Antioxidants attenuate MK-801-induced cortical neurotoxicity in the rat

Neuroprotective thiourea derivative uncouples mitochondria and exerts weak protonophoric action on lipid membranes

The isothiourea derivative NT-1505 is known as a neuroprotector and cognition enhancer in animal models of neurodegenerative diseases. Bearing in mind possible relation of the NT-1505-mediated neuroprotection to mitochondrial uncoupling activity, here, we examine NT-1505 effects on mitochondria functioning. At concentrations starting from 10 μM, NT-1505 prevented Ca2+-induced mitochondrial swelling, similar to common uncouplers. Alongside the inhibition of the mitochondrial permeability transition, NT-1505 caused a decrease in mitochondrial membrane potential and an increase in respiration rate in both isolated mammalian mitochondria and cell cultures, which resulted in the reduction of energy-dependent Ca2+ uptake by mitochondria. Based on the oppositely directed effects of bovine serum albumin and palmitate, we suggest the involvement of fatty acids in the NT-1505-mediated mitochondrial uncoupling. In addition, we measured the induction of electrical current across planar bilayer lipid membrane upon the addition of NT-1505 to the bathing solution. Importantly, introduction of the palmitic acid into the lipid bilayer composition led to weak proton selectivity of the NT-1505-mediated BLM current. Thus, the present study revealed an ability of NT-1505 to cause moderate protonophoric uncoupling of mitochondria, which could contribute to the neuroprotective effect of this compound.

Effects of ortho-eugenol on anxiety, working memory and oxidative stress in mice

Ortho-eugenol is a synthetic derivative from eugenol, the major compound of clove essential oil, which has demonstrated antidepressant and antinociceptive effects in pioneering studies. Additionally, its effects appear to be dependent on the noradrenergic and dopaminergic systems. Depression and anxiety disorders are known to share a great overlap in their pathophysiology, and many drugs are effective in the treatment of both diseases. Furthermore, high levels of anxiety are related to working memory deficits and increased oxidative stress. Thus, in this study we investigated the effects of acute treatment of ortho-eugenol, at 50, 75 and 100 mg/kg, on anxiety, working memory and oxidative stress in male Swiss mice. Our results show that the 100 mg/kg dose increased the number of head-dips and reduced the latency in the hole-board test. The 50 mg/kg dose reduced malondialdehyde levels in the prefrontal cortex and the number of Y-maze entries compared to the MK-801-induced hyperlocomotion group. All doses reduced nitrite levels in the hippocampus. It was also possible to assess a statistical correlation between the reduction of oxidative stress and hyperlocomotion after the administration of ortho-eugenol. However, acute treatment was not able to prevent working memory deficits. Therefore, the present study shows that ortho-eugenol has an anxiolytic and antioxidant effect, and was able to prevent substance-induced hyperlocomotion. Our results contribute to the elucidation of the pharmacological profile of ortho-eugenol, as well as to direct further studies that seek to investigate its possible clinical applications.

The Impact of the Combined Administration of 1MeTIQ and MK-801 on Cell Viability, Oxidative Stress Markers, and Glutamate Release in the Rat Hippocampus

MK-801, as an N-methyl-D-aspartate (NMDA) receptor inhibitor, causes elevation in glutamate release, which may lead to an increase in excitotoxicity, oxidative stress and, consequently, cell death. 1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) shows antioxidant activity. The aim of the present study was to evaluate the effect of combined treatment with 1MeTIQ and MK-801 on cell viability, antioxidant enzyme activity, and glutamate release in the rat hippocampus. Cytotoxicity was measured using lactate dehydrogenase leakage assay (LDH) and the methyl tetrazolium (MTT) assay; antioxidant enzyme activity (glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD), and catalase (CAT)) were measured by ELISA kits. The release of glutamate in the rat hippocampus was measured using in vivo microdialysis methodology. An in vitro study showed that MK-801 induced cell death in a concentration-dependent manner and that 1MeTIQ partially reduced this adverse effect of MK-801. An ex vivo study indicated that MK-801 produced an increase in antioxidant enzyme activity (GPx, GR, and SOD), whereas coadministration of MK-801 and 1MeTIQ restored the activity of these enzymes to the control level. An in vivo microdialysis study demonstrated that combined treatment with both drugs decreased the release of glutamate in the rat hippocampus. The above results revealed that 1MeTIQ shows limited neuroprotective activity under conditions of glutamate-induced neurotoxicity.

Para-Substituted α-Phenyl-N-tert-butyl Nitrones: Spin-Trapping, Redox and Neuroprotective Properties

In this work, a series of para-substituted α-phenyl-N-tert-butyl nitrones (PBN) were studied. Their radical-trapping properties were evaluated by electron paramagnetic resonance, with 4-CF₃-PBN being the fastest derivative to trap the hydroxymethyl radical (^•CH₂OH). The redox properties of the nitrones were further investigated by cyclic voltammetry, and 4-CF₃-PBN was the easiest to reduce and the hardest to oxidize. This is due to the presence of the electron-withdrawing CF₃ group. Very good correlations between the Hammett constants (σ_p) of the substituents and both spin-trapping rates and redox potentials were observed. These correlations were further supported by computationally determined ionization potentials and atom charge densities. Finally, the neuroprotective effect of these derivatives was studied using two different in vitro models of cell death on primary cortical neurons injured by glutamate exposure or on glial cells exposed to ^t BuOOH. Trends between the protection afforded by the nitrones and their lipophilicity were observed. 4-CF₃-PBN was the most potent agent against ^t BuOOH-induced oxidative stress on glial cells, while 4-Me₂N-PBN showed potency in both models.

N-Methyl-D aspartate receptor-mediated effect on glucose transporter-3 levels of high glucose exposed-SH-SY5Y dopaminergic neurons

High glucose and insulin lead to neuronal insulin resistance. Glucose transport into the neurons is achieved by regulatory induction of surface glucose transporter-3 (GLUT3) instead of the insulin. N-methyl-D aspartate (NMDA) receptor activity increases GLUT3 expression. This study explored whether an endogenous NMDA receptor antagonist, kynurenic acid (KynA) affects the neuronal cell viability at high glucose concentrations. SH-SY5Y neuroblastoma cells were exposed to 150-250 mg/dL glucose and 40 μU/mL insulin. In KynA and N-nitro-l-arginine methyl ester (L-NAME) supplemented cultures, oxidative stress, mitochondrial metabolic activity (MTT), nitric oxide as nitrite+nitrate (NOx) and GLUT3 were determined at the end of 24 and 48-h incubation periods. Viable cells were counted by trypan blue dye. High glucose-exposed SH-SY5Y cells showed two-times more GLUT3 expression at second 24-h period. While GLUT3-stimulated glucose transport and oxidative stress was increased, total mitochondrial metabolic activity was significantly reduced. Insulin supplementation to high glucose decreased NOx synthesis and GLUT3 levels, in contrast oxidative stress increased three-fold. KynA significantly reduced oxidative stress, and increased MTT by regulating NOx production and GLUT3 expression. KynA is a noteworthy compound, as an endogenous, specific NMDA receptor antagonist; it significantly reduces oxidative stress, while increasing cell viability at high glucose and insulin concentrations.

Differential Effects of Olanzapine and Haloperidol on MK-801-induced Memory Impairment in Mice

OBJECTIVE

We investigated the differential effects of the antipsychotic drugs olanzapine and haloperidol on MK-801-induced memory impairment and neurogenesis in mice.

METHODS

MK-801 (0.1 mg/kg) was administered 20 minutes prior to behavioral testing over 9 days. Beginning on the sixth day of MK-801 treatment, either olanzapine (0.05 mg/kg) or haloperidol (0.05 mg/kg) was administered 40 minutes prior to MK-801 for the final 4 days. Spatial memory performance was measured using a Morris water maze (MWM) test for 9 days (four trials/day). Immunohistochemistry with bromodeoxyuridine (BrdU) was used to identify newborn cells labeled in tissue sections from the dentate gyrus of the hippocampus.

RESULTS

MK-801 administration over 9 days significantly impaired memory performance in the MWM test compared to untreated controls (p＜0.05) and these deficits were blocked by treatment with olanzapine (p＜0.05) but not haloperidol. The administration of MK-801 also resulted in a decrease in the number of BrdU-labeled cells in the dentate gyrus (28.6%; p＜0.01), which was prevented by treatment with olanzapine (p＜0.05) but not haloperidol.

CONCLUSION

These results suggest that olanzapine has a protective effect against cognitive impairments induced by MK-801 in mice via the stimulating effects of neurogenesis.

Pathological Implications of Oxidative Stress in Patients and Animal Models with Schizophrenia: The Role of Epidermal Growth Factor Receptor Signaling

Proinflammatory cytokines perturb brain development and neurotransmission and are implicated in various psychiatric diseases, such as schizophrenia and depression. These cytokines often induce the production of reactive oxygen species (ROS) and regulate not only cell survival and proliferation but also inflammatory process and neurotransmission. Under physiological conditions, ROS are moderately produced in mitochondria but are rapidly scavenged by reducing agents in cells. However, brain injury, ischemia, infection, or seizure-like neural activities induce inflammatory cytokines and trigger the production of excessive amounts of ROS, leading to abnormal brain functions and psychiatric symptoms. Protein phosphatases, which are involved in the basal silencing of cytokine receptor activation, are the major targets of ROS. Consistent with this, several ROS scavengers, such as polyphenols and unsaturated fatty acids, attenuate both cytokine signaling and psychiatric abnormalities. In this review, we list the inducers, producers, targets, and scavengers of ROS in the brain and discuss the interaction between ROS and cytokine signaling implicated in schizophrenia and its animal models. In particular, we present an animal model of schizophrenia established by perinatal exposure to epidermal growth factor and illustrate the pathological role of ROS and antipsychotic actions of ROS scavengers, such as emodin and edaravone.

Investigation of Mechanisms for MK-801-Induced Neurotoxicity Utilizing Metabolomic Approach

Single treatment of rats with the noncompetitive N-methyl-D-aspartate receptor antagonist MK-801 induces neuronal cell degeneration and death in the retrosplenial/posterior cingulate cortex (RS/PC) region, along with local cerebral glucose utilization. However, the relationship between this neuronal cell degeneration and death and glucose utilization remains unclear. To investigate the mechanism of MK-801-induced neurotoxicity and its relation to glucose utilization, changes in endogenous metabolites in the RS/PC region of MK-801 treated rats were assessed using metabolomics. Inverse correlation between citrulline and arginine levels suggested increased nitric oxide (NO) production. In addition, decreased levels of purine metabolites suggested enhanced xanthine oxidase activity accompanied with reactive oxygen species (ROS) production. Histopathological analysis confirmed that the production of ROS in the RS/PC region was increased by MK-801 and that the nonspecific NO synthase inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) prevented MK-801-induced neuronal cell death. These results suggest that NO increases oxidative stress-related cell death. Increased levels of metabolites of glucose metabolism suggested enhanced energy production via glycolysis. To confirm the relationship between NO and glucose utilization, positron emission tomography (PET) imaging with [(18)F] fluoro-2-deoxy-d-glucose ([(18)F] FDG) was conducted. [(18)F] FDG-PET imaging accompanied by co-treatment of L-NAME with MK-801 demonstrated that L-NAME ameliorated MK-801-induced glucose utilization.In conclusion, MK-801 induces NO and ROS production in the RS/PC region, which might subsequently induce oxidative stress and in turn neuronal cell death. In addition, MK-801-induced NO production increased glucose utilization and affected glucose metabolism, the imbalance of which might generate additional oxidative stress related to neuronal cell death.

Methanol extract of Ficus platyphylla ameliorates seizure severity, cognitive deficit and neuronal cell loss in pentylenetetrazole-kindled mice

Decoctions of Ficus plathyphylla are used in Nigeria's folk medicine to manage epilepsy for many years and their efficacies are widely acclaimed among the rural communities of Northern Nigeria. In this study, we examined the ameliorative effects of the standardized methanol extract of Ficus platyphylla (FP) stem bark on seizure severity, cognitive deficit and neuronal cell loss in pentylenetetrazole-kindled mice. The (35)S-GTPγS, glutamate and γ-aminobutyric acid receptors binding properties of the extract were also evaluated. Male CD-1 mice were kindled with an initial subeffective dose of pentylenetetrazole (PTZ, 37.5mg/kg, i.p.) for a total of 13 convulsant injections and the treatment groups concurrently received FP (100 and 200mg/kg). Control animals received the same number of saline injections. Twenty-four h after kindling completion the animals' learning performance was tested in a two-way shuttle-box. The animals were challenged with another subeffective dose of PTZ (32.5mg/kg, i.p.) on day 7 after kindling completion. Animals were sacrificed a day after the challenged experiment and the brains were processed for histological investigation. FP ameliorates seizure severity, cognitive deficits and neuronal cell loss in PTZ kindled mice. Components of the extract showed affinity for GABAergic and glutamatergic receptors. Glutamate release was diminished and the (35)S-GTPγS binding assay revealed no intrinsic activity at glutamatergic receptors. Our results revealed that FP contains psychoactive secondary metabolites with anticonvulsant properties, thus supporting the isolation and development of the biologically active components of this medicinal plant as antiepileptic agents.

Potential implication of the chemical properties and bioactivity of nitrone spin traps for therapeutics

Nitrone therapeutics has been employed in the treatment of oxidative stress-related diseases such as neurodegeneration, cardiovascular disease and cancer. The nitrone-based compound NXY-059, which is the first drug to reach clinical trials for the treatment of acute ischemic stroke, has provided promise for the development of more robust pharmacological agents. However, the specific mechanism of nitrone bioactivity remains unclear. In this review, we present a variety of nitrone chemistry and biological activity that could be implicated for the nitrone's pharmacological activity. The chemistries of spin trapping and spin adduct reveal insights on the possible roles of nitrones for altering cellular redox status through radical scavenging or nitric oxide donation, and their biological effects are presented. An interdisciplinary approach towards the development of novel synthetic antioxidants with improved pharmacological properties encompassing theoretical, synthetic, biochemical and in vitro/in vivo studies is covered.

Metabonomic studies of schizophrenia and psychotropic medications: focus on alterations in CNS energy homeostasis

Schizophrenia is a severe neuropsychiatric disorder with a poorly understood etiology and progression. We and other research groups have found that energy metabolic pathways in the CNS are perturbed in many subjects with this disorder. Antipsychotic drugs that generally target neurotransmission are currently used for clinical management of the disorder, although these can also have marked effects on energy metabolism in the CNS and periphery. Recent proteomic and metabonomic studies have shown that molecular pathways associated with brain energy metabolism are altered in both the disorder and by antipsychotic treatments. This review focuses on discussion of these molecular alterations. Increased knowledge in this area could facilitate biomarker identification and drug discovery based on improving brain energy metabolism in this debilitating disorder.

Clinical physiology and mechanism of dizocilpine (MK-801): electron transfer, radicals, redox metabolites and bioactivity

Dizocilpine (MK-801), an extensively investigated drug possessing secondary amine and benzenoid functions, displays a wide array of biological properties, including anticonvulsant and anesthetic. There is scant discussion of biomechanism. A relevant, important finding is formation of oxidative metabolites in the hydroxylamine and phenolic categories. Analogy to cocaine metabolites suggests participation of redox entities, such as, hydroxylamine, nitroxide and nitrosonium, which can lead to electron transfer and radical formation. There is also similarity to metabolism by 3,3′-iminodipropionitrile and phencyclidine. Alternatively, the phenolic metabolites are well-known precursors of ET quinones. The review documents various physiological effects, mainly involving the central nervous system. Also of interest are the pro- and anti-oxidant properties. Considerable attention has been paid to MK-801 as an antagonist of the N-methyl-D-aspartate receptor in the glutamate category. This aspect is often associated with effects on the central nervous system. The review also provides recent literature dealing with MK-801/NMDA receptor in various areas of bioactivity. Studies were made of MK-801 involvement in working memory processing. Deficits in behavior were noted after administration of the drug. Treatment of mice with dizocilpine induced learning impairment. The influence of MK-801 on fear has been investigated. The substance is known to exert an analgesic effect in pain control. A number of reports deal with anesthetic properties.

Protective effect of melatonin against hippocampal injury of rats with intermittent hypoxia

Obstructive sleep apnea (OSA) patients suffer from intermittent hypoxia (IH) and neuropsychologic impairments. Oxidative stress is involved in the pathogenesis of OSA, so the application of an antioxidant may be useful. We evaluated the hypothesis that melatonin would reduce IH-induced hippocampal injury via an increased expression of antioxidant enzymes. Adult Sprague-Dawley rats that had received a daily injection of melatonin or vehicle were exposed to IH for 8 hr/day for 7 or 14 days. The serum and hippocampus were harvested for the measurement of malondialdehyde (MDA). Apoptotic cell death was studied histologically in hippocampal sections. The mRNA expression of inflammatory mediators including tumor necrosis factor-alpha, inducible nitric oxide synthase, cyclooxygenase-2 and antioxidant enzymes including glutathione peroxidase, catalase and copper/zinc superoxide dismutase were examined in the hippocampus by RT-PCR. The results show significant increases in levels of serum and hippocampal MDA, apoptotic cell death and mRNA levels of inflammatory mediators in hypoxic rats when compared with the normoxic controls. Also, mRNA levels of the antioxidant enzymes were decreased in hypoxic animals. In the melatonin-treated hypoxic rats, serum MDA levels were comparable with those in normoxic control rats. Also, melatonin treatment significantly reduced hippocampal MDA levels and totally prevented apoptosis. Moreover, there were a decreased expression of the inflammatory mediators and an elevated expression of antioxidant enzymes in the melatonin injected rats when compared with vehicle-treated animals. These results indicate that melatonin mitigates oxidative stress and the pathogenesis of IH-induced hippocampal injury via its antioxidant and anti-inflammatory properties which includes stimulation of transcriptional regulation of antioxidant enzymes.

Role of IFN-gamma in an experimental murine model of West Nile virus-induced seizures

Seizures are a major complication of viral encephalitis. However, the mechanisms of seizure-associated neuronal dysfunction remain poorly understood. We report that intranasal inoculation with West Nile virus (WNV) (Sarafend) causes limbic seizures in C57BL/6 mice, but not in interferon (IFN)-gamma-deficient (IFN-gamma-/-) mice. Both strains showed similar levels of virus in the brain, as well as similar concentrations of the cytokines, tumor necrosis factor and interleukin-6, both of which can alter neuronal excitability. Experiments in chimeric IFN-gamma-/- mice reconstituted with IFN-gamma-producing leukocytes showed that IFN-gamma is not required during central nervous system infection for limbic seizure development, suggesting a role for IFN-gamma in the developing brain. This was supported responses to pentylenetetrazole, kainic acid (KA), and N-methyl-d-aspartate (NMDA). Both strains of mice exhibited similar behavior after pentylenetetrazole challenge. However, while NMDA and KA treatment resulted in characteristic seizures in C57BL/6 mice, these responses were diminished (NMDA treatment) or absent (KA treatment) in IFN-gamma-/- mice. Furthermore, NMDA-receptor blockade with MK-801 in WNV-infected C57BL/6 mice abrogated seizures and prolonged survival. Our data show that IFN-gamma plays an important role in the development of the excitatory seizure pathways in the brain and that these cascades become pathogenic in encephalitic WNV infection.

Oxidative stress in prefrontal cortex of rat exposed to MK-801 and protective effects of CAPE

MK-801 was shown to be one of the most neurotoxic non-competitive NMDA receptor antagonists. It is known that repeated injection of MK-801 was proposed in an animal model in psychosis. The aims of this study are to investigate the contributing effect of oxidative stress in MK-801-induced experimental psychosis model, and to show that prevention of oxidative stress may improve prognosis. Furthermore, there is evidence that oxygen free radicals play an important role in the pathophysiology of schizophrenia. In this study, Wistar Albino rats were divided into three groups: 1st group: Control, 2nd group: MK-801, 3rd group: MK-801+CAPE (Caffeic acid phenethyl ester) group. MK-801 was given intraperitoneally at the dose of 0.5 mg/kg/day for 5 days. CAPE was given to the treatment group while exposed to MK-801. In control group, saline was given intraperitoneally at the same time. After 7 days, rats were killed by decapitation. Prefrontal cortex (PFC) of rats was removed for biochemical and histological analyses. As a result, malondialdehyde (MDA), protein carbonyl (PC), nitric oxide (NO) levels and superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and xanthine oxidase (XO) and adenosine deaminase (AD) enzyme activities were found to be increased significantly in prefrontal cortex (PFC) of MK-801 group (p<0.0001) compared to control group. In CAPE treated rats, prefrontal tissue MDA, PC, NO levels and, GSH-Px, XO, AD enzyme activities were significantly decreased when compared to MK-801 groups (p<0.0001) whereas catalase (CAT) enzyme activity was not changed. Moreover, in the light of microscopic examination of MK-801 groups, a great number of apoptotic cells were observed. CAPE treatment decreased the apoptotic cell count in PFC. The results of this study showed that MK-801-induced neurotoxicity caused oxidative stress in PFC of rats. This experimental study may also provide some evidences for the new treatment strategies with antioxidants in schizophrenia.