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

Nitroxidative Signaling Mechanisms in Pathological Pain

Tissue injury can initiate bidirectional signaling between neurons, glia, and immune cells that creates and amplifies pain. While the ability for neurotransmitters, neuropeptides, and cytokines to initiate and maintain pain has been extensively studied, recent work has identified a key role for reactive oxygen and nitrogen species (ROS/RNS; nitroxidative species), including superoxide, peroxynitrite, and hydrogen peroxide. In this review we describe how nitroxidative species are generated after tissue injury and the mechanisms by which they enhance neuroexcitability in pain pathways. Finally, we discuss potential therapeutic strategies for normalizing nitroxidative signaling, which may also enhance opioid analgesia, to help to alleviate the enormous burden of pathological pain.

Therapeutic potential of peroxynitrite decomposition catalysts: a patent review

INTRODUCTION

Peroxynitrite is a cytotoxic oxidant species implicated in a host of pathologies, including inflammatory and neurodegenerative diseases, cancer, radiation injury and chronic pain. With the recognition of the role of peroxynitrite in disease, numerous experimental and therapeutic tools have arisen to probe peroxyntirite's pathophysiological contribution and attenuate its oxidative damage. Peroxynitrite decomposition catalysts (PNDCs) are redox-active compounds that detoxify peroxynitrite by catalyzing its isomerization or reduction to nitrate or nitrite.

AREAS COVERED

This review discusses recent research articles and patents published 1995 - 2014 on the development and therapeutic use of PNDCs. Iron and manganese metalloporphyrin PNDCs attenuate the toxic effects of peroxynitrite and are currently being developed for clinical applications. Additionally, some Mn porphyrin-based PNDCs have optimized pharmaceutical properties such that they exhibit greater peroxynitrite selectivity. Other classes of PNDC agents, including bis(hydroxyphenyl)dipyrromethenes and metallocorroles, have demonstrated preclinical efficacy, oral availability and reduced toxicity risk.

EXPERT OPINION

Interest in the drug-like properties of peroxynitrite-neutralizing agents has grown with the realization that PNDCs will be powerful tools in the treatment of disease. The design of compounds with enhanced oral availability and peroxynitrite selectivity is a critical step toward the availability of safe, effective and selective redox modulators for the treatment of peroxynitrite-associated pathologies.

Abandon the mouse research ship? Not just yet!

Many preclinical studies in critical care medicine and related disciplines rely on hypothesis-driven research in mice. The underlying premise posits that mice sufficiently emulate numerous pathophysiologic alterations produced by trauma/sepsis and can serve as an experimental platform for answering clinically relevant questions. Recently, the lay press severely criticized the translational relevance of mouse models in critical care medicine. A series of provocative editorials were elicited by a highly publicized research report in the Proceedings of the National Academy of Sciences (PNAS; February 2013), which identified an unrecognized gene expression profile mismatch between human and murine leukocytes following burn/trauma/endotoxemia. Based on their data, the authors concluded that mouse models of trauma/inflammation are unsuitable for studying corresponding human conditions. We believe this conclusion was not justified. In conjunction with resulting negative commentary in the popular press, it can seriously jeopardize future basic research in critical care medicine. We will address some limitations of that PNAS report to provide a framework for discussing its conclusions and attempt to present a balanced summary of strengths/weaknesses of use of mouse models. While many investigators agree that animal research is a central component for improved patient outcomes, it is important to acknowledge known limitations in clinical translation from mouse to man. The scientific community is responsible to discuss valid limitations without overinterpretation. Hopefully, a balanced view of the strengths/weaknesses of using animals for trauma/endotoxemia/critical care research will not result in hasty discount of the clear need for using animals to advance treatment of critically ill patients.

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.

Simple biological systems for assessing the activity of superoxide dismutase mimics

SIGNIFICANCE

Half a century of research provided unambiguous proof that superoxide and species derived from it-reactive oxygen species (ROS)-play a central role in many diseases and degenerative processes. This stimulated the search for pharmaceutical agents that are capable of preventing oxidative damage, and methods of assessing their therapeutic potential.

RECENT ADVANCES

The limitations of superoxide dismutase (SOD) as a therapeutic tool directed attention to small molecules, SOD mimics, that are capable of catalytically scavenging superoxide. Several groups of compounds, based on either metal complexes, including metalloporphyrins, metallocorroles, Mn(II) cyclic polyamines, and Mn(III) salen derivatives, or non-metal based compounds, such as fullerenes, nitrones, and nitroxides, have been developed and studied in vitro and in vivo. Very few entered clinical trials.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Development of SOD mimics requires in-depth understanding of their mechanisms of biological action. Elucidation of both molecular features, essential for efficient ROS-scavenging in vivo, and factors limiting the potential side effects requires biologically relevant and, at the same time, relatively simple testing systems. This review discuses the advantages and limitations of genetically engineered SOD-deficient unicellular organisms, Escherichia coli and Saccharomyces cerevisiae as tools for investigating the efficacy and mechanisms of biological actions of SOD mimics. These simple systems allow the scrutiny of the minimal requirements for a functional SOD mimic: the association of a high catalytic activity for superoxide dismutation, low toxicity, and an efficient cellular uptake/biodistribution.

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.

Differential coordination demands in Fe versus Mn water-soluble cationic metalloporphyrins translate into remarkably different aqueous redox chemistry and biology

The different biological behavior of cationic Fe and Mn pyridylporphyrins in Escherichia coli and mouse studies prompted us to revisit and compare their chemistry. For that purpose, the series of ortho and meta isomers of Fe(III) meso-tetrakis-N-alkylpyridylporphyrins, alkyl being methyl to n-octyl, were synthesized and characterized by elemental analysis, UV/vis spectroscopy, mass spectrometry, lipophilicity, protonation equilibria of axial waters, metal-centered reduction potential, E(1/2) for M(III)P/M(II)P redox couple (M = Fe, Mn, P = porphyrin), kcat for the catalysis of O2(•-) dismutation, stability toward peroxide-driven porphyrin oxidative degradation (produced in the catalysis of ascorbate oxidation by MP), ability to affect growth of SOD-deficient E. coli, and toxicity to mice. Electron-deficiency of the metal site is modulated by the porphyrin ligand, which renders Fe(III) porphyrins ≥5 orders of magnitude more acidic than the analogous Mn(III) porphyrins, as revealed by the pKa1 of axially coordinated waters. The 5 log units difference in the acidity between the Mn and Fe sites in porphyrin translates into the predominance of tetracationic (OH)(H2O)FeP complexes relative to pentacationic (H2O)2MnP species at pH ∼7.8. This is additionally evidenced in large differences in the E(1/2) values of M(III)P/M(II)P redox couples. The presence of hydroxo ligand labilizes trans-axial water which results in higher reactivity of Fe relative to Mn center. The differences in the catalysis of O2(•-) dismutation (log kcat) between Fe and Mn porphyrins is modest, 2.5-5-fold, due to predominantly outer-sphere, with partial inner-sphere character of two reaction steps. However, the rate constant for the inner-sphere H2O2-based porphyrin oxidative degradation is 18-fold larger for (OH)(H2O)FeP than for (H2O)2MnP. The in vivo consequences of the differences between the Fe and Mn porphyrins were best demonstrated in SOD-deficient E. coli growth. On the basis of fairly similar log kcat(O2(•-)) values, a very similar effect on the growth of SOD-deficient E. coli was anticipated by both metalloporphyrins. Yet, while (H2O)2MnTE-2-PyP(5+) was fully efficacious at ≥20 μM, the Fe analogue (OH)(H2O)FeTE-2-PyP(4+) supported SOD-deficient E. coli growth at as much as 200-fold lower doses in the range of 0.1-1 μM. Moreover the pattern of SOD-deficient E. coli growth was different with Mn and Fe porphyrins. Such results suggested a different mode of action of these metalloporphyrins. Further exploration demonstrated that (1) 0.1 μM (OH)(H2O)FeTE-2-PyP(4+) provided similar growth stimulation as the 0.1 μM Fe salt, while the 20 μM Mn salt provides no protection to E. coli; and (2) 1 μM Fe porphyrin is fully degraded by 12 h in E. coli cytosol and growth medium, while Mn porphyrin is not. Stimulation of the aerobic growth of SOD-deficient E. coli by the Fe porphyrin is therefore due to iron acquisition. Our data suggest that in vivo, redox-driven degradation of Fe porphyrins resulting in Fe release plays a major role in their biological action. Possibly, iron reconstitutes enzymes bearing [4Fe-4S] clusters as active sites. Under the same experimental conditions, (OH)(H2O)FePs do not cause mouse arterial hypotension, whereas (H2O)2MnPs do, which greatly limits the application of Mn porphyrins in vivo.

Administration of a peroxynitrite decomposition catalyst into the bronchial artery attenuates pulmonary dysfunction after smoke inhalation and burn injury in sheep

Reactive nitrogen species such as peroxynitrite play a significant role in burn and smoke inhalation injury. The bronchial circulation increases more than 10-fold in response to this combination injury. We hypothesized that direct delivery of low-dose WW-85, a peroxynitrite decomposition catalyst, into the bronchial artery would attenuate burn- and smoke inhalation-induced acute lung injury. In adult female sheep (n = 17), the bronchial artery was cannulated in preparation surgery. After a 5- to 7-day recovery period, sheep were subjected to a burn (40% total body surface area, third degree) and inhalation injury (48 breaths of cotton smoke, <40°C). The animals were divided into three groups following the injury: (i) WW-85 group: 1 h after injury, WW-85 (0.002 mg/kg per hour) was continuously infused into the bronchial artery, n = 5; (ii) control group: 1 h after injury, an equivalent amount of saline was injected into the bronchial artery, n = 6; (iii) sham group: no injury, no treatment, same operation and anesthesia, n = 6. All animals were mechanically ventilated and fluid resuscitated equally. In the control group, the injury induced a severe deterioration of pulmonary oxygenation and shunting and an increase in pulmonary microvascular permeability toward sham. The injury was further associated with an increase in reactive nitrogen species in lung tissues of the control group. All these alterations were significantly attenuated in the WW-85 group. We demonstrated that a low dosage of WW-85 directly administered into the bronchial artery attenuated pulmonary dysfunction to the same extent as higher systemically administered doses in previous experiments. Our data strongly suggest that local airway production of peroxynitrite contributes to pulmonary dysfunction following smoke inhalation and burn injury.

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.

Acute molecular perturbation of inducible nitric oxide synthase with an antisense approach enhances neuronal preservation and functional recovery after contusive spinal cord injury

Inducible nitric oxide synthase (iNOS) is a key mediator of inflammation and oxidative stress produced during pathological conditions, including neurodegenerative diseases and central nervous system (CNS) injury. iNOS is responsible for the formation of high levels of nitric oxide (NO). The production of highly reactive and cytotoxic NO species, such as peroxynitrite, plays an important role in secondary tissue damage. We have previously demonstrated that acute administration of iNOS antisense oligonucleotides (ASOs) 3 h after moderate contusive spinal cord injury (SCI) potently inhibits iNOS-mediated increases in NO levels, leading to reduced blood-spinal cord barrier permeability, decreased neutrophil accumulation, and less neuronal cell death. In the current study we investigated if iNOS ASOs could also provide long-term (10-week) histological and behavioral improvements after moderate thoracic T8 contusive SCI. Adult rats were randomly assigned to three groups (n=10/group): SCI alone, SCI and mixed base control oligonucleotides (MBOs), or SCI and iNOS ASOs (200 nM). Oligonucleotides were administered by spinal superfusion 3 h after injury. Behavioral analysis (Basso-Beattie-Bresnahan [BBB] score and subscore) was employed weekly for 10 weeks post-SCI. Although animals treated with iNOS ASOs demonstrated no significant differences in BBB scores compared to controls, subscore analysis revealed a significant improvement in foot positioning, trunk stability, and tail clearance. Histologically, while no gross improvement in preserved white and gray matter was observed, greater numbers of surviving neurons were present adjacent to the lesion site in iNOS ASO-treated animals than controls. These results support the effectiveness of targeting iNOS acutely as a therapeutic approach after 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.

Effects of a potent peroxynitrite decomposition catalyst in murine models of endotoxemia and sepsis

Excessive free-radical production due to various bacterial components released during bacterial infection has been linked to cell death and tissue injury. Peroxynitrite is a highly reactive oxidant produced by the combination of nitric oxide (NO) and superoxide anion, which has been implicated in cell death and tissue injury in various forms of critical illness. Pharmacological decomposition of peroxynitrite may represent a potential therapeutic approach in diseases associated with the overproduction of NO and superoxide. In the present study, we tested the effect of a potent peroxynitrite decomposition catalyst in murine models of endotoxemia and sepsis. Mice were injected i.p. with LPS 40 mg/kg with or without FP15 [Fe(III) tetrakis-2-(N-triethylene glycol monomethyl ether)pyridyl porphyrin] (0.1, 0.3, 1, 3, or 10 mg/kg per hour). Mice were killed 12 h later, followed by the harvesting of samples from the lung, liver, and gut for malondialdehyde and myeloperoxidase measurements. In other subsets of animals, blood samples were obtained by cardiac puncture at 1.5, 4, and 8 h after LPS administration for cytokine (TNF-α, IL-1β, and IL-10), nitrite/nitrate, alanine aminotransferase, and blood urea nitrogen measurements. Endotoxemic animals showed an increase in survival from 25% to 80% at the FP15 doses of 0.3 and 1 mg/kg per hour. The same dose of FP15 had no effect on plasma levels of nitrite/nitrate. There was a reduction in liver and lung malondialdehyde in the endotoxemic animals pretreated with FP15, as well as in hepatic myeloperoxidase and biochemical markers of liver and kidney damage (alanine aminotransferase and blood urea nitrogen). In a bacterial model of sepsis induced by cecal ligation and puncture, FP15 treatment (0.3 mg/kg per day) significantly protected against mortality. The current data support the view that peroxynitrite is a critical factor mediating liver, gut, and lung injury in endotoxemia and septic shock: its pharmacological neutralization may be of therapeutic benefit.

The peroxynitrite catalyst WW-85 improves pulmonary function in ovine septic shock

Systemic inflammatory response syndrome is associated with excessive production of nitric oxide (NO·) and superoxide (O2), forming peroxynitrite, which in turn, acts as a terminal mediator of cellular injury by producing cell necrosis and apoptosis. We examined the effect of the peroxynitrite decomposition catalyst, WW-85, in a sheep model of acute lung injury and septic shock. Eighteen sheep were operatively prepared and randomly allocated to the sham, control, or WW-85 group (n = 6 each). After a tracheotomy, acute lung injury was produced in the control and WW-85 groups by insufflation of four sets of 12 breaths of cotton smoke. Then, a 30-mL suspension of live Pseudomonas aeruginosa bacteria (containing 2 - 5 × 10¹¹ colony-forming units) was instilled into the lungs according to an established protocol. The sham group received only the vehicle (30 mL saline). The sheep were studied in awake state for 24 h and ventilated with 100% oxygen. WW-85 was administered 1 h after injury as bolus infusion (0.1 mg/kg), followed by a continuous infusion of 0.02 mg·kg⁻¹·h⁻¹ until the end of the 24-h experimental period. Compared with injured but untreated controls, WW-85-treated animals had significantly improved gas exchange, reductions in airway obstruction, shunt formation, lung myeloperoxidase concentrations, lung malondialdehyde concentrations, lung 3-nitrotyrosine concentrations, and plasma nitrate-to-nitrite levels. Animals treated with WW-85 exhibited less microvascular leakage and improvements in pulmonary function. These results provide evidence that blockade of the nitric oxide-peroxynitrite pathway improves disturbances from septic shock, as demonstrated in a clinically relevant ovine experimental model.

The peroxynitrite catalyst WW-85 improves microcirculation in ovine smoke inhalation injury and septic shock

This prospective, randomized, controlled experimental study examined the effects of the peroxynitrite decomposition catalyst WW-85 on global hemodynamics and regional microvascular blood flow (RMBF) in an established ovine model of septic shock following severe smoke inhalation injury. Twenty-one sheep were randomized into a sham group (no injury), a control group (smoke/sepsis), and a treatment group (smoke/sepsis/WW-85; n=7 each). WW-85 was administered 1h after injury as a bolus (0.1 mg/kg), followed by a continuous infusion of 0.02 mg/kg/h RMBF was analyzed using colored microspheres. All control animals developed a hypotensive, hyperdynamic circulation and increased plasma levels of nitrate/-nitrite (NOx). All hemodynamic variables and NOx levels were significantly improved in the treatment group. In visceral organs of controls, blood flow to trachea, ileum, and spleen significantly increased (p<0.05). Blood flow to kidneys and pancreas significantly decreased (p<0.05). Treatment with WW-85 stabilized blood flow to ileum, spleen, and kidneys on baseline levels and was significantly improved compared to controls (p<0.05). Cerebral blood flow deteriorated in controls, but was significantly improved in cerebral cortex, cerebellum, pons, medulla oblongata, and thalamus (p<0.05) by WW-85. These results provide evidence that WW-85 blocks NO production, thereby improving cardiovascular function and microcirculation.

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.