Antioxidants, but not cAMP or high K+, prevent arachidonic acid toxicity on neuronal cultures

Polyunsaturated Fatty Acid-Enriched Lipid Fingerprint of Glioblastoma Proliferative Regions Is Differentially Regulated According to Glioblastoma Molecular Subtype

Glioblastoma (GBM) represents one of the deadliest tumors owing to a lack of effective treatments. The adverse outcomes are worsened by high rates of treatment discontinuation, caused by the severe side effects of temozolomide (TMZ), the reference treatment. Therefore, understanding TMZ’s effects on GBM and healthy brain tissue could reveal new approaches to address chemotherapy side effects. In this context, we have previously demonstrated the membrane lipidome is highly cell type-specific and very sensitive to pathophysiological states. However, little remains known as to how membrane lipids participate in GBM onset and progression. Hence, we employed an ex vivo model to assess the impact of TMZ treatment on healthy and GBM lipidome, which was established through imaging mass spectrometry techniques. This approach revealed that bioactive lipid metabolic hubs (phosphatidylinositol and phosphatidylethanolamine plasmalogen species) were altered in healthy brain tissue treated with TMZ. To better understand these changes, we interrogated RNA expression and DNA methylation datasets of the Cancer Genome Atlas database. The results enabled GBM subtypes and patient survival to be linked with the expression of enzymes accounting for the observed lipidome, thus proving that exploring the lipid changes could reveal promising therapeutic approaches for GBM, and ways to ameliorate TMZ side effects.

Endocrine disruptors also function as nervous disruptors and can be renamed endocrine and nervous disruptors (ENDs)

Endocrine disruption (ED) and endocrine disruptors (EDs) emerged as scientific concepts in 1995, after numerous chemical pollutants were found to be responsible for reproductive dysfunction. The World Health Organization established in the United Nations Environment Programme a list of materials, plasticizers, pesticides, and various pollutants synthesized from petrochemistry that impact not only reproduction, but also hormonal functions, directly or indirectly. Cells communicate via either chemical or electrical signals transmitted within the endocrine or nervous systems. To investigate whether hormone disruptors may also interfere directly or indirectly with the development or functioning of the nervous system through either a neuroendocrine or a more general mechanism, we examined the scientific literature to ascertain the effects of EDs on the nervous system, specifically in the categories of neurotoxicity, cognition, and behaviour. To date, we demonstrated that all of the 177 EDs identified internationally by WHO are known to have an impact on the nervous system. Furthermore, the precise mechanisms underlying this neurodisruption have also been established. It was previously believed that EDs primarily function via the thyroid. However, this study presents substantial evidence that approximately 80 % of EDs operate via other mechanisms. It thus outlines a novel concept: EDs are also neurodisruptors (NDs) and can be collectively termed endocrine and nervous disruptors (ENDs). Most of ENDs are derived from petroleum residues, and their various mechanisms of action are similar to those of "spam" in electronic communications technologies. Therefore, ENDs can be considered as an instance of spam in a biological context.

Glutathione depletion and oxidative stress

Oxidative stress is believed to contribute to the pathogenesis of Parkinson's disease. One of the indices of oxidative stress is the depletion of the antioxidant glutathione (GSH), which may occur early in the development of Parkinson's disease. To study the role of GSH depletion in the survival of dopamine neurons we treated mesencephalic cultures with the GSH synthesis inhibitor L-buthionine sulfoximine. Our studies have shown that the depletion of GSH causes a cascade of events, which ultimately may result in cell death. An early event following GSH depletion is a phospholipase A(2)-dependent release of arachidonic acid. Arachidonic acid can cause damage to the GSH-depleted cells through its metabolism by lipoxygenase. The generation of superoxide radicals during the metabolism of arachidonic acid is likely to play an important role in the toxic events that follow GSH depletion.

Influence of antioxidants on the blood-brain barrier permeability during epileptic seizures

Pentylenetetrazol-induced seizures in rats lead to the breakdown of the blood-brain barrier. We compared the disruption of the blood-brain barrier during epileptic seizure in untreated rats and in rats treated with vitamin E or selenium. The rats were supplemented with nontoxic doses of sodium selenite (4 pp) in drinking water for 3 months, or vitamin E (70 mg/kg) was given intraperitoneally for 30 min before the pentylenetetrazole injection. Evans-blue was used as a blood-brain barrier tracer and was given intravenously at a dose of 4 ml/kg of a 2% solution. The rats were divided into four experimental groups. Group I: control (n = 24); Group II: pentylenetetrazole-induced seizure (n = 12); Group III: vitamin E injected + seizure (n = 12); Group IV: Selenium supplemented + seizure (n = 12). The rats subjected to epileptic seizures showed Evans-blue albumin extravasations especially in the thalamic nuclei, brainstem, occipital, and frontal cortex. Mean values for Evans-blue dye were found to be 0.28 +/- 0.04 mg % brain tissue in control rats and 1.6 +/- 0.2 mg % brain tissue after epileptic seizures (P < 0.01). The magnitude of distribution of the blood-brain barrier during epileptic seizures was significantly less in rats treated with vitamin E or selenium. The mean value for Evans-blue dye was found to be 1.2 +/- 0.1 mg % brain tissue in selenium supplemented rats and 1.2 +/- 0.1 mg % brain tissue in vitamin E injected rats after epileptic seizures. This difference between treated and untreated animals was found to be significant (P < 0.05). The findings of the present study suggest that free radicals contribute to disruption of the blood-brain barrier during pentylenetetrazol-induced seizures.

4-Hydroxynonenal induces oxidative stress and death of cultured spinal cord neurons

Primary spinal cord trauma can trigger a cascade of secondary processes leading to delayed and amplified injury to spinal cord neurons. Release of fatty acids, in particular arachidonic acid, from cell membranes is believed to contribute significantly to these events. Mechanisms of fatty acid-induced injury to spinal cord neurons may include lipid peroxidation. One of the major biologically active products of arachidonic acid peroxidation is 4-hydroxynonenal (HNE). The levels of HNE-protein conjugates in cultured spinal cord neurons increased in a dose-dependent manner after a 24-h exposure to arachidonic acid. To study cellular effects of HNE, spinal cord neurons were treated with different doses of HNE, and cellular oxidative stress, intracellular calcium, and cell viability were determined. A 3-h exposure to 10 microM HNE caused approximately 80% increase in oxidative stress and 30% elevation of intracellular calcium. Exposure of spinal cord neurons to HNE caused a dramatic loss of cellular viability, indicated by a dose-dependent decrease in MTS [3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-s ulfophenyl)- 2H-tetrazolium, inner salt] conversion. The cytotoxic effect of HNE was diminished by pretreating neurons with ebselen or N-acetylcysteine. These data support the hypothesis that formation of HNE may be responsible, at least in part, for the cytotoxic effects of membrane-released arachidonic acid to spinal cord neurons.

The role of volume transmission of adaptogenic signals in forming the adaptive reactions of the brain

This review presents published data and results from our own studies providing evidence for the important role of volume, non-synaptic transmission of adaptogenic signals in the mechanisms forming the long-term adaptive reactions of the brain. The importance of chemical factors involved in volume transmission and secreted by cells in this process is discussed. Special attention is paid to peptides-possible mediators of volume transmission of adaptive-type signals. Evidence has been obtained for the presence of peptides and their role in the mechanism of development of adaptive brain reactions of different origins, especially those arising in response to tetanic stimulation of neurons and transient hypoxic stress. An original method for testing for the effects of neuromodulator factors released by cells in donor slices subjected to these treatments on recipient slices was used to show that these factors had pronounced effects on synaptic transmission and could induce long-term potentiation of synaptic transmission, protecting against functional derangements due to prolonged anoxia. Blockade of protein synthesis in donor slices subjected to adaptogenic treatments suppressed the appearance of these effects. The review concludes with a discussion of the mechanisms of interaction of the synaptic and volume transmission of signals involved in forming long-term adaptive brain reactions.

Nicotine attenuates arachidonic acid-induced overexpression of nitric oxide synthase in cultured spinal cord neurons

Primary spinal cord trauma can initiate a cascade of pathophysiologic events which markedly contribute to the expansion and amplification of the primary insult. The detailed mechanisms of these secondary neurochemical reactions are largely unknown; however, they involve membrane lipid derangements with the release of free fatty acids, in particular, arachidonic acid (AA). AA can induce several injury effects on spinal cord neurons. We hypothesize that upregulation of nitric oxide synthase (NOS) is among the most important mechanisms of arachidonic-acid-induced neuronal dysfunction and that nicotine can attenuate this effect. To study these hypotheses, spinal cord neurons were exposed to AA and/or nicotine, and several markers of neuronal nitric oxide synthase (nNOS) metabolism were measured. In addition, cotreatments with either inhibitors of nicotinic receptors or inhibitors of specific NOS isoforms were employed. Treatment with AA markedly increased activity of nNOS, as well as mRNA and protein levels of this enzyme. Changes in nNOS expression were accompanied by an increase in cellular cGMP and medium nitrite levels. Pretreatment with nicotine decreased AA-induced overexpression of nNOS and elevation of nitrite levels. In addition, it appeared that these nicotine effects could be partially modulated both by the alpha7 nicotinic receptors or by nonreceptor mechanisms. Alternatively, the observed changes could also be mediated by an alternate nicotinic receptor mechanism which is not blocked by alpha-bungarotoxin or mecamylamine. Results of the present study indicate that exposure to AA can lead to induction of nNOS in cultured spinal cord neurons. In addition, nicotine can exert a neuroprotective effect by attenuation of AA-induced upregulation of nNOS metabolism. These data may have therapeutic implications for the treatment of acute spinal cord trauma.

Regulation of renal epithelial cell affinity for calcium oxalate monohydrate crystals

The binding and internalization of calcium oxalate monohydrate (COM) crystals by tubular epithelial cells may be a critical step leading to kidney stone formation. Exposure of MDCK cells to arachidonic acid (AA) for 3 days, but not oleic or linoleic acid, decreased COM crystal adhesion by 55%. Exogenous prostaglandin PGE(1) or PGE(2) decreased crystal binding 96% within 8 h, as did other agents that raise intracellular cAMP. Actinomycin D, cycloheximide, or tunicamycin each blocked the action of PGE(2), suggesting that gene transcription, protein synthesis, and N-glycosylation were required. Blockade of crystal binding by AA was not prevented by the cyclooxygenase inhibitor flurbiprofen, and was mimicked by the nonmetabolizable AA analog eicosatetryanoic acid (ETYA), suggesting that generation of PGE from AA is not the pathway by which AA exerts its effect. These studies provide new evidence that binding of COM crystals to renal cells is regulated by physiological signals that could modify exposure of cell surface molecules to which the crystals bind. Intrarenal AA, PGs, and/or other agents that raise the intracellular concentration of cAMP may serve a protective function by preventing crystal adhesion along the nephron, thereby defending the kidney against crystal retention and stone formation.

Arachidonic acid-induced oxidative injury to cultured spinal cord neurons

Spinal cord trauma can cause a marked release of free fatty acids, in particular, arachidonic acid (AA), from cell membranes. Free fatty acids, and AA by itself, may lead to secondary damage to spinal cord neurons. To study this hypothesis, cultured spinal cord neurons were exposed to increasing concentrations of AA (0.01-10 microM). AA-induced injury to spinal cord neurons was assessed by measurements of cellular oxidative stress, intracellular calcium levels, activation of nuclear factor-KB (NF-kappaB), and cell viability. AA treatment increased intracellular calcium concentrations and decreased cell viability. Oxidative stress increased significantly in neurons exposed to 1 and 10 microM AA. In addition, AA treatment activated NF-kappaB and decreased levels of the inhibitory subunit, IKB. It is interesting that manganese superoxide dismutase protein levels and levels of intracellular total glutathione increased in neurons exposed to this fatty acid for 24 h, consistent with a compensatory response to increased oxidative stress. These results strongly support the hypothesis that free fatty acids contribute to the tissue injury observed following spinal cord trauma.

Glial cells mediate toxicity in glutathione-depleted mesencephalic cultures

We have examined the role of glial cells in the toxicity that results from inhibition of reduced glutathione (GSH) synthesis by L-buthionine sulfoximine (BSO) in mesencephalic cell cultures. We show that GSH depletion, to levels that cause total cell loss in cultures containing neurons and glial cells, has no effect on cell viability in enriched neuronal cultures. An increase in the plating cell density sensitizes glia-containing cultures to GSH depletion-induced toxicity. This suggests that cell death in this model is the consequence of events that are induced by GSH depletion and are mediated by glial cells. The antioxidant ascorbic acid and the lipoxygenase (LOX) inhibitor nordihydroguaiaretic acid (1-10 microM) provide full protection from BSO toxicity, indicating that arachidonic acid metabolism through the LOX pathway and the generation of reactive oxygen species play a role in the loss of cell viability. In contrast, inhibition of nitric oxide (NO) synthase affords only partial protection from BSO toxicity, suggesting that increased NO production cannot entirely account for cell death in this model. Our data provide evidence that GSH depletion in the presence of glial cells leads to neuronal degeneration that can be prevented by inhibition of LOX. This may have relevance to the pathogenesis of Parkinson's disease, where glial activation and depletion of GSH have been found in the substantia nigra pars compacta.

Cell death, calcium mobilization, and immunostaining for phosphorylated eukaryotic initiation factor 2-alpha (eIF2alpha) in neuronally differentiated NB-104 cells: arachidonate and radical-mediated injury mechanisms

These experiments examine the effects of arachidonate with respect to cell death, radical-mediated injury, Ca2+ mobilization, and formation of ser-51-phosphorylated eukaryotic initiation factor 2alpha [eIF2alpha(P)]. It is known that during brain ischemia the concentration of free arachidonate can reach 180 microM, and during reperfusion oxidative metabolism of arachidonate leads to generation of superoxide that can reduce stored ferric iron and promote lipid peroxidation. During early brain reperfusion, we have shown an approximately 20-fold increase in eIF2alpha(P) which maps to vulnerable neurons that display inhibition of protein synthesis. Here in neuronally differentiated NB-104 cells, equivalent cell death (assessed by LDH release) was induced by 40 microM arachidonate and 20 microM cumene hydroperoxide (CumOOH, a known alkoxyl radical generator). In these injury models (1) radical inhibitors (BHA, BHT, and the lipophilic iron chelator EMHP) block CumOOH-induced cell death but do not block arachidonate-induced death; (2) 40 microM arachidonate (but not up to 40 microM CumOOH) rapidly induces Ca2+ release from intracellular stores; (3) both 40 microM arachidonate and 20 microM CumOOH induce intense immunostaining for eIF2alpha(P); and (4) the elF2alpha(P) immunostaining induced by CumOOH but not that induced by arachidonate is completely blocked by anti-radical intervention with EMHP. Arachidonate-induced formation of eIF2alpha(P) and cell death do not require iron-mediated radical mechanisms and are associated with Ca2+ release from intracellular stores; however, radical-mediated injury also induces both eIF2alpha(P) and cell death without release of intracellular Ca2+. Our data link eIF2alpha(P) formation during brain reperfusion to two established injury mechanisms that may operate concurrently.

Venom phospholipase A2-induced impairment of glutamate uptake: an indirect and nonselective effect related to phospholipid hydrolysis

In a nominally calcium-free medium, a toxic phospholipase A2, paradoxin, PDX (1-200nM) was able to significantly decrease glutamate uptake by rat hippocampal mini-slices. Under the same experimental conditions, PDX could also inhibit the reuptake of choline and dopamine, suggesting a nonselective action. Furthermore, we found no evidence of competition between PDX and [3H]L-Aspartate described as a marker of glutamate carrier proteins. A direct blockage of glutamate uptake by binding to the glutamate transporters is thus unlikely to occur. Implication of the free fatty acids (FFAs), or their metabolites, was clearly shown by the total suppression of PDX effect on reuptake in a medium inhibiting its catalytic activity (EGTA/Sr2+ buffer). Moreover, analysis of the FFAs liberated showed a significant increase in polyunsaturated fatty acid (PUFA) levels. Arachidonic acid (AA) concentration reached in the water phase, though in the low micromolar range, may be especially relevant in explaining this effect. Much higher concentrations are found in the membranes and may also participate in the action on reuptake. Evidence for the involvement of FFAs was also provided by the antagonistic, although partial, action of bovine serum albumine (BSA, 1%). Finally, free radicals or eicosanoids did not seem to play a significant role given the persistence of inhibition in the presence of NDGA (1 microM) or indomethacin (10 microM), inhibitors of the two major AA metabolic pathways. Altogether, PDX-induced uptake impairment may thus be related to the direct action of AA and other PUFAs on the glutamate transporter, as well as through less selective actions.

Arachidonic acid as a neurotoxic and neurotrophic substance

In this article we summarize a wide variety of properties of arachidonic acid (AA) in the mammalian nervous system especially in the brain. AA serves as a biologically-active signaling molecule as well as an important component of membrane lipids. Esterified AA is liberated from the membrane by phospholipase activity which is stimulated by various signals such as neurotransmitter-mediated rise in intracellular Ca2+. AA exerts many biological actions which include modulation of the activities of protein kinases and ion channels, inhibition of neurotransmitter uptake, and enhancement of synaptic transmission. AA serves also as a precursor of a variety of eicosanoids, which are formed by oxidative metabolism of AA. AA cascade is activated under several pathological conditions in the brain such as ischemia and seizures, and may be involved in irreversible tissue damage. On the other hand, AA can show beneficial influences on brain tissues and cells in several situations. In a recent study using cultured brain neurons, we have found that AA shows quite distinct actions at a narrow concentration range, such as induction of cell death, promotion of cell survival and enhancement of neurite extension. The neurotoxic action is mediated by free radicals generated by AA metabolism, whereas the neurotrophic actions are exerted by AA itself. The observed in vitro actions of AA might be related to important roles of AA in brain pathogenesis and neural development.