Neuroprotection by the stable nitroxide 3-carbamoyl-proxyl during reperfusion in a rat model of transient focal ischemia

Cerium Oxide Nanoparticles Improve Outcome after In Vitro and In Vivo Mild Traumatic Brain Injury

Mild traumatic brain injury results in aberrant free radical generation, which is associated with oxidative stress, secondary injury signaling cascades, mitochondrial dysfunction, and poor functional outcome. Pharmacological targeting of free radicals with antioxidants has been examined as an approach to treatment, but has met with limited success in clinical trials. Conventional antioxidants that are currently available scavenge a single free radical before they are destroyed in the process. Here, we report for the first time that a novel regenerative cerium oxide nanoparticle antioxidant reduces neuronal death and calcium dysregulation after in vitro trauma. Further, using an in vivo model of mild lateral fluid percussion brain injury in the rat, we report that cerium oxide nanoparticles also preserve endogenous antioxidant systems, decrease macromolecular free radical damage, and improve cognitive function. Taken together, our results demonstrate that cerium oxide nanoparticles are a novel nanopharmaceutical with potential for mitigating neuropathological effects of mild traumatic brain injury and modifying the course of recovery.

In vivo redox metabolic imaging of mitochondria assesses disease progression in non-alcoholic steatohepatitis

Given the rising incidence of non-alcoholic fatty liver disease (NAFLD) in both adults and children, the development of a non-invasive diagnostic method for assessing disease progression to non-alcoholic steatohepatitis (NASH) has become an important research goal. Currently available non-invasive imaging technologies are only able to assess fat accumulation in the liver. Therefore, these methods are not suitable for a precise diagnosis of NASH. The standard diagnostic technique for NASH, liver biopsy, has several drawbacks, including the higher risk of complications that accompanies invasive procedures. Here, we demonstrated that in vivo mitochondrial redox metabolism was dramatically altered at an early stage, before histopathological changes, and NASH could be accurately diagnosed by in vivo dynamic nuclear polarization-magnetic resonance imaging, with carbamoyl-PROXYL as a molecular imaging probe. In addition, this technique was feasible for the diagnosis of NASH compared with histopathological findings from biopsies. Our data reveal a novel method for monitoring the dynamics of redox metabolic changes in NAFLD/NASH.

Kinetics of oxidation of nitrosodisulfonate anion radical with a metallo-superoxide

The metal bound superoxide in μ-superoxo-bis[pentaamminecobalt(III)](5+) (1) oxidizes the nitrosodisulfonate anion radical (NDS(2-)) by two electrons. Oxidized NDS(2-) quickly decomposes to SO(4)(2-) and NO. 1 is itself reduced to the corresponding hydroperoxo complex which also decomposes fast to Co(ii), NH(4)(+) ions and oxygen. 1.5 moles of volatile products formed per mole of 1 mixed with excess NDS(2-). In the absence of superoxide in a bridged complex, e.g. the μ-amido-bis[pentaamminecobalt(III)](5+) complex fails to oxidize the nitroxyl radicals, NDS(2-), TEMPO and 4-oxo TEMPO. With excess NDS(2-) over 1, the reaction is first-order with respect to [1], [NDS(2-)] and inverse first order in [H(+)]. The activation entropy, ΔS(≠), is largely negative, increased ionic strength decreased the rate and a Brønsted plot is fairly linear with a negative slope. Oxidant μ-superoxo-bis[(ethylenediamine)(diethylenetriamine)cobalt(III)](5+) has ligands sterically more crowded though more basic than ammonia in 1. It oxidizes NDS(2-) much more slowly. No solvent kinetic isotope effect (k(H(2)O/D(2)O)≈ 1) could be seen; a spin-adduct formation by the conjugate base of 1 followed by electron transfer is postulated.

Cellular effects of photogenerated oxidants and long-lived, reactive, hydroperoxide photoproducts

Reaction of radicals and singlet oxygen ((1)O(2)) with proteins results in both direct damage and the formation of long-lived reactive hydroperoxides. Elevated levels of protein hydroperoxide-derived products have been detected in multiple human pathologies, suggesting that these secondary oxidants contribute to tissue damage. Previous studies have provided evidence for protein hydroperoxide-mediated inhibition of thiol-dependent enzymes and modulation of signaling processes in isolated systems. In this study (1)O(2) and hydroperoxides have been generated in J774A.1 macrophage-like cells using visible light and the photosensitizer rose bengal, with the consequences of oxidant formation examined both immediately and after subsequent (dark-phase) incubation. Significant losses of GSH (≤50%), total thiols (≤20%), and activity of thiol-dependent proteins (GAPDH, thioredoxin, protein tyrosine phosphatases, creatine kinase, and cathepsins B and L; 10-50% inhibition) were detected after 1 or 2 min photo-oxidation. Non-thiol-dependent enzymes were not affected. In contrast, NADPH levels increased, together with the activity of glutathione reductase, glutathione peroxidase, and thioredoxin reductase; these increases may be components of a rapid global cytoprotective cellular response to stress. Neither oxidized thioredoxin nor radical-mediated protein oxidation products were detected at significant levels. Further decreases in thiol levels and enzyme activity occurred during dark-phase incubation, with this accompanied by decreased cell viability. These secondary events are ascribed to the reactions of long-lived hydroperoxides, generated by (1)O(2)-mediated reactions. Overall, this study provides novel insights into early cellular responses to photo-oxidative damage and indicates that long-lived hydroperoxides can play a significant role in cellular damage.

Tempol-mediated activation of latent iron regulatory protein activity prevents symptoms of neurodegenerative disease in IRP2 knockout mice

In mammals, two homologous cytosolic regulatory proteins, iron regulatory protein 1 (also known as IRP1 and Aco1) and iron regulatory protein 2 (also known as IRP2 and Ireb2), sense cytosolic iron levels and posttranscriptionally regulate iron metabolism genes, including transferrin receptor 1 (TfR1) and ferritin H and L subunits, by binding to iron-responsive elements (IREs) within target transcripts. Mice that lack IRP2 develop microcytic anemia and neurodegeneration associated with functional cellular iron depletion caused by low TfR1 and high ferritin expression. IRP1 knockout (IRP1(-/-)) animals do not significantly misregulate iron metabolism, partly because IRP1 is an iron-sulfur protein that functions mainly as a cytosolic aconitase in mammalian tissues and IRP2 activity increases to compensate for loss of the IRE binding form of IRP1. The neurodegenerative disease of IRP2(-/-) animals progresses slowly as the animals age. In this study, we fed IRP2(-/-) mice a diet supplemented with a stable nitroxide, Tempol, and showed that the progression of neuromuscular impairment was markedly attenuated. In cell lines derived from IRP2(-/-) animals, and in the cerebellum, brainstem, and forebrain of animals maintained on the Tempol diet, IRP1 was converted from a cytosolic aconitase to an IRE binding protein that stabilized the TfR1 transcript and repressed ferritin synthesis. We suggest that Tempol protected IRP2(-/-) mice by disassembling the cytosolic iron-sulfur cluster of IRP1 and activating IRE binding activity, which stabilized the TfR1 transcript, repressed ferritin synthesis, and partially restored normal cellular iron homeostasis in the brain.

Statistical mapping of effects of middle cerebral artery occlusion (MCAO) on blood flow and oxygen consumption in porcine brain

The volume of cerebral tissue perturbed in experimental models of middle cerebral artery occlusion (MCAO) can be highly variable. Thus, the territories of reduced cerebral blood flow (CBF) or oxygen consumption (CMRO(2)) following MCAO might properly be defined using statistical parametric mapping within a population. In order to establish such a method, we mapped CBF and CMRO(2) in 18 pigs with acute MCAO. Parametric maps were flipped about the axis of symmetry, and CBF and CMRO(2) in the infarcted hemisphere were calculated as percentages of the magnitudes in mirror-image pixels. There were log-linear relationships between the volumes of affected tissue and the percentages of normal CFB or CMRO(2). This graphical analysis showed that the volume of the core deficit was smaller for CBF that for CMRO(2), but expanded more rapidly with decreasing CBF deficit than did the corresponding volumes of reduced CMRO(2). Thus, acute changes in CBF and CMRO(2) following MCAO in the pig can be defined as probabilistic volumes.

Tempol, a Nitroxide Antioxidant, Improves Locomotor and Histological Outcomes after Spinal Cord Contusion in Rats

We have determined whether the nitroxide antioxidant, tempol, can oppose tissue loss and improve recovery of locomotor function following contusion injury of the spinal cord. Contusion injury was produced in rats at the level of T10 with a weight-drop device and locomotor recovery was determined with the 21-point Basso, Beattie and Bresnahan (BBB) scale. Locomotor function recovered progressively during the 6-week postinjury observation period and was significantly greater in tempol-treated (275 mg/kg i.p., 20 min postinjury) compared to vehicle-treated rats (final BBB scores: 9.1 versus 6.4). Similarly enhanced locomotor recovery was observed with doses of tempol in the range of 138-550, but not 69 mg/kg, and with injection at 48 h postinjury indicating a therapeutic time-window of at least several days. The extent of recovery correlated with measurements of sparing of spinal cord white matter in a region several millimeters in length extending rostrally from the contusion epicenter. In contrast, loss of gray matter was unaffected by tempol treatment. Since tempol acts by scavenging reactive oxygen species (ROS) such as superoxide and hydroxyl radicals, the improved locomotor recovery and spared spinal cord tissue following contusion injury provides evidence of a direct role of ROS-mediated neurodegeneration in spinal cord injury.

Factors influencing nitroxide reduction and cytotoxicity in vitro

Nitroxides have been shown to be effective antioxidants, radiation protectors, and redox-active probes for functional electron paramagnetic resonance (EPR) imaging. More recently, the nitroxide 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-N-oxyl (Tempol) has been shown to exert differential cytotoxicity to tumor compared with normal cell counterparts. Nitroxides are readily reduced in tissues to their respective hydroxylamines, which exhibit less cytotoxicity in vitro and do not provide radiation protection or an EPR-detectable signal for imaging. In order to better understand factors that influence nitroxide reduction, the rate of reduction of Tempol in mouse and human cell lines and in primary cultures of tumor cells was measured using EPR spectroscopy. Additionally, the cytotoxicity of high concentrations of Tempol and the hydroxylamine of Tempol (Tempol-H) was evaluated in wild-type and glucose-6-phosphate dehydrogenase (G6PD)-deficient Chinese hamster ovary cells. The results show that in general Tempol was reduced at a faster rate when cells were under hypoxic compared with aerobic conditions. Neither depletion of intracellular glutathione nor treatment of cells with sodium cyanide influenced Tempol reduction rates. G6PD-deficient cells were found to reduce Tempol at a significantly slower rate than wild-type cells. Likewise, Tempol-induced cytotoxicity was markedly less for G6PD-deficient cells compared with wild-type cells. Tempol-H exhibited no cytotoxicity to either cell type. Tempol-mediated cytotoxicity was enhanced by glutathione depletion and inhibition of 6-phosphogluconate dehydrogenase in wild-type cells, but was unaltered in G6PD-deficient cells. Collectively, the results indicate that while the bioreduction of Tempol can be influenced by a number of factors, the hexose monophosphate shunt appears to be involved in both nitroxide reduction as well as cytotoxicity induced by high levels of exposure to Tempol.

Application of in vivo ESR spectroscopy to measurement of cerebrovascular ROS generation in stroke

This study used an in vivo ESR spectroscopy/spin probe technique to measure directly the generation of reactive oxygen species (ROS) in the brain after cerebral ischemia-reperfusion. Transient middle cerebral artery occlusion (MCAO) was induced in rats by inserting a nylon thread into the internal carotid artery for 1 h. The in vivo generation of ROS and its location in the brain were analyzed from the enhanced ESR signal decay data of three intra-arterially injected spin probes with different membrane permeabilities. The ESR signal decay of the probe with intermediate permeability was significantly enhanced 30 min after reperfusion following MCAO, whereas no enhancement was observed with the other probes or in the control group. The enhanced in vivo signal decay was significantly suppressed by superoxide dismutase (SOD). Brain damage was barely discernible until 3 h of reperfusion, and was clearly suppressed with the probe of intermediate permeability. The antioxidant MCI-186 completely suppressed the enhanced in vivo signal decay after transient MCAO. These results clearly demonstrate that ROS are generated at the interface of the cerebrovascular cell membrane when reperfusion follows MCAO in rats, and that the ROS generated during the initial stages of transient MCAO cause brain injury.