N-methyl bases of ethanolamine prevent apoptotic cell death induced by oxidative stress in cells of oligodendroglia origin

Docosahexaenoic acid supplementation induces dose and time dependent oxidative changes in C6 glioma cells

In view of the promising use of n-3 polyunsaturated fatty acids (PUFAs) in the prevention and treatment of neurological diseases, it is necessary to ascertain the lack of detrimental oxidative effects. We evaluated short- and long-term effects of 25, 50 and 75 muM docosahexaenoic acid (DHA) supplementation on the oxidative status of C6 glial cells. DHA was incorporated into cells dose and time dependently without any cytotoxic effect. Reactive oxygen species (ROS) level was related to DHA dose and supplementation time. At the lowest dose no significant increase in ROS values was observed at hour 24. Low doses of DHA strengthened the cellular antioxidant defence system as highlighted by a raise in both GPX and catalase activity, and the decreased levels of lipid peroxidation. This effect was pronounced at 24 h of supplementation, almost disappeared at hour 48, while after 72 h an opposite effect was observed: lipid peroxidation increased concomitantly with DHA doses. Therefore, the final effect of DHA on cellular redox status is dependent on dose and time supplementation.

Docosahexaenoic acid-dependent iron accumulation in oligodendroglia cells protects from hydrogen peroxide-induced damage

Iron, a transition metal and essential nutrient, is a typical pro-oxidant forming free radicals, lipid peroxides and causing cell damage when added at high (> or = 50 microM) concentrations to oligodendroglia-like OLN-93 cells that have been enriched for 3 days with 10 microM docosahexaenoic acid (DHA, 22 : 6 n-3). At low (5 microM) iron concentrations lipid peroxides were still formed, but cells turned resistant to 250 microM H2O2, a secondary genotoxic stress. This has been attributed most likely to a time-dependent (16 h preconditioning) increase of cellular antioxidant enzyme activities i.e., glutathione peroxidase (38%) and glutathione reductase (26%). DHA but not arachidonic acid (20 : 4 n-6) supplements induced 3-fold increase in gene expression of divalent metal transporter-1, a transporter protein presumably responsible for the increase in intracellular iron. Elevated iron levels triggered a transient scrambling of membrane lipid asymmetry as evident by an accelerated ethanolamine phosphoglyceride translocation to the outer cell surface. Ethanolamine phosphoglyceride reorientation is proposed to activate certain signaling cascades leading to changes in nuclear transcription, a reaction that could represent a mechanism of preconditioning. These findings may have important implications for understanding the interactive role of iron and DHA in nutritional deficiencies, losses of polyunsaturated fatty acids in the aging brain or excessive iron accumulation in degenerative disorders.

Effect of ingested sulfite on hippocampus antioxidant enzyme activities in sulfite oxidase competent and deficient rats

Animal tissues are exposed to sulfite used as a preservative in food and drugs, and generated from the catabolism of sulfur-containing amino acids. Sulfite, which is a very reactive and potentially toxic molecule, is detoxified by the enzyme sulfite oxidase (SOX). Laboratory animals can be made deficient in SOX by the administration of a high-tungsten/low molybdenum regimen. It has been suggested that SOX deficient rats might be used as a model for the prediction of sulfite toxicity in humans. The aim of this study was to investigate the effects of ingested sulfite on hippocampus superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities in SOX competent and deficient rats. Hippocampus SOD, CAT and GPx activities were found to be significantly increased by sulfite treatment in SOX competent groups. On the other hand, exposure to sulfite had no effect on antioxidant status in hippocampus of SOX deficient rats. In conclusion, these results suggest that hippocampus antioxidant capacity where defense mechanism against the oxidative challenge is up regulated by sulfite in SOX competent rats. This up regulation mechanism in antioxidant enzymes against to sulfite related oxidative stress is not observed in SOX deficient rats and remains to be explained.

Docosahexaenoic Acid Enhances Iron Uptake by Modulating Iron Transporters and Accelerates Apoptotic Death in PC12 Cells

The effect of docosahexaenoic acid (DHA; 22:6 n-3) on Fe(2+)-mediated and/or H(2)O(2)-mediated oxidative stress (OS) was investigated in a PC12 pheochromocytoma cell line in the presence or absence of 50 ng/ml nerve growth factor (NGF). DHA-supplemented cells showed enhanced Fe(2+)-induced cell damage as evident by increased lipid peroxides formation (10-fold) and reduced neutral red (NR) dye uptake in a NGF-independent fashion. DHA caused a nearly 10-fold increase in free iron uptake in NGF-treated cells and doubled iron uptake in nondifferentiated cells. DHA-enrichment induced an elevation in the transferrin receptor protein in the nondifferentiated cells whereas NGF-treatment led to a substantial increase in the ubiquitous divalent metal ion transporter 1 (DMT-1) as detected by mRNA levels using qRT-PCR. The mechanism of action of DHA to accelerate cell death may be associated with the externalization of amino-phosphoglycerides (PG) species of which, increased ethanolamine plasmalogen levels, may be essential for cell rescue as noted in NGF-treated PC12 cells.

Anandamide protects from low serum-induced apoptosis via its degradation to ethanolamine

Anandamide (AEA) is a lipid molecule belonging to the family of endocannabinoids. Various studies report neuroprotective activity of AEA against toxic insults, such as ischemic conditions and excitotoxicity, whereas some show that AEA has pro-apoptotic effects. Here we have shown that AEA confers a protective activity in N18TG2 murine neuroblastoma cells subjected to low serum-induced apoptosis. We have demonstrated that the protection from apoptosis by AEA is not mediated via the CB1 receptor, the CB2 receptor, or the vanilloid receptor 1. Interestingly, breakdown of AEA by fatty acid amide hydrolase is required for the protective effect of AEA. Furthermore, the ethanolamine (EA) generated in this reaction is the metabolite responsible for the protective response. The elevation in the levels of reactive oxygen species during low serum-induced apoptosis is not affected by AEA or EA. On the other hand, AEA and EA reduce caspase 3/7 activity, and AEA attenuates the cleavage of PARP-1. Taken together, our results demonstrate a role for AEA and EA in the protection against low serum-induced apoptosis.

Versatile roles of docosahexaenoic acid in the prenatal brain: from pro- and anti-oxidant features to regulation of gene expression

Docosahexaenoic acid (DHA) is the most ubiquitous polyunsaturated fatty acid (FA) in brain tissue. It is selectively esterified to amino phospholipids (PL) and therefore it is highly prevalent at the cytofacial site of the plasma membrane where it may specifically participate in intracellular events. A highly selective DHA accumulation prior to birth is the result of maternal supply via the placenta through a bio-magnification process. Supplements of DHA via the intra-amniotic route to the fetal rat increase brain DHA levels and also confer neuroprotection to fetuses subjected to global ischemic stress. The protective effect has been attributed to an enhanced free radical scavenging capacity of DHA. Dietary deprivation of linolenic acid (LNA) during the perinatal life on the other hand, resulted in losses of DHA from cerebral PLs [M. Schiefermeier, E. Yavin, n-3 deficient and DHA-enriched diets during critical periods of the developing prenatal rat brain, J. Lipid Res. 43 (2002) 124-131]. LNA deprivation also caused changes in a number of gene markers the identification of which was attained by a labor-intensive suppression subtractive hybridization protocol using mRNA from 2-week-old postnatal brains [E. Yakubov, P. Dinerman, F. Kuperstein, S. Saban, E. Yavin, Improved representation of gene markers on microarray by PCR-select subtracted cDNA targets, Mol. Brain Res. 137 (2005) 110-118]. Most notable was a remarkable elevation of dopamine (DA) receptor (D1 and D2) genes as evaluated by quantitative RT-PCR, SDS-PAGE gel electrophoresis and immunochemical staining [F. Kuperstein, E. Yakubov, P. Dinerman, S. Gil, R. Eylam, N. Salem Jr., E. Yavin, Overexpression of dopamine receptor genes and their products in the postnatal rat brain following maternal n-3 FA dietary deficiency, J. Neurochem. 95 (2005) 1550-1562]. Over-expression of DA receptors has been attributed to a compensatory mechanism resulting from impairment in DA neurotransmitter production, storage and processing. In conclusion, DHA is a versatile molecule with a wide range of actions spanning from participation in cellular oxidative processes and intracellular signaling to modulatory roles in gene expression and growth regulation.

Translocation of Ethanolamine Phosphoglyceride is Required for Initiation of Apoptotic Death in OLN-93 Oligodendroglial Cells

The possible interplay between extracellular signal-regulated protein kinase (ERK) activation and ethanolamine phosphoglycerides (PG) membrane bilayer translocation following oxidative stress (OS) (0.5 mM H2O2/0.05 mM Fe2+), was examined in oligodendroglia, OLN93, cells with altered plasma membrane PG composition. Cells supplemented with 50 microM docosahexaenoic acid (DHA, 22:6n3) to increase the number of potential double bond targets for OS in ethanolamine-PG (EPG) were compared to cells with diminished content of EPG, attained by the addition of 0.5 mM N,N-dimethylethanolamine (dEa). After 30 min OS, EPG translocation accompanied by sustained ERK activation and nuclear translocation culminating in apoptosis was found in DHA-supplemented cells in contrast to no EPG translocation, a brief ERK activation, but no nuclear translocation, and no cell death in DHA/dEa-supplemented cells. DHA/dEa-supplemented cells pretreated with the protein-tyrosine phosphatases inhibitor Na3VO4 followed by OS, although expressing a sustained ERK activation and nuclear translocation, failed to show apoptosis and lacked EPG translocation. In DHA-supplemented cells U0126, a MEK inhibitor, prevented ERK activation and EPG translocation and protected from cell death. These findings most likely indicate that ERK activation is an indispensable component for the signaling cascades leading to EPG translocation but only activation of the latter is leading to OS-induced apoptotic cell death.

Synthesis and biological evaluation of lipophilic iron chelators as protective agents from oxidative stress

Lipophilic Fe(III) chelators were synthesized and shown to protect oligodendrial cells from oxidative damage induced by Fe(III) and hydrogen peroxide.

Stimulation of myelin proteolipid protein gene expression by eicosapentaenoic acid in C6 glioma cells

In this study, the role of exogenous fatty acids in the regulation of proteolipid protein (PLP) gene expression was investigated using the following model culture system: C6 glioma cells expressing the green-fluorescent protein (eGFP) driven by different segments of PLP promoter. Eicosapentanoic acid (EPA; 20:5 n-3), but not arachidonic acid (AA; 20:4 n-6), induced a significant increase in medium fluorescence intensity (MFI) determined by fluorescence-activated cell sorting (FACS). The induction of PLP promoter was time-dependent showing maximal activity between 24 and 48 h after EPA exposure. PLP promoter activation was dependent on fatty acid concentration, with maximum activation at 200 microM. Northern blot analysis confirmed the fluorescence data in C6 cells incubated with EPA. Furthermore, this treatment increased the adenylyl cyclase-cyclic AMP (cAMP) levels and the mitogen-activated protein kinase (MAPK) activation in C6 cells. PLP promoter activity was inhibited by pre-treatment with H89 (protein kinase A (PKA) inhibitor), but not with PD98059 (MAPK inhibitor), suggesting that EPA stimulates the expression of PLP via cAMP-mediated pathways.

Pro-apoptotic signaling in neuronal cells following iron and amyloid beta peptide neurotoxicity

In a previous report, we characterized several oxidative stress parameters during the course of amyloid beta (Abeta) peptide/Fe2+-induced apoptotic death in neuronal cells. In extending these findings, we now report a marked decrease in protein kinase C (PKC) isoforms, reduced Akt serine/threonine kinase activity, Bcl 2-associated death promoter (BAD) phosphorylation and enhanced p38 mitogen-activated protein kinase (MAPK) and caspase-9 and -3 activation, 12 h after addition of both 5 micro m Abeta and 5 micro m Fe2+. These activities reminiscent for a pro-apoptotic cellular course were blocked in the presence of the iron chelator deferroxamine. Abeta alone, increased PKC isoform levels between three- and four-fold after 12 h, enhanced Akt activity approximately eight-fold and Ser136 BAD phosphorylation two-fold, suggesting that by itself is not toxic. Fe2+ alone transiently enhanced p38 MAPK and caspase-9 and -3 enzymes indicative for cell damage, but was not sufficient to cause cell death as previously indicated. GF, a PKC inhibitor or wortmannin, a blocker of the Akt pathway enhanced Abeta/Fe2+-induced toxicity, while SB, a p38 MAPK inhibitor, prevented cell damage and apoptosis. These findings further support the hypothesis that metal ion chelation and inhibitors of pro-apoptotic kinase cascades may be beneficial for Alzheimer's disease therapy.

The Cu,Zn superoxide dismutase in neuroblastoma SK-N-BE cells is exported by a microvesicles dependent pathway

The antioxidant enzyme Cu,Zn superoxide dismutase has so far been considered costitutively expressed and exclusively localized into cytosol. In this paper we investigated Cu,Zn superoxide dismutase export in neuroblastoma SK-N-BE cells by flow cytometry analysis, confocal immunofluorescence analysis and enzyme-linked immunosorbed assay. Immunofluorescence analysis shows that the enzyme is exported by microvesicular granules; moreover the treatment of cells with brefeldin A and with 2-deoxy-D-glucose and sodium azide strongly decreases the amount of CuZn superoxide dismutase detected in the medium. Therefore the involvement of ATP-dependent mechanisms, likely including BFA-sensitive intracytoplasmic vesicles in Cu,Zn SOD export from SK-N-BE cells, has to be hypothesized. Microvesicular-mediated Cu,Zn SOD export in neurons could represent a relevant phenomenon able to influence cell excitability that is affected by reactive oxygen species.

ERK activation and nuclear translocation in amyloid-beta peptide- and iron-stressed neuronal cell cultures

Oxidative stress in the human brain has been strongly implicated as the cause of neuronal cell losses in Alzheimer's disease patients, but the exact mechanism still remains unknown. In this report several oxidative stress parameters and an associated signalling transduction cascade predating neuronal cell death in cultures treated with the oxidative stressors Fe(2+) (5 microm) and the amyloid beta (A beta(1-40)) peptide (5 microm) were studied. Production of reactive oxygen species as detected by dichlorofluorescein staining was apparent within 5 min in the presence of both agents. Lipid peroxide content increased by approximately 10-fold after 2 h, while mitochondrial activity was impaired by 40% after 6 h. Caspase-3 activity was elevated 5-6 fold, all indicative of oxidative cell stress. The combined presence of A beta(1-40) and Fe(2+) resulted in a rapid (5 min) ERK activation followed by a decline by 30 min and a second activation that continued up to 24 h when nuclear translocation was noticed. Neither treatment with Fe(2+) nor that with A beta(1-40) alone caused similar changes. Addition of either deferroxamine (DFe, 25 microm), catalase (0.4 mg/mL) or N-acetyl cysteine (0.5 mm) - the last two known as suppressants of oxidative stress - attenuated ERK activation and nuclear translocation. The mitogen-activated protein/ERK kinase (MEK) inhibitor U0126 blocked ERK and caspase 3 activation, suppressed ERK translocation and reduced the number of apoptotic cells, suggesting a central role for the ERK signalling cascade in A beta(1-40) plus Fe(2+) (A beta(1-40)/Fe(2+)) -induced apoptotic death. The full peptide A beta(1-42) was very effective at 0.5 microm while the inverse peptide A beta(40-1) at 5 microm was ineffective. The acetyl-amyloid-beta protein amide fragment 15-20 (V-pep) known to be an A beta aggregation inhibitor, prevented A beta(1-40)/Fe(2+)-induced toxicity. These findings indicate that metal ions chelators and antioxidants suppress the A beta(1-40)/Fe(2+)-induced oxidative stress cascade and may be beneficial in reducing the severity of Alzheimer's disease.

Early ethanolamine phospholipid translocation marks stress-induced apoptotic cell death in oligodendroglial cells

The consequences of H(2)O(2)/Fe(2+)-induced oxidative stress on translocation of ethanolamine phosphoglyceride (EPG) and serine phosphoglyceride (SPG) were studied in an oligodendroglia-like cell line (OLN 93) following 3 days of supplementation with 0.1 mM docosahexaenoic acid (DHA) and a series of polar head group precursors, including N-monomethyl- and N,N-dimethylethanolamine at millimolar concentrations. Added DHA was predominantly esterified in EPG species and those cells enriched in DHA showed enhanced sensitivity to oxidative stress and eventually died by apoptosis. Co-supplements with ethanolamine and DHA resulted in a rapid, but transient, EPG translocation with a maximum at 30 min following stress, as characterized by a trinitrobenzenesulfonic acid reagent. There was no significant translocation of SPG as evidenced by annexin V binding. Unlike SPG, which is usually irreversibly translocated to subserve as a tag for phagocytosis, EPG acted as a signaling molecule with biphasic kinetic characteristics. N-Monomethyl- and N,N-dimethylethanolamine supplements reduced EPG synthesis, prevented its externalization and rescued cells from apoptotic death. Following stress, the fatty acid profile of the externalized EPG showed marked losses in polyunsaturated fatty acids and aldehydes compared with the remaining intracellular EPG. Prevention of EPG species selective translocation to the outer membrane leaflet by altering phospholipid asymmetry may be important in the mechanism of rescue from cell death.

Walker-256 tumor growth causes oxidative stress in rat brain

The elevated rate of oxygen consumption and high amount of polyunsaturated fatty acids make the central nervous system vulnerable to oxidative stress. The effect of Walker-256 tumor growth on oxi-reduction indexes in the hypothalamus (HT), cortex (CT), hippocampus (HC) and cerebellum (CB) of male Wistar rats was investigated. The presence of the tumor caused an increase in thiobarbituric acid reactant substances (TBARs) in the HT, CB and HC. Due to tumor growth, the activity of glucose-6-phosphate dehydrogenase increased in the HT and CB, whereas citrate synthase activity was reduced in the HT, CT and CB. Therefore, the potential for generation of reducing power is increased in the cytosol and decreased in the mitochondria of various brain regions of Walker-256 tumor-bearing rats. These changes occurred concomitantly with an unbalance in the brain enzymatic antioxidant system. The tumor decreased the activities of catalase in the HT and CB and of glutathione peroxidase in the HT, CB and HC, and raised the CuZn-superoxide dismutase activity in the HT, CB and HC. These combined findings indicate that Walker-256 tumor growth causes oxidative stress in the brain.

A review of the causes of central pontine myelinosis: yet another apoptotic illness?

One of the well recognized stimuli for central pontine myelinosis (CPM) is the rapid correction of chronic hyponatraemia. Conventionally this has been perceived to lead to pontine glial cell swelling through osmosis and eventually to cell death. However, although a purely osmotic argument has been central to any patho-physiological understanding of CPM, there are deficiencies in this approach that do not account for why certain individuals develop CPM with relatively mild osmotic insults. Here we review the varying aetiologies of CPM and propose a novel hypothesis for CPM causation by suggesting that individuals predisposed to CPM have inadequate energy provision as well as other factors that result in a pro-apoptotic drive, which renders them susceptible to brain injury from diverse causes. In CPM, the precipitant of brain injury appears to be osmotic stress. Furthermore, this model suggests a number of therapeutic interventions that may prevent or at least mitigate the consequences of CPM.

Lipid constituents in oligodendroglial cells alter susceptibility to H2O2-induced apoptotic cell death via ERK activation

The present work examines the effect of membrane lipid composition on activation of extracellular signal-regulated protein kinases (ERK) and cell death following oxidative stress. When subjected to 50 microM docosahexaenoic acid (DHA, 22 : 6 n-3), cellular phospholipids of OLN 93 cells, a clonal line of oligodendroglia origin low in DHA, were enriched with this polyunsaturated fatty acid. In the presence of 1 mM N,N-dimethylethanolamine (dEa) a new phospholipid species analog was formed in lieu of phosphatidylcholine. Exposure of DHA-enriched cells to 0.5 mM H2O2, caused sustained activation of ERK up to 24 h. At this time massive apoptotic cell death was demonstrated by ladder and TUNEL techniques. H2O2-induced stress applied to dEa or DHA/dEa co-supplemented cells showed only a transient ERK activation and no cell death after 24 h. Moreover, while ERK was rapidly translocated into the nucleus in DHA-enriched cells, dEa supplements completely blocked ERK nuclear translocation. This study suggests that H2O2-induced apoptotic cell death is associated with prolonged ERK activation and nuclear translocation in DHA-enriched OLN 93 cells, while both phenomena are prevented by dEa supplements. Thus, the membrane lipid composition ultimately modulates ERK activation and translocation and therefore can promote or prevent apoptotic cell death.