Role of reactive oxygen species and protein kinase C in ischemic tolerance in the brain

The Mfn1-βIIPKC Interaction Regulates Mitochondrial Dysfunction via Sirt3 Following Experimental Subarachnoid Hemorrhage

Neuronal injury following subarachnoid hemorrhage (SAH) has been shown to be associated with mitochondrial dysfunction and oxidative stress. βIIPKC, a subtype of protein kinase C (PKC), accumulates on the mitochondrial outer membrane and phosphorylates mitofusin 1 (Mfn1) at serine 86. Here, we investigated the role of Mfn1-βIIPKC interaction in brain damage and neurological function in both in vivo and in vitro experimental SAH models. The expression of βIIPKC protein and the interaction of Mfn1-βIIPKC were found to be increased after OxyHb treatment in primary cultured cortical neurons and were also observed in the brain following SAH in rats. Treatment with the βIIPKC inhibitor βIIV5-3 or SAMβA, a peptide that selectively antagonizes Mfn1-βIIPKC association, significantly attenuated the OxyHb-induced neuronal injury and apoptosis. These protective effects were accompanied by inhibited mitochondrial dysfunction and preserved mitochondrial biogenesis. The results of western blot showed that βIIV5-3 or SAMβA markedly increased the expression of Sirt3 and enhanced the activities of its downstream mitochondrial antioxidant enzymes in OxyHb-treated neurons. Knockdown of Sirt3 via specific targeted small interfering RNA (siRNA) partially prevented the βIIV5-3- or SAMβA-induced protection and antioxidative effects. In addition, treatment with βIIV5-3 or SAMβA in vivo was found to obviously reduce brain edema, alleviate neuroinflammation, and preserve neurological function after experimental SAH in rats. In congruent with in vitro data, the protection induced by βIIV5-3 or SAMβA was reduced by Sirt3 knockdown in vivo. In summary, our present results showed that blocking Mfn1-βIIPKC interaction protects against brain damage and mitochondrial dysfunction via Sirt3 following experimental SAH.

Morphine pretreatment protects against cerebral ischemic injury via a cPKCγ-mediated anti-apoptosis pathway

It has been reported that morphine pretreatment (MP) can exert neuroprotective effects, and that protein kinase C (PKC) participates in the initiation and development of ischemic/hypoxic preconditioning in the brain. However, it remains unknown whether PKC is involved in MP-induced neuroprotection. The aim of the present study, which included in vivo and in vitro experiments, was to determine whether the conventional γ isoform of PKC (cPKCγ) was involved in the protective effects of MP against cerebral ischemic injury. The present study included an in vivo experiment using a mouse model of middle cerebral artery occlusion and an in vitro experiment using neuroblastoma N2a cells with oxygen-glucose deprivation (OGD). Furthermore, a cPKCγ antagonist, Go6983, was used to determine the involvement of cPKCγ in the protective effects of MP against cerebral ischemic injury. In the in vivo experiment, neurological deficits, ischemic infarct volume, neural cell damage, apoptosis and caspase-3 activation were evaluated. In the in vitro experiment, flow cytometry was used to determine the activation of caspase-3 in N2a cells with OGD. It was found that MP protected against cerebral ischemic injury. However, intracerebroventricular injection of the cPKCγ antagonist before MP attenuated the neuroprotective effect of MP and increased the activation of cleaved caspase-3. These findings suggested that MP may provide protection against cerebral ischemic injury via a cPKCγ-mediated anti-apoptosis pathway.

GPR68 Contributes to Persistent Acidosis-Induced Activation of AGC Kinases and Tyrosine Phosphorylation in Organotypic Hippocampal Slices

Persistent acidosis occurs in ischemia and multiple neurological diseases. In previous studies, acidic stimulation leads to rapid increase in intracellular calcium in neurons. However, it remains largely unclear how a prolonged acidosis alters neuronal signaling. In our previous study, we found that GPR68-mediated PKC activities are protective against acidosis-induced injury in cortical slices. Here, we first asked whether the same principle holds true in organotypic hippocampal slices. Our data showed that 1-h pH 6 induced PKC phosphorylation in a GPR68-dependent manner. Go6983, a PKC inhibitor worsened acidosis-induced neuronal injury in wild type (WT) but had no effect in GPR68^−/− slices. Next, to gain greater insights into acid signaling in brain tissue, we treated organotypic hippocampal slices with pH 6 for 1-h and performed a kinome profiling analysis by Western blot. Acidosis had little effect on cyclin-dependent kinase (CDK) or casein kinase 2 activity, two members of the CMGC family, or Ataxia telangiectasia mutated (ATM)/ATM and RAD3-related (ATR) activity, but reduced the phosphorylation of MAPK/CDK substrates. In contrast, acidosis induced the activation of CaMKIIα, PKA, and Akt. Besides these serine/threonine kinases, acidosis also induced tyrosine phosphorylation. Since GPR68 is widely expressed in brain neurons, we asked whether GPR68 contributes to acidosis-induced signaling. Deleting GPR68 had no effect on acidosis-induced CaMKII phosphorylation, attenuated that of phospho-Akt and phospho-PKA substrates, while abolishing acidosis-induced tyrosine phosphorylation. These data demonstrate that prolonged acidosis activates a network of signaling cascades, mediated by AGC kinases, CaMKII, and tyrosine kinases. GPR68 is the primary mediator for acidosis-induced activation of PKC and tyrosine phosphorylation, while both GPR68-dependent and -independent mechanisms contribute to the activation of PKA and Akt.

Bridging the Gap Between Diabetes and Stroke in Search of High Clinical Relevance Therapeutic Targets

Diabetes affects more than 425 million people worldwide, a scale approaching pandemic proportion. Diabetes represents a major risk factor for stroke, and therefore is actively addressed for stroke prevention. However, how diabetes affects stroke severity has not yet been extensively considered, which is surprising given the evident but understudied common mechanistic features of both pathologies. The increase in number of diabetic people, incidence of stroke in the presence of this specific risk factor, and the exacerbation of ischemic brain damage in diabetic conditions (at least in animal models) warrants the need to integrate this comorbidity in preclinical studies of brain ischemia to develop novel therapeutic approaches. Therefore, a better understanding of the commonalties involved in the course of both diseases would offer the promise of discovering novel neuroprotective pathways that would be more appropriated to clinical scenarios. In this article, we will review the relevant mechanisms that have been identified as common traits of both pathologies and that could be, to our knowledge, potential targets in both pathologies.

Age-Dependent Levels of Protein Kinase Cs in Brain: Reduction of Endogenous Mechanisms of Neuroprotection

Neurodegenerative diseases are among the leading causes of mortality and disability worldwide. However, current therapeutic approaches have failed to reach significant results in their prevention and cure. Protein Kinase Cs (PKCs) are kinases involved in the pathophysiology of neurodegenerative diseases, such as Alzheimer's Disease (AD) and cerebral ischemia. Specifically ε, δ, and γPKC are associated with the endogenous mechanism of protection referred to as ischemic preconditioning (IPC). Existing modulators of PKCs, in particular of εPKC, such as ψεReceptor for Activated C-Kinase (ψεRACK) and Resveratrol, have been proposed as a potential therapeutic strategy for cerebrovascular and cognitive diseases. PKCs change in expression during aging, which likely suggests their association with IPC-induced reduction against ischemia and increase of neuronal loss occurring in senescent brain. This review describes the link between PKCs and cerebrovascular and cognitive disorders, and proposes PKCs modulators as innovative candidates for their treatment. We report original data showing εPKC reduction in levels and activity in the hippocampus of old compared to young rats and a reduction in the levels of δPKC and γPKC in old hippocampus, without a change in their activity. These data, integrated with other findings discussed in this review, demonstrate that PKCs modulators may have potential to restore age-related reduction of endogenous mechanisms of protection against neurodegeneration.

Ischemic postconditioning prevents surge of presynaptic glutamate release by activating mitochondrial ATP-dependent potassium channels in the mouse hippocampus

A mild ischemic load applied after a lethal ischemic insult reduces the subsequent ischemia–reperfusion injury, and is called ischemic postconditioning (PostC). We studied the effect of ischemic PostC on synaptic glutamate release using a whole-cell patch-clamp technique. We recorded spontaneous excitatory post-synaptic currents (sEPSCs) from CA1 pyramidal cells in mouse hippocampal slices. The ischemic load was perfusion of artificial cerebrospinal fluid (ACSF) equilibrated with mixed gas (95% N₂ and 5% CO₂). The ischemic load was applied for 7.5 min, followed by ischemic PostC 30 s later, consisting of three cycles of 15 s of reperfusion and 15 s of re-ischemia. We found that a surging increase in sEPSCs frequency occurred during the immediate-early reperfusion period after the ischemic insult. We found a significant positive correlation between cumulative sEPSCs and the number of dead CA1 neurons (r = 0.70; p = 0.02). Ischemic PostC significantly suppressed this surge of sEPSCs. The mitochondrial K_ATP (mito-K_ATP) channel opener, diazoxide, also suppressed the surge of sEPSCs when applied for 15 min immediately after the ischemic load. The mito-K_ATP channel blocker, 5-hydroxydecanoate (5-HD), significantly attenuated the suppressive effect of both ischemic PostC and diazoxide application on the surge of sEPSCs. These results suggest that the opening of mito-K_ATP channels is involved in the suppressive effect of ischemic PostC on synaptic glutamate release and protection against neuronal death. We hypothesize that activation of mito-K_ATP channels prevents mitochondrial malfunction and breaks mutual facilitatory coupling between glutamate release and Ca²⁺ entry at presynaptic sites.

Early antioxidant responses via the concerted activation of NF-κB and Nrf2 characterize the gamma-radiation-induced adaptive response in quiescent human peripheral blood mononuclear cells

The radiation-induced adaptive response (RI-AR) is a non-targeted effect which is outside the scope of the classical Linear-No-Threshold (LNT) dose-response paradigm. However, the mechanisms of the RI-AR are not well understood. We have studied the RI-AR in quiescent human peripheral blood mononuclear cells (PBMCs). PBMCs in G₀ phase were 'primed' with a low dose (100 mGy gamma radiation) and then, after an 'adaptive window' of 4 h, 'challenged' with a high dose (2 Gy). A small (5.7%) increase in viability and a decrease in DNA strand breaks were seen in primed cells, compared to non-primed cells. This was consistent with lower levels of reactive oxygen species, higher mitochondrial membrane potential, and increased activity of antioxidant enzymes such as catalase, superoxide dismutase, thioredoxin reductase, and glutathione peroxidase, in the primed cells. Reduced oxidative stress in primed PBMCs correlated with greater nuclear translocation of the redox-sensitive transcription factors Nuclear factor kappa B (NF-κB) and Nuclear factor E2-related factor 2 (Nrf2). Distinct differences in responses were seen in PBMCs irradiated with low dose (100 mGy) and high dose (2 Gy). These findings provide insight into the mechanisms of radioadaptation in human cells.

Tanshinol borneol ester on nanostructured lipid carriers has longer brain and systemic effector retention and better antioxidant activity in vivo

Background

Tanshinol borneol ester (DBZ) is a hybrid of danshensu (DSS) and borneol and has anti-ischemic activity in animals. However, its low water solubility and short half-life limit its clinical application.

Methods

We prepared polyethylene glycol (PEG)-modified and DBZ-loaded nanostructured lipid carriers (DBZ-PEG-NLC) and DBZ-NLC, and examined their physical characteristics, such as particle size, zeta potential, entrapment efficiency and drug loading. The in vitro stability and pharmacokinetics in rats as well as antioxidant activity of DBZ-PEG-NLC and DBZ-NLC in a C57BL/6 mouse model of ischemia/reperfusion-related brain injury were investigated. The levels of DBZ and its hydrolyzed DSS in rat plasma and brain microdialysates were determined by liquid chromatography-mass spectroscopy/mass spectroscopy analysis.

Results

We found that the mean particle size and entrapment efficacy of DBZ-PEG-NLC were similar to that of DBZ-NLC. The DBZ-PEG-NLC, like DBZ-NLC, released DBZ in a biphasic manner with initially burst release and then prolonged slow release in vitro. Intravenous injection of DBZ-PEG-NLC resulted in significantly higher levels and longer retention periods of DBZ and DSS in plasma and the brains than DBZ-NLC and DBZ in rats. Finally, treatment with DBZ-PEG-NLC achieved a better antioxidant activity than DBZ or DBZ-NLC in mouse model of ischemia/reperfusion by reducing the levels of brain malondialdehyde, but increasing the levels of brain superoxide dismutase and glutathione.

Conclusion

DBZ-PEG-NLC is a preferable option to deliver DBZ for sustainable release of DSS and borneol in vivo, and may serve as a promising drug for effective therapy of ischemic cardiovascular and cerebrovascular diseases.

Protective effect of nicotinamide adenine dinucleotide (NAD+) against spinal cord ischemia-reperfusion injury via reducing oxidative stress-induced neuronal apoptosis

As previous studies demonstrate that oxidative stress and apoptosis play crucial roles in ischemic pathogenesis and nicotinamide adenine dinucleotide (NAD⁺) treatment attenuates oxidative stress-induced cell death among primary neurons and astrocytes as well as significantly reduce cerebral ischemic injury in rats. We used a spinal cord ischemia injury (SCII) model in rats to verify our hypothesis that NAD⁺ could ameliorate oxidative stress-induced neuronal apoptosis. Adult male rats were subjected to transient spinal cord ischemia for 60min, and different doses of NAD⁺ were administered intraperitoneally immediately after the start of reperfusion. Neurological function was determined by Basso, Beattie, Bresnahan (BBB) scores. The oxidative stress level was assessed by superoxide dismutase (SOD) activity and malondialdehyde (MDA) content. The degree of apoptosis was analyzed by deoxyuridinetriphosphate nick-end labeling (TUNEL) staining and protein levels of cleaved caspase-3 and AIF (apoptosis inducing factor). The results showed that NAD⁺ at 50 or 100mg/kg significantly decreased the oxidative stress level and neuronal apoptosis in the spinal cord of ischemia-reperfusion rats compared with saline, as accompanied with the decreased oxidative stress, NAD⁺ administration significantly restrained the neuronal apoptosis after ischemia injury while improved the neurological and motor function. These findings suggested that NAD⁺ might protect against spinal cord ischemia-reperfusion via reducing oxidative stress-induced neuronal apoptosis.

Role of Mitochondria in Cerebral Vascular Function: Energy Production, Cellular Protection, and Regulation of Vascular Tone

Mitochondria not only produce energy in the form of ATP to support the activities of cells comprising the neurovascular unit, but mitochondrial events, such as depolarization and/or ROS release, also initiate signaling events which protect the endothelium and neurons against lethal stresses via pre-/postconditioning as well as promote changes in cerebral vascular tone. Mitochondrial depolarization in vascular smooth muscle (VSM), via pharmacological activation of the ATP-dependent potassium channels on the inner mitochondrial membrane (mitoKATP channels), leads to vasorelaxation through generation of calcium sparks by the sarcoplasmic reticulum and subsequent downstream signaling mechanisms. Increased release of ROS by mitochondria has similar effects. Relaxation of VSM can also be indirectly achieved via actions of nitric oxide (NO) and other vasoactive agents produced by endothelium, perivascular and parenchymal nerves, and astroglia following mitochondrial activation. Additionally, NO production following mitochondrial activation is involved in neuronal preconditioning. Cerebral arteries from female rats have greater mitochondrial mass and respiration and enhanced cerebral arterial dilation to mitochondrial activators. Preexisting chronic conditions such as insulin resistance and/or diabetes impair mitoKATP channel relaxation of cerebral arteries and preconditioning. Surprisingly, mitoKATP channel function after transient ischemia appears to be retained in the endothelium of large cerebral arteries despite generalized cerebral vascular dysfunction. Thus, mitochondrial mechanisms may represent the elusive signaling link between metabolic rate and blood flow as well as mediators of vascular change according to physiological status. Mitochondrial mechanisms are an important, but underutilized target for improving vascular function and decreasing brain injury in stroke patients. © 2016 American Physiological Society. Compr Physiol 6:1529-1548, 2016.

Environmental Correlation Analysis for Genes Associated with Protection against Malaria

Genome-wide searches for loci involved in human resistance to malaria are currently being conducted on a large scale in Africa using case-control studies. Here, we explore the utility of an alternative approach-"environmental correlation analysis, ECA," which tests for clines in allele frequencies across a gradient of an environmental selection pressure-to identify genes that have historically protected against death from malaria. We collected genotype data from 12,425 newborns on 57 candidate malaria resistance loci and 9,756 single nucleotide polymorphisms (SNPs) selected at random from across the genome, and examined their allele frequencies for geographic correlations with long-term malaria prevalence data based on 84,042 individuals living under different historical selection pressures from malaria in coastal Kenya. None of the 57 candidate SNPs showed significant (P < 0.05) correlations in allele frequency with local malaria transmission intensity after adjusting for population structure and multiple testing. In contrast, two of the random SNPs that had highly significant correlations (P < 0.01) were in genes previously linked to malaria resistance, namely, CDH13, encoding cadherin 13, and HS3ST3B1, encoding heparan sulfate 3-O-sulfotransferase 3B1. Both proteins play a role in glycoprotein-mediated cell-cell adhesion which has been widely implicated in cerebral malaria, the most life-threatening form of this disease. Other top genes, including CTNND2 which encodes δ-catenin, a molecular partner to cadherin, were significantly enriched in cadherin-mediated pathways affecting inflammation of the brain vascular endothelium. These results demonstrate the utility of ECA in the discovery of novel genes and pathways affecting infectious disease.

The Timing of Raf/ERK and AKT Activation in Protecting PC12 Cells against Oxidative Stress

Acute brain injuries such as ischemic stroke or traumatic brain injury often cause massive neural death and irreversible brain damage with grave consequences. Previous studies have established that a key participant in the events leading to neural death is the excessive production of reactive oxygen species. Protecting neuronal cells by activating their endogenous defense mechanisms is an attractive treatment strategy for acute brain injuries. In this work, we investigate how the precise timing of the Raf/ERK and the AKT pathway activation affects their protective effects against oxidative stress. For this purpose, we employed optogenetic systems that use light to precisely and reversibly activate either the Raf/ERK or the AKT pathway. We find that preconditioning activation of the Raf/ERK or the AKT pathway immediately before oxidant exposure provides significant protection to cells. Notably, a 15-minute transient activation of the Raf/ERK pathway is able to protect PC12 cells against oxidant strike that is applied 12 hours later, while the transient activation of the AKT pathway fails to protect PC12 cells in such a scenario. On the other hand, if the pathways are activated after the oxidative insult, i.e. postconditioning, the AKT pathway conveys greater protective effect than the Raf/ERK pathway. We find that postconditioning AKT activation has an optimal delay period of 2 hours. When the AKT pathway is activated 30min after the oxidative insult, it exhibits very little protective effect. Therefore, the precise timing of the pathway activation is crucial in determining its protective effect against oxidative injury. The optogenetic platform, with its precise temporal control and its ability to activate specific pathways, is ideal for the mechanistic dissection of intracellular pathways in protection against oxidative stress.

Tissue plasminogen activator followed by antioxidant-loaded nanoparticle delivery promotes activation/mobilization of progenitor cells in infarcted rat brain

Inherent neuronal and circulating progenitor cells play important roles in facilitating neuronal and functional recovery post stroke. However, this endogenous repair process is rather limited, primarily due to unfavorable conditions in the infarcted brain involving reactive oxygen species (ROS)-mediated oxidative stress and inflammation following ischemia/reperfusion injury. We hypothesized that during reperfusion, effective delivery of antioxidants to ischemic brain would create an environment without such oxidative stress and inflammation, thus promoting activation and mobilization of progenitor cells in the infarcted brain. We administered recombinant human tissue-type plasminogen activator (tPA) via carotid artery at 3 h post stroke in a thromboembolic rat model, followed by sequential administration of the antioxidants catalase (CAT) and superoxide dismutase (SOD), encapsulated in biodegradable nanoparticles (nano-CAT/SOD). Brains were harvested at 48 h post stroke for immunohistochemical analysis. Ipsilateral brain slices from animals that had received tPA + nano-CAT/SOD showed a widespread distribution of glial fibrillary acidic protein-positive cells (with morphology resembling radial glia-like neural precursor cells) and nestin-positive cells (indicating the presence of immature neurons); such cells were considerably fewer in untreated animals or those treated with tPA alone. Brain sections from animals receiving tPA + nano-CAT/SOD also showed much greater numbers of SOX2- and nestin-positive progenitor cells migrating from subventricular zone of the lateral ventricle and entering the rostral migratory stream than in t-PA alone treated group or untreated control. Further, animals treated with tPA + nano-CAT/SOD showed far fewer caspase-positive cells and fewer neutrophils than did other groups, as well as an inhibition of hippocampal swelling. These results suggest that the antioxidants mitigated the inflammatory response, protected neuronal cells from undergoing apoptosis, and inhibited edema formation by protecting the blood-brain barrier from ROS-mediated reperfusion injury. A longer-term study would enable us to determine if our approach would assist progenitor cells to undergo neurogenesis and to facilitate neurological and functional recovery following stroke and reperfusion injury.

Spatial, temporal, and quantitative manipulation of intracellular hydrogen peroxide in cultured cells

Hydrogen peroxide (H2O2) is produced endogenously in a number of cellular compartments, including the mitochondria, the endoplasmic reticulum, peroxisomes, and at the plasma membrane, and can play divergent roles as a second messenger or a pathological toxin. It is assumed that the tuned production of H2O2 within neuronal and nonneuronal cells regulates a discreet balance between survival and death. However, a major challenge in understanding the physiological versus pathological role of H2O2 in cells has been the lack of validated methods that can spatially, temporally, and quantitatively modulate H2O2 production. A promising means of regulating endogenous H2O2 is through the expression of peroxide-producing enzyme d-amino acid oxidase (DAAO from Rhodotorula gracilis lacking a peroxisomal targeting sequence). Using viral vectors to express DAAO in distinct cell types and using targeting sequences to target DAAO to distinct subcellular sites, we can manipulate H2O2 production by applying the substrate d-alanine or permeable analogs of d-alanine. In this chapter, we describe the use of DAAO to produce H2O2 in culture models and the real-time visual validation of this technique using two-photon microscopy and chemoselective fluorescent probes.

Revisiting Cerebral Postischemic Reperfusion Injury: New Insights in Understanding Reperfusion Failure, Hemorrhage, and Edema

Cerebral postischemic reperfusion injury is defined as deterioration of ischemic brain tissue that parallels and antagonizes the benefits of restoring cerebral circulation after therapeutic thrombolysis for acute ischemic stroke. To understand the paradox of injury caused by treatment, we first emphasize the phenomenon in which recanalization of an occluded artery does not lead to tissue reperfusion. Additionally, no-reflow after recanalization may be due to injury of the neurovascular unit, distal microthrombosis, or both, and certainly worsens outcome. We examine the mechanism of molecular and sub-cellular damage in the neurovascular unit, notably oxidative stress, mitochondrial dysfunction, and apoptosis. At the level of the neurovascular unit, which mediates crosstalk between the damaged brain and systemic responses in blood, we summarize emerging evidence demonstrating that individual cell components play unique and cumulative roles that lead to damage of the blood–brain barrier and neurons. Furthermore, we review the latest developments in establishing a link between the immune system and microvascular dysfunction during ischemic reperfusion. Progress in assessing reperfusion injury has also been made, and we review imaging studies using various magnetic resonance imaging modalities. Lastly, we explore potential treatment approaches, including ischemic preconditioning, postconditioning, pharmacologic agents, and hypothermia.

Pretreatment with 2-(4-methoxyphenyl)ethyl-2-acetamido-2-deoxy-β-D-pyranoside attenuates cerebral ischemia/reperfusion-induced injury in vitro and in vivo

Salidroside, extracted from the root of Rhodiola rosea L, is known for its pharmacological properties, in particular its neuroprotective effects. 2-(4-Methoxyphenyl) ethyl-2-acetamido-2-deoxy-β-D-pyranoside (GlcNAc-Sal), an analog of salidroside, was recently synthesized and shown to possess neuroprotective properties. The purpose of the current study was to investigate the neuroprotective effects of GlcNAc-Sal against oxygen-glucose deprivation-reperfusion (OGD-R)-induced neurotoxicity in vitro and global cerebral ischemia-reperfusion (GCI-R) injury in vivo. Cell viability tests and Hoechst 33342 staining confirmed that GlcNAc-Sal pretreatment markedly attenuated OGD-R induced apoptotic cell death in immortalized mouse hippocampal HT22 cells. Western blot, immunofluorescence and PCR analyses revealed that GlcNAc-Sal pretreatment restored the balance of pro- and anti-apoptotic proteins and inhibited the activation of caspase-3 and PARP induced by OGD-R treatment. Further analyses showed that GlcNAc-Sal pretreatment antagonized reactive oxygen species (ROS) generation, iNOS-derived NO production and NO-related apoptotic cell death during OGD-R stimulation. GCI-R was induced by bilateral common carotid artery occlusion (BCCAO) and reperfusion in mice in vivo. Western blot analysis showed that GlcNAc-Sal pretreatment decreased the expression of caspase-3 and increased the expression of Bcl-2 (B-cell lymphoma 2)/Bax (Bcl-2-associated X protein) induced by GCI-R treatment. Our findings suggest that GlcNAc-Sal pretreatment prevents brain ischemia reperfusion injury by the direct or indirect suppression of cell apoptosis and GlcNAc-Sal could be developed as a broad-spectrum agent for the prevention and/or treatment of cerebral ischemic injury.

Mitochondrial mechanisms in cerebral vascular control: shared signaling pathways with preconditioning

Mitochondrial-initiated events protect the neurovascular unit against lethal stress via a process called preconditioning, which independently promotes changes in cerebrovascular tone through shared signaling pathways. Activation of adenosine triphosphate (ATP)-dependent potassium channels on the inner mitochondrial membrane (mitoKATP channels) is a specific and dependable way to induce protection of neurons, astroglia, and cerebral vascular endothelium. Through the opening of mitoKATP channels, mitochondrial depolarization leads to activation of protein kinases and transient increases in cytosolic calcium (Ca(2+)) levels that activate terminal mechanisms that protect the neurovascular unit against lethal stress. The release of reactive oxygen species from mitochondria has similar protective effects. Signaling elements of the preconditioning pathways also are involved in the regulation of vascular tone. Activation of mitoKATP channels in cerebral arteries causes vasodilation, with cell-specific contributions from the endothelium, vascular smooth muscles, and nerves. Preexisting chronic conditions, such as insulin resistance and/or diabetes, prevent preconditioning and impair relaxation to mitochondrial-centered responses in cerebral arteries. Surprisingly, mitochondrial activation after anoxic or ischemic stress appears to protect cerebral vascular endothelium and promotes the restoration of blood flow; therefore, mitochondria may represent an important, but underutilized target in attenuating vascular dysfunction and brain injury in stroke patients.

Mitochondrial stress signaling promotes cellular adaptations

Mitochondrial dysfunction has been implicated in the aetiology of many complex diseases, as well as the ageing process. Much of the research on mitochondrial dysfunction has focused on how mitochondrial damage may potentiate pathological phenotypes. The purpose of this review is to draw attention to the less well-studied mechanisms by which the cell adapts to mitochondrial perturbations. This involves communication of stress to the cell and successful induction of quality control responses, which include mitophagy, unfolded protein response, upregulation of antioxidant and DNA repair enzymes, morphological changes, and if all else fails apoptosis. The mitochondrion is an inherently stressful environment and we speculate that dysregulation of stress signaling or an inability to switch on these adaptations during times of mitochondrial stress may underpin mitochondrial dysfunction and hence amount to pathological states over time.

Methods for studying oxidative regulation of protein kinase C

The protein kinase C (PKC) family of isoenzymes may be a crucial player in transducing H2O2-induced signaling in a wide variety of physiological and pathophysiological processes. PKCs contain unique structural features that make them highly susceptible to oxidative modification. Depending on the site of oxidation and the extent to which it is modified, PKC can be either activated or inactivated by H2O2. The N-terminal regulatory domain contains zinc-binding, cysteine-rich motifs that are readily oxidized by H2O2. When oxidized, the autoinhibitory function of the regulatory domain is compromised, and as a result, PKC is activated in a lipid cofactor-independent manner. The C-terminal catalytic domain contains several reactive cysteine residues, which when oxidized with a higher concentration of H2O2 leads to an inactivation of PKC. Here, we describe the methods used to induce oxidative modification of purified PKC isoenzymes by H2O2 and the methods to assess the extent of this modification. Protocols are given for isolating oxidatively activated PKC isoenzymes from cells treated with H2O2. Furthermore, we describe the methods used to assess indirect regulation of PKC isoenzymes by determining their cytosol to membrane or mitochondrial translocation and tyrosine phosphorylation of PKCδ in response to sublethal levels of H2O2. Finally, as an example, we describe the methods used to demonstrate the role of H2O2-mediated cell signaling of PKCɛ in green tea polyphenol-induced preconditioning against neuronal cell death caused by oxygen-glucose deprivation and reoxygenation, an in vitro model for cerebral ischemic/reperfusion injury.

Green tea polyphenols precondition against cell death induced by oxygen-glucose deprivation via stimulation of laminin receptor, generation of reactive oxygen species, and activation of protein kinase Cε

As the development of synthetic drugs for the prevention of stroke has proven challenging, utilization of natural products capable of preconditioning neuronal cells against ischemia-induced cell death would be a highly useful complementary approach. In this study using an oxygen-glucose deprivation and reoxygenation (OGD/R) model in PC12 cells, we show that 2-day pretreatment with green tea polyphenols (GTPP) and their active ingredient, epigallocatechin-3-gallate (EGCG), protects cells from subsequent OGD/R-induced cell death. A synergistic interaction was observed between GTPP constituents, with unfractionated GTPP more potently preconditioning cells than EGCG. GTPP-induced preconditioning required the 67-kDa laminin receptor (67LR), to which EGCG binds with high affinity. 67LR also mediated the generation of reactive oxygen species (ROS) via activation of NADPH oxidase. An exogenous ROS-generating system bypassed 67LR to induce preconditioning, suggesting that sublethal levels of ROS are indeed an important mediator in GTPP-induced preconditioning. This role for ROS was further supported by the fact that antioxidants blocked GTPP-induced preconditioning. Additionally, ROS induced an activation and translocation of protein kinase C (PKC), particularly PKCε from the cytosol to the membrane/mitochondria, which was also blocked by antioxidants. The crucial role of PKC in GTPP-induced preconditioning was supported by use of its specific inhibitors. Preconditioning was increased by conditional overexpression of PKCε and decreased by its knock-out with siRNA. Collectively, these results suggest that GTPP stimulates 67LR and thereby induces NADPH oxidase-dependent generation of ROS, which in turn induces activation of PKC, particularly prosurvival isoenzyme PKCε, resulting in preconditioning against cell death induced by OGD/R.

Neuroglobin, a novel target for endogenous neuroprotection against stroke and neurodegenerative disorders

Brain neurons and tissues respond to sublethal injury by activating endogenous protective pathways. Recently, following the failure of a large number of clinical trials for protective strategies against stroke that aim to inhibit a specific ischemia response pathway, endogenous neuroprotection has emerged as a more promising and hopeful strategy for development of therapeutics against stroke and neurodegenerative disorders. Neuroglobin (Ngb) is an oxygen-binding globin protein that is highly and specifically expressed in brain neurons. Accumulating evidence have clearly demonstrated that Ngb is an endogenous neuroprotective molecule against hypoxic/ischemic and oxidative stress-related insults in cultured neurons and animals, as well as neurodegenerative disorders such as Alzheimer’s disease, thus any pharmacological strategy that can up-regulate endogenous Ngb expression may lead to novel therapeutics against these brain disorders. In this review, we summarize recent studies about the biological function, regulation of gene expression, and neuroprotective mechanisms of Ngb. Furthermore, strategies for identification of chemical compounds that can up-regulate endogenous Ngb expression for neuroprotection against stroke and neurodegenerative disorders are discussed.

Lipocalin-type prostaglandin D synthase protects against oxidative stress-induced neuronal cell death

L-PGDS [lipocalin-type PGD (prostaglandin D) synthase] is a dual-functional protein, acting as a PGD2-producing enzyme and a lipid transporter. L-PGDS is a member of the lipocalin superfamily and can bind a wide variety of lipophilic molecules. In the present study we demonstrate the protective effect of L-PGDS on H2O2-induced apoptosis in neuroblastoma cell line SH-SY5Y. L-PGDS expression was increased in H2O2-treated neuronal cells, and the L-PGDS level was highly associated with H2O2-induced apoptosis, indicating that L-PGDS protected the neuronal cells against H2O2-mediated cell death. A cell viability assay revealed that L-PGDS protected against H2O2-induced cell death in a concentration-dependent manner. Furthermore, the titration of free thiols in H2O2-treated L-PGDS revealed that H2O2 reacted with the thiol of Cys65 of L-PGDS. The MALDI-TOF (matrix-assisted laser-desorption ionization-time-of-flight)-MS spectrum of H2O2-treated L-PGDS showed a 32 Da increase in the mass relative to that of the untreated protein, showing that the thiol was oxidized to sulfinic acid. The binding affinities of oxidized L-PGDS for lipophilic molecules were comparable with those of untreated L-PGDS. Taken together, these results demonstrate that L-PGDS protected against neuronal cell death by scavenging reactive oxygen species without losing its ligand-binding function. The novel function of L-PGDS could be useful for the suppression of oxidative stress-mediated neurodegenerative diseases.

Differential effects of delta and epsilon protein kinase C in modulation of postischemic cerebral blood flow

Cerebral ischemia causes cerebral blood flow (CBF) derangements resulting in neuronal damage by enhanced protein kinase C delta (δPKC) levels leading to hippocampal and cortical neuronal death after ischemia. Contrarily, activation of εPKC mediates ischemic tolerance by decreasing vascular tone providing neuroprotection. However, whether part of this protection is due to the role of differential isozymes of PKCs on CBF following cerebral ischemia remains poorly understood. Rats pretreated with a δPKC specific inhibitor (δV1-1, 0.5 mg/kg) exhibited attenuation of hyperemia and latent hypoperfusion characterized by vasoconstriction followed by vasodilation of microvessels after two-vessel occlusion plus hypotension. In an asphyxial cardiac arrest (ACA) model, rats treated with δ V1-1 (pre- and postischemia) exhibited improved perfusion after 24 h and less hippocampal CA1 and cortical neuronal death 7 days after ACA. On the contrary, εPKC-selective peptide activator, conferred neuroprotection in the CA1 region of the rat hippocampus 30 min before induction of global cerebral ischemia and decreased regional CBF during the reperfusion phase. These opposing effects of δ v. εPKC suggest a possible therapeutic potential by modulating CBF preventing neuronal damage after cerebral ischemia.

Redox regulation of intracellular zinc: molecular signaling in the life and death of neurons

Zn(2+) has emerged as a major regulator of neuronal physiology, as well as an important signaling agent in neural injury. The intracellular concentration of this metal is tightly regulated through the actions of Zn(2+) transporters and the thiol-rich metal binding protein metallothionein, closely linking the redox status of the cell to cellular availability of Zn(2+). Accordingly, oxidative and nitrosative stress during ischemic injury leads to an accumulation of neuronal free Zn(2+) and the activation of several downstream cell death processes. While this Zn(2+) rise is an established signaling event in neuronal cell death, recent evidence suggests that a transient, sublethal accumulation of free Zn(2+) can also play a critical role in neuroprotective pathways activated during ischemic preconditioning. Thus, redox-sensitive proteins, like metallothioneins, may play a critical role in determining neuronal cell fate by regulating the localization and concentration of intracellular free Zn(2+).

Protective effects of quercetin against hydrogen peroxide-induced apoptosis in human neuronal SH-SY5Y cells

Hydrogen peroxide (H(2)O(2)) is a major reactive oxygen species that has been implicated in various neurodegenerative diseases. Quercetin, one of the plant flavonoids, has been reported to harbor various physiological properties including antioxidant activity. In this study, we investigated the neuroprotective effects of quercetin against H(2)O(2)-induced apoptosis in human neuronal SH-SY5Y cells. H(2)O(2)-mediated cytotoxicity and lactate dehydrogenase release were suppressed in a quercetin concentration-dependent manner. In addition, quercetin repressed the expression of the pro-apoptotic Bax gene and enhanced that of the anti-apoptotic Bcl-2 gene in SH-SY5Y cells. Moreover, quercetin effectively inhibited the activation of the caspase cascade that leads to DNA fragmentation, a key feature of apoptosis, and subsequent cell death. These results indicate the importance of quercetin in protecting against H(2)O(2)-mediated neuronal cell death. Thus, quercetin might potentially serve as an agent for prevention of neurodegenerative diseases caused by oxidative stress and apoptosis.

Activation of protein kinase C delta following cerebral ischemia leads to release of cytochrome C from the mitochondria via bad pathway

BACKGROUND

The release of cytochrome c from the mitochondria following cerebral ischemia is a key event leading to cell death. The goal of the present study was to determine the mechanisms involved in post-ischemic activation of protein kinase c delta (δPKC) that lead to cytochrome c release.

METHODS/FINDINGS

We used a rat model of cardiac arrest as an in vivo model, and an in vitro analog, oxygen glucose deprivation (OGD) in rat hippocampal synaptosomes. Cardiac arrest triggered translocation of δPKC to the mitochondrial fraction at 1 h reperfusion. In synaptosomes, the peptide inhibitor of δPKC blocked OGD-induced translocation to the mitochondria. We tested two potential pathways by which δPKC activation could lead to cytochrome c release: phosphorylation of phospholipid scramblase-3 (PLSCR3) and/or protein phosphatase 2A (PP2A). Cardiac arrest increased levels of phosphorlyated PLSCR3; however, inhibition of δPKC translocation failed to affect the OGD-induced increase in PLSCR3 in synaptosomal mitochondria suggesting the post-ischemic phosphorylation of PLSCR3 is not mediated by δPKC. Inhibition of either δPKC or PP2A decreased cytochrome c release from synaptosomal mitochondria. Cardiac arrest results in the dephosphorylation of Bad and Bax, both downstream targets of PP2A promoting apoptosis. Inhibition of δPKC or PP2A prevented OGD-induced Bad, but not Bax, dephosphorylation. To complement these studies, we used proteomics to identify novel mitochondrial substrates of δPKC.

CONCLUSIONS

We conclude that δPKC initiates cytochrome c release via phosphorylation of PP2A and subsequent dephosphorylation of Bad and identified δPKC, PP2A and additional mitochondrial proteins as potential therapeutic targets for ischemic neuroprotection.

Neurovascular protection by ischaemic tolerance: role of nitric oxide

Nitric oxide (NO) has emerged as a key mediator in the mechanisms of ischaemic tolerance induced by a wide variety of preconditioning stimuli. NO is involved in the brain protection that develops either early (minutes-hours) or late (days-weeks) after the preconditioning stimulus. However, the sources of NO and the mechanisms underlying the protective effects differ substantially. While in early preconditioning NO is produced by the endothelial and neuronal isoform of NO synthase, in delayed preconditioning NO is synthesized by the inducible or 'immunological' isoform of NO synthase. Furthermore, in early preconditioning, NO acts through the canonical cGMP pathway, possibly through protein kinase G and opening of mitochondrial K(ATP) channels. In late preconditioning, the protection is mediated by peroxynitrite formed by the reaction of NO with superoxide derived from the enzyme NADPH oxidase. The mechanisms by which peroxynitrite exerts its protective effect may include improvement of post-ischaemic cerebrovascular function, leading to enhancement of blood flow to the ischaemic territory, and expression of prosurvival genes resulting in cytoprotection. The evidence suggests that NO can engage highly effective and multifunctional prosurvival pathways, which could be exploited for the prevention and treatment of cerebrovascular pathologies.

Lipid peroxidation-derived reactive aldehydes directly and differentially impair spinal cord and brain mitochondrial function

Mitochondrial bioenergetic dysfunction in traumatic spinal cord and brain injury is associated with post-traumatic free radical-mediated oxidative damage to proteins and lipids. Lipid peroxidation by-products, such as 4-hydroxy-2-nonenal and acrolein, can form adducts with proteins and exacerbate the effects of direct free radical-induced protein oxidation. The aim of the present investigation was to determine and compare the direct contribution of 4-hydroxy-2-nonenal and acrolein to spinal cord and brain mitochondrial dysfunction. Ficoll gradient-isolated mitochondria from normal rat spinal cords and brains were treated with carefully selected doses of 4-hydroxy-2-nonenal or acrolein, followed by measurement of complex I- and complex II-driven respiratory rates. Both compounds were potent inhibitors of mitochondrial respiration in a dose-dependent manner. 4-Hydroxy-2-nonenal significantly compromised spinal cord mitochondrial respiration at a 0.1-muM concentration, whereas 10-fold greater concentrations produced a similar effect in brain. Acrolein was more potent than 4-hydroxy-2-nonenal, significantly decreasing spinal cord and brain mitochondrial respiration at 0.01 muM and 0.1 muM concentrations, respectively. The results of this study show that 4-hydroxy-2-nonenal and acrolein can directly and differentially impair spinal cord and brain mitochondrial function, and that the targets for the toxic effects of aldehydes appear to include pyruvate dehydrogenase and complex I-associated proteins. Furthermore, they suggest that protein modification by these lipid peroxidation products may directly contribute to post-traumatic mitochondrial damage, with spinal cord mitochondria showing a greater sensitivity than those in brain.

Anti-oxidative effects of the biennial flower of Panax notoginseng against H2O2-induced cytotoxicity in cultured PC12 cells

Background

Radix notoginseng is used in Chinese medicine to improve blood circulation and clotting; however, the pharmacological activities of other parts of Panax notoginseng have yet to be explored. The present study reports the anti-oxidative effects of various parts of Panax notoginseng.

Methods

Various parts of Panax notoginseng, including the biennial flower, stem-leaf, root-rhizome, fiber root and sideslip, were used to prepare extracts and analyzed for their anti-oxidation effects, namely suppressing xanthine oxidase activity, H₂O₂-induced cytotoxicity and H₂O₂-induced ROS formation.

Results

Among various parts of the herb (biennial flower, stem-leaf, root-rhizome, fiber root and sideslip), the water extract of the biennial flower showed the strongest effects in (i) inhibiting the enzymatic activity of xanthine oxidase and (ii) protecting neuronal PC12 cells against H₂O₂-induced cytotoxicity. Only the water extracts demonstrated such anti-oxidative effects while the ethanol extracts did not exert significant effects in suppressing xanthine oxidase and H₂O₂-induced neuronal cytotoxicity.

Conclusions

The present study demonstrates the biennial flower of Panax notoginseng to have neuroprotection effect on cultured neurons and the underlying protection mechanism may involve anti-oxidation.

Calcium and mitochondrial reactive oxygen species generation: how to read the facts

A number of recent discoveries indicate that abnormal Ca2+ signaling, oxidative stress, and mitochondrial dysfunction are involved in the neuronal damage in Alzheimer's disease. However, the literature on the interactions between these factors is controversial especially in the interpretation of the cause-effect relationship between mitochondrial damage induced by Ca2+ overload and the production of reactive oxygen species (ROS). In this review, we survey the experimental observations on the Ca2+-induced mitochondrial ROS production, explain the sources of controversy in interpreting these results, and discuss the different molecular mechanisms underlying the effect of Ca2+ on the ROS emission by brain mitochondria.

Mitochondria: the missing link between preconditioning and neuroprotection

The quote "what does not kill you makes you stronger" perfectly describes the preconditioning phenomenon - a paradigm that affords robust brain tolerance in the face of neurodegenerative insults. Over the last few decades, many attempts have been made to identify the molecular mechanisms involved in preconditioning-induced protective responses, and recent data suggests that many of these mechanisms converge on the mitochondria, positing mitochondria as master regulators of preconditioning-triggered endogenous neuroprotection. In this review, we critically discuss evidence for the involvement of mitochondria within the preconditioning paradigm. We will highlight the crucial targets and mediators by which mitochondria are integrated into neuroprotective signaling pathways that underlie preconditioning, putting focus on mitochondrial respiratory chain and mitochondrial reactive oxygen species, mitochondrial ATP-sensitive potassium channels, mitochondrial permeability transition pore, uncoupling proteins, and mitochondrial antioxidant enzyme manganese superoxide dismutase. We also discuss the role of mitochondria in the induction of hypoxia-inducible factor-1, a transcription factor engaged in preconditioning-mediated neuroprotective effects. The identification of intrinsic mitochondrial mechanisms involved in preconditioning will provide new insights which can be translated into potential pharmacological interventions aimed at counteracting neurodegeneration.

Neuron specific metabolic adaptations following multi-day exposures to oxygen glucose deprivation

Prior exposure to sub toxic insults can induce a powerful endogenous neuroprotective program known as ischemic preconditioning. Current models typically rely on a single stress episode to induce neuroprotection whereas the clinical reality is that patients may experience multiple transient ischemic attacks (TIAs) prior to suffering a stroke. We sought to develop a neuron-enriched preconditioning model using multiple oxygen glucose deprivation (OGD) episodes to assess the endogenous protective mechanisms neurons implement at the metabolic and cellular level. We found that neurons exposed to a five minute period of glucose deprivation recovered oxygen utilization and lactate production using novel microphysiometry techniques. Using the non-toxic and energetically favorable five minute exposure, we developed a preconditioning paradigm where neurons are exposed to this brief OGD for three consecutive days. These cells experienced a 45% greater survival following an otherwise lethal event and exhibited a longer lasting window of protection in comparison to our previous in vitro preconditioning model using a single stress. As in other models, preconditioned cells exhibited mild caspase activation, an increase in oxidized proteins and a requirement for reactive oxygen species for neuroprotection. Heat shock protein 70 was upregulated during preconditioning, yet the majority of this protein was released extracellularly. We believe coupling this neuron-enriched multi-day model with microphysiometry will allow us to assess neuronal specific real-time metabolic adaptations necessary for preconditioning.

Identification of a voltage-gated potassium channel in gerbil hippocampal mitochondria

Transient cerebral ischemia is known to induce endogenous mechanisms that can prevent or delay neuronal injury, such as the activation of mitochondrial potassium channels. However, the molecular mechanism of this effect remains unclear. In this study, the single-channel activity was measured using the patch-clamp technique of the mitoplasts isolated from gerbil hippocampus. In 70% of all patches, a potassium-selective current with the properties of a voltage-gated Kv-type potassium channel was recorded with mean conductance 109+/-6pS in a symmetrical solution. The channel was blocked at negative voltages and irreversibly by margatoxin, a specific Kv1.3 channel inhibitor. The ATP/Mg(2+) complex and Ca(2+) ions had no effect on channel activity. Additionally, agitoxin-2, a potent inhibitor of voltage-gated potassium channels, had no effect on mitochondrial channel activity. This observation suggests that in contrast to surface membrane channels, the mitochondrial voltage-gated potassium channel could have a different molecular structure with no affinity to agitoxin-2. Western blots of gerbil hippocampal mitochondria and immunohistochemistry on gerbil brain sections confirmed the expression of the Kv1.3 protein in mitochondria. Our findings indicate that gerbil brain mitochondria contain a voltage-gated potassium channel that can influence the function of mitochondria in physiological and pathological conditions and that has properties similar to the surface membrane Kv1.3 channel.

Ischemic preconditioning mediates cyclooxygenase-2 expression via nuclear factor-kappa B activation in mixed cortical neuronal cultures

Nuclear factor-kappaB (NF-κB) activation occurs following ischemic preconditioning (IPC) in brain. However, the upstream signaling messengers and down-stream targets of NF-κB required for induction of IPC remain undefined. In a previous study, we demonstrated that epsilon protein kinase c (εPKC) was a key mediator of IPC in brain. Activation of εPKC induced cyclooygenase-2 (COX-2) expression and conferred ischemic tolerance in the neuronal and hippocampal slice models. Here, we hypothesized that IPC-mediated COX-2 expression was mediated by NF-κB. We tested this hypothesis in mixed cortical neuron/astrocyte cell cultures. To simulate IPC or ischemia, cell cultures were exposed to 1 or 4 h of oxygen-glucose deprivation, respectively. Our results demonstrated translocation of p65 and p50 subunits of NF-κB into nucleus following IPC or εPKC activation. NF-κB inhibition with pyrrolidine dithiocarbamate (10 μM) abolished IPC or εPKC activator-mediated neuroprotection indicating that NF-κB activation was involved in ischemic tolerance. In parallel studies, inhibition of either εPKC or the extracellular signal-regulated kinase (ERK 1/2) pathway reduced IPC-induced NF-κB activation. Finally, inhibition of NF-κB blocked IPC-induced COX-2 expression. In conclusion, we demonstrated that IPC-signaling cascade comprises εPKC activation→ERK1/2 activation→NF-κB translocation to nucleus→COX-2 expression resulting in neuroprotection in mixed neuronal culture.

Brain plasticity after ischemic episode

Brain plasticity describes the potential of the organ for adaptive changes involved in various phenomena in health and disease. A substantial amount of experimental evidence, received in animal and cell models, shows that a cascade of plastic changes at the molecular, cellular, and tissue levels, is initiated in different regions of the postischemic brain. Underlying mechanisms include neurochemical alterations, functional changes in excitatory and inhibitory synapses, axonal and dendritic sprouting, and reorganization of sensory and motor central maps. Multiple lines of evidence indicate numerous points in which the process of postischemic recovery may be influenced with the aim to restore the full capacity of the brain tissue injured by an ischemic episode.

Measurement of mitochondrial ROS production

The significance of reactive oxygen species (ROS) as aggravating or primary factors in numerous pathologies is widely recognized, with mitochondria being considered the major intracellular source of ROS. It is not yet possible to routinely measure mitochondrial ROS in animals or cultured cells with a reasonable degree of certainty. However, at the level of isolated mitochondria, one can easily monitor and quantify the rate of ROS production, identify major sites of ROS production, and compare the rates of ROS production in mitochondria isolated from normal and diseased tissue. In this chapter, we describe in detail the most recent and reliable method to measure mitochondrial ROS as the rate of H2O2 emission. This method may be employed with minimal modifications to measure H2O2 production by mitochondria isolated from various tissues and under a wide variety of experimental conditions.

Protein kinase C epsilon activation delays neuronal depolarization during cardiac arrest in the euthermic arctic ground squirrel

During the pre-hibernation season, arctic ground squirrels (AGS) can tolerate 8 min of asphyxial cardiac arrest (CA) without detectable brain pathology. Better understanding of the mechanisms regulating innate ischemia tolerance in AGS has the potential to facilitate the development of novel prophylactic agents to induce ischemic tolerance in patients at risk of stroke or CA. We hypothesized that neuroprotection in AGS involves robust maintenance of ion homeostasis similar to anoxia-tolerant turtles. Ion homeostasis was assessed by monitoring ischemic depolarization (ID) in cerebral cortex during CA in vivo and during oxygen glucose deprivation in vitro in acutely prepared hippocampal slices. In both models, the onset of ID was significantly delayed in AGS compared with rats. The epsilon protein kinase C (epsilonPKC) is a key mediator of neuroprotection and inhibits both Na+/K+-ATPase and voltage-gated sodium channels, primary mediators of the collapse of ion homeostasis during ischemia. The selective peptide inhibitor of epsilonPKC (epsilonV1-2) shortened the time to ID in brain slices from AGS but not in rats despite evidence that epsilonV1-2 decreased activation of epsilonPKC in brain slices from both rats and AGS. These results support the hypothesis that epsilonPKC activation delays the collapse of ion homeostasis during ischemia in AGS.

Repeated exposure to MDMA provides neuroprotection against subsequent MDMA-induced serotonin depletion in brain

Repeated exposure to sub-lethal insults has been reported to result in neuroprotection against a subsequent deleterious insult. The purpose of this study was to evaluate whether repeated exposure (preconditioning) to a non-5-HT depleting dose of MDMA in adult rats provides neuroprotection against subsequent MDMA-induced 5-HT depletion. Treatment of rats with MDMA (10 mg/kg, ip every 2 h for 4 injections) resulted in a 50-65% depletion of 5-HT in the striatum, hippocampus and cortex, and these depletions were significantly attenuated in rats that received a preconditioning regimen of MDMA (10 mg/kg, ip daily for 4 days). The 5-HT depleting regimen of MDMA also resulted in a 40-80% reduction in 5-HT transporter immunoreactivity (SERT(ir)), and the reduction in SERT(ir) also was completely attenuated in MDMA-preconditioned animals. Preconditioning with MDMA (10 mg/kg, ip) daily for 4 days provided neuroprotection against methamphetamine-induced 5-HT depletion, but not dopamine depletion, in the striatum. Additional studies were conducted to exclude the possibility that alterations in MDMA pharmacokinetics or MDMA-induced hyperthermia in rats previously exposed to MDMA contribute towards neuroprotection. During the administration of the 5-HT depleting regimen of MDMA, there was no difference in the extracellular concentration of the drug in the striatum of rats that had received 4 prior, daily injections of vehicle or MDMA. Moreover, there was no difference in the hyperthermic response to the 5-HT depleting regimen of MDMA in rats that had earlier received 4 daily injections of vehicle or MDMA. Furthermore, hyperthermia induced by MDMA during preconditioning appears not to contribute towards neuroprotection, inasmuch as preconditioning with MDMA at a low ambient temperature at which hyperthermia was absent did not alter the neuroprotection provided by the preconditioning regimen. Thus, prior exposure to MDMA affords protection against the long-term depletion of brain 5-HT produced by subsequent MDMA administration. The mechanisms underlying preconditioning-induced neuroprotection for MDMA remain to be determined.

Neuroprotective roles and mechanisms of neuroglobin

OBJECTIVE

The objectives of this work were to update and summarize recent experimental works on neuroglobin, mainly focus on its neuroprotective effects and the mechanisms.

METHODS

The literature was reviewed using PubMed database, and some of the recent findings from our laboratory were included.

RESULTS

Neuroglobin is a recently discovered tissue globin with a high affinity for oxygen and is widely and specifically expressed in neurons of vertebrate's central and peripheral nervous systems. Investigations in the past several years have advanced our knowledge on the functions and mechanisms of neuroglobin, but many issues remain unclear. Emerging reports have shown that overexpression of neuroglobin confers neuroprotection against neuronal hypoxia or ischemia-induced damage in cultured neurons and in cerebral ischemic animal models. Accumulating findings suggest several possible neuroprotective roles and mechanisms including ligand binding and oxygen sensing, modulation of cell signaling pathways and maintenance of mitochondria function.

CONCLUSION

Emerging experimental works suggest that neuroglobin is neuroprotective against hypoxic/ischemic insults, probably via ligand binding and oxygen sensing, modulation of cell signaling pathways and maintenance of mitochondria function.

Preconditioning and tolerance against cerebral ischaemia: from experimental strategies to clinical use

Neuroprotection and brain repair in patients after acute brain damage are still major unfulfilled medical needs. Pharmacological treatments are either ineffective or confounded by adverse effects. Consequently, endogenous mechanisms by which the brain protects itself against noxious stimuli and recovers from damage are being studied. Research on preconditioning, also known as induced tolerance, over the past decade has resulted in various promising strategies for the treatment of patients with acute brain injury. Several of these strategies are being tested in randomised clinical trials. Additionally, research into preconditioning has led to the idea of prophylactically inducing protection in patients such as those undergoing brain surgery and those with transient ischaemic attack or subarachnoid haemorrhage who are at high risk of brain injury in the near future. In this Review, we focus on the clinical issues relating to preconditioning and tolerance in the brain; specifically, we discuss the clinical situations that might benefit from such procedures. We also discuss whether preconditioning and tolerance occur naturally in the brain and assess the most promising candidate strategies that are being investigated.

Effects of neuroglobin overexpression on mitochondrial function and oxidative stress following hypoxia/reoxygenation in cultured neurons

Neuroglobin (Ngb) is a recently discovered tissue globin with a high affinity for oxygen that is widely and specifically expressed in neurons of vertebrate central and peripheral nervous systems. Our laboratory and others have shown Ngb overexpression can protect neurons against hypoxic/ischemic insults, but the underlying mechanisms remain poorly understood. In this study, we examined the effects of Ngb overexpression on mitochondrial function, oxidative stress, and neurotoxicity in primary cortical neurons following hypoxia/reoxygenation (H/R). Ngb-overexpressing transgenic neurons (Ngb-Tg) were significantly protected against H/R-induced cell death. Rates of decline in ATP levels, MTT reduction, and mitochondrial membrane potential were significantly ameliorated in Ngb-Tg neurons. Furthermore, Ngb overexpression reduced superoxide anion generation after H/R, whereas glutathione levels were significantly improved compared with WT controls. Taken together, these data suggest that Ngb is neuroprotective against hypoxia, in part by improving mitochondria function and decreasing oxidative stress.

Resveratrol pretreatment protects rat brain from cerebral ischemic damage via a sirtuin 1-uncoupling protein 2 pathway

Resveratrol is a natural polyphenol found in grapes and wine and has been associated with protective effects against cardiovascular diseases. In vitro, both resveratrol preconditioning (RPC) and ischemic preconditioning (IPC) require activation of sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase, to induce neuroprotection against cerebral ischemia. In the present study, we tested two hypotheses: (a) that neuroprotection against cerebral ischemia can be induced by RPC in vivo; and (b) that RPC neuroprotection involves alterations in mitochondrial function via the SIRT1 target mitochondrial uncoupling protein 2 (UCP2). IPC was induced by 2 min of global ischemia (temporary bilateral carotid artery occlusion with hypotension), and RPC, by i.p. injection of resveratrol at 10, 50 and 100 mg/kg dosages. Forty-eight hours later, we compared the neuroprotective efficacy of RPC and IPC in vulnerable cornu ammonis 1 hippocampal pyramidal neurons using a rat model of asphyxial cardiac arrest (ACA). SIRT1 activity was measured using a SIRT1-specific fluorescent enzyme activity assay. In hippocampal mitochondria isolated 48 h after IPC or RPC, we measured UCP2 levels, membrane potential, respiration, and the mitochondrial ATP synthesis efficiency (ADP/O ratio). Both IPC and RPC induced tolerance against brain injury induced by cardiac arrest in this in vivo model. IPC increased SIRT1 activity at 48 h, while RPC increased SIRT1 activity at 1 h but not 48 h after treatment in hippocampus. Resveratrol significantly decreased UCP2 levels by 35% compared to sham-treated rats. The SIRT1-specific inhibitor sirtinol abolished the neuroprotection afforded by RPC and the decrease in UCP2 levels. Finally, RPC significantly increased the ADP/O ratio in hippocampal mitochondria reflecting enhanced ATP synthesis efficiency. In conclusion, in vivo resveratrol pretreatment confers neuroprotection similar to IPC via the SIRT1-UCP2 pathway.

Mitochondrial-mediated suppression of ROS production upon exposure of neurons to lethal stress: mitochondrial targeted preconditioning

Preconditioning represents the condition where transient exposure of cells to an initiating event leads to protection against subsequent, potentially lethal stimuli. Recent studies have established that mitochondrial-centered mechanisms are important mediators in promoting development of the preconditioning response. However, many details concerning these mechanisms are unclear. The purpose of this review is to describe the initiating and subsequent intracellular events involving mitochondria which can lead to neuronal preconditioning. These mitochondrial specific targets include: 1) potassium channels located on the inner mitochondrial membrane; 2) respiratory chain enzymes; and 3) oxidative phosphorylation. Following activation of mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels and/or increased production of reactive oxygen species (ROS) resulting from the disruption of the respiratory chain or during energy substrate deprivation, morphological changes or signaling events involving protein kinases confer immediate or delayed preconditioning on neurons that will allow them to survive otherwise lethal insults. While the mechanisms involved are not known with certainty, the results of preconditioning are the enhanced neuronal viability, the attenuated influx of intracellular calcium, the reduced availability of ROS, the suppression of apoptosis, and the maintenance of ATP levels during and following stress.