Oxidative stress induces a form of programmed cell death with characteristics of both apoptosis and necrosis in neuronal cells

Increased apoptosis of neutrophils in induced sputum of COPD patients

AIM

The aim of the current study was to evaluate apoptosis in induced sputum neutrophils and to investigate the relationship between the number of apoptotic cells and clinical parameters in COPD patients.

METHODS

Twenty-four COPD ex-smoker patients and 10 healthy controls were included in the study. All subjects underwent clinical evaluation and sputum induction. Sputum cell in situ apoptosis was identified using white light microscopy and TUNEL assay technique. Apoptosis of neutrophils obtained by sputum induction was expressed as apoptotic rate (AR=percentage of apoptotic neutrophils over the number of neutrophils measured).

RESULTS

TUNEL assay revealed statistically significant higher AR in COPD patients than controls (p=0.004). Patients with FEV(1)<50%pred had significantly higher median (IQR) AR (%) compared to patients with FEV(1)>or=50% [26.3 (16-29) vs 13.1 (8.6-21), p=0.01]. No significant association was found between the number of apoptotic cells and age, symptoms or medication used.

CONCLUSION

The significantly increased apoptotic rate of neutrophils that were found in COPD patients with advanced disease compared to controls might reflect either a deregulation of apoptosis of neutrophils or, a reduced clearance of apoptotic neutrophils from the airways. The pathophysiologic significance of the observed phenomenon has to be further explored.

Ethanol withdrawal provokes opening of the mitochondrial membrane permeability transition pore in an estrogen-preventable manner

We have reported that the major endogenous estrogen, 17beta-estradiol (E2), protects against oxidative injury during ethanol withdrawal (EW) in a cultured hippocampal cell line (HT22). Here, we investigated whether the pro-oxidant nature of EW mediates opening of the mitochondrial membrane permeability transition pore (PTP) in a manner protected by E2. Excess PTP opening provokes mitochondrial membrane swelling (MMS) and the collapse of membrane potential (DeltaPsim). HT22 cells were collected at the end of ethanol exposure (100 mM) for 24 h or at 4 h of EW to assess MMS by monitoring absorbance decline at 540 nm and to assess DeltaPsim using flow cytometry. Protective effects of E2 on PTP were compared with an antioxidant butylated hydroxytoluene (BHT) and an E2 analog, ZYC26 [(3-hydroxy-2-adamantyl(1)-4-methyl-estra-1,3,5(10)-17-one], with higher antioxidant potency than E2. To assess cellular consequences of PTP opening, effects of a PTP inhibitor (cyclosporin A) on EW-induced cell death were assessed using the calcein assay. Major findings were that: 1) EW resulted in rapid MMS and DeltaPsim collapse; 2) cyclosporin A attenuated EW-induced cell death; and 3) E2 treatment restricted to the EW phase protected against the PTP opening more prominently than BHT and to a similar degree to ZYC26. These findings suggest that EW provokes PTP opening partly but not entirely through the pro-oxidant nature and that E2 counteracts EW-associated factors to protect against the PTP opening.

p75NTR antagonistic cyclic peptide decreases the size of beta amyloid-induced brain inflammation

Amyloid beta (Abeta) was shown to bind the 75 kD neurotrophin receptor (p75(NTR)) to induce neuronal death. We synthesized a p75(NTR) antagonistic peptide (CATDIKGAEC) that contains the KGA motif that is present in the toxic part of Abeta and closely resembles the binding site of NGF for p75(NTR). In vivo injections of Abeta into the cerebral cortex of B57BL/6 mice together with the peptide produced significantly less inflammation than simultaneous injections of Abeta and a control (CKETIADGAC, scrambled) peptide injected into the contralateral cortex. These data suggest that blocking the binding of Abeta to p75(NTR) may reduce neuronal loss in Alzheimer's disease.

Opposing roles for caspase and calpain death proteases in L-glutamate-induced oxidative neurotoxicity

Oxidative glutamate toxicity in HT22 murine hippocampal cells is a model for neuronal death by oxidative stress. We have investigated the role of proteases in HT22 cell oxidative glutamate toxicity. L-glutamate-induced toxicity was characterized by cell and nuclear shrinkage and chromatin condensation, yet occurred in the absence of either DNA fragmentation or mitochondrial cytochrome c release. Pretreatment with the selective caspase inhibitors either benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (pan-caspase), N-acetyl-Leu-Glu-His-Asp-aldehyde (caspase 9) or N-acetyl-Ile-Glu-Thr-Asp-aldehyde (caspase 8), significantly increased L-glutamate-induced cell death with a corresponding increase in observed nuclear shrinkage and chromatin condensation. This enhancement of glutamate toxicity correlated with an increase in L-glutamate-dependent production of reactive oxygen species (ROS) as a result of caspase inhibition. Pretreating the cells with N-acetyl-L-cysteine prevented ROS production, cell shrinkage and cell death from L-glutamate as well as that associated with the presence of the pan-caspase inhibitor. In contrast, the caspase-3/-7 inhibitor N-acetyl-Asp-Glu-Val-Asp aldehyde was without significant effect. However, pretreating the cells with the calpain inhibitor N-acetyl-Leu-Leu-Nle-CHO, but not the cathepsin B inhibitor CA-074, prevented cell death. The cytotoxic role of calpains was confirmed further by: 1) cytotoxic dependency on intracellular Ca(2+) increase, 2) increased cleavage of the calpain substrate Suc-Leu-Leu-Val-Tyr-AMC and 3) immunoblot detection of the calpain-selective 145 kDa alpha-fodrin cleavage fragment. We conclude that oxidative L-glutamate toxicity in HT22 cells is mediated via calpain activation, whereas inhibition of caspases-8 and -9 may exacerbate L-glutamate-induced oxidative neuronal damage through increased oxidative stress.

Pharmacological properties of BN82451: a novel multitargeting neuroprotective agent

BN82451 belongs to a new family of small molecules designated as multitargeting or hybrid molecules. BN82451 is orally active, has good central nervous system penetration, and elicits potent neuronal protection and antiinflammatory properties. Neuronal protection is due to Na+ channel blockade, antioxidant properties, and mitochondria-protecting activity, whereas inhibition of cyclooxygenases is mostly responsible for its antiinflammatory activity. BN82451 has been shown to exert a potent neuroprotective effect in various in vitro and in vivo animal models. BN82451 was found to exert a significant protection in experimental animal models mimicking aspects of cerebral ischemia, Parkinson disease, Huntington disease, and more particularly amyotrophic lateral sclerosis. Collectively, its pharmacological properties designate BN82451 as a promising neuroprotective agent.

Selenium attenuates ROS-mediated apoptotic cell death of injured spinal cord through prevention of mitochondria dysfunction; in vitro and in vivo study

The primary objective of this study was to determine the possible apoptotic cell death preventive effects of the antioxidant selenium using an experimental rat spinal cord injury (SCI) model and cultured spinal cord-derived neural progenitor cells (NPCs). Sodium selenite treatment exerted a profound preventive effect on apoptotic cell death, including p-P38, p-SAPK/JNK, caspases, and PARP activity, and ameliorated astrogliosis and hypomyelination, which occurs in regions of active cell death in the spinal cords of SCI rats. The foremost protective effect of selenite in SCI would therefore be manifested in the suppression of acute secondary apoptotic cell death. However, selenite does not appear to exert an anti-inflammatory function associated with active microglia and macrophage propagation or infiltration into the lesion site. Selenite-mediated neuroprotection has been linked to selenite's attenuation or inhibition of p38 mitogen-activated protein kinase, pSAPK/JNK, and Bax activation in in vitro and in vivo SCI lesion sites. Selenite also attenuated cell death via the prevention of cytochrome c release, caspase activation, and ROS accumulation in the cytosol. Also, our study showed that selenite administered immediately after SCI significantly diminishes functional deficits. The selenite-treated group recovered hind limb reflexes more rapidly, and a higher percentage of these rats regained responses to a greater degree than was seen in the untreated injured rats. Our data indicate that the therapeutic outcome of selenite is most likely the consequence of its comprehensive apoptotic cell death blocking effects, resulting in the protection of white matter, oligodendrocytes, and neurons, and the inhibition of astrogliosis. The finding that the administration of selenite prevents secondary pathological events in traumatic spinal cord injuries, and promotes the recovery of motor function in an animal model. Its efficacy may facilitate the development of novel drug targets for the treatment of SCI.

Necrostatin-1 protects against glutamate-induced glutathione depletion and caspase-independent cell death in HT-22 cells

Glutamate, a major excitatory neurotransmitter in the CNS, plays a critical role in neurological disorders such as stroke and Parkinson's disease. Recent studies have suggested that glutamate excess can result in a form of cell death called glutamate-induced oxytosis. In this study, we explore the protective effects of necrostatin-1 (Nec-1), an inhibitor of necroptosis, on glutamate-induced oxytosis. We show that Nec-1 inhibits glutamate-induced oxytosis in HT-22 cells through a mechanism that involves an increase in cellular glutathione (GSH) levels as well as a reduction in reactive oxygen species production. However, Nec-1 had no protective effect on free radical-induced cell death caused by hydrogen peroxide or menadione, which suggests that Nec-1 has no antioxidant effects. Interestingly, the protective effect of Nec-1 was still observed when cellular GSH was depleted by buthionine sulfoximine, a specific and irreversible inhibitor of glutamylcysteine synthetase. Our study further demonstrates that Nec-1 significantly blocks the nuclear translocation of apoptosis-inducing factor (a marker of caspase-independent programmed cell death) and inhibits the integration of Bcl-2/adenovirus E1B 19 kDa-interacting protein 3 (a pro-death member of the Bcl-2 family) into the mitochondrial membrane. Taken together, these results demonstrate for the first time that Nec-1 prevents glutamate-induced oxytosis in HT-22 cells through GSH related as well as apoptosis-inducing factor and Bcl-2/adenovirus E1B 19 kDa-interacting protein 3-related pathways.

Phosphoproteomic analysis of neuronal cell death by glutamate-induced oxidative stress

Oxidative stress is one of the major causes of neuronal cell death in disorders such as perinatal hypoxia and ischemia. Protein phosphorylation is the most significant PTM of proteins and plays an important role in stress-induced signal transduction. Thus, the analysis of alternative protein phosphorylation states which occur during oxidative stress-induced cell death could provide valuable information regarding cell death. In this study, a reference phosphoproteome map of the mouse hippocampal cell line HT22 was constructed based on 125 spots that were identified by MALDI-TOF or LC-ESI-Q-TOF-MS analysis. In addition, proteins of HT22 cells at various stages of oxidative stress-induced cell death were separated by 2-DE and alterations in phosphoproteins were detected by Pro-Q Diamond staining. A total of 17 spots showing significant quantitative changes and seven newly appearing spots were identified after glutamate treatment. Splicing factor 2, peroxiredoxin 2, S100 calcium binding protein A11, and purine nucleoside phosphorylase were identified as up- or down-regulated proteins. CDC25A, caspase-8, and cyp51 protein appeared during oxidative stress-induced cell death. The data in this study from phosphoproteomic analysis provide a valuable resource for the understanding of HT22 cell death mechanisms mediated by oxidative stress.

Nanomolar concentrations of anabolic-androgenic steroids amplify excitotoxic neuronal death in mixed mouse cortical cultures

The use of anabolic-androgenic steroids (AASs) in the world of sport has raised a major concern for the serious, sometimes life-threatening, side effects associated with these drugs. Most of the CNS effects are of psychiatric origin, and whether or not AASs are toxic to neurons is yet unknown. We compared the effect of testosterone with that of the AASs, 19-nortestosterone (nandrolone), stanozolol, and gestrinone, on excitotoxic neuronal death induced by N-methyl-d-aspartate (NMDA) in primary cultures of mouse cortical cells. In the most relevant experiments, steroids were applied to the cultures once daily during the 4 days preceding the NMDA pulse. Under these conditions, testosterone amplified excitotoxic neuronal death only at very high concentrations (10 muM), whereas it was protective at concentrations of 10 nM and inactive at intermediate concentrations. Low concentrations of testosterone became neurotoxic in the presence of the aromatase inhibitors, i.e. anastrozole and aminoglutethimide, suggesting that the intrinsic toxicity of testosterone was counterbalanced by its aromatization into 17beta-estradiol. As opposed to testosterone, nortestosterone, stanozolol and gestrinone amplified NMDA toxicity at nanomolar concentrations; their action was insensitive to aromatase inhibitors, but was abrogated by the androgen receptor antagonist, flutamide. None of the AASs were toxic in the absence of NMDA. These data suggest that AASs increase neuronal vulnerability to an excitotoxic insult and may therefore facilitate neuronal death associated with acute or chronic CNS disorders.

Secretory PLA2-IIA and ROS generation in peripheral mitochondria are critical for neuronal death

In this study the role of mitochondrial secretory PLA2-IIA in glutamate-induced cell death in cultured cerebellar granule neurons has been investigated. Inhibition of secretory PLA2-IIA blocked glutamate-induced cell death. Since PLA2 may generate reactive oxygen species (ROS), we have investigated ROS production, detected as dihydrorhodamine 123 oxidation and nitrotyrosine modifications of proteins, following glutamate treatment in the absence or presence of an inhibitor of secretory PLA2-IIA. There was an increased generation of ROS in both glutamate- and buffer-treated neurons compared to untreated neurons. Scavenging with dihydrorhodamine 123 reduced glutamate-induced death (60%), showing that ROS detected in glutamate-treated neurons were associated with cell death. However, ROS detected in buffer-treated neurons were not associated with toxicity. Glutamate treatment led to ROS production predominantly in peripheral mitochondria, whereas buffer treatment led to ROS production in somal mitochondria. Inhibition of secretory PLA2-IIA (i) reduced the generation of ROS after glutamate treatment, (ii) reduced the ROS production in peripheral mitochondria in glutamate-treated neurons, consistent with the fact that calcium entry through glutamate (NMDA) receptors has a privileged access to peripheral mitochondria, and (iii) did not reduce the generation of ROS after buffer treatment. In conclusion, activation of NMDA receptors induces ROS, which is critical for neuronal death, due to secretory PLA2-IIA associated with peripheral mitochondria.

siRNA delivery by a transferrin-associated lipid-based vector: a non-viral strategy to mediate gene silencing

BACKGROUND

RNA interference provides a powerful technology for specific gene silencing. Therapeutic applications of small interfering RNA (siRNA) however require efficient vehicles for stable complexation, protection, and extra- and intracellular delivery of these nucleic acids. Here, we evaluated the potential of transferrin (Tf)-associated liposomes for siRNA complexation and gene silencing.

METHODS

Cationic liposomes composed of DOTAP : Cholesterol associated with or without transferrin (Tf) were complexed with siRNA at different lipid/siRNA charge ratios. Complexation and protection of siRNA from enzymatic degradation was assessed with the PicoGreen intercalation assay and gel electrophoresis. Cellular internalization of these siRNA Tf-lipoplexes was detected by confocal microscopy. Luciferase assay, immunoblot and fluorescence-activated cell sorting (FACS) analysis were used to evaluate reporter gene silencing in Huh-7 hepatocarcinoma and U-373 glioma cells. c-Jun knockdown in HT-22 cells was evaluated by quantitative real-time polymerase chain reaction (RT-PCR). Cytotoxicity of the siRNA complexes was assessed by Alamar blue, lactate dehydrogenase and MTT assays.

RESULTS

Complexation of siRNA with the cationic liposomes in the presence of Tf results in the formation of stable particles and prevents serum-mediated degradation. Confocal microscopy showed fast cellular internalization of the Tf-lipoplexes via endocytosis. In the GFP glioma cells Tf-lipoplexes showed enhanced gene silencing at minimum toxicity in comparison to Tf-free lipoplexes. Targeting luciferase in the hepatocarcinoma cell line resulted in more than 70% reduction of luciferase activity, while in HT-22 cells 50% knockdown of endogenous c-Jun resulted in a significant protection from glutamate-mediated toxicity.

CONCLUSIONS

Cationic liposomes associated with Tf form stable siRNA lipoplexes with reduced toxicity and enhanced specific gene knockdown activity compared to conventional lipoplexes. Thus, such formulations may constitute efficient delivery systems for therapeutic siRNA applications.

Mechanisms of cell death in oxidative stress

Reactive oxygen or nitrogen species (ROS/RNS) generated endogenously or in response to environmental stress have long been implicated in tissue injury in the context of a variety of disease states. ROS/RNS can cause cell death by nonphysiological (necrotic) or regulated pathways (apoptotic). The mechanisms by which ROS/RNS cause or regulate apoptosis typically include receptor activation, caspase activation, Bcl-2 family proteins, and mitochondrial dysfunction. Various protein kinase activities, including mitogen-activated protein kinases, protein kinases-B/C, inhibitor-of-I-kappaB kinases, and their corresponding phosphatases modulate the apoptotic program depending on cellular context. Recently, lipid-derived mediators have emerged as potential intermediates in the apoptosis pathway triggered by oxidants. Cell death mechanisms have been studied across a broad spectrum of models of oxidative stress, including H2O2, nitric oxide and derivatives, endotoxin-induced inflammation, photodynamic therapy, ultraviolet-A and ionizing radiations, and cigarette smoke. Additionally ROS generated in the lung and other organs as the result of high oxygen therapy or ischemia/reperfusion can stimulate cell death pathways associated with tissue damage. Cells have evolved numerous survival pathways to counter proapoptotic stimuli, which include activation of stress-related protein responses. Among these, the heme oxygenase-1/carbon monoxide system has emerged as a major intracellular antiapoptotic mechanism.

Proteomic analysis of glutamate-induced toxicity in HT22 cells

In the present study, we have investigated the proteome changes associated with glutamate-induced HT22 cell death, a model system to study oxidative stress-mediated toxicity. Among a number of HT22 proteins exhibiting altered expression, several molecular chaperones demonstrated substantial changes. For example, the levels of Hsp90 and Hsp70 decreased as cell death progressed whereas that of Hsp60 increased dramatically. Interestingly, cytosolic Hsp60 increased more prominently than mitochondrial Hsp60. Concomitantly, the accumulation of poly-ubiquitylated proteins and differential regulation of the peptidase activities and the subunits of 26S proteasomes were observed in glutamate-treated HT22 cells. Our findings that the molecular chaperones and the ubiquitin-proteasome system undergo changes during glutamate-induced HT22 cell death may suggest the importance of a protein quality control system in oxidative damage-mediated toxicity.

A proteomic analysis of the effect of MAPK pathway activation on L-glutamate-induced neuronal cell death

Oxidative stress has been implicated in the pathogenesis of neuronal degenerative diseases. It is also widely known that oxidative stress induces mitogen-activated protein kinase (MAPK) signaling cascades. In this study, we used proteomic analysis to investigate the role of the MAPK pathway in oxidative stress-induced neuronal cell death. The results demonstrated that several proteins, including eukaryotic translation elongation factor 2 (eEF2) and enolase I, showed a differential expression pattern during the neuronal cell death process, and this was MAPK pathway dependent. Several chaperone and cytoskeletal proteins including heat shock protein 70, calreticulin, vimentin, prolyl 4-hydroxylase β polypeptide, and transgelin 2 were up-or down-regulated, despite their expressions not depending on the MAPK pathway. These findings strongly suggest that the expressions of proteins which play protective roles are independent of the MAPK pathway. On the other hand, eEF2 and enolase I may be the downstream targets of the MAPK pathway.

Estrogen protects neuronal cells from amyloid beta-induced apoptosis via regulation of mitochondrial proteins and function

BACKGROUND

Neurodegeneration in Alzheimer's disease is associated with increased apoptosis and parallels increased levels of amyloid beta, which can induce neuronal apoptosis. Estrogen exposure prior to neurotoxic insult of hippocampal neurons promotes neuronal defence and survival against neurodegenerative insults including amyloid beta. Although all underlying molecular mechanisms of amyloid beta neurotoxicity remain undetermined, mitochondrial dysfunction, including altered calcium homeostasis and Bcl-2 expression, are involved in neurodegenerative vulnerability.

RESULTS

In this study, we investigated the mechanism of 17beta-estradiol-induced prevention of amyloid beta-induced apoptosis of rat hippocampal neuronal cultures. Estradiol treatment prior to amyloid beta exposure significantly reduced the number of apoptotic neurons and the associated rise in resting intracellular calcium levels. Amyloid beta exposure provoked down regulation of a key antiapoptotic protein, Bcl-2, and resulted in mitochondrial translocation of Bax, a protein known to promote cell death, and subsequent release of cytochrome c. E2 pretreatment inhibited the amyloid beta-induced decrease in Bcl-2 expression, translocation of Bax to the mitochondria and subsequent release of cytochrome c. Further implicating the mitochondria as a target of estradiol action, in vivo estradiol treatment enhanced the respiratory function of whole brain mitochondria. In addition, estradiol pretreatment protected isolated mitochondria against calcium-induced loss of respiratory function.

CONCLUSION

Therefore, we propose that estradiol pretreatment protects against amyloid beta neurotoxicity by limiting mitochondrial dysfunction via activation of antiapoptotic mechanisms.

Depletion of CBP is directly linked with cellular toxicity caused by mutant huntingtin

Huntington's disease is a neurodegenerative disease caused by an expanded polyglutamine stretch within the huntingtin protein. Transfection of mutant huntingtin causes cell toxicity and depletion of CREB binding protein (CBP) or its recruitment into huntingtin aggregates. However, the role of CBP has been controversial and the relationship between polyglutamine-induced toxicity and CBP depletion has not been examined on an individual cell basis. Using a single-cell based assay, we found that, in HT22 cells or primary neurons transfected with mutant huntingtin, cell toxicity was accompanied by CBP depletion, rather than merely recruitment. Transfection with a htt exon1 construct containing uninterrupted polyglutamine or a polyglutamine region engineered to form a compact beta structure resulted in cell toxicity. CBP depletion was accompanied by histone hypo-acetylation. CBP overexpression rescued both acetylated histone levels and cell toxicity. These data suggest that CBP dysfunction and altered gene transcription contribute to mutant htt-induced neurotoxicity.

ω-3 Polyunsaturated fatty acids and ionizing radiation: Combined cytotoxicity on human colorectal adenocarcinoma cells

OBJECTIVE

This study evaluated whether omega-3 polyunsaturated fatty acids (PUFAs) could enhance the radiosensitivity of three different human colorectal adenocarcinoma cell lines. To understand the underlying mechanisms, the effects of omega-3 PUFAs on the cell growth, survival, and apoptosis were evaluated alone or in combination with an antioxidant (vitamin E) and compared with the effects of omega-6 PUFAs.

METHODS

LS174T, CO112, and Caco-2 cell survival was assessed by clonogenic assay after a 3-d pretreatment with omega-3/omega-6 PUFAs and/or vitamin E before a single X-ray exposure to 4 Gy. Cell growth and viability were measured by double fluorescence-activated cell sorter analyses using propidium iodide and fluorescein isothiocyanate-conjugated annexin V. Student's t test or multivariable linear regression analyses were used for comparison.

RESULTS

Preincubation with 30 to 100 micromol/L of omega-3 PUFAs induced a dose-dependent additive decrease in cell survival after irradiation (P < 0.05). Evaluation of the underlying mechanisms indicated that omega-3 PUFAs mainly decreased the cell number via apoptosis induction. Moreover, formation of lipid peroxidation products and modulation of cyclooxygenase II activity seemed to be involved, because coincubation with 10 micromol/L vitamin E abolished the effect of 50 micromol/L of omega-3 PUFAs (P < 0.05), whereas omega-6 PUFAs could partly mimic omega-3 PUFA effects.

CONCLUSION

These observations suggest that omega-3 PUFAs may be potential candidates as nutritional adjuvants to enhance the efficacy of human colorectal cancer radiotherapy.

Gypenosides protect primary cultures of rat cortical cells against oxidative neurotoxicity

Gypenosides (GPs) were tested for their ability to protect primary cultures of immature cortical cells against oxidative glutamate toxicity. In immature neural cells, glutamate cytotoxicity is known to be mediated by the inhibition of cystine uptake, leading to depletion of intracellular glutathione (GSH). The depletion of GSH impairs cellular antioxidant defenses resulting in oxidative stress and cell death. We found that pretreatment with GPs (100-400 microg/ml) significantly protected cells from glutamate-induced cell death. It was therefore of interest to investigate whether GPs protect cortical cells against glutamate-induced oxidative injury through preventing GSH depletion. Results show that GPs significantly up-regulated mRNAs encoding gamma-glutamylcysteine synthetase (gamma-GCS) and glutathione reductase (GR) and enhanced their activities for GSH synthesis as well as recycle. Furthermore, GPs lowered the consumption of GSH through decreased accumulation of intracellular peroxides, leading to an increase in the intracellular GSH content. GPs were also found to prevent lipid peroxidation and reduce the influx of Ca(2+) which routinely follows glutamate oxidative challenge. GPs treatment significantly blocked glutamate-induced decrease in levels of Bcl-2 and increase in Bax, leading to a decrease in glutamate-induced apoptosis. Thus, we conclude that GPs protect cortical cells by multiple antioxidative actions via enhancing intracellular GSH, suppressing glutamate-induced cytosolic Ca(2+) elevation and blocking glutamate-induced apoptosis. The novel role of GPs implies their remarkable preventative and therapeutic potential in treatment of neurological diseases involving glutamate and oxidative stress.

Ganglioside GM3 is involved in neuronal cell death

Gangliosides abundant in the nervous system have been implicated in a broad range of biological functions, including the regulation of cell proliferation and death. Glutamate-induced cell death, which is accompanied by an accumulation of reactive oxygen species (ROS), is a major contributor to pathological cell death within the nervous system. However, the mechanism underlying this neuronal cell death has not been fully elucidated. In this study, we report that ganglioside GM3 is involved in neuronal cell death. GM3 was up-regulated in the mouse hippocampal cell line HT22 death caused by glutamate. Increment in GM3 levels by both the exogenous addition of GM3 and the overexpression of the GM3 synthase gene induced neuronal cell death. Overexpression of GM3 synthase by microinjecting mRNA into zebrafish embryos resulted in neuronal cell death in the central nervous system (CNS). Conversely, RNA interference-mediated silencing of GM3 synthase rescued glutamate-induced neuronal death, as evidenced by the inhibition of massive ROS production and intracellular calcium ion influx. 12-lipoxygenase (12-lipoxygenase) (12-LOX) was recruited to glycosphingolipid-enriched microdomains (GEM) in a GM3-dependent manner during oxidative glutamate toxicity. Our findings suggest that GM3 acts as not only a mediator of oxidative HT22 death by glutamate but also a modulator of in vivo neuronal cell death.

Oxidative metabolism, apoptosis and perinatal brain injury

Perinatal hypoxic-ischaemic injury (HII) is a significant cause of neurodevelopmental impairment and disability. Studies employing 31P magnetic resonance spectroscopy to measure phosphorus metabolites in situ in the brains of newborn infants and animals have demonstrated that transient hypoxia-ischaemia leads to a delayed disruption in cerebral energy metabolism, the magnitude of which correlates with the subsequent neurodevelopmental impairment. Prominent among the biochemical features of HII is the loss of cellular ATP, resulting in increased intracellular Na+ and Ca2+, and decreased intracellular K+. These ionic imbalances, together with a breakdown in cellular defence systems following HII, can contribute to oxidative stress with a net increase in reactive oxygen species. Subsequent damage to lipids, proteins, and DNA and inactivation of key cellular enzymes leads ultimately to cell death. Although the precise mechanisms of neuronal loss are unclear, it is now clear both apoptosis and necrosis are the significant components of cell death following HII. A number of different factors influence whether a cell will undergo apoptosis or necrosis, including the stage of development, cell type, severity of mitochondrial injury and the availability of ATP for apoptotic execution. This review will focus on some pathological mechanisms of cell death in which there is a disruption to oxidative metabolism. The first sections will discuss the process of damage to oxidative metabolism, covering the data collected both from human infants and from animal models. Following sections will deal with the molecular mechanisms that may underlie cerebral energy failure and cell death in this form of brain injury, with a particular emphasis on the role of apoptosis and mitochondria.

Maltol Inhibits Apoptosis of Human Neuroblastoma Cells Induced by Hydrogen Peroxide

To analyze the effect of Maltol on the apoptosis of Human Neuroblastoma Cells (SH-SY5Y) treated by free radical which was generated from Hydrogen Peroxide (H2O2), flow cytometry analysis on Phosphatidylserine (PS) inverting percentage was applied to determine the apoptosis. MTT (3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl-tetrazolium bromide) assay was employed to analyze the cell viability. DNA electrophoresis was used to detect DNA fragmentation. Moreover intracellular calcium of concentration ([Ca2+]i) was measured by fluorescence emission. Flow cytometry analysis on the function of mitochondria and Western blot analysis of NF-kappaB. The results showed that the pretreatment with maltol for 2 hours could prevent the H2O2-induced apoptosis. Maltol could reduce the inverting percentage of PS, DNA fragmentation and [Ca2+]i, and enhance the cellular function of mitochondria. NF-kappaB activated by H2O2 is reduced. The experiments suggest that maltol could effectively inhibit the apoptosis induced by H2O2. As a novel anti-oxidant, maltol is a new promising drug in protecting the neurological cells from the damage by free radical.

Oxygen-glucose deprivation decreases glutathione levels and glutamate uptake in rat hippocampal slices

Ischemia is a transitory or permanent reduction of blood flow that may provoke an excessive release of glutamate. In that condition, increased reactive oxygen species generation and/or decreased cerebral antioxidant capacity may induce cell death. Antioxidant enzymes and thiols play an important role in the cellular defenses against oxidative stress. The purpose of this study was to evaluate cell viability, glutamate uptake and antioxidant status in rat hippocampal slices exposed to oxygen-glucose deprivation (OGD), an in vitro model of ischemia. After 15 min or 1 h of OGD, hippocampal slices showed a significant reduction of cell viability. Reperfusion during 1 or 2 h did not increase cell death. In this condition, the activities of antioxidant enzymes catalase, glutathione reductase, and peroxidase did not change. However, slices exposed to 15 min OGD and reperfused for 1 or 2 h showed higher superoxide dismutase activity. A significant reduction of glutathione levels was observed after 1 or 2 h of reperfusion in slices previously exposed to 1 h of OGD, although the protein-thiol content was unchanged. Slices exposed to 1 h of OGD and reperfused for 2 h showed reduced sodium-dependent l-[(3)H]glutamate uptake. The reduction of glutamate uptake was partially reversed by dl-dithiothreitol (DTT), a thiol-reducing agent, which may reduce thiol groups in glutamate transporters. Therefore, higher glutamate levels in the synaptic cleft could promote transporter reversal and impair glutamate uptake. Increased extracellular glutamate levels associated with decreased glutathione levels might exacerbate cell damage induced by oxygen and glucose deprivation.

Distribution of the cystine/glutamate antiporter system xc- in the brain, kidney, and duodenum

System x(c)(-), one of the main transporters responsible for central nervous system cystine transport, is comprised of two subunits, xCT and 4F2hc. The transport of cystine into cells is rate limiting for glutathione synthesis, the major antioxidant and redox cofactor in the brain. Alterations in glutathione status are prevalent in numerous neurodegenerative diseases, emphasizing the importance of proper cystine homeostasis. However, the distribution of xCT and 4F2hc within the brain and other areas has not been described. Using specific antibodies, both xCT and 4F2hc were localized predominantly to neurons in the mouse and human brain, but some glial cells were labeled as well. Border areas between the brain proper and periphery including the vascular endothelial cells, ependymal cells, choroid plexus, and leptomeninges were also highly positive for the system x(c)(-) components. xCT and 4F2hc are also present at the brush border membranes in the kidney and duodenum. These results indicate that system x(c)(-) is likely to play a role in cellular health throughout many areas of the brain as well as other organs by maintaining intracellular cystine levels, thereby resulting in low levels of oxidative stress.

Proteome analysis of cortical neuronal cultures following cycloheximide, heat stress and MK801 preconditioning

Studying endogenous neuroprotective mechanisms induced by preconditioning may provide drug leads to reduce ischemic neuronal death. In this study, we used 2-DE to examine protein expression following cycloheximide, heat stress, and MK801 preconditioning in rat cortical neuronal cultures. Of 150 differentially expressed protein spots selected for identification the protein or tentative protein(s) were identified in 84 cases, representing 50 different proteins. Different protein spots representing the same protein or closely related protein(s) occurred for 21 of the identified proteins and are likely to represent PTMs or proteolytic fragments of the protein. Six protein spots (actin, elongation factor 1-alpha 1, peptidyl-prolyl cis-transisomerase A, Cu/Zn superoxide dismutase, stathmin, tropomyosin) were differentially expressed in all three preconditioning treatments. Twenty-seven protein spots were differentially expressed in two preconditioning treatments, while 51 spots were differentially expressed in one treatment. Three proteins heterogeneous nuclear ribonucleoproteins A2/B1, mitochondrial stress-70 protein, and tropomyosin were detected in control neuronal cultures, but not following one or more preconditioning treatments, while a posttranslational modified form of the voltage dependent anion channel 1 was only detected following cycloheximide preconditioning. In summary, this study has revealed multiple protein changes potentially involved in neuroprotective and neurodamaging pathways, which require further characterization.

Mood stabilizing drug lithium increases expression of endoplasmic reticulum stress proteins in primary cultured rat cerebral cortical cells

The mood stabilizing drug lithium is a highly effective treatment for bipolar disorder. Previous studies in our laboratory found that chronic treatment with the mood stabilizing drug valproate in rat brain increased the expression of endoplasmic reticulum (ER) stress proteins GRP78, GRP94 and calreticulin. We report here that in primary cultured rat cerebral cortical cells, expression of GRP78, GRP94 and calreticulin are increased not only by valproate, but also by lithium after chronic treatment for 1 week at therapeutically relevant concentrations. However, two other mood stabilizing drugs carbamazepine and lamotrigine had no effect on expression of GRP78, GRP94 or calreticulin. Chronic treatment with lithium for 1 week increased both mRNA and protein levels of ER stress proteins. In contrast to a classic GRP78 inducer thapsigargin, an inhibitor of the ER Ca2+ -ATPase, chronic treatment with lithium or valproate for 1 week modestly increased GRP78 expression in neuronal cells, had no effect on basal intracellular free Ca2+ concentration and does not induce cell death. These results indicate that lithium and valproate may increase expression of GRP78, GRP94 and calreticulin in primary cultured rat cerebral cortical cells without causing cell damage. These results also suggest that the mechanism of GRP78 increase induced by lithium and valproate may be different from that of thapsigargin.

Distinct nuclear factor-kappaB/Rel proteins have opposing modulatory effects in glutamate-induced cell death in HT22 cells

Members of the nuclear factor-kappaB (NF-kappaB)/Rel family (p50, p52, p65 (RelA), RelB and c-Rel) is sequestered in the cytoplasm through its tight association with the inhibitor of NF-kappaB (IkappaB). NF-kappaB has been shown to function as key regulators of either cell death or survival in neurons after activation of the cells by various extracellular signals. In the study presented here, we investigated whether the selective activation of diverse NF-kappaB/Rel family members in HT22 cells might lead to distinct effects on glutamate-induced cell death. Exposing HT22 cells to glutamate, which blocks cystine uptake into the cells via inhibition of the glutamate-cystine antiporter, resulted in a transient activation of IkappaB and NF-kappaB/Rel and caused delayed cell death. Aspirin, which has been shown to block phosphorylation of the IkappaB component of the cytoplasmic NF-kappaB complex, significantly suppressed glutamate-induced cell death, whereas the NF-kappaB decoy oligonucleotide potentiated it. The inhibition of NF-kappaB/Rel protein expression by antisense oligonucleotides showed that p65 is involved in glutamate-mediated cell death, whereas p50 is involved in inhibitory pathways of the cell death. These findings suggest that in HT22 cells, the balance between promoting and presenting cell death to glutamate-induced oxidative stress relies on the activation of distinct NF-kappaB proteins.

Suppression of protein kinase Cepsilon mediates 17beta-estradiol-induced neuroprotection in an immortalized hippocampal cell line

Although estrogens are neuroprotective in a variety of neuroprotection models, the precise underlying mechanisms are currently not well understood. Here, we examined the role of protein kinase C (PKC) in mediating estrogen-induced neuroprotection in the HT-22 immortalized hippocampal cell line. The neuroprotection model utilized calcein fluorescence to quantitate cell viability following glutamate insults. 17beta-Estradiol (betaE2) protected HT-22 cells when treatment was initiated before or after the glutamate insult. The inhibition of PKC by bis-indolylmaleimide mimicked and enhanced betaE2-induced neuroprotection. In contrast, the inhibition of specific PKC isozymes (alpha and beta) by Go6976, inhibition of 1-phosphatidylinositol 3 kinase by wortmannin, or inhibition of protein kinase A by H-89, did not alter cell viability, suggesting a specific involvement of PKC in an isozyme-dependent manner. We further examined whether estrogen interacts with PKC in a PKC isozyme-specific manner. Protein levels and activity of PKC isozymes (alpha, delta, epsilon, and zeta) were assessed by western blot analysis and radiolabeled phosphorylation assays respectively. Among the isozymes tested, betaE2 altered only PKCepsilon; it reduced the activity and membrane translocation of PKCepsilon in a manner that correlated with its protection against glutamate toxicity. Furthermore, betaE2 reversed the increased activity of membrane PKCepsilon induced by glutamate. These data suggest that the neuroprotective effects of estrogens are mediated in part by inhibition of PKCepsilon activity and membrane translocation.

Conjugation of catechins with cysteine generates antioxidant compounds with enhanced neuroprotective activity

Antioxidant compounds derived from the conjugation of (-)-epicatechin and (-)-epicatechin 3-O-gallate with cysteine and cysteine derivatives protected HT-22 nerve cells (EC50 between 36 and 65 microM) from death triggered by glutamate while underivatized (-)-epicatechin was almost inactive (EC50=610 microM). Differences in free radical scavenging capacity (DPPH assay) could not account for the improvement in neuroprotective activity upon derivatization of (-)-epicatechin with thiols. Moreover, while the gallate-containing compounds are more efficient radical scavengers than their non-galloylated counterparts, they are only equally or less potent as neuroprotective agents. Although all of the conjugates were able to scavenge mitochondrially generated reactive oxygen species (ROS) inside the cells, the majority of their neuroprotective activity appeared to be dependent upon their ability to maintain glutathione levels. These results suggest that a mechanism other than ROS scavenging is involved in the neuroprotective action exerted by the epicatechin conjugates.

Overexpression of glutathione peroxidase protects immature murine neurons from oxidative stress

Neuronal enzyme systems involved in free radical detoxification are developmentally regulated such that intracellular glutathione peroxidase (GPx-1) activity is low in the newborn mouse brain. We hypothesized that neurons expressing a higher level of GPx-1 will be more resistant to hydrogen peroxide (H(2)O(2)) exposure. We show a dose-dependent protection against H(2)O(2) in primary neuronal cultures from fetuses overexpressing human GPx-1 compared to wild types of the same genetic background. Exogenous antioxidants completely protected neurons, even at extremely high H(2)O(2 )concentrations and regardless of the genotype. Specific depletion of glutathione with buthionine sulfoximine increased cell death in transgenic cultures exposed to 200 microM H(2)O(2), reducing protection afforded by increased GPx-1 activity. Increased GPx-1 expression in immature cortical neurons confers protection from oxidative stress, but availability of reducing equivalents determines susceptibility to oxidative cell death.

Neuroprotective Properties of Afobazol in Vitro

The effects of a novel selective anxiolytic afobazol on survival of HT-22 neurons were studied in the model of oxidative stress and glutamate toxicity. In both models, the neuroprotective effect of afobazol was established.

Tyrosine phosphorylation regulates the proteolytic activation of protein kinase Cdelta in dopaminergic neuronal cells

Oxidative stress is a key apoptotic stimulus in neuronal cell death and has been implicated in the pathogenesis of many neurodegenerative disorders, including Parkinson disease (PD). Recently, we demonstrated that protein kinase C-delta (PKCdelta) is an oxidative stress-sensitive kinase that can be activated by caspase-3-dependent proteolytic cleavage to induce apoptotic cell death in cell culture models of Parkinson disease (Kaul, S., Kanthasamy, A., Kitazawa, M., Anantharam, V., and Kanthasamy, A. G. (2003) Eur. J. Neurosci. 18, 1387-1401 and Kanthasamy, A. G., Kitazawa, M., Kanthasamy, A., and Anantharam, V. (2003) Antioxid. Redox. Signal. 5, 609-620). Here we showed that the phosphorylation of a tyrosine residue in PKCdelta can regulate the proteolytic activation of the kinase during oxidative stress, which consequently influences the apoptotic cell death in dopaminergic neuronal cells. Exposure of a mesencephalic dopaminergic neuronal cell line (N27 cells) to H(2)O(2)(0-300 microm) induced a dose-dependent increase in cytotoxicity, caspase-3 activation and PKCdelta cleavage. H(2)O(2)-induced proteolytic activation of PKC was delta mediated by the activation of caspase-3. Most interestingly, both the general Src tyrosine kinase inhibitor genistein (25 microm) and the p60(Src) tyrosine-specific kinase inhibitor (TSKI; 5 microm) dramatically inhibited H(2)O(2) and the Parkinsonian toxin 1-methyl-4-phenylpyridinium-induced PKCdelta cleavage, kinase activation, and apoptotic cell death. H(2)O(2) treatment also increased phosphorylation of PKCdelta at tyrosine site 311, which was effectively blocked by co-treatment with TSKI. Furthermore, N27 cells overexpressing a PKCdelta(Y311F) mutant protein exhibited resistance to H(2)O(2)-induced PKCdelta cleavage, caspase activation, and apoptosis. To our knowledge, these data demonstrate for the first time that phosphorylation of Tyr-311 on PKCdelta can regulate the proteolytic activation and proapoptotic function of the kinase in dopaminergic neuronal cells.

Proteasome inhibition protects HT22 neuronal cells from oxidative glutamate toxicity

Oxidative stress caused by glutathione depletion after prolonged exposure to extracellular glutamate leads to a form of neuronal cell death that exhibits morphologically mixed features of both apoptosis and necrosis. However, specific downstream executioners involved in this form of cell death have yet to be identified. We report here that glutamate exposure does not activate caspase-3 in the HT22 neuronal cell line. Furthermore, no cytoprotection was achieved with either the pan-caspase inhibitor Z-VAD-fmk or the caspase-3-specific inhibitor DEVD-CHO. In contrast, inhibition of the proteasome by lactacystin protected both HT22 cells and rat primary neuronal cells against cell lysis. In parallel, oxidatively altered and ubiquitinated proteins accumulated in the mitochondrial fraction of cells after proteasome inhibition. These findings suggest that caspases can be decoupled from oxidative stress under some conditions, and implicate the ubiquitin/proteasome pathway in neuronal cell death caused by oxidative glutamate toxicity.

Prosurvival and Prodeath Effects of Hypoxia-inducible Factor-1α Stabilization in a Murine Hippocampal Cell Line

Hypoxia-inducible factor-1 (HIF-1) is a transcriptional activator involved in adaptation to hypoxic stress. Previous studies from our laboratory demonstrated that pharmacological activators of HIF-1 (e.g. deferoxamine, cobalt chloride) could also protect cultured primary neurons or an immortalized hippocampal neuroblast line (HT22) from oxidative stress-induced death. However, whether HIF-1 activation is sufficient to abrogate neuronal death resulting from oxidative stress or other hypoxia-independent death inducers remains unclear. To address this question we utilized a HIF-1alpha fusion protein that partially lacks the domain required for oxygen-dependent degradation of HIF-1alpha and that has a VP16 transcriptional activation domain from herpes simplex virus. HT22 cells were infected with a retrovirus encoding either the HIF-1alpha-VP16 fusion protein or the activation domain of the VP16 protein alone as a control. Expression of HIF-1alpha-VP16, but not VP16 alone, increased luciferase activity driven by a canonical hypoxia response element, increased mRNA of established HIF-1 target genes, and increased activity of one of these HIF-1 target genes. Unexpectedly, enhanced HIF-1 activity in HT22 cells enhanced sensitivity to oxidative death induced by glutathione depletion. Accordingly, suppression of HIF-1alpha expression using RNA interference prevented oxidative death. By contrast, HIF-1alpha-VP16-expressing HT22 cells were more resistant to DNA damage (induced by camptothecin) or endoplasmic reticulum stress (induced by thapsigargin and tunicamycin) than were VP16-expressing cells, and suppression of HIF-1alpha expression using RNA interference rendered HT22 cells more sensitive to death induced by DNA damage or endoplasmic reticulum stress. Together, these data demonstrate that HIF-1 can mediate prodeath or prosurvival responses in the same cell type depending on the injury stimulus.

Glutathione depletion-induced chromosomal DNA fragmentation associated with apoptosis and necrosis

Chromosomal DNA and mitochondrial dysfunctions play a role on mammalian cell death induced by oxidative stress. The major biochemical dysfunction of chromosome is the presence of an ordered cleavage of the DNA backborn, which is separated and visualized as an electrophoretic pattern of fragments. Oxidative stress provides chromatin dysfunction such as single strand and double strand DNA fragmentation leading to cell death. More than 1 Mb of giant DNA, 200-800 kb or 50-300 kb high molecular weight (HMW) DNA and internucleosomal DNA fragments are produced during apoptosis or necrosis induced by oxidative stress such as glutathione (GSH) depletion in several types of mammalian cells. Reactive oxygen species (ROS)-mediated DNA fragmentation is enhanced by polyunsaturated fatty acids including arachidonic acid or their hydroperoxides, leading to necrosis. Mitochondrial dysfunction on decrease of trans membrane potential, accumulation of ROS, membrane permeability transition and release of apoptotic factors during apoptosis or necrosis has been implicated. This review refers to the correlation of chromosomal DNA fragmentation and apoptosis or necrosis induced by GSH depletion, and the possible mechanisms of oxidative stress-induced cell death.

Gliotoxicity in hippocampal cultures is induced by transportable, but not by nontransportable, glutamate uptake inhibitors

Extracellular glutamate is kept below a toxic level by glial and neuronal glutamate transporters. Here we show that the transportable glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylate (t-PDC) induced cell death in mature, but not in immature, hippocampal neuron-enriched cultures. The cell death produced by a 24-hr treatment with t-PDC was dose-dependent and reached 85% of the cell population at a 250 microM concentration at 23 days in vitro (DIV). Immunocytochemistry experiments showed that, under these experimental conditions, t-PDC killed not only neurons as expected but also glial cells. The N-methyl-D-aspartate (NMDA) antagonist D-2-aminophosphonovalerate (D-APV; 250 microM) only partially reversed this toxicity, completely protecting the neuronal cell population but not the glial population. The antioxidant compounds alpha-tocopherol or Trolox, used at concentrations that reverse the oxidative stress-induced toxicity, did not block the gliotoxicity specifically produced by t-PDC in the presence of D-APV. The nontransportable glutamate uptake inhibitor DL-threo-beta-benzyloxyaspartate (TBOA) elicited cell death only in mature, but not in immature, hippocampal cultures. The TBOA toxic effect was dose dependent and reached a plateau at 100 microM in 23-DIV cultures. About 50% of the cell population died. TBOA affected essentially the neuronal population. D-APV (250 microM) completely reversed this toxicity. It is concluded that nontransportable glutamate uptake inhibitors are neurotoxic via overactivation of NMDA receptors, whereas transportable glutamate uptake inhibitors induce both an NMDA-dependent neurotoxicity and an NMDA- and oxidative stress-independent gliotoxicity, but only in mature hippocampal cultures.

Effects of gender on neurologic and functional recovery after spinal cord injury

OBJECTIVE

To assess gender differences in neurologic and functional outcome measures in persons with spinal cord injury (SCI).

DESIGN

Case series.

SETTINGS

Model Spinal Cord Injury Systems (MSCIS) throughout the United States.

PARTICIPANTS

People (N=14,433) admitted to an MSCIS within 30 days of injury.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Improvement in American Spinal Injury Association (ASIA) motor index score, ASIA Impairment Scale, level of injury, and FIM instrument scores after SCI.

RESULTS

When examining subjects grouped by severity of injury, changes in ASIA motor index total scores, from system admission to 1-year anniversary, were significantly greater for women than men with either complete ( P =.035) or incomplete ( P =.031) injuries. Functional comparison of men and women, using the FIM motor subscale, revealed that men had higher FIM motor scores at rehabilitation discharge among those with motor-complete injuries, except for those with C1-4 and C6 neurologic levels. Women with motor-incomplete high tetraplegia (C1-4 levels) had higher discharge FIM motor scores than did similarly afflicted men. There were no significant differences in FIM motor scores among men and women with other levels of motor incomplete SCI.

CONCLUSIONS

Gender differences in SCI were seen in several areas. Women may have more natural neurologic recovery than men; however, for a given level and degree of neurologic injury, men tend to do better functionally than women at time of discharge from rehabilitation. Future prospective study of the effects of estrogen on neurologic recovery and the effects of gender on functional potential are recommended.

A cytosolic source of calcium unveiled by hydrogen peroxide with relevance for epithelial cell death

Oxidative stress releases intracellular calcium, which plays a pathogenic role in mammalian cell death. Here we report a search for the source of oxidative calcium in HeLa cells based on confocal epifluorescence microscopy. H(2)O(2) caused a rapid increase in cytosolic calcium, which was followed by mitochondrial Ca(2+) loading. Combined mitochondrial uncoupling with full depletion of thapsigargin-sensitive stores abrogated inositol 1,4,5-trisphosphate-mediated calcium release but failed to inhibit H(2)O(2)-induced calcium release, observation that was confirmed in MDCK cells. Prevention of peroxide-induced acidification with a pH clamp was also ineffective, discarding a role for endosomal/lysosomal Ca(2+)/H(+) exchange. Lysosomal integrity was not affected by H(2)O(2). Mature human erythrocytes also reacted to peroxide by releasing intracellular calcium, thus directly demonstrating the cytosolic source. Glutathione depletion markedly sensitized cells to H(2)O(2), an effect opposite to that achieved by DTT. Iron chelation was ineffective. In summary, our results show the existence of a previously unrecognized sulfhydryl-sensitive source of pathogenic calcium in the cytosol of mammalian cells.

?Dark? (compacted) neurons may not die through the necrotic pathway

"Dark" neurons were produced in the cortex of the rat brain by hypoglycemic convulsions. In the somatodendritic domain of each affected neuron, the ultrastructural elements, except for disturbed mitochondria, were remarkably preserved during the acute stage, but the distances between them were reduced dramatically (ultrastructural compaction). Following a 1-min convulsion period, only a few neurons were involved and their environment appeared undamaged. In contrast, 1-h convulsions affected many neurons and caused swelling of astrocytic processes and neuronal dendrites (excitotoxic neuropil). A proportion of "dark" neurons recovered the normal structure in 2 days. The non-recovering "dark" neurons were removed from the brain cortex through two entirely different pathways. In the case of 1-h convulsions, their organelles swelled, then disintegrated and finally dispersed into the neuropil through large gaps in the plasma membrane (necrotic-like removal). Following a 1-min convulsion period, the non-recovering "dark" neurons fell apart into membrane-bound fragments that retained the compacted interior even after being engulfed by astrocytes or microglial cells (apoptotic-like removal). Consequently, in contrast to what is generally accepted, the "dark" neurons produced by 1-min hypoglycemic convulsions do not die as a consequence of necrosis. As regards the case of 1-h convulsions, it is assumed that a necrotic-like removal process is imposed, by an excitotoxic environment, on "dark" neurons that previously died through a non-necrotic pathway. Apoptotic neurons were produced in the hippocampal dentate gyrus by intraventricularly administered colchicine. After the biochemical processes had been completed and the chromatin condensation in the nucleus had reached an advanced phase, the ultrastructural elements in the somatodendritic cytoplasm of the affected cells became compacted. If present in an apparently undamaged environment such apoptotic neurons were removed from the dentate gyrus through the apoptotic sequence of morphological changes, whereas those present in an impaired environment were removed through a necrotic-like sequence of morphological changes. This suggests that the removal pathway may depend on the environment and not on the death pathway, as also assumed in the case of the "dark" neurons produced by hypoglycemic convulsions.

l-Cysteine-induced brain damage in adult rats

The time-dependent brain damage induced in adult rats by a single dose of L-cysteine was examined morphologically. Five-week-old male Sprague-Dawley rats that received 1500 mg/kg of L-cysteine by intraperitoneal injection were examined at 12 and 24 h and 3, 7, and 14 days after administration. Pathological changes were seen in the cerebral and cerebellar cortex. Neuronal karyopyknosis was observed in the granular and molecular layers of the superficial cerebellar cortex at 12 h, and well-demarcated infarct-like lesions were seen with a widespread distribution in the cerebral cortex at 24 h. A large number of lipid phagocytes and glial cell proliferation were noted in the affected regions on days 3 to 14. The neuronal cell death observed in the cerebellar granular layer cells was demonstrated to be due to apoptosis by histopathological and ultrastructural examinations as well as by the terminal deoxyribonucleotide transferase-mediated dUTP nick-end labeling (TUNEL) method and agarose gel electrophoresis for DNA laddering. It was found that L-cysteine induced brain lesions mainly in the cerebral and cerebellar cortex in adult rats, in contrast to lesions in various regions as observed in neonatal rats. The histopathological findings reported here suggest that the pathogenesis of the brain damage induced by L-cysteine in adult rats differs from that in neonatal rats. It appears likely that L-cysteine-induced brain damage is secondary to impairment of blood flow or other unknown factors that are responsible for the subsequent development of brain lesions.

The spread of cell death from impact damaged cartilage: lack of evidence for the role of nitric oxide and caspases

Over 21 days in culture, cell death spreads, both radially and transversely, from loaded to surrounding cartilage. This spread was prevented by physical separation and separate culture post-impact.

OBJECTIVE

One aim was to determine if nitric oxide (NO) is the intercellular signal mediating cell death. Another aim was to clarify the nature of the cell death, whether caspase mediated apoptosis or necrosis.

DESIGN

Cyclic impacts were applied to the central 2 mm core of 4 mm canine articular cartilage discs. Post-impact culturing was for 21 days in the presence or absence of the iNOS inhibitor, L-NAME, or the broad-spectrum caspase inhibitor, Z-VAD FMK. Cell death was quantified using the TUNEL assay. Culture media were collected every 2 days for measurements of glycosaminoglycan (GAG) and NO release.

RESULTS

Cell death spread from the loaded core into the surrounding ring over 21 days in culture. Although L-NAME significantly reduced nitrite release into the culture media of both loaded and control cartilage, the spread of cell death was not prevented. Neither was the spread of cell death prevented by Z-VAD FMK.

CONCLUSIONS

These data indicate that NO is not acting as an intercellular signalling factor in this in vitro system and that the cell death post-impact is not caspase mediated.

Cytoprotection by pre-emptive conditional phosphorylation of translation initiation factor 2

Transient phosphorylation of the alpha-subunit of translation initiation factor 2 (eIF2alpha) represses translation and activates select gene expression under diverse stressful conditions. Defects in the eIF2alpha phosphorylation-dependent integrated stress response impair resistance to accumulation of malfolded proteins in the endoplasmic reticulum (ER stress), to oxidative stress and to nutrient deprivations. To study the hypothesized protective role of eIF2alpha phosphorylation in isolation of parallel stress signaling pathways, we fused the kinase domain of pancreatic endoplasmic reticulum kinase (PERK), an ER stress-inducible eIF2alpha kinase that is normally activated by dimerization, to a protein module that binds a small dimerizer molecule. The activity of this artificial eIF2alpha kinase, Fv2E-PERK, is subordinate to the dimerizer and is uncoupled from upstream stress signaling. Fv2E-PERK activation enhanced the expression of numerous stress-induced genes and protected cells from the lethal effects of oxidants, peroxynitrite donors and ER stress. Our findings indicate that eIF2alpha phosphorylation can initiate signaling in a cytoprotective gene expression pathway independently of other parallel stress-induced signals and that activation of this pathway can single-handedly promote a stress-resistant preconditioned state.

Regeneration of supraspinal axons after complete transection of the thoracic spinal cord in neonatal opossums (Monodelphis domestica)

These studies define the time table and origin of supraspinal axons regenerating across a complete spinal transection in postnatal Monodelphis domestica. After lumbar (L1) spinal cord injection of fluorophore-dextran amine conjugate on postnatal (P) day 4, a consistent number of neurons could be labeled. The numbers of labeled neurons remained stable for several weeks, but subsequently declined by P60 in control animals and by P35 in animals with complete spinal transection (T4-T6) performed at P7. In control animals, 25-40% of neurons labeled with a fluorophore injected (L1) at P4 could also be double-labeled by a second fluorophore injected (T8-T10) at different older ages. In spinally transected animals, total numbers of neurons labeled with the second marker were initially lower compared with age-matched controls, but were not significantly different by 3 weeks after injury. The proportion of double-labeled neurons in spinally transected animals increased from approximately 2% 1 week after injury (P14) to approximately 50% by P60, indicating that a substantial proportion of neurons with axons transected at P7 is able to regenerate and persist into adulthood. However, the proportion of axons originating from regenerating neurons made only a small contribution at older ages to total numbers of fibers growing through the injury site, because much of development of the spinal cord occurs after P7. Evidence was obtained that degenerating neurons with both apoptotic and necrotic morphologies were present in brainstem nuclei; the number of neurons with necrotic morphology was much greater in the brainstem of animals with spinal cords transected at P7.

Activation of stimulatory heterotrimeric G proteins increases glutathione and protects neuronal cells against oxidative stress

Oxidative glutamate toxicity in the neuronal cell line HT22 is a model for cell death by oxidative stress, where an excess of extracellular glutamate inhibits import of cystine, a building block of the antioxidant glutathione. The subsequent decrease in glutathione then leads to the accumulation of reactive oxygen species (ROS) and programmed cell death. We used pharmacological compounds known to interact with heterotrimeric G-protein signalling and studied their effects on cell survival, morphology, and intracellular events that ultimately lead to cell death. Cholera toxin and phorbol esters were most effective and prevented cell death through independent pathways. Treating HT22 cells with cholera toxin attenuated the glutamate-induced accumulation of ROS and calcium influx. This was, at least in part, caused by an increase in glutathione due to improved uptake of cystine mediated by the induction of the glutamate/cystine-antiporter subunit xCT or, additionally, by the up-regulation of the antiapoptotic protein Bcl-2. Gs activation also protected HT22 cells from hydrogen peroxide or inhibition of glutathione synthesis by buthionine sulfoximine, and immature cortical neurones from oxidative glutamate toxicity. Thus, this pathway might be more generally implicated in protection from neuronal death by oxidative stress.

Chromosomal DNA fragmentation in apoptosis and necrosis induced by oxidative stress

Chromosomal DNA dysfunction plays a role in mammalian cell death. Oxidative stress producing reactive oxygen species (ROS) induces chromatin dysfunction such as single- and double-strand DNA fragmentation leading to cell death through apoptosis or necrosis. More than 1 Mbp giant DNA, 200-800 or 50-300 kbp high molecular weight (HMW) DNA and internucleosomal DNA fragments are produced by oxidative stress and by some agents producing ROS during apoptosis or necrosis in several types of mammalian cells. Some nucleases involved in the chromosomal DNA fragmentation in apoptosis or necrosis are classified. ROS-mediated DNA fragmentation is caused and enhanced by polyunsaturated fatty acids (PUFAs) or their hydroperoxides through lipid peroxidation. A reduction of intracellular GSH levels induced by the inhibition of cystein transport or GSH biosynthesis leads to cell death through over production and accumulation of ROS in some types of mammalian cells. The ROS accumulation system has been used as a model of oxidative stress to discuss whether ROS-mediated DNA fragmentation associated with cell death is based on apoptosis or necrosis.

Brain expression of apurinic/apyrimidinic endonuclease (APE/Ref-1) multifunctional DNA repair enzyme gene in the mouse with special reference to the suprachiasmatic nucleus

Multifunctional mammalian apurinic/apyrimidinic endonuclease (APE, also known as redox factor-1; Ref-1) repairs baseless sites of damaged DNA caused by oxidative stress and regulates the redox state of various DNA binding proteins. Here, we examined the expression of APE/Ref-1 m-RNA in the mouse brain by in situ hybridization. We detected APE/Ref-1 transcripts throughout the mouse brain particularly in the clock oscillating neurons of the suprachiasmatic nucleus (SCN), hippocampal pyramidal cells, granular cells, and in monoaminergic neurons. In the circadian center SCN, levels of APE/ref-1 mRNA transcripts were constantly high, and were not influenced by either circadian rhythms or by exposure to light.

Necrotic cell death induced by delta-aminolevulinic acid in mouse astrocytes. Protective role of melatonin and other antioxidants

Accumulation of delta-aminolevulinic acid (ALA), as it occurs in acute intermittent porphyria (AIP), is the origin of an endogenous source of reactive oxygen species (ROS), which can exert oxidative damage to cell structures. In the present work we examined the ability of different antioxidants to revert ALA-promoted damage, by incubating mouse astrocytes with 1.0 mM ALA for different times (1-4 hr) in the presence of melatonin (2.5 mM), superoxide dismutase (25 units/mL), catalase (200 units/mL) or glutathione (0.5 mM). The defined relative index [(malondialdehyde levels/accumulated ALA) x 100], decreases with incubation time, reaching values of 76% for melatonin and showing that the different antioxidants tested can protect astrocytes against ALA-promoted lipid peroxidation. Concerning porphyrin biosynthesis, no effect was observed with catalase and superoxide dismutase whereas increases of 57 and 87% were obtained with glutathione and melatonin, respectively, indicating that these antioxidants may prevent the oxidation of porphobilinogen deaminase, reactivating so that the AIP genetically reduced enzyme. Here we showed that ALA induces cell death displaying a pattern of necrosis. This pattern was revealed by loss of cell membrane integrity, marked nuclear swelling and double labeling with annexin V and propidium iodide. In addition, no caspase 3-like activity was detected. These findings provide the first experimental evidence of the involvement of ALA-promoted ROS in the damage of proteins related to porphyrin biosynthesis and the induction of necrotic cell death in astrocytes. Interestingly, melatonin decreases the number of enlarged nuclei and shows a protective effect on cellular morphology.

Activation of extracellular signal-regulated kinases (ERK) during reperfusion of ischemic spinal cord

The extracellular signal-regulated kinases (ERK) participate in numerous signaling pathways and are abundantly expressed in the CNS. It has been proposed that ERK activation promotes survival in models of neuronal injury. Inhibition of MEK, the upstream kinase that activates ERK, however, leads to neuroprotection in models of cerebral ischemia and trauma, suggesting that in this context ERK activation contributes to cellular damage. The effect of ischemia and reperfusion on activity and expression of ERK was investigated using a reversible model of rabbit spinal cord ischemia. Active ERK was observed in nai;ve animals, which decreased during 15 to 60 min of ischemia. Upon reperfusion, a robust activation of ERK was observed in animals occluded for 60 min that remained permanently paraplegic. Immunohistochemical analyses revealed increased staining of phosphorylated ERK (pERK) in glial cells and faint nuclear staining in motor neurons of animals occluded for 60 min and reperfused for 18 h. In contrast ERK activity did not increase in animals occluded for 15 min that regained motor function. No evidence of increased pERK immunoreactivity in motor neurons or nuclear translocation was noted in these animals. ERK1 was demonstrated to be identical to a p46 c-Jun/ATF-2 kinase previously shown to be activated by reperfusion after a 60-min occlusion. The results suggest that activation of ERK during reperfusion of ischemic spinal cord participates in the cellular pathways leading to neuronal damage.