salicylates and Nerve-Degeneration

The in vivo generation of .OH free radicals in specific brain regions can be measured by intracerebral microdialysis perfusion of salicylate, avoiding many of the pitfalls inherent in systemic administration of salicylate. Direct infusion of salicylate into the brain can minimize the hepatic hydroxylation of salicylate and its contribution to brain levels of 2,5-DHBA. Levels of 2,5-DHBA detected in the brain dialysate may reflect the .OH adduct plus some enzymatic hydroxylation of salicylate in the brain. After minimizing the contribution of enzyme and/or blood-borne 2,5-DHBA, the present data demonstrate the validity of the use of 2,3-DHBA and apparently 2,5-DHBA as indices of .OH formation in the brain. Therefore, intracranial microdialysis of salicylic acid and measurement of 2,3-DHBA appears to be a useful .OH trapping procedure for monitoring the time course of .OH generation in the extracellular fluid of the brain. These results indicate that nonenzymatic and/or enzymatic oxidation of the dopamine released by MPTP analogues in the extracellular fluid may play a key role in the generation of .OH free radicals in the iron-rich basal ganglia. Moreover, a site-specific generation of cytotoxic .OH free radicals and quinone/semiquinone radicals in the striatum may cause the observed lipid peroxidation, calcium overload, and retrograde degeneration of nigrostriatal neurons. This free-radical-induced nigral injury can be suppressed by antioxidants (i.e., U-78517F, DMSO, and deprenyl) and possibly hypothermia as well. In the future, this in vivo detection of .OH generation may be useful in answering some of the fundamental questions concerning the relevance of oxidants and antioxidants in neurodegenerative disorders during aging. It could also pave the way for the research and development of novel neuroprotective antioxidants and strategies for the early or preventive treatment of neurodegenerative disorders, such as Parkinson's disease (Wu et al., this issue), amyotrophic lateral sclerosis, head trauma, and possibly Alzheimer's cognitive dysfunction as well. In conclusion, this in vivo free-radical trapping procedure provides evidence to support a current working hypothesis that a site-specific formation of cytotoxic .OH free radicals in the basal ganglia may be one of the neurotoxic mechanisms underlying nigrostriatal degeneration and Parkinsonism caused by the dopaminergic neurotoxin MPTP. Addendum added in proof: The controversy concerning possible neuro

Topics: Animals; Antioxidants; Basal Ganglia; Corpus Striatum; Dopamine; Free Radical Scavengers; Free Radicals; Humans; Hydroxyl Radical; Melanins; MPTP Poisoning; Nerve Degeneration; Parkinson Disease; Rats; Salicylates; Selegiline; Substantia Nigra

Striatal neurons are highly vulnerable to hypoxia-ischemia (HI) in term newborns. In a piglet model of HI, striatal neurons develop oxidative stress and organelle disruption by 3-6 h of recovery and ischemic cytopathology over 6-24 h of recovery. We tested the hypothesis that early treatment with the antioxidants EUK-134 (a manganese-salen derivative that acts as a scavenger of superoxide, hydrogen peroxide, nitric oxide or NO and peroxynitrite) or edaravone (MCI-186, a scavenger of hydroxyl radical and NO) protects striatal neurons from HI. Anesthetized newborn piglets were subjected to 40 min of hypoxia and 7 min of airway occlusion. At 30 min after resuscitation, the piglets received vehicle, EUK-134 or edaravone. Drug treatment did not affect arterial blood pressure, blood gases, blood glucose or rectal temperature. At 4 days of recovery, the density of viable neurons in the putamen of vehicle-treated piglets was 12 ± 6% (±SD) of sham-operated control density. Treatment with EUK-134 increased viability to 41 ± 17%, and treatment with edaravone increased viability to 39 ± 19%. In the caudate nucleus, neuronal viability was increased from 54 ± 11% in the vehicle group to 78 ± 15% in the EUK-134 group and to 73 ± 13% in the edaravone group. Antioxidant drug treatment accelerated recovery from neurologic deficits and decreased oxidative and nitrative damage to nucleic acids. Treatment with EUK-134 reduced the HI-induced formation of protein carbonyl groups and tyrosine nitration at 3 h of recovery. We conclude that systemic administration of antioxidant agents by 30 min after resuscitation from HI can reduce oxidative stress and salvage neurons in the highly vulnerable striatum in a large-animal model of neonatal HI. Therefore, oxidative stress is an important mechanism for this injury, and antioxidant therapy is a rational, mechanism-based approach to neuroprotection in the newborn brain.

Topics: Animals; Animals, Newborn; Antioxidants; Antipyrine; Corpus Striatum; Edaravone; Free Radical Scavengers; Hypoxia-Ischemia, Brain; Nerve Degeneration; Neuroprotective Agents; Organometallic Compounds; Oxidative Stress; Salicylates; Swine

We previously demonstrated that elevation of astrocytic monoamine oxidase B (MAO-B) levels in a doxycycline (dox)-inducible transgenic mouse model following 14 days of dox induction results in several neuropathologic features similar to those observed in the Parkinsonian midbrain (Mallajosyula et al., 2008). These include a specific, selective and progressive loss of dopaminergic neurons of the substantia nigra (SN), selective decreases in mitochondrial complex I (CI) activity and increased oxidative stress. Here, we report that the temporal sequence of events following MAO-B elevation initially involves increased oxidative stress followed by CI inhibition and finally neurodegeneration. Furthermore, dox removal (DR) at days 3 and 5 of MAO-B induction was sufficient to arrest further increases in oxidative stress as well as subsequent neurodegenerative events. In order to assess the contribution of MAO-B-induced oxidative stress to later events, we compared the impact of DR which reverses the MAO-B increase with treatment of animals with the lipophilic antioxidant compound EUK-189. EUK-189 was found to be as effective as DR in halting downstream CI inhibition and also significantly attenuated SN DA cell loss as a result of astrocytic MAO-B induction. This suggests that MAO-B-mediated ROS contributes to neuropathology associated with this model and that antioxidant treatment can arrest further progression of dopaminergic cell death. This has implications for early intervention therapies.

Topics: Animals; Anti-Bacterial Agents; Antioxidants; Astrocytes; Disease Models, Animal; Disease Progression; Dopamine; Doxycycline; Electron Transport Complex I; Mesencephalon; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mitochondrial Diseases; Monoamine Oxidase; Nerve Degeneration; Neurons; Organometallic Compounds; Oxidative Stress; Parkinson Disease; Prognosis; Salicylates; Substantia Nigra; Time Factors; Treatment Outcome

Microglial cells, known to play key roles in neuroinflammation, can be immunotoxically eliminated from hippocampal slice cultures by treatment with saporin coupled to the microglial receptor Mac1. Considering microglial cells as a target for anti-inflammatory treatment we studied the effects of microglial depletion on anti-inflammatory treatment of mouse hippocampal slice cultures subjected to ischemia-like neurodegeneration, induced by oxygen-glucose deprivation (OGD). Hippocampal slice cultures, derived from 7-day-old mice and grown for 2 weeks, were divided into 8 groups: (1) control cultures; (2) sham-OGD cultures; (3) OGD cultures; (4) OGD cultures treated with triflusal during OGD; (5) microglia-depleted control cultures; (6) microglia-depleted sham-OGD cultures; (7) microglia-depleted OGD cultures; and (8) microglia-depleted OGD cultures treated with triflusal during OGD. The resulting neurodegeneration was quantified by densitometric measurements of cellular uptake of propidium iodide (PI), with focus on the hippocampal CA1 subfield. Subjection of regular cultures to OGD for 30 min induced a significant increase in PI uptake in the CA1 pyramidal cell layer, compared to control cultures. The presence of 100 microM triflusal during OGD protected against OGD-induced neurodegeneration, and reduced the number of OGD-induced NFkB positive-cells correspondingly. Cultures treated with the Mac1-saporin complex for 7 days displayed an almost total loss of microglial cells. When subjected to OGD after microglial depletion, these cultures displayed a significant increase in OGD-induced PI uptake compared to non-depleted cultures. The presence of triflusal during OGD of these cultures reduced neurodegeneration of the irrespective absence of microglia. In accordance with that, the presence of triflusal during OGD significantly inhibited the increase in the number of reactive microglia and proliferative cells in the CA1 pyramidal and dentate granule cell layers. We conclude that immunotoxic microglia depletion significantly increases the susceptibility of CA1 pyramidal cells to neurodegeneration and that the anti-inflammatory drug triflusal still can exert its neuroprotective role following depletion of microglia.

Topics: Analysis of Variance; Animals; Animals, Newborn; Cell Count; Cell Death; Cell Movement; Cell Proliferation; Dose-Response Relationship, Drug; Glucose; Hippocampus; Ischemia; Mice; Mice, Inbred C57BL; Microglia; Nerve Degeneration; Neurons; Neuroprotective Agents; NF-kappa B; Plant Lectins; Propidium; Salicylates; Tissue Culture Techniques

Extensive epidemiological data in humans and studies in animal models of Parkinson's disease (PD) suggest that sporadic forms of the disorder are not strictly genetic in nature but most likely because of combined environmental exposures over the period of the life-span coupled with increased genetic susceptibilities. Environmental paraquat and neonatal iron exposure have both been separately suggested as potential risk factors for sporadic forms of the disease. In this study, we demonstrate that combined environmental exposure to these two agents results in accelerated age-related degeneration of nigrostriatal dopaminergic neurons. Furthermore, pretreatment with the synthetic superoxide dismutase/catalase mimetic, EUK-189, significantly attenuated neuronal death mediated by combined paraquat and iron treatment. These findings support the notion that environmental PD risk factors may act synergistically to produce neurodegeneration associated with the disorder and that iron and paraquat may act via common oxidative stress-mediated mechanisms.

Topics: Aging; Animals; Cell Line; Cells, Cultured; Drug Synergism; Environmental Exposure; Herbicides; Iron; Male; Mice; Mice, Inbred C57BL; Nerve Degeneration; Neurons; Neuroprotective Agents; Organometallic Compounds; Paraquat; Parkinson Disease; Rats; Salicylates; Substantia Nigra; Superoxide Dismutase

Topics: Adenosine Triphosphatases; Adenosine Triphosphate; Animals; Calpain; Cell Death; Cell Survival; Cyclic N-Oxides; Free Radical Scavengers; Free Radicals; Iron; L-Lactate Dehydrogenase; Lipid Peroxidation; Nerve Degeneration; Nitrogen Oxides; PC12 Cells; Pyrophosphatases; Rats; Salicylates; Salicylic Acid; Thiobarbituric Acid Reactive Substances; Xanthine Oxidase

Topics: Aging; Audiometry; Deafness; Humans; Labyrinth Diseases; Labyrinthine Fluids; Meniere Disease; Nerve Degeneration; Organ of Corti; Perceptual Disorders; Prognosis; Salicylates