Prostaglandin E2 and microsomal prostaglandin E synthase-2 expression are decreased in the cyclooxygenase-2-deficient mouse brain despite compensatory induction of cyclooxygenase-1 and Ca2+-dependent phospholipase A2

Targeting memory loss with aspirin, a molecular mechanism perspective for future therapeutic approaches

Acetylsalicylic acid (ASA), also known as aspirin, was discovered in 1897 as an acetylated form of salicylate. It has been widely used for its anti-inflammatory and antiplatelet effects. It is commonly used for its cardiovascular benefits and is prescribed as secondary prophylaxis after a heart attack. Furthermore, low-dose, long-term ASA is used to reduce the risk of heart attack and stroke in individuals without prior cardiovascular disease. Acetylsalicylic acid acts as a non-selective inhibitor of cyclooxygenase (COX), which inhibits the synthesis of prostaglandins and prevents pro-inflammatory cytokines. Findings suggest that targeting cytokines and growth factors could be a potential therapeutic strategy for reducing neuroinflammation and slowing down the progression of dementia. Additionally, prostaglandins contribute to synaptic plasticity and can act as retrograde messengers in synapses. Research has implicated COX-1, one of the isoforms of the enzyme, in neuroinflammation and neurodegenerative disorders. The inhibition of COX-1 might potentially prevent impairments in working memory and reduce neuroinflammation caused by beta-amyloid proteins in some conditions, such as Alzheimer's disease (AD). Cyclooxygenase-2, an inducible form of the enzyme, is expressed in cortical and hippocampal neurons and is associated with long-term synaptic plasticity. The inhibition or knockout of COX-2 has been shown to decrease long-term potentiation, a process involved in memory formation. Studies have also demonstrated that the administration of COX-2 inhibitors impairs cognitive function and memory acquisition and recall in animal models. There remains a debate regarding the effects of aspirin on dementia and cognitive decline. Although some studies suggest a possible protective effect of non-steroidal anti-inflammatory drugs, including aspirin, against the development of AD, others have shown inconsistent evidence. This review provides an overview of the effects of ASA or its active metabolite salicylate on learning, memory, and synaptic plasticity.

The crucial role that hippocampus Cyclooxygenase-2 plays in memory

It is generally accepted that Cyclooxygenase-2 (COX-2) is activated to cause inflammation. However, COX-2 is also constitutively expressed at the postsynaptic dendrites and excitatory terminals of the cortical and spinal cord neurons. Although some evidence suggests that COX-2 release during neuronal signalling may be pivotal for regulating the function of memory, the significance of constitutively expressed COX-2 in neuron is still unclear. This research aims to discover the role of COX-2 in memory beyond neuroinflammation and to determine whether the inhibition of COX-2 can cause cognitive dysfunction by influencing dendritic plasticity and its underlying mechanism. We found COX-2 gene knockout (KO) could significantly impact the learning and memory ability, cause neuronal structure disorder and influence gamma oscillations. These might be mediated by the inhibition of prostaglandin (PG) E2/cAMP pathway and phosphorylated protein kinase A (p-PKA)-phosphorylated cAMP response element binding protein (p-CREB)-brain derived neurotrophic factor (BDNF) axis. It suggested COX-2 might play a critical role in learning, regulating neuronal structure and gamma oscillations in the hippocampus CA1 by regulating COX-2/BDNF signalling pathway.

Transcriptome of human neuroblastoma SH-SY5Y cells in response to 2B protein of enterovirus-A71

Infection with enterovirus-A71 (EV-A71) can cause hand-foot-mouth disease associated with fatal neurological complications. The host response to EV-A71 has not yet been fully elucidated, thus, hampering the development of a precise therapeutic approach. A nonstructural 2B protein of EV-A71 has been reported to involve with calcium dysregulation and apoptosis induction in human neuroblastoma SH-SY5Y cells. However, the molecular mechanism has not been delineated. To address this, comprehensive study of the gene expression from SH-SY5Y cells transfected with EV-A71 2B was carried out by RNA sequencing and transcriptomic analysis. It was found that the signature of the upregulated genes of SH-SY5Y cells expressing EV-A71 2B involved the Ca²⁺-related signaling pathways participating gene expression, inflammatory response, apoptosis, and long-term potentiation of the neuron. Protein-protein interaction network analysis revealed that the products encoded by CCL2, RELB, BIRC3, and TNFRSF9 were the most significant hub proteins in the network. It indicated that EV-A71 2B protein might play a role in immunopathogenesis of the central nervous system (CNS) which probably associated with the non-canonical NF-κB pathway. The data suggest that transcriptomic profiling can provide novel information source for studying the neuropathogenesis of EV-A71 infection leading to development of an effective therapeutic measure for CNS complications.

Abnormal dendritic morphology in the cerebellum of cyclooxygenase-2- knockin mice

Prostaglandin E2 (PGE2) is a bioactive signalling molecule metabolized from the phospholipid membranes by the enzymatic activity of cycloxygenase-2 (COX-2). In the developing brain, COX-2 constitutively regulates the production of PGE2, which is important in neuronal development. However, abnormal COX-2/PGE2 signalling has been linked to neurodevelopmental disorders including autism spectrum disorders (ASDs). We have previously demonstrated that COX-2^- -KI mice show autism-related behaviours including social deficits, repetitive behaviours and anxious behaviours. COX-2-deficient mice also have deficits in pathways involved in synaptic transmission and dendritic spine formation. In this study, we use a Golgi-COX staining method to examine sex-dependent differences in dendritic and dendritic spine morphology in neurons of COX-2^- -KI mice cerebellum compared with wild-type (WT) matched controls at postnatal day 25 (P25). We show that COX-2^- -KI mice have increased dendritic arborization closer to the cell soma and increased dendritic looping. We also observed a sex-dependent effect of the COX-2^- -KI on dendritic thickness, dendritic spine density, dendritic spine morphology, and the expression of β-actin and the actin-binding protein spinophilin. Our findings show that changes in COX-2/PGE2 signalling lead to impaired morphology of dendrites and dendritic spines in a sex-dependant manner and may contribute the pathology of the cerebellum seen in individuals with ASD. This study provides further evidence that the COX-2^- -KI mouse model can be used to study a subset of ASD pathologies.

The Role of Brain Cyclooxygenase-2 (Cox-2) Beyond Neuroinflammation: Neuronal Homeostasis in Memory and Anxiety

Cyclooxygenases are a group of heme-containing isozymes (namely Cox-1 and Cox-2) that catalyze the conversion of arachidonic acid to largely bioactive prostaglandins (PGs). Cox-1 is the ubiquitous housekeeping enzyme, and the mitogen-inducible Cox-2 is activated to cause inflammation. Interestingly, Cox-2 is constitutively expressed in the brain at the postsynaptic dendrites and excitatory terminals of the cortical and spinal cord neurons. Neuronal Cox-2 is activated in response to synaptic excitation to yield PGE₂, the predominant Cox-2 metabolite in the brain, which in turn stimulates the release of glutamate and neuronal firing in a retrograde fashion. Cox-2 is also engaged in the metabolism of new endocannabinoids from 2-arachidonoyl-glycerol to modulate their actions at presynaptic terminals. In addition to these interactions, the induction of neuronal Cox-2 is coupled to the trans-synaptic activation of the dopaminergic mesolimbic system and some serotoninergic receptors, which might contribute to the development of emotional behavior. Although much of the focus regarding the induction of Cox-2 in the brain has been centered on neuroinflammation-related neurodegenerative and psychiatric disorders, some evidence also suggests that Cox-2 release during neuronal signaling may be pivotal for the fine tuning of cortical networks to regulate behavior. This review compiles the evidence supporting the homeostatic role of neuronal Cox-2 in synaptic transmission and plasticity, since neuroinflammation is originally triggered by the induction of glial Cox-2 expression. The goal is to provide perspective on the roles of Cox-2 beyond neuroinflammation, such as those played in memory and anxiety, and whose evidence is still scant.

Muramyl dipeptide-mediated immunomodulation on monocyte subsets exerts therapeutic effects in a mouse model of Alzheimer's disease

Background

Muramyl dipeptide (MDP) is a component derived from minimal peptidoglycan motif from bacteria, and it is a ligand for the NOD2 receptor. Peripheral administration of MDP converts Ly6C^high into Ly6C^low monocytes. Previously, we have shown that Ly6C^low monocytes play crucial roles in the pathology of a mouse model of Alzheimer’s disease (AD). However, medications with mild immunomodulatory effects that solely target specific monocyte subsets, without triggering microglial activation, are rare.

Methods

Three months old APP_swe/PS1 transgenic male mice and age-matched C57BL/6 J mice were used for high frequency (2 times/week) over 6 months and low frequency (once a week) over 3 months of intraperitoneally MDP (10 mg/kg) administrations. Flow cytometry analysis of monocyte subsets in blood, and behavioral and postmortem analyses were performed.

Results

Memory tests showed mild to a strong improvement in memory function, increased expression levels of postsynaptic density protein 95 (PSD95), and low-density lipoprotein receptor-related protein 1 (LRP1), which are involved in synaptic plasticity and amyloid-beta (Aβ) elimination, respectively. In addition, we found monocyte chemoattractant protein-1(MCP-1) levels significantly increased, whereas intercellular adhesion molecule-1(ICAM-1) significantly decreased, and microglial marker (Iba1) did not change in the treatment group compared to the control. In parallel, we discovered elevated cyclooxygenase-2 (COX2) expression levels in the treated group, which might be a positive factor for synaptic activity.

Conclusions

Our results demonstrate that MDP is beneficial in both the early phase and, to some extent, later phases of the pathology in the mouse model of AD. These data open the way for potential MDP-based medications for AD.

Autism-related behaviors in the cyclooxygenase-2-deficient mouse model

Prostaglandin E2 (PGE2) is an endogenous lipid molecule involved in normal brain development. Cyclooxygenase-2 (COX2) is the main regulator of PGE2 synthesis. Emerging clinical and molecular research provides compelling evidence that abnormal COX2/PGE2 signaling is associated with autism spectrum disorder (ASD). We previously found that COX2 knockout mice had dysregulated expression of many ASD genes belonging to important biological pathways for neurodevelopment. The present study is the first to show the connection between irregular COX2/PGE2 signaling and autism-related behaviors in male and female COX2-deficient knockin, (COX)-2^- , mice at young (4-6 weeks) or adult (8-11 weeks) ages. Autism-related behaviors were prominent in male (COX)-2^- mice for most behavioral tests. In the open field test, (COX)-2^- mice traveled more than controls and adult male (COX)-2^- mice spent less time in the center indicating elevated hyperactive and anxiety-linked behaviors. (COX)-2^- mice also buried more marbles, with males burying more than females, suggesting increased anxiety and repetitive behaviors. Young male (COX)-2^- mice fell more frequently in the inverted screen test revealing motor deficits. The three-chamber sociability test found that adult female (COX)-2^- mice spent less time in the novel mouse chamber indicative of social abnormalities. In addition, male (COX)-2^- mice showed altered expression of several autism-linked genes: Wnt2, Glo1, Grm5 and Mmp9. Overall, our findings offer new insight into the involvement of disrupted COX2/PGE2 signaling in ASD pathology with age-related differences and greater impact on males. We propose that (COX)-2^- mice might serve as a novel model system to study specific types of autism.

AH6809 decreases production of inflammatory mediators by PGE2 - EP2 - cAMP signaling pathway in an experimentally induced pure cerebral concussion in rats

Increasing evidence suggests that PGE₂ metabolic pathway is involved in pathological changes of the secondary brain injury after traumatic brain injury. However, the underlying mechanisms, in particular, the correlation between various key enzymes and the brain injury, has remained to be fully explored. More specifically, it remains to be ascertained whether AH6809 (an EP2 receptor antagonist) would interfere with the downstream of the PGE₂, regulate the inflammatory mediators and improve neuronal damage in the hippocampus by PGE₂ - EP2 - cAMP signaling pathway. The expression and pathological changes of cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), microsomal prostaglandin-E synthase-1 (mPGES-1), E-prostanoid receptor 2 (EP2), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and inducible nitricoxide synthase (iNOS) in the CA1 area of hippocampus were evaluated by immunohistochemistry, Western blot and RT-PCR after pure cerebral concussion (PCC) induced by a metal pendulum closed brain injury in rats followed by AH6809 treatment. The morphology and number of neurons in CA1 region were analyzed by cresyl violet staining. The concentration of prostaglandin E₂ (PGE₂) and cyclic adenosine monophosphate (cAMP) was assayed by ELISA. Many neurons in hippocampal CA1 area appeared to undergo necrosis and the number of neurons was concomitantly reduced after PCC injury. With the passage of time, the protein and mRNA expression of various key enzymes including COX-1, COX-2 and mPGES-1, EP2 receptor, and inflammatory mediators including TNF-α, IL-1β and iNOS was increased; meanwhile, the concentration of PGE₂ and cAMP was enhanced. After PCC injury given AH6809 intervention, injury of neurons in hippocampal CA1 area was attenuated. The protein and mRNA expression of COX-1, COX-2, mPGES-1, EP2, TNF-α, IL-1β and iNOS was decreased, this was coupled with reduction of PGE₂ and cAMP. The results suggest that PGE₂ metabolic pathway is involved in secondary pathological changes of PCC. AH6809 improves the recovery of injured neurons in the hippocampal CA1 area and downregulates the inflammatory mediators by PGE₂ - EP2 - cAMP signaling pathway.

Genetic and Histological Alterations Reveal Key Role of Prostaglandin Synthase and Cyclooxygenase 1 and 2 in Traumatic Brain Injury-Induced Neuroinflammation in the Cerebral Cortex of Rats Exposed to Moderate Fluid Percussion Injury

After the initial insult in traumatic brain injury (TBI), secondary neurodegeneration occurs that is intimately associated with neuroinflammation. Prostaglandin (PG) synthases and cyclooxygenase (COX) 1 and 2 may contribute to inflammation in the brain. Temporal and spatial expression features of PG and COX1 and 2 following trauma may guide the development of antineuroinflammation strategies. Here, we examined PG synthase signaling and COX1 and 2 gene expression levels and COX-1- and 2-positive cell types and their temporal localization in TBI-induced brain in an effort to reveal their participation in the disease’s evolving neuroinflammation. Using brain samples from the cerebral cortex of rats subjected to TBI model of lateral moderate fluid percussion injury (FPI), we sought to characterize the temporal (subacute TBI) and spatial (lateral cortical lesion) brain alterations accompanying the disease progression. Temporal gene expression changes of PG synthase signaling were compared between sham-operated and TBI-treated rats using microarray pathway analysis. Moreover, we examined COX1 and 2 expression patterns and their intracellular distribution in sham-operated and TBI-treated rats by immunohistochemistry. After FPI, COX1 and 2 gene expression levels, and PGE₂ synthase increased while PGD₂ synthase decreased, suggesting that PGE₂ and PGD₂ afforded contraindicative effects of inflammation and anti-inflammation, respectively. Immunohistochemical analyses showed that both COX1 and COX2 increased in a time-dependent manner in the brain, specifically in degenerating neurons of the cortex. Interestingly, the expression of COX cell type was cell-specific, in that COX1 was particularly increased in degenerating neurons while COX2 was expressed in macrophages. In view of the dynamic temporal and spatial expression of PG, COX1 and 2 gene expression and localization in the injured brain regulating PG synthase and COX1 and 2 activity will require a careful disease-specific tailoring of treatments to abrogate the neuroinflammation-plagued secondary cell death due to TBI.

Prenatal exposure to the organophosphate insecticide chlorpyrifos enhances brain oxidative stress and prostaglandin E2 synthesis in a mouse model of idiopathic autism

BACKGROUND

Autism spectrum disorders (ASD) are emerging as polygenic and multifactorial disorders in which complex interactions between defective genes and early exposure to environmental stressors impact on the correct neurodevelopment and brain processes. Organophosphate insecticides, among which chlorpyrifos (CPF), are widely diffused environmental toxicants associated with neurobehavioral deficits and increased risk of ASD occurrence in children. Oxidative stress and dysregulated immune responses are implicated in both organophosphate neurodevelopmental effects and ASD etiopathogenesis. BTBR T+tf/J mice, a well-studied model of idiopathic autism, show several behavioral and immunological alterations found in ASD children, and we recently showed that CPF gestational exposure strengthened some of these autistic-like traits. In the present study, we aimed at investigating whether the behavioral effects of gestational CPF administration are associated with brain increased oxidative stress and altered lipid mediator profile.

METHODS

Brain levels of F2-isoprostanes (15-F2t-IsoP), as index of in vivo oxidative stress, and prostaglandin E2 (PGE2), a major arachidonic acid metabolite released by immune cells and by specific glutamatergic neuron populations mainly in cortex and hippocampus, were assessed by specific enzyme-immuno assays in brain homogenates from BTBR T+tf/J and C57Bl6/J mice, exposed during gestation to either vehicle or CPF. Measures were performed in mice of both sexes, at different postnatal stages (PNDs 1, 21, and 70).

RESULTS

At birth, BTBR T+tf/J mice exhibited higher baseline 15-F2t-IsoP levels as compared to C57Bl6/J mice, suggestive of greater oxidative stress processes. Gestational treatment with CPF-enhanced 15-F2t-IsoP and PGE2 levels in strain- and age-dependent manner, with 15-F2t-IsoP increased in BTBR T+tf/J mice at PNDs 1 and 21, and PGE2 elevated in BTBR T+tf/J mice at PNDs 21 and 70. At PND 21, CPF effects were sex-dependent being the increase of the two metabolites mainly associated with male mice. CPF treatment also induced a reduction of somatic growth, which reached statistical significance at PND 21.

CONCLUSIONS

These findings indicate that the autistic-like BTBR T+tf/J strain is highly vulnerable to environmental stressors during gestational period. The results further support the hypothesis that oxidative stress might be the link between environmental neurotoxicants such as CPF and ASD. The increased levels of oxidative stress during early postnatal life could result in delayed and long-lasting alterations in specific pathways relevant to ASD, of which PGE2 signaling represents an important one.

Formation of the early canine CL and the role of prostaglandin E2 (PGE2) in regulation of its function: an in vivo approach

The mechanisms governing corpus luteum (CL) function in domestic dogs remain not fully elucidated. The upregulated expression of cyclooxygenase 2 and prostaglandin (PG) E2 synthase (PGES) at the beginning of the canine luteal phase indicated their luteotrophic roles, and the steroidogenic activity of PGE2 in the early canine CL has been confirmed in vitro. Recently, by applying a cyclooxygenase 2 (COX2)-specific inhibitor (firocoxib [Previcox]; Merial) from the day of ovulation until the midluteal phase, the luteotrophic effects of PGs have been shown in vivo. This is a follow-up study investigating the underlying endocrine mechanisms associated with the firocoxib-mediated effects on the canine CL. Experimental groups were formed with ovariohysterectomies performed on Days 5, 10, 20, or 30 of firocoxib treatments (10 mg/kg bw/24h; TGs = treated groups). Untreated dogs served as controls. A decrease of steroidogenic acute regulatory (STAR) protein expression was observed in TGs. The expression of PGE2 synthase was significantly suppressed in TGs 5 and 10, and both PGE2 and PGF2α levels were decreased in luteal homogenates, particularly from CL in TG 5. Similarly, expression of the prolactin receptor (PRLR) was diminished in TGs 5 and 20. The expression of PGE2 receptors PTGER2 (EP2) and PTGER4 (EP4), the PG- transporter (PGT), and 15-hydroxy PG dehydrogenase (HPGD) was not affected in TGs. Our results substantiate a direct luteotrophic role of PGs in the early canine CL, i.e., by upregulating the steroidogenic machinery. Additionally, the possibility of an indirect effect on PRL function arises from the increased prolactin receptor expression in response to PGE2 treatment in canine lutein cells observed in vitro.

Lack of Microsomal Prostaglandin E 2 Synthase-1 in Bone Marrow–Derived Myeloid Cells Impairs Left Ventricular Function and Increases Mortality After Acute Myocardial Infarction

Background—

Microsomal prostaglandin E 2 synthase-1 (mPGES-1), encoded by the Ptges gene, catalyzes prostaglandin E 2 biosynthesis and is expressed by leukocytes, cardiac myocytes, and cardiac fibroblasts. Ptges −/− mice develop more left ventricle (LV) dilation, worse LV contractile function, and higher LV end-diastolic pressure than Ptges +/+ mice after myocardial infarction. In this study, we define the role of mPGES-1 in bone marrow–derived leukocytes in the recovery of LV function after coronary ligation.

Methods and Results—

Cardiac structure and function in Ptges +/+ mice with Ptges +/+ bone marrow ( BM +/+ ) and Ptges +/+ mice with Ptges −/− BM ( BM −/− ) were assessed by morphometric analysis, echocardiography, and invasive hemodynamics before and 7 and 28 days after myocardial infarction. Prostaglandin levels and prostaglandin biosynthetic enzyme gene expression were measured by liquid chromatography–tandem mass spectrometry and real-time polymerase chain reaction, immunoblotting, immunohistochemistry, and immunofluorescence microscopy, respectively. After myocardial infarction, BM −/− mice had more LV dilation, worse LV systolic and diastolic function, higher LV end-diastolic pressure, more cardiomyocyte hypertrophy, and higher mortality but similar infarct size and pulmonary edema compared with BM +/+ mice. BM −/− mice also had higher levels of COX-1 protein and more leukocytes in the infarct, but not the viable LV, than BM +/+ mice. Levels of prostaglandin E 2 were higher in the infarct and viable myocardium of BM −/− mice than in BM +/+ mice.

Conclusions—

Lack of mPGES-1 in bone marrow–derived leukocytes negatively regulates COX-1 expression, prostaglandin E 2 biosynthesis, and inflammation in the infarct and leads to impaired LV function, adverse LV remodeling, and decreased survival after acute myocardial infarction.

Disturbed brain phospholipid and docosahexaenoic acid metabolism in calcium-independent phospholipase A(2)-VIA (iPLA(2)β)-knockout mice

Calcium-independent phospholipase A(2) group VIA (iPLA(2)β) releases docosahexaenoic acid (DHA) from phospholipids in vitro. Mutations in the iPLA(2)β gene, PLA2G6, are associated with dystonia-parkinsonism and infantile neuroaxonal dystrophy. To understand the role of iPLA(2)β in brain, we applied our in vivo kinetic method using radiolabeled DHA in 4 to 5-month-old wild type (iPLA(2)β(+/+)) and knockout (iPLA(2)β(-/-)) mice, and measured brain DHA kinetics, lipid concentrations, and expression of PLA(2), cyclooxygenase (COX), and lipoxygenase (LOX) enzymes. Compared to iPLA(2)β(+/+) mice, iPLA(2)β(-/-) mice showed decreased rates of incorporation of unesterified DHA from plasma into brain phospholipids, reduced concentrations of several fatty acids (including DHA) esterified in ethanolamine- and serine-glycerophospholipids, and increased lysophospholipid fatty acid concentrations. DHA turnover in brain phospholipids did not differ between genotypes. In iPLA(2)β(-/-) mice, brain levels of iPLA(2)β mRNA, protein, and activity were decreased, as was the iPLA(2)γ (Group VIB PLA(2)) mRNA level, while levels of secretory sPLA(2)-V mRNA, protein, and activity and cytosolic cPLA(2)-IVA mRNA were increased. Levels of COX-1 protein were decreased in brain, while COX-2 protein and mRNA were increased. Levels of 5-, 12-, and 15-LOX proteins did not differ significantly between genotypes. Thus, a genetic iPLA(2)β deficiency in mice is associated with reduced DHA metabolism, profound changes in lipid-metabolizing enzyme expression (demonstrating lack of redundancy) and of phospholipid fatty acid content of brain (particularly of DHA), which may be relevant to neurologic abnormalities in humans with PLA2G6 mutations.

Imaging brain signal transduction and metabolism via arachidonic and docosahexaenoic acid in animals and humans

The polyunsaturated fatty acids (PUFAs), arachidonic acid (AA, 20:4n-6) and docosahexaenoic acid (DHA, 22:6n-3), important second messengers in brain, are released from membrane phospholipid following receptor-mediated activation of specific phospholipase A(2) (PLA(2)) enzymes. We developed an in vivo method in rodents using quantitative autoradiography to image PUFA incorporation into brain from plasma, and showed that their incorporation rates equal their rates of metabolic consumption by brain. Thus, quantitative imaging of unesterified plasma AA or DHA incorporation into brain can be used as a biomarker of brain PUFA metabolism and neurotransmission. We have employed our method to image and quantify effects of mood stabilizers on brain AA/DHA incorporation during neurotransmission by muscarinic M(1,3,5), serotonergic 5-HT(2A/2C), dopaminergic D(2)-like (D(2), D(3), D(4)) or glutamatergic N-methyl-d-aspartic acid (NMDA) receptors, and effects of inhibition of acetylcholinesterase, of selective serotonin and dopamine reuptake transporter inhibitors, of neuroinflammation (HIV-1 and lipopolysaccharide) and excitotoxicity, and in genetically modified rodents. The method has been extended for the use with positron emission tomography (PET), and can be employed to determine how human brain AA/DHA signaling and consumption are influenced by diet, aging, disease and genetics.

The role of nitric oxide in prostaglandin biology; update

The biosynthesis of nitric oxide (NO) and prostaglandin share many similarities. Two major forms of nitric oxide synthase (NOS) and cyclooxygenase (COX) have been identified: constitutive versus inducible. In general, the constitutive form functions in housekeeping and physiologic roles whereas the inducible form is up-regulated by mitogenic or inflammatory stimuli and is responsible for pathophysiological responses. The cross talk between the COX and NOS pathways was initially reported in 1993 and since then, numerous studies have been undertaken to delineate the functional consequences of this interaction as well as the potential mechanism by which each pathway interacts. This review will focus in particular on recent advances in this field that extend our understanding of these two pathways under various systems.

Cyclooxygenase expression and prostaglandin levels in central nervous system tissues during the course of chronic relapsing experimental autoimmune encephalomyelitis (EAE)

OBJECTIVE

Multiple sclerosis (MS) and its animal counterpart experimental autoimmune encephalomyelitis (EAE) have a major inflammatory component that drives and orchestrates both diseases. One particular group of mediators are the prostaglandins (PGs), which we have previously shown, through quantitation and pharmacological intervention, to be closely involved in the pathology of MS and EAE. The aim of the current study was to determine the expression of the PG-generating cyclooxygenase (COX) enzymes and the profile of PGE(2) and PGD(2), in selected central nervous system (CNS) tissues, with the development of the chronic relapsing (CR) form of EAE. In particular, the work investigates the possible relationship between the expression of COX isoenzymes and PG levels during the neurological phases of CR EAE.

METHODS

CR EAE was induced in Biozzi mice with inoculum containing lyophilised, syngeneic spinal cord emulsified in complete Freund's adjuvant. The cerebral cortex, cerebellum and spinal cord were dissected from mice during the acute, remission and relapse stages of disease with a minimum of five animals per treatment. The expression of COX-1, COX-1b variant and COX-2, in pooled samples, was determined by Western blotting. PGE(2) and PGD(2) levels in extracted samples were measured using commercial enzyme immunoassay kits.

RESULTS

COX-2 expression in spinal cords during acute disease remained unaltered and was in contrast to an enhancement of the enzyme, together with COX-1 and COX-1b, in all other sampled areas. PGE(2) and PGD(2) levels remained unchanged during the acute phase and the subsequent remission of symptoms. COX-1 and COX-1b expression was elevated in tissues during the relapse stage of CR EAE and concentrations of the prostanoids were markedly increased.

CONCLUSIONS

The study examines the implications of COX isoenzyme expression over the course of CR EAE and discusses the reported relationship between PGE(2) and PGD(2) in the instigation and resolution of CNS inflammation. Consideration is also given to the treatment of CR EAE and suggests that drugs designed to limit the inflammatory effects of the PGs should be administered prior to or during the relapse phase of the disease.

Endothelial microsomal prostaglandin E synthase-1 facilitates neurotoxicity by elevating astrocytic Ca2+ levels

Recurrent seizures may cause neuronal damage in the hippocampus. As neurons form intimate interactions with astrocytes via glutamate, this neuron-glia circuit may play a pivotal role in neuronal excitotoxicity following such seizures. On the other hand, astrocytes contact vascular endothelia with their endfeet. Recently, we found kainic acid (KA) administration induced microsomal prostaglandin E synthase-1 (mPGES-1) and prostaglandin E(2) (PGE(2)) receptor EP3 in venous endothelia and on astrocytes, respectively. In addition, mice deficient in mPGES-1 exhibited an improvement in KA-induced neuronal loss, suggesting that endothelial PGE(2) might modulate neuronal damage via astrocytes. In this study, we therefore investigated whether the functional associations between endothelia and astrocytes via endothelial mPGES-1 lead to neuronal injury using primary cultures of hippocampal slices. We first confirmed the delayed induction of endothelial mPGES-1 in the wild-type (WT) slices after KA-treatment. Next, we examined the effects of endothelial mPGES-1 on Ca(2+) levels in astrocytes, subsequent glutamate release and neuronal injury using cultured slices prepared from WT and mPGES-1 knockout mice. Moreover, we investigated which EP receptor on astrocytes was activated by PGE(2). We found that endothelial mPGES-1 produced PGE(2) that enhanced astrocytic Ca(2+) levels via EP3 receptors and increased Ca(2+)-dependent glutamate release, aggravating neuronal injury. This novel endothelium-astrocyte-neuron signaling pathway may be crucial for neuronal damage after repetitive seizures, and hence could be a new target for drug development.

Cyclooxygenase-2/microsomal prostaglandin E synthase-1 complex in the preoptic-anterior hypothalamus of the mouse: involvement through fever to intravenous lipopolysaccharide

AIM

Prostaglandin E₂ (PGE₂) is now well established as a central effector of pyrogen fever. However, questions remain on the source, local vs. blood-borne, of the compound for the early phase of the typically biphasic fever (Phases 1 and 2) to i.v. pyrogens. To verify the role of centrally formed PGE₂, we examined the cyclooxygenase (COX)/prostaglandin E synthase (PGES) complex through fever to i.v. lipopolysaccharide (LPS).

METHODS

Experiments were carried out in the conscious mouse and LPS effect was ascertained on all steps of expression - gene, protein, catalytic activity - of individual enzymes. The analysis was limited to the preoptic-anterior hypothalamus (AH/POA).

RESULTS

We found upregulation of the COX2 transcript together with an upward trend for the mPGES1 transcript during Phase 1. Coincidentally, there was a progressive increase in COX2 and mPGES1 protein expression through Phases 1 and 2. Catalytic activity for COX1 and COX2 combined was instead enhanced only in Phase 2, while mPGES1 activity remained steady at an intrinsically high level. Other COX and PGES enzymes were not modified through either Phase, and COX2/mPGES1 changes subsided with fever defervescence.

CONCLUSION

The findings confirm a key function of COX2 and mPGES1 for the synthesis of pyrogenic PGE₂ and, at the same time, document their early response to LPS. We conclude that locally formed PGE₂ in AH/POA is qualified for a role in the initiation of fever.

Cyclooxygenase-2 deficiency attenuates adipose tissue differentiation and inflammation in mice

Obesity is associated with a variety of disorders and is a significant health problem in developed countries. One factor controlling the level of adiposity is the differentiation of cells into adipocytes. Adipocyte differentiation requires expression of peroxisome proliferator-activated receptor γ (PPARγ), which is activated by ligands to regulate expression of genes involved in adipocyte differentiation. Although 15-deoxy-Δ(12,14)-prostaglandin (PG) J(2) (15d-PGJ(2)) has long been known to be a potent activator of PPARγ, the importance of its synthesis in adipose tissue in vivo is not clear. The current study utilized mice deficient in cyclooxygenase-2 (COX-2) to examine the role of COX-2-derived PGs as in vivo modulators of adiposity. As compared with strain- and age-matched wild-type controls, the genetic deficiency of COX-2 resulted in a significant reduction in total body weight and percent body fat. Although there were no significant differences in food consumption between groups, COX-2-deficient mice showed increased metabolic activity. Epididymal adipose tissue from wild-type mice produced a significantly greater level of 15d-PGJ(2), as compared with adipose tissue isolated from mice deficient in COX-2. Furthermore, production of the precursor required for 15d-PGJ(2) formation, PGD(2), was also significantly reduced in COX-2-deficient adipose tissue. The expression of markers for differentiated adipocytes was significantly reduced in adipose tissue from COX-2-deficient mice, whereas preadipocyte marker expression was increased. Macrophage-dependent inflammation was also significantly reduced in adipose tissue of COX-2-deficient mice. These findings suggest that reduced adiposity in COX-2-deficient mice results from attenuated PPARγ ligand production and adipocyte differentiation.

Cerebrovascular cyclooxygenase-1 expression, regulation, and role in hypothalamic-pituitary-adrenal axis activation by inflammatory stimuli

Systemic injection of lipopolysaccharide (LPS) is a widely used model of immune/inflammatory challenge, which can invoke a host of CNS responses, including activation of the hypothalamic-pituitary-adrenal (HPA) axis. Inducible vascular prostaglandin E(2) (PGE(2)) synthesis by endothelial (ECs) and/or perivascular cells (PVCs) (a macrophage-derived vascular cell type) is implicated in the engagement of HPA and other CNS responses, by virtue of their capacity to express cyclooxygenase-2 (COX-2) and microsomal PGE(2) synthase-1. Evidence from genetic and pharmacologic studies also supports a role for the constitutively expressed COX-1 in inflammation-induced activation of the HPA axis, although histochemical evidence to support relevant localization(s) and regulation of COX-1 expression is lacking. The present experiments fill this void in showing that COX-1 immunoreactivity (IR) and mRNA are detectable in identified PVCs and parenchymal microglia under basal conditions and is robustly expressed in these and ECs 1-3 h after intravenous injection of LPS (2 microg/kg). Confocal and electron microscopic analyses indicate distinct cellular/subcellular localizations of COX-1-IR in the three cell types. Interestingly, COX-1 expression is enhanced in ECs of brain PVC-depleted rats, supporting an anti-inflammatory role of the latter cell type. Functional involvement of COX-1 is indicated by the observation that central, but not systemic, pretreatment with the selective COX-1 inhibitor SC-560 attenuated the early phase of LPS-induced increases in adrenocorticotropin and corticosterone secretion. These findings support an involvement of COX-1 in bidirectional interplay between ECs and PVCs in initiating vascular PGE(2) and downstream HPA response to proinflammatory challenges.

Expression of cyclooxygenase-1/-2, microsomal prostaglandin-E synthase-1 and E-prostanoid receptor 2 and regulation of inflammatory mediators by PGE(2) in the amoeboid microglia in hypoxic postnatal rats and murine BV-2 cells

This study aimed to investigate the effect of hypoxia on the expression of cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), microsomal prostaglandin-E synthase (mPGES-1), E-prostanoid receptor 2 (EP2) in microglia; and the roles of EP2-cyclic adenosine monophosphate (cAMP) signaling pathway in the prostaglandin E(2) (PGE(2)) regulation of inflammatory mediators released by hypoxic BV-2 cells. Immunoexpression of COX-1, COX-2, mPGES-1 and EP2 was localized in the amoeboid microglial cells (AMC), a nascent brain macrophage in the developing brain, as confirmed by double labeling with OX-42 and lectin, specific markers of microglia. AMC emitted a more intense immunofluorescence in hypoxic rats when compared with the matching controls. In postnatal rats subjected to hypoxia, mRNA and protein expression levels of COX-1, COX-2 and mPGES-1 along with tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), inducible nitric-oxide synthase (iNOS) and PGE(2) product in the callosal tissue were significantly increased. The results were shared in the BV-2 cells except for COX-1 mRNA and protein whose levels remained unaltered. Interestingly, treatment with EP2 antagonist AH-6809 resulted in suppression of hypoxia induced EP2, IL-1beta and iNOS mRNA and protein expression, TNF-alpha protein expression and intracellular cAMP level in BV-2 cells. It is suggested that PGE(2) may regulate above inflammatory mediators in the activated microglia via EP2-cAMP signaling pathway in hypoxic conditions.

Microsomal prostaglandin E synthase-2: cellular distribution and expression in Alzheimer's disease

Nonsteroidal anti-inflammatory drugs, such as cyclooxygenase (COX)-2 inhibitors, have been unsuccessful in slowing or reversing Alzheimer's disease (AD). Thus, understanding the expression patterns of the downstream effectors for the regulation of prostaglandin synthesis may be important for understanding the pathological processes involved in AD and formulating more effective pharmacotherapeutics for this disease. In this study, we used immunofluorescence, immunohistochemistry, and Western blot analysis to compare patterns of microsomal prostaglandin E synthase (mPGES)-2 expression in the middle frontal gyrus (MFG) of AD patients and age-matched controls. In control human brain sections, mPGES-2 immunoreactivity was observed in neurons, activated microglia, and endothelium, but not in resting microglia, astrocytes, or smooth muscle cells. Microsomal PGES-2 immunoreactivity was particularly elevated in the pyramidal neurons of brains from three of five sporadic and four of five familial AD patients compared with four of five age-matched control brains that showed minimal immunoreactivity. In contrast, Western blot analysis revealed no difference in mPGES-2 levels between end-stage AD brain tissue and control brain tissue. These results suggest that in human cortex, mPGES-2 is constitutive in neurons and endothelium and induced in activated microglia. Furthermore, the high immunoreactivity of mPGES-2 in pyramidal neurons of AD brains indicates that it might have a potential role in the functional replacement of cytosolic PGES or inactive mPGES-1 in later stages of AD.

Bipolar disorder and mechanisms of action of mood stabilizers

Bipolar disorder (BD) is a major medical and social burden, whose cause, pathophysiology and treatment are not agreed on. It is characterized by recurrent periods of mania and depression (Bipolar I) or of hypomania and depression (Bipolar II). Its inheritance is polygenic, with evidence of a neurotransmission imbalance and disease progression. Patients often take multiple agents concurrently, with incomplete therapeutic success, particularly with regard to depression. Suicide is common. Of the hypotheses regarding the action of mood stabilizers in BD, the "arachidonic acid (AA) cascade" hypothesis is presented in detail in this review. It is based on evidence that chronic administration of lithium, carbamazepine, sodium valproate, or lamotrigine to rats downregulated AA turnover in brain phospholipids, formation of prostaglandin E(2), and/or expression of AA cascade enzymes, including cytosolic phospholipase A(2), cyclooxygenase-2 and/or acyl-CoA synthetase. The changes were selective for AA, since brain docosahexaenoic or palmitic acid metabolism, when measured, was unaffected, and topiramate, ineffective in BD, did not modify the rat brain AA cascade. Downregulation of the cascade by the mood stabilizers corresponded to inhibition of AA neurotransmission via dopaminergic D(2)-like and glutamatergic NMDA receptors. Unlike the mood stabilizers, antidepressants that increase switching of bipolar depression to mania upregulated the rat brain AA cascade. These observations suggest that the brain AA cascade is a common target of mood stabilizers, and that bipolar symptoms, particularly mania, are associated with an upregulated cascade and excess AA signaling via D(2)-like and NMDA receptors. This review presents ways to test these suggestions.

Imaging elevated brain arachidonic acid signaling in unanesthetized serotonin transporter (5-HTT)-deficient mice

Certain polymorphisms reduce serotonin (5-HT) reuptake transporter (5-HTT) function and increase susceptibility to psychiatric disorders. Heterozygous (5-HTT(+/-))-deficient mice, models for humans with these polymorphisms, have elevated brain 5-HT concentrations and behavioral abnormalities. As postsynaptic 5-HT(2A/2C) receptors are coupled to cytosolic phospholipase A(2) (cPLA(2)), which releases arachidonic acid (AA) from membrane phospholipid, 5-HTT-deficient mice may have altered brain AA signaling and metabolism. To test this hypothesis, signaling was imaged as an AA incorporation coefficient k(*) in unanesthetized homozygous knockout (5-HTT(-/-)), 5-HTT(+/-) and wild-type (5-HTT(+/+)), mice following saline (baseline) or 1.5 mg/kg s.c. DOI, a partial 5-HT(2A/2C) receptor agonist. Enzyme activities, metabolite concentrations, and head-twitch responses to DOI were also measured. Baseline k(*) was widely elevated by 20-70% in brains of 5-HTT(+/-) and 5-HTT(-/-) compared to 5-HTT(+/+) mice. DOI increased k(*) in 5-HTT(+/+) mice, but decreased k(*) in 5-HTT-deficient mice. Brain cPLA(2) activity was elevated in 5-HTT-deficient mice; cyclooxygenase activity and prostaglandin E(2) and F(2alpha) and thromboxane B(2) concentrations were reduced. Head-twitch responses to DOI, although robust in 5-HTT(+/+) and 5-HTT(+/-) mice, were markedly fewer in 5-HTT(-/-) mice. Pretreatment with para-chlorophenylalanine, a 5-HT synthesis inhibitor, restored head twitches in 5-HTT(-/-) mice to levels in 5-HTT(+/+) mice. We propose that increased baseline values of k(*) in 5-HTT-deficient mice reflect tonic cPLA(2) stimulation through 5-HT(2A/2C) receptors occupied by excess 5-HT, and that reduced k(*) and head-twitch responses to DOI reflected displacement of receptor-bound 5-HT by DOI with a lower affinity. Increased baseline AA signaling in humans having polymorphisms with reduced 5-HTT function might be identified using positron emission tomography.

Prostaglandin E2 synthases in neurologic homeostasis and disease

Prostaglandin E(2) synthases (PGES) currently comprise a group of three structurally and biologically distinct molecules. These enzymes are part of an important and complex paracrine signaling system involved in a wide range of biological processes. This review focuses on the normal physiological and pathological roles of these enzymes in the nervous system. Specific topics include the role of PGES(s) in fever and sickness behavior, inflammatory pain, and neural disease. Although the field is in its early stages, ongoing development of selective PGES inhibitors for possible use in people creates a significant need for more fully understanding the biological roles of these important enzymes.

The distinct roles of cyclooxygenase-1 and -2 in neuroinflammation: implications for translational research

Cyclooxygenases (COX-1 and COX-2) are key enzymes in the conversion of arachidonic acid to prostaglandins and other lipid mediators. Because it can be induced by inflammatory stimuli, COX-2 has been classically considered as the most appropriate target for anti-inflammatory drugs. However, recent data indicate that COX-2 can mediate neuroprotection and that COX-1 is a major player in the neuroinflammatory process. We discuss the specific contributions of COX-1 and COX-2 in various neurodegenerative diseases and in models of neuroinflammation. We suggest that, owing to its predominant localization in microglia, COX-1 might be the major player in neuroinflammation, whereas COX-2, which is localized in neurons, might have a major role in models in which the neurons are directly challenged. Overall, the benefit of using COX-2 inhibitors should be carefully evaluated and COX-1 preferential inhibitors should be further investigated as a potential therapeutic approach in neurodegenerative diseases with an inflammatory component.

Cytosolic PLA2 is required for CTL-mediated immunopathology of celiac disease via NKG2D and IL-15

IL-15 and NKG2D promote autoimmunity and celiac disease by arming cytotoxic T lymphocytes (CTLs) to cause tissue destruction. However, the downstream signaling events underlying these functional properties remain unclear. Here, we identify cytosolic phospholipase A₂ (cPLA₂) as a central molecule in NKG2D-mediated cytolysis in CTLs. Furthermore, we report that NKG2D induces, upon recognition of MIC⁺ target cells, the release of arachidonic acid (AA) by CTLs to promote tissue inflammation in association with target killing. Interestingly, IL-15, which licenses NKG2D-mediated lymphokine killer activity in CTLs, cooperates with NKG2D to induce cPLA₂ activation and AA release. Finally, cPLA₂ activation in intraepithelial CTLs of celiac patients provides an in vivo pathophysiological dimension to cPLA₂ activation in CTLs. These results reveal an unrecognized link between NKG2D and tissue inflammation, which may underlie the emerging role of NKG2D in various immunopathological conditions and define new therapeutic targets.

Glucocorticoid-regulated crosstalk between arachidonic acid and endocannabinoid biochemical pathways coordinates cognitive-, neuroimmune-, and energy homeostasis-related adaptations to stress

Arachidonic acid and its derivatives constitute the major group of signaling molecules involved in the innate immune response and its communication with all cellular and systemic aspects involved on homeostasis maintenance. Glucocorticoids spread throughout the organism their influences over key enzymatic steps of the arachidonic acid biochemical pathways, leading, in the central nervous system, to a shift favoring the synthesis of anti-inflammatory endocannabinoids over proinflammatory metabolites, such as prostaglandins. This shift modifies local immune-inflammatory response and neuronal activity to ultimately coordinate cognitive, behavioral, neuroendocrine, neuroimmune, physiological, and metabolic adjustments to basal and stress conditions. In the hypothalamus, a reciprocal feedback between glucocorticoids and arachidonate-containing molecules provides a mechanism for homeostatic control. This neurochemical switch is susceptible to fine-tuning by neuropeptides, cytokines, and hormones, such as leptin and interleukin-1beta, assuring functional integration between energy homeostasis control and the immune/stress response.

Cyclooxygenase-2 in synaptic signaling

Cyclooxygenase-2 (COX-2), a rate-limiting enzyme converting arachidonic acid to prostaglandins and a key player in neuroinflammation, has been implicated in the pathogenesis of neurodegenerative diseases such as multiple sclerosis, Parkinson's and Alzheimer's diseases, and in traumatic brain injury- and ischemia-induced neuronal damage, and epileptogenesis. Accumulated information suggests that the contribution of COX-2 to neuropathology is associated with its involvement in synaptic modification. Inhibition or elevation of COX-2 has been shown to suppress or enhance excitatory glutamatergic neurotransmission and long-term potentiation (LTP). These events are mainly mediated via PGE(2), the predominant reaction product of COX-2, and the PGE(2) subtype 2 receptor (EP(2))-protein kinase A pathway. Recent evidence shows that endogenous cannabinoids are substrates for COX-2 and can be oxygenated by COX-2 to form new classes of prostaglandins (prostaglandin glycerol esters and prostaglandin ethanolamides). These COX-2 oxidative metabolites of endocannabinoids, as novel signaling mediators, modulate synaptic transmission and plasticity and cause neurodegeneration. The actions of these COX-2 metabolites are likely mediated by mitogen-activated protein kinase (MAPK) and inositol 1,4,5-trisphosphate (IP(3)) signal transduction pathways. These discoveries suggest that the contributions of COX-2 to neurotransmission and brain malfunction result not only from its conversion of arachidonic acid to classic prostaglandins but also from its oxidative metabolism of endocannabinoids to novel prostaglandins. Thus, elucidation of COX-2 in synaptic signaling may provide a mechanistic basis for designing new drugs aimed at preventing, treating or alleviating neuroinflammation-associated neurological disorders.

Neuroinflammatory response to lipopolysaccharide is exacerbated in mice genetically deficient in cyclooxygenase-2

Background

Cyclooxygenases (COX) -1 and -2 are key mediators of the inflammatory response in the central nervous system. Since COX-2 is inducible by inflammatory stimuli, it has been traditionally considered as the most appropriate target for anti-inflammatory drugs. However, the specific roles of COX-1 and COX-2 in modulating a neuroinflammatory response are unclear. Recently, we demonstrated that COX-1 deficient mice show decreased neuroinflammatory response and neuronal damage in response to lipopolysaccharide (LPS).

Methods

In this study, we investigated the role of COX-2 in the neuroinflammatory response to intracerebroventricular-injected LPS (5 μg), a model of direct activation of innate immunity, using COX-2 deficient (COX-2^-/-) and wild type (COX-2^+/+) mice, as well as COX-2^+/+ mice pretreated for 6 weeks with celecoxib, a COX-2 selective inhibitor.

Results

Twenty-four hours after LPS injection, COX-2^-/- mice showed increased neuronal damage, glial cell activation, mRNA and protein expression of markers of inflammation and oxidative stress, such as cytokines, chemokines, iNOS and NADPH oxidase. Brain protein levels of IL-1β, NADPH oxidase subunit p67^phox, and phosphorylated-signal transducer and activator of transcription 3 (STAT3) were higher in COX-2^-/- and in celecoxib-treated mice, compared to COX-2^+/+ mice. The increased neuroinflammatory response in COX-2^-/- mice was likely mediated by the upregulation of STAT3 and suppressor of cytokine signaling 3 (SOCS3).

Conclusion

These results show that inhibiting COX-2 activity can exacerbate the inflammatory response to LPS, possibly by increasing glial cells activation and upregulating the STAT3 and SOCS3 pathways in the brain.

Lipopolysaccharide and a social stressor influence behaviour, corticosterone and cytokine levels: divergent actions in cyclooxygenase-2 deficient mice and wild type controls

Administration of the endotoxin, lipopolysaccharide (LPS) diminished motor activity and increased plasma corticosterone as well as circulating levels of interleukin-1beta (IL-1beta), IL-6, tumor necrosis-factor-alpha (TNF-alpha) and IL-10. Among cyclooxygenase-2 (COX-2) knockout mice the behavioural, corticosterone and cytokine variations promoted by LPS were moderately (home cage activity, corticosterone, TNF-alpha) or largely (IL-6) reduced. However, if mice were exposed to a psychosocial stressor (social disruption associated with grouping mice with novel cage-mates after a period of isolation) coupled with LPS treatment, then the effects of the COX-2 deletion were absent, or there was a synergistic or additive elevation apparent (e.g., in the case of TNF-alpha, IL-6 and corticosterone). Evidently, COX-2 deletion may have either pro- or anti-inflammatory actions, depending upon the psychosocial context in which immune activation occurs.

Clinical significance of prostaglandin E synthase expression in gastric cancer tissue

Studies have linked microsomal prostaglandin E synthase (mPGES)-1 with gastric cancer. The purpose of this study was to determine mPGES-1, mPGES-2, and cytosolic PGES (cPGES) expression in gastric cancer and to evaluate the correlation between mPGES-1 and mPGES-2 expression and clinicopathological factors and cyclooxygenase-2 expression. PGES protein expression was examined by Western blot in gastric cancer cell lines and in biopsy samples from patients with gastric cancer. mPGES-1, mPGES-2, and cPGES protein localizations were examined immunohistochemically in 129 archival gastric cancer surgical resections. mPGES-1 protein expression was found in gastric cancer biopsies and cancer cell lines with differentiated or undifferentiated adenocarcinoma. There was no mPGES-1 expression in nonneoplastic biopsies. All cell lines and tissue samples expressed mPGES-2 and cPGES. Immunohistochemical analysis showed cancer cells expressed mPGES-1 in 47% of cases. mPGES-2 immunoreactivity was seen both in nonneoplastic glandular epithelium and cancer cells; however, cancer cell immunoreactivity was significantly more pronounced in 29% of cases. cPGES expression was constitutive both in nonneoplastic and neoplastic tissues, with no significant variation among cases. mPGES-1 and mPGES-2 expression correlated with cyclooxygenase-2 expression. mPGES-1 and mPGES-2 expression, and tumor-node-metastasis stage had independent prognostic significance under multivariate analysis in patients with gastric cancer overall and in patients with differentiated cancers. However, only tumor-node-metastasis stage and mPGES-2 expression retained independent prognostic significance in patients with poorly differentiated cancers. mPGES-1 and mPGES-2 correlate with clinicopathological factors and may be valuable prognostic factors in gastric cancer.

Altered GABAergic neurotransmission is associated with increased kainate-induced seizure in prostaglandin-endoperoxide synthase-2 deficient mice

Excitotoxicity involves over activation of brain excitatory glutamate receptors and has been implicated in neurological, neurodegenerative and neuropsychiatric diseases. Metabolism of arachidonic acid (AA) through the phospholipase A(2) (PLA(2))/prostaglandin-endoperoxide synthase (PTGS) pathway is increased after excitotoxic stimulation. However, the individual roles of the PTGS isoforms in this process are not well established. We assessed the role of the PTGS isoforms in the process of excitotoxicity by exposing mice deficient in either PTGS-1 (PTGS-1(-/-)) or PTGS-2 (PTGS-2(-/-)) to the prototypic excitotoxin, kainic acid (KA). Seizure intensity and neuronal damage were significantly elevated in KA-exposed PTGS-2(-/-), but not in PTGS-1(-/-), mice. The increased susceptibility was not associated with an alteration in KA receptor binding activity or mediated through the CB1 endocannabinoid receptor. The frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) was decreased in the CA1 pyramidal neurons of PTGS-2(-/-) mice, suggesting an alteration of GABAergic function. In wild-type mice, six weeks treatment with the PTGS-2 selective inhibitor celecoxib recapitulated the increased susceptibility to KA-induced excitotoxicity observed in PTGS-2(-/-) mice, further supporting the role of PTGS-2 in the excitotoxic process. The increased susceptibility to KA was also associated with decreased brain levels of PGE(2), a biomarker of PTGS-2 activity. Our results suggest that PTGS-2 activity and its specific products may modulate neuronal excitability by affecting GABAergic neurotransmission. Further, inhibition of PTGS-2, but not PTGS-1, may increase the susceptibility to seizures.

Chronic carbamazepine administration reduces N-methyl-D-aspartate receptor-initiated signaling via arachidonic acid in rat brain

BACKGROUND

Lithium and carbamazepine (CBZ) are used to treat mania in bipolar disorder. When given chronically to rats, both agents reduce arachidonic acid (AA) turnover in brain phospholipids and downstream AA metabolism. Lithium in rats also attenuates brain N-methyl-D-aspartic acid receptor (NMDAR) signaling via AA. We hypothesized that, like chronic lithium, chronic CBZ administration to rats would reduce NMDAR-mediated signaling via AA.

METHODS

We used our fatty acid method with quantitative autoradiography to image the regional brain incorporation coefficient k* of AA, a marker of AA signaling, in unanesthetized rats that had been given 25 mg/kg/day I.P. CBZ or vehicle for 30 days, then injected with NMDA (25 mg/kg I.P.) or saline. We also measured brain concentrations of two AA metabolites, prostaglandin E(2) (PGE(2)) and thromboxane B(2) (TXB(2)).

RESULTS

In chronic vehicle-treated rats, NMDA compared with saline increased k* significantly in 69 of 82 brain regions examined, but did not change k* significantly in any region in CBZ-treated rats. In vehicle- but not CBZ-treated rats, NMDA also increased brain concentrations of PGE(2) and TXB(2).

CONCLUSIONS

Chronic CBZ administration to rats blocks increments in the AA signal k*, and in PGE(2) and TXB(2) concentrations that are produced by NMDA in vehicle-treated rats. The clinical action of antimanic drugs might involve inhibition of brain NMDAR-mediated signaling involving AA and its metabolites.

Regulation of prostaglandin E synthases: Effects of siRNA-mediated inhibition of microsomal prostaglandin E synthase-1

Prostaglandin E2 (PGE2) is a key mediator involved in several inflammatory conditions. In this study, we investigated the expression and regulation of the terminal PGE2 synthesizing enzyme prostaglandin E synthases (mPGES-1, mPGES-2 and cPGES) in gingival fibroblasts stimulated with pro-inflammatory cytokines. We used siRNA knockdown of mPGES-1 to elucidate the impact of mPGES-1 inhibition on mPGES-2 and cPGES expression, as well as on PGE2 production. The cytokines TNFalpha and IL-1beta increased protein expression and activity of mPGES-1, accompanied by increased COX-2 expression and PGE2 production. The isoenzymes mPGES-2 and cPGES, constitutively expressed at mRNA and protein levels, were unaffected by the pro-inflammatory cytokines. We show for the first time that treatment with mPGES-1 siRNA down-regulated the cytokine-induced mPGES-1 protein expression and activity. Interestingly, mPGES-1 siRNA did not affect the cytokine-stimulated PGE2 production, whereas PGF(2alpha) levels were enhanced. Neither mPGES-2 nor cPGES expression was affected by siRNA silencing of mPGES-1. Dexamethasone and MK-886 both inhibited the cytokine-induced mPGES-1 expression while mPGES-2 and cPGES expression remained unaffected. In conclusion, mPGES-1 siRNA down-regulates mPGES-1 expression, and neither mPGES-2 nor cPGES substituted for mPGES-1 in a knockdown setting in gingival fibroblasts. Moreover, mPGES-1 siRNA did not affect PGE2 levels, whereas PGF(2alpha) increased, suggesting a compensatory pathway of PGE2 synthesis when mPGES-1 is knocked down.

In search of cyclooxygenase inhibitors, anti-Mycobacterium tuberculosis and anti-malarial drugs from Thai flora and microbes

Malaria continues to be a major infectious disease of the developing world and the problem is compounded not only by the emergence of drug resistant strains but also from a lack of a vaccine. The situation for tuberculosis (TB) infection is equally problematic. Once considered a "treatable" disease for which eradication was predicted, TB has re-emerged as highly lethal, multi-drug resistant strains after the outbreak of AIDS. Worldwide, the disease causes millions of deaths annually. Similarly, treatments for chronic inflammatory diseases such as arthritis have been impeded due to the potentially lethal side effects of the new and widely prescribed non-steroidal anti-inflammatory compounds. Thais have utilized bioresources from plants and some microorganisms for medicine for thousands of years. Because of the need for new drugs to fight malaria and TB, with radically different chemical structures and mode of actions other than existing drugs, efforts have been directed towards searching for new drugs from bioresources. This is also true for anti-inflammatories. Although Thailand is considered species-rich, only a small number of potential bioresources has been investigated. This article briefly describes the pathogenesis of 2 infectious diseases, malaria and TB, and modern medicines employed in chemotherapy. Diversities of Thai flora and fungi and their chemical constituents with antagonistic properties against these 2 diseases are described in detail. Similarly, anti-inflammatory compounds, mostly cyclooxygenase (COX) inhibitors, are also described herein to demonstrate the potential of Thai bioresources to provide a wide array of compounds for treatment of diseases of a different nature.

Flurbiprofen, A Cyclooxygenase Inhibitor, Reduces the Brain Arachidonic Acid Signal in Response to the Cholinergic Muscarinic Agonist, Arecoline, in Awake Rats

Cholinergic muscarinic receptors, when stimulated by arecoline, can activate cytosolic phospholipase A(2) (cPLA(2)) to release arachidonic acid (AA) from membrane phospholipid. This signal can be imaged in the brain in vivo using quantitative autoradiography following the intravenous injection of radiolabeled AA, as an increment in a regional brain AA incorporation coefficient k*. Arecoline increases k* significantly in brain regions having muscarinic M(1,3,5) receptors in wild-type but not in cyclooxygenase (COX)-2 knockout mice. To further clarify the roles of COX enzymes in the AA signal, in this paper we imaged k* following arecoline (5 mg/kg i.p.) or saline in each of 81 brain regions of unanesthetized rats pretreated 6 h earlier with the non-selective COX inhibitor flurbiprofen (FB, 60 mg/kg s.c.) or with vehicle. Baseline values of k* were unaffected by FB treatment, which however reduced by 80% baseline brain concentrations of prostaglandin E(2) (PGE(2)) and thromboxane B(2) (TXB(2)), eicosanoids preferentially derived from AA via COX-2 and COX-1, respectively. In vehicle-pretreated rats, arecoline increased the brain PGE(2) but not TXB(2) concentration, as well as values for k* in 77 of the 81 brain regions. FB-pretreatment prevented these arecoline-provoked changes. These results and those reported in COX-2 knockout mice suggest that the AA released in brain following muscarinic receptor-mediated activation is lost via COX-2 to PGE(2) but not via COX-1 to TXB(2), and that increments in k* following arecoline largely represent replacement by unesterified plasma AA of this loss.

The roles of NADPH oxidase and phospholipases A2 in oxidative and inflammatory responses in neurodegenerative diseases

Reactive oxygen species (ROS) are produced in mammalian cells through enzymic and non-enzymic mechanisms. Although some ROS production pathways are needed for specific physiological functions, excessive production is detrimental and is regarded as the basis of numerous neurodegenerative diseases. Among enzymes producing superoxide anions, NADPH oxidase is widespread in mammalian cells and is an important source of ROS in mediating physiological and pathological processes in the cardiovascular and the CNS. ROS production is linked to the alteration of intracellular calcium homeostasis, activation of Ca(2+)-dependent enzymes, alteration of cytoskeletal proteins, and degradation of membrane glycerophospholipids. There is evolving evidence that ROS produced by NADPH oxidase regulate neuronal functions and degrade membrane phospholipids through activation of phospholipases A(2) (PLA(2)). This review is intended to cover recent studies describing ROS generation from NADPH oxidase in the CNS and its downstream activation of PLA(2), namely, the group IV cytosolic cPLA(2) and the group II secretory sPLA(2). A major focus is to elaborate the dual role of NADPH oxidase and PLA(2) in mediating the oxidative and inflammatory responses in neurodegenerative diseases, including cerebral ischemia and Alzheimer's disease. Elucidation of the signaling pathways linking NADPH oxidase with the multiple forms of PLA(2) will be important in understanding the oxidative and degradative mechanisms that underline neuronal damage and glial activation and will facilitate development of therapeutic intervention for prevention and treatment of these and other neurodegenerative diseases.

Differential gene expression patterns in cyclooxygenase-1 and cyclooxygenase-2 deficient mouse brain

Microarray analysis of gene expression in the cerebral cortex and hippocampus of mice deficient in cyclooxygenase-1 or cyclooxygenase-2 reveals that the two enzymes differentially modulate brain gene expression.

Background

Cyclooxygenase (COX)-1 and COX-2 produce prostanoids from arachidonic acid and are thought to have important yet distinct roles in normal brain function. Deletion of COX-1 or COX-2 results in profound differences both in brain levels of prostaglandin E₂ and in activation of the transcription factor nuclear factor-κB, suggesting that COX-1 and COX-2 play distinct roles in brain arachidonic acid metabolism and regulation of gene expression. To further elucidate the role of COX isoforms in the regulation of the brain transcriptome, microarray analysis of gene expression in the cerebral cortex and hippocampus of mice deficient in COX-1 (COX-1^-/-) or COX-2 (COX-2^-/-) was performed.

Results

A majority (>93%) of the differentially expressed genes in both the cortex and hippocampus were altered in one COX isoform knockout mouse but not the other. The major gene function affected in all genotype comparisons was 'transcriptional regulation'. Distinct biologic and metabolic pathways that were altered in COX^-/- mice included β oxidation, methionine metabolism, janus kinase signaling, and GABAergic neurotransmission.

Conclusion

Our findings suggest that COX-1 and COX-2 differentially modulate brain gene expression. Because certain anti-inflammatory and analgesic treatments are based on inhibition of COX activity, the specific alterations observed in this study further our understanding of the relationship of COX-1 and COX-2 with signaling pathways in brain and of the therapeutic and toxicologic consequences of COX inhibition.

Arachidonic acid metabolism in brain physiology and pathology: lessons from genetically altered mouse models

The arachidonic acid (AA) cascade involves the release of AA from the membrane phospholipids by a phospholipase A(2), followed by its subsequent metabolism to bioactive prostanoids by cyclooxygenases coupled with terminal synthases. Altered brain AA metabolism has been implicated in neurological, neurodegenerative, and psychiatric disorders. The development of genetically altered mice lacking specific enzymes of the AA cascade has helped to elucidate the individual roles of these enzymes in brain physiology and pathology. The roles of AA and its metabolites in brain physiology, with a particular emphasis on the phospholipase A(2)/cyclooxygenases pathway, are summarized, and the specific phenotypes of genetically altered mice relevant to brain physiology and neurotoxic models are discussed.

Chronic lithium administration attenuates up-regulated brain arachidonic acid metabolism in a rat model of neuroinflammation

Neuroinflammation, caused by a 6-day intracerebroventricular infusion of lipopolysaccharide (LPS) in rats, is associated with the up-regulation of brain arachidonic acid (AA) metabolism markers. Because chronic LiCl down-regulates markers of brain AA metabolism, we hypothesized that it would attenuate increments of these markers in LPS-infused rats. Incorporation coefficients k* of AA from plasma into brain, and other brain AA metabolic markers, were measured in rats that had been fed a LiCl or control diet for 6 weeks, and subjected in the last 6 days on the diet to intracerebroventricular infusion of artificial CSF or of LPS. In rats on the control diet, LPS compared with CSF infusion increased k* significantly in 28 regions, whereas the LiCl diet prevented k* increments in 18 of these regions. LiCl in CSF infused rats increased k* in 14 regions, largely belonging to auditory and visual systems. Brain cytoplasmic phospholipase A(2) activity, and prostaglandin E(2) and thromboxane B(2) concentrations, were increased significantly by LPS infusion in rats fed the control but not the LiCl diet. Chronic LiCl administration attenuates LPS-induced up-regulation of a number of brain AA metabolism markers. To the extent that this up-regulation has neuropathological consequences, lithium might be considered for treating human brain diseases accompanied by neuroinflammation.

Prostaglandin E2 synthesis in cartilage explants under compression: mPGES-1 is a mechanosensitive gene

Knee osteoarthritis (OA) results, at least in part, from overloading and inflammation leading to cartilage degradation. Prostaglandin E2 (PGE₂) is one of the main catabolic factors involved in OA. Its synthesis is the result of cyclooxygenase (COX) and prostaglandin E synthase (PGES) activities whereas NAD+-dependent 15 hydroxy prostaglandin dehydrogenase (15-PGDH) is the key enzyme implicated in the catabolism of PGE₂. For both COX and PGES, three isoforms have been described: in cartilage, COX-1 and cytosolic PGES are constitutively expressed whereas COX-2 and microsomal PGES type 1 (mPGES-1) are inducible in an inflammatory context. COX-3 (a variant of COX-1) and mPGES-2 have been recently cloned but little is known about their expression and regulation in cartilage, as is also the case for 15-PGDH. We investigated the regulation of the genes encoding COX and PGES isoforms during mechanical stress applied to cartilage explants. Mouse cartilage explants were subjected to compression (0.5 Hz, 1 MPa) for 2 to 24 hours. After determination of the amount of PGE₂ released in the media (enzyme immunoassay), mRNA and proteins were extracted directly from the cartilage explants and analyzed by real-time RT-PCR and western blotting respectively. Mechanical compression of cartilage explants significantly increased PGE₂ production in a time-dependent manner. This was not due to the synthesis of IL-1, since pretreatment with interleukin 1 receptor antagonist (IL1-Ra) did not alter the PGE₂ synthesis. Interestingly, COX-2 and mPGES-1 mRNA expression significantly increased after 2 hours, in parallel with protein expression, whereas COX-3 and mPGES-2 mRNA expression was not modified. Moreover, we observed a delayed overexpression of 15-PGDH just before the decline of PGE₂ synthesis after 18 hours, suggesting that PGE₂ synthesis could be altered by the induction of 15-PGDH expression. We conclude that, along with COX-2, dynamic compression induces mPGES-1 mRNA and protein expression in cartilage explants. Thus, the mechanosensitive mPGES-1 enzyme represents a potential therapeutic target in osteoarthritis.

Role of COX-2 in inflammatory and degenerative brain diseases

In the last decade, the potential role of cyclooxygenase-2 (COX-2) and prostaglandins (PGs) in brain diseases has been extensively studied. COX-2 over-expression has been associated with neurotoxiticy in acute conditions, such as hypoxia/ischemia and seizures, as well as in inflammatory chronic diseases, including Creutzfeldt-Jakob disease (CJD) and Alzheimer's disease (AD). However, the role played by COX-2 in neurodegenerative diseases is still controversial and further clinical and experimental studies are warranted. In addition, the emerging role of COX-2 in behavioural and cognitive functions strongly indicates that studies aimed at improving our knowledge of the physiological role of COX-2 in the central nervous system are crucial to fully understand the pros and cons of its manipulation in disabling neurological diseases.

Chronic fluoxetine increases cytosolic phospholipase A(2) activity and arachidonic acid turnover in brain phospholipids of the unanesthetized rat

RATIONALE

Fluoxetine is used to treat unipolar depression and is thought to act by increasing the concentration of serotonin (5-HT) in the synaptic cleft, leading to increased serotonin signaling. The 5-HT(2A/2C) receptor subtypes are coupled to a phospholipase A(2) (PLA(2)). We hypothesized that chronic fluoxetine would increase the brain activity of PLA(2) and the turnover rate of arachidonic acid (AA) in phospholipids of the unanesthetized rat.

MATERIALS AND METHODS

To test this hypothesis, rats were administered fluoxetine (10 mg/kg) or vehicle intraperitoneally daily for 21 days. In the unanesthetized rat, [1-(14)C]AA was infused intravenously and arterial blood plasma was sampled until the animal was killed at 5 min and its brain was subjected to chemical, radiotracer, or enzyme analysis.

RESULTS

Using equations from our fatty acid model, we found that chronic fluoxetine compared with vehicle increased the turnover rate of AA within several brain phospholipids by 75-86%. The activity and protein levels of brain cytosolic PLA(2) (cPLA(2)) but not of secretory or calcium-independent PLA(2) were increased in rats administered fluoxetine. In a separate group of animals that received chronic fluoxetine followed by a 3-day saline washout, the turnover of AA and activity and protein levels of cPLA(2) were not significantly different from controls. The protein levels of cyclooxygenases 1 and 2 as well as the concentration of prostaglandin E(2) in rats chronically administered fluoxetine did not differ significantly from controls.

CONCLUSION

The results support the hypothesis that fluoxetine increases the cPLA(2)-mediated turnover of AA within brain phospholipids.