclude that (1) the role of H2O2 in secondary SCI is pro-oxidation and pro-cell death, (2) apoptosis is a pathway for SCI-elevated [H2O2] to induce cell death, (3) caspase activation is a mechanism of H2O2-induced apoptosis after SCI, and (4) MnTBAP treatment significantly decreased H2O2-induced oxidation, cell loss, and apoptosis to the levels of ACSF controls, further supporting MnTBAP's ability to scavenge H2O2 by in vivo evidence.

Rational design of superoxide dismutase (SOD) mimics: the evaluation of the therapeutic potential of new cationic Mn porphyrins with linear and cyclic substituents

Our goal herein has been to gain further insight into the parameters which control porphyrin therapeutic potential. Mn porphyrins (MnTnOct-2-PyP(5+), MnTnHexOE-2-PyP(5+), MnTE-2-PyPhP(5+), and MnTPhE-2-PyP(5+)) that bear the same positive charge and same number of carbon atoms at meso positions of porphyrin core were explored. The carbon atoms of their meso substituents are organized to form either linear or cyclic structures of vastly different redox properties, bulkiness, and lipophilicities. These Mn porphyrins were compared to frequently studied compounds, MnTE-2-PyP(5+), MnTE-3-PyP(5+), and MnTBAP(3-). All Mn(III) porphyrins (MnPs) have metal-centered reduction potential, E1/2 for Mn(III)P/Mn(II)P redox couple, ranging from -194 to +340 mV versus NHE, log kcat(O2(•-)) from 3.16 to 7.92, and log kred(ONOO(-)) from 5.02 to 7.53. The lipophilicity, expressed as partition between n-octanol and water, log POW, was in the range -1.67 to -7.67. The therapeutic potential of MnPs was assessed via: (i) in vitro ability to prevent spontaneous lipid peroxidation in rat brain homogenate as assessed by malondialdehyde levels; (ii) in vivo O2(•-) specific assay to measure the efficacy in protecting the aerobic growth of SOD-deficient Saccharomyces cerevisiae; and (iii) aqueous solution chemistry to measure the reactivity toward major in vivo endogenous antioxidant, ascorbate. Under the conditions of lipid peroxidation assay, the transport across the cellular membranes, and in turn shape and size of molecule, played no significant role. Those MnPs of E1/2 ∼ +300 mV were the most efficacious, significantly inhibiting lipid peroxidation in 0.5-10 μM range. At up to 200 μM, MnTBAP(3-) (E1/2 = -194 mV vs NHE) failed to inhibit lipid peroxidation, while MnTE-2-PyPhP(5+) with 129 mV more positive E1/2 (-65 mV vs NHE) was fully efficacious at 50 μM. The E1/2 of Mn(III)P/Mn(II)P redox couple is proportional to the log kcat(O2(•-)), i.e., the SOD-like activity of MnPs. It is further proportional to kred(ONOO(-)) and the ability of MnPs to prevent lipid peroxidation. In turn, the inhibition of lipid peroxidation by MnPs is also proportional to their SOD-like activity. In an in vivo S. cerevisiae assay, however, while E1/2 predominates, lipophilicity significantly affects the efficacy of MnPs. MnPs of similar log POW and E1/2, that have linear alkyl or alkoxyalkyl pyridyl substituents, distribute more easily within a cell and in turn provide higher protection to S. cerevisiae in comparison to MnP with bulky cyclic substituents. The bell-shape curve, with MnTE-2-PyP(5+) exhibiting the highest ability to catalyze ascorbate oxidation, has been established and discussed. Our data support the notion that the SOD-like activity of MnPs parallels their therapeutic potential, though species other than O2(•-), such as peroxynitrite, H2O2, lipid reactive species, and cellular reductants, may be involved in their mode(s) of action(s).

Mn porphyrin-based SOD mimic, MnTnHex-2-PyP(5+), and non-SOD mimic, MnTBAP(3-), suppressed rat spinal cord ischemia/reperfusion injury via NF-κB pathways

Herein we have demonstrated that both superoxide dismutase (SOD) mimic, cationic Mn(III) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin (MnTnHex-2-PyP(5+)), and non-SOD mimic, anionic Mn(III) meso-tetrakis(4-carboxylatophenyl)porphyrin (MnTBAP(3-)), protect against oxidative stress caused by spinal cord ischemia/reperfusion via suppression of nuclear factor kappa B (NF-κB) pro-inflammatory pathways. Earlier reports showed that Mn(III) N-alkylpyridylporphyrins were able to prevent the DNA binding of NF-κB in an aqueous system, whereas MnTBAP(3-) was not. Here, for the first time, in a complex in vivo system-animal model of spinal cord injury-a similar impact of MnTBAP(3-), at a dose identical to that of MnTnHex-2-PyP(5+), was demonstrated in NF-κB downregulation. Rats were treated subcutaneously at 1.5 mg/kg starting at 30 min before ischemia/reperfusion, and then every 12 h afterward for either 48 h or 7 days. The anti-inflammatory effects of both Mn porphyrins (MnPs) were demonstrated in the spinal cord tissue at both 48 h and 7 days. The downregulation of NF-κB, a major pro-inflammatory signaling protein regulating astrocyte activation, was detected and found to correlate well with the suppression of astrogliosis (as glial fibrillary acidic protein) by both MnPs. The markers of oxidative stress, lipid peroxidation and protein carbonyl formation, were significantly reduced by MnPs. The favorable impact of both MnPs on motor neurons (Tarlov score and inclined plane test) was assessed. No major changes in glutathione peroxidase- and SOD-like activities were demonstrated, which implies that none of the MnPs acted as SOD mimic. Increasing amount of data on the reactivity of MnTBAP(3-) with reactive nitrogen species (RNS) (.NO/HNO/ONOO(-)) suggests that RNS/MnTBAP(3-)-driven modification of NF-κB protein cysteines may be involved in its therapeutic effects. This differs from the therapeutic efficacy of MnTnHex-2-PyP(5+) which presumably occurs via reactive oxygen species and relates to NF-κB thiol oxidation; the role of RNS cannot be excluded.

Cytokine pathways regulating glial and leukocyte function after spinal cord and peripheral nerve injury

Injury to the nervous system causes the almost immediate release of cytokines by glial cells and neurons. These cytokines orchestrate a complex array of responses leading to microgliosis, immune cell recruitment, astrogliosis, scarring, and the clearance of cellular debris, all steps that affect neuronal survival and repair. This review will focus on cytokines released after spinal cord and peripheral nerve injury and the primary signalling pathways triggered by these inflammatory mediators. Notably, the following cytokine families will be covered: IL-1, TNF, IL-6-like, TGF-β, and IL-10. Whether interfering with cytokine signalling could lead to novel therapies will also be discussed. Finally, the review will address whether manipulating the above-mentioned cytokine families and signalling pathways could exert distinct effects in the injured spinal cord versus peripheral nerve.

Metalloporphyrins as therapeutic catalytic oxidoreductants in central nervous system disorders

SIGNIFICANCE

Metalloporphyrins, characterized by a redox-active transitional metal (Mn or Fe) coordinated to a cyclic porphyrin core ligand, mitigate oxidative/nitrosative stress in biological systems. Side-chain substitutions tune redox properties of metalloporphyrins to act as potent superoxide dismutase mimics, peroxynitrite decomposition catalysts, and redox regulators of transcription factor function. With oxidative/nitrosative stress central to pathogenesis of CNS injury, metalloporphyrins offer unique pharmacologic activity to improve the course of disease.

RECENT ADVANCES

Metalloporphyrins are efficacious in models of amyotrophic lateral sclerosis, Alzheimer's disease, epilepsy, neuropathic pain, opioid tolerance, Parkinson's disease, spinal cord injury, and stroke and have proved to be useful tools in defining roles of superoxide, nitric oxide, and peroxynitrite in disease progression. The most substantive recent advance has been the synthesis of lipophilic metalloporphyrins offering improved blood-brain barrier penetration to allow intravenous, subcutaneous, or oral treatment.

CRITICAL ISSUES

Insufficient preclinical data have accumulated to enable clinical development of metalloporphyrins for any single indication. An improved definition of mechanisms of action will facilitate preclinical modeling to define and validate optimal dosing strategies to enable appropriate clinical trial design. Due to previous failures of "antioxidants" in clinical trials, with most having markedly less biologic activity and bioavailability than current-generation metalloporphyrins, a stigma against antioxidants has discouraged the development of metalloporphyrins as CNS therapeutics, despite the consistent definition of efficacy in a wide array of CNS disorders.

FUTURE DIRECTIONS

Further definition of the metalloporphyrin mechanism of action, side-by-side comparison with "failed" antioxidants, and intense effort to optimize therapeutic dosing strategies are required to inform and encourage clinical trial design.

Traumatic brain injury in vivo and in vitro contributes to cerebral vascular dysfunction through impaired gap junction communication between vascular smooth muscle cells

Gap junctions (GJs) contribute to cerebral vasodilation, vasoconstriction, and, perhaps, to vascular compensatory mechanisms, such as autoregulation. To explore the effects of traumatic brain injury (TBI) on vascular GJ communication, we assessed GJ coupling in A7r5 vascular smooth muscle (VSM) cells subjected to rapid stretch injury (RSI) in vitro and VSM in middle cerebral arteries (MCAs) harvested from rats subjected to fluid percussion TBI in vivo. Intercellular communication was evaluated by measuring fluorescence recovery after photobleaching (FRAP). In VSM cells in vitro, FRAP increased significantly (p<0.05 vs. sham RSI) after mild RSI, but decreased significantly (p<0.05 vs. sham RSI) after moderate or severe RSI. FRAP decreased significantly (p<0.05 vs. sham RSI) 30 min and 2 h, but increased significantly (p<0.05 vs. sham RSI) 24 h after RSI. In MCAs harvested from rats 30 min after moderate TBI in vivo, FRAP was reduced significantly (p<0.05), compared to MCAs from rats after sham TBI. In VSM cells in vitro, pretreatment with the peroxynitrite (ONOO(-)) scavenger, 5,10,15,20-tetrakis(4-sulfonatophenyl)prophyrinato iron[III], prevented RSI-induced reductions in FRAP. In isolated MCAs from rats treated with the ONOO(-) scavenger, penicillamine, GJ coupling was not impaired by fluid percussion TBI. In addition, penicillamine treatment improved vasodilatory responses to reduced intravascular pressure in MCAs harvested from rats subjected to moderate fluid percussion TBI. These results indicate that TBI reduced GJ coupling in VSM cells in vitro and in vivo through mechanisms related to generation of the potent oxidant, ONOO(-).

Genetic ablation of receptor for advanced glycation end products promotes functional recovery in mouse model of spinal cord injury

Spinal cord injury (SCI) results in a loss of normal motor and sensory function, leading to severe disability and reduced quality of life. The aim of this work was to investigate the effect of receptor for advanced glycation end products (RAGE) deficiency on the function recovery in a mouse model of SCI. Mice received a mid-thoracic spinal contusion injury. Upregulation of RAGE protein expression in spinal cord tissue was evident at 12 h after SCI and continued at 2 and 5 days. Furthermore, we showed that locomotor recovery was improved and lesion pathology was reduced after SCI in RAGE-deficient mice. RAGE deficiency in mice attenuated apoptosis after SCI through inhibiting p53/Bax/caspase-3 pathway. RAGE deficiency in mice inhibited inflammation after SCI, marked by reduced myeloperoxidase activity, NFκB nuclear translocation, and TNF-α, IL-1β, and IL-6 mRNA and protein levels. RAGE deficiency in mice exposed to SCI suppressed the upregulation of inducible nitric oxide synthase (iNOS) and gp91-phox and attenuated oxidative and nitrosative stresses, marked by reduced formation of malondialdehyde, reactive oxygen species, peroxynitrite (OONO(-)), and 3-nitrotyrosine. RAGE deficiency in mice exposed to SCI attenuated glial scar at the injury site, marked by decreased expression of glial fibrillary acidic protein. These data indicate that the RAGE plays an important role in the development of SCI and might provide a therapeutic target to promote recovery from SCI.

The temporal and spatial profiles of cell loss following experimental spinal cord injury: effect of antioxidant therapy on cell death and functional recovery

Background

Traumatic spinal cord injury (SCI)-induced overproduction of endogenous deleterious substances triggers secondary cell death to spread damage beyond the initial injury site. Substantial experimental evidence supports reactive species (RS) as important mediators of secondary cell death after SCI. This study established quantitative temporal and spatial profiles of cell loss, characterized apoptosis, and evaluated the effectiveness of a broad spectrum RS scavenger - Mn (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP) and a combination of MnTBAP plus nitro-L-arginine to prevent cell loss and neurological dysfunction following contusion SCI to the rat spinal cord.

Results

By counting the number of surviving cells in spinal cord sections removed at 1, 6, 12, 24, 48, 72 h and 1 week post-SCI and at 0 – 4 mm from the epicenter, the temporal and spatial profiles of motoneuron and glia loss were established. Motoneurons continued to disappear over a week and the losses decreased with increasing distance from the epicenter. Significant glia loss peaked at 24 to 48 h post-SCI, but only at sections 0–1.5 mm from the epicenter. Apoptosis of neurons, motoneurons and astrocytes was characterized morphologically by double immuno-staining with cell-specific markers and apoptosis indicators and confirmed by transmission electron microscopy. DNA laddering, ELISA quantitation and caspase-3 activation in the spinal cord tissue indicated more intense DNA fragments and greater caspase-3 activation in the epicenter than at 1 and 2 cm away from the epicenter or the sham-operated sections. Intraperitoneal treatment with MnTBAP + nitro-L-arginine significantly reduced motoneuron and cell loss and apoptosis in the gray and white matter compared with the vehicle-treated group. MnTBAP alone significantly reduced the number of apoptotic cells and improved functional recovery as evaluated by three behavioral tests.

Conclusions

Our temporal and spatial profiles of cell loss provide data bases for determining the time and location for pharmacological intervention. Our demonstration that apoptosis follows SCI and that MnTBAP alone or MnTBAP + nitro-L-arginine significantly reduces apoptosis correlates SCI-induced apoptosis with RS overproduction. MnTBAP significantly improved functional recovery, which strongly supports the important role of antioxidant therapy in treating SCI and the candidacy of MnTBAP for such treatment.

Immunization with a neural-derived peptide protects the spinal cord from apoptosis after traumatic injury

Apoptosis is one of the most destructive mechanisms that develop after spinal cord (SC) injury. Immunization with neural-derived peptides (INDPs) such as A91 has shown to reduce the deleterious proinflammatory response and the amount of harmful compounds produced after SC injury. With the notion that the aforementioned elements are apoptotic inducers, we hypothesized that INDPs would reduce apoptosis after SC injury. In order to test this assumption, adult rats were subjected to SC contusion and immunized either with A91 or phosphate buffered saline (PBS; control group). Seven days after injury, animals were euthanized to evaluate the number of apoptotic cells at the injury site. Apoptosis was evaluated using DAPI and TUNEL techniques; caspase-3 activity was also evaluated. To further elucidate the mechanisms through which A91 exerts this antiapoptotic effects we quantified tumor necrosis factor-alpha (TNF-α). To also demonstrate that the decrease in apoptotic cells correlated with a functional improvement, locomotor recovery was evaluated. Immunization with A91 significantly reduced the number of apoptotic cells and decreased caspase-3 activity and TNF-α concentration. Immunization with A91 also improved the functional recovery of injured rats. The present study shows the beneficial effect of INDPs on preventing apoptosis and provides more evidence on the neuroprotective mechanisms exerted by this strategy.

Stability, disposition, and penetration of catalytic antioxidants Mn-porphyrin and Mn-salen and of methylprednisolone in spinal cord injury

This study measured the time courses of concentration changes following administration of the catalytic antioxidants Mn (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP) and Mn (III) 3-methoxy N, N' bis (salicyclidene) ethylenediamine chloride (EUK-134) in blood and cerebrospinal fluid (CSF) of rats with a spinal cord injury (SCI) and sham controls. Parallel measurements were made for methylprednisolone, the only drug presently used clinically for treating SCI. The time courses kinetically characterized the agents in their stability, disposition, and ability to penetrate the blood-spinal cord barrier (BSB). In both the SCI and control groups, MnTBAP was stable in CSF and in blood across the collection periods (10 h and 24 h, respectively) following administration. In the blood, [EUK-134] and [methylprednisolone] rapidly declined to near basal concentrations at 4 h and 2 h, respectively, post-administration. Therefore the order of stability in CSF and blood was MnTBAP >> EUK-134 > methylprednisolone. The maximum CSF/blood concentration ratios for EUK-134, methylprednisolone and MnTBAP post-administration were: 32 ± 3.1%, 19.2 ± 6.4%, and 4.42 ± 0.73% in the injured rats, and 22 ± 6.5%, 17.8 ± 2.9%, and 1.0 ± 0.5% in the sham control animals. This suggests an order of BSB penetration of EUK-134 > methylprednisolone >> MnTBAP. Despite much lower penetration by MnTBAP compared with EUK-134 and methylprednisolone, a lower dose of MnTBAP because of its stability provided a higher concentration in CSF than did the other agents given at higher doses. This finding supports further exploration of MnTBAP as a potential treatment for SCI.

Effect of melatonin on the functional recovery from experimental traumatic compression of the spinal cord

Spinal cord injury is an extremely severe condition with no available effective therapies. We examined the effect of melatonin on traumatic compression of the spinal cord. Sixty male adult Wistar rats were divided into three groups: sham-operated animals and animals with 35 and 50% spinal cord compression with a polycarbonate rod spacer. Each group was divided into two subgroups, each receiving an injection of vehicle or melatonin (2.5 mg/kg, intraperitoneal) 5 min prior to and 1, 2, 3, and 4 h after injury. Functional recovery was monitored weekly by the open-field test, the Basso, Beattie and Bresnahan locomotor scale and the inclined plane test. Histological changes of the spinal cord were examined 35 days after injury. Motor scores were progressively lower as spacer size increased according to the motor scale and inclined plane test evaluation at all times of assessment. The results of the two tests were correlated. The open-field test presented similar results with a less pronounced difference between the 35 and 50% compression groups. The injured groups presented functional recovery that was more evident in the first and second weeks. Animals receiving melatonin treatment presented more pronounced functional recovery than vehicle-treated animals as measured by the motor scale or inclined plane. NADPH-d histochemistry revealed integrity of the spinal cord thoracic segment in sham-operated animals and confirmed the severity of the lesion after spinal cord narrowing. The results obtained after experimental compression of the spinal cord support the hypothesis that melatonin may be considered for use in clinical practice because of its protective effect on the secondary wave of neuronal death following the primary wave after spinal cord injury.

Nitration of Hsp90 induces cell death

Oxidative stress is a widely recognized cause of cell death associated with neurodegeneration, inflammation, and aging. Tyrosine nitration in these conditions has been reported extensively, but whether tyrosine nitration is a marker or plays a role in the cell-death processes was unknown. Here, we show that nitration of a single tyrosine residue on a small proportion of 90-kDa heat-shock protein (Hsp90), is sufficient to induce motor neuron death by the P2X7 receptor-dependent activation of the Fas pathway. Nitrotyrosine at position 33 or 56 stimulates a toxic gain of function that turns Hsp90 into a toxic protein. Using an antibody that recognizes the nitrated Hsp90, we found immunoreactivity in motor neurons of patients with amyotrophic lateral sclerosis, in an animal model of amyotrophic lateral sclerosis, and after experimental spinal cord injury. Our findings reveal that cell death can be triggered by nitration of a single protein and highlight nitrated Hsp90 as a potential target for the development of effective therapies for a large number of pathologies.

Mn (III) tetrakis (4-benzoic acid) porphyrin scavenges reactive species, reduces oxidative stress, and improves functional recovery after experimental spinal cord injury in rats: comparison with methylprednisolone

BACKGROUND

Substantial experimental evidence supports that reactive species mediate secondary damage after traumatic spinal cord injury (SCI) by inducing oxidative stress. Removal of reactive species may reduce secondary damage following SCI. This study explored the effectiveness of a catalytic antioxidant - Mn (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP) - in removing reactive oxygen species (ROS), reducing oxidative stress, and improving functional recovery in vivo in a rat impact SCI model. The efficiency of MnTBAP was also compared with that of methylprednisolone - the only drug used clinically in treating acute SCI.

RESULTS

In vivo measurements of time courses of ROS production by microdialysis and microcannula sampling in MnTBAP, methylprednisolone, and saline (as vehicle control)-treated SCI rats showed that both agents significantly reduced the production of hydrogen peroxide, but only MnTBAP significantly reduced superoxide elevation after SCI. In vitro experiments further demonstrated that MnTBAP scavenged both of the preceding ROS, whereas methylprednisolone had no effect on either. By counting the immuno-positive neurons in the spinal cord sections immunohistochemically stained with anti-nitrotyrosine and anti-4-hydroxy-nonenal antibodies as the markers of protein nitration and membrane lipid peroxidation, we demonstrated that MnTBAP significantly reduced the numbers of 4-hydroxy-nonenal-positive and nitrotyrosine-positive neurons in the sections at 1.55 to 2.55 mm and 1.1 to 3.1 mm, respectively, rostral to the injury epicenter compared to the vehicle-treated animals. By behavioral tests (open field and inclined plane tests), we demonstrated that at 4 hours post-SCI treatment with MnTBAP and the standard methylprednisolone regimen both significantly increased test scores compared to those produced by vehicle treatment. However, the outcomes for MnTBAP-treated rats were significantly better than those for methylprednisolone-treated animals.

CONCLUSIONS

This study demonstrated for the first time in vivo and in vitro that MnTBAP significantly reduced the levels of SCI-elevated ROS and that MnTBAP is superior to methylprednisolone in removing ROS. Removal of ROS by MnTBAP significantly reduced protein nitration and membrane lipid peroxidation in neurons. MnTBAP more effectively reduced neurological deficits than did methylprednisolone after SCI - the first most important criterion for assessing SCI treatments. These results support the therapeutic potential of MnTBAP in treating SCI.

Nitrous oxide myelopathy posing as spinal cord injury

The authors describe a patient who presented with acute tetraparesis and a proposed acute traumatic spinal cord injury that was the result of nitrous oxide myelopathy. This 19-year-old man sustained a traumatic fall off a 6-ft high wall. His examination was consistent with a central cord syndrome with the addition of dorsal column impairment. Cervical MRI demonstrated an isolated dorsal column signal that was suggestive of a nontraumatic etiology. The patient's symptoms resolved entirely over the course of 48 hours.

Nitrous oxide abuse is increasing in prevalence. Its toxic side effects can mask vitamin B12 and folate deficiency and central cord syndrome. The patient's history and radiographic presentation are key to establishing a diagnosis.

Inhibition of the Ca²⁺-dependent K⁺ channel, KCNN4/KCa3.1, improves tissue protection and locomotor recovery after spinal cord injury

Spinal cord injury (SCI) triggers inflammatory responses that involve neutrophils, macrophages/microglia and astrocytes and molecules that potentially cause secondary tissue damage and functional impairment. Here, we assessed the contribution of the calcium-dependent K⁺ channel KCNN4 (KCa3.1, IK1, SK4) to secondary damage after moderate contusion lesions in the lower thoracic spinal cord of adult mice. Changes in KCNN4 mRNA levels (RT-PCR), KCa3.1 protein expression (Western blots), and cellular expression (immunofluorescence) in the mouse spinal cord were monitored between 1 and 28 d after SCI. KCNN4 mRNA and KCa3.1 protein rapidly increased after SCI; double labeling identified astrocytes as the main cellular source accounting for this upregulation. Locomotor function after SCI, evaluated for 28 d in an open-field test using the Basso Mouse Scale, was improved in a dose-dependent manner by treating mice with a selective inhibitor of KCa3.1 channels, TRAM-34 (triarylmethane-34). Improved locomotor function was accompanied by reduced tissue loss at 28 d and increased neuron and axon sparing. The rescue of tissue by TRAM-34 treatment was preceded by reduced expression of the proinflammatory mediators, tumor necrosis factor-α and interleukin-1β in spinal cord tissue at 12 h after injury, and reduced expression of inducible nitric oxide synthase at 7 d after SCI. In astrocytes in vitro, TRAM-34 inhibited Ca²⁺ signaling in response to metabotropic purinergic receptor stimulation. These results suggest that blocking the KCa3.1 channel could be a potential therapeutic approach for treating secondary damage after spinal cord injury.

Immunization with A91 peptide or copolymer-1 reduces the production of nitric oxide and inducible nitric oxide synthase gene expression after spinal cord injury

Immunization with neurally derived peptides (INDP) boosts the action of an autoreactive immune response that has been shown to induce neuroprotection in several neurodegenerative diseases, especially after spinal cord (SC) injury. This strategy provides an environment that promotes neuronal survival and tissue preservation. The mechanisms by which this autoreactive response exerts its protective effects is not totally understood at the moment. A recent study showed that INDP reduces lipid peroxidation. Lipid peroxidation is a neurodegenerative phenomenon caused by the increased production of reactive nitrogen species such as nitric oxide (NO). It is possible that INDP could be interfering with NO production. To test this hypothesis, we examined the effect of INDP on the amount of NO produced by glial cells when cocultured with autoreactive T cells. We also evaluated the amount of NO and the expression of the inducible form of nitric oxide synthase (iNOS) at the injury site of SC-injured animals. The neural-derived peptides A91 and Cop-1 were used to immunize mice and rats with SC injury. In vitro studies showed that INDP significantly reduces the production of NO by glial cells. This observation was substantiated by in vivo experiments demonstrating that INDP decreases the amount of NO and iNOS gene expression at the site of injury. The present study provides substantial evidence on the inhibitory effect of INDP on NO production, helpingour understanding of the mechanisms through which protective autoimmunity promotes neuroprotection.

Inhibition of inflammation and oxidative stress by Angelica dahuricae radix extract decreases apoptotic cell death and improves functional recovery after spinal cord injury

Inflammation and oxidative stress play major roles in the pathogenesis after spinal cord injury (SCI). Here, we examined the neuroprotective effects of Angelica dahuricae radix (ADR) extract after SCI. ADR extract significantly decreased the levels of proinflammatory factors such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) in a lipopolysaccharide (LPS)-activated microglial cell line, BV2 cells. ADR extract also significantly alleviated the level of reactive oxygen species in LPS-activated BV2 cells. To examine the neuroprotective effect of ADR extract after SCI, spinally injured rats were administered ADR extract orally at a dose of 100 mg/kg for 14 days. ADR extract treatment significantly reduced the levels of TNF-α, IL-1β, IL-6, iNOS, and COX-2. The levels of superoxide anion (O(2·)(-)) and protein nitration were also significantly decreased by ADR extract. In addition, ADR extract inhibited p38 mitogen-activated protein kinase activation and pronerve growth factor expression in microglia after SCI. Furthermore, ADR extract significantly inhibited caspase-3 activation following apoptotic cell death of neurons and oligodendrocytes, thereby improving functional recovery after injury. Thus, our data suggest that ADR extract provides neuroprotection by alleviating inflammation and oxidative stress and can be used as an orally administered therapeutic agent for acute SCI.

Antioxidant therapies for acute spinal cord injury

One of the most investigated molecular mechanisms involved in the secondary pathophysiology of acute spinal cord injury (SCI) is free radical-induced, iron-catalyzed lipid peroxidation (LP) and protein oxidative/nitrative damage to spinal neurons, glia, and microvascular cells. The reactive nitrogen species peroxynitrite and its highly reactive free radicals are key initiators of LP and protein nitration in the injured spinal cord, the biochemistry, and pathophysiology of which are first of all reviewed in this article. This is followed by a presentation of the antioxidant mechanistic approaches and pharmacological compounds that have been shown to have neuroprotective properties in preclinical SCI models. Two of these, which act by inhibition of LP, are high-dose treatment with the glucocorticoid steroid methylprednisolone (MP) and the nonglucocorticoid 21-aminosteroid tirilazad, have been demonstrated in the multicenter NASCIS clinical trials to produce at least a modest improvement in neurological recovery when administered within the first 8 hours after SCI. Although these results have provided considerable validation of oxidative damage as a clinically practical neuroprotective target, there is a need for the discovery of safer and more effective antioxidant compounds for acute SCI.

Mitogen-activated protein kinase-activated protein kinase 2 (MK2) contributes to secondary damage after spinal cord injury

The inflammatory response contributes importantly to secondary tissue damage and functional deficits after spinal cord injury (SCI). In this work, we identified mitogen-activated protein kinase (MAPK)-activated protein kinase 2 (MAPKAPK2 or MK2), a downstream substrate of p38 MAPK, as a potential target using microarray analysis of contused spinal cord tissue taken at the peak of the inflammatory response. There was increased expression and phosphorylation of MK2 after SCI, with phospho-MK2 expressed in microglia/macrophages, neurons and astrocytes. We examined the role of MK2 in spinal cord contusion injury using MK2(-/-) mice. These results show that locomotor recovery was significantly improved in MK2(-/-) mice, compared with wild-type controls. MK2(-/-) mice showed reduced neuron and myelin loss, and increased sparing of serotonergic fibers in the ventral horn caudal to the injury site. We also found differential expression of matrix metalloproteinase-2 and 9 in MK2(-/-) and wild-type mice after SCI. Significant reduction was also seen in the expression of proinflammatory cytokines and protein nitrosylation in the injured spinal cord of MK2(-/-) mice. Our previous work has shown that macrophages lacking MK2 have an anti-inflammatory phenotype. We now show that there is no difference in the number of macrophages in the injured spinal cord between the two mouse strains and little if any difference in their phagocytic capacity, suggesting that macrophages lacking MK2 have a beneficial phenotype. These findings suggest that a lack of MK2 can reduce tissue damage after SCI and improve locomotor recovery. MK2 may therefore be a useful target to treat acute SCI.

Temporal and spatial dynamics of peroxynitrite-induced oxidative damage after spinal cord contusion injury

The reactive nitrogen species peroxynitrite (PN) has been suggested to be an important mediator of the secondary oxidative damage that occurs following acute spinal cord injury (SCI). The PN decomposition products nitrogen dioxide (*NO(2)), hydroxyl radical (*OH), and carbonate radical (*CO(3)) are highly reactive with cellular lipids and proteins. In this immunohistochemical study, we examined the temporal (3, 24, and 72 h, and 1 and 2 weeks) and spatial relationships of PN-mediated oxidative damage in the contusion-injured rat thoracic spinal cord (IH device, 200 kdyn, T10) using 3-nitrotyrosine (3-NT), a marker for protein nitration by PN-derived *NO(2) and 4-hydroxynonenal (4-HNE), an indicator of lipid peroxidation (LP) initiated by any of the PN radicals. Minimal 3-NT or 4-HNE immunostaining was seen in sham, non-injured spinal cords. In contrast, both markers showed a substantial increase at 3 h post-injury at the epicenter, that extended throughout the gray matter and into the surrounding white matter. At 24 and 72 h, the oxidative damage expanded circumferentially to involve all but a small rim of white matter tissue at the injury site, and longitudinally as much as 6-9 mm in the rostral and caudal directions. The staining was observed in neuronal soma, axons, and microvessels. At all time points except 3 h, there was no significant difference in the mean rostral or caudal extent of 3-NT and 4-HNE staining. By 1, and more so at 2 weeks, the longitudinal extent of the oxidative damage staining was greatly decreased. The spatial and temporal overlap of 3-NT and 4-HNE staining supports the concept that PN is involved in both damage produced by lipid peroxidation and protein nitration, and that antioxidant agents that target PN or PN-derived radicals should be effective neuroprotectants for acute SCI if administered during the first post-injury hours.

NO mediates microglial response to acute spinal cord injury under ATP control in vivo

To understand the pathomechanisms of spinal cord injuries will be a prerequisite to develop efficient therapies. By investigating acute lesions of spinal cord white matter in anesthetized mice with fluorescently labeled microglia and axons using in vivo two-photon laser-scanning microscopy (2P-LSM), we identified the messenger nitric oxide (NO) as a modulator of injury-activated microglia. Local tissue damages evoked by high-power laser pulses provoked an immediate attraction of microglial processes. Spinal superfusion with NO synthase and guanylate cyclase inhibitors blocked these extensions. Furthermore, local injection of the NO-donor spermine NONOate (SPNO) or the NO-dependent second messenger cGMP induced efficient migration of microglial cells toward the injection site. High-tissue levels of NO, achieved by uniform superfusion with SPNO and mimicking extended tissue damage, resulted in a fast conversion of the microglial shape from ramified to ameboid indicating cellular activation. When the spinal white matter was preconditioned by increased, ambient ATP (known as a microglial chemoattractant) levels, the attraction of microglial processes to local NO release was augmented, whereas it was abolished at low levels of tissue ATP. Because both signaling molecules, NO and ATP, mediate acute microglial reactions, coordinated pharmacological targeting of NO and purinergic pathways will be an effective mean to influence the innate immune processes after spinal cord injury.

Immunization with neural-derived antigens inhibits lipid peroxidation after spinal cord injury

Lipid peroxidation (LP) is one of the most harmful mechanisms developed after spinal cord (SC) injury. Several strategies have been explored in order to control this phenomenon. Protective autoimmunity is a physiological process based on the modulation of inflammatory cells that can be boosted by immunizing with neural-derived peptides, such as A91. Since inflammatory cells are among the main contributors to lipid peroxidation, we hypothesized that protective autoimmunity could reduce LP after SC injury. In order to test this hypothesis, we designed two experiments in SC contused rats. First, animals were immunized with a neural-derived peptide seven days before injury. With the aim of inducing the functional elimination of CNS-specific T cells, for the second experiment, animals were tolerized against SC-protein extract and thereafter subjected to a SC injury. The lipid-soluble fluorescent products were used as an index of lipid peroxidation and were assessed after injury. Immunization with neural-derived peptides reduced lipid peroxidation after SC injury. Functional elimination of CNS-specific T cells avoided the beneficial effect induced by protective autoimmunity. The present study demonstrates the beneficial effect of immunizing with neural-derived peptides on lipid peroxidation inhibition; besides this, it also provides evidence on the neuroprotective mechanisms exerted by protective autoimmunity.

Mitochondrial targeting of electron scavenging antioxidants: Regulation of selective oxidation vs random chain reactions

Effective regulation of highly compartmentalized production of reactive oxygen species and peroxidation reactions in mitochondria requires targeting of small molecule antioxidants and antioxidant enzymes into the organelles. This review describes recently developed approaches to mitochondrial targeting of small biologically active molecules based on: (i) preferential accumulation in mitochondria because of their hydrophobicity and positive charge (hydrophobic cations), (ii) binding with high affinity to an intra-mitochondrial constituent, and (iii) metabolic conversions by specific mitochondrial enzymes to reveal an active entity. In addition, targeted delivery of antioxidant enzymes via expression of leader sequences directing the proteins into mitochondria is considered. Examples of successful antioxidant and anti-apoptotic protection based on the ability of targeted cargoes to inhibit cytochrome c-catalyzed peroxidation of a mitochondria-specific phospholipid cardiolipin, in vitro and in vivo are presented. Particular emphasis is placed on the employment of triphenylphosphonium- and hemi-gramicidin S-moieties as two effective vehicles for mitochondrial delivery of antioxidants.

Effects of a metalloporphyrinic peroxynitrite decomposition catalyst, ww-85, in a mouse model of spinal cord injury

The aim of the present study was to assess the effect of a metalloporphyrinic peroxynitrite decomposition catalyst, ww-85, in the pathophysiology of spinal cord injury (SCI) in mice. Spinal cord trauma was induced by the application of vascular clips to the dura via a four-level T5-T8 laminectomy. SCI in mice resulted in severe trauma characterized by oedema, neutrophil infiltration, production of inflammatory mediators, tissue damage and apoptosis. ww-85 treatment (30-300 microg/kg, i.p. 1 h after the SCI) significantly reduced in a dose-dependent manner: (1) the degree of spinal cord inflammation and tissue injury, (2) neutrophil infiltration (myeloperoxidase activity), (3) nitrotyrosine formation and PARP activation, (4) pro-inflammatory cytokines expression, (5) NF-kappaB activation and (6) apoptosis. Moreover, ww-85 significantly ameliorated the recovery of limb function (evaluated by motor recovery score) in a dose-dependent manner. The results demonstrate that ww-85 treatment reduces the development of inflammation and tissue injury associated with spinal cord trauma.