Free radicals are involved in the damage to protein synthesis after anoxia/aglycemia and NMDA exposure

Role of quercetin and caloric restriction on the biomolecular composition of aged rat cerebral cortex: An FTIR study

Aging brain is characterized by a change in biomolecular composition leading to a diverse range of neurological diseases. Anti-aging research is of current interest, to lessen the burden of age-related macromolecular damage through antioxidant supplementation and caloric restriction. However, data concerning the effect of these anti-aging regimens on age-related biomolecular changes in rat brain is still lacking. In the present study, for the first time, we employed Fourier transform infrared (FTIR) spectroscopy, to investigate the effect of quercetin, caloric restriction (CR) and combination of both on alterations in the composition of lipids and proteins of aged rat brain cerebral cortex. Aged male Wistar rats (21 months old) were divided into four groups: Control (CONT), fed pellet diet; Quercetin (QUER), fed quercetin (50 mg/kg/day); CR (caloric restriction) (fed 40% reduced CONT), and CRQ (40% CR and 50 mg/kg/day QUER). Three-month-old rats served as young control (YOUNG). Our short-term study (45 days) shows decreased band area of unsaturated lipids, decreased area ratios of olefinic/lipid and CH₂ antisymmetric stretching (2925 cm^-1)/lipids in CONT group compared to young rats, suggesting age-associated lipid peroxidation in aged rats. A slight decrease in the frequency of CH₂ antisymmetric mode of lipids (whereas no change in CH₂ symmetric mode), but a decrease in bandwidths of both CH₂ antisymmetric and symmetric modes of lipids was observed for CONT group compared to YOUNG. Further, a significant decrease in the peak area of infrared bands of proteins and an increase in the peak area of the CO band of lipids was observed in the CONT group. Our data also show that lower levels of α-helical structures and higher levels of random coils, representing altered protein secondary structure composition in the CONT group compared to YOUNG group. Reduction in neuronal cell density and shrinked nucleus was also observed in aged rats. Increase in the accumulation of oxidative mediated damage to macromolecules and diminished antioxidant levels, could be the possible reason for the age-related alterations in the composition of lipids and proteins. However, the combination of quercetin and CR, but not either treatment alone, significantly prevented the age associated alterations in the lipid and protein profiles in the rat cerebral cortex. Further, our results help to understand the mechanism of action of antioxidants under non-restriction and CR conditions, this might help in the development of novel anti-aging treatments to ameliorate oxidative stress in age-related disorders.

Hyperglycemia / hypoglycemia-induced mitochondrial dysfunction and cerebral ischemic damage in diabetics

Enhancement of ischemic brain damage is one of the most serious complications of diabetes. Studies from various in vivo and in vitro models of cerebral ischemia have led to an understanding of the role of mitochondria and complex interrelated mitochondrial biochemical pathways leading to the aggravation of ischemic neuronal damage. Advancements in the elucidation of the mechanisms of ischemic brain damage in diabetic subjects have revealed a number of key mitochondrial targets that have been hypothesized to participate in enhancement of brain damage. The present review initially discusses the neurobiology of ischemic neuronal injury, with special emphasis on the central role of mitochondria in mediating its pathogenesis and therapeutic targets. Later it further details the potential role of various biochemical mediators and second messengers causing widespread ischemic brain damage among diabetics via mitochondrial pathways. The present review discusses preclinical data which validates the significance of mitochondrial mechanisms in mediating the aggravation of ischemic cerebral injury in diabetes. Exploitation of these targets may provide effective therapeutic agents for the management of diabetes-related aggravation of ischemic neuronal damage.

Superoxide dismutase mRNA and protein level in human colorectal cancer

Impairments of antioxidant enzyme expression are often concomitant with the onset of cancer. Due to epigenetic factors causing an inflammatory state the gastrointestinal tract can become exposed to reactive oxygen species. The purpose of our work was to evaluate mRNA and protein levels of superoxide dismutase isoenzymes in human colorectal adenocarcinoma due to its clinical advancement, and in colorectal cancer liver metastases. Evaluation of SOD expression in regard to CRC advancement, seems useful for clinical applications due to different tumor cells sensitivity to reactive oxygen species based treatment. Studies were conducted on a group of 27 patients: 15 diagnosed with colorectal adenocarcinoma and 12 diagnosed with colorectal cancer liver metastases. The mRNA level was determined by RT-PCR, and protein level by Western blotting. We observed significant (P≤0.05) changes of mRNA and protein level of SOD isoenzymes in subsequent stages of colorectal adenocarcinoma advancement and in colorectal cancer liver metastases. Differences in mRNA and protein level of SOD isoenzymes in colorectal adenocarcinoma and its liver metastases indicates that SOD participate in adaptation of tumor cells to oxidative stress, and maintain certain level of ROS, necessary for appropriate cell proliferation. Expression of superoxide dismutase isoenzymes seems to be regulated not only at transcriptional level, but also posttranscriptional.

Establishing a physiological environment for visualized in vitro brain slice recordings by increasing oxygen supply and modifying aCSF content

Our insights into the basic characteristics of neuronal function were significantly advanced by combining the in vitro slice technique with the visualization of neurons and their processes. The visualization through water immersion objectives requires keeping slices submerged in recording chambers where delivering artificial cerebro-spinal fluid (aCSF) at flow rates of 2-3 ml/min results in a limited oxygen supply [Hájos N, Ellender TJ, Zemankovics R, Mann EO, Exley R, Cragg SJ, et al. Maintaining network activity in submerged hippocampal slices: importance of oxygen supply. Eur J Neurosci 2009;29:319-27]. Here we review two methods aimed at providing sufficient oxygen levels to neurons in submerged slices to enable high energy consuming processes such as elevated firing rates or network oscillations. The use of these methods may also influence the outcome of other electrophysiological experiments in submerged slices including the study of intercellular signaling pathways. In addition, we also emphasize the importance of various aCSF constituents used in in vitro experiments.

Lysosomal release of cathepsins causes ischemic damage in the rat hippocampal slice and depends on NMDA-mediated calcium influx, arachidonic acid metabolism, and free radical production

NMDA-mediated calcium entry and reactive oxygen species (ROS) production are well-recognized perpetrators of ischemic neuronal damage. The current studies show that these events lead to the release of the protein hydrolase, cathepsin B, from lysosomes 2 h following 5-min oxygen-glucose deprivation in the rat hippocampal slice. This release reflects a lysosomal membrane permeabilization (LMP) and was measured as the appearance of diffuse immunolabeled cathepsin B in the cytosol of CA1 pyramidal neurons. Necrotic neuronal damage begins after the release of cathepsins and is prevented by inhibitors of either cathepsin B or D indicating that the release of cathepsins is an important mediator of severe damage. There was an increase in superoxide levels, measured by dihydroethidium fluorescence, at the same time as LMP and reducing ROS levels with antioxidants, Trolox or N-tert-butyl-alpha-phenyl nitrone, blocked LMP. Both LMP and ROS production were blocked by an NMDA channel blocker (MK-801) and by inhibitors of mitogen-activated protein kinase kinase (U0126), calcium-dependent/independent phospholipases A2 (methyl arachidonyl fluorophosphonate) but not calcium-independent phospholipases A2 (bromoenol lactone) and cyclooxygenase-2 (NS398). A cell-permeant specific inhibitor of calpain (PD150606) prevented LMP, but not ROS production. It is concluded that LMP results in part from calcium-initiated and extracellular signal-regulated kinase-initiated arachidonic acid metabolism, which produces free radicals; it also requires the action of calpain.

Edaravone inhibits lipid peroxidation in neonatal hypoxic-ischemic rats: An in vivo microdialysis study

The occurrence of hypoxia-ischemia (HI) during early fetal or neonatal stages of an individual leads to the damaging of immature neurons resulting in behavioral and psychological dysfunctions. Free radical-mediated lipid peroxidation is the main cause of neurotoxicity including neonatal brain damage. Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) is a novel anti-oxidant agent and the drug of choice in the treatment of acute ischemic brain disorders in adult patient. The purpose of this study is to determine the direct effects of edaravone in inhibiting the lipid peroxidation production in the neonatal rat brains during hypoxic-ischemic insult by electron paramagnetic resonance (EPR) spectoroscopy and in vivo brain microdialysis. Seven-day-old Wistar rats were subjected to left common carotid artery ligation and a probe was inserted in the rat hippocampus. Edaravone (5, 50, or 100 microM) or saline was perfused with a spin trap agent (alpha-(4-pyridyl-N-oxide)-N-tert-butylnitrone; POBN) before, during and after hypoxia (1h of 8% O2 exposure) and then analyzed by EPR. Edaravone (100 microM) did not show any EPR evidence of POBN adduct formation during and after hypoxic-ischemic insult. However, the EPR signal increased, but not significantly during the hypoxic period in the hypoxic and edaravone 50 microM-treated groups compared to control. Edaravone at 5 microM significantly increased the EPR signals compared to control. This study shows that edaravone directly and dose-dependently inhibited the formation of lipid free radicals produced during hypoxic-ischemic insult in the neonatal rat brain. These results suggest that edaravone is able to attenuate neuronal damage in the rat neonatal brain by inhibiting the formation of lipid radicals.

Chelation of intracellular calcium reduces cell death after hyperglycemic in vitro ischemia in murine hippocampal slice cultures

The aggravating effect of high glucose levels during cerebral ischemia has been extensively documented in clinical studies and in vivo models of global and focal ischemia. Detailed mechanistic studies of hyperglycemic ischemia have so far been hampered by the lack of in vitro models since glucose during anoxia in vitro is highly protective. We have previously reported glucose toxicity in murine hippocampal organotypic slice cultures exposed to anoxia in an acidotic medium containing high potassium and low calcium. In the present study, we compared the importance of calcium, nitric oxide and free radicals during in vitro ischemia (IVI) and hyperglycemic (40 mM) IVI. Extracellular calcium was a ubiquitous factor for cell death after IVI, but its removal from the medium had no effect on cell death after hyperglycemic IVI. When intracellular calcium was chelated by the 1,2-Bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl) ester (BAPTA-AM) cell death appeared earlier but was mitigated in hyperglycemic IVI, while it was increased in glucose-free IVI. Addition of the nitric oxide synthase (NOS) inhibitor N(omega)-Nitro-L-arginine methyl ester hydrochloride (L-NAME) or the free radical scavengers N-tert-butyl-alpha-phenylnitrone (PBN), deferoxamine and N-acetyl-L-cysteine (NAC) did not affect cell damage in either paradigm. We conclude that the aggravating effect of hyperglycemia during in vitro ischemia is partially mediated by calcium ions released from intracellular stores.

Generation of lipid radicals in the hippocampus of neonatal rats after acute hypoxic-ischemic brain damage

Free radical-mediated lipid peroxidation has been strongly suggested to be the main cause of neuronal toxicity in the rat brain, including neonatal brain damage. The primary objective of this experiment was to see if the generation of free radicals occurred in the acute phase of ischemic-hypoxic insult in neonatal rats, by electron paramagnetic resonance (EPR) spectroscopy and in vivo brain microdialysis. A spin trap agent, alpha-(4-pyridyl-N-oxide)-N-tert-butylnitrone was perfused through a probe in the hippocampus before and after hypoxia and then an analysis was performed by EPR. From the EPR analysis of spin adduct in the dialysates, we obtained the EPR spectrum of six line spectra for which the hyperfine coupling constants corresponded to those of the EPR signal from the lipoxygenase/linoleic acid (LPX/LA), a lipid radical generating system, increased transiently just after hypoxia. The results of our in vivo study show the lipid peroxidation of the neuronal membrane to progress during neonatal ischemic-hypoxic insult. We hypothesize that an increased formation of lipid radicals may participate in the cascade of reactions leading to neuronal damage in the hippocampus following ischemic-hypoxic insult in neonatal rats.

N-methyl-D-aspartate receptors are involved in the quinolinic acid, but not in the malonate pro-oxidative activity in vitro

Oxidative stress plays a significant role in the neurotoxicity of a variety of agents that interact with the N-methyl-D-aspartate (NMDA) receptors. Here we investigated in a comparative way the pro-oxidative effects of quinolinic acid (QA) and malonate, two neurotoxic substances that act through distinct primary molecular mechanisms on the production of thiobarbituric acid reactive species (TBARS) by brain homogenates. In fact, QA is thought to activate directly the NMDA receptor, whereas malonate seems to act primarily by inhibiting oxidative metabolism. The malonate-induced TBARS formation was not modified by cyanide (CN-) or 2,4-dinitrophenol. MK-801 did not reduce basal or malonate induced-TBARS production in fresh tissues preparations. However, in heat-treated preparations a significant effect of MK-801 against basal TBARS production was observed, but not on the malonate induced-TBARS production. QA induced-TBARS production was significantly prevented by MK-801 either in fresh or heat-treated preparations. The antioxidant effect of MK-801 on basal and QA-induced TBARS production increased as the temperatures used to treat S1 were increased. Succinate dehydrogenase (SDH) was inhibited by malonate but not by QA. Malonate was able to chelate iron(II) and the malonate-iron complex(es) is(are) active as measured by its(their) activity on deoxyribose degradation assay. These findings indicate that direct interactions of malonate with NMDA receptors are not involved in malonate pro-oxidative activity in vitro. QA pro-oxidative activity in vitro was related, at least in part, to its capability in stimulate NMDA receptors. Taken together, these findings indicated that malonate pro-oxidative activity in vitro could be attributed to its capability of changing the ratio Fe2+/Fe3+, which is essential to TBARS production.

Succinate causes oxidative damage through N-methyl-d-aspartate-mediated mechanisms

In this study we investigated whether succinate, the accumulating substrate in succinate dehydrogenase (SDH) deficiencies and SDH inhibitor intoxication, causes lipoperoxidation and protein carbonylation, and if NMDA receptors are involved in the succinate-induced oxidative damage. Adult male mice (30-40 g) received an intracerebroventricular injection of succinic acid (0.7, 1.0 and 1.7 micromol/5 microl) or 0.9% NaCl (5 microl) and had their exploratory behavior assessed in an open field for 10 min. Succinate (0.7 and 1.0 micromol/5 microl) decreased locomotor activity behavior and increased thiobarbituric acid reactive substances (TBARS) and protein carbonylation in the forebrain. Conversely, 1.7 micromol of succinate did not alter locomotor activity or oxidative damage parameters. The involvement of NMDA receptors in the succinate-induced increase of total protein carbonylation content and exploratory behavior inhibition was assessed by co-administrating MK-801 (7 nmol/2.5 microl icv), a noncompetitive NMDA receptor antagonist, with succinate (1 micromol/2.5 microl icv). The co-administration of MK-801 protected against succinate-induced increase of total protein carbonylation and decrease of locomotor activity. These results suggest the involvement of NMDA receptors in these effects of succinate, which may of particular relevance for succinate-accumulating conditions, such as SDH inhibitors intoxication and inherited SDH deficiencies.

Effect of vitamin E treatment on N-methyl-D-aspartate receptor at different ages in the rat brain

A comparative study using membrane homogenate binding, autoradiography, and Western blot assays was carried out to determine the age-related changes in N-methyl-D-aspartate (NMDA) receptors in 4-, 12- and 24-month-old male Wistar rats, treated or not with vitamin E. Vitamin E treatment was 20 mg/kg i.p. daily for 15 days. [(3)H] 5-methyl-10,11-dihydro-5H-dibenzo (a,d) cycloheptan-5,10-imine maleate (MK-801) binding was significantly increased in all areas studied (cortex and hippocampus) at all ages when rats received this treatment. A Western blot study in vitamin-E-treated rats and their controls did not reveal significant differences in the amounts of NR2A, an NMDA receptor subunit widely distributed in the brain mainly in cortex and hippocampus. We conclude that the effect of vitamin E on NMDA receptors is largely age independent. Previous reports and our data have described the presence of age-dependent NMDA receptor changes. The effect of vitamin E in aging is considered to be mediated by free radical scavenging, but from our data, we conclude that this mechanism is not relevant for age-dependent NMDA receptor changes. Our results also support that age or vitamin E treatment have no relevant effects on NR2A subunit, at least until 24 months in rats.

Effects of purslane herb on stress ability of aging mice induced by D-galactose

OBJECTIVE

To investigate the effects of purslane herb aquenous extracts (PHAS) on the stress ability of aging mice induced by D-galactose.

METHODS

We observed the survival time to hypoxia and heat survival rate of the mice treated with different doses of PHAS and vitamin E. The contents of lipofuscin and malondialdehyde (MDA), and the activity of superoxide dismutase (SOD) and catalase (CAT) in the brain and liver of the mice were tested.

RESULTS

As compared with vitamin E, three doses of PHAS (1.6, 0.8 and 0.4 ml/d) prolonged the survival time to hypoxia and the pole climbing time and increased the heat survival rate, and the 0.8 ml/d PHAS had the best effect. In the group of 0.8 ml/d PHAS, the activity of SOD and CAT decreased less, and the contents of lipofuscin and MDA decreased significantly. The effect of vitamin E was not as good as the PHAS.

CONCLUSION

PHAS can prevent the stress ability of the aging mice. One of its mechanisms may be increasing the activity of SOD and CAT, hence decreasing the damage of the oxidation products to the body.

Primary cortical neuronal cultures reduce cellular energy utilization during anoxic energy deprivation

It has been widely hypothesized that neurons reduce cellular energy use in response to periods of energy deprivation. To test this hypothesis, we measured rates of energy use under normoxia and anoxia in immature (6 days in vitro) and mature (13 days in vitro) neuronal cultures. During anoxic incubation immature and mature cultures reduced cellular energy use by 80% and 45%, respectively. Reduced cellular energy use dramatically affected ATP depletion in neuronal cultures under anoxia. Intracellular ATP stores were expected to deplete within 3 min of anoxia. However, ATP was maintained at decreased but stabilized concentrations for at least 3 h. The capacity of neuronal cultures to reduce cellular energy use during anoxia correlated with their sensitivity towards simulated ischemia. Immature cultures, with the largest capacity to reduce cellular energy use, survived simulated ischemia 2.5 times longer than mature cultures. The addition of glutamate receptor antagonists to mature cultures further decreased cellular energy use during anoxia and significantly extended their survival time under simulated ischemia. This study verifies that primary cortical neuronal cultures reduce cellular energy use during energy deprivation. Additionally, we show that maturation of glutamate receptor activity increases non-depressible energy demand in neuronal cultures.

Microtubule-associated protein 2 (MAP2) associates with the NMDA receptor and is spatially redistributed within rat hippocampal neurons after oxygen-glucose deprivation

MAP2 (microtubule-associated protein 2) is a cytoskeletal phosphoprotein that regulates the dynamic assembly characteristics of microtubules and appears to provide scaffolding for organelle distribution into the dendrites and for the localization of signal transduction apparatus in dendrites, particularly near spines. MAP2 is degraded after ischemia and other metabolic insults, but the time course and initial triggers of that breakdown are not fully understood. This study determined that MAP2 resides in a complex with the NMDA receptor, suggesting that spatially localized changes may be important in the mechanism of MAP2 redistribution and breakdown after oxygen-glucose deprivation (OGD). Using OGD in the adult rat hippocampal slice as a model system, this study demonstrated that MAP2 breakdown occurs very early after OGD, with the first statistical decrease in MAP2 levels within the first 30 min after the insult. There is a dramatic redistribution of MAP2 to the somata of pyramidal neurons, particularly neurons at the CA1-subiculum border. Free radicals and nitric oxide are not involved in the damage to MAP2. NMDA-receptor activation plays a prominent role in the MAP2 breakdown. In direct response to NMDA receptor activation, calcium influx, likely through the receptor ion channel complex, as well as release of calcium from the mitochondria through activation of the 2Na(+)-Ca(2+) exchanger of mitochondria, triggers MAP2 degradation. The proteolysis of MAP2 is limited by endogenous calpain activity, likely via the spatial access of calpain to MAP2.

Expression of neuronal plasticity markers in hypoglycemia induced brain injury

The expression of neuroplasticity markers was analyzed in four brain regions, namely cerebral hemispheres (CH), cerebellum (CB), brain stem (BS) and diencephalon (DC) from insulin-induced hypoglycemic young adult rats. Significant decrease in neural cell adhesion molecule (NCAM) isoforms and growth-associated protein-43 (GAP-43) was observed following hypoglycemic injury from majority of brain regions studied. The glial fibrillary acidic protein (GFAP) level increased significantly in cerebral hemispheres and diencephalon regions, whereas, synaptophysin level increased in cerebellum, brain stem and diencephalon regions. The selective downregulation of the neuronal plasticity marker proteins (GAP-43 and NCAM), and enhanced expression of GFAP and synaptophysin suggests that in acute hypoglycemia, mechanisms other than energy failure may also contribute to neuronal cell damage in the brain.

Nitric oxide and hydroxyl radicals initiate lipid peroxidation by NMDA receptor activation

In this experiment, we used direct electron paramagnetic resonance (EPR) spectra to measure lipid peroxidation by hydroxyl radical (.OH), nitric oxide (.NO) and lipid radical (.L). NMDA-receptor associated lipid peroxidation is thought to act through .OH in induction of neurotoxicity. The origin of .OH generation was found to arise mainly from peroxynitrite anion produced from O(2)(-) and .NO rather than from Fenton's reaction. This study verified that .OH generation from interactive reactions between .NO and O(2)(-) initiates NMDA-induced lipid peroxidation of PC12 cells.

Profound molecular changes following hippocampal slice preparation: loss of AMPA receptor subunits and uncoupled mRNA/protein expression

The acute hippocampal slice preparation is a convenient, in vitro model widely used to study the biological basis of synaptic plasticity. Although slices may preserve their electrophysiological properties for several hours, profound molecular changes in response to the injury caused by the slicing procedure are likely to occur. To determine the magnitude and duration of these changes we examined the post-slicing expression kinetics of three classes of genes known to be implicated in long-term synaptic plasticity: glutamate AMPA receptors (GluR), transcription factors and neurotrophins. Slicing resulted in a striking loss of GluR1 and GluR3, but not of GluR2 proteins suggesting that rapid changes in the composition of major neurotransmitter receptors may occur. Slicing caused a significant induction of the transcription factors c-fos, zif268, CCAAT enhancer binding protein (C/EBP ) beta and delta mRNAs and of the neurotrophin brain-derived neurothophic factor (BDNF ) mRNA. In contrast, there was no augmentation, and sometimes a decline, in the levels of the corresponding proteins. These data reveal that significant discrepancies exist between the slice preparation and the intact hippocampus in terms of the metabolism of molecular components known to be involved in synaptic plasticity.

Retinoic acid reduces apoptosis and oxidative stress by preservation of SOD protein level

Retinoic acid (RA) has already been shown to exert antiapoptotic and antioxidative activity in various cells. In this study, we determined the effect of RA on the mRNA and protein levels of the Cu-,Zn-superoxide dismutase (SOD-1) and Mn-superoxide dismutase (SOD-2) during staurosporine-induced apoptosis in primary cultures from neonatal rat hippocampus. Exposure to staurosporine (300 nM, 24 h) increased the percentage of apoptotic neurons to 62% compared with 18% in controls. We determined an increase in the reactive oxygen species (ROS) content from 4 up to 48 h after the induction of the injury. Treatment with staurosporine did not significantly change the mRNA levels of SOD-1 and SOD-2. However, the SOD-1 and SOD-2 protein levels markedly decreased 24 and 48 h after the addition of staurosporine. Compared with staurosporine-exposed controls, RA (10 nM)-treated cultures showed a significant increase in neuronal survival, a reduced neuronal ROS content, and enhanced protein levels of SOD-1 and SOD-2 24 and 48 h after the start of the exposure to staurosporine. The results suggest that RA reduced staurosporine-induced oxidative stress and apoptosis by preventing the decrease in the protein levels of SOD-1 and SOD-2, and thus supported the antioxidant defense system.