Memory impairments and oxidative stress in the hippocampus of in-utero cocaine-exposed rats

We examined whether significant oxidative stress is induced in the brain of juvenile rats exposed in utero to cocaine, and contributes to their mnesic difficulties. We measured nitric oxide generation, using electron paramagnetic resonance, and the thiobarbituric acid reactive species as specific indexes of lipid peroxidation. Both nitric oxide and lipid peroxidation were elevated in the hippocampus of in-utero cocaine-exposed rats as compared with control animals. In-utero cocaine-exposed rats developed significant learning impairments in the water-maze, shown by probe test retrieval deficits. In parallel, behavioural sessions resulted in increases of thiobarbituric acid reactive species levels only in control animals. Therefore, in-utero cocaine exposure resulted in a significant oxidative stress in basal conditions, which may be related to impaired learning ability.     

S-nitrosothiols and nitric oxide,but not sodium nitroprusside,protect nigrostriatal dopamine neurons against iron-induced oxidative stress in vivo

Intranigral infusion of ferrous citrate (4.2 nmol) induced an acute lipid peroxidation in the substantia nigra and a chronic dopamine depletion in the striatum of rat nigrostriatal system. Coinfusion of 8.4 nmol nitric oxide donors such as S-nitroso-glutathione (GSNO) and S-nitroso-N-acetylpenicillamine (SNAP) or nitric oxide (∼2 nmol) protected nigrostriatal neurons against iron-induced lipid peroxidation and associated oxidative injury. However, sodium nitroprusside (SNP, 8.4 nmol) augmented dopamine depletion caused by ferrous citrate because SNP is a ferricyanide complex. The present in vivo results indicate that nitric oxide and S-nitrosothiols are antioxidants which can protect brain dopamine neurons against oxidant stress/damage. © 1996 Wiley-Liss, Inc.     

Oxidative stress is associated with region-specific neuronal death during thiamine deficiency.

Thiamine deficiency (TD) is a model of chronic impairment of oxidative metabolism and selective neuronal loss. TD leads to region-specific neuronal death and elevation of inducible nitric oxide synthase (iNOS) in macrophages/microglia in mouse brain. Identification of the initial site of neuronal death in the submedial thalamic nucleus allowed us to test the role of iNOS and oxidative stress in TD-induced neuronal death. The pattern of neuronal loss, which begins after 9 days of TD, overlapped with induction of the oxidative stress marker heme oxygenase-1 (HO-1) in microglia. Neuronal death and microglial HO-1 induction spread to engulf the whole thalamus after 11 days of TD. As in past studies, reactive iron and ferritin accumulated in microglia beginning on day 10. The lipid peroxidation product, 4-hydroxynonenal (HNE) accumulated in the remaining thalamic neurons only after 11 days of TD. These responses were not likely mediated by iNOS because HO-1 induction and HNE accumulation were comparable in iNOS knockout mice and wild-type controls. These results show that region and cell specific oxidative stress is associated with selective neurodegeneration during TD. Thus, TD is a useful model to help elucidate neuron-microglial interaction in neurodegenerative diseases associated with oxidative stress.     

Neurodegeneration in multiple sclerosis: the role of oxidative stress and excitotoxicity

In multiple sclerosis (MS) disability results from neuronal and axonal loss, the hallmark of neurodegenerative diseases (ND). Neurodegeneration is initiated by microglia activation and mediated by oxidative stress and excitotoxicity. The same sequence of events has been consistently observed in MS. However, microglia activation correlates with a marked cell infiltration in MS but not in ND. In both pathological states, peroxynitrite is the common initiating factor of oxidative stress and excitotoxicity and is thus a potential interesting therapeutic target. Oxidative stress leads to multiple lipid and protein damages via peroxidation and nitration processes. The pathomechanisms of excitotoxicity are complex involving glutamate overload, ionic channel dysfunction, calcium overload, mitochondriopathy, proteolytic enzyme production and activation of apoptotic pathways. The inflammatory component in MS is important for the design of therapeutic strategies. Inflammation not only causes axonal and neuronal loss but it also initiates the degenerative cascade in the early stage of MS. Potent anti-inflammatory agents are now available and it is not unreasonable to think that an early blockade of inflammatory processes might also block associated degenerative mechanisms and delay disability progression. The development of neuroprotective drugs is more problematic. Indeed, given the multiple and parallel mechanisms involved in neurodegeneration, modulation of a single specific pathway will likely yield a partial benefit if any.     

Glutathione elevation by gamma-glutamyl cysteine ethyl ester as a potential therapeutic strategy for preventing oxidative stress in brain mediated by in vivo administration of adriamycin: Implication for chemobrain

Oxidative stress in heart and brain by the cancer chemotherapeutic drug adriamycin (ADR), used for treating solid tumors, is well established. Long-term treatment with ADR in breast cancer patients has led to symptoms of cardiomyopathy. Less well recognized, but increasingly well documented, is cognitive dysfunction. After chemotherapy, free radical-mediated oxidative stress has been reported in both heart and brain. We recently showed a significant increase in protein oxidation and lipid peroxidation in brain isolated from mice injected intraperitonially (i.p) with ADR. Systemic administration of ADR also induces tumor necrosis factor-alpha (TNF-alpha), which leads to production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in brain. Circulating TNF also causes mitochondrial dysfunction, leading to apoptotic pathways in brain. Inducible nitric oxide synthase also plays a role in ADR-induced TNF-mediated neurotoxicity. In addition, we previously showed a significant decrease in glutathione (GSH) levels in brain isolated from ADR injected mice, along with increased expression of multidrug-resistant protein-1 (MRP-1), glutathione-S-transferase (GST), glutathione peroxidase (GPx), and glutathione reductase (GR). There was a significant decrease in activity of brain GST. The present study was designed to test the hypothesis that, by elevating brain levels of GSH, the brain would be protected against oxidative stress in ADR-injected mice. gamma-Glutamyl cysteine ethyl ester (GCEE), a precursor of glutathione, injected i.p. (150 mg/ kg body weight) 4 hr prior ADR injection (20 mg/kg body weight) led to significantly decreased protein oxidation and lipid peroxidation in subsequently isolated mice brain compared with brain isolated from ADR-injected mice without GCEE. The GSH levels were restored to the level of brain isolated from saline-injected mice. Furthermore, the enzyme activity of GST was increased in brain isolated from ADR-injected mice previously injected with GCEE compared with the brain isolated from ADR-injected mice previously injected with saline. These results are discussed with regard to potential pharmacological prevention of brain cognitive dysfunction in patients receiving ADR chemotherapy.     

Intermittent Hypobaric Hypoxia Induces Neuroprotection in Kainate-Induced Oxidative Stress in Rats

Severe hypoxia induces oxidative stress, which can lead to brain injury. In this study, we wanted to determine whether intermittent hypobaric hypoxia induces oxidative stress in the brain. In adult rats exposed to 380 mmHg in a hypobaric chamber for 3 h/day for 6 days, we determined the levels of malondialdehyde and nitric oxide derivatives in the brain, which indicated that there was no oxidative stress. The levels of N-acetylaspartate indicated that there was no neuronal loss or mitochondrial dysfunction and finally because apoptotic proteins such as caspase-3 and nuclear factor-kappa B (NF-κB) were not activated, apoptosis was probably not induced. The increase in the expression of erythropoietin (EPO) in the brain of rats exposed to hypoxia confirms the efficacy of the method used to induce hypoxia in the brain. Because EPO have antioxidant effects on the brain, the results suggest that intermittent hypoxia can increase the antioxidant capacity of the brain. This effect of intermittent hypoxia was studied using the systemic administration of kainate, as a model of brain oxidative stress. Kainate treatment induces oxidative stress in the brain, which is measured by an increase in lipid peroxidation and nitric oxide. Furthermore, in rats treated with kainate, both caspase-3 and NF-κB activity increased. However, in rats previously exposed to intermittent hypobaric hypoxia, 3 h per day for 6 days, the effect of kainate treatment resulted in the reduction of both oxidative stress and apoptotic activity. This study demonstrates that intermittent hypobaric hypoxia can increase brain antioxidant capacity in rats and induces neuroprotection in kainate-induced oxidative injury.     

Neuroprotective strategies in parkinson’s disease: protection against progressive nigral damage induced by free radicals

Brain undergoes neurodegeneration when excess free radicals overwhelm antioxidative defense systems during senescence, head trauma and/or neurotoxic insults. A site-specific accumulation of ferrous citrate-iron complexes in the substantia nigra dopaminergic neurons could lead to exaggerated dopamine turnover, dopamine auto-oxidation, free radical generation, and oxidant stress. Eventually, this iron-catalyzed dopamine auto-oxidation results in the accumulation of neuromelanin, a progressive loss of nigral neurons, and the development of Parkinson's disease when brain dopamine depletion is greater than 80%. Emerging evidence indicates that free radicals such as hydroxyl radicals ((.-)OH) and nitric oxide ((.-)NO) may play opposite role in cell and animal models of parkinsonism. (.-)OH is a cytotoxic oxidant whereas oNO is an atypical neuroprotective antioxidant. (.-)NO and S-nitrosoglutathione (GSNO) protect nigral neurons against oxidative stress caused by 1-methyl-4-phenylpyridinium (MPP(+)), dopamine, ferrous citrate, hemoglobin, sodium nitroprusside and peroxynitrite. MPP(+), the toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), increases the nigral uptake of iron complexes and dopamine overflow leading to the generation of (.-)OH, protein oxidation, lipid peroxidation, and associated retrograde degeneration. In addition to GSNO, MPP(+)-induced oxidative neurotoxicity can be prevented by antioxidants including selegiline, 7-nitroindazole, 17beta-estradiol, melatonin, alpha-phenyl-tert-butylnitrone and U78517F. Similar to selegiline, 7-nitroindazole is a MAO-B inhibitor, which blocks the bio-activation of MPTP and oxidative stress. Freshly prepared but not light exposed, (.-)NO-exhausted GSNO is about 100 times more potent than the classic antioxidant glutathione. Via S-nitrosylation, GSNO also inhibits proteolysis and cytotoxicity caused by caspases and HIV-1 protease. Furthermore, in addition to protection against serum deprivation stress, the induction of neuronal NOS1 in human cells increases tolerance to MPP(+)-induced neuro-toxicity since newly synthesized (.-)NO prevents apoptosis possibly through up-regulation of bcl-2 and down regulation of p66(shc). In conclusion, reactive oxygen species are unavoidable by-products of iron-catalyzed dopamine auto-oxidation, which can initiate lipid peroxidation, protein oxidation, DNA damage, and nigral loss, all of which can be prevented by endogenous and exogenous (.-)NO. Natural and man-made antioxidants can be employed as part of preventative or neuroprotective treatments in Parkinson's disease and perhaps dementia complexes as well. For achieving neuroprotection and neuro-rescue in early clinical parkinsonian stages, a cocktail therapy of multiple neuroprotective agents may be more effective than the current treatment with extremely high doses of a single antioxidative agent.     

Myelophil ameliorates brain oxidative stress in mice subjected to restraint stress

We evaluated the pharmacological effects of Myelophil, a 30% ethanol extract of a mix of Astragali Radix and Salviae Radix, on oxidative stress-induced brain damage in mice caused by restraint stress. C57BL/6 male mice (eight weeks old) underwent daily oral administration of distilled water, Myelophil (25, 50, or 100 mg/kg), or ascorbic acid (100 mg/kg) 1 h before induction of restraint stress, which involved 3 h of immobilization per day for 21 days. Nitric oxide levels, lipid peroxidation, activities of antioxidant enzymes (superoxide dismutase, catalase, and glutathione redox system enzymes), and concentrations of adrenaline, corticosterone, and interferon-γ, were measured in brain tissues and/or sera. Restraint stress-induced increases in nitric oxide levels (serum and brain tissues) and lipid peroxidation (brain tissues) were significantly attenuated by Myelophil treatment. Restraint stress moderately lowered total antioxidant capacity, catalase activity, glutathione content, and the activities of glutathione reductase, glutathione peroxidase, and glutathione S-transferase; all these responses were reversed by Myelophil. Myelophil significantly attenuated the elevated serum concentrations of adrenaline and corticosterone and restored serum and brain interferon-γ levels. Moreover, Myelophil normalized expression of the genes encoding monoamine oxidase A, catechol-O-methyltransferase, and phenylethanolamine N-methyltransferase, which was up-regulated by restraint stress in brain tissues. These results suggest that Myelophil has pharmacological properties protects brain tissues against stress-associated oxidative stress damage, perhaps in part through regulation of stress hormones.     

Genetic elimination of eNOS reduces secondary complications of experimental subarachnoid hemorrhage

Delayed complications of subarachnoid hemorrhage (SAH) such as angiographic vasospasm, cortical spreading ischemia, microcirculatory dysfunction, and microthrombosis are reported in both patients and animal models of SAH. We demonstrated previously that SAH is associated with increased oxidative stress in the brain parenchyma, and that this correlates with dysfunction of endothelial nitric oxide synthase (eNOS) (homodimeric uncoupling). Uncoupling of eNOS exacerbated oxidative stress and enhanced nitric oxide (NO) depletion, and was associated with multiple secondary complications such as microthrombosis, neuronal apoptosis, and release of reactive oxygen species. Thus, we hypothesized that genetic abbrogation of eNOS would confer a beneficial effect on the brain after SAH. Using a prechiasmatic injection model of SAH, we show here that eNOS knockout (KO) significantly alleviates vasospasm of the middle cerebral artery and reduces superoxide production. Endothelial nitric oxide synthase KO also affected other nitric oxide synthase isoforms. It significantly increases neuron nitric oxide synthase expression but has no effect on inducible nitric oxide synthase. Endothelial nitric oxide synthase KO decreases Zn²⁺ release after SAH, reduces microthrombi formation, and prevent neuronal degeneration. This work is consistent with our findings where, after SAH, increased oxidative stress can uncouple eNOS via Zn²⁺ thiolate oxidation, or theoretically by depletion or oxidation of tetrahydrobiopterin, resulting in a paradoxical release of superoxide anion radical, further exacerbating oxidative stress and microvascular damage.     

Spatial and temporal patterns of oxidative stress in the brain of gerbils submitted to different duration of global cerebral ischemia

The present study was undertaken to examine spatial and temporal patterns of oxidative stress rate in the brain of Mongolian gerbils submitted to different duration of global ischemia/reperfusion. The common carotid arteries of gerbils were occluded for 5, 10, or 15 min. We followed the temporal ischemia-induced oxidative stress rate, the most important factor that exacerbates brain damage by reperfusion, starting from 24 h up to 28 days after reperfusion. The spatial ischemia-induced oxidative stress distribution was measured parallely in different brain regions: forebrain cortex, striatum, hippocampus and cerebellum. Post-ischemic effects were followed in vivo by monitoring the neurological status of whole animals and at the intracellular level by standard biochemical assays in different brain regions. We measured superoxide production, superoxide dismutase activity, nitric oxide production, index of lipid peroxidation, and reduced glutathione. Our results revealed a pattern of dynamic changes in each oxidative stress parameter that corresponded with ischemia duration in all tested brain structures. The highest levels were obtained in the first 24 h after the insult. After that, they slowly returned to nearly control values 28 days after reperfusion (with the exception of SOD activity that returned to control values at fourth day after reperfusion). The most sensitive oxidative stress parameter was index of lipid peroxidation. Our study confirmed spatial distribution of ischemia-induced oxidative stress. Tested brain structures showed different sensitivity to each oxidative stress parameter, although their basal levels were similar. These new findings could be valuable for creation and strategy of post-ischemic therapy.     

In vivo protective effects of ferulic acid ethyl ester against amyloid-beta peptide 1-42-induced oxidative stress

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the deposition of amyloid-beta peptide (Abeta), a peptide that as both oligomers and fibrils is believed to play a central role in the development and progress of AD by inducing oxidative stress in brain. Therefore, treatment with antioxidants might, in principle, prevent propagation of tissue damage and neurological dysfunction. The aim of the present study was to investigate the in vivo protective effect of the antioxidant compound ferulic acid ethyl ester (FAEE) against Abeta-induced oxidative damage on isolated synaptosomes. Gerbils were injected intraperitoneally (i.p.) with FAEE or with dimethylsulfoxide, and synaptosomes were isolated from the brain. Synaptosomes isolated from FAEE-injected gerbils and then treated ex vivo with Abeta(1-42) showed a significant decrease in oxidative stress parameters: reactive oxygen species levels, protein oxidation (protein carbonyl and 3-nitrotyrosine levels), and lipid peroxidation (4-hydroxy-2-nonenal levels). Consistent with these results, both FAEE and Abeta(1-42) increased levels of antioxidant defense systems, evidenced by increased levels of heme oxygenase 1 and heat shock protein 72. FAEE led to decreased levels of inducible nitric oxide synthase. These results are discussed with potential therapeutic implications of FAEE, a brain accessible, multifunctional antioxidant compound, for AD involving modulation of free radicals generated by Abeta.     

Antioxidant effect of acetylsalicylic and salicylic acid in rat brain slices subjected to hypoxia

Acetylsalicylic acid (ASA) reduces the incidence of ischemic stroke mainly through its antithrombotic action; however, it also has a direct neuroprotective effect. The present study was designed to evaluate the effect of ASA on oxidative stress and the activity of nitric oxide synthase (NOS) in an in vitro model of hypoxia in rat brain slices. Rat brain slices were perfused with nitrogen (hypoxia) for a maximum of 120 min, after which we measured lipid peroxidation, glutathione levels, glutathione-related enzyme activities, and constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) activities. In brain tissue subjected to hypoxia, ASA reduced oxidative stress and iNOS activity (all increased by hypoxia), but only when used at higher concentrations. The effects of salicylic acid (SA) were similar but more intense than were those of ASA. After oral administration, the effect of SA was much greater than that of ASA, and the decrease in cell death with SA was seen much more clearly. In view of the greater effect of SA compared to ASA on changes in oxidative stress parameters in a model of hypoxia, and higher brain concentrations of SA when it is administered alone than when ASA is given (undetectable levels), we conclude that SA plays an important role in the cytoprotective effect in brain tissue after ASA administration.     

D-2-hydroxyglutaric acid induces oxidative stress in cerebral cortex of young rats

Large amounts of d-2-hydroxyglutaric acid (DGA) accumulate in d-2-hydroxyglutaric aciduria (D-2-OHGA), an inherited neurometabolic disorder characterized by severe neurological dysfunction and cerebral atrophy. Despite the significant brain abnormalities, the neurotoxic mechanisms of brain injury in this disease are virtually unknown. In this work, the in vitro effect of DGA on various parameters of oxidative stress was investigated; namely chemiluminescence, thiobarbituric acid-reactive substances (TBA-RS), total radical-trapping antioxidant potential (TRAP), total antioxidant reactivity (TAR) and the activities of the antioxidant enzymes catalase, glutathione peroxidase and superoxide dismutase in cerebral cortex from 30-day-old-rats. DGA significantly increased chemiluminescence and TBA-RS and decreased TAR values in the cortical supernatants. In contrast, TRAP and the antioxidant enzyme activities were not altered by the metabolite. Furthermore, the DGA-induced increase of TBA-RS was fully prevented by the free radical scavengers ascorbic acid plus Trolox (water-soluble alpha-tocopherol) and attenuated by the inhibitor of nitric oxide synthase Nomega-nitro-L-arginine methyl ester (L-NAME), suggesting the role of superoxide, hydroxyl and nitric oxide radicals in this action. The data indicate a stimulation of lipid peroxidation through the production of free radicals and a reduction of the brain capacity to efficiently modulate the damage associated with the enhanced generation of free radicals by DGA. In the case that these findings also occur in human D-2-OHGA, it is feasible that oxidative stress may be involved in the pathophysiology of the brain injury observed in patients with this disease.     

Implications for atypical antioxidative properties of manganese in iron-induced brain lipid peroxidation and copper-dependent low density lipoprotein conjugation.

Our group recently observed that manganese prevents oxidative brain injury in the iron-induced parkinsonian animal model. It has also been suggested that manganese retards while copper promotes the development of atherosclerosis. In this report, we provide further evidence to support a controversial notion that manganese is an atypical antioxidant. Among transition metals, Cu2+ and Fe2+ (0.1 to 125 microM), but not Mn2+, converted hydrogen peroxide to reactive hydroxyl radicals via the Fenton reaction at pH 7.4. Iron's pro-oxidative rate is relatively slow, but it is accelerated further by ascorbate (50 microM) in 37 degrees C Dulbecco's phosphate buffered saline. Moreover, Mn2+ (0-80 microM) concentration dependently retarded diene conjugation of human low density lipoproteins stimulated by 5 microM Cu2+. This new result is consistent with our recent finding that Mn2+ (0 to 20 microM) does not initiate brain lipid peroxidation while it inhibits iron-induced peroxidation of polyunsaturated fatty acids. These unexpected manganese results are somewhat at odds with a prominent theory that manganese is a prooxidative transition metal. Furthermore, iron and copper induced free radical generation and lipid peroxidation are suppressed by lowering the incubation temperature; this suggests that hypothermia may decrease the oxidative stress and damage in vivo. In conclusion, normal dietary intake of manganese may protect cells and neurons from oxidant stress through the inhibition of propagation of lipid peroxidation caused by hydroxyl radicals generated by pro-oxidative transition metals such as iron and copper. Potential therapeutical uses of manganese, manganese SOD mimetics and hypothermia for protecting brain neurons and vascular endothelial cells against oxidative stress and damage have been successfully demonstrated in both animal models and clinical trials.     

Antioxidant and Anti-Apoptotic Activity of Vasoactive Intestinal Peptide (VIP) Against 6-Hydroxy Dopamine Toxicity in the Rat Corpus Striatum

6-Hydroxydopamine (6-OHDA) is an oxidative stress neurotoxin, which is oxidized in neurons, causes respiratory inhibition, and induces free radical formation and oxidative stress. Therefore, a 6-OHDA-induced Parkinson's disease (PD) experimental model can be used to test a candidate molecule for use as an antioxidant that could be a promising therapeutic for treating Parkinson's disease. Recent studies have shown that vasoactive intestinal peptide (VIP) might be a good candidate agent for the treatment of PD. In this study, the anti-apoptotic and antioxidant actions of VIP were investigated using the 6-OHDA-lesioned rat model for PD. Twenty-four young adult Sprague–Dawley rats were used. The rats were separated into the following groups: group I (n = 8), sham operated; group II (n = 8), 6-OHDA lesioned; group III (n = 8), 6-OHDA lesioned + i.p. VIP—injected (25 ng/kg) every 2 days for 15 days. The first i.p. injection of VIP was made 1 h after the intrastriatal 6-OHDA microinjection. Antioxidant enzymatic activity [super oxide dismutase (SOD) and catalase (CAT)], lipid peroxidation, nitric oxide and DNA fragmentation were measured from homogenates isolated from the corpus striatum. SOD, CAT, malondialdehyde, and DNA fragmentation were measured using a spectrophotometer, and nitric oxide (NO) levels were measured by capillary electrophoresis. 6-OHDA significantly induced oxidative stress, lipid peroxidation, and DNA fragmentation in the corpus striatum of rats. VIP significantly protected neuronal tissue from oxidative stress and apoptosis by reducing lipid peroxidation and DNA fragmentation. 6-OHDA toxicity did not cause significant changes in NO production in the corpus striatum. However, VIP treatment significantly reduced NO levels in brain tissue.     

Effect of Zen Meditation on serum nitric oxide activity and lipid peroxidation

This study was designed to investigate the effect of Zen Meditation on serum nitric oxide activity (NO) and oxidative stress (lipid peroxidation). The experimental group included 20 subjects who had practiced the Zen Meditation program in Meditation Center located in Seoul, South Korea. The control group included 20 subjects who did not practice any formal stress management technique and were age and sex matched with experimental group. To provide an assessment of nitric oxide production, the serum level of nitrate/nitrite was determined using the Griess reagent. Malondialdehyde (MDA) concentration was measured as a convenient index of lipid peroxidation by thiobarbituric acid (TBA) method. Meditation group showed a significant higher level of serum nitrate+nitrite concentration and a significant reduced level of serum malondialdehyde (MDA) than control group. A comprehensive randomized controlled trial should be performed to prove the causal relationship between meditation and level of nitric oxide or oxidative stress in reducing cardiovascular risk factors.     

Psychological stress-induced enhancement of brain lipid peroxidation via nitric oxide systems and its modulation by anxiolytic and anxiogenic drugs in mice

We investigated the effect of psychological stress on lipid peroxidation activity in the mouse brain, the mechanism underlying the psychological stress-induced change in the activity, and the effects of anxiolytic and anxiogenic drugs on the activity in psychologically-stressed animals. Psychological stress exposure using a communication box paradigm for 2-16 h significantly increased the content of thiobarbituric acid reactive substance (TBARS), an index of lipid peroxidation activity, in the brain, and the effect was maximal after peaked by a 4-h stress exposure. In the animals stressed for over 4 h, the increased brain TBARS content lasted for 30 min after the stress exposure, while no significant increase of the TBARS content was observed in the liver or serum. Trolox (67.6 mg/kg, i.p.), an antioxidant drug, but not monoamine oxidase inhibitors, clorgyline (2.5-5 mg/kg, i.p.) or 5-(4-benzylphenyl)-3-(2-cyanoethyl)-(3H)-1,3,4-oxadiazol-2-o ne (1-5 mg/kg, i.p.), significantly suppressed the effect of psychological stress. The non-selective nitric oxide (NO) synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 10-100 mg/kg, i.p.) and the selective neuronal NOS inhibitor 7-nitroindazole (25 and 50 mg/kg, i.p.), but not the inducible NOS inhibitor aminoguanidine (1-100 mg/kg, i.p.), dose dependently suppressed the psychological stress-induced enhancement of lipid peroxidation in the brain. L-Arginine (300 mg/kg, i.p.), a substrate of NOS, antagonized the effect of L-NAME. Measurements of NO metabolites revealed a significant increase of NO production in the brains of stressed mice. The benzodiazepine (BZD) receptor agonist diazepam (0.05-0.5 mg/kg, i.p.), the 5-HT(1A) receptor agonists (+/-)-8-hydroxy-di-propylaminotetralin and buspirone (0.1-1 mg/kg, i. p.), but not the 5-HT(3) receptor agonist MDL72222, dose-dependently suppressed the psychological stress-induced enhancement of brain lipid peroxidation. In contrast, the administration of anxiogenic drugs, FG7142 (an inverse BZD agonist: 1-10 mg/kg, i.p.) and 1-(3-chlorophenyl)piperazine (a mixed 5-HT(2A/2B/2C) agonist: 0.1-1 mg/kg, i.p.), potentiated it. The effects of diazepam and FG7142 were abolished by the BZD receptor antagonist flumazenil (10 mg/kg, i.p.). These results indicate that psychological stress causes oxidative damage to the brain lipid via enhancing constitutive NOS-mediated production of NO, and that drugs with a BZD or 5-HT(1A) receptor agonist profile have a protective effect on oxidative brain membrane damage induced by psychological stress.     

Hyperammonemia-induced toxicity for the developing central nervous system

In pediatric patients, hyperammonemia can be caused by various acquired or inherited disorders such as urea cycle deficiencies or organic acidemias. The brain is much more susceptible to the deleterious effects of ammonium during development than in adulthood. Hyperammonemia can provoke irreversible damages to the developing central nervous system that lead to cortical atrophy, ventricular enlargement and demyelination, responsible for cognitive impairment, seizures and cerebral palsy. Until recently, the mechanisms leading to these irreversible cerebral damages were poorly understood. Using experimental models allowing the analysis of the neurotoxic effects of ammonium on the developing brain, these last years have seen the emergence of new clues showing that ammonium exposure alters several amino acid pathways and neurotransmitter systems, as well as cerebral energy metabolism, nitric oxide synthesis, oxidative stress, mitochondrial permeability transition and signal transduction pathways. Those alterations may explain neuronal loss and impairment of axonal and dendritic growth observed in the different models of congenital hyperammonemia. Some neuroprotective strategies such as the potential use of NMDA receptor antagonists, nitric oxide inhibitors, creatine and acetyl-l-carnitine have been suggested to counteract these toxic effects. Unraveling the molecular mechanisms involved in the chain of events leading to neuronal dysfunction under hyperammonemia may be useful to develop new potential strategies for neuroprotection.     

Neuro-oxidative-nitrosative stress in sepsis

Neuro-oxidative-nitrosative stress may prove the molecular basis underlying brain dysfunction in sepsis. In the current review, we describe how sepsis-induced reactive oxygen and nitrogen species (ROS/RNS) trigger lipid peroxidation chain reactions throughout the cerebrovasculature and surrounding brain parenchyma, due to failure of the local antioxidant systems. ROS/RNS cause structural membrane damage, induce inflammation, and scavenge nitric oxide (NO) to yield peroxynitrite (ONOO⁻). This activates the inducible NO synthase, which further compounds ONOO⁻ formation. ROS/RNS cause mitochondrial dysfunction by inhibiting the mitochondrial electron transport chain and uncoupling oxidative phosphorylation, which ultimately leads to neuronal bioenergetic failure. Furthermore, in certain ‘at risk'' areas of the brain, free radicals may induce neuronal apoptosis. In the present review, we define a role for ROS/RNS-mediated neuronal bioenergetic failure and apoptosis as a primary mechanism underlying sepsis-associated encephalopathy and, in sepsis survivors, permanent cognitive deficits.     

Melatonin and its brain metabolite N1‐acetyl‐5‐methoxykynuramine prevent mitochondrial nitric oxide synthase induction in parkinsonian mice

Melatonin prevents mitochondrial failure in models of sepsis through its ability to inhibit the expression and activity of both cytosolic (iNOS) and mitochondrial (i‐mtNOS) inducible nitric oxide synthases. Because Parkinson's disease (PD), like sepsis, is associated with iNOS induction, we assessed the existence of changes in iNOS/i‐mtNOS and their relation with mitochondrial dysfunction in the MPTP model of PD, which also displays increased iNOS expression. We also evaluated the role of melatonin (aMT) and its brain metabolite, N¹‐acetyl‐5‐methoxykynuramine (AMK), in preventing i‐mtNOS induction and mitochondrial failure in this model of PD. Mitochondria from substantia nigra (SN) and, to a lesser extent, from striatum (ST) showed a significant increase in i‐mtNOS activity, nitrite levels, oxidative stress, and complex I inhibition after MPTP treatment. MPTP‐induced i‐mtNOS was probably related to mitochondrial failure, because its prevention by aMT and AMK reduced oxidative/nitrosative stress and restored complex I activity. These findings represent the first experimental evidence of a potential role for i‐mtNOS in the mitochondrial failure of PD and support a novel mechanism in the neuroprotective effects of aMT and AMK. © 2009 Wiley‐Liss, Inc.