Temporal and spatial profiles of cell loss after spinal cord injury: Reduction by a metalloporphyrin

Protection of the Vascular System by Polyethylene Glycol Reduces Secondary Injury Following Spinal Cord Injury in Rats

BACKGROUND

Polyethylene glycol (PEG) is a hydrophilic polymer, which has been known to have a neuroprotective effect by sealing the ruptured cell membrane, but PEG effects on the vascular systems and its underlying mechanisms remain unclear. Here, we showed the neuroprotective effect of PEG by preventing damage to the vascular system.

METHODS

A spinal contusion was made at the T11 segment in male Sprague-Dawley rats. PEG was injected into the subdural space immediately after SCI. Vascular permeability was assessed for 24 h after SCI using intraperitoneally injected Evans blue dye. Junctional complexes were stained with CD31 and ZO-1. Infarct size was analyzed using triphenyltetrazolium chloride, and blood vessels were counted in the epicenter. Behavioral tests for motor and sensory function were performed for 6 weeks. And then the tissue-sparing area was assessed.

RESULTS

Immediately applied PEG significantly reduced the vascular permeability at 6, 12, and 24 h after SCI when it compared to saline, and infarct size was also reduced at 0, 6, and 24 h after SCI. In addition, a great number of blood vessels were observed in PEG group at 6 and 24 h after SCI compared to those of the saline group. The PEG group also showed a significant improvement in motor function. And tissue-sparing areas in the PEG were greater than those of the saline group.

CONCLUSION

The present results provide preclinical evidence for the neuroprotective effects of PEG as a promising therapeutic agent for reducing secondary injury following SCI through vascular protection.

Coaxial 3D printing of hierarchical structured hydrogel scaffolds for on-demand repair of spinal cord injury

After spinal cord injury (SCI), endogenous neural stem cells (NSCs) near the damaged site are activated, but few NSCs migrate to the injury epicenter and differentiate into neurons because of the harsh microenvironment. It has demonstrated that implantation of hydrogel scaffold loaded with multiple cues can enhance the function of endogenous NSCs. However, programming different cues on request remains a great challenge. Herein, a time-programmed linear hierarchical structure scaffold is developed for spinal cord injury recovery. The scaffold is obtained through coaxial 3D printing by encapsulating a dual-network hydrogel (composed of hyaluronic acid derivatives and N-cadherin modified sodium alginate, inner layer) into a temperature responsive gelatin/cellulose nanofiber hydrogel (Gel/CNF, outer layer). The reactive species scavenger, metalloporphyrin, loaded in the outer layer is released rapidly by the degradation of Gel/CNF, inhibiting the initial oxidative stress at lesion site to protect endogenous NSCs; while the inner hydrogel with appropriate mechanical support, linear topology structure and bioactive cues facilitates the migration and neuronal differentiation of NSCs at the later stage of SCI treatment, thereby promoting motor functional restorations in SCI rats. This study offers an innovative strategy for fabrication of multifunctional nerve regeneration scaffold, which has potential for clinical treatment of SCI. STATEMENT OF SIGNIFICANCE: Two major challenges facing the recovery from spinal cord injury (SCI) are the low viability of endogenous neural stem cells (NSCs) within the damaged microenvironment, as well as the difficulty of neuronal regeneration at the injured site. To address these issues, a spinal cord-like coaxial scaffold was fabricated with free radical scavenging agent metalloporphyrin Mn (III) tetrakis (4-benzoic acid) porphyrin and chemokine N-cadherin. The scaffold was constructed by 3D bioprinting for time-programmed protection and modulation of NSCs to effectively repair SCI. This 3D coaxially bioprinted biomimetic construct enables multi-factor on-demand repair and may be a promising therapeutic strategy for SCI.

Ferrostatin-1 Alleviates White Matter Injury Via Decreasing Ferroptosis Following Spinal Cord Injury

Spinal cord injury (SCI), a devastating neurological impairment, usually imposes a long-term psychological stress and high socioeconomic burden for the sufferers and their family. Recent researchers have paid arousing attention to white matter injury and the underlying mechanism following SCI. Ferroptosis has been revealed to be associated with diverse diseases including stroke, cancer, and kidney degeneration. Ferrostatin-1, a potent inhibitor of ferroptosis, has been illustrated to curb ferroptosis in neurons, subsequently improving functional recovery after traumatic brain injury (TBI) and SCI. However, the role of ferroptosis in white matter injury and the therapeutic effect of ferrostatin-1 on SCI are still unknown. Here, our results indicated that ferroptosis played a pivotal role in the secondary white matter injury, and ferrostatin-1 could reduce iron and reactive oxygen species (ROS) accumulation and downregulate the ferroptosis-related genes and its products of IREB2 and PTGS2 to further inhibit ferroptosis in oligodendrocyte, finally reducing white matter injury and promoting functional recovery following SCI in rats. Meanwhile, the results demonstrated that ferrostatin-1 held the potential of inhibiting the activation of reactive astrocyte and microglia. Mechanically, the present study deciphers the potential mechanism of white matter damage, which enlarges the therapeutic effects of ferrostatin-1 on SCI and even in other central nervous system (CNS) diseases existing ferroptosis.

Temporal Progression of Acute Spinal Cord Injury Mechanisms in a Rat Model: Contusion, Dislocation, and Distraction

Traumatic spinal cord injuries (SCIs) occur due to different spinal column injury patterns, including burst fracture, dislocation, and flexion-distraction. Pre-clinical studies modeling different SCI mechanisms have shown distinct histological differences between these injuries both acutely (3 h and less) and chronically (8 weeks), but there remains a temporal gap. Different rates of injury progression at specific regions of the spinal cord may provide insight into the pathologies that are initiated by specific SCI mechanisms. Therefore, the objective of this study was to evaluate the temporal progression of injury at specific tracts within the white matter, for time-points of 3 h, 24 h, and 7 days, for three distinct SCI mechanisms. In this study, 96 male Sprague Dawley rats underwent one of three SCI mechanisms: contusion, dislocation, or distraction. Animals were sacrificed at one of three times post-injury: 3 h, 24 h, or 7 days. Histological analysis using eriochrome cyanide and immunostaining for MBP, SMI-312, neurofilament-H (NF-H), and β-III tubulin were used to characterize white matter sparing and axon and myelinated axon counts. The regions analyzed were the gracile fasciculus, cuneate fasciculus, dorsal corticospinal tract, and ventrolateral white matter. Contusion, dislocation, and distraction SCIs demonstrated distinct damage patterns that progressed differently over time. Myelinated axon counts were significantly reduced after dislocation and contusion injuries in most locations and time-points analyzed (compared with sham). This indicates early myelin damage often within 3 h. Myelinated axon counts after distraction dropped early and did not demonstrate any significant progression over the next 7 days. Important differences in white matter degeneration were identified between injury types, with distraction injuries showing the least variability across time-points These findings and the observation that white matter injury occurs early, and in many cases, without much dynamic change, highlight the importance of injury type in SCI research-both clinically and pre-clinically.

Microtubule Stabilization Promotes Microcirculation Reconstruction After Spinal Cord Injury

Spinal cord microcirculation plays an important role in maintaining the function of spinal cord neurons and other cells. Previous studies have largely focused on the ability of microtubule stabilization to inhibit the fibroblast migration and promote axon regeneration after spinal cord injury (SCI). However, the effect of microtubule stabilization treatment on microcirculation reconstruction after SCI remains unclear. By using immunofluorescence, we found that microtubule stabilization treatment improved microcirculation reconstruction via increasing the number of microvessels, pericytes, and the perfused microvessels after SCI. To clarify the underlying mechanisms, rat brain microvascular endothelial cells and pericytes were subjected to glucose oxygen deprivation. By using flow cytometry and western blotting, we found that microtubule stabilization treatment inhibited apoptosis and migration of endothelial cells and pericytes but promoted proliferation and survival of endothelial cells and pericytes through upregulated expression of vascular endothelial growth factor A (VEGFA), VEGF receptor 2, platelet-derived growth factor-B (PDGFB), PDGF receptor β, and angiopoietin-1 after SCI. Taken together, this study provides evidence for the mechanisms underlying the promotion of microcirculation reconstruction after SCI by microtubule stabilization treatment. Importantly, this study suggests the potential of microtubule stabilization as a therapeutic target to reduce microcirculation dysfunction after SCI in the clinic.

Elevated TRPV4 Levels Contribute to Endothelial Damage and Scarring in Experimental Spinal Cord Injury

Currently, the role of transient receptor potential vanilloid type 4 (TRPV4), a nonselective cation channel in the pathology of spinal cord injury (SCI), is not recognized. Herein, we report the expression and contribution of TRPV4 in the pathology of scarring and endothelial and secondary damage after SCI. TRPV4 expression increased during the inflammatory phase in female rats after SCI and was expressed primarily by cells at endothelial-microglial junctions. Two-photon microscopy of intracellular-free Ca2+ levels revealed a biphasic increase at similar time points after SCI. Expression of TRPV4 at the injury epicenter, but not intracellular-free Ca2+, progressively increases with the severity of the injury. Activation of TRPV4 with specific agonist altered the organization of endothelial cells, affected tight junctions in the hCMEC/D3 BBB cell line in vitro, and increases the scarring in rat spinal cord as well as induced endothelial damage. By contrast, suppression of TRPV4 with a specific antagonist or in female Trpv4 KO mouse attenuated inflammatory cytokines and chemokines, prevented the degradation of tight junction proteins, and preserve blood-spinal cord barrier integrity, thereby attenuate the scarring after SCI. Likewise, secondary damage was reduced, and behavioral outcomes were improved in Trpv4 KO mice after SCI. These results suggest that increased TRPV4 expression disrupts endothelial cell organization during the early inflammatory phase of SCI, resulting in tissue damage, vascular destabilization, blood-spinal cord barrier breakdown, and scarring. Thus, TRPV4 inhibition/knockdown represents a promising therapeutic strategy to stabilize/protect endothelial cells, attenuate nociception and secondary damage, and reduce scarring after SCI.SIGNIFICANCE STATEMENT TRPV4, a calcium-permeable nonselective cation channel, is widely expressed in both excitable and nonexcitable cells. Spinal cord injury (SCI) majorly caused by trauma/accidents is associated with changes in osmolarity, mechanical injury, and shear stress. After SCI, TRPV4 was increased and were found to be linked with the severity of injury at the epicenter at the time points that were reported to be critical for repair/treatment. Activation of TRPV4 was damaging to endothelial cells that form the blood-spinal cord barrier and thus contributes to scarring (glial and fibrotic). Importantly, inhibition/knockdown of TRPV4 prevented these effects. Thus, the manipulation of TRPV4 signaling might lead to new therapeutic strategies or combinatorial therapies to protect endothelial cells and enhance repair after SCI.

Attenuation of White Matter Damage Following Deferoxamine Treatment in Rats After Spinal Cord Injury

BACKGROUND

With little information available on axonal and myelin damage surrounding the contusion, the study of spinal cord injury (SCI) so far has focused on neuronal death. In this study, we investigated the role of iron overload in long-term oligodendroglia death and progressive white matter damage to rats after SCI using the iron chelator, deferoxamine (DFX).

METHODS

Female Sprague-Dawley rats received either a contusion at T10 or sham-surgery. The rats were treated with DFX or vehicle. All rats were evaluated in behavioral assessments and then euthanized at different time points. Spinal cords were analyzed by diaminobenzidine-enhanced Perls' staining, non-heme iron measurements, Western blotting, immunohistochemistry, and transmission electron microscopy.

RESULTS

Iron accumulation after SCI resulted in the upregulation of transferrin receptor and divalent metal transporter 1, which exacerbated the intracellular iron overload. DFX treatment reduced iron overload-induced delayed oligodendrocyte death (e.g., 21 days: 47.12 ± 10.5 vs. 20.02 ± 9.4 x 10³/mm² in the vehicle-treated group, n = 4, P < 0.05). After SCI, the markers of axonal damage and demyelination were increased in white matter in the vehicle-treated group compared with the DFX-treated group (P < 0.05).

CONCLUSIONS

Iron overload plays an important role in progressive white matter damage after SCI. DFX may be an effective treatment for white matter damage after SCI.

Neutrophil elastase inhibition effectively rescued angiopoietin-1 decrease and inhibits glial scar after spinal cord injury

After spinal cord injury (SCI), neutrophil elastase (NE) released at injury site disrupts vascular endothelium integrity and stabilization. Angiopoietins (ANGPTs) are vascular growth factors that play an important role in vascular stabilization. We hypothesized that neutrophil elastase is one of the key determinants of vascular endothelium disruption/destabilization and affects angiopoietins expression after spinal cord injury. To test this, tubule formation and angiopoietins expression were assessed in endothelial cells exposed to different concentrations of recombinant neutropil elastase. Then, the expression of angiopoietin-1, angiopoietin-2, and neutrophil elastase was determined at 3 h and at 1, 3, 5, 7, 14, 21, and 28 days in a clinically relevant model of moderate compression (35 g for 5 min at T10) spinal cord injury. A dichotomy between the levels of angiopoietin-1 and angiopoietin-2 was observed; thus, we utilized a specific neutrophil elastase inhibitor (sivelestat sodium; 30 mg/kg, i.p., b.i.d.) after spinal cord injury. The expression levels of neutropil elastase and angiopoietin-2 increased, and that of angiopoietin-1 decreased after spinal cord injury in rats. The sivelestat regimen, optimized via a pharmacokinetics study, had potent effects on vascular stabilization by upregulating angiopoietin-1 via the AKT pathway and preventing tight junction protein degradation. Moreover, sivelestat attenuated the levels of inflammatory cytokines and chemokines after spinal cord injury and hence subsequently alleviated secondary damage observed as a reduction in glial scar formation and the promotion of blood vessel formation and stabilization. As a result, hindlimb locomotor function significantly recovered in the sivelestat-treated animals as determined by the Basso, Beattie, and Bresnahan scale and footprint analyses. Furthermore, sivelestat treatment attenuated neuropathic pain as assessed by responses to von Frey filaments after spinal cord injury. Thus, our result suggests that inhibiting neutropil elastase by administration of sivelestat is a promising therapeutic strategy to inhibit glial scar and promote functional recovery by upregulating angiopoietin-1 after spinal cord injury.

The Function of FGFR1 Signalling in the Spinal Cord: Therapeutic Approaches Using FGFR1 Ligands after Spinal Cord Injury

Extensive research is ongoing that concentrates on finding therapies to enhance CNS regeneration after spinal cord injury (SCI) and to cure paralysis. This review sheds light on the role of the FGFR pathway in the injured spinal cord and discusses various therapies that use FGFR activating ligands to promote regeneration after SCI. We discuss studies that use peripheral nerve grafts or Schwann cell grafts in combination with FGF1 or FGF2 supplementation. Most of these studies show evidence that these therapies successfully enhance axon regeneration into the graft. Further they provide evidence for partial recovery of sensory function shown by electrophysiology and motor activity evidenced by behavioural data. We also present one study that indicates that combination with additional, synergistic factors might further drive the system towards functional regeneration. In essence, this review summarises the potential of nerve and cell grafts combined with FGF1/2 supplementation to improve outcome even after severe spinal cord injury.

Novel mouse model of spinal cord injury-induced heterotopic ossification

Heterotopic ossification (HO) develops in about 20% to 30% of patients with spinal cord injury (SCI) and significantly impairs their rehabilitation. There is no effective prevention or treatment for this condition at this time. Our current understanding of its etiology and pathophysiology is limited partially due to the lack of clinically relevant animal models. In this study, we report a novel mouse model of SCI-induced HO by administering a subthreshold dose of bone morphogenetic protein (BMP)-2 to muscles in mice after SCI. Micro-computed tomography scanning showed that an intramuscular injection of 0.25 micrograms of BMP-2 causes significant HO in mice with SCI but not in control (sham surgery) mice. Our analysis of gene expression showed significantly increased BMP signaling in quadriceps following SCI, suggesting that BMP signaling may play a role in SCI-induced HO. Administering 0.25 micrograms of BMP-2 to the front arms of the mice with SCI also results in the development of significant HO but not in control mice. This suggests that SCI causes a systematic osteogenic effect, which is not limited to paralyzed limbs. This novel mouse model will serve as a powerful tool in exploring the molecular mechanisms of SCI-induced HO, which may lead to novel treatment for this disease.

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.

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.

Delayed administration of a bio-engineered zinc-finger VEGF-A gene therapy is neuroprotective and attenuates allodynia following traumatic spinal cord injury

Following spinal cord injury (SCI) there are drastic changes that occur in the spinal microvasculature, including ischemia, hemorrhage, endothelial cell death and blood-spinal cord barrier disruption. Vascular endothelial growth factor-A (VEGF-A) is a pleiotropic factor recognized for its pro-angiogenic properties; however, VEGF has recently been shown to provide neuroprotection. We hypothesized that delivery of AdV-ZFP-VEGF--an adenovirally delivered bio-engineered zinc-finger transcription factor that promotes endogenous VEGF-A expression--would result in angiogenesis, neuroprotection and functional recovery following SCI. This novel VEGF gene therapy induces the endogenous production of multiple VEGF-A isoforms; a critical factor for proper vascular development and repair. Briefly, female Wistar rats--under cyclosporin immunosuppression--received a 35 g clip-compression injury and were administered AdV-ZFP-VEGF or AdV-eGFP at 24 hours post-SCI. qRT-PCR and Western Blot analysis of VEGF-A mRNA and protein, showed significant increases in VEGF-A expression in AdV-ZFP-VEGF treated animals (p<0.001 and p<0.05, respectively). Analysis of NF200, TUNEL, and RECA-1 indicated that AdV-ZFP-VEGF increased axonal preservation (p<0.05), reduced cell death (p<0.01), and increased blood vessels (p<0.01), respectively. Moreover, AdV-ZFP-VEGF resulted in a 10% increase in blood vessel proliferation (p<0.001). Catwalk™ analysis showed AdV-ZFP-VEGF treatment dramatically improves hindlimb weight support (p<0.05) and increases hindlimb swing speed (p<0.02) when compared to control animals. Finally, AdV-ZFP-VEGF administration provided a significant reduction in allodynia (p<0.01). Overall, the results of this study indicate that AdV-ZFP-VEGF administration can be delivered in a clinically relevant time-window following SCI (24 hours) and provide significant molecular and functional benefits.

Characterization of vascular disruption and blood-spinal cord barrier permeability following traumatic spinal cord injury

Significant vascular changes occur subsequent to spinal cord injury (SCI), which contribute to progressive pathophysiology. In the present study, we used female Wistar rats (300-350 g) and a 35-g clip-compression injury at T6 to T7 to characterize the spatial and temporal vascular changes that ensue post-SCI. Before sacrifice, animals were injected with vascular tracing dyes (2% Evans Blue (EB) or fluorescein isothiocyanate/Lycopersicon esculentum agglutinin [FITC-LEA]) to assess blood-spinal cord barrier (BSCB) integrity or vascular architecture, respectively. Spectrophotometry of EB tissue showed maximal BSCB disruption at 24 h postinjury, with significant disruption observed until 5 days postinjury (p<0.01). FITC-LEA-identified functional vasculature was dramatically reduced by 24 h. Similarly, RECA-1 immunohistochemistry showed a significant decrease in the number of vessels at 24 h postinjury, compared to uninjured animals (p<0.01), with slight increases in endogenous revascularization by 10 days postinjury. White versus gray matter (GM) quantification showed that GM vessels are more susceptible to SCI. Finally, we observed an endogenous angiogenic response between 3 and 7 days postinjury: maximal endothelial cell proliferation was observed at day 5. These data indicate that BSCB disruption and endogenous revascularization occur at specific time points after injury, which may be important for developing effective therapeutic interventions for 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.

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.

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.

Design, mechanism of action, bioavailability and therapeutic effects of mn porphyrin-based redox modulators

Based on aqueous redox chemistry and simple in vivo models of oxidative stress, Escherichia coli and Saccharomyces cerevisiae, the cationic Mn(III) N-substituted pyridylporphyrins (MnPs) have been identified as the most potent cellular redox modulators within the porphyrin class of drugs; their efficacy in animal models of diseases that have oxidative stress in common is based on their high ability to catalytically remove superoxide, peroxynitrite, carbonate anion radical, hypochlorite, nitric oxide, lipid peroxyl and alkoxyl radicals, thus suppressing the primary oxidative event. While doing so MnPs could couple with cellular reductants and redox-active proteins. Reactive species are widely accepted as regulators of cellular transcriptional activity: minute, nanomolar levels are essential for normal cell function, while submicromolar or micromolar levels impose oxidative stress, which is evidenced in increased inflammatory and immune responses. By removing reactive species, MnPs affect redox-based cellular transcriptional activity and consequently secondary oxidative stress, and in turn inflammatory processes. The equal ability to reduce and oxidize superoxide during the dismutation process and recently accumulated results suggest that pro-oxidative actions of MnPs may also contribute to their therapeutic effects. All our data identify the superoxide dismutase-like activity, estimated by log k(cat)O2-*), as a good measure for the therapeutic efficacy of MnPs. Their accumulation in mitochondria and their ability to cross the blood-brain barrier contribute to their remarkable efficacy. We summarize herein the therapeutic effects of MnPs in cancer, central nervous system injuries, diabetes, their radioprotective action and potential for imaging. Few of the most potent modulators of cellular redox-based pathways, MnTE2-PyP5+, MnTDE-2-ImP5+, MnTnHex-2-PyP5+ and MnTnBuOE-2-PyP5+, are under preclinical and clinical development.

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.

Emodin and [6]-gingerol lessen hypoxia-induced embryotoxicities in cultured mouse whole embryos via upregulation of hypoxia-inducible factor 1α and intracellular superoxide dismutases

Excess hypoxia during embryonic organogenesis leads to developmental abnormalities and postnatal deficits. To determine whether emodin and [6]-gingerol affects hypoxia-induced anomalies during embryonic organogenesis, we cultured embryonic day 8.5 mouse embryos under hypoxic conditions (5% O(2)) for 2 days with or without emodin (1 × 10(-8) μg/mL), [6]-gingerol (1 × 10(-9) μg/mL), and SOD mimetics MnTBAP (1 × 10(2) nM/mL) and then investigated the developmental changes and expression patterns of hypoxia-inducible factor 1α (HIF-1α), cytoplasmic superoxide dismutase (SOD1), and mitochondrial SOD (SOD2) in the embryos. Hypoxic conditions induced various developmental anomalies in the growth stages and remarkably low levels of HIF-1α, SOD1 and SOD2 mRNAs, and SOD activity in the embryos; however, these effects were significantly reversed by treatment with emodin, [6]-gingerol, and MnTBAP, respectively. Our findings indicate that antioxidants such as emodin, [6]-gingerol, and MnTBAP lessen hypoxia-induced embryotoxicities via upregulation of HIF-1α and intracellular SODs.

Superoxide dismutase mimics: chemistry, pharmacology, and therapeutic potential

Oxidative stress has become widely viewed as an underlying condition in a number of diseases, such as ischemia-reperfusion disorders, central nervous system disorders, cardiovascular conditions, cancer, and diabetes. Thus, natural and synthetic antioxidants have been actively sought. Superoxide dismutase is a first line of defense against oxidative stress under physiological and pathological conditions. Therefore, the development of therapeutics aimed at mimicking superoxide dismutase was a natural maneuver. Metalloporphyrins, as well as Mn cyclic polyamines, Mn salen derivatives and nitroxides were all originally developed as SOD mimics. The same thermodynamic and electrostatic properties that make them potent SOD mimics may allow them to reduce other reactive species such as peroxynitrite, peroxynitrite-derived CO(3)(*-), peroxyl radical, and less efficiently H(2)O(2). By doing so SOD mimics can decrease both primary and secondary oxidative events, the latter arising from the inhibition of cellular transcriptional activity. To better judge the therapeutic potential and the advantage of one over the other type of compound, comparative studies of different classes of drugs in the same cellular and/or animal models are needed. We here provide a comprehensive overview of the chemical properties and some in vivo effects observed with various classes of compounds with a special emphasis on porphyrin-based compounds.

Proteomic and phosphoproteomic analyses of the soluble fraction following acute spinal cord contusion in rats

Traumatic spinal cord injury (SCI) causes marked neuropathological changes in the spinal cord, resulting in limited functional recovery. Currently, there are no effective treatments, and the mechanisms underlying these neuropathological changes are not completely understood. In this study, two-dimensional gel electrophoresis coupled with mass spectrometry was used to investigate injury-related changes in the abundance (SYPRO Ruby stain) and phosphorylation (Pro-Q Diamond stain) of proteins from the soluble fraction of the lesion epicenter at 24 h following SCI. Over 1500 SYPRO Ruby-stained spots and 100 Pro-Q Diamond-stained spots were examined. We identified 26 unique proteins within 38 gel spots that differentially changed in abundance, phosphorylation, or both in response to SCI. Protein redundancies among the gel spots were likely due to differences in proteolysis, post-translational modifications, and the existence of isoforms. The proteins affected were blood-related proteins, heat-shock proteins, glycolytic enzymes, antioxidants, and proteins that function in cell structure, cell signaling, DNA damage, and protein degradation. These protein changes post injury may suggest additional avenues of investigation into the underlying molecular mechanisms responsible for the pathophysiological consequences of SCI.

NCAM-mediated locomotor recovery from spinal cord contusion injury involves neuroprotection, axon regeneration, and synaptogenesis

The expression level of neural cell adhesion molecule (NCAM), which plays a critical role in pathways involving development and plasticity of the nervous system, changes markedly after spinal cord injury (SCI). However, the significance of NCAM-involved mechanisms in SCI remains elusive. The present study demonstrates that NCAM-deficient (ND) mice exhibited significantly poorer locomotor activity than wildtype (WT) littermates with the same injury intensity by the contusion model. To determine detailed contribution of NCAM, quantitative immunohistochemistry examination was performed on the injured spinal cord of 6mm along the rostrocaudal axis in the animals for up to 5 weeks after SCI. Overall level of NCAM decreased initially in the lesion site but increased around the center of the injury thereafter. At acute stage, more apoptotic cells were found in the gray and white matter in ND mice. Between the two animal groups, no obvious difference in expression levels of GFAP (astrocytosis marker) and MBP (remyelination marker) was detected. However, diverse expression trends of NF200 (axon marker), GAP-43 (synaptogenesis indicator) and phosphorylated ERK (active signal molecule) were observed in the area encompassing the lesion site, and remarkable differences were illustrated between WT mice and ND littermates. Detailed analysis indicates that NCAM-mediated pathways may be involved in the activation of ERK at acute stages and bi-phasic upregulation of GAP-43 expression at acute and sub-acute stages after SCI to promote cell survival, outgrowth of regenerated axons, synaptogenesis, and function recovery.

Neuroproteomic methods in spinal cord injury

Spinal cord injury (SCI) is a major public health problem with no known effective treatment. Traumatic injury to the spinal cord initiates a host of pathophysiological events that are secondary to the initial insult leading to neuronal dysfunction and death; yet, the molecular mechanisms underlying its dysfunction are poorly understood. Furthermore, while use of imaging methods (e.g., computed tomography scans and magnetic resonance imaging) may help define injury severity and location, they do not elucidate biological mechanisms of SCI progression. The lack of comparable biomarkers for monitoring SCI makes accurate diagnosis and evaluation of SCI progression difficult. Spinal cord contusion is an extensively used SCI model in rats that best represents the etiology of SCI in humans. In this chapter, we describe a two-dimensional (2D) gel electrophoresis-based proteomic approach to investigate the injury-related differences in the proteome and phosphoproteome of spinal cord lesion epicenter at 24 h after spinal cord contusion in rats. The purpose of this study is to elucidate the mechanisms of acute spinal cord dysfunction, as well as discover novel biomarker candidates to evaluate the biological mechanisms of SCI progression and the injury severity.

Inhibition of MMP2/MMP9 after spinal cord trauma reduces apoptosis

STUDY DESIGN

Randomized controlled trial.

OBJECTIVE

To characterize the increase in gelatinase A (MMP2) activity after spinal cord injury (SCI) in the mouse model, and the effects of MMP2/MMP9 inhibition on apoptotic cells.

SUMMARY OF BACKGROUND DATA

Clinical consequences of SCI are due to a series of secondary injury cascades. Matrix metalloproteinases are thought play a key role in this, leading to apoptotic cell death.

METHODS

SCI via a drop tower in mice was used. MMP2 beta-gal reporter mice were used to quantify the level of MMP2 after SCI. In a follow-up experiment, mice which underwent SCI were randomized to daily SQ injections of MMP2/MMP9 inhibitor versus placebo. MMP2 levels were quantified and histology was performed with TUNEL and Luxol fast blue staining.

RESULTS

MMP2 transcription was significantly upregulated after SCI, by the beta-gal assay. Inhibition of MMP2/MMP9 activity after SCI led to statistically significant decreases in apoptosis within the zone of injury. There was a trend towards preservation of myelin by preserved luxol fast blue staining.

CONCLUSION

After SCI, MMP2 is upregulated along with neuron and glial cells apoptosis. The level of apoptosis could be reduced with MMP2/MMP9 inhibition. This supports MMP2 as cause for apoptosis after SCI with the potential for therapeutic intervention as apoptosis can be reduced with MMP2 inhibition.