Prevention of ischemia/reperfusion-induced alterations in synaptosomal membrane-associated proteins and lipids by N-tert-butyl-alpha-phenylnitrone and difluoromethylornithine

The protective effect of melatonin on brain ischemia and reperfusion in rats and humans: In vivo assessment and a randomized controlled trial

Carotid endarterectomy (CEA) is the treatment of choice for carotid stenosis. Some patients develop ischemia and reperfusion (I/R) injury after CEA. This study was designed to investigate the neuroprotective effects of melatonin on I/R injury in both rats and humans. To this end, 36 male rats were evaluated, and a double-blind randomized controlled trial (RCT) including 60 patients was performed. A rat model of middle cerebral artery occlusion was used to mimic cerebral I/R. After 2 hour of occlusion and 24 hour of reperfusion, blood samples and brain tissues were harvested for further assessments. Compared with the vehicle treatment, melatonin decreased the expression of nuclear factor κ light-chain-enhancer of activated B cells (NF-κB) and S100 calcium-binding protein β (S100β) (P < 0.05) and markedly increased the expression of nuclear erythroid 2-related factor 2 (Nrf2), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) (P < 0.05). The participants in the RCT took 6 mg/d melatonin orally from 3 days before surgery to 3 days after surgery. Blood samples were drawn at the following times: baseline; pre-anesthesia; carotid reconstruction completion; and 6, 24, and 72 hour after CEA. Compared with the oral placebo treatment, melatonin decreased the expression of NF-κB, tumor necrosis factor-α, interleukin-6 (IL-6), and S100β (P < 0.05) and increased the expression of Nrf2, SOD, CAT, and GPx (P < 0.05) in patients after CEA. Our findings suggested that melatonin could ameliorate brain I/R injury after CEA and that this outcome was essentially due to the antioxidant and anti-inflammatory effects of melatonin.

The antioxidative property of melatonin against brain ischemia

INTRODUCTION

This review briefly summarizes some of the large amount of data documenting the ability of melatonin to limit molecular and organ tissue damage in neural ischemia-reperfusion injury (stroke), where free radicals are generally considered as being responsible for much of the resulting tissue destruction.

AREA COVERED

Melatonin actions that have been identified include its ability to directly neutralize a number of toxic reactants and stimulate antioxidative enzymes. Furthermore, several of its metabolites such as N(1)-acetyl-N(2)-formyl-5- methoxykynuramine (AFMK) and N(1)-acetyl-5-methoxykynuramine (AMF), are themselves scavengers suggesting that there is a cascade of reactions that greatly increase the efficacy of melatonin. Expert Commentary: However, the mechanisms by which melatonin is protective in such widely diverse areas of the cell and different organs are likely not yet all identified.

Identification of nitrated proteins in Alzheimer's disease brain using a redox proteomics approach

Nitric oxide (NO) has been implicated in the pathophysiology of a number of neurodegenerative diseases including Alzheimer's disease (AD). In the present study, using a proteomics approach, we identified enolase, glyceraldehyde-3-phosphate dehydrogenase, ATP synthase alpha chain, carbonic anhydrase-II, and voltage-dependent anion channel-protein as the targets of nitration in AD hippocampus, a region that shows a extensive deposition of amyloid beta-peptide, compared with the age-matched control brains. Immunoprecipitation and Western blotting techniques were used to validate the correct identification of these proteins. Our results are discussed in context of the role of oxidative stress as one of the important mechanisms of neurodegeneration in AD.

The role of superoxide dismutase and α-tocopherol in the development of seizures and kindling induced by pentylenetetrazol - influence of the radical scavenger α-phenyl-N-tert-butyl nitrone

Previous experiments have shown that the generation of free hydroxyl radicals in rat brain homogenates is increased following pentylenetetrazol (PTZ) kindling. The present study was performed in order to evaluate the involvement of endogeneous radical defence systems as the superoxide dismutase (SOD) and the level of alpha-tocopherol, an important lipid-soluble and membrane-bound antioxidant in brain homogenate of rats after acute seizure and kindling induced by PTZ. The activities of the total SOD were significantly reduced after acute seizure and tend towards an enhancement in kindled animals. Western blot analysis shows an upregulation of Mn-SOD in rat brain homogenates after kindling. The level of the chain-breaking antioxidant alpha-tocopherol was reduced in acutely convulsing rats and was not modified in kindled rats. Second, we studied the influence of exogeneously supplied radical scavenger alpha-phenyl-N-tert-butyl-nitrone (PBN) on seizure and kindling following PTZ treatment. After a single injection of PTZ at a dose evoking clonic-tonic seizures, PBN did not modify either the formation of free hydroxyl radicals measured by the levels of 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA or the susceptibility to PTZ. In the kindling group, subchronic treatment with PBN (over a period of 4 weeks) prevented the increase in the formation of free hydroxyl radicals, and the susceptibility to PTZ was transiently decreased during the development of kindling, but PBN did not influence the susceptibility to PTZ in fully kindled rats. Pretreatment with PBN increased the activities of total SOD and the protein content of Mn-SOD and decreased the level of alpha-tocopherol in comparison to saline controls. The results suggest that the formation of free hydroxyl radicals is not reflected by an enhanced susceptibility to PTZ classified according to the modified RACINE scale. Additionally, it may be assumed that the increased generation of hydroxyl radicals in kindled animals is not primary caused by an exhaustion of both the defence systems measured. Adaptive mechanisms, as the induction of Mn-SOD, may be taken into consideration to counteract oxidative stress-mediated free radical formation.

Melatonin ameliorates neurologic damage and neurophysiologic deficits in experimental models of stroke

This review summarizes the numerous reports that have documented the neuroprotective actions of melatonin in experimental models of ischemia/reperfusion injury (stroke). In these investigations, which have used three species (rat, gerbil, and cat), melatonin was universally found to reduce brain damage that normally occurs as a consequence of the temporary interruption of blood flow followed by the reflow of oxygenated blood to the brain. The exogenous administration of melatonin in these experimental stroke models reduced infarct volume, lowered the frequency of apoptosis, increased the number of surviving neurons, reduced reactive gliosis, lowered the oxidation of neural lipids and oxidatively damaged DNA, induced bcl-2 gene expression (the activity of which improves cell survival), upregulated excision repair cross-complementing factor 6 (an essential gene for preferential DNA excision repair), restrained poly(ADP ribose) synthetase (which depletes cellular NAD resulting in the loss of ATP) activity, and improved neurophysiologic outcomes. Under no circumstances did melatonin exacerbate the damage associated with ischemia/reperfusion injury. As well as the beneficial pharmacologic actions of melatonin, several studies show that a relative deficiency of endogenous melatonin exaggerates neural damage due to stroke; this suggests that even physiologic concentrations of melatonin normally serve to protect the brain against damage. The primary action to explain melatonin's protective effects may relate to its ubiquitous direct and indirect antioxidative actions, although other beneficial functions of melatonin are not precluded.

The antioxidants alpha-lipoic acid and N-acetylcysteine reverse memory impairment and brain oxidative stress in aged SAMP8 mice

Oxidative stress may play a crucial role in age-related neurodegenerative disorders. Here, we examined the ability of two antioxidants, alpha-lipoic acid (LA) and N-acetylcysteine (NAC), to reverse the cognitive deficits found in the SAMP8 mouse. By 12 months of age, this strain develops elevated levels of Abeta and severe deficits in learning and memory. We found that 12-month-old SAMP8 mice, in comparison with 4-month-old mice, had increased levels of protein carbonyls (an index of protein oxidation), increased TBARS (an index of lipid peroxidation) and a decrease in the weakly immobilized/strongly immobilized (W/S) ratio of the protein-specific spin label MAL-6 (an index of oxidation-induced conformational changes in synaptosomal membrane proteins). Chronic administration of either LA or NAC improved cognition of 12-month-old SAMP8 mice in both the T-maze footshock avoidance paradigm and the lever press appetitive task without inducing non-specific effects on motor activity, motivation to avoid shock, or body weight. These effects probably occurred directly within the brain, as NAC crossed the blood-brain barrier and accumulated in the brain. Furthermore, treatment of 12-month-old SAMP8 mice with LA reversed all three indexes of oxidative stress. These results support the hypothesis that oxidative stress can lead to cognitive dysfunction and provide evidence for a therapeutic role for antioxidants.

Increased protein oxidation and decreased creatine kinase BB expression and activity after spinal cord contusion injury

Traumatic injury to the spinal cord triggers several secondary effects, including oxidative stress and compromised energy metabolism, which play a major role in biochemical and pathological changes in spinal cord tissue. Free radical generation and lipid peroxidation have been shown to be early events subsequent to spinal cord injury. In the present study, we demonstrated that protein oxidation increases in rat spinal cord tissue after experimental injury. As early as h after injury, the level of protein carbonyls at the injury epicenter was significantly higher than in control (169%, p < 0.05) and increased gradually over the next 4 weeks to 1260% of control level. Both caudal and rostral parts of the injured spinal cord demonstrated a mild increase of protein carbonyls by 4 weeks postinjury (135-138%, p < 0.05). Immunocytochemical analysis of protein carbonyls in the spinal cord cross-sections showed increased protein carbonyl immunoreactivity in the epicenter section compared to rostral and caudal sections of the same animal or control laminectomy animals. Increased protein carbonyl formation in damaged spinal cord tissue was associated with changes in activity and expression of an oxidative sensitive enzyme, creatine kinase BB, which plays an important role in the maintenance of ATP level in the CNS tissue. Damage to CK function in the CNS may severely aggravate the impairment of energy metabolism. The results of our study indicate that events associated with oxidative damage are triggered immediately after spinal cord trauma but continue to occur over the subsequent 4 weeks. These results suggest that antioxidant therapeutic strategies may be beneficial to lessen the consequences of the injury and potentially improve the restoration of neurological function.

Heterogeneity affecting outcome from acute stroke therapy: making reperfusion worse

BACKGROUND

Stroke patients are heterogeneous not only with respect to etiology but also in terms of preexisting clinical conditions. Approximately one fifth of patients with acute stroke are hyperglycemic and/or have had a recent infectious or inflammatory condition. Summary of Review-- Experimental research indicates that these factors can alter and accelerate the evolution of stroke and reperfusion injury, although these effects are complex and some may have a favorable impact. Both conditions involve activation of inflammatory and reactive oxygen mechanisms. In addition, hyperglycemia has concomitant deleterious vascular and metabolic effects that worsen infarct size and encourage hemorrhagic transformation in reperfusion models. Clinical data are less extensive but in general support an adverse impact on outcome.

CONCLUSIONS

After examining these data in detail, we concluded that the presence of these clinical conditions could assist in identification of those at increased risk for complications of reperfusion therapy. Furthermore, consideration of these factors may provide a rational basis for combination therapy and improve the clinical relevance of experimental stroke models.

Elevated oxidative stress in models of normal brain aging and Alzheimer's disease

Age-associated neurodegenerative disorders are becoming more prevalent as the mean age of the population increases in the United States over the next few decades. Both normal brain aging and Alzheimer's disease (AD) are associated with oxidative stress. Our laboratory has used a wide variety of physical and biochemical methods to investigate free radical oxidative stress in several models of aging and AD. Beta-amyloid (A beta), the peptide that constitutes the central core of senile plaques in AD brain, is associated with free radical oxidative stress and is toxic to neurons. This review summarizes some of our studies in aging and A beta-associated free radical oxidative stress and on the modulating effects of free radical scavengers on neocortical synaptosomal membrane damage found in aging and A beta-treated systems.

Molecular mechanisms of ischemic neuronal injury

Brain ischemia triggers a complex cascade of molecular events that unfolds over hours to days. Identified mechanisms of postischemic neuronal injury include altered Ca(2+) homeostasis, free radical formation, mitochondrial dysfunction, protease activation, altered gene expression, and inflammation. Although many of these events are well characterized, our understanding of how they are integrated into the causal pathways of postischemic neuronal death remains incomplete. The primary goal of this review is to provide an overview of molecular injury mechanisms currently believed to be involved in postischemic neuronal death specifically highlighting their time course and potential interactions.

Effect of exogenous and endogenous antioxidants on 3-nitropionic acid-induced in vivo oxidative stress and striatal lesions: insights into Huntington's disease

3-Nitropropionic acid (3-NP) is an irreversible inhibitor of complex II in the mitochondria. 3-NP toxicity has gained acceptance as an animal model of Huntington's disease (HD). In the present study, we confirmed that rats injected with 3-NP (20 mg/kg, i.p., daily for 4 days) exhibit increased oxidative stress in both striatum and cortical synaptosomes as well as lesions in the striatum. Synaptosomal membrane proteins from rats injected with 3-NP exhibited a decrease in W/S ratio, the relevant electron paramagnetic resonance (EPR) parameter used to determine levels of protein oxidation, and western blot analysis for protein carbonyls revealed direct evidence of increased synaptosomal protein oxidation. Treatment of rats with the brain-accessible free radical spin trap 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO; 30 mg/kg, i.p., daily 2 h before 3-NP injection) or with N-acetylcysteine (NAC; 100 mg/kg, i.p., daily 2 h before 3-NP injection), a known glutathione precursor, before 3-NP treatments protects against oxidative damage induced by 3-NP as measured by EPR and western blot analysis for protein carbonyls. Furthermore, both DEMPMPO and NAC treatments before 3-NP administration significantly reduce striatal lesion volumes. These data suggest oxidative damage is a prerequisite for striatal lesion formation and that antioxidant treatment may be a useful therapeutic strategy against 3-NP neurotoxicity and perhaps against HD as well.

Review: Alzheimer's amyloid beta-peptide-associated free radical oxidative stress and neurotoxicity

Alzheimer's disease, the major dementing disorder of the elderly that affects over 4 million Americans, is related to amyloid beta-peptide, the principal component of senile plaques in Alzheimer's disease brain. Oxidative stress, manifested by protein oxidation and lipid peroxidation, among other alterations, is a characteristic of Alzheimer's disease brain. Our laboratory united these two observations in a model to account for neurodegeneration in Alzheimer's disease brain, the amyloid beta-peptide-associated oxidative stress model for neurotoxicity in Alzheimer's disease. Under this model, the aggregated peptide, perhaps in concert with bound redox metal ions, initiates free radical processes resulting in protein oxidation, lipid peroxidation, reactive oxygen species formation, cellular dysfunction leading to calcium ion accumulation, and subsequent neuronal death. Free radical antioxidants abrogate these findings. This review outlines the substantial evidence from multiidisciplinary approaches for amyloid beta-peptide-associated free radical oxidative stress and neurotoxicity and protection against these oxidative processes and cell death by free radical scavengers. In addition, we review the strong evidence supporting the notion that the single methionine residue of amyloid beta-peptide is vital to the oxidative stress and neurotoxicological properties of this peptide. Further, we discuss studies that support the hypothesis that aggregated soluble amyloid beta-peptide and not fibrils per se are necessary for oxidative stress and neurotoxicity associated with amyloid beta-peptide.

3-nitropropionic acid induced in vivo protein oxidation in striatal and cortical synaptosomes: insights into Huntington's disease

3-nitropropionic acid (3-NP) administered systemically daily for 4 days to rats inhibits mitochondrial oxidative phosphorylation and induces selective lesions in the striatum in a manner reminiscent of Huntington's disease (HD). To investigate the potential oxidative nature of these lesions, rats were injected with 3-NP (20 mg/kg, i.p. daily for 4 days) and subsequently isolated brain synaptosomal membranes were examined for evidence of oxidative stress. Brain synaptosomal membrane proteins from rats injected with 3-NP exhibited a decreased in W/S ratio, the relevant electron paramagnetic resonance (EPR) parameter used to determine levels of protein oxidation (76% of control), and Western blot analysis for protein carbonyls revealed direct evidence of increased synaptosomal membrane protein oxidation (248% of control). Similar results were obtained in synaptosomes isolated from striatum and from cerebral cortex, demonstrating that the oxidative changes are not restricted to the lesion site. Moreover, increased oxidative stress was evident prior to the appearance of morphological lesions. These data are consistent with the hypothesis that 3-NP-induced striatal lesions, and perhaps those in HD, are associated with oxidative processes.

Identification of components of Prunus africana extract that inhibit lipid peroxidation

Extractive and chromatographic separations were performed on V-1326, a chloroform extract from the bark of Prunus africana (also referred to as Pygeum africanum), which is used to treat the symptoms associated with benign prostate hyperplasia (BPH). The relative amounts of eleven identified constituents in crude V-1326 and in separated fractions were determined using gas chromatographic analysis. The ability of V-1326 and its separated fractions to inhibit ferrous ion-induced stimulation of lipid peroxidation in microsomal preparations from rabbit livers was evaluated. The extract, V-1326, and fractions containing high levels of myristic acid potently inhibited lipid peroxidation.

Fatty acid profiles in normal and obstructed rabbit bladder smooth muscle and mucosa

Partial bladder outlet obstruction results in progressive loss in contractile and specific cellular and subcellular membrane functions. There is evidence that ischemic activation of proteolytic and lipolytic enzymes play a major role in the etiology of bladder dysfunction secondary to partial outlet obstruction. The specific aims of the current study were to determine the fatty acid profiles in normal rabbit bladder smooth muscle and mucosa and to determine the effect of partial outlet obstruction on the distribution and content of free and total fatty acids. Fatty acids were isolated by extraction from obstructed and normal bladder smooth muscle and mucosal homogenates, and samples were analyzed by gas chromatography. All samples contained palmitic, stearic, oleic, linoleic, and arachidonic acids. A 100% increase in total fatty acid concentration was observed in the obstructed bladder muscle tissue relative to normal bladders, although the concentration of total arachidonic acid remained constant in the two groups. Significantly higher levels of free arachidonic acid were observed in the obstructed bladder muscle group compared to the normal group. No changes were observed in fatty acid concentrations or distributions in bladder mucosa. These data show that fatty acid composition is altered as a result of bladder obstruction and support the idea that obstruction increases the activity of lipase activity and/or decreases acyl transferase activity. Neurourol. Urodynam. 18:697-711, 1999.

Effect of α-phenyl-N-tert-butylnitrone on diabetes and lipid peroxidation in BB rats

Oxygen free radicals have been shown to interfere with pancreatic islet beta cell function and integrity, and have been implicated in autoimmune type 1 diabetes. We hypothesized that the spontaneous autoimmune type 1 diabetes of the BB rat would be prevented by in vivo administration of a free-radical spin trap, α-phenyl-N-tert-butylnitrone (PBN). Twenty-eight diabetes-prone (BBdp) and 13 non-diabetes-prone (BBn) rats received PBN (10 mg/kg) subcutaneously twice daily, and 27 BBdp and 12 BBn rats received saline as controls. Rats were treated from age 47 ± 6 days until diabetes onset or age 118 ± 7 days. PBN caused no growth, biochemical, or hematological side effects. Sixteen control BBdp rats became diabetic (BBd, mean age 77 ± 6 days) and six demonstrated impaired glucose tolerance (IGT rats). The incidence of diabetes and IGT was not different in PBN-treated BBdp rats. Saline-treated rats showed no differences in pancreatic malondialdehyde (MDA) contents of BBd, IGT rats, and the BBdp that did not develop diabetes, versus BBn rats (2.38 ± 0.35 nmoL/g). Among rats receiving PBN, BBn had lower pancreatic MDA than BBd and IGT rats (1.38 ± 0.15 vs. 1.88 ± 0.15 and 2.02 ± 0.24 nmoL/g, p < 0.05), but not than BBdp rats (1.78 ± 0.12 nmoL/g, ns). BBn rats receiving PBN also had lower pancreatic MDA than the saline controls (p < 0.05). Thus, PBN is remarkably nontoxic and is able to decrease MDA in the absence of the autoimmune process, but does not prevent diabetes. A combination of PBN with other complementary antioxidant agents may hold better promise for disease prevention.Key words: α-phenyl-N-tert-butylnitrone, type 1 diabetes mellitus, BB rats, lipid peroxidation, malondialdehyde, spin traps.

Antioxidants protect against reactive oxygen species associated with adriamycin-treated cardiomyocytes

Adriamycin (ADM) is a broad-spectrum antineoplastic antibiotic used to treat cancer patients. However, the usefulness of this drug is presently limited by the development of a dose-dependent cardiotoxicity. A current hypothesis for the ADM-induced cardiotoxicity is the production of reactive oxygen radicals by the drug. We utilized the fluorescent indicator 2',7'-dichlorodihydrofluorescein diacetate (DCFH/DA), in which fluorescence appears if reactive oxygen species (ROS) are present, to investigate the ability of ADM to generate reactive oxygen species and the potential protective effect of antioxidants in a cultured cardiomyocyte model. All three of the antioxidants (alpha-phenyl-tert-butyl nitrone (PBN), trolox, and 5-aminosalicylic acid (5-ASA)) tested in our ADM-treated myocytes provided protection against the oxidative stress induced by the drug. These findings suggest that antioxidants modulate ADM-induced oxidative stress, and they are discussed in terms of a possible therapeutic strategy in the prevention of cardiotoxicity resulting from ADM administration.

Structural and functional changes in proteins induced by free radical-mediated oxidative stress and protective action of the antioxidants N-tert-butyl-alpha-phenylnitrone and vitamin E

The free radical theory of aging proposes that reactive oxygen species (ROS) cause oxidative damage over the lifetime of the subject. It is the cumulative and potentially increasing amount of accumulated damage that accounts for the dysfunctions and pathologies seen in normal aging. We have previously demonstrated that both normal rodent brain aging and normal human brain aging are associated with an increase in oxidative modification of proteins and in changes in plasma membrane lipids. Several lines of investigation indicate that one of the likely sources of ROS is the mitochondria. There is an increase in oxidative damage to the mitochondrial genome in aging and a decreased expression of mitochondrial mRNA in aging. We have used a multidisciplinary approach to the characterization of the changes that occur in aging and in the modeling of brain aging, both in vitro and in vivo. Exposure of rodents to acute normobaric hyperoxia for up to 24 h results in oxidative modifications in cytosolic proteins and loss of activity for the oxidation-sensitive enzymes glutamine synthetase and creatine kinase. Cytoskeletal protein spin labeling also reveals synaptosomal membrane protein oxidation following hyperoxia. These changes are similar to the changes seen in senescent brains, compared to young adult controls. The antioxidant spin-trapping compound N-tert-butyl-alpha-phenylnitrone (PBN) was effective in preventing all of these changes. In a related study, we characterized the changes in brain protein spin labeling and cytosolic enzyme activity in a series of phenotypically selected senescence-accelerated mice (SAMP), compared to a resistant line (SAMR1) that was derived from the same original parents. In general, the SAM mice demonstrated greater oxidative changes in brain proteins. In a sequel study, a group of mice from the SAMP8-sensitive line were compared to the SAMR1-resistant mice following 14 days of daily PBN treatment at a dose of 30 mg/kg. PBN treatment resulted in an improvement in the cytoskeletal protein labeling toward that of the normal control line (SAMR1). The results of these and related studies indicate that the changes in brain function seen in several different studies may be related to the progressive oxidation of critical brain proteins and lipids. These components may be critical targets for the beneficial effects of gerontotherapeutics both in normal aging and in disease of aging.

The free radical antioxidant vitamin E protects cortical synaptosomal membranes from amyloid beta-peptide(25-35) toxicity but not from hydroxynonenal toxicity: relevance to the free radical hypothesis of Alzheimer's disease

Amyloid beta-peptide (Abeta) is a key factor in the neurotoxicity of Alzheimer's disease (AD). Recent research has shown that Abeta-mediated neurotoxicity involves free radicals and that Abeta peptides can initiate multiple membrane alterations, including protein oxidation and lipid peroxidation, eventually leading to neuronal cell death. Research also has emphasized the role of 4-hydroxynonenal (HNE), a downstream product of lipid peroxidation, in being able to mimic some of the effects of Abeta peptides. In the current investigation, electron paramagnetic resonance (EPR) studies of spin labeled cortical synaptosomal membrane proteins has been employed to study conformational changes in proteins, spectrophotometric methods have been used to measure protein carbonyl content, and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for mitochondrial function has been used to study the effect of vitamin E on samples that were treated with Abeta or HNE. The free radical dependence of beta-amyloid-associated toxicity was confirmed by the ability of the free radical scavenger vitamin E to prevent the toxic effects of Abeta. In contrast, HNE was still toxic in the presence of vitamin E. These results support our Abeta-associated free radical model for neurotoxicity in AD brain and are discussed with reference to potential therapeutic strategies for AD.

Mechanism of brain protection by nitroxide radicals in experimental model of closed-head injury

Reactive oxygen-derived species were previously implicated in mediation of post-traumatic brain damage; however, the efficacy of traditional antioxidants in preventing/reversing the damage is sometimes limited. The present work focused on the mechanisms underlying the neuroprotective activity of cell permeable, nontoxic, antioxidants, namely stable nitroxide radicals in an experimental model of rat closed-head injury. Brain damage was induced by the weight-drop method and the clinical status was evaluated according to a neurological severity score at 1 h and 24 h, where the difference between these scores reflects the extent of recovery. The metal chelator deferoxamine as well as three nitroxide derivatives, differing in hydrophilicity and charge, and one hydroxylamine (a reduced nitroxide) facilitated the clinical recovery and decreased the brain edema. The nitroxides, but neither the hydroxylamine nor deferoxamine, protected the integrity of the blood-brain barrier. Superoxide dismutase also improved the clinical recovery but did not affect brain edema or the blood-brain barrier. The results suggest that by switching back and forth between themselves, the nitroxide and hydroxylamine act catalytically as self-replenishing antioxidants, and protect brain tissue by terminating radical-chain reactions, oxidizing deleterious metal ions, and by removal of intracellular superoxide.

Abeta25-35 induces rapid lysis of red blood cells: contrast with Abeta1-42 and examination of underlying mechanisms

Amyloid beta-peptide (A beta) is produced by many different cell types and circulates in blood and cerebrospinal fluid in a soluble form. In Alzheimer's disease (AD), A beta forms insoluble fibrillar aggregates that accumulate in association with cells of the brain parenchyma and vasculature. Both full-length A beta (A beta1-40/42) and the A beta25-35 fragment can damage and kill neurons by a mechanism that may involve oxidative stress and disruption of calcium homeostasis. Circulating blood cells are exposed to soluble A beta1-40/42 and may also be exposed to A beta aggregates associated with the luminal surfaces of cerebral microvessels. We therefore examined the effects of A beta25-35 and A beta1-42 on human red blood cells (RBCs) and report that A beta25-35, in contrast to A beta1-42, induces rapid (10-60 min) lysis of RBCs. The mechanism of RBC lysis by A beta25-35 involved ion channel formation and calcium influx, but did not involve oxidative stress because antioxidants did not prevent cell lysis. In contrast, A beta1-42 induced a delayed (4-24 h) damage to RBCs which was attenuated by antioxidants. The damaging effects of both A beta25-35 and A beta1-42 towards RBCs were completely prevented by Congo red indicating a requirement for peptide fibril formation. A beta1-42 induced membrane lipid peroxidation in RBC, and basal levels of lipid peroxidation in RBCs from AD patients were significantly greater than in age-matched controls, suggesting a possible role for A beta1-42 in previously reported alterations in RBCs from AD patients.

Effect of 2-cyclohexene-1-one-induced glutathione diminution on ischemia/reperfusion-induced alterations in the physical state of brain synaptosomal membrane proteins and lipids

Glutathione is able to protect membrane proteins from oxidative stress. In ischemia/reperfusion injury, free radicals cause synaptosomal membrane protein and lipid oxidation that is prevented by the free radical scavenger N-tert-butyl-alpha-phenylnitrone (Hall N. C. et al. (1995) Neuroscience 64, 81-89; 69, 591-600). We wondered if diminution of glutathione would lead to further membrane alterations. Accordingly, the effects of glutathione depletion, by intraperitoneal administration of 2-cyclohexene-1-one, on the physical state of cortical synaptosomal membrane proteins and lipids, with and without global ischemia/reperfusion, were studied in vivo and in vitro in adult and aged gerbils utilizing electron paramagnetic resonance spectrometry. 2-Cyclohexene-1-one (100 mg/kg, i.p.) was administered 30 min prior to 10-min ischemia followed by 1 or 14 h reperfusion. This glutathione reduction agent was also administered to gerbils under the same temporal schedule in the absence of ischemia and compared to untreated controls. Synaptosomal membranes were labeled with a protein-specific spin label, 2,2,6,6-tetramethyl-4-maleimidopiperidine-1-oxyl, or a lipid-specific spin probe, 5-doxylstearic acid. There were no significant changes in the physical state of the lipid portion of synaptosomal membranes when comparing ischemia reperfusion and 2-cyclohexene-1-one-treated ischemia reperfusion in either the adult or aged gerbils. However, glutathione depletion without ischemia/reperfusion caused significant changes in the physical state of the protein portion of cortical synaptosomal membranes in both the adult and aged models. Glutathione depletion, without ischemia/reperfusion, in the adult model showed a maximum change at 3 h that returned to control values by 14 h. In contrast, the aged model showed significant changes at 1 h reperfusion, which did not return to control values by 14 h reperfusion. Glutathione depletion combined with ischemia/reperfusion caused initial protein change in both adult and aged models at 1 h reperfusion, which did not return toward control values by 14 h reperfusion. The results of this study suggest that glutathione depletion increases the severity of membrane protein damage associated with ischemia/reperfusion injury.

Free radical oxidation of brain proteins in accelerated senescence and its modulation by N-tert-butyl-alpha-phenylnitrone

According to the free radical theory of aging, reactive oxygen species cause oxidative damage, proposed to be an underlying factor of the aging process. In the current study, we have used electron paramagnetic resonance spin labeling, measurements of protein carbonyl content, an index of protein oxidation, and determination of the activity of glutamine synthetase (an oxidatively sensitive enzyme) to report that cortical synaptosomal membranes from the senescence accelerated-prone (SAMP8) mouse showed structural characteristics of free radical oxidative stress relative to the senescence accelerated-resistant (SAMR1) mouse. The SAMP8 mouse exhibited a decrease in the relevant EPR parameter consistent with oxidative stress (P < 0.002), a decreased glutamine synthetase activity (P < 0.05), and an increased protein carbonyl content (P < 0.01) compared with these parameters in the SAMR1 mouse. Further, because free radical trapping compounds have been demonstrated to extend maximum life span and improve cognition in SAMP8 mice, we investigated the protective nature of the known free radical scavenger, N-tert-butyl-alpha-phenylnitrone (PBN), on the physical state of cortical synaptosomal membrane proteins. For 14 days, SAMR1 and SAMP8 mice were injected with 30 mg/kg PBN while the controls were injected with the corresponding volume of saline. Characteristic of less oxidized systems, cortical synaptosomal membranes from the PBN-injected SAMP8 mouse exhibited a return toward normal values of the relevant EPR parameter [the M1 = +1 low-field weakly immobilized line/M1 = +1 low-field strongly immobilized line (W/S) ratio of a protein-specific spin label] (P < 0.001) compared with that from saline-injected SAMP8 mice. In SAMR1 mice, in contrast to SAMP8, there was no significant change in the conformation of membrane proteins or protein carbonyl content of cortical synaptosomal membranes from the PBN-injected and saline-injected SAMR1 mice, showing that PBN itself did not induce conformational changes in cortical synaptosomal membrane proteins. The results are discussed with reference to the use of free radical scavengers as potential anti-aging agents.

Structural alterations in synaptosomal membrane-associated proteins and lipids by transient middle cerebral artery occlusion in the cat

We have previously reported that ischemia reperfusion injury results from free radical generation following transient global ischemia, and that this radical induced damage is evident in the synaptosomal membrane of the gerbil. [Hall et al, (1995) Neuroscience 64: 81-89]. In the present study we have extended these observations to transient focal ischemia in the cat. We prepared synaptosomal membranes from frontal, parietal-temporal, and occipital regions of the cat cerebral cortex with reperfusion times of 1 and 3 hours following 1 hour right middle cerebral artery occlusion. The membranes were selectively labeled with protein and lipid specific paramagnetic spin labels and analyzed using electron paramagnetic resonance spectrometry. There were significant motional changes of both the protein and lipid specific spin labels in the parietal-temporal and occipital regions with 1 hour reperfusion; but, both parameters returned to control values by 3 hours reperfusion. No significant changes were observed in the normally perfused frontal pole at either reperfusion time. These results support the argument that free radicals play a critical role in cell damage at early reperfusion times following ischemia.