Potential role of prostaglandins and leukotrienes in multiple sclerosis and experimental allergic encephalomyelitis

Montelukast as a repurposable additive drug for standard-efficacy multiple sclerosis treatment: Emulating clinical trials with retrospective administrative health claims data

BACKGROUND

Effective and safe treatment options for multiple sclerosis (MS) are still needed. Montelukast, a leukotriene receptor antagonist (LTRA) currently indicated for asthma or allergic rhinitis, may provide an additional therapeutic approach.

OBJECTIVE

The study aimed to evaluate the effects of montelukast on the relapses of people with MS (pwMS).

METHODS

In this retrospective case-control study, two independent longitudinal claims datasets were used to emulate randomized clinical trials (RCTs). We identified pwMS aged 18-65 years, on MS disease-modifying therapies concomitantly, in de-identified claims from Optum's Clinformatics® Data Mart (CDM) and IQVIA PharMetrics® Plus for Academics. Cases included 483 pwMS on montelukast and with medication adherence in CDM and 208 in PharMetrics Plus for Academics. We randomly sampled controls from 35,330 pwMS without montelukast prescriptions in CDM and 10,128 in PharMetrics Plus for Academics. Relapses were measured over a 2-year period through inpatient hospitalization and corticosteroid claims. A doubly robust causal inference model estimated the effects of montelukast, adjusting for confounders and censored patients.

RESULTS

pwMS treated with montelukast demonstrated a statistically significant 23.6% reduction in relapses compared to non-users in 67.3% of emulated RCTs.

CONCLUSION

Real-world evidence suggested that montelukast reduces MS relapses, warranting future clinical trials and further research on LTRAs' potential mechanism in MS.

The ketogenic diet for the treatment of glioma: insights from genetic profiling

Seizures, particularly first onset seizures in adults, are a diagnostic hallmark of brain tumors (Giglio and Villano, 2010). Unfortunately, malignant brain tumors are almost uniformly fatal due, in part, to the limitations of available therapies. Improvement in the survival of brain cancer patients requires the design of new therapeutic modalities including those that enhance currently available therapies. One potential strategy is to exploit differences in metabolic regulation between normal cells and tumor cells through dietary approaches. Previous studies have shown that a high-fat, low-carbohydrate ketogenic diet (KD) extends survival in animal models of glioma; however, the mechanism for this effect is not entirely known. We examined the effects of an experimental KD on a mouse model of glioma, and compared patterns of gene expression in tumors versus contralateral non-tumor containing brain from animals fed either a KD or a standard diet. We found that the KD reduced reactive oxygen species (ROS) production in tumor cells. Gene expression profiling demonstrated that the KD induces an overall reversion to expression patterns seen in non-tumor specimens, and a number of genes involved in modulating ROS levels and oxidative stress were altered in tumor cells. In addition, there was reduced expression of genes involved in signal transduction from growth factors known to be involved in glioma growth. These results suggest that the anti-tumor effect of the KD is multifactorial, and elucidation of genes whose expression is altered will help identify mechanisms through which ketones inhibit tumor growth, reduce seizure activity and provide neuroprotection.

COX-2 inhibitors modulate IL-12 signaling through JAK-STAT pathway leading to Th1 response in experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is a Th1 cell-mediated autoimmune disease model of multiple sclerosis (MS). IL-12 plays a crucial role in the pathogenesis of EAE/MS and inhibition of IL-12 production or IL-12 signaling was effective in preventing EAE. Cyclooxygenase (COX-2) is a key enzyme promoting inflammation in rheumatoid arthritis and tumor induced angiogenesis. Recent studies have shown that COX-2 inhibitors prevent EAE, however, their mechanism of action is not fully understood. In this study, we show that in vivo treatment (i.p.) with 100 mug COX-2 selective inhibitors (LM01, LM08, LM11, and NS398), on every other day from day 0 to 30, significantly reduced the incidence and severity of EAE in SJL/J and C57BL/6 mice. Further analyses showed that the COX-2 inhibitors reduced neural antigen-induced IL-12 production, T cell proliferation and Th1 differentiation ex vivo and in vitro. The COX-2 inhibitors also decreased IL-12-induced T cell responses through blocking tyrosine phosphorylation of JAK2, TYK2, STAT3, and STAT4 proteins in T cells. These results demonstrate that COX-2 inhibitors ameliorate EAE in association with the modulation of IL-12 signaling through JAK-STAT pathway leading to Th1 differentiation and suggest their use in the treatment of MS and other Th1 cell-mediated autoimmune diseases.

Regulation of the cyclooxygenase-2 system by interleukin-1beta through mitogen-activated protein kinase signaling pathways: a comparative study of human neuroglioma and neuroblastoma cells

Glial activation and inflammation following brain injury may initiate and maintain the process of neurodegeneration. Both glia and neurons synthesize proinflammatory mediators such as interleukin 1 beta (IL-1beta), cytosolic phospholipase A2 (cPLA2), cyclooxygenase-2 (COX-2), and prostaglandins. The molecular mechanisms by which IL-1beta regulates inflammatory genes such as cPLA2 and COX-2 in glial and neuronal cells are poorly understood. We have studied IL-1beta-mediated gene regulation in an established glial and neuronal human cell lines. We report that IL-1beta induced cPLA2 and COX-2 mRNA and protein expression and subsequent prostaglandin E2 (PGE2) release in a time-dependent manner in H4 neuroglioma cells. Both SB203580 and PD98059 [p38 and p42/44 mitogen-activated protein kinase (MAPKs) inhibitors, respectively] reduced IL-1beta-induced PGE2 production, while only SB203580 reduced both cPLA2 and COX-2 expression. Similarly, in SKNSH neuroblastoma cells, both SB203580 and PD98059 reduced IL-1beta-induced PGE2 release, with no detectable COX-2 and cPLA2 protein expression in these cells. Our results indicate that the signaling mechanisms of p38 and p42/44 MAPKs play a role in IL-1beta-mediated PGE2 release in both of these cell lines, with differences upstream at the level of cPLA(2)/COX-2 expression. IL-1beta-induced cPLA2 and COX-2 gene expression is modulated through the p38 MAPK pathway in both neuroglioma and neuroblastoma cells. Understanding the signaling mechanisms involved in IL-1beta-mediated inflammatory processes in both glia and neuronal cells may provide potential targets for therapeutic intervention for neurological disorders.

Differential modulation of microglia superoxide anion and thromboxane B2 generation by the marine manzamines

BACKGROUND

Thromboxane B2 (TXB2) and superoxide anion (O2-) are neuroinflammatory mediators that appear to be involved in the pathogenesis of several neurodegenerative diseases. Because activated-microglia are the main source of TXB2 and O2- in these disorders, modulation of their synthesis has been hypothesized as a potential therapeutic approach for neuroinflammatory disorders. Marine natural products have become a source of novel agents that modulate eicosanoids and O2- generation from activated murine and human leukocytes. With the exception of manzamine C, all other manzamines tested are characterized by a complex pentacyclic diamine linked to C-1 of the beta-carboline moiety. These marine-derived alkaloids have been reported to possess a diverse range of bioactivities including anticancer, immunostimulatory, insecticidal, antibacterial, antimalarial and antituberculosis activities. The purpose of this investigation was to conduct a structure-activity relationship study with manzamines (MZ) A, B, C, D, E and F on agonist-stimulated release of TXB2 and O2- from E. coli LPS-activated rat neonatal microglia in vitro.

RESULTS

The manzamines differentially attenuated PMA (phorbol 12-myristate 13-acetate)-stimulated TXB2 generation in the following order of decreasing potency: MZA (IC50 < 0.016 microM) > MZD (IC50 = 0.23 microM) > MZB (IC50 = 1.6 microM) > MZC (IC50 = 2.98 microM) > MZE and F (IC50 > 10 microM). In contrast, there was less effect on OPZ (opsonized zymosan)-stimulated TXB2 generation: MZB (IC50 = 1.44 microM) > MZA (IC50 = 3.16 microM) > MZC (IC50 = 3.34 microM) > MZD, MZE and MZF (IC50 > 10 microM). Similarly, PMA-stimulated O2- generation was affected differentially as follows: MZD (apparent IC50 < 0.1 microM) > MZA (IC50 = 0.1 microM) > MZB (IC50 = 3.16 microM) > MZC (IC50 = 3.43 microM) > MZE and MZF (IC50 > 10 microM). In contrast, OPZ-stimulated O2- generation was minimally affected: MZB (IC50 = 4.17 microM) > MZC (IC50 = 9.3 microM) > MZA, MZD, MZE and MZF (IC50 > 10 microM). From the structure-activity relationship perspective, contributing factors to the observed differential bioactivity on TXB2 and O2- generation are the solubility or ionic forms of MZA and D as well as changes such as saturation or oxidation of the beta carboline or 8-membered amine ring. In contrast, the fused 13-membered macrocyclic and isoquinoline ring system, and any substitutions in these rings would not appear to be factors contributing to bioactivity.

CONCLUSION

To our knowledge, this is the first experimental study that demonstrates that MZA, at in vitro concentrations that are non toxic to E. coli LPS-activated rat neonatal microglia, potently modulates PMA-stimulated TXB2 and O2- generation. MZA may thus be a lead candidate for the development of novel therapeutic agents for the modulation of TXB2 and O2- release in neuroinflammatory diseases. Marine natural products provide a novel and rich source of chemical diversity that can contribute to the design and development of new and potentially useful anti-inflammatory agents to treat neurodegenerative diseases.

Cyclooxygenase-2 (COX-2) in Inflammatory and Degenerative Brain Diseases

Cyclooxygenase (COX) catalyses the first committed step in the synthesis of prostanoids, a large family of arachidonic acid metabolites comprising prostaglandins, prostacyclin, and thromboxanes, and is a major target of non-steroidal anti-inflammatory drugs (NSAIDs). COX exists as constitutive and inducible isoforms. COX-2 is the inducible isoform, rapidly expressed in several cell types in response to growth factors, cytokines, and pro-inflammatory molecules. Since its discovery in the early 1990s, COX-2 has emerged as a major player in inflammatory reactions in peripheral tissues. By extension, COX-2 expression in brain has been associated with pro-inflammatory activities, thought to be instrumental in neurodegenerative processes of several acute and chronic diseases. However, 2 major aspects should be borne in mind. First, in the central nervous system, COX-2 is expressed under normal conditions and contributes to fundamental brain functions, such as synaptic activity, memory consolidation, and functional hyperemia. Second, "neuroinflammation" is a much more controlled reaction than inflammation in peripheral tissues, and in many cases is triggered and sustained by activation of resident cells, particularly microglia. In spite of the intense research of the last decade, the evidence of a direct role of COX-2 in neurodegenerative events is still controversial. This article will review new data in this area, focusing on some major human neurological diseases, such as multiple sclerosis, amyotrophic lateral sclerosis, Parkinson disease, Creutzfeldt-Jakob disease, and Alzheimer disease. Furthermore, the emerging role of COX-2 in behavioral and cognitive functions will be discussed.

γ-Mangostin Inhibits Inhibitor-κB Kinase Activity and Decreases Lipopolysaccharide-Induced Cyclooxygenase-2 Gene Expression in C6 Rat Glioma Cells

We investigated the effect of gamma-mangostin purified from the fruit hull of the medicinal plant Garcinia mangostana on spontaneous prostaglandin E(2) (PGE(2)) genase release and inducible cyclooxy-2 (COX-2) gene expression in C6 rat glioma cells. An 18-h treatment with gamma-mangostin potently inhibited spontaneous PGE(2) release in a concentration-dependent manner with the IC(50) value of approximately 2 microM, without affecting the cell viability even at 30 microM. By immunoblotting and reverse-transcription polymerase chain reaction, we showed that gamma-mangostin concentration-dependently inhibited lipopolysaccharide (LPS)-induced expression of COX-2 protein and its mRNA, but not those of constitutive COX-1 cyclooxygenase. Because LPS is known to stimulate inhibitor kappaB (IkappaB) kinase (IKK)-mediated phosphorylation of IkappaB followed by its degradation, which in turn induces nuclear factor (NF)-kappaB nuclear translocation leading to transcriptional activation of COX-2 gene, the effect of gamma-mangostin on the IKK/IkappaB cascade controlling the NF-kappaB activation was examined. An in vitro IKK assay using IKK protein immunoprecipitated from C6 cell extract showed that this compound inhibited IKK activity in a concentration-dependent manner, with the IC(50) value of approximately 10 microM. Consistently gamma-mangostin was also observed to decrease the LPS-induced IkappaB degradation and phosphorylation in a concentration-dependent manner, as assayed by immunoblotting. Furthermore, luciferase reporter assays showed that gamma-mangostin reduced the LPS-inducible activation of NF-kappaB-and human COX-2 gene promoter region-dependent transcription. gamma-Mangostin also inhibited rat carrageenan-induced paw edema. These results suggest that gamma-mangostin directly inhibits IKK activity and thereby prevents COX-2 gene transcription, an NF-kappaB target gene, probably to decrease the inflammatory agent-stimulated PGE(2) production in vivo, and is a new useful lead compound for anti-inflammatory drug development.

Soluble factors released by Toxoplasma gondii-infected astrocytes down-modulate nitric oxide production by gamma interferon-activated microglia and prevent neuronal degeneration

The maintenance of a benign chronic Toxoplasma gondii infection is mainly dependent on the persistent presence of gamma interferon (IFN-gamma) in the central nervous system (CNS). However, IFN-gamma-activated microglia are paradoxically involved in parasitism control and in tissue damage during a broad range of CNS pathologies. In this way, nitric oxide (NO), the main toxic metabolite produced by IFN-gamma-activated microglia, may cause neuronal injury during T. gondii infection. Despite the potential NO toxicity, neurodegeneration is not a common finding during chronic T. gondii infection. In this work, we describe a significant down-modulation of NO production by IFN-gamma-activated microglia in the presence of conditioned medium of T. gondii-infected astrocytes (CMi). The inhibition of NO production was paralleled with recovery of neurite outgrowth when neurons were cocultured with IFN-gamma-activated microglia in the presence of CMi. Moreover, the modulation of NO secretion and the neuroprotective effect were shown to be dependent on prostaglandin E(2) (PGE(2)) production by T. gondii-infected astrocytes and autocrine secretion of interleukin-10 (IL-10) by microglia. These events were partially eliminated when infected astrocytes were treated with aspirin and cocultures were treated with anti-IL-10 neutralizing antibodies and RP-8-Br cyclic AMP (cAMP), a protein kinase A inhibitor. Further, the modulatory effects of CMi were mimicked by the presence of exogenous PGE(2) and by forskolin, an adenylate cyclase activator. Altogether, these data point to a T. gondii-triggered regulatory mechanism involving PGE(2) secretion by astrocytes and cAMP-dependent IL-10 secretion by microglia. This may reduce host tissue inflammation, thus avoiding neuron damage during an established Th1 protective immune response.

A synthetic heparin-mimicking polyanionic compound inhibits central nervous system inflammation

The immunomodulating capacity of heparin led us to test the effect of the synthetic heparin-mimicking and low anticoagulant compound RG-13577 on the course of experimental autoimmune encephalomyelitis (EAE) and central nervous system (CNS) inflammation. EAE was induced in SJL mice by inoculation with whole mouse spinal cord homogenate. RG-13577, delivered intraperitoneally, inhibited the clinical signs of acute EAE and markedly ameliorated inflammation in the spinal cord, primarily by inhibiting heparanase activity in lymphocytes and astrocytes and thus impairing lymphocyte traffic. RG-13577 treatment was effective when started on day of disease induction or day 7 after induction. The low molecular weight heparin, enoxaparin, tested under the same conditions, exerted only a minor insignificant inhibitory effect. RG-13577 also inhibited the tyrosine phosphorylation of several proteins, particularly Erk1 and Erk2 of the MAP kinase signaling pathways associated with inflammation and cell proliferation. RG-13577 blocked the activity of sPLA(2) and inhibited CNS PGE(2) production both in vivo and in vitro.

Distinct roles of eicosanoids in the immune response to viral encephalitis: or why you should take NSAIDS

Prostaglandins (PGs) and leukotrienes (LTs) are important proinflammatory mediators. They are both derived from arachidonic acid (AA). Cyclooxygenase (COX), the key enzyme in transforming AA into PGs, has two isoforms: COX-1 is constitutively expressed, and COX-2, is inducible. Lipoxygenase (5-LO) is the key enzyme for LT production. PGs and LTs have been intensively studied. Release of these molecules is associated with mucus secretion, redness, pain, fever and other inflammatory manifestations. Both PGs and LTs are involved in host defense against various pathogens. In addition to mediating inflammatory symptoms, PGs might suppress some innate immune factors, including nitric oxide (NO) production. PGs also suppress a TH1 response. LTs have pathologic potential, especially in asthma. LTs also have been found to have positive roles in host defense, either against virus or bacteria. Finally, PGs and LTs might regulate the production of each other, possibly at the level of substrate competition by their enzymes. Because they are clinically important molecules, a further understanding of the roles that PGs and LTs played in host defense will have great impact on therapeutic research.

Theiler's virus infection induces the expression of cyclooxygenase-2 in murine astrocytes: inhibition by the anti-inflammatory cytokines interleukin-4 and interleukin-10

Theiler's murine encephalomyelitis virus (TMEV) causes an acute encephalomyelitis followed by a persistent infection of the central nervous system (CNS) resulting in a chronic inflammation and axonal demyelination in susceptible strains of mice. The pathogenesis of TMEV-induced demyelinating disease remains unknown, but infection of brain glial cells is a critical factor for virus persistence in the CNS. In the present study we investigated the effects of the anti-inflammatory cytokines interleukin-4 (IL-4) and interleukin-10 (IL-10) on the production of inflammatory mediators, such as prostaglandins, after infection of primary astroglial SJL/J murine cultures with TMEV. This infection resulted in a time-dependent transcription of the gene encoding cyclooxygenase-2 (COX-2) and an increased production of prostaglandin E2 (PGE(2)). Both, IL-4 but mainly, IL-10 (1 and 10 ng/ml) decreased the TMEV-induced expression of COX-2 as well as the synthesis of PGE(2). Interestingly, treatment with IL-10 completely abrogated COX-2 induction. The molecular mechanisms involved in the regulation of COX-2 expression by TMEV are unknown, but the effects of anti-inflammatory cytokines may involve the inhibition of the transcription factor nuclear factor B activity and lead to strategies capable of interrupting the inflammatory cascade triggered by TMEV in brain glial cells.

Selective inhibition of COX-2 is beneficial to mice infected intranasally with VSV

Cyclooxygenase (COX) is the key enzyme for prostaglandin (PG) synthesis. PGs are mediators of many critical physiological and inflammatory responses. There are two isoforms, COX-1 and COX-2, both of which are constitutively expressed in the central nervous system (CNS). Studies have shown that COX-1 and COX-2 are involved in physiological and pathological conditions of the brain. However, little is known about the role(s) of COX in the host defense system against a viral infection in the CNS. In this report, we used Vesicular Stomatitis Virus (VSV) induced acute encephalitis to distinguish between the contribution(s) of the two isoforms. COX-2 activity was inhibited with a COX-2 selective drug, celecoxib (Celebrex), and COX-1 was antagonized with SC560. We found that inhibition of COX-2 led to decreased viral titers, while COX-1 antagonism did not have the same effect at day 1 post infection. 5-lipooxygenase (5-LO) expression and neutrophil recruitment in the CNS were increased in celecoxib-inhibited mice. Furthermore, mice treated with celecoxib expressed more Nitric Oxide Synthase-1 (NOS-1), a crucial component of the innate immune system in the restriction of VSV propagation. The expression of type 1 cytokines, IFN-gamma and IL-12, were also increased in celecoxib-treated mice.

Inhibition of cyclooxygenase and prostaglandin E2 synthesis by gamma-mangostin, a xanthone derivative in mangosteen, in C6 rat glioma cells

The fruit hull of mangosteen, Garcinia mangostana L., has been used for many years as a medicine for treatment of skin infection, wounds, and diarrhea in Southeast Asia. In the present study, we examined the effect of gamma-mangostin, a tetraoxygenated diprenylated xanthone contained in mangosteen, on arachidonic acid (AA) cascade in C6 rat glioma cells. gamma-Mangostin had a potent inhibitory activity of prostaglandin E2 (PGE2) release induced by A23187, a Ca2+ ionophore. The inhibition was concentration-dependent, with the IC50 value of about 5 microM. gamma-Mangostin had no inhibitory effect on A23187-induced phosphorylation of p42/p44 extracellular signal regulated kinase/mitogen-activated protein kinase or on the liberation of [14C]-AA from the cells labeled with [14C]-AA. However, gamma-mangostin concentration-dependently inhibited the conversion of AA to PGE2 in microsomal preparations, showing its possible inhibition of cyclooxygenase (COX). In enzyme assay in vitro, gamma-mangostin inhibited the activities of both constitutive COX (COX-1) and inducible COX (COX-2) in a concentration-dependent manner, with the IC50 values of about 0.8 and 2 microM, respectively. Lineweaver-Burk plot analysis indicated that gamma-mangostin competitively inhibited the activities of both COX-1 and -2. This study is a first demonstration that gamma-mangostin, a xanthone derivative, directly inhibits COX activity.

Leukotrienes in patients with clinically active multiple sclerosis

OBJECTIVES

The role of leukotrienes (LTs) in the pathophysiology of multiple sclerosis (MS) has been controversially discussed in the past. Studies of LTs in the cerebrospinal fluid (CSF) revealed different results mainly because of analytical difficulties.

MATERIAL AND METHODS

In the present study we used highly sensitive and specific analytical methods for measuring LTs in the CSF as well as in urine samples from 20 patients with active MS and 20 control patients with noninflammatory neurological disorders.

RESULTS

LTB4 concentrations in CSF were almost twice as high in MS patients compared with controls (P < 0.001). CSF concentrations of the cysteinyl-LTs (LTC4, LTD4 and LTE4) as well as urinary LTE4 showed no significant differences compared with controls (P > 0.05). In addition, there was no significant association between CSF pleocytosis, clinical severity or time of disease onset.

CONCLUSIONS

The increased concentration of LTB4 in the CSF of MS patients may indicate a biological importance for this mediator in MS.

Induction of COX-2 and PGE(2) biosynthesis by IL-1beta is mediated by PKC and mitogen-activated protein kinases in murine astrocytes

Interleukin-1 (IL-1) is an important mediator of immunoinflammatory responses in the brain. In the present study, we examined whether prostaglandin E(2) (PGE(2)) production after IL-1beta stimulation is dependent upon activation of protein kinases in astroglial cells. Astrocyte cultures stimulated with IL-1beta or the phorbol ester, PMA significantly increased PGE(2) secretion. The stimulatory action of IL-1beta on PGE(2) production was totally abolished by NS-398, a specific inhibitor of cyclo-oxygenase-2 activity, as well as by the protein synthesis inhibitor cycloheximide, and the glucocorticoid dexamethasone. Furthermore, IL-1beta induced the expression of COX-2 mRNA. This occurred early at 2 h, with a maximum at 4 h and declined at 12 h. IL-1 beta treatment also induced the expression of COX-2 protein as determined by immunoblot analysis. In that case the expression of the protein remained high at least up to 12 h. Treatment of cells with protein kinase C inhibitors (H-7, bisindolylmaleimide and calphostin C) inhibited IL-1beta stimulation of PGE(2). In addition, PKC-depleted astrocyte cultures by overnight treatment with PMA no longer responded to PMA or IL-1. The ablation of the effects of PMA and IL-1beta on PGE(2) production, likely results from down-regulation of phorbol ester sensitive-PKC isoenzymes. Immunoblot analysis demonstrated the translocation of the conventional isoform cPKC-alpha from cytosol to membrane following treatment with IL-1beta. In addition, IL-1beta treatment led to activation of extracellular signal-regulated kinase (ERK1/2) and p38 subgroups of MAP kinases in astroglial cells. Interestingly, the inhibition of ERK kinase with PD 98059, as well as the inhibition of p38 MAPK with SB 203580, prevented IL-1beta-induced PGE(2) release. ERK1/2 activation by IL-1beta was sensitive to inhibition by the PKC inhibitor bisindolylmaleimide suggesting that ERK phosphorylation is a downstream signal of PKC activation. These results suggest key roles for PKC as well as for ERK1/2 and p38 MAP kinase cascades in the biosynthesis of PGE(2), likely by regulating the induction of cyclo-oxygenase-2, in IL-1beta-stimulated astroglial cells.

Protein kinase C activation reduces microglial cyclic AMP response to prostaglandin E2 by interfering with EP2 receptors

We studied the modulation by protein kinase C (PKC) of the cyclic AMP (cAMP) accumulation induced by prostaglandin (PG) E2 in rat neonatal microglial cultures. Short pretreatment of microglia with phorbol 12-myristate 13-acetate (PMA) or 4beta-phorbol 12,13-didecanoate, which activate PKC, but not with the inactive 4alpha-phorbol 12,13-didecanoate, substantially reduced cAMP accumulation induced by 1 microM PGE2. The action of PMA was dose and time dependent, and the maximal inhibition (approximately 85%) was obtained after 10-min preincubation with 100 nM PMA. The inhibitory effect of PMA was mimicked by diacylglycerol and was prevented by the PKC inhibitor calphostin C. As PMA did not affect isoproterenol- or forskolin-stimulated cAMP accumulation, we investigated whether activation of PKC decreased cAMP production by acting directly at PGE2 EP receptors. Neither sulprostone (10(-9)-10(-5) M), a potent agonist at EP3 receptors (coupled to adenylyl cyclase inhibition), nor 17-phenyl-PGE2 (10(-6)-10(-5) M), an agonist of EP1 receptors, modified cAMP accumulation induced by forskolin. On the contrary, 11-deoxy-16,16-dimethyl PGE2, which does not discriminate between EP2 and EP4 receptors, both coupled to the activation of adenylyl cyclase, and butaprost, a selective EP2 agonist, induced a dose-dependent elevation of cAMP that was largely reduced by PMA pretreatment, as in the case of PGE2. These results indicated EP2 receptors as a possible target of PKC and suggest that PKC-activating agents present in the pathological brain may prevent the cAMP-mediated microglia-deactivating function of PGE2.

Interleukin-6 expression and regulation in astrocytes

The physiological function of interleukin-6 (IL-6) within the central nervous system (CNS) is complex; IL-6 exerts neurotrophic and neuroprotective effects, and yet can also function as a mediator of inflammation, demyelination, and astrogliosis, depending on the cellular context. In the normal brain, IL-6 levels remain low. However, elevated expression occurs in injury, infection, stroke, and inflammation. Given the diverse biological functions of IL-6 and its expression in numerous CNS conditions, it is critical to understand its regulation in the brain in order to control its expression and ultimately its effects. Accumulating data demonstrate that the predominant CNS source of IL-6 is the activated astrocyte. Furthermore, a wide range of factors have been demonstrated to be involved in IL-6 regulation by astrocytes. In this review, we summarize information concerning IL-6 regulation in astrocytes, focusing on the role of proinflammatory factors, neurotransmitters, and second messengers.

Opposite effects of interferon-gamma and prostaglandin E2 on tumor necrosis factor and interleukin-10 production in microglia: a regulatory loop controlling microglia pro- and anti-inflammatory activities

Following brain injury, microglial cells produce pro- and anti-inflammatory cytokines, such as tumor necrosis factor (TNF) and interleukin-10 (IL-10). IL-10 provides an efficient autocrine mechanism for controlling microglia activation. To elucidate the mechanisms that regulate the cytokine profile of microglia, we examined the effects of several immunomodulators on IL-10 and TNF production by cultured mouse microglia. Lipopolysaccharide (LPS) was the only inducer of IL-10 and TNF gene expression and secretion. The T helper 1-type cytokine interferon-gamma (IFN-gamma) induced TNF transcripts, but not TNF secretion, and suppressed LPS-induced IL-10 mRNA and secretion by microglia. Opposite to IFN-gamma, the lipid mediator prostaglandin E2 (PGE2) enhanced the LPS-induced production of IL-10 and inhibited that of TNF. The effects of PGE2 on cytokine gene expression and secretion were antagonized by IFN-gamma. Agents that increase cAMP levels mimicked the action of PGE2 on cytokine secretion, indicating the involvement of cAMP-coupled prostaglandin receptors. In conclusion, IFN-gamma and PGE2, two mediators released at inflammatory sites, differentially regulate the production of a proinflammatory and an anti-inflammatory cytokine in microglia. We suggest that the activity and role of microglia in the damaged CNS could be finely tuned by the local concentration ratio of these mediators.

CD40-CD154 Interaction and IFN-γ Are Required for IL-12 But Not Prostaglandin E2 Secretion by Microglia During Antigen Presentation to Th1 Cells

IL-12 and PGE2 promote and inhibit, respectively, the development of Th1 responses. Production of these mediators by APC residing in the central nervous system (CNS) may be involved in the local regulation of the T cell phenotype during infectious and autoimmune CNS diseases. In the present study we have examined IL-12 and PGE2 secretion by cultured microglia and astrocytes from the mouse brain upon Ag-dependent interaction with I-Ad-restricted, OVA323–339 specific TCR transgenic Th1 and Th2 cell lines. We show that microglia, which restimulate efficiently both Th1 and Th2 cells, secrete IL-12 upon Ag-dependent interaction with Th1, but not with Th2 cells. Th1-driven IL-12 production depends on TCR ligation by MHC class II/peptide complexes, CD40 engagement on microglia, and IFN-γ secretion by activated Th1 cells. Th1 and, to a lesser extent, Th2 cells also stimulate the production of PGE2 by microglia. T cell-mediated induction of PGE2 requires MHC class II/peptide/TCR interactions but does not depend on CD40 engagement or on the presence of IFN-γ. Astrocytes, which preferentially activate Th2 cells, fail to produce IL-12 and secrete negligible amounts of PGE2 upon interaction with either Th1 or Th2 cells. These results suggest that during CNS infection or immunopathology, IL-12 produced by microglia upon Ag-specific interaction with Th1 cells may further skew the immune response to Th1, whereas the T cell-dependent production of PGE2 by microglia may represent a negative feedback mechanism, limiting the propagation of Th1 responses.

Regulation of prostanoid synthesis in microglial cells and effects of prostaglandin E2 on microglial functions

Brain prostanoid levels are normally low but can increase after ischemia and during inflammatory and infectious diseases. High prostanoid levels can affect brain function in several ways. In particular, prostaglandin E2 (PGE2) might exert both immunodepressive and proinflammatory actions. The present short review focuses on the regulation of prostanoid synthesis in microglial cultures and on the possible role of PGE2 in the down-regulation of microglial activation induced by lipopolysaccharide (LPS). Our studies were carried out using purified mouse or rat microglial cultures. LPS induced a dose-dependent expression of the inducible isoform of cyclooxygenase (COX-2), both in neonatal and adult microglial cultures. In the latter, the inducibility of COX-2 increased with time in culture, paralleling the acquisition of a more 'activated' microglial phenotype, and appeared to account for the time-dependent increase in the PGE2/TXB2 production ratio. The LPS-induced COX-2 expression and prostanoid production were down-regulated by potentially neurotoxic agents, such as nitric oxide (NO), the proinflammatory cytokine IFN-gamma (which acted both directly and indirectly, through its NO-inducing activity) and the HIV regulatory protein tat. On the other hand, COX-2 expression was up-regulated by the macrophage-deactivating cytokine TGF-beta 1, by exogenous PGE2 itself, which acted through EP2 receptors linked to cyclic AMP generation, and by non steroidal anti-inflammatory drugs. Interestingly, PGE2 utilized the same EP2 receptor-mediated signal transduction mechanism to down-regulate the expression of the inducible NO synthase and the production of NO. Largely, but not exclusively, through its effect on cyclic AMP, PGE2 can also: i) depress the expression of major histocompatibility complex class II antigens and of the costimulatory molecule B7-2; ii) down-regulate TNF and up-regulate IL-10 microglial production; iii) inhibit microglial IL-12 secretion. These observations, together with literature data on in vivo models of central nervous system (CNS) diseases, suggest a neuroprotective role of PGE2 in pathological conditions.

Effect of endotoxin and interleukin-1beta on corticotropin-releasing-factor and prostaglandin release by rat brainstem slices

This study investigated the effects of lipopolysaccharide (LPS) and interleukin-1beta (IL-1beta) on corticotropin releasing factor (CRF) and prostaglandin E2 (PGE2) release by brainstem slices in vitro. First, we characterized our experimental model and demonstrated that high potassium stimulates CRF release from rat brainstem slices in a calcium dependent way. The direct stimulation of brainstem slices with IL-1beta (3-25 pM) did not modify basal or potassium-stimulated CRF release, although IL-1beta at the dose of 25 pM increased PGE2 production. Peripheral injection (i.p.) of LPS (1-10 microg/kg) or IL-1beta (1-10 microg/kg) evoked a dose-related potentiation of the ex-vivo release of CRF and PGE2 from brainstem slices. However, central (i.c.v.) administration of LPS (10-500 ng/rat) potentiated the release of CRF and PGE2 only at the dose of 500 ng/rat, whereas IL-1beta (1-100 ng/rat) failed to modify significantly the ex vivo production of both CRF and PGE2. The results of the present study provide evidence that peripheral, rather than central, endotoxin and IL-1beta administration induce the activation of brainstem CRF and PGE2, supporting the hypothesis that peripheral cytokine signalling to the CNS is mediated by stimulation of peripheral afferents.

Opposite regulation of prostaglandin E2 synthesis by transforming growth factor-beta1 and interleukin 10 in activated microglial cultures

We have recently shown that prostaglandin E2 (PGE2) synthesis in activated microglia is tightly regulated by several substances (NO, neurotransmitters, pro-inflammatory cytokines), that might originate from intrinsic brain cells or from hematogenous cells infiltrating the brain in the course of inflammatory diseases. In view of the important immunoregulatory and neuroprotective functions recently attributed to PGE2, in the present study we extended our analysis of factors regulating PGE2 synthesis in rat microglial cultures to two anti-inflammatory and immunosuppressive cytokines, transforming growth factor beta1 (TGF-beta1) and interleukin 10 (IL-10), which share with PGE2 the ability to strongly deactivate peripheral macrophages and microglial cells. Moreover, we looked at the effect of the two cytokines on nitric oxide (NO) synthesis, another important microglial effector, whose synthesis is linked to that of PGE2 by complex feed-back mechanisms. We found that while both cytokines inhibited LPS-induced NO release, they had distinct and opposite regulatory activities on PGE2 production. In fact, while TGF-beta1 enhanced LPS-induced PGE2 synthesis, IL-10 showed an inhibitory effect. The two cytokines acted mainly by regulating the LPS-induced expression of the rate limiting enzymes of the two metabolic pathways, cyclooxygenase-2 (COX-2) and inducible NO synthase (iNOS). Moreover, TGF-beta1 counteracted the effect of the pro-inflammatory cytokine interferon-gamma, which in the same cultures has been shown to downregulate PGE2 and to upregulate NO synthesis. Although the present in vitro observations cannot be directly extrapolated to the in vivo situation, they may provide a novel clue for understanding the specific role of TGF-beta1 and IL-10 in several neurological diseases such as multiple sclerosis, in which their cerebral level was found to be elevated.

Functional characterization of substance P receptors on cultured human spinal cord astrocytes: synergism of substance P with cytokines in inducing interleukin-6 and prostaglandin E2 production

Following brain injury, astrocytes express receptors for cytokines and neuropeptides and secrete several regulatory mediators that have a well established role in inflammation, immunity, and tissue development or repair. To elucidate the role of substance P (SP), a neurotransmitter peptide of the tachykinin family, in inducing astrocyte secretory activities, we have examined the expression of SP receptors and the functional consequences of their activation in cultured astrocytes from the human embryonic brain or spinal cord. Radioligand binding studies revealed that only one type of SP receptors, the high affinity NK-1 receptor, was present on human astrocytes and that spinal cord astrocytes expressed about 6 times as many SP binding sites as brain astrocytes. Following SP treatment, a substantial inositol phosphate formation was observed in spinal cord astrocytes only. Stimulation of spinal cord astrocytes with SP alone did not induce secretion of cytokines [interleukin-6 (IL-6), granulocyte-macrophage-CSF, macrophage chemoattractant protein-1 or leukemia inhibitory factor] or prostaglandin E2 (PGE2). Interestingly, however, SP selectively potentiated the inducing effect of IL-1beta on IL-6 and PGE2 secretion by spinal cord astrocytes without affecting the IL-1-beta-evoked secretion of other cytokines. SP also enhanced the small inducing effect of tumor necrosis factor-alpha (TNF-alpha) on IL-6 and PGE2 secretion and that of transforming growth factor-beta on PGE2 secretion. These results suggest that SP can enhance immunoregulatory and neurotrophic astroglial functions mediated by IL-6 and PGE2 by acting in concert with a set of cytokines whose cerebral expression has been reported during development and in a variety of diseases.

Expression and regulation of cyclooxygenase-2 in rat microglia

Increased levels of prostanoids have been implicated in various neuropathological diseases, although little is known about their cellular sources inside the brain. In this study, we analyzed the expression of cyclooxygenase-2 (COX-2), a key enzyme in arachidonic acid metabolism, in rat microglia. COX-2 mRNA and protein as well as prostaglandin E2 formation were almost undetectable in unstimulated microglial cultures but were found to be strongly upregulated in response to lipopolysaccharide. However, in contrast to most peripheral cells, proinflammatory cytokines such as tumor necrosis factor alpha, interleukin-1 beta or interleukin-6 failed to markedly induce COX-2 expression. Similar effects were observed by analyzing transcription nuclear factor-kappa B (NF-kappa B) which was strongly activated in microglia by lipopolysaccharide but not by incubation with cytokines. Moreover, known inhibitors of NF-kappa B activation, such as dexamethasone and the antioxidant pyrrolidine dithiocarbamate, as well as the protein kinase C (PKC) inhibitor Gö6976, strongly reduced lipopolysaccharide-induced COX-2 transcription, indicating the involvement of NF-kappa B and PKC in COX-2 expression. Our results suggest that microglia may represent an important source of prostanoids in the brain, thus reinforcing their prominent role in cerebral inflammatory processes.

Multiple sclerosis: sunlight, diet, immunology and aetiology

Multiple sclerosis is more common in temperate latitudes, and migration studies indicate the involvement of an aetiological environmental factor in pre-pubertal life; the precise nature of this factor has never been identified and may perhaps have been overlooked. Here we suggest a simple explanation for the latitude gradient of multiple sclerosis, i.e. that it can be explained by the immunosuppressant effects of sunlight mediated via suppression of the secretion of the immunostimulatory neurohormone melatonin from the pineal gland. The effects of dietary fatty acids in multiple sclerosis also indicate the involvement of anti-inflammatory eicosanoids in its pathogenesis. We further suggest that the exceptions to the latitude gradient (e.g. Japan), which have previously been attributed to genetic factors, may in fact have a dietary basis. Since sunlight also influences the metabolism of fatty acids in the retina, it may also influence the development of retrobulbar optic neuritis-a common antecedent of multiple sclerosis. We suggest a re-examination of the epidemiology of multiple sclerosis based on an understanding of the immunological consequences of illumination of the retina by sunlight.

Arachidonic acid and its metabolites increase Cai in cultured rat oligodendrocytes

Fluorescence measurements of intracellular calcium (Cai) were made on cultured rat spinal cord oligodendrocytes (OLGs) using the dye fura-2. Exposure of OLGs to arachidonic acid (AA) (5-50 microM) elicited a concentration-dependent increase in Cai that was derived mainly from extracellular Ca2+. AA at 50 microM also released Ca2+ from intracellular stores. The response to AA was not decreased by nifedipine or by inhibition of Na(+)-Ca2+ exchange. AA-induced Ca2+ influx pathway was permeable to Mn2+ and Co2+ but not to Ba2+ and was not markedly influenced by depolarization, suggesting that AA activates a voltage-independent, not strictly selective, Ca2+ channel. The Cai response to AA was partially attenuated in the presence of indomethacin, indicating that the Cai response was mediated in part by cyclooxygenase products of AA. However, the AA-induced Cai response far exceeded that induced by prostaglandins and was mimicked by linoleic acid. We conclude that AA modulates Cai of OLGs via two mechanisms: 1) indirectly via cyclooxygenase pathway and 2) directly via membrane lipid-protein interaction.