Preconditioning-induced neuroprotection is mediated by reactive oxygen species and activation of the transcription factor nuclear factor-kappaB

Intermittent Hypobaric Hypoxic Preconditioning Provides Neuroprotection by Increasing Antioxidant Activity, Erythropoietin Expression and Preventing Apoptosis and Astrogliosis in the Brain of Adult Rats Exposed to Acute Severe Hypoxia

BACKGROUND

Exposure to intermittent hypoxia has been demonstrated to be an efficient tool for hypoxic preconditioning, preventing damage to cells and demonstrating therapeutic benefits. We aimed to evaluate the effects of respiratory intermittent hypobaric hypoxia (IHH) to avoid brain injury caused by exposure to acute severe hypoxia (ASH).

METHODS

biomarkers of oxidative damage, mitochondrial apoptosis, and transcriptional factors in response to hypoxia were assessed by Western blot and immunohistochemistry in brain tissue. Four groups of rats were used: (1) normoxic (NOR), (2) exposed to ASH (FiO2 7% for 6 h), (3) exposed to IHH for 3 h per day over 8 days at 460 mmHg, and (4) ASH preconditioned after IHH.

RESULTS

ASH animals underwent increased oxidative-stress-related parameters, an upregulation in apoptotic proteins and had astrocytes with phenotype forms compatible with severe diffuse reactive astrogliosis. These effects were attenuated and even prevented when the animals were preconditioned with IHH. These changes paralleled the inhibition of NF-κB expression and the increase of erythropoietin (EPO) levels in the brain.

CONCLUSIONS

IHH exerted neuroprotection against ASH-induced oxidative injury by preventing oxidative stress and inhibiting the apoptotic cascade, which was associated with NF-κB downregulation and EPO upregulation.

CNS function and dysfunction during exposure to hyperbaric oxygen in operational and clinical settings

Hyperbaric oxygen (HBO2) is breathed during hyperbaric oxygen therapy and during certain undersea pursuits in diving and submarine operations. What limits exposure to HBO2 in these situations is the acute onset of central nervous system oxygen toxicity (CNS-OT) following a latent period of safe oxygen breathing. CNS-OT presents as various non-convulsive signs and symptoms, many of which appear to be of brainstem origin involving cranial nerve nuclei and autonomic and cardiorespiratory centers, which ultimately spread to higher cortical centers and terminate as generalized tonic-clonic seizures. The initial safe latent period makes the use of HBO2 practical in hyperbaric and undersea medicine; however, the latent period is highly variable between individuals and within the same individual on different days, making it difficult to predict onset of toxic indications. Consequently, currently accepted guidelines for safe HBO2 exposure are highly conservative. This review examines the disorder of CNS-OT and summarizes current ideas on its underlying pathophysiology, including specific areas of the CNS and fundamental neural and redox signaling mechanisms that are thought to be involved in seizure genesis and propagation. In addition, conditions that accelerate the onset of seizures are discussed, as are current mitigation strategies under investigation for neuroprotection against redox stress while breathing HBO2 that extend the latent period, thus enabling safer and longer exposures for diving and medical therapies.

Neuronal-like differentiated SH-SY5Y cells adaptation to a mild and transient H2 O2 -induced oxidative stress

Preconditioning (PC) is a cell adaptive response to oxidative stress and, with regard to neurons, can be considered as a neuroprotective strategy. The aim of the present study was to verify how neuronal-like differentiated SH-SY5Y cells adapt to a mild and transient H₂ O₂ -induced oxidative stress and, hence, whether may be considered as more sensitive cell model to study PC pathways. A first screening allowed to define H₂ O₂ concentrations for PC (10μM-50μM), applied before damage(100μM H₂ O₂ ). Cell viability measured 24 hours after 100μM H₂ O₂ -induced damage was ameliorated by 24-hour pre-exposure to low-concentration H₂ O₂ (10μM-30μM) with cell size as well restored. Markers for apoptosis (Bcl-2 and Bad), inflammation (iNOS), and redox system (MnSOD) were also determined, showing that, in cells pre-exposed to 10μM H₂ O₂ and then submitted to 100μM H₂ O₂ , Bcl-2 levels were higher, Bad and iNOS levels were lower than those observed in damaged cells, and MnSOD levels were unchanged. Such findings show that (1) neuronal-like differentiated SH-SY5Y cells are a suitable model to investigate PC response and more sensitive to the effect of a mild and transient H₂ O₂ -induced oxidative stress with respect to other neuronal cells; (2) 10μM H₂ O₂ -induced PC is mediated by apoptotic and inflammatory pathways, unlike antioxidant system; (3) such neuroprotective strategy and underlying signals proven in neuronal-like differentiated SH-SY5Y cells may contribute to understand in vivo PC mechanisms and to define a window for pharmacological intervention, namely, related to ischemic brain damage.

SIGNIFICANCE OF THE STUDY

Neuronal-like differentiated SH-SY5Y cells are a suitable model to investigate PC, an endogenous neuroprotective response to a mild and transient H₂ O₂ -induced oxidative stress, elicited by 24-hour exposure to very low H₂ O₂ concentrations and mediated by both apoptotic and inflammatory pathways. This model reflects in vivo PC mechanisms occurring after brain trauma and provides novel information about pathways and time of protection useful for an appropriate pharmacological intervention.

Dietary phytochemicals and neuro-inflammaging: from mechanistic insights to translational challenges

An extensive literature describes the positive impact of dietary phytochemicals on overall health and longevity. Dietary phytochemicals include a large group of non-nutrients compounds from a wide range of plant-derived foods and chemical classes. Over the last decade, remarkable progress has been made to realize that oxidative and nitrosative stress (O&NS) and chronic, low-grade inflammation are major risk factors underlying brain aging. Accumulated data strongly suggest that phytochemicals from fruits, vegetables, herbs, and spices may exert relevant negative immunoregulatory, and/or anti-O&NS activities in the context of brain aging. Despite the translational gap between basic and clinical research, the current understanding of the molecular interactions between phytochemicals and immune-inflammatory and O&NS (IO&NS) pathways could help in designing effective nutritional strategies to delay brain aging and improve cognitive function. This review attempts to summarise recent evidence indicating that specific phytochemicals may act as positive modulators of IO&NS pathways by attenuating pro-inflammatory pathways associated with the age-related redox imbalance that occurs in brain aging. We will also discuss the need to initiate long-term nutrition intervention studies in healthy subjects. Hence, we will highlight crucial aspects that require further study to determine effective physiological concentrations and explore the real impact of dietary phytochemicals in preserving brain health before the onset of symptoms leading to cognitive decline and inflammatory neurodegeneration.

Neuroprotection by Polynitrogen Manganese Complexes: Regulation of Reactive Oxygen Species-Related Pathways

Cell death in the central nervous system causes neurologic diseases, in which reactive oxygen species (ROS) play a critical role by either inducing cellular oxidative stress or by increasing the cell tolerance against insult. Neurologic diseases may potentially be treated by regulating ROS levels in a certain range with small molecules. We studied preconditioning with two polynitrogen manganese complexes (1 and 2) to regulate intracellular ROS levels in the protection of both the differentiated rat pheochromocytoma cell line (PC12 cells) and neurons against H₂O₂-induced apoptosis. Pre-treatment with the two complexes attenuated the cell apoptosis caused by H₂O₂. And the ROS-related neuroprotective mechanisms were explored. Both complexes activate the hypoxia inducible factor-related pathways and increase the cell adaptation to oxidative stress. Pre-treatment with complex 1 eliminated intracellular ROS, which also activated antioxidase system, while short-term incubation of complex 2, generated low levels of ROS leading to cell survival.

Novel Cellular Mechanisms for Neuroprotection in Ischemic Preconditioning: A View from Inside Organelles

Ischemic preconditioning represents an important adaptation mechanism of CNS, which results in its increased tolerance to the lethal cerebral ischemia. The molecular mechanisms responsible for the induction and maintenance of ischemic tolerance in the brain are complex and not yet completely clarified. In the last 10 years, great attention has been devoted to unravel the intracellular pathways activated by preconditioning and responsible for the establishing of the tolerant phenotype. Indeed, recent papers have been published supporting the hypothesis that mitochondria might act as master regulators of preconditioning-triggered endogenous neuroprotection due to their ability to control cytosolic calcium homeostasis. More interestingly, the demonstration that functional alterations in the ability of mitochondria and endoplasmic reticulum (ER) managing calcium homeostasis during ischemia, opened a new line of research focused to the role played by mitochondria and ER cross-talk in the pathogenesis of cerebral ischemia in order to identify new molecular mechanisms involved in the ischemic tolerance. In line with these findings and considering that the expression of the three isoforms of the sodium calcium exchanger (NCX), NCX1, NCX2, and NCX3, mainly responsible for the regulation of Ca²⁺ homeostasis, was reduced during cerebral ischemia, it was investigated whether these proteins might play a role in neuroprotection induced by ischemic tolerance. In this review, evidence supporting the involvement of ER and mitochondria interaction within the preconditioning paradigm will be provided. In particular, the key role played by NCXs in the regulation of Ca²⁺-homeostasis at the different subcellular compartments will be discussed as new molecular mechanism proposed for the establishing of ischemic tolerant phenotype.

Signaling pathways leading to ischemic mitochondrial neuroprotection

There is extensive evidence that ischemic/reperfusion mediated mitochondrial dysfunction is a major contributor to ischemic damage. However data also indicates that mild ischemic stress induces mitochondrial dependent activation of ischemic preconditioning. Ischemic preconditioning is a neuroprotective mechanism which is activated upon a brief sub-injurious ischemic exposure and is sufficient to provide protection against a subsequent lethal ischemic insult. Current research demonstrates that mitochondria are not only the inducers of but are also an important target of ischemic preconditioning mediated protection. Numerous proteins and signaling pathways are activated by ischemic preconditioning which protect the mitochondria against ischemic damage. In this review we examine some of the proteins activated by ischemic precondition which counteracts the deleterious effects of ischemia/reperfusion thereby maintaining normal mitochondrial activity and lead to ischemic tolerance.

Role of iron, zinc and reduced glutathione in oxidative stress induction by low pH in rat brain synaptosomes

Brain ischemia leads to a decrease in pH_o. We have shown previously in synaptosomes that the extracellular acidification induces depolarization of mitochondria followed by synthesis of superoxide anions and oxidative stress. Here, we investigated the effects of lowered pH_o on oxidative stress and membrane potentials in synaptosomes treated by the iron chelator deferoxamine and zinc chelator TPEN. We demonstrated that chelating of metals has no impact on superoxide anion synthesis and intrasynaptosomal mitochondria depolarization. Meanwhile, deferoxamine was able to inhibit oxidative stress induced by low pH_o and hydrogen peroxide application. Compared to deferoxamine, TPEN was less effective but it decreased the DCF fluorescence induced by pH_o 6.0 which had no effects in other oxidative stress models. We found that the chelators were able to inhibit slightly plasma membrane depolarization. Synaptosomes preincubation at low pH_o caused no effects on the reduced glutathione level. Depletion of glutathione by CDNB produced no additional increase in the DCF fluorescence induced by pH_o 7.0. Our results suggest that free iron is crucial for the development of oxidative stress elicited by acidification in synaptosomes. Chelating of this metal seems to be a promising strategy for protecting the neuronal presynaptic terminals against oxidative stress developed at stroke.

Preconditioning strategy in stem cell transplantation therapy

Stem cell transplantation therapy has emerged as a promising regenerative medicine for ischemic stroke and other neurodegenerative disorders. However, many issues and problems remain to be resolved before successful clinical applications of the cell-based therapy. To this end, some recent investigations have sought to benefit from well-known mechanisms of ischemic/hypoxic preconditioning. Ischemic/hypoxic preconditioning activates endogenous defense mechanisms that show marked protective effects against multiple insults found in ischemic stroke and other acute attacks. As in many other cell types, a sub-lethal hypoxic exposure significantly increases the tolerance and regenerative properties of stem cells and progenitor cells. So far, a variety of preconditioning triggers have been tested on different stem cells and progenitor cells. Preconditioned stem cells and progenitors generally show much better cell survival, increased neuronal differentiation, enhanced paracrine effects leading to increased trophic support, and improved homing to the lesion site. Transplantation of preconditioned cells helps to suppress inflammatory factors and immune responses, and promote functional recovery. Although the preconditioning strategy in stem cell therapy is still an emerging research area, accumulating information from reports over the last few years already indicates it as an attractive, if not essential, prerequisite for transplanted cells. It is expected that stem cell preconditioning and its clinical applications will attract more attention in both the basic research field of preconditioning as well as in the field of stem cell translational research. This review summarizes the most important findings in this active research area, covering the preconditioning triggers, potential mechanisms, mediators, and functional benefits for stem cell transplant therapy.

An Immunological Approach to Increase the Brain's Resilience to Insults

We have previously demonstrated the therapeutic potential of inducing a humoral response with autoantibodies to the N-methyl D-aspartate (NMDA) receptor using a genetic approach. In this study, we generated three recombinant proteins to different functional domains of the NMDA receptor, which is implicated in mediating brain tolerance, specifically NR1[21-375], NR1[313-619], NR1[654-800], and an intracellular scaffolding protein, Homer1a, with a similar anatomical expression pattern. All peptides showed similar antigenicity and antibody titers following systemic vaccination, and all animals thrived. Two months following vaccination, rats were administered the potent neurotoxin, kainic acid. NR1[21-375] animals showed an antiepileptic phenotype but no neuroprotection. Remarkably, despite ineffective antiepileptic activity, 6 of 7 seizing NR1[654-800] rats showed absolutely no injury with only minimal changes in the remaining animal, whereas the majority of persistently seizing rats in the other groups showed moderate to severe hippocampal injury. CREB, BDNF, and HSP70, proteins associated with preconditioning, were selectively upregulated in the hippocampus of NR1[654-800] animals, consistent with the observed neuroprotective phenotype. These results identify NR1 epitopes important in conferring anticonvulsive and neuroprotective effects and support the concept of an immunological strategy to induce a chronic state of tolerance in the brain.

In vivo inhibition of the mitochondrial H+-ATP synthase in neurons promotes metabolic preconditioning

A key transducer in energy conservation and signaling cell death is the mitochondrial H(+)-ATP synthase. The expression of the ATPase inhibitory factor 1 (IF1) is a strategy used by cancer cells to inhibit the activity of the H(+)-ATP synthase to generate a ROS signal that switches on cellular programs of survival. We have generated a mouse model expressing a mutant of human IF1 in brain neurons to assess the role of the H(+)-ATP synthase in cell death in vivo. The expression of hIF1 inhibits the activity of oxidative phosphorylation and mediates the shift of neurons to an enhanced aerobic glycolysis. Metabolic reprogramming induces brain preconditioning affording protection against quinolinic acid-induced excitotoxicity. Mechanistically, preconditioning involves the activation of the Akt/p70S6K and PARP repair pathways and Bcl-xL protection from cell death. Overall, our findings provide the first in vivo evidence highlighting the H(+)-ATP synthase as a target to prevent neuronal cell death.

Upregulation of HIF-1α via activation of ERK and PI3K pathway mediated protective response to microwave-induced mitochondrial injury in neuron-like cells

Microwave-induced learning and memory deficits in animal models have been gaining attention in recent years, largely because of increasing public concerns on growing environmental influences. The data from our group and others have showed that the injury of mitochondria, the major source of cellular adenosine triphosphate (ATP) in primary neurons, could be detected in the neuron cells of microwave-exposed rats. In this study, we provided some insights into the cellular and molecular mechanisms behind mitochondrial injury in PC12 cell-derived neuron-like cells. PC12 cell-derived neuron-like cells were exposed to 30 mW/cm(2) microwave for 5 min, and damages of mitochondrial ultrastructure could be observed by using transmission electron microscopy. Impairments of mitochondrial function, indicated by decrease of ATP content, reduction of succinate dehydrogenase (SDH) and cytochrome c oxidase (COX) activities, decrease of mitochondrial membrane potential (MMP), and increase of reactive oxygen species (ROS) production, could be detected. We also found that hypoxia-inducible factor-1 (HIF-1α), a key regulator responsible for hypoxic response of the mammalian cells, was upregulated in microwave-exposed neuron-like cells. Furthermore, HIF-1α overexpression protected mitochondria from injury by increasing the ATP contents and MMP, while HIF-1α silence promoted microwave-induced mitochondrial damage. Finally, we demonstrated that both ERK and PI3K signaling activation are required in microwave-induced HIF-1α activation and protective response. In conclusion, we elucidated a regulatory connection between impairments of mitochondrial function and HIF-1α activation in microwave-exposed neuron-like cells. By modulating mitochondrial function and protecting neuron-like cells against microwave-induced mitochondrial injury, HIF-1α represents a promising therapeutic target for microwave radiation injury.

AIF depletion provides neuroprotection through a preconditioning effect

Previous studies established a major role for apoptosis inducing factor (AIF) in neuronal cell death after acute brain injury. For example, AIF translocation from mitochondria to the nucleus determined delayed neuronal death, whereas reduced AIF expression provided neuroprotective effects in models of cerebral ischemia or brain trauma. The question remains, however, why reduced AIF levels are sufficient to mediate neuroprotection, since only very little AIF translocation to the nucleus is required for induction of cell death. Thus, the present study addresses the question, whether AIF gene silencing affects intrinsic death pathways upstream of nuclear translocation at the level of the mitochondria. Using MTT assays and real-time cell impedance measurements we confirmed the protective effect of AIF siRNA against glutamate toxicity in immortalized mouse hippocampal HT-22 neurons. Further, AIF siRNA prevented glutamate-induced mitochondrial fragmentation and loss of mitochondrial membrane potential. The protection of mitochondrial integrity was associated with preserved ATP levels, attenuated increases in lipid peroxidation and reduced complex I expression levels. Notably, low concentrations of the complex I inhibitor rotenone (20 nM), provided similar protective effects against glutamate toxicity at the mitochondrial level. These results expose a preconditioning effect as a mechanism for neuroprotection mediated by AIF depletion. In particular, they point out an association between mitochondrial complex I and AIF, which regulate each other's stability in mitochondria. Overall, these findings postulate that AIF depletion mediates a preconditioning effect protecting neuronal cells from subsequent glutamate toxicity through reduced levels of complex I protein.

Using a novel in vivo model to study the function of nuclear factor kappa B in cerebral ischemic injury

Background

Cerebral ischemia is a situation with a deficit blood supply to the brain, which eventually leads to cell death, inflammation, and tissue damage. Nuclear factor kappa B (NF-κB) plays an important role in inflammation and immune regulation. The aim of this study was to test the function of the activation of NF-κB in vivo in cerebral ischemic injury.

Material/Methods

We generated an animal model that used the method of occlusion of the middle cerebral artery (MCAO). The 60 traits were equally divided into 5 groups to investigate the role of NAC pretreatment: (1) sham-operation (control), (2) ischemia for 6 hours, (3) ischemia for 6 hours and NAC pretreatment, (4) ischemia for 24 hours, (5) ischemia for 24 hours and NAC pretreatment. The 36 rats were divided randomly into 3 groups: (A) recombinant adenovirus expressing wild-type κBα (AdIκBαM) group, (B) recombinant adenovirus expressing wild-type IκBα (AdIκBα) group, and (C) simple ischemia group. Triphenyltetrazolium chloride (TTC) was used to measure infarct volume. Detection of expression of NF-κB was by Immunohistochemistry analysis.

Results

The infarct size of the 24-hours ischemia groups were bigger than those of 6-hours ischemia groups (P<0.01). The infarct size of using NAC pretreatment groups was obviously reduced compared with saline control groups (P<0.01).The percentage of cortical p65-positive cells of the group of (A) were significantly less than the groups of (B) and (C).

Conclusions

Our data suggest that N-acetylcysteine (NAC) and Ad-IκBα-Mut can inhibit the activation of NF-κB in vivo, reduce the focal infarct size, and protect the brain tissue in ischemia.

Influence of intra- and extracellular acidification on free radical formation and mitochondria membrane potential in rat brain synaptosomes

Brain ischemia is accompanied by lowering of intra- and extracellular pH. Stroke often leads to irreversible damage of synaptic transmission by unknown mechanism. We investigated an influence of lowering of pH(i) and pH(o) on free radical formation in synaptosomes. Three models of acidosis were used: (1) pH(o) 6.0 corresponding to pH(i) decrease down to 6.04; (2) pH(o) 7.0 corresponding to the lowering of pH(i) down to 6.92: (3) 1 mM amiloride corresponding to pH(i) decrease down to 6.65. We have shown that both types of extracellular acidification, but not intracellular acidification, increase 2',7'-dichlorodihydrofluorescein diacetate fluorescence that reflects free radical formation. These three treatments induce the rise of the dihydroethidium fluorescence that reports synthesis of superoxide anion. However, the impact of amiloride on superoxide anion synthesis was less than that induced by moderate extracellular acidification. Superoxide anion synthesis at pH(o) 7.0 was almost completely eliminated by mitochondrial uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone. Furthermore, using fluorescent dyes JC-1 and rhodamine-123, we confirmed that pH(o) lowering, but not intracellular acidification, led to depolarization of intrasynaptosomal mitochondria. We have shown that pH(o) but not pH(i) lowering led to oxidative stress in neuronal presynaptic endings that might underlie the long-term irreversible changing in synaptic transmission.

Threefold exposure to moderate hypobaric hypoxia decreases the expression of Cu,Zn-superoxide dismutase in some regions of rat hippocampus

The effect of moderate hypobaric hypoxia on the expression of a peptide antioxidant Cu,Zn-superoxide dismutase in rat hippocampal neurons was evaluated in an immunocytochemical study. The expression of Cu,Zn-superoxide dismutase decreased significantly in the dorsal hippocampus (CA1 and CA2) and tended to decrease in ventral regions (CA3 and dentate gyrus) by the 24th hour after 3-fold exposure to hypoxia.

Low concentrations of methamphetamine can protect dopaminergic cells against a larger oxidative stress injury: mechanistic study

Mild stress can protect against a larger insult, a phenomenon termed preconditioning or tolerance. To determine if a low intensity stressor could also protect cells against intense oxidative stress in a model of dopamine deficiency associated with Parkinson disease, we used methamphetamine to provide a mild, preconditioning stress, 6-hydroxydopamine (6-OHDA) as a source of potentially toxic oxidative stress, and MN9D cells as a model of dopamine neurons. We observed that prior exposure to subtoxic concentrations of methamphetamine protected these cells against 6-OHDA toxicity, whereas higher concentrations of methamphetamine exacerbated it. The protection by methamphetamine was accompanied by decreased uptake of both [(3)H] dopamine and 6-OHDA into the cells, which may have accounted for some of the apparent protection. However, a number of other effects of methamphetamine exposure suggest that the drug also affected basic cellular survival mechanisms. First, although methamphetamine preconditioning decreased basal pERK1/2 and pAkt levels, it enhanced the 6-OHDA-induced increase in these phosphokinases. Second, the apparent increase in pERK1/2 activity was accompanied by increased pMEK1/2 levels and decreased activity of protein phosphatase 2. Third, methamphetamine upregulated the pro-survival protein Bcl-2. Our results suggest that exposure to low concentrations of methamphetamine cause a number of changes in dopamine cells, some of which result in a decrease in their vulnerability to subsequent oxidative stress. These observations may provide insights into the development of new therapies for prevention or treatment of PD.

Ischemic preconditioning-like effect of polyunsaturated fatty acid-rich diet on hepatic ischemia/reperfusion injury

AIM

The aim of this study was to investigate a possible preconditioning effect of oral diet enriched with polyunsaturated fatty acids (PUFAs) on liver ischemia/reperfusion (I/R) injuries.

METHODS

Wistar male rats were fed a standard diet or polyunsaturated fatty acid-rich diet (PRD) enriched with (GII) or without (GIII) ω-3 PUFA. Rats were submitted to partial liver ischemia during 1 h and evaluated in pre- and post-I/R conditions. In pre-I/R condition, livers were collected for determination of fatty acid composition, liver mitochondrial function, malondialdehyde (MDA) content, and histological analysis. Four hours after liver reperfusion serum activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), serum levels of tumor necrosis factor-alpha, interleukin-6, interleukin-10, and prostaglandin-E2, liver mitochondrial function, MDA content, and histology were evaluated.

RESULTS

In the pre-I/R condition, GII and GIII groups had an increase on PUFA content and exhibited slight increased macrosteatosis and microsteatosis in the liver. After 4 h of reperfusion, PRD-fed rats showed a marked decrease on steatosis, diminished necrosis, an increase in MDA formation, and mitochondrial uncoupling. We also observed a marked decrease in plasma levels of cytokines and ALT and AST activities in post-I/R condition in PRD groups.

CONCLUSION

In this experimental model in the rat, PRD has a preconditioning effect protecting the liver from I/R injury and should be object of future clinical studies.

Cell signaling in NMDA preconditioning and neuroprotection in convulsions induced by quinolinic acid

The search for novel, less invasive therapeutic strategies to treat neurodegenerative diseases has stimulated scientists to investigate the mechanisms involved in preconditioning. Preconditioning has been report to occur in many organs and tissues. In the brain, the modulation of glutamatergic transmission is an important and promising target to the use of effective neuroprotective agents. The glutamatergic excitotoxicity is a factor common to neurodegenerative diseases and acute events such as cerebral ischemia, traumatic brain injury and epilepsy. In this review we focus on the neuroprotection and preconditioning by chemical agents. Specially, chemical preconditioning models using N-methyl-d-aspartate (NMDA) pre-treatment, which has demonstrated to lead to neuroprotection against seizures and damage to neuronal tissue induced by quinolinic acid (QA). Here we attempted to gather important results obtained in the study of cellular and molecular mechanisms involved in NMDA preconditioning and neuroprotection.

Neuroprotection against cobalt chloride-induced cell apoptosis of primary cultured cortical neurons by salidroside

Salidroside, a phenol glycoside of plant origin, has been documented to possess a broad spectrum of pharmacological properties, including protective effects against neuronal death induced by different insults. To provide further insights into the neuroprotective functions peculiar to salidroside, this study used primary cultured cortical neurons of rats as a cell model to examine whether salidroside was able to prevent against cell damage after exposure to cobalt chloride (CoCl(2)), a hypoxia-inducing agent. The data from 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test, Hoechst33342 staining, terminal deoxynucleotidyl transferase dUTP-mediated nicked end labeling assay, and Bax/Bcl-2 ratio analysis indicated that salidroside pretreatment attenuated hypoxia-induced apoptotic cell death of primary cultured cortical neurons in a dose-dependent manner. Moreover, preliminary exploration of the possible mechanisms suggested that the protective effects of salidroside, shown in our experimental setting, might probably be mediated by enhancing the expression of hypoxia-inducible factor-1α, alleviating the increase of intracellular reactive oxygen species levels, and inhibiting over-expression of nuclear factor-kappa B protein.

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.

Mitochondrial preconditioning: a potential neuroprotective strategy

Mitochondria have long been known as the powerhouse of the cell. However, these organelles are also pivotal players in neuronal cell death. Mitochondrial dysfunction is a prominent feature of chronic brain disorders, including Alzheimer's disease (AD) and Parkinson's disease (PD), and cerebral ischemic stroke. Data derived from morphologic, biochemical, and molecular genetic studies indicate that mitochondria constitute a convergence point for neurodegeneration. Conversely, mitochondria have also been implicated in the neuroprotective signaling processes of preconditioning. Despite the precise molecular mechanisms underlying preconditioning-induced brain tolerance are still unclear, mitochondrial reactive oxygen species generation and mitochondrial ATP-sensitive potassium channels activation have been shown to be involved in the preconditioning phenomenon. This review intends to discuss how mitochondrial malfunction contributes to the onset and progression of cerebral ischemic stroke and AD and PD, two major neurodegenerative disorders. The role of mitochondrial mechanisms involved in the preconditioning-mediated neuroprotective events will be also discussed. Mitochondrial targeted preconditioning may represent a promising therapeutic weapon to fight neurodegeneration.

Lifelong protection from global cerebral ischemia and reperfusion in long-lived Mclk1(+/)(-) mutants

To achieve a long life span, animals must be resistant to various injuries as well as avoid or delay lethality from age-dependent diseases. Reduced expression of the mitochondrial enzyme CLK-1/MCLK1 (a.k.a. Coq7), a mitochondrial hydroxylase that is necessary for the biosynthesis of ubiquinone (UQ), extends lifespan in Caenorhabditiselegans and in mice. Here, we show that long-lived Mclk1(+/)(-) mutants have enhanced resistance to neurological damage following global cerebral ischemia-reperfusion (I/R) injury induced by transient bilateral common carotid artery occlusion (BCCAO). Both young ( approximately 100days old) and relatively aged ( approximately 450days old) mutants display increased resistance as indicated by a significant decrease in the amount of degenerating cells observed in forebrain cortex and in hippocampal areas after ischemia and reperfusion. Furthermore, less oxidative damage resulting from the procedure was measured in the brain of young Mclk1(+/)(-) animals. The finding that both young and old mutants are protected indicates that this is a basic phenotype of these mutants and not a secondary consequence of their slow rate of aging. Thus, the partial resistance to I/R injury suggests that Mclk1(+/)(-) mutants have an enhanced recovery potential following age-dependant vascular accidents, which correlates well with their longer survival. By relating this neuroprotective effect to previously reported characteristics of the Mclk1(+/)(-) phenotype, including altered mitochondrial metabolism and increased HIF-1alpha expression, this study establishes these mutants as useful models to analyze the mechanisms underlying tolerance to ischemia, particularly those associated with ischemic preconditioning, as well as to clarify the relation between aging and age-dependent diseases.

The neuroprotective mechanism of brain ischemic preconditioning

Brain ischemia is one of the most common causes of death and the leading cause of adult disability in the world. Brain ischemic preconditioning (BIP) refers to a transient, sublethal ischemia which results in tolerance to later, otherwise lethal, cerebral ischemia. Many attempts have been made to understand the molecular and cellular mechanisms underlying the neuroprotection offered by ischemic preconditioning. Many studies have shown that neuroprotective mechanisms may involve a series of molecular regulatory pathways including activation of the N-methyl-D-aspartate (NMDA) and adenosine receptors; activation of intracellular signaling pathways such as mitogen activated protein kinases (MAPK) and other protein kinases; upregulation of Bcl-2 and heat shock proteins (HSPs); and activation of the ubiquitin-proteasome pathway and the autophagic-lysosomal pathway. A better understanding of the processes that lead to cell death after stroke as well as of the endogenous neuroprotective mechanisms by which BIP protects against brain ischemic insults could help to develop new therapeutic strategies for this devastating neurological disease. The purpose of the present review is to summarize the neuroprotective mechanisms of BIP and to discuss the possibility of mimicking ischemic preconditioning as a new strategy for preventive treatment of ischemia.

TNF-alpha preconditioning protects neurons via neuron-specific up-regulation of CREB-binding protein

Despite being a proinflammatory cytokine, TNF-alpha preconditions neurons against various toxic insults. However, underlying molecular mechanisms are poorly understood. The present study identifies the importance of CREB-binding protein (CBP) in facilitating TNF-alpha-mediated preconditioning in neurons. Treatment of rat primary neurons with fibrillar amyloid beta1-42 (Abeta) resulted in the loss of CBP protein. However, this loss was compensated by TNF-alpha preconditioning as the expression of neuronal CBP was up-regulated in response to TNF-alpha treatment. The induction of CBP by TNF-alpha was observed only in neurons, but not in astroglia and microglia, and it was contingent on the activation of transcription factor NF-kappaB. Interestingly, antisense knockdown of CBP abrogated the TNF-alpha-mediated preconditioning of neurons against Abeta and glutamate toxicity. Similarly in vivo, preadministration of TNF-alpha in mouse neocortex prevented Abeta-induced apoptosis and loss of choline acetyltransferase-positive cholinergic neurons. However, coadministration of cbp antisense, but not scrambled oligonucleotides, negated the protective effect of TNF-alpha against Abeta neurotoxicity. This study illustrates a novel biological role of TNF-alpha in increasing neuron-specific expression of CBP for preconditioning that may have therapeutic potential against neurodegenerative disorders.

Transcriptional regulation of PSA-NCAM expression by NMDA receptor activation in RA-differentiated C6 glioma cultures

N-Methyl-d-aspartate (NMDA) receptors exhibit a dichotomy of signaling with both toxic and plastic responses. Recent reports have shown that exposure to subtoxic concentration of NMDA results in a neuroprotective state that was measured when these neurons were subsequently challenged with toxic doses of glutamate or kainate. Control of polysialylated neural cell adhesion molecule (PSA-NCAM) expression by NMDA receptor activation has been described in several systems, suggesting a functional link between these two proteins. The perception of glial role in CNS function has changed dramatically over the past few years from simple trophic functions to that of cells with important roles in development and maintenance of CNS in cooperation with neurons. We report here the transcriptional regulation of PSA-NCAM expression by subtoxic dose of NMDA in retinoic acid differentiated C6 glioma cell cultures. C6 glioma cell cultures differentiated with retinoic acid (10microM) were exposed to NMDA (100microM) or to antagonist MK-801 (200nM) prior to treatment with NMDA and cells were harvested after 24h of treatment to study the expression of total NCAM, PSA-NCAM, nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1) by Western blotting and dual immunocytofluorescence and expression of PST mRNA by fluorescent in situ hybridization (FISH). Significant increase in the levels of PSA-NCAM, NF-kappaB, AP-1 and PST mRNA was observed in NMDA treated cultures. Treatment of cultures with MK-801, a non-competitive NMDA receptor antagonist, prior to NMDA exposure prevented the NMDA-mediated changes indicating the involvement of NMDA receptor activation. The results elucidate the possible cellular and molecular mechanisms of regulation of PSA-NCAM expression in astroglial cultures by extracellular signals.

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

BACKGROUND

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation.

REVIEW

We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation).The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible.This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles.Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here.

CONCLUSION

Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets.

Thioredoxin-1 expression levels in rat hippocampal neurons in moderate hypobaric hypoxia

Previous studies have demonstrated that preconditioning (PC) with three sessions of moderate hypoxia significantly increases the expression of the antioxidant protein thioredoxin-1 (Trx-1) in the rat hippocampus by 3 h after subsequent acute severe hypoxia as compared with non-preconditioned animals. However, it remained unclear whether this increase in Trx-1 accumulation during PC is induced before severe hypoxia or is a modification of the response to severe hypoxia. This question was addressed in the present investigation using experiments on 12 adult male Wistar rats with studies of Trx-1 expression after PC without subsequent severe hypoxia. Immunocytochemical studies were performed 3 and 24 h after three episodes of moderate hypobaric hypoxia (three sessions of 2 h at 360 mmHg with 24-h intervals). Immunoreactivity to Trx-1 24 h after the last session was significantly decreased in neurons in all the areas of the hippocampus studied (CA1, CA2, CA3, and the dentate gyrus). Immunoreactivity in CA3 was also decreased 3 h after hypoxia. These results provide evidence that moderate preconditioning hypoxia itself not only does not increase, but even significantly decreases Trx-1 expression. Thus, increases in Trx-1 contents in the hippocampus of preconditioned animals after severe hypoxia are not associated with the accumulation of this protein during PC, but with a PC-induced modification of the reaction to severe hypoxia.

Implications of oxidative stress in the pathophysiology of obstructive uropathy

Although the functional and clinical alterations occurring in patients with obstructive uropathy are not well understood, it has been suggested that oxidative stress could contribute in the mechanism responsible for the impairment of sodium and water balance. This study aimed to test the hypothesis that red wine administration causes an amelioration of both the renal damage and impairment of renal Na(+), K(+)-ATPase activity occurring after ureteral obstruction in the rat. Twenty-four male Wistar adult rats weighting 200-250 g were used. Half of them received a 10-week treatment with wine as the sole fluid source, while the other group received water. Both groups were subjected to 24-h unilateral ureteral obstruction (UUO). Kidney tissue was collected following the relief of the ligature to perform the biochemical assessments. Urine and blood samples were taken at baseline and after the relief. Results show that the treatment with red wine significantly enhances the activity of antioxidant enzymes, and thus reduces renal lipid peroxidation secondary to UUO, which correlated negatively with Na(+), K(+)-ATPase activity. Based on this and other previous data, it could be suggested that red wine administration may prevent renal damage secondary to UUO by inducing enhanced antioxidant potential.

Nitric oxide triggers delayed anesthetic preconditioning-induced cardiac protection via activation of nuclear factor-kappaB and upregulation of inducible nitric oxide synthase

Nitric oxide (NO) plays a pivotal role both in triggering and mediating delayed protection against myocardial I/R injury during anesthetic-induced preconditioning (APC). However, the signaling mechanisms that underlie this phenomenon remain unclear. Using isoflurane as a representative anesthetic, the present study tested the hypothesis that NO released after anesthetic-induced preconditioning initiates delayed cardioprotection via activation of nuclear transcription factor-kappaB (NF-kappaB), leading to myocardial adaptation by upregulation of iNOS and increase in production of NO. Sprague-Dawley rats that received open-chest surgery under pentobarbital anesthesia were subject to 30 min of left coronary artery occlusion, followed by 120 min of reperfusion. Exposure to 60 min of 2.1% isoflurane inhalation with oxygen 24 h before ischemia significantly reduced I/R-induced myocardial infarct size that was associated with overexpression of iNOS protein and increased NO content in the heart. These protective effects were abolished by pretreatment with a NOS inhibitor, N-nitro-L-arginine methyl ester, an NF-kappaB blocker, diethyldithiocarbamate, before isoflurane, or a selective iNOS inhibitor, S-methylisothiourea, before left coronary artery occlusion. Isoflurane exposure also evoked a robust increase in myocardial NO content, followed by nucleus-bound translocation of p65 or p50 subunit of NF-kappaB and increase in NF-kappaB DNA-binding activity in heart tissues. These molecular events after isoflurane exposure were blocked by pretreatment with N-nitro-L-arginine methyl ester. We conclude that NO generated immediately after isoflurane exposure triggers downstream activation of NF-kappaB, resulting in subsequent upregulation of iNOS expression and NO synthesis that mediate APC-induced delayed cardioprotection.

Preconditioning induces prolonged expression of transcription factors pCREB and NF-kappa B in the neocortex of rats before and following severe hypobaric hypoxia

Preconditioning using mild repetitive hypobaric hypoxia is known to increase a tolerance of brain neurons to severe hypoxia and other injurious exposures. In the present study, the effects of mild hypoxic preconditioning on the expression of transcription factors NF-kappaB and phosphorylated CREB (pCREB) has been studied in the neocortex of rats exposed to severe hypobaric hypoxia. As revealed by quantitative immunocytochemistry, the injurious severe hypobaric hypoxia (180 Torr, 3 h) remarkably reduced the neocortical levels of pCREB and NF-kappaB. The three-trial hypoxic preconditioning (360 Torr, 2 h, 3 days) induced persistent up-regulation of pCREB and NF-kappaB expression in the neocortex of rats 3-24 h following the severe hypoxia. In addition, the preconditioning alone which was not followed by the severe hypoxia, considerably increased neocortical pCREB and NF-kappaB levels. The findings suggest a role for transcription factors cAMP response element-binding protein and NF-kappaB in the neuroprotective mechanisms activated by the hypoxic preconditioning.

Preconditioning with NMDA protects against toxicity of 3-nitropropionic acid or glutamate in cultured cerebellar granule neurons

A brief sub-lethal ischaemic stimulus has been reported to protect against subsequent ischaemic damage in vivo, and in vitro following periods of hypoxia or oxygen-glucose deprivation (OGD). Preconditioning against neurotoxic stimuli has been linked to N-methyl-d-aspartate (NMDA) receptors, since receptor blockade prevents the protection afforded by OGD, and low doses of NMDA treatment are capable of preconditioning. The current study demonstrated that NMDA preconditioning also protects against 3-nitropropionic acid (3-NPA), a generator of both excitotoxic and oxidative damage, in addition to glutamate. Cerebellar granule neuronal (CGN) cultures prepared from 8-day neonatal Sprague-Dawley rats were maintained for 8 days prior to NMDA stimulation for 6h. At 9 days in vitro (DIV), preconditioned and control cultures were subjected to a toxic insult (1 microM-10 mM glutamate or 1 microM-10 mM 3-NPA). Neuronal viability was assessed by use of a fluorescein diacetate assay. Protection was effective with 100 microM NMDA preconditioning for 6 h against 1-100 microM glutamate, and also against 1-500 microM 3-NPA. The study demonstrates that NMDA preconditioning can be beneficial against excitotoxic treatments, even when these are potentially complicated by associated oxidative damage and metabolic compromise, as is the case for 3-NPA.

Normobaric hyperoxia induces ischemic tolerance and upregulation of glutamate transporters in the rat brain and serum TNF-alpha level

Recent studies suggest that intermittent and prolonged normobaric hyperoxia (HO) results in ischemic tolerance to reduce ischemic brain injury. In this research, we attempted to see changes in excitatory amino acid transporters (EAATs) and TNF-alpha levels following prolonged and intermittent hyperoxia preconditioning. Rats were divided into four experimental groups, each of 21 animals. The first two were exposed to 95% inspired HO for 4 h/day for 6 consecutive days (intermittent HO, InHO) or for 24 continuous hours (prolonged HO, PrHO). The second two groups acted as controls, and were exposed to 21% oxygen in the same chamber. Each main group was subdivided to middle cerebral artery occlusion (MCAO-operated), sham-operated (without MCAO), and intact (without any surgery) subgroups. After 24 h from pretreatment, MCAO-operated subgroups were subjected to 60 min of right MCAO. After 24 h reperfusion, neurologic deficit score (NDS) and infarct volume were measured in MCAO-operated subgroups. EAATs expression and serum TNF-alpha levels were assessed in sham-operated and intact subgroups. Preconditioning with prolonged and intermittent HO decreased NDS and upregulated EAAT1, EAAT2, and EAAT3 and increased serum TNF-alpha levels significantly. Although further studies are needed to clarify the mechanisms of ischemic tolerance, the intermittent and prolonged HO seems to partly exert their effects via increase serum TNF-alpha levels and upregulation of EAATs.