Effects of oxidative stress on phospholipid signaling in rat cultured astrocytes and brain slices

Vitamin K - sources, physiological role, kinetics, deficiency, detection, therapeutic use, and toxicity

Vitamin K is traditionally connected with blood coagulation, since it is needed for the posttranslational modification of 7 proteins involved in this cascade. However, it is also involved in the maturation of another 11 or 12 proteins that play different roles, encompassing in particular the modulation of the calcification of connective tissues. Since this process is physiologically needed in bones, but is pathological in arteries, a great deal of research has been devoted to finding a possible link between vitamin K and the prevention of osteoporosis and cardiovascular diseases. Unfortunately, the current knowledge does not allow us to make a decisive conclusion about such a link. One possible explanation for this is the diversity of the biological activity of vitamin K, which is not a single compound but a general term covering natural plant and animal forms of vitamin K (K₁ and K₂) as well as their synthetic congeners (K₃ and K₄). Vitamin K₁ (phylloquinone) is found in several vegetables. Menaquinones (MK₄–MK₁₃, a series of compounds known as vitamin K₂) are mostly of a bacterial origin and are introduced into the human diet mainly through fermented cheeses. Current knowledge about the kinetics of different forms of vitamin K, their detection, and their toxicity are discussed in this review.

Mitochondrial hydrogen peroxide positively regulates neuropeptide secretion during diet-induced activation of the oxidative stress response

Mitochondria play a pivotal role in the generation of signals coupling metabolism with neurotransmitter release, but a role for mitochondrial-produced ROS in regulating neurosecretion has not been described. Here we show that endogenously produced hydrogen peroxide originating from axonal mitochondria (mtH2O2) functions as a signaling cue to selectively regulate the secretion of a FMRFamide-related neuropeptide (FLP-1) from a pair of interneurons (AIY) in C. elegans. We show that pharmacological or genetic manipulations that increase mtH2O2 levels lead to increased FLP-1 secretion that is dependent upon ROS dismutation, mitochondrial calcium influx, and cysteine sulfenylation of the calcium-independent PKC family member PKC-1. mtH2O2-induced FLP-1 secretion activates the oxidative stress response transcription factor SKN-1/Nrf2 in distal tissues and protects animals from ROS-mediated toxicity. mtH2O2 levels in AIY neurons, FLP-1 secretion and SKN-1 activity are rapidly and reversibly regulated by exposing animals to different bacterial food sources. These results reveal a previously unreported role for mtH2O2 in linking diet-induced changes in mitochondrial homeostasis with neuropeptide secretion.

Role of Phospholipase D-Derived Phosphatidic Acid in Regulated Exocytosis and Neurological Disease

Lipids play a vital role in numerous cellular functions starting from a structural role as major constituents of membranes to acting as signaling intracellular or extracellular entities. Accordingly, it has been known for decades that lipids, especially those coming from diet, are important to maintain normal physiological functions and good health. On the other side, the exact molecular nature of these beneficial or deleterious lipids, as well as their precise mode of action, is only starting to be unraveled. This recent improvement in our knowledge is largely resulting from novel pharmacological, molecular, cellular, and genetic tools to study lipids in vitro and in vivo. Among these important lipids, phosphatidic acid plays a unique and central role in a great variety of cellular functions. This review will focus on the proposed functions of phosphatidic acid generated by phospholipase D in the last steps of regulated exocytosis with a specific emphasis on hormonal and neurotransmitter release and its potential impact on different neurological diseases.

Single-Cell RNA-seq Reveals Profound Alterations in Mechanosensitive Dorsal Root Ganglion Neurons with Vitamin E Deficiency

Ninety percent of Americans consume less than the estimated average requirements of dietary vitamin E (vitE). Severe vitE deficiency due to genetic mutations in the tocopherol transfer protein (TTPA) in humans results in ataxia with vitE deficiency (AVED), with proprioceptive deficits and somatosensory degeneration arising from dorsal root ganglia neurons (DRGNs). Single-cell RNA-sequencing of DRGNs was performed in Ttpa^−/− mice, an established model of AVED. In stark contrast to expected changes in proprioceptive neurons, Ttpa^−/− DRGNs showed marked upregulation of voltage-gated Ca²⁺ and K⁺ channels in mechanosensitive, tyrosine-hydroxylase positive (TH+) DRGNs. The ensuing significant conductance changes resulted in reduced excitability in mechanosensitive Ttpa^−/− DRGNs. A highly supplemented vitE diet (600 mg dl-α-tocopheryl acetate/kg diet) prevented the cellular and molecular alterations and improved mechanosensation. VitE deficiency profoundly alters the molecular signature and functional properties of mechanosensitive TH+ DRGN, representing an intriguing shift of the prevailing paradigm from proprioception to mechanical sensation.

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vitE deficiency alters gene expression in DRGs

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Mechanosensitive TH+ DRG neurons are most affected

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K⁺ and Ca²⁺ current densities are increased in vitE-deficient TH+ DRG neurons

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High-dose vitE supplementation prevents the molecular phenotype

UPLC-QTOF/MS-Based Metabolomics Reveals the Protective Mechanism of Hydrogen on Mice with Ischemic Stroke

As a reductive gas, hydrogen plays an antioxidant role by selectively scavenging oxygen free radicals. It has been reported that hydrogen has protective effects against nerve damage caused by ischemia-reperfusion in stroke, but the specific mechanism is still unclear. Therefore, this study aims to investigate the protective effects of hydrogen on stroke-induced ischemia-reperfusion injury and its detailed mechanism. Two weeks after the inhalation of high concentrations (66.7%) of hydrogen, middle cerebral artery occlusion (MCAO) was induced in mice using the thread occlusion technique to establish an animal model of the focal cerebral ischemia-reperfusion. Then, a metabolomics analysis of mouse cerebral cortex tissues was first performed by ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS) to study the metabolic changes and protective mechanisms of hydrogen on stroke ischemia-reperfusion injury. According to the metabolomic profiling of cortex tissues, 29 different endogenous metabolites were screened, including palmitoyl-L-carnitine, citric acid, glutathione, taurine, acetyl-L-carnitine, N-acetylaspartylglutamic acid (NAAG), L-aspartic acid, lysophosphatidylcholine (LysoPC) and lysophosphatidylethanolamine (LysoPE). Through pathway analysis, the metabolic pathways were concentrate on the glutathione pathway and the taurine pathway, mitochondrial energy metabolism and phospholipid metabolism that related to the oxidative stress process. This result reveals that hydrogen may protect against ischemic stroke by reducing oxidative stress during ischemia-reperfusion, thereby protecting nerve cells from reactive oxygen species(ROS).

Lipid-Mediated Modulation of Intracellular Ion Channels and Redox State: Physiopathological Implications

Significance: Ion channels play an important role in the regulation of organelle function within the cell, as proven by increasing evidence pointing to a link between altered function of intracellular ion channels and different pathologies ranging from cancer to neurodegenerative diseases, ischemic damage, and lysosomal storage diseases. Recent Advances: A link between these pathologies and redox state as well as lipid homeostasis and ion channel function is in the focus of current research. Critical Issues: Ion channels are target of modulation by lipids and lipid messengers, although in most cases the mechanistic details have not been clarified yet. Ion channel function importantly impacts production of reactive oxygen species (ROS), especially in the case of mitochondria and lysosomes. ROS, in turn, may modulate the function of intracellular channels triggering thereby a feedback control under physiological conditions. If produced in excess, ROS can be harmful to lipids and may produce oxidized forms of these membrane constituents that ultimately affect ion channel function by triggering a "circulus vitiosus." Future Directions: The present review summarizes our current knowledge about the contribution of intracellular channels to oxidative stress and gives examples of how these channels are modulated by lipids and how this modulation may affect ROS production in ROS-related diseases. Future studies need to address the importance of the regulation of intracellular ion channels and related oxidative stress by lipids in various physiological and pathological contexts. Antioxid. Redox Signal. 28, 949-972.

The influence of oxidative stress on symptom occurrence, severity, and distress during childhood leukemia treatment

PURPOSE/OBJECTIVES

To explore the symptom trajectory during the first 16 months of childhood leukemia treatment and any associations with the oxidative stress pathway measured by cerebrospinal fluid (CSF) concentration of oxidized phosphatidylcholine (PC), the predominant glycerophospholipid in the brain and cell membranes.

DESIGN

Prospective, longitudinal design.

SETTING

Two cancer centers in the southwestern United States.

SAMPLE

36 children (aged 3-14 years) newly diagnosed with acute lymphoblastic leukemia.

METHODS

Symptoms were measured using the Memorial Symptom Assessment Scale at six specific time points during treatment. Biochemical changes in oxidative stress were measured by oxidized PC in the CSF.

MAIN RESEARCH VARIABLES

Childhood cancer symptoms, oxidized PC.

FINDINGS

Significant differences were found in the number of symptoms experienced during the three phases of treatment. Symptom trajectory changes and influence of the oxidative stress pathway on symptom experiences were identified.

CONCLUSIONS

Symptoms experienced during treatment for childhood leukemia are associated with increased oxidative stress.

IMPLICATIONS FOR NURSING

Children with leukemia experience symptoms throughout treatment. Physiologic measures indicate the influence of oxidative stress on symptoms.

Lipid peroxidation is essential for phospholipase C activity and the inositol-trisphosphate-related Ca²⁺ signal

Reactive oxygen species (ROS) are produced in enzymatic and non-enzymatic reactions and have important roles in cell signalling but also detrimental effects. ROS-induced damage has been implicated in a number of neurological diseases; however, antioxidant therapies targeting brain diseases have been unsuccessful. Such failure might be related to inhibition of ROS-induced signalling in the brain. Using direct kinetic measures of lipid peroxidation in astrocytes and measurements of lipid peroxidation products in brain tissue, we here show that phospholipase C (PLC) preferentially cleaves oxidised lipids. Because of this, an increase in the rate of lipid peroxidation leads to increased Ca(2+) release from endoplasmic reticulum (ER) stores in response to physiological activation of purinoreceptors with ATP. Both vitamin E and its water-soluble analogue Trolox, potent ROS scavengers, were able to suppress PLC activity, therefore dampening intracellular Ca(2+) signalling. This implies that antioxidants can compromise intracellular Ca(2+) signalling through inhibition of PLC, and that PLC plays a dual role - signalling and antioxidant defence.

Phagocytic microglial phenotype induced by glibenclamide improves functional recovery but worsens hyperalgesia after spinal cord injury in adult rats

Microglial cell plays a crucial role in the development and establishment of chronic neuropathic pain after spinal cord injuries. As neuropathic pain is refractory to many treatments and some drugs only present partial efficacy, it is essential to study new targets and mechanisms to ameliorate pain signs. For this reason we have used glibenclamide (GB), a blocker of KATP channels that are over expressed in microglia under activation conditions. GB has already been used to trigger the early scavenger activity of microglia, so we administer it to promote a better removal of dead cells and myelin debris and support the microglia neuroprotective phenotype. Our results indicate that a single dose of GB (1 μg) injected after spinal cord injury is sufficient to promote long-lasting functional improvements in locomotion and coordination. Nevertheless, the Randall-Selitto test measurements indicate that these improvements are accompanied by enhanced mechanical hyperalgesia. In vitro results indicate that GB may influence microglial phagocytosis and therefore this action may be at the basis of the results obtained in vivo.

Effects of hydrogen peroxide on diazepam and xylazine sedation in chicks

Oxidative stress may cause various neuronal dysfunctions and modulate responses to many centrally acting drugs. This study examines the effects of oxidative stress produced by hydrogen peroxide (H₂O₂) on sedation induced by diazepam or xylazine as assessed in 7–14 day-old chicks. Day-old chicks were provided with either plane tap water (control group) or H₂O₂ in tap water as 0.5% v/v drinking solution for two weeks in order to produce oxidative stress. Spectrophotometric methods were used to determine glutathione and malondialdehyde concentrations in plasma and whole brain. Drug-induced sedation in the chicks was assessed by monitoring the occurrence of signs of sedation manifested as drooping of the head, closed eyelids, reduced motility or immotility, decreased distress calls, and recumbency. The latency to onset of sedation and its duration were also recorded. H₂O₂ treatment for two weeks significantly decreased glutathione and increased malondialdehyde concentrations in plasma and whole brain of the chicks on days 7, 10 and 14 as compared with respective age-matched control groups. H₂O₂ decreased the median effective doses of diazepam and xylazine for the induction of sedation in chicks by 46% and 63%, respectively. Injection of diazepam at 2.5, 5 and 10 mg/kg, i.m. or xylazine at 2, 4 and 8 mg/kg, i.m. induced sedation in both control and H₂O₂-treated chicks in a dose dependent manner, manifested by the above given signs of sedation. H₂O₂ significantly decreased the latency to onset of sedation in chicks treated with diazepam at 5 and 10 mg/kg, increased the duration of sedation and prolonged the total recovery time in comparison with respective non-stressed control chicks. A similar trend occurred with xylazine in the H₂O₂-treated chicks, though the differences from control counterparts did not attain the statistical significance, except for the recovery time of the lowest dose of the drug. The data suggest that H₂O₂-induced oxidative stress sensitizes the chicks to the depressant action of the sedatives diazepam and xylazine. Further studies are needed to examine the potential role of oxidative stress in modulating the actions of therapeutic agents on the brain.

Reactive oxygen species enhance TLR10 expression in the human monocytic cell line THP-1

We investigated TLR10 expression in human monocytes, THP-1 cells, cultured in hypoxia (3% O₂). Levels of both TLR10 mRNA and protein in THP-1 cells cultured in hypoxia were significantly higher than those cultured in normoxia (20% O₂). We examined intracellular reactive oxygen species (ROS) content in hypoxic cells, and TLR10 expression in cells treated with hydrogen peroxide (H₂O₂), to determine whether the increase in TLR10 expression observed with hypoxia was due to an increase in intracellular ROS levels. We found that the level of intracellular ROS in cells subject to hypoxia was significantly higher than in normoxia. Experiments with ROS synthesis inhibitors revealed that hypoxia induced ROS production is mainly due to NADPH oxidase activity. TLR10 mRNA expression was increased by treatment with H₂O₂ at concentrations ranging from 50 to 250 μM. We screened the TLR10 promoter and found putative binding sites for transcription factors (TFs), such as NF-κB, NF-AT and AP-1. Next, we examined TF activities using a luciferase reporter assay. Activities of NF-κB, NF-AT and AP-1 in the cells treated with H₂O₂ were significantly higher than in untreated cells. The experiment with TF inhibitors revealed that ROS-induced upregulation of TLR10 expression is mainly due to NF-κB activation. Overall, our results suggest that hypoxia or ROS increase TLR10 expression in human monocytes and the transcriptional activities of NF-κB are involved in this process. Therefore, it is suggested that ROS produced by various exogenous stimuli may play a crucial role in the regulation of expression and function of TLR10 as second messengers.

Crosstalk between calcium and redox signaling: from molecular mechanisms to health implications

Studies done many years ago established unequivocally the key role of calcium as a universal second messenger. In contrast, the second messenger roles of reactive oxygen and nitrogen species have emerged only recently. Therefore, their contributions to physiological cell signaling pathways have not yet become universally accepted, and many biological researchers still regard them only as cellular noxious agents. Furthermore, it is becoming increasingly apparent that there are significant interactions between calcium and redox species, and that these interactions modify a variety of proteins that participate in signaling transduction pathways and in other fundamental cellular functions that determine cell life or death. This review article addresses first the central aspects of calcium and redox signaling pathways in animal cells, and continues with the molecular mechanisms that underlie crosstalk between calcium and redox signals under a number of physiological or pathological conditions. To conclude, the review focuses on conditions that, by promoting cellular oxidative stress, lead to the generation of abnormal calcium signals, and how this calcium imbalance may cause a variety of human diseases including, in particular, degenerative diseases of the central nervous system and cardiac pathologies.

Oxidative stress in the spinal cord is an important contributor in capsaicin-induced mechanical secondary hyperalgesia in mice

Recent studies indicate that reactive oxygen species (ROS) are critically involved in persistent pain primarily through spinal mechanisms, thus suggesting ROS involvement in central sensitization. To investigate ROS involvement in central sensitization, the effects of ROS scavengers and donors on pain behaviors were examined in mice. Capsaicin- induced hyperalgesia was used as a pain model since it has 2 distinctive pain components, primary and secondary hyperalgesia representing peripheral and central sensitization, respectively. Capsaicin (25 microg/5 microl) was injected intradermally into the left hind foot. Foot withdrawal frequencies in response to von Frey filament stimuli were measured and used as an indicator of mechanical hyperalgesia. The production of ROS was examined by using a ROS sensitive dye, MitoSox. Mice developed primary and secondary mechanical hyperalgesia after capsaicin injection. A systemic or intrathecal post-treatment with either phenyl-N-tert-butylnitrone (PBN) or 4-hydroxy-2,2,6,6-tetramethylpiperidine-1 oxyl (TEMPOL), ROS scavengers, significantly reduced secondary hyperalgesia, but not primary hyperalgesia, in a dose-dependent manner. Pretreatment with ROS scavengers also significantly reduced the magnitude and duration of capsaicin-induced secondary hyperalgesia. On the other hand, intrathecal injection of tert-butylhydroperoxide (t-BOOH, 5 microl), a ROS donor, produced a transient hyperalgesia in a dose-dependent manner. The number of MitoSox positive dorsal horn neurons was increased significantly after capsaicin treatment. This study suggests that ROS mediates the development and maintenance of capsaicin-induced hyperalgesia in mice, mainly through central sensitization and that the elevation of spinal ROS is most likely due to increased production of mitochondrial superoxides in the dorsal horn neurons.

Conversion of phylloquinone (Vitamin K1) into menaquinone-4 (Vitamin K2) in mice: two possible routes for menaquinone-4 accumulation in cerebra of mice

There are two forms of naturally occurring vitamin K, phylloquinone and the menaquinones. Phylloquinone (vitamin K(1)) is a major type (>90%) of dietary vitamin K, but its concentrations in animal tissues are remarkably low compared with those of the menaquinones, especially menaquinone-4 (vitamin K(2)), the major form (>90%) of vitamin K in tissues. Despite this great difference, the origin of tissue menaquinone-4 has yet to be exclusively defined. It is postulated that phylloquinone is converted into menaquinone-4 and accumulates in extrahepatic tissues. To clarify this, phylloquinone with a deuterium-labeled 2-methyl-1,4-naphthoquinone ring was given orally to mice, and cerebra were collected for D NMR and liquid chromatography-tandem mass spectrometry analyses. We identified the labeled menaquinone-4 that was converted from the given phylloquinone, and this conversion occurred following an oral or enteral administration, but not parenteral or intracerebroventricular administration. By the oral route, the phylloquinone with the deuterium-labeled side chain in addition to the labeled 2-methyl-1,4-naphthoquinone was clearly converted into a labeled menaquinone-4 with a non-deuterium-labeled side chain, implying that phylloquinone was converted into menaquinone-4 via integral side-chain removal. The conversion also occurred in cerebral slice cultures and primary cultures. Deuterium-labeled menadione was consistently converted into the labeled menaquinone-4 with all of the administration routes and the culture conditions tested. Our results suggest that cerebral menaquinone-4 originates from phylloquinone intake and that there are two routes of accumulation, one is the release of menadione from phylloquinone in the intestine followed by the prenylation of menadione into menaquinone-4 in tissues, and another is cleavage and prenylation within the cerebrum.

Effect of Oxidative Stress on Glial Cell Volume

Cytotoxic brain edema is a major contributor of tissue damage following cerebral ischemia and traumatic brain injury. The pathophysiology of cytotoxic edema formation is still not well understood. Although it is widely believed that oxidative stress causes cytotoxic brain edema, experimental proof is lacking. The aim of the present study was therefore to examine the effect of oxidative stress on cell volume of glial cells. C6 glial cells were exposed to hydrogen peroxide and the superoxide forming complex hypoxanthine/xanthine oxidase (HX/XO). Exposure to hydrogen peroxide (0.5-5 mM) resulted in initial cell shrinkage by 5.7 +/- 1.5% (mean +/- SEM; p < 0.05) and was followed by a dose-dependent recovery to baseline. Exposure to superoxide anions generated by HX/XO provoked a delayed, but sustained decrease of cell volume by 11.8 +/- 0.9% (p < 0.05). Cell volume showed no tendency to recover upon sustained exposure to superoxide. Neither hydrogen peroxide nor HX/XO exposure was associated with a decrease of cell viability. Thereby, the present study demonstrates that oxidative stress by hydrogen peroxide and superoxide anions does not induce cytotoxic cell swelling and suggests that free radicals are not directly involved in the formation of cytotoxic brain edema.

Reactive oxygen species cerebral autoregulation in health and disease

Reactive oxygen species (ROS) are a family of oxygen-derived free radicals that are produced in mammalian cells under normal and pathologic conditions. Many ROS, such as the superoxide anion (O2-) and hydrogen peroxide (H2O2), act as cellular signaling molecules within blood vessels, altering mechanisms mediating mechanical signal transduction and autoregulation of cerebral blood flow. This article focuses on the actions of ROS, such as O2.- and H2O2, and how they influence mechanisms responsible for the modulation of pressure-induced myogenic tone in the cerebral circulation and blood flow autoregulation in response to elevated arterial pressure. ROS may be a key target for therapeutic interventions in pediatric patients who have hypoxic injury or altered cerebral metabolism induced by trauma or infection.

SNAP25 is a pre-synaptic target for the depressant action of reactive oxygen species on transmitter release

Reactive oxygen species (ROS) participate in various physiological and pathological processes in the nervous system, but the specific pathways that mediate ROS signalling remain largely unknown. Using electrophysiological techniques and biochemical evaluation of isolated fusion proteins, we explored the sensitivity to standard oxidative stress of the entire synapse, the pre-synaptic machinery and essential fusion proteins underlying transmitter exocytosis. Oxidative stress induced by H(2)O(2) plus Fe(2+) inhibited both evoked and spontaneous quantal release from frog or mouse motor nerve endings, while it left post-synaptic sensitivity unchanged. The depressant effect of H(2)O(2) on acetylcholine release was pertussis toxin-insensitive, ruling out G-protein cascades. Experiments with ionomycin, a Ca(2+) ionophore, revealed that ROS directly impaired the function of releasing machinery. In line with this, SNAP25, one of three essential fusion proteins, showed a selectively high sensitivity to the oxidative signals. Several ROS scavengers enhanced evoked synaptic transmission, consistent with tonic inhibition by endogenous ROS. Our data suggest that ROS-induced impairment of releasing machinery is mediated by SNAP25, which appears to be a pre-synaptic ROS sensor. This mechanism of ROS signalling could have widespread implications in the nervous system and might contribute to the pathogenesis of neurodegenerative diseases.

Critical role of phospholipase Cgamma1 in the generation of H2O2-evoked [Ca2+]i oscillations in cultured rat cortical astrocytes

Reactive oxygen species, such as the superoxide anion, H2O2, and the hydroxyl radical, have been considered as cytotoxic by-products of cellular metabolism. However, recent studies have provided evidence that H2O2 serves as a signaling molecule modulating various physiological functions. Here we investigated the effect of H2O2 on the regulation of intracellular Ca2+ signaling in rat cortical astrocytes. H2O2 triggered the generation of oscillations of intracellular Ca2+ concentration ([Ca2+]i) in a concentration-dependent manner over the range 10-100 microM. The H2O2-induced [Ca2+]i oscillations persisted in the absence of extracellular Ca2+ and were prevented by depletion of intracellular Ca2+ stores with thapsigargin. The H2O2-induced [Ca2+]i oscillations were not inhibited by pretreatment with ryanodine but were prevented by 2-aminoethoxydiphenyl borate and caffeine, known antagonists of inositol 1,4,5-trisphosphate receptors. H2O2 activated phospholipase C (PLC) gamma1 in a dose-dependent manner, and U73122, an inhibitor of PLC, completely abolished the H2O2-induced [Ca2+]i oscillations. In addition, RNA interference against PLCgamma1 and the expression of the inositol 1,4,5-trisphosphate-sequestering "sponge" prevented the generation of [Ca2+]i oscillations. H2O2-induced [Ca2+]i oscillations and PLC1 phosphorylation were inhibited by pretreatment with dithiothreitol, a sulfhydryl-reducing agent. Finally, epidermal growth factor induced H2O2 production, PLCgamma1 activation, and [Ca2+]i increases, which were attenuated by N-acetylcysteine and diphenyleneiodonium and by the overexpression of peroxiredoxin type II. Therefore, we conclude that low concentrations of exogenously applied H2O2 generate [Ca2+]i oscillations by activating PLCgamma1 through sulfhydryl oxidation-dependent mechanisms. Furthermore, we show that this mechanism underlies the modulatory effect of endogenously produced H2O2 on epidermal growth factor-induced Ca2+ signaling in rat cortical astrocytes.

Peroxiredoxin II functions as a signal terminator for H2O2-activated phospholipase D1

Phospholipase D1 (PLD1) is a signal-transduction regulated enzyme which regulates several cell intrinsic processes including activation of NAPDH oxidase, which elevates intracellular H2O2. Several proteins have been reported to interact with PLD1 in resting cells. We sought to identify proteins that interact with PLD1 after phorbol 12-myristate 13-acetate (PMA) stimulation. A novel interaction with peroxiredoxin II (PrxII), an enzyme that eliminates cellular H2O2, which is a known stimulator of PLD1, was identified by PLD1-affinity pull-down and MS. PMA stimulation was confirmed to promote physical interaction between PLD1 and PrxII and to cause PLD1 and PrxII to colocalize subcellularly. Functional significance of the interaction was suggested by the observation that over-expression of PrxII specifically reduces the response of PLD1 to stimulation by H2O2. These results indicate that PrxII may have a signal-terminating role for PLD1 by being recruited to sites containing activated PLD1 after cellular stimulation involving production of H2O2.

Functions and pathophysiological roles of phospholipase D in the brain

Ten years after the isoforms of mammalian phospholipase D (PLD), PLD1 and 2, were cloned, their roles in the brain remain speculative but several lines of evidence now implicate these enzymes in basic cell functions such as vesicular trafficking as well as in brain development. Many mitogenic factors, including neurotransmitters and growth factors, activate PLD in neurons and astrocytes. Activation of PLD downstream of protein kinase C seems to be a required step for astroglial proliferation. The characteristic disruption of the PLD signaling pathway by ethanol probably contributes to the delay of brain growth in fetal alcohol syndrome. The post-natal increase of PLD activities concurs with synapto- and myelinogenesis in the brain and PLD is apparently involved in neurite formation. In the adult and aging brain, PLD activity has antiapoptotic properties suppressing ceramide formation. Increased PLD activities in acute and chronic neurodegeneration as well as in inflammatory processes are evidently due to astrogliosis and may be associated with protective responses of tissue repair and remodeling. ARF-regulated PLD participates in receptor endocytosis as well as in exocytosis of neurotransmitters where PLD seems to favor vesicle fusion by modifications of the shape and charge of lipid membranes. Finally, PLD activities contribute free choline for the synthesis of acetylcholine in the brain. Novel tools such as RNA interference should help to further elucidate the roles of PLD isoforms in brain physiology and pathology.

Glutamate-mediated influx of extracellular Ca2+ is coupled with reactive oxygen species generation in cultured hippocampal neurons but not in astrocytes

Generation of reactive oxygen species (ROS) in brain tissue leads to neurodegeneration. The major source of ROS is the mitochondrial respiratory chain. We studied regulation of Ca2+ level, mitochondrial potential, and ROS generation in defined mixed hippocampal cell cultures exposed to glutamate (100 microM). Recordings were made from individually identified astrocytes and neurons to compare the physiologic responses in both cell types. Neurons identified by synaptotagmin immunoreactivity were characterized functionally by the fast Ca2+ increase with K+ (50 mM) stimulation, and the astrocytes identified by glial fibrillary acidic protein (GFAP) staining had the functional characteristic of a transient Ca2+ peak in response to ATP (10 microM) stimulation. We found that the glutamate-mediated Ca2+ response in neurons is due largely to influx of extracellular Ca2+. This is consistent with our finding that in cultured hippocampal neurons, stores depending on the activity of the sarcoendoplasmic reticulum Ca2+ ATPase (SERCA) pump had a low Ca2+ content, regardless of whether the neurons were challenged or not with K+ before applying the SERCA inhibitor cyclopiazonic acid (CPA). Astrocytes displayed a large CPA-mediated Ca2 response, indicating a high level of Ca2+ load in the stores in astrocytes. Importantly, the rise in ROS generation due to glutamate application was cell-type specific. In neurons, glutamate induced a marked rise in generation of ROS, but not in astrocytes. In both astrocytes and neurons, the mitochondrial potential was increased in response to glutamate challenge. We conclude that in neurons, Ca2+ influx accounts for the increased ROS generation in response to glutamate. This might explain the high vulnerability of neurons to glutamate challenge compared to the vulnerability of astrocytes. The high resistance of astrocytes is accompanied by an efficient downregulation of cytosolic Ca2+, which is not found in neurons.

Reactive oxygen species contribute to the presynaptic action of extracellular ATP at the frog neuromuscular junction

During normal cell metabolism the production of intracellular ATP is associated with the generation of reactive oxygen species (ROS), which appear to be important signalling molecules. Both ATP and ROS can be released extracellularly by skeletal muscle during intense activity. Using voltage clamp recording combined with imaging and biochemical assay of ROS, we tested the hypothesis that at the neuromuscular junction extracellular ATP generates ROS to inhibit transmitter release from motor nerve endings. We found that ATP produced the presynaptic inhibitory action on multiquantal end-plate currents. The inhibitory action of ATP (but not that of adenosine) was significantly reduced by several antioxidants or extracellular catalase, which breaks down H2O2. Consistent with these data, the depressant effect of ATP was dramatically potentiated by the pro-oxidant Fe2+. Exogenous H2O2 reproduced the depressant effects of ATP and showed similar sensitivity to anti- and pro-oxidants. While NO also inhibited synaptic transmission, inhibitors of the NO-producing cascade did not prevent the depressant action of ATP. The ferrous oxidation in xylenol orange assay showed the increase of ROS production by ATP and 2-MeSADP but not by adenosine. Suramin, a non-selective antagonist of P2 receptors, and pertussis toxin prevented the action of ATP on ROS production. Likewise, imaging with the ROS-sensitive dye carboxy-2',7'-dichlorodihydrofluorescein revealed increased production of ROS in the muscle treated with ATP or ADP while UTP or adenosine had no effect. Thus, generation of ROS contributed to the ATP-mediated negative feedback mechanism controlling quantal secretion of ACh from the motor nerve endings.

Cytoprotection against oxidative stress-induced damage of astrocytes by extracellular ATP via P2Y1 receptors

Oxidative stress is the main cause of neuronal damage in traumatic brain injury, hypoxia/reperfusion injury, and neurodegenerative disorders. Although extracellular nucleosides, especially adenosine, are well known to protect against neuronal damage in such pathological conditions, the effects of these nucleosides or nucleotides on glial cell damage remain largely unknown. We report that ATP but not adenosine protects against the cell death of cultured astrocytes induced by hydrogen peroxide (H2O2). ATP ameliorated the H2O2-induced decrease in cell viability of astrocytes in an incubation time- and concentration-dependent fashion. Protection by ATP was inhibited by P2 receptor antagonists and was mimicked by P2Y1 receptor agonists but not by adenosine. The expressions of P2Y1 mRNAs and functional P2Y1 receptors in astrocytes were confirmed. Thus, ATP, acting on P2Y1 receptors in astrocytes, showed a protective action against H2O2. The astrocytic protection by the P2Y1 receptor agonist 2-methylthio-ADP was inhibited by an intracellular Ca2+ chelator and a blocker of phospholipase C, indicating the involvement of intracellular signals mediated by Gq/11-coupled P2Y1 receptors. The ATP-induced protection was inhibited by cycloheximide, a protein synthesis inhibitor, and it took more than 12 h for the onset of the protective action. In the DNA microarray analysis, ATP induced a dramatic upregulation of various oxidoreductase genes. Taken together, ATP acts on P2Y1 receptors coupled to Gq/11, resulting in the upregulation of oxidoreductase genes, leading to the protection of astrocytes against H2O2.

Expression and localization of diacylglycerol kinase isozymes and enzymatic features in rat lung

Diacylglycerol kinase (DGK) catalyzes phosphorylation of diacylglycerol to generate phosphatidic acid, and both molecules are known to serve as second messengers as well as important intermediates for the synthesis of various lipids. In this study, we investigated the spatiotemporal expression patterns of DGK isozymes together with the developmental changes of the mRNA expression and enzymatic property in rat lung. Northern blot and RT-PCR analyses showed that mRNAs for DGKalpha, -epsilon, and -zeta were detected in the lung. By immunohistochemical examination, DGKalpha and -zeta were shown to be coexpressed in alveolar type II cells and macrophages. Interestingly, these isozymes were localized at distinct subcellular locations, i.e., DGKalpha in the cytoplasm and DGKzeta in the nucleus, suggesting different roles for these isozymes. In the developing lung, the expression for DGKalpha and -zeta was transiently elevated on embryonic day 21 (E21) to levels approximately two- to threefold higher than on postnatal day 0 (P0). On the other hand, the expression for DGKepsilon was inversely elevated approximately twofold on P0 compared with that on E21. These unique changes in the expression pattern during the perinatal period suggest that each isozyme may play a distinct role in the adaptation of the lung to air or oxygen breathing at birth.

Increased expression of phospholipase D1 in the brains of scrapie-infected mice

Mitochondrial dysfunction and free radical-induced oxidative damage are critical factors in the pathogenesis of neurodegenerative diseases. Recently, phospholipid breakdown by phospholipase D (PLD) has been recognized as an important signalling pathway in the nervous system. Here, we examined the expression of PLD and alteration of membrane phospholipid in scrapie brain. We have found that protein expression and enzyme activity of PLD1 were increased in scrapie brains compared with controls; in particular, there was an increase in the mitochondrial fraction. PLD1 in mitochondrial membranes from scrapie brains, but not from control brains, was tyrosine phosphorylated. Furthermore, the concentration of mitochondrial phospholipids such as phosphatidylcholine and phosphatidylethanolamine was increased and the content of phosphatidic acid, a product of PLD activity, was up-regulated in the mitochondrial membrane fractions. Immunohistochemically, PLD1 immunoreactivity was significantly increased in activated astrocytes in both cerebral cortex and hippocampus of scrapie brains. Taken together, these results suggest that PLD activation might induce alterations in mitochondrial lipids and, in turn, mediate mitochondrial dysfunction in the brains of scrapie-infected mice.

Phospholipase C is involved in the adenosine-activated signal transduction pathway conferring protection against iodoacetic acid-induced injury in primary rat neuronal cultures

We have demonstrated before that exposure of neuronal cultures to poisoning by iodoacetic acid, followed by "reperfusion" (iodoacetate-"reperfusion" insult; IAA-R insult), results in severe cytotoxicity. This insult was found to be associated with ATP depletion and generation of reactive oxygen species. The cultured neurons could be protected against the insult by activation of the adenosine A1 receptors and by presence of antioxidants. Previous studies in our laboratory demonstrated that the adenosine-activated signal transduction pathway (Ado-STP) conferring protection against the IAA-R insult, involves activation of protein kinase C-epsilon (PKCepsilon) and opening of ATP sensitive potassium (K(ATP)) channels. In this respect, the adenosine-activated protective mechanism against the IAA-R insult is similar to the Ado-STP in the neurons and in cardiomyocytes against ischemia-reperfusion injury. Phospholipase C (PLC) is an additional component demonstrated recently to participate in the myocardial Ado-STP protecting against ischemia-reperfusion. Here we provide proof for the involvement of PLC also in the neuronal Ado-STP protecting against the IAA-R insult. Primary rat neuronal cultures were exposed to the IAA-R insult. The neurons could be protected against this insult by activation of the adenosine A1 receptors by N6-(R)-phenylisopropyladenosine (R-PIA), a specific A1 adenosine receptor agonist. Exposure of the cultures to the PLC inhibitor U73122, abrogated the protection. The exposure of the cultures to R-PIA was found to enhance PLC activity, an effect that could be abrogated by presence of U73122. The R-PIA-induced increase in PLC activity was short-lived, in the range of minutes. These results demonstrate that activation of PLC is a vital step in the neuronal protective Ado-STP, but that it does not contribute directly to the relatively long time window of the protection signal shown previously to characterize the neuronal mechanism. The results also support the suggestion that the Ado-STP protecting against the IAA-R insult and that protecting against ischemia-reperfusion may represent the same mechanism.

Phospholipase A2 in the central nervous system

Phospholipase A2 (PLA2) belongs to a family of enzymes that catalyze the cleavage of fatty acids from the sn-2 position of phospholipids. There are more than 19 different isoforms of PLA2 in the mammalian system, but recent studies have focused on three major groups, namely, the group IV cytosolic PLA2, the group II secretory PLA2 (sPLA2), and the group VI Ca(2+)-independent PLA2. These PLA2s are involved in a complex network of signaling pathways that link receptor agonists, oxidative agents, and proinflammatory cytokines to the release of arachidonic acid (AA) and the synthesis of eicosanoids. PLA2s acting on membrane phospholipids have been implicated in intracellular membrane trafficking, differentiation, proliferation, and apoptotic processes. All major groups of PLA2 are present in the central nervous system (CNS). Therefore, this review is focused on PLA2 and AA release in neural cells, especially in astrocytes and neurons. In addition, because many neurodegenerative diseases are associated with increased oxidative and inflammatory responses, an attempt was made to include studies on PLA2 in cerebral ischemia, Alzheimer's disease, and neuronal injury due to excitotoxic agents. Information from these studies has provided clear evidence for the important role of PLA2 in regulating physiological and pathological functions in the CNS.

Copper-induced oxidative damage on astrocytes: protective effect exerted by human high density lipoproteins

In the present study, we confirmed that copper ions induce oxidative damage in human astrocytes in culture, as demonstrated by the significant increase in the levels of hydroperoxides and in the fluorescence intensity of the fluorescent probe dichloro-dihydrofluorescein diacetate (H(2)DCFDA). The compositional changes were associated with a significant decrease in cell viability in astrocytes treated with 10 microM Cu(++) with respect to control cells. Astrocytes incubated with copper ions in the presence of high density lipoproteins (HDL) isolated from plasma of normolipemic subjects showed lower levels of hydroperoxides and a higher cell viability with respect to cells oxidized alone. Moreover, a significant decrease in the levels of hydroperoxides was observed in oxidized astrocytes treated with HDL. These results demonstrate that HDL exert a protective role against lipid peroxidation. The protective effect could be related to the ability of HDL to bind metal ions at the lipoprotein surface and/or to a stimulation of the efflux of lipid hydroperoxides from cell membranes as demonstrated in other cell types. Oxidative damage of astrocytes was induced at a copper concentration similar to that observed in cerebrospinal fluid (CSF) of patients affected by neurodegenerative diseases such as Alzheimer's (AD) and Parkinson's diseases (PD). Lipoprotein particles similar for density and chemical composition to plasma HDL were recently isolated in human CSF, therefore, the protective role exerted by HDL against Cu(++)-induced oxidative damage of astrocytes could be of physiological relevance.

Dual action of hydrogen peroxide on synaptic transmission at the frog neuromuscular junction

There is evidence that reactive oxygen species (ROS) are produced and released during neuromuscular activity, but their role in synaptic transmission is not known. Using a two-electrode voltage-clamp technique, at frog neuromuscular junctions, the action H2O2 on end-plate currents (EPC) was studied to determine the targets for this membrane-permeable ROS. In curarized or cut muscles, micromolar concentrations of H2O2 increased the amplitude of EPCs. Higher (> 30 microM) doses inhibited EPCs and prolonged current decay. These effects were presynaptic since H2O2 did not change the amplitude or duration of miniature EPCs (although it reduced the rate of spontaneous release at high concentrations). Quantal analysis and deconvolution methods showed that facilitation of EPCs was due to increased quantal release, while depression was accompanied by temporal dispersion of evoked release. Extracellular recordings revealed prolonged presynaptic Ca2+ entry in the presence of high H2O2. Both low and high H2O2 increased presynaptic potentiation during high-frequency stimulation. Pro-oxidant Fe2+ did not affect facilitation by low doses of H2O2 but augmented the inhibition of EPCs by high H2O2, indicating involvement of hydroxyl radicals. High Mg2+ and the ROS scavenger N-acetylcysteine eliminated both the facilitatory and depressant effects of H2O2. The facilitatory effect of H2O2 was prevented by protein kinase C (PKC) inhibitors and 4beta-phorbol 12-myristate, 13-acetate (PMA), an activator of PKC. PKC inhibitors but not PMA also abolished the depressant effect of H2O2. Our data suggest complex presynaptic actions of H2O2, which could serve as a fast feedback modulator of intense neuromuscular transmission.

Opposed effects of lithium on the MEK-ERK pathway in neural cells: inhibition in astrocytes and stimulation in neurons by GSK3 independent mechanisms

Lithium is widely used in the treatment of bipolar disorder, but despite its proven therapeutic efficacy, the molecular mechanisms of action are not fully understood. The present study was undertaken to explore lithium effects of the MEK/ERK cascade of protein kinases in astrocytes and neurons. In asynchronously proliferating rat cortical astrocytes, lithium decreased time- and dose-dependently the phosphorylation of MEK and ERK, with 1 mM concentrations achieving 60 and 50% inhibition of ERK and MEK, respectively, after a 7-day exposure. Lithium also inhibited [3H]thymidine incorporation into DNA and induced a G2/M cell cycle arrest. In serum-deprived, quiescent astrocytes, pre-exposure to lithium resulted in the inhibition of cell cycle re-entry as stimulated by the mitogen endothelin-1: under this experimental setting, lithium did not affect the rapid, peak phosphorylation of MEK taking place after 3-5 min, but was effective in inhibiting the long-term, sustained phosphorylation of MEK. Lithium inhibition of the astrocyte MEK/ERK pathway was independent of inositol depletion. Further, compound SB216763 inhibited Tau phosphorylation at Ser396 and stabilized cytosolic beta-catenin, consistent with the inhibition of glycogen synthase kinase-3 beta (GSK-3 beta), but failed to reproduce lithium effects on MEK and ERK phosphorylation and cell cycle arrest. In cerebellar granule neurons, millimolar concentrations of lithium enhanced MEK and ERK phosphorylation in a concentration-dependent manner, again through an inositol and GSK-3 beta independent mechanism. These opposing effects in astrocytes and neurons make lithium treatment a promising strategy to favour neural repair and reduce reactive gliosis after traumatic injury.

Oxidant-mediated AA release from astrocytes involves cPLA(2) and iPLA(2)

Excessive generation of reactive oxygen species (ROS) in the central nervous system (CNS) is a leading cause of neuronal injury. Despite yet unknown mechanisms, oxidant compounds such as H(2)O(2) have been shown to stimulate the release of arachidonic acid (AA) in a number of cell systems. In this study, H(2)O(2) and menadione, a compound known to release H(2)O(2) intracellularly, were used to examine the phospholipases A(2) (PLA(2)) responsible for AA release from primary murine astrocytes. Both H(2)O(2) and menadione dose-dependently stimulated AA release, and the release mediated by H(2)O(2) was completely inhibited by catalase. H(2)O(2) also stimulated phosphorylation of extracellular signal-regulated kinases (ERK1/2) and cytosolic phospholipase A(2) (cPLA(2)). However, complete inhibition of cPLA(2) phosphorylation by U0126, an inhibitor for mitogen-activated protein kinase kinase (MEK) and GF109203x, a nonselective PKC inhibitor preferring the conventional and novel isoforms, only reduced H(2)O(2)-stimulated AA release by 50%. MAFP, a selective, active, site-directed, irreversible inhibitor of both cPLA(2) and the Ca(2+)-independent iPLA(2), nearly completely inhibited H(2)O(2)-mediated AA release; but, HELSS, a potent irreversible inhibitor of iPLA(2), only inhibited H(2)O(2)-mediated AA release by 40%. Along with the observation that H(2)O(2)-mediated AA release was only partially inhibited upon chelating intracellular Ca(2+) by BAPTA, these results indicate the involvement of both cPLA(2) and iPLA(2) in H(2)O(2)-mediated AA release in murine astrocytes.

Cytoprotection of pyruvic acid and reduced beta-nicotinamide adenine dinucleotide against hydrogen peroxide toxicity in neuroblastoma cells

Elevated production of hydrogen peroxide (H2O2) in the central nervous system has been implicated in the pathogenesis of several neurodegenerative diseases, including Parkinson's disease, ischemic reperfusion, stroke, and Alzheimer's disease. Pyruvic acid has a critical role in energy metabolism and a capability to nonenzymatically decarboxylate H2O2 into H2O. This study examined the effects of glycolytic regulation of pyruvic acid on H2O2 toxicity in murine neuroblastoma cells. Glycolytic energy substrates including D-(+)-glucose, D-(-) fructose and the adenosine transport blocker dipyridamole, were not effective in providing protection against H2O2 toxicity, negating energy as a factor. On the other hand, pyruvic acid completely prevented H2O2 toxicity, restoring the loss of ATP and cell viability. H2O2 toxicity was also attenuated by D-fructose 1,6 diphosphate (FBP), phospho (enol) pyruvate (PEP), niacinamide, beta-nicotinamide adenine dinucleotide (beta-NAD+), and reduced form (beta-NADH). Both FBP and PEP exerted positive kinetic effects on pyruvate kinase (PK) activity. Interestingly, only pyruvic acid and beta-NADH exhibited powerful stoichiometric H2O2 antioxidant properties. Further, beta-NADH may exert positive effects on PK activity. Subsequent pyruvic acid accumulation can lead to the recycling of beta-NAD+ through lactate dehydrogenase and beta-NADH through glyceraldehyde-3-phosphate dehydrogenase. It was concluded from these studies that intracellular pyruvic acid and beta-NADH appear to act in concert through glycolysis, to enhance H2O2 intracellular antioxidant capacity in neuroblastoma cells. Future research will be required to examine whether similar effects are observed in primary neuronal culture or intact tissue.

How does glucose generate oxidative stress in peripheral nerve?

Diabetes-associated oxidative stress is clearly manifest in peripheral nerve, dorsal root, and sympathetic ganglia of the peripheral nervous system and endothelial cells and is implicated in nerve blood flow and conduction deficits, impaired neurotrophic support, changes in signal transduction and metabolism, and morphological abnormalities characteristic of peripheral diabetic neuropathy (diabetic peripheral neuropathy). Hyperglycemia has a key role in oxidative stress in diabetic nerve, whereas the contribution of other factors, such as endoneurial hypoxia, transition metal imbalance, and hyperlipidemia, has not been rigorously proven. It has been suggested that oxidative stress, particularly mitochondrial superoxide production, is responsible for sorbitol pathway hyperactivity, nonenzymatic glycation/glycooxidation, and activation of protein kinase C. However, this concept is not supported by in vivo studies demonstrating the lack of any inhibition of the sorbitol pathway activity in peripheral nerve, retina, and lens by antioxidants, including potent superoxide scavengers. Its has been also hypothesized that aldose reductase (AR) detoxifies lipid peroxidation products, and therefore, the enzyme inhibition in diabetes is detrimental rather than benefical. However, the role for AR in lipid peroxdation product metabolism has never been demonstrated in vivo, and the effects of aldose reductase inhibitors and antioxidants on diabetic peripheral neuropathy are unidirectional, i.e., both classes of agents prevent and correct functional, metabolic, neurotrophic, and morphological changes in diabetic nerve. Growing evidence indicates that AR has a key role in oxidative stress in the peripheral nerve and contributes to superoxide production by the vascular endothelium. The potential mechanisms of this phenonmenon are discussed.

ROS and NO trigger early preconditioning: relationship to mitochondrial KATP channel

Reactive oxygen species (ROS) and nitric oxide (NO) are implicated in induction of ischemic preconditioning. However, the relationship between these oxidant signals and opening of the mitochondrial ATP-dependent potassium (K(ATP)) channel during early preconditioning is not fully understood. We observed preconditioning protection by hypoxia, exogenous H(2)O(2), or PKC activator PMA in cardiomyocytes subjected to 1-h ischemia and 3-h reperfusion. Protection was abolished by K(ATP) channel blocker 5-hydroxydecanoate (5-HD) in each case, indicating that these triggers must act upstream from the K(ATP) channel. Inhibitors of NO synthase abolished protection in preconditioned cells, suggesting that NO is also required for protection. DAF-2 fluorescence (NO sensitive) increased during hypoxic triggering. This was amplified by pinacidil and inhibited by 5-HD, indicating that NO is generated subsequent to K(ATP) channel activation. Exogenous NO during the triggering phase conferred protection blocked by 5-HD. Exogenous NO also restored protection abolished by 5-HD or N(omega)-nitro-l-arginine methyl ester in preconditioned cells. Antioxidants given during pinacidil or NO triggering abolished protection, confirming that ROS are generated by K(ATP) channel activation. Coadministration of H(2)O(2) and NO restored PMA-induced protection in 5-HD-treated cells, indicating that ROS and NO are required downstream from the K(ATP) channel. We conclude that ROS can trigger preconditioning by causing activation of the K(ATP) channel, which then induces generation of ROS and NO that are both required for preconditioning protection.

PARP expression is increased in astrocytes but decreased in motor neurons in the spinal cord of sporadic ALS patients

The evidence for increased oxidative stress and DNA damage in amyotrophic lateral sclerosis (ALS) prompted studies to determine if the expression of poly(ADP-ribose) polymerase (PARP) is increased in ALS. Using Western analyses of postmortem tissue, we demonstrated that PARP-immunoreactivity (PARP-IR) was increased 3-fold in spinal cord tissues of sporadic ALS (sALS) patients compared with non-neurological disease controls. Despite the increased PARP-IR, PARP mRNA expression was not increased significantly. Immunohistochemical analyses revealed PARP-IR was increased in both white and gray matter of sALS spinal cord. While PARP-IR was predominantly seen in astrocytes, large motor neurons displayed reduced staining compared with controls. This result contrasts sharply to the staining of Alzheimer and MPTP-induced Parkinson diseased tissue, where poly(ADP-ribose) (PAR)-IR was seen mostly in neurons, with little astrocytic staining. PARP-IR was increased in the pellet fraction of sALS homogenates compared with control homogenates, representing potential PARP binding to chromatin or membranes and suggesting a possible mechanism of PARP stabilization. The present results demonstrate glial alterations in sALS spinal cord tissue and support the role of glial alterations in sALS pathogenesis. Additionally, these results demonstrate differences in sALS spinal motor neurons and astrocytes compared to brain neurons and astrocytes in Alzheimer disease and MPTP-induced Parkinson disease despite the presence of markers for oxidative stress in all 3 diseases.

Role of Ca(2+) on TNF-alpha and IL-6 secretion from RBL-2H3 mast cells

Ca2+ acts as an important second messenger in mast cells. However, the mechanisms involved in the secretion of inflammatory cytokines from activated mast cells are unknown. In this study, we examined the signaling pathway involved in calcium-related cytokine secretion in a mast cell line, RBL-2H3 cells. We report that treatment with 1,2-bis (2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM), a chelator of intracellular calcium, can inhibit IgE-stimulated TNF-alpha and IL-6 secretion in a concentration-dependent manner with IC50 values of 0.41 and 0.014 microM, respectively. Maximal inhibition of TNFalpha- and IL-6 secretion was 58.5 +/- 3% and 87 +/- 8% in BAPTA-AM, respectively. BAPTA-AM also completely inhibited the IgE-induced TNF-alpha and IL-6 mRNA levels. In activated RBL-2H3 cells, the expression level of NF-kappaB/Rel A protein increased in the nucleus. However, the level of NF-kappaB/Rel A in nucleus was decreased by treatment of BAPTA-AM. In addition, BAPTA-AM completely inhibited the IgE-induced IkappaB kinase beta (IKKbeta) activation and IkappaBalpha phosphorylation. These observations demonstrate that the intracellular Ca2+ may play an important role in IgE-induced TNF-alpha and IL-6 secretion from mast cells via IKKbeta activation.

Taurine counteracts oxidative stress and nerve growth factor deficit in early experimental diabetic neuropathy

Oxidative stress has a key role in the pathogenesis of diabetic complications. We have previously reported that taurine (T), which is known to counteract oxidative stress in tissues (lens, kidney, retina) of diabetic rats, attenuates nerve blood flow and conduction deficits in early experimental diabetic neuropathy (EDN). The purpose of this study was to evaluate whether dietary T supplementation counteracts oxidative stress and the nerve growth factor (NGF) deficit in the diabetic peripheral nerve. The experiments were performed in control rats and streptozotocin-diabetic rats fed standard or 1% T-supplemented diets for 6 weeks. All measurements were performed in the sciatic nerve. Malondialdehyde (MDA) plus 4-hydroxyalkenals (4-HA) were quantified with N-methyl-2-phenylindole. GSH, GSSG, dehydroascorbate (DHAA), and ascorbate (AA) were assayed spectrofluorometrically, T by reverse-phase HPLC, and NGF by ELISA. MDA plus 4-HA concentration (mean +/- SEM) was increased in diabetic rats (0.127 +/- 0.006 vs 0.053 +/- 0.003 micromol/g in controls, P < 0.01), and this increase was partially prevented by T (0.096 +/- 0.004, P < 0.01 vs untreated diabetic group). GSH levels were similarly decreased in diabetic rats treated with or without taurine vs controls. GSSG levels were similar in control and diabetic rats but were lower in diabetic rats treated with T (P < 0.05 vs controls). AA levels were decreased in diabetic rats (0.133 +/- 0.015 vs 0.219 +/- 0.023 micromol/g in controls, P < 0.05), and this deficit was prevented by T. DHAA/AA ratio was increased in diabetic rats vs controls (P < 0.05), and this increase was prevented by T. T levels were decreased in diabetic rats (2.7 +/- 0.16 vs 3.8 +/- 0.1 micromol/g in controls, P < 0.05) and were repleted by T supplementation (4.2 +/- 0.3). NGF levels were decreased in diabetic rats (2.35 +/- 0.20 vs 3.57 +/- 0.20 ng/g in controls, P < 0.01), and this decrease was attenuated by T treatment (3.16 +/- 0.28, P < 0.05 vs diabetic group). In conclusion, T counteracts oxidative stress and the NGF deficit in early EDN. Antioxidant effects of T in peripheral nerve are, at least in part, mediated through the ascorbate system of antioxidative defense. The findings are consistent with the important role for oxidative stress in impaired neurotrophic support in EDN.