Cyclopentenone prostaglandins PGA2 and 15-deoxy-delta12,14 PGJ2 suppress activation of murine microglia and astrocytes: implications for multiple sclerosis

Arachidonic acid-derived lipid mediators in multiple sclerosis pathogenesis: fueling or dampening disease progression?

BACKGROUND

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS), characterized by neuroinflammation, demyelination, and neurodegeneration. Considering the increasing prevalence among young adults worldwide and the disabling phenotype of the disease, a deeper understanding of the complexity of the disease pathogenesis is needed to ultimately improve diagnosis and personalize treatment opportunities. Recent findings suggest that bioactive lipid mediators (LM) derived from ω-3/-6 polyunsaturated fatty acids (PUFA), also termed eicosanoids, may contribute to MS pathogenesis. For example, disturbances in LM profiles and especially those derived from the ω-6 PUFA arachidonic acid (AA) have been reported in people with MS (PwMS), where they may contribute to the chronicity of neuroinflammatory processes. Moreover, we have previously shown that certain AA-derived LMs also associated with neurodegenerative processes in PwMS, suggesting that AA-derived LMs are involved in more pathological events than solely neuroinflammation. Yet, to date, a comprehensive overview of the contribution of these LMs to MS-associated pathological processes remains elusive.

MAIN BODY

This review summarizes and critically evaluates the current body of literature on the eicosanoid biosynthetic pathway and its contribution to key pathological hallmarks of MS during different disease stages. Various parts of the eicosanoid pathway are highlighted, namely, the prostanoid, leukotriene, and hydroxyeicosatetraenoic acids (HETEs) biochemical routes that include specific enzymes of the cyclooxygenases (COXs) and lipoxygenases (LOX) families. In addition, cellular sources of LMs and their potential target cells based on receptor expression profiles will be discussed in the context of MS. Finally, we propose novel therapeutic approaches based on eicosanoid pathway and/or receptor modulation to ultimately target chronic neuroinflammation, demyelination and neurodegeneration in MS.

SHORT CONCLUSION

The eicosanoid pathway is intrinsically linked to specific aspects of MS pathogenesis. Therefore, we propose that novel intervention strategies, with the aim of accurately modulating the eicosanoid pathway towards the biosynthesis of beneficial LMs, can potentially contribute to more patient- and MS subtype-specific treatment opportunities to combat MS.

Type 3 secretion system induced leukotriene B4 synthesis by leukocytes is actively inhibited by Yersinia pestis to evade early immune recognition

Subverting the host immune response to inhibit inflammation is a key virulence strategy of Yersinia pestis. The inflammatory cascade is tightly controlled via the sequential action of lipid and protein mediators of inflammation. Because delayed inflammation is essential for Y. pestis to cause lethal infection, defining the Y. pestis mechanisms to manipulate the inflammatory cascade is necessary to understand this pathogen's virulence. While previous studies have established that Y. pestis actively inhibits the expression of host proteins that mediate inflammation, there is currently a gap in our understanding of the inflammatory lipid mediator response during plague. Here we used the murine model to define the kinetics of the synthesis of leukotriene B4 (LTB4), a pro-inflammatory lipid chemoattractant and immune cell activator, within the lungs during pneumonic plague. Furthermore, we demonstrated that exogenous administration of LTB4 prior to infection limited bacterial proliferation, suggesting that the absence of LTB4 synthesis during plague contributes to Y. pestis immune evasion. Using primary leukocytes from mice and humans further revealed that Y. pestis actively inhibits the synthesis of LTB4. Finally, using Y. pestis mutants in the Ysc type 3 secretion system (T3SS) and Yersinia outer protein (Yop) effectors, we demonstrate that leukocytes recognize the T3SS to initiate the rapid synthesis of LTB4. However, several Yop effectors secreted through the T3SS effectively inhibit this host response. Together, these data demonstrate that Y. pestis actively inhibits the synthesis of the inflammatory lipid LTB4 contributing to the delay in the inflammatory cascade required for rapid recruitment of leukocytes to sites of infection.

Inhibition of Lipopolysaccharide-Induced Inflammatory Signaling by Soft Coral-Derived Prostaglandin A2 in RAW264.7 Cells

Lipopolysaccharide (LPS) is a component of the outer membrane of Gram-negative bacteria and causes inflammatory diseases. We searched MeOH extracts of collected marine organisms for inhibitors of LPS-induced nitric oxide (NO) production in RAW264.7 cells and identified prostaglandin A₂ (PGA₂) as an active compound from the MeOH extract of the soft coral Lobophytum sp. PGA₂ inhibited the production of NO and reduced the expression of inducible NO synthase (iNOS) in LPS-stimulated RAW264.7 cells. Although short preincubation with PGA₂ did not inhibit LPS-induced degradation and resynthesis of IκBα, the suppressive effect of PGA₂ was observed only after a prolonged incubation period prior to LPS treatment. In addition, PGA₂-inhibited NO production was negated by the addition of the EP4 antagonist L161982. Thus, PGA₂ was identified as an inhibitor of LPS-induced inflammatory signaling in RAW264.7 cells.

Neuroinflammatory contribution of microglia and astrocytes in fetal alcohol spectrum disorders

Ethanol exposure to the fetus during pregnancy can result in fetal alcohol spectrum disorders (FASD). These disorders vary in severity, can affect multiple organ systems, and can lead to lifelong disabilities. Damage to the central nervous system (CNS) is common in FASD, and can result in altered behavior and cognition. The incidence of FASD is alarmingly high, resulting in significant personal and societal costs. There are no cures for FASD. Alcohol can directly alter the function of neurons in the developing CNS. In addition, ethanol can alter the function of CNS glial cells including microglia and astrocytes which normally maintain homeostasis in the CNS. These glial cells can function as resident immune cells in the CNS to protect against pathogens and other insults. However, activation of glia can also damage CNS cells and lead to aberrant CNS function. Ethanol exposure to the developing brain can result in the activation of glia and neuroinflammation, which may contribute to the pathology associated with FASD. This suggests that anti-inflammatory agents may be effective in the treatment of FASD.

A Systematic Review on the Role of Arachidonic Acid Pathway in Multiple Sclerosis

BACKGROUND & OBJECTIVE

Multiple sclerosis (MS) is an inflammatory neurodegenerative disease characterized by destruction of oligodendrocytes, immune cell infiltration and demyelination. Inflammation plays a significant role in MS, and the inflammatory mediators such as eicosanoids, leukotrienes, superoxide radicals are involved in pro-inflammatory responses in MS. In this systematic review we tried to define and discuss all the findings of in vivo animal studies and human clinical trials on the potential association between arachidonic acid (AA) pathway and multiple sclerosis.

METHODS

A systematic literature search across Pubmed, Scopus, Embase and Cochrane database was conducted. This systematic review was performed according to PRISMA guidelines.

RESULTS

A total of 146 studies were included, of which 34 were conducted in animals, 58 in humans, and 60 studies reported the role of different compounds that target AA mediators or their corresponding enzymes/ receptors, and can have a therapeutic effect in MS. These results suggest that eicosanoids have significant roles in experimental autoimmune encephalomyelitis (EAE) and MS. The data from animal and human studies elucidated that PGI2, PGF2α, PGD2, isoprostanes, PGE2, PLA2, LTs are increased in MS. PLA2 inhibition modulates the progression of the disease. PGE1 analogues can be a useful option in the treatment of MS.

CONCLUSIONS

All studies reported the beneficial effects of COX and LOX inhibitors in MS. The hybrid compounds, such as COX-2 inhibitors/TP antagonists and 5-LOX inhibitors can be an innovative approach for multiple sclerosis treatment. Future work in MS should shed light in synthesizing new compounds targeting arachidonic acid pathway.

The chemistry, biology and pharmacology of the cyclopentenone prostaglandins

The cyclopentenone prostaglandins (CyPGs) are a small group compounds that are a subset of the eicosanoid superfamily, which are metabolites of arachidonic acid as well as other polyunsaturated fatty acids. The CyPGs are defined by a structural feature, namely, a five-membered carbocyclic ring containing an alfa-beta unsaturated keto group. The two most studied members are PGA₂ and 15d-PGJ₂ (15-deoxy-Δ12,14-prostaglandin J₂); other less studied members are PGA₁, Δ¹²-PGJ₂, and PGJ₂. They are involved in a number of biological activities including the ability to resolve chronic inflammation and the growth and survival of cells, particularly those of cancerous or neurological origin. Also, they can activate the prostaglandin DP2 receptor as well as the ligand-dependent transcription factor PPAR-gamma. Their ability to promote the resolution of chronic inflammation makes it of particular interest to have a good understanding of their actions. Since their discovery, the literature on the CyPGs has greatly expanded both in size and in scope; these reports are covered in the current review.

Mass spectrometry-based urinary metabolomics for the investigation on the mechanism of action of Eleutherococcus senticosus (Rupr. & Maxim.) Maxim. leaves against ischemic stroke in rats

ETHNOPHARMACOLOGICAL RELEVANCE

As a traditional Chinese medicine, Eleutherococcus senticosus (Rupr. & Maxim.) Maxim. leaves (ESL) can treat ischemic, neurasthenia, and hypertension diseases. However, only few studies have been conducted on the mechanism of action of ESL for ischemic disease treatment.

AIM OF THE STUDY

This study aimed to discover the potential biomarkers in the rats caused by ischemic stroke and build a gene-enzyme-biomarker network to explore the mechanism of ESL treatment on ischemic stroke further.

MATERIALS AND METHODS

The urinary metabolomics strategy was developed by combining UPLC-Q-TOF/MS with multivariate data analysis. The gene-enzyme-biomarker network was built by Cytoscape 3.6.0 on the basis of the potential biomarkers filtered out via urinary metabolomic analysis. Then, the potential target enzymes of ESL in the treatment of ischemic stroke were selected for further validation analysis via the ELISA kits.

RESULTS

A total of 42 biomarkers associated with ischemic stroke have been identified, among which 38 species can be adjusted by ESL, including 5'-methylthioadenosine, prostaglandin A2, l-methionine, aldosterone, 11b-hydroxyprogesterone, prostaglandin E3, dehydroepiandrosterone, taurine, 5-methoxyindoleacetate, and p-cresol glucuronide. These biomarkers were involved in several metabolic pathways, including taurine and hypotaurine, arachidonic acid, cysteine and methionine, steroid hormone biosynthesis, tryptophan, and tyrosine metabolism pathways. The gene-enzyme-biomarker network was built, and three predicted target proteins, including cyclooxygenase-2 (COX-2), monoamine oxidase (MAO), and nitric oxide synthase (NOS), were selected as the potential target enzymes for ESL in ischemic stroke treatment.

CONCLUSIONS

All results showed that ESL can play a therapeutic role in treating ischemic stroke through different pathways. This study will provide an overall view of the mechanism underlying the action of ESL against ischemic stroke.

Integrated communications between cyclooxygenase-2 and Alzheimer's disease

Elevated levels of cyclooxygenase-2 (COX-2) and prostaglandins (PGs) are involved in the pathogenesis of Alzheimer's disease (AD), which is characterized by the accumulation of β-amyloid protein (Aβ) and tau hyperphosphorylation. However, the gaps in our knowledge of the roles of COX-2 and PGs in AD have not been filled. Here, we summarized the literature showing that COX-2 dysregulation obviously influences abnormal cleavage of β-amyloid precursor protein, aggregation and deposition of Aβ in β-amyloid plaques and the inclusion of phosphorylated tau in neurofibrillary tangles. Neuroinflammation, oxidative stress, synaptic plasticity, neurotoxicity, autophagy, and apoptosis have been assessed to elucidate the mechanisms of COX-2 regulation of AD. Notably, an imbalance of these factors ultimately produces cognitive decline. The current review substantiates our understanding of the mechanisms of COX-2-induced AD and establishes foundations for the design of feasible therapeutic strategies to treat AD.-Guan, P.-P., Wang, P. Integrated communications between cyclooxygenase-2 and Alzheimer's disease.

Regulation of Immune Cell Function by PPARs and the Connection with Metabolic and Neurodegenerative Diseases

Increasing evidence points towards the existence of a bidirectional interconnection between metabolic disease and neurodegenerative disorders, in which inflammation is linking both together. Activation of members of the peroxisome proliferator-activated receptor (PPAR) family has been shown to have beneficial effects in these interlinked pathologies, and these improvements are often attributed to anti-inflammatory effects of PPAR activation. In this review, we summarize the role of PPARs in immune cell function, with a focus on macrophages and T cells, and how this was shown to contribute to obesity-associated inflammation and insulin resistance, atherosclerosis, and neurodegenerative disorders. We address gender differences as a potential explanation in observed contradictory results, and we highlight PPAR-induced metabolic changes as a potential mechanism of regulation of immune cell function through these nuclear receptors. Together, immune cell-specific activation of PPARs present a promising therapeutic approach to treat both metabolic and neurodegenerative diseases.

Astrocytes synthesize primary and cyclopentenone prostaglandins that are negative regulators of their proliferation

Recently, the modulation of cellular inflammatory responses via endogenous regulators became a major focus of medically relevant investigations. Prostaglandins (PGs) are attractive regulatory molecules, but their synthesis and mechanisms of action in brain cells are still unclear. Astrocytes are involved in manifestation of neuropathology and their proliferation is an important part of astrogliosis, a cellular neuroinflammatory response. The aims of our study were to measure synthesis of PGs by astrocytes, and evaluate their influence on proliferation in combination with addition of inflammatory pathway inhibitors. With UPLC-MS/MS analysis we detected primary PGs (1410 ± 36 pg/mg PGE₂, 344 ± 24 PGD₂) and cyclopentenone PGs (cyPGs) (87 ± 17 15d-PGJ₂, 308 ± 23 PGA₂) in the extracellular medium after 24-h lipopolysaccharide (LPS) stimulation of astrocytes. PGs reduced astrocytic proliferation with the following order of potencies (measured as inhibition at 20 μM): most potent 15d-PGJ₂ (90%) and PGA₂ (80%), > PGD₂ (40%) > 15d-PGA₂ (20%) > PGE₂ (5%), the least potent. However, PGF_2α and 2-cyclopenten-1-one, and ciglitazone and rosiglitazone (synthetic agonists of PPARγ) had no effect. Combinations of cyPGs with SC-560 or NS-398 (specific anti-inflammatory inhibitors of cyclooxygenase-1 and -2, respectively) were not effective; while GW9662 (PPARγ antagonist) or MK-741 (inhibitor of multidrug resistance protein-1, MRP1, and CysLT1 receptors) amplified the inhibitory effect of PGA₂ and 15d-PGJ₂. Although concentrations of individual PGs and cyPGs are low, all of them, as well as primary PGs suppress proliferation. Thus, the effects are potentially additive, and activated PGs synthesis suppresses proliferation in astrocytes.

Peroxisome proliferator-activated receptor γ (PPARγ): A master gatekeeper in CNS injury and repair

Peroxisome proliferator-activated receptor γ (PPARγ) is a widely expressed ligand-modulated transcription factor that governs the expression of genes involved in inflammation, redox equilibrium, trophic factor production, insulin sensitivity, and the metabolism of lipids and glucose. Synthetic PPARγ agonists (e.g. thiazolidinediones) are used to treat Type II diabetes and have the potential to limit the risk of developing brain injuries such as stroke by mitigating the influence of comorbidities. If brain injury develops, PPARγ serves as a master gatekeeper of cytoprotective stress responses, improving the chances of cellular survival and recovery of homeostatic equilibrium. In the acute injury phase, PPARγ directly restricts tissue damage by inhibiting the NFκB pathway to mitigate inflammation and stimulating the Nrf2/ARE axis to neutralize oxidative stress. During the chronic phase of acute brain injuries, PPARγ activation in injured cells culminates in the repair of gray and white matter, preservation of the blood-brain barrier, reconstruction of the neurovascular unit, resolution of inflammation, and long-term functional recovery. Thus, PPARγ lies at the apex of cell fate decisions and exerts profound effects on the chronic progression of acute injury conditions. Here, we review the therapeutic potential of PPARγ in stroke and brain trauma and highlight the novel role of PPARγ in long-term tissue repair. We describe its structure and function and identify the genes that it targets. PPARγ regulation of inflammation, metabolism, cell fate (proliferation/differentiation/maturation/survival), and many other processes also has relevance to other neurological diseases. Therefore, PPARγ is an attractive target for therapies against a number of progressive neurological disorders.

Regulation of lung endothelial permeability and inflammatory responses by prostaglandin A2: role of EP4 receptor

PGA2 exhibits anti-inflammatory and barrier-protective effects on endothelial cells and in two mouse models of acute lung injury. PGA2-induced cytoskeletal remodeling and suppression of the NFκB pathway is mediated by prostanoid receptor EP4. Endothelial-specific EP4 knockout abolishes PGA2-protective effects in vitro and in vivo.

The role of prostaglandin A2 (PGA2) in modulation of vascular endothelial function is unknown. We investigated effects of PGA2 on pulmonary endothelial cell (EC) permeability and inflammatory activation and identified a receptor mediating these effects. PGA2 enhanced the EC barrier and protected against barrier dysfunction caused by vasoactive peptide thrombin and proinflammatory bacterial wall lipopolysaccharide (LPS). Receptor screening using pharmacological and molecular inhibitory approaches identified EP4 as a novel PGA2 receptor. EP4 mediated barrier-protective effects of PGA2 by activating Rap1/Rac1 GTPase and protein kinase A targets at cell adhesions and cytoskeleton: VE-cadherin, p120-catenin, ZO-1, cortactin, and VASP. PGA2 also suppressed LPS-induced inflammatory signaling by inhibiting the NFκB pathway and expression of EC adhesion molecules ICAM1 and VCAM1. These effects were abolished by pharmacological or molecular inhibition of EP4. In vivo, PGA2 was protective in two distinct models of acute lung injury (ALI): LPS-induced inflammatory injury and two-hit ALI caused by suboptimal mechanical ventilation and injection of thrombin receptor–activating peptide. These protective effects were abolished in mice with endothelial-specific EP4 knockout. The results suggest a novel role for the PGA2–EP4 axis in vascular EC protection that is critical for improvement of pathological states associated with increased vascular leakage and inflammation.

Pioglitazone rapidly reduces neuropathic pain through astrocyte and nongenomic PPARγ mechanisms

Repeated administration of peroxisome proliferator-activated receptor gamma (PPARγ) agonists reduces neuropathic pain-like behavior and associated changes in glial activation in the spinal cord dorsal horn. As PPARγ is a nuclear receptor, sustained changes in gene expression are widely believed to be the mechanism of pain reduction. However, we recently reported that a single intrathecal (i.t.) injection of pioglitazone, a PPARγ agonist, reduced hyperalgesia within 30 minutes, a time frame that is typically less than that required for genomic mechanisms. To determine the very rapid antihyperalgesic actions of PPARγ activation, we administered pioglitazone to rats with spared nerve injury and evaluated hyperalgesia. Pioglitazone inhibited hyperalgesia within 5 minutes of injection, consistent with a nongenomic mechanism. Systemic or i.t. administration of GW9662, a PPARγ antagonist, inhibited the antihyperalgesic actions of intraperitoneal or i.t. pioglitazone, suggesting a spinal PPARγ-dependent mechanism. To further address the contribution of nongenomic mechanisms, we blocked new protein synthesis in the spinal cord with anisomycin. When coadministered intrathecally, anisomycin did not change pioglitazone antihyperalgesia at an early 7.5-minute time point, further supporting a rapid nongenomic mechanism. At later time points, anisomycin reduced pioglitazone antihyperalgesia, suggesting delayed recruitment of genomic mechanisms. Pioglitazone reduction of spared nerve injury-induced increases in GFAP expression occurred more rapidly than expected, within 60 minutes. We are the first to show that activation of spinal PPARγ rapidly reduces neuropathic pain independent of canonical genomic activity. We conclude that acute pioglitazone inhibits neuropathic pain in part by reducing astrocyte activation and through both genomic and nongenomic PPARγ mechanisms.

Peroxisome proliferator-activated receptor agonists modulate neuropathic pain: a link to chemokines?

Chronic pain presents a widespread and intractable medical problem. While numerous pharmaceuticals are used to treat chronic pain, drugs that are safe for extended use and highly effective at treating the most severe pain do not yet exist. Chronic pain resulting from nervous system injury (neuropathic pain) is common in conditions ranging from multiple sclerosis to HIV-1 infection to type II diabetes. Inflammation caused by neuropathy is believed to contribute to the generation and maintenance of neuropathic pain. Chemokines are key inflammatory mediators, several of which (MCP-1, RANTES, MIP-1α, fractalkine, SDF-1 among others) have been linked to chronic, neuropathic pain in both human conditions and animal models. The important roles chemokines play in inflammation and pain make them an attractive therapeutic target. Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear receptors known for their roles in metabolism. Recent research has revealed that PPARs also play a role in inflammatory gene repression. PPAR agonists have wide-ranging effects including inhibition of chemokine expression and pain behavior reduction in animal models. Experimental evidence suggests a connection between the pain ameliorating effects of PPAR agonists and suppression of inflammatory gene expression, including chemokines. In early clinical research, one PPARα agonist, palmitoylethanolamide (PEA), shows promise in relieving chronic pain. If this link can be better established, PPAR agonists may represent a new drug therapy for neuropathic pain.

Anti-inflammatory prostaglandins for the prevention of preterm labour

Preterm birth occurs in 10-12% of pregnancies and is the primary cause of neonatal mortality and morbidity. Tocolytic therapies have long been the focus for the prevention of preterm labour, yet they do not significantly improve neonatal outcome. A direct causal link exists between infection-induced inflammation and preterm labour. As inflammation and infection are independent risk factors for poor neonatal outcome, recent research focus has been shifted towards exploring the potential for anti-inflammatory strategies. Nuclear factor kappa B (NFκB) is a transcription factor that controls the expression of many labour-associated genes including PTGS2 (COX2), prostaglandins (PGs) and the oxytocin receptor (OXTR) as well as key inflammatory genes. Targeting the inhibition of NFκB is therefore an attractive therapeutic approach for both the prevention of preterm labour and for reducing neonatal exposure to inflammation. While PGs are considered to be pro-labour and pro-inflammatory, the cyclopentenone PG 15-deoxy-Δ(12,14)PGJ2 (15d-PGJ2) exhibits anti-inflammatory properties via the inhibition of NFκB in human amniocytes, myocytes and peripheral blood mononuclear cells in vitro. 15d-PGJ2 also delays inflammation-induced preterm labour in the mouse and significantly increases pup survival. This review examines the current understanding of inflammation in the context of labour and discusses how anti-inflammatory PGs may hold promise for the prevention of preterm labour and improved neonatal outcome.

Fetal alcohol spectrum disorders and neuroimmune changes

The behavioral consequences of fetal alcohol spectrum disorders (FASD) are serious and persist throughout life. The causative mechanisms underlying FASD are poorly understood. However, much has been learned about FASD from human structural and functional studies as well as from animal models, which have provided a greater understanding of the mechanisms underlying FASD. Using animal models of FASD, it has been recently discovered that ethanol induces neuroimmune activation in the developing brain. The resulting microglial activation, production of proinflammatory molecules, and alteration in expression of developmental genes are postulated to alter neuron survival and function and lead to long-term neuropathological and cognitive defects. It has also been discovered that microglial loss occurs, reducing microglia's ability to protect neurons and contribute to neuronal development. This is important, because emerging evidence demonstrates that microglial depletion during brain development leads to long-term neuropathological and cognitive defects. Interestingly, the behavioral consequences of microglial depletion and neuroimmune activation in the fetal brain are particularly relevant to FASD. This chapter reviews the neuropathological and behavioral abnormalities of FASD and delineates correlates in animal models. This serves as a foundation to discuss the role of the neuroimmune system in normal brain development, the consequences of microglial depletion and neuroinflammation, the evidence of ethanol induction of neuroinflammatory processes in animal models of FASD, and the development of anti-inflammatory therapies as a new strategy for prevention or treatment of FASD. Together, this knowledge provides a framework for discussion and further investigation of the role of neuroimmune processes in FASD.

PPAR agonists as therapeutics for CNS trauma and neurological diseases

Traumatic injury or disease of the spinal cord and brain elicits multiple cellular and biochemical reactions that together cause or are associated with neuropathology. Specifically, injury or disease elicits acute infiltration and activation of immune cells, death of neurons and glia, mitochondrial dysfunction, and the secretion of substrates that inhibit axon regeneration. In some diseases, inflammation is chronic or non-resolving. Ligands that target PPARs (peroxisome proliferator-activated receptors), a group of ligand-activated transcription factors, are promising therapeutics for neurologic disease and CNS injury because their activation affects many, if not all, of these interrelated pathologic mechanisms. PPAR activation can simultaneously weaken or reprogram the immune response, stimulate metabolic and mitochondrial function, promote axon growth and induce progenitor cells to differentiate into myelinating oligodendrocytes. PPAR activation has beneficial effects in many pre-clinical models of neurodegenerative diseases and CNS injury; however, the mechanisms through which PPARs exert these effects have yet to be fully elucidated. In this review we discuss current literature supporting the role of PPAR activation as a therapeutic target for treating traumatic injury and degenerative diseases of the CNS.

Lipidomic profiling of influenza infection identifies mediators that induce and resolve inflammation

Bioactive lipid mediators play a crucial role in the induction and resolution of inflammation. To elucidate their involvement during influenza infection, liquid chromatography/mass spectrometry lipidomic profiling of 141 lipid species was performed on a mouse influenza model using two viruses of significantly different pathogenicity. Infection by the low-pathogenicity strain X31/H3N2 induced a proinflammatory response followed by a distinct anti-inflammatory response; infection by the high-pathogenicity strain PR8/H1N1 resulted in overlapping pro- and anti-inflammatory states. Integration of the large-scale lipid measurements with targeted gene expression data demonstrated that 5-lipoxygenase metabolites correlated with the pathogenic phase of the infection, whereas 12/15-lipoxygenase metabolites were associated with the resolution phase. Hydroxylated linoleic acid, specifically the ratio of 13- to 9-hydroxyoctadecadienoic acid, was identified as a potential biomarker for immune status during an active infection. Importantly, some of the findings from the animal model were recapitulated in studies of human nasopharyngeal lavages obtained during the 2009-2011 influenza seasons.

Fluid shear stress-induced osteoarthritis: roles of cyclooxygenase-2 and its metabolic products in inducing the expression of proinflammatory cytokines and matrix metalloproteinases

The mechanical overloading of cartilage is involved in the pathophysiology of osteoarthritis (OA) by both biochemical and mechanical pathways. The application of fluid shear stress to chondrocytes recapitulates the earmarks of OA, as evidenced by the release of proinflammatory cytokines (PICs), matrix metalloproteinases (MMPs), and apoptotic factors. Dysregulations or mutations in these genes might directly cause OA in addition to determining the stage at which OA becomes apparent, the joint sites involved, and the severity of the disease and how rapidly it progresses. However, the underlying mechanisms remain unknown. In this review, we propose that the dysregulation of cyclooxygenase-2 (COX-2) is associated with fluid shear stress-induced OA via its metabolic products at different stages of the disease. Indeed, high fluid shear stress rapidly induces the production of PICs and MMPs via COX-2-derived prostaglandin (PG)E2 at the early stage of OA. In contrast, prolonged shear exposure (>12 h) aggravates the condition by concurrently up-regulating the expression of proapoptotic genes and down-regulating the expression of antiapoptotic genes in a 15-deoxy-Δ (12,14)-prostaglandin J2 (15d-PGJ2)-dependent manner at the late stage of disease. These observations may help to resolve long-standing questions in OA progression and provide insight for development of strategies to treat and combat OA.

Cigarette smoke-induced cerebral cortical interleukin-6 elevation is not mediated through oxidative stress

The author group has previously established an in vivo subchronic cigarette smoke (CS) exposure rat model, in which the systemic oxidative burden as well as the modulation of local anti-oxidative enzymes in the lung has been demonstrated. Oxidative stress has been shown to induce pro-inflammatory cytokine release, including interleukin (IL)-6 in the airways. In this study, we aimed to investigate the changes in IL-6 production, as well as the oxidative/anti-oxidative responses in the cerebral cortex using the same in vivo model. IL-6 was determined by RT-PCR and western-blot analysis. Local oxidative and anti-oxidative responses were determined by measuring cerebral cortical malondialdehyde (MDA) and advanced oxidation protein product (AOPP) levels, superoxide dismutase (SOD) and catalase activities, and the reduced to oxidized glutathione (GSH/GSSG) ratio. Nitrite level was measured by fluorescent spectrophotometry. Our results demonstrated a significant increase in both IL-6 mRNA and protein levels. Reductions of SOD activity and manganese (Mn)SOD protein level were observed together with the increased level of superoxide measured by chemiluminescent signal, after 56 days of CS exposure. There were no significant changes in the cerebral cortical levels of MDA, AOPP, catalase activity, and the GSH/GSSG ratio. Nitrite level was significantly reduced, together with the decreased protein level of nNOS in the cerebral cortex, after 56 days of CS exposure. Our results suggest that exposure to CS induces IL-6 expression in the cerebral cortex, which is not mediated by the oxidative/anti-oxidative imbalance.

PPAR-gamma: Therapeutic Potential for Multiple Sclerosis

The role of peroxisome proliferator-activated receptors (PPARs) in altering lipid and glucose metabolism is well established. More recent studies indicate that PPARs also play critical roles in controlling immune responses. We and others have previously demonstrated that PPAR-γ agonists modulate the development of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). This review will discuss the cellular and molecular mechanisms by which these agonists are believed to modulate disease. The therapeutic potential of PPAR-γ agonists in the treatment of multiple sclerosis will also be considered.

PPAR-gamma, Microglial Cells, and Ocular Inflammation: New Venues for Potential Therapeutic Approaches

The last decade has witnessed an increasing interest for the role played by the peroxisome proliferator-activated receptor-γ (PPAR-γ) in controlling inflammation in peripheral organs as well as in the brain. Activation of PPAR-γ has been shown to control the response of microglial cells, the main macrophage population found in brain parenchyma, and limit the inflammation. The anti-inflammatory capacity of PPAR-γ agonists has led to the hypothesis that PPAR-γ might be targeted to modulate degenerative brain diseases in which inflammation has been increasingly recognized as a significant component. Recent experimental evidence suggests that PPAR-γ agonists could be exploited to treat ocular diseases such as diabetic retinopathy, age-related macular degeneration, autoimmune uveitis, and optic neuritis where inflammation has relevant role. Additional PPAR-γ agonist beneficial effects could involve amelioration of retinal microcirculation and inhibition of neovascularization. However, PPAR-γ activation could, in some instances, aggravate the ocular pathology, for example, by increasing the synthesis of vascular endothelial growth factor, a proangiogenic factor that could trigger a vicious circle and further deteriorate retinal perfusion. The development of new in vivo and in vitro models to study ocular inflammation and how to modulate for the eye benefit will be instrumental for the search of effective therapies.

PPAR Regulation of Inflammatory Signaling in CNS Diseases

Central nervous system (CNS) is an immune privileged site, nevertheless inflammation associates with many CNS diseases. Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear hormone receptors that regulate immune and inflammatory responses. Specific ligands for PPARα, γ, and δ isoforms have proven effective in the animal models of multiple sclerosis (MS), Alzheimer's disease, Parkinson's disease, and trauma/stroke, suggesting their use in the treatment of neuroinflammatory diseases. The activation of NF-κB and Jak-Stat signaling pathways and secretion of inflammatory cytokines are critical in the pathogenesis of CNS diseases. Interestingly, PPAR agonists mitigate CNS disease by modulating inflammatory signaling network in immune cells. In this manuscript, we review the current knowledge on how PPARs regulate neuroinflammatory signaling networks in CNS diseases.

Regulation of Immune Responses and Autoimmune Encephalomyelitis by PPARs

PPARs are members of the steroid hormone nuclear receptor superfamily and play an important role in regulating inflammation as well as lipid metabolism. The PPAR subfamily has been defined as PPARα, PPARβ/δ, and PPARγ, each with different ligands, target genes, and biological roles. PPARs regulate the expression of target inflammatory genes through mechanisms involving both transactivation and transrepression. The anti-inflammatory properties of PPAR agonists have led to the investigation of PPAR functions in regulating autoimmune encephalomyelitis. This paper will summarize some of the general mechanisms by which PPARs regulate inflammatory gene expression and focus on the recent advances of PPAR regulation of autoimmune encephalomyelitis.

Prostaglandins in pathogenesis and treatment of multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS) characterized by inflammation, demyelination, axonal loss, and gliosis. The inflammatory lesions are manifested by a large infiltration and a heterogeneous population of cellular and soluble mediators of the immune system, such as T cells, B cells, macrophages, and microglia, as well as a broad range of cytokines, chemokines, antibodies, complement, and other toxic substances. Prostaglandins (PGs) are arachidonic acid-derived autacoids that have a role in the modulation of many physiological systems including the CNS, respiratory, cardiovascular, gastrointestinal, genitourinary, endocrine, and immune systems. PG production is associated with inflammation, a major feature in MS that is characterized by the loss of myelinating oligodendrocytes in the CNS. With respect to the role of PGs in the induction of inflammation, they can be effective mediators in the pathophysiology of MS. Thus use of agonists or antagonists of PG receptors may be considered as a new therapeutic protocol in MS. In this review, we try to clarify the role of PGs in immunopathology and treatment of MS.

Effects of the PPAR-beta agonist GW501516 in an in vitro model of brain inflammation and antibody-induced demyelination

Background

Brain inflammation plays a central role in numerous brain pathologies, including multiple sclerosis (MS). Microglial cells and astrocytes are the effector cells of neuroinflammation. They can be activated also by agents such as interferon-γ (IFN-γ) and lipopolysaccharide (LPS). Peroxisome proliferator-associated receptor (PPAR) pathways are involved in the control of the inflammatory processes, and PPAR-β seems to play an important role in the regulation of central inflammation. In addition, PPAR-β agonists were shown to have trophic effects on oligodendrocytes in vitro, and to confer partial protection in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. In the present work, a three-dimensional brain cell culture system was used as in vitro model to study antibody-induced demyelination and inflammatory responses. GW 501516, a specific PPAR-β agonist, was examined for its capacity to protect from antibody-mediated demyelination and to prevent inflammatory responses induced by IFN-γ and LPS.

Methods

Aggregating brain cells cultures were prepared from embryonal rat brain, and used to study the inflammatory responses triggered by IFN-γ and LPS and by antibody-mediated demyelination induced by antibodies directed against myelin-oligodendrocyte glycoprotein (MOG). The effects of GW 501516 on cellular responses were characterized by the quantification of the mRNA expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), inducible NO synthase (i-NOS), PPAR-β, PPAR-γ, glial fibrillary acidic protein (GFAP), myelin basic protein (MBP), and high molecular weight neurofilament protein (NF-H). GFAP expression was also examined by immunocytochemistry, and microglial cells were visualized by isolectin B4 (IB4) and ED1 labeling.

Results

GW 501516 decreased the IFN-γ-induced up-regulation of TNF-α and iNOS in accord with the proposed anti-inflammatory effects of this PPAR-β agonist. However, it increased IL-6 m-RNA expression. In demyelinating cultures, reactivity of both microglial cells and astrocytes was observed, while the expression of the inflammatory cytokines and iNOS remained unaffected. Furthermore, GW 501516 did not protect against the demyelination-induced changes in gene expression.

Conclusion

Although GW 501516 showed anti-inflammatory activity, it did not protect against antibody-mediated demyelination. This suggests that the protective effects of PPAR-β agonists observed in vivo can be attributed to their anti-inflammatory properties rather than to a direct protective or trophic effect on oligodendrocytes.

The importance of NAD in multiple sclerosis

The etiology of multiple sclerosis (MS) is unknown but it manifests as a chronic inflammatory demyelinating disease in the central nervous system (CNS). During chronic CNS inflammation, nicotinamide adenine dinucleotide (NAD) concentrations are altered by (T helper) Th1-derived cytokines through the coordinated induction of both indoleamine 2,3-dioxygenase (IDO) and the ADP cyclase CD38 in pathogenic microglia and lymphocytes. While IDO activation may keep auto-reactive T cells in check, hyper-activation of IDO can leave neuronal CNS cells starving for extracellular sources of NAD. Existing data indicate that glia may serve critical functions as an essential supplier of NAD to neurons during times of stress. Administration of pharmacological doses of non-tryptophan NAD precursors ameliorates pathogenesis in animal models of MS. Animal models of MS involve artificially stimulated autoimmune attack of myelin by experimental autoimmune encephalomyelitis (EAE) or by viral-mediated demyelination using Thieler's murine encephalomyelitis virus (TMEV). The Wld(S) mouse dramatically resists razor axotomy mediated axonal degeneration. This resistance is due to increased efficiency of NAD biosynthesis that delays stress-induced depletion of axonal NAD and ATP. Although the Wld(S) genotype protects against EAE pathogenesis, TMEV-mediated pathogenesis is exacerbated. In this review, we contrast the role of NAD in EAE versus TMEV demyelinating pathogenesis to increase our understanding of the pharmacotherapeutic potential of NAD signal transduction pathways. We speculate on the importance of increased SIRT1 activity in both PARP-1 inhibition and the potentially integral role of neuronal CD200 interactions through glial CD200R with induction of IDO in MS pathogenesis. A comprehensive review of immunomodulatory control of NAD biosynthesis and degradation in MS pathogenesis is presented. Distinctive pharmacological approaches designed for NAD-complementation or targeting NAD-centric proteins (SIRT1, SIRT2, PARP-1, GPR109a, and CD38) are outlined towards determining which approach may work best in the context of clinical application.

15-deoxy-delta12,14-prostaglandin J2 attenuates endothelial-monocyte interaction: implication for inflammatory diseases

BACKGROUND

The Infiltration of leukocytes across the brain endothelium is a hallmark of various neuroinflammatory disorders. Under inflammatory conditions, there is increased expression of specific cell adhesion molecules (CAMs) on activated vascular endothelial cells which increases the adhesion and infiltration of leukocytes. TNFalpha is one of the major proinflammatory cytokines that causes endothelial dysfunction by various mechanisms including activation of transcription factor NF-kappaB, a key transcription factor that regulates expression of CAMs. Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear hormone superfamily of ligand-activated transcriptional factors. 15-deoxy-delta 12, 14-prostaglandin J2 (15d-PGJ2) is a well recognized natural ligand of PPARgamma and possesses anti-inflammatory properties both in vitro and in vivo. This study aims to elucidate the mechanism of 15-PGJ2 on the adhesion of mononuclear cells to activated endothelial cells.

METHODS

To delineate the signaling pathway of 15d-PGJ2 mediated effects, we employed an in vitro adhesion assay model of endothelial-monocyte interaction. Expression of CAMs was examined using flow cytometry and real time PCR techniques. To define the mechanism of 15d-PGJ2, we explored the role of NF-kappaB by EMSA (Electrophoretic Mobility Shift Assay) gels, NF-kappaB reporter and p65-transcriptional activities by transient transfection in the brain-derived endothelial cell line (bEND.3).

RESULTS

Using an in vitro adhesion assay model, we demonstrate that 15d-PGJ2 inhibits TNFalpha induced monocyte adhesion to endothelial cells, which is mediated by downregulation of endothelial cell adhesion molecules in a PPARgamma independent manner. 15d-PGJ2 modulated the adhesion process by inhibiting the TNFalpha induced IKK-NF-kappaB pathway as evident from EMSA, NF-kappaB reporter and p65 mediated transcriptional activity results in bEND.3 cells.

CONCLUSION

These findings suggest that 15d-PGJ2 inhibits inflammation at multiple steps and thus is a potential therapeutic target for various inflammatory diseases.

Augmentation of endogenous cannabinoid tone modulates lipopolysaccharide-induced alterations in circulating cytokine levels in rats

The endogenous cannabinoid system plays an important role in regulating the immune system. Modulation of endogenous cannabinoids represents an attractive alternative for the treatment of inflammatory disorders. This study investigated the effects of URB597, a selective inhibitor of fatty acid amide hydrolase (FAAH), the enzyme catalysing degradation of the endogenous cannabinoid anandamide, and AM404, an inhibitor of anandamide transport, on lipopolysaccharide (LPS)-induced increases in plasma cytokine levels in rats. Both URB597 and AM404 potentiated the LPS-induced increase in plasma tumour necrosis factor-alpha (TNF-alpha) levels. The peroxisome proliferator-activated receptor gamma (PPARgamma) antagonist, GW9662, attenuated the AM404-induced augmentation of TNF-alpha levels. Furthermore, the selective cannabinoid CB1 and CB2 receptor antagonists, AM251 and AM630 respectively, and the transient receptor potential vanilloid receptor-1 (TRPV1) antagonist, SB366791, reduced LPS-induced TNF-alpha plasma levels both alone and in combination with AM404. In contrast, AM404 inhibited LPS-induced increases in circulating interleukin-1beta (IL-1beta) and IL-6. AM251 attenuated the immunosuppressive effect of AM404 on IL-1beta. None of the antagonists altered the effect of AM404 on LPS-induced IL-6. Moreover, AM251, AM630 and SB366791, administered alone, inhibited LPS-induced increases in plasma IL-1beta and IL-6 levels. In conclusion, inhibition of endocannabinoid degradation or transport in vivo potentiates LPS-induced increases in circulating TNF-alpha levels, an effect which may be mediated by PPARgamma and is also reduced by pharmacological blockade of CB1, CB2 and TRPV1. The immunosuppressive effect of AM404 on IL-1beta levels is mediated by the cannabinoid CB1 receptor. Improved understanding of endocannabinoid-mediated regulation of immune function has fundamental physiological and potential therapeutic significance.

Anti-inflammatory constituents of the red alga Gracilaria verrucosa and their synthetic analogues

A chemical study on the anti-inflammatory components of the red alga Gracilaria verrucosa led to the isolation of new 11-deoxyprostaglandins ( 1- 4), a ceramide ( 5), and a C 16 keto fatty acid ( 6), along with known oxygenated fatty acids ( 7- 14). Their structures were elucidated on the basis of NMR and MS data. The absolute configurations of compounds 1- 5 were determined by Mosher's method. The anti-inflammatory activity of the isolated compounds ( 1- 14) was evaluated by determining their inhibitory effects on the production of pro-inflammatory mediators (NO, IL-6, and TNF-alpha) in lipopolysaccharide (LPS)-activated RAW 264.7 murine macrophage cells. Compounds 9 and 10 exhibited the most potent activity. In the evaluation of these two compounds and derivatized analogues ( 15- 40), the anti-inflammatory activity was enhanced in some synthetic analogues. These enone fatty acids were investigated as potential anti-inflammatory leads for the first time.

15d-PGJ2 induces apoptosis of mouse oligodendrocyte precursor cells

Background

Prostaglandin (PG) production is associated with inflammation, a major feature in multiple sclerosis (MS) that is characterized by the loss of myelinating oligodendrocytes in the CNS. While PGs have been shown to have relevance in MS, it has not been determined whether PGs have a direct effect on cells within the oligodendrocyte lineage.

Methods

Undifferentiated or differentiated mouse oligodendrocyte precursor (mOP) cells were treated with PGE2, PGF2α, PGD2 or 15-deoxy-^Δ12,14-PGJ2 (15d-PGJ2). Cell growth and survival following treatment were examined using cytotoxicity assays and apoptosis criteria. The membrane receptors for PGD2 and the nuclear receptor peroxisome proliferator-activated receptor (PPAR)γ, as well as reactive oxygen species (ROS) in the death mechanism were examined.

Results

PGE2 and PGF2α had minimal effects on the growth and survival of mOP cells. In contrast, PGD2 and 15d-PGJ2 induced apoptosis of undifferentiated mOP cells at relatively low micromolar concentrations. 15d-PGJ2 was less toxic to differentiated mOP cells. Apoptosis was independent of membrane receptors for PGD2 and the nuclear receptor PPARγ. The cytotoxicity of 15d-PGJ2 was associated with the production of ROS and was inversely related to intracellular glutathione (GSH) levels. However, the cytotoxicity of 15d-PGJ2 was not decreased by the free radical scavengers ascorbic acid or α-tocopherol.

Conclusion

Taken together, these results demonstrated that 15d-PGJ2 is toxic to early stage OP cells, suggesting that 15d-PGJ2 may represent a deleterious factor in the natural remyelination process in MS.

Peroxisome proliferator-activated receptor-gamma agonists suppress the production of IL-12 family cytokines by activated glia

The IL-12 family of cytokines, which include IL-12, IL-23, and IL-27, play critical roles in the differentiation of Th1 cells and are believed to contribute to the development of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Relatively little is known concerning the expression of IL-12 family cytokines by cells of the CNS, the affected tissue in MS. Previously, we and others demonstrated that peroxisome proliferator-activated receptor (PPAR)-gamma agonists suppress the development of EAE, alter T cell proliferation and phenotype, and suppress the activation of APCs. The present studies demonstrated that PPAR-gamma agonists, including the naturally occurring 15-deoxy-Delta(12,14)-PGJ(2) and the synthetic thiazoladinedione rosiglitazone, inhibited the induction of IL-12p40, IL-12p70 (p35/p40), IL-23 (p19/p40), and IL-27p28 proteins by LPS-stimulated primary microglia. In primary astrocytes, LPS induced the production of IL-12p40, IL-23, and IL-27p28 proteins. However, IL-12p70 production was not detected in these cells. The 15-deoxy-Delta(12,14)-PGJ(2) potently suppressed IL-12p40, IL-23, and IL-27p28 production by primary astrocytes, whereas rosiglitazone suppressed IL-23 and IL-27p28, but not IL-12p40 in these cells. These novel observations suggest that PPAR-gamma agonists modulate the development of EAE, at least in part, by inhibiting the production of IL-12 family cytokines by CNS glia. In addition, we demonstrate that PPAR-gamma agonists inhibit TLR2, MyD88, and CD14 expression in glia, suggesting a possible mechanism by which these agonists modulate IL-12 family cytokine expression. Collectively, these studies suggest that PPAR-gamma agonists may be beneficial in the treatment of MS.

Janus faces of microglia in multiple sclerosis

Multiple sclerosis (MS) is the most common cause of neurological disability in young adults. The disease is characterized by inflammatory reactions, demyelination and axonal loss in the brain, spinal cord and optic nerves. Microglia seem to play an important role in the inflammatory processes in MS, since they are found in actively demyelinating lesions. Their role in the differentiation of T cells could led to the expansion of inflammation and tissue destruction. However, microglia are also involved in the termination of an inflammatory response and produce protective factors. To be able to therapeutically manipulate microglia, their exact function in the onset and development of MS needs to be clarified. This review provides an overview of the functions of the most important microglia-associated molecules in MS, being CD40, B7-1 and B7-2, interferon-gamma, tumor necrosis factor-alpha, chemokines, prostanoids, and nitric oxide.

15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) and ciglitazone modulate Staphylococcus aureus-dependent astrocyte activation primarily through a PPAR-gamma-independent pathway

Brain abscesses arise from a focal parenchymal infection by various pathogens, particularly Staphylococcus aureus. We have shown that astrocytes are activated upon exposure to S. aureus and may contribute to the excessive tissue damage characteristic of brain abscess. Therefore, modulating astrocyte activation may facilitate a reduction in brain abscess severity. Peroxisome proliferator activated receptor-gamma (PPAR-gamma) agonists are potent inhibitors of microglial activation; however, the effects of these compounds on S. aureus-dependent astrocyte activation have not yet been examined. Here, we demonstrate that two chemically distinct PPAR-gamma agonists, 15-deoxy-delta12,14-prostaglandin J2 (15d-PGJ2) and ciglitazone, suppress the production of several pro-inflammatory molecules in S. aureus-stimulated astrocytes including interleukin-1beta and nitric oxide (NO). Interestingly, 15d-PGJ2 attenuated Toll-like receptor 2 (TLR2) and inducible nitric oxide synthase expression, but failed to modulate macrophage inflammatory protein-2 (MIP-2/CXCL2) production, suggesting that 15d-PGJ2 is not a global inhibitor of astrocyte activation. Another novel finding of this study was the fact that both 15d-PGJ2 and ciglitazone were capable of attenuating pre-existing astrocyte activation, indicating their potential benefit in a therapeutic setting. Importantly, 15d-PGJ2 and ciglitazone were still capable of inhibiting S. aureus-induced pro-inflammatory mediator release in PPAR-gamma-deficient astrocytes, supporting PPAR-gamma-independent effects of these compounds. Collectively, these results suggest that 15d-PGJ2 and ciglitazone exert their anti-inflammatory actions on astrocytes primarily independent of the PPAR-gamma pathway.

Liver X receptor and retinoid X receptor agonists inhibit inflammatory responses of microglia and astrocytes

Liver X receptors (LXRs) are nuclear receptors previously identified to be important in lipid metabolism. Recent reports suggest that LXR agonists also exhibit anti-inflammatory properties in mouse models of atherosclerosis and contact dermatitis. In the present study, we investigated the effects of LXR agonists on mouse microglia and astrocytes. When chronically activated, these resident-CNS glia have been implicated in the pathology of neuroinflammatory disorders including multiple sclerosis (MS). Our studies demonstrated for the first time that LXR agonists inhibited the production of nitric oxide, the pro-inflammatory cytokines IL-1beta and IL-6 and the chemokine MCP-1 from LPS-stimulated microglia and astrocytes. Furthermore, LXR agonists inhibited LPS-induction of nuclear factor-kappa B (NF-kappaB) DNA-binding activity. These agonists also blocked LPS-induction of IkappaB-alpha protein degradation in microglia, suggesting a mechanism by which these agonists modulate NF-kappaB DNA-binding activity. These studies suggest that LXR agonists suppress the production of pro-inflammatory molecules by CNS glia, at least in part, by modulating NF-kappaB-signaling pathways. Retinoid X receptors (RXRs) physically interact with LXR receptors, and the resulting obligate heterodimer regulates the expression of LXR-responsive genes. Interestingly, a combination of LXR and RXR agonists additively suppressed the production of NO by microglia and astrocytes. Collectively, these studies suggest that LXR agonists may be effective in the treatment of neuroinflammatory diseases including MS.

Toward prevention of Alzheimers disease--potential nutraceutical strategies for suppressing the production of amyloid beta peptides

Alzheimers disease (AD) can be viewed as a vicious cycle in which excess production and deposition of amyloid beta (Abeta) peptides promote microglial activation, and the resultant production of inflammatory mediators further boosts Abeta production while inducing death and dysfunction of neurons. Abeta production is mediated by beta- and gamma-secretase activities; it is prevented by alpha-secretase activity, and insulin-degrading enzyme (IDE) catabolizes Abeta. High cellular cholesterol content increases Abeta synthesis by boosting beta-secretase activity; inhibition of cholesterol syntheses and/or stimulation of cholesterol export thus diminishes Abeta production. PPARgamma activity decreases Abeta production by promoting harmless catabolism of amyloid precursor protein while blocking the up-regulatory impact of cytokines on beta-secretase expression. Nitric oxide produced by the healthy cerebral microvasculature can suppress Abeta production by boosting expression of alpha-secretase while suppressing that of beta-secretase; conversely, cerebral ischemia provokes increased APP expression. Good insulin sensitivity and efficient brain insulin function protect by inhibiting gamma-secretase activity and increasing expression of IDE. The DHA provided by fish oil diminishes cerebral Abeta deposition in rodent AD models, for unclear reasons. Various measures which oppose microglial activation can inhibit up-regulation of beta-secretase and gamma-secretase by oxidants and cytokines, respectively. These considerations suggest that a number of nutraceutical or lifestyle measures may have potential for preventing or slowing AD: policosanol; 9-cis-beta-carotene; isomerized hops extract; DHA; measures which promote efficient endothelial NO generation, such as low-salt/potassium-rich diets, exercise training, high-dose folate, and flavanol-rich cocoa; chromium picolinate and cinnamon extract as aids for insulin sensitivity; and various agents which can oppose microglial activation, including vitamin D, genistein, and sesamin. The impact of these measures on Abeta production in rodent models of AD should be evaluated, with the intent of defining practical strategies for AD prevention.

Peroxisome proliferator-activated receptor-α and retinoid X receptor agonists inhibit inflammatory responses of astrocytes

The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) plays a key role in lipid metabolism and inflammation. Recently, we demonstrated that administration of the PPAR-alpha agonists gemfibrozil and fenofibrate, inhibit the clinical signs of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). In the present study, we investigated the effects of PPAR-alpha agonists on primary mouse astrocytes, a cell type implicated in the pathology of MS and EAE. Our studies demonstrated that the PPAR-alpha agonists fenofibrate, and WY 14643 inhibited NO production by LPS-stimulated astrocytes in a dose-dependent manner. Additionally, PPAR-alpha agonists inhibited the secretion of the pro-inflammatory cytokines TNF-alpha, IL-1beta, and IL-6 by LPS-stimulated astrocytes. Fenofibrate inhibited NF-kappaB DNA binding activity, suggesting a mechanism by which PPAR-alpha agonists may regulate the expression of genes encoding these pro-inflammatory molecules. Retinoid X receptors (RXRs) physically interact with PPAR-alpha receptors, and the resulting heterodimers regulate the expression of PPAR-responsive genes. Interestingly, a combination of 9-cis RA and the PPAR-alpha agonists fenofibrate or gemfibrozil cooperatively inhibited NO, TNF-alpha, IL-1beta, IL-6, and MCP-1 production by these cells. Collectively, these results raise the possibility that PPAR-alpha and RXR agonists might be effective in the treatment of MS, where activated astrocytes are believed to contribute to disease pathology.

15d-Prostaglandin J2 activates peroxisome proliferator-activated receptor-gamma, promotes expression of catalase, and reduces inflammation, behavioral dysfunction, and neuronal loss after intracerebral hemorrhage in rats

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a transcription factor that regulates the expression of various gene products that are essential in lipid and glucose metabolism, as well as that of the peroxisome-enriched antioxidant enzyme, catalase. Activation of PPARgamma is linked to anti-inflammatory activities and is beneficial for cardiovascular diseases. However, little is known about its role in intracerebral hemorrhage (ICH). 15-Deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) acts as a physiologic agonist for PPARgamma. In this study, we found that injection of 15d-PGJ2 into the locus of striatal hematoma increased PPARgamma-deoxyribonucleic acid (DNA) binding activity and the expression of catalase messenger ribonucleic acid (mRNA) and protein in the perihemorrhagic area. Additionally, 15d-PGJ2 significantly reduced nuclear factor-kappaB (NF-kappaB) activation and prevented neutrophil infiltration measured by myeloperoxidase (MPO) immunoassay, and also reduced cell apoptosis measured by terminal deoxynucleotide transferase dUTP nick-end labeling (TUNEL). In addition, 15d-PGJ2 reduced behavioral dysfunction produced by the ICH. Altogether, our findings indicate that injection of 15d-PGJ2 at the onset of ICH is associated with activation of PPARgamma and elevation of catalase expression, suppression of NF-kappaB activity, and restricted neutrophil infiltration. All these events predicted reduced behavioral deficit and neuronal damage.

Down-regulation of microglial activation may represent a practical strategy for combating neurodegenerative disorders

Chronic neurodegenerative disorders are characterized by activation of microglia in the affected neural pathways. Peroxynitrite, prostanoids, and cytokines generated by these microglia can potentiate the excitotoxicity that contributes to neuronal death and dysfunction in these disorders--both by direct effects on neurons, and by impairing the capacity of astrocytes to sequester and metabolize glutamate. This suggests a vicious cycle in which the death of neurons leads to microglial activation, which in turn potentiates neuronal damage. If this model is correct, measures which down-regulate microglial activation may have a favorable effect on the induction and progression of neurodegenerative disease, independent of the particular trigger or target involved in a given disorder. Consistent with this possibility, the antibiotic minocycline, which inhibits microglial activation, shows broad utility in rodent models of neurodegeneration. Other agents which may have potential in this regard include PPARgamma agonists, genistein, vitamin D, COX-2 inhibitors, statins (and possibly policosanol), caffeine, cannabinoids, and sesamin; some of these agents could also be expected to be directly protective to neurons threatened with excitotoxicity. To achieve optimal clinical outcomes, regimens which down-regulate microglial activation could be used in conjunction with complementary measures which address other aspects of excitotoxicity.