Differential roles of cyclooxygenase isoforms after kainic acid-induced prostaglandin E(2) production and neurodegeneration in cortical and hippocampal cell cultures

Protein Arginine Methyltransferases in Cardiovascular and Neuronal Function

The methylation of arginine residues by protein arginine methyltransferases (PRMTs) is a type of post-translational modification which is important for numerous cellular processes, including mRNA splicing, DNA repair, signal transduction, protein interaction, and transport. PRMTs have been extensively associated with various pathologies, including cancer, inflammation, and immunity response. However, the role of PRMTs has not been well described in vascular and neurological function. Aberrant expression of PRMTs can alter its metabolic products, asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA). Increased ADMA levels are recognized as an independent risk factor for cardiovascular disease and mortality. Recent studies have provided considerable advances in the development of small-molecule inhibitors of PRMTs to study their function under normal and pathological states. In this review, we aim to elucidate the particular roles of PRMTs in vascular and neuronal function as a potential target for cardiovascular and neurological diseases.

Apolipoprotein D Overexpression Protects Against Kainate-Induced Neurotoxicity in Mice

Excitotoxicity due to the excessive activation of glutamatergic receptors leads to neuronal dysfunction and death. Excitotoxicity has been implicated in the pathogenesis of a myriad of neurodegenerative diseases with distinct etiologies such as Alzheimer's and Parkinson's. Numerous studies link apolipoprotein D (apoD), a secreted glycoprotein highly expressed in the central nervous system (CNS), to maintain and protect neurons in various mouse models of acute stress and neurodegeneration. Here, we used a mouse model overexpressing human apoD in neurons (H-apoD Tg) to test the neuroprotective effects of apoD in the kainic acid (KA)-lesioned hippocampus. Our results show that apoD overexpression in H-apoD Tg mice induces an increased resistance to KA-induced seizures, significantly attenuates inflammatory responses and confers protection against KA-induced cell apoptosis in the hippocampus. The apoD-mediated protection against KA-induced toxicity is imputable in part to increased plasma membrane Ca2+ ATPase type 2 expression (1.7-fold), decreased N-methyl-D-aspartate receptor (NMDAR) subunit NR2B levels (30 %) and lipid metabolism alterations. Indeed, we demonstrate that apoD can attenuate intracellular cholesterol content in primary hippocampal neurons and in brain of H-apoD Tg mice. In addition, apoD can be internalised by neurons and this internalisation is accentuated in ageing and injury conditions. Our results provide additional mechanistic information on the apoD-mediated neuroprotection in neurodegenerative conditions.

Kainic Acid-Induced Excitotoxicity Experimental Model: Protective Merits of Natural Products and Plant Extracts

Excitotoxicity is well recognized as a major pathological process of neuronal death in neurodegenerative diseases involving the central nervous system (CNS). In the animal models of neurodegeneration, excitotoxicity is commonly induced experimentally by chemical convulsants, particularly kainic acid (KA). KA-induced excitotoxicity in rodent models has been shown to result in seizures, behavioral changes, oxidative stress, glial activation, inflammatory mediator production, endoplasmic reticulum stress, mitochondrial dysfunction, and selective neurodegeneration in the brain upon KA administration. Recently, there is an emerging trend to search for natural sources to combat against excitotoxicity-associated neurodegenerative diseases. Natural products and plant extracts had attracted a considerable amount of attention because of their reported beneficial effects on the CNS, particularly their neuroprotective effect against excitotoxicity. They provide significant reduction and/or protection against the development and progression of acute and chronic neurodegeneration. This indicates that natural products and plants extracts may be useful in protecting against excitotoxicity-associated neurodegeneration. Thus, targeting of multiple pathways simultaneously may be the strategy to maximize the neuroprotection effect. This review summarizes the mechanisms involved in KA-induced excitotoxicity and attempts to collate the various researches related to the protective effect of natural products and plant extracts in the KA model of neurodegeneration.

Synergistic effects of celecoxib and bupropion in a model of chronic inflammation-related depression in mice

This study was aimed to characterize the depression-like behaviour in the classical model of chronic inflammation induced by Complete Freund's Adjuvant (CFA). Male Swiss mice received an intraplantar (i.pl.) injection of CFA (50 µl/paw) or vehicle. Behavioural and inflammatory responses were measured at different time-points (1 to 4 weeks), and different pharmacological tools were tested. The brain levels of IL-1β and BDNF, or COX-2 expression were also determined. CFA elicited a time-dependent edema formation and mechanical allodynia, which was accompanied by a significant increase in the immobility time in the tail suspension (TST) or forced-swimming (FST) depression tests. Repeated administration of the antidepressants imipramine (10 mg/kg), fluoxetine (20 mg/kg) and bupropion (30 mg/kg) significantly reversed depression-like behaviour induced by CFA. Predictably, the anti-inflammatory drugs dexamethasone (0.5 mg/kg), indomethacin (10 mg/kg) and celecoxib (30 mg/kg) markedly reduced CFA-induced edema. The oral treatment with the analgesic drugs dipyrone (30 and 300 mg/kg) or pregabalin (30 mg/kg) significantly reversed the mechanical allodyinia induced by CFA. Otherwise, either dipyrone or pregabalin (both 30 mg/kg) did not significantly affect the paw edema or the depressive-like behaviour induced by CFA, whereas the oral treatment with dipyrone (300 mg/kg) was able to reduce the immobility time in TST. Noteworthy, CFA-induced edema was reduced by bupropion (30 mg/kg), and depression behaviour was prevented by celecoxib (30 mg/kg). The co-treatment with bupropion and celecoxib (3 mg/kg each) significantly inhibited both inflammation and depression elicited by CFA. The same combined treatment reduced the brain levels of IL-1β, as well as COX-2 immunopositivity, whilst it failed to affect the reduction of BDNF levels. We provide novel evidence on the relationship between chronic inflammation and depression, suggesting that combination of antidepressant and anti-inflammatory agents bupropion and celecoxib might represent an attractive therapeutic strategy for depression.

Kainic Acid-induced neurotoxicity: targeting glial responses and glia-derived cytokines

Glutamate excitotoxicity contributes to a variety of disorders in the central nervous system, which is triggered primarily by excessive Ca²⁺ influx arising from overstimulation of glutamate receptors, followed by disintegration of the endoplasmic reticulum (ER) membrane and ER stress, the generation and detoxification of reactive oxygen species as well as mitochondrial dysfunction, leading to neuronal apoptosis and necrosis. Kainic acid (KA), a potent agonist to the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate class of glutamate receptors, is 30-fold more potent in neuro-toxicity than glutamate. In rodents, KA injection resulted in recurrent seizures, behavioral changes and subsequent degeneration of selective populations of neurons in the brain, which has been widely used as a model to study the mechanisms of neurodegenerative pathways induced by excitatory neurotransmitter. Microglial activation and astrocytes proliferation are the other characteristics of KA-induced neurodegeneration. The cytokines and other inflammatory molecules secreted by activated glia cells can modify the outcome of disease progression. Thus, anti-oxidant and anti-inflammatory treatment could attenuate or prevent KA-induced neurodegeneration. In this review, we summarized updated experimental data with regard to the KA-induced neurotoxicity in the brain and emphasized glial responses and glia-oriented cytokines, tumor necrosis factor-α, interleukin (IL)-1, IL-12 and IL-18.

Role of CNS efflux drug transporters in antiepileptic drug delivery: overcoming CNS efflux drug transport

Experimental support for the transporter hypothesis of drug resistance in epilepsies has triggered efforts developing and validating approaches to overcome enhanced blood-brain barrier efflux transport. Testing in rodent models has rendered proof-of-concept for an add-on therapy with antiepileptic drugs. However, further development of the approach would require tolerability considerations as efflux transporters serve an important protective function throughout the body limiting distribution of harmful xenobiotics. Relevant progress has been made in the elucidation of mechanisms driving up-regulation of the multidrug transporter P-glycoprotein in response to seizure activity. Based on this knowledge, novel strategies have been evaluated targeting the signaling cascade that regulates P-glycoprotein in the epileptic brain. Further concepts might include by-passing blood-brain barrier transporters by intracerebral administration or by encapsulation of antiepileptic drugs in nano-sized carrier systems. It is important to note that the future perspectives of respective approaches are still questionable based on the limited evidence for a clinical relevance of transporter expression. Thus, techniques are urgently needed for non-invasive assessment of blood-brain barrier transporter function. Respective techniques would allow testing for a clinical correlation between pharmacosensitivity and transporter function, validating therapeutic strategies targeting efflux transporters and selecting patients with transporter over-expression for respective clinical trials. Provided that further clinical data render support for the transporter hypothesis, the main question remains whether patients exist in which transporter over-expression is the predominant mechanism of drug resistance and in which overcoming drug efflux is equivalent with overcoming drug resistance. Imaging techniques might provide a tool to address these questions in clinical epileptology. However, the complex pharmacological interactions between antiepileptic drugs, radiotracers, and transporter modulators used in these approaches as well as interindividual differences in the brain pathology might hamper clear-cut conclusions and limit the diagnostic significance.

Indomethacin ameliorates trimethyltin-induced neuronal damage in vivo by attenuating oxidative stress in the dentate gyrus of mice

The organotin trimethyltin (TMT) is well known to cause neuronal degeneration in the hippocampal dentate gyrus of mice. The first purpose of the present study was to examine whether the cyclooxygenase (COX) inhibitor indomethacin could ameliorate neuronal degeneration in the dentate gyrus of mice following TMT treatment in vivo. The systemic injection into mice of TMT at 2.8 mg/kg produced activation of endogenous caspase-3 and calpain, enhanced the gene expression of COX-1 and COX-2, activated microglial cells, and caused the formation of the lipid peroxidation product 4-hydroxynonenal in the hippocampus. Given at 12-h post-TMT treatment, the systemic injection of indomethacin (5 or 10 mg/kg, subcutaneously) significantly decreased the TMT-induced damage to neurons having active caspase-3 and single-stranded DNA in the dentate granule cell layer of the hippocampus. The results of the α-Fodrin degradation test revealed that the post-treatment with indomethacin was effective in attenuating TMT-induced activation of endogenous caspases and calpain in the hippocampus. In TMT-treated animals, interestingly, the post-treatment with indomethacin produced not only activation of microglial cells in the dentate gyrus but also the formation of 4-hydroxynonenal in the dentate granule cell layer. Taken together, our data suggest that COX inhibition by indomethacin ameliorated TMT-induced neuronal degeneration in the dentate gyrus by attenuating intensive oxidative stress.

Kainic acid-induced neurodegenerative model: potentials and limitations

Excitotoxicity is considered to be an important mechanism involved in various neurodegenerative diseases in the central nervous system (CNS) such as Alzheimer's disease (AD). However, the mechanism by which excitotoxicity is implicated in neurodegenerative disorders remains unclear. Kainic acid (KA) is an epileptogenic and neuroexcitotoxic agent by acting on specific kainate receptors (KARs) in the CNS. KA has been extensively used as a specific agonist for ionotrophic glutamate receptors (iGluRs), for example, KARs, to mimic glutamate excitotoxicity in neurodegenerative models as well as to distinguish other iGluRs such as α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors and N-methyl-D-aspartate receptors. Given the current knowledge of excitotoxicity in neurodegeneration, interventions targeted at modulating excitotoxicity are promising in terms of dealing with neurodegenerative disorders. This paper summarizes the up-to-date knowledge of neurodegenerative studies based on KA-induced animal model, with emphasis on its potentials and limitations.

Kainic acid-induced neurodegeneration and activation of inflammatory processes in organotypic hippocampal slice cultures: treatment with cyclooxygenase-2 inhibitor does not prevent neuronal death

In the postnatal rodent hippocampus status epilepticus (SE) leads to age- and region-specific excitotoxic neuronal damage, the precise mechanisms of which are still incompletely known. Recent studies suggest that the activation of inflammatory responses together with glial cell reactivity highly contribute to excitotoxic neuronal damage. However, pharmacological tools to attenuate their activation in the postnatal brain are still poorly elucidated. In this study, we investigated the role of inflammatory mediators in kainic acid (KA)-induced neuronal damage in organotypic hippocampal slice cultures (OHCs). A specific cyclooxygenase-2 (COX-2) inhibitor N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide (NS-398) was used to study whether or not it could ameliorate neuronal death. Our results show that KA treatment (24 h) resulted in a dose-dependent degeneration of CA3a/b pyramidal neurons. Furthermore, COX-2 immunoreactivity was pronouncedly enhanced particularly in CA3c pyramidal neurons, microglial and astrocyte morphology changed from a resting to active appearance, the expression of the microglial specific protein, Iba1, increased, and prostaglandin E₂ (PGE₂) production increased. These indicated the activation of inflammatory processes. However, the expression of neither proinflammatory cytokines, i.e. tumour necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β), nor the anti-inflammatory cytokine IL-10 mRNA was significantly altered by KA treatment as studied by real-time PCR. Despite activation of an array of inflammatory processes, neuronal damage could not be rescued either with the combined pre- and co-treatment with a specific COX-2 inhibitor, NS-398. Our results suggest that KA induces activation of a repertoire of inflammatory processes in immature OHCs, and that the timing of anti-inflammatory treatment to achieve neuroprotection is a challenge due to developmental properties and the complexity of inflammatory processes activated by noxious stimuli. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.

Modulating P-glycoprotein regulation: future perspectives for pharmacoresistant epilepsies?

Enhanced brain efflux of antiepileptic drugs by the blood-brain barrier transporter P-glycoprotein is discussed as one mechanism contributing to pharmacoresistance of epilepsies. P-glycoprotein overexpression has been proven to occur as a consequence of seizure activity. Therefore, blocking respective signaling events should help to improve brain penetration and efficacy of P-glycoprotein substrates. A series of recent studies revealed key signaling factors involved in seizure-associated transcriptional activation of P-glycoprotein. These data suggested several interesting targets, including the N-methyl-d-aspartate (NMDA) receptor, the inflammatory enzyme cyclooxygenase-2, and the prostaglandin E2 EP1 receptor. These targets have been further evaluated in rodent models, demonstrating that targeting these factors can control P-glycoprotein expression, improve antiepileptic drug brain penetration, and help to overcome pharmacoresistance. In general, the approach offers particular advantages over transporter inhibition as it preserves basal transporter function. In this review the different strategies for blocking P-glycoprotein upregulation, including their therapeutic promise and drawbacks are discussed. Moreover, pros and cons of the approach are compared to those of alternative strategies to overcome transporter-associated resistance. Regarding future perspectives of the novel approach, there is an obvious need to more clearly define the clinical relevance of transporter overexpression. In this context current efforts are discussed, including the development of imaging tools that allow an evaluation of P-glycoprotein function in individual patients.

Platelet kainate receptor signaling promotes thrombosis by stimulating cyclooxygenase activation

RATIONALE

Glutamate is a major signaling molecule that binds to glutamate receptors including the ionotropic glutamate receptors; kainate (KA) receptor (KAR), the N-methyl-d-aspartate receptor, and the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor. Each is well characterized in the central nervous system, but glutamate has important signaling roles in peripheral tissues as well, including a role in regulating platelet function.

OBJECTIVE

Our previous work has demonstrated that glutamate is released by platelets in high concentrations within a developing thrombus and increases platelet activation and thrombosis. We now show that platelets express a functional KAR that drives increased agonist induced platelet activation.

METHODS AND RESULTS

KAR induced increase in platelet activation is in part the result of activation of platelet cyclooxygenase in a mitogen-activated protein kinase-dependent manner. Platelets derived from KAR subunit knockout mice (GluR6(-/-)) are resistant to KA effects and have a prolonged time to thrombosis in vivo. Importantly, we have also identified polymorphisms in KAR subunits that are associated with phenotypic changes in platelet function in a large group of whites and blacks.

CONCLUSIONS

Our data demonstrate that glutamate regulation of platelet activation is in part cyclooxygenase-dependent and suggest that the KAR is a novel antithrombotic target.

Alterations in excitotoxicity and prostaglandin metabolism in a transgenic mouse model of Alzheimer's disease

To address the potential impact of presenilin mutations on the prostaglandin metabolism in a neurodegenerative model of glutamatergic excitotoxicity, we injected kainic acid intraperitoneally (30mg/kg body weight) into mice over-expressing the human N141I mutation of presenilin-2, which is known to cause an early-onset form of Alzheimer's disease. We compared the seizure activity as well as seizure lethality in 2- and 6-month-old mice, transgenic for the above-mentioned point mutation, and their wildtype littermates and found that mice harboring the hN141I mutation showed a relative resistance to excitotoxic treatment. This was associated with a constituitively reduced expression of the cyclooxygenases COX-1 and COX-2 in the hippocampus of N141I presenilin-2 mice and a reduced induction of COX-2 expression post-kainate injection. In the past, clinical trials have suggested that both non-steroidal anti-inflammatory drugs, which impact upon a cell's prostaglandin metabolism, and glutamatergic antagonists might be of benefit to patients suffering from Alzheimer's-type dementias. Yet, the exact mechanism by which these drugs are beneficial remains unclear, although it seems possible that presenilins might be implicated in the process, at least in the case of early-onset forms. The data presented here strongly support the notion of an implication of presenilins in the alterations in the prostaglandin system, which have been observed in Alzheimer's disease and may contribute to the underlying pathogenesis of the disease.

Prostaglandins compromise basal forebrain cholinergic neuron differentiation and survival: action at EP1/3 receptors results in AIF-induced death

Activated microglia produce a factor or cocktail of factors that promotes cholinergic neuronal differentiation of undifferentiated precursors in the embryonic basal forebrain (BF) in vitro. To determine whether microglial prostaglandins mediate this action, microglia were stimulated in the presence of the cyclooxygenase inhibitor ibuprofen, and microglial conditioned medium (CM) was used to culture rat BF precursors at embryonic day 15. Choline acetyltransferase (ChAT) activity served as a measure of cholinergic differentiation. While inhibition of prostaglandin biosynthesis did not affect the ability of microglial CM to promote ChAT activity, treatment of microglia with prostaglandin E2 (PGE2) inhibited it. Agonists of E prostanoid receptors EP2 (butaprost) and EP1/3 (sulprostone) mimicked PGE2, while misoprostol (E1-4) actually enhanced the action of CM. PGE2 added directly to BF cultures together with microglial CM also inhibited ChAT activity. While BF cultures expressed all four prostanoid receptors, direct addition of sulprostone but not butaprost mimicked PGE2, suggesting that PGE2 engaged EP1/3 receptors in the BF. Neither PKA inhibition by H89 nor cAMP induction by forskolin or dibutyrl-cAMP altered the action of sulprostone. Sulprostone severely compromised ChAT activity, dendrite number, axonal length and axonal branching, but caspase inhibition did not restore these. However, sulprostone resulted in increased staining intensity and nuclear translocation of apoptosis-inducing factor (AIF) suggesting caspase-independent cell death. We have found that PGE2 action at microglial EP2 receptors inhibits the microglial production of the cholinergic differentiating cocktail, while action at neuronal EP3 receptors has a deleterious effect on cholinergic neurons causing neurite retraction and cell death.

Interactions between CB(1) receptors and TRPV1 channels mediated by 12-HPETE are cytotoxic to mesencephalic dopaminergic neurons

BACKGROUND AND PURPOSES

We recently proposed the existence of neurotoxic interactions between the cannabinoid type 1 (CB(1)) receptor and transient receptor potential vanilloid 1 (TRPV1) channels in rat mesencephalic cultures. This study seeks evidence for the mediator(s) and mechanisms underlying the neurotoxic interactions between CB(1) receptors and TRPV1 in vitro and in vivo.

EXPERIMENTAL APPROACH

The mediator(s) and mechanism(s) for the interactions between CB(1) receptors and TRPV1 were evaluated by cell viability assays, immunocytochemistry, Fura-2 calcium imaging, mitochondrial morphology assay, ELISA and Western blot assay in vitro in neuron-enriched mesencephalic cultures. Injections into the substantia nigra and subsequent cell counts were also used to confirm these interactions in vivo.

KEY RESULTS

The neurotoxic interactions were mediated by 12(S)-hydroperoxyeicosatetraenoic acid (12(S)-HPETE), an endogenous TRPV1 agonist. CB(1) receptor agonists (HU210 and WIN55,212-2) increased the level of 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), a downstream metabolite of 12(S)-HPETE, which stimulates TRPV1-mediated death of mesencephalic neurons, both in vitro and in vivo. The neurotoxicity was mediated by increased intracellular Ca(2+) concentration ([Ca(2+)](i)) through TRPV1, consequently leading to mitochondrial damage and was attenuated by baicalein, a 12-lipoxygenase inhibitor.

CONCLUSION AND IMPLICATIONS

Activation of CB(1) receptors in rat mesencephalic neurons was associated with biosynthesis of 12(S)-HPETE, which in turn stimulated TRPV1 activity, leading to increased [Ca(2+)](i), mitochondrial damage and neuronal death.

Endocannabinoid 2-arachidonoylglycerol protects neurons by limiting COX-2 elevation

Endocannabinoids are involved in synaptic signaling and neuronal protection; however, our understanding of the mechanisms by which endocannabinoids protect neurons from harmful insults remains elusive. 2-Arachidonoylglycerol (2-AG), the most abundant endogenous cannabinoid and a full agonist for cannabinoid receptors (CB1 and CB2), is a substrate for cyclooxygenase-2 (COX-2) and can be metabolized by COX-2. Here we show, however, that 2-AG is also capable of suppressing elevation of hippocampal COX-2 expression in response to proinflammatory and excitotoxic stimuli. 2-AG prevents neurodegeneration from toxic assaults that elevate COX-2 expression and inhibits the COX-2 elevation-enhanced excitatory glutamatergic synaptic transmission. The action of 2-AG on suppression of COX-2 appeared to be mediated via the pertussis toxin-sensitive G protein-coupled CB1 receptor and MAPK/NF-kappaB signaling pathways. Our results reveal that 2-AG functions as an endogenous COX-2 inhibitor protecting neurons from harmful insults by preventing excessive expression of COX-2, which provides a mechanistic basis for opening up new therapeutic approaches for protecting neurons from inflammation- and excitotoxicity-induced neurodegeneration.

Possible glutamatergic and lipid signalling mechanisms in ECT-induced retrograde amnesia: experimental evidence for involvement of COX-2, and review of literature

We sought to explore nonselective vs. selective COX mechanisms in ECS-induced retrograde amnesia using indomethacin and celecoxib as in vivo probes. Adult Wistar rats (n=72) which showed adequate learning on a passive avoidance task received 5 once-daily 30 mC true or sham ECS. During the learning and ECS periods, indomethacin (4 mg/kg/day), celecoxib (15 mg/kg/day), or vehicle were orally administered. One day after the fifth ECS, recall of pre-ECS learning was tested. There were no baseline or pre-ECS differences in learning between groups. ECS seizure duration did not differ across groups. ECS-treated rats showed impaired recall in the vehicle but not indomethacin and celecoxib groups. Celecoxib but not indomethacin significantly protected against ECS-induced retrograde amnesia. We interpret these results as follows: ECS may impair cognition by pathologically upregulating glutmatergic signalling, thereby causing cation and water influx, oxidative stress, and saturation of hippocampal LTP. These may result from glutamatergic disinhibition through COX-2-mediated removal of endogenous cannabinoids, and by ECS-activated, NMDA-mediated upregulation of platelet activating factor and COX-2 signalling pathways. Thus, indomethacin and celecoxib, by inhibiting COX-2, may protect against ECS-induced amnesia. Furthermore, COX-2 mediated increase in hippocampal kynurenic acid may impair glutamate-dependent learning and memory processes at ionotropic glutamatergic receptor sites; the inhibition of kynurenic acid synthesis by celecoxib and its induction by indomethacin may explain the greater benefits with celecoxib. These findings suggest new avenues for the study of the neurobiology of ECT-induced amnesia and the attenuation thereof.

Neuroprotective effect of nimesulide, a preferential COX-2 inhibitor, against pentylenetetrazol (PTZ)-induced chemical kindling and associated biochemical parameters in mice

Brain cyclooxygenases (COX), the rate-limiting enzyme in prostaglandin synthesis, is rapidly and transiently induced by convulsions in hippocampal and cortical neurons. Previous studies have explored the protective effect of naproxen (non-selective COX-inhibitor) or rofecoxib (selective COX-2 inhibitor) against chemical kindling in mice. With this background, the present study was designed to explore the possible effect of nimesulide (a preferential COX-2 inhibitor) against pentylenetetrazol (PTZ)-induced kindling epilepsy in mice. To induce kindling, PTZ was injected in a subconvulsive dose (40 mg/kg, i.p.) every other day for 15 days. Nimesulide (2.5 or 5 mg/kg, p.o.) was administered each day 45 min before either PTZ or vehicle challenge. The intensity of kindling was assessed immediately after PTZ administration according to a prevalidated scoring scale. On 16th day i.e. 24 h after the last dose of PTZ, animals were sacrificed and various biochemical parameters were assessed in the whole brain. Compared with normal control group, PTZ-kindled mice had significantly higher levels of malondialdehyde, nitrite, myeloperoxidase but had lower levels of reduced glutathione in the whole brain homogenate. Chronic treatment with nimesulide (2.5 or 5 mg/kg, p.o.) for 15 days showed significant decrease in kindling score and could play a role in controlling the accompanying biochemical alterations due to PTZ. These results suggested that nimesulide, a preferential COX-2 inhibitor offered neuroprotection against PTZ-induced kindling in mice.

Striatal and nigral COX-2 expression after chronic typical and atypical neuroleptic administration in rats

Haloperidol, but not clozapine, induces dopaminergic nigrostriatal degeneration. However, the mechanisms by which haloperidol causes neurotoxicity are not fully understood. An increase in cyclooxygenase-2 (COX-2) expression has been observed correlated with nigrostriatal degeneration. We investigated the modifications of striatal and nigral COX-2 expression induced by chronic haloperidol and clozapine administration. Rats were treated for 21 days with: haloperidol (1 mg/kg), clozapine (1 mg/kg) or saline. No significant differences were observed in striatal and nigral COX-2 expression between haloperidol and clozapine-treated animals. This observation might suggest that nigral COX-2 expression is not the underlying mechanisms involved in haloperidol-induced dopaminergic neurodegeneration.

Ischemic preconditioning via epsilon protein kinase C activation requires cyclooxygenase-2 activation in vitro

The signaling pathway of cyclooxygenase-2 (COX-2) induction following ischemic preconditioning (IPC) in brain remains undefined. To determine role of COX-2 in ischemic preconditioning, we used two in vitro models: mixed cortical neuron/astrocyte cell cultures and organotypic hippocampal slice cultures. We simulated IPC by exposing cell or slice cultures to 1 h or 15 min of oxygen/glucose deprivation (OGD), respectively, 48 h prior to ischemia. To mimic ischemia in vitro, we exposed cell or slice cultures to OGD of 4 h or 40 min, respectively. In cell cultures, these experiments revealed that COX-2 induction peaked at 24 h following IPC in cell culture. Inhibition of COX-2 activation with 50 microM NS-398 (a COX-2 selective inhibitor) abolished IPC-mediated neuroprotection in both in vitro models. Next, we tested whether epsilon protein kinase C (epsilonPKC) and extracellular signal regulated kinase 1/2 (ERK1/2) activation was involved in IPC-mediated neuroprotection and COX-2 expression in cell culture. Cell cultures were treated with an epsilonPKC-specific activating peptide (psiepsilonRACK, 100 nM) for 1 h, and 48 h later were exposed to OGD. epsilonPKC activation increased ERK1/2 phosphorylation and COX-2 induction and conferred neuroprotection similar to IPC. Additionally, inhibition of either epsilonPKC or ERK1/2 activation abolished COX-2 expression and neuroprotection due to ischemic preconditioning. These results demonstrate a crucial role for the epsilonPKC-->ERK1/2-->COX-2 pathway in the induction of neuroprotection via ischemic preconditioning.

Effect of cyclooxygenase inhibitors on pentylenetetrazol (PTZ)-induced convulsions: Possible mechanism of action

Cyclooxygenase (COX) is reported to play a significant role in neurodegenerative and neuropsychiatric disorders, and may play a significant role in the pathogenesis of epilepsy. Various neurotransmitter abnormalities, especially of GABA and glutamate, have been reported to play a key role in the pathophysiology of epilepsy. The objective of the present study was to elucidate the effect of cyclooxygenase inhibitors on pentylenetetrazol (PTZ)-induced (80 mg/kg) convulsions in mice with possible mechanism of action. Various COX-inhibitors were administered 45 min prior to the PTZ administration. Onset, duration of clonic convulsions and percentage mortality/recovery were recorded. Pretreatment with COX-inhibitors aspirin (10 and 20 mg/kg, p.o.), naproxen (7 and 14 mg/kg, p.o.), nimesulide (1-5 mg/kg, p.o.) or rofecoxib (1-4 mg/kg, p.o.) dose-dependently showed protection against PTZ-induced convulsions. COX-2 inhibitors were more effective as compared to non-selective COX-inhibitors. Rofecoxib (1 mg/kg) or nimesulide (1 mg/kg) also enhanced the sub-protective effect of diazepam or muscimol showing GABAergic modulation of COX-2 inhibitors. COX-2 inhibitors also antagonized the effect of flumazenil (4 mg/kg)- against PTZ-induced convulsions further confirming the GABAergic mechanism. In conclusion, the results of the present study strongly suggest the possible role of cyclooxygenase isoenzymes in the pathophysiology of epilepsy and the use of COX-inhibitors as an adjuvant therapy in the treatment of epilepsy.

Different parkinsonism models produce a time-dependent induction of COX-2 in the substantia nigra of rats

The present study investigated the effects on general activity, COX-2 and TH protein expression of intranigral neurotoxins LPS, MPTP or 6-OHDA infusion in rats. Results indicate that LPS produced an increase in locomotion frequency (3 and 7 days after surgery) and a strong up-regulation of COX-2 protein 16 and 24 h after surgery, as observed in the substantia nigra (SN). The MPTP model generated impairment in locomotion frequency 24 h after surgery. Besides, MPTP caused a marked up-regulation in COX-2 protein observed in the SN 16 h after surgery. Moreover, the 6-OHDA model produced severe motor impairment indicated by the decrease in locomotion (24 h) and rearing (24 h, 3 and 7 days) frequencies and also an increase in latency (24 h, 3 and 7 days) and immobility (24 h and 3 days) times. We also demonstrated an up-regulation of COX-2, which occurred in the SN 4-24 h after surgery. TH protein did not appear to be reduced in the striatum in the groups lesioned with the neurotoxins. In contrast, the TH content of SN was significantly reduced in the groups lesioned with the very same neurotoxins. For all the models analyzed, we observed no statistical differences in the expression of COX-2 in the striatum along the time-points. The results of the present study suggest that COX-2 induction patterns differ in function of the neurotoxin tested. Such time-dependent induction has been found to be relatively constant, a fact of great significance considering the importance of the neuroinflammatory process in Parkinson's disease.

Prostaglandin D2-mediated microglia/astrocyte interaction enhances astrogliosis and demyelination in twitcher

Prostaglandin (PG) D2 is well known as a mediator of inflammation. Hematopoietic PGD synthase (HPGDS) is responsible for the production of PGD2 involved in inflammatory responses. Microglial activation and astrogliosis are commonly observed during neuroinflammation, including that which occurs during demyelination. Using the genetic demyelination mouse twitcher, a model of human Krabbe's disease, we discovered that activated microglia expressed HPGDS and activated astrocytes expressed the DP1 receptor for PGD2 in the brain of these mice. Cultured microglia actively produced PGD2 by the action of HPGDS. Cultured astrocytes expressed two types of PGD2 receptor, DP1 and DP2, and showed enhanced GFAP production after stimulation of either receptor with its respective agonist. These results suggest that PGD2 plays an important role in microglia/astrocyte interaction. We demonstrated that the blockade of the HPGDS/PGD2/DP signaling pathway using HPGDS- or DP1-null twitcher mice, and twitcher mice treated with an HPGDS inhibitor, HQL-79 (4-benzhydryloxy-1-[3-(1H-tetrazol-5-yl)-propyl]piperidine), resulted in remarkable suppression of astrogliosis and demyelination, as well as a reduction in twitching and spasticity. Furthermore, we found that the degree of oligodendroglial apoptosis was also reduced in HPGDS-null and HQL-79-treated twitcher mice. These results suggest that PGD2 is the key neuroinflammatory molecule that heightens the pathological response to demyelination in twitcher mice.

Hippocampal upregulation of the cyclooxygenase-2 gene following neonatal clomipramine treatment (a model of depression)

Although a putative role has been attributed to inflammation in the pathogenesis of depressive disorders, the relationship of prostaglandins, known mediators of inflammation, and depression has not been elucidated. Clomipramine is an antidepressive drug with a pro-depressive paradoxical effect in adult rats when administrated neonatally. Using this effect as a model of depression, we investigated the differential expression of the cyclooxygenase (COX-2) gene in rat brains. Rats injected neonatally with clomipramine showed depressive-like symptoms in adulthood, as well as decreased levels of the brain-derived neurotrophic factor (BDNF) and a quantitative differential expression of the COX-2 gene (Real Time PCR) and protein (immunohistochemistry) in the hippocampus. As evidenced, the relationship between a key enzyme in the prostaglandin synthesis and biological and behavioral depression-like changes opens an interesting line of investigation regarding the molecular bases of depression and its potential treatment through immunomodulatory drugs.

Profiling of eicosanoid production in the rat hippocampus during kainic acid-induced seizure: dual phase regulation and differential involvement of COX-1 and COX-2

Kainic acid (KA)-induced seizure in rat involves eicosanoid production in the brain, but their production mechanism and biological functions are poorly understood. We profiled the eicosanoid production during KA-induced seizure by a comprehensive lipidomics analysis using liquid chromatography-tandem mass spectrometry. Systemic KA administration caused production of large amounts of prostaglandin (PG) F(2alpha) and PGD(2) in the hippocampus, with smaller amounts of other PGs and hydroxyeicosatetraenoic acids. The production was biphasic, which consisted of an initial burst in the first 30 min and a sustained late phase production. The initial phase was specific to the hippocampus and was blocked by intracerebroventricular administration of KA receptor antagonists. A selective cyclooxygenase (COX)-2 inhibitor, NS398, completely inhibited the initial phase productions, except for PGD(2) and thromboxane B(2), whose productions were also dependent on COX-1. These results suggest that KA signals directly stimulate the arachidonic acid cascade in the initial phase and that COX-1 and COX-2, both constitutively expressed at low levels, differentially contribute to PG productions. In the late phase, a sustained PG production in hippocampus appears due to the increased COX-2 levels even with a limited arachidonic acid supply. The present study demonstrates a dual phase regulatory mechanism of eicosanoid production during KA-induced seizure, providing a biochemical basis for understanding the biosynthesis and roles of eicosanoids in the brain.

COX-2 inhibitors as adjunctive therapy in schizophrenia: rationale for use and evidence to date

A better understanding of the human immune system and its complex interactions has resulted in new insights into the pathoaetiological mechanisms of psychiatric disorders. As a result, new treatment options are being explored. Several findings suggest that an imbalanced immune response is involved in the pathophysiology of schizophrenia. COX-2 inhibitors are known to influence the immune system in a way that may redirect this imbalance. Based on these suggestions, the COX-2 inhibitor celecoxib has been tested as a possible adjunctive therapeutic approach in the treatment of schizophrenia. While the first trial using celecoxib as add-on therapy to an atypical antipsychotic showed a significant beneficial effect, recent studies demonstrated that this effect may be limited to patients with recent-onset schizophrenia.

Combining exercise and cyclooxygenase-2 inhibition does not ameliorate learning deficits after brain insult, despite an increase in BDNF levels

Neurodegeneration can produce behavioral impairments. Previously, we have found that inhibition of cyclooxygenase-2 activity or physical activity was neuroprotective during kainic-acid-induced neural loss. Here, we investigated the combined effect of exercise pre-insult and cyclooxygenase inhibitor treatment post-kainate-induced brain damage. However, in spite of an increase in BDNF levels, the combination did not improve behavioral performance in Morris watermaze and object exploration tasks.

Modulation of prostaglandin biosynthesis by nitric oxide and nitric oxide donors

The biosynthesis and release of nitric oxide (NO) and prostaglandins (PGs) share a number of similarities. Two major forms of nitric-oxide synthase (NOS) and cyclooxygenase (COX) enzymes have been identified to date. Under normal circumstances, the constitutive isoforms of these enzymes (constitutive NOS and COX-1) are found in virtually all organs. Their presence accounts for the regulation of several important physiological effects (e.g. antiplatelet activity, vasodilation, and cytoprotection). On the other hand, in inflammatory setting, the inducible isoforms of these enzymes (inducible NOS and COX-2) are detected in a variety of cells, resulting in the production of large amounts of proinflammatory and cytotoxic NO and PGs. The release of NO and PGs by the inducible isoforms of NOS and COX has been associated with the pathological roles of these mediators in disease states as evidenced by the use of selective inhibitors. An important link between the NOS and COX pathways was made in 1993 by Salvemini and coworkers when they demonstrated that the enhanced release of PGs, which follows inflammatory mechanisms, was nearly entirely driven by NO. Such studies raised the possibility that COX enzymes represent important endogenous "receptor" targets for modulating the multifaceted roles of NO. Since then, numerous papers have been published extending the observation across various cellular systems and animal models of disease. Furthermore, other studies have highlighted the importance of such interaction in physiology as well as in the mechanism of action of drugs such as organic nitrates. More importantly, mechanistic studies of how NO switches on/off the PG/COX pathway have been undertaken and additional pathways through which NO modulates prostaglandin production unraveled. On the other hand, NO donors conjugated with COX inhibitors have recently found new interest in the understanding of NO/COX reciprocal interaction and potential clinical use. The purpose of this article is to cover the advances which have occurred over the years, and in particular, to summarize experimental data that outline how the discovery that NO modulates prostaglandin production has impacted and extended our understanding of these two systems in physiopathological events.

Post-treatment, but not pre-treatment, with the selective cyclooxygenase-2 inhibitor celecoxib markedly enhances functional recovery from kainic acid-induced neurodegeneration

We have investigated the role of inflammation in the excitotoxicity induced by overstimulation of glutamate receptors using kainic acid, an important tool for studying functions related to excitatory amino acid transmission and for producing neuronal death, especially in areas CA1 and CA3 of the hippocampus. We hypothesised that by inhibiting one of the major components of the neuroinflammation response, after kainic acid injection, that there would be less inflammation and therefore a reduction in cell loss, an enhancement of cognitive function (using spatial learning and object exploration tasks) or both. We examined brain-derived neurotrophic factor levels, expecting that there would be a correlation between its level and subsequent recovery. Our results confirmed our hypothesis: the kainic acid injected-rats treated with celecoxib (after kainic injection) performed better in the spatial and non-spatial tasks than the kainic acid-treated group. However, there was not any improvement if celecoxib was given before kainic acid treatment, underlining also the importance of the production of prostaglandin at the beginning of inflammation.

Secretory phospholipases A2 induce neurite outgrowth in PC12 cells

sPLA(2)s (secretory phospholipases A(2)) belong to a broad and structurally diverse family of enzymes that hydrolyse the sn -2 ester bond of glycerophospholipids. We previously showed that a secreted fungal 15 kDa protein, named p15, as well as its orthologue from Streptomyces coelicolor (named Scp15) induce neurite outgrowth in PC12 cells at nanomolar concentrations. We report here that both p15 and Scp15 are members of a newly identified group of fungal/bacterial sPLA(2)s. The phospholipid-hydrolysing activity of p15 is absolutely required for neurite outgrowth induction. Mutants with a reduced PLA(2) activity exhibited a comparable reduction in neurite-inducing activity, and the ability to induce neurites closely matched the capacity of various p15 forms to promote fatty acid release from live PC12 cells. A structurally divergent member of the sPLA(2) family, bee venom sPLA(2), also induced neurites in a phospholipase activity-dependent manner, and the same effect was elicited by mouse group V and X sPLA(2)s, but not by group IB and IIA sPLA(2)s. Lysophosphatidylcholine, but not other lysophospholipids, nor arachidonic acid, elicited neurite outgrowth in an L-type Ca(2+) channel activity-dependent manner. In addition, p15-induced neuritogenesis was unaffected by various inhibitors that block arachidonic acid conversion into bioactive eicosanoids. Altogether, these results delineate a novel, Ca(2+)- and lysophosphatidylcholine-dependent neurotrophin-like role of sPLA(2)s in the nervous system.

Relationship between cyclooxygenase-2 and nitric oxide synthase-2 in rat cortex after stress

Many studies have focused on the relationships between distinct enzymatic sources of oxidative mediators. Recently, we have shown that cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (NOS-2) isoforms are up-regulated and account for oxidative damage in brain after stress. To assess the time course of these events, we have used adult male Wistar rats, some of which were immobilized for 6 h. Whereas pretreatment with the specific COX-2 inhibitor NS-398 (5 mg/kg i.p.) decreased Ca2+-independent NOS activity after 6 h of stress, pretreatment with the specific NOS-2 inhibitor 1400 W (4 mg/kg i.p.) did not decrease prostaglandin E2 (PGE2) accumulation induced by stress after 6 h. The observed effects of NS-398 and 1400 W were independent of the general response to stress--neither drug modified stress-induced corticosterone response--which might indicate a possible adaptive role for COX-2 and NOS-2 pathways in this situation. These findings are discussed as possible therapeutic targets in the context of neuropsychiatric disorders related to stress.

Induction of cyclooxygenase-2 accounts for restraint stress-induced oxidative status in rat brain

Cyclooxygenase (COX) is the rate-limiting enzyme in the metabolism of arachidonic acid into prostanoids. Although it is constitutively expressed in brain neurons, the inducible isoform (COX-2) is also upregulated in pathological conditions such as seizures, ischemia or some degenerative diseases. To assess whether COX-2 is regulated after stress, we have used adult male Wistar rats, some of which were immobilized during 6 h. An increase in PGE2 concentration occurs in brain cortex after 2-6 h of the onset of stress as well as an enhancement of COX-2 protein. Immunohistochemical studies indicate that COX-2 is expressed in the cortex and hippocampus after stress in cells with morphology of neurons. Administration of PDTC (150 mg/kg), an inhibitor of the transcription factor NF-kappaB or MK-801 (0.2 mg/kg), an N-methyl-D-aspartate receptor blocker, prevents both stress-induced increase in COX-2 activity and protein levels, suggesting an implication of these factors in the mechanism by which stress induces COX-2 in brain. To assess if COX-2 accounts for the oxidative status seen in brain after stress, a group of animals were i.p. injected with NS-398, a specific COX-2 inhibitor 1 h prior to the onset of stress. NS-398 (5 mg/kg) decreases stress-induced malondialdehyde accumulation in cortex as well as prevents the stress-induced oxidation of glutathione. Finally, NS-398 reduced Ca2+-independent inducible nitric oxide synthase (iNOS, NOS-2) activity and lowered the stress-induced accumulation of NO metabolite levels in cortex. These effects of NS-398 seem to be due to the specific inhibition of COX-2, since it has no effect on stress-induced corticosterone release, glutamate release, and NF-kappaB activation. These findings are discussed as possible damaging and/or adaptive roles for stress-induced COX-2 in the brain.

Cyclooxygenase 2 and intermittent hypoxia-induced spatial deficits in the rat

Intermittent hypoxia (IH) during sleep, a critical feature of sleep apnea, induces significant neurobehavioral deficits in the rat. Cyclooxygenase (COX)-2 is induced during stressful conditions such as cerebral ischemia and could play an important role in IH-induced learning deficits. We therefore examined COX-1 and COX-2 genes and COX-2 protein expression and activity (prostaglandin E2 [PGE2] tissue concentration) in cortical regions of rat brain after exposure to either IH (10% O2 alternating with 21% O2 every 90 seconds) or sustained hypoxia (10% O2). In addition, the effect of selective COX-2 inhibition with NS-398 on IH-induced neurobehavioral deficits was assessed. IH was associated with increased COX-2 protein and gene expression from Day 1 to Day 14 of exposure. No changes were found in COX-1 gene expression after exposure to hypoxia. IH-induced COX-2 upregulation was associated with increased PGE2 tissue levels, neuronal apoptosis, and neurobehavioral deficits. Administration of NS-398 abolished IH-induced apoptosis and PGE2 increases without modifying COX-2 mRNA expression. Furthermore, NS-398 treatment attenuated IH-induced deficits in the acquisition and retention of a spatial task in the water maze. We conclude that IH induces upregulation and activation of COX-2 in rat cortex and that COX-2 may play a role in IH-mediated neurobehavioral deficits.

Thrombin-induced microglial activation produces degeneration of nigral dopaminergic neurons in vivo

The present study examined whether thrombin-induced microglial activation could contribute to death of dopaminergic neurons in the rat substantia nigra (SN) in vivo. Seven days after thrombin injection into the SN, tyrosine hydroxylase immunohistochemistry showed a significant loss of nigral dopaminergic neurons. In parallel, thrombin-activated microglia, visualized by immunohistochemical staining using antibodies against the complement receptor type 3 (OX-42) and the major histocompatibility complex class II antigens were also observed in the SN, where degeneration of nigral neurons was found. Reverse transcription PCR at various time points demonstrated that activated microglia in vivo exhibited an early and transient expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and several proinflammatory cytokines, including interleukin 1beta (IL-1beta), IL-6, and tumor necrosis factor alpha. Western blot analysis and double-label immunohistochemistry showed an increase in the expression of iNOS and COX-2 and the colocalization of these proteins within microglia. The thrombin-induced loss of SN dopaminergic neurons was partially inhibited by NG-nitro-L-arginine methyl ester hydrochloride, an NOS inhibitor, and by DuP-697, a COX-2 inhibitor. Additional studies demonstrated that extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK) were activated in the SN as early as 30 min after thrombin injection, and that these kinases were localized within microglia. Inhibition of ERK1/2 and p38 MAPK reduced iNOS and COX-2 mRNA expression and rescued dopaminergic neurons in the SN. The present results strongly suggest that microglial activation triggered by endogenous compound(s) such as thrombin may be involved in the neuropathological processes of dopaminergic neuronal cell death that occur in Parkinson's disease.

Prostaglandin E2 is increased in amyotrophic lateral sclerosis patients

OBJECTIVES

Oxidative stress and glutamate-mediated excitotoxicity may play an important role in the etiopathogenesis of amyotrophic lateral sclerosis (ALS). Prostaglandin E2 (PGE2) activity can be associated with motor neuron death by inducing free radical formation and glutamate release from astrocytes. The aim of this study was to determine PGE2 concentration in the serum and cerebrospinal fluid (CSF) of ALS patients.

MATERIAL AND METHODS

PGE2 concentration was measured by the enzyme-linked immunosorbent method in the serum and CSF from ALS and control group patients.

RESULTS

Serum and CSF PGE2 concentration was significantly higher in the whole group of ALS patients compared with the control group patients (P < 0.05). There was no relationship between PGE2 concentration and clinical parameters of the disease, such as clinical state, type of ALS onset, and duration of the disease (P > 0.05). A significant correlation between CSF PGE2 concentration and age of control group patients was found (P < 0.05).

CONCLUSIONS

A significant increase in serum and CSF PGE2 concentration, in ALS patients observed in this study, indicates that PGE2 may play a role in neurodegeneration of ALS through oxidative damage of neurons and glutamate-mediated excitotoxicity. It suggests that inhibition of PGE2 synthesis could prevent motor neuron death. However, serum and CSF PGE2 cannot be a marker of the type of ALS onset, clinical state of patients, or the duration of the disease.

Deficits in spatial learning and synaptic plasticity induced by the rapid and competitive broad-spectrum cyclooxygenase inhibitor ibuprofen are reversed by increasing endogenous brain-derived neurotrophic factor

Cyclooxygenase (COX), which is present in two isoforms (COX1 and 2), synthesizes prostaglandins from arachidonic acid; it plays a crucial role in inflammation in both central and peripheral tissues. Here, we describe its role in synaptic plasticity and spatial learning in vivo via an effect on brain-derived neurotrophic factor (BDNF) and prostaglandin E2 (PGE2; both measured by Elisa). We found that broad-spectrum COX inhibition (BSCI) inhibits the induction of long-term potentiation (LTP; the major contemporary model of synaptic plasticity), and causes substantial and sustained deficits in spatial learning in the watermaze. Increases in BDNF and PGE2 following spatial learning and LTP were also blocked. Importantly, 4 days of prior exercise in a running wheel increased endogenous BDNF levels sufficiently to reverse the BSCI of LTP and spatial learning, and restored a parallel increase in LTP and learning-related BDNF and PGE2. In control experiments, we found that BSCI had no effect on baseline synaptic transmission or on the nonhippocampal visible-platform task; there was no evidence of gastric ulceration from BSCI. COX2 is inhibited by glucorticoids; there was no difference in blood corticosterone levels as measured by radioimmunoassay in any condition. Thus, COX plays a previously undescribed, permissive role in synaptic plasticity and spatial learning via a BDNF-associated mechanism.

Prostaglandin E2 rescues cortical neurons from amyloid beta protein-induced apoptosis

Cerebrospinal fluid prostaglandin E(2) (PGE(2)) levels are elevated in patients with Alzheimer's disease (AD), suggesting an involvement of PGE(2) in the neurodegeneration. AD is characterized by deposits of amyloid beta protein (Abeta) in various regions of the brain, e.g. the cerebral cortex. In the present study, we investigated the effects of PGE(2) on neuronal survival in primary cultures of rat cortical neurons. PGE(2) had no effect on neuronal cell viability or its morphology. Therefore, we examined the synergistic effects of PGE(2) with Abeta, a neurotoxin. Abeta caused neuronal cell death via apoptosis. PGE(2) significantly suppressed Abeta neurotoxicity, but did not promote the neurotoxicity. Furthermore, PGE(2) ameliorated Abeta-induced apoptotic features such as the condensation of chromatin and the fragmentation of DNA. Abeta increased the influx of Ca(2+) into neurons before cell death. Nimodipine, an inhibitor of the L-type voltage-sensitive calcium channel (L-VSCC), significantly reduced Abeta-potentiated Ca(2+) uptake. On the other hand, there was no effect on the Abeta-induced Ca(2+) influx by an N-VSCC blocker or P/Q-VSCC blockers. Moreover, the inhibitor of L-VSCC suppressed Abeta-induced neuronal cell death, whereas neither an N-VSCC blocker nor P/Q-VSCC blockers affected the neurotoxicity of Abeta. PGE(2) also suppressed the Abeta-induced Ca(2+) influx in a concentration-dependent manner. This study demonstrated that PGE(2) rescues cortical neurons from Abeta-induced apoptosis by reducing Ca(2+) influx in the primary culture. Furthermore, the present study suggested that the inhibition of L-VSCC contributes to the neuroprotective effect of PGE(2).

Gene transfer of the Caenorhabditis elegans n-3 fatty acid desaturase inhibits neuronal apoptosis

Previous studies have shown that n-3 polyunsaturated fatty acids (PUFAs) can exert an antiapoptotic effect on neurons. The present study was designed to investigate whether the Caenorhabditis elegans fat-1 gene encoding an n-3 fatty acid desaturase (an enzyme that converts n-6 PUFAs to corresponding n-3 PUFAs) can be expressed functionally in rat cortical neurons and whether its expression can change the ratio of n-6 : n-3 fatty acids in the cell membrane and exert an effect on neuronal apoptosis. Infection of primary rat cortical cultures with Ad-fat-1 resulted in high expression of the fat-1 gene. Lipid analysis indicated a decrease in the ratio of n-6 : n-3 PUFAs from 5.9 : 1 in control cells, to 1.45 : 1 in cells expressing the n-3 fatty acid desaturase. Accordingly, the levels of prostaglandin E2, an eicosanoid derived from n-6 PUFA, were significantly lower in cells infected with Ad-fat-1 when compared with control cells. Finally, there was a significant inhibition of growth factor withdrawal-induced apoptotic cell death in neurons expressing the fat-1 gene. These results demonstrate that expression of the fat-1 gene can inhibit apoptotic cell death in neurons and suggest that the change in the n-6 : n-3 fatty acid ratio may play a key role in this protective effect.